WorldWideScience

Sample records for longitudinal relaxation times

  1. A method for longitudinal relaxation time measurement in inhomogeneous fields

    Science.gov (United States)

    Chen, Hao; Cai, Shuhui; Chen, Zhong

    2017-08-01

    The spin-lattice relaxation time (T1) plays a crucial role in the study of spin dynamics, signal optimization and data quantification. However, the measurement of chemical shift-specific T1 constants is hampered by the magnetic field inhomogeneity due to poorly shimmed external magnetic fields or intrinsic magnetic susceptibility heterogeneity in samples. In this study, we present a new protocol to determine chemical shift-specific T1 constants in inhomogeneous fields. Based on intermolecular double-quantum coherences, the new method can resolve overlapped peaks in inhomogeneous fields. The measurement results are in consistent with the measurements in homogeneous fields using the conventional method. Since spatial encoding technique is involved, the experimental time for the new method is very close to that for the conventional method. With the aid of T1 knowledge, some concealed information can be exploited by T1 weighting experiments.

  2. Investigation of microenvironmental factors influencing the longitudinal relaxation times of drugs and other compounds

    DEFF Research Database (Denmark)

    Dzik-Jurasz, A.S.K.; Leach, M.O.; Rowland, Ian John

    2004-01-01

    demonstrated that in the presence of competitive binding of other ligands for common binding sites on albumin, the 19F longitudinal relaxation time of 5-fluorouracil can increase by up to 340% from its value in the absence of the competing ligand. The relevance of the findings to in vivo studies is discussed...

  3. Magnetization Transfer Induced Biexponential Longitudinal Relaxation

    Science.gov (United States)

    Prantner, Andrew M.; Bretthorst, G. Larry; Neil, Jeffrey J.; Garbow, Joel R.; Ackerman, Joseph J.H.

    2009-01-01

    Longitudinal relaxation of brain water 1H magnetization in mammalian brain in vivo is typically analyzed on a per voxel basis using a monoexponential model, thereby assigning a single relaxation time constant to all 1H magnetization within a given voxel. This approach was tested by obtaining inversion recovery data from grey matter of rats at 64 exponentially-spaced recovery times. Using Bayesian probability for model selection, brain water data were best represented by a biexponential function characterized by fast and slow relaxation components. At 4.7 T, the amplitude fraction of the rapidly relaxing component is 3.4 ± 0.7 % with a rate constant of 44 ± 12 s-1 (mean ± SD; 174 voxels from 4 rats). The rate constant of the slow relaxing component is 0.66 ± 0.04 s-1. At 11.7 T, the corresponding values are 6.9 ± 0.9 %, 19 ± 5 s-1, and 0.48 ± 0.02 s-1 (151 voxels from 4 rats). Several putative mechanisms for biexponential relaxation behavior were evaluated, and magnetization transfer between bulk water protons and non-aqueous protons was determined to be the source of biexponential longitudinal relaxation. MR methods requiring accurate quantification of longitudinal relaxation may need to take this effect explicitly into account. PMID:18759367

  4. Comparison of longitudinal metabolite relaxation times in different regions of the human brain at 1.5 and 3 Tesla.

    Science.gov (United States)

    Ethofer, Thomas; Mader, Irina; Seeger, Uwe; Helms, Gunther; Erb, Michael; Grodd, Wolfgang; Ludolph, Albert; Klose, Uwe

    2003-12-01

    In vivo longitudinal relaxation times of N-acetyl compounds (NA), choline-containing substances (Cho), creatine (Cr), myo-inositol (mI), and tissue water were measured at 1.5 and 3 T using a point-resolved spectroscopy (PRESS) sequence with short echo time (TE). T(1) values were determined in six different brain regions: the occipital gray matter (GM), occipital white matter (WM), motor cortex, frontoparietal WM, thalamus, and cerebellum. The T(1) relaxation times of water protons were 26-38% longer at 3 T than at 1.5 T. Significantly longer metabolite T(1) values at 3 T (11-36%) were found for NA, Cho, and Cr in the motor cortex, frontoparietal WM, and thalamus. The amounts of GM, WM, and cerebrospinal fluid (CSF) within the voxel were determined by segmentation of a 3D image data set. No influence of tissue composition on metabolite T(1) values was found, while the longitudinal relaxation times of water protons were strongly correlated with the relative GM content. Copyright 2003 Wiley-Liss, Inc.

  5. Measurement of 15N longitudinal relaxation rates in 15NH4+ spin systems to characterise rotational correlation times and chemical exchange

    Science.gov (United States)

    Hansen, D. Flemming

    2017-06-01

    Many chemical and biological processes rely on the movement of monovalent cations and an understanding of such processes can therefore only be achieved by characterising the dynamics of the involved ions. It has recently been shown that 15N-ammonium can be used as a proxy for potassium to probe potassium binding in bio-molecules such as DNA quadruplexes and enzymes. Moreover, equations have been derived to describe the time-evolution of 15N-based spin density operator elements of 15NH4+ spin systems. Herein NMR pulse sequences are derived to select specific spin density matrix elements of the 15NH4+ spin system and to measure their longitudinal relaxation in order to characterise the rotational correlation time of the 15NH4+ ion as well as report on chemical exchange events of the 15NH4+ ion. Applications to 15NH4+ in acidic aqueous solutions are used to cross-validate the developed pulse sequence while measurements of spin-relaxation rates of 15NH4+ bound to a 41 kDa domain of the bacterial Hsp70 homologue DnaK are presented to show the general applicability of the derived pulse sequence. The rotational correlation time obtained for 15N-ammonium bound to DnaK is similar to the correlation time that describes the rotation about the threefold axis of a methyl group. The methodology presented here provides, together with the previous theoretical framework, an important step towards characterising the motional properties of cations in macromolecular systems.

  6. Hydrogen-1 NMR relaxation time studies in membrane: anesthetic systems; Variacao dos tempos de relaxacao longitudinal de protons em sistemas membranares contendo anestesicos locais

    Energy Technology Data Exchange (ETDEWEB)

    Pinto, L.M.A.; Fraceto, L.; Paula, E. de [Universidade Estadual de Campinas, SP (Brazil). Dept. de Bioquimica; Franzoni, L.; Spisni, A. [Universita degli Studi di Parma, Parma (Italy). Ist. di Chimica Biologica

    1997-12-31

    The study of local anesthetics`(LA) interaction with model phospholipid membranes is justified by the direct correlation between anesthetic`s hydrophobicity and its potency/toxicity. By the same reason, uncharged LA species seems to play a crucial role in anesthesia. Most clinically used LA are small amphiphilics with a protonated amine group (pKa around 8). Although both charged (protonated) and uncharged forms can coexist at physiological pH, it has been shown (Lee, Biochim. Biophys. Acta 514:95, 1978; Screier et al. Biochim. Biophys. Acta 769:231, 1984) that the real anesthetic pka can be down-shifted, due to differential partition into membranes, increasing the ratio of uncharged species at pH 7.4. We have measured {sup 1}H-NMR longitudinal relaxation times (T{sub 1}) for phospholipid and three local anesthetics (tetracaine, lidocaine, benzocaine), in sonicated vesicles at a 3:1 molar ratio. All the LA protons have shown smaller T{sub 1} in this system than in isotropic phases, reflecting LA immobilization caused by insertion in the membrane. T{sub 1} values for the lipid protons in the presence of LA were analyzed, in an attempt to identify specific LA:lipid contact regions. (author) 13 refs., 3 figs., 1 tabs.

  7. Heteronuclear transverse and longitudinal relaxation in AX4 spin systems: Application to 15N relaxations in 15NH4 +

    OpenAIRE

    Werbeck, Nicolas D; Hansen, D. Flemming

    2014-01-01

    The equations that describe the time-evolution of transverse and longitudinal 15N magnetisations in tetrahedral ammonium ions, 15NH4 +, are derived from the Bloch-Wangsness-Redfield density operator relaxation theory. It is assumed that the relaxation of the spin-states is dominated by (1) the intra-molecular 15N–1H and 1H–1H dipole–dipole interactions and (2) interactions of the ammonium protons with remote spins, which also include the contribution to the relaxations that arise from the exc...

  8. A rapid inversion technique for the measurement of longitudinal relaxation times of brain metabolites: application to lactate in high-grade gliomas at 3 T.

    Science.gov (United States)

    Landheer, Karl; Sahgal, Arjun; Myrehaug, Sten; Chen, Albert P; Cunningham, Charles H; Graham, Simon J

    2016-10-01

    The aim of this study was to develop a time-efficient inversion technique to measure the T1 relaxation time of the methyl group of lactate (Lac) in the presence of contaminating lipids and to measure T1 at 3 T in a cohort of primary high-grade gliomas. Three numerically optimized inversion times (TIs) were chosen to minimize the expected error in T1 estimates for a given input total scan duration (set to be 30 min). A two-cycle spectral editing scheme was used to suppress contaminating lipids. The T1 values were then estimated from least-squares fitting of signal measurements versus TI. Lac T1 was estimated as 2000 ± 280 ms. After correcting for T1 (and T2 from literature values), the mean absolute Lac concentration was estimated as 4.3 ± 2.6 mm. The technique developed agrees with the results obtained by standard inversion recovery and can be used to provide rapid T1 estimates of other spectral components as required. Lac T1 exhibits similar variations to other major metabolites observable by MRS in high-grade gliomas. The T1 estimate provided here will be useful for future MRS studies wishing to report relaxation-corrected estimates of Lac concentration as an objective tumor biomarker. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

  9. Time of relaxation in dusty plasma model

    Science.gov (United States)

    Timofeev, A. V.

    2015-11-01

    Dust particles in plasma may have different values of average kinetic energy for vertical and horizontal motion. The partial equilibrium of the subsystems and the relaxation processes leading to this asymmetry are under consideration. A method for the relaxation time estimation in nonideal dusty plasma is suggested. The characteristic relaxation times of vertical and horizontal motion of dust particles in gas discharge are estimated by analytical approach and by analysis of simulation results. These relaxation times for vertical and horizontal subsystems appear to be different. A single hierarchy of relaxation times is proposed.

  10. Relaxation time in disordered molecular systems

    Energy Technology Data Exchange (ETDEWEB)

    Rocha, Rodrigo P. [Departamento de Física, Universidade Federal de Santa Catarina, 88040-900 Florianópolis-SC (Brazil); Freire, José A., E-mail: jfreire@fisica.ufpr.br [Departamento de Física, Universidade Federal do Paraná, 81531-990 Curitiba-PR (Brazil)

    2015-05-28

    Relaxation time is the typical time it takes for a closed physical system to attain thermal equilibrium. The equilibrium is brought about by the action of a thermal reservoir inducing changes in the system micro-states. The relaxation time is intuitively expected to increase with system disorder. We derive a simple analytical expression for this dependence in the context of electronic equilibration in an amorphous molecular system model. We find that the disorder dramatically enhances the relaxation time but does not affect its independence of the nature of the initial state.

  11. Heteronuclear transverse and longitudinal relaxation in AX4 spin systems: Application to 15N relaxations in 15NH4+

    Science.gov (United States)

    Werbeck, Nicolas D.; Hansen, D. Flemming

    2014-01-01

    The equations that describe the time-evolution of transverse and longitudinal 15N magnetisations in tetrahedral ammonium ions, 15NH4+, are derived from the Bloch-Wangsness-Redfield density operator relaxation theory. It is assumed that the relaxation of the spin-states is dominated by (1) the intra-molecular 15N–1H and 1H–1H dipole–dipole interactions and (2) interactions of the ammonium protons with remote spins, which also include the contribution to the relaxations that arise from the exchange of the ammonium protons with the bulk solvent. The dipole–dipole cross-correlated relaxation mechanisms between each of the 15N–1H and 1H–1H interactions are explicitly taken into account in the derivations. An application to 15N-ammonium bound to a 41 kDa domain of the protein DnaK is presented, where a comparison between experiments and simulations show that the ammonium ion rotates rapidly within its binding site with a local correlation time shorter than approximately 1 ns. The theoretical framework provided here forms the basis for further investigations of dynamics of AX4 spin systems, with ammonium ions in solution and bound to proteins of particular interest. PMID:25128779

  12. Heteronuclear transverse and longitudinal relaxation in AX4 spin systems: application to (15)N relaxations in (15)NH4(+).

    Science.gov (United States)

    Werbeck, Nicolas D; Hansen, D Flemming

    2014-09-01

    The equations that describe the time-evolution of transverse and longitudinal (15)N magnetisations in tetrahedral ammonium ions, (15)NH4(+), are derived from the Bloch-Wangsness-Redfield density operator relaxation theory. It is assumed that the relaxation of the spin-states is dominated by (1) the intra-molecular (15)N-(1)H and (1)H-(1)H dipole-dipole interactions and (2) interactions of the ammonium protons with remote spins, which also include the contribution to the relaxations that arise from the exchange of the ammonium protons with the bulk solvent. The dipole-dipole cross-correlated relaxation mechanisms between each of the (15)N-(1)H and (1)H-(1)H interactions are explicitly taken into account in the derivations. An application to (15)N-ammonium bound to a 41kDa domain of the protein DnaK is presented, where a comparison between experiments and simulations show that the ammonium ion rotates rapidly within its binding site with a local correlation time shorter than approximately 1ns. The theoretical framework provided here forms the basis for further investigations of dynamics of AX4 spin systems, with ammonium ions in solution and bound to proteins of particular interest.

  13. Rounded stretched exponential for time relaxation functions.

    Science.gov (United States)

    Powles, J G; Heyes, D M; Rickayzen, G; Evans, W A B

    2009-12-01

    A rounded stretched exponential function is introduced, C(t)=exp{(tau(0)/tau(E))(beta)[1-(1+(t/tau(0))(2))(beta/2)]}, where t is time, and tau(0) and tau(E) are two relaxation times. This expression can be used to represent the relaxation function of many real dynamical processes, as at long times, t>tau(0), the function converges to a stretched exponential with normalizing relaxation time, tau(E), yet its expansion is even or symmetric in time, which is a statistical mechanical requirement. This expression fits well the shear stress relaxation function for model soft soft-sphere fluids near coexistence, with tau(E)Cole-Cole plots for dielectric and shear stress relaxation (both the modulus and viscosity forms). It is shown that both the dielectric spectra and dynamic shear modulus imaginary parts approach the real axis with a slope equal to 0 at high frequency, whereas the dynamic viscosity has an infinite slope in the same limit. This indicates that inertial effects at high frequency are best discerned in the modulus rather than the viscosity Cole-Cole plot. As a consequence of the even expansion in time of the shear stress relaxation function, the value of the storage modulus derived from it at very high frequency exceeds that in the infinite frequency limit (i.e., G(infinity)).

  14. Rapid parametric mapping of the longitudinal relaxation time T1 using two-dimensional variable flip angle magnetic resonance imaging at 1.5 Tesla, 3 Tesla, and 7 Tesla.

    Science.gov (United States)

    Dieringer, Matthias A; Deimling, Michael; Santoro, Davide; Wuerfel, Jens; Madai, Vince I; Sobesky, Jan; von Knobelsdorff-Brenkenhoff, Florian; Schulz-Menger, Jeanette; Niendorf, Thoralf

    2014-01-01

    Visual but subjective reading of longitudinal relaxation time (T1) weighted magnetic resonance images is commonly used for the detection of brain pathologies. For this non-quantitative measure, diagnostic quality depends on hardware configuration, imaging parameters, radio frequency transmission field (B1+) uniformity, as well as observer experience. Parametric quantification of the tissue T1 relaxation parameter offsets the propensity for these effects, but is typically time consuming. For this reason, this study examines the feasibility of rapid 2D T1 quantification using a variable flip angles (VFA) approach at magnetic field strengths of 1.5 Tesla, 3 Tesla, and 7 Tesla. These efforts include validation in phantom experiments and application for brain T1 mapping. T1 quantification included simulations of the Bloch equations to correct for slice profile imperfections, and a correction for B1+. Fast gradient echo acquisitions were conducted using three adjusted flip angles for the proposed T1 quantification approach that was benchmarked against slice profile uncorrected 2D VFA and an inversion-recovery spin-echo based reference method. Brain T1 mapping was performed in six healthy subjects, one multiple sclerosis patient, and one stroke patient. Phantom experiments showed a mean T1 estimation error of (-63±1.5)% for slice profile uncorrected 2D VFA and (0.2±1.4)% for the proposed approach compared to the reference method. Scan time for single slice T1 mapping including B1+ mapping could be reduced to 5 seconds using an in-plane resolution of (2×2) mm2, which equals a scan time reduction of more than 99% compared to the reference method. Our results demonstrate that rapid 2D T1 quantification using a variable flip angle approach is feasible at 1.5T/3T/7T. It represents a valuable alternative for rapid T1 mapping due to the gain in speed versus conventional approaches. This progress may serve to enhance the capabilities of parametric MR based lesion detection and

  15. Gadolinium oxide nanoplates with high longitudinal relaxivity for magnetic resonance imaging.

    Science.gov (United States)

    Cho, Minjung; Sethi, Richa; Narayanan, Jeyarama Subramanian Ananta; Lee, Seung Soo; Benoit, Denise N; Taheri, Nasim; Decuzzi, Paolo; Colvin, Vicki L

    2014-11-21

    Molecular-based contrast agents for magnetic resonance imaging (MRI) are often characterized by insufficient relaxivity, thus requiring the systemic injection of high doses to induce sufficient contrast enhancement at the target site. In this work, gadolinium oxide (Gd2O3) nanoplates are produced via a thermal decomposition method. The nanoplates have a core diameter varying from 2 to 22 nm, a thickness of 1 to 2 nm and are coated with either an oleic acid bilayer or an octylamine modified poly(acrylic acid) (PAA-OA) polymer layer. For the smaller nanoplates, longitudinal relaxivities (r1) of 7.96 and 47.2 (mM s)(-1) were measured at 1.41 T for the oleic acid bilayer and PAA-OA coating, respectively. These values moderately reduce as the size of the Gd2O3 nanoplates increases, and are always larger for the PAA-OA coating. Cytotoxicity studies on human dermal fibroblast cells documented no significant toxicity, with 100% cell viability preserved up to 250 μM for the PAA-OA coated Gd2O3 nanoplates. Given the 10 times increase in longitudinal relaxivity over the commercially available Gd-based molecular agents and the favorable toxicity profile, the 2 nm PAA-OA coated Gd2O3 nanoplates could represent a new class of highly effective T1 MRI contrast agents.

  16. NMR longitudinal relaxation enhancement in metal halides by heteronuclear polarization exchange during magic-angle spinning.

    Science.gov (United States)

    Shmyreva, Anna A; Safdari, Majid; Furó, István; Dvinskikh, Sergey V

    2016-06-14

    Orders of magnitude decrease of (207)Pb and (199)Hg NMR longitudinal relaxation times T1 upon magic-angle-spinning (MAS) are observed and systematically investigated in solid lead and mercury halides MeX2 (Me = Pb, Hg and X = Cl, Br, I). In lead(ii) halides, the most dramatic decrease of T1 relative to that in a static sample is in PbI2, while it is smaller but still significant in PbBr2, and not detectable in PbCl2. The effect is magnetic-field dependent but independent of the spinning speed in the range 200-15 000 Hz. The observed relaxation enhancement is explained by laboratory-frame heteronuclear polarization exchange due to crossing between energy levels of spin-1/2 metal nuclei and adjacent quadrupolar-spin halogen nuclei. The enhancement effect is also present in lead-containing organometal halide perovskites. Our results demonstrate that in affected samples, it is the relaxation data recorded under non-spinning conditions that characterize the local properties at the metal sites. A practical advantage of fast relaxation at slow MAS is that spectral shapes with orientational chemical shift anisotropy information well retained can be acquired within a shorter experimental time.

  17. Relaxation time estimation in surface NMR

    Science.gov (United States)

    Grunewald, Elliot D.; Walsh, David O.

    2017-03-21

    NMR relaxation time estimation methods and corresponding apparatus generate two or more alternating current transmit pulses with arbitrary amplitudes, time delays, and relative phases; apply a surface NMR acquisition scheme in which initial preparatory pulses, the properties of which may be fixed across a set of multiple acquisition sequence, are transmitted at the start of each acquisition sequence and are followed by one or more depth sensitive pulses, the pulse moments of which are varied across the set of multiple acquisition sequences; and apply processing techniques in which recorded NMR response data are used to estimate NMR properties and the relaxation times T.sub.1 and T.sub.2* as a function of position as well as one-dimensional and two-dimension distributions of T.sub.1 versus T.sub.2* as a function of subsurface position.

  18. Relaxation time estimation in surface NMR

    Energy Technology Data Exchange (ETDEWEB)

    Grunewald, Elliot D.; Walsh, David O.

    2017-03-21

    NMR relaxation time estimation methods and corresponding apparatus generate two or more alternating current transmit pulses with arbitrary amplitudes, time delays, and relative phases; apply a surface NMR acquisition scheme in which initial preparatory pulses, the properties of which may be fixed across a set of multiple acquisition sequence, are transmitted at the start of each acquisition sequence and are followed by one or more depth sensitive pulses, the pulse moments of which are varied across the set of multiple acquisition sequences; and apply processing techniques in which recorded NMR response data are used to estimate NMR properties and the relaxation times T.sub.1 and T.sub.2* as a function of position as well as one-dimensional and two-dimension distributions of T.sub.1 versus T.sub.2* as a function of subsurface position.

  19. Probing relaxation times in graphene quantum dots

    Science.gov (United States)

    Volk, Christian; Neumann, Christoph; Kazarski, Sebastian; Fringes, Stefan; Engels, Stephan; Haupt, Federica; Müller, André; Stampfer, Christoph

    2013-01-01

    Graphene quantum dots are attractive candidates for solid-state quantum bits. In fact, the predicted weak spin-orbit and hyperfine interaction promise spin qubits with long coherence times. Graphene quantum dots have been extensively investigated with respect to their excitation spectrum, spin-filling sequence and electron-hole crossover. However, their relaxation dynamics remain largely unexplored. This is mainly due to challenges in device fabrication, in particular concerning the control of carrier confinement and the tunability of the tunnelling barriers, both crucial to experimentally investigate decoherence times. Here we report pulsed-gate transient current spectroscopy and relaxation time measurements of excited states in graphene quantum dots. This is achieved by an advanced device design that allows to individually tune the tunnelling barriers down to the low megahertz regime, while monitoring their asymmetry. Measuring transient currents through electronic excited states, we estimate a lower bound for charge relaxation times on the order of 60–100 ns. PMID:23612294

  20. Relaxation time measurements by an electronic method.

    Science.gov (United States)

    Brousseau, R.; Vanier, J.

    1973-01-01

    Description of a simple electronic system that permits the direct measurement of time constants of decaying signals. The system was used in connection with relaxation experiments on hydrogen and rubidium masers and was found to operate well. The use of a computing counter in the systems gives the possibility of making averages on several experiments and obtaining the standard deviation of the results from the mean. The program for the computing counter is given.

  1. Nuclear magnetic relaxation induced by exchange-mediated orientational randomization: Longitudinal relaxation dispersion for a dipole-coupled spin-1/2 pair

    Science.gov (United States)

    Chang, Zhiwei; Halle, Bertil

    2013-10-01

    In complex biological or colloidal samples, magnetic relaxation dispersion (MRD) experiments using the field-cycling technique can characterize molecular motions on time scales ranging from nanoseconds to microseconds, provided that a rigorous theory of nuclear spin relaxation is available. In gels, cross-linked proteins, and biological tissues, where an immobilized macromolecular component coexists with a mobile solvent phase, nuclear spins residing in solvent (or cosolvent) species relax predominantly via exchange-mediated orientational randomization (EMOR) of anisotropic nuclear (electric quadrupole or magnetic dipole) couplings. The physical or chemical exchange processes that dominate the MRD typically occur on a time scale of microseconds or longer, where the conventional perturbation theory of spin relaxation breaks down. There is thus a need for a more general relaxation theory. Such a theory, based on the stochastic Liouville equation (SLE) for the EMOR mechanism, is available for a single quadrupolar spin I = 1. Here, we present the corresponding theory for a dipole-coupled spin-1/2 pair. To our knowledge, this is the first treatment of dipolar MRD outside the motional-narrowing regime. Based on an analytical solution of the spatial part of the SLE, we show how the integral longitudinal relaxation rate can be computed efficiently. Both like and unlike spins, with selective or non-selective excitation, are treated. For the experimentally important dilute regime, where only a small fraction of the spin pairs are immobilized, we obtain simple analytical expressions for the auto-relaxation and cross-relaxation rates which generalize the well-known Solomon equations. These generalized results will be useful in biophysical studies, e.g., of intermittent protein dynamics. In addition, they represent a first step towards a rigorous theory of water 1H relaxation in biological tissues, which is a prerequisite for unravelling the molecular basis of soft

  2. Estimation of Hot Electron Relaxation Time in GaN Using Hot Electron Transistors

    Science.gov (United States)

    Dasgupta, Sansaptak; Lu, Jing; Nidhi; Raman, Ajay; Hurni, Christophe; Gupta, Geetak; Speck, James S.; Mishra, Umesh K.

    2013-03-01

    In this paper, we report for the first time an estimation of hot electron relaxation time in GaN using electrical measurements. Hot electron transistors (HETs) with GaN as the base layer and different base-emitter barrier-height configurations and base thicknesses were fabricated. Common-base measurements were performed to extract the differential transfer ratio, and an exponential decay of the transfer ratio with increasing base thickness was observed. A hot electron mean free path was extracted from the corresponding exponential fitting and a relaxation time was computed, which, for low energy injection, matched well with theoretically predicted relaxation times based on longitudinal optical (LO) phonon scattering.

  3. RELAXATION TIME LIMITS PROBLEM FOR HYDRODYNAMIC MODELS IN SEMICONDUCTOR SCIENCE

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    In this article, two relaxation time limits, namely, the momentum relaxation time limit and the energy relaxation time limit are considered. By the compactness argument, it is obtained that the smooth solutions of the multidimensional nonisentropic Euler-Poisson problem converge to the solutions of an energy transport model or a drift diffusion model, respectively, with respect to different time scales.

  4. A theoretical and numerical consideration of the longitudinal and transverse relaxations in the rotating frame.

    Science.gov (United States)

    Murase, Kenya

    2013-11-01

    We previously derived a simple equation for solving time-dependent Bloch equations by a matrix operation. The purpose of this study was to present a theoretical and numerical consideration of the longitudinal (R1ρ=1/T1ρ) and transverse relaxation rates in the rotating frame (R2ρ=1/T2ρ), based on this method. First, we derived an equation describing the time evolution of the magnetization vector (M(t)) by expanding the matrix exponential into the eigenvalues and the corresponding eigenvectors using diagonalization. Second, we obtained the longitudinal magnetization vector in the rotating frame (M1ρ(t)) by taking the inner product of M(t) and the eigenvector with the smallest eigenvalue in modulus, and then we obtained the transverse magnetization vector in the rotating frame (M2ρ(t)) by subtracting M1ρ(t) from M(t). For comparison, we also computed the spin-locked magnetization vector. We derived the exact solutions for R1ρ and R2ρ from the eigenvalues, and compared them with those obtained numerically from M1ρ(t) and M2ρ(t), respectively. There was excellent agreement between them. From the exact solutions for R1ρ and R2ρ, R2ρ was found to be given by R2ρ=(2R2+R1)/2-R1ρ/2, where R1 and R2 denote the conventional longitudinal and transverse relaxation rates, respectively. We also derived M1ρ(t) and M2ρ(t) for bulk water protons, in which the effect of chemical exchange was taken into account using a 2-pool chemical exchange model, and we compared the R1ρ and R2ρ values obtained from the eigenvalues and those obtained numerically from M1ρ(t) and M2ρ(t). There was also excellent agreement between them. In conclusion, this study will be useful for better understanding of the longitudinal and transverse relaxations in the rotating frame and for analyzing the contrast mechanisms in T1ρ- and T2ρ-weighted MRI.

  5. First Passage Times, Lifetimes, and Relaxation Times of Unfolded Proteins

    Science.gov (United States)

    Dai, Wei; Sengupta, Anirvan M.; Levy, Ronald M.

    2015-01-01

    The dynamics of proteins in the unfolded state can be quantified in computer simulations by calculating a spectrum of relaxation times which describes the time scales over which the population fluctuations decay to equilibrium. If the unfolded state space is discretized we can evaluate the relaxation time of each state. We derive a simple relation that shows the mean first passage time to any state is equal to the relaxation time of that state divided by the equilibrium population. This explains why mean first passage times from state to state within the unfolded ensemble can be very long but the energy landscape can still be smooth (minimally frustrated). In fact, when the folding kinetics is two-state, all of the unfolded state relaxation times within the unfolded free energy basin are faster than the folding time. This result supports the well-established funnel energy landscape picture and resolves an apparent contradiction between this model and the recently proposed kinetic hub model of protein folding. We validate these concepts by analyzing a Markov State Model of the kinetics in the unfolded state and folding of the mini-protein NTL9 constructed from a 2.9 millisecond simulation provided by D. E. Shaw Research. PMID:26252709

  6. Gadolinium oxide nanoplates with high longitudinal relaxivity for magnetic resonance imaging

    Science.gov (United States)

    Cho, Minjung; Sethi, Richa; Ananta Narayanan, Jeyarama Subramanian; Lee, Seung Soo; Benoit, Denise N.; Taheri, Nasim; Decuzzi, Paolo; Colvin, Vicki L.

    2014-10-01

    Molecular-based contrast agents for magnetic resonance imaging (MRI) are often characterized by insufficient relaxivity, thus requiring the systemic injection of high doses to induce sufficient contrast enhancement at the target site. In this work, gadolinium oxide (Gd2O3) nanoplates are produced via a thermal decomposition method. The nanoplates have a core diameter varying from 2 to 22 nm, a thickness of 1 to 2 nm and are coated with either an oleic acid bilayer or an octylamine modified poly(acrylic acid) (PAA-OA) polymer layer. For the smaller nanoplates, longitudinal relaxivities (r1) of 7.96 and 47.2 (mM s)-1 were measured at 1.41 T for the oleic acid bilayer and PAA-OA coating, respectively. These values moderately reduce as the size of the Gd2O3 nanoplates increases, and are always larger for the PAA-OA coating. Cytotoxicity studies on human dermal fibroblast cells documented no significant toxicity, with 100% cell viability preserved up to 250 μM for the PAA-OA coated Gd2O3 nanoplates. Given the 10 times increase in longitudinal relaxivity over the commercially available Gd-based molecular agents and the favorable toxicity profile, the 2 nm PAA-OA coated Gd2O3 nanoplates could represent a new class of highly effective T1 MRI contrast agents.Molecular-based contrast agents for magnetic resonance imaging (MRI) are often characterized by insufficient relaxivity, thus requiring the systemic injection of high doses to induce sufficient contrast enhancement at the target site. In this work, gadolinium oxide (Gd2O3) nanoplates are produced via a thermal decomposition method. The nanoplates have a core diameter varying from 2 to 22 nm, a thickness of 1 to 2 nm and are coated with either an oleic acid bilayer or an octylamine modified poly(acrylic acid) (PAA-OA) polymer layer. For the smaller nanoplates, longitudinal relaxivities (r1) of 7.96 and 47.2 (mM s)-1 were measured at 1.41 T for the oleic acid bilayer and PAA-OA coating, respectively. These values

  7. Internal relaxation time in immersed particulate materials

    CERN Document Server

    Rognon, P; Gay, C

    2009-01-01

    We study the dynamics of the solid to liquid transition for a model material made of elastic particles immersed in a viscous fluid. The interaction between particle surfaces includes their viscous lubrication, a sharp repulsion when they get closer than a tuned steric length and their elastic deflection induced by those two forces. We use Soft Dynamics to simulate the dynamics of this material when it experiences a step increase in the shear stress and a constant normal stress. We observe a long creep phase before a substantial flow eventually establishes. We find that the typical creep time relies on an internal relaxation process, namely the separation of two particles driven by the applied stress and resisted by the viscous friction. This mechanism should be relevant for granular pastes, living cells, emulsions and wet foams.

  8. Effects of relaxed static longitudinal stability on a single-stage-to-orbit vehicle design

    Science.gov (United States)

    Freeman, D. C., Jr.; Wilhite, A. W.

    1979-01-01

    The effects of relaxing longitudinal stability requirements on single stage to orbit space vehicles is studied. A comparison of the mass and performance characteristics of two vehicles, one designed for positive levels of longitudinal stability and the other designed with relaxed stability requirements in a computer aided design process is presented. Both vehicles, required to meet the same mission characteristics are described. Wind tunnel tests, conducted over a Mach number range from 0.3 to 4.63 to verify estimated aerodynamic characteristics, are discussed.

  9. Ultrafast NMR T1 relaxation measurements: probing molecular properties in real time.

    Science.gov (United States)

    Smith, Pieter E S; Donovan, Kevin J; Szekely, Or; Baias, Maria; Frydman, Lucio

    2013-09-16

    The longitudinal relaxation properties of NMR active nuclei carry useful information about the site-specific chemical environments and about the mobility of molecular fragments. Molecular mobility is in turn a key parameter reporting both on stable properties, such as size, as well as on dynamic ones, such as transient interactions and irreversible aggregation. In order to fully investigate the latter, a fast sampling of the relaxation parameters of transiently formed molecular species may be needed. Nevertheless, the acquisition of longitudinal relaxation data is typically slow, being limited by the requirement that the time for which the nucleus relaxes be varied incrementally until a complete build-up curve is generated. Recently, a number of single-shot-inversion-recovery methods have been developed capable of alleviating this need; still, these may be challenged by either spectral resolution restrictions or when coping with very fast relaxing nuclei. Here, we present a new experiment to measure the T1s of multiple nuclear spins that experience fast longitudinal relaxation, while retaining full high-resolution chemical shift information. Good agreement is observed between T1s measured with conventional means and T1s measured using the new technique. The method is applied to the real-time investigation of the reaction between D-xylose and sodium borate, which is in turn elucidated with the aid of ancillary ultrafast and conventional 2D TOCSY measurements. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Immersed boundary lattice Boltzmann model based on multiple relaxation times.

    Science.gov (United States)

    Lu, Jianhua; Han, Haifeng; Shi, Baochang; Guo, Zhaoli

    2012-01-01

    As an alterative version of the lattice Boltzmann models, the multiple relaxation time (MRT) lattice Boltzmann model introduces much less numerical boundary slip than the single relaxation time (SRT) lattice Boltzmann model if some special relationship between the relaxation time parameters is chosen. On the other hand, most current versions of the immersed boundary lattice Boltzmann method, which was first introduced by Feng and improved by many other authors, suffer from numerical boundary slip as has been investigated by Le and Zhang. To reduce such a numerical boundary slip, an immerse boundary lattice Boltzmann model based on multiple relaxation times is proposed in this paper. A special formula is given between two relaxation time parameters in the model. A rigorous analysis and the numerical experiments carried out show that the numerical boundary slip reduces dramatically by using the present model compared to the single-relaxation-time-based model.

  11. Longitudinal spin relaxation of donor-bound electrons in direct band-gap semiconductors

    Science.gov (United States)

    Linpeng, Xiayu; Karin, Todd; Durnev, M. V.; Barbour, Russell; Glazov, M. M.; Sherman, E. Ya.; Watkins, S. P.; Seto, Satoru; Fu, Kai-Mei C.

    2016-09-01

    We measure the donor-bound electron longitudinal spin-relaxation time (T1) as a function of magnetic field (B ) in three high-purity direct band-gap semiconductors: GaAs, InP, and CdTe, observing a maximum T1 of 1.4, 0.4, and 1.2 ms, respectively. In GaAs and InP at low magnetic field, up to ˜2 T, the spin-relaxation mechanism is strongly density and temperature dependent and is attributed to the random precession of the electron spin in hyperfine fields caused by the lattice nuclear spins. In all three semiconductors at high magnetic field, we observe a power-law dependence T1∝B-ν with 3 ≲ν ≲4 . Our theory predicts that the direct spin-phonon interaction is important in all three materials in this regime in contrast to quantum dot structures. In addition, the "admixture" mechanism caused by Dresselhaus spin-orbit coupling combined with single-phonon processes has a comparable contribution in GaAs. We find excellent agreement between high-field theory and experiment for GaAs and CdTe with no free parameters, however a significant discrepancy exists for InP.

  12. General Solution to Gradient Induced Transverse and Longitudinal Relaxation of Spins Undergoing Restricted Diffusion

    CERN Document Server

    Zheng, W; Liu, J -G; Zhang, Y; Ye, Q; Swank, C; 10.1103/PhysRevA.84.053411

    2012-01-01

    We develop an approach, by calculating the autocorrelation function of spins, to derive the magnetic field gradient induced transverse ($T_2$) relaxation of spins undergoing restricted diffusion. This approach is an extension to the method adopted by McGregor. McGregor's approach solves the problem only in the fast diffusion limit; however, our approach yields a single analytical solution suitable in all diffusion regimes, including the intermediate regime. This establishes a direct connection between the well-known Torrey's slow diffusion result and the fast diffusion result. We also perform free induction decay measurements on spin-exchange optically polarized $^3$He gas with different diffusion constants. The transverse relaxation profiles are compared with the theory and satisfactory agreement has been found throughout all diffusion regimes. In addition to the transverse relaxation, this approach is also applicable to solving the longitudinal relaxation ($T_1$) regardless of the diffusion limits. It turns...

  13. In Vitro Longitudinal Relaxivity Profile of Gd(ABE-DTTA, an Investigational Magnetic Resonance Imaging Contrast Agent.

    Directory of Open Access Journals (Sweden)

    Akos Varga-Szemes

    Full Text Available MRI contrast agents (CA whose contrast enhancement remains relatively high even at the higher end of the magnetic field strength range would be desirable. The purpose of this work was to demonstrate such a desired magnetic field dependency of the longitudinal relaxivity for an experimental MRI CA, Gd(ABE-DTTA.The relaxivity of 0.5mM and 1mM Gd(ABE-DTTA was measured by Nuclear Magnetic Relaxation Dispersion (NMRD in the range of 0.0002 to 1T. Two MRI and five NMR instruments were used to cover the range between 1.5 to 20T. Parallel measurement of a Gd-DTPA sample was performed throughout as reference. All measurements were carried out at 37°C and pH 7.4.The relaxivity values of 0.5mM and 1mM Gd(ABE-DTTA measured at 1.5, 3, and 7T, within the presently clinically relevant magnetic field range, were 15.3, 11.8, 12.4 s-1mM-1 and 18.1, 16.7, and 13.5 s-1mM-1, respectively. The control 4 mM Gd-DTPA relaxivities at the same magnetic fields were 3.6, 3.3, and 3.0 s-1mM-1, respectively.The longitudinal relaxivity of Gd(ABE-DTTA measured within the presently clinically relevant field range is three to five times higher than that of most commercially available agents. Thus, Gd(ABE-DTTA could be a practical choice at any field strength currently used in clinical imaging including those at the higher end.

  14. Quantitative Measurement of Longitudinal and Transverse Cross-Relaxation Rates: An Application to the Analysis of the Internal Dynamics of Ranalexin in Water and Trifluoroethanol

    Science.gov (United States)

    Malliavin, T. E.; Desvaux, H.; Aumelas, A.; Chavanieu, A.; Delsuc, M. A.

    1999-09-01

    We describe a quantitative processing method which gives access to the longitudinal and transverse cross-relaxation rates from off-resonance ROESY intensities. This method takes advantage of the dependence of the off-resonance ROESY experiments at any mixing time and any spin-lock angle θ on two relaxation matrices, the longitudinal and the transverse ones. This allows one to take into account multistep magnetization transfers even if the measurements are performed only at one or two mixing times. The ratio of the longitudinal to transverse cross-relaxation rates can then be used as a local indicator of the internal dynamics, without assuming a structure or a model of motion. After validation of this processing method by numerical simulations, it is applied to the analysis of the dynamics of the peptide ranalexin dissolved in pure water and in water/TFE.

  15. Time scales of relaxation dynamics during transient conditions in two-phase flow: RELAXATION DYNAMICS

    Energy Technology Data Exchange (ETDEWEB)

    Schlüter, Steffen [School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis Oregon USA; Department Soil Physics, Helmholtz-Centre for Environmental Research-UFZ, Halle Germany; Berg, Steffen [Shell Global Solutions International B.V., Rijswijk Netherlands; Li, Tianyi [School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis Oregon USA; Vogel, Hans-Jörg [Department Soil Physics, Helmholtz-Centre for Environmental Research-UFZ, Halle Germany; Institut für Agrar- und Ernährungswissenschaften, Martin-Luther-Universität Halle-Wittenberg, Halle Germany; Wildenschild, Dorthe [School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis Oregon USA

    2017-06-01

    The relaxation dynamics toward a hydrostatic equilibrium after a change in phase saturation in porous media is governed by fluid reconfiguration at the pore scale. Little is known whether a hydrostatic equilibrium in which all interfaces come to rest is ever reached and which microscopic processes govern the time scales of relaxation. Here we apply fast synchrotron-based X-ray tomography (X-ray CT) to measure the slow relaxation dynamics of fluid interfaces in a glass bead pack after fast drainage of the sample. The relaxation of interfaces triggers internal redistribution of fluids, reduces the surface energy stored in the fluid interfaces, and relaxes the contact angle toward the equilibrium value while the fluid topology remains unchanged. The equilibration of capillary pressures occurs in two stages: (i) a quick relaxation within seconds in which most of the pressure drop that built up during drainage is dissipated, a process that is to fast to be captured with fast X-ray CT, and (ii) a slow relaxation with characteristic time scales of 1–4 h which manifests itself as a spontaneous imbibition process that is well described by the Washburn equation for capillary rise in porous media. The slow relaxation implies that a hydrostatic equilibrium is hardly ever attained in practice when conducting two-phase experiments in which a flux boundary condition is changed from flow to no-flow. Implications for experiments with pressure boundary conditions are discussed.

  16. Reactor flush time correction in relaxation experiments

    NARCIS (Netherlands)

    den Otter, M.W.; Bouwmeester, Henricus J.M.; Boukamp, Bernard A.; Verweij, H.

    2001-01-01

    The present paper deals with the analysis of experimental data from conductivity relaxation experiments. It is shown that evaluation of the chemical diffusion and surface transfer coefficients for oxygen by use of this technique is possible only if accurate data for the conductivity transient can be

  17. Determination of Relaxation Time of a Josephson Tunnel Junction

    Institute of Scientific and Technical Information of China (English)

    WEN Xue-Da; YU Yang

    2008-01-01

    We propose a non-stationary method to measure the energy relaxation time of Josephson tunnel junctions from microwave enhanced escape phenomena.Compared with the previous methods,our method possesses simple and accurate features.Moreover,having determined the energy relaxation time,we can further obtain the coupling strength between the microwave source and the junction by changing the microwave power.

  18. Correlation of transverse relaxation time with structure of biological tissue

    Science.gov (United States)

    Furman, Gregory B.; Meerovich, Victor M.; Sokolovsky, Vladimir L.

    2016-09-01

    Transverse spin-spin relaxation of liquids entrapped in nanocavities with different orientational order is theoretically investigated. Based on the bivariate normal distribution of nanocavities directions, we have calculated the anisotropy of the transverse relaxation time for biological systems, such as collagenous tissues, articular cartilage, and tendon. In the framework of the considered model, the dipole-dipole interaction is determined by a single coupling constant. The calculation results for the transverse relaxation time explain the angular dependence observed in MRI experiments with biological objects. The good agreement with the experimental data is obtained by adjustment of only one parameter which characterizes the disorder in fiber orientations. The relaxation time is correlated with the degree of ordering in biological tissues. Thus, microstructure of the tissues can be revealed from the measurement of relaxation time anisotropy. The clinical significance of the correlation, especially in the detection of damage must be evaluated in a large prospective clinical trials.

  19. Anomalous longitudinal relaxation of nuclear spins in CaF{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Kropf, Chahan M. [Institute of Physics, University of Freiburg, Hermann-Herder-Str. 3, D-79104, Freiburg (Germany); Kohlrautz, Jonas; Haase, Juergen [University of Leipzig, Faculty of Physics and Earth Sciences, Linnestr. 5, 04103, Leipzig (Germany); Fine, Boris V. [Skolkovo Institute of Science and Technology, 100 Novaya Str., Skolkovo, Moscow Region, 143025 (Russian Federation); Institute for Theoretical Physics, University of Heidelberg, Philosophenweg 12, 69120, Heidelberg (Germany)

    2017-06-15

    We consider the effect of non-secular resonances for interacting nuclear spins in solids which were predicted theoretically to exist in the presence of strong static and strong radio-frequency magnetic fields. These resonances imply corrections to the standard secular approximation for the nuclear spin-spin interaction in solids, which, in turn, should lead to an anomalous longitudinal relaxation in nuclear magnetic resonance experiments. In this article, we investigate the feasibility of the experimental observation of this anomalous longitudinal relaxation in calcium fluoride (CaF{sub 2}) and conclude that such an observation is realistic. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  20. Chemical relaxation times in a hadron gas at finite temperature

    CERN Document Server

    Goity, J L

    1993-01-01

    The relaxation times of particle numbers in hot hadronic matter with vanishing baryon number are estimated using the ideal gas approximation and taking into account resonance decays and annihilation processes as the only sources of particle number fluctuations. Near the QCD critical temperature the longest relaxation times turn out to be of the order of 10 fm and grow roughly exponentially to become of the order of $10^{3}$ fm at temperatures around 100 MeV. As a consequence of such long relaxation times, a clear departure from chemical equilibrium must be observed in the momentum distribution of secondary particles produced in high energy nuclear collisions.

  1. Real-time Relaxation of Condensates and Kinetics in Hot Scalar QED Landau Damping

    CERN Document Server

    Boyanovsky, D; Holman, R; Kumar, S P; Pisarski, R D; Boyanovsky, Daniel; Vega, Hector J. de; Holman, Richard; Pisarski, Robert D.

    1998-01-01

    The real time evolution of field condensates with soft length scales k^{-1}>(eT)^{-1} is solved in hot scalar electrodynamics. We rederive the HTL effective action using the techniques of non-equilibrium field theory for small amplitude condensates. We find that transverse gauge invariant condensates relax as 1/t^2 and longitudinal condensates associated with plasmon (charge density) excitations relax with 1/[t log^2 t ] behavior to asymptotic amplitudes that are determined by the quasiparticle poles. The relaxational dynamics and relevant time scales are determined by the global analytic structure of the retarded propagators. To leading order, the long-time behaviour is determined by the Landau discontinuities associated with off-shell processes. Landau damping follows from the contribution of such discontinuities. We derive the influence functional for the soft (gauge invariant) degrees of freedom by integrating out the hard scales in the HTL approximation and obtain consistently the Langevin equation, the ...

  2. Immersed Boundary-Lattice Boltzmann Method Using Two Relaxation Times

    Directory of Open Access Journals (Sweden)

    Kosuke Hayashi

    2012-06-01

    Full Text Available An immersed boundary-lattice Boltzmann method (IB-LBM using a two-relaxation time model (TRT is proposed. The collision operator in the lattice Boltzmann equation is modeled using two relaxation times. One of them is used to set the fluid viscosity and the other is for numerical stability and accuracy. A direct-forcing method is utilized for treatment of immersed boundary. A multi-direct forcing method is also implemented to precisely satisfy the boundary conditions at the immersed boundary. Circular Couette flows between a stationary cylinder and a rotating cylinder are simulated for validation of the proposed method. The method is also validated through simulations of circular and spherical falling particles. Effects of the functional forms of the direct-forcing term and the smoothed-delta function, which interpolates the fluid velocity to the immersed boundary and distributes the forcing term to fixed Eulerian grid points, are also examined. As a result, the following conclusions are obtained: (1 the proposed method does not cause non-physical velocity distribution in circular Couette flows even at high relaxation times, whereas the single-relaxation time (SRT model causes a large non-physical velocity distortion at a high relaxation time, (2 the multi-direct forcing reduces the errors in the velocity profile of a circular Couette flow at a high relaxation time, (3 the two-point delta function is better than the four-point delta function at low relaxation times, but worse at high relaxation times, (4 the functional form of the direct-forcing term does not affect predictions, and (5 circular and spherical particles falling in liquids are well predicted by using the proposed method both for two-dimensional and three-dimensional cases.

  3. Increasing the sensitivity of NMR diffusion measurements by paramagnetic longitudinal relaxation enhancement, with application to ribosome–nascent chain complexes

    Energy Technology Data Exchange (ETDEWEB)

    Chan, Sammy H. S.; Waudby, Christopher A.; Cassaignau, Anaïs M. E.; Cabrita, Lisa D.; Christodoulou, John, E-mail: j.christodoulou@ucl.ac.uk [University College London and Birkbeck College, Institute of Structural and Molecular Biology (United Kingdom)

    2015-10-15

    The translational diffusion of macromolecules can be examined non-invasively by stimulated echo (STE) NMR experiments to accurately determine their molecular sizes. These measurements can be important probes of intermolecular interactions and protein folding and unfolding, and are crucial in monitoring the integrity of large macromolecular assemblies such as ribosome–nascent chain complexes (RNCs). However, NMR studies of these complexes can be severely constrained by their slow tumbling, low solubility (with maximum concentrations of up to 10 μM), and short lifetimes resulting in weak signal, and therefore continuing improvements in experimental sensitivity are essential. Here we explore the use of the paramagnetic longitudinal relaxation enhancement (PLRE) agent NiDO2A on the sensitivity of {sup 15}N XSTE and SORDID heteronuclear STE experiments, which can be used to monitor the integrity of these unstable complexes. We exploit the dependence of the PLRE effect on the gyromagnetic ratio and electronic relaxation time to accelerate recovery of {sup 1}H magnetization without adversely affecting storage on N{sub z} during diffusion delays or introducing significant transverse relaxation line broadening. By applying the longitudinal relaxation-optimized SORDID pulse sequence together with NiDO2A to 70S Escherichia coli ribosomes and RNCs, NMR diffusion sensitivity enhancements of up to 4.5-fold relative to XSTE are achieved, alongside ∼1.9-fold improvements in two-dimensional NMR sensitivity, without compromising the sample integrity. We anticipate these results will significantly advance the use of NMR to probe dynamic regions of ribosomes and other large, unstable macromolecular assemblies.Graphical Abstract.

  4. Ice sheet growth with laterally varying bedrock relaxation time

    Science.gov (United States)

    van der Wal, Wouter; Vizcaino Rubio, Pablo; De Boer, Bas; van de Wal, Roderik

    2017-04-01

    Isostatic response of the bedrock, or glacial isostatic adjustment (GIA) in included in most ice sheet models. This is important because the surface elevation determines the mass balance and thereby implicitly also the strength of the mass balance feedback where higher surface elevation yields lower temperatures implying less melt and vice versa. Usually a single relaxation time or a set of relaxation times is used to model the response everywhere on Earth or at least for an entire ice sheet. In reality the viscosity in the Earth's mantle, and hence the relaxation time experienced by the ice, varies with location. Seismic studies indicate that several regions that were covered by ice during the last glacial cycle are underlain by mantle in which viscosity varies with orders of magnitude, such as Antarctica and North America. The question is whether such a variation of viscosity influences ice evolution. Several GIA models exist that can deal with 3D viscosity, but their large computation times make it nearly impossible to couple them to ice sheet models. Here we use the ANICE ice-sheet model (de Boer et al. 2013) with a simple bedrock-relaxation model in which a different relaxation time is used for separate regions. A temperature anomaly is applied to grow a schematic ice sheet on a flat earth, with other forcing mechanisms neglected. It is shown that in locations with a fast relaxation time of 300 years the equilibrium ice sheet is significantly thinner and narrower but also ice thickness in neighbouring regions (with the more standard relaxation time of 3000 years) is affected.

  5. Mindfulness meditation and relaxation training increases time sensitivity.

    Science.gov (United States)

    Droit-Volet, S; Fanget, M; Dambrun, M

    2015-01-01

    Two experiments examined the effect of mindfulness meditation and relaxation on time perception using a temporal bisection task. In Experiment 1, the participants performed a temporal task before and after exercises of mindfulness meditation or relaxation. In Experiment 2, the procedure was similar than that used in Experiment 1, except that the participants were trained to mediate or relax every day over a period of several weeks. The results showed that mindfulness meditation exercises increased sensitivity to time and lengthened perceived time. However, this temporal improvement with meditation exercises was primarily observed in the experienced meditators. Our results also showed the experienced meditators were less anxious than the novice participants, and that the sensitivity to time increased when the level of anxiety decreased. Our results were explained by the practice of mindfulness technique that had developed individuals' abilities in devoting more attention resources to temporal information processing.

  6. Electron-phonon relaxation time in ultrathin tungsten silicon film

    CERN Document Server

    Sidorova, M; Korneev, A; Chulkova, G; Korneeva, Yu; Mikhailov, M; Devizenko, Yu; Kozorezov, A; Goltsman, G

    2016-01-01

    Using amplitude-modulated absorption of sub-THz radiation (AMAR) method, we studied electron-phonon relaxation in thin disordered films of tungsten silicide. We found a response time ~ 800 ps at critical temperature Tc = 3.4 K, which scales as minus 3 in the temperature range from 1.8 to 3.4 K. We discuss mechanisms, which can result in a strong phonon bottle-neck effect in a few nanometers thick film and yield a substantial difference between the measured time, characterizing response at modulation frequency, and the inelastic electron-phonon relaxation time. We estimate the electron-phonon relaxation time to be in the range ~ 100-200 ps at 3.4 K.

  7. Parameterization of NMR relaxation curves in terms of logarithmic moments of the relaxation time distribution

    Science.gov (United States)

    Petrov, Oleg V.; Stapf, Siegfried

    2017-06-01

    This work addresses the problem of a compact and easily comparable representation of multi-exponential relaxation data. It is often convenient to describe such data in a few parameters, all being of physical significance and easy to interpret, and in such a way that enables a model-free comparison between different groups of samples. Logarithmic moments (LMs) of the relaxation time constitute a set of parameters which are related to the characteristic relaxation time on the log-scale, the width and the asymmetry of an underlying distribution of exponentials. On the other hand, the calculation of LMs does not require knowing the actual distribution function and is reduced to a numerical integration of original data. The performance of this method has been tested on both synthetic and experimental NMR relaxation data which differ in a signal-to-noise ratio, the sampling range and the sampling rate. The calculation of two lower-order LMs, the log-mean time and the log-variance, has proved robust against deficiencies of the experiment such as scattered data point and incomplete sampling. One may consider using them as such to monitor formation of a heterogeneous structure, e.g., in phase separation, vitrification, polymerization, hydration, aging, contrast agent propagation processes. It may also assist in interpreting frequency and temperature dependences of relaxation, revealing a crossover from slow to fast exchange between populations. The third LM was found to be a less reliable quantity due to its susceptibility to the noise and must be used with caution.

  8. Experimental study on relaxation time in direction changing movement

    Science.gov (United States)

    Liu, Chi; Song, Weiguo; Fu, Libi; Lian, Liping; Lo, Siuming

    2017-02-01

    Controlled experiments were conducted to clarify the movement characteristics of pedestrians in direction changing processes. We track pedestrians' trajectories and map them into real space coordinates by the direct linear transformation method. In the acceleration process, the relaxation time and free moving speed in our experiments respectively equal 0.659 s and 1.540 m/s, which are consistent with those for Chinese participants in other experiments. Meanwhile, the values of relaxation time in the direction changing process are calculated by a derived equation from the concept of the social force model. It is observed that the relaxation time is not an invariable parameter, and tends to increase with an increase in the angular difference. Furthermore, results show that pedestrians are insensitive to a tiny angular difference between instantaneous velocity and desired velocity. These experimental results presented in this work can be applied in model development and validation.

  9. Longitudinal relaxation in dipole-coupled homonuclear three-spin systems: Distinct correlations and odd spectral densities

    Science.gov (United States)

    Chang, Zhiwei; Halle, Bertil

    2015-12-01

    A system of three dipole-coupled spins exhibits a surprisingly intricate relaxation behavior. Following Hubbard's pioneering 1958 study, many authors have investigated different aspects of this problem. Nevertheless, on revisiting this classic relaxation problem, we obtain several new results, some of which are at variance with conventional wisdom. Most notably from a fundamental point of view, we find that the odd-valued spectral density function influences longitudinal relaxation. We also show that the effective longitudinal relaxation rate for a non-isochronous three-spin system can exhibit an unusual inverted dispersion step. To clarify these and other issues, we present a comprehensive theoretical treatment of longitudinal relaxation in a three-spin system of arbitrary geometry and with arbitrary rotational dynamics. By using the Liouville-space formulation of Bloch-Wangsness-Redfield theory and a basis of irreducible spherical tensor operators, we show that the number of relaxation components in the different cases can be deduced from symmetry arguments. For the isochronous case, we present the relaxation matrix in analytical form, whereas, for the non-isochronous case, we employ a computationally efficient approach based on the stochastic Liouville equation.

  10. Longitudinal relaxation in dipole-coupled homonuclear three-spin systems: Distinct correlations and odd spectral densities

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Zhiwei; Halle, Bertil, E-mail: bertil.halle@bpc.lu.se [Department of Chemistry, Division of Biophysical Chemistry, Lund University, P.O. Box 124, SE-22100 Lund (Sweden)

    2015-12-21

    A system of three dipole-coupled spins exhibits a surprisingly intricate relaxation behavior. Following Hubbard’s pioneering 1958 study, many authors have investigated different aspects of this problem. Nevertheless, on revisiting this classic relaxation problem, we obtain several new results, some of which are at variance with conventional wisdom. Most notably from a fundamental point of view, we find that the odd-valued spectral density function influences longitudinal relaxation. We also show that the effective longitudinal relaxation rate for a non-isochronous three-spin system can exhibit an unusual inverted dispersion step. To clarify these and other issues, we present a comprehensive theoretical treatment of longitudinal relaxation in a three-spin system of arbitrary geometry and with arbitrary rotational dynamics. By using the Liouville-space formulation of Bloch-Wangsness-Redfield theory and a basis of irreducible spherical tensor operators, we show that the number of relaxation components in the different cases can be deduced from symmetry arguments. For the isochronous case, we present the relaxation matrix in analytical form, whereas, for the non-isochronous case, we employ a computationally efficient approach based on the stochastic Liouville equation.

  11. The short-time intramolecular dynamics of solutes in liquids. II. Vibrational population relaxation

    Science.gov (United States)

    Goodyear, Grant; Stratt, Richard M.

    1997-08-01

    Events such as the vibrational relaxation of a solute are often well described by writing an effective equation of motion—a generalized Langevin equation—which expresses the surrounding medium's influence on the intramolecular dynamics in terms of a friction and a fluctuating force acting on the solute. These quantities, though, can be obtained from the instantaneous normal modes (INMs) of the system when the relaxation takes place in a fluid, suggesting that we should be able to analyze in some detail the solvent motions driving the relaxation, at least for short times. In this paper we show that this promise can indeed be realized for the specific case of a vibrating diatomic molecule dissolved in an atomic solvent. Despite the relatively long times typical of vibrational population relaxation, it turns out that understanding the behavior of the vibrational friction at the short times appropriate to INMs (a few hundred femtoseconds) often suffices to predict T1 times. We use this observation to probe the dependence of these relaxation rates on thermodynamic conditions and to look at the molecular mechanisms underlying the process. We find that raising the temperature at any given density or raising the density at any given temperature will invariably increase the rate of energy relaxation. However, since these two trends may be in conflict in a typical constant-pressure laboratory experiment, we also find that it is possible to make sense of the "anomalous" inverted temperature dependence recently seen experimentally. We find, as well, that the INM theory—which has no explicit collisions built into it—predicts exactly the same density dependence as the venerable independent-binary-collision (IBC) theory (an intriguing result in view of recent claims that experimental observations of this kind of dependence provide support for the IBC theory). The actual mechanisms behind vibrational population relaxation are revealed by looking in detail at the

  12. Magnetic resonance spectroscopy in vivo of neurochemicals in a transgenic model of Alzheimer's disease: a longitudinal study of metabolites, relaxation time, and behavioral analysis in TASTPM and wild-type mice.

    Science.gov (United States)

    Forster, Duncan; Davies, Karen; Williams, Steve

    2013-04-01

    Alzheimer's disease (AD) is the most common form of dementia in the elderly. Due to ongoing advances in our understanding of the underlying pathology of AD, many potential new targets for therapeutics are becoming available. Transgenic mouse models of AD have helped in furthering our understanding of AD and also provide a vehicle for preclinical testing of new, putative disease-modifying therapeutics, which may have potential for translation to use in clinical trials. To identify possible translational biomarkers, we have studied the longitudinal cerebral metabolic pattern of the TASTPM transgenic AD mouse, a double transgenic mouse overexpressing human mutant amyloid precursor protein (hAPP695swe) and presenilin-1 (M146V) by (1) H magnetic resonance spectroscopy, along with concurrent brain T1 /T2 mapping and behavioral testing. We found significant differences in creatine, glutamate, N-acetylaspartate, choline-containing compounds, and myo-inositol between TASTPM and wild-type mice. In the case of N-acetylaspartate and myo-inositol, there were similarities to differences detected in human AD. T1 /T2 values were shorter overall in TASTPM mice, indicating possible differences in water content between TASTPM and wild-type mice. In older TASTPM mice, exploratory behavior became more random, indicating a possible memory deficiency. The decrease in behavioral performance correlated in the transgenic group with higher expression of myo-inositol. Copyright © 2012 Wiley Periodicals, Inc.

  13. Relaxation Characteristics of 828 DGEBA Epoxy Over Long Time Periods

    Science.gov (United States)

    Hoo, Jasmine; Reprogle, Riley C.; Wisler, Brian; Arechederra, Gabriel K.; McCoy, John D.; Kropka, Jamie M.; Long, Kevin N.

    The mechanical relaxation response in uniaxial compression of a diglycidyl ether of bisphenol-A epoxy was studied over long time periods. The epoxy, 828DEA, was Epon 828 cured with diethanolamine (DEA). A sample was compressed at constant strain rate and held at various strain levels for days to allow the sample to relax. The sample was then compressed further and held once more. The relaxation curves were fit with a stretched exponential function. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  14. Distribution of relaxation times of relaxors: comparison with dipolar glasses

    Energy Technology Data Exchange (ETDEWEB)

    Banys, Juras; Grigalaitis, Robertas; Mikonis, Andrejus; Keburis, Povilas [Faculty of Physics, Vilnius University, Sauletekio 9, 10222 Vilnius (Lithuania); Macutkevic, Jan [Semiconductor Physics Institute, A. Gostauto 11, 01108 Vilnius (Lithuania)

    2009-12-15

    In the present publication we report the results of dielectric spectroscopy investigations of two classes of materials - relaxor and dipolar glasses. As model relaxor was chosen (Pb{sub 1-x}La{sub x})(Zr{sub y}Ti{sub 1-y})O{sub 3} (PLZT 100(x/y/1-y)). The real distribution function of the relaxation times f ({tau}) of the relaxor ferroelectric ceramics PLZT 8/65/35 and 9.5/65/35 was calculated from the dielectric measurements results in the wide frequency range (10{sup 1}-10{sup 12} Hz). Below the Burns temperature T{sub B} {approx_equal} 620 K, when the clusters begin to appear on cooling, the distribution function of the relaxation times is symmetrically shaped. On cooling the dispersion and loss spectra strongly broaden and slow down, the f ({tau}) function becomes asymmetrically shaped and the second maximum appears. The width of the f ({tau}) function was calculated at different temperatures. The longest relaxation times diverge according to the Vogel-Fulcher law with the freezing temperature 299 K and 252 K for the 8/65/35 and 9.5/65/35 samples, respectively. The shortest relaxation time is about 10{sup -12} s and it remains almost temperature independent. Similar behaviour was observed in dipolar glasses betaine phosphate betaine phosphite (BP/BPI). Much more information was obtained from two dimensional distribution of the relaxation times. This confirmed Meyer-Neldel law in relaxors and dipolar glasses. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  15. Inversion of generalized relaxation time distributions with optimized damping parameter

    Science.gov (United States)

    Florsch, Nicolas; Revil, André; Camerlynck, Christian

    2014-10-01

    Retrieving the Relaxation Time Distribution (RDT), the Grains Size Distribution (GSD) or the Pore Size Distribution (PSD) from low-frequency impedance spectra is a major goal in geophysics. The “Generalized RTD” generalizes parametric models like Cole-Cole and many others, but remains tricky to invert since this inverse problem is ill-posed. We propose to use generalized relaxation basis function (for instance by decomposing the spectra on basis of generalized Cole-Cole relaxation elements instead of the classical Debye basis) and to use the L-curve approach to optimize the damping parameter required to get smooth and realistic inverse solutions. We apply our algorithm to three examples, one synthetic and two real data sets, and the program includes the possibility of converting the RTD into GSD or PSD by choosing the value of the constant connecting the relaxation time to the characteristic polarization size of interest. A high frequencies (typically above 1 kHz), a dielectric term in taken into account in the model. The code is provided as an open Matlab source as a supplementary file associated with this paper.

  16. An analytical model which determines the apparent T1 for Modified Look-Locker Inversion Recovery - Analysis of the longitudinal relaxation under the influence of discontinuous balanced (classical MOLLI) and spoiled gradient echo readouts.

    Science.gov (United States)

    Kampf, Thomas; Reiter, Theresa; Bauer, Wolfgang Rudolf

    2017-08-09

    Quantitative nuclear magnetic resonance imaging (MRI) shifts more and more into the focus of clinical research. Especially determination of relaxation times without/and with contrast agents becomes the foundation of tissue characterization, e.g. in cardiac MRI for myocardial fibrosis. Techniques which assess longitudinal relaxation times rely on repetitive application of readout modules, which are interrupted by free relaxation periods, e.g. the Modified Look-Locker Inversion Recovery = MOLLI sequence. These discontinuous sequences reveal an apparent relaxation time, and, by techniques extrapolated from continuous readout sequences, a putative real T1 is determined. What is missing is a rigorous analysis of the dependence of the apparent relaxation time on its real partner, readout sequence parameters and biological parameters as heart rate. This is provided in this paper for the discontinuous balanced steady state free precession (bSSFP) and spoiled gradient echo readouts. It turns out that the apparent longitudinal relaxation rate is the time average of the relaxation rates during the readout module, and free relaxation period. Knowing the heart rate our results vice versa allow to determine the real T1 from its measured apparent partner. Copyright © 2017. Published by Elsevier GmbH.

  17. Hyperpolarized nanodiamond with long spin-relaxation times

    Science.gov (United States)

    Rej, Ewa; Gaebel, Torsten; Boele, Thomas; Waddington, David E. J.; Reilly, David J.

    2015-10-01

    The use of hyperpolarized agents in magnetic resonance, such as 13C-labelled compounds, enables powerful new imaging and detection modalities that stem from a 10,000-fold boost in signal. A major challenge for the future of the hyperpolarization technique is the inherently short spin-relaxation times, typically nanodiamond can be hyperpolarized at cryogenic and room temperature without the use of free radicals, and, owing to their solid-state environment, exhibit relaxation times exceeding 1 h. Combined with the already established applications of nanodiamonds in the life sciences as inexpensive fluorescent markers and non-cytotoxic substrates for gene and drug delivery, these results extend the theranostic capabilities of nanoscale diamonds into the domain of hyperpolarized magnetic resonance.

  18. Carrier relaxation time divergence in single and double layer cuprates

    Science.gov (United States)

    Schneider, M. L.; Rast, S.; Onellion, M.; Demsar, J.; Taylor, A. J.; Glinka, Y.; Tolk, N. H.; Ren, Y. H.; Lüpke, G.; Klimov, A.; Xu, Y.; Sobolewski, R.; Si, W.; Zeng, X. H.; Soukiassian, A.; Xi, X. X.; Abrecht, M.; Ariosa, D.; Pavuna, D.; Krapf, A.; Manzke, R.; Printz, J. O.; Williamsen, M. S.; Downum, K. E.; Guptasarma, P.; Bozovic, I.

    2003-12-01

    We report the transient optical pump-probe reflectivity measurements on single and double layer cuprate single crystals and thin films of ten different stoichiometries. We find that with sufficiently low fluence the relaxation time (tauR) of all samples exhibits a power law divergence with temperature (T): tauR ∝ T^{-3 ± 0.5}. Further, the divergence has an onset temperature above the superconducting transition temperature for all superconducting samples. Possible causes of this divergence are discussed.

  19. Relaxation Time and the Problem of the Pleistocene

    Directory of Open Access Journals (Sweden)

    Steven M. Holland

    2013-04-01

    Full Text Available Although changes in habitat area, driven by changes in sea level, have long been considered as a possible cause of marine diversity change in the Phanerozoic, the lack of Pleistocene extinction in the Californian Province has raised doubts, given the large and rapid sea-level changes during the Pleistocene. Neutral models of metacommunities presented here suggest that diversity responds rapidly to changes in habitat area, with relaxation times of a few hundred to a few thousand years. Relaxation time is controlled partly by metacommunity size, implying that different provinces or trophic levels might have measurably different responses to changes in habitable area. Geologically short relaxation times imply that metacommunities should be able to stay nearly in equilibrium with all but the most rapid changes in area. A simulation of the Californian Province during the Pleistocene confirms this, with the longest lags in diversity approaching 20 kyr. The apparent lack of Pleistocene extinction in the Californian Province likely results from the difficulty of sampling rare species, coupled with repopulation from adjacent deep-water or warm-water regions.

  20. Group epitope mapping considering relaxation of the ligand (GEM-CRL): Including longitudinal relaxation rates in the analysis of saturation transfer difference (STD) experiments

    Science.gov (United States)

    Kemper, Sebastian; Patel, Mitul K.; Errey, James C.; Davis, Benjamin G.; Jones, Jonathan A.; Claridge, Timothy D. W.

    2010-03-01

    In the application of saturation transfer difference (STD) experiments to the study of protein-ligand interactions, the relaxation of the ligand is one of the major influences on the experimentally observed STD factors, making interpretation of these difficult when attempting to define a group epitope map (GEM). In this paper, we describe a simplification of the relaxation matrix that may be applied under specified experimental conditions, which results in a simplified equation reflecting the directly transferred magnetisation rate from the protein onto the ligand, defined as the summation over the whole protein of the protein-ligand cross-relaxation multiplied by with the fractional saturation of the protein protons. In this, the relaxation of the ligand is accounted for implicitly by inclusion of the experimentally determined longitudinal relaxation rates. The conditions under which this "group epitope mapping considering relaxation of the ligand" (GEM-CRL) can be applied were tested on a theoretical model system, which demonstrated only minor deviations from that predicted by the full relaxation matrix calculations (CORCEMA-ST) [7]. Furthermore, CORCEMA-ST calculations of two protein-saccharide complexes (Jacalin and TreR) with known crystal structures were performed and compared with experimental GEM-CRL data. It could be shown that the GEM-CRL methodology is superior to the classical group epitope mapping approach currently used for defining ligand-protein proximities. GEM-CRL is also useful for the interpretation of CORCEMA-ST results, because the transferred magnetisation rate provides an additional parameter for the comparison between measured and calculated values. The independence of this parameter from the above mentioned factors can thereby enhance the value of CORCEMA-ST calculations.

  1. Krylov-subspace acceleration of time periodic waveform relaxation

    Energy Technology Data Exchange (ETDEWEB)

    Lumsdaine, A. [Univ. of Notre Dame, IN (United States)

    1994-12-31

    In this paper the author uses Krylov-subspace techniques to accelerate the convergence of waveform relaxation applied to solving systems of first order time periodic ordinary differential equations. He considers the problem in the frequency domain and presents frequency dependent waveform GMRES (FDWGMRES), a member of a new class of frequency dependent Krylov-subspace techniques. FDWGMRES exhibits many desirable properties, including finite termination independent of the number of timesteps and, for certain problems, a convergence rate which is bounded from above by the convergence rate of GMRES applied to the static matrix problem corresponding to the linear time-invariant ODE.

  2. Longitudinal proton relaxation rates in rabbit tissues after intravenous injection of free and chelated Mn2+

    Energy Technology Data Exchange (ETDEWEB)

    Spiller, M.; Brown, R.D. III; Koenig, S.H.; Wolf, G.L.

    1988-11-01

    The factors that determine the field-dependent increase in 1/T1 of tissue water protons were investigated for MnCl2 and Mn2+ (PDTA) (1,3-propylenediamine-N,N',N'',N'''-tetraacetic acid) introduced intravenously into rabbits. Mn2+ was used in preference to other paramagnetic ions in part because of the distinct NMRD profiles (magnetic field dependence of 1/T1) of free Mn2+ ions, their small chelate complexes, and their macromolecular conjugates, and in part because the relatively low toxicity of Mn2+ is favorable for animal studies. Tissue content of Mn2+ was determined in all samples by inductively coupled plasma analyses the state of Mn2+ in excised tissues was determined from the form of the 1/T1 NMRD profile of water protons; and distribution of contrast agent within tissue and access of water on a T1 time scale were determined by double-exponential analyses of proton relaxation behavior in intact doped tissue, as well as by the change of single-exponential relaxation rates and proton signal intensity upon gentle disruption of the tissue. MnCl2 is found in all tissues, except fat and skeletal muscle, but liver is most avid at low dose, and Mn2+ accumulates in spleen after high doses. Chelation targets Mn2+ to liver and kidney, saturating the liver chemically at relatively low dose. We suggest that pronounced increase in tissue relaxivity results from irrotationally bound Mn2+, ostensibly associated with the polar head groups of cell membranes. Compartmentalization of contrast agent and restricted diffusion of tissue water influences the maximum relaxation rates attainable, so that there is an optimal dose of these contrast agents which is rather low.

  3. Longitudinal proton relaxation rates in rabbit tissues after intravenous injection of free and chelated Mn2+.

    Science.gov (United States)

    Spiller, M; Brown, R D; Koenig, S H; Wolf, G L

    1988-11-01

    The factors that determine the field-dependent increase in 1/T1 of tissue water protons were investigated for MnCl2 and Mn2+ (PDTA) (1,3-propylenediamine-N,N',N'',N'''-tetraacetic acid) introduced intravenously into rabbits. Mn2+ was used in preference to other paramagnetic ions in part because of the distinct NMRD profiles (magnetic field dependence of 1/T1) of free Mn2+ ions, their small chelate complexes, and their macromolecular conjugates, and in part because the relatively low toxicity of Mn2+ is favorable for animal studies. Tissue content of Mn2+ was determined in all samples by inductively coupled plasma analyses the state of Mn2+ in excised tissues was determined from the form of the 1/T1 NMRD profile of water protons; and distribution of contrast agent within tissue and access of water on a T1 time scale were determined by double-exponential analyses of proton relaxation behavior in intact doped tissue, as well as by the change of single-exponential relaxation rates and proton signal intensity upon gentle disruption of the tissue. MnCl2 is found in all tissues, except fat and skeletal muscle, but liver is most avid at low dose, and Mn2+ accumulates in spleen after high doses. Chelation targets Mn2+ to liver and kidney, saturating the liver chemically at relatively low dose. We suggest that pronounced increase in tissue relaxivity results from irrotationally bound Mn2+, ostensibly associated with the polar head groups of cell membranes. Compartmentalization of contrast agent and restricted diffusion of tissue water influences the maximum relaxation rates attainable, so that there is an optimal dose of these contrast agents which is rather low.

  4. Circular and longitudinal muscles shortening indicates sliding patterns during peristalsis and transient lower esophageal sphincter relaxation.

    Science.gov (United States)

    Patel, Nirali; Jiang, Yanfen; Mittal, Ravinder K; Kim, Tae Ho; Ledgerwood, Melissa; Bhargava, Valmik

    2015-09-01

    Esophageal axial shortening is caused by longitudinal muscle (LM) contraction, but circular muscle (CM) may also contribute to axial shortening because of its spiral morphology. The goal of our study was to show patterns of contraction of CM and LM layers during peristalsis and transient lower esophageal sphincter (LES) relaxation (TLESR). In rats, esophageal and LES morphology was assessed by histology and immunohistochemistry, and function with the use of piezo-electric crystals and manometry. Electrical stimulation of the vagus nerve was used to induce esophageal contractions. In 18 healthy subjects, manometry and high frequency intraluminal ultrasound imaging during swallow-induced esophageal contractions and TLESR were evaluated. CM and LM thicknesses were measured (40 swallows and 30 TLESRs) as markers of axial shortening, before and at peak contraction, as well as during TLESRs. Animal studies revealed muscular connections between the LM and CM layers of the LES but not in the esophagus. During vagal stimulated esophageal contraction there was relative movement between the LM and CM. Human studies show that LM-to-CM (LM/CM) thickness ratio at baseline was 1. At the peak of swallow-induced contraction LM/CM ratio decreased significantly (2). The pattern of contraction of CM and LM suggests sliding of the two muscles. Furthermore, the sliding patterns are in the opposite direction during peristalsis and TLESR.

  5. Multiple-relaxation-time model for the correct thermohydrodynamic equations.

    Science.gov (United States)

    Zheng, Lin; Shi, Baochang; Guo, Zhaoli

    2008-08-01

    A coupling lattice Boltzmann equation (LBE) model with multiple relaxation times is proposed for thermal flows with viscous heat dissipation and compression work. In this model the fixed Prandtl number and the viscous dissipation problems in the energy equation, which exist in most of the LBE models, are successfully overcome. The model is validated by simulating the two-dimensional Couette flow, thermal Poiseuille flow, and the natural convection flow in a square cavity. It is found that the numerical results agree well with the analytical solutions and/or other numerical results.

  6. Direct Timing Method for Longitudinal Coordinate Determination in Straws

    OpenAIRE

    Makhankin, A. M.; Myalkovsky, V. V.; Peshekhonov, V. D.; Vasilyev, S. E.

    2013-01-01

    The considering different technics of measuring the longitudinal coordinates by the drift tubes. It is shown that the determination of the longitudinal coordinate by the direct time method provides the best longitudinal resolution. The realization of this method enables the development of coordinate detectors based on the straw with two-dimensional readout, which can be fast enough and not very complex.

  7. Effective rotational correlation times of proteins from NMR relaxation interference

    Science.gov (United States)

    Lee, Donghan; Hilty, Christian; Wider, Gerhard; Wüthrich, Kurt

    2006-01-01

    Knowledge of the effective rotational correlation times, τc, for the modulation of anisotropic spin-spin interactions in macromolecules subject to Brownian motion in solution is of key interest for the practice of NMR spectroscopy in structural biology. The value of τc enables an estimate of the NMR spin relaxation rates, and indicates possible aggregation of the macromolecular species. This paper reports a novel NMR pulse scheme, [ 15N, 1H]-TRACT, which is based on transverse relaxation-optimized spectroscopy and permits to determine τc for 15N- 1H bonds without interference from dipole-dipole coupling of the amide proton with remote protons. [ 15N, 1H]-TRACT is highly efficient since only a series of one-dimensional NMR spectra need to be recorded. Its use is suggested for a quick estimate of the rotational correlation time, to monitor sample quality and to determine optimal parameters for complex multidimensional NMR experiments. Practical applications are illustrated with the 110 kDa 7,8-dihydroneopterin aldolase from Staphylococcus aureus, the uniformly 15N-labeled Escherichia coli outer membrane protein X (OmpX) in 60 kDa mixed OmpX/DHPC micelles with approximately 90 molecules of unlabeled 1,2-dihexanoyl- sn-glycero-3-phosphocholine (DHPC), and the 16 kDa pheromone-binding protein from Bombyx mori, which cover a wide range of correlation times.

  8. The structure of precipitation fronts for finite relaxation time

    Energy Technology Data Exchange (ETDEWEB)

    Stechmann, Samuel N.; Majda, Andrew J. [New York University, Department of Mathematics and Center for Atmosphere Ocean Science, Courant Institute of Mathematical Sciences, New York, NY (United States)

    2006-11-15

    When convection is parameterized in an atmospheric circulation model, what types of waves are supported by the parameterization? Several studies have addressed this question by finding the linear waves of simplified tropical climate models with convective parameterizations. In this paper's simplified tropical climate model, convection is parameterized by a nonlinear precipitation term, and the nonlinearity gives rise to precipitation front solutions. Precipitation fronts are solutions where the spatial domain is divided into two regions, and the precipitation (and other model variables) changes abruptly at the boundary of the two regions. In one region the water vapor is below saturation and there is no precipitation, and in the other region the water vapor is above saturation level and precipitation is nonzero. The boundary between the two regions is a free boundary that moves at a constant speed. It is shown that only certain front speeds are allowed. The three types of fronts that exist for this model are drying fronts, slow moistening fronts, and fast moistening fronts. Both types of moistening fronts violate Lax's stability criterion, but they are robustly realizable in numerical experiments that use finite relaxation times. Remarkably, here it is shown that all three types of fronts are robustly realizable analytically for finite relaxation time. All three types of fronts may be physically unreasonable if the front spans an unrealistically large physical distance; this depends on various model parameters, which are investigated below. From the viewpoint of applied mathematics, these model equations exhibit novel phenomena as well as features in common with the established applied mathematical theories of relaxation limits for conservation laws and waves in reacting gas flows. (orig.)

  9. Hydration Dependence of Energy Relaxation Time for Cytochrome C

    Science.gov (United States)

    Ye, Shuji; Chen, Jing-Yin; Knab, Joseph R.; Markelz, Andrea

    2006-03-01

    Hydration plays a critical role in protein dynamics. Here we consider the effects of hydration on energy relaxation for an electronically excited heme protein cytochrome c. We measure the hydration dependence of energy relaxation time of cytochrome C films after photoexcitation in the Soret regionusing two-color pump/probe time resolved transmission measurements. Thin films were prepared from cytochrome C/ Trizma buffer solutions and mounted in a hydration controlled cell. We used 400nm (˜3 mW) to pump the B band and 800 nm (˜1 mW) to probe the III band. The III band corresponds to the charge-transfer transition between heme π and iron d orbital, and is assigned to the ground electronic state of the heme. Therefore this band can be used to probe the ground state population. Three separate dynamic components were observed: a very fast transient τ1 ˜ 200 fs; a several hundred femtosecond component (τ2); and a recovery of the ground state absorption(τ3). We find τ3 apparently decreases with decreasing hydration while τ1 and τ2 are independent of hydration.

  10. Time course of corticospinal excitability and intracortical inhibition just before muscle relaxation

    Directory of Open Access Journals (Sweden)

    Tomotaka eSuzuki

    2016-01-01

    Full Text Available Using transcranial magnetic stimulation (TMS, we investigated how short-interval intracortical inhibition (SICI was involved with transient motor cortex excitability changes observed just before the transition from muscle contraction to muscle relaxation. Ten healthy participants performed a simultaneous relaxation task of the ipsilateral finger and foot, relaxing from 10% of their maximal voluntary contraction force after the go signal. In the simple reaction time paradigm, single or paired TMS pulses were randomly delivered after the go signal, and motor evoked potentials were recorded from the right first dorsal interosseous muscle. We analyzed the time course prior to the estimated relaxation reaction time, defined here as the onset of voluntary relaxation. SICI decreased in the 80–100 ms before relaxation reaction time, and motor evoked potentials were significantly greater in amplitude in the 60–80 ms period before relaxation reaction time than in the other intervals in single-pulse trials. TMS pulses did not effectively increase relaxation reaction time. These results show that cortical excitability in the early stage, before muscle relaxation, plays an important role in muscle relaxation control. SICI circuits may vary between decreased and increased activation to continuously maintain muscle relaxation during or after a relaxation response. With regard to motor cortex excitability dynamics, we suggest that SICI also dynamically changes throughout the muscle relaxation process.

  11. Relaxation therapy for insomnia: nighttime and day time effects.

    Science.gov (United States)

    Means, M K; Lichstein, K L; Epperson, M T; Johnson, C T

    2000-07-01

    We compared day time functioning in college students with and without insomnia and explored changes in day time functioning after progressive relaxation (PR) treatment for insomnia. Students with insomnia (SWI; n = 57) were compared to a control group of students not complaining of insomnia (SNI; n = 61) on self-reported sleep variables and five questionnaires: Insomnia Impact Scale (IIS), Dysfunctional Beliefs and Attitudes About Sleep Scale (DBAS), Epworth Sleepiness Scale (ESS), Fatigue Severity Scale (FSS), and Penn State Worry Questionnaire (PSWQ). SWI demonstrated significant impairment on all day time functioning and sleep measures compared to SNI. To investigate treatment effects on day time functioning, 28 SWI were randomly assigned to PR. Treated SWI were compared to untreated SWI and SNI at posttreatment. Treated participants improved sleep in comparison to untreated SWI, but failed to show significant improvements in day time functioning. Insomnia treatments focused on improving sleep may not improve day time functioning, or day time gains may emerge more slowly than sleep gains. This study documents the wide range of day time functioning complaints in young adults with insomnia and suggests that the goal of insomnia treatment should be to not only improve sleep but also to improve the subjective experience of day time functioning.

  12. Relaxation time effects of wave ripples on tidal beaches

    Science.gov (United States)

    Austin, M. J.; Masselink, G.; O'Hare, T. J.; Russell, P. E.

    2007-08-01

    Seabed roughness due to wave ripples is a key factor in controlling sediment transport processes in the nearshore zone. Roughness is commonly considered a function of the ripple geometry, which in turn, can be predicted from sediment and hydrodynamic parameters. Existing ripple predictors consider the bed morphology to be in equilibrium with the hydrodynamics, whereas recent laboratory measurements show that the time scale for ripple development is of the order of tens of minutes to hours. Here we show that wave ripples on tidal beaches are significantly affected by relaxation time effects, with ripple height and length progressively increasing during the rising tide and remaining constant during the falling tide. Moreover, we examine the ripples in the context of existing empirical models and suggest how the temporal evolution over a tidal cycle may be predicted.

  13. Generalized dynamic scaling for quantum critical relaxation in imaginary time.

    Science.gov (United States)

    Zhang, Shuyi; Yin, Shuai; Zhong, Fan

    2014-10-01

    We study the imaginary-time relaxation critical dynamics of a quantum system with a vanishing initial correlation length and an arbitrary initial order parameter M0. We find that in quantum critical dynamics, the behavior of M0 under scale transformations deviates from a simple power law, which was proposed for very small M0 previously. A universal characteristic function is then suggested to describe the rescaled initial magnetization, similar to classical critical dynamics. This characteristic function is shown to be able to describe the quantum critical dynamics in both short- and long-time stages of the evolution. The one-dimensional transverse-field Ising model is employed to numerically determine the specific form of the characteristic function. We demonstrate that it is applicable as long as the system is in the vicinity of the quantum critical point. The universality of the characteristic function is confirmed by numerical simulations of models belonging to the same universality class.

  14. A 1-year time course study of the relaxation times and histology for irradiated rat lungs

    Energy Technology Data Exchange (ETDEWEB)

    Shioya, S.; Haida, M.; Fukuzaki, M.; Ono, Y.; Tsuda, M.; Ohta, Y.; Yamabayashi, H. (Tokai Univ. School of Medicine, Kanagawa (Japan))

    1990-05-01

    To investigate the NMR relaxation times for irradiated rat lung tissue, we measured T1 and T2 at 11 different times during the injury's 1-year time course. A biexponential analysis of T2 was used to determine T2 fast (T2f) and T2 slow (T2s). In addition, we measured water content and correlated changes in the relaxation times with pathological changes. The correlation indicates the following: (1) Shortly after irradiation, the biexponential T2 decay for 1/3 of the samples became monoexponential and there were no noticeable pathological changes observed using light microscopy. (2) During radiation pneumonitis, T2f and T2s were prolonged. This accompanied acute edematous changes and inflammatory cell infiltration. (3) Finally, during radiation fibrosis T1 shortened and collagen increased. We observed no significant correlation between relaxation time changes and water content changes throughout the 1-year time course.

  15. Upper D region chemical kinetic modeling of LORE relaxation times

    Science.gov (United States)

    Gordillo-Vázquez, F. J.; Luque, A.; Haldoupis, C.

    2016-04-01

    The recovery times of upper D region electron density elevations, caused by lightning-induced electromagnetic pulses (EMP), are modeled. The work was motivated from the need to understand a recently identified narrowband VLF perturbation named LOREs, an acronym for LOng Recovery Early VLF events. LOREs associate with long-living electron density perturbations in the upper D region ionosphere; they are generated by strong EMP radiated from large peak current intensities of ±CG (cloud to ground) lightning discharges, known also to be capable of producing elves. Relaxation model scenarios are considered first for a weak enhancement in electron density and then for a much stronger one caused by an intense lightning EMP acting as an impulsive ionization source. The full nonequilibrium kinetic modeling of the perturbed mesosphere in the 76 to 92 km range during LORE-occurring conditions predicts that the electron density relaxation time is controlled by electron attachment at lower altitudes, whereas above 79 km attachment is balanced totally by associative electron detachment so that electron loss at these higher altitudes is controlled mainly by electron recombination with hydrated positive clusters H+(H2O)n and secondarily by dissociative recombination with NO+ ions, a process which gradually dominates at altitudes >88 km. The calculated recovery times agree fairly well with LORE observations. In addition, a simplified (quasi-analytic) model build for the key charged species and chemical reactions is applied, which arrives at similar results with those of the full kinetic model. Finally, the modeled recovery estimates for lower altitudes, that is <79 km, are in good agreement with the observed short recovery times of typical early VLF events, which are known to be associated with sprites.

  16. Rapid and simple determination of T1 relaxation times in time-domain NMR by Continuous Wave Free Precession sequence

    Science.gov (United States)

    Moraes, Tiago Bueno; Monaretto, Tatiana; Colnago, Luiz Alberto

    2016-09-01

    Longitudinal (T1) and transverse (T2) relaxation times have been widely used in time-domain NMR (TD-NMR) to determine several physicochemical properties of petroleum, polymers, and food products. The measurement of T2 through the CPMG pulse sequence has been used in most of these applications because it denotes a rapid, robust method. On the other hand, T1 has been occasionally used in TD-NMR due to the long measurement time required to collect multiple points along the T1 relaxation curve. Recently, several rapid methods to measure T1 have been proposed. Those methods based upon single shot, known as Continuous Wave Free Precession (CWFP) pulse sequences, have been employed in the simultaneous measurement of T1 and T2 in a rapid fashion. However, these sequences can be used exclusively in instrument featuring short dead time because the magnitude of the signal at thermal equilibrium is required. In this paper, we demonstrate that a special CWFP sequence with a low flip angle can be a simple and rapid method to measure T1 regardless of instruments dead time. Experimental results confirmed that the method called CWFP-T1 may be used to measure both single T1 value and T1 distribution in heterogeneous samples. Therefore, CWFP-T1 sequence can be a feasible alternative to CPMG in the determination of physicochemical properties, particularly in processes where fast protocols are requested such as industrial applications.

  17. Anomalous divergence of a relaxation time in discontinuous shear thickening suspensions

    CERN Document Server

    Maharjan, Rijan

    2016-01-01

    We investigated the transient relaxation of a Discontinuous Shear Thickening (DST) suspension of cornstarch in water. Starting from a steady shear in a parallel plate rheometer, we stopped the top plate rotation and measured the transient stress relaxation. We found that at low effective packing fraction $\\phi_{eff}$, the suspensions exhibited a relaxation behavior consistent with a rheometric fluid in which the relaxation is determined by the steady-state viscosity. However, for larger $\\phi_{eff}$, we find up to two exponential relaxation regimes, which both become distinct from the rheometric model. The discrepancy between the measured relaxation times and the rheometric prediction was found to be as large as 4 orders of magnitude and diverges in the limit as $\\phi_{eff} \\rightarrow \\phi_c$, corresponding to the liquid solid transition, as the measured relaxation times diverge to infinity while the rheometric prediction approaches 0. In this limit, the measured relaxation time scales are on the order of $\\...

  18. Chiral Relaxation Time at the Chiral Crossover of Quantum Chromodynamics

    CERN Document Server

    Ruggieri, M; Chernodub, M

    2016-01-01

    We study microscopic processes responsible for chirality flips in the thermal bath of Quantum Chromodynamics at finite temperature and zero baryon chemical potential. We focus on the temperature range where the crossover from chirally broken phase to quark-gluon plasma takes place, namely $T \\simeq (150, 200)$ MeV. The processes we consider are quark-quark scatterings mediated by collective excitations with the quantum number of pions and $\\sigma$-meson, hence we refer to these processes simply as \\sugg{to} one-pion (one-$\\sigma$) exchange\\sugg{s}. We use a Nambu-Jona-Lasinio model to compute equilibrium properties of the thermal bath, as well as the relevant scattering kernel to be used in the collision integral to estimate the chiral relaxation time $\\tau$. We find $\\tau\\simeq 0.1 \\div 1$ fm/c around the chiral crossover.

  19. Implicit versus explicit momentum relaxation time solution for semiconductor nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Marin, E. G., E-mail: egmarin@ugr.es; Ruiz, F. G., E-mail: franruiz@ugr.es; Godoy, A., E-mail: agodoy@ugr.es; Tienda-Luna, I. M.; Gámiz, F. [Departamento de Electrónica, Universidad de Granada, Av. Fuentenueva S/N, 18071–Granada (Spain)

    2015-07-14

    We discuss the necessity of the exact implicit Momentum Relaxation Time (MRT) solution of the Boltzmann transport equation in order to achieve reliable carrier mobility results in semiconductor nanowires. Firstly, the implicit solution for a 1D electron gas with a isotropic bandstructure is presented resulting in the formulation of a simple matrix system. Using this solution as a reference, the explicit approach is demonstrated to be inaccurate for the calculation of inelastic anisotropic mechanisms such as polar optical phonons, characteristic of III-V materials. Its validity for elastic and isotropic mechanisms is also evaluated. Finally, the implications of the MRT explicit approach inaccuracies on the total mobility of Si and III-V NWs are studied.

  20. Ovarian chocolate cysts. Staging with relaxation time in MR imaging

    Energy Technology Data Exchange (ETDEWEB)

    Sugimura, Kazuro; Ishida, Tetsuya; Takemori, Masayuki; Kitagaki, Hajime; Tanaka, Yutaka; Yamasaki, Katsuhito; Shimizu, Tadafumi; Kono, Michio.

    1988-10-01

    Accurate preoperative staging of ovarian chocolate cysts is very important because recent hormonal therapy has been effective in low stage patients. However, it has been difficult to assess the preoperative stage of ovarian chocolate cysts. We evaluated the diagnostic potential of MRI in preoperative staging of 15 overian chocolate cysts. It was well known that the older the ovarian chocolate cyst was the more iron content it had. We examined the iron contents effect on T1 and T2 relaxation times in surgically confirmed chocolate cysts (stage II: 3 cases, stage III: 3 cases and stage IV: 9 cases by AFS classification, 1985) employing the 0.15-T MR system and 200 MHz spectrometer. There was a positive linear relation between T1 of the lesion using the MR system (T1) and T1 of the resected contents using the spectrometer (sp-T1); r = 0.93. The same relation was revealed between T2 and sp-T2; r = 0.87. It was indicated that T1 and T2 using the MR system was accurate. There was a negative linear relation between T1 and the iron contents ( r = -0.81) but no relation between T2 and the iron contents. T1 was 412 +- 91 msec for stage II, 356 +- 126 msec for stage III and 208 +- 30 msec for stage IV. T1 for stage IV was shorter than that for stage II and III, statistically significant differences were noted (p < 0.05). Thus, T1 was useful in differentiating a fresh from an old ovarian chocolate cyst. We concluded that T1 relaxation time using the MR system was useful for the staging of an ovarian chocolate cyst without surgery.

  1. Convex quadratic programming relaxations for parallel machine scheduling with controllable processing times subject to release times

    Institute of Scientific and Technical Information of China (English)

    ZHANG Feng; CHEN Feng; TANG Guochun

    2004-01-01

    Scheduling unrelated parallel machines with controllable processing times subject to release times is investigated. Based on the convex quadratic programming relaxation and the randomized rounding strategy, a 2-approximation algorithm is obtained for a special case with the all-or-none property and then a 3-approximation algorithm is presented for general problem.

  2. A nonlinear BOLD model accounting for refractory effect by applying the longitudinal relaxation in NMR to the linear BOLD model.

    Science.gov (United States)

    Jung, Kwan-Jin

    2009-09-01

    A mathematical model to regress the nonlinear blood oxygen level-dependent (BOLD) fMRI signal has been developed by incorporating the refractory effect into the linear BOLD model of the biphasic gamma variate function. The refractory effect was modeled as a relaxation of two separate BOLD capacities corresponding to the biphasic components of the BOLD signal in analogy with longitudinal relaxation of magnetization in NMR. When tested with the published fMRI data of finger tapping, the nonlinear BOLD model with the refractory effect reproduced the nonlinear BOLD effects such as reduced poststimulus undershoot and saddle pattern in a prolonged stimulation as well as the reduced BOLD signal for repetitive stimulation.

  3. Determination of T1- and T2-relaxation times in the spleen of patients with splenomegaly

    DEFF Research Database (Denmark)

    Thomsen, C; Josephsen, P; Karle, H

    1990-01-01

    Twenty-nine patients with known splenomegaly and seven healthy volunteers were examined. The T1 and T2 relaxation times were read out from a region of interest centrally in the spleen. Even though different mean T1 and T2 relaxation times were found between the groups, the great scatter and the c...... and the considerable overlap between the groups makes the contribution of relaxation time measurements to the differential diagnosis of splenomegaly of limited value....

  4. Reconstruction of relaxation time distribution from linear electrochemical impedance spectroscopy

    Science.gov (United States)

    Zhang, Yanxiang; Chen, Yu; Yan, Mufu; Chen, Fanglin

    2015-06-01

    Linear electrochemical impedance spectroscopy (EIS), and in particular its representation of distribution of relaxation time (DRT), enables the identification of the number of processes and their nature involved in electrochemical cells. With the advantage of high frequency resolution, DRT has recently drawn increasing attention for applications in solid oxide fuel cells (SOFCs). However, the method of DRT reconstruction is not yet presented clearly in terms of what mathematical treatments and theoretical assumptions have been made. Here we present unambiguously a method to reconstruct DRT function of impedance based on Tikhonov regularization. By using the synthetic impedances and analytic DRT functions of RQ element, generalized finite length Warburg element, and Gerischer element with physical quantities representative to those of SOFC processes, we show that the quality of DRT reconstruction is sensitive to the sampling points per decade (ppd) of frequency from the impedance measurement. The robustness of the DRT reconstruction to resist noise imbedded in impedance data and numerical calculations can be accomplished by optimizing the weighting factor λ according to well defined criterion.

  5. Water sorption-induced crystallization, structural relaxations and strength analysis of relaxation times in amorphous lactose/whey protein systems

    OpenAIRE

    Fan, Fanghui; Mou, Tian; Nurhadi, Bambang; Roos, Yrjö H.

    2016-01-01

    Water sorption-induced crystallization, α-relaxations and relaxation times of freeze-dried lactose/whey protein isolate (WPI) systems were studied using dynamic dewpoint isotherms (DDI) method and dielectric analysis (DEA), respectively. The fractional water sorption behavior of lactose/WPI mixtures shown at aw ≤ 0.44 and the critical aw for water sorption-related crystallization (aw(cr)) of lactose were strongly affected by protein content based on DDI data. DEA results showed that the α-rel...

  6. The time dependence of rock healing as a universal relaxation process, a tutorial

    Science.gov (United States)

    Snieder, Roel; Sens-Schönfelder, Christoph; Wu, Renjie

    2017-01-01

    The material properties of earth materials often change after the material has been perturbed (slow dynamics). For example, the seismic velocity of subsurface materials changes after earthquakes, and granular materials compact after being shaken. Such relaxation processes are associated by observables that change logarithmically with time. Since the logarithm diverges for short and long times, the relaxation can, strictly speaking, not have a log-time dependence. We present a self-contained description of a relaxation function that consists of a superposition of decaying exponentials that has log-time behaviour for intermediate times, but converges to zero for long times, and is finite for t = 0. The relaxation function depends on two parameters, the minimum and maximum relaxation time. These parameters can, in principle, be extracted from the observed relaxation. As an example, we present a crude model of a fracture that is closing under an external stress. Although the fracture model violates some of the assumptions on which the relaxation function is based, it follows the relaxation function well. We provide qualitative arguments that the relaxation process, just like the Gutenberg-Richter law, is applicable to a wide range of systems and has universal properties.

  7. Time Course of Corticospinal Excitability and Intracortical Inhibition Just before Muscle Relaxation.

    Science.gov (United States)

    Suzuki, Tomotaka; Sugawara, Kenichi; Ogahara, Kakuya; Higashi, Toshio

    2016-01-01

    Using transcranial magnetic stimulation (TMS), we investigated how short-interval intracortical inhibition (SICI) was involved with transient motor cortex (M1) excitability changes observed just before the transition from muscle contraction to muscle relaxation. Ten healthy participants performed a simultaneous relaxation task of the ipsilateral finger and foot, relaxing from 10% of their maximal voluntary contraction (MVC) force after the go signal. In the simple reaction time (RT) paradigm, single or paired TMS pulses were randomly delivered after the go signal, and motor evoked potentials (MEPs) were recorded from the right first dorsal interosseous (FDI) muscle. We analyzed the time course prior to the estimated relaxation reaction time (RRT), defined here as the onset of voluntary relaxation. SICI decreased in the 80-100 ms before RRT, and MEPs were significantly greater in amplitude in the 60-80 ms period before RRT than in the other intervals in single-pulse trials. TMS pulses did not effectively increase RRT. These results show that cortical excitability in the early stage, before muscle relaxation, plays an important role in muscle relaxation control. SICI circuits may vary between decreased and increased activation to continuously maintain muscle relaxation during or after a relaxation response. With regard to M1 excitability dynamics, we suggest that SICI also dynamically changes throughout the muscle relaxation process.

  8. Time Course of Corticospinal Excitability and Intracortical Inhibition Just before Muscle Relaxation

    Science.gov (United States)

    Suzuki, Tomotaka; Sugawara, Kenichi; Ogahara, Kakuya; Higashi, Toshio

    2016-01-01

    Using transcranial magnetic stimulation (TMS), we investigated how short-interval intracortical inhibition (SICI) was involved with transient motor cortex (M1) excitability changes observed just before the transition from muscle contraction to muscle relaxation. Ten healthy participants performed a simultaneous relaxation task of the ipsilateral finger and foot, relaxing from 10% of their maximal voluntary contraction (MVC) force after the go signal. In the simple reaction time (RT) paradigm, single or paired TMS pulses were randomly delivered after the go signal, and motor evoked potentials (MEPs) were recorded from the right first dorsal interosseous (FDI) muscle. We analyzed the time course prior to the estimated relaxation reaction time (RRT), defined here as the onset of voluntary relaxation. SICI decreased in the 80–100 ms before RRT, and MEPs were significantly greater in amplitude in the 60–80 ms period before RRT than in the other intervals in single-pulse trials. TMS pulses did not effectively increase RRT. These results show that cortical excitability in the early stage, before muscle relaxation, plays an important role in muscle relaxation control. SICI circuits may vary between decreased and increased activation to continuously maintain muscle relaxation during or after a relaxation response. With regard to M1 excitability dynamics, we suggest that SICI also dynamically changes throughout the muscle relaxation process. PMID:26858619

  9. Multiple-relaxation-time lattice Boltzmann kinetic model for combustion.

    Science.gov (United States)

    Xu, Aiguo; Lin, Chuandong; Zhang, Guangcai; Li, Yingjun

    2015-04-01

    To probe both the hydrodynamic nonequilibrium (HNE) and thermodynamic nonequilibrium (TNE) in the combustion process, a two-dimensional multiple-relaxation-time (MRT) version of lattice Boltzmann kinetic model (LBKM) for combustion phenomena is presented. The chemical energy released in the progress of combustion is dynamically coupled into the system by adding a chemical term to the LB kinetic equation. Aside from describing the evolutions of the conserved quantities, the density, momentum, and energy, which are what the Navier-Stokes model describes, the MRT-LBKM presents also a coarse-grained description on the evolutions of some nonconserved quantities. The current model works for both subsonic and supersonic flows with or without chemical reaction. In this model, both the specific-heat ratio and the Prandtl number are flexible, the TNE effects are naturally presented in each simulation step. The model is verified and validated via well-known benchmark tests. As an initial application, various nonequilibrium behaviors, including the complex interplays between various HNEs, between various TNEs, and between the HNE and TNE, around the detonation wave in the unsteady and steady one-dimensional detonation processes are preliminarily probed. It is found that the system viscosity (or heat conductivity) decreases the local TNE, but increases the global TNE around the detonation wave, that even locally, the system viscosity (or heat conductivity) results in two kinds of competing trends, to increase and to decrease the TNE effects. The physical reason is that the viscosity (or heat conductivity) takes part in both the thermodynamic and hydrodynamic responses.

  10. Change over Time: Conducting Longitudinal Studies of Children's Cognitive Development.

    Science.gov (United States)

    Grammer, Jennie K; Coffman, Jennifer L; Ornstein, Peter A; Morrison, Frederick J

    2013-10-01

    Developmental scientists have argued that the implementation of longitudinal methods is necessary for obtaining an accurate picture of the nature and sources of developmental change (Magnusson & Cairns, 1996; Morrison & Ornstein, 1996; Magnusson & Stattin, 2006). Developmentalists studying cognition have been relatively slow to embrace longitudinal research, and thus few exemplar studies have tracked individual children's cognitive performance over time and even fewer have examined contexts that are associated with this growth. In this article we first outline some of the benefits of implementing longitudinal designs. Using illustrations from existing studies of children's basic cognitive development and of their school-based academic performance, we discuss when it may be appropriate to employ longitudinal (versus other) methods. We then outline methods for integrating longitudinal data into one's research portfolio, contrasting the leveraging of existing longitudinal data sets with the launching of new longitudinal studies in order to address specific questions concerning cognitive development. Finally, for those who are interested in conducting longitudinal investigations of their own, we provide practical on-the-ground guidelines for designing and carrying out such studies of cognitive development.

  11. Quantitative Assessment of the T2 Relaxation Time of the Gluteus Muscles in Children with Duchenne Muscular Dystrophy: a Comparative Study Before and After Steroid Treatment

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hee Kyung; Laor, Tal; Wong, Brenda [Cincinnati Children' s Hospital Medical Center, Cincinnati (United States); Horn, Paul S. [University of Cincinnati, Cincinnati (United States)

    2010-06-15

    To determine the feasibility of using T2 mapping as a quantitative method to longitudinally follow the disease activity in children with Duchenne muscular dystrophy (DMD) who are treated with steroids. Eleven boys with DMD (age range: 5-14 years) underwent evaluation with the clinical functional score (CFS), and conventional pelvic MRI and T2 mapping before and during steroid therapy. The gluteus muscle inflammation and fatty infiltration were evaluated on conventional MRI. The histograms and mean T2 relaxation times were obtained from the T2 maps. The CFS, the conventional MRI findings and the T2 values were compared before and during steroid therapy. None of the patients showed interval change of their CFSs. On conventional MRI, none of the images showed muscle inflammation. During steroid treatment, two boys showed increased fatty infiltration on conventional MRI, and both had an increase of the mean T2 relaxation time (p < 0.05). The remaining nine boys had no increase in fatty infiltration. Of these, three showed an increased mean T2 relaxation time (p < 0.05), two showed no change and four showed a decreased mean T2 relaxation time (p < 0.05). T2 mapping is a feasible technique to evaluate the longitudinal muscle changes in those children who receive steroid therapy for DMD. The differences of the mean T2 relaxation time may reflect alterations in disease activity, and even when the conventional MRI and CFS remain stable.

  12. Relaxation Time of the Particle Beam with an Anisotropic Velocity Distribution

    Directory of Open Access Journals (Sweden)

    V.P. Vechirka

    2012-11-01

    Full Text Available The computer experiment for study of the relaxation time of the beam particles with an anisotropic velocity distribution is performed by the molecular dynamics. Obtained results agree with the characteristic times of thermal relaxation in plasma for the electronic coolers in modern storage rings.

  13. Evaluation of relaxation time measurements by magnetic resonance imaging. A phantom study

    DEFF Research Database (Denmark)

    Kjaer, L; Thomsen, C; Henriksen, O

    1987-01-01

    Several circumstances may explain the great variation in reported proton T1 and T2 relaxation times usually seen. This study was designed to evaluate the accuracy of relaxation time measurements by magnetic resonance imaging (MRI) operating at 1.5 tesla. Using a phantom of nine boxes with different...

  14. Stretched Exponential Relaxation in Disordered Complex Systems: Fractal Time Random Walk Model

    Institute of Scientific and Technical Information of China (English)

    Ekrem Aydmer

    2007-01-01

    We have analytically derived the relaxation function for one-dimensional disordered complex systems in terms of autocorrelation function of fractal time random walk by using operator formalism. We have shown that the relaxation function has stretched exponential, i.e. the Kohlrausch-Williams-Watts character for a fractal time random walk process.

  15. NMR T1 relaxation time measurements and calculations with translational and rotational components for liquid electrolytes containing LiBF4 and propylene carbonate

    Science.gov (United States)

    Richardson, P. M.; Voice, A. M.; Ward, I. M.

    2013-12-01

    Longitudinal relaxation (T1) measurements of 19F, 7Li, and 1H in propylene carbonate/LiBF4 liquid electrolytes are reported. Comparison of T1 values with those for the transverse relaxation time (T2) confirm that the measurements are in the high temperature (low correlation time) limit of the T1 minimum. Using data from pulsed field gradient measurements of self-diffusion coefficients and measurements of solution viscosity measured elsewhere, it is concluded that although in general there are contributions to T1 from both translational and rotational motions. For the lithium ions, this is mainly translational, and for the fluorine ions mainly rotational.

  16. Time-parallel iterative methods for parabolic PDES: Multigrid waveform relaxation and time-parallel multigrid

    Energy Technology Data Exchange (ETDEWEB)

    Vandewalle, S. [Caltech, Pasadena, CA (United States)

    1994-12-31

    Time-stepping methods for parabolic partial differential equations are essentially sequential. This prohibits the use of massively parallel computers unless the problem on each time-level is very large. This observation has led to the development of algorithms that operate on more than one time-level simultaneously; that is to say, on grids extending in space and in time. The so-called parabolic multigrid methods solve the time-dependent parabolic PDE as if it were a stationary PDE discretized on a space-time grid. The author has investigated the use of multigrid waveform relaxation, an algorithm developed by Lubich and Ostermann. The algorithm is based on a multigrid acceleration of waveform relaxation, a highly concurrent technique for solving large systems of ordinary differential equations. Another method of this class is the time-parallel multigrid method. This method was developed by Hackbusch and was recently subject of further study by Horton. It extends the elliptic multigrid idea to the set of equations that is derived by discretizing a parabolic problem in space and in time.

  17. Short-Time Beta Relaxation in Glass-Forming Liquids Is Cooperative in Nature

    Science.gov (United States)

    Karmakar, Smarajit; Dasgupta, Chandan; Sastry, Srikanth

    2016-02-01

    Temporal relaxation of density fluctuations in supercooled liquids near the glass transition occurs in multiple steps. Using molecular dynamics simulations for three model glass-forming liquids, we show that the short-time β relaxation is cooperative in nature. Using finite-size scaling analysis, we extract a growing length scale associated with beta relaxation from the observed dependence of the beta relaxation time on the system size. We find, in qualitative agreement with the prediction of the inhomogeneous mode coupling theory, that the temperature dependence of this length scale is the same as that of the length scale that describes the spatial heterogeneity of local dynamics in the long-time α -relaxation regime.

  18. TU-EF-BRA-02: Longitudinal Proton Spin Relaxation and T1-Imaging

    Energy Technology Data Exchange (ETDEWEB)

    Lemen, L. [Univ Cincinnati (United States)

    2015-06-15

    NMR, and Proton Density MRI of the 1D Patient - Anthony Wolbarst Net Voxel Magnetization, m(x,t). T1-MRI; The MRI Device - Lisa Lemen ‘Classical’ NMR; FID Imaging in 1D via k-Space - Nathan Yanasak Spin-Echo; S-E/Spin Warp in a 2D Slice - Ronald Price Magnetic resonance imaging not only reveals the structural, anatomic details of the body, as does CT, but also it can provide information on the physiological status and pathologies of its tissues, like nuclear medicine. It can display high-quality slice and 3D images of organs and vessels viewed from any perspective, with resolution better than 1 mm. MRI is perhaps most extraordinary and notable for the plethora of ways in which it can create unique forms of image contrast, reflective of fundamentally different biophysical phenomena. As with ultrasound, there is no risk from ionizing radiation to the patient or staff, since no X-rays or radioactive nuclei are involved. Instead, MRI harnesses magnetic fields and radio waves to probe the stable nuclei of the ordinary hydrogen atoms (isolated protons) occurring in water and lipid molecules within and around cells. MRI consists, in essence, of creating spatial maps of the electromagnetic environments around these hydrogen nuclei. Spatial variations in the proton milieus can be related to clinical differences in the biochemical and physiological properties and conditions of the associated tissues. Imaging of proton density (PD), and of the tissue proton spin relaxation times known as T1 and T2, all can reveal important clinical information, but they do so with approaches so dissimilar from one another that each is chosen for only certain clinical situations. T1 and T2 in a voxel are determined by different aspects of the rotations and other motions of the water and lipid molecules involved, as constrained by the local biophysical surroundings within and between its cells – and they, in turn, depend on the type of tissue and its state of health. Three other common

  19. TRANSVERSAL INERTIAL EFFECT ON RELAXATION/RETARDATION TIME OF CEMENT MORTAR UNDER HARMONIC WAVE

    Institute of Scientific and Technical Information of China (English)

    Jue Zhu; Yonghui Cao; Jiankang Chen

    2008-01-01

    Under dynamic loading, the constitutive relation of the cement mortar will be signif-icantly affected by the transversal inertial effect of specimens with large diameters. In this paper,one-dimensional theoretical analysis is carried out to determine the transversal inertial effect on the relaxation/retardation time of the cement mortar under the harmonic wave. Relaxation time or retardation time is obtained by means of the wave velocity, attenuation coefficient and the frequency of the harmonic wave. Thus, the transversal inertial effect on the relaxation time from Maxwell model, as well as on retardation time from Voigt model is analyzed. The results show that the transversal inertial effect may lead to the increase of the relaxation time, but induce the decrease of the retardation time. Those should be taken into account when eliminating the transversal inertial effect in applications.

  20. Time-fractional derivatives in relaxation processes: a tutorial survey

    CERN Document Server

    Mainardi, Francesco

    2008-01-01

    The aim of this tutorial survey is to revisit the basic theory of relaxation processes governed by linear differential equations of fractional order. The fractional derivatives are intended both in the Rieamann-Liouville sense and in the Caputo sense. After giving a necessary outline of the classical theory of linear viscoelasticity, we contrast these two types of fractional derivatives in their ability to take into account initial conditions in the constitutive equations of fractional order. We also provide historical notes on the origins of the Caputo derivative and on the use of fractional calculus in viscoelasticity.

  1. The relaxation time of processes in a FitzHugh-Nagumo neural system with time delay

    Energy Technology Data Exchange (ETDEWEB)

    Gong Ailing; Zeng Chunhua [Faculty of Science, Kunming University of Science and Technology, Kunming 650093 (China); Wang Hua, E-mail: zchh2009@126.com [Province Engineering Research Center of Industrial Energy Conservation and New Technology, Kunming University of Science and Technology, Kunming, Yunnan 650093 (China)

    2011-08-01

    In this paper, we study the relaxation time (RT) of the steady-state correlation function in a FitzHugh-Nagumo neural system under the presence of multiplicative and additive white noises and time delay. The noise correlation parameter {lambda} can produce a critical behavior in the RT as functions of the multiplicative noise intensity D, the additive noise intensity Q and the time delay {tau}. That is, the RT decreases as the noise intensities D and Q increase, and increases as the time delay {tau} increases below the critical value of {lambda}. However, above the critical value, the RT first increases, reaches a maximum, and then decreases as D, Q and {tau} increase, i.e. a noise intensity D or Q and a time delay {tau} exist, at which the time scales of the relaxation process are at their largest. In addition, the additive noise intensity Q can also produce a critical behavior in the RT as a function of {lambda}. The noise correlation parameter {lambda} first increases the RT of processes, then decreases it below the critical value of Q. Above the critical value, {lambda} increases it.

  2. Active open boundary forcing using dual relaxation time-scales in downscaled ocean models

    Science.gov (United States)

    Herzfeld, M.; Gillibrand, P. A.

    2015-05-01

    Regional models actively forced with data from larger scale models at their open boundaries often contain motion at different time-scales (e.g. tidal and low frequency). These motions are not always individually well specified in the forcing data, and one may require a more active boundary forcing while the other exert less influence on the model interior. If a single relaxation time-scale is used to relax toward these data in the boundary equation, then this may be difficult. The method of fractional steps is used to introduce dual relaxation time-scales in an open boundary local flux adjustment scheme. This allows tidal and low frequency oscillations to be relaxed independently, resulting in a better overall solution than if a single relaxation parameter is optimized for tidal (short relaxation) or low frequency (long relaxation) boundary forcing. The dual method is compared to the single relaxation method for an idealized test case where a tidal signal is superimposed on a steady state low frequency solution, and a real application where the low frequency boundary forcing component is derived from a global circulation model for a region extending over the whole Great Barrier Reef, and a tidal signal subsequently superimposed.

  3. Spin relaxation time dependence on optical pumping in GaAs:Mn

    Science.gov (United States)

    Burobina, Veronika; Binek, Christian

    2015-03-01

    We analyze the dependence of electron spin relaxation time on optical pumping in a partially-compensated acceptor semiconductor GaAs:Mn using analytic solutions for the kinetic equations of the charge carrier concentrations. Our results are applied to previous experimental data of spin-relaxation time vs. excitation power for magnetic concentrations of approximately 1017cm-3. The agreement of our analytic solutions with the experimental data supports the mechanism of the earlier-reported atypically long electron-spin relaxation time in the magnetic semiconductor.

  4. Spin relaxation time dependence on optical pumping intensity in GaAs:Mn

    Energy Technology Data Exchange (ETDEWEB)

    Burobina, V. [Department of Physics and Astronomy, University of Utah, 115 South 1400 East, Salt Lake City, Utah 84112-0830 (United States); Binek, Ch. [Department of Physics and Astronomy, Nebraska Center for Materials and Nanoscience, Theodore Jorgensen Hall, 855 North 16th Street, University of Nebraska, P.O. Box 880299, Lincoln, Nebraska 68588-0299 (United States)

    2014-04-28

    We analyze the dependence of electron spin relaxation time on optical pumping intensity in a partially compensated acceptor semiconductor GaAs:Mn using analytic solutions for the kinetic equations of the charge carrier concentrations. Our results are applied to previous experimental data of spin-relaxation time vs. excitation power for magnetic concentrations of approximately 10{sup 17} cm{sup −3}. The agreement of our analytic solutions with the experimental data supports the mechanism of the earlier-reported atypically long electron-spin relaxation time in the magnetic semiconductor.

  5. Spin relaxation time dependence on optical pumping intensity in GaAs:Mn

    Science.gov (United States)

    Burobina, V.; Binek, Ch.

    2014-04-01

    We analyze the dependence of electron spin relaxation time on optical pumping intensity in a partially compensated acceptor semiconductor GaAs:Mn using analytic solutions for the kinetic equations of the charge carrier concentrations. Our results are applied to previous experimental data of spin-relaxation time vs. excitation power for magnetic concentrations of approximately 1017 cm-3. The agreement of our analytic solutions with the experimental data supports the mechanism of the earlier-reported atypically long electron-spin relaxation time in the magnetic semiconductor.

  6. Large lateral photovoltaic effect with ultrafast relaxation time in SnSe/Si junction

    Science.gov (United States)

    Wang, Xianjie; Zhao, Xiaofeng; Hu, Chang; Zhang, Yang; Song, Bingqian; Zhang, Lingli; Liu, Weilong; Lv, Zhe; Zhang, Yu; Tang, Jinke; Sui, Yu; Song, Bo

    2016-07-01

    In this paper, we report a large lateral photovoltaic effect (LPE) with ultrafast relaxation time in SnSe/p-Si junctions. The LPE shows a linear dependence on the position of the laser spot, and the position sensitivity is as high as 250 mV mm-1. The optical response time and the relaxation time of the LPE are about 100 ns and 2 μs, respectively. The current-voltage curve on the surface of the SnSe film indicates the formation of an inversion layer at the SnSe/p-Si interface. Our results clearly suggest that most of the excited-electrons diffuse laterally in the inversion layer at the SnSe/p-Si interface, which results in a large LPE with ultrafast relaxation time. The high positional sensitivity and ultrafast relaxation time of the LPE make the SnSe/p-Si junction a promising candidate for a wide range of optoelectronic applications.

  7. Longitudinal relaxation of mechanically clamped KH2PO4 type crystals

    Directory of Open Access Journals (Sweden)

    R.R. Levitskii

    2012-10-01

    Full Text Available Within the framework of a modified proton ordering model of the KH2PO4 family ferroelectric crystals, taking into account a linear over the strain ϵ6 contribution into the proton system energy, we obtain an expression for longitudinal dynamic dielectric permittivity of a mechanically clamped crystal using the four-particle cluster approximation and the dynamic Glauber approach. At a proper choice of the model parameters, we obtain a good quantitative description of available experimental data for these crystals.

  8. Relaxation in distal and proximal arm muscles: a reaction time study.

    Science.gov (United States)

    Buccolieri, A; Avanzino, L; Trompetto, C; Abbruzzese, G

    2003-02-01

    To investigate whether the same mechanisms underlie muscle relaxation in proximal and distal arm muscles of normal subjects. Fourteen healthy subjects were studied using a simple visual reaction time paradigm. Relaxation reaction time (R-RT) and contraction reaction time (C-RT) were compared across different tasks involving distal (first dorsal interosseus, FDI, flexor carpi radialis, FCR) and proximal (biceps brachii, BB, triceps brachii, TR) arm muscles. Changes of FCR H-reflex before and during voluntary relaxation were investigated in two subjects. No significant difference was observed between R-RT and C-RT in the distal muscles. The R-RT was significantly shorter than C-RT in both the BB and TR muscles. The relaxation latency (R-RT) was significantly correlated to the subjects' age in all the muscles except the FDI. No inhibition of the FCR H-reflex could be observed in the 20 ms preceding muscle relaxation. Our findings suggest that neural mechanisms contribute differently to the relaxation of muscles with a different functional role. Voluntary relaxation in distal arm muscles is mainly related to the reduction of motor cortical output, while in proximal muscles a spinal disfacilitation is also present and possibly sustained by the modulation of presynaptic inhibition.

  9. Source of non-arrhenius average relaxation time in glass-forming liquids

    DEFF Research Database (Denmark)

    Dyre, Jeppe

    1998-01-01

    A major mystery of glass-forming liquids is the non-Arrhenius temperature-dependence of the average relaxation time. This paper briefly reviews the classical phenomenological models for non-Arrhenius behavior – the free volume model and the entropy model – and critiques against these models. We...... are anharmonic, the non-Arrhenius temperature-dependence of the average relaxation time is a consequence of the fact that the instantaneous shear modulus increases upon cooling....

  10. Effects of in-pulse transverse relaxation in 3D ultrashort echo time sequences: analytical derivation, comparison to numerical simulation and experimental application at 3T.

    Science.gov (United States)

    Springer, Fabian; Steidle, Günter; Martirosian, Petros; Claussen, Claus D; Schick, Fritz

    2010-09-01

    The introduction of ultrashort-echo-time-(UTE)-sequences to clinical whole-body MR scanners has opened up the field of MR characterization of materials or tissues with extremely fast signal decay. If the transverse relaxation time is in the range of the RF-pulse duration, approximation of the RF-pulse by an instantaneous rotation applied at the middle of the RF-pulse and immediately followed by free relaxation will lead to a distinctly underestimated echo signal. Thus, the regular Ernst equation is not adequate to correctly describe steady state signal under those conditions. The paper presents an analytically derived modified Ernst equation, which correctly describes in-pulse relaxation of transverse magnetization under typical conditions: The equation is valid for rectangular excitation pulses, usually applied in 3D UTE sequences. Longitudinal relaxation time of the specimen must be clearly longer than RF-pulse duration, which is fulfilled for tendons and bony structures as well as many solid materials. Under these conditions, the proposed modified Ernst equation enables adequate and relatively simple calculation of the magnetization of materials or tissues. Analytically derived data are compared to numerical results obtained by using an established Runge-Kutta-algorithm based on the Bloch equations. Validity of the new approach was also tested by systematical measurements of a solid polymeric material on a 3T whole-body MR scanner. Thus, the presented modified Ernst equation provides a suitable basis for T1 measurements, even in tissues with T2 values as short as the RF-pulse duration: independent of RF-pulse duration, the 'variable flip angle method' led to consistent results of longitudinal relaxation time T1, if the T2 relaxation time of the material of interest is known as well.

  11. Attractors of relaxation discrete-time systems with chaotic dynamics on a fast time scale

    Energy Technology Data Exchange (ETDEWEB)

    Maslennikov, Oleg V.; Nekorkin, Vladimir I. [Institute of Applied Physics of RAS, Nizhny Novgorod (Russian Federation)

    2016-07-15

    In this work, a new type of relaxation systems is considered. Their prominent feature is that they comprise two distinct epochs, one is slow regular motion and another is fast chaotic motion. Unlike traditionally studied slow-fast systems that have smooth manifolds of slow motions in the phase space and fast trajectories between them, in this new type one observes, apart the same geometric objects, areas of transient chaos. Alternating periods of slow regular motions and fast chaotic ones as well as transitions between them result in a specific chaotic attractor with chaos on a fast time scale. We formulate basic properties of such attractors in the framework of discrete-time systems and consider several examples. Finally, we provide an important application of such systems, the neuronal electrical activity in the form of chaotic spike-burst oscillations.

  12. Attractors of relaxation discrete-time systems with chaotic dynamics on a fast time scale.

    Science.gov (United States)

    Maslennikov, Oleg V; Nekorkin, Vladimir I

    2016-07-01

    In this work, a new type of relaxation systems is considered. Their prominent feature is that they comprise two distinct epochs, one is slow regular motion and another is fast chaotic motion. Unlike traditionally studied slow-fast systems that have smooth manifolds of slow motions in the phase space and fast trajectories between them, in this new type one observes, apart the same geometric objects, areas of transient chaos. Alternating periods of slow regular motions and fast chaotic ones as well as transitions between them result in a specific chaotic attractor with chaos on a fast time scale. We formulate basic properties of such attractors in the framework of discrete-time systems and consider several examples. Finally, we provide an important application of such systems, the neuronal electrical activity in the form of chaotic spike-burst oscillations.

  13. Time-dependent Jahn-Teller problem: Phonon-induced relaxation through conical intersection

    Energy Technology Data Exchange (ETDEWEB)

    Pae, Kaja, E-mail: kaja.pae@gmail.com; Hizhnyakov, Vladimir [Institute of Physics University of Tartu, Tartu (Estonia)

    2014-12-21

    A theoretical study of time-dependent dynamical Jahn-Teller effect in an impurity center in a solid is presented. We are considering the relaxation of excited states in the E⊗e-problem through the conical intersection of the potential energy. A strict quantum-mechanical treatment of vibronic interactions with both the main Jahn-Teller active vibration and the nontotally symmetric phonons causing the energy loss is given. The applied method enables us to calculate the time-dependence of the distribution function of the basic configurational coordinate. We have performed a series of numerical calculations allowing us, among other relaxation features, to visualise the details of the relaxation through the conical intersection. In particular, we elucidate how the Slonczewski quantization of the states in the conical intersection affects the relaxation.

  14. Time-dependent Jahn-Teller problem: phonon-induced relaxation through conical intersection.

    Science.gov (United States)

    Pae, Kaja; Hizhnyakov, Vladimir

    2014-12-21

    A theoretical study of time-dependent dynamical Jahn-Teller effect in an impurity center in a solid is presented. We are considering the relaxation of excited states in the E⊗e-problem through the conical intersection of the potential energy. A strict quantum-mechanical treatment of vibronic interactions with both the main Jahn-Teller active vibration and the nontotally symmetric phonons causing the energy loss is given. The applied method enables us to calculate the time-dependence of the distribution function of the basic configurational coordinate. We have performed a series of numerical calculations allowing us, among other relaxation features, to visualise the details of the relaxation through the conical intersection. In particular, we elucidate how the Slonczewski quantization of the states in the conical intersection affects the relaxation.

  15. SEMI-DEFINITE RELAXATION ALGORITHM FOR SINGLE MACHINE SCHEDULING WITH CONTROLLABLE PROCESSING TIMES

    Institute of Scientific and Technical Information of China (English)

    CHEN FENG; ZHANG LIANSHENG

    2005-01-01

    The authors present a semi-definite relaxation algorithm for the scheduling problem with controllable times on a single machine. Their approach shows how to relate this problem with the maximum vertex-cover problem with kernel constraints (MKVC).The established relationship enables to transfer the approximate solutions of MKVCinto the approximate solutions for the scheduling problem. Then, they show how to obtain an integer approximate solution for MKVC based on the semi-definite relaxation and randomized rounding technique.

  16. Time-Dependent Behaviors of Granite: Loading-Rate Dependence, Creep, and Relaxation

    Science.gov (United States)

    Hashiba, K.; Fukui, K.

    2016-07-01

    To assess the long-term stability of underground structures, it is important to understand the time-dependent behaviors of rocks, such as their loading-rate dependence, creep, and relaxation. However, there have been fewer studies on crystalline rocks than on tuff, mudstone, and rock salt, because the high strength of crystalline rocks makes the detection of their time-dependent behaviors much more difficult. Moreover, studies on the relaxation, temporal change of stress and strain (TCSS) conditions, and relations between various time-dependent behaviors are scarce for not only granites, but also other rocks. In this study, previous reports on the time-dependent behaviors of granites were reviewed and various laboratory tests were conducted using Toki granite. These tests included an alternating-loading-rate test, creep test, relaxation test, and TCSS test. The results showed that the degree of time dependence of Toki granite is similar to other granites, and that the TCSS resembles the stress-relaxation curve and creep-strain curve. A viscoelastic constitutive model, proposed in a previous study, was modified to investigate the relations between the time-dependent behaviors in the pre- and post-peak regions. The modified model reproduced the stress-strain curve, creep, relaxation, and the results of the TCSS test. Based on a comparison of the results of the laboratory tests and numerical simulations, close relations between the time-dependent behaviors were revealed quantitatively.

  17. Mechanical spectra of glass-forming liquids. II. Gigahertz-frequency longitudinal and shear acoustic dynamics in glycerol and DC704 studied by time-domain Brillouin scattering

    DEFF Research Database (Denmark)

    Klieber, Christoph; Hecksher, Tina; Pezeril, Thomas;

    2013-01-01

    of the shear acoustic relaxation time agrees well with literature data for dielectric measurements. In DC704, combining the new data with data from measurements obtained previously by piezo-ceramic transducers yields figures showing the longitudinal and shear sound velocities at frequencies from mHz to GHz...

  18. A theoretical study of the stress relaxation in HMX on the picosecond time scale

    Science.gov (United States)

    Long, Yao; Chen, Jun

    2015-12-01

    The stress relaxation model of β-HMX on the picosecond time scale is studied by a theoretical approach. The relaxation of normal stress is contributed by lattice vibration, and the relaxation of shear stress is contributed by molecular rotation. Based on this model, the energy dissipation rule of the elastic wave and the profile of the shock wave are investigated. We find at low frequency the dissipation rate of the elastic wave is proportional to the power function of frequency, and under high speed shock loading the width of the stress relaxation zone is less than 0.3 μm there is a pressure peak with a height of 14 GPa near the wave front.

  19. Space and time dynamical heterogeneity in glassy relaxation. The role of democratic clusters

    Energy Technology Data Exchange (ETDEWEB)

    Appignanesi, G A; Rodriguez Fris, J A [Fisicoquimica, Departamento de Quimica, Universidad Nacional del Sur, Avenida Alem 1253, 8000 BahIa Blanca (Argentina); Seccion de Fisicoquimica, Instituto de Quimica de la Universidad Nacional del Sur, INQUISUR-UNS-CONICET, Universidad Nacional del Sur, Avenida Alem 1253, 8000 BahIa Blanca (Argentina)], E-mail: appignan@criba.edu.ar

    2009-05-20

    In this work we review recent computational advances in the understanding of the relaxation dynamics of supercooled glass-forming liquids. In such a supercooled regime these systems experience a striking dynamical slowing down which can be rationalized in terms of the picture of dynamical heterogeneities, wherein the dynamics can vary by orders of magnitude from one region of the sample to another and where the sizes and timescales of such slowly relaxing regions are expected to increase considerably as the temperature is decreased. We shall focus on the relaxation events at a microscopic level and describe the finding of the collective motions of particles responsible for the dynamical heterogeneities. In so doing, we shall demonstrate that the dynamics in different regions of the system is not only heterogeneous in space but also in time. In particular, we shall be interested in the events relevant to the long-time structural relaxation or {alpha} relaxation. In this regard, we shall focus on the discovery of cooperatively relaxing units involving the collective motion of relatively compact clusters of particles, called 'democratic clusters' or d-clusters. These events have been shown to trigger transitions between metabasins of the potential energy landscape (collections of similar configurations or structures) and to consist of the main steps in the {alpha} relaxation. Such events emerge in systems quite different in nature such as simple model glass formers and supercooled amorphous water. Additionally, another relevant issue in this context consists in the determination of a link between structure and dynamics. In this context, we describe the relationship between the d-cluster events and the constraints that the local structure poses on the relaxation dynamics, thus revealing their role in reformulating structural constraints. (topical review)

  20. Combined quantification of fatty infiltration, T 1-relaxation times and T 2*-relaxation times in normal-appearing skeletal muscle of controls and dystrophic patients.

    Science.gov (United States)

    Leporq, Benjamin; Le Troter, Arnaud; Le Fur, Yann; Salort-Campana, Emmanuelle; Guye, Maxime; Beuf, Olivier; Attarian, Shahram; Bendahan, David

    2017-08-01

    To evaluate the combination of a fat-water separation method with an automated segmentation algorithm to quantify the intermuscular fatty-infiltrated fraction, the relaxation times, and the microscopic fatty infiltration in the normal-appearing muscle. MR acquisitions were performed at 1.5T in seven patients with facio-scapulo-humeral dystrophy and eight controls. Disease severity was assessed using commonly used scales for the upper and lower limbs. The fat-water separation method provided proton density fat fraction (PDFF) and relaxation times maps (T 2* and T 1). The segmentation algorithm distinguished adipose tissue and normal-appearing muscle from the T 2* map and combined active contours, a clustering analysis, and a morphological closing process to calculate the index of fatty infiltration (IFI) in the muscle compartment defined as the relative amount of pixels with the ratio between the number of pixels within IMAT and the total number of pixels (IMAT + normal appearing muscle). In patients, relaxation times were longer and a larger fatty infiltration has been quantified in the normal-appearing muscle. T 2* and PDFF distributions were broader. The relaxation times were correlated to the Vignos scale whereas the microscopic fatty infiltration was linked to the Medwin-Gardner-Walton scale. The IFI was linked to a composite clinical severity scale gathering the whole set of scales. The MRI indices quantified within the normal-appearing muscle could be considered as potential biomarkers of dystrophies and quantitatively illustrate tissue alterations such as inflammation and fatty infiltration.

  1. Association of MRI T1 relaxation time with neuropsychological test performance in manganese- exposed welders.

    Science.gov (United States)

    Bowler, R M; Yeh, C-L; Adams, S W; Ward, E J; Ma, R E; Dharmadhikari, S; Snyder, S A; Zauber, S E; Wright, C W; Dydak, U

    2017-06-03

    This study examines the results of neuropsychological testing of 26 active welders and 17 similar controls and their relationship to welders' shortened MRI T1 relaxation time, indicative of increased brain manganese (Mn) accumulation. Welders were exposed to Mn for an average duration of 12.25 years to average levels of Mn in air of 0.11±0.05mg/m(3). Welders scored significantly worse than controls on Fruit Naming and the Parallel Lines test of graphomotor tremor. Welders had shorter MRI T1 relaxation times than controls in the globus pallidus, substantia nigra, caudate nucleus, and the anterior prefrontal lobe. 63% of the variation in MRI T1 relaxation times was accounted for by exposure group. In welders, lower relaxation times in the caudate nucleus and substantia nigra were associated with lower neuropsychological test performance on tests of verbal fluency (Fruit Naming), verbal learning, memory, and perseveration (WHO-UCLA AVLT). Results indicate that verbal function may be one of the first cognitive domains affected by brain Mn deposition in welders as reflected by MRI T1 relaxation times. Copyright © 2017 Elsevier B.V. All rights reserved.

  2. Multigrid waveform relaxation for the time-fractional heat equation

    NARCIS (Netherlands)

    F.J. Gaspar Lorenz (Franscisco); C. Rodrigo (Carmen)

    2017-01-01

    textabstractIn this work, we propose an efficient and robust multigrid method for solving the time-fractional heat equation. Due to the nonlocal property of fractional differential operators, numerical methods usually generate systems of equations for which the coefficient matrix is dense.

  3. T2 relaxation time mapping of the cartilage cap of osteochondromas

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hee Kyung; Horn, Paul; Laor, Tal [Cincinnati Children' s Hospital Medical Center, Cincinnati (United States); Daedzinski, Bernard J. [Dept. of Radiology, Children' s Hospital of Philadelphia, University of Pennsylvania, Philadelphia (United States); Kim, Dong Hoon [Dept. of Radiology, Pharmacology, Korea University College of Medicine, Seoul (Korea, Republic of)

    2016-02-15

    Our aim was to evaluate the cartilage cap of osteochondromas using T2 maps and to compare these values to those of normal patellar cartilage, from age and gender matched controls. This study was approved by the Institutional Review Board and request for informed consent was waived. Eleven children (ages 5-17 years) with osteochondromas underwent MR imaging, which included T2-weighted fat suppressed and T2 relaxation time mapping (echo time = 9-99/repetition time = 1500 msec) sequences. Lesion origins were femur (n = 5), tibia (n = 3), fibula (n = 2), and scapula (n = 1). Signal intensity of the cartilage cap, thickness, mean T2 relaxation times, and T2 spatial variation (mean T2 relaxation times as a function of distance) were evaluated. Findings were compared to those of patellar cartilage from a group of age and gender matched subjects. The cartilage caps showed a fluid-like high T2 signal, with mean thickness of 4.8 mm. The mean value of mean T2 relaxation times of the osteochondromas was 264.0 ± 80.4 msec (range, 151.0-366.0 msec). Mean T2 relaxation times were significantly longer than the values from patellar cartilage (39.0 msec) (p < 0.0001). These findings were observed with T2 spatial variation plots across the entire distance of the cartilage cap, with the most pronounced difference in the middle section of the cartilage. Longer T2 relaxation times of the cartilage caps of osteochondromas should be considered as normal, and likely to reflect an increased water content, different microstructure and component.

  4. Time Resolved Broadband Terahertz Relaxation Dynamics of Electron in Water

    DEFF Research Database (Denmark)

    Wang, Tianwu; Iwaszczuk, Krzysztof; Cooke, David G.;

    We investigated the transient response of the solvated electron in water ejected by photodetachment from potassium ferrocyanide using time resolved terahertz spectroscopy (TSTS). Ultrabroadband THz transients are generated and detected by a two-color femtosecond-induced air plasma and air biased...... coherent detection, respectively. We find that the measured frequency dependent conductivity can be well described by a Drude-Smith model, supplemented by a Lorentz model oscillating near 5 THz....

  5. ARTICLES: Time-Dependent Stokes Shift from Solvent Dielectric Relaxation

    Science.gov (United States)

    Xu, Jing; Wang, Quan-de; Zhu, Quan; Fu, Ke-xiang; He, Fu-cheng; Li, Xiang-yuan

    2010-06-01

    The Stokes shift response function, which is related to the time dependent solvation energy, is calculated with the dielectric response function and a novel expression of nonequilibrium solvation energy. In the derivation, relationship between the polarization and the dielectric response function is used. With the dipole-in-a-sphere model applied to the system coumarin 343 and water as the solvent, encouraging agreement with the experimental data from Jimenez et al. is obtained [Nature 369, 471 (1994)].

  6. Immiscible multicomponent lattice Boltzmann model for fluids with high relaxation time ratio

    Indian Academy of Sciences (India)

    Tao Jiang; Qiwei Gong; Ruofan Qiu; Anlin Wang

    2014-10-01

    An immiscible multicomponent lattice Boltzmann model is developed for fluids with high relaxation time ratios, which is based on the model proposed by Shan and Chen (SC). In the SC model, an interaction potential between particles is incorporated into the discrete lattice Boltzmann equation through the equilibrium velocity. Compared to the SC model, external forces in our model are discretized directly into the discrete lattice Boltzmann equation, as proposed by Guo et al. We develop it into a new multicomponent lattice Boltzmann (LB) model which has the ability to simulate immiscible multicomponent fluids with relaxation time ratio as large as 29.0 and to reduce `spurious velocity’. In this work, the improved model is validated and studied using the central bubble case and the rising bubble case. It finds good applications in both static and dynamic cases for multicomponent simulations with different relaxation time ratios.

  7. DIRECT MEASUREMENT OF TRANSVERSE RELAXATION TIME OF INTERMOLECULAR MULTIPLE QUANTUM COHERENCES IN NMR

    Institute of Scientific and Technical Information of China (English)

    ZHENG SHAO-KUAN; CHEN ZHONG; CHEN ZHI-WEI; ZHONG JIAN-HUI

    2001-01-01

    A one-dimensional NMR method is presented for measuring the transverse relaxation time, T2,n, of intermolecular multiple quantum coherences (IMQCs) of coherence order n in highly polarized spin systems. The pulse sequence proposed in this paper effectively suppresses the effects of radiation damping, molecular diffusion, inhomogeneity of magnetic field, and variations of dipolar correlation distance, all of which may affect quantitation of T2,n. This pulse sequence can be used to measure not only IMQC transverse relaxation time T2,n(n > 1) quickly and directly, but also the conventional transverse relaxation time. Experimental results demonstrate that the quantitative relationship between T2,n(n≥1) and T2 is T2,n≈T2/n. These results will be helpful for understanding the fundamental properties and mechanisms of IMQCs.

  8. Conductivity and relaxation time of porous silicon using the Kramers-Kronig relation

    Energy Technology Data Exchange (ETDEWEB)

    Dariani, R.S., E-mail: dariani@alzahra.ac.ir; Tavakoli, F.

    2015-01-01

    To review the dielectric characteristics of porous silicon samples with various porosities, an equivalent circuit including a capacitor and parallel resistance was used. By applying AC voltage with a constant amplitude of 200 mV to the circuit and using impedance measurements of the samples between 10–100 KHz, the variations in the capacitance, dielectric function, refractive index, and resistance for the samples at room temperature and up to 350 °C were studied. The dielectric characteristics of the samples decreased with increasing frequency. In addition, with increasing temperature, the pore diameters increased, and the dielectric characteristics varied. In this paper, we demonstrate that the relaxation time and DC conductivity could be obtained using the Kramers-Kronig function and Hilbert transformation. Our results indicate that the relaxation time and DC conductivity increase with increasing porosity, and with increasing temperature, the relaxation time decreases and the DC conductivity increases.

  9. Relaxation Study of N-Submitted Amides with Alcohol Mixtures by Time Domain Reflectometry

    Directory of Open Access Journals (Sweden)

    A. Arunkumar

    2016-08-01

    Full Text Available Using Time Domain Reflectometry (TDR, dielectric relaxation studies have been carried out on binary mixtures of amides (N-methylacetamide, N,N-dimethylacetamide with alcohols (1-butanol, 1-pentanol for various concentrations over the frequency range from 10 MHz to 10 GHz at 303 K. The Kirkwood correlation factor and excess dielectric constant properties were determined and discussed to yield information on the molecular interactions of the systems. The relaxation time is vary with the chain length of alcohols and substituted amides are noticed. The Bruggeman plot shows a deviation from linearity. This deviation was attributed to some sort of molecular interaction which may take place between the alcohols and substituted amides. The excess static permittivity and excess inverse relaxation time values vary from negative to positive for all the systems indicating the solute-solvent interaction to exist between alcohols and substituted amides for all the dynamics of the mixture.

  10. Effects of cross-correlated noises on the relaxation time of the bistable system

    Institute of Scientific and Technical Information of China (English)

    谢崇伟; 梅冬成

    2003-01-01

    The stationary correlation function and the associated relaxation time for a general system driven by crosscorrelated white noises are derived, by virtue of a Stratonovich-like ansatz. The effects of correlated noises on the relaxation time of a bistable kinetic model coupled to an additive and a multiplicative white noises are studied. It is proved that for small fluctuations the relaxation time Tc as a function of λ (the correlated intensity between noises)exhibits very different behaviours for α< D and for α> D (α and D, respectively, stand for the intensities of additive and multiplicative noises). When α> D, Tc increases with increasing λ. But when α< D, Tc increases with λ for the case of weak correlated noises and sharply decreases with λ for the case of strong correlated noises, and thus Tc-λ curve behaves with one extremum.

  11. Source of non-arrhenius average relaxation time in glass-forming liquids

    DEFF Research Database (Denmark)

    Dyre, Jeppe

    1998-01-01

    then discuss a recently proposed model according to which the activation energy of the average relaxation time is determined by the work done in shoving aside the surrounding liquid to create space needed for a "flow event". In this model, which is based on the fact that intermolecular interactions......A major mystery of glass-forming liquids is the non-Arrhenius temperature-dependence of the average relaxation time. This paper briefly reviews the classical phenomenological models for non-Arrhenius behavior – the free volume model and the entropy model – and critiques against these models. We...... are anharmonic, the non-Arrhenius temperature-dependence of the average relaxation time is a consequence of the fact that the instantaneous shear modulus increases upon cooling....

  12. On-chip Brownian relaxation measurements of magnetic nanobeads in the time domain

    DEFF Research Database (Denmark)

    Østerberg, Frederik Westergaard; Rizzi, Giovanni; Hansen, Mikkel Fougt

    2013-01-01

    magnetic fields are needed. First, the method is demonstrated on Brownian relaxation measurements of beads with nominal sizes of 40, 80, 130, and 250 nm. The results are found to compare well to those obtained by an already established measurement technique in the frequency domain. Next, we demonstrate......We present and demonstrate a new method for on-chip Brownian relaxation measurements on magnetic nanobeads in the time domain using magnetoresistive sensors. The beads are being magnetized by the sensor self-field arising from the bias current passed through the sensors and thus no external...... the time and frequency domain methods on Brownian relaxation detection of clustering of streptavidin coated magnetic beads in the presence of different concentrations of biotin-conjugated bovine serum albumin and obtain comparable results. In the time domain, a measurement is carried out in less than 30 s...

  13. Photoacoustic Determination of Non-radiative Relaxation Time of Absorbing Centers in Maize Seeds

    Science.gov (United States)

    Domínguez-Pacheco, A.; Hernández-Aguilar, C.; Cruz-Orea, A.

    2017-07-01

    Using non-destructive photothermal techniques, it is possible to characterize non-homogenous materials to obtain its optical and thermal properties through photoacoustic spectroscopy (PAS). In photoacoustic (PA) phenomena, there are transient states of thermal excitation, when samples absorb the incident light; these states manifest an excitation process that generates the PA signal, being in direct relation with the non-radiative relaxation times with the sample absorbent centers. The objective of this study was to determine the non-radiative relaxation times associated with different absorbent centers of corn seeds ( Zea mays L.), by using PAS. A frequency scan was done at different wavelengths (350 nm, 470 nm and 650 nm) in order to obtain the non-radiative relaxation times with different types of maize seeds.

  14. Time to trust: longitudinal integrated clerkships and entrustable professional activities.

    Science.gov (United States)

    Hirsh, David A; Holmboe, Eric S; ten Cate, Olle

    2014-02-01

    Medical education shaped by the learning sciences can better serve medical students, residents, faculty, health care institutions, and patients. With increasing innovation in undergraduate and graduate medical education and more focused attention on educational principles and how people learn, this era of educational transformation offers promise. Principles manifest in "educational continuity" are informing changes in educational structures and venues and are enriching new discourse in educational pedagogy, assessment, and scholarship. The articles by Myhre and colleagues and Woloschuk and colleagues in this issue, along with mounting evidence preceding these works, should reassure that principle-driven innovation in medical education is not only possible but can be achieved safely. In this commentary, the authors draw from these works and the wider literature on longitudinal integrated educational design. They suggest that the confluences of movements for longitudinal integrated clerkships and entrustable professional activities open new possibilities for other educational and practice advancements in quality and safety. With the advent of competency-based education, explicit milestones, and improved assessment regimens, overseers will increasingly evaluate students, trainees, and other learners on their ability rather than relying solely on time spent in an activity. The authors suggest that, for such oversight to have the most value, assessors and learners need adequate oversight time, and redesign of educational models will serve this operational imperative. As education leaders are reassessing old medical school and training models, rotational blocks, and other barriers to progress, the authors explore the dynamic interplay between longitudinal integrated learning models and entrustment.

  15. Time derivatives of the spectrum: Relaxing the stationarity assumption

    Science.gov (United States)

    Prieto, G. A.; Thomson, D. J.; Vernon, F. L.

    2005-12-01

    Spectrum analysis of seismic waveforms has played a significant role towards the understanding of multiple aspects of Earth structure and earthquake source physics. In recent years the multitaper spectrum estimation approach (Thomson, 1982) has been applied to geophysical problems providing not only reliable estimates of the spectrum, but also estimates of spectral uncertainties (Thomson and Chave, 1991). However, these improved spectral estimates were developed under the assumption of local stationarity and provide an incomplete description of the observed process. It is obvious that due to the intrinsic attenuation of the Earth, the amplitudes, and thus the frequency contents are changing with time as waves pass through a seismic station. There have been incredible improvements in different techniques to analyze non-stationary signals, including wavelet decomposition, Wigner-Ville spectrum and the dual-frequency spectrum. We apply one of the recently developed techniques, the Quadratic Inverse Theory (Thomson, 1990, 1994), combined with the multitaper technique to look at the time derivatives of the spectrum. If the spectrum is reasonably white in a certain bandwidth, using QI theory, we can estimate the derivatives of the spectrum at each frequency. We test synthetic signals to corroborate the approach and apply it the records of small earthquakes at local distances. This is a first approach to try and combine the classical spectrum analysis without the assumption of stationarity that is generally taken.

  16. Deconfinement Phase Transition in an Expanding Quark system in Relaxation Time Approximation

    CERN Document Server

    Yang, Z; Yang, Zhenwei; Zhuang, Pengfei

    2004-01-01

    We investigated the effects of nonequilibrium and collision terms on the deconfinement phase transition of an expanding quark system in Friedberg-Lee model in relaxation time approximation. By calculating the effective quark potential, the critical temperature of the phase transition is dominated by the mean field, while the collisions among quarks and mesons change the time structure of the phase transition significantly.

  17. Comparing Entropic and Multiple Relaxation Times Lattice Boltzmann Methods for blood flow simulations

    NARCIS (Netherlands)

    Geerdink, J.B.W.; Hoekstra, A.G.

    2009-01-01

    We compare the Lattice BGK, the Multiple Relaxation Times and the Entropic Lattice Boltzmann Methods for time harmonic flows. We measure the stability, speed and accuracy of the three models for Reynolds and Womersley numbers that are representative for human arteries. The Lattice BGK shows

  18. Only through perturbation can relaxation times be estimated

    DEFF Research Database (Denmark)

    Ditlevsen, Susanne; Lansky, Petr

    2012-01-01

    Estimation of model parameters is as important as model building, but is often neglected in model studies. Here we show that despite the existence of well known results on parameter estimation in a simple homogenous Ornstein-Uhlenbeck process, in most practical situations the methods suffer greatly...... from finite sample sizes and especially the estimator of the time constant of the system is degraded. Therefore an alternative solution is of paramount importance. We present such a solution based on perturbation of the system, observing trajectories far from equilibrium. The results are illustrated...... on computer experiments based on applications in neuroscience and pharmacokinetics, which show a striking improvement of the quality of estimation. The results are important for judicious designs of experiments to obtain maximal information from each data point, especially when samples are expensive...

  19. Option pricing during post-crash relaxation times

    Science.gov (United States)

    Dibeh, Ghassan; Harmanani, Haidar M.

    2007-07-01

    This paper presents a model for option pricing in markets that experience financial crashes. The stochastic differential equation (SDE) of stock price dynamics is coupled to a post-crash market index. The resultant SDE is shown to have stock price and time dependent volatility. The partial differential equation (PDE) for call prices is derived using risk-neutral pricing. European call prices are then estimated using Monte Carlo and finite difference methods. Results of the model show that call option prices after the crash are systematically less than those predicted by the Black-Scholes model. This is a result of the effect of non-constant volatility of the model that causes a volatility skew.

  20. Dielectric relaxation time and structure of bound water in biological materials

    Energy Technology Data Exchange (ETDEWEB)

    Mashimo, S.; Kuwabara, S.; Yagihara, S.; Higasi, K.

    1987-12-03

    The dielectric behavior of living tissues and a number of biological materials was examined by new equipment of the time domain reflectometry method in a wide frequency range of 10/sup 7/-10/sup 10/ Hz. The authors found two peaks of Debye absorption around 100 MHz and 20 GHz for all the materials. The low-frequency absorption is probably due to bound water while the high-frequency absorption to free water. From the observed relaxation times of bound water a hypothesis is ventured on the structure of bound water and its relaxation mechanism.

  1. Non-Fermi liquid behavior of thermal relaxation time in degenerate electron gas

    CERN Document Server

    Sarkar, Sreemoyee

    2012-01-01

    The thermal relaxation time ($\\tau_{\\kappa_{ee}}$) for the degenerate electron plasma has been calculated by incorporating non-Fermi liquid (NFL) corrections both for the thermal conductivity and specific heat capacity. Perturbative results are presented by making expansion in $T/m_D$ with next to leading order corrections. It is seen that unlike the normal Fermi liquid (FL) result where $\\tau_{\\kappa_{ee}}\\propto 1/T^2$, NFL corrections in leading order (LO) changes the temperature dependence of $\\tau_{\\kappa_{ee}}$ to 1/T. Incorporation of the phase space correction driven by the medium modified Fermion dispersion relation increases the relaxation time further.

  2. Molecular motions and phase transitions. NMR relaxation times studies of several lecithins.

    OpenAIRE

    Bar-Adon, R; Gilboa, H

    1981-01-01

    The spin-lattice relaxation time, T1, and the dipolar energy relaxation time, TD, were measured as a function of temperature. The materials studied were samples of anhydrous L-dipalmitoyl lecithin, DL-dipalmitoyl lecithin, L-dimyristoyl lecithin, DL-dimyristoyl lecithin and their monohydrates, and of anhydrous egg yolk lecithin. It is shown that TD is a much more sensitive parameter than T1 for the determination of the Chapman phase transition. Comparison between T1 and TD provides informatio...

  3. Estimating mean first passage time of biased random walks with short relaxation time on complex networks.

    Directory of Open Access Journals (Sweden)

    Zhuo Qi Lee

    Full Text Available Biased random walk has been studied extensively over the past decade especially in the transport and communication networks communities. The mean first passage time (MFPT of a biased random walk is an important performance indicator in those domains. While the fundamental matrix approach gives precise solution to MFPT, the computation is expensive and the solution lacks interpretability. Other approaches based on the Mean Field Theory relate MFPT to the node degree alone. However, nodes with the same degree may have very different local weight distribution, which may result in vastly different MFPT. We derive an approximate bound to the MFPT of biased random walk with short relaxation time on complex network where the biases are controlled by arbitrarily assigned node weights. We show that the MFPT of a node in this general case is closely related to not only its node degree, but also its local weight distribution. The MFPTs obtained from computer simulations also agree with the new theoretical analysis. Our result enables fast estimation of MFPT, which is useful especially to differentiate between nodes that have very different local node weight distribution even though they share the same node degrees.

  4. Nanosecond spin relaxation times in single layer graphene spin valves with hexagonal boron nitride tunnel barriers

    Science.gov (United States)

    Singh, Simranjeet; Katoch, Jyoti; Xu, Jinsong; Tan, Cheng; Zhu, Tiancong; Amamou, Walid; Hone, James; Kawakami, Roland

    2016-09-01

    We present an experimental study of spin transport in single layer graphene using atomic sheets of hexagonal boron nitride (h-BN) as a tunnel barrier for spin injection. While h-BN is expected to be favorable for spin injection, previous experimental studies have been unable to achieve spin relaxation times in the nanosecond regime, suggesting potential problems originating from the contacts. Here, we investigate spin relaxation in graphene spin valves with h-BN barriers and observe room temperature spin lifetimes in excess of a nanosecond, which provides experimental confirmation that h-BN is indeed a good barrier material for spin injection into graphene. By carrying out measurements with different thicknesses of h-BN, we show that few layer h-BN is a better choice than monolayer for achieving high non-local spin signals and longer spin relaxation times in graphene.

  5. Increasing energy relaxation time of superconducting qubits with nonmagnetic infrared filter and shield

    Science.gov (United States)

    Yuhao, Liu; Mengmeng, Li; Dong, Lan; Guangming, Xue; Xinsheng, Tan; Haifeng, Yu; Yang, Yu

    2016-05-01

    One of the primary origins of the energy relaxation in superconducting qubits is the quasiparticle loss. The quasiparticles can be excited remarkably by infrared radiation. In order to minimize the density of quasiparticle and increase the qubit relaxation time, we design and fabricate the infrared filter and shield for superconducting qubits. In comparison with previous filters and shields, a nonmagnetic dielectric is used as the infrared absorbing material, greatly suppressing the background magnetic fluctuations. The filters can be made to impedance-match with other microwave devices. Using the as-fabricated infrared filter and shield, we increased the relaxation time of a transmon qubit from 519 ns to 1125 ns. Project supported by the National Natural Science Foundation of China (Grant Nos. 91321310, 11274156, 11474152, 11474153, 61521001, and 11504165) and the State Key Program for Basic Research of China (Grant Nos. 2011CB922104 and 2011CBA00205).

  6. Determination of protein rotational correlation time from NMR relaxation data at various solvent viscosities

    Energy Technology Data Exchange (ETDEWEB)

    Korchuganov, Denis S.; Gagnidze, Ivan E.; Tkach, Elena N.; Schulga, Alexey A.; Kirpichnikov, Mikhail P.; Arseniev, Alexander S. [Russian Academy of Sciences, Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry (Russian Federation)], E-mail: aars@nmr.ru

    2004-12-15

    An accurate determination of the overall rotation of a protein plays a crucial role in the investigation of its internal motions by NMR. In the present work, an innovative approach to the determination of the protein rotational correlation time {tau}{sub R} from the heteronuclear relaxation data is proposed. The approach is based on a joint fit of relaxation data acquired at several viscosities of a protein solution. The method has been tested on computer simulated relaxation data as compared to the traditional {tau}{sub R} determination method from T{sub 1}/T{sub 2} ratio. The approach has been applied to ribonuclease barnase from Bacillus amyloliquefaciens dissolved in an aqueous solution and deuterated glycerol as a viscous component. The resulting rotational correlation time of 5.56 {+-} 0.01 ns and other rotational diffusion tensor parameters are in good agreement with those determined from T{sub 1}/T{sub 2} ratio.

  7. Fragile-strong fluid crossover and universal relaxation times in a confined hard-disk fluid.

    Science.gov (United States)

    Yamchi, Mahdi Zaeifi; Ashwin, S S; Bowles, Richard K

    2012-11-30

    We show that a system of hard disks confined to a narrow channel exhibits a fragile-strong fluid crossover located at the maximum of the isobaric heat capacity and that the relaxation times for different channel widths fall onto a single master curve when rescaled by the relaxation times and temperatures of the crossover. Calculations of the configurational entropy and the inherent structure equation of state find that the crossover is related to properties of the jamming landscape for the model but that the Adam-Gibbs relation does not predict the relaxation behavior. We also show that a facilitated dynamics description of the system, where kinetically excited regions are identified with local packing arrangements of the disks, successfully describes the fragile-strong crossover.

  8. T2 star relaxation times for assessment of articular cartilage at 3 T: a feasibility study.

    Science.gov (United States)

    Mamisch, Tallal Charles; Hughes, Timothy; Mosher, Timothy J; Mueller, Christoph; Trattnig, Siegfried; Boesch, Chris; Welsch, Goetz Hannes

    2012-03-01

    T2 mapping techniques use the relaxation constant as an indirect marker of cartilage structure, and the relaxation constant has also been shown to be a sensitive parameter for cartilage evaluation. As a possible additional robust biomarker, T2* relaxation time is a potential, clinically feasible parameter for the biochemical evaluation of articular cartilage. The knees of 15 healthy volunteers and 15 patients after microfracture therapy (MFX) were evaluated with a multi-echo spin-echo T2 mapping technique and a multi-echo gradient-echo T2* mapping sequence at 3.0 Tesla MRI. Inline maps, using a log-linear least squares fitting method, were assessed with respect to the zonal dependency of T2 and T2* relaxation for the deep and superficial regions of healthy articular cartilage and cartilage repair tissue. There was a statistically significant correlation between T2 and T2* values. Both parameters demonstrated similar spatial dependency, with longer values measured toward the articular surface for healthy articular cartilage. No spatial variation was observed for cartilage repair tissue after MFX. Within this feasibility study, both T2 and T2* relaxation parameters demonstrated a similar response in the assessment of articular cartilage and cartilage repair tissue. The potential advantages of T2*-mapping of cartilage include faster imaging times and the opportunity for 3D acquisitions, thereby providing greater spatial resolution and complete coverage of the articular surface.

  9. T2 star relaxation times for assessment of articular cartilage at 3 T: a feasibility study

    Energy Technology Data Exchange (ETDEWEB)

    Mamisch, Tallal Charles [University Bern, Department of Orthopedic Surgery, Inselspital, Bern (Switzerland); University Bern, Magnetic Resonance Spectroscopy and Methodology, Department of Clinical Research, Bern (Switzerland); Hughes, Timothy [Siemens Medical Solutions, Erlangen (Germany); Mosher, Timothy J. [Penn State University College of Medicine, Musculoskeletal Imaging and MRI, Department of Radiology, Hershey, PA (United States); Mueller, Christoph [University of Erlangen, Department of Trauma Surgery, Erlangen (Germany); Trattnig, Siegfried [Medical University of Vienna, MR Center - High Field MR, Department of Radiology, Vienna (Austria); Boesch, Chris [University Bern, Magnetic Resonance Spectroscopy and Methodology, Department of Clinical Research, Bern (Switzerland); Welsch, Goetz Hannes [University of Erlangen, Department of Trauma Surgery, Erlangen (Germany); Medical University of Vienna, MR Center - High Field MR, Department of Radiology, Vienna (Austria)

    2012-03-15

    T2 mapping techniques use the relaxation constant as an indirect marker of cartilage structure, and the relaxation constant has also been shown to be a sensitive parameter for cartilage evaluation. As a possible additional robust biomarker, T2* relaxation time is a potential, clinically feasible parameter for the biochemical evaluation of articular cartilage. The knees of 15 healthy volunteers and 15 patients after microfracture therapy (MFX) were evaluated with a multi-echo spin-echo T2 mapping technique and a multi-echo gradient-echo T2* mapping sequence at 3.0 Tesla MRI. Inline maps, using a log-linear least squares fitting method, were assessed with respect to the zonal dependency of T2 and T2* relaxation for the deep and superficial regions of healthy articular cartilage and cartilage repair tissue. There was a statistically significant correlation between T2 and T2* values. Both parameters demonstrated similar spatial dependency, with longer values measured toward the articular surface for healthy articular cartilage. No spatial variation was observed for cartilage repair tissue after MFX. Within this feasibility study, both T2 and T2* relaxation parameters demonstrated a similar response in the assessment of articular cartilage and cartilage repair tissue. The potential advantages of T2*-mapping of cartilage include faster imaging times and the opportunity for 3D acquisitions, thereby providing greater spatial resolution and complete coverage of the articular surface. (orig.)

  10. Longitudinal T1 relaxation rate (R1) captures changes in short-term Mn exposure in welders.

    Science.gov (United States)

    Lewis, Mechelle M; Flynn, Michael R; Lee, Eun-Young; Van Buren, Scott; Van Buren, Eric; Du, Guangwei; Fry, Rebecca C; Herring, Amy H; Kong, Lan; Mailman, Richard B; Huang, Xuemei

    2016-12-01

    We demonstrated recently that the T1 relaxation rate (R1) captured short-term Mn exposure in welders with chronic, relatively low exposure levels in a cross-sectional study. In the current study, we used a longitudinal design to examine whether R1 values reflect the short-term dynamics of Mn exposure. Twenty-nine welders were evaluated at baseline and 12 months. Occupational questionnaires estimated short-term welding exposure using welding hours in the 90days prior to each study visit (HrsW90). In addition, blood Mn levels, the pallidal index (PI; globus pallidus T1-weighted intensity (T1WI)/frontal white matter T1WI), and R1 values in brain regions of interest (ROIs) were determined as Mn biomarkers at each visit. Associations between changes in estimated welding exposure and changes in purported Mn biomarkers were assessed by Spearman's correlations with adjustment for age and baseline R1, HrsW90, and blood Mn values. Changes in welding hours (HrsW90: the short-term welding exposure estimate), was associated significantly with changes in R1 values in the putamen (r=0.541, p=0.005), caudate (R=0.453, p=0.023), globus pallidus (R=0.430, p=0.032), amygdala (R=0.461, p=0.020), and hippocampus (R=0.447, p=0.025), but not with changes in blood Mn levels or the PI. Changes in R1 values correlated with changes in the short-term welding exposure estimate, but not with more traditional measures of Mn exposure (blood Mn levels or PI). These results suggest that R1 may serve as a useful marker to capture the short-term dynamics in Mn brain accumulation related to welding exposure. Copyright © 2016 Elsevier B.V. All rights reserved.

  11. Invariance of conductivity relaxation under pressure and temperature variations at constant conductivity relaxation time in 0.4Ca(NO₃)₂-0.6KNO₃.

    Science.gov (United States)

    Wojnarowska, Z; Ngai, K L; Paluch, M

    2014-12-01

    The article reports the dependence of the conductivity relaxation on temperature T and pressure P in the canonical ionic glass former 0.4Ca(NO(3))(2)-0.6KNO(3)(CKN). At constant conductivity relaxation time τ(σ), the entire conductivity relaxation spectra obtained at widely different combinations of T and P superpose almost perfectly, and thus it is the ion-ion interaction but not thermodynamics that determines the frequency dispersion. Moreover, on vitrifying CKN by either elevating P or decreasing T, changes of P or T dependence of τ(σ) at the glass transition pressure P(g) and temperature T(g) are observed to occur at the same value, i.e., τ(σ)(P(g))=τ(σ)(T(g)), indicating that the relation between τ(σ) and the structural relaxation time τ(α) is also independent of P and T.

  12. Highly biocompatible TiO2:Gd3+ nano-contrast agent with enhanced longitudinal relaxivity for targeted cancer imaging

    Science.gov (United States)

    Chandran, Parwathy; Sasidharan, Abhilash; Ashokan, Anusha; Menon, Deepthy; Nair, Shantikumar; Koyakutty, Manzoor

    2011-10-01

    We report the development of a novel magnetic nano-contrast agent (nano-CA) based on Gd3+ doped amorphous TiO2 of size ~25 nm, exhibiting enhanced longitudinal relaxivity (r1) and magnetic resonance (MR) contrasting together with excellent biocompatibility. Quantitative T1 mapping of phantom samples using a 1.5 T clinical MR imaging system revealed that the amorphous phase of doped titania has the highest r1 relaxivity which is ~2.5 fold higher than the commercially used CA Magnevist™. The crystalline (anatase) samples formed by air annealing at 250 °C and 500 °C showed significant reduction in r1 values and MR contrast, which is attributed to the loss of proton-exchange contribution from the adsorbed water and atomic re-arrangement of Gd3+ ions in the crystalline host lattice. Nanotoxicity studies including cell viability, plasma membrane integrity, reactive oxygen stress and expression of pro-inflammatory cytokines, performed on human primary endothelial cells (HUVEC), human blood derived peripheral blood mononuclear cells (PBMC) and nasopharyngeal epidermoid carcinoma (KB) cell line showed excellent biocompatibility up to relatively higher doses of 200 μg ml-1. The potential of this nano-CA to cause hemolysis, platelet aggregation and plasma coagulation were studied using human peripheral blood samples and found no adverse effects, illustrating the possibility of the safe intravenous administration of these agents for human applications. Furthermore, the ability of these agents to specifically detect cancer cells by targeting molecular receptors on the cell membrane was demonstrated on folate receptor (FR) positive oral carcinoma (KB) cells, where the folic acid conjugated nano-CA showed receptor specific accumulation on cell membrane while leaving the normal fibroblast cells (L929) unstained. This study reveals that the Gd3+ doped amorphous TiO2 nanoparticles having enhanced magnetic resonance contrast and high biocompatibility is a promising candidate for

  13. Predicting permeability from the characteristic relaxation time and intrinsic formation factor of complex conductivity spectra

    Science.gov (United States)

    Revil, A.; Binley, A.; Mejus, L.; Kessouri, P.

    2015-08-01

    Low-frequency quadrature conductivity spectra of siliclastic materials exhibit typically a characteristic relaxation time, which either corresponds to the peak frequency of the phase or the quadrature conductivity or a typical corner frequency, at which the quadrature conductivity starts to decrease rapidly toward lower frequencies. This characteristic relaxation time can be combined with the (intrinsic) formation factor and a diffusion coefficient to predict the permeability to flow of porous materials at saturation. The intrinsic formation factor can either be determined at several salinities using an electrical conductivity model or at a single salinity using a relationship between the surface and quadrature conductivities. The diffusion coefficient entering into the relationship between the permeability, the characteristic relaxation time, and the formation factor takes only two distinct values for isothermal conditions. For pure silica, the diffusion coefficient of cations, like sodium or potassium, in the Stern layer is equal to the diffusion coefficient of these ions in the bulk pore water, indicating weak sorption of these couterions. For clayey materials and clean sands and sandstones whose surface have been exposed to alumina (possibly iron), the diffusion coefficient of the cations in the Stern layer appears to be 350 times smaller than the diffusion coefficient of the same cations in the pore water. These values are consistent with the values of the ionic mobilities used to determine the amplitude of the low and high-frequency quadrature conductivities and surface conductivity. The database used to test the model comprises a total of 202 samples. Our analysis reveals that permeability prediction with the proposed model is usually within an order of magnitude from the measured value above 0.1 mD. We also discuss the relationship between the different time constants that have been considered in previous works as characteristic relaxation time, including

  14. Determining the structural relaxation times deep in the glassy state of the pharmaceutical Telmisartan

    Science.gov (United States)

    Adrjanowicz, K.; Paluch, M.; Ngai, K. L.

    2010-03-01

    By using the dielectric relaxation method proposed recently by Casalini and Roland (2009 Phys. Rev. Lett. 102 035701), we were able to determine the structural α-relaxation times deep in the glassy state of the pharmaceutical, Telmisartan. Normally, deep in the glassy state τα is so long that it cannot be measured but τβ, which is usually much shorter, can be directly determined. The method basically takes advantage of the connection between the α-relaxation and the secondary β-relaxation of the Johari-Goldstein kind, including a relation between their relaxation times τα and τβ, respectively. Thus, τα of Telmisartan were determined by monitoring the change of the dielectric β-loss, ɛ'', with physical aging time at temperatures well below the vitrification temperature. The values of τα were compared with those expected by the coupling model (CM). Unequivocal comparison cannot be made in the case of Telmisartan because its β-loss peak is extremely broad, and the CM predicts only an order of magnitude agreement between the primitive relaxation frequency and the β-peak frequency. We also made an attempt to analyze all isothermal and aging susceptibility data after transformation into the electric modulus representation. The τα found in the glass state by using the method of Casalini and Roland in the modulus representation are similar to those obtained in the susceptibility representation. However, it is remarkable that the stretching parameter βKWW - M = 0.51 in the electric modulus representation gives more precise fits to the aging data than in the susceptibility representation with βKWW = 0.61. Our results suggest that the electric modulus representation may be useful as an alternative to analyze aging data, especially in the case of highly polar glassformers having a large ratio of low frequency and high frequency dielectric constants, such as the Telmisartan studied.

  15. Relationship between the crystallization rates of amorphous nifedipine, phenobarbital, and flopropione, and their molecular mobility as measured by their enthalpy relaxation and (1)H NMR relaxation times.

    Science.gov (United States)

    Aso, Y; Yoshioka, S; Kojima, S

    2000-03-01

    Isothermal crystallization of amorphous nifedipine, phenobarbital, and flopropione was studied at temperatures above and below their glass transition temperatures (T(g)). A sharp decrease in the crystallization rate with decreasing temperature was observed for phenobarbital and flopropione, such that no crystallization was observed at temperatures 20-30 degrees C lower than their T(g) within ordinary experimental time periods. In contrast, the crystallization rate of nifedipine decreased moderately with decreasing temperature, and considerable crystallization was observed at 40 degrees C below its T(g) within 4 months. The molecular mobility of these amorphous drugs was assessed by enthalpy relaxation and (1)H-NMR relaxation measurements. The enthalpy relaxation time of nifedipine was smaller than that of phenobarbital or flopropinone at the same T - T(g) values, suggesting higher molecular mobility of nifedipine. The spin-lattice relaxation time in the rotating frame (T(1rho)) decreased markedly at temperature above T(g). The slope of the Arrhenius type plot of the T(1rho) for nifedipine protons changed at about 10 degrees C below the T(g), whereas the slope for phenobarbital protons became discontinuous at about 10 degrees C above the T(g). Even at temperatures below its T(g), the spin-spin relaxation process of nifedipine could be described by the sum of its Gaussian relaxation, which is characteristic of solid protons, and its Lorentzian relaxation, which is characteristic of protons with higher mobility. In contrast, no Lorentzian relaxation was observed for phenobarbital or flopropione at temperatures below their T(g). These results also suggest that nifedipine has higher molecular mobility than phenobarbital and flopropione at temperatures below T(g). The faster crystallization of nifedipine than that of phenobarbital or flopropione observed at temperatures below its T(g) may be partly ascribed to its higher molecular mobility at these temperatures.

  16. Capacity enhancement of wavelength/time/space asynchronous optical CDMA with relaxed cross-correlation

    Science.gov (United States)

    Singh, Jaswinder

    2013-12-01

    The analysis of a three-dimensional (3-D) wavelength/time/space (W-T-S) asynchronous optical CDMA code family is presented considering MAI only under relaxed cross-correlation (λc ⩾ 1). Based on the code performance, it is shown that for code-limited systems (when W and/or T are non-prime), the number of generated codes and hence the supported users can be significantly increased by relaxing the cross-correlation constraint if a slight degradation in code performance can be tolerated.

  17. Temperature dependence of the spin relaxation time of Fe3O4 and hemozoin superparamagnetic nanocrystals

    Science.gov (United States)

    Khmelinskii, I.; Makarov, V.

    2017-08-01

    We report experimental temperature and concentration dependences of the natural spin relaxation time of superparamagnetic Fe3O4 and hemozoin nanocrystals. We recorded the 1H NMR spectrum of 0.5% benzene dissolved in CS2 in function of superparamagnetic particle concentration and temperature, interpreting the 7.261 ± 0.002 ppm benzene line broadening. Our model for the line broadening includes natural, hyperfine magnetic dipole-dipole, and contact hyperfine contributions. The latter arises due to exchange interaction between benzene molecules and suspended nanoparticles. Estimated frequency of fluctuation in the 1 cm3 sample volume is in the 107 Hz scale. Estimated natural electron spin-lattice relaxation frequencies of the superparamagnetic nanocrystals using frequency of fluctuations, and developed theoretical model applied to analysis of experimental data are in good agreement between each other. Thus the presently developed approach may be used to study fluctuations and natural spin-lattice relaxation frequencies in different media.

  18. Optimized Schwarz waveform relaxation and discontinuous Galerkin time stepping for heterogeneous problems

    CERN Document Server

    Halpern, Laurence; Japhet, Caroline

    2010-01-01

    We design and analyze a Schwarz waveform relaxation algorithm for domain decomposition of advection-diffusion-reaction problems with strong heterogeneities. The interfaces are curved, and we use optimized Robin or Ventcell transmission conditions. We analyze the semi-discretization in time with Discontinuous Galerkin as well. We also show two-dimensional numerical results using generalized mortar finite elements in space.

  19. MR pulse sequences for selective relaxation time measurements: a phantom study

    DEFF Research Database (Denmark)

    Thomsen, C; Jensen, K E; Jensen, M

    1990-01-01

    a Siemens Magnetom wholebody magnetic resonance scanner operating at 1.5 Tesla was used. For comparison six imaging pulse sequences for relaxation time measurements were tested on the same phantom. The spectroscopic pulse sequences all had an accuracy better than 10% of the reference values....

  20. Elastic models for the non-Arrhenius relaxation time of glass-forming liquids

    DEFF Research Database (Denmark)

    Dyre, Jeppe

    We first review the phenomenology of viscous liquids and the standard models used for explaining the non-Arrhenius average relaxation time. Then the focus is turned to the so-called elastic models, arguing that these models are all equivalent in the Einstein approximation (where the short...

  1. Elastic models for the Non-Arrhenius Relaxation Time of Glass-Forming Liquids

    DEFF Research Database (Denmark)

    Dyre, J. C.

    2006-01-01

    We first review the phenomenology of viscous liquids and the standard models used for explaining the non-Arrhenius average relaxation time. Then the focus is turned to the so-called elastic models, arguing that these models are all equivalent in the Einstein approximation (where the short...

  2. Changes in P-31-relaxation times during organ preservation : Observations on cold stored human donor livers

    NARCIS (Netherlands)

    Wolf, RFE; Slooff, MJH; Go, KG; Kamman, RL

    1997-01-01

    During cold preservation for transplantation the tissue hydration state changes, It is not known whether such changes lead to altered relaxation times of P-31 nuclei with potential consequences for the quantification of tissue metabolites, Therefore, P-31 spectroscopic and proton T-1 relaxometric

  3. Interfacial layers from the protein HFBII hydrophobin: Dynamic surface tension, dilatational elasticity and relaxation times

    NARCIS (Netherlands)

    Alexandrov, N.A.; Marinova, K.G.; Gurkov, T.D.; Danov, K.D.; Kralchevsky, P.A.; Stoyanov, S.D.; Blijdenstein, T.B.J.; Arnaudov, L.N.; Pelan, E.G.; Lips, A.

    2012-01-01

    The pendant-drop method (with drop-shape analysis) and Langmuir trough are applied to investigate the characteristic relaxation times and elasticity of interfacial layers from the protein HFBII hydrophobin. Such layers undergo a transition from fluid to elastic solid films. The transition is

  4. Time stepping free numerical solution of linear differential equations: Krylov subspace versus waveform relaxation

    NARCIS (Netherlands)

    Bochev, Mikhail A.; Oseledets, I.V.; Tyrtyshnikov, E.E.

    2013-01-01

    The aim of this paper is two-fold. First, we propose an efficient implementation of the continuous time waveform relaxation method based on block Krylov subspaces. Second, we compare this new implementation against Krylov subspace methods combined with the shift and invert technique.

  5. Iterative across-time solution of linear differential equations: Krylov subspace versus waveform relaxation

    NARCIS (Netherlands)

    Bochev, Mikhail A.; Oseledets, I.V.; Tyrtyshnikov, E.E.

    The aim of this paper is two-fold. First, we propose an efficient implementation of the continuous time waveform relaxation (WR) method based on block Krylov subspaces. Second, we compare this new WR-Krylov implementation against Krylov subspace methods combined with the shift and invert (SAI)

  6. Analysis and Application of Distribution of Relaxation Times in Solid State Ionics

    NARCIS (Netherlands)

    Boukamp, B.A.; Rolle, A.

    2017-01-01

    Three methods for obtaining a Distribution (Function) of Relaxation Times (DFRT) are compared, Fourier transform (FT), Tikhonov regularization (TR) and a multiple-(RQ) CNLS-fit. The FT method was written in the programming package ‘Borland Delphi’, for the Tikhonov regularization (TR) a freely avail

  7. A high-precision approach to reconstruct distribution of relaxation times from electrochemical impedance spectroscopy

    Science.gov (United States)

    Zhang, Yanxiang; Chen, Yu; Li, Mei; Yan, Mufu; Ni, Meng; Xia, Changrong

    2016-03-01

    A new Tikhonov regularization approach without adjusting parameters is proposed for reconstructing distribution of relaxation time (DRT). It is capable of eliminating the pseudo peaks and capturing discontinuities in the DRT, making it feasible to resolve the number and the nature of electrochemical processes without making assumptions.

  8. Determining optimal ultrasound off time with micropulse longitudinal phacoemulsification.

    Science.gov (United States)

    Jensen, Jason D; Kirk, Kevin R; Gupta, Isha; Ronquillo, Cecinio; Farukhi, M Aabid; Stagg, Brian C; Pettey, Jeff H; Olson, Randall J

    2015-02-01

    To evaluate the optimum off time for the most efficient removal of lens fragments using micropulse ultrasound (US). John A. Moran Eye Center Laboratories, University of Utah, Salt Lake City, Utah, USA. Experimental study. Porcine lens nuclei were soaked in formalin for 2 hours and then cut into 2.0 mm cubes using the Signature US machine with a bent 0.9 mm phaco tip with a 30-degree bevel. The on time was 7 milliseconds (ms), and the off time was varied from 2 to 20 ms in 2 ms steps. Phacoemulsification efficiency (time for fragment removal) and chatter (number of times the fragment bounced from the tip) were measured. A nonsignificant linear increase in efficiency was observed with 2 to 6 ms of off time (R(2) = .87, P = .24). A significant linear decrease in efficiency was observed with 6 to 20 ms (R(2) = .74, P = .006). With micropulse longitudinal US, 6 to 7 ms of off time was as efficient as shorter off times; longer off times (8 to 20 ms) showed decreased efficiency. Chatter was minimal and statistically similar throughout. To maximize phacoemulsification US efficiency, an off-time setting of 6 ms is recommended. No author has a financial or proprietary interest in any material or method mentioned. Copyright © 2015 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  9. Estimation of T2 relaxation time of breast cancer: Correlation with clinical, imaging and pathological features

    Energy Technology Data Exchange (ETDEWEB)

    Seo, Mirinae; Sohn, Yu Mee [Dept. of Radiology, Kyung Hee University Hospital, College of Medicine, Kyung Hee University, Seoul (Korea, Republic of); Ryu, Jung Kyu; Jahng, Geon Ho; Rhee, Sun Jung; Oh, Jang Hoon; Won, Kyu Yeoun [Kyung Hee University Hospital at Gangdong, College of Medicine, Kyung Hee University, Seoul (Korea, Republic of)

    2017-01-15

    The purpose of this study was to estimate the T2* relaxation time in breast cancer, and to evaluate the association between the T2* value with clinical-imaging-pathological features of breast cancer. Between January 2011 and July 2013, 107 consecutive women with 107 breast cancers underwent multi-echo T2*-weighted imaging on a 3T clinical magnetic resonance imaging system. The Student's t test and one-way analysis of variance were used to compare the T2* values of cancer for different groups, based on the clinical-imaging-pathological features. In addition, multiple linear regression analysis was performed to find independent predictive factors associated with the T2* values. Of the 107 breast cancers, 92 were invasive and 15 were ductal carcinoma in situ (DCIS). The mean T2* value of invasive cancers was significantly longer than that of DCIS (p = 0.029). Signal intensity on T2-weighted imaging (T2WI) and histologic grade of invasive breast cancers showed significant correlation with T2* relaxation time in univariate and multivariate analysis. Breast cancer groups with higher signal intensity on T2WI showed longer T2* relaxation time (p = 0.005). Cancer groups with higher histologic grade showed longer T2* relaxation time (p = 0.017). The T2* value is significantly longer in invasive cancer than in DCIS. In invasive cancers, T2* relaxation time is significantly longer in higher histologic grades and high signal intensity on T2WI. Based on these preliminary data, quantitative T2* mapping has the potential to be useful in the characterization of breast cancer.

  10. Optically-detected spin-echo method for relaxation times measurements in a Rb atomic vapor

    Science.gov (United States)

    Gharavipour, M.; Affolderbach, C.; Gruet, F.; Radojičić, I. S.; Krmpot, A. J.; Jelenković, B. M.; Mileti, G.

    2017-06-01

    We introduce and demonstrate an experimental method, optically-detected spin-echo (ODSE), to measure ground-state relaxation times of a rubidium (Rb) atomic vapor held in a glass cell with buffer-gas. The work is motivated by our studies on high-performance Rb atomic clocks, where both population and coherence relaxation times (T 1 and T 2, respectively) of the ‘clock transition’ (52S1/2 | {F}g = 1,{m}F=0> ≤ftrightarrow | {F}g=2,{m}F=0> ) are relevant. Our ODSE method is inspired by classical nuclear magnetic resonance spin-echo method, combined with optical detection. In contrast to other existing methods, like continuous-wave double-resonance (CW-DR) and Ramsey-DR, principles of the ODSE method allow suppression of decoherence arising from the inhomogeneity of the static magnetic field across the vapor cell, thus enabling measurements of intrinsic relaxation rates, as properties of the cell alone. Our experimental result for the coherence relaxation time, specific for the clock transition, measured with the ODSE method is in good agreement with the theoretical prediction, and the ODSE results are validated by comparison to those obtained with Franzen, CW-DR and Ramsey-DR methods. The method is of interest for a wide variety of quantum optics experiments with optical signal readout.

  11. Pore size distribution, survival probability, and relaxation time in random and ordered arrays of fibers

    Science.gov (United States)

    Tomadakis, Manolis M.; Robertson, Teri J.

    2003-07-01

    We present a random walk based investigation of the pore size probability distribution and its moments, the survival probability and mean survival time, and the principal relaxation time, for random and ordered arrays of cylindrical fibers of various orientation distributions. The dimensionless mean survival time, principal relaxation time, mean pore size, and mean square pore size are found to increase with porosity, remain practically independent of the directionality of random fiber beds, and attain lower values for ordered arrays. Wide pore size distributions are obtained for random fiber structures and relatively narrow for ordered square arrays, all in very good agreement with theoretically predicted limiting values. Analytical results derived for the pore size probability and its lower moments for square arrays of fibers practically coincide with the corresponding simulation results. Earlier variational bounds on the mean survival time and principal relaxation time are obeyed by our numerical results in all cases, and are found to be quite sharp up to very high porosities. Dimensionless groups representing the deviation of such bounds from our simulation results vary in practically the same range as the corresponding values reported earlier for beds of spherical particles. A universal scaling expression of the literature relating the mean survival time to the mean pore size [S. Torquato and C. L. Y. Yeong, J. Chem. Phys. 106, 8814 (1997)] agrees very well with our results for all types of fiber structures, thus validated for the first time for anisotropic porous media.

  12. Impaired left ventricular global longitudinal strain in patients with heart failure with preserved ejection fraction: insights from the RELAX trial.

    Science.gov (United States)

    DeVore, Adam D; McNulty, Steven; Alenezi, Fawaz; Ersboll, Mads; Vader, Justin M; Oh, Jae K; Lin, Grace; Redfield, Margaret M; Lewis, Gregory; Semigran, Marc J; Anstrom, Kevin J; Hernandez, Adrian F; Velazquez, Eric J

    2017-07-01

    While abnormal left ventricular (LV) global longitudinal strain (GLS) has been described in patients with heart failure with preserved ejection fraction (HFpEF), its prevalence and clinical significance are poorly understood. Patients enrolled in the RELAX trial of sildenafil in HFpEF (LV ejection fraction ≥50%) in whom two-dimensional, speckle-tracking LV GLS was possible (n = 187) were analysed. The distribution of LV GLS and its associations with clinical characteristics, LV structure and function, biomarkers, exercise capacity and quality of life were assessed. Baseline median LV GLS was -14.6% (25th and 75th percentile, -17.0% and -11.9%, respectively) and abnormal (≥ - 16%) in 122/187 (65%) patients. Patients in the tertile with the best LV GLS had lower N-terminal pro-brain natriuretic peptide (NT-proBNP) [median 505 pg/mL (161, 1065) vs. 875 pg/mL (488, 1802), P = 0.008) and lower collagen III N-terminal propeptide (PIIINP) levels [median 6.7 µg/L (5.1, 8.1) vs. 8.1 µg/L (6.5, 10.5), P = 0.001] compared with the tertile with the worst LV GLS. There was also a modest linear relationship with LV GLS and log-transformed NT-proBNP and PIIINP (r = 0.29, P < 0.001 and r = 0.19, P = 0.009, respectively). We observed no linear association of LV GLS with Minnesota Living with Heart Failure scores, 6-min walk distance, peak oxygen consumption, or expiratory minute ventilation/carbon dioxide excretion slope. Impaired LV GLS is common among HFpEF patients, indicating the presence of covert systolic dysfunction despite normal LV ejection fraction. Impaired LV GLS was associated with biomarkers of wall stress and collagen synthesis and diastolic dysfunction but not with quality of life or exercise capacity, suggesting other processes may be more responsible for these aspects of the HFpEF syndrome. © 2017 The Authors. European Journal of Heart Failure © 2017 European Society of Cardiology.

  13. Problematics of Time and Timing in the Longitudinal Study of Human Development: Theoretical and Methodological Issues.

    Science.gov (United States)

    Lerner, Richard M; Schwartz, Seth J; Phelps, Erin

    2009-02-01

    Studying human development involves describing, explaining, and optimizing intraindividual change and interindividual differences in such change and, as such, requires longitudinal research. The selection of the appropriate type of longitudinal design requires selecting the option that best addresses the theoretical questions asked about developmental process and the use of appropriate statistical procedures to best exploit data derived from theory-predicated longitudinal research. This paper focuses on several interrelated problematics involving the treatment of time and the timing of observations that developmental scientists face in creating theory-design fit and in charting in change-sensitive ways developmental processes across life. We discuss ways in which these problematics may be addressed to advance theory-predicated understanding of the role of time in processes of individual development.

  14. Time-resolved torsional relaxation of spider draglines by an optical technique.

    OpenAIRE

    Emile, Olivier; Le Floch, Albert; Vollrath, F.

    2007-01-01

    International audience; The sensitivity of the torsional pendulum demonstrates the self-shape-memory effect in different types of spider draglines. Here we report the time-resolved noncovalent bonds recovery in the protein structure. The torsional dynamics of such multilevel structure governed by reversible interactions are described in the frame of a nested model. Measurement of three different relaxation times confirms the existence of three energy storage levels in such two protein spidroi...

  15. Determination of relaxation modulus of time-dependent materials using neural networks

    Science.gov (United States)

    Aulova, Alexandra; Govekar, Edvard; Emri, Igor

    2016-10-01

    Health monitoring systems for plastic based structures require the capability of real time tracking of changes in response to the time-dependent behavior of polymer based structures. The paper proposes artificial neural networks as a tool of solving inverse problem appearing within time-dependent material characterization, since the conventional methods are computationally demanding and cannot operate in the real time mode. Abilities of a Multilayer Perceptron (MLP) and a Radial Basis Function Neural Network (RBFN) to solve ill-posed inverse problems on an example of determination of a time-dependent relaxation modulus curve segment from constant strain rate tensile test data are investigated. The required modeling data composed of strain rate, tensile and related relaxation modulus were generated using existing closed-form solution. Several neural networks topologies were tested with respect to the structure of input data, and their performance was compared to an exponential fitting technique. Selected optimal topologies of MLP and RBFN were tested for generalization and robustness on noisy data; performance of all the modeling methods with respect to the number of data points in the input vector was analyzed as well. It was shown that MLP and RBFN are capable of solving inverse problems related to the determination of a time dependent relaxation modulus curve segment. Particular topologies demonstrate good generalization and robustness capabilities, where the topology of RBFN with data provided in parallel proved to be superior compared to other methods.

  16. Determination of relaxation modulus of time-dependent materials using neural networks

    Science.gov (United States)

    Aulova, Alexandra; Govekar, Edvard; Emri, Igor

    2017-08-01

    Health monitoring systems for plastic based structures require the capability of real time tracking of changes in response to the time-dependent behavior of polymer based structures. The paper proposes artificial neural networks as a tool of solving inverse problem appearing within time-dependent material characterization, since the conventional methods are computationally demanding and cannot operate in the real time mode. Abilities of a Multilayer Perceptron (MLP) and a Radial Basis Function Neural Network (RBFN) to solve ill-posed inverse problems on an example of determination of a time-dependent relaxation modulus curve segment from constant strain rate tensile test data are investigated. The required modeling data composed of strain rate, tensile and related relaxation modulus were generated using existing closed-form solution. Several neural networks topologies were tested with respect to the structure of input data, and their performance was compared to an exponential fitting technique. Selected optimal topologies of MLP and RBFN were tested for generalization and robustness on noisy data; performance of all the modeling methods with respect to the number of data points in the input vector was analyzed as well. It was shown that MLP and RBFN are capable of solving inverse problems related to the determination of a time dependent relaxation modulus curve segment. Particular topologies demonstrate good generalization and robustness capabilities, where the topology of RBFN with data provided in parallel proved to be superior compared to other methods.

  17. One-Shot Measurement of Spin-Lattice Relaxation Times in the Off-Resonance Rotating Frame of Reference with Applications to Breast

    Science.gov (United States)

    Fairbanks, Ethan Jefferson

    1994-01-01

    Off-resonance spin locking makes use of the novel relaxation time T_{1rho} ^{rm off}, which may be useful in characterizing breast disease. Knowledge of T _{rm 1rho}^{rm off} is essential for optimization of spin -locking imaging methods. The purpose of this work was to develop an optimal imaging technique for in vivo measurement of T_{rm 1rho}^ {rm off}. Measurement of T _{1rho}^{rm off } using conventional methods requires long exam times which are not suitable for patients. Exam time may be shortened by utilizing a one-shot method developed by Look and Locker, making in vivo measurements possible. The imaging method consisted of a 180^circ inversion pulse followed by a series of small-angle alpha pulses to tip a portion of the longitudinal magnetization into the transverse plane for readout. During each relaxation interval (between alpha pulses), a spin-locking pulse was applied off-resonance to achieve T_ {1rho}^{rm off} relaxation. The value of T_{rm 1rho}^{rm off} was then determined using a three-parameter non-linear least-squares fitting procedure. Values of T_ {1rho}^{rm off} were measured for normal and pathologic breast tissues at several resonant offsets. These measurements revealed that image contrast can be manipulated by altering the resonant offset of the spin-locking pulse. Whereas T _1 relaxation times were nearly identical for normal and cancerous tissues, T_{1 rho}^{rm off} relaxation times differed significantly. These results may be useful in improving image contrast in magnetic resonance imaging.

  18. Optimal Configuration for Relaxation Times Estimation in Complex Spin Echo Imaging

    Directory of Open Access Journals (Sweden)

    Fabio Baselice

    2014-01-01

    Full Text Available Many pathologies can be identified by evaluating differences raised in the physical parameters of involved tissues. In a Magnetic Resonance Imaging (MRI framework, spin-lattice T1 and spin-spin T2 relaxation time parameters play a major role in such an identification. In this manuscript, a theoretical study related to the evaluation of the achievable performances in the estimation of relaxation times in MRI is proposed. After a discussion about the considered acquisition model, an analysis on the ideal imaging acquisition parameters in the case of spin echo sequences, i.e., echo and repetition times, is conducted. In particular, the aim of the manuscript consists in providing an empirical rule for optimal imaging parameter identification with respect to the tissues under investigation. Theoretical results are validated on different datasets in order to show the effectiveness of the presented study and of the proposed methodology.

  19. A new approach for calculation of relaxation time and magnetic anisotropy of ferrofluids containing superparmagnetic nanoparticles

    Directory of Open Access Journals (Sweden)

    Ahmadi R.

    2012-01-01

    Full Text Available In this work, a new approach is described for the calculation of the relaxation time and magnetic anisotropy energy of magnetic nanoparticles. Ferrofluids containing monodispersed magnetite nanoparticles were synthesized via hydrothermal method and then heated using the 10 kA/m external AC magnetic fields in three different frequencies: 10, 50 and 100 kHz. By measuring the temperature variations during the application of the magnetic field, the total magnetic time constant including both Brownian and Neel relaxation times can be calculated. By measuring the magnetic core size and hydrodynamic size of particles, the magnetic anisotropy can be calculated too. Synthesized ferrofluids were characterized via TEM, XRD, VSM and PCS techniques and the results were used for the mentioned calculations.

  20. Relaxation and self-sustained oscillations in the time elapsed neuron network model

    CERN Document Server

    Pakdaman, Khashayar; Salort, Delphine

    2011-01-01

    The time elapsed model describes the firing activity of an homogeneous assembly of neurons thanks to the distribution of times elapsed since the last discharge. It gives a mathematical description of the probability density of neurons structured by this time. In an earlier work, based on generalized relative entropy methods, it is proved that for highly or weakly connected networks the model exhibits relaxation to the steady state and for moderately connected networks it is obtained numerical evidence of appearance of self-sustained periodic solutions. Here, we go further and, using the particular form of the model, we quantify the regime where relaxation to a stationary state occurs in terms of the network connectivity. To introduce our methodology, we first consider the case where the neurons are not connected and we give a new statement showing that total asynchronous firing of neurons appears asymptotically. In a second step, we consider the case with connections and give a low connectivity condition that...

  1. Investigation of dielectric relaxation in systems with hierarchical organization: From time to frequency domain and back again

    Energy Technology Data Exchange (ETDEWEB)

    Yokoi, Koki [Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, WI (United States); Raicu, Valerică, E-mail: vraicu@uwm.edu [Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, WI (United States); Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI (United States)

    2017-06-28

    Relaxation in fractal structures was investigated theoretically starting from a simple model of a Cantorian tree and kinetic equations linking the change in the number of particles (e.g., electrical charges) populating each branch of the tree and their transfer to other branches or to the ground state. We numerically solved the system of differential equations obtained and determined the so-called cumulative distribution function of particles, which, in dielectric or mechanical relaxation parlance, is the same as the relaxation function of the system. As a physical application, we studied the relationship between the dielectric relaxation in time-domain and the dielectric dispersion in the frequency-domain. Upon choosing appropriate rate constants, our model described accurately well-known non-exponential and non-Debye time- and frequency-domain functions, such as stretched exponentials, Havrilliak–Negami, and frequency power law. Our approach opens the door to applying kinetic models to describe a wide array of relaxation processes, which traditionally have posed great challenges to theoretical modeling based on first principles. - Highlights: • Relaxation was investigated for a system of particles flowing through a Cantorian tree. • A set of kinetic equations was formulated and used to compute the relaxation function of the system. • The dispersion function of the system was computed from the relaxation function. • An analytical method was used to recover the original relaxation function from the dispersion function. • This formalism was used to study dielectric relaxation and dispersion in fractal structures.

  2. Impact of electron-impurity scattering on the spin relaxation time in graphene: a first-principles study.

    Science.gov (United States)

    Fedorov, Dmitry V; Gradhand, Martin; Ostanin, Sergey; Maznichenko, Igor V; Ernst, Arthur; Fabian, Jaroslav; Mertig, Ingrid

    2013-04-12

    The effect of electron-impurity scattering on momentum and spin relaxation times in graphene is studied by means of relativistic ab initio calculations. Assuming carbon and silicon adatoms as natural impurities in graphene, we are able to simulate fast spin relaxation observed experimentally. We investigate the dependence of the relaxation times on the impurity position and demonstrate that C or Si adatoms act as real-space spin hot spots inducing spin-flip rates about 5 orders of magnitude larger than those of in-plane impurities. This fact confirms the hypothesis that the adatom-induced spin-orbit coupling leads to fast spin relaxation in graphene.

  3. Measurement of interfacial area from NMR time dependent diffusion and relaxation measurements.

    Science.gov (United States)

    Fleury, M

    2017-09-07

    The interfacial area between two immiscible phases in porous media is an important parameter for describing and predicting 2 phase flow. Although present in several models, experimental investigations are sparse due to the lack of appropriate measurement techniques. We propose two NMR techniques for the measurement of oil-water interfacial area: (i) a time dependent NMR diffusion technique applicable in static conditions, similar to those used for the measurement of the solid specific surface of a porous media, and (ii) a fast relaxation technique applicable in dynamic conditions while flowing, based on an interfacial relaxation mechanism induced by the inclusion of paramagnetic salts in the water phase. For dodecane relaxing on doped water, we found an oil interfacial relaxivity of 1.8μm/s, large enough to permit the measurement of specific interfacial surface as small as 1000cm(2)/cm(3). We demonstrate both NMR techniques in drainage followed by imbibition, in a model porous media with a narrow pore size distribution. While flowing, we observe that the interfacial area is larger in imbibition than in drainage, implying a different organization of the oil phase. In a carbonate sample with a wide pore size distribution, we evidence the gradual invasion of the smallest pores as the oil-water pressure difference is increased. Copyright © 2017. Published by Elsevier Inc.

  4. In vivo measurements of T1 relaxation times of 31P-metabolites in human skeletal muscle

    DEFF Research Database (Denmark)

    Thomsen, C; Jensen, K E; Henriksen, O

    1989-01-01

    The T1 relaxation times were estimated for 31P-metabolites in human skeletal muscle. Five healthy volunteers were examined in a 1.5 Tesla wholebody imaging system using an inversion recovery pulse sequence. The calculated T1 relaxation times ranged from 5.517 sec for phosphocreatine to 3.603 sec...

  5. Menstrual variation of breast volume and T{sub 2} relaxation times in cyclical mastalgia

    Energy Technology Data Exchange (ETDEWEB)

    Hussain, Zainab [Department of Medical Imaging, University of Liverpool, Johnstone Building, Brownlow Hill, P.O. Box 147, Liverpool, Merseyside L69 3GB (United Kingdom); Magnetic Resonance and Image Analysis Research Centre, University of Liverpool, Johnstone Building, Brownlow Hill, P.O. Box 147, Liverpool, Merseyside L69 3GB (United Kingdom)], E-mail: zay@liverpool.ac.uk; Brooks, Jonathan [Magnetic Resonance and Image Analysis Research Centre, University of Liverpool, Johnstone Building, Brownlow Hill, P.O. Box 147, Liverpool, Merseyside L69 3GB (United Kingdom); Department of Human Anatomy and Genetics, University of Oxford, Oxford (United Kingdom); Percy, Dave [Centre for Operational Research and Applied Statistics, University of Salford, Salford, Greater Manchester M5 4WT (United Kingdom)

    2008-02-15

    Purpose: Hormonal activity causes breast volume to change during the menstrual cycle. One possible cause of this volume change is thought to be due to water retention or oedema within the tissues. We used magnetic resonance imaging (MRI) to study the variation in breast volume and {sup 1}H Magnetic Resonance Spectroscopy (MRS) to measure T{sub 2} relaxation times which are known to increase with increasing tissue water content. We hypothesised that an increase in breast volume will elevate T{sub 2} relaxation due to the presence of an increased water content within the breast. T{sub 2} Relaxation time and volume were studied in fifteen control subjects and in a cohort of eight patients with cyclical mastalgia in order to determine whether changes in breast volume and T{sub 2} relaxation times differed in controls and patients during menses, ovulation and premenses. Method: Breast volume was determined by the Cavalieri method in combination with point counting techniques on MR images and T{sub 2} relaxation times of the water and fat in a voxel of breast tissue were obtained using {sup 1}H Magnetic Resonance Spectroscopy (MRS). Results: Statistical analysis (ANOVA) demonstrated highly significant differences in breast volume between the three stages of the cycle (p < 0.0005) with breast volume being greatest premenstrually. Patients did not exhibit an increase in volume premenstrually, significantly above controls. T{sub 2} of fat or water did not depend on stage of cycle. T-tests demonstrated no significant differences in T{sub 2} of water or fat between patient and control groups. The average T{sub 2} relaxation time of water was lowest in the patient and control groups during ovulation and highest in the patient group during premenses. Conclusion: We have performed the first combined volumetric and spectroscopic study of women with cyclical mastalgia and demonstrated that the global changes in volumes and T{sub 2} were not significantly different from normal

  6. Ground-state atomic polarization relaxation-time measurement of Rb filled hypocycloidal core-shaped Kagome HC-PCF

    CERN Document Server

    Bradley, T D; McFerran, J J; Jouin, J; Debord, B; Alharbi, M; Thomas, P; Gerome, F; Benabid, F

    2015-01-01

    We report on the measurement of ground state atomic polarization relaxation tile of Rb vapor confined in five different hypocycloidal core shape Kagome hollow core photonic crystal fibers made with uncoated silica glass. We are able to distinguish between wall-collision and transit-time effects in optical waveguide and deduce the contribution of the atom's dwell time at the core wall surface. In contrast with convetional macroscopic atomic cell configuration, and in agreement with Monte Carlo simulations, the measured relaxation times were found to be at least one order of magnitude longer than the limit set by the atom-wall collisional relaxation from thermal atoms. This extended relaxation time is explained by the combination of a stronger contribution of the slow atoms in the atomic polarization build-up, and of the relatively significant contribution of dwell time to the relaxation process of the ground state polarization.

  7. Shear viscosity to relaxation time ratio in SU(3) lattice gauge theory

    CERN Document Server

    Kohno, Yasuhiro; Kitazawa, Masakiyo

    2011-01-01

    We evaluate the ratio of the shear viscosity to the relaxation time of the shear flux above but near the critical temperature $T_c$ in SU(3) gauge theory on the lattice. The ratio is related to Kubo's canonical correlation of the energy-momentum tensor in Euclidean space with the relaxation time approximation and an appropriate regularization. Using this relation, the ratio is evaluated by direct measurements of the Euclidean observables on the lattice. We obtained the ratio with reasonable statistics for the range of temperature $1.3T_c \\lesssim T \\lesssim 4T_c$. We also found that the characteristic speed of the transverse plane wave in gluon media is almost constant, $v \\simeq 0.5$, for $T \\gtrsim 1.5T_c$, which is compatible with the causality in the second order dissipative hydrodynamics.

  8. Accuracy and Numerical Stabilty Analysis of Lattice Boltzmann Method with Multiple Relaxation Time for Incompressible Flows

    Science.gov (United States)

    Pradipto; Purqon, Acep

    2017-07-01

    Lattice Boltzmann Method (LBM) is the novel method for simulating fluid dynamics. Nowadays, the application of LBM ranges from the incompressible flow, flow in the porous medium, until microflows. The common collision model of LBM is the BGK with a constant single relaxation time τ. However, BGK suffers from numerical instabilities. These instabilities could be eliminated by implementing LBM with multiple relaxation time. Both of those scheme have implemented for incompressible 2 dimensions lid-driven cavity. The stability analysis has done by finding the maximum Reynolds number and velocity for converged simulations. The accuracy analysis is done by comparing the velocity profile with the benchmark results from Ghia, et al and calculating the net velocity flux. The tests concluded that LBM with MRT are more stable than BGK, and have a similar accuracy. The maximum Reynolds number that converges for BGK is 3200 and 7500 for MRT respectively.

  9. The generalized Phillips-Twomey method for NMR relaxation time inversion.

    Science.gov (United States)

    Gao, Yang; Xiao, Lizhi; Zhang, Yi; Xie, Qingming

    2016-10-01

    The inversion of NMR relaxation time involves the Fredholm integral equation of the first kind. Due to its ill-posedness, numerical solutions to this type of equations are often found much less accurate and bear little resemblance to the true solution. There has been a strong interest in finding a well-posed method for this ill-posed problem since 1950s. In this paper, we prove the existence, the uniqueness, the stability and the convergence of the generalized Phillips-Twomey regularization method for solving this type of equations. Numerical simulations and core analyses arising from NMR transverse relaxation time inversion are conducted to show the effectiveness of the generalized Phillips-Twomey method. Both the simulation results and the core analyses agree well with the model and the realities.

  10. Enthalpy Relaxation of a DGEBA Epoxy as a function of Time, Temperature, and Cooling Rate

    Science.gov (United States)

    Clarkson, Caitlyn M.; McCoy, John D.; Kropka, Jamie M.

    2015-03-01

    Enthalpy relaxation resulting from physical aging of a DGEBA epoxy, Epon 828, cross-linked with an amine curative, Jeffamine T-403, was studied for two isothermal aging temperatures at sequential aging times up to two weeks. Results were analyzed using the peak shift method to obtain the relaxation parameters β, δ (H*), and χ. The individual effects of cooling rate from the equilibrated state, aging time, and aging temperature were isolated to understand the initial state of the glassy epoxy and its evolution during physical aging. [Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  11. Spin time-relaxation within strongly coupled paramagnetic systems exhibiting paramagnetic-ferrimagnetic transitions

    Energy Technology Data Exchange (ETDEWEB)

    Chahid, M.; Benhamou, M. E-mail: benhamou.mabrouk@caramail.com

    2000-08-01

    The purpose of the present work is a quantitative study of the spin time relaxation within superweak ferrimagnetic materials exhibiting a paramagnetic-ferrimagnetic transition, when the temperature is changed from an initial value T{sub i} to a final one T{sub f} very close to the critical temperature T{sub c}. From a magnetic point of view, the material under investigation is considered to be made of two strongly coupled paramagnetic sublattices of respective moments phi (cursive,open) Greek and {psi}. Calculations are made within a Landau mean-field theory, whose free energy involves, in addition to quadratic and quartic terms in both moments phi (cursive,open) Greek and {psi}, a lowest-order coupling - Cphi (cursive,open) Greek{psi}, where C<0 stands for the coupling constant measuring the interaction between the two sublattices. We first determine the time dependence of the shifts of the order parameters {delta}phi (cursive,open) Greek and {delta}{psi} from the equilibrium state. We find that this time dependence is completely controlled by two kinds of relaxation times {tau}{sub 1} and {tau}{sub 2}. The former is a long time and the second a short one, and they are associated, respectively, with long and local wavelength fluctuations. We find that, only the first relaxation time is relevant for physics, since it drives the system to undergo a phase transition. Spatial fluctuations are also taken into account. In this case, we find an explicit expression of the relaxation times, which are functions of temperature T, coupling constant C and wave vector q. We find that the critical mode is that given by the zero scattering-angle limit, i.e. q=0. Finally, we emphasize that the appearance of these two relaxation times is in good agreement with results reported in recent experimental work dealt with the Curie-Weiss paramagnet compound Li{sub x}Ni{sub 2-x}O{sub 2}, where the composition x is very close to 1.

  12. Remarks concerning bulk viscosity of hadron matter in relaxation time ansatz

    Energy Technology Data Exchange (ETDEWEB)

    Khvorostukhin, A.S., E-mail: hvorost@theor.jinr.ru [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Institute of Applied Physics, Moldova Academy of Science, MD-2028 Kishineu (Moldova, Republic of); Toneev, V.D. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Voskresensky, D.N. [National Research Nuclear University “MEPhI”, Kashirskoe sh. 31, Moscow 115409 (Russian Federation)

    2013-10-03

    The bulk viscosity is calculated for hadron matter produced in heavy-ion collisions, being described in the relaxation time approximation within the relativistic mean-field-based model with scaled hadron masses and couplings. We show how different approximations used in the literature affect the result. Numerical evaluations of the bulk viscosity with three considered models deviate not much from each other confirming earlier results.

  13. Implicit-correction-based immersed boundary-lattice Boltzmann method with two relaxation times

    Science.gov (United States)

    Seta, Takeshi; Rojas, Roberto; Hayashi, Kosuke; Tomiyama, Akio

    2014-02-01

    In the present paper, we verify the effectiveness of the two-relaxation-time (TRT) collision operator in reducing boundary slip computed by the immersed boundary-lattice Boltzmann method (IB-LBM). In the linear collision operator of the TRT, we decompose the distribution function into symmetric and antisymmetric components and define the relaxation parameters for each part. The Chapman-Enskog expansion indicates that one relaxation time for the symmetric component is related to the kinematic viscosity. Rigorous analysis of the symmetric shear flows reveals that the relaxation time for the antisymmetric part controls the velocity gradient, the boundary velocity, and the boundary slip velocity computed by the IB-LBM. Simulation of the symmetric shear flows, the symmetric Poiseuille flows, and the cylindrical Couette flows indicates that the profiles of the numerical velocity calculated by the TRT collision operator under the IB-LBM framework exactly agree with those of the multirelaxation time (MRT). The TRT is as effective in removing the boundary slip as the MRT. We demonstrate analytically and numerically that the error of the boundary velocity is caused by the smoothing technique using the δ function used in the interpolation method. In the simulation of the flow past a circular cylinder, the IB-LBM based on the implicit correction method with the TRT succeeds in preventing the flow penetration through the solid surface as well as unphysical velocity distortion. The drag coefficient, the wake length, and the separation points calculated by the present IB-LBM agree well with previous studies at Re = 10, 20, and 40.

  14. In-vivo T2-relaxation times of asymptomatic cervical intervertebral discs

    Energy Technology Data Exchange (ETDEWEB)

    Driscoll, Sean J.; Mao, Haiqing; Li, Guoan [Massachusetts General Hospital/Harvard Medical School, Bioengineering Laboratory, Department of Orthopaedic Surgery, Boston, MA (United States); Zhong, Weiye [Massachusetts General Hospital/Harvard Medical School, Bioengineering Laboratory, Department of Orthopaedic Surgery, Boston, MA (United States); Second Xiangya Hospital and Central South University, Department of Spinal Surgery, Changsha, Hunan (China); Torriani, Martin [Massachusetts General Hospital/Harvard Medical School, Musculoskeletal Imaging and Intervention, Department of Radiology, Boston, MA (United States); Wood, Kirkham B.; Cha, Thomas D. [Massachusetts General Hospital/Harvard Medical School, Spine Service, Department of Orthopaedic Surgery, Boston, MA (United States)

    2016-03-15

    Limited research exists on T2-mapping techniques for cervical intervertebral discs and its potential clinical utility. The objective of this research was to investigate the in-vivo T2-relaxation times of cervical discs, including C2-C3 through C7-T1. Ten asymptomatic subjects were imaged using a 3.0 T MR scanner and a sagittal multi-slice multi-echo sequence. Using the mid-sagittal image, intervertebral discs were divided into five regions-of-interest (ROIs), centered along the mid-line of the disc. Average T2 relaxation time values were calculated for each ROI using a mono-exponential fit. Differences in T2 values between disc levels and across ROIs of the same disc were examined. For a given ROI, the results showed a trend of increasing relaxation times moving down the spinal column, particularly in the middle regions (ROIs 2, 3 and 4). The C6-C7 and C7-T1 discs had significantly greater T2 values compared to superior discs (discs between C2 and C6). The results also showed spatial homogeneity of T2 values in the C3-C4, C4-C5, and C5-C6 discs, while C2-C3, C6-C7, and C7-T1 showed significant differences between ROIs. The findings indicate there may be inherent differences in T2-relaxation time properties between different cervical discs. Clinical evaluations utilizing T2-mapping techniques in the cervical spine may need to be level-dependent. (orig.)

  15. Influence of Heat Sources and Relaxation Time on Temperature Distribution in Tissues

    Directory of Open Access Journals (Sweden)

    Sharma S.

    2014-05-01

    Full Text Available In the present study, the temperature fluctuations in tissues based on Penne’s bio-heat transfer equation is investigated by applying the Laplace and Hankel transforms. To get the solution in a physical form, a numerical inversion technique has been applied. The temporal and spatial distribution of temperature is investigated with the effect of relaxation time and is presented graphically.

  16. Determining the structural relaxation times deep in the glassy state of the pharmaceutical Telmisartan

    Energy Technology Data Exchange (ETDEWEB)

    Adrjanowicz, K; Paluch, M [Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice (Poland); Ngai, K L [Naval Research Laboratory, Washington, DC 20375-5320 (United States)

    2010-03-31

    By using the dielectric relaxation method proposed recently by Casalini and Roland (2009 Phys. Rev. Lett. 102 035701), we were able to determine the structural alpha-relaxation times deep in the glassy state of the pharmaceutical, Telmisartan. Normally, deep in the glassy state tau{sub a}lpha is so long that it cannot be measured but tau{sub b}eta, which is usually much shorter, can be directly determined. The method basically takes advantage of the connection between the alpha-relaxation and the secondary beta-relaxation of the Johari-Goldstein kind, including a relation between their relaxation times tau{sub a}lpha and tau{sub b}eta, respectively. Thus, tau{sub a}lpha of Telmisartan were determined by monitoring the change of the dielectric beta-loss, epsilon'', with physical aging time at temperatures well below the vitrification temperature. The values of tau{sub a}lpha were compared with those expected by the coupling model (CM). Unequivocal comparison cannot be made in the case of Telmisartan because its beta-loss peak is extremely broad, and the CM predicts only an order of magnitude agreement between the primitive relaxation frequency and the beta-peak frequency. We also made an attempt to analyze all isothermal and aging susceptibility data after transformation into the electric modulus representation. The tau{sub a}lpha found in the glass state by using the method of Casalini and Roland in the modulus representation are similar to those obtained in the susceptibility representation. However, it is remarkable that the stretching parameter beta{sub KWWM} = 0.51 in the electric modulus representation gives more precise fits to the aging data than in the susceptibility representation with beta{sub KWW} = 0.61. Our results suggest that the electric modulus representation may be useful as an alternative to analyze aging data, especially in the case of highly polar glassformers having a large ratio of low frequency and high frequency dielectric

  17. Pseudopotential multi-relaxation-time lattice Boltzmann model for cavitation bubble collapse with high density ratio

    Science.gov (United States)

    Shan, Ming-Lei; Zhu, Chang-Ping; Yao, Cheng; Yin, Cheng; Jiang, Xiao-Yan

    2016-10-01

    The dynamics of the cavitation bubble collapse is a fundamental issue for the bubble collapse application and prevention. In the present work, the modified forcing scheme for the pseudopotential multi-relaxation-time lattice Boltzmann model developed by Li Q et al. [Li Q, Luo K H and Li X J 2013 Phys. Rev. E 87 053301] is adopted to develop a cavitation bubble collapse model. In the respects of coexistence curves and Laplace law verification, the improved pseudopotential multi-relaxation-time lattice Boltzmann model is investigated. It is found that the thermodynamic consistency and surface tension are independent of kinematic viscosity. By homogeneous and heterogeneous cavitation simulation, the ability of the present model to describe the cavitation bubble development as well as the cavitation inception is verified. The bubble collapse between two parallel walls is simulated. The dynamic process of a collapsing bubble is consistent with the results from experiments and simulations by other numerical methods. It is demonstrated that the present pseudopotential multi-relaxation-time lattice Boltzmann model is applicable and efficient, and the lattice Boltzmann method is an alternative tool for collapsing bubble modeling. Project supported by the National Natural Science Foundation of China (Grant Nos. 11274092 and 1140040119) and the Natural Science Foundation of Jiangsu Province, China (Grant No. SBK2014043338).

  18. Second-order hydrodynamics for fermionic cold atoms: Detailed analysis of transport coefficients and relaxation times

    CERN Document Server

    Kikuchi, Yuta; Kunihiro, Teiji

    2016-01-01

    We give a detailed derivation of the second-order (local) hydrodynamics for Boltzmann equation with an external force by using the renormalization group method. In this method, we solve the Boltzmann equation faithfully to extract the hydrodynamics without recourse to any ansatz. Our method leads to microscopic expressions of not only all the transport coefficients that are of the same form as those in Chapman-Enskog method but also those of the viscous relaxation times $\\tau_i$ that admit physically natural interpretations. As an example, we apply our microscopic expressions to calculate the transport coefficients and the relaxation times of the cold fermionic atoms in a quantitative way, where the transition probability in the collision term is given explicitly in terms of the $s$-wave scattering length $a_s$. We thereby discuss the quantum statistical effects, temperature dependence, and scattering-length dependence of the first-order transport coefficients and the viscous relaxation times: It is shown tha...

  19. Relaxation time and excess entropy in viscous liquids: Electric field versus temperature as control parameter

    Science.gov (United States)

    Richert, Ranko

    2017-02-01

    On the basis of adiabatic calorimetry data and results obtained from dielectric relaxation studies in the presence of a high static electric field, the effects of temperature and electric field induced changes of the excess entropy are compared for the same sample: supercooled cresolphthalein dimethylether. A field induced reduction of the excess entropy by 45 mJ K-1 mol-1 at constant temperature increases the structural relaxation time by 0.75%, while the same entropy change originating from lowering the temperature at constant field increases the time constant by 3.5%. Therefore, there is no simple link connecting excess entropy and relaxation time that is independent of the control parameter that is used to modify the entropy. A consequence is that the Adam-Gibbs approach does not provide a quantitative prediction for how the dynamics of liquids depend on the electric field, and, more generally, on excess entropy. This work compares the dynamics for temperature versus field induced changes of isobaric excess entropy, thereby eliminating previous uncertainties arising from isochoric versus isobaric conditions and from unknown relations between thermodynamic, excess, and configurational entropies.

  20. Viscosity, relaxation time, and dynamics within a model asphalt of larger molecules

    Science.gov (United States)

    Li, Derek D.; Greenfield, Michael L.

    2014-01-01

    The dynamics properties of a new "next generation" model asphalt system that represents SHRP AAA-1 asphalt using larger molecules than past models is studied using molecular simulation. The system contains 72 molecules distributed over 12 molecule types that range from nonpolar branched alkanes to polar resins and asphaltenes. Molecular weights range from 290 to 890 g/mol. All-atom molecular dynamics simulations conducted at six temperatures from 298.15 to 533.15 K provide a wealth of correlation data. The modified Kohlrausch-Williams-Watts equation was regressed to reorientation time correlation functions and extrapolated to calculate average rotational relaxation times for individual molecules. The rotational relaxation rate of molecules decreased significantly with increasing size and decreasing temperature. Translational self-diffusion coefficients followed an Arrhenius dependence. Similar activation energies of ˜42 kJ/mol were found for all 12 molecules in the model system, while diffusion prefactors spanned an order of magnitude. Viscosities calculated directly at 533.15 K and estimated at lower temperatures using the Debye-Stokes-Einstein relationship were consistent with experimental data for asphalts. The product of diffusion coefficient and rotational relaxation time showed only small changes with temperature above 358.15 K, indicating rotation and translation that couple self-consistently with viscosity. At lower temperatures, rotation slowed more than diffusion.

  1. Viscosity, relaxation time, and dynamics within a model asphalt of larger molecules

    Energy Technology Data Exchange (ETDEWEB)

    Li, Derek D.; Greenfield, Michael L., E-mail: greenfield@egr.uri.edu [Department of Chemical Engineering, University of Rhode Island, Kingston, Rhode Island 02881 (United States)

    2014-01-21

    The dynamics properties of a new “next generation” model asphalt system that represents SHRP AAA-1 asphalt using larger molecules than past models is studied using molecular simulation. The system contains 72 molecules distributed over 12 molecule types that range from nonpolar branched alkanes to polar resins and asphaltenes. Molecular weights range from 290 to 890 g/mol. All-atom molecular dynamics simulations conducted at six temperatures from 298.15 to 533.15 K provide a wealth of correlation data. The modified Kohlrausch-Williams-Watts equation was regressed to reorientation time correlation functions and extrapolated to calculate average rotational relaxation times for individual molecules. The rotational relaxation rate of molecules decreased significantly with increasing size and decreasing temperature. Translational self-diffusion coefficients followed an Arrhenius dependence. Similar activation energies of ∼42 kJ/mol were found for all 12 molecules in the model system, while diffusion prefactors spanned an order of magnitude. Viscosities calculated directly at 533.15 K and estimated at lower temperatures using the Debye-Stokes-Einstein relationship were consistent with experimental data for asphalts. The product of diffusion coefficient and rotational relaxation time showed only small changes with temperature above 358.15 K, indicating rotation and translation that couple self-consistently with viscosity. At lower temperatures, rotation slowed more than diffusion.

  2. The modified relaxation time function: A novel analysis technique for relaxation processes. Application to high-temperature molybdenum internal friction peaks

    Energy Technology Data Exchange (ETDEWEB)

    Matteo, C.L. [Departamento de Fisica, Facultad de Ingenieria, Universidad de Buenos Aires, Avda. Paseo Colon 850, 1063 Buenos Aires (Argentina); Lambri, O.A. [Instituto de Fisica Rosario, Facultad de Ciencias Exactas, Ingenieria y Agrimensura, Laboratorio de Materiales, Escuela de Ing. Electrica, Universidad Nacional de Rosario, Avda. Pellegrini 250, (2000) Rosario (Argentina)], E-mail: olambri@fceia.unr.edu.ar; Zelada-Lambri, G.I. [Instituto de Fisica Rosario, Facultad de Ciencias Exactas, Ingenieria y Agrimensura, Laboratorio de Materiales, Escuela de Ing. Electrica, Universidad Nacional de Rosario, Avda. Pellegrini 250, (2000) Rosario (Argentina); Sorichetti, P.A. [Departamento de Fisica, Facultad de Ingenieria, Universidad de Buenos Aires, Avda. Paseo Colon 850, 1063 Buenos Aires (Argentina); Garcia, J.A. [Departamento de Fisica Aplicada II, Facultad de Ciencias y Tecnologia, Universidad del Pais Vasco, Apdo. 644, 48080 Bilbao, Pais Vasco (Spain)

    2008-07-01

    The modified relaxation time (MRT) function, which is based on a general linear viscoelastic formalism, has several important mathematical properties that greatly simplify the analysis of relaxation processes. In this work, the MRT is applied to the study of the relaxation damping peaks in deformed molybdenum at high temperatures. The dependence of experimental data from these relaxation processes with temperature are adequately described by a Havriliak-Negami (HN) function, and the MRT makes it possible to find a relation between the parameters of the HN function and the activation energy of the process. The analysis reveals that for the relaxation peak appearing at temperatures below 900 K, the physical mechanism is related to a vacancy-diffusion-controlled movement of dislocations. In contrast, when the peak appears at temperatures higher than 900 K, the damping is controlled by a mechanism of diffusion in the low-temperature tail of the peak, and in the high-temperature tail of the peak the creation plus diffusion of vacancies at the dislocation line occurs.

  3. Direct Time-domain Observation of Conformational Relaxation in Gas-phase Cold Collisions

    CERN Document Server

    Drayna, Garrett K; Wang, Kenneth; Domingos, Sergio R; Eibengerber, Sandra; Doyle, John M; Patterson, David

    2016-01-01

    Cooling molecules in the gas phase is important for precision spectroscopy, cold molecule physics, and physical chemistry. Measurements of conformational relaxation cross sections shed important light on potential energy surfaces and energy flow within a molecule. However, gas-phase conformational cooling has not been previously observed directly. In this work, we directly observe conformational dynamics of 1,2-propanediol in cold (6K) collisions with atomic helium using microwave spectroscopy and buffer-gas cooling. Precise knowledge and control of the collisional environment in the buffer-gas allows us to measure the absolute collision cross-section for conformational relaxation. Several conformers of 1,2-propanediol are investigated and found to have relaxation cross-sections with He ranging from $\\sigma=4.7(3.0)\\times10^{-18}\\:\\mathrm{cm}^{2}$ to $\\sigma>5\\times10^{-16}\\:\\mathrm{cm}^{2}$. Our method is applicable to a broad class of molecules and could be used to provide information about the potential en...

  4. Dynamical theory of spin noise and relaxation - prospects for real time NMR measurements

    Science.gov (United States)

    Field, Timothy

    2014-03-01

    The dynamics of a spin system is usually calculated using the density matrix. However, the usual formulation in terms of the density matrix predicts that the signal will decay to zero, and does not address the stochastic dynamics of individual spins. Spin fluctuations are to be viewed as an intrinsic quantum mechanical property of such systems immersed in random magnetic environments, and are observed as ``spin noise'' in the absence of any radio frequency (RF) excitation. Using stochastic calculus we develop a dynamical theory of spin noise and relaxation whose origins lie in the component spin fluctuations. This entails consideration of random pure states for individual protons, and how these pure states are correctly combined when the density matrix is formulated. Both the lattice and the spins are treated quantum mechanically. Such treatment incorporates both the processes of spin-spin and (finite temperature) spin-lattice relaxation. Our results reveal the intimate connections between spin noise and conventional spin relaxation, in terms of a modified spin density (MSD), distinct from the density matrix, which is necessary to describe non-ensemble averaged properties of spin systems. With the prospect of ultra-fast digitization, the role of spin noise in real time parameter extraction for (NMR) spin systems, and the advantage over standard techniques, is of essential importance, especially for systems containing a small number of spins. In this presentation we outline prospects for harnessing the recent dynamical theory in terms of spin noise measurement, with attention to real time properties.

  5. Relaxation time diagram for identifying heat generation mechanisms in magnetic fluid hyperthermia

    Energy Technology Data Exchange (ETDEWEB)

    Lima, Enio, E-mail: lima@cab.cnea.gov.ar; De Biasi, Emilio; Zysler, Roberto D.; Vasquez Mansilla, Marcelo; Mojica-Pisciotti, Mary L. [Centro Atómico Bariloche/CONICET (Argentina); Torres, Teobaldo E.; Calatayud, M. Pilar; Marquina, C.; Ricardo Ibarra, M.; Goya, Gerardo F. [Universidad de Zaragoza, Instituto de Nanociencia de Aragón INA (Spain)

    2014-12-15

    We present a versatile diagram to envisage the dominant relaxation mechanism of single-domain magnetic nanoparticles (MNPs) under alternating magnetic fields, as those used in magnetic fluid hyperthermia (MFH). The diagram allows estimating the heating efficiency, measured by the Specific Power Absorption (SPA), originated in the magnetic and viscous relaxation times of single-domain MNPs for a given frequency of the ac magnetic field (AFM). The diagram has been successfully applied to different colloids, covering a wide variety of MNPs with different magnetic anisotropy and particle size, and dispersed in different viscous liquid carriers. From the general diagram, we derived a specific chart based on the Linear Response Theory in order to easily estimate the experimental condition for the optimal SPA values of most colloids currently used in MFH.

  6. Assessment of the time constant of relaxation: insights from simulations and hemodynamic measurements

    Science.gov (United States)

    De Mey, S.; Thomas, J. D.; Greenberg, N. L.; Vandervoort, P. M.; Verdonck, P. R.

    2001-01-01

    The objective of this study was to use high-fidelity animal data and numerical simulations to gain more insight into the reliability of the estimated relaxation constant derived from left ventricular pressure decays, assuming a monoexponential model with either a fixed zero or free moving pressure asymptote. Comparison of the experimental data with the results of the simulations demonstrated a trade off between the fixed zero and the free moving asymptote approach. The latter method more closely fits the pressure curves and has the advantage of producing an extra coefficient with potential diagnostic information. On the other hand, this method suffers from larger standard errors on the estimated coefficients. The method with fixed zero asymptote produces values of the time constant of isovolumetric relaxation (tau) within a narrow confidence interval. However, if the pressure curve is actually decaying to a nonzero pressure asymptote, this method results in an inferior fit of the pressure curve and a biased estimation of tau.

  7. Biogeographic kinetics: estimation of relaxation times for avifaunas of southwest pacific islands.

    Science.gov (United States)

    Diamond, J M

    1972-11-01

    When species diversity S on an island is displaced from the equilibrium value by injection or removal of species, S relaxes to equilibrium by an imbalance between immigration and extinction rates. Estimates of exponential relaxation times, t(r), for avifaunas of New Guinea satellite islands are calculated from analysis of four "experiments of nature": recolonization of exploded volcanoes, contraction in island area due to rising sea level, severing of land bridges, and disappearance of landbridge relict species. t(r) is in the range 3,000-18,000 years for avifaunas of islands of 50-3000 square miles (130-7800 km(2)), and increases with island area. Immigration coefficients decrease and extinction coefficients increase with increasing S. The results may be relevant to the design of rainforest preserves.

  8. Interfacial layers from the protein HFBII hydrophobin: dynamic surface tension, dilatational elasticity and relaxation times.

    Science.gov (United States)

    Alexandrov, Nikola A; Marinova, Krastanka G; Gurkov, Theodor D; Danov, Krassimir D; Kralchevsky, Peter A; Stoyanov, Simeon D; Blijdenstein, Theodorus B J; Arnaudov, Luben N; Pelan, Eddie G; Lips, Alex

    2012-06-15

    The pendant-drop method (with drop-shape analysis) and Langmuir trough are applied to investigate the characteristic relaxation times and elasticity of interfacial layers from the protein HFBII hydrophobin. Such layers undergo a transition from fluid to elastic solid films. The transition is detected as an increase in the error of the fit of the pendant-drop profile by means of the Laplace equation of capillarity. The relaxation of surface tension after interfacial expansion follows an exponential-decay law, which indicates adsorption kinetics under barrier control. The experimental data for the relaxation time suggest that the adsorption rate is determined by the balance of two opposing factors: (i) the barrier to detachment of protein molecules from bulk aggregates and (ii) the attraction of the detached molecules by the adsorption layer due to the hydrophobic surface force. The hydrophobic attraction can explain why a greater surface coverage leads to a faster adsorption. The relaxation of surface tension after interfacial compression follows a different, square-root law. Such behavior can be attributed to surface diffusion of adsorbed protein molecules that are condensing at the periphery of interfacial protein aggregates. The surface dilatational elasticity, E, is determined in experiments on quick expansion or compression of the interfacial protein layers. At lower surface pressures (<11 mN/m) the experiments on expansion, compression and oscillations give close values of E that are increasing with the rise of surface pressure. At higher surface pressures, E exhibits the opposite tendency and the data are scattered. The latter behavior can be explained with a two-dimensional condensation of adsorbed protein molecules at the higher surface pressures. The results could be important for the understanding and control of dynamic processes in foams and emulsions stabilized by hydrophobins, as well as for the modification of solid surfaces by adsorption of such

  9. Joint Models for Longitudinal and Time-to-Event Data With Applications in R

    CERN Document Server

    Rizopoulos, Dimitris

    2012-01-01

    In longitudinal studies it is often of interest to investigate how a marker that is repeatedly measured in time is associated with a time to an event of interest, e.g., prostate cancer studies where longitudinal PSA level measurements are collected in conjunction with the time-to-recurrence. Joint Models for Longitudinal and Time-to-Event Data: With Applications in R provides a full treatment of random effects joint models for longitudinal and time-to-event outcomes that can be utilized to analyze such data. The content is primarily explanatory, focusing on applications of joint modeling, but

  10. Thermoelastic Thick Plate under Illumination of a Uniform Laser Beam with one Relaxation time

    Directory of Open Access Journals (Sweden)

    Ezzat. F. Henain

    2013-05-01

    Full Text Available The problem of thermoelasticity, based on the theory of Lord and Shulman (L-S with one relaxation time, is used to solve a one dimensional boundary value problem of a thick plate. The upper surface of the medium is taken as traction free and heated by a pulsed laser beam. The lower surface of the medium rests on a rigid and thermally isolated. The general solution is obtained in the Laplace transform domain. Approximate small time analytical solutions to temperature, stress and displacement are obtained. Results of this problem are presented graphically.

  11. Elastic models for the non-Arrhenius relaxation time of glass-forming liquids

    DEFF Research Database (Denmark)

    Dyre, Jeppe

    We first review the phenomenology of viscous liquids and the standard models used for explaining the non-Arrhenius average relaxation time. Then the focus is turned to the so-called elastic models, arguing that these models are all equivalent in the Einstein approximation (where the short......-time elastic properties are all determined by just one effective, temperature-dependent force constant). We finally discuss the connection between the elastic models and two well-established research fields of condensed-matter physics: point defects in crystals and solid-state diffusion....

  12. Elastic models for the Non-Arrhenius Relaxation Time of Glass-Forming Liquids

    DEFF Research Database (Denmark)

    Dyre, J. C.

    2006-01-01

    We first review the phenomenology of viscous liquids and the standard models used for explaining the non-Arrhenius average relaxation time. Then the focus is turned to the so-called elastic models, arguing that these models are all equivalent in the Einstein approximation (where the short......-time elastic properties are all determined by just one effective, temperature-dependent force constant). We finally discuss the connection between the elastic models and two well-established research fields of condensed-matter physics: point defects in crystals and solid-state diffusion....

  13. Time-Resolved Torsional Relaxation of Spider Draglines by an Optical Technique

    Science.gov (United States)

    Emile, O.; Floch, A. Le; Vollrath, F.

    2007-04-01

    The sensitivity of the torsional pendulum demonstrates the self-shape-memory effect in different types of spider draglines. Here we report the time-resolved noncovalent bonds recovery in the protein structure. The torsional dynamics of such multilevel structure governed by reversible interactions are described in the frame of a nested model. Measurement of three different relaxation times confirms the existence of three energy storage levels in such two protein spidroin systems. Torsion opens the way to further investigations towards unraveling the tiny torque effects in biological molecules.

  14. Elastic Models for the Non-Arrhenius Relaxation Time of Glass-Forming Liquids

    Science.gov (United States)

    Dyre, Jeppe C.

    2006-05-01

    We first review the phenomenology of viscous liquids and the standard models used for explaining the non-Arrhenius average relaxation time. Then the focus is turned to the so-called elastic models, arguing that these models are all equivalent in the Einstein approximation (where the short-time elastic properties are all determined by just one effective, temperature-dependent force constant). We finally discuss the connection between the elastic models and two well-established research fields of condensed-matter physics: point defects in crystals and solid-state diffusion.

  15. T(2) relaxation time of hyaline cartilage in presence of different gadolinium-based contrast agents.

    Science.gov (United States)

    Wiener, Edzard; Settles, Marcus; Diederichs, Gerd

    2010-01-01

    The transverse relaxation time, T(2), of native cartilage is used to quantify cartilage degradation. T(2) is frequently measured after contrast administration, assuming that the impact of gadolinium-based contrast agents on cartilage T(2) is negligible. To verify this assumption the depth-dependent variation of T(2) in the presence of gadopentetate dimeglumine, gadobenate dimeglumine and gadoteridol was investigated. Furthermore, the r(2)/r(1) relaxivity ratios were quantified in different cartilage layers to demonstrate differences between T(2) and T(1) relaxation effects. Transverse high-spatial-resolution T(1)- and T(2)-maps were simultaneously acquired on a 1.5 T MR scanner before and after contrast administration in nine bovine patellae using a turbo-mixed sequence. The r(2)/r(1) ratios were calculated for each contrast agent in cartilage. Profiles of T(1), T(2) and r(2)/r(1) across cartilage thickness were generated in the absence and presence of contrast agent. The mean values in different cartilage layers were compared for global variance using the Kruskal-Wallis test and pairwise using the Mann-Whitney U-test. T(2) of unenhanced cartilage was 98 +/- 5 ms at 1 mm and 65 +/- 4 ms at 3 mm depth. Eleven hours after contrast administration significant differences (p cartilage thickness were close to 1.0 (range 0.9-1.3). At 1.5 T, T(2) decreased significantly in the presence of contrast agents, more pronounced in superficial than in deep cartilage. The change in T(2) relaxation rate was similar to the change in T(1). Cartilage T(2) measurements after contrast administration will lead to systematic errors in the quantification of cartilage degradation. 2010 John Wiley & Sons, Ltd.

  16. Ground-state atomic polarization relaxation-time measurement of Rb filled hypocycloidal core-shaped Kagome HC-PCF

    Science.gov (United States)

    Bradley, T. D.; Ilinova, E.; McFerran, J. J.; Jouin, J.; Debord, B.; Alharbi, M.; Thomas, P.; Gérôme, F.; Benabid, F.

    2016-09-01

    We report on the measurement of ground-state atomic polarization relaxation time of Rb vapor confined in five different hypocycloidal core-shape Kagome hollow-core photonic crystal fibers made with uncoated silica glass. We are able to distinguish between wall-collision and transit-time effects in an optical waveguide and deduce the contribution of the atom’s dwell time at the core wall surface. In contrast with conventional macroscopic atomic cell configuration, and in agreement with Monte Carlo simulations, the measured relaxation times were found to be at least one order of magnitude longer than the limit set by atom-wall collisional from thermal atoms. This extended relaxation time is explained by the combination of a stronger contribution of the slow atoms in the atomic polarization build-up, and of the relatively significant contribution of dwell time to the relaxation process of the ground state polarization.

  17. Experimental proposal for accurate determination of the phase relaxation time in highly excited quantum many-body systems

    CERN Document Server

    Bienert, M; Kun, S Yu

    2006-01-01

    We estimate how accurate the phase relaxation time of quantum many-body systems can be determined from data on forward peaking of evaporating protons from a compound nucleus. The angular range and accuracy of the data needed for a reliable determination of the phase relaxation time are evaluated. The general method is applied to analyze the inelastic scattering of 18 MeV protons from Pt for which previously measured double differential cross sections for two angles in the evaporating domain of the spectra show a strong forward peaking. A new experiment for an improved determination of the phase relaxation time is proposed.

  18. Molecular dynamics simulations of proton transverse relaxation times in suspensions of magnetic nanoparticles.

    Science.gov (United States)

    Panczyk, Tomasz; Konczak, Lukasz; Zapotoczny, Szczepan; Szabelski, Pawel; Nowakowska, Maria

    2015-01-01

    In this work we have analyzed the influence of various factors on the transverse relaxation times T2 of water protons in suspension of magnetic nanoparticles. For that purpose we developed a full molecular dynamics force field which includes the effects of dispersion interactions between magnetic nanoparticles and water molecules, electrostatic interactions between charged nanoparticles and magnetic dipole-dipole and dipole-external field interactions. We also accounted for the magnetization reversal within the nanoparticles body frames due to finite magnetic anisotropy barriers. The force field together with the Langevin dynamics imposed on water molecules and the nanoparticles allowed us to monitor the dephasing of water protons in real time. Thus, we were able to determine the T2 relaxation times including the effects of the adsorption of water on the nanoparticles' surfaces, thermal fluctuations of the orientation of nanoparticles' magnetizations as well as the effects of the core-shell architecture of nanoparticles and their agglomeration into clusters. We found that there exists an optimal cluster size for which T2 is minimized and that the retardation of water molecules motion, due to adsorption on the nanoparticles surfaces, has some effect in the measured T2 times. The typical strengths of the external magnetic fields in MRI are enough to keep the magnetizations fixed along the field direction, however, in the case of low magnetic fields, we observed significant enhancement of T2 due to thermal fluctuations of the orientations of magnetizations. Copyright © 2014 Elsevier Inc. All rights reserved.

  19. Relaxation time of the Cooper pairs near Tc in cuprate superconductors

    Science.gov (United States)

    Ramallo, M. V.; Carballeira, C.; Viña, J.; Veira, J. A.; Mishonov, T.; Pavuna, D.; Vidal, F.

    1999-10-01

    It is first shown that the thermal fluctuation effects on the transport and on the thermodynamic observables above the superconducting transition may provide, when they are analyzed simultaneously and consistently, a powerful tool to access the relaxation time, τ0, of the Cooper pairs with wave vector k = 0 in high-temperature cuprate superconductors (HTSC). Then, we apply this procedure to optimally doped YBa2Cu3O7 - δ (Y-123) crystals. It is found that in this HTSC τ0 follows, within 20% accuracy, the BCS temperature behaviour and amplitude given by τ0 = πhbar/[8kB(T - Tc0)].

  20. Intensity Correlation Function and Associated Relaxation Time of a Saturation Laser Model with Correlated Noises

    Institute of Scientific and Technical Information of China (English)

    ZHU Ping; CHEN Shi-Bo; MEI Dong-Cheng

    2006-01-01

    We investigate the intensity correlation function C(s) and its associated relaxation time Tc for a saturation model of single-mode laser with correlated noises.The expressions of C(s) and Tc are derived by means of the projection operator method,and effects of correlations between an additive noise and a multiplicative noise are discussed by numerical calculation.Based on the calculated results,it is found that the correlation strength λ between the additive noise and the multiplicative noise can enhance the fluctuation decay of the laser intensity.

  1. One-Dimensional Problem of a Conducting Viscous Fluid with One Relaxation Time

    Directory of Open Access Journals (Sweden)

    Angail A. Samaan

    2011-01-01

    Full Text Available We introduce a magnetohydrodynamic model of boundary-layer equations for conducting viscous fluids. This model is applied to study the effects of free convection currents with thermal relaxation time on the flow of a viscous conducting fluid. The method of the matrix exponential formulation for these equations is introduced. The resulting formulation together with the Laplace transform technique is applied to a variety problems. The effects of a plane distribution of heat sources on the whole and semispace are studied. Numerical results are given and illustrated graphically for the problem.

  2. A Novel Statistical Approach for Brain MR Images Segmentation Based on Relaxation Times

    Directory of Open Access Journals (Sweden)

    Fabio Baselice

    2015-01-01

    Full Text Available Brain tissue segmentation in Magnetic Resonance Imaging is useful for a wide range of applications. Classical approaches exploit the gray levels image and implement criteria for differentiating regions. Within this paper a novel approach for brain tissue joint segmentation and classification is presented. Starting from the estimation of proton density and relaxation times, we propose a novel method for identifying the optimal decision regions. The approach exploits the statistical distribution of the involved signals in the complex domain. The technique, compared to classical threshold based ones, is able to globally improve the classification rate. The effectiveness of the approach is evaluated on both simulated and real datasets.

  3. The Frequency-Dependence of the NMR Longitudinal Relaxation Rate, T(1)(-1), of Water in Cysts of the Brine Shrimp

    Science.gov (United States)

    Egan, Thomas F.

    The NMR spin-lattice relaxation rate, T(,1)(' -1), of water is independent of the Larmor frequency, (omega)/2(pi), in the normal rf range. However, T(,1)('-1) of intracellular water in biological systems, which accounts for as much as 80% of the cell mass, is frequency-dependent. This indicates that the NMR properties of water in the cellular environment are influenced by long-correlation time processes due to the interaction of water with proteins and other macromolecular constituents of the cell. In this research, the relaxation rate T(,1)(' -1) of water in the Artemia (brine shrimp) cyst is examined as a function of: (1) the proton NMR Larmor frequency for .01 Artemia cysts between 10 and 500 MHz. At lower Larmor frequencies, below 1 MHz, the relaxation rates of water in brine shrimp cysts are influenced by additional relexation mechanisms; translational diffusion of hydration water is one possibility.

  4. Longitudinal and transverse exciton-spin relaxation in a single InAsP quantum dot embedded inside a standing InP nanowire using photoluminescence spectroscopy

    NARCIS (Netherlands)

    Sasakura, H.; Hermannstädter, C.; Dorenbos, S.N.; Akopian, N.; Van Kouwen, M.P.; Motohisa, J.; Kobayashi, Y.; Kumano, H.; Kondo, K.; Tomioka, K.; Fukui, T.; Suemune, I.; Zwiller, V.

    2012-01-01

    We have investigated the optical properties of a single InAsP quantum dot embedded in a standing InP nanowire. Elongation of the transverse exciton-spin relaxation time of the exciton state with decreasing excitation power was observed by first-order photon correlation measurements. This behavior is

  5. Density Relaxation in Time-Dependent Density Functional Theory: Combining Relaxed Density Natural Orbitals and Multireference Perturbation Theories for an Improved Description of Excited States.

    Science.gov (United States)

    Ronca, Enrico; Angeli, Celestino; Belpassi, Leonardo; De Angelis, Filippo; Tarantelli, Francesco; Pastore, Mariachiara

    2014-09-09

    Making use of the recently developed excited state charge displacement analysis [E. Ronca et al., J. Chem. Phys. 140, 054110 (2014)], suited to quantitatively characterize the charge fluxes coming along an electronic excitation, we investigate the role of the density relaxation effects in the overall description of electronically excited states of different nature, namely, valence, ionic, and charge transfer (CT), considering a large set of prototypical small and medium-sized molecular systems. By comparing the response densities provided by time-dependent density functional theory (TDDFT) and the corresponding relaxed densities obtained by applying the Z-vector postlinear-response approach [N. C. Handy and H. F. Schaefer, J. Chem. Phys. 81, 5031 (1984)] with those obtained by highly correlated state-of-the-art wave function calculations, we show that the inclusion of the relaxation effects is imperative to get an accurate description of the considered excited states. We also examine what happens at the quality of the response function when an increasing amount of Hartree-Fock (HF) exchange is included in the functional, showing that the usually improved excitation energies in the case of CT states are not always the consequence of an improved description of their overall properties. Remarkably, we find that the relaxation of the response densities is always able to reproduce, independently of the extent of HF exchange in the functional, the benchmark wave function densities. Finally, we propose a novel and computationally convenient strategy, based on the use of the natural orbitals derived from the relaxed TDDFT density to build zero-order wave function for multireference perturbation theory calculations. For a significant set of different excited states, the proposed approach provided accurate excitation energies, comparable to those obtained by computationally demanding ab initio calculations.

  6. Extending the EGP constitutive model for polymer glasses to multiple relaxation times

    Science.gov (United States)

    van Breemen, L. C. A.; Klompen, E. T. J.; Govaert, L. E.; Meijer, H. E. H.

    2011-10-01

    The one-mode EGP (Eindhoven glassy polymer) model captures the plastic flow at yield and post-yield quantitatively, but behaves poor in the non-linear viscoelastic pre-yield region. Since a proper description here is important in cases of complex loading and unloading situations, such as e.g. in indentation and scratching, an extension to non-linear modeling is required using a spectrum of relaxation times. It is shown that such a reference spectrum can be obtained from simple tensile tests. It shifts to shorter times under the influence of stress and is independent of the two important time-dependent processes in polymers: the strain rate applied during testing and the aging time during storage and use. The multi-mode model is critically tested and proves quantitative in describing the intrinsic polymer response and, based thereupon, in predicting the correct response in tensile testing, including necking, in flat tip indentation and in notched loading.

  7. Survival and relaxation time, pore size distribution moments, and viscous permeability in random unidirectional fiber structures

    Science.gov (United States)

    Tomadakis, Manolis M.; Robertson, Teri J.

    2005-03-01

    Computer simulation results are presented for the mean survival time, principal relaxation time, mean pore size, and mean square pore size, for random porous structures consisting of parallel nonoverlapping or partially overlapping fibers. The numerical procedure is based on a discrete step-by-step random walk mechanism simulating the Brownian diffusion trajectories of molecules in the porous media. Numerical results on the viscous permeability of these structures are computed with a method based on electrical conduction principles and compared to a variational bound derived from the mean survival time. The results show that nonoverlapping fiber structures exhibit lower values of the dimensionless mean survival time, principal relaxation time, mean pore size, and mean square pore size than randomly overlapping fiber structures of the same porosity, while partially overlapping fiber structures show behavior intermediate to those of the two extreme cases. The mean square pore size (second moment of the pore size distribution) is found to be a very good predictor of the mean survival time for non-, partially, and randomly overlapping fiber structures. Dimensionless groups representing the deviation of variational bounds from our simulation results vary in practically the same range as the corresponding values reported earlier for beds of spherical particles. A universal scaling expression of the literature relating the mean survival time to structural properties [S. Torquato and C. L. Y. Yeong, J. Chem. Phys. 106, 8814 (1997)] agrees very well with our results for all examined fiber structures, thus validated for the first time for porous media formed by partially overlapping particles. The permeability behavior of partially overlapping fiber structures resembles that of nonoverlapping fiber structures for flow parallel to the fibers, but not for transverse flow, where percolation phenomena prevail. The permeability results for beds of unidirectional partially

  8. Acceleration of carbon-13 spin-lattice relaxation times in amino acids by electrolytes

    Institute of Scientific and Technical Information of China (English)

    Tian Jinping; Yin Yingwu

    2004-01-01

    A series of amino acids and carboxylic acids were determined by 13C NMR spectroscopy.The results showed that addition of 3M MgCl2 led to the 13C NMR integral area of samples being well proportional to number of carbon atoms that produce the particular signal with reliability over 95%. Measurements of 13C spin-lattice relaxation times (T1's) are reported for a number of amino acids. T1's of all the carbons in amino acids generally tend to decrease with the increase of the concentration of electrolytes, and the presence of magnesium slats is of significant. Carboxylic carbons in amino acids are the most sensitive "acceptor" of the 13C spin-lattice relaxation accelerating effects in electrolytes, and the 13C spin-lattice relaxation accelerating ability of electrolytes is Mg(ClO4)2 >MgCl2 >CaCl2 >NaCl >KCl >LiClO4 >NaOH. In general, T1's of C1 carbons in nonpolar a-amino acids are higher than those in polar and basic a-amino acids both in aqueous and 3M MgCl2 medium. In aliphatic straight-chain amino acids, a-, a-, a-, ai- and a- amino acids, T1's of C1 carbons tend to reduce with the increase of inserted carbon numbers between amino and carboxylic groups compared with Gly. T1's can be decreased even more when amino acids are mixed in 3M MgCl2, but T1's of carbons in amino acids decrease slightly with increase of the concentration of amino acids in 3M MgCl2. The mechanisms of the observed phenomena are discussed in terms of intermolecular interaction and paramagnetic impurity in electrolytes, large contributions of intermolecular interaction which is enhanced in electrolytes concentrate on the incoming "unsaturation" of the primary solvation shell of cations with the increase of electrolytes concentration and complexes formation of amino acids with metal ions. In electrolytes, amino acids are "anchored" to cations and molecule tumbling is slowed down, molecular rigidity is increased and molecular size is "enlarged", all of these are helpful to accelerate

  9. Evaluation of PHB/Clay nanocomposite by spin-lattice relaxation time

    Directory of Open Access Journals (Sweden)

    Mariana Bruno

    2008-12-01

    Full Text Available Poly(3-hydroxybutyrate (PHB based on nanocomposites containing different amounts of a commercial organically modified clay (viscogel B7 were prepared employing solution intercalation method. Three solvents, such as: CHCl3, dimethylchloride (DMC and tetrahydrofuran (THF were used. The relationship among the processing conditions; molecular structure and intermolecular interaction, between both nanocomposite components, were investigated using a nuclear magnetic resonance (NMR, as a part of characterization methodology, which has been used by Tavares et al. It involves the hydrogen spin-lattice relaxation time, T1H, by solid state nuclear magnetic resonance, employing low field NMR. X ray diffraction was also employed because it is a conventional technique, generally used to obtain the first information on nanocomposite formation. Changes in PHB crystallinity were observed after the organophilic nanoclay had been incorporated in the polymer matrix. These changes, in the microstructure, were detected by the variation of hydrogen nuclear relaxation time values and by X ray, which showed an increase in the clay interlamelar space due to the intercalation of the polymer in the clay between lamellae. It was also observed, for both techniques, that the solvents affect directly the organization of the crystalline region, promoting a better intercalation, considering that they behave like a plasticizer.

  10. MRI-Based Visualization of the Relaxation Times of Early Somatic Embryos

    Directory of Open Access Journals (Sweden)

    Mikulka J.

    2016-04-01

    Full Text Available The large set of scientific activities supported by MRI includes, among others, the research of water and mineral compounds transported within a plant, the investigation of cellular processes, and the examination of the growth and development of plants. MRI is a method of major importance for the measurement of early somatic embryos (ESE during cultivation, and in this respect it offers several significant benefits discussed within this paper. We present the following procedures: non-destructive measurement of the volume and content of water during cultivation; exact three-dimensional differentiation between the ESEs and the medium; investigation of the influence of ions and the change of relaxation times during cultivation; and multiparametric segmentation of MR images to differentiate between embryogenic and non-embryogenic cells. An interesting technique consists in two-parameter imaging of the relaxation times of the callus; this method is characterized by tissue changes during cultivation at a microscopic level, which can be monitored non-destructively.

  11. Kinetic lattice Boltzmann method for microscale gas flows: issues on boundary condition, relaxation time, and regularization.

    Science.gov (United States)

    Niu, Xiao-Dong; Hyodo, Shi-Aki; Munekata, Toshihisa; Suga, Kazuhiko

    2007-09-01

    It is well known that the Navier-Stokes equations cannot adequately describe gas flows in the transition and free-molecular regimes. In these regimes, the Boltzmann equation (BE) of kinetic theory is invoked to govern the flows. However, this equation cannot be solved easily, either by analytical techniques or by numerical methods. Hence, in order to efficiently maneuver around this equation for modeling microscale gas flows, a kinetic lattice Boltzmann method (LBM) has been introduced in recent years. This method is regarded as a numerical approach for solving the BE in discrete velocity space with Gauss-Hermite quadrature. In this paper, a systematic description of the kinetic LBM, including the lattice Boltzmann equation, the diffuse-scattering boundary condition for gas-surface interactions, and definition of the relaxation time, is provided. To capture the nonlinear effects due to the high-order moments and wall boundaries, an effective relaxation time and a modified regularization procedure of the nonequilibrium part of the distribution function are further presented based on previous work [Guo et al., J. Appl. Phys. 99, 074903 (2006); Shan et al., J. Fluid Mech. 550, 413 (2006)]. The capability of the kinetic LBM of simulating microscale gas flows is illustrated based on the numerical investigations of micro Couette and force-driven Poiseuille flows.

  12. Enhancing Web applications in radiology with Java: estimating MR imaging relaxation times.

    Science.gov (United States)

    Dagher, A P; Fitzpatrick, M; Flanders, A E; Eng, J

    1998-01-01

    Java is a relatively new programming language that has been used to develop a World Wide Web-based tool for estimating magnetic resonance (MR) imaging relaxation times, thereby demonstrating how Java may be used for Web-based radiology applications beyond improving the user interface of teaching files. A standard processing algorithm coded with Java is downloaded along with the hypertext markup language (HTML) document. The user (client) selects the desired pulse sequence and inputs data obtained from a region of interest on the MR images. The algorithm is used to modify selected MR imaging parameters in an equation that models the phenomenon being evaluated. MR imaging relaxation times are estimated, and confidence intervals and a P value expressing the accuracy of the final results are calculated. Design features such as simplicity, object-oriented programming, and security restrictions allow Java to expand the capabilities of HTML by offering a more versatile user interface that includes dynamic annotations and graphics. Java also allows the client to perform more sophisticated information processing and computation than is usually associated with Web applications. Java is likely to become a standard programming option, and the development of stand-alone Java applications may become more common as Java is integrated into future versions of computer operating systems.

  13. Nuclear magnetic resonance and proton relaxation times in experimental heterotopic heart transplantation

    Energy Technology Data Exchange (ETDEWEB)

    Eugene, M.; Lechat, P.; Hadjiisky, P.; Teillac, A.; Grosgogeat, Y.; Cabrol, C.

    1986-01-01

    It should be possible to detect heart transplant rejection by nuclear magnetic resonance (NMR) imaging if it induces myocardial T1 and T2 proton relaxation time alterations or both. We studied 20 Lewis rats after a heterotopic heart transplantation. In vitro measurement of T1 and T2 was performed on a Minispec PC20 (Bruker) 3 to 9 days after transplantation. Histologic analysis allowed the quantification of rejection process based on cellular infiltration and myocardiolysis. Water content, a major determinant of relaxation time, was also studied. T1 and T2 were significantly prolonged in heterotopic vs orthotopic hearts (638 +/- 41 msec vs 606 +/- 22 msec for T1, p less than 0.01 and 58.2 +/- 8.4 msec vs 47.4 +/- 1.9 msec for T2, p less than 0.001). Water content was also increased in heterotopic hearts (76.4 +/- 2.3 vs 73.8 +/- 1.0, p less than 0.01). Most importantly, we found close correlations between T1 and especially T2 vs water content, cellular infiltration, and myocardiolysis. We conclude that rejection reaction should be noninvasively detected by NMR imaging, particularly with pulse sequences emphasizing T2.

  14. Nuclear magnetic resonance relaxation times for human lung cancer and lung tissues

    Energy Technology Data Exchange (ETDEWEB)

    Matsuura, Yoshifumi; Shioya, Sumie; Kurita, Daisaku; Ohta, Takashi; Haida, Munetaka; Ohta, Yasuyo [Tokai Univ., Isehara, Kanagawa (Japan). School of Medicine; Suda, Syuichi; Fukuzaki, Minoru

    1994-12-01

    We investigated the nuclear magnetic resonance (NMR) relaxation times, T{sub 1} and T{sub 2}, for lung cancer tissue, and other samples of lung tissue obtained from surgical specimens. The samples were nine squamous cell carcinomas, five necrotic squamous cell carcinomas, 15 adenocarcinomas, two benign mesotheliomas, and 13 fibrotic lungs. The relaxation times were measured with a 90 MHz NMR spectrometer and the results were correlated with histological changes. The values of T{sub 1} and T{sub 2} for squamous cell carcinoma and mesothelioma were significantly longer than those of adenocarcinoma and fibrotic lung tissue. There were no significant differences in values of T{sub 1} and T{sub 2} between adenocarcinoma and lung tissue. The values of T{sub 1} and T{sub 2} for benign mesothelioma were similar to those of squamous cell carcinoma, which suggested that increases in T{sub 1} and T{sub 2} are not specific to malignant tissues. (author).

  15. Average-atom treatment of relaxation time in x-ray Thomson scattering from warm dense matter.

    Science.gov (United States)

    Johnson, W R; Nilsen, J

    2016-03-01

    The influence of finite relaxation times on Thomson scattering from warm dense plasmas is examined within the framework of the average-atom approximation. Presently most calculations use the collision-free Lindhard dielectric function to evaluate the free-electron contribution to the Thomson cross section. In this work, we use the Mermin dielectric function, which includes relaxation time explicitly. The relaxation time is evaluated by treating the average atom as an impurity in a uniform electron gas and depends critically on the transport cross section. The calculated relaxation rates agree well with values inferred from the Ziman formula for the static conductivity and also with rates inferred from a fit to the frequency-dependent conductivity. Transport cross sections determined by the phase-shift analysis in the average-atom potential are compared with those evaluated in the commonly used Born approximation. The Born approximation converges to the exact cross sections at high energies; however, differences that occur at low energies lead to corresponding differences in relaxation rates. The relative importance of including relaxation time when modeling x-ray Thomson scattering spectra is examined by comparing calculations of the free-electron dynamic structure function for Thomson scattering using Lindhard and Mermin dielectric functions. Applications are given to warm dense Be plasmas, with temperatures ranging from 2 to 32 eV and densities ranging from 2 to 64 g/cc.

  16. Temperature dependence of proton NMR relaxation times at earth's magnetic field

    Science.gov (United States)

    Niedbalski, Peter; Kiswandhi, Andhika; Parish, Christopher; Ferguson, Sarah; Cervantes, Eduardo; Oomen, Anisha; Krishnan, Anagha; Goyal, Aayush; Lumata, Lloyd

    The theoretical description of relaxation processes for protons, well established and experimentally verified at conventional nuclear magnetic resonance (NMR) fields, has remained untested at low fields despite significant advances in low field NMR technology. In this study, proton spin-lattice relaxation (T1) times in pure water and water doped with varying concentrations of the paramagnetic agent copper chloride have been measured from 6 to 92oC at earth's magnetic field (1700 Hz). Results show a linear increase of T1 with temperature for each of the samples studied. Increasing the concentration of the copper chloride greatly reduced T1 and reduced dependence on temperature. The consistency of the results with theory is an important confirmation of past results, while the ability of an ultra-low field NMR system to do contrast-enhanced magnetic resonance imaging (MRI) is promising for future applicability to low-cost medical imaging and chemical identification. This work is supported by US Dept of Defense Award No. W81XWH-14-1-0048 and the Robert A. Welch Foundation Grant No. AT-1877.

  17. NMR relaxation times of trabecular bone-reproducibility, relationships to tissue structure and effects of sample freezing

    Energy Technology Data Exchange (ETDEWEB)

    Prantner, Viktoria; Isaksson, Hanna; Nissi, Mikko J; Jurvelin, Jukka S [Department of Physics and Mathematics, University of Eastern Finland, PO Box 1627, 70211 Kuopio (Finland); Naervaeinen, Johanna; Groehn, Olli H J [Department of Neurobiology, A I Virtanen Institute for Molecular Sciences, University of Eastern Finland, PO Box 1627, 70211 Kuopio (Finland); Lammentausta, Eveliina [Department of Diagnostic Radiology, Oulu University Hospital, PO Box 50, 90029 OYS, Oulu (Finland); Avela, Janne, E-mail: hanna.isaksson@uef.f [Department of Biology of Physical Activity, University of Jyvaeskylae, PO Box 35, 40014 Jyvaeskylae (Finland)

    2010-12-07

    Nuclear magnetic resonance (NMR) spectroscopy provides a potential tool for non-invasive evaluation of the trabecular bone structure. The objective of this study was to determine the reproducibility of the NMR relaxation parameters (T{sub 2}, Carr-Purcel-T{sub 2}, T{sub 1}{rho}) for fat and water and relate those to the structural parameters obtained by micro-computed tomography ({mu}CT). Especially, we aimed to evaluate the effect of freezing on the relaxation parameters. For storing bone samples, freezing is the standard procedure during which the biochemical and cellular organization of the bone marrow may be affected. Bovine trabecular bone samples were stored at -20 {sup 0}C for 7 days and measured by NMR spectroscopy before and after freezing. The reproducibility of NMR relaxation parameters, as expressed by the coefficient of variation, ranged from 3.1% to 27.9%. In fresh samples, some correlations between NMR and structural parameters (Tb.N, Tb.Sp) were significant (e.g. the relaxation rate for T{sub 2} of fat versus Tb.Sp: r = -0.716, p < 0.01). Freezing did not significantly change the NMR relaxation times but the correlations between relaxation parameters and the {mu}CT structural parameters were not statistically significant after freezing, suggesting some nonsystematic alterations of the marrow structure. Therefore, the use of frozen bone samples for NMR relaxation studies may provide inferior information about the trabecular bone structure.

  18. Longitudinal variability of time-location/activity patterns of population at different ages: a longitudinal study in California

    Directory of Open Access Journals (Sweden)

    Cassady Diana L

    2011-09-01

    Full Text Available Abstract Background Longitudinal time-activity data are important for exposure modeling, since the extent to which short-term time-activity data represent long-term activity patterns is not well understood. This study was designed to evaluate longitudinal variations in human time-activity patterns. Method We report on 24-hour recall diaries and questionnaires collected via the internet from 151 parents of young children (mostly under age 55, and from 55 older adults of ages 55 and older, for both a weekday and a weekend day every three months over an 18-month period. Parents also provided data for their children. The self-administrated diary and questionnaire distinguished ~30 frequently visited microenvironments and ~20 activities which we selected to represent opportunities for exposure to toxic environmental compounds. Due to the non-normal distribution of time-location/activity data, we employed generalized linear mixed-distribution mixed-effect models to examine intra- and inter-individual variations. Here we describe variation in the likelihood of and time spent engaging in an activity or being in a microenvironment by age group, day-type (weekday/weekend, season (warm/cool, sex, employment status, and over the follow-up period. Results As expected, day-type and season influence time spent in many location and activity categories. Longitudinal changes were also observed, e.g., young children slept less with increasing follow-up, transit time increased, and time spent on working and shopping decreased during the study, possibly related to human physiological changes with age and changes in macro-economic factors such as gas prices and the economic recession. Conclusions This study provides valuable new information about time-activity assessed longitudinally in three major age groups and greatly expands our knowledge about intra- and inter-individual variations in time-location/activity patterns. Longitudinal variations beyond weekly and

  19. Dependence of the time of the appearance of a Stark echo response on irreversible relaxation of a system

    Science.gov (United States)

    Akhmedshina, E. N.; Nefed'ev, L. A.; Garnaeva, G. I.

    2016-09-01

    The dependence of the time of the appearance of a Stark (gradient) echo response on the irreversible transverse relaxation time of a system in the nanosecond range and on the width of the excitation region of an inhomogeneously broadened line has been investigated. It has been shown that the use of nonresonant laser pulses with an artificially created spatial inhomogeneity makes it possible to determine the relaxation time in the nanosecond range from the time of the appearance of a Stark (gradient) echo response, which is a more accurate method than the method of determining the relaxation time from the decay of the intensity by varying time intervals of the exposure to inhomogeneous electromagnetic fields.

  20. Characterization of the uncertainty of divergence time estimation under relaxed molecular clock models using multiple loci.

    Science.gov (United States)

    Zhu, Tianqi; Dos Reis, Mario; Yang, Ziheng

    2015-03-01

    Genetic sequence data provide information about the distances between species or branch lengths in a phylogeny, but not about the absolute divergence times or the evolutionary rates directly. Bayesian methods for dating species divergences estimate times and rates by assigning priors on them. In particular, the prior on times (node ages on the phylogeny) incorporates information in the fossil record to calibrate the molecular tree. Because times and rates are confounded, our posterior time estimates will not approach point values even if an infinite amount of sequence data are used in the analysis. In a previous study we developed a finite-sites theory to characterize the uncertainty in Bayesian divergence time estimation in analysis of large but finite sequence data sets under a strict molecular clock. As most modern clock dating analyses use more than one locus and are conducted under relaxed clock models, here we extend the theory to the case of relaxed clock analysis of data from multiple loci (site partitions). Uncertainty in posterior time estimates is partitioned into three sources: Sampling errors in the estimates of branch lengths in the tree for each locus due to limited sequence length, variation of substitution rates among lineages and among loci, and uncertainty in fossil calibrations. Using a simple but analogous estimation problem involving the multivariate normal distribution, we predict that as the number of loci ([Formula: see text]) goes to infinity, the variance in posterior time estimates decreases and approaches the infinite-data limit at the rate of 1/[Formula: see text], and the limit is independent of the number of sites in the sequence alignment. We then confirmed the predictions by using computer simulation on phylogenies of two or three species, and by analyzing a real genomic data set for six primate species. Our results suggest that with the fossil calibrations fixed, analyzing multiple loci or site partitions is the most effective way

  1. JM: An R package for the joint modelling of longitudinal and time-to-event data

    NARCIS (Netherlands)

    D. Rizopoulos (Dimitris)

    2010-01-01

    textabstractIn longitudinal studies measurements are often collected on different types of outcomes for each subject. These may include several longitudinally measured responses (such as blood values relevant to the medical condition under study) and the time at which an event of particular interest

  2. Knee Cartilage Thickness, T1ρ and T2 Relaxation Time Are Related to Articular Cartilage Loading in Healthy Adults

    Science.gov (United States)

    Van Rossom, Sam; Smith, Colin Robert; Zevenbergen, Lianne; Thelen, Darryl Gerard; Vanwanseele, Benedicte; Van Assche, Dieter; Jonkers, Ilse

    2017-01-01

    Cartilage is responsive to the loading imposed during cyclic routine activities. However, the local relation between cartilage in terms of thickness distribution and biochemical composition and the local contact pressure during walking has not been established. The objective of this study was to evaluate the relation between cartilage thickness, proteoglycan and collagen concentration in the knee joint and knee loading in terms of contact forces and pressure during walking. 3D gait analysis and MRI (3D-FSE, T1ρ relaxation time and T2 relaxation time sequence) of fifteen healthy subjects were acquired. Experimental gait data was processed using musculoskeletal modeling to calculate the contact forces, impulses and pressure distribution in the tibiofemoral joint. Correlates to local cartilage thickness and mean T1ρ and T2 relaxation times of the weight-bearing area of the femoral condyles were examined. Local thickness was significantly correlated with local pressure: medial thickness was correlated with medial condyle contact pressure and contact force, and lateral condyle thickness was correlated with lateral condyle contact pressure and contact force during stance. Furthermore, average T1ρ and T2 relaxation time correlated significantly with the peak contact forces and impulses. Increased T1ρ relaxation time correlated with increased shear loading, decreased T1ρ and T2 relaxation time correlated with increased compressive forces and pressures. Thicker cartilage was correlated with higher condylar loading during walking, suggesting that cartilage thickness is increased in those areas experiencing higher loading during a cyclic activity such as gait. Furthermore, the proteoglycan and collagen concentration and orientation derived from T1ρ and T2 relaxation measures were related to loading. PMID:28076431

  3. All-electrical measurement of the triplet-singlet spin relaxation time in self-assembled quantum dots

    Science.gov (United States)

    Eltrudis, K.; Al-Ashouri, A.; Beckel, A.; Ludwig, A.; Wieck, A. D.; Geller, M.; Lorke, A.

    2017-08-01

    We have measured the spin relaxation time of an excited two-electron spin-triplet state into its singlet ground state in self-assembled InAs/GaAs quantum dots. We use a time-resolved measurement scheme that combines transconductance spectroscopy with spin-to-charge conversion to address the |s ↑,p ↑ 〉 triplet state, where one electron is in the quantum dot s-shell and a second one in the p-shell. The evaluation of the state-selective tunneling times from the dots into a nearby two-dimensional electron gas allows us to determine the s- and p-shell occupation and extract the relaxation time from a rate equation model. A comparably long triplet-to-singlet spin relaxation time of 25 μs is found.

  4. Extensional Relaxation Times and Pinch-off Dynamics of Dilute Polymer Solutions

    Science.gov (United States)

    Dinic, Jelena; Zhang, Yiran; Jimenez, Leidy; Sharma, Vivek

    2015-11-01

    We show that visualization and analysis of capillary-driven thinning and pinch-off dynamics of the columnar neck in an asymmetric liquid bridge created by dripping-onto-substrate can be used for characterizing the extensional rheology of complex fluids. Using a particular example of dilute, aqueous PEO solutions, we show the measurement of both the extensional relaxation time and extensional viscosity of weakly elastic, polymeric complex fluids with low shear viscosity ηsessile drop to a nozzle is detected optically, and the extensional response for viscoelastic fluids is characterized by analyzing their elastocapillary self-thinning, we refer to this technique as optically-detected elastocapillary self-thinning dripping-onto-substrate (ODES-DOS) extensional rheometry.

  5. A new multiple-relaxation-time lattice Boltzmann model for incompressible flows in porous media

    CERN Document Server

    Liu, Qing; He, Chao

    2013-01-01

    In this paper, a two-dimensional eight-velocity (D2Q8) multiple-relaxation-time (MRT) lattice Boltzmann (LB) model is proposed for incompressible porous flows at the representative elementary volume scale based on the Brinkman-Forchheimer-extended Darcy formulation. In the MRT-LB model, newly defined equilibrium moments are employed to account for the porosity of the porous media, and the linear and nonlinear drag forces of the media are incorporated into the model by adding a forcing term to the MRT-LB equation in the moment space. The model is validated by simulating the 2D Poiseuille flow, Couette flow and lid-driven cavity flow in porous media. The numerical results are in excellent agreement with the analytical solutions and/or the well-documented data available in the literature.

  6. Time-resolved photoluminescence study of excitonic relaxation in one-dimensional systems

    Science.gov (United States)

    Tanino, H.; Rühle, W. W.; Takahashi, K.

    1988-12-01

    Self-trapped exciton luminescence of quasi-one-dimensional (1D) halogen-bridged mixed-valence platinum complexes [Pt(II) (EA)4][Pt(IV)Cl2(EA)4] Cl4.4H2O (EA=ethylamine) and [Pt(II)(en)2] [Pt(IV)Cl2(en)2](ClO4)4 (en=1,2-diaminoethane) are studied by time-resolved photoluminescence experiments. The lifetimes of the luminescence of self-trapped exciton are exceptionally short, of the order of 100 psec. We interpret the short lifetime by a ``giant oscillator strength'' caused by a strong coupling between the electron and hole of the 1D charge transfer exciton and an extended polaronlike character of the 1D state. The lifetimes of the broad luminescence and of the resonant Raman lines during the barrier-free relaxation process are both faster than 7 psec.

  7. Probe Spin-Velocity Dependent New Interactions by Spin Relaxation Times of Polarized $^{3}He$ Gas

    CERN Document Server

    Zhang, Y; Peng, S M; Fu, C B; Guo, Hao; Liu, B Q; Yan, H

    2014-01-01

    We have studied how to constrain the $\\alpha\\vec{\\sigma}\\cdot\\vec{v}$ type interactions with the relaxation time of spin polarized noble gases in magnetic fields. Using the longest $T_{2}$ measured in the laboratory and the earth as the source, we obtained constraints on three new interactions. We present a new experimental upper bound to the vector-axial-vector($V_{VA}$) type interaction for ranges between $1\\sim10^{8}$m. In combination with the previous result, we set the most stringent experiment limits on $g_{V}g_{A}$ ranging from $\\sim\\mu m$ to $\\sim10^{8}$m. We improve the laboratory limit to the axial-axial-vector($V_{AA}$) type interaction by $\\sim2$ orders or more for distances below $\\sim1$cm. To our best knowledge, we report the first experiment upper limit on torsion induced by the earth on its surface.

  8. Relaxation time of the Cooper pairs near T{sub c} in cuprate superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Ramallo, M.V.; Carballeira, C.; Vina, J.; Veira, J.A.; Mishonov, T.; Pavuna, D.; Vidal, F. [Santiago de Compostela Univ. (Spain). Lab. de Bajas Temperaturas y Superconductividad

    1999-10-01

    It is first shown that the thermal fluctuation effects on the transport and on the thermodynamic observables above the superconducting transition may provide, when they are analyzed simultaneously and consistently, a powerful tool to access the relaxation time, {tau}{sub 0}, of the Cooper pairs with wave vector k = 0 in high-temperature cuprate superconductors (HTSC). Then, we apply this procedure to optimally doped YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (Y-123) crystals. It is found that in this HTSC {tau}{sub 0} follows, within 20% accuracy, the BCS temperature behaviour and amplitude given by {tau}{sub 0} = {pi}{Dirac_h}[8k{sub B}(T-T{sub c0})]. (orig.)

  9. Non-orthogonal multiple-relaxation-time lattice Boltzmann method for incompressible thermal flows

    CERN Document Server

    Liu, Qing; Li, Dong

    2015-01-01

    In this paper, a non-orthogonal multiple-relaxation-time (MRT) lattice Boltzmann (LB) method for simulating incompressible thermal flows is presented. In the method, the incompressible Navier-Stokes equations and temperature equation (or convection-diffusion equation) are solved separately by two different MRT-LB models, which are proposed based on non-orthogonal transformation matrices constructed in terms of some proper non-orthogonal basis vectors obtained from the combinations of the lattice velocity components. The macroscopic equations for incompressible thermal flows can be recovered from the present method through the Chapman-Enskog analysis in the incompressible limit. Numerical simulations of several typical two-dimensional problems are carried out to validate the present method. It is found that the present numerical results are in good agreement with the analytical solutions or other numerical results of previous studies. Furthermore, the grid convergence tests indicate that the present MRT-LB met...

  10. Intracerebral pH affects the T2 relaxation time of brain tissue

    Energy Technology Data Exchange (ETDEWEB)

    Schilling, A.M.; Blankenburg, F.B.; Bernarding, J.; Heidenreich, J.O.; Wolf, K.J. [Department of Radiology, University Hospital Benjamin Franklin, Free University Berlin, Hindenburgdamm 30, 12200 Berlin (Germany)

    2002-12-01

    Signal changes in activated brain areas are detectable by MRI and MR spectroscopy (MRS). Shifts in pH occur during brain activation. Our aim was to investigate the relationship between changes in pH and T2 relaxation times. T2 was determined in vitro at 24 MHz in various liquids at different pH using a Carr-Purcell-Meiboom-Gill (CPMG) spin-echo sequence. We also studied five Fisher rats were studied at 2.4 tesla with a double-tuneable surface coil. After baseline measurements, potassium cyanide was injected, producing intracerebral acidosis. Alternating series of 1H CPMG spin-echo sequences and 31P spectra were acquired. True T2 relaxation times were calculated from a CPMG multi-echo train. Changes in intracellular pH determined from 31P spectra. In vitro measurements demonstrated a correlation between T2 and pH that could be described by a quadratic fit curve. Depending on the initial pH, changes of 0.2 induced changes in T2 of up to 150 ms. In vivo measurements confirmed these findings. After intraperitoneal injection of a sublethal dose of cyanide, T2 decreased by about 5% in four cases, followed by recovery after 2 h. The in vitro measurements demonstrated that changes in pH can lead to significant signal change on T2- or T2*- weighted images. The dependence of T2 on pH in vitro was confirmed in vivo; it may contribute to signal change in activated brain areas. (orig.)

  11. Development of rapid methods for relaxation time mapping and motion estimation using magnetic resonance imaging

    Energy Technology Data Exchange (ETDEWEB)

    Gilani, Syed Irtiza Ali

    2008-09-15

    Recent technological developments in the field of magnetic resonance imaging have resulted in advanced techniques that can reduce the total time to acquire images. For applications such as relaxation time mapping, which enables improved visualisation of in vivo structures, rapid imaging techniques are highly desirable. TAPIR is a Look- Locker-based sequence for high-resolution, multislice T{sub 1} relaxation time mapping. Despite the high accuracy and precision of TAPIR, an improvement in the k-space sampling trajectory is desired to acquire data in clinically acceptable times. In this thesis, a new trajectory, termed line-sharing, is introduced for TAPIR that can potentially reduce the acquisition time by 40 %. Additionally, the line-sharing method was compared with the GRAPPA parallel imaging method. These methods were employed to reconstruct time-point images from the data acquired on a 4T high-field MR research scanner. Multislice, multipoint in vivo results obtained using these methods are presented. Despite improvement in acquisition speed, through line-sharing, for example, motion remains a problem and artefact-free data cannot always be obtained. Therefore, in this thesis, a rapid technique is introduced to estimate in-plane motion. The presented technique is based on calculating the in-plane motion parameters, i.e., translation and rotation, by registering the low-resolution MR images. The rotation estimation method is based on the pseudo-polar FFT, where the Fourier domain is composed of frequencies that reside in an oversampled set of non-angularly, equispaced points. The essence of the method is that unlike other Fourier-based registration schemes, the employed approach does not require any interpolation to calculate the pseudo-polar FFT grid coordinates. Translation parameters are estimated by the phase correlation method. However, instead of two-dimensional analysis of the phase correlation matrix, a low complexity subspace identification of the phase

  12. MECHANICAL RELAXATION TIME OF A TWO-COMPONENT EPOXY NETWORK-LiClO4 POLYMER ELECTROLYTE

    Institute of Scientific and Technical Information of China (English)

    PENG Xinsheng; WU Shuyun; CHEN Donglin

    1993-01-01

    The mechanical relaxation time of a two-component epoxy network-LiClO4 system as a polymer electrolyte was investigated.The network is composed of diglycidyl ether of polyethylene glycol (DGEPEG) and triglycidyl ether of glycerol (TGEG),wherein LiClO4 was incorporated and acts as both the ionic carrier and the curing catalyst.As the relaxation time is informative to the segmental mobility,which is known to be essential for ionic conductivity,the average relaxation times of the specimens were determined through master curve construction.Experimental results showed that the salt concentration,molecular weight of PEG in DGEPEG and DGEPEG/TGEG ratio have profound effect on the relaxation time of the specimen.Among these factors,the former reinforces the network hains,leading to lengthen the relaxation time,whereas the latter two are in favour of the chain flexibility and show an opposite effect.The findings was rationalized in terms of the free volume concept.

  13. Dielectric relaxation studies of binary mixture of β-picoline and methanol using time domain reflectometry at different temperatures

    Science.gov (United States)

    Trivedi, C. M.; Rana, V. A.; Hudge, P. G.; Kumbharkhane, A. C.

    2016-08-01

    Complex permittivity spectra of binary mixtures of varying concentrations of β-picoline and Methanol (MeOH) have been obtained using time domain reflectometry (TDR) technique over frequency range 10 MHz to 25 GHz at 283.15, 288.15, 293.15 and 298.15 K temperatures. The dielectric relaxation parameters namely static permittivity (ɛ0), high frequency limit permittivity (ɛ∞1) and the relaxation time (τ) were determined by fitting complex permittivity data to the single Debye/Cole-Davidson model. Complex nonlinear least square (CNLS) fitting procedure was carried out using LEVMW software. The excess permittivity (ɛ0E) and the excess inverse relaxation time (1/τ)E which contain information regarding molecular structure and interaction between polar-polar liquids were also determined. From the experimental data, parameters such as effective Kirkwood correlation factor (geff), Bruggeman factor (fB) and some thermo dynamical parameters have been calculated. Excess parameters were fitted to the Redlich-Kister polynomial equation. The values of static permittivity and relaxation time increase nonlinearly with increase in the mol-fraction of MeOH at all temperatures. The values of excess static permittivity (ɛ0E) and the excess inverse relaxation time (1/τ)E are negative for the studied β-picoline — MeOH system at all temperatures.

  14. Relaxation time: a proton NMR-based approach as a metric to measure reactivity of engineered nanomaterials

    Science.gov (United States)

    Paruthi, Archini; Misra, Superb K.

    2017-08-01

    The toxicological impact of engineered nanoparticles in environmental or biological milieu is very difficult to predict and control because of the complexity of interactions of nanoparticles with the varied constituents in the suspended media. Nanoparticles are different from their bulk counterparts due to their high surface area-to-volume ratio per unit mass, which plays a vital role in bioavailability of these nanoparticles to its surroundings. This study explores how changes in the spin-spin nuclear relaxation time can be used to gauge the availability of surface area and suspension stability of selected nanoparticles (CuO, ZnO, and SiO2), in a range of simulated media. Spin-spin nuclear relaxation time can be mathematically correlated to wetted surface area, which is well backed up by the data of hydrodynamic size measurements and suspension stability. We monitored the change in spin-spin relaxation time for all the nanoparticles, over a range of concentrations (2.5 -100 ppm) in deionized water and artificial seawater. Selective concentrations of nanoparticle suspensions were subjected for temporal studies over a period of 48 hrs to understand the concept of spin-spin nuclear relaxation time-based reactivity of nanoparticle suspension. The nanoparticles showed high degree of agglomeration, when suspended in artificial seawater. This was captured by a decrease in spin-spin nuclear relaxation time and also an increment in the hydrodynamic size of the nanoparticles.

  15. Quadriceps and hamstrings morphology is related to walking mechanics and knee cartilage MRI relaxation times in young adults.

    Science.gov (United States)

    Kumar, Deepak; Subburaj, Karupppasamy; Lin, Wilson; Karampinos, Dimitrios C; McCulloch, Charles E; Li, Xiaojuan; Link, Thomas M; Souza, Richard B; Majumdar, Sharmila

    2013-12-01

    Controlled laboratory study using a cross-sectional design. To analyze the relationship of quadriceps-hamstrings and medial-lateral quadriceps anatomical cross-sectional area (ACSA) ratios with knee loads during walking and articular and meniscal cartilage composition in young, healthy subjects. Muscle forces affect knee loading during walking, but it is not known if muscle morphology is associated with walking mechanics and cartilage composition in young subjects. Forty-two knees from 27 young, healthy, active volunteers (age, 20-35 years; body mass index, relaxation times and for quadriceps and hamstrings muscle ACSA. Frontal plane kinetics during the stance phase of walking was calculated. Generalized estimating equation models were used to identify muscle variables that predicted MRI and gait parameters. Quadriceps-hamstrings and medial-lateral quadriceps ACSA ratios were positively related to frontal plane loading (β = .21-.54, P≤.006), global articular cartilage relaxation times (β = .22-.28, P≤.041), and the medial-lateral ratio of meniscus T1rho relaxation time (β = .26-.36, P≤.049). The medial-lateral quadriceps ACSA ratio was positively related to global meniscus T1rho relaxation times (β = .30, P = .046). Higher quadriceps-hamstrings and medial-lateral quadriceps ACSA ratios were associated with higher frontal plane loading during walking and with articular and meniscal cartilage T1rho and T2 relaxation times. These findings highlight the relationships between different knee tissues and knee mechanics in young, healthy individuals.

  16. Joint modeling of longitudinal data and discrete-time survival outcome.

    Science.gov (United States)

    Qiu, Feiyou; Stein, Catherine M; Elston, Robert C

    2016-08-01

    A predictive joint shared parameter model is proposed for discrete time-to-event and longitudinal data. A discrete survival model with frailty and a generalized linear mixed model for the longitudinal data are joined to predict the probability of events. This joint model focuses on predicting discrete time-to-event outcome, taking advantage of repeated measurements. We show that the probability of an event in a time window can be more precisely predicted by incorporating the longitudinal measurements. The model was investigated by comparison with a two-step model and a discrete-time survival model. Results from both a study on the occurrence of tuberculosis and simulated data show that the joint model is superior to the other models in discrimination ability, especially as the latent variables related to both survival times and the longitudinal measurements depart from 0.

  17. Understanding generalized inversions of nuclear magnetic resonance transverse relaxation time in porous media

    Science.gov (United States)

    Mitchell, J.; Chandrasekera, T. C.

    2014-12-01

    The nuclear magnetic resonance transverse relaxation time T2, measured using the Carr-Purcell-Meiboom-Gill (CPMG) experiment, is a powerful method for obtaining unique information on liquids confined in porous media. Furthermore, T2 provides structural information on the porous material itself and has many applications in petrophysics, biophysics, and chemical engineering. Robust interpretation of T2 distributions demands appropriate processing of the measured data since T2 is influenced by diffusion through magnetic field inhomogeneities occurring at the pore scale, caused by the liquid/solid susceptibility contrast. Previously, we introduced a generic model for the diffusion exponent of the form -ant_e^k (where n is the number and te the temporal separation of spin echoes, and a is a composite diffusion parameter) in order to distinguish the influence of relaxation and diffusion in CPMG data. Here, we improve the analysis by introducing an automatic search for the optimum power k that best describes the diffusion behavior. This automated method is more efficient than the manual trial-and-error grid search adopted previously, and avoids variability through subjective judgments of experimentalists. Although our method does not avoid the inherent assumption that the diffusion exponent depends on a single k value, we show through simulation and experiment that it is robust in measurements of heterogeneous systems that violate this assumption. In this way, we obtain quantitative T2 distributions from complicated porous structures and demonstrate the analysis with examples of ceramics used for filtration and catalysis, and limestone of relevance to the construction and petroleum industries.

  18. Understanding generalized inversions of nuclear magnetic resonance transverse relaxation time in porous media

    Energy Technology Data Exchange (ETDEWEB)

    Mitchell, J., E-mail: JMitchell16@slb.com [Schlumberger Gould Research, High Cross, Madingley Road, Cambridge CB3 0EL (United Kingdom); Chandrasekera, T. C. [Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2 3RA (United Kingdom)

    2014-12-14

    The nuclear magnetic resonance transverse relaxation time T{sub 2}, measured using the Carr-Purcell-Meiboom-Gill (CPMG) experiment, is a powerful method for obtaining unique information on liquids confined in porous media. Furthermore, T{sub 2} provides structural information on the porous material itself and has many applications in petrophysics, biophysics, and chemical engineering. Robust interpretation of T{sub 2} distributions demands appropriate processing of the measured data since T{sub 2} is influenced by diffusion through magnetic field inhomogeneities occurring at the pore scale, caused by the liquid/solid susceptibility contrast. Previously, we introduced a generic model for the diffusion exponent of the form −ant{sub e}{sup k} (where n is the number and t{sub e} the temporal separation of spin echoes, and a is a composite diffusion parameter) in order to distinguish the influence of relaxation and diffusion in CPMG data. Here, we improve the analysis by introducing an automatic search for the optimum power k that best describes the diffusion behavior. This automated method is more efficient than the manual trial-and-error grid search adopted previously, and avoids variability through subjective judgments of experimentalists. Although our method does not avoid the inherent assumption that the diffusion exponent depends on a single k value, we show through simulation and experiment that it is robust in measurements of heterogeneous systems that violate this assumption. In this way, we obtain quantitative T{sub 2} distributions from complicated porous structures and demonstrate the analysis with examples of ceramics used for filtration and catalysis, and limestone of relevance to the construction and petroleum industries.

  19. Electron--electron double resonance study of magnetic energy transfer between trapped electrons and radicals in organic glasses: Relation between dipolar cross relaxation times and dipolar interaction distances

    Energy Technology Data Exchange (ETDEWEB)

    Lin, D.P.; Feng, D.F.; Ngo, F.Q.H.; Kevan, L.

    1976-11-15

    Electron--electron double resonance (ELDOR) has been used to measure cross-relaxation times between trapped electrons and trapped radicals produced by ..gamma.. irradiation of 2-methyltetrahydrofuran and 3-methylhexane organic glasses. The cross-relaxation times are measured as a function of temperature, radiation dose, and the frequency difference ..delta..f of the microwave frequencies used. The cross-relaxation times are nearly temperature independent and depend on ..delta..f/sup 2/ at doses where the spin concentrations approach uniformity; these features indicate the dominance of single step over multistep cross-relaxation processes. Equations have been derived to relate the dipolar cross-relaxation distance to the measured cross-relaxation times, and it is suggested that the cross-relaxation line shape is Lorentzian in magnetically dilute systems. Typical electron--radical correlation distances in these organic glasses are 10 A. (AIP)

  20. Solid State NMR Study of Polystyrene Nanolatex Particles(I) 13C Spin-Lattice Relaxation Time

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    13C spin-lattice relaxtion times for polystyrene nanolatex particles have been investigated. It was found that the dramatic increase at 80℃ annealing temperature is well below the Tg temperature of bulk polystyrene, the increase of relaxation time of aromatic carbons is larger than that of for aliphatic carbons at transition annealing temperature.

  1. Spin time-relaxation within strongly coupled paramagnetic systems exhibiting paramagnetic-ferrimagnetic transitions

    CERN Document Server

    Chahid, M

    2000-01-01

    The purpose of the present work is a quantitative study of the spin time relaxation within superweak ferrimagnetic materials exhibiting a paramagnetic-ferrimagnetic transition, when the temperature is changed from an initial value T sub i to a final one T sub f very close to the critical temperature T sub c. From a magnetic point of view, the material under investigation is considered to be made of two strongly coupled paramagnetic sublattices of respective moments phi (cursive,open) Greek and psi. Calculations are made within a Landau mean-field theory, whose free energy involves, in addition to quadratic and quartic terms in both moments phi (cursive,open) Greek and psi, a lowest-order coupling - Cphi (cursive,open) Greek psi, where C<0 stands for the coupling constant measuring the interaction between the two sublattices. We first determine the time dependence of the shifts of the order parameters delta phi (cursive,open) Greek and delta psi from the equilibrium state. We find that this time dependence ...

  2. Highly biocompatible TiO₂:Gd³⁺ nano-contrast agent with enhanced longitudinal relaxivity for targeted cancer imaging.

    Science.gov (United States)

    Chandran, Parwathy; Sasidharan, Abhilash; Ashokan, Anusha; Menon, Deepthy; Nair, Shantikumar; Koyakutty, Manzoor

    2011-10-05

    We report the development of a novel magnetic nano-contrast agent (nano-CA) based on Gd(3+) doped amorphous TiO(2) of size ∼25 nm, exhibiting enhanced longitudinal relaxivity (r(1)) and magnetic resonance (MR) contrasting together with excellent biocompatibility. Quantitative T1 mapping of phantom samples using a 1.5 T clinical MR imaging system revealed that the amorphous phase of doped titania has the highest r(1) relaxivity which is ∼2.5 fold higher than the commercially used CA Magnevist™. The crystalline (anatase) samples formed by air annealing at 250 °C and 500 °C showed significant reduction in r(1) values and MR contrast, which is attributed to the loss of proton-exchange contribution from the adsorbed water and atomic re-arrangement of Gd(3+) ions in the crystalline host lattice. Nanotoxicity studies including cell viability, plasma membrane integrity, reactive oxygen stress and expression of pro-inflammatory cytokines, performed on human primary endothelial cells (HUVEC), human blood derived peripheral blood mononuclear cells (PBMC) and nasopharyngeal epidermoid carcinoma (KB) cell line showed excellent biocompatibility up to relatively higher doses of 200 μg ml(-1). The potential of this nano-CA to cause hemolysis, platelet aggregation and plasma coagulation were studied using human peripheral blood samples and found no adverse effects, illustrating the possibility of the safe intravenous administration of these agents for human applications. Furthermore, the ability of these agents to specifically detect cancer cells by targeting molecular receptors on the cell membrane was demonstrated on folate receptor (FR) positive oral carcinoma (KB) cells, where the folic acid conjugated nano-CA showed receptor specific accumulation on cell membrane while leaving the normal fibroblast cells (L929) unstained. This study reveals that the Gd(3+) doped amorphous TiO(2) nanoparticles having enhanced magnetic resonance contrast and high biocompatibility is a

  3. Real-Time Observation of Ultrafast Intraband Relaxation and Exciton Multiplication in PbS Quantum Dots

    KAUST Repository

    El-Ballouli, Ala’a O.

    2014-03-19

    We examine ultrafast intraconduction band relaxation and multiple-exciton generation (MEG) in PbS quantum dots (QDs) using transient absorption spectroscopy with 120 fs temporal resolution. The intraconduction band relaxation can be directly and excellently resolved spectrally and temporally by applying broadband pump-probe spectroscopy to excite and detect the wavelengths around the exciton absorption peak, which is located in the near-infrared region. The time-resolved data unambiguously demonstrate that the intraband relaxation time progressively increases as the pump-photon energy increases. Moreover, the relaxation time becomes much shorter as the size of the QDs decreases, indicating the crucial role of spatial confinement in the intraband relaxation process. Additionally, our results reveal the systematic scaling of the intraband relaxation time with both excess energy above the effective energy band gap and QD size. We also assess MEG in different sizes of the QDs. Under the condition of high-energy photon excitation, which is well above the MEG energy threshold, ultrafast bleach recovery due to the nonradiative Auger recombination of the multiple electron-hole pairs provides conclusive experimental evidence for the presence of MEG. For instance, we achieved quantum efficiencies of 159, 129 and 106% per single-absorbed photon at pump photoexcition of three times the band gap for QDs with band gaps of 880 nm (1.41 eV), 1000 nm (1.24 eV) and 1210 nm (1.0 eV), respectively. These findings demonstrate clearly that the efficiency of transferring excess photon energy to carrier multiplication is significantly increased in smaller QDs compared with larger ones. Finally, we discuss the Auger recombination dynamics of the multiple electron-hole pairs as a function of QD size.

  4. Lineshape theory of pigment-protein complexes: How the finite relaxation time of nuclei influences the exciton relaxation-induced lifetime broadening.

    Science.gov (United States)

    Dinh, Thanh-Chung; Renger, Thomas

    2016-07-21

    In pigment-protein complexes, often the excited states are partially delocalized and the exciton-vibrational coupling in the basis of delocalized states contains large diagonal and small off-diagonal elements. This inequality may be used to introduce potential energy surfaces (PESs) of exciton states and to treat the inter-PES coupling in Markov and secular approximations. The resulting lineshape function consists of a Lorentzian peak that is broadened by the finite lifetime of the exciton states caused by the inter-PES coupling and a vibrational sideband that results from the mutual displacement of the excitonic PESs with respect to that of the ground state. So far analytical expressions have been derived that relate the exciton relaxation-induced lifetime broadening to the Redfield [T. Renger and R. A. Marcus, J. Chem. Phys. 116, 9997 (2002)] or modified Redfield [M. Schröder, U. Kleinekathöfer, and M. Schreiber, J. Chem. Phys. 124, 084903 (2006)] rate constants of exciton relaxation, assuming that intra-PES nuclear relaxation is fast compared to inter-PES transfer. Here, we go beyond this approximation and provide an analytical expression, termed Non-equilibrium Modified Redfield (NeMoR) theory, for the lifetime broadening that takes into account the finite nuclear relaxation time. In an application of the theory to molecular dimers, we find that, for a widely used experimental spectral density of the exciton-vibrational coupling of pigment-protein complexes, the NeMoR spectrum at low-temperatures (T theory. At room temperature, the lifetime broadening obtained with Redfield theory underestimates the NeMoR broadening, whereas modified Redfield theory overestimates it by a similar amount. A fortuitous error compensation in Redfield theory is found to explain the good performance of this theory at low temperatures. Since steady state spectra of PPCs are often measured at low temperatures, Redfield theory still provides a numerically efficient alternative to Ne

  5. Wide-ranging molecular mobilities of water in active pharmaceutical ingredient (API) hydrates as determined by NMR relaxation times.

    Science.gov (United States)

    Yoshioka, Sumie; Aso, Yukio; Osako, Tsutomu; Kawanishi, Toru

    2008-10-01

    In order to examine the possibility of determining the molecular mobility of hydration water in active pharmaceutical ingredient (API) hydrates by NMR relaxation measurement, spin-spin relaxation and spin-lattice relaxation were measured for the 11 API hydrates listed in the Japanese Pharmacopeia using pulsed (1)H-NMR. For hydration water that has relatively high mobility and shows Lorentzian decay, molecular mobility as determined by spin-spin relaxation time (T(2)) was correlated with ease of evaporation under both nonisothermal and isothermal conditions, as determined by DSC and water vapor sorption isotherm analysis, respectively. Thus, T(2) may be considered a useful parameter which indicates the molecular mobility of hydration water. In contrast, for hydration water that has low mobility and shows Gaussian decay, T(2) was found not to correlate with ease of evaporation under nonisothermal conditions, which suggests that in this case, the molecular mobility of hydration water was too low to be determined by T(2). A wide range of water mobilities was found among API hydrates, from low mobility that could not be evaluated by NMR relaxation time, such as that of the water molecules in pipemidic acid hydrate, to high mobility that could be evaluated by this method, such as that of the water molecules in ceftazidime hydrate. (c) 2008 Wiley-Liss, Inc. and the American Pharmacists Association

  6. Multiple-relaxation-time lattice Boltzmann simulation for flow, mass transfer, and adsorption in porous media

    Science.gov (United States)

    Ma, Qiang; Chen, Zhenqian; Liu, Hao

    2017-07-01

    In this paper, to predict the dynamics behaviors of flow and mass transfer with adsorption phenomena in porous media at the representative elementary volume (REV) scale, a multiple-relaxation-time (MRT) lattice Boltzmann (LB) model for the convection-diffusion equation is developed to solve the transfer problem with an unsteady source term in porous media. Utilizing the Chapman-Enskog analysis, the modified MRT-LB model can recover the macroscopic governing equations at the REV scale. The coupled MRT-LB model for momentum and mass transfer is validated by comparing with the finite-difference method and the analytical solution. Moreover, using the MRT-LB method coupled with the linear driving force model, the fluid transfer and adsorption behaviors of the carbon dioxide in a porous fixed bed are explored. The breakthrough curve of adsorption from MRT-LB simulation is compared with the experimental data and the finite-element solution, and the transient concentration distributions of the carbon dioxide along the porous fixed bed are elaborated upon in detail. In addition, the MRT-LB simulation results show that the appearance time of the breakthrough point in the breakthrough curve is advanced as the mass transfer resistance in the linear driving force model increases; however, the saturation point is prolonged inversely.

  7. Optimal timing for initiation of biofeedback-assisted relaxation training in hospitalized coronary heart disease patients with sleep disturbances.

    Science.gov (United States)

    Wang, Li-Na; Tao, Hong; Zhao, Yue; Zhou, Yu-Qiu; Jiang, Xiu-Rong

    2014-07-01

    Clinical studies have shown that biofeedback-assisted relaxation positively influences the treatment outcomes of sleep disturbance. However, there are only few studies reporting the timing of relaxation training initiation, and the relationships between the timing of initiation and the effectiveness of relaxation remain unclear. The aim of this study was to determine the optimal timing for initiating nurse-led biofeedback-assisted relaxation on hospitalized coronary heart disease patients with sleep disturbance. An experimental pretest and repeated posttest design was used to compare the effectiveness of nurse-led biofeedback-assisted relaxation. A total of 128 patients with coronary heart disease were randomly assigned to 1 of 4 groups: morning group, night group, morning-night group, or control group. Outcome measures included self-report of sleep-related indicators, the scores of the Pittsburgh Sleep Quality Index (PSQI) and the Zung's Self-rating Anxiety Scale (SAS), and the dosage of sleep medication used. A 2-way analysis of variance and a simple effect test were used to analyze the differences among the 4 groups. No significant differences could be detected at baseline. Compared with the control group, the nurse-led biofeedback-assisted relaxation yielded a greater benefit for patients in the 3 intervention groups. Group and time factors (pretest-protest) could explain the variation in the effectiveness of this program (main effect P sleep latency, experienced fewer awakenings, reported higher sleep quality, and used significantly fewer sleep medications than the morning group did (F = 32.97, P sleep quality and decrease the need for of sleep medications in hospitalized patients with sleep disturbance.

  8. Neural Networks-Based Real-Time Determination of the Laser Beam Spatial Profile and Vibrational-to-Translational Relaxation Time Within Pulsed Photoacoustics

    Science.gov (United States)

    Lukić, M.; Ćojbašić, Ž.; Rabasović, M. D.; Markushev, D. D.; Todorović, D. M.

    2013-09-01

    This paper concerns with the possibilities of computational intelligence application for simultaneous determination of the laser beam spatial profile and vibrational-to-translational relaxation time of the polyatomic molecules in gases by pulsed photoacoustics. Results regarding the application of neural computing through the use of feed-forward multilayer perception networks are presented. Feed-forward multilayer perception networks are trained in an offline batch training regime to estimate simultaneously, and in real-time, the laser beam spatial profile (profile shape class) and the vibrational-to-translational relaxation time from given (theoretical) photoacoustic signals. The proposed method significantly shortens the time required for the simultaneous determination of the laser beam spatial profile and relaxation time and has the advantage of accurately calculating the aforementioned quantities.

  9. Revisiting spin-lattice relaxation time measurements for dilute spins in high-resolution solid-state NMR spectroscopy

    Science.gov (United States)

    Fu, Riqiang; Li, Jun; Cui, Jingyu; Peng, Xinhua

    2016-07-01

    Numerous nuclear magnetic resonance (NMR) measurements of spin-lattice relaxation times (T1S) for dilute spins such as 13C have led to investigations of the motional dynamics of individual functional groups in solid materials. In this work, we revisit the Solomon equations and analyze how the heteronuclear cross relaxation between the dilute S (e.g. 13C) and abundant I (e.g. 1H) spins affects the measured T1S values in solid-state NMR in the absence of 1H saturation during the recovery time. It is found theoretically that at the beginning of the S spin magnetization recovery, the existence of non-equilibrium I magnetization introduces the heteronuclear cross relaxation effect onto the recovery of the S spin magnetization and confirmed experimentally that such a heteronuclear cross relaxation effect results in the recovery overshoot phenomena for the dilute spins when T1S is on the same order of T1H, leading to inaccurate measurements of the T1S values. Even when T1S is ten times larger than T1H, the heteronuclear cross relaxation effect on the measured T1S values is still noticeable. Furthermore, this cross relaxation effect on recovery trajectory of the S spins can be manipulated and even suppressed by preparing the initial I and S magnetization, so as to obtain the accurate T1S values. A sample of natural abundance L-isoleucine powder has been used to demonstrate the T1S measurements and their corresponding measured T1C values under various experimental conditions.

  10. TIME-COURSE OF ACTION AND ENDOTRACHEAL INTUBATING CONDITIONS OF ORG-9487, A NEW SHORT-ACTING STEROIDAL MUSCLE-RELAXANT - A COMPARISON WITH SUCCINYLCHOLINE

    NARCIS (Netherlands)

    WIERDA, JMKH; VANDENBROEK, L; PROOST, JH; VERBAAN, BW; HENNIS, PJ

    1993-01-01

    In a randomized study, we evaluated lag time (time from the end of injection of muscle relaxant until the first depression of the train-of-four response [TOF]), onset time (time from the end of injection of muscle relaxant until the maximum depression of the first twitch of the TOF [T1]), neuromuscu

  11. Existence of the transverse relaxation time in optically excited bulk semiconductors

    Institute of Scientific and Technical Information of China (English)

    Zhang Hai-Chao; Lin Wei-Zhu; Wang Yu-Zhu

    2006-01-01

    Two basic types of depolarization mechanisms,carrier-carrier (CC) and carrier-phonon (CP) scattering,are investigated in optically excited bulk semiconductors (3D),in which the existence of the transverse relaxation time is proven based on the vector property of the interband transition matrix elements.The dephasing rates for both CC and CP scattering are determined to be equal to one half of the total scattering-rate-integrals weighted by the factors (1-COSx),wherex are the scattering angles.Analytical expressions of the polarization dephasing due to CC scattering are established by using an uncertainty broadening approach,and analytical ones due to both the polar optical-phonon and non-polar deformation potential scattering (including inter-valley scattering) are also presented by using the sharp spectral functions in the dephasing rate calculations.These formulas,which reveal the trivial role of the Coulomb screening effect in the depolarization processes,are used to explain the experimental results at hand and provide a clear physical picture that is difficult to extract from numerical treatments.

  12. Structural relaxation time and cooling rate of a melt in the glass transition region

    Science.gov (United States)

    Sanditov, D. S.; Sydykov, B. S.

    2015-03-01

    The nature of the parameter involved in the Bartenev equation qτg = C relating the cooling rate of a glass-forming melt to its structural relaxation time in the glass transition region is discussed on the basis of the Volkenshtein-Ptitsyn theory using a number of known relationships. It is established that parameter C for amorphous substances with the same fragility is linearly temperature dependent. This parameter is shown to equal the narrow temperature range δ T g characterizing the liquid-glass transition region (by Nemilov); i.e., C = δ T g. It is concluded that δ T g for most glassy systems is only ˜0.7% of the glass transition temperature T g. The narrowness of temperature range δ T g is explained by the small fluctuation volume fraction f g "frozen" at the glass transition temperature. The concept of a close relationship between constant C and the structural order at T g (i.e., the characteristic of the inner state of a nonequilibrium "frozen" amorphous system) is developed.

  13. Diffusion relaxation times of nonequilibrium isolated small bodies and their solid phase ensembles to equilibrium states

    Science.gov (United States)

    Tovbin, Yu. K.

    2017-08-01

    The possibility of obtaining analytical estimates in a diffusion approximation of the times needed by nonequilibrium small bodies to relax to their equilibrium states based on knowledge of the mass transfer coefficient is considered. This coefficient is expressed as the product of the self-diffusion coefficient and the thermodynamic factor. A set of equations for the diffusion transport of mixture components is formulated, characteristic scales of the size of microheterogeneous phases are identified, and effective mass transfer coefficients are constructed for them. Allowing for the developed interface of coexisting and immiscible phases along with the porosity of solid phases is discussed. This approach can be applied to the diffusion equalization of concentrations of solid mixture components in many physicochemical systems: the mutual diffusion of components in multicomponent systems (alloys, semiconductors, solid mixtures of inert gases) and the mass transfer of an absorbed mobile component in the voids of a matrix consisting of slow components or a mixed composition of mobile and slow components (e.g., hydrogen in metals, oxygen in oxides, and the transfer of molecules through membranes of different natures, including polymeric).

  14. Relaxing the closure assumption in single-season occupancy models: staggered arrival and departure times

    Science.gov (United States)

    Kendall, William L.; Hines, James E.; Nichols, James D.; Grant, Evan H. Campbell

    2013-01-01

    Occupancy statistical models that account for imperfect detection have proved very useful in several areas of ecology, including species distribution and spatial dynamics, disease ecology, and ecological responses to climate change. These models are based on the collection of multiple samples at each of a number of sites within a given season, during which it is assumed the species is either absent or present and available for detection while each sample is taken. However, for some species, individuals are only present or available for detection seasonally. We present a statistical model that relaxes the closure assumption within a season by permitting staggered entry and exit times for the species of interest at each site. Based on simulation, our open model eliminates bias in occupancy estimators and in some cases increases precision. The power to detect the violation of closure is high if detection probability is reasonably high. In addition to providing more robust estimation of occupancy, this model permits comparison of phenology across sites, species, or years, by modeling variation in arrival or departure probabilities. In a comparison of four species of amphibians in Maryland we found that two toad species arrived at breeding sites later in the season than a salamander and frog species, and departed from sites earlier.

  15. Energy-dependent relaxation time in quaternary amorphous oxide semiconductors probed by gated Hall effect measurements

    Science.gov (United States)

    Socratous, Josephine; Watanabe, Shun; Banger, Kulbinder K.; Warwick, Christopher N.; Branquinho, Rita; Barquinha, Pedro; Martins, Rodrigo; Fortunato, Elvira; Sirringhaus, Henning

    2017-01-01

    Despite the success of exploiting the properties of amorphous oxide semiconductors for device applications, the charge transport in these materials is still not clearly understood. The observation of a definite Hall voltage suggests that electron transport in the conduction band is free-electron-like. However, the temperature dependence of the Hall and field-effect mobilities cannot be explained using a simple bandlike model. Here, we perform gated Hall effect measurements in field-effect transistors, which allow us to make two independent estimates of the charge carrier concentration and determine the Hall factor providing information on the energy dependence of the relaxation time. We demonstrate that the Hall factor in a range of sputtered and solution-processed quaternary amorphous oxides, such as a-InGaZnO, is close to two, while in ternary oxides, such as InZnO, it is near unity. This suggests that quaternary elements like Ga act as strong ionized impurity scattering centers in these materials.

  16. Intraindividual comparison of T1 relaxation times after gadobutrol and Gd-DTPA administration for cardiac late enhancement imaging

    Energy Technology Data Exchange (ETDEWEB)

    Doeblin, Patrick, E-mail: Patrick.doeblin@charite.de [Department of Cardiology, Charité – Universitätsmedizin Berlin, Charité Campus Benjamin Franklin, Berlin (Germany); Schilling, Rene, E-mail: rene.schilling@charite.de [Department of Radiology, Charité – Universitätsmedizin Berlin, Charité Campus Mitte, Berlin (Germany); Wagner, Moritz, E-mail: moritz.wagner@charite.de [Department of Radiology, Charité – Universitätsmedizin Berlin, Charité Campus Mitte, Berlin (Germany); Luhur, Reny, E-mail: renyluhur@yahoo.com [Department of Radiology, Charité – Universitätsmedizin Berlin, Charité Campus Mitte, Berlin (Germany); Huppertz, Alexander, E-mail: alexander.huppertz@charite.de [Department of Radiology, Charité – Universitätsmedizin Berlin, Charité Campus Mitte, Berlin (Germany); Imaging Science Institute, Charité, Berlin (Germany); Hamm, Bernd, E-mail: bernd.hamm@charite.de [Department of Radiology, Charité – Universitätsmedizin Berlin, Charité Campus Mitte, Berlin (Germany); Taupitz, Matthias, E-mail: matthias.taupitz@harite.de [Department of Radiology, Charité – Universitätsmedizin Berlin, Charité Campus Mitte, Berlin (Germany); and others

    2014-04-15

    Purpose: To evaluate T1-relaxation times of chronic myocardial infarction (CMI) using gadobutrol and gadopentetate dimeglumine (Gd-DTPA) over time and to determine the optimal imaging window for late enhancement imaging with both contrast agents. Material and methods: Twelve patients with CMI were prospectively included and examined on a 1.5 T magnetic resonance (MR) system using relaxivity-adjusted doses of gadobutrol (0.15 mmol/kg) and Gd-DTPA (0.2 mmol/kg) in random order. T1-relaxation times of remote myocardium (RM), infarcted myocardium (IM), and left ventricular cavity (LVC) were assessed from short-axis TI scout imaging using the Look–Locker approach and compared intraindividually using a Wilcoxon paired signed-rank test (α < 0.05). Results: Within 3 min of contrast agent administration (CA), IM showed significantly lower T1-relaxation times than RM with both contrast agents, indicating beginning cardiac late enhancement. Differences between gadobutrol and Gd-DTPA in T1-relaxation times of IM and RM were statistically not significant through all time points. However, gadobutrol led to significantly higher T1-relaxation times of LVC than Gd-DTPA from 6 to 9 min (220 ± 15 ms vs. 195 ± 30 ms p < 0.01) onwards, resulting in a significantly greater ΔT1 of IM to LVC at 9–12 min (−20 ± 35 ms vs. 0 ± 35 ms, p < 0.05) and 12–15 min (−25 ± 45 ms vs. −10 ± 60 ms, p < 0.05). Using Gd-DTPA, comparable ΔT1 values were reached only after 25–35 min. Conclusion: This study indicates good delineation of IM to RM with both contrast agents as early as 3 min after administration. However, we found significant differences in T1 relaxation times with greater ΔT1 IM–LVC using 0.15 mmol/kg gadobutrol compared to 0.20 mmol/kg Gd-DTPA after 9–15 min post-CA suggesting earlier differentiability of IM and LVC using gadobutrol.

  17. Long Spin Relaxation and Coherence Times of Electrons In Gated Si/SiGe Quantum Dots

    Science.gov (United States)

    He, Jianhua; Tyryshkin, A. M.; Lyon, S. A.; Lee, C.-H.; Huang, S.-H.; Liu, C. W.

    2012-02-01

    Single electron spin states in semiconductor quantum dots are promising candidate qubits. We report the measurement of 250 μs relaxation (T1) and coherence (T2) times of electron spins in gated Si/SiGe quantum dots at 350 mK. The experiments used conventional X-band (10 GHz) pulsed electron spin resonance (pESR), on a large area (3.5 x 20 mm^2) dual-gate undoped high mobility Si/SiGe heterostructure sample, which was patterned with 2 x 10^8 quantum dots using e-beam lithography. Dots having 150 nm radii with a 700 nm period are induced in a natural Si quantum well by the gates. The measured T1 and T2 at 350 mK are much longer than those of free 2D electrons, for which we measured T1 to be 10 μs and T2 to be 6.5 μs in this gated sample. The results provide direct proof that the effects of a fluctuating Rashba field have been greatly suppressed by confining the electrons in quantum dots. From 0.35 K to 0.8 K, T1 of the electron spins in the quantum dots shows little temperature dependence, while their T2 decreased to about 150 μs at 0.8 K. The measured 350 mK spin coherence time is 10 times longer than previously reported for any silicon 2D electron-based structures, including electron spins confined in ``natural quantum dots'' formed by potential disorder at the Si/SiO2ootnotetextS. Shankar et al., Phys. Rev. B 82, 195323 (2010) or Si/SiGe interface, where the decoherence appears to be controlled by spin exchange.

  18. Comparison of different pulse sequences for in vivo determination of T1 relaxation times in the human brain

    DEFF Research Database (Denmark)

    Kjaer, L; Henriksen, O

    1988-01-01

    (PSIR) sequence with TR varying between 0.24 and 8.0 s. The median T1 relaxation times obtained in cortical grey matter and cerebrospinal fluid were significantly shorter in the IR experiments at TR = 2 s than in those carried out at TR = 4 s. Concerning white matter the discrepancy was much less...

  19. Effects of age and timing of augmented feedback on learning muscle relaxation while performing a gross motor task

    NARCIS (Netherlands)

    van Dijk, H; Hermens, Hermanus J.

    Objective: To examine the combined effect of age and timing of augmented feedback on learning muscle relaxation. Performing a gross motor task, subjects had to lower their trapezius muscle activity using the electromyographic signal as visual myofeedback. Design: Healthy subjects (16 young adults:

  20. Sensitivity of the simulated precipitation to changes in convective relaxation time scale

    Directory of Open Access Journals (Sweden)

    S. K. Mishra

    2010-10-01

    Full Text Available The paper describes the sensitivity of the simulated precipitation to changes in convective relaxation time scale (TAU of Zhang and McFarlane (ZM cumulus parameterization, in NCAR-Community Atmosphere Model version 3 (CAM3. In the default configuration of the model, the prescribed value of TAU, a characteristic time scale with which convective available potential energy (CAPE is removed at an exponential rate by convection, is assumed to be 1 h. However, some recent observational findings suggest that, it is larger by around one order of magnitude. In order to explore the sensitivity of the model simulation to TAU, two model frameworks have been used, namely, aqua-planet and actual-planet configurations. Numerical integrations have been carried out by using different values of TAU, and its effect on simulated precipitation has been analyzed.

    The aqua-planet simulations reveal that when TAU increases, rate of deep convective precipitation (DCP decreases and this leads to an accumulation of convective instability in the atmosphere. Consequently, the moisture content in the lower- and mid- troposphere increases. On the other hand, the shallow convective precipitation (SCP and large-scale precipitation (LSP intensify, predominantly the SCP, and thus capping the accumulation of convective instability in the atmosphere. The total precipitation (TP remains approximately constant, but the proportion of the three components changes significantly, which in turn alters the vertical distribution of total precipitation production. The vertical structure of moist heating changes from a vertically extended profile to a bottom heavy profile, with the increase of TAU. Altitude of the maximum vertical velocity shifts from upper troposphere to lower troposphere. Similar response was seen in the actual-planet simulations. With an increase in TAU from 1 h to 8 h, there was a significant improvement in the simulation of the seasonal mean precipitation. The

  1. Feedback control strategy of longitudinal temperature and finished carbonization time for coke oven and its application

    Institute of Scientific and Technical Information of China (English)

    Fang Huo; Zhi Wen; Dong Chen; Yueling Shen; Yongqin Zhang; Xiaoming Zhi

    2004-01-01

    Based on the detailed analysis of the third coke oven in BaoSteel, a feedback control strategy of longitudinal temperature and finished carbonization time of coke ovens was proposed and it was applied to the third coke oven in BaoSteel. As a result, the ratio of the instance that the absolute deviation of the longitudinal temperature is within ±7°C and the finished carbonization time within ± 10 rain is more than 80%, having acquired the patent saving effect of an energy consumption lowered by 2.92%. At the same time, it can provide an example for the same coke ovens inside and outside the nation.

  2. Measurement of the relaxation time of hot electrons in laser-solid interaction at relativistic laser intensities

    Energy Technology Data Exchange (ETDEWEB)

    Chen, H; Shepherd, R; Chung, H K; Dyer, G; Faenov, A; Fournier, K B; Hansen, S B; Hunter, J; Kemp, A; Pikuz, T; Ping, Y; Widmann, K; Wilks, S C; Beiersdorfer, P

    2006-08-22

    The authors have measured the relaxation time of hot electrons in short pulse laser-solid interactions using a picosecond time-resolved x-ray spectrometer and a time-integrated electron spectrometer. Employing laser intensities of 10{sup 17}, 10{sup 18}, and 10{sup 19} W/cm{sup 2}, they find increased laser coupling to hot electrons as the laser intensity becomes relativistic and thermalization of hot electrons at timescales on the order of 10 ps at all laser intensities. They propose a simple model based on collisional coupling and plasma expansion to describe the rapid relaxation of hot electrons. The agreement between the resulting K{sub {alpha}} time-history from this model with the experiments is best at highest laser intensity and less satisfactory at the two lower laser intensities.

  3. Relaxation times and modes of disturbed aggregate distribution in micellar solutions with fusion and fission of micelles

    Energy Technology Data Exchange (ETDEWEB)

    Zakharov, Anatoly I.; Adzhemyan, Loran Ts.; Shchekin, Alexander K., E-mail: akshch@list.ru [Department of Statistical Physics, Faculty of Physics, St. Petersburg State University, Ulyanovskaya 1, Petrodvoretz, St. Petersburg 198504 (Russian Federation)

    2015-09-28

    We have performed direct numerical calculations of the kinetics of relaxation in the system of surfactant spherical micelles under joint action of the molecular mechanism with capture and emission of individual surfactant molecules by molecular aggregates and the mechanism of fusion and fission of the aggregates. As a basis, we have taken the difference equations of aggregation and fragmentation in the form of the generalized kinetic Smoluchowski equations for aggregate concentrations. The calculations have been made with using the droplet model of molecular surfactant aggregates and two modified Smoluchowski models for the coefficients of aggregate-monomer and aggregate-aggregate fusions which take into account the effects of the aggregate size and presence of hydrophobic spots on the aggregate surface. A full set of relaxation times and corresponding relaxation modes for nonequilibrium aggregate distribution in the aggregation number has been found. The dependencies of these relaxation times and modes on the total concentration of surfactant in the solution and the special parameter controlling the probability of fusion in collisions of micelles with other micelles have been studied.

  4. Changes in transverse relaxation time of quadriceps femoris muscles after active recovery exercises with different intensities.

    Science.gov (United States)

    Mukaimoto, Takahiro; Semba, Syun; Inoue, Yosuke; Ohno, Makoto

    2014-01-01

    The purpose of this study was to examine the changes in the metabolic state of quadriceps femoris muscles using transverse relaxation time (T2), measured by muscle functional magnetic resonance (MR) imaging, after inactive or active recovery exercises with different intensities following high-intensity knee-extension exercise. Eight healthy men performed recovery sessions with four different conditions for 20 min after high-intensity knee-extension exercise on separate days. During the recovery session, the participants conducted a light cycle exercise for 20 min using a cycle (50%, 70% and 100% of the lactate threshold (LT), respectively: active recovery), and inactive recovery. The MR images of quadriceps femoris muscles were taken before the trial and after the recovery session every 30 min for 120 min. The percentage changes in T2 for the rectus femoris and vastus medialis muscles after the recovery session in 50% LT and 70% LT were significantly lower than those in either inactive recovery or 100% LT. There were no significant differences in those for vastus lateralis and vastus intermedius muscles among the four trials. The percentage changes in T2 of rectus femoris and vastus medialis muscles after the recovery session in 50% LT and 70% LT decreased to the values before the trial faster than those in either inactive recovery or 100% LT. Those of vastus lateralis and vastus intermedius muscles after the recovery session in 50% LT and 70% LT decreased to the values before the trial faster than those in 100% LT. Although the changes in T2 after active recovery exercises were not uniform in exercised muscles, the results of this study suggest that active recovery exercise with the intensities below LT are more effective to recover the metabolic state of quadriceps femoris muscles after intense exercise than with either intensity at LT or inactive recovery.

  5. The use of time-resolved X-ray diffraction and sample techniques for studying the muscle structure during relaxation

    Science.gov (United States)

    Vazina, A. A.; Gadzhiev, A. M.; Gerasimov, V. S.; Gorbunova, N. P.; Sergienko, P. M.; Korneev, V. N.; Aulchenko, V. M.; Baru, S. E.

    1995-02-01

    The use of the modern time-resolved X-ray diffraction and sample technique has played an important role in studying muscle structures during contraction at various physiological conditions. We represent time-resolved X-ray data on equatorial diffraction and tension response of the frog sartorius muscle during relaxation. The measurements of the time-course of the intensity change of reflections (1,0), (1,1) and the background under them give a possibility to study the effect of potentiation of contraction by repetitive stimulation in fresh and tired muscles. Model calculations of meridional diffraction patterns for various configurations of cross-bridges in the relaxation phase were carried out.

  6. Predicting How Nanoconfinement Changes the Relaxation Time of a Supercooled Liquid

    DEFF Research Database (Denmark)

    Ingebrigtsen, Trond; Errington, Jeff; Truskett, Tom;

    2013-01-01

    asymmetric dumbbell-shaped molecules, which can be deeply supercooled without crystallizing. We find that the dimensionless structural relaxation times—spanning six decades as a function of temperature, density, and degree of confinement—collapse when plotted versus excess entropy. The data also collapse...

  7. A stable and accurate relaxation technique using multiple penalty terms in space and time

    Science.gov (United States)

    Frenander, Hannes; Nordström, Jan

    2017-09-01

    A new method for data relaxation based on weak imposition of external data is introduced. The technique is simple, easy to implement, and the resulting numerical scheme is unconditionally stable. Numerical experiments show that the error growth naturally present in long term simulations can be prevented by using the new technique.

  8. DEVICE FOR MEASURMENT OF RELAXATION TIME OF THE BLEACHED STATE OF OPTICAL MATERIALS BY THE «PUMP-PROBE» METHOD IN SUB-ΜS TIME DOMAIN

    Directory of Open Access Journals (Sweden)

    I. V. Glazunov

    2016-01-01

    Full Text Available The use of passive shutters to control the duration of the light pulses is an important aspect in the miniature and microchip lasers. One of the key spectroscopic characteristics which determine the properties of the material, which can be used as a passive shutter is relaxation time of its bleached state.We describe a device for determination of relaxation time of the bleached state in optical materials by the «pump-probe» method in the sub-μs time domain. This device allows one to determine relaxation times for materials which absorb at the light wavelength of 1.5 μm, e.g., materials doped with cobalt ions Co2+. The results of test examinations of the device are described, and the relaxation time of the bleached state of Co2+ ions is measured for a novel material – transparent glass-ceramics with Co2+:Ga2 O3 nanophase – amounting to 190 ± 6 ns. 

  9. An open-source software tool for the generation of relaxation time maps in magnetic resonance imaging

    Directory of Open Access Journals (Sweden)

    Kühne Titus

    2010-07-01

    Full Text Available Abstract Background In magnetic resonance (MR imaging, T1, T2 and T2* relaxation times represent characteristic tissue properties that can be quantified with the help of specific imaging strategies. While there are basic software tools for specific pulse sequences, until now there is no universal software program available to automate pixel-wise mapping of relaxation times from various types of images or MR systems. Such a software program would allow researchers to test and compare new imaging strategies and thus would significantly facilitate research in the area of quantitative tissue characterization. Results After defining requirements for a universal MR mapping tool, a software program named MRmap was created using a high-level graphics language. Additional features include a manual registration tool for source images with motion artifacts and a tabular DICOM viewer to examine pulse sequence parameters. MRmap was successfully tested on three different computer platforms with image data from three different MR system manufacturers and five different sorts of pulse sequences: multi-image inversion recovery T1; Look-Locker/TOMROP T1; modified Look-Locker (MOLLI T1; single-echo T2/T2*; and multi-echo T2/T2*. Computing times varied between 2 and 113 seconds. Estimates of relaxation times compared favorably to those obtained from non-automated curve fitting. Completed maps were exported in DICOM format and could be read in standard software packages used for analysis of clinical and research MR data. Conclusions MRmap is a flexible cross-platform research tool that enables accurate mapping of relaxation times from various pulse sequences. The software allows researchers to optimize quantitative MR strategies in a manufacturer-independent fashion. The program and its source code were made available as open-source software on the internet.

  10. Relaxation times of nanoscale deformations on the surface of a polymer thin film near and below the glass transition

    Science.gov (United States)

    Papaléo, R. M.; Leal, R.; Carreira, W. H.; Barbosa, L. G.; Bello, I.; Bulla, A.

    2006-09-01

    We report on measurements of relaxation times of nanometer-sized deformations resulting from the impact of individual energetic ions on poly(methyl methacrylate) surfaces at temperatures close to and below the glass transition Tg . The temporal evolution of the dimensions of the deformations is well described by a stretched exponential function, but with relaxation times τ(T) many orders of magnitude smaller than bulk values at the same T . The local Tg was around 86°C , roughly 30°C below the conventional bulk Tg . At the vicinity of the local Tg , τ(T) follows the Vogel-Fulcher type of T dependence, but at lower T a transition towards a less steep behavior is seen.

  11. Double multiple-relaxation-time lattice Boltzmann model for solid-liquid phase change with natural convection in porous media

    Science.gov (United States)

    Liu, Qing; He, Ya-Ling

    2015-11-01

    In this paper, a double multiple-relaxation-time lattice Boltzmann model is developed for simulating transient solid-liquid phase change problems in porous media at the representative elementary volume scale. The model uses two different multiple-relaxation-time lattice Boltzmann equations, one for the flow field and the other for the temperature field with nonlinear latent heat source term. The model is based on the generalized non-Darcy formulation, and the solid-liquid interface is traced through the liquid fraction which is determined by the enthalpy-based method. The present model is validated by numerical simulations of conduction melting in a semi-infinite space, solidification in a semi-infinite corner, and convection melting in a square cavity filled with porous media. The numerical results demonstrate the efficiency and accuracy of the present model for simulating transient solid-liquid phase change problems in porous media.

  12. Double multiple-relaxation-time lattice Boltzmann model for solid-liquid phase change with natural convection in porous media

    CERN Document Server

    Liu, Qing

    2015-01-01

    In this paper, a double multiple-relaxation-time lattice Boltzmann model is developed for simulating transient solid-liquid phase change problems in porous media at the representative elementary volume scale. The model uses two different multiple-relaxation-time lattice Boltzmann equations, one for the flow field and the other for the temperature field with nonlinear latent heat source term. The model is based on the generalized non-Darcy formulation, and the solid-liquid phase change interface is traced through the liquid fraction which is determined by the enthalpy method. The model is validated by numerical simulations of conduction melting in a semi-infinite space, solidification in a semi-infinite corner, and convection melting in a square cavity filled with porous media. The numerical results demonstrate the efficiency and accuracy of the present model for simulating transient solid-liquid phase change problems in porous media.

  13. Intraband relaxation time in wurtzite InGaN quantum-well lasers and comparison with experiment

    CERN Document Server

    Park, S H

    1999-01-01

    The intraband relaxation time for wurtzite (WZ) 3.5-nm In sub 0 sub . sub 1 sub 5 Ga sub 0 sub . sub 8 sub 5 N/In sub 0 sub . sub 0 sub 2 Ga sub 0 sub . sub 9 sub 8 N quantum well (QW) lasers is investigated theoretically. The results are also compared with those obtained from fitting the experimental data with a non-Markovian gain model with many-body effects. An intraband relaxation time of 25 fs is obtained from the comparison with experiment, which is in reasonably good agreement with the calculated value of 20 fs at the subband edge. These values are significantly shorter than those (40 - 100 sf) reported for zinc-blende crystals, such as InP and GaAs. This is because the hole effective masses of GaN are larger than those of GaAs and InP.

  14. Bayesian joint modeling of longitudinal measurements and time-to-event data using robust distributions.

    Science.gov (United States)

    Baghfalaki, T; Ganjali, M; Hashemi, R

    2014-01-01

    Distributional assumptions of most of the existing methods for joint modeling of longitudinal measurements and time-to-event data cannot allow incorporation of outlier robustness. In this article, we develop and implement a joint modeling of longitudinal and time-to-event data using some powerful distributions for robust analyzing that are known as normal/independent distributions. These distributions include univariate and multivariate versions of the Student's t, the slash, and the contaminated normal distributions. The proposed model implements a linear mixed effects model under a normal/independent distribution assumption for both random effects and residuals of the longitudinal process. For the time-to-event process a parametric proportional hazard model with a Weibull baseline hazard is used. Also, a Bayesian approach using the Markov-chain Monte Carlo method is adopted for parameter estimation. Some simulation studies are performed to investigate the performance of the proposed method under presence and absence of outliers. Also, the proposed methods are applied for analyzing a real AIDS clinical trial, with the aim of comparing the efficiency and safety of two antiretroviral drugs, where CD4 count measurements are gathered as longitudinal outcomes. In these data, time to death or dropout is considered as the interesting time-to-event outcome variable. Different model structures are developed for analyzing these data sets, where model selection is performed by the deviance information criterion (DIC), expected Akaike information criterion (EAIC), and expected Bayesian information criterion (EBIC).

  15. SU-E-I-64: Transverse Relaxation Time in Methylene Protons of Non-Alcoholic Fatty Liver Disease Rats

    Energy Technology Data Exchange (ETDEWEB)

    Song, K-H; Lee, D-W; Choe, B-Y [Department of Biomedical Engineering, Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul, Seoul (Korea, Republic of)

    2015-06-15

    Purpose: The aim of this study was to evaluate transverse relaxation time of methylene resonance compared to other lipid resonances. Methods: The examinations were performed using a 3.0 T scanner with a point — resolved spectroscopy (PRESS) sequence. Lipid relaxation time in a lipid phantom filled with canola oil was estimated considering repetition time (TR) as 6000 msec and echo time (TE) as 40 — 550 msec. For in vivo proton magnetic resonance spectroscopy ({sup 1}H — MRS), eight male Sprague — Dawley rats were given free access to a normal - chow (NC) and eight other male Sprague-Dawley rats were given free access to a high — fat (HF) diet. Both groups drank water ad libitum. T{sub 2} measurements in the rats’ livers were conducted at a fixed TR of 6000 msec and TE of 40 – 220 msec. Exponential curve fitting quality was calculated through the coefficients of determination (R{sup 2}). Results: A chemical analysis of phantom and liver was not performed but a T{sub 2} decay curve was acquired. The T{sub 2} relaxation time of methylene resonance was estimated as follows: NC rats, 37.07 ± 4.32 msec; HF rats, 31.43 ± 1.81 msec (p < 0.05). The extrapolated M0 values were higher in HF rats than in NC rats (p < 0.005). Conclusion: This study of {sup 1}H-MRS led to sufficient spectral resolution and signal — to — noise ratio differences to characterize all observable resonances for yielding T{sub 2} relaxation times of methylene resonance. {sup 1}H — MRS relaxation times may be useful for quantitative characterization of various liver diseases, including fatty liver disease. This study was supported by grant (2012-007883 and 2014R1A2A1A10050270) from the Mid-career Researcher Program through the NRF funded by Ministry of Science. In addition, this study was supported by the Industrial R&D of MOTIE/KEIT (10048997, Development of the core technology for integrated therapy devices based on real-time MRI-guided tumor tracking)

  16. The application of T1 and T2 relaxation time and magnetization transfer ratios to the early diagnosis of patellar cartilage osteoarthritis

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Weiwu; Qu, Nan; Lu, Zhihua; Yang, Shixun [Shanghai Jiaotong University, Department of Radiology, Shanghai (China)

    2009-11-15

    We compare the T1 and T2 relaxation times and magnetization transfer ratios (MTRs) of normal subjects and patients with osteoarthritis (OA) to evaluate the ability of these techniques to aid in the early diagnosis and treatment of OA. The knee joints in 11 normal volunteers and 40 patients with OA were prospectively evaluated using T1 relaxation times as measured using delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), T2 relaxation times (multiple spin-echo sequence, T2 mapping), and MTRs. The OA patients were further categorized into mild, moderate, and severe OA. The mean T1 relaxation times of the four groups (normal, mild OA, moderate OA, and severe OA) were: 487.3{+-}27.7, 458.0{+-}55.9, 405.9{+-}57.3, and 357.9{+-}36.7 respectively (p<0.001). The mean T2 relaxation times of the four groups were: 37.8{+-}3.3, 44.0{+-}8.5, 50.9{+-}9.5, and 57.4{+-}4.8 respectively (p<0.001). T1 relaxation time decreased and T2 relaxation time increased with worsening degeneration of patellar cartilage. The result of the covariance analysis showed that the covariate age had a significant influence on T2 relaxation time (p<0.001). No significant differences between the normal and OA groups using MTR were noted. T1 and T2 relaxation times are relatively sensitive to early degenerative changes in the patellar cartilage, whereas the MTR may have some limitations with regard to early detection of OA. In addition, The T1 and T2 relaxation times negatively correlate with each other, which is a novel finding. (orig.)

  17. Concise review of relaxations and approximation algorithms for nonidentical parallel-machine scheduling to minimize total weighted completion times

    Institute of Scientific and Technical Information of China (English)

    Li Kai; Yang Shanlin

    2008-01-01

    A class of nonidentical parallel machine scheduling problems are considered in which the goal is to minimize the total weighted completion time.Models and relaxations are collected.Most of these problems are NP-hard,in the strong sense,or open problems,therefore approximation algorithms are studied.The review reveals that there exist some potential areas worthy of further research.

  18. Algorithmic developments of the kinetic activation-relaxation technique: Accessing long-time kinetics of larger and more complex systems

    Science.gov (United States)

    Trochet, Mickaël; Sauvé-Lacoursière, Alecsandre; Mousseau, Normand

    2017-10-01

    In spite of the considerable computer speed increase of the last decades, long-time atomic simulations remain a challenge and most molecular dynamical simulations are limited to 1 μ s at the very best in condensed matter and materials science. There is a need, therefore, for accelerated methods that can bridge the gap between the full dynamical description of molecular dynamics and experimentally relevant time scales. This is the goal of the kinetic Activation-Relaxation Technique (k-ART), an off-lattice kinetic Monte-Carlo method with on-the-fly catalog building capabilities based on the topological tool NAUTY and the open-ended search method Activation-Relaxation Technique (ART nouveau) that has been applied with success to the study of long-time kinetics of complex materials, including grain boundaries, alloys, and amorphous materials. We present a number of recent algorithmic additions, including the use of local force calculation, two-level parallelization, improved topological description, and biased sampling and show how they perform on two applications linked to defect diffusion and relaxation after ion bombardement in Si.

  19. Polarized alkali vapor with minute-long transverse spin-relaxation time

    CERN Document Server

    Balabas, Misha; Ledbetter, Micah; Budker, Dmitry

    2010-01-01

    We demonstrate lifetimes of atomic populations and coherences in excess of 60 seconds in alkali vapor cells with inner walls coated with an alkene material. This represents two orders of magnitude improvement over the best paraffin coatings. Such anti-relaxation properties will likely lead to substantial improvements in atomic clocks, magnetometers, quantum memory, and enable sensitive studies of collisional effects and precision measurements of fundamental symmetries.

  20. Measurement of relaxation times by NMR-CT of electric superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Shimizu, Koji; Yoshitoshi, Motosada (Shimadzu Corp., Kyoto (Japan)); Narise, Shoji; Hirakawa, Kogi

    1984-08-01

    Relaxation curves of T/sub 1/ in various tissues of the brain in patients with cerebral tumor and in healthy controls were obtained by saturation-recovery and inversion-recovery methods, whereby T/sub 1/ values were calculated. The results obtained were in good agreement with in vitro measurement results of excised brain tissues. Prolongation of T/sub 1/ values was evidently observed with increasing the strength of static magnetic field.

  1. Using the Relaxation Test to Study Variation in the Time-Dependent Property of Rock and the Consequent Effect on Time-Dependent Roof Failure

    Science.gov (United States)

    Xue, Yuting; Mishra, Brijes; Gao, Danqing

    2017-09-01

    Field observations have demonstrated that roof failure occurs spatially in a mine from the time of excavation. It is suspected that time-dependent deformation propagates failure in the rock mass. In this paper, the relaxation test is used to study variation in the time-dependent property of rock and the consequent effect on time-dependent roof failure. This investigation uses a numerical simulation in 3DEC. The relaxation equation is developed from Burgers model. Variations in the time-dependent property in the post-failure region show negligible variation and, therefore, are averaged to represent the time-dependent property of the failed rock. Finally, these parameters are used in the numerical simulation of underground excavations. Two groups of parameters are used to represent the time-dependent property for pre- and post-failure conditions. FISH functions within 3DEC are used to monitor the state of each zone. Once failure is detected, the parameters are changed to the values corresponding to failed rock. The results show that the new relaxation model accurately predicts the time-dependent propagation of the failure zone. The variation of the time-dependent parameters significantly affects the rock mass behavior and roof convergence.

  2. On the suppression of background signals originating from NMR hardware components. Application to zero echo time imaging and relaxation time analysis.

    Science.gov (United States)

    Dreher, Wolfgang; Bardenhagen, Ingo; Huang, Li; Bäumer, Marcus

    2016-04-01

    Modern NMR imaging systems used for biomedical research are equipped with B0 gradient systems with strong maximum gradient strength and short switching time enabling (1)H NMR measurements of samples with very short transverse relaxation times. However, background signal originating from non-optimized RF coils may hamper experiments with ultrashort delays between RF excitation and signal reception. We demonstrate that two simple means, outer volume suppression and the use of shaped B0 fields produced by higher-order shim coils, allow a considerable suppression of disturbing background signals. Thus, the quality of NMR images acquired at ultrashort or zero echo time is improved and systematic errors in quantitative data evaluation are avoided. Fields of application comprise MRI with ultrashort echo time or relaxation time analysis, for both biomedical research and characterizing porous media filled with liquids or gases.

  3. The value of time in longitudinal studies of ageing. Lessons from the Australian Longitudinal Study on Women's Health.

    Science.gov (United States)

    Byles, Julie E; Dobson, Annette

    2011-10-01

    The Australian Longitudinal Study on Women's Health (ALSWH) involves three cohorts of women born in 1921-1926, 1946-1951 and 1973-1978, who have been surveyed every 3 years since 1996. We describe how the 1921-1926 cohort have changed over time. We also describe trends in health risks among the younger cohorts, providing an indication of future health threats. By Survey 5, 28.4% of the 1921-1926 cohort had died. Among those who survived and remained in the study, 61% maintained high physical function scores over time. Chronic conditions such as arthritis, diabetes, heart disease and stroke were associated with lower physical function scores and decline in scores over time. ALSWH will continue to provide information on changes in health and health service use as we follow the oldest cohort through their 90 s, and as younger cohorts accumulate increasing burden of disease and disability as they age. © 2011 The Authors. Australasian Journal on Ageing © 2011 ACOTA.

  4. Effects of attitude dissimilarity and time on social integration : A longitudinal panel study

    NARCIS (Netherlands)

    Van der Vegt, GS

    2002-01-01

    A longitudinal panel study in 25 work groups of elementary school teachers examined the effect of attitudinal dissimilarity and time on social integration across a 9-month period. In line with the prediction based on both the similarity-attraction approach and social identity theory, cross-lagged re

  5. A Longitudinal Study of Speech Timing in Young Children Later Found to Have Reading Disability

    Science.gov (United States)

    Smith, Allan B.; Smith, Susan Lambrecht; Locke, John L.; Bennett, Jane

    2008-01-01

    Purpose: This study examined the development of timing characteristics in early spontaneous speech of children who were later identified as having reading disability (RD). Method: Child-adult play sessions were recorded longitudinally at 2 and 3 years of age in 27 children, most of whom were at high familial risk for RD. For each speaking turn,…

  6. A Longitudinal Study of Speech Timing in Young Children Later Found to Have Reading Disability

    Science.gov (United States)

    Smith, Allan B.; Smith, Susan Lambrecht; Locke, John L.; Bennett, Jane

    2008-01-01

    Purpose: This study examined the development of timing characteristics in early spontaneous speech of children who were later identified as having reading disability (RD). Method: Child-adult play sessions were recorded longitudinally at 2 and 3 years of age in 27 children, most of whom were at high familial risk for RD. For each speaking turn,…

  7. Very short NMR relaxation times of anions in ionic liquids: new pulse sequence to eliminate the acoustic ringing.

    Science.gov (United States)

    Klimavicius, Vytautas; Gdaniec, Zofia; Balevicius, Vytautas

    2014-11-11

    NMR relaxation processes of anions were studied in two neat imidazolium-based room temperature ionic liquids (RTILs) 1-decyl-3-methyl-imidazolium bromide- and chloride. The spin-lattice and spin-spin relaxations of 81Br and 35Cl nuclei were found to be extremely fast due to very strong quadrupolar interactions. The determined relaxation rates are comparable with those observed in the solids or in some critical organic solute/water/salt systems. In order to eliminate the acoustic ringing of the probe-head during relaxation times measurements the novel pulse sequence has been devised. It is based on the conventional inversion recovery pulse sequence, however, instead of the last 90° pulse the subsequence of three 90° pulses applied along axes to fulfill the phase cycling condition is used. Using this pulse sequence it was possible to measure T1 for both studied nuclei. The viscosity measurements have been carried out and the rotational correlation times were calculated. The effective 35Cl quadrupolar coupling constant was found to be almost one order lower than that for 81Br, i.e. 1.8 MHz and 16.0 MHz, respectively. Taking into account the facts that the ratio of (Q(35Cl)/Q(81Br))2≈0.1 and EFG tensors on the anions are quite similar, analogous structural organizations are expected for both RTILs. The observed T1/T2 (1.27-1.44) ratios were found to be not sufficiently high to confirm the presence of long-living (on the time scale of ≥10(-8) s) mesoscopic structures or heterogeneities in the studied neat ionic liquids.

  8. Distribution of relaxation times from dielectric spectroscopy using Monte Carlo simulated annealing: Application to α-PVDF

    Science.gov (United States)

    Bello, A.; Laredo, E.; Grimau, M.

    1999-11-01

    The existence of a distribution of relaxation times has been widely used to describe the relaxation function versus frequency in glass-forming liquids. Several empirical distributions have been proposed and the usual method is to fit the experimental data to a model that assumes one of these functions. Another alternative is to extract from the experimental data the discrete profile of the distribution function that best fits the experimental curve without any a priori assumption. To test this approach a Monte Carlo algorithm using the simulated annealing is used to best fit simulated dielectric loss data, ɛ''(ω), generated with Cole-Cole, Cole-Davidson, Havriliak-Negami, and Kohlrausch-Williams-Watts (KWW) functions. The relaxation times distribution, G(ln(τ)), is obtained as an histogram that follows very closely the analytical expression for the distributions that are known in these cases. Also, the temporal decay functions, φ(t), are evaluated and compared to a stretched exponential. The method is then applied to experimental data for α-polyvinylidene fluoride over a temperature range 233 Kflouride (PVDF) is found to be 87, which characterizes this polymer as a relatively structurally strong material.

  9. In vivo relaxation time measurements on a murine tumor model--prolongation of T1 after photodynamic therapy.

    Science.gov (United States)

    Liu, Y H; Hawk, R M; Ramaprasad, S

    1995-01-01

    RIF tumors implanted on mice feet were investigated for changes in relaxation times (T1 and T2) after photodynamic therapy (PDT). Photodynamic therapy was performed using Photofrin II as the photosensitizer and laser light at 630 nm. A home-built proton solenoid coil in the balanced configuration was used to accommodate the tumors, and the relaxation times were measured before, immediately after, and up to several hours after therapy. Several control experiments were performed untreated tumors, tumors treated with Photofrin II alone, or tumors treated with laser light alone. Significant increases in T1s of water protons were observed after PDT treatment. In all experiments, 31P spectra were recorded before and after the therapy to study the tumor status and to confirm the onset of PDT. These studies show significant prolongation of T1s after the PDT treatment. The spin-spin relaxation measurements, on the other hand, did not show such prolongation in T2 values after PDT treatment.

  10. In vivo field dependence of proton relaxation times in human brain, liver and skeletal muscle: a multicenter study

    DEFF Research Database (Denmark)

    Henriksen, O; de Certaines, J D; Spisni, A;

    1993-01-01

    T1 and T2 relaxation times are fundamental parameters for signal contrast behaviour in MRI. A number of ex vivo relaxometry studies have dealt with the magnetic field dispersion of T1. By means of multicenter study within the frame of the COMAC BME Concerted Action on Tissue Characterization by MRI...... and MRS, the in vivo field dispersion of T1 and T2 has been measured in order to evaluate whether ex vivo data are representative for the in vivo situation. Brain, skeletal muscle, and liver of healthy human volunteers were studied. Fifteen MR units with a field strength ranging from 0.08 T to 1.5 T took...... part in the trial, which comprised 218 volunteers. All the MR systems were tested for measurement accuracy using the Eurospin TO5 test object. The measured relaxation data were subsequently corrected according to the obtained calibration curves. The results showed a clear field dispersion of T1...

  11. 1H metabolite relaxation times at 3.0 tesla: Measurements of T1 and T2 values in normal brain and determination of regional differences in transverse relaxation.

    Science.gov (United States)

    Träber, Frank; Block, Wolfgang; Lamerichs, Rolf; Gieseke, Jürgen; Schild, Hans H

    2004-05-01

    To measure 1H relaxation times of cerebral metabolites at 3 T and to investigate regional variations within the brain. Investigations were performed on a 3.0-T clinical whole-body magnetic resonance (MR) system. T2 relaxation times of N-acetyl aspartate (NAA), total creatine (tCr), and choline compounds (Cho) were measured in six brain regions of 42 healthy subjects. T1 relaxation times of these metabolites and of myo-inositol (Ins) were determined in occipital white matter (WM), the frontal lobe, and the motor cortex of 10 subjects. T2 values of all metabolites were markedly reduced with respect to 1.5 T in all investigated regions. T2 of NAA was significantly (P motor cortex (247 +/- 13 msec) than in occipital WM (301 +/- 18 msec). T2 of the tCr methyl resonance showed a corresponding yet less pronounced decrease (162 +/- 16 msec vs. 178 +/- 9 msec, P = 0.021). Even lower T2 values for all metabolites were measured in the basal ganglia. Metabolite T1 relaxation times at 3.0 T were not significantly different from the values at 1.5 T. Transverse relaxation times of the investigated cerebral metabolites exhibit an inverse proportionality to magnetic field strength, and especially T2 of NAA shows distinct regional variations at 3 T. These can be attributed to differences in relative WM/gray matter (GM) contents and to local paramagnetism. Copyright 2004 Wiley-Liss, Inc.

  12. Propagation of plane waves in thermoelastic cubic crystal material with two relaxation times

    Institute of Scientific and Technical Information of China (English)

    Rajneesh Kumar; Manjeet Singh

    2007-01-01

    A problem concerned with the reflection and refraction of thermoelastic plane waves an imperfect interface between two generalized thermally conducting cutimes has been investigated.The generalized thermoelastic theory with two relaxation of retiected and refracted waves to the amplitude of incident waves are obtained for an imperfect boundary and deduced for normal stiffness,transverse stiffness,themlal contact conductance,slip and welded boundaries. Amplitude ratios of different reflected and graphically for different incident waves.It is observed that the amplitude ratios of reflected and refracted waves are affected by the stiffness and thermal properties of the media.

  13. Rapid spin-lattice relaxation time mapping incorporating flip angle calibration in quantitative magnetic resonance imaging

    Institute of Scientific and Technical Information of China (English)

    Zhongliang Zu; Qi Liu; Yanming Yu; Song Gao; Shanglian Bao

    2008-01-01

    Driven equilibrium single pulse observation of T1(DESPOT1)is a rapid spin-lattice relaxation constant(T1)mapping technique in magnetic resonance imaging(MRI).However,DESPOT1 is very sensitive to flip angle(FA)inhomogeneity,resulting in T1 inaccuracy.Here,a five-point DESPOTl method is proposed to reduce the sensitivity to FA inhomogeneity through FA measurement and calibra-tion.Phantom and in vivo experiments are performed to validate the technique.As a result.a rapid and accurate T1 mapping is acquired by using the proposed five-point DESPOT1 method.

  14. Time scales and mechanisms of relaxation in the energy landscape of polymer glass under deformation: direct atomistic modeling.

    Science.gov (United States)

    Lyulin, Alexey V; Michels, M A J

    2007-08-24

    Molecular-dynamics simulation is used to explore the influence of thermal and mechanical history of typical glassy polymers on their deformation. Polymer stress-strain and energy-strain developments have been followed for different deformation velocities, also in closed extension-recompression loops. The latter simulate for the first time the experimentally observed mechanical rejuvenation and overaging of polymers, and energy partitioning reveals essential differences between mechanical and thermal rejuvenation. All results can be qualitatively interpreted by considering the ratios of the relevant time scales: for cooling down, for deformation, and for segmental relaxation.

  15. Screen time and physical activity during adolescence: longitudinal effects on obesity in young adulthood

    Directory of Open Access Journals (Sweden)

    Gordon-Larsen Penny

    2007-06-01

    Full Text Available Abstract Background The joint impact of sedentary behavior and physical activity on obesity has not been assessed in a large cohort followed from adolescence to adulthood. Methods Nationally representative longitudinal data from Waves II (1995; mean age: 15.9 and III (2001; mean age: 21.4 of the National Longitudinal Study of Adolescent Health (n = 9,155 were collected. Sex-stratified multivariate logistic regression analysis assessed the odds of obesity associated with Wave II MVPA and screen time, controlling for sociodemographic characteristics and change in MVPA and screen time from Wave II to III. Obesity was defined using body mass index (BMI, kg/m2 International Obesity Task Force cut-points at Wave II and adult cut-points at Wave III (BMI ≥ 30. Results In males, adjusted odds of prevalent obesity was strongly predicted by MVPA bouts [OR (95% CI: OR6 vs. 1 MVPA bouts = 0.50 (0.40, 0.62; OR4 vs. 40 hrs screen time = 0.83 (0.69, 1.00]. In females, greater MVPA bouts and lower screen time correlated with lower prevalent obesity [OR (95% CI: OR6 vs. 1 MVPA bouts = 0.67 (0.49, 0.91; OR4 vs. 40 hrs screen time = 0.67 (0.53, 0.85]. Longitudinally, adolescent screen time hours had a stronger influence on incident obesity in females [OR (95% CI: OR4 vs. 40 hrs = 0.58 (0.43, 0.80] than males [OR (95% CI: OR4 vs. 40 hrs = 0.78 (0.61, 0.99]. Longitudinal activity patterns were not predictive of incident obesity. Conclusion Reducing screen time during adolescence and into adulthood may be a promising strategy for reducing obesity incidence, especially in females.

  16. Single-frequency dielectric relaxation used to characterize the glass transition time of polydextrose

    Science.gov (United States)

    Buehler, Martin G.; Campbell, Zachary J.; Carter, Brady P.

    2017-02-01

    Dielectric relaxation methods are applicable to powdery materials such as carbohydrates. These materials have relaxations that occur in the milli-Hz range while samples are held at fixed temperatures and fixed water activities, a w, (relativity humidity). Under proper conditions these materials undergo physical changes where the initially glassy powder transitions to an amorphous equilibrium state at the glass transition temperature, T g. Determining this transition involves characterizing the boundary curve (T g versus a w) which determines T g and a w conditions where materials are stable with long-shelf life or unstable with very a short shelf-life. This paper serves to illustrate multiple methodologies which can be used to characterize glass transition from frequency-spectra. Three methodologies are described: peak-broadening, peak-shift, and single-frequency. The new single frequency method not only provides results that identical to those of the peak-shift method but increases the data acquisition speeds by a factor of 5. This method is illustrated on polydextrose, a common sugar substitute. The information gathered can then be used to construct the boundary curve which is used to characterize the shelf-life of a material at various conditions.

  17. Motional Spin Relaxation in Large Electric Fields

    CERN Document Server

    Schmid, Riccardo; Filippone, B W

    2008-01-01

    We discuss the precession of spin-polarized Ultra Cold Neutrons (UCN) and $^{3}\\mathrm{He}$ atoms in uniform and static magnetic and electric fields and calculate the spin relaxation effects from motional $v\\times E$ magnetic fields. Particle motion in an electric field creates a motional $v\\times E$ magnetic field, which when combined with collisions, produces variations of the total magnetic field and results in spin relaxation of neutron and $^{3}\\mathrm{He}$ samples. The spin relaxation times $T_{1}$ (longitudinal) and $T_{2}$ (transverse) of spin-polarized UCN and $^{3}\\mathrm{He}$ atoms are important considerations in a new search for the neutron Electric Dipole Moment at the SNS \\emph{nEDM} experiment. We use a Monte Carlo approach to simulate the relaxation of spins due to the motional $v\\times E$ field for UCN and for $^{3}\\mathrm{He}$ atoms at temperatures below $600 \\mathrm{mK}$. We find the relaxation times for the neutron due to the $v\\times E$ effect to be long compared to the neutron lifetime, ...

  18. Dielectric relaxation and hydrogen bonding studies of 1,3-propanediol–dioxane mixtures using time domain reflectometry technique

    Indian Academy of Sciences (India)

    Madhukar N Shinde; Ravindra B Talware; Pravin G Hudge; Yogesh S Joshi; Ashok C Kumbharkhane

    2012-02-01

    The complex permittivity, static dielectric constant and relaxation time for 1,3-propanediol, 1,4-dioxane and their mixtures have been studied using time domain reflectometry (TDR). The excess permittivity, excess inverse relaxation time and Kirkwood correlation factor have also been determined at various concentrations of dioxane. Hydrogen bonded theory was applied to compute the correlation terms for the mixtures. The Bruggeman model for the nonlinear case has been fitted to the dielectric data for mixtures.

  19. Magnetic relaxation in anisotropic magnets

    DEFF Research Database (Denmark)

    Lindgård, Per-Anker

    1971-01-01

    The line shape and the kinematic and thermodynamic slowing down of the critical and paramagnetic relaxation in axially anisotropic materials are discussed. Kinematic slowing down occurs only in the longitudinal relaxation function. The thermodynamic slowing down occurs in either the transverse or...

  20. The effect of timing of intravenous muscle relaxant on the quality of double-contrast barium enema

    Energy Technology Data Exchange (ETDEWEB)

    Elson, E.M.; Campbell, D.M.; Halligan, S.; Shaikh, I.; Davitt, S.; Bartram, C.I

    2000-05-01

    AIM: To determine whether the timing of buscopan administration during double-contrast barium enema examination (DCBE) affects diagnostic quality. MATERIALS AND METHODS: In a prospective setting, 100 consecutive adult out-patients referred for DCBE received 20 mg buscopan (hyoscine-N-butylbromide) intravenously, either before infusion of barium suspension (Group A) or after barium infusion and gas insufflation (Group B). A subjective assessment of ease of contrast medium infusion was made at the time of examination and the films subsequently analysed by two radiologists unaware of the mode of relaxant administration, who noted the quality of mucosal coating and made subjective and objective measurements of segmental distension. RESULTS: There was no significant difference in screening times, infusion difficulty or colonic contrast medium coating between the two groups. Subjective assessment of distension of the caecum, ascending colon, transverse colon and rectum were not significantly different. Patients receiving intravenous relaxant after barium and gas infusion had less subjective descending (P = 0.05) and sigmoid (P = 0.04) colon distension, but there was no significant difference with respect to maximal bowel diameter in any of the segments measured. CONCLUSION: The timing of intravenous administration during DCBE is likely to have no significant effect on the diagnostic quality of the study. Elson, E.M. (2000)

  1. A Study of Concrete Hydration and Dielectric Relaxation Mechanism Using Ground Penetrating Radar and Short-Time Fourier Transform

    Directory of Open Access Journals (Sweden)

    Lai WL

    2010-01-01

    Full Text Available Abstract Ground penetrating radar (GPR was used to characterize the frequency-dependent dielectric relaxation phenomena in ordinary Portland cement (OPC hydration in concrete changing from fresh to hardened state. The study was experimented by measuring the changes of GPR A-scan waveforms over a period of 90 days, and processed the waveforms with short-time Fourier transform (STFT in joint time-frequency analysis (JTFA domain rather than a conventional time or frequency domain alone. The signals of the direct wave traveled at the concrete surface and the reflected wave from an embedded steel bar were transformed with STFT, in which the changes of peak frequency over ages were tracked. The peak frequencies were found to increase with ages and the patterns were found to match closely with primarily the well-known OPC hydration process and secondarily, the evaporation effect. The close match is contributed to the simultaneous effects converting free to bound water over time, on both conventional OPC hydration and dielectric relaxation mechanisms.

  2. Relaxed clocks and inferences of heterogeneous patterns of nucleotide substitution and divergence time estimates across whales and dolphins (Mammalia: Cetacea).

    Science.gov (United States)

    Dornburg, Alex; Brandley, Matthew C; McGowen, Michael R; Near, Thomas J

    2012-02-01

    Various nucleotide substitution models have been developed to accommodate among lineage rate heterogeneity, thereby relaxing the assumptions of the strict molecular clock. Recently developed "uncorrelated relaxed clock" and "random local clock" (RLC) models allow decoupling of nucleotide substitution rates between descendant lineages and are thus predicted to perform better in the presence of lineage-specific rate heterogeneity. However, it is uncertain how these models perform in the presence of punctuated shifts in substitution rate, especially between closely related clades. Using cetaceans (whales and dolphins) as a case study, we test the performance of these two substitution models in estimating both molecular rates and divergence times in the presence of substantial lineage-specific rate heterogeneity. Our RLC analyses of whole mitochondrial genome alignments find evidence for up to ten clade-specific nucleotide substitution rate shifts in cetaceans. We provide evidence that in the uncorrelated relaxed clock framework, a punctuated shift in the rate of molecular evolution within a subclade results in posterior rate estimates that are either misled or intermediate between the disparate rate classes present in baleen and toothed whales. Using simulations, we demonstrate abrupt changes in rate isolated to one or a few lineages in the phylogeny can mislead rate and age estimation, even when the node of interest is calibrated. We further demonstrate how increasing prior age uncertainty can bias rate and age estimates, even while the 95% highest posterior density around age estimates decreases; in other words, increased precision for an inaccurate estimate. We interpret the use of external calibrations in divergence time studies in light of these results, suggesting that rate shifts at deep time scales may mislead inferences of absolute molecular rates and ages.

  3. Factorial Invariance within Longitudinal Structural Equation Models: Measuring the Same Construct across Time

    Science.gov (United States)

    Widaman, Keith F.; Ferrer, Emilio; Conger, Rand D.

    2009-01-01

    Charting change in behavior as a function of age and investigating longitudinal relations among constructs are primary goals of developmental research. Traditionally, researchers rely on a single measure (e.g., scale score) for a given construct for each person at each occasion of measurement, assuming that measure reflects the same construct at each occasion. With multiple indicators of a latent construct at each time of measurement, the researcher can evaluate whether factorial invariance holds. If factorial invariance constraints are satisfied, latent variable scores at each time of measurement are on the same metric and stronger conclusions are warranted. In this paper we discuss factorial invariance in longitudinal studies, contrasting analytic approaches and highlighting strengths of the multiple-indicator approach to modeling developmental processes. PMID:20369028

  4. Simplex-TSDC spectroscopy: An efficient tool to measure the relaxation time of the isothermal transient depolarization current in organic dielectrics

    Energy Technology Data Exchange (ETDEWEB)

    Benchenane-Mehor, Halima, E-mail: halima_mehor_2000@yahoo.fr [Laboratoire CaSiCCE, Département de Génie Electrique, ENSET-Oran, B.P. 1523, El M’Naouer, 31000 Oran (Algeria); Laboratoire de Microphysique et de Nanophysique (LaMiN), Département de Physique-Chimie, ENSET-Oran, B.P. 1523 EL M’Naouer, 31000 Oran (Algeria); Soufi, Manil M.; Saiter, Jean-Marc; Benzohra, Mohamed [Laboratoire LECAP-AMME, EA 4528, Université de Rouen, Faculté des Sciences, Avenue de l' Université BP 12, 76801 Saint Etienne du Rouvray (France)

    2013-03-01

    The temporal technique analysis by a simplex optimization method of isothermal transient depolarization current measurements (Simplex-TSDC) is presented for the study of the glass transition domain of different polymers. The advantage of the present method compared to the classical TSDC is that it gives direct results comparable to the experiment and allows a good estimate of the relaxation time close to the glass transition temperature in dielectric thin films. The present method also allows a direct determination of two relaxation times corresponding to a fast and a slow dynamics; and then confirms the heterogeneous character of the molecular relaxation dynamics.

  5. Time-optimal control of spin 1/2 particles in the presence of radiation damping and relaxation.

    Science.gov (United States)

    Zhang, Y; Lapert, M; Sugny, D; Braun, M; Glaser, S J

    2011-02-07

    We consider the time-optimal control of an ensemble of uncoupled spin 1/2 particles in the presence of relaxation and radiation damping effects, whose dynamics is governed by nonlinear equations generalizing the standard linear Bloch equations. For a single spin, the optimal control strategy can be fully characterized analytically. However, in order to take into account the inhomogeneity of the static magnetic field, an ensemble of isochromats at different frequencies must be considered. For this case, numerically optimized pulse sequences are computed and the dynamics under the corresponding optimal field is experimentally demonstrated using nuclear magnetic resonance techniques.

  6. Prediction of Mass Transfer Time Relaxation Parameter for Boiling Simulation on the Shell-Side of LNG Spiral Wound Heat Exchanger

    Directory of Open Access Journals (Sweden)

    Zhi-Yong Wu

    2014-07-01

    Full Text Available The objective of this present study is to propose an approach to predict mass transfer time relaxation parameter for boiling simulation on the shell-side of LNG spiral wound heat exchanger (SWHE. The numerical model for the shell-side of LNG SWHE was established. For propane and ethane, a predicted value of mass transfer time relaxation parameter was presented through the equivalent evaporation simulations and was validated by the Chisholm void fraction correlation recommended under various testing conditions. In addition, heat transfer deviations between simulations using the predicted value of mass transfer time relaxation parameter and experiments from Aunan were investigated. The boiling characteristics of SWHE shell-side were also visualized based on the simulations with VOF model. The method of predicting mass transfer time relaxation parameter may be well applicable to various phase change simulations.

  7. A Bayesian approach to joint analysis of multivariate longitudinal data and parametric accelerated failure time.

    Science.gov (United States)

    Luo, Sheng

    2014-02-20

    Impairment caused by Parkinson's disease (PD) is multidimensional (e.g., sensoria, functions, and cognition) and progressive. Its multidimensional nature precludes a single outcome to measure disease progression. Clinical trials of PD use multiple categorical and continuous longitudinal outcomes to assess the treatment effects on overall improvement. A terminal event such as death or dropout can stop the follow-up process. Moreover, the time to the terminal event may be dependent on the multivariate longitudinal measurements. In this article, we consider a joint random-effects model for the correlated outcomes. A multilevel item response theory model is used for the multivariate longitudinal outcomes and a parametric accelerated failure time model is used for the failure time because of the violation of proportional hazard assumption. These two models are linked via random effects. The Bayesian inference via MCMC is implemented in 'BUGS' language. Our proposed method is evaluated by a simulation study and is applied to DATATOP study, a motivating clinical trial to determine if deprenyl slows the progression of PD. © 2013 The authors. Statistics in Medicine published by John Wiley & Sons, Ltd.

  8. The effect of the magnetic nanoparticle's size dependence of the relaxation time constant on the specific loss power of magnetic nanoparticle hyperthermia

    Science.gov (United States)

    Harabech, Mariem; Leliaert, Jonathan; Coene, Annelies; Crevecoeur, Guillaume; Van Roost, Dirk; Dupré, Luc

    2017-03-01

    Magnetic nanoparticle hyperthermia is a cancer treatment in which magnetic nanoparticles (MNPs) are subjected to an alternating magnetic field to induce heat in the tumor. The generated heat of MNPs is characterized by the specific loss power (SLP) due to relaxation phenomena of the MNP. Up to now, several models have been proposed to predict the SLP, one of which is the Linear Response Theory. One parameter in this model is the relaxation time constant. In this contribution, we employ a macrospin model based on the Landau-Lifshitz-Gilbert equation to investigate the relation between the Gilbert damping parameter and the relaxation time constant. This relaxation time has a pre-factor τ0 which is often taken as a fixed value ranging between 10-8 and 10-12 s. However, in reality it has small size dependence. Here, the influence of this size dependence on the calculation of the SLP is demonstrated, consequently improving the accuracy of this estimate.

  9. Television viewing time and risk of incident diabetes mellitus: the English Longitudinal Study of Ageing.

    Science.gov (United States)

    Smith, L; Hamer, M

    2014-12-01

    To investigate the longitudinal association between television viewing time and risk of incident diabetes mellitus in an elderly sample of adults in England. Analyses of data from the English Longitudinal Study of Ageing. At baseline (2008), participants reported their television viewing time and physical activity level. Diabetes mellitus was recorded from self-reported physician diagnosis at 2-year follow-up. Associations between television viewing time and combined television viewing time and physical activity level with risk of incident diabetes mellitus at follow-up were examined using adjusted logistic regression models. A total of 5964 participants (mean ± sd age 65 ± 9 years at baseline, 44% male) were included in the analyses. There was an association between baseline television viewing time and risk of incident diabetes mellitus at 2-year follow-up (≥ 6 h/day compared with diabetes mellitus at 2-year follow-up than those who were active/had low television viewing time (fully adjusted odds ratio 1.94, 95% CI 1.02, 3.68), although active participants reporting high television viewing were not at risk. Interventions to reduce the incidence of diabetes in the elderly that focus on both increasing physical activity and reducing television viewing time might prove useful. © 2014 The Authors. Diabetic Medicine published by John Wiley & Sons Ltd on behalf of Diabetes UK.

  10. Quantifying millisecond time-scale exchange in proteins by CPMG relaxation dispersion NMR spectroscopy of side-chain carbonyl groups

    Energy Technology Data Exchange (ETDEWEB)

    Hansen, Alexandar L.; Kay, Lewis E., E-mail: kay@pound.med.utoronto.ca [University of Toronto, Departments of Molecular Genetics, Biochemistry and Chemistry (Canada)

    2011-08-15

    A new pulse sequence is presented for the measurement of relaxation dispersion profiles quantifying millisecond time-scale exchange dynamics of side-chain carbonyl groups in uniformly {sup 13}C labeled proteins. The methodology has been tested using the 87-residue colicin E7 immunity protein, Im7, which is known to fold via a partially structured low populated intermediate that interconverts with the folded, ground state on the millisecond time-scale. Comparison of exchange parameters extracted for this folding 'reaction' using the present methodology with those obtained from more 'traditional' {sup 15}N and backbone carbonyl probes establishes the utility of the approach. The extracted excited state side-chain carbonyl chemical shifts indicate that the Asx/Glx side-chains are predominantly unstructured in the Im7 folding intermediate. However, several crucial salt-bridges that exist in the native structure appear to be already formed in the excited state, either in part or in full. This information, in concert with that obtained from existing backbone and side-chain methyl relaxation dispersion experiments, will ultimately facilitate a detailed description of the structure of the Im7 folding intermediate.

  11. Effects of Liver Fibrosis Progression on Tissue Relaxation Times in Different Mouse Models Assessed by Ultrahigh Field Magnetic Resonance Imaging.

    Science.gov (United States)

    Müller, Andreas; Hochrath, Katrin; Stroeder, Jonas; Hittatiya, Kanishka; Schneider, Günther; Lammert, Frank; Buecker, Arno; Fries, Peter

    2017-01-01

    Recently, clinical studies demonstrated that magnetic resonance relaxometry with determination of relaxation times T1 and T2(⁎) may aid in staging and management of liver fibrosis in patients suffering from viral hepatitis and steatohepatitis. In the present study we investigated T1 and T2(⁎) in different models of liver fibrosis to compare alternate pathophysiologies in their effects on relaxation times and to further develop noninvasive quantification methods of liver fibrosis. MRI was performed with a fast spin echo sequence for measurement of T1 and a multigradient echo sequence for determination of T2(⁎). Toxic liver fibrosis was induced by injections of carbon tetrachloride (1.4 mL CCl4 per kg bodyweight and week, for 3 or 6 weeks) in BALB/cJ mice. Chronic sclerosing cholangitis was mimicked using the ATP-binding cassette transporter B4 knockout (Abcb4 (-/-)) mouse model. Untreated BALB/cJ mice served as controls. To assess hepatic fibrosis, we ascertained collagen contents and fibrosis scores after Sirius red staining. T1 and T2(⁎) correlate differently to disease severity and etiology of liver fibrosis. T2(⁎) shows significant decrease correlating with fibrosis in CCl4 treated animals, while demonstrating significant increase with disease severity in Abcb4 (-/-) mice. Measurements of T1 and T2(⁎) may therefore facilitate discrimination between different stages and causes of liver fibrosis.

  12. Effects of Liver Fibrosis Progression on Tissue Relaxation Times in Different Mouse Models Assessed by Ultrahigh Field Magnetic Resonance Imaging

    Science.gov (United States)

    Müller, Andreas; Hochrath, Katrin; Stroeder, Jonas; Hittatiya, Kanishka; Schneider, Günther; Lammert, Frank; Buecker, Arno

    2017-01-01

    Recently, clinical studies demonstrated that magnetic resonance relaxometry with determination of relaxation times T1 and T2⁎ may aid in staging and management of liver fibrosis in patients suffering from viral hepatitis and steatohepatitis. In the present study we investigated T1 and T2⁎ in different models of liver fibrosis to compare alternate pathophysiologies in their effects on relaxation times and to further develop noninvasive quantification methods of liver fibrosis. MRI was performed with a fast spin echo sequence for measurement of T1 and a multigradient echo sequence for determination of T2⁎. Toxic liver fibrosis was induced by injections of carbon tetrachloride (1.4 mL CCl4 per kg bodyweight and week, for 3 or 6 weeks) in BALB/cJ mice. Chronic sclerosing cholangitis was mimicked using the ATP-binding cassette transporter B4 knockout (Abcb4 −/−) mouse model. Untreated BALB/cJ mice served as controls. To assess hepatic fibrosis, we ascertained collagen contents and fibrosis scores after Sirius red staining. T1 and T2⁎ correlate differently to disease severity and etiology of liver fibrosis. T2⁎ shows significant decrease correlating with fibrosis in CCl4 treated animals, while demonstrating significant increase with disease severity in Abcb4 −/− mice. Measurements of T1 and T2⁎ may therefore facilitate discrimination between different stages and causes of liver fibrosis. PMID:28194423

  13. Effects of Liver Fibrosis Progression on Tissue Relaxation Times in Different Mouse Models Assessed by Ultrahigh Field Magnetic Resonance Imaging

    Directory of Open Access Journals (Sweden)

    Andreas Müller

    2017-01-01

    Full Text Available Recently, clinical studies demonstrated that magnetic resonance relaxometry with determination of relaxation times T1 and T2⁎ may aid in staging and management of liver fibrosis in patients suffering from viral hepatitis and steatohepatitis. In the present study we investigated T1 and T2⁎ in different models of liver fibrosis to compare alternate pathophysiologies in their effects on relaxation times and to further develop noninvasive quantification methods of liver fibrosis. MRI was performed with a fast spin echo sequence for measurement of T1 and a multigradient echo sequence for determination of T2⁎. Toxic liver fibrosis was induced by injections of carbon tetrachloride (1.4 mL CCl4 per kg bodyweight and week, for 3 or 6 weeks in BALB/cJ mice. Chronic sclerosing cholangitis was mimicked using the ATP-binding cassette transporter B4 knockout (Abcb4 -/- mouse model. Untreated BALB/cJ mice served as controls. To assess hepatic fibrosis, we ascertained collagen contents and fibrosis scores after Sirius red staining. T1 and T2⁎ correlate differently to disease severity and etiology of liver fibrosis. T2⁎ shows significant decrease correlating with fibrosis in CCl4 treated animals, while demonstrating significant increase with disease severity in Abcb4 -/- mice. Measurements of T1 and T2⁎ may therefore facilitate discrimination between different stages and causes of liver fibrosis.

  14. The effects of proteoglycan and type II collagen on T1rho relaxation time of articular cartilage

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Won Seok; Yoo, Hye Jin; Hong, Sung Hwan; Choi, Ja Young [Dept. of Radiology and Institute of Radiation Medicine, Seoul National University Hospital, Seoul National University College of Medicine, Seoul (Korea, Republic of)

    2015-02-15

    To evaluate the effects of proteoglycan and type II collagen within articular cartilage on T1rho relaxation time of articular cartilage. This study was exempted by the institutional and animal review boards, and informed consent was not required. Twelve porcine patellae were assigned to three groups of control, trypsin-treated (proteoglycan-degraded), or collagenase-treated (collagen-degraded). The T1rho images were obtained with a 3 tesla magnetic resonance imaging scanner with a single loop coil. Statistical differences were detected by analysis of variance to evaluate the effects of the enzyme on T1rho relaxation time. Safranin-O was used to stain proteoglycan in the articular cartilage and immunohistochemical staining was performed for type II collagen. Mean T1rho values of the control, trypsin-treated, and collagenase-treated groups were 37.72 +/- 5.82, 57.53 +/- 8.24, and 45.08 +/- 5.31 msec, respectively (p < 0.001). Histology confirmed a loss of proteoglycan and type II collagen in the trypsin- and collagenase-treated groups. Degradation of proteoglycans and collagen fibers in the articular cartilage increased the articular cartilage T1rho value.

  15. Excited state dynamics in SO2. I. Bound state relaxation studied by time-resolved photoelectron-photoion coincidence spectroscopy.

    Science.gov (United States)

    Wilkinson, Iain; Boguslavskiy, Andrey E; Mikosch, Jochen; Bertrand, Julien B; Wörner, Hans Jakob; Villeneuve, David M; Spanner, Michael; Patchkovskii, Serguei; Stolow, Albert

    2014-05-28

    The excited state dynamics of isolated sulfur dioxide molecules have been investigated using the time-resolved photoelectron spectroscopy and time-resolved photoelectron-photoion coincidence techniques. Excited state wavepackets were prepared in the spectroscopically complex, electronically mixed (B̃)(1)B1/(Ã)(1)A2, Clements manifold following broadband excitation at a range of photon energies between 4.03 eV and 4.28 eV (308 nm and 290 nm, respectively). The resulting wavepacket dynamics were monitored using a multiphoton ionisation probe. The extensive literature associated with the Clements bands has been summarised and a detailed time domain description of the ultrafast relaxation pathways occurring from the optically bright (B̃)(1)B1 diabatic state is presented. Signatures of the oscillatory motion on the (B̃)(1)B1/(Ã)(1)A2 lower adiabatic surface responsible for the Clements band structure were observed. The recorded spectra also indicate that a component of the excited state wavepacket undergoes intersystem crossing from the Clements manifold to the underlying triplet states on a sub-picosecond time scale. Photoelectron signal growth time constants have been predominantly associated with intersystem crossing to the (c̃)(3)B2 state and were measured to vary between 750 and 150 fs over the implemented pump photon energy range. Additionally, pump beam intensity studies were performed. These experiments highlighted parallel relaxation processes that occurred at the one- and two-pump-photon levels of excitation on similar time scales, obscuring the Clements band dynamics when high pump beam intensities were implemented. Hence, the Clements band dynamics may be difficult to disentangle from higher order processes when ultrashort laser pulses and less-differential probe techniques are implemented.

  16. Time-varying effect modeling with longitudinal data truncated by death: conditional models, interpretations, and inference.

    Science.gov (United States)

    Estes, Jason P; Nguyen, Danh V; Dalrymple, Lorien S; Mu, Yi; Şentürk, Damla

    2016-05-20

    Recent studies found that infection-related hospitalization was associated with increased risk of cardiovascular (CV) events, such as myocardial infarction and stroke in the dialysis population. In this work, we develop time-varying effects modeling tools in order to examine the CV outcome risk trajectories during the time periods before and after an initial infection-related hospitalization. For this, we propose partly conditional and fully conditional partially linear generalized varying coefficient models (PL-GVCMs) for modeling time-varying effects in longitudinal data with substantial follow-up truncation by death. Unconditional models that implicitly target an immortal population is not a relevant target of inference in applications involving a population with high mortality, like the dialysis population. A partly conditional model characterizes the outcome trajectory for the dynamic cohort of survivors, where each point in the longitudinal trajectory represents a snapshot of the population relationships among subjects who are alive at that time point. In contrast, a fully conditional approach models the time-varying effects of the population stratified by the actual time of death, where the mean response characterizes individual trends in each cohort stratum. We compare and contrast partly and fully conditional PL-GVCMs in our aforementioned application using hospitalization data from the United States Renal Data System. For inference, we develop generalized likelihood ratio tests. Simulation studies examine the efficacy of estimation and inference procedures.

  17. The relative efficiency of time-to-threshold and rate of change in longitudinal data.

    Science.gov (United States)

    Donohue, M C; Gamst, A C; Thomas, R G; Xu, R; Beckett, L; Petersen, R C; Weiner, M W; Aisen, P

    2011-09-01

    Randomized, placebo-controlled trials often use time-to-event as the primary endpoint, even when a continuous measure of disease severity is available. We compare the power to detect a treatment effect using either rate of change, as estimated by linear models of longitudinal continuous data, or time-to-event estimated by Cox proportional hazards models. We propose an analytic inflation factor for comparing the two types of analyses assuming that the time-to-event can be expressed as a time-to-threshold of the continuous measure. We conduct simulations based on a publicly available Alzheimer's disease data set in which the time-to-event is algorithmically defined based on a battery of assessments. A Cox proportional hazards model of the time-to-event endpoint is compared to a linear model of a single assessment from the battery. The simulations also explore the impact of baseline covariates in either analysis.

  18. Longitudinal Outcomes of Start Time Delay on Sleep, Behavior, and Achievement in High School

    Science.gov (United States)

    Thacher, Pamela V.; Onyper, Serge V.

    2016-01-01

    Study Objectives: To establish whether sleep, health, mood, behavior, and academics improved after a 45-minute delay in high school start time, and whether changes persisted longitudinally. Methods: We collected data from school records and student self-report across a number of domains at baseline (May 2012) and at two follow-up time points (November 2012 and May 2013), at a public high school in upstate New York. Students enrolled during academic years (AY) 2011–2012 and 2012–2013 completed the Pittsburgh Sleep Quality Index; the DASS-21; the “Owl-Lark” Scale; the Daytime Sleepiness Index; and a brief self-report of health. Reports from school records regarding attendance, tardiness, disciplinary violations, and academic performance were collected for AY 2010–2011 through 2013–2014. Results: Students delayed but did not extend their sleep period; we found lasting improvements in tardiness and disciplinary violations after the start-time delay, but no changes to other variables. At the first follow-up, students reported 20 minutes longer sleep, driven by later rise times and stable bed times. At the second follow-up, students maintained later rise times but delayed bedtimes, returning total sleep to baseline levels. A delay in rise time, paralleling the delay in the start time that occurred, resulted in less tardiness and decreased disciplinary incidents, but larger improvements to sleep patterns may be necessary to affect health, attendance, sleepiness, and academic performance. Conclusions: Later start times improved tardiness and disciplinary issues at this school district. A delay in start time may be a necessary but not sufficient means to increase sleep time and may depend on preexisting individual differences. Commentary: A commentary on this article appears in this issue on page 267. Citation: Thacher PV, Onyper SV. Longitudinal outcomes of start time delay on sleep, behavior, and achievement in high school. SLEEP 2016;39(2):271–281. PMID

  19. Engineering estimation of time-dependent deformation characteristics as bending moment relaxation and released unfolding motion of creased paperboard

    Science.gov (United States)

    Nagasawa, Sh

    2017-02-01

    Paperboards are recognized to be important raw materials for packaging industry due to their advantages such as high strength-to-weight ratio, recyclability. Regarding the development of advanced packaging materials and the requirement of smart formed products, a study of sheet’s response behaviour is necessary for expanding the advanced converting industry. After introducing a couple of past research works concerned crease technologies, a fundamental mechanisms of crease deformation is reviewed using the scoring depth and the folding angle of a paperboard. Since one of important forming characteristics is a time-dependent stress relaxation or time-delayed strain during a fold/unfold process, the author’s experimental approaches for estimating a short term (less than 10 seconds) dynamic deformation behaviour of creased paperboard are discussed.

  20. Spin and Time-Reversal Symmetries of Superconducting Electron Pairs Probed by the Muon Spin Rotation and Relaxation Technique

    Science.gov (United States)

    Higemoto, Wataru; Aoki, Yuji; MacLaughlin, Douglas E.

    2016-09-01

    Unconventional superconductivity based on the strong correlation of electrons is one of the central issues of solid-state physics. Although many experimental techniques are appropriate for investigating unconventional superconductivity, a complete perspective has not been established yet. The symmetries of electron pairs are crucial properties for understanding the essential state of unconventional superconductivity. In this review, we discuss the investigation of the time-reversal and spin symmetries of superconducting electron pairs using the muon spin rotation and relaxation technique. By detecting a spontaneous magnetic field under zero field and/or the temperature dependence of the muon Knight shift in the superconducting phase, the time-reversal symmetry and spin parity of electron pairs have been determined for several unconventional superconductors.

  1. Concentration Regimes of Biopolymers Xanthan, Tara, and Clairana, Comparing Dynamic Light Scattering and Distribution of Relaxation Time

    Science.gov (United States)

    Oliveira, Patrícia D.; Michel, Ricardo C.; McBride, Alan J. A.; Moreira, Angelita S.; Lomba, Rosana F. T.; Vendruscolo, Claire T.

    2013-01-01

    The aim of this work was to evaluate the utilization of analysis of the distribution of relaxation time (DRT) using a dynamic light back-scattering technique as alternative method for the determination of the concentration regimes in aqueous solutions of biopolymers (xanthan, clairana and tara gums) by an analysis of the overlap (c*) and aggregation (c**) concentrations. The diffusion coefficients were obtained over a range of concentrations for each biopolymer using two methods. The first method analysed the behaviour of the diffusion coefficient as a function of the concentration of the gum solution. This method is based on the analysis of the diffusion coefficient versus the concentration curve. Using the slope of the curves, it was possible to determine the c* and c** for xanthan and tara gum. However, it was not possible to determine the concentration regimes for clairana using this method. The second method was based on an analysis of the DRTs, which showed different numbers of relaxation modes. It was observed that the concentrations at which the number of modes changed corresponded to the c* and c**. Thus, the DRT technique provided an alternative method for the determination of the critical concentrations of biopolymers. PMID:23671627

  2. Master equation for the Unruh-DeWitt detector and the universal relaxation time in de Sitter space

    CERN Document Server

    Fukuma, Masafumi; Sugishita, Sotaro

    2013-01-01

    de Sitter space is known to have a thermal character. This can be best seen by an Unruh-DeWitt detector which stays in the Poincare patch and interacts with a scalar field in the Bunch-Davies vacuum. However, since the Bunch-Davies vacuum is the ground state only at the infinite past, if the scalar field starts in the ground state at a finite past, an Unruh-DeWitt detector then will feel as if it is in a medium that is not in thermodynamic equilibrium and that undergoes a relaxation to the equilibrium corresponding to the Bunch-Davies vacuum. In this paper, we first develop a general framework to treat such circumstances and write down the master equation which completely describes the finite time evolution of the density matrix of an Unruh-DeWitt detector in arbitrary background geometry. We then apply this framework to an ideal detector in de Sitter space which can get adjusted to its environment instantaneously, and show that the density distribution of the detector certainly exhibits a relaxation to the G...

  3. Slow Dynamics in Berea Sandstone: a Non-logarithmic Relaxation at Early Times Revealed by Dynamic Acousto-Elasticity.

    Science.gov (United States)

    Riviere, J. V.; Shokouhi, P.; Marone, C.; Elsworth, D.; Guyer, R. A.; Johnson, P. A.

    2015-12-01

    We study nonlinear elastic/acoustic phenomena in rocks at the laboratory scale, with the goal of understanding observations at crustal scales, for instance during strong ground motion and earthquake slip processes. In particular, a long-term goal is to relate microstructure of rocks/gouge to nonlinear acoustic properties. A dynamic perturbation with modest (i.e. acoustic) strain amplitude (10-6 Berea sandstone to explore short-term relaxation, down to 10-4s (DAE is the dynamic equivalent of measuring acoustic velocity as a function of applied pressure). We find that early recovery does not follow a logarithmic law, while some earlier studies based on resonance techniques and at times larger than 1s do exhibit log(t)-recovery. From this non-log(t) dataset, we extract a spectrum of relaxation rates and discuss the potential relation between characteristic rates and rock microstructure. We also discuss the possible links between transient elastic softening and transient increase in permeability due to dynamic perturbation.

  4. Concentration regimes of biopolymers xanthan, tara, and clairana, comparing dynamic light scattering and distribution of relaxation time.

    Directory of Open Access Journals (Sweden)

    Patrícia D Oliveira

    Full Text Available The aim of this work was to evaluate the utilization of analysis of the distribution of relaxation time (DRT using a dynamic light back-scattering technique as alternative method for the determination of the concentration regimes in aqueous solutions of biopolymers (xanthan, clairana and tara gums by an analysis of the overlap (c* and aggregation (c** concentrations. The diffusion coefficients were obtained over a range of concentrations for each biopolymer using two methods. The first method analysed the behaviour of the diffusion coefficient as a function of the concentration of the gum solution. This method is based on the analysis of the diffusion coefficient versus the concentration curve. Using the slope of the curves, it was possible to determine the c* and c** for xanthan and tara gum. However, it was not possible to determine the concentration regimes for clairana using this method. The second method was based on an analysis of the DRTs, which showed different numbers of relaxation modes. It was observed that the concentrations at which the number of modes changed corresponded to the c* and c**. Thus, the DRT technique provided an alternative method for the determination of the critical concentrations of biopolymers.

  5. Molecular relaxation in supersonic free jets of N2 and CH4 from stimulated Raman spectroscopy and time-of-flight measurements

    OpenAIRE

    Abad, Laura; Bermejo, Dionisio; Herrero, Víctor J.; Santos, J.; Tanarro, Isabel

    1997-01-01

    The relaxation of the energy stored in the translational and rotational degrees of freedom of N2 and CH4 in the course of free jet expansions has been experimentally studied. Rotational temperatures along the expansion axis were obtained by means of stimulated Raman spectroscopy, and terminal flow velocities and translational temperatures were determined from supersonic beam time-of-flight measurements. From these measurements low-temperature cross sections for rotational relaxation have been...

  6. Climate change relaxes the time constraints for late-born offspring in a long-distance migrant.

    Science.gov (United States)

    Tomotani, Barbara M; Gienapp, Phillip; Beersma, Domien G M; Visser, Marcel E

    2016-09-28

    Animals in seasonal environments need to fit their annual-cycle stages, such as moult and migration, in a tight schedule. Climate change affects the phenology of organisms and causes advancements in timing of these annual-cycle stages but not necessarily at the same rates. For migratory birds, this can lead to more severe or more relaxed time constraints in the time from fledging to migration, depending on the relative shifts of the different stages. We tested how a shift in hatch date, which has advanced due to climate change, impacts the organization of the birds' whole annual cycle. We experimentally advanced and delayed the hatch date of pied flycatcher chicks in the field and then measured the timing of their annual-cycle stages in a controlled laboratory environment. Hatch date affected the timing of moult and pre-migratory fattening, but not migration. Early-born birds hence had a longer time to fatten up than late-born ones; the latter reduced their interval between onset of fattening and migration to be able to migrate at the same time as the early-born birds. This difference in time constraints for early- and late-born individuals may explain why early-born offspring have a higher probability to recruit as a breeding bird. Climate change-associated advancements of avian egg-lay dates, which in turn advances hatch dates, can thus reduce the negative fitness consequences of reproducing late, thereby reducing the selection for early egg-laying migratory birds.

  7. Physical Activity and Spatial Differences in Medial Knee T1rho and T2 Relaxation Times in Knee Osteoarthritis

    Science.gov (United States)

    KUMAR, DEEPAK; SOUZA, RICHARD B.; SINGH, JUSTIN; CALIXTO, NATHANIEL E.; NARDO, LORENZO; LINK, THOMAS M.; LI, XIAOJUAN; MAJUMDAR, SHARMILA

    2015-01-01

    STUDY DESIGN Cross-sectional. OBJECTIVES To investigate the association between knee loading–related osteoarthritis (OA) risk factors (obesity, malalignment, and physical activity) and medial knee laminar (superficial and deep) T1rho and T2 relaxation times. BACKGROUND The interaction of various modifiable loading-related knee risk factors and cartilage health in knee OA is currently not well known. METHODS Participants with and without knee OA (n = 151) underwent magnetic resonance imaging at 3 T for superficial and deep cartilage T1rho and T2 magnetic resonance relaxation times in the medial femur (MF) and medial tibia (MT). Other variables included radiographic Kellgren-Lawrence (KL) grade, alignment, pain and symptoms using the Knee injury and Osteoarthritis Outcome Score, and physical activity using the International Physical Activity Questionnaire (IPAQ). Individuals with a KL grade of 4 were excluded. Group differences were calculated using 1-way analysis of variance, adjusting for age and body mass index. Linear regression models were created with age, sex, body mass index, alignment, KL grade, and the IPAQ scores to predict the laminar T1rho and T2 times. RESULTS Total IPAQ scores were the only significant predictors among the loading-related variables for superficial MF T1rho (P = .005), deep MT T1rho (P = .026), and superficial MF T2 (P = .049). Additionally, the KL grade predicted the superficial MF T1rho (P = .023) and deep MT T1rho (P = .022). CONCLUSION Higher physical activity levels and worse radiographic severity of knee OA, but not obesity or alignment, were associated with worse cartilage composition. PMID:25353261

  8. More relaxed condition for dynamics of discrete time delayed Hopfield neural networks

    Institute of Scientific and Technical Information of China (English)

    Zhang Qiang

    2008-01-01

    The dynamics of discrete time delayed Hopfield neural networks is investigated.By using a difference inequality combining with the linear matrix inequality,a sufficient condition ensuring global exponential stability of the unique equilibrium point of the networks is found.The result obtained holds not only for constant delay but also for time-varying delays.

  9. Multi-relaxation-time Lattice Boltzman model for uniform-shear flow over a rotating circular cylinder

    Directory of Open Access Journals (Sweden)

    Nemati Hasan

    2011-01-01

    Full Text Available A numerical investigation of the two-dimensional laminar flow and heat transfer a rotating circular cylinder with uniform planar shear, where the free-stream velocity varies linearly across the cylinder using Multi-Relaxation-Time Lattice Boltzmann method is conducted. The effects of variation of Reynolds number, rotational speed ratio at shear rate 0.1, blockage ratio 0.1 and Prandtl number 0.71 are studied. The Reynolds number changing from 50 to 160 for three rotational speed ratios of 0, 0.5, 1 is investigated. Results show that flow and heat transfer depends significantly on the rotational speed ratio as well as the Reynolds number. The effect of Reynolds number on the vortex-shedding frequency and period-surface Nusselt numbers is overall very strong compared with rotational speed ratio. Flow and heat conditions characteristics such as lift and drag coefficients, Strouhal number and Nusselt numbers are studied.

  10. Knee muscle strength correlates with joint cartilage T2 relaxation time in young participants with risk factors for osteoarthritis.

    Science.gov (United States)

    Macías-Hernández, Salvador Israel; Miranda-Duarte, Antonio; Ramírez-Mora, Isabel; Cortés-González, Socorro; Morones-Alba, Juan Daniel; Olascoaga-Gómez, Andrea; Coronado-Zarco, Roberto; Soria-Bastida, María de Los Angeles; Nava-Bringas, Tania Inés; Cruz-Medina, Eva

    2016-08-01

    The objective of this study is to correlate T2 relaxation time (T2RT), measured by magnetic resonance imaging (MRI) with quadriceps and hamstring strength in young participants with risk factors for knee osteoarthritis (OA). A descriptive cross-sectional study was conducted with participants between 20 and 40 years of age, without diagnosis of knee OA. Their T2 relaxation time was measured through MRI, and their muscle strength (MS) was measured with an isokinetic dynamometer. Seventy-one participants were recruited, with an average age of 28.3 ± 5.5 years; 39 (55 %) were females. Negative correlations were found between T2RT and quadriceps peak torque (QPT) in males in the femur r = -0.46 (p = 0.01), tibia r = -0.49 (p = 0.02), and patella r = -0.44 (p = 0.01). In women, correlations were found among the femur r = -0.43 (p = 0.01), tibia r = -0.61 (p = 0.01), and patella r = -0.32 (p = 0.05) and among hamstring peak torque (HPT), in the femur r = -0.46 (p = 0.01), hamstring total work (HTW) r = -0.42 (p = 0.03), and tibia r = -0.33 (p = 0.04). Linear regression models showed good capacity to predict T2RT through QPT in both genders. The present study shows that early changes in femoral, tibial, and patellar cartilage are significantly correlated with MS, mainly QPT, and that these early changes might be explained by MS, which could play an important role in pre-clinical phases of the disease.

  11. Impact of different coils on biochemical T2 and T2* relaxation time mapping of articular patella cartilage.

    Science.gov (United States)

    Pachowsky, Milena L; Trattnig, Siegfried; Apprich, Sebastian; Mauerer, Andreas; Zbyn, Stephan; Welsch, Goetz H

    2013-11-01

    The purpose of our study was to assess T2 and T2* relaxation time values of patella cartilage in healthy volunteers using three different coils at 3.0 Tesla MRI and their influence on the quantitative values. Fifteen volunteers were examined on the same 3-Tesla MR unit using three different coils: (i) a dedicated eight-channel knee phased-array coil; (ii) an eight-channel multi-purpose coil, and (iii) a one-channel 1H surface coil. T2 and T2* relaxation time measurements were prepared by a multi-echo spinecho respectively a gradient-echo sequence. A semi-automatic region-of-interest analysis was performed for patella cartilage. To allow stratification, a subregional analysis was carried out (deep-superficial cartilage layer). Statistical analysis-of-variance was performed. The mean quantitative T2 values showed statistically significant differences in all comparison combinations. The differences between the mean quantitative T2* values were slightly less pronounced than the T2 evaluation and only the comparison between (i) and (ii) showed a significant difference. The results of T2 and T2* values showed, independent of the used coil, higher values in the superficial zone compared to the deep zone (p < 0.05). Looking at the signal alterations, all coils showed clearly higher values (and thus more signal alterations as a sign of noise) in the deep layer. The validation of the reliability showed a high intra-class correlation coefficient and hence a very high plausibility (ICC was between 0.870 and 0.905 for T2 mapping and between 0.879 and 0.888 for T2* mapping). The present results demonstrate that biochemical T2 and T2* mapping is significantly dependent on the utilized coil.

  12. Native T1 Relaxation Time and Extracellular Volume Fraction as Accurate Markers of Diffuse Myocardial Fibrosis in Heart Valve Disease - Comparison With Targeted Left Ventricular Myocardial Biopsy.

    Science.gov (United States)

    Kockova, Radka; Kacer, Petr; Pirk, Jan; Maly, Jiri; Sukupova, Lucie; Sikula, Viktor; Kotrc, Martin; Barciakova, Lucia; Honsova, Eva; Maly, Marek; Kautzner, Josef; Sedmera, David; Penicka, Martin

    2016-04-25

    The aim of our study was to investigate the relationship between the cardiac magnetic resonance (CMR)-derived native T1 relaxation time and myocardial extracellular volume (ECV) fraction and the extent of diffuse myocardial fibrosis (DMF) on targeted myocardial left ventricular (LV) biopsy. The study population consisted of 40 patients (age 63±8 years, 65% male) undergoing valve and/or ascending aorta surgery for severe aortic stenosis (77.5%), root dilatation (7.5%) or valve regurgitation (15%). The T1 relaxation time was assessed in the basal interventricular septum pre- and 10-min post-contrast administration using the modified Look-Locker Inversion recovery sequence prior to surgery. LV myocardial biopsy specimen was obtained during surgery from the basal interventricular septal segment matched with the T1 mapping assessment. The percentage of myocardial collagen was quantified using picrosirius red staining. The average percentage of myocardial collagen was 22.0±14.8%. Both native T1 relaxation time with cutoff value ≥1,010 ms (sensitivity=90%, specificity=73%, area under the curve=0.82) and ECV with cutoff value ≥0.32 (sensitivity=80%, specificity=90%, area under the curve=0.85) showed high accuracy to identify severe (>30%) DMF. The native T1 relaxation time showed significant correlation with LV mass (P<0.01). Native T1 relaxation time and ECV at 10 min after contrast administration are accurate markers of DMF. (Circ J 2016; 80: 1202-1209).

  13. A Longitudinal Study of Usability in Health Care - Does Time Heal?

    DEFF Research Database (Denmark)

    Kjeldskov, Jesper; Skov, Mikael B.; Stage, Jan

    2007-01-01

    We report from a longitudinal laboratory-based usability evaluation of a health care information system. A usability evaluation was conducted with novice users when an electronic patient record system was being deployed in a large hospital. After the nurses had used the system in their daily work...... for 15 months, we repeated the evaluation. Our aim was to inquire into the nature of usability problems experienced by novice and expert users, and to see to what extend usability problems of a health care information system may or may not disappear over time, as the nurses get more familiar...... with it – if time heals poor design. On the basis of our study, we present findings on the usability of the electronic patient system as experienced by the nurses at these two different points in time and discuss implications for evaluating usability in health care....

  14. Chemical reaction, thermal relaxation time and internal material parameter effects on MHD viscoelastic fluid with internal structure using the Cattaneo-Christov heat flux equation

    Science.gov (United States)

    Khan, Sabeel M.; Hammad, M.; Sunny, D. A.

    2017-08-01

    In this article, the influence of thermal relaxation time and chemical reaction is studied on the MHD upper-convected viscoelastic fluid with internal structure using the Cattaneo-Christov heat flux equation for the first time in the literature. The flow-governing equations are formulated and are converted into their respective ordinary differential equations (ODEs) with the application of similarity functions. The resulting system of coupled nonlinear ODEs is solved along with the prescribed conditions at boundary using a finite-difference code in MATLAB. Influence of chemical reaction, thermal relaxation time and internal material parameter on the macroscopic and micropolar velocities as well as on the temperature and concentration profiles is examined along with other physical parameters ( e.g., magnetic parameter, Eckert number, Prandtl number and fluid relaxation time). The accuracy of the obtained numerical solution is shown by comparing the physical parameters of interest with particular cases of existing results in the literature.

  15. Improved differentiation between knees with cartilage lesions and controls using 7T relaxation time mapping

    Directory of Open Access Journals (Sweden)

    Cory Wyatt

    2015-10-01

    Conclusion: T1ρ imaging at 7T has been established as a viable imaging method for the differentiation of degenerated cartilage despite previous concerns over specific absorption rate and imaging time. The potential increased sensitivity of T1ρ and T2 imaging at 7T may be useful for future studies in the development of OA.

  16. Impact of neonate haematocrit variability on the longitudinal relaxation time of blood: Implications for arterial spin labelling MRI

    Directory of Open Access Journals (Sweden)

    J.B. De Vis

    2014-01-01

    Conclusion: We demonstrated a wide variability of the T1b in neonates and the implications it could have in methods relying on the actual T1b as for instance ASL. It was concluded that arterial-drawn Hct values obtained from a point-of-care device can be used to infer the T1b whereas our data did not support the use of capillary-drawn Hct for T1b correction.

  17. Estimation of divergence times in litostomatean ciliates (Ciliophora: Intramacronucleata), using Bayesian relaxed clock and 18S rRNA gene.

    Science.gov (United States)

    Vďačný, Peter

    2015-08-01

    The class Litostomatea comprises a diverse assemblage of free-living and endosymbiotic ciliates. To understand diversification dynamic of litostomateans, divergence times of their main groups were estimated with the Bayesian molecular dating, a technique allowing relaxation of molecular clock and incorporation of flexible calibration points. The class Litostomatea very likely emerged during the Cryogenian around 680 Mya. The origin of the subclass Rhynchostomatia is dated to about 415 Mya, while that of the subclass Haptoria to about 654 Mya. The order Pleurostomatida, emerging about 556 Mya, was recognized as the oldest group within the subclass Haptoria. The order Spathidiida appeared in the Paleozoic about 442 Mya. The three remaining haptorian orders evolved in the Paleozoic/Mesozoic periods: Didiniida about 419 Mya, Lacrymariida about 269 Mya, and Haptorida about 194 Mya. The subclass Trichostomatia originated from a spathidiid ancestor in the Mesozoic about 260 Mya. A further goal of this study was to investigate the impact of various settings on posterior divergence time estimates. The root placement and tree topology as well as the priors of the rate-drift model, birth-death process and nucleotide substitution rate, had no significant effect on calculation of posterior divergence time estimates. However, removal of calibration points could significantly change time estimates at some nodes.

  18. Longitudinal beta regression models for analyzing health-related quality of life scores over time

    Directory of Open Access Journals (Sweden)

    Hunger Matthias

    2012-09-01

    Full Text Available Abstract Background Health-related quality of life (HRQL has become an increasingly important outcome parameter in clinical trials and epidemiological research. HRQL scores are typically bounded at both ends of the scale and often highly skewed. Several regression techniques have been proposed to model such data in cross-sectional studies, however, methods applicable in longitudinal research are less well researched. This study examined the use of beta regression models for analyzing longitudinal HRQL data using two empirical examples with distributional features typically encountered in practice. Methods We used SF-6D utility data from a German older age cohort study and stroke-specific HRQL data from a randomized controlled trial. We described the conceptual differences between mixed and marginal beta regression models and compared both models to the commonly used linear mixed model in terms of overall fit and predictive accuracy. Results At any measurement time, the beta distribution fitted the SF-6D utility data and stroke-specific HRQL data better than the normal distribution. The mixed beta model showed better likelihood-based fit statistics than the linear mixed model and respected the boundedness of the outcome variable. However, it tended to underestimate the true mean at the upper part of the distribution. Adjusted group means from marginal beta model and linear mixed model were nearly identical but differences could be observed with respect to standard errors. Conclusions Understanding the conceptual differences between mixed and marginal beta regression models is important for their proper use in the analysis of longitudinal HRQL data. Beta regression fits the typical distribution of HRQL data better than linear mixed models, however, if focus is on estimating group mean scores rather than making individual predictions, the two methods might not differ substantially.

  19. A pseudopotential-based multiple-relaxation-time lattice Boltzmann model for multicomponent/multiphase flows

    Institute of Scientific and Technical Information of China (English)

    Zhen-Hua Chai; Tian-Shou Zhao

    2012-01-01

    In this paper,a pseudopotential-based multiplerelaxation-time lattice Boltzmann model is proposed for multicomponent/multiphase flow systems.Unlike previous models in the literature,the present model not only enables the study of multicomponent flows with different molecular weights,different viscosities and different Schmidt numbers,but also ensures that the distribution function of each component evolves on the same square lattice without invoking additional interpolations.Furthermore,the Chapman-Enskog analysis shows that the present model results in the correct hydrodynamic equations,and satisfies the indifferentiability principle.The numerical validation exercises further demonstrate that the favorable performance of the present model.

  20. Estimation of the left ventricular relaxation time constant tau requires consideration of the pressure asymptote.

    Science.gov (United States)

    Langer, S F J; Habazettl, H; Kuebler, W M; Pries, A R

    2005-01-01

    The left ventricular isovolumic pressure decay, obtained by cardiac catheterization, is widely characterized by the time constant tau of the exponential regression p(t)=Pomega+(P0-Pomega)exp(-t/tau). However, several authors prefer to prefix Pomega=0 instead of coestimating the pressure asymptote empirically; others present tau values estimated by both methods that often lead to discordant results and interpretation of lusitropic changes. The present study aims to clarify the relations between the tau estimates from both methods and to decide for the more reliable estimate. The effect of presetting a zero asymptote on the tau estimate was investigated mathematically and empirically, based on left ventricular pressure decay data from isolated ejecting rat and guinea pig hearts at different preload and during spontaneous decrease of cardiac function. Estimating tau with preset Pomega=0 always yields smaller values than the regression with empirically estimated asymptote if the latter is negative and vice versa. The sequences of tau estimates from both methods can therefore proceed in reverse direction if tau and Pomega change in opposite directions between the measurements. This is exemplified by data obtained during an increasing preload in spontaneously depressed isolated hearts. The estimation of the time constant of isovolumic pressure fall with a preset zero asymptote is heavily biased and cannot be used for comparing the lusitropic state of the heart in hemodynamic conditions with considerably altered pressure asymptotes.

  1. Timing of retinal neuronal and axonal loss in MS: a longitudinal OCT study.

    Science.gov (United States)

    Balk, Lisanne J; Cruz-Herranz, Andrés; Albrecht, Philipp; Arnow, Sam; Gelfand, Jeffrey M; Tewarie, Prejaas; Killestein, Joep; Uitdehaag, Bernard M J; Petzold, Axel; Green, Ari J

    2016-07-01

    The objective of the study was to investigate the timing of central nervous system tissue atrophy in MS by evaluating longitudinal retinal volume changes in a broadly representative cohort with disease duration across the entire arc of disease. In this longitudinal study, 135 patients with MS and 16 healthy reference subjects underwent spectral-domain optical coherence tomography (OCT) at baseline and 2 years later. Following OCT quality control, automated segmentation of the peripapillary retinal nerve fiber layer (pRNFL), macular ganglion cell-inner plexiform layer (mGCIPL) and macular inner nuclear layer (mINL) was performed. Generalized estimation equations were used to analyze longitudinal changes and associations with disease duration and clinical measures. Participants had a median disease duration at baseline of 16.4 years (range 0.1-45.4). Nearly half (44 %) of the MS patients had previously experienced MS-related optic neuritis (MSON) more than 6 months prior. The MS patients demonstrated a significant decrease over 2 years of the pRNFL (-1.1 µm, 95 % CI 1.4-0.7, p < 0.001) and mGCIPL (-1.1 µm, 95 % CI -1.4 to -0.8, p < 0.001). This thinning was most pronounced early in the course of disease. These findings were irrespective of previous episodes of MSON. No consistent pattern of change was observed for the mINL (-0.03 µm, 95 % CI -0.2 to 0.2, p = 0.795). This longitudinal study demonstrated that injury of the innermost retinal layers is found in MS and that this damage occurs most rapidly during the early stages of disease. The attenuation of atrophy with longer disease duration is suggestive of a plateau effect. These findings emphasize the importance of early intervention to prevent such injury.

  2. Adversity, time, and well-being: A longitudinal analysis of time perspective in adulthood.

    Science.gov (United States)

    Holman, E Alison; Silver, Roxane Cohen; Mogle, Jacqueline A; Scott, Stacey B

    2016-09-01

    Despite the prominence of time in influential aging theories and the ubiquity of stress across the life span, research addressing how time perspective (TP) and adversity are associated with well-being across adulthood is rare. Examining the role of TP in coping with life events over the life span would be best accomplished after large-scale population-based exposure to a specific event, with repeated assessments to examine within- and between-person differences over time. A national sample aged 18-91 years (N = 722, M = 49.4 years) was followed for 3 years after the September 11, 2001 (9/11) terrorist attacks. Respondents completed assessments of 9/11-related television (TV) exposure 9-21 days after the attacks, temporal disintegration 2 months post-9/11, and TP, ongoing stress, and well-being at 12, 24, and 36 months post-9/11. Results provided support for measurement invariance of TP across time and across age. Early 9/11-related TV exposure was significantly associated with greater temporal disintegration. Temporal disintegration and ongoing stress, in turn, were associated with between- and within-person variation in past TP. This effect was qualified by an age interaction that indicated a stronger relationship between ongoing stress and past TP for younger compared with older adults. Past and future TP were significantly and independently related to individual differences and within-person variation in psychological well-being, regardless of age. Future work should incorporate adversity as an important correlate of TP across adulthood. (PsycINFO Database Record

  3. The search for negative amplitude components in quasi-continuous distributions of relaxation times: the example of 1H magnetization exchange in articular cartilage and hydrated collagen

    Science.gov (United States)

    Fantazzini, Paola; Galassi, Francesca; Bortolotti, Villiam; Brown, Robert J. S.; Vittur, Franco

    2011-06-01

    When inverting nuclear magnetic resonance relaxation data in order to obtain quasi-continuous distributions of relaxation times for fluids in porous media, it is common practice to impose a non-negative (NN) constraint on the distributions. While this approach can be useful in reducing the effects of data distortion and/or preventing wild oscillations in the distributions, it may give misleading results in the presence of real negative amplitude components. Here, some examples of valid negative components for articular cartilage and hydrated collagen are given. Articular cartilage is a connective tissue, consisting mainly of collagen, proteoglycans and water, which can be considered, in many aspects, as a porous medium. Separate T1 relaxation data are obtained for low-mobility ('solid') macromolecular 1H and for higher-mobility ('liquid') 1H by the separation of these components in free induction decays, with α denoting the solid/liquid 1H ratio. When quasi-continuous distributions of relaxation times (T1) of the solid and liquid signal components of cartilage or collagen are computed from experimental relaxation data without imposing the usual NN constraint, valid negative peaks may appear. The features of the distributions, in particular negative peaks, and the fact that peaks at longer times for macromolecular and water protons are at essentially the same T1, are interpreted as the result of a magnetization exchange between these two spin pools. For the only-slightly-hydrated collagen samples, with α>1, the exchange leads to small negative peaks at short T1 times for the macromolecular component. However, for the cartilage, with substantial hydration or for a strongly hydrated collagen sample, both with αLt1, the behavior is reversed, with a negative peak for water at short times. The validity of a negative peak may be accepted (dismissed) by a high (low) cost of NN in error of fit. Computed distributions for simulated data using observed signal

  4. Hyaline articular cartilage: relaxation times, pulse-sequence parameters and MR appearance at 1.5 T

    Energy Technology Data Exchange (ETDEWEB)

    Chalkias, S.M. [Dept. of Radiology, A.H.E.P.A. General Hospital of the Aristotelian Univ., Thessaloniki (Greece); Pozzi-Mucelli, R.S. [Dept. of Radiology, Univ. of Trieste (Italy); Pozzi-Mucelli, M. [Orthopaedic Clinic, Univ. of Trieste (Italy); Frezza, F. [Dept. of Radiology, Univ. of Trieste (Italy); Longo, R. [Dept. of Radiology, Univ. of Trieste (Italy)

    1994-08-01

    In order to optimize the parameters for the best visualization of the internal architecture of the hyaline articular cartilage a study both ex vivo and in vivo was performed. Accurate T1 and T2 relaxation times of articular cartilage were obtained with a particular mixed sequence and then used for the creation of isocontrast intensity graphs. These graphs subsequently allowed in all pulse sequences (spin echo, SE and gradient echo, GRE) the best combination of repetition time (TR), echo time (TE) and flip angle (FA) for optimization of signal differences between MR cartilage zones. For SE sequences maximum contrast between cartilage zones can be obtained by using a long TR (> 1,500 ms) with a short TE (< 30 ms), whereas for GRE sequences maximum contrast is obtained with the shortest TE (< 15 ms) combined with a relatively long TR (> 400 ms) and an FA greater than 40 . A trilaminar appearance was demonstrated with a superficial and deep hypointense zone in all sequences and an intermediate zone that was moderately hyperintense on SE T1-weighted images, slightly more hyperintense on proton density Rho and SE T2-weighted images and even more hyperintense on GRE images. (orig.)

  5. Social Activity and Cognitive Functioning Over Time: A Coordinated Analysis of Four Longitudinal Studies

    Directory of Open Access Journals (Sweden)

    Cassandra L. Brown

    2012-01-01

    Full Text Available Social activity is typically viewed as part of an engaged lifestyle that may help mitigate the deleterious effects of advanced age on cognitive function. As such, social activity has been examined in relation to cognitive abilities later in life. However, longitudinal evidence for this hypothesis thus far remains inconclusive. The current study sought to clarify the relationship between social activity and cognitive function over time using a coordinated data analysis approach across four longitudinal studies. A series of multilevel growth models with social activity included as a covariate is presented. Four domains of cognitive function were assessed: reasoning, memory, fluency, and semantic knowledge. Results suggest that baseline social activity is related to some, but not all, cognitive functions. Baseline social activity levels failed to predict rate of decline in most cognitive abilities. Changes in social activity were not consistently associated with cognitive functioning. Our findings do not provide consistent evidence that changes in social activity correspond to immediate benefits in cognitive functioning, except perhaps for verbal fluency.

  6. Modeling Intensive Longitudinal Data With Mixtures of Nonparametric Trajectories and Time-Varying Effects

    Science.gov (United States)

    Dziak, John J.; Li, Runze; Tan, Xianming; Shiffman, Saul; Shiyko, Mariya P.

    2015-01-01

    Behavioral scientists increasingly collect intensive longitudinal data (ILD), in which phenomena are measured at high frequency and in real time. In many such studies, it is of interest to describe the pattern of change over time in important variables as well as the changing nature of the relationship between variables. Individuals' trajectories on variables of interest may be far from linear, and the predictive relationship between variables of interest and related covariates may also change over time in a nonlinear way. Time-varying effect models (TVEMs; see Tan, Shiyko, Li, Li, & Dierker, 2012) address these needs by allowing regression coefficients to be smooth, nonlinear functions of time rather than constants. However, it is possible that not only observed covariates but also unknown, latent variables may be related to the outcome. That is, regression coefficients may change over time and also vary for different kinds of individuals. Therefore, we describe a finite mixture version of TVEM for situations in which the population is heterogeneous and in which a single trajectory would conceal important, inter-individual differences. This extended approach, MixTVEM, combines finite mixture modeling with non- or semi-parametric regression modeling, in order to describe a complex pattern of change over time for distinct latent classes of individuals. The usefulness of the method is demonstrated in an empirical example from a smoking cessation study. We provide a versatile SAS macro and R function for fitting MixTVEMs. PMID:26390169

  7. Simulations of Bingham plastic flows with the multiple-relaxation-time lattice Boltzmann model

    Science.gov (United States)

    Chen, SongGui; Sun, QiCheng; Jin, Feng; Liu, JianGuo

    2014-03-01

    Fresh cement mortar is a type of workable paste, which can be well approximated as a Bingham plastic and whose flow behavior is of major concern in engineering. In this paper, Papanastasiou's model for Bingham fluids is solved by using the multiplerelaxation-time lattice Boltzmann model (MRT-LB). Analysis of the stress growth exponent m in Bingham fluid flow simulations shows that Papanastasiou's model provides a good approximation of realistic Bingham plastics for values of m > 108. For lower values of m, Papanastasiou's model is valid for fluids between Bingham and Newtonian fluids. The MRT-LB model is validated by two benchmark problems: 2D steady Poiseuille flows and lid-driven cavity flows. Comparing the numerical results of the velocity distributions with corresponding analytical solutions shows that the MRT-LB model is appropriate for studying Bingham fluids while also providing better numerical stability. We further apply the MRT-LB model to simulate flow through a sudden expansion channel and the flow surrounding a round particle. Besides the rich flow structures obtained in this work, the dynamics fluid force on the round particle is calculated. Results show that both the Reynolds number Re and the Bingham number Bn affect the drag coefficients C D , and a drag coefficient with Re and Bn being taken into account is proposed. The relationship of Bn and the ratio of unyielded zone thickness to particle diameter is also analyzed. Finally, the Bingham fluid flowing around a set of randomly dispersed particles is simulated to obtain the apparent viscosity and velocity fields. These results help simulation of fresh concrete flowing in porous media.

  8. sup 31 P spin-lattice relaxation time measurements in biological systems; Heart, liver, kidney and erythrocytes of rat

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, Eiji; Maeda, Munehiro; Kuki, Satoru; Tsukamoto, Kenji; Kawakami, Tsuyoshi; Seo, Yoshiteru; Murakami, Masataka; Watari, Hiroshi (National Inst. for Physiological Sciences, Okazaki, Aichi (Japan))

    1989-08-01

    Spin-lattice relaxation time (T{sub 1}) of phosphorus compounds in the perfused heart, liver, kidney and erythrocytes of rats were measured by the DESPOT (Driven-equilibrium single-pulse observation of T{sub 1}) method at 8.45 T. This method is a rapid and accurate technique for the measurement of T{sub 1} values. T{sub 1} values of phosphomonoesters (PME), 2, 3-diphosphoglycerate (DPG), inorganic phosphate (Pi), phosphodiesters (PDE), phosphocreatine (PCr) and three phosphates of ATP were ranged from 0.15 {plus minus} 0.02 sec (beta-ATP in the liver) to 8.5 {plus minus} 1.6 sec (PDE in the kidney). T{sub 1} value of beta-ATP in the liver was 1/4-1/5 of those in the mandibular gland, heart, erythrocytes and kidney. T{sub 1} values obtained from biological materials are useful for selecting the optimal pulse repetition times and pulse angles to maximize the signal-to-noise ratio of {sup 13}P spectra, and for correcting distortions of signal intensities in the spectra. (author).

  9. Magnetic Properties of Transverse Ising Model under a Time Oscillating Longitudinal Field

    Institute of Scientific and Technical Information of China (English)

    SHI Xiao-Ling; WANG Li; WEI Guo-Zhu

    2011-01-01

    A transverse Ising spin system, in the presence of time-dependent longitudinal field, is studied by the effective-field theory (EFT). The effective-field equations of motion of the average magnetization are given for the simple cubic lattice (Z = 6) and the honeycomb lattice (Z = 3). The Liapunov exponent λ is calculated for discussing the stability of the magnetization and it is used to determine the phase boundary. The dynamic phase transition diagrams in ho/ZJ - Γ/ZJ plane and in ho/ZJ - T/ZJ plane have been drawn, and there is no dynamical tricritical point on the dynamic phase transition boundary. The effect of the thermal fluctuations upon the dynamic phase boundary has been discussed.

  10. Time domain System Identification of Longitudinal Dynamics of Single Rotor Model Helicopter using SIDPAC

    Directory of Open Access Journals (Sweden)

    Arbab Nighat Khizer

    2015-01-01

    Full Text Available This paper presents a time-domain approach for identification of longitudinal dynamics of single rotor model helicopter. A frequency sweep excitation input signal is applied for hover flying mode widely used for space state linearized model. A fully automated programmed flight test method provides high quality flight data for system identification using the computer controlled flight simulator X-plane©. The flight test data were recorded, analyzed and reduced using the SIDPAC (System Identification Programs for Air Craft toolbox for MATLAB, resulting in an aerodynamic model of single rotor helicopter. Finally, the identified model of single rotor helicopter is validated on Raptor 30-class model helicopter at hover showing the reliability of proposed approach

  11. Acoustic Longitudinal Field NIF Optic Feature Detection Map Using Time-Reversal & MUSIC

    Energy Technology Data Exchange (ETDEWEB)

    Lehman, S K

    2006-02-09

    We developed an ultrasonic longitudinal field time-reversal and MUltiple SIgnal Classification (MUSIC) based detection algorithm for identifying and mapping flaws in fused silica NIF optics. The algorithm requires a fully multistatic data set, that is one with multiple, independently operated, spatially diverse transducers, each transmitter of which, in succession, launches a pulse into the optic and the scattered signal measured and recorded at every receiver. We have successfully localized engineered ''defects'' larger than 1 mm in an optic. We confirmed detection and localization of 3 mm and 5 mm features in experimental data, and a 0.5 mm in simulated data with sufficiently high signal-to-noise ratio. We present the theory, experimental results, and simulated results.

  12. Investigation of the longitudinal relaxation rate of blood after gadobenate dimeglumine administration: sequence optimization, dynamic acquisition, and clinical impact for contrast-enhanced MR angiography of the carotid arteries.

    Science.gov (United States)

    Neira, Cristina; Anzidei, Michele; Napoli, Alessandro; Kirchin, Miles A; Cavallo Marincola, Beatrice; Zaccagna, Fulvio; Catalano, Carlo; Passariello, Roberto; Tedoldi, Fabio

    2011-12-01

    To optimize the image acquisition parameters for improved steady-state (SS) contrast-enhanced magnetic resonance angiography (CE-MRA) of the carotid arteries with gadobenate dimeglumine. An inversion recovery fast low-angle shot (IR-FLASH) sequence for ultrafast determination of the longitudinal relaxation rate R1 was first optimized on phantoms and tested against a routine variable repetition time (TR) spin echo sequence used as reference standard. Different combinations of flip angle (FA, between 6 and 14 degrees) and inversion time (between 134 and 9000 milliseconds) were evaluated to achieve the best trade off between speed and accuracy. The optimized sequence was thereafter used in vivo in 5 subjects to determine the time evolution of blood R1 at 1.5 T after administration of gadobenate dimeglumine at 0.1 mmol/kg bodyweight. An optimal FA for angiographic measurement was thereafter derived from the Ernst equation based on experimental values of R1 previously determined in vivo. Finally, steady-state CE-MRA examinations were performed in 20 subjects to evaluate the improved contrast achieved after optimization of the FA for maximal blood signal enhancement. An ultrafast IR-FLASH sequence with a flip angle of 8 degrees and a properly defined set of inversion time values was shown to give in vitro R1 determinations that were in good agreement with those obtained using a routine, time consuming, variable-TR spin echo sequence. The use of this ultrafast IR-FLASH sequence in vivo allowed the blood signal behavior in the carotid arteries after gadobenate dimeglumine administration to be monitored. Using this sequence, the R1 decreased from 8.7±0.96 s⁻¹ at 30 seconds after injection to 3.8±0.24 s⁻¹ at 10 minutes after injection. Based on these data for R1, the optimal FA for SS CE-MRA was calculated to be 18 degrees for a gradient echo acquisition protocol with TR=7.5 milliseconds, when gadobenate dimeglumine is used. Significantly higher blood signal to noise

  13. Numerical simulation of convection and heat transfer in Czochralski crystal growth by multiple-relaxation-time LBM

    Science.gov (United States)

    Liu, Ding; Huang, Weichao; Zhang, Ni

    2017-07-01

    A two-dimensional axisymmetric swirling model based on the lattice Boltzmann method (LBM) in a pseudo Cartesian coordinate system is posited to simulate Czochralski (Cz) crystal growth in this paper. Specifically, the multiple-relaxation-time LBM (MRT-LBM) combined with the finite difference method (FDM) is used to analyze the melt convection and heat transfer in the process of Cz crystal growth. An incompressible axisymmetric swirling MRT-LB D2Q9 model is applied to solve for the axial and radial velocities by inserting thermal buoyancy and rotational inertial force into the two-dimensional lattice Boltzmann equation. In addition, the melt temperature and the azimuthal velocity are solved by MRT-LB D2Q5 models, and the crystal temperature is solved by FDM. The comparison results of stream functions values of different methods demonstrate that our hybrid model can be used to simulate the fluid-thermal coupling in the axisymmetric swirling model correctly and effectively. Furthermore, numerical simulations of melt convection and heat transfer are conducted under the conditions of high Grashof (Gr) numbers, within the range of 105 ˜ 107, and different high Reynolds (Re) numbers. The experimental results show our hybrid model can obtain the exact solution of complex crystal-growth models and analyze the fluid-thermal coupling effectively under the combined action of natural convection and forced convection.

  14. Numerical simulation of convection and heat transfer in Czochralski crystal growth by multiple-relaxation-time LBM

    Directory of Open Access Journals (Sweden)

    Ding Liu

    2017-07-01

    Full Text Available A two-dimensional axisymmetric swirling model based on the lattice Boltzmann method (LBM in a pseudo Cartesian coordinate system is posited to simulate Czochralski (Cz crystal growth in this paper. Specifically, the multiple-relaxation-time LBM (MRT-LBM combined with the finite difference method (FDM is used to analyze the melt convection and heat transfer in the process of Cz crystal growth. An incompressible axisymmetric swirling MRT-LB D2Q9 model is applied to solve for the axial and radial velocities by inserting thermal buoyancy and rotational inertial force into the two-dimensional lattice Boltzmann equation. In addition, the melt temperature and the azimuthal velocity are solved by MRT-LB D2Q5 models, and the crystal temperature is solved by FDM. The comparison results of stream functions values of different methods demonstrate that our hybrid model can be used to simulate the fluid-thermal coupling in the axisymmetric swirling model correctly and effectively. Furthermore, numerical simulations of melt convection and heat transfer are conducted under the conditions of high Grashof (Gr numbers, within the range of 105 ∼ 107, and different high Reynolds (Re numbers. The experimental results show our hybrid model can obtain the exact solution of complex crystal-growth models and analyze the fluid-thermal coupling effectively under the combined action of natural convection and forced convection.

  15. Chain Dynamics, Relaxation Times, and Conductivities of Bithiophene--Acene Copolymers Measured Using High Frequency Saturation Transfer EPR.

    Science.gov (United States)

    Fraind, Alicia M; Ryzhkov, Lev R; Tovar, John D

    2016-02-11

    We present a study to probe the formation of localized aromatic sextets and their effects on the charge transport properties in polymers with acene cores. Bithiophene-acene copolymers containing benzene, naphthalene, or anthracene as acene cores were synthesized using Yamamoto polymerization. Drop-casted polymer films were chemically doped and analyzed using high frequency saturation transfer EPR (HF ST-EPR), a method which has proven useful in the study of conducting polymers. The spin-spin and spin-lattice relaxation times were determined for these polymers at low temperatures (4 to 20 K) and used to obtain inter- and intrachain spin diffusion rates and conductivities. Similar interchain spin diffusion rates were seen across all polymer systems; however, anthracene containing polymer poly(hexylTTATT) was found to have the largest intrachain spin diffusion rate. The poly(hexylTTATT) intrachain spin diffusion rate may be artificially high if the anthracene ring restricts the diffusion of spin to the hexylated quaterthiophene segment in poly(hexylTTATT) whereas the spins diffuse through the acene cores in the benzene and naphthalene derivatives. Alternatively, as both the spin diffusion rates and conductivities vary unpredictably with temperature, it is possible that the π-electron localization previously seen in the anthracene core could be relieved at lower temperatures.

  16. High homogeneity B(1) 30.2 MHz Nuclear Magnetic Resonance Probe for off-resonance relaxation times measurements.

    Science.gov (United States)

    Baranowski, M; Woźniak-Braszak, A; Jurga, K

    2011-01-01

    This paper reports on design and construction of a double coil high-homogeneity ensuring Nuclear Magnetic Resonance Probe for off-resonance relaxation time measurements. NMR off-resonance experiments pose unique technical problems. Long irradiation can overheat the sample, dephase the spins because of B(1) field inhomogeneity and degrade the signal received by requiring the receiver bandwidth to be broader than that needed for normal experiment. The probe proposed solves these problems by introducing a separate off-resonance irradiation coil which is larger than the receiver coil and is wound up on the dewar tube that separates it from the receiver coil thus also thermally protects the sample from overheating. Large size of the irradiation coil also improves the field homogeneity because as a ratio of the sample diameter to the magnet (coil) diameter increases, the field inhomogeneity also increases (Blümich et al., 2008) [1]. The small receiver coil offers maximization of the filling factor and a high signal to the noise ratio. Copyright © 2010 Elsevier Inc. All rights reserved.

  17. A multiphase three-dimensional multi-relaxation time (MRT) lattice Boltzmann model with surface tension adjustment

    Science.gov (United States)

    Ammar, Sami; Pernaudat, Guillaume; Trépanier, Jean-Yves

    2017-08-01

    The interdependence of surface tension and density ratio is a weakness of pseudo-potential based lattice Boltzmann models (LB). In this paper, we propose a 3D multi-relaxation time (MRT) model for multiphase flows at large density ratios. The proposed model is capable of adjusting the surface tension independently of the density ratio. We also present the 3D macroscopic equations recovered by the proposed forcing scheme. A high order of isotropy for the interaction force is used to reduce the amplitude of spurious currents. The proposed 3D-MRT model is validated by verifying Laplace's law and by analyzing its thermodynamic consistency and the oscillation period of a deformed droplet. The model is then applied to the simulation of the impact of a droplet on a dry surface. Impact dynamics are determined and the maximum spread factor calculated for different Reynolds and Weber numbers. The numerical results are in agreement with data published in the literature. The influence of surface wettability on the spread factor is also investigated. Finally, our 3D-MRT model is applied to the simulation of the impact of a droplet on a wet surface. The propagation of transverse waves is observed on the liquid surface.

  18. Study of the relaxation process during InGaAs/GaAs (001) growth from in situ real-time stress measurements

    OpenAIRE

    González Sagardoy, María Ujué; González Díez, Yolanda; González Sotos, Luisa

    2002-01-01

    Strain evolution during In0.2Ga0.8As/GaAs (001) growth by molecular beam epitaxy has been monitored in real time. We have detected that three main relaxation stages, related to different mechanisms, take place during growth, and we have obtained the thickness range where those mechanisms are active. The in situ measured relaxation behavior in the plastic stages has been described by means of a simple equilibrium model that takes into account dislocations generation and interaction between the...

  19. Relationship between thermodynamic parameter and thermodynamic scaling parameter for orientational relaxation time for flip-flop motion of nematic liquid crystals.

    Science.gov (United States)

    Satoh, Katsuhiko

    2013-03-07

    Thermodynamic parameter Γ and thermodynamic scaling parameter γ for low-frequency relaxation time, which characterize flip-flop motion in a nematic phase, were verified by molecular dynamics simulation with a simple potential based on the Maier-Saupe theory. The parameter Γ, which is the slope of the logarithm for temperature and volume, was evaluated under various conditions at a wide range of temperatures, pressures, and volumes. To simulate thermodynamic scaling so that experimental data at isobaric, isothermal, and isochoric conditions can be rescaled onto a master curve with the parameters for some liquid crystal (LC) compounds, the relaxation time was evaluated from the first-rank orientational correlation function in the simulations, and thermodynamic scaling was verified with the simple potential representing small clusters. A possibility of an equivalence relationship between Γ and γ determined from the relaxation time in the simulation was assessed with available data from the experiments and simulations. In addition, an argument was proposed for the discrepancy between Γ and γ for some LCs in experiments: the discrepancy arises from disagreement of the value of the order parameter P2 rather than the constancy of relaxation time τ1(*) on pressure.

  20. A Peak in Density Dependence of Electron Spin Relaxation Time in n-Type Bulk GaAs in the Metallic Regime

    Institute of Scientific and Technical Information of China (English)

    SHEN Ka

    2009-01-01

    We demonstrate that the peak in the density dependence of electron spin relaxation time in n-type bulk GaAs in the metallic regime predicted by Jiang and Wu[Phys.Rev.B 79 (2009) 125206]has been realized experimentally in the latest work[arXiv:0902.0270]by Krauβ et al.

  1. Relationship between the Carotid Plaque T1 Relaxation Time and the Plaque-to-Muscle Signal Intensity Ratio on Black-Blood Magnetic Resonance Imaging Scans.

    Science.gov (United States)

    Eto, Ayumu; Kinoshita, Yoshimasa; Matsumoto, Yoshihisa; Kiyomi, Fumiaki; Iko, Minoru; Nii, Kouhei; Tsutsumi, Masanori; Sakamoto, Kimiya; Aikawa, Hiroshi; Kazekawa, Kiyoshi

    2016-11-01

    Black-blood magnetic resonance imaging (BB-MRI) is useful for the characterization and assessment of carotid artery plaques. The plaque-to-muscle signal intensity (SI) ratio (plaque/muscle ratio [PMR]) is used widely to evaluate plaques. However, the correlation between the PMR and the T1 relaxation time needs to be determined. We measured the T1 relaxation time of carotid plaques using T1 mapping and compared the results with the PMR on BB-MRI scans. Between April 2014 and July 2015, 20 patients with carotid artery stenosis were treated by carotid artery stenting. All patients underwent preoperative magnetic resonance plaque imaging. The ratio of the plaque SI to the sternocleidomastoid muscle was calculated on T1-weighted BB-MRI scans. T1 mapping was performed in the region where the vessel was narrowest using the inversion recovery technique. The T1 relaxation time was recorded to determine whether there was a correlation with the PMR. The plaque T1 value was 577.3 ± 143.2 milliseconds; the PMR value obtained on BB-MRI scans was 1.23 ± .27. There was a statistically significant decrease in the T1 value as the PMR increased (P relaxation time was well correlated with the PMR on BB-MRI scans, the evaluation of vulnerable plaques using the PMR was reliable and convenient. Copyright © 2016 National Stroke Association. Published by Elsevier Inc. All rights reserved.

  2. The Dual Impact of Gender and the Influence of Timing of Parenthood on Men's and Women's Career Development: Longitudinal Findings

    Science.gov (United States)

    Abele, Andrea E.; Spurk, Daniel

    2011-01-01

    This study investigated the impact of gender, the gender-related self-concept (agency and communion), and the timing of parenthood on objective career success of 1,015 highly educated professionals. Hypotheses derived from a dual-impact model of gender and career-related processes were tested in a 5-wave longitudinal study over a time span of 10…

  3. Weight variation over time and its association with tuberculosis treatment outcome: a longitudinal analysis.

    Directory of Open Access Journals (Sweden)

    Antonio Bernabe-Ortiz

    Full Text Available OBJECTIVE: Weight variation during therapy has been described as a useful marker to predict TB treatment outcome. No previous study has used longitudinal analysis to corroborate this finding. The goal of this study was to evaluate change and trends of patients' bodyweight over time depending on TB treatment outcome. METHODS AND FINDINGS: A retrospective cohort study with all TB cases diagnosed from 2000 to 2006 was carried out. Information from 5 public tuberculosis treatment facilities at Pampas de San Juan de Miraflores, Lima, Peru was analyzed. Poor outcome was defined as failure or death during TB therapy, and compared to good outcome defined as cured. Longitudinal analysis with a pre-specified marginal model was fitted using Generalized Estimating Equations to compare weight trends for patients with good and poor outcome adjusting for potential confounders. A total of 460 patients (55.4% males, mean age: 31.6 years were included in the analysis: 42 (9.1% had a poor outcome (17 failed and 25 died. Weight at baseline was not different comparing outcome groups (p = 0.17. After adjusting for age, gender, type of TB, scheme of treatment, HIV status and sputum variation during follow-up, after the first month of treatment, patients with good outcome gained, on average, almost 1 kg compared to their baseline weight (p<0.001, whereas those with poor outcome lost 1 kg (p = 0.003. Similarly, after 4 months, a patient with good outcome increased 3 kg on average (p<0.001, while those with poor outcome only gained 0.2 kg (p = 0.02. CONCLUSIONS: Weight variation during tuberculosis therapy follow-up can predict treatment outcome. Patients losing weight during TB treatment, especially in the first month, should be more closely followed as they are at risk of failure or death.

  4. Emotional intelligence increases over time: A longitudinal study of Australian pre-registration nursing students.

    Science.gov (United States)

    Foster, Kim; Fethney, Judith; McKenzie, Heather; Fisher, Murray; Harkness, Emily; Kozlowski, Desirée

    2017-08-01

    Emotional intelligence (EI) has been associated with positive outcomes for nursing students. Higher EI is associated with personal wellbeing and stress management, higher academic performance, stronger nursing leadership and practice performance, and greater patient safety. While there is an increasing body of evidence on nursing students' EI, there is minimal evidence on EI over time during pre-registration programs. To measure EI in pre-registration nursing students from program commencement to conclusion to ascertain EI over time and examine the relationship between EI and academic performance. Longitudinal repeated measures study between March 2010-February 2013 at a metropolitan university in Australia. 111 nursing students (74.8% female) contributed data on at least two occasions. Participants were enrolled in a pre-registration Master of Nursing degree. Half the cohort (55.0%) comprised Graduate Entry students who completed the course in two years full time. The other 45% were enrolled in an undergraduate degree in arts, science or health science, combined with the same pre-registration Master of Nursing Degree. These students completed their Combined Degree program in four years full time. Participants had a mean age of 24.7years (SD=7.36). EI was measured for commencing students (T1) using the Assessing Emotions Scale (AES), then a further three times: end of first year (T2; 9 months follow up); beginning of second year (12 months follow up; T3) and end of the program (T4; 24/36 months follow up). Students' EI was found to increase across the program; one subscale of EI (managing others' emotions) was related to higher academic performance; and there was a significant increase in the Utilising Emotions subscale scores over time. Pre-registration nurse education contributes to strengthening students' EI over time. Specific EI education scaffolded throughout programs is recommended in pre-registration curricula. Copyright © 2017. Published by Elsevier Ltd.

  5. Time-Course Gene Set Analysis for Longitudinal Gene Expression Data.

    Directory of Open Access Journals (Sweden)

    Boris P Hejblum

    2015-06-01

    Full Text Available Gene set analysis methods, which consider predefined groups of genes in the analysis of genomic data, have been successfully applied for analyzing gene expression data in cross-sectional studies. The time-course gene set analysis (TcGSA introduced here is an extension of gene set analysis to longitudinal data. The proposed method relies on random effects modeling with maximum likelihood estimates. It allows to use all available repeated measurements while dealing with unbalanced data due to missing at random (MAR measurements. TcGSA is a hypothesis driven method that identifies a priori defined gene sets with significant expression variations over time, taking into account the potential heterogeneity of expression within gene sets. When biological conditions are compared, the method indicates if the time patterns of gene sets significantly differ according to these conditions. The interest of the method is illustrated by its application to two real life datasets: an HIV therapeutic vaccine trial (DALIA-1 trial, and data from a recent study on influenza and pneumococcal vaccines. In the DALIA-1 trial TcGSA revealed a significant change in gene expression over time within 69 gene sets during vaccination, while a standard univariate individual gene analysis corrected for multiple testing as well as a standard a Gene Set Enrichment Analysis (GSEA for time series both failed to detect any significant pattern change over time. When applied to the second illustrative data set, TcGSA allowed the identification of 4 gene sets finally found to be linked with the influenza vaccine too although they were found to be associated to the pneumococcal vaccine only in previous analyses. In our simulation study TcGSA exhibits good statistical properties, and an increased power compared to other approaches for analyzing time-course expression patterns of gene sets. The method is made available for the community through an R package.

  6. Relaxation rates of low-field gas-phase ^129Xe storage cells

    Science.gov (United States)

    Limes, Mark; Saam, Brian

    2010-10-01

    A study of longitudinal nuclear relaxation rates T1 of ^129Xe and Xe-N2 mixtures in a magnetic field of 3.8 mT is presented. In this regime, intrinsic spin relaxation is dominated by the intramolecular spin-rotation interaction due to persistent xenon dimers, a mechanism that can be quelled by introducing large amounts of N2 into the storage cell. Extrinsic spin relaxation is dominated by the wall-relaxation rate, which is the primary quantity of interest for the various low-field storage cells and coatings that we have tested. Previous group work has shown that extremely long gas-phase relaxation times T1 can be obtained, but only at large magnetic fields and low xenon densities. The current work is motivated by the practical benefits of retaining hyperpolarized ^129Xe for extended periods of time in a small magnetic field.

  7. Quantitative study of MR T1 and T2 relaxation times and 1 HMRS in gray matter of normal adult brain

    Institute of Scientific and Technical Information of China (English)

    范国光; 吴振华; 潘诗农; 郭启勇

    2003-01-01

    Objective To evaluate magnetic resonance (MR) Imaging and 1 H magnetic resonance spectroscopy (1 HMRS) in the study of normal biochemical process of the brain, as well as differentiation of normal senile brain from cerebral diseases related to senility. Methods One hundred and eighty healthy adult volunteers were selected for MR examination and 60 other healthy subjects for 1 HMRS examination. Ages of subjects ranged from 18 to 80 years. They were divided into six age groups. A 0.35 T superconductive MR system was used to perform MR examination. Point resolved spectroscopy sequence was required for 1 HMRS. The metabolites in the spectra included: N-acetylaspartate (NAA), choline compounds (CHO), creatine compounds (CR), myo-inositol (MI), glutamate and glutamine (Glu-n). Results In 180 cases of MR, the shortest T2 relaxation time occurred in the deep gray matter within the same age group while the length of T1 relaxation time was ordered from low to high compared to age groups. T2 relaxation time decreased as age increased. The peaks, ordered from high to low, were as follows in 60 cases of 1 HMRS: NAA, CR, CHO, MI, Glu-n. The ratios of NAA/CR and Glu-n/CR were higher in the senile age group, while that of MI/CR was lower. The ratio of CHO/CR was increased as age decreased. The ratio of NAA/CR and MI/CR gradually decreased in relation to movement from the anterior to the posterior part of the brain; the ratio of CHO/CR was highest in the occipital cortex. Correlation of T1 relaxation time and partial metabolite ratios to age were present in gray matter.Conclusions Quantitative studies of MR T1 and T2 relaxation times and 1 HMRS are essential to evaluation of normal myelinization processes, neuronal integrity and age-related biochemical changes in the brain.

  8. Membrane fluidity profiles as deduced by saturation-recovery EPR measurements of spin-lattice relaxation times of spin labels.

    Science.gov (United States)

    Mainali, Laxman; Feix, Jimmy B; Hyde, James S; Subczynski, Witold K

    2011-10-01

    There are no easily obtainable EPR spectral parameters for lipid spin labels that describe profiles of membrane fluidity. The order parameter, which is most often used as a measure of membrane fluidity, describes the amplitude of wobbling motion of alkyl chains relative to the membrane normal and does not contain explicitly time or velocity. Thus, this parameter can be considered as nondynamic. The spin-lattice relaxation rate (T(1)(-1)) obtained from saturation-recovery EPR measurements of lipid spin labels in deoxygenated samples depends primarily on the rotational correlation time of the nitroxide moiety within the lipid bilayer. Thus, T(1)(-1) can be used as a convenient quantitative measure of membrane fluidity that reflects local membrane dynamics. T(1)(-1) profiles obtained for 1-palmitoyl-2-(n-doxylstearoyl)phosphatidylcholine (n-PC) spin labels in dimyristoylphosphatidylcholine (DMPC) membranes with and without 50 mol% cholesterol are presented in parallel with profiles of the rotational diffusion coefficient, R(⊥), obtained from simulation of EPR spectra using Freed's model. These profiles are compared with profiles of the order parameter obtained directly from EPR spectra and with profiles of the order parameter obtained from simulation of EPR spectra. It is shown that T(1)(-1) and R(⊥) profiles reveal changes in membrane fluidity that depend on the motional properties of the lipid alkyl chain. We find that cholesterol has a rigidifying effect only to the depth occupied by the rigid steroid ring structure and a fluidizing effect at deeper locations. These effects cannot be differentiated by profiles of the order parameter. All profiles in this study were obtained at X-band (9.5 GHz).

  9. Nonlogarithmic magnetization relaxation at the initial time intervals and magnetic field dependence of the flux creep rate in Bi2Sr2Ca(sub I)Cu2Ox single crystals

    Science.gov (United States)

    Moshchalcov, V. V.; Zhukov, A. A.; Kuznetzov, V. D.; Metlushko, V. V.; Leonyuk, L. I.

    1990-01-01

    At the initial time intervals, preceding the thermally activated flux creep regime, fast nonlogarithmic relaxation is found. The fully magnetic moment Pm(t) relaxation curve is shown. The magnetic measurements were made using SQUID-magnetometer. Two different relaxation regimes exist. The nonlogarithmic relaxation for the initial time intervals may be related to the viscous Abrikosov vortices flow with j is greater than j(sub c) for high enough temperature T and magnetic field induction B. This assumption correlates with Pm(t) measurements. The characteristic time t(sub O) separating two different relaxation regimes decreases as temperature and magnetic field are lowered. The logarithmic magnetization relaxation curves Pm(t) for fixed temperature and different external magnetic field inductions B are given. The relaxation rate dependence on magnetic field, R(B) = dPm(B, T sub O)/d(1nt) has a sharp maximum which is similar to that found for R(T) temperature dependences. The maximum shifts to lower fields as temperature goes up. The observed sharp maximum is related to a topological transition in shielding critical current distribution and, consequently, in Abrikosov vortices density. The nonlogarithmic magnetization relaxation for the initial time intervals is found. This fast relaxation has almost an exponentional character. The sharp relaxation rate R(B) maximum is observed. This maximum corresponds to a topological transition in Abrikosov vortices distribution.

  10. A longitudinal assessment of sleep timing, circadian phase, and phase angle of entrainment across human adolescence.

    Science.gov (United States)

    Crowley, Stephanie J; Van Reen, Eliza; LeBourgeois, Monique K; Acebo, Christine; Tarokh, Leila; Seifer, Ronald; Barker, David H; Carskadon, Mary A

    2014-01-01

    The aim of this descriptive analysis was to examine sleep timing, circadian phase, and phase angle of entrainment across adolescence in a longitudinal study design. Ninety-four adolescents participated; 38 (21 boys) were 9-10 years ("younger cohort") and 56 (30 boys) were 15-16 years ("older cohort") at the baseline assessment. Participants completed a baseline and then follow-up assessments approximately every six months for 2.5 years. At each assessment, participants wore a wrist actigraph for at least one week at home to measure self-selected sleep timing before salivary dim light melatonin onset (DLMO) phase - a marker of the circadian timing system - was measured in the laboratory. Weekday and weekend sleep onset and offset and weekend-weekday differences were derived from actigraphy. Phase angles were the time durations from DLMO to weekday sleep onset and offset times. Each cohort showed later sleep onset (weekend and weekday), later weekend sleep offset, and later DLMO with age. Weekday sleep offset shifted earlier with age in the younger cohort and later in the older cohort after age 17. Weekend-weekday sleep offset differences increased with age in the younger cohort and decreased in the older cohort after age 17. DLMO to sleep offset phase angle narrowed with age in the younger cohort and became broader in the older cohort. The older cohort had a wider sleep onset phase angle compared to the younger cohort; however, an age-related phase angle increase was seen in the younger cohort only. Individual differences were seen in these developmental trajectories. This descriptive study indicated that circadian phase and self-selected sleep delayed across adolescence, though school-day sleep offset advanced until no longer in high school, whereupon offset was later. Phase angle changes are described as an interaction of developmental changes in sleep regulation interacting with psychosocial factors (e.g., bedtime autonomy).

  11. A longitudinal assessment of sleep timing, circadian phase, and phase angle of entrainment across human adolescence.

    Directory of Open Access Journals (Sweden)

    Stephanie J Crowley

    Full Text Available The aim of this descriptive analysis was to examine sleep timing, circadian phase, and phase angle of entrainment across adolescence in a longitudinal study design. Ninety-four adolescents participated; 38 (21 boys were 9-10 years ("younger cohort" and 56 (30 boys were 15-16 years ("older cohort" at the baseline assessment. Participants completed a baseline and then follow-up assessments approximately every six months for 2.5 years. At each assessment, participants wore a wrist actigraph for at least one week at home to measure self-selected sleep timing before salivary dim light melatonin onset (DLMO phase - a marker of the circadian timing system - was measured in the laboratory. Weekday and weekend sleep onset and offset and weekend-weekday differences were derived from actigraphy. Phase angles were the time durations from DLMO to weekday sleep onset and offset times. Each cohort showed later sleep onset (weekend and weekday, later weekend sleep offset, and later DLMO with age. Weekday sleep offset shifted earlier with age in the younger cohort and later in the older cohort after age 17. Weekend-weekday sleep offset differences increased with age in the younger cohort and decreased in the older cohort after age 17. DLMO to sleep offset phase angle narrowed with age in the younger cohort and became broader in the older cohort. The older cohort had a wider sleep onset phase angle compared to the younger cohort; however, an age-related phase angle increase was seen in the younger cohort only. Individual differences were seen in these developmental trajectories. This descriptive study indicated that circadian phase and self-selected sleep delayed across adolescence, though school-day sleep offset advanced until no longer in high school, whereupon offset was later. Phase angle changes are described as an interaction of developmental changes in sleep regulation interacting with psychosocial factors (e.g., bedtime autonomy.

  12. Longitudinal uniformity, time performances and irradiation test of pure CsI crystals

    Energy Technology Data Exchange (ETDEWEB)

    Angelucci, M. [Laboratori Nazionali di Frascati dell' INFN, Frascati (Italy); Atanova, O. [Joint Institute for Nuclear Research, Dubna (Russian Federation); Baccaro, S.; Cemmi, A. [ENEA UTTMAT-IRR, Casaccia R.C., Roma (Italy); Cordelli, M. [Laboratori Nazionali di Frascati dell' INFN, Frascati (Italy); Donghia, R., E-mail: raffaella.donghia@lnf.infn.it [Laboratori Nazionali di Frascati dell' INFN, Frascati (Italy); Dipartimento di Fisica, Universitá Roma Tre, Roma (Italy); Giovannella, S.; Happacher, F.; Miscetti, S.; Sarra, I.; Soleti, S.R. [Laboratori Nazionali di Frascati dell' INFN, Frascati (Italy)

    2016-07-11

    To study an alternative to BaF{sub 2}, as the crystal choice for the Mu2e calorimeter, 13 pure CsI crystals from Opto Materials and ISMA producers have been characterized by determining their light yield (LY) and longitudinal response uniformity (LRU), when read with a UV extended PMT. The crystals show a LY of ~100 p.e./MeV (~150 p.e./MeV) when wrapped with Tyvek and coupled to the PMT without (with) optical grease. The LRU is well represented by a linear slope that is on average δ~ −0.6%/cm. The timing performances of the Opto Materials crystal, read with a UV extended MPPC, have been evaluated with minimum ionizing particles. A timing resolution of ~330 ps (~ 440 ps) is achieved when connecting the photosensor to the MPPC with (without) optical grease. The crystal radiation hardness to a ionization dose has also been studied for one pure CsI crystal from SICCAS. After exposing it to a dose of 900 Gy, a decrease of 33% in the LY is observed while the LRU remains unchanged.

  13. Longitudinal uniformity, time performance and irradiation test of pure CsI crystals

    CERN Document Server

    Angelucci, M; Baccaro, S; Cemmi, A; Cordelli, M; Donghia, R; Giovannella, S; Happacher, F; Miscetti, S; Sarra, I; Soleti, S R

    2016-01-01

    To study an alternative to BaF2, as the crystal choice for the Mu2e calorimeter, thirteen pure CsI crystals from Opto Materials and ISMA producers have been characterized by determining their light yield (LY) and longitudinal response uniformity (LRU), when read with a UV extended PMT. The crystals show a LY of ~ 100 p.e./MeV (~ 150 p.e./MeV) when wrapped with Tyvek and coupled to the PMT without (with) optical grease. The LRU is well represented by a linear slope that is on average around -0.6 %/cm. The timing performances of the Opto Materials crystal, read with a UV extended MPPC, have been evaluated with minimum ionizing particles. A timing resolution of ~ 330 ps (~ 440 ps) is achieved when connecting the photosensor to the MPPC with (without) optical grease. The crystal radiation hardness to a ionization dose has also been studied for one pure CsI crystal from SICCAS. After exposing it to a dose of 900 Gy, a decrease of 33% in the LY is observed while the LRU remains unchanged.

  14. The effect of the polymer relaxation time on the nonlinear energy cas- cade and dissipation of statistically steady and decaying homogeneous isotropic turbulence

    Science.gov (United States)

    Valente, Pedro C.; da Silva, Carlos B.; Pinho, Fernando T.

    2013-11-01

    We report a numerical study of statistically steady and decaying turbulence of FENE-P fluids for varying polymer relaxation times ranging from the Kolmogorov dissipation time-scale to the eddy turnover time. The total turbulent kinetic energy dissipation is shown to increase with the polymer relaxation time in both steady and decaying turbulence, implying a ``drag increase.'' If the total power input in the statistically steady case is kept equal in the Newtonian and the viscoelastic simulations the increase in the turbulence-polymer energy transfer naturally lead to the previously reported depletion of the Newtonian, but not the overall, kinetic energy dissipation. The modifications to the nonlinear energy cascade with varying Deborah/Weissenberg numbers are quantified and their origins investigated. The authors acknowledge the financial support from Fundação para a Ciência e a Tecnologia under grant PTDC/EME-MFE/113589/2009.

  15. Differences in time to peak carbachol-induced contractions between circular and longitudinal smooth muscles of mouse ileum.

    Science.gov (United States)

    Azuma, Yasu-Taka; Samezawa, Nanako; Nishiyama, Kazuhiro; Nakajima, Hidemitsu; Takeuchi, Tadayoshi

    2016-01-01

    The muscular layer in the GI tract consists of an inner circular muscular layer and an outer longitudinal muscular layer. Acetylcholine (ACh) is the representative neurotransmitter that causes contractions in the gastrointestinal tracts of most animal species. There are many reports of muscarinic receptor-mediated contraction of longitudinal muscles, but few studies discuss circular muscles. The present study detailed the contractile response in the circular smooth muscles of the mouse ileum. We used small muscle strips (0.2 mm × 1 mm) and large muscle strips (4 × 4 mm) isolated from the circular and longitudinal muscle layers of the mouse ileum to compare contraction responses in circular and longitudinal smooth muscles. The time to peak contractile responses to carbamylcholine (CCh) were later in the small muscle strips (0.2 × 1 mm) of circular muscle (5.7 min) than longitudinal muscles (0.4 min). The time to peak contractile responses to CCh in the large muscle strips (4 × 4 mm) were also later in the circular muscle (3.1 min) than the longitudinal muscle (1.4 min). Furthermore, a muscarinic M2 receptor antagonist and gap junction inhibitor significantly delayed the time to peak contraction of the large muscle strips (4 × 4 mm) from the circular muscular layer. Our findings indicate that muscarinic M2 receptors in the circular muscular layer of mouse ileum exert a previously undocumented function in gut motility via the regulation of gap junctions.

  16. Experimental deformation and recrystallization of olivine – processes and time scales of damage healing during postseismic relaxation at mantle depths

    Directory of Open Access Journals (Sweden)

    C. A. Trepmann

    2013-04-01

    Full Text Available Experiments comprising sequences of deformation (at 300 or 600 °C and annealing at varying temperature (700 to 1100 °C, time (up to 144 h and stress (up to 1.5 GPa were carried out in a Griggs-type apparatus on natural olivine-rich peridotite samples to simulate deformation and recrystallization processes in deep shear zones that reach mantle depth as continuations of seismically active faults. The resulting olivine microfabrics were analysed by polarization and electron microscopy. Core-and-mantle like microstructures are the predominant result of our experiments simulating rapid stress relaxation (without or with minor creep after a high-stress deformation event: porphyroclasts (> 100 μm are surrounded by defect-poor recrystallized grains with a wide range in size (2 to 40 μm. Areas with smaller recrystallized grains (> 10 μm trace former high-strain zones generated during initial high-stress deformation even after annealing at a temperature of 1100 °C for 70 h. A weak crystallographic preferred orientation (CPO of recrystallized olivine grains is related to the orientation of the host crystals but appears unrelated to the strain field. Based on these findings, we propose that olivine microstructures in natural shear-zone peridotites with a large range in recrystallized grain size, localized fine-grained zones, and a weak CPO not related to the strain field are diagnostic for a sequence of high-stress deformation followed by recrystallization at low stresses, as to be expected in areas of seismic activity. We extended the classic Avrami-kinetics equation by accounting for time-dependent growth kinetics and constrained the involved parameters relying on our results and previously reported kinetics parameters. Extrapolation to natural conditions suggests that the observed characteristic microstructure may develop within as little as tens of years and less than ten thousands of years. These recrystallization microstructures have a great

  17. Comparison of the dietary intakes of new parents, second-time parents, and nonparents: a longitudinal cohort study.

    Science.gov (United States)

    Nasuti, Gabriella; Blanchard, Chris; Naylor, Patti-Jean; Levy-Milne, Ryna; Warburton, Darren E R; Benoit, Cecilia; Symons Downs, Danielle; Rhodes, Ryan E

    2014-03-01

    The objective of this study was to examine the dietary intake profiles of first-time parents, second-time parents, and couples without children; once during pregnancy, then at 6- and 12-months postpartum. This was an observational, longitudinal, cohort study. Participants were a community-based sample of 153 couples aged 25 to 40 years. Data were collected between 2007 and 2011. Dietary intake was recorded using 3-day dietary recall. Hierarchical linear modeling was used to compare the dietary intakes of groups (ie, parent, sex, and couple days) over time. Percentage of participants per group meeting recommended daily dietary guidelines was also analyzed, as were variables that influenced meeting overall recommended guidelines using a multivariate analysis of variance. First-time mothers had higher overall energy, fat, sugar, fruit, and milk intake compared with women without children, and longitudinally first-time mothers decreased their fruit intake. Second-time mothers had higher overall energy, fat, sugar, and fruit intake compared with nonparent women, and longitudinally second-time mothers increased their meat intake. First-time fathers had overall higher bread intake compared with second-time fathers and men without children, and first-time fathers consumed less sugar than second-time fathers. Longitudinally, first-time fathers increased their fiber intake. At any stage of data collection, from pregnancy to 12-months postpartum, only 2% to 16% of all mothers met recommended overall daily dietary guidelines. The only variable investigated that influenced meeting overall daily dietary guidelines at baseline was parent status.

  18. Dependence of transverse relaxation time T{sub 2} of biologic tissues on the interpulse delay time in Carr-Purcell-Meiboom-Gill (CPMG) measurements

    Energy Technology Data Exchange (ETDEWEB)

    Shioya, Sumie; Kurita, Daisaku; Haida, Munetaka; Tanigaki, Toshimori; Kutsuzawa, Tomoko; Ohta, Yasuyo [Tokai Univ., Isehara, Kanagawa (Japan). School of Medicine; Fukuzaki, Minoru

    1997-05-01

    To determine the transverse relaxation time (T{sub 2}) of biological tissues in nuclear magnetic resonance measurements, the Carr-Purcell-Meiboom-Gill (CPMG) method has been recommended to avoid the effect of external magnetic field inhomogeneity on T{sub 2} values. However, a dependence of T{sub 2} on the interpulse delay time (IPDT) in the CPMG measurements has been shown for biological tissues. The present study examined the dependence of the T{sub 2} on IPDT for muscle, lung (passively collapsed or degassed), and brain tissues. It was found that the CPMG T{sub 2} of the lung was strongly dependent upon the IPDT, in contrast to muscle and brain tissues. The IPDT dependence of the CPMG T{sub 2} for lung tissue, which was lessened by degassing, was affected by the magnetic field inhomogeneity due to air-tissue interfaces, but not by the spin-locking effect, since the T{sub 2} measured by the Carr-Purcell-Freeman-Hill (CPFH) method did not show this dependence. These results should aid in the evaluation of T{sub 2} values for biological tissues measured under various conditions and by different techniques. (author)

  19. Longitudinal measurement invariance of the metabolic syndrome: is the assessment of the metabolic syndrome stable over time?

    Science.gov (United States)

    Barbosa-Leiker, Celestina; Wright, Bruce R; Burns, G Leonard; Parks, Craig D; Strand, Paul S

    2011-02-01

    Without verification of longitudinal measurement invariance, researchers cannot be certain whether observed change in the metabolic syndrome reflects true change or changes in assessment or structure of the construct over time. This research tested longitudinal measurement invariance of a 1-factor model of the metabolic syndrome during the course of 6 years. Tests of longitudinal measurement invariance (configural, metric, and scalar) were conducted on 604 men and women who participated in the Spokane Heart Study from 1996 to 2006. Metabolic syndrome indicators included body mass index, triglycerides, high-density lipoprotein, diastolic blood pressure, and fasting glucose. Sequential configural and metric invariance models demonstrated adequate model fit, but the scalar invariance model led to a decrement in fit. Therefore, the theoretical framework of the syndrome and the relationships between the syndrome construct and the indicators appear to be equivalent over time. However, observed values of the metabolic syndrome indicators may differ across time when there is a constant level of the syndrome. Because longitudinal invariance was not fully demonstrated, interpretation of change in the metabolic syndrome over time may be misleading because change may be partly attributable to measurement properties of the indicators. However, a cross-sectional 1-factor model of the metabolic syndrome is supported. Copyright © 2011 Elsevier Inc. All rights reserved.

  20. Longitudinal studies of semantic dementia: the relationship between structural and functional changes over time.

    Science.gov (United States)

    Bright, P; Moss, H E; Stamatakis, E A; Tyler, L K

    2008-01-01

    The pattern of brain atrophy in semantic dementia and its associated cognitive effects have attracted a considerable body of research, but the nature of core impairments remains disputed. A key issue is whether the disease encompasses one neurocognitive network (semantics) or two (language and semantics). In order to address these conflicting perspectives, we conducted a longitudinal investigation of two semantic dementia patients, in which behavioural performance across a range of measures of language and semantic performance was assessed and interpreted in the context of annually acquired MRI scans. Our results indicated a core semantic impairment in early stages of the disease, associated with atrophy of the inferior, anterior temporal cortex. Linguistic impairments emerged later, and were contingent on atrophy having spread into areas widely believed to subserve core language processes (left posterior perisylvian, inferior frontal and insular cortex). We claim, therefore, that phonological, syntactic and morphological processing deficits in semantic dementia reflect damage to core language areas. Further, we propose that much of the current controversy over the nature of deficits in semantic dementia reflect a tendency in the literature to adopt a static perspective on what is a progressive disease. An approach in which the relationship between progressive neural changes and behavioural change over time is carefully mapped, offers a more constraining data-set from which to draw inferences about the relationship between language, semantics and the brain.

  1. The Arrow of Time in the Collapse of Collisionless Self-gravitating Systems: Non-validity of the Vlasov–Poisson Equation during Violent Relaxation

    Science.gov (United States)

    Beralso e Silva, Leandro; de Siqueira Pedra, Walter; Sodré, Laerte; Perico, Eder L. D.; Lima, Marcos

    2017-09-01

    The collapse of a collisionless self-gravitating system, with the fast achievement of a quasi-stationary state, is driven by violent relaxation, with a typical particle interacting with the time-changing collective potential. It is traditionally assumed that this evolution is governed by the Vlasov–Poisson equation, in which case entropy must be conserved. We run N-body simulations of isolated self-gravitating systems, using three simulation codes, NBODY-6 (direct summation without softening), NBODY-2 (direct summation with softening), and GADGET-2 (tree code with softening), for different numbers of particles and initial conditions. At each snapshot, we estimate the Shannon entropy of the distribution function with three different techniques: Kernel, Nearest Neighbor, and EnBiD. For all simulation codes and estimators, the entropy evolution converges to the same limit as N increases. During violent relaxation, the entropy has a fast increase followed by damping oscillations, indicating that violent relaxation must be described by a kinetic equation other than the Vlasov–Poisson equation, even for N as large as that of astronomical structures. This indicates that violent relaxation cannot be described by a time-reversible equation, shedding some light on the so-called “fundamental paradox of stellar dynamics.” The long-term evolution is well-described by the orbit-averaged Fokker–Planck model, with Coulomb logarithm values in the expected range 10{--}12. By means of NBODY-2, we also study the dependence of the two-body relaxation timescale on the softening length. The approach presented in the current work can potentially provide a general method for testing any kinetic equation intended to describe the macroscopic evolution of N-body systems.

  2. Evidence of alpha fluctuations in myoglobin's denaturation in the high temperature region: Average relaxation time from an Adam-Gibbs perspective.

    Science.gov (United States)

    Olivares-Quiroz, Luis; Garcia-Colin, Leopoldo S

    2009-10-01

    In this work, we derive an analytical expression for the relaxation time tau as a function of temperature T for myoglobin protein (Mb, PDB:1MBN) in the high temperature limit (T>T(g)=200K). The method is based on a modified version of the Adam-Gibbs theory (AG theory) for the glass transition in supercooled liquids and an implementation of differential geometry techniques. This modified version of the AG theory takes into account that the entropic component in protein's denaturation has two major sources: a configurational contribution DeltaS(c) due to the unfolding of the highly ordered native state N and a hydration contribution DeltaS(hyd) arising from the exposure of non-polar residues to direct contact with solvent polar molecules. Our results show that the configurational contribution DeltaS(c) is temperature-independent and one order of magnitude smaller than its hydration counterpart DeltaS(hyd) in the temperature range considered. The profile obtained for log tau(T) from T=200 K to T=300 K exhibits a non-Arrhenius behavior characteristic of alpha relaxation mechanisms in hydrated proteins and glassy systems. This result is in agreement with recent dielectric spectroscopy data obtained for hydrated myoglobin, where at least two fast relaxation processes in the high temperature limit have been observed. The connection between the relaxation process calculated here and the experimental results is outlined.

  3. The contrasting roles of creep and stress relaxation in the time-dependent deformation during in-situ cooling of a nickel-base single crystal superalloy.

    Science.gov (United States)

    Panwisawas, Chinnapat; D'Souza, Neil; Collins, David M; Bhowmik, Ayan

    2017-09-11

    Time dependent plastic deformation in a single crystal nickel-base superalloy during cooling from casting relevant temperatures has been studied using a combination of in-situ neutron diffraction, transmission electron microscopy and modelling. Visco-plastic deformation during cooling was found to be dependent on the stress and constraints imposed to component contraction during cooling, which mechanistically comprises creep and stress relaxation. Creep results in progressive work hardening with dislocations shearing the γ' precipitates, a high dislocation density in the γ channels and near the γ/γ' interface and precipitate shearing. When macroscopic contraction is restricted, relaxation dominates. This leads to work softening from a decreased dislocation density and the presence of long segment stacking faults in γ phase. Changes in lattice strains occur to a similar magnitude in both the γ and γ' phases during stress relaxation, while in creep there is no clear monotonic trend in lattice strain in the γ phase, but only a marginal increase in the γ' precipitates. Using a visco-plastic law derived from in-situ experiments, the experimentally measured and calculated stresses during cooling show a good agreement when creep predominates. However, when stress relaxation dominates accounting for the decrease in dislocation density during cooling is essential.

  4. Multiple breath-hold proton spectroscopy of human liver at 3T: Relaxation times and concentrations of glycogen, choline, and lipids.

    Science.gov (United States)

    Weis, Jan; Kullberg, Joel; Ahlström, Håkan

    2017-04-17

    To evaluate the feasibility of an expiration multiple breath-hold (1) H-MRS technique to measure glycogen (Glycg), choline-containing compounds (CCC), and lipid relaxation times T1 , T2 , and their concentrations in normal human liver. Thirty healthy volunteers were recruited. Experiments were performed at 3T. Multiple expiration breath-hold single-voxel point-resolved spectroscopy (PRESS) technique was used for localization. Water-suppressed spectra were used for the estimation of Glycg, CCC, lipid methylene (CH2 )n relaxation times and concentrations. Residual water lines were removed by the Hankel Lanczos singular value decomposition filter. After phase correction and frequency alignment, spectra were averaged and processed by LCModel. Summed signals of Glycg resonances H2H4', H3, and H5 between 3.6 and 4 ppm were used to estimate their apparent relaxation times and concentration. Glycg, CCC, and lipid content were estimated from relaxation corrected spectral intensity ratios to unsuppressed water line. Relaxation times were measured for liver Glycg (T1 , 892 ± 126 msec; T2 , 13 ± 4 msec), CCC (T1 , 842 ± 75 msec; T2 , 50 ± 5 msec), lipid (CH2 )n (T1 , 402 ± 19 msec; T2 , 52 ± 3 msec), and water (T1 , 990 ± 89 msec; T2 , 30 ± 2 msec). Mean CCC and lipid concentrations of healthy liver were 7.8 ± 1.3 mM and 15.8 ± 23.6 mM, respectively. Glycg content was found lower in the morning (48 ± 21 mM) compared to the afternoon (145 ± 50 mM). Multiple breath-hold (1) H-MRS together with dedicated postprocessing is a feasible technique for the quantification of liver Glycg, CCC, and lipid relaxation times and concentrations. 1 J. Magn. Reson. Imaging 2017. © 2017 International Society for Magnetic Resonance in Medicine.

  5. The search for negative amplitude components in quasi-continuous distributions of relaxation times: the example of {sup 1}H magnetization exchange in articular cartilage and hydrated collagen

    Energy Technology Data Exchange (ETDEWEB)

    Fantazzini, Paola; Galassi, Francesca [Department of Physics, University of Bologna, Viale Berti Pichat 6/2, 40127 Bologna (Italy); Bortolotti, Villiam [Department of DICAM, University of Bologna, Viale del Risorgimento 2, 40136 Bologna (Italy); Brown, Robert J S [953 West Bonita Avenue, Claremont, CA 91711-4193 (United States); Vittur, Franco, E-mail: paola.fantazzini@unibo.it [Department of Life Sciences, University of Trieste, via Giorgeri 1, 24137 (Italy)

    2011-06-15

    When inverting nuclear magnetic resonance relaxation data in order to obtain quasi-continuous distributions of relaxation times for fluids in porous media, it is common practice to impose a non-negative (NN) constraint on the distributions. While this approach can be useful in reducing the effects of data distortion and/or preventing wild oscillations in the distributions, it may give misleading results in the presence of real negative amplitude components. Here, some examples of valid negative components for articular cartilage and hydrated collagen are given. Articular cartilage is a connective tissue, consisting mainly of collagen, proteoglycans and water, which can be considered, in many aspects, as a porous medium. Separate T{sub 1} relaxation data are obtained for low-mobility ('solid') macromolecular {sup 1}H and for higher-mobility ('liquid') {sup 1}H by the separation of these components in free induction decays, with {alpha} denoting the solid/liquid {sup 1}H ratio. When quasi-continuous distributions of relaxation times (T{sub 1}) of the solid and liquid signal components of cartilage or collagen are computed from experimental relaxation data without imposing the usual NN constraint, valid negative peaks may appear. The features of the distributions, in particular negative peaks, and the fact that peaks at longer times for macromolecular and water protons are at essentially the same T{sub 1}, are interpreted as the result of a magnetization exchange between these two spin pools. For the only-slightly-hydrated collagen samples, with {alpha}>1, the exchange leads to small negative peaks at short T{sub 1} times for the macromolecular component. However, for the cartilage, with substantial hydration or for a strongly hydrated collagen sample, both with {alpha}<<1, the behavior is reversed, with a negative peak for water at short times. The validity of a negative peak may be accepted (dismissed) by a high (low) cost of NN in error of fit

  6. Chemical shift and spin-lattice relaxation time for two crystallographically inequivalent 133Cs sites in Cs2BBr4 (B=57Co, 63Cu, and 65Zn) using magic-angle spinning nuclear magnetic resonance

    Science.gov (United States)

    Lim, Ae Ran; Kim, Sun Ha

    2017-05-01

    The structural geometry around the 133Cs nuclei in Cs2BBr4 (B = 57Co, 63Cu, and 65Zn) was investigated by examining the chemical shifts and spin-lattice relaxation times in a rotating frame. Two crystallographically inequivalent Cs(1) and Cs(2) sites were differentiated. The spin-lattice relaxation times T1ρ of 133Cs nuclei in three crystals were measured to obtain detailed information about their structural dynamics. Cs(1) surrounded by eleven bromide ions was found to have a longer relaxation time than Cs(2) surrounded by nine bromide ions. The nuclear magnetic resonance (NMR) results were compared to previously reported results for Cs2BCl4. The halogen species in Cs2BX4 (X = Br, Cl) was not found to influence the relaxation time, whereas the B metal ion (B = Co, Cu, and Zn) was found to alter the relaxation time mechanism.

  7. A Technique for Determining Relaxation Times by Free-Flight Tests of Low-Fineness-Ratio Cones; with Experimental Results for Air at Equilibrium Temperatures up to 3440 K

    Science.gov (United States)

    Stephenson, Jack D.

    1960-01-01

    This report describes a technique which combines theory and experiments for determining relaxation times in gases. The technique is based on the measurement of shapes of the bow shock waves of low-fineness-ratio cones fired from high-velocity guns. The theory presented in the report provides a means by which shadowgraph data showing the bow waves can be analyzed so as to furnish effective relaxation times. Relaxation times in air were obtained by this technique and the results have been compared with values estimated from shock tube measurements in pure oxygen and nitrogen. The tests were made at velocities ranging from 4600 to 12,000 feet per second corresponding to equilibrium temperatures from 35900 R (19900 K) to 6200 R (34400 K), under which conditions, at all but the highest temperatures, the effective relaxation times were determined primarily by the relaxation time for oxygen and nitrogen vibrations.

  8. Determination of intra-axial brain tumors cellularity through the analysis of T2 Relaxation time of brain tumors before surgery using MATLAB software.

    Science.gov (United States)

    Abdolmohammadi, Jamil; Shafiee, Mohsen; Faeghi, Fariborz; Arefan, Douman; Zali, Alireza; Motiei-Langroudi, Rouzbeh; Farshidfar, Zahra; Nazarlou, Ali Kiani; Tavakkoli, Ali; Yarham, Mohammad

    2016-08-01

    Timely diagnosis of brain tumors could considerably affect the process of patient treatment. To do so, para-clinical methods, particularly MRI, cannot be ignored. MRI has so far answered significant questions regarding tumor characteristics, as well as helping neurosurgeons. In order to detect the tumor cellularity, neuro-surgeons currently have to sample specimens by biopsy and then send them to the pathology unit. The aim of this study is to determine the tumor cellularity in the brain. In this cross-sectional study, 32 patients (18 males and 14 females from 18-77 y/o) were admitted to the neurosurgery department of Shohada-E Tajrish Hospital in Tehran, Iran from April 2012 to February 2014. In addition to routine pulse sequences, T2W Multi echo pulse sequences were taken and the images were analyzed using the MATLAB software to determine the brain tumor cellularity, compared with the biopsy. These findings illustrate the need for more T2 relaxation time decreases, the higher classes of tumors will stand out in the designed table. In this study, the results show T2 relaxation time with a 85% diagnostic weight, compared with the biopsy, to determine the brain tumor cellularity (p<0.05). Our results indicate that the T2 relaxation time feature is the best method to distinguish and present the degree of intra-axial brain tumors cellularity (85% accuracy compared to biopsy). The use of more data is recommended in order to increase the percent accuracy of this techniques.

  9. Simulating high Reynolds number flow in two-dimensional lid-driven cavity by multi-relaxation-time lattice Boltzmann method

    Institute of Scientific and Technical Information of China (English)

    Chai Zhen-Hua; Shi Bao-Chang; Zheng Lin

    2006-01-01

    By coupling the non-equilibrium extrapolation scheme for boundary condition with the multi-relaxation-time lattice Boltzmann method, this paper finds that the stability of the multi-relaxation-time model can be improved greatly, especially on simulating high Reynolds number (Re) flow. As a discovery, the super-stability analysed by Lallemand and Luo is verified and the complex structure of the cavity flow is also exhibited in our numerical simulation when Re is high enough. To the best knowledge of the authors, the maximum of Re which has been investigated by direct numerical simulation is only around 50 000 in the literature; however, this paper can readily extend the maximum to 1000 000 with the above combination.

  10. Relaxation time and impurity effects on linear and nonlinear refractive index changes in (In,Ga)N-GaN spherical QD

    Science.gov (United States)

    El Ghazi, Haddou; Jorio, Anouar

    2014-10-01

    By means of a combination of Quantum Genetic Algorithm and Hartree-Fock-Roothaan method, the changes in linear, third-order nonlinear and total refractive index associated with intra-conduction band transition are investigated with and without shallow-donor impurity in wurtzite (In,Ga)N-GaN spherical quantum dot. For both cases with and without impurity, the calculation is performed within the framework of single band effective-mass and parabolic band approximations. Impurity's position and relaxation time effects are investigated. It is found that the modulation of the refractive index changes, suitable for good performance optical modulators and various infra-red optical device applications can be easily obtained by tailoring the relaxation time and the position of the impurity.

  11. Relaxation time and impurity effects on linear and nonlinear refractive index changes in (In,Ga)N–GaN spherical QD

    Energy Technology Data Exchange (ETDEWEB)

    El Ghazi, Haddou, E-mail: hadghazi@gmail.com [LPS, Faculty of Science, Dhar El Mehrez, BP 1796 Fes-Atlas (Morocco); Special Mathematics, CPGE My Youssef, Rabat (Morocco); Jorio, Anouar [LPS, Faculty of Science, Dhar El Mehrez, BP 1796 Fes-Atlas (Morocco)

    2014-10-01

    By means of a combination of Quantum Genetic Algorithm and Hartree–Fock–Roothaan method, the changes in linear, third-order nonlinear and total refractive index associated with intra-conduction band transition are investigated with and without shallow-donor impurity in wurtzite (In,Ga)N–GaN spherical quantum dot. For both cases with and without impurity, the calculation is performed within the framework of single band effective-mass and parabolic band approximations. Impurity's position and relaxation time effects are investigated. It is found that the modulation of the refractive index changes, suitable for good performance optical modulators and various infra-red optical device applications can be easily obtained by tailoring the relaxation time and the position of the impurity.

  12. Acoustic multipole sources for the regularized lattice Boltzmann method: Comparison with multiple-relaxation-time models in the inviscid limit.

    Science.gov (United States)

    Zhuo, Congshan; Sagaut, Pierre

    2017-06-01

    In this paper, a variant of the acoustic multipole source (AMS) method is proposed within the framework of the lattice Boltzmann method. A quadrupole term is directly included in the stress system (equilibrium momentum flux), and the dependency of the quadrupole source in the inviscid limit upon the fortuitous discretization error reported in the works of E. M. Viggen [Phys. Rev. E 87, 023306 (2013)PLEEE81539-375510.1103/PhysRevE.87.023306] is removed. The regularized lattice Boltzmann (RLB) method with this variant AMS method is presented for the 2D and 3D acoustic problems in the inviscid limit, and without loss of generality, the D3Q19 model is considered in this work. To assess the accuracy and the advantage of the RLB scheme with this AMS for acoustic point sources, the numerical investigations and comparisons with the multiple-relaxation-time (MRT) models and the analytical solutions are performed on the 2D and 3D acoustic multipole point sources in the inviscid limit, including monopoles, x dipoles, and xx quadrupoles. From the present results, the good precision of this AMS method is validated, and the RLB scheme exhibits some superconvergence properties for the monopole sources compared with the MRT models, and both the RLB and MRT models have the same accuracy for the simulations of acoustic dipole and quadrupole sources. To further validate the capability of the RLB scheme with AMS, another basic acoustic problem, the acoustic scattering from a solid cylinder presented at the Second Computational Aeroacoustics Workshop on Benchmark Problems, is numerically considered. The directivity pattern of the acoustic field is computed at r=7.5; the present results agree well with the exact solutions. Also, the effects of slip and no-slip wall treatments within the regularized boundary condition on this pure acoustic scattering problem are tested, and compared with the exact solution, the slip wall treatment can present a better result. All simulations demonstrate

  13. Prevalence for the universal distribution of relaxation times near the glass transitions in experimental model systems: Rodlike liquid crystals and orientationally disordered crystals

    OpenAIRE

    Martínez García, Julio Cesar; Tamarit Mur, José Luis; Rzosca, S. J.

    2011-01-01

    Recently, Nielsen et al. [J. Chem. Phys. 130, 154508 (2009); Philos. Mag. 88, 4101 (2008)] demonstrated a universal pattern for the high frequency wing of the loss curve for primary relaxation time on approaching the glass transition for organic liquids. In this contribution it is presented that a similar universality occurs for glass-forming liquid crystals and orientationally disordered crystals (plastic crystals). Empirical correlations of the found behavior are also briefly di...

  14. Frequency dependence of electron spin relaxation times in aqueous solution for a nitronyl nitroxide radical and perdeuterated-tempone between 250 MHz and 34 GHz.

    Science.gov (United States)

    Biller, Joshua R; Meyer, Virginia M; Elajaili, Hanan; Rosen, Gerald M; Eaton, Sandra S; Eaton, Gareth R

    2012-12-01

    Electron spin relaxation times of perdeuterated tempone (PDT) 1 and of a nitronyl nitroxide (2-(4-carboxy-phenyl)-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl) 2 in aqueous solution at room temperature were measured by 2-pulse electron spin echo (T(2)) or 3-pulse inversion recovery (T(1)) in the frequency range of 250 MHz to 34 GHz. At 9 GHz values of T(1) measured by long-pulse saturation recovery were in good agreement with values determined by inversion recovery. Below 9 GHz for 1 and below 1.5 GHz for 2,T(1)~T(2), as expected in the fast tumbling regime. At higher frequencies T(2) was shorter than T(1) due to incomplete motional averaging of g and A anisotropy. The frequency dependence of 1/T(1) is modeled as the sum of spin rotation, modulation of g and A-anisotropy, and a thermally-activated process that has maximum contribution at about 1.5 GHz. The spin lattice relaxation times for the nitronyl nitroxide were longer than for PDT by a factor of about 2 at 34 GHz, decreasing to about a factor of 1.5 at 250 MHz. The rotational correlation times, τ(R) are calculated to be 9 ps for 1 and about 25 ps for 2. The longer spin lattice relaxation times for 2 than for 1 at 9 and 34 GHz are due predominantly to smaller contributions from spin rotation that arise from slower tumbling. The smaller nitrogen hyperfine couplings for the nitronyl 2 than for 1 decrease the contribution to relaxation due to modulation of A anisotropy. However, at lower frequencies the slower tumbling of 2 results in a larger value of ωτ(R) (ω is the resonance frequency) and larger values of the spectral density function, which enhances the contribution from modulation of anisotropic interactions for 2 to a greater extent than for 1.

  15. Initial evaluation of hepatic T1 relaxation time as an imaging marker of liver disease associated with autosomal recessive polycystic kidney disease (ARPKD).

    Science.gov (United States)

    Gao, Ying; Erokwu, Bernadette O; DeSantis, David A; Croniger, Colleen M; Schur, Rebecca M; Lu, Lan; Mariappuram, Jose; Dell, Katherine M; Flask, Chris A

    2016-01-01

    Autosomal recessive polycystic kidney disease (ARPKD) is a potentially lethal multi-organ disease affecting both the kidneys and the liver. Unfortunately, there are currently no non-invasive methods to monitor liver disease progression in ARPKD patients, limiting the study of potential therapeutic interventions. Herein, we perform an initial investigation of T1 relaxation time as a potential imaging biomarker to quantitatively assess the two primary pathologic hallmarks of ARPKD liver disease: biliary dilatation and periportal fibrosis in the PCK rat model of ARPKD. T1 relaxation time results were obtained for five PCK rats at 3 months of age using a Look-Locker acquisition on a Bruker BioSpec 7.0 T MRI scanner. Six three-month-old Sprague-Dawley (SD) rats were also scanned as controls. All animals were euthanized after the three-month scans for histological and biochemical assessments of bile duct dilatation and hepatic fibrosis for comparison. PCK rats exhibited significantly increased liver T1 values (mean ± standard deviation = 935 ± 39 ms) compared with age-matched SD control rats (847 ± 26 ms, p = 0.01). One PCK rat exhibited severe cholangitis (mean T1  = 1413 ms), which occurs periodically in ARPKD patients. The observed increase in the in vivo liver T1 relaxation time correlated significantly with three histological and biochemical indicators of biliary dilatation and fibrosis: bile duct area percent (R = 0.85, p = 0.002), periportal fibrosis area percent (R = 0.82, p = 0.004), and hydroxyproline content (R = 0.76, p = 0.01). These results suggest that hepatic T1 relaxation time may provide a sensitive and non-invasive imaging biomarker to monitor ARPKD liver disease.

  16. Prevalence for the universal distribution of relaxation times near the glass transitions in experimental model systems: Rodlike liquid crystals and orientationally disordered crystals

    OpenAIRE

    2011-01-01

    Recently, Nielsen et al. [J. Chem. Phys. 130, 154508 (2009); Philos. Mag. 88, 4101 (2008)] demonstrated a universal pattern for the high frequency wing of the loss curve for primary relaxation time on approaching the glass transition for organic liquids. In this contribution it is presented that a similar universality occurs for glass-forming liquid crystals and orientationally disordered crystals (plastic crystals). Empirical correlations of the found behavior are also briefly di...

  17. Differences in patellar cartilage thickness, transverse relaxation time, and deformational behavior: a comparison of young women with and without patellofemoral pain.

    Science.gov (United States)

    Farrokhi, Shawn; Colletti, Patrick M; Powers, Christopher M

    2011-02-01

    The origin of patellofemoral pain (PFP) may be associated with the inability of the patellofemoral joint cartilage to absorb and distribute patellofemoral joint forces. When compared with a pain-free control group, young active women with PFP will demonstrate differences in their baseline patellar cartilage thickness and transverse (T2) relaxation time, as well as a less adaptive response to an acute bout of joint loading. Controlled laboratory study; Level of evidence, 3. Ten women between the ages of 23 to 37 years with PFP and 10 sex-, age-, and activity-matched pain-free controls participated. Quantitative magnetic resonance imaging of the patellofemoral joint was performed at baseline and after participants performed 50 deep knee bends. Differences in baseline cartilage thickness and T2 relaxation time, as well as the postexercise change in patellar cartilage thickness and T2 relaxation time, were compared between groups. Individuals with PFP demonstrated reductions in baseline cartilage thickness of 14.0% and 14.1% for the lateral patellar facet and total patellar cartilage, respectively. Similarly, individuals with PFP exhibited significantly lower postexercise cartilage thickness change for the lateral patellar facet (2.1% vs 8.9%) and the total patellar cartilage (4.4% vs 10.0%) when compared with the control group. No group differences in baseline or postexercise change in T2 relaxation time were found. The findings suggest that a baseline reduction in patellar cartilage thickness and a reduced deformational behavior of patellar cartilage following an acute bout of loading are associated with presence of PFP symptoms.

  18. Implications of Electron Momentum Relaxation Time Scales for Modeling of Transient Electric Fields in the Lower Ionosphere

    Science.gov (United States)

    Pasko, V. P.

    2009-12-01

    Thomas et al. [JGR, A12306, 2008] has reported lightning-driven electric (E) field pulses at 75-130 km altitude recorded during rocket experiment in 1995 from Wallops Island, Virginia. The measurements were compared to a 2D electromagnetic model of Cho and Rycroft [JASTP, 60,871,1998]. Thomas et al.[2008] indicated that the observed field magnitudes were an order of magnitude lower than predicted by the model and questioned validity of the electromagnetic pulse mechanism of elves. The goal of the present work, which utilizes Monte Carlo and FDTD electromagnetic modeling, is to emphasize range of validity of the local field approximation (LFA) employed in the Cho and Rycroft's [1998] model and other similar models for the cases when weak (~10 mV/m as reported in [Thomas et al., 2008]) E field pulses are considered. Glukhov et al. [GRL, 23, 2193, 1996] and Sukhorukov et al. [GRL, 23, 2911, 1996] performed Monte Carlo simulations for large E fields ~10V/m at typical altitudes of elves, which fully confirmed validity of models of elves based on LFA [Taranenko et al., GRL, 20, 2675, 1993; Inan et al., GRL, 23, 133, 1996]. We demonstrate that the time of relaxation of the momentum of the electron distributions subjected to the external E field scales approximately as 1/E and exceeds 10s of microseconds for E1 V/m when fast (10 kHz) processes are considered. The models of elves relying on LFA [e.g., Taranenko et al., 1993; Inan et al., 1996] generally require E>1 V/m for production of observable optical emissions at lower ionospheric altitudes and therefore remain valid, in agreement with original conclusions reached by Glukhov et al. [1996] and Sukhorukov et al. [1996]. Two additional factors may have contributed to the low field magnitudes reported in [Thomas et al., 2008]: 1) The measurements were conducted on September 2, 1995 around evening hours (9:22 PM local time) at which the lower ionosphere likely exhibited enhancement of electron density in comparison with

  19. Relaxation and phase space singularities in time series of human magnetoencephalograms can serve as an indicator of the photosensitive epilepsy

    CERN Document Server

    Yulmetyev, R M; Hänggi, P; Khusaenova, E V; Shimojo, S; Yulmetyeva, D G

    2006-01-01

    To analyze the crucial role of the fluctuation and relaxational effects in the human brain functioning we have studied a some statistical quantifiers that support the informational characteristics of neuromagnetic responses of magnetoencephalographic (MEG) signals. The signals to a flickering stimulus of different color combinations has been obtained from a group of control subjects which is contrasted with those for a patient with photosensitive epilepsy (PSE). We have revealed that the existence of the specific stratification of the phase clouds and the concomitant relaxation singularities of the corresponding nonequilibrium processes of chaotic behavior of the signals in the separate areas for a patient most likely shows the pronounced zones responsible the appearance of PSE.

  20. New technique for single-scan T1 measurements using solid echoes. [for spin-lattice relaxation time

    Science.gov (United States)

    Burum, D. P.; Elleman, D. D.; Rhim, W. K.

    1978-01-01

    A simple technique for single-scan T1 measurements in solids is proposed and analyzed for single exponential spin-lattice relaxation. In this technique, the direct spin heating caused by the sampling process is significantly reduced in comparison with conventional techniques by utilizing the 'solid echo' to refocus the magnetization. The applicability of this technique to both the solid and liquid phases is demonstrated.

  1. Influence of aging time of oleate precursor on the magnetic relaxation of cobalt ferrite nanoparticles synthesized by the thermal decomposition method

    Energy Technology Data Exchange (ETDEWEB)

    Herrera, Adriana P.; Polo-Corrales, Liliana [Department of Chemical Engineering, University of Puerto Rico, Mayagueez, Puerto Rico, PR 00681-9000 (United States); Chavez, Ermides; Cabarcas-Bolivar, Jari [Department of Physics, University of Puerto Rico, Mayagueez, Puerto Rico, PR 00681-9000 (United States); Uwakweh, Oswald N.C. [Department of General Engineering, University of Puerto Rico, Mayagueez, Puerto Rico, PR 00681-9000 (United States); Rinaldi, Carlos, E-mail: crinaldi@uprm.edu [Department of Chemical Engineering, University of Puerto Rico, Mayagueez, Puerto Rico, PR 00681-9000 (United States)

    2013-02-15

    Cobalt ferrite nanoparticles are of interest because of their room temperature coercivity and high magnetic anisotropy constant, which make them attractive in applications such as sensors based on the Brownian relaxation mechanism and probes to determine the mechanical properties of complex fluids at the nanoscale. These nanoparticles can be synthesized with a narrow size distribution by the thermal decomposition of an iron-cobalt oleate precursor in a high boiling point solvent. We studied the influence of aging time of the iron-cobalt oleate precursor on the structure, chemical composition, size, and magnetic relaxation of cobalt ferrite nanoparticles synthesized by the thermal decomposition method. The structure and thermal behavior of the iron-cobalt oleate was studied during the aging process. Infrared spectra indicated a shift in the coordination state of the oleate and iron/cobalt ions from bidentate to bridging coordination. Aging seemed to influence the thermal decomposition of the iron-cobalt oleate as determined from thermogravimmetric analysis and differential scanning calorimetry, where shifts in the temperatures corresponding to decomposition events and a narrowing of the endotherms associated with these events were observed. Aging promoted formation of the spinel crystal structure, as determined from X-ray diffraction, and influenced the nanoparticle magnetic properties, resulting in an increase in blocking temperature and magnetocrystalline anisotropy. Mossbauer spectra also indicated changes in the magnetic properties resulting from aging of the precursor oleate. Although all samples exhibited some degree of Brownian relaxation, as determined from complex susceptibility measurements in a liquid medium, aging of the iron-cobalt oleate precursor resulted in crossing of the in-phase {chi} Prime and out-of-phase {chi} Double-Prime components of the complex susceptibility at the frequency of the Brownian magnetic relaxation peak, as expected for

  2. Isotope ratio of Cl NQR spin-lattice relaxation times in 1D hydrogen-bonding system of tetramethylpyrazine-chloranilic acid at high temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Asaji, Tetsuo, E-mail: asaji@chs.nihon-u.ac.jp [Nihon University, Department of Chemistry, College of Humanities and Sciences (Japan)

    2013-05-15

    The temperature dependences of spin-lattice relaxation time T{sub 1} of {sup 35}Cl and {sup 37}Cl NQR were studied for the co-crystal of tetramethylpyrazine (TMP) with chloranilic acid (H{sub 2}ca), TMP-H{sub 2}ca, in which one-dimensional hydrogen bonding is formed by alternate arrangement of TMP and H{sub 2}ca. The isotope ratio {sup 37}Cl T{sub 1} / {sup 35}Cl T{sub 1} was determined to be 1.0 {+-} 0.1 above ca. 290 K where a steep decrease of spin-lattice relaxation time T{sub 1} with increasing temperature was observed. In this temperature range it is suggested that the relaxation is originated from the slow fluctuation of electric field gradient (EFG). Beside EFG fluctuation due to the external-charge-density fluctuation, the small angle reorientation of the quantization axis triggered by a proton transfer motion between N...H-O and N-H...O hydrogen bonding states is proposed.

  3. Temperature- and pressure-dependent study of 35Cl NQR frequency and spin lattice relaxation time in 2,3-dichloroanisole.

    Science.gov (United States)

    Ramu, L; Ramesh, K P; Ramananda, D; Chandramani, R

    2010-08-01

    The temperature and pressure dependence of (35)Cl NQR frequency and spin lattice relaxation time (T(1)) were investigated in 2,3-dichloroanisole. Two NQR signals were observed throughout the temperature and pressure range studied. T(1) were measured in the temperature range from 77 to 300 K and from atmospheric pressure to 5 kbar. Relaxation was found to be due to the torsional motion of the molecule and also reorientation of motion of the CH(3) group. T(1) versus temperature data were analyzed on the basis of Woessner and Gutowsky model, and the activation energy for the reorientation of the CH(3) group was estimated. The temperature dependence of the average torsional lifetimes of the molecules and the transition probabilities were also obtained. NQR frequency shows a nonlinear behavior with pressure, indicating both dynamic and static effects of pressure. The pressure coefficients were observed to be positive for both the lines. A thermodynamic analysis of the data was carried out to determine the constant volume temperature coefficients of the NQR frequency. The variation of spin lattice time with pressure was very small, showing that the relaxation is mainly due to the torsional motions of the molecules.

  4. 实时脉冲光声法用于分子弛豫时间的测定%Real-time pulsed photoacoustics-molecular relaxation time measurements

    Institute of Scientific and Technical Information of China (English)

    Markushev Dragan; Rabasovic Mihailo; Lukic Mladena; Cojbasic Zarko; Todorovic Dragan

    2013-01-01

    脉冲光声光谱法一个重要的应用是确定气体分子的振动—平动弛豫时间τV-T.因激光光束的空间分布R(r)对光声测量有显著影响,我们发展了同时测定R(r)和τV-T的方法.本方法基于光声脉冲的实时信号和一种用于光声成像的数学运算法则.本文讨论了智能计算用于多原子气体分子的R(r)和τV-T同时和实时测定的可能性.进一步利用前馈多层神经网络的离线批训练法,结合一个理论光声信号对R(r)和τV-T进行了同时和实时分析.本方法可明显缩短确定上述参数所需时间.%Determination of the vibrational-to-translational relaxation time rv-T in gases is one of the applications of pulsed photoacoustic spectroscopy.Because the spatial profile of the laser beam R (r)can significantly influence the accuracy of the photoacoustic measurements,we developed the method for simultaneous determination of the R(r)and τv T.It is based on the temporal shape of the photoacoustic pulse and utilizes a mathematical algorithm developed for photoacoustic tomography.The possibilities of computational intelligence application for simultaneous and real-time determination of R(r)and rv-T values of polyatomic molecules in gases by pulsed photoacoustic are also discussed.Feed forward multilayer perception networks are trained in an offline batch training regime to estimate simultaneously,and in real-time,R(r) (profile shape class) and τv T from a given (theoretical) photoacoustic signals.Proposed method significantly shortens the time required for the simultaneous determination of the afore mentioned quantities.

  5. A 3-year longitudinal analysis of changes in fitness, physical activity, fatness and screen time

    DEFF Research Database (Denmark)

    Aires, L; Andersen, Lars Bo; Mendonça, D

    2010-01-01

    in fitness. METHODS: This is a 3-year longitudinal study of 345 high school students aged 11-19 years. Students performed curl-ups, push-ups and 20-m shuttle run tests from Fitnessgram. PA and ST were evaluated using a standard questionnaire. Standardized scores of fitness tests were summed. Changes over...

  6. Speech Perception and Production by Sequential Bilingual Children: A Longitudinal Study of Voice Onset Time Acquisition

    Science.gov (United States)

    McCarthy, Kathleen M.; Mahon, Merle; Rosen, Stuart; Evans, Bronwen G.

    2014-01-01

    The majority of bilingual speech research has focused on simultaneous bilinguals. Yet, in immigrant communities, children are often initially exposed to their family language (L1), before becoming gradually immersed in the host country's language (L2). This is typically referred to as sequential bilingualism. Using a longitudinal design, this…

  7. Molecular Relaxation in Liquids

    CERN Document Server

    Bagchi, Biman

    2012-01-01

    This book brings together many different relaxation phenomena in liquids under a common umbrella and provides a unified view of apparently diverse phenomena. It aligns recent experimental results obtained with modern techniques with recent theoretical developments. Such close interaction between experiment and theory in this area goes back to the works of Einstein, Smoluchowski, Kramers' and de Gennes. Development of ultrafast laser spectroscopy recently allowed study of various relaxation processes directly in the time domain, with time scales going down to picosecond (ps) and femtosecond (fs

  8. Linear regulator design for stochastic systems by a multiple time scales method. [with application to F-8 aircraft longitudinal control

    Science.gov (United States)

    Teneketzis, D.; Sandell, N. R., Jr.

    1976-01-01

    This paper develops a hierarchically-structured, suboptimal controller for a linear stochastic system composed of fast and slow subsystems. It is proved that the controller is optimal in the limit as the separation of time scales of the subsystems becomes infinite. The methodology is illustrated by design of a controller to suppress the phugoid and short period modes of the longitudinal dynamics of the F-8 aircraft.

  9. Joint analyses of longitudinal and time-to-event data in research on aging: Implications for predicting health and survival

    Directory of Open Access Journals (Sweden)

    Konstantin G. Arbeev

    2014-11-01

    Full Text Available Longitudinal data on aging, health and longevity provide a wealth of information to investigate different aspects of the processes of aging and development of diseases leading to death. Statistical methods aimed at analyses of time-to-event data jointly with longitudinal measurements became known as the joint models (JM. An important point to consider in analyses of such data in the context of studies on aging, health, and longevity is how to incorporate knowledge and theories about mechanisms and regularities of aging-related changes that accumulate in the research field into respective analytic approaches. In the absence of specific observations of longitudinal dynamics of relevant biomarkers manifesting such mechanisms and regularities, traditional approaches have a rather limited utility to estimate respective parameters that can be meaningfully interpreted from the biological point of view. A conceptual analytic framework for these purposes, the stochastic process model of aging (SPM, has been recently developed in the biodemographic literature. It incorporates available knowledge about mechanisms of aging-related changes which may be hidden in the individual longitudinal trajectories of physiological variables and this allows for analyzing their indirect impact on risks of diseases and death. Despite, essentially, serving similar purposes, JM and SPM developed in parallel in different disciplines with very limited cross-referencing. Although there were several publications separately reviewing these two approaches, there were no publications presenting both these approaches in some detail. Here we overview both approaches jointly and provide some new modifications of SPM. We discuss the use of stochastic processes to capture biological variation and heterogeneity in longitudinal patterns and important and promising (but still largely underused applications of JM and SPM to predictions of individual and population mortality and health

  10. Multilevel modeling versus cross-sectional analysis for assessing the longitudinal tracking of cardiovascular risk factors over time.

    Science.gov (United States)

    Xanthakis, Vanessa; Sullivan, Lisa M; Vasan, Ramachandran S

    2013-12-10

    Correlated data are obtained in longitudinal epidemiological studies, where repeated measurements are taken on individuals or groups over time. Such longitudinal data are ideally analyzed using multilevel modeling approaches, which appropriately account for the correlations in repeated responses in the same individual. Commonly used regression models are inappropriate as they assume that measurements are independent. In this tutorial, we use multilevel modeling to demonstrate its use for analysis of correlated data obtained from serial examinations on individuals. We focus on cardiovascular epidemiological research where investigators are often interested in quantifying the relations between clinical risk factors and outcome measures (X and Y, respectively), where X and Y are measured repeatedly over time, for example, using serial observations on participants attending multiple examinations in a longitudinal cohort study. For instance, it may be of interest to evaluate the relations between serial measures of left ventricular mass (outcome) and of its potential determinants (i.e., body mass index and blood pressure), both of which are measured over time. In this tutorial, we describe the application of multilevel modeling to cardiovascular risk factors and outcome data (using serial echocardiographic data as an example of an outcome). We suggest an analytical approach that can be implemented to evaluate relations between any potential outcome of interest and risk factors, including assessment of random effects and nonlinear relations. We illustrate these steps using echocardiographic data from the Framingham Heart Study with SAS PROC MIXED.

  11. Longitudinal Serum Creatinine Levels in Relation to Graft Loss Following Renal Transplantation: Robust Joint Modeling of Longitudinal Measurements and Survival Time Data

    Directory of Open Access Journals (Sweden)

    Younespour

    2016-08-01

    Full Text Available Background Chronic kidney disease (CKD is a major public health problem that may lead to end-stage renal disease (ESRD. Renal transplantation has become the treatment modality of choice for the majority of patients with ESRD. It is therefore necessary to monitor the disease progression of patients who have undergone renal transplantation. In order to monitor the disease progression, the continuous assessment of kidney function over time is considered. Objectives This study aimed to investigate the etiological role of recipient characteristics in serum creatinine changes within the follow-up period and in relation to the graft failure risk, as well as to evaluate whether or not the serum creatinine level represents an indicator of graft failure following renal transplantation. Methods This retrospective cohort study was conducted at the department of nephrology, Baqiyatallah Hospital, Baqiyatallah University of Medical Sciences, between April 2005 and December 2008. The study involved 413 renal transplantation patients. The primary outcomes were the determination of the serum creatinine levels at each attendance and the time to graft failure. Robust joint modeling of the longitudinal measurements (serum creatinine level and time-to-event data (time to graft failure were used for the analysis in the presence of outliers in the serum creatinine levels. The data analysis was implemented in WinBUGS 1.4.3. Results There was a positive association between the serum creatinine level and graft failure (HR = 5.13, P < 0.001. A one unit increase in the serum creatinine level suggests an increased risk of graft failure of up to 5.13 times. The serum creatinine level significantly decreased over time (95% CI: (-1.58, -1.08. The recipient’s age was negatively associated with the serum creatinine level (95% CI: (-0.02, -0.001. Conclusions Graft failure is more likely to occur in patients with higher serum creatinine levels.

  12. Properties of the relaxation time distribution underlying the Kohlrausch-Williams-Watts photoionization of the DX centers in Cd{sub 1-x}Mn{sub x}Te mixed crystals

    Energy Technology Data Exchange (ETDEWEB)

    Trzmiel, J; Weron, K; Placzek-Popko, E [Institute of Physics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland); Janczura, J [Hugo Steinhaus Center for Stochastic Methods and Institute of Mathematics and Computer Science, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland)

    2009-08-26

    In this paper we clarify the relationship between the relaxation rate and relaxation time distributions underlying the Kohlrausch-Williams-Watts (KWW) photoconductivity build-ups in indium- and gallium-doped Cd{sub 1-x}Mn{sub x}Te mixed crystals. We discuss the role of asymptotic properties of the corresponding probability density functions. We show that the relaxation rate distribution, as a completely asymmetric alpha-stable distribution, leads to an infinite mean value of the effective relaxation rate. In contrast, the relaxation time distribution related to it leads to a finite mean value of the effective relaxation time. It follows from the experimental data analysis that for all the investigated samples the KWW exponent alpha decreases linearly with increasing photon flux in the range of (0.6-0.99) and its values are more spread in the case of gallium-doped material. We also observe a linear dependence of the mean relaxation time on the characteristic material time constant, which is consistent with the theoretical model.

  13. Discrimination of benign from malignant hepatic lesions based on their T2-relaxation times calculated from moderately T2-weighted turbo SE sequence

    Energy Technology Data Exchange (ETDEWEB)

    Cieszanowski, Andrzej; Szeszkowski, Wojciech; Golebiowski, Marek; Bielecki, Dennis K.; Pruszynski, Bogdan [2. Department of Clinical Radiology, Medical University of Warsaw, ul.Banacha 1a, 02097, Warsaw (Poland); Grodzicki, Mariusz [Department of Surgery and Liver Disease, Medical University of Warsaw, ul.Banacha 1a, 02097, Warsaw (Poland)

    2002-09-01

    The differentiation of hemangioma from other hepatic neoplasms using MRI usually relies on the evaluation of heavily T2-weighted images. The aim of this study was to assess the value of T2-relaxation times calculated from moderately T2-weighted turbo spin-echo (TSE) sequence in characterization of focal hepatic lesions, including hepatic malignancies, focal nodular hyperplasia (FNH), hemangioma, and cyst. Fifty-two patients with 114 proven lesions (61 malignant masses, 6 focal nodular hyperplasias, 28 hemangiomas, 19 cystic lesions) were examined on 1.5-T system using a double-echo TSE sequence (TR=1800 ms; TE{sub eff} 1=40 ms; TE{sub eff} 2=120 ms). Signal intensities (SI) of the liver as well as SI of all lesions were measured, and then the T2-relaxation times were calculated. The mean T2 time for the liver was 54 ms ({+-}8 ms), for FNH 66 ms ({+-}7 ms), for malignant hepatic lesions 85 ms ({+-}17 ms), for hemangiomas 155 ms ({+-}35 ms), and for cystic lesions 583 ms ({+-}369) ms. Most malignant hepatic lesions were best differentiated between the thresholds of 67 and 116 ms, generating a sensitivity of 90% and a specificity of 94%. There were six false-negative diagnoses of malignant tumor and three false-positive cases (two hemangiomas and one FNH). Calculation of the T2-relaxation times obtained from the double-echo TSE sequence with moderate T2-weighting allowed differentiation between malignant and benign hepatic lesions with high sensitivity and specificity. (orig.)

  14. The contribution of time-dependent stress relaxation in protein gels to the recoverable energy that is used as a tool to describe food texture

    Science.gov (United States)

    de Jong, Saskia; van Vliet, Ton; de Jongh, Harmen H. J.

    2015-11-01

    The recoverable energy (RE), defined as the ratio of the work exerted on a test specimen during compression and recovered upon subsequent decompression, has been shown to correlate to sensory profiling of protein-based food products. Understanding the mechanism determining the time-dependency of RE is primordial. This work aims to identify the protein-specific impact on the recoverable energy by stress dissipation via relaxation of (micro)structural rearrangements within protein gels. To this end, caseinate and gelatin gels are studied for their response to time-dependent mechanical deformation as they are known to develop structurally distinct network morphologies. This work shows that in gelatin gels no significant stress relaxation occurs on the seconds timescale, and consequently no time-dependency of the amount of energy stored in this material is observed. In caseinate gels, however, the energy dissipation via relaxation processes does contribute significantly to the time-dependency of reversible stored energy in the network. This can explain the obtained RE as a function of applied deformation at slow deformation rates. At faster deformation, an additional contribution to the dissipated energy is apparent, that increases with the deformation rate, which might point to the role of energy dissipation related to friction of the serum entrapped by the protein-network. This work shows that engineering strategies focused on controlling viscous flow in protein gels could be more effective to dictate the ability to elastically store energy in protein gels than routes that direct protein-specific aggregation and/or network-assembly.

  15. Spousal interrelations in happiness in the Seattle Longitudinal Study: considerable similarities in levels and change over time.

    Science.gov (United States)

    Hoppmann, Christiane A; Gerstorf, Denis; Willis, Sherry L; Schaie, K Warner

    2011-01-01

    Development does not take place in isolation and is often interrelated with close others such as marital partners. To examine interrelations in spousal happiness across midlife and old age, we used 35-year longitudinal data from both members of 178 married couples in the Seattle Longitudinal Study. Latent growth curve models revealed sizeable spousal similarities not only in levels of happiness but also in how happiness changed over time. These spousal interrelations were considerably larger in size than those found among random pairs of women and men from the same sample. Results are in line with life-span theories emphasizing an interactive minds perspective by showing that adult happiness waxes and wanes in close association with the respective spouse. Our findings also complement previous individual-level work on age-related changes in well-being by pointing to the importance of using the couple as the unit of analysis.

  16. Timed Up & Go as a measure for longitudinal change in mobility after stroke - Postural Stroke Study in Gothenburg (POSTGOT).

    Science.gov (United States)

    Persson, Carina U; Danielsson, Anna; Sunnerhagen, Katharina S; Grimby-Ekman, Anna; Hansson, Per-Olof

    2014-05-09

    A frequently used clinical test to assess mobility after stroke is the Timed Up & Go. Knowledge regarding whether or not the Timed Up & Go is able to detect change over time in patients with stroke, whether improvements in mobility exist after the first three months and whether or not longitudinal change in mobility after stroke depend on the patients' age, is limited or unclear. The objectives were to investigate the distribution-based responsiveness of the Timed Up & Go (TUG) during the first three months after a first event of stroke, to measure the longitudinal change in TUG time during the first year after stroke and to establish whether recovery in TUG time differs between different age groups. Ninety-one patients with first-ever stroke were assessed using the Timed Up & Go at the 1st week and at 3, 6 and 12 months after stroke. The non-parametric sign-test, the parametric t-test and a mixed model approach to linear regression for repeated measurements (Proc mixed) were used for the statistical analyses. The median TUG time was reduced from 17 to 12 seconds (p time between 3 and 12 months after stroke, while patients time). The Timed Up & Go demonstrates ability to detect change in mobility over time in patients with stroke. A significant improvement in TUG time from the 1st week to 3 months after stroke was found, as expected, but thereafter no statistically significant change was detected. After 3 months, patients ≥80 years tended to deteriorate in terms of TUG time, while the younger patients did not.

  17. Timed Up & Go as a measure for longitudinal change in mobility after stroke – Postural Stroke Study in Gothenburg (POSTGOT)

    Science.gov (United States)

    2014-01-01

    Background A frequently used clinical test to assess mobility after stroke is the Timed Up & Go. Knowledge regarding whether or not the Timed Up & Go is able to detect change over time in patients with stroke, whether improvements in mobility exist after the first three months and whether or not longitudinal change in mobility after stroke depend on the patients’ age, is limited or unclear. The objectives were to investigate the distribution-based responsiveness of the Timed Up & Go (TUG) during the first three months after a first event of stroke, to measure the longitudinal change in TUG time during the first year after stroke and to establish whether recovery in TUG time differs between different age groups. Methods Ninety-one patients with first-ever stroke were assessed using the Timed Up & Go at the 1st week and at 3, 6 and 12 months after stroke. The non-parametric sign-test, the parametric t-test and a mixed model approach to linear regression for repeated measurements (Proc mixed) were used for the statistical analyses. Results The median TUG time was reduced from 17 to 12 seconds (p time between 3 and 12 months after stroke, while patients time). Conclusion The Timed Up & Go demonstrates ability to detect change in mobility over time in patients with stroke. A significant improvement in TUG time from the 1st week to 3 months after stroke was found, as expected, but thereafter no statistically significant change was detected. After 3 months, patients ≥80 years tended to deteriorate in terms of TUG time, while the younger patients did not. PMID:24885868

  18. Non-Equilibrium Real-Time Dynamics of Quantum Fields Linear and Non-Linear Relaxation in Scalar and Gauge Theories

    CERN Document Server

    Boyanovsky, D; Holman, R; Kumar, S P; Pisarski, R D; Salgado, J; Pisarski, Rob D.

    1998-01-01

    The real time evolution of field condensates is solved for small and large field amplitudes in scalar theories.For small amplitudes,the quantum equations of motion for the condensate can be linearized and solved by Laplace transform. The late time evolution turns to be determined by the singularities in the complex plane (one-particle poles, two- and multi- particle cuts, Landau cuts for non-zero initial temperature). In hot scalar electrodynamics, we solve the real time evolution of field condensates with soft length scales \\sim k^{-1}>(eT)^{-1}. Transverse gauge invariant condensates relax as 1/t^2 to amplitudes determined by the quasiparticle poles. We rederive the HTL action using the non-equilibrium field theory techniques.In the nonlinear regime (for large initial energy densities) we analyze the dynamics of dissipation and relaxation in scalar theory after linear unstabilities are shut-off by the quantum back-reaction. A new time scale emerges that separates the linear from the non-linear regimes. This...

  19. Multiple-relaxation-time lattice Boltzmann model for incompressible miscible flow with large viscosity ratio and high Péclet number

    Science.gov (United States)

    Meng, Xuhui; Guo, Zhaoli

    2015-10-01

    A lattice Boltzmann model with a multiple-relaxation-time (MRT) collision operator is proposed for incompressible miscible flow with a large viscosity ratio as well as a high Péclet number in this paper. The equilibria in the present model are motivated by the lattice kinetic scheme previously developed by Inamuro et al. [Philos. Trans. R. Soc. London, Ser. A 360, 477 (2002), 10.1098/rsta.2001.0942]. The fluid viscosity and diffusion coefficient depend on both the corresponding relaxation times and additional adjustable parameters in this model. As a result, the corresponding relaxation times can be adjusted in proper ranges to enhance the performance of the model. Numerical validations of the Poiseuille flow and a diffusion-reaction problem demonstrate that the proposed model has second-order accuracy in space. Thereafter, the model is used to simulate flow through a porous medium, and the results show that the proposed model has the advantage to obtain a viscosity-independent permeability, which makes it a robust method for simulating flow in porous media. Finally, a set of simulations are conducted on the viscous miscible displacement between two parallel plates. The results reveal that the present model can be used to simulate, to a high level of accuracy, flows with large viscosity ratios and/or high Péclet numbers. Moreover, the present model is shown to provide superior stability in the limit of high kinematic viscosity. In summary, the numerical results indicate that the present lattice Boltzmann model is an ideal numerical tool for simulating flow with a large viscosity ratio and/or a high Péclet number.

  20. I. Low frequency noise in metal films at the superconducting transition. II. Resistance of superconductor - normal metal- superconductor sandwiches and the quasiparticle relaxation time

    Energy Technology Data Exchange (ETDEWEB)

    Hsiang, T.Y.

    1977-07-01

    Measurements of the noise power spectra of tin and lead films at the superconducting transition in the frequency range of 0.1 Hz to 5k Hz are reported. Two types of samples were made. Type A were evaporated directly onto glass substrate, while Type B were evaporated onto glass or sapphire substrate with a 50A aluminum underlay. The results were consistent with a thermal diffusion model which attributes the noise to the intrinsic temperature fluctuation in the metal film driven with a random energy flux source. In both types of metal films, the noise power was found to be proportional to (V-bar)/sup 2/ ..beta../sup 2//..cap omega.., where V-bar was the mean voltage across the sample, ..beta.. was the temperature coefficient of resistance and ..cap omega.. was the volume of the sample. Correlation of noises in two regions of the metal film a distance d apart was detected at frequencies less than or = D/..pi..d/sup 2/. A possible explanation of the noises using quantitative boundary conditions and implications of this work for device applications are discussed. Theoretical and experimental investigation are reported on the resistance of superconductor-normal metal-superconductor sandwiches near T/sub c/. The increase in SNS resistance is attributed to the penetration of normal electric current in the superconductor. It is proved from first principles that an electric field can exist inside the superconductor when quasiparticles are not equally populated on the two branches of the excitation spectrum, and such is the case in a current biased SNS junction. The electric field inside S decays according to a diffusion law. The diffusion length is determined by the quasiparticle ''branch-crossing'' relaxation time. The branch-crossing relaxation times were measured. Impurity-doping of tin was found to decrease this relaxation time.

  1. Density relaxation and particle motion characteristics in a non-ionic deep eutectic solvent (acetamide + urea): Time-resolved fluorescence measurements and all-atom molecular dynamics simulations

    Energy Technology Data Exchange (ETDEWEB)

    Das, Anuradha; Das, Suman; Biswas, Ranjit, E-mail: ranjit@bose.res.in [Chemical, Biological and Macromolecular Sciences, S. N. Bose National Centre for Basic Sciences, Block-JD, Sector-III, Salt Lake, Kolkata, West Bengal 700098 (India)

    2015-01-21

    Temperature dependent relaxation dynamics, particle motion characteristics, and heterogeneity aspects of deep eutectic solvents (DESs) made of acetamide (CH{sub 3}CONH{sub 2}) and urea (NH{sub 2}CONH{sub 2}) have been investigated by employing time-resolved fluorescence measurements and all-atom molecular dynamics simulations. Three different compositions (f) for the mixture [fCH{sub 3}CONH{sub 2} + (1 − f)NH{sub 2}CONH{sub 2}] have been studied in a temperature range of 328-353 K which is ∼120-145 K above the measured glass transition temperatures (∼207 K) of these DESs but much lower than the individual melting temperature of either of the constituents. Steady state fluorescence emission measurements using probe solutes with sharply different lifetimes do not indicate any dependence on excitation wavelength in these metastable molten systems. Time-resolved fluorescence anisotropy measurements reveal near-hydrodynamic coupling between medium viscosity and rotation of a dissolved dipolar solute. Stokes shift dynamics have been found to be too fast to be detected by the time-resolution (∼70 ps) employed, suggesting extremely rapid medium polarization relaxation. All-atom simulations reveal Gaussian distribution for particle displacements and van Hove correlations, and significant overlap between non-Gaussian (α{sub 2}) and new non-Gaussian (γ) heterogeneity parameters. In addition, no stretched exponential relaxations have been detected in the simulated wavenumber dependent acetamide dynamic structure factors. All these results are in sharp contrast to earlier observations for ionic deep eutectics with acetamide [Guchhait et al., J. Chem. Phys. 140, 104514 (2014)] and suggest a fundamental difference in interaction and dynamics between ionic and non-ionic deep eutectic solvent systems.

  2. Liquid-state paramagnetic relaxation from first principles

    Science.gov (United States)

    Rantaharju, Jyrki; Vaara, Juha

    2016-10-01

    We simulate nuclear and electron spin relaxation rates in a paramagnetic system from first principles. Sampling a molecular dynamics trajectory with quantum-chemical calculations produces a time series of the instantaneous parameters of the relevant spin Hamiltonian. The Hamiltonians are, in turn, used to numerically solve the Liouville-von Neumann equation for the time evolution of the spin density matrix. We demonstrate the approach by studying the aqueous solution of the Ni2 + ion. Taking advantage of Kubo's theory, the spin-lattice (T1) and spin-spin (T2) relaxation rates are extracted from the simulations of the time dependence of the longitudinal and transverse magnetization, respectively. Good agreement with the available experimental data is obtained by the method.

  3. Organic semiconductors: What makes the spin relax?

    Science.gov (United States)

    Bobbert, Peter A.

    2010-04-01

    Spin relaxation in organic materials is expected to be slow because of weak spin-orbit coupling. The effects of deuteration and coherent spin excitation show that the spin-relaxation time is actually limited by hyperfine fields.

  4. Parenting, relational aggression, and borderline personality features: associations over time in a Russian longitudinal sample.

    Science.gov (United States)

    Nelson, David A; Coyne, Sarah M; Swanson, Savannah M; Hart, Craig H; Olsen, Joseph A

    2014-08-01

    Crick, Murray-Close, and Woods (2005) encouraged the study of relational aggression as a developmental precursor to borderline personality features in children and adolescents. A longitudinal study is needed to more fully explore this association, to contrast potential associations with physical aggression, and to assess generalizability across various cultural contexts. In addition, parenting is of particular interest in the prediction of aggression or borderline personality disorder. Early aggression and parenting experiences may differ in their long-term prediction of aggression or borderline features, which may have important implications for early intervention. The currrent study incorporated a longitudinal sample of preschool children (84 boys, 84 girls) living in intact, two-parent biological households in Voronezh, Russia. Teachers provided ratings of children's relational and physical aggression in preschool. Mothers and fathers also self-reported their engagement in authoritative, authoritarian, permissive, and psychological controlling forms of parenting with their preschooler. A decade later, 70.8% of the original child participants consented to a follow-up study in which they completed self-reports of relational and physical aggression and borderline personality features. The multivariate results of this study showed that preschool relational aggression in girls predicted adolescent relational aggression. Preschool aversive parenting (i.e., authoritarian, permissive, and psychologically controlling forms) significantly predicted aggression and borderline features in adolescent females. For adolescent males, preschool authoritative parenting served as a protective factor against aggression and borderline features, whereas authoritarian parenting was a risk factor for later aggression.

  5. Resolving the Impact of Biological Processes on DNAPL Transport in Unsaturated Porous Media Through Nuclear Magnetic Resonance Relaxation Time Measurements

    Science.gov (United States)

    Hertzog, R. C.; Geesey, G.; White, T.; Oram, L.; Seymour, J.; Codd, S.; Straley, C.; Bryar, T.

    2003-12-01

    This research leads to a better understanding of how physical and biological properties of porous media influence water and dense non-aqueous phase liquid (DNAPL) distributions under saturated and unsaturated conditions. Knowing how environmental properties affect DNAPL solvent flow in the subsurface is essential for developing models of flow and transport needed for designing remediation and long-term stewardship strategies. We investigate the capability and limitations of low-field nuclear magnetic resonance (NMR) relaxation decay-rate measurements for determining environmental properties affecting DNAPL solvent flow in the subsurface. For in-situ subsurface environmental applications, low-field proton NMR measurements are preferred to conventional high-field techniques commonly used to obtain chemical shift data, because low field measurements are much less degraded by magnetic susceptibility variations between rock grains and pore fluids that significantly interfere with high-field NMR measurements. The research scope includes discriminating DNAPLs in water-wet or solvent-wet environments and the impact of biological processes on their transport mechanisms in porous media. Knowledge of the in situ flow properties and pore distributions of organic contaminants are critical to understanding where and when these fluids will enter subsurface aquifers. Experiments determined that commonly found subsurface DNAPLs containing hydrogen, such as trichloroethylene and dichloroethylene, are detectable and distinguished from water in soils. Related experiments concern the effects of bacterial accumulation in saturated and unsaturated porous media on water and DNAPL pore-size distributions. These include synthetic bio-film matrix as a surrogate bio-film and sand, biological agents to grow biofilms, and multiple pore sizes to determine if bio-films prefer certain pore-size ranges. NMR microscopy focused on imaging a single biofilm in a 1 mm capillary reactor. This system

  6. (31)P-MRS of healthy human brain: ATP synthesis, metabolite concentrations, pH, and T1 relaxation times.

    Science.gov (United States)

    Ren, Jimin; Sherry, A Dean; Malloy, Craig R

    2015-11-01

    The conventional method for measuring brain ATP synthesis is (31)P saturation transfer (ST), a technique typically dependent on prolonged pre-saturation with γ-ATP. In this study, ATP synthesis rate in resting human brain is evaluated using EBIT (exchange kinetics by band inversion transfer), a technique based on slow recovery of γ-ATP magnetization in the absence of B1 field following co-inversion of PCr and ATP resonances with a short adiabatic pulse. The unidirectional rate constant for the Pi → γ-ATP reaction is 0.21 ± 0.04 s(-1) and the ATP synthesis rate is 9.9 ± 2.1 mmol min(-1)  kg(-1) in human brain (n = 12 subjects), consistent with the results by ST. Therefore, EBIT could be a useful alternative to ST in studying brain energy metabolism in normal physiology and under pathological conditions. In addition to ATP synthesis, all detectable (31)P signals are analyzed to determine the brain concentration of phosphorus metabolites, including UDPG at around 10 ppm, a previously reported resonance in liver tissues and now confirmed in human brain. Inversion recovery measurements indicate that UDPG, like its diphosphate analogue NAD, has apparent T1 shorter than that of monophosphates (Pi, PMEs, and PDEs) but longer than that of triphosphate ATP, highlighting the significance of the (31)P-(31)P dipolar mechanism in T1 relaxation of polyphosphates. Another interesting finding is the observation of approximately 40% shorter T1 for intracellular Pi relative to extracellular Pi, attributed to the modulation by the intracellular phosphoryl exchange reaction Pi ↔ γ-ATP. The sufficiently separated intra- and extracellular Pi signals also permit the distinction of pH between intra- and extracellular environments (pH 7.0 versus pH 7.4). In summary, quantitative (31)P MRS in combination with ATP synthesis, pH, and T1 relaxation measurements may offer a promising tool to detect biochemical alterations at early stages of brain dysfunctions and diseases.

  7. Natural relaxation

    Science.gov (United States)

    Marzola, Luca; Raidal, Martti

    2016-11-01

    Motivated by natural inflation, we propose a relaxation mechanism consistent with inflationary cosmology that explains the hierarchy between the electroweak scale and Planck scale. This scenario is based on a selection mechanism that identifies the low-scale dynamics as the one that is screened from UV physics. The scenario also predicts the near-criticality and metastability of the Standard Model (SM) vacuum state, explaining the Higgs boson mass observed at the Large Hadron Collider (LHC). Once Majorana right-handed neutrinos are introduced to provide a viable reheating channel, our framework yields a corresponding mass scale that allows for the seesaw mechanism as well as for standard thermal leptogenesis. We argue that considering singlet scalar dark matter extensions of the proposed scenario could solve the vacuum stability problem and discuss how the cosmological constant problem is possibly addressed.

  8. Theoretical study of built-in-polarization effect on relaxation time and mean free path of phonons in Al$_x$Ga$_{1−x}$N alloy

    Indian Academy of Sciences (India)

    B K SAHOO; A PANSARI

    2016-12-01

    In this article we have investigated theoretically the effect of built-in-polarization field on various phonon scattering mechanisms in AlxGa1−xN alloy. The built-in-polarization field of AlxGa1−xN modifies the elastic constant,group velocity of phonons and Debye temperature. As a result, various phonon scattering mechanisms are changed. Important phonon scattering mechanisms such as normal scattering, Umklapp scattering, point defect scattering, dislocation scattering and phonon–electron scattering processes have been considered in the computation. The combined relaxation time due to above-mentioned scattering mechanisms has also been computed as afunction of phonon frequency for various Al compositions at room temperature. It is found that combined relaxation time is enhanced due to built-in-polarization effect and makes phonon mean free path longer, which is required forhigher optical, electrical and thermal transport processes. The result can be used to determine the effect of built-inpolarization field on optical and thermal properties of Al$_x$Ga$_{1−x}$N and will be useful, particularly, for improvementof thermoelectric performance of Al$_x$Ga$_{1−x}$N alloy through polarization engineering.

  9. A multiple-relaxation-time lattice-boltzmann model for bacterial chemotaxis: effects of initial concentration, diffusion, and hydrodynamic dispersion on traveling bacterial bands.

    Science.gov (United States)

    Yan, Zhifeng; Hilpert, Markus

    2014-10-01

    Bacterial chemotaxis can enhance the bioremediation of contaminants in aqueous and subsurface environments if the contaminant is a chemoattractant that the bacteria degrade. The process can be promoted by traveling bands of chemotactic bacteria that form due to metabolism-generated gradients in chemoattractant concentration. We developed a multiple-relaxation-time (MRT) lattice-Boltzmann method (LBM) to model chemotaxis, because LBMs are well suited to model reactive transport in the complex geometries that are typical for subsurface porous media. This MRT-LBM can attain a better numerical stability than its corresponding single-relaxation-time LBM. We performed simulations to investigate the effects of substrate diffusion, initial bacterial concentration, and hydrodynamic dispersion on the formation, shape, and propagation of bacterial bands. Band formation requires a sufficiently high initial number of bacteria and a small substrate diffusion coefficient. Uniform flow does not affect the bands while shear flow does. Bacterial bands can move both upstream and downstream when the flow velocity is small. However, the bands disappear once the velocity becomes too large due to hydrodynamic dispersion. Generally bands can only be observed if the dimensionless ratio between the chemotactic sensitivity coefficient and the effective diffusion coefficient of the bacteria exceeds a critical value, that is, when the biased movement due to chemotaxis overcomes the diffusion-like movement due to the random motility and hydrodynamic dispersion.

  10. Softening temperature of lyophilized bovine serum albumin and gamma-globulin as measured by spin-spin relaxation time of protein protons.

    Science.gov (United States)

    Yoshioka, S; Aso, Y; Kojima, S

    1997-04-01

    We investigated the usefulness of the spin-spin relaxation time (T2) of protein protons as a probe for evaluating the molecular flexibility of freeze-dried protein formulations. It is proposed that the microscopic softening temperature determined from changes in the T2 of protein protons (Ts(T2)) is an important characteristic of freeze-dried protein formulations, the glass transition temperature (Tg) of which is generally difficult to determine by differential scanning calorimetry. We determined the molecular flexibility of lyophilized bovine serum albumin (BSA) and bovine gamma-globulin (BGG) by measuring the T2 of protein and water protons as well as the spin-lattice relaxation time (T1) of the latter as a function of temperature. The flexibility of freeze-dried BSA and BGG cakes markedly varied at temperatures above and below the Ts(T2), affecting the stability of the proteins. The denaturation and subsequent aggregation of lyophilized BSA and BGG cakes with a relatively high water content was enhanced in the softened state at temperatures above the Ts(T2). Lyophilized cakes with an extremely low water content were significantly denatured, even in the unsoftened state at temperatures below the Ts(T2), probably due to the thermodynamically unstable structures of protein molecules generated by a loss of structural water.

  11. Temperature dependence of the damping constant and the relaxation time close to the tetragonal-cubic phase transition in SrZrO3

    Science.gov (United States)

    Yurtseven, H.; Kiraci, A.

    2017-01-01

    The damping constant Γsp due to the pseudospin-phonon coupling is calculated as a function of temperature using the pseudospin-phonon coupled model and the energy fluctuation model close to the tetragonal-cubic transition (TC = 1443 K) in SrZrO3. Using the observed Raman frequencies and the linewidth (FWHM) of the soft modes (Eg and A1g) from the literature, predictions of both models studied, are examined for the tetragonal-cubic transition in this crystalline system. Values of the activation energy U are extracted and also the inverse relaxation time is predicted as a function of temperature close to the phase transition studied in SrZrO3. Divergence behaviour of the damping constant (FWHM) of the soft modes is predicted from both models as also observed experimentally when TC is approached from the tetragonal to the cubic phase in SrZrO3. The relaxation time also diverges close to the TC in this crystal. It is indicated that the tetragonal-cubic transition is of a second order as predicted from both models studied here, as also observed experimentally in SrZrO3.

  12. In vivo measurement of a new source of contrast, the dipolar relaxation time, T1D , using a modified inhomogeneous magnetization transfer (ihMT) sequence.

    Science.gov (United States)

    Varma, Gopal; Girard, Olivier M; Prevost, Valentin H; Grant, Aaron K; Duhamel, Guillaume; Alsop, David C

    2017-10-01

    This paper describes a technique that can be used in vivo to measure the dipolar relaxation time, T1D , of macromolecular protons contributing to magnetization transfer (MT) in tissues and to produce quantitative T1D maps. The technique builds upon the inhomogeneous MT (ihMT) technique that is particularly sensitive to tissue components with long T1D . A standard ihMT experiment was altered to introduce a variable time for switching between positive and negative offset frequencies for RF saturation. A model for the dependence of ihMT was developed and used to fit data acquired in vivo. Application of the method to images from brains of healthy volunteers produced values of T1D  = (5.9 ± 1.2) ms in gray matter and T1D  = (6.2 ± 0.4) ms in white matter regions and provided maps of the T1D parameter. The model and experiments described provide access to a new relaxation characteristic of tissue with potentially unique diagnostic information. Magn Reson Med 78:1362-1372, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  13. Studying common-pool resources over time: A longitudinal case study of the Buen Hombre fishery in the Dominican Republic.

    Science.gov (United States)

    Wilson, Margaret; Pavlowich, Tyler; Cox, Michael

    2016-03-01

    Like many small-scale fishing communities around the world, the community of Buen Hombre in the Dominican Republic is dealing with a set of challenges to reconcile its fishing activities with the ecology on which it depends. Also like many such communities, this case has been examined at a particular period in time by a group of social scientists, but not over substantial lengths of time in order to examine the longitudinal validity of the conclusions made during this period. In this paper we combine data from previous anthropological work with our own primary social and ecological data to conduct a longitudinal case study of the Buen Hombre fishery. Our over-time comparison focuses on a suite of mostly social and institutional variables to explain what we find to be a continued degradation of the fishery, and we conclude the analysis by presenting a causal-loop diagram, summarizing our inferences regarding the complex interactions among these variables. We find that a mix of factors, notably changes in gear and fishing sites used, the number of fishermen and their livelihood diversity, as well as an increased connectivity between Buen Hombre and its external environment, have contributed to the decline of the condition of Buen Hombre coral reef fishery. We conclude with a discussion of what may lie ahead for this particular case and others like it.

  14. High-field 1H T1 and T2 NMR relaxation time measurements of H2O in homeopathic preparations of quartz, sulfur, and copper sulfate

    Science.gov (United States)

    Baumgartner, Stephan; Wolf, Martin; Skrabal, Peter; Bangerter, Felix; Heusser, Peter; Thurneysen, André; Wolf, Ursula

    2009-09-01

    Quantitative meta-analyses of randomized clinical trials investigating the specific therapeutic efficacy of homeopathic remedies yielded statistically significant differences compared to placebo. Since the remedies used contained mostly only very low concentrations of pharmacologically active compounds, these effects cannot be accounted for within the framework of current pharmacology. Theories to explain clinical effects of homeopathic remedies are partially based upon changes in diluent structure. To investigate the latter, we measured for the first time high-field (600/500 MHz) 1H T1 and T2 nuclear magnetic resonance relaxation times of H2O in homeopathic preparations with concurrent contamination control by inductively coupled plasma mass spectrometry (ICP-MS). Homeopathic preparations of quartz (10 c-30 c, n = 21, corresponding to iterative dilutions of 100-10-100-30), sulfur (13 x-30 x, n = 18, 10-13-10-30), and copper sulfate (11 c-30 c, n = 20, 100-11-100-30) were compared to n = 10 independent controls each (analogously agitated dilution medium) in randomized and blinded experiments. In none of the samples, the concentration of any element analyzed by ICP-MS exceeded 10 ppb. In the first measurement series (600 MHz), there was a significant increase in T1 for all samples as a function of time, and there were no significant differences between homeopathic potencies and controls. In the second measurement series (500 MHz) 1 year after preparation, we observed statistically significant increased T1 relaxation times for homeopathic sulfur preparations compared to controls. Fifteen out of 18 correlations between sample triplicates were higher for controls than for homeopathic preparations. No conclusive explanation for these phenomena can be given at present. Possible hypotheses involve differential leaching from the measurement vessel walls or a change in water molecule dynamics, i.e., in rotational correlation time and/or diffusion. Homeopathic preparations

  15. Longitudinal associations between personality profile stability and adjustment in college students: distinguishing among overall stability, distinctive stability, and within-time normativeness.

    Science.gov (United States)

    Klimstra, Theo A; Luyckx, Koen; Hale, William W; Goossens, Luc; Meeus, Wim H J

    2010-08-01

    In the present study, longitudinal associations of 3 aspects of personality profile stability (i.e., overall stability, distinctive stability, and within-time normativeness) with 3 adjustment measures (i.e., depressive symptoms, self-esteem, and delinquency) were examined, using 4 waves of longitudinal data on a Belgian college sample (N=565). Longitudinal path models revealed strong longitudinal associations between adjustment and overall stability. Subsequent analyses showed that it is not the degree to which one's personality profile consistently diverges from the average personality profile within a population (i.e., distinctive stability) that is related to adjustment but the degree to which a personality profile of an individual matches the average personality profile within the sample at a certain point in time (i.e., within-time normativeness). The current study thereby underscores the importance of distinguishing normativeness and distinctiveness when examining personality profile stability.

  16. Capturing molecular multimode relaxation processes in excitable gases based on decomposition of acoustic relaxation spectra

    Science.gov (United States)

    Zhu, Ming; Liu, Tingting; Wang, Shu; Zhang, Kesheng

    2017-08-01

    Existing two-frequency reconstructive methods can only capture primary (single) molecular relaxation processes in excitable gases. In this paper, we present a reconstructive method based on the novel decomposition of frequency-dependent acoustic relaxation spectra to capture the entire molecular multimode relaxation process. This decomposition of acoustic relaxation spectra is developed from the frequency-dependent effective specific heat, indicating that a multi-relaxation process is the sum of the interior single-relaxation processes. Based on this decomposition, we can reconstruct the entire multi-relaxation process by capturing the relaxation times and relaxation strengths of N interior single-relaxation processes, using the measurements of acoustic absorption and sound speed at 2N frequencies. Experimental data for the gas mixtures CO2-N2 and CO2-O2 validate our decomposition and reconstruction approach.

  17. Effect of gel firmness at cutting time, pH, and temperature on rennet coagulation and syneresis: an in situ 1H NMR relaxation study.

    Science.gov (United States)

    Hansen, Christian Lyndgaard; Rinnan, Asmund; Engelsen, Søren Balling; Janhøj, Thomas; Micklander, Elisabeth; Andersen, Ulf; van den Berg, Frans

    2010-01-13

    The objective of this study was to monitor rennet-induced milk gel formation and mechanically induced gel syneresis in situ by low-field NMR. pH, temperature, and gel firmness at cutting time were varied in a factorial design. The new curve-fitting method Doubleslicing revealed that during coagulation two proton populations with distinct transverse relaxation times (T2,1=181, T2,2=465 ms) were present in fractions (f1=98.9%, f2=1.1%). Mechanical cutting of the gel in the NMR tube induced macrosyneresis, which led to the appearance of an additional proton population (T2,3=1500-2200 ms) identified as whey. On the basis of NMR quantification of whey water the syneresis rate was calculated and found to be significantly dependent on pH and temperature.

  18. Structural Dependence of the Ising-type Magnetic Anisotropy and of the Relaxation Time in Mononuclear Trigonal Bipyramidal Co(II) Single Molecule Magnets.

    Science.gov (United States)

    Shao, Feng; Cahier, Benjamin; Rivière, Eric; Guillot, Régis; Guihéry, Nathalie; Campbell, Victoria E; Mallah, Talal

    2017-02-06

    This paper describes the correlation between Ising-type magnetic anisotropy and structure in trigonal bipyramidal Co(II) complexes. Three sulfur-containing trigonal bipyramidal Co(II) complexes were synthesized and characterized. It was shown that we can engineer the magnitude of the Ising anisotropy using ligand field theory arguments in conjunction with structural parameters. To prepare this series of compounds, we used, on the one hand, a tetradentate ligand containing three sulfur atoms and one amine (NS3(tBu)) and on the other hand three different axial ligands, namely, Cl(-), Br(-), and NCS(-). The organic ligand imposes a trigonal bipyramidal arrangement with the three sulfur atoms lying in the trigonal plane with long Co-S bond distances. The magnetic properties of the compounds were measured, and ab initio calculations were used to analyze the anisotropy parameters and perform magneto-structural correlations. We demonstrate that a smaller axial zero-field splitting parameter leads to slower relaxation time when the symmetry is strictly axial, while the presence of very weak rhombicity decreases the energy barrier and speeds the relaxation of the magnetization.

  19. Changes in spectral measures and voice-onset time with age: a cross-sectional and a longitudinal study.

    Science.gov (United States)

    Decoster, W; Debruyne, F

    1997-01-01

    In this study, we searched for changes in spectral features (during the sustained vowels [a] and [i]) and the voice onset time (VOT, of [pa] and [ka]) of the ageing voice. A longitudinal study (on 20 participants) and a cross-sectional study (on 265 participants) were conducted. The spectral parameters under consideration were: the difference in amplitude between the first and the second harmonic, the energy difference between the frequency band below 1 kHz and 2-4 kHz, and the energy difference between vowels [a] and [i]. A relatively stronger spectral level was found between 4 and 5 kHz in elderly men and women (60+) for [i] compared to young men and women (20-29 years). Significant differences in the longitudinal study were not identical to those of the cross-sectional study. After a time interval of 30 years, 20 men produced a relatively weaker 2- to 4-kHz part of the spectrum and the VOT became much longer. It was impossible to attribute the changes purely to the process of ageing. Situations and emotions also play an important role and contribute to the different findings of the two groups of participants under consideration.

  20. A Simple, Inexpensive Model to Demonstrate How Contraction of GI Longitudinal Smooth Muscle Promotes Propulsion

    Science.gov (United States)

    Lujan, Heidi L.; DiCarlo, Stephen E.

    2015-01-01

    Peristalis is a propulsive activity that involves both circular and longitudinal muscle layers of the esophagus, distal stomach, and small and large intestines. During peristalsis, the circular smooth muscle contracts behind (on the orad side) the bolus and relaxes in front (on the aborad side) of the bolus. At the same time, the longitudinal…

  1. The dependence of the ultrafast relaxation kinetics of the S2 and S1 states in β-carotene homologs and lycopene on conjugation length studied by femtosecond time-resolved absorption and Kerr-gate fluorescence spectroscopies

    Science.gov (United States)

    Kosumi, Daisuke; Fujiwara, Masazumi; Fujii, Ritsuko; Cogdell, Richard J.; Hashimoto, Hideki; Yoshizawa, Masayuki

    2009-06-01

    The ultrafast relaxation kinetics of all-trans-β-carotene homologs with varying numbers of conjugated double bonds n(n =7-15) and lycopene (n =11) has been investigated using femtosecond time-resolved absorption and Kerr-gate fluorescence spectroscopies, both carried out under identical excitation conditions. The nonradiative relaxation rates of the optically allowed S2(1Bu+1) state were precisely determined by the time-resolved fluorescence. The kinetics of the optically forbidden S1(2Ag-1) state were observed by the time-resolved absorption measurements. The dependence of the S1 relaxation rates upon the conjugation length is adequately described by application of the energy gap law. In contrast to this, the nonradiative relaxation rates of S2 have a minimum at n =9 and show a reverse energy gap law dependence for values of n above 11. This anomalous behavior of the S2 relaxation rates can be explained by the presence of an intermediate state (here called the Sx state) located between the S2 and S1 states at large values of n (such as n =11). The presence of such an intermediate state would then result in the following sequential relaxation pathway S2→Sx→S1→S0. A model based on conical intersections between the potential energy curves of these excited singlet states can readily explain the measured relationships between the decay rates and the energy gaps.

  2. Does Viewing Pornography Reduce Marital Quality Over Time? Evidence from Longitudinal Data.

    Science.gov (United States)

    Perry, Samuel L

    2017-02-01

    Numerous studies have examined the connection between pornography viewing and marital quality, with findings most often revealing a negative association. Data limitations, however, have precluded establishing directionality with a representative sample. This study is the first to draw on nationally representative, longitudinal data (2006-2012 Portraits of American Life Study) to test whether more frequent pornography use influences marital quality later on and whether this effect is moderated by gender. In general, married persons who more frequently viewed pornography in 2006 reported significantly lower levels of marital quality in 2012, net of controls for earlier marital quality and relevant correlates. Pornography's effect was not simply a proxy for dissatisfaction with sex life or marital decision-making in 2006. In terms of substantive influence, frequency of pornography use in 2006 was the second strongest predictor of marital quality in 2012. Interaction effects revealed, however, that the negative effect of porn use on marital quality applied to husbands, but not wives. In fact, post-estimation predicted values indicated that wives who viewed pornography more frequently reported higher marital quality than those who viewed it less frequently or not at all. The implications and limitations of this study are discussed.

  3. Plasmon-mediated energy relaxation in graphene

    Energy Technology Data Exchange (ETDEWEB)

    Ferry, D. K. [School of Electrical, Computer, and Energy Engineering, Arizona State University, Tempe, Arizona 85287-5706 (United States); Somphonsane, R. [Department of Physics, King Mongkut' s Institute of Technology, Ladkrabang, Bangkok 10520 (Thailand); Ramamoorthy, H.; Bird, J. P. [Department of Electrical Engineering, University at Buffalo, the State University of New York, Buffalo, New York 14260-1500 (United States)

    2015-12-28

    Energy relaxation of hot carriers in graphene is studied at low temperatures, where the loss rate may differ significantly from that predicted for electron-phonon interactions. We show here that plasmons, important in the relaxation of energetic carriers in bulk semiconductors, can also provide a pathway for energy relaxation in transport experiments in graphene. We obtain a total loss rate to plasmons that results in energy relaxation times whose dependence on temperature and density closely matches that found experimentally.

  4. Time-to-event analysis of individual variables associated with nursing students' academic failure: a longitudinal study.

    Science.gov (United States)

    Dante, Angelo; Fabris, Stefano; Palese, Alvisa

    2013-12-01

    Empirical studies and conceptual frameworks presented in the extant literature offer a static imagining of academic failure. Time-to-event analysis, which captures the dynamism of individual factors, as when they determine the failure to properly tailor timely strategies, impose longitudinal studies which are still lacking within the field. The aims of this longitudinal study were to investigate the time which elapses from a nursing student's admission to a Bachelor of Nursing program to their academic failure and to estimate the predictive power of individual variables on academic failure. Enrolled students (n = 170) in two Italian nursing degree programs during academic year 2008-2009, received at the beginning of each years a questionnaire which evaluated individual variables. Academic failure rate was 37.2 %. Time-to-event analysis has shown that academic failure occurred after an average of 664.52 days of course attendance ((95 %)CI = 623.2-705.8). Kaplan-Meier analyses demonstrated a high likelihood of failure among males (χ(2) 7.790, p 0.005) and among those who had obtained a final average grade in their secondary education ≤73/100 (χ(2)11.676, p 0.001). Cox regression analysis confirmed an increased likelihood of failure over time among males as compared to females (HR 1.931, (95 %)CI = 1.017-3.670), and among students living more than a 30 min commute from their place of study (HR 1.898, (95 %)CI = 1.015-3.547). The effect of these two factors on academic failure has been seen to manifest primarily toward the end of students' second academic year; students at risk might be supported by the appropriate university staff prior to this period.

  5. Longitudinal study of posttraumatic stress disorder, depression, and changes in traumatic memories over time in Bosnian refugees.

    Science.gov (United States)

    Mollica, Richard F; Caridad, Kathleen Rey; Massagli, Michael P

    2007-07-01

    This longitudinal study examined traumatic memory consistency over a 3-year period among a sample of highly traumatized Bosnian refugees, focusing on demographic factors, types of trauma, and posttraumatic stress disorder (PTSD) and depression. In 1996 and 1999, 376 Bosnian refugees were interviewed about 54 wartime trauma and torture events, and symptoms of PTSD and depression. Reports were compared for both time periods, and changed responses were analyzed for significance. Overall, there was consistency in reporting over time; when change occurred it was in the direction of decreased reports at follow-up. This downward trend was not associated with any particular diagnosis. However, PTSD alone, without comorbid symptoms of depression, was uniquely associated with the group that exhibited an upward trend. This implies that increased reporting is related specifically to the presence of PTSD symptoms, and that PTSD may be distinctly associated with the failed extinction of traumatic memories.

  6. Parity-time symmetry optics for modal selection in transverse and longitudinal waves (Conference Presentation)

    Science.gov (United States)

    Benisty, Henri; Lupu, Anatole

    2017-05-01

    The evolving field of optics for information and communication is currently seeking directions to expand the data rates in all concerned devices, fiber-based or on chips. We describe here two possibilities where the new concept of PT-symmetry in optics [1,2] can be exploited to help high data rate operation, considering either transverse or longitudinal aspects of modal selection, and assuming that data are carried using precise modes. The first aspect is transverse multimode transport. In this case, a fiber or a waveguide carries a few modes, say 4 to 16, and at nodes, they have to undergo a demux/mux operation to add or drop a subset of them, as much as possible without affecting the others. We shall consider to this end the operation as described in ref. [3] : if a PT-symmetric "potential", which essentially consists of a transverse gain-loss profile with antisymmetry, is applied to a waveguide, it has a very different impact on the different modes and mode families in the waveguide. One can in particular find situations where only two modes of the passive waveguide to be analyzed may enter into a gain regime, and not the other ones. From this scheme and others [4], we will discuss what is the road left towards an actual device, either in dielectrics or in case plasmonics is envisioned [5], i.e. with rather constant losses, but the possible advantage of miniaturization. The second aspect is longitudinal mode selection. The special transport properties of PT-symmetric Bragg gratings are now well established. In order to be used within a data management system, attention has to be paid to the rejection rate of Bragg gratings, and to the flatness of their response in the targeted window. To this end, a slow modulation of both real and imaginary parts of the periodic pattern of the basically PT-symmetric waveguide can help, in the general spirit of "apodization", but now with more parameters. We will detail some aspects of the designs introduced in [6] , notably

  7. Lower white matter microstructure in the superior longitudinal fasciculus is associated with increased response time variability in adults with attention-deficit/ hyperactivity disorder

    OpenAIRE

    Wolfers, T.; Onnink, A.M.; Zwiers, M.P.; Arias Vasquez, A.; Hoogman, M.; Mostert, J.C.; Kan, C C; Slaats-Willemse, D.I.E.; Buitelaar, J.; Franke, B

    2015-01-01

    BACKGROUND: Response time variability (RTV) is consistently increased in patients with attention-deficit/hyperactivity disorder (ADHD). A right-hemispheric frontoparietal attention network model has been implicated in these patients. The 3 main connecting fibre tracts in this network, the superior longitudinal fasciculus (SLF), inferior longitudinal fasciculus (ILF) and the cingulum bundle (CB), show microstructural abnormalities in patients with ADHD. We hypothesized that the microstructural...

  8. Tracking of leisure-time physical activity during adolescence and young adulthood: a 10-year longitudinal study

    Directory of Open Access Journals (Sweden)

    Torsheim Torbjørn

    2008-12-01

    Full Text Available Abstract Background The purpose of this study was to show how participation in leisure-time physical activity changes between ages 13 to 23, and to what extent engaging in specific types of sports tracks into young adulthood. Methods The sample comprised 630 subjects who responded to questionnaires at age 13, with seven follow-ups over a 10-year period in the Norwegian Longitudinal Health Behaviour Study. The associations between adolescent participation in global and specific types of leisure-time physical activity were examined by analyses of variance, regression analysis and growth curve analysis. Results The findings suggest that the transition from adolescence to adulthood is, on average, a period of decline in physical activity, but with the decline levelling off into adulthood. The decline was significantly greater among males than females. There were substantial individual differences in the amount of change, in particular among males. Jogging alone and cycling, recreational activities such as skiing and hiking, and ball games, showed a high degree of tracking from age 15 to 23. The findings indicate low associations between participation in specific types of activities during adolescence and global leisure-time physical activity in young adulthood, while participation in several adolescent physical activities simultaneously was moderately related to later activity. Thus, being involved in various types of physical activity may offer good opportunities for establishing lifelong involvement in physical activity, independent of the specific type of activity. Conclusion The observed variation in change might suggest a need for a more targeted approach, with a focus on subgroups of individuals. The group of inactive youth may be considered as a high risk group, and the findings suggest that adolescent males who are inactive early seem likely to continue to be inactive later. The observed heterogeneity in change highlights the limitation of

  9. Assessing the Impact of Exposure Time and Incapacitation on Longitudinal Trajectories of Criminal Offending.

    Science.gov (United States)

    Piquero, Alex; Blumstein, Alfred; Brame, Robert; Haapanen, Rudy; Mulvey, Edward P.; Nagin, Daniel S.

    2001-01-01

    Examined effect of accounting for exposure (incarceration) time on arrest rate of 272 paroled serious offenders followed through age 33. Analysis without exposure time adjustments suggested that over 92 percent exhibited highest arrest activity in late teens and early 20s. Adjusted for exposure time, about 72 percent showed a decline in arrest…

  10. Longitudinal research databases in medical education: facilitating the study of educational outcomes over time and across institutions.

    Science.gov (United States)

    Cook, David A; Andriole, Dorothy A; Durning, Steven J; Roberts, Nicole K; Triola, Marc M

    2010-08-01

    Many education research questions cannot be answered using participants from one institution or short periods of follow-up. In response to societal demands for accountability and evidence of effectiveness, new models of research must be developed to study the outcomes of educational activities. Following the 2007 Millennium Conference on Medical Education Research, organizers assigned a task force to explore the use of longitudinal databases in education research. This article summarizes the task force's findings. Similar to the Framingham studies in clinical medicine, longitudinal databases assemble prospectively collected information to retrospectively answer questions of interest. Many studies using such databases have been published. The task force identified three general approaches to database-type research. First, institutions can obtain identified information from existing sources, link it with school-specific information and other identified information, deidentify it, and merge it with similar information from other collaborating schools. Second, researchers can obtain from existing sources deidentified information on large samples and explore associations within this dataset. Third, investigators can design and implement databases to prospectively collect trainee information over time and across multiple institutions for the purpose of education research. Although costly, such comprehensive, purpose-built databases would ensure the availability of information needed to answer a variety of medical education research questions. Millennium Conference participants believed that stakeholders should explore the funding and development of such prospective databases. In the meantime, education researchers should use existing sources of individualized learner data to better understand how to develop competent, compassionate clinicians.

  11. A general model to calculate the spin-lattice (T1) relaxation time of blood, accounting for haematocrit, oxygen saturation and magnetic field strength.

    Science.gov (United States)

    Hales, Patrick W; Kirkham, Fenella J; Clark, Christopher A

    2016-02-01

    Many MRI techniques require prior knowledge of the T1-relaxation time of blood (T1bl). An assumed/fixed value is often used; however, T1bl is sensitive to magnetic field (B0), haematocrit (Hct), and oxygen saturation (Y). We aimed to combine data from previous in vitro measurements into a mathematical model, to estimate T1bl as a function of B0, Hct, and Y. The model was shown to predict T1bl from in vivo studies with a good accuracy (± 87 ms). This model allows for improved estimation of T1bl between 1.5-7.0 T while accounting for variations in Hct and Y, leading to improved accuracy of MRI-derived perfusion measurements.

  12. Time Out-of-Home and Cognitive, Physical, and Emotional Wellbeing of Older Adults: A Longitudinal Mixed Effects Model.

    Directory of Open Access Journals (Sweden)

    Johanna Petersen

    Full Text Available Time out-of-home has been linked with numerous health outcomes, including cognitive decline, poor physical ability and low emotional state. Comprehensive characterization of this important health metric would potentially enable objective monitoring of key health outcomes. The objective of this study is to determine the relationship between time out-of-home and cognitive status, physical ability and emotional state.Participants included 85 independent older adults, age 65-96 years (M = 86.36; SD = 6.79 who lived alone, from the Intelligent Systems for Assessing Aging Changes (ISAAC and the ORCATECH Life Laboratory cohorts. Factors hypothesized to affect time out-of-home were assessed on three different temporal levels: yearly (cognitive status, loneliness, clinical walking speed, weekly (pain and mood or daily (time out-of-home, in-home walking speed, weather, and season. Subject characteristics including age, race, and gender were assessed at baseline. Total daily time out-of-home in hours was assessed objectively and unobtrusively for up to one year using an in-home activity sensor platform. A longitudinal tobit mixed effects regression model was used to relate daily time out-of-home to cognitive status, physical ability and emotional state. More hours spend outside the home was associated with better cognitive function as assessed using the Clinical Dementia Rating (CDR Scale, where higher scores indicate lower cognitive function (βCDR = -1.69, p<0.001. More hours outside the home was also associated with superior physical ability (βPain = -0.123, p<0.001 and improved emotional state (βLonely = -0.046, p<0.001; βLow mood = -0.520, p<0.001. Weather, season, and weekday also affected the daily time out-of-home.These results suggest that objective longitudinal monitoring of time out-of-home may enable unobtrusive assessment of cognitive, physical and emotional state. In addition, these results indicate that the factors affecting out

  13. Twitch potentiation influences the time course of twitch depression in muscle relaxant studies : A pharmacokinetic-pharmacodynamic explanation

    NARCIS (Netherlands)

    Eleveld, Douglas J.; Proost, Johannes H.; Wierda, J. Mark K. H.

    2006-01-01

    The time course of twitch depression following neuromuscular blocking agent (NMBA) administration is influenced by the duration of control neuromuscular monitoring (twitch stabilization). The physiological mechanism for this interaction is not known. During twitch stabilization twitch response often

  14. A longitudinal study on time perspectives: relations with academic delay of gratification and learning environment

    NARCIS (Netherlands)

    Peetsma, T.; Schuitema, J.; van der Veen, I.

    2012-01-01

    After they start secondary school (at age 12 in the Netherlands), students' time perspectives on school and professional career and self-regulated learning decrease, while their perspectives on leisure increase. We aimed to investigate relations in the developments in time perspectives and delay of

  15. Climate change relaxes the time constraints for late-born offspring in a long-distance migrant

    NARCIS (Netherlands)

    Tomotani, Barbara M.; Gienapp, Phillip; Beersma, Domien G. M.; Visser, Marcel E.

    2016-01-01

    Animals in seasonal environments need to fit their annual-cycle stages, such as moult and migration, in a tight schedule. Climate change affects the phenology of organisms and causes advancements in timing of these annual-cycle stages but not necessarily at the same rates. For migratory birds, this

  16. Climate change relaxes the time constraints for late-born offspring in a long-distance migrant

    NARCIS (Netherlands)

    Tomotani, Barbara M; Gienapp, Phillip; Beersma, Domien G M; Visser, Marcel E

    2016-01-01

    Animals in seasonal environments need to fit their annual-cycle stages, such as moult and migration, in a tight schedule. Climate change affects the phenology of organisms and causes advancements in timing of these annual-cycle stages but not necessarily at the same rates. For migratory birds, this

  17. A comparison of multiple imputation methods for handling missing values in longitudinal data in the presence of a time-varying covariate with a non-linear association with time: a simulation study

    National Research Council Canada - National Science Library

    Anurika Priyanjali De Silva; Margarita Moreno-Betancur; Alysha Madhu De Livera; Katherine Jane Lee; Julie Anne Simpson

    2017-01-01

    ...)) treat repeated measurements of the same time-dependent variable as just another ‘distinct’ variable for imputation and therefore do not make the most of the longitudinal structure of the data...

  18. Effects of incentive size and timing on response rates to a follow-up wave of a longitudinal mailed survey.

    Science.gov (United States)

    Collins, R L; Ellickson, P L; Hays, R D; McCaffrey, D F

    2000-08-01

    Young adults who had previously participated in a longitudinal survey of youth were sent a questionnaire. They were randomly assigned to receive a $20 prepayment, a $20 postpayment, or a $25 postpayment for participation in the latest survey. Those in the large incentive condition were 7 percentage points more likely to return a survey than those in the smaller, postpayment group. Prepayment had a smaller, less reliable effect. Effects of incentive magnitude and timing were consistent at each month of the study period; only better high school grades distinguished early responders from late responders. Nonresponders had characteristics suggestive of low social conformity and were more likely than responders to be African American and male and have low SES. The discussion centers on motivations for participating in research and differences in the incentives likely to promote continued response versus initial study enrollment.

  19. Effect of healthy aging on left ventricular relaxation and diastolic suction.

    Science.gov (United States)

    Carrick-Ranson, Graeme; Hastings, Jeffrey L; Bhella, Paul S; Shibata, Shigeki; Fujimoto, Naoki; Palmer, M Dean; Boyd, Kara; Levine, Benjamin D

    2012-08-01

    Doppler ultrasound measures of left ventricular (LV) active relaxation and diastolic suction are slowed with healthy aging. It is unclear to what extent these changes are related to alterations in intrinsic LV properties and/or cardiovascular loading conditions. Seventy carefully screened individuals (38 female, 32 male) aged 21-77 were recruited into four age groups (young: relaxation, including isovolumic relaxation time and the time constant of isovolumic pressure decay increased progressively, whereas peak early mitral annular longitudinal velocity decreased with advancing age (P relaxation and diastolic suction were not attenuated significantly when PCWP was increased in older subjects or reduced in the younger subjects. There is an early slowing of LV relaxation and diastolic suction beginning in early middle age, with the greatest reduction observed in seniors. Because age-related differences in LV dynamic diastolic filling parameters were not diminished significantly with significant changes in LV loading conditions, a decline in ventricular relaxation is likely responsible for the alterations in LV diastolic filling with senescence.

  20. Nuclear magnetic relaxation studies of water in frozen biological tissues. Cross-relaxation effects between protein and bound water protons

    Science.gov (United States)

    Escanyé, J. M.; Canet, D.; Robert, J.

    Water proton longitudinal relaxation has been investigated in frozen mouse tissues including tumors. The nonfreezable water which gives rise to a relatively sharp NMR signal at this temperature (263 K) is identified as water bound to macromolecules. Measurements have been carried out by the nonselective inversion-recovery method at 90 and 6 MHz. Partially selective inversion has been achieved at 90 MHz by the DANTE sequence. The experimental data are analyzed by means of Solomon-type equations. This analysis provides the cross-relaxation term from which the dipolar contribution to water relaxation rate, arising from interactions with macromolecular protons, is calculated. This contribution seems to be dominant. The number of water protons interacting with a given macromolecular proton is found to be of the order of 10. The data at both frequencies can be consistently interpreted in terms of water diffusion, with a characteristic time of about 10 -9 sec. These conclusions are valid for all the tissues investigated here, their relaxation parameters exhibiting only slight differences.

  1. Conformational exchange of aromatic side chains characterized by L-optimized TROSY-selected {sup 13}C CPMG relaxation dispersion

    Energy Technology Data Exchange (ETDEWEB)

    Weininger, Ulrich; Respondek, Michal; Akke, Mikael, E-mail: mikael.akke@bpc.lu.se [Center for Molecular Protein Science, Lund University, Department of Biophysical Chemistry (Sweden)

    2012-09-15

    Protein dynamics on the millisecond time scale commonly reflect conformational transitions between distinct functional states. NMR relaxation dispersion experiments have provided important insights into biologically relevant dynamics with site-specific resolution, primarily targeting the protein backbone and methyl-bearing side chains. Aromatic side chains represent attractive probes of protein dynamics because they are over-represented in protein binding interfaces, play critical roles in enzyme catalysis, and form an important part of the core. Here we introduce a method to characterize millisecond conformational exchange of aromatic side chains in selectively {sup 13}C labeled proteins by means of longitudinal- and transverse-relaxation optimized CPMG relaxation dispersion. By monitoring {sup 13}C relaxation in a spin-state selective manner, significant sensitivity enhancement can be achieved in terms of both signal intensity and the relative exchange contribution to transverse relaxation. Further signal enhancement results from optimizing the longitudinal relaxation recovery of the covalently attached {sup 1}H spins. We validated the L-TROSY-CPMG experiment by measuring fast folding-unfolding kinetics of the small protein CspB under native conditions. The determined unfolding rate matches perfectly with previous results from stopped-flow kinetics. The CPMG-derived chemical shift differences between the folded and unfolded states are in excellent agreement with those obtained by urea-dependent chemical shift analysis. The present method enables characterization of conformational exchange involving aromatic side chains and should serve as a valuable complement to methods developed for other types of protein side chains.

  2. Negative magnetic relaxation in superconductors

    Directory of Open Access Journals (Sweden)

    Krasnoperov E.P.

    2013-01-01

    Full Text Available It was observed that the trapped magnetic moment of HTS tablets or annuli increases in time (negative relaxation if they are not completely magnetized by a pulsed magnetic field. It is shown, in the framework of the Bean critical-state model, that the radial temperature gradient appearing in tablets or annuli during a pulsed field magnetization can explain the negative magnetic relaxation in the superconductor.

  3. 时域反射光谱法研究酰胺-醇混合物的介电驰豫%Dielectric Relaxation Study of Amide-Alcohol Mixtures by Using Time Domain Reflectometry

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Using time domain reflectometry (TDR), dielectric relaxation studies were carried out on binary mixtures of amides (N-methyfformamide (NMF) and N,N-dimethylformamide (DMF)) with alcohols (1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, and 1-decanol) for various concentrations over the frequency range from 10 MHz to 10 GHz at 303 K. The Kirkwood correlation factor and excess dielectric constant properties were determined and discussed to yield information on the molecular interactions of the systems. The relaxation time varied with the chain length of alcohols and substituted amides were noticed. The Bruggeman plot shows a deviation from linearity. This deviation was attributed to some sort of molecular interaction which may take place between the alcohols and substituted amides. The excess static permittivity and excess inverse relaxation time values varied from negative to positive for all the systems indicating that the solute-solvent interaction existed between alcohols and substituted amides for all the dynamics of the mixture.

  4. Fast mapping of the T2 relaxation time of cerebral metabolites using proton echo-planar spectroscopic imaging (PEPSI).

    Science.gov (United States)

    Tsai, Shang-Yueh; Posse, Stefan; Lin, Yi-Ru; Ko, Cheng-Wen; Otazo, Ricardo; Chung, Hsiao-Wen; Lin, Fa-Hsuan

    2007-05-01

    Metabolite T2 is necessary for accurate quantification of the absolute concentration of metabolites using long-echo-time (TE) acquisition schemes. However, lengthy data acquisition times pose a major challenge to mapping metabolite T2. In this study we used proton echo-planar spectroscopic imaging (PEPSI) at 3T to obtain fast T2 maps of three major cerebral metabolites: N-acetyl-aspartate (NAA), creatine (Cre), and choline (Cho). We showed that PEPSI spectra matched T2 values obtained using single-voxel spectroscopy (SVS). Data acquisition for 2D metabolite maps with a voxel volume of 0.95 ml (32 x 32 image matrix) can be completed in 25 min using five TEs and eight averages. A sufficient spectral signal-to-noise ratio (SNR) for T2 estimation was validated by high Pearson's correlation coefficients between logarithmic MR signals and TEs (R2 = 0.98, 0.97, and 0.95 for NAA, Cre, and Cho, respectively). In agreement with previous studies, we found that the T2 values of NAA, but not Cre and Cho, were significantly different between gray matter (GM) and white matter (WM; P PEPSI and SVS scans was less than 9%. Consistent spatial distributions of T2 were found in six healthy subjects, and disagreement among subjects was less than 10%. In summary, the PEPSI technique is a robust method to obtain fast mapping of metabolite T2.

  5. Modeling Time-Dependent Association in Longitudinal Data: A Lag as Moderator Approach

    Science.gov (United States)

    Selig, James P.; Preacher, Kristopher J.; Little, Todd D.

    2012-01-01

    We describe a straightforward, yet novel, approach to examine time-dependent association between variables. The approach relies on a measurement-lag research design in conjunction with statistical interaction models. We base arguments in favor of this approach on the potential for better understanding the associations between variables by…

  6. Dating Violence, Bullying, and Sexual Harassment: Longitudinal Profiles and Transitions over Time

    Science.gov (United States)

    Miller, Shari; Williams, Jason; Cutbush, Stacey; Gibbs, Deborah; Clinton-Sherrod, Monique; Jones, Sarah

    2013-01-01

    Although there is growing recognition of the problem of dating violence, little is known about how it unfolds among young adolescents who are just beginning to date. This study examined classes (subgroups) and transitions between classes over three time points based on dating violence, bullying, and sexual harassment perpetration and victimization…

  7. Enhancing student motivation: a longitudinal intervention study based on future time perspective theory

    NARCIS (Netherlands)

    Schuitema, J.; Peetsma, T.; van der Veen, I.

    2014-01-01

    The authors investigated the effects of an intervention developed to enhance student motivation in the first years of secondary education. The intervention, based on future time perspective (FTP) theory, has been found to be effective in prevocational secondary education (T. T. D. Peetsma & I. Van

  8. Relaxation Dynamics in Heme Proteins.

    Science.gov (United States)

    Scholl, Reinhard Wilhelm

    A protein molecule possesses many conformational substates that are likely arranged in a hierarchy consisting of a number of tiers. A hierarchical organization of conformational substates is expected to give rise to a multitude of nonequilibrium relaxation phenomena. If the temperature is lowered, transitions between substates of higher tiers are frozen out, and relaxation processes characteristic of lower tiers will dominate the observational time scale. This thesis addresses the following questions: (i) What is the energy landscape of a protein? How does the landscape depend on the environment such as pH and viscosity, and how can it be connected to specific structural parts? (ii) What relaxation phenomena can be observed in a protein? Which are protein specific, and which occur in other proteins? How does the environment influence relaxations? (iii) What functional form best describes relaxation functions? (iv) Can we connect the motions to specific structural parts of the protein molecule, and are these motions important for the function of the protein?. To this purpose, relaxation processes after a pressure change are studied in carbonmonoxy (CO) heme proteins (myoglobin-CO, substrate-bound and substrate-free cytochrome P450cam-CO, chloroperoxidase-CO, horseradish peroxidase -CO) between 150 K and 250 K using FTIR spectroscopy to monitor the CO bound to the heme iron. Two types of p -relaxation experiments are performed: p-release (200 to ~eq40 MPa) and p-jump (~eq40 to 200 MPa) experiments. Most of the relaxations fall into one of three groups and are characterized by (i) nonexponential time dependence and non-Arrhenius temperature dependence (FIM1( nu), FIM1(Gamma)); (ii) exponential time dependence and non-Arrhenius temperature dependence (FIM0(A_{i}to A_{j})); exponential time dependence and Arrhenius temperature dependence (FIMX( nu)). The influence of pH is studied in myoglobin-CO and shown to have a strong influence on the substate population of the

  9. Relaxation Dynamics in Photoexcited Chiral Molecules Studied by Time-Resolved Photoelectron Circular Dichroism: Toward Chiral Femtochemistry

    CERN Document Server

    Comby, Antoine; Boggio-Pasqua, Martial; Descamps, Dominique; Légaré, Francois; Nahon, Laurent; Petit, Stéphane; Pons, Bernard; Fabre, Baptiste; Mairesse, Yann; Blanchet, Valérie

    2016-01-01

    Unravelling the main initial dynamics responsible for chiral recognition is a key stepin the understanding of many biological processes. However this challenging task requires a sensitive enantiospecic probe to investigate molecular dynamics on their natural femtosecond timescale. Here we show that, in the gas phase, the ultrafast relaxationdynamics of photoexcited chiral molecules can be tracked by recording Time-ResolvedPhotoElectron Circular Dichroism (TR-PECD) resulting from the photoionisation bya circularly polarized probe pulse. A large forward/backward asymmetry along theprobe propagation axis is observed in the photoelectron angular distribution. Its evolution with pump-probe delay reveals ultrafast dynamics that are inaccessible in theangle-integrated photoelectron spectrum nor via the usual electron emission anisotropyparameter ($\\beta$). PECD, which originates from the electron scattering in the chiral molecular potential, appears as a new sensitive observable for ultrafast molecular dynamicsin ch...

  10. Young People outside the Labour Force and Full-Time Education: Activities and Profiles. Longitudinal Surveys of Australian Youth. Research Report 45

    Science.gov (United States)

    Hillman, Kylie

    2005-01-01

    This report focuses on a group of young people who are not involved in full-time education or the labour force, that is, they are not studying full-time, nor are they working or looking for work. The data used in this report are drawn from the Longitudinal Surveys of Australian Youth (LSAY), which studies the progress of cohorts of young…

  11. How the optical timing system,the longitudinal diagnostics and the associated feedback systems provide femtosecond stable operation at the FERMI free electron laser

    Institute of Scientific and Technical Information of China (English)

    Mario Ferianis; Enrico Allaria; Eugenio Ferrari; Giulio Gaio; Giuseppe Penco; Fabio Rossi; Marco Veronese

    2016-01-01

    FERMI, the seeded free electron laser(FEL) in operation in Italy, is providing the User Community with unique fully coherent radiation, in the wavelength range 100–4 nm. FERMI is the first FEL fully synchronized by means of optical fibers. The optical timing system ensures an ultra-stable phase reference to its distributed clients. Several femtosecond longitudinal diagnostics verify the achieved performance; the bunch length monitor(BLM) and the bunch arrival monitor(BAM) will be presented in this paper. Feedback systems play a crucial role to guarantee the needed longterm electron beam stability. A real-time infrastructure allows shot-to-shot communication between front-end computers and the servers. Orbit feedbacks are useful in machine tuning, whereas longitudinal feedbacks control electron energy,compression and arrival time. A flexible software framework allows a rapid implementation of heterogeneous multiinput–multi-output(MIMO) longitudinal loops simply by selecting the appropriate sensors and actuators.

  12. Longitudinal dispersion with time-dependent source concentration in semi-infinite aquifer

    Indian Academy of Sciences (India)

    Mritunjay Kumar Singh; Nav Kumar Mahato; Premlata Singh

    2008-12-01

    An analytical solution is obtained to predict the contaminant concentration along unsteady ground-water flow in semi-in finite aquifer. Initially,the aquifer is not supposed to be solute free ,i.e.,aquifer is not clean.A time-dependent source concentration is considered at the origin of the aquifer and at the other end of the aquifer, it is supposed to be zero. The time-dependent forms of unsteady velocities are considered in which one such form ,i.e., sinusoidal form represents the seasonal pattern in a year in tropical regions. The Laplace Transformation Technique (LTT)is used to get an analytical solution and a graphical representation is made through MATLAB.

  13. Longitudinal analysis of intrinsic motivation and competence beliefs: is there a relation over time?

    Science.gov (United States)

    Spinath, Birgit; Steinmayr, Ricarda

    2008-01-01

    The present study explored whether competence beliefs and intrinsic motivation for different school domains show reciprocal effects over time. A sample of 670 German elementary school pupils (M= 8.8 years, SD= 0.51) was followed over 1 year. At 4 measurement occasions, children completed self-reports on their intrinsic motivation and competence beliefs for math, German, and school in general. Latent growth models revealed that intrinsic motivation and competence beliefs decreased over time. Comparing correlational and cross-lagged structural equation models yielded only weak evidence for cross-lagged influences between the 2 constructs. Results suggest that the developmental curves of competence beliefs and intrinsic motivation might be less inextricably interwoven than frequently assumed.

  14. Metal enrichment of the intra-cluster medium over a Hubble time for merging and relaxed galaxy clusters

    CERN Document Server

    Kapferer, W; Weratschnig, J; Schindler, S; Domainko, W; Van Kampen, E; Kimeswenger, S; Mair, M; Ruffert, M

    2007-01-01

    We investigate the efficiency of galactic mass loss, triggered by ram-pressure stripping and galactic winds of cluster galaxies, on the chemical enrichment of the intra-cluster medium (ICM). We combine N-body and hydrodynamic simulations with a semi-numerical galaxy formation model. By including simultaneously different enrichment processes, namely ram-pressure stripping and galactic winds, in galaxy-cluster simulations, we are able to reproduce the observed metal distribution in the ICM. We find that the mass loss by galactic winds in the redshift regime z>2 is ~10% to 20% of the total galactic wind mass loss, whereas the mass loss by ram-pressure stripping in the same epoch is up to 5% of the total ram-pressure stripping mass loss over the whole simulation time. In the cluster formation epochs z<2 ram-pressure stripping becomes more dominant than galactic winds. We discuss the non-correlation between the evolution of the mean metallicity of galaxy clusters and the galactic mass losses. For comparison wit...

  15. Peripubertal Caffeine Exposure Impairs Longitudinal Bone Growth in Immature Male Rats in a Dose- and Time-Dependent Manner.

    Science.gov (United States)

    Choi, Yun-Young; Choi, Yuri; Kim, Jisook; Choi, Hyeonhae; Shin, Jiwon; Roh, Jaesook

    2016-01-01

    This study investigated the dose- and time-dependent effects of caffeine consumption throughout puberty in peripubertal rats. A total of 85 male SD rats were randomly divided into four groups: control and caffeine-fed groups with 20, 60, or 120 mg/kg/day through oral gavage for 10, 20, 30, or 40 days. Caffeine decreased body weight gain and food consumption in a dose- and time-dependent manner, accompanied by a reduction in muscle and body fat. In addition, it caused a shortening and lightening of leg bones and spinal column. The total height of the growth plate decreased sharply at 40 days in the controls, but not in the caffeine-fed groups, and the height of hypertrophic zone in the caffeine-fed groups was lower than in the control. Caffeine increased the height of the secondary spongiosa, whereas parameters related to bone formation, such as bone area ratio, thickness and number of trabeculae, and bone perimeter, were significantly reduced. Furthermore, serum levels of IGF-1, estradiol, and testosterone were also reduced by the dose of caffeine exposure. Our results demonstrate that caffeine consumption can dose- and time-dependently inhibit longitudinal bone growth in immature male rats, possibly by blocking the physiologic changes in body composition and hormones relevant to bone growth.

  16. OS044. Morphological differences in murine placenta detected by magneticresonance imaging measurements of T2 relaxation times in mouse models ofpreeclampsia.

    Science.gov (United States)

    Bobek, G; Stait-Gardner, T; Surmon, L; Makris, A; Price, W S; Hennessy, A

    2012-07-01

    We have demonstrated that morphologically distinct regions of the murine placenta can be detected by magnetic resonance imaging (MRI), with image contrast arising from the variation in T2 relaxation times between regions and dependent upon blood flow. Previous studies of human placenta by other groups have shown a homogeneous tissue with correlation of relaxation times with gestational age and a trend for shorter relaxation times in pregnancies complicated by preeclampsia and fetal growth restriction. The ability to detect morphological changes and alterations in blood flow in experimental models of preeclampsia would be a significant boost in understanding the relationship between abnormal placental implantation, reduced placental perfusion, inflammatory cytokines, angiogenic molecules and other factors that may play a role in the syndrome. The aim of this study was to investigate whether morphological changes or abnormalities can be detected by T2 mapping in the placenta of mice subject to two experimental models of preeclampsia (reduced uterine perfusion pressure (RUPP) model and TNF-α induced model). Pregnant C57BL/6JArc mice were, on day 13.5 of gestation, either subject to a unilateral ligation of the right uterine artery (RUPP) (n=2) or given an infusion of TNF-α by subcutaneous insertion of a mini-osmotic pump primed to deliver 500ng/kg/day for 4days (n=2). Controls were normal pregnant (n=2), sham-operated (n=1) or saline infused animals(n=1). MRI images were acquired on anaesthetised mice on day 17.5 of gestation using a Bruker Avance 11.7 Tesla wide-bore spectrometer with micro-imaging probe capable of generating gradients of 0.45T/m. T2 measurements were acquired using an MSME sequence protocol (Bruker MSME-T2-map) with an in-plane resolution of 0.1-0.2mm. Matlab was used to generate R2 (i.e.,1/T2) maps from the acquired data with the T2 values being calculated from selected regions of interest from 2-6 individual placenta from each mouse. Differences

  17. Spousal Interrelations in Happiness in the Seattle Longitudinal Study: Considerable Similarities in Levels and Change over Time

    Science.gov (United States)

    Hoppmann, Christiane A.; Gerstorf, Denis; Willis, Sherry L.; Schaie, K. Warner

    2011-01-01

    Development does not take place in isolation and is often interrelated with close others such as marital partners. To examine interrelations in spousal happiness across midlife and old age, we used 35-year longitudinal data from both members of 178 married couples in the Seattle Longitudinal Study. Latent growth curve models revealed sizeable…

  18. Spousal Interrelations in Happiness in the Seattle Longitudinal Study: Considerable Similarities in Levels and Change over Time

    Science.gov (United States)

    Hoppmann, Christiane A.; Gerstorf, Denis; Willis, Sherry L.; Schaie, K. Warner

    2011-01-01

    Development does not take place in is