DEFF Research Database (Denmark)
Berg, Rune W.; Ditlevsen, Susanne
2013-01-01
and excitation and their confidence limits from single sweep trials. The estimates are based on the mean membrane potential, (V) , and the membrane time constant,τ. The time constant provides the total conductance (G = capacitance/τ) and is extracted from the autocorrelation of V. The synaptic conductances can....... The method gives best results if the synaptic input is large compared to other conductances, the intrinsic conductances have little or no time dependence or are comparably small, the ligand gated kinetics is faster than the membrane time constant, and the majority of synaptic contacts are electrotonically...
Energy Technology Data Exchange (ETDEWEB)
Shirakashi, Ryo [Tokyo Univ., Inst. of Industrial Science, Tokyo (Japan); Sukhorukov, Vladimir L.; Zimmermann, Ulrich [Wuerzburg Univ. Biozentrum, Lehrstuhl fuer Biotechnologie, Wuerzburg (Germany); Tanasawa, Ichiro [Nihon Univ., Dept. of Mechanical Engineering, Koriyama (Japan)
2004-10-01
In this study a new method is presented for measuring the transient permeability of mammalian cell membranes to sugar and electrolyte molecules based on the volumetric response of cells subjected to electroporation. The time constant of membrane resealing was determined independently by flow cytometry using a fluorescent dye as the reporter molecule. The volumetric and dye uptake data were analyzed with a model relating the cell volume changes to the solute transport across the reversibly permeabilized cell membrane. The experimental approach developed here might be useful for estimating the amount of electroinjected molecules, which are difficult to measure directly. (Author)
Berg, Rune W; Ditlevsen, Susanne
2013-08-01
When recording the membrane potential, V, of a neuron it is desirable to be able to extract the synaptic input. Critically, the synaptic input is stochastic and nonreproducible so one is therefore often restricted to single-trial data. Here, we introduce means of estimating the inhibition and excitation and their confidence limits from single sweep trials. The estimates are based on the mean membrane potential, V, and the membrane time constant, τ. The time constant provides the total conductance (G = capacitance/τ) and is extracted from the autocorrelation of V. The synaptic conductances can then be inferred from V when approximating the neuron as a single compartment. We further employ a stochastic model to establish limits of confidence. The method is verified on models and experimental data, where the synaptic input is manipulated pharmacologically or estimated by an alternative method. The method gives best results if the synaptic input is large compared with other conductances, the intrinsic conductances have little or no time dependence or are comparably small, the ligand-gated kinetics is faster than the membrane time constant, and the majority of synaptic contacts are electrotonically close to soma (recording site). Although our data are in current clamp, the method also works in V-clamp recordings, with some minor adaptations. All custom made procedures are provided in Matlab.
Prestin-driven cochlear amplification is not limited by the outer hair cell membrane time constant.
Johnson, Stuart L; Beurg, Maryline; Marcotti, Walter; Fettiplace, Robert
2011-06-23
Outer hair cells (OHCs) provide amplification in the mammalian cochlea using somatic force generation underpinned by voltage-dependent conformational changes of the motor protein prestin. However, prestin must be gated by changes in membrane potential on a cycle-by-cycle basis and the periodic component of the receptor potential may be greatly attenuated by low-pass filtering due to the OHC time constant (τ(m)), questioning the functional relevance of this mechanism. Here, we measured τ(m) from OHCs with a range of characteristic frequencies (CF) and found that, at physiological endolymphatic calcium concentrations, approximately half of the mechanotransducer (MT) channels are opened at rest, depolarizing the membrane potential to near -40 mV. The depolarized resting potential activates a voltage-dependent K+ conductance, thus minimizing τ(m) and expanding the membrane filter so there is little receptor potential attenuation at the cell's CF. These data suggest that minimal τ(m) filtering in vivo ensures optimal activation of prestin.
Directory of Open Access Journals (Sweden)
Agnieszka I Wlodarczyk
2013-12-01
Full Text Available Because of a complex dendritic structure, pyramidal neurons have a large membrane surface relative to other cells and so a large electrical capacitance and a large membrane time constant (τm. This results in slow depolarizations in response to excitatory synaptic inputs, and consequently increased and variable action potential latencies, which may be computationally undesirable. Tonic activation of GABAA receptors increases membrane conductance and thus regulates neuronal excitability by shunting inhibition. In addition, tonic increases in membrane conductance decrease the membrane time constant (τm, and improve the temporal fidelity of neuronal firing. Here we performed whole-cell current clamp recordings from hippocampal CA1 pyramidal neurons and found that bath application of 10 µM GABA indeed decreases τm in these cells. GABA also decreased first spike latency and jitter (standard deviation of the latency produced by current injection of 2 rheobases (500 ms. However, when larger current injections (3-6 rheobases were used, GABA produced no significant effect on spike jitter, which was low. Using mathematical modelling we demonstrate that the tonic GABAA conductance decreases rise time, decay time and half-width of EPSPs in pyramidal neurons. A similar effect was observed on EPSP/IPSP pairs produced by stimulation of Schaffer collaterals: the EPSP part of the response became shorter after application of GABA. Consistent with the current injection data, a significant decrease in spike latency and jitter was obtained in cell attached recordings only at near-threshold stimulation (50% success rate, S50. When stimulation was increased to 2- or 3- times S50, GABA significantly affected neither spike latency nor spike jitter. Our results suggest that a decrease in τm associated with elevations in ambient GABA can improve EPSP-spike precision at near-threshold synaptic inputs.
Wlodarczyk, Agnieszka I; Xu, Chun; Song, Inseon; Doronin, Maxim; Wu, Yu-Wei; Walker, Matthew C; Semyanov, Alexey
2013-01-01
Because of a complex dendritic structure, pyramidal neurons have a large membrane surface relative to other cells and so a large electrical capacitance and a large membrane time constant (τm). This results in slow depolarizations in response to excitatory synaptic inputs, and consequently increased and variable action potential latencies, which may be computationally undesirable. Tonic activation of GABAA receptors increases membrane conductance and thus regulates neuronal excitability by shunting inhibition. In addition, tonic increases in membrane conductance decrease the membrane time constant (τm), and improve the temporal fidelity of neuronal firing. Here we performed whole-cell current clamp recordings from hippocampal CA1 pyramidal neurons and found that bath application of 10μM GABA indeed decreases τm in these cells. GABA also decreased first spike latency and jitter (standard deviation of the latency) produced by current injection of 2 rheobases (500 ms). However, when larger current injections (3-6 rheobases) were used, GABA produced no significant effect on spike jitter, which was low. Using mathematical modeling we demonstrate that the tonic GABAA conductance decreases rise time, decay time and half-width of EPSPs in pyramidal neurons. A similar effect was observed on EPSP/IPSP pairs produced by stimulation of Schaffer collaterals: the EPSP part of the response became shorter after application of GABA. Consistent with the current injection data, a significant decrease in spike latency and jitter was obtained in cell attached recordings only at near-threshold stimulation (50% success rate, S50). When stimulation was increased to 2- or 3- times S50, GABA significantly affected neither spike latency nor spike jitter. Our results suggest that a decrease in τm associated with elevations in ambient GABA can improve EPSP-spike precision at near-threshold synaptic inputs.
Song, Yang; Li, S Kevin; Peck, Kendall D; Zhu, Honggang; Ghanem, Abdel-Halim; Higuchi, William I
2002-01-31
An experimental protocol, using an initial 1 min direct current (DC) applied potential of 4 V followed by alternating current (AC), was established to: (a) increase conductance and permeability and decrease lag time for human epidermal membrane (HEM) relative to unaltered HEM and; (b) maintain constant conductance and permeability during flux studies. The protocol allowed specific permeation parameters of the membrane to be characterized under electrically enhanced, constant flux conditions. The permeability, lag time, and effective membrane thickness were determined using a nonionic polar permeant, urea, while the enhanced conductance was maintained at a constant level with AC. A tortuous pore pathway model was employed to analyze the data. The AC protocol increased membrane permeability, and decreased lag time and effective membrane thickness relative to similar parameters obtained in previous studies from unaltered HEM. Lag times ranged from 32.0 to 105.5 min, and permeability coefficients calculated from steady state fluxes ranged from 1.68 to 6.03x10(-7) cm/s for HEM samples with electrical resistance values during transport of 2.3-8.0 kOmega x cm2. Effective membrane thicknesses were calculated to range from 0.34 to 0.61 cm during AC iontophoresis. Significant additional results were obtained when the protocol was applied for two consecutive runs using the same HEM sample, with time for the HEM sample to recover between runs. During the second run, the applied potential was adjusted to reproduce the conductance obtained on the first run. Under these conditions, the consecutive runs yielded essentially the same lag time, permeability and effective membrane thickness values. These results suggest that constant fluxes can be achieved by keeping HEM electrical conductance constant during AC iontophoresis.
Villain, Maud; Marrot, Benoît
2013-01-01
Food to microorganisms ratio (F/M) and sludge retention time (SRT) are known to affect in different ways biomass growth, bioactivities and foulants characteristics. Thus the aim of this study was to dissociate the effects of SRT from those of F/M ratio on lab-scale membrane bioreactors performances during stable and unstable state. Two acclimations were stabilized at a SRT of either 20 or 50 d with a constant F/M ratio of 0.2 kg(COD)kg(MLVSS)(-1) d(-1). During stable state, a higher N-NH(4)(+) removal rate (78%) was obtained at SRT of 50 d as an easier autotroph development was observed. Soluble microbial products (SMPs) release was double at 50 d with a majority of polysaccharides (49% of total SMP). The unstable conditions consisted in F/M ratio changes and operation without air and nutrient. Autotrophs were highly affected by the tested disturbances and SMP retention on membrane surface exhibited consistent changes during the performed stresses.
Time-Varying Fundamental Constants
Olive, Keith
2003-04-01
Recent data from quasar absorption systems can be interpreted as arising from a time variation in the fine-structure constant. However, there are numerous cosmological, astro-physical, and terrestrial bounds on any such variation. These includes bounds from Big Bang Nucleosynthesis (from the ^4He abundance), the Oklo reactor (from the resonant neutron capture cross-section of Sm), and from meteoretic lifetimes of heavy radioactive isotopes. The bounds on the variation of the fine-structure constant are significantly strengthened in models where all gauge and Yukawa couplings vary in a dependent manner, as would be expected in unified theories. Models which are consistent with all data are severly challenged when Equivalence Principle constraints are imposed.
Cryptography in constant parallel time
Applebaum, Benny
2013-01-01
Locally computable (NC0) functions are 'simple' functions for which every bit of the output can be computed by reading a small number of bits of their input. The study of locally computable cryptography attempts to construct cryptographic functions that achieve this strong notion of simplicity and simultaneously provide a high level of security. Such constructions are highly parallelizable and they can be realized by Boolean circuits of constant depth.This book establishes, for the first time, the possibility of local implementations for many basic cryptographic primitives such as one-way func
Naturally Time Dependent Cosmological Constant
Gregori, A
2004-01-01
In the light of the proposal of hep-th/0207195, we discuss in detail the issue of the cosmological constant, explaining how can string theory naturally predict the value which is experimentally observed, without low-energy supersymmetry.
Coasting cosmologies with time dependent cosmological constant
Pimentel, L O; Pimentel, Luis O.
1999-01-01
The effect of a time dependent cosmological constant is considered in a family of scalar tensor theories. Friedmann-Robertson-Walker cosmological models for vacumm and perfect fluid matter are found. They have a linear expansion factor, the so called coasting cosmology, the gravitational "constant" decreace inversely with time; this model satisfy the Dirac hipotesis. The cosmological "constant" decreace inversely with the square of time, therefore we can have a very small value for it at present time.
Cosmic Time Variation of the Gravitational Constant
Tomaschitz, R
2000-01-01
A pre-relativistic cosmological approach to electromagnetism and gravitation is explored that leads to a cosmic time variation of the fundamental constants. Space itself is supposed to have physical substance, which manifests by its permeability. The scale factors of the permeability tensor induce a time variation of the fundamental constants. Atomic radii, periods, and energy levels scale in cosmic time, which results in dispersionless redshifts without invoking a space expansion. Hubble constant and deceleration parameter are reviewed in this context. The time variation of the gravitational constant at the present epoch can be expressed in terms of these quantities. This provides a completely new way to restrain the deceleration parameter from laboratory bounds on the time variation of the gravitational constant. This variation also affects the redshift dependence of angular diameters and the surface brightness, and we study in some detail the redshift scaling of the linear sizes of radio sources. The effec...
The time constant of the somatogravic illusion.
Correia Grácio, B J; de Winkel, K N; Groen, E L; Wentink, M; Bos, J E
2013-02-01
Without visual feedback, humans perceive tilt when experiencing a sustained linear acceleration. This tilt illusion is commonly referred to as the somatogravic illusion. Although the physiological basis of the illusion seems to be well understood, the dynamic behavior is still subject to discussion. In this study, the dynamic behavior of the illusion was measured experimentally for three motion profiles with different frequency content. Subjects were exposed to pure centripetal accelerations in the lateral direction and were asked to indicate their tilt percept by means of a joystick. Variable-radius centrifugation during constant angular rotation was used to generate these motion profiles. Two self-motion perception models were fitted to the experimental data and were used to obtain the time constant of the somatogravic illusion. Results showed that the time constant of the somatogravic illusion was on the order of two seconds, in contrast to the higher time constant found in fixed-radius centrifugation studies. Furthermore, the time constant was significantly affected by the frequency content of the motion profiles. Motion profiles with higher frequency content revealed shorter time constants which cannot be explained by self-motion perception models that assume a fixed time constant. Therefore, these models need to be improved with a mechanism that deals with this variable time constant. Apart from the fundamental importance, these results also have practical consequences for the simulation of sustained accelerations in motion simulators.
On a time varying fine structure constant
Berman, M S; Berman, Marcelo S.; Trevisan, Luis A.
2001-01-01
By employing Dirac LNH, and a further generalization by Berman (GLNH), we estimate how should vary the total number of nucleons, the energy density, Newton Gravitational constant, the cosmological constant, the magnetic permeability and electric permitivity, of the Universe,in order to account for the experimentally observed time variation of the fine structure constant. As a bonus,we find an acceptable value for the deceleration parameter of the present Universe, compatible with the Supernovae observations.
Compact phase space, cosmological constant, discrete time
Rovelli, Carlo
2015-01-01
We study the quantization of geometry in the presence of a cosmological constant, using a discretiza- tion with constant-curvature simplices. Phase space turns out to be compact and the Hilbert space finite dimensional for each link. Not only the intrinsic, but also the extrinsic geometry turns out to be discrete, pointing to discreetness of time, in addition to space. We work in 2+1 dimensions, but these results may be relevant also for the physical 3+1 case.
Inflationary Phase with Time Varying Fundamental Constants
Berman, M S; Berman, Marcelo S.; Trevisan, Luis A.
2002-01-01
Following Barrow, and Barrow and collaborators, we find a cosmological JBD model, with varying speed of light and varying fine structure constant, where the deceleration parameter is -1,causing acceleration of the Universe.Indeed, we have an exponential inflationary phase. Plancks time, energy, length,etc.,might have had different numerical values in the past, than those available in the litterature, due to the varying values for speed of light, and gravitational constant.
Physical Basis for a Constant Lag Time
Socrates, Aristotle
2012-01-01
We show that the constant time lag prescription for tidal dissipation follows directly from the equations of motion of a tidally-forced fluid body, given some basic assumptions. They are (i) the equilibrium structure of the forced body is spherically-symmetric (ii) the tidal forcing is weak and non-resonant (iii) dissipation is weak. The lag time is an intrinsic property of the tidally-forced body and is independent of the orbital configuration.
Time constant determination for electrical equivalent of biological cells
Dubey, Ashutosh Kumar; Dutta-Gupta, Shourya; Kumar, Ravi; Tewari, Abhishek; Basu, Bikramjit
2009-04-01
The electric field interactions with biological cells are of significant interest in various biophysical and biomedical applications. In order to study such important aspect, it is necessary to evaluate the time constant in order to estimate the response time of living cells in the electric field (E-field). In the present study, the time constant is evaluated by considering the hypothesis of electrical analog of spherical shaped cells and assuming realistic values for capacitance and resistivity properties of cell/nuclear membrane, cytoplasm, and nucleus. In addition, the resistance of cytoplasm and nucleoplasm was computed based on simple geometrical considerations. Importantly, the analysis on the basis of first principles shows that the average values of time constant would be around 2-3 μs, assuming the theoretical capacitance values and the analytically computed resistance values. The implication of our analytical solution has been discussed in reference to the cellular adaptation processes such as atrophy/hypertrophy as well as the variation in electrical transport properties of cellular membrane/cytoplasm/nuclear membrane/nucleoplasm.
Isothermal titration calorimetry in nanoliter droplets with subsecond time constants.
Lubbers, Brad; Baudenbacher, Franz
2011-10-15
We reduced the reaction volume in microfabricated suspended-membrane titration calorimeters to nanoliter droplets and improved the sensitivities to below a nanowatt with time constants of around 100 ms. The device performance was characterized using exothermic acid-base neutralizations and a detailed numerical model. The finite element based numerical model allowed us to determine the sensitivities within 1% and the temporal dynamics of the temperature rise in neutralization reactions as a function of droplet size. The model was used to determine the optimum calorimeter design (membrane size and thickness, junction area, and thermopile thickness) and sensitivities for sample volumes of 1 nL for silicon nitride and polymer membranes. We obtained a maximum sensitivity of 153 pW/(Hz)(1/2) for a 1 μm SiN membrane and 79 pW/(Hz)(1/2) for a 1 μm polymer membrane. The time constant of the calorimeter system was determined experimentally using a pulsed laser to increase the temperature of nanoliter sample volumes. For a 2.5 nanoliter sample volume, we experimentally determined a noise equivalent power of 500 pW/(Hz)(1/2) and a 1/e time constant of 110 ms for a modified commercially available infrared sensor with a thin-film thermopile. Furthermore, we demonstrated detection of 1.4 nJ reaction energies from injection of 25 pL of 1 mM HCl into a 2.5 nL droplet of 1 mM NaOH.
Hu, Jinglei; Lipowsky, Reinhard; Weikl, Thomas R
2013-09-17
Cell adhesion and the adhesion of vesicles to the membranes of cells or organelles are pivotal for immune responses, tissue formation, and cell signaling. The adhesion processes depend sensitively on the binding constant of the membrane-anchored receptor and ligand proteins that mediate adhesion, but this constant is difficult to measure in experiments. We have investigated the binding of membrane-anchored receptor and ligand proteins with molecular dynamics simulations. We find that the binding constant of the anchored proteins strongly decreases with the membrane roughness caused by thermally excited membrane shape fluctuations on nanoscales. We present a theory that explains the roughness dependence of the binding constant for the anchored proteins from membrane confinement and that relates this constant to the binding constant of soluble proteins without membrane anchors. Because the binding constant of soluble proteins is readily accessible in experiments, our results provide a useful route to compute the binding constant of membrane-anchored receptor and ligand proteins.
Ventricular fibrillation time constant for swine.
Wu, Jiun-Yan; Nimunkar, Amit J; Sun, Hongyu; O'Rourke, Ann; Huebner, Shane; Will, James A; Webster, John G
2008-10-01
The strength-duration curve for cardiac excitation can be modeled by a parallel resistor-capacitor circuit that has a time constant. Experiments on six pigs were performed by delivering current from the X26 Taser dart at a distance from the heart to cause ventricular fibrillation (VF). The X26 Taser is an electromuscular incapacitation device (EMD), which generates about 50 kV and delivers a pulse train of about 15-19 pulses s(-1) with a pulse duration of about 150 micros and peak current about 2 A. Similarly a continuous 60 Hz alternating current of the amplitude required to cause VF was delivered from the same distance. The average current and duration of the current pulse were estimated in both sets of experiments. The strength-duration equation was solved to yield an average time constant of 2.87 ms +/- 1.90 (SD). Results obtained may help in the development of safety standards for future electromuscular incapacitation devices (EMDs) without requiring additional animal tests.
Measuring the RC time constant with Arduino
Pereira, N. S. A.
2016-11-01
In this work we use the Arduino UNO R3 open source hardware platform to assemble an experimental apparatus for the measurement of the time constant of an RC circuit. With adequate programming, the Arduino is used as a signal generator, a data acquisition system and a basic signal visualisation tool. Theoretical calculations are compared with direct observations from an analogue oscilloscope. Data processing and curve fitting is performed on a spreadsheet. The results obtained for the six RC test circuits are within the expected interval of values defined by the tolerance of the components. The hardware and software prove to be adequate to the proposed measurements and therefore adaptable to a laboratorial teaching and learning context.
Time constant of the cerebral arterial bed.
Kasprowicz, Magdalena; Diedler, Jennifer; Reinhard, Matthias; Carrera, Emmanuel; Smielewski, Peter; Budohoski, Karol P; Sorrentino, Enrico; Haubrich, Christina; Kirkpatrick, Peter J; Pickard, John D; Czosnyka, Marek
2012-01-01
We have defined a novel cerebral hemodynamic index, a time constant of the cerebral arterial bed (τ), the product of arterial compliance (C(a)) and cerebrovascular resistance (CVR). C(a) and CVR were calculated based on the relationship between pulsatile arterial blood pressure (ABP) and transcranial Doppler cerebral blood flow velocity. This new parameter theoretically estimates how fast the cerebral arterial bed is filled by blood volume after a sudden change in ABP during one cardiac cycle. We have explored this concept in 11 volunteers and in 25 patients with severe stenosis of the internal carotid artery (ICA). An additional group of 15 subjects with non-vascular dementia was studied to assess potential age dependency of τ. The τ was shorter (p = 0.011) in ICA stenosis, both unilateral (τ = 0.18 ± 0.04 s) and bilateral (τ = 0.16 ± 0.03 s), than in controls (τ = 0.22 ± 0.0 s). The τ correlated with the degree of stenosis (R = -0.62, p = 0.001). In controls, τ was independent of age. Further study during cerebrovascular reactivity tests is needed to establish the usefulness of τ for quantitative estimation of haemodynamics in cerebrovascular disease.
Kaya, Ahmet; Onac, Canan; Alpoguz, H Korkmaz
2016-11-05
In this study, the use of polymer inclusion membrane under constant electric current for the removal of Cr(VI) from water has investigated for the first time. Transport of Cr(VI) is performed by an electric current from the donor phase to the acceptor phase with a constant electric current of 0.5A. The optimized membrane includes of 12.1% 2-nitrophenyl octyl ether (2-NPOE), 77.6% cellulose triacetate (CTA), 10.3% tricapryl-methylammonium chloride (Aliquat 336) as a carrier. We tested the applicability of the selected membrane for Cr(VI) removal in real environmental water samples and evaluated its reusability. Electro membrane experiments were carried out under various parameters, such as the effect of electro membrane voltage at constant DC electric current; electro membrane current at constant voltage, acceptor phase pH, and stable electro membrane; and a comparison of polymer inclusion membrane and electro membrane transport studies. The Cr(VI) transport was achieved 98.33% after 40min under optimized conditions. An alternative method has been employed that eliminates the changing of electrical current by the application of constant electric current for higher reproducibility of electro membrane extraction experiments by combining the excellent selective and long-term use features of polymer inclusion membrane.
The time constant of the somatogravic illusion
Correia Grácio, B.J.; Winkel, K.N. de; Groen, E.L.; Wentink, M.; Bos, J.E.
2013-01-01
Met desdemona hebben we gevonden dat de tijd constante van de somatografische illusie rond twee seconden is. Dit resultaat verschilt van wat was gevonden in ander onderzoek dat gebruikt maakt van een gewone centrifuge
Do the fundamental constants change with time ?
Kanekar, Nissim
2008-01-01
Comparisons between the redshifts of spectral lines from cosmologically-distant galaxies can be used to probe temporal changes in low-energy fundamental constants like the fine structure constant and the proton-electron mass ratio. In this article, I review the results from, and the advantages and disadvantages of, the best techniques using this approach, before focussing on a new method, based on conjugate satellite OH lines, that appears to be less affected by systematic effects and hence holds much promise for the future.
Implications of a Time-Varying Fine Structure Constant
Alfonso-Faus, A
2002-01-01
Much work has been done after the possibility of a fine structure constant being time-varying. It has been taken as an indication of a time-varying speed of light. Here we prove that this is not the case. We prove that the speed of light may or may not vary with time, independently of the fine structure constant being constant or not. Time variations of the speed of light, if present, have to be derived by some other means and not from the fine structure constant. No implications based on the possible variations of the fine structure constant can be imposed on the speed of light.
A crossflow filtration system for constant permeate flux membrane fouling characterization
Miller, Daniel J.; Paul, Donald R.; Freeman, Benny D.
2013-03-01
Membrane fouling is often characterized using a crossflow filtration apparatus. Typically, the transmembrane pressure (TMP) difference is fixed, and the flux is allowed to decline as the membrane fouls and the resistance to mass transfer increases. However, as flux varies, so too does the rate at which foulants are brought to the membrane surface, so the observed fouling behavior is not solely the result of membrane/foulant interactions. Constant flux experiments, where the permeate flux is fixed and the TMP difference varies, minimize such variations in the hydrodynamic conditions at the membrane surface, but constant TMP difference experiments dominate the fouling literature because they are more straightforward to execute than constant flux experiments. Additionally, most industrial water purification membrane installations operate at constant flux rather than at constant TMP. Here, we describe the construction and operation of a constant flux crossflow fouling apparatus. System measurement accuracy was validated by comparison of pure water permeance measurements to values specified by the membrane manufacturer, reported elsewhere, and measured by another technique. Fouling experiments were performed with two membrane/foulant systems: polysulfone ultrafiltration membranes with a soybean oil emulsion foulant and PVDF microfiltration membranes with a polystyrene latex bead suspension foulant. Automatic permeate flux control facilitated flux stepping experiments, which are commonly used to determine the threshold flux or critical flux of a membrane/foulant pair. Comparison of a flux stepping experiment with a literature report yielded good agreement.
Moura, Clarissa de Almeida; Lima, Jéssica Polyana da Silva; Silveira, Vanessa Augusta Magalhães; Miguel, Mário André Leocadio; Luchiari, Ana Carolina
2017-02-20
The ability to learn about the signs of variability in space and time is known as time place learning (TPL). To adjust their circadian rhythms, animals use stimuli that change regularly, such as the light-dark cycle, temperature, food availability or even social stimuli. Because light-dark cycle is the most important environmental temporal cue, we asked how a diurnal animal would perform TPL if this cue was removed. Zebrafish has been extensively studied in the chronobiology area due to it diurnal chronotype, thus, we studied the effects of constant light and constant dark on the time-place learning and activity profile in zebrafish. Our data show that while under constant light and dark condition zebrafish was not able of TPL, after 30days under the constant conditions, constant light led to higher activity level and less significant (robust) 24h rhythm.
Using Constant Time Delay to Teach Braille Word Recognition
Hooper, Jonathan; Ivy, Sarah; Hatton, Deborah
2014-01-01
Introduction: Constant time delay has been identified as an evidence-based practice to teach print sight words and picture recognition (Browder, Ahlbrim-Delzell, Spooner, Mims, & Baker, 2009). For the study presented here, we tested the effectiveness of constant time delay to teach new braille words. Methods: A single-subject multiple baseline…
Time constant of the cerebral arterial bed in normal subjects.
Kasprowicz, Magdalena; Diedler, Jennifer; Reinhard, Matthias; Carrera, Emmanuel; Steiner, Luzius A; Smielewski, Peter; Budohoski, Karol P; Haubrich, Christina; Pickard, John D; Czosnyka, Marek
2012-07-01
The time constant of cerebral arterial bed (in brief time constant) is a product of brain arterial compliance (C(a)) and resistance (CVR). We tested the hypothesis that in normal subjects, changes in end-tidal CO(2) (EtCO(2)) affect the value of the time constant. C(a) and CVR were estimated using mathematical transformations of arterial pressure (ABP) and transcranial Doppler (TCD) cerebral blood flow velocity waveforms. Responses of the time constant to controlled changes in EtCO(2) were compared in 34 young volunteers. Hypercapnia shortened the time constant (0.22 s [0.17, 0.26] vs. 0.16 s [0.13, 0.20]; p = 0.000001), while hypocapnia lengthened the time constant (0.22 s [0.17, 0.26] vs. 0.23 s [0.19, 0.32]; p time constant was negatively correlated with changes in EtCO(2) (R(partial) = -0.68, p time constant shortens with increasing EtCO(2). Its potential role in cerebrovascular investigations needs further studies.
Energy consumption and constant current operation in membrane capacitive deionization
Zhao, R.; Biesheuvel, P.M.; Wal, van der A.F.
2012-01-01
Membrane capacitive deionization (MCDI) is a water desalination technology based on applying a cell voltage between two oppositely placed porous electrodes sandwiching a spacer channel that transports the water to be desalinated. In the salt removal step, ions are adsorbed at the carbon–water interf
Stability of neutral equations with constant time delays
Barker, L. K.; Whitesides, J. L.
1976-01-01
A method was developed for determining the stability of a scalar neutral equation with constant coefficients and constant time delays. A neutral equation is basically a differential equation in which the highest derivative appears both with and without a time delay. Time delays may appear also in the lower derivatives or the independent variable itself. The method is easily implemented, and an illustrative example is presented.
Thermocouple time constant measurement by cross power spectra
Strahle, W. C.; Muthukrishnan, M.
1976-01-01
A method of measuring thermocouple time constants is outlined which requires Fourier signal processing. In this method, two thermocouples of differing time constants are placed in a gas flow as closely as possible to one another, and the time constant of the first thermocouple is determined directly from the extremum of the imaginary part of the ratio of the ensemble averaged cross-power spectrum to the ensemble averaged auto-power spectrum of that thermocouple. A coherence function is given for assuring the quality of the data, and results are presented for an experimental test of the method. Some problems with the method are briefly noted.
Climatic response to a time varying solar constant
North, G. R.; Short, D. A.; Mengel, J. G.
1983-01-01
Recent measurements of the solar constant, theoretical arguments, and climatic measurements combined with signal processing suggest the possibility that the solar constant varies significantly on time scales ranging from billions of years to 11-yr (sunspot) cycles, and even to scales of a few weeks. Simple climate models with a time varying solar constant are examined here, with emphasis on the heat balance models (North et al., 1981). Linear heat balance model results are presented for high (10 cycles/yr) and low (0.1 cycle/yr) frequencies, providing a useful guide in estimating the direct heat response to solar variability.
Time optimal paths for a constant speed unicycle
Energy Technology Data Exchange (ETDEWEB)
Reister, D.B.
1991-01-01
This paper uses the Pontryagin maximum principle to find time optimal paths for a constant speed unicycle. The time optimal paths consist of sequences of arcs of circles and straight lines. The maximum principle introduced concepts (dual variables, bang-bang solutions, singular solutions, and transversality conditions) that provide important insight into the nature of the time optimal paths. 10 refs., 6 figs.
Possible Cosmological Implications of Time Varying Fine Structure Constant
Berman, M S; Berman, Marcelo S.; Trevisan, Luis A.
2001-01-01
We make use of Dirac LNH and results for a time varying fine structure constant in order to derive possible laws of variation for speed of light, the number of nucleons in the Universe, energy density and gravitational constant. By comparing with experimental bounds on G variation, we find that the deceleration paramenter of the present Universe is negative. This is coherent with recent Supernovae observations.
Simple Model with Time-Varying Fine-Structure ``Constant''
Berman, M. S.
2009-10-01
Extending the original version written in colaboration with L.A. Trevisan, we study the generalisation of Dirac's LNH, so that time-variation of the fine-structure constant, due to varying electrical and magnetic permittivities is included along with other variations (cosmological and gravitational ``constants''), etc. We consider the present Universe, and also an inflationary scenario. Rotation of the Universe is a given possibility in this model.
Ma, Weina; Yang, Liu; Lv, Yanni; Fu, Jia; Zhang, Yanmin; He, Langchong
2017-06-23
The equilibrium dissociation constant (KD) of drug-membrane receptor affinity is the basic parameter that reflects the strength of interaction. The cell membrane chromatography (CMC) method is an effective technique to study the characteristics of drug-membrane receptor affinity. In this study, the KD value of CMC relative standard method for the determination of drug-membrane receptor affinity was established to analyze the relative KD values of drugs binding to the membrane receptors (Epidermal growth factor receptor and angiotensin II receptor). The KD values obtained by the CMC relative standard method had a strong correlation with those obtained by the frontal analysis method. Additionally, the KD values obtained by CMC relative standard method correlated with pharmacological activity of the drug being evaluated. The CMC relative standard method is a convenient and effective method to evaluate drug-membrane receptor affinity. Copyright © 2017 Elsevier B.V. All rights reserved.
A Parallel Priority Queue with Constant Time Operations
DEFF Research Database (Denmark)
Brodal, Gerth Stølting; Träff, Jesper Larsson; Zaroliagis, Christos D.
1998-01-01
We present a parallel priority queue that supports the following operations in constant time:parallel insertionof a sequence of elements ordered according to key,parallel decrease keyfor a sequence of elements ordered according to key,deletion of the minimum key element, anddeletion of an arbitrary...... element. Our data structure is the first to support multi-insertion and multi-decrease key in constant time. The priority queue can be implemented on the EREW PRAM and can perform any sequence ofnoperations inO(n) time andO(mlogn) work,mbeing the total number of keyes inserted and/or updated. A main...
Approximate Range Emptiness in Constant Time and Optimal Space
DEFF Research Database (Denmark)
Goswami, Mayank; Jørgensen, Allan Grønlund; Larsen, Kasper Green
2015-01-01
that the query time can be improved greatly, to constant time, while matching our space lower bound up to a lower order additive term. This result is achieved through a succinct data structure for (non-approximate 1d) range emptiness/reporting queries, which may be of independent interest....
Generating k-independent variables in constant time
DEFF Research Database (Denmark)
Christiani, Tobias Lybecker; Pagh, Rasmus
2014-01-01
time addition and multiplication in F, and present the first nontrivial construction of a generator that outputs each value in constant time, not dependent on k. Our generator has period length |F| poly log k and uses k poly (log k) log |F| bits of space, which is optimal up to a poly log k factor. We...
Generating k-independent variables in constant time
DEFF Research Database (Denmark)
Christiani, Tobias Lybecker; Pagh, Rasmus
2014-01-01
time addition and multiplication in F, and present the first nontrivial construction of a generator that outputs each value in constant time, not dependent on k. Our generator has period length |F| poly log k and uses k poly (log k) log |F| bits of space, which is optimal up to a poly log k factor. We...
Single time point isothermal drug stability experiments at constant humidity.
Tao, Jian-Lin; Zhan, Xian-Cheng; Li, Lin-Li; Lin, Bing; Jiang, Lu
2009-03-01
A single time point isothermal drug stability experiments at constant humidity is introduced. In the new method, kinetic parameters related to both moisture and temperature were obtained by a single pair of experiments: these related to moisture by one with a group of testing humidities and a fixed temperature, those related to temperature by the other with a group of testing temperatures and a constant humidity. By a simulation, the estimates for the kinetic parameters (E(a), m, A) obtained by the proposed method and the reported programmed humidifying and heating method were statistically evaluated and were compared with those obtained by the isothermal measurements at constant humidity. Results indicated that under the same experimental conditions, the estimates obtained by the proposed method were significantly more precise than those obtained by the reported programmed humidifying and heating method. The estimates obtained by the isothermal method at constant humidity were somewhat more precise than those obtained by the proposed method. However, the experimental period needed by the isothermal method at constant humidity was greatly longer than that needed by the proposed method. The stability of dicloxacillin sodium, as a solid state model, was investigated by the single time point isothermal drug stability experiments at constant humidity. The results indicated that the kinetic parameters obtained by the proposed method were comparable to those from the reported.
Automated real time constant-specificity surveillance for disease outbreaks
Directory of Open Access Journals (Sweden)
Brownstein John S
2007-06-01
Full Text Available Abstract Background For real time surveillance, detection of abnormal disease patterns is based on a difference between patterns observed, and those predicted by models of historical data. The usefulness of outbreak detection strategies depends on their specificity; the false alarm rate affects the interpretation of alarms. Results We evaluate the specificity of five traditional models: autoregressive, Serfling, trimmed seasonal, wavelet-based, and generalized linear. We apply each to 12 years of emergency department visits for respiratory infection syndromes at a pediatric hospital, finding that the specificity of the five models was almost always a non-constant function of the day of the week, month, and year of the study (p Conclusion Modeling the variance of visit patterns enables real-time detection with known, constant specificity at all times. With constant specificity, public health practitioners can better interpret the alarms and better evaluate the cost-effectiveness of surveillance systems.
Fuzzy logic estimator of rotor time constant in induction motors
Energy Technology Data Exchange (ETDEWEB)
Alminoja, J. [Tampere University of Technology (Finland). Control Engineering Laboratory; Koivo, H. [Helsinki University of Technology, Otaniemi (Finland). Control Engineering Laboratory
1997-12-31
Vector control of AC machines is a well-known and widely used technique in induction machine control. It offers an exact method for speed control of induction motors, but it is also sensitive to the changes in machine parameters. E.g. rotor time constant has a strong dependence on temperature. In this paper a fuzzy logic estimator is developed, with which the rotor time constant can be estimated when the machine has a load. It is more simple than the estimators proposed in the literature. The fuzzy estimator is tested by simulation when step-wise abrupt changes and slow drifting occurs. (orig.) 7 refs.
Early Universe Constraints on Time Variation of Fundamental Constants
Landau, Susana J; Scoccola, Claudia G; Vucetich, Hector
2008-01-01
We study the time variation of fundamental constants in the early Universe. Using data from primordial light nuclei abundances, CMB and the 2dFGRS power spectrum, we put constraints on the time variation of the fine structure constant $\\alpha$, and the Higgs vacuum expectation value $$ without assuming any theoretical framework. A variation in $$ leads to a variation in the electron mass, among other effects. Along the same line, we study the variation of $\\alpha$ and the electron mass $m_e$. In a purely phenomenological fashion, we derive a relationship between both variations.
Fine structure constant variation or space-time anisotropy?
Chang, Zhe; Li, Xin
2011-01-01
Recent observations on quasar absorption spectra supply evidences for variation of fine structure constant $\\alpha$. In this paper, we propose another interpretation of the observational data on quasar absorption spectra: a scenario with space-time inhomogeneity and anisotropy but uniform fine structure constant. Maybe the space-time is characterized by Finsler geometry instead of Riemann one. Finsler geometry admits less symmetries than Riemann geometry does. We investigate the Finslerian geodesic equations in Randers space-time (a special Finsler space-time). It is found that the cosmological redshift in this space-time is deviated from the one in general relativity. The modification term to redshift could be generally revealed as a monopole plus dipole function about space-time locations and directions. We suggest that this modification corresponds to the observed spatial monopole and Australian Dipole in quasar absorption spectra.
The cosmological constant and the time of its dominance
Garriga Torres, Jaume; Livio, Mario; Vilenkin, A.
1999-01-01
We explore a model in which the cosmological constant $\\Lambda$ and the density contrast at the time of recombination $\\sigma_{rec}$ are random variables, whose range and {\\it a priori} probabilities are determined by the laws of physics. (Such models arise naturally in the framework of inflationary cosmology.) Based on the assumption that we are typical observers, we show that the order of magnitude coincidence among the three timescales: the time of galaxy formation, the time when the cosmo...
Low Redundancy in Static Dictionaries with Constant Query Time
DEFF Research Database (Denmark)
Pagh, Rasmus
2001-01-01
A static dictionary is a data structure for storing subsets of a finite universe U, so that membership queries can be answered efficiently. We study this problem in a unit cost RAM model with word size Ω(log |U|), and show that for n-element subsets, constant worst case query time can be obtained...
The Cosmological Constant Problem and Re-interpretation of Time
Luo, M J
2013-01-01
We abandon the interpretation that time is a global parameter in quantum mechanics, replace it by a quantum dynamical variable playing the role of time. This operational re-interpretation of time provides a solution to the cosmological constant problem. The expectation value of the zero-point energy under the new time variable vanishes. The fluctuation of the vacuum energy as the leading contribution to the gravitational effect gives the correct order of the observed "dark energy". The effective vacuum energy density is always comparable to the matter energy density. Conceptual consequences of the re-interpretation of time are also discussed.
The cosmological constant and the time of its dominance
Garriga, J; Vilenkin, A; Garriga, Jaume; Livio, Mario; Vilenkin, Alexander
2000-01-01
We explore a model in which the cosmological constant $\\Lambda$ and the density contrast at the time of recombination $\\sigma_{rec}$ are random variables, whose range and {\\it a priori} probabilities are determined by the laws of physics. (Such models arise naturally in the framework of inflationary cosmology.) Based on the assumption that we are typical observers, we show that the order of magnitude coincidence among the three timescales: the time of galaxy formation, the time when the cosmological constant starts to dominate the cosmic energy density, and the present age of the universe, finds a natural explanation. We also discuss the probability distribution for $\\sigma_{rec}$, and find that it is peaked near the observationally suggested values, for a wide class of {\\it a priori} distributions.
Isothermal Titration Calorimetry in Nanoliter Droplets with Sub-Second Time Constants
2011-01-01
We reduced the reaction volume in microfabricated suspended-membrane titration calorimeters to nanoliter droplets and improved the sensitivities to below a nanowatt with time constants of around 100ms, The device performance was characterized using exothermic acid-base neutralizations and a detailed numerical model. The finite element based numerical model allowed us to determine the sensitivities within 1% and the temporal dynamics of the temperature rise in neutralization reactions as a fun...
Approximate Range Emptiness in Constant Time and Optimal Space
DEFF Research Database (Denmark)
Goswami, Mayank; Jørgensen, Allan Grønlund; Larsen, Kasper Green;
2015-01-01
that the query time can be improved greatly, to constant time, while matching our space lower bound up to a lower order additive term. This result is achieved through a succinct data structure for (non-approximate 1d) range emptiness/reporting queries, which may be of independent interest.......{Bloom filters} from single point queries to any interval length L. Setting the false positive rate to ε/L and performing L queries, Bloom filters yield a solution to this problem with space O(nlg(L/ε)) bits, false positive probability bounded by ε for intervals of length up to L, using query time O...
ROTATING RINDLER SPACE TIME WITH CONSTANT ANGULAR VELOCITY
Institute of Scientific and Technical Information of China (English)
WANG YONG-CHENG
2000-01-01
A new space time metric is derived from Kerr metric if its mass and location approach to infinite in an appropriate way. The new space-time is an infinitesimal neighborhood nearby one of the two horizon poles of an infinite Kerr black hole. In other words, it is the second order infinitesimal neighborhood nearby one of the two horizon poles of a Kerr black hole. It is fiat and has event horizon and infinite red shift surface. We prove that it is a rotating Rindler space time with constant angular velocity.
Fluorescence decay-time constants in organic liquid scintillators.
Marrodán Undagoitia, T; von Feilitzsch, F; Oberauer, L; Potzel, W; Ulrich, A; Winter, J; Wurm, M
2009-04-01
The fluorescence decay-time constants have been measured for several scintillator mixtures based on phenyl-o-xylylethane (PXE) and linear alkylbenzene (LAB) solvents. The resulting values are of relevance for the physics performance of the proposed large-volume liquid scintillator detector Low Energy Neutrino Astronomy (LENA). In particular, the impact of the measured values to the search for proton decay via p-->K(+)nu is evaluated in this work.
Cerebrovascular Time Constant in Patients with Head Injury.
Trofimov, Alex; Kalentiev, George; Gribkov, Alexander; Voennov, Oleg; Grigoryeva, Vera
2016-01-01
The cerebrovascular time constant (τ) theoretically estimates how fast the cerebral arterial bed is filled by blood volume after a sudden change in arterial blood pressure during one cardiac cycle. The aim of this study was to assess the time constant of the cerebral arterial bed in patients with traumatic brain injury (TBI) with and without intracranial hematomas (IH). We examined 116 patients with severe TBI (mean 35 ± 15 years, 61 men, 55 women). The first group included 58 patients without IH and the second group included 58 patients with epidural (7), subdural (48), and multiple (3) hematomas. Perfusion computed tomography (PCT) was performed 1-12 days after TBI in the first group and 2-8 days after surgical evacuation of the hematoma in the second group. Arteriovenous amplitude of regional cerebral blood volume oscillation was calculated as the difference between arterial and venous blood volume in the "region of interest" of 1 cm(2). Mean arterial pressure was measured and the flow rate of the middle cerebral artery was recorded with transcranial Doppler ultrasound after PCT. The time constant was calculated by the formula modified by Kasprowicz. The τ was shorter (p = 0.05) in both groups 1 and 2 in comparison with normal data. The time constant in group 2 was shorter than in group 1, both on the side of the former hematoma (р = 0.012) and on the contralateral side (р = 0.044). The results indicate failure of autoregulation of cerebral capillary blood flow in severe TBI, which increases in patients with polytrauma and traumatic IH.
Hubble Constant, Lensing, and Time Delay in Relativistic MOND
2012-01-01
Time delay in galaxy gravitational lensing systems has been used to determine the value of Hubble constant. As in other dynamical phenomena at the scale of galaxy, dark matter is often invoked in gravitational lensing to account for the "missing mass" (the apparent discrepancy between the dynamical mass and the luminous mass). Alternatively, modified gravity can be used to explain the discrepancy. In this paper we adopt the Tensor-Vector-Scalar gravity (TeVeS), a relativistic version of MOdif...
The cosmological constant problem and re-interpretation of time
Energy Technology Data Exchange (ETDEWEB)
Luo, M.J.
2014-07-15
We abandon the interpretation that time is a global parameter in quantum mechanics, replace it by a quantum dynamical variable playing the role of time. This operational re-interpretation of time provides a solution to the cosmological constant problem. The expectation value of the zero-point energy under the new time variable vanishes. The fluctuation of the vacuum energy as the leading contribution to the gravitational effect gives a correct order to the observed “dark energy”. The “dark energy” as a mirage is always seen comparable with the matter energy density by an observer using the internal clock time. Conceptual consequences of the re-interpretation of time are also discussed.
Constant Power Control of a Proton Exchange Membrane Fuel Cell through Adaptive Fuzzy Sliding Mode
Directory of Open Access Journals (Sweden)
Minxiu Yan
2013-05-01
Full Text Available Fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. The paper describes a mathematical model of proton exchange membrane fuel cells by analyzing the working mechanism of the proton exchange membrane fuel cell. Furthermore, an adaptive fuzzy sliding mode controller is designed for the constant power output of PEMFC system. Simulation results prove that adaptive fuzzy sliding mode control has better control effect than conventional fuzzy sliding mode control.
Analysis of constant tension-induced rupture of lipid membranes using activation energy.
Karal, Mohammad Abu Sayem; Levadnyy, Victor; Yamazaki, Masahito
2016-05-11
The stretching of biomembranes and lipid membranes plays important roles in various physiological and physicochemical phenomena. Here we analyzed the rate constant kp of constant tension-induced rupture of giant unilamellar vesicles (GUVs) as a function of tension σ using their activation energy Ua. To determine the values of kp, we applied constant tension to a GUV membrane using the micropipette aspiration method and observed the rupture of GUVs, and then analyzed these data statistically. First, we investigated the temperature dependence of kp for GUVs of charged lipid membranes composed of negatively charged dioleoylphosphatidylglycerol (DOPG) and electrically neutral dioleoylphosphatidylcholine (DOPC). By analyzing this result, the values of Ua of tension-induced rupture of DOPG/DOPC-GUVs were obtained. Ua decreased with an increase in σ, supporting the classical theory of tension-induced pore formation. The analysis of the relationship between Ua and σ using the theory on the electrostatic interaction effects on the tension-induced rupture of GUVs provided the equation of Ua including electrostatic interaction effects, which well fits the experimental data of the tension dependence of Ua. A constant which does not depend on tension, U0, was also found to contribute significantly to Ua. The Arrhenius equations for kp using the equation of Ua and the parameters determined by the above analysis fit well to the experimental data of the tension dependence of kp for DOPG/DOPC-GUVs as well as for DOPC-GUVs. On the basis of these results, we discussed the possible elementary processes underlying the tension-induced rupture of GUVs of lipid membranes. These results indicate that the Arrhenius equation using the experimentally determined Ua is useful in the analysis of tension-induced rupture of GUVs.
Time-dependent polymer rheology under constant stress and under constant shear conditions.
Lee, K. H.; Brodkey, R. S.
1971-01-01
A kinetic rate theory previously presented for describing non-Newtonian phenomena has been further modified to predict the flow behavior of viscoelastic materials under constant stress conditions. The thixotropic shear stress or shear rate is predicted by the kinetic theory, and the experimental stress or shear rate is obtained by modifying the thixotropic value by a stress or shear rate retardation term. The retardation term stems from a Maxwellian approach for stress retardation. In order to test the validity of this approach, transient and steady-state data were obtained for two solutions of polymethylmethacrylate in diethylphthalate. Both constant stress measurements and constant shear rate data were taken over a broad range.
Zhu, Honggang; Peck, Kendall D; Miller, David J; Liddell, Mark R; Yan, Guang; Higuchi, William I; Li, S Kevin
2003-04-14
Previous studies in our laboratory have shown that enhanced, constant permeant fluxes across human skin can be achieved by applying an alternating current (AC) to maintain skin electrical conductance at a constant level. Relative to conventional direct current (DC) iontophoresis, for which current is maintained at a constant level, this newly developed constant conductance alternating current (CCAC) method achieves constant fluxes with less inter- and intra-sample variability. The present study focused upon further investigating the permeability properties of human skin during CCAC iontophoresis at a variety of target resistance/conductance values. A three-stage experimental protocol was used with flux measurements determined on 3 consecutive days. Stage I was an AC only protocol (symmetrical AC square-wave signal), stage II was an AC plus DC protocol (AC square-wave with DC offset voltage), and stage III was a repeat of stage I. During this three-stage protocol, the skin electrical resistance was maintained at a constant target value by manually adjusting the applied AC voltage. Radiolabeled mannitol and urea were model permeants in all experiments. Their fluxes were determined and used to characterize the permeability properties of human skin. The results from the present study established that: (i) the CCAC protocol made it possible to reduce HEM electrical resistance to different target levels as low as 0.8 kOmega cm(2) and maintain the specific resistance level throughout the flux experiment, (ii) permeant fluxes are proportional to skin electrical conductance, (iii) under the studied CCAC passive conditions, membrane pore size tends to increase as skin resistance decreases, and (iv) as the membrane breaks down, its pore sizes become larger.
A Digitally Programmable Differential Integrator with Enlarged Time Constant
Directory of Open Access Journals (Sweden)
S. K. Debroy
1994-12-01
Full Text Available A new Operational Amplifier (OA-RC integrator network is described. The novelties of the design are used of single grounded capacitor, ideal integration function realization with dual-input capability and design flexibility for extremely large time constant involving an enlargement factor (K using product of resistor ratios. The aspect of the digital control of K through a programmable resistor array (PRA controlled by a microprocessor has also been implemented. The effect of the OA-poles has been analyzed which indicates degradation of the integrator-Q at higher frequencies. An appropriate Q-compensation design scheme exhibiting 1 : |A|2 order of Q-improvement has been proposed with supporting experimental observations.
Certificateless Public Auditing Protocol with Constant Verification Time
Directory of Open Access Journals (Sweden)
Dongmin Kim
2017-01-01
Full Text Available To provide the integrity of outsourced data in the cloud storage services, many public auditing schemes which allow a user to check the integrity of the outsourced data have been proposed. Since most of the schemes are constructed on Public Key Infrastructure (PKI, they suffer from several concerns like management of certificates. To resolve the problems, certificateless public auditing schemes also have been studied in recent years. In this paper, we propose a certificateless public auditing scheme which has the constant-time verification algorithm. Therefore, our scheme is more efficient than previous certificateless public auditing schemes. To prove the security of our certificateless public auditing scheme, we first define three formal security models and prove the security of our scheme under the three security models.
Cosmological Constant, Quantum Measurement, and the Problem of Time
Banerjee, Shreya; Singh, Tejinder P
2015-01-01
Three of the big puzzles of theoretical physics are the following: (i) There is apparently no time evolution in the dynamics of quantum general relativity, because the allowed quantum states must obey the Hamiltonian constraint. (ii) During a quantum measurement, the state of the quantum system randomly collapses from being in a linear superposition of the eigenstates of the measured observable, to just one of the eigenstates, in apparent violation of the predictions of the deterministic, linear Schr\\"{o}dinger equation. (iii) The observed value of the cosmological constant is exceedingly small, compared to its natural value, creating a serious fine-tuning problem. In this essay we propose a novel idea to show how the three problems help solve each other.
Fong, Yeong Yin; Bhatia, Subhash
The semiconductor industry needs low dielectric constant (low k-value) materials for more advance microprocessor and chips by reducing the size of the device features. In fabricating these contents, a new material with lower k-value than conventional silica (k = 3.9-4.2) is needed in order to improve the circuit performance. The choice of the inorganic zeolite membrane is an attractive option for low k material and suitable for microprocessor applications. A pure silica zeolite beta membrane was synthesized and coated on non-porous stainless steel support using insitu crystallization in the presence of tetraethylammonium hydroxide, TEA (OH), as structure directing agent, fumed silica, HF and deionized water at pH value of 9. The crystallization was carried out for the duration of 14 days under hydrothermal conditions at 130°C. The membrane was characterized by thermogravimetric analysis (TGA), nitrogen adsorption and Scanning Electron Microscope (SEM). SEM results show a highly crystalline; with a truncated square bipyramidal morphology of pure silica zeolite beta membrane strongly adhered on the non-porous stainless steel support. In the present work, the k-value of the membrane was measured as 2.64 which make it suitable for the microprocessor applications.
Time-dependent cell membrane damage under mechanical tension: Experiments and modeling
Lu, Bo; Chang, Jay Han-Chieh; Tai, Yu-Chong
2011-01-01
This paper reports a study of cancer cell membrane damage during filtration caused by cell membrane tension. The membrane tension was induced when cells were captured on a microfabricated parylene-C filter during the constant-pressure-driven filtration. This work includes both experiments and modeling to explore the underlying biomechanics of the cell membrane damage. The developed model not only agrees with our time-dependent cell damage data, but also fits well with previous results on red ...
Limits on the space-time variations of fundamental constants
Levshakov, S A; Reimers, D; Molaro, P
2013-01-01
We report on new tests that improve our previous (2009-2010) estimates of the electron-to-proton mass ratio variation, mu = m_e/m_p. Subsequent observations (2011-2013) at the Effelsberg 100-m telescope of a sample of eight molecular cores from the Milky Way disk reveal systematic errors in the measured sky frequencies varying with an amplitude +/-0.01 km/s during the exposure time. The averaged offset between the radial velocities of the NH3(1,1), HC3N(2-1), HC5N(9-8), HC7N(16-15), HC7N(21-20), and HC7N(23-22) transitions gives Delta V = 0.002 +/- 0.015 km/s (3 sigma C.L.). This value, when interpreted in terms of Delta mu/mu = (mu_obs - mu_lab)/mu_lab constraints the mu-variation at the level of Delta mu/mu < 2x10^{-8} (3 sigma C.L.), which is the most stringent limit on the fractional changes in mu based on radio astronomical observations. If variation of the fine-structure constant alpha is coupled with mu, then within the grand unification model one may expect locally the spacial changes |Delta alpha/...
Minimizing the area required for time constants in integrated circuits
Lyons, J. C.
1972-01-01
When a medium- or large-scale integrated circuit is designed, efforts are usually made to avoid the use of resistor-capacitor time constant generators. The capacitor needed for this circuit usually takes up more surface area on the chip than several resistors and transistors. When the use of this network is unavoidable, the designer usually makes an effort to see that the choice of resistor and capacitor combinations is such that a minimum amount of surface area is consumed. The optimum ratio of resistance to capacitance that will result in this minimum area is equal to the ratio of resistance to capacitance which may be obtained from a unit of surface area for the particular process being used. The minimum area required is a function of the square root of the reciprocal of the products of the resistance and capacitance per unit area. This minimum occurs when the area required by the resistor is equal to the area required by the capacitor.
Embedding and Distributing Constant Time Delay in Circle Time and Transitions.
Wolery, Mark; Anthony, Leslie; Caldwell, Nicola K.; Snyder, Erin D.; Morgante, James D.
2002-01-01
This study evaluated embedding and distributing constant time delay instructional trials into circle time and transitions between activities in a summer camp program. Three boys (ages 5-8) with disabilities or behavior problems participated. Results indicated the children acquired the behaviors they were taught and generalized the learned…
Li, S Kevin; Higuchi, William I; Kochambilli, Rajan P; Zhu, Honggang
2004-04-01
Although constant current iontophoresis is supposed to provide constant transdermal transport, significant flux variability and/or time-dependent flux drifts are observed during iontophoresis with human skin in vitro and human studies in vivo. The objectives of the present study were to determine (a) the causes of flux variability in constant current dc transdermal iontophoresis and (b) the relationships of flux variabilities among permeants of different physicochemical properties. Changes in the human epidermal membrane (HEM) effective pore size and/or electroosmosis during constant current dc iontophoresis were examined. Tetraethylammonium ion (TEA), urea, and mannitol were the model permeants. For the neutral permeants, the results in the present study showed a significant increase of fluxes with time in a given experiment and large HEM sample-to-sample variability. Although both effective pore size and pore charge density variations contributed to the time-dependent flux drifts observed in electroosmotic transport, the significant flux drifts observed were found to be primarily a result of the time-dependent increase in effective pore charge density. For the ionic permeant, the observed flux variability was smaller than that of the neutral permeants and was believed to be primarily due to effective pore size alteration in HEM during iontophoresis as suggested in a previous study. The different extents of flux variability observed between neutral and ionic permeants are consistent with the different iontophoretically enhanced transport mechanisms for the neutral and ionic permeants (i.e. electroosmosis and electrophoresis, respectively). The results of the present study also demonstrate that flux variability of two neutral permeants are inter-related, so the flux of one neutral permeant can be predicted if the permeability coefficient of the other neutral permeant is known.
Cranor, W.L.; Alvarez, D.A.; Huckins, J.N.; Petty, J.D.
2009-01-01
To fully utilize semipermeable membrane devices (SPMDs) as passive samplers in air monitoring, data are required to accurately estimate airborne concentrations of environmental contaminants. Limited uptake rate constants (kua) and no SPMD air partitioning coefficient (Ksa) existed for vapor-phase contaminants. This research was conducted to expand the existing body of kinetic data for SPMD air sampling by determining kua and Ksa for a number of airborne contaminants including the chemical classes: polycyclic aromatic hydrocarbons, organochlorine pesticides, brominated diphenyl ethers, phthalate esters, synthetic pyrethroids, and organophosphate/organosulfur pesticides. The kuas were obtained for 48 of 50 chemicals investigated and ranged from 0.03 to 3.07??m3??g-1??d-1. In cases where uptake was approaching equilibrium, Ksas were approximated. Ksa values (no units) were determined or estimated for 48 of the chemicals investigated and ranging from 3.84E+5 to 7.34E+7. This research utilized a test system (United States Patent 6,877,724 B1) which afforded the capability to generate and maintain constant concentrations of vapor-phase chemical mixtures. The test system and experimental design employed gave reproducible results during experimental runs spanning more than two years. This reproducibility was shown by obtaining mean kua values (n??=??3) of anthracene and p,p???-DDE at 0.96 and 1.57??m3??g-1??d-1 with relative standard deviations of 8.4% and 8.6% respectively.
Determination and discussion hydraulic retention time in membrane bioreactor system
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
Based on the microorganism kinetic model, the formulafor computing hydraulic retention time in a membrane bioreactorsystem (MBR) is derived. With considering HRT as an evaluationindex a combinational approach was used to discuss factors whichhave an effect on MBR. As a result, the influencing factors werelisted in order from strength to weakness as: maximum specificremoval rate K, saturation constant Ks, maintenance coefficient m,Moreover, the formula was simplified, whose parameters wereexperimentally determined in petrochemical wastewater treatment. The simplified formula is (=1.1((1/(-1)(Ks+S)/KX0, forpetrochemical wastewater treatment K and Ks equaled 0.185 and154.2, respectively.
Time Variation of the Fine Structure Constant Driven by Quintessence
Anchordoqui, L A; Anchordoqui, Luis; Goldberg, Haim
2003-01-01
There are indications from the study of quasar absorption spectra that the fine structure constant $\\alpha$ may have been measurably smaller for redshifts $z>2.$ Analyses of other data ($^{149}$Sm fission rate for the Oklo natural reactor, variation of $^{187}$Re $\\beta$-decay rate in meteorite studies, atomic clock measurements) which probe variations of $\\alpha$ in the more recent past imply much smaller deviations from its present value. In this work we tie the variation of $\\alpha$ to the evolution of the quintessence field proposed by Albrecht and Skordis, and show that agreement with all these data, as well as consistency with WMAP observations, can be achieved for a range of parameters. Some definite predictions follow for upcoming space missions searching for violations of the equivalence principle.
Time variation of the fine structure constant driven by quintessence
Anchordoqui, Luis; Goldberg, Haim
2003-10-01
There are indications from the study of quasar absorption spectra that the fine structure constant α may have been measurably smaller for redshifts z>2. Analyses of other data (149Sm fission rate for the Oklo natural reactor, variation of 187Re β-decay rate in meteorite studies, atomic clock measurements) which probe variations of α in the more recent past imply much smaller deviations from its present value. In this work we tie the variation of α to the evolution of the quintessence field proposed by Albrecht and Skordis, and show that agreement with all these data, as well as consistency with Wilkinson Microwave Anisotropy Probe observations, can be achieved for a range of parameters. Some definite predictions follow for upcoming space missions searching for violations of the equivalence principle.
Mark-recapture models with parameters constant in time.
Jolly, G M
1982-06-01
The Jolly-Seber method, which allows for both death and immigration, is easy to apply but often requires a larger number of parameters to be estimated tha would otherwise be necessary. If (i) survival rate, phi, or (ii) probability of capture, p, or (iii) both phi and p can be assumed constant over the experimental period, models with a reduced number of parameters are desirable. In the present paper, maximum likelihood (ML) solutions for these three situations are derived from the general ML equations of Jolly [1979, in Sampling Biological Populations, R. M. Cormack, G. P. Patil and D. S. Robson (eds), 277-282]. A test is proposed for heterogeneity arising from a breakdown of assumptions in the general Jolly-Seber model. Tests for constancy of phi and p are provided. An example is given, in which these models are fitted to data from a local butterfly population.
The photochemical time constants of minor constituents and their families in the middle atmosphere
Shimazaki, T.
1984-01-01
A comprehensive formula is worked out for the photochemical time constant of minor constituents in the middle atmosphere. The formula is particularly useful for evaluating the time constants for families of some chemical species that are strongly coupled by rapid exchange reactions. Height profiles of photochemical time constants are calculated for individual species and their families based on the chemical reaction rate constants recommended in the recent WMO and JPL reports. Potential exchange reactions among various family members are discussed, and the effects of the choice of family membership on the time constant are evaluated.
Is the Galactic Cosmic Ray Spectrum Constant in Time?
Eichler, David; Pohl, Martin
2013-01-01
The hypothesis is considered that the present Galactic cosmic ray spectrum is at present softer than its time average due to source intermittency. Measurements of muogenic nuclides underground could provide an independent measurement of the time averaged spectrum. Source intermittency could also account for the surprising low anisotropy reported by the IceCube collaboration. Predictions for Galactic emission of ultrahigh-energy quanta, such as UHE gamma rays and neutrinos, might be higher or lower than previously estimated.
Dark energy models with time-dependent gravitational constant
Ray, S; Ray, Saibal; Mukhopadhyay, Utpal
2005-01-01
Two phenomenological models of $\\Lambda$, viz. $\\Lambda \\sim (\\dot a/a)^2$ and $\\Lambda \\sim \\ddot a/a$ are studied under the assumption that $G$ is a time-variable parameter. Both models show that $G$ is inversely proportional to time as suggested earlier by others including Dirac. The models considered here can be matched with observational results by properly tuning the parameters of the models. Our analysis shows that $\\Lambda \\sim \\ddot a/a$ model corresponds to a repulsive situation and hence correlates with the present status of the accelerating Universe. The other model $\\Lambda \\sim (\\dot a/a)^2$ is, in general, attractive in nature. Moreover, it is seen that due to the combined effect of time-variable $\\Lambda$ and $G$ the Universe evolved with acceleration as well as deceleration. This later one indicates a Big Crunch.
Dark Energy Models with a Time-Dependent Gravitational Constant
Ray, Saibal; Mukhopadhyay, Utpal; Choudhury, S. B. Dutta
Two phenomenological models of Λ, viz. Λ ˜ (˙ a/a)2 and Λ ˜ ḋ a/a, are studied under the assumption that G is a time-variable parameter. Both models show that G is inversely proportional to time, as suggested earlier by others, including Dirac. The models considered here can be matched with observational results by properly tuning the parameters of the models. Our analysis shows that the Λ ˜ ḋ a/a model corresponds to a repulsive situation and hence correlates with the present status of the accelerating Universe. The other model, Λ ˜ (˙ a/a)2, is in general attractive in nature. Moreover, it is seen that due to the combined effect of time-variable Λ and G the Universe evolved with acceleration as well as deceleration. Deceleration indicates a "big crunch".
Dynamic maintenance of majority information in constant time per update
DEFF Research Database (Denmark)
Frandsen, Gudmund Skovbjerg; Skyum, Sven
1997-01-01
We show how to maintain information about the existence of a majority colour in a set of elements under insertion and deletion of single elements using O(1) time and at most 4 equality tests on colours per update. No ordering information is used....
Constant pressure and temperature discrete-time Langevin molecular dynamics.
Grønbech-Jensen, Niels; Farago, Oded
2014-11-21
We present a new and improved method for simultaneous control of temperature and pressure in molecular dynamics simulations with periodic boundary conditions. The thermostat-barostat equations are built on our previously developed stochastic thermostat, which has been shown to provide correct statistical configurational sampling for any time step that yields stable trajectories. Here, we extend the method and develop a set of discrete-time equations of motion for both particle dynamics and system volume in order to seek pressure control that is insensitive to the choice of the numerical time step. The resulting method is simple, practical, and efficient. The method is demonstrated through direct numerical simulations of two characteristic model systems-a one-dimensional particle chain for which exact statistical results can be obtained and used as benchmarks, and a three-dimensional system of Lennard-Jones interacting particles simulated in both solid and liquid phases. The results, which are compared against the method of Kolb and Dünweg [J. Chem. Phys. 111, 4453 (1999)], show that the new method behaves according to the objective, namely that acquired statistical averages and fluctuations of configurational measures are accurate and robust against the chosen time step applied to the simulation.
Design verification of large time constant thermal shields for optical reference cavities.
Zhang, J; Wu, W; Shi, X H; Zeng, X Y; Deng, K; Lu, Z H
2016-02-01
In order to achieve high frequency stability in ultra-stable lasers, the Fabry-Pérot reference cavities shall be put inside vacuum chambers with large thermal time constants to reduce the sensitivity to external temperature fluctuations. Currently, the determination of thermal time constants of vacuum chambers is based either on theoretical calculation or time-consuming experiments. The first method can only apply to simple system, while the second method will take a lot of time to try out different designs. To overcome these limitations, we present thermal time constant simulation using finite element analysis (FEA) based on complete vacuum chamber models and verify the results with measured time constants. We measure the thermal time constants using ultrastable laser systems and a frequency comb. The thermal expansion coefficients of optical reference cavities are precisely measured to reduce the measurement error of time constants. The simulation results and the experimental results agree very well. With this knowledge, we simulate several simplified design models using FEA to obtain larger vacuum thermal time constants at room temperature, taking into account vacuum pressure, shielding layers, and support structure. We adopt the Taguchi method for shielding layer optimization and demonstrate that layer material and layer number dominate the contributions to the thermal time constant, compared with layer thickness and layer spacing.
Thermal time constant of a terminating type MEMS microwave power sensor
Institute of Scientific and Technical Information of China (English)
Xu Yinglin; Liao Xiaoping
2009-01-01
A terminating type MEMS microwave power sensor based on the Seebeck effect and compatible with the GaAs MMIC process is presented. An electrothermal model is introduced to simulate the thermal time constant. An analytical result, about 160 ms, of the thermal time constant from the non-stationary Fourier heat equations for the structure of the sensor is also given. The sensor measures the microwave power jumping from 15 to 20 dBm at a constant frequency 15 GHz, and the experimental thermal time constant result is 180 ms. The frequency is also changed from 20 to 10 GHz with a constant power 20 dBm, and the result is also 180 ms. Compared with the analytical and experimental results, the model is verified.
Dynamics of Perceived Exertion in Constant-Power Cycling: Time- and Workload-Dependent Thresholds
Balagué, Natàlia; Hristovski, Robert; García, Sergi; Aguirre, Cecilia; Vázquez, Pablo; Razon, Selen; Tenenbaum, Gershon
2015-01-01
Purpose: The purpose of this study was to test the dynamics of perceived exertion shifts (PES) as a function of time and workload during constant-power cycling. Method: Fifty-two participants assigned to 4 groups performed a cycling task at 4 different constant workloads corresponding to their individual rates of perceived exertion (RPEs = 13, 15,…
Dynamics of Perceived Exertion in Constant-Power Cycling: Time- and Workload-Dependent Thresholds
Balagué, Natàlia; Hristovski, Robert; García, Sergi; Aguirre, Cecilia; Vázquez, Pablo; Razon, Selen; Tenenbaum, Gershon
2015-01-01
Purpose: The purpose of this study was to test the dynamics of perceived exertion shifts (PES) as a function of time and workload during constant-power cycling. Method: Fifty-two participants assigned to 4 groups performed a cycling task at 4 different constant workloads corresponding to their individual rates of perceived exertion (RPEs = 13, 15,…
Constant scalar curvature hypersurfaces in the extended Schwarzschild space-time
Pareja, M J
2006-01-01
In this paper we study the spherically symmetric constant scalar curvature hypersurfaces of the extended Schwarzschild space-time. Especially, we analyse the embedding equation and we find the family of solutions or slices that results varying a parameter "c" for fixed constant scalar curvature parameter and fixed time-translation parameter. The parameter "c" represents the amount of variation of volume of the 3-geometry during the 'time'-evolution.
Time of flight and range of the motion of a projectile in a constant gravitational field
Directory of Open Access Journals (Sweden)
P. A. Karkantzakos
2009-01-01
Full Text Available In this paper we study the classical problem of the motion of a projectile in a constant gravitational field under the influenceof a retarding force proportional to the velocity. Specifically, we express the time of flight, the time of fall and the range ofthe motion as a function of the constant of resistance per unit mass of the projectile. We also prove that the time of fall isgreater than the time of rise with the exception of the case of zero constant of resistance where we have equality. Finally weprove a formula from which we can compute the constant of resistance per unit mass of the projectile from time of flight andrange of the motion when the acceleration due to gravity and the initial velocity of the projectile are known.
Effect of coefficient changes on stability of linear retarded systems with constant time delays
Barker, L. K.
1977-01-01
A method is developed to determine the effect of coefficient changes on the stability of a retarded system with constant time delays. The method, which uses the tau-decomposition method of stability analysis, is demonstrated by an example.
MacKenzie Ross, Robert V; Toshner, Mark R; Soon, Elaine; Naeije, Robert; Pepke-Zaba, Joanna
2013-07-15
This study analyzed the relationship between pulmonary vascular resistance (PVR) and pulmonary arterial compliance (Ca) in patients with idiopathic pulmonary arterial hypertension (IPAH) and proximal chronic thromboembolic pulmonary hypertension (CTEPH). It has recently been shown that the time constant of the pulmonary circulation (RC time constant), or PVR × Ca, remains unaltered in various forms and severities of pulmonary hypertension, with the exception of left heart failure. We reasoned that increased wave reflection in proximal CTEPH would be another cause of the decreased RC time constant. We conducted a retrospective analysis of invasive pulmonary hemodynamic measurements in IPAH (n = 78), proximal CTEPH (n = 91) before (pre) and after (post) pulmonary endarterectomy (PEA), and distal CTEPH (n = 53). Proximal CTEPH was defined by a postoperative mean pulmonary artery pressure (PAP) of ≤25 mmHg. Outcome measures were the RC time constant, PVR, Ca, and relationship between systolic and mean PAPs. The RC time constant for pre-PEA CTEPH was 0.49 ± 0.11 s compared with post-PEA-CTEPH (0.37 ± 0.11 s, P time constant was associated with a disproportionate decrease in systolic PAP with respect to mean PAP. We concluded that the pulmonary RC time constant is decreased in proximal CTEPH compared with IPAH, pre- and post-PEA, which may be explained by increased wave reflection but also, importantly, by persistent structural changes after the removal of proximal obstructions. A reduced RC time constant in CTEPH is in accord with a wider pulse pressure and hence greater right ventricular work for a given mean PAP.
Kleist, Thomas J; Luan, Sheng
2016-03-01
Despite substantial variation and irregularities in their environment, plants must conform to spatiotemporal demands on the molecular composition of their cytosol. Cell membranes are the major interface between organisms and their environment and the basis for controlling the contents and intracellular organization of the cell. Membrane transport proteins (MTPs) govern the flow of molecules across membranes, and their activities are closely monitored and regulated by cell signalling networks. By continuously adjusting MTP activities, plants can mitigate the effects of environmental perturbations, but effective implementation of this strategy is reliant on precise coordination among transport systems that reside in distinct cell types and membranes. Here, we examine the role of calcium signalling in the coordination of membrane transport, with an emphasis on potassium transport. Potassium is an exceptionally abundant and mobile ion in plants, and plant potassium transport has been intensively studied for decades. Classic and recent studies have underscored the importance of calcium in plant environmental responses and membrane transport regulation. In reviewing recent advances in our understanding of the coding and decoding of calcium signals, we highlight established and emerging roles of calcium signalling in coordinating membrane transport among multiple subcellular locations and distinct transport systems in plants, drawing examples from the CBL-CIPK signalling network. By synthesizing classical studies and recent findings, we aim to provide timely insights on the role of calcium signalling networks in the modulation of membrane transport and its importance in plant environmental responses.
A high-linearity digital-to-time converter technique: constant-slope charging
Ru, Jiayoon Zhiyu; Palattella, Claudia; Geraedts, Paul; Klumperink, Eric; Nauta, Bram
2015-01-01
A digital-to-time converter (DTC) controls time delay by a digital code, which is useful, for example, in a sampling oscilloscope, fractional-N PLL, or time-interleaved ADC. This paper proposes constant-slope charging as a method to realize a DTC with intrinsically better integral non-linearity (INL
Running vacuum in the Universe and the time variation of the fundamental constants of Nature
Energy Technology Data Exchange (ETDEWEB)
Fritzsch, Harald [Nanyang Technological University, Institute for Advanced Study, Singapore (Singapore); Universitaet Muenchen, Physik-Department, Munich (Germany); Sola, Joan [Nanyang Technological University, Institute for Advanced Study, Singapore (Singapore); Universitat de Barcelona, Departament de Fisica Quantica i Astrofisica, Barcelona, Catalonia (Spain); Universitat de Barcelona (ICCUB), Institute of Cosmos Sciences, Barcelona, Catalonia (Spain); Nunes, Rafael C. [Universidade Federal de Juiz de Fora, Dept. de Fisica, Juiz de Fora, MG (Brazil)
2017-03-15
We compute the time variation of the fundamental constants (such as the ratio of the proton mass to the electron mass, the strong coupling constant, the fine-structure constant and Newton's constant) within the context of the so-called running vacuum models (RVMs) of the cosmic evolution. Recently, compelling evidence has been provided that these models are able to fit the main cosmological data (SNIa+BAO+H(z)+LSS+BBN+CMB) significantly better than the concordance ΛCDM model. Specifically, the vacuum parameters of the RVM (i.e. those responsible for the dynamics of the vacuum energy) prove to be nonzero at a confidence level >or similar 3σ. Here we use such remarkable status of the RVMs to make definite predictions on the cosmic time variation of the fundamental constants. It turns out that the predicted variations are close to the present observational limits. Furthermore, we find that the time evolution of the dark matter particle masses should be crucially involved in the total mass variation of our Universe. A positive measurement of this kind of effects could be interpreted as strong support to the ''micro-macro connection'' (viz. the dynamical feedback between the evolution of the cosmological parameters and the time variation of the fundamental constants of the microscopic world), previously proposed by two of us (HF and JS). (orig.)
On the use of measured time delays in gravitational lenses to determine the Hubble constant
Alcock, C.; Anderson, N.
1985-01-01
Gravitational lenses are rare in the known samples of quasars, indicating that the conditions involved in their formation are unusual. In particular, the distribution of matter along the light rays from the observer through the deflector to the quasar may be very different from mean conditions. It is shown that reasonable deviations in the density of matter along the beams can significantly alter the relationship between time delays and the Hubble constant, and it is concluded that gravitational lenses are not promising estimators of this constant. However, should an independent, precise determination of the Hubble constant become available, gravitational lenses could be used to probe long-range density fluctuations.
Queueing systems with constant service time and evaluation of M/D/1,k
DEFF Research Database (Denmark)
Iversen, Villy Bæk
1997-01-01
Systems with constant service times have the particular property that the customers leave the servers in the same order in which they areaccepted for service. Probabilitites of integral waiting times can be expressed by the state probabilities, and non-integral waiting timescan be expressed...
The Finite-time Ruin Probability for the Jump-Diffusion Model with Constant Interest Force
Institute of Scientific and Technical Information of China (English)
Tao Jiang; Hai-feng Yan
2006-01-01
In this paper, we consider the finite-time ruin probability for the jump-diffusion Poisson process.Under the assumptions that the claimsizes are subexponentially distributed and that the interest force is constant, we obtain an asymptotic formula for the finite-time ruin probability. The results we obtain extends the
Time-variability of the coupling constants of fundamental particles and Oklo phenomena
Energy Technology Data Exchange (ETDEWEB)
Fujii, Yasunori [Nihon Fukushi Univ., Handa, Aichi (Japan); Iwamoto, Akira; Hidaka, Hiroshi
2000-09-01
About 60 years ago, Dirac, P.A.M. presented that gravitational constant was not a constant but varied with a time in universe. As it has not obtained any determining proof experimentally, a fundamental concept on physical constants was disturbed since then, which has been succeeded to trials on the present integral theory. In special, some interesting researches on what is called coupling constants of fundamental particles, such as if fundamental charge of an electron changes actually, are continued. As proof on this change was not established, the observing and experimental upper values contain some important suggestions. The most serious result as its upper limit was obtained as well by an investigation on a surprising fact (a natural reactor) that uranium naturally reached a criticality at a place (Oklo) on the earth two billion years ago. Here were introduced on some their recent researches. (G.K.)
Competing bounds on the present-day time variation of fundamental constants
Dent, Thomas; Wetterich, Christof
2008-01-01
We compare the sensitivity of a recent bound on time variation of the fine structure constant from optical clocks with bounds on time varying fundamental constants from atomic clocks sensitive to the electron-to-proton mass ratio, from radioactive decay rates in meteorites, and from the Oklo natural reactor. Tests of the Weak Equivalence Principle also lead to comparable bounds on present variations of constants. The "winner in sensitivity" depends on what relations exist between the variations of different couplings in the standard model of particle physics, which may arise from the unification of gauge interactions. WEP tests are currently the most sensitive within unified scenarios. A detection of time variation in atomic clocks would favour dynamical dark energy and put strong constraints on the dynamics of a cosmological scalar field.
Competing bounds on the present-day time variation of fundamental constants
Dent, Thomas; Stern, Steffen; Wetterich, Christof
2009-04-01
We compare the sensitivity of a recent bound on time variation of the fine structure constant from optical clocks with bounds on time-varying fundamental constants from atomic clocks sensitive to the electron-to-proton mass ratio, from radioactive decay rates in meteorites, and from the Oklo natural reactor. Tests of the weak equivalence principle also lead to comparable bounds on present variations of constants. The “winner in sensitivity” depends on what relations exist between the variations of different couplings in the standard model of particle physics, which may arise from the unification of gauge interactions. Weak equivalence principle tests are currently the most sensitive within unified scenarios. A detection of time variation in atomic clocks would favor dynamical dark energy and put strong constraints on the dynamics of a cosmological scalar field.
Measurements of the time constant for steady ionization in shaped-charge barium releases
Hoch, Edward L.; Hallinan, Thomas J.
1993-01-01
Quantitative measurements of three solar illuminated shaped-charge barium releases injected at small angles to the magnetic field were made using a calibrated color television camera. Two of the releases were from 1989. The third release, a reanalysis of an event included in Hallinan's 1988 study of three 1986 releases, was included to provide continuity between the two studies. Time constants for ionization, measured during the first 25 s of each release, were found to vary considerably. The two 1989 time constants differed substantially, and both were significantly less than any of the 1986 time constants. On the basis of this variability, we conclude that the two 1989 releases showed evidence of continuous nonsolar ionization. One release showed nonsolar ionization which could not he attributed to Alfven's critical ionization velocity process, which requires a component of velocity perpendicular to the magnetic field providing a perpendicular energy greater than the ionization potential.
Structural Requirements for Membrane Assembly of Proteins Spanning the Membrane Several Times
Lipp, Joachim; Flint, Nicholas; Haeuptle, Marie-Theres; Dobberstein, Bernhard
1989-01-01
We have investigated the structural requirements for the biogenesis of proteins spanning the membrane several times. Proteins containing various combinations of topological signals (signal anchor and stop transfer sequences) were synthesized in a cell-free translation system and their membrane topology was determined. Proteins spanning the membrane twice were obtained when a signal anchor sequence was followed by either a stop transfer sequence or a second signal anchor sequence. Thus, a sig...
Estimation of the Plant Time Constant of Current-Controlled Voltage Source Converters
DEFF Research Database (Denmark)
Vidal, Ana; Yepes, Alejandro G.; Malvar, Jano
2014-01-01
Precise knowledge of the plant time constant is essential to perform a thorough analysis of the current control loop in voltage source converters (VSCs). As the loop behavior can be significantly influenced by the VSC working conditions, the effects associated to converter losses should be included...... of the VSC interface filter measured at rated conditions. This paper extends that method so that both parameters of the plant time constant (resistance and inductance) are estimated. Such enhancement is achieved through the evaluation of the closed-loop transient responses of both axes of the synchronous...
Time-dependent water permeation behavior of concrete under constant hydraulic pressure
Institute of Scientific and Technical Information of China (English)
Fang Yonghao; Wang Zhongli; Zhou Yue
2008-01-01
In the present work, a concrete permeability testing setup was designed to study the behavior of hydraulic concrete subjected to constant hydraulic pressure. The results show that when concrete is subjected to high enough constant hydraulic pressure, it will be permeated, and after it reaches its maximum permeation rate, the permeability coefficient will gradually decrease towards a stable value. A time-dependent model of permeability coefficient for concrete subjected to hydraulic pressure is proposed. It is indicated that the decrease of the permeability coefficient with permeation time conforms well to the negative-exponential decrease model.
Running vacuum in the Universe and the time variation of the fundamental constants of Nature
Fritzsch, Harald; Sola, Joan
2016-01-01
We compute the time variation of the fundamental constants (such as the ratio of the proton mass to the electron mass, the strong coupling constant, the fine structure constant and Newton's constant) within the context of the so-called running vacuum models (RVM's) of the cosmic evolution. Recently, compelling evidence has been provided showing that these models are able to fit the main cosmological data (SNIa+BAO+H(z)+LSS+BBN+CMB) significantly better than the concordance $\\Lambda$CDM model. Specifically, the vacuum parameters of the RVM (i.e. those responsible for the dynamics of the vacuum energy) prove to be nonzero at a confidence level of $\\gtrsim3\\sigma$. Here we use such remarkable status of the RVM's to make definite predictions on the cosmic time variation of the fundamental constants. It turns out that the predicted variations are close to the present observational limits. Furthermore, we find that the time variation of the dark matter particles should be necessarily involved in the total mass vari...
Geometric optimal design of MR damper considering damping force, control energy and time constant
Energy Technology Data Exchange (ETDEWEB)
Nguyen, Q H; Choi, S B [Smart Structures and Systems Laboratory, Department of Mechanical Engineering, INHA University, Incheon 402-751 (Korea, Republic of); Kim, K S [Department of Mechanical and Automotive Engineering, Kongju National University, Chonan 330-240 (Korea, Republic of)], E-mail: seungbok@inha.ac.kr
2009-02-01
This paper presents an optimal design of magnetorheological (MR) damper based on finite element analysis. The MR damper is constrained in a specific volume and the optimization problem identifies geometric dimensions of the damper that minimizes an objective function. The objective function is proposed by considering the damping force, dynamic range and the inductive time constant of the damper. After describing the configuration of the MR damper, a quasi-static modelling of the damper is performed based on Bingham model of MR fluid. The initial geometric dimensions of the damper are then determined based on the assumption of constant magnetic flux density throughout the magnetic circuit of the damper. Subsequently, the optimal design variables that minimize the objective function are determined using a golden-section algorithm and a local quadratic fitting technique via commercial finite element method parametric design language. A comparative work on damping force and time constant between the initial and optimal design is undertaken.
Institute of Scientific and Technical Information of China (English)
Prashant Singh Baghel; Jagdish Prasad Singh
2012-01-01
We consider spatially homogeneous and anisotropic Bianchi type Ⅴ space-time with a bulk viscous fluid source,and time varying gravitational constant G and cosmological term A.The coefficient of bulk viscosity ζ is assumed to be a simple linear function of the Hubble parameter H (i.e.ζ=ζ0 + ζ1H,where ζ0 and ζ1 are constants).The Einstein field equations are solved explicitly by using a law of variation for the Hubble parameter,which yields a constant value of the deceleration parameter.Physical and kinematical parameters of the models are discussed.The models are found to be compatible with the results of astronomical observations.
Estimation of the Plant Time Constant of Current-Controlled Voltage Source Converters
DEFF Research Database (Denmark)
Vidal, Ana; Yepes, Alejandro G.; Malvar, Jano;
2014-01-01
Precise knowledge of the plant time constant is essential to perform a thorough analysis of the current control loop in voltage source converters (VSCs). As the loop behavior can be significantly influenced by the VSC working conditions, the effects associated to converter losses should be included...... of the VSC interface filter measured at rated conditions. This paper extends that method so that both parameters of the plant time constant (resistance and inductance) are estimated. Such enhancement is achieved through the evaluation of the closed-loop transient responses of both axes of the synchronous...... in the model, through an equivalent series resistance. In a recent work, an algorithm to identify this parameter was developed, considering the inductance value as known and practically constant. Nevertheless, the plant inductance can also present important uncertainties with respect to the inductance...
Farias, Elizabeth L; Howe, Kerry J; Thomson, Bruce M
2014-02-01
The effect of the solids retention time (SRT) in a membrane bioreactor (MBR) on the fouling of the membranes in a subsequent reverse osmosis (RO) process used for wastewater reuse was studied experimentally using a pilot-scale treatment system. The MBR-RO pilot system was fed effluent from the primary clarifiers at a large municipal wastewater treatment plant. The SRT in the MBRs was adjusted to approximately 2, 10, and 20 days in three experiments. The normalized specific flux through the MBR and RO membranes was evaluated along with inorganic and organic constituents in the influent and effluent of each process. Increasing the SRT in the MBR led to an increase in the removal of bulk DOC, protein, and carbohydrates, as has been observed in previous studies. Increasing the SRT led to a decrease in the fouling of the MBR membranes, which is consistent with previous studies. However, the opposite trend was observed for fouling of the RO membranes; increasing the SRT of the MBR resulted in increased fouling of the RO membranes. These results indicate that the constituents that foul MBR membranes are not the same as those that foul RO membranes; to be an RO membrane foulant in a MBR-RO system, the constituents must first pass through the MBR membranes without being retained. Thus, an intermediate value of SRT may be best choice of operating conditions in an MBR when the MBR is followed by RO for wastewater reuse.
Mizuno, Ju; Matsubara, Hiromi; Mohri, Satoshi; Shimizu, Juichiro; Suzuki, Shunsuke; Mikane, Takeshi; Araki, Junichi; Hanaoka, Kazuo; Akins, Robert; Morita, Shigeho
2008-03-01
Temperature changes influence cardiac diastolic function. The monoexponential time constant (tauE), which is a conventional lusitropic index of the rate of left ventricular (LV) pressure fall, increases with cooling and decreases with warming. We have proposed that a half-logistic time constant (tauL) is a better lusitropic index than tauE at normothermia. In the present study, we investigated whether tauL can remain a superior measure as temperature varies. The isovolumic relaxation LV pressure curves from the minimum of the first time derivative of LV pressure (dP/dtmin) to the LV end-diastolic pressure were analyzed at 30, 33, 36, 38, and 40 degrees C in excised, cross-circulated canine hearts. tauL and tauE were evaluated by curve-fitting using the least squares method and applying the half-logistic equation, P(t) = PA/[1 + exp(t/tauL)] + PB, and the monoexponential equation, P(t) = P0exp(-t/tauE) + Pinfinity. Both tauL and tauE increased significantly with decreasing temperature and decreased with increasing temperature. The half-logistic correlation coefficient (r) values were significantly higher than the monoexponential r values at the 5 above-mentioned temperatures. This implies that the superiority of the goodness of the half-logistic fit is not temperature dependent. The half-logistic model characterizes the amplitude and time course of LV pressure fall more reliably than the monoexponential model. Hence, we concluded that tauL is a more useful lusitropic index regardless of temperature.
A simple biophysically plausible model for long time constants in single neurons.
Tiganj, Zoran; Hasselmo, Michael E; Howard, Marc W
2015-01-01
Recent work in computational neuroscience and cognitive psychology suggests that a set of cells that decay exponentially could be used to support memory for the time at which events took place. Analytically and through simulations on a biophysical model of an individual neuron, we demonstrate that exponentially decaying firing with a range of time constants up to minutes could be implemented using a simple combination of well-known neural mechanisms. In particular, we consider firing supported by calcium-controlled cation current. When the amount of calcium leaving the cell during an interspike interval is larger than the calcium influx during a spike, the overall decay in calcium concentration can be exponential, resulting in exponential decay of the firing rate. The time constant of the decay can be several orders of magnitude larger than the time constant of calcium clearance, and it could be controlled externally via a variety of biologically plausible ways. The ability to flexibly and rapidly control time constants could enable working memory of temporal history to be generalized to other variables in computing spatial and ordinal representations.
Analysis of distributed power control under constant and time-varying delays
Campos-delgado, Daniel U.; Luna-rivera, J. Martin; Bonilla, Isela
2013-10-01
This work studies the distributed power control algorithm proposed in 1993 by Foschini-Miljanic, standardised for universal mobile telecommunication systems. Continuous and discrete time versions of this algorithm are analysed. First, the stability of the distributed power allocation schemes was studied, where sufficient conditions to guarantee stability and convergence to a desired quality of service were provided. In this study, the channel gains are assumed to be slowly time-varying or piece-wise constant. For closed-loop control, a proportional controller is then employed under integral action in order to achieve good tracking despite time-varying and unknown channel gains. Next, the effects of constant and time-varying time delays in the closed-loop structure are studied. Explicit stability regions for the control gains in the Foschini-Miljanic scheme are derived for both the continuous and discrete-time versions of the algorithm, under constant and time-varying delays. For time-varying scenario, the resulting stability regions do not impose limitations on the rate change of the time-varying profiles. A comprehensive evaluation using simulations is performed to validate the analytical derivations described in the paper.
Cylindrically bounded constant mean curvature surfaces in $\\mathbb{H}^2\\times\\mathbb{R}$
Mazet, Laurent
2012-01-01
In this paper we prove that a properly embedded constant mean curvature surface in $\\mathbb{H}^2\\times\\mathbb{R}$ which has finite topology and stays at a finite distance from a vertical geodesic line is invariant by rotation around a vertical geodesic line.
On the Calculation of Reactor Time Constants Using the Monte Carlo Method
Energy Technology Data Exchange (ETDEWEB)
Leppaenen, Jaakko [VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT (Finland)
2008-07-01
Full-core reactor dynamics calculation involves the coupled modelling of thermal hydraulics and the time-dependent behaviour of core neutronics. The reactor time constants include prompt neutron lifetimes, neutron reproduction times, effective delayed neutron fractions and the corresponding decay constants, typically divided into six or eight precursor groups. The calculation of these parameters is traditionally carried out using deterministic lattice transport codes, which also produce the homogenised few-group constants needed for resolving the spatial dependence of neutron flux. In recent years, there has been a growing interest in the production of simulator input parameters using the stochastic Monte Carlo method, which has several advantages over deterministic transport calculation. This paper reviews the methodology used for the calculation of reactor time constants. The calculation techniques are put to practice using two codes, the PSG continuous-energy Monte Carlo reactor physics code and MORA, a new full-core Monte Carlo neutron transport code entirely based on homogenisation. Both codes are being developed at the VTT Technical Research Centre of Finland. The results are compared to other codes and experimental reference data in the CROCUS reactor kinetics benchmark calculation. (author)
Using a Constant Time Delay Procedure to Teach Foundational Swimming Skills to Children with Autism
Rogers, Laura; Hemmeter, Mary Louise; Wolery, Mark
2010-01-01
The purpose of this study was to evaluate the effectiveness of using a constant time delay procedure to teach foundational swimming skills to three children with autism. The skills included flutter kick, front-crawl arm strokes, and head turns to the side. A multiple-probe design across behaviors and replicated across participants was used.…
Time constant measurement for control of induction heating processes for thixoforming
Gerlach, O.; Lechler, A.; Verl, A.
2015-02-01
In controlling induction heating systems, several measurement methods exist for controlled heating of metal billets into the semi-solid state for thixoforming. The most common approach is to measure the billet temperature, which suffers from various drawbacks leading to difficulties in process stability. The main disadvantages are the small temperature range of the process window and the alloy composition dependency of the correlation between temperature and liquid fraction. An alternative is to determine the liquid fraction of the billet by measuring the time constant of the load. Although time constant measurement is not affected by the mentioned problems, it is difficult to use it as a controlled variable. This paper shows that disturbances affecting time constant measurement are mainly caused by semiconductor losses inside the inverter. A method is introduced to compensate these losses. This method was implemented and tested in the embedded system of an induction heating unit, thereby showing that it is possible to use time constant measurement to determine the liquid fraction of a billet during induction heating.
Partially persistent data structures of bounded degree with constant update time
DEFF Research Database (Denmark)
Brodal, Gerth Stølting
1996-01-01
The problem of making bounded in-degree and out-degree data structures partially persistent is considered. The node copying method of Driscoll et al. is extended so that updates can be performed in worst-case constant time on the pointer machine model. Previously it was only known to be possible...
Using a Constant Time Delay Procedure to Teach Aquatic Play Skills to Children with Autism
Yilmaz, Ilker; Birkan, Bunyamin; Konukman, Ferman; Erkan, Mert
2005-01-01
Effects of a constant time delay procedure on aquatic play skills of children with autism was investigated. A single subject multiple probe model across behaviors with probe conditions was used. Participants were four boys, 7-9 years old. Data were collected over a 10-week period using the single opportunity method as an intervention. Results…
A Comparison of Flexible Prompt Fading and Constant Time Delay for Five Children with Autism
Soluaga, Doris; Leaf, Justin B.; Taubman, Mitchell; McEachin, John; Leaf, Ron
2008-01-01
Given the increasing rates of autism, identifying prompting procedures that can assist in the development of more optimal learning opportunities for this population is critical. Extensive empirical research exists supporting the effectiveness of various prompting strategies. Constant time delay (CTD) is a highly implemented prompting procedure…
Concept for sleeve induction motor with 1-msec mechanical time constant
Wiegand, D. E.
1968-01-01
Conductive sleeve induction motor having a 1-msec mechanical time constant is used with solid-state devices to control all-electric servo power systems. The servomotor rotor inertia is small compared to the maximum force rating of the servo motion, permitting high no-load acceleration.
A Comparison of Simultaneous Prompting and Constant Time Delay Procedures in Teaching State Capitals
Head, Kenneth David; Collins, Belva C.; Schuster, John W.; Ault, Melinda Jones
2011-01-01
This investigation compared the effectiveness and efficiency of constant time delay (CTD) and simultaneous prompting (SP) procedures in teaching discrete social studies facts to 4 high school students with learning and behavior disorders using an adapted alternating treatments design nested within a multiple probe design. The results indicated…
Jameson, J. Matt; McDonnell, John; Polychronis, Shamby; Riesen, Tim
2008-01-01
This study investigated the effects of a training package (written manual, individual training session, and ongoing verbal feedback) on middle school peer tutors' use of embedded, constant time delay procedures and on the learning outcomes for students with significant cognitive disabilities in general education settings. The study data showed…
Learning to Effectively Implement Constant Time Delay Procedures To Teach Spelling.
Hughes, Trudie A.; Fredrick, Laura D.; Keel, Marie C.
2002-01-01
A study examined the effectiveness of a training procedure in teaching a special educator the constant time delay procedure and the effectiveness of the procedure in teaching spelling to a 12-year-old with learning disabilities. The teacher successfully implemented the procedure and the student learned to spell all 15 words. (Contains references.)…
Hughes, Trudie A.; Fredrick, Laura D.
2006-01-01
This study examined the effectiveness and efficiency of combining classwide peer tutoring (CWPT) and constant time delay (CTD) on the academic performance of 3 students with learning disabilities (LD) and 15 students without LD enrolled in an inclusive sixth-grade language arts class. Treatment integrity checklists were used to measure the extent…
Walker, Gabriela
2008-01-01
A review of 22 empirical studies examining the use of constant (CTD) and progressive (PTD) time delay procedures employed with children with autism frames an indirect analysis of the demographic, procedural, methodological, and outcome parameters of existing research. None of the previous manuscripts compared the two response prompting procedures.…
The ruin probability of a discrete time risk model under constant interest rate with heavy tails
Tang, Q.
2004-01-01
This paper investigates the ultimate ruin probability of a discrete time risk model with a positive constant interest rate. Under the assumption that the gross loss of the company within one year is subexponentially distributed, a simple asymptotic relation for the ruin probability is derived and co
Influence of a constant magnetic field on thrombocytes. [delay of blood coagulation time
Meyerova, Y. A.
1974-01-01
In an experiment on white mice it was found that a constant electromagnetic field with strength of 250-275 oersteds is biologically active at an exposure of 55 minutes. Qualitative and morphological changes in thrombocytes 1-3 days following exposure reduced their numbers, prolonged blood coagulation time and increased the number of leucocytes.
Using a Constant Time Delay Procedure to Teach Foundational Swimming Skills to Children with Autism
Rogers, Laura; Hemmeter, Mary Louise; Wolery, Mark
2010-01-01
The purpose of this study was to evaluate the effectiveness of using a constant time delay procedure to teach foundational swimming skills to three children with autism. The skills included flutter kick, front-crawl arm strokes, and head turns to the side. A multiple-probe design across behaviors and replicated across participants was used.…
Bekenstein model and the time variation of the strong coupling constant
Chamoun, N; Vucetich, H
2001-01-01
We propose to generalize Bekenstein model for the time variation of the fine structure "constant" $\\alpha_{em}$ to QCD strong coupling constant $\\alpha_S$. We find that, except for a ``fine tuned'' choice of the free parameters, the extension can not be performed trivially without being in conflict with experimental constraints and this rules out $\\alpha_S$ variability. This is due largely to the huge numerical value of the QCD vacuum gluon condensate when compared to the mass density of the universe.
In vivo Target Residence Time and Kinetic Selectivity: The Association Rate Constant as Determinant.
de Witte, Wilhelmus E A; Danhof, Meindert; van der Graaf, Piet H; de Lange, Elizabeth C M
2016-10-01
It is generally accepted that, in conjunction with pharmacokinetics, the first-order rate constant of target dissociation is a major determinant of the time course and duration of in vivo target occupancy. Here we show that the second-order rate constant of target association can be equally important. On the basis of the commonly used mathematical models for drug-target binding, it is shown that a high target association rate constant can increase the (local) concentration of the drug, which decreases the rate of decline of target occupancy. The increased drug concentration can also lead to increased off-target binding and decreased selectivity. Therefore, the kinetics of both target association and dissociation need to be taken into account in the selection of drug candidates with optimal pharmacodynamic properties. Copyright © 2016 Elsevier Ltd. All rights reserved.
Gravitational lensing effects in a time-variable cosmological 'constant' cosmology
Ratra, Bharat; Quillen, Alice
1992-01-01
A scalar field phi with a potential V(phi) varies as phi exp -alpha(alpha is greater than 0) has an energy density, behaving like that of a time-variable cosmological 'constant', that redshifts less rapidly than the energy densities of radiation and matter, and so might contribute significantly to the present energy density. We compute, in this spatially flat cosmology, the gravitational lensing optical depth, and the expected lens redshift distribution for fixed source redshift. We find, for the values of alpha of about 4 and baryonic density parameter Omega of about 0.2 consistent with the classical cosmological tests, that the optical depth is significantly smaller than that in a constant-Lambda model with the same Omega. We also find that the redshift of the maximum of the lens distribution falls between that in the constant-Lambda model and that in the Einstein-de Sitter model.
Delay decomposition at a single server queue with constant service time and multiple inputs
Ziegler, C.; Schilling, D. L.
1978-01-01
Two network consisting of single server queues, each with a constant service time, are considered. The external inputs to each network are assumed to follow some general probability distribution. Several interesting equivalencies that exist between the two networks considered are derived. This leads to the introduction of an important concept in delay decomposition. It is shown that the waiting time experienced by a customer can be decomposed into two basic components called self-delay and interference delay.
In search of lost time constants and of non-Michaelis–Menten parameters
Directory of Open Access Journals (Sweden)
Maria F. Pinto
2016-12-01
Full Text Available Upon completing 100 years since it was published, the work Die Kinetik der Invertinwirkung by Michaelis and Menten (MM was celebrated during the 6th Beilstein ESCEC Symposium 2013. As the 7th Beilstein ESCEC Symposium 2015 debates enzymology in the context of complex biological systems, a post-MM approach is required to address cell-like conditions that are well beyond the steady-state limitations. The present contribution specifically addresses two hitherto ambiguous constants whose interest was, however, intuited in the original MM paper: (i the characteristic time constant τ∞, which can be determined using the late stages of any progress curve independently of the substrate concentration adopted; and (ii the dissociation constant KS, which is indicative of the enzyme–substrate affinity and completes the kinetic portrayal of the Briggs–Haldane reaction scheme. The rationale behind τ∞ and KS prompted us to revise widespread concepts of enzyme's efficiency, defined by the specificity constant kcat/KM, and of the Michaelis constant KM seen as the substrate concentration yielding half-maximal rates. The alternative definitions here presented should help recovering the wealth of published kcat/KM and KM data from the criticism that they are subjected. Finally, a practical method is envisaged for objectively determining enzyme's activity, efficiency and affinity – (EA2 – from single progress curves. The (EA2 assay can be conveniently applied even when the concentrations of substrate and enzyme are not accurately known.
Małek, D; Drobniak, S; Gozdek, A; Pawlik, K; Kramarz, P
2015-07-01
Temperature has profound effects on biological functions at all levels of organization. In ectotherms, body size is usually negatively correlated with ambient temperature during development, a phenomenon known as The Temperature-Size Rule (TSR). However, a growing number of studies have indicated that temperature fluctuations have a large influence on life history traits and the implications of such fluctuations for the TSR are unknown. Our study investigated the effect of different constant and fluctuating temperatures on the body mass and development time of red flour beetles (Tribolium castaneum Herbst, 1797); we also examined whether the sexes differed in their responses to thermal conditions. We exposed the progeny of half-sib families of a T. castaneum laboratory strain to one of four temperature regimes: constant 30°C, constant 25°C, fluctuating with a daily mean of 30°C, or fluctuating with a daily mean of 25°C. Sex-specific development time and body mass at emergence were determined. Beetles developed the fastest and had the greatest body mass upon emergence when they were exposed to a constant temperature of 30°C. This pattern was reversed when beetles experienced a constant temperature of 25°C: slowest development and lowest body mass upon emergence were observed. Fluctuations changed those effects significantly - impact of temperature on development time was smaller, while differences in body mass disappeared completely. Our results do not fit TSR predictions. Furthermore, regardless of the temperature regime, females acquired more mass, while there were no differences between sexes in development time to eclosion. This finding fails to support one of the explanations for smaller male size: that selection favors the early emergence of males. We found no evidence of genotype × environment interactions for selected set of traits.
How Strongly does Dating Meteorites Constrain the Time-Dependence of the Fine-Structure Constant?
Fujii, Yasunori; Iwamoto, Akira
We review our argument on the nature of the so-called meteorite constraint on the possible time-dependence of the fine-structure constant, emphasizing that dating meteorites at the present time is different in principle from searching directly for the traces in the past, as in the Oklo phenomenon and the QSO absorption lines. In the related literature, we still find some arguments not necessarily consistent with this difference to be taken properly into account. It does not immediately follow that any model-dependent approaches are useless in practice, though we cannot help suspecting that dating meteorites is no match for the Oklo and the QSO in probing the time-variability of the fine-structure constant, at this moment. Some of the relevance to the QSO data particularly in terms of the scalar field will be discussed.
Gan, Qifeng; Seoud, Lama; Ben Tahar, Houssem; Langlois, J. M. Pierre
2016-04-01
Spatial Averaging Filters (SAF) are extensively used in image processing for image smoothing and denoising. Their latest implementations have already achieved constant time computational complexity regardless of kernel size. However, all the existing O(1) algorithms require additional memory for temporary data storage. In order to minimize memory usage in embedded systems, we introduce a new two-dimensional recursive SAF. It uses previous resultant pixel values along both rows and columns to calculate the current one. It can achieve constant time computational complexity without using any additional memory usage. Experimental comparisons with previous SAF implementations shows that the proposed 2D-Recursive SAF does not require any additional memory while offering a computational time similar to the most efficient existing SAF algorithm. These features make it especially suitable for embedded systems with limited memory capacity.
How strongly does dating meteorites constrain the time-dependence of the fine-structure constant?
Fujii, Y; Fujii, Yasunori; Iwamoto, Akira
2005-01-01
We review our argument on the nature of the so-called meteorite constraint on the possible time-dependence of the fine-structure constant, emphasizing that dating meteorites at the present time is different in principle from searching directly for the traces in the past, as in the Oklo phenomenon and the QSO absorption lines. In the related literature, we still find some arguments not necessarily consistent with this difference to be taken properly into account. This does not imply that any of the model-dependent approaches are useless in practice, though we cannot help guessing that dating meteorites is no match for the Oklo and the QSO in probing time-dependence of the fine-structure constant, at this moment. Some of the relevance to the QSO data particularly in terms of the scalar field will be discussed.
Directory of Open Access Journals (Sweden)
Tay C.C.
2013-06-01
Full Text Available Purpose: The paper is primarily done on the purpose of introducing new concept in defining the Overall Equipment Effectiveness (OEE with the consideration of both machine utilization and customer demand requested. Previous literature concerning the limitation and difficulty of OEE implementation has been investigated in order to track out the potential opportunities to be improved, since the OEE has been widely accepted by most of the industries regardless their manufacturing environment.Design/methodology/approach: The paper is conducting the study based on literature review and the computerized data collection. In details, the novel definition and method of processing the computerized data are all interpreted based on similar studies performed by others and supported by related journals in proving the validation of the output. Over the things, the computerized data are the product amount and total time elapsed on each production which is automatically recorded by the system at the manufacturing site.Findings: The finding of this paper is firstly the exposure and emphasis of limitation exists in current implementation of OEE, which showing that high utilization of the machine is encouraged regardless of the customer demand and is having conflict with the inventory handling cost. This is certainly obvious with overproduction issue especially during low customer demand period. The second limitation in general implementation of OEE is the difficulty in obtaining the ideal cycle time, especially those equipments with constant process time. The section of this paper afterward comes out with the proposed solution in fixing this problem through the definition of performance ratio and then usage of this definition in measuring the machine utilization from time to time. Before this, the time available for the production is calculated incorporating the availability of OEE, which is then used to get the Takt time.Research limitations/implications: Future
Directory of Open Access Journals (Sweden)
Pieprzyca J.
2015-04-01
Full Text Available A common method used in identification of hydrodynamics phenomena occurring in Continuous Casting (CC device's tundish is to determine the RTD curves of time. These curves allows to determine the way of the liquid steel flowing and mixing in the tundish. These can be identified either as the result of numerical simulation or by the experiments - as the result of researching the physical models. Special problem is to objectify it while conducting physical research. It is necessary to precisely determine the time constants which characterize researched phenomena basing on the data acquired in the measured change of the concentration of the tracer in model liquid's volume. The mathematical description of determined curves is based on the approximate differential equations formulated in the theory of fluid mechanics. Solving these equations to calculate the time constants requires a special software and it is very time-consuming. To improve the process a method was created to calculate the time constants with use of automation elements. It allows to solve problems using algebraic method, which improves interpretation of the research results of physical modeling.
King, Adam C; Newell, Karl M
2013-06-01
This experiment was set up to investigate the influence of constant and variable practice on performance accuracy and the time- and frequency-dependent structure of the force output dynamics in the learning of an irregular isometric force pattern. Traditional approaches to the variability of practice hypothesis have demonstrated benefits of task-induced variability at the outcome level of behavior, but there have been limited investigations of the effect of practice conditions on movement execution and particularly the multiple time scale processes of force output. During the practice phase, variability was induced along the force-time dimension of the target pattern for the variable practice condition (different wave forms), but the wave forms exhibited the same distributional properties of the frequency content (1/f noise: β = -1.5) as the constant practice condition. The results showed that both practice conditions exhibited similar reductions in task error as a function of practice. However, constant practice produced greater changes in the time- and frequency-dependent properties of force output than variable practice, including a higher relative change in the contribution from faster (4-12 Hz) time scale mechanisms. Generalization tests to novel target patterns revealed that the task dynamics had a greater influence than the effect of practice conditions. Collectively, the findings support the adaptive nature of force output structure and the perspective that practice conditions can produce differential effects on the outcome and execution levels of motor behavior.
Wang, Shilong; Yin, Changchun; Lin, Jun; Yang, Yu; Hu, Xueyan
2016-03-01
Cooperative work of multiple magnetic transmitting sources is a new trend in the development of transient electromagnetic system. The key is the bipolar current waves shutdown, concurrently in the inductive load. In the past, it was difficult to use the constant clamping voltage technique to realize the synchronized shutdown of currents with different peak values. Based on clamping voltage technique, we introduce a new controlling method with constant shutdown time. We use the rising time to control shutdown time and use low voltage power source to control peak current. From the viewpoint of the circuit energy loss, by taking the high-voltage capacitor bypass resistance and the capacitor of the passive snubber circuit into account, we establish the relationship between the rising time and the shutdown time. Since the switch is not ideal, we propose a new method to test the shutdown time by the low voltage, the high voltage and the peak current. Experimental results show that adjustment of the current rising time can precisely control the value of the clamp voltage. When the rising time is fixed, the shutdown time is unchanged. The error for shutdown time deduced from the energy consumption is less than 6%. The new controlling method on current shutdown proposed in this paper can be used in the cooperative work of borehole and ground transmitting system.
Wang, Shilong; Yin, Changchun; Lin, Jun; Yang, Yu; Hu, Xueyan
2016-03-01
Cooperative work of multiple magnetic transmitting sources is a new trend in the development of transient electromagnetic system. The key is the bipolar current waves shutdown, concurrently in the inductive load. In the past, it was difficult to use the constant clamping voltage technique to realize the synchronized shutdown of currents with different peak values. Based on clamping voltage technique, we introduce a new controlling method with constant shutdown time. We use the rising time to control shutdown time and use low voltage power source to control peak current. From the viewpoint of the circuit energy loss, by taking the high-voltage capacitor bypass resistance and the capacitor of the passive snubber circuit into account, we establish the relationship between the rising time and the shutdown time. Since the switch is not ideal, we propose a new method to test the shutdown time by the low voltage, the high voltage and the peak current. Experimental results show that adjustment of the current rising time can precisely control the value of the clamp voltage. When the rising time is fixed, the shutdown time is unchanged. The error for shutdown time deduced from the energy consumption is less than 6%. The new controlling method on current shutdown proposed in this paper can be used in the cooperative work of borehole and ground transmitting system.
Constant time distance queries in planar unweighted graphs with subquadratic preprocessing time
DEFF Research Database (Denmark)
Wulff-Nilsen, C.
2013-01-01
) time with O(n) space. The techniques that we apply allow us to build, within the same time bound, an oracle for exact distance queries in G. More generally, for any parameter S is an element of [(log n/log log n)(2), n(2/5)], distance queries can be answered in O (root S log S/log n) time per query...
A constant travel time budget? In search for explanations for an increase in average travel time
Rietveld, P.; Wee, van B.
2002-01-01
Recent research suggests that during the past decades the average travel time of the Dutch population has probably increased. However, different datasources show different levels of increase. Possible causes of the increase in average travel time are presented here. Increased incomes have probablyre
A constant travel time budget? In search for explanations for an increase in average travel time
Rietveld, P.; Wee, van B.
2002-01-01
Recent research suggests that during the past decades the average travel time of the Dutch population has probably increased. However, different datasources show different levels of increase. Possible causes of the increase in average travel time are presented here. Increased incomes have
A constant travel time budget? In search for explanations for an increase in average travel time
Rietveld, P.; Wee, van B.
2002-01-01
Recent research suggests that during the past decades the average travel time of the Dutch population has probably increased. However, different datasources show different levels of increase. Possible causes of the increase in average travel time are presented here. Increased incomes have probablyre
On the thermal inertia and time constant of single-family houses
Energy Technology Data Exchange (ETDEWEB)
Hedbrant, J.
2001-08-01
Since the 1970s, electricity has become a common heating source in Swedish single-family houses. About one million small houses can use electricity for heating, about 600.000 have electricity as the only heating source, A liberalised European electricity market would most likely raise the Swedish electricity prices during daytime on weekdays and lower it at other times. In the long run, electrical heating of houses would be replaced by fuels, but in the shorter perspective, other strategies may be considered. This report evaluates the use of electricity for heating a dwelling, or part of it, at night when both the demand and the price are low. The stored heat is utilised in the daytime some hours later, when the electricity price is high. Essential for heat storage is the thermal time constant. The report gives a simple theoretical framework for the calculation of the time constant for a single-family house with furniture. Furthermore the comfort time constant, that is, the time for a house to cool down from a maximum to a minimum acceptable temperature, is derived. Two theoretical model houses are calculated, and the results are compared to data from empirical studies in three inhabited test houses. The results show that it was possible to store about 8 kWh/K in a house from the seventies and about 5 kWh/K in a house from the eighties. The time constants were 34 h and 53 h, respectively. During winter conditions with 0 deg C outdoor, the 'comfort' time constants with maximum and minimum indoor temperatures of 23 and 20 deg C were 6 h and 10 h. The results indicate that the maximum load-shifting potential of an average single family house is about 1 kw during 16 daytime hours shifted into 2 kw during 8 night hours. Upscaled to the one million Swedish single-family houses that can use electricity as a heating source, the maximum potential is 1000 MW daytime time-shifted into 2000 MW at night.
Ziegler, C.; Schilling, D. L.
1977-01-01
Two networks consisting of single server queues, each with a constant service time, are considered. The external inputs to each network are assumed to follow some general probability distribution. Several interesting equivalencies that exist between the two networks considered are derived. This leads to the introduction of an important concept in delay decomposition. It is shown that the waiting time experienced by a customer can be decomposed into two basic components called self delay and interference delay.
Constant-net-time headway as a key mechanism behind pedestrian flow dynamics.
Johansson, Anders
2009-08-01
We show that keeping a constant lower limit on the net-time headway is the key mechanism behind the dynamics of pedestrian streams. There is a large variety in flow and speed as functions of density for empirical data of pedestrian streams obtained from studies in different countries. The net-time headway, however, stays approximately constant over all these different data sets. By using this fact, we demonstrate how the underlying dynamics of pedestrian crowds, naturally follows from local interactions. This means that there is no need to come up with an arbitrary fit function (with arbitrary fit parameters) as has traditionally been done. Further, by using not only the average density values but the variance as well, we show how the recently reported stop-and-go waves [Helbing, Phys. Rev. E 75, 046109 (2007)] emerge when local density variations take values exceeding a certain maximum global (average) density, which makes pedestrians stop.
Simulating diffusion processes in discontinuous media: A numerical scheme with constant time steps
Energy Technology Data Exchange (ETDEWEB)
Lejay, Antoine, E-mail: Antoine.Lejay@iecn.u-nancy.fr [Universite de Lorraine, IECN, UMR 7502, Vandoeuvre-les-Nancy, F-54500 (France); CNRS, IECN, UMR 7502, Vandoeuvre-les-Nancy, F-54500 (France); Inria, Villers-les-Nancy, F-54600 (France); IECN, BP 70238, F-54506 Vandoeuvre-les-Nancy Cedex (France); Pichot, Geraldine, E-mail: Geraldine.Pichot@inria.fr [Inria, Rennes - Bretagne Atlantique, Campus de Beaulieu, 35042 Rennes Cedex (France); INRIA, Campus de Beaulieu, 35042 Rennes Cedex (France)
2012-08-30
In this article, we propose new Monte Carlo techniques for moving a diffusive particle in a discontinuous media. In this framework, we characterize the stochastic process that governs the positions of the particle. The key tool is the reduction of the process to a Skew Brownian motion (SBM). In a zone where the coefficients are locally constant on each side of the discontinuity, the new position of the particle after a constant time step is sampled from the exact distribution of the SBM process at the considered time. To do so, we propose two different but equivalent algorithms: a two-steps simulation with a stop at the discontinuity and a one-step direct simulation of the SBM dynamic. Some benchmark tests illustrate their effectiveness.
Directory of Open Access Journals (Sweden)
Veysel Hatipoglu
2015-09-01
Full Text Available In this study, we present a practical matrix method to find an approximate solution of higher order linear difference equation with constant coefficients under the initial-boundary conditions in terms of Taylor polynomials. To obtain this goal, we first present time scale extension of previous polynomial approach, then restrict the formula to the Integers with h step. This method converts the difference equation to a matrix equation, which may be considered as a system of linear algebraic equations.
Re/Os Constraint on the Time Variability of the Fine-Structure Constant
Fujii, Yasunori; Iwamoto, Akira
2003-12-01
We argue that the accuracy by which the isochron parameters of the decay 187Re→187Os are determined by dating iron meteorites may constrain the possible time dependence of the decay rate and hence of the fine-structure constant α, not directly but only in a model-dependent manner. From this point of view, some of the attempts to analyze the Oklo constraint and the results of the quasistellar-object absorption lines are reexamined.
Re/Os constraint on the time-variability of the fine-structure constant
Fujii, Y; Fujii, Yasunori; Iwamoto, Akira
2003-01-01
We argue that the accuracy by which the isochron parameters of the decay $^{187}{\\rm Re}\\to ^{187}{\\rm Os}$ are determined by dating iron meteorites may not directly constrain the possible time-dependence of the decay rate and hence of the fine-structure constant $\\alpha$. From this point of view, some of the attempts to analyze the Oklo constraint and the results of the QSO absorption lines are re-examined.
Measurement of Thermocouple Time Constant%热电偶时间常数的测量
Institute of Scientific and Technical Information of China (English)
傅元; 董宇哲; 李德健; 董健
2012-01-01
为准确测量出热电偶的时间常数，根据热电偶对阶跃温度的响应，用单指数曲线描述过渡过程的数学模型，对记录的过渡过程曲线进行拟合，拟合后单指数曲线的时间常数就是被测热电偶的时间常数。对多种热电偶和同一热电偶的反复测试表明这种方法准确，相对于其它方法适应性更强。%In order to accurately measure the time constant of the thermocouple, according to the temperature of the thermocouple to a step response, single exponential curve with a mathematical model of the transition process described, record of the transition pro- cess of fitting curves, after fitting a single exponential curve is the measured time constant time constant thermocouples. A variety of thermocouples and thermocouple repeated the same test shows that this method is accurate, compared to other methods more adaptive.
Buis, Arjan
2016-01-01
Elevated skin temperature at the body/device interface of lower-limb prostheses is one of the major factors that affect tissue health. The heat dissipation in prosthetic sockets is greatly influenced by the thermal conductive properties of the hard socket and liner material employed. However, monitoring of the interface temperature at skin level in lower-limb prosthesis is notoriously complicated. This is due to the flexible nature of the interface liners used which requires consistent positioning of sensors during donning and doffing. Predicting the residual limb temperature by monitoring the temperature between socket and liner rather than skin and liner could be an important step in alleviating complaints on increased temperature and perspiration in prosthetic sockets. To predict the residual limb temperature, a machine learning algorithm – Gaussian processes is employed, which utilizes the thermal time constant values of commonly used socket and liner materials. This Letter highlights the relevance of thermal time constant of prosthetic materials in Gaussian processes technique which would be useful in addressing the challenge of non-invasively monitoring the residual limb skin temperature. With the introduction of thermal time constant, the model can be optimised and generalised for a given prosthetic setup, thereby making the predictions more reliable. PMID:27695626
Myers, Jerry G.; Hussey, Sam W.; Yee, Glenda F.; Kim, Jungho
2003-01-01
Investigations into single bubble pool boiling phenomena are often complicated by the difficulties in obtaining time and space resolved information in the bubble region. This usually occurs because the heaters and diagnostics used to measure heat transfer data are often on the order of, or larger than, the bubble characteristic length or region of influence. This has contributed to the development of many different and sometimes contradictory models of pool boiling phenomena and dominant heat transfer mechanisms. Recent investigations by Yaddanapyddi and Kim and Demiray and Kim have obtained time and space resolved heat transfer information at the bubble/heater interface under constant temperature conditions using a novel micro-heater array (10x10 array, each heater 100 microns on a side) that is semi-transparent and doubles as a measurement sensor. By using active feedback to maintain a state of constant temperature at the heater surface, they showed that the area of influence of bubbles generated in FC-72 was much smaller than predicted by standard models and that micro-conduction/micro-convection due to re-wetting dominated heat transfer effects. This study seeks to expand on the previous work by making time and space resolved measurements under bubbles nucleating on a micro-heater array operated under constant heat flux conditions. In the planned investigation, wall temperature measurements made under a single bubble nucleation site will be synchronized with high-speed video to allow analysis of the bubble energy removal from the wall.
Khurshudyan, M; Momeni, D; Myrzakulov, R; Raza, M
2014-01-01
The subject of this paper is to investigate the weak regime covariant scalar-tensor-vector gravity (STVG) theory, known as the MOdified gravity (MOG) theory of gravity. First, we show that the MOG in the absence of scalar fields is converted into $\\Lambda(t),G(t)$ models. Time evolution of the cosmological parameters for a family of viable models have been investigated. Numerical results with the cosmological data have been adjusted. We've introduced a model for dark energy (DE) density and cosmological constant which involves first order derivatives of Hubble parameter. To extend this model, correction terms including the gravitational constant are added. In our scenario, the cosmological constant is a function of time. To complete the model,interaction terms between dark energy and dark matter (DM) manually entered in phenomenological form. Instead of using the dust model for DM, we have proposed DM equivalent to a barotropic fluid. Time evolution of DM is a function of other cosmological parameters. Using ...
Nassar, Antonio B; Miret-Artés, Salvador
2013-10-11
This Letter proposes an answer to a challenge posed by Bell on the lack of clarity in regards to the dividing line between the quantum and classical regimes in a measurement problem. To this end, a generalized logarithmic nonlinear Schrödinger equation is proposed to describe the time evolution of a quantum dissipative system under continuous measurement. Within the Bohmian mechanics framework, a solution to this equation reveals a novel result: it displays a time constant that should represent the dividing line between the quantum and classical trajectories. It is shown that continuous measurements and damping not only disturb the particle but compel the system to converge in time to a Newtonian regime. While the width of the wave packet may reach a stationary regime, its quantum trajectories converge exponentially in time to classical trajectories. In particular, it is shown that damping tends to suppress further quantum effects on a time scale shorter than the relaxation time of the system. If the initial wave packet width is taken to be equal to 2.8×10(-15) m (the approximate size of an electron), the Bohmian time constant is found to have an upper limit, i.e., τ(Bmax)=10(-26) s.
Constant-momentum acceleration time-of-flight mass spectrometry with energy focusing.
Dennis, Elise A; Ray, Steven J; Gundlach-Graham, Alexander W; Enke, Christie G; Barinaga, Charles J; Koppenaal, David W; Hieftje, Gary M
2013-12-01
Fundamental aspects of constant-momentum acceleration time-of-flight mass spectrometry (CMA-TOFMS) are explored as a means to improve mass resolution. By accelerating all ions to the same momentum rather than to the same energy, the effects of the initial ion spatial and energy distributions upon the total ion flight time are decoupled. This decoupling permits the initial spatial distribution of ions in the acceleration region to be optimized independently, and energy focus, including ion turn-around-time error, to be accomplished with a linear-field reflectron. Constant-momentum acceleration also linearly disperses ions across time according to mass-to-charge (m/z) ratio, instead of the quadratic relationship between flight time and m/z found in conventional TOFMS. Here, CMA-TOFMS is shown to achieve simultaneous spatial and energy focusing over a selected portion of the mass spectrum. An orthogonal-acceleration time-of-flight system outfitted with a reduced-pressure DC glow discharge (GD) ionization source is used to demonstrate CMA-TOFMS with atomic ions. The influence of experimental parameters such as the amplitude and width of the time-dependent CMA pulse on mass resolution is investigated, and a useful CMA-TOFMS focusing window of 2 to 18 Da is found for GD-CMA-TOFMS.
Model-independent determination of the carrier multiplication time constant in CdSe nanocrystals.
Califano, Marco
2009-11-21
The experimental determination of the carrier multiplication (CM) time constant is complicated by the fact that this process occurs within the initial few hundreds of femtoseconds after excitation and, in transient-absorption experiments, cannot be separated from the buildup time of the 1p-state population. This work provides an accurate theoretical determination of the electron relaxation lifetime during the last stage of the p-state buildup, in CdSe nanocrystals, in the presence of a single photogenerated hole (no CM) and of a hole plus an additional electron-hole pair (following CM). From the invariance of the 1p buildup time observed experimentally for excitations above and below the CM threshold producing hot carriers with the same average per-exciton excess energy, and the calculated corresponding variations in the electron decay time in the two cases, an estimate is obtained for the carrier multiplication time constant. Unlike previous estimates reported in the literature so far, this result is model-independent, i.e., is obtained without making any assumption on the nature of the mechanism governing carrier multiplication. It is then compared with the time constant calculated, as a function of the excitation energy, assuming an impact-ionization-like process for carrier multiplication (DCM). The two results are in good agreement and show that carrier multiplication can occur on timescales of the order of tens of femtoseconds at energies close to the observed onset. These findings, which are compatible with the fastest lifetime estimated experimentally, confirm the suitability of the impact-ionization model to explain carrier multiplication in CdSe nanocrystals.
Time Variation of the Fine Structure Constant in the Spacetime of a Cosmic Domain Wall
Campanelli, L.; Cea, P.; Tedesco, L.
The gravitational field produced by a domain wall acts as a medium with spacetime-dependent permittivity ɛ. Therefore, the fine structure constant α=e2/4πɛ will be a time-dependent function at fixed position. The most stringent constraint on the time-variation of α comes from the natural reactor Oklo and gives |˙ α /α | < few × 10-17 yr-1. This limit constrains the tension of a cosmic domain wall to be less than σ ≲ 10-2 MeV3, and then represents the most severe limit on the energy density of a cosmic wall stretching our Universe.
Time Variation of the Fine Structure Constant in the Spacetime of a Domain Wall
Campanelli, L; Tedesco, L
2005-01-01
The gravitational field produced by a domain wall acts as a medium with spacetime-dependent permittivity \\epsilon. Therefore, the fine structure constant \\alpha = e^2/4 \\pi \\epsilon will be a time-dependent function at fixed position. The most stringent constraint on the time-variation of \\alpha comes from the natural reactor Oklo and gives |\\dot{\\alpha}/\\alpha| < few 10^{-17} yr^{-1}. This limit constrains the tension of a cosmic domain wall to be less than \\sigma \\lesssim 10^{-2} MeV^3, and then represents the most severe limit on the energy density of a cosmic wall stretching our Universe.
Global structure of Robinson-Trautman radiative space-times with cosmological constant
Bicák, J
1997-01-01
Robinson-Trautman radiative space-times of Petrov type II with a non-vanishing cosmological constant Lambda and mass parameter m>0 are studied using analytical methods. They are shown to approach the corresponding spherically symmetric Schwarzschild-de Sitter or Schwarzschild-anti-de Sitter solution at large retarded times. Their global structure is analyzed, and it is demonstrated that the smoothness of the extension of the metrics across the horizon, as compared with the case Lambda=0, is increased for Lambda>0 and decreased for Lambda0 exhibit explicitly the cosmic no-hair conjecture under the presence of gravitational waves.
HUBBLE CONSTANT, LENSING, AND TIME DELAY IN RELATIVISTIC MODIFIED NEWTONIAN DYNAMICS
Energy Technology Data Exchange (ETDEWEB)
Tian, Yong [Department of Physics, National Central University, Jhongli, Taiwan 320 (China); Ko, Chung-Ming [Institute of Astronomy, Department of Physics and Center for Complex Systems, National Central University, Jhongli, Taiwan 320 (China); Chiu, Mu-Chen, E-mail: yonngtian@gmail.com, E-mail: cmko@astro.ncu.edu.tw, E-mail: mcc@roe.ac.uk [Scottish University Physics Alliance, Institute for Astronomy, the Royal Observatory, University of Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ (United Kingdom)
2013-06-20
The time delay in galaxy gravitational lensing systems has been used to determine the value of the Hubble constant. As with other dynamical phenomena on the galaxy scale, dark matter is often invoked in gravitational lensing to account for the 'missing mass' (the apparent discrepancy between the dynamical mass and the luminous mass). Alternatively, modified gravity can be used to explain the discrepancy. In this paper, we adopt the tensor-vector-scalar gravity (TeVe S), a relativistic version of Modified Newtonian Dynamics, to study gravitational lensing phenomena and derive the formulae needed to evaluate the Hubble constant. We test our method on quasar lensing by elliptical galaxies in the literature. We focus on double-image systems with time delay measurement. Three candidates are suitable for our study: HE 2149-2745, FBQ J0951+2635, and SBS 0909+532. The Hubble constant obtained is consistent with the value used to fit the cosmic microwave background result in a neutrino cosmological model.
Measuring JHH values with a selective constant-time 2D NMR protocol
Lin, Liangjie; Wei, Zhiliang; Lin, Yanqin; Chen, Zhong
2016-11-01
Proton-proton scalar couplings play important roles in molecule structure elucidation. However, measurements of JHH values in complex coupled spin systems remain challenging. In this study, we develop a selective constant-time (SECT) 2D NMR protocol with which scalar coupling networks involving chosen protons can be revealed, and corresponding JHH values can be measured through doublets along the F1 dimension. All JHH values within a network of n fully coupled protons can be separately determined with (n - 1) SECT experiments. Additionally, the proposed pulse sequence possesses satisfactory sensitivity and handy implementation. Therefore, it will interest scientists who intend to address structural analyzes of molecules with overcrowded spectra, and may greatly facilitate the applications of scalar-coupling constants in molecule structure studies.
The Oklo Natural Reactor and the Time Variability of the Fundamental Constants of Nature
Energy Technology Data Exchange (ETDEWEB)
Lamoreaux, Steve (LANL)
2005-11-07
Natural nuclear reactors? Changes in the speed of light? If either of these concepts seem implausible to you now they certainly won't once Dr. Steve Lamoreaux (LANL) delivers his SLAC Colloquium lecture in the Panofsky Auditorium on November 7th at 4:15 pm entitled The Oklo Natural Reactor and the Time Variability of the Fundamental Constants of Nature. This lecture is a rare opportunity to learn not only about Oklo's incredible natural nuclear reactors but also to gain understanding about how the present-day study of these sites may alter our understanding of fundamental constants such as the speed of light. This event is a must-see for the curious!
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.
Maynard, N. C.; Evans, D. S.; Troim, J.
1982-01-01
The Polar 5 electric field results are reviewed, and the transients from Polar 3 are presented. The phenomena are discussed from the standpoint of space charge. On the basis of the Polar 5 results, the large magnitude of the electric field from Polar 3 is seen as indicating that the observed space charge was probably within a few km or less of the payload. Reference is made to Cole's prediction (1960) that charges in the ionosphere would reach equilibrium with a time constant of the order of a few microsec. The processes involved in the two cases presented here require time constants of the order of ms. If the sheath dimensions are taken to be between 50 and 100 m, which is not considered unreasonable in view of the electric field measurements, then a qualitative estimate of the neutralization time would be the transit time for ions across the sheath. Since the kinetic velocity of a 1-eV proton is approximately 14 m/s, it would traverse the distance in 4 to 8 ms, assuming freedom of movement across magnetic field lines. This is the order of the decay times observed on Polar 5.
Short time Fourier analysis of the electromyogram - Fast movements and constant contraction
Hannaford, Blake; Lehman, Steven
1986-01-01
Short-time Fourier analysis was applied to surface electromyograms (EMG) recorded during rapid movements, and during isometric contractions at constant forces. A portion of the data to be transformed by multiplying the signal by a Hamming window was selected, and then the discrete Fourier transform was computed. Shifting the window along the data record, a new spectrum was computed each 10 ms. The transformed data were displayed in spectograms or 'voiceprints'. This short-time technique made it possible to see time-dependencies in the EMG that are normally averaged in the Fourier analysis of these signals. Spectra of EMGs during isometric contractions at constant force vary in the short (10-20 ms) term. Short-time spectra from EMGs recorded during rapid movements were much less variable. The windowing technique picked out the typical 'three-burst pattern' in EMG's from both wrist and head movements. Spectra during the bursts were more consistent than those during isometric contractions. Furthermore, there was a consistent shift in spectral statistics in the course of the three bursts. Both the center frequency and the variance of the spectral energy distribution grew from the first burst to the second burst in the same muscle. The analogy between EMGs and speech signals is extended to argue for future applicability of short-time spectral analysis of EMG.
Influence of the Gilbert damping constant on the flux rise time of write head fields
Energy Technology Data Exchange (ETDEWEB)
Ertl, Othmar [Institute of Applied and Technical Physics, Vienna University of Technology, Wiedner Hauptstrasse 8-10/138, A-1040 Vienna (Austria); Schrefl, Thomas [Institute of Applied and Technical Physics, Vienna University of Technology, Wiedner Hauptstrasse 8-10/138, A-1040 Vienna (Austria) and Department of Engineering Materials, University of Sheffield, Mappin Street, Sheffield, S1 3JD (United Kingdom)]. E-mail: thomas.schrefl@tuwien.ac.at; Suess, Dieter [Institute of Applied and Technical Physics, Vienna University of Technology, Wiedner Hauptstrasse 8-10/138, A-1040 Vienna (Austria); Schabes, Manfred E. [Hitachi Global Storage Technologies, Hitachi San Jose Research Center, San Jose, CA (United States)
2005-04-15
Magnetic recording at fast data rates requires write heads with rapid rise times of the magnetic flux during the write process. We present three-dimensional (3D) micromagnetic finite element calculations of an entire ring head including 3D coil geometry during the writing of magnetic bits in granular media. The simulations demonstrate how input current profiles translate into magnetization processes in the head and which in turn generate the write head field. The flux rise time significantly depends on the Gilbert damping constant of the head material. Low damping causes incoherent magnetization processes, leading to long rise times and low head fields. High damping leads to coherent reversal of the magnetization in the head. As a consequence, the gap region can be quickly saturated which causes high head fields with short rise times.
Time variation of the fine structure constant α from realistic models of Oklo reactors.
Gould, C. R.; Sharapov, E. I.; Lamoreaux, S. K.
2006-11-01
The topic of whether the fundamental constants of nature vary with time has been a subject of great interest since Dirac originally proposed the possibility that GN˜1/tuniverse. Recent observations of absorption spectra lines from distant quasars appeared to indicate a possible increase in the fine structure constant α over ten billion years. Contrarily, analyses of the time evolution of α from Oklo natural nuclear reactor data have yielded inconsistent results, some indicating a decrease over two billion years while others indicated no change. We have used known Oklo reactor epithermal spectral indices as criteria for selecting realistic reactor models. Reactors RZ2 and RZ10 were modeled with MCNP and the resulting neutron spectra were used to calculate the change in the ^149Sm capture cross section as a function of a possible shift in the energy of the 97.3-meV resonance. Our study resolves the contradictory situation with previous Oklo α-results. Our suggested 2 σ bound on a possible time variation of α over two billion years is stringent: -0.11 <=δαα <=0.24, in units of 10-7, but model dependent in that it assumes only α has varied over time.
Protopopescu, V; Barhen, J
2003-01-01
A constant-time solution of the continuous global optimization problem (GOP) is obtained by using an ensemble algorithm. We show that under certain assumptions, the solution can be guaranteed by mapping the GOP onto a discrete unsorted search problem, whereupon Brueschweiler's ensemble search algorithm is applied. For adequate sensitivities of the measurement technique, the query complexity of the ensemble search algorithm depends linearly on the size of the function's domain. Advantages and limitations of an eventual NMR implementation are discussed. (letter to the editor)
Estimation of Nutation Time Constant Model Parameters for On-Axis Spinning Spacecraft
Schlee, Keith; Sudermann, James
2008-01-01
Calculating an accurate nutation time constant for a spinning spacecraft is an important step for ensuring mission success. Spacecraft nutation is caused by energy dissipation about the spin axis. Propellant slosh in the spacecraft fuel tanks is the primary source for this dissipation and can be simulated using a forced motion spin table. Mechanical analogs, such as pendulums and rotors, are typically used to simulate propellant slosh. A strong desire exists for an automated method to determine these analog parameters. The method presented accomplishes this task by using a MATLAB Simulink/SimMechanics based simulation that utilizes the Parameter Estimation Tool.
Oklo Constraint on the Time-Variability of the Fine-Structure Constant
Fujii, Y
2003-01-01
The Oklo phenomenon, natural fission reactors which had taken place in Gabon about 2 billion years ago, porvides one of the most stringent constraints on the possible time-variability of the fine-structure constant $\\alpha$. We first review briefly what it is and how reliable it is in constraining $\\alpha$. We then compare the result with a more recent result on the nonzero change of $\\alpha$ obtained from the observation of the QSO absoorption lines. We suggest a possible way to make these results consistent with each other in terms of the behavior of a scalar field which is expected to be responsible for the accelaration of the universe.
Oklo Constraint on the Time-Variabilityof the Fine-Structure Constant
Fujii, Yasunori
The Oklo phenomenon, natural fission reactors which had taken place in Gabon about 2 billion years ago, provides one of the most stringent constraints on the possible time-variability of the fine-structure constant . We first review briefly what it is and how reliable it is in constraining . We then compare the result with a more recent result on the nonzero change of obtained from the observation of the QSO absorption lines. We suggest a possible way to make these results consistent with each other in terms of the behavior of a scalar field which is expected to be responsible for the acceleration of the universe.
Nuclear Data in Oklo and Time-Variability of Fundamental Coupling Constants
Fujii, Y; Fukahori, T; Ohnuki, T; Nakagawa, M; Hidaka, H; Oura, Y; Møller, P; Fujii, Yasunori; Iwamoto, Akira; Fukahori, Tokio; Ohnuki, Toshihiko; Nakagawa, Masayuki; Hidaka, Hiroshi; Oura, Yasuji; Moller, Peter
2001-01-01
We re-examined Shlyakhter's analysis of the Sm data in Oklo. With a special care of minimizing contamination due to the inflow of the isotope after the end of the reactor activity, we confirmed that his result on the time-variability of the fine-structure constant, $|\\dot{\\alpha}/\\alpha |\\lsim 10^{-17}{\\rm y}^{-1}$, was basically correct. In addition to this upper bound, however, we obtained another result that indicates a different value of $\\alpha$ 2 billion years ago. We add comments on the recent result from QSO's.
Constant-time parallel sorting algorithm and its optical implementation using smart pixels
Louri, Ahmed; Hatch, James A., Jr.; Na, Jongwhoa
1995-06-01
Sorting is a fundamental operation that has important implications in a vast number of areas. For instance, sorting is heavily utilized in applications such as database machines, in which hashing techniques are used to accelerate data-processing algorithms. It is also the basis for interprocessor message routing and has strong implications in video telecommunications. However, high-speed electronic sorting networks are difficult to implement with VLSI technology because of the dense, global connectivity required. Optics eliminates this bottleneck by offering global interconnects, massive parallelism, and noninterfering communications. We present a parallel sorting algorithm and its efficient optical implementation. The algorithm sorts n data elements in few steps, independent of the number of elements to be sorted. Thus it is a constant-time sorting algorithm [i.e., O(1) time]. We also estimate the system's performance to show that the proposed sorting algorithm can provide at least 2 orders of magnitude improvement in execution time over conventional electronic algorithms.
Directory of Open Access Journals (Sweden)
Shumin Bian
Full Text Available Prestin (SLC26a5 is the outer hair cell integral membrane motor protein that drives cochlear amplification, and has been described as an obligate tetramer. We studied in real time the delivery of YFP-prestin to the plasma membrane of cells from a tetracycline-inducible cell line. Following the release of temperature block to reinstate trans Golgi network delivery of the integral membrane protein, we measured nonlinear capacitance (NLC and membrane fluorescence during voltage clamp. Prestin was delivered exponentially to the plasma membrane with a time constant of less than 10 minutes, with both electrical and fluorescence methods showing high temporal correlation. However, based on disparity between estimates of prestin density derived from either fluorescence or NLC, we conclude that sub-tetrameric forms of prestin contribute to our electrical and fluorescence measures. Thus, in agreement with previous observations we find that functional prestin is not an obligate tetramer.
DEFF Research Database (Denmark)
Al Shakhshir, Saher; Berning, Torsten; Kær, Søren Knudsen
2016-01-01
A novel method to obtain an ad-hoc and real time electrical signal of the PEMFC water balance by employing a constant temperature hot wire anemometry has been developed by our fuel cell research group. In this work, the effect of nitrogen-cross over on this method is experimentally demonstrated....... This is due to the effect of 1% nitrogen on power law constant’s “m” which can be used in determining the water balance as explained in previous work was extremely low. Thus, the hot wire technique for measuring the PEMFC water balance is still accurate with the nitrogen cross-over...
Constant time tensor correlation experiments by non-gamma-encoded recoupling pulse sequences.
Mou, Yun; Tsai, Tim W T; Chan, Jerry C C
2012-10-28
Constant-time tensor correlation under magic-angle spinning conditions is an important technique in solid-state nuclear magnetic resonance spectroscopy for the measurements of backbone or side-chain torsion angles of polypeptides and proteins. We introduce a general method for the design of constant-time tensor correlation experiments under magic-angle spinning. Our method requires that the amplitude of the average Hamiltonian must depend on all the three Euler angles bringing the principal axis system to the rotor-fixed frame, which is commonly referred to as non-gamma encoding. We abbreviate this novel approach as COrrelation of Non-Gamma-Encoded Experiment (CONGEE), which exploits the orientation-dependence of non-gamma-encoded sequences with respect to the magic-angle rotation axis. By manipulating the relative orientation of the average Hamiltonians created by two non-gamma-encoded sequences, one can obtain a modulation of the detected signal, from which the structural information can be extracted when the tensor orientations relative to the molecular frame are known. CONGEE has a prominent feature that the number of rf pulses and the total pulse sequence duration can be maintained to be constant so that for torsion angle determination the effects of systematic errors owing to the experimental imperfections and/or T(2) effects could be minimized. As a proof of concept, we illustrate the utility of CONGEE in the correlation between the C' chemical shift tensor and the C(α)-H(α) dipolar tensor for the backbone psi angle determination. In addition to a detailed theoretical analysis, numerical simulations and experiments measured for [U-(13)C, (15)N]-L-alanine and N-acetyl-[U-(13)C, (15)N]-D,L-valine are used to validate our approach at a spinning frequency of 20 kHz.
A Different Look at Dark Energy and the Time Variation of Fundamental Constants
Energy Technology Data Exchange (ETDEWEB)
Weinstein, Marvin; /SLAC
2011-02-07
This paper makes the simple observation that a fundamental length, or cutoff, in the context of Friedmann-Lemaitre-Robertson-Walker (FRW) cosmology implies very different things than for a static universe. It is argued that it is reasonable to assume that this cutoff is implemented by fixing the number of quantum degrees of freedom per co-moving volume (as opposed to a Planck volume) and the relationship of the vacuum-energy of all of the fields in the theory to the cosmological constant (or dark energy) is re-examined. The restrictions that need to be satisfied by a generic theory to avoid conflicts with current experiments are discussed, and it is shown that in any theory satisfying these constraints knowing the difference between w and minus one allows one to predict w. It is argued that this is a robust result and if this prediction fails the idea of a fundamental cutoff of the type being discussed can be ruled out. Finally, it is observed that, within the context of a specific theory, a co-moving cutoff implies a predictable time variation of fundamental constants. This is accompanied by a general discussion of why this is so, what are the strongest phenomenological limits upon this predicted variation, and which limits are in tension with the idea of a co-moving cutoff. It is pointed out, however, that a careful comparison of the predicted time variation of fundamental constants is not possible without restricting to a particular model field-theory and that is not done in this paper.
Fletcher, Stephen; Kirkpatrick, Iain; Dring, Roderick; Puttock, Robert; Thring, Rob; Howroyd, Simon
2017-03-01
Supercapacitors are an emerging technology with applications in pulse power, motive power, and energy storage. However, their carbon electrodes show a variety of non-ideal behaviours that have so far eluded explanation. These include Voltage Decay after charging, Voltage Rebound after discharging, and Dispersed Kinetics at long times. In the present work, we establish that a vertical ladder network of RC components can reproduce all these puzzling phenomena. Both software and hardware realizations of the network are described. In general, porous carbon electrodes contain random distributions of resistance R and capacitance C, with a wider spread of log R values than log C values. To understand what this implies, a simplified model is developed in which log R is treated as a Gaussian random variable while log C is treated as a constant. From this model, a new family of equivalent circuits is developed in which the continuous distribution of log R values is replaced by a discrete set of log R values drawn from a geometric series. We call these Pascal Equivalent Circuits. Their behaviour is shown to resemble closely that of real supercapacitors. The results confirm that distributions of RC time constants dominate the behaviour of real supercapacitors.
The cosmological constant problem in heterotic-M-theory and the orbifold of time
Zanzi, Andrea
2016-01-01
Chameleon fields are quantum fields with an increasing mass as a function of the matter density of the environment. Recently chameleon fields have been exploited to solve the cosmological constant problem in the Modified Fujii's Model - MFM [Phys Rev D82 (2010) 044006]. However, gravity has been treated basically at a semiclassical level in that paper. In this article the stringy origin of the MFM is further discussed: as we will see, the MFM can be obtained from heterotic-M-theory. Consequently, a quantum description of gravity is obtained and the theory is finite because we choose the string mass as our UV cut-off. This stringy origin of the MFM creates stronger theoretical grounds for our solution to the cosmological constant problem. In our analysis, time will be compactified on a $S^1/Z_2$ orbifold and this peculiar compactification of time has a number of consequences. For example, as we will see, quantum gravity and a quantum gauge theory are actually the same theory in the sense that gravity is the ti...
Real-Time Simulation and Analysis of the Induction Machine Performances Operating at Flux Constant
Directory of Open Access Journals (Sweden)
Aziz Derouich
2014-05-01
Full Text Available In this paper, we are interested, in a first time, at the study and the implementation of a V/f control for induction machine in real time. After, We are attached to a comparison of the results by simulation and experiment for, speed responses, flux and currents of the real machine, with a DSPACE card and model established by classical identification (Direct Current test , blocked-rotor test, no-load test , synchronous test, to ensure the validity of the established model. The scalar controlled induction motor allows operation of the motor with the maximum torque by simultaneous action on the frequency and amplitude of the stator voltage, with conservation of the ratio V/f. Speed reference imposes a frequency at the inverter supplying the voltages needed to power the motor, which determines the speed of rotation. The maximum torque of the machine is proportional to the square of the supply voltage and inversely proportional to the frequency voltage. So, Keep V/f constant implies a operating with maximum constant torque. The results obtained for the rotor flux and the stator currents are especially satisfactory steady.
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.
Accelerating universe and the time-dependent fine-structure constant
Fujii, Yasunori
2010-11-01
I start with assuming a gravitational scalar field as the dark-energy supposed to be responsible for the accelerating universe. Also from the point of view of unification, a scalar field implies a time-variability of certain “constants” in Nature. In this context I once derived a relation for the time-variability of the fine-structure constant α: Δα/α =ζ Ƶ(α/π) Δσ, where ζ and Ƶ are the constants of the order one, while σ on the right-hand side is the scalar field in action in the accelerating universe. I use the reduced Planckian units with c=ℏ =MP(=(8π G)-1/2)=1. I then compared the dynamics of the accelerating universe, on one hand, and Δα/α derived from the analyses of QSO absorption lines, Oklo phenomenon, also different atomic clocks in the laboratories, on the other hand. I am here going to discuss the theoretical background of the relation, based on the scalar-tensor theory invented first by Jordan in 1955.
Origin and control of the dominant time constant of salamander cone photoreceptors.
Zang, Jingjing; Matthews, Hugh R
2012-08-01
Recovery of the light response in vertebrate photoreceptors requires the shutoff of both active intermediates in the phototransduction cascade: the visual pigment and the transducin-phosphodiesterase complex. Whichever intermediate quenches more slowly will dominate photoresponse recovery. In suction pipette recordings from isolated salamander ultraviolet- and blue-sensitive cones, response recovery was delayed, and the dominant time constant slowed when internal [Ca(2+)] was prevented from changing after a bright flash by exposure to 0Ca(2+)/0Na(+) solution. Taken together with a similar prior observation in salamander red-sensitive cones, these observations indicate that the dominance of response recovery by a Ca(2+)-sensitive process is a general feature of amphibian cone phototransduction. Moreover, changes in the external pH also influenced the dominant time constant of red-sensitive cones even when changes in internal [Ca(2+)] were prevented. Because the cone photopigment is, uniquely, exposed to the external solution, this may represent a direct effect of protons on the equilibrium between its inactive Meta I and active Meta II forms, consistent with the notion that the process dominating recovery of the bright flash response represents quenching of the active Meta II form of the cone photopigment.
Ivy, Sarah E.; Guerra, Jennifer A.; Hatton, Deborah D.
2017-01-01
Introduction: Constant time delay is an evidence-based practice to teach sight word recognition to students with a variety of disabilities. To date, two studies have documented its effectiveness for teaching braille. Methods: Using a multiple-baseline design, we evaluated the effectiveness of constant time delay to teach highly motivating words to…
Knight, Melissa G.; Ross, Denise E.; Taylor, Ronald L.; Ramasamy, Rangasamy
2003-01-01
This study compared efficacy and efficiency of constant time delay and interspersal of known items to teach sight words to four students with mild mental retardation and learning disabilities. Results support effectiveness of constant time delay and suggest that interspersal of known items was more effective with students with learning…
Flores, Margaret M.; Houchins, David E.; Shippen, Margaret E.
2006-01-01
The purpose of this series of case studies was to compare the impact of Constant Time Delay and Strategic Instruction on the maintenance and generalization of learning. Four middle school students with learning disabilities were effectively taught two different groups of multiplication facts using Constant Time Delay and Strategic instruction. The…
Visualization of membrane fusion, one particle at a time.
Otterstrom, Jason; van Oijen, Antoine M
2013-03-12
Protein-mediated fusion between phospholipid bilayers is a fundamental and necessary mechanism for many cellular processes. The short-lived nature of the intermediate states visited during fusion makes it challenging to capture precise kinetic information using classical, ensemble-averaging biophysical techniques. Recently, a number of single-particle fluorescence microscopy-based assays that allow researchers to obtain highly quantitative data about the fusion process by observing individual fusion events in real time have been developed. These assays depend upon changes in the acquired fluorescence signal to provide a direct readout for transitions between the various fusion intermediates. The resulting data yield meaningful and detailed kinetic information about the transitory states en route to productive membrane fusion. In this review, we highlight recent in vitro and in vivo studies of membrane fusion at the single-particle level in the contexts of viral membrane fusion and SNARE-mediated synaptic vesicle fusion. These studies afford insight into mechanisms of coordination between fusion-mediating proteins as well as coordination of the overall fusion process with other cellular processes. The development of single-particle approaches to investigate membrane fusion and their successful application to a number of model systems have resulted in a new experimental paradigm and open up considerable opportunities to extend these methods to other biological processes that involve membrane fusion.
Nitrocellulose membrane sample holder using for terahertz time domain spectroscopy
Zhao, Xiaojing; Liu, Shangjian; Wang, Cuicui; Zuo, Jian; Zhang, Cunlin
2016-11-01
Terahertz (THz) technology has promising applications for the detection and identification of materials because it has a great advantage in measuring material fingerprint spectrum. Terahertz time-domain spectroscopy (THz-TDS) is a key technique that is applied to spectroscopic measurement of materials. However, it is difficult to press a pellet with small mass of sample and a bulking medium such as polyethylene (PE) powder usually need to be added. Characteristic absorption peaks of the solution in liquid cell is hard to be observed due to the interaction between materials and water molecules. Therefore, one method using the hydrophilic nitrocellulose (NC) membrane as a sample holder was applied to detect samples in an aqueous medium by THz-TDS. In this study, the α-lactose samples were mixed with 20 μl of deionized water and then applied directly onto the double-layered NC membrane sample holder. This mixture is located on the gap of two piece of NC membranes. Firstly the NC membranes with different pore sizes were tested in the experiment. And then the α-lactose solutions with different concentrations were measured on the NC with different pore sizes. Consequently, the small mass of samples can be detected and the characteristic absorption peaks become stronger with the increase of NC pore size. Moreover, compared to the traditional pellet-making and liquid cell detection, this membrane method is more convenient and easy to operate.
Ranjbaran, Mina; Katsarkas, Athanasios; Galiana, Henrietta L.
2016-01-01
The vestibulo-ocular reflex (VOR) is essential in our daily life to stabilize retinal images during head movements. Balanced vestibular functionality secures optimal reflex performance which otherwise can be distorted by peripheral vestibular lesions. Luckily, vestibular compensation in different neuronal sites restores VOR function to some extent over time. Studying vestibular compensation gives insight into the possible mechanisms for plasticity in the brain. In this work, novel experimental analysis tools are employed to reevaluate the VOR characteristics following unilateral vestibular lesions and compensation. Our results suggest that following vestibular lesions, asymmetric performance of the VOR is not only limited to its gain. Vestibular compensation also causes asymmetric dynamics, i.e., different time constants for the VOR during leftward or rightward passive head rotation. Potential mechanisms for these experimental observations are provided using simulation studies. PMID:27065839
Energy Technology Data Exchange (ETDEWEB)
Jaeger, Markus, E-mail: jaeger@informatik.uni-leipzig.de [Faculty of Mathematics and Computer Science, University of Leipzig, PF 100920, 04009 Leipzig (Germany); Butz, Tilman, E-mail: butz@physik.uni-leipzig.de [Faculty of Physics and Earth Sciences, University of Leipzig, Linnestr. 5, 04103 Leipzig (Germany)
2012-05-11
In a recent development of a fully digital spectrometer for time differential perturbed angular correlations a true constant fraction trigger (CFT) algorithm was implemented that, however, allowed for integer delays, i.e. integer multiples of the sampling interval, only. With a sampling rate of 1 GS/s and BaF{sub 2} scintillators this turned out to be insufficient. Here, we present an extension of the algorithm to fractional delays implemented in field programmable gate arrays (FPGAs). Furthermore, we derive a criterion for the delay for optimum timing based on the steepest slope of the CFT signal. Experimental data are given for LaBr{sub 3}(Ce) scintillators and 511 keV-511 keV prompt coincidences that corroborate the theoretical result.
Directory of Open Access Journals (Sweden)
Mohammad Javad Namazifar
2015-09-01
Full Text Available The Freeze-Tag Problem (FTP arises in the study of swarm robotics. The FTP is a combinatorial optimization problem that starts by locating a set of robots in a Euclidean plane. Here, we are given a swarm of n asleep (frozen or inactive robots and a single awake (active robot. In order to activate an inactive robot in FTP, the active robot should either be in the physical proximity to the inactive robot or ``touch`` it. The new activated robot starts moving and can wake up other inactive robots. The goal is to ﬁnd an optimal activating schedule with the minimum time required for activating all robots. In general, FTP is an NP-Hard problem and in the Euclidean space is an open problem. In this paper, we present a recursive approximation algorithm with a constant approximation factor and a linear running time for the Euclidean Freeze-Tag Problem.
Asymptotics with a positive cosmological constant: II. Linear fields on de Sitter space-time
Ashtekar, Abhay; Kesavan, Aruna
2015-01-01
Linearized gravitational waves in de Sitter space-time are analyzed in detail to obtain guidance for constructing the theory of gravitational radiation in presence of a positive cosmological constant in full, nonlinear general relativity. Specifically: i) In the exact theory, the intrinsic geometry of $\\scri$ is often assumed to be conformally flat in order to reduce the asymptotic symmetry group from $\\Diff$ to the de Sitter group. Our {results show explicitly} that this condition is physically unreasonable; ii) We obtain expressions of energy-momentum and angular momentum fluxes carried by gravitational waves in terms of fields defined at $\\scrip$; iii) We argue that, although energy of linearized gravitational waves can be arbitrarily negative in general, gravitational waves emitted by physically reasonable sources carry positive energy; and, finally iv) We demonstrate that the flux formulas reduce to the familiar ones in Minkowski space-time in spite of the fact that the limit $\\Lambda \\to 0$ is discontin...
Ranjbaran, Mina; Katsarkas, Athanasios; Galiana, Henrietta L
2016-01-01
The vestibulo-ocular reflex (VOR) is essential in our daily life to stabilize retinal images during head movements. Balanced vestibular functionality secures optimal reflex performance which otherwise can be distorted by peripheral vestibular lesions. Luckily, vestibular compensation in different neuronal sites restores VOR function to some extent over time. Studying vestibular compensation gives insight into the possible mechanisms for plasticity in the brain. In this work, novel experimental analysis tools are employed to reevaluate the VOR characteristics following unilateral vestibular lesions and compensation. Our results suggest that following vestibular lesions, asymmetric performance of the VOR is not only limited to its gain. Vestibular compensation also causes asymmetric dynamics, i.e., different time constants for the VOR during leftward or rightward passive head rotation. Potential mechanisms for these experimental observations are provided using simulation studies.
Directory of Open Access Journals (Sweden)
Mina eRanjbaran
2016-03-01
Full Text Available The vestibulo-ocular reflex (VOR is essential in our daily life to stabilize retinal images during head movements. Balanced vestibular functionality secures optimal reflex performance which can be distorted in case of peripheral vestibular lesions. Luckily, vestibular compensation in different neuronal sites restores VOR function to some extent over time. Studying vestibular compensation gives insight into the possible mechanisms for plasticity in the brain.In this work, novel experimental analysis tools are employed to reevaluate the VOR characteristics following unilateral vestibular lesions and compensation. Our results suggest that following vestibular lesions, asymmetric performance of the VOR is not only limited to its gain. Vestibular compensation also causes asymmetric dynamics, i.e. different time constants for the VOR during leftward or rightward passive head rotation. Potential mechanisms for these experimental observations are provided using simulation studies.
The Oklo bound on the time variation of the fine-structure constant revisited
Damour, Thibault Marie Alban Guillaume; Damour, Thibault; Dyson, Freeman
1996-01-01
It has been pointed out by Shlyakhter that data from the natural fission reactors which operated about two billion years ago at Oklo (Gabon) had the potential of providing an extremely tight bound on the variability of the fine-structure constant alpha. We revisit the derivation of such a bound by: (i) reanalyzing a large selection of published rare-earth data from Oklo, (ii) critically taking into account the very large uncertainty of the temperature at which the reactors operated, and (iii) connecting in a new way (using isotope shift measurements) the Oklo-derived constraint on a possible shift of thermal neutron-capture resonances with a bound on the time variation of alpha. Our final (95% C.L.) results are: -0.9 \\times 10^{-7} <(alpha^{Oklo} - alpha^{now})/alpha <1.2\\times 10^{-7} and -6.7 \\times 10^{-17} {yr}^{-1} < {\\dot alpha}^{averaged}/alpha <5.0\\times10^{-17} {yr}^{-1}.
Myers, Jerry G.; Hussey, Sam W.; Yee, Glenda F.; Yerramilli, Vamsee K.; Kim, Jungho
2005-01-01
The lack of temporally and spatially resolved measurements under nucleate bubbles has complicated efforts to fully explain pool-boiling phenomena. The objective of this current work is to acquire time and space resolved temperature distributions under nucleate bubbles on a constant heat flux surface. This was performed using a microheater array with 100 micron resolution that allowed effectively simultaneous measurements of surface temperature while supplying a constant dissipative heat flux. This data is then correlated with high speed (> 1000Hz) visual recordings of the bubble growth and departure from the heater surface acquired from below and from the side of the heater. The data indicate that a significant source of energy during bubble nucleation and initial growth is the superheated layer around the bubble. Bubble coalescence was not observed to decrease surface temperature as significantly as bubble departure from the surface. Since bubble departure is typically followed by a sharp increase in the heater surface temperature, it is surmised that the departing bubble effectively removes the superheated layer, allowing a high local heat transfer rate with the bulk fluid through transient conduction/micro-convection during rewetting.
Carvalheda, Catarina A; Campos, Sara R R; Baptista, António M
2015-10-26
Pulmonary surfactant protein C (SP-C) is a small peptide with two covalently linked fatty acyl chains that plays a crucial role in the formation and stabilization of the pulmonary surfactant reservoirs during the compression and expansion steps of the respiratory cycle. Although its function is known to be tightly related to its highly hydrophobic character and key interactions maintained with specific lipid components, much is left to understand about its molecular mechanism of action. Also, although it adopts a mainly helical structure while associated with the membrane, factors as pH variation and deacylation have been shown to affect its stability and function. In this work, the conformational behavior of both the acylated and deacylated SP-C isoforms was studied in a DPPC bilayer under different pH conditions using constant-pH molecular dynamics simulations. Our findings show that both protein isoforms are remarkably stable over the studied pH range, even though the acylated isoform exhibits a labile helix-turn-helix motif rarely observed in the other isoform. We estimate similar tilt angles for the two isoforms over the studied pH range, with a generally higher degree of internalization of the basic N-terminal residues in the deacylated case, and observe and discuss some protonation-conformation coupling effects. Both isoforms establish contacts with the surrounding lipid molecules (preferentially with the sn-2 ester bonds) and have a local effect on the conformational behavior of the surrounding lipid molecules, the latter being more pronounced for acylated SP-C.
Motoneuron membrane potentials follow a time inhomogeneous jump diffusion process
DEFF Research Database (Denmark)
Jahn, Patrick; Berg, Rune W; Hounsgaard, Jørn
2011-01-01
Stochastic leaky integrate-and-fire models are popular due to their simplicity and statistical tractability. They have been widely applied to gain understanding of the underlying mechanisms for spike timing in neurons, and have served as building blocks for more elaborate models. Especially...... models can only be applied over short time windows. However, experimental data show varying time constants, state dependent noise, a graded firing threshold and time-inhomogeneous input. In the present study we build a jump diffusion model that incorporates these features, and introduce a firing...
Effects of constant voltage on time evolution of propagating concentration polarization.
Zangle, Thomas A; Mani, Ali; Santiago, Juan G
2010-04-15
We extend the analytical theory of propagating concentration polarization (CP) to describe and compare the effects of constant-voltage versus constant-current conditions on the transient development of CP enrichment and depletion zones. We support our analysis with computational and experimental results. We find that at constant voltage, enrichment and depletion regions spread as t(1/2) as opposed to the previously observed t(1) scaling for constant current conditions. At low, constant voltages, the growth and propagation of CP zones can easily be misinterpreted as nonpropagating behavior.
Precision Measurements: Testing the Time Variation of the Fine Structure Constant
Lamoreaux, Steve
2004-05-01
Often, precision measurements from diverse fields can be used to learn new facts about the universe. The usual definition of "precision" is based on improvements over previous measurements. A review of the present state of knowledge regarding the possible time variation of the fine structure constant α will be presented; "precise" data from natural phenomena, which include an apparent shift in the red-shift-scaled fine structure in the absorption spectra of quasar light, and the isotopic abundances in the fission products of a prehistoric natural reactor in Oklo, Gabon. Prospects to improve the accuracy for the constancy of α with laboratory experiments will be discussed. Our two experimental investigations currently being developed are based on optical spectroscopy of trapped ions and on radiofrequency spectroscopy of an atomic dysprosium beam. A sensitivity of dotα/α≈ 10-18/yr is anticipated. Because this accuracy exceeds that by which the second is defined, these measurements will necessarily be differential.
Constraints on the time variation of the fine structure constant by the 5-year WMAP data
Nakashima, Masahiro; Yokoyama, Jun'ichi
2008-01-01
The constraints on the time variation of the fine structure constant at recombination epoch relative to its present value, $\\Delta\\alpha/\\alpha \\equiv (\\alpha_{\\mathrm{rec}} - \\alpha_{\\mathrm{now}})/\\alpha_{\\mathrm{now}}$, are obtained from the analysis of the 5-year WMAP cosmic microwave background data. As a result of Markov-Chain Monte-Carlo analysis, it is found that, contrary to the analysis based on the previous WMAP data, the mean value of $\\Delta\\alpha/\\alpha=-0.0009$ does not change significantly whether we use the Hubble Space Telescope (HST) measurement of the Hubble parameter as a prior or not. The resultant 95% confidence ranges of $\\Delta\\alpha/\\alpha$ are $-0.028 < \\Delta\\alpha/\\alpha < 0.026$ with HST prior and $-0.050 < \\Delta\\alpha/\\alpha < 0.042$ without HST prior.
Yerramilli, Vamsee K.; Myers, Jerry G.; Hussey, Sam W.; Yee, Glenda F.; Kim, Jungho
2005-01-01
The lack of temporally and spatially resolved measurements under nucleate bubbles has complicated efforts to fully explain pool-boiling phenomena. The objective of this current work was to acquire time and space resolved temperature distributions under nucleating bubbles on a constant heat flux surface using a microheater array with 100x 100 square microns resolution, then numerically determine the wall to liquid heat flux. This data was then correlated with high speed (greater than l000Hz) visual recordings of The bubble growth and departure from the heater surface acquired from below and from the side of the heater. The data indicate that microlayer evaporation and contact line heat transfer are not major heat transfer mechanisms for bubble growth. The dominant heat transfer mechanism appears to be transient conduction into the liquid as the liquid rewets the wall during the bubble departure process.
Time-of-flight PET data determine the attenuation sinogram up to a constant.
Defrise, Michel; Rezaei, Ahmadreza; Nuyts, Johan
2012-02-21
In positron emission tomography (PET), a quantitative reconstruction of the tracer distribution requires accurate attenuation correction. We consider situations where a direct measurement of the attenuation coefficient of the tissues is not available or is unreliable, and where one attempts to estimate the attenuation sinogram directly from the emission data by exploiting the consistency conditions that must be satisfied by the non-attenuated data. We show that in time-of-flight PET, the attenuation sinogram is determined by the emission data except for a constant and that its gradient can be estimated efficiently using a simple analytic algorithm. The stability of the method is illustrated numerically by means of a 2D simulation.
van Toor, Thijs; Verschuure, Hans
2002-10-01
The objectives of the study were to evaluate the effect of different settings with regard to speech intelligibility in noise both objectively and subjectively and thus determine a favoured setting of compression time parameters, pre-set program (high-frequency emphasis) or combination for each individual user in a prospective study. Another objective was to evaluate the relationship between patient characteristics (e.g. slope of hearing loss) and favoured settings. In total, 38 subjects divided over five audiological centres were fitted with the Philips Spaceline D71-40 BTE digital hearing aid. Subjects were asked to compare three predefined compression algorithms with different time constants, slow (indicated by the manufacturer as AVC), intermediate (NORMAL) and fast (SYLLABIC) over two 4-week periods using the intermediate setting in both comparisons and randomizing over the fast and slow conditions. A randomization determined whether a subject started with the comfort-oriented pre-set program (AUTO) or the speech intelligibility-oriented setting with high-frequency emphasis (SPIN). In a third 4-week period, the pre-sets AUTO and SPIN were compared using the setting of the compression time constants that gave the best results during the first two periods. Comparisons were made using a standard speech-in-noise test with three types of noise: continuous speaker noise, modulated ICRA-4 noise, and car noise. The patients were also asked to fill in a Dutch translation and adaptation of the APHAB questionnaire to indicate their impression of performance. The results indicate that no compression algorithm, pre-set or combination is favoured overall. The largest improvement in speech-in-noise scores was found with syllabic compression. The advantageous effect of high-frequency emphasis after optimization of compression timing is small. The APHAB showed that users tend to prefer the SPIN setting. We found no relationship between favoured compression or pre-set and the
Evolution of the magnetospheric storm-ring current with a constant time delay
Energy Technology Data Exchange (ETDEWEB)
Cluadegonzalez, A.L.; Gonzalez, W.D.; Detman, T.R.; Joselyn, J.A. [National Oceanic and Atmospheric Administration, Boulder, CO (United States)
1994-01-01
Using the energy balance equation for the ring current during magnetic storms, a theoretical study of the response of this current is done, for the case of a constant time decay tau. The input energy function for the balance equation is assumed to be described by a simple time variation during the injection time, such that an analytical response can be obtained. The model is used for 5 of the 10 intense storms in the interval August 1978-December 1979, for which the ISEE-3 interplanetary data are available. The energy input function for these 5 events (those with less data gaps) is assumed to be one of both, the azimuthal interplanetary electric field or the Akasofu`s coupling function. These input functions are approximated by one of the simple mentioned input functions and the solution obtained from the energy balance equation, for different values of tau, is compared to the actual evolution of the ring current (derived from the geomagnetic index Dst). The sets of input functions and tau values that better reproduce the observed storm evolution are adopted as the best approximation. As a conclusion, it is found that the more appropriate values of tau are longer than those determined in previous studies, especially for the case of more intense storms.
Pradhan, Anirudh; Rikhvitsky, Victor
2013-01-01
The present study deals with the exact solutions of the Einstein's field equations with variable gravitational and cosmological "constants" for a spatially homogeneous and anisotropic Bianchi type-I space-time. To study the transit behaviour of Universe, we consider a law of variation of scale factor $a(t) = \\left(t^{k} e^{t}\\right)^{\\frac{1}{n}}$ which yields a time dependent deceleration parameter (DP) $q = - 1 + \\frac{nk}{(k + t)^{2}}$, comprising a class of models that depicts a transition of the universe from the early decelerated phase to the recent accelerating phase. We find that the time dependent DP is reasonable for the present day Universe and give an appropriate description of the evolution of the universe. For $n = 0.27k$, we obtain $q_{0} = -0.73$ which is similar to observed value of DP at present epoch. It is also observed that for $n \\geq 2$ and $k = 1$, we obtain a class of transit models of the universe from early decelerating to present accelerating phase. For $k = 0$, the universe has no...
Effect of temporal acquisition parameters on image quality of strain time constant elastography.
Nair, Sanjay; Varghese, Joshua; Chaudhry, Anuj; Righetti, Raffaella
2015-04-01
Ultrasound methods to image the time constant (TC) of elastographic tissue parameters have been recently developed. Elastographic TC images from creep or stress relaxation tests have been shown to provide information on the viscoelastic and poroelastic behavior of tissues. However, the effect of temporal ultrasonic acquisition parameters and input noise on the image quality of the resultant strain TC elastograms has not been fully investigated yet. Understanding such effects could have important implications for clinical applications of these novel techniques. This work reports a simulation study aimed at investigating the effects of varying windows of observation, acquisition frame rate, and strain signal-to-noise ratio (SNR) on the image quality of elastographic TC estimates. A pilot experimental study was used to corroborate the simulation results in specific testing conditions. The results of this work suggest that the total acquisition time necessary for accurate strain TC estimates has a linear dependence to the underlying strain TC (as estimated from the theoretical strain-vs.-time curve). The results also indicate that it might be possible to make accurate estimates of the elastographic TC (within 10% error) using windows of observation as small as 20% of the underlying TC, provided sufficiently fast acquisition rates (>100 Hz for typical acquisition depths). The limited experimental data reported in this study statistically confirm the simulation trends, proving that the proposed model can be used as upper bound guidance for the correct execution of the experiments.
Stability and Relative Stability of Linear Systems with Many Constant Time Delays. Ph.D. Thesis
Barker, Larry Keith
1976-01-01
A method of determining the stability of linear systems with many constant time delays is developed. This technique, an extension of the tau-decomposition method, is used to examine not only the stability but also the relative stability of retarded systems with many delays and a class of neutral equations with one delay. Analytical equations are derived for partitioning the delay space of a retarded system with two time delays. The stability of the system in each of the regions defined by the partitioning curves in the parameter plane is determined using the extended tau-decomposition method. In addition, relative stability boundaries are defined using the extended tau-decompositon method in association with parameter plane techniques. Several applications of the extended tau-decomposition method are presented and compared with stability results obtained from other analyses. In all cases the results obtained using the method outlined herein coincide with and extend those of previous investigations. The extended tau-decomposition method applied to systems with time delays requires less computational effort and yields more complete stability analyses than previous techniques.
Energetically optimal nonstationary mode of flow along tube with constant and time-varying radius
Directory of Open Access Journals (Sweden)
Sergey G. Chefranov
2016-11-01
Full Text Available Derived is a new modification of hydrodynamic equations of viscous incompressible fluid flowing along the tube with radius changing in time. Obtained are exact non-stationary solutions of these equations generalizing a well-known classic stationary solution for Hagen–Poiseuille flow in the tube with radius constant in time. It is demonstrated that the law of changing the tube radius in time may be determined basing on the condition of minimality of the work expended for flowing the set fluid volume along such a tube during the period of radius change cycle. Obtained is the solution of the corresponding variational (isoperimetric problem on conditional extremum determining the limits to dimensionless quantity of the cycle duration set by the specified dimensionless value of the flowed fluid volume. Identified is the generalization of well-known model of optimal branching pipeline (F.L. Chernous’ko, 1977 in which the Poiseuille law modification is used for a new exact non-stationary solution of hydrodynamic equation instead of the law itself. It is demonstrated that the energetically favorable non-stationary modes with negative hydraulic resistance are permissible in certain conditions. The obtained conclusions may be used for development of the hydrodynamic basis of modelling the energy-optimal blood flow realized in the cardiovascular system in norm.
Microgrid Restoration after Major Faults in Main Grid with Automatic and Constant Time Switching
Directory of Open Access Journals (Sweden)
Elyas Zare
2013-09-01
Full Text Available When a microgrid and distributed generation resources are disconnected from the grid for protection reasons, the restoration of microgrid (restoring distributed generation resources to feed the loads in microgrid causes to increase the reliability of microgrid. When a fault occurs in the main grid, the reliability of islanded microgrid will be increased. In this paper a novel method for restoration of the microgrid is proposed when the fault occurred in the main grid. Therefore, we can take advantage of selling power energy during the fault. In addition, because of increasing in reliability, the price of energy will be increased. This paper selected a microgrid with two type of distributed generation resources, power electronic based distributed generation and small gas turbine with synchronous generator. Another purpose of this paper is to reduce restoration time. The proposed algorithm for automatic switching time is provided. This paper selected a microgrid system in medium voltage. The limitation voltage and frequency is according to IEEE 1547 standards, and simulation will be done by EMTP-RV with automatic and constant time switching separately.
Time resolved multiphoton excited fluorescence probes in model membranes
Bai, Y
2000-01-01
Using the time-correlated single-photon counting technique, this thesis reports on a time-resolved fluorescence study of several fluorescent probes successfully employed in membrane research. Concentration and temperature effects on fluorescence anisotropy parameters are demonstrated by DPH, p-terphenyl, alpha-NPO and PPO in DPPC lipid bilayers. Fluorescence anisotropy has shown that trans-stilbene and Rhd 800 have a two-site location in membranes. Multiphoton induced fluorescence of DPH, p-terphenyl, alpha-NPO and v-biphenyl in liposomes was measured using 800nm excitation with a femtosecond Ti:Sapphire laser. P-terphenyl, alpha-NPO and v-biphenyl are new probes for membranes. Comparison of one and multiphoton excitation results has demonstrated higher initial anisotropy with multiphoton excitation than with one-photon excitation. The rotational times were identical for one and multiphoton excitation, indicating the absence of significant local heating or sample perturbation. Excimer formation of alpha-NPO w...
Herda, T J; Costa, P B; Walter, A A; Ryan, E D; Cramer, J T
2014-02-01
The purpose of the present study was to examine the time course of passive range of motion (PROM), passive torque (PASTQ), and musculo-tendinous stiffness (MTS) responses during constant-angle (CA) and constant-torque (CT) stretching of the leg flexors. Eleven healthy men [mean ± standard deviation (SD): age = 21.5 ± 2.3 years] performed 16 30-s bouts of CA and CT stretching of the leg flexors. PROM, PASTQ , and MTS were measured during stretches 1, 2, 4, 8, and 16. For PROM and PASTQ , there were no differences between CA and CT stretching treatments (P > 0.05); however, there were stretch-related differences (P stretching (collapsed across CA and CT stretching) with additional increases up to 8 min of stretching. PASTQ decreased following one 30-s bout of stretching (collapsed across CA and CT stretching) and continued to decrease up to 4 min of stretching. In contrast, only the CT stretching treatment resulted in changes to MTS (P stretching, with subsequent decreases in MTS up to 6 min of stretching. These results suggested that CT stretching may be more appropriate than a stretch held at a constant muscle length for decreasing MTS.
Cerebral Arterial Time Constant Recorded from the MCA and PICA in Normal Subjects.
Kasprowicz, Magdalena; Czosnyka, Marek; Poplawska, Karolina; Reinhard, Matthias
2016-01-01
Cerebral arterial time constant (τ) estimates how quickly the cerebral arterial bed distal to the point of insonation is filled with arterial blood following a cardiac contraction. It is not known how τ behaves in different vascular territories in the brain. We therefore investigated the differences in τ of two cerebral arteries: the posterior inferior cerebellar artery (PICA) and the middle cerebral artery (MCA).Transcranial Doppler cerebral blood flow velocity (CBFV) in the PICA and left MCA along with Finapres arterial blood pressure (ABP) were simultaneously recorded in 35 young healthy volunteers. τ was estimated using mathematical transformations of pulse waveforms of ABP and the CBFV of the MCA and the PICA. Since τ is independent from the vessel radius, its comparison in different cerebral arteries was feasible. Mean ABP was 76.1 ± 9.6 mmHg. The CBFV of the MCA was higher than that of the PICA (59.7 ± 7.7 vs. 41.0 ± 4.5 cm/s; p time is needed to fill it with arterial blood volume. This study thus confirms the physiological validity of the τ concept.
Iorio, Lorenzo
2016-01-01
A sinusoidally time-varying pattern for the values of the Newton's constant of gravitation $G$ measured in Earth-based laboratories over the latest decades has been recently reported in the literature. Its amplitude and period amount to $A_G=1.619\\times 10^{-14} \\textrm{kg}^{-1} \\textrm{m}^3 \\textrm{s}^{-2}, P_G=5.899 \\textrm{yr}$, respectively. Given the fundamental role played by $G$ in the currently accepted theory of gravitation and the attempts to merge it with quantum mechanics, it is important to put to the test the hypothesis that the aforementioned harmonic variation may pertain $G$ itself in a direct and independent way. The bounds on $\\dot G/G$ existing in the literature may not be extended straightforwardly to the present case since they were inferred by considering just secular variations. Thus, we numerically integrated the ad-hoc modified equations of motion of the major bodies of the Solar System by finding that the orbits of the planets would be altered by an unacceptably larger amount in vie...
Institute of Scientific and Technical Information of China (English)
OUYANG Ke; LIU Junxin
2009-01-01
Three identical membrane bioreactors (MBRs) were operated over 2 years at different sludge retention times (SRT) of 10, 40 d and no sludge withdrawal (NS), respectively, to elucidate and quantify the effect of SRT on the sludge characteristics and membrane fouling. The hydraulic retention times of these MBRs were controlled at 12 h. With increasing SRT, the sludge concentrations in the MBRs increased, whereas the ratio of volatile suspended solid to the total solid decreased, and the size of sludge granule diminished in the meantime. A higher sludge concentration at long SRT could maintain a better organic removal efficiency, and a longer SRT was propitious to the growth of nitrifiers. The performance of these MBRs for the removal of COD and NH4+-N did not change much with different SRTs. However, the bioactivity decreased as SRT increased. The measurements of specific oxygen uptake rates (SOUR) and fluorescence in situ hybridization (FISH) with rRNA-targeted oligonucleotide probes testified that SOUR and the proportion of the bacteria-specific probe EUB338 in all DAPI-stainable bacteria decreased with increasing SRT. The concentrations of total organic carbon, protein, polysaccharides and soluble extracellular polymeric substance (EPS) in the mixed liquor supernatant decreased too with increasing SRT. The membrane fouling rate was higher at shorter SRT, and the highest fouling rate appeared at a SRT of 10 d. Both the sludge cake layer and gel layer had contribution to the fouling resistance, but the relative contribution of the gel layer decreased as SRT increased.
2008-01-01
Calculating an accurate nutation time constant (NTC), or nutation rate of growth, for a spinning upper stage is important for ensuring mission success. Spacecraft nutation, or wobble, is caused by energy dissipation anywhere in the system. Propellant slosh in the spacecraft fuel tanks is the primary source for this dissipation and, if it is in a state of resonance, the NTC can become short enough to violate mission constraints. The Spinning Slosh Test Rig (SSTR) is a forced-motion spin table where fluid dynamic effects in full-scale fuel tanks can be tested in order to obtain key parameters used to calculate the NTC. We accomplish this by independently varying nutation frequency versus the spin rate and measuring force and torque responses on the tank. This method was used to predict parameters for the Genesis, Contour, and Stereo missions, whose tanks were mounted outboard from the spin axis. These parameters are incorporated into a mathematical model that uses mechanical analogs, such as pendulums and rotors, to simulate the force and torque resonances associated with fluid slosh.
Guarin, Diego L; Kearney, Robert E
2015-01-01
Dynamic joint stiffness defines the torque generated at the joint in response to position perturbations. Dynamic stiffness is modulated by the angular position and the muscle activation level, making it difficult to estimate during large movements and/or time-varying muscle contractions. This paper presents a new methodology for estimating dynamic joint stiffness during movement and muscle activation. For this, we formulate a novel, nonlinear, dynamic joint stiffness model and present a new algorithm to estimate its parameters. The algorithm assumes that the variability in the model parameters is a function of the mean joint position. Using this methodology we estimated the dynamic joint stiffness at the ankle throughout ramp and hold displacements during a constant muscle contraction. The estimated model accurately predicted the intrinsic and reflex torques produced at the ankle as a response to small position perturbations during large displacement with muscle activation. Preliminary results show that during muscle contraction, ankle intrinsic stiffness estimated during movement is significantly lower than that estimated during quasi-stationary experiments.
Strength-Duration Time Constant in Peripheral Nerve: No Abnormality in Multiple Sclerosis
Directory of Open Access Journals (Sweden)
Gençer Genç
2012-01-01
Full Text Available Objectives. To investigate the properties of the strength-duration time constant (SDTC in multiple sclerosis (MS patients. Methods. The SDTC and rheobase in 16 MS patients and 19 healthy controls were obtained following stimulation of the right median nerve at the wrist. Results. SDTC and rheobase values were 408.3±60.0 μs and 4.0±1.8 mA in MS patients, versus 408.0±62.4 μs and 3.8±2.1 mA in controls. The differences were not significant in SDTC or rheobase values between the patients and controls (=0.988 for SDTC and =0.722 for rheobase. Conclusion. Our study showed no abnormality in relapsing remitting MS patients in terms of SDTC, which gives some indirect information about peripheral Na+ channel function. This may indicate that alterations in the Na+ channel pattern in central nervous system (CNS couldnot be shown in the peripheral nervous system (PNS in the MS patients by SDTC. The opinion that MS can be a kind of channelopathy might be proven by performing other axonal excitability tests or SDTC in progressive forms of MS.
Direct test of the time-independence of fundamental nuclear constants using the Oklo natural reactor
Shlyakhter, A I
The positions of neutron resonances have been shown to be highly sensitive to the variation of fundamental nuclear constants. The analysis of the measured isotopic shifts in the natural fossil reactor at Oklo gives the following restrictions on the possible rates of the interaction constants variation: strong ~2x10^-19 yr^-1, electromagnetic ~5x10^-18 yr^-1, weak ~10^-12 yr^-1. These limits permit to exclude all the versions of nuclear constants contemporary variation discussed in the literature. URL: http://alexonline.info >. For more recent analyses see hep-ph/9606486, hep-ph/0205206 and astro-ph/0204069 .
Glancy, Brian; Barstow, Thomas; Willis, Wayne T
2008-01-01
Following the onset of moderate aerobic exercise, the rate of oxygen consumption (J(o)) rises monoexponentially toward the new steady state with a time constant (tau) in the vicinity of 30 s. The mechanisms underlying this delay have been studied over several decades. Meyer's electrical analog model proposed the concept that the tau is given by tau = R(m) x C, where R(m) is mitochondrial resistance to energy transfer, and C is metabolic capacitance, determined primarily by the cellular total creatine pool (TCr = phosphocreatine + creatine). The purpose of this study was to evaluate in vitro the J(o) kinetics of isolated rat skeletal muscle mitochondria at various levels of TCr and mitochondrial protein. Mitochondria were incubated in a medium containing 5.0 mM ATP, TCr pools of 0-1.5 mM, excess creatine kinase, and an ATP-splitting system of glucose + hexokinase (HK). Pyruvate and malate (1 mM each) were present as oxidative substrates. J(o) was measured across time after HK was added to elicit one of two levels of J(o) (40 and 60% of state 3). At TCr levels (in mM) of 0.1, 0.2, 0.3, 0.75, and 1.5, the corresponding tau values (s, means +/- SE) were 22.2 +/- 3.0, 36.3 +/- 2.2, 65.7 +/- 4.3, 168.1 +/- 22.2, and 287.3 +/- 25.9. Thus tau increased linearly with TCr (R(2) = 0.916). Furthermore, the experimentally observed tau varied linearly and inversely with the mitochondrial protein added. These in vitro results consistently conform to the predictions of Meyer's electrical analog model.
Conditioned reinforcement in chain schedules when time to reinforcement is held constant.
Bell, Matthew C; Williams, Ben A
2013-03-01
Two alternative approaches describe determinants of responding to a stimulus temporally distant from primary reinforcement. One emphasizes the temporal relation of each stimulus to the primary reinforcer, with relative proximity of the stimulus determining response rate. A contrasting view emphasizes immediate consequences of responding to the stimulus, the key factor being the conditioned reinforcement value of those immediate consequences. To contrast these approaches, 4 pigeons were exposed to a two-component multiple schedule with three-link chain schedules in each component. Only middle-link stimuli differed between chains. Baseline reinforcement probabilities were 0.50 for both chains; during discrimination phases it was 1.0 for one chain and 0.0 for the other. During discrimination phases pigeons responded more to the reinforcement-correlated middle link than to the extinction-correlated middle link, demonstrating that responding was affected by the probability change. Terminal link responding was also higher in the reinforced chain, even though the terminal link stimulus was identical in both chains. Of greatest interest is initial link responding, which was temporally most distant from reinforcement. Initial link responding, necessarily equal in the two chains, was significantly higher during the 1.0/0.0 discrimination phases, even though overall reinforcement probability remained constant. For 3 of 4 birds, in fact, initial-link response rates were higher than terminal-link response rates, an outcome that can be ascribed only to the potent conditioned reinforcement properties of the middle-link stimulus during the discrimination phases. Results are incompatible with any account of chain behavior based solely on relative time to reinforcement.
Does Newton’s gravitational constant vary sinusoidally with time? Orbital motions say no
Iorio, Lorenzo
2016-02-01
A sinusoidally time-varying pattern of the values of Newton’s constant of gravitation G measured in Earth-based laboratories over the last few decades has been recently reported in the literature. We put to the test the hypothesis that the aforementioned harmonic variation may pertain to G itself in a direct and independent way. We numerically integrated the ad hoc modified equations of motion of the major bodies of the Solar System, finding that the orbits of the planets would be altered by an unacceptably larger amount in view of the present-day high accuracy astrometric measurements. In the case of Saturn, its geocentric right ascension α, declination δ and range ρ would be affected by up to {10}4-{10}5 milliarcseconds and 105 km, respectively; the present-day residuals of such observables are as little as about 4 milliarcseconds and 10-1 km, respectively. We analytically calculated the long-term orbital effects induced by the putative harmonic variation of G at hand, finding non-zero rates of change for the semimajor axis a, the eccentricity e and the argument of pericenter ω of a test particle. For the LAGEOS satellite, an orbital increase as large as 3.9 m yr-1 is predicted, in contrast with the observed decay of -0.203 ± 0.035 m yr-1. An anomalous perihelion precession as large as 14 arcseconds per century is implied for Saturn, while latest observations constrain it to the 10-4 arcseconds per century level. The rejection level provided by the Mercury’s perihelion rate is of the same order of magnitude.
2002-01-01
The solution proposed by Zhao & Qin to the apparent conflict between gravitational lens time delays, local estimates of the Hubble constant and current expectations for the structure of CDM halos is discussed. Two essential points emerge. First, the degeneracy is exactly the same as the local surface density degeneracy previously discussed in the literature. Second, the proposed mass distribution is inconsistent with CDM halo models. The Hubble constant is raised by making the dark matter far...
OPTIMAL TIME FOR SUBSTITUTION OF Eucalyptus spp POPULATIONS – THE CASE OF CONSTANT TECHNOLOGY
Directory of Open Access Journals (Sweden)
Álvaro Nogueira de Souza1;
2001-01-01
Full Text Available The few studies on renewal of Eucalyptus spp populations done in Brazil consider constant technology. This is done this way for facilitating the modeling of how variables affect this activity, such as income, costs, rates of discount and yield. The reason for not considering the gains earned through technological progress is the lack of a specific dynamic model. This study was carried out aiming to get to know the forest rotation with values from the sixties (beginning of tax exemption programme and current values (nineties aiming to obtain wood for cellulose and charcoal production; to determine the moment of substitution of a population which presents the same yield and the same cost structure through time as well as to determine how many cuttings should be done until the final cycle; to determine how many cuttings should be done until substitution (substitution chain; to verify the sensitivity of the substitution time to variations in the discount rates, wood prices, yield, land costs, harvesting costs and coppice yield. The results were tested in a case study, employing the Gompertz Function to determine the population yield. The Current Net Value Method was used as a crieterion of economic decision. It has been concluded that: The forest rotation to produce charcoal in the sixties was at 13 years of age; the current rotation is at 7 years of age; the final cycle allows up to 13 cuttings, but considering the possibility of land leasing, the best alternative is to conduce the sproutings up to the third cutting; an increase in factors such as discount rates, wood prices and yield caused reduction of the cutting age; increase in land costs did not affect the cutting ages; increase in the logging cost increased the cutting ages; the substitution of population now a days happens after 3 cuttings, while in the sixties it happened after 2 cuttings due to the lesser loss; an increase in factors such as discount rates, wood prices, logging costs and
Variation of fundamental constants in space and time: theory and observations
Flambaum, V V
2008-01-01
Review of recent works devoted to the temporal and spatial variation of the fundamental constants and dependence of the fundamental constants on the gravitational potential (violation of local position invariance) is presented. We discuss the variation of the fine structure constant $\\alpha=e^2/\\hbar c$, strong interaction and fundamental masses (Higgs vacuum), e.g. the electron-to-proton mass ratio $\\mu=m_e/M_p$ or $X_e=m_e/\\Lambda_{QCD}$ and $X_q=m_q/\\Lambda_{QCD}$. We also present new results from Big Bang nucleosynthesis and Oklo natural nuclear reactor data and propose new measurements of enhanced effects in atoms, nuclei and molecules, both in quasar and laboratory spectra.
The Time Constant Problem of Servo Motor%伺服电动机的时间常数问题
Institute of Scientific and Technical Information of China (English)
张文海
2012-01-01
The definitions of electric time constant, mechanical time constant, electromechanical time constant of servo motor were summarized. The reason that high speed servo motor can obtain low speed and high torque through reducer, but its mechanical time constant is usually higher than which of permanent magnet DC torque motor was analyzed. And the formulas to calculate mechanical time constant of DC & AC servo motors were explained.%概述了伺服电动机的电气时间常数、机械时间常数和机电时间常数的定义；分析了高速伺服电动机经减速器减速后可获得低速大转矩,但其机械时间常数比永磁直流力矩电动机大的原因；并解释了直流伺服电动机与交流伺服电动机的机械时间常数计算公式.
Variation of fundamental constants in space and time: Theory and observations
Flambaum, V. V.
2008-10-01
Review of recent works devoted to the temporal and spatialvariation of the fundamental constants and dependence of the fundamentalconstants on the gravitational potential (violation of local position invariance) is presented. We discuss the variation of the fine structure constant α=e2/ħc, strong interaction andfundamental masses (Higgs vacuum), e.g. the electron-to-proton mass ratioμ=me/Mp or Xe=me/ΛQCD and Xq=mq/ΛQCD.We also present new results from Big Bang nucleosynthesisand Oklo natural nuclear reactor data and propose new measurements of enhanced effects in atoms, nuclei and molecules, both in quasar and laboratory spectra.
Brandt, Julie A. Ackerlund; Weinkauf, Sara; Zeug, Nicole; Klatt, Kevin P.
2016-01-01
Previous research has shown that various prompting procedures are effective in teaching skills to children and adults with developmental disabilities. Simultaneous prompting includes proving a prompt immediately following an instruction; whereas constant time-delay procedures include a set time delay (i.e., 5 s or 10 s) prior to delivering a…
Bozkurt, Funda; Gursel, Oguz
2005-01-01
A multiple probe design with probe conditions across behaviors was used to evaluate effectiveness of constant time delay on teaching snack and drink preparation skills to children with mental retardation. In addition, generalization effects across settings, time, and materials, and maintenance effects were examined. Three students between the ages…
1976-12-01
The time dependent solution is presented for the dynamical behavior of the one dimensional electron boundary layer formed when X-rays knock photoelectrons out of a material surface. The X-ray flux is taken to be either linearly rising in time or constant in time . Two electron energy spectra are considered-exponential and linear-times-exponential. The electrons are assumed to have a cos theta
Time-Variation of the Gravitational Constant and the Machian Solution in the Brans-Dicke Theory
Miyazaki, A
2001-01-01
The Machian cosmological solution satisfying $\\phi =O(\\rho /\\omega)$ for the perfect-fluid with negative pressure is discussed. When the coefficient of the equation of state $\\gamma \\to -1/3$, the gravitational constant approaches to constant. If we assume the present mass density $\\rho_{0}\\sim \\rho_{c}$ (critical density), the parameter $\\epsilon$ ($\\gamma =(\\epsilon -1)/3$) has a value of order $10^{-3}$ to support the present gravitational constant. The closed model is valid for $\\omega <-3/2\\epsilon$ and exhibits the slow accelerating expansion. We understand why the coupling parameter $| \\omega |$ is so large ($\\omega \\sim -10^{3}$). The time-variation of the gravitational constant $| \\dot{G}/G| \\sim 10^{-13} yr^{-1}$ at present is derived in this model.
Real-Time Monitoring of Reverse Osmosis Membrane Integrity
Surawanvijit, Sirikarn
2015-01-01
Reverse osmosis (RO) membrane desalination is the primary technology for seawater and brackish water desalination, agricultural drainage desalting, as well as municipal wastewater recycling for potable water reuse applications. RO membranes achieve high salt rejection (>95%) and in principle should provide a complete physical barrier to nanosize pathogens (e.g., waterborne enteric viruses). However, in the presence of imperfections and/or membrane damage, membrane breaches as small as 20-30 n...
DEFF Research Database (Denmark)
Fedosov, Sergey; Belousova, Lubov; Plesner, Igor
1993-01-01
The quantitative aspects of mitochondrial creatinekinase (mitCK) binding to mitochondrial membranes were investigated. A simple adsorption and binding model was used for data fitting, taking into account the influence of protein concentration, pH, ionic strength and substrate concentration on the...
Chaos Time Series Prediction Based on Membrane Optimization Algorithms
Directory of Open Access Journals (Sweden)
Meng Li
2015-01-01
Full Text Available This paper puts forward a prediction model based on membrane computing optimization algorithm for chaos time series; the model optimizes simultaneously the parameters of phase space reconstruction (τ,m and least squares support vector machine (LS-SVM (γ,σ by using membrane computing optimization algorithm. It is an important basis for spectrum management to predict accurately the change trend of parameters in the electromagnetic environment, which can help decision makers to adopt an optimal action. Then, the model presented in this paper is used to forecast band occupancy rate of frequency modulation (FM broadcasting band and interphone band. To show the applicability and superiority of the proposed model, this paper will compare the forecast model presented in it with conventional similar models. The experimental results show that whether single-step prediction or multistep prediction, the proposed model performs best based on three error measures, namely, normalized mean square error (NMSE, root mean square error (RMSE, and mean absolute percentage error (MAPE.
Pan, Jiangjiang
2011-12-01
Organic micropollutants (OMPs) have received more and more attention in recent years due to their potential harmful effects on public health and aquatic ecosystems, and eliminating OMPs in wastewater treatment systems is an important solution to control OMPs wastage. An innovative hybrid process, anaerobic membrane bioreactor with nanofiltration (AnMBR-NF), in which enhanced OMPs removal is possible based on the concept of compound retention time (CRT) through coupling anaerobic biodegradation and NF rejection, is proposed and examined in terms of preliminary feasibility in this study. First, NF membrane screening through sludge water dead-end filtration tests demonstrated that KOCH NF200 (molecular weight cut-off (MWCO) 200 Da, acid/base stable) performed best in organic matter rejection. Then, selected OMPs (ketobrofen and naproxen) in MQ water and a biologically treated wastewater matrix were filtered through NF200 under constant-pressure dead-end mode, with and without stirring, and several methods (contact angle, scanning electronic microscopy, Zeta potential, Fourier transform infra-red spectroscopy) were used to characterize membranes. Results show selected OMPs in MQ could be rejected (about 40%) by a clean NF200 membrane. The main rejection mechanism was initial absorption by the membrane followed by size exclusion (electric charge interaction plays a less important role). The wastewater matrix could enhance the rejection significantly (up to 90%) because effluent organic matter (EfOM) enhanced size exclusion and electric charge interaction through blocking membrane pores and forming a gel layer as well as binding some OMPs through partitioning followed by retention by NF. Third, an anaerobic bioreactor was set up to evaluate the anaerobic biodegradability of selected OMPs. Results showed selected OMPs could be absorbed by sludge and reached equilibrium within one day, and then were consumed by anaerobic microorganism with a half life 9.4 days for
A Time Varying Strong Coupling Constant as a Model of Inflationary Universe
Chamoun, N; Vucetich, H
2000-01-01
We consider a scenario where the strong coupling constant was changing in the early universe. We attribute this change to a variation in the colour charge within a Bekenstein-like model. Allowing for a large value for the vacuum gluon condensate $\\sim 10^{22}GeV^4$, we could generate inflation with the required properties to solve the fluctuation and other standard cosmology problems. A possible approach to end the inflation is suggested.
Time variation of the fine structure constant in the early universe and the Bekenstein model
Mosquera, Mercedes E; Landau, Susana J; Vucetich, Hector
2007-01-01
We use observational primordial abundances of $\\De$, $\\Het$, $\\He$ and $\\Li$, recent data from the Cosmic Microwave Background and the 2dFGRS power spectrum, to put limits on the variation of the fine structure constant in the early universe. Furthermore, we use these constraints together with other astronomical and geophysical bounds from the late universe to test Bekenstein's model for the variation of $\\alpha$. The model is not able to fit all observational and experimental data.
Avelino, P P
2016-01-01
We critically assess recent claims suggesting that upper limits on the time variation of the fine-structure constant tightly constrain the coupling of a dark energy scalar field to the electromagnetic sector, and, indirectly, the violation of the weak equivalence principle. We show that such constraints depend crucially on the assumed priors, even if the dark energy was described by a dynamical scalar field with a constant equation of state parameter $w$ linearly coupled to the electromagnetic sector through a dimensionless coupling $\\zeta$. We find that, although local atomic clock tests, as well as other terrestrial, astrophysical and cosmological data, put stringent bounds on $|\\zeta| {\\sqrt {|w+1|}}$, the time variation of the fine-structure constant cannot be used to set or to improve upper limits on $|\\zeta|$ or $|w+1|$ without specifying priors, consistent but not favoured by current data, which strongly disfavour low values of $|w+1|$ or $|\\zeta|$, respectively. We briefly discuss how this might chang...
Rashid, M.
2011-01-01
A circularly orbiting electromagnetic harmonic wave may appear when a 1S electron encounters a decelerating stopping positively charged hole inside a semiconductor. The circularly orbiting electromagnetic harmonic wave can have an interaction with a conducting electron which has a constant time inde
Zhang, Jiabei; Cote, Bridget; Chen, Shihui; Liu, John
2004-01-01
The purpose of this study was to examine the effect of a constant time delay (CTD) procedure on teaching a recreational bowling skill to a 39-year-old male with severe mental retardation. The CTD procedure used 5 seconds as delay interval, task direction as target stimulus, physical assistance as controlling prompt, and oral praise as reinforcer.…
Appelman, Michelle; Vail, Cynthia O.; Lieberman-Betz, Rebecca G.
2014-01-01
The authors of this study evaluated the acquisition of instructive feedback information presented to four kindergarten children with mild delays taught in dyads using a constant time delay (CTD) procedure. They also assessed the learning of observational (dyadic partner) information within this instructional arrangement. A multiple probe design…
Yang, Tao; Wang, Xu; Saberi, Ali; Stoorvogel, Anton A.
2013-01-01
In this paper, we consider synchronization problems for heterogeneous networks of introspective, right-invertible, discrete-time linear agents with uniform constant communication delay. We first design decentralized controllers for solving the output synchronization problem for a set of network topo
Stevens, Kay B.; Lingo, Amy S.
2005-01-01
Teachers of students with emotional and behavioral disorders (EBD) understand conceptually, emotionally, and legally the importance of using research-based procedures as well as positive behavioral supports. One way to provide positive behavioral support for students with EBD is constant time delay (CTD). CTD is an instructional delivery procedure…
Seward, Jannike; Schuster, John W.; Ault, Melinda Jones; Collins, Belva C.; Hall, Meada
2014-01-01
We compared the effects of simultaneous prompting and constant time delay in teaching two solitaire card games to five high school students with moderate intellectual disability. An adapted alternating treatments within a multiple probe design was used to evaluate the effectiveness and efficiency of the procedures. Both procedures were effective…
Kurt, Onur; Tekin-Iftar, Elif
2008-01-01
An adapted alternating-treatments design was used to compare the effectiveness and efficiency of constant time delay and simultaneous prompting procedures within an embedded instruction format on the acquisition of various leisure skills by four preschool students with autism. The results showed that both procedures were effective in promoting the…
Zisimopoulos, Dimitrios; Sigafoos, Jeff; Koutromanos, George
2011-01-01
We evaluated a video prompting and a constant time delay procedure for teaching three primary school students with moderate intellectual disabilities to access the Internet and download pictures related to participation in a classroom History project. Video clips were used as an antecedent prompt and as an error correction technique within a…
Zhang, Jiabei; Cote, Bridget; Chen, Shihui; Liu, John
2004-01-01
The purpose of this study was to examine the effect of a constant time delay (CTD) procedure on teaching a recreational bowling skill to a 39-year-old male with severe mental retardation. The CTD procedure used 5 seconds as delay interval, task direction as target stimulus, physical assistance as controlling prompt, and oral praise as reinforcer.…
Dogoe, Maud; Banda, Devender R.
2009-01-01
We reviewed twelve studies that used the constant time delay (CTD) procedure to teach chained tasks to individuals with developmental disabilities from years 1996-2006. Variables analyzed include types of tasks that have been taught with the procedure, how effective CTD has been in teaching participants, and whether researchers have investigated…
Redhair, Emily I.; McCoy, Kathleen M.; Zucker, Stanley H.; Mathur, Sarup R.; Caterino, Linda
2013-01-01
This study compared a stimulus fading (SF) procedure with a constant time delay (CTD) procedure for identification of consonant-vowel-consonant (CVC) nonsense words for a participant with autism. An alternating treatments design was utilized through a computer-based format. Receptive identification of target words was evaluated using a computer…
Dogoe, Maud S.; Banda, Devender R.; Lock, Robin H.; Feinstein, Rita
2011-01-01
This study examined the effectiveness of the constant timed delay procedure for teaching two young adults with autism to read, define, and state the contextual meaning of keywords on product warning labels of common household products. Training sessions were conducted in the dyad format using flash cards. Results indicated that both participants…
Yilmaz, Ilker; Konukman, Ferman; Birkan, Binyamin; Ozen, Arzu; Yanardag, Mehmet; Camursoy, Ilhan
2010-01-01
Effects of a constant time delay procedure on the Halliwick's method of swimming rotation skills (i.e., vertical and lateral rotation) for children with autism were investigated. A single subject multiple baseline model across behaviors with probe conditions was used. Participants were three boys, 8-9 years old. Data were collected over a 10-week…
Hua, Youjia; Woods-Groves, Suzanne; Kaldenberg, Erica R.; Scheidecker, Bethany J.
2013-01-01
We investigated the effectiveness of using constant time delay (CTD) with young adults with intellectual disability on their vocabulary acquisition and retention, as well as expository reading comprehension. Four learners, ages 19 to 21 years, from a postsecondary education program for individuals with disabilities participated in the study.…
Yilmaz, Ilker; Konukman, Ferman; Birkan, Binyamin; Ozen, Arzu; Yanardag, Mehmet; Camursoy, Ilhan
2010-01-01
Effects of a constant time delay procedure on the Halliwick's method of swimming rotation skills (i.e., vertical and lateral rotation) for children with autism were investigated. A single subject multiple baseline model across behaviors with probe conditions was used. Participants were three boys, 8-9 years old. Data were collected over a 10-week…
Chruściel, Piotr T.; Delay, Erwann
2017-08-01
We construct infinite-dimensional families of non-singular static space-times, solutions of the vacuum Einstein-Maxwell equations with a negative cosmological constant. The families include an infinite-dimensional family of solutions with the usual AdS conformal structure at conformal infinity.
Rashid, M.
2011-01-01
A circularly orbiting electromagnetic harmonic wave may appear when a 1S electron encounters a decelerating stopping positively charged hole inside a semiconductor. The circularly orbiting electromagnetic harmonic wave can have an interaction with a conducting electron which has a constant time
Recent measurements of the gravitational constant as a function of time
Schlamminger, S; Newman, R D
2015-01-01
A recent publication (J.D. Anderson et. al., EPL 110, 1002) presented a strong correlation between the measured values of the gravitational constant $G$ and the 5.9-year oscillation of the length of day. Here, we provide a compilation of all published measurements of $G$ taken over the last 35 years. A least squares regression to a sine with a period of 5.9 years still yields a better fit than a straight line. However, our additions and corrections to the G data reported by Anderson {\\it et al.} significantly weaken the correlation.
Time Evolution of the Fine Structure Constant in a Two-Field Quintessence Model
Bento, M C; Santos, N M C
2004-01-01
We examine the variation of the fine structure constant in the context of a two-field quintessence model. We find that, for solutions that lead to a transient late period of accelerated expansion, it is possible to fit the data arising from quasar spectra and comply with the bounds on the variation of $\\alpha$ from the Oklo reactor, meteorite analysis, atomic clock measurements, Cosmic Microwave Background Radiation and Big Bang Nucleosynthesis. That is more difficult if we consider solutions corresponding to a late period of permanent accelerated expansion.
Time evolution of the fine structure constant in a two-field quintessence model
Bento, M. C.; Bertolami, O.; Santos, N. M.
2004-11-01
We examine the variation of the fine structure constant in the context of a two-field quintessence model. We find that, for solutions that lead to a transient late period of accelerated expansion, it is possible to fit the data arising from quasar spectra and comply with the bounds on the variation of α from the Oklo reactor, meteorite analysis, atomic clock measurements, cosmic microwave background radiation, and big bang nucleosynthesis. That is more difficult if we consider solutions corresponding to a late period of permanent accelerated expansion.
Karam, Ayman M.
2015-09-21
This paper presents a real time optimization scheme for a solar powered direct contact membrane distillation (DCMD) water desalination system. The sun and weather conditions vary and are inconsistent throughout the day. Therefore, the solar powered DCMD feed inlet temperature is never constant, which influences the distilled water flux. The problem of DCMD process optimization has not been studied enough. In this work, the response of the process under various feed inlet temperatures is investigated, which demonstrates the need for an optimal controller. To address this issue, we propose a multivariable Newton-based extremum seeking controller which optimizes the inlet feed and permeate mass flow rates as the feed inlet temperature varies. Results are presented and discussed for a realistic temperature profile.
Fujii, Y
2003-01-01
The data from the QSO absorption lines indicating a nonzero time-variability of the fine-structure constant has been re-analyzed on the basis of a "damped-oscillator" fit, as motivated by the same type of behavior of a scalar field, dilaton, which mimics a cosmological constant to understand the accelerating universe. We find nearly as good fit to the latest data as the simple weighted mean. In this way, we offer a way to fit the more stringent result from the Oklo phenomenon, as well.
Fujii, Yasunori
2003-10-01
The data from the QSO absorption lines indicating a nonzero time-variability of the fine-structure constant has been re-analyzed on the basis of a ``damped-oscillator'' fit, as motivated by the same type of behavior of a scalar field, dilaton, which mimics a cosmological constant to understand the accelerating universe. We find nearly as good fit to the latest data as the simple weighted mean. In this way, we offer a way to fit the more stringent result from the Oklo phenomenon, as well.
Yu, Huarong; Xu, Guoren; Qu, Fangshu; Li, Guibai; Liang, Heng
2016-09-01
Solid retention time (SRT) is one of the most important operational parameters in membrane bioreactor (MBR), which significantly influences membrane fouling. It is widely recognized that SRT mainly changes biomass characteristics, and then, influences membrane fouling. Effect of SRT on quorum sensing (QS) in MBR, which could also influence fouling by coordinating biofilm formation, has not been reported. In this study, fouling, QS, soluble microbial products (SMP), and extracellular polymer substances (EPS) in MBRs operated under SRTs of 4, 10, and 40 days were investigated. The results showed that as SRT increased, the abundance of quorum quenching (QQ) bacteria increased, the quorum signal degradation activity of activated sludge increased, the concentrations of signal molecules in MBR decreased, the excretion of SMP and EPS decreased, and thus membrane biofouling was alleviated. Therefore, besides altering the biomass physiochemical properties, SRT also changed the balance between QS and QQ in MBR, and in this way, influenced membrane biofouling.
Quantum logic gates from time-dependent global magnetic field in a system with constant exchange
Energy Technology Data Exchange (ETDEWEB)
Nenashev, A. V., E-mail: nenashev@isp.nsc.ru; Dvurechenskii, A. V. [Rzhanov Institute of Semiconductor Physics SB RAS, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, 630090 Novosibirsk (Russian Federation); Zinovieva, A. F. [Rzhanov Institute of Semiconductor Physics SB RAS, 630090 Novosibirsk (Russian Federation); Gornov, A. Yu.; Zarodnyuk, T. S. [Institute for System Dynamics and Control Theory SB RAS, 664033 Irkutsk (Russian Federation)
2015-03-21
We propose a method that implements a universal set of one- and two-quantum-bit gates for quantum computation in a system of coupled electron pairs with constant non-diagonal exchange interaction. In our proposal, suppression of the exchange interaction is performed by the continual repetition of single-spin rotations. A small g-factor difference between the electrons allows for addressing qubits and avoiding strong magnetic field pulses. Numerical experiments were performed to show that, to implement the one- and two-qubit operations, it is sufficient to change the strength of the magnetic field by a few Gauss. This introduces one and then the other electron in a resonance. To determine the evolution of the two-qubit system, we use the algorithms of optimal control theory.
Institute of Scientific and Technical Information of China (English)
Xin-yu Lai; Nan-rong Zhao
2013-01-01
Time-dependent diffusion coefficient and conventional diffusion constant are calculated and analyzed to study diffusion of nanoparticles in polymer melts.A generalized Langevin equation is adopted to describe the diffusion dynamics.Mode-coupling theory is employed to calculate the memory kernel of friction.For simplicity,only microscopic terms arising from binary collision and coupling to the solvent density fluctuation are included in the formalism.The equilibrium structural information functions of the polymer nanocomposites required by mode-coupling theory are calculated on the basis of polymer reference interaction site model with Percus-Yevick closure.The effect of nanoparticle size and that of the polymer size are clarified explicitly.The structural functions,the friction kernel,as well as the diffusion coefficient show a rich variety with varying nanoparticle radius and polymer chain length.We find that for small nanoparticles or short chain polymers,the characteristic short time non-Markov diffusion dynamics becomes more prominent,and the diffusion coefficient takes longer time to approach asymptotically the conventional diffusion constant.This constant due to the microscopic contributions will decrease with the increase of nanoparticle size,while increase with polymer size.Furthermore,our result of diffusion constant from modecoupling theory is compared with the value predicted from the Stokes-Einstein relation.It shows that the microscopic contributions to the diffusion constant are dominant for small nanoparticles or long chain polymers.Inversely,when nanonparticle is big,or polymer chain is short,the hydrodynamic contribution might play a significant role.
Succinct Dynamic Cardinal Trees with Constant Time Operations for Small Alphabet
DEFF Research Database (Denmark)
Davoodi, Pooya; Satti, Srinivasa Rao
2011-01-01
) bits and performs the following operations in O(1) time: parent, child(i), label-child(alpha), degree, subtree-size, preorder, is-ancestor(x), insert-leaf (alpha), delete-leaf(alpha). The update times are amortized. The space is close to the information theoretic lower bound. The operations...... are performed in the course of traversing the tree. This improves the succinct dynamic $k$-ary cardinal trees representation of Arroyuelo [1] for small alphabet, by speeding up both the query time of O(loglog n), and the update time of O((log log n)^2/logloglog n) to O(1), solving an open problem in [1...
Membrane bioreactor sludge rheology at different solid retention times.
Laera, G; Giordano, C; Pollice, A; Saturno, D; Mininni, G
2007-10-01
Rheological characterization is of crucial importance in sludge management both in terms of biomass dewatering and stabilization properties and in terms of design parameters for sludge handling operations. The sludge retention time (SRT) has a significant influence on biomass properties in biological wastewater treatment systems and in particular in membrane bioreactors (MBRs). The aim of this work is to compare the rheological behaviour of the biomass in a MBR operated under different SRTs. A bench-scale MBR was operated for 4 years under the same conditions except for the SRT, which ranged from 20 days to complete sludge retention. The rheological properties were measured over time and the apparent viscosity was correlated with the concentration of solid material when equilibrium conditions were reached and maintained. The three models most commonly adopted for rheological simulations were evaluated and compared in terms of their parameters. Then, steady-state average values of these parameters were related to the equilibrium biomass concentration (MLSS). The models were tested to select the one better fitting the experimental data in terms of mean root square error (MRSE). The relationship between the apparent viscosity and the shear rate, as a function of solid concentration, was determined and is proposed here. Statistical analysis showed that, in general, the Bingham model provided slightly better results than the Ostwald one. However, considering that a strong correlation between the two parameters of the Ostwald model was found for all the SRTs tested, both in the transient growth phases and under steady-state conditions, this model might be used more conveniently. This feature suggests that the latter model is easier to be used for the determination of the sludge apparent viscosity.
A Different Look at Dark Energy and the Time Variation of Fundamental Constants
Weinstein, Marvin
2011-01-01
This paper makes the simple observation that a fundamental length, or cutoff, in the context of Friedmann-Lema\\^itre-Robertson-Walker (FRW) cosmology implies very different things than for a static universe. It is argued that it is reasonable to assume that this cutoff is implemented by fixing the number of quantum degrees of freedom per co-moving volume (as opposed to a Planck volume) and the relationship of the vacuum-energy of all of the fields in the theory to the cosmological constant (or dark energy) is re-examined. The restrictions that need to be satisfied by a generic theory to avoid conflicts with current experiments are discussed, and it is shown that in any theory satisfying these constraints knowing the difference between $w$ and minus one allows one to predict $\\dot{w}$. It is argued that this is a robust result and if this prediction fails the idea of a fundamental cutoff of the type being discussed can be ruled out. Finally, it is observed that, within the context of a specific theory, a co-mo...
Domain Structure of Black Hole Space-Times with a Cosmological Constant
Armas, Jay; Harmark, Troels
2011-01-01
We generalize the domain structure for stationary black hole space-times to include asymptotically de Sitter and Anti-de Sitter space-times. Given a set of commuting Killing vector fields of a space-time the domain structure lives on the submanifold of the orbit space on which at least one of the Killing vector fields has zero norm. In general the domain structure provides topological and geometrical invariants of black hole space-times that in specific cases have proven to be a crucial part of a full characterization leading to uniqueness theorems. In four and five dimensions the domain structure generalizes the rod structure. We examine in detail the domain structure for four, five, six and seven-dimensional black hole space-times including a very general class of spherically symmetric and static black hole space-times as well as the exact solutions for Kerr-(Anti)-de Sitter black holes. While for asymptotically Anti-de Sitter space-times the domain structures resemble that of asymptotically flat space-time...
Energy Technology Data Exchange (ETDEWEB)
Yabu-uti, B.F.C., E-mail: yabuuti@ifi.unicamp.br [Instituto de Fisica ' Gleb Wataghin' , Universidade Estadual de Campinas, 13083-970 Campinas, SP (Brazil); Roversi, J.A., E-mail: roversi@ifi.unicamp.br [Instituto de Fisica ' Gleb Wataghin' , Universidade Estadual de Campinas, 13083-970 Campinas, SP (Brazil)
2011-08-22
We propose an alternative scheme to implement a two-qubit controlled-R (rotation) gate in the hybrid atom-CCA (coupled cavities array) system. Our scheme results in a constant gating time and, with an adjustable qubit-bus coupling (atom-resonator), one can specify a particular rotation R on the target qubit. We believe that this proposal may open promising perspectives for networking quantum information processors and implementing distributed and scalable quantum computation. -- Highlights: → We propose an alternative two-qubit controlled-rotation gate implementation. → Our gate is realized in a constant gating time for any rotation. → A particular rotation on the target qubit can be specified by an adjustable qubit-bus coupling. → Our proposal may open promising perspectives for implementing distributed and scalable quantum computation.
Xu, Bin
2012-01-01
By using laboratory experimental data, we test the uncertainty of social strategy transitions in various competing environments of fixed paired two-person constant sum $2 \\times 2$ games. It firstly shows that, the distributions of social strategy transitions are not erratic but obey the principle of the maximum entropy (MaxEnt). This finding indicates that human subject social systems and natural systems could have wider common backgrounds.
Yabu-uti, Bruno F C
2011-01-01
We propose an alternative scheme to implement a two-qubits Controlled-U gate in the hybrid system atom-$CCA$ (coupled cavities array). Our scheme results in a constant gating time and, with an adjustable qubit-bus coupling (atom-resonator), one can specify a particular transformation $U$ on the target qubit. We believe that this proposal may open promising perspectives for networking quantum information processors and implementing distributed and scalable quantum computation.
Nakashima, Masahiro; Nagata, Ryo; Yokoyama, Jun'ichi
2009-01-01
We investigate constraints on the time variation of the fine structure constant between the recombination epoch and the present epoch, $\\Delta\\alpha/\\alpha \\equiv (\\alpha_{rec} - \\alpha_{now})/\\alpha_{now}$, from cosmic microwave background (CMB) taking into account simultaneous variation of other physical constants, namely the electron mass $m_{e}$ and the proton mass $m_{p}$. In other words, we consider the variation of Yukawa coupling and the QCD scale $\\Lambda_{QCD}$ in addition to the electromagnetic coupling. We clarify which parameters can be determined from CMB temperature anisotropy in terms of singular value decomposition. Assuming a relation among variations of coupling constants governed by a single scalar field (the dilaton), the 95 % confidence level (C.L.) constraint on $\\Delta\\alpha/\\alpha$ is found to be $-8.28 \\times 10^{-3} < \\Delta\\alpha/\\alpha < 1.81 \\times 10^{-3}$, which is tighter than the one obtained by considering only the change of $\\alpha$ and $m_{e}$. We also obtain the con...
Reith, Lorenz M; Schlagnitweit, Judith; Smrecki, Vilko; Knör, Günther; Müller, Norbert; Schoefberger, Wolfgang
2011-03-01
A constant-time TOCSY difference experiment for the determination of (3)J((1)H3'-(31)P) coupling constants in non-isotope-labelled DNA oligonucleotides is presented. The method is tested on a DNA octamer and compared with the established constant-time NOESY difference method. Each (3)J((1)H3'-(31)P) coupling constant is determined from amplitude changes caused by phosphorous decoupling, which are observable on multiple cross-peaks, thus leading to a high accuracy of the value of the (3)J((1)H3'-(31)P) coupling constant. The new experiment delivers up to three times the sensitivity compared with previously reported methods.
Comparison of Cole-Cole and Constant Phase Angle modeling in time-domain induced polarization
DEFF Research Database (Denmark)
Lajaunie, Myriam; Maurya, Pradip Kumar; Fiandaca, Gianluca
is reflected in TDIP data, and therefore, at identifying (1) if and when it is possible to distinguish, in time domain, between a Cole-Cole description and a CPA one, and (2) if features of time domain data exist in order to know, from a simple data inspection, which model will be the most adapted to the data......, forward modeling of quadrupolar sequences on 1D and 2D heterogeneous CPA models shows that the CPA decays differ among each other only by a multiplication factor. Consequently, the inspection of field data in log-log plots gives insight on the modeling needed for fitting them: the CPA inversion cannot...
A compensatory algorithm for the slow-down effect on constant-time-separation approaches
Abbott, Terence S.
1991-01-01
In seeking methods to improve airport capacity, the question arose as to whether an electronic display could provide information which would enable the pilot to be responsible for self-separation under instrument conditions to allow for the practical implementation of reduced separation, multiple glide path approaches. A time based, closed loop algorithm was developed and simulator validated for in-trail (one aircraft behind the other) approach and landing. The algorithm was designed to reduce the effects of approach speed reduction prior to landing for the trailing aircraft as well as the dispersion of the interarrival times. The operational task for the validation was an instrument approach to landing while following a single lead aircraft on the same approach path. The desired landing separation was 60 seconds for these approaches. An open loop algorithm, previously developed, was used as a basis for comparison. The results showed that relative to the open loop algorithm, the closed loop one could theoretically provide for a 6 pct. increase in runway throughput. Also, the use of the closed loop algorithm did not affect the path tracking performance and pilot comments indicated that the guidance from the closed loop algorithm would be acceptable from an operational standpoint. From these results, it is concluded that by using a time based, closed loop spacing algorithm, precise interarrival time intervals may be achievable with operationally acceptable pilot workload.
A Comparison of Constant Time Delay Instruction with High and Low Treatment Integrity
Tekin Iftar, Elif; Kurt, Onur; Cetin, Ozlem
2011-01-01
Time delay (TD) procedure is an effective procedure in teaching various skills to children with developmental disabilities. Moreover, research has shown that it is used with high treatment integrity (HTI). However, there are several barriers which may prevent delivery instruction with HTI. Therefore, this study was designed to compare the…
A two-dimensional model of the plasmasphere - Refilling time constants
Rasmussen, Craig E.; Guiter, Steven M.; Thomas, Steven G.
1993-01-01
A 2D model of the plasmasphere has been developed to study the temporal evolution of plasma density in the equatorial plane of the magnetosphere. This model includes the supply and loss of hydrogen ions due to ionosphere-magnetosphere coupling as well as the effects of E x B convection. A parametric model describing the required coupling fluxes has been developed which utilizes empirical models of the neutral atmosphere, the ionosphere and the saturated plasmasphere. The plasmaspheric model has been used to examine the time it takes for the plasmasphere to refill after it has been depleted by a magnetic storm. The time it takes for the plasmasphere to reach 90 percent of its equilibrium level ranges from 3 days at L = 3 during solar minimum to as high as 100 days at L = 5 during solar maximum. Refilling is also dependent on the month of the year, with refilling requiring a longer period of time at solar maximum during June than during December for L greater than 3.2.
Are fMRI event-related response constant in time? A model selection answer.
Donnet, Sophie; Lavielle, Marc; Poline, Jean-Baptiste
2006-07-01
An accurate estimation of the hemodynamic response function (HRF) in functional magnetic resonance imaging (fMRI) is crucial for a precise spatial and temporal estimate of the underlying neuronal processes. Recent works have proposed non-parametric estimation of the HRF under the hypotheses of linearity and stationarity in time. Biological literature suggests, however, that response magnitude may vary with attention or ongoing activity. We therefore test a more flexible model that allows for the variation of the magnitude of the HRF with time in a maximum likelihood framework. Under this model, the magnitude of the HRF evoked by a single event may vary across occurrences of the same type of event. This model is tested against a simpler model with a fixed magnitude using information theory. We develop a standard EM algorithm to identify the event magnitudes and the HRF. We test this hypothesis on a series of 32 regions (4 ROIS on eight subjects) of interest and find that the more flexible model is better than the usual model in most cases. The important implications for the analysis of fMRI time series for event-related neuroimaging experiments are discussed.
Novel membrane-based electrochemical sensor for real-time bio-applications
DEFF Research Database (Denmark)
Al Atraktchi, Fatima Al-Zahraa; Bakmand, Tanya; Dimaki, Maria
2014-01-01
This article presents a novel membrane-based sensor for real-time electrochemical investigations of cellular- or tissue cultures. The membrane sensor enables recording of electrical signals from a cell culture without any signal dilution, thus avoiding loss of sensitivity. Moreover, the porosity...... of the membrane provides optimal culturing conditions similar to existing culturing techniques allowing more efficient nutrient uptake and molecule release. The patterned sensor electrodes were fabricated on a porous membrane by electron-beam evaporation. The electrochemical performance of the membrane electrodes...
Capacity of Discrete-Time Wiener Phase Noise Channels to Within a Constant Gap
Barletta, Luca; Rini, Stefano
2017-01-01
The capacity of the discrete-time channel affected by both additive Gaussian noise and Wiener phase noise is studied. Novel inner and outer bounds are presented, which differ of at most $6.65$ bits per channel use for all channel parameters. The capacity of this model can be subdivided in three regimes: (i) for large values of the frequency noise variance, the channel behaves similarly to a channel with circularly uniform iid phase noise; (ii) when the frequency noise variance is small, the e...
DEFF Research Database (Denmark)
Bach, Finn
2009-01-01
Notatet giver en kort introduktion til den statiske virkemåde af membraner og membrankonstruktioner......Notatet giver en kort introduktion til den statiske virkemåde af membraner og membrankonstruktioner...
Theoretical determination of chemical rate constants using novel time-dependent methods
Dateo, Christopher E.
1994-01-01
The work completed within the grant period 10/1/91 through 12/31/93 falls primarily in the area of reaction dynamics using both quantum and classical mechanical methodologies. Essentially four projects have been completed and have been or are in preparation of being published. The majority of time was spent in the determination of reaction rate coefficients in the area of hydrocarbon fuel combustion reactions which are relevant to NASA's High Speed Research Program (HSRP). These reaction coefficients are important in the design of novel jet engines with low NOx emissions, which through a series of catalytic reactions contribute to the deterioration of the earth's ozone layer. A second area of research studied concerned the control of chemical reactivity using ultrashort (femtosecond) laser pulses. Recent advances in pulsed-laser technologies have opened up a vast new field to be investigated both experimentally and theoretically. The photodissociation of molecules adsorbed on surfaces using novel time-independent quantum mechanical methods was a third project. And finally, using state-of-the-art, high level ab initio electronic structure methods in conjunction with accurate quantum dynamical methods, the rovibrational energy levels of a triatomic molecule with two nonhydrogen atoms (HCN) were calculated to unprecedented levels of agreement between theory and experiment.
Time-resolved GISAXS and cryo-microscopy characterization of block copolymer membrane formation
Marques, Debora S.
2014-03-01
Time-resolved grazing-incidence small-angle X-ray scattering (GISAXS) and cryo-microscopy were used for the first time to understand the pore evolution by copolymer assembly, leading to the formation of isoporous membranes with exceptional porosity and regularity. The formation of copolymer micelle strings in solution (in DMF/DOX/THF and DMF/DOX) was confirmed by cryo field emission scanning electron microscopy (cryo-FESEM) with a distance of 72 nm between centers of micelles placed in different strings. SAXS measurement of block copolymer solutions in DMF/DOX indicated hexagonal assembly with micelle-to-micelle distance of 84-87 nm for 14-20 wt% copolymer solutions. GISAXS in-plane peaks were detected, revealing order close to hexagonal. The d-spacing corresponding to the first peak in this case was 100-130 nm (lattice constant 115-150 nm) for 17 wt% copolymer solutions evaporating up to 100 s. Time-resolved cryo-FESEM showed the formation of incipient pores on the film surface after 4 s copolymer solution casting with distances between void centers of 125 nm. © 2014 Elsevier Ltd. All rights reserved.
Zhang, Xiaomei; Yue, Xiuping; Liu, Zhiqiang; Li, Qingqing; Hua, Xiufu
2015-06-01
Anaerobic-oxic membrane bioreactor (AOMBR) has been proposed as a highly effective method in municipal and industrial wastewater treatment. In this study, according to the sewage treatment system in a campus, long-term experiments were conducted to assess the impacts of the sludge retention time (SRT) on sludge characteristics and membrane fouling, and the sludge parameters include biomass concentration, particle size distribution, extracellular polymeric substances (EPS), soluble microbial products (SMPs), and specific resistance to filtration (SRF). Our results clearly demonstrated that SRT was one of the most important factors influencing sludge characteristics, and different sludge characteristics resulted in different membrane fouling degrees. A better treatment and filtration performances were observed at the SRT of 30 days compared to two SRTs of 10 and 90 days. Among these parameters, SMP had the most significant correlation with the membrane fouling rate (dTMP/dt), and it had a negative impact on membrane filtration performance. The impact of SRT on membrane fouling process was discussed further by filtration models. At 10 days SRT, the complete-standard blocking model curve had a comparatively higher goodness-of-fit with the fouling process, and at 30 and 90 days SRT, the cake-standard blocking model curve had a relatively higher goodness-of-fit with respective fouling process.
Oknyanskij, V. L.
The Optical-to-Near-infrared variability time delay have already been reported for a small number (˜ 7) of AGNs and has been firmly established only for 5 of them. The time delay is probably increasing with the IR wavelengths. The most naturally this time delay can be interpreted by the model where IR emission is attributed to circumnuclear dust heated by the nuclear radiation. In given model a suggestion on narrowness of the near-infrared (NIR) emission region is quite natural, as far as the dust can be not saved on distances from the nucleus closer then some critical value, on which it is reached the sublimation temperature for graphite particles (Barvainis, 1987). For NGC 4151 case it has been shown that the NIR region has a form of thin ring or torus. The radius of this ring correlates with level of the nucleus activity (Oknyanskij et al. 1999). This dependency of radius of the NIR emission region from luminosity reveals itself as under object variability (as in the case of NGC4151), and also when objects with high and low luminosity are considered. We assume that the observed time delays allow us to derive a redshift independent luminosity distances to AGNs and estimate a Hubble constant. Some problems of using this strategy for the Hubble constant determination are discussed.
Snyder, Jeff; Hanstock, Chris C.; Wilman, Alan H.
2009-10-01
A general in vivo magnetic resonance spectroscopy editing technique is presented to detect weakly coupled spin systems through subtraction, while preserving singlets through addition, and is applied to the specific brain metabolite γ-aminobutyric acid (GABA) at 4.7 T. The new method uses double spin echo localization (PRESS) and is based on a constant echo time difference spectroscopy approach employing subtraction of two asymmetric echo timings, which is normally only applicable to strongly coupled spin systems. By utilizing flip angle reduction of one of the two refocusing pulses in the PRESS sequence, we demonstrate that this difference method may be extended to weakly coupled systems, thereby providing a very simple yet effective editing process. The difference method is first illustrated analytically using a simple two spin weakly coupled spin system. The technique was then demonstrated for the 3.01 ppm resonance of GABA, which is obscured by the strong singlet peak of creatine in vivo. Full numerical simulations, as well as phantom and in vivo experiments were performed. The difference method used two asymmetric PRESS timings with a constant total echo time of 131 ms and a reduced 120° final pulse, providing 25% GABA yield upon subtraction compared to two short echo standard PRESS experiments. Phantom and in vivo results from human brain demonstrate efficacy of this method in agreement with numerical simulations.
Reschke, M. F.; Kozlovskaya, I. B.; Kofman, I. S.; Tomilovskaya, E. S.; Cerisano, J. M.; Bloomberg, J. J.; Stenger, M. B.; Platts, S. H.; Rukavishnikov, I. V.; Fomina, E. V.; Lee, S. M. C.; Wood, S. J.; Mulavara, A. P.; Feiveson, A. H.; Fisher, E. A.
2015-01-01
INTRODUCTION Testing of crew responses following long-duration flights has not been previously possible until a minimum of more than 24 hours after landing. As a result, it has not been possible to determine the trend of the early recovery process, nor has it been possible to accurately assess the full impact of the decrements associated with long-duration flight. To overcome these limitations, both the Russian and U.S. programs have implemented joint testing at the Soyuz landing site. This International Space Station research effort has been identified as the functional Field Test, and represents data collect on NASA, Russian, European Space Agency, and Japanese Aerospace Exploration Agency crews. RESEARCH The primary goal of this research is to determine functional abilities associated with long-duration space flight crews beginning as soon after landing as possible on the day of landing (typically within 1 to 1.5 hours). This goal has both sensorimotor and cardiovascular elements. To date, a total of 15 subjects have participated in a 'pilot' version of the full 'field test'. The full version of the 'field test' will assess functional sensorimotor measurements included hand/eye coordination, standing from a seated position (sit-to-stand), walking normally without falling, measurement of dynamic visual acuity, discriminating different forces generated with the hands (both strength and ability to judge just noticeable differences of force), standing from a prone position, coordinated walking involving tandem heel-to-toe placement (tested with eyes both closed and open), walking normally while avoiding obstacles of differing heights, and determining postural ataxia while standing (measurement of quiet stance). Sensorimotor performance has been obtained using video records, and data from body worn inertial sensors. The cardiovascular portion of the investigation has measured blood pressure and heart rate during a timed stand test in conjunction with postural ataxia
Apparent horizons of an N-black-hole system in a space-time with a cosmological constant
Nakao, Ken-ichi; Yamamoto, Kazuhiro; Maeda, Kei-ichi
1993-01-01
We present the analytic solution of N Einstein-Rosen bridges ("N black holes") in the space-time with a cosmological constant Λ and analyze it for one- and two-bridge systems. We discuss the three kinds of apparent horizons: i.e., the black-hole, white-hole, and cosmological apparent horizons. In the case of two Einstein-Rosen bridges, when the "total mass" is larger than a critical value, the black-hole apparent horizon surrounding two Einstein-Rosen bridges is not formed even if the distanc...
Effect of evaporation time on cellulose acetate membrane for gas separation
Jami'an, W. N. R.; Hasbullah, H.; Mohamed, F.; Yusof, N.; Ibrahim, N.; Ali, R. R.
2016-06-01
Throughout this decades, membrane technology has been the desirable option among the others gas separation technologies. However, few issues have been raised regarding the membrane gas separation application including the trade-off between its permeability and selectivity and also its effects towards environment. Therefore, for this research, a biopolymer membrane for gas separation application will be developed with reasonably high on both permeability and selectivity. The main objective of this research is to study the effect of solvent evaporation time on the flat sheet asymmetric membrane morphology and gas separation performance. The membranes were produced by a simple dry/wet phase inversion technique using a pneumatically controlled casting system. The dope solution for the membrane casting was prepared by dissolving the cellulose acetate (CA) polymer in N-Methyl-2-pyrrolidone (NMP) and the solvent evaporation time was varied. Permeability and selectivity of the membrane was performed by using pure gases of carbon dioxide, CO2 and methane, CH4. The increase in solvent evaporation time had improved the membrane morphologies as the porosity of the membrane surface decrease and formation of a more mature skin layer. The gas permeation tests determined that increasing in solvent evaporation time had increased the selectivity of CO2/CH4 but reduce the permeability of both gases
Nair, S P; Righetti, R
2015-05-07
Recent elastography techniques focus on imaging information on properties of materials which can be modeled as viscoelastic or poroelastic. These techniques often require the fitting of temporal strain data, acquired from either a creep or stress-relaxation experiment to a mathematical model using least square error (LSE) parameter estimation. It is known that the strain versus time relationships for tissues undergoing creep compression have a non-linear relationship. In non-linear cases, devising a measure of estimate reliability can be challenging. In this article, we have developed and tested a method to provide non linear LSE parameter estimate reliability: which we called Resimulation of Noise (RoN). RoN provides a measure of reliability by estimating the spread of parameter estimates from a single experiment realization. We have tested RoN specifically for the case of axial strain time constant parameter estimation in poroelastic media. Our tests show that the RoN estimated precision has a linear relationship to the actual precision of the LSE estimator. We have also compared results from the RoN derived measure of reliability against a commonly used reliability measure: the correlation coefficient (CorrCoeff). Our results show that CorrCoeff is a poor measure of estimate reliability for non-linear LSE parameter estimation. While the RoN is specifically tested only for axial strain time constant imaging, a general algorithm is provided for use in all LSE parameter estimation.
Pagnamenta, Alberto; Vanderpool, Rebecca; Brimioulle, Serge; Naeije, Robert
2013-06-01
The time constant of the pulmonary circulation, or product of pulmonary vascular resistance (PVR) and compliance (Ca), called the RC-time, has been reported to remain constant over a wide range of pressures, etiologies of pulmonary hypertension, and treatments. We wondered if increased wave reflection on proximal pulmonary vascular obstruction, like in operable chronic thromboembolic pulmonary hypertension, might also decrease the RC-time and thereby increase pulse pressure and right ventricular afterload. Pulmonary hypertension of variable severity was induced either by proximal obstruction (pulmonary arterial ensnarement) or distal obstruction (microembolism) eight anesthetized dogs. Pulmonary arterial pressures (Ppa) were measured with high-fidelity micromanometer-tipped catheters, and pulmonary flow with transonic technology. Pulmonary ensnarement increased mean Ppa, PVR, and characteristic impedance, decreased Ca and the RC-time (from 0.46 ± 0.07 to 0.30 ± 0.03 s), and increased the oscillatory component of hydraulic load (Wosc/Wtot) from 25 ± 2 to 29 ± 2%. Pulmonary microembolism increased mean Ppa and PVR, with no significant change in Ca and characteristic impedance, increased RC-time from 0.53 ± 0.09 to 0.74 ± 0.05 s, and decreased Wosc/Wtot from 26 ± 2 to 13 ± 2%. Pulse pressure increased more after pulmonary ensnarement than after microembolism. Concomitant measurements with fluid-filled catheters showed the same functional differences between the two types of pulmonary hypertension, with, however, an underestimation of Wosc. We conclude that pulmonary hypertension caused by proximal vs. distal obstruction is associated with a decreased RC-time and increased pulsatile component of right ventricular hydraulic load.
Vandergrift, Gregory W; Krogh, Erik T; Gill, Chris G
2017-05-16
Condensed phase membrane introduction mass spectrometry (CP-MIMS) is an online, in situ analysis technique for low volatility analytes. Analytes diffuse through a hollow fiber membrane, where they are then dissolved by a liquid (condensed) acceptor phase flowing through the membrane lumen. Permeating analytes are entrained to an atmospheric pressure ionization source for subsequent measurement by a mass spectrometer. Larger analytes, with inherently lower diffusivities, suffer from lengthy response times and lower sensitivity, limiting the use of CP-MIMS for their online, real-time measurement. We present the use of a heptane cosolvent in a methanol acceptor phase in combination with a polydimethylsiloxane (PDMS) membrane. The heptane generates an in situ polymer inclusion membrane (PIM) with the PDMS. We report improved measurement response times and greater sensitivity across a suite of analytes studied (gemfibrozil, nonylphenol, triclosan, 2,4,6-trichlorophenol, and naphthenic acids), with detection limits in the low parts per trillion (ppt) range. These improvements are attributed to increasing analyte diffusivities, as well as increased analyte partitioning across the PIM. Response times are ∼3× faster for the larger analytes studied, and calibration sensitivity is improved by up to ∼3.5× using 0.046 mole fraction heptane in the methanol acceptor. We report the use of short sample exposure times and the use of non-steady-state signals to reduce the analytical duty cycle, and illustrate that the use of a PIM provides a simple and robust variant of CP-MIMS amenable to rapid screening of analytes in complex samples.
Singh, Trailokyanath; Mishra, Pandit Jagatananda; Pattanayak, Hadibandhu
2017-04-01
In this paper, an economic order quantity (EOQ) inventory model for a deteriorating item is developed with the following characteristics: (i) The demand rate is deterministic and two-staged, i.e., it is constant in first part of the cycle and linear function of time in the second part. (ii) Deterioration rate is time-proportional. (iii) Shortages are not allowed to occur. The optimal cycle time and the optimal order quantity have been derived by minimizing the total average cost. A simple solution procedure is provided to illustrate the proposed model. The article concludes with a numerical example and sensitivity analysis of various parameters as illustrations of the theoretical results.
Souza, Kristopher Mendes; de Lucas, Ricardo Dantas; do Nascimento Salvador, Paulo Cesar; Guglielmo, Luiz Guilherme Antonacci; Caritá, Renato Aparecido Corrêa; Greco, Camila Coelho; Denadai, Benedito Sérgio
2015-09-01
The aim of this study was to investigate whether the maximal power output (Pmax) during an incremental test was dependent on the curvature constant (W') of the power-time relationship. Thirty healthy male subjects (maximal oxygen uptake = 3.58 ± 0.40 L·min(-1)) performed a ramp incremental cycling test to determine the maximal oxygen uptake and Pmax, and 4 constant work rate tests to exhaustion to estimate 2 parameters from the modeling of the power-time relationship (i.e., critical power (CP) and W'). Afterwards, the participants were ranked according to their magnitude of W'. The median third was excluded to form a high W' group (HIGH, n = 10), and a low W' group (LOW, n = 10). Maximal oxygen uptake (3.84 ± 0.50 vs. 3.49 ± 0.37 L·min(-1)) and CP (213 ± 22 vs. 200 ± 29 W) were not significantly different between HIGH and LOW, respectively. However, Pmax was significantly greater for the HIGH (337 ± 23 W) than for the LOW (299 ± 40 W). Thus, in physically active individuals with similar aerobic parameters, W' influences the Pmax during incremental testing.
Higgs potential from extended Brans–Dicke theory and the time-evolution of the fundamental constants
Solà, Joan; Karimkhani, Elahe; Khodam-Mohammadi, A.
2017-01-01
Despite the enormous significance of the Higgs potential in the context of the standard model of electroweak interactions and in grand unified theories, its ultimate origin is fundamentally unknown and must be introduced by hand in accordance with the underlying gauge symmetry and the requirement of renormalizability. Here we propose a more physical motivation for the structure of the Higgs potential, which we derive from a generalized Brans–Dicke (BD) theory containing two interacting scalar fields. One of these fields is coupled to curvature as in the BD formulation, whereas the other is coupled to gravity both derivatively and non-derivatively through the curvature scalar and the Ricci tensor. By requiring that the cosmological solutions of the model are consistent with observations, we show that the effective scalar field potential adopts the Higgs potential form with a mildly time-evolving vacuum expectation value. This residual vacuum dynamics could be responsible for the possible time variation of the fundamental constants, and is reminiscent of former Bjorken’s ideas on the cosmological constant problem.
Coleman, Mari Beth; Hurley, Kevin J.; Cihak, David F.
2012-01-01
The purpose of this study was to compare the effectiveness and efficiency of teacher-directed and computer-assisted constant time delay strategies for teaching three students with moderate intellectual disability to read functional sight words. Target words were those found in recipes and were taught via teacher-delivered constant time delay or…
Noutsi, Pakiza
2016-06-30
Cell membrane is made up of a complex structure of lipids and proteins that diffuse laterally giving rise to what we call membrane fluidity. During cellular development, such as differentiation cell membranes undergo dramatic fluidity changes induced by proteins such as ARC and Cofilin among others. In this study we used the generalized polarization (GP) property of fluorescent probe Laurdan using two-photon microscopy to determine membrane fluidity as a function of time and for various cell lines. A low GP value corresponds to a higher fluidity and a higher GP value is associated with a more rigid membrane. Four different cell lines were monitored such as hN2, NIH3T3, HEK293 and L6 cells. Membrane fluidity was measured at 12h, 72h and 92 h. Our results show significant changes in membrane fluidity among all cell types at different time points. GP values tend to increase significantly within 92 h in hN2 cells and 72 h in NIH3T3 cells and only at 92 h in HEK293 cells. L6 showed a marked decrease in membrane fluidity at 72 h and starts to increase at 92 h. As expected, NIH3T3 cells have more rigid membrane at earlier time points. On the other hand, neurons tend to have the highest membrane fluidity at early time points emphasizing its correlation with plasticity and the need for this malleability during differentiation. This study sheds light on the involvement of membrane fluidity during neuronal differentiation and development of other cell lines.
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Pakiza Noutsi
Full Text Available Cell membrane is made up of a complex structure of lipids and proteins that diffuse laterally giving rise to what we call membrane fluidity. During cellular development, such as differentiation cell membranes undergo dramatic fluidity changes induced by proteins such as ARC and Cofilin among others. In this study we used the generalized polarization (GP property of fluorescent probe Laurdan using two-photon microscopy to determine membrane fluidity as a function of time and for various cell lines. A low GP value corresponds to a higher fluidity and a higher GP value is associated with a more rigid membrane. Four different cell lines were monitored such as hN2, NIH3T3, HEK293 and L6 cells. Membrane fluidity was measured at 12h, 72h and 92 h. Our results show significant changes in membrane fluidity among all cell types at different time points. GP values tend to increase significantly within 92 h in hN2 cells and 72 h in NIH3T3 cells and only at 92 h in HEK293 cells. L6 showed a marked decrease in membrane fluidity at 72 h and starts to increase at 92 h. As expected, NIH3T3 cells have more rigid membrane at earlier time points. On the other hand, neurons tend to have the highest membrane fluidity at early time points emphasizing its correlation with plasticity and the need for this malleability during differentiation. This study sheds light on the involvement of membrane fluidity during neuronal differentiation and development of other cell lines.
Institute of Scientific and Technical Information of China (English)
罗少盈; 刘琦
2014-01-01
In this article, we concern the motion of relativistic membranes and null mem-branes in the Reissner-Nordstr¨om space-time. The equation of relativistic membranes moving in the Reissner-Nordstr¨om space-time is derived and some properties are discussed. Spherical symmetric solutions for the motion are illustrated and some interesting physical phenomena are discovered. The equations of the null membranes are derived and the exact solutions are also given. Spherical symmetric solutions for null membranes are just the two horizons of Reissner-Nordstr¨om space-time.
Gornyi, I. V.; Dmitriev, A. P.; Mirlin, A. D.; Protopopov, I. V.
2016-08-01
We have studied the motion of an electron in a membrane under the influence of flexural vibrations with a correlator that decreases upon an increase in the distance in accordance with the law r-2η. We have conducted a detailed consideration of the case with η < 1/2, in which the perturbation theory is inapplicable, even for an arbitrarily weak interaction. It is shown that, in this case, reciprocal quantum time 1/τ q is proportional to g 1/(1-η) T (2-η)/(2-2η), where g is the electron-phonon interaction constant and T is the temperature. The method developed here is applied for calculating the electron density of states in a magnetic field perpendicular to the membrane. In particular, it is shown that the Landau levels in the regime with ω c τ q » 1 have a Gaussian shape with a width that depends on the magnetic field as B η. In addition, we calculate the time τφ of dephasing of the electron wave function that emerges due to the interaction with flexural phonons for η < 1/2. It has been shown that, in several temperature intervals, quantity 1/τφ can be expressed by various power functions of the electron-phonon interaction constant, temperature, and electron energy.
Takou, E; Takou, Etienne; Noutchegueme, Norbert
2005-01-01
We prove a global in time existence theorem for the initial values problem for the Einstein-Boltzmann system with cosmological constant and arbitrarily large initial data, in the spatially homogeneous case, in a Robertson-Walker space-time.
Energy Technology Data Exchange (ETDEWEB)
Vedia, V., E-mail: mv.vedia@ucm.es [Grupo de Física Nuclear, Facultad de CC. Físicas, Universidad Complutense, CEI Moncloa, ES-28040 Madrid (Spain); Mach, H. [Grupo de Física Nuclear, Facultad de CC. Físicas, Universidad Complutense, CEI Moncloa, ES-28040 Madrid (Spain); National Centre for Nuclear Research, Division for Nuclear Physics, BP1, PL-00-681 Warsaw (Poland); Fraile, L.M.; Udías, J.M. [Grupo de Física Nuclear, Facultad de CC. Físicas, Universidad Complutense, CEI Moncloa, ES-28040 Madrid (Spain); Lalkovski, S. [Faculty of Physics, University of Sofia, St. Kliment Ohridski, BG-1164 Sofia (Bulgaria)
2015-09-21
We have characterized in depth the time response of three detectors equipped with cylindrical LaBr{sub 3}(Ce) crystals with dimensions of 1-in. in height and 1-in. in diameter, and having nominal Ce doping concentration of 5%, 8% and 10%. Measurements were performed at {sup 60}Co and {sup 22}Na γ-ray energies against a fast BaF{sub 2} reference detector. The time resolution was optimized by the choice of the photomultiplier bias voltage and the fine tuning of the parameters of the constant fraction discriminator, namely the zero-crossing and the external delay. We report here on the optimal time resolution of the three crystals. It is observed that timing properties are influenced by the amount of Ce doping and the crystal homogeneity. For the crystal with 8% of Ce doping the use of the ORTEC 935 CFD at very shorts delays in addition to the Hamamatsu R9779 PMT has made it possible to improve the LaBr{sub 3}(Ce) time resolution from the best literature value at {sup 60}Co photon energies to below 100 ps.
Ghahraman Afshar, Majid; Crespo, Gastón A; Bakker, Eric
2012-10-16
Ion-selective membranes based on porous polypropylene membranes doped with an ionophore and a lipophilic cation-exchanger are used here in a new tandem measurement mode that combines dynamic electrochemistry and zero current potentiometry into a single protocol. Open circuit potential measurements yield near-nernstian response slopes in complete analogy to established ion-selective electrode methodology. Such measurements are well established to give direct information on the so-called free ion concentration (strictly, activity) in the sample. The same membrane is here also operated in a constant current mode, in which the localized ion depletion at a transition time is visualized by chronopotentiometry. This dynamic electrochemistry methodology gives information on the labile ion concentration in the sample. The sequential protocol is established on potassium and calcium ion-selective membranes. An increase of the ionophore concentration in the membrane to 180 mM makes it possible to determine calcium concentrations as high as 3 mM by chronopotentiometry, thereby making it possible to directly detect total calcium in undiluted blood samples. Recovery times after current perturbation depend on the current amplitude but can be kept to below 1 min for the polypropylene based ion-selective membranes studied here. Plasticized PVC as membrane material is less suited for this protocol, especially when the measurement at elevated concentrations is desired. An analysis of current amplitudes, transition times, and concentrations shows that the data are described by the Sand equation and that migration effects are insignificant. A numerical model describes the experimental findings with good agreement and gives guidance on the required selectivity in order to observe a well-resolved transition time and on the expected errors due to insufficient selectivity. The simulations suggest that the methodology compares well to that of open circuit potentiometry, despite giving
Dizge, Nadir; Koseoglu-Imer, Derya Y; Karagunduz, Ahmet; Keskinler, Bulent
2013-01-01
The objective of this study was to investigate the influence of sludge retention time (SRT) on membrane bio-fouling. An activated sludge reactor was operated at three different SRTs (10, 30, and 50 days). Submerged membrane experiments were performed when the mixed liquor suspended solids (MLSS) concentration reached the steady state conditions. MLSS concentrations reached the steady state at 3,109 ± 194, 6,209 ± 123 and 6,609 ± 280 mg/L for SRTs of 10, 30 and 50 days, respectively. The total soluble microbial products (SMP) were 20.1 ± 3.7, 16.2 ± 7.2 and 28.2 ± 8.4 mg/L at SRTs of 10, 30, and 50 days, respectively. The carbohydrate concentration in the supernatant was about two times more for SRT of 10 days than that for 50 days. The total amount of extracellular polymeric substances (EPS) extracted from the flocs were approximately 74.9 ± 11.9, 67.8 ± 15.0 and 67.5 ± 17.4 mg/g MLSS at three SRTs (10, 30, and 50 days) under the same organic loading rate. The viscosity of the biomass increased with the increasing SRT. The results of flux stepping tests showed that the membrane fouling at SRT 10 days was always higher than that of 30 and 50 days. Four different microfiltration membranes (cellulose acetate, polyethersulfone, mixed ester, and polycarbonate) with three different pore sizes (0.45, 0.22, 0.10 μm) were tested. Filtration resistances were determined for each membrane. Cake resistance was observed to be the most significant fouling mechanism for all membranes.
Yu, Hao; Gupta, Amar Nath; Liu, Xia; Neupane, Krishna; Brigley, Angela M; Sosova, Iveta; Woodside, Michael T
2012-09-04
Protein folding is described conceptually in terms of diffusion over a configurational free-energy landscape, typically reduced to a one-dimensional profile along a reaction coordinate. In principle, kinetic properties can be predicted directly from the landscape profile using Kramers theory for diffusive barrier crossing, including the folding rates and the transition time for crossing the barrier. Landscape theory has been widely applied to interpret the time scales for protein conformational dynamics, but protein folding rates and transition times have not been calculated directly from experimentally measured free-energy profiles. We characterized the energy landscape for native folding of the prion protein using force spectroscopy, measuring the change in extension of a single protein molecule at high resolution as it unfolded/refolded under tension. Key parameters describing the landscape profile were first recovered from the distributions of unfolding and refolding forces, allowing the diffusion constant for barrier crossing and the transition path time across the barrier to be calculated. The full landscape profile was then reconstructed from force-extension curves, revealing a double-well potential with an extended, partially unfolded transition state. The barrier height and position were consistent with the previous results. Finally, Kramers theory was used to predict the folding rates from the landscape profile, recovering the values observed experimentally both under tension and at zero force in ensemble experiments. These results demonstrate how advances in single-molecule theory and experiment are harnessing the power of landscape formalisms to describe quantitatively the mechanics of folding.
Liu, Tao; Yan, Shaoze; Zhang, Wei
2016-06-01
Deployable structures have been widely used in on-orbit servicing spacecrafts, and the vibration properties of such structures have become increasingly important in the aerospace industry. The constant-Q nonstationary Gabor transform (CQ-NSGT) is introduced in this paper to accurately evaluate the variation in the frequency and amplitude of vibration signals along with time. First, an example signal is constructed on the basis of the vibration properties of deployable structures and is processed by the short-time Fourier transform, Wigner-Ville distribution, Hilbert-Huang transform, and CQ-NSGT. Results show that time and frequency resolutions are simultaneously fine only by employing CQ-NSGT. Subsequently, a zero padding operation is conducted to correct the calculation error at the end of the transform results. Finally, a set of experimental devices is constructed. The vibration signal of the experimental mode is processed by CQ-NSGT. On this basis, the experimental signal properties are discussed. This time-frequency method may be useful for formulating the dynamics for complex deployable structures.
Glawe, G. E.; Holanda, R.; Krause, L. N.
1978-01-01
Performance characteristics were experimentally determined for several sizes of a shielded and unshielded thermocouple probe design. The probes are of swaged construction and were made of type K wire with a stainless steel sheath and shield and MgO insulation. The wire sizes ranged from 0.03- to 1.02-mm diameter for the unshielded design and from 0.16- to 0.81-mm diameter for the shielded design. The probes were tested through a Mach number range of 0.2 to 0.9, through a temperature range of room ambient to 1420 K, and through a total-pressure range of 0.03 to 0.2.2 MPa (0.3 to 22 atm). Tables and graphs are presented to aid in selecting a particular type and size. Recovery corrections, radiation corrections, and time constants were determined.
Gupta, Sharad; Gui, Dong; Zandi, Roya; Gill, Sarjeet; Mohideen, Umar
2014-03-01
Melittin is an anti-bacterial and hemolytic toxic peptide found in bee venom. Cell lysis behavior of peptides has been widely investigated, but the exact interaction mechanism of lytic peptides with lipid membranes and its constituents has not been understood completely. In this paper we study the melittin interaction with lipid plasma membranes in real time using non-invasive and non-contact fluorescence interference contrast microscopy (FLIC). Particularly the interaction of melittin with plasma membranes was studied in a controlled molecular environment, where these plasma membrane were composed of saturated lipid, 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) and unsaturated lipid, 1,2-dioleoyl-sn-glycero-3-phosphocholine(DOPC) with and without cholesterol. We found out that melittin starts to form nanometer size pores in the plasma membranes shortly after interacting with membranes. But the addition of cholesterol in plasma membrane slows down the pore formation process. Our results show that inclusion of cholesterol to the plasma membranes make them more resilient towards pore formation and lysis of membrane.
Dennis, Elise A; Gundlach-Graham, Alexander W; Ray, Steven J; Enke, Christie G; Barinaga, Charles J; Koppenaal, David W; Hieftje, Gary M
2014-11-01
In this study, we demonstrate the performance of a new mass spectrometry concept called zoom time-of-flight mass spectrometry (zoom-TOFMS). In our zoom-TOFMS instrument, we combine two complementary types of TOFMS: conventional, constant-energy acceleration (CEA) TOFMS and constant-momentum acceleration (CMA) TOFMS to provide complete mass-spectral coverage as well as enhanced resolution and duty factor for a narrow, targeted mass region, respectively. Alternation between CEA- and CMA-TOFMS requires only that electrostatic instrument settings (i.e., reflectron and ion optics) and ion acceleration conditions be changed. The prototype zoom-TOFMS instrument has orthogonal-acceleration geometry, a total field-free distance of 43 cm, and a direct-current glow-discharge ionization source. Experimental results demonstrate that the CMA-TOFMS "zoom" mode offers resolution enhancement of 1.6 times over single-stage acceleration CEA-TOFMS. For the atomic mass range studied here, the maximum resolving power at full-width half-maximum observed for CEA-TOFMS was 1,610 and for CMA-TOFMS the maximum was 2,550. No difference in signal-to-noise (S/N) ratio was observed between the operating modes of zoom-TOFMS when both were operated at equivalent repetition rates. For a 10-kHz repetition rate, S/N values for CEA-TOFMS varied from 45 to 990 and from 67 to 10,000 for CMA-TOFMS. This resolution improvement is the result of a linear TOF-to-mass scale and the energy-focusing capability of CMA-TOFMS. Use of CMA also allows ions outside a given m/z range to be rejected by simple ion-energy barriers to provide a substantial improvement in duty factor.
Novel Membrane-Based Electrochemical Sensor for Real-Time Bio-Applications
Directory of Open Access Journals (Sweden)
Fatima AlZahra'a Alatraktchi
2014-11-01
Full Text Available This article presents a novel membrane-based sensor for real-time electrochemical investigations of cellular- or tissue cultures. The membrane sensor enables recording of electrical signals from a cell culture without any signal dilution, thus avoiding loss of sensitivity. Moreover, the porosity of the membrane provides optimal culturing conditions similar to existing culturing techniques allowing more efficient nutrient uptake and molecule release. The patterned sensor electrodes were fabricated on a porous membrane by electron-beam evaporation. The electrochemical performance of the membrane electrodes was characterized by cyclic voltammetry and chronoamperometry, and the detection of synthetic dopamine was demonstrated down to a concentration of 3.1 pM. Furthermore, to present the membrane-sensor functionality the dopamine release from cultured PC12 cells was successfully measured. The PC12 cells culturing experiments showed that the membrane-sensor was suitable as a cell culturing substrate for bio-applications. Real-time measurements of dopamine exocytosis in cell cultures were performed, where the transmitter release was recorded at the point of release. The developed membrane-sensor provides a new functionality to the standard culturing methods, enabling sensitive continuous in vitro monitoring and closely mimicking the in vivo conditions.
Morimoto, Ryota; Hirata, Akimasa; Laakso, Ilkka; Ziskin, Marvin C.; Foster, Kenneth R.
2017-03-01
This study computes the time constants of the temperature elevations in human head and body models exposed to simulated radiation from dipole antennas, electromagnetic beams, and plane waves. The frequency range considered is from 1 to 30 GHz. The specific absorption rate distributions in the human models are first computed using the finite-difference time-domain method for the electromagnetics. The temperature elevation is then calculated by solving the bioheat transfer equation. The computational results show that the thermal time constants (defined as the time required to reach 63% of the steady state temperature elevation) decrease with the elevation in radiation frequency. For frequencies higher than 4 GHz, the computed thermal time constants are smaller than the averaging time prescribed in the ICNIRP guidelines, but larger than the averaging time in the IEEE standard. Significant differences between the different head models are observed at frequencies higher than 10 GHz, which is attributable to the heat diffusion from the power absorbed in the pinna. The time constants for beam exposures become large with the increase in beam diameter. The thermal time constant in the brain is larger than that in the superficial tissues at high frequencies, because the brain temperature elevation is caused by the heat conduction of energy absorbed in the superficial tissue. The thermal time constant is minimized with an ideal beam with a minimum investigated diameter of 10 mm this minimal time constant is approximately 30 s and is almost independent of the radiation frequency, which is supported by analytic methods. In addition, the relation between the time constant, as defined in this paper, and ‘averaging time’ as it appears in the exposure limits is discussed, especially for short intense pulses. Similar to the laser guidelines, provisions should be included in the limits to limit the fluence for such pulses.
Berezhkovskii, Alexander M.; Hummer, Gerhard; Bezrukov, Sergey M.
2006-07-01
We study the distribution of direct translocation times for particles passing through membrane channels connecting two reservoirs. The direct translocation time is a conditional first-passage time defined as the residence time of the particle in the channel while passing to the other side of the membrane directly, i.e., without returning to the reservoir from which it entered. We show that the distributions of direct translocation times are identical for translocation in both directions, independent of any asymmetry in the potential across the channel and, hence, the translocation probabilities.
Directory of Open Access Journals (Sweden)
W. Zhang
2015-03-01
Full Text Available Abstract This work examines the influence of the residence-time distribution (RTD of surface elements on a model of cross-flow microfiltration that has been proposed recently (Hasan et al., 2013. Along with the RTD from the previous work (Case 1, two other RTD functions (Cases 2 and 3 are used to develop theoretical expressions for the permeate-flux decline and cake buildup in the filter as a function of process time. The three different RTDs correspond to three different startup conditions of the filtration process. The analytical expressions for the permeate flux, each of which contains three basic parameters (membrane resistance, specific cake resistance and rate of surface renewal, are fitted to experimental permeate flow rate data in the microfiltration of fermentation broths in laboratory- and pilot-scale units. All three expressions for the permeate flux fit the experimental data fairly well with average root-mean-square errors of 4.6% for Cases 1 and 2, and 4.2% for Case 3, respectively, which points towards the constructive nature of the model - a common feature of theoretical models used in science and engineering.
Directory of Open Access Journals (Sweden)
Yoon-Ho Kim
2016-01-01
Full Text Available The equivalent test circuit that can deliver both short-circuit current and recovery voltage is used to verify the performance of high-voltage circuit breakers. Most of the parameters in this circuit can be obtained by using a simple calculation or a simulation program. The ratings of the circuit breaker include rated short-circuit breaking current, rated short-circuit making current, rated operating sequence of the circuit breaker and rated short-time current. Among these ratings, the short-circuit making capacity of the circuit breaker is expressed in peak value and not in RMS value similar to breaking capacity. A series resistor or super-excitation is used to control the peak value of the short-circuit current in the equivalent test circuit. When using a series resistor, a higher rating of circuit breakers leads to a higher thermal capacity, thereby requiring additional space. Therefore, an effective, optimal design of the series resistor is essential. This paper proposes a method for reducing thermal capacity and selecting the optimal resistance to limit the making current by controlling the DC time constant of the test circuit.
Directory of Open Access Journals (Sweden)
Daisuke Miyashiro
2015-01-01
Full Text Available During their chemotactic swimming toward eggs, sperm cells detect their species-specific chemoattractant and sense concentration gradients by unknown mechanisms. After sensing the attractant, sperm cells commonly demonstrate a series of responses involving different swimming patterns by changing flagellar beats, gradually approaching a swimming path toward the eggs, which is the source of chemoattractants. Shiba et al. observed a rapid increase in intracellular Ca2+ concentrations in Ciona spermatozoa after sensing chemoattractants; however, the biochemical processes occurring inside the sperm cells are unclear. In the present study, we focused on the timing and sensing mechanism of chemical signal detection in Ciona. One of the most crucial problems to be solved is defining the initial epoch of chemotactic responses. We adopted a high rate of video recording (600 Hz for detailed analysis of sperm motion and a novel method for detecting subtle signs of beat forms and moving paths of sperm heads. From these analyses, we estimated a virtual sensing point of the attractant before initiation of motility responses and found that the time delay from sensing to motility responses was almost constant. To evaluate the efficiency of this constant delay model, we performed computer simulation of chemotactic behaviors of Ciona spermatozoa.
Miyashiro, Daisuke; Shiba, Kogiku; Miyashita, Tahahiro; Baba, Shoji A.; Yoshida, Manabu; Kamimura, Shinji
2015-01-01
ABSTRACT During their chemotactic swimming toward eggs, sperm cells detect their species-specific chemoattractant and sense concentration gradients by unknown mechanisms. After sensing the attractant, sperm cells commonly demonstrate a series of responses involving different swimming patterns by changing flagellar beats, gradually approaching a swimming path toward the eggs, which is the source of chemoattractants. Shiba et al. observed a rapid increase in intracellular Ca2+ concentrations in Ciona spermatozoa after sensing chemoattractants; however, the biochemical processes occurring inside the sperm cells are unclear. In the present study, we focused on the timing and sensing mechanism of chemical signal detection in Ciona. One of the most crucial problems to be solved is defining the initial epoch of chemotactic responses. We adopted a high rate of video recording (600 Hz) for detailed analysis of sperm motion and a novel method for detecting subtle signs of beat forms and moving paths of sperm heads. From these analyses, we estimated a virtual sensing point of the attractant before initiation of motility responses and found that the time delay from sensing to motility responses was almost constant. To evaluate the efficiency of this constant delay model, we performed computer simulation of chemotactic behaviors of Ciona spermatozoa. PMID:25572419
Miyashiro, Daisuke; Shiba, Kogiku; Miyashita, Tahahiro; Baba, Shoji A; Yoshida, Manabu; Kamimura, Shinji
2015-01-08
During their chemotactic swimming toward eggs, sperm cells detect their species-specific chemoattractant and sense concentration gradients by unknown mechanisms. After sensing the attractant, sperm cells commonly demonstrate a series of responses involving different swimming patterns by changing flagellar beats, gradually approaching a swimming path toward the eggs, which is the source of chemoattractants. Shiba et al. observed a rapid increase in intracellular Ca(2+) concentrations in Ciona spermatozoa after sensing chemoattractants; however, the biochemical processes occurring inside the sperm cells are unclear. In the present study, we focused on the timing and sensing mechanism of chemical signal detection in Ciona. One of the most crucial problems to be solved is defining the initial epoch of chemotactic responses. We adopted a high rate of video recording (600 Hz) for detailed analysis of sperm motion and a novel method for detecting subtle signs of beat forms and moving paths of sperm heads. From these analyses, we estimated a virtual sensing point of the attractant before initiation of motility responses and found that the time delay from sensing to motility responses was almost constant. To evaluate the efficiency of this constant delay model, we performed computer simulation of chemotactic behaviors of Ciona spermatozoa.
Poudel, Kumud R.; Dong, Yongming; Yu, Hang; Su, Allen; Ho, Thuong; Liu, Yan; Schulten, Klaus; Bai, Jihong
2016-01-01
Numerous proteins act in concert to sculpt membrane compartments for cell signaling and metabolism. These proteins may act as curvature sensors, membrane benders, and scaffolding molecules. Here we show that endophilin, a critical protein for rapid endocytosis, quickly transforms from a curvature sensor into an active bender upon membrane association. We find that local membrane deformation does not occur until endophilin inserts its amphipathic helices into lipid bilayers, supporting an active bending mechanism through wedging. Our time-course studies show that endophilin continues to drive membrane changes on a seconds-to-minutes time scale, indicating that the duration of endocytosis events constrains the mode of endophilin action. Finally, we find a requirement of coordinated activities between wedging and scaffolding for endophilin to produce stable membrane tubules in vitro and to promote synaptic activity in vivo. Together these data demonstrate that endophilin is a multifaceted molecule that precisely integrates activities of sensing, bending, and stabilizing curvature to sculpt membranes with speed. PMID:27170174
Best timing for replacement of membrane of ion-exchange membrane electrolyzer%离子膜电解槽的最佳换膜时机
Institute of Scientific and Technical Information of China (English)
王宏
2012-01-01
介绍了离子膜电解装置中离子膜的经济使用寿命，分析计算了更换离子膜的最佳时机。合理确定离子膜换膜时间，有利于离子膜制碱能源利用效率的提高，降低生产成本。%Introduced the economic life of the ion-exchange membrane in manufacture of ion-exchange membrane alkaline. Analyzed and calculated the best time to be replaced ion-exchange membrane in our company. The drop in market price of ion-exchange membrane causes changing ion-exchange membrane time ahead of time, improves energy utilization efficiency in manufacture of ion-exchange membrane caustic soda and reduces the production costs.
DEFF Research Database (Denmark)
Al Shakhshir, Saher; Berning, Torsten; Kær, Søren Knudsen
2016-01-01
by introducing 1% of nitrogen concentration to the dry and humidified hydrogen flow simulating the PEMFC anode outlet. The hot wire voltage is measured with and without nitrogen and it was slightly lower with the presence of nitrogen. The effect of the voltage reduction on the measured water balance is small....... This is due to the effect of 1% nitrogen on power law constant’s “m” which can be used in determining the water balance as explained in previous work was extremely low. Thus, the hot wire technique for measuring the PEMFC water balance is still accurate with the nitrogen cross-over......A novel method to obtain an ad-hoc and real time electrical signal of the PEMFC water balance by employing a constant temperature hot wire anemometry has been developed by our fuel cell research group. In this work, the effect of nitrogen-cross over on this method is experimentally demonstrated...
Sasaoka, K; Ogawa, K
1990-11-01
Some of our earlier reports have dealt with experiments on the central caudal arteries of a series of anesthetized rats. The results of these experiments were expressed by a relationship derived from the Windkessel theory where f(t) = alpha dz(t)/dt + beta z(t). When this theory is used, the measured blood flow forms f(t) and calculated wave forms alpha dz(t)/dt + beta z(t) agree closely. In these studies, we discovered that, when blood flow adz(t)/dt + beta z(t) agree closely. In these studies, we discovered that, when blood flow decreases, CR (time constant tau, the product of the blood vessel compliance C and the peripheral resistance R) values increase and vary widely. In the present study, 1) we investigated changes in CR when blood flow increases, and, 2) the method of least squares was used in calculating the formula given above. We achieved a better conformity between measured blood flow and calculated blood flow and perceived a clearer relationship between mean blood flow and CR than when they were calculated by the old method.
Boyle, Patrick J; Büchner, Andreas; Stone, Michael A; Lenarz, Thomas; Moore, Brian C J
2009-04-01
Cochlear implants usually employ an automatic gain control (AGC) system as a first stage of processing. AGC1 was a fast-acting (syllabic) compressor. AGC2 was a dual-time-constant system; it usually performed as a slow-acting compressor, but incorporated an additional fast-acting system to provide protection from sudden increases in sound level. Six experienced cochlear-implant users were tested in a counterbalanced order, receiving one-month of experience with a given AGC type before switching to the other type. Performance was evaluated shortly after provision of a given AGC type and after one-month of experience with that AGC type. Questionnaires, mainly relating to listening in quiet situations, did not reveal significant differences between the two AGC types. However, fixed-level and roving-level tests of sentence identification in noise both revealed significantly better performance for AGC2. It is suggested that the poorer performance for AGC1 occurred because AGC1 introduced cross-modulation between the target speech and background noise, which made perceptual separation of the target and background more difficult.
Plein, Michaela; Längsfeld, Laura; Neuschulz, Eike Lena; Schultheiss, Christina; Ingmann, Lili; Töpfer, Till; Böhning-Gaese, Katrin; Schleuning, Matthias
2013-06-01
along gradients of structural diversity at the landscape scale. Although seasonal fluctuations influenced the functional diversity of avian frugivore communities, we found constant interaction diversity of plant-frugivore networks in space and time, probably due to the functional redundancy of frugivorous birds. These findings indicate a high robustness of avian frugivory to moderate levels of human-induced landscape modification in temperate ecosystems and call for studies testing the generality of these findings for ultimate avian seed dispersal functions.
Berengut, J. C.; Dzuba, V. A.; Flambaum, V. V.; King, J. A.; Kozlov, M. G.; Murphy, M. T.; Webb, J. K.
2010-11-01
Current theories that seek to unify gravity with the other fundamental interactions suggest that spatial and temporal variation of fundamental constants is a possibility, or even a necessity, in an expanding Universe. Several studies have tried to probe the values of constants at earlier stages in the evolution of the Universe, using tools such as big-bang nucleosynthesis, the Oklo natural nuclear reactor, quasar absorption spectra, and atomic clocks (see, e.g. Flambaum & Berengut (2009)).
Directory of Open Access Journals (Sweden)
Martin Andrew R
2012-05-01
Full Text Available Abstract Background Expiratory time constants are used to quantify emptying of the lung as a whole, and emptying of individual lung compartments. Breathing low-density helium/oxygen mixtures may modify regional time constants so as to redistribute ventilation, potentially reducing gas trapping and hyperinflation for patients with obstructive lung disease. In the present work, bench and mathematical models of the lung were used to study the influence of heterogeneous patterns of obstruction on compartmental and whole-lung time constants. Methods A two-compartment mechanical test lung was used with the resistance in one compartment held constant, and a series of increasing resistances placed in the opposite compartment. Measurements were made over a range of lung compliances during ventilation with air or with a 78/22% mixture of helium/oxygen. The resistance imposed by the breathing circuit was assessed for both gases. Experimental results were compared with predictions of a mathematical model applied to the test lung and breathing circuit. In addition, compartmental and whole-lung time constants were compared with those reported by the ventilator. Results Time constants were greater for larger minute ventilation, and were reduced by substituting helium/oxygen in place of air. Notably, where time constants were long due to high lung compliance (i.e. low elasticity, helium/oxygen improved expiratory flow even for a low level of resistance representative of healthy, adult airways. In such circumstances, the resistance imposed by the external breathing circuit was significant. Mathematical predictions were in agreement with experimental results. Time constants reported by the ventilator were well-correlated with those determined for the whole-lung and for the low-resistance compartment, but poorly correlated with time constants determined for the high-resistance compartment. Conclusions It was concluded that breathing a low-density gas mixture, such
Hasegawa, Taisuke
2016-11-07
We propose a novel molecular dynamics (MD) algorithm for approximately dealing with a nuclear quantum dynamics in a real-time MD simulation. We have found that real-time dynamics of the ensemble of classical particles acquires quantum nature by introducing a constant quantum mechanical uncertainty constraint on its classical dynamics. The constant uncertainty constraint is handled by the Lagrange multiplier method and implemented into a conventional MD algorithm. The resulting constant uncertainty molecular dynamics (CUMD) is applied to the calculation of quantum position autocorrelation functions on quartic and Morse potentials. The test calculations show that CUMD gives better performance than ring-polymer MD because of the inclusion of the quantum zero-point energy during real-time evolution as well as the quantum imaginary-time statistical effect stored in an initial condition. The CUMD approach will be a possible starting point for new real-time quantum dynamics simulation in condensed phase.
Directory of Open Access Journals (Sweden)
G. T. Kulakov
2008-01-01
Full Text Available The paper is devoted to computational investigation of influence relative time constant of an object which changes in broad band on quality of steam temperature control behind a boiler with due account of value of regulating action in the system with PI- and PID- regulator. The simulation has been based on a single-loop automatic control system (ACS. It has been revealed that the less value of the relative time constant of an object leads to more integral control error in system with PID- regulator while operating external ACS perturbation. Decrease of numerical value of relative time constant of an object while operating external perturbation causes decrease of relative time concerning appearance of maximum dynamic control error from common relative control time.
Hasegawa, Taisuke
2016-11-01
We propose a novel molecular dynamics (MD) algorithm for approximately dealing with a nuclear quantum dynamics in a real-time MD simulation. We have found that real-time dynamics of the ensemble of classical particles acquires quantum nature by introducing a constant quantum mechanical uncertainty constraint on its classical dynamics. The constant uncertainty constraint is handled by the Lagrange multiplier method and implemented into a conventional MD algorithm. The resulting constant uncertainty molecular dynamics (CUMD) is applied to the calculation of quantum position autocorrelation functions on quartic and Morse potentials. The test calculations show that CUMD gives better performance than ring-polymer MD because of the inclusion of the quantum zero-point energy during real-time evolution as well as the quantum imaginary-time statistical effect stored in an initial condition. The CUMD approach will be a possible starting point for new real-time quantum dynamics simulation in condensed phase.
Directory of Open Access Journals (Sweden)
Natalia Mendez
Full Text Available Surprisingly, in our modern 24/7 society, there is scant information on the impact of developmental chronodisruption like the one experienced by shift worker pregnant women on fetal and postnatal physiology. There are important differences between the maternal and fetal circadian systems; for instance, the suprachiasmatic nucleus is the master clock in the mother but not in the fetus. Despite this, several tissues/organs display circadian oscillations in the fetus. Our hypothesis is that the maternal plasma melatonin rhythm drives the fetal circadian system, which in turn relies this information to other fetal tissues through corticosterone rhythmic signaling. The present data show that suppression of the maternal plasma melatonin circadian rhythm, secondary to exposure of pregnant rats to constant light along the second half of gestation, had several effects on fetal development. First, it induced intrauterine growth retardation. Second, in the fetal adrenal in vivo it markedly affected the mRNA expression level of clock genes and clock-controlled genes as well as it lowered the content and precluded the rhythm of corticosterone. Third, an altered in vitro fetal adrenal response to ACTH of both, corticosterone production and relative expression of clock genes and steroidogenic genes was observed. All these changes were reversed when the mother received a daily dose of melatonin during the subjective night; supporting a role of melatonin on overall fetal development and pointing to it as a 'time giver' for the fetal adrenal gland. Thus, the present results collectively support that the maternal circadian rhythm of melatonin is a key signal for the generation and/or synchronization of the circadian rhythms in the fetal adrenal gland. In turn, low levels and lack of a circadian rhythm of fetal corticosterone may be responsible of fetal growth restriction; potentially inducing long term effects in the offspring, possibility that warrants further
Lotosh, T A; Vinogradova, I A; Iliukha, V A; Khizhkin, E A
2013-06-01
The influence of constant lightening on biomarkers of ageing and rates of male rats aging was studied. It was revealed that the maintenance of rats in the constant lightening regime starting from the age of one month results in accelerated ageing of the organism, the reduction of the phases progressive and stable growth, early occurrence of presenile and senile periods, to the earlier occurrence of water-and-salt metabolism imbalance, accelerate the process of "aging" of the antioxidant system in comparison with the rates of the control group. On the contrary, the maintenance of rats in the constant lightening regime starting from the age of fourteen months slows ageing of the organism, increases body growth, delays appearance of pathological changes in the urine, slows down the "aging" of the enzymatic components of the antioxidant system.
Damour, Thibault Marie Alban Guillaume
2003-01-01
We review some string-inspired theoretical models which incorporate a correlated spacetime variation of coupling constants while remaining naturally compatible both with phenomenological constraints coming from geochemical data (Oklo; Rhenium decay) and with present equivalence principle tests. Barring unnatural fine-tunings of parameters, a variation of the fine-structure constant as large as that recently ``observed'' by Webb et al. in quasar absorption spectra appears to be incompatible with these phenomenological constraints. Independently of any model, it is emphasized that the best experimental probe of varying constants are high-precision tests of the universality of free fall, such as MICROSCOPE and STEP. Recent claims by Bekenstein that fine-structure-constant variability does not imply detectable violations of the equivalence principle are shown to be untenable.
Cover, Keith S
2008-01-01
While the multiexponential nature of T2 decays measured in vivo is well known, characterizing T2 decays by a single time constant is still very useful when differentiating among structures and pathologies in MRI images. A novel, robust, fast and very simple method is presented for both estimating and displaying the average time constant for the T2 decay of each pixel from a multiecho MRI sequence. The average time constant is calculated from the average of the values measured from the T2 decay over many echoes. For a monoexponential decay, the normalized decay average varies monotonically with the time constant. Therefore, it is simple to map any normalized decay average to an average time constant. This method takes advantage of the robustness of the normalized decay average to both artifacts and multiexponential decays. Color intensity projections (CIPs) were used to display 32 echoes acquired at a 10ms spacing as a single color image. The brightness of each pixel in each color image was determined by the i...
Cell membrane-anchored biosensors for real-time monitoring of the cellular microenvironment.
Qiu, Liping; Zhang, Tao; Jiang, Jianhui; Wu, Cuichen; Zhu, Guizhi; You, Mingxu; Chen, Xigao; Zhang, Liqin; Cui, Cheng; Yu, Ruqin; Tan, Weihong
2014-09-24
Cell membrane-anchored biochemical sensors that allow real-time monitoring of the interactions of cells with their microenvironment would be powerful tools for studying the mechanisms underlying various biological processes, such as cell metabolism and signaling. Despite the significance of these techniques, unfortunately, their development has lagged far behind due to the lack of a desirable membrane engineering method. Here, we propose a simple, efficient, biocompatible, and universal strategy for one-step self-construction of cell-surface sensors using diacyllipid-DNA conjugates as the building and sensing elements. The sensors exploit the high membrane-insertion capacity of a diacyllipid tail and good sensing performance of the DNA probes. Based on this strategy, we have engineered specific DNAzymes on the cell membrane for metal ion assay in the extracellular microspace. The immobilized DNAzyme showed excellent performance for reporting and semiquantifying both exogenous and cell-extruded target metal ions in real time. This membrane-anchored sensor could also be used for multiple target detection by having different DNA probes inserted, providing potentially useful tools for versatile applications in cell biology, biomedical research, drug discovery, and tissue engineering.
Evolution of a Rippled Membrane during Phospholipase A2 Hydrolysis Studied by Time-Resolved AFM
DEFF Research Database (Denmark)
Leidy, Chad; Mouritsen, Ole G.; Jørgensen, Kent;
2004-01-01
The sensitivity of phospholipase A2 (PLA2) for lipid membrane curvature is explored by monitoring, through time-resolved atomic force microscopy, the hydrolysis of supported double bilayers in the ripple phase. The ripple phase presents a corrugated morphology. PLA2 is shown to have higher activi...
Yu, Meina; Zhou, Xiaochen; Jiang, Jinghua; Yang, Huai; Yang, Deng-Ke
2016-05-11
Chiral nematic liquid crystals possess a self-assembled helical structure and exhibit unique selective reflection in visible and infrared light regions. Their optical properties can be electrically tuned. The tuning involves the unwinding and restoring of the helical structure. We carried out an experimental study on the mechanism of the restoration of the helical structure. We constructed chiral nematic liquid crystals with variable elastic constants by doping bent-dimers and studied their impact on the restoration. With matched twist and bend elastic constants, the helical structure can be restored dramatically fast from the field-induced homeotropic state. Furthermore, defects can be eliminated to produce a perfect planar state which exhibits high selective reflection.
A Linear Time Complexity of Breadth-First Search Using P System with Membrane Division
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Einallah Salehi
2013-01-01
Full Text Available One of the known methods for solving the problems with exponential time complexity such as NP-complete problems is using the brute force algorithms. Recently, a new parallel computational framework called Membrane Computing is introduced which can be applied in brute force algorithms. The usual way to find a solution for the problems with exponential time complexity with Membrane Computing techniques is by P System with active membrane using division rule. It makes an exponential workspace and solves the problems with exponential complexity in a polynomial (even linear time. On the other hand, searching is currently one of the most used methods for finding solution for problems in real life, that the blind search algorithms are accurate, but their time complexity is exponential such as breadth-first search (BFS algorithm. In this paper, we proposed a new approach for implementation of BFS by using P system with division rule technique for first time. The theorem shows time complexity of BSF in this framework on randomly binary trees reduced from O(2d to O(d.
Odluyurt, Serhat
2011-01-01
The general purpose of this study was to examine the effectiveness of constant time delay embedded in activities for teaching clothes name for preschool children with developmental disabilities. This study included four participants having Down syndrome with an age range of 43-46 months. All experimental sessions were conducted in one to one…
Mizuta, Sora; Saito, Itsuro; Isoyama, Takashi; Hara, Shintaro; Yurimoto, Terumi; Li, Xinyang; Murakami, Haruka; Ono, Toshiya; Mabuchi, Kunihiko; Abe, Yusuke
2017-05-17
1/R control is a physiological control method of the total artificial heart (TAH) with which long-term survival was obtained with animal experiments. However, 1/R control occasionally diverged in the undulation pump TAH (UPTAH) animal experiment. To improve the control stability of the 1/R control, appropriate control time constant in relation to characteristics of the baroreflex vascular system was investigated with frequency analysis and numerical simulation. In the frequency analysis, data of five goats in which the UPTAH was implanted were analyzed with first Fourier transform technique to examine the vasomotion frequency. The numerical simulation was carried out repeatedly changing baroreflex parameters and control time constant using the elements-expanded Windkessel model. Results of the frequency analysis showed that the 1/R control tended to diverge when very low frequency band that was an indication of the vasomotion frequency was relative high. In numerical simulation, divergence of the 1/R control could be reproduced and the boundary curves between the divergence and convergence of the 1/R control varied depending on the control time constant. These results suggested that the 1/R control tended to be unstable when the TAH recipient had high reflex speed in the baroreflex vascular system. Therefore, the control time constant should be adjusted appropriately with the individual vasomotion frequency.
Akmanoglu, Nurgul; Kurt, Onur; Kapan, Alper
2015-01-01
The aim of the current study was to compare simultaneous prompting (SP) and constant time delay (CTD) in terms of their effectiveness and efficiency in teaching children with autism how to respond to questions about personal information. The adapted alternating treatments model was used in the study. Three male students with autism aged 4, 6, and…
Swain, Rasheeda; Lane, Justin D.; Gast, David L.
2015-01-01
Constant time delay (CTD) and simultaneous prompting (SP) are effective response prompting procedures for teaching students with moderate to severe disabilities. The purpose of this study was to compare the efficiency of CTD and SP when teaching functional sight words to four students, 8-11 years of age, with moderate intellectual disability (ID)…
Aykut, Cigil
2012-01-01
This study is aimed at comparing the effectiveness and efficiency of constant-time delay and most-to-least prompt procedures in teaching daily living skills to children with mental retardation. Adapted alternating treatment design was used. The outcome shows that both procedures were equally effective in teaching the daily living skills. However,…
Tucker Cohen, Elisabeth; Heller, Kathryn Wolff; Alberto, Paul; Fredrick, Laura D.
2008-01-01
The use of a three-step decoding strategy with constant time delay for teaching decoding and word reading to students with mild and moderate mental retardation was investigated in this study. A multiple probe design was used to examine the percentage of words correctly decoded and read as well as the percentage of sounds correctly decoded. The…
Nifant'eva, T I; Shkinev, V M; Spivakov, B Y; Burba, P
1999-02-01
The assessment of conditional stability constants of aquatic humic substance (HS) metal complexes is overviewed with special emphasis on the application of ultrafiltration methods. Fundamentals and limitations of stability functions in the case of macromolecular and polydisperse metal-HS species in aquatic environments are critically discussed. The review summarizes the advantages and application of ultrafiltration for metal-HS complexation studies, discusses the comparibility and reliability of stability constants. The potential of ultrafiltration procedures for characterizing the lability of metal-HS species is also stressed.
Energy Technology Data Exchange (ETDEWEB)
Ikeya, Tomohiko; Mita, Yuichi; Ishihara, Kaoru [Central Research Inst. of Electric Power Industry, Tokyo (Japan); Sawada, Nobuyuki [Hokkaido Electric Power, Sapporo (Japan); Takagi, Sakae; Murakami, Jun-ichi [Tohoku Electric Power, Sendai (Japan); Kobayashi, Kazuyuki [Tokyo Electric Power, Yokohama (Japan); Sakabe, Tetsuya [Chubu Electric Power, Nagoya (Japan); Kousaka, Eiichi [Hokuriku Electric Power, Toyama (Japan); Yoshioka, Haruki [The Kansai Electric Power, Osaka (Japan); Kato, Satoru [The Chugoku Electric Power, Hiroshima (Japan); Yamashita, Masanori [Shikoku Research Inst., Takamatsu (Japan); Narisoko, Hayato [The Okinawa Electric Power, Naha (Japan); Nishiyama, Kazuo [The Central Electric Power Council, Tokyo (Japan); Adachi, Kazuyuki [Kyushu Electric Power, Fukuoka (Japan)
1998-09-01
For the popularization of electric vehicles (EVs), the conditions for charging EV batteries with available current patterns should allow complete charging in a short time, i.e., less than 5 to 8 h. Therefore, in this study, a new charging condition is investigated for the EV valve-regulated lead/acid battery system, which should allow complete charging of EV battery systems with multi-step constant currents in a much shorter time with longer cycle life and higher energy efficiency compared with two-step constant-current charging. Although a high magnitude of the first current in the two-step constant-current method prolongs cycle life by suppressing the softening of positive active material, too large a charging current magnitude degrades cells due to excess internal evolution of heat. A charging current magnitude of approximately 0.5 C is expected to prolong cycle life further. Three-step charging could also increase the magnitude of charging current in the first step without shortening cycle life. Four-or six-step constant-current methods could shorten the charging time to less than 5 h, as well as yield higher energy efficiency and enhanced cycle life of over 400 cycles compared with two-step charging with the first step current of 0.5 C. Investigation of the degradation mechanism of the batteries revealed that the conditions of multi-step constant-current charging suppressed softening of positive active material and sulfation of negative active material, but, unfortunately, advanced the corrosion of the grids in the positive plates. By adopting improved grids and cooling of the battery system, the multistep constant-current method may enhance the cycle life. (orig.)
Mahdavi, Alireza; Haghighat, Fariborz; Bahloul, Ali; Brochot, Clothilde; Ostiguy, Claude
2015-06-01
It is necessary to investigate the efficiencies of filtering facepiece respirators (FFRs) exposed to ultrafine particles (UFPs) for long periods of time, since the particle loading time may potentially affect the efficiency of FFRs. This article aims to investigate the filtration efficiency for a model of electrostatic N95 FFRs with constant and 'inhalation-only' cyclic flows, in terms of particle loading time effect, using different humidity conditions. Filters were exposed to generated polydisperse NaCl particles. Experiments were performed mimicking an 'inhalation-only' scenario with a cyclic flow of 85 l min(-1) as the minute volume [or 170 l min(-1) as mean inhalation flow (MIF)] and for two constant flows of 85 and 170 l min(-1), under three relative humidity (RH) levels of 10, 50, and 80%. Each test was performed for loading time periods of 6h and the particle penetration (10-205.4nm in electrical mobility diameter) was measured once every 2h. For a 10% RH, the penetration of smaller size particles (time for both constant and cyclic flows. For 50 and 80% RH levels, the changes in penetration were typically observed in an opposite direction with less magnitude. The penetrations at MPPS increased with respect to loading time under constant flow conditions (85 and 170 l min(-1)): it did not substantially increase under cyclic flows. The comparison of the cyclic flow (85 l min(-1) as minute volume) and constant flow equal to the cyclic flow minute volume indicated that, for all conditions the penetration was significantly less for the constant flow than that of cyclic flow. The comparison between the cyclic (170 l min(-1) as MIF) and constant flow equal to cyclic flow MIF indicated that, for the initial stage of loading, the penetrations were almost equal, but they were different for the final stages of the loading time. For a 10% RH, the penetration of a wide range of sizes was observed to be higher with the cyclic flow (170 as MIF) than with the equivalent
Davidson, J. A.; Sadowski, C. M.; Schiff, H. I.; Howard, C. J.; Schmeltekopf, A. L.; Jennings, D. A.; Streit, G. E.
1976-01-01
Absolute rate constants for the deactivation of O(1D) atoms by some atmospheric gases have been determined by observing the time-resolved emission of O(1D) at 630 nm. O(1D) atoms were produced by the dissociation of ozone via repetitive laser pulses at 266 nm. Absolute rate constants for the relaxation of O(1D) at 298 K are reported for N2, O2, CO2, O3, H2, D2, CH4, HCl, NH3, H2O, N2O, and Ne. The results obtained are compared with previous relative and absolute measurements reported in the literature.
Energy Technology Data Exchange (ETDEWEB)
Robinson, H.P.; Potter, Elinor
1971-03-01
This collection of mathematical data consists of two tables of decimal constants arranged according to size rather than function, a third table of integers from 1 to 1000, giving some of their properties, and a fourth table listing some infinite series arranged according to increasing size of the coefficients of the terms. The decimal values of Tables I and II are given to 20 D.
Sparavigna, Amelia Carolina
2012-01-01
As proposed in a previous paper, the decorations of ancient objects can provide some information on the approximate evaluations of constant {\\pi}, the ratio of circumference to diameter. Here we discuss some disks found in the tomb of Hemaka, the chancellor of a king of the First Dynasty of Egypt, about 3000 BC. The discussion is based on measurements of the dimensionless ratio of lengths.
Tan, Songwen; Hou, Yang; Cui, Chunzhi; Chen, Xuncai; Li, Weiguo
2017-01-01
This work presents a novel, fast and simple monitoring-responding method at the very early stages of membrane bio-fouling in a membrane bioreactor (MBR) during saline wastewater treatment. The impacts of multiple environmental shocks on membrane fouling were studied. The transmembrane pressure exceeded the critical fouling pressure within 8days in the case of salinity shock or temperature shock. In the case of DO shock, the transmembrane pressure exceeded the critical fouling pressure after 16days, showing the lower impact of DO shock on the MBR. In another study, the membrane fouling was observed within 4days responding to mixed environmental shocks. To decrease the potential of membrane bio-fouling, another bioreactor was integrated immediately with the MBR as a quickly-responded countermeasure, when an early warning of membrane bio-fouling was provided. After the bioreactor enhancement, the time required for membrane fouling increased from 4 to 10days.
Directory of Open Access Journals (Sweden)
De Rosa Matteo
2017-03-01
Full Text Available In our previous research we have observed that the fluorescence emission from water solutions of Single-Walled Carbon Nano-Tubes (SWCNT, excited by a laser with a wavelength of 830nm, diminishes with the time. We have already proved that such a fading is a function of the storage time and the storage temperature. In order to study the emission of the SWCNT as a function of these two parameters we have designed and realized a special measurement compartment with a cuvette holder where the SWCNT solutions can be measured and stored at a fixed constant temperature for periods of time as long as several weeks. To maintain the measurement setup under a constant temperature we have designed special experimental setup based on two Peltier cells with electronic temperature control.
De Rosa, Matteo; De Nardo, Laura; Bello, Michele; Uzunov, Nikolay
2017-03-01
In our previous research we have observed that the fluorescence emission from water solutions of Single-Walled Carbon Nano-Tubes (SWCNT), excited by a laser with a wavelength of 830nm, diminishes with the time. We have already proved that such a fading is a function of the storage time and the storage temperature. In order to study the emission of the SWCNT as a function of these two parameters we have designed and realized a special measurement compartment with a cuvette holder where the SWCNT solutions can be measured and stored at a fixed constant temperature for periods of time as long as several weeks. To maintain the measurement setup under a constant temperature we have designed special experimental setup based on two Peltier cells with electronic temperature control.
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.
Learning of Precise Spike Times with Homeostatic Membrane Potential Dependent Synaptic Plasticity.
Directory of Open Access Journals (Sweden)
Christian Albers
Full Text Available Precise spatio-temporal patterns of neuronal action potentials underly e.g. sensory representations and control of muscle activities. However, it is not known how the synaptic efficacies in the neuronal networks of the brain adapt such that they can reliably generate spikes at specific points in time. Existing activity-dependent plasticity rules like Spike-Timing-Dependent Plasticity are agnostic to the goal of learning spike times. On the other hand, the existing formal and supervised learning algorithms perform a temporally precise comparison of projected activity with the target, but there is no known biologically plausible implementation of this comparison. Here, we propose a simple and local unsupervised synaptic plasticity mechanism that is derived from the requirement of a balanced membrane potential. Since the relevant signal for synaptic change is the postsynaptic voltage rather than spike times, we call the plasticity rule Membrane Potential Dependent Plasticity (MPDP. Combining our plasticity mechanism with spike after-hyperpolarization causes a sensitivity of synaptic change to pre- and postsynaptic spike times which can reproduce Hebbian spike timing dependent plasticity for inhibitory synapses as was found in experiments. In addition, the sensitivity of MPDP to the time course of the voltage when generating a spike allows MPDP to distinguish between weak (spurious and strong (teacher spikes, which therefore provides a neuronal basis for the comparison of actual and target activity. For spatio-temporal input spike patterns our conceptually simple plasticity rule achieves a surprisingly high storage capacity for spike associations. The sensitivity of the MPDP to the subthreshold membrane potential during training allows robust memory retrieval after learning even in the presence of activity corrupted by noise. We propose that MPDP represents a biophysically plausible mechanism to learn temporal target activity patterns.
Energy Technology Data Exchange (ETDEWEB)
Chamoun, N [Departamento de Fisica, Universidad Nacional de La Plata, cc67, 1900 La Plata (Argentina); Landau, S J [Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque, cp 1900 La Plata (Argentina); Mosquera, M E [Facultad de Ciencias Astronomicas y GeofIsicas, Universidad Nacional de La Plata, Paseo del Bosque, cp 1900 La Plata (Argentina); Vucetich, Hector [Departamento de Fisica, Universidad Nacional de La Plata, cc67, 1900 La Plata (Argentina)
2007-02-15
We use the semi-analytic method of Esmailzadeh et al (1991 Astrophys. J. 378 504-18) to calculate the abundances of helium and deuterium produced during Big Bang nucleosynthesis assuming the fine structure constant and the Higgs vacuum expectation value may vary in time. We analyse the dependence on the fundamental constants of the nucleon mass, nuclear binding energies and cross sections involved in the calculation of the abundances. Unlike previous works, we do not assume the chiral limit of QCD. Rather, we take into account the quark masses and consider the one-pion exchange potential, within perturbation theory, for the proton-neutron scattering. However, we do not consider the time variation of the strong interactions scale but attribute the changes in the quark masses to the temporal variation of the Higgs vacuum expectation value. Using the observational data of the helium and deuterium, we put constraints on the variation of the fundamental constants between the time of nucleosynthesis and the present time.
On Neuron Membrane Potential Distributions for Voltage and Time Dependent Current Modulation
Salig, J. B.; Carpio-Bernido, M. V.; Bernido, C. C.; Bornales, J. B.
Tracking variations of neuronal membrane potential in response to multiple synaptic inputs remains an important open field of investigation since information about neural network behavior and higher brain functions can be inferred from such studies. Much experimental work has been done, with recent advances in multi-electrode recordings and imaging technology giving exciting results. However, experiments have also raised questions of compatibility with available theoretical models. Here we show how methods of modern infinite dimensional analysis allow closed form expressions for important quantities rich in information such as the conditional probability density (cpd). In particular, we use a Feynman integral approach where fluctuations in the dynamical variable are parametrized with Hida white noise variables. The stochastic process described then gives variations in time of the relative membrane potential defined as the difference between the neuron membrane and firing threshold potentials. We obtain the cpd for several forms of current modulation coefficients reflecting the flow of synaptic currents, and which are analogous to drift coefficients in the configuration space Fokker-Planck equation. In particular, we consider cases of voltage and time dependence for current modulation for periodic and non-periodic oscillatory current modulation described by sinusoidal and Bessel functions.
Zaim, Slimane
2015-01-01
We study the effect of the non-commutativity on the creation of scalar particles from vacuum in the anisotropic universe space-time. We derive the deformed Klein-Gordon equation up to second order in the non-commutativity parameter using the general modified field equation. Then the canonical method based on Bogoliubov transformation is applied to calculate the probability of particle creation in vacuum and the corresponding number density in the $k$ mode. We deduce that the non-commutative space-time introduces a new source of particle creation.
Elliott, Mark A.; du Bois, Naomi
2017-01-01
From the point of view of the cognitive dynamicist the organization of brain circuitry into assemblies defined by their synchrony at particular (and precise) oscillation frequencies is important for the correct correlation of all independent cortical responses to the different aspects of a given complex thought or object. From the point of view of anyone operating complex mechanical systems, i.e., those comprising independent components that are required to interact precisely in time, it follows that the precise timing of such a system is essential – not only essential but measurable, and scalable. It must also be reliable over observations to bring about consistent behavior, whatever that behavior is. The catastrophic consequence of an absence of such precision, for instance that required to govern the interference engine in many automobiles, is indicative of how important timing is for the function of dynamical systems at all levels of operation. The dynamics and temporal considerations combined indicate that it is necessary to consider the operating characteristic of any dynamical, cognitive brain system in terms, superficially at least, of oscillation frequencies. These may, themselves, be forensic of an underlying time-related taxonomy. Currently there are only two sets of relevant and necessarily systematic observations in this field: one of these reports the precise dynamical structure of the perceptual systems engaged in dynamical binding across form and time; the second, derived both empirically from perceptual performance data, as well as obtained from theoretical models, demonstrates a timing taxonomy related to a fundamental operator referred to as the time quantum. In this contribution both sets of theory and observations are reviewed and compared for their predictive consistency. Conclusions about direct comparability are discussed for both theories of cognitive dynamics and time quantum models. Finally, a brief review of some experimental data
Improving dynamic performance of proton-exchange membrane fuel cell system using time delay control
Energy Technology Data Exchange (ETDEWEB)
Kim, Young-Bae [Mechanical Engineering Department, Chonnam National University, Gwangju (Korea)
2010-10-01
Transient behaviour is a key parameter for the vehicular application of proton-exchange membrane (PEM) fuel cell. The goal of this presentation is to construct better control technology to increase the dynamic performance of a PEM fuel cell. The PEM fuel cell model comprises a compressor, an injection pump, a humidifier, a cooler, inlet and outlet manifolds, and a membrane-electrode assembly. The model includes the dynamic states of current, voltage, relative humidity, stoichiometry of air and hydrogen, cathode and anode pressures, cathode and anode mass flow rates, and power. Anode recirculation is also included with the injection pump, as well as anode purging, for preventing anode flooding. A steady-state, isothermal analytical fuel cell model is constructed to analyze the mass transfer and water transportation in the membrane. In order to prevent the starvation of air and flooding in a PEM fuel cell, time delay control is suggested to regulate the optimum stoichiometry of oxygen and hydrogen, even when there are dynamical fluctuations of the required PEM fuel cell power. To prove the dynamical performance improvement of the present method, feed-forward control and Linear Quadratic Gaussian (LQG) control with a state estimator are compared. Matlab/Simulink simulation is performed to validate the proposed methodology to increase the dynamic performance of a PEM fuel cell system. (author)
Improving dynamic performance of proton-exchange membrane fuel cell system using time delay control
Kim, Young-Bae
Transient behaviour is a key parameter for the vehicular application of proton-exchange membrane (PEM) fuel cell. The goal of this presentation is to construct better control technology to increase the dynamic performance of a PEM fuel cell. The PEM fuel cell model comprises a compressor, an injection pump, a humidifier, a cooler, inlet and outlet manifolds, and a membrane-electrode assembly. The model includes the dynamic states of current, voltage, relative humidity, stoichiometry of air and hydrogen, cathode and anode pressures, cathode and anode mass flow rates, and power. Anode recirculation is also included with the injection pump, as well as anode purging, for preventing anode flooding. A steady-state, isothermal analytical fuel cell model is constructed to analyze the mass transfer and water transportation in the membrane. In order to prevent the starvation of air and flooding in a PEM fuel cell, time delay control is suggested to regulate the optimum stoichiometry of oxygen and hydrogen, even when there are dynamical fluctuations of the required PEM fuel cell power. To prove the dynamical performance improvement of the present method, feed-forward control and Linear Quadratic Gaussian (LQG) control with a state estimator are compared. Matlab/Simulink simulation is performed to validate the proposed methodology to increase the dynamic performance of a PEM fuel cell system.
Energy Technology Data Exchange (ETDEWEB)
Guerrero, C. [Centro de Investigaciones Medioambientales, Energéticas y Tecnológicas (CIEMAT), Madrid (Spain); Departamento de Física Atómica, Molecular y Nuclear, Universidad de Sevilla (Spain); Cano-Ott, D.; Mendoza, E. [Centro de Investigaciones Medioambientales, Energéticas y Tecnológicas (CIEMAT), Madrid (Spain); Wright, T. [University of Manchester, Manchester (United Kingdom)
2015-03-21
The effect of dead-time and pile-up in counting experiments may become a significant source of uncertainty if not properly taken into account. Although analytical solutions to this problem have been proposed for simple set-ups with one or two detectors, these are limited when it comes to arrays where time correlation between the detector modules is used, and also in situations of variable counting rates. In this paper we describe the dead-time and pile-up corrections applied to the n-TOF Total Absorption Calorimeter (TAC), a 4π γ-ray detector made of 40 BaF{sub 2} modules operating at the CERN n-TOF facility. Our method is based on the simulation of the complete signal detection and event reconstruction processes and can be applied as well in the case of rapidly varying counting rates. The method is discussed in detail and then we present its successful application to the particular case of the measurement of {sup 238}U(n, γ) reactions with the TAC detector.
Hong, S. D.; Fedors, R. F.; Schwarzl, F.; Moacanin, J.; Landel, R. F.
1981-01-01
A theoretical analysis of the tensile stress-strain relation of elastomers at constant strain rate is presented which shows that the time and the stress effect are separable if the experimental time scale coincides with a segment of the relaxation modulus that can be described by a single power law. It is also shown that time-strain separability is valid if the strain function is linearly proportional to the Cauchy strain, and that when time-strain separability holds, two strain-dependent quantities can be obtained experimentally. In the case where time and strain effect are not separable, superposition can be achieved only by using temperature and strain-dependent shift factors.
Higgs potential from extended Brans-Dicke theory and the time-evolution of the fundamental constants
Sola, Joan; Khodam-Mohammadi, A
2016-01-01
Despite the enormous significance of the Higgs potential in the context of the Standard Model of electroweak interactions and in Grand Unified Theories, its ultimate origin is fundamentally unknown and must be introduced by hand in accordance with the underlying gauge symmetry and the requirement of renormalizability. Here we propose a more physical motivation for the structure of the Higgs potential, which we link to gravity, and more specifically to an extended Brans-Dicke (BD) theory containing two interacting scalar fields. One of these fields is coupled to curvature as in the BD formulation, whereas the other is coupled to gravity both derivatively and non-derivatively through the curvature scalar and the Ricci tensor. By requiring that the cosmological solutions of the model are consistent with observations, we show that the effective scalar field potential adopts the Higgs potential form with a mildly time-evolving vacuum expectation value. Such residual vacuum dynamics could be responsible for the pos...
Institute of Scientific and Technical Information of China (English)
CAO ZhanPing; ZHANG JingLi; ZHANG HongWe
2008-01-01
Here the effect of solid retention time (SRT) on the concentration of the mixed liquor suspend solid (MLSS), the sludge characteristics, the content of extra-cellular polymeric substances (EPS), the viscosity of mixed liquor and effluent quality in the immersed membrane bioreactor (IMBR) was investigated. The results indicate that the increase of the EPS content is the main reason for the increase of mixed liquor viscosity, the former is positively correlated with the latter (R2 = 0.9751). The size distribution profile of particles in the mixed liquor presents double-peak shape at SRT more than 30 days. The filtration resistance of membrane in IMBR is mainly caused by the tiny particles and the viscosity of the mixed liquor. In this study, the extension of SRT can hardly affect the removal efficiency of Chemical Oxygen Demand (COD) and NH+4-N, and when SRT is below 30 days, silt density index (SDI15) is less than 3, the effluent can be deeply treated by using reverse osmosis system (RO) or nano-filtration system (NF). The method of controlling SRT is put forward by analyzing the relationship between SRT and the minimum generation-time of dominant bacteria (at the maximum specific growth rate under the operation temperature).
Lucke, Robert L.; Sirlin, Samuel W.; San Martin, A. M.
1992-01-01
For most imaging sensors, a constant (dc) pointing error is unimportant (unless large), but time-dependent (ac) errors degrade performance by either distorting or smearing the image. When properly quantified, the separation of the root-mean-square effects of random line-of-sight motions into dc and ac components can be used to obtain the minimum necessary line-of-sight stability specifications. The relation between stability requirements and sensor resolution is discussed, with a view to improving communication between the data analyst and the control systems engineer.
Design of Digital AGC Loops with Constant Settling Time%恒定建立时间数字AGC环路设计
Institute of Scientific and Technical Information of China (English)
周三文; 卢满宏; 黄建国
2013-01-01
针对传统恒定建立时间数字AGC(自动增益控制)环路实现方式复杂、成本高的问题,基于AGC环路的对数模型,推导出AGC环路建立时间恒定的条件,提出采用线性放大器实现恒定建立时间AGC环路的方法,该方法能够在数字实现上省去传统方式的指数运算单元,降低了实现复杂度和成本.另外,对于非突跳或突跳幅度较小输入信号,利用输出信号平方检测代替对数功率检测,省去传统方式的对数运算单元,进一步降低了实现复杂度和成本.通过上述2种改进,提出了一种简单的恒定建立时间数字AGC环路设计方法.Simulink仿真证明了该设计方法的正确性.该方法应用于无线数字接收机中,能够简化设计,节约成本.%Based on the logarithmic model of AGC (Automatic Gain Control),conditions for keeping constant settling time of AGC loops have been derived and a method using a linear amplifier to achieve a constant settling time AGC loop is proposed to simplify the design and reduce the cost of conventional constant settling time digital AGC loops.The exponential computing unit of the conventional method is eliminated,thus reducing the complexity and cost of implementation.Furthermore,square detection is used instead of the conventional logarithmic power detection for non-sudden jump or slight sudden jump input signals,and this lowers the cost further.Based on the two improvements,a simplified design method is proposed for constant settling time digital AGC loops.Correctness of the design method is proved by the simulation results.The method can be used in wireless digital receivers to simplify design and to save cost.
Energy Technology Data Exchange (ETDEWEB)
Bassler, M.; Pensl, G. [Erlangen-Nuernberg Univ., Erlangen (Germany). Inst. fuer Angewandte Physik
1999-07-30
A long-time constant-capacitance deep level transient spectroscopy (LT-CC-DLTS) method has been established to investigate the energy distribution D{sub it} and the capture-cross-section {sigma}{sub n/p} of states at the interface of 6H SiC/MOS structures. A comparison of dry and wet oxidation (1120 C) reveals a change in the distribution of interface states and a different magnitude of capture-cross-sections indicating that the interface states consist of at least two types of defects. (orig.)
Xu, Dandan; Schneider, Peter; Springel, Volker; Vogelsberger, Mark; Nelson, Dylan; Hernquist, Lars
2015-01-01
The combination of dynamical and strong gravitational lensing studies of massive galaxies shows that their total density profile in the central region (i.e. up to a few half-light radius) can be described by a power law, $\\rho(r)\\propto r^{-\\gamma}$. Therefore, such a power-law model is employed for a large number of strong-lensing applications, including the so-called time-delay technique used to infer the Hubble constant $H_0$. However, since the radial scale at which strong lensing features are formed (i.e., the Einstein radius) corresponds to the transition from the dominance of baryonic matter to dark matter, there is no known reason why galaxies should follow a power law in density. The assumption of a power law artificially breaks the mass-sheet degeneracy, a well-known invariance transformation in gravitational lensing which affects the product of Hubble constant and time delay and can therefore cause a bias in the determination of $H_0$ from the time-delay technique. In this paper, we use the Illustr...
Lind, Tania Kjellerup; Zielińska, Paulina; Wacklin, Hanna Pauliina; Urbańczyk-Lipkowska, Zofia; Cárdenas, Marité
2014-01-28
In this paper, an amphiphilic peptide dendrimer with potential applications against multi-resistant bacteria such as Staphylococcus aureus was synthesized and studied on model cell membranes. The combination of quartz crystal microbalance and atomic force microscopy imaging during continuous flow allowed for in situ monitoring of the very initial interaction processes and membrane transformations on longer time scales. We used three different membrane compositions of low and high melting temperature phospholipids to vary the membrane properties from a single fluid phase to a pure gel phase, while crossing the phase coexistence boundaries at room temperature. The interaction mechanism of the dendrimer was found to be time-dependent and to vary remarkably with the fluidity and coexistence of liquid-solid phases in the membrane. Spherical micelle-like dendrimer-lipid aggregates were formed in the fluid-phase bilayer and led to partial solubilization of the membrane, while in gel-phase membranes, the dendrimers caused areas of local depressions followed by redeposition of flexible lipid patches. Domain coexistence led to a sequence of events initiated by the formation of a ribbon-like network and followed by membrane solubilization via spherical aggregates from the edges of bilayer patches. Our results show that the dendrimer molecules were able to destroy the membrane integrity through different mechanisms depending on the lipid phase and morphology and shed light on their antimicrobial activity. These findings could have an impact on the efficacy of the dendrimers since lipid membranes in certain bacteria have transition temperatures very close to the host body temperature.
The Interacting and Non-constant Cosmological Constant
Verma, Murli Manohar
2009-01-01
We propose a time-varying cosmological constant with a fixed equation of state, which evolves mainly through its interaction with the background during most of the long history of the universe. However, such interaction does not exist in the very early and the late-time universe and produces the acceleration during these eras when it becomes very nearly a constant. It is found that after the initial inflationary phase, the cosmological constant, that we call as lambda parameter, rolls down from a large constant value to another but very small constant value and further dominates the present epoch showing up in form of the dark energy driving the acceleration.
Real-Time Monitoring of Membrane-Protein Reconstitution by Isothermal Titration Calorimetry
2013-01-01
Phase diagrams offer a wealth of thermodynamic information on aqueous mixtures of bilayer-forming lipids and micelle-forming detergents, providing a straightforward means of monitoring and adjusting the supramolecular state of such systems. However, equilibrium phase diagrams are of very limited use for the reconstitution of membrane proteins because of the occurrence of irreversible, unproductive processes such as aggregation and precipitation that compete with productive reconstitution. Here, we exemplify this by dissecting the effects of the K+ channel KcsA on the process of bilayer self-assembly in a mixture of Escherichia coli polar lipid extract and the nonionic detergent octyl-β-d-glucopyranoside. Even at starting concentrations in the low micromolar range, KcsA has a tremendous impact on the supramolecular organization of the system, shifting the critical lipid/detergent ratios at the onset and completion of vesicle formation by more than 2-fold. Thus, equilibrium phase diagrams obtained for protein-free lipid/detergent mixtures would be misleading when used to guide the reconstitution process. To address this issue, we demonstrate that, even under such nonequilibrium conditions, high-sensitivity isothermal titration calorimetry can be exploited to monitor the progress of membrane-protein reconstitution in real time, in a noninvasive manner, and at high resolution to yield functional proteoliposomes with a narrow size distribution for further downstream applications. PMID:24354292
Development of a portable time-of-flight membrane inlet mass spectrometer for environmental analysis
White, A. J.; Blamire, M. G.; Corlett, C. A.; Griffiths, B. W.; Martin, D. M.; Spencer, S. B.; Mullock, S. J.
1998-02-01
The benefits of on-site analysis of environmental pollutants are well known, with such techniques increasing sample throughput and reducing the overall cost of pollution level monitoring. This article describes a transportable time-of-flight (TOF) mass spectrometer, based upon a converging, annular TOF (CAT) arrangement. The instrument, the transportable CAT or T-CAT is battery powered and self-contained. The vacuum chamber is never vented and is kept at a very low pressure, even during analysis. Sample gases are admitted to the mass spectrometer via a membrane inlet system. Data collection and analysis are accomplished via a portable PC. The T-CAT is capable of detection limits approaching those of more conventional, nonportable design. The device shows reasonable linearity over wide concentration ranges. Initial results indicate that the T-CAT will be capable of use in a wide range of applications, particularly for environmental monitoring. This article describes the features of the T-CAT, and presents initial results from the membrane inlet/T-CAT system.
基于 NANM AC 热电偶的时间常数测试技术研究%Research on measuring time constant of NANMAC thermocouple
Institute of Scientific and Technical Information of China (English)
冯浩; 张志杰; 黄晓敏; 张晋文
2014-01-01
The theory for measuring the time constant of thermocouple was introduced ,and the method for measuring the time constant of NANMAC thermocouple by using dynamic calibration system of transient surface temperature sensor was proposed .In this system ,static and dynamic calibrations were conducted for infrared detectors and thermocouples ,and then both temperature-time curves were obtained .Since the frequency response of infrared detector is superior to that of calibrat -ed thermocouple ,the values measured by infrared detectors are taken as true values .Through dividing the values measured with thermocouples by those with infrared detectors ,a normalized curve was obtained ,based on which the time constant of thermocouple was measured .With this method ,the experiments were carried out with NANMAC thermocouple to obtain its time constant .The results show that the method for measuring the time constant is feasible and the dynamic calibration of thermocouples can be achieved at microsecond and millisecond level .This research has a certain reference value for research and application of NANMAC thermocouple temperature sensor .%本文介绍了热电偶时间常数的测试理论，提出了运用瞬态表面温度传感器动态校准系统实现对NANMAC 热电偶时间常数的测试方法。该系统对红外探测器和热电偶进行了静态校准和动态校准，得到两者的温度－时间曲线。由于红外探测器的频率响应优于被校准热电偶的频率响应，因此，以红外探测器测得的值作为真值，用热电偶测得的值与红外探测器测得的值相比得到一条归一化的曲线，并由归一化曲线求得热电偶的时间常数。利用该方法对 NANMAC 热电偶进行时间常数的测试实验，得到了该热电偶的时间常数。实验结果表明：该时间常数测试方法是可行的，可以实现对微秒、毫秒量级热电偶的动态校准，这对于 NANMAC 热电偶温度传感器的研究
Quantum Theory without Planck's Constant
Ralston, John P
2012-01-01
Planck's constant was introduced as a fundamental scale in the early history of quantum mechanics. We find a modern approach where Planck's constant is absent: it is unobservable except as a constant of human convention. Despite long reference to experiment, review shows that Planck's constant cannot be obtained from the data of Ryberg, Davisson and Germer, Compton, or that used by Planck himself. In the new approach Planck's constant is tied to macroscopic conventions of Newtonian origin, which are dispensable. The precision of other fundamental constants is substantially improved by eliminating Planck's constant. The electron mass is determined about 67 times more precisely, and the unit of electric charge determined 139 times more precisely. Improvement in the experimental value of the fine structure constant allows new types of experiment to be compared towards finding "new physics." The long-standing goal of eliminating reliance on the artifact known as the International Prototype Kilogram can be accompl...
Baker, Robert G. V.
2017-02-01
Self-similar matrices of the fine structure constant of solar electromagnetic force and its inverse, multiplied by the Carrington synodic rotation, have been previously shown to account for at least 98% of the top one hundred significant frequencies and periodicities observed in the ACRIM composite irradiance satellite measurement and the terrestrial 10.7cm Penticton Adjusted Daily Flux data sets. This self-similarity allows for the development of a time-space differential equation (DE) where the solutions define a solar model for transmissions through the core, radiative, tachocline, convective and coronal zones with some encouraging empirical and theoretical results. The DE assumes a fundamental complex oscillation in the solar core and that time at the tachocline is smeared with real and imaginary constructs. The resulting solutions simulate for tachocline transmission, the solar cycle where time-line trajectories either 'loop' as Hermite polynomials for an active Sun or 'tail' as complementary error functions for a passive Sun. Further, a mechanism that allows for the stable energy transmission through the tachocline is explored and the model predicts the initial exponential coronal heating from nanoflare supercharging. The twisting of the field at the tachocline is then described as a quaternion within which neutrinos can oscillate. The resulting fractal bubbles are simulated as a Julia Set which can then aggregate from nanoflares into solar flares and prominences. Empirical examples demonstrate that time and space fractals are important constructs in understanding the behaviour of the Sun, from the impact on climate and biological histories on Earth, to the fractal influence on the spatial distributions of the solar system. The research suggests that there is a fractal clock underpinning solar frequencies in packages defined by the fine structure constant, where magnetic flipping and irradiance fluctuations at phase changes, have periodically impacted on the
Directory of Open Access Journals (Sweden)
Ziaei Poor Hamed
2016-01-01
Full Text Available This article focuses on temperature response of skin tissue due to time-dependent surface heat fluxes. Analytical solution is constructed for DPL bio-heat transfer equation with constant, periodic and pulse train heat flux conditions on skin surface. Separation of variables and Duhamel’s theorem for a skin tissue as a finite domain are employed. The transient temperature responses for constant and time-dependent boundary conditions are obtained and discussed. The results show that there is major discrepancy between the predicted temperature of parabolic (Pennes bio-heat transfer, hyperbolic (thermal wave and DPL bio-heat transfer models when high heat flux accidents on the skin surface with a short duration or propagation speed of thermal wave is finite. The results illustrate that the DPL model reduces to the hyperbolic model when τT approaches zero and the classic Fourier model when both thermal relaxations approach zero. However for τq = τT the DPL model anticipates different temperature distribution with that predicted by the Pennes model. Such discrepancy is due to the blood perfusion term in energy equation. It is in contrast to results from the literature for pure conduction material, where the DPL model approaches the Fourier heat conduction model when τq = τT . The burn injury is also investigated.
Ren, Jinjun; Eckert, Hellmut
2015-11-01
A new pulse sequence entitled DQ-DRENAR (Double-Quantum based Dipolar Recoupling Effects Nuclear Alignment Reduction) was recently described for the quantitative measurement of magnetic dipole-dipole interactions in homonuclear spin-1/2 systems involving multiple nuclei. As described in the present manuscript, the efficiency and performance of this sequence can be significantly improved, if the measurement is done in the constant-time mode. We describe both the theoretical analysis of this method and its experimental validation of a number of crystalline model compounds, considering both symmetry-based and back-to-back (BABA) DQ-coherence excitation schemes. Based on the combination of theoretical analysis and experimental results we discuss the effect of experimental parameters such as the chemical shift anisotropy (CSA), the spinning rate, and the radio frequency field inhomogeneity upon its performance. Our results indicate that constant-time (CT-) DRENAR is a method of high efficiency and accuracy for compounds with multiple homonuclear spin systems with particular promise for the analysis of stronger-coupled and short T2 spin systems.
Albareti, Franco D; Gutiérrez, Carlos M; Prada, Francisco; Pâris, Isabelle; Schlegel, David; López-Corredoira, Martín; Schneider, Donald P; Manchado, Arturo; García-Hernández, D A; Petitjean, Patrick; Ge, Jian
2015-01-01
From the Sloan Digital Sky Survey Data Release 12, which covers the full Baryonic Oscillation Spectroscopic Survey (BOSS) footprint, we investigate the possible variation of the fine-structure constant over cosmological time scales. We analyze the largest quasar sample considered so far in the literature, which contains 10,363 spectra with $z<1$. All the BOSS quasar spectra are selected from a visually inspected quasar catalog. We apply the emission line method on the [O III] doublet (4960, 5008 A) and obtain $\\Delta\\alpha/\\alpha= \\left(1.4 \\pm 2.3\\right)\\times10^{-5}$ for the relative variation of the fine-structure constant. We also investigate the possible sources of systematics: misidentification of the lines, sky OH lines, H$\\beta$ and broad line contamination, optimal wavelength range for the Gaussian fits, chosen polynomial order for the continuum spectrum, signal-to-noise ratio and good quality of the fits. The uncertainty of the measurement is dominated by the sky subtraction. The results presente...
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.
Directory of Open Access Journals (Sweden)
Weihua Liu
2014-01-01
Full Text Available In mass customization logistics service, reasonable scheduling of the logistics service supply chain (LSSC, especially time scheduling, is benefit to increase its competitiveness. Therefore, the effect of a customer order decoupling point (CODP on the time scheduling performance should be considered. To minimize the total order operation cost of the LSSC, minimize the difference between the expected and actual time of completing the service orders, and maximize the satisfaction of functional logistics service providers, this study establishes an LSSC time scheduling model based on the CODP. Matlab 7.8 software is used in the numerical analysis for a specific example. Results show that the order completion time of the LSSC can be delayed or be ahead of schedule but cannot be infinitely advanced or infinitely delayed. Obtaining the optimal comprehensive performance can be effective if the expected order completion time is appropriately delayed. The increase in supply chain comprehensive performance caused by the increase in the relationship coefficient of logistics service integrator (LSI is limited. The relative concern degree of LSI on cost and service delivery punctuality leads to not only changes in CODP but also to those in the scheduling performance of the LSSC.
Liu, Weihua; Yang, Yi; Xu, Haitao; Liu, Xiaoyan; Wang, Yijia; Liang, Zhicheng
2014-01-01
In mass customization logistics service, reasonable scheduling of the logistics service supply chain (LSSC), especially time scheduling, is benefit to increase its competitiveness. Therefore, the effect of a customer order decoupling point (CODP) on the time scheduling performance should be considered. To minimize the total order operation cost of the LSSC, minimize the difference between the expected and actual time of completing the service orders, and maximize the satisfaction of functional logistics service providers, this study establishes an LSSC time scheduling model based on the CODP. Matlab 7.8 software is used in the numerical analysis for a specific example. Results show that the order completion time of the LSSC can be delayed or be ahead of schedule but cannot be infinitely advanced or infinitely delayed. Obtaining the optimal comprehensive performance can be effective if the expected order completion time is appropriately delayed. The increase in supply chain comprehensive performance caused by the increase in the relationship coefficient of logistics service integrator (LSI) is limited. The relative concern degree of LSI on cost and service delivery punctuality leads to not only changes in CODP but also to those in the scheduling performance of the LSSC.
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.
Directory of Open Access Journals (Sweden)
Parneet Paul
2013-02-01
Full Text Available The computer modelling and simulation of wastewater treatment plant and their specific technologies, such as membrane bioreactors (MBRs, are becoming increasingly useful to consultant engineers when designing, upgrading, retrofitting, operating and controlling these plant. This research uses traditional phenomenological mechanistic models based on MBR filtration and biochemical processes to measure the effectiveness of alternative and novel time series models based upon input–output system identification methods. Both model types are calibrated and validated using similar plant layouts and data sets derived for this purpose. Results prove that although both approaches have their advantages, they also have specific disadvantages as well. In conclusion, the MBR plant designer and/or operator who wishes to use good quality, calibrated models to gain a better understanding of their process, should carefully consider which model type is selected based upon on what their initial modelling objectives are. Each situation usually proves unique.
Effect of time-varying humidity on the performance of a polymer electrolyte membrane fuel cells
Energy Technology Data Exchange (ETDEWEB)
Noorani, Shamsuddin [Department of Mechanical Engineering, University of Michigan-Dearborn (United States); Shamim, Tariq [Mechanical Engineering, Masdar Institute of Science and Technology (United Arab Emirates)], E-mail: tshamim@masdar.ac.ae
2011-07-01
In the energy sector, fuel cells constitute a promising solution for the future due to their energy-efficient and environment-friendly characteristics. However, the performance of fuel cells is very much affected by the humidification level of the reactants, particularly in hot regions. The aim of this paper is to develop a better understanding of the effect of driving conditions on the performance of fuel cells. A macroscopic single-fuel-cell-based, one dimensional, isothermal model was used on a polymer electrolyte membrane fuel cell to carry out a computational study of the impact of humidity conditions which vary over time. It was found that the variation of humidity has a significant effect on water distribution but a much lower impact on power and current densities. This paper provided useful information on fuel cells' performance under varying conditions which could be used to improve their design for mobile applications.
Growth cone travel in space and time: the cellular ensemble of cytoskeleton, adhesion, and membrane.
Vitriol, Eric A; Zheng, James Q
2012-03-22
Growth cones, found at the tip of axonal projections, are the sensory and motile organelles of developing neurons that enable axon pathfinding and target recognition for precise wiring of the neural circuitry. To date, many families of conserved guidance molecules and their corresponding receptors have been identified that work in space and time to ensure billions of axons to reach their targets. Research in the past two decades has also gained significant insight into the ways in which growth cones translate extracellular signals into directional migration. This review aims to examine new progress toward understanding the cellular mechanisms underlying directional motility of the growth cone and to discuss questions that remain to be addressed. Specifically, we will focus on the cellular ensemble of cytoskeleton, adhesion, and membrane and examine how the intricate interplay between these processes orchestrates the directed movement of growth cones.
Shavorskiy, Andrey; Neppl, Stefan; Slaughter, Daniel S; Cryan, James P; Siefermann, Katrin R; Weise, Fabian; Lin, Ming-Fu; Bacellar, Camila; Ziemkiewicz, Michael P; Zegkinoglou, Ioannis; Fraund, Matthew W; Khurmi, Champak; Hertlein, Marcus P; Wright, Travis W; Huse, Nils; Schoenlein, Robert W; Tyliszczak, Tolek; Coslovich, Giacomo; Robinson, Joseph; Kaindl, Robert A; Rude, Bruce S; Ölsner, Andreas; Mähl, Sven; Bluhm, Hendrik; Gessner, Oliver
2014-09-01
An apparatus for sub-nanosecond time-resolved ambient-pressure X-ray photoelectron spectroscopy studies with pulsed and constant wave X-ray light sources is presented. A differentially pumped hemispherical electron analyzer is equipped with a delay-line detector that simultaneously records the position and arrival time of every single electron at the exit aperture of the hemisphere with ~0.1 mm spatial resolution and ~150 ps temporal accuracy. The kinetic energies of the photoelectrons are encoded in the hit positions along the dispersive axis of the two-dimensional detector. Pump-probe time-delays are provided by the electron arrival times relative to the pump pulse timing. An average time-resolution of (780 ± 20) ps (FWHM) is demonstrated for a hemisphere pass energy E(p) = 150 eV and an electron kinetic energy range KE = 503-508 eV. The time-resolution of the setup is limited by the electron time-of-flight (TOF) spread related to the electron trajectory distribution within the analyzer hemisphere and within the electrostatic lens system that images the interaction volume onto the hemisphere entrance slit. The TOF spread for electrons with KE = 430 eV varies between ~9 ns at a pass energy of 50 eV and ~1 ns at pass energies between 200 eV and 400 eV. The correlation between the retarding ratio and the TOF spread is evaluated by means of both analytical descriptions of the electron trajectories within the analyzer hemisphere and computer simulations of the entire trajectories including the electrostatic lens system. In agreement with previous studies, we find that the by far dominant contribution to the TOF spread is acquired within the hemisphere. However, both experiment and computer simulations show that the lens system indirectly affects the time resolution of the setup to a significant extent by inducing a strong dependence of the angular spread of electron trajectories entering the hemisphere on the retarding ratio. The scaling of the angular spread with
Rivero Santamaría, Alejandro; Dayou, Fabrice; Rubayo-Soneira, Jesus; Monnerville, Maurice
2017-02-15
The dynamics of the Si((3)P) + OH(X(2)Π) → SiO(X(1)Σ(+)) + H((2)S) reaction is investigated by means of the time-dependent wave packet (TDWP) approach using an ab initio potential energy surface recently developed by Dayou et al. ( J. Chem. Phys. 2013 , 139 , 204305 ) for the ground X(2)A' electronic state. Total reaction probabilities have been calculated for the first 15 rotational states j = 0-14 of OH(v=0,j) at a total angular momentum J = 0 up to a collision energy of 1 eV. Integral cross sections and state-selected rate constants for the temperature range 10-500 K were obtained within the J-shifting approximation. The reaction probabilities display highly oscillatory structures indicating the contribution of long-lived quasibound states supported by the deep SiOH/HSiO wells. The cross sections behave with collision energies as expected for a barrierless reaction and are slightly sensitive to the initial rotational excitation of OH. The thermal rate constants show a marked temperature dependence below 200 K with a maximum value around 15 K. The TDWP results globally agree with the results of earlier quasi-classical trajectory (QCT) calculations carried out by Rivero-Santamaria et al. ( Chem. Phys. Lett. 2014 , 610-611 , 335 - 340 ) with the same potential energy surface. In particular, the thermal rate constants display a similar temperature dependence, with TDWP values smaller than the QCT ones over the whole temperature range.
Baker, R P; Urban, S
2017-01-01
Intramembrane proteases are an ancient and diverse group of multispanning membrane proteins that cleave transmembrane substrates inside the membrane to effect a wide range of biological processes. As proteases, a clear understanding of their function requires kinetic dissection of their catalytic mechanism, but this is difficult to achieve for membrane proteins. Kinetic measurements in detergent systems are complicated by micelle fusion/exchange, which introduces an additional kinetic step and imposes system-specific behaviors (e.g., cooperativity). Conversely, kinetic analysis in proteoliposomes is hindered by premature substrate cleavage during coreconstitution, and lack of methods to quantify proteolysis in membranes in real time. In this chapter, we describe a method for the real-time kinetic analysis of intramembrane proteolysis in model liposomes. Our assay is inducible, because the enzyme is held inactive by low pH during reconstitution, and fluorogenic, since fluorescence emission from the substrate is quenched near lipids but restored upon proteolytic release from the membrane. The precise measurement of initial reaction velocities continuously in real time facilitates accurate steady-state kinetic analysis of intramembrane proteolysis and its inhibition inside the membrane environment. Using real data we describe a step-by-step strategy to implement this assay for essentially any intramembrane protease.
Finger, W; Martin, C; Pareto, A
1988-08-31
Single channel currents activated by glutamate were recorded by means of the patch-clamp technique in the abdominal superficial extensor muscle and the claw opener muscle of small (1-3 months old) and large (greater than 16 months old) crayfish. It was found that in small crayfish the time course of glutamate-operated single channel currents was prolonged by a factor of about 4 in these two preparations. In the abdominal superficial extensor muscle, single channel currents activated by 5 mmol/l glutamate had a mean burst length of tau = 2-3 ms in large crayfish and a mean burst length of tau = 8-9 ms in small crayfish. In the claw opener, for large crayfish tau congruent to 0.5 ms and for small crayfish tau = 1.5-2.5 ms resulted (500 mumol/l glutamate). Moreover, single channel currents with long time courses often slowly increased their amplitudes during the open time of the channel and current amplitudes did not decline completely to the baseline after channel closing. In addition, single channel currents with relatively constant amplitude were often followed by a small increasing and decreasing membrane current. The latter results suggest that glutamate channel gating might trigger a membrane current.
Scott, Tricia
2015-11-01
Compassion is a powerful word that describes an intense feeling of commiseration and a desire to help those struck by misfortune. Most people know intuitively how and when to offer compassion to relieve another person's suffering. In health care, compassion is a constant; it cannot be rationed because emergency nurses have limited time or resources to manage increasing demands.
Piquette, Jean C; McLaughlin, Elizabeth A
2007-06-01
A complex material-constant theory of lossy piezoelectrics is fully solved for crystal class 3m for harmonic time dependence of the fields and stresses. A new demonstration that the theory's eigen coupling factor equation applies to the lossy alternating current (AC) case also is given. The solution presented for crystal class 3m provides a complete orthonormal set of eigenvectors and eigenvalues for the eigen coupling factor problem, and it also provides a complete orthonormal set of eigenvectors and eigenvalues for the eigen loss tangent problem, for this crystal class. It is shown that two positive coupling factors are sufficient to express an arbitrary 3m crystal state. Despite the complex nature of the material constants, the Holland-EerNisse theory produces fully real expressions for the coupling factors. The loss tangent eigenvalues also are fully real and positive. The loss eigenstates are important because driving a crystal in a loss eigenstate tends to minimize the impact of material losses. Given also is a set of loss inequalities for crystal class 3m. The loss inequalities of crystal class 6mm are recovered from these when d22 and s(E)14 both vanish.
Iihama, Satoshi; Sakuma, Akimasa; Naganuma, Hiroshi; Oogane, Mikihiko; Mizukami, Shigemi; Ando, Yasuo
2016-11-01
We have systematically investigated the Gilbert damping constant α for L 10 -FePd films using the time-resolved magneto-optical Kerr effect (TRMOKE). The field angle dependence of TRMOKE signals was measured and analyzed. The field angle dependence of the lifetime of magnetization precession was explained by evaluating extrinsic contributions such as the anisotropy distribution and two-magnon scattering. The crystalline uniaxial perpendicular magnetic anisotropy constant Ku and α values were evaluated for FePd films for various L 10 order parameters S . Ku values of approximately 15 Merg/cm3 were obtained for films with large-S values (i.e., over 0.8). In addition, α for the low-S film was found to be approximately 0.007 and decreased with increasing S . Smaller values of α (of 0.002-0.004) were obtained for films with S values of approximately 0.6-0.8. Results revealed that FePd films have both large-Ku and small-α values, which is a useful property for low-power magnetization switching while maintaining high thermal stability in spin-transfer-torque magnetoresistive random access memory applications.
Welsch, Ralph; Manthe, Uwe
2012-12-28
The multi-layer extension of the multi-configurational time-dependent Hartree (MCTDH) approach is applied to the investigation of elementary bimolecular chemical reactions. Cumulative reaction probabilities and thermal rate constants of the H + CH(4) → H(2) + CH(3) reaction are calculated using flux correlation functions and the quantum transition state concept. Different coordinate systems and potential energy surfaces (PESs) are studied. The convergence properties of different layerings are investigated and the efficiency of multi-layer MCTDH approach is compared to the standard MCTDH approach. It is found that the multi-layer approach can decrease the numerical effort by more than an order of magnitude. The increased efficiency resulting from the multi-layer MCTDH approach is crucial for quantum dynamical calculations on recent global H + CH(4) → H(2) + CH(3) PESs, e.g., the ZBB3-PES [Z. Xie, J. M. Bowman, and X. Zhang, J. Chem. Phys. 125, 133120 (2006)] based on permutational invariant polynomials, which are numerically more demanding than earlier PESs. The results indicate that an accurate description of all transition state frequencies is important to obtain accurate thermal rate constants.
Directory of Open Access Journals (Sweden)
M. Petrillo
2015-09-01
Full Text Available Due to the large size and highly heterogeneous spatial distribution of deadwood, the time scales involved in the coarse woody debris (CWD decay of Picea abies (L. Karst. and Larix decidua Mill. in Alpine forests have been poorly investigated and are largely unknown. We investigated the CWD decay dynamics in an Alpine valley in Italy using the five-decay class system commonly employed for forest surveys, based on a macromorphological and visual assessment. For the decay classes 1 to 3, most of the dendrochronological samples were cross-dated to assess the time that had elapsed since tree death, but for decay classes 4 and 5 (poorly preserved tree rings and some others not having enough tree rings, radiocarbon dating was used. In addition, density, cellulose and lignin data were measured for the dated CWD. The decay rate constants for spruce and larch were estimated on the basis of the density loss using a single negative exponential model. In the decay classes 1 to 3, the ages of the CWD were similar varying between 1 and 54 years for spruce and 3 and 40 years for larch with no significant differences between the classes; classes 1–3 are therefore not indicative for deadwood age. We found, however, distinct tree species-specific differences in decay classes 4 and 5, with larch CWD reaching an average age of 210 years in class 5 and spruce only 77 years. The mean CWD rate constants were 0.012 to 0.018 yr−1 for spruce and 0.005 to 0.012 yr−1 for larch. Cellulose and lignin time trends half-lives (using a multiple-exponential model could be derived on the basis of the ages of the CWD. The half-lives for cellulose were 21 yr for spruce and 50 yr for larch. The half-life of lignin is considerably higher and may be more than 100 years in larch CWD.
Characterization of a constant current charge detector.
Mori, Masanobu; Chen, Yongjing; Ohira, Shin-Ichi; Dasgupta, Purnendu K
2012-12-15
Ion exchangers are ionic equivalents of doped semiconductors, where cations and anions are equivalents of holes and electrons as charge carriers in solid state semiconductors. We have previously demonstrated an ion exchange membrane (IEM) based electrolyte generator which behaves similar to a light-emitting diode and a charge detector (ChD) which behaves analogous to a p-i-n photodiode. The previous work on the charge detector, operated at a constant voltage, established its unique ability to respond to the charge represented by the analyte ions regardless of their redox properties, rather than to their conductivities. It also suggested that electric field induced dissociation (EFID) of water occurs at one or both ion exchange membranes. A logical extension is to study the behavior of the same device, operated in a constant current mode (ChD(i)). The evidence indicates that in the present operational mode the device also responds to the charge represented by the analytes and not their conductivity. Injection of a base into a charge detector operated in the constant voltage mode was not previously examined; in the constant current mode, base injection appears to inhibit EFID. The effects of applied current, analyte residence time and outer channel fluid composition were individually examined; analyte ions of different mobilities as well as affinities for the respective IEMs were used. While the exact behavior is somewhat dependent on the applied current, strong electrolytes, both acids and salts, respond the highest and in a near-uniform fashion, weak acids and their salts respond in an intermediate fashion and bases produce the lowest responses. A fundamentally asymmetric behavior is observed. Injected bases but not injected acids produce a poor response; the effects of incorporating a strong base as the electrolyte in the anion exchange membrane (AEM) compartment is far greater than incorporating an acid in the cation exchange membrane (CEM) compartment. These
WAKUNO, Ai; MAEDA, Tatsuya; KODAIRA, Kazumichi; KIKUCHI, Takuya; OHTA, Minoru
2017-01-01
ABSTRACT A three-year old Thoroughbred racehorse was anesthetized with sevoflurane and oxygen inhalation anesthesia combined with constant rate infusion (CRI) of alfaxalone-medetomidine for internal fixation of a third metacarpal bone fracture. After premedication with intravenous (IV) injections of medetomidine (6.0 µg/kg IV), butorphanol (25 µg/kg IV), and midazolam (20 µg/kg IV), anesthesia was induced with 5% guaifenesin (500 ml/head IV) followed immediately by alfaxalone (1.0 mg/kg IV). Anesthesia was maintained with sevoflurane and CRIs of alfaxalone (1.0 mg/kg/hr) and medetomidine (3.0 µg/kg/hr). The total surgical time was 180 min, and the total inhalation anesthesia time was 230 min. The average end-tidal sevoflurane concentration during surgery was 1.8%. The mean arterial blood pressure was maintained above 70 mmHg throughout anesthesia, and the recovery time was 65 min. In conclusion, this anesthetic technique may be clinically applicable for Thoroughbred racehorses undergoing a long-time orthopedic surgery. PMID:28955163
Energy Technology Data Exchange (ETDEWEB)
Monzo, Jose M. [Digital Systems Design (DSD) Group, ITACA Institute, Universidad Politecnica de Valencia, Camino de Vera s/n, 46022 Valencia (Spain)], E-mail: jmonfer@aaa.upv.es; Lerche, Christoph W.; Martinez, Jorge D.; Esteve, Raul; Toledo, Jose; Gadea, Rafael; Colom, Ricardo J.; Herrero, Vicente; Ferrando, Nestor; Aliaga, Ramon J.; Mateo, Fernando [Digital Systems Design (DSD) Group, ITACA Institute, Universidad Politecnica de Valencia, Camino de Vera s/n, 46022 Valencia (Spain); Sanchez, Filomeno [Nuclear Medical Physics Group, IFIC Institute, Consejo Superior de Investigaciones Cientificas (CSIC), 46980 Paterna (Spain); Mora, Francisco J. [Digital Systems Design (DSD) Group, ITACA Institute, Universidad Politecnica de Valencia, Camino de Vera s/n, 46022 Valencia (Spain); Benlloch, Jose M. [Nuclear Medical Physics Group, IFIC Institute, Consejo Superior de Investigaciones Cientificas (CSIC), 46980 Paterna (Spain); Sebastia, Angel [Digital Systems Design (DSD) Group, ITACA Institute, Universidad Politecnica de Valencia, Camino de Vera s/n, 46022 Valencia (Spain)
2009-06-01
PET systems need good time resolution to improve the true event rate, random event rejection, and pile-up rejection. In this study we propose a digital procedure for this task using a low pass filter interpolation plus a Digital Constant Fraction Discriminator (DCFD). We analyzed the best way to implement this algorithm on our dual head PET system and how varying the quality of the acquired signal and electronic noise analytically affects timing resolution. Our detector uses two continuous LSO crystals with a position sensitive PMT. Six signals per detector are acquired using an analog electronics front-end and these signals are processed using an in-house digital acquisition board. The test bench developed simulates the electronics and digital algorithms using Matlab. Results show that electronic noise and other undesired effects have a significant effect on the timing resolution of the system. Interpolated DCFD gives better results than non-interpolated DCFD. In high noise environments, differences are reduced. An optimum delay selection, based on the environment noise, improves time resolution.
Ziganshin, Ayrat M; Schmidt, Thomas; Lv, Zuopeng; Liebetrau, Jan; Richnow, Hans Hermann; Kleinsteuber, Sabine; Nikolausz, Marcell
2016-10-01
The effects of hydraulic retention time (HRT) reduction at constant high organic loading rate on the activity of hydrogen-producing bacteria and methanogens were investigated in reactors digesting thin stillage. Stable isotope fingerprinting was additionally applied to assess methanogenic pathways. Based on hydA gene transcripts, Clostridiales was the most active hydrogen-producing order in continuous stirred tank reactor (CSTR), fixed-bed reactor (FBR) and anaerobic sequencing batch reactor (ASBR), but shorter HRT stimulated the activity of Spirochaetales. Further decreasing HRT diminished Spirochaetales activity in systems with biomass retention. Based on mcrA gene transcripts, Methanoculleus and Methanosarcina were the predominantly active in CSTR and ASBR, whereas Methanosaeta and Methanospirillum activity was more significant in stably performing FBR. Isotope values indicated the predominance of aceticlastic pathway in FBR. Interestingly, an increased activity of Methanosaeta was observed during shortening HRT in CSTR and ASBR despite high organic acids concentrations, what was supported by stable isotope data.
Tobar, M E; Tobar, Michael Edmund; Hartnett, John Gideon
2003-01-01
A new experiment to test for the time independence of the fine structure constant, alpha, is proposed. The experiment utilizes orthogonally polarized Transverse Electric and Transverse Magnetic Whispering Gallery Modes in a single sapphire resonator tuned to similar frequencies. When configured as a dual mode sapphire clock, we show that the anisotropy of sapphire makes it is possible to undertake a sensitive measurement from the beat frequency between the two modes. At infrared frequencies this is possible due to the different effect of the lowest phonon frequency on the two orthogonally polarized modes. At microwave frequencies we show that the phonon effect is too small. We show that the Electron Spin Resonance of paramagnetic impurities (such as Cr3+) in the lattice effects only one polarization with an alpha^6 dependence. This enables an enhancement of the sensitivity to temporal changes in a at microwave frequencies.
Nuansawan, Nararatchporn; Boonnorat, Jarungwit; Chiemchaisri, Wilai; Chiemchaisri, Chart
2016-06-01
Methane (CH4) and nitrous oxide (N2O) emissions and responsible microorganisms during the treatment of municipal solid waste leachate in two-stage membrane bioreactor (MBR) was investigated. The MBR system, consisting of anaerobic and aerobic stages, were operated at hydraulic retention time (HRT) of 5 and 2.5days in each reactor under the presence and absence of sludge recirculation. Organic and nitrogen removals were more than 80% under all operating conditions during which CH4 emission were found highest under no sludge recirculation condition at HRT of 5days. An increase in hydraulic loading resulted in a reduction in CH4 emission from anaerobic reactor but an increase from the aerobic reactor. N2O emission rates were found relatively constant from anaerobic and aerobic reactors under different operating conditions. Diversity of CH4 and N2O producing microorganisms were found decreasing when hydraulic loading rate to the reactors was increased.
Hayashi, J.; Nakatsuka, N.; Morimoto, I.; Akamatsu, F.
2017-02-01
The lean combustion is one of the key techniques for the advanced internal combustion systems due to the requirement of the higher thermal efficiency. Since the successful ignition must be guaranteed even in the lean combustion, advanced ignition systems have been developed in this decade. Laser ignition is one of the advanced ignition systems which have the profits of the flexibility in the position and the timing of ignition. To develop this ignition system for the actual combustion system, it is required to reveal the underlying physics of the laser ignition. Particularly, the time evolution of high temperature region formed by laser induced breakdown should be discussed. In this study, therefore, the time evolution of the high temperature region formed by the laser induced breakdown and the development of flame kernel were observed by using high-speed imaging. The ignition trials of methane/air lean premixed mixture were carried out in the constant volume combustion vessel to obtain minimum laser pulse energy for ignition (MPE). Results showed that the light emission from plasma formed by laser induced breakdown remained at least in several tens nano-seconds. In addition, there were large differences between the breakdown threshold and the MPE, which meant that the breakdown threshold did not determine the minimum pulse energy for ignition.
Ghaithan, Hamid M.; Qaid, Saif M.; Hezam, Mahmoud; Siddique, Muhemmad B.; Bedja, Idriss M.; Aldwayyana, Abdullah S.
2015-08-01
Dye-sensitized solar cells (DSSCs) have been considered as one of the most promising new generation solar cells. Enormous research efforts have been invested to improve the efficiency of solar energy conversion which is determined by the light harvesting efficiency, electron injection efficiency and undesirable electron lifetime. A simple, cheap and trustable laser-induced photovoltage and photocurrent decay (LIPVCD) technique is adopted in this work in order to determine the electron lifetime (τe) and electron transport (τtr) in DSSCs. In LIPVCD technique, DSSC is illuminated by a small squared intensity-modulated laser beam. Time-based response of the DSSC is recorded using a transient digitized oscilloscope for further analysis. Frequency-based response was also investigated in this work. The frequency-dependent measurements turned out to be a powerful method to determine electron time constants in a fast, real-time fashion. Measurements were carried out using a standard dye-sensitized solar cell, and results were in excellent agreement with results obtained from traditional IMVS-MPS measurements. Measurements were also performed for a variety of DSSCs, having various electrodes including TiO2 nanoparticles, TiO2 nanosheets with exposed {001} facets and ZnO vertically aligned nanowires. Results will also be presented and discussed in this work.
Vamvakeros, A; Jacques, S D M; Middelkoop, V; Di Michiel, M; Egan, C K; Ismagilov, I Z; Vaughan, G B M; Gallucci, F; van Sint Annaland, M; Shearing, P R; Cernik, R J; Beale, A M
2015-08-18
We report the results from an operando XRD-CT study of a working catalytic membrane reactor for the oxidative coupling of methane. These results reveal the importance of the evolving solid state chemistry during catalytic reaction, particularly the chemical interaction between the catalyst and the oxygen transport membrane.
Petrillo, Marta; Cherubini, Paolo; Fravolini, Giulia; Marchetti, Marco; Ascher-Jenull, Judith; Schärer, Michael; Synal, Hans-Arno; Bertoldi, Daniela; Camin, Federica; Larcher, Roberto; Egli, Markus
2016-03-01
Due to the large size (e.g. sections of tree trunks) and highly heterogeneous spatial distribution of deadwood, the timescales involved in the coarse woody debris (CWD) decay of Picea abies (L.) Karst. and Larix decidua Mill. in Alpine forests are largely unknown. We investigated the CWD decay dynamics in an Alpine valley in Italy using the chronosequence approach and the five-decay class system that is based on a macromorphological assessment. For the decay classes 1-3, most of the dendrochronological samples were cross-dated to assess the time that had elapsed since tree death, but for decay classes 4 and 5 (poorly preserved tree rings) radiocarbon dating was used. In addition, density, cellulose, and lignin data were measured for the dated CWD. The decay rate constants for spruce and larch were estimated on the basis of the density loss using a single negative exponential model, a regression approach, and the stage-based matrix model. In the decay classes 1-3, the ages of the CWD were similar and varied between 1 and 54 years for spruce and 3 and 40 years for larch, with no significant differences between the classes; classes 1-3 are therefore not indicative of deadwood age. This seems to be due to a time lag between the death of a standing tree and its contact with the soil. We found distinct tree-species-specific differences in decay classes 4 and 5, with larch CWD reaching an average age of 210 years in class 5 and spruce only 77 years. The mean CWD rate constants were estimated to be in the range 0.018 to 0.022 y-1 for spruce and to about 0.012 y-1 for larch. Snapshot sampling (chronosequences) may overestimate the age and mean residence time of CWD. No sampling bias was, however, detectable using the stage-based matrix model. Cellulose and lignin time trends could be derived on the basis of the ages of the CWD. The half-lives for cellulose were 21 years for spruce and 50 years for larch. The half-life of lignin is considerably higher and may be more than
Macháň, Radek; Jurkiewicz, Piotr; Olżyńska, Agnieszka; Olšinová, Marie; Cebecauer, Marek; Marquette, Arnaud; Bechinger, Burkhard; Hof, Martin
2014-06-03
Positioning of peptides with respect to membranes is an important parameter for biological and biophysical studies using model systems. Our experiments using five different membrane peptides suggest that the time-dependent fluorescence shift (TDFS) of Laurdan can help when distinguishing between peripheral and integral membrane binding and can be a useful, novel tool for studying the impact of transmembrane peptides (TMP) on membrane organization under near-physiological conditions. This article focuses on LAH4, a model α-helical peptide with high antimicrobial and nucleic acid transfection efficiencies. The predominantly helical peptide has been shown to orient in supported model membranes parallel to the membrane surface at acidic and, in a transmembrane manner, at basic pH. Here we investigate its interaction with fully hydrated large unilamellar vesicles (LUVs) by TDFS and fluorescence correlation spectroscopy (FCS). TDFS shows that at acidic pH LAH4 does not influence the glycerol region while at basic pH it makes acyl groups at the glycerol level of the membrane less mobile. TDFS experiments with antimicrobial peptides alamethicin and magainin 2, which are known to assume transmembrane and peripheral orientations, respectively, prove that changes in acyl group mobility at the glycerol level correlate with the orientation of membrane-associated peptide molecules. Analogous experiments with the TMPs LW21 and LAT show similar effects on the mobility of those acyl groups as alamethicin and LAH4 at basic pH. FCS, on the same neutral lipid bilayer vesicles, shows that the peripheral binding mode of LAH4 is more efficient in bilayer permeation than the transmembrane mode. In both cases, the addition of LAH4 does not lead to vesicle disintegration. The influence of negatively charged lipids on the bilayer permeation is also addressed.
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).
Time Resolved Neutron Reflectivity During Supported Membrane Formation by Vesicle Fusion.
Koutsioubas, Alexandros; Appavou, Marie-Sousai; Lairez, Didier
2017-09-05
The formation of supported lipid bilayers (SLB) on hydrophilic substrates through the method of unilamelar vesicle fusion is used routinely in a wide range of biophysical studies. In an effort to control and better understand the fusion process on the substrate, many experimental studies employing different techniques have been devoted to the elucidation of the fusion mechanism. In the present work we follow the kinetics of membrane formation using time-resolved (TR) neutron reflectivity, focussing at the structural changes near the solid/liquid interface. A clear indication of stacked bilayer structure is observed during the intermediate phase of SLB formation. Adsorbed lipid mass decrease is also measured at the final stage of the process. We have found that it is essential for the analysis of the experimental results to treat theoretically the shape of adsorbed lipid vesicles on an attractive substrate. The overall findings are discussed in relation to proposed fusion mechanisms from previous literature, while we argue that our observations favour a model involving enhanced adhesion of incoming vesicles on the edges of already formed bilayer patches.
Xue, Hongqi; Wu, Hulin; 10.1214/09-AOS784
2010-01-01
This article considers estimation of constant and time-varying coefficients in nonlinear ordinary differential equation (ODE) models where analytic closed-form solutions are not available. The numerical solution-based nonlinear least squares (NLS) estimator is investigated in this study. A numerical algorithm such as the Runge--Kutta method is used to approximate the ODE solution. The asymptotic properties are established for the proposed estimators considering both numerical error and measurement error. The B-spline is used to approximate the time-varying coefficients, and the corresponding asymptotic theories in this case are investigated under the framework of the sieve approach. Our results show that if the maximum step size of the $p$-order numerical algorithm goes to zero at a rate faster than $n^{-1/(p\\wedge4)}$, the numerical error is negligible compared to the measurement error. This result provides a theoretical guidance in selection of the step size for numerical evaluations of ODEs. Moreover, we h...
Bellofiore, A; Wang, Z; Chesler, N C
2015-06-01
Compliance (C) and resistance (R) maintain a unique, inverse relationship in the pulmonary circulation, resulting in a constant characteristic time [Formula: see text] that has been observed in healthy subjects as well as patients with pulmonary arterial hypertension (PAH). However, little is known about the dependence of right ventricular (RV) function on the coupled changes in R and C in the context of this inverse relationship. We hypothesized three simple dependencies of RV ejection fraction (RVEF) on R and C. The first model (linear-R) assumes a linear RVEF-R relation; the second (linear-C) assumes a linear RVEF-C relation; and the third one combines the former two in a mixed linear model. We found that the linear-R model and the mixed linear model are in good agreement with clinical evidence. A conclusive validation of these models will require more clinical data. Longitudinal data in particular are needed to identify the time course of ventricular-vascular impairment in PAH. Simple models like the ones we present here, once validated, will advance our understanding of the mechanisms of RV failure, which could improve strategies to manage RV dysfunction in PAH.
van Esch, Sadie; Struijk, Dirk G; Krediet, Raymond T
2016-01-01
♦ The quality of the peritoneal membrane can deteriorate over time. Exposure to glucose-based dialysis solutions is the most likely culprit. Because peritonitis is a common complication of peritoneal dialysis (PD), distinguishing between the effect of glucose exposure and a possible additive effect of peritonitis is difficult. The aim of the present study was to compare the time-course of peritoneal transport characteristics in patients without a single episode of peritonitis-representing the natural course-and in patients who experienced 1 or more episodes of peritonitis during long-term follow-up. ♦ This prospective, single-center cohort study enrolled incident adult PD patients who started PD during 1990-2010. A standard peritoneal permeability analysis was performed in the first year of PD treatment and was repeated every year. The results in patients without a single episode of peritonitis ("no-peritonitis group") were compared with the results obtained in patients who experienced 1 or more peritonitis episodes ("peritonitis group") during a follow-up of 4 years. ♦ The 124 patients analyzed included 54 in the no-peritonitis group and 70 in the peritonitis group. The time-course of small-solute transport was different in the groups, with the peritonitis group showing an earlier and more pronounced increase in the mass transfer area coefficient for creatinine (p = 0.07) and in glucose absorption (p = 0.048). In the no-peritonitis group, the net ultrafiltration rate (NUFR) and the transcapillary ultrafiltration rate (TCUFR) both showed a steep increase from the 1st to the 2nd year of PD that was absent in the peritonitis group. Both groups showed a decrease in the NUFR after year 3. A decrease in the TCUFR occurred only in the peritonitis group. That decrease was already present after the year 1 in patients with severe peritonitis. The time-course of free water transport showed a continuous increase in the patients without peritonitis, but a decrease in the
Influence of solids retention time on continuous H{sub 2} production using membrane bioreactor
Energy Technology Data Exchange (ETDEWEB)
Lee, Dong-Yeol [Research Center for Material Cycles and Waste Management, National Institute for Environmental Studies,16-2 Onogawa, Tsukuba, Ibaraki 305 8506 (Japan); Li, Yu-You [Department of Environmental Science, Tohoku University, 6-6-06 Aoba, Sendai, Miyagi 980 8579 (Japan); Noike, Tatsuya [Advanced Research Institute for the Sciences and Humanities, Nihon University 12-5, Goban-cho, Chiyoda-ku, Tokyo 102 8251 (Japan)
2010-01-15
The influence of solids retention time (SRT) on continuous H{sub 2} production in a submerged membrane bioreactor (MBR) was investigated using mixed mesophilic microflora. The bioreactor was continuously operated at the four SRTs of 2, 4, 12.5 and 90 d on a glucose medium under the hydraulic retention time (HRT) of 9 h and the mesophilic condition of 35 C {+-} 0.5. Stable biogas production with H{sub 2} content of 50.8%-60% was achieved at SRTs ranging from 2 to 12.5 d. No methane gas was observed in monitoring the experimental conditions. The H{sub 2} production increased from 17.62 to 26.1 l-H{sub 2}/d when the SRT increased from 2 to 12.5 d, but decreased to 9.1 l-H{sub 2}/d at the 90 d SRT. The best H{sub 2} yield, 1.19 mol-H{sub 2}/mol-glucose, was observed at the SRT of 2 d and the highest H{sub 2} production rate, 5.8 l-H{sub 2}/l/d, was obtained at the SRT of 12.5 d. Stable H{sub 2} production was achieved by maintaining the SRT in the range of 2 - 12.5 d, regardless of the fermentative pathway related to higher lactate production. The decrease in H{sub 2} yield was observed at long SRTs due to the low volatile suspended solids/total suspended solids (VSS/TSS) as well as the high extracellular polymeric substances (EPS) concentrations. These results suggest that the SRT is the key factor enabling sustainable H{sub 2} fermentation in MBR, and that an SLR value of around 1.6 kg-DOC/kg-VSS/d might be the specific condition for achieving optimum H{sub 2} production. (author)
String Scale Cosmological Constant
Chalmers, Gordon
2006-01-01
The cosmological constant is an unexplained until now phenomena of nature that requires an explanation through string effects. The apparent discrepancy between theory and experiment is enourmous and has already been explained several times by the author including mechanisms. In this work the string theory theory of abolished string modes is documented and given perturbatively to all loop orders. The holographic underpinning is also exposed. The matching with the data of the LIGO and D0 experi...
Kehoe, E. James; Ludvig, Elliot A.; Sutton, Richard S.
2010-01-01
Using interstimulus intervals (ISIs) of 125, 250, and 500 msec in trace conditioning of the rabbit nictitating membrane response, the offset times and durations of conditioned responses (CRs) were collected along with onset and peak latencies. All measures were proportional to the ISI, but only onset and peak latencies conformed to the criterion…
Institute of Scientific and Technical Information of China (English)
涂一新; 万泓; 余新春
2001-01-01
根据热电偶的响应特性，利用采样点的温度数据，采用在线式实时处理算法，能较准确地求解出热电偶使用时刻的时间常数。而且利用相关的算法，可较大幅度的减小测量的动态误差，并且缩短测量时间。%Base on response characteristic of the thermocouple, with the temperature data of sampling point and algorithm of real-time-on-line data processing,can evaluation time-constant of thermocouple's usage-time.It not only reducing dynamic-error of measurement with related algorithm，but contraction time of measurement.
Institute of Scientific and Technical Information of China (English)
张全禹
2014-01-01
文章给出了一种测量RC积分电路时间常数的实验方法。利用信号源幅值与电容两端电压之间的比例关系，解决了不能在RC积分电路响应波形图中利用常规方法测量时间常数的问题。%Determination of the time constant of the RC integrator circuit is a difficult point in the first-order RC circuit response testing experiments. It is very difficult to detect the RC time constant through conventional methods. For this problem, this paper gives an experimental method for measuring time constant of the RC integrator circuit, which uses the proportional relationship between the amplitude of the signal source and the voltage across the capacitor to solve the problem that the time constant can't be measured through conventional methods in the RC integrator circuit output waveform diagram. The experimental results show that: the time constant measured through this method is close to the theoretical value with the relative error less than 10%. The method is simple and practical and provides reference for the time constant estimation of the first-order RC integrator circuit.
Karthikayan, S; Sankaranarayanan, G; Karthikeyan, R
2015-11-01
Present energy strategies focus on environmental issues, especially environmental pollution prevention and control by eco-friendly green technologies. This includes, increase in the energy supplies, encouraging cleaner and more efficient energy management, addressing air pollution, greenhouse effect, global warming, and climate change. Biofuels provide the panorama of new fiscal opportunities for people in rural area for meeting their need and also the demand of the local market. Biofuels concern protection of the environment and job creation. Renewable energy sources are self-reliance resources, have the potential in energy management with less emissions of air pollutants. Biofuels are expected to reduce dependability on imported crude oil with connected economic susceptibility, reduce greenhouse gases, other pollutants and invigorate the economy by increasing demand and prices for agricultural products. The use of neat paradise tree oil and induction of eco-friendly material Hydrogen through inlet manifold in a constant pressure heat addition cycle engine (diesel engine) with optimized engine operating parameters such as injection timing, injection pressure and compression ratio. The results shows the heat utilization efficiency for neat vegetable oil is 29% and neat oil with 15% Hydrogen as 33%. The exhaust gas temperature (EGT) for 15% of H2 share as 450°C at full load and the heat release of 80J/deg. crank angle for 15% Hydrogen energy share. Copyright © 2015 Elsevier Inc. All rights reserved.
Directory of Open Access Journals (Sweden)
Ninić Marko
2017-01-01
Full Text Available A novel 60 GHz RF/DC power harvesting system is presented. The system consists of RF to DC rectifier and a DC/DC Buck converter based on constant ON/OFF time (COOT control. The rectifier has a structure of voltage doubler, but employs diodes that have lower parasitics compared to those of the standard MOSFET diodes, resulting in improved power conversion efficiency. The peak efficiency of the rectifier obtained with the extracted parasitics for the output power of 1 mW is about 25%. In order to keep the output voltage of the system to 1.2 V, the COOT control in the Buck converter is used. COOT control has much better efficiency at low output powers compared to the PWM systems. For correct operation of the COOT control, auxiliary sub-blocks: a low power high-speed comparator, a hysteresis comparator, and a high-speed voltage reference are designed and presented. The maximum switching frequency in the Buck converter is about 100MHz and the whole control system has very low static power consumption. The efficiency of the overall system for the output power of 1mW is about 21%. The system is designed in 65 nm CMOS technology.
Song, In-Kyung; Lee, Ji-Hyun; Jung, SungAe; Kim, Jin-Tae; Kim, Hee-Soo
2015-01-01
Although targeting the effect site concentration may offer advantages over the traditional forms of administering intravenous anesthetics, it is not applicable for sufentanil in children because its plasma effect site equilibration rate constant (ke0) is not known yet. We estimated ke0 of sufentanil in children using the time to peak effect (t peak) method. Under general anesthesia, sufentanil t peak was measured after administration of a submaximal bolus dose by means of the decrease in heart rate, blood pressure and calculated approximate entropy (ApEn) of electroencephalogram in 105 children (age range: 3-11 years). ke0 was estimated using t peak and known sufentanil pharmacokinetic parameters in normal children. The mean t peaks were measured as 44 ± 22 s and 227 ± 91 s by heart rate and by mean blood pressure respectively. The estimated ke0 were 5.16/min and 0.49/min by heart rate and blood pressure respectively. t peak could not be measured using the ApEn, thus ke0 could not be calculated by ApEn in children. Shorter measured sufentanil t peak by heart rate compared to blood pressure indicate that the heart rate decrease faster than decreasing of blood pressure. Moreover, the calculated sufentanil ke0 in children depends on the pharmacodynamics parameters.
Directory of Open Access Journals (Sweden)
Zhiyan Zhang
Full Text Available Hematological traits are important indicators of immune function and have been commonly examined as biomarkers of disease and disease severity in humans. Pig is an ideal biomedical model for human diseases due to its high degree of similarity with human physiological characteristics. Here, we conducted genome-wide association studies (GWAS for 18 hematological traits at three growth stages (days 18, 46 and 240 in a White Duroc × Erhualian F2 intercross. In total, we identified 38 genome-wide significant regions containing 185 genome-wide significant SNPs by single-marker GWAS or LONG-GWAS. The significant regions are distributed on pig chromosomes (SSC 1, 4, 5, 7, 8, 10, 11, 12, 13, 17 and 18, and most of significant SNPs reside on SSC7 and SSC8. Of the 38 significant regions, 7 show constant effects on hematological traits across the whole life stages, and 6 regions have time-specific effects on the measured traits at early or late stages. The most prominent locus is the genomic region between 32.36 and 84.49 Mb on SSC8 that is associated with multiple erythroid traits. The KIT gene in this region appears to be a promising candidate gene. The findings improve our understanding of the genetic architecture of hematological traits in pigs. Further investigations are warranted to characterize the responsible gene(s and causal variant(s especially for the major loci on SSC7 and SSC8.
Tagusari, Junta; Matsui, Toshihito
2016-03-25
Chronic sleep disturbance induced by traffic noise is considered to cause environmental sleep disorder, which increases the risk of cardiovascular disease, stroke, diabetes and other stress-related diseases. However, noise indices for the evaluation of sleep disturbance are not based on the neurophysiological process of awakening regulated by the brainstem. In this study, through the neurophysiological approach, we attempted (1) to investigate the thresholds of awakening due to external stimuli in the brainstem; (2) to evaluate the dynamic characteristics in the brainstem and (3) to verify the validity of existing noise indices. Using the mathematical Phillips-Robinson model, we obtained thresholds of awakening in the brainstem for different durations of external stimuli. The analysis revealed that the brainstem seemed insensitive to short stimuli and that the response to external stimuli in the brainstem could be approximated by a first-order lag system with a time constant of 10-100 s. These results suggest that the brainstem did not integrate sound energy as external stimuli, but neuroelectrical signals from auditory nerve. To understand the awakening risk accumulated in the brainstem, we introduced a new concept of "awakening potential" instead of sound energy.
Institute of Scientific and Technical Information of China (English)
H.M.Baran; A.Tataro(g)lu
2013-01-01
The frequency dependence of admittance measurements (capacitance-voltage (C-V) and conductance-voltage (G/ω-V)) of Au/SnO2/n-Si (MOS) capacitors was investigated by taking into account the effects of the interface states (Nss) and series resistance (Rs) at room temperature.Admittance measurements were carried out in frequency and bias voltage ranges of 1 kHz-1 MHz and (-5 V)-(+9 V),respectively.The values of Nss and Rs were determined by using a conductance method and estimating from the admittance measurements of the MOS capacitors.At low frequencies,the interface states can follow the AC signal and yield excess capacitance and conductance.In addition,the parallel conductance (Gp/ω)versus log(f) curves at various voltages include a peak due to the presence of interface states.It is observed that the Nss and their time constant (τ) range from 1.23 × 1012 eV-1.cm-2 to 1.47 × 1012 eV-1 cm-2 and from 7.29 × 10-5 s to 1.81 × 10-5 s,respectively.
Kehoe, E. James; Ludvig, Elliot A.; Sutton, Richard S.
2014-01-01
The present experiment tested whether or not the time course of a conditioned eyeblink response, particularly its duration, would expand and contract, as the magnitude of the conditioned response (CR) changed massively during acquisition, extinction, and reacquisition. The CR duration remained largely constant throughout the experiment, while CR…
Time-dependent effects of o-xylene on rat lung and liver microsomal membrane structure and function.
Park, S H; AuCoin, T A; Silverman, D M; Schatz, R A
1994-12-01
The present study investigates the time-dependent effect of acute intraperitoneal o-xylene administration (1 g/kg) on rat hepatic and pulmonary mixed-function oxidase (MFO) content and activity and microsomal membrane structural parameters for up to 12 h postadministration. The purpose of this study was to determine whether o-xylene has similar effects on these parameters as those previously observed for the m and p isomers. o-xylene decreased total pulmonary cytochrome P-450 content and aryl hydrocarbon hydroxylase (AHH) activity at all time points examined with maximal inhibition occurring at 3 h postdose. The isozyme-specific MFO activity responsible for AHH activity was examined using benzyloxyresorufin O-dealkylation (BROD) as a measure of CYP2B1 activity and ethoxyresorufin O-dealkylation (EROD) as a measure of CYP1A1 activity. Reduced pulmonary activity for both EROD and BROD was noted for the 12-h postexposure period, in agreement with the decreases in total cytochrome P-450 content and AHH activity data. In contrast, increased hepatic cytochrome P-450 content was noted at 6 and 12 h with slightly increased EROD activity and markedly increased BROD activity. Conjugated diene (CD) formation, and index of membrane peroxidation, and phospholipid (PL) and cholesterol (CL) content of the microsomal membranes were also examined in lung and liver to assess membrane structural integrity. Pulmonary CD formation was increased only at the 12-h time point, while hepatic CD formation was increased from 3 to 12 h. An increase in pulmonary microsomal PL and CL content was noted as early as 1 h postdose. In liver, PL content was increased as early as 3 h, with no change in CL content. An increase in the PL/CL ratio, suggesting an increase in membrane fluidity, was observed in pulmonary microsomes 12 h after dosing, and in hepatic microsomes at 3, 6, and 12 h postdose. There was no correlation between solvent tissue levels and MFO or membrane changes. It seems unlikely that
Energy Technology Data Exchange (ETDEWEB)
Judd, Ellen M.; Comolli, Luis R.; Chen, Joseph C.; Downing,Kenneth H.; Moerner, W.E.; McAdams, Harley H.
2005-05-01
Cryo-electron microscope tomography (cryoEM) and a fluorescence loss in photobleaching (FLIP) assay were used to characterize progression of the terminal stages of Caulobacter crescentus cell division. Tomographic cryoEM images of the cell division site show separate constrictive processes closing first the inner, and then the outer, membrane in a manner distinctly different from septum-forming bacteria. The smallest observed pre-fission constrictions were 60 nm for both the inner and outer membrane. FLIP experiments had previously shown cytoplasmic compartmentalization, when cytoplasmic proteins can no longer diffuse between the two nascent progeny cell compartments, occurring 18 min before daughter cell separation in a 135 min cell cycle. Here, we used FLIP experiments with membrane-bound and periplasmic fluorescent proteins to show that (1) periplasmic compartmentalization occurs after cytoplasmic compartmentalization, consistent with the cryoEM observations, and (2) inner membrane and periplasmic proteins can diffuse past the FtsZ constriction site, indicating that the cell division machinery does not block membrane diffusion.
Glassman, R B
2000-02-01
1. The capacity of working memory (WM) for about 7+/-2 ("the magical number") serially organized simple verbal items may represent a fundamental constant of cognition. Indeed, there is the same capacity for sense of familiarity of a number of recently encountered places, observed in radial maze performance both of lab rats and of humans. 2. Moreover, both species show a peculiar capacity for retaining WM of place over delays. The literature also describes paradoxes of extended time duration in certain human verbal recall tasks. Certain bird species have comparable capacity for delayed recall of about 4 to 8 food caches in a laboratory room. 3. In addition to these paradoxes of the time dimension with WM (still sometimes called "short-term" memory) there are another set of paradoxes of dimensionality for human judgment of magnitudes, noted by Miller in his classic 1956 paper on "the magical number." We are able to reliably refer magnitudes to a rating scale of up to about seven divisions. Remarkably, that finding is largely independent of perceptual modality or even of the extent of a linear interval selected within any given modality. 4. These paradoxes suggest that "the magical number 7+/2" depends on fundamental properties of mammalian brains. 5. This paper theorizes that WM numerosity is conserved as a fundamental constant, by means of elasticity of cognitive dimensionality, including the temporal pace of arrival of significant items of cognitive information. 6. A conjectural neural code for WM item-capacity is proposed here, which extends the hypothetical principle of binding-by-synchrony. The hypothesis is that several coactive frequencies of brain electrical rhythms each mark a WM item. 7. If, indeed, WM does involve a brain wave frequency code (perhaps within the gamma frequency range that has often been suggested with the binding hypothesis) mathematical considerations suggest additional relevance of harmonic relationships. That is, if copresent sinusoids
Reinsperger, Tony; Luy, Burkhard
2014-02-01
Heteronuclear one-bond couplings are of interest for various aspects of structural analysis of small organic molecules, including for example the distinction of axial and equatorial protons or the use of RDCs as angular constraints. Such couplings are most easily measured from pure doublets in HSQC-type spectra. Recently, the fully decoupled RESET HSQC experiment was reported and several other so-called pure-shift methods followed that allow for the removal of splittings due to homonuclear scalar interactions in one and two-dimensional NMR. In this work we present broadband homonuclear decoupled CLIP/CLAP-RESET experiments based on an isotope-selective BIRD filter element using a recently reported improved version of Zangger-Sterk data chunking. The concatenated FIDs result in multiplets in which most homonuclear splittings are removed while the heteronuclear one-bond couplings are retained. Couplings can be extracted in an IPAP fashion without scaling of subspectra by the use of optimized coherence transfer elements like the COB-INEPT. The method leads to complete homonuclear decoupling for CH groups and CH3 groups in isotropic samples, but leaves residual splittings with antiphase contributions for e.g. CH2 groups due to (2)JHH coupling evolution that is not affected by the BIRD element. For this case we present a constant-time version of the proposed BIRD decoupling scheme with full homonuclear decoupling. In addition, the effects of strong coupling are discussed. Strong coupling artifacts cannot be circumvented, but the proposed experiments allow their distinct recognition.
Pathophysiological advances in membranous nephropathy: time for a shift in patient's care.
Ronco, Pierre; Debiec, Hanna
2015-05-16
Membranous nephropathy is a major cause of nephrotic syndrome of non-diabetic origin in adults. It is the second or third leading cause of end-stage renal disease in patients with primary glomerulonephritis, and is the leading glomerulopathy that recurs after kidney transplantation (occurring in about 40% of patients). Treatment with costly and potentially toxic drugs remains controversial and challenging, partly because of insufficient insight into the pathogenesis of the disease and absence of sensitive biomarkers of disease activity. The disease is caused by the formation of immune deposits on the outer aspect of the glomerular basement membrane, which contain podocyte or planted antigens and circulating antibodies specific to those antigens, resulting in complement activation. In 2002, podocyte neutral endopeptidase was identified as an antigenic target of circulating antibodies in alloimmune neonatal nephropathy, and in 2009, podocyte phospholipase A2 receptor (PLA2R) was reported as an antigenic target in autoimmune adult membranous nephropathy. These major breakthroughs were translated to clinical practice very quickly. Measurement of anti-PLA2R antibodies in serum and detection of PLA2R antigen in glomerular deposits can now be done routinely. Anti-PLA2R antibodies have high specificity (close to 100%), sensitivity (70-80%), and predictive value. PLA2R detection in immune deposits allows for retrospective diagnosis of PLA2R-related membranous nephropathy in archival kidney biopsies. These tests already have a major effect on diagnosis and monitoring of treatment, including after transplantation.
A Constant Off-time Controlled Boost Converter%一种固定关断时间控制模式的升压变换器
Institute of Scientific and Technical Information of China (English)
程林; 倪金华; 洪志良; 刘洋
2011-01-01
采用0.5 μm 40 V BCD工艺,实现了一款基于固定关断时间控制模式的升压型直流-直流转换器.采取了输出电压双路反馈的方式,既提高了瞬态响应速度,也简化了补偿网络的设计.同时提出了一种新型的频率控制电路,克服了固定关断时间控制模式开关频率不固定的缺点.测试结果表明,当芯片输人电压为5 V,输出电压为15 V时,峰值效率达到了89.7%,最大输出电流达到500 mA.在300mA的负载跳变下,过冲或欠压小于140 mV,响应时间小于82μs.开关频率变化在目标频率1%以内.%A constant off-time controlled boost converter is realized in 0.5μm 40 V BCD technology. The adopted two-path feedback method not only speeds the transient response, but also simplifies the compensation network. A novel frequency control circuit is also proposed to compensate switching frequency variation. Measurement results at 5 V input and 15 V output show that the peak power efficiency is 89.7％, the maximum load current is 500 mA. The overshoot and undershoot are less than 140 mV and recovery time is shorter than 82 μs with 300 mA load current step. The switching frequency variation of 1 ％ can be obtained.
Vuissoz, C.; Courbin, F.; Sluse, D.; Meylan, G.; Chantry, V.; Eulaers, E.; Morgan, C.; Eyler, M. E.; Kochanek, C. S.; Coles, J.; Saha, P.; Magain, P.; Falco, E. E.
2008-09-01
Gravitationally lensed quasars can be used to map the mass distribution in lensing galaxies and to estimate the Hubble constant H0 by measuring the time delays between the quasar images. Here we report the measurement of two independent time delays in the quadruply imaged quasar WFI J2033-4723 (z = 1.66). Our data consist of R-band images obtained with the Swiss 1.2 m EULER telescope located at La Silla and with the 1.3 m SMARTS telescope located at Cerro Tololo. The light curves have 218 independent epochs spanning 3 full years of monitoring between March 2004 and May 2007, with a mean temporal sampling of one observation every 4th day. We measure the time delays using three different techniques, and we obtain Δ tB-A = 35.5 ± 1.4 days (3.8%) and Δ tB-C = 62.6+ 4.1- 2.3~days ~ (+ 6.5%- 3.7%), where A is a composite of the close, merging image pair. After correcting for the time delays, we find R-band flux ratios of FA/FB = 2.88 ± 0.04, FA/FC = 3.38 ± 0.06, and FA1/FA2 = 1.37 ± 0.05 with no evidence for microlensing variability over a time scale of three years. However, these flux ratios do not agree with those measured in the quasar emission lines, suggesting that longer term microlensing is present. Our estimate of H0 agrees with the concordance value: non-parametric modeling of the lensing galaxy predicts H0 = 67+13-10 km s-1 Mpc-1, while the Single Isothermal Sphere model yields H0 = 63+7-3 km s-1 Mpc-1 (68% confidence level). More complex lens models using a composite de Vaucouleurs plus NFW galaxy mass profile show twisting of the mass isocontours in the lensing galaxy, as do the non-parametric models. As all models also require a significant external shear, this suggests that the lens is a member of the group of galaxies seen in field of view of WFI J2033-4723. Based on observations obtained with the 1.2 m EULER Swiss Telescope, the 1.3 m Small and Moderate Aperture Research Telescope System (SMARTS) which is operated by the SMARTS Consortium, and the
2013-07-01
single-point flow velocity and membrane vibration velocity measurements were recorded via a hotwire (HW) anemometer and laser vibrometer (LV...solvent in the primer to evaporate for approximately 30 minutes, the two parts of raw silicone (Dragon Skin Shore 20A) were mixed in a separate cup to... anemometer and laser vibrometer measurements permitted coherence analysis between the two time-resolved data series. Coherence assessment between the two
Directory of Open Access Journals (Sweden)
Feride Aylin Kantarci
2014-08-01
Full Text Available AIM: To investigate the permeability of amniotic membrane in herpes virus cell culture to acyclovir with real time polymerase chain reaction (RT-PCR.METHODS: Madin-Darby Bovine Kidney (MDBK cell culture and Bovine Herpes Virus (BHV1 type 1 were used in the study. Cell cultures were grouped into two on the basis of herpes virus inoculation. Each group was sub-grouped into three. Amniotic membrane (V-HAM, acyclovir (V-A, and amniotic membrane and acyclovir (V-HAM-A were applied to these subgroup cultures, respectively. After the application of the membrane and the drug, the cultures were evaluated at 24 and 48h for cytopathic effect positive (CPE+ with a tissue culture microscope. In the CPE (+ samples, the DNA was extracted for viral DNA analysis by RT-PCR.RESULTS: In control cultures without herpes virus CPE was not detected. Besides, amniotic membrane and acyclovir did not have cytotoxic effect on cell cultures. CPE were detected in Bovine Herpesvirus type-1 inoculated cell cultures after amniotic membrane and/or acyclovir application. DNA analysis with RT-PCR indicated that Cycle threshold (Ct values were lower in the BHV1 and membrane applied group (amniotic membrane group< acyclovir group< membrane and acyclovir group. This showed that membrane did not have antiviral effect. The membrane and acyclovir cell culture groups with high Ct values indicated that membrane was permeable and had a low barrier effect to drug,CONCLUSION: In our in-vitro study, we found that amniotic membrane, which can be used in the treatment of corneal diseases, did not have antiviral effect. Besides, we detected that amniotic membrane was permeable to acyclovir in BHV-1 inoculated MDBK cell culture. However, more studies are necessary to investigate the quantitative effects of amniotic membrane and acyclovir.
Constant-time 2D and 3D through-bond correlation NMR spectroscopy of solids under 60 kHz MAS
Energy Technology Data Exchange (ETDEWEB)
Zhang, Rongchun; Ramamoorthy, Ayyalusamy, E-mail: ramamoor@umich.edu [Biophysics and Department of Chemistry, The University of Michigan, Ann Arbor, Michigan 48109-1055 (United States)
2016-01-21
Establishing connectivity and proximity of nuclei is an important step in elucidating the structure and dynamics of molecules in solids using magic angle spinning (MAS) NMR spectroscopy. Although recent studies have successfully demonstrated the feasibility of proton-detected multidimensional solid-state NMR experiments under ultrafast-MAS frequencies and obtaining high-resolution spectral lines of protons, assignment of proton resonances is a major challenge. In this study, we first re-visit and demonstrate the feasibility of 2D constant-time uniform-sign cross-peak correlation (CTUC-COSY) NMR experiment on rigid solids under ultrafast-MAS conditions, where the sensitivity of the experiment is enhanced by the reduced spin-spin relaxation rate and the use of low radio-frequency power for heteronuclear decoupling during the evolution intervals of the pulse sequence. In addition, we experimentally demonstrate the performance of a proton-detected pulse sequence to obtain a 3D {sup 1}H/{sup 13}C/{sup 1}H chemical shift correlation spectrum by incorporating an additional cross-polarization period in the CTUC-COSY pulse sequence to enable proton chemical shift evolution and proton detection in the incrementable t{sub 1} and t{sub 3} periods, respectively. In addition to through-space and through-bond {sup 13}C/{sup 1}H and {sup 13}C/{sup 13}C chemical shift correlations, the 3D {sup 1}H/{sup 13}C/{sup 1}H experiment also provides a COSY-type {sup 1}H/{sup 1}H chemical shift correlation spectrum, where only the chemical shifts of those protons, which are bonded to two neighboring carbons, are correlated. By extracting 2D F1/F3 slices ({sup 1}H/{sup 1}H chemical shift correlation spectrum) at different {sup 13}C chemical shift frequencies from the 3D {sup 1}H/{sup 13}C/{sup 1}H spectrum, resonances of proton atoms located close to a specific carbon atom can be identified. Overall, the through-bond and through-space homonuclear/heteronuclear proximities determined from the
Constant-time 2D and 3D through-bond correlation NMR spectroscopy of solids under 60 kHz MAS.
Zhang, Rongchun; Ramamoorthy, Ayyalusamy
2016-01-21
Establishing connectivity and proximity of nuclei is an important step in elucidating the structure and dynamics of molecules in solids using magic angle spinning (MAS) NMR spectroscopy. Although recent studies have successfully demonstrated the feasibility of proton-detected multidimensional solid-state NMR experiments under ultrafast-MAS frequencies and obtaining high-resolution spectral lines of protons, assignment of proton resonances is a major challenge. In this study, we first re-visit and demonstrate the feasibility of 2D constant-time uniform-sign cross-peak correlation (CTUC-COSY) NMR experiment on rigid solids under ultrafast-MAS conditions, where the sensitivity of the experiment is enhanced by the reduced spin-spin relaxation rate and the use of low radio-frequency power for heteronuclear decoupling during the evolution intervals of the pulse sequence. In addition, we experimentally demonstrate the performance of a proton-detected pulse sequence to obtain a 3D (1)H/(13)C/(1)H chemical shift correlation spectrum by incorporating an additional cross-polarization period in the CTUC-COSY pulse sequence to enable proton chemical shift evolution and proton detection in the incrementable t1 and t3 periods, respectively. In addition to through-space and through-bond (13)C/(1)H and (13)C/(13)C chemical shift correlations, the 3D (1)H/(13)C/(1)H experiment also provides a COSY-type (1)H/(1)H chemical shift correlation spectrum, where only the chemical shifts of those protons, which are bonded to two neighboring carbons, are correlated. By extracting 2D F1/F3 slices ((1)H/(1)H chemical shift correlation spectrum) at different (13)C chemical shift frequencies from the 3D (1)H/(13)C/(1)H spectrum, resonances of proton atoms located close to a specific carbon atom can be identified. Overall, the through-bond and through-space homonuclear/heteronuclear proximities determined from the 3D (1)H/(13)C/(1)H experiment would be useful to study the structure and dynamics of
Directory of Open Access Journals (Sweden)
Ramkumar Menon
2017-08-01
Full Text Available Human parturition is an inflammatory process that involves both fetal and maternal compartments. The precise immune cell interactions have not been well delineated in human uterine tissues during parturition, but insights into human labor initiation have been informed by studies in animal models. Unfortunately, the timing of parturition relative to fetal maturation varies among viviparous species—indicative of different phylogenetic clocks and alarms—but what is clear is that important common pathways must converge to control the birth process. Herein, we hypothesize a novel signaling mechanism initiated by human fetal membrane aging and senescence-associated inflammation. Programmed events of fetal membrane aging coincide with fetal growth and organ maturation. Mechanistically, senescence involves in telomere shortening and activation of p38 mitogen-activated signaling kinase resulting in aging-associated phenotypic transition. Senescent tissues release inflammatory signals that are propagated via exosomes to cause functional changes in maternal uterine tissues. In vitro, oxidative stress causes increased release of inflammatory mediators (senescence-associated secretory phenotype and damage-associated molecular pattern markers that can be packaged inside the exosomes. These exosomes traverse through tissues layers, reach maternal tissues to increase overall inflammatory load transitioning them from a quiescent to active state. Animal model studies have shown that fetal exosomes can travel from fetal to the maternal side. Thus, aging fetal membranes and membrane-derived exosomes cargo fetal signals to the uterus and cervix and may trigger parturition. This review highlights a novel hypothesis in human parturition research based on data from ongoing research using human fetal membrane model system.
Menon, Ramkumar; Mesiano, Sam; Taylor, Robert N
2017-01-01
Human parturition is an inflammatory process that involves both fetal and maternal compartments. The precise immune cell interactions have not been well delineated in human uterine tissues during parturition, but insights into human labor initiation have been informed by studies in animal models. Unfortunately, the timing of parturition relative to fetal maturation varies among viviparous species-indicative of different phylogenetic clocks and alarms-but what is clear is that important common pathways must converge to control the birth process. Herein, we hypothesize a novel signaling mechanism initiated by human fetal membrane aging and senescence-associated inflammation. Programmed events of fetal membrane aging coincide with fetal growth and organ maturation. Mechanistically, senescence involves in telomere shortening and activation of p38 mitogen-activated signaling kinase resulting in aging-associated phenotypic transition. Senescent tissues release inflammatory signals that are propagated via exosomes to cause functional changes in maternal uterine tissues. In vitro, oxidative stress causes increased release of inflammatory mediators (senescence-associated secretory phenotype and damage-associated molecular pattern markers) that can be packaged inside the exosomes. These exosomes traverse through tissues layers, reach maternal tissues to increase overall inflammatory load transitioning them from a quiescent to active state. Animal model studies have shown that fetal exosomes can travel from fetal to the maternal side. Thus, aging fetal membranes and membrane-derived exosomes cargo fetal signals to the uterus and cervix and may trigger parturition. This review highlights a novel hypothesis in human parturition research based on data from ongoing research using human fetal membrane model system.
Menon, Ramkumar; Mesiano, Sam; Taylor, Robert N.
2017-01-01
Human parturition is an inflammatory process that involves both fetal and maternal compartments. The precise immune cell interactions have not been well delineated in human uterine tissues during parturition, but insights into human labor initiation have been informed by studies in animal models. Unfortunately, the timing of parturition relative to fetal maturation varies among viviparous species—indicative of different phylogenetic clocks and alarms—but what is clear is that important common pathways must converge to control the birth process. Herein, we hypothesize a novel signaling mechanism initiated by human fetal membrane aging and senescence-associated inflammation. Programmed events of fetal membrane aging coincide with fetal growth and organ maturation. Mechanistically, senescence involves in telomere shortening and activation of p38 mitogen-activated signaling kinase resulting in aging-associated phenotypic transition. Senescent tissues release inflammatory signals that are propagated via exosomes to cause functional changes in maternal uterine tissues. In vitro, oxidative stress causes increased release of inflammatory mediators (senescence-associated secretory phenotype and damage-associated molecular pattern markers) that can be packaged inside the exosomes. These exosomes traverse through tissues layers, reach maternal tissues to increase overall inflammatory load transitioning them from a quiescent to active state. Animal model studies have shown that fetal exosomes can travel from fetal to the maternal side. Thus, aging fetal membranes and membrane-derived exosomes cargo fetal signals to the uterus and cervix and may trigger parturition. This review highlights a novel hypothesis in human parturition research based on data from ongoing research using human fetal membrane model system. PMID:28861041
The fundamental constants a mystery of physics
Fritzsch, Harald
2009-01-01
The speed of light, the fine structure constant, and Newton's constant of gravity — these are just three among the many physical constants that define our picture of the world. Where do they come from? Are they constant in time and across space? In this book, physicist and author Harald Fritzsch invites the reader to explore the mystery of the fundamental constants of physics in the company of Isaac Newton, Albert Einstein, and a modern-day physicist
Decay constants in geochronology
Institute of Scientific and Technical Information of China (English)
IgorM.Villa; PaulR.Renne
2005-01-01
Geologic time is fundamental to the Earth Sciences, and progress in many disciplines depends critically on our ability to measure time with increasing accuracy and precision. Isotopic geochronology makes use of the decay of radioactive nuclides as a help to quantify the histories of rock, minerals, and other materials. Both accuracy and precision of radioisotopic ages are, at present, limited by those of radioactive decay constants. Modem mass spectrometers can measure isotope ratios with a precision of 10-4 or better. On the other hand, the uncertainties associated with direct half-life determinations are, in most cases, still at the percent level. The present short note briefly summarizes progress and problems that have been encountered during the Working Group's activity.
[Kinetics of in vitro drug release from chitosan and N-alkyl chitosan membranes].
Li, M; Xin, M; Wang, Q; Yao, K
2001-03-01
By using the so-called "lag-time" method, we studied the effect of membrane thickness(h), initial drug concentration(Co) and flow rate(V) on the difusion coefficient(D) of model drug in membranes. The experiment indicates that D increases as h and v increase; D Keeps constant when C0 changes; Under the same condition, the D value of N-alkyl chitosan membrane is bigger than that of pure chitosan membrane.
Institute of Scientific and Technical Information of China (English)
Feride; Aylin; Kantarci; Ali; Reza; Faraji; Aykut; Ozkul; Fikret; Akata
2014-01-01
·AIM: To investigate the permeability of amniotic membrane in herpes virus cell culture to acyclovir with real time polymerase chain reaction(RT-PCR).·METHODS: Madin-Darby Bovine Kidney(MDBK) cell culture and Bovine Herpes Virus(BHV1) type 1 were used in the study. Cell cultures were grouped into two on the basis of herpes virus inoculation. Each group was sub-grouped into three. Amniotic membrane(V-HAM),acyclovir(V-A), and amniotic membrane and acyclovir(V-HAM-A) were applied to these subgroup cultures,respectively. After the application of the membrane and the drug, the cultures were evaluated at 24 and 48 h for cytopathic effect positive(CPE +) with a tissue culture microscope. In the CPE(+) samples, the DNA was extracted for viral DNA analysis by RT-PCR.·RESULTS: In control cultures without herpes virus CPE was not detected. Besides, amniotic membrane and acyclovir did not have cytotoxic effect on cell cultures.CPE were detected in Bovine Herpesvirus type-1inoculated cell cultures after amniotic membrane and/or acyclovir application. DNA analysis with RT-PCR indicated that Cycle threshold(Ct) values were lower in the BHV1 and membrane applied group(amniotic membrane group < acyclovir group < membrane and acyclovir group). This showed that membrane did not have antiviral effect. The membrane and acyclovir cell culture groups with high Ct values indicated thatmembrane was permeable and had a low barrier effect to drug.·CONCLUSION: In our in-vitro study, we found that amniotic membrane, which can be used in the treatment of corneal diseases, did not have antiviral effect. Besides,we detected that amniotic membrane was permeable to acyclovir in BHV-1 inoculated MDBK cell culture.However, more studies are necessary to investigate the quantitative effects of amniotic membrane and acyclovir.
Felmy, Felix; Neher, Erwin; Schneggenburger, Ralf
2003-12-09
Ca2+ influx through voltage-gated Ca2+ channels and the resulting elevation of intracellular Ca2+ concentration, [Ca2+]i, triggers transmitter release in nerve terminals. However, it is controversial whether in addition to the opening of Ca2+ channels, membrane potential directly affects transmitter release. Here, we assayed the influence of membrane potential on transmitter release at the calyx of Held nerve terminals. Transmitter release was evoked by presynaptic Ca2+ uncaging, or by presynaptic Ca2+ uncaging paired with presynaptic voltage-clamp depolarizations to +80 mV, under pharmacological block of voltage-gated Ca2+ channels. Such a change in membrane potential did not alter the Ca2+ dependence of transmitter release rates or synaptic delays. We also found, by varying the amount of Ca2+ influx during Ca2+ tail-currents, that the time course of phasic transmitter release is not invariant to changes in release probability. Rather, the time difference between peak Ca2+ current and peak transmitter release became progressively shorter with increasing Ca2+ current amplitude. When this time difference was plotted as a function of the estimated local [Ca2+]i at the sites of vesicle fusion, a slope of approximately 100 micros per 10 microM [Ca2+]i was found, in reasonable agreement with a model of cooperative Ca2+ binding and vesicle fusion. Thus, the amplitude and time course of the [Ca2+]i signal at the sites of vesicle fusion controls the timing and the amount of transmitter release, both under conditions of brief periods of Ca2+ influx, as well as during step-like elevations of [Ca2+]i produced by Ca2+ uncaging.
Directory of Open Access Journals (Sweden)
S. Chelliapan
2011-03-01
Full Text Available The present investigation was aimed at determining the impact of the macrolide antibiotic Tylosin in reduced HRT at constant organic loading rate (OLR by varying feed substrate concentration in an up-flow anaerobic stage reactor (UASR. The antibiotic concentration was maintained at 200 mg.L-1, at constant OLR of 1.88 kg COD.m-3.d-1, by varying feed substrate concentration to the UASR and the HRT was decreased gradually from 4 to 1 d. Throughout the operation period, brewery wastewater was used as simple feed substrate to elevate the concentration of easily biodegradable carbon in comparison with the concentrations of more recalcitrant Tylosin substrate. The reactor alkalinity was controlled in all the stages of UASR by adding 1000 - 2000 mg.L-1 CaCO3. Results showed the total COD removal efficiency at 4 d HRT was around 92%, after which point there was a slight decrease at 3 and 2 d HRT (average 82%, and this was reduced further (average 77% at a HRT of 1 d. The UASR showed stable operation with effluent volatile fatty acid (VFA less than 300 mg.L-1 throughout the experimental period (HRT 4 - 1 d. Moreover, the average methane yield (CH4.kg CODr-1 showed a relatively constant profile and was largely unaffected by HRT in all the stages of UASR. These results show that bacteria were readily adapted to wastewater containing Tylosin at lower HRTs and did not affect the reactor performance substantially.
Ganguly, Gaurab; Mukherjee, Manas; Paul, Ankan
2014-01-01
Based on the spectroscopic constants derived from highly accurate potential energy surfaces, the SeD radical is identified as a spectroscopic probe for measuring spatial and temporal variation of fundamental physical constants such as the fine-structure constant (denoted as $\\alpha=\\frac{e^2}{\\hbar c}$) and the proton-to-electron mass ratio (denoted as $\\mu=\\frac{m_p}{m_e}$). The ground state of SeD ($X^2\\Pi$), due to spin-orbit coupling, splits into two fine structure multiplets $^2\\Pi_{\\frac{3}{2}}$ and $^2\\Pi_{\\frac{1}{2}}$. The potential energy surfaces of these spin-orbit components are derived from a state of the art electronic structure method, MRCI+Q inclusive of scalar relativistic effects with the spin-orbit effects accounted through the Breit-Pauli operator. The relevant spectroscopic data are evaluated using Murrel-Sorbie fit to the potential energy surfaces. The spin-orbit splitting($\\omega_f$) between the two multiplets is similar in magnitude with the harmonic frequency ($\\omega_e$) of the diat...
Varying constants, Gravitation and Cosmology
Uzan, Jean-Philippe
2010-01-01
Fundamental constants are a cornerstone of our physical laws. Any constant varying in space and/or time would reflect the existence of an almost massless field that couples to matter. This will induce a violation of the universality of free fall. It is thus of utmost importance for our understanding of gravity and of the domain of validity of general relativity to test for their constancy. We thus detail the relations between the constants, the tests of the local position invariance and of the universality of free fall. We then review the main experimental and observational constraints that have been obtained from atomic clocks, the Oklo phenomenon, Solar system observations, meteorites dating, quasar absorption spectra, stellar physics, pulsar timing, the cosmic microwave background and big bang nucleosynthesis. At each step we describe the basics of each system, its dependence with respect to the constants, the known systematic effects and the most recent constraints that have been obtained. We then describ...
Untangling Fixed Effects and Constant Regressors
Klaassen, F.; Teulings, R.
2015-01-01
Fixed effects (FE) in panel data models overlap each other and prohibit the identification of the impact of "constant" regressors. Think of regressors that are constant across countries in a country-time panel with time FE. The traditional approach is to drop some FE and constant regressors by
Untangling Fixed Effects and Constant Regressors
Klaassen, F.; Teulings, R.
2015-01-01
Fixed effects (FE) in panel data models overlap each other and prohibit the identification of the impact of "constant" regressors. Think of regressors that are constant across countries in a country-time panel with time FE. The traditional approach is to drop some FE and constant regressors by norma
Ion exchange equilibrium constants
Marcus, Y
2013-01-01
Ion Exchange Equilibrium Constants focuses on the test-compilation of equilibrium constants for ion exchange reactions. The book first underscores the scope of the compilation, equilibrium constants, symbols used, and arrangement of the table. The manuscript then presents the table of equilibrium constants, including polystyrene sulfonate cation exchanger, polyacrylate cation exchanger, polymethacrylate cation exchanger, polysterene phosphate cation exchanger, and zirconium phosphate cation exchanger. The text highlights zirconium oxide anion exchanger, zeolite type 13Y cation exchanger, and
Directory of Open Access Journals (Sweden)
Kusworo Tutuk Djoko
2017-01-01
Full Text Available The coastal areas in Indonesia often have a problem of clean water lack, because the water is classified as brackish water. Therefore, this research investigated the fabrication of CA membranes using phase inversion method for brackish water treatment. Investigation was conducted to study the effect of combination dope composition and evaporation time on separation performance and morphology of the memrbane. Membrane was fabricated by dry-wet phase inversion technique with variation of polymer concentration 17, 18 and 20 wt% in the total solid and evaporation time of 5, 10 and 15 seconds, respectively. The asymmetric membranes were characterized by permeability test through rejection and flux measurements using brackish water as feed. The experimental results from SEM images analysis showed that all the membranes have a thin small porous layer and thicker sub-structure of larger porous layer formed asymmetric membrane. Moreover, the greater polymer concentration is resulting smaller pore size and smaller membrane porosity. The longer evaporation time was also resulted in denser membrane active layer. The best membrane performance was observed at the composition of 20 wt% CA polymer, 1 wt % polyethylene glycol with the solvent evaporation time of 15 seconds.
Takechi-Haraya, Yuki; Aki, Kenzo; Tohyama, Yumi; Harano, Yuichi; Kawakami, Toru; Saito, Hiroyuki; Okamura, Emiko
2017-04-15
Glycosaminoglycans (GAGs), which are covalently-linked membrane proteins at the cell surface have recently been suggested to involve in not only endocytic cellular uptake but also non-endocytic direct cell membrane translocation of arginine-rich cell-penetrating peptides (CPPs). However, in-situ comprehensive observation and the quantitative analysis of the direct membrane translocation processes are challenging, and the mechanism therefore remains still unresolved. In this work, real-time in-cell NMR spectroscopy was applied to investigate the direct membrane translocation of octaarginine (R8) into living cells. By introducing 4-trifluoromethyl-l-phenylalanine to the N terminus of R8, the non-endocytic membrane translocation of (19)F-labeled R8 ((19)F-R8) into a human myeloid leukemia cell line was observed at 4 °C with a time resolution in the order of minutes. (19)F NMR successfully detected real-time R8 translocation: the binding to anionic GAGs at the cell surface, followed by the penetration into the cell membrane, and the entry into cytosol across the membrane. The NMR concentration analysis enabled quantification of how much of R8 was staying in the respective translocation processes with time in situ. Taken together, our in-cell NMR results provide the physicochemical rationale for spontaneous penetration of CPPs in cell membranes.
Temporal variation of coupling constants and nucleosynthesis
Oberhummer, Heinz; Fairbairn, M; Schlattl, H; Sharma, M M
2003-01-01
We investigate the triple-alpha process and the Oklo phenomenon to obtain constraints on possible cosmological time variations of fundamental constants. Specifically we study cosmological temporal constraints for the fine structure constant and nucleon and meson masses.
Temporal variation of coupling constants and nucleosynthesis
Oberhummer, H.; Csótó, A.; Fairbairn, M.; Schlattl, H.; Sharma, M. M.
2003-05-01
We investigate the triple-alpha process and the Oklo phenomenon to obtain constraints on possible cosmological time variations of fundamental constants. Specifically we study cosmological temporal constraints for the fine structure constant and nucleon and meson masses.
Energy Technology Data Exchange (ETDEWEB)
Bitler, Arkady, E-mail: arkady.bitler@weizmann.ac.il [Department of Chemical Research Support (Israel); Lev, Naama; Fridmann-Sirkis, Yael; Blank, Lior [Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100 (Israel); Cohen, Sidney R. [Department of Chemical Research Support (Israel); Shai, Yechiel [Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100 (Israel)
2010-05-15
One of the most important steps in the process of viral infection is a fusion between cell membrane and virus, which is mediated by the viral envelope glycoprotein. The study of activity of the glycoprotein in the post-fusion state is important for understanding the progression of infection. Here we present a first real-time kinetic study of the activity of gp41 (the viral envelope glycoprotein of human immunodeficiency virus-HIV) and its two mutants in the post-fusion state with nanometer resolution by atomic force microscopy (AFM). Tracking the changes in the phosphatidylcholine (PC) and phosphatidylcholine-phosphatidylserine (PC:PS) membrane integrity over one hour by a set of AFM images revealed differences in the interaction of the three types of protein with zwitterionic and negatively charged membranes. A quantitative analysis of the slow kinetics of hole formation in the negatively charged lipid bilayer is presented. Specifically, analysis of the rate of roughness change for the three types of proteins suggests that they exhibit different types of kinetic behavior.
Energy Technology Data Exchange (ETDEWEB)
Beiu, V.
1997-04-01
In this paper the authors discuss several complexity aspects pertaining to neural networks, commonly known as the curse of dimensionality. The focus will be on: (1) size complexity and depth-size tradeoffs; (2) complexity of learning; and (3) precision and limited interconnectivity. Results have been obtained for each of these problems when dealt with separately, but few things are known as to the links among them. They start by presenting known results and try to establish connections between them. These show that they are facing very difficult problems--exponential growth in either space (i.e. precision and size) and/or time (i.e., learning and depth)--when resorting to neural networks for solving general problems. The paper will present a solution for lowering some constants, by playing on the depth-size tradeoff.
Spatial Variations of Fundamental Constants
Barrow, John D; Barrow, John D.; Toole, Chris O'
1999-01-01
We show that observational limits on the possible time variation of constants of Nature are significantly affected by allowing for both space and time variation. Bekenstein's generalisation of Maxwell's equations to allow for cosmological variation of $alpha$ is investigated in a universe containing spherically symmetric inhomogeneities. The time variation of $alpha$ is determined by the local matter density and hence limits obtained in high-density geophysical enviroments are far more constraining than those obtained at high redshift. This new feature is expected to be a property of a wide class of theories for the variation of constants.
Benard, P
2003-01-01
The linearization of the meteorological equations around a specified reference state, usually applied in NWP to define the linear system of constant-coefficients semi-implicit schemes, is outlined as an unnecessarily restrictive approach which may be detrimental in terms of stability. It is shown theoretically that an increased robustness can sometimes be obtained by choosing the reference linear system in a wider set of possibilities. The potential benefits of this new approach are illustrated in two simple examples. The advantage in robustness is not obtained at the price of an increased error or complexity.
Cosmological Constant, Fine Structure Constant and Beyond
Wei, Hao; Li, Hong-Yu; Xue, Dong-Ze
2016-01-01
In this work, we consider the cosmological constant model $\\Lambda\\propto\\alpha^{-6}$, which is well motivated from three independent approaches. As is well known, the evidence of varying fine structure constant $\\alpha$ was found in 1998. If $\\Lambda\\propto\\alpha^{-6}$ is right, it means that the cosmological constant $\\Lambda$ should be also varying. In this work, we try to develop a suitable framework to model this varying cosmological constant $\\Lambda\\propto\\alpha^{-6}$, in which we view it from an interacting vacuum energy perspective. We propose two types of models to describe the evolutions of $\\Lambda$ and $\\alpha$. Then, we consider the observational constraints on these models, by using the 293 $\\Delta\\alpha/\\alpha$ data from the absorption systems in the spectra of distant quasars, and the data of type Ia supernovae (SNIa), cosmic microwave background (CMB), baryon acoustic oscillation (BAO). We find that the model parameters can be tightly constrained to the narrow ranges of ${\\cal O}(10^{-5})$ t...
DEFF Research Database (Denmark)
Parhamifar, Ladan; Moghimi, Seyed Moien
2012-01-01
Nanoparticulate systems are widely used for site-specific drug and gene delivery as well as for medical imaging. The mode of nanoparticle-cell interaction may have a significant effect on the pathway of nanoparticle internalization and subsequent intracellular trafficking. Total internal reflection...... fluorescence (TIRF) microscopy allows for real-time monitoring of nanoparticle-membrane interaction events, which can provide vital information in relation to design and surface engineering of therapeutic nanoparticles for cell-specific targeting. In contrast to other microscopy techniques, the bleaching...
Effective cosmological constant induced by stochastic fluctuations of Newton's constant
de Cesare, Marco; Lizzi, Fedele; Sakellariadou, Mairi
2016-09-01
We consider implications of the microscopic dynamics of spacetime for the evolution of cosmological models. We argue that quantum geometry effects may lead to stochastic fluctuations of the gravitational constant, which is thus considered as a macroscopic effective dynamical quantity. Consistency with Riemannian geometry entails the presence of a time-dependent dark energy term in the modified field equations, which can be expressed in terms of the dynamical gravitational constant. We suggest that the late-time accelerated expansion of the Universe may be ascribed to quantum fluctuations in the geometry of spacetime rather than the vacuum energy from the matter sector.
Effective cosmological constant induced by stochastic fluctuations of Newton's constant
de Cesare, Marco; Sakellariadou, Mairi
2016-01-01
We consider implications of the microscopic dynamics of spacetime for the evolution of cosmological models. We argue that quantum geometry effects may lead to stochastic fluctuations of the gravitational constant, which is thus considered as a macroscopic effective dynamical quantity. Consistency with Riemannian geometry entails the presence of a time-dependent dark energy term in the modified field equations, which can be expressed in terms of the dynamical gravitational constant. We suggest that the late-time accelerated expansion of the Universe may be ascribed to quantum fluctuations in the geometry of spacetime rather than the vacuum energy from the matter sector.
Varying Constants, Gravitation and Cosmology
Directory of Open Access Journals (Sweden)
Jean-Philippe Uzan
2011-03-01
Full Text Available Fundamental constants are a cornerstone of our physical laws. Any constant varying in space and/or time would reflect the existence of an almost massless field that couples to matter. This will induce a violation of the universality of free fall. Thus, it is of utmost importance for our understanding of gravity and of the domain of validity of general relativity to test for their constancy. We detail the relations between the constants, the tests of the local position invariance and of the universality of free fall. We then review the main experimental and observational constraints that have been obtained from atomic clocks, the Oklo phenomenon, solar system observations, meteorite dating, quasar absorption spectra, stellar physics, pulsar timing, the cosmic microwave background and big bang nucleosynthesis. At each step we describe the basics of each system, its dependence with respect to the constants, the known systematic effects and the most recent constraints that have been obtained. We then describe the main theoretical frameworks in which the low-energy constants may actually be varying and we focus on the unification mechanisms and the relations between the variation of different constants. To finish, we discuss the more speculative possibility of understanding their numerical values and the apparent fine-tuning that they confront us with.
Varying Constants, Gravitation and Cosmology.
Uzan, Jean-Philippe
2011-01-01
Fundamental constants are a cornerstone of our physical laws. Any constant varying in space and/or time would reflect the existence of an almost massless field that couples to matter. This will induce a violation of the universality of free fall. Thus, it is of utmost importance for our understanding of gravity and of the domain of validity of general relativity to test for their constancy. We detail the relations between the constants, the tests of the local position invariance and of the universality of free fall. We then review the main experimental and observational constraints that have been obtained from atomic clocks, the Oklo phenomenon, solar system observations, meteorite dating, quasar absorption spectra, stellar physics, pulsar timing, the cosmic microwave background and big bang nucleosynthesis. At each step we describe the basics of each system, its dependence with respect to the constants, the known systematic effects and the most recent constraints that have been obtained. We then describe the main theoretical frameworks in which the low-energy constants may actually be varying and we focus on the unification mechanisms and the relations between the variation of different constants. To finish, we discuss the more speculative possibility of understanding their numerical values and the apparent fine-tuning that they confront us with.
Varying Constants, Gravitation and Cosmology
Uzan, Jean-Philippe
2011-12-01
Fundamental constants are a cornerstone of our physical laws. Any constant varying in space and/or time would reflect the existence of an almost massless field that couples to matter. This will induce a violation of the universality of free fall. Thus, it is of utmost importance for our understanding of gravity and of the domain of validity of general relativity to test for their constancy. We detail the relations between the constants, the tests of the local position invariance and of the universality of free fall. We then review the main experimental and observational constraints that have been obtained from atomic clocks, the Oklo phenomenon, solar system observations, meteorite dating, quasar absorption spectra, stellar physics, pulsar timing, the cosmic microwave background and big bang nucleosynthesis. At each step we describe the basics of each system, its dependence with respect to the constants, the known systematic effects and the most recent constraints that have been obtained. We then describe the main theoretical frameworks in which the low-energy constants may actually be varying and we focus on the unification mechanisms and the relations between the variation of different constants. To finish, we discuss the more speculative possibility of understanding their numerical values and the apparent fine-tuning that they confront us with.
Chand, H; Srianand, R; Aracil, B; Chand, Hum; Petitjean, Patrick; Srianand, Raghunathan; Aracil, Bastien
2004-01-01
We report a new constraint on the variation of the fine-structure constant based on the analysis of 15 Si IV doublets selected from a ESO-UVES sample. We find \\Delta\\alpha/\\alpha= +(0.15 +/- 0.43) 10^{-5} over a redshift range of 1.59< z < 2.92 which is consistent with no variation in \\alpha. This result represents a factor three improvement on the constraint on \\Delta\\alpha/\\alpha based on Si IV doublets compared to the published results in the literature. Alkali doublet method used here avoids the implicit assumptions used in the many-multiplet method that chemical and ionization homogeneities are negligible and isotopic abundances are close to the terrestrial value.
Generalized Pickands constants
Debicki, K.G.
2001-01-01
Pickands constants play an important role in the exact asymptotic of extreme values for Gaussian stochastic processes. By the {it generalized Pickands constant ${cal H_{eta$ we mean the limit begin{eqnarray* {cal H_{eta= lim_{T to inftyfrac{ {cal H_{eta(T){T, end{eqnarray* where ${cal H_{eta(T)= Exp
Learning Read-constant Polynomials of Constant Degree modulo Composites
DEFF Research Database (Denmark)
Chattopadhyay, Arkadev; Gavaldá, Richard; Hansen, Kristoffer Arnsfelt;
2011-01-01
Boolean functions that have constant degree polynomial representation over a fixed finite ring form a natural and strict subclass of the complexity class \\textACC0ACC0. They are also precisely the functions computable efficiently by programs over fixed and finite nilpotent groups. This class...... is not known to be learnable in any reasonable learning model. In this paper, we provide a deterministic polynomial time algorithm for learning Boolean functions represented by polynomials of constant degree over arbitrary finite rings from membership queries, with the additional constraint that each variable...
Belghith, Akram; Bowd, Christopher; Medeiros, Felipe A; Hammel, Naama; Yang, Zhiyong; Weinreb, Robert N; Zangwill, Linda M
2016-02-01
We determined if the Bruch's membrane opening (BMO) location changes over time in healthy eyes and eyes with progressing glaucoma, and validated an automated segmentation algorithm for identifying the BMO in Cirrus high-definition coherence tomography (HD-OCT) images. We followed 95 eyes (35 progressing glaucoma and 60 healthy) for an average of 3.7 ± 1.1 years. A stable group of 50 eyes had repeated tests over a short period. In each B-scan of the stable group, the BMO points were delineated manually and automatically to assess the reproducibility of both segmentation methods. Moreover, the BMO location variation over time was assessed longitudinally on the aligned images in 3D space point by point in x, y, and z directions. Mean visual field mean deviation at baseline of the progressing glaucoma group was -7.7 dB. Mixed-effects models revealed small nonsignificant changes in BMO location over time for all directions in healthy eyes (the smallest P value was 0.39) and in the progressing glaucoma eyes (the smallest P value was 0.30). In the stable group, the overall intervisit-intraclass correlation coefficient (ICC) and coefficient of variation (CV) were 98.4% and 2.1%, respectively, for the manual segmentation and 98.1% and 1.9%, respectively, for the automated algorithm. Bruch's membrane opening location was stable in normal and progressing glaucoma eyes with follow-up between 3 and 4 years indicating that it can be used as reference point in monitoring glaucoma progression. The BMO location estimation with Cirrus HD-OCT using manual and automated segmentation showed excellent reproducibility.
Blanco, J.M.; Long, J.A.; Gee, G.; Donoghue, A.M.; Wildt, D.E.
2008-01-01
Potential factors influencing sperm survival under hypertonic conditions were evaluated in the Sandhill crane (Grus canadensis) and turkey (Meleagridis gallopavo). Sperm osmotolerance (300-3000 mOsm/kg) was evaluated after: (1) equilibration times of 2, 10, 45 and 60 min at 4 ?C versus 21 ?C; (2) pre-equilibrating with dimethylacetamide (DMA) or dimethylsulfoxide (Me2SO) at either 4 ?C or 21 ?C; and (3) inhibition of the Na+/K+ and the Na+/H+ antiporter membrane ionic pumps. Sperm viability was assessed using the eosin-nigrosin live/dead stain. Species-specific differences occurred in response to hypertonic conditions with crane sperm remaining viable under extreme hypertonicity (3000 mOsm/kg), whereas turkey sperm viability was compromised with only slightly hypertonic (500 mOsm/kg) conditions. The timing of spermolysis under hypertonic conditions was also species-specific, with a shorter interval for turkey (2 min) than crane (10 min) sperm. Turkey sperm osmotolerance was slightly improved by lowering the incubation temperature from 21 to 4 ?C. Pre-equilibrating sperm with DMA reduced the incidence of hypertonic spermolysis only in the crane, at both room and refrigeration temperature. Inhibiting the Na+/K+ and the Na+/H+ antiporter membrane ion pumps did not impair resistance of crane and turkey spermatozoa to hypertonic stress; pump inhibition actually increased turkey sperm survival compared to control sperm. Results demonstrate marked species specificity in osmotolerance between crane and turkey sperm, as well as in the way temperature and time of exposure affect sperm survival under hypertonic conditions. Differences are independent of the role of osmotic pumps in these species.
Wessling, M.; Huisman, I.; Boomgaard, van den Th.; Smolders, C.A.
1995-01-01
The time-dependent permeation behavior of a glassy polyimide is studied above and below the plasticization pressure with carbon dioxide as the permeating gas. The work particularly focuses on the quantification of the slow increase in permeability at feed pressures above the plasticization pressure.
Modeling electrically active viscoelastic membranes.
Directory of Open Access Journals (Sweden)
Sitikantha Roy
Full Text Available The membrane protein prestin is native to the cochlear outer hair cell that is crucial to the ear's amplification and frequency selectivity throughout the whole acoustic frequency range. The outer hair cell exhibits interrelated dimensional changes, force generation, and electric charge transfer. Cells transfected with prestin acquire unique active properties similar to those in the native cell that have also been useful in understanding the process. Here we propose a model describing the major electromechanical features of such active membranes. The model derived from thermodynamic principles is in the form of integral relationships between the history of voltage and membrane resultants as independent variables and the charge density and strains as dependent variables. The proposed model is applied to the analysis of an active force produced by the outer hair cell in response to a harmonic electric field. Our analysis reveals the mechanism of the outer hair cell active (isometric force having an almost constant amplitude and phase up to 80 kHz. We found that the frequency-invariance of the force is a result of interplay between the electrical filtering associated with prestin and power law viscoelasticity of the surrounding membrane. Paradoxically, the membrane viscoelasticity boosts the force balancing the electrical filtering effect. We also consider various modes of electromechanical coupling in membrane with prestin associated with mechanical perturbations in the cell. We consider pressure or strains applied step-wise or at a constant rate and compute the time course of the resulting electric charge. The results obtained here are important for the analysis of electromechanical properties of membranes, cells, and biological materials as well as for a better understanding of the mechanism of hearing and the role of the protein prestin in this mechanism.
Institute of Scientific and Technical Information of China (English)
吴明仁
2012-01-01
It analyzes cause of deviation between experiment measured value of time constant and theoretical one in transient process of RLC series circuit.The loss resistance of inductor and capacitor is measured by the sinusoidal wave of the same frequency as the oscillating one of the underdamped oscillating wave.The theoretic value of time constant is corrected,and the agreement between the corrected theoretic value of time constant and the measured one can be obtained.%本文分析了RLC串联电路暂态过程时间常数τ的实验测量值与理论值偏差的原因,以频率为振荡频率的正弦波代替欠阻尼振荡波,测出电路电容和电感上的损耗电阻,对时间常数的理论值进行修正,可使τ的理论修正值与实验测量值基本吻合。
Bouncing universes with varying constants
Energy Technology Data Exchange (ETDEWEB)
Barrow, John D [DAMTP, Centre for Mathematical Sciences, Cambridge University, Wilberforce Road, Cambridge CB3 0WA (United Kingdom); Kimberly, Dagny [Theoretical Physics, Blackett Laboratory, Imperial College, Prince Consort Road, London SW7 2BZ (United Kingdom); Magueijo, Joao [Theoretical Physics, Blackett Laboratory, Imperial College, Prince Consort Road, London SW7 2BZ (United Kingdom)
2004-09-21
We investigate the behaviour of exact closed bouncing Friedmann universes in theories with varying constants. We show that the simplest BSBM varying alpha theory leads to a bouncing universe. The value of alpha increases monotonically, remaining approximately constant during most of each cycle, but increasing significantly around each bounce. When dissipation is introduced we show that in each new cycle the universe expands for longer and to a larger size. We find a similar effect for closed bouncing universes in Brans-Dicke theory, where G also varies monotonically in time from cycle to cycle. Similar behaviour occurs also in varying speed of light theories.
Bouncing Universes with Varying Constants
Barrow, J D; Magueijo, J; Barrow, John D.; Kimberly, Dagny; Magueijo, Joao
2004-01-01
We investigate the behaviour of exact closed bouncing Friedmann universes in theories with varying constants. We show that the simplest BSBM varying-alpha theory leads to a bouncing universe. The value of alpha increases monotonically, remaining approximately constant during most of each cycle, but increasing significantly around each bounce. When dissipation is introduced we show that in each new cycle the universe expands for longer and to a larger size. We find a similar effect for closed bouncing universes in Brans-Dicke theory, where $G$ also varies monotonically in time from cycle to cycle. Similar behaviour occurs also in varying speed of light theories.
Gravitational Instantons and Cosmological Constant
Cyriac, Josily
2015-01-01
The cosmological dynamics of an otherwise empty universe in the presence of vacuum fields is considered. Quantum fluctuations at the Planck scale leads to a dynamical topology of space-time at very small length scales, which is dominated by compact gravitational instantons. The Planck scale vacuum energy acts as a source for the curvature of the these compact gravitational instantons and decouples from the large scale energy momentum tensor of the universe, thus making the observable cosmological constant vanish. However, a Euclidean functional integral over all possible topologies of the gravitational instantons generates a small non-zero value for the large scale cosmological constant, which agrees with the present observations.
Ye, Shuji; Nguyen, Khoi Tan; Le Clair, Stéphanie V.; Chen, Zhan
2009-01-01
Sum frequency generation (SFG) vibrational spectroscopy has been demonstrated to be a powerful technique to study the molecular structures of surfaces and interfaces in different chemical environments. This review summarizes recent SFG studies on hybrid bilayer membranes and substrate-supported lipid monolayers and bilayers, the interaction between peptides/proteins and lipid monolayers/bilayers, and bilayer perturbation induced by peptides/proteins. To demonstrate the ability of SFG to determine the orientations of various secondary structures, studies on the interaction between different peptides/proteins (melittin, G proteins, almethicin, and tachyplesin I) and lipid bilayers are discussed. Molecular level details revealed by SFG in these studies show that SFG can provide a unique understanding on the interactions between a lipid monolayer/bilayer and peptides/proteins in real time, in situ and without any exogenous labeling. PMID:19306928
Her, Cheenou; Alonzo, Aaron P.; Vang, Justin Y.; Torres, Ernesto; Krishnan, V. V.
2015-01-01
Enzyme kinetics is an essential part of a chemistry curriculum, especially for students interested in biomedical research or in health care fields. Though the concept is routinely performed in undergraduate chemistry/biochemistry classrooms using other spectroscopic methods, we provide an optimized approach that uses a real-time monitoring of the…
Her, Cheenou; Alonzo, Aaron P.; Vang, Justin Y.; Torres, Ernesto; Krishnan, V. V.
2015-01-01
Enzyme kinetics is an essential part of a chemistry curriculum, especially for students interested in biomedical research or in health care fields. Though the concept is routinely performed in undergraduate chemistry/biochemistry classrooms using other spectroscopic methods, we provide an optimized approach that uses a real-time monitoring of the…
Fuel cell membranes and crossover prevention
Masel, Richard I.; York, Cynthia A.; Waszczuk, Piotr; Wieckowski, Andrzej
2009-08-04
A membrane electrode assembly for use with a direct organic fuel cell containing a formic acid fuel includes a solid polymer electrolyte having first and second surfaces, an anode on the first surface and a cathode on the second surface and electrically linked to the anode. The solid polymer electrolyte has a thickness t:.gtoreq..times..times..times..times. ##EQU00001## where C.sub.f is the formic acid fuel concentration over the anode, D.sub.f is the effective diffusivity of the fuel in the solid polymer electrolyte, K.sub.f is the equilibrium constant for partition coefficient for the fuel into the solid polymer electrolyte membrane, I is Faraday's constant n.sub.f is the number of electrons released when 1 molecule of the fuel is oxidized, and j.sub.f.sup.c is an empirically determined crossover rate of fuel above which the fuel cell does not operate.
Mosgaard, Lars D; Heimburg, Thomas
2013-01-01
Membranes are two-dimensional structures embedded in a three-dimensional heat reservoir. At constant temperature, the heat capacity is proportional to the enthalpy fluctuations. However, when the membrane is embedded in a finite aqueous reservoir, the enthalpy and temperature fluctuations of the reservoir are intimately coupled to the enthalpy fluctuations of the membrane. Employing Monte Carlo simulations, we show that membranes embedded in water reservoirs of various sizes display different enthalpy fluctuations and fluctuation time scales. In particular, larger water reservoirs result in a larger enthalpy fluctuations of the membrane and in slower fluctuation time scales (relaxation times). In periodic processes such as sound propagation in membranes, the membrane has only a finite time available to exchange heat with the medium. A larger frequency therefore reduces the accessible volume of the reservoir. We discuss the relevance of these considerations for the frequency dependence of the compressibility a...
Gerencser, Akos A; Mookerjee, Shona A; Jastroch, Martin; Brand, Martin D
2016-01-01
The aim of this study was to simplify, improve and validate quantitative measurement of the mitochondrial membrane potential (ΔψM) in pancreatic β-cells. This built on our previously introduced calculation of the absolute magnitude of ΔψM in intact cells, using time-lapse imaging of the non-quench mode fluorescence of tetramethylrhodamine methyl ester and a bis-oxonol plasma membrane potential (ΔψP) indicator. ΔψM is a central mediator of glucose-stimulated insulin secretion in pancreatic β-cells. ΔψM is at the crossroads of cellular energy production and demand, therefore precise assay of its magnitude is a valuable tool to study how these processes interplay in insulin secretion. Dispersed islet cell cultures allowed cell type-specific, single-cell observations of cell-to-cell heterogeneity of ΔψM and ΔψP. Glucose addition caused hyperpolarization of ΔψM and depolarization of ΔψP. The hyperpolarization was a monophasic step increase, even in cells where the ΔψP depolarization was biphasic. The biphasic response of ΔψP was associated with a larger hyperpolarization of ΔψM than the monophasic response. Analysis of the relationships between ΔψP and ΔψM revealed that primary dispersed β-cells responded to glucose heterogeneously, driven by variable activation of energy metabolism. Sensitivity analysis of the calibration was consistent with β-cells having substantial cell-to-cell variations in amounts of mitochondria, and this was predicted not to impair the accuracy of determinations of relative changes in ΔψM and ΔψP. Finally, we demonstrate a significant problem with using an alternative ΔψM probe, rhodamine 123. In glucose-stimulated and oligomycin-inhibited β-cells the principles of the rhodamine 123 assay were breached, resulting in misleading conclusions.
Pacheco-Ruiz, Santiago; Heaven, Sonia; Banks, Charles J
2017-05-01
Kinetic control of Mean Cell Residence Time (MCRT) was shown to have a significant impact on membrane flux under steady-state conditions. Two laboratory-scale flat-plate submerged anaerobic membrane bioreactors were operated for 245 days on a low-to-intermediate strength substrate with high suspended solids. Transmembrane pressure was maintained at 2.2 kPa throughout four experimental phases, while MCRT in one reactor was progressively reduced. This allowed very accurate measurement of sustainable membrane flux rates at different MCRTs, and hence the degree of membrane fouling. Performance data were gathered on chemical oxygen demand (COD) removal efficiency, and a COD mass balance was constructed accounting for carbon converted into new biomass and that lost in the effluent as dissolved methane. Measurements of growth yield at each MCRT were made, with physical characterisation of each mixed liquor based on capillary suction time. The results showed membrane flux and MLSS filterability was highest at short MCRT, although specific methane production (SMP) was lower since a proportion of COD removal was accounted for by higher biomass yield. There was no advantage in operating at an MCRT <25 days. When considering the most suitable MCRT there is thus a trade-off between membrane performance, SMP and waste sludge yield.
Varying Fine-Structure Constant and the Cosmological Constant Problem
Fujii, Y
2003-01-01
We start with a brief account of the latest analysis of the Oklo phenomenon providing the still most stringent constraint on time-variability of the fine- structure constant $\\alpha$. Comparing this with the recent result from the measurement of distant QSO's appears to indicate a non-uniform time-dependence, which we argue to be related to another recent finding of the accelerating universe. This view is implemented in terms of the scalar-tensor theory, applied specifically to the small but nonzero cosmological constant. Our detailed calculation shows that these two phenomena can be understood in terms of a common origin, a particular behavior of the scalar field, dilaton. We also sketch how this theoretical approach makes it appropriate to revisit non- Newtonian gravity featuring small violation of Weak Equivalence Principle at medium distances.
Varying Fine-Structure Constant and the Cosmological Constant Problem
Fujii, Yasunori
We start with a brief account of the latest analysis of the Oklo phenomenon providing the still most stringent constraint on time variability of the fine-structure constant α. Comparing this with the recent result from the measurement of distant QSO's appears to indicate a non-uniform time-dependence, which we argue to be related to another recent finding of the accelerating universe. This view is implemented in terms of the scalar-tensor theory, applied specifically to the small but nonzero cosmological constant. Our detailed calculation shows that these two phenomena can be understood in terms of a common origin, a particular behavior of the scalar field, dilaton. We also sketch how this theoretical approach makes it appropriate to revisit non-Newtonian gravity featuring small violation of Weak Equivalence Principle at medium distances.
Variation of Fundamental Constants
Flambaum, V. V.
2006-11-01
Theories unifying gravity with other interactions suggest temporal and spatial variation of the fundamental ``constants'' in expanding Universe. The spatial variation can explain a fine tuning of the fundamental constants which allows humans (and any life) to appear. We appeared in the area of the Universe where the values of the fundamental constants are consistent with our existence. We present a review of recent works devoted to the variation of the fine structure constant α, strong interaction and fundamental masses. There are some hints for the variation in quasar absorption spectra. Big Bang nucleosynthesis, and Oklo natural nuclear reactor data. A very promising method to search for the variation of the fundamental constants consists in comparison of different atomic clocks. Huge enhancement of the variation effects happens in transition between accidentally degenerate atomic and molecular energy levels. A new idea is to build a ``nuclear'' clock based on the ultraviolet transition between very low excited state and ground state in Thorium nucleus. This may allow to improve sensitivity to the variation up to 10 orders of magnitude! Huge enhancement of the variation effects is also possible in cold atomic and molecular collisions near Feshbach resonance.
Wang, Luying; Dumont, Randall S.; Dickson, James M.
2013-03-01
Nonequilibrium molecular dynamics (NEMD) simulations are presented to investigate the effect of water-membrane interactions on the transport properties of pressure-driven water flow passing through carbon nanotube (CNT) membranes. The CNT membrane is modified with different physical properties to alter the van der Waals interactions or the electrostatic interactions between water molecules and the CNT membranes. The unmodified and modified CNT membranes are models of simplified nanofiltration (NF) membranes at operating conditions consistent with real NF systems. All NEMD simulations are run with constant pressure difference (8.0 MPa) temperature (300 K), constant pore size (0.643 nm radius for CNT (12, 12)), and membrane thickness (6.0 nm). The water flow rate, density, and velocity (in flow direction) distributions are obtained by analyzing the NEMD simulation results to compare transport through the modified and unmodified CNT membranes. The pressure-driven water flow through CNT membranes is from 11 to 21 times faster than predicted by the Navier-Stokes equations. For water passing through the modified membrane with stronger van der Waals or electrostatic interactions, the fast flow is reduced giving lower flow rates and velocities. These investigations show the effect of water-CNT membrane interactions on water transport under NF operating conditions. This work can help provide and improve the understanding of how these membrane characteristics affect membrane performance for real NF processes.
Wang, Luying; Dumont, Randall S; Dickson, James M
2013-03-28
Nonequilibrium molecular dynamics (NEMD) simulations are presented to investigate the effect of water-membrane interactions on the transport properties of pressure-driven water flow passing through carbon nanotube (CNT) membranes. The CNT membrane is modified with different physical properties to alter the van der Waals interactions or the electrostatic interactions between water molecules and the CNT membranes. The unmodified and modified CNT membranes are models of simplified nanofiltration (NF) membranes at operating conditions consistent with real NF systems. All NEMD simulations are run with constant pressure difference (8.0 MPa) temperature (300 K), constant pore size (0.643 nm radius for CNT (12, 12)), and membrane thickness (6.0 nm). The water flow rate, density, and velocity (in flow direction) distributions are obtained by analyzing the NEMD simulation results to compare transport through the modified and unmodified CNT membranes. The pressure-driven water flow through CNT membranes is from 11 to 21 times faster than predicted by the Navier-Stokes equations. For water passing through the modified membrane with stronger van der Waals or electrostatic interactions, the fast flow is reduced giving lower flow rates and velocities. These investigations show the effect of water-CNT membrane interactions on water transport under NF operating conditions. This work can help provide and improve the understanding of how these membrane characteristics affect membrane performance for real NF processes.
Peselnick, L.; Robie, R.A.
1962-01-01
The recent measurements of the elastic constants of calcite by Reddy and Subrahmanyam (1960) disagree with the values obtained independently by Voigt (1910) and Bhimasenachar (1945). The present authors, using an ultrasonic pulse technique at 3 Mc and 25??C, determined the elastic constants of calcite using the exact equations governing the wave velocities in the single crystal. The results are C11=13.7, C33=8.11, C44=3.50, C12=4.82, C13=5.68, and C14=-2.00, in units of 1011 dyncm2. Independent checks of several of the elastic constants were made employing other directions and polarizations of the wave velocities. With the exception of C13, these values substantially agree with the data of Voigt and Bhimasenachar. ?? 1962 The American Institute of Physics.
Yang, Sun A.; Choi, Yong Chan; Bu, Sang Don
2012-11-01
We investigated the effect of etching time on the bottom surface morphologies of ultrathin porous alumina membranes (UT-PAMs) anodized in oxalic and phosphoric acid. The morphology of the bottom surface clearly changed and a unique surface undulation was observed during the etching process. Such an undulation regarding the bottom surface is attributed to the different etching rates between the dome-shaped barrier layer and the hexagonal cell walls. The results suggest that the bottom morphology of UT-PAMs formed after the barrier layer is opened significantly affects the contact area of the bottom side with the substrate. During the initial stage of the opening process for the barrier layer, the porous section will contact the substrate rather than the walls. However, as the etching time increases, the height of the porous section becomes considerably lower than that of the walls, which means that the walls will contact the substrate with a gap between the pores and the substrate. Based on our experimental results, we propose a possible schematic diagram describing the effects of UT-PAMs with differently-shaped bottom surfaces on the shapes of fabricated nanodots when the UT-PAMs are used as masks.
Algorithm for structure constants
Paiva, F M
2011-01-01
In a $n$-dimensional Lie algebra, random numerical values are assigned by computer to $n(n-1)$ especially selected structure constants. An algorithm is then created, which calculates without ambiguity the remaining constants, obeying the Jacobi conditions. Differently from others, this algorithm is suitable even for poor personal computer. ------------- En $n$-dimensia algebro de Lie, hazardaj numeraj valoroj estas asignitaj per komputilo al $n(n-1)$ speciale elektitaj konstantoj de strukturo. Tiam algoritmo estas kreita, kalkulante senambigue la ceterajn konstantojn, obeante kondicxojn de Jacobi. Malsimile al aliaj algoritmoj, tiu cxi tauxgas ecx por malpotenca komputilo.
Radiographic constant exposure technique
DEFF Research Database (Denmark)
Domanus, Joseph Czeslaw
1985-01-01
The constant exposure technique has been applied to assess various industrial radiographic systems. Different X-ray films and radiographic papers of two producers were compared. Special attention was given to fast film and paper used with fluorometallic screens. Radiographic image quality...... was tested by the use of ISO wire IQI's and ASTM penetrameters used on Al and Fe test plates. Relative speed and reduction of kilovoltage obtained with the constant exposure technique were calculated. The advantages of fast radiographic systems are pointed out...
Bosma, Wieb
2009-01-01
The average value of log s(n)/n taken over the first N even integers is shown to converge to a constant lambda when N tends to infinity; moreover, the value of this constant is approximated and proven to be less than 0. Here s(n) sums the divisors of n less than n. Thus the geometric mean of s(n)/n, the growth factor of the function s, in the long run tends to be less than 1. This could be interpreted as probabilistic evidence that aliquot sequences tend to remain bounded.
Ye, Shuji; Li, Hongchun; Wei, Feng; Jasensky, Joshua; Boughton, Andrew P; Yang, Pei; Chen, Zhan
2012-04-11
Ion channels play crucial roles in transport and regulatory functions of living cells. Understanding the gating mechanisms of these channels is important to understanding and treating diseases that have been linked to ion channels. One potential model peptide for studying the mechanism of ion channel gating is alamethicin, which adopts a split α/3(10)-helix structure and responds to changes in electric potential. In this study, sum frequency generation vibrational spectroscopy (SFG-VS), supplemented by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), has been applied to characterize interactions between alamethicin (a model for larger channel proteins) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid bilayers in the presence of an electric potential across the membrane. The membrane potential difference was controlled by changing the pH of the solution in contact with the bilayer and was measured using fluorescence spectroscopy. The orientation angle of alamethicin in POPC lipid bilayers was then determined at different pH values using polarized SFG amide I spectra. Assuming that all molecules adopt the same orientation (a δ distribution), at pH = 6.7 the α-helix at the N-terminus and the 3(10)-helix at the C-terminus tilt at about 72° (θ(1)) and 50° (θ(2)) versus the surface normal, respectively. When pH increases to 11.9, θ(1) and θ(2) decrease to 56.5° and 45°, respectively. The δ distribution assumption was verified using a combination of SFG and ATR-FTIR measurements, which showed a quite narrow distribution in the angle of θ(1) for both pH conditions. This indicates that all alamethicin molecules at the surface adopt a nearly identical orientation in POPC lipid bilayers. The localized pH change in proximity to the bilayer modulates the membrane potential and thus induces a decrease in both the tilt and the bend angles of the two helices in alamethicin. This is the first reported application of SFG
Amaral, Pauline; Partlan, Erin; Li, Mengfei; Lapolli, Flavio; Mefford, O Thompson; Karanfil, Tanju; Ladner, David A
2016-09-01
In microfiltration processes for drinking water treatment, one method of removing trace contaminants is to add powdered activated carbon (PAC). Recently, a version of PAC called superfine PAC (S-PAC) has been under development. S-PAC has a smaller particle size and thus faster adsorption kinetics than conventionally sized PAC. Membrane coating performance of various S-PAC samples was evaluated by measuring adsorption of atrazine, a model micropollutant. S-PACs were created in-house from PACs of three different materials: coal, wood, and coconut shell. Milling time was varied to produce S-PACs pulverized with different amounts of energy. These had different particles sizes, but other properties (e.g. oxygen content), also differed. In pure water the coal based S-PACs showed superior atrazine adsorption; all milled carbons had over 90% removal while the PAC had only 45% removal. With addition of calcium and/or NOM, removal rates decreased, but milled carbons still removed more atrazine than PAC. Oxygen content and specific external surface area (both of which increased with longer milling times) were the most significant predictors of atrazine removal. S-PAC coatings resulted in loss of filtration flux compared to an uncoated membrane and smaller particles caused more flux decline than larger particles; however, the data suggest that NOM fouling is still more of a concern than S-PAC fouling. The addition of calcium improved the flux, especially for the longer-milled carbons. Overall the data show that when milling S-PAC with different levels of energy there is a tradeoff: smaller particles adsorb contaminants better, but cause greater flux decline. Fortunately, an acceptable balance may be possible; for example, in these experiments the coal-based S-PAC after 30 min of milling achieved a fairly high atrazine removal (overall 80%) with a fairly low flux reduction (under 30%) even in the presence of NOM. This suggests that relatively short duration (low energy
基于阶跃温度响应的热电偶时间常数测试系统%Test system of time constant based on step temperature response
Institute of Scientific and Technical Information of China (English)
滕士雷; 孔喜梅
2011-01-01
为了更方便地测试热电偶时间常数,设计了一套热电偶时间常数测试系统,包括工控机、信号调理电路、A/D采集、数据采集处理软件和打印机等.根据热电偶对阶跃温度的响应,提出了一种全新的热电偶时间常数测试方法,设计功能完善的信号调理电路,通过PCL818L数据采集卡将采集的数据送交上位机应用软件进行分析处理,得到所需要的热电偶参数,应用软件提供各类报表输出及数据打印功能.%In order to facilitate the test of thermocouple time constant, a thermocouple time constant test system was designed.The system is composed of IPC, signal conditioning circuit, A/ D collecting card, data processing software and printer.In addition, a new method for testing the time constant of thermocouple was proposed according to its response to phase step temperature.By the PCL818L card, the data was collected and transferred to application software for analysis, by which the desired parameters of thermocouple can be obtained.The application software provides all types of reporting forms output and data printing.
Schmiedeberg, Michael
2013-05-01
By using molecular-dynamics simulations, we determine the jamming phase diagrams at high densities for a bidisperse mixture of soft spheres that interact according to repulsive power-law pair potentials. We observe that the relaxation time varies nonmonotonically as a function of density at constant temperature. Therefore, the jamming phase diagrams contain multiple reentrant glass transitions if temperature and density are used as control parameters. However, if we consider a new formulation of the jamming phase diagrams where temperature over pressure and pressure are employed as control parameters, no nonmonotonic behavior is observed.
Grohs, Jacob R.; Li, Yongqiang; Dillard, David A.; Case, Scott W.; Ellis, Michael W.; Lai, Yeh-Hung; Gittleman, Craig S.
Temperature and humidity fluctuations in operating fuel cells impose significant biaxial stresses in the constrained proton exchange membranes (PEMs) of a fuel cell stack. The strength of the PEM, and its ability to withstand cyclic environment-induced stresses, plays an important role in membrane integrity and consequently, fuel cell durability. In this study, a pressure loaded blister test is used to characterize the biaxial strength of Gore-Select ® series 57 over a range of times and temperatures. Hencky's classical solution for a pressurized circular membrane is used to estimate biaxial strength values from burst pressure measurements. A hereditary integral is employed to construct the linear viscoelastic analog to Hencky's linear elastic exact solution. Biaxial strength master curves are constructed using traditional time-temperature superposition principle techniques and the associated temperature shift factors show good agreement with shift factors obtained from constitutive (stress relaxation) and fracture (knife slit) tests of the material.
DEFF Research Database (Denmark)
Vistisen, Bodil; Høy, Carl-Erik
2004-01-01
The purpose of the present study was to examine the short-term effect of dietary specific structured triacylglycerols (MLM, M = 8:0, L = 18:2n-6), LLL and MMM on the fatty acid composition of brush border membrane (BBM) phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Rats were...... administered intragastrically a bolus of ML*M, M*LM*, L*L*L* or M*M*M* (* = C-13- labeled fatty acid). Rats were decapitated 2 hours and 6 hours later, and the fatty acid composition and C-13-enrichment of BBM-PC and -PE were determined. C-13-enriched 18:2n-6 was observed in BBM-PC after intragastric...... fatty acids in the two phospholipid pools. Minor effects on BBM-PC and BBM-PE fatty acid profiles (mole-%) were observed. The present study demonstrated for the first time incorporation of C-13-labeled 18:2n-6 into BBM-PC 2 hours and 6 hours after intragastric administration of L*L*L* or ML...