WorldWideScience

Sample records for stable density gradient

  1. Validation of classical density-dependent solute transport theory for stable, high-concentration-gradient brine displacements in coarse and medium sands

    Science.gov (United States)

    Watson, S. J.; Barry, D. A.; Schotting, R. J.; Hassanizadeh, S. M.

    A series of careful laboratory soil column experiments was carried out for the purpose of providing data for testing recently presented theories of miscible density-dependent flow and transport. In particular, modifications to the standard theory involve extensions to both Darcy's (for flow) and Fick's laws (for diffusive/dispersive solute flux). Both coarse- and medium-grained sands were used in the experiments. All experiments concerned upward (i.e., stable) displacement of fresh water within the soil by a brine solution, under either constant head or constant volume flux conditions. The experimental data were analysed using accurate numerical solutions of the standard governing flow and transport model, as well as models with modified Darcy's and Fick's laws. Model parameters were determined by a step-wise fitting procedure based on the least-squares criterion. The results show clearly that, for large density contrasts, an extended Darcy's law was not necessary. On the other hand, an extension to Fick's Law was needed to model the experimental data accurately.

  2. Microinstabilities in weak density gradient tokamak systems

    International Nuclear Information System (INIS)

    Tang, W.M.; Rewoldt, G.; Chen, L.

    1986-04-01

    A prominent characteristic of auxiliary-heated tokamak discharges which exhibit improved (''H-mode type'') confinement properties is that their density profiles tend to be much flatter over most of the plasma radius. Depsite this favorable trend, it is emphasized here that, even in the limit of zero density gradient, low-frequency microinstabilities can persist due to the nonzero temperature gradient

  3. Microinstabilities in weak density gradient tokamak systems

    Energy Technology Data Exchange (ETDEWEB)

    Tang, W.M.; Rewoldt, G.; Chen, L.

    1986-04-01

    A prominent characteristic of auxiliary-heated tokamak discharges which exhibit improved (''H-mode type'') confinement properties is that their density profiles tend to be much flatter over most of the plasma radius. Depsite this favorable trend, it is emphasized here that, even in the limit of zero density gradient, low-frequency microinstabilities can persist due to the nonzero temperature gradient.

  4. Molecular fractionation of starch by density-gradient ultracentrifugation.

    Science.gov (United States)

    Yoon, Jae Wook; Lim, Seung Taik

    2003-03-28

    Amylose and amylopectin in corn and potato starches were fractionated by centrifugation at 124,000g for 3-72 h at 40 degrees C in a gradient media, Nycodenz, based on their sedimentation rate differences. The fractions were collected from a centrifuge tube, and then analyzed by the phenol-sulfuric acid method and iodine-binding test. Amylopectin, a large and highly branched starch molecule, migrated faster than amylose and quickly reached its isopycnic point with a buoyant density of about 1.25 g/mL, exhibiting a sharp and stable carbohydrate peak. Amylose, which is a relatively small and linear molecule, however, migrated slowly in a broad density range and continued moving to higher density regions, eventually overlapping with amylopectin peak as the centrifugation continued. This could indicate that the buoyant density of amylose is similar to that of amylopectin. Under centrifugal conditions of 3 h and 124,000g, amylose and amylopectin molecules were clearly separated, and the presence of intermediate starch molecules (11.5 and 7.7% for corn and potato starch, respectively) was also observed between amylose and amylopectin fractions. The amylose content of corn and potato starches was 22.6 and 21.1%, respectively, based on the total carbohydrate analysis after the ultracentrifugation for 3 h. In alkaline gradients (pH 11 or 12.5), the sedimentation rate of starch molecules and the buoyant density of amylopectin were reduced, possibly due to the structural changes induced by alkali.

  5. Density Gradient Stabilization of Electron Temperature Gradient Driven Turbulence in a Spherical Tokamak

    Energy Technology Data Exchange (ETDEWEB)

    Ren, Y; Mazzucato, E; Guttenfelder, W; Bell, R E; Domier, C W; LeBlanc, B P; Lee, K C; Luhmann Jr, N C; Smith, D R

    2011-03-21

    In this letter we report the first clear experimental observation of density gradient stabilization of electron temperature gradient driven turbulence in a fusion plasma. It is observed that longer wavelength modes, k⊥ρs ≤10, are most stabilized by density gradient, and the stabilization is accompanied by about a factor of two decrease in the plasma effective thermal diffusivity.

  6. Density gradients in ceramic pellets measured by computed tomography

    International Nuclear Information System (INIS)

    Sawicka, B.D.; Palmer, B.J.F.

    1986-07-01

    Density gradients are of fundamental importance in ceramic processing and computed tomography (CT) can provide accurate measurements of density profiles in sintered and unsintered ceramic parts. As a demonstration of this potential, the density gradients in an unsintered pellet pressed from an alumina powder were measured by CT scanning. To detect such small density gradients, the CT images must have good density resolution and be free from beam-hardening effects. This was achieved by measuring high-contrast (low-noise) images with the use of an Ir-192 isotopic source. A beam-hardening correction was applied. The resulting images are discussed relative to the transmission of forces through the powder mass during the pelletizing process

  7. Density-Gradient Determination of Osmotic Potential in Plant Cells

    Science.gov (United States)

    Nabors, Murray W.

    1973-01-01

    Describes a method for measuring osmotic potential which is suitable for high school and college biology classes. This method introduces students to the hard-to-visualize technique of using density gradients to separate cells or cell constituents of differing densities. (JR)

  8. Gas density gradient for three dark interstellar clouds

    International Nuclear Information System (INIS)

    Fulkerson, S.A.; Clark, F.O.

    1984-01-01

    A grid of models has been constructed of the surface brightness of selected transitions of interstellar formal-dehyde for three interstellar clouds. The grid included radial gas density gradients over a considerable range from uniform to very steep. The model results were then compared to observations of the interstellar dark clouds B361, L183, and L134. In all three cases, the comparison indicates that the gas is centrally condensed and follows a gradient in density which closely approximates an inverse square law. This result offers a hint that the dust may be more centrally condensed than the gas in B361

  9. Enhancement of electric and magnetic wave fields at density gradients

    Directory of Open Access Journals (Sweden)

    A. Reiniusson

    2006-03-01

    Full Text Available We use Freja satellite data to investigate irregular small-scale density variations. The observations are made in the auroral region at about 1000-1700 km. The density variations are a few percent, and the structures are found to be spatial down to a scale length of a few ion gyroradii. Irregular density variations are often found in an environment of whistler mode/lower hybrid waves and we show that at the density gradients both the electric and magnetic wave fields are enhanced.

  10. Effect of Crustal Density Structures on GOCE Gravity Gradient Observables

    Directory of Open Access Journals (Sweden)

    Robert Tenzer Pavel Novák

    2013-01-01

    Full Text Available We investigate the gravity gradient components corrected for major known anomalous density structures within the Earth¡¦s crust. Heterogeneous mantle density structures are disregarded. The gravimetric forward modeling technique is utilized to compute the gravity gradients based on methods for a spherical harmonic analysis and synthesis of a gravity field. The Earth¡¦s gravity gradient components are generated using the global geopotential model GOCO-03s. The topographic and stripping gravity corrections due to the density contrasts of the ocean and ice are computed from the global topographic/bathymetric model DTM2006.0 (which also includes the ice-thickness dataset. The discrete data of sediments and crust layers taken from the CRUST2.0 global crustal model are then used to apply the additional stripping corrections for sediments and remaining anomalous crustal density structures. All computations are realized globally on a one arc-deg geographical grid at a mean satellite elevation of 255 km. The global map of the consolidated crust-stripped gravity gradients reveals distinctive features which are attributed to global tectonics, lithospheric plate configuration, lithosphere structure and mantle dynamics (e.g., glacial isostatic adjustment, mantle convection. The Moho signature, which is the most pronounced signal in these refined gravity gradients, is superimposed over a weaker gravity signal of the lithospheric mantle. An interpretational quality of the computed (refined gravity gradient components is mainly limited by a low accuracy and resolution of the CRUST2.0 sediment and crustal layer data and unmodeled mantle structures.

  11. [Content trends of pollutants in street dust of Beijing along the urban-rural gradient and road density gradient].

    Science.gov (United States)

    Tang, Rong-Li; Ma, Ke-Ming; Zhang, Yu-Xin; Mao, Qi-Zheng

    2013-01-01

    In the article, pollutant content of 220 road dust samples within the sixth ring road of Beijing have been investigated by using grid stationing sampling method. The changing characteristics of road nude number per unit area, road network density and pollutant content within buffering areas along urban to rural gradient were also studied. Three following variation trends are presented as each index varies widely within the research areas. Firstly, road nude number per unit area, road network density and Cu, Cr, Pb content decrease along urban to rural gradient, and they decrease sharply in the beginning. Secondly, Mn, Cd content change a little along urban to rural gradient, and mean value remains stable. Thirdly, the content of Ni, TOC, TN decreases along with the distance fluctuations in the beginning and their mean values are then rising slowly in the suburbs. The turning point of pollutant content are found in places 15-20 km away from city center. The article shows that the road index and Cd content are irrelevant, and weak correlations are found between road index, TS, Mn and pH. And other relevance ranking are described as follows: Cu > TN > TOC > Pb > Ni > Cr. In contrast with road network density, higher correlations between road nude number per unit area and each element are fond, and element pollution of Cu, TN, TOC, Pb, Ni and Cr could be indicated by these indicators.

  12. Gram-scale fractionation of nanodiamonds by density gradient ultracentrifugation

    KAUST Repository

    Peng, Wei

    2013-01-01

    Size is a defining characteristic of nanoparticles; it influences their optical and electronic properties as well as their interactions with molecules and macromolecules. Producing nanoparticles with narrow size distributions remains one of the main challenges to their utilization. At this time, the number of practical approaches to optimize the size distribution of nanoparticles in many interesting materials systems, including diamond nanocrystals, remains limited. Diamond nanocrystals synthesized by detonation protocols-so-called detonation nanodiamonds (DNDs)-are promising systems for drug delivery, photonics, and composites. DNDs are composed of primary particles with diameters mainly <10 nm and their aggregates (ca. 10-500 nm). Here, we introduce a large-scale approach to rate-zonal density gradient ultracentrifugation to obtain monodispersed fractions of nanoparticles in high yields. We use this method to fractionate a highly concentrated and stable aqueous solution of DNDs and to investigate the size distribution of various fractions by dynamic light scattering, analytical ultracentrifugation, transmission electron microscopy and powder X-ray diffraction. This fractionation method enabled us to separate gram-scale amounts of DNDs into several size ranges within a relatively short period of time. In addition, the high product yields obtained for each fraction allowed us to apply the fractionation method iteratively to a particular size range of particles and to collect various fractions of highly monodispersed primary particles. Our method paves the way for in-depth studies of the physical and optical properties, growth, and aggregation mechanism of DNDs. Applications requiring DNDs with specific particle or aggregate sizes are now within reach. © 2013 The Royal Society of Chemistry.

  13. Gram-scale fractionation of nanodiamonds by density gradient ultracentrifugation.

    Science.gov (United States)

    Peng, Wei; Mahfouz, Remi; Pan, Jun; Hou, Yuanfang; Beaujuge, Pierre M; Bakr, Osman M

    2013-06-07

    Size is a defining characteristic of nanoparticles; it influences their optical and electronic properties as well as their interactions with molecules and macromolecules. Producing nanoparticles with narrow size distributions remains one of the main challenges to their utilization. At this time, the number of practical approaches to optimize the size distribution of nanoparticles in many interesting materials systems, including diamond nanocrystals, remains limited. Diamond nanocrystals synthesized by detonation protocols - so-called detonation nanodiamonds (DNDs) - are promising systems for drug delivery, photonics, and composites. DNDs are composed of primary particles with diameters mainly <10 nm and their aggregates (ca. 10-500 nm). Here, we introduce a large-scale approach to rate-zonal density gradient ultracentrifugation to obtain monodispersed fractions of nanoparticles in high yields. We use this method to fractionate a highly concentrated and stable aqueous solution of DNDs and to investigate the size distribution of various fractions by dynamic light scattering, analytical ultracentrifugation, transmission electron microscopy and powder X-ray diffraction. This fractionation method enabled us to separate gram-scale amounts of DNDs into several size ranges within a relatively short period of time. In addition, the high product yields obtained for each fraction allowed us to apply the fractionation method iteratively to a particular size range of particles and to collect various fractions of highly monodispersed primary particles. Our method paves the way for in-depth studies of the physical and optical properties, growth, and aggregation mechanism of DNDs. Applications requiring DNDs with specific particle or aggregate sizes are now within reach.

  14. Role of turbulence regime on determining the local density gradient

    Science.gov (United States)

    Wang, X.; Mordijck, S.; Doyle, E. J.; Zeng, L.; Staebler, G. M.; Meneghini, O.; Smith, S. P.

    2018-01-01

    In this paper we show that the local density gradient in the plasma core depends on the calculated mode-frequency of the most unstable linear mode and reaches a maximum when this frequency is close to zero. Previous theoretical and experimental work on AUG has shown that the ratio of electron to ion temperature, and as such the frequency of the dominant linear gyrokinetic mode, affects the local density gradient close to ρ = 0.3 (Fable et al 2010 Plasma Phys. Control. Fusion 52 015007, Angioni et al 2011 Nucl. Fusion 51 023006). On DIII-D we find that by adding electron cyclotron heating, we modify the dominant unstable linear gyrokinetic mode from an ion temperature gradient (ITG) mode to a trapped electron mode (TEM), which means that the frequency of the dominant mode changes sign (from the ion to the electron direction). Local density peaking around mid-radius increases by 50% right around the cross-over between the ITG and TEM regimes. By comparing how the particle flux changes, through the derivative of the electron density, n e , with respect to time, \\partial n_e/\\partial t , we find that the particle flux also exhibits the same trend versus mode frequency. As a result, we find that the changes in local particle transport are inversely proportional to the changes in electron density, indicating that the changes are driven by a change in thermo-diffusive pinch.

  15. Interacting Eigenmodes of a plasma diode with a density gradient

    International Nuclear Information System (INIS)

    Loefgren, T.; Gunell, H.

    1997-08-01

    The formation of narrow high frequency electric field spikes in plasma density gradients is investigated using one-dimensional particle in cell simulations. It is found that the shape of the plasma density gradient is very important for the spike formation. The spike appears also in simulations with immobile ions showing that a coupling to the ion motion, as for example in wave interactions, is not necessary for the formation of HF spikes. However, the HF spike influences the ion motion, and ion waves are seen in the simulations. It has been found, in experiments and simulations, that the electron velocity distribution function deviates from the Maxwellian distribution. Dispersion relations are calculated using realistic distribution functions. The spike can be seen as a coupled system of two Eigenmodes of a plasma diode fed by the beam-plasma interaction. Based on a simplified fluid description of such Eigenmodes, explanations for the localization of the spike, spatially and in frequency, are given. The density amplitude is comparable with the DC density level close to the cathode. Space charge limits of waves in this region seem to determine the amplitude of the spike through the Poisson's equation

  16. Analytical gradients for density functional calculations with approximate spin projection.

    Science.gov (United States)

    Saito, Toru; Thiel, Walter

    2012-11-08

    We have derived and implemented analytical gradients for broken-symmetry unrestricted density functional calculations (BS-UDFT) with removal of spin contamination by Yamaguchi's approximate spin projection method. Geometry optimizations with these analytical gradients (AGAP-opt) yield results consistent with those obtained with the previously available numerical gradients (NAP-opt). The AGAP-opt approach is found to be more precise, efficient, and robust than NAP-opt. It allows full geometry optimizations for large open-shell systems. We report results for three types of organic diradicals and for a binuclear vanadium(II) complex to demonstrate the merits of removing the spin contamination effects during geometry optimization (AGAP-opt vs BS-UDFT) and to illustrate the superior performance of the analytical gradients (AGAP-opt vs NAP-opt). The results for the vanadium(II) complex indicate that the AGAP-opt method is capable of handling pronounced spin contamination effects in large binuclear transition metal complexes with two magnetic centers.

  17. Density gradients in the solar plasma observed by interplanetary scintillation

    International Nuclear Information System (INIS)

    Gapper, G.R.; Hewish, A.

    1981-01-01

    A new technique is described which overcomes the limitation set by Fresnel filtering in previous IPS studies of the small-scale density irregularities in the solar plasma. Phase gradients introduced by irregularities larger than the Fresnel limit cause transverse displacements of the small-scale scintillation pattern. In the presence of the solar wind, such refraction effects may be revealed by simultaneous measurements of intensity scintillation at two radio frequencies. Observations show that the structure corresponding to temporal frequencies approximately 0.02 Hz is in agreement with an extrapolation of the Kolmogorov spectrum derived from spacecraft data at lower frequencies. (author)

  18. Density Measurement of Silicon Carbide Layers of Simulated Coated Particles by Using a Density Gradient Column

    International Nuclear Information System (INIS)

    Kim, Woong Ki; Lee, Young Woo; Kim, Weon Ju; Kim, Young Min; Kim, Yeon Ku; Oh, Seung Chul; Jeong, Kyung Chai; Cho, Moon Sung

    2009-01-01

    The TRISO-coated fuel particle for a HTGR(high temperature gas-cooled reactor) is composed of a nuclear fuel kernel and outer coating layers. The coating layers consist of a buffer PyC(pyrolytic carbon) layer, inner PyC(I-PyC) layer, SiC(silicon carbide) layer, and outer PyC(O-PyC) layer. The SiC coating layer acts as the primary barrier to the release of metallic fission products as well as fission gas and iodine. The density of SiC layer is one of the most important material properties for evaluating the soundness of SiC layer. The SiC fragments are acquired by oxidizing the broken coated particles. The SiC fragments are so small and irregular that it is not easy to measure the weight and volume of the SiC fragments. Density gradient column and standard floats can be used to measure such a small fragment. Xray radiography is one of the alternatives to measure the density of coating layer. It is very difficult to calibrate the density by using the X-ray image. In this study, the densities of the SiC specimens of simulated TRISO-coated particles with ZrO 2 kernel were measured by a density gradient column with a density gradient solution

  19. Mineral Density Volume Gradients in Normal and Diseased Human Tissues

    Science.gov (United States)

    Djomehri, Sabra I.; Candell, Susan; Case, Thomas; Browning, Alyssa; Marshall, Grayson W.; Yun, Wenbing; Lau, S. H.; Webb, Samuel; Ho, Sunita P.

    2015-01-01

    Clinical computed tomography provides a single mineral density (MD) value for heterogeneous calcified tissues containing early and late stage pathologic formations. The novel aspect of this study is that, it extends current quantitative methods of mapping mineral density gradients to three dimensions, discretizes early and late mineralized stages, identifies elemental distribution in discretized volumes, and correlates measured MD with respective calcium (Ca) to phosphorus (P) and Ca to zinc (Zn) elemental ratios. To accomplish this, MD variations identified using polychromatic radiation from a high resolution micro-computed tomography (micro-CT) benchtop unit were correlated with elemental mapping obtained from a microprobe X-ray fluorescence (XRF) using synchrotron monochromatic radiation. Digital segmentation of tomograms from normal and diseased tissues (N=5 per group; 40-60 year old males) contained significant mineral density variations (enamel: 2820-3095mg/cc, bone: 570-1415mg/cc, cementum: 1240-1340mg/cc, dentin: 1480-1590mg/cc, cementum affected by periodontitis: 1100-1220mg/cc, hypomineralized carious dentin: 345-1450mg/cc, hypermineralized carious dentin: 1815-2740mg/cc, and dental calculus: 1290-1770mg/cc). A plausible linear correlation between segmented MD volumes and elemental ratios within these volumes was established, and Ca/P ratios for dentin (1.49), hypomineralized dentin (0.32-0.46), cementum (1.51), and bone (1.68) were observed. Furthermore, varying Ca/Zn ratios were distinguished in adapted compared to normal tissues, such as in bone (855-2765) and in cementum (595-990), highlighting Zn as an influential element in prompting observed adaptive properties. Hence, results provide insights on mineral density gradients with elemental concentrations and elemental footprints that in turn could aid in elucidating mechanistic processes for pathologic formations. PMID:25856386

  20. Mineral density volume gradients in normal and diseased human tissues.

    Directory of Open Access Journals (Sweden)

    Sabra I Djomehri

    Full Text Available Clinical computed tomography provides a single mineral density (MD value for heterogeneous calcified tissues containing early and late stage pathologic formations. The novel aspect of this study is that, it extends current quantitative methods of mapping mineral density gradients to three dimensions, discretizes early and late mineralized stages, identifies elemental distribution in discretized volumes, and correlates measured MD with respective calcium (Ca to phosphorus (P and Ca to zinc (Zn elemental ratios. To accomplish this, MD variations identified using polychromatic radiation from a high resolution micro-computed tomography (micro-CT benchtop unit were correlated with elemental mapping obtained from a microprobe X-ray fluorescence (XRF using synchrotron monochromatic radiation. Digital segmentation of tomograms from normal and diseased tissues (N=5 per group; 40-60 year old males contained significant mineral density variations (enamel: 2820-3095 mg/cc, bone: 570-1415 mg/cc, cementum: 1240-1340 mg/cc, dentin: 1480-1590 mg/cc, cementum affected by periodontitis: 1100-1220 mg/cc, hypomineralized carious dentin: 345-1450 mg/cc, hypermineralized carious dentin: 1815-2740 mg/cc, and dental calculus: 1290-1770 mg/cc. A plausible linear correlation between segmented MD volumes and elemental ratios within these volumes was established, and Ca/P ratios for dentin (1.49, hypomineralized dentin (0.32-0.46, cementum (1.51, and bone (1.68 were observed. Furthermore, varying Ca/Zn ratios were distinguished in adapted compared to normal tissues, such as in bone (855-2765 and in cementum (595-990, highlighting Zn as an influential element in prompting observed adaptive properties. Hence, results provide insights on mineral density gradients with elemental concentrations and elemental footprints that in turn could aid in elucidating mechanistic processes for pathologic formations.

  1. Density-dependent adaptive resistance allows swimming bacteria to colonize an antibiotic gradient

    NARCIS (Netherlands)

    Hol, F.J.H.; Hubert, A.W.R.; Dekker, C.; Keymer Vergara, J.E.

    2016-01-01

    During antibiotic treatment, antibiotic concentration gradients develop. Little is know regarding the effects of antibiotic gradients on populations of nonresistant bacteria. Using a microfluidic device, we show that high-density motile Escherichia coli populations composed of nonresistant

  2. Nonlinear density waves in a marginally stable gravitating disk

    International Nuclear Information System (INIS)

    Korchagin, V.I.

    1986-01-01

    The evolution of short nonlinear density waves in a disk at the stability limit is studied for arbitrary values of the radial wave number k/sub r/. For waves with wave numbers that do not lie at the minimum of the dispersion curve, the behavior of the amplitude is described by a nonlinear parabolic equation; however, stationary soliton solutions cannot exist in such a system since there is no dispersion spreading of a packet. For wave numbers lying at the minimum of the dispersion curve, soliton structures with determined amplitude are possible. In stable gravitating disks and in a disk at the stability limit, two physically different types of soliton can exist

  3. Modelling CO2-Brine Interfacial Tension using Density Gradient Theory

    KAUST Repository

    Ruslan, Mohd Fuad Anwari Che

    2018-03-01

    Knowledge regarding carbon dioxide (CO2)-brine interfacial tension (IFT) is important for petroleum industry and Carbon Capture and Storage (CCS) strategies. In petroleum industry, CO2-brine IFT is especially importance for CO2 – based enhanced oil recovery strategy as it affects phase behavior and fluid transport in porous media. CCS which involves storing CO2 in geological storage sites also requires understanding regarding CO2-brine IFT as this parameter affects CO2 quantity that could be securely stored in the storage site. Several methods have been used to compute CO2-brine interfacial tension. One of the methods employed is by using Density Gradient Theory (DGT) approach. In DGT model, IFT is computed based on the component density distribution across the interface. However, current model is only applicable for modelling low to medium ionic strength solution. This limitation is due to the model only considers the increase of IFT due to the changes of bulk phases properties and does not account for ion distribution at interface. In this study, a new modelling strategy to compute CO2-brine IFT based on DGT was proposed. In the proposed model, ion distribution across interface was accounted for by separating the interface to two sections. The saddle point of tangent plane distance where ( ) was defined as the boundary separating the two sections of the interface. Electrolyte is assumed to be present only in the second section which is connected to the bulk liquid phase side. Numerical simulations were performed using the proposed approach for single and mixed salt solutions for three salts (NaCl, KCl, and CaCl2), for temperature (298 K to 443 K), pressure (2 MPa to 70 MPa), and ionic strength (0.085 mol·kg-1 to 15 mol·kg-1). The simulation result shows that the tuned model was able to predict with good accuracy CO2-brine IFT for all studied cases. Comparison with current DGT model showed that the proposed approach yields better match with the experiment data

  4. Destabilizing effect of density gradient on the Kelvin-Helmholtz instability

    International Nuclear Information System (INIS)

    Wang, L. F.; Xue, C.; Ye, W. H.; Li, Y. J.

    2009-01-01

    In this paper, we derive explicit analytic formulas for the linear growth rate and frequency of the Kelvin-Helmholtz instability in fluids with the density gradient. The analytic formulas are in excellent agreement with the results of two-dimensional numerical simulation. We found that the density gradient effect enforces (destabilizes) the Kelvin-Helmholtz instability by increasing its linear growth rate in the direction normal to the perturbed interface. The frequency is reduced (stabilized) by the density gradient effect, i.e., the density gradient decreases the transmission of the perturbation in the direction along to the perturbed interface. In most cases, the combined effect of density and velocity gradients stabilizes the Kelvin-Helmholtz instability.

  5. General approach for solving the density gradient theory in the interfacial tension calculations

    DEFF Research Database (Denmark)

    Liang, Xiaodong; Michelsen, Michael Locht

    2017-01-01

    Within the framework of the density gradient theory, the interfacial tension can be calculated by finding the density profiles that minimize an integral of two terms over the system of infinite width. It is found that the two integrands exhibit a constant difference along the interface for a finite...... property evaluations compared to other methods. The performance of the algorithm with recommended parameters is analyzed for various systems, and the efficiency is further compared with the geometric-mean density gradient theory, which only needs to solve nonlinear algebraic equations. The results show...... that the algorithm is only 5-10 times less efficient than solving the geometric-mean density gradient theory....

  6. Magnetohydrodynamically stable plasma with supercritical current density at the axis

    Science.gov (United States)

    Burdakov, A. V.; Postupaev, V. V.; Sudnikov, A. V.

    2014-05-01

    In this work, an analysis of magnetic perturbations in the GOL-3 experiment is given. In GOL-3, plasma is collectively heated in a multiple-mirror trap by a high-power electron beam. During the beam injection, the beam-plasma interaction maintains a high-level microturbulence. This provides an unusual radial profile of the net current (that consists of the beam current, current of the preliminary discharge, and the return current). The plasma core carries supercritical current density with the safety factor well below unity, but as a whole, the plasma is stable with q(a) ≈ 4. The net plasma current is counter-directed to the beam current; helicities of the magnetic field in the core and at the edge are of different signs. This forms a system with a strong magnetic shear that stabilizes the plasma core in good confinement regimes. We have found that the most pronounced magnetic perturbation is the well-known n = 1, m = 1 mode for both stable and disruptive regimes.

  7. Magnetohydrodynamically stable plasma with supercritical current density at the axis

    International Nuclear Information System (INIS)

    Burdakov, A. V.; Postupaev, V. V.; Sudnikov, A. V.

    2014-01-01

    In this work, an analysis of magnetic perturbations in the GOL-3 experiment is given. In GOL-3, plasma is collectively heated in a multiple-mirror trap by a high-power electron beam. During the beam injection, the beam-plasma interaction maintains a high-level microturbulence. This provides an unusual radial profile of the net current (that consists of the beam current, current of the preliminary discharge, and the return current). The plasma core carries supercritical current density with the safety factor well below unity, but as a whole, the plasma is stable with q(a) ≈ 4. The net plasma current is counter-directed to the beam current; helicities of the magnetic field in the core and at the edge are of different signs. This forms a system with a strong magnetic shear that stabilizes the plasma core in good confinement regimes. We have found that the most pronounced magnetic perturbation is the well-known n = 1, m = 1 mode for both stable and disruptive regimes

  8. Cell Growth on ("Janus") Density Gradients of Bifunctional Zeolite L Crystals.

    Science.gov (United States)

    Kehr, Nermin Seda; Motealleh, Andisheh; Schäfer, Andreas H

    2016-12-28

    Nanoparticle density gradients on surfaces have attracted interest as two-dimensional material surfaces that can mimic the complex nano-/microstructure of the native extracellular matrix, including its chemical and physical gradients, and can therefore be used to systematically study cell-material interactions. In this respect, we report the preparation of density gradients made of bifunctional zeolite L crystals on glass surfaces and the effects of the density gradient and biopolymer functionalization of zeolite L crystals on cell adhesion. We also describe how we created "Janus" density gradient surfaces by gradually depositing two different types of zeolite L crystals that were functionalized and loaded with different chemical groups and guest molecules onto the two distinct sides of the same glass substrate. Our results show that more cells adhered on the density gradient of biopolymer-coated zeolites than on uncoated ones. The number of adhered cells increased up to a certain surface coverage of the glass by the zeolite L crystals, but then it decreased beyond the zeolite density at which a higher surface coverage decreased fibroblast cell adhesion and spreading. Additionally, cell experiments showed that cells gradually internalized the guest-molecule-loaded zeolite L crystals from the underlying density gradient containing bifunctional zeolite L crystals.

  9. Gram-scale fractionation of nanodiamonds by density gradient ultracentrifugation

    Science.gov (United States)

    Peng, Wei; Mahfouz, Remi; Pan, Jun; Hou, Yuanfang; Beaujuge, Pierre M.; Bakr, Osman M.

    2013-05-01

    -called detonation nanodiamonds (DNDs) - are promising systems for drug delivery, photonics, and composites. DNDs are composed of primary particles with diameters mainly size distribution of various fractions by dynamic light scattering, analytical ultracentrifugation, transmission electron microscopy and powder X-ray diffraction. This fractionation method enabled us to separate gram-scale amounts of DNDs into several size ranges within a relatively short period of time. In addition, the high product yields obtained for each fraction allowed us to apply the fractionation method iteratively to a particular size range of particles and to collect various fractions of highly monodispersed primary particles. Our method paves the way for in-depth studies of the physical and optical properties, growth, and aggregation mechanism of DNDs. Applications requiring DNDs with specific particle or aggregate sizes are now within reach. Electronic supplementary information (ESI) available: Discussion of the influence of sample solution concentrations on DLS measurements, comparisons of the size distributions of our raw milled particles and NanoAmando particles, a detailed description of the RZDGU procedure, discussion of the influences of the gradients and centrifugation times on fractionation, TEM images, zeta potentials, AUC analysis and determination of mpDND density. See DOI: 10.1039/c3nr00990d

  10. Lowering coefficient of friction in Cu alloys with stable gradient nanostructures.

    Science.gov (United States)

    Chen, Xiang; Han, Zhong; Li, Xiuyan; Lu, K

    2016-12-01

    The coefficient of friction (COF) of metals is usually high, primarily because frictional contacts induce plastic deformation underneath the wear surface, resulting in surface roughening and formation of delaminating tribolayers. Lowering the COF of metals is crucial for improving the reliability and efficiency of metal contacts in engineering applications but is technically challenging. Refining the metals' grains to nanoscale cannot reduce dry-sliding COFs, although their hardness may be elevated many times. We report that a submillimeter-thick stable gradient nanograined surface layer enables a significant reduction in the COF of a Cu alloy under high-load dry sliding, from 0.64 (coarse-grained samples) to 0.29, which is smaller than the COFs of many ceramics. The unprecedented stable low COF stems from effective suppression of sliding-induced surface roughening and formation of delaminating tribolayer, owing to the stable gradient nanostructures that can accommodate large plastic strains under repeated sliding for more than 30,000 cycles.

  11. The influence of mineral matter on the separation of amorphous marine kerogens using density gradient centrifugation

    OpenAIRE

    Sinninghe Damsté, J.S.; Hartgers, W.A.; Leeuw, J.W. de; Ling, Y.; Crelling, J.C.

    1995-01-01

    Three relatively immature amorphous marine kerogens were subjected to density gradient centrifugation (DGC). The density fractions obtained were analyzed by Curie-point pyrolysis in combination with gas chromatography (Py-GC) and with gas chromatography-mass spectrometry (Py-GC-MS). Despite the variations in density, no significant variations were observed in chemical compositions of the flash pyrolysates of the density fractions of each kerogen. The variations in density were due to varying ...

  12. Depth perception: cuttlefish (Sepia officinalis) respond to visual texture density gradients.

    Science.gov (United States)

    Josef, Noam; Mann, Ofri; Sykes, António V; Fiorito, Graziano; Reis, João; Maccusker, Steven; Shashar, Nadav

    2014-11-01

    Studies concerning the perceptual processes of animals are not only interesting, but are fundamental to the understanding of other developments in information processing among non-humans. Carefully used visual illusions have been proven to be an informative tool for understanding visual perception. In this behavioral study, we demonstrate that cuttlefish are responsive to visual cues involving texture gradients. Specifically, 12 out of 14 animals avoided swimming over a solid surface with a gradient picture that to humans resembles an illusionary crevasse, while only 5 out of 14 avoided a non-illusionary texture. Since texture gradients are well-known cues for depth perception in vertebrates, we suggest that these cephalopods were responding to the depth illusion created by the texture density gradient. Density gradients and relative densities are key features in distance perception in vertebrates. Our results suggest that they are fundamental features of vision in general, appearing also in cephalopods.

  13. A model for sedimentation in inhomogeneous media. I. Dynamic density gradients from sedimenting co-solutes.

    Science.gov (United States)

    Schuck, Peter

    2004-03-01

    Macromolecular sedimentation in inhomogeneous media is of great practical importance. Dynamic density gradients have a long tradition in analytical ultracentrifugation, and are frequently used in preparative ultracentrifugation. In this paper, a new theoretical model for sedimentation in inhomogeneous media is presented, based on finite element solutions of the Lamm equation with spatial and temporal variation of the local solvent density and viscosity. It is applied to macromolecular sedimentation in the presence of a dynamic density gradient formed by the sedimentation of a co-solute at high concentration. It is implemented in the software SEDFIT for the analysis of experimental macromolecular concentration distributions. The model agrees well with the measured sedimentation profiles of a protein in a dynamic cesium chloride gradient, and may provide a measure for the effects of hydration or preferential solvation parameters. General features of protein sedimentation in dynamic density gradients are described.

  14. Density functional theory for molecular and periodic systems using density fitting and continuous fast multipole method: Analytical gradients.

    Science.gov (United States)

    Łazarski, Roman; Burow, Asbjörn Manfred; Grajciar, Lukáš; Sierka, Marek

    2016-10-30

    A full implementation of analytical energy gradients for molecular and periodic systems is reported in the TURBOMOLE program package within the framework of Kohn-Sham density functional theory using Gaussian-type orbitals as basis functions. Its key component is a combination of density fitting (DF) approximation and continuous fast multipole method (CFMM) that allows for an efficient calculation of the Coulomb energy gradient. For exchange-correlation part the hierarchical numerical integration scheme (Burow and Sierka, Journal of Chemical Theory and Computation 2011, 7, 3097) is extended to energy gradients. Computational efficiency and asymptotic O(N) scaling behavior of the implementation is demonstrated for various molecular and periodic model systems, with the largest unit cell of hematite containing 640 atoms and 19,072 basis functions. The overall computational effort of energy gradient is comparable to that of the Kohn-Sham matrix formation. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

  15. Species density and diversity along geomorphic gradient in ...

    African Journals Online (AJOL)

    The relevance of geomorphic forms to the conservation and protection of plant species and their territorial habitats in the Gashaka-Gumti National Park (GGNP) Nigeria was examined. The study analyzed and stratified the geomorphic features of the Park and observed species types, density and diversity distribution pattern.

  16. Virus purification by CsCl density gradient using general centrifugation.

    Science.gov (United States)

    Nasukawa, Tadahiro; Uchiyama, Jumpei; Taharaguchi, Satoshi; Ota, Sumire; Ujihara, Takako; Matsuzaki, Shigenobu; Murakami, Hironobu; Mizukami, Keijirou; Sakaguchi, Masahiro

    2017-11-01

    Virus purification by cesium chloride (CsCl) density gradient, which generally requires an expensive ultracentrifuge, is an essential technique in virology. Here, we optimized virus purification by CsCl density gradient using general centrifugation (40,000 × g, 2 h, 4 °C), which showed almost the same purification ability as conventional CsCl density gradient ultracentrifugation (100,000 × g, 1 h, 4 °C) using phages S13' and φEF24C. Moreover, adenovirus strain JM1/1 was also successfully purified by this method. We suggest that general centrifugation can become a less costly alternative to ultracentrifugation for virus purification by CsCl densiy gradient and will thus encourage research in virology.

  17. The influence of mineral matter on the separation of amorphous marine kerogens using density gradient centrifugation

    NARCIS (Netherlands)

    Sinninghe Damsté, J.S.; Hartgers, W.A.; Leeuw, J.W. de; Ling, Y.; Crelling, J.C.

    1995-01-01

    Three relatively immature amorphous marine kerogens were subjected to density gradient centrifugation (DGC). The density fractions obtained were analyzed by Curie-point pyrolysis in combination with gas chromatography (Py-GC) and with gas chromatography-mass spectrometry (Py-GC-MS). Despite the

  18. Density-Gradient-Driven trapped-electron-modes in improved-confinement RFP plasmas

    Science.gov (United States)

    Duff, James; Sarff, John; Ding, Weixing; Brower, David; Parke, Eli; Chapman, Brett; Terry, Paul; Pueschel, M. J.; Williams, Zach

    2017-10-01

    Short wavelength density fluctuations in improved-confinement MST plasmas exhibit multiple features characteristic of the trapped-electron-mode (TEM). Core transport in the RFP is normally governed by magnetic stochasticity stemming from long wavelength tearing modes that arise from current profile peaking, which are suppressed via inductive control for this work. The improved confinement is associated with an increase in the pressure gradient that can destabilize drift waves. The measured density fluctuations have f 50 kHz, kϕρs sharp decrease in global tearing mode associated fluctuations, their amplitude increases with local density gradient, and they exhibit a density-gradient threshold at R /Ln 15 . The GENE code, modified for the RFP, predicts the onset of density-gradient-driven TEM for these strong-gradient plasma conditions. While nonlinear analysis shows a large Dimits shift associated with predicted strong zonal flows, the inclusion of residual magnetic fluctuations, comparable to experimental magnetic fluctuations, causes a collapse of the zonal flows and an increase in the predicted transport to a level close to the experimentally measured heat flux. Work supported by US DOE.

  19. Density-dependent adaptive resistance allows swimming bacteria to colonize an antibiotic gradient.

    Science.gov (United States)

    Hol, Felix J H; Hubert, Bert; Dekker, Cees; Keymer, Juan E

    2016-01-01

    During antibiotic treatment, antibiotic concentration gradients develop. Little is know regarding the effects of antibiotic gradients on populations of nonresistant bacteria. Using a microfluidic device, we show that high-density motile Escherichia coli populations composed of nonresistant bacteria can, unexpectedly, colonize environments where a lethal concentration of the antibiotic kanamycin is present. Colonizing bacteria establish an adaptively resistant population, which remains viable for over 24 h while exposed to the antibiotic. Quantitative analysis of multiple colonization events shows that collectively swimming bacteria need to exceed a critical population density in order to successfully colonize the antibiotic landscape. After colonization, bacteria are not dormant but show both growth and swimming motility under antibiotic stress. Our results highlight the importance of motility and population density in facilitating adaptive resistance, and indicate that adaptive resistance may be a first step to the emergence of genetically encoded resistance in landscapes of antibiotic gradients.

  20. Effect of density gradient centrifugation on reactive oxygen species in human semen.

    Science.gov (United States)

    Takeshima, Teppei; Yumura, Yasushi; Kuroda, Shinnosuke; Kawahara, Takashi; Uemura, Hiroji; Iwasaki, Akira

    2017-06-01

    Density gradient centrifugation can separate motile sperm from immotile sperm and other cells for assisted reproduction, but may also remove antioxidants from seminal plasma, resulting in oxidative stress. Therefore, we investigated reactive oxygen species (ROS) concentrations and distribution in semen before and after density gradient centrifugation. We assessed semen volume, sperm concentration, sperm motility, and ROS levels before and after density gradient centrifugation (300 x g for 20 minutes) in 143 semen samples from 118 patients. The ROS removal rate was evaluated in ROS-positive samples and ROS formation rate in ROS-negative samples. Thirty-eight of 143 untreated samples (26.6%) were ROS-positive; sperm motility was significantly lower in these samples than in ROS-negative samples (p centrifugation, only seven of the 38 ROS-positive samples (18.42%) exhibited a ROS-positive lower layer (containing motile sperm) with a ROS removal rate of 81.58%, whereas the upper layer was ROS-positive in 24 samples (63.16%). In the ROS-negative group (n = 105), ROS was detected in 19 samples after centrifugation (18.10%, ROS generation rate), of which 18 were ROS-positive only in the upper layer or interface and the other was ROS-positive in both layers. Density gradient centrifugation can separate motile sperm from immotile sperm as well as remove ROS (including newly generated ROS). This data supports the view that density gradient centrifugation can select motile spermatozoa without enhancing oxidative stress. ROS: reactive oxygen species; SOD: superoxide dismutase; GPx: glutathione peroxidase; DNA: deoxyribonucleic acid; DGC: density gradient centrifugation; IUI: intrauterine insemination; IVF: in vitro fertilization; HEPES: 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid; EDTA: ethylenediaminetetraacetic acid; HTF: HEPES-buffered human tubal fluid; IMSI: intracytoplasmic morphologically selected sperm injection; SMAS: sperm motility analyzing system; CASA

  1. Generation of a wakefield undulator in plasma with transverse density gradient

    Science.gov (United States)

    Stupakov, G.

    2017-11-01

    We show that a short relativistic electron beam propagating in a plasma with a density gradient perpendicular to the direction of motion generates a wakefield in which a witness bunch experiences a transverse force. A density gradient oscillating along the beam path would create a periodically varying force—an undulator, with an estimated strength of the equivalent magnetic field more than 10 T. This opens an avenue for the creation of a high-strength, short-period undulator, which eventually may lead to all-plasma, free electron lasers where a plasma wakefield acceleration is naturally combined with a plasma undulator in a unifying, compact setup.

  2. Stable Isotope Systematics in Grasshopper Assemblages Along an Elevation Gradient, Colorado

    Science.gov (United States)

    Kohn, M. J.; Evans, S.; Dean, J.; Nufio, C.

    2012-12-01

    Insects comprise over three quarters of all animal species, yet studies of body water isotopic composition are limited to only the cockroach, the hoverfly, and chironomid flies. These studies suggest that oxygen and hydrogen isotopic compositions in body water are primarily controlled by dietary water sources, with modification from respiratory and metabolic processes. In particular, outward diffusion of isotopically depleted water vapor through insect spiracles at low humidity enriches residual body water in 18O and 2H (D). Stable isotope compositions (δ18O and δD) also respond to gradients in elevation and humidity, but these influences remain poorly understood. In this study, we measured grasshopper body water and local vegetation isotopic compositions along an elevation gradient in Colorado to evaluate three hypotheses: 1) Insect body water isotopic composition is directly related to food source water composition 2) Water vapor transport alters body water isotopic compositions relative to original diet sources, and 3) Elevation gradients influence isotopic compositions in insect body water. Thirty-five species of grasshopper were collected from 14 locations in Colorado grasslands, ranging in elevation from 450 to 800 meters (n=131). Body water was distilled from previously frozen grasshopper specimens using a vacuum extraction line, furnaces (90 °C), and liquid nitrogen traps. Water samples were then analyzed for δ18O and δD on an LGR Liquid Water Isotope Analyzer, housed in the Department of Geosciences, Boise State University. Grasshopper body water isotopic compositions show wide variation, with values ranging between -76.64‰ to +42.82‰ in δD and -3.06‰ to +26.78‰ in δ18O. Precipitation δ18O values over the entire Earth excluding the poles vary by approximately 30‰, comparable to the total range measured in our single study area. Most grasshopper values deviate from the global meteoric water line relating δ18O and δD in precipitation

  3. Critical density gradients for small-scale plasma irregularity generation in the E and F regions

    Science.gov (United States)

    Makarevich, Roman A.

    2017-09-01

    Electron density gradients that can make plasma unstable in the ionospheric E and F regions are analyzed. We focus on critical gradient values required for plasma instability to become operational to produce decameter-scale plasma irregularities observed by the Super Dual Auroral Radar Network (SuperDARN) without any nonlinear wave cascade. Analytic expressions are developed for the critical gradients using a recently developed general formalism for arbitrary geometry and with the ion inertia and stabilizing thermal diffusion effects included. It is demonstrated that the problem can be analyzed using a single equation applicable in both the E and F regions that only differs in the sign of the main term related to convection strength. Analytic expressions are obtained, and results are presented for (1) critical gradient strength for arbitrary gradient and propagation directions, (2) range of propagation directions with unstable primary waves, (3) most favorable configuration and minimum critical gradient, and (4) most favorable propagation direction for arbitrary gradient direction. It is shown that the most favorable configuration is achieved for propagation along the differential drift and gradient perpendicular to it and that an unexpected exception is the F region under strong convection when propagation and gradient are both rotated by a certain angle. It is estimated that in the F region, from which most of the SuperDARN backscatter comes, primary decameter waves can be generated for gradient scales as large as 100 km for favorable orientations and strong plasma convection >500 m/s and that much smaller scales of 200-1000 m are required for unfavorable orientations.

  4. Potential impacts of climate change on stable flies, investigated along an altitudinal gradient.

    Science.gov (United States)

    Gilles, J; David, J-F; Duvallet, G; Tillard, E

    2008-03-01

    Adult populations of stable flies were sampled along an altitudinal transect in Reunion Island to determine whether higher temperatures were associated with: (a) higher numbers of flies; (b) a longer season of infestation, and/or (c) different responses to warming in the cosmopolitan Stomoxys calcitrans (L) and the tropical Stomoxys niger niger Macquart (Diptera: Muscidae). Flies of both species were trapped at seven farms situated at four altitudes (100-1600 m a.s.l.) over a 90-week period. For both species, there were no relationships between the maximum or mean fly abundance and altitude. Only minimum abundance in winter was significantly higher at lower altitudes. Maximum and mean abundances differed significantly between nearby farms under similar climatic conditions. Seasonal fluctuations in fly abundance changed along the gradient. At lower altitudes, population growth started earlier after the winter but abundance declined earlier in summer, which resulted in a shift of the season of infestation. Seasonal fluctuations of both species were strongly related to climate variables at high altitude, mainly temperature. However, climate variables explained a decreasing proportion of the variations in abundance at lower altitudes. Stomoxys calcitrans was the most abundant species overall, but the proportion of S. n. niger increased significantly at lower altitudes and this species became predominant at 100 m a.s.l. It is concluded that stable fly infestations are unlikely to worsen in response to global warming. Maximum abundance is limited by local factors, possibly larval resources, which suggests that adequate husbandry practices could override the impact of climate change. Because S. n. niger tends to be the predominant pest at elevated temperatures, it is recommended that this species should not be introduced in areas where climate is changing.

  5. Vertical density gradient in the eastern North Atlantic during the last 30,000 years

    Energy Technology Data Exchange (ETDEWEB)

    Rogerson, M.; Ramirez, J. [University of Hull, Geography Department, Hull (United Kingdom); Bigg, G.R. [University of Sheffield, Department of Geography, Sheffield (United Kingdom); Rohling, E.J. [University of Southampton, National Oceanography Centre, School of Ocean and Earth Science, Southampton (United Kingdom)

    2012-08-15

    Past changes in the density and momentum structure of oceanic circulation are an important aspect of changes in the Atlantic Meridional Overturning Circulation and consequently climate. However, very little is known about past changes in the vertical density structure of the ocean, even very extensively studied systems such as the North Atlantic. Here we exploit the physical controls on the settling depth of the dense Mediterranean water plume derived from the Strait of Gibraltar to obtain the first robust, observations-based, probabilistic reconstruction of the vertical density gradient in the eastern North Atlantic during the last 30,000 years. We find that this gradient was weakened by more than 50%, relative to the present, during the last Glacial Maximum, and that changes in general are associated with reductions in AMOC intensity. However, we find only a small change during Heinrich Event 1 relative to the Last Glacial Maximum, despite strong evidence that overturning was substantially altered. This implies that millennial-scale changes may not be reflected in vertical density structure of the ocean, which may be limited to responses on an ocean-overturning timescale or longer. Regardless, our novel reconstruction of Atlantic density structure can be used as the basis for a dynamical measure for validation of model-based AMOC reconstructions. In addition, our general approach is transferrable to other marginal sea outflow plumes, to provide estimates of oceanic vertical density gradients in other locations. (orig.)

  6. Modified method for labeling human platelets with indium-111 oxine using albumin density-gradient separation

    International Nuclear Information System (INIS)

    Bunting, R.W.; Callahan, R.J.; Finkelstein, S.; Lees, R.S.; Strauss, H.W.

    1982-01-01

    When labeling platelets with indium-111 oxine, albumin density-gradient separation minimizes the time spent to resuspend those platelets that have been centrifuged against a hard surface. Labeling efficiency or platelet viability, as measured by platelet survival or aggregation with adenosine diphosphate, are not adversely affected

  7. Enrichment of unlabeled human Langerhans cells from epidermal cell suspensions by discontinuous density gradient centrifugation

    NARCIS (Netherlands)

    Teunissen, M. B.; Wormmeester, J.; Kapsenberg, M. L.; Bos, J. D.

    1988-01-01

    In this report we introduce an alternative procedure for enrichment of human epidermal Langerhans cells (LC) from epidermal cell suspensions of normal skin. By means of discontinuous Ficoll-Metrizoate density gradient centrifugation, a fraction containing high numbers of viable, more than 80% pure

  8. Effect of intraband variability on stable isotope and density time ...

    Indian Academy of Sciences (India)

    Density, 18O and 13C were measured along two tracks, one close to the central growth axis and the other, ∼20° off the axis, in a coral (Porites lutea) collected from the Stanley Reef, Central Great Barrier Reef, Australia. The 18O variations in the coral are well correlated with sea surface temperature changes.

  9. Bone marrow-derived cells for cardiovascular cell therapy: an optimized GMP method based on low-density gradient improves cell purity and function.

    Science.gov (United States)

    Radrizzani, Marina; Lo Cicero, Viviana; Soncin, Sabrina; Bolis, Sara; Sürder, Daniel; Torre, Tiziano; Siclari, Francesco; Moccetti, Tiziano; Vassalli, Giuseppe; Turchetto, Lucia

    2014-09-27

    Cardiovascular cell therapy represents a promising field, with several approaches currently being tested. The advanced therapy medicinal product (ATMP) for the ongoing METHOD clinical study ("Bone marrow derived cell therapy in the stable phase of chronic ischemic heart disease") consists of fresh mononuclear cells (MNC) isolated from autologous bone marrow (BM) through density gradient centrifugation on standard Ficoll-Paque. Cells are tested for safety (sterility, endotoxin), identity/potency (cell count, CD45/CD34/CD133, viability) and purity (contaminant granulocytes and platelets). BM-MNC were isolated by density gradient centrifugation on Ficoll-Paque. The following process parameters were optimized throughout the study: gradient medium density; gradient centrifugation speed and duration; washing conditions. A new manufacturing method was set up, based on gradient centrifugation on low density Ficoll-Paque, followed by 2 washing steps, of which the second one at low speed. It led to significantly higher removal of contaminant granulocytes and platelets, improving product purity; the frequencies of CD34+ cells, CD133+ cells and functional hematopoietic and mesenchymal precursors were significantly increased. The methodological optimization described here resulted in a significant improvement of ATMP quality, a crucial issue to clinical applications in cardiovascular cell therapy.

  10. Microfluidic Adaptation of Density-Gradient Centrifugation for Isolation of Particles and Cells

    Directory of Open Access Journals (Sweden)

    Yuxi Sun

    2017-08-01

    Full Text Available Density-gradient centrifugation is a label-free approach that has been extensively used for cell separations. Though elegant, this process is time-consuming (>30 min, subjects cells to high levels of stress (>350 g and relies on user skill to enable fractionation of cells that layer as a narrow band between the density-gradient medium and platelet-rich plasma. We hypothesized that microfluidic adaptation of this technique could transform this process into a rapid fractionation approach where samples are separated in a continuous fashion while being exposed to lower levels of stress (<100 g for shorter durations of time (<3 min. To demonstrate proof-of-concept, we designed a microfluidic density-gradient centrifugation device and constructed a setup to introduce samples and medium like Ficoll in a continuous, pump-less fashion where cells and particles can be exposed to centrifugal force and separated via different outlets. Proof-of-concept studies using binary mixtures of low-density polystyrene beads (1.02 g/cm3 and high-density silicon dioxide beads (2.2 g/cm3 with Ficoll–Paque (1.06 g/cm3 show that separation is indeed feasible with >99% separation efficiency suggesting that this approach can be further adapted for separation of cells.

  11. High frequency electric field spikes formed by electron beam-plasma interaction in plasma density gradients

    International Nuclear Information System (INIS)

    Gunell, H.; Loefgren, T.

    1997-02-01

    In the electron beam-plasma interaction at an electric double layer the beam density is much higher than in the classical beam-plasma experiments. The wave propagation takes place along the density gradient, that is present at the high potential side of the double layer. Such a case is studied experimentally by injecting the electron beam from a plane cathode, without any grids suppressing the gradient, and by particle simulations. The high frequency field concentrates in a sharp 'spike' with a half width of the order of one wavelength. The spike is found to be a standing wave surrounded by regions dominated by propagating waves. It forms at a position where its frequency is close to the local plasma frequency. The spike forms also when the electric field is well below the threshold for modulational instability, and long before a density cavity is formed in the simulations. Particle simulations reveal that, at the spike, there is a backward travelling wave that, when it is strongly damped, accelerates electrons back towards the cathode. In a simulation of a homogeneous plasma without the density gradient no spike is seen, and the wave is purely travelling instead of standing. 9 refs

  12. Electric field spikes formed by electron beam endash plasma interaction in plasma density gradients

    International Nuclear Information System (INIS)

    Gunell, H.; Loefgren, T.

    1997-01-01

    In the electron beam endash plasma interaction at an electric double layer the beam density is much higher than in the classical beam endash plasma experiments. The wave propagation takes place along the density gradient that is present at the high potential side of the double layer. Such a case is studied experimentally by injecting the electron beam from a plane cathode, without any grids suppressing the gradient, and by particle simulations. The high frequency field concentrates in a sharp open-quotes spikeclose quotes with a half width of the order of one wavelength. The spike is found to be a standing wave surrounded by regions dominated by propagating waves. It forms at a position where its frequency is close to the local plasma frequency. The spike forms also when the electric field is well below the threshold for modulational instability, and long before a density cavity is formed in the simulations. Particle simulations reveal that, at the spike, there is a backward traveling wave that, when it is strongly damped, accelerates electrons back towards the cathode. In a simulation of a homogeneous plasma without the density gradient no spike is seen, and the wave is purely travelling instead of standing. copyright 1997 American Institute of Physics

  13. Co-isolation of extracellular vesicles and high-density lipoproteins using density gradient ultracentrifugation

    NARCIS (Netherlands)

    Yuana, Yuana; Levels, Johannes; Grootemaat, Anita; Sturk, Auguste; Nieuwland, Rienk

    2014-01-01

    Extracellular vesicles (EVs) facilitate intercellular communication by carrying bioactive molecules such as proteins, messenger RNA, and micro (mi)RNAs. Recently, high-density lipoproteins (HDL) isolated from human plasma were also reported to transport miRNA to other cells. HDL, when isolated from

  14. Noninvasive prenatal diagnosis. Use of density gradient centrifugation, magnetically activated cell sorting and in situ hybridization

    DEFF Research Database (Denmark)

    Campagnoli, C; Multhaupt, H A; Ludomirski, A

    1997-01-01

    centrifugation and dual antibody labeling methods. The protocol was designed to compare the efficacy of antitransferrin receptor (CD71)/antiglycophorin A (GPA) antibodies with antithrom-bospondin receptor (CD36)/anti-GPA antibodies in identifying nucleated erythrocytes in maternal blood. Cytospin preparations...... cells recovered did not differ. Seven of seven male pregnancies were correctly identified. One case of trisomy 21 was detected. CONCLUSION: The in situ hybridization analysis of fetal nucleated erythrocytes isolated from maternal blood using single density gradient centrifugation, anti-CD71/anti......OBJECTIVE: To develop a noninvasive method suitable for clinical prenatal diagnosis. STUDY DESIGN: Fetal nucleated erythrocytes were separated from peripheral blood of 17 healthy pregnant women using small magnetically activated cell sorting columns (MiniMACS) following density gradient...

  15. Preparation of monodisperse silicon nanocrystals through density-gradient unltracentrifugation in organic solvents

    Science.gov (United States)

    Miller, Joseph B.; van Sickle, Austin; Iyer, Swathi; Anthony, Rebecca A.; Kortshagen, Uwe R.; Hobbie, Erik K.

    2011-03-01

    Monodisperse colloidal suspensions of ligand-coated silicon nanocrystals, synthesized through a nonthermal low-pressure plasma reaction, have been prepared through density-gradient ultracentrifugation in mixed organic solvents. Density-gradient profiles of mixed chloroform and m-xylene are used to tune and control the settling speed of the nanoparticles and hence optimize their transient separation by size along the depth of polyoxymethylene ultracentrifuge tubes. The mean size and polydispersity of the extracted fractions are characterized through photoluminescence spectroscopy and transmission electron microscopy, and the self-assembly of fractions into close-packed crystal lattices is achieved using an immiscible two-fluid evaporation scheme. The photophysical properties of the nanocrystal lattices are compared with those of the starting materials and suspensions, and the influence of atmospheric oxygen on the stability of the nanocrystal photoluminescence is measured. Supported by the DOE through DE-FG36-08GO88160.

  16. Analytic calculations of hyper-Raman spectra from density functional theory hyperpolarizability gradients

    Energy Technology Data Exchange (ETDEWEB)

    Ringholm, Magnus; Ruud, Kenneth [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø – The Arctic University of Norway, 9037 Tromsø (Norway); Bast, Radovan [Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of Technology, AlbaNova University Center, S-10691 Stockholm (Sweden); PDC Center for High Performance Computing, Royal Institute of Technology, S-10044 Stockholm (Sweden); Oggioni, Luca [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø – The Arctic University of Norway, 9037 Tromsø (Norway); Department of Physics G. Occhialini, University of Milano Bicocca, Piazza della scienza 3, 20126 Milan (Italy); Ekström, Ulf [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, 0315 Oslo (Norway)

    2014-10-07

    We present the first analytic calculations of the geometrical gradients of the first hyperpolarizability tensors at the density-functional theory (DFT) level. We use the analytically calculated hyperpolarizability gradients to explore the importance of electron correlation effects, as described by DFT, on hyper-Raman spectra. In particular, we calculate the hyper-Raman spectra of the all-trans and 11-cis isomers of retinal at the Hartree-Fock (HF) and density-functional levels of theory, also allowing us to explore the sensitivity of the hyper-Raman spectra on the geometrical characteristics of these structurally related molecules. We show that the HF results, using B3LYP-calculated vibrational frequencies and force fields, reproduce the experimental data for all-trans-retinal well, and that electron correlation effects are of minor importance for the hyper-Raman intensities.

  17. Processing of semen by density gradient centrifugation selects spermatozoa with longer telomeres for assisted reproduction techniques.

    Science.gov (United States)

    Yang, Qingling; Zhang, Nan; Zhao, Feifei; Zhao, Wanli; Dai, Shanjun; Liu, Jinhao; Bukhari, Ihtisham; Xin, Hang; Niu, Wenbing; Sun, Yingpu

    2015-07-01

    The ends of eukaryotic chromosomes contain specialized chromatin structures called telomeres, the length of which plays a key role in early human embryonic development. Although the effect of sperm preparation techniques on major sperm characteristics, such as concentration, motility and morphology have been previously documented, the possible status of telomere length and its relation with sperm preparation techniques is not well-known for humans. The aim of this study was to investigate the role of density gradient centrifugation in the selection of spermatozoa with longer telomeres for use in assisted reproduction techniques in 105 samples before and after sperm processing. After density gradient centrifugation, the average telomere length of the sperm was significantly longer (6.51 ± 2.54 versus 5.16 ± 2.29, P technique for selection of sperm with longer telomeres. Copyright © 2015 Reproductive Healthcare Ltd. Published by Elsevier Ltd. All rights reserved.

  18. Landscape Patterns of Wood Density and Aboveground Biomass Along a Tropical Elevation Gradient in Costa Rica

    Science.gov (United States)

    Robinson, C. M.

    2015-12-01

    This research sought to understand how tree wood density and taxonomic diversity relate to topography and three-dimensional vegetation structure in the tropical montane forest of Braulio Carrillo National Park in Costa Rica. The study utilized forest inventory and botanical data from twenty 1-ha plots ranging from 55 m to 2800 m above sea level and remote sensing data from an airborne lidar sensor (NASA's Land, Vegetation, and Ice Sensor [LVIS]) to quantify variations in forest structure. There is growing evidence that ecosystem structure may help to control the functional variations across landscapes. This study relates patterns of tree functional wood density and alpha diversity to three-dimensional structure using remote sensing observations of forest structure. We were able to test the effect of the gradient on wood density measured from collected tree cores and on the subsequent aboveground biomass estimations. We sought to determine if there was a significant pattern of wood density across the altitudinal gradient, which has implications for conservation of both ecosystem services and biodiversity. We also wanted to determine how many random individuals could be sampled to accurately estimate aboveground biomass in a one-hectare plot. Our results indicate that there is a strong relationship between LVIS-derived forest 3D-structure and alpha diversity, likely controlled by variations in abiotic factors and topography along the elevation. Using spatial analysis with the aid of remote sensing data, we found patterns along the environmental gradients defining species composition and forest structure. Wood density values were found to vary significantly from database values for the same species. This variation in tree growth has repercussions on overall forest structure, and subsequent carbon estimates extrapolated from field measurements. Because these wood density values are directly tied to biomass estimates, it is possible that carbon storage has been

  19. Separation of Bacteria, Protozoa and Carbon Nanotubes by Density Gradient Centrifugation

    Directory of Open Access Journals (Sweden)

    Monika Mortimer

    2016-10-01

    Full Text Available Sustainable production and use of carbon nanotube (CNT-enabled materials require efficient assessment of CNT environmental hazards, including the potential for CNT bioaccumulation and biomagnification in environmental receptors. Microbes, as abundant organisms responsible for nutrient cycling in soil and water, are important ecological receptors for studying the effects of CNTs. Quantification of CNT association with microbial cells requires efficient separation of CNT-associated cells from individually dispersed CNTs and CNT agglomerates. Here, we designed, optimized, and demonstrated procedures for separating bacteria (Pseudomonas aeruginosa from unbound multiwall carbon nanotubes (MWCNTs and MWCNT agglomerates using sucrose density gradient centrifugation. We demonstrate separation of protozoa (Tetrahymena thermophila from MWCNTs, bacterial agglomerates, and protozoan fecal pellets by centrifugation in an iodixanol solution. The presence of MWCNTs in the density gradients after centrifugation was determined by quantification of 14C-labeled MWCNTs; the recovery of microbes from the density gradient media was confirmed by optical microscopy. Protozoan intracellular contents of MWCNTs and of bacteria were also unaffected by the designed separation process. The optimized methods contribute to improved efficiency and accuracy in quantifying MWCNT association with bacteria and MWCNT accumulation in protozoan cells, thus supporting improved assessment of CNT bioaccumulation.

  20. Separation of Bacteria, Protozoa and Carbon Nanotubes by Density Gradient Centrifugation

    Science.gov (United States)

    Mortimer, Monika; Petersen, Elijah J.; Buchholz, Bruce A.; Holden, Patricia A.

    2016-01-01

    Sustainable production and use of carbon nanotube (CNT)-enabled materials require efficient assessment of CNT environmental hazards, including the potential for CNT bioaccumulation and biomagnification in environmental receptors. Microbes, as abundant organisms responsible for nutrient cycling in soil and water, are important ecological receptors for studying the effects of CNTs. Quantification of CNT association with microbial cells requires efficient separation of CNT-associated cells from individually dispersed CNTs and CNT agglomerates. Here, we designed, optimized, and demonstrated procedures for separating bacteria (Pseudomonas aeruginosa) from unbound multiwall carbon nanotubes (MWCNTs) and MWCNT agglomerates using sucrose density gradient centrifugation. We demonstrate separation of protozoa (Tetrahymena thermophila) from MWCNTs, bacterial agglomerates, and protozoan fecal pellets by centrifugation in an iodixanol solution. The presence of MWCNTs in the density gradients after centrifugation was determined by quantification of 14C-labeled MWCNTs; the recovery of microbes from the density gradient media was confirmed by optical microscopy. Protozoan intracellular contents of MWCNTs and of bacteria were also unaffected by the designed separation process. The optimized methods contribute to improved efficiency and accuracy in quantifying MWCNT association with bacteria and MWCNT accumulation in protozoan cells, thus supporting improved assessment of CNT bioaccumulation. PMID:27917301

  1. Isolation of human salivary extracellular vesicles by iodixanol density gradient ultracentrifugation and their characterizations

    Directory of Open Access Journals (Sweden)

    Kazuya Iwai

    2016-05-01

    Full Text Available Diagnostic methods that focus on the extracellular vesicles (EVs present in saliva have been attracting great attention because of their non-invasiveness. EVs contain biomolecules such as proteins, messenger RNA (mRNA and microRNA (miRNA, which originate from cells that release EVs, making them an ideal source for liquid biopsy. Although there have been many reports on density-based fractionation of EVs from blood and urine, the number of reports on EVs from saliva has been limited, most probably because of the difficulties in separating EVs from viscous saliva using density gradient centrifugation. This article establishes a protocol for the isolation of EVs from human saliva using density gradient centrifugation. The fractionated salivary EVs were characterized by atomic force microscopy, western blot and reverse transcription polymerase chain reaction. The results indicate that salivary EVs have a smaller diameter (47.8±12.3 nm and higher density (1.11 g/ml than EVs isolated from conditioned cell media (74.0±23.5 nm and 1.06 g/ml, respectively. Additionally, to improve the throughput of density-based fractionation of EVs, the original protocol was further modified by using a fixed angle rotor instead of a swinging rotor. It was also confirmed that several miRNAs were expressed strongly in the EV-marker-expressing fractions.

  2. VERTICAL GRADIENTS IN REGIONAL LUNG DENSITY AND PERFUSION IN THE SUPINE HUMAN LUNG: THE SLINKY® EFFECT

    Science.gov (United States)

    Hopkins, Susan R.; Henderson, A. Cortney; Levin, David L.; Yamada, Kei; Arai, Tatsuya; Buxton, Richard B.; Prisk., G. Kim

    2008-01-01

    In-vivo radioactive tracer and microsphere studies have differing conclusions as to the magnitude of the gravitational effect on the distribution of pulmonary blood flow. We hypothesized that some of the apparent vertical perfusion gradient in-vivo is due to compression of dependent lung increasing local lung density and therefore perfusion/volume. To test this, 6 normal subjects underwent functional MRI with arterial spin labeling during a breath-hold at functional residual capacity, and perfusion quantified in non-overlapping 15mm sagittal slices covering most of the right lung. Lung proton density was measured in the same slices using a short echo 2D-FLASH sequence. Mean perfusion was 1.7 ± 0.6 ml/min/cm3 and was related to vertical height above the dependent lung (slope = −3%/cm, p Slinky®, a deformable spring distorting under its own weight. The greater density of lung tissue in the dependent regions of the lung is analogous to a greater number of coils in the dependent portion of the vertically oriented spring. This implies that measurements of perfusion in-vivo will be influenced by density distributions and will differ from excised lungs where density gradients are reduced by processing. PMID:17395757

  3. Vertical gradients in regional lung density and perfusion in the supine human lung: the Slinky effect.

    Science.gov (United States)

    Hopkins, Susan R; Henderson, A Cortney; Levin, David L; Yamada, Kei; Arai, Tatsuya; Buxton, Richard B; Prisk, G Kim

    2007-07-01

    In vivo radioactive tracer and microsphere studies have differing conclusions as to the magnitude of the gravitational effect on the distribution of pulmonary blood flow. We hypothesized that some of the apparent vertical perfusion gradient in vivo is due to compression of dependent lung increasing local lung density and therefore perfusion/volume. To test this, six normal subjects underwent functional magnetic resonance imaging with arterial spin labeling during breath holding at functional residual capacity, and perfusion quantified in nonoverlapping 15 mm sagittal slices covering most of the right lung. Lung proton density was measured in the same slices using a short echo 2D-Fast Low-Angle SHot (FLASH) sequence. Mean perfusion was 1.7 +/- 0.6 ml x min(-1) x cm(-3) and was related to vertical height above the dependent lung (slope = -3%/cm, P Slinky (Slinky is a registered trademark of Poof-Slinky Incorporated), a deformable spring distorting under its own weight. The greater density of lung tissue in the dependent regions of the lung is analogous to a greater number of coils in the dependent portion of the vertically oriented spring. This implies that measurements of perfusion in vivo will be influenced by density distributions and will differ from excised lungs where density gradients are reduced by processing.

  4. Space charge profiles in low density polyethylene samples containing a permittivity/conductivity gradient

    DEFF Research Database (Denmark)

    Bambery, K.R.; Fleming, R.J.; Holbøll, Joachim

    2001-01-01

    Laser induced pressure pulse space charge measurements were made on 1.5 mm thick plaques of high purity low density polyethylene equipped with vacuum-evaporated aluminium electrodes. Temperature differences up to 20 °C were maintained across the samples, which were subjected to dc fields up to 1.......5×107 V m-1. Current density was also measured as a function of temperature and field. Space charge due exclusively to the temperature gradient was detected, with density of order 0.01 C m-3. The activation energy associated with the transport of electrons through the bulk was calculated as 0.09 e...... were inferred by combining the space charge and current density measurements...

  5. Medicinal Plants Density Along an Altitudinal Gradient in and Around Ayubia National Park

    International Nuclear Information System (INIS)

    Tariq, A.; Adnan, M.; Begum, S.

    2016-01-01

    Medicinal plants are an essential source of livelihood for many rural populations and are currently facing several threats of extinction in temperate Himalaya, such as excessive grazing and collection along altitudinal gradients. The present study was designed to investigate the species density of medicinal plants at different mid-altitude levels (2200, 2300, 2400, and 2500 m above the sea level (a.s.l.) between two forest-use types and to examine the possible association between medicinal plant densities and forest-stand structural variables along the altitudinal gradient. Factorial design analysis of variance showed that the densities of all medicinal plants differed significantly between the forest-use types (p<0.00) and elevation (p<0.00). Moreover, a significant interaction (p<0.04) was also observed between the forest-use types and elevation. In the old-growth forest, density of medicinal plants was 290/40 m/sup 2/ at the higher altitude (2500 m a.s.l.), approximately 1.5-fold less than the 475/40 m/sup 2/ density observed at lower altitude (2200 m a.s.l.). However, in derived woodland, density of medicinal plants at higher altitude was approximately 4-fold less than that at the lower altitude. At these altitudinal levels, medicinal plants densities, such as Valeriana jatamansi, were significantly higher under old-growth forest compared to derived woodland, where they were almost nonexistent. A rapid vulnerability assessment has also shown that Valeriana jatamansi and Viola canescens were highly vulnerable species. Litter cover was the influential variable that was most likely related to medicinal plant density. In conclusion, abundance of medicinal plants decreased along mid-altitude levels in both of the forest-use types. However, this decrease was extremely marked in the derived woodland, and this decline may be due to human activity. Hence, these factors must be considered in future studies to suggest protective measures that can be applied along

  6. Pitfalls of using the geometric-mean combining rule in the density gradient theory

    DEFF Research Database (Denmark)

    Liang, Xiaodong; Michelsen, Michael Locht; Kontogeorgis, Georgios

    2016-01-01

    . It has been found that the solution profile passes a saddle point of the tangent plane distance, which is independent of the influence parameters. It has been shown that the numerical pitfalls could occur for both vapor liquid and liquid liquid equilibrium systems. Shape density change inside......It is popular and attractive to model the interfacial tension using the density gradient theory with the geometric-mean combining rule, in which the same equation of state is used for the interface and bulk phases. The computational efficiency is the most important advantage of this theory....... In this work, it has been mathematically shown that the theory fails if the solution profile is not monotonic in the path function, which is defined as the summation of the density multiplied by the square root of the influence parameter over all components. A computational solution procedure is then presented...

  7. Plasma membrane temperature gradients and multiple cell permeabilization induced by low peak power density femtosecond lasers

    Directory of Open Access Journals (Sweden)

    Allen L. Garner

    2016-03-01

    Full Text Available Calculations indicate that selectively heating the extracellular media induces membrane temperature gradients that combine with electric fields and a temperature-induced reduction in the electropermeabilization threshold to potentially facilitate exogenous molecular delivery. Experiments by a wide-field, pulsed femtosecond laser with peak power density far below typical single cell optical delivery systems confirmed this hypothesis. Operating this laser in continuous wave mode at the same average power permeabilized many fewer cells, suggesting that bulk heating alone is insufficient and temperature gradients are crucial for permeabilization. This work suggests promising opportunities for a high throughput, low cost, contactless method for laser mediated exogenous molecule delivery without the complex optics of typical single cell optoinjection, for potential integration into microscope imaging and microfluidic systems.

  8. Chemical bond as a test of density-gradient expansions for kinetic and exchange energies

    International Nuclear Information System (INIS)

    Perdew, J.P.; Levy, M.; Painter, G.S.; Wei, S.; Lagowski, J.B.

    1988-01-01

    Errors in kinetic and exchange contributions to the molecular bonding energy are assessed for approximate density functionals by reference to near-exact Hartree-Fock values. From the molecular calculations of Allan et al. and of Lee and Ghosh, it is demonstrated that the density-gradient expansion does not accurately describe the noninteracting kinetic contribution to the bonding energy, even when this expansion is carried to fourth order and applied in its spin-density-functional form to accurate Hartree-Fock densities. In a related study, it is demonstrated that the overbinding of molecules such as N 2 and F 2 , which occurs in the local-spin-density (LSD) approximation for the exchange-correlation energy, is not attributable to errors in the self-consistent LSD densities. Contrary to expectations based upon the Gunnarsson-Jones nodality argument, it is found that the LSD approximation for the exchange energy can seriously overbind a molecule even when bonding does not create additional nodes in the occupied valence orbitals. LSD and exact values for the exchange contribution to the bonding energy are displayed and discussed for several molecules

  9. Large polarization gradients and temperature-stable responses in compositionally-graded ferroelectrics

    Science.gov (United States)

    Damodaran, Anoop R.; Pandya, Shishir; Qi, Yubo; Hsu, Shang-Lin; Liu, Shi; Nelson, Christopher; Dasgupta, Arvind; Ercius, Peter; Ophus, Colin; Dedon, Liv R.; Agar, Josh C.; Lu, Hongling; Zhang, Jialan; Minor, Andrew M.; Rappe, Andrew M.; Martin, Lane W.

    2017-05-01

    A range of modern applications require large and tunable dielectric, piezoelectric or pyroelectric response of ferroelectrics. Such effects are intimately connected to the nature of polarization and how it responds to externally applied stimuli. Ferroelectric susceptibilities are, in general, strongly temperature dependent, diminishing rapidly as one transitions away from the ferroelectric phase transition (TC). In turn, researchers seek new routes to manipulate polarization to simultaneously enhance susceptibilities and broaden operational temperature ranges. Here, we demonstrate such a capability by creating composition and strain gradients in Ba1-xSrxTiO3 films which result in spatial polarization gradients as large as 35 μC cm-2 across a 150 nm thick film. These polarization gradients allow for large dielectric permittivity with low loss (εr~775, tan δ<0.05), negligible temperature-dependence (13% deviation over 500 °C) and high-dielectric tunability (greater than 70% across a 300 °C range). The role of space charges in stabilizing polarization gradients is also discussed.

  10. The tempered one-sided stable density: a universal model for hydrological transport?

    International Nuclear Information System (INIS)

    Cvetkovic, Vladimir

    2011-01-01

    A generalized distribution for the water residence time in hydrological transport is proposed in the form of the tempered one-sided stable (TOSS) density. It is shown that limiting cases of the TOSS distribution recover virtually all distributions that have been considered in the literature for hydrological transport, from plug flow to flow reactor, the advection-dispersion model, and the gamma and Levy densities. The stable property of TOSS is particularly important, enabling a seamless transition between a time-domain random walk, and the Lagrangian (trajectory) approach along hydrological transport pathways.

  11. Analytical gradients for subsystem density functional theory within the slater-function-based amsterdam density functional program.

    Science.gov (United States)

    Schlüns, Danny; Franchini, Mirko; Götz, Andreas W; Neugebauer, Johannes; Jacob, Christoph R; Visscher, Lucas

    2017-02-05

    We present a new implementation of analytical gradients for subsystem density-functional theory (sDFT) and frozen-density embedding (FDE) into the Amsterdam Density Functional program (ADF). The underlying theory and necessary expressions for the implementation are derived and discussed in detail for various FDE and sDFT setups. The parallel implementation is numerically verified and geometry optimizations with different functional combinations (LDA/TF and PW91/PW91K) are conducted and compared to reference data. Our results confirm that sDFT-LDA/TF yields good equilibrium distances for the systems studied here (mean absolute deviation: 0.09 Å) compared to reference wave-function theory results. However, sDFT-PW91/PW91k quite consistently yields smaller equilibrium distances (mean absolute deviation: 0.23 Å). The flexibility of our new implementation is demonstrated for an HCN-trimer test system, for which several different setups are applied. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

  12. Isolating peripheral lymphocytes by density gradient centrifugation and magnetic cell sorting.

    Science.gov (United States)

    Brosseron, Frederic; Marcus, Katrin; May, Caroline

    2015-01-01

    Combining density gradient centrifugation with magnetic cell sorting provides a powerful tool to isolate blood cells with high reproducibility, yield, and purity. It also allows for subsequent separation of multiple cell types, resulting in the possibility to analyze different purified fractions from one donor's sample. The centrifugation step divides whole blood into peripheral blood mononuclear cells (PBMC), erythrocytes, and platelet-rich plasma. In the following, lymphocyte subtypes can be consecutively isolated from the PBMC fraction. This chapter describes enrichment of erythrocytes, CD14-positive monocytes and CD3-positive T lymphocytes. Alternatively, other cell types can be targeted by using magnetic beads specific for the desired subpopulation.

  13. Noninvasive prenatal diagnosis. Use of density gradient centrifugation, magnetically activated cell sorting and in situ hybridization

    DEFF Research Database (Denmark)

    Campagnoli, C; Multhaupt, H A; Ludomirski, A

    1997-01-01

    centrifugation and dual antibody labeling methods. The protocol was designed to compare the efficacy of antitransferrin receptor (CD71)/antiglycophorin A (GPA) antibodies with antithrom-bospondin receptor (CD36)/anti-GPA antibodies in identifying nucleated erythrocytes in maternal blood. Cytospin preparations...... cells recovered did not differ. Seven of seven male pregnancies were correctly identified. One case of trisomy 21 was detected. CONCLUSION: The in situ hybridization analysis of fetal nucleated erythrocytes isolated from maternal blood using single density gradient centrifugation, anti-CD71/anti...

  14. Method and means for a spatial and temporal probe for laser-generated plumes based on density gradients

    Science.gov (United States)

    Yeung, E.S.; Chen, G.

    1990-05-01

    A method and means are disclosed for a spatial and temporal probe for laser generated plumes based on density gradients includes generation of a plume of vaporized material from a surface by an energy source. The probe laser beam is positioned so that the plume passes through the probe laser beam. Movement of the probe laser beam caused by refraction from the density gradient of the plume is monitored. Spatial and temporal information, correlated to one another, is then derived. 15 figs.

  15. Probability density based gradient projection method for inverse kinematics of a robotic human body model.

    Science.gov (United States)

    Lura, Derek; Wernke, Matthew; Alqasemi, Redwan; Carey, Stephanie; Dubey, Rajiv

    2012-01-01

    This paper presents the probability density based gradient projection (GP) of the null space of the Jacobian for a 25 degree of freedom bilateral robotic human body model (RHBM). This method was used to predict the inverse kinematics of the RHBM and maximize the similarity between predicted inverse kinematic poses and recorded data of 10 subjects performing activities of daily living. The density function was created for discrete increments of the workspace. The number of increments in each direction (x, y, and z) was varied from 1 to 20. Performance of the method was evaluated by finding the root mean squared (RMS) of the difference between the predicted joint angles relative to the joint angles recorded from motion capture. The amount of data included in the creation of the probability density function was varied from 1 to 10 subjects, creating sets of for subjects included and excluded from the density function. The performance of the GP method for subjects included and excluded from the density function was evaluated to test the robustness of the method. Accuracy of the GP method varied with amount of incremental division of the workspace, increasing the number of increments decreased the RMS error of the method, with the error of average RMS error of included subjects ranging from 7.7° to 3.7°. However increasing the number of increments also decreased the robustness of the method.

  16. A microfluidic device to establish concentration gradients using reagent density differences.

    Science.gov (United States)

    Kong, Qingjun; Able, Richard A; Dudu, Veronica; Vazquez, Maribel

    2010-12-01

    Microfabrication has become widely utilized to generate controlled microenvironments that establish chemical concentration gradients for a variety of engineering and life science applications. To establish microfluidic flow, the majority of existing devices rely upon additional facilities, equipment, and excessive reagent supplies, which together limit device portability as well as constrain device usage to individuals trained in technological disciplines. The current work presents our laboratory-developed bridged μLane system, which is a stand-alone device that runs via conventional pipette loading and can operate for several days without need of external machinery or additional reagent volumes. The bridged μLane is a two-layer polydimethylsiloxane microfluidic device that is able to establish controlled chemical concentration gradients over time by relying solely upon differences in reagent densities. Fluorescently labeled Dextran was used to validate the design and operation of the bridged μLane by evaluating experimentally measured transport properties within the microsystem in conjunction with numerical simulations and established mathematical transport models. Results demonstrate how the bridged μLane system was used to generate spatial concentration gradients that resulted in an experimentally measured Dextran diffusivity of (0.82 ± 0.01) × 10(-6) cm(2)/s.

  17. Effects of population density and chemical environment on the behavior of Escherichia coli in shallow temperature gradients

    International Nuclear Information System (INIS)

    Demir, Mahmut; Yoney, Anna; Salman, Hanna; Douarche, Carine; Libchaber, Albert

    2011-01-01

    In shallow temperature gradients, changes in temperature that bacteria experience occur over long time scales. Therefore, slow processes such as adaptation, metabolism, chemical secretion and even gene expression become important. Since these are cellular processes, the cell density is an important parameter that affects the bacteria's response. We find that there are four density regimes with distinct behaviors. At low cell density, bacteria do not cause changes in their chemical environment; however, their response to the temperature gradient is strongly influenced by it. In the intermediate cell-density regime, the consumption of nutrients becomes significant and induces a gradient of nutrients opposing the temperature gradient due to higher consumption rate at the high temperature. This causes the bacteria to drift toward low temperature. In the high cell-density regime, interactions among bacteria due to secretion of an attractant lead to a strong local accumulation of bacteria. This together with the gradient of nutrients, resulted from the differential consumption rate, creates a fast propagating pulse of bacterial density. These observations are a result of classical nonlinear population dynamics. At extremely high cell density, a change in the physiological state of the bacteria is observed. The bacteria, at the individual level, become cold seeking. This appears initially as a result of a change in the methylation level of the two most abundant sensing receptors, Tsr and Tar. It is further enforced at an even higher cell density by a change in the expression level of these receptors. (perspective)

  18. The effect of shear flow and the density gradient on the Weibel instability growth rate in the dense plasma

    Science.gov (United States)

    Amininasab, S.; Sadighi-Bonabi, R.; Khodadadi Azadboni, F.

    2018-02-01

    Shear stress effect has been often neglected in calculation of the Weibel instability growth rate in laser-plasma interactions. In the present work, the role of the shear stress in the Weibel instability growth rate in the dense plasma with density gradient is explored. By increasing the density gradient, the shear stress threshold is increasing and the range of the propagation angles of growing modes is limited. Therefore, by increasing steps of the density gradient plasma near the relativistic electron beam-emitting region, the Weibel instability occurs at a higher stress flow. Calculations show that the minimum value of the stress rate threshold for linear polarization is greater than that of circular polarization. The Wiebel instability growth rate for linear polarization is 18.3 times circular polarization. One sees that for increasing stress and density gradient effects, there are smaller maximal growth rates for the range of the propagation angles of growing modes /π 2 stress and density gradient tend to stabilize the Weibel instability for /k c ω p stress and density gradient tend to stabilize the Weibel instability for the range of the propagation angles of growing modes /π 2 < θ m i n < π and /3 π 2 < θ m i n < 2 π in circular polarized plasma.

  19. Noninvasive prenatal diagnosis. Use of density gradient centrifugation, magnetically activated cell sorting and in situ hybridization.

    Science.gov (United States)

    Campagnoli, C; Multhaupt, H A; Ludomirski, A; Haut, M J; Warhol, M J

    1997-04-01

    To develop a noninvasive method suitable for clinical prenatal diagnosis. Fetal nucleated erythrocytes were separated from peripheral blood of 17 healthy pregnant women using small magnetically activated cell sorting columns (MiniMACS) following density gradient centrifugation and dual antibody labeling methods. The protocol was designed to compare the efficacy of antitransferrin receptor (CD71)/antiglycophorin A (GPA) antibodies with antithrom-bospondin receptor (CD36)/anti-GPA antibodies in identifying nucleated erythrocytes in maternal blood. Cytospin preparations of the isolated cells were subjected to in situ hybridization with specific DNA probes for the Y chromosome and chromosome 21 to confirm the fetal origin. After MiniMACS the enrichment factors for the CD71/GPA- and CD36/GPA-positive cells from maternal blood were similar, and the percentages of fetal cells recovered did not differ. Seven of seven male pregnancies were correctly identified. One case of trisomy 21 was detected. The in situ hybridization analysis of fetal nucleated erythrocytes isolated from maternal blood using single density gradient centrifugation, anti-CD71/anti-GPA immunostaining and MiniMACS could be an accurate, sensitive and noninvasive method for prenatal diagnosis.

  20. Ficoll-400 density gradient method as an effective sperm preparation technique for assisted reproductive techniques.

    Science.gov (United States)

    Highland, Hyacinth N; Rishika, A Sharma; Almira, S Shaikh; Kanthi, P Bansal

    2016-01-01

    Infertility being a burning issue, the male itself contributes about 40% as a cause, as evident by statistical data. However, Assisted Reproductive Technology (ART) has emerged as a powerful tool in the management of infertility. Sperm preparation techniques govern the selection procedure to separate functional spermatozoa which can then be used in IUI, IVF, and ART and for cryopreservation. The present study was aimed at evaluation of sperm preparation techniques for reliability, performance and to determine the most effective, feasible and economical technique. The subjects under study includes males with normal proven fertility (n=40) and the males with unexplained infertility (n=40). Four sperm separation techniques, viz., Swim-up, Swim-down, Sucrose and Ficoll-400 density gradient techniques were evaluated for their efficacy in separation of good quality fraction of spermatozoa. Sperm viability, morphology and maturation status of spermatozoa were taken as evaluation parameters following the standard methods (WHO 2010). Data was analyzed using student's t -test and the four selected techniques were compared with the normal semen samples for scoring the efficiency of the techniques. Out of the several techniques used, Ficoll-400 was found to be more efficient method for separation of spermatozoa. The percentage of change in each parameter was calculated and taken as the index for recovery of potent sperm from the original sperm. Ficoll-400 density gradient yielded higher percentage of live, mature, morphologically normal spermatozoa in an isolated fraction as compared to other three techniques. It was observed that a combination of Ficoll-400 gradient separation with Swim-up technique could give quality spermatozoa which in-turn would directly have an impact on the success of IVF and other ART techniques.

  1. Controls on stand transpiration and soil water utilization along a tree density gradient in a Neotropical savanna

    Science.gov (United States)

    Sandra J. Bucci; Fabian G. Scholz; Guillermo Goldstein; William A. Hoffmann; Frederick C. Meinzer; Augusto C. Franco; Thomas Giambelluca; Fernando Miralles-Wilhelm

    2008-01-01

    Environmental controls of stand-level tree transpiration (E) and seasonal patterns of soil water utilization were studied in five central Brazilian savanna (Cerrado) sites differing in tree density. Tree density of Cerrado vegetation in the study area consistently changes along topographic gradients from ~1,000 trees ha-1 in open savannas (campo...

  2. Effects of density gradients and fluctuations at the plasma edge on ECEI measurements at ASDEX Upgrade

    Science.gov (United States)

    Vanovac, B.; Wolfrum, E.; Denk, S. S.; Mink, F.; Laggner, F. M.; Birkenmeier, G.; Willensdorfer, M.; Viezzer, E.; Hoelzl, M.; Freethy, S. J.; Dunne, M. G.; Lessig, A.; Luhmann, N. C., Jr.; the ASDEX Upgrade Team; the EUROfusion MST1 Team

    2018-04-01

    Electron cyclotron emission imaging (ECEI) provides measurements of electron temperature (T e ) and its fluctuations (δT e ). However, when measuring at the plasma edge, in the steep gradient region, radiation transport effects must be taken into account. It is shown that due to these effects, the scrape-off layer region is not accessible to the ECEI measurements in steady state conditions and that the signal is dominated by the shine-through emission. Transient effects, such as filaments, can change the radiation transport locally, but cannot be distinguished from the shine-through. Local density measurements are essential for the correct interpretation of the electron cyclotron emission, since the density fluctuations influence the temperature measurements at the plasma edge. As an example, a low frequency 8 kHz mode, which causes 10%-15% fluctuations in the signal level of the ECEI, is analysed. The same mode has been measured with the lithium beam emission spectroscopy density diagnostic, and is very well correlated in time with high frequency magnetic fluctuations. With radiation transport modelling of the electron cyclotron radiation in the ECEI geometry, it is shown that the density contributes significantly to the radiation temperature (T rad) and the experimental observations have shown the amplitude modulation in both density and temperature measurements. The poloidal velocity of the low frequency mode measured by the ECEI is 3 km s-1. The calculated velocity of the high frequency mode measured with the magnetic pick-up coils is about 25 km s-1. Velocities are compared with the E × B background flow velocity and possible explanations for the origin of the low frequency mode are discussed.

  3. COLLEMBOLA DENSITY AND DIVERSITY ALONG A GRADIENT OF LAND- USE TYPES IN EMBU DISTRICT, EASTERN KENYA

    Directory of Open Access Journals (Sweden)

    Jamleck M. Muturi

    2009-10-01

    Full Text Available Populations of soil-dwelling Collembola were monitored on a land use gradient ranging from Natural forests to intensively cultivated land during the wet season October-November, 2007 and dry season February-March, 2008. Eight land use types (LUTs which included stands of; Eucalyptus saligna, Vitex keniensis, Pennisetum purpureum, indigenous forest, fallow fields, Cammelia sinensis, Coffea africana and Zea mays intercropped with beans were sampled for Collembola in Embu district.. Collembola population densities of (15,111 M² were collected in the study area. The Collembolan populations were lower in all sites during the dry season (5,445 M², compared to those of wet season (9,666 M². However, the highest collembolan population was observed in undisturbed indigenous forest (38,089 M² during the dry season. A total of seventeen genera in seven families were recorded. The genus Isotomiella was the most abundant followed by Cryptopygus, Folsomina and Parisotoma respectively. Results from this study revealed that abundance, diversity and species richness decreased along land use gradient with agro-based LUTs presenting an impoverished community. The level of organic matter as indicated by proportion of Carbon and Nitrogen in LUTs such as Indigenous forest, Eucalyptus forest and Cammelia sinensis seemed to influence highly collembolan assemblages. The study concludes that land use intensification (land disturbance negatively influences the abundance and species richness of soil Collembolan communities

  4. Purification of Sarcocystis neurona sporocysts from opossum (Didelphis virginiana) using potassium bromide discontinuous density gradient centrifugation.

    Science.gov (United States)

    Elsheikha, Hany M; Murphy, Alice J; Fitzgerald, Scott D; Mansfield, Linda S; Massey, Jeffrey P; Saeed, Mahdi A

    2003-06-01

    This report describes a new, inexpensive procedure for the rapid and efficient purification of Sarcocystis neurona sporocysts from opossum small intestine. S. neurona sporocysts were purified using a discontinuous potassium bromide density gradient. The procedure provides a source of sporocyst wall and sporozoites required for reliable biochemical characterization and for immunological studies directed at characterizing antigens responsible for immunological responses by the host. The examined isolates were identified as S. neurona using random amplified polymorphic DNA primers and restriction endonuclease digestion assays. This method allows the collection of large numbers of highly purified S. neurona sporocysts without loss of sporocyst viability as indicated by propidium iodide permeability and cell culture infectivity assays. In addition, this technique might also be used for sporocyst purification of other Sarcocystis spp.

  5. Resistance scaling for composite fermions in the presence of a density gradient

    International Nuclear Information System (INIS)

    Stormer, H. L.; Tsui, Daniel Chee; Pan, Wei; West, Ken W.; Baldwin, K. W.; Pfeiffer, Loren N.

    2006-01-01

    The magnetoresistance, R xx , at even-denominator fractional fillings, of an ultra high quality two-dimensional electron system at T ∼ 35 mK is observed to be strictly linear in magnetic field, B. While at 35 mK R xx is dominated by the integer and fractional quantum Hall states, at T ≅ 1.2 K an almost perfect linear relationship between R xx and B emerges over the whole magnetic field range except for spikes at the integer quantum Hall states. This linear R xx cannot be understood within the Composite Fermion model, but can be explained through the existence of a density gradient in our sample

  6. Density Dependence, Landscape, and Weather Impacts on Aquatic Aedes japonicus japonicus (Diptera: Culicidae) Abundance Along an Urban Altitudinal Gradient.

    Science.gov (United States)

    Chaves, Luis Fernando; Moji, Kazuhiko

    2018-02-28

    The Asian Bush Mosquito, Aedes (Finlaya) japonicus japonicus (Theobald) is an important globally invasive mosquito species. In comparison with other major invasive mosquitoes, relatively little is known about Ae. j. japonicus population dynamics in the field. Here, we present results from a 54-biweek long study of Ae. j. japonicus abundance in ovitraps set across the altitudinal gradient of Mt. Konpira, Nagasaki, Japan. Spatially, we found that Ae. j. japonicus fourth instar larvae (Aj4il) were more abundant at the base and top of Mt. Konpira and in ovitraps with more platykurtic water temperature (WT) distributions. In contrast, we found that temporally Aj4il were more abundant when ovitrap WT was more leptokurtic with 2 weeks of lag, and with high relative humidity SD with 2 months of lag. We also found that Aj4il were unlikely present when ovitrap WT was below 12.41°C. Parameter estimates for the Ricker model suggested that Ae. j. japonicus population growth was under density-dependence regulation, with a stable population dynamics whose fluctuations were associated with changes in ovitrap WT kurtosis and demographic stochasticity. Our results suggest that Aj4il abundance is more sensitive to temperature changes in kurtosis than mean values, potentially limiting the predictive ability of Ae. j. japonicus niche models based on the increase of average temperatures with global warming, and suggesting this mosquito species has a relatively coarse-grained response to temperature changes.

  7. Solute dispersion for stable density-driven flow in randomly heterogeneous porous media

    Science.gov (United States)

    Dell'Oca, Aronne; Riva, Monica; Carrera, Jesus; Guadagnini, Alberto

    2018-01-01

    We present a theoretical investigation on the processes underpinning the reduced longitudinal spreading documented in stable variable density flows, as opposed to constant density settings, within heterogeneous porous media. We do so by decomposing velocity and pressure in terms of stationary and dynamic components. The former corresponds to the solution of the constant density flow problem, while the latter accounts for the effects induced by density variability. We focus on a stable flow configuration and analyze the longitudinal spread of saltwater injected from the bottom of a column formed by a heterogeneous porous medium initially fully saturated by freshwater. We adopt a perturbation expansion approach and derive the equations satisfied by section-averaged concentrations and their ensemble mean values. These formulations are respectively characterized by a single realization and an ensemble dispersive flux, which we determine through appropriate closure equations. The latter are solved via semi-analytical and numerical approaches. Our formulations and associated results enable us to discriminate the relative impact on the density-driven solute displacement of (a) covariance of the permeability of the porous medium, (b) cross-covariance between permeability and concentration, which is in turn linked to the coupling of flow and transport problems, and (c) cross-covariance between the dynamic and stationary velocities.

  8. Measuring Density Profiles of Electrons and Heavy Particles in a Stable Axially Blown Arc

    Science.gov (United States)

    Carstensen, J.; Stoller, P.; Galletti, B.; Doiron, C. B.; Sokolov, A.

    2017-08-01

    Two-color spatial carrier wave interferometry employing pulsed 532- and 671-nm lasers is used to measure the electron-density and heavy-particle-density profiles in the stagnation point of a stable, axially blown arc in argon for currents of 50 to 200 A and stagnation point pressures of 0.2 to 16 bar. This technique takes advantage of the fact that the free-electron contribution to the refractive index depends strongly on the wavelength, while that of the heavy particles does not. The high spatial resolution achieved allows the hot core of the arc to be readily distinguished from the surrounding boundary layer. A custom-built test device is used to ensure flow conditions that lead to a stable, axisymmetric arc; this permits the reconstruction of the density and temperature profiles using a single projection (interferometric image) of the refractive-index distribution through the arc (at two wavelengths). The arc radius determined from the heavy-particle density decreases with increasing stagnation pressure and increases with the current. These measurements are in good agreement with a simple axially blown arc model taking into account Ohmic heating, radiation losses, and enthalpy flow for core temperatures of approximately 16 500 K. The measured electron density at the center of the arc agrees well with a prediction based on local thermodynamic equilibrium.

  9. Biogenic gradients in algal density affect the emergent properties of spatially self-organized mussel beds.

    Science.gov (United States)

    Liu, Quan-Xing; Weerman, Ellen J; Gupta, Rohit; Herman, Peter M J; Olff, Han; van de Koppel, Johan

    2014-07-06

    Theoretical models highlight that spatially self-organized patterns can have important emergent effects on the functioning of ecosystems, for instance by increasing productivity and affecting the vulnerability to catastrophic shifts. However, most theoretical studies presume idealized homogeneous conditions, which are rarely met in real ecosystems. Using self-organized mussel beds as a case study, we reveal that spatial heterogeneity, resulting from the large-scale effects of mussel beds on their environment, significantly alters the emergent properties predicted by idealized self-organization models that assume homogeneous conditions. The proposed model explicitly considers that the suspended algae, the prime food for the mussels, are supplied by water flow from the seaward boundary of the bed, which causes in combination with consumption a gradual depletion of algae over the simulated domain. Predictions of the model are consistent with properties of natural mussel patterns observed in the field, featuring a decline in mussel biomass and a change in patterning. Model analyses reveal a fundamental change in ecosystem functioning when this self-induced algal depletion gradient is included in the model. First, no enhancement of secondary productivity of the mussels comparing with non-patterns states is predicted, irrespective of parameter setting; the equilibrium amount of mussels is entirely set by the input of algae. Second, alternate stable states, potentially present in the original (no algal gradient) model, are absent when gradual depletion of algae in the overflowing water layer is allowed. Our findings stress the importance of including sufficiently realistic environmental conditions when assessing the emergent properties of self-organized ecosystems.

  10. Versatile van der Waals Density Functional Based on a Meta-Generalized Gradient Approximation

    Directory of Open Access Journals (Sweden)

    Haowei Peng

    2016-10-01

    Full Text Available A “best-of-both-worlds” van der Waals (vdW density functional is constructed, seamlessly supplementing the strongly constrained and appropriately normed (SCAN meta-generalized gradient approximation for short- and intermediate-range interactions with the long-range vdW interaction from rVV10, the revised Vydrov–van Voorhis nonlocal correlation functional. The resultant SCAN+rVV10 is the only vdW density functional to date that yields excellent interlayer binding energies and spacings, as well as intralayer lattice constants in 28 layered materials. Its versatility for various kinds of bonding is further demonstrated by its good performance for 22 interactions between molecules; the cohesive energies and lattice constants of 50 solids; the adsorption energy and distance of a benzene molecule on coinage-metal surfaces; the binding energy curves for graphene on Cu(111, Ni(111, and Co(0001 surfaces; and the rare-gas solids. We argue that a good semilocal approximation should (as SCAN does capture the intermediate-range vdW through its exchange term. We have found an effective range of the vdW interaction between 8 and 16 Å for systems considered here, suggesting that this interaction is negligibly small at the larger distances where it reaches its asymptotic power-law decay.

  11. Implementation of Molecular Gradients for Local Hybrid Density Functionals Using Seminumerical Integration Techniques.

    Science.gov (United States)

    Klawohn, Sascha; Bahmann, Hilke; Kaupp, Martin

    2016-09-13

    We present the first implementation of the derivative of the local hybrid exchange-correlation energy with respect to the displacement of nuclei in a Gaussian-type atomic basis set. This extends a recent efficient implementation of local hybrid functionals for self-consistent Kohn-Sham and linear-response TDDFT calculations into the TURBOMOLE program package. In contrast to seminumerical schemes for global exact-exchange admixtures and to the related SCF and TDDFT implementations of local hybrid functionals, additional analytical integrals have to be evaluated at each grid point in the case of molecular gradients. The overall efficiency of the present scheme is improved through prescreening with the density matrix (P-junctions), as well as with spherical overlap estimates (S-junctions). Comparative timings for structure optimizations with local vs global hybrid functionals are discussed while gauging the accuracy for S- and P-junctions using varying thresholds. Local hybrids are furthermore assessed for structure optimization and harmonic vibrational frequency calculations (using numerical second derivatives) of a selection of test systems, comparing with experimental data and some widely used density functionals.

  12. A gradient stable scheme for a phase field model for the moving contact line problem

    KAUST Repository

    Gao, Min

    2012-02-01

    In this paper, an efficient numerical scheme is designed for a phase field model for the moving contact line problem, which consists of a coupled system of the Cahn-Hilliard and Navier-Stokes equations with the generalized Navier boundary condition [1,2,4]. The nonlinear version of the scheme is semi-implicit in time and is based on a convex splitting of the Cahn-Hilliard free energy (including the boundary energy) together with a projection method for the Navier-Stokes equations. We show, under certain conditions, the scheme has the total energy decaying property and is unconditionally stable. The linearized scheme is easy to implement and introduces only mild CFL time constraint. Numerical tests are carried out to verify the accuracy and stability of the scheme. The behavior of the solution near the contact line is examined. It is verified that, when the interface intersects with the boundary, the consistent splitting scheme [21,22] for the Navier Stokes equations has the better accuracy for pressure. © 2011 Elsevier Inc.

  13. Changes in home range sizes and population densities of carnivore species along the natural to urban habitat gradient

    Czech Academy of Sciences Publication Activity Database

    Šálek, Martin; Drahníková, L.; Tkadlec, Emil

    2015-01-01

    Roč. 45, č. 1 (2015), s. 1-14 ISSN 0305-1838 Institutional support: RVO:68081766 Keywords : Carnivores * home range size * natural–urban gradient * population density * review Subject RIV: EG - Zoology Impact factor: 4.116, year: 2015

  14. EUROMECH colloquium 377. Stability and control of shear flows with strong temperature or density gradients. Book of abstracts

    International Nuclear Information System (INIS)

    1998-10-01

    The topics discussed comprise the onset of instability in heated free jets and jets with density gradients, flow past heated/cooled boundaries, atmospheric shear flow, and mathematical modeling of laminar-turbulent transition phenomena. Three contributions have been input to INIS. (P.A.)

  15. arXiv Interferometer-based high-accuracy white light measurement of neutral rubidium density and gradient at AWAKE

    CERN Document Server

    Batsch, Fabian; Oez, Erdem; Moody, Joshua; Gschwendtner, Edda; Caldwell, Allen; Muggli, Patric

    The AWAKE experiment requires an automated online rubidium (Rb) plasma density and gradient diagnostic for densities between 1 and 10$\\cdot$10$^{14}$ cm$^{-3}$. A linear density gradient along the plasma source at the percent level may be useful to improve the electron acceleration process. Because of full laser ionization of Rb vapor to Rb$^{+}$ within a radius of 1 mm, the plasma density equals the vapor density. We measure the Rb vapor densities at both ends of the source, with high precision using, white light interferometry. At either source end, broadband laser light passes a remotely controlled Mach-Zehnder interferometer built out of single mode fibers. The resulting interference signal, influenced by dispersion in the vicinity of the Rb D1 and D2 transitions, is dispersed in wavelength by a spectrograph. Fully automated Fourier-based signal conditioning and a fit algorithm yield the density with an uncertainty between the measurements at both ends of 0.11 to 0.46 $\\%$ over the entire density range. T...

  16. Density-Dependent Regulation of Brook Trout Population Dynamics along a Core-Periphery Distribution Gradient in a Central Appalachian Watershed

    Science.gov (United States)

    Huntsman, Brock M.; Petty, J. Todd

    2014-01-01

    Spatial population models predict strong density-dependence and relatively stable population dynamics near the core of a species' distribution with increasing variance and importance of density-independent processes operating towards the population periphery. Using a 10-year data set and an information-theoretic approach, we tested a series of candidate models considering density-dependent and density-independent controls on brook trout population dynamics across a core-periphery distribution gradient within a central Appalachian watershed. We sampled seven sub-populations with study sites ranging in drainage area from 1.3–60 km2 and long-term average densities ranging from 0.335–0.006 trout/m. Modeled response variables included per capita population growth rate of young-of-the-year, adult, and total brook trout. We also quantified a stock-recruitment relationship for the headwater population and coefficients of variability in mean trout density for all sub-populations over time. Density-dependent regulation was prevalent throughout the study area regardless of stream size. However, density-independent temperature models carried substantial weight and likely reflect the effect of year-to-year variability in water temperature on trout dispersal between cold tributaries and warm main stems. Estimated adult carrying capacities decreased exponentially with increasing stream size from 0.24 trout/m in headwaters to 0.005 trout/m in the main stem. Finally, temporal variance in brook trout population size was lowest in the high-density headwater population, tended to peak in mid-sized streams and declined slightly in the largest streams with the lowest densities. Our results provide support for the hypothesis that local density-dependent processes have a strong control on brook trout dynamics across the entire distribution gradient. However, the mechanisms of regulation likely shift from competition for limited food and space in headwater streams to competition for

  17. Density-dependent regulation of brook trout population dynamics along a core-periphery distribution gradient in a central Appalachian watershed.

    Science.gov (United States)

    Huntsman, Brock M; Petty, J Todd

    2014-01-01

    Spatial population models predict strong density-dependence and relatively stable population dynamics near the core of a species' distribution with increasing variance and importance of density-independent processes operating towards the population periphery. Using a 10-year data set and an information-theoretic approach, we tested a series of candidate models considering density-dependent and density-independent controls on brook trout population dynamics across a core-periphery distribution gradient within a central Appalachian watershed. We sampled seven sub-populations with study sites ranging in drainage area from 1.3-60 km(2) and long-term average densities ranging from 0.335-0.006 trout/m. Modeled response variables included per capita population growth rate of young-of-the-year, adult, and total brook trout. We also quantified a stock-recruitment relationship for the headwater population and coefficients of variability in mean trout density for all sub-populations over time. Density-dependent regulation was prevalent throughout the study area regardless of stream size. However, density-independent temperature models carried substantial weight and likely reflect the effect of year-to-year variability in water temperature on trout dispersal between cold tributaries and warm main stems. Estimated adult carrying capacities decreased exponentially with increasing stream size from 0.24 trout/m in headwaters to 0.005 trout/m in the main stem. Finally, temporal variance in brook trout population size was lowest in the high-density headwater population, tended to peak in mid-sized streams and declined slightly in the largest streams with the lowest densities. Our results provide support for the hypothesis that local density-dependent processes have a strong control on brook trout dynamics across the entire distribution gradient. However, the mechanisms of regulation likely shift from competition for limited food and space in headwater streams to competition for

  18. Density-dependent regulation of brook trout population dynamics along a core-periphery distribution gradient in a central Appalachian watershed.

    Directory of Open Access Journals (Sweden)

    Brock M Huntsman

    Full Text Available Spatial population models predict strong density-dependence and relatively stable population dynamics near the core of a species' distribution with increasing variance and importance of density-independent processes operating towards the population periphery. Using a 10-year data set and an information-theoretic approach, we tested a series of candidate models considering density-dependent and density-independent controls on brook trout population dynamics across a core-periphery distribution gradient within a central Appalachian watershed. We sampled seven sub-populations with study sites ranging in drainage area from 1.3-60 km(2 and long-term average densities ranging from 0.335-0.006 trout/m. Modeled response variables included per capita population growth rate of young-of-the-year, adult, and total brook trout. We also quantified a stock-recruitment relationship for the headwater population and coefficients of variability in mean trout density for all sub-populations over time. Density-dependent regulation was prevalent throughout the study area regardless of stream size. However, density-independent temperature models carried substantial weight and likely reflect the effect of year-to-year variability in water temperature on trout dispersal between cold tributaries and warm main stems. Estimated adult carrying capacities decreased exponentially with increasing stream size from 0.24 trout/m in headwaters to 0.005 trout/m in the main stem. Finally, temporal variance in brook trout population size was lowest in the high-density headwater population, tended to peak in mid-sized streams and declined slightly in the largest streams with the lowest densities. Our results provide support for the hypothesis that local density-dependent processes have a strong control on brook trout dynamics across the entire distribution gradient. However, the mechanisms of regulation likely shift from competition for limited food and space in headwater streams to

  19. Highly transparent, stable, and superhydrophobic coatings based on gradient structure design and fast regeneration from physical damage

    Science.gov (United States)

    Chen, Zao; Liu, Xiaojiang; Wang, Yan; Li, Jun; Guan, Zisheng

    2015-12-01

    Optical transparency, mechanical flexibility, and fast regeneration are important factors to expand the application of superhydrophobic surfaces. Herein, we fabricated highly transparent, stable, and superhydrophobic coatings through a novel gradient structure design by versatile dip-coating of silica colloid particles (SCPs) and diethoxydimethysiliane cross-linked silica nanoparticles (DDS-SNPs) on polyethylene terephthalate (PET) film and glass, followed by the modification of octadecyltrichlorosiliane (OTCS). When the DDS concentration reached 5 wt%, the modified SCPs/DDS-SNPs coating exhibited a water contact angle (WCA) of 153° and a sliding angle (SA) superhydrophobic coating on PET film and glass was increased by 2.7% and 1% in the visible wavelength, respectively. This superhydrophobic coating also showed good robustness and stability against water dropping impact, ultrasonic damage, and acid solution. Moreover, the superhydrophobic PET film after physical damage can quickly regain the superhydrophobicity by one-step spray regenerative solution of dodecyltrichlorosilane (DTCS) modified silica nanoparticles at room temperature. The demonstrated method for the preparation and regeneration of superhydrophobic coating is available for different substrates and large-scale production at room temperature.

  20. Vitality of oligozoospermic semen samples is improved by both swim-up and density gradient centrifugation before cryopreservation.

    Science.gov (United States)

    Counsel, Madeleine; Bellinge, Rhys; Burton, Peter

    2004-05-01

    To ascertain whether washing sperm from oligozoospermic and normozoospermic samples before cryopreservation improves post-thaw vitality. Normozoospermic (n = 18) and oligozoospermic (n = 16) samples were divided into three aliquots. The first aliquot remained untreated and the second and third aliquots were subjected to the swim-up and discontinuous density gradient sperm washing techniques respectively. Vitality staining was performed, samples mixed with cryopreservation media and frozen. Spermatozoa were thawed, stained, and vitality quantified and expressed as the percentage of live spermatozoa present. Post-thaw vitality in untreated aliquots from normozoospermic samples (24.9% +/- 2.3; mean +/- SEM) was significantly higher (unpaired t-tests; P vitality was significantly higher after swim-up in normozoospermic samples (35.6% +/- 2.1; P vitality in oligozoospermic (22.4% +/- 1.0; P vitality in cryopreserved oligozoospermic samples was improved by both the swim-up and density gradient centrifugation washing techniques prior to freezing.

  1. Costs of coexistence along a gradient of competitor densities: an experiment with arvicoline rodents.

    Science.gov (United States)

    Eccard, Jana A; Ylönen, Hannu

    2007-01-01

    1. Costs of coexistence for species with indirect resource competition usually increase monotonically with competitor numbers. Very little is known though about the shape of the cost function for species with direct interference competition. 2. Here we report the results of an experiment with two vole species in artificial coexistence in large enclosures, where density of the dominant competitor species (Microtus agrestis) was manipulated. Experimental populations of the subordinate vole species (Clethrionomys glareolus) were composed of same aged individuals to study distribution of costs of coexistence with a dominant species within an age-cohort. 3. Survival and space use decreased gradually with increasing field vole numbers. Thus, responses to interference competition in our system appeared to be similar as expected from resource competition. The total number of breeders was stable. Reproductive characteristics such as the timing of breeding, and the litter size were not affected. In the single species enclosures a proportion of surviving individuals were not able to establish a breeding territory against stronger conspecifics. Under competition with heterospecifics such nonbreeders suffered high mortality, whereas the breeders survived. 4. Combined interference of dominant conspecifics and heterospecifics probably increased the frequency of aggressive interactions, social stress and mortality for the weaker individuals within a homogeneous age cohort of the subordinate competitor population. 5. Our results suggest, that in open systems where bank voles are outcompeted over the breeding season by faster reproducing field voles, animals able to establish a territory may be able to withstand competitor pressure, while nonbreeding bank vole individuals are forced to emigrate to suboptimal forest habitats.

  2. Sedimentation properties in density gradients correspond with levels of sperm DNA fragmentation, chromatin compaction and binding affinity to hyaluronic acid

    OpenAIRE

    Torabi, F; Binduraihem, A; Miller, D

    2017-01-01

    Mature spermatozoa bind hyaluronic acid in the extracellular matrix via hyaladherins. Immature spermatozoa may be unable to interact because they do not express the appropriate hyaladherins on their surface. Fresh human semen samples were fractionated using differential density gradient centrifugation (DDGC) and the ability of these fractions to bind hyaluronic acid was evaluated. The presence of sperm hyaladherins was also assessed. CD44 was located mainly on the acrosome and equatorial segm...

  3. Interaction of rate- and size-effect using a dislocation density based strain gradient viscoplasticity model

    Science.gov (United States)

    Nguyen, Trung N.; Siegmund, Thomas; Tomar, Vikas; Kruzic, Jamie J.

    2017-12-01

    Size effects occur in non-uniform plastically deformed metals confined in a volume on the scale of micrometer or sub-micrometer. Such problems have been well studied using strain gradient rate-independent plasticity theories. Yet, plasticity theories describing the time-dependent behavior of metals in the presence of size effects are presently limited, and there is no consensus about how the size effects vary with strain rates or whether there is an interaction between them. This paper introduces a constitutive model which enables the analysis of complex load scenarios, including loading rate sensitivity, creep, relaxation and interactions thereof under the consideration of plastic strain gradient effects. A strain gradient viscoplasticity constitutive model based on the Kocks-Mecking theory of dislocation evolution, namely the strain gradient Kocks-Mecking (SG-KM) model, is established and allows one to capture both rate and size effects, and their interaction. A formulation of the model in the finite element analysis framework is derived. Numerical examples are presented. In a special virtual creep test with the presence of plastic strain gradients, creep rates are found to diminish with the specimen size, and are also found to depend on the loading rate in an initial ramp loading step. Stress relaxation in a solid medium containing cylindrical microvoids is predicted to increase with decreasing void radius and strain rate in a prior ramp loading step.

  4. Landscape and forest structural controls on wood density and aboveground biomass along a tropical elevation gradient in Costa Rica

    Science.gov (United States)

    Robinson, C. M.; Saatchi, S. S.; Clark, D. B.; Gillespie, T. W.; Andelman, S.

    2014-12-01

    This research seeks to understand how tree wood density and taxonomic diversity relate to topography and three-dimensional vegetation structure in the tropical montane forest of Braulio Carrillo National Park in Costa Rica. The study utilized forest inventory and botanical data from twenty 1-ha plots ranging from 55 m to 2800 m above sea level and remote sensing data from an airborne lidar sensor (NASA's Land, Vegetation, and Ice Sensor [LVIS]) to quantify variations in forest structure. There is growing evidence that ecosystem structure plays an important role in defining patterns of species diversity and help to control the phenotypic and functional variations across landscapes. Elevation gradients along mountains provide landscape-size scales through which variations in topography, climate, and edaphic conditions as drivers of biodiversity can be tested. In this study we report on the effectiveness of relating patterns of tree wood density and alpha diversity to three-dimensional structure of a tropical montane forest using remote sensing observations of forest structure. Wood density is an important parameter for aboveground biomass and carbon estimations. Tree cores were analyzed for wood density and compared to existing database values for the same species. In this manner we were able to test the effect of the gradient on wood density and on the subsequent aboveground biomass estimations. Understanding these patterns has implications for conservation of both ecosystem services and biodiversity. Our results indicate that there is a strong relationship between LVIS-derived forest 3D-structure and alpha diversity, likely controlled controlled by variations in abiotic factors and topography along the elevation. Using spatial analysis with the aid of remote sensing data, we found distinct patterns along the environmental gradients defining species composition and forest structure. Wood density values were found to vary significantly from database values for the

  5. A modified gradient approach for the growth of low-density InAs quantum dot molecules by molecular beam epitaxy

    Science.gov (United States)

    Sharma, Nandlal; Reuter, Dirk

    2017-11-01

    Two vertically stacked quantum dots that are electronically coupled, so called quantum dot molecules, are of great interest for the realization of solid state building blocks for quantum communication networks. We present a modified gradient approach to realize InAs quantum dot molecules with a low areal density so that single quantum dot molecules can be optically addressed. The individual quantum dot layers were prepared by solid source molecular beam epitaxy depositing InAs on GaAs(100). The bottom quantum dot layer has been grown without substrate rotation resulting in an In-gradient across the surface, which translated into a density gradient with low quantum dot density in a certain region of the wafer. For the top quantum dot layer, separated from the bottom quantum dot layer by a 6 nm thick GaAs barrier, various InAs amounts were deposited without an In-gradient. In spite of the absence of an In-gradient, a pronounced density gradient is observed for the top quantum dots. Even for an In-amount slightly below the critical thickness for a single dot layer, a density gradient in the top quantum dot layer, which seems to reproduce the density gradient in the bottom layer, is observed. For more or less In, respectively, deviations from this behavior occur. We suggest that the obvious influence of the bottom quantum dot layer on the growth of the top quantum dots is due to the strain field induced by the buried dots.

  6. Comparative efficacy of density gradient and swim-up methods of semen preparation in intrauterine insemination cycles.

    Science.gov (United States)

    Butt, Amjad; Chohan, Muhammad Arshad

    2016-08-01

    To see the efficacy of different methods of intrauterine insemination preparation for sperm recovery and conception rate. This prospective observational study was carried out at Chohan Reproduction and Assisted Fertility Treatment Centre, Lahore, Pakistan, from January 2014 to July 2014, and comprised infertile couples undergoing intrauterine insemination cycles. Method of sperm preparation for intrauterine insemination during super-ovulation was randomly assigned for swim-up and density gradient techniques. Total sperm count, percentage recovery of motile sperm count, conception rate and cycle fecundity (live births, miscarriages, ectopic pregnancy) were measured.Mean percentages of sperm recovery and motility were compared. SPSS 21 was used for data analysis. Of the 220 couples who underwent 440 cycles, 138(62.7%) suffered from primary infertility and 82(37.27%) from secondary infertility. The mean age of women was 31.75±5.47 years, while that of men was 35.78±5.27 years. Mean duration of infertility in these couples was 5.50±3.51 years. Intrauterine insemination was performed at the first attempt in 180(81.8%) couples, at the second attempt in 37(16.8%) and at the third attempt in 3(1.3%) couples. Mean percentage of sperm motility in post-preparation of density gradient procedure was 83.88±15.02 (day 1) and 84.02±18.51 (day 2) while in swim-up procedure it was 91.02±11.85 (day 1) and 92.28±9.89 (day 2). Mean percentage of sperm concentration after processing in density gradient procedure was higher than swim-up (p=0.368 day 1; p=0.225 day 2) but mean percentage of sperm motility in post-preparation of density gradient procedure was less than swim-up procedure (p=0.000 day 1; p=0.000 day 2). Recovery rates in density gradient were 50.89% on day 1 and 5 13% on day 2compared to 36.69% on day 1 and 37.5%on day 2in swim-up technique (p=0.02). Conception rate was 15%. Despite the difference in percentage recovery of motile sperms in different techniques, cycle

  7. Development of gradient-corrected exchange-correlation functionals in the density functional theory; Developpement de fonctionnelles corrigees du gradient en theorie de la fonctionnelle de la densite

    Energy Technology Data Exchange (ETDEWEB)

    Lembarki, A.

    1994-12-01

    In this work, we have developed some gradient-corrected exchange-correlation functionals. This study is in keeping with the density functional theory (DFT) formalism. In the first part of this memory, a description of Hartree-Fock (HF), post-HF and density functional theories is given. The second part is devoted the study the different approximations of DFT exchange-correlation functionals which have been proposed in the last years. In particular, we have underlined the approximations used for the construction of these functionals. The third part of this memory consists in the development of new gradient-corrected functionals. In this study, we have established a new relation between exchange energy, correlation energy and kinetic energy. We have deduced two new possible forms of exchange or correlation functionals, respectively. In the fourth part, we have studied the exchange potential, for which the actual formulation does not satisfy some theoretical conditions, such as the asymptotic behavior -1/r. Our contribution lies in the development of an exchange potential with a correct asymptotic -1/r behavior for large values of r. In this chapter, we have proposed a model which permits the obtention of the exchange energy from the exchange potential, using the virial theorem. The fifth part of this memory is devoted the application of these different functionals to simple systems (H{sub 2}O, CO, N{sub 2}O, H{sub 3}{sup +} and H{sub 5}{sup +}) in order to characterize the performance of DFT calculations in regards to those obtained with post-HF methods. (author). 215 refs., 8 figs., 28 tabs.

  8. Excited state geometry optimizations by analytical energy gradient of long-range corrected time-dependent density functional theory.

    Science.gov (United States)

    Chiba, Mahito; Tsuneda, Takao; Hirao, Kimihiko

    2006-04-14

    An analytical excitation energy gradient of long-range corrected time-dependent density functional theory (LC-TDDFT) is presented. This is based on a previous analytical TDDFT gradient formalism, which avoids solving the coupled-perturbed Kohn-Sham equation for each nuclear degree of freedom. In LC-TDDFT, exchange interactions are evaluated by combining the short-range part of a DFT exchange functional with the long-range part of the Hartree-Fock exchange integral. This LC-TDDFT gradient was first examined by calculating the excited state geometries and adiabatic excitation energies of small typical molecules and a small protonated Schiff base. As a result, we found that long-range interactions play a significant role even in valence excited states of small systems. This analytical LC-TDDFT gradient was also applied to the investigations of small twisted intramolecular charge transfer (TICT) systems. By comparing with calculated ab initio multireference perturbation theory and experimental results, we found that LC-TDDFT gave much more accurate absorption and fluorescence energies of these systems than those of conventional TDDFTs using pure and hybrid functionals. For optimized excited state geometries, LC-TDDFT provided fairly different twisting and wagging angles of these small TICT systems in comparison with conventional TDDFT results.

  9. Density gradient localization of vanadate- and NO-3-sensitive ATPase from sterile cultures of Spirodela polyrrhiza (L. Schleiden

    Directory of Open Access Journals (Sweden)

    Józef Buczek

    2014-01-01

    Full Text Available The present work deals with the separation and some characteristics of ATPase activities bound with plant membanes prepared from sterile cultures of Spirodela polyrrhiza. The membrane-bound ATPases were separated on sucrose gradients and distinguished by membrane density and sensitivity to several inhibitors. The results showed that N0-3-sensitive ATPase activity associated with the tonoplast was localized at a sucrose density between 1.095-1.117 g•cm-3. The vanadate-sensitive ATPase activity bound with the plasma membrane showed a density between 1.127-1.151 g•cm-3. Both ATPases were insensitive to azide and oligomycin and were separable from markers for mitochondria.

  10. COLLEMBOLA DENSITY AND DIVERSITY ALONG A GRADIENT OF LAND- USE TYPES IN EMBU DISTRICT, EASTERN KENYA

    OpenAIRE

    Jamleck M. Muturi; J. P. Mbugi; Jones M. Mueke; Jan Lagerlóf; Joseph Mungatu; Gideon Nyamasyo; Mary Gikungu

    2009-01-01

    Populations of soil-dwelling Collembola were monitored on a land use gradient ranging from Natural forests to intensively cultivated land during the wet season October-November, 2007 and dry season February-March, 2008. Eight land use types (LUTs) which included stands of; Eucalyptus saligna, Vitex keniensis, Pennisetum purpureum, indigenous forest, fallow fields, Cammelia sinensis, Coffea africana and Zea mays intercropped with beans were sampled for Collembola in Embu district.. Collembola ...

  11. Characterization of a silica-PVA hybrid for high density and stable silver dissolution

    Energy Technology Data Exchange (ETDEWEB)

    Dorin, Bryce, E-mail: bryce.dorin@postgrad.manchester.ac.uk [The Photon Science Institute, The University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom); School of Chemical Engineering and Analytical Science, The University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom); Zhu, Guangyu, E-mail: g.zhu@liverpool.ac.uk [Lairdside Laser Engineering Centre, The University of Liverpool, Campbeltown Road, Merseyside, CH41 9HP (United Kingdom); Parkinson, Patrick, E-mail: patrick.parkinson@manchester.ac.uk [The Photon Science Institute, The University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom); School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom); Perrie, Walter, E-mail: wpfemto1@liverpool.ac.uk [Lairdside Laser Engineering Centre, The University of Liverpool, Campbeltown Road, Merseyside, CH41 9HP (United Kingdom); Benyezzar, Med, E-mail: med.benyezzar@manchester.ac.uk [The Photon Science Institute, The University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom); Scully, Patricia, E-mail: patricia.scully@manchester.ac.uk [The Photon Science Institute, The University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom); School of Chemical Engineering and Analytical Science, The University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom)

    2016-07-01

    A silica and polyvinyl alcohol (PVA) hybrid material mixed with a high density of silver ions is synthesised and characterized in this work. The hybrid material can be cast into thick films, which we determined to be homogeneous using Raman spectroscopy. We observed that the silver ions remain stable in the material over time and at temperatures of 100 °C, which represents a marked improvement over previous solid solutions of silver. Differential scanning calorimetry and thermogravimetric analysis indicate the rapid activation of silver at 173 °C, resulting in a dense formation of silver nanoparticles within the hybrid. The activation of silver was also demonstrated in 3-dimensional geometries using femtosecond duration laser pulses. These results illustrate the silica-PVA hybrid is an attractive material for developing silver-insulator composites. - Highlights: • A novel PVA-silica hybrid is developed for silver ion dissolution. • The hybrid exhibits a high silver saturation point and good silver stability. • Heating and laser irradiation are capable of converting the silver ions to metal. • The hybrid material enables the fabrication of 3D metal-insulator composites.

  12. Spatial variation of the stable nitrogen isotope ratio of woody plants along a topoedaphic gradient in a subtropical savanna.

    Science.gov (United States)

    Bai, Edith; Boutton, Thomas W; Liu, Feng; Wu, X Ben; Archer, Steven R; Hallmark, C Thomas

    2009-03-01

    Variation in the stable N isotope ratio (delta15N) of plants and soils often reflects the influence of environment on the N cycle. We measured leaf delta15N and N concentration ([N]) on all individuals of Prosopis glandulosa (deciduous tree legume), Condalia hookeri (evergreen shrub), and Zanthoxylum fagara (evergreen shrub) present within a belt transect 308 m long x 12 m wide in a subtropical savanna ecosystem in southern Texas, USA in April and August 2005. Soil texture, gravimetric water content (GWC), total N and delta15N were also measured along the transect. At the landscape scale, leaf delta15N was negatively related to elevation for all the three species along this topoedaphic sequence. Changes in soil delta15N, total N, and GWC appeared to contribute to this spatial pattern of leaf delta15N. In lower portions of the landscape, greater soil N availability and GWC are associated with relatively high rates of both N mineralization and nitrification. Both soil delta15N and leaf [N] were positively correlated with leaf delta15N of non-N2 fixing plants. Leaf delta15N of P. glandulosa, an N2-fixing legume, did not correlate with leaf [N]; the delta15N of P. glandulosa's leaves were closer to atmospheric N2 and significantly lower than those of C. hookeri and Z. fagara. Additionally, at smaller spatial scales, a proximity index (which reflected the density and distance of surrounding P. glandulosa trees) was negatively correlated with leaf delta15N of C. hookeri and Z. fagara, indicating the N2-fixing P. glandulosa may be important to the N nutrition of nearby non-N2-fixing species. Our results indicate plant 15N natural abundance can reflect the extent of N retention and help us better understand N dynamics and plant-soil interactions at ecosystem and landscape scales.

  13. Reservoir longitudinal gradient promotes ordered losses on diversity and density of Ephemeroptera community.

    Science.gov (United States)

    Melo, S M; Pinha, G D; Ragonha, F H; Fontes-Junior, H M; Takeda, A M

    2018-02-05

    Reservoir operations alter, eliminate or restrain the natural hydrologic cycles. Biotic community has become subject to these non-cyclic events, responding by reducing the species diversity. Ephemeroptera species present distinct responses to environmental deterioration such that poses this assemblage between the most useful groups in biomonitoring programs. We hypothesized an alteration in beta diversity at the longitudinal species gradient, which will be influenced mainly by species losses between zones. Changes in temporal beta diversity is also expected, but the main drivers of such alterations will be the species turnover between the sampling period. Ephemeroptera community was monitored in nine sampling points from Itaipu Reservoir, where were installed three sets of substrates composed by a float and 2 wooden substrates. We took biological samples in triplicates monthly, from June-01 to August-02. Our initial hypothesis was partially supported and with significant variations only for spatial approach, between the Reservoir zones. The generated ordering from Non-Metric Dimensional Scale - NMDS - corroborated with spatial analyzes, with the formation of two groups along the gradient zonation of the reservoir. The temporal ordination showed no clear pattern. As expected, the contribution to beta diversity was different for our two approaches, such that the loss of species was more important along the spatial gradient and despite of no significant result, the species replacement was more important among months. The spatial results lead us to infer that differences in limnological characteristics between zones are important for determining differences in Ephemeroptera composition and can reflect the dependency degree of the species in relation to the lentic and sometimes-lotic conditions, mainly in the riverine zone of reservoirs. On the other hand, the absence of a temporal pattern can be result of chaotic variations in the physical and chemical attributes

  14. Reservoir longitudinal gradient promotes ordered losses on diversity and density of Ephemeroptera community

    Directory of Open Access Journals (Sweden)

    S. M. Melo

    2018-02-01

    Full Text Available Abstract Reservoir operations alter, eliminate or restrain the natural hydrologic cycles. Biotic community has become subject to these non-cyclic events, responding by reducing the species diversity. Ephemeroptera species present distinct responses to environmental deterioration such that poses this assemblage between the most useful groups in biomonitoring programs. We hypothesized an alteration in beta diversity at the longitudinal species gradient, which will be influenced mainly by species losses between zones. Changes in temporal beta diversity is also expected, but the main drivers of such alterations will be the species turnover between the sampling period. Ephemeroptera community was monitored in nine sampling points from Itaipu Reservoir, where were installed three sets of substrates composed by a float and 2 wooden substrates. We took biological samples in triplicates monthly, from June-01 to August-02. Our initial hypothesis was partially supported and with significant variations only for spatial approach, between the Reservoir zones. The generated ordering from Non-Metric Dimensional Scale – NMDS - corroborated with spatial analyzes, with the formation of two groups along the gradient zonation of the reservoir. The temporal ordination showed no clear pattern. As expected, the contribution to beta diversity was different for our two approaches, such that the loss of species was more important along the spatial gradient and despite of no significant result, the species replacement was more important among months. The spatial results lead us to infer that differences in limnological characteristics between zones are important for determining differences in Ephemeroptera composition and can reflect the dependency degree of the species in relation to the lentic and sometimes-lotic conditions, mainly in the riverine zone of reservoirs. On the other hand, the absence of a temporal pattern can be result of chaotic variations in the

  15. Fast-electron self-collimation in a plasma density gradient

    International Nuclear Information System (INIS)

    Yang, X. H.; Borghesi, M.; Robinson, A. P. L.

    2012-01-01

    A theoretical and numerical study of fast electron transport in solid and compressed fast ignition relevant targets is presented. The principal aim of the study is to assess how localized increases in the target density (e.g., by engineering of the density profile) can enhance magnetic field generation and thus pinching of the fast electron beam through reducing the rate of temperature rise. The extent to which this might benefit fast ignition is discussed.

  16. Droplet and bubble nucleation modeled by density gradient theory – cubic equation of state versus saft model

    Directory of Open Access Journals (Sweden)

    Hrubý Jan

    2012-04-01

    Full Text Available The study presents some preliminary results of the density gradient theory (GT combined with two different equations of state (EoS: the classical cubic equation by van der Waals and a recent approach based on the statistical associating fluid theory (SAFT, namely its perturbed-chain (PC modification. The results showed that the cubic EoS predicted for a given surface tension the density profile with a noticeable defect. Bulk densities predicted by the cubic EoS differed as much as by 100 % from the reference data. On the other hand, the PC-SAFT EoS provided accurate results for density profile and both bulk densities in the large range of temperatures. It has been shown that PC-SAFT is a promising tool for accurate modeling of nucleation using the GT. Besides the basic case of a planar phase interface, the spherical interface was analyzed to model a critical cluster occurring either for nucleation of droplets (condensation or bubbles (boiling, cavitation. However, the general solution for the spherical interface will require some more attention due to its numerical difficulty.

  17. Thermodynamic, energy efficiency, and power density analysis of reverse electrodialysis power generation with natural salinity gradients.

    Science.gov (United States)

    Yip, Ngai Yin; Vermaas, David A; Nijmeijer, Kitty; Elimelech, Menachem

    2014-05-06

    Reverse electrodialysis (RED) can harness the Gibbs free energy of mixing when fresh river water flows into the sea for sustainable power generation. In this study, we carry out a thermodynamic and energy efficiency analysis of RED power generation, and assess the membrane power density. First, we present a reversible thermodynamic model for RED and verify that the theoretical maximum extractable work in a reversible RED process is identical to the Gibbs free energy of mixing. Work extraction in an irreversible process with maximized power density using a constant-resistance load is then examined to assess the energy conversion efficiency and power density. With equal volumes of seawater and river water, energy conversion efficiency of ∼ 33-44% can be obtained in RED, while the rest is lost through dissipation in the internal resistance of the ion-exchange membrane stack. We show that imperfections in the selectivity of typical ion exchange membranes (namely, co-ion transport, osmosis, and electro-osmosis) can detrimentally lower efficiency by up to 26%, with co-ion leakage being the dominant effect. Further inspection of the power density profile during RED revealed inherent ineffectiveness toward the end of the process. By judicious early discontinuation of the controlled mixing process, the overall power density performance can be considerably enhanced by up to 7-fold, without significant compromise to the energy efficiency. Additionally, membrane resistance was found to be an important factor in determining the power densities attainable. Lastly, the performance of an RED stack was examined for different membrane conductivities and intermembrane distances simulating high performance membranes and stack design. By thoughtful selection of the operating parameters, an efficiency of ∼ 37% and an overall gross power density of 3.5 W/m(2) represent the maximum performance that can potentially be achieved in a seawater-river water RED system with low

  18. Density and community structure of soil- and bark-dwelling microarthropods along an altitudinal gradient in a tropical montane rainforest

    Science.gov (United States)

    Illig, Jens; Norton, Roy A.; Scheu, Stefan

    2010-01-01

    Microarthropod communities in the soil and on the bark of trees were investigated along an elevation gradient (1,850, 2,000, 2,150, 2,300 m) in a tropical montane rain forest in southern Ecuador. We hypothesised that the density of microarthropods declines with depth in soil and increases with increasing altitude mainly due to the availability of resources, i.e. organic matter. In addition, we expected bark and soil communities to differ strongly, since the bark of trees is more exposed to harsher factors. In contrast to our hypothesis, the density of major microarthropod groups (Collembola, Oribatida, Gamasina, Uropodina) was generally low and decreased with altitude. However, as we predicted the density of each of the groups decreased with soil depth. Density of microarthropods on tree bark was lower than in soil. Overall, 43 species of oribatid mites were found, with the most abundant higher taxa being Poronota, pycnonotic Apheredermata, Mixonomata and Eupheredermata. The oribatid mite community on bark did not differ significantly from that in soil. The number of oribatid mite species declined with altitude (24, 23, 17 and 13 species at 1,850, 2,000, 2,150 and 2,300 m, respectively). Rarefaction curves indicate that overall about 50 oribatid mite species are to be expected along the studied altitudinal gradient. Results of this study indicate (1) that microarthropods may be limited by the quality of resources at high altitudes and by the amount of resources at deeper soil layers, and (2) that the bark of trees and the soil are habitats of similar quality for oribatid mites. Electronic supplementary material The online version of this article (doi:10.1007/s10493-010-9348-x) contains supplementary material, which is available to authorized users. PMID:20229099

  19. Optically abrupt localized surface plasmon resonances in si nanowires by mitigation of carrier density gradients.

    Science.gov (United States)

    Chou, Li-Wei; Boyuk, Dmitriy S; Filler, Michael A

    2015-02-24

    Spatial control of carrier density is critical for engineering and exploring the interactions of localized surface plasmon resonances (LSPRs) in nanoscale semiconductors. Here, we couple in situ infrared spectral response measurements and discrete dipole approximation (DDA) calculations to show the impact of axially graded carrier density profiles on the optical properties of mid-infrared LSPRs supported by Si nanowires synthesized by the vapor-liquid-solid technique. The region immediately adjacent to each intentionally encoded resonator (i.e., doped segment) can exhibit residual carrier densities as high as 10(20) cm(-3), which strongly modifies both near- and far-field behavior. Lowering substrate temperature during the spacer segment growth reduces this residual carrier density and results in a spectral response that is indistinguishable from nanowires with ideal, atomically abrupt carrier density profiles. Our experiments have important implications for the control of near-field plasmonic phenomena in semiconductor nanowires, and demonstrate methods for determining and controlling axial dopant profile in these systems.

  20. Relaxation of a steep density gradient in a simple fluid: Comparison between atomistic and continuum modeling

    Energy Technology Data Exchange (ETDEWEB)

    Pourali, Meisam; Maghari, Ali [Department of Physical Chemistry, School of Chemistry, College of Science, University of Tehran, Tehran (Iran, Islamic Republic of); Meloni, Simone, E-mail: simone.meloni@epfl.ch [Laboratory of Computational Chemistry and Biochemistry, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne (Switzerland); Magaletti, Francesco; Casciola, Carlo Massimo [Dipartimento di Ingegneria Meccanica e Aerospaziale, Università La Sapienza, Via Eudossiana 18, 00184 Rome (Italy); Ciccotti, Giovanni [Dipartimento di Fisica and CNISM, Università La Sapienza, P.le A. Moro 5, 00185 Rome (Italy)

    2014-10-21

    We compare dynamical nonequilibrium molecular dynamics and continuum simulations of the dynamics of relaxation of a fluid system characterized by a non-uniform density profile. Results match quite well as long as the lengthscale of density nonuniformities are greater than the molecular scale (∼10 times the molecular size). In presence of molecular scale features some of the continuum fields (e.g., density and momentum) are in good agreement with atomistic counterparts, but are smoother. On the contrary, other fields, such as the temperature field, present very large difference with respect to reference (atomistic) ones. This is due to the limited accuracy of some of the empirical relations used in continuum models, the equation of state of the fluid in the present example.

  1. Relaxation of a steep density gradient in a simple fluid: Comparison between atomistic and continuum modeling

    International Nuclear Information System (INIS)

    Pourali, Meisam; Maghari, Ali; Meloni, Simone; Magaletti, Francesco; Casciola, Carlo Massimo; Ciccotti, Giovanni

    2014-01-01

    We compare dynamical nonequilibrium molecular dynamics and continuum simulations of the dynamics of relaxation of a fluid system characterized by a non-uniform density profile. Results match quite well as long as the lengthscale of density nonuniformities are greater than the molecular scale (∼10 times the molecular size). In presence of molecular scale features some of the continuum fields (e.g., density and momentum) are in good agreement with atomistic counterparts, but are smoother. On the contrary, other fields, such as the temperature field, present very large difference with respect to reference (atomistic) ones. This is due to the limited accuracy of some of the empirical relations used in continuum models, the equation of state of the fluid in the present example

  2. Evaluation of the impact of density gradient centrifugation on fetal cell loss during enrichment from maternal peripheral blood.

    Science.gov (United States)

    Emad, Ahmed; Drouin, Régen

    2014-09-01

    Physical separation by density gradient centrifugation (DGC) is usually used as an initial step of multistep enrichment protocols for purification of fetal cells (FCs) from maternal blood. Many protocols were designed but no single approach was efficient enough to provide noninvasive prenatal diagnosis. Procedures and methods were difficult to compare because of the nonuniformity of protocols among different groups. Recovery of FCs is jeopardized by their loss during the process of enrichment. Any loss of FCs must be minimized because of the multiplicative effect of each step of the enrichment process. The main objective of this study was to evaluate FC loss caused by DGC. Fetal cells were quantified in peripheral blood samples obtained from both euploid and aneuploid pregnancies before and after enrichment by buoyant DGC using Histopaque 1.119 g/mL. Density gradient centrifugation results in major loss of 60% to 80% of rare FCs, which may further complicate subsequent enrichment procedures. Eliminating aggressive manipulations can significantly minimize FC loss. Data obtained raise questions about the appropriateness of the DGC step for the enrichment of rare FCs and argues for the use of the alternative nonaggressive version of the procedure presented here or prioritizing other methods of enrichments. © 2014 John Wiley & Sons, Ltd.

  3. A process study of the interaction of tidal currents, tidal mixing and density gradients in a region of freshwater influence

    Science.gov (United States)

    Xing, Jiuxing; Chen, Shengli

    2017-08-01

    A three dimensional unstructured grid model of the west coast of Britain is used to study the process of the interaction of tidal currents, tidal mixing and density gradient in the Liverpool Bay region. Calculations with M2 tidal forcing and omitting freshwater discharge show that tidal currents in the region are strong (of order 1 ms- 1), with tidal current ellipses essentially rectilinear in the surface and bottom. In the absence of tidal forcing, the freshwater is confined to a thin surface layer. With the inclusion of tidal mixing the surface layer thickens, and in the shallow water area mixed layer occupies the whole water depth. This has a significant effect of reducing its lateral spread. A detailed study of time series of velocity, salinity and turbulence reveals that at flood tide, more saline water is advected into the coastal region and rapid vertical mixing occurs, whereas at ebb tide, fresher water is advected over more saline water. The induced strong pycnocline uncouples surface and bottom layers leading to more circular tidal ellipses which rotate in opposite directions in the vertical, as found in observations. The three dimensional nature of the model reveals that this process involves both horizontal and vertical density gradients, and shows significant horizontal variability in the Liverpool Bay region.

  4. Density gradient instabilities in a neutron inhomogeneous guiding-centre plasma

    International Nuclear Information System (INIS)

    Shoucri, M.M.; Gagne, R.R.J.

    1977-01-01

    The guiding-centre equations for a plasma of cold ions and thermal electrons admit neutral and non-neutral inhomogeneous equilibrium solutions, and the linear stability of these solutions has been recently investigated numerically by Shoucri and Knorr (1975). With arbitrary density profiles, numerical techniques appear to be the only practical way to study the linear stability of the inhomogeneous equilibrium solutions for the guiding centre plasma. However, analytical methods can be applied to some simple types of density profiles. The purpose of the present note is to present some analytical results on the linear instabilities of an inhomogeneous neutral guiding centre plasma. (U.K.)

  5. Damping-Growth Transition for Ion-Acoustic Waves in a Density Gradient

    DEFF Research Database (Denmark)

    D'Angelo, N.; Michelsen, Poul; Pécseli, Hans

    1975-01-01

    A damping-growth transition for ion-acoustic waves propagating in a nonuniform plasma (e-folding length for the density ln) is observed at a wavelength λ∼2πln. This result supports calculations performed in connection with the problem of heating of the solar corona by ion-acoustic waves generated...... in the solar photosphere....

  6. Numerical Studies of Electron Acceleration Behind Self-Modulating Proton Beam in Plasma with a Density Gradient

    CERN Document Server

    Petrenko, A.; Sosedkin, A.

    2016-01-01

    Presently available high-energy proton beams in circular accelerators carry enough momentum to accelerate high-intensity electron and positron beams to the TeV energy scale over several hundred meters of the plasma with a density of about 1e15 1/cm^3. However, the plasma wavelength at this density is 100-1000 times shorter than the typical longitudinal size of the high-energy proton beam. Therefore the self-modulation instability (SMI) of a long (~10 cm) proton beam in the plasma should be used to create the train of micro-bunches which would then drive the plasma wake resonantly. Changing the plasma density profile offers a simple way to control the development of the SMI and the acceleration of particles during this process. We present simulations of the possible use of a plasma density gradient as a way to control the acceleration of the electron beam during the development of the SMI of a 400 GeV proton beam in a 10 m long plasma. This work is done in the context of the AWAKE project --- the proof-of-prin...

  7. Extension of SMAC scheme for variable density flows under strong temperature gradient

    Science.gov (United States)

    Anwer, S. F.; Khan, H. Naushad; Sanghi, S.; Ahmad, A.; Yahya, S. M.

    2012-06-01

    An extension of SMAC scheme is proposed for variable density flows under low Mach number approximation. The algorithm is based on a predictor-corrector time integration scheme that employs a projection method for the momentum equation. A constant-coefficient Poisson equation is solved for the pressure following both the predictor and corrector steps to satisfy the continuity equation at each time step. Spatial discretization is performed on a collocated grid system that offers computational simplicity and straight forward extension to curvilinear coordinate systems. To avoid the pressure odd-even decoupling that is typically encountered in such grids, a flux interpolation technique is introduced for the equations governing variable density flows. An important characteristic of the proposed algorithm is that it can be applied to flows in both open and closed domains. Its robustness and accuracy are illustrated with a non-isothermal, turbulent channel flow at temperature ratio of 1.01 and 2.

  8. Species-specific gradients of juvenile fish density and size in pelagic areas of temperate reservoirs

    Czech Academy of Sciences Publication Activity Database

    Jůza, Tomáš; Ricard, Daniel; Blabolil, Petr; Čech, Martin; Draštík, Vladislav; Frouzová, Jaroslava; Muška, Milan; Peterka, Jiří; Prchalová, Marie; Říha, Milan; Sajdlová, Zuzana; Šmejkal, Marek; Tušer, Michal; Vašek, Mojmír; Vejřík, Lukáš; Kubečka, Jan

    2015-01-01

    Roč. 762, č. 1 (2015), s. 169-181 ISSN 0018-8158 R&D Projects: GA MŠk(CZ) EE2.3.20.0204; GA MŠk(CZ) EE2.3.30.0032; GA MŠk(CZ) 7F14316 Institutional support: RVO:60077344 Keywords : trawling * juvenile density * horizontal distribution * vertical distribution * tributary area Subject RIV: EH - Ecology, Behaviour Impact factor: 2.051, year: 2015

  9. Weak turbulence theory of ion temperature gradient modes for inverted density plasmas

    International Nuclear Information System (INIS)

    Hahm, T.S.; Tang, W.M.

    1989-09-01

    Typical profiles measured in H-mode (''high confinement'') discharges from tokamaks such as JET and DIII-D suggest that the ion temperature gradient instability threshold parameter η i (≡dlnT i /dlnn i ) could be negative in many cases. Previous linear theoretical calculations have established the onset conditions for these negative η i -modes and the fact that their growth rate is much smaller than their real frequency over a wide range of negative η i values. This has motivated the present nonlinear weak turbulence analysis to assess the relevance of such instabilities for confinement in H-mode plasmas. The nonlinear eigenmode equation indicates that the 3-wave coupling to shorter wavelength modes is the dominant nonlinear saturation mechanism. It is found that both the saturation level for these fluctuations and the magnitude of the associated ion thermal diffusivity are considerably smaller than the strong turbulence mixing length type estimates for the more conventional positive-η i -instabilities. 19 refs., 3 figs

  10. Measuring the electron density gradients of dense plasmas by deflectometry using short-wavelength probe

    Czech Academy of Sciences Publication Activity Database

    Nejdl, J.; Kozlová, Michaela; Mocek, Tomáš; Rus, Bedřich

    2010-01-01

    Roč. 17, č. 12 (2010), 122705/1-122705/6 ISSN 1070-664X R&D Projects: GA MŠk(CZ) 7E08099; GA ČR GA202/08/1734; GA MŠk(CZ) 7E09092 Grant - others:AVČR(CZ) M100100911 Institutional research plan: CEZ:AV0Z10100523 Keywords : plasma density * plasma diagnostics * plasma electromagnetic wave propagation * plasma production by laser Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.320, year: 2010 http://pop.aip.org/resource/1/phpaen/v17/i12/p122705_s1?isAuthorized=no

  11. Multi-Dimensional Quantum Effect Simulation Using a Density-Gradient Model and Script-Level Programming Techniques

    Science.gov (United States)

    Rafferty, Connor S.; Biegel, Bryan A.; Yu, Zhi-Ping; Ancona, Mario G.; Bude, J.; Dutton, Robert W.; Saini, Subhash (Technical Monitor)

    1998-01-01

    A density-gradient (DG) model is used to calculate quantum-mechanical corrections to classical carrier transport in MOS (Metal Oxide Semiconductor) inversion/accumulation layers. The model is compared to measured data and to a fully self-consistent coupled Schrodinger and Poisson equation (SCSP) solver. Good agreement is demonstrated for MOS capacitors with gate oxide as thin as 21 A. It is then applied to study carrier distribution in ultra short MOSFETs (Metal Oxide Semiconductor Field Effect Transistor) with surface roughness. This work represents the first implementation of the DG formulation on multidimensional unstructured meshes. It was enabled by a powerful scripting approach which provides an easy-to-use and flexible framework for solving the fourth-order PDEs (Partial Differential Equation) of the DG model.

  12. Density-gradient centrifugation enables the purification of cultured corneal endothelial cells for cell therapy by eliminating senescent cells

    Science.gov (United States)

    Okumura, Naoki; Kusakabe, Ayaka; Hirano, Hiroatsu; Inoue, Ryota; Okazaki, Yugo; Nakano, Shinichiro; Kinoshita, Shigeru; Koizumi, Noriko

    2015-01-01

    The corneal endothelium is essential for maintaining corneal transparency; therefore, corneal endothelial dysfunction causes serious vision loss. Tissue engineering-based therapy is potentially a less invasive and more effective therapeutic modality. We recently started a first-in-man clinical trial of cell-based therapy for treating corneal endothelial dysfunction in Japan. However, the senescence of corneal endothelial cells (CECs) during the serial passage culture needed to obtain massive quantities of cells for clinical use is a serious technical obstacle preventing the push of this regenerative therapy to clinical settings. Here, we show evidence from an animal model confirming that senescent cells are less effective in cell therapy. In addition, we propose that density-gradient centrifugation can eliminate the senescent cells and purify high potency CECs for clinical use. This simple technique might be applicable for other types of cells in the settings of regenerative medicine. PMID:26443440

  13. Seasonal leaf dynamics across a tree density gradient in a Brazilian savanna.

    Science.gov (United States)

    Hoffmann, William A; da Silva, Edson Rangel; Machado, Gustavo C; Bucci, Sandra J; Scholz, Fabian G; Goldstein, Guillermo; Meinzer, Frederick C

    2005-09-01

    Interactions between trees and grasses that influence leaf area index (LAI) have important consequences for savanna ecosystem processes through their controls on water, carbon, and energy fluxes as well as fire regimes. We measured LAI, of the groundlayer (herbaceous and woody plants 1-m tall), in the Brazilian cerrado over a range of tree densities from open shrub savanna to closed woodland through the annual cycle. During the dry season, soil water potential was strongly and positively correlated with grass LAI, and less strongly with tree and shrub LAI. By the end of the dry season, LAI of grasses, groundlayer dicots and trees declined to 28, 60, and 68% of mean wet-season values, respectively. We compared the data to remotely sensed vegetation indices, finding that field measurements were more strongly correlated to the enhanced vegetation index (EVI, r (2)=0.71) than to the normalized difference vegetation index (NDVI, r (2)=0.49). Although the latter has been more widely used in quantifying leaf dynamics of tropical savannas, EVI appears better suited for this purpose. Our ground-based measurements demonstrate that groundlayer LAI declines with increasing tree density across sites, with savanna grasses being excluded at a tree LAI of approximately 3.3. LAI averaged 4.2 in nearby gallery (riparian) forest, so savanna grasses were absent, thereby greatly reducing fire risk and permitting survival of fire-sensitive forest tree species. Although edaphic conditions may partly explain the larger tree LAI of forests, relative to savanna, biological differences between savanna and forest tree species play an important role. Overall, forest tree species had 48% greater LAI than congeneric savanna trees under similar growing conditions. Savanna and forest species play distinct roles in the structure and dynamics of savanna-forest boundaries, contributing to the differences in fire regimes, microclimate, and nutrient cycling between savanna and forest ecosystems.

  14. Impact of Ficoll density gradient centrifugation on major and trace element concentrations in erythrocytes and blood plasma.

    Science.gov (United States)

    Lu, Ying; Ahmed, Sultan; Harari, Florencia; Vahter, Marie

    2015-01-01

    Ficoll density gradient centrifugation is widely used to separate cellular components of human blood. We evaluated the suitability to use erythrocytes and blood plasma obtained from Ficoll centrifugation for assessment of elemental concentrations. We determined 22 elements (from Li to U) in erythrocytes and blood plasma separated by direct or Ficoll density gradient centrifugation, using inductively coupled plasma mass spectrometry. Compared with erythrocytes and blood plasma separated by direct centrifugation, those separated by Ficoll had highly elevated iodine and Ba concentration, due to the contamination from the Ficoll-Paque medium, and about twice as high concentrations of Sr and Mo in erythrocytes. On the other hand, the concentrations of Ca in erythrocytes and plasma were markedly reduced by the Ficoll separation, to some extent also Li, Co, Cu, and U. The reduced concentrations were probably due to EDTA, a chelator present in the Ficoll medium. Arsenic concentrations seemed to be lowered by Ficoll, probably in a species-specific manner. The concentrations of Mg, P, S, K, Fe, Zn, Se, Rb, and Cs were not affected in the erythrocytes, but decreased in plasma. Concentrations of Mn, Cd, and Pb were not affected in erythrocytes, but in plasma affected by EDTA and/or pre-analytical contamination. Ficoll separation changed the concentrations of Li, Ca, Co, Cu, As, Mo, I, Ba, and U in erythrocytes and blood plasma, Sr in erythrocytes, and Mg, P, S, K, Fe, Zn, Se, Rb and Cs in blood plasma, to an extent that will invalidate evaluation of deficiencies or excess intakes. Copyright © 2014 Elsevier GmbH. All rights reserved.

  15. Stabilization of the Rayleigh-Taylor instability by convection and thermal conduction in smooth density gradient: WKB analysis

    International Nuclear Information System (INIS)

    Bud'ko, A.B.; Liberman, M.A.; Bondarenko, E.A.

    1992-01-01

    Since development of the RT modes in the ablatively accelerated plasma of laser targets imposes crucial limitations on symmetry of spherical implosions and hence on energy cumulation, it has been the subject of intensive numerical and analytical analysis in the recent years, particularly in the context of inertial confinement fusion. Recent thin-foil ablative-acceleration experiments as well as the results of 2D numerical simulations demonstrated substantial reduction of the instability growth rates compared with the classical theory predictions up to the total stabilization in the short-wavelength limit. The numerical results indicated that the main stabilization mechanism is convection. To derive the scaling laws for the RT growth rates and cut-off wavenumbers in the wide range of flow parameters, analytical solutions attract special interest. The analytical approach based on the discontinuity model was developed to analyze the reduction of the RT growth rates by the plasma convective flow and the thermal conductivity effects. The following major problem arises in the discontinuity approximation, which leaves the solution undetermined: the number of the boundary conditions on the perturbed ablation surface is not sufficient to derive the dispersion equation. One needs additional boundary conditions not associated with the conservation laws on the discontinuity surface to close the system of linearized equations for small perturbations. The stabilization effect of highly structured hydrodynamic profiles was studied by Mikaelian and Munro for a stationary plasma. Nevertheless, no reasonable analytical model was constructed taking into account the combined convective, thermal conductivity and density gradient reduction of the RT growth rates. In this report we develop the analytical approach based on the WKB approximation to analyze the stabilization of the RT modes in plasma with smooth density and velocity gradients. (author) 9 refs., 1 fig

  16. Thermocapillary migration of liquid droplets in a temperature gradient in a density matched system

    Science.gov (United States)

    Rashidnia, N.; Balasubramaniam, R.

    1991-01-01

    An experimental investigation of thermocapillary flow in droplets of a vegetable oil (partially hydrogenated soybean oil) immersed in silicone oil was conducted in a test cell with a heated top wall and a cooled bottom wall. The liquids are nearly immiscible and have equal densities at a temperature below the room temperature, thus providing a simulation of low-gravity conditions by reducing the buoyancy forces. The interfacial tension between the two oils was measured in the temperature range 20 to 50 C using a capillary tube and (d sigma)/(d T) was determined to be negative. Droplets ranging in sizes from 3 mm to 1 cm diameter were injected into the silicone oil. The vertical temperature profile in the bulk liquid (silicone oil) produces temperature variations along the interface which induce variations in the interfacial tension. The flow inside the droplet driven by the resulting interfacial shear stresses was observed using a laser light-sheet flow visualization technique. The flow direction is consistent with the sign of (d sigma)/(d T). The observed maximum surface velocities are compared to the theoretical predictions of Young et al. (1959).

  17. Proton elastic scattering from stable and unstable nuclei - Extraction of nuclear densities

    Science.gov (United States)

    Sakaguchi, H.; Zenihiro, J.

    2017-11-01

    Progress in proton elastic scattering at intermediate energies to determine nuclear density distributions is reviewed. After challenges of about 15 years to explain proton elastic scattering and associated polarization phenomena at intermediate energies, we have reached to some conclusions regarding proton elastic scattering as a means of obtaining nuclear densities. During this same period, physics of unstable nuclei has become of interest, and the density distributions of protons and neutrons play more important roles in unstable nuclei, since the differences in proton and neutron numbers and densities are expected to be significant. As such, proton elastic scattering experiments at intermediate energies using the inverse kinematic method have started to determine density distributions of unstable nuclei. In the region of unstable nuclei, we are confronted with a new problem when attempting to find proton and neutron densities separately from elastic proton scattering data, since electron scattering data for unstable nuclei are not presently available. We introduce a new means of determining proton and neutron densities separately by double-energy proton elastic scattering at intermediate energies.

  18. Assessment of Gradient-Based Similarity Functions in the Stable Boundary Layer Derived from a Large-Eddy Simulation

    Science.gov (United States)

    Sorbjan, Zbigniew

    2017-06-01

    Gradient-based similarity functions, evaluated based on data generated by a large-eddy simulation model of the stably stratified boundary layer, are compared with analogous similarity functions, derived from field observations in the surface layer during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment in the Arctic. The comparison is performed in terms of explicit and implicit local scaling systems, for the temperature and momentum fluxes, standard deviations of the vertical velocity and of temperature, as well as dissipation rates for the turbulent kinetic energy and for the temperature variance. The comparison shows the best agreement of the SHEBA-based similarity functions with analogous functions evaluated using the large-eddy simulation data in the range of the Richardson number 0.01<{ Ri}< 0.1.

  19. Identification of burrowing shrimp food sources along an estuarine gradient using fatty acid analysis and stable isotope ratios

    Science.gov (United States)

    Two species of burrowing shrimps occur in high densities in U.S. West Coast estuaries, the ghost shrimp (Neotrypaea californiensis) and the blue mud shrimp (Upogebia pugettensis). Both species of shrimp are considered ecosystem engineers as they bioturbate and irrigate extensive galleries in the sed...

  20. Chemically and Thermally Stable High Energy Density Silicone Composites, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — Thermal energy storage systems with 300 -- 1000 kJ/kg energy density through either phase changes or chemical heat absorption are sought by NASA. This proposed...

  1. Dual-capillary backscatter interferometry for high-sensitivity nanoliter-volume refractive index detection with density gradient compensation.

    Science.gov (United States)

    Wang, Zhanling; Bornhop, Darryl J

    2005-12-15

    A simple, stable, ultrasensitive dual-capillary dual-bicell (DCDB) microinterferometic backscattering detection (MIBD) system was developed. In DCDB MIBD, a He-Ne laser beam passes through a half-wave plate onto the cross section of two capillaries, one for reference and another for sensing analyte. The position of the backscattered fringe from each capillary, which are in proximity or essentially identical thermal environments, was detected with matched bicell photodetectors. The configuration was found to effectively compensate for thermal drift, which is normally the major source of noise in refractive index (RI) detection systems. It is shown that passive environmental compensation leads to greatly enhanced signal in nanoscale refractometry preformed by MIBD. An order of magnitude improvement in detection limits over single channel configurations is possible. Performance reaches the 10(-9) RIU level for like solvents in the presence in extremely large thermally induced RI gradients. At this level of detectability, DCDB MIBD could facilitate nanoliter-volume, femtomole-level universal detection in applications ranging from mu-HPLC and on-chip CE to scanning microcalorimetry.

  2. Charge density modification of carboxylated cellulose nanocrystals for stable silver nanoparticles suspension preparation

    International Nuclear Information System (INIS)

    Hoeng, Fanny; Denneulin, Aurore; Neuman, Charles; Bras, Julien

    2015-01-01

    Synthesis of silver nanoparticles using cellulose nanocrystals (CNC) has been found to be a great method for producing metallic particles in a sustainable way. In this work, we propose to evaluate the influence of the charge density of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-oxidized CNC on the morphology and the stability of synthetized silver nanoparticles. Silver nanoparticles were obtained by sol–gel reaction using borohydride reduction, and charge density of TEMPO-oxidized CNC was tuned by an amine grafting. The grafting was performed at room temperature and neutral pH. Crystallinity and morphology were kept intact during the peptidic reaction on CNC allowing knowing the exact impact of the charge density. Charge density has been found to have a strong impact on shape, organization, and suspension stability of resulting silver particles. Results show an easy way to tune the charge density of CNC and propose a sustainable way to control the morphology and stability of silver nanoparticles in aqueous suspension

  3. Modified internal state variable models of plasticity using nonlocal integrals in damage and gradients in dislocation density

    Science.gov (United States)

    Ahad, Fazle Rabbi

    To enhance material performance at different length scales, this study strives to develop a reliable analytical and computational tool with the help of internal state variables spanning micro and macro-level behaviors. First, the practical relevance of a nonlocal damage integral added to an internal state variable (BCJ) model is studied to alleviate numerical instabilities associated within the post-bifurcation regime. The characteristic length scale in the nonlocal damage, which is mathematical in nature, can be calibrated using a series of notch tensile tests. Then the same length scale from the notch tests is used in solving the problem of a high-velocity (between 89 and 107 m/s) rigid projectile colliding against a 6061-T6 aluminum-disk. The investigation indicates that incorporating a characteristic length scale to the constitutive model eliminates the pathological mesh-dependency associated with material instabilities. In addition, the numerical calculations agree well with experimental data. Next, an effort is made rather to introduce a physically motivated length scale than to apply a mathematical-one in the deformation analysis. Along this line, a dislocation based plasticity model is developed where an intrinsic length scale is introduced in the forms of spatial gradients of mobile and immobile dislocation densities. The spatial gradients are naturally invoked from balance laws within a consistent kinematic and thermodynamic framework. An analytical solution of the model variables is derived at homogenous steady state using the linear stability and bifurcation analysis. The model qualitatively captures the formation of dislocation cell-structures through material instabilities at the microscopic level. Finally, the model satisfactorily predicts macroscopic mechanical behaviors - e.g., multi-strain rate uniaxial compression, simple shear, and stress relaxation - and validates experimental results.

  4. Localization of the Ethylene-Receptor Signaling Complex to the Endoplasmic Reticulum: Analysis by Two-Phase Partitioning and Density-Gradient Centrifugation.

    Science.gov (United States)

    Schaller, G Eric

    2017-01-01

    Ethylene receptors and other elements of the ethylene-signal transduction pathway localize to membranes of the endoplasmic reticulum (ER). New players in the ethylene signaling pathway continue to be discovered and so it is important to have methods by which to diagnose their cellular localization. Two methods for microsome isolation and fractionation are described here that can assist in determining if a protein localizes to the ER: aqueous two-phase partitioning and equilibrium density-gradient centrifugation. Two-phase partitioning serves to purify plasma membrane away from other cellular membranes and can thus discriminate whether a protein is localized to the plasma membrane or not. Equilibrium density-gradient centrifugation is particularly useful for resolving if a protein is localized to the ER. Ribosomes are associated with the rough ER in the presence of Mg 2+ but are stripped away when Mg 2+ is removed from the medium, resulting in a reduction in the ER membrane density and a diagnostic shift in migration when analyzed by equilibrium density-gradient centrifugation. A method for growing plants in liquid culture is also provided because these microsomal membranes exhibit consistent fractionation by both two-phase partitioning and density-gradient centrifugation.

  5. Lidar and Ground Assessment of Diversity, Wood Density, and Aboveground Biomass Along an Elevation Gradient in Tropical Montane Forest of Costa Rica

    Science.gov (United States)

    Robinson, C. M.; Saatchi, S. S.; Clark, D.; Andelman, S.; Gillespie, T.

    2013-12-01

    This research seeks to understand how tree diversity relates to three-dimensional vegetation structure along environmental gradients in the tropical montane forest of Braulio Carrillo National Park in Costa Rica. Elevation gradients along mountains provide landscape-size scales through which variations in topography and climatic conditions can be tested as drivers of biodiversity. In this study we report on the effectiveness of relating patterns of tree alpha diversity to three-dimensional structure of a tropical montane forest using remote sensing observations of forest structure. The study was utilized forest inventory and botanical data from nine 1-ha plots ranging from 100m-2800m above sea level and remote sensing data from an airborne lidar sensor (NASA's Land, Vegetation, and Ice Sensor [LVIS]) to quantify variations in forest structure. In addition to calculating alpha diversity, we report on the variations in wood density with elevation, important for biomass and carbon estimations. Tree cores were analyzed for wood density and compared to existing database values for the same species, often collected only in the lowlands. In this manner we were able to test the effect of the gradient on effective wood density. Through the comparison to the lidar, our results show that there is a strong relationship between forest 3D structure and alpha diversity controlled by variations in abiotic factors along the elevational gradient. Using spatial analysis with the aid of remote sensing data, we found distinct patterns along the environmental gradients defining species composition. Wood density values with elevation change were found to vary significantly from database values for the same species. These wood density values are directly tied to biomass estimates, and it is possible that carbon storage has been overestimated along this gradient using prior methods. This variation in individual tree growth has repercussions on overall forest structure, as well as

  6. The ideal free distribution as an evolutionarily stable state in density-dependent population games

    Czech Academy of Sciences Publication Activity Database

    Cressman, R.; Křivan, Vlastimil

    2010-01-01

    Roč. 119, č. 8 (2010), s. 1231-1242 ISSN 0030-1299 R&D Projects: GA AV ČR IAA100070601 Institutional research plan: CEZ:AV0Z50070508 Keywords : density-dependent population games Subject RIV: EH - Ecology, Behaviour Impact factor: 3.393, year: 2010

  7. Density gradient centrifugation: Application to the separation of macerals of type I, II, and III sedimentary organic matter

    Science.gov (United States)

    Stankiewicz, B.A.; Kruge, M.A.; Crelling, J.C.; Salmon, G.L.

    1994-01-01

    Samples of organic matter from nine well-known geological units (Green River Fm., Tasmanian Tasmanite, Lower Toarcian Sh. of the Paris Basin, Duwi Fm., New Albany Sh., Monterey Fm., Herrin No. 6 coal, Eocene coal, and Miocene lignite from Kalimantan) were processed by density gradient centrifugation (DGC) to isolate the constituent macerals. Optimal separation, as well as the liberation of microcrystalline pyrite from the organic matter, was obtained by particle size minimization prior to DGC by treatment with liquid N2 and micronization in a fluid energy mill. The resulting small particle size limits the use of optical microscopy, thus microfluorimetry and analytical pyrolysis were also employed to assess the quality and purity of the fractions. Each of the samples exhibits one dominant DGC peak (corresponding to alginite in the Green River Fm., amorphinite in the Lower Toarcian Sh., vitrinite in the Herrin No. 6, etc.) which shifts from 1.05 g mL-1 for the Type I kerogens to between 1.18 and 1.23 g mL-1 for Type II and II-S. The characteristic densities for Type III organic matter are greater still, being 1.27 g mL-1 for the hydrogen-rich Eocene coal, 1.29 g mL-1 for the Carboniferous coal and 1.43 g mL-1 for the oxygen-rich Miocene lignite. Among Type II kerogens, the DGC profile represents a compositional continuum from undegraded alginite through (bacterial) degraded amorphinite; therefore chemical and optical properties change gradually with increasing density. The separation of useful quantities of macerals that occur in only minor amounts is difficult. Such separations require large amounts of starting material and require multiple processing steps. Complete maceral separation for some samples using present methods seems remote. Samples containing macerals with significant density differences due to heteroatom diversity (e.g., preferential sulfur or oxygen concentration in the one maceral), on the other hand, may be successfully separated (e.g., coals and

  8. Multiconfiguration Pair-Density Functional Theory Spectral Calculations Are Stable to Adding Diffuse Basis Functions.

    Science.gov (United States)

    Hoyer, Chad E; Gagliardi, Laura; Truhlar, Donald G

    2015-11-05

    Time-dependent Kohn-Sham density functional theory (TD-KS-DFT) is useful for calculating electronic excitation spectra of large systems, but the low-energy spectra are often complicated by artificially lowered higher-energy states. This affects even the lowest energy excited states. Here, by calculating the lowest energy spin-conserving excited state for atoms from H to K and for formaldehyde, we show that this problem does not occur in multiconfiguration pair-density functional theory (MC-PDFT). We use the tPBE on-top density functional, which is a translation of the PBE exchange-correlation functional. We compare to a robust multireference method, namely, complete active space second-order perturbation theory (CASPT2), and to TD-KS-DFT with two popular exchange-correlation functionals, PBE and PBE0. We find for atoms that the mean unsigned error (MUE) of MC-PDFT with the tPBE functional improves from 0.42 to 0.40 eV with a double set of diffuse functions, whereas the MUEs for PBE and PBE0 drastically increase from 0.74 to 2.49 eV and from 0.45 to 1.47 eV, respectively.

  9. Preparation and flammability of high density polyethylene/paraffin/organophilic montmorillonite hybrids as a form stable phase change material

    International Nuclear Information System (INIS)

    Cai, Yibing; Hu, Yuan; Song, Lei; Kong, Qinghong; Yang, Rui; Zhang, Yinping; Chen, Zuyao; Fan, Weicheng

    2007-01-01

    A kind of form stable phase change material (PCM) based on high density polyethylene (HDPE), paraffin, organophilic montmorillonite (OMT) and intumescent flame retardant (IFR) hybrids is prepared by using a twin screw extruder technique. This kind of form stable PCM is made of paraffin as a dispersed phase change material and HDPE as a supporting material. The structure of the montmorillonite (MMT) and OMT is characterized by X-ray diffraction (XRD) and high resolution electron microscopy (HREM). The analysis indicates that the MMT is a kind of lamellar structure, and the structure does not change after organic modification. However, the structure of the hybrid is evidenced by the XRD and scanning electronic microscope (SEM). Its thermal stability, latent heat and flame retardant properties are given by the Thermogravimetry analysis (TGA), differential scanning calorimeter (DSC) method and cone calorimeter, respectively. Synergy is observed between the OMT and IFR. The XRD result indicates that the paraffin intercalates into the silicate layers of the OMT, thus forming a typically intercalated hybrid. The SEM investigation and DSC result show that the additives of OMT and IFR have hardly any effect on the HDPE/paraffin three dimensional netted structure and the latent heat. In TGA curves, although the onset of weight loss of flame-retardant form stable PCMs occur at a lower temperature than that of form stable PCM, flame-retardant form stable PCMs produce a large amount of char residue at 700 o C. The synergy between OMT and IFR leads to the decrease of the heat release rate (HRR), contributing to improvement of the flammability performance

  10. An enriched stable isotope technique to estimate the availability of soil zinc to Lumbricus terrestris (L.) across a salinization gradient.

    Science.gov (United States)

    Rodgers, Derek W; Lev, Steven M; Snodgrass, Joel W; Ownby, David R; Prince, Lisa M; Casey, Ryan E

    2011-03-01

    An enriched stable isotope approach was developed to evaluate Zn bioavailability to Lumbricus terrestris. The decrease in (68)Zn/(66) Zn in organ tissues was used to assess the relative magnitude of the bioavailable soil Zn pool. This tool was then used to specifically evaluate bioavailability as a function of soil cation distribution. Storm-water pond soils were modified using two treatment regimens whereby H(2)O-extractable Zn was varied either by different ZnCl(2) amendments or by constant ZnCl(2) amendment followed by varying the soil cation distribution through salt amendments (NaCl or CaCl(2)). Earthworms previously equilibrated in (68) Zn-spiked soil were introduced to experimental soils, and after 2 d, removed for analysis of isotopic ratios in specific tissues. Despite a wide range of H(2)O-extractable Zn values produced by the salt treatments (0.007-24.3 mg/kg), a significant relationship between Zn turnover rate in earthworm tissues and H(2)O-extractable Zn in the salt-treated soils was not observed. Rather, considering both treatment regimens, turnover rate better correlated with Zn present in broader pools, such as that extracted by 6M HNO(3). The bioavailability of trace metals to earthworms may be poorly characterized by loosely bound fractions such as the pore water. Additionally, the turnover rate of (68)Zn in anterior organ tissues may be an effective tool to evaluate the relative magnitude of the bioavailable soil Zn pool. Copyright © 2010 SETAC.

  11. Space Electron Density Gradient Studies using a 3D Embedded Reconfigurable Sounder and ESA/NASA CLUSTER Mission

    Science.gov (United States)

    Dekoulis, George

    2016-07-01

    This paper provides a direct comparison between data captured by a new embedded reconfigurable digital sounder, different ground-based ionospheric sounders spread around Europe and the ESA/NASA CLUSTER mission. The CLUSTER mission consists of four identical space probes flying in a formation that allows measurements of the electron density gradient in the local magnetic field. Both the ground-based and the spacecraft instrumentations assist in studying the motion, geometry and boundaries of the plasmasphere. The comparison results are in accordance to each other. Some slight deviations among the captured data were expected from the beginning of this investigation. These small discrepancies are reasonable and seriatim analyzed. The results of this research are significant, since the level of the plasma's ionization, which is related to the solar activity, dominates the propagation of electromagnetic waves through it. Similarly, unusually high solar activity presents serious hazards to orbiting satellites, spaceborne instrumentation, satellite communications and infrastructure located on the Earth's surface. Long-term collaborative study of the data is required to continue, in order to identify and determine the enhanced risk in advance. This would allow scientists to propose an immediate cure.

  12. Sexagem de espermatozoides bovinos por centrifugação em gradiente descontínuo de densidade de Percoll Sex selection in bovine spermatozoa by using Percoll discontinuos density gradient centrifugation

    Directory of Open Access Journals (Sweden)

    Vera Fernanda Martins Hossepian de Lima

    2011-08-01

    Full Text Available O objetivo neste trabalho foi desenvolver um método de seleção do sexo de espermatozoides bovinos por centrifugação em gradiente de densidade de Percoll. Utilizou-se sêmen congelado de touros mantidos em regime de colheita de sêmen. A fração de espermatozoides X ou Y foi separada por centrifugação em treze diferentes gradientes de densidade de Percoll formados por 1 a 12 camadas com densidades que variaram de 1,004 g/mL a 1,123 g/mL. As soluções com diferentes densidades foram preparadas misturando-se, em proporções diferentes, meio de cultura Hank's e uma solução estoque composta de NaCl 1,5 M e Percoll (1:9, v/v. Sobre cada gradiente foi colocado um total de 50 × 10(6 espermatozoides descongelados em 0,7 mL de meio Hank's e centrifugados a 250 X g por 30 minutos, em rotor horizontal, a 25°C. Os espermatozoides das frações superior e inferior foram tratados com Quinacrina Mustarda e analisados (200 deles quanto à presença do corpúsculo-F. Dos espermatozoides encontrados no sedimento de dois gradientes, compostos de 8 e 12 frações com densidades variando entre 1,050 a 1,120 g/mL e 1,044 a 1,123 g/mL, respectivamente, visualizaram-se 25% com corpúsculo-F e os 75% restantes prováveis portadores do cromossomo X. O aumento na porcentagem de espermatozoides X após a centrifugação em gradiente de densidade permitirá que esse método de sexagem seja usado em larga escala na produção comercial de carne e leite bem como no teste de progênie.The objective of this work was to develop a bovine spermatozoid sex selection method by using Percoll density gradient centrifugation. It was used frozen semen of bulls kept in semen collection regime. Fraction X or Y was separated by centrifugation in three different Percoll density gradient formed by 1 to 12 layers with densities varying from 1.004 g/mL to 1.123 g/mL. Solutions with different densities were prepared by mixing, at different proportions, Hank's culture medium and a

  13. Charge and spin density in s-stable rare earth intermetallic compounds

    International Nuclear Information System (INIS)

    Graaf, H. de.

    1982-01-01

    This thesis deals with a study of the electronic structure of rare earth intermetallic compounds, in particular the electronic charge and spin density distribution. These are closely related to the properties of the rare earth ions, which carry the partly filled 4f shell. In chapter 1 a survey of the theory of hyperfine interaction as far as it has a bearing on the Moessbauer effect of 155 Gd and 151 Eu is given. Also some details of the Moessbauer spectra, which have practical importance are discussed. In chapter 2 the experimental set-up is described. Special attention is paid to the gamma radiation source and gamma detection requirements. In chapter 3 the author introduces the theoretical framework which will be used to interpret the measurements. In chapter 4 the results of the 155 Gd Moessbauer measurements are presented. Also it is discussed how the result can be understood in terms of the charge and spin density in rare earth intermetallic compounds. In order to lend support to the picture emerging from the previous chapter, in chapter 5 the conduction electron band structure of some representative Gd intermetallics is computed with an approximate semi-empirical LCAO method. The results are compared with those from chapter 4. Finally, in chapter 6, the 151 Eu resonance is used to investigate the temperature dependence of the hyperfine field and line width in the Eu intermetallic compounds Eu 2 Mg 17 and EuMg 5 . (Auth.)

  14. Latitudinal Gradients in the Stable Carbon and Oxygen Isotopes of Tree-Ring Cellulose Reveal Differential Climate Influences of the North American Monsoon

    Science.gov (United States)

    Szejner, P.; Wright, W. E.; Babst, F.; Belmecheri, S.; Trouet, V.; Ehleringer, J. R.; Leavitt, S. W.; Monson, R. K.

    2015-12-01

    Summer rainfall plays an important role sustaining different types of ecosystems in the Southwestern US. The arrival of the monsoon breaks the early summer hyper-arid period in the region providing unique seasonal conditions for these ecosystems to thrive. It is unknown to what extent monsoon rainfall is used by Ponderosa pine forests, which occupy many mountain ecosystems in the Western US. While these forests clearly rely on winter snowpack to drive much of their annual net primary productivity, the extent to which they supplement winter moisture, with summer monsoon moisture needs to be clarified. It is likely that there are north-south gradients in the degree to which forests rely on monsoon moisture, as the summer monsoon system tends to become diminished as it moves progressively northward. We addressed these gaps in our knowledge about the monsoon by studying stable Carbon and Oxygen isotopes in earlywood and latewood α-cellulose from cores taken from trees in eleven sites along a latitudinal gradient extending from Southern Arizona and New Mexico toward Utah. Here we show evidence that Ponderosa pine trees from most of these sites use monsoon water to support growth during the late summer, and the fractional use of monsoon precipitation is strongest in the southernmost sites. This study provides new physiological evidence on the influence of the North American monsoon and winter precipitation on tree growth in montane ecosystems of the Western US. Using these results, we predict differences in the susceptibility of southern and northern montane forests to future climate change. ACKNOWLEDGMENTS: This work was funded by an NSF Macrosystems Grant #1065790

  15. Pressure-induced stable BeN4 as a high-energy density material

    Science.gov (United States)

    Zhang, Shoutao; Zhao, Ziyuan; Liu, Lulu; Yang, Guochun

    2017-10-01

    Polynitrogens are the ideal rocket fuels or propellants. Due to strong triple N≡N bond in N2, the direct polymerization of nitrogen is rather difficult (i.e. extreme high temperature and high pressure). However, the use of nitrides as precursors or the reaction of N2 with other elements has been proved to be an effective way to obtain polynitrogens. Here, with assistance of the advanced first-principles swarm-intelligence structure searches, we found that P 1 bar -BeN4, containing infinite zigzag-like polymeric nitrogen chains, can be synthesized by compressing the mixture of Be3N2 and N2 at 25.4 GPa, which is greatly lower than 110 GPa for synthesizing cubic gauche nitrogen and other polynitrogen compounds (e.g. bulk CNO at 52 GPa and SN4 at 49 GPa). Its structural stability can be attributed to the coexistence of ionic Be-N and covalent N-N bonds. Intriguingly, this phase has high kinetic stability and remains metastable at ambient pressure. The exceptional properties, including high energy density (3.60 kJ g-1), high nitrogen content (86.1%), high dynamical stability, and low polymerization pressure, make P 1 bar -structured BeN4 a promising high energy material. Infinite nitrogen chains in P 1 bar -BeN4 transform to N10 rings network in P21/c phase at 115.1 GPa. P 1 bar -BeN4 is metallic, while P21/c-BeN4 is an insulator.

  16. An analysis of the gradient-induced electric fields and current densities in human models when situated in a hybrid MRI-LINAC system

    Science.gov (United States)

    Liu, Limei; Trakic, Adnan; Sanchez-Lopez, Hector; Liu, Feng; Crozier, Stuart

    2014-01-01

    MRI-LINAC is a new image-guided radiotherapy treatment system that combines magnetic resonance imaging (MRI) with a linear accelerator (LINAC) in a single unit. One drawback is that the pulsing of the split gradient coils of the system induces an electric field and currents in the patient which need to be predicted and evaluated for patient safety. In this novel numerical study the in situ electric fields and associated current densities were evaluated inside tissue-accurate male and female human voxel models when a number of different split-geometry gradient coils were operated. The body models were located in the MRI-LINAC system along the axial and radial directions in three different body positions. Each model had a region of interest (ROI) suitable for image-guided radiotherapy. The simulation results show that the amplitudes and distributions of the field and current density induced by different split x-gradient coils were similar with one another in the ROI of the body model, but varied outside of the region. The fields and current densities induced by a split classic coil with the surface unconnected showed the largest deviation from those given by the conventional non-split coils. Another finding indicated that the distributions of the peak current densities varied when the body position, orientation or gender changed, while the peak electric fields mainly occurred in the skin and fat tissues.

  17. Collagen density gradient on three-dimensional printed poly(ε-caprolactone) scaffolds for interface tissue engineering.

    Science.gov (United States)

    D'Amora, Ugo; D'Este, Matteo; Eglin, David; Safari, Fatemeh; Sprecher, Christoph M; Gloria, Antonio; De Santis, Roberto; Alini, Mauro; Ambrosio, Luigi

    2018-02-01

    The ability to engineer scaffolds that resemble the transition between tissues would be beneficial to improve repair of complex organs, but has yet to be achieved. In order to mimic tissue organization, such constructs should present continuous gradients of geometry, stiffness and biochemical composition. Although the introduction of rapid prototyping or additive manufacturing techniques allows deposition of heterogeneous layers and shape control, the creation of surface chemical gradients has not been explored on three-dimensional (3D) scaffolds obtained through fused deposition modelling technique. Thus, the goal of this study was to introduce a gradient functionalization method in which a poly(ε-caprolactone) surface was first aminolysed and subsequently covered with collagen via carbodiimide reaction. The 2D constructs were characterized for their amine and collagen contents, wettability, surface topography and biofunctionality. Finally, chemical gradients were created in 3D printed scaffolds with controlled geometry and porosity. The combination of additive manufacturing and surface modification is a viable tool for the fabrication of 3D constructs with controlled structural and chemical gradients. These constructs can be employed for mimicking continuous tissue gradients for interface tissue engineering. Copyright © 2017 John Wiley & Sons, Ltd.

  18. A Breast Cell Atlas: Organelle analysis of the MDA-MB-231 cell line by density-gradient fractionation using isotopic marking and label-free analysis

    Directory of Open Access Journals (Sweden)

    Marianne Sandin

    2015-09-01

    Full Text Available Protein translocation between organelles in the cell is an important process that regulates many cellular functions. However, organelles can rarely be isolated to purity so several methods have been developed to analyse the fractions obtained by density gradient centrifugation. We present an analysis of the distribution of proteins amongst organelles in the human breast cell line, MDA-MB-231 using two approaches: an isotopic labelling and a label-free approach.

  19. Study of homogeneous bubble nucleation in liquid carbon dioxide by a hybrid approach combining molecular dynamics simulation and density gradient theory

    Science.gov (United States)

    Langenbach, K.; Heilig, M.; Horsch, M.; Hasse, H.

    2018-03-01

    A new method for predicting homogeneous bubble nucleation rates of pure compounds from vapor-liquid equilibrium (VLE) data is presented. It combines molecular dynamics simulation on the one side with density gradient theory using an equation of state (EOS) on the other. The new method is applied here to predict bubble nucleation rates in metastable liquid carbon dioxide (CO2). The molecular model of CO2 is taken from previous work of our group. PC-SAFT is used as an EOS. The consistency between the molecular model and the EOS is achieved by adjusting the PC-SAFT parameters to VLE data obtained from the molecular model. The influence parameter of density gradient theory is fitted to the surface tension of the molecular model. Massively parallel molecular dynamics simulations are performed close to the spinodal to compute bubble nucleation rates. From these simulations, the kinetic prefactor of the hybrid nucleation theory is estimated, whereas the nucleation barrier is calculated from density gradient theory. This enables the extrapolation of molecular simulation data to the whole metastable range including technically relevant densities. The results are tested against available experimental data and found to be in good agreement. The new method does not suffer from typical deficiencies of classical nucleation theory concerning the thermodynamic barrier at the spinodal and the bubble size dependence of surface tension, which is typically neglected in classical nucleation theory. In addition, the density in the center of critical bubbles and their surface tension is determined as a function of their radius. The usual linear Tolman correction to the capillarity approximation is found to be invalid.

  20. High density of tree-cavities and snags in tropical dry forest of western Mexico raises questions for a latitudinal gradient.

    Directory of Open Access Journals (Sweden)

    Leopoldo Vázquez

    Full Text Available It has been suggested that a latitudinal gradient exists of a low density of snags and high density of naturally-formed tree-cavities in tropical vs. temperate forests, though few cavities may have characteristics suitable for nesting by birds. We determined snag and cavity density, characteristics, and suitability for birds in a tropical dry forest biome of western Mexico, and evaluated whether our data fits the trend of snag and cavity density typically found in tropical moist and wet forests. We established five 0.25-ha transects to survey and measure tree-cavities and snags in each of three vegetation types of deciduous, semi-deciduous, and mono-dominant Piranhea mexicana forest, comprising a total of 3.75 ha. We found a high density of 77 cavities/ha, with 37 cavities suitable for birds/ha, where density, and characteristics of cavities varied significantly among vegetation types. Lowest abundance of cavities occurred in deciduous forest, and these were in smaller trees, at a lower height, and with a narrower entrance diameter. Only 8.6% of cavities were excavated by woodpeckers, and only 11% of cavities were occupied, mainly by arthropods, though 52% of all cavities were unsuitable for birds. We also found a high density of 56 snags/ha, with greatest density in deciduous forest (70 snags/ha, though these were of significantly smaller diameter, and snags of larger diameter were more likely to contain cavities. The Chamela-Cuixmala tropical dry forest had the highest density of snags recorded for any tropical or temperate forest, and while snag density was significantly correlated with mean snag dbh, neither latitude nor mean dbh predicted snag density in ten forest sites. The high spatial aggregation of snag and cavity resources in tropical dry forest may limit their availability, particularly for large-bodied cavity adopters, and highlights the importance of habitat heterogeneity in providing resources for primary and secondary cavity-nesters.

  1. High density of tree-cavities and snags in tropical dry forest of western Mexico raises questions for a latitudinal gradient.

    Science.gov (United States)

    Vázquez, Leopoldo; Renton, Katherine

    2015-01-01

    It has been suggested that a latitudinal gradient exists of a low density of snags and high density of naturally-formed tree-cavities in tropical vs. temperate forests, though few cavities may have characteristics suitable for nesting by birds. We determined snag and cavity density, characteristics, and suitability for birds in a tropical dry forest biome of western Mexico, and evaluated whether our data fits the trend of snag and cavity density typically found in tropical moist and wet forests. We established five 0.25-ha transects to survey and measure tree-cavities and snags in each of three vegetation types of deciduous, semi-deciduous, and mono-dominant Piranhea mexicana forest, comprising a total of 3.75 ha. We found a high density of 77 cavities/ha, with 37 cavities suitable for birds/ha, where density, and characteristics of cavities varied significantly among vegetation types. Lowest abundance of cavities occurred in deciduous forest, and these were in smaller trees, at a lower height, and with a narrower entrance diameter. Only 8.6% of cavities were excavated by woodpeckers, and only 11% of cavities were occupied, mainly by arthropods, though 52% of all cavities were unsuitable for birds. We also found a high density of 56 snags/ha, with greatest density in deciduous forest (70 snags/ha), though these were of significantly smaller diameter, and snags of larger diameter were more likely to contain cavities. The Chamela-Cuixmala tropical dry forest had the highest density of snags recorded for any tropical or temperate forest, and while snag density was significantly correlated with mean snag dbh, neither latitude nor mean dbh predicted snag density in ten forest sites. The high spatial aggregation of snag and cavity resources in tropical dry forest may limit their availability, particularly for large-bodied cavity adopters, and highlights the importance of habitat heterogeneity in providing resources for primary and secondary cavity-nesters.

  2. Tree stocking affects winter bird densities across a gradient of savanna, woodland, and forest in the Missouri Ozarks

    Science.gov (United States)

    Sarah W. Kendrick; Frank R., III Thompson

    2013-01-01

    Savanna and woodland were historically prevalent in the midwestern United States, and managers throughout the area are currently attempting to restore these communities. Better knowledge of the responses of breeding and non-breeding birds to savanna and woodland restoration is needed to inform management.We surveyed abundance of winter resident birds across a gradient...

  3. The Purification Method Using Iodixanol (Optiprep)-Based Density Gradient Significantly Reduces Cytokine/Chemokine Production from Human Islet Preparations, Leading to Prolong β-Cell Survival During Culture

    Science.gov (United States)

    Mita, Atsuyoshi; Ricordi, Camillo; Miki, Atsushi; Barker, Scott; Khan, Aisha; Alvarez, Alejandro; Hashikura, Yasuhiko; Miyagawa, Shin-ichi; Ichii, Hirohito

    2009-01-01

    Improved islet isolation has still been important to obtain adequate islet numbers for islet transplantation. Although Ficol-based density gradient is widely used for purification in most islet processing centers, OptiPrep-based density gradient is recently used in the limited centers and their clinical outcomes are excellent. Cytokine/chemokine production from islet preparations for transplantation widely varies. Some cytokines/chemokines have been reported to cause apoptosis in human islet preparations after isolation. Reducing cytokine/chemokine production is a key to improve islet numbers after isolation and islet transplantation outcome. The aim of current study is to investigate the variability of pro-inflammatory cytokine/chemokine production from islet preparations purified by different density gradient. After digestion of human pancreata, pre-purification digests were devided into two groups and purified using semi-automated cell processor with Ficoll-based and OptiPrep-based density gradient. Islet preparations were cultured for 2 days and assessed regarding islet cell viability (FDA/PI), fractional β-cell viability and β-cell content. Cytokine/chemokine production from islet preparations was also examined. After purification, purity, post-purification IEQ and islet recovery rate were comparable between two groups. Although FDA/PI and fractional β-cell viability showed no significant differences, β-cell survival during culture significantly increased in OptiPrep-based density gradient group when compared to Ficoll-based density gradient group. TNF-α, IL-1β, IFN-γ, IL-6 and MIP-1β production from OptiPrep-based density gradient group significantly decreased. OptiPrep-based density gradient can reduce cytokine-production when compared to Ficoll-based density gradient, resulting in improvement of quantity of β-cell mass. Cytokine profiling could spot new light on assessment of islet preparations before transplantation. PMID:19249543

  4. High-latitude GPS phase scintillation from E region electron density gradients during the 20-21 December 2015 geomagnetic storm

    Science.gov (United States)

    Loucks, Diana; Palo, Scott; Pilinski, Marcin; Crowley, Geoff; Azeem, Irfan; Hampton, Don

    2017-07-01

    A novel operating mode for Poker Flat Incoherent Scatter Radar (PFISR) has been developed to support the study of GPS L1 scintillations arising from electron density gradients over Alaska. Previous authors have combined GPS scintillation data with either PFISR or multispectral imagery in this region. This analysis combines all three techniques to determine both gradient parameters as well as the most likely ionospheric source, including a conjunction analysis between GPS signals and known PFISR beams. This approach was used to study scintillation events observed in December 2015. These events were recorded during the recovery phase of a geomagnetic storm that ensued on 20 December when the Earth passed through the path of a solar CME (DST minimum near -170 nT, Kp peak of 7). Two scintillation events were detected through analysis of the phase scintillation index (σϕ), calculated from an Atmospheric and Space Technology Research Associates' Connected Autonomous Space Environment Sensor GPS receiver at Poker Flat. Values of σϕ≃0.5 and σϕ≃1.6 cycles were recorded for these events. Concurrently, an experiment on PFISR was run to discern the electron density along the GPS signal line of site, and the imager observed the 428.7 nm, 557.7 nm, and 630.0 nm emission lines during the experiment window. From the ratios of derived emission intensities, estimates of precipitating particle energies were made allowing confirmation of the altitudes associated with the electron density peaks determined using raw radar returns from PFISR. Results indicate that temporal and spatial electron density gradients existed along the signal's path during periods of highest scintillation, which resulted from impact ionization from auroral particle precipitation at E region altitudes.

  5. Convergent sum of gradient expansion of the kinetic-energy density functional up to the sixth order term using Padé approximant

    Science.gov (United States)

    Sergeev, A.; Alharbi, F. H.; Jovanovic, R.; Kais, S.

    2016-04-01

    The gradient expansion of the kinetic energy density functional, when applied to atoms or finite systems, usually grossly overestimates the energy in the fourth order and generally diverges in the sixth order. We avoid the divergence of the integral by replacing the asymptotic series including the sixth order term in the integrand by a rational function. Padé approximants show moderate improvements in accuracy in comparison with partial sums of the series. The results are discussed for atoms and Hooke’s law model for two-electron atoms.

  6. Comparison of Conjugate Gradient Density Matrix Search and Chebyshev Expansion Methods for Avoiding Diagonalization in Large-Scale Electronic Structure Calculations

    Science.gov (United States)

    Bates, Kevin R.; Daniels, Andrew D.; Scuseria, Gustavo E.

    1998-01-01

    We report a comparison of two linear-scaling methods which avoid the diagonalization bottleneck of traditional electronic structure algorithms. The Chebyshev expansion method (CEM) is implemented for carbon tight-binding calculations of large systems and its memory and timing requirements compared to those of our previously implemented conjugate gradient density matrix search (CG-DMS). Benchmark calculations are carried out on icosahedral fullerenes from C60 to C8640 and the linear scaling memory and CPU requirements of the CEM demonstrated. We show that the CPU requisites of the CEM and CG-DMS are similar for calculations with comparable accuracy.

  7. MR imaging of iliofemoral peripheral vascular calcifications using proton density-weighted, in-phase three-dimensional stack-of-stars gradient echo.

    Science.gov (United States)

    Ferreira Botelho, Marcos P; Koktzoglou, Ioannis; Collins, Jeremy D; Giri, Shivraman; Carr, James C; Gupta, NavYash; Edelman, Robert R

    2017-06-01

    The presence of vascular calcifications helps to determine percutaneous access for interventional vascular procedures and has prognostic value for future cardiovascular events. Unlike CT, standard MRI techniques are insensitive to vascular calcifications. In this prospective study, we tested a proton density-weighted, in-phase (PDIP) three-dimensional (3D) stack-of-stars gradient-echo pulse sequence with approximately 1 mm 3 isotropic spatial resolution at 1.5 Tesla (T) and 3T to detect iliofemoral peripheral vascular calcifications and correlated MR-determined lesion volumes with CT angiography (CTA). The study was approved by the Institutional Review Board. The prototype PDIP stack-of-stars pulse sequence was applied in 12 patients with iliofemoral peripheral vascular calcifications who had undergone CTA. Vascular calcifications were well visualized in all subjects, excluding segments near prostheses or stents. The location, size, and shape of the calcifications were similar to CTA. Quantitative analysis showed excellent correlation (r 2  = 0.84; P stars outperformed cartesian 3D gradient-echo and point-wise encoding time reduction with radial acquisition (PETRA). In this pilot study, a PDIP 3D stack-of-stars gradient-echo pulse sequence with high spatial resolution provided excellent image quality and accurately depicted the location and volume of iliofemoral vascular calcifications. Magn Reson Med 77:2146-2152, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  8. An oscillating extracellular voltage gradient reduces the density and influences the orientation of astrocytes in injured mammalian spinal cord.

    Science.gov (United States)

    Moriarty, L J; Borgens, R B

    2001-01-01

    We have studied the cellular basis for recovery from acute spinal cord injury induced by applied electric fields. We have emphasized this recovery is due to the regeneration of spinal axons around and through the lesion, and have begun to evaluate the contribution of other cells to the recovery process. We have imposed a voltage gradient of about 320 microV/mm across puncture wounds to the adult rat spinal cord in order to study the accumulation and orientation of GFAP+ astrocytes within and adjacent to the lesion. This electric field was imposed by a miniaturized electronic implant designed to alternate the polarity of the field every 15 minutes. Astrocytes are known to undergo hyperplastic transformation within injured mammalian cords forming a major component of the scar that forms in response to injury. We have made three observations using a new computer based morphometry technique: First, we note a slight shift in the orientation of astrocytes parallel to the long axis of the spinal cord towards an imaginary reference perpendicular to this axis by approximately 10 degrees--but only in undamaged white matter near the lesion. Second, the relative number of astrocytes was markedly, and statistically significantly, reduced within electrically--treated spinal cords, particularly in the lesion. Third, the imposed voltage gradient statistically reduced the numbers of astrocytes possessing oriented cell processes within the injury site compared to adjacent undamaged regions of spinal cord.

  9. A one-step separation of human serum high density lipoproteins 2 and 3 by rate-zonal density gradient ultracentrifugation in a swinging bucket rotor

    NARCIS (Netherlands)

    Groot, P.H.E.; Scheek, L.M.; Havekes, L.; Noort, W.L. van; Hooft, F.M. van 't

    1982-01-01

    A method was developed for the separation of the high density lipoprotein subclasses HDL2 and HDL3 from human serum. Six serum samples are fractionated in a single-step ultracentrifugal procedure using the Beckman (SW-40) swinging bucket rotor. The method is based on a difference in flotation rate

  10. Comparative validation using quantitative real-time PCR (qPCR and conventional PCR of bovine semen centrifuged in continuous density gradient

    Directory of Open Access Journals (Sweden)

    M.V. Resende

    2011-06-01

    Full Text Available The objective of the present study was to determine the sperm enrichment with X-bearing spermatozoa, after one centrifugation in a Percoll or OptiPrep continuous density gradient, using quantitative real-time polymerase chain reaction (qPCR of sperm DNA and resultant in vitro-produced bovine embryos by PCR. Frozen/thawed sperm was layered on density gradients and the tubes were centrifuged. Supernatants were gently aspirated and the sperm recovered from the bottom of the tubes. Cleavage and blastocyst rates were determined through in vitro production of embryos and PCR was performed to identify the embryos' genetic sex. A difference in blastocyst rate was found in the Percoll treatment compared to OptiPrep (P<0.05. The percentage of female embryos in the Percoll and OptiPrep groups was 62.0% and 47.1%, respectively. These results were confirmed by qPCR of spermatozoa DNA and underestimation was seen only in the Percoll group. It was possible to sexing sperm using simple approach.

  11. Mapping axonal density and average diameter using non-monotonic time-dependent gradient-echo MRI

    DEFF Research Database (Denmark)

    Nunes, Daniel; Cruz, Tomás L; Jespersen, Sune N

    2017-01-01

    Abstract White Matter (WM) microstructures, such as axonal density and average diameter, are crucial to the normal function of the Central Nervous System (CNS) as they are closely related with axonal conduction velocities. Conversely, disruptions of these microstructural features may result......, the axonal density can be extracted. We then experimentally demonstrate that maps derived from MGE acquired at 16.4 T in ex-vivo spinal cords, where the different tracts characterized by different microstructures are clearly contrasted in parametric maps extracted by fitting the MGE decay to the model. When...

  12. How Do Vegetation Density and Transportation Network Density Affect Crime across an Urban Central-Peripheral Gradient? A Case Study in Kitchener—Waterloo, Ontario

    Directory of Open Access Journals (Sweden)

    Yikang Du

    2016-07-01

    Full Text Available The relationship between vegetation, transportation networks, and crime has been under debate. Vegetation has been positively correlated with fear of crime; however, the actual correlation between vegetation and occurrences of crime is uncertain. Transportation networks have also been connected with crime occurrence but their impact on crime tends to vary over different circumstances. By conducting spatial analyses, this study explores the associations between crime and vegetation as well as transportation networks in Kitchener-Waterloo. Further, geographically weighted regression modeling and a dummy urban variable representing the urban center/other urban areas were employed to explore the associations across an urban central-peripheral gradient. Associations were analyzed for crimes against persons and crimes against property for four specific crime types (assaults, vehicle theft, sex offences, and drugs. Results suggest that vegetation has a reverse association with crimes against persons and crimes against property while transportation networks have a positive relationship with these two types of crime. Additionally, vegetation can be a deterrent to vehicle theft crime and drugs, while transportation networks can be a facilitator of drug-related crimes. Besides, these two associations appear stronger in the urban center compared to the urban periphery.

  13. Ecohydrologic controls on vegetation density and evapotranspiration partitioning across the climatic gradients of the central United States

    OpenAIRE

    Kochendorfer, J. P.; Ramírez, J. A.

    2008-01-01

    International audience; The soil-water balance and plant water use are investigated over a domain encompassing the central United States using the Statistical-Dynamical Ecohydrology Model (SDEM). The seasonality in the model and its use of the two-component Shuttleworth-Wallace canopy model allow for application of an ecological optimality hypothesis in which vegetation density, in the form of peak green leaf area index (LAI), is maximized, within upper and lower bounds, such that, in a typic...

  14. Linking Soil Physical Parameters Along a Density Gradient in a Loess-Soil Long-Term Experiment

    DEFF Research Database (Denmark)

    Eden, Marie; Møldrup, Per; Schjønning, Per

    2012-01-01

    It is important to understand the impact of texture and organic carbon (OC) on soil structure development. Only few studies investigated this for silt-dominated soils. In this study, soil physical properties were determined on samples from a controlled experiment (Static Fertilization Experiment,...... coefficient data; the model pore-connectivity factor was fairly constant, whereas the water blockage factor was markedly different. Water and air parameters both implied that change in bulk density was the major driver for diffusive and convective parameters in the experiment....

  15. A Centrifugal Microfluidic Platform That Separates Whole Blood Samples into Multiple Removable Fractions Due to Several Discrete but Continuous Density Gradient Sections

    Science.gov (United States)

    Moen, Scott T.; Hatcher, Christopher L.; Singh, Anup K.

    2016-01-01

    We present a miniaturized centrifugal platform that uses density centrifugation for separation and analysis of biological components in small volume samples (~5 μL). We demonstrate the ability to enrich leukocytes for on-disk visualization via microscopy, as well as recovery of viable cells from each of the gradient partitions. In addition, we simplified the traditional Modified Wright-Giemsa staining by decreasing the time, volume, and expertise involved in the procedure. From a whole blood sample, we were able to extract 95.15% of leukocytes while excluding 99.8% of red blood cells. This platform has great potential in both medical diagnostics and research applications as it offers a simpler, automated, and inexpensive method for biological sample separation, analysis, and downstream culturing. PMID:27054764

  16. Forward calculation of gravity and its gradient using polyhedral representation of density interfaces: an application of spherical or ellipsoidal topographic gravity effect

    Science.gov (United States)

    Zhang, Yi; Chen, Chao

    2018-02-01

    A density interface modeling method using polyhedral representation is proposed to construct 3-D models of spherical or ellipsoidal interfaces such as the terrain surface of the Earth and applied to forward calculating gravity effect of topography and bathymetry for regional or global applications. The method utilizes triangular facets to fit undulation of the target interface. The model maintains almost equal accuracy and resolution at different locations of the globe. Meanwhile, the exterior gravitational field of the model, including its gravity and gravity gradients, is obtained simultaneously using analytic solutions. Additionally, considering the effect of distant relief, an adaptive computation process is introduced to reduce the computational burden. Then features and errors of the method are analyzed. Subsequently, the method is applied to an area for the ellipsoidal Bouguer shell correction as an example and the result is compared to existing methods, which shows our method provides high accuracy and great computational efficiency. Suggestions for further developments and conclusions are drawn at last.

  17. Ecohydrologic controls on vegetation density and evapotranspiration partitioning across the climatic gradients of the central United States

    Directory of Open Access Journals (Sweden)

    J. P. Kochendorfer

    2010-10-01

    Full Text Available The soil-water balance and plant water use are investigated over a domain encompassing the central United States using the Statistical-Dynamical Ecohydrology Model (SDEM. The seasonality in the model and its use of the two-component Shuttleworth-Wallace canopy model allow for application of an ecological optimality hypothesis in which vegetation density, in the form of peak green leaf area index (LAI, is maximized, within upper and lower bounds, such that, in a typical season, soil moisture in the latter half of the growing season just reaches the point at which water stress is experienced. Via a comparison to large-scale estimates of grassland productivity, modeled-determined peak green LAI for these systems is seen to be at least as accurate as the unaltered satellite-based observations on which they are based. A related feature of the SDEM is its partitioning of evapotranspiration into transpiration, evaporation from canopy interception, and evaporation from the soil surface. That partitioning is significant for the soil-water balance because the dynamics of the three processes are very different. Surprising little dependence on climate and vegetation type is found for the percentage of total evapotranspiration that is soil evaporation, with most of the variation across the study region attributable to soil texture and the resultant differences in vegetation density. While empirical evidence suggests that soil evaporation in the forested regions of the most humid part of the study region is somewhat overestimated, model results are in excellent agreement with observations from croplands and grasslands. The implication of model results for water-limited vegetation is that the higher (lower soil moisture content in wetter (drier climates is more-or-less completely offset by the greater (lesser amount of energy available at the soil surface. This contrasts with other modeling studies which show a strong dependence of evapotranspiration

  18. Density-Gradient Mediated Band Extraction of Leukocytes from Whole Blood Using Centrifugo-Pneumatic Siphon Valving on Centrifugal Microfluidic Discs

    Science.gov (United States)

    Kearney, Sinéad M.; Kilcawley, Niamh A.; Early, Philip L.; Glynn, Macdara T.; Ducrée, Jens

    2016-01-01

    Here we present retrieval of Peripheral Blood Mononuclear Cells by density-gradient medium based centrifugation for subsequent analysis of the leukocytes on an integrated microfluidic “Lab-on-a-Disc” cartridge. Isolation of white blood cells constitutes a critical sample preparation step for many bioassays. Centrifugo-pneumatic siphon valves are particularly suited for blood processing as they function without need of surface treatment and are ‘low-pass’, i.e., holding at high centrifugation speeds and opening upon reduction of the spin rate. Both ‘hydrostatically’ and ‘hydrodynamically’ triggered centrifugo-pneumatic siphon valving schemes are presented. Firstly, the geometry of the pneumatic chamber of hydrostatically primed centrifugo-pneumatic siphon valves is optimised to enable smooth and uniform layering of blood on top of the density-gradient medium; this feature proves to be key for efficient Peripheral Blood Mononuclear Cell extraction. A theoretical analysis of hydrostatically primed valves is also presented which determines the optimum priming pressure for the individual valves. Next, ‘dual siphon’ configurations for both hydrostatically and hydrodynamically primed centrifugo-pneumatic siphon valves are introduced; here plasma and Peripheral Blood Mononuclear Cells are extracted through a distinct siphon valve. This work represents a first step towards enabling on disc multi-parameter analysis. Finally, the efficiency of Peripheral Blood Mononuclear Cells extraction in these structures is characterised using a simplified design. A microfluidic mechanism, which we termed phase switching, is identified which affects the efficiency of Peripheral Blood Mononuclear Cell extraction. PMID:27167376

  19. Efficient enrichment of hepatic cancer stem-like cells from a primary rat HCC model via a density gradient centrifugation-centered method.

    Directory of Open Access Journals (Sweden)

    Wei-hui Liu

    Full Text Available BACKGROUND: Because few definitive markers are available for hepatic cancer stem cells (HCSCs, based on physical rather than immunochemical properties, we applied a novel method to enrich HCSCs. METHODOLOGY: After hepatic tumor cells (HTCs were first isolated from diethylinitrosamine-induced F344 rat HCC model using percoll discontinuous gradient centrifugation (PDGC and purified via differential trypsinization and differential attachment (DTDA, they were separated into four fractions using percoll continuous gradient centrifugation (PCGC and sequentially designated as fractions I-IV (FI-IV. Morphological characteristics, mRNA and protein levels of stem cell markers, proliferative abilities, induced differentiation, in vitro migratory capacities, in vitro chemo-resistant capacities, and in vivo malignant capacities were determined for the cells of each fraction. FINDINGS: As the density of cells increased, 22.18%, 11.62%, 4.73% and 61.47% of primary cultured HTCs were segregated in FI-FIV, respectively. The cells from FIII (density between 1.041 and 1.062 g/ml displayed a higher nuclear-cytoplasmic ratio and fewer organelles and expressed higher levels of stem cell markers (AFP, EpCAM and CD133 than cells from other fractions (P<0.01. Additionally, in vitro, the cells from FIII showed a greater capacity to self-renew, differentiate into mature HTCs, transit across membranes, close scratches, and carry resistance to chemotherapy than did cells from any other fraction; in vivo, injection of only 1×10(4 cells from FIII could generate tumors not only in subcutaneous tissue but also in the livers of nude mice. CONCLUSIONS: Through our novel method, HCSC-like cells were successfully enriched in FIII. This study will greatly contribute to two important areas of biological interest: CSC isolation and HCC therapy.

  20. Reconstructions of Climatic and Topographic Gradients in the Sierra Nevada during the early Eocene using compound-specific stable isotopes and organic molecular temperature proxies

    Science.gov (United States)

    Hren, M. T.; Pagani, M.; Brandon, M.; Erwin, D. M.

    2008-12-01

    Terrestrial sediments from the early Cenozoic provide important records of continental temperature gradients during periods of high global temperatures and PCO2, yet these records are often interpreted in terms of either climatic or orographic effects. As a result, linking models of past global climate with terrestrial temperature information is hampered by a lack of detailed information on paleoelevation. Organic molecular proxies provide new tools to help distinguish between climatic and orographic information in terrestrial sediments. For this study, we used organic molecular proxies to determine paleoelevation and paleotemperature gradients in the Sierra Nevada during the early Eocene warm period. Specifically, we analyzed the hydrogen and carbon isotopes of n-alkanes in bulk sediments and fossil angiosperm leaf cuticle in overbank deposits of major drainages of the Eocene Sierra Nevada to quantify the changes in the isotopic composition of leaf water that potentially reflect changes in paleoelevation. We coupled this data with paleotemperature measurements across this landscape using the MBT/CBT organic molecular temperature proxy, as well as thermodynamic models of the isotopic evolution of rainwater during orographic ascent. Hydrogen isotopes of n-alkanes systematically decrease by more than 30 per mil with distance from the Eocene shoreline and temperature data show a decrease of more than 8 degrees across this ancient range, with temperatures near the ocean margin exceeding 22 degrees. Isotopic and temperature data provide evidence for steep topography and high temperature lapse rates at the California margin during the early Eocene. These results support model estimates of temperature and relative humidity for the early Eocene based on a four time doubling of atmospheric CO2.

  1. Deciphering the kinetic binding mechanism of dimeric ligands using a potent plasma-stable dimeric inhibitor of postsynaptic density protein-95 as an example

    DEFF Research Database (Denmark)

    Chi, Celestine N; Bach, Anders; Gottschalk, Marie

    2010-01-01

    Dimeric ligands can be potent inhibitors of protein-protein or enzyme-substrate interactions. They have increased affinity and specificity toward their targets due to their ability to bind two binding sites simultaneously and are therefore attractive in drug design. However, few studies have...... addressed the kinetic mechanism of interaction of such bivalent ligands. We have investigated the binding interaction of a recently identified potent plasma-stable dimeric pentapeptide and PDZ1-2 of postsynaptic density protein-95 (PSD-95) using protein engineering in combination with fluorescence...

  2. Preparation and properties studies of halogen-free flame retardant form-stable phase change materials based on paraffin/high density polyethylene composites

    International Nuclear Information System (INIS)

    Cai Yibing; Wei Qufu; Huang Fenglin; Gao Weidong

    2008-01-01

    The halogen-free flame retardant form-stable phase change materials (PCM) based on paraffin/high density polyethylene (HDPE) composites were prepared by using twin-screw extruder technique. The structures and properties of the form-stable PCM composites based on intumescent flame retardant system with expandable graphite (EG) and different synergistic additives, such as ammonium polyphosphate (APP) and zinc borate (ZB) were characterized by scanning electronic microscope (SEM), thermogravimetric analyses (TGA), dynamic Fourier-transform infrared (FTIR) spectra, differential scanning calorimeter (DSC) and Cone calorimeter test. The TGA results showed that the halogen-free flame retardant form-stable PCM composites produced a larger amount of charred residue at 700 deg. C, although the onset of weight loss of the halogen-free flame retardant form-stable PCM composites occurred at a lower temperature due to the thermal decomposition of flame retardant. The DSC measurements indicated that the additives of flame retardant had little effect on the thermal energy storage property, and the temperatures of phase change peaks and the latent heat of the paraffin showed better occurrence during the freezing process. The dynamic FTIR monitoring results revealed that the breakdowns of main chains (HDPE and paraffin) and formations of various residues increased with increasing thermo-oxidation temperature. It was also found from the Cone calorimeter tests that the peak of heat release rate (PHRR) decreased significantly. Both the decrease of the PHRR and the structure of charred residue after combustion indicated that there was a synergistic effect between the EG and APP, contributing to the improved flammability of the halogen-free flame retardant form-stable PCM composites

  3. Calorific value of Prosopis africana and Balanites aegyptiaca wood: Relationships with tree growth, wood density and rainfall gradients in the West African Sahel

    Energy Technology Data Exchange (ETDEWEB)

    Montes, Carmen Sotelo; Weber, John C. [World Agroforestry Centre (ICRAF), Sahel Office, B.P. E 5118 Bamako (Mali); Silva, Dimas Agostinho da; Bolzon de Muniz, Graciela Ines [Universidade Federal do Parana (UFPR), Av. Lothario Meissner, 900, CEP.: 80270-170-Curitiba (Brazil); Garcia, Rosilei A. [Universidade Federal Rural do Rio de Janeiro (UFRRJ), Instituto de Florestas, Departamento de Produtos Florestais, BR 465, km 07, 23890-000, Seropedica, Rio de Janeiro (Brazil)

    2011-01-15

    Prosopis africana and Balanites aegyptiaca are native tree species in the West African Sahel and provide wood for fuel, construction and other essential products. A provenance/progeny test of each species was established at one relatively dry site in Niger, and evaluated at 13 years. Gross calorific value of the wood was determined for a random sample of trees in each test: gross CV and CVm{sup 3} = gross calorific value in MJ kg{sup -1} and MJ m{sup -3}, respectively. The major objectives were to determine if gross CV was positively correlated with wood density and tree growth, and if gross CV and/or CVm{sup 3} varied with rainfall gradients in the sample region. Provenances were grouped into a drier and more humid zone, and correlations were computed among all trees and separately in each zone. Results indicated that gross CV was not significantly correlated with density in either species. Gross CV was positively correlated with growth of P. africana (but not B. aegyptiaca) only in the drier zone. Gross CVm{sup 3} was positively correlated with growth of both species, and the correlations were stronger in the drier zone. Multiple regressions with provenance latitude, longitude and elevation indicated that provenance means for gross CV increased, in general, from the drier to the more humid zones. Regressions with gross CVm{sup 3} were not significant. Results are compared with earlier research reports from the provenance/progeny tests and with other tropical hardwood species; and practical implications are presented for tree improvement and conservation programs in the region. (author)

  4. Tail lobe ion composition at energies of 0.1 to 16 keV/e: Evidence for mass-dependent density gradients

    Science.gov (United States)

    Lennartsson, O. W.

    1994-01-01

    A large set of energetic (0.1 to 16 keV/e) ion composition data from the central magnetotail, obtained by the ISEE 1 spacecraft between 10 and 23R(sub E) from Earth, is sorted according to measured total ion beta value, in order to investigate whether bulk properties of different ions vary in different ways between plasma sheets and lobes, as suggested by a comparison of certain experimental and theoretical results in the literature. Despite inevitable difficulties with extracting statistically valid data at very low beta (10(exp -2) or lower), the results seem to support a recent theoretical model suggesting that lighter ions have a steeper density gradient than heavier ions, especially when comparing H(+) ions with O(+) ions. The results also indicate that ion velocity distributions are fairly isotropic even at low beta, at least those of H(+) ions, although field-aligned flows are common. The results are evaluated in the context of plasma transport and are found to lend some support to the notion that tail lobe convection may be directed inward from the dawn and dusk flanks.

  5. Instability of spiral and scroll waves in the presence of a gradient in the fibroblast density: the effects of fibroblast-myocyte coupling

    Science.gov (United States)

    Zimik, Soling; Pandit, Rahul

    2016-12-01

    Fibroblast-myocyte coupling can modulate electrical-wave dynamics in cardiac tissue. In diseased hearts, the distribution of fibroblasts is heterogeneous, so there can be gradients in the fibroblast density (henceforth we call this GFD) especially from highly injured regions, like infarcted or ischemic zones, to less-wounded regions of the tissue. Fibrotic hearts are known to be prone to arrhythmias, so it is important to understand the effects of GFD in the formation and sustenance of arrhythmic re-entrant waves, like spiral or scroll waves. Therefore, we investigate the effects of GFD on the stability of spiral and scroll waves of electrical activation in a state-of-the-art mathematical model for cardiac tissue in which we also include fibroblasts. By introducing GFD in controlled ways, we show that spiral and scroll waves can be unstable in the presence of GFDs because of regions with varying spiral- or scroll-wave frequency ω, induced by the GFD. We examine the effects of the resting membrane potential of the fibroblast and the number of fibroblasts attached to the myocytes on the stability of these waves. Finally, we show that the presence of GFDs can lead to the formation of spiral waves at high-frequency pacing.

  6. Clinical efficacy of a combination of Percoll continuous density gradient and swim-up techniques for semen processing in HIV-1 serodiscordant couples

    Directory of Open Access Journals (Sweden)

    Osamu Inoue

    2017-01-01

    Full Text Available To evaluate the clinical efficacy of a procedure comprising a combination of Percoll continuous density gradient and modified swim-up techniques for the removal of human immunodeficiency virus type 1 (HIV-1 from the semen of HIV-1 infected males, a total of 129 couples with an HIV-1 positive male partner and an HIV-1 negative female partner (serodiscordant couples who were treated at Keio University Hospital between January 2002 and April 2012 were examined. A total of 183 ejaculates from 129 HIV-1 infected males were processed. After swim-up, we successfully collected motile sperms at a recovery rate as high as 100.0% in cases of normozoospermia (126/126 ejaculates, oligozoospermia (6/6, and asthenozoospermia (36/36. The recovery rate of oligoasthenozoospermia was 86.7% (13/15. In processed semen only four ejaculates (4/181:2.2% showed viral nucleotide sequences consistent with those in the blood of the infected males. After using these sperms, no horizontal infections of the female patients and no vertical infections of the newborns were observed. Furthermore, no obvious adverse effects were observed in the offspring. This protocol allowed us to collect HIV-1 negative motile sperms at a high rate, even in male factor cases. We concluded that our protocol is clinically effective both for decreasing HIV-1 infections and for yielding a healthy child.

  7. A fully discrete energy stable scheme for a phase filed moving contact line model with variable densities and viscosities

    KAUST Repository

    Zhu, Guangpu

    2018-01-26

    In this paper, a fully discrete scheme which considers temporal and spatial discretizations is presented for the coupled Cahn-Hilliard equation in conserved form with the dynamic contact line condition and the Navier-Stokes equation with the generalized Navier boundary condition. Variable densities and viscosities are incorporated in this model. A rigorous proof of energy stability is provided for the fully discrete scheme based on a semi-implicit temporal discretization and a finite difference method on the staggered grids for the spatial discretization. A splitting method based on the pressure stabilization is implemented to solve the Navier-Stokes equation, while the stabilization approach is also used for the Cahn-Hilliard equation. Numerical results in both 2-D and 3-D demonstrate the accuracy, efficiency and decaying property of discrete energy of the proposed scheme.

  8. Design of stable polyether-magnetite complexes in aqueous media: effects of the anchor group, molecular weight, and chain density.

    Science.gov (United States)

    Miles, William C; Huffstetler, Philip P; Goff, Jonathan D; Chen, Alfred Y; Riffle, J S; Davis, Richey M

    2011-05-03

    The colloidal stability of polymer-stabilized nanoparticles is critical for therapeutic use. However, phosphates in physiological media can induce polymer desorption and consequently flocculation. Colloidal characteristics of PEO-magnetite nanoparticles with different anchors for attaching PEO to magnetite were examined in PBS. The effects of the number of anchors, PEO molecular weight, and chain density were examined. It was observed that ammonium phosphonates anchored PEO to magnetite effectively in phosphate-containing solutions because of interactions between the phosphonates and magnetite. Additionally, a method to estimate the magnetite surface coverage was developed and was found to be critical to the prediction of colloidal stability. This is key to understanding how functionalized surfaces interact with their environment.

  9. Form-stable paraffin/high density polyethylene composites as solid-liquid phase change material for thermal energy storage: preparation and thermal properties

    International Nuclear Information System (INIS)

    Sari, Ahmet

    2004-01-01

    This paper deals with the preparation of paraffin/high density polyethylene (HDPE) composites as form-stable, solid-liquid phase change material (PCM) for thermal energy storage and with determination of their thermal properties. In such a composite, the paraffin (P) serves as a latent heat storage material and the HDPE acts as a supporting material, which prevents leakage of the melted paraffin because of providing structural strength. Therefore, it is named form-stable composite PCM. In this study, two kinds of paraffins with melting temperatures of 42-44 deg. C (type P1) and 56-58 deg. C (type P2) and latent heats of 192.8 and 212.4 J g -1 were used. The maximum weight percentage for both paraffin types in the PCM composites without any seepage of the paraffin in the melted state were found as high as 77%. It is observed that the paraffin is dispersed into the network of the solid HDPE by investigation of the structure of the composite PCMs using a scanning electronic microscope (SEM). The melting temperatures and latent heats of the form-stable P1/HDPE and P2/HDPE composite PCMs were determined as 37.8 and 55.7 deg. C, and 147.6 and 162.2 J g -1 , respectively, by the technique of differential scanning calorimetry (DSC). Furthermore, to improve the thermal conductivity of the form-stable P/HDPE composite PCMs, expanded and exfoliated graphite (EG) by heat treatment was added to the samples in the ratio of 3 wt.%. Thereby, the thermal conductivity was increased about 14% for the form-stable P1/HDPE and about 24% for the P2/HDPE composite PCMs. Based on the results, it is concluded that the prepared form-stable P/HDPE blends as composite type PCM have great potential for thermal energy storage applications in terms of their satisfactory thermal properties and improved thermal conductivity. Furthermore, these composite PCMs added with EG can be considered cost effective latent heat storage materials since they do not require encapsulation and extra cost to enhance

  10. Characterization of Growing Soil Bacterial Communities across a pH gradient Using H218O DNA-Stable Isotope Probing

    Science.gov (United States)

    Welty-Bernard, A. T.; Schwartz, E.

    2014-12-01

    Recent studies have established consistent relationships between pH and bacterial diversity and community structure in soils from site-specific to landscape scales. However, these studies rely on DNA or PLFA extraction techniques from bulk soils that encompass metabolically active and inactive, or dormant, communities, and loose DNA. Dormant cells may comprise up to 80% of total live cells. If dormant cells dominate a particular environment, it is possible that previous interpretations of the soil variables assumed to drive communities could be profoundly affected. We used H218O stable isotope probing and bar-coded illumina sequencing of 16S rRNA genes to monitor the response of actively growing communities to changes in soil pH in a soil microcosm over 14 days. This substrate-independent approach has several advantages over 13C or 15N-labelled molecules in that all growing bacteria should be able to make use of water, allowing characterization of whole communities. We hypothesized that Acidobacteria would increasingly dominate the growing community and that Actinobacteria and Bacteroidetes would decline, given previously established responses by these taxa to soil pH. Instead, we observed the reverse. Actinobacteria abundance increased three-fold from 26 to 76% of the overall community as soil pH fell from pH 5.6 to pH 4.6. Shifts in community structure and decreases in diversity with declining soil pH were essentially driven by two families, Streptomyceaca and Microbacteracea, which collectively increased from 2 to 40% of the entire community. In contrast, Acidobacteria as a whole declined although numbers of subdivision 1 remained stable across all soil pH levels. We suggest that the brief incubation period in this SIP study selected for growth of acid-tolerant Actinobacteria over Acidobacteria. Taxa within Actinomycetales have been readily cultured over short time frames, suggesting rapid growth patterns. Conversely, taxa within Acidobacteria have been

  11. Sperm quality after swim up and density gradient centrifugation sperm preparation with supplementation of alpha lipoic acid (ALA): A preliminary study

    Science.gov (United States)

    Lestari, Silvia W.; Lestari, Sarah H.; Pujianto, Dwi A.

    2018-02-01

    Intra uterine insemination (IUI) as one of the treatment for infertility, persists low success rate. A factor that contributes to the unsuccessful of IUI is sperm preparation, performed through Swim-up (SU) and Density Gradient Centrifugation (DGC) methods. Furthermore, studies have shown that Alpha Lipoic Acid (ALA) is a potent antioxidant that could enhance the sperm motility and protect the DNA integrity of the sperm [1]. This study is aimed to re-evaluate the efficiency of the DGC and SU methods in selecting sperm before being transferred for IUI by the supplementation of ALA based on the sperm DNA integrity. Semen samples were obtained from 13 men from partners of women who are infertile (normozoospermia) and underwent IUI. Semen analysis based on the guideline of World Health Organization (WHO) 2010 was performed to measure the sperm motility and velocity, before and after sperm preparation. Then, samples were incubated with Alpha Lipoic Acid (ALA) in 0.625 mg (ALA 1), 1.25 mg (ALA 2) and 2.5 mg (ALA 3). The Sperm Chromatin Dispersion (SCD) test was performed to evaluate the sperm DNA Fragmentation Index (DFI). The percentage of motile sperm was higher in prepared sperm (post-DGC and post-SU) than in whole semen. Furthermore, the percentage of motile sperm was higher in post-DGC compared to post-SU. The level of DFI after the supplementation of ALA was decreased in prepared sperm compared to the whole semen. ALA was proved capable to select the better sperm quality with decreased sperm DNA fragmentation of prepared sperm in the all of DFI category.

  12. Form-stable crystalline polymer pellets for thermal energy storage: high density polyethylene intermediate products. Final report, October 1, 1977--January 31, 1978

    Energy Technology Data Exchange (ETDEWEB)

    Botham, R.A.; Ball, G.L. III; Jenkins, G.H.; Salyer, I.O.

    1978-01-01

    The primary objectives of this program were to demonstrate: (1) that form-stable high density polyethylene (HDPE), which has been shown to have desirable properties as a phase-change type of thermal energy storage material, could be produced by processing in a polyethylene plant for a projected price near 26 cents/lb; and (2) that the raw material, ethylene, will be available in the very long-term from alternate sources (other than petroleum and natural gas). These objectives were accomplished. Production of useful, form-stable HDPE pellets by radiation cross-linking was demonstrated. Such pellets are estimated to be obtainable at 26 cents/lb, using large-volume (> or equal to 10,000,000 lb/yr) in-plant processing. Well-developed technologies exist for obtaining ethylene from coal and plant (or biomass) sources, thus assuring its long-term availability and therefore that of polyethylene. A cost-benefit analysis of the HDPE thermal energy storage system was conducted over its 120 to 140/sup 0/C optimum operating range which is most suited for absorption air conditioning. The HDPE is more cost effective than either rocks, ethylene glycol, or pressurized water and is even competitive with a hypothetical 5 cents/lb salt-hydrate melting in this temperature range. These results applied, as appropriate, to both air and liquid transfer systems.

  13. Cultivo de células mesenquimais do sangue de cordão umbilical com e sem uso do gradiente de densidade Ficoll-Paque Blood mesenchymal stem cell culture from the umbilical cord with and without Ficoll-Paque density gradient method

    Directory of Open Access Journals (Sweden)

    Rosa Sayoko Kawasaki-Oyama

    2008-03-01

    Ficoll-Paque gradient density method (d=1.077g/ml. METHODS: Ten samples of the umbilical cord blood obtained from full-term deliveries were submitted to two different procedures of mesenchymal stem cell culture: a Method without the Ficoll-Paque density gradient, which concentrates all nucleated cells; b Method with the Ficoll-Paque density gradient, which selects only low-density mononuclear cells. Cells were initially plated into 25 cm² cultures flasks at a density of 1x10(7 nucleated cells/cm² and 1x10(6 mononuclear cells/cm². RESULTS: It was obtained 2-13x10(7 (median = 2.35x10(7 nucleated cells/cm² by the method without the Ficoll-Paque gradient density, and 3.7-15.7x10(6 (median = 7.2x10(6 mononuclear cells/cm² by the method with the Ficoll-Paque gradient density. In all cultures adherent cells were observed 24 hours after being cultured. Cells presented fibroblastoid and epithelioid morphology. In most of the cultures, cell proliferation occurred in the first week, but after the second week only some cultures - derived from the method without the Ficoll-Paque gradient density - maintained the growth rate reaching confluence. Those cultures were submitted to trypsinization with 0.25% trypsin/EDTA solution and cultured for two to three months. CONCLUSION: In the samples analyzed, cell separation and mesenchymal stem cell culture techniques from human umbilical cord blood by the method without the Ficoll-Paque density gradient was more efficient than the method with the Ficoll-Paque density gradient.

  14. Sperm Na+, K+-ATPase and Ca2+-ATPase activity: A preliminary study of comparison of swim up and density gradient centrifugation methods for sperm preparation

    Science.gov (United States)

    Lestari, Silvia W.; Larasati, Manggiasih D.; Asmarinah, Mansur, Indra G.

    2018-02-01

    As one of the treatment for infertility, the success rate of Intrauterine Insemination (IUI) is still relatively low. Several sperm preparation methods, swim-up (SU) and the density-gradient centrifugation (DGC) are frequently used to select for better sperm quality which also contribute to IUI failure. Sperm selection methods mainly separate the motile from the immotile sperm, eliminating the seminal plasma. The sperm motility involves the structure and function of sperm membrane in maintaining the balance of ion transport system which is regulated by the Na+, K+-ATPase, and Ca2+-ATPase enzymes. This study aims to re-evaluate the efficiency of these methods in selecting for sperm before being used for IUI and based the evaluation on sperm Na+,K+-ATPase and Ca2+-ATPase activities. Fourteen infertile men from couples who underwent IUI were involved in this study. The SU and DGC methods were used for the sperm preparation. Semen analysis was performed based on the reference value of World Health Organization (WHO) 2010. After isolating the membrane fraction of sperms, the Na+, K+-ATPase activity was defined as the difference in the released inorganic phosphate (Pi) with and without the existence of 10 mM ouabain in the reaction, while the Ca2+-ATPase was determined as the difference in Pi contents with and without the existence of 55 µm CaCl2. The prepared sperm demonstrated a higher percentage of motile sperm compared to sperm from the whole semen. Additionally, the percentage of motile sperm of post-DGC showed higher result than the sperm from post-SU. The velocity of sperm showed similar pattern with the percentage of motile sperm, in which the velocity of prepared sperm was higher than the sperm from whole semen. Furthermore, the sperm velocity of post-DGC was higher compared to the sperm from post-SU. The Na+, K+-ATPase activity of prepared sperm was higher compared to whole semen, whereas Na+, K+-ATPase activity in the post DGC was higher than post SU. The Ca2

  15. Differences in below-ground bud bank density and composition along a climatic gradient in the temperate steppe of northern China

    Czech Academy of Sciences Publication Activity Database

    Qian, J.; Wang, Z.; Klimešová, Jitka; Lü, X.; Kuang, W.; Liu, Z.; Han, X.

    2017-01-01

    Roč. 120, č. 5 (2017), s. 755-764 ISSN 0305-7364 R&D Projects: GA ČR GB14-36079G Institutional support: RVO:67985939 Keywords : Bud Bank * Precipitation gradient * Stepic vegetation Subject RIV: EH - Ecology, Behaviour OBOR OECD: Ecology Impact factor: 4.041, year: 2016

  16. Surface Tension of Binary Mixtures Including Polar Components Modeled by the Density Gradient Theory Combined with the PC-SAFT Equation of State

    Czech Academy of Sciences Publication Activity Database

    Vinš, Václav; Planková, Barbora; Hrubý, Jan

    2013-01-01

    Roč. 34, č. 5 (2013), s. 792-812 ISSN 0195-928X R&D Projects: GA AV ČR IAA200760905; GA ČR(CZ) GPP101/11/P046; GA ČR GA101/09/1633 Institutional research plan: CEZ:AV0Z20760514 Institutional support: RVO:61388998 Keywords : chemical polarity * gradient theory * surface tension Subject RIV: BJ - Thermodynamics Impact factor: 0.623, year: 2013 http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1007/s10765-012-1207-z

  17. Desvio da proporção de sexo e da integridade do DNA dos espermatozóides bovinos centrifugados em gradientes de densidade contínuos Alteration of sex ratio and DNA integrity of bovine sperm centrifuged in continuous density gradients

    Directory of Open Access Journals (Sweden)

    Alberto Lopes Gusmão

    2010-03-01

    Full Text Available O objetivo, neste trabalho, foi verificar o desvio da proporção de sexo e a presença de fragmentação do DNA, pela técnica de TUNEL (“In situ terminal deoxinucleotidyl transferase mediated dUTP nick end labeling assay”, em espermatozoides bovinos centrifugados em gradientes de densidade de Percoll ou OptiPrep durante a separação espermática. Doses de sêmen de touros foram descongeladas, e cerca de 40 milhões de espermatozoides foram depositados sobre cada gradiente de densidade compostos por Percoll ou OptiPrep com três camadas entre 1.110g/mL e 1.123g/mL, em tubos de 15mL, em que permaneceram por 24h a 4°C antes da deposição dos espermatozoides. Os tubos foram centrifugados a 500xg por 15min a 22°C. Os sobrenadantes foram aspirados, e os sedimentos, recuperados para verificação da fragmentação do DNA pela técnica de TUNEL. Obteve-se um desvio dos embriões produzidos in vitro para fêmeas no gradiente de Percoll (62% de fêmeas, em relação aos grupos OptiPrep e Controle (47,1 e 48,7% de fêmeas, respectivamente. Não foi detectada fragmentação do DNA dos espermatozoides nas amostras centrifugadas, tanto no gradiente de Percoll quanto de OptiPrep. Dessa forma, foi possível realizar a sexagem espermática, com uma maior porcentagem de espermatozoides X do que o grupo controle, por meio de metodologia mais simples e sem provocar danos ao DNA dos espermatozoides.The objective of the present study was to verify the sex ratio and presence of DNA fragmentation by TUNEL technique (In situ terminal deoxinucleotidyl transferase mediated dUTP nick end labeling assay in bovine spermatozoa centrifuged in density gradients of Percoll or OptiPrep during the sperm separation. Approximately 40 million of frozen/thawed bovine spermatozoa were deposited on each density gradient composed of Percoll or OptiPrep with three layers ranging from 1.110g/mL to 1.123g/mL in polystyrene tubes of 15mL. The tubes were kept at 4°C for 24h before

  18. Keutuhan Membran Spermatozoa Disekuensing Sentrifugasi Gradien Densitas Percoll Berpengencer Andromed dan CEP-2 yang Ditambahkan Kuning Telur (MEMBRANE INTACT OF SPERMATOZOA FOLLOWING SEXING USING PERCOLL DENSITY GRADIENT CENTRIFUGATION IN ANDROMED AND C

    Directory of Open Access Journals (Sweden)

    Yudha Fika Diliyana

    2014-05-01

    Full Text Available The aim of this study was to observe the best extender in protecting the membrane of bovine spermatozoafollowing sexing by percoll density gradient centrifugation. Freshly collected semen were obtained fromBalai Besar Inseminasi Buatan Singosari-Malang. The semen were diluted in andromed and CaudalEpididymal Plasma-2 (CEP-2 added with 10% egg yolk extenders.The sperm membrane integrity wasobserved using Hypo-osmotic Swelling Test (HOST. Sperm capacitation and acrososome reaction wereassessed using Chlortetracycline Fluorescence Assay.The results showed that andromed and CEP-2 addedwith 10% egg yolk were able to retain the sperm membrane integrity, whereas sperm capacitation andacrosome reaction were kept low. Caudal Epididymal Plasma-2 (CEP-2 added with 10% egg yolk seemedto give better protection towards the sperm membrane intact in comparison to andromed extender.

  19. Irradiance gradients

    International Nuclear Information System (INIS)

    Ward, G.J.; Heckbert, P.S.; Technische Hogeschool Delft

    1992-04-01

    A new method for improving the accuracy of a diffuse interreflection calculation is introduced in a ray tracing context. The information from a hemispherical sampling of the luminous environment is interpreted in a new way to predict the change in irradiance as a function of position and surface orientation. The additional computation involved is modest and the benefit is substantial. An improved interpolation of irradiance resulting from the gradient calculation produces smoother, more accurate renderings. This result is achieved through better utilization of ray samples rather than additional samples or alternate sampling strategies. Thus, the technique is applicable to a variety of global illumination algorithms that use hemicubes or Monte Carlo sampling techniques

  20. Preparation, thermal and flammability properties of a novel form-stable phase change materials based on high density polyethylene/poly(ethylene-co-vinyl acetate)/organophilic montmorillonite nanocomposites/paraffin compounds

    International Nuclear Information System (INIS)

    Cai Yibing; Song Lei; He Qingliang; Yang Dandan; Hu Yuan

    2008-01-01

    The paraffin is one of important thermal energy storage materials with many desirable characteristics (i.e., high heat of fusion, varied phase change temperature, negligible supercooling, self-nucleating, no phase segregation and cheap, etc.), but has low thermal stability and flammable. Hence, a novel form-stable phase change materials (PCM) based on high density polyethylene (HDPE)/poly(ethylene-co-vinyl acetate) (EVA)/organophilic montmorillonite (OMT) nanocomposites and paraffin are prepared by twin-screw extruder technique. The structures of the HDPE-EVA/OMT nanocomposites and the form-stable PCM are evidenced by the X-ray diffraction (XRD), transmission electronic microscopy (TEM) and scanning electronic microscope (SEM). The results of XRD and TEM show that the HDPE-EVA/OMT nanocomposites form the ordered intercalated nanomorphology. The form-stable PCM consists of the paraffin, which acts as a dispersed phase change material and the HDPE-EVA/OMT nanocomposites, which acts as the supporting material. The paraffin disperses in the three-dimensional net structure formed by HDPE-EVA/OMT nanocomposites. The thermal stability, latent heat and flammability properties are characterized by thermogravimetry analysis (TGA), dynamic Fourier-transform infrared (FTIR), differential scanning calorimeter (DSC) and cone calorimeter, respectively. The TGA and dynamic FTIR analyses indicate that the incorporation of suitable amount of OMT into the form-stable PCM increase the thermal stability. The DSC results show that the latent heat of the form-stable PCM has a certain degree decrease. The cone calorimeter shows that the heat release rate (HRR) has remarkably decreases with loading of OMT in the form-stable PCM, contributing to the improved flammability properties

  1. Formation of large-scale structures with sharp density gradient through Rayleigh-Taylor growth in a two-dimensional slab under the two-fluid and finite Larmor radius effects

    International Nuclear Information System (INIS)

    Goto, R.; Hatori, T.; Miura, H.; Ito, A.; Sato, M.

    2015-01-01

    Two-fluid and the finite Larmor effects on linear and nonlinear growth of the Rayleigh-Taylor instability in a two-dimensional slab are studied numerically with special attention to high-wave-number dynamics and nonlinear structure formation at a low β-value. The two effects stabilize the unstable high wave number modes for a certain range of the β-value. In nonlinear simulations, the absence of the high wave number modes in the linear stage leads to the formation of the density field structure much larger than that in the single-fluid magnetohydrodynamic simulation, together with a sharp density gradient as well as a large velocity difference. The formation of the sharp velocity difference leads to a subsequent Kelvin-Helmholtz-type instability only when both the two-fluid and finite Larmor radius terms are incorporated, whereas it is not observed otherwise. It is shown that the emergence of the secondary instability can modify the outline of the turbulent structures associated with the primary Rayleigh-Taylor instability

  2. Stable isotopes

    International Nuclear Information System (INIS)

    Evans, D.K.

    1986-01-01

    Seventy-five percent of the world's stable isotope supply comes from one producer, Oak Ridge Nuclear Laboratory (ORNL) in the US. Canadian concern is that foreign needs will be met only after domestic needs, thus creating a shortage of stable isotopes in Canada. This article describes the present situation in Canada (availability and cost) of stable isotopes, the isotope enrichment techniques, and related research programs at Chalk River Nuclear Laboratories (CRNL)

  3. Highly-stable and low-state-density Al2O3/GaN interfaces using epitaxial n-GaN layers grown on free-standing GaN substrates

    Science.gov (United States)

    Kaneki, Shota; Ohira, Joji; Toiya, Shota; Yatabe, Zenji; Asubar, Joel T.; Hashizume, Tamotsu

    2016-10-01

    Interface characterization was carried out on Al2O3/GaN structures using epitaxial n-GaN layers grown on free-standing GaN substrates with relatively low dislocation density (capacitance-voltage (C-V) curves at reverse bias, showing high-density interface states in the range of 1012 cm-1 eV-1. On the other hand, excellent C-V characteristics with negligible frequency dispersion were observed from the MOS sample after annealing under a reverse bias at 300 °C in air for 3 h. The reverse-bias-annealed sample showed state densities less than 1 × 1011 cm-1 eV-1 and small shifts of flat-band voltage. In addition, the C-V curve measured at 200 °C remained essentially similar compared with the room-temperature C-V curves. These results indicate that the present process realizes a stable Al2O3/GaN interface with low interface state densities.

  4. Rev1, Rev3, or Rev7 siRNA Abolishes Ultraviolet Light-Induced Translesion Replication in HeLa Cells: A Comprehensive Study Using Alkaline Sucrose Density Gradient Sedimentation

    Directory of Open Access Journals (Sweden)

    Jun Takezawa

    2010-01-01

    Full Text Available When a replicative DNA polymerase stalls upon encountering a lesion on the template strand, it is relieved by other low-processivity polymerase(s, which insert nucleotide(s opposite the lesion, extend by a few nucleotides, and dissociate from the 3′-OH. The replicative polymerase then resumes DNA synthesis. This process, termed translesion replication (TLS or replicative bypass, may involve at least five different polymerases in mammals, although the participating polymerases and their roles have not been entirely characterized. Using siRNAs originally designed and an alkaline sucrose density gradient sedimentation technique, we verified the involvement of several polymerases in ultraviolet (UV light-induced TLS in HeLa cells. First, siRNAs to Rev3 or Rev7 largely abolished UV-TLS, suggesting that these 2 gene products, which comprise Polζ, play a main role in mutagenic TLS. Second, Rev1-targeted siRNA also abrogated UV-TLS, indicating that Rev1 is also indispensable to mutagenic TLS. Third, Polη-targeted siRNA also prevented TLS to a greater extent than our expectations. Forth, although siRNA to Polι had no detectable effect, that to Polκ delayed UV-TLS. To our knowledge, this is the first study reporting apparent evidence for the participation of Polκ in UV-TLS.

  5. Stability of gradient semigroups under perturbations

    Science.gov (United States)

    Aragão-Costa, E. R.; Caraballo, T.; Carvalho, A. N.; Langa, J. A.

    2011-07-01

    In this paper we prove that gradient-like semigroups (in the sense of Carvalho and Langa (2009 J. Diff. Eqns 246 2646-68)) are gradient semigroups (possess a Lyapunov function). This is primarily done to provide conditions under which gradient semigroups, in a general metric space, are stable under perturbation exploiting the known fact (see Carvalho and Langa (2009 J. Diff. Eqns 246 2646-68)) that gradient-like semigroups are stable under perturbation. The results presented here were motivated by the work carried out in Conley (1978 Isolated Invariant Sets and the Morse Index (CBMS Regional Conference Series in Mathematics vol 38) (RI: American Mathematical Society Providence)) for groups in compact metric spaces (see also Rybakowski (1987 The Homotopy Index and Partial Differential Equations (Universitext) (Berlin: Springer)) for the Morse decomposition of an invariant set for a semigroup on a compact metric space).

  6. a Modified Denitrifying Bacteria Method for Dual Stable Isotopic Analysis of of Soil Nitrate in Kcl Extracts: Identification of Bioindicators of Nitrogen Deposition Along a Gradient in the Sonoran Desert

    Science.gov (United States)

    Bell, M. D.; Sickman, J. O.; Allen, E. B.

    2011-12-01

    Previous studies performing dual isotopic analysis of nitrate in KCl soil extracts using denitrifying bacteria have not incorporated alterations in the method to compensate for the increased N2O blank produced when the bacteria are exposed to KCl in solution. When 1M KCl is used as a blank, the amount of N2O released from the concentrated bacteria solution is more than four times as high as when using a DI water blank. The excess N2O produced is not an artifact of nitrate impurity in the KCl, although the blank increases with the molarity of KCl up to 1M. The introduction of N2O gas is significant enough to alter the values of IAEA USGS standards (3 μg in 3ml KCl) which in turn results in an inaccurate regression for unknown samples. We reduced the size of the KCl blank and its effect on the standards by adding 3ml of KCl to the bacteria solution prior to purging the sample with He gas. This removes the N2O gas which is released by the bacteria when they initially come in contact with the KCl, and allows for standards to be calibrated to a precision of ± 0.1 % δ15N and ± 0.2 % δ18O. Using this new method, we measured δ15N and δ18O of nitrate in 1M KCl soil extracts taken from surface soil (5cm cores) along a nitrogen deposition gradient spanning the Coachella Valley in the western Sonoran Desert during the summer. Early germinating winter annual plant species (Schismus barbatus, Chaenactic fremontii, and Malacothrix glabrata) were collected as seedlings early in the growing season and again in late spring before senescence. Leaves from the dominant shrub, Larrea tridentata, were also collected from each site. Soil nitrogen from sites on the eastern edge of the valley had δ18O values between +30 and +41%, indicating an influence of atmospheric nitrate in plant available nitrate. There was an inverse correlation (r2=0.907) between soil δ18O and the δ15N of the C.fremontii leaf tissue, which suggests that in areas of high N deposition, some seedlings are

  7. Stable particles

    International Nuclear Information System (INIS)

    Samios, N.P.

    1994-01-01

    I have been asked to review the subject of stable particles, essentially the particles that eventually comprised the meson and baryon octets, with a few more additions - with an emphasis on the contributions made by experiments utilizing the bubble chamber technique. In this activity, much work had been done by the photographic emulsion technique and cloud chambers - exposed to cosmic rays as well as accelerator based beams. In fact, many if not most of the stable particles were found by these latter two techniques, however, the foree of the bubble chamber (coupled with the newer and more powerful accelerators) was to verify, and reinforce with large statistics, the existence of these states, to find some of the more difficult ones, mainly neutrals and further to elucidate their properties, i.e., spin, parity, lifetimes, decay parameters, etc. (orig.)

  8. Stable particles

    International Nuclear Information System (INIS)

    Samios, N.P.

    1993-01-01

    I have been asked to review the subject of stable particles, essentially the particles that eventually comprised the meson and baryon octets. with a few more additions -- with an emphasis on the contributions made by experiments utilizing the bubble chamber technique. In this activity, much work had been done by the photographic emulsion technique and cloud chambers-exposed to cosmic rays as well as accelerator based beams. In fact, many if not most of the stable particles were found by these latter two techniques, however, the forte of the bubble chamber (coupled with the newer and more powerful accelerators) was to verify, and reinforce with large statistics, the existence of these states, to find some of the more difficult ones, mainly neutrals and further to elucidate their properties, i.e., spin, parity, lifetimes, decay parameters, etc

  9. Convection induced by thermal gradients on thin reaction fronts

    Science.gov (United States)

    Ruelas Paredes, David R. A.; Vasquez, Desiderio A.

    2017-09-01

    We present a thin front model for the propagation of chemical reaction fronts in liquids inside a Hele-Shaw cell or porous media. In this model we take into account density gradients due to thermal and compositional changes across a thin interface. The front separating reacted from unreacted fluids evolves following an eikonal relation between the normal speed and the curvature. We carry out a linear stability analysis of convectionless flat fronts confined in a two-dimensional rectangular domain. We find that all fronts are stable to perturbations of short wavelength, but they become unstable for some wavelengths depending on the values of compositional and thermal gradients. If the effects of these gradients oppose each other, we observe a range of wavelengths that make the flat front unstable. Numerical solutions of the nonlinear model show curved fronts of steady shape with convection propagating faster than flat fronts. Exothermic fronts increase the temperature of the fluid as they propagate through the domain. This increment in temperature decreases with increasing speed.

  10. Dynamical attraction to stable processes

    OpenAIRE

    Fisher, Albert M.; Talet, Marina

    2012-01-01

    We apply dynamical ideas within probability theory, proving an almost-sure invariance principle in log density for stable processes. The familiar scaling property (self-similarity) of the stable process has a stronger expression, that the scaling flow on Skorokhod path space is a Bernoulli flow. We prove that typical paths of a random walk with i.i.d. increments in the domain of attraction of a stable law can be paired with paths of a stable process so that, after applying a non-random regula...

  11. Stable beams

    CERN Multimedia

    2015-01-01

    Stable beams: two simple words that carry so much meaning at CERN. When LHC page one switched from "squeeze" to "stable beams" at 10.40 a.m. on Wednesday, 3 June, it triggered scenes of jubilation in control rooms around the CERN sites, as the LHC experiments started to record physics data for the first time in 27 months. This is what CERN is here for, and it’s great to be back in business after such a long period of preparation for the next stage in the LHC adventure.   I’ve said it before, but I’ll say it again. This was a great achievement, and testimony to the hard and dedicated work of so many people in the global CERN community. I could start to list the teams that have contributed, but that would be a mistake. Instead, I’d simply like to say that an achievement as impressive as running the LHC – a machine of superlatives in every respect – takes the combined effort and enthusiasm of everyone ...

  12. SEPARATION OF X-BEARING BOVINE SPERM BY CENTRIFUGATION IN CONTINUOUS PERCOLL AND OPTIPREP DENSITY GRADIENT: EFFECT IN SPERM VIABILITY AND IN VITRO EMBRYO PRODUCTION SEPARAÇÃO DE ESPERMATOZOIDES PORTADORES DO CROMOSSOMO X BOVINO POR CENTRIFUGAÇÃO EM GRADIENTE DE DENSIDADE CONTÍNUO DE PERCOLL E OPTIPREP: EFEITO SOBRE A VIABILIDADE ESPERMÁTICA E NA PRODUÇÃO IN VITRO DE EMBRIÕES

    Directory of Open Access Journals (Sweden)

    Aline Costa Lucio

    2009-07-01

    Full Text Available

    The aim of this study was to separate X-bearing bovine sperm by continuous Percoll and OptiPrep density gradients and to validate the sexing of resultant in vitro produced embryos by Polimerase Chain Reaction (PCR. Frozen/thawed sperm was layered on density gradients which were previously prepared in polystyrene tubes, 24 h before procedures and maintained at 4 °C. The tubes were centrifuged at 500 x g for 15 min at 22 °C. Supernatants were gently aspirated and the sperm recovered from the bottom of the tubes. Viability and integrity of sperm were evaluated by Trypan Blue/Giemsa stain. Cleavage and blastocyst rates were determined by in vitro production of embryos and PCR was performed for identification of the embryos’ genetic sex. No damage in viability and acrossomal integrity and in cleavage and blastocyst rates was found in the Percoll and OptiPrep treatment compared to the non-centrifuged group (P>0.05. The percentage of female embryos in the Percoll and OptiPrep group was 63.0 and 47.6%, respectively. The female embryos in control group were 48.7%. A sexual deviation in the Percoll density gradient was achieved without reduction of sperm viability and in vitro production rates.

    KEY WORDS: Bovine, centrifugation, in vitro production of embryos, PCR, X-bearing sperm.

    O objetivo deste estudo foi separar espermatozoides bovinos portadores do cromossomo X pela centrifugação em gradiente de densidade contínuo de Percoll e OptiPrep, e validar a sexagem pela reação em cadeia da polimerase (PCR, dos embriões produzidos in vitro. Para a sexagem, espermatozoides descongelados foram depositados nos gradientes de densidade, previamente preparados, em tubos de poliestireno, 24 horas antes da sexagem e mantidos a 4°C. Centrifugou-se a 500 x g por quinze minutos a 22°C. Os sobrenadantes foram aspirados, e os espermatozoides recuperados do

  13. Unstable ion-temperature-gradient modes in the Wendelstein 7-X stellarator configuration

    Science.gov (United States)

    Rafiq, T.; Kleiber, R.; Nadeem, M.; Persson, M.

    2002-12-01

    The linear stability of the ion-temperature-gradient modes (ITG) in the electrostatic limit is examined in the short wavelength region by using a two fluid reactive model in fully three-dimensional Wendelstein 7-X (W7-X) stellarator [G. Grieger et al., Plasma Physics and Controlled Nuclear Fusion Research, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 525] geometry. The spectrum of stable and unstable modes and their real frequencies and eigenfunctions are calculated. The effects of density gradients, temperature gradients, temperature ratios, wavevector, ballooning angle, curvature and local magnetic shear on the ITG mode are also investigated. The frequency and growth rate of the most unstable ITG mode is calculated and visualized for a specific magnetic flux surface. For the equilibrium under investigation both localized and extended eigenmodes are found. The effect of small and large temperature ratios, small and large density gradients as well as large local magnetic shear are all found to be stabilizing. The highest growth rates are found at the outer part of the surface where the local magnetic shear is small and normal curvature is unfavorable.

  14. Multilayer ceramic capacitors based on relaxor BaTiO3-Bi(Zn1/2Ti1/2)O3 for temperature stable and high energy density capacitor applications

    Science.gov (United States)

    Kumar, Nitish; Ionin, Aleksey; Ansell, Troy; Kwon, Seongtae; Hackenberger, Wesley; Cann, David

    2015-06-01

    The need for miniaturization without compromising cost and performance continues to motivate research in advanced capacitor devices. In this report, multilayer ceramic capacitors based on relaxor BaTiO3-Bi(Zn1/2Ti1/2)O3 (BT-BZT) were fabricated and characterized. In bulk ceramic embodiments, BT-BZT has been shown to exhibit relative permittivities greater than 1000, high resistivities (ρ > 1 GΩ-cm at 300 °C), and negligible saturation up to fields as high as 150 kV/cm. Multilayer capacitor embodiments were fabricated and found to exhibit similar dielectric and resistivity properties. The energy density for the multilayer ceramics reached values of ˜2.8 J/cm3 at room temperature at an applied electric field of ˜330 kV/cm. This represents a significant improvement compared to commercially available multilayer capacitors. The dielectric properties were also found to be stable over a wide range of temperatures with a temperature coefficient of approximately -2000 ppm/K measured from 50 to 350 °C, an important criteria for high temperature applications. Finally, the compatibility of inexpensive Ag-Pd electrodes with these ceramics was also demonstrated, which can have implications on minimizing the device cost.

  15. Self-organization of intracellular gradients during mitosis

    Directory of Open Access Journals (Sweden)

    Fuller Brian G

    2010-01-01

    Full Text Available Abstract Gradients are used in a number of biological systems to transmit spatial information over a range of distances. The best studied are morphogen gradients where information is transmitted over many cell lengths. Smaller mitotic gradients reflect the need to organize several distinct events along the length of the mitotic spindle. The intracellular gradients that characterize mitosis are emerging as important regulatory paradigms. Intracellular gradients utilize intrinsic auto-regulatory feedback loops and diffusion to establish stable regions of activity within the mitotic cytosol. We review three recently described intracellular mitotic gradients. The Ran GTP gradient with its elaborate cascade of nuclear transport receptors and cargoes is the best characterized, yet the dynamics underlying the robust gradient of Ran-GTP have received little attention. Gradients of phosphorylation have been observed on Aurora B kinase substrates both before and after anaphase onset. In both instances the phosphorylation gradient appears to result from a soluble gradient of Aurora B kinase activity. Regulatory properties that support gradient formation are highlighted. Intracellular activity gradients that regulate localized mitotic events bare several hallmarks of self-organizing biologic systems that designate spatial information during pattern formation. Intracellular pattern formation represents a new paradigm in mitotic regulation.

  16. DOUBLE-DIFFUSIVE MIXING IN STELLAR INTERIORS IN THE PRESENCE OF HORIZONTAL GRADIENTS

    Energy Technology Data Exchange (ETDEWEB)

    Medrano, M.; Garaud, P. [Department of Applied Mathematics and Statistics, Baskin School of Engineering, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95060 (United States); Stellmach, S. [Institut für Geophysik, Westfälische Wilhelms-Universität Münster, Münster D-48149 (Germany)

    2014-09-10

    We have identified a potentially important source of mixing in stellar radiation zones which would arise whenever two conditions are satisfied: (1) the presence of an inverse vertical compositional gradient, and (2) the presence of density-compensating horizontal gradients of temperature and composition. The former can be caused by off-center nuclear burning, atomic diffusion, or surface accretion. The latter could be caused by rotation, tides, meridional flows, etc. The linear instability and its nonlinear development have been studied in an oceanographic context. It is known to drive the formation of stacks of fingering layers separated by diffusive interfaces, called intrusions. Using three-dimensional numerical simulations of the process in the astrophysically relevant region of parameter space, we find similar results and demonstrate that the material transport in the intrusive regime can be highly enhanced compared with pure diffusion, even in systems which would otherwise be stable to fingering (thermohaline) convection.

  17. Aluminum and gallium nuclei as microscopic probes for pulsed electron-nuclear double resonance diagnostics of electric-field gradient and spin density in garnet ceramics doped with paramagnetic ions

    Science.gov (United States)

    Uspenskaya, Yu. A.; Mamin, G. V.; Babunts, R. A.; Badalyan, A. G.; Edinach, E. V.; Asatryan, H. R.; Romanov, N. G.; Orlinskii, S. B.; Khanin, V. M.; Wieczorek, H.; Ronda, C.; Baranov, P. G.

    2018-03-01

    The presence of aluminum and gallium isotopes with large nuclear magnetic and quadrupole moments in the nearest environment of impurity ions Mn2+ and Ce3+ in garnets made it possible to use hyperfine and quadrupole interactions with these ions to determine the spatial distribution of the unpaired electron and the gradient of the electric field at the sites of aluminum and gallium in the garnet lattice. High-frequency (94 GHz) electron spin echo detected electron paramagnetic resonance and electron-nuclear double resonance measurements have been performed. Large difference in the electric field gradient and quadrupole splitting at octahedral and tetrahedral sites allowed identifying the positions of aluminum and gallium ions in the garnet lattice and proving that gallium first fills tetrahedral positions in mixed aluminum-gallium garnets. This should be taken into account in the development of garnet-based scintillators and lasers. It is shown that the electric field gradient at aluminum nuclei near Mn2+ possessing an excess negative charge in the garnet lattice is ca. 2.5 times larger than on aluminum nuclei near Ce3+.

  18. Three gradients and the perception of flat and curved surfaces.

    Science.gov (United States)

    Cutting, J E; Millard, R T

    1984-06-01

    Researchers of visual perception have long been interested in the perceived slant of a surface and in the gradients that purportedly specify it. Slant is the angle between the line of sight and the tangent to the planar surface at any point, also called the surface normal. Gradients are the sources of information that grade, or change, with visual angle as one looks from one's feet upward to the horizon. The present article explores three gradients--perspective, compression, and density--and the phenomenal impression of flat and curved surfaces. The perspective gradient is measured at right angles to the axis of tilt at any point in the optic array; that is, when looking down a hallway at the tiles of a floor receding in the distance, perspective is measured by the x-axis width of each tile projected on the image plane orthogonal to the line of sight. The compression gradient is the ratio of y/x axis measures on the projected plane. The density gradient is measured by the number of tiles per unit solid visual angle. For flat surfaces and many others, perspective and compression gradients decrease with distance, and the density gradient increases. We discuss the manner in which these gradients change for various types of surfaces. Each gradient is founded on a different assumption about textures on the surfaces around us. In Experiment 1, viewers assessed the three-dimensional character of projections of flat and curved surfaces receding in the distance. They made pairwise judgments of preference and of dissimilarity among eight stimuli in each of four sets. The presence of each gradient was manipulated orthogonally such that each stimulus had zero, one, two, or three gradients appropriate for either a flat surface or a curved surface. Judgments were made were made for surfaces with both regularly shaped and irregularly shaped textures scattered on them. All viewer assessment were then scaled in one dimension. Multiple correlation and regression on the scale values

  19. Generalized Gradient Approximation Made Simple

    International Nuclear Information System (INIS)

    Perdew, J.P.; Burke, K.; Ernzerhof, M.

    1996-01-01

    Generalized gradient approximations (GGA close-quote s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. copyright 1996 The American Physical Society

  20. Generation of tunable and pulsatile concentration gradients via microfluidic network

    KAUST Repository

    Zhou, Bingpu

    2014-06-04

    We demonstrate a compact Polydimethylsiloxane microfluidic chip which can quickly generate ten different chemical concentrations simultaneously. The concentration magnitude of each branch can be flexibly regulated based on the flow rate ratios of the two injecting streams. The temporal/pulsatile concentration gradients are achieved by integrating on-chip pneumatic actuated valves controlled by the external signals. The temporal concentration gradients can also be tuned precisely by varying applied frequency and duty cycle of the trigger signal. It is believed that such microdevice will be potentially used for some application areas of producing stable chemical gradients as well as allowing fast, pulsatile gradient transformation in seconds.

  1. Pancreatic islet isolation by mechanical-enzymatic separation, stationary collagenase digestion and dextran discontinuous density gradient purification: experimental study in dogs Isolamento das ilhotas pancreáticas pela separação mecânica-enzimática digestão estacionária com colagenase e purificação com gradiente de densidade descontínua de dextran: estudo experimental em cães

    Directory of Open Access Journals (Sweden)

    Jaques Waisberg

    2002-04-01

    Full Text Available The prospects for allotransplantation of pancreatic islets in man depend on the development of methods that provide sufficient quantities of pancreatic islets from a single donor, which are capable, when transplanted, of achieve the normalization of carbohydrate metabolism. Objective: Evaluate the efficacy of the isolation of Langerhans islets from dogs, by means of mechanical-enzymatic separation technique with stationary digestion using collagenase, and purification with a discontinuous dextran density gradient. Methods: The counting of islet numbers and evaluation of their sizes was accomplished by staining with diphenylthiocarbazone and using stereoscopic microscopes equipped with eyepiece reticule for the measurement of average diameters of stained islets. Results: The results disclosed that the average number of islets isolated was 81032.20 ± 24736.79 and the average number of islets isolated per kg of body weight was 6938.70 ± 1392.43. The average number of islets isolated per kg of body weight showed significant correlation with body weight and weight of the pancreas resected. Conclusion: The number of islets isolated, of a single donor, by mechanical-enzymatic separation, stationary collagenase digestion and discontinuous dextran density gradient purification can be sufficient to success of pancreatic islets transplant in dogs.A perspectiva do alotransplante de ilhotas pancreáticas no homem está na dependência do desenvolvimento de métodos que propiciem quantidades suficientes de ilhotas pancreáticas, originadas de doador único, capazes de, quando transplantadas, levarem à normalização do metabolismo dos hidratos de carbono. Objetivo: Avaliar, em cães, a eficácia do isolamento das ilhotas de Langerhans por meio da técnica de separação mecânica-enzimática, digestão estacionária com colagenase e purificação pelo gradiente de densidade descontínua de dextran. Métodos: A contagem do número e avaliação do tamanho

  2. Stereo vision with distance and gradient recognition

    Science.gov (United States)

    Kim, Soo-Hyun; Kang, Suk-Bum; Yang, Tae-Kyu

    2007-12-01

    Robot vision technology is needed for the stable walking, object recognition and the movement to the target spot. By some sensors which use infrared rays and ultrasonic, robot can overcome the urgent state or dangerous time. But stereo vision of three dimensional space would make robot have powerful artificial intelligence. In this paper we consider about the stereo vision for stable and correct movement of a biped robot. When a robot confront with an inclination plane or steps, particular algorithms are needed to go on without failure. This study developed the recognition algorithm of distance and gradient of environment by stereo matching process.

  3. Subduction zones seen by GOCE gravity gradients

    DEFF Research Database (Denmark)

    Švarc, Mario; Herceg, Matija; Cammarano, Fabio

    . Few pattern recognition methods were tested on all 6 gravity gradient tensor components represented as global scale maps with resolution of 100km (corresponds to the resolution of the GOCE satellite data). By adjusting pattern recognition methods’ features and optimizing various input patterns...... and used as starting point for analysis based on image processing. On obtained maps, locations of known subduction zones were represented with characteristic elongated patterns and cross-sections. Cross sections of well-known subduction zones were used as input patterns for pattern recognition method......, the best method was applied. That is a combination of methods based on SURF (Speeded Up Robust Features) and MSER (Maximally Stable Extremal Regions) algorithms provided in MATLAB’s Computer Vision System Toolbox. Based on 6 gravity gradient components, the global gradient anomaly maps were produced...

  4. Inversion gradients for acoustic VTI wavefield tomography

    KAUST Repository

    Li, Vladimir

    2017-03-21

    Wavefield tomography can handle complex subsurface geology better than ray-based techniques and, ultimately, provide a higher resolution. Here, we implement forward and adjoint wavefield extrapolation for VTI (transversely isotropic with a vertical symmetry axis) media using a generalized pseudospectral operator based on a separable approximation for the P-wave dispersion relation. This operator is employed to derive the gradients of the differential semblance optimization (DSO) and modified image-power objective functions. We also obtain the gradient expressions for a data-domain objective function that can more easily incorporate borehole information necessary for stable VTI velocity analysis. These gradients are similar to the ones obtained with a space-time finite-difference (FD) scheme for a system of coupled wave equations but the pseudospectral method is not hampered by the imprint of the shear-wave artifact. Numerical examples also show the potential advantages of the modified image-power objective function in estimating the anellipticity parameter η.

  5. Travelling gradient thermocouple calibration

    International Nuclear Information System (INIS)

    Broomfield, G.H.

    1975-01-01

    A short discussion of the origins of the thermocouple EMF is used to re-introduce the idea that the Peltier and Thompson effects are indistinguishable from one another. Thermocouples may be viewed as devices which generate an EMF at junctions or as integrators of EMF's developed in thermal gradients. The thermal gradient view is considered the more appropriate, because of its better accord with theory and behaviour, the correct approach to calibration, and investigation of service effects is immediately obvious. Inhomogeneities arise in thermocouples during manufacture and in service. The results of travelling gradient measurements are used to show that such effects are revealed with a resolution which depends on the length of the gradient although they may be masked during simple immersion calibration. Proposed tests on thermocouples irradiated in a nuclear reactor are discussed

  6. Electron density analysis of 1-butyl-3-methylimidazolium chloride ionic liquid.

    Science.gov (United States)

    del Olmo, Lourdes; Morera-Boado, Cercis; López, Rafael; García de la Vega, José M

    2014-06-01

    An analysis of the electron density of different conformers of the 1-butyl-3-methylimidazolium chloride (bmimCl) ionic liquid by using DFT through the BVP86 density functional has been obtained within the framework of Bader's atom in molecules (AIM), localized orbital locator (LOL), natural bond orbital (NBO), and deformed atoms in molecules (DAM). We also present an analysis of the reduced density gradients that deliver the non-covalent interaction regions and allow to understand the nature of intermolecular interactions. The most polar conformer can be characterized as ionic by AIM, LOL, and DAM methods while the most stable and the least polar shows shared-type interactions. The NBO method allows to comprehend what causes the stabilization of the most stable conformer based on analysis of the second-order perturbative energy and the charge transferred among the natural orbitals involved in the interaction.

  7. Gradient Alloy for Optical Packaging

    Data.gov (United States)

    National Aeronautics and Space Administration — Advances in additive manufacturing, such as Laser Engineered Net Shaping (LENS), enables the fabrication of compositionally gradient microstructures, i.e. gradient...

  8. Stable Isotope Data

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Tissue samples (skin, bone, blood, muscle) are analyzed for stable carbon, stable nitrogen, and stable sulfur analysis. Many samples are used in their entirety for...

  9. Uniform gradient expansions

    Directory of Open Access Journals (Sweden)

    Massimo Giovannini

    2015-06-01

    Full Text Available Cosmological singularities are often discussed by means of a gradient expansion that can also describe, during a quasi-de Sitter phase, the progressive suppression of curvature inhomogeneities. While the inflationary event horizon is being formed the two mentioned regimes coexist and a uniform expansion can be conceived and applied to the evolution of spatial gradients across the protoinflationary boundary. It is argued that conventional arguments addressing the preinflationary initial conditions are necessary but generally not sufficient to guarantee a homogeneous onset of the conventional inflationary stage.

  10. Uniform gradient expansions

    CERN Document Server

    Giovannini, Massimo

    2015-01-01

    Cosmological singularities are often discussed by means of a gradient expansion that can also describe, during a quasi-de Sitter phase, the progressive suppression of curvature inhomogeneities. While the inflationary event horizon is being formed the two mentioned regimes coexist and a uniform expansion can be conceived and applied to the evolution of spatial gradients across the protoinflationary boundary. It is argued that conventional arguments addressing the preinflationary initial conditions are necessary but generally not sufficient to guarantee a homogeneous onset of the conventional inflationary stage.

  11. High gradient superconducting quadrupoles

    International Nuclear Information System (INIS)

    Lundy, R.A.; Brown, B.C.; Carson, J.A.; Fisk, H.E.; Hanft, R.H.; Mantsch, P.M.; McInturff, A.D.; Remsbottom, R.H.

    1987-07-01

    Prototype superconducting quadrupoles with a 5 cm aperture and gradient of 16 kG/cm have been built and tested as candidate magnets for the final focus at SLC. The magnets are made from NbTi Tevatron style cable with 10 inner and 14 outer turns per quadrant. Quench performance and multipole data are presented. Design and data for a low current, high gradient quadrupole, similar in cross section but wound with a cable consisting of five insulated conductors are also discussed

  12. Density games.

    Science.gov (United States)

    Novak, Sebastian; Chatterjee, Krishnendu; Nowak, Martin A

    2013-10-07

    The basic idea of evolutionary game theory is that payoff determines reproductive rate. Successful individuals have a higher payoff and produce more offspring. But in evolutionary and ecological situations there is not only reproductive rate but also carrying capacity. Individuals may differ in their exposure to density limiting effects. Here we explore an alternative approach to evolutionary game theory by assuming that the payoff from the game determines the carrying capacity of individual phenotypes. Successful strategies are less affected by density limitation (crowding) and reach higher equilibrium abundance. We demonstrate similarities and differences between our framework and the standard replicator equation. Our equation is defined on the positive orthant, instead of the simplex, but has the same equilibrium points as the replicator equation. Linear stability analysis produces the classical conditions for asymptotic stability of pure strategies, but the stability properties of internal equilibria can differ in the two frameworks. For example, in a two-strategy game with an internal equilibrium that is always stable under the replicator equation, the corresponding equilibrium can be unstable in the new framework resulting in a limit cycle. Copyright © 2013 The Authors. Published by Elsevier Ltd.. All rights reserved.

  13. Stable convergence and stable limit theorems

    CERN Document Server

    Häusler, Erich

    2015-01-01

    The authors present a concise but complete exposition of the mathematical theory of stable convergence and give various applications in different areas of probability theory and mathematical statistics to illustrate the usefulness of this concept. Stable convergence holds in many limit theorems of probability theory and statistics – such as the classical central limit theorem – which are usually formulated in terms of convergence in distribution. Originated by Alfred Rényi, the notion of stable convergence is stronger than the classical weak convergence of probability measures. A variety of methods is described which can be used to establish this stronger stable convergence in many limit theorems which were originally formulated only in terms of weak convergence. Naturally, these stronger limit theorems have new and stronger consequences which should not be missed by neglecting the notion of stable convergence. The presentation will be accessible to researchers and advanced students at the master's level...

  14. Spatial patterns of habitat distribution of Corvidae (the case of urban-rural gradient

    Directory of Open Access Journals (Sweden)

    А. A. Zimaroyeva

    2016-09-01

    was 2.4 birds/km2 and varied significantly in different settlements, although the fluctuation range was small (0.1–9.3 birds/km2. We registered an expansion in the breeding distribution of Eurasian Jays in recent years i.e. the birds began to nest in old urban neighborhoods and small central parks of large cities. However, the number of birds naturally decreased along the gradient of landscape transformation. The impact of urban-rural gradient on Eurasian Jay density was significant but the correlation was weak and negative. The density of this species was highest in small villages (4.9 birds/km2 and the lowest in medium-sized cities (1.5 birds/km2. The seasonal density of Jays varied significantly and the greatest value was registered in the post-breeding period. In urban areas the birds’ density was much higher in winter compared to the nesting period, and in villages we observed the reverse situation. The number of Eurasian Jays remained almost stable in all the settlements during the study period indicating the stability of the local populations. The average density of the Common Raven was 1.3 birds/km2 and the highest density was registered in small villages (2.2 birds/km2, the lowest – in the townships (small urban type settlements (0.6 birds/km2. The urban-rural gradient significantly affected the spatial distribution of Common Ravens, but we cannot claim an increase or decrease in their numbers along the gradient of urbanization, since the value of this indicator also depended on habitat conditions in each specific settlement. The spatial distribution of Common Ravens varied seasonally and the highest density was typical in winter due to food migrations towards human settlements.

  15. Velocity Gradient Power Functional for Brownian Dynamics

    Science.gov (United States)

    de las Heras, Daniel; Schmidt, Matthias

    2018-01-01

    We present an explicit and simple approximation for the superadiabatic excess (over ideal gas) free power functional, admitting the study of the nonequilibrium dynamics of overdamped Brownian many-body systems. The functional depends on the local velocity gradient and is systematically obtained from treating the microscopic stress distribution as a conjugate field. The resulting superadiabatic forces are beyond dynamical density functional theory and are of a viscous nature. Their high accuracy is demonstrated by comparison to simulation results.

  16. Gradient computation for VTI acoustic wavefield tomography

    KAUST Repository

    Li, Vladimir

    2016-09-06

    Wavefield tomography can handle complex subsurface geology better than ray-based techniques and, ultimately, provide a higher resolution. Here, we implement forward and adjoint wavefield extrapolation for VTI (transversely isotropic with a vertical symmetry axis) media using a pseudospectral operator that employes a separable approximation of the P-wave dispersion relation. This operator is employed to derive the gradients of the differential semblance optimization (DSO) and modified stack-power objective functions. We also obtain the gradient expressions for the data-domain objective function, which can incorporate borehole information necessary for stable VTI velocity analysis. These gradients are compared to the ones obtained with a space-time finite-difference (FD) scheme for a system of coupled wave equations. Whereas the kernels computed with the two wave-equation operators are similar, the pseudospectral method is not hampered by the imprint of the shear-wave artifact. Numerical examples also show that the modified stack-power objective function produces cleaner gradients than the more conventional DSO operator.

  17. Feldspar tunneling by Fungi along natural productivity gradients

    NARCIS (Netherlands)

    Hoffland, E.; Giesler, R.; Jongmans, A.G.; Breemen, van N.

    2003-01-01

    Recently, it was hypothesized that ectomycorrhizas hyphae are involved in mineral tunneling. We evaluated the role of ectomycorrhizas in mineral weathering and the ecosystem influx of basic cations by correlating mineral tunnel density to ectomycorrhizas density in two forest productivity gradients.

  18. Colloidal attraction induced by a temperature gradient.

    Science.gov (United States)

    Di Leonardo, R; Ianni, F; Ruocco, G

    2009-04-21

    Colloidal crystals are of extreme importance for applied research and for fundamental studies in statistical mechanics. Long-range attractive interactions, such as capillary forces, can drive the spontaneous assembly of such mesoscopic ordered structures. However, long-range attractive forces are very rare in the colloidal realm. Here we report a novel strong, long-ranged attraction induced by a thermal gradient in the presence of a wall. By switching the thermal gradient on and off, we can rapidly and reversibly form stable hexagonal 2D crystals. We show that the observed attraction is hydrodynamic in nature and arises from thermally induced slip flow on particle surfaces. We used optical tweezers to measure the force law directly and compare it to an analytical prediction based on Stokes flow driven by Marangoni-like forces.

  19. stableGP

    Data.gov (United States)

    National Aeronautics and Space Administration — The code in the stableGP package implements Gaussian process calculations using efficient and numerically stable algorithms. Description of the algorithms is in the...

  20. Temperature-gradient-induced

    Science.gov (United States)

    Park, Cheol; Glaser, Matt; Maclennan, Joe; Clark, Noel; Trittel, Torsten; Stannarius, Ralf

    Freely-suspended smectic films of sub-micrometer thickness and lateral extensions of several millimeters were used to study thermally driven migration and convection in the film plane. Film experiments were performed during the 6 minute microgravity phase of a TEXUS suborbital rocket flight (Texus 52, launched April 27, 2015). We have found an attraction of the smectic material towards the cold edge of the film in a temperature gradient, similar to the Soret effect. This process is reversed when this edge is heated up again. Thermal convection driven by two thermocontacts in the film is practically absent, even at temperature gradients up to 10 K/mm, with thermally driven convection only setting in when the hot post reaches the transition temperature to the nematic phase. The Observation and Analysis of Smectic Islands in Space (OASIS) flight hardware was launched on SpaceX-6 in April 2015 and experiments on smectic bubbles were carried out on the International Space Station using four different smectic A and C liquid crystal materials in separate sample chambers. We observed that smectic islands on the surface of the bubbles migrated towards the colder part of the bubble in a temperature gradient. This work was supported by NASA Grant No. NNX-13AQ81G, by the Soft Materials Research Center under NSF MRSEC Grants No. DMR-0820579 and No. DMR-1420736, and by DLR Grants 50WM1127 and 50WM1430.

  1. Density structures inside the plasmasphere: Cluster observations

    DEFF Research Database (Denmark)

    Darrouzet, F.; Decreau, P.M.E.; De Keyser, J.

    2004-01-01

    on the plasmasphere crossing on I I April 2002, during which Cluster observed several density irregularities inside the plasmasphere, as well as a plasmaspheric plume. We derive the density gradient vectors from simultaneous density measurements by the four spacecraft. We also determine the normal velocity...

  2. Stable atomic hydrogen: Polarized atomic beam source

    International Nuclear Information System (INIS)

    Niinikoski, T.O.; Penttilae, S.; Rieubland, J.M.; Rijllart, A.

    1984-01-01

    We have carried out experiments with stable atomic hydrogen with a view to possible applications in polarized targets or polarized atomic beam sources. Recent results from the stabilization apparatus are described. The first stable atomic hydrogen beam source based on the microwave extraction method (which is being tested ) is presented. The effect of the stabilized hydrogen gas density on the properties of the source is discussed. (orig.)

  3. The Galactic metallicity gradient

    Science.gov (United States)

    Rolleston, W. R. J.; Smartt, S. J.; Dufton, P. L.; Ryans, R. S. I.

    2000-11-01

    We have previously published intermediate to high resolution spectroscopic observations of approximately 80 early B-type main-sequence stars situated in 19 Galactic open clusters/associations with Galactocentric distances distributed over 6Twarog et al. \\cite{twa97}). However, there is no evidence to suggest that our data would be better fitted with a two-zone model. Moreover, we observe a N/O gradient of -0.04+/-0.02 dex kpc-1 which is consistent with that found for other spiral galaxies (Vila-Costas & Edmunds \\cite{vil93}).

  4. [Translaminar Gradient and Glaucoma].

    Science.gov (United States)

    Čmelo, J

    2017-01-01

    The cribriform plate is a threshold of the intraocular pressure (VOT) and of the intracranial pressure (IKT). The difference between the VOT and IKT is referred to as translaminar gradient (TLG). The goal was to evaluate the Glaucoma progression (visual field, fundus examination, HRT) with / without topical anti-glaucomatous therapy) in relation to the TLG. the significance of TLG has been studied in two groups. I. Group: 57 patients diagnosed and treatment of Primary Open-Angle Glaucoma (PGOU), 10 patients with Ocular hypertension (OH), 7 patients with Normal-Tension Glaucoma (NTG), and 75 healthy without glaucoma. The examinations of TLG were carried out once and retrospectively. In II. group there were prospectively studied 14 patients with OH and 24 patients with newly detected PGOU without local therapy. The examinations were performed 4 times at intervals of 10 to 11 months. All tests included a basic eye examination, ORA tonometry, HRT examination, gonioscopy, Color Doppler sonography of blood vessels of the eye and orbit. Venous pulsation pressure (VPT) has been recorded by the Ophthalmodynamometer Meditron (D-ODM). In case of spontaneous retinal venous pulsation, VPT was considered as the same pressure as the VOT. The TLG was calculated with formula of Querfurth: ICT = 0.29 + 0.74 (VOT / PI (AO)). [PI(AO) - Pulsatility index of the Ophthalmic artery (AO)]. I. group: TLG was in the control group without Glaucoma: 12.2 ± 2.0 torr. The NTG group: 9.0 ± 1.70 mm Hg. PGOU: 11.1 ± 1.91 mm Hg. OH: 12.6 ± 0.85 mm Hg. IKT alone does not show a significant relationship to the presence of glaucoma, ocular hypertension. II. Group: The average TLG in Ocular Hypertension (14 patients) has been 3.8 ± 1.2 torr. 2 patients (OH) had TLG 10 torr. and 15 torr. After 4 years in one of them (TLG = 15 torr.) there was recorded Glaucoma progression. In the PGOU group before antiglaucoma therapy, TLG was 15.0 ± 4.8 torr for all patients. After setting up local anti

  5. Temperature Versus Salinity Gradients Below the Ocean Mixed Layer

    Science.gov (United States)

    2012-05-03

    13] The effects of density compensated gradients below the mixed layer are not limited to ocean circulation and cli- mate. Since sound speed and...The Impact of Spice on Ocean circulation . The second is the 6.2 program element 62435N Full Column Mixing for Numerical Ocean Models. The authors would...and F. Paparella (2003), Compensation and alignment of thermohaline gradients in the ocean mixed layer, J. Phys. Oceanogr., 33, 2214–2223, doi

  6. Trace element concentrations in soils along urbanization gradients in the city of Wien, Austria.

    Science.gov (United States)

    Simon, Edina; Vidic, Andreas; Braun, Mihály; Fábián, István; Tóthmérész, Béla

    2013-02-01

    Urban soil is an important component of urban ecosystems. This study focuses on heavy metal contamination in soils of Wien (Austria) and results are compared to those for a few large European cities. We analysed the elemental contents of 96 samples of topsoil from urban, suburban and rural areas in Wien along a dynamic (floodplain forest) and a stable (oak-hornbeam forest) urbanization gradient. The following elements were quantified using ICP-OES technique: Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Pb, P, S and Zn. For heavy metals PI (pollution index) values were used to assess the level of pollution. The PI values indicated high level of pollution by Pb in the suburban and rural area of stable gradient and in the urban area of dynamic gradient; moderate level of pollution was indicated for Cd in the urban area of stable gradient. The level of pollution was moderate for Co in the suburban and rural area of the stable gradient, and for Cu in suburban area of stable gradient, and urban area of dynamic gradient. The pollution level of Zn was moderate in all areas. Urban soils, especially in urban parks and green areas may have a direct influence on human health. Thus, the elemental analysis of soil samples is one of the best ways to study the effects of urbanization. Our results indicated that the heavy metal contamination was higher in Wien than in a few large European cities.

  7. Color Gradient in the King Type Globular Cluster NGC 7089

    Directory of Open Access Journals (Sweden)

    Young-Jong Sohn

    1999-12-01

    Full Text Available We use BV CCD images to investigate the reality of the color gradient within a King type globular cluster NGC 7089. Surface photometry shows that there is a strong radial color gradient in the central region of the cluster in the sense of bluer center with the amplitude of -0.39 +/- 0.07 mag/arcsec2 in (B - V. In the outer region of the cluster, however, the radial color gradient shows a reverse case, i.e., redder toward the center. (B - V color profile which was derived from resolved stars in VGC 7089 field also shows a significant color gradient in the central region of the clusters, indicating that lights from the combination of red giant stars and blue horizontal branch stars cause the radial color gradient. Color gradient of the outer region of NGC 7089 may be due to the unresolved background of the cluster. Similar color gradients in the central area of clusters have been previously observed exserved exclusively in highly concentrated systems classified as post core collapse clusters. We caution, however, to confirm the reality of the color gradient from resolved stars, we need more accurate imaging data of the cluster with exceptional seeing condition because the effect of completeness correlates with local density of stars.

  8. Generalized conjugate gradient squared

    Energy Technology Data Exchange (ETDEWEB)

    Fokkema, D.R.; Sleijpen, G.L.G. [Utrecht Univ. (Netherlands)

    1994-12-31

    In order to solve non-symmetric linear systems of equations, the Conjugate Gradient Squared (CGS) is a well-known and widely used iterative method. In practice the method converges fast, often twice as fast as the Bi-Conjugate Gradient method. This is what you may expect, since CGS uses the square of the BiCG polynomial. However, CGS may suffer from its erratic convergence behavior. The method may diverge or the approximate solution may be inaccurate. BiCGSTAB uses the BiCG polynomial and a product of linear factors in an attempt to smoothen the convergence. In many cases, this has proven to be very effective. Unfortunately, the convergence of BiCGSTAB may stall when a linear factor (nearly) degenerates. BiCGstab({ell}) is designed to overcome this degeneration of linear factors. It generalizes BiCGSTAB and uses both the BiCG polynomial and a product of higher order factors. Still, CGS may converge faster than BiCGSTAB or BiCGstab({ell}). So instead of using a product of linear or higher order factors, it may be worthwhile to look for other polynomials. Since the BiCG polynomial is based on a three term recursion, a natural choice would be a polynomial based on another three term recursion. Possibly, a suitable choice of recursion coefficients would result in method that converges faster or as fast as CGS, but less erratic. It turns out that an algorithm for such a method can easily be formulated. One particular choice for the recursion coefficients leads to CGS. Therefore one could call this algorithm generalized CGS. Another choice for the recursion coefficients leads to BiCGSTAB. It is therefore possible to mix linear factors and some polynomial based on a three term recursion. This way one may get the best of both worlds. The authors will report on their findings.

  9. Stable isotopes labelled compounds

    International Nuclear Information System (INIS)

    1982-09-01

    The catalogue on stable isotopes labelled compounds offers deuterium, nitrogen-15, and multiply labelled compounds. It includes: (1) conditions of sale and delivery, (2) the application of stable isotopes, (3) technical information, (4) product specifications, and (5) the complete delivery programme

  10. Stable Boundary Layer Issues

    NARCIS (Netherlands)

    Steeneveld, G.J.

    2012-01-01

    Understanding and prediction of the stable atmospheric boundary layer is a challenging task. Many physical processes are relevant in the stable boundary layer, i.e. turbulence, radiation, land surface coupling, orographic turbulent and gravity wave drag, and land surface heterogeneity. The

  11. Evolutionary Stable Strategy

    Indian Academy of Sciences (India)

    IAS Admin

    After Maynard-Smith and Price [1] mathematically derived why a given behaviour or strategy was adopted by a certain proportion of the population at a given time, it was shown that a strategy which is currently stable in a population need not be stable in evolutionary time (across generations). Additionally it was sug-.

  12. Gradient Boosting Machines, A Tutorial

    Directory of Open Access Journals (Sweden)

    Alexey eNatekin

    2013-12-01

    Full Text Available Gradient boosting machines are a family of powerful machine-learning techniques that have shown considerable success in a wide range of practical applications. They are highly customizable to the particular needs of the application, like being learned with respect to different loss functions. This article gives a tutorial introduction into the methodology of gradient boosting methods. A theoretical information is complemented with many descriptive examples and illustrations which cover all the stages of the gradient boosting model design. Considerations on handling the model complexity are discussed. A set of practical examples of gradient boosting applications are presented and comprehensively analyzed.

  13. Theory of resistivity-gradient-driven turbulence

    Energy Technology Data Exchange (ETDEWEB)

    Garcia, L.; Diamond, P.H.; Carreras, B.A.; Callen, J.D.

    1985-07-01

    A theory of the nonlinear evolution and saturation of resistivity driven turbulence, which evolves from linear rippling instabilities, is presented. The nonlinear saturation mechanism is identified both analytically and numerically. Saturation occurs when the turbulent diffusion of the resistivity is large enough so that dissipation due to parallel electron thermal conduction balances the nonlinearly modified resistivity gradient driving term. The levels of potential, resistivity, and density fluctuations at saturation are calculated. A combination of computational modeling and analytic treatment is used in this investigation.

  14. Normal modified stable processes

    DEFF Research Database (Denmark)

    Barndorff-Nielsen, Ole Eiler; Shephard, N.

    2002-01-01

    This paper discusses two classes of distributions, and stochastic processes derived from them: modified stable (MS) laws and normal modified stable (NMS) laws. This extends corresponding results for the generalised inverse Gaussian (GIG) and generalised hyperbolic (GH) or normal generalised inverse...... Gaussian (NGIG) laws. The wider framework thus established provides, in particular, for added flexibility in the modelling of the dynamics of financial time series, of importance especially as regards OU based stochastic volatility models for equities. In the special case of the tempered stable OU process...

  15. Applications of stable isotopes

    International Nuclear Information System (INIS)

    Letolle, R.; Mariotti, A.; Bariac, T.

    1991-06-01

    This report reviews the historical background and the properties of stable isotopes, the methods used for their measurement (mass spectrometry and others), the present technics for isotope enrichment and separation, and at last the various present and foreseeable application (in nuclear energy, physical and chemical research, materials industry and research; tracing in industrial, medical and agronomical tests; the use of natural isotope variations for environmental studies, agronomy, natural resources appraising: water, minerals, energy). Some new possibilities in the use of stable isotope are offered. A last chapter gives the present state and forecast development of stable isotope uses in France and Europe

  16. Denaturing gradient gel electrophoresis

    International Nuclear Information System (INIS)

    Kocherginskaya, S.A.; Cann, I.K.O.; Mackie, R.I.

    2005-01-01

    It is worthwhile considering that only some 30 species make up the bulk of the bacterial population in human faeces at any one time based on the classical cultivation-based approach. The situation in the rumen is similar. Thus, it is practical to focus on specific groups of interest within the complex community. These may be the predominant or the most active species, specific physiological groups or readily identifiable (genetic) clusters of phylogenetically related organisms. Several 16S rDNA fingerprinting techniques can be invaluable for selecting and monitoring sequences or phylogenetic groups of interest and are described below. Over the past few decades, considerable attention was focussed on the identification of pure cultures of microbes on the basis of genetic polymorphisms of DNA encoding rRNA such as ribotyping, amplified fragment length polymorphism and randomly amplified polymorphic DNA. However, many of these methods require prior cultivation and are less suitable for use in analysis of complex mixed populations although important in describing cultivated microbial diversity in molecular terms. Much less attention was given to molecular characterization of complex communities. In particular, research into diversity and community structure over time has been revolutionized by the advent of molecular fingerprinting techniques for complex communities. Denaturing or temperature gradient gel electrophoresis (DGGE/TGGE) methods have been successfully applied to the analysis of human, pig, cattle, dog and rodent intestinal populations

  17. Multishot echo-planar MREIT for fast imaging of conductivity, current density, and electric field distributions.

    Science.gov (United States)

    Chauhan, Munish; Vidya Shankar, Rohini; Ashok Kumar, Neeta; Kodibagkar, Vikram D; Sadleir, Rosalind

    2018-01-01

    Magnetic resonance electrical impedance tomography (MREIT) sequences typically use conventional spin or gradient echo-based acquisition methods for reconstruction of conductivity and current density maps. Use of MREIT in functional and electroporation studies requires higher temporal resolution and faster sequences. Here, single and multishot echo planar imaging (EPI) based MREIT sequences were evaluated to see whether high-quality MREIT phase data could be obtained for rapid reconstruction of current density, conductivity, and electric fields. A gel phantom with an insulating inclusion was used as a test object. Ghost artifact, geometric distortion, and MREIT correction algorithms were applied to the data. The EPI-MREIT-derived phase-projected current density and conductivity images were compared with simulations and spin-echo images as a function of EPI shot number. Good agreement among measures in simulated, spin echo, and EPI data was achieved. Current density errors were stable and below 9% as the shot number decreased from 64 to 2, but increased for single-shot images. Conductivity reconstruction relative contrast ratios were stable as the shot number decreased. The derived electric fields also agreed with the simulated data. The EPI methods can be combined successfully with MREIT reconstruction algorithms to achieve fast imaging of current density, conductivity, and electric field. Magn Reson Med 79:71-82, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  18. Characterization of gradient control systems

    NARCIS (Netherlands)

    Cortés, Jorge; van der Schaft, Arjan; Crouch, Peter E.

    2005-01-01

    Given a general nonlinear affine control system with outputs and a torsion-free affine connection defined on its state space, we investigate the gradient realization problem: we give necessary and sufficient conditions under which the control system can be written as a gradient control system

  19. Sobolev gradients and differential equations

    CERN Document Server

    Neuberger, J W

    2010-01-01

    A Sobolev gradient of a real-valued functional on a Hilbert space is a gradient of that functional taken relative to an underlying Sobolev norm. This book shows how descent methods using such gradients allow a unified treatment of a wide variety of problems in differential equations. For discrete versions of partial differential equations, corresponding Sobolev gradients are seen to be vastly more efficient than ordinary gradients. In fact, descent methods with these gradients generally scale linearly with the number of grid points, in sharp contrast with the use of ordinary gradients. Aside from the first edition of this work, this is the only known account of Sobolev gradients in book form. Most of the applications in this book have emerged since the first edition was published some twelve years ago. What remains of the first edition has been extensively revised. There are a number of plots of results from calculations and a sample MatLab code is included for a simple problem. Those working through a fair p...

  20. Road density

    Data.gov (United States)

    U.S. Environmental Protection Agency — Road density is generally highly correlated with amount of developed land cover. High road densities usually indicate high levels of ecological disturbance. More...

  1. The geomagnetic field gradient tensor

    DEFF Research Database (Denmark)

    Kotsiaros, Stavros; Olsen, Nils

    2012-01-01

    We develop the general mathematical basis for space magnetic gradiometry in spherical coordinates. The magnetic gradient tensor is a second rank tensor consisting of 3 × 3 = 9 spatial derivatives. Since the geomagnetic field vector B is always solenoidal (∇ · B = 0) there are only eight independent...... tensor elements. Furthermore, in current free regions the magnetic gradient tensor becomes symmetric, further reducing the number of independent elements to five. In that case B is a Laplacian potential field and the gradient tensor can be expressed in series of spherical harmonics. We present properties...... of the magnetic gradient tensor and provide explicit expressions of its elements in terms of spherical harmonics. Finally we discuss the benefit of using gradient measurements for exploring the Earth’s magnetic field from space, in particular the advantage of the various tensor elements for a better determination...

  2. Analysing Stable Time Series

    National Research Council Canada - National Science Library

    Adler, Robert

    1997-01-01

    We describe how to take a stable, ARMA, time series through the various stages of model identification, parameter estimation, and diagnostic checking, and accompany the discussion with a goodly number...

  3. Lung density

    DEFF Research Database (Denmark)

    Garnett, E S; Webber, C E; Coates, G

    1977-01-01

    The density of a defined volume of the human lung can be measured in vivo by a new noninvasive technique. A beam of gamma-rays is directed at the lung and, by measuring the scattered gamma-rays, lung density is calculated. The density in the lower lobe of the right lung in normal man during quiet...

  4. Gradient zone boundary control in salt gradient solar ponds

    Energy Technology Data Exchange (ETDEWEB)

    Hull, John R. (Downers Grove, IL)

    1984-01-01

    A method and apparatus for suppressing zone boundary migration in a salt gradient solar pond includes extending perforated membranes across the pond at the boundaries, between the convective and non-convective zones, the perforations being small enough in size to prevent individual turbulence disturbances from penetrating the hole, but being large enough to allow easy molecular diffusion of salt thereby preventing the formation of convective zones in the gradient layer. The total area of the perforations is a sizable fraction of the membrane area to allow sufficient salt diffusion while preventing turbulent entrainment into the gradient zone.

  5. Multiconfiguration Pair-Density Functional Theory.

    Science.gov (United States)

    Li Manni, Giovanni; Carlson, Rebecca K; Luo, Sijie; Ma, Dongxia; Olsen, Jeppe; Truhlar, Donald G; Gagliardi, Laura

    2014-09-09

    We present a new theoretical framework, called Multiconfiguration Pair-Density Functional Theory (MC-PDFT), which combines multiconfigurational wave functions with a generalization of density functional theory (DFT). A multiconfigurational self-consistent-field (MCSCF) wave function with correct spin and space symmetry is used to compute the total electronic density, its gradient, the on-top pair density, and the kinetic and Coulomb contributions to the total electronic energy. We then use a functional of the total density, its gradient, and the on-top pair density to calculate the remaining part of the energy, which we call the on-top-density-functional energy in contrast to the exchange-correlation energy of Kohn-Sham DFT. Because the on-top pair density is an element of the two-particle density matrix, this goes beyond the Hohenberg-Kohn theorem that refers only to the one-particle density. To illustrate the theory, we obtain first approximations to the required new type of density functionals by translating conventional density functionals of the spin densities using a simple prescription, and we perform post-SCF density functional calculations using the total density, density gradient, and on-top pair density from the MCSCF calculations. Double counting of dynamic correlation or exchange does not occur because the MCSCF energy is not used. The theory is illustrated by applications to the bond energies and potential energy curves of H2, N2, F2, CaO, Cr2, and NiCl and the electronic excitation energies of Be, C, N, N(+), O, O(+), Sc(+), Mn, Co, Mo, Ru, N2, HCHO, C4H6, c-C5H6, and pyrazine. The method presented has a computational cost and scaling similar to MCSCF, but a quantitative accuracy, even with the present first approximations to the new types of density functionals, that is comparable to much more expensive multireference perturbation theory methods.

  6. Earthworm communities along an elevation gradient in Northeastern Puerto Rico.

    Science.gov (United States)

    Grizelle Gonzalez; Emerita Garcia; Veronica Cruz; Sonia Borges; Marcela Zalamea; Maria M. Rivera

    2007-01-01

    In this study, we describe earthworm communities along an elevation gradient of eight forest types in Northeastern Puerto Rico, and determine whether their abundance, biomass and/or diversity is related to climatic, soil physical/chemical and/or biotic characteristics. We found that the density, biomass, and diversity of worms varied significantly among forest types....

  7. Growth and deformation structure of gradient and layer-gradient Ti-Al-Si-Cu-N coatings

    Energy Technology Data Exchange (ETDEWEB)

    Ovchinnikov, Stanislav V., E-mail: ovm@spti.tsu.ru; Pinzhin, Yurii P., E-mail: pinzhin@phys.tsu.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); Korotaev, Alexandr D., E-mail: korotaev@phys.tsu.ru [National Research Tomsk State University, Tomsk, 634050 (Russian Federation)

    2014-11-14

    The features of the growth structure and modification of gradient and layer-gradient Ti-Al-Si-Cu-N coatings in the areas of deformation and fracture during indentation and scratch testing were investigated using transmission and scanning electron microscopy methods. The influence of the concentration of alloying elements and displacement potential in the substrate on the secondary sputtering, phase composition and the level of combined torsion and bending of the crystal lattice of doped TiN were determined. It was found out that the size of the crystals in deformation location bands grows with deformation of gradient nanocrystal coatings. The article shows that layer-gradient coatings combining submicrocrystalline and nanocrystalline structures have the increased plasticity and fracture toughness due to enhanced density of interfaces and formation of the soft metal phase (Cu) in the surface layer.

  8. Growth and deformation structure of gradient and layer-gradient Ti-Al-Si-Cu-N coatings

    International Nuclear Information System (INIS)

    Ovchinnikov, Stanislav V.; Pinzhin, Yurii P.; Korotaev, Alexandr D.

    2014-01-01

    The features of the growth structure and modification of gradient and layer-gradient Ti-Al-Si-Cu-N coatings in the areas of deformation and fracture during indentation and scratch testing were investigated using transmission and scanning electron microscopy methods. The influence of the concentration of alloying elements and displacement potential in the substrate on the secondary sputtering, phase composition and the level of combined torsion and bending of the crystal lattice of doped TiN were determined. It was found out that the size of the crystals in deformation location bands grows with deformation of gradient nanocrystal coatings. The article shows that layer-gradient coatings combining submicrocrystalline and nanocrystalline structures have the increased plasticity and fracture toughness due to enhanced density of interfaces and formation of the soft metal phase (Cu) in the surface layer

  9. Abundance gradients in low surface brightness spirals: clues on the origin of common gradients in galactic discs

    Science.gov (United States)

    Bresolin, F.; Kennicutt, R. C.

    2015-12-01

    We acquired spectra of 141 H II regions in 10 late-type low surface brightness galaxies (LSBGs). The analysis of the chemical abundances obtained from the nebular emission lines shows that metallicity gradients are a common feature of LSBGs, contrary to previous claims concerning the absence of such gradients in this class of galaxies. The average slope, when expressed in units of the isophotal radius, is found to be significantly shallower in comparison to galaxies of high surface brightness. This result can be attributed to the reduced surface brightness range measured across their discs, when combined with a universal surface mass density-metallicity relation. With a similar argument we explain the common abundance gradient observed in high surface brightness galaxy (HSBG) discs and its approximate dispersion. This conclusion is reinforced by our result that LSBGs share the same common abundance gradient with HSBGs, when the slope is expressed in terms of the exponential disc scalelength.

  10. Strain gradient crystal plasticity: A continuum mechanics approach to modeling micro-structural evolution

    DEFF Research Database (Denmark)

    El-Naaman, Salim Abdallah; Nielsen, Kim Lau; Niordson, Christian Frithiof

    2015-01-01

    In agreement with dislocation theory, recent experiments show, both quantitatively and qualitatively, how geometrically necessary dislocations (GNDs) distribute in dislocation wall and cell structures. Hence, GND density fields are highly localized with large gradients and discontinuities occurri....... A phenomenological back stress formulation is proposed, through which the effect of the GND gradient exponent can be studied. It is shown that this model can lead to more localized GND distributions.......In agreement with dislocation theory, recent experiments show, both quantitatively and qualitatively, how geometrically necessary dislocations (GNDs) distribute in dislocation wall and cell structures. Hence, GND density fields are highly localized with large gradients and discontinuities occurring...... between the cells. This behavior is not typical for strain gradient crystal plasticity models. The present study employs a higher order extension of conventional crystal plasticity theory in which the viscous slip rate is influenced by the gradients of GND densities through a back stress...

  11. Effect of composition gradient on magnetothermal instability modified by shear and rotation

    Science.gov (United States)

    Gupta, Himanshu; Chaudhuri, Anya; Sadhukhan, Shubhadeep; Chakraborty, Sagar

    2018-02-01

    We model the intracluster medium as a weakly collisional plasma that is a binary mixture of the hydrogen and the helium ions, along with free electrons. When, owing to the helium sedimentation, the gradient of the mean-molecular weight (or equivalently, composition or helium ions' concentration) of the plasma is not negligible, it can have appreciable influence on the stability criteria of the thermal convective instabilities, e.g. the heat-flux-buoyancy instability and the magnetothermal instability (MTI). These instabilities are consequences of the anisotropic heat conduction occurring preferentially along the magnetic field lines. In this paper, without ignoring the magnetic tension, we first present the mathematical criterion for the onset of composition gradient modified MTI. Subsequently, we relax the commonly adopted equilibrium state in which the plasma is at rest, and assume that the plasma is in a sheared state which may be due to differential rotation. We discuss how the concentration gradient affects the coupling between the Kelvin-Helmholtz instability and the MTI in rendering the plasma unstable or stable. We derive exact stability criterion by working with the sharp boundary case in which the physical variables - temperature, mean-molecular weight, density and magnetic field - change discontinuously from one constant value to another on crossing the boundary. Finally, we perform the linear stability analysis for the case of the differentially rotating plasma that is thermally and compositionally stratified as well. By assuming axisymmetric perturbations, we find the corresponding dispersion relation and the explicit mathematical expression determining the onset of the modified MTI.

  12. Thermoelectric properties of high electron concentration materials under large temperature gradients

    International Nuclear Information System (INIS)

    Bulat, L.P.; Stefansky, V.A.

    1994-01-01

    Theoretical methods of investigating of transport properties in solids under large temperature gradients are grounded. The nonlinear and non-local expressions for current density and heat flow are obtained with degenerated of current carriers gas. A number of new effects with large temperature gradients have been tested. Use of large temperature gradients leads to the increasing of the thermoelectric figure of merit. copyright 1995 American Institute of Physics

  13. Leaf water stable isotopes and water transport outside the xylem.

    Science.gov (United States)

    Barbour, M M; Farquhar, G D; Buckley, T N

    2017-06-01

    How water moves through leaves, and where the phase change from liquid to vapour occurs within leaves, remain largely mysterious. Some time ago, we suggested that the stable isotope composition of leaf water may contain information on transport pathways beyond the xylem, through differences in the development of gradients in enrichment within the various pathways. Subsequent testing of this suggestion provided ambiguous results and even questioned the existence of gradients in enrichment within the mesophyll. In this review, we bring together recent theoretical developments in understanding leaf water transport pathways and stable isotope theory to map a path for future work into understanding pathways of water transport and leaf water stable isotope composition. We emphasize the need for a spatially, anatomically and isotopically explicit model of leaf water transport. © 2016 John Wiley & Sons Ltd.

  14. Calcium stable isotope geochemistry

    Energy Technology Data Exchange (ETDEWEB)

    Gausonne, Nikolaus [Muenster Univ. (Germany). Inst. fuer Mineralogie; Schmitt, Anne-Desiree [Strasbourg Univ. (France). LHyGeS/EOST; Heuser, Alexander [Bonn Univ. (Germany). Steinmann-Inst. fuer Geologie, Mineralogie und Palaeontologie; Wombacher, Frank [Koeln Univ. (Germany). Inst. fuer Geologie und Mineralogie; Dietzel, Martin [Technische Univ. Graz (Austria). Inst. fuer Angewandte Geowissenschaften; Tipper, Edward [Cambridge Univ. (United Kingdom). Dept. of Earth Sciences; Schiller, Martin [Copenhagen Univ. (Denmark). Natural History Museum of Denmark

    2016-08-01

    This book provides an overview of the fundamentals and reference values for Ca stable isotope research, as well as current analytical methodologies including detailed instructions for sample preparation and isotope analysis. As such, it introduces readers to the different fields of application, including low-temperature mineral precipitation and biomineralisation, Earth surface processes and global cycling, high-temperature processes and cosmochemistry, and lastly human studies and biomedical applications. The current state of the art in these major areas is discussed, and open questions and possible future directions are identified. In terms of its depth and coverage, the current work extends and complements the previous reviews of Ca stable isotope geochemistry, addressing the needs of graduate students and advanced researchers who want to familiarize themselves with Ca stable isotope research.

  15. Strain gradients in epitaxial ferroelectrics

    International Nuclear Information System (INIS)

    Catalan, G.; Noheda, B.; McAneney, J.; Sinnamon, L.J.; Gregg, J.M.

    2005-01-01

    X-ray analysis of ferroelectric thin layers of Ba 1/2 Sr 1/2 TiO 3 with different thicknesses reveals the presence of strain gradients across the films and allows us to propose a functional form for the internal strain profile. We use this to calculate the influence of strain gradient, through flexoelectric coupling, on the degradation of the ferroelectric properties of films with decreasing thickness, in excellent agreement with the observed behavior. This paper shows that strain relaxation can lead to smooth, continuous gradients across hundreds of nanometers, and it highlights the pressing need to avoid such strain gradients in order to obtain ferroelectric films with bulklike properties

  16. Optimization for getting stable plasma initiation in JT-60

    International Nuclear Information System (INIS)

    Yoshino, Ryuji; Neyatani, Yuzuru; Abe, T.

    1988-06-01

    This paper analyses the plasma current build-up just after the breakdown, and investigates the method for obtaining more stable plasma initiation with reduced Volt-second consumption. Control of the amount of particles contained in the wall is necessary for getting the optimum plasma density just after the breakdown, and is essential for obtaining the stable current build-up. (author)

  17. Gradient Index Optics at DARPA

    Science.gov (United States)

    2013-11-01

    sodium, is submerged into a bath of molten salt containing a different ion, such as lithium bromide. Ions from the salt bath diffuse into the glass...molecules, creating a gradient of index of refraction (Mohr et al. 1979). • Crystal growing. From a silver- chloride /sodium- chloride bath, starting with a...sodium chloride seed, a crystal is pulled that begins to deplete the sodium in the bath and starts to pull silver, forming a gradient (Houde-Walter

  18. Stochastic Gradient Monomial Gamma Sampler

    OpenAIRE

    Zhang, Yizhe; Chen, Changyou; Gan, Zhe; Henao, Ricardo; Carin, Lawrence

    2017-01-01

    Recent advances in stochastic gradient techniques have made it possible to estimate posterior distributions from large datasets via Markov Chain Monte Carlo (MCMC). However, when the target posterior is multimodal, mixing performance is often poor. This results in inadequate exploration of the posterior distribution. A framework is proposed to improve the sampling efficiency of stochastic gradient MCMC, based on Hamiltonian Monte Carlo. A generalized kinetic function is leveraged, delivering ...

  19. A tunable microplasma gradient-index lens for millimeter waves

    Energy Technology Data Exchange (ETDEWEB)

    Venkattraman, Ayyaswamy [School of Engineering, University of California Merced, Merced, California 95343 (United States)

    2015-10-15

    This work presents proof of concept of a novel application of field emission assisted (FEA) microplasmas that exploits the relatively high plasma number densities encountered in these devices. We hypothesize that the number density gradients and the resulting gradient in the microplasma relative permittivity/refractive index can be utilized as a tunable diverging lens with on/off ability to defocus waves in the Terahertz regime. Electron number density profiles obtained from one-dimensional particle-in-cell with Monte Carlo collisions simulations for a typical FEA microplasma are used to determine the relative permittivity and conductivity profiles. Frequency domain wave propagation simulations using these profiles show that sub-mm waves can be controlled using the microplasma lens with the degree of defocusing depending on the wavelength. In spite of the non-zero conductivity, the medium is not significantly lossy at the frequencies considered.

  20. Evolutionary Stable Strategy

    Indian Academy of Sciences (India)

    2016-08-26

    Aug 26, 2016 ... Home; Journals; Resonance – Journal of Science Education; Volume 21; Issue 9. Evolutionary Stable Strategy: Application of Nash Equilibrium in Biology. General ... Using some examples of classical games, we show how evolutionary game theory can help understand behavioural decisions of animals.

  1. The Stable Concordance Genus

    OpenAIRE

    Kearney, M. Kate

    2013-01-01

    The concordance genus of a knot is the least genus of any knot in its concordance class. Although difficult to compute, it is a useful invariant that highlights the distinction between the three-genus and four-genus. In this paper we define and discuss the stable concordance genus of a knot, which describes the behavior of the concordance genus under connected sum.

  2. Manifolds admitting stable forms

    Czech Academy of Sciences Publication Activity Database

    Le, Hong-Van; Panák, Martin; Vanžura, Jiří

    2008-01-01

    Roč. 49, č. 1 (2008), s. 101-11 ISSN 0010-2628 R&D Projects: GA ČR(CZ) GP201/05/P088 Institutional research plan: CEZ:AV0Z10190503 Keywords : stable forms * automorphism groups Subject RIV: BA - General Mathematics

  3. Stable isotope studies

    International Nuclear Information System (INIS)

    Ishida, T.

    1992-01-01

    The research has been in four general areas: (1) correlation of isotope effects with molecular forces and molecular structures, (2) correlation of zero-point energy and its isotope effects with molecular structure and molecular forces, (3) vapor pressure isotope effects, and (4) fractionation of stable isotopes. 73 refs, 38 figs, 29 tabs

  4. Interactive Stable Ray Tracing

    DEFF Research Database (Denmark)

    Dal Corso, Alessandro; Salvi, Marco; Kolb, Craig

    2017-01-01

    Interactive ray tracing applications running on commodity hardware can suffer from objectionable temporal artifacts due to a low sample count. We introduce stable ray tracing, a technique that improves temporal stability without the over-blurring and ghosting artifacts typical of temporal post-pr...

  5. The stable subgroup graph

    Directory of Open Access Journals (Sweden)

    Behnaz Tolue

    2018-07-01

    Full Text Available In this paper we introduce stable subgroup graph associated to the group $G$. It is a graph with vertex set all subgroups of $G$ and two distinct subgroups $H_1$ and $H_2$ are adjacent if $St_{G}(H_1\\cap H_2\

  6. An energy stable evolution method for simulating two-phase equilibria of multi-component fluids at constant moles, volume and temperature

    KAUST Repository

    Kou, Jisheng

    2016-02-25

    In this paper, we propose an energy-stable evolution method for the calculation of the phase equilibria under given volume, temperature, and moles (VT-flash). An evolution model for describing the dynamics of two-phase fluid system is based on Fick’s law of diffusion for multi-component fluids and the Peng-Robinson equation of state. The mobility is obtained from diffusion coefficients by relating the gradient of chemical potential to the gradient of molar density. The evolution equation for moles of each component is derived using the discretization of diffusion equations, while the volume evolution equation is constructed based on the mechanical mechanism and the Peng-Robinson equation of state. It is proven that the proposed evolution system can well model the VT-flash problem, and moreover, it possesses the property of total energy decay. By using the Euler time scheme to discretize this evolution system, we develop an energy stable algorithm with an adaptive choice strategy of time steps, which allows us to calculate the suitable time step size to guarantee the physical properties of moles and volumes, including positivity, maximum limits, and correct definition of the Helmhotz free energy function. The proposed evolution method is also proven to be energy-stable under the proposed time step choice. Numerical examples are tested to demonstrate efficiency and robustness of the proposed method.

  7. Volume based vs. time based chromatograms: reproducibility of data for gradient separations under high and low pressure conditions.

    Science.gov (United States)

    Stankovich, Joseph J; Gritti, Fabrice; Stevenson, Paul G; Vajda, Péter; Beaver, Lois Ann; Guiochon, Georges

    2014-05-23

    A critical aspect in fast gradient separations carried out under constant pressure, in the very high pressure liquid chromatography (VHPLC) mode is that time-based chromatograms may not yield highly reproducible separations. A proposed solution to improve the reproducibility of these separations involves plotting the chromatograms as functions of the volume eluted vs. UV absorbance instead of time vs. UV. To study the consequences of using the volume-based rather than the time-based chromatograms, separations were first performed under low pressures that do not generate significant amounts of heat and for which the variations of the eluent density along the columns are negligible. Secondly, they were performed under very high pressures that do generate heat and measurable variations of the local retention factor and eluent density along the column. Comparison of the results provides estimates of the improvements obtained when volume based chromatograms are used in gradient analyses. Using a column packed with fully porous particles, four different types of methods and several sets for each method were used to perform the gradient elution runs: two sets of constant flow rate operations, four sets of constant pressure operations, two sets of constant pressure operations with programmed flow rate, and one set using the constant heat loss approach. The differences between time-based and volume-based chromatograms are demonstrated by using eight replicates of early, middle, and last eluting peaks. The results show that volume-based chromatograms improve the retention time reproducibility of the four constant pressure methods by a factor of 3.7 on average. If the column is not thermally conditioned prior to performing a long series of separations, flow controlled methods (constant flow rate, programmed constant pressure, and constant wall heat approaches) are more precise. If one gradient run is used to bring the column to a relatively stable temperature, constant

  8. Stable isotope analysis

    International Nuclear Information System (INIS)

    Tibari, Elghali; Taous, Fouad; Marah, Hamid

    2014-01-01

    This report presents results related to stable isotopes analysis carried out at the CNESTEN DASTE in Rabat (Morocco), on behalf of Senegal. These analyzes cover 127 samples. These results demonstrate that Oxygen-18 and Deuterium in water analysis were performed by infrared Laser spectroscopy using a LGR / DLT-100 with Autosampler. Also, the results are expressed in δ values (‰) relative to V-SMOW to ± 0.3 ‰ for oxygen-18 and ± 1 ‰ for deuterium.

  9. Forensic Stable Isotope Biogeochemistry

    Science.gov (United States)

    Cerling, Thure E.; Barnette, Janet E.; Bowen, Gabriel J.; Chesson, Lesley A.; Ehleringer, James R.; Remien, Christopher H.; Shea, Patrick; Tipple, Brett J.; West, Jason B.

    2016-06-01

    Stable isotopes are being used for forensic science studies, with applications to both natural and manufactured products. In this review we discuss how scientific evidence can be used in the legal context and where the scientific progress of hypothesis revisions can be in tension with the legal expectations of widely used methods for measurements. Although this review is written in the context of US law, many of the considerations of scientific reproducibility and acceptance of relevant scientific data span other legal systems that might apply different legal principles and therefore reach different conclusions. Stable isotopes are used in legal situations for comparing samples for authenticity or evidentiary considerations, in understanding trade patterns of illegal materials, and in understanding the origins of unknown decedents. Isotope evidence is particularly useful when considered in the broad framework of physiochemical processes and in recognizing regional to global patterns found in many materials, including foods and food products, drugs, and humans. Stable isotopes considered in the larger spatial context add an important dimension to forensic science.

  10. Gradient hydrogel coatings for medical applications

    Science.gov (United States)

    Chinnayan Kannan, Pandiyarajan; Genzer, Jan

    Mussel byssus is a typical example for gradient material that demonstrates a continues variation in mechanical property (or modulus), i . e . , soft (proximal) part is connected to mussel, while the stiffer (distal) part facilitates the attachment of mussel to a stone. Mimicking such materials is highly demanding especially in the areas of artificial implants. We developed a simple synthetic route to produce gradient hydrogels that are covalently anchored to the substrate. N-isopropylacrylamide has been copolymerized with 5 mole% of photo-active (methacrylyloxybenzophenone) and/or 5% of thermally-active (styrenesulfonylazide) crosslinkers. The incorporation of photo and/or thermal crosslinkers allows us for a complete control over the network properties in orthogonal directions. A systematic investigation towards the gel kinetics, swelling, crosslink density, elasticity and protein adsorption was performed. Our results instigate that weakly crosslinked (low modulus) gels swell strong in aqueous medium than the densely crosslinked (high modulus) gels. The results of protein adsorption are discussed based on the previously developed model entropic shielding and size exclusion effect.

  11. Polyacrylamide temperature gradient gel electrophoresis.

    Science.gov (United States)

    Viglasky, Viktor

    2013-01-01

    Temperature Gradient Gel Electrophoresis (TGGE) is a form of electrophoresis in which temperature gradient is used to denature molecules as they move through either acrylamide or agarose gel. TGGE can be applied to analyze DNA, RNA, protein-DNA complexes, and, less commonly, proteins. Separation of double-stranded DNA molecules during TGGE relies on temperature-dependent melting of the DNA duplex into two single-stranded DNA molecules. Therefore, the mobility of DNA reflects not only the size of the molecule but also its nucleotide composition, thereby allowing separation of DNA molecules of similar size with different sequences. Depending on the relative orientation of electric field and temperature gradient, TGGE can be performed in either a parallel or a perpendicular mode. The former is used to analyze multiple samples in the same gel, whereas the later allows detailed analysis of a single sample. This chapter is focused on analysis of DNA by polyacrylamide TGGE using the perpendicular mode.

  12. T-junction cross-flow mixing with thermally driven density stratification

    Energy Technology Data Exchange (ETDEWEB)

    Kickhofel, John, E-mail: jkickhofel@gmail.com [Laboratory of Nuclear Energy Systems, ETH Zurich, Sonneggstrasse 3, 8057 Zurich (Switzerland); Prasser, Horst-Michael, E-mail: prasser@lke.mavt.ethz.ch [Laboratory of Nuclear Energy Systems, ETH Zurich, Sonneggstrasse 3, 8057 Zurich (Switzerland); Selvam, P. Karthick, E-mail: karthick.selvam@ike.uni-stuttgart.de [Institute of Nuclear Technology and Energy Systems (IKE), University of Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart (Germany); Laurien, Eckart, E-mail: eckart.laurien@ike.uni-stuttgart.de [Institute of Nuclear Technology and Energy Systems (IKE), University of Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart (Germany); Kulenovic, Rudi, E-mail: rudi.kulenovic@ike.uni-stuttgart.de [Institute of Nuclear Technology and Energy Systems (IKE), University of Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart (Germany)

    2016-12-01

    Highlights: • Mesh sensor for realistic nuclear thermal hydraulic scenarios is demonstrated. • Flow temperature behavior across a wide range of Richardson numbers measured. • Upstream stratified flow in the T-junction results in a thermal shock scenario. • Large, stable near-wall thermal gradients exist in spite of turbulent flows. - Abstract: As a means of further elucidating turbulence- and stratification-driven thermal fatigue in the vicinity of T-junctions in nuclear power plants, a series of experiments have been conducted at the high temperature high pressure fluid–structure interaction T-junction facility of the University of Stuttgart with novel fluid measurement instrumentation. T-junction mixing with large fluid temperature gradients results in complex flow behavior, the result of density driven effects. Deionized water mixing at temperature differences of up to 232 K at 7 MPa pressure have been investigated in a T-junction with main pipe diameter 71.8 mm and branch line diameter 38.9 mm. The experiments have been performed with fixed flow rates of 0.4 kg/s in the main pipe and 0.1 kg/s in the branch line. A novel electrode-mesh sensor compatible with the DN80 PN100 pipeline upstream and downstream of the T-junction has been utilized as a temperature sensor providing a high density information in the pipe cross-section in both space and time. Additionally, in-flow and in-wall thermocouples quantify the damping of thermal fluctuations by the wall material. The results indicate that large inflow temperature differences lead to strong turbulence damping, and ultimately stable stratification extending both downstream and upstream of the T-junction resulting in large local thermal gradients.

  13. Molecular evolution and the latitudinal biodiversity gradient.

    Science.gov (United States)

    Dowle, E J; Morgan-Richards, M; Trewick, S A

    2013-06-01

    Species density is higher in the tropics (low latitude) than in temperate regions (high latitude) resulting in a latitudinal biodiversity gradient (LBG). The LBG must be generated by differential rates of speciation and/or extinction and/or immigration among regions, but the role of each of these processes is still unclear. Recent studies examining differences in rates of molecular evolution have inferred a direct link between rate of molecular evolution and rate of speciation, and postulated these as important drivers of the LBG. Here we review the molecular genetic evidence and examine the factors that might be responsible for differences in rates of molecular evolution. Critical to this is the directionality of the relationship between speciation rates and rates of molecular evolution.

  14. Migration of inclusions in solids in stress gradients

    International Nuclear Information System (INIS)

    Olander, D.R.

    1980-01-01

    A theoretical method of assessing the influence of stress and temperature gradients on the motion of inclusions in solids is developed. In nonuniform stress fields, the stress distribution on the surface of the cavity must be calculated and transformed to a potential gradient for driving a surface atom flux. The bubble migration velocity is the first Legendre coefficient of the surface flux. Higher order components represent distortion. The stress gradient effect appears only in small-magnitude terms in the surface chemical potential, specifically in the stress effect on the solid atomic volume and in the elastic energy density. The migration velocities of spherical and faceted bubbles in solids are computed and the extent of distortion of a spherical bubble is estimated. The role of vacancy exchange with the bulk solid on the migration velocity is assessed. (author)

  15. Computational Strain Gradient Crystal Plasticity

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Kysar, Jeffrey W.

    2011-01-01

    element solution method is presented, which delivers the slip-rate field and the velocity-field based on two minimum principles. Some plane deformation problems relevant for certain specific orientations of a face centered cubic crystal under plane loading conditions are studied, and effective in......A model for strain gradient crystal visco-plasticity is formulated along the lines proposed by Fleck andWillis (2009) for isotropic plasticity. Size-effects are included in the model due to the addition of gradient terms in both the free energy as well as through a dissipation potential. A finite...

  16. Optimization of gradient coil technology for human magnetic resonance imaging

    Science.gov (United States)

    Chronik, Blaine Alexander

    The general problem of identifying the optimal gradient coil design for any given application is addressed in this thesis. The problem is divided into stages. The first step is the development of an optimal mathematical solution for single designs conforming to some set of constraints. The second step is the systematic implementation of the mathematical algorithm to search for the optimal set of design constraints for an intended application, two examples of which are investigated. The final step is the consideration of gradient coil dependent physiological limits specific to the application of strong gradient fields in human subjects. A modified minimum inductance target field method that allows the placement of a set of constraints on the final current density is developed. This constrained current minimum inductance (CCMI) method is derived in the context of previous target field methods. The method has been fully implemented on computer and applied to the design of both central and edge uniformity gradient coils. A three axis gradient coil set that utilizes interleaved, multilayer axes to achieve maximum gradient strengths of over 2000mT/m in rise times of less than 50μs with an inner coil diameter of 5cm was designed. Water cooling was incorporated into the coil to assist in thermal management. The duty cycle for the most extreme cases of single shot EPI is limited by the thermal response and expressions for maximum rates of image collection are given for burst and continuous modes of operation. A three axis gradient coil set with an imaging region extending outside the physical edge of the coil was designed, constructed, and tested. The configuration is compatible with both neck and brain imaging in humans. The coil produces a cylindrical imaging region 16cm in diameter and 16cm in length. The coil axes produce gradient strengths between 80mT/m and 100mT/m at 250A peak current, with minimum rise times of approximately 400μs. Heating tests were performed

  17. Acoustic Force Density Acting on Inhomogeneous Fluids in Acoustic Fields

    DEFF Research Database (Denmark)

    Karlsen, Jonas Tobias; Augustsson, Per; Bruus, Henrik

    2016-01-01

    We present a theory for the acoustic force density acting on inhomogeneous fluids in acoustic fields on time scales that are slow compared to the acoustic oscillation period. The acoustic force density depends on gradients in the density and compressibility of the fluid. For microfluidic systems...

  18. Compositional gradients in Gramineae genes

    DEFF Research Database (Denmark)

    Wong, Gane Ka-Shu; Wang, Jun; Tao, Lin

    2002-01-01

    In this study, we describe a property of Gramineae genes, and perhaps all monocot genes, that is not observed in eudicot genes. Along the direction of transcription, beginning at the junction of the 5'-UTR and the coding region, there are gradients in GC content, codon usage, and amino-acid usage...

  19. Thermal gradient migration of brine inclusions in salt crystals

    International Nuclear Information System (INIS)

    Yagnik, S.K.

    1982-01-01

    Natural salt deposits, which are being considered for high-level nuclear wastes repositories, contain a small volume fraction of water in the form of brine inclusions distributed throughout the salt. Radioactive decay heating of the nuclear wastes will impose a temperature gradient on the surrounding salt which mobilizes the brine inclusions. Inclusions filled completely with brine (the all-liquid inclusions) migrate up the temperature gradient and eventually accumulate brine near the buried waste forms. The brine may slowly corrode or degrade the waste forms which is undesirable. In the present work, thermal gradient migration of both all-liquid and gas-liquid inclusions was experimentally studied in synthetic single crystals of NaCl and KCl using a hot-stage attachment to an optical microscope which was capable of imposing temperature gradients and axial compressive loads on the crystals. The migration velocities of the inclusions were found to be dependent on temperature, temperature gradient, and inclusion shape and size. The velocities were also dictated by the interfacial mass transfer resistance at brine/solid interface. This interfacial resistance depends on the dislocation density in the crystal, which in turn, depends on the axial compressive loading of the crystal. At low axial loads, the dependence between the velocity and temperature gradient is nonlinear. At high axial loads, however, the interfacial resistance is reduced and the migration velocity depends linearly on the temperature gradient. All-liquid inclusions filled with mixed brines were also studied. For gas-liquid inclusions, three different gas phases (helium, air and argon) were compared. Migration studies were also conducted on single crystallites of natural salt as well as in polycrystalline natural salt samples. The behavior of the inclusions at large angle grain boudaries was observed

  20. Thermal-gradient migration of brine inclusions in salt crystals

    International Nuclear Information System (INIS)

    Yagnik, S.K.

    1982-09-01

    It has been proposed that high-level nuclear waste be disposed in a geologic repository. Natural-salt deposits, which are being considered for this purpose, contain a small volume fraction of water in the form of brine inclusions distributed throughout the salt. Radioactive-decay heating of the nuclear wastes will impose a temperature gradient on the surrounding salt which mobilizes the brine inclusions. Inclusions filled completely with brine migrate up the temperature gradient and eventually accumulate brine near the buried waste forms. The brine may slowly corrode or degrade the waste forms which is undesirable. In this work, thermal gradient migration of both all-liquid and gas-liquid inclusions was experimentally studied in synthetic single crystals of NaCl and KCl using a hot-stage attachment to an optical microscope which was capable of imposing temperature gradients and axial compressive loads on the crystals. The migration velocities of the inclusions were found to be dependent on temperature, temperature gradient, and inclusion shape and size. The velocities were also dictated by the interfacial mass transfer resistance at brine/solid interface. This interfacial resistance depends on the dislocation density in the crystal, which in turn, depends on the axial compressive loading of the crystal. At low axial loads, the dependence between the velocity and temperature gradient is non-linear.At high axial loads, however, the interfacial resistance is reduced and the migration velocity depends linearly on the temperature gradient. All-liquid inclusions filled with mixed brines were also studied. For gas-liquid inclusions, three different gas phases (helium, air and argon) were compared. Migration studies were also conducted on single crystallites of natural salt as well as in polycrystalline natural salt samples. The behavior of the inclusions at large angle grain boundaries was observed. 35 figures, 3 tables

  1. An assessment of an environmental gradient using coral geochemical records, Whitsunday Islands, Great Barrier Reef, Australia

    International Nuclear Information System (INIS)

    Lewis, S.E.; Brodie, J.E.; McCulloch, M.T.; Mallela, J.; Jupiter, S.D.; Stuart Williams, H.; Lough, J.M.; Matson, E.G.

    2012-01-01

    Coral cores were collected along an environmental and water quality gradient through the Whitsunday Island group, Great Barrier Reef (Australia), for trace element and stable isotope analysis. The primary aim of the study was to examine if this gradient could be detected in coral records and, if so, whether the gradient has changed over time with changing land use in the adjacent river catchments. Y/Ca was the trace element ratio which varied spatially across the gradient, with concentrations progressively decreasing away from the river mouths. The Ba/Ca and Y/Ca ratios were the only indicators of change in the gradient through time, increasing shortly after European settlement. The Mn/Ca ratio responded to local disturbance related to the construction of tourism infrastructure. Nitrogen isotope ratios showed no apparent trend over time. This study highlights the importance of site selection when using coral records to record regional environmental signals.

  2. Stable patterns for fourth-order parabolic equations

    OpenAIRE

    van den Berg, J. B.; Vandervorst, R. C.

    2002-01-01

    We consider fourth-order parabolic equations of gradient type. For the sake of simplicity, the analysis is carried out for the specific equation $u\\sb t=-\\gamma\\ u\\sb {xxxx}+\\beta u\\sb {xx}-F\\sp \\prime(u)$ with $(t,x)\\in (0,\\infty)\\times(0, L)$ and $\\gamma,\\beta>0$ and where $F(u)$ is a bistable potential. We study its stable equilibria as a function of the ratio $\\gamma/beta\\sp 2$. As the ratio $\\gamma/beta\\sp 2$ crosses an explicit threshold value, the number of stable ...

  3. Gradient Plasticity Model and its Implementation into MARMOT

    Energy Technology Data Exchange (ETDEWEB)

    Barker, Erin I.; Li, Dongsheng; Zbib, Hussein M.; Sun, Xin

    2013-08-01

    The influence of strain gradient on deformation behavior of nuclear structural materials, such as boby centered cubic (bcc) iron alloys has been investigated. We have developed and implemented a dislocation based strain gradient crystal plasticity material model. A mesoscale crystal plasticity model for inelastic deformation of metallic material, bcc steel, has been developed and implemented numerically. Continuum Dislocation Dynamics (CDD) with a novel constitutive law based on dislocation density evolution mechanisms was developed to investigate the deformation behaviors of single crystals, as well as polycrystalline materials by coupling CDD and crystal plasticity (CP). The dislocation density evolution law in this model is mechanism-based, with parameters measured from experiments or simulated with lower-length scale models, not an empirical law with parameters back-fitted from the flow curves.

  4. Low Bone Density

    Science.gov (United States)

    ... Bone Density Exam/Testing › Low Bone Density Low Bone Density Low bone density is when your bone ... to people with normal bone density. Detecting Low Bone Density A bone density test will determine whether ...

  5. Elemental gradients in macrophytes from a reactor effluent gradient

    International Nuclear Information System (INIS)

    Grace, J.B.; Tilly, L.J.

    1978-01-01

    The tissues of submersed macrophtes from along the thermal gradient were analyzed for phosphorus to determine whether any pattern correspondent to standing crop distributions could be detected. Although water concentrations of phosphorus showed no detectable relationship to the thermal effluent, tissue concentrations of this element in submersed macrophytes declined with distance from the effluent entry point. The occurrence of this concentration pattern suggests that phosphorus availability is greater near the discharge. Because phosphorus is the element most often determined to limit aquatic productivity, its greater availability may partially account for the apparent enhancement of macrophte growth near the thermal discharge. A patter of macrophyte abundance which indicated enchancement related to the discharge gradient in the reactor-cooling reservoir, Par Pond is reported. Correlative data tended to implicate light and temperature as important in influencing the differential abundance pattern

  6. Early impact of oil palm planting density on vegetative and oil yield variables in West Africa

    Directory of Open Access Journals (Sweden)

    Bonneau Xavier

    2014-07-01

    Full Text Available A range of various different planting distances (from 7.5 to 9.5 m between oil palms were tested using an equilateral triangle design in a plantation density experiment which was settled in an oil palm commercial plantation in Nigeria. Climatic conditions were quite stable, with two seasons and around 2000 mm of annual rainfall. The soil was of desaturated ferralitic type, sandy on the surface, deep and without coarse elements. The early impact of plantation density was analysed at eight years after planting. Some early signs of depressive effect on yields were found for high planting densities (180 and 205 p/ha. Such a negative impact was not severe enough to counteract the effects of a higher number of palms per hectare. As a consequence, a gradient could be observed as yields (in tons of bunches per hectare increased with density. We can anticipate that the competition effect between palms will increase over time with high densities, so that the counteracting point ought to be reached in a few years. A thinning treatment has been included in the protocol. Thinning was carried out at the end of the eight-year period.

  7. Gradient-driven flux-tube simulations of ion temperature gradient turbulence close to the non-linear threshold

    Energy Technology Data Exchange (ETDEWEB)

    Peeters, A. G.; Rath, F.; Buchholz, R.; Grosshauser, S. R.; Strintzi, D.; Weikl, A. [Physics Department, University of Bayreuth, Universitätsstrasse 30, Bayreuth (Germany); Camenen, Y. [Aix Marseille Univ, CNRS, PIIM, UMR 7345, Marseille (France); Candy, J. [General Atomics, PO Box 85608, San Diego, California 92186-5608 (United States); Casson, F. J. [CCFE, Culham Science Centre, Abingdon OX14 3DB, Oxon (United Kingdom); Hornsby, W. A. [Max Planck Institut für Plasmaphysik, Boltzmannstrasse 2 85748 Garching (Germany)

    2016-08-15

    It is shown that Ion Temperature Gradient turbulence close to the threshold exhibits a long time behaviour, with smaller heat fluxes at later times. This reduction is connected with the slow growth of long wave length zonal flows, and consequently, the numerical dissipation on these flows must be sufficiently small. Close to the nonlinear threshold for turbulence generation, a relatively small dissipation can maintain a turbulent state with a sizeable heat flux, through the damping of the zonal flow. Lowering the dissipation causes the turbulence, for temperature gradients close to the threshold, to be subdued. The heat flux then does not go smoothly to zero when the threshold is approached from above. Rather, a finite minimum heat flux is obtained below which no fully developed turbulent state exists. The threshold value of the temperature gradient length at which this finite heat flux is obtained is up to 30% larger compared with the threshold value obtained by extrapolating the heat flux to zero, and the cyclone base case is found to be nonlinearly stable. Transport is subdued when a fully developed staircase structure in the E × B shearing rate forms. Just above the threshold, an incomplete staircase develops, and transport is mediated by avalanche structures which propagate through the marginally stable regions.

  8. Marginally Stable Nuclear Burning

    Science.gov (United States)

    Strohmayer, Tod E.; Altamirano, D.

    2012-01-01

    Thermonuclear X-ray bursts result from unstable nuclear burning of the material accreted on neutron stars in some low mass X-ray binaries (LMXBs). Theory predicts that close to the boundary of stability oscillatory burning can occur. This marginally stable regime has so far been identified in only a small number of sources. We present Rossi X-ray Timing Explorer (RXTE) observations of the bursting, high- inclination LMXB 4U 1323-619 that reveal for the first time in this source the signature of marginally stable burning. The source was observed during two successive RXTE orbits for approximately 5 ksec beginning at 10:14:01 UTC on March 28, 2011. Significant mHz quasi- periodic oscillations (QPO) at a frequency of 8.1 mHz are detected for approximately 1600 s from the beginning of the observation until the occurrence of a thermonuclear X-ray burst at 10:42:22 UTC. The mHz oscillations are not detected following the X-ray burst. The average fractional rms amplitude of the mHz QPOs is 6.4% (3 - 20 keV), and the amplitude increases to about 8% below 10 keV.This phenomenology is strikingly similar to that seen in the LMXB 4U 1636-53. Indeed, the frequency of the mHz QPOs in 4U 1323-619 prior to the X-ray burst is very similar to the transition frequency between mHz QPO and bursts found in 4U 1636-53 by Altamirano et al. (2008). These results strongly suggest that the observed QPOs in 4U 1323-619 are, like those in 4U 1636-53, due to marginally stable nuclear burning. We also explore the dependence of the energy spectrum on the oscillation phase, and we place the present observations within the context of the spectral evolution of the accretion-powered flux from the source.

  9. Consolidation by Prefabricated Vertical Drains with a Threshold Gradient

    Directory of Open Access Journals (Sweden)

    Xiao Guo

    2014-01-01

    Full Text Available This paper shows the development of an approximate analytical solution of radial consolidation by prefabricated vertical drains with a threshold gradient. To understand the effect of the threshold gradient on consolidation, a parametric analysis was performed using the present solution. The applicability of the present solution was demonstrated in two cases, wherein the comparisons with Hansbo’s results and observed data were conducted. It was found that (1 the flow with the threshold gradient would not occur instantaneously throughout the whole unit cell. Rather, it gradually occurs from the vertical drain to the outside; (2 the moving boundary would never reach the outer radius of influence if R+1stable value at the end of consolidation; (4 the larger the threshold gradient is, the greater the long-term excess pore pressure will be; and (5 the present solution could predict the consolidation behavior in soft clay better than previous methods.

  10. Mapping land cover gradients through analysis of hyper-temporal NDVI imagery

    NARCIS (Netherlands)

    Ali, A.; de Bie, C.A.J.M.; Skidmore, A.K.; Scarrott, R.G.; Hamad, A.A.; Venus, V.; Lymberakis, P.

    2013-01-01

    The green cover of the earth exhibits various spatial gradients that represent gradual changes in space of vegetation density and/or in species composition. To date, land cover mapping methods differentiate at best, mapping units with different cover densities and/or species compositions, but

  11. A gradient enhanced plasticity-damage microplane model for concrete

    Science.gov (United States)

    Zreid, Imadeddin; Kaliske, Michael

    2018-03-01

    Computational modeling of concrete poses two main types of challenges. The first is the mathematical description of local response for such a heterogeneous material under all stress states, and the second is the stability and efficiency of the numerical implementation in finite element codes. The paper at hand presents a comprehensive approach addressing both issues. Adopting the microplane theory, a combined plasticity-damage model is formulated and regularized by an implicit gradient enhancement. The plasticity part introduces a new microplane smooth 3-surface cap yield function, which provides a stable numerical solution within an implicit finite element algorithm. The damage part utilizes a split, which can describe the transition of loading between tension and compression. Regularization of the model by the implicit gradient approach eliminates the mesh sensitivity and numerical instabilities. Identification methods for model parameters are proposed and several numerical examples of plain and reinforced concrete are carried out for illustration.

  12. Vertebrate pressure-gradient receivers

    DEFF Research Database (Denmark)

    Christensen-Dalsgaard, Jakob

    2011-01-01

    The eardrums of all terrestrial vertebrates (tetrapods) are connected through Eustachian tubes or interaural canals. In some of the animals, these connections create pressure-gradient directionality, an enhanced directionality by interaction of sound arriving at both sides of the eardrum and stro......The eardrums of all terrestrial vertebrates (tetrapods) are connected through Eustachian tubes or interaural canals. In some of the animals, these connections create pressure-gradient directionality, an enhanced directionality by interaction of sound arriving at both sides of the eardrum....... Recent vertebrates form a continuum from perfect interaural transmission (0 dB in a certain frequency band) and pronounced eardrum directionality (30-40 dB) in the lizards, over somewhat attenuated transmission and limited directionality in birds and frogs, to the strongly attenuated interaural...

  13. Enviromental Effects on Internal Color Gradients of Early-Type Galaxies

    Science.gov (United States)

    La Barbera, F.; de Carvalho, R. R.; Gal, R. R.; Busarello, G.; Haines, C. P.; Mercurio, A.; Merluzzi, P.; Capaccioli, M.; Djorgovski, S. G.

    2007-05-01

    One of the most debated issues of observational and theoretical cosmology is that of how the environment affects the formation and evolution of galaxies. To gain new insight into this subject, we have derived surface photometry for a sample of 3,000 early-type galaxies belonging to 163 clusters with different richness, spanning a redshift range of 0.05 to 0.25. This large data-set is used to analyze how the color distribution inside galaxies depends on several parameters, such as cluster richness, local galaxy density, galaxy luminosity and redshift. We find that the internal color profile of galaxies strongly depends on the environment where galaxies reside. Galaxies in poor and rich clusters are found to follow two distinct trends in the color gradient vs. redshift diagram, with color gradients beeing less steep in rich rather than in poor clusters. No dependence of color gradients on galaxy luminosity is detected both for poor and rich clusters. We find that color gradients strongly depend on local galaxy density, with more shallow gradients in high density regions. Interestingly, this result holds only for low richness clusters, with color gradients of galaxies in rich clusters showing no dependence on local galaxy density. Our results support a reasonable picture whereby young early-type galaxies form in a dissipative collapse process, and then undergo increased (either major or minor) merging activity in richer rather than in poor clusters.

  14. Primordial vorticity and gradient expansion

    CERN Document Server

    Giovannini, Massimo

    2012-01-01

    The evolution equations of the vorticities of the electrons, ions and photons in a pre-decoupling plasma are derived, in a fully inhomogeneous geometry, by combining the general relativistic gradient expansion and the drift approximation within the Adler-Misner-Deser decomposition. The vorticity transfer between the different species is discussed in this novel framework and a set of general conservation laws, connecting the vorticities of the three-component plasma with the magnetic field intensity, is derived. After demonstrating that a source of large-scale vorticity resides in the spatial gradients of the geometry and of the electromagnetic sources, the total vorticity is estimated to lowest order in the spatial gradients and by enforcing the validity of the momentum constraint. By acknowledging the current bounds on the tensor to scalar ratio in the (minimal) tensor extension of the $\\Lambda$CDM paradigm the maximal comoving magnetic field induced by the total vorticity turns out to be, at most, of the or...

  15. Evaluation of the Field Gradient Lattice Detector

    CERN Document Server

    AUTHOR|(CDS)2072983

    A novel Micro Pattern Gas Detector, named the Field Gradient Lattice Detector, has been implemented using technologies available to CERN’s Printed Circuit Workshop. Numerous prototypes based on various materials were constructed in different geometries and their gain performance has been studied using 55Fe and 109Cd X-ray sources in Argon-CO2 gas mixtures. Two axis (2D) prototype structures have been shown to provide stable gains of around 1000 while a 3D design, based on the same polyimide foils used in other MPGD elements, holds a gain of 5000 for 8.9 keV X-rays even at high rates of 22 kHz/mm2. At a gain of 3100, the device has been tested up to 1 MHz/mm2 and shows no signs of degradation in performance. The energy resolution of the 3D-in-polyimide is modest, around 40% for 5.9 keV X-rays and 30% if the source is collimated indicating a variation in gain over the 3x3 cm2 active area. Having the most promise for future applications, the 3D-in-polyimide design has been selected for testing with a custom-bu...

  16. Advanced compositional gradient and compartmentalization analysis

    Energy Technology Data Exchange (ETDEWEB)

    Canas, Jesus A.; Petti, Daniela; Mullins, Oliver [Schlumberger Servicos de Petroleo Ltda., Rio de Janeiro, RJ (Brazil)

    2008-07-01

    Acquisition of hydrocarbons samples from the reservoir prior to oil or gas production is essential in order to design production strategies and production facilities. In addition, reservoir compartmentalization and hydrocarbon compositional grading magnify the necessity to map fluid properties vertically and laterally in the reservoir prior to production. Formation testers supply a wealth of information to observe and predict the state of fluids in hydrocarbon reservoirs, through detailed pressure and fluid analysis measurements. With the correct understanding of the state of fluids in the reservoirs, reserve calculations and adequate development plans can be prepared. Additionally, flow barriers may then be revealed. This paper describes a new Downhole Fluid Analysis technology (DFA) for improved reservoir management. DFA is a unique process that combines new fluid identification sensors, which allow real time monitoring of a wide range of parameters as GOR, fluid density, viscosity, fluorescence and composition (CH{sub 4}, C2- C5, C6 +, CO{sub 2}), free gas and liquid phases detection, saturation pressure, as well WBM and OBM filtrate differentiation and pH. This process is not limited to light fluid evaluation and we extended to heavy oil (HO) reservoirs analysis successfully. The combination of DFA Fluid Profiling with pressure measurements has shown to be very effective for compartmentalization characterization. The ability of thin barriers to hold off large depletion pressures has been established, as the gradual variation of hydrocarbon quality in biodegraded oils. In addition, heavy oils can show large compositional variation due to variations in source rock charging but without fluid mixing. Our findings indicates that steep gradients are common in gas condensates or volatile oils, and that biodegradation is more common in HO than in other hydrocarbons, which generate fluid gradients and heavy ends tars near the OWC, limiting the aquifer activity and

  17. Instabilities in power law gradient hardening materials

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Tvergaard, Viggo

    2005-01-01

    Tension and compression instabilities are investigated for specimens with dimensions in the micron range. A finite strain generalization of a higher order strain gradient plasticity theory is implemented in a finite element scheme capable of modeling power law hardening materials. Effects...... of gradient hardening are found to delay the onset of localization under plane strain tension, and significantly reduce strain gradients in the localized zone. For plane strain compression gradient hardening is found to increase the load-carrying capacity significantly....

  18. Conjugate gradient heat bath for ill-conditioned actions.

    Science.gov (United States)

    Ceriotti, Michele; Bussi, Giovanni; Parrinello, Michele

    2007-08-01

    We present a method for performing sampling from a Boltzmann distribution of an ill-conditioned quadratic action. This method is based on heat-bath thermalization along a set of conjugate directions, generated via a conjugate-gradient procedure. The resulting scheme outperforms local updates for matrices with very high condition number, since it avoids the slowing down of modes with lower eigenvalue, and has some advantages over the global heat-bath approach, compared to which it is more stable and allows for more freedom in devising case-specific optimizations.

  19. Bistable gradient networks. II. Storage capacity and behavior near saturation

    Science.gov (United States)

    McGraw, Patrick N.; Menzinger, Michael

    2003-01-01

    We examine numerically the storage capacity and the behavior near saturation of an attractor neural network consisting of bistable elements with an adjustable coupling strength, the bistable gradient network. For strong coupling, we find evidence of a first-order “memory blackout” phase transition, as in the Hopfield network. For weak coupling, on the other hand, there is no evidence of such a transition and memorized patterns can be stable even at high levels of loading. The enhanced storage capacity comes, however, at the cost of imperfect retrieval of the patterns from corrupted versions.

  20. Biomaterials with persistent growth factor gradients in vivo accelerate vascularized tissue formation.

    Science.gov (United States)

    Akar, Banu; Jiang, Bin; Somo, Sami I; Appel, Alyssa A; Larson, Jeffery C; Tichauer, Kenneth M; Brey, Eric M

    2015-12-01

    Gradients of soluble factors play an important role in many biological processes, including blood vessel assembly. Gradients can be studied in detail in vitro, but methods that enable the study of spatially distributed soluble factors and multi-cellular processes in vivo are limited. Here, we report on a method for the generation of persistent in vivo gradients of growth factors in a three-dimensional (3D) biomaterial system. Fibrin loaded porous poly (ethylene glycol) (PEG) scaffolds were generated using a particulate leaching method. Platelet derived growth factor BB (PDGF-BB) was encapsulated into poly (lactic-co-glycolic acid) (PLGA) microspheres which were placed distal to the tissue-material interface. PLGA provides sustained release of PDGF-BB and its diffusion through the porous structure results in gradient formation. Gradients within the scaffold were confirmed in vivo using near-infrared fluorescence imaging and gradients were present for more than 3 weeks. The diffusion of PDGF-BB was modeled and verified with in vivo imaging findings. The depth of tissue invasion and density of blood vessels formed in response to the biomaterial increased with magnitude of the gradient. This biomaterial system allows for generation of sustained growth factor gradients for the study of tissue response to gradients in vivo. Published by Elsevier Ltd.

  1. Symbol recognition with kernel density matching.

    Science.gov (United States)

    Zhang, Wan; Wenyin, Liu; Zhang, Kun

    2006-12-01

    We propose a novel approach to similarity assessment for graphic symbols. Symbols are represented as 2D kernel densities and their similarity is measured by the Kullback-Leibler divergence. Symbol orientation is found by gradient-based angle searching or independent component analysis. Experimental results show the outstanding performance of this approach in various situations.

  2. Gradient remediability in linear distributed parabolic systems ...

    African Journals Online (AJOL)

    The aim of this paper is the introduction of a new concept that concerned the analysis of a large class of distributed parabolic systems. It is the general concept of gradient remediability. More precisely, we study with respect to the gradient observation, the existence of an input operator (gradient efficient actuators) ensuring ...

  3. Estimation of gradients from scattered data

    Energy Technology Data Exchange (ETDEWEB)

    Stead, S.E.

    1984-01-01

    Many techniques for producing a surface from scattered data require gradients at the data points. Since only positional data are usually known, the gradients must be estimated before the surface can be computed. The quality of the surface depends on the estimated gradients; so it is important to compute accurate estimates.

  4. An education gradient in health, a health gradient in education, or a confounded gradient in both?

    Science.gov (United States)

    Lynch, Jamie L; von Hippel, Paul T

    2016-04-01

    There is a positive gradient associating educational attainment with health, yet the explanation for this gradient is not clear. Does higher education improve health (causation)? Do the healthy become highly educated (selection)? Or do good health and high educational attainment both result from advantages established early in the life course (confounding)? This study evaluates these competing explanations by tracking changes in educational attainment and Self-rated Health (SRH) from age 15 to age 31 in the National Longitudinal Study of Youth, 1997 cohort. Ordinal logistic regression confirms that high-SRH adolescents are more likely to become highly educated. This is partly because adolescent SRH is associated with early advantages including adolescents' academic performance, college plans, and family background (confounding); however, net of these confounders adolescent SRH still predicts adult educational attainment (selection). Fixed-effects longitudinal regression shows that educational attainment has little causal effect on SRH at age 31. Completion of a high school diploma or associate's degree has no effect on SRH, while completion of a bachelor's or graduate degree have effects that, though significant, are quite small (less than 0.1 points on a 5-point scale). While it is possible that educational attainment would have greater effect on health at older ages, at age 31 what we see is a health gradient in education, shaped primarily by selection and confounding rather than by a causal effect of education on health. Copyright © 2016 Elsevier Ltd. All rights reserved.

  5. Gradient approximated exchange energy functionals with improved performances for two-dimensional quantum dot systems

    Science.gov (United States)

    Jana, Subrata; Patra, Abhilash; Samal, Prasanjit

    2018-03-01

    Semilocal exchange-correlation functionals are frequently used to accurately describe the complex many-electron effects of two-dimensional quantum systems. Most of these functionals are designed using the reduced density gradient as the main ingredient. A semilocal functional for the exchange and the corresponding enhancement factor is constructed using the inhomogeneity parameter of the generalized gradient approximations by analyzing the small and large-density gradient expansion of the exchange hole. This exchange functional significantly reduces the error compared to the existing gradient approximations. Performance of the proposed semilocal functional is demonstrated by considering parabolic and Gaussian quantum dots with varying particle number and confinement strength. The results are also compared with that of the exact exchange formalism by considering it as the standard.

  6. Analysis of physical mechanisms underlying density-dependent transport in porous media

    NARCIS (Netherlands)

    Landman, A.J.

    2005-01-01

    In this thesis, the interaction between (large) density gradients and flow and transport in porous media is studied. Large gradients in the density of groundwater exist for example near deep salt rock formations, which are considered as possible long-term storage sites for radioactive waste.

  7. High precision and stable structures for particle detectors

    CERN Document Server

    Da Mota Silva, S; Hauviller, Claude

    1999-01-01

    The central detectors used in High Energy Physics Experiments require the use of light and stable structures capable of supporting delicate and precise radiation detection elements. These structures need to be highly stable under environmental conditions where external vibrations, high radiation levels, temperature and humidity gradients should be taken into account. Their main design drivers are high dimension and dynamic stability, high stiffness to mass ratio and large radiation length. For most applications, these constraints lead us to choose Carbon Fiber Reinforced Plastics ( CFRP) as structural element. The construction of light and stable structures with CFRP for these applications can be achieved by careful design engineering and further confirmation at the prototyping phase. However, the experimental environment can influence their characteristics and behavior. In this case, theuse of adaptive structures could become a solution for this problem. We are studying structures in CFRP with bonded piezoel...

  8. Influence of precipitating light elements on stable stratification below the core/mantle boundary

    Science.gov (United States)

    O'Rourke, J. G.; Stevenson, D. J.

    2017-12-01

    Stable stratification below the core/mantle boundary is often invoked to explain anomalously low seismic velocities in this region. Diffusion of light elements like oxygen or, more slowly, silicon could create a stabilizing chemical gradient in the outermost core. Heat flow less than that conducted along the adiabatic gradient may also produce thermal stratification. However, reconciling either origin with the apparent longevity (>3.45 billion years) of Earth's magnetic field remains difficult. Sub-isentropic heat flow would not drive a dynamo by thermal convection before the nucleation of the inner core, which likely occurred less than one billion years ago and did not instantly change the heat flow. Moreover, an oxygen-enriched layer below the core/mantle boundary—the source of thermal buoyancy—could establish double-diffusive convection where motion in the bulk fluid is suppressed below a slowly advancing interface. Here we present new models that explain both stable stratification and a long-lived dynamo by considering ongoing precipitation of magnesium oxide and/or silicon dioxide from the core. Lithophile elements may partition into iron alloys under extreme pressure and temperature during Earth's formation, especially after giant impacts. Modest core/mantle heat flow then drives compositional convection—regardless of thermal conductivity—since their solubility is strongly temperature-dependent. Our models begin with bulk abundances for the mantle and core determined by the redox conditions during accretion. We then track equilibration between the core and a primordial basal magma ocean followed by downward diffusion of light elements. Precipitation begins at a depth that is most sensitive to temperature and oxygen abundance and then creates feedbacks with the radial thermal and chemical profiles. Successful models feature a stable layer with low seismic velocity (which mandates multi-component evolution since a single light element typically

  9. Shape reconstruction from gradient data.

    Science.gov (United States)

    Ettl, Svenja; Kaminski, Jürgen; Knauer, Markus C; Häusler, Gerd

    2008-04-20

    We present a generalized method for reconstructing the shape of an object from measured gradient data. A certain class of optical sensors does not measure the shape of an object but rather its local slope. These sensors display several advantages, including high information efficiency, sensitivity, and robustness. For many applications, however, it is necessary to acquire the shape, which must be calculated from the slopes by numerical integration. Existing integration techniques show drawbacks that render them unusable in many cases. Our method is based on an approximation employing radial basis functions. It can be applied to irregularly sampled, noisy, and incomplete data, and it reconstructs surfaces both locally and globally with high accuracy.

  10. Temperature Gradient in Hall Thrusters

    International Nuclear Information System (INIS)

    Staack, D.; Raitses, Y.; Fisch, N.J.

    2003-01-01

    Plasma potentials and electron temperatures were deduced from emissive and cold floating probe measurements in a 2 kW Hall thruster, operated in the discharge voltage range of 200-400 V. An almost linear dependence of the electron temperature on the plasma potential was observed in the acceleration region of the thruster both inside and outside the thruster. This result calls into question whether secondary electron emission from the ceramic channel walls plays a significant role in electron energy balance. The proportionality factor between the axial electron temperature gradient and the electric field is significantly smaller than might be expected by models employing Ohmic heating of electrons

  11. On Nonconvex Decentralized Gradient Descent

    Science.gov (United States)

    2016-08-01

    difference between each local point and their global average is subject to a bound proportional to the step size. This note then establishes similar...estimation, and control. When fi’s are convex, the existing algorithms include the (sub)gradient meth- ods [5], [7], [10], [11], [18], [14], [15], and the...set of n nodes and E is the edge set. Any edge (i, j) ∈ E represents an arc between node i and node j. Let x(i) ∈ Rp denote the local copy of x at node

  12. Stringy bounces and gradient instabilities

    CERN Document Server

    Giovannini, Massimo

    2017-01-01

    Bouncing solutions are obtained from a generally covariant action characterized by a potential which is a nonlocal functional of the dilaton field at two separated space-time points. Gradient instabilities are shown to arise in this context but they are argued to be nongeneric. After performing a gauge-invariant and frame-invariant derivation of the evolution equations of the fluctuations, a heuristic criterium for the avoidance of pathological instabilities is proposed and corroborated by a number of explicit examples that turn out to be compatible with a quasi-flat spectrum of curvature inhomogeneities for typical wavelengths larger than the Hubble radius.

  13. Velocity Gradients as a Tracer for Magnetic Fields

    Science.gov (United States)

    González-Casanova, Diego F.; Lazarian, A.

    2017-01-01

    Strong Alfvénic turbulence develops eddy-like motions perpendicular to the local direction of magnetic fields. This local alignment induces velocity gradients perpendicular to the local direction of the magnetic field. We use this fact to propose a new technique of studying the direction of magnetic fields from observations, which we call the velocity gradient technique. We test our idea by employing the synthetic observations obtained via 3D magnetohydrodynamical (MHD) numerical simulations for different sonic and Alfvén Mach numbers. We calculate the velocity gradient, {\\boldsymbol{Ω }}, using the velocity centroids. We find that {\\boldsymbol{Ω }} traces the projected magnetic field best for the synthetic maps obtained with sub-Alfvénic simulations and provides good point-wise correspondence between the magnetic field direction and the direction of {\\boldsymbol{Ω }}. The reported alignment is much better than the alignment between the density gradients and the magnetic field, and we demonstrate that it can be used to find the magnetic field strength with an analog of the Chandrasekhar-Fermi method. This new technique does not require dust polarimetry, and our study opens up a new way of studying magnetic fields using spectroscopic data.

  14. First-row diatomics: Calculation of the geometry and energetics using self-consistent gradient-functional approximations

    International Nuclear Information System (INIS)

    Kutzler, F.W.; Painter, G.S.

    1992-01-01

    A fully self-consistent series of nonlocal (gradient) density-functional calculations has been carried out using the augmented-Gaussian-orbital method to determine the magnitude of gradient corrections to the potential-energy curves of the first-row diatomics, Li 2 through F 2 . Both the Langreth-Mehl-Hu and the Perdew-Wang gradient-density functionals were used in calculations of the binding energy, bond length, and vibrational frequency for each dimer. Comparison with results obtained in the local-spin-density approximation (LSDA) using the Vosko-Wilk-Nusair functional, and with experiment, reveals that bond lengths and vibrational frequencies are rather insensitive to details of the gradient functionals, including self-consistency effects, but the gradient corrections reduce the overbinding commonly observed in the LSDA calculations of first-row diatomics (with the exception of Li 2 , the gradient-functional binding-energy error is only 50--12 % of the LSDA error). The improved binding energies result from a large differential energy lowering, which occurs in open-shell atoms relative to the diatomics. The stabilization of the atom arises from the use of nonspherical charge and spin densities in the gradient-functional calculations. This stabilization is negligibly small in LSDA calculations performed with nonspherical densities

  15. Strain gradient effects on cyclic plasticity

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Legarth, Brian Nyvang

    2010-01-01

    Size effects on the cyclic shear response are studied numerically using a recent higher order strain gradient visco-plasticity theory accounting for both dissipative and energetic gradient hardening. Numerical investigations of the response under cyclic pure shear and shear of a finite slab between...... rigid platens have been carried out, using the finite element method. It is shown for elastic–perfectly plastic solids how dissipative gradient effects lead to increased yield strength, whereas energetic gradient contributions lead to increased hardening as well as a Bauschinger effect. For linearly...... hardening materials it is quantified how dissipative and energetic gradient effects promote hardening above that of conventional predictions. Usually, increased hardening is attributed to energetic gradient effects, but here it is found that also dissipative gradient effects lead to additional hardening...

  16. GRADIENTES TÉRMICOS NATURAIS NA ESTIMATIVA DO FLUXO DE SEIVA PELO MÉTODO GRANIER

    Directory of Open Access Journals (Sweden)

    LUCAS MELO VELLAME

    2011-01-01

    Full Text Available The effects of thermal gradients on stem add one methodological constraint for estimating sap flow through the Granier method (thermal dissipation probe. The present work studied the effect of natural thermal gradients on estimates of sap flow by using thermal dissipation probe in mango plants. The study was carried by using mango plants of the cultivar Tommy Atkins during two development stages: (a during the initial development phase of plants with leaf area of 0.66, 0.73, 1.78 m2 , planted in 15 and 50 liters pots. The study was carried in a greenhouse environment and in the field. Different thermal shields were used around the stem of plants in pots in order to minimize the effects of thermal natural gradients. The measurements of thermal differences were obtained from an adult plant with high leaf density and small exposition of branches to solar radiation. Sensors placed in stems of adult plant with high leaf density provided smaller thermal gradients compared to those inserted in young plant stems. It is necessary to cover the whole branch with neoprene and a shield (skirt type of aluminum paper above and below the location of probe insertion for exposed branches. The air temperature at 2 m height may be used efficiently to correct thermal gradients. It is indispensable the correction of natural thermal gradients in the stem for adequate estimating sap flow density by the Granier method.

  17. A Linear Gradient Theory Model for Calculating Interfacial Tensions of Mixtures

    DEFF Research Database (Denmark)

    Zou, You-Xiang; Stenby, Erling Halfdan

    1996-01-01

    containing supercritical methane, argon, nitrogen, and carbon dioxide gases at high pressure. With this model it is unnecessary to solve the time-consuming density profile equations of the gradient theory model. The model has been tested on a number of mixtures at low and high pressures. The results show...... with proper scaling behavior at the critical point is at least required.Key words: linear gradient theory; interfacial tension; equation of state; influence parameter; density profile.......In this research work, we assumed that the densities of each component in a mixture are linearly distributed across the interface between the coexisting vapor and liquid phases, and we developed a linear gradient theory model for computing interfacial tensions of mixtures, especially mixtures...

  18. Density functional study of manganese atom adsorption on hydrogen-terminated armchair boron nitride nanoribbons

    International Nuclear Information System (INIS)

    Abdullahi, Yusuf Zuntu; Rahman, Md. Mahmudur; Shuaibu, Alhassan; Abubakar, Shamsu; Zainuddin, Hishamuddin; Muhida, Rifki; Setiyanto, Henry

    2014-01-01

    In this paper, we have investigated stable structural, electric and magnetic properties of manganese (Mn) atom adsorption on armchair hydrogen edge-terminated boron nitride nanoribbon (A-BNNRs) using first principles method based on density-functional theory with the generalized gradient approximation. Calculation shows that Mn atom situated on the ribbons of A-BNNRs is the most stable configuration, where the bonding is more pronounced. The projected density of states (PDOS) of the favored configuration has also been computed. It has been found that the covalent bonding of boron (B), nitrogen (N) and Mn is mainly contributed by s, d like-orbitals of Mn and partially occupied by the 2p like-orbital of N. The difference in energy between the inner and the edge adsorption sites of A-BNNRs shows that Mn atoms prefer to concentrate at the edge sites. The electronic structures of the various configurations are wide, narrow-gap semiconducting and half-metallic, and the magnetic moment of Mn atoms are well preserved in all considered configurations. This has shown that the boron nitride (BN) sheet covered with Mn atoms demonstrates additional information on its usefulness in future spintronics, molecular magnet and nanoelectronics devices.

  19. Physisorbed Polymer-Tethered Lipid Bilayer with Lipopolymer Gradient

    Directory of Open Access Journals (Sweden)

    Christoph A. Naumann

    2012-11-01

    Full Text Available Physisorbed polymer-tethered lipid bilayers consisting of phospholipids and lipopolymers represent an attractive planar model membrane platform, in which bilayer fluidity and membrane elastic properties can be regulated through lipopolymer molar concentration. Herein we report a method for the fabrication of such a planar model membrane system with a lateral gradient of lipopolymer density. In addition, a procedure is described, which leads to a sharp boundary between regions of low and high lipopolymer molar concentrations. Resulting gradients and sharp boundaries are visualized on the basis of membrane buckling structures at elevated lipopolymer concentrations using epifluorescence microscopy and atomic force microscopy. Furthermore, results from spot photobleaching experiments are presented, which provide insight into the lipid lateral fluidity in these model membrane architectures. The presented experimental data highlight a planar, solid-supported membrane characterized by fascinating length scale-dependent dynamics and elastic properties with remarkable parallels to those observed in cellular membranes.

  20. Temperature dependency of silicon structures for magnetic field gradient sensing

    Science.gov (United States)

    Dabsch, Alexander; Rosenberg, Christoph; Stifter, Michael; Keplinger, Franz

    2018-02-01

    This work describes the temperature dependence of two sensors for magnetic field gradient sensors and demonstrates a structure to compensate for the drift of resonance frequency over a wide temperature range. The temperature effect of the sensing element is based on internal stresses induced by the thermal expansion of material, therefore FEM is used to determine the change of the eigenvalues of the sensing structure. The experimental setup utilizes a Helmholtz coil system to generate the magnetic field and to excite the MEMS structure with Lorentz forces. The MEMS structure is placed on a plate heated with resistors and cooled by a Peltier element to control the plate temperature. In the second part, we describe how one can exploit temperature sensitivity for temperature measurements and we show the opportunity to include the temperature effect to increase the sensitivity of single-crystal silicon made flux density gradient sensors.

  1. Control of colloids with gravity, temperature gradients, and electric fields

    CERN Document Server

    Sullivan, M; Harrison, C; Austin, R H; Megens, M; Hollingsworth, A; Russel, W B; Cheng Zhen; Mason, T; Chaikin, P M

    2003-01-01

    We have used a variety of different applied fields to control the density, growth, and structure of colloidal crystals. Gravity exerts a body force proportional to the buoyant mass and in equilibrium produces a height-dependent concentration profile. A similar body force can be obtained with electric fields on charged particles (electrophoresis), a temperature gradient on all particles, or an electric field gradient on uncharged particles (dielectrophoresis). The last is particularly interesting since its magnitude and sign can be changed by tuning the applied frequency. We study these effects in bulk (making 'dielectrophoretic bottles' or traps), to control concentration profiles during nucleation and growth and near surfaces. We also study control of non-spherical and optically anisotropic particles with the light field from laser tweezers.

  2. A case study for sustainable development action using financial gradients

    International Nuclear Information System (INIS)

    Bose, Arnab; Ramji, Aditya; Singh, Jarnail; Dholakia, Dhairya

    2012-01-01

    Energy access is critical for sustainable development and therefore financing energy access is a necessity. The key is whether to focus on grants or public finance for sustainable development projects or move to a more diffused financing mechanism, involving investment grade financing sources like debt and equity. In other words, financing sustainable development action via grants is becoming a constraint. To address this constraint, it is important to consider the relationship between the nature and sources of financial flows. The concept of ‘financial gradients’ emerged while analysing the financial and business strategy developed for Lighting a Billion Lives (LaBL) campaign. This paper espouses the idea of ‘financial gradients’ which is a potential financial mechanism for sustainable development action. Financial gradients, can contribute in three different ways—first, as an approach to analyse financial flows in projects; second, as a tool to generate a single, long term and stable inflow of finance; third, as a financial mechanism to help in creating long term strategies to sustain projects. This paper will concentrate on financial gradients as a potential approach to analyse financial flows in a sustainable development programme. - Highlights: ► Financial stability is a key challenge for sustainable development programmes. ► Development action via public funds is limited, need for investment grade finance. ► Need to understand financial flows with relation to nature and sources of finance. ► Financial gradients is an innovative tool for ensuring health of programmes.

  3. Detonation of Meta-stable Clusters

    Energy Technology Data Exchange (ETDEWEB)

    Kuhl, Allen; Kuhl, Allen L.; Fried, Laurence E.; Howard, W. Michael; Seizew, Michael R.; Bell, John B.; Beckner, Vincent; Grcar, Joseph F.

    2008-05-31

    We consider the energy accumulation in meta-stable clusters. This energy can be much larger than the typical chemical bond energy (~;;1 ev/atom). For example, polymeric nitrogen can accumulate 4 ev/atom in the N8 (fcc) structure, while helium can accumulate 9 ev/atom in the excited triplet state He2* . They release their energy by cluster fission: N8 -> 4N2 and He2* -> 2He. We study the locus of states in thermodynamic state space for the detonation of such meta-stable clusters. In particular, the equilibrium isentrope, starting at the Chapman-Jouguet state, and expanding down to 1 atmosphere was calculated with the Cheetah code. Large detonation pressures (3 and 16 Mbar), temperatures (12 and 34 kilo-K) and velocities (20 and 43 km/s) are a consequence of the large heats of detonation (6.6 and 50 kilo-cal/g) for nitrogen and helium clusters respectively. If such meta-stable clusters could be synthesized, they offer the potential for large increases in the energy density of materials.

  4. Stable carbon isotope time series from tropical tree rings indicate a precipitation signal

    OpenAIRE

    E. Fichtler; Gerhard Helle; M. Worbes

    2010-01-01

    Although studies on stable-carbon isotopes in trees from temperate zones provide abundant paleoclimatic data, tropical trees are still understudied in this context. Therefore this study examined the variability of intra- and inter-annual stable-carbon isotopic pattern in several tree species from various tropical climates. The delta C-13 Values of samples of 12 broadleaved trees (seven species) from various paleotropical and neotropical sites along a climatic moisture gradient were investigat...

  5. Wavefront reconstruction from its gradients.

    Science.gov (United States)

    Talmi, Amos; Ribak, Erez N

    2006-02-01

    Wavefronts reconstructed from measured gradients are composed of a straightforward integration of the measured data, plus a correction term that disappears when there are no measurement errors. For regions of any shape, this term is a solution of Poisson's equation with Dirichlet conditions (V = 0 on the boundaries). We show that for rectangular regions, the correct solution is not a periodic one, but one expressed with Fourier cosine series. The correct solution has a lower variance than the periodic Fourier transform solution. Similar formulas exist for a circular region with obscuration. We present a near-optimal solution that is much faster than fast-Fourier-transform methods. By use of diagonal multigrid methods, a single iteration brings the correction term to within a standard deviation of 0.08, two iterations, to within 0.0064, etc.

  6. Analysis of surface degradation of high density polyethylene (HDPE ...

    Indian Academy of Sciences (India)

    Unknown

    Analysis of surface degradation of high density polyethylene (HDPE) insulation ... ammonium chloride as the contaminant, in high density polyethylene ..... liquid in the material. When diffusion is driven by the concentration gradient and if there is no chemical change between liquid and material, this would result in mass.

  7. Applicability of Stokes method for measuring viscosity of mixtures with concentration gradient

    Directory of Open Access Journals (Sweden)

    César Medina

    2017-12-01

    Full Text Available After measuring density and viscosity of a mixture of glycerin and water contained in a vertical pipe, a variation of these properties according to depth is observed. These gradients are typical of non-equilibrium states related to the lower density of water and the fact that relatively long times are necessary to achieve homogeneity. In the same pipe, the falling velocity of five little spheres is measured as a function of depth, and then a numerical fit is performed which agrees very well with experimental data. Based on the generalization of these results, the applicability of Stokes method is discussed for measuring viscosity of mixtures with a concentration gradient.

  8. RNA–Stable-Isotope Probing Shows Utilization of Carbon from Inulin by Specific Bacterial Populations in the Rat Large Bowel

    Science.gov (United States)

    Lawley, Blair; Munro, Karen; Sims, Ian M.; Lee, Julian; Butts, Christine A.; Roy, Nicole

    2014-01-01

    Knowledge of the trophisms that underpin bowel microbiota composition is required in order to understand its complex phylogeny and function. Stable-isotope (13C)-labeled inulin was added to the diet of rats on a single occasion in order to detect utilization of inulin-derived substrates by particular members of the cecal microbiota. Cecal digesta from Fibruline-inulin-fed rats was collected prior to (0 h) and at 6, 12, 18 and 24 h following provision of the [13C]inulin diet. RNA was extracted from these cecal specimens and fractionated in isopycnic buoyant density gradients in order to detect 13C-labeled nucleic acid originating in bacterial cells that had metabolized the labeled dietary constituent. RNA extracted from specimens collected after provision of the labeled diet was more dense than 0-h RNA. Sequencing of 16S rRNA genes amplified from cDNA obtained from these fractions showed that Bacteroides uniformis, Blautia glucerasea, Clostridium indolis, and Bifidobacterium animalis were the main users of the 13C-labeled substrate. Culture-based studies of strains of these bacterial species enabled trophisms associated with inulin and its hydrolysis products to be identified. B. uniformis utilized Fibruline-inulin for growth, whereas the other species used fructo-oligosaccharide and monosaccharides. Thus, RNA–stable-isotope probing (RNA-SIP) provided new information about the use of carbon from inulin in microbiota metabolism. PMID:24487527

  9. Jupiter's evolution with primordial composition gradients

    OpenAIRE

    Vazan, A.; Helled, R.; Guillot, T.

    2018-01-01

    Recent formation and structure models of Jupiter suggest that the planet can have composition gradients and not be fully convective (adiabatic). This possibility directly affects our understanding of Jupiter's bulk composition and origin. In this Letter we present Jupiter's evolution with a primordial structure consisting of a relatively steep heavy-element gradient of 40 Earth masses. We show that for a primordial structure with composition gradients, most of the mixing occurs in the outer p...

  10. Thermal conduction down steep temperature gradients

    International Nuclear Information System (INIS)

    Bell, A.R.; Evans, R.G.; Nicholas, D.J.

    1980-08-01

    The Fokker-Planck equation has been solved numerically in one spatial and two velocity dimensions in order to study thermal conduction in large temperature gradients. An initially cold plasma is heated at one end of the spatial grid producing temperature gradients with scale lengths of a few times the electron mean free path. The heat flow is an order of magnitude smaller than that predicted by the classical theory which is valid in the limit of small temperature gradients. (author)

  11. Testing the limits of gradient sensing.

    Directory of Open Access Journals (Sweden)

    Vinal Lakhani

    2017-02-01

    Full Text Available The ability to detect a chemical gradient is fundamental to many cellular processes. In multicellular organisms gradient sensing plays an important role in many physiological processes such as wound healing and development. Unicellular organisms use gradient sensing to move (chemotaxis or grow (chemotropism towards a favorable environment. Some cells are capable of detecting extremely shallow gradients, even in the presence of significant molecular-level noise. For example, yeast have been reported to detect pheromone gradients as shallow as 0.1 nM/μm. Noise reduction mechanisms, such as time-averaging and the internalization of pheromone molecules, have been proposed to explain how yeast cells filter fluctuations and detect shallow gradients. Here, we use a Particle-Based Reaction-Diffusion model of ligand-receptor dynamics to test the effectiveness of these mechanisms and to determine the limits of gradient sensing. In particular, we develop novel simulation methods for establishing chemical gradients that not only allow us to study gradient sensing under steady-state conditions, but also take into account transient effects as the gradient forms. Based on reported measurements of reaction rates, our results indicate neither time-averaging nor receptor endocytosis significantly improves the cell's accuracy in detecting gradients over time scales associated with the initiation of polarized growth. Additionally, our results demonstrate the physical barrier of the cell membrane sharpens chemical gradients across the cell. While our studies are motivated by the mating response of yeast, we believe our results and simulation methods will find applications in many different contexts.

  12. STOCHASTIC GRADIENT METHODS FOR UNCONSTRAINED OPTIMIZATION

    Directory of Open Access Journals (Sweden)

    Nataša Krejić

    2014-12-01

    Full Text Available This papers presents an overview of gradient based methods for minimization of noisy functions. It is assumed that the objective functions is either given with error terms of stochastic nature or given as the mathematical expectation. Such problems arise in the context of simulation based optimization. The focus of this presentation is on the gradient based Stochastic Approximation and Sample Average Approximation methods. The concept of stochastic gradient approximation of the true gradient can be successfully extended to deterministic problems. Methods of this kind are presented for the data fitting and machine learning problems.

  13. Wireless SAW Based Temperature Gradient Sensor Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Prime Photonics proposes design and development of a surface acoustic wave (SAW) based temperature gradient sensor for instrumentation of thermal protection systems...

  14. Community and ecosystem responses to elevational gradients

    DEFF Research Database (Denmark)

    Sundqvist, Maja K.; Sanders, Nate; Wardle, David A.

    2013-01-01

    elevational gradients for understanding community and ecosystem responses to global climate change at much larger spatial and temporal scales than is possible through conventional ecological experiments. However, future studies that integrate elevational gradient approaches with experimental manipulations...... will provide powerful information that can improve predictions of climate change impacts within and across ecosystems.......Community structure and ecosystem processes often vary along elevational gradients. Their responses to elevation are commonly driven by changes in temperature, and many community- and ecosystem-level variables therefore frequently respond similarly to elevation across contrasting gradients...

  15. On lower order strain gradient plasticity theories

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Hutchinson, J. W.

    2003-01-01

    the tangent moduli governing increments of stress and strain. It is shown that the modification is far from benign from a mathematical standpoint, changing the qualitative character of solutions and leading to a new type of localization that is at odds with what is expected from a strain gradient theory......By way of numerical examples, this paper explores the nature of solutions to a class of strain gradient plasticity theories that employ conventional stresses, equilibrium equations and boundary conditions. Strain gradients come into play in these modified conventional theories only to alter....... The findings raise questions about the physical acceptability of this class of strain gradient theories....

  16. Methanotrophic bacteria in warm geothermal spring sediments identified using stable-isotope probing.

    Science.gov (United States)

    Sharp, Christine E; Martínez-Lorenzo, Azucena; Brady, Allyson L; Grasby, Stephen E; Dunfield, Peter F

    2014-10-01

    We investigated methanotrophic bacteria in sediments of several warm geothermal springs ranging in temperature from 22 to 45 °C. Methane oxidation was measured at potential rates up to 141 μmol CH4 d(-1) g(-1) sediment. Active methanotrophs were identified using (13) CH4 stable-isotope probing (SIP) incubations performed at close to in situ temperatures for each site. Quantitative (q) PCR of pmoA genes identified the position of the heavy ((13) C-labelled) DNA fractions in density gradients, and 16S rRNA gene pyrotag sequencing of the heavy fractions was performed to identify the active methanotrophs. Methanotroph communities identified in heavy fractions of all samples were predominated by species similar (≥ 95% 16S rRNA gene identities) to previously characterized Gammaproteobacteria and Alphaproteobacteria methanotrophs. Among the five hottest samples (45 °C), members of the Gammaproteobacteria genus Methylocaldum dominated in two cases, while three others were dominated by an OTU closely related (96.8% similarity) to the Alphaproteobacteria genus Methylocapsa. These results suggest that diverse methanotroph groups are adapted to warm environments, including the Methylocapsa-Methylocella-Methyloferula group, which has previously only been detected in cooler sites. © 2014 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved.

  17. Entropy stable modeling of non-isothermal multi-component diffuse-interface two-phase flows with realistic equations of state

    KAUST Repository

    Kou, Jisheng

    2018-02-25

    In this paper, we consider mathematical modeling and numerical simulation of non-isothermal compressible multi-component diffuse-interface two-phase flows with realistic equations of state. A general model with general reference velocity is derived rigorously through thermodynamical laws and Onsager\\'s reciprocal principle, and it is capable of characterizing compressibility and partial miscibility between multiple fluids. We prove a novel relation among the pressure, temperature and chemical potentials, which results in a new formulation of the momentum conservation equation indicating that the gradients of chemical potentials and temperature become the primary driving force of the fluid motion except for the external forces. A key challenge in numerical simulation is to develop entropy stable numerical schemes preserving the laws of thermodynamics. Based on the convex-concave splitting of Helmholtz free energy density with respect to molar densities and temperature, we propose an entropy stable numerical method, which solves the total energy balance equation directly, and thus, naturally satisfies the first law of thermodynamics. Unconditional entropy stability (the second law of thermodynamics) of the proposed method is proved by estimating the variations of Helmholtz free energy and kinetic energy with time steps. Numerical results validate the proposed method.

  18. Shelf-Stable Food Safety

    Science.gov (United States)

    ... is an MRE? Is an MRE shelf stable? What foods are packaged in retort packages? What is aseptic ... type of package is used for aseptic processing? What foods are packaged in aseptic packages? Can I microwave ...

  19. Pharmaceuticals labelled with stable isotopes

    International Nuclear Information System (INIS)

    Krumbiegel, P.

    1986-11-01

    The relatively new field of pharmaceuticals labelled with stable isotopes is reviewed. Scientific, juridical, and ethical questions are discussed concerning the application of these pharmaceuticals in human medicine. 13 C, 15 N, and 2 H are the stable isotopes mainly utilized in metabolic function tests. Methodical contributions are given to the application of 2 H, 13 C, and 15 N pharmaceuticals showing new aspects and different states of development in the field under discussion. (author)

  20. Stable isotope research pool inventory

    International Nuclear Information System (INIS)

    1984-03-01

    This report contains a listing of electromagnetically separated stable isotopes which are available at the Oak Ridge National Laboratory for distribution for nondestructive research use on a loan basis. This inventory includes all samples of stable isotopes in the Research Materials Collection and does not designate whether a sample is out on loan or is in reprocessing. For some of the high abundance naturally occurring isotopes, larger amounts can be made available; for example, Ca-40 and Fe-56

  1. Canonical trivialization of gravitational gradients

    International Nuclear Information System (INIS)

    Niedermaier, Max

    2017-01-01

    A one-parameter family of canonical transformations is constructed that reduces the Hamiltonian form of the Einstein–Hilbert action to its strong coupling limit where dynamical spatial gradients are absent. The parameter can alternatively be viewed as the overall scale of the spatial metric or as a fractional inverse power of Newton’s constant. The generating function of the canonical transformation is constructed iteratively as a powerseries in the parameter to all orders. The algorithm draws on Lie–Deprit transformation theory and defines a ‘trivialization map’ with several bonus properties: (i) Trivialization of the Hamiltonian constraint implies that of the action while the diffeomorphism constraint is automatically co-transformed. (ii) Only a set of ordinary differential equations needs to be solved to drive the iteration via a homological equation where no gauge fixing is required. (iii) In contrast to (the classical limit of) a Lagrangian trivialization map the algorithm also produces series solutions of the field equations. (iv) In the strong coupling theory temporal gauge variations are abelian, nevertheless the map intertwines with the respective gauge symmetries on the action, the field equations, and their solutions. (paper)

  2. Canonical trivialization of gravitational gradients

    Science.gov (United States)

    Niedermaier, Max

    2017-06-01

    A one-parameter family of canonical transformations is constructed that reduces the Hamiltonian form of the Einstein-Hilbert action to its strong coupling limit where dynamical spatial gradients are absent. The parameter can alternatively be viewed as the overall scale of the spatial metric or as a fractional inverse power of Newton’s constant. The generating function of the canonical transformation is constructed iteratively as a powerseries in the parameter to all orders. The algorithm draws on Lie-Deprit transformation theory and defines a ‘trivialization map’ with several bonus properties: (i) Trivialization of the Hamiltonian constraint implies that of the action while the diffeomorphism constraint is automatically co-transformed. (ii) Only a set of ordinary differential equations needs to be solved to drive the iteration via a homological equation where no gauge fixing is required. (iii) In contrast to (the classical limit of) a Lagrangian trivialization map the algorithm also produces series solutions of the field equations. (iv) In the strong coupling theory temporal gauge variations are abelian, nevertheless the map intertwines with the respective gauge symmetries on the action, the field equations, and their solutions.

  3. The influence of density distribution on the stability of beams

    International Nuclear Information System (INIS)

    Guy, F.W.; Lapostolle, P.M.; Wangler, T.P.

    1987-01-01

    We examine the effect of various density distributions in four-dimensional phase space and their projections in real and velocity space on the stability of continuous beams in alternating-gradient transport lines using particle-following computer simulations. We discuss the susceptibility of three different distributions (Kapchinskii-Vladimirskii, bicylinder, and thermal) to third- and higher-order mode instabilities. These distributions are all uniform in real space, but their velocity distributions are different; they also react differently to structure resonances. Velocity distributions of high-current beams tend to evolve to a peaked Gaussian-like form. Is there a specific velocity distribution that is stable and, therefore, the preferred injection distribution for minimizing emittance growth? Forced smoothness or uniformity in real space is necessary for setting up particle simulations of high-current beams so that spurious charge-redistribution emittance growth can be avoided. Is forced smoothness also desirable in four dimensions for continuous beams and possibly in six dimensions for bunched beams? We consider these and related questions

  4. 3D joint inversion of gravity-gradient and borehole gravity data

    Science.gov (United States)

    Geng, Meixia; Yang, Qingjie; Huang, Danian

    2017-12-01

    Borehole gravity is increasingly used in mineral exploration due to the advent of slim-hole gravimeters. Given the full-tensor gradiometry data available nowadays, joint inversion of surface and borehole data is a logical next step. Here, we base our inversions on cokriging, which is a geostatistical method of estimation where the error variance is minimised by applying cross-correlation between several variables. In this study, the density estimates are derived using gravity-gradient data, borehole gravity and known densities along the borehole as a secondary variable and the density as the primary variable. Cokriging is non-iterative and therefore is computationally efficient. In addition, cokriging inversion provides estimates of the error variance for each model, which allows direct assessment of the inverse model. Examples are shown involving data from a single borehole, from multiple boreholes, and combinations of borehole gravity and gravity-gradient data. The results clearly show that the depth resolution of gravity-gradient inversion can be improved significantly by including borehole data in addition to gravity-gradient data. However, the resolution of borehole data falls off rapidly as the distance between the borehole and the feature of interest increases. In the case where the borehole is far away from the target of interest, the inverted result can be improved by incorporating gravity-gradient data, especially all five independent components for inversion.

  5. Gradient Flow Convolutive Blind Source Separation

    DEFF Research Database (Denmark)

    Pedersen, Michael Syskind; Nielsen, Chinton Møller

    2004-01-01

    Experiments have shown that the performance of instantaneous gradient flow beamforming by Cauwenberghs et al. is reduced significantly in reverberant conditions. By expanding the gradient flow principle to convolutive mixtures, separation in a reverberant environment is possible. By use of a circ...

  6. Preconditioning the modified conjugate gradient method ...

    African Journals Online (AJOL)

    In this paper, the convergence analysis of the conventional conjugate Gradient method was reviewed. And the convergence analysis of the modified conjugate Gradient method was analysed with our extension on preconditioning the algorithm. Convergence of the algorithm is a function of the condition number of M-1A.

  7. 40 CFR 230.25 - Salinity gradients.

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 24 2010-07-01 2010-07-01 false Salinity gradients. 230.25 Section 230.25 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) OCEAN DUMPING SECTION 404(b... Physical and Chemical Characteristics of the Aquatic Ecosystem § 230.25 Salinity gradients. (a) Salinity...

  8. Patterns of macromycete community assemblage along an elevation gradient: options for fungal gradient and metacommunity analyse

    Science.gov (United States)

    Marko Gómez-Hernández; Guadalupe Williams-Linera; Roger Guevara; D. Jean Lodge

    2012-01-01

    Gradient analysis is rarely used in studies of fungal communities. Data on macromycetes from eight sites along an elevation gradient in central Veracruz, Mexico, were used to demonstrate methods for gradient analysis that can be applied to studies of communities of fungi. Selected sites from 100 to 3,500 m altitude represent tropical dry forest, tropical montane cloud...

  9. Dense Bicoid hubs accentuate binding along the morphogen gradient.

    Science.gov (United States)

    Mir, Mustafa; Reimer, Armando; Haines, Jenna E; Li, Xiao-Yong; Stadler, Michael; Garcia, Hernan; Eisen, Michael B; Darzacq, Xavier

    2017-09-01

    Morphogen gradients direct the spatial patterning of developing embryos; however, the mechanisms by which these gradients are interpreted remain elusive. Here we used lattice light-sheet microscopy to perform in vivo single-molecule imaging in early Drosophila melanogaster embryos of the transcription factor Bicoid that forms a gradient and initiates patterning along the anteroposterior axis. In contrast to canonical models, we observed that Bicoid binds to DNA with a rapid off rate throughout the embryo such that its average occupancy at target loci is on-rate-dependent. We further observed Bicoid forming transient "hubs" of locally high density that facilitate binding as factor levels drop, including in the posterior, where we observed Bicoid binding despite vanishingly low protein levels. We propose that localized modulation of transcription factor on rates via clustering provides a general mechanism to facilitate binding to low-affinity targets and that this may be a prevalent feature of other developmental transcription factors. © 2017 Mir et al.; Published by Cold Spring Harbor Laboratory Press.

  10. Soliton formation in electron-temperature-gradient-driven magnetoplasma

    Science.gov (United States)

    M Yaqub, KHAN; Javed, IQBAL

    2018-02-01

    Electron-temperature-gradient (ETG)-driven solitons are studied in a plasma. We derive the linear dispersion relation and an admitted solitary wave solution Korteweg–de Vries-type equation (KdV) for the ETG mode in the nonlinear regime by using the Braginskii model and a transformation. It is found that the ETG mode supports only rarefactive solitons. It is also observed that the ratio of electron-to-ion temperature τ ={T}{{e}}/{T}{{i}}, the ratio of gradient scale lengths {η }{{e}}={L}n/{L}T, and the magnetic field B affect both the amplitude and width of a soliton. It is found that the soliton profile changes with variation in these parameters. We apply the homotopy perturbation method to the derived KdV equation. It is found this method is computationally attractive and the results are very impressive. This work may be useful to study the low electrostatic modes in inhomogeneous electron–ion plasma with density and ETG gradients. For illustration, the model has been applied to tokamak plasma.

  11. Density Distributions of Cyclotrimethylenetrinitramines (RDX)

    International Nuclear Information System (INIS)

    Hoffman, D M

    2002-01-01

    As part of the US Army Foreign Comparative Testing (FCT) program the density distributions of six samples of class 1 RDX were measured using the density gradient technique. This technique was used in an attempt to distinguish between RDX crystallized by a French manufacturer (designated insensitive or IRDX) from RDX manufactured at Holston Army Ammunition Plant (HAAP), the current source of RDX for Department of Defense (DoD). Two samples from different lots of French IRDX had an average density of 1.7958 ± 0.0008 g/cc. The theoretical density of a perfect RDX crystal is 1.806 g/cc. This yields 99.43% of the theoretical maximum density (TMD). For two HAAP RDX lots the average density was 1.786 ± 0.002 g/cc, only 98.89% TMD. Several other techniques were used for preliminary characterization of one lot of French IRDX and two lot of HAAP RDX. Light scattering, SEM and polarized optical microscopy (POM) showed that SNPE and Holston RDX had the appropriate particle size distribution for Class 1 RDX. High performance liquid chromatography showed quantities of HMX in HAAP RDX. French IRDX also showed a 1.1 C higher melting point compared to HAAP RDX in the differential scanning calorimetry (DSC) consistent with no melting point depression due to the HMX contaminant. A second part of the program involved characterization of Holston RDX recrystallized using the French process. After reprocessing the average density of the Holston RDX was increased to 1.7907 g/cc. Apparently HMX in RDX can act as a nucleating agent in the French RDX recrystallization process. The French IRDX contained no HMX, which is assumed to account for its higher density and narrower density distribution. Reprocessing of RDX from Holston improved the average density compared to the original Holston RDX, but the resulting HIRDX was not as dense as the original French IRDX. Recrystallized Holston IRDX crystals were much larger (3-500 (micro)m or more) then either the original class 1 HAAP RDX or French

  12. Approximate error conjugation gradient minimization methods

    Science.gov (United States)

    Kallman, Jeffrey S

    2013-05-21

    In one embodiment, a method includes selecting a subset of rays from a set of all rays to use in an error calculation for a constrained conjugate gradient minimization problem, calculating an approximate error using the subset of rays, and calculating a minimum in a conjugate gradient direction based on the approximate error. In another embodiment, a system includes a processor for executing logic, logic for selecting a subset of rays from a set of all rays to use in an error calculation for a constrained conjugate gradient minimization problem, logic for calculating an approximate error using the subset of rays, and logic for calculating a minimum in a conjugate gradient direction based on the approximate error. In other embodiments, computer program products, methods, and systems are described capable of using approximate error in constrained conjugate gradient minimization problems.

  13. Bauschinger Effect and Back Stress in Gradient Cu-Ge Alloy

    Science.gov (United States)

    Hu, Xianzhi; Jin, Shenbao; Zhou, Hao; Yin, Zhe; Yang, Jian; Gong, Yulan; Zhu, Yuntian; Sha, Gang; Zhu, Xinkun

    2017-09-01

    Using surface mechanical attrition treatment (SMAT), a gradient structure composed of two gradient structure (GS) layers and a coarse grain (CG) layer was generated from a Cu-5.7 wt pct Ge alloy, significantly improving the yield strength of the sample. Unloading-reloading tests showed an unusual Bauschinger effect in these GS samples. The back stresses caused by the accumulated geometrically necessary dislocations (GNDs) on the GS/CG border increased with increasing strain. As found by electron backscatter diffraction (EBSD), the GNDs are mainly distributed in the gradient structured layer, and the density of the GNDs increase with increasing SMAT time. The effect of the back stress increased with increasing SMAT processing time due to the increase in the strain gradient. The pronounced Bauschinger effect in a GS sample can improve the resistance to forward plastic flow and finally contributes to the high strength of GS samples.

  14. Exploring Nf=2 +1 QCD thermodynamics from the gradient flow

    Science.gov (United States)

    Taniguchi, Yusuke; Ejiri, Shinji; Iwami, Ryo; Kanaya, Kazuyuki; Kitazawa, Masakiyo; Suzuki, Hiroshi; Umeda, Takashi; Wakabayashi, Naoki; WHOT-QCD Collaboration

    2017-07-01

    The energy-momentum tensor plays an important role in QCD thermodynamics. Its expectation value contains information of the pressure and the energy density as its diagonal part. Further properties like viscosity and specific heat can be extracted from its correlation function. A nonperturbative evaluation of it on the lattice is called. Recently, a new method based on the gradient flow was introduced to calculate the energy-momentum tensor on the lattice and has been successfully applied to quenched QCD. In this paper, we apply the gradient flow method to calculate the energy-momentum tensor in (2 +1 )-flavor QCD adopting a nonperturbatively O (a )-improved Wilson quark action and the renormalization group-improved Iwasaki gauge action. As the first application of the method with dynamical quarks, we study at a single but fine lattice spacing a ≃0.07 fm with heavy u and d quarks (mπ/mρ≃0.63 ) and approximately physical s quark (mηss/mϕ≃0.74 ). With the fixed-scale approach, temperature is varied by the temporal lattice size Nt at a fixed lattice spacing. Performing simulations on lattices with Nt=16 to 4, the temperature range of T ≃174 - 697 MeV is covered. We find that the results of the pressure and the energy density by the gradient flow method are consistent with the previous results using the T -integration method at T ≲280 MeV (Nt≳10 ), while the results show disagreement at T ≳350 MeV (Nt≲8 ), presumably due to the small-Nt lattice artifact of O ((a T )2) =O (1 /Nt2) . We also apply the gradient flow method to evaluate the chiral condensate taking advantage of the gradient flow method that renormalized quantities can be directly computed avoiding the difficulty of explicit chiral violation with lattice quarks. We compute the renormalized chiral condensate in the MS ¯ scheme at renormalization scale μ =2 GeV with a high precision to study the temperature dependence of the chiral condensate and its disconnected susceptibility. Even with

  15. Asymmetric transmission of acoustic waves in a layer thickness distribution gradient structure using metamaterials

    Directory of Open Access Journals (Sweden)

    Jung-San Chen

    2016-09-01

    Full Text Available This research presents an innovative asymmetric transmission design using alternate layers of water and metamaterial with complex mass density. The directional transmission behavior of acoustic waves is observed numerically inside the composite structure with gradient layer thickness distribution and the rectifying performance of the present design is evaluated. The layer thickness distributions with arithmetic and geometric gradients are considered and the effect of gradient thickness on asymmetric wave propagation is systematically investigated using finite element simulation. The numerical results indicate that the maximum pressure density and transmission through the proposed structure are significantly influenced by the wave propagation direction over a wide range of audible frequencies. Tailoring the thickness of the layered structure enables the manipulation of asymmetric wave propagation within the desired frequency range. In conclusion, the proposed design offers a new possibility for developing directional-dependent acoustic devices.

  16. Stable Boundary Layer Education (STABLE) Final Campaign Summary

    Energy Technology Data Exchange (ETDEWEB)

    Turner, David D. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2016-03-01

    The properties of, and the processes that occur in, the nocturnal stable boundary layer are not well understood, making it difficult to represent adequately in numerical models. The nocturnal boundary layer often is characterized by a temperature inversion and, in the Southern Great Plains region, a low-level jet. To advance our understanding of the nocturnal stable boundary layer, high temporal and vertical resolution data on the temperature and wind properties are needed, along with both large-eddy simulation and cloud-resolving modeling.

  17. Calculation of Surface Tensions of Polar Mixtures with a Simplified Gradient Theory Model

    DEFF Research Database (Denmark)

    Zuo, You-Xiang; Stenby, Erling Halfdan

    1996-01-01

    Key Words: Thermodynamics, Simplified Gradient Theory, Surface Tension, Equation of state, Influence Parameter.In this work, assuming that the number densities of each component in a mixture across the interface between the coexisting vapor and liquid phases are linearly distributed, we developed...

  18. Comparison of termite assemblages along a landuse gradient on peat areas in Sarawak, Malaysia.

    NARCIS (Netherlands)

    Vaessen, T.; Verwer, C.; Demies, M.; Kaliang, H.; Meer, van der P.J.

    2011-01-01

    VAESSEN T, VERWER C, DEMIES M, KALIANG H & VAN DER MEER PJ. 2011. Comparison of termite assemblages along a landuse gradient on peat areas in Sarawak, Malaysia. In this study we assessed the species density and relative abundance of termites in peat land in Sarawak, Malaysia. Termites were

  19. Ab-initio calculations of electric field gradient in Ru compounds and ...

    Indian Academy of Sciences (India)

    S N Mishra

    2017-07-11

    Jul 11, 2017 ... useful for the precise determination of quadrupole moment of high spin states in other Ru isotopes and is likely to stimulate further shell model calculations for an improved understanding of nuclear shape in these nuclei. Keywords. Hyperfine field; electric field gradient; density functional calculation; nuclear ...

  20. Intracellular chemical gradients: morphing principle in bacteria

    Directory of Open Access Journals (Sweden)

    Endres Robert G

    2012-09-01

    Full Text Available Abstract Advances in computational biology allow systematic investigations to ascertain whether internal chemical gradients can be maintained in bacteria – an open question at the resolution limit of fluorescence microscopy. While it was previously believed that the small bacterial cell size and fast diffusion in the cytoplasm effectively remove any such gradient, a new computational study published in BMC Biophysics supports the emerging view that gradients can exist. The study arose from the recent observation that phosphorylated CtrA forms a gradient prior to cell division in Caulobacter crescentus, a bacterium known for its complicated cell cycle. Tropini et al. (2012 postulate that such gradients can provide an internal chemical compass, directing protein localization, cell division and cell development. More specifically, they describe biochemical and physical constraints on the formation of such gradients and explore a number of existing bacterial cell morphologies. These chemical gradients may limit in vitro analyses, and may ensure timing control and robustness to fluctuations during critical stages in cell development.

  1. Satellite gravity gradient grids for geophysics.

    Science.gov (United States)

    Bouman, Johannes; Ebbing, Jörg; Fuchs, Martin; Sebera, Josef; Lieb, Verena; Szwillus, Wolfgang; Haagmans, Roger; Novak, Pavel

    2016-02-11

    The Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite aimed at determining the Earth's mean gravity field. GOCE delivered gravity gradients containing directional information, which are complicated to use because of their error characteristics and because they are given in a rotating instrument frame indirectly related to the Earth. We compute gravity gradients in grids at 225 km and 255 km altitude above the reference ellipsoid corresponding to the GOCE nominal and lower orbit phases respectively, and find that the grids may contain additional high-frequency content compared with GOCE-based global models. We discuss the gradient sensitivity for crustal depth slices using a 3D lithospheric model of the North-East Atlantic region, which shows that the depth sensitivity differs from gradient to gradient. In addition, the relative signal power for the individual gradient component changes comparing the 225 km and 255 km grids, implying that using all components at different heights reduces parameter uncertainties in geophysical modelling. Furthermore, since gravity gradients contain complementary information to gravity, we foresee the use of the grids in a wide range of applications from lithospheric modelling to studies on dynamic topography, and glacial isostatic adjustment, to bedrock geometry determination under ice sheets.

  2. Particle acceleration in near critical density plasma

    International Nuclear Information System (INIS)

    Gu, Y.J.; Kong, Q.; Kawata, S.; Izumiyama, T.; Nagashima, T.

    2013-01-01

    Charged particle acceleration schemes driven by ultra intense laser and near critical density plasma interactions are presented. They include electron acceleration in a plasma channel, ion acceleration by the Coulomb explosion and high energy electron beam driven ion acceleration. It is found that under the near critical density plasma both ions and electrons are accelerated with a high acceleration gradient. The electron beam containing a large charge quantity is accelerated well with 23 GeV/cm. The collimated ion bunch reaches 1 GeV. The investigations and discussions are based on 2.5D PIC (particle-in-cell) simulations. (author)

  3. Forecasting gypsy moth egg-mass density

    Science.gov (United States)

    Robert W. Campbell; Robert W. Campbell

    1973-01-01

    Several multiple regression models for gypsy moth egg-mass density were developed from data accumulated in eastern New England between 1911 and 1931. Analysis of these models indicates that: (1) The gypsy moth population system was relatively stable in either the OUTBREAK phase or the INNOCUOUS one; (2) Several naturally occurring processes that could terminate the...

  4. Free water transport, small pore transport and the osmotic pressure gradient.

    Science.gov (United States)

    Parikova, Alena; Smit, Watske; Zweers, Machteld M; Struijk, Dirk G; Krediet, Raymond T

    2008-07-01

    Water transport in peritoneal dialysis (PD) patients occurs through the small pores and water channels, the latter allowing free water transport (FWT). The osmotic gradient is known to be one of the major determinants of water transport. The objective of the study was to analyse the relation between each transport route and the osmotic gradient. The 4-h standard peritoneal permeability analyses of 80 stable PD patients were studied. Small pore transport (SPT) was calculated based on the transported amount of sodium. FWT was calculated by subtracting SPT from transcapillary ultrafiltration (TCUF). Water transport rates were determined. The osmotic gradient was calculated. The slope of the relation between FWT rate and osmotic gradient (slope(FWT)), and the elimination constant (K(e)) of the exponential relation between SPT rate and osmotic gradient (K(SPT)) were calculated for every patient. The FWT rate was related to the osmotic gradient (P = 0.001). A similar correlation was also found between the SPT rate and osmotic gradient when fitted exponentially (P = 0.005). The rates of FWT decreased significantly between each time point during the whole dwell. The SPT rates decreased significantly within the first half of the dwell and levelled off thereafter. No correlations were found between the slope(FWT), K(SPT) and PD duration. The slope(FWT) of the relationship between the FWT and the osmotic gradient is an indirect measurement of the amount of functioning water channels. Similarly, the K(SPT) value represents the number of functioning small pores. The absence of a relationship of these parameters with the duration of PD suggests opposing mechanisms, for instance a lower number of functioning pores in combination with an increased vascular surface area. Conclusion. The curves of the relationship between FWR, SPT and OG support the assumption that FWR is much more dependent on the OG than SPT. Non-osmotic determinants are likely to be important in small pore fluid

  5. Sound beam manipulation based on temperature gradients

    Energy Technology Data Exchange (ETDEWEB)

    Qian, Feng [Key Laboratory of Modern Acoustics, Institute of Acoustics and School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093 (China); School of Physics & Electronic Engineering, Changshu Institute of Technology, Changshu 215500 (China); Quan, Li; Liu, Xiaozhou, E-mail: xzliu@nju.edu.cn; Gong, Xiufen [Key Laboratory of Modern Acoustics, Institute of Acoustics and School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093 (China)

    2015-10-28

    Previous research with temperature gradients has shown the feasibility of controlling airborne sound propagation. Here, we present a temperature gradients based airborne sound manipulation schemes: a cylindrical acoustic omnidirectional absorber (AOA). The proposed AOA has high absorption performance which can almost completely absorb the incident wave. Geometric acoustics is used to obtain the refractive index distributions with different radii, which is then utilized to deduce the desired temperature gradients. Since resonant units are not applied in the scheme, its working bandwidth is expected to be broadband. The scheme is temperature-tuned and easy to realize, which is of potential interest to fields such as noise control or acoustic cloaking.

  6. On fracture in finite strain gradient plasticity

    DEFF Research Database (Denmark)

    Martínez Pañeda, Emilio; Niordson, Christian Frithiof

    2016-01-01

    predictions. These differences increase significantly when large strains are taken into account, as a consequence of the contribution of strain gradients to the work hardening of the material. The magnitude of stress elevation at the crack tip and the distance ahead of the crack where GNDs significantly alter......In this work a general framework for damage and fracture assessment including the effect of strain gradients is provided. Both mechanism-based and phenomenological strain gradient plasticity (SGP) theories are implemented numerically using finite deformation theory and crack tip fields...

  7. Speciation gradients and the distribution of biodiversity.

    Science.gov (United States)

    Schluter, Dolph; Pennell, Matthew W

    2017-05-31

    Global patterns of biodiversity are influenced by spatial and environmental variations in the rate at which new species form. We relate variations in speciation rates to six key patterns of biodiversity worldwide, including the species-area relationship, latitudinal gradients in species and genetic diversity, and between-habitat differences in species richness. Although they sometimes mirror biodiversity patterns, recent rates of speciation, at the tip of the tree of life, are often highest where species richness is low. Speciation gradients therefore shape, but are also shaped by, biodiversity gradients and are often more useful for predicting future patterns of biodiversity than for interpreting the past.

  8. Sound beam manipulation based on temperature gradients

    International Nuclear Information System (INIS)

    Qian, Feng; Quan, Li; Liu, Xiaozhou; Gong, Xiufen

    2015-01-01

    Previous research with temperature gradients has shown the feasibility of controlling airborne sound propagation. Here, we present a temperature gradients based airborne sound manipulation schemes: a cylindrical acoustic omnidirectional absorber (AOA). The proposed AOA has high absorption performance which can almost completely absorb the incident wave. Geometric acoustics is used to obtain the refractive index distributions with different radii, which is then utilized to deduce the desired temperature gradients. Since resonant units are not applied in the scheme, its working bandwidth is expected to be broadband. The scheme is temperature-tuned and easy to realize, which is of potential interest to fields such as noise control or acoustic cloaking

  9. Areal-averaged trace gas emission rates from long-range open-path measurements in stable boundary layer conditions

    Directory of Open Access Journals (Sweden)

    K. Schäfer

    2012-07-01

    Full Text Available Measurements of land-surface emission rates of greenhouse and other gases at large spatial scales (10 000 m2 are needed to assess the spatial distribution of emissions. This can be readily done using spatial-integrating micro-meteorological methods like flux-gradient methods which were evaluated for determining land-surface emission rates of trace gases under stable boundary layers. Non-intrusive path-integrating measurements are utilized. Successful application of a flux-gradient method requires confidence in the gradients of trace gas concentration and wind, and in the applicability of boundary-layer turbulence theory; consequently the procedures to qualify measurements that can be used to determine the flux is critical. While there is relatively high confidence in flux measurements made under unstable atmospheres with mean winds greater than 1 m s−1, there is greater uncertainty in flux measurements made under free convective or stable conditions. The study of N2O emissions of flat grassland and NH3 emissions from a cattle lagoon involves quality-assured determinations of fluxes under low wind, stable or night-time atmospheric conditions when the continuous "steady-state" turbulence of the surface boundary layer breaks down and the layer has intermittent turbulence. Results indicate that following the Monin-Obukhov similarity theory (MOST flux-gradient methods that assume a log-linear profile of the wind speed and concentration gradient incorrectly determine vertical profiles and thus flux in the stable boundary layer. An alternative approach is considered on the basis of turbulent diffusivity, i.e. the measured friction velocity as well as height gradients of horizontal wind speeds and concentrations without MOST correction for stability. It is shown that this is the most accurate of the flux-gradient methods under stable conditions.

  10. Spin and orbital magnetism of coinage metal trimers (Cu3, Ag3, Au3: A relativistic density functional theory study

    Directory of Open Access Journals (Sweden)

    Mahdi Afshar

    2013-11-01

    Full Text Available We have demonstrated electronic structure and magnetic properties of Cu3, Ag3 and Au3 trimers using a full potential local orbital method in the framework of relativistic density functional theory. We have also shown that the non-relativistic generalized gradient approximation for the exchange-correlation energy functional gives reliable magnetic properties in coinage metal trimers compared to experiment. In addition we have indicated that the spin-orbit coupling changes the structure and magnetic properties of gold trimer while the structure and magnetic properties of copper and silver trimers are marginally affected. A significant orbital moment of 0.21μB was found for most stable geometry of the gold trimer whereas orbital magnetism is almost quenched in the copper and silver trimers.

  11. Conspecific negative density dependence and forest diversity.

    Science.gov (United States)

    Johnson, Daniel J; Beaulieu, Wesley T; Bever, James D; Clay, Keith

    2012-05-18

    Conspecific negative density-dependent establishment, in which local abundance negatively affects establishment of conspecific seedlings through host-specific enemies, can influence species diversity of plant communities, but the generality of this process is not well understood. We tested the strength of density dependence using the United States Forest Service's Forest Inventory and Analysis database containing 151 species from more than 200,000 forest plots spanning 4,000,000 square kilometers. We found that most species experienced conspecific negative density dependence (CNDD), but there was little effect of heterospecific density. Additionally, abundant species exhibited weaker CNDD than rarer species, and species-rich regions exhibited stronger CNDD than species-poor regions. Collectively, our results provide evidence that CNDD is a pervasive mechanism driving diversity across a gradient from boreal to subtropical forests.

  12. Determination of Resistant Starch Assimilating Bacteria in Fecal Samples of Mice by In vitro RNA-Based Stable Isotope Probing

    Directory of Open Access Journals (Sweden)

    Elena Herrmann

    2017-07-01

    Full Text Available The impact of the intestinal microbiota on human health is becoming increasingly appreciated in recent years. In consequence, and fueled by major technological advances, the composition of the intestinal microbiota in health and disease has been intensively studied by high throughput sequencing approaches. Observations linking dysbiosis of the intestinal microbiota with a number of serious medical conditions including chronic inflammatory disorders and allergic diseases suggest that restoration of the composition and activity of the intestinal microbiota may be a treatment option at least for some of these diseases. One possibility to shape the intestinal microbiota is the administration of prebiotic carbohydrates such as resistant starch (RS. In the present study, we aim at establishing RNA-based stable isotope probing (RNA-SIP to identify bacterial populations that are involved in the assimilation of RS using anaerobic in vitro fermentation of murine fecal material with stable [U13C] isotope-labeled potato starch. Total RNA from these incubations was extracted, processed by gradient ultracentrifugation and fractionated by density. 16S rRNA gene sequences were amplified from reverse transcribed RNA of high and low density fractions suspected to contain labeled and unlabeled RNA, respectively. Phylogenetic analysis of the obtained sequences revealed a distinct subset of the intestinal microbiota involved in starch metabolism. The results suggest Bacteroidetes, in particular genera affiliated with Prevotellaceae, as well as members of the Ruminococcacea family to be primary assimilators of resistant starch due to a significantly higher relative abundance in higher density fractions in RNA samples isolated after 2 h of incubation. Using high performance liquid chromatography coupled to isotope ratio mass spectrometry (HPLC-IRMS analysis, some stable isotope label was recovered from acetate, propionate and butyrate. Here, we demonstrate the

  13. Instabilities in the Nuclear Energy Density Functional

    Energy Technology Data Exchange (ETDEWEB)

    Kortelainen, Erno M [ORNL; Lesinski, Thomas [ORNL

    2010-01-01

    In the field of Energy Density Functionals (EDF) used in nuclear structure and dynamics, one of the unsolved issues is the stability of the functional. Numerical issues aside, some EDFs are unstable with respect to particular perturbations of the nuclear ground-state density. The aim of this contribution is to raise questions about the origin and nature of these instabilities, the techniques used to diagnose and prevent them, and the domain of density functions in which one should expect a nuclear EDF to be stable.

  14. Wideband quin-stable energy harvesting via combined nonlinearity

    Directory of Open Access Journals (Sweden)

    Chen Wang

    2017-04-01

    Full Text Available In this work, we propose a wideband quintuple-well potential piezoelectric-based vibration energy harvester using a combined nonlinearity: the magnetic nonlinearity induced by magnetic force and the piecewise-linearity produced by mechanical impact. With extra stable states compared to other multi-stable harvesters, the quin-stable harvester can distribute its potential energy more uniformly, which provides shallower potential wells and results in lower excitation threshold for interwell motion. The mathematical model of this quin-stable harvester is derived and its equivalent piecewise-nonlinear restoring force is measured in the experiment and identified as piecewise polynomials. Numerical simulations and experimental verifications are performed in different levels of sinusoid excitation ranging from 1 to 25 Hz. The results demonstrate that, with lower potential barriers compared with tri-stable counterpart, the quin-stable arrangement can escape potential wells more easily for doing high-energy interwell motion over a wider band of frequencies. Moreover, by utilizing the mechanical stoppers, this harvester can produce significant output voltage under small tip deflections, which results in a high power density and is especially suitable for a compact MEMS approach.

  15. Coaxial two-channel high-gradient dielectric wakefield accelerator

    Directory of Open Access Journals (Sweden)

    G. V. Sotnikov

    2009-06-01

    Full Text Available A new scheme for a dielectric wakefield accelerator is proposed that employs a cylindrical multizone dielectric structure configured as two concentric dielectric tubes with outer and inner vacuum channels for drive and accelerated bunches. Analytical and numerical studies have been carried out for such coaxial dielectric-loaded structures (CDS for high-gradient acceleration. An analytical theory of wakefield excitation by particle bunches in a multizone CDS has been formulated. Numerical calculations are presented for an example of a CDS using dielectric tubes with dielectric permittivity 5.7, having external diameters of 2.121 and 0.179 mm with inner diameters of 2.095 and 0.1 mm. An annular 5 GeV, 6 nC electron bunch with rms length of 0.035 mm energizes a wakefield on the structure axis having an accelerating gradient of ∼600  MeV/m with a transformer ratio ∼8∶1. The period of the accelerating field is ∼0.33  mm. If the width of the drive bunch channel is decreased, it is possible to obtain an accelerating gradient of >1  GeV/m while keeping the transformer ratio approximately the same. Full numerical simulations using a particle-in-cell code have confirmed results of the linear theory and furthermore have shown the important influence of the quenching wave that restricts the region of the wakefield to within several periods following the drive bunch. Numerical simulations for another example have shown nearly stable transport of drive and accelerated bunches through the CDS, using a short train of drive bunches.

  16. High-gradient two-beam accelerator structure

    Directory of Open Access Journals (Sweden)

    S. Yu Kazakov

    2010-07-01

    Full Text Available A novel cavity structure is described that could be the basis for a two-beam, high-gradient, accelerator. Versions of the structure could be used for acceleration of beams of electrons, positrons, muons, protons, or heavier ions; with either electron or proton drive beams. The structure embodies cavities that are excited in several harmonically related eigenmodes, such that rf fields reach their peak values only during small portions of each basic rf period. This feature could help raise breakdown and pulse heating thresholds. The two-beam accelerator structure comprises chains of these cavities. In this configuration, no transfer elements are needed to couple rf energy from the drive beam to the accelerated beam, since both beams traverse the same cavities. Purposeful cavity detuning is used to provide much smaller deceleration for a high-current drive beam, than acceleration for a low-current accelerated beam, i.e., to provide a high transformer ratio. A self-consistent theory is presented to calculate idealized acceleration gradient, transformer ratio, and efficiency for energy transfer from the drive beam to the accelerated beam, for either parallel or antiparallel motion of the beams. The theory has been cast in dimensionless quantities so as to facilitate optimization with respect to efficiency, acceleration gradient, or transformer ratio, and to illuminate the interdependence of these parameters. Means for dramatically shortening the structure fill time are also described. However, no beam dynamics analysis is presented, so the range of parameters within which this new acceleration concept can be used will remain uncertain until it is established that stable beam transport along the structure using an appropriate focusing system is possible.

  17. Radiation-stable polyolefin compositions

    International Nuclear Information System (INIS)

    Rekers, J.W.

    1986-01-01

    This invention relates to compositions of olefinic polymers suitable for high energy radiation treatment. In particular, the invention relates to olefinic polymer compositions that are stable to sterilizing dosages of high energy radiation such as a gamma radiation. Stabilizers are described that include benzhydrol and benzhydrol derivatives; these stabilizers may be used alone or in combination with secondary antioxidants or synergists

  18. Monitoring of stable glaucoma patients

    NARCIS (Netherlands)

    K.M. Holtzer-Goor (Kim); N.S. Klazinga (Niek); M.A. Koopmanschap (Marc); H.G. Lemij (Hans); T. Plochg; E. van Sprundel (Esther)

    2010-01-01

    textabstractA high workload for ophthalmologists and long waiting lists for patients challenge the organization of ophthalmic care. Tasks that require less specialized skills, like the monitoring of stable (well controlled) glaucoma patients could be substituted from ophthalmologists to other

  19. A new type of descent conjugate gradient method with exact line search

    Science.gov (United States)

    Hajar, Nurul; Mamat, Mustafa; Rivaie, Mohd.; Jusoh, Ibrahim

    2016-06-01

    Nowadays, conjugate gradient (CG) methods are impressive for solving nonlinear unconstrained optimization problems. In this paper, a new CG method is proposed and analyzed. This new CG method satisfies descent condition and its global convergence is established using exact line search. Numerical results show that this new CG method substantially outperforms the previous CG methods. This new CG method is considered robust, efficient and provided faster and stable convergence.

  20. Are pine plantations valid tools for restoring Mediterranean forests? An assessment along abiotic and biotic gradients.

    Science.gov (United States)

    Gómez-Aparicio, Lorena; Zavala, Miguel A; Bonet, Francisco J; Zamora, Regino

    2009-12-01

    The ecological impacts of forest plantations are a focus of intense debate, from studies that consider plantations as "biological deserts" to studies showing positive effects on plant diversity and dynamics. This lack of consensus might be influenced by the scarcity of studies that examine how the ecological characteristics of plantations vary along abiotic and biotic gradients. Here we conducted a large-scale assessment of plant regeneration and diversity in plantations of southern Spain. Tree seedling and sapling density, plant species richness, and Shannon's (H') diversity index were analyzed in 442 pine plantation plots covering a wide gradient of climatic conditions, stand density, and distance to natural forests that act as seed sources. Pronounced variation in regeneration and diversity was found in plantation understories along the gradients explored. Low- to mid-altitude plantations showed a diverse and abundant seedling bank dominated by Quercus ilex, whereas high-altitude plantations showed a virtually monospecific seeding bank of Pinus sylvestris. Regeneration was null in plantations with stand densities exceeding 1500 pines/ha. Moderate plantation densities (500-1000 pines/ha) promoted recruitment in comparison to low or null canopy cover, suggesting the existence of facilitative interactions. Quercus ilex recruitment diminished exponentially with distance to the nearest Q. ilex forest. Richness and H' index values showed a hump-shaped distribution along the altitudinal and radiation gradients and decreased monotonically along the stand density gradient. From a management perspective, different strategies will be necessary depending on where a plantation lies along the gradients explored. Active management will be required in high-density plantations with arrested succession and low diversity. Thinning could redirect plantations toward more natural densities where facilitation predominates. Passive management might be recommended for low- to moderate-density

  1. Improving GOCE cross-track gravity gradients

    Science.gov (United States)

    Siemes, Christian

    2018-01-01

    The GOCE gravity gradiometer measured highly accurate gravity gradients along the orbit during GOCE's mission lifetime from March 17, 2009, to November 11, 2013. These measurements contain unique information on the gravity field at a spatial resolution of 80 km half wavelength, which is not provided to the same accuracy level by any other satellite mission now and in the foreseeable future. Unfortunately, the gravity gradient in cross-track direction is heavily perturbed in the regions around the geomagnetic poles. We show in this paper that the perturbing effect can be modeled accurately as a quadratic function of the non-gravitational acceleration of the satellite in cross-track direction. Most importantly, we can remove the perturbation from the cross-track gravity gradient to a great extent, which significantly improves the accuracy of the latter and offers opportunities for better scientific exploitation of the GOCE gravity gradient data set.

  2. Vegetation patterns and environmental gradients in Benin

    NARCIS (Netherlands)

    Adomou, A.

    2005-01-01

    Key words: West Africa, Benin, vegetation patterns, floristic areas, phytogeography, chorology, floristic gradients, climatic factors, water availability, Dahomey Gap, threatened plants, biodiversity, conservation.Understanding plant species distribution patterns and the underlying factors is a

  3. Flexoelectricity: strain gradient effects in ferroelectrics

    Energy Technology Data Exchange (ETDEWEB)

    Ma Wenhui [Department of Physics, Shantou Unversity, Shantou, Guangdong 515063 (China)

    2007-12-15

    Mechanical strain gradient induced polarization effect or flexoelectricity in perovskite-type ferroelectric and relaxor ferroelectric ceramics was investigated. The flexoelectric coefficients measured at room temperature ranged from about 1 {mu} C m{sup -1} for lead zirconate titanate to 100 {mu} C m{sup -1} for barium strontium titanate. Flexoelectric effects were discovered to be sensitive to chemical makeup, phase symmetry, and domain structures. Based on phenomenological discussion and experimental data on flexoelectricity, the present study proposed that mechanical strain gradient field could influence polarization responses in a way analogous to electric field. Flexoelectric coefficients were found to be nonlinearly enhanced by dielectric permittivity and strain gradient. Interfacial mismatch in epitaxial thin films can give rise to high strain gradients, enabling flexoelectric effects to make a significant impact in properly engineered ferroelectric heterostructure systems.

  4. Flexoelectricity: strain gradient effects in ferroelectrics

    International Nuclear Information System (INIS)

    Ma Wenhui

    2007-01-01

    Mechanical strain gradient induced polarization effect or flexoelectricity in perovskite-type ferroelectric and relaxor ferroelectric ceramics was investigated. The flexoelectric coefficients measured at room temperature ranged from about 1 μ C m -1 for lead zirconate titanate to 100 μ C m -1 for barium strontium titanate. Flexoelectric effects were discovered to be sensitive to chemical makeup, phase symmetry, and domain structures. Based on phenomenological discussion and experimental data on flexoelectricity, the present study proposed that mechanical strain gradient field could influence polarization responses in a way analogous to electric field. Flexoelectric coefficients were found to be nonlinearly enhanced by dielectric permittivity and strain gradient. Interfacial mismatch in epitaxial thin films can give rise to high strain gradients, enabling flexoelectric effects to make a significant impact in properly engineered ferroelectric heterostructure systems

  5. Integral Field Spectroscopy Surveys: Oxygen Abundance Gradients

    Science.gov (United States)

    Sánchez, S. F.; Sánchez-Menguiano, L.

    2017-07-01

    We present here the recent results on our understanding of oxygen abundance gradients derived using Integral Field Spectroscopic surveys. In particular we analyzed more than 2124 datacubes corresponding to individual objects observed by the CALIFA (˜ 734 objects) and the public data by MaNGA (˜ 1390 objects), deriving the oxygen abundance gradient for each galaxy. We confirm previous results that indicate that the shape of this gradient is very similar for all galaxies with masses above 109.5M⊙, presenting in average a very similar slope of ˜ -0.04 dex within 0.5-2.0 re, with a possible drop in the inner regions (r109.5M⊙) the gradient seems to be flatter than for more massive ones. All these results agree with an inside-out growth of massive galaxies and indicate that low mass ones may still be growing in an outside in phase.

  6. Unimodal and crossmodal gradients of spatial attention

    DEFF Research Database (Denmark)

    Föcker, J.; Hötting, K.; Gondan, Matthias

    2010-01-01

    Behavioral and event-related potential (ERP) studies have shown that spatial attention is gradually distributed around the center of the attentional focus. The present study compared uni- and crossmodal gradients of spatial attention to investigate whether the orienting of auditory and visual...... spatial attention is based on modality specific or supramodal representations of space. Auditory and visual stimuli were presented from five speaker locations positioned in the right hemifield. Participants had to attend to the innermost or outmost right position in order to detect either visual...... or auditory deviant stimuli. Detection rates and event-related potentials (ERPs) indicated that spatial attention is distributed as a gradient. Unimodal spatial ERP gradients correlated with the spatial resolution of the modality. Crossmodal spatial gradients were always broader than the corresponding...

  7. Photosynthetic and gas exchange characteristics of dominant woody plants on a moisture gradient in an African savanna

    NARCIS (Netherlands)

    Midgley, G.F.; Aranibar, J.N.; Mantlana, K.B.; Macko, S.

    2004-01-01

    We determined key photosynthetic gas exchange parameters, and their temperature dependence, in dominant woody plants at four savanna sites on a moisture gradient in Botswana, southern Africa. Leaf stable carbon and nitrogen (N) isotope and morphological measures were made concurrently. Sampling of

  8. Tolman temperature gradients in a gravitational field

    OpenAIRE

    Santiago, Jessica; Visser, Matt

    2018-01-01

    Tolman's relation for the temperature gradient in an equilibrium self-gravitating general relativistic fluid is broadly accepted within the general relativity community. However, the concept of temperature gradients in thermal equilibrium continues to cause confusion in other branches of physics, since it contradicts naive versions of the laws of classical thermodynamics. In this paper we discuss the crucial role of the universality of free fall, and how thermodynamics emphasises the great di...

  9. Ultimate gradient in solid-state accelerators

    Energy Technology Data Exchange (ETDEWEB)

    Whittum, D.H.

    1998-08-01

    The authors recall the motivation for research in high-gradient acceleration and the problems posed by a compact collider. They summarize the phenomena known to appear in operation of a solid-state structure with large fields, and research relevant to the question of the ultimate gradient. They take note of new concepts, and examine one in detail, a miniature particle accelerator based on an active millimeter-wave circuit and parallel particle beams.

  10. Ultimate gradient in solid-state accelerators

    International Nuclear Information System (INIS)

    Whittum, D.H.

    1998-08-01

    The authors recall the motivation for research in high-gradient acceleration and the problems posed by a compact collider. They summarize the phenomena known to appear in operation of a solid-state structure with large fields, and research relevant to the question of the ultimate gradient. They take note of new concepts, and examine one in detail, a miniature particle accelerator based on an active millimeter-wave circuit and parallel particle beams

  11. Intratumoral oxygen gradients mediate sarcoma cell invasion

    Science.gov (United States)

    Lewis, Daniel M.; Park, Kyung Min; Tang, Vitor; Xu, Yu; Pak, Koreana; Eisinger-Mathason, T. S. Karin; Simon, M. Celeste; Gerecht, Sharon

    2016-01-01

    Hypoxia is a critical factor in the progression and metastasis of many cancers, including soft tissue sarcomas. Frequently, oxygen (O2) gradients develop in tumors as they grow beyond their vascular supply, leading to heterogeneous areas of O2 depletion. Here, we report the impact of hypoxic O2 gradients on sarcoma cell invasion and migration. O2 gradient measurements showed that large sarcoma mouse tumors (>300 mm3) contain a severely hypoxic core [≤0.1% partial pressure of O2 (pO2)] whereas smaller tumors possessed hypoxic gradients throughout the tumor mass (0.1–6% pO2). To analyze tumor invasion, we used O2-controllable hydrogels to recreate the physiopathological O2 levels in vitro. Small tumor grafts encapsulated in the hydrogels revealed increased invasion that was both faster and extended over a longer distance in the hypoxic hydrogels compared with nonhypoxic hydrogels. To model the effect of the O2 gradient accurately, we examined individual sarcoma cells embedded in the O2-controllable hydrogel. We observed that hypoxic gradients guide sarcoma cell motility and matrix remodeling through hypoxia-inducible factor-1α (HIF-1α) activation. We further found that in the hypoxic gradient, individual cells migrate more quickly, across longer distances, and in the direction of increasing O2 tension. Treatment with minoxidil, an inhibitor of hypoxia-induced sarcoma metastasis, abrogated cell migration and matrix remodeling in the hypoxic gradient. Overall, we show that O2 acts as a 3D physicotactic agent during sarcoma tumor invasion and propose the O2-controllable hydrogels as a predictive system to study early stages of the metastatic process and therapeutic targets. PMID:27486245

  12. The density-salinity relation of standard seawater

    Science.gov (United States)

    Schmidt, Hannes; Seitz, Steffen; Hassel, Egon; Wolf, Henning

    2018-01-01

    The determination of salinity by means of electrical conductivity relies on stable salt proportions in the North Atlantic Ocean, because standard seawater, which is required for salinometer calibration, is produced from water of the North Atlantic. To verify the long-term stability of the standard seawater composition, it was proposed to perform measurements of the standard seawater density. Since the density is sensitive to all salt components, a density measurement can detect any change in the composition. A conversion of the density values to salinity can be performed by means of a density-salinity relation. To use such a relation with a target uncertainty in salinity comparable to that in salinity obtained from conductivity measurements, a density measurement with an uncertainty of 2 g m-3 is mandatory. We present a new density-salinity relation based on such accurate density measurements. The substitution measurement method used is described and density corrections for uniform isotopic and chemical compositions are reported. The comparison of densities calculated using the new relation with those calculated using the present reference equations of state TEOS-10 suggests that the density accuracy of TEOS-10 (as well as that of EOS-80) has been overestimated, as the accuracy of some of its underlying density measurements had been overestimated. The new density-salinity relation may be used to verify the stable composition of standard seawater by means of routine density measurements.

  13. Correlations of the energy-momentum tensor via gradient flow in SU(3) Yang-Mills theory at finite temperature

    Science.gov (United States)

    Kitazawa, Masakiyo; Iritani, Takumi; Asakawa, Masayuki; Hatsuda, Tetsuo

    2017-12-01

    Euclidean two-point correlators of the energy-momentum tensor (EMT) in SU(3) gauge theory on the lattice are studied on the basis of the Yang-Mills gradient flow. The entropy density and the specific heat obtained from the two-point correlators are shown to be in good agreement with those from the one-point functions of EMT. These results constitute a first step toward the first principle simulations of the transport coefficients with the gradient flow.

  14. Electropolishing of Stainless Steel Implants for Stable Functional Osteosynthesis

    Directory of Open Access Journals (Sweden)

    Omel’chuk, A.О.

    2016-01-01

    Full Text Available A new method for the electropolishing stainless steel for stable functional osteosynthesis has been developed. The polishing of implants was carried out in solutions, based on the ternary system H2SO4—H3PO4—H2O with stepwise decreasing the current density and increasing the orthophosphoric acid concentration. The optimal polishing conditions (current density, solution composition, temperature and duration have been determined. The developed method improves the quality and mechanical properties of the surface.

  15. Stable corrugated state of the two-dimensional electron gas

    International Nuclear Information System (INIS)

    Mendez-Moreno, R.M.; Moreno, M.; Ortiz, M.A.

    1991-01-01

    A corrugated and stable ground state is found for the two-dimensional electron gas in both the normal paramagnetic and the fully polarized phases. The self-consistent Hartree-Fock method is used with a modulated set of trial wave functions within the deformable jellium model. The results for high metallic densities reproduce the usual noncorrugated ferromagnetic electron-gas behavior. A transition to a paramagnetic corrugated state for values of r s ∼6.5 is predicted. At lower densities r s ∼30, a second transition to a corrugated ferromagnetic phase is suggested

  16. Oxidatively stable polyaniline:polyacid electrodes for electrochemical energy storage.

    Science.gov (United States)

    Jeon, Ju-Won; Ma, Yuguang; Mike, Jared F; Shao, Lin; Balbuena, Perla B; Lutkenhaus, Jodie L

    2013-06-28

    Conjugated polymers, such as polyaniline, have been widely explored as sensors, electrodes, and conductive fillers. As an electrode material in electrochemical energy storage systems, polyaniline can be subject to irreversible oxidation that reduces cycle life and electrode capacity, thus, limiting its widespread application. Here we present a simple route to produce and prepare polyaniline-based electrodes that are oxidatively stable up to 4.5 V vs. Li/Li(+). The route uses a polyacid to stabilize the fully oxidized pernigraniline salt form of polyaniline, which is normally highly unstable as a homopolymer. The result is an organic electrode of exceptionally high capacity, energy density, power density, and cycle life. We demonstrate that the polyaniline:polyacid electrode stores 230 mA h g(-1) of polyaniline for over 800 cycles, far surpassing homopolymer polyaniline under equivalent conditions. This approach provides a highly stable, electrochemically reversible replacement for conventional polyaniline.

  17. Magnetoelectric Transverse Gradient Sensor with High Detection Sensitivity and Low Gradient Noise

    OpenAIRE

    Zhang, Mingji; Or, Siu Wing

    2017-01-01

    We report, theoretically and experimentally, the realization of a high detection performance in a novel magnetoelectric (ME) transverse gradient sensor based on the large ME effect and the magnetic field gradient (MFG) technique in a pair of magnetically-biased, electrically-shielded, and mechanically-enclosed ME composites having a transverse orientation and an axial separation. The output voltage of the gradient sensor is directly obtained from the transverse MFG-induced difference in ME vo...

  18. Oribatid mite communities along an elevational gradient in Sairme gorge (Caucasus).

    Science.gov (United States)

    Mumladze, Levan; Murvanidze, Maka; Maraun, Mark; Salakaia, Meri

    2015-05-01

    Many aboveground animals and plant communities have been studied along elevational gradients whereas studies on soil animals are scarce. Here, we studied oribatid mite community distribution along an elevational gradient from 600 to 2200 m in forest ecosystems of the Western Lesser Caucasus Mountains in Georgia. Overall, 86 oribatid mite species were found at the study sites. Oribatid mite densities were generally low (~9800 ind./m(2)), and 74% of all species reproduced sexually indicating that resource conditions at the study sites are generally poor. Oribatids mainly comprised Brachypylina (76%), Mixonomata (13%), Desmonomata (6%) and Enarthronota (5%). Oribatid mite community structure changed along the elevational gradient and the changes correlated with temperature, pH, litter thickness and density of the herb layer. The dominance of sexually reproducing taxa and low overall abundance indicate that the studied elevational gradient is characterized by poor resource conditions for soil microarthropods. Oribatid mite species richness and density declined with elevation suggesting that decreasing temperature in concert with resource limitation is a main driver of oribatid mite communities whereas stochastic factors (such as mid-domain effects) are of minor importance.

  19. Toward Practical Secure Stable Matching

    Directory of Open Access Journals (Sweden)

    Riazi M. Sadegh

    2017-01-01

    Full Text Available The Stable Matching (SM algorithm has been deployed in many real-world scenarios including the National Residency Matching Program (NRMP and financial applications such as matching of suppliers and consumers in capital markets. Since these applications typically involve highly sensitive information such as the underlying preference lists, their current implementations rely on trusted third parties. This paper introduces the first provably secure and scalable implementation of SM based on Yao’s garbled circuit protocol and Oblivious RAM (ORAM. Our scheme can securely compute a stable match for 8k pairs four orders of magnitude faster than the previously best known method. We achieve this by introducing a compact and efficient sub-linear size circuit. We even further decrease the computation cost by three orders of magnitude by proposing a novel technique to avoid unnecessary iterations in the SM algorithm. We evaluate our implementation for several problem sizes and plan to publish it as open-source.

  20. New AB Initio Based Density Functional Methods for Molecules, Polymers, and Crystals

    National Research Council Canada - National Science Library

    Bartlett, Rodney

    2000-01-01

    My efforts in the Density Functional Theory (DFT) project of Dr. Bartlett's research group have been limited to the implementation of analytical energy gradients with respect to nuclear displacement in ACES2...

  1. Gradient ultrafine-grained titanium: Computational study of mechanical and damage behavior

    DEFF Research Database (Denmark)

    Liu, Hongsheng; Mishnaevsky, Leon

    2014-01-01

    A computational model of ultrafine-grained (UFG) titanium with random and gradient distribution based on Voronoi tessellation and the composite model of nanomaterials is developed. The effect of grain size, non-equilibrium state of the grain boundary phase (characterized by the initial dislocation...... density and diffusion coefficient) and gradient of grain sizes on the mechanical behavior and damage initiation of the UFG titanium are studied in numerical experiments. Using computational experiments, the authors determined the likely damage criterion (dislocation-based model) and found several effects...

  2. Towards stable acceleration in LINACS

    CERN Document Server

    Dubrovskiy, A D

    2014-01-01

    Ultra-stable and -reproducible high-energy particle beams with short bunches are needed in novel linear accelerators and, in particular, in the Compact Linear Collider CLIC. A passive beam phase stabilization system based on a bunch compression with a negative transfer matrix element R56 and acceleration at a positive off-crest phase is proposed. The motivation and expected advantages of the proposed scheme are outlined.

  3. An assessment of an environmental gradient using coral geochemical records, Whitsunday Islands, Great Barrier Reef, Australia.

    Science.gov (United States)

    Lewis, S E; Brodie, J E; McCulloch, M T; Mallela, J; Jupiter, S D; Williams, H Stuart; Lough, J M; Matson, E G

    2012-01-01

    Coral cores were collected along an environmental and water quality gradient through the Whitsunday Island group, Great Barrier Reef (Australia), for trace element and stable isotope analysis. The primary aim of the study was to examine if this gradient could be detected in coral records and, if so, whether the gradient has changed over time with changing land use in the adjacent river catchments. Y/Ca was the trace element ratio which varied spatially across the gradient, with concentrations progressively decreasing away from the river mouths. The Ba/Ca and Y/Ca ratios were the only indicators of change in the gradient through time, increasing shortly after European settlement. The Mn/Ca ratio responded to local disturbance related to the construction of tourism infrastructure. Nitrogen isotope ratios showed no apparent trend over time. This study highlights the importance of site selection when using coral records to record regional environmental signals. Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.

  4. Perturbations of the solar wind flow by radial and latitudinal pick-up ion pressure gradients

    Directory of Open Access Journals (Sweden)

    H. J. Fahr

    2004-06-01

    Full Text Available It has been found that pick-up ions at their dynamical incorporation into the solar wind modify the original conditions of the asymptotic solar wind plasma flow. In this respect, it has meanwhile been revealed in many papers that these type of solar wind modifications, i.e. deceleration and decrease of effective Mach number, are not only due to the pick-up ion loading effects, but also to the action of pick-up ion pressure gradients. Up to now only the effects of radial pick-up ion pressure gradients were considered, however, analogously but latitudinal pressure gradients also appear to be important. Here we study the effects of radial and latitudinal pick-up ion pressure gradients, occurring especially during solar minimum conditions at mid-latitude regions where slow solar wind streams change to fast solar wind streams. First, we give estimates of the latitudinal wind components connected with these gradients, and then after revealing its importance, present a more quantitative calculation of solar wind velocity and density perturbations resulting from these pressure forces. It is shown that the relative density perturbations near and in the ecliptic increase with radial distance and thus may well explain the measured non-spherically symmetric density decrease with distance. We also show that the solar wind decelerations actually seen with Voyager-1/2 are in conciliation with interstellar hydrogen densities of nH∞≥0.1cm-3, in contrast to earlier claims for nH∞=0.05cm-3.

  5. Perturbations of the solar wind flow by radial and latitudinal pick-up ion pressure gradients

    Directory of Open Access Journals (Sweden)

    H. J. Fahr

    2004-06-01

    Full Text Available It has been found that pick-up ions at their dynamical incorporation into the solar wind modify the original conditions of the asymptotic solar wind plasma flow. In this respect, it has meanwhile been revealed in many papers that these type of solar wind modifications, i.e. deceleration and decrease of effective Mach number, are not only due to the pick-up ion loading effects, but also to the action of pick-up ion pressure gradients. Up to now only the effects of radial pick-up ion pressure gradients were considered, however, analogously but latitudinal pressure gradients also appear to be important. Here we study the effects of radial and latitudinal pick-up ion pressure gradients, occurring especially during solar minimum conditions at mid-latitude regions where slow solar wind streams change to fast solar wind streams. First, we give estimates of the latitudinal wind components connected with these gradients, and then after revealing its importance, present a more quantitative calculation of solar wind velocity and density perturbations resulting from these pressure forces. It is shown that the relative density perturbations near and in the ecliptic increase with radial distance and thus may well explain the measured non-spherically symmetric density decrease with distance. We also show that the solar wind decelerations actually seen with Voyager-1/2 are in conciliation with interstellar hydrogen densities of nH∞≥0.1cm-3, in contrast to earlier claims for nH∞=0.05cm-3.

  6. On the joint statistics of stable random processes

    International Nuclear Information System (INIS)

    Hopcraft, K I; Jakeman, E

    2011-01-01

    A utilitarian continuous bi-variate random process whose first-order probability density function is a stable random variable is constructed. Results paralleling some of those familiar from the theory of Gaussian noise are derived. In addition to the joint-probability density for the process, these include fractional moments and structure functions. Although the correlation functions for stable processes other than Gaussian do not exist, we show that there is coherence between values adopted by the process at different times, which identifies a characteristic evolution with time. The distribution of the derivative of the process, and the joint-density function of the value of the process and its derivative measured at the same time are evaluated. These enable properties to be calculated analytically such as level crossing statistics and those related to the random telegraph wave. When the stable process is fractal, the proportion of time it spends at zero is finite and some properties of this quantity are evaluated, an optical interpretation for which is provided. (paper)

  7. On the density limit of Tokamaks

    International Nuclear Information System (INIS)

    Lehnert, B.

    1982-12-01

    Under the conditions of so far performed quasi-steady tokamak experiments near the density limit, the plasma pressure gradient in the outer layers of the plasma body becomes mainly determined by the plasma-neutral gas balance. An earlier analysis of ballooning instabilities driven by this gradient in regions of bad curvature has been extended to deduce an explicit stability criterion which determines the density limit. This criterion is closely related to the empirical Murakami limit. At relevant tokamak data, the deduced limit becomes proportional to J(sub)zR(sup)1/2 where J(sub)z is the average current density and R the major plasma radius. It is further found to be independent of the toroidal magnetic field strength and anomalous transport, as well as to be a slow function of the outer layer temperature and the mass number. The deduced stability criterion is consistent with so far performed experiments. Provided that the present analysis can be extrapolated to a wider range of parameter data and be combined with Alcator scaling, conditions near ignition appear to become realizable in small tokamaks by ohmic heating alone. These conditions can be satisfied at relevant magnetic field strengths and plasma currents, by imposing a high plasma current density. (author)

  8. CO2 laser diagnostics for measurements of the plasma density profile and plasma density fluctuations on LHD

    International Nuclear Information System (INIS)

    Vyacheslavov, L.N.; Tanaka, K.; Kawahata, K.

    2001-04-01

    A CO 2 laser based diagnostics complimentary to the existing FIR interferometer is proposed. It combines interferometry for plasma density profile measurement under conditions of large density gradients, and both imaging and scattering techniques for observation of plasma fluctuations. Two-colour interferometer with a slablike probe beam and a single multichannel linear detector array provide observation of plasma density profile and density fluctuations at two locations along the probe beam. Basic characteristics of the diagnostics are considered as well as some effects that include dispersion and are critical for two colour imaging technique. The results of the bench-top experiments with the prototype of the interferometer are presented. (author)

  9. Eye patches: Protein assembly of index-gradient squid lenses

    Energy Technology Data Exchange (ETDEWEB)

    Cai, J.; Townsend, J. P.; Dodson, T. C.; Heiney, P. A.; Sweeney, A. M.

    2017-08-10

    A parabolic relationship between lens radius and refractive index allows spherical lenses to avoid spherical aberration. We show that in squid, patchy colloidal physics resulted from an evolutionary radiation of globular S-crystallin proteins. Small-angle x-ray scattering experiments on lens tissue show colloidal gels of S-crystallins at all radial positions. Sparse lens materials form via low-valence linkages between disordered loops protruding from the protein surface. The loops are polydisperse and bind via a set of hydrogen bonds between disordered side chains. Peripheral lens regions with low particle valence form stable, volume-spanning gels at low density, whereas central regions with higher average valence gel at higher densities. The proteins demonstrate an evolved set of linkers for self-assembly of nanoparticles into volumetric materials.

  10. Jupiter's evolution with primordial composition gradients

    Science.gov (United States)

    Vazan, Allona; Helled, Ravit; Guillot, Tristan

    2018-02-01

    Recent formation and structure models of Jupiter suggest that the planet can have composition gradients and not be fully convective (adiabatic). This possibility directly affects our understanding of Jupiter's bulk composition and origin. In this Letter we present Jupiter's evolution with a primordial structure consisting of a relatively steep heavy-element gradient of 40 M⊕. We show that for a primordial structure with composition gradients, most of the mixing occurs in the outer part of the gradient during the early evolution (several 107 yr), leading to an adiabatic outer envelope (60% of Jupiter's mass). We find that the composition gradient in the deep interior persists, suggesting that 40% of Jupiter's mass can be non-adiabatic with a higher temperature than the one derived from Jupiter's atmospheric properties. The region that can potentially develop layered convection in Jupiter today is estimated to be limited to 10% of the mass. Movies associated to Figs. 1-3 are available at http://https://www.aanda.org

  11. Variation in wood nutrients along a tropical soil fertility gradient.

    Science.gov (United States)

    Heineman, Katherine D; Turner, Benjamin L; Dalling, James W

    2016-07-01

    Wood contains the majority of the nutrients in tropical trees, yet controls over wood nutrient concentrations and their function are poorly understood. We measured wood nutrient concentrations in 106 tree species in 10 forest plots spanning a regional fertility gradient in Panama. For a subset of species, we quantified foliar nutrients and wood density to test whether wood nutrients scale with foliar nutrients at the species level, or wood nutrient storage increases with wood density as predicted by the wood economics spectrum. Wood nutrient concentrations varied enormously among species from fourfold in nitrogen (N) to > 30-fold in calcium (Ca), potassium (K), magnesium (Mg) and phosphorus (P). Community-weighted mean wood nutrient concentrations correlated positively with soil Ca, K, Mg and P concentrations. Wood nutrients scaled positively with leaf nutrients, supporting the hypothesis that nutrient allocation is conserved across plant organs. Wood P was most sensitive to variation in soil nutrient availability, and significant radial declines in wood P indicated that tropical trees retranslocate P as sapwood transitions to heartwood. Wood P decreased with increasing wood density, suggesting that low wood P and dense wood are traits associated with tree species persistence on low fertility soils. Substantial variation among species and communities in wood nutrient concentrations suggests that allocation of nutrients to wood, especially P, influences species distributions and nutrient dynamics in tropical forests. © 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.

  12. Laboratory Density Functionals

    OpenAIRE

    Giraud, B. G.

    2007-01-01

    We compare several definitions of the density of a self-bound system, such as a nucleus, in relation with its center-of-mass zero-point motion. A trivial deconvolution relates the internal density to the density defined in the laboratory frame. This result is useful for the practical definition of density functionals.

  13. Tubing-Electrospinning: A One-Step Process for Fabricating Fibrous Matrices with Spatial, Chemical, and Mechanical Gradients.

    Science.gov (United States)

    Kim, Jung-Suk; Im, Byung Gee; Jin, Gyuhyung; Jang, Jae-Hyung

    2016-08-31

    Guiding newly generated tissues in a gradient pattern, thereby precisely mimicking inherent tissue morphology and subsequently arranging the intimate networks between adjacent tissues, is essential to raise the technical levels of tissue engineering and facilitate its transition into the clinic. In this study, a straightforward electrospinning method (the tubing-electrospinning technique) was developed to create fibrous matrices readily with diverse gradient patterns and to induce patterned cellular responses. Gradient fibrous matrices can be produced simply by installing a series of polymer-containing lengths of tubing into an electrospinning circuit and sequentially processing polymers without a time lag. The loading of polymer samples with different characteristics, including concentration, wettability, and mechanical properties, into the tubing system enabled unique features in fibrous matrices, such as longitudinal gradients in fiber density, surface properties, and mechanical stiffness. The resulting fibrous gradients were shown to arrange cellular migration and residence in a gradient manner, thereby offering efficient cues to mediate patterned tissue formation. The one-step process using tubing-electrospinning apparatus can be used without significant modifications regardless of the type of fibrous gradient. Hence, the tubing-electrospinning system can serve as a platform that can be readily used by a wide-range of users to induce patterned tissue formation in a gradient manner, which will ultimately improve the functionality of tissue engineering scaffolds.

  14. Classically Stable Nonsingular Cosmological Bounces

    Science.gov (United States)

    Ijjas, Anna; Steinhardt, Paul J.

    2016-09-01

    One of the fundamental questions of theoretical cosmology is whether the Universe can undergo a nonsingular bounce, i.e., smoothly transit from a period of contraction to a period of expansion through violation of the null energy condition (NEC) at energies well below the Planck scale and at finite values of the scale factor such that the entire evolution remains classical. A common claim has been that a nonsingular bounce either leads to ghost or gradient instabilities or a cosmological singularity. In this Letter, we consider a well-motivated class of theories based on the cubic Galileon action and present a procedure for explicitly constructing examples of a nonsingular cosmological bounce without encountering any pathologies and maintaining a subluminal sound speed for comoving curvature modes throughout the NEC violating phase. We also discuss the relation between our procedure and earlier work.

  15. Evidence of counter-gradient growth in western pond turtles (Actinemys marmorata) across thermal gradients

    Science.gov (United States)

    Snover, Melissa; Adams, Michael J.; Ashton, Donald T.; Bettaso, Jamie B.; Welsh, Hartwell H.

    2015-01-01

    Counter-gradient growth, where growth per unit temperature increases as temperature decreases, can reduce the variation in ectothermic growth rates across environmental gradients. Understanding how ectothermic species respond to changing temperatures is essential to their conservation and management due to human-altered habitats and changing climates.

  16. An x-ray backlit Talbot-Lau deflectometer for high-energy-density electron density diagnostics

    Science.gov (United States)

    Valdivia, M. P.; Stutman, D.; Stoeckl, C.; Theobald, W.; Mileham, C.; Begishev, I. A.; Bromage, J.; Regan, S. P.

    2016-02-01

    X-ray phase-contrast techniques can measure electron density gradients in high-energy-density plasmas through refraction induced phase shifts. An 8 keV Talbot-Lau interferometer consisting of free standing ultrathin gratings was deployed at an ultra-short, high-intensity laser system using K-shell emission from a 1-30 J, 8 ps laser pulse focused on thin Cu foil targets. Grating survival was demonstrated for 30 J, 8 ps laser pulses. The first x-ray deflectometry images obtained under laser backlighting showed up to 25% image contrast and thus enabled detection of electron areal density gradients with a maximum value of 8.1 ± 0.5 × 1023 cm-3 in a low-Z millimeter sized sample. An electron density profile was obtained from refraction measurements with an error of x-ray source-size, similar to conventional radiography.

  17. Energy approach to brittle fracture in strain-gradient modelling

    Science.gov (United States)

    Placidi, Luca; Barchiesi, Emilio

    2018-02-01

    In this paper, we exploit some results in the theory of irreversible phenomena to address the study of quasi-static brittle fracture propagation in a two-dimensional isotropic continuum. The elastic strain energy density of the body has been assumed to be geometrically nonlinear and to depend on the strain gradient. Such generalized continua often arise in the description of microstructured media. These materials possess an intrinsic length scale, which determines the size of internal boundary layers. In particular, the non-locality conferred by this internal length scale avoids the concentration of deformations, which is usually observed when dealing with local models and which leads to mesh dependency. A scalar Lagrangian damage field, ranging from zero to one, is introduced to describe the internal state of structural degradation of the material. Standard Lamé and second-gradient elastic coefficients are all assumed to decrease as damage increases and to be locally zero if the value attained by damage is one. This last situation is associated with crack formation and/or propagation. Numerical solutions of the model are provided in the case of an obliquely notched rectangular specimen subjected to monotonous tensile and shear loading tests, and brittle fracture propagation is discussed.

  18. Vascular Extraction Using MRA Statistics and Gradient Information

    Directory of Open Access Journals (Sweden)

    Shifeng Zhao

    2018-01-01

    Full Text Available Brain vessel segmentation is a fundamental component of cerebral disease screening systems. However, detecting vessels is still a challenging task owing to their complex appearance and thinning geometry as well as the contrast decrease from the root of the vessel to its thin branches. We present a method for segmentation of the vasculature in Magnetic Resonance Angiography (MRA images. First, we apply volume projection, 2D segmentation, and back-projection procedures for first stage of background subtraction and vessel reservation. Those labeled as background or vessel voxels are excluded from consideration in later computation. Second, stochastic expectation maximization algorithm (SEM is used to estimate the probability density function (PDF of the remaining voxels, which are assumed to be mixture of one Rayleigh and two Gaussian distributions. These voxels can then be classified into background, middle region, or vascular structure. Third, we adapt the K-means method which is based on the gradient of remaining voxels to effectively detect true positives around boundaries of vessels. Experimental results on clinical cerebral data demonstrate that using gradient information as a further step improves the mixture model based segmentation of cerebral vasculature, in particular segmentation of the low contrast vasculature.

  19. Antiherbivory defense mechanisms along an environmental gradient in restinga

    Directory of Open Access Journals (Sweden)

    Maiara Matilde da Silva

    2017-09-01

    Full Text Available ABSTRACT Plant-herbivore interactions have directed the evolution of defense mechanisms in plants, which can vary intraspecifically according to environmental quality. This study evaluated variation in the production of antiherbivory defenses in plant species distributed along an environmental gradient of restinga. The study was performed in Parque Estadual Acaraí, state of Santa Catarina, Brazil. Three species of four plant formations with different abiotic conditions were selected for study. Specific leaf area; water, nitrogen and carbon content; and presence of phenols, tannins, lignin and alkaloids, were evaluated in leaves of ten plants per species per plant formation. The results indicated that Symphyopappus casarettoi possesses Low Nutritional Quality Syndrome, characterized by low specific leaf area, presence of secondary metabolites and low nitrogen content. Dodonaea viscosa and Varronia curassavica possess Nutrition and Defense Syndrome, characterized by a balance between nutritional quality (high nitrogen content and lower C:N ratio and protection (greater thickness of leaves and higher density of trichomes. The results did not confirm the Resource Availability Hypothesis. The absence of a pattern in antiherbivory response due to the environmental gradient may indicate that the investment in defense by plants is not unidirectional and that certain morpho-anatomical attributes are typically related to conservation of resources.

  20. Symptomatic Raccoon Dogs and Sarcoptic Mange Along an Urban Gradient.

    Science.gov (United States)

    Saito, Masayuki U; Sonoda, Yoichi

    2017-06-01

    We quantitatively evaluated the effects of landscape factors on the distribution of symptomatic raccoon dogs with sarcoptic mange along an urban gradient. We used 246 camera traps (182 traps from April 2005 to December 2006; 64 traps from September 2009 to October 2010) to record the occurrence of asymptomatic and symptomatic raccoon dogs at 21 survey sites along an urban-rural gradient in the Tama Hills area of Tokyo. Each occurrence was explained in terms of the surrounding forest, agricultural, and grassland areas and additional factors (i.e., seasonal variations and survey methods) at various spatial scales using a generalized additive mixed model (GAMM). In our analysis, a 1000-m radius was identified as the important spatial scale for asymptomatic and symptomatic raccoon dog occurrence. The peak of the predicted occurrence probability of asymptomatic raccoon dogs appeared in the intermediate forest landscape as opposed to non-forest and forest landscapes. However, a high occurrence probability of symptomatic raccoon dogs was detected in non-forest and intermediate forest landscapes (i.e., urban and suburban) as opposed to a forest landscape, presumably because of animals occurring at much higher densities in more urbanized areas. Therefore, our results suggest that human-modified landscapes play an important role in the high occurrence of sarcoptic mange in raccoon dogs.

  1. Reflectance analysis of porosity gradient in nanostructured silicon layers

    Science.gov (United States)

    Jurečka, Stanislav; Imamura, Kentaro; Matsumoto, Taketoshi; Kobayashi, Hikaru

    2017-12-01

    In this work we study optical properties of nanostructured layers formed on silicon surface. Nanostructured layers on Si are formed in order to reach high suppression of the light reflectance. Low spectral reflectance is important for improvement of the conversion efficiency of solar cells and for other optoelectronic applications. Effective method of forming nanostructured layers with ultralow reflectance in a broad interval of wavelengths is in our approach based on metal assisted etching of Si. Si surface immersed in HF and H2O2 solution is etched in contact with the Pt mesh roller and the structure of the mesh is transferred on the etched surface. During this etching procedure the layer density evolves gradually and the spectral reflectance decreases exponentially with the depth in porous layer. We analyzed properties of the layer porosity by incorporating the porosity gradient into construction of the layer spectral reflectance theoretical model. Analyzed layer is splitted into 20 sublayers in our approach. Complex dielectric function in each sublayer is computed by using Bruggeman effective media theory and the theoretical spectral reflectance of modelled multilayer system is computed by using Abeles matrix formalism. Porosity gradient is extracted from the theoretical reflectance model optimized in comparison to the experimental values. Resulting values of the structure porosity development provide important information for optimization of the technological treatment operations.

  2. Theory of neoclassical ion temperature-gradient-driven turbulence

    Science.gov (United States)

    Kim, Y. B.; Diamond, P. H.; Biglari, H.; Callen, J. D.

    1991-02-01

    The theory of collisionless fluid ion temperature-gradient-driven turbulence is extended to the collisional banana-plateau regime. Neoclassical ion fluid evolution equations are developed and utilized to investigate linear and nonlinear dynamics of negative compressibility ηi modes (ηi≡d ln Ti/d ln ni). In the low-frequency limit (ωB2p. As a result of these modifications, growth rates are dissipative, rather than sonic, and radial mode widths are broadened [i.e., γ˜k2∥c2s(ηi -(2)/(3) )/μi, Δx˜ρs(Bt/Bp) (1+ηi)1/2, where k∥, cs, and ρs are the parallel wave number, sound velocity, and ion gyroradius, respectively]. In the limit of weak viscous damping, enhanced neoclassical polarization persists and broadens radial mode widths. Linear mixing length estimates and renormalized turbulence theory are used to determine the ion thermal diffusivity in both cases. In both cases, a strong favorable dependence of ion thermal diffusivity on Bp (and hence plasma current) is exhibited. Furthermore, the ion thermal diffusivity for long wavelength modes exhibits favorable density scaling. The possible role of neoclassical ion temperature-gradient-driven modes in edge fluctuations and transport in L-phase discharges and the L to H transition is discussed.

  3. Learning Deep Generative Models With Doubly Stochastic Gradient MCMC.

    Science.gov (United States)

    Du, Chao; Zhu, Jun; Zhang, Bo

    2017-06-28

    Deep generative models (DGMs), which are often organized in a hierarchical manner, provide a principled framework of capturing the underlying causal factors of data. Recent work on DGMs focussed on the development of efficient and scalable variational inference methods that learn a single model under some mean-field or parameterization assumptions. However, little work has been done on extending Markov chain Monte Carlo (MCMC) methods to Bayesian DGMs, which enjoy many advantages compared with variational methods. We present doubly stochastic gradient MCMC, a simple and generic method for (approximate) Bayesian inference of DGMs in a collapsed continuous parameter space. At each MCMC sampling step, the algorithm randomly draws a mini-batch of data samples to estimate the gradient of log-posterior and further estimates the intractable expectation over hidden variables via a neural adaptive importance sampler, where the proposal distribution is parameterized by a deep neural network and learnt jointly along with the sampling process. We demonstrate the effectiveness of learning various DGMs on a wide range of tasks, including density estimation, data generation, and missing data imputation. Our method outperforms many state-of-the-art competitors.

  4. Using Spatial Gradients to Model Localization Phenomena

    Energy Technology Data Exchange (ETDEWEB)

    D.J.Bammann; D.Mosher; D.A.Hughes; N.R.Moody; P.R.Dawson

    1999-07-01

    We present the final report on a Laboratory-Directed Research and Development project, Using Spatial Gradients to Model Localization Phenomena, performed during the fiscal years 1996 through 1998. The project focused on including spatial gradients in the temporal evolution equations of the state variables that describe hardening in metal plasticity models. The motivation was to investigate the numerical aspects associated with post-bifurcation mesh dependent finite element solutions in problems involving damage or crack propagation as well as problems in which strain Localizations occur. The addition of the spatial gradients introduces a mathematical length scale that eliminates the mesh dependency of the solution. In addition, new experimental techniques were developed to identify the physical mechanism associated with the numerical length scale.

  5. Nonlinear conjugate gradient methods in micromagnetics

    Directory of Open Access Journals (Sweden)

    J. Fischbacher

    2017-04-01

    Full Text Available Conjugate gradient methods for energy minimization in micromagnetics are compared. The comparison of analytic results with numerical simulation shows that standard conjugate gradient method may fail to produce correct results. A method that restricts the step length in the line search is introduced, in order to avoid this problem. When the step length in the line search is controlled, conjugate gradient techniques are a fast and reliable way to compute the hysteresis properties of permanent magnets. The method is applied to investigate demagnetizing effects in NdFe12 based permanent magnets. The reduction of the coercive field by demagnetizing effects is μ0ΔH = 1.4 T at 450 K.

  6. Substrate curvature gradient drives rapid droplet motion.

    Science.gov (United States)

    Lv, Cunjing; Chen, Chao; Chuang, Yin-Chuan; Tseng, Fan-Gang; Yin, Yajun; Grey, Francois; Zheng, Quanshui

    2014-07-11

    Making small liquid droplets move spontaneously on solid surfaces is a key challenge in lab-on-chip and heat exchanger technologies. Here, we report that a substrate curvature gradient can accelerate micro- and nanodroplets to high speeds on both hydrophilic and hydrophobic substrates. Experiments for microscale water droplets on tapered surfaces show a maximum speed of 0.42  m/s, 2 orders of magnitude higher than with a wettability gradient. We show that the total free energy and driving force exerted on a droplet are determined by the substrate curvature and substrate curvature gradient, respectively. Using molecular dynamics simulations, we predict nanoscale droplets moving spontaneously at over 100  m/s on tapered surfaces.

  7. Conjugate gradient algorithms using multiple recursions

    Energy Technology Data Exchange (ETDEWEB)

    Barth, T.; Manteuffel, T.

    1996-12-31

    Much is already known about when a conjugate gradient method can be implemented with short recursions for the direction vectors. The work done in 1984 by Faber and Manteuffel gave necessary and sufficient conditions on the iteration matrix A, in order for a conjugate gradient method to be implemented with a single recursion of a certain form. However, this form does not take into account all possible recursions. This became evident when Jagels and Reichel used an algorithm of Gragg for unitary matrices to demonstrate that the class of matrices for which a practical conjugate gradient algorithm exists can be extended to include unitary and shifted unitary matrices. The implementation uses short double recursions for the direction vectors. This motivates the study of multiple recursion algorithms.

  8. Orientations of Liquid Crystals in Contact with Surfaces that Present Continuous Gradients of Chemical Functionality

    International Nuclear Information System (INIS)

    Clare, B.; Efimenko, K.; Fischer, D.; Genzer, J.; Abbott, N.

    2006-01-01

    We report the formation of continuous spatial gradients in the density of grafted semifluorinated chains on silicon oxide surfaces by vapor-phase diffusion of semifluorinated silanes. We quantify the orientations of the nematic liquid crystal (LC) 4-cyano-4'-pentylbiphenyl on these surfaces as a function of local surface composition obtained by using NEXAFS. These measurements demonstrate that it is possible to obtain the full range of tilt angles of a LC on these surfaces. We also use the data provided by these gradient surfaces to test hypotheses regarding the nature of the interaction between the LC and surfaces that give rise to the range of tilted orientations of the LC. We conclude that the orientations of the LC are not determined solely by the density of grafted semifluorinated chains or by the density of residual hydroxyl groups presented at these surfaces following reactions with the silanes. Instead, our results raise the possibility that the tilt angles of the semifluorinated chains on these surfaces (which are a function of the density of the grafted chains) may influence the orientation of the LC. These results, when combined, demonstrate the potential utility of gradient surfaces for screening surface chemistries that achieve desired orientations of LCs as well as for rapidly assembling experimental data sets that can be used to test propositions regarding mechanisms of anchoring LCs at surfaces

  9. Ion temperature gradient driven turbulence with strong trapped ion resonance

    Energy Technology Data Exchange (ETDEWEB)

    Kosuga, Y., E-mail: kosuga@riam.kyushu-u.ac.jp [Institute for Advanced Study, Kyushu University, Fukuoka (Japan); Research Institute for Applied Mechanics, Kyushu University, Fukuoka (Japan); Itoh, S.-I. [Research Center for Plasma Turbulence, Kyushu University, Fukuoka (Japan); Research Institute for Applied Mechanics, Kyushu University, Fukuoka (Japan); Diamond, P. H. [CASS and CMTFO, University of California at San Diego, La Jolla, California 92093 (United States); WCI Center for Fusion Theory, National Fusion Research Institute, Daejeon (Korea, Republic of); Itoh, K. [National Institute for Fusion Science, Gifu (Japan); Research Center for Plasma Turbulence, Kyushu University, Fukuoka (Japan); Lesur, M. [Research Institute for Applied Mechanics, Kyushu University, Fukuoka (Japan)

    2014-10-15

    A theory to describe basic characterization of ion temperature gradient driven turbulence with strong trapped ion resonance is presented. The role of trapped ion granulations, clusters of trapped ions correlated by precession resonance, is the focus. Microscopically, the presence of trapped ion granulations leads to a sharp (logarithmic) divergence of two point phase space density correlation at small scales. Macroscopically, trapped ion granulations excite potential fluctuations that do not satisfy dispersion relation and so broaden frequency spectrum. The line width from emission due only to trapped ion granulations is calculated. The result shows that the line width depends on ion free energy and electron dissipation, which implies that non-adiabatic electrons are essential to recover non-trivial dynamics of trapped ion granulations. Relevant testable predictions are summarized.

  10. Brief introduction of fabrication technique for flier-plate with gradient wave impedance in laser-induced quasi-isentropic compression

    International Nuclear Information System (INIS)

    Du Ai; Zhou Bin; Shen Yang; Shen Jun; Huang Xiuguang; Ye Junjian; Xie Zhiyong; Fu Sizu

    2014-01-01

    The flier-plate is the key element for achieving quasi-isentropic compression. In this paper, the developments and preparation methods of three kinds of porous flier-plates with gradient wave impedance were introduced as emphasis, based on the materials selection and design. Among them, gradient aerogels were considered as the flier- plate materials with good applicability, because of their nano-scale homogeneity and continuous adjustability of the density and thickness. At last, the problems of accurate impedance measurement and noncontinuous distribution were introduced. The accurate measurements of the density and sound velocity and three kinds of methods for preparing gradient flier-plate (including gradient sol co-gelation method, diffusion corrosion method and interface diffusion method) were suggested to solve these problems. The development of porous flier-plate with gradient wave impedance will help to prolong the loading time, improve the efficiency of the energy, and finally achieve higher loading pressure. (authors)

  11. Review of new shapes for higher gradients

    International Nuclear Information System (INIS)

    Geng, R.L.

    2006-01-01

    High-gradient superconducting RF (SRF) cavities are needed for energy frontier superconducting accelerators. Progress has been made over the past decades and the accelerating gradient E acc has been increased from a few MV/m to ∼42 MV/m in SRF niobium cavities. The corresponding peak RF magnetic field H pk on the niobium cavity surface is approaching the intrinsic RF critical magnetic field H crit,RF , a hard physical limit at which superconductivity breaks down. Pushing the gradient envelope further by adopting new cavity shapes with a lower ratio of H pk /E acc has been recently proposed. For a reduced H pk /E acc , a higher ultimate E acc is sustained when H pk finally strikes H crit,RF . The new cavity geometry include the re-entrant shape conceived at Cornell University and the so-called 'Low-loss' shape proposed by a DESY/JLAB/KEK collaboration. Experimental work is being pursued at Cornell, KEK and JLAB. Results of single-cell cavities are encouraging. A record gradient of 47 MV/m was first demonstrated in a 1.3 GHz re-entrant niobium cavity at Cornell University. At the time of writing, a new record of 52 MV/m has been realized with another 1.3 GHz re-entrant cavity, designed and built at Cornell and processed and tested at KEK. Single-cell low-loss cavities have reached equally high gradients in the range of 45-51 MV/m at KEK and JLAB. Owing to their higher gradient potential and the encouraging single-cell cavity results, the new cavity shapes are becoming attractive for their possible use in the international linear collider (ILC). Experimental work on multi-cell niobium cavities of new shapes is currently under active exploration

  12. Frequency Analysis of Gradient Estimators in Volume Rendering

    NARCIS (Netherlands)

    Bentum, Marinus Jan; Lichtenbelt, Barthold B.A.; Malzbender, Tom

    1996-01-01

    Gradient information is used in volume rendering to classify and color samples along a ray. In this paper, we present an analysis of the theoretically ideal gradient estimator and compare it to some commonly used gradient estimators. A new method is presented to calculate the gradient at arbitrary

  13. Stable Hemiaminals: 2-Aminopyrimidine Derivatives

    Directory of Open Access Journals (Sweden)

    Anna Kwiecień

    2015-08-01

    Full Text Available Stable hemiaminals can be obtained in the one-pot reaction between 2-aminopyrimidine and nitrobenzaldehyde derivatives. Ten new hemiaminals have been obtained, six of them in crystal state. The molecular stability of these intermediates results from the presence of both electron-withdrawing nitro groups as substituents on the phenyl ring and pyrimidine ring, so no further stabilisation by intramolecular interaction is required. Hemiaminal molecules possess a tetrahedral carbon atom constituting a stereogenic centre. As the result of crystallisation in centrosymmetric space groups both enantiomers are present in the crystal structure.

  14. Organic synthesis with stable isotopes

    International Nuclear Information System (INIS)

    Daub, G.H.; Kerr, V.N.; Williams, D.L.; Whaley, T.W.

    1978-01-01

    Some general considerations concerning organic synthesis with stable isotopes are presented. Illustrative examples are described and discussed. The examples include DL-2-amino-3-methyl- 13 C-butanoic-3,4- 13 C 2 acid (DL-valine- 13 C 3 ); methyl oleate-1- 13 C; thymine-2,6- 13 C 2 ; 2-aminoethanesulfonic- 13 C acid (taurine- 13 C); D-glucose-6- 13 C; DL-2-amino-3-methylpentanoic-3,4- 13 C 2 acid (DL-isoleucine- 13 C 2 ); benzidine- 15 N 2 ; and 4-ethylsulfonyl-1-naphthalene-sulfonamide- 15 N

  15. Stable agents for imaging investigations

    International Nuclear Information System (INIS)

    Tofe, A.J.

    1976-01-01

    This invention concerns highly stable compounds useful in preparing technetium 99m based scintiscanning exploration agents. The compounds of this invention include a pertechnetate reducing agent or a solution of oxidized pertechnetate and an efficient proportion, sufficient to stabilize the compounds in the presence of oxygen and of radiolysis products, of ascorbic acid or a pharmaceutically acceptable salt or ester of this acid. The invention also concerns a perfected process for preparing a technetium based exploration agent, consisting in codissolving the ascorbic acid or a pharmaceutically acceptable salt or ester of such an acid and a pertechnetate reducing agent in a solution of oxidized pertechnetate [fr

  16. Statistics of the perceived velocity gradient tensor in a rotating turbulent flow

    International Nuclear Information System (INIS)

    Naso, Aurore; Godeferd, Fabien S

    2012-01-01

    The dynamics and structure of rotating homogeneous turbulence is investigated through the statistical properties of the ‘perceived’ velocity gradient tensor, defined by interpolation from the locations and velocities of a set of four particles. The results of direct numerical simulations of forced homogeneous rotating turbulence at different Rossby numbers are presented. We thus provide a multi-scale analysis of the dynamics of rotating turbulence and some of its important features. We present scaling laws for second- and third-order moments of the perceived velocity gradient tensor. We relate the distribution of the enstrophy and strain variance, and of their production terms, to the topology of the flow, thanks to conditional probability density functions. These quantities demonstrate the role played by the Zeman scale in the elementary processes of rotating turbulence, when compared to the scale at which the perceived velocity gradient tensor is measured. (paper)

  17. Structure of the optimized effective Kohn-Sham exchange potential and its gradient approximations

    International Nuclear Information System (INIS)

    Gritsenko, O.; Van Leeuwen, R.; Baerends, E.J.

    1996-01-01

    An analysis of the structure of the optimized effective Kohn-Sham exchange potential v, and its gradient approximations is presented. The potential is decomposed into the Slater potential v s and the response of v s to density variations, v resp . The latter exhibits peaks that reflect the atomic shell structure. Kohn-Sham exchange potentials derived from current gradient approaches for the exchange energy are shown to be quite reasonable for the Slater potential, but they fail to approximate the response part, which leads to poor overall potentials. Improved potentials are constructed by a direct fit of v x with a gradient-dependent Pade approximant form. The potentials obtained possess proper asymptotic and scaling properties and reproduce the shell structure of the exact v x . 44 refs., 7 figs., 4 tabs

  18. A finite deformation theory of higher-order gradient crystal plasticity

    DEFF Research Database (Denmark)

    Kuroda, Mitsutoshi; Tvergaard, Viggo

    2008-01-01

    For higher-order gradient crystal plasticity, a finite deformation formulation is presented. The theory does not deviate much from the conventional crystal plasticity theory. Only a back stress effect and additional differential equations for evolution of the geometrically necessary dislocation...... (GND) densities supplement the conventional theory within a non-work-conjugate framework in which there is no need to introduce higher-order microscopic stresses that would be work-conjugate to slip rate gradients. We discuss its connection to a work-conjugate type of finite deformation gradient...... for the small deformation theory. As in a previous formulation for small deformation, the present formulation applies to the context of multiple and three-dimensional slip deformations. (C) 2008 Elsevier Ltd. All rights reserved....

  19. Measurement of gradient magnetic field temporal characteristics

    International Nuclear Information System (INIS)

    Bartusek, K.; Jflek, B.

    1994-01-01

    We describe a technique of measuring the time dependence and field distortions of magnetic fields due to eddy currents (EC) produced by time-dependent magnetic field gradients. The EC measuring technique makes use of a large volume sample and selective RF excitation pulses and free induction decay (FID) (or a spin or gradient echo) to measure the out-of-phase component of the FID, which is proportional to γδB, i.e. the amount the signal is off resonance. The measuring technique is sensitive, easy to implement and interpret, and used for determining pre-emphasis compensation parameters

  20. Relativistic klystron research for high gradient accelerators

    International Nuclear Information System (INIS)

    Allen, M.A.; Callin, R.S.; Deruyter, H.

    1988-06-01

    Relativistic klystrons are being developed as a power source for high gradient accelerator applications which include large linear electron--positron colliders, compact accelerators, and FEL sources. We have attained 200MW peak power at 11.4 GHz from a relativistic klystron, and 140 MV/m longitudinal gradient in a short 11.4 GHz accelerator section. We report here on the design of our first klystrons, the results of our experiments so far, and some of our plans for the near future. 5 refs., 7 figs

  1. Crack Tip Mechanics in Distortion Gradient Plasticity

    DEFF Research Database (Denmark)

    Fuentes-Alonso, Sandra; Martínez Pañeda, Emilio

    2017-01-01

    The important role of geometrically necessary dislocations in structural integrity assessment has encouraged an extensive use of strain gradient plasticity theories to characterize the behavior at the small scales involved in crack tip deformation. However, despite the popularity of Distortion...... Gradient Plasticity (DGP), the influence on crack tip mechanics of DGP's distinguishing features that entail superior modelling capabilities has not been investigated yet. In this work crack tip fields are thoroughly examined by implementing the higher order theory of DGP in an implicit finite element...

  2. Gradient Learning Algorithms for Ontology Computing

    Science.gov (United States)

    Gao, Wei; Zhu, Linli

    2014-01-01

    The gradient learning model has been raising great attention in view of its promising perspectives for applications in statistics, data dimensionality reducing, and other specific fields. In this paper, we raise a new gradient learning model for ontology similarity measuring and ontology mapping in multidividing setting. The sample error in this setting is given by virtue of the hypothesis space and the trick of ontology dividing operator. Finally, two experiments presented on plant and humanoid robotics field verify the efficiency of the new computation model for ontology similarity measure and ontology mapping applications in multidividing setting. PMID:25530752

  3. Realizable planar gradient-index solar lenses.

    Science.gov (United States)

    Kotsidas, Panagiotis; Modi, Vijay; Gordon, Jeffrey M

    2012-04-01

    The design of single element planar hemispherical gradient-index solar lenses that can accommodate the constraints of realistic materials and fabrication techniques are presented, and simulated with an extended and polychromatic solar source for concentrator photovoltaics at flux concentration values exceeding 1000 suns. The planar hemispherical far-field lens is created from a near-field unit magnification spherical gradient-index design, and illustrated with an f/1.40 square solar lens that allows lossless packing within a concentrator module.

  4. Gradient Elasticity Formulations for Micro/Nanoshells

    Directory of Open Access Journals (Sweden)

    Bohua Sun

    2014-01-01

    Full Text Available The focus of this paper is on illustrating how to extend the second author’s gradient theory of elasticity to shells. Three formulations are presented based on the implicit gradient elasticity constitutive relation 1 -ld2∇2σij=Cijkl(1-ls2∇2εkl and its two approximations 1+ls2∇2-ld2∇2σij=Cijklεkl and σij=Cijkl(1+ld2∇2-ls2∇2εkl.

  5. Gradient learning algorithms for ontology computing.

    Science.gov (United States)

    Gao, Wei; Zhu, Linli

    2014-01-01

    The gradient learning model has been raising great attention in view of its promising perspectives for applications in statistics, data dimensionality reducing, and other specific fields. In this paper, we raise a new gradient learning model for ontology similarity measuring and ontology mapping in multidividing setting. The sample error in this setting is given by virtue of the hypothesis space and the trick of ontology dividing operator. Finally, two experiments presented on plant and humanoid robotics field verify the efficiency of the new computation model for ontology similarity measure and ontology mapping applications in multidividing setting.

  6. Improving dimensionality reduction with spectral gradient descent.

    Science.gov (United States)

    Memisevic, Roland; Hinton, Geoffrey

    2005-01-01

    We introduce spectral gradient descent, a way of improving iterative dimensionality reduction techniques. The method uses information contained in the leading eigenvalues of a data affinity matrix to modify the steps taken during a gradient-based optimization procedure. We show that the approach is able to speed up the optimization and to help dimensionality reduction methods find better local minima of their objective functions. We also provide an interpretation of our approach in terms of the power method for finding the leading eigenvalues of a symmetric matrix and verify the usefulness of the approach in some simple experiments.

  7. On lower order strain gradient plasticity theories

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Hutchinson, J. W.

    2002-01-01

    By way of numerical examples, this paper explores the nature of solutions to a class of strain gradient plasticity theories that employ conventional stresses, equilibrium equations and boundary conditions. Strain gradients come into play in these modified conventional theories only to alter...... the tangential moduli governing increments of stress and strain. It is shown that the modification is far from benign from a mathematical standpoint, changing the qualitative character of solutions and leading to a new type of localization that appears to be unphysical....

  8. Gradient Learning Algorithms for Ontology Computing

    Directory of Open Access Journals (Sweden)

    Wei Gao

    2014-01-01

    Full Text Available The gradient learning model has been raising great attention in view of its promising perspectives for applications in statistics, data dimensionality reducing, and other specific fields. In this paper, we raise a new gradient learning model for ontology similarity measuring and ontology mapping in multidividing setting. The sample error in this setting is given by virtue of the hypothesis space and the trick of ontology dividing operator. Finally, two experiments presented on plant and humanoid robotics field verify the efficiency of the new computation model for ontology similarity measure and ontology mapping applications in multidividing setting.

  9. A density functional study on the adsorption of hydrogen molecule ...

    Indian Academy of Sciences (India)

    An all-electron scalar relativistic calculation on the adsorption of hydrogen molecule onto small copper clusters has been performed by using density functional theory with the generalized gradient approximation (GGA) at PW91 level. Our results reveal that after adsorption of H2 molecule, the Cu-Cu interaction is ...

  10. A density functional study on the adsorption of hydrogen molecule

    Indian Academy of Sciences (India)

    An all-electron scalar relativistic calculation on the adsorption of hydrogen molecule onto small copper clusters has been performed by using density functional theory with the generalized gradient approximation (GGA) at PW91 level. Our results reveal that after adsorption of H2 molecule, the Cu-Cu interaction is ...

  11. A density functional study on the adsorption of hydrogen molecule ...

    Indian Academy of Sciences (India)

    Abstract. An all-electron scalar relativistic calculation on the adsorption of hydrogen molecule onto small copper clusters has been performed by using density functional theory with the generalized gradient approxi- mation (GGA) at PW91 level. Our results reveal that after adsorption of H2 molecule, the Cu–Cu interaction.

  12. Ground-state properties of third-row elements with nonlocal density functionals

    International Nuclear Information System (INIS)

    Bagno, P.; Jepsen, O.; Gunnarsson, O.

    1989-01-01

    The cohesive energy, the lattice parameter, and the bulk modulus of third-row elements are calculated using the Langreth-Mehl-Hu (LMH), the Perdew-Wang (PW), and the gradient expansion functionals. The PW functional is found to give somewhat better results than the LMH functional and both are found to typically remove half the errors in the local-spin-density (LSD) approximation, while the gradient expansion gives worse results than the local-density approximation. For Fe both the LMH and PW functionals correctly predict a ferromagnetic bcc ground state, while the LSD approximation and the gradient expansion predict a nonmagnetic fcc ground state

  13. Stable cosmology in chameleon bigravity

    Science.gov (United States)

    De Felice, Antonio; Mukohyama, Shinji; Oliosi, Michele; Watanabe, Yota

    2018-02-01

    The recently proposed chameleonic extension of bigravity theory, by including a scalar field dependence in the graviton potential, avoids several fine-tunings found to be necessary in usual massive bigravity. In particular it ensures that the Higuchi bound is satisfied at all scales, that no Vainshtein mechanism is needed to satisfy Solar System experiments, and that the strong coupling scale is always above the scale of cosmological interest all the way up to the early Universe. This paper extends the previous work by presenting a stable example of cosmology in the chameleon bigravity model. We find a set of initial conditions and parameters such that the derived stability conditions on general flat Friedmann background are satisfied at all times. The evolution goes through radiation-dominated, matter-dominated, and de Sitter eras. We argue that the parameter space allowing for such a stable evolution may be large enough to encompass an observationally viable evolution. We also argue that our model satisfies all known constraints due to gravitational wave observations so far and thus can be considered as a unique testing ground of gravitational wave phenomenologies in bimetric theories of gravity.

  14. Evidence of chronic anthropogenic nutrient within coastal lagoon reefs adjacent to urban and tourism centers, Kenya: A stable isotope approach.

    Science.gov (United States)

    Mwaura, Jelvas; Umezawa, Yu; Nakamura, Takashi; Kamau, Joseph

    2017-06-30

    The source of anthropogenic nutrient and its spatial extent in three fringing reefs with differing human population gradients in Kenya were investigated using stable isotope approaches. Nutrient concentrations and nitrate-δ 15 N in seepage water indicated that population density and tourism contributed greatly to the extent of nutrient loading to adjacent reefs. Although water-column nutrient analyses did not show any significant difference among the reefs, higher δ 15 N and N contents in macrophytes showed terrestrial nutrients affected primary producers in onshore areas in Nyali and Bamburi reefs, but were mitigated by offshore water intrusion especially at Nyali. On the offshore reef flat, where the same species of macroalgae were not available, complementary use of δ 15 N in sedimentary organic matter suggested inputs of nutrients originated from the urban city of Mombasa. If population increases in the future, nutrient conditions in the shallower reef, Vipingo, may be dramatically degraded due to lower water exchange ratio. Copyright © 2017 Elsevier Ltd. All rights reserved.

  15. Detection of Sialic Acid-Utilising Bacteria in a Caecal Community Batch Culture Using RNA-Based Stable Isotope Probing

    Directory of Open Access Journals (Sweden)

    Wayne Young

    2015-03-01

    Full Text Available Sialic acids are monosaccharides typically found on cell surfaces and attached to soluble proteins, or as essential components of ganglioside structures that play a critical role in brain development and neural transmission. Human milk also contains sialic acid conjugated to oligosaccharides, glycolipids, and glycoproteins. These nutrients can reach the large bowel where they may be metabolised by the microbiota. However, little is known about the members of the microbiota involved in this function. To identify intestinal bacteria that utilise sialic acid within a complex intestinal community, we cultured the caecal microbiota from piglets in the presence of 13C-labelled sialic acid. Using RNA-based stable isotope probing, we identified bacteria that consumed 13C-sialic acid by fractionating total RNA in isopycnic buoyant density gradients followed by 16S rRNA gene analysis. Addition of sialic acid caused significant microbial community changes. A relative rise in Prevotella and Lactobacillus species was accompanied by a corresponding reduction in the genera Escherichia/Shigella, Ruminococcus and Eubacterium. Inspection of isotopically labelled RNA sequences suggests that the labelled sialic acid was consumed by a wide range of bacteria. However, species affiliated with the genus Prevotella were clearly identified as the most prolific users, as solely their RNA showed significantly higher relative shares among the most labelled RNA species. Given the relevance of sialic acid in nutrition, this study contributes to a better understanding of their microbial transformation in the intestinal tract with potential implications for human health.

  16. Apparent deposition velocity and compensation point of ammonia inferred from gradient measurements above and through alfalfa

    Science.gov (United States)

    Dabney, Seth M.; Bouldin, David R.

    Understanding the cycling of ammonia between croplands and the atmosphere is of importance to agriculturalists and atmospheric scientists. Flux densities of gaseous ammonia (NH 3), particulate ammonium (NH 4+), and total ammoniacal nitrogen (AN) were measured using an aerodynamic method above an alfalfa ( Medicago sativa, L.) canopy between April and July 1981 at a rural location in central New York State. In air not influenced by local sources, NH 3 and NH 4+ averaged 1.5 and 3.0 ppb, respectively, at 1 m above the crop. Ambient NH 4+ varied consistently with synoptic air masses, being lowest (2.3 ppb) for NW and highest (6.4 ppb) for SW flows. Concentrations and gradients of both species were higher during periods of hay harvest. Gradients of NH 3 were much steeper than those of NH 4+ within the alfalfa canopy, but NH 4+ contributed appreciably (36% on average) to above-canopy AN gradients. Alfalfa's NH 3 compensation point was estimated by combining concentration and gradient data with transport resistances. Gaseous gradients indicated a compensation point of 2 ppb, lower than previously published estimates. Conversion of NH 3 to NH 4+ within the canopy air could have reduced NH 3 gradients and caused a low estimate of the compensation point. Acidic aerosols, by keeping NH 3 levels low, may compete with plants for NH 3. Future studies of ammonia exchange should distinguish between NH 3 and NH 4+ if flux densities are to be related to ambient conditions. Total AN level is a poor predictor of soil-plant-atmosphere ammonia exchange since high AN was frequently associated with low NH 3, and NH 3 is more surface reactive than NH 4+.

  17. Up-gradient transport in a probabilistic transport model

    DEFF Research Database (Denmark)

    Gavnholt, J.; Juul Rasmussen, J.; Garcia, O.E.

    2005-01-01

    The transport of particles or heat against the driving gradient is studied by employing a probabilistic transport model with a characteristic particle step length that depends on the local concentration or heat gradient. When this gradient is larger than a prescribed critical value, the standard....... These results supplement recent works by van Milligen [Phys. Plasmas 11, 3787 (2004)], which applied Levy distributed step sizes in the case of supercritical gradients to obtain the up-gradient transport. (c) 2005 American Institute of Physics....

  18. A mechanistic analysis of density dependence in algal population dynamics

    Directory of Open Access Journals (Sweden)

    Adrian eBorlestean

    2015-04-01

    Full Text Available Population density regulation is a fundamental principle in ecology, but the specific process underlying functional expression of density dependence remains to be fully elucidated. One view contends that patterns of density dependence are largely fixed across a species irrespective of environmental conditions, whereas another is that the strength and expression of density dependence are fundamentally variable depending on the nature of exogenous or endogenous constraints acting on the population. We conducted a study investigating the expression of density dependence in Chlamydomonas spp. grown under a gradient from low to high nutrient density. We predicted that the relationship between per capita growth rate (pgr and population density would vary from concave up to concave down as nutrient density became less limiting and populations experienced weaker density regulation. Contrary to prediction, we found that the relationship between pgr and density became increasingly concave-up as nutrient levels increased. We also found that variation in pgr increased, and pgr levels reached higher maxima in nutrient-limited environments. Most likely, these results are attributable to population growth suppression in environments with high intraspecific competition due to limited nutrient resources. Our results suggest that density regulation is strongly variable depending on exogenous and endogenous processes acting on the population, implying that expression of density dependence depends extensively on local conditions. Additional experimental work should reveal the mechanisms influencing how the expression of density dependence varies across populations through space and time.

  19. Large Airborne Full Tensor Gradient Data Inversion Based on a Non-Monotone Gradient Method

    Science.gov (United States)

    Sun, Yong; Meng, Zhaohai; Li, Fengting

    2018-03-01

    Following the development of gravity gradiometer instrument technology, the full tensor gravity (FTG) data can be acquired on airborne and marine platforms. Large-scale geophysical data can be obtained using these methods, making such data sets a number of the "big data" category. Therefore, a fast and effective inversion method is developed to solve the large-scale FTG data inversion problem. Many algorithms are available to accelerate the FTG data inversion, such as conjugate gradient method. However, the conventional conjugate gradient method takes a long time to complete data processing. Thus, a fast and effective iterative algorithm is necessary to improve the utilization of FTG data. Generally, inversion processing is formulated by incorporating regularizing constraints, followed by the introduction of a non-monotone gradient-descent method to accelerate the convergence rate of FTG data inversion. Compared with the conventional gradient method, the steepest descent gradient algorithm, and the conjugate gradient algorithm, there are clear advantages of the non-monotone iterative gradient-descent algorithm. Simulated and field FTG data were applied to show the application value of this new fast inversion method.

  20. Annular beam with segmented phase gradients

    Directory of Open Access Journals (Sweden)

    Shubo Cheng

    2016-08-01

    Full Text Available An annular beam with a single uniform-intensity ring and multiple segments of phase gradients is proposed in this paper. Different from the conventional superposed vortices, such as the modulated optical vortices and the collinear superposition of multiple orbital angular momentum modes, the designed annular beam has a doughnut intensity distribution whose radius is independent of the phase distribution of the beam in the imaging plane. The phase distribution along the circumference of the doughnut beam can be segmented with different phase gradients. Similar to a vortex beam, the annular beam can also exert torques and rotate a trapped particle owing to the orbital angular momentum of the beam. As the beam possesses different phase gradients, the rotation velocity of the trapped particle can be varied along the circumference. The simulation and experimental results show that an annular beam with three segments of different phase gradients can rotate particles with controlled velocities. The beam has potential applications in optical trapping and optical information processing.

  1. Subspace learning from image gradient orientations

    NARCIS (Netherlands)

    Tzimiropoulos, Georgios; Zafeiriou, Stefanos; Pantic, Maja

    2012-01-01

    We introduce the notion of subspace learning from image gradient orientations for appearance-based object recognition. As image data is typically noisy and noise is substantially different from Gaussian, traditional subspace learning from pixel intensities fails very often to estimate reliably the

  2. Considerations of ion temperature gradient driven turbulence

    International Nuclear Information System (INIS)

    Cowley, S.C.; Kulsrud, R.M.

    1991-02-01

    The ion temperature gradient driven instability is considered in this paper. Physical pictures are presented to clarify the nature of the instability. The saturation of a single eddy is modeled by a simple nonlinear equation. We show that eddies which are elongated in the direction of the temperature gradient are the most unstable and have the highest saturation amplitudes. In a sheared magnetic field, such elongated eddies twist with the field lines. This structure is shown to be alternative to the usual Fourier mode picture in which the mode is localized around the surface where k parallel = 0. We show how these elongated twisting eddies, which are an integral part of the ''ballooning mode'' structure, could survive in a torus. The elongated eddies are shown to be unstable to secondary instabilities that are driven by the large gradients in the long eddy. We argue that this mechanism isotropizes ion temperature gradient turbulence. We further argue that the ''mixing length'' is set by this nonlinear process, not by a linear eigenmode width. 17 refs., 6 figs

  3. Gradient realization of nonlinear control systems

    NARCIS (Netherlands)

    Cortes monforte, J.; Cortés, J.; Crouch, P.E.; Astolfi, A.; van der Schaft, Arjan; Gordillo, F.

    2003-01-01

    We investigate necessary and su?cient conditions under which a nonlinear afine control system with outputs can be written as a gradient control system corresponding to some pseudo-Riemannian metric defined on the state space. The results rely on a suitable notion of compatibility of the system with

  4. Joining of Tungsten Armor Using Functional Gradients

    International Nuclear Information System (INIS)

    John Scott O'Dell

    2006-01-01

    The joining of low thermal expansion armor materials such as tungsten to high thermal expansion heat sink materials has been a major problem in plasma facing component (PFC) development. Conventional planar bonding techniques have been unable to withstand the high thermal induced stresses resulting from fabrication and high heat flux testing. During this investigation, innovative functional gradient joints produced using vacuum plasma spray forming techniques have been developed for joining tungsten armor to copper alloy heat sinks. A model was developed to select the optimum gradient architecture. Based on the modeling effort, a 2mm copper rich gradient was selected. Vacuum plasma pray parameters and procedures were then developed to produce the functional gradient joint. Using these techniques, dual cooling channel, medium scale mockups (32mm wide x 400mm length) were produced with vacuum plasma spray formed tungsten armor. The thickness of the tungsten armor was up to 5mm thick. No evidence of debonding at the interface between the heat sink and the vacuum plasma sprayed material was observed.

  5. Joining of Tungsten Armor Using Functional Gradients

    Energy Technology Data Exchange (ETDEWEB)

    John Scott O' Dell

    2006-12-31

    The joining of low thermal expansion armor materials such as tungsten to high thermal expansion heat sink materials has been a major problem in plasma facing component (PFC) development. Conventional planar bonding techniques have been unable to withstand the high thermal induced stresses resulting from fabrication and high heat flux testing. During this investigation, innovative functional gradient joints produced using vacuum plasma spray forming techniques have been developed for joining tungsten armor to copper alloy heat sinks. A model was developed to select the optimum gradient architecture. Based on the modeling effort, a 2mm copper rich gradient was selected. Vacuum plasma pray parameters and procedures were then developed to produce the functional gradient joint. Using these techniques, dual cooling channel, medium scale mockups (32mm wide x 400mm length) were produced with vacuum plasma spray formed tungsten armor. The thickness of the tungsten armor was up to 5mm thick. No evidence of debonding at the interface between the heat sink and the vacuum plasma sprayed material was observed.

  6. Lactate uptake against a concentration gradient

    DEFF Research Database (Denmark)

    Nordström, Carl-Henrik; Nielsen, Troels Halfeld; Nielsen, Hans Boye

    2014-01-01

    The recently published article by Jalloh et al (Jalloh I, Helmy A, Shannon RJ, Gallagher CN, Menon D, Carpenter K, Hutchinson P. Lactate uptake by the injured human brain - evidence from an arterio-venous gradient and cerebral microdialysis study. J Neurotrauma. 2013 Aug 22. [Epub ahead of print]...... is of fundamental importance the misconception should be corrected....

  7. Instabilities in power law gradient hardening materials

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Tvergaard, Viggo

    2005-01-01

    Tension and compression instabilities are investigated for specimens with dimensions in the micron range. A finite strain generalization of a higher order strain gradient plasticity theory is implemented in a finite element scheme capable of modeling power law hardening materials. Effects...

  8. Gradient based filtering of digital elevation models

    DEFF Research Database (Denmark)

    Knudsen, Thomas; Andersen, Rune Carbuhn

    We present a filtering method for digital terrain models (DTMs). The method is based on mathematical morphological filtering within gradient (slope) defined domains. The intention with the filtering procedure is to improbé the cartographic quality of height contours generated from a DTM based on ...

  9. Stochastic gradient versus recursive least squares learning

    Czech Academy of Sciences Publication Activity Database

    Slobodyan, Sergey; Bogomolova, Anna; Kolyuzhnov, Dmitri

    -, č. 309 (2006), s. 1-21 ISSN 1211-3298 Institutional research plan: CEZ:AV0Z70850503 Keywords : constant gain adaptive learning * stochastic gradient learning * recursive least squares Subject RIV: AH - Economics http://www.cerge-ei.cz/pdf/wp/Wp309.pdf

  10. Stable isotope mass spectrometry in petroleum exploration

    International Nuclear Information System (INIS)

    Mathur, Manju

    1997-01-01

    The stable isotope mass spectrometry plays an important role to evaluate the stable isotopic composition of hydrocarbons. The isotopic ratios of certain elements in petroleum samples reflect certain characteristics which are useful for petroleum exploration

  11. Housing price gradient and immigrant population: Data from the Italian real estate market.

    Science.gov (United States)

    Antoniucci, Valentina; Marella, Giuliano

    2018-02-01

    The database presented here was collected by Antoniucci and Marella to analyze the correlation between the housing price gradient and the immigrant population in Italy during 2016. It may also be useful in other statistical analyses, be they on the real estate market or in another branches of social science. The data sample relates to 112 Italian provincial capitals. It provides accurate information on urban structure, and specifically on urban density. The two most significant variables are original indicators constructed from official data sources: the housing price gradient, or the ratio between average prices in the center and suburbs by city; and building density, which is the average number of housing units per residential building. The housing price gradient is calculated for the two residential sub-markets, new-build and existing units, providing an original and detailed sample of the Italian residential market. Rather than average prices, the housing price gradient helps to identify potential divergences in residential market trends. As well as house prices, two other data clusters are considered: socio-economic variables, which provide a framework of each city, in terms of demographic and economic information; and various data on urban structure, which are rarely included in the same database.

  12. A sandwich-designed temperature-gradient incubator for studies of microbial temperature responses.

    Science.gov (United States)

    Elsgaard, Lars; Jørgensen, Leif Wagner

    2002-03-01

    A temperature-gradient incubator (TGI) is described, which produces a thermal gradient over 34 aluminium modules (15x30x5 cm) intersected by 2-mm layers of partly insulating graphite foil (SigraFlex Universal). The new, sandwich-designed TGI has 30 rows of six replicate sample wells for incubation of 28-ml test tubes. An electric plate heats one end of the TGI, and the other end is cooled by thermoelectric Peltier elements in combination with a liquid cooling system. The TGI is equipped with 24 calibrated Pt-100 temperature sensors and insulated by polyurethane plates. A PC-operated SCADA (Supervisory Control And Data Acquisition) software (Genesis 4.20) is applied for temperature control using three advanced control loops. The precision of the TGI temperature measurements was better than +/-0.12 degrees C, and for a 0-40 degrees C gradient, the temperature at the six replicate sample wells varied less than +/-0.04 degrees C. Temperatures measured in incubated water samples closely matched the TGI temperatures, which showed a linear relationship to the sample row number. During operation for 8 days with a gradient of 0-40 degrees C, the temperature at the cold end was stable within +/-0.02 degrees C, while the temperatures at the middle and the warm end were stable within +/-0.08 degrees C (n=2370). Using the new TGI, it was shown that the fine-scale (1 degrees C) temperature dependence of S(o) oxidation rates in agricultural soil (0-29 degrees C) could be described by the Arrhenius relationship. The apparent activation energy (E(a)) for S(o) oxidation was 79 kJ mol(-1), which corresponded to a temperature coefficient (Q(10)) of 3.1. These data demonstrated that oxidation of S(o) in soil is strongly temperature-dependent. In conclusion, the new TGI allowed a detailed study of microbial temperature responses as it produced a precise, stable, and certifiable temperature gradient by the new and combined use of sandwich-design, thermoelectric cooling, and advanced

  13. Experimental study of particle transport and density fluctuation in LHD

    International Nuclear Information System (INIS)

    Tanaka, K.; Michael, C.; Sanin, A.

    2005-01-01

    A variety of electron density (n e ) profiles have been observed in Large Helical Device (LHD). The density profiles change dramatically with heating power and toroidal magnetic field (B t ) under the same line averaged density. The particle transport coefficients, i.e., diffusion coefficient (D) and convection velocity (V) are experimentally obtained in the standard configuration from density modulation experiments. The values of D and V are estimated separately in the core and edge. The diffusion coefficients are found to be a strong function of electron temperature (T e ) and are proportional to T e 1.7±0.9 in the core and T e 1.1±0.14 in the edge. Edge diffusion coefficients are proportional to B t -2.08 . It is found that the scaling of D in the edge is close to gyro-Bohm-like in nature. Non-zero V is observed and it is found that the electron temperature gradient can drive particle convection, particularly in the core region. The convection velocity in the core reverses direction from inward to outward as the T e gradient increases. In the edge, convection is inward directed in most cases of the present data set. It shows a modest tendency, being proportional to T e gradient and remaining inward directed. However, the toroidal magnetic field also significantly affects the value and direction of V. The density fluctuation spectrum varies with heating power suggesting that it has an influence on particle transport. The value of K sub(perpendicular) ρ i is around 0.1, as expected for gyro-Bohm diffusion. Fluctuations are localized in both positive and negative density gradient regions of the hollow density profiles. The fluctuation power in each region is clearly distinguished having different phase velocity profiles. (author)

  14. Comparison of Corneal Riboflavin Gradients Using Dextran and HPMC Solutions.

    Science.gov (United States)

    Ehmke, Tobias; Seiler, Theo G; Fischinger, Isaak; Ripken, Tammo; Heisterkamp, Alexander; Frueh, Beatrice E

    2016-12-01

    To determine the riboflavin concentration gradient in the anterior corneal stroma when using hydroxypropyl methylcellulose (HPMC) or dextran as the carrier agent. Four different groups of porcine corneas (5 each) were compared regarding the riboflavin concentration in the anterior stroma. Prior to all experiments, stable hydration conditions were established for the corresponding solution. The dextran groups were treated with 0.1% riboflavin in 20% dextran for 10 and 30 minutes and the HPMC groups with 0.1% riboflavin in 1.1% HPMC for 10 and 30 minutes. After imbibition, nonlinear microscopy and consecutive image analysis were used to determine two-photon fluorescence intensities. To determine the riboflavin concentration, corneas were saturated and measured a second time by two-photon microscopy. With this measurement, a proper correction for absorption and scattering could be performed. Ultraviolet-A (UVA) transmission was measured after the application time for each group. Riboflavin concentration decreased with increasing depth and increased with longer application times in all groups. Comparing the dextran for 30 minutes and HPMC for 10 minutes groups, a significantly higher stromal riboflavin concentration was found within the most anterior 70 µm in the dextran group for 30 minutes, whereas deeper than 260 µm HPMC-assisted imbibition for 10 minutes yielded higher concentrations. In dextran-treated corneas, values obtained from pachymetry were substantially reduced, whereas HPMC-assisted imbibition led to a decent swelling. UVA transmission values were higher in dextran-assisted imbibition than in HPMC-assisted imbibition. Stromal riboflavin gradients are similar when applied in dextran for 30 minutes and HPMC for 10 minutes. When using HPMC solutions, a shallower cross-linked volume is expected due to a higher corneal hydration. [J Refract Surg. 2016;32(12):798-802.]. Copyright 2016, SLACK Incorporated.

  15. Stable rotating dipole solitons in nonlocal media

    DEFF Research Database (Denmark)

    Lopez-Aguayo, Servando; Skupin, Stefan; Desyatnikov, Anton S.

    2006-01-01

    We present the first example of stable rotating two-soliton bound states in nonlinear optical media with nonlocal response. We show that, in contrast to media with local response, nonlocality opens possibilities to generate stable azimuthons.......We present the first example of stable rotating two-soliton bound states in nonlinear optical media with nonlocal response. We show that, in contrast to media with local response, nonlocality opens possibilities to generate stable azimuthons....

  16. The production and characterization of topologically and mechanically gradient open-cell thermoplastic foams

    International Nuclear Information System (INIS)

    Sanami, M; Alderson, K L; Mottershead, B; Alderson, A; McDonald, S A; Withers, P J

    2014-01-01

    The development of longitudinally and radially gradient open-cell polyurethane foams is reported. Local and global mechanical properties and pore structure have been characterized using video extensometry with x−y strain-mapping capability, and x-ray microtomography (CT) and scanning electron microscopy (SEM), respectively. The local axial Poisson’s ratio varies in a smoothly continuous manner along the length of the longitudinally gradient foam from large negative (auxetic), through zero, to positive (conventional) values. The production of radially gradient foams having a coaxial core–sheath structure is reported for the first time. Two radially gradient foams have been produced, each displaying similar global negative axial Poisson’s ratio responses but with markedly different local axial Poisson’s ratio and local axial Young’s modulus behaviours. One of the radially gradient foams displays a positive Poisson’s ratio core and an auxetic sheath resulting from conventional and higher density re-entrant open-cell pore structures, respectively. (paper)

  17. Spin imaging in solids using synchronously rotating field gradients and samples

    International Nuclear Information System (INIS)

    Wind, R.A.; Yannoni, C.S.

    1983-01-01

    A method for spin-imaging in solids using nuclear magnetic resonance (NMR) spectroscopy is described. With this method, the spin density distribution of a two- or three-dimensional object such as a solid can be constructed resulting in an image of the sample. This method lends itself to computer control to map out an image of the object. This spin-imaging method involves the steps of placing a solid sample in the rf coil field and the external magnetic field of an NMR spectrometer. A magnetic field gradient is superimposed across the sample to provide a field gradient which results in a varying DC field that has different values over different parts of the sample. As a result, nuclei in different parts of the sample have different resonant NMR frequencies. The sample is rotated about an axis which makes a particular angle of 54.7 degrees with the static external magnetic field. The magnetic field gradient which has a spatial distribution related to the sample spinning axis is then rotated synchronously with the sample. Data is then collected while performing a solid state NMR line narrowing procedure. The next step is to change the phase relation between the sample rotation and the field gradient rotation. The data is again collected as before while the sample and field gradient are synchronously rotated. The phase relation is changed a number of times and data collected each time. The spin image of the solid sample is then reconstructed from the collected data

  18. Extracellular Processing of Molecular Gradients by Eukaryotic Cells Can Improve Gradient Detection Accuracy

    Science.gov (United States)

    Segota, Igor; Franck, Carl

    2017-12-01

    Eukaryotic cells sense molecular gradients by measuring spatial concentration variation through the difference in the number of occupied receptors to which molecules can bind. They also secrete enzymes that degrade these molecules, and it is presently not well understood how this affects the local gradient perceived by cells. Numerical and analytical results show that these enzymes can substantially increase the signal-to-noise ratio of the receptor difference and allow cells to respond to a much broader range of molecular concentrations and gradients than they would without these enzymes.

  19. Extracellular Processing of Molecular Gradients by Eukaryotic Cells Can Improve Gradient Detection Accuracy.

    Science.gov (United States)

    Segota, Igor; Franck, Carl

    2017-12-15

    Eukaryotic cells sense molecular gradients by measuring spatial concentration variation through the difference in the number of occupied receptors to which molecules can bind. They also secrete enzymes that degrade these molecules, and it is presently not well understood how this affects the local gradient perceived by cells. Numerical and analytical results show that these enzymes can substantially increase the signal-to-noise ratio of the receptor difference and allow cells to respond to a much broader range of molecular concentrations and gradients than they would without these enzymes.

  20. The effects of slope length and slope gradient on the size distributions of loess slides: Field observations and simulations

    Science.gov (United States)

    Qiu, Haijun; Cui, Peng; Regmi, Amar Deep; Hu, Sheng; Wang, Xingang; Zhang, Yuzhu

    2018-01-01

    In this study, we characterize and consider the effects of slope length and slope gradient on the size distributions of loess slides. To carry out this study, we employ data on 275 loess slides within Zhidan County, Central Loess Plateau, China. These data were collected in the field and supplemented by the interpretation of remote sensing images. Both the field observations and slope stability analysis show that loess slide size increases with the slope length. Slide sizes is significantly correlated with slope length, showing a power law relationship in both cases. However, the simulation results show that slope gradient is not associated with loess slide size. The main part of the link between slope gradient and slide size seen in the observations is only apparent, as indicated by the strong connection between slope gradient and length. Statistical analysis of the field observations reveals that slope gradient decreases with increasing slope length, and this correlation interferes with the potential relationship between landslide sizes and slope gradient seen in the field observations. In addition, the probability densities of the areas of loess slides occurring on slopes of different slope lengths are determined using kernel density estimation. This analysis shows that slope length controls the rollover of the frequency-size distribution of loess slides. The scaling exponent increases with slope length.