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Sample records for zeldovich gradient mechanism

  1. Cosmological collapse and the improved Zel'dovich approximation.

    NASA Astrophysics Data System (ADS)

    Salopek, D. S.; Stewart, J. M.; Croudace, K. M.; Parry, J.

    Using a general relativistic formulation, the authors show how to compute the higher order terms in the Zel'dovich approximation which describes cosmological collapse. They evolve the 3-metric in a spatial gradient expansion. Their method is an advance over earlier work because it is local at each order. Using the improved Zel'dovich approximation, they compute the epoch of collapse.

  2. zeldovich-PLT: Zel'dovich approximation initial conditions generator

    NASA Astrophysics Data System (ADS)

    Eisenstein, Daniel; Garrison, Lehman

    2016-05-01

    zeldovich-PLT generates Zel'dovich approximation (ZA) initial conditions (i.e. first-order Lagrangian perturbation theory) for cosmological N-body simulations, optionally applying particle linear theory (PLT) corrections.

  3. Unraveling Deformation Mechanisms in Gradient Structured Metals

    NASA Astrophysics Data System (ADS)

    Moering, Jordan Alexander

    Gradient structures have demonstrated high strength and high ductility, introducing new mechanisms to challenge conventional mechanics. This work develops a method for characterizing the shear strain in gradient structured steel and presents evidence of a texture gradient that develops in Surface Mechanical Attrition Treatment (SMAT). Mechanics underlying some theories of the strengthening mechanisms in gradient structured metals are introduced, followed by the fabrication and testing of gradient structured aluminum rod. The round geometry is intrinsically different from its flat counterparts, which leads to a multiaxial stress state evolving in tension. The aluminum exhibits strengthening beyond rule of mixtures, and texture evolution in the post-mortem sample indicates that out of plane stresses operate within the gradient. Finally, another gradient structured aluminum rod is shown to exhibit higher strength and higher elongation to failure in a variety of sample diameters and processing conditions. The GND density and microstructural evolution showed no significant changes during mechanical testing, and high resolution strain mapping was successfully completed within the core of the material. These discoveries and contributions to the field should help continue unraveling the deformation mechanisms of gradient structured metals.

  4. Yakov Zeldovich and the Cosmic Web Paradigm

    NASA Astrophysics Data System (ADS)

    Einasto, Jaan

    2016-10-01

    I discuss the formation of the modern cosmological paradigm. In more detail I describe the early study of dark matter and cosmic web and the role of Yakov Zeldovich in the formation of the present concepts on these subjects.

  5. PLETHORA gradient formation mechanism separates auxin responses.

    PubMed

    Mähönen, Ari Pekka; Ten Tusscher, Kirsten; Siligato, Riccardo; Smetana, Ondřej; Díaz-Triviño, Sara; Salojärvi, Jarkko; Wachsman, Guy; Prasad, Kalika; Heidstra, Renze; Scheres, Ben

    2014-11-06

    During plant growth, dividing cells in meristems must coordinate transitions from division to expansion and differentiation, thus generating three distinct developmental zones: the meristem, elongation zone and differentiation zone. Simultaneously, plants display tropisms, rapid adjustments of their direction of growth to adapt to environmental conditions. It is unclear how stable zonation is maintained during transient adjustments in growth direction. In Arabidopsis roots, many aspects of zonation are controlled by the phytohormone auxin and auxin-induced PLETHORA (PLT) transcription factors, both of which display a graded distribution with a maximum near the root tip. In addition, auxin is also pivotal for tropic responses. Here, using an iterative experimental and computational approach, we show how an interplay between auxin and PLTs controls zonation and gravitropism. We find that the PLT gradient is not a direct, proportionate readout of the auxin gradient. Rather, prolonged high auxin levels generate a narrow PLT transcription domain from which a gradient of PLT protein is subsequently generated through slow growth dilution and cell-to-cell movement. The resulting PLT levels define the location of developmental zones. In addition to slowly promoting PLT transcription, auxin also rapidly influences division, expansion and differentiation rates. We demonstrate how this specific regulatory design in which auxin cooperates with PLTs through different mechanisms and on different timescales enables both the fast tropic environmental responses and stable zonation dynamics necessary for coordinated cell differentiation.

  6. Mechanical Properties of Gradient Structure Mg Alloy

    NASA Astrophysics Data System (ADS)

    Chen, Hongliang; Yang, Jiang; Zhou, Hao; Moering, Jordan; Yin, Zhe; Gong, Yulan; Zhao, KunYu

    2017-09-01

    In this work, a surface mechanical attrition treatment (SMAT) process was applied to AZ31B magnesium alloy at room temperature. This method produced a gradient structure on the treated AZ31B, in which the grains of the topmost layer are refined to nanoscale sizes. A combination of nanocrystallites at the surface and coarse-grains in the center are the main features of this structure. This structure results in an excellent combination of both strength and ductility. The highest yield strength for the 30 minutes SMAT AZ31B samples increased to 249 ± 5 MPa and the uniform elongation decreased to 9.3 ± 0.8 pct, whereas the original yield strength was only 147 ± 4 MPa and the uniform elongation was 15.4 ± 1.1 pct. Microstructural observations, stress relaxation tests, and hardness tests were used to verify the results. Additionally, there is a specific volume fraction of gradient structure to achieve the best mechanical performance, which is shown to be in the range of 9.3 to 14 pct for the AZ31B alloy.

  7. Applying the Zel'dovich approximation to general relativity

    NASA Astrophysics Data System (ADS)

    Croudace, K. M.; Parry, J.; Salopek, D. S.; Stewart, J. M.

    1994-03-01

    Starting from general relativity, we give a systematic derivation of the Zel'dovich approximation describing the nonlinear evolution of collisionless dust. We begin by evolving dust along world lines, and we demonstrate that the Szekeres line element is an exact but apparently unstable solution of the evolution equations describing pancake collapse. Next, we solve the Einstein field equations by employing Hamilton-Jacobi techniques and a spatial gradient expansion. We give a prescription for evolving a primordial or 'seed' metric up to the formation of pancakes, and demonstrate its validity by rederiving the Szekeres solution approximately at third order and exactly at fifth order in spatial gradients. Finally we show that the range of validity of the expansion can be improved quite significantly if one notes that the 3-metric must have nonnegative eigenvalues. With this improvement the exact Szekeres solution is obtained after only one iteration.

  8. Ya B Zeldovich and nuclear power

    NASA Astrophysics Data System (ADS)

    Ponomarev, L. I.

    2014-03-01

    The idea on a homogeneous nuclear reactor, first suggested by Ya B Zeldovich and Yu B Khariton in 1939, has since had its ups and downs and is now re-emerging, enriched with the knowledge and experience accumulated over the years having past. One of the current versions of the idea, the fast molten-salt reactor with a U-Pu fuel cycle, is presented in this paper.

  9. Morphogengineering roots: comparing mechanisms of morphogen gradient formation

    PubMed Central

    2012-01-01

    Background In developmental biology, there has been a recent focus on the robustness of morphogen gradients as possible providers of positional information. It was shown that functional morphogen gradients present strong biophysical constraints and lack of robustness to noise. Here we explore how the details of the mechanism which underlies the generation of a morphogen gradient can influence those properties. Results We contrast three gradient-generating mechanisms, (i) a source-decay mechanism; and (ii) a unidirectional transport mechanism; and (iii) a so-called reflux-loop mechanism. Focusing on the dynamics of the phytohormone auxin in the root, we show that only the reflux-loop mechanism can generate a gradient that would be adequate to supply functional positional information for the Arabidopsis root, for biophysically reasonable kinetic parameters. Conclusions We argue that traits that differ in spatial and temporal time-scales can impose complex selective pressures on the mechanism of morphogen gradient formation used for the development of the particular organism. PMID:22583698

  10. Molecular mechanisms for generating transmembrane proton gradients

    PubMed Central

    Gunner, M.R.; Amin, Muhamed; Zhu, Xuyu; Lu, Jianxun

    2013-01-01

    Membrane proteins use the energy of light or high energy substrates to build a transmembrane proton gradient through a series of reactions leading to proton release into the lower pH compartment (P-side) and proton uptake from the higher pH compartment (N-side). This review considers how the proton affinity of the substrates, cofactors and amino acids are modified in four proteins to drive proton transfers. Bacterial reaction centers (RCs) and photosystem II (PSII) carry out redox chemistry with the species to be oxidized on the P-side while reduction occurs on the N-side of the membrane. Terminal redox cofactors are used which have pKas that are strongly dependent on their redox state, so that protons are lost on oxidation and gained on reduction. Bacteriorhodopsin is a true proton pump. Light activation triggers trans to cis isomerization of a bound retinal. Strong electrostatic interactions within clusters of amino acids are modified by the conformational changes initiated by retinal motion leading to changes in proton affinity, driving transmembrane proton transfer. Cytochrome c oxidase (CcO) catalyzes the reduction of O2 to water. The protons needed for chemistry are bound from the N-side. The reduction chemistry also drives proton pumping from N- to P-side. Overall, in CcO the uptake of 4 electrons to reduce O2 transports 8 charges across the membrane, with each reduction fully coupled to removal of two protons from the N-side, the delivery of one for chemistry and transport of the other to the P-side. PMID:23507617

  11. Zeldovich pancakes in observational data are cold

    SciTech Connect

    Brinckmann, Thejs; Lindholmer, Mikkel; Hansen, Steen

    The present day universe consists of galaxies, galaxy clusters, one-dimensional filaments and two-dimensional sheets or pancakes, all of which combine to form the cosmic web. The so called ''Zeldovich pancakes' are very difficult to observe, because their overdensity is only slightly greater than the average density of the universe. Falco et al. [1] presented a method to identify Zeldovich pancakes in observational data, and these were used as a tool for estimating the mass of galaxy clusters. Here we expand and refine that observational detection method. We study two pancakes on scales of 10 Mpc, identified from spectroscopically observed galaxiesmore » near the Coma cluster, and compare with twenty numerical pancakes.We find that the observed structures have velocity dispersions of about 100 km/sec, which is relatively low compared to typical groups and filaments. These velocity dispersions are consistent with those found for the numerical pancakes. We also confirm that the identified structures are in fact two-dimensional structures. Finally, we estimate the stellar to total mass of the observational pancakes to be 2 · 10{sup −4}, within one order of magnitude, which is smaller than that of clusters of galaxies.« less

  12. Gradients in Wall Mechanics and Polysaccharides along Growing Inflorescence Stems.

    PubMed

    Phyo, Pyae; Wang, Tuo; Kiemle, Sarah N; O'Neill, Hugh; Pingali, Sai Venkatesh; Hong, Mei; Cosgrove, Daniel J

    2017-12-01

    At early stages of Arabidopsis ( Arabidopsis thaliana ) flowering, the inflorescence stem undergoes rapid growth, with elongation occurring predominantly in the apical ∼4 cm of the stem. We measured the spatial gradients for elongation rate, osmotic pressure, cell wall thickness, and wall mechanical compliances and coupled these macroscopic measurements with molecular-level characterization of the polysaccharide composition, mobility, hydration, and intermolecular interactions of the inflorescence cell wall using solid-state nuclear magnetic resonance spectroscopy and small-angle neutron scattering. Force-extension curves revealed a gradient, from high to low, in the plastic and elastic compliances of cell walls along the elongation zone, but plots of growth rate versus wall compliances were strikingly nonlinear. Neutron-scattering curves showed only subtle changes in wall structure, including a slight increase in cellulose microfibril alignment along the growing stem. In contrast, solid-state nuclear magnetic resonance spectra showed substantial decreases in pectin amount, esterification, branching, hydration, and mobility in an apical-to-basal pattern, while the cellulose content increased modestly. These results suggest that pectin structural changes are connected with increases in pectin-cellulose interaction and reductions in wall compliances along the apical-to-basal gradient in growth rate. These pectin structural changes may lessen the ability of the cell wall to undergo stress relaxation and irreversible expansion (e.g. induced by expansins), thus contributing to the growth kinematics of the growing stem. © 2017 American Society of Plant Biologists. All Rights Reserved.

  13. Polarized Sunyaev Zel'dovich tomography

    NASA Astrophysics Data System (ADS)

    Deutsch, Anne-Sylvie; Johnson, Matthew C.; Münchmeyer, Moritz; Terrana, Alexandra

    2018-04-01

    Secondary CMB polarization is induced by the late-time scattering of CMB photons by free electrons on our past light cone. This polarized Sunyaev Zel'dovich (pSZ) effect is sensitive to the electrons' locally observed CMB quadrupole, which is sourced primarily by long wavelength inhomogeneities. By combining the remote quadrupoles measured by free electrons throughout the Universe after reionization, the pSZ effect allows us to obtain additional information about large scale modes beyond what can be learned from our own last scattering surface. Here we determine the power of pSZ tomography, in which the pSZ effect is cross-correlated with the density field binned at several redshifts, to provide information about the long wavelength Universe. The signal we explore here is a power asymmetry in the cross-correlation between E or B mode CMB polarization and the density field. We compare this to the cosmic variance limited noise: the random chance to get a power asymmetry in the absence of a large scale quadrupole field. By computing the necessary transfer functions and cross-correlations, we compute the signal-to-noise ratio attainable by idealized next generation CMB experiments and galaxy surveys. We find that a signal-to-noise ratio of ~ 1‑10 is in principle attainable over a significant range of power multipoles, with the strongest signal coming from the first multipoles in the lowest redshift bins. These results prompt further assessment of realistically measuring the pSZ signal and the potential impact for constraining cosmology on large scales.

  14. Pauli-Zeldovich cancellation of the vacuum energy divergences, auxiliary fields and supersymmetry

    NASA Astrophysics Data System (ADS)

    Kamenshchik, Alexander Yu.; Starobinsky, Alexei A.; Tronconi, Alessandro; Vardanyan, Tereza; Venturi, Giovanni

    2018-03-01

    We have considered the Pauli-Zeldovich mechanism for the cancellation of the ultraviolet divergences in vacuum energy. This mechanism arises because bosons and fermions give contributions of the opposite signs. In contrast with the preceding papers devoted to this topic wherein mainly free fields were studied, here we have taken their interactions into account to the lowest order of perturbation theory. We have constructed some simple toy models having particles with spin 0 and spin 1 / 2, where masses of the particles are equal while the interactions can be quite non-trivial.

  15. Bone scaffolds with homogeneous and discrete gradient mechanical properties.

    PubMed

    Jelen, C; Mattei, G; Montemurro, F; De Maria, C; Mattioli-Belmonte, M; Vozzi, G

    2013-01-01

    Bone TE uses a scaffold either to induce bone formation from surrounding tissue or to act as a carrier or template for implanted bone cells or other agents. We prepared different bone tissue constructs based on collagen, gelatin and hydroxyapatite using genipin as cross-linking agent. The fabricated construct did not present a release neither of collagen neither of genipin over its toxic level in the surrounding aqueous environment. Each scaffold has been mechanically characterized with compression, swelling and creep tests, and their respective viscoelastic mechanical models were derived. Mechanical characterization showed a practically elastic behavior of all samples and that compressive elastic modulus basically increases as content of HA increases, and it is strongly dependent on porosity and water content. Moreover, by considering that gradients in cellular and extracellular architecture as well as in mechanical properties are readily apparent in native tissues, we developed discrete functionally graded scaffolds (discrete FGSs) in order to mimic the graded structure of bone tissue. These new structures were mechanically characterized showing a marked anisotropy as the native bone tissue. Results obtained have shown FGSs could represent valid bone substitutes. Copyright © 2012 Elsevier B.V. All rights reserved.

  16. Exploring Molecular and Mechanical Gradients in Structural Bioscaffolds†

    PubMed Central

    Waite, J. Herbert; Lichtenegger, Helga C.; Stucky, Galen D.; Hansma, Paul

    2007-01-01

    Most organisms consist of a functionally adaptive assemblage of hard and soft tissues. Despite the obvious advantages of reinforcing soft protoplasm with a hard scaffold, such composites can lead to tremendous mechanical stresses where the two meet. Although little is known about how nature relieves these stresses, it is generally agreed that fundamental insights about molecular adaptation at hard/soft interfaces could profoundly influence how we think about biomaterials. Based on two noncellular tissues, mussel byssus and polychaete jaws, recent studies suggest that one natural strategy to minimize interfacial stresses between adjoining stiff and soft tissue appears to be the creation of a “fuzzy” boundary, which avoids abrupt changes in mechanical properties. Instead there is a gradual mechanical change that accompanies the transcendence from stiff to soft and vice versa. In byssal threads, the biochemical medium for achieving such a gradual mechanical change involves the elegant use of collagen-based self-assembling block copolymers. There are three distinct diblock copolymer types in which one block is always collagenous, whereas the other can be either elastin-like (soft), amorphous polyglycine (intermediate), or silk-like (stiff). Gradients of these are made by an incrementally titrated expression of the three proteins in secretory cells the titration phenotype of which is linked to their location. Thus, reflecting exactly the composition of each thread, the distal cells secrete primarily the silk– and polyglycine–collagen diblocks, whereas the proximal cells secrete the elastin– and polyglycine–collagen diblocks. Those cells in between exhibit gradations of collagens with silk or elastin blocks. Spontaneous self-assembly appears to be by pH triggered metal binding by histidine (HIS)-rich sequences at both the amino and carboxy termini of the diblocks. In the polychaete jaws, HIS-rich sequences are expanded into a major block domain. Histidine

  17. Systems biology derived source-sink mechanism of BMP gradient formation

    PubMed Central

    Zinski, Joseph; Bu, Ye; Wang, Xu; Dou, Wei

    2017-01-01

    A morphogen gradient of Bone Morphogenetic Protein (BMP) signaling patterns the dorsoventral embryonic axis of vertebrates and invertebrates. The prevailing view in vertebrates for BMP gradient formation is through a counter-gradient of BMP antagonists, often along with ligand shuttling to generate peak signaling levels. To delineate the mechanism in zebrafish, we precisely quantified the BMP activity gradient in wild-type and mutant embryos and combined these data with a mathematical model-based computational screen to test hypotheses for gradient formation. Our analysis ruled out a BMP shuttling mechanism and a bmp transcriptionally-informed gradient mechanism. Surprisingly, rather than supporting a counter-gradient mechanism, our analyses support a fourth model, a source-sink mechanism, which relies on a restricted BMP antagonist distribution acting as a sink that drives BMP flux dorsally and gradient formation. We measured Bmp2 diffusion and found that it supports the source-sink model, suggesting a new mechanism to shape BMP gradients during development. PMID:28826472

  18. Systems biology derived source-sink mechanism of BMP gradient formation.

    PubMed

    Zinski, Joseph; Bu, Ye; Wang, Xu; Dou, Wei; Umulis, David; Mullins, Mary C

    2017-08-09

    A morphogen gradient of Bone Morphogenetic Protein (BMP) signaling patterns the dorsoventral embryonic axis of vertebrates and invertebrates. The prevailing view in vertebrates for BMP gradient formation is through a counter-gradient of BMP antagonists, often along with ligand shuttling to generate peak signaling levels. To delineate the mechanism in zebrafish, we precisely quantified the BMP activity gradient in wild-type and mutant embryos and combined these data with a mathematical model-based computational screen to test hypotheses for gradient formation. Our analysis ruled out a BMP shuttling mechanism and a bmp transcriptionally-informed gradient mechanism. Surprisingly, rather than supporting a counter-gradient mechanism, our analyses support a fourth model, a source-sink mechanism, which relies on a restricted BMP antagonist distribution acting as a sink that drives BMP flux dorsally and gradient formation. We measured Bmp2 diffusion and found that it supports the source-sink model, suggesting a new mechanism to shape BMP gradients during development.

  19. Mechanisms of detonation formation due to a temperature gradient

    NASA Astrophysics Data System (ADS)

    Kapila, A. K.; Schwendeman, D. W.; Quirk, J. J.; Hawa, T.

    2002-12-01

    Emergence of a detonation in a homogeneous, exothermically reacting medium can be deemed to occur in two phases. The first phase processes the medium so as to create conditions ripe for the onset of detonation. The actual events leading up to preconditioning may vary from one experiment to the next, but typically, at the end of this stage the medium is hot and in a state of nonuniformity. The second phase consists of the actual formation of the detonation wave via chemico-gasdynamic interactions. This paper considers an idealized medium with simple, rate-sensitive kinetics for which the preconditioned state is modelled as one with an initially prescribed linear gradient of temperature. Accurate and well-resolved numerical computations are carrried out to determine the mode of detonation formation as a function of the size of the initial gradient. For shallow gradients, the result is a decelerating supersonic reaction wave, a weak detonation, whose trajectory is dictated by the initial temperature profile, with only weak intervention from hydrodynamics. If the domain is long enough, or the gradient less shallow, the wave slows down to the Chapman-Jouguet speed and undergoes a swift transition to the ZND structure. For sharp gradients, gasdynamic nonlinearity plays a much stronger role. Now the path to detonation is through an accelerating pulse that runs ahead of the reaction wave and rearranges the induction-time distribution there to one that bears little resemblance to that corresponding to the initial temperature gradient. The pulse amplifies and steepens, transforming itself into a complex consisting of a lead shock, an induction zone, and a following fast deflagration. As the pulse advances, its three constituent entities attain progressively higher levels of mutual coherence, to emerge as a ZND detonation. For initial gradients that are intermediate in size, aspects of both the extreme scenarios appear in the path to detonation. The novel aspect of this study

  20. Ya.B. Zel''dovich (1914-1987). Chemist, Nuclear Physicist, Cosmologist

    NASA Astrophysics Data System (ADS)

    Sahni, Varun

    2011-06-01

    A scientific biography of the outstanding Soviet Chemist, Physicist and Cosmologist Yakov Borisovich Zeldovich (1914-1987) has been given by one of his pupils. A special concern has been given to cosmological works by Zel'dovich. Figures 4,Bibliography: 9.

  1. Chandra Observations of the Brightest Sunyaev-Zeldovich Effect Cluster

    NASA Astrophysics Data System (ADS)

    Hughes, John

    2011-10-01

    We propose deep Chandra observations of ACT-CL J0102-4915, the brightest Sunyaev-Zeldovich effect cluster discovered by the Atacama Cosmology Telescope and South Pole Telescope surveys. These surveys covered approximately 3000 square degrees and are essentially complete to high redshift. Our recent Chandra and VLT optical data reveal ACL-CL J0102-4915 to be undergoing a major merger. It is likely a high redshift {z=0.870} counterpart to the famous A?A?bulletA?A? cluster. New Chandra data will determine the properties of the merger shock and the HST/ACS data will provide a weak lensing mass map.

  2. Chandra Observations of the Brightest Sunyaev-Zeldovich Effect Cluster

    NASA Astrophysics Data System (ADS)

    Hughes, John

    2011-09-01

    We propose deep Chandra observations of ACT-CL J0102-4915, the brightest Sunyaev-Zeldovich effect cluster discovered by the Atacama Cosmology Telescope and South Pole Telescope surveys. These surveys covered approximately 3000 square degrees and are essentially complete to high redshift. Our recent Chandra and VLT optical data reveal ACL-CL J0102-4915 to be undergoing a major merger. It is likely a high redshift (z=0.870) counterpart to the famous ``bullet'' cluster. New Chandra data will determine the properties of the merger shock and the HST/ACS data will provide a weak lensing mass map.

  3. The Zeldovich & Adhesion approximations and applications to the local universe

    NASA Astrophysics Data System (ADS)

    Hidding, Johan; van de Weygaert, Rien; Shandarin, Sergei

    2016-10-01

    The Zeldovich approximation (ZA) predicts the formation of a web of singularities. While these singularities may only exist in the most formal interpretation of the ZA, they provide a powerful tool for the analysis of initial conditions. We present a novel method to find the skeleton of the resulting cosmic web based on singularities in the primordial deformation tensor and its higher order derivatives. We show that the A 3 lines predict the formation of filaments in a two-dimensional model. We continue with applications of the adhesion model to visualise structures in the local (z < 0.03) universe.

  4. Collective gradient sensing: fundamental bounds, cluster mechanics, and cell-to-cell variability

    NASA Astrophysics Data System (ADS)

    Camley, Brian

    Many eukaryotic cells chemotax, sensing and following chemical gradients. However, experiments have shown that even under conditions when single cells do not chemotax, small clusters may still follow a gradient. Similar collective motion is also known to occur in response to gradients in substrate stiffness or electric potential (collective durotaxis or galvanotaxis). How can cell clusters sense a gradient that individual cells ignore? I discuss possible ``collective guidance'' mechanisms underlying this motion, where individual cells measure the mean value of the attractant, but need not measure its gradient to give rise to directional motility for a cell cluster. I show that the collective guidance hypothesis can be directly tested by looking for strong orientational effects in pairs of cells chemotaxing. Collective gradient sensing also has a new wrinkle in comparison to single-cell chemotaxis: to accurately determine a gradient direction, a cluster must integrate information from cells with highly variable properties. When is cell-to-cell variation a limiting factor in sensing accuracy? I provide some initial answers, and discuss how cell clusters can sense gradients in a way that is robust to cell-to-cell variation. Interestingly, these strategies may depend on the cluster's mechanics; I develop a bound that links the cluster's chemotactic accuracy and its rheology. This suggests that in some circumstances, mechanical transitions (e.g. unjamming) can control tactic accuracy. Work supported by NIH Grant No. P01 GM078586, NIH Grant No. F32GM110983.

  5. Direct measurement of optical trapping force gradient on polystyrene microspheres using a carbon nanotube mechanical resonator.

    PubMed

    Yasuda, Masaaki; Takei, Kuniharu; Arie, Takayuki; Akita, Seiji

    2017-06-06

    Optical tweezers based on optical radiation pressure are widely used to manipulate nanoscale to microscale particles. This study demonstrates direct measurement of the optical force gradient distribution acting on a polystyrene (PS) microsphere using a carbon nanotube (CNT) mechanical resonator, where a PS microsphere with 3 μm diameter is welded at the CNT tip using laser heating. With the CNT mechanical resonator with PS microsphere, we measured the distribution of optical force gradient with resolution near the thermal noise limit of 0.02 pN/μm in vacuum, in which condition enables us to high accuracy measurement using the CNT mechanical resonator because of reduced mechanical damping from surrounding fluid. The obtained force gradient and the force gradient distribution agree well with theoretical values calculated using Lorenz-Mie theory.

  6. The mechanism of thermal-gradient mass transfer in the sodium hydroxide-nickel system

    NASA Technical Reports Server (NTRS)

    May, Charles E

    1958-01-01

    "Thermal-gradient mass transfer" was investigated in the molten sodium hydroxide-nickel system. Possible mechanisms (physical, electrochemical, and chemical) are discussed in terms of experimental and theoretical evidence. Experimental details are included in appendixes.

  7. Gravitropic mechanisms derived from space experiments and magnetic gradients.

    NASA Astrophysics Data System (ADS)

    Hasenstein, Karl H.; Park, Myoung Ryoul

    2016-07-01

    Gravitropism is the result of a complex sequence of events that begins with the movement of dense particles, typically starch-filled amyloplasts in response to reorientation. Although these organelles change positions, it is not clear whether the critical signal is derived from sedimentation or dynamic interactions of amyloplasts with relevant membranes. Substituting gravity by high-gradient magnetic fields (HGMF) provides a localized stimulus for diamagnetic starch that is specific for amyloplasts and comparable to gravity without affecting other organelles. Experiments with Brassica rapa showed induction of root curvature by HGMF when roots moved sufficiently close to the magnetic gradient-inducing foci. The focused and short-range effectiveness of HGMFs provided a gravity-like stimulus and affected related gene expression. Root curvature was sensitive to the mutual alignment between roots and HGMF direction. Unrelated to any HGMF effects, the size of amyloplasts in space-grown roots increased by 30% compared to ground controls and suggests enhanced sensitivity in a gravity-reduced environment. Accompanying gene transcription studies showed greater differences between HGMF-exposed and space controls than between space and ground controls. This observation may lead to the identification of gravitropism-relevant genes. However, space grown roots showed stronger transcription of common reference genes such as actin and ubiquitin in magnetic fields than in non-magnetic conditions. In contrast, α-amylase, glucokinase and PIN encoding genes were transcribed stronger under non-magnetic conditions than under HGMF. The large number of comparisons between space, ground, and HGMF prompted the assessment of transcription differences between root segments, root-shoot junction, and seeds. Because presumed transcription of reference genes varied more than genes of interest, changes in gene expression cannot be based on reference genes. The data provide an example of complex

  8. Noise reduction in the intracellular pom1p gradient by a dynamic clustering mechanism.

    PubMed

    Saunders, Timothy E; Pan, Kally Z; Angel, Andrew; Guan, Yinghua; Shah, Jagesh V; Howard, Martin; Chang, Fred

    2012-03-13

    Chemical gradients can generate pattern formation in biological systems. In the fission yeast Schizosaccharomyces pombe, a cortical gradient of pom1p (a DYRK-type protein kinase) functions to position sites of cytokinesis and cell polarity and to control cell length. Here, using quantitative imaging, fluorescence correlation spectroscopy, and mathematical modeling, we study how its gradient distribution is formed. Pom1p gradients exhibit large cell-to-cell variability, as well as dynamic fluctuations in each individual gradient. Our data lead to a two-state model for gradient formation in which pom1p molecules associate with the plasma membrane at cell tips and then diffuse on the membrane while aggregating into and fragmenting from clusters, before disassociating from the membrane. In contrast to a classical one-component gradient, this two-state gradient buffers against cell-to-cell variations in protein concentration. This buffering mechanism, together with time averaging to reduce intrinsic noise, allows the pom1p gradient to specify positional information in a robust manner. Copyright © 2012 Elsevier Inc. All rights reserved.

  9. Fgf8 morphogen gradient forms by a source-sink mechanism with freely diffusing molecules.

    PubMed

    Yu, Shuizi Rachel; Burkhardt, Markus; Nowak, Matthias; Ries, Jonas; Petrásek, Zdenek; Scholpp, Steffen; Schwille, Petra; Brand, Michael

    2009-09-24

    It is widely accepted that tissue differentiation and morphogenesis in multicellular organisms are regulated by tightly controlled concentration gradients of morphogens. How exactly these gradients are formed, however, remains unclear. Here we show that Fgf8 morphogen gradients in living zebrafish embryos are established and maintained by two essential factors: fast, free diffusion of single molecules away from the source through extracellular space, and a sink function of the receiving cells, regulated by receptor-mediated endocytosis. Evidence is provided by directly examining single molecules of Fgf8 in living tissue by fluorescence correlation spectroscopy, quantifying their local mobility and concentration with high precision. By changing the degree of uptake of Fgf8 into its target cells, we are able to alter the shape of the Fgf8 gradient. Our results demonstrate that a freely diffusing morphogen can set up concentration gradients in a complex multicellular tissue by a simple source-sink mechanism.

  10. Theoretical analysis of degradation mechanisms in the formation of morphogen gradients

    NASA Astrophysics Data System (ADS)

    Bozorgui, Behnaz; Teimouri, Hamid; Kolomeisky, Anatoly B.

    2015-07-01

    Fundamental biological processes of development of tissues and organs in multicellular organisms are governed by various signaling molecules, which are called morphogens. It is known that spatial and temporal variations in the concentration profiles of signaling molecules, which are frequently referred as morphogen gradients, lead to a cell differentiation via activating specific genes in a concentration-dependent manner. It is widely accepted that the establishment of the morphogen gradients involves multiple biochemical reactions and diffusion processes. One of the critical elements in the formation of morphogen gradients is a degradation of signaling molecules. We develop a new theoretical approach that provides a comprehensive description of the degradation mechanisms. It is based on the idea that the degradation works as an effective potential that drives the signaling molecules away from the source region. Utilizing the method of first-passage processes, the dynamics of the formation of morphogen gradients for various degradation mechanisms is explicitly evaluated. It is found that linear degradation processes lead to a dynamic behavior specified by times to form the morphogen gradients that depend linearly on the distance from the source. This is because the effective potential due to the degradation is quite strong. At the same time, nonlinear degradation mechanisms yield a quadratic scaling in the morphogen gradients formation times since the effective potentials are much weaker. Physical-chemical explanations of these phenomena are presented.

  11. Stronger tests of mechanisms underlying geographic gradients of biodiversity: insights from the dimensionality of biodiversity.

    PubMed

    Stevens, Richard D; Tello, J Sebastián; Gavilanez, María Mercedes

    2013-01-01

    Inference involving diversity gradients typically is gathered by mechanistic tests involving single dimensions of biodiversity such as species richness. Nonetheless, because traits such as geographic range size, trophic status or phenotypic characteristics are tied to a particular species, mechanistic effects driving broad diversity patterns should manifest across numerous dimensions of biodiversity. We develop an approach of stronger inference based on numerous dimensions of biodiversity and apply it to evaluate one such putative mechanism: the mid-domain effect (MDE). Species composition of 10,000-km(2) grid cells was determined by overlaying geographic range maps of 133 noctilionoid bat taxa. We determined empirical diversity gradients in the Neotropics by calculating species richness and three indices each of phylogenetic, functional and phenetic diversity for each grid cell. We also created 1,000 simulated gradients of each examined metric of biodiversity based on a MDE model to estimate patterns expected if species distributions were randomly placed within the Neotropics. For each simulation run, we regressed the observed gradient onto the MDE-expected gradient. If a MDE drives empirical gradients, then coefficients of determination from such an analysis should be high, the intercept no different from zero and the slope no different than unity. Species richness gradients predicted by the MDE fit empirical patterns. The MDE produced strong spatially structured gradients of taxonomic, phylogenetic, functional and phenetic diversity. Nonetheless, expected values generated from the MDE for most dimensions of biodiversity exhibited poor fit to most empirical patterns. The MDE cannot account for most empirical patterns of biodiversity. Fuller understanding of latitudinal gradients will come from simultaneous examination of relative effects of random, environmental and historical mechanisms to better understand distribution and abundance of the current biota.

  12. Stronger Tests of Mechanisms Underlying Geographic Gradients of Biodiversity: Insights from the Dimensionality of Biodiversity

    PubMed Central

    Stevens, Richard D.; Tello, J. Sebastián; Gavilanez, María Mercedes

    2013-01-01

    Inference involving diversity gradients typically is gathered by mechanistic tests involving single dimensions of biodiversity such as species richness. Nonetheless, because traits such as geographic range size, trophic status or phenotypic characteristics are tied to a particular species, mechanistic effects driving broad diversity patterns should manifest across numerous dimensions of biodiversity. We develop an approach of stronger inference based on numerous dimensions of biodiversity and apply it to evaluate one such putative mechanism: the mid-domain effect (MDE). Species composition of 10,000-km2 grid cells was determined by overlaying geographic range maps of 133 noctilionoid bat taxa. We determined empirical diversity gradients in the Neotropics by calculating species richness and three indices each of phylogenetic, functional and phenetic diversity for each grid cell. We also created 1,000 simulated gradients of each examined metric of biodiversity based on a MDE model to estimate patterns expected if species distributions were randomly placed within the Neotropics. For each simulation run, we regressed the observed gradient onto the MDE-expected gradient. If a MDE drives empirical gradients, then coefficients of determination from such an analysis should be high, the intercept no different from zero and the slope no different than unity. Species richness gradients predicted by the MDE fit empirical patterns. The MDE produced strong spatially structured gradients of taxonomic, phylogenetic, functional and phenetic diversity. Nonetheless, expected values generated from the MDE for most dimensions of biodiversity exhibited poor fit to most empirical patterns. The MDE cannot account for most empirical patterns of biodiversity. Fuller understanding of latitudinal gradients will come from simultaneous examination of relative effects of random, environmental and historical mechanisms to better understand distribution and abundance of the current biota. PMID

  13. Research of Mechanical Property Gradient Distribution of Al-Cu Alloy in Centrifugal Casting

    NASA Astrophysics Data System (ADS)

    Sun, Zhi; Sui, Yanwei; Liu, Aihui; Li, Bangsheng; Guo, Jingjie

    Al-Cu alloy castings are obtained using centrifugal casting. The regularity of mechanical property gradient distribution of Al-Cu alloy castings with the same centrifugal radius at different positions is investigated. The result shows that the tensile strength, yield strength, elongation and microscope hardness exhibit the following gradient distribution characteristic — high on both sides and low on the center. The trend of mechanical property gradient distribution of Al-Cu alloy increases with the increase in the rotation speed. Moreover, the mechanical properties of casting centerline two sides have asymmetry. The reason is that the grain size of casting centerline two sides and Al2Cu phase and Cu content change correspondingly.

  14. 3D Printing of Materials with Tunable Failure via Bioinspired Mechanical Gradients.

    PubMed

    Kokkinis, Dimitri; Bouville, Florian; Studart, André R

    2018-05-01

    Mechanical gradients are useful to reduce strain mismatches in heterogeneous materials and thus prevent premature failure of devices in a wide range of applications. While complex graded designs are a hallmark of biological materials, gradients in manmade materials are often limited to 1D profiles due to the lack of adequate fabrication tools. Here, a multimaterial 3D-printing platform is developed to fabricate elastomer gradients spanning three orders of magnitude in elastic modulus and used to investigate the role of various bioinspired gradient designs on the local and global mechanical behavior of synthetic materials. The digital image correlation data and finite element modeling indicate that gradients can be effectively used to manipulate the stress state and thus circumvent the weakening effect of defect-rich interfaces or program the failure behavior of heterogeneous materials. Implementing this concept in materials with bioinspired designs can potentially lead to defect-tolerant structures and to materials whose tunable failure facilitates repair of biomedical implants, stretchable electronics, or soft robotics. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Engineering mechanical gradients in next generation biomaterials - Lessons learned from medical textile design.

    PubMed

    Ng, Joanna L; Collins, Ciara E; Knothe Tate, Melissa L

    2017-07-01

    Nonwoven and textile membranes have been applied both externally and internally to prescribe boundary conditions for medical conditions as diverse as oedema and tissue defects. Incorporation of mechanical gradients in next generation medical membrane design offers great potential to enhance function in a dynamic, physiological context. Yet the gradient properties and resulting mechanical performance of current membranes are not well described. To bridge this knowledge gap, we tested and compared the mechanical properties of bounding membranes used in both external (compression sleeves for oedema, exercise bands) and internal (surgical membranes) physiological contexts. We showed that anisotropic compression garment textiles, isotropic exercise bands and surgical membranes exhibit similar ranges of resistance to tension under physiologic strains. However, their mechanical gradients and resulting stress-strain relationships show differences in work capacity and energy expenditure. Exercise bands' moduli of elasticity and respective thicknesses allow for controlled, incremental increases in loading to facilitate healing as injured tissues return to normal structure and function. In contrast, the gradients intrinsic to compression sleeve design exhibit gaps in the middle range (1-5N) of physiological strains and also inconsistencies along the length of the sleeve, resulting in less than optimal performance of these devices. These current shortcomings in compression textile and garment design may be addressed in the future through implementation of novel approaches. For example, patterns, fibre compositions, and fibre anisotropy can be incorporated into biomaterial design to achieve seamless mechanical gradients in structure and resulting dynamic function, which would be particularly useful in physiological contexts. These concepts can be applied further to biomaterial design to deliver pressure gradients during movement of oedematous limbs (compression garments) and

  16. The Sunyaev-Zeldovich Effect in Abell 370

    NASA Technical Reports Server (NTRS)

    Grego, Laura; Carlstrom, John E.; Joy, Marshall K.; Reese, Erik D.; Holder, Gilbert P.; Patel, Sandeep; Cooray, Asantha R.; Holzappel, William L.

    2000-01-01

    We present interferometric measurements of the Sunyaev-Zeldovich (SZ) effect toward the galaxy cluster Abell 370. These measurements, which directly probe the pressure of the cluster's gas, show the gas distribution to be strongly aspherical, as do the X-ray and gravitational lensing observations. We calculate the cluster's gas mass fraction in two ways. We first compare the gas mass derived from the SZ measurements to the lensing-derived gravitational mass near the critical lensing radius. We also calculate the gas mass fraction from the SZ data by deprojecting the three-dimensional gas density distribution and deriving the total mass under the assumption that the gas is in hydrostatic equilibrium (HSE). We test the assumptions in the HSE method by comparing the total cluster mass implied by the two methods and find that they agree within the errors of the measurement. We discuss the possible system- atic errors in the gas mass fraction measurement and the constraints it places on the matter density parameter, Omega(sub M).

  17. Infiltration of chitin by protein coacervates defines the squid beak mechanical gradient.

    PubMed

    Tan, YerPeng; Hoon, Shawn; Guerette, Paul A; Wei, Wei; Ghadban, Ali; Hao, Cai; Miserez, Ali; Waite, J Herbert

    2015-07-01

    The beak of the jumbo squid Dosidicus gigas is a fascinating example of how seamlessly nature builds with mechanically mismatched materials. A 200-fold stiffness gradient begins in the hydrated chitin of the soft beak base and gradually increases to maximum stiffness in the dehydrated distal rostrum. Here, we combined RNA-Seq and proteomics to show that the beak contains two protein families. One family consists of chitin-binding proteins (DgCBPs) that physically join chitin chains, whereas the other family comprises highly modular histidine-rich proteins (DgHBPs). We propose that DgHBPs play multiple key roles during beak bioprocessing, first by forming concentrated coacervate solutions that diffuse into the DgCBP-chitin scaffold, and second by inducing crosslinking via an abundant GHG sequence motif. These processes generate spatially controlled desolvation, resulting in the impressive biomechanical gradient. Our findings provide novel molecular-scale strategies for designing functional gradient materials.

  18. Surface-Plasmon-Mediated Gradient Force Enhancement and Mechanical State Transitions of Graphene Sheets

    SciTech Connect

    Zhang, Peng; Shen, Nian-Hai; Koschny, Thomas

    Graphene, a two-dimensional material possessing extraordinary properties in electronics as well as mechanics, provides a great platform for various optoelectronic and opto-mechanical devices. Here in this article, we theoretically study the optical gradient force arising from the coupling of surface plasmon modes on parallel graphene sheets, which can be several orders stronger than that between regular dielectric waveguides. Furthermore, with an energy functional optimization model, possible force-induced deformation of graphene sheets is calculated. We show that the significantly enhanced optical gradient force may lead to mechanical state transitions of graphene sheets, which are accompanied by abrupt changes in reflection andmore » transmission spectra of the system. Our demonstrations illustrate the potential for a broader graphene-related applications such as force sensors and actuators.« less

  19. Surface-Plasmon-Mediated Gradient Force Enhancement and Mechanical State Transitions of Graphene Sheets

    DOE PAGES

    Zhang, Peng; Shen, Nian-Hai; Koschny, Thomas; ...

    2016-12-16

    Graphene, a two-dimensional material possessing extraordinary properties in electronics as well as mechanics, provides a great platform for various optoelectronic and opto-mechanical devices. Here in this article, we theoretically study the optical gradient force arising from the coupling of surface plasmon modes on parallel graphene sheets, which can be several orders stronger than that between regular dielectric waveguides. Furthermore, with an energy functional optimization model, possible force-induced deformation of graphene sheets is calculated. We show that the significantly enhanced optical gradient force may lead to mechanical state transitions of graphene sheets, which are accompanied by abrupt changes in reflection andmore » transmission spectra of the system. Our demonstrations illustrate the potential for a broader graphene-related applications such as force sensors and actuators.« less

  20. Effect of Vertical Concentration Gradient on Globally Planar Detonation with Detailed Reaction Mechanism

    NASA Astrophysics Data System (ADS)

    Song, Qingguana; Wang, Cheng; Han, Yong; Gao, Dayuan; Duan, Yingliang

    2017-06-01

    Since detonation often initiates and propagates in the non-homogeneous mixtures, investigating its behavior in non-uniform mixtures is significant not only for the industrial explosion in the leakage combustible gas, but also for the experimental investigations with a vertical concentration gradient caused by the difference in the molecular weight of gas mixture. Objective of this work is to show the detonation behavior in the mixture with different concentration gradients with detailed chemical reaction mechanism. A globally planar detonation in H2-O2 system is simulated by a high-resolution code based on the fifth-order weighted essentially non-oscillatory (WENO) scheme in spatial discretization and the third-order Additive Runge-Kutta schemes in time discretization. The different shocked combustion modes appear in the rich-fuel and poor-fuel layers due to the concentration gradient effect. Globally, for the cases with the lower gradient detonation can be sustained in a way of the alternation of the multi-heads mode and single-head mode, whereas for the cases with the higher gradient detonation propagates with a single-head mode. Institute of Chemical Materials, CAEP.

  1. Microstructure and mechanical characteristics of gradient structured Cu and Cu alloys processed by surface mechanical attrition treatment

    NASA Astrophysics Data System (ADS)

    Hu, XZ; Cheng, LP; Chen, HL; Yin, Z.; Zhang, Z.; Shu, BP; Gong, YL; Zhu, XK

    2017-05-01

    Cu-Al-Zn alloys with different stacking fault energy (SFE) were processed by surface mechanical attrition treatment (SMAT) at cryogenic temperature (CT), mechanical properties of gradient structured Cu-Al-Zn alloys were investigated in this study. Al and Zn content in alloys, which result in the decrease of SFE, can contribute to the increase in strength. Cu-4.5wt%Al-14.3wt%Zn alloy with the lower SFE shows that the strength increased, the ductility did not decrease significantly with increasing processing time, and the strength can be improved by a thicker gradient structure (GS) layer. The better combination of strength and ductility was achieved in Cu-4.5wt%Al-14.3wt%Zn alloy with lower SFE.

  2. Dark Energy Constraints from the Thermal Sunyaev Zeldovich Power Spectrum

    NASA Astrophysics Data System (ADS)

    Bolliet, Boris; Comis, Barbara; Komatsu, Eiichiro; Macías-Pérez, Juan Francisco

    2018-03-01

    We constrain the dark energy equation of state parameter, w, using the power spectrum of the thermal Sunyaev-Zeldovich (tSZ) effect. We improve upon previous analyses by taking into account the trispectrum in the covariance matrix and marginalising over the foreground parameters, the correlated noise, the mass bias B in the Planck universal pressure profile, and all the relevant cosmological parameters (i.e., not just Ωm and σ8). We find that the amplitude of the tSZ power spectrum at ℓ ≲ 103 depends primarily on F ≡ σ8(Ωm/B)0.40h-0.21, where B is related to more commonly used variable b by B = (1 - b)-1. We measure this parameter with 2.6% precision, F = 0.460 ± 0.012 (68% CL). By fixing the bias to B = 1.25 and adding the local determination of the Hubble constant H0 and the amplitude of the primordial power spectrum constrained by the Planck Cosmic Microwave Background (CMB) data, we find w = -1.10 ± 0.12, σ8 = 0.802 ± 0.037, and Ωm = 0.265 ± 0.022 (68% CL). Our limit on w is consistent with and is as tight as that from the distance-alone constraint from the CMB and H0. Finally, by combining the tSZ power spectrum and the CMB data we find, in the Λ Cold Dark Matter (CDM) model, the mass bias of B = 1.71 ± 0.17, i.e., 1 - b = 0.58 ± 0.06 (68% CL).

  3. Inherent interfacial mechanical gradients in 3D hydrogels influence tumor cell behaviors.

    PubMed

    Rao, Shreyas S; Bentil, Sarah; DeJesus, Jessica; Larison, John; Hissong, Alex; Dupaix, Rebecca; Sarkar, Atom; Winter, Jessica O

    2012-01-01

    Cells sense and respond to the rigidity of their microenvironment by altering their morphology and migration behavior. To examine this response, hydrogels with a range of moduli or mechanical gradients have been developed. Here, we show that edge effects inherent in hydrogels supported on rigid substrates also influence cell behavior. A Matrigel hydrogel was supported on a rigid glass substrate, an interface which computational techniques revealed to yield relative stiffening close to the rigid substrate support. To explore the influence of these gradients in 3D, hydrogels of varying Matrigel content were synthesized and the morphology, spreading, actin organization, and migration of glioblastoma multiforme (GBM) tumor cells were examined at the lowest (<50 µm) and highest (>500 µm) gel positions. GBMs adopted bipolar morphologies, displayed actin stress fiber formation, and evidenced fast, mesenchymal migration close to the substrate, whereas away from the interface, they adopted more rounded or ellipsoid morphologies, displayed poor actin architecture, and evidenced slow migration with some amoeboid characteristics. Mechanical gradients produced via edge effects could be observed with other hydrogels and substrates and permit observation of responses to multiple mechanical environments in a single hydrogel. Thus, hydrogel-support edge effects could be used to explore mechanosensitivity in a single 3D hydrogel system and should be considered in 3D hydrogel cell culture systems.

  4. Relativistic Corrections to the Sunyaev-Zeldovich Effect for Clusters of Galaxies. III. Polarization Effect

    NASA Astrophysics Data System (ADS)

    Itoh, Naoki; Nozawa, Satoshi; Kohyama, Yasuharu

    2000-04-01

    We extend the formalism of relativistic thermal and kinematic Sunyaev-Zeldovich effects and include the polarization of the cosmic microwave background photons. We consider the situation of a cluster of galaxies moving with a velocity β≡v/c with respect to the cosmic microwave background radiation. In the present formalism, polarization of the scattered cosmic microwave background radiation caused by the proper motion of a cluster of galaxies is naturally derived as a special case of the kinematic Sunyaev-Zeldovich effect. The relativistic corrections are also included in a natural way. Our results are in complete agreement with the recent results of relativistic corrections obtained by Challinor, Ford, & Lasenby with an entirely different method, as well as the nonrelativistic limit obtained by Sunyaev & Zeldovich. The relativistic correction becomes significant in the Wien region.

  5. Gradient plasticity for thermo-mechanical processes in metals with length and time scales

    NASA Astrophysics Data System (ADS)

    Voyiadjis, George Z.; Faghihi, Danial

    2013-03-01

    A thermodynamically consistent framework is developed in order to characterize the mechanical and thermal behavior of metals in small volume and on the fast transient time. In this regard, an enhanced gradient plasticity theory is coupled with the application of a micromorphic approach to the temperature variable. A physically based yield function based on the concept of thermal activation energy and the dislocation interaction mechanisms including nonlinear hardening is taken into consideration in the derivation. The effect of the material microstructural interface between two materials is also incorporated in the formulation with both temperature and rate effects. In order to accurately address the strengthening and hardening mechanisms, the theory is developed based on the decomposition of the mechanical state variables into energetic and dissipative counterparts which endowed the constitutive equations to have both energetic and dissipative gradient length scales for the bulk material and the interface. Moreover, the microstructural interaction effect in the fast transient process is addressed by incorporating two time scales into the microscopic heat equation. The numerical example of thin film on elastic substrate or a single phase bicrystal under uniform tension is addressed here. The effects of individual counterparts of the framework on the thermal and mechanical responses are investigated. The model is also compared with experimental results.

  6. Mechanisms of high-gradient microwave breakdown on metal surfaces in high power microwave source

    NASA Astrophysics Data System (ADS)

    Xie, Jialing; Chen, Changhua; Chang, Chao; Wu, Cheng; Huo, Yankun

    2017-12-01

    A breakdown cavity was designed to study the high-gradient microwave breakdown on a metal surface. The breakdown cavity can be distinguished into an electron emission boundary and a bombardment boundary as there is an evident difference in amplitude of the electric field between the two planes in the cavity. Breakdown tracks on the cavity were studied with an electron scanning microscope. The tracks on the electron emission boundary with the higher electric field were eroded; a component analysis indicates that these tracks contain an emission boundary material. On the bombardment boundary with a lower electric field, two kinds of tracks exist: an erosion track containing a bombardment boundary material and a sputtered track containing an emission boundary material. From these tracks, the mechanisms of high-gradient microwave breakdown on a metal surface have been analyzed.

  7. A study of microindentation hardness tests by mechanism-based strain gradient plasticity

    SciTech Connect

    Huang, Y.; Xue, Z.; Gao, H.

    2000-08-01

    We recently proposed a theory of mechanism-based strain gradient (MSG) plasticity to account for the size dependence of plastic deformation at micron- and submicron-length scales. The MSG plasticity theory connects micron-scale plasticity to dislocation theories via a multiscale, hierarchical framework linking Taylor's dislocation hardening model to strain gradient plasticity. Here we show that the theory of MSG plasticity, when used to study micro-indentation, indeed reproduces the linear dependence observed in experiments, thus providing an important self-consistent check of the theory. The effects of pileup, sink-in, and the radius of indenter tip have been taken into account in the indentation model.more » In accomplishing this objective, we have generalized the MSG plasticity theory to include the elastic deformation in the hierarchical framework. (c) 2000 Materials Research Society.« less

  8. Representing Matrix Cracks Through Decomposition of the Deformation Gradient Tensor in Continuum Damage Mechanics Methods

    NASA Technical Reports Server (NTRS)

    Leone, Frank A., Jr.

    2015-01-01

    A method is presented to represent the large-deformation kinematics of intraply matrix cracks and delaminations in continuum damage mechanics (CDM) constitutive material models. The method involves the additive decomposition of the deformation gradient tensor into 'crack' and 'bulk material' components. The response of the intact bulk material is represented by a reduced deformation gradient tensor, and the opening of an embedded cohesive interface is represented by a normalized cohesive displacement-jump vector. The rotation of the embedded interface is tracked as the material deforms and as the crack opens. The distribution of the total local deformation between the bulk material and the cohesive interface components is determined by minimizing the difference between the cohesive stress and the bulk material stress projected onto the cohesive interface. The improvements to the accuracy of CDM models that incorporate the presented method over existing approaches are demonstrated for a single element subjected to simple shear deformation and for a finite element model of a unidirectional open-hole tension specimen. The material model is implemented as a VUMAT user subroutine for the Abaqus/Explicit finite element software. The presented deformation gradient decomposition method reduces the artificial load transfer across matrix cracks subjected to large shearing deformations, and avoids the spurious secondary failure modes that often occur in analyses based on conventional progressive damage models.

  9. Transmural gradients of myocardial structure and mechanics: Implications for fiber stress and strain in pressure overload.

    PubMed

    Carruth, Eric D; McCulloch, Andrew D; Omens, Jeffrey H

    2016-12-01

    Although a truly complete understanding of whole heart activation, contraction, and deformation is well beyond our current reach, a significant amount of effort has been devoted to discovering and understanding the mechanisms by which myocardial structure determines cardiac function to better treat patients with cardiac disease. Several experimental studies have shown that transmural fiber strain is relatively uniform in both diastole and systole, in contrast to predictions from traditional mechanical theory. Similarly, mathematical models have largely predicted uniform fiber stress across the wall. The development of this uniform pattern of fiber stress and strain during filling and ejection is due to heterogeneous transmural distributions of several myocardial structures. This review summarizes these transmural gradients, their contributions to fiber mechanics, and the potential functional effects of their remodeling during pressure overload hypertrophy. Copyright © 2016 Elsevier Ltd. All rights reserved.

  10. Tubing-Electrospinning: A One-Step Process for Fabricating Fibrous Matrices with Spatial, Chemical, and Mechanical Gradients.

    PubMed

    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.

  11. Elevational Gradients in β-Diversity Reflect Variation in the Strength of Local Community Assembly Mechanisms across Spatial Scales

    PubMed Central

    Tello, J. Sebastián; Myers, Jonathan A.; Macía, Manuel J.; Fuentes, Alfredo F.; Cayola, Leslie; Arellano, Gabriel; Loza, M. Isabel; Torrez, Vania; Cornejo, Maritza; Miranda, Tatiana B.; Jørgensen, Peter M.

    2015-01-01

    Despite long-standing interest in elevational-diversity gradients, little is known about the processes that cause changes in the compositional variation of communities (β-diversity) across elevations. Recent studies have suggested that β-diversity gradients are driven by variation in species pools, rather than by variation in the strength of local community assembly mechanisms such as dispersal limitation, environmental filtering, or local biotic interactions. However, tests of this hypothesis have been limited to very small spatial scales that limit inferences about how the relative importance of assembly mechanisms may change across spatial scales. Here, we test the hypothesis that scale-dependent community assembly mechanisms shape biogeographic β-diversity gradients using one of the most well-characterized elevational gradients of tropical plant diversity. Using an extensive dataset on woody plant distributions along a 4,000-m elevational gradient in the Bolivian Andes, we compared observed patterns of β-diversity to null-model expectations. β-deviations (standardized differences from null values) were used to measure the relative effects of local community assembly mechanisms after removing sampling effects caused by variation in species pools. To test for scale-dependency, we compared elevational gradients at two contrasting spatial scales that differed in the size of local assemblages and regions by at least an order of magnitude. Elevational gradients in β-diversity persisted after accounting for regional variation in species pools. Moreover, the elevational gradient in β-deviations changed with spatial scale. At small scales, local assembly mechanisms were detectable, but variation in species pools accounted for most of the elevational gradient in β-diversity. At large spatial scales, in contrast, local assembly mechanisms were a dominant force driving changes in β-diversity. In contrast to the hypothesis that variation in species pools alone

  12. Cyclic Failure Mechanisms of Thermal and Environmental Barrier Coating Systems Under Thermal Gradient Test Conditions

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Lee, Kang N.; Miller, Robert A.

    2002-01-01

    Plasma-sprayed ZrO2-8wt%Y2O3 and mullite+BSAS/Si multilayer thermal and environmental barrier coating (TBC-EBC) systems on SiC/SiC ceramic matrix composite (CMC) substrates were thermally cyclic tested under high thermal gradients using a laser high-heat-flux rig in conjunction with furnace exposure in water-vapor environments. Coating sintering and interface damage were assessed by monitoring the real-time thermal conductivity changes during the laser heat-flux tests and by examining the microstructural changes after exposure. Sintering kinetics of the coating systems were also independently characterized using a dilatometer. It was found that the coating failure involved both the time-temperature dependent sintering and the cycle frequency dependent cyclic fatigue processes. The water vapor environments not only facilitated the initial coating conductivity increases due to enhanced sintering and interface reaction, but also promoted later conductivity reductions due to the accelerated coating cracking and delamination. The failure mechanisms of the coating systems are also discussed based on the cyclic test results and are correlated to the sintering and thermal stress behavior under the thermal gradient test conditions.

  13. A Continuum Damage Mechanics Model to Predict Kink-Band Propagation Using Deformation Gradient Tensor Decomposition

    NASA Technical Reports Server (NTRS)

    Bergan, Andrew C.; Leone, Frank A., Jr.

    2016-01-01

    A new model is proposed that represents the kinematics of kink-band formation and propagation within the framework of a mesoscale continuum damage mechanics (CDM) model. The model uses the recently proposed deformation gradient decomposition approach to represent a kink band as a displacement jump via a cohesive interface that is embedded in an elastic bulk material. The model is capable of representing the combination of matrix failure in the frame of a misaligned fiber and instability due to shear nonlinearity. In contrast to conventional linear or bilinear strain softening laws used in most mesoscale CDM models for longitudinal compression, the constitutive response of the proposed model includes features predicted by detailed micromechanical models. These features include: 1) the rotational kinematics of the kink band, 2) an instability when the peak load is reached, and 3) a nonzero plateau stress under large strains.

  14. Failure Mechanisms and Life Prediction of Thermal and Environmental Barrier Coatings under Thermal Gradients

    NASA Technical Reports Server (NTRS)

    Zju, Dongming; Ghosn, Louis J.; Miller, Robert A.

    2008-01-01

    Ceramic thermal and environmental barrier coatings (TEBCs) will play an increasingly important role in gas turbine engines because of their ability to further raise engine temperatures. However, the issue of coating durability is of major concern under high-heat-flux conditions. In particular, the accelerated coating delamination crack growth under the engine high heat-flux conditions is not well understood. In this paper, a laser heat flux technique is used to investigate the coating delamination crack propagation under realistic temperature-stress gradients and thermal cyclic conditions. The coating delamination mechanisms are investigated under various thermal loading conditions, and are correlated with coating dynamic fatigue, sintering and interfacial adhesion test results. A coating life prediction framework may be realized by examining the crack initiation and propagation driving forces for coating failure under high-heat-flux test conditions.

  15. Pressure-coupled combustion response model for solid propellants based on Zeldovich-Novozhilov approach

    NASA Technical Reports Server (NTRS)

    Harstad, K. G.; Strand, L. D.

    1987-01-01

    An exact analytical solution is given to the problem of long-time propellant thermal response to a specified pressure oscillation. Coupling to the gas phase is made using the quasisteady Zeldovich-Novozhilov approximation. Explicit linear and lowest order (quadratic) nonlinear expressions for propellant response are obtained from the implicit nonlinear solutions. Using these expressions, response curves are presented for an ammonium perchlorate composite propellant and HMX monopropellant.

  16. Changes in the distribution of mechanically dependent plants along a gradient of past hurricane impact

    PubMed Central

    Batke, Sven P.; Kelly, Daniel L.

    2015-01-01

    The severity of the effects that large disturbance events such as hurricanes can have on the forest canopy and the associated mechanically dependent plant community (epiphytes, climbers, etc.) is dependent on the frequency and intensity of the disturbance events. Here we investigate the effects of different structural and environmental properties of the host trees and previously modelled past hurricanes on dependent plants in Cusuco National Park, Honduras. Tree-climbing methods were employed to sample different dependent life-forms in ten 150 × 150 m plots. We identified 7094 individuals of dependent plants from 214 different species. For holo- and hemi-epiphytes, we found that diversity was significantly negatively related to past hurricane impact. The abundance of dependent plants was greatly influenced by their position in tree canopy and hurricane disturbance regimes. The relationship between abundance and mean branch height shifts across a gradient of hurricane impact (from negative to positive), which might result from a combination of changes in abundance of individual species and composition of the dependent flora across sites. Mechanically dependent plants also responded to different structural and environmental conditions along individual branches. The variables that explained much of the community differences of life-forms and families among branches were branch surface area and bryophyte cover. The factors that explained most variation at a plot level were mean vapour pressure deficit and elevation. At the level of the individual tree, the most important factors were canopy openness and past hurricane impact. We believe that more emphasis needs to be placed on the effects that past disturbance events have on mechanically dependent plant communities, particularly in areas that are prone to catastrophic perturbations. PMID:26286220

  17. A pressure-gradient mechanism for vortex shedding in constricted channels

    PubMed Central

    Boghosian, M. E.; Cassel, K. W.

    2013-01-01

    Numerical simulations of the unsteady, two-dimensional, incompressible Navier–Stokes equations are performed for a Newtonian fluid in a channel having a symmetric constriction modeled by a two-parameter Gaussian distribution on both channel walls. The Reynolds number based on inlet half-channel height and mean inlet velocity ranges from 1 to 3000. Constriction ratios based on the half-channel height of 0.25, 0.5, and 0.75 are considered. The results show that both the Reynolds number and constriction geometry have a significant effect on the behavior of the post-constriction flow field. The Navier–Stokes solutions are observed to experience a number of bifurcations: steady attached flow, steady separated flow (symmetric and asymmetric), and unsteady vortex shedding downstream of the constriction depending on the Reynolds number and constriction ratio. A sequence of events is described showing how a sustained spatially growing flow instability, reminiscent of a convective instability, leads to the vortex shedding phenomenon via a proposed streamwise pressure-gradient mechanism. PMID:24399860

  18. Corrosion behaviour and mechanical properties of functionally gradient materials developed for possible hard-tissue applications.

    PubMed

    Becker, B S; Bolton, J D

    1997-12-01

    Artificial hip joints have an average lifetime of 10 years due to aseptic loosening of the femoral stem attributed to polymeric wear debris; however, there is a steadily increasing demand from younger osteoarthritis patients aged between 15 and 40 year for a longer lasting joint of 25 years or more. Compliant layers incorporated into the acetabular cup generate elastohydrodynamic lubrication conditions between the bearing surfaces, reduce joint friction coefficients and wear debris production and could increase the average life of total hip replacements, and other human load-bearing joint replacements, i.e. total knee replacements. Poor adhesion between a fully dense substrate and the compliant layer has so far prevented any further exploitation. This work investigated the possibility of producing porous metallic, functionally gradient type acetabular cups using powder metallurgy techniques - where a porous surface was supported by a denser core - into which the compliant layers could be incorporated. The corrosion behaviour and mechanical properties of three biomedically approved alloys containing two levels of total porosity (>30% and <10%) were established, resulting in Ti-6Al-4V being identified as the most promising biocompatible functionally graded material, not only for this application but for other hard-tissue implants.

  19. Mechanical and tribological properties of gradient a-C:H/Ti coatings

    NASA Astrophysics Data System (ADS)

    Batory, D.; Szymański, W.; Cłapa, M.

    2013-08-01

    The unusual combination of high hardness and very low friction coefficient are the most attractive tribological parameters of DLC (diamond-like carbon) layers. However, their usability is strongly restricted by the limited thickness due to high residual stress. The main goal of the presented work was to obtain thick, wear resistant and well adherent DLC layers while keeping their perfect friction parameters. As a proposed solution a Ti-Ti x C y gradient layer was manufactured as the adhesion improving interlayer followed by a thick diamond-like carbon film. This kind of combination seems to be very promising for many applications, where dry friction conditions for highly loaded elements can be observed. Both layers were obtained in one process using a hybrid deposition system combining PVD and CVD techniques in one reaction chamber. The investigation was performed on nitrided samples made from X53CrMnNiN21-9 valve steel. Structural features, surface topography, tribological and mechanical properties of manufactured layers were evaluated. The results of the investigation confirmed that the presented deposition technique makes it possible to manufacture thick and well adherent carbon layers with high hardness and very good tribological parameters. Preliminary investigation results prove the possibility of application of presented technology in automotive industry.

  20. Combinatorial Study of Gradient Ag-Al Thin Films: Microstructure, Phase Formation, Mechanical and Electrical Properties.

    PubMed

    Mao, Fang; Taher, Mamoun; Kryshtal, Oleksandr; Kruk, Adam; Czyrska-Filemonowicz, Aleksandra; Ottosson, Mikael; Andersson, Anna M; Wiklund, Urban; Jansson, Ulf

    2016-11-09

    A combinatorial approach is applied to rapidly deposit and screen Ag-Al thin films to evaluate the mechanical, tribological, and electrical properties as a function of chemical composition. Ag-Al thin films with large continuous composition gradients (6-60 atom % Al) were deposited by a custom-designed combinatorial magnetron sputtering system. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning and transmission electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS), nanoindentation, and four-point electrical resistance screening were employed to characterize the chemical composition, structure, and physical properties of the films in a time-efficient way. For low Al contents (<13 atom %), a highly (111)-textured fcc phase was formed. At higher Al contents, a (002)-textured hcp solid solution phase was formed followed by a fcc phase in the most Al-rich regions. No indication of a μ phase was observed. The Ag-Al films with fcc-Ag matrix is prone to adhesive material transfer leading to a high friction coefficient (>1) and adhesive wear, similar to the behavior of pure Ag. In contrast, the hexagonal solid solution phase (from ca. 15 atom %Al) exhibited dramatically reduced friction coefficients (about 15% of that of the fcc phase) and dramatically reduced adhesive wear when tested against the pure Ag counter surface. The increase in contact resistance of the Ag-Al films is limited to only 50% higher than a pure Ag reference sample at the low friction and low wear region (19-27 atom %). This suggests that a hcp Ag-Al alloy can have a potential use in sliding electrical contact applications and in the future will replace pure Ag in specific electromechanical applications.

  1. Concentration gradients at the mineral-solution interface: implications for understanding dissolution mechanisms

    NASA Astrophysics Data System (ADS)

    Ruiz-Agudo, Encarnacion; Patiño-López, Luis David; Putnis, Christine V.; Rodriguez-Navarro, Carlos; Putnis, Andrew

    2014-05-01

    Dissolution is a key process in fluid-rock interactions, such as in chemical weathering, CO2 carbonation reactions, metasomatism, and metamorphism. Many multicomponent rock-forming minerals are reported to dissolve incongruently, because the elemental molar ratios, measured in the fluid during dissolution experiments, that differ from those in the solid. This frequently results in the formation of chemically and structurally altered zones at the fluid-solid interface of varying thickness that are depleted in some elements relative to the bulk mineral composition. Although the mechanisms of the formation of these altered layers is still a matter of debate (see e.g. Ruiz-Agudo et al. 2012 and Schott et al. 2012), recent AFM studies on the dissolution of two multicomponent minerals, dolomite, Ca0.5Mg0.5CO3 (Urosevic et al. 2012), and wollastonite, CaSiO3 (Ruiz-Agudo et al. 2012), provide experimental evidence showing that these layers are formed in a two-step process: (i) stoichiometric dissolution of the pristine mineral surfaces and (ii) precipitation of a secondary phase. This occurs despite the fact that the bulk solution is undersaturated with respect to such a phase. It has been suggested that after stoichiometric dissolution of the mineral, a boundary layer of fluid in contact with the surface becomes supersaturated with respect to a secondary phase that then precipitates. Here we present in situ observations of the evolution of the fluid composition at the interface during dissolution in acidic solutions (pH 1.5) of dolomite and wollastonite using real-time phase-shift interferometry. We show that immediately when the sparingly soluble dolomite or wollastonite crystals are in contact with the solution, the refractive index of the solution at the crystal surface sharply increases. A steep refractive index gradient (i.e., concentration gradient) develops as a consequence of mineral dissolution producing an interfacial fluid with a different composition to the

  2. Optical Identifications of High-Redshift Galaxy Clusters from the Planck Sunyaev-Zeldovich Survey

    NASA Astrophysics Data System (ADS)

    Burenin, R. A.; Bikmaev, I. F.; Khamitov, I. M.; Zaznobin, I. A.; Khorunzhev, G. A.; Eselevich, M. V.; Afanasiev, V. L.; Dodonov, S. N.; Rubiño-Martín, J.-A.; Aghanim, N.; Sunyaev, R. A.

    2018-05-01

    We present the results of optical identifications and spectroscopic redshift measurements for galaxy clusters from the second Planck catalogue of Sunyaev-Zeldovich sources (PSZ2) located at high redshifts, z ≈ 0.7-0.9. We used the data of optical observations with the Russian-Turkish 1.5-mtelescope (RTT-150), the Sayan Observatory 1.6-m telescope, the Calar Alto 3.5-m telescope, and the 6-m SAO RAS telescope (BTA). The spectroscopic redshift measurements were obtained for seven galaxy clusters, including one cluster, PSZ2 G126.57+51.61, from the cosmological sample of the PSZ2 catalogue. In the central regions of two clusters, PSZ2 G069.39+68.05 and PSZ2 G087.39-34.58, we detected arcs of strong gravitational lensing of background galaxies, one of which is at redshift z = 4.262. The data presented below roughly double the number of known galaxy clusters in the second Planck catalogue of Sunyaev-Zeldovich sources at high redshifts, z ≈ 0.8.

  3. Proton Gradients as a Key Physical Factor in the Evolution of the Forced Transport Mechanism Across the Lipid Membrane.

    PubMed

    Strbak, Oliver; Kanuchova, Zuzana; Krafcik, Andrej

    2016-11-01

    A critical phase in the transition from prebiotic chemistry to biological evolution was apparently an asymmetric ion flow across the lipid membrane. Due to imbalance in the ion flow, the early lipid vesicles could selectively take the necessary molecules from the environment, and release the side-products from the vesicle. Natural proton gradients played a definitively crucial role in this process, since they remain the basis of energy transfer in the present-day cells. On the basis of this supposition, and the premise of the early vesicle membrane's impermeability to protons, we have shown that the emergence of the proton gradient in the lipid vesicle could be a key physical factor in the evolution of the forced transport mechanism (pore formation and active transport) across the lipid bilayer. This driven flow of protons across the membrane is the result of the electrochemical proton gradient and osmotic pressures on the integrity of the lipid vesicle. At a critical number of new lipid molecules incorporated into the vesicle, the energies associated with the creation of the proton gradient exceed the bending stiffness of the lipid membrane, and overlap the free energy of the lipid bilayer pore formation.

  4. Temperature sensitivity and enzymatic mechanisms of soil organic matter decomposition along an altitudinal gradient on Mount Kilimanjaro

    NASA Astrophysics Data System (ADS)

    Blagodatskaya, Evgenia; Blagodatsky, Sergey; Khomyakov, Nikita; Myachina, Olga; Kuzyakov, Yakov

    2016-02-01

    Short-term acceleration of soil organic matter decomposition by increasing temperature conflicts with the thermal adaptation observed in long-term studies. Here we used the altitudinal gradient on Mt. Kilimanjaro to demonstrate the mechanisms of thermal adaptation of extra- and intracellular enzymes that hydrolyze cellulose, chitin and phytate and oxidize monomers (14C-glucose) in warm- and cold-climate soils. We revealed that no response of decomposition rate to temperature occurs because of a cancelling effect consisting in an increase in half-saturation constants (Km), which counteracts the increase in maximal reaction rates (Vmax with temperature). We used the parameters of enzyme kinetics to predict thresholds of substrate concentration (Scrit) below which decomposition rates will be insensitive to global warming. Increasing values of Scrit, and hence stronger canceling effects with increasing altitude on Mt. Kilimanjaro, explained the thermal adaptation of polymer decomposition. The reduction of the temperature sensitivity of Vmax along the altitudinal gradient contributed to thermal adaptation of both polymer and monomer degradation. Extrapolating the altitudinal gradient to the large-scale latitudinal gradient, these results show that the soils of cold climates with stronger and more frequent temperature variation are less sensitive to global warming than soils adapted to high temperatures.

  5. Møller-Plesset perturbation theory gradient in the generalized hybrid orbital quantum mechanical and molecular mechanical method

    NASA Astrophysics Data System (ADS)

    Jung, Jaewoon; Sugita, Yuji; Ten-no, S.

    2010-02-01

    An analytic gradient expression is formulated and implemented for the second-order Møller-Plesset perturbation theory (MP2) based on the generalized hybrid orbital QM/MM method. The method enables us to obtain an accurate geometry at a reasonable computational cost. The performance of the method is assessed for various isomers of alanine dipepetide. We also compare the optimized structures of fumaramide-derived [2]rotaxane and cAMP-dependent protein kinase with experiment.

  6. Life in the salinity gradient: Discovering mechanisms behind a new biodiversity pattern

    NASA Astrophysics Data System (ADS)

    Telesh, Irena; Schubert, Hendrik; Skarlato, Sergei

    2013-12-01

    A recently discovered paradoxical maximum of planktonic protistan species in the salinity gradient of the Baltic Sea revealed an inverse trend of species number/salinity relation in comparison to the previously accepted species-minimum model for macrozoobenthos. Here, we review long-term data on organisms of different size classes and ecological groups to show that eukaryotic and prokaryotic microbes in plankton demonstrate a maximum species richness in the challenging zone of the critical salinity 5-8, where the large-bodied bottom dwellers (macrozoobenthos, macroalgae and aquatic higher plants) experience large-scale salinity stress which leads to an impoverished diversity. We propose a new conceptual model to explain why the diversity of small, fast-developing, rapidly evolving unicellular plankton organisms benefits from relative vacancy of brackish-water ecological niches and impaired competitiveness therein. The ecotone theory, Hutchinson's Ecological Niche Concept, species-area relationships and the Intermediate Disturbance Hypothesis are considered as a theoretical framework for understanding extinctions, speciation and variations in the evolution rates of different aquatic species in ecosystems with the pronounced salinity gradient.

  7. Analysis of the intraocular jet flows and pressure gradients induced by air and fluid infusion: mechanism of focal chorioretinal damage.

    PubMed

    Kim, Yong Joon; Jo, Sungkil; Moon, Daruchi; Joo, Youngcheol; Choi, Kyung Seek

    2014-05-01

    To comprehend the mechanism of focal chorioretinal damage by analysis of the pressure distribution and dynamic pressure induced by infused air during fluid-air exchange. A precise simulation featuring a model eye and a fluid circuit was designed to analyze fluid-air exchange. The pressure distribution, flow velocity, and dynamic pressure induced by infusion of air into an air-filled eye were analyzed using an approach based on fluid dynamics. The size of the port and the infusion pressure were varied during simulated iterations. We simulated infusion of an air-filled eye with balanced salt solution (BSS) to better understand the mechanism of chorioretinal damage induced by infused air. Infused air was projected straight toward a point on the retina contralateral to the infusion port (the "vulnerable point"). The highest pressure was evident at the vulnerable point, and the lowest pressure was recorded on most retinal areas. Simulations using greater infusion pressure and a port of larger size were associated with elevations in dynamic pressure and the pressure gradient. The pressure gradients were 2.8 and 5.1 mm Hg, respectively, when infusion pressures of 30 and 50 mm Hg were delivered through a 20-gauge port. The pressure gradient associated with BSS infusion was greater than that created by air, but lasted for only a moment. Our simulation explains the mechanism of focal chorioretinal damage in numerical terms. Infused air induces a prolonged increase in focal pressure on the vulnerable point, and this may be responsible for visual field defects arising after fluid-air exchange. Copyright 2014 The Association for Research in Vision and Ophthalmology, Inc.

  8. Planck 2015 results: XXII. A map of the thermal Sunyaev-Zeldovich effect

    SciTech Connect

    Aghanim, N.; Arnaud, M.; Ashdown, M.

    In this article, we have constructed all-sky Compton parameters maps, y-maps, of the thermal Sunyaev-Zeldovich (tSZ) effect by applying specifically tailored component separation algorithms to the 30 to 857 GHz frequency channel maps from the Planck satellite. These reconstructed y-maps are delivered as part of the Planck 2015 release. The y-maps are characterized in terms of noise properties and residual foreground contamination, mainly thermal dust emission at large angular scales, and cosmic infrared background and extragalactic point sources at small angular scales. Specific masks are defined to minimize foreground residuals and systematics. Using these masks, we compute the y-map angularmore » power spectrum and higher order statistics. From these we conclude that the y-map is dominated by tSZ signal in the multipole range, 20« less

  9. N-point statistics of large-scale structure in the Zel'dovich approximation

    SciTech Connect

    Tassev, Svetlin, E-mail: tassev@astro.princeton.edu

    2014-06-01

    Motivated by the results presented in a companion paper, here we give a simple analytical expression for the matter n-point functions in the Zel'dovich approximation (ZA) both in real and in redshift space (including the angular case). We present numerical results for the 2-dimensional redshift-space correlation function, as well as for the equilateral configuration for the real-space 3-point function. We compare those to the tree-level results. Our analysis is easily extendable to include Lagrangian bias, as well as higher-order perturbative corrections to the ZA. The results should be especially useful for modelling probes of large-scale structure in the linear regime,more » such as the Baryon Acoustic Oscillations. We make the numerical code used in this paper freely available.« less

  10. Planck 2015 results: XXII. A map of the thermal Sunyaev-Zeldovich effect

    DOE PAGES

    Aghanim, N.; Arnaud, M.; Ashdown, M.; ...

    2016-09-20

    In this article, we have constructed all-sky Compton parameters maps, y-maps, of the thermal Sunyaev-Zeldovich (tSZ) effect by applying specifically tailored component separation algorithms to the 30 to 857 GHz frequency channel maps from the Planck satellite. These reconstructed y-maps are delivered as part of the Planck 2015 release. The y-maps are characterized in terms of noise properties and residual foreground contamination, mainly thermal dust emission at large angular scales, and cosmic infrared background and extragalactic point sources at small angular scales. Specific masks are defined to minimize foreground residuals and systematics. Using these masks, we compute the y-map angularmore » power spectrum and higher order statistics. From these we conclude that the y-map is dominated by tSZ signal in the multipole range, 20« less

  11. Quantum mechanical/molecular mechanical/continuum style solvation model: linear response theory, variational treatment, and nuclear gradients.

    PubMed

    Li, Hui

    2009-11-14

    Linear response and variational treatment are formulated for Hartree-Fock (HF) and Kohn-Sham density functional theory (DFT) methods and combined discrete-continuum solvation models that incorporate self-consistently induced dipoles and charges. Due to the variational treatment, analytic nuclear gradients can be evaluated efficiently for these discrete and continuum solvation models. The forces and torques on the induced point dipoles and point charges can be evaluated using simple electrostatic formulas as for permanent point dipoles and point charges, in accordance with the electrostatic nature of these methods. Implementation and tests using the effective fragment potential (EFP, a polarizable force field) method and the conductorlike polarizable continuum model (CPCM) show that the nuclear gradients are as accurate as those in the gas phase HF and DFT methods. Using B3LYP/EFP/CPCM and time-dependent-B3LYP/EFP/CPCM methods, acetone S(0)-->S(1) excitation in aqueous solution is studied. The results are close to those from full B3LYP/CPCM calculations.

  12. Dual-reference digital holographic interferometry for analyzing high-density gradients in fluid mechanics.

    PubMed

    Desse, Jean-Michel; Olchewsky, François

    2018-04-15

    This Letter proposes a dual-reference digital holographic interferometer for analyzing the high refractive index encountered in transonic and supersonic flows. For that, a Wollaston prism is inserted in the reference arm in order to simultaneously generate two orthogonally polarized reference waves. As a consequence, recorded interferograms contain two crossed and perpendicular interference patterns that give two orders fully separated in the Fourier spectrum. It is then possible to analyze a transparent object regardless of the orientation of the refractive index gradient using the two phase maps reconstructed with each of the two first interference orders. Fusion of the phase maps yields a single phase map in which the phase singularities are removed. Experimental results demonstrate the suitability of the proposed approach for analyzing shock waves in the unsteady wake flow around a circular cylinder at Mach 0.75.

  13. Tailored Height Gradients in Vertical Nanowire Arrays via Mechanical and Electronic Modulation of Metal-Assisted Chemical Etching.

    PubMed

    Otte, M A; Solis-Tinoco, V; Prieto, P; Borrisé, X; Lechuga, L M; González, M U; Sepulveda, B

    2015-09-02

    In current top-down nanofabrication methodologies the design freedom is generally constrained to the two lateral dimensions, and is only limited by the resolution of the employed nanolithographic technique. However, nanostructure height, which relies on certain mask-dependent material deposition or etching techniques, is usually uniform, and on-chip variation of this parameter is difficult and generally limited to very simple patterns. Herein, a novel nanofabrication methodology is presented, which enables the generation of high aspect-ratio nanostructure arrays with height gradients in arbitrary directions by a single and fast etching process. Based on metal-assisted chemical etching using a catalytic gold layer perforated with nanoholes, it is demonstrated how nanostructure arrays with directional height gradients can be accurately tailored by: (i) the control of the mass transport through the nanohole array, (ii) the mechanical properties of the perforated metal layer, and (iii) the conductive coupling to the surrounding gold film to accelerate the local electrochemical etching process. The proposed technique, enabling 20-fold on-chip variation of nanostructure height in a spatial range of a few micrometers, offers a new tool for the creation of novel types of nano-assemblies and metamaterials with interesting technological applications in fields such as nanophotonics, nanophononics, microfluidics or biomechanics. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Variational and perturbative formulations of quantum mechanical/molecular mechanical free energy with mean-field embedding and its analytical gradients.

    PubMed

    Yamamoto, Takeshi

    2008-12-28

    Conventional quantum chemical solvation theories are based on the mean-field embedding approximation. That is, the electronic wavefunction is calculated in the presence of the mean field of the environment. In this paper a direct quantum mechanical/molecular mechanical (QM/MM) analog of such a mean-field theory is formulated based on variational and perturbative frameworks. In the variational framework, an appropriate QM/MM free energy functional is defined and is minimized in terms of the trial wavefunction that best approximates the true QM wavefunction in a statistically averaged sense. Analytical free energy gradient is obtained, which takes the form of the gradient of effective QM energy calculated in the averaged MM potential. In the perturbative framework, the above variational procedure is shown to be equivalent to the first-order expansion of the QM energy (in the exact free energy expression) about the self-consistent reference field. This helps understand the relation between the variational procedure and the exact QM/MM free energy as well as existing QM/MM theories. Based on this, several ways are discussed for evaluating non-mean-field effects (i.e., statistical fluctuations of the QM wavefunction) that are neglected in the mean-field calculation. As an illustration, the method is applied to an S(N)2 Menshutkin reaction in water, NH(3)+CH(3)Cl-->NH(3)CH(3) (+)+Cl(-), for which free energy profiles are obtained at the Hartree-Fock, MP2, B3LYP, and BHHLYP levels by integrating the free energy gradient. Non-mean-field effects are evaluated to be <0.5 kcal/mol using a Gaussian fluctuation model for the environment, which suggests that those effects are rather small for the present reaction in water.

  15. Determination of Cluster Distances from Chandra Imaging Spectroscopy and Sunyaev-Zeldovich Effect Measurements. I; Analysis Methods and Initial Results

    NASA Technical Reports Server (NTRS)

    Bonamente, Massimiliano; Joy, Marshall K.; Carlstrom, John E.; LaRoque, Samuel J.

    2004-01-01

    X-ray and Sunyaev-Zeldovich Effect data ca,n be combined to determine the distance to galaxy clusters. High-resolution X-ray data are now available from the Chandra Observatory, which provides both spatial and spectral information, and interferometric radio measurements of the Sunyam-Zeldovich Effect are available from the BIMA and 0VR.O arrays. We introduce a Monte Carlo Markov chain procedure for the joint analysis of X-ray and Sunyaev-Zeldovich Effect data. The advantages of this method are the high computational efficiency and the ability to measure the full probability distribution of all parameters of interest, such as the spatial and spectral properties of the cluster gas and the cluster distance. We apply this technique to the Chandra X-ray data and the OVRO radio data for the galaxy cluster Abell 611. Comparisons with traditional likelihood-ratio methods reveal the robustness of the method. This method will be used in a follow-up paper to determine the distance of a large sample of galaxy clusters for which high-resolution Chandra X-ray and BIMA/OVRO radio data are available.

  16. Planck intermediate results: XXXVII. Evidence of unbound gas from the kinetic Sunyaev-Zeldovich effect

    DOE PAGES

    Ade, P. A. R.; Aghanim, N.; Arnaud, M.; ...

    2016-02-09

    By looking at the kinetic Sunyaev-Zeldovich effect (kSZ) in Planck nominal mission data, we present in this paper a significant detection of baryons participating in large-scale bulk flows around central galaxies (CGs) at redshift z ≈ 0.1. We estimate the pairwise momentum of the kSZ temperature fluctuations at the positions of the Central Galaxy Catalogue (CGC) samples extracted from Sloan Digital Sky Survey (SDSS-DR7) data. For the foreground-cleaned SEVEM, SMICA, NILC, and COMMANDER maps, we find 1.8–2.5σ detections of the kSZ signal, which are consistent with the kSZ evidence found in individualPlanck raw frequency maps, although lower than found inmore » the WMAP-9yr W-band (3.3σ). We further reconstruct the peculiar velocity field from the CG density field, and compute for the first time the cross-correlation function between kSZ temperature fluctuations and estimates of CG radial peculiar velocities. This correlation function yields a 3.0–3.7σ detection of the peculiar motion of extended gas on Mpc scales in flows correlated up to distances of 80–100 h -1 Mpc. Both the pairwise momentum estimates and the kSZ temperature-velocity field correlation find evidence for kSZ signatures out to apertures of 8 arcmin and beyond, corresponding to a physical radius of >1 Mpc, more than twice the mean virial radius of halos. This is consistent with the predictions from hydrodynamical simulations that most of the baryons are outside the virialized halos. We fit a simple model, in which the temperature-velocity cross-correlation is proportional to the signal seen in a semi-analytic model built upon N-body simulations, and interpret the proportionality constant as an effective optical depth to Thomson scattering. Finally, we find τT = (1.4 ± 0.5) × 10 -4; the simplest interpretation of this measurement is that much of the gas is in a diffuse phase, which contributes little signal to X-ray or thermal Sunyaev-Zeldovich observations.« less

  17. Parent-related mechanisms underlying the social gradient of childhood overweight and obesity: a systematic review.

    PubMed

    Mech, P; Hooley, M; Skouteris, H; Williams, J

    2016-09-01

    Low socio-economic status (SES) is a significant risk factor for childhood overweight and obesity (COWOB) in high-income countries. Parents to young children buffer and accentuate social and cultural influences, and are central to the development of this disease. An understanding of the parent-related mechanisms that underlie the SES-COWOB relationship is needed to improve the efficacy of prevention and intervention efforts. A systematic review of relevant literature was conducted to investigate the mechanisms by which levels of SES (low, middle and high) are associated to COWOB, by exploring mediation and interaction effects. Six electronic databases were searched yielding 5155 initial records, once duplicates were removed. Studies were included if they investigated COWOB, SES, parent-related factors and the multivariate relationship between these factors. Thirty studies were included. Factors found to be mediating the SES-COWOB relationship or interacting with SES to influence COWOB were categorized according to an ecological systems framework, at child, parent, household and social system level factors. High parent body mass index, ethnicity, child-care attendance, high TV time (mother and child), breastfeeding (early weaning), food intake behaviours and birthweight potentially mediate the relationship between SES and COWOB. Different risk factors for COWOB in different SES groups were found. For low SES families, parental obesity and maternal depressive symptoms were strong risk factors for COWOB, whereas long maternal working hours and a permissive parenting style were risk factors for higher SES families. None of the studies investigated parental psychological attributes such as attitudes, beliefs, self-esteem and so on as potential mechanisms/risk factors. Families from different SES groups have different risk and protective factors for COWOB. Prevention and intervention efforts may have improved efficacy if they are tailored to address specific risk factors

  18. The Zeldovich approximation and wide-angle redshift-space distortions

    NASA Astrophysics Data System (ADS)

    Castorina, Emanuele; White, Martin

    2018-06-01

    The contribution of line-of-sight peculiar velocities to the observed redshift of objects breaks the translational symmetry of the underlying theory, modifying the predicted 2-point functions. These `wide angle effects' have mostly been studied using linear perturbation theory in the context of the multipoles of the correlation function and power spectrum . In this work we present the first calculation of wide angle terms in the Zeldovich approximation, which is known to be more accurate than linear theory on scales probed by the next generation of galaxy surveys. We present the exact result for dark matter and perturbatively biased tracers as well as the small angle expansion of the configuration- and Fourier-space two-point functions and the connection to the multi-frequency angular power spectrum. We compare different definitions of the line-of-sight direction and discuss how to translate between them. We show that wide angle terms can reach tens of percent of the total signal in a measurement at low redshift in some approximations, and that a generic feature of wide angle effects is to slightly shift the Baryon Acoustic Oscillation scale.

  19. Planck 2015 results: XXVII. The second Planck catalogue of Sunyaev-Zeldovich sources

    DOE PAGES

    Ade, P. A. R.; Aghanim, N.; Arnaud, M.; ...

    2016-09-20

    Here, we present the all-sky Planck catalogue of Sunyaev-Zeldovich (SZ) sources detected from the 29 month full-mission data. The catalogue (PSZ2) is the largest SZ-selected sample of galaxy clusters yet produced and the deepest systematic all-sky surveyof galaxy clusters. It contains 1653 detections, of which 1203 are confirmed clusters with identified counterparts in external data sets, and is the first SZ-selected cluster survey containing >103 confirmed clusters. We present a detailed analysis of the survey selection function in terms of its completeness and statistical reliability, placing a lower limit of 83% on the purity. Using simulations, we find that themore » estimates of the SZ strength parameter Y5R500are robust to pressure-profile variation and beam systematics, but accurate conversion to Y500 requires the use of prior information on the cluster extent. We describe the multi-wavelength search for counterparts in ancillary data, which makes use of radio, microwave, infra-red, optical, and X-ray data sets, and which places emphasis on the robustness of the counterpart match. We discuss the physical properties of the new sample and identify a population of low-redshift X-ray under-luminous clusters revealed by SZ selection. These objects appear in optical and SZ surveys with consistent properties for their mass, but are almost absent from ROSAT X-ray selected samples.« less

  20. Planck 2013 results. XXXII. The updated Planck catalogue of Sunyaev-Zeldovich sources

    NASA Astrophysics Data System (ADS)

    Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Aussel, H.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Barrena, R.; Bartelmann, M.; Bartlett, J. G.; Battaner, E.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bikmaev, I.; Bobin, J.; Bock, J. J.; Böhringer, H.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Bridges, M.; Bucher, M.; Burenin, R.; Burigana, C.; Butler, R. C.; Cardoso, J.-F.; Carvalho, P.; Catalano, A.; Challinor, A.; Chamballu, A.; Chary, R.-R.; Chen, X.; Chiang, H. C.; Chiang, L.-Y.; Chon, G.; Christensen, P. R.; Churazov, E.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Comis, B.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Da Silva, A.; Dahle, H.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J.-M.; Démoclès, J.; Désert, F.-X.; Dickinson, C.; Diego, J. M.; Dolag, K.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Dupac, X.; Efstathiou, G.; Enßlin, T. A.; Eriksen, H. K.; Feroz, F.; Ferragamo, A.; Finelli, F.; Flores-Cacho, I.; Forni, O.; Frailis, M.; Franceschi, E.; Fromenteau, S.; Galeotta, S.; Ganga, K.; Génova-Santos, R. T.; Giard, M.; Giardino, G.; Gilfanov, M.; Giraud-Héraud, Y.; González-Nuevo, J.; Górski, K. M.; Grainge, K. J. B.; Gratton, S.; Gregorio, A.; Groeneboom, N., E.; Gruppuso, A.; Hansen, F. K.; Hanson, D.; Harrison, D.; Hempel, A.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Hurier, G.; Hurley-Walker, N.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Khamitov, I.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Knox, L.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Laureijs, R. J.; Lawrence, C. R.; Leahy, J. P.; Leonardi, R.; León-Tavares, J.; Lesgourgues, J.; Li, C.; Liddle, A.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; MacTavish, C. J.; Maffei, B.; Maino, D.; Mandolesi, N.; Maris, M.; Marshall, D. J.; Martin, P. G.; Martínez-González, E.; Masi, S.; Massardi, M.; Matarrese, S.; Matthai, F.; Mazzotta, P.; Mei, S.; Meinhold, P. R.; Melchiorri, A.; Melin, J.-B.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mikkelsen, K.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nastasi, A.; Nati, F.; Natoli, P.; Nesvadba, N. P. H.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; O'Dwyer, I. J.; Olamaie, M.; Osborne, S.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paoletti, D.; Pasian, F.; Patanchon, G.; Pearson, T. J.; Perdereau, O.; Perotto, L.; Perrott, Y. C.; Perrotta, F.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Popa, L.; Poutanen, T.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Roudier, G.; Rowan-Robinson, M.; Rubiño-Martín, J. A.; Rumsey, C.; Rusholme, B.; Sandri, M.; Santos, D.; Saunders, R. D. E.; Savini, G.; Schammel, M. P.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Shimwell, T. W.; Spencer, L. D.; Starck, J.-L.; Stolyarov, V.; Stompor, R.; Streblyanska, A.; Sudiwala, R.; Sunyaev, R.; Sureau, F.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Tavagnacco, D.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tramonte, D.; Tristram, M.; Tucci, M.; Tuovinen, J.; Türler, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vibert, L.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; White, M.; White, S. D. M.; Yvon, D.; Zacchei, A.; Zonca, A.

    2015-09-01

    We update the all-sky Planck catalogue of 1227 clusters and cluster candidates (PSZ1) published in March 2013, derived from detections of the Sunyaev-Zeldovich (SZ) effect using the first 15.5 months of Planck satellite observations. As an addendum, we deliver an updated version of the PSZ1 catalogue, reporting the further confirmation of 86 Planck-discovered clusters. In total, the PSZ1 now contains 947 confirmed clusters, of which 214 were confirmed as newly discovered clusters through follow-up observations undertaken by the Planck Collaboration. The updated PSZ1 contains redshifts for 913 systems, of which 736 (~ 80.6%) are spectroscopic, and associated mass estimates derived from the Yz mass proxy. We also provide a new SZ quality flag for the remaining 280 candidates. This flag was derived from a novel artificial neural-network classification of the SZ signal. Based on this assessment, the purity of the updated PSZ1 catalogue is estimated to be 94%. In this release, we provide the full updated catalogue and an additional readme file with further information on the Planck SZ detections. The catalogue is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/581/A14

  1. The Zel'dovich approximation: key to understanding cosmic web complexity

    NASA Astrophysics Data System (ADS)

    Hidding, Johan; Shandarin, Sergei F.; van de Weygaert, Rien

    2014-02-01

    We describe how the dynamics of cosmic structure formation defines the intricate geometric structure of the spine of the cosmic web. The Zel'dovich approximation is used to model the backbone of the cosmic web in terms of its singularity structure. The description by Arnold et al. in terms of catastrophe theory forms the basis of our analysis. This two-dimensional analysis involves a profound assessment of the Lagrangian and Eulerian projections of the gravitationally evolving four-dimensional phase-space manifold. It involves the identification of the complete family of singularity classes, and the corresponding caustics that we see emerging as structure in Eulerian space evolves. In particular, as it is instrumental in outlining the spatial network of the cosmic web, we investigate the nature of spatial connections between these singularities. The major finding of our study is that all singularities are located on a set of lines in Lagrangian space. All dynamical processes related to the caustics are concentrated near these lines. We demonstrate and discuss extensively how all 2D singularities are to be found on these lines. When mapping this spatial pattern of lines to Eulerian space, we find a growing connectedness between initially disjoint lines, resulting in a percolating network. In other words, the lines form the blueprint for the global geometric evolution of the cosmic web.

  2. Planck 2015 results. XXVII. The second Planck catalogue of Sunyaev-Zeldovich sources

    NASA Astrophysics Data System (ADS)

    Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Barrena, R.; Bartlett, J. G.; Bartolo, N.; Battaner, E.; Battye, R.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bikmaev, I.; Böhringer, H.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Bucher, M.; Burenin, R.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cardoso, J.-F.; Carvalho, P.; Catalano, A.; Challinor, A.; Chamballu, A.; Chary, R.-R.; Chiang, H. C.; Chon, G.; Christensen, P. R.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Combet, C.; Comis, B.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Dahle, H.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Désert, F.-X.; Dickinson, C.; Diego, J. M.; Dolag, K.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Eisenhardt, P. R. M.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Falgarone, E.; Fergusson, J.; Feroz, F.; Ferragamo, A.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Génova-Santos, R. T.; Giard, M.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Grainge, K. J. B.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Hansen, F. K.; Hanson, D.; Harrison, D. L.; Hempel, A.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jin, T.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Khamitov, I.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leonardi, R.; Lesgourgues, J.; Levrier, F.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maggio, G.; Maino, D.; Mak, D. S. Y.; Mandolesi, N.; Mangilli, A.; Martin, P. G.; Martínez-González, E.; Masi, S.; Matarrese, S.; Mazzotta, P.; McGehee, P.; Mei, S.; Melchiorri, A.; Melin, J.-B.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nastasi, A.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Olamaie, M.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paoletti, D.; Pasian, F.; Patanchon, G.; Pearson, T. J.; Perdereau, O.; Perotto, L.; Perrott, Y. C.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rozo, E.; Rubiño-Martín, J. A.; Rumsey, C.; Rusholme, B.; Rykoff, E. S.; Sandri, M.; Santos, D.; Saunders, R. D. E.; Savelainen, M.; Savini, G.; Schammel, M. P.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Shimwell, T. W.; Spencer, L. D.; Stanford, S. A.; Stern, D.; Stolyarov, V.; Stompor, R.; Streblyanska, A.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tramonte, D.; Tristram, M.; Tucci, M.; Tuovinen, J.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; White, S. D. M.; Wright, E. L.; Yvon, D.; Zacchei, A.; Zonca, A.

    2016-09-01

    We present the all-sky Planck catalogue of Sunyaev-Zeldovich (SZ) sources detected from the 29 month full-mission data. The catalogue (PSZ2) is the largest SZ-selected sample of galaxy clusters yet produced and the deepest systematic all-sky surveyof galaxy clusters. It contains 1653 detections, of which 1203 are confirmed clusters with identified counterparts in external data sets, and is the first SZ-selected cluster survey containing >103 confirmed clusters. We present a detailed analysis of the survey selection function in terms of its completeness and statistical reliability, placing a lower limit of 83% on the purity. Using simulations, we find that the estimates of the SZ strength parameter Y5R500are robust to pressure-profile variation and beam systematics, but accurate conversion to Y500 requires the use of prior information on the cluster extent. We describe the multi-wavelength search for counterparts in ancillary data, which makes use of radio, microwave, infra-red, optical, and X-ray data sets, and which places emphasis on the robustness of the counterpart match. We discuss the physical properties of the new sample and identify a population of low-redshift X-ray under-luminous clusters revealed by SZ selection. These objects appear in optical and SZ surveys with consistent properties for their mass, but are almost absent from ROSAT X-ray selected samples.

  3. Planck 2015 results. XXII. A map of the thermal Sunyaev-Zeldovich effect

    NASA Astrophysics Data System (ADS)

    Planck Collaboration; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Bartolo, N.; Battaner, E.; Battye, R.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cardoso, J.-F.; Catalano, A.; Challinor, A.; Chiang, H. C.; Christensen, P. R.; Churazov, E.; Clements, D. L.; Colombo, L. P. L.; Combet, C.; Comis, B.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Désert, F.-X.; Dickinson, C.; Diego, J. M.; Dolag, K.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Fergusson, J.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Génova-Santos, R. T.; Giard, M.; González-Nuevo, J.; Górski, K. M.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Hansen, F. K.; Harrison, D. L.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Holmes, W. A.; Hornstrup, A.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kneissl, R.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lacasa, F.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Leonardi, R.; Lesgourgues, J.; Levrier, F.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Macías-Pérez, J. F.; Maffei, B.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Maris, M.; Martin, P. G.; Martínez-González, E.; Masi, S.; Matarrese, S.; Melchiorri, A.; Melin, J.-B.; Migliaccio, M.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Noviello, F.; Novikov, D.; Novikov, I.; Paci, F.; Pagano, L.; Pajot, F.; Paoletti, D.; Pasian, F.; Patanchon, G.; Perdereau, O.; Perotto, L.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Pratt, G. W.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rossetti, M.; Roudier, G.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Sauvé, A.; Savelainen, M.; Savini, G.; Scott, D.; Spencer, L. D.; Stolyarov, V.; Stompor, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tramonte, D.; Tristram, M.; Tucci, M.; Tuovinen, J.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; Yvon, D.; Zacchei, A.; Zonca, A.

    2016-09-01

    We have constructed all-sky Compton parameters maps, y-maps, of the thermal Sunyaev-Zeldovich (tSZ) effect by applying specifically tailored component separation algorithms to the 30 to 857 GHz frequency channel maps from the Planck satellite. These reconstructed y-maps are delivered as part of the Planck 2015 release. The y-maps are characterized in terms of noise properties and residual foreground contamination, mainly thermal dust emission at large angular scales, and cosmic infrared background and extragalactic point sources at small angular scales. Specific masks are defined to minimize foreground residuals and systematics. Using these masks, we compute the y-map angular power spectrum and higher order statistics. From these we conclude that the y-map is dominated by tSZ signal in the multipole range, 20 <ℓ< 600. We compare the measured tSZ power spectrum and higher order statistics to various physically motivated models and discuss the implications of our results in terms of cluster physics and cosmology.

  4. Sunyaev-Zeldovich Effect-Derived Distances to the High-Redshift Clusters

    NASA Technical Reports Server (NTRS)

    Reese, Erik D.; Mohr, Joseph J.; Carlstrom, John E.; Joy, Marshall; Grego, Laura; Holder, Gilbert P.; Holzapfel, William L.; Hughes, John P.; Patel, Sandeep K.; Donahue, Megan

    2000-01-01

    We determine the distances to the z approximately equals 0.55 galaxy clusters MS 0451.6 - 0305 and Cl 0016 + 16 from a maximum-likelihood joint fit to interferometric Sunyaev-Zeldovich effect (SZE) and X-ray observations. We model the intracluster medium (ICM) using a spherical isothermal beta model. We quantify the statistical and systematic uncertainties inherent to these direct distance measurements, and we determine constraints on the Hubble parameter for three different cosmologies. For an Omega(sub M) = 0.3, Omega(sub lambda) = 0.7 cosmology, these distances imply a Hubble constant of 63(sup +12) (sub -9) (sup + 21) (sub -21) km/s Mp/c, where the uncertainties correspond to statistical followed by systematic at 68% confidence. The best-fit H(sub 0) is 57 km/s Mp/c for an open (Omega(sub M) = 0.3) universe and 52 km/s Mp/c for a flat (Omega(sub M) = 1) universe.

  5. Discovery of the surface polarity gradient on iridescent Morpho butterfly scales reveals a mechanism of their selective vapor response

    PubMed Central

    Potyrailo, Radislav A.; Starkey, Timothy A.; Vukusic, Peter; Ghiradella, Helen; Vasudev, Milana; Bunning, Timothy; Naik, Rajesh R.; Tang, Zhexiong; Larsen, Michael; Deng, Tao; Zhong, Sheng; Palacios, Manuel; Grande, James C.; Zorn, Gilad; Goddard, Gregory; Zalubovsky, Sergey

    2013-01-01

    For almost a century, the iridescence of tropical Morpho butterfly scales has been known to originate from 3D vertical ridge structures of stacked periodic layers of cuticle separated by air gaps. Here we describe a biological pattern of surface functionality that we have found in these photonic structures. This pattern is a gradient of surface polarity of the ridge structures that runs from their polar tops to their less-polar bottoms. This finding shows a biological pattern design that could stimulate numerous technological applications ranging from photonic security tags to self-cleaning surfaces, gas separators, protective clothing, sensors, and many others. As an important first step, this biomaterial property and our knowledge of its basis has allowed us to unveil a general mechanism of selective vapor response observed in the photonic Morpho nanostructures. This mechanism of selective vapor response brings a multivariable perspective for sensing, where selectivity is achieved within a single chemically graded nanostructured sensing unit, rather than from an array of separate sensors. PMID:24019497

  6. Assessment of trans-aortic pressure gradient using a coronary pressure wire in patients with mechanical aortic and mitral valve prostheses.

    PubMed

    Kherada, Nisharahmed; Brenes, Juan Carlos; Kini, Annapoorna S; Dangas, George D

    2017-03-15

    Accurate evaluation of trans-aortic valvular pressure gradients is challenging in cases where dual mechanical aortic and mitral valve prostheses are present. Non-invasive Doppler echocardiographic imaging has its limitations due to multiple geometric assumptions. Invasive measurement of trans-valvular gradients with cardiac catheterization can provide further information in patients with two mechanical valves, where simultaneous pressure measurements in the left ventricle and ascending aorta must be obtained. Obtaining access to the left ventricle via the mitral valve after a trans-septal puncture is not feasible in the case of a concomitant mechanical mitral valve, whereas left ventricular apical puncture technique is associated with high procedural risks. Retrograde crossing of a bileaflet mechanical aortic prosthesis with standard catheters is associated with the risk of catheter entrapment and acute valvular regurgitation. In these cases, the assessment of trans-valvular gradients using a 0.014˝ diameter coronary pressure wire technique has been described in a few case reports. We present the case of a 76-year-old female with rheumatic valvular heart disease who underwent mechanical aortic and mitral valve replacement in the past. She presented with decompensated heart failure and echocardiographic findings suggestive of elevated pressure gradient across the mechanical aortic valve prosthesis. The use of a high-fidelity 0.014˝ diameter coronary pressure guidewire resulted in the detection of a normal trans-valvular pressure gradient across the mechanical aortic valve. This avoided a high-risk third redo valve surgery in our patient. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  7. Planck's view on the spectrum of the Sunyaev-Zeldovich effect

    NASA Astrophysics Data System (ADS)

    Erler, Jens; Basu, Kaustuv; Chluba, Jens; Bertoldi, Frank

    2018-05-01

    We present a detailed analysis of the stacked frequency spectrum of a large sample of galaxy clusters using Planck data, together with auxiliary data from the AKARI and IRAS missions. Our primary goal is to search for the imprint of relativistic corrections to the thermal Sunyaev-Zeldovich effect (tSZ) spectrum, which allow to measure the temperature of the intracluster medium. We remove Galactic and extragalactic foregrounds with a matched filtering technique, which is validated using simulations with realistic mock data sets. The extracted spectra show the tSZ signal at high significance and reveal an additional far-infrared (FIR) excess, which we attribute to thermal emission from the galaxy clusters themselves. This excess FIR emission from clusters is accounted for in our spectral model. We are able to measure the tSZ relativistic corrections at 2.2σ by constraining the mean temperature of our cluster sample to 4.4^{+2.1}_{-2.0} keV. We repeat the same analysis on a subsample containing only the 100 hottest clusters, for which we measure the mean temperature to be 6.0^{+3.8}_{-2.9} keV, corresponding to 2.0σ. The temperature of the emitting dust grains in our FIR model is constrained to ≃20 K, consistent with previous studies. Control for systematic biases is done by fitting mock clusters, from which we also show that using the non-relativistic spectrum for SZ signal extraction will lead to a bias in the integrated Compton parameter Y, which can be up to 14% for the most massive clusters. We conclude by providing an outlook for the upcoming CCAT-prime telescope, which will improve upon Planck with lower noise and better spatial resolution.

  8. Measurement of the pairwise kinematic Sunyaev-Zeldovich effect with Planck and BOSS data

    NASA Astrophysics Data System (ADS)

    Li, Yi-Chao; Ma, Yin-Zhe; Remazeilles, Mathieu; Moodley, Kavilan

    2018-01-01

    We present a new measurement of the kinetic Sunyaev-Zeldovich effect (kSZ) using Planck cosmic microwave background (CMB) and Baryon Oscillation Spectroscopic Survey (BOSS) data. Using the "LowZ North/South" galaxy catalogue from BOSS DR12, and the group catalogue from BOSS DR13, we evaluate the mean pairwise kSZ temperature associated with BOSS galaxies. We construct a "Central Galaxies Catalogue" (CGC) which consists of isolated galaxies from the original BOSS data set, and apply the aperture photometry (AP) filter to suppress the primary CMB contribution. By constructing a halo model to fit the pairwise kSZ function, we constrain the mean optical depth to be τ ¯=(0.53 ±0.32 )×10-4(1.65 σ ) for LowZ North CGC, τ ¯ =(0.30 ±0.57 )×10-4(0.53 σ ) for LowZ South CGC, and τ ¯ =(0.43 ±0.28 )×10-4(1.53 σ ) for DR13 Group. In addition, we vary the radius of the AP filter and find that the AP size of 7 arcmin gives the maximum detection for τ ¯. We also investigate the dependence of the signal with halo mass and find τ ¯ =(0.32 ±0.36 )×10-4(0.8 σ ) and τ ¯ =(0.67 ±0.46 )×10-4(1.4 σ ) for DR13 Group with halo mass restricted to, respectively, less and greater than its median halo mass, 1 012 h-1M⊙ . For the LowZ North CGC sample restricted to Mh≳1014 h-1M⊙ there is no detection of the kSZ signal because these high mass halos are associated with the high-redshift galaxies of the LowZ North catalogue, which have limited contribution to the pairwise kSZ signals.

  9. Testing eternal inflation with the kinetic Sunyaev Zel'dovich effect

    NASA Astrophysics Data System (ADS)

    Zhang, Pengjie; Johnson, Matthew C.

    2015-06-01

    Perhaps the most controversial idea in modern cosmology is that our observable universe is contained within one bubble among many, all inhabiting the eternally inflating multiverse. One of the few way to test this idea is to look for evidence of the relic inhomogeneities left by the collisions between other bubbles and our own. Such relic inhomogeneities will induce a coherent bulk flow over Gpc scales. Therefore, bubble collisions leave unique imprints in the cosmic microwave background (CMB) through the kinetic Sunyaev Zel'dovich (kSZ) effect, temperature anisotropies induced by the scattering of photons from coherently moving free electrons in the diffuse intergalactic medium. The kSZ signature produced by bubble collisions has a unique directional dependence and is tightly correlated with the galaxy distribution; it can therefore be distinguished from other contributions to the CMB anisotropies. An important advantage of the kSZ signature is that it peaks on arcminute angular scales, where the limiting factors in making a detection are instrumental noise and foreground subtraction. This is in contrast to the collision signature in the primary CMB, which peaks on angular scales much larger than one degree, and whose detection is therefore limited by cosmic variance. In this paper, we examine the prospects for probing the inhomogeneities left by bubble collisions using the kSZ effect. We provide a forecast for detection using cross-correlations between CMB and galaxy surveys, finding that the detectability using the kSZ effect can be competitive with constraints from CMB temperature and polarization data.

  10. Dissecting the thermal Sunyaev-Zeldovich-gravitational lensing cross-correlation with hydrodynamical simulations

    SciTech Connect

    Hojjati, Alireza; Harnois-Deraps, Joachim; Waerbeke, Ludovic Van

    2015-10-01

    We use the cosmo-OWLS suite of cosmological hydrodynamical simulations, which includes different galactic feedback models, to predict the cross-correlation signal between weak gravitational lensing and the thermal Sunyaev-Zeldovich (tSZ) y-parameter. The predictions are compared to the recent detection reported by van Waerbeke and collaborators. The simulations reproduce the weak lensing-tSZ cross-correlation, ξ{sub yκ}(θ), well. The uncertainty arising from different possible feedback models appears to be important on small scales only (0θ ∼< 1 arcmin), while the amplitude of the correlation on all scales is sensitive to cosmological parameters that control the growth rate of structure (such as σ{sub 8}, Ω{sub m} andmore » Ω{sub b}). This study confirms our previous claim (in Ma et al.) that a significant proportion of the signal originates from the diffuse gas component in low-mass (M{sub halo} ∼< 10{sup 14} M{sub ⊙}) clusters as well as from the region beyond the virial radius. We estimate that approximately 20% of the detected signal comes from low-mass clusters, which corresponds to about 30% of the baryon density of the Universe. The simulations also suggest that more than half of the baryons in the Universe are in the form of diffuse gas outside halos (∼> 5 times the virial radius) which is not hot or dense enough to produce a significant tSZ signal or be observed by X-ray experiments. Finally, we show that future high-resolution tSZ-lensing cross-correlation observations will serve as a powerful tool for discriminating between different galactic feedback models.« less

  11. Galaxy Cluster Gas Mass Fractions From Sunyaev-Zeldovich Effect Measurements: Constraints on Omega(M)

    NASA Technical Reports Server (NTRS)

    Grego, Laura; Carlstrom, John E.; Reese, Erik D.; Holder, Gilbert P.; Holzapfel, William L.; Joy, Marshall K.; Mohr, Joseph J.; Patel, Sandeep

    2001-01-01

    Using sensitive centimeter-wave receivers mounted on the Owens Valley Radio Observatory and Berkeley-Illinois-Maryland-Association millimeter arrays, we have obtained interferometric measurements of the Sunyaev-Zeldovich(SZ) effect toward massive galaxy clusters. We use the SZ data to determine the pressure distribution of the cluster gas and, in combination with published X-ray temperatures, to infer the gas mass and total gravitational mass of 18 clusters. The gas mass fraction, f(g), is calculated for each cluster and is extrapolated to the fiducial radius r(500) using the results of numerical simulations. The mean f(g) within r(500) is 0.081(+ 0.009 / - 0.011) per h(100) (statistical uncertainty at 68% confidence level, assuming Omega(M) = 0.3, Omega(Lambda) = 0.7). We discuss possible sources of systematic errors in the mean f(sub g) measurement. We derive an upper limit for Omega(M) from this sample under the assumption that the mass composition of clusters within r(500) reflects the universal mass composition: Omega(M)h is less than or equal to Omega(B)/f(g). The gas mass fractions depend on cosmology through the angular diameter distance and the r(500) correction factors. For a flat universe (Omega(Lambda) is identical with 1 - Omega(M)) and h = 0.7, we find the measured gas mass fractions are consistent with Omega(M) is less than 0.40, at 68% confidence. Including estimates of the baryons contained in galaxies and the baryons which failed to become bound during the cluster formation process, we find Omega(M) is approximately equal to 0.25.

  12. Testing eternal inflation with the kinetic Sunyaev Zel'dovich effect

    SciTech Connect

    Zhang, Pengjie; Johnson, Matthew C., E-mail: zhangpj@sjtu.edu.cn, E-mail: mjohnson@perimeterinstitute.ca

    2015-06-01

    Perhaps the most controversial idea in modern cosmology is that our observable universe is contained within one bubble among many, all inhabiting the eternally inflating multiverse. One of the few way to test this idea is to look for evidence of the relic inhomogeneities left by the collisions between other bubbles and our own. Such relic inhomogeneities will induce a coherent bulk flow over Gpc scales. Therefore, bubble collisions leave unique imprints in the cosmic microwave background (CMB) through the kinetic Sunyaev Zel'dovich (kSZ) effect, temperature anisotropies induced by the scattering of photons from coherently moving free electrons in themore » diffuse intergalactic medium. The kSZ signature produced by bubble collisions has a unique directional dependence and is tightly correlated with the galaxy distribution; it can therefore be distinguished from other contributions to the CMB anisotropies. An important advantage of the kSZ signature is that it peaks on arcminute angular scales, where the limiting factors in making a detection are instrumental noise and foreground subtraction. This is in contrast to the collision signature in the primary CMB, which peaks on angular scales much larger than one degree, and whose detection is therefore limited by cosmic variance. In this paper, we examine the prospects for probing the inhomogeneities left by bubble collisions using the kSZ effect. We provide a forecast for detection using cross-correlations between CMB and galaxy surveys, finding that the detectability using the kSZ effect can be competitive with constraints from CMB temperature and polarization data.« less

  13. Planck 2015 results: XXIII. The thermal Sunyaev-Zeldovich effect-cosmic infrared background correlation

    DOE PAGES

    Ade, P. A. R.; Aghanim, N.; Arnaud, M.; ...

    2016-09-20

    In this paper, we use Planck data to detect the cross-correlation between the thermal Sunyaev-Zeldovich (tSZ) effect and the infrared emission from the galaxies that make up the the cosmic infrared background (CIB). We first perform a stacking analysis towards Planck-confirmed galaxy clusters. We detect infrared emission produced by dusty galaxies inside these clusters and demonstrate that the infrared emission is about 50% more extended than the tSZ effect. Modelling the emission with a Navarro-Frenk-White profile, we find that the radial profile concentration parameter is c 500 = 1.00 +0.18 -0.15 . This indicates that infrared galaxies in the outskirtsmore » of clusters have higher infrared flux than cluster-core galaxies. We also study the cross-correlation between tSZ and CIB anisotropies, following three alternative approaches based on power spectrum analyses: (i) using a catalogue of confirmed clusters detected in Planck data; (ii) using an all-sky tSZ map built from Planck frequency maps; and (iii) using cross-spectra between Planck frequency maps. With the three different methods, we detect the tSZ-CIB cross-power spectrum at significance levels of (i) 6σ; (ii) 3σ; and (iii) 4σ. We model the tSZ-CIB cross-correlation signature and compare predictions with the measurements. The amplitude of the cross-correlation relative to the fiducial model is A tSZ-CIB = 1.2 ± 0.3. Finally, this result is consistent with predictions for the tSZ-CIB cross-correlation assuming the best-fit cosmological model from Planck 2015 results along with the tSZ and CIB scaling relations.« less

  14. Planck 2015 results. XXIII. The thermal Sunyaev-Zeldovich effect-cosmic infrared background correlation

    NASA Astrophysics Data System (ADS)

    Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Bartolo, N.; Battaner, E.; Benabed, K.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Burigana, C.; Butler, R. C.; Calabrese, E.; Catalano, A.; Chamballu, A.; Chiang, H. C.; Christensen, P. R.; Churazov, E.; Clements, D. L.; Colombo, L. P. L.; Combet, C.; Comis, B.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Dickinson, C.; Diego, J. M.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Finelli, F.; Flores-Cacho, I.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Galeotta, S.; Galli, S.; Ganga, K.; Génova-Santos, R. T.; Giard, M.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Hansen, F. K.; Harrison, D. L.; Helou, G.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Langer, M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leonardi, R.; Levrier, F.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maffei, B.; Maggio, G.; Maino, D.; Mak, D. S. Y.; Mandolesi, N.; Mangilli, A.; Maris, M.; Martin, P. G.; Martínez-González, E.; Masi, S.; Matarrese, S.; Melchiorri, A.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, J. A.; Nati, F.; Natoli, P.; Noviello, F.; Novikov, D.; Novikov, I.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paoletti, D.; Partridge, B.; Pasian, F.; Pearson, T. J.; Perdereau, O.; Perotto, L.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Pratt, G. W.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Spencer, L. D.; Stolyarov, V.; Stompor, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; Welikala, N.; Yvon, D.; Zacchei, A.; Zonca, A.

    2016-09-01

    We use Planck data to detect the cross-correlation between the thermal Sunyaev-Zeldovich (tSZ) effect and the infrared emission from the galaxies that make up the the cosmic infrared background (CIB). We first perform a stacking analysis towards Planck-confirmed galaxy clusters. We detect infrared emission produced by dusty galaxies inside these clusters and demonstrate that the infrared emission is about 50% more extended than the tSZ effect. Modelling the emission with a Navarro-Frenk-White profile, we find that the radial profile concentration parameter is c500 = 1.00+0.18-0.15 . This indicates that infrared galaxies in the outskirts of clusters have higher infrared flux than cluster-core galaxies. We also study the cross-correlation between tSZ and CIB anisotropies, following three alternative approaches based on power spectrum analyses: (I) using a catalogue of confirmed clusters detected in Planck data; (II) using an all-sky tSZ map built from Planck frequency maps; and (III) using cross-spectra between Planck frequency maps. With the three different methods, we detect the tSZ-CIB cross-power spectrum at significance levels of (I) 6σ; (II) 3σ; and (III) 4σ. We model the tSZ-CIB cross-correlation signature and compare predictions with the measurements. The amplitude of the cross-correlation relative to the fiducial model is AtSZ-CIB = 1.2 ± 0.3. This result is consistent with predictions for the tSZ-CIB cross-correlation assuming the best-fit cosmological model from Planck 2015 results along with the tSZ and CIB scaling relations.

  15. Planck 2015 results. XXIV. Cosmology from Sunyaev-Zeldovich cluster counts

    NASA Astrophysics Data System (ADS)

    Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Bartolo, N.; Battaner, E.; Battye, R.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cardoso, J.-F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chary, R.-R.; Chiang, H. C.; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Combet, C.; Comis, B.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Désert, F.-X.; Diego, J. M.; Dolag, K.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Falgarone, E.; Fergusson, J.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Giard, M.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Hansen, F. K.; Hanson, D.; Harrison, D. L.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leonardi, R.; Lesgourgues, J.; Levrier, F.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Maris, M.; Martin, P. G.; Martínez-González, E.; Masi, S.; Matarrese, S.; McGehee, P.; Meinhold, P. R.; Melchiorri, A.; Melin, J.-B.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Pearson, T. J.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Popa, L.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Roman, M.; Rosset, C.; Rossetti, M.; Roudier, G.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Spencer, L. D.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Türler, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; Weller, J.; White, S. D. M.; Yvon, D.; Zacchei, A.; Zonca, A.

    2016-09-01

    We present cluster counts and corresponding cosmological constraints from the Planck full mission data set. Our catalogue consists of 439 clusters detected via their Sunyaev-Zeldovich (SZ) signal down to a signal-to-noise ratio of 6, and is more than a factor of 2 larger than the 2013 Planck cluster cosmology sample. The counts are consistent with those from 2013 and yield compatible constraints under the same modelling assumptions. Taking advantage of the larger catalogue, we extend our analysis to the two-dimensional distribution in redshift and signal-to-noise. We use mass estimates from two recent studies of gravitational lensing of background galaxies by Planck clusters to provide priors on the hydrostatic bias parameter, (1-b). In addition, we use lensing of cosmic microwave background (CMB) temperature fluctuations by Planck clusters as an independent constraint on this parameter. These various calibrations imply constraints on the present-day amplitude of matter fluctuations in varying degrees of tension with those from the Planck analysis of primary fluctuations in the CMB; for the lowest estimated values of (1-b) the tension is mild, only a little over one standard deviation, while it remains substantial (3.7σ) for the largest estimated value. We also examine constraints on extensions to the base flat ΛCDM model by combining the cluster and CMB constraints. The combination appears to favour non-minimal neutrino masses, but this possibility does little to relieve the overall tension because it simultaneously lowers the implied value of the Hubble parameter, thereby exacerbating the discrepancy with most current astrophysical estimates. Improving the precision of cluster mass calibrations from the current 10%-level to 1% would significantly strengthen these combined analyses and provide a stringent test of the base ΛCDM model.

  16. Planck 2015 results: XXIII. The thermal Sunyaev-Zeldovich effect-cosmic infrared background correlation

    SciTech Connect

    Ade, P. A. R.; Aghanim, N.; Arnaud, M.

    In this paper, we use Planck data to detect the cross-correlation between the thermal Sunyaev-Zeldovich (tSZ) effect and the infrared emission from the galaxies that make up the the cosmic infrared background (CIB). We first perform a stacking analysis towards Planck-confirmed galaxy clusters. We detect infrared emission produced by dusty galaxies inside these clusters and demonstrate that the infrared emission is about 50% more extended than the tSZ effect. Modelling the emission with a Navarro-Frenk-White profile, we find that the radial profile concentration parameter is c 500 = 1.00 +0.18 -0.15 . This indicates that infrared galaxies in the outskirtsmore » of clusters have higher infrared flux than cluster-core galaxies. We also study the cross-correlation between tSZ and CIB anisotropies, following three alternative approaches based on power spectrum analyses: (i) using a catalogue of confirmed clusters detected in Planck data; (ii) using an all-sky tSZ map built from Planck frequency maps; and (iii) using cross-spectra between Planck frequency maps. With the three different methods, we detect the tSZ-CIB cross-power spectrum at significance levels of (i) 6σ; (ii) 3σ; and (iii) 4σ. We model the tSZ-CIB cross-correlation signature and compare predictions with the measurements. The amplitude of the cross-correlation relative to the fiducial model is A tSZ-CIB = 1.2 ± 0.3. Finally, this result is consistent with predictions for the tSZ-CIB cross-correlation assuming the best-fit cosmological model from Planck 2015 results along with the tSZ and CIB scaling relations.« less

  17. Dark energy constraints from the thermal Sunyaev-Zeldovich power spectrum

    NASA Astrophysics Data System (ADS)

    Bolliet, Boris; Comis, Barbara; Komatsu, Eiichiro; Macías-Pérez, Juan Francisco

    2018-07-01

    We constrain the dark energy equation of state parameter, {w}, using the power spectrum of the thermal Sunyaev-Zeldovich (tSZ) effect. We improve upon previous analyses by taking into account the trispectrum in the covariance matrix and marginalizing over the foreground parameters, the correlated noise, the mass bias B in the Planck universal pressure profile, and all the relevant cosmological parameters (i.e. not just Ωm and σ8). We find that the amplitude of the tSZ power spectrum at ℓ ≲ 103 depends primarily on F ≡ σ8(Ωm/B)0.40h-0.21, where B is related to more commonly used variable b by B = (1 - b)-1. We measure this parameter with 2.6 per cent precision, F = 0.460 ± 0.012 (68 per cent CL). By fixing the bias to B = 1.25 and adding the local determination of the Hubble constant H0 and the amplitude of the primordial power spectrum constrained by the Planck cosmic microwave background (CMB) data, we find {w} = -1.10 ± 0.12, σ8 = 0.802 ± 0.037, and Ωm = 0.265 ± 0.022 (68 per cent CL). Our limit on {w} is consistent with and is as tight as that from the distance-alone constraint from the CMB and H0. Finally, by combining the tSZ power spectrum and the CMB data we find, in the Λ cold dark matter model, the mass bias of B = 1.71 ± 0.17, i.e. 1 - b = 0.58 ± 0.06 (68 per cent CL).

  18. Planck 2015 results: XXIV. Cosmology from Sunyaev-Zeldovich cluster counts

    DOE PAGES

    Ade, P. A. R.; Aghanim, N.; Arnaud, M.; ...

    2016-09-20

    In this work, we present cluster counts and corresponding cosmological constraints from the Planck full mission data set. Our catalogue consists of 439 clusters detected via their Sunyaev-Zeldovich (SZ) signal down to a signal-to-noise ratio of 6, and is more than a factor of 2 larger than the 2013 Planck cluster cosmology sample. The counts are consistent with those from 2013 and yield compatible constraints under the same modelling assumptions. Taking advantage of the larger catalogue, we extend our analysis to the two-dimensional distribution in redshift and signal-to-noise. We use mass estimates from two recent studies of gravitational lensing ofmore » background galaxies by Planck clusters to provide priors on the hydrostatic bias parameter, (1-b). In addition, we use lensing of cosmic microwave background (CMB) temperature fluctuations by Planck clusters as an independent constraint on this parameter. These various calibrations imply constraints on the present-day amplitude of matter fluctuations in varying degrees of tension with those from the Planck analysis of primary fluctuations in the CMB; for the lowest estimated values of (1-b) the tension is mild, only a little over one standard deviation, while it remains substantial (3.7σ) for the largest estimated value. We also examine constraints on extensions to the base flat ΛCDM model by combining the cluster and CMB constraints. The combination appears to favour non-minimal neutrino masses, but this possibility does little to relieve the overall tension because it simultaneously lowers the implied value of the Hubble parameter, thereby exacerbating the discrepancy with most current astrophysical estimates. In conclusion, improving the precision of cluster mass calibrations from the current 10%-level to 1% would significantly strengthen these combined analyses and provide a stringent test of the base ΛCDM model.« less

  19. Planck 2015 results: XXIV. Cosmology from Sunyaev-Zeldovich cluster counts

    SciTech Connect

    Ade, P. A. R.; Aghanim, N.; Arnaud, M.

    In this work, we present cluster counts and corresponding cosmological constraints from the Planck full mission data set. Our catalogue consists of 439 clusters detected via their Sunyaev-Zeldovich (SZ) signal down to a signal-to-noise ratio of 6, and is more than a factor of 2 larger than the 2013 Planck cluster cosmology sample. The counts are consistent with those from 2013 and yield compatible constraints under the same modelling assumptions. Taking advantage of the larger catalogue, we extend our analysis to the two-dimensional distribution in redshift and signal-to-noise. We use mass estimates from two recent studies of gravitational lensing ofmore » background galaxies by Planck clusters to provide priors on the hydrostatic bias parameter, (1-b). In addition, we use lensing of cosmic microwave background (CMB) temperature fluctuations by Planck clusters as an independent constraint on this parameter. These various calibrations imply constraints on the present-day amplitude of matter fluctuations in varying degrees of tension with those from the Planck analysis of primary fluctuations in the CMB; for the lowest estimated values of (1-b) the tension is mild, only a little over one standard deviation, while it remains substantial (3.7σ) for the largest estimated value. We also examine constraints on extensions to the base flat ΛCDM model by combining the cluster and CMB constraints. The combination appears to favour non-minimal neutrino masses, but this possibility does little to relieve the overall tension because it simultaneously lowers the implied value of the Hubble parameter, thereby exacerbating the discrepancy with most current astrophysical estimates. In conclusion, improving the precision of cluster mass calibrations from the current 10%-level to 1% would significantly strengthen these combined analyses and provide a stringent test of the base ΛCDM model.« less

  20. Root gravitropism is regulated by a transient lateral auxin gradient controlled by a tipping-point mechanism

    PubMed Central

    Band, Leah R.; Wells, Darren M.; Larrieu, Antoine; Sun, Jianyong; Middleton, Alistair M.; French, Andrew P.; Brunoud, Géraldine; Sato, Ethel Mendocilla; Wilson, Michael H.; Péret, Benjamin; Oliva, Marina; Swarup, Ranjan; Sairanen, Ilkka; Parry, Geraint; Ljung, Karin; Beeckman, Tom; Garibaldi, Jonathan M.; Estelle, Mark; Owen, Markus R.; Vissenberg, Kris; Hodgman, T. Charlie; Pridmore, Tony P.; King, John R.; Vernoux, Teva; Bennett, Malcolm J.

    2012-01-01

    Gravity profoundly influences plant growth and development. Plants respond to changes in orientation by using gravitropic responses to modify their growth. Cholodny and Went hypothesized over 80 years ago that plants bend in response to a gravity stimulus by generating a lateral gradient of a growth regulator at an organ's apex, later found to be auxin. Auxin regulates root growth by targeting Aux/IAA repressor proteins for degradation. We used an Aux/IAA-based reporter, domain II (DII)-VENUS, in conjunction with a mathematical model to quantify auxin redistribution following a gravity stimulus. Our multidisciplinary approach revealed that auxin is rapidly redistributed to the lower side of the root within minutes of a 90° gravity stimulus. Unexpectedly, auxin asymmetry was rapidly lost as bending root tips reached an angle of 40° to the horizontal. We hypothesize roots use a “tipping point” mechanism that operates to reverse the asymmetric auxin flow at the midpoint of root bending. These mechanistic insights illustrate the scientific value of developing quantitative reporters such as DII-VENUS in conjunction with parameterized mathematical models to provide high-resolution kinetics of hormone redistribution. PMID:22393022

  1. Root gravitropism is regulated by a transient lateral auxin gradient controlled by a tipping-point mechanism.

    PubMed

    Band, Leah R; Wells, Darren M; Larrieu, Antoine; Sun, Jianyong; Middleton, Alistair M; French, Andrew P; Brunoud, Géraldine; Sato, Ethel Mendocilla; Wilson, Michael H; Péret, Benjamin; Oliva, Marina; Swarup, Ranjan; Sairanen, Ilkka; Parry, Geraint; Ljung, Karin; Beeckman, Tom; Garibaldi, Jonathan M; Estelle, Mark; Owen, Markus R; Vissenberg, Kris; Hodgman, T Charlie; Pridmore, Tony P; King, John R; Vernoux, Teva; Bennett, Malcolm J

    2012-03-20

    Gravity profoundly influences plant growth and development. Plants respond to changes in orientation by using gravitropic responses to modify their growth. Cholodny and Went hypothesized over 80 years ago that plants bend in response to a gravity stimulus by generating a lateral gradient of a growth regulator at an organ's apex, later found to be auxin. Auxin regulates root growth by targeting Aux/IAA repressor proteins for degradation. We used an Aux/IAA-based reporter, domain II (DII)-VENUS, in conjunction with a mathematical model to quantify auxin redistribution following a gravity stimulus. Our multidisciplinary approach revealed that auxin is rapidly redistributed to the lower side of the root within minutes of a 90° gravity stimulus. Unexpectedly, auxin asymmetry was rapidly lost as bending root tips reached an angle of 40° to the horizontal. We hypothesize roots use a "tipping point" mechanism that operates to reverse the asymmetric auxin flow at the midpoint of root bending. These mechanistic insights illustrate the scientific value of developing quantitative reporters such as DII-VENUS in conjunction with parameterized mathematical models to provide high-resolution kinetics of hormone redistribution.

  2. Search for Candidate Objects with the Sunyaev–Zeldovich Effect in the Radio Source Vicinities—galaxies: clusters: general

    NASA Astrophysics Data System (ADS)

    Verkhodanov, O. V.; Verkhodanova, N. V.; Ulakhovich, O. S.; Solovyov, D. I.; Khabibullina, M. L.

    2018-01-01

    Based on the data from the Westerbork Northern Sky Survey performed at a frequency of 325 MHz in the range of right ascensions 0h ≤ α < 2h and declinations 29° < δ < 78° and using multi-frequency Planck maps, we selected candidate objects with the Sunyaev-Zeldovich effect. The list of the most probable candidates includes 381 sources. It is shown that the search for such objects can be accelerated by using a priori data on the negative level of fluctuations in the CMB map with removed low multipoles in the direction to radio sources.

  3. Constraining the Thermal Contents of X-Ray Cavities in Galaxy Clusters with Sunyaev Zel'dovich Effect Observations

    NASA Astrophysics Data System (ADS)

    Abdulla, Zubair M.

    We use Sunyaev Zel'dovich Effect observations at 30 GHz with the Combined Array for Research in Millimeter Astronomy (CARMA) to probe the thermal contents of X-ray cavities in the galaxy cluster MS 0735+741 (MS0735). The hot (3-10 keV), diffuse X-ray emitting atmospheres of galaxy clusters should quickly radiate away its thermal energy via radiative cooling. However, high-resolution X-ray observations from Chandra and XMM have shown that the gas is not cooling to low temperatures at the rates expected, suggesting that the radiative cooling is being balanced by non-gravitational sources of heating. Of primary interest is the energy output from active galactic nuclei (AGN), outbursts from accreting super massive black holes at the center of clusters, which drive radio jets into the atmospheres of clusters and terminate in spectacular radio lobes. High resolution X-ray images have revealed giant cavities produced by the radio lobes displacing the X-ray emitting gas, providing a gauge for the mean mechanical power output of the AGN. These measured powers are enough to offset radiative cooling at the center of relaxed clusters, however, little beyond the energetics of the outbursts is known. The relative balance and efficiency of heating mechanisms for converting the mechanical energy from the AGN into thermal energy in the cluster atmosphere is not well understood, nor are the details of the jets whose contents inflate and support the X-ray cavities. The Sunyaev-Zel'dovich (SZ) effect, which is proportional to the line-of-sight pressure of the electrons of the hot gas in galaxy clusters, can shed light on these outstanding issues by directly constraining the thermal contents of the radio-filled X-ray cavities. In this work, we describe the assembly and commissioning of 1-cm cryogenic receivers for CARMA, which are vital for the high-fidelity SZ observations required for the proposed measurements. CARMA is a 23-element heterogeneous radio interferometer in Cedar Flat

  4. Planck intermediate results: XL. The Sunyaev-Zeldovich signal from the Virgo cluster

    DOE PAGES

    Ade, P. A. R.; Aghanim, N.; Arnaud, M.; ...

    2016-12-12

    The Virgo cluster is the largest Sunyaev-Zeldovich (SZ) source in the sky, both in terms of angular size and total integrated flux. Planck’s wide angular scale and frequency coverage, together with its high sensitivity, enable a detailed study of this big object through the SZ effect. Virgo is well resolved by Planck, showing an elongated structure that correlates well with the morphology observed from X-rays, but extends beyond the observed X-ray signal. We find good agreement between the SZ signal (or Compton parameter, y c) observed by Planck and the expected signal inferred from X-ray observations and simple analytical models.more » Owing to its proximity to us, the gas beyond the virial radius in Virgo can be studied with unprecedented sensitivity by integrating the SZ signal over tens of square degrees. In this paper, we study the signal in the outskirts of Virgo and compare it with analytical models and a constrained simulation of the environment of Virgo. Planck data suggest that significant amounts of low-density plasma surround Virgo, out to twice the virial radius. We find the SZ signal in the outskirts of Virgo to be consistent with a simple model that extrapolates the inferred pressure at lower radii, while assuming that the temperature stays in the keV range beyond the virial radius. The observed signal is also consistent with simulations and points to a shallow pressure profile in the outskirts of the cluster. This reservoir of gas at large radii can be linked with the hottest phase of the elusivewarm/hot intergalactic medium. Taking the lack of symmetry of Virgo into account, we find that a prolate model is favoured by the combination of SZ and X-ray data, in agreement with predictions. In conclusion, based on the combination of the same SZ and X-ray data, we constrain the total amount of gas in Virgo. Under the hypothesis that the abundance of baryons in Virgo is representative of the cosmic average, we also infer a distance for Virgo of

  5. Planck intermediate results. XL. The Sunyaev-Zeldovich signal from the Virgo cluster

    NASA Astrophysics Data System (ADS)

    Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartolo, N.; Battaner, E.; Benabed, K.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cardoso, J.-F.; Catalano, A.; Chamballu, A.; Chiang, H. C.; Christensen, P. R.; Churazov, E.; Clements, D. L.; Colombo, L. P. L.; Combet, C.; Comis, B.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Dickinson, C.; Diego, J. M.; Dolag, K.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Galeotta, S.; Galli, S.; Ganga, K.; Giard, M.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Hansen, F. K.; Harrison, D. L.; Helou, G.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leonardi, R.; Levrier, F.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maffei, B.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Marcos-Caballero, A.; Maris, M.; Martin, P. G.; Martínez-González, E.; Masi, S.; Matarrese, S.; Mazzotta, P.; Meinhold, P. R.; Melchiorri, A.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Noviello, F.; Novikov, D.; Novikov, I.; Oppermann, N.; Oxborrow, C. A.; Pagano, L.; Pajot, F.; Paoletti, D.; Pasian, F.; Pearson, T. J.; Perdereau, O.; Perotto, L.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Pratt, G. W.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Schaefer, B. M.; Scott, D.; Soler, J. D.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; Weller, J.; Yvon, D.; Zacchei, A.; Zonca, A.

    2016-12-01

    The Virgo cluster is the largest Sunyaev-Zeldovich (SZ) source in the sky, both in terms of angular size and total integrated flux. Planck's wide angular scale and frequency coverage, together with its high sensitivity, enable a detailed study of this big object through the SZ effect. Virgo is well resolved by Planck, showing an elongated structure that correlates well with the morphology observed from X-rays, but extends beyond the observed X-ray signal. We find good agreement between the SZ signal (or Compton parameter, yc) observed by Planck and the expected signal inferred from X-ray observations and simple analytical models. Owing to its proximity to us, the gas beyond the virial radius in Virgo can be studied with unprecedented sensitivity by integrating the SZ signal over tens of square degrees. We study the signal in the outskirts of Virgo and compare it with analytical models and a constrained simulation of the environment of Virgo. Planck data suggest that significant amounts of low-density plasma surround Virgo, out to twice the virial radius. We find the SZ signal in the outskirts of Virgo to be consistent with a simple model that extrapolates the inferred pressure at lower radii, while assuming that the temperature stays in the keV range beyond the virial radius. The observed signal is also consistent with simulations and points to a shallow pressure profile in the outskirts of the cluster. This reservoir of gas at large radii can be linked with the hottest phase of the elusivewarm/hot intergalactic medium. Taking the lack of symmetry of Virgo into account, we find that a prolate model is favoured by the combination of SZ and X-ray data, in agreement with predictions. Finally, based on the combination of the same SZ and X-ray data, we constrain the total amount of gas in Virgo. Under the hypothesis that the abundance of baryons in Virgo is representative of the cosmic average, we also infer a distance for Virgo of approximately 18 Mpc, in good

  6. An international conference in honour of the centennial of the birth of Ya.B. Zeldovich, "Subatomic Particles, Nucleons, Atoms, the Universe: Processes and Structure"

    NASA Astrophysics Data System (ADS)

    Kilin, S. Ya.; Ruffini, R.; Vereshchagin, G.

    2015-06-01

    An international conference in honour of the centennial of the birth of Ya.B. Zeldovich, "Subatomic Particles, Nucleons, Atoms, the Universe: Processes and Structure" was held in Minsk, Belarus on March 10-14, 2014. Scientific papers based on plenary presentations made at this conference are being published in Volumes 6 and 7, 2015 of "Astronomy Reports."

  7. Mechanism of How Salt-Gradient-Induced Charges Affect the Translocation of DNA Molecules through a Nanopore

    PubMed Central

    He, Yuhui; Tsutsui, Makusu; Scheicher, Ralph H.; Fan, Chun; Taniguchi, Masateru; Kawai, Tomoji

    2013-01-01

    Experiments using nanopores demonstrated that a salt gradient enhances the capture rate of DNA and reduces its translocation speed. These two effects can help to enable electrical DNA sequencing with nanopores. Here, we provide a quantitative theoretical evaluation that shows the positive net charges, which accumulate around the pore entrance due to the salt gradient, are responsible for the two observed effects: they reinforce the electric capture field, resulting in promoted molecule capture rate; and they induce cationic electroosmotic flow through the nanopore, thus significantly retarding the motion of the anionic DNA through the nanopore. Our multiphysical simulation results show that, during the polymer trapping stage, the former effect plays the major role, thus resulting in promoted DNA capture rate, while during the nanopore-penetrating stage the latter effect dominates and consequently reduces the DNA translocation speed significantly. Quantitative agreement with experimental results has been reached by further taking nanopore wall surface charges into account. PMID:23931325

  8. Regular and chaotic dynamics of non-spherical bodies. Zeldovich's pancakes and emission of very long gravitational waves

    NASA Astrophysics Data System (ADS)

    Bisnovatyi-Kogan, G. S.; Tsupko, O. Yu.

    2015-10-01

    > In this paper we review a recently developed approximate method for investigation of dynamics of compressible ellipsoidal figures. Collapse and subsequent behaviour are described by a system of ordinary differential equations for time evolution of semi-axes of a uniformly rotating, three-axis, uniform-density ellipsoid. First, we apply this approach to investigate dynamic stability of non-spherical bodies. We solve the equations that describe, in a simplified way, the Newtonian dynamics of a self-gravitating non-rotating spheroidal body. We find that, after loss of stability, a contraction to a singularity occurs only in a pure spherical collapse, and deviations from spherical symmetry prevent the contraction to the singularity through a stabilizing action of nonlinear non-spherical oscillations. The development of instability leads to the formation of a regularly or chaotically oscillating body, in which dynamical motion prevents the formation of the singularity. We find regions of chaotic and regular pulsations by constructing a Poincaré diagram. A real collapse occurs after damping of the oscillations because of energy losses, shock wave formation or viscosity. We use our approach to investigate approximately the first stages of collapse during the large scale structure formation. The theory of this process started from ideas of Ya. B. Zeldovich, concerning the formation of strongly non-spherical structures during nonlinear stages of the development of gravitational instability, known as `Zeldovich's pancakes'. In this paper the collapse of non-collisional dark matter and the formation of pancake structures are investigated approximately. Violent relaxation, mass and angular momentum losses are taken into account phenomenologically. We estimate an emission of very long gravitational waves during the collapse, and discuss the possibility of gravitational lensing and polarization of the cosmic microwave background by these waves.

  9. Assembly processes under severe abiotic filtering: adaptation mechanisms of weed vegetation to the gradient of soil constraints.

    PubMed

    Nikolic, Nina; Böcker, Reinhard; Kostic-Kravljanac, Ljiljana; Nikolic, Miroslav

    2014-01-01

    Effects of soil on vegetation patterns are commonly obscured by other environmental factors; clear and general relationships are difficult to find. How would community assembly processes be affected by a substantial change in soil characteristics when all other relevant factors are held constant? In particular, can we identify some functional adaptations which would underpin such soil-induced vegetation response? Eastern Serbia: fields partially damaged by long-term and large-scale fluvial deposition of sulphidic waste from a Cu mine; subcontinental/submediterranean climate. We analysed the multivariate response of cereal weed assemblages (including biomass and foliar analyses) to a strong man-made soil gradient (from highly calcareous to highly acidic, nutrient-poor soils) over short distances (field scale). The soil gradient favoured a substitution of calcicoles by calcifuges, and an increase in abundance of pseudometallophytes, with preferences for Atlantic climate, broad geographical distribution, hemicryptophytic life form, adapted to low-nutrient and acidic soils, with lower concentrations of Ca, and very narrow range of Cu concentrations in leaves. The trends of abundance of the different ecological groups of indicator species along the soil gradient were systematically reflected in the maintenance of leaf P concentrations, and strong homeostasis in biomass N:P ratio. Using annual weed vegetation at the field scale as a fairly simple model, we demonstrated links between gradients in soil properties (pH, nutrient availability) and floristic composition that are normally encountered over large geographic distances. We showed that leaf nutrient status, in particular the maintenance of leaf P concentrations and strong homeostasis of biomass N:P ratio, underpinned a clear functional response of vegetation to mineral stress. These findings can help to understand assembly processes leading to unusual, novel combinations of species which are typically observed as a

  10. Assembly Processes under Severe Abiotic Filtering: Adaptation Mechanisms of Weed Vegetation to the Gradient of Soil Constraints

    PubMed Central

    Nikolic, Nina; Böcker, Reinhard; Kostic-Kravljanac, Ljiljana; Nikolic, Miroslav

    2014-01-01

    Questions Effects of soil on vegetation patterns are commonly obscured by other environmental factors; clear and general relationships are difficult to find. How would community assembly processes be affected by a substantial change in soil characteristics when all other relevant factors are held constant? In particular, can we identify some functional adaptations which would underpin such soil-induced vegetation response? Location Eastern Serbia: fields partially damaged by long-term and large-scale fluvial deposition of sulphidic waste from a Cu mine; subcontinental/submediterranean climate. Methods We analysed the multivariate response of cereal weed assemblages (including biomass and foliar analyses) to a strong man-made soil gradient (from highly calcareous to highly acidic, nutrient-poor soils) over short distances (field scale). Results The soil gradient favoured a substitution of calcicoles by calcifuges, and an increase in abundance of pseudometallophytes, with preferences for Atlantic climate, broad geographical distribution, hemicryptophytic life form, adapted to low-nutrient and acidic soils, with lower concentrations of Ca, and very narrow range of Cu concentrations in leaves. The trends of abundance of the different ecological groups of indicator species along the soil gradient were systematically reflected in the maintenance of leaf P concentrations, and strong homeostasis in biomass N:P ratio. Conclusion Using annual weed vegetation at the field scale as a fairly simple model, we demonstrated links between gradients in soil properties (pH, nutrient availability) and floristic composition that are normally encountered over large geographic distances. We showed that leaf nutrient status, in particular the maintenance of leaf P concentrations and strong homeostasis of biomass N:P ratio, underpinned a clear functional response of vegetation to mineral stress. These findings can help to understand assembly processes leading to unusual, novel combinations

  11. Study of adhesion and friction properties on a nanoparticle gradient surface: transition from JKR to DMT contact mechanics.

    PubMed

    Ramakrishna, Shivaprakash N; Nalam, Prathima C; Clasohm, Lucy Y; Spencer, Nicholas D

    2013-01-08

    We have previously investigated the dependence of adhesion on nanometer-scale surface roughness by employing a roughness gradient. In this study, we correlate the obtained adhesion forces on nanometer-scale rough surfaces to their frictional properties. A roughness gradient with varying silica particle (diameter ≈ 12 nm) density was prepared, and adhesion and frictional forces were measured across the gradient surface in perfluorodecalin by means of atomic force microscopy with a polyethylene colloidal probe. Similarly to the pull-off measurements, the frictional forces initially showed a reduction with decreasing particle density and later an abrupt increase as the colloidal sphere began to touch the flat substrate beneath, at very low particle densities. The friction-load relation is found to depend on the real contact area (A(real)) between the colloid probe and the underlying particles. At high particle density, the colloidal sphere undergoes large deformations over several nanoparticles, and the contact adhesion (JKR type) dominates the frictional response. However, at low particle density (before the colloidal probe is in contact with the underlying surface), the colloidal sphere is suspended by a few particles only, resulting in local deformations of the colloid sphere, with the frictional response to the applied load being dominated by long-range, noncontact (DMT-type) interactions with the substrate beneath.

  12. Fast ion stabilization of the ion temperature gradient driven modes in the Joint European Torus hybrid-scenario plasmas: a trigger mechanism for internal transport barrier formation

    NASA Astrophysics Data System (ADS)

    Romanelli, M.; Zocco, A.; Crisanti, F.; Contributors, JET-EFDA

    2010-04-01

    Understanding and modelling turbulent transport in thermonuclear fusion plasmas are crucial for designing and optimizing the operational scenarios of future fusion reactors. In this context, plasmas exhibiting state transitions, such as the formation of an internal transport barrier (ITB), are particularly interesting since they can shed light on transport physics and offer the opportunity to test different turbulence suppression models. In this paper, we focus on the modelling of ITB formation in the Joint European Torus (JET) [1] hybrid-scenario plasmas, where, due to the monotonic safety factor profile, magnetic shear stabilization cannot be invoked to explain the transition. The turbulence suppression mechanism investigated here relies on the increase in the plasma pressure gradient in the presence of a minority of energetic ions. Microstability analysis of the ion temperature gradient driven modes (ITG) in the presence of a fast-hydrogen minority shows that energetic ions accelerated by the ion cyclotron resonance heating (ICRH) system (hydrogen, nH,fast/nD,thermal up to 10%, TH,fast/TD,thermal up to 30) can increase the pressure gradient enough to stabilize the ITG modes driven by the gradient of the thermal ions (deuterium). Numerical analysis shows that, by increasing the temperature of the energetic ions, electrostatic ITG modes are gradually replaced by nearly electrostatic modes with tearing parity at progressively longer wavelengths. The growth rate of the microtearing modes is found to be lower than that of the ITG modes and comparable to the local E × B-velocity shearing rate. The above mechanism is proposed as a possible trigger for the formation of ITBs in this type of discharges.

  13. Modeling Study: Mechanism of Foam Propagation in Porous Media at Different Levels of Minimum Mobilization Pressure Gradient

    NASA Astrophysics Data System (ADS)

    Izadi, M.; Kam, S.

    2017-12-01

    Scope: Numerous laboratory and field tests revealed that foam can effectively control gas mobility and improve sweep efficiency in enhanced-oil-recovery and subsurface-remediation processes, if correctly designed. The objective of this study is to answer (i) how mechanistic foam model parameters can be determined by fitting lab experiments in a step-by-step manner; (ii) how different levels of mobilization pressure gradient for foam generation affects the fundamentals of foam propagation; and (iii) how foam propagation distance can be estimated in the subsurface. This study for the first time shows why, and by how much, supercritical CO2 foams are advantaged over other types of foams such as N2 foam. Methods: First of all, by borrowing experimental data existing in the literature, this study shows how to capture mechanistic foam model parameters. The model, then, is applied to a wide range of mobilization pressure gradient to represent different types of foams that have been applied in the field (Note that supercritical CO2 foams exhibit much lower mobilization pressure compared to other types of foams (N2, steam, air, etc.). Finally, the model and parameters are used to evaluate different types of foam injection scenarios in order to predict how far foams can propagate with what properties in the field condition. Results and Conclusions: The results show that (i) the presence of three different foam states (strong, weak, intermediate) as well as two different strong-foam flow regimes (high-quality and low-quality regimes) plays a key role in model fit and field-scale propagation prediction and (ii) the importance of complex non-Newtonian foam rheology should not be underestimated. More specifically, this study finds that (i) supercritical CO2 foams can propagate a few hundreds of feet easily, which is a few orders of magnitude higher than other foams such as N2 foams; (ii) for dry foams (or, strong foams in the high-quality regime), the higher gas fractions the

  14. Do Work-Related Mechanical and Psychosocial Factors Contribute to the Social Gradient in Low Back Pain?: A 3-Year Follow-Up Study of the General Working Population in Norway.

    PubMed

    Sterud, Tom; Johannessen, Håkon A; Tynes, Tore

    2016-07-01

    A prospective cohort study. The aim of the study was to investigate the extent to which work-related factors contribute to the social gradient in low back pain (LBP). A social gradient in LBP is well established, but only a few studies have examined the extent to which exposure to mechanical and psychosocial work environment factors is a pathway for this gradient. A randomly drawn cohort from the general population in Norway aged 18 to 66 years was followed up for 3 years (n = 12,550, response rate at baseline = 67%). Eligible respondents were in paid work during 2006 and 2009 (n = 6819). Based on administrative register data respondents were coded into five educational levels (university/college ≥4 years was set as the reference group). Outcome of interest was self-reported moderate or severe LBP at follow-up adjusted for baseline LBP. In total, 11.2% (397 individuals) men and 14.5% (461 individual) women reported LBP at follow-up. There was a strong social gradient ranging from 16.4% (elementary) to 6.4% (university/college ≥4 years). The corresponding figures among women were 22.4% and 7.5%. Corrected for age, LBP at baseline and working hours, educational level was a significant predictor of LBP at follow-up (odds ratios 1.8-2.3 in men and 1.7-3.1 in women). Adjusting for mechanical factors reduced the gradient by 39% to 43% in men and 28% to 34% in women. Adjusting for psychosocial factors reduced the gradient by 5% to 12% in men and increased the gradient by 7% to 11% in women. Work-related mechanical factors contributed substantially to the social gradient in LBP among both men and women. The impact of psychosocial factors was modest among men and contributed to an increased gradient among women. 3.

  15. Autocrine A2 in the T-System of Ventricular Myocytes Creates Transmural Gradients in Ion Transport: A Mechanism to Match Contraction with Load?

    PubMed Central

    Gao, Junyuan; Sun, Xiurong; Potapova, Irina A.; Cohen, Ira S.; Mathias, Richard T.; Kim, Jeremy H.

    2014-01-01

    Transmural heterogeneities in Na/K pump current (IP), transient outward K+-current (Ito), and Ca2+-current (ICaL) play an important role in regulating electrical and contractile activities in the ventricular myocardium. Prior studies indicated angiotensin II (A2) may determine the transmural gradient in Ito, but the effects of A2 on IP and ICaL were unknown. In this study, myocytes were isolated from five muscle layers between epicardium and endocardium. We found a monotonic gradient in both Ip and Ito, with the lowest currents in ENDO. When AT1Rs were inhibited, EPI currents were unaffected, but ENDO currents increased, suggesting endogenous extracellular A2 inhibits both currents in ENDO. IP- and Ito-inhibition by A2 yielded essentially the same K0.5 values, so they may both be regulated by the same mechanism. A2/AT1R-mediated inhibition of IP or Ito or stimulation of ICaL persisted for hours in isolated myocytes, suggesting continuous autocrine secretion of A2 into a restricted diffusion compartment, like the T-system. Detubulation brought EPI IP to its low ENDO value and eliminated A2 sensitivity, so the T-system lumen may indeed be the restricted diffusion compartment. These studies showed that 33–50% of IP, 57–65% of Ito, and a significant fraction of ICaL reside in T-tubule membranes where they are transmurally regulated by autocrine secretion of A2 into the T-system lumen and activation of AT1Rs. Increased AT1R activation regulates each of these currents in a direction expected to increase contractility. Endogenous A2 activation of AT1Rs increases monotonically from EPI to ENDO in a manner similar to reported increases in passive tension when the ventricular chamber fills with blood. We therefore hypothesize load is the signal that regulates A2-activation of AT1Rs, which create a contractile gradient that matches the gradient in load. PMID:24896115

  16. Evolutionary trade-offs between drought resistance mechanisms across a precipitation gradient in a seasonally dry tropical oak (Quercus oleoides).

    PubMed

    Ramírez-Valiente, Jose A; Cavender-Bares, Jeannine

    2017-07-01

    In seasonally dry tropical forest regions, drought avoidance during the dry season coupled with high assimilation rates in the wet season is hypothesized to be an advantageous strategy for forest trees in regions with severe and long dry seasons. In contrast, where dry seasons are milder, drought tolerance coupled with a conservative resource-use strategy is expected to maximize carbon assimilation throughout the year. Tests of this hypothesis, particularly at the intraspecific level, have been seldom conducted. In this study, we tested the extent to which drought resistance mechanisms and rates of carbon assimilation have evolved under climates with varying dry season length and severity within Quercus oleoidesCham. and Schlect., a tropical dry forest species that is widely distributed in Central America. For this purpose, we conducted a greenhouse experiment where seedlings originating from five populations that vary in rainfall patterns were grown under different watering treatments. Our results revealed that populations from xeric climates with more severe dry seasons exhibited large mesophyllous leaves (with high specific leaf area, SLA), and leaf abscission in response to drought, consistent with a drought-avoidance strategy. In contrast, populations from more mesic climates with less severe dry seasons had small and thick sclerophyllous leaves with low SLA and reduced water potential at the turgor loss point (πtlp), consistent with a drought-tolerance strategy. Mesic populations also showed high plasticity in πtlp in response to water availability, indicating that osmotic adjustment to drought is an important component of this strategy. However, populations with mesophyllous leaves did not have higher maximum carbon assimilation rates under well-watered conditions. Furthermore, SLA was negatively associated with mass-based photosynthetic rates, contrary to expectations of the leaf economics spectrum, indicating that drought-resistance strategies are not

  17. Do work-related mechanical and psychosocial factors contribute to the social gradient in long-term sick leave: a prospective study of the general working population in Norway.

    PubMed

    Sterud, Tom; Johannessen, Håkon A

    2014-05-01

    A social gradient in long-term sick leave (LTSL) rates is well established, but only a few studies have examined to what extent this gradient may be explained by mechanical and psychosocial work environment factors. A randomly drawn cohort from the general population in Norway, aged 18-69 years, was interviewed in the second half of 2009 (n=12,255, response at baseline 60.9%) and followed up in national registries to the end of 2010. Eligible respondents were registered with an active employee relationship of at least 100 actual working days in 2009 and 2010 (n=6758). Based on administrative register data, respondents were coded into five educational levels (university/college ≥4 years was set as the reference group). Eight work-related psychosocial factors and 10 mechanical exposures were measured. The outcome of interest was medically confirmed LTSL ≥40 working days during 2010. In total, 9.4% (635 individuals) were classified with LTSL during 2010. There was a strong social gradient ranging from 12.4% (elementary) to 3.3% (university/college ≥4 years) among men. The corresponding figures among women were 15.4 and 4.6%. Adjusting for work-related mechanical and psychosocial factors explained between 41 and 44% of the social gradient in men. Among women, the corresponding figures were 31 and 54%. Work-related mechanical and psychosocial factors contribute to the social gradient in LTSL. The work-related factors that accounted for this gradient were rather similar for men and women.

  18. Zel'dovich Λ and Weinberg's relation: an explanation for the cosmological coincidences

    NASA Astrophysics Data System (ADS)

    Alfonso-Faus, Antonio

    2008-11-01

    In 1937 Dirac proposed the large number hypothesis (LNH). The idea was to explain that these numbers were large because the Universe is old. A time variation of certain “constants” was assumed. So far, no experimental evidence has significantly supported this time variation. Here we present a simplified cosmological model. We propose a new cosmological system of units, including a cosmological Planck’s constant that “absorbs” the well known large number 10120. With this new Planck’s constant no large numbers appear at the cosmological level. They appear at lower levels, e.g. at the quantum world. We note here that Zel’dovich formula, for the cosmological constant Λ, is equivalent to the Weinberg’s relation. The immediate conclusion is that the speed of light c must be proportional to the Hubble parameter H, and therefore decrease with time. We find that the gravitational radius of the Universe and its size are one and the same constant (Mach’s principle). The usual cosmological Ω’s parameters for mass, lambda and curvature turn out to be all constants of order one. The anthropic principle is not necessary in this theory. It is shown that a factor of 1061 converts in this theory a Planck fluctuation (a quantum black hole) into a cosmological quantum black hole: the Universe today. General relativity and quantum mechanics give the same local solution of an expanding Universe with the law a( t)≈constṡ t. This constant is just the speed of light today. Then the Hubble parameter is exactly H= a( t)'/ a( t)=1/ t.

  19. Comparison of two equation-of-state models for partially ionized aluminum: Zel'dovich and Raizer's model versus the activity expansion code

    NASA Astrophysics Data System (ADS)

    Harrach, Robert J.; Rogers, Forest J.

    1981-09-01

    Two equation-of-state (EOS) models for multipy ionized matter are evaluated for the case of an aluminum plasma in the temperature range from about one eV to several hundred eV, spanning conditions of weak to strong ionization. Specifically, the simple analytical mode of Zel'dovich and Raizer and the more comprehensive model comprised by Rogers' plasma physics avtivity expansion code (ACTEX) are used to calculate the specific internal energy ɛ and average degree of ionization Z¯*, as functons of temperature T and density ρ. In the absence of experimental data, these results are compared against each other, covering almost five orders-of-magnitude variation in ɛ and the full range of Z¯* We find generally good agreement between the two sets of results, especially for low densities and for temperatures near the upper end of the rage. Calculated values of ɛ(T) agree to within ±30% over nearly the full range in T for densities below about 1 g/cm3. Similarly, the two models predict values of Z¯*(T) which track each other fairly well; above 20 eV the discrepancy is less than ±20% fpr ρ≲1 g/cm3. Where the calculations disagree, we expect the ACTEX code to be more accurate than Zel'dovich and Raizer's model, by virtue of its more detailed physics content.

  20. Effect and mechanism of a High Gradient Magnetic Separation (HGMS) and Ultraviolet (UV) composite process on the inactivation of microbes in ballast water.

    PubMed

    Ren, Zhijun; Zhang, Lin; Shi, Yue; Leng, Xiaodong; Shao, Jingchao

    2016-07-15

    The patented technology of a High Gradient Magnetic Separation (HGMS)-Ultraviolet (UV) composite process was used to treat ballast water. Staphylococcus aureus (S. aureus) was selected as the reference bacteria. After treatment by the HGMS-UV process, the concentration of S. aureus on the log 10 scale was lower than 2 at different flow rates, S. aureus suffered the most serious damage, and K(+) leakage of the bacteria was 1.73mg/L higher than separate 60min UV irradiation (1.17mg/L) and HGMS (0.12mg/L) processes. These results demonstrated that the HGMS-UV composite process was an effective approach to treat ballast water. Further, the HGMS process had synergistic action on the subsequent UV irradiation process and accelerated cell membrane damage. Meanwhile, the results of superoxide dismutase (SOD) activities of bacteria and DNA band analyses indicated that the inactivation mechanisms were different for HGMS and UV irradiation. Copyright © 2016 Elsevier Ltd. All rights reserved.

  1. Gradient-based optimization with B-splines on sparse grids for solving forward-dynamics simulations of three-dimensional, continuum-mechanical musculoskeletal system models.

    PubMed

    Valentin, J; Sprenger, M; Pflüger, D; Röhrle, O

    2018-05-01

    Investigating the interplay between muscular activity and motion is the basis to improve our understanding of healthy or diseased musculoskeletal systems. To be able to analyze the musculoskeletal systems, computational models are used. Albeit some severe modeling assumptions, almost all existing musculoskeletal system simulations appeal to multibody simulation frameworks. Although continuum-mechanical musculoskeletal system models can compensate for some of these limitations, they are essentially not considered because of their computational complexity and cost. The proposed framework is the first activation-driven musculoskeletal system model, in which the exerted skeletal muscle forces are computed using 3-dimensional, continuum-mechanical skeletal muscle models and in which muscle activations are determined based on a constraint optimization problem. Numerical feasibility is achieved by computing sparse grid surrogates with hierarchical B-splines, and adaptive sparse grid refinement further reduces the computational effort. The choice of B-splines allows the use of all existing gradient-based optimization techniques without further numerical approximation. This paper demonstrates that the resulting surrogates have low relative errors (less than 0.76%) and can be used within forward simulations that are subject to constraint optimization. To demonstrate this, we set up several different test scenarios in which an upper limb model consisting of the elbow joint, the biceps and triceps brachii, and an external load is subjected to different optimization criteria. Even though this novel method has only been demonstrated for a 2-muscle system, it can easily be extended to musculoskeletal systems with 3 or more muscles. Copyright © 2018 John Wiley & Sons, Ltd.

  2. Study on the effects of gradient mechanical pressures on the proliferation, apoptosis, chondrogenesis and hypertrophy of mandibular condylar chondrocytes in vitro.

    PubMed

    Li, Hui; Huang, Linjian; Xie, Qianyang; Cai, Xieyi; Yang, Chi; Wang, Shaoyi; Zhang, Min

    2017-01-01

    To investigate the effects of gradient mechanical pressure on chondrocyte proliferation, apoptosis, and the expression of markers of chondrogenesis and chondrocyte hypertrophy. Mandibular condylar chondrocytes from 5 rabbits were cultured in vitro, and pressed with static pressures of 50kPa, 100kPa, 150kPa and 200kPa for 3h, respectively. The chondrocytes cultured without pressure (0kPa) were used as control. Cell proliferation, apoptosis, and the expression of aggrecan (AGG), collagen II (COL2), collagen X (COL10), alkaline phosphatase (ALP) were investigated. Ultrastructures of the pressurized chondrocytes under transmission electron microscopy (TEM) were observed. Chondrocyte proliferation increased at 100kPa and decreased at 200kPa. Chondrocyte apoptosis increased with peak pressure at 200kPa in a dose-dependent manner. Chondrocyte necrosis increased at 200kPa. The expression of AGG increased at 200kPa. The expression of COL2 decreased at 50kPa and increased at 150kPa. The expression of COL10 and ALP increased at 150kPa. Ultrastructure of the pressurized chondrocytes under TEM showed: at 100kPa, cells were enlarged with less cellular microvillus and a bigger nucleus; at 200kPa, cells shrank with the sign of apoptosis, and apoptosis cells were found. The mechanical loading of 150kPa is the moderate pressure for chondrocyte: cell proliferation and apoptosis is balanced, necrosis is reduced, and chondrogenesis and chondrocyte hypertrophy are promoted. When the pressure is lower, chondrogenesis and chondrocyte hypertrophy are inhibited. At 200kPa, degeneration of cartilage is implied. Copyright © 2016 Elsevier Ltd. All rights reserved.

  3. Optimum gradient of mountain paths.

    PubMed

    Minetti, A E

    1995-11-01

    By combining the experiment results of R. Margaria (Atti Accad. Naz. Lincei Memorie 7: 299-368, 1938), regarding the metabolic cost of gradient locomotion, together with recent insights on gait biomechanics, a prediction about the most economical gradient of mountain paths (approximately 25%) is obtained and interpreted. The pendulum-like mechanism of walking produces a waste of mechanical work against gravity within the gradient range of up to 15% (the overall efficiency is dominated by the low transmission efficiency), whereas for steeper values only the muscular efficiency is responsible for the (slight) metabolic change (per meter of vertical displacement) with respect to gradient. The speeds at the optimum gradient turned out to be approximately 0.65 m/s (+0.16 m/s vertical) and 1.50 m/s (-0.36 m/s vertical), for uphill and downhill walking, respectively, and the ascensional energy expenditure was 0.4 and 2.0 ml O2.kg body mass-1.vertical m-1 climbed or descended. When the metabolic power becomes a burden, as in high-altitude mountaineering, the optimum gradient should be reduced. A sample of real mountain path gradients, experimentally measured, mimics the obtained predictions.

  4. The Linear Bias in the Zeldovich Approximation and a Relation between the Number Density and the Linear Bias of Dark Halos

    NASA Astrophysics Data System (ADS)

    Fan, Zuhui

    2000-01-01

    The linear bias of the dark halos from a model under the Zeldovich approximation is derived and compared with the fitting formula of simulation results. While qualitatively similar to the Press-Schechter formula, this model gives a better description for the linear bias around the turnaround point. This advantage, however, may be compromised by the large uncertainty of the actual behavior of the linear bias near the turnaround point. For a broad class of structure formation models in the cold dark matter framework, a general relation exists between the number density and the linear bias of dark halos. This relation can be readily tested by numerical simulations. Thus, instead of laboriously checking these models one by one, numerical simulation studies can falsify a whole category of models. The general validity of this relation is important in identifying key physical processes responsible for the large-scale structure formation in the universe.

  5. Elevational Gradient in Species Richness Pattern of Epigaeic Beetles and Underlying Mechanisms at East Slope of Balang Mountain in Southwestern China

    PubMed Central

    Yu, Xiao-Dong; Lü, Liang; Luo, Tian-Hong; Zhou, Hong-Zhang

    2013-01-01

    We report on the species richness patterns of epigaeic beetles (Coleoptera: Carabidae and Staphylinidae) along a subtropical elevational gradient of Balang Mountain, southwestern China. We tested the roles of environmental factors (e.g. temperature, area and litter cover) and direct biotic interactions (e.g. foods and antagonists) that shape elevational diversity gradients. Beetles were sampled at 19 sites using pitfall traps along the studied elevational gradient ranging from 1500 m–4000 m during the 2004 growing season. A total of 74416 specimens representing 260 species were recorded. Species richness of epigaeic beetles and two families showed unimodal patterns along the elevational gradient, peaking at mid-elevations (c. 2535 m), and the ranges of most beetle species were narrow along the gradient. The potential correlates of both species richness and environmental variables were examined using linear and second order polynomial regressions. The results showed that temperature, area and litter cover had strong explanatory power of beetle species richness for nearly all richness patterns, of beetles as a whole and of Carabidae and Staphylinidae, but the density of antagonists was associated with species richness of Carabidae only. Multiple regression analyses suggested that the three environmental factors combined contributed most to richness patterns for most taxa. The results suggest that environmental factors associated with temperature, area and habitat heterogeneity could account for most variation in richness pattern of epigaeic beetles. Additionally, the mid-elevation peaks and the small range size of most species indicate that conservation efforts should give attention to the entire gradient rather than just mid-elevations. PMID:23874906

  6. The turbulent boundary layer on a porous plate: An experimental study of the fluid mechanics for adverse free stream pressure gradients

    NASA Technical Reports Server (NTRS)

    Anderson, P. S.; Kays, W. M.; Moffat, R. J.

    1972-01-01

    An experimental investigation of transpired turbulent boundary layers in zero and adverse pressure gradients has been carried out. Profiles of: (1) the mean velocity, (2) the three intensities of the turbulent fluctuations, and (3) the Reynolds stress were obtained by hot-wire anemometry. The friction coefficients were measured by using an integrated form of the boundary layer equation to extrapolate the measured shear stress profiles to the wall.

  7. The Distance and Mass of the Galaxy Cluster Abell 1995 Derived from Sunyaev-Zeldovich Effect and X-Ray Measurements

    NASA Technical Reports Server (NTRS)

    Patel, Sandeep K.; Joy, Marshall; Carlstrom, John E.; Holder, Gilbert P.; Reese, Erik D.; Gomez, Percy L.; Hughes, John P.; Grego, Laura; Holzapfel, William L.

    2000-01-01

    We present multiwavelength observations of the Abell 1995 galaxy cluster. From an analysis of X-ray spectroscopy and imaging data, we derive the electron temperature, cluster core radius, and central electron number density. Using optical spectroscopy of 15 cluster members, we derive an accurate cluster redshift and velocity dispersion. Finally, the interferometric imaging of the Sunyaev-Zeldovich effect toward Abell 1995 at 28.5 GHz provides a measure of the integrated pressure through the cluster. The X-ray and Sunyaev-Zeldovich effect observations are combined to determine the angular diameter distance to the cluster of D(sub A) = 1294(sup +294 +438, sub -283 -458) Mpc (Statistical followed by systematic uncertainty), implying a Hubble constant of H(sub 0) = 52.2(sup +11.4 +18.5, sub -11.9 -17.7) km/s.Mpc for Omega(sub M) = 0.3 and Omega(sub lambda) = 0.7. We find a best-fit H(sub 0) of 46 km/s.Mpc for the Omega(sub M) = 1 and Omega(sub lambda) = 0 cosmology, and 48 km/s.Mpc for Omega(sub M) = 0.3 and Omega(sub lambda) = 0.0. The X-ray data are also used to derive a total cluster mass of M(sup HSE, sub tot)(r(sub 500)) = 5.18(sup +0.62, sub -0.48) x 10(exp 14)/h solar mass; the optical velocity dispersion yields an independent and consistent estimate of M(sup virial, sub tot)(r(sub 500)) = 6.35(sup +1.51, sub -1.19) X 10(exp 14) /h solar mass. Both of the total mass estimates are evaluated at a fiducial radius, r(sub 500) = 830 /h kpc, where the overdensity is 500 times the critical density. The total cluster mass is then combined with gas mass measurements to determine a cluster gas mass fraction of F(sub g) = 0.056(sup +0.010, sub -0.013) /h(sup 3/2) in combination with recent baryon density constraints, the measured gas mass fraction yields an upper limit on the mass density parameter of Omega(sub M) h(sup 1/2) <= 0.34(sup +/0.06, sub 0.05.

  8. Analyzing the cosmic variance limit of remote dipole measurements of the cosmic microwave background using the large-scale kinetic Sunyaev Zel'dovich effect

    SciTech Connect

    Terrana, Alexandra; Johnson, Matthew C.; Harris, Mary-Jean, E-mail: aterrana@perimeterinstitute.ca, E-mail: mharris8@perimeterinstitute.ca, E-mail: mjohnson@perimeterinstitute.ca

    Due to cosmic variance we cannot learn any more about large-scale inhomogeneities from the primary cosmic microwave background (CMB) alone. More information on large scales is essential for resolving large angular scale anomalies in the CMB. Here we consider cross correlating the large-scale kinetic Sunyaev Zel'dovich (kSZ) effect and probes of large-scale structure, a technique known as kSZ tomography. The statistically anisotropic component of the cross correlation encodes the CMB dipole as seen by free electrons throughout the observable Universe, providing information about long wavelength inhomogeneities. We compute the large angular scale power asymmetry, constructing the appropriate transfer functions, andmore » estimate the cosmic variance limited signal to noise for a variety of redshift bin configurations. The signal to noise is significant over a large range of power multipoles and numbers of bins. We present a simple mode counting argument indicating that kSZ tomography can be used to estimate more modes than the primary CMB on comparable scales. A basic forecast indicates that a first detection could be made with next-generation CMB experiments and galaxy surveys. This paper motivates a more systematic investigation of how close to the cosmic variance limit it will be possible to get with future observations.« less

  9. Weak-Lensing Mass Calibration of the Atacama Cosmology Telescope Equatorial Sunyaev-Zeldovich Cluster Sample with the Canada-France-Hawaii Telescope Stripe 82 Survey

    NASA Technical Reports Server (NTRS)

    Battaglia, N.; Leauthaud, A.; Miyatake, H.; Hasseleld, M.; Gralla, M. B.; Allison, R.; Bond, J. R.; Calabrese, E.; Crichton, D.; Devlin, M. J.; hide

    2016-01-01

    Mass calibration uncertainty is the largest systematic effect for using clustersof galaxies to constrain cosmological parameters. We present weak lensing mass measurements from the Canada-France-Hawaii Telescope Stripe 82 Survey for galaxy clusters selected through their high signal-to-noise thermal Sunyaev-Zeldovich (tSZ) signal measured with the Atacama Cosmology Telescope (ACT). For a sample of 9 ACT clusters with a tSZ signal-to-noise greater than five, the average weak lensing mass is (4.8 plus or minus 0.8) times 10 (sup 14) solar mass, consistent with the tSZ mass estimate of (4.7 plus or minus 1.0) times 10 (sup 14) solar mass, which assumes a universal pressure profile for the cluster gas. Our results are consistent with previous weak-lensing measurements of tSZ-detected clusters from the Planck satellite. When comparing our results, we estimate the Eddington bias correction for the sample intersection of Planck and weak-lensing clusters which was previously excluded.

  10. Weak-lensing mass calibration of the Atacama Cosmology Telescope equatorial Sunyaev-Zeldovich cluster sample with the Canada-France-Hawaii telescope stripe 82 survey

    SciTech Connect

    Battaglia, N.; Miyatake, H.; Hasselfield, M.

    Mass calibration uncertainty is the largest systematic effect for using clusters of galaxies to constrain cosmological parameters. We present weak lensing mass measurements from the Canada-France-Hawaii Telescope Stripe 82 Survey for galaxy clusters selected through their high signal-to-noise thermal Sunyaev-Zeldovich (tSZ) signal measured with the Atacama Cosmology Telescope (ACT). For a sample of 9 ACT clusters with a tSZ signal-to-noise greater than five the average weak lensing mass is (4.8±0.8) ×10{sup 14} M{sub ⊙}, consistent with the tSZ mass estimate of (4.70±1.0) ×10{sup 14} M{sub ⊙} which assumes a universal pressure profile for the cluster gas. Our results are consistentmore » with previous weak-lensing measurements of tSZ-detected clusters from the Planck satellite. When comparing our results, we estimate the Eddington bias correction for the sample intersection of Planck and weak-lensing clusters which was previously excluded.« less

  11. The Atacama Cosmology Telescope: High-Resolution Sunyaev-Zeldovich Array Observations of ACT SZE-Selected Clusters from the Equatorial Strip

    NASA Technical Reports Server (NTRS)

    Reese, Erik; Mroczkowski, Tony; Menateau, Felipe; Hilton, Matt; Sievers, Jonathan; Aguirre, Paula; Appel, John William; Baker, Andrew J.; Bond, J. Richard; Das, Sudeep; hide

    2011-01-01

    We present follow-up observations with the Sunyaev-Zel'dovich Array (SZA) of optically-confirmed galaxy clusters found in the equatorial survey region of the Atacama Cosmology Telescope (ACT): ACT-CL J0022-0036, ACT-CL J2051+0057, and ACT-CL J2337+0016. ACT-CL J0022-0036 is a newly-discovered, massive ( approximately equals 10(exp 15) Solar M), high-redshift (z = 0.81) cluster revealed by ACT through the Sunyaev-Zeldovich effect (SZE). Deep, targeted observations with the SZA allow us to probe a broader range of cluster spatial scales, better disentangle cluster decrements from radio point source emission, and derive more robust integrated SZE flux and mass estimates than we can with ACT data alone. For the two clusters we detect with the SZA we compute integrated SZE signal and derive masses from the SZA data only. ACT-CL J2337+0016, also known as Abell 2631, has archival Chandra data that allow an additional X-ray-based mass estimate. Optical richness is also used to estimate cluster masses and shows good agreement with the SZE and X-ray-based estimates. Based on the point sources detected by the SZA in these three cluster fields and an extrapolation to ACT's frequency, we estimate that point sources could be contaminating the SZE decrement at the approx < 20% level for some fraction of clusters.

  12. Biomimetic Gradient Polymers with Enhanced Damping Capacities.

    PubMed

    Wang, Dong; Zhang, Huan; Guo, Jing; Cheng, Beichen; Cao, Yuan; Lu, Shengjun; Zhao, Ning; Xu, Jian

    2016-04-01

    Designing gradient structures, mimicking biological materials, such as pummelo peels and tendon, is a promising strategy for developing advanced materials with superior energy damping capacities. Here a facile and effective approach for fabricating polymers with composition gradients at millimeter length scale is presented. The gradient thiol-ene polymers (TEPs) are created by the use of density difference of ternary thiol-ene-ene precursors and the subsequent photo-crosslinking via thiol-ene reaction. The compositional gradients are analyzed via differential scanning calorimeter (DSC), compressive modulus testing, atomic force microscopy (AFM) indentation, and swelling measurements. In contrast to homogeneous TEPs networks, the resultant gradient polymer shows a broader effective damping temperature range combining with good mechanical properties. The present result provides an effective route toward high damping materials by the fabrication of gradient structures. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Testing the limits of gradient sensing

    PubMed Central

    Lakhani, Vinal

    2017-01-01

    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. PMID:28207738

  14. Protein gradient films of fibroin and gelatine.

    PubMed

    Claussen, Kai U; Lintz, Eileen S; Giesa, Reiner; Schmidt, Hans-Werner; Scheibel, Thomas

    2013-10-01

    Gradients are a natural design principle in biological systems that are used to diminish stress concentration where materials of differing mechanical properties connect. An interesting example of a natural gradient material is byssus, which anchors mussels to rocks and other hard substrata. Building upon previous work with synthetic polymers and inspired by byssal threads, protein gradient films are cast using glycerine-plasticized gelatine and fibroin exhibiting a highly reproducible and smooth mechanical gradient, which encompasses a large range of modulus from 160 to 550 MPa. The reproducible production of biocompatible gradient films represents a first step towards medical applications. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Mechanical Properties and Real-Time Damage Evaluations of Environmental Barrier Coated SiC/SiC CMCs Subjected to Tensile Loading Under Thermal Gradients

    NASA Technical Reports Server (NTRS)

    Appleby, Matthew; Zhu, Dongming; Morscher, Gregory

    2015-01-01

    SiC/SiC ceramic matrix composites (CMCs) require new state-of-the art environmental barrier coatings (EBCs) to withstand increased temperature requirements and high velocity combustion corrosive combustion gasses. The present work compares the response of coated and uncoated SiC/SiC CMC substrates subjected to simulated engine environments followed by high temperature mechanical testing to asses retained properties and damage mechanisms. Our focus is to explore the capabilities of electrical resistance (ER) measurements as an NDE technique for testing of retained properties under combined high heat-flux and mechanical loading conditions. Furthermore, Acoustic Emission (AE) measurements and Digital Image Correlation (DIC) were performed to determine material damage onset and accumulation.

  16. $L_{0}$ Gradient Projection.

    PubMed

    Ono, Shunsuke

    2017-04-01

    Minimizing L 0 gradient, the number of the non-zero gradients of an image, together with a quadratic data-fidelity to an input image has been recognized as a powerful edge-preserving filtering method. However, the L 0 gradient minimization has an inherent difficulty: a user-given parameter controlling the degree of flatness does not have a physical meaning since the parameter just balances the relative importance of the L 0 gradient term to the quadratic data-fidelity term. As a result, the setting of the parameter is a troublesome work in the L 0 gradient minimization. To circumvent the difficulty, we propose a new edge-preserving filtering method with a novel use of the L 0 gradient. Our method is formulated as the minimization of the quadratic data-fidelity subject to the hard constraint that the L 0 gradient is less than a user-given parameter α . This strategy is much more intuitive than the L 0 gradient minimization because the parameter α has a clear meaning: the L 0 gradient value of the output image itself, so that one can directly impose a desired degree of flatness by α . We also provide an efficient algorithm based on the so-called alternating direction method of multipliers for computing an approximate solution of the nonconvex problem, where we decompose it into two subproblems and derive closed-form solutions to them. The advantages of our method are demonstrated through extensive experiments.

  17. Constraining the optical depth of galaxies and velocity bias with cross-correlation between the kinetic Sunyaev-Zeldovich effect and the peculiar velocity field

    NASA Astrophysics Data System (ADS)

    Ma, Yin-Zhe; Gong, Guo-Dong; Sui, Ning; He, Ping

    2018-03-01

    We calculate the cross-correlation function < (Δ T/T)({v}\\cdot \\hat{n}/σ _v) > between the kinetic Sunyaev-Zeldovich (kSZ) effect and the reconstructed peculiar velocity field using linear perturbation theory, with the aim of constraining the optical depth τ and peculiar velocity bias of central galaxies with Planck data. We vary the optical depth τ and the velocity bias function bv(k) = 1 + b(k/k0)n, and fit the model to the data, with and without varying the calibration parameter y0 that controls the vertical shift of the correlation function. By constructing a likelihood function and constraining the τ, b and n parameters, we find that the quadratic power-law model of velocity bias, bv(k) = 1 + b(k/k0)2, provides the best fit to the data. The best-fit values are τ = (1.18 ± 0.24) × 10-4, b=-0.84^{+0.16}_{-0.20} and y0=(12.39^{+3.65}_{-3.66})× 10^{-9} (68 per cent confidence level). The probability of b > 0 is only 3.12 × 10-8 for the parameter b, which clearly suggests a detection of scale-dependent velocity bias. The fitting results indicate that the large-scale (k ≤ 0.1 h Mpc-1) velocity bias is unity, while on small scales the bias tends to become negative. The value of τ is consistent with the stellar mass-halo mass and optical depth relationship proposed in the literature, and the negative velocity bias on small scales is consistent with the peak background split theory. Our method provides a direct tool for studying the gaseous and kinematic properties of galaxies.

  18. Gradient Driven Fluctuations

    NASA Technical Reports Server (NTRS)

    Cannell, David

    2005-01-01

    We have worked with our collaborators at the University of Milan (Professor Marzio Giglio and his group-supported by ASI) to define the science required to measure gradient driven fluctuations in the microgravity environment. Such a study would provide an accurate test of the extent to which the theory of fluctuating hydrodynamics can be used to predict the properties of fluids maintained in a stressed, non-equilibrium state. As mentioned above, the results should also provide direct visual insight into the behavior of a variety of fluid systems containing gradients or interfaces, when placed in the microgravity environment. With support from the current grant, we have identified three key systems for detailed investigation. These three systems are: 1) A single-component fluid to be studied in the presence of a temperature gradient; 2) A mixture of two organic liquids to be studied both in the presence of a temperature gradient, which induces a steady-state concentration gradient, and with the temperature gradient removed, but while the concentration gradient is dying by means of diffusion; 3) Various pairs of liquids undergoing free diffusion, including a proteidbuffer solution and pairs of mixtures having different concentrations, to allow us to vary the differences in fluid properties in a controlled manner.

  19. Full Gradient Solution to Adaptive Hybrid Control

    NASA Technical Reports Server (NTRS)

    Bean, Jacob; Schiller, Noah H.; Fuller, Chris

    2016-01-01

    This paper focuses on the adaptation mechanisms in adaptive hybrid controllers. Most adaptive hybrid controllers update two filters individually according to the filtered-reference least mean squares (FxLMS) algorithm. Because this algorithm was derived for feedforward control, it does not take into account the presence of a feedback loop in the gradient calculation. This paper provides a derivation of the proper weight vector gradient for hybrid (or feedback) controllers that takes into account the presence of feedback. In this formulation, a single weight vector is updated rather than two individually. An internal model structure is assumed for the feedback part of the controller. The full gradient is equivalent to that used in the standard FxLMS algorithm with the addition of a recursive term that is a function of the modeling error. Some simulations are provided to highlight the advantages of using the full gradient in the weight vector update rather than the approximation.

  20. Full Gradient Solution to Adaptive Hybrid Control

    NASA Technical Reports Server (NTRS)

    Bean, Jacob; Schiller, Noah H.; Fuller, Chris

    2017-01-01

    This paper focuses on the adaptation mechanisms in adaptive hybrid controllers. Most adaptive hybrid controllers update two filters individually according to the filtered reference least mean squares (FxLMS) algorithm. Because this algorithm was derived for feedforward control, it does not take into account the presence of a feedback loop in the gradient calculation. This paper provides a derivation of the proper weight vector gradient for hybrid (or feedback) controllers that takes into account the presence of feedback. In this formulation, a single weight vector is updated rather than two individually. An internal model structure is assumed for the feedback part of the controller. The full gradient is equivalent to that used in the standard FxLMS algorithm with the addition of a recursive term that is a function of the modeling error. Some simulations are provided to highlight the advantages of using the full gradient in the weight vector update rather than the approximation.

  1. Advanced Gradient Heating Facility

    NASA Technical Reports Server (NTRS)

    2004-01-01

    The Advanced Gradient Heating Facility (AGHF) is a European Space Agency (ESA) developed hardware. The AGHF was flown on STS-78, which featured four European PI's and two NASA PI's. The AGHFsupports the production of advanced semiconductor materials and alloys using the directional process, which depends on establishing a hot side and a cold side in the sample.

  2. Gradient Refractive Index Lenses.

    ERIC Educational Resources Information Center

    Morton, N.

    1984-01-01

    Describes the nature of gradient refractive index (GRIN) lenses, focusing on refraction in these materials, focal length of a thin Wood lens, and on manufacturing of such lenses. Indicates that GRIN lenses of small cross section are in limited production with applications suggested for optical communication and photocopying fields. (JN)

  3. Manipulating the Gradient

    ERIC Educational Resources Information Center

    Gaze, Eric C.

    2005-01-01

    We introduce a cooperative learning, group lab for a Calculus III course to facilitate comprehension of the gradient vector and directional derivative concepts. The lab is a hands-on experience allowing students to manipulate a tangent plane and empirically measure the effect of partial derivatives on the direction of optimal ascent. (Contains 7…

  4. Gradient Sun [still

    NASA Image and Video Library

    2017-12-08

    To view a video of the Gradient Sun go to: www.flickr.com/photos/gsfc/8103212817 Looking at a particularly beautiful image of the sun helps show how the lines between science and art can sometimes blur. But there is more to the connection between the two disciplines: science and art techniques are often quite similar, indeed one may inform the other or be improved based on lessons from the other arena. One such case is a technique known as a "gradient filter" – recognizable to many people as an option available on a photo-editing program. Gradients are, in fact, a mathematical description that highlights the places of greatest physical change in space. A gradient filter, in turn, enhances places of contrast, making them all the more obviously different, a useful tool when adjusting photos. Scientists, too, use gradient filters to enhance contrast, using them to accentuate fine structures that might otherwise be lost in the background noise. On the sun, for example, scientists wish to study a phenomenon known as coronal loops, which are giant arcs of solar material constrained to travel along that particular path by the magnetic fields in the sun's atmosphere. Observations of the loops, which can be more or less tangled and complex during different phases of the sun's 11-year activity cycle, can help researchers understand what's happening with the sun's complex magnetic fields, fields that can also power great eruptions on the sun such as solar flares or coronal mass ejections. The still here shows an unfiltered image from the sun next to one that has been processed using a gradient filter. Note how the coronal loops are sharp and defined, making them all the more easy to study. On the other hand, gradients also make great art. NASA/Goddard Space Flight Center To download this video go to: svs.gsfc.nasa.gov/goto?11112 NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics

  5. High Gradient Accelerator Research

    SciTech Connect

    Temkin, Richard

    The goal of the MIT program of research on high gradient acceleration is the development of advanced acceleration concepts that lead to a practical and affordable next generation linear collider at the TeV energy level. Other applications, which are more near-term, include accelerators for materials processing; medicine; defense; mining; security; and inspection. The specific goals of the MIT program are: • Pioneering theoretical research on advanced structures for high gradient acceleration, including photonic structures and metamaterial structures; evaluation of the wakefields in these advanced structures • Experimental research to demonstrate the properties of advanced structures both in low-power microwave coldmore » test and high-power, high-gradient test at megawatt power levels • Experimental research on microwave breakdown at high gradient including studies of breakdown phenomena induced by RF electric fields and RF magnetic fields; development of new diagnostics of the breakdown process • Theoretical research on the physics and engineering features of RF vacuum breakdown • Maintaining and improving the Haimson / MIT 17 GHz accelerator, the highest frequency operational accelerator in the world, a unique facility for accelerator research • Providing the Haimson / MIT 17 GHz accelerator facility as a facility for outside users • Active participation in the US DOE program of High Gradient Collaboration, including joint work with SLAC and with Los Alamos National Laboratory; participation of MIT students in research at the national laboratories • Training the next generation of Ph. D. students in the field of accelerator physics.« less

  6. Oxygen gradients in the microcirculation.

    PubMed

    Pittman, R N

    2011-07-01

    Early in the last century August Krogh embarked on a series of seminal studies to understand the connection between tissue metabolism and mechanisms by which the cardiovascular system supplied oxygen to meet those needs. Krogh recognized that oxygen was supplied from blood to the tissues by passive diffusion and that the most likely site for oxygen exchange was the capillary network. Studies of tissue oxygen consumption and diffusion coefficient, coupled with anatomical studies of capillarity in various tissues, led him to formulate a model of oxygen diffusion from a single capillary. Fifty years after the publication of this work, new methods were developed which allowed the direct measurement of oxygen in and around microvessels. These direct measurements have confirmed the predictions by Krogh and have led to extensions of his ideas resulting in our current understanding of oxygenation within the microcirculation. Developments during the last 40 years are reviewed, including studies of oxygen gradients in arterioles, capillaries, venules, microvessel wall and surrounding tissue. These measurements were made possible by the development and use of new methods to investigate oxygen in the microcirculation, so mention is made of oxygen microelectrodes, microspectrophotometry of haemoglobin and phosphorescence quenching microscopy. Our understanding of oxygen transport from the perspective of the microcirculation has gone from a consideration of oxygen gradients in capillaries and tissue to the realization that oxygen has the ability to diffuse from any microvessel to another location under the conditions that there exists a large enough PO(2) gradient and that the permeability for oxygen along the intervening pathway is sufficient. © 2011 The Author. Acta Physiologica © 2011 Scandinavian Physiological Society.

  7. Oxygen Gradients in the Microcirculation

    PubMed Central

    Pittman, Roland N.

    2010-01-01

    Early in the last century August Krogh embarked on a series of seminal studies to understand the connection between tissue metabolism and mechanisms by which the cardiovascular system supplied oxygen to meet those needs. Krogh recognized that oxygen was supplied from blood to the tissues by passive diffusion and that the most likely site for oxygen exchange was the capillary network. Studies of tissue oxygen consumption and diffusion coefficient, coupled with anatomical studies of capillarity in various tissues, led him to formulate a model of oxygen diffusion from a single capillary. Fifty years after the publication of this work, new methods were developed which allowed the direct measurement of oxygen in and around microvessels. These direct measurements have confirmed the predictions by Krogh and have led to extensions of his ideas resulting in our current understanding of oxygenation within the microcirculation. Developments during the last 40 years are reviewed, including studies of oxygen gradients in arterioles, capillaries, venules, microvessel wall and surrounding tissue. These measurements were made possible by the development and use of new methods to investigate oxygen in the microcirculation, so mention is made of oxygen microelectrodes, microspectrophotometry of haemoglobin and phosphorescence quenching microscopy. Our understanding of oxygen transport from the perspective of the microcirculation has gone from a consideration of oxygen gradients in capillaries and tissue to the realization that oxygen has the ability to diffuse from any microvessel to another location under the conditions that there exists a large enough PO2 gradient and that the permeability for oxygen along the intervening pathway is sufficient. PMID:21281453

  8. Gradient magnetometer system balloons

    NASA Astrophysics Data System (ADS)

    Korepanov, Valery; Tsvetkov, Yury

    2005-08-01

    Earth's magnetic field study still remains one of the leading edges of experimental geophysics. Thus study is executed on the Earth surface, including ocean bottom, and on satellite heights using component, mostly flux-gate magnetometers. But balloon experiments with component magnetometers are very seldom, first of all because of great complexity of data interpretation. This niche still waits for new experimental ideology, which will allow to get the measurements results with high accuracy, especially in gradient mode. The great importance of precise balloon-borne component magnetic field gradient study is obvious. Its technical realization is based both on the available at the marked high-precision non-magnetic tiltmeters and on recent achievements of flux-gate magnetometry. The scientific goals of balloon-borne magnetic gradiometric experiment are discussed and its practical realization is proposed.

  9. Gradient-Modulated SWIFT

    PubMed Central

    Zhang, Jinjin; Idiyatullin, Djaudat; Corum, Curtis A.; Kobayashi, Naoharu; Garwood, Michael

    2017-01-01

    Purpose Methods designed to image fast-relaxing spins, such as sweep imaging with Fourier transformation (SWIFT), often utilize high excitation bandwidth and duty cycle, and in some applications the optimal flip angle cannot be used without exceeding safe specific absorption rate (SAR) levels. The aim is to reduce SAR and increase the flexibility of SWIFT by applying time-varying gradient-modulation (GM). The modified sequence is called GM-SWIFT. Theory and Methods The method known as gradient-modulated offset independent adiabaticity was used to modulate the radiofrequency (RF) pulse and gradients. An expanded correlation algorithm was developed for GM-SWIFT to correct the phase and scale effects. Simulations and phantom and in vivo human experiments were performed to verify the correlation algorithm and to evaluate imaging performance. Results GM-SWIFT reduces SAR, RF amplitude, and acquisition time by up to 90%, 70%, and 45%, respectively, while maintaining image quality. The choice of GM parameter influences the lower limit of short T2* sensitivity, which can be exploited to suppress unwanted image haze from unresolvable ultrashort T2* signals originating from plastic materials in the coil housing and fixatives. Conclusions GM-SWIFT reduces peak and total RF power requirements and provides additional flexibility for optimizing SAR, RF amplitude, scan time, and image quality. PMID:25800547

  10. Temperature-gradient-induced

    NASA Astrophysics Data System (ADS)

    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.

  11. Magnetoelectric Transverse Gradient Sensor with High Detection Sensitivity and Low Gradient Noise.

    PubMed

    Zhang, Mingji; Or, Siu Wing

    2017-10-25

    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 voltage between the two ME composites and is calibrated against transverse MFGs to give a high detection sensitivity of 0.4-30.6 V/(T/m), a strong common-mode magnetic field noise rejection rate of <-14.5 dB, a small input-output nonlinearity of <10 ppm, and a low gradient noise of 0.16-620 nT/m/ Hz in a broad frequency range of 1 Hz-170 kHz under a small baseline of 35 mm. An analysis of experimental gradient noise spectra obtained in a magnetically-unshielded laboratory environment reveals the domination of the pink (1/ f ) noise, dielectric loss noise, and power-frequency noise below 3 kHz, in addition to the circuit noise above 3 kHz, in the gradient sensor. The high detection performance, together with the added merit of passive and direct ME conversion by the large ME effect in the ME composites, makes the gradient sensor suitable for the passive, direct, and broadband detection of transverse MFGs.

  12. A new method of determining moisture gradient in wood

    Treesearch

    Zhiyong Cai

    2008-01-01

    Moisture gradient in wood and wood composites is one of most important factors that affects both physical stability and mechanical performance. This paper describes a method for measuring moisture gradient in lumber and engineering wood composites as it varies across material thickness. This innovative method employs a collimated radiation beam (x rays or [gamma] rays...

  13. Motion Driven by Strain Gradient Fields

    PubMed Central

    Wang, Chao; Chen, Shaohua

    2015-01-01

    A new driving mechanism for direction-controlled motion of nano-scale objects is proposed, based on a model of stretching a graphene strip linked to a rigid base with linear springs of identical stiffness. We find that the potential energy difference induced by the strain gradient field in the graphene strip substrate can generate sufficient force to overcome the static and kinetic friction forces between the nano-flake and the strip substrate, resulting in the nanoscale flake motion in the direction of gradient reduction. The dynamics of the nano-flake can be manipulated by tuning the stiffness of linear springs, stretching velocity and the flake size. This fundamental law of directional motion induced by strain gradient could be very useful for promising designs of nanoscale manipulation, transportation and smart surfaces. PMID:26323603

  14. MEMS cantilever based magnetic field gradient sensor

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

    This paper describes major contributions to a MEMS magnetic field gradient sensor. An H-shaped structure supported by four arms with two circuit paths on the surface is designed for measuring two components of the magnetic flux density and one component of the gradient. The structure is produced from silicon wafers by a dry etching process. The gold leads on the surface carry the alternating current which interacts with the magnetic field component perpendicular to the direction of the current. If the excitation frequency is near to a mechanical resonance, vibrations with an amplitude within the range of 1-103 nm are expected. Both theoretical (simulations and analytic calculations) and experimental analysis have been carried out to optimize the structures for different strength of the magnetic gradient. In the same way the impact of the coupling structure on the resonance frequency and of different operating modes to simultaneously measure two components of the flux density were tested. For measuring the local gradient of the flux density the structure was operated at the first symmetrical and the first anti-symmetrical mode. Depending on the design, flux densities of approximately 2.5 µT and gradients starting from 1 µT mm-1 can be measured.

  15. Adaptive microfluidic gradient generator for quantitative chemotaxis experiments.

    PubMed

    Anielski, Alexander; Pfannes, Eva K B; Beta, Carsten

    2017-03-01

    Chemotactic motion in a chemical gradient is an essential cellular function that controls many processes in the living world. For a better understanding and more detailed modelling of the underlying mechanisms of chemotaxis, quantitative investigations in controlled environments are needed. We developed a setup that allows us to separately address the dependencies of the chemotactic motion on the average background concentration and on the gradient steepness of the chemoattractant. In particular, both the background concentration and the gradient steepness can be kept constant at the position of the cell while it moves along in the gradient direction. This is achieved by generating a well-defined chemoattractant gradient using flow photolysis. In this approach, the chemoattractant is released by a light-induced reaction from a caged precursor in a microfluidic flow chamber upstream of the cell. The flow photolysis approach is combined with an automated real-time cell tracker that determines changes in the cell position and triggers movement of the microscope stage such that the cell motion is compensated and the cell remains at the same position in the gradient profile. The gradient profile can be either determined experimentally using a caged fluorescent dye or may be alternatively determined by numerical solutions of the corresponding physical model. To demonstrate the function of this adaptive microfluidic gradient generator, we compare the chemotactic motion of Dictyostelium discoideum cells in a static gradient and in a gradient that adapts to the position of the moving cell.

  16. Wetting of flat gradient surfaces.

    PubMed

    Bormashenko, Edward

    2018-04-01

    Gradient, chemically modified, flat surfaces enable directed transport of droplets. Calculation of apparent contact angles inherent for gradient surfaces is challenging even for atomically flat ones. Wetting of gradient, flat solid surfaces is treated within the variational approach, under which the contact line is free to move along the substrate. Transversality conditions of the variational problem give rise to the generalized Young equation valid for gradient solid surfaces. The apparent (equilibrium) contact angle of a droplet, placed on a gradient surface depends on the radius of the contact line and the values of derivatives of interfacial tensions. The linear approximation of the problem is considered. It is demonstrated that the contact angle hysteresis is inevitable on gradient surfaces. Electrowetting of gradient surfaces is discussed. Copyright © 2018 Elsevier Inc. All rights reserved.

  17. Bigravity from gradient expansion

    SciTech Connect

    Yamashita, Yasuho; Tanaka, Takahiro; Department of Physics, Kyoto University,606-8502, Kyoto

    2016-05-04

    We discuss how the ghost-free bigravity coupled with a single scalar field can be derived from a braneworld setup. We consider DGP two-brane model without radion stabilization. The bulk configuration is solved for given boundary metrics, and it is substituted back into the action to obtain the effective four-dimensional action. In order to obtain the ghost-free bigravity, we consider the gradient expansion in which the brane separation is supposed to be sufficiently small so that two boundary metrics are almost identical. The obtained effective theory is shown to be ghost free as expected, however, the interaction between two gravitons takesmore » the Fierz-Pauli form at the leading order of the gradient expansion, even though we do not use the approximation of linear perturbation. We also find that the radion remains as a scalar field in the four-dimensional effective theory, but its coupling to the metrics is non-trivial.« less

  18. Reassessing Pliocene temperature gradients

    NASA Astrophysics Data System (ADS)

    Tierney, J. E.

    2017-12-01

    With CO2 levels similar to present, the Pliocene Warm Period (PWP) is one of our best analogs for climate change in the near future. Temperature proxy data from the PWP describe dramatically reduced zonal and meridional temperature gradients that have proved difficult to reproduce with climate model simulations. Recently, debate has emerged regarding the interpretation of the proxies used to infer Pliocene temperature gradients; these interpretations affect the magnitude of inferred change and the degree of inconsistency with existing climate model simulations of the PWP. Here, I revisit the issue using Bayesian proxy forward modeling and prediction that propagates known uncertainties in the Mg/Ca, UK'37, and TEX86 proxy systems. These new spatiotemporal predictions are quantitatively compared to PWP simulations to assess probabilistic agreement. Results show generally good agreement between existing Pliocene simulations from the PlioMIP ensemble and SST proxy data, suggesting that exotic changes in the ocean-atmosphere are not needed to explain the Pliocene climate state. Rather, the spatial changes in SST during the Pliocene are largely consistent with elevated CO2 forcing.

  19. Stability of boundary layer flow based on energy gradient theory

    NASA Astrophysics Data System (ADS)

    Dou, Hua-Shu; Xu, Wenqian; Khoo, Boo Cheong

    2018-05-01

    The flow of the laminar boundary layer on a flat plate is studied with the simulation of Navier-Stokes equations. The mechanisms of flow instability at external edge of the boundary layer and near the wall are analyzed using the energy gradient theory. The simulation results show that there is an overshoot on the velocity profile at the external edge of the boundary layer. At this overshoot, the energy gradient function is very large which results in instability according to the energy gradient theory. It is found that the transverse gradient of the total mechanical energy is responsible for the instability at the external edge of the boundary layer, which induces the entrainment of external flow into the boundary layer. Within the boundary layer, there is a maximum of the energy gradient function near the wall, which leads to intensive flow instability near the wall and contributes to the generation of turbulence.

  20. Chemotaxis of Molecular Dyes in Polymer Gradients in Solution.

    PubMed

    Guha, Rajarshi; Mohajerani, Farzad; Collins, Matthew; Ghosh, Subhadip; Sen, Ayusman; Velegol, Darrell

    2017-11-08

    Chemotaxis provides a mechanism for directing the transport of molecules along chemical gradients. Here, we show the chemotactic migration of dye molecules in response to the gradients of several different neutral polymers. The magnitude of chemotactic response depends on the structure of the monomer, polymer molecular weight and concentration, and the nature of the solvent. The mechanism involves cross-diffusion up the polymer gradient, driven by favorable dye-polymer interaction. Modeling allows us to quantitatively evaluate the strength of the interaction and the effect of the various parameters that govern chemotaxis.

  1. Stereo transparency and the disparity gradient limit

    NASA Technical Reports Server (NTRS)

    McKee, Suzanne P.; Verghese, Preeti

    2002-01-01

    Several studies (Vision Research 15 (1975) 583; Perception 9 (1980) 671) have shown that binocular fusion is limited by the disparity gradient (disparity/distance) separating image points, rather than by their absolute disparity values. Points separated by a gradient >1 appear diplopic. These results are sometimes interpreted as a constraint on human stereo matching, rather than a constraint on fusion. Here we have used psychophysical measurements on stereo transparency to show that human stereo matching is not constrained by a gradient of 1. We created transparent surfaces composed of many pairs of dots, in which each member of a pair was assigned a disparity equal and opposite to the disparity of the other member. For example, each pair could be composed of one dot with a crossed disparity of 6' and the other with uncrossed disparity of 6', vertically separated by a parametrically varied distance. When the vertical separation between the paired dots was small, the disparity gradient for each pair was very steep. Nevertheless, these opponent-disparity dot pairs produced a striking appearance of two transparent surfaces for disparity gradients ranging between 0.5 and 3. The apparent depth separating the two transparent planes was correctly matched to an equivalent disparity defined by two opaque surfaces. A test target presented between the two transparent planes was easily detected, indicating robust segregation of the disparities associated with the paired dots into two transparent surfaces with few mismatches in the target plane. Our simulations using the Tsai-Victor model show that the response profiles produced by scaled disparity-energy mechanisms can account for many of our results on the transparency generated by steep gradients.

  2. Role of spatial averaging in multicellular gradient sensing.

    PubMed

    Smith, Tyler; Fancher, Sean; Levchenko, Andre; Nemenman, Ilya; Mugler, Andrew

    2016-05-20

    Gradient sensing underlies important biological processes including morphogenesis, polarization, and cell migration. The precision of gradient sensing increases with the length of a detector (a cell or group of cells) in the gradient direction, since a longer detector spans a larger range of concentration values. Intuition from studies of concentration sensing suggests that precision should also increase with detector length in the direction transverse to the gradient, since then spatial averaging should reduce the noise. However, here we show that, unlike for concentration sensing, the precision of gradient sensing decreases with transverse length for the simplest gradient sensing model, local excitation-global inhibition. The reason is that gradient sensing ultimately relies on a subtraction of measured concentration values. While spatial averaging indeed reduces the noise in these measurements, which increases precision, it also reduces the covariance between the measurements, which results in the net decrease in precision. We demonstrate how a recently introduced gradient sensing mechanism, regional excitation-global inhibition (REGI), overcomes this effect and recovers the benefit of transverse averaging. Using a REGI-based model, we compute the optimal two- and three-dimensional detector shapes, and argue that they are consistent with the shapes of naturally occurring gradient-sensing cell populations.

  3. Role of spatial averaging in multicellular gradient sensing

    NASA Astrophysics Data System (ADS)

    Smith, Tyler; Fancher, Sean; Levchenko, Andre; Nemenman, Ilya; Mugler, Andrew

    2016-06-01

    Gradient sensing underlies important biological processes including morphogenesis, polarization, and cell migration. The precision of gradient sensing increases with the length of a detector (a cell or group of cells) in the gradient direction, since a longer detector spans a larger range of concentration values. Intuition from studies of concentration sensing suggests that precision should also increase with detector length in the direction transverse to the gradient, since then spatial averaging should reduce the noise. However, here we show that, unlike for concentration sensing, the precision of gradient sensing decreases with transverse length for the simplest gradient sensing model, local excitation-global inhibition. The reason is that gradient sensing ultimately relies on a subtraction of measured concentration values. While spatial averaging indeed reduces the noise in these measurements, which increases precision, it also reduces the covariance between the measurements, which results in the net decrease in precision. We demonstrate how a recently introduced gradient sensing mechanism, regional excitation-global inhibition (REGI), overcomes this effect and recovers the benefit of transverse averaging. Using a REGI-based model, we compute the optimal two- and three-dimensional detector shapes, and argue that they are consistent with the shapes of naturally occurring gradient-sensing cell populations.

  4. Gradient optimization and nonlinear control

    NASA Technical Reports Server (NTRS)

    Hasdorff, L.

    1976-01-01

    The book represents an introduction to computation in control by an iterative, gradient, numerical method, where linearity is not assumed. The general language and approach used are those of elementary functional analysis. The particular gradient method that is emphasized and used is conjugate gradient descent, a well known method exhibiting quadratic convergence while requiring very little more computation than simple steepest descent. Constraints are not dealt with directly, but rather the approach is to introduce them as penalty terms in the criterion. General conjugate gradient descent methods are developed and applied to problems in control.

  5. Escalation of polymerization in a thermal gradient

    PubMed Central

    Mast, Christof B.; Schink, Severin; Gerland, Ulrich; Braun, Dieter

    2013-01-01

    For the emergence of early life, the formation of biopolymers such as RNA is essential. However, the addition of nucleotide monomers to existing oligonucleotides requires millimolar concentrations. Even in such optimistic settings, no polymerization of RNA longer than about 20 bases could be demonstrated. How then could self-replicating ribozymes appear, for which recent experiments suggest a minimal length of 200 nt? Here, we demonstrate a mechanism to bridge this gap: the escalated polymerization of nucleotides by a spatially confined thermal gradient. The gradient accumulates monomers by thermophoresis and convection while retaining longer polymers exponentially better. Polymerization and accumulation become mutually self-enhancing and result in a hyperexponential escalation of polymer length. We describe this escalation theoretically under the conservative assumption of reversible polymerization. Taking into account the separately measured thermophoretic properties of RNA, we extrapolate the results for primordial RNA polymerization inside a temperature gradient in pores or fissures of rocks. With a dilute, nanomolar concentration of monomers the model predicts that a pore length of 5 cm and a temperature difference of 10 K suffice to polymerize 200-mers of RNA in micromolar concentrations. The probability to generate these long RNAs is raised by a factor of >10600 compared with polymerization in a physical equilibrium. We experimentally validate the theory with the reversible polymerization of DNA blocks in a laser-driven thermal trap. The results confirm that a thermal gradient can significantly enlarge the available sequence space for the emergence of catalytically active polymers. PMID:23630280

  6. Gradient Material Strategies for Hydrogel Optimization in Tissue Engineering Applications

    PubMed Central

    2018-01-01

    Although a number of combinatorial/high-throughput approaches have been developed for biomaterial hydrogel optimization, a gradient sample approach is particularly well suited to identify hydrogel property thresholds that alter cellular behavior in response to interacting with the hydrogel due to reduced variation in material preparation and the ability to screen biological response over a range instead of discrete samples each containing only one condition. This review highlights recent work on cell–hydrogel interactions using a gradient material sample approach. Fabrication strategies for composition, material and mechanical property, and bioactive signaling gradient hydrogels that can be used to examine cell–hydrogel interactions will be discussed. The effects of gradients in hydrogel samples on cellular adhesion, migration, proliferation, and differentiation will then be examined, providing an assessment of the current state of the field and the potential of wider use of the gradient sample approach to accelerate our understanding of matrices on cellular behavior. PMID:29485612

  7. Sound control by temperature gradients

    NASA Astrophysics Data System (ADS)

    Sánchez-Dehesa, José; Angelov, Mitko I.; Cervera, Francisco; Cai, Liang-Wu

    2009-11-01

    This work reports experiments showing that airborne sound propagation can be controlled by temperature gradients. A system of two heated tubes is here used to demonstrate the collimation and focusing of an ultrasonic beam by the refractive index profile created by the temperature gradients existing around the tubes. Numerical simulations supporting the experimental findings are also reported.

  8. Density Gradients in Chemistry Teaching

    ERIC Educational Resources Information Center

    Miller, P. J.

    1972-01-01

    Outlines experiments in which a density gradient might be used to advantage. A density gradient consists of a column of liquid, the composition and density of which varies along its length. The procedure can be used in analysis of solutions and mixtures and in density measures of solids. (Author/TS)

  9. Thermal Gradient Fining of Glass

    NASA Technical Reports Server (NTRS)

    Wilcox, W.

    1983-01-01

    Molten glass fined (cleared of bubbles) by heating with suitable temperature gradient, according to preliminary experiments. Temperature gradient produces force on gas bubbles trapped in molten glass pushing bubbles to higher temperature region where they are collected. Concept demonstrated in experiments on Earth and on rocket.

  10. Magnetoelectric Transverse Gradient Sensor with High Detection Sensitivity and Low Gradient Noise

    PubMed Central

    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 voltage between the two ME composites and is calibrated against transverse MFGs to give a high detection sensitivity of 0.4–30.6 V/(T/m), a strong common-mode magnetic field noise rejection rate of <−14.5 dB, a small input-output nonlinearity of <10 ppm, and a low gradient noise of 0.16–620 nT/m/Hz in a broad frequency range of 1 Hz–170 kHz under a small baseline of 35 mm. An analysis of experimental gradient noise spectra obtained in a magnetically-unshielded laboratory environment reveals the domination of the pink (1/f) noise, dielectric loss noise, and power-frequency noise below 3 kHz, in addition to the circuit noise above 3 kHz, in the gradient sensor. The high detection performance, together with the added merit of passive and direct ME conversion by the large ME effect in the ME composites, makes the gradient sensor suitable for the passive, direct, and broadband detection of transverse MFGs. PMID:29068428

  11. Bioinspired conical copper wire with gradient wettability for continuous and efficient fog collection.

    PubMed

    Ju, Jie; Xiao, Kai; Yao, Xi; Bai, Hao; Jiang, Lei

    2013-11-06

    Inspired by the efficient fog collection on cactus spines, conical copper wires with gradient wettability are fabricated through gradient electrochemical corrosion and subsequent gradient chemical modification. These dual-gradient copper wires' fog-collection ability is demonstrated to be higher than that of conical copper wires with pure hydrophobic surfaces or pure hydrophilic surfaces, and the underlying mechanism is also analyzed. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Gradient zone boundary control in salt gradient solar ponds

    DOEpatents

    Hull, John R.

    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.

  13. Designing gradient coils with reduced hot spot temperatures.

    PubMed

    While, Peter T; Forbes, Larry K; Crozier, Stuart

    2010-03-01

    Gradient coil temperature is an important concern in the design and construction of MRI scanners. Closely spaced gradient coil windings cause temperature hot spots within the system as a result of Ohmic heating associated with large current being driven through resistive material, and can strongly affect the performance of the coils. In this paper, a model is presented for predicting the spatial temperature distribution of a gradient coil, including the location and extent of temperature hot spots. Subsequently, a method is described for designing gradient coils with improved temperature distributions and reduced hot spot temperatures. Maximum temperature represents a non-linear constraint and a relaxed fixed point iteration routine is proposed to adjust coil windings iteratively to minimise this coil feature. Several examples are considered that assume different thermal material properties and cooling mechanisms for the gradient system. Coil winding solutions are obtained for all cases considered that display a considerable drop in hot spot temperature (>20%) when compared to standard minimum power gradient coils with equivalent gradient homogeneity, efficiency and inductance. The method is semi-analytical in nature and can be adapted easily to consider other non-linear constraints in the design of gradient coils or similar systems. Crown Copyright (c) 2009. Published by Elsevier Inc. All rights reserved.

  14. Colloidal attraction induced by a temperature gradient.

    PubMed

    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.

  15. Social gradients in periodontal diseases among adolescents.

    PubMed

    López, Rodrigo; Fernández, Olaya; Baelum, Vibeke

    2006-06-01

    To investigate the association between socioeconomic position and periodontal diseases among adolescents. Data were obtained from 9203 Chilean high school students. Clinical examinations included direct recordings of clinical attachment level and the necrotizing ulcerative gingival lesions. Students answered a questionnaire on various dimensions of socioeconomic position. Seven periodontal outcomes were analyzed. Logistic regression analyses were used to identify socioeconomic variables associated with the periodontal outcomes. The occurrence of all periodontal outcomes investigated followed social gradients, and paternal income and parental education were the most influential variables. The study demonstrates the existence of significant social gradients in periodontal diseases already among adolescents. This is worrying, and indicates a new potential for further insight into the mechanisms of periodontal disease causation.

  16. Combining Step Gradients and Linear Gradients in Density.

    PubMed

    Kumar, Ashok A; Walz, Jenna A; Gonidec, Mathieu; Mace, Charles R; Whitesides, George M

    2015-06-16

    Combining aqueous multiphase systems (AMPS) and magnetic levitation (MagLev) provides a method to produce hybrid gradients in apparent density. AMPS—solutions of different polymers, salts, or surfactants that spontaneously separate into immiscible but predominantly aqueous phases—offer thermodynamically stable steps in density that can be tuned by the concentration of solutes. MagLev—the levitation of diamagnetic objects in a paramagnetic fluid within a magnetic field gradient—can be arranged to provide a near-linear gradient in effective density where the height of a levitating object above the surface of the magnet corresponds to its density; the strength of the gradient in effective density can be tuned by the choice of paramagnetic salt and its concentrations and by the strength and gradient in the magnetic field. Including paramagnetic salts (e.g., MnSO4 or MnCl2) in AMPS, and placing them in a magnetic field gradient, enables their use as media for MagLev. The potential to create large steps in density with AMPS allows separations of objects across a range of densities. The gradients produced by MagLev provide resolution over a continuous range of densities. By combining these approaches, mixtures of objects with large differences in density can be separated and analyzed simultaneously. Using MagLev to add an effective gradient in density also enables tuning the range of densities captured at an interface of an AMPS by simply changing the position of the container in the magnetic field. Further, by creating AMPS in which phases have different concentrations of paramagnetic ions, the phases can provide different resolutions in density. These results suggest that combining steps in density with gradients in density can enable new classes of separations based on density.

  17. High field gradient particle accelerator

    DOEpatents

    Nation, J.A.; Greenwald, S.

    1989-05-30

    A high electric field gradient electron accelerator utilizing short duration, microwave radiation, and capable of operating at high field gradients for high energy physics applications or at reduced electric field gradients for high average current intermediate energy accelerator applications is disclosed. Particles are accelerated in a smooth bore, periodic undulating waveguide, wherein the period is so selected that the particles slip an integral number of cycles of the r.f. wave every period of the structure. This phase step of the particles produces substantially continuous acceleration in a traveling wave without transverse magnetic or other guide means for the particle. 10 figs.

  18. High field gradient particle accelerator

    DOEpatents

    Nation, John A.; Greenwald, Shlomo

    1989-01-01

    A high electric field gradient electron accelerator utilizing short duration, microwave radiation, and capable of operating at high field gradients for high energy physics applications or at reduced electric field gradients for high average current intermediate energy accelerator applications. Particles are accelerated in a smooth bore, periodic undulating waveguide, wherein the period is so selected that the particles slip an integral number of cycles of the r.f. wave every period of the structure. This phase step of the particles produces substantially continuous acceleration in a traveling wave without transverse magnetic or other guide means for the particle.

  19. Spatial gradient tuning in metamaterials

    NASA Astrophysics Data System (ADS)

    Driscoll, Tom; Goldflam, Michael; Jokerst, Nan; Basov, Dimitri; Smith, David

    2011-03-01

    Gradient Index (GRIN) metamaterials have been used to create devices inspired by, but often surpassing the potential of, conventional GRIN optics. The unit-cell nature of metamaterials presents the opportunity to exert much greater control over spatial gradients than is possible in natural materials. This is true not only during the design phase but also offers the potential for real-time reconfiguration of the metamaterial gradient. This ability fits nicely into the picture of transformation-optics, in which spatial gradients can enable an impressive suite of innovative devices. We discuss methods to exert control over metamaterial response, focusing on our recent demonstrations using Vanadium Dioxide. We give special attention to role of memristance and mem-capacitance observed in Vanadium Dioxide, which simplify the demands of stimuli and addressing, as well as intersecting metamaterials with the field of memory-materials.

  20. Gravity Gradients Frame Oceanus Procellarum

    NASA Image and Video Library

    2014-10-01

    Topography of Earth moon generated from data NASA LRO, with the gravity anomalies bordering the Procellarum region superimposed in blue. The border structures are shown using gravity gradients calculated with data from NASA GRAIL mission.

  1. Broadband absorption with gradient metasurfaces

    NASA Astrophysics Data System (ADS)

    Kwon, Hoyeong; Chalabi, Hamidreza; Alù, Andrea

    2018-03-01

    A metasurface with appropriately designed transverse spatial inhomogeneities can provide the desired phase redistribution in response to an incident wave with arbitrary incident angle. This property of gradient metasurfaces has been used to modify light propagation in unusual manners, to transform the impinging optical wavefront with large flexibility. In this work, we show how gradient metasurfaces can be tailored to offer high absorption in thin absorptive layers, and how to design realistic metasurfaces for this purpose using dielectric materials.

  2. Dose gradient curve: A new tool for evaluating dose gradient.

    PubMed

    Sung, KiHoon; Choi, Young Eun

    2018-01-01

    Stereotactic radiotherapy, which delivers an ablative high radiation dose to a target volume for maximum local tumor control, requires a rapid dose fall-off outside the target volume to prevent extensive damage to nearby normal tissue. Currently, there is no tool to comprehensively evaluate the dose gradient near the target volume. We propose the dose gradient curve (DGC) as a new tool to evaluate the quality of a treatment plan with respect to the dose fall-off characteristics. The average distance between two isodose surfaces was represented by the dose gradient index (DGI) estimated by a simple equation using the volume and surface area of isodose levels. The surface area was calculated by mesh generation and surface triangulation. The DGC was defined as a plot of the DGI of each dose interval as a function of the dose. Two types of DGCs, differential and cumulative, were generated. The performance of the DGC was evaluated using stereotactic radiosurgery plans for virtual targets. Over the range of dose distributions, the dose gradient of each dose interval was well-characterized by the DGC in an easily understandable graph format. Significant changes in the DGC were observed reflecting the differences in planning situations and various prescription doses. The DGC is a rational method for visualizing the dose gradient as the average distance between two isodose surfaces; the shorter the distance, the steeper the dose gradient. By combining the DGC with the dose-volume histogram (DVH) in a single plot, the DGC can be utilized to evaluate not only the dose gradient but also the target coverage in routine clinical practice.

  3. Dose gradient curve: A new tool for evaluating dose gradient

    PubMed Central

    Choi, Young Eun

    2018-01-01

    Purpose Stereotactic radiotherapy, which delivers an ablative high radiation dose to a target volume for maximum local tumor control, requires a rapid dose fall-off outside the target volume to prevent extensive damage to nearby normal tissue. Currently, there is no tool to comprehensively evaluate the dose gradient near the target volume. We propose the dose gradient curve (DGC) as a new tool to evaluate the quality of a treatment plan with respect to the dose fall-off characteristics. Methods The average distance between two isodose surfaces was represented by the dose gradient index (DGI) estimated by a simple equation using the volume and surface area of isodose levels. The surface area was calculated by mesh generation and surface triangulation. The DGC was defined as a plot of the DGI of each dose interval as a function of the dose. Two types of DGCs, differential and cumulative, were generated. The performance of the DGC was evaluated using stereotactic radiosurgery plans for virtual targets. Results Over the range of dose distributions, the dose gradient of each dose interval was well-characterized by the DGC in an easily understandable graph format. Significant changes in the DGC were observed reflecting the differences in planning situations and various prescription doses. Conclusions The DGC is a rational method for visualizing the dose gradient as the average distance between two isodose surfaces; the shorter the distance, the steeper the dose gradient. By combining the DGC with the dose-volume histogram (DVH) in a single plot, the DGC can be utilized to evaluate not only the dose gradient but also the target coverage in routine clinical practice. PMID:29698471

  4. Variable high gradient permanent magnet quadrupole (QUAPEVA)

    NASA Astrophysics Data System (ADS)

    Marteau, F.; Ghaith, A.; N'Gotta, P.; Benabderrahmane, C.; Valléau, M.; Kitegi, C.; Loulergue, A.; Vétéran, J.; Sebdaoui, M.; André, T.; Le Bec, G.; Chavanne, J.; Vallerand, C.; Oumbarek, D.; Cosson, O.; Forest, F.; Jivkov, P.; Lancelot, J. L.; Couprie, M. E.

    2017-12-01

    Different applications such as laser plasma acceleration, colliders, and diffraction limited light sources require high gradient quadrupoles, with strength that can reach up to 200 T/m for a typical 10 mm bore diameter. We present here a permanent magnet based quadrupole (so-called QUAPEVA) composed of a Halbach ring and surrounded by four permanent magnet cylinders. Its design including magnetic simulation modeling enabling us to reach 201 T/m with a gradient variability of 45% and mechanical issues are reported. Magnetic measurements of seven systems of different lengths are presented and confirmed the theoretical expectations. The variation of the magnetic center while changing the gradient strength is ±10 μm. A triplet of QUAPEVA magnets is used to efficiently focus a beam with large energy spread and high divergence that is generated by a Laser Plasma Acceleration source for a free electron laser demonstration and has enabled us to perform beam based alignment and control the dispersion of the beam.

  5. Air temperature gradient in large industrial hall

    NASA Astrophysics Data System (ADS)

    Karpuk, Michał; Pełech, Aleksander; Przydróżny, Edward; Walaszczyk, Juliusz; Szczęśniak, Sylwia

    2017-11-01

    In the rooms with dominant sensible heat load, volume airflow depends on many factors incl. pre-established temperature difference between exhaust and supply airflow. As the temperature difference is getting higher, airflow volume drops down, consequently, the cost of AHU is reduced. In high industrial halls with air exhaust grids located under the ceiling additional temperature gradient above working zone should be taken into consideration. In this regard, experimental research of the vertical air temperature gradient in high industrial halls were carried out for the case of mixing ventilation system The paper presents the results of air temperature distribution measurements in high technological hall (mechanically ventilated) under significant sensible heat load conditions. The supply airflow was delivered to the hall with the help of the swirl diffusers while exhaust grids were located under the hall ceiling. Basing on the air temperature distribution measurements performed on the seven pre-established levels, air temperature gradient in the area between 2.0 and 7.0 m above the floor was calculated and analysed.

  6. Measurement and Perturbation of Morphogen Lifetime: Effects on Gradient Shape

    PubMed Central

    Drocco, Jeffrey A.; Grimm, Oliver; Tank, David W.; Wieschaus, Eric

    2011-01-01

    Protein lifetime is of critical importance for most biological processes and plays a central role in cell signaling and embryonic development, where it impacts the absolute concentration of signaling molecules and, potentially, the shape of morphogen gradients. Early conceptual and mathematical models of gradient formation proposed that steady-state gradients are established by an equilibration between the lifetime of a morphogen and its rates of synthesis and diffusion, though whether gradients in fact reach steady state before being read out is a matter of controversy. In any case, this class of models predicts that protein lifetime is a key determinant of both the time to steady state and the spatial extent of a gradient. Using a method that employs repeated photoswitching of a fusion of the morphogen Bicoid (Bcd) and the photoconvertible fluorescent protein Dronpa, we measure and modify the lifetime of Dronpa-Bcd in living Drosophila embryos. We find that the lifetime of Bcd is dynamic, changing from 50 min before mitotic cycle 14 to 15 min during cellularization. Moreover, by measuring total quantities of Bcd over time, we find that the gradient does not reach steady state. Finally, using a nearly continuous low-level conversion to the dark state of Dronpa-Bcd to mimic the effect of increased degradation, we demonstrate that perturbation of protein lifetime changes the characteristic length of the gradient, providing direct support for a mechanism based on synthesis, diffusion, and degradation. PMID:22004733

  7. Development and implementation of an 84-channel matrix gradient coil.

    PubMed

    Littin, Sebastian; Jia, Feng; Layton, Kelvin J; Kroboth, Stefan; Yu, Huijun; Hennig, Jürgen; Zaitsev, Maxim

    2018-02-01

    Design, implement, integrate, and characterize a customized coil system that allows for generating spatial encoding magnetic fields (SEMs) in a highly-flexible fashion. A gradient coil with a high number of individual elements was designed. Dimensions of the coil were chosen to mimic a whole-body gradient system, scaled down to a head insert. Mechanical shape and wire layout of each element were optimized to increase the local gradient strength while minimizing eddy current effects and simultaneously considering manufacturing constraints. Resulting wire layout and mechanical design is presented. A prototype matrix gradient coil with 12 × 7 = 84 elements consisting of two element types was realized and characterized. Measured eddy currents are <1% of the original field. The coil is shown to be capable of creating nonlinear, and linear SEMs. In a DSV of 0.22 m gradient strengths between 24 mT∕m and 78 mT∕m could be realized locally with maximum currents of 150 A. Initial proof-of-concept imaging experiments using linear and nonlinear encoding fields are demonstrated. A shielded matrix gradient coil setup capable of generating encoding fields in a highly-flexible manner was designed and implemented. The presented setup is expected to serve as a basis for validating novel imaging techniques that rely on nonlinear spatial encoding fields. Magn Reson Med 79:1181-1191, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  8. Optimal disturbances in boundary layers subject to streamwise pressure gradient

    NASA Technical Reports Server (NTRS)

    Ashpis, David E.; Tumin, Anatoli

    2003-01-01

    An analysis of the optimal non-modal growth of perturbations in a boundary layer in the presence of a streamwise pressure gradient is presented. The analysis is based on PSE equations for an incompressible fluid. Examples with Falkner-Scan profiles indicate that a favorable pressure gradient decreases the non-modal growth, while an unfavorable pressure gradient leads to an increase of the amplification. It is suggested that the transient growth mechanism be utilized to choose optimal parameters of tripping elements on a low-pressure turbine (LPT) airfoil. As an example, a boundary layer flow with a streamwise pressure gradient corresponding to the pressure distribution over a LPT airfoil is considered. It is shown that there is an optimal spacing of the tripping elements and that the transient growth effect depends on the starting point.

  9. Directional Bleb Formation in Spherical Cells under Temperature Gradient

    PubMed Central

    Oyama, Kotaro; Arai, Tomomi; Isaka, Akira; Sekiguchi, Taku; Itoh, Hideki; Seto, Yusuke; Miyazaki, Makito; Itabashi, Takeshi; Ohki, Takashi; Suzuki, Madoka; Ishiwata, Shin'ichi

    2015-01-01

    Living cells sense absolute temperature and temporal changes in temperature using biological thermosensors such as ion channels. Here, we reveal, to our knowledge, a novel mechanism of sensing spatial temperature gradients within single cells. Spherical mitotic cells form directional membrane extensions (polar blebs) under sharp temperature gradients (≥∼0.065°C μm−1; 1.3°C temperature difference within a cell), which are created by local heating with a focused 1455-nm laser beam under an optical microscope. On the other hand, multiple nondirectional blebs are formed under gradual temperature gradients or uniform heating. During heating, the distribution of actomyosin complexes becomes inhomogeneous due to a break in the symmetry of its contractile force, highlighting the role of the actomyosin complex as a sensor of local temperature gradients. PMID:26200871

  10. Anterior-Posterior Cerebral Blood Volume Gradient in Human Subiculum

    PubMed Central

    Talati, Pratik; Rane, Swati; Kose, Samet; Gore, John; Heckers, Stephan

    2014-01-01

    The human hippocampal formation is characterized by anterior-posterior gradients of cell density, neurochemistry and hemodynamics. In addition, some functions are associated with specific subfields (subiculum, CA1–4, dentate gyrus) and regions (anterior and posterior). We performed contrast-enhanced, high-resolution T1-weighted 3T steady state (SS) imaging to investigate cerebral blood volume (CBV) gradients of the hippocampal formation. We studied 14 healthy subjects and found significant CBV gradients (anterior > posterior) in the subiculum but not in other hippocampal subfields. Since CBV is a marker of basal metabolism, these results indicate a greater baseline activity in the anterior compared to the posterior subiculum. This gradient might be related to the role of the subiculum as the main outflow station of the hippocampal formation and might have implications for the mechanisms of neuropsychiatric disorders. PMID:24677295

  11. Rapid Gradient-Echo Imaging

    PubMed Central

    Hargreaves, Brian

    2012-01-01

    Gradient echo sequences are widely used in magnetic resonance imaging (MRI) for numerous applications ranging from angiography to perfusion to functional MRI. Compared with spin-echo techniques, the very short repetition times of gradient-echo methods enable very rapid 2D and 3D imaging, but also lead to complicated “steady states.” Signal and contrast behavior can be described graphically and mathematically, and depends strongly on the type of spoiling: fully balanced (no spoiling), gradient spoiling, or RF-spoiling. These spoiling options trade off between high signal and pure T1 contrast while the flip angle also affects image contrast in all cases, both of which can be demonstrated theoretically and in image examples. As with spin-echo sequences, magnetization preparation can be added to gradient-echo sequences to alter image contrast. Gradient echo sequences are widely used for numerous applications such as 3D perfusion imaging, functional MRI, cardiac imaging and MR angiography. PMID:23097185

  12. Low-gradient aortic stenosis.

    PubMed

    Clavel, Marie-Annick; Magne, Julien; Pibarot, Philippe

    2016-09-07

    An important proportion of patients with aortic stenosis (AS) have a 'low-gradient' AS, i.e. a small aortic valve area (AVA <1.0 cm(2)) consistent with severe AS but a low mean transvalvular gradient (<40 mmHg) consistent with non-severe AS. The management of this subset of patients is particularly challenging because the AVA-gradient discrepancy raises uncertainty about the actual stenosis severity and thus about the indication for aortic valve replacement (AVR) if the patient has symptoms and/or left ventricular (LV) systolic dysfunction. The most frequent cause of low-gradient (LG) AS is the presence of a low LV outflow state, which may occur with reduced left ventricular ejection fraction (LVEF), i.e. classical low-flow, low-gradient (LF-LG), or preserved LVEF, i.e. paradoxical LF-LG. Furthermore, a substantial proportion of patients with AS may have a normal-flow, low-gradient (NF-LG) AS: i.e. a small AVA-low-gradient combination but with a normal flow. One of the most important clinical challenges in these three categories of patients with LG AS (classical LF-LG, paradoxical LF-LG, and NF-LG) is to differentiate a true-severe AS that generally benefits from AVR vs. a pseudo-severe AS that should be managed conservatively. A low-dose dobutamine stress echocardiography may be used for this purpose in patients with classical LF-LG AS, whereas aortic valve calcium scoring by multi-detector computed tomography is the preferred modality in those with paradoxical LF-LG or NF-LG AS. Although patients with LF-LG severe AS have worse outcomes than those with high-gradient AS following AVR, they nonetheless display an important survival benefit with this intervention. Some studies suggest that transcatheter AVR may be superior to surgical AVR in patients with LF-LG AS. Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2016. For permissions please email: journals.permissions@oup.com.

  13. Extreme Events on a Low-Gradient River and Delta: Evidence for Sediment Mass Movements on the Subaqueous Delta and a Mechanism for Creating Hyperpycnal Flow onto the Shelf

    NASA Astrophysics Data System (ADS)

    Dellapenna, T. M.; Carlin, J. A.; Williams, J. R.

    2016-02-01

    The Brazos River empties into the Gulf of Mexico (GOM) forming a wave-influenced, muddy, subaqueous delta (SAD). Recent research in the estuarine reach of the river and on the SAD, however, found evidence for significant mass wasting of the delta-front and potential evidence of hyperpycnal flow, a processes typically associated with higher gradient and higher sediment yield rivers. The study used high-resolution geophysics on the SAD and water-column profiling in the lower river to investigate the transfer to and fate of fluvial sediment on the shelf. The SAD side scan mosaic combined with core data reveal that the eastern portion was dominated by exposed relict, consolidated sediment; an erosional scarp along the upper shoreface; and a thinning of the Holocene strata immediately downslope of the scarp. Holocene strata thickness increases into deeper water. These features suggest sediment mass wasting on the delta front. After rapidly prograding during the early and mid 20th century, reductions in sediment load due anthropogenic influences, and a shift in the primary depocenter lead to erosion on these abandoned portions of the delta. During an elevated fluvial discharge event, a >1 m thick fluid mud layer was found along a 6 km span of the river 2 km upstream from the mouth. The river's salt wedge was shown to inhibit sediment export from the river to the GOM, and facilitate deposition of mud in the lower river. We believe that the mud layer in the lower river builds during moderate and low discharge periods and remobilized during increased discharge, potentially resulting in hyperpyncnal flow to the shelf. We observed suspended sediment concentrations up to 100 g/l in the fluid mud layer during this event. While our observations did not capture the transition from fluid mud to hyperpycnal flow, we believe that with persistent increased discharge the fluid mud layer could transition to hyperpycnal flow.

  14. Dense Bicoid hubs accentuate binding along the morphogen gradient

    PubMed Central

    Mir, Mustafa; Reimer, Armando; Haines, Jenna E.; Li, Xiao-Yong; Stadler, Michael; Garcia, Hernan

    2017-01-01

    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. PMID:28982761

  15. Proton electrochemical gradient: Driving and regulating neurotransmitter uptake.

    PubMed

    Farsi, Zohreh; Jahn, Reinhard; Woehler, Andrew

    2017-05-01

    Accumulation of neurotransmitters in the lumen of synaptic vesicles (SVs) relies on the activity of the vacuolar-type H + -ATPase. This pump drives protons into the lumen, generating a proton electrochemical gradient (Δμ H+ ) across the membrane. Recent work has demonstrated that the balance between the chemical (ΔpH) and electrical (ΔΨ) components of Δμ H+ is regulated differently by some distinct vesicle types. As different neurotransmitter transporters use ΔpH and ΔΨ with different relative efficiencies, regulation of this gradient balance has the potential to influence neurotransmitter uptake. Nevertheless, the underlying mechanisms responsible for this regulation remain poorly understood. In this review, we provide an overview of current neurotransmitter uptake models, with a particular emphasis on the distinct roles of the electrical and chemical gradients and current hypotheses for regulatory mechanisms. © 2017 WILEY Periodicals, Inc.

  16. Orderings for conjugate gradient preconditionings

    NASA Technical Reports Server (NTRS)

    Ortega, James M.

    1991-01-01

    The effect of orderings on the rate of convergence of the conjugate gradient method with SSOR or incomplete Cholesky preconditioning is examined. Some results also are presented that help to explain why red/black ordering gives an inferior rate of convergence.

  17. Gradient Tempering Of Bearing Races

    NASA Technical Reports Server (NTRS)

    Parr, Richardson A.

    1991-01-01

    Gradient-tempering process increases fracture toughness and resistance to stress-corrosion cracking of ball-bearing races made of hard, strong steels and subject to high installation stresses and operation in corrosive media. Also used in other applications in which local toughening of high-strength/low-toughness materials required.

  18. Low-gradient aortic stenosis

    PubMed Central

    Clavel, Marie-Annick; Magne, Julien; Pibarot, Philippe

    2016-01-01

    Abstract An important proportion of patients with aortic stenosis (AS) have a ‘low-gradient’ AS, i.e. a small aortic valve area (AVA <1.0 cm2) consistent with severe AS but a low mean transvalvular gradient (<40 mmHg) consistent with non-severe AS. The management of this subset of patients is particularly challenging because the AVA-gradient discrepancy raises uncertainty about the actual stenosis severity and thus about the indication for aortic valve replacement (AVR) if the patient has symptoms and/or left ventricular (LV) systolic dysfunction. The most frequent cause of low-gradient (LG) AS is the presence of a low LV outflow state, which may occur with reduced left ventricular ejection fraction (LVEF), i.e. classical low-flow, low-gradient (LF-LG), or preserved LVEF, i.e. paradoxical LF-LG. Furthermore, a substantial proportion of patients with AS may have a normal-flow, low-gradient (NF-LG) AS: i.e. a small AVA—low-gradient combination but with a normal flow. One of the most important clinical challenges in these three categories of patients with LG AS (classical LF-LG, paradoxical LF-LG, and NF-LG) is to differentiate a true-severe AS that generally benefits from AVR vs. a pseudo-severe AS that should be managed conservatively. A low-dose dobutamine stress echocardiography may be used for this purpose in patients with classical LF-LG AS, whereas aortic valve calcium scoring by multi-detector computed tomography is the preferred modality in those with paradoxical LF-LG or NF-LG AS. Although patients with LF-LG severe AS have worse outcomes than those with high-gradient AS following AVR, they nonetheless display an important survival benefit with this intervention. Some studies suggest that transcatheter AVR may be superior to surgical AVR in patients with LF-LG AS. PMID:27190103

  19. Gradient biomaterials and their influences on cell migration

    PubMed Central

    Wu, Jindan; Mao, Zhengwei; Tan, Huaping; Han, Lulu; Ren, Tanchen; Gao, Changyou

    2012-01-01

    Cell migration participates in a variety of physiological and pathological processes such as embryonic development, cancer metastasis, blood vessel formation and remoulding, tissue regeneration, immune surveillance and inflammation. The cells specifically migrate to destiny sites induced by the gradually varying concentration (gradient) of soluble signal factors and the ligands bound with the extracellular matrix in the body during a wound healing process. Therefore, regulation of the cell migration behaviours is of paramount importance in regenerative medicine. One important way is to create a microenvironment that mimics the in vivo cellular and tissue complexity by incorporating physical, chemical and biological signal gradients into engineered biomaterials. In this review, the gradients existing in vivo and their influences on cell migration are briefly described. Recent developments in the fabrication of gradient biomaterials for controlling cellular behaviours, especially the cell migration, are summarized, highlighting the importance of the intrinsic driving mechanism for tissue regeneration and the design principle of complicated and advanced tissue regenerative materials. The potential uses of the gradient biomaterials in regenerative medicine are introduced. The current and future trends in gradient biomaterials and programmed cell migration in terms of the long-term goals of tissue regeneration are prospected. PMID:23741610

  20. Imaging the Buried Chicxulub Crater with Gravity Gradients and Cenotes

    NASA Astrophysics Data System (ADS)

    Hildebrand, A. R.; Pilkington, M.; Halpenny, J. F.; Ortiz-Aleman, C.; Chavez, R. E.; Urrutia-Fucugauchi, J.; Connors, M.; Graniel-Castro, E.; Camara-Zi, A.; Vasquez, J.

    1995-09-01

    the other terrestrial planets. A modeled fault of 1.5 km displacement (slightly slumped block exterior and impact breccia interior) reproduces the steepest gradient feature. This model is incompatible with models that place these gradient features inside the collapsed transient cavity. Locations of the karst features of the northern Yucatan region were digitized from 1:50,000 topographic maps, which show most but not all the water-filled sinkholes (locally known as cenotes). A prominent ring of cenotes is visible over the crater that is spatially correlated to the outer steep gravity gradient feature. The mapped cenotes constitute an unbiased sampling of the region's karst surface features of >50 m diameter. The gradient maximum and the cenote ring both meander with amplitudes of up to 2 km. The wiggles in the gradient feature and the cenote distribution probably correspond to the "scalloping" observed at the headwall of terraces in large complex craters. A second partial cenote ring exterior to the southwest side of the main ring corresponds to a less-prominent gravity gradient feature. No concentric structure is observable in the distribution of karst features at radii >90 km. The cenote ring is bounded by the outer peripheral steep gradient feature and must be related to it; the slump faults must have been reactivated sufficiently to create fracturing in the overlying and much younger sediment. Long term subsidence, as found at other terrestrial craters is a possible mechanism for the reactivation. Such long term subsidence may be caused by differential compaction or thermal relaxation. Elevations acquired during gravity surveys show that the cenote ring also corresponds to a topographic low along some of its length that probably reflects preferential erosion.

  1. Stem cell migration and mechanotransduction on linear stiffness gradient hydrogels

    PubMed Central

    Hadden, William J.; Young, Jennifer L.; Holle, Andrew W.; McFetridge, Meg L.; Kim, Du Yong; Wijesinghe, Philip; Taylor-Weiner, Hermes; Wen, Jessica H.; Lee, Andrew R.; Bieback, Karen; Vo, Ba-Ngu; Sampson, David D.; Kennedy, Brendan F.; Spatz, Joachim P.; Choi, Yu Suk

    2017-01-01

    The spatial presentation of mechanical information is a key parameter for cell behavior. We have developed a method of polymerization control in which the differential diffusion distance of unreacted cross-linker and monomer into a prepolymerized hydrogel sink results in a tunable stiffness gradient at the cell–matrix interface. This simple, low-cost, robust method was used to produce polyacrylamide hydrogels with stiffness gradients of 0.5, 1.7, 2.9, 4.5, 6.8, and 8.2 kPa/mm, spanning the in vivo physiological and pathological mechanical landscape. Importantly, three of these gradients were found to be nondurotactic for human adipose-derived stem cells (hASCs), allowing the presentation of a continuous range of stiffnesses in a single well without the confounding effect of differential cell migration. Using these nondurotactic gradient gels, stiffness-dependent hASC morphology, migration, and differentiation were studied. Finally, the mechanosensitive proteins YAP, Lamin A/C, Lamin B, MRTF-A, and MRTF-B were analyzed on these gradients, providing higher-resolution data on stiffness-dependent expression and localization. PMID:28507138

  2. Modeling Yeast Cell Polarization Induced by Pheromone Gradients

    NASA Astrophysics Data System (ADS)

    Yi, Tau-Mu; Chen, Shanqin; Chou, Ching-Shan; Nie, Qing

    2007-07-01

    Yeast cells respond to spatial gradients of mating pheromones by polarizing and projecting up the gradient toward the source. It is thought that they employ a spatial sensing mechanism in which the cell compares the concentration of pheromone at different points on the cell surface and determines the maximum point, where the projection forms. Here we constructed the first spatial mathematical model of the yeast pheromone response that describes the dynamics of the heterotrimeric and Cdc42p G-protein cycles, which are linked in a cascade. Two key performance objectives of this system are (1) amplification—converting a shallow external gradient of ligand to a steep internal gradient of protein components and (2) tracking—following changes in gradient direction. We used simulations to investigate amplification mechanisms that allow tracking. We identified specific strategies for regulating the spatial dynamics of the protein components (i.e. their changing location in the cell) that would enable the cell to achieve both objectives.

  3. Elevation Gradients and Climatic Consequences

    NASA Astrophysics Data System (ADS)

    Redmond, K. T.

    2006-12-01

    Steep topography usually results in gradients in surface meteorological elements. Sometimes these gradients are extremely sharp. Frequent or persistent gradients are expressed in climatic statistics as well. Most commonly, higher elevations are wetter and cooler than lower elevations. The magnitude of these climate gradients vary both spatially and temporally, generally on smaller scales for the former and on a greater variety of scales for the latter. Orographic contributions to precipitation vary on hourly to annual scales, and temperature inversions of different durations can alter or reverse the vertical temperature lapse rate normally found in the atmosphere. The presence of these factors affects the probability distributions of climate elements as a function of elevation. This leads in turn to consequences for ecology, resource management, and data. Orographic enhancement of Sierra precipitation varies by a factor of about three on seasonal time scales, and more on shorter scales. Particularly strong gradients in temperature climate are observed along the California coast, resulting in large changes in long-term climatological probability distributions over quite short distances in elevation. These have significant implications for plant life. For specific noteworthy events, such as the California heat wave of July 2006, striking differences were seen over a horizontal distance of merely 2-3 km along the Big Sur Coast, related entirely to elevation. There is evidence of differential warming with elevation between California's Central Valley and the Sierra Nevada. As a practical matter, the three-dimensional correlation fields of weather and climate elements in topographically diverse regions, on differing time scales, have complex structure, but also have certain regularities. This makes quality control of weather and climate data sets in highly diverse topography much more challenging. Quality control decisions that do not properly take this correlation

  4. Spatial temperature gradients guide axonal outgrowth

    PubMed Central

    Black, Bryan; Vishwakarma, Vivek; Dhakal, Kamal; Bhattarai, Samik; Pradhan, Prabhakar; Jain, Ankur; Kim, Young-tae; Mohanty, Samarendra

    2016-01-01

    Formation of neural networks during development and regeneration after injury depends on accuracy of axonal pathfinding, which is primarily believed to be influenced by chemical cues. Recently, there is growing evidence that physical cues can play crucial role in axonal guidance. However, detailed mechanism involved in such guidance cues is lacking. By using weakly-focused near-infrared continuous wave (CW) laser microbeam in the path of an advancing axon, we discovered that the beam acts as a repulsive guidance cue. Here, we report that this highly-effective at-a-distance guidance is the result of a temperature field produced by the near-infrared laser light absorption. Since light absorption by extracellular medium increases when the laser wavelength was red shifted, the threshold laser power for reliable guidance was significantly lower in the near-infrared as compared to the visible spectrum. The spatial temperature gradient caused by the near-infrared laser beam at-a-distance was found to activate temperature-sensitive membrane receptors, resulting in an influx of calcium. The repulsive guidance effect was significantly reduced when extracellular calcium was depleted or in the presence of TRPV1-antagonist. Further, direct heating using micro-heater confirmed that the axonal guidance is caused by shallow temperature-gradient, eliminating the role of any non-photothermal effects. PMID:27460512

  5. Spatial temperature gradients guide axonal outgrowth

    NASA Astrophysics Data System (ADS)

    Black, Bryan; Vishwakarma, Vivek; Dhakal, Kamal; Bhattarai, Samik; Pradhan, Prabhakar; Jain, Ankur; Kim, Young-Tae; Mohanty, Samarendra

    2016-07-01

    Formation of neural networks during development and regeneration after injury depends on accuracy of axonal pathfinding, which is primarily believed to be influenced by chemical cues. Recently, there is growing evidence that physical cues can play crucial role in axonal guidance. However, detailed mechanism involved in such guidance cues is lacking. By using weakly-focused near-infrared continuous wave (CW) laser microbeam in the path of an advancing axon, we discovered that the beam acts as a repulsive guidance cue. Here, we report that this highly-effective at-a-distance guidance is the result of a temperature field produced by the near-infrared laser light absorption. Since light absorption by extracellular medium increases when the laser wavelength was red shifted, the threshold laser power for reliable guidance was significantly lower in the near-infrared as compared to the visible spectrum. The spatial temperature gradient caused by the near-infrared laser beam at-a-distance was found to activate temperature-sensitive membrane receptors, resulting in an influx of calcium. The repulsive guidance effect was significantly reduced when extracellular calcium was depleted or in the presence of TRPV1-antagonist. Further, direct heating using micro-heater confirmed that the axonal guidance is caused by shallow temperature-gradient, eliminating the role of any non-photothermal effects.

  6. Bacterial accumulation in viscosity gradients

    NASA Astrophysics Data System (ADS)

    Waisbord, Nicolas; Guasto, Jeffrey

    2016-11-01

    Cell motility is greatly modified by fluid rheology. In particular, the physical environments in which cells function, are often characterized by gradients of viscous biopolymers, such as mucus and extracellular matrix, which impact processes ranging from reproduction to digestion to biofilm formation. To understand how spatial heterogeneity of fluid rheology affects the motility and transport of swimming cells, we use hydrogel microfluidic devices to generate viscosity gradients in a simple, polymeric, Newtonian fluid. Using video microscopy, we characterize the random walk motility patterns of model bacteria (Bacillus subtilis), showing that both wild-type ('run-and-tumble') cells and smooth-swimming mutants accumulate in the viscous region of the fluid. Through statistical analysis of individual cell trajectories and body kinematics in both homogeneous and heterogeneous viscous environments, we discriminate passive, physical effects from active sensing processes to explain the observed cell accumulation at the ensemble level.

  7. Utility of a novel error-stepping method to improve gradient-based parameter identification by increasing the smoothness of the local objective surface: a case-study of pulmonary mechanics.

    PubMed

    Docherty, Paul D; Schranz, Christoph; Chase, J Geoffrey; Chiew, Yeong Shiong; Möller, Knut

    2014-05-01

    Accurate model parameter identification relies on accurate forward model simulations to guide convergence. However, some forward simulation methodologies lack the precision required to properly define the local objective surface and can cause failed parameter identification. The role of objective surface smoothness in identification of a pulmonary mechanics model was assessed using forward simulation from a novel error-stepping method and a proprietary Runge-Kutta method. The objective surfaces were compared via the identified parameter discrepancy generated in a Monte Carlo simulation and the local smoothness of the objective surfaces they generate. The error-stepping method generated significantly smoother error surfaces in each of the cases tested (p<0.0001) and more accurate model parameter estimates than the Runge-Kutta method in three of the four cases tested (p<0.0001) despite a 75% reduction in computational cost. Of note, parameter discrepancy in most cases was limited to a particular oblique plane, indicating a non-intuitive multi-parameter trade-off was occurring. The error-stepping method consistently improved or equalled the outcomes of the Runge-Kutta time-integration method for forward simulations of the pulmonary mechanics model. This study indicates that accurate parameter identification relies on accurate definition of the local objective function, and that parameter trade-off can occur on oblique planes resulting prematurely halted parameter convergence. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

  8. Bidirectional transport model of morphogen gradient formation via cytonemes

    NASA Astrophysics Data System (ADS)

    Bressloff, Paul C.; Kim, Hyunjoong

    2018-03-01

    Morphogen protein gradients play an important role in the spatial regulation of patterning during embryonic development. The most commonly accepted mechanism for gradient formation is diffusion from a source combined with degradation. Recently, there has been growing interest in an alternative mechanism, which is based on the direct delivery of morphogens along thin, actin-rich cellular extensions known as cytonemes. In this paper, we develop a bidirectional motor transport model for the flux of morphogens along cytonemes, linking a source cell to a one-dimensional array of target cells. By solving the steady-state transport equations, we show how a morphogen gradient can be established, and explore how the mean velocity of the motors affects properties of the morphogen gradient such as accumulation time and robustness. In particular, our analysis suggests that in order to achieve robustness with respect to changes in the rate of synthesis of morphogen, the mean velocity has to be negative, that is, retrograde flow or treadmilling dominates. Thus the potential targeting precision of cytonemes comes at an energy cost. We then study the effects of non-uniformly allocating morphogens to the various cytonemes projecting from a source cell. This competition for resources provides a potential regulatory control mechanism not available in diffusion-based models.

  9. Active-passive gradient shielding for MRI acoustic noise reduction.

    PubMed

    Edelstein, William A; Kidane, Tesfaye K; Taracila, Victor; Baig, Tanvir N; Eagan, Timothy P; Cheng, Yu-Chung N; Brown, Robert W; Mallick, John A

    2005-05-01

    An important source of MRI acoustic noise-magnet cryostat warm-bore vibrations caused by eddy-current-induced forces-can be mitigated by a passive metal shield mounted on the outside of a vibration-isolated, vacuum-enclosed shielded gradient set. Finite-element (FE) calculations for a z-gradient indicate that a 2-mm-thick Cu layer wrapped on the gradient assembly can decrease mechanical power deposition in the warm bore and reduce warm-bore acoustic noise production by about 25 dB. Eliminating the conducting warm bore and other magnet parts as significant acoustic noise sources could lead to the development of truly quiet, fully functioning MRI systems with noise levels below 70 dB. Copyright 2005 Wiley-Liss, Inc.

  10. Experiments with conjugate gradient algorithms for homotopy curve tracking

    NASA Technical Reports Server (NTRS)

    Irani, Kashmira M.; Ribbens, Calvin J.; Watson, Layne T.; Kamat, Manohar P.; Walker, Homer F.

    1991-01-01

    There are algorithms for finding zeros or fixed points of nonlinear systems of equations that are globally convergent for almost all starting points, i.e., with probability one. The essence of all such algorithms is the construction of an appropriate homotopy map and then tracking some smooth curve in the zero set of this homotopy map. HOMPACK is a mathematical software package implementing globally convergent homotopy algorithms with three different techniques for tracking a homotopy zero curve, and has separate routines for dense and sparse Jacobian matrices. The HOMPACK algorithms for sparse Jacobian matrices use a preconditioned conjugate gradient algorithm for the computation of the kernel of the homotopy Jacobian matrix, a required linear algebra step for homotopy curve tracking. Here, variants of the conjugate gradient algorithm are implemented in the context of homotopy curve tracking and compared with Craig's preconditioned conjugate gradient method used in HOMPACK. The test problems used include actual large scale, sparse structural mechanics problems.

  11. Visualization of an endogenous retinoic acid gradient across embryonic development.

    PubMed

    Shimozono, Satoshi; Iimura, Tadahiro; Kitaguchi, Tetsuya; Higashijima, Shin-Ichi; Miyawaki, Atsushi

    2013-04-18

    In vertebrate development, the body plan is determined by primordial morphogen gradients that suffuse the embryo. Retinoic acid (RA) is an important morphogen involved in patterning the anterior-posterior axis of structures, including the hindbrain and paraxial mesoderm. RA diffuses over long distances, and its activity is spatially restricted by synthesizing and degrading enzymes. However, gradients of endogenous morphogens in live embryos have not been directly observed; indeed, their existence, distribution and requirement for correct patterning remain controversial. Here we report a family of genetically encoded indicators for RA that we have termed GEPRAs (genetically encoded probes for RA). Using the principle of fluorescence resonance energy transfer we engineered the ligand-binding domains of RA receptors to incorporate cyan-emitting and yellow-emitting fluorescent proteins as fluorescence resonance energy transfer donor and acceptor, respectively, for the reliable detection of ambient free RA. We created three GEPRAs with different affinities for RA, enabling the quantitative measurement of physiological RA concentrations. Live imaging of zebrafish embryos at the gastrula and somitogenesis stages revealed a linear concentration gradient of endogenous RA in a two-tailed source-sink arrangement across the embryo. Modelling of the observed linear RA gradient suggests that the rate of RA diffusion exceeds the spatiotemporal dynamics of embryogenesis, resulting in stability to perturbation. Furthermore, we used GEPRAs in combination with genetic and pharmacological perturbations to resolve competing hypotheses on the structure of the RA gradient during hindbrain formation and somitogenesis. Live imaging of endogenous concentration gradients across embryonic development will allow the precise assignment of molecular mechanisms to developmental dynamics and will accelerate the application of approaches based on morphogen gradients to tissue engineering and

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

    PubMed

    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.

  13. Derivative Free Gradient Projection Algorithms for Rotation

    ERIC Educational Resources Information Center

    Jennrich, Robert I.

    2004-01-01

    A simple modification substantially simplifies the use of the gradient projection (GP) rotation algorithms of Jennrich (2001, 2002). These algorithms require subroutines to compute the value and gradient of any specific rotation criterion of interest. The gradient can be difficult to derive and program. It is shown that using numerical gradients…

  14. Formation of the long range Dpp morphogen gradient.

    PubMed

    Schwank, Gerald; Dalessi, Sascha; Yang, Schu-Fee; Yagi, Ryohei; de Lachapelle, Aitana Morton; Affolter, Markus; Bergmann, Sven; Basler, Konrad

    2011-07-01

    The TGF-β homolog Decapentaplegic (Dpp) acts as a secreted morphogen in the Drosophila wing disc, and spreads through the target tissue in order to form a long range concentration gradient. Despite extensive studies, the mechanism by which the Dpp gradient is formed remains controversial. Two opposing mechanisms have been proposed: receptor-mediated transcytosis (RMT) and restricted extracellular diffusion (RED). In these scenarios the receptor for Dpp plays different roles. In the RMT model it is essential for endocytosis, re-secretion, and thus transport of Dpp, whereas in the RED model it merely modulates Dpp distribution by binding it at the cell surface for internalization and subsequent degradation. Here we analyzed the effect of receptor mutant clones on the Dpp profile in quantitative mathematical models representing transport by either RMT or RED. We then, using novel genetic tools, experimentally monitored the actual Dpp gradient in wing discs containing receptor gain-of-function and loss-of-function clones. Gain-of-function clones reveal that Dpp binds in vivo strongly to the type I receptor Thick veins, but not to the type II receptor Punt. Importantly, results with the loss-of-function clones then refute the RMT model for Dpp gradient formation, while supporting the RED model in which the majority of Dpp is not bound to Thick veins. Together our results show that receptor-mediated transcytosis cannot account for Dpp gradient formation, and support restricted extracellular diffusion as the main mechanism for Dpp dispersal. The properties of this mechanism, in which only a minority of Dpp is receptor-bound, may facilitate long-range distribution.

  15. Application of gradient elasticity to benchmark problems of beam vibrations

    NASA Astrophysics Data System (ADS)

    Kateb, K. M.; Almitani, K. H.; Alnefaie, K. A.; Abu-Hamdeh, N. H.; Papadopoulos, P.; Askes, H.; Aifantis, E. C.

    2016-04-01

    The gradient approach, specifically gradient elasticity theory, is adopted to revisit certain typical configurations on mechanical vibrations. New results on size effects and scale-dependent behavior not captured by classical elasticity are derived, aiming at illustrating the usefulness of this approach to applications in advanced technologies. In particular, elastic prismatic straight beams in bending are discussed using two different governing equations: the gradient elasticity bending moment equation (fourth order) and the gradient elasticity deflection equation (sixth order). Different boundary/support conditions are examined. One problem considers the free vibrations of a cantilever beam loaded by an end force. A second problem is concerned with a simply supported beam disturbed by a concentrated force in the middle of the beam. Both problems are solved analytically. Exact free vibration frequencies and mode shapes are derived and presented. The difference between the gradient elasticity solution and its classical counterpart is revealed. The size ratio c/L (c denotes internal length and L is the length of the beam) induces significant effects on vibration frequencies. For both beam configurations, it turns out that as the ratio c/L increases, the vibration frequencies decrease, a fact which implies lower beam stiffness. Numerical examples show this behavior explicitly and recover the classical vibration behavior for vanishing size ratio c/L.

  16. Strain gradient drives shear banding in metallic glasses

    NASA Astrophysics Data System (ADS)

    Tian, Zhi-Li; Wang, Yun-Jiang; Chen, Yan; Dai, Lan-Hong

    2017-09-01

    Shear banding is a nucleation-controlled process in metallic glasses (MGs) involving multiple temporal-spatial scales, which hinders a concrete understanding of its structural origin down to the atomic scale. Here, inspired by the morphology of composite materials, we propose a different perspective of MGs as a hard particle-reinforced material based on atomic-scale structural heterogeneity. The local stable structures indicated by a high level of local fivefold symmetry (L5FS) act as hard "particles" which are embedded in the relatively soft matrix. We demonstrate this concept by performing atomistic simulations of shear banding in CuZr MG. A shear band is prone to form in a sample with a high degree of L5FS which is slowly quenched from the liquid. An atomic-scale analysis on strain and the structural evolution reveals that it is the strain gradient effect that has originated from structural heterogeneity that facilitates shear transformation zones (STZs) to mature shear bands. An artificial composite model with a high degree of strain gradient, generated by inserting hard MG strips into a soft MG matrix, demonstrates a great propensity for shear banding. It therefore confirms the critical role strain gradient plays in shear banding. The strain gradient effect on shear banding is further quantified with a continuum model and a mechanical instability analysis. These physical insights might highlight the strain gradient as the hidden driving force in transforming STZs into shear bands in MGs.

  17. Interpretation of the FGF8 morphogen gradient is regulated by endocytic trafficking.

    PubMed

    Nowak, Matthias; Machate, Anja; Yu, Shuizi Rachel; Gupta, Mansi; Brand, Michael

    2011-02-01

    Forty years ago, it was proposed that during embryonic development and organogenesis, morphogen gradients provide positional information to the individual cells within a tissue leading to specific fate decisions. Recently, much insight has been gained into how such morphogen gradients are formed and maintained; however, which cellular mechanisms govern their interpretation within target tissues remains debated. Here we used in vivo fluorescence correlation spectroscopy and automated image analysis to assess the role of endocytic sorting dynamics on fibroblast growth factor 8 (Fgf8) morphogen gradient interpretation. By interfering with the function of the ubiquitin ligase Cbl, we found an expanded range of Fgf target gene expression and a delay of Fgf8 lysosomal transport. However, the extracellular Fgf8 morphogen gradient remained unchanged, indicating that the observed signalling changes are due to altered gradient interpretation. We propose that regulation of morphogen signalling activity through endocytic sorting allows fast feedback-induced changes in gradient interpretation during the establishment of complex patterns.

  18. Dai-Kou type conjugate gradient methods with a line search only using gradient.

    PubMed

    Huang, Yuanyuan; Liu, Changhe

    2017-01-01

    In this paper, the Dai-Kou type conjugate gradient methods are developed to solve the optimality condition of an unconstrained optimization, they only utilize gradient information and have broader application scope. Under suitable conditions, the developed methods are globally convergent. Numerical tests and comparisons with the PRP+ conjugate gradient method only using gradient show that the methods are efficient.

  19. Ternary gradient metal-organic frameworks.

    PubMed

    Liu, Chong; Rosi, Nathaniel L

    2017-09-08

    Gradient MOFs contain directional gradients of either structure or functionality. We have successfully prepared two ternary gradient MOFs based on bMOF-100 analogues, namely bMOF-100/102/106 and bMOF-110/100/102, via cascade ligand exchange reactions. The cubic unit cell parameter discrepancy within an individual ternary gradient MOF crystal is as large as ∼1 nm, demonstrating the impressive compatibility and flexibility of the component MOF materials. Because of the presence of a continuum of unit cells, the pore diameters within individual crystals also change in a gradient fashion from ∼2.5 nm to ∼3.0 nm for bMOF-100/102/106, and from ∼2.2 nm to ∼2.7 nm for bMOF-110/100/102, indicating significant porosity gradients. Like previously reported binary gradient MOFs, the composition of the ternary gradient MOFs can be easily controlled by adjusting the reaction conditions. Finally, X-ray diffraction and microspectrophotometry were used to analyse fractured gradient MOF crystals by comparing unit cell parameters and absorbance spectra at different locations, thus revealing the profile of heterogeneity (i.e. gradient distribution of properties) and further confirming the formation of ternary gradient MOFs.

  20. The ion temperature gradient: An intrinsic property of Earth's magnetotail

    NASA Astrophysics Data System (ADS)

    Lu, San; Artemyev, A. V.; Angelopoulos, V.; Lin, Y.; Wang, X. Y.

    2017-08-01

    Although the ion temperature gradient along (XGSM) and across (ZGSM) the Earth's magnetotail, which plays a key role in generating the cross-tail current and establishing pressure balance with the lobes, has been extensively observed by spacecraft, the mechanism responsible for its formation is still unknown. We use multispacecraft observations and three-dimensional (3-D) global hybrid simulations to reveal this mechanism. Using THEMIS (Time History of Events and Macroscale Interactions during Substorms), Geotail, and ARTEMIS (Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun) observations during individual, near-simultaneous plasma sheet crossings from 10 to 60 RE, we demonstrate that the ion temperature ZGSM profile is bell-shaped at different geocentric distances. This ZGSM profile is also prevalent in statistics of 200 THEMIS current sheet crossings in the near-Earth region. Using 3-D global hybrid simulations, we show that mapping of the XGSM gradient of ion temperature along magnetic field lines produces such a bell-shaped profile. The ion temperature mapping along magnetic field lines in the magnetotail enables construction of two-dimensional distributions of these quantities from vertical (north-south) spacecraft crossings. Our findings suggest that the ion temperature gradient is an intrinsic property of the magnetotail that should be considered in kinetic descriptions of the magnetotail current sheet. Toward this goal, we use theoretical approaches to incorporate the temperature gradient into kinetic current sheet models, making them more realistic.

  1. Design keys for paper-based concentration gradient generators.

    PubMed

    Schaumburg, Federico; Urteaga, Raúl; Kler, Pablo A; Berli, Claudio L A

    2018-08-03

    The generation of concentration gradients is an essential operation for several analytical processes implemented on microfluidic paper-based analytical devices. The dynamic gradient formation is based on the transverse dispersion of chemical species across co-flowing streams. In paper channels, this transverse flux of molecules is dominated by mechanical dispersion, which is substantially different than molecular diffusion, which is the mechanism acting in conventional microchannels. Therefore, the design of gradient generators on paper requires strategies different from those used in traditional microfluidics. This work considers the foundations of transverse dispersion in porous substrates to investigate the optimal design of microfluidic paper-based concentration gradient generators (μPGGs) by computer simulations. A set of novel and versatile μPGGs were designed in the format of numerical prototypes, and virtual experiments were run to explore the ranges of operation and the overall performance of such devices. Then physical prototypes were fabricated and experimentally tested in our lab. Finally, some basic rules for the design of optimized μPGGs are proposed. Apart from improving the efficiency of mixers, diluters and μPGGs, the results of this investigation are relevant to attain highly controlled concentration fields on paper-based devices. Copyright © 2018 Elsevier B.V. All rights reserved.

  2. Gradient Measurements of Nitrous Acid (hono)

    NASA Astrophysics Data System (ADS)

    Kleffmann, J.; Kurtenbach, R.; Lörzer, J.; Wiesen, P.; Kalthoff, N.; Vogel, B.; Vogel, H.

    Nitrous acid (HONO) plays an important role in photochemical air pollution due to its photodissociation by solar UV radiation into hydroxyl radicals and thus significantly enhances photooxidation processes. Furthermore, HONO is an important indoor pol- lutant, which can react with amines leading to nitrosamines, which are known to be carcinogenic. Despite its importance in atmospheric chemistry the mechanisms lead- ing to HONO formation are still not completely understood at present. Although it is commonly proposed that HONO is formed by heterogeneous processes, i.e. by the conversion of NO2 on wet surfaces, it is still under discussion whether HONO produc- tion is dominated by the surface of particles or by the ground surface. Simultaneous vertical profile measurements of HONO, the precursor NO2 and the aerosol surface area, which could answer this question are not available at present. Accordingly, in the present study night-time HONO, NO2 and particle surface area gradients in the altitude range 10-190 m were measured on the meteorological tower at the Forschungszentrum Karlsruhe/Germany using a new, very sensitive HONO in- strument (LOPAP), a commercial NOx monitor and a SMPS system. For all gradient measurements during the campaign it was observed that the [HONO]/[NO2] ratio decreased with increasing altitude. In contrast, the particle sur- face area was found to be more or less constant. Accordingly, no correlation between the [HONO]/[NO2] ratio and the particle surface area was observed showing that HONO formation was dominated by processes on ground surfaces and that signifi- cant HONO formation on particle surfaces could be excluded for the measurement site.

  3. Influence of two-dimensional hygrothermal gradients on interlaminar stresses near free edges

    NASA Technical Reports Server (NTRS)

    Farley, G. L.; Herakovich, C. T.

    1977-01-01

    Interlaminar stresses are determined for mechanical loading, uniform hygrothermal loading, and gradient moisture loading through implementation of a finite element computer code. Nonuniform two-dimensional hygroscopic gradients are obtained from a finite difference solution of the diffusion equation. It is shown that hygroscopic induced stresses can be larger than those resulting from mechanical and thermal loading, and that the distribution of the interlaminar normal stress may be changed significantly in the presence of a two-dimensional moisture gradient in the boundary layer of a composite laminate.

  4. Strength gradient enhances fatigue resistance of steels

    NASA Astrophysics Data System (ADS)

    Ma, Zhiwei; Liu, Jiabin; Wang, Gang; Wang, Hongtao; Wei, Yujie; Gao, Huajian

    2016-02-01

    Steels are heavily used in infrastructure and the transportation industry, and enhancing their fatigue resistance is a major challenge in materials engineering. In this study, by introducing a gradient microstructure into 304 austenitic steel, which is one of the most widely used types of stainless steel, we show that a strength gradient substantially enhances the fatigue life of the material. Pre-notched samples with negative strength gradients in front of the notch’s tip endure many more fatigue cycles than do samples with positive strength gradients during the crack initiation stage, and samples with either type of gradient perform better than do gradient-free samples with the same average yield strength. However, as a crack grows, samples with positive strength gradients exhibit better resistance to fatigue crack propagation than do samples with negative gradients or no gradient. This study demonstrates a simple and promising strategy for using gradient structures to enhance the fatigue resistance of materials and complements related studies of strength and ductility.

  5. Strength gradient enhances fatigue resistance of steels

    PubMed Central

    Ma, Zhiwei; Liu, Jiabin; Wang, Gang; Wang, Hongtao; Wei, Yujie; Gao, Huajian

    2016-01-01

    Steels are heavily used in infrastructure and the transportation industry, and enhancing their fatigue resistance is a major challenge in materials engineering. In this study, by introducing a gradient microstructure into 304 austenitic steel, which is one of the most widely used types of stainless steel, we show that a strength gradient substantially enhances the fatigue life of the material. Pre-notched samples with negative strength gradients in front of the notch’s tip endure many more fatigue cycles than do samples with positive strength gradients during the crack initiation stage, and samples with either type of gradient perform better than do gradient-free samples with the same average yield strength. However, as a crack grows, samples with positive strength gradients exhibit better resistance to fatigue crack propagation than do samples with negative gradients or no gradient. This study demonstrates a simple and promising strategy for using gradient structures to enhance the fatigue resistance of materials and complements related studies of strength and ductility. PMID:26907708

  6. Combinational concentration gradient confinement through stagnation flow.

    PubMed

    Alicia, Toh G G; Yang, Chun; Wang, Zhiping; Nguyen, Nam-Trung

    2016-01-21

    Concentration gradient generation in microfluidics is typically constrained by two conflicting mass transport requirements: short characteristic times (τ) for precise temporal control of concentration gradients but at the expense of high flow rates and hence, high flow shear stresses (σ). To decouple the limitations from these parameters, here we propose the use of stagnation flows to confine concentration gradients within large velocity gradients that surround the stagnation point. We developed a modified cross-slot (MCS) device capable of feeding binary and combinational concentration sources in stagnation flows. We show that across the velocity well, source-sink pairs can form permanent concentration gradients. As source-sink concentration pairs are continuously supplied to the MCS, a permanently stable concentration gradient can be generated. Tuning the flow rates directly controls the velocity gradients, and hence the stagnation point location, allowing the confined concentration gradient to be focused. In addition, the flow rate ratio within the MCS rapidly controls (τ ∼ 50 ms) the location of the stagnation point and the confined combinational concentration gradients at low flow shear (0.2 Pa < σ < 2.9 Pa). The MCS device described in this study establishes the method for using stagnation flows to rapidly generate and position low shear combinational concentration gradients for shear sensitive biological assays.

  7. Chemotactic cell trapping in controlled alternating gradient fields

    PubMed Central

    Meier, Börn; Zielinski, Alejandro; Weber, Christoph; Arcizet, Delphine; Youssef, Simon; Franosch, Thomas; Rädler, Joachim O.; Heinrich, Doris

    2011-01-01

    Directed cell migration toward spatio-temporally varying chemotactic stimuli requires rapid cytoskeletal reorganization. Numerous studies provide evidence that actin reorganization is controlled by intracellular redistribution of signaling molecules, such as the PI4,5P2/PI3,4,5P3 gradient. However, exploring underlying mechanisms is difficult and requires careful spatio-temporal control of external chemotactic stimuli. We designed a microfluidic setup to generate alternating chemotactic gradient fields for simultaneous multicell exposure, greatly facilitating statistical analysis. For a quantitative description of intracellular response dynamics, we apply alternating time sequences of spatially homogeneous concentration gradients across 300 μm, reorienting on timescales down to a few seconds. Dictyostelium discoideum amoebae respond to gradient switching rates below 0.02 Hz by readapting their migration direction. For faster switching, cellular repolarization ceases and is completely stalled at 0.1 Hz. In this “chemotactically trapped” cell state, external stimuli alternate faster than intracellular feedback is capable to respond by onset of directed migration. To investigate intracellular actin cortex rearrangement during gradient switching, we correlate migratory cell response with actin repolymerization dynamics, quantified by a fluorescence distribution moment of the GFP fusion protein LimEΔcc. We find two fundamentally different cell polarization types and we could reveal the role of PI3-Kinase for cellular repolarization. In the early aggregation phase, PI3-Kinase enhances the capability of D. discoideum cells to readjust their polarity in response to spatially alternating gradient fields, whereas in aggregation competent cells the effect of PI3-Kinase perturbation becomes less relevant. PMID:21709255

  8. Gradient Plasticity Model and its Implementation into MARMOT

    SciTech Connect

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

    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 thismore » 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.« less

  9. Asymmetrical Macromolecular Complex Formation of Lysophosphatidic Acid Receptor 2 (LPA2) Mediates Gradient Sensing in Fibroblasts*

    PubMed Central

    Ren, Aixia; Moon, Changsuk; Zhang, Weiqiang; Sinha, Chandrima; Yarlagadda, Sunitha; Arora, Kavisha; Wang, Xusheng; Yue, Junming; Parthasarathi, Kaushik; Heil-Chapdelaine, Rick; Tigyi, Gabor; Naren, Anjaparavanda P.

    2014-01-01

    Chemotactic migration of fibroblasts toward growth factors relies on their capacity to sense minute extracellular gradients and respond to spatially confined receptor-mediated signals. Currently, mechanisms underlying the gradient sensing of fibroblasts remain poorly understood. Using single-particle tracking methodology, we determined that a lysophosphatidic acid (LPA) gradient induces a spatiotemporally restricted decrease in the mobility of LPA receptor 2 (LPA2) on chemotactic fibroblasts. The onset of decreased LPA2 mobility correlates to the spatial recruitment and coupling to LPA2-interacting proteins that anchor the complex to the cytoskeleton. These localized PDZ motif-mediated macromolecular complexes of LPA2 trigger a Ca2+ puff gradient that governs gradient sensing and directional migration in response to LPA. Disruption of the PDZ motif-mediated assembly of the macromolecular complex of LPA2 disorganizes the gradient of Ca2+ puffs, disrupts gradient sensing, and reduces the directional migration of fibroblasts toward LPA. Our findings illustrate that the asymmetric macromolecular complex formation of chemoattractant receptors mediates gradient sensing and provides a new mechanistic basis for models to describe gradient sensing of fibroblasts. PMID:25542932

  10. Interrelationship between flexoelectricity and strain gradient elasticity in ferroelectric nanofilms: A phase field study

    NASA Astrophysics Data System (ADS)

    Jiang, Limei; Xu, Xiaofei; Zhou, Yichun

    2016-12-01

    With the development of the integrated circuit technology and decreasing of the device size, ferroelectric films used in nano ferroelectric devices become thinner and thinner. Along with the downscaling of the ferroelectric film, there is an increasing influence of two strain gradient related terms. One is the strain gradient elasticity and the other one is flexoelectricity. To investigate the interrelationship between flexoelectricity and strain gradient elasticity and their combined effect on the domain structure in ferroelectric nanofilms, a phase field model of flexoelectricity and strain gradient elasticity on the ferroelectric domain evolution is developed based on Mindlin's theory of strain-gradient elasticity. Weak form is derived and implemented in finite element formulations for numerically solving the model equations. The simulation results show that upper bounds for flexoelectric coefficients can be enhanced by increasing strain gradient elasticity coefficients. While a large flexoelectricity that exceeds the upper bound can induce a transition from a ferroelectric state to a modulated/incommensurate state, a large enough strain gradient elasticity may lead to a conversion from an incommensurate state to a ferroelectric state. Strain gradient elasticity and the flexoelectricity have entirely opposite effects on polarization. The observed interrelationship between the strain gradient elasticity and flexoelectricity is rationalized by an analytical solution of the proposed theoretical model. The model proposed in this paper could help us understand the mechanism of phenomena observed in ferroelectric nanofilms under complex electromechanical loads and provide some guides on the practical application of ferroelectric nanofilms.

  11. The Educational Gradient in Health in China

    PubMed Central

    Chen, Qiulin; Eggleston, Karen; Zhang, Wei; Zhao, Jiaying; Zhou, Sen

    2017-01-01

    It has been well established that better educated individuals enjoy better health and longevity. In theory, the educational gradients in health could be flattening if diminishing returns to improved average education levels and the influence of earlier population health interventions outweigh the gradient-steepening effects of new medical and health technologies. This paper documents how the gradients are evolving in China, a rapidly developing country, about which little is known on this topic. Based on recent mortality data and nationally representative health surveys, we find large and, in some cases, steepening educational gradients. We also find that the gradients vary by cohort, gender and region. Further, we find that the gradients can only partially be accounted for by economic factors. These patterns highlight the double disadvantage of those with low education, and suggest the importance of policy interventions that foster both aspects of human capital for them. PMID:29056815

  12. Automated Quantification of Gradient Defined Features

    DTIC Science & Technology

    2008-09-01

    defined features in submarine environments. The technique utilizes MATLAB scripts to convert bathymetry data into a gradient dataset, produce gradient...maps, and most importantly, automate the process of defining and characterizing gradient defined features such as flows, faults, landslide scarps, folds...convergent plate margin hosts a series of large serpentinite mud volcanoes (Fig. 1). One of the largest of these active mud volcanoes is Big Blue

  13. Gradient Nanostructured Tantalum by Thermal-Mechanical Ultrasonic Impact Energy.

    PubMed

    Chae, Jong-Min; Lee, Keun-Oh; Amanov, Auezhan

    2018-03-20

    Microstructural evolution and wear performance of Tantalum (Ta) treated by ultrasonic nanocrystalline surface modification (UNSM) at 25 and 1000 °C were reported. The UNSM treatment modified a surface along with subsurface layer with a thickness in the range of 20 to 150 µm, which depends on the UNSM treatment temperature, via the surface severe plastic deformation (S²PD) method. The cross-sectional microstructure of the specimens was observed by electron backscattered diffraction (EBSD) in order to confirm the microstructural alteration in terms of effective depth and refined grain size. The surface hardness measurement results, including depth profile, revealed that the hardness of the UNSM-treated specimens at both temperatures was increased in comparison with those of the untreated ones. The increase in UNSM treatment temperature led to a further increase in hardness. Moreover, both the UNSM-treated specimens with an increased hardness resulted in a higher resistance to wear in comparison with those of the untreated ones under dry conditions. The increase in hardness and induced compressive residual stress that depend on the formation of severe plastically deformed layer with the refined nano-grains are responsible for the enhancement in wear resistance. The findings of this study may be implemented in response to various industries that are related to strength improvement and wear enhancement issues of Ta.

  14. Gradient Nanostructured Tantalum by Thermal-Mechanical Ultrasonic Impact Energy

    PubMed Central

    Chae, Jong-Min; Lee, Keun-Oh; Amanov, Auezhan

    2018-01-01

    Microstructural evolution and wear performance of Tantalum (Ta) treated by ultrasonic nanocrystalline surface modification (UNSM) at 25 and 1000 °C were reported. The UNSM treatment modified a surface along with subsurface layer with a thickness in the range of 20 to 150 µm, which depends on the UNSM treatment temperature, via the surface severe plastic deformation (S2PD) method. The cross-sectional microstructure of the specimens was observed by electron backscattered diffraction (EBSD) in order to confirm the microstructural alteration in terms of effective depth and refined grain size. The surface hardness measurement results, including depth profile, revealed that the hardness of the UNSM-treated specimens at both temperatures was increased in comparison with those of the untreated ones. The increase in UNSM treatment temperature led to a further increase in hardness. Moreover, both the UNSM-treated specimens with an increased hardness resulted in a higher resistance to wear in comparison with those of the untreated ones under dry conditions. The increase in hardness and induced compressive residual stress that depend on the formation of severe plastically deformed layer with the refined nano-grains are responsible for the enhancement in wear resistance. The findings of this study may be implemented in response to various industries that are related to strength improvement and wear enhancement issues of Ta. PMID:29558402

  15. Molecular Quantum Mechanics: Analytic Gradients and Beyond - Program and Abstracts

    DTIC Science & Technology

    2007-06-03

    Kutzelnigg (Bochum, Germany) Chair: Pekka Pyykko (Helsinki, Finland) Which Masses are Vibrating or Rotating in a Molecule? 15:40-16:15 O30...Krylov (Los Angeles, CA, U.S.A.) Multiconfigurational Quantum Chemistry for Actinide Containing Systems: From Isolated Molecules to Condensed...the genetic algorithm will be critically assessed. For B4n, the double rings are notably stable. The DFT calculations provide strong indications of

  16. Nanofiber scaffold gradients for interfacial tissue engineering.

    PubMed

    Ramalingam, Murugan; Young, Marian F; Thomas, Vinoy; Sun, Limin; Chow, Laurence C; Tison, Christopher K; Chatterjee, Kaushik; Miles, William C; Simon, Carl G

    2013-02-01

    We have designed a 2-spinnerette device that can directly electrospin nanofiber scaffolds containing a gradient in composition that can be used to engineer interfacial tissues such as ligament and tendon. Two types of nanofibers are simultaneously electrospun in an overlapping pattern to create a nonwoven mat of nanofibers containing a composition gradient. The approach is an advance over previous methods due to its versatility - gradients can be formed from any materials that can be electrospun. A dye was used to characterize the 2-spinnerette approach and applicability to tissue engineering was demonstrated by fabricating nanofibers with gradients in amorphous calcium phosphate nanoparticles (nACP). Adhesion and proliferation of osteogenic cells (MC3T3-E1 murine pre-osteoblasts) on gradients was enhanced on the regions of the gradients that contained higher nACP content yielding a graded osteoblast response. Since increases in soluble calcium and phosphate ions stimulate osteoblast function, we measured their release and observed significant release from nanofibers containing nACP. The nanofiber-nACP gradients fabricated herein can be applied to generate tissues with osteoblast gradients such as ligaments or tendons. In conclusion, these results introduce a versatile approach for fabricating nanofiber gradients that can have application for engineering graded tissues.

  17. Optimal Disturbances in Boundary Layers Subject to Streamwise Pressure Gradient

    NASA Technical Reports Server (NTRS)

    Ashpis, David E.; Tumin, Anatoli

    2003-01-01

    An analysis of the non-modal growth of perturbations in a boundary layer in the presence of a streamwise pressure gradient is presented. The analysis is based on PSE equations for an incompressible fluid. Examples with Falkner- Skan profiles indicate that a favorable pressure gradient decreases the non-modal growth while an unfavorable pressure gradient leads to an increase of the amplification. It is suggested that the transient growth mechanism be utilized to choose optimal parameters of tripping elements on a low-pressure turbine (LPT) airfoil. As an example, a boundary-layer flow with a streamwise pressure gradient corresponding to the pressure distribution over a LPT airfoil is considered. It is shown that there is an optimal spacing of the tripping elements and that the transient growth effect depends on the starting point. The amplification is found to be small at the LPT s very low Reynolds numbers, but there is a possibility to enhance the transient energy growth by means of wall cooling.

  18. Gravity gradient preprocessing at the GOCE HPF

    NASA Astrophysics Data System (ADS)

    Bouman, J.; Rispens, S.; Gruber, T.; Schrama, E.; Visser, P.; Tscherning, C. C.; Veicherts, M.

    2009-04-01

    One of the products derived from the GOCE observations are the gravity gradients. These gravity gradients are provided in the Gradiometer Reference Frame (GRF) and are calibrated in-flight using satellite shaking and star sensor data. In order to use these gravity gradients for application in Earth sciences and gravity field analysis, additional pre-processing needs to be done, including corrections for temporal gravity field signals to isolate the static gravity field part, screening for outliers, calibration by comparison with existing external gravity field information and error assessment. The temporal gravity gradient corrections consist of tidal and non-tidal corrections. These are all generally below the gravity gradient error level, which is predicted to show a 1/f behaviour for low frequencies. In the outlier detection the 1/f error is compensated for by subtracting a local median from the data, while the data error is assessed using the median absolute deviation. The local median acts as a high-pass filter and it is robust as is the median absolute deviation. Three different methods have been implemented for the calibration of the gravity gradients. All three methods use a high-pass filter to compensate for the 1/f gravity gradient error. The baseline method uses state-of-the-art global gravity field models and the most accurate results are obtained if star sensor misalignments are estimated along with the calibration parameters. A second calibration method uses GOCE GPS data to estimate a low degree gravity field model as well as gravity gradient scale factors. Both methods allow to estimate gravity gradient scale factors down to the 10-3 level. The third calibration method uses high accurate terrestrial gravity data in selected regions to validate the gravity gradient scale factors, focussing on the measurement band. Gravity gradient scale factors may be estimated down to the 10-2 level with this method.

  19. Enhanced protective role in materials with gradient structural orientations: Lessons from Nature.

    PubMed

    Liu, Zengqian; Zhu, Yankun; Jiao, Da; Weng, Zhaoyong; Zhang, Zhefeng; Ritchie, Robert O

    2016-10-15

    Living organisms are adept at resisting contact deformation and damage by assembling protective surfaces with spatially varied mechanical properties, i.e., by creating functionally graded materials. Such gradients, together with multiple length-scale hierarchical structures, represent the two prime characteristics of many biological materials to be translated into engineering design. Here, we examine one design motif from a variety of biological tissues and materials where site-specific mechanical properties are generated for enhanced protection by adopting gradients in structural orientation over multiple length-scales, without manipulation of composition or microstructural dimension. Quantitative correlations are established between the structural orientations and local mechanical properties, such as stiffness, strength and fracture resistance; based on such gradients, the underlying mechanisms for the enhanced protective role of these materials are clarified. Theoretical analysis is presented and corroborated through numerical simulations of the indentation behavior of composites with distinct orientations. The design strategy of such bioinspired gradients is outlined in terms of the geometry of constituents. This study may offer a feasible approach towards generating functionally graded mechanical properties in synthetic materials for improved contact damage resistance. Living organisms are adept at resisting contact damage by assembling protective surfaces with spatially varied mechanical properties, i.e., by creating functionally-graded materials. Such gradients, together with multiple length-scale hierarchical structures, represent the prime characteristics of many biological materials. Here, we examine one design motif from a variety of biological tissues where site-specific mechanical properties are generated for enhanced protection by adopting gradients in structural orientation at multiple length-scales, without changes in composition or microstructural

  20. 40 CFR 230.25 - Salinity gradients.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... gradients form where salt water from the ocean meets and mixes with fresh water from land. (b) Possible loss... those organisms that are adapted to freshwater environments. It may also affect municipal water supplies... fresh or salt water may change existing salinity gradients. For example, partial blocking of the...

  1. Announcing Workshop on High Gradient RF

    Science.gov Websites

    Cavities at Argonne National Laboratory Workshop on High Gradient RF October 7-9, 2003 Agenda Accommodation Argonne Guest House SLAC Workshop August 2000 Attendees ANL Map High energy physics and other the gradient limits of these devices. Although the limits on high fields in rf cavities have been

  2. An Inexpensive Digital Gradient Controller for HPLC.

    ERIC Educational Resources Information Center

    Brady, James E.; Carr, Peter W.

    1983-01-01

    Use of gradient elution techniques in high performance liquid chromatography (HPLC) is often essential for direct separation of complex mixtures. Since most commercial controllers have features that are of marginal value for instructional purposes, a low-cost controller capable of illustrating essential features of gradient elution was developed.…

  3. Patterns of macromycete community assemblage along an elevation gradient: options for fungal gradient and metacommunity analyse

    Treesearch

    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...

  4. Convective Electrokinetic Instability With Conductivity Gradients

    NASA Astrophysics Data System (ADS)

    Chen, Chuan-Hua; Lin, Hao; Lele, Sanjiva; Santiago, Juan

    2003-11-01

    Electrokinetic flow instability has been experimentally identified and quantified in a glass T-junction microchannel system with a cross section of 11 um x 155 um. In this system, buffers of different conductivities were electrokinetically driven into a common mixing channel by a DC electric field. A convective instability was observed with a threshold electric field of 0.45 kV/cm for a 10:1 conductivity ratio. A physical model has been developed which consists of a modified Ohmic model formulation for electrolyte solutions and the Navier-Stokes equations with an electric body force term. The model and experiments show that bulk charge accumulation in regions of conductivity gradients is the key mechanism of such instabilities. A linear stability analysis was performed in a convective framework, and Briggs-Bers criteria were applied to determine the nature of instability. The analysis shows the instability is governed by two key parameters: the ratio of molecular diffusion to electroviscous time scale which governs the onset of instability, and the ratio of electroviscous to electroosmotic velocity which governs whether the instability is convective or absolute. The model predicted critical electric field, growth rate, wavelength, and phase speed which were comparable to experimental data.

  5. Bioinspired adaptive gradient refractive index distribution lens

    NASA Astrophysics Data System (ADS)

    Yin, Kezhen; Lai, Chuan-Yar; Wang, Jia; Ji, Shanzuo; Aldridge, James; Feng, Jingxing; Olah, Andrew; Baer, Eric; Ponting, Michael

    2018-02-01

    Inspired by the soft, deformable human eye lens, a synthetic polymer gradient refractive index distribution (GRIN) lens with an adaptive geometry and focal power has been demonstrated via multilayer coextrusion and thermoforming of nanolayered elastomeric polymer films. A set of 30 polymer nanolayered films comprised of two thermoplastic polyurethanes having a refractive index difference of 0.05 were coextruded via forced-assembly technique. The set of 30 nanolayered polymer films exhibited transmission near 90% with each film varying in refractive index by 0.0017. An adaptive GRIN lens was fabricated from a laminated stack of the variable refractive index films with a 0.05 spherical GRIN. This lens was subsequently deformed by mechanical ring compression of the lens. Variation in the optical properties of the deformable GRIN lens was determined, including 20% variation in focal length and reduced spherical aberration. These properties were measured and compared to simulated results by placido-cone topography and ANSYS methods. The demonstration of a solid-state, dynamic focal length, GRIN lens with improved aberration correction was discussed relative to the potential future use in implantable devices.

  6. Competition along productivity gradients: news from heathlands.

    PubMed

    Delerue, Florian; Gonzalez, Maya; Achat, David L; Puzos, Luc; Augusto, Laurent

    2018-05-01

    The importance of competition in low productive habitats is still debated. Studies which simultaneously evaluate preemption of resources and consequences for population dynamics are needed for a comprehensive view of competitive outcomes. We cultivated two emblematic species of European heathlands (Calluna vulgaris and Molinia caerulea) in a nursery for 2 years at two fertility levels, reproducing the productivity gradient found in phosphorus (P)-depleted heathlands in southwest France. The second year, we planted Ulex europaeus seedlings, a ubiquitous heathland species, under the cover of the two species to evaluate its ability to regenerate. Half of the seedlings were placed in tubes for exclusion of competitor roots. We measured the development of the competitors aboveground and belowground and their interception of resources (light, water, inorganic P). Ulex seedlings' growth and survival were also measured. Our results on resources interception were consistent with species distribution in heathlands. Molinia, which dominates rich heathlands, was the strongest competitor for light and water in the rich soil. Calluna, which dominates poor heathlands, increased its root allocation in the poor soil, decreasing water and inorganic P availability. However, the impact of total competition and root competition on Ulex seedlings decreased in the poor soil. Other mechanisms, especially decrease of water stress under neighbouring plant cover, appeared to have more influence on the seedlings' response. We found no formal contradiction between Tilman and Grime's theories. Root competition has a primary role in acquisition of soil resources in poor habitats. However, the importance of competition decreases with decreasing fertility.

  7. Applying Gradient Descent in Convolutional Neural Networks

    NASA Astrophysics Data System (ADS)

    Cui, Nan

    2018-04-01

    With the development of the integrated circuit and computer science, people become caring more about solving practical issues via information technologies. Along with that, a new subject called Artificial Intelligent (AI) comes up. One popular research interest of AI is about recognition algorithm. In this paper, one of the most common algorithms, Convolutional Neural Networks (CNNs) will be introduced, for image recognition. Understanding its theory and structure is of great significance for every scholar who is interested in this field. Convolution Neural Network is an artificial neural network which combines the mathematical method of convolution and neural network. The hieratical structure of CNN provides it reliable computer speed and reasonable error rate. The most significant characteristics of CNNs are feature extraction, weight sharing and dimension reduction. Meanwhile, combining with the Back Propagation (BP) mechanism and the Gradient Descent (GD) method, CNNs has the ability to self-study and in-depth learning. Basically, BP provides an opportunity for backwardfeedback for enhancing reliability and GD is used for self-training process. This paper mainly discusses the CNN and the related BP and GD algorithms, including the basic structure and function of CNN, details of each layer, the principles and features of BP and GD, and some examples in practice with a summary in the end.

  8. Surface-attached orthogonal gradient hydrogels

    NASA Astrophysics Data System (ADS)

    Chinnayan Kannan, Pandiyarajan; Genzer, Jan

    Gradient materials play a significant role in the creation of artificial implants due to their potential to reduce stress concentration when two or more structures with different mechanical properties are joined together, e . g . , tendon, a fibrous protein that connects the soft and hard muscle tissues in our body. We employ free radical polymerization to synthesize random copolymers containing 90% of N-isopropyl acrylamide (NIPAAm), 5% photo-active methacrylyloxybenzophenone (MABP) and 5% thermally-active styrenesulfonylazide (SSAz) crosslinkers. The presence of MABP and SSAz facilitates adjusting gel density on a flat support in two orthogonal directions by spatially and independently controlling UV dosage and temperature. The swelling behavior (α) of the gels in water and methanol is examined using a spectroscopic ellipsometry and the degree of swelling depends on the extent of crosslinking that ranges from α = 1-1.2 (highly crosslinked gels) to α = 4-5 (loosely crosslinked gels). We compare the network properties surface-attached gels and un-attached identical counterparts and confirm that the linear swelling ratio of surface-attached networks is higher than that of the corresponding un-attached gels.

  9. Spatially Different Tissue-Scale Diffusivity Shapes ANGUSTIFOLIA3 Gradient in Growing Leaves.

    PubMed

    Kawade, Kensuke; Tanimoto, Hirokazu; Horiguchi, Gorou; Tsukaya, Hirokazu

    2017-09-05

    The spatial gradient of signaling molecules is pivotal for establishing developmental patterns of multicellular organisms. It has long been proposed that these gradients could arise from the pure diffusion process of signaling molecules between cells, but whether this simplest mechanism establishes the formation of the tissue-scale gradient remains unclear. Plasmodesmata are unique channel structures in plants that connect neighboring cells for molecular transport. In this study, we measured cellular- and tissue-scale kinetics of molecular transport through plasmodesmata in Arabidopsis thaliana developing leaf primordia by fluorescence recovery assays. These trans-scale measurements revealed biophysical properties of diffusive molecular transport through plasmodesmata and revealed that the tissue-scale diffusivity, but not the cellular-scale diffusivity, is spatially different along the leaf proximal-to-distal axis. We found that the gradient in cell size along the developmental axis underlies this spatially different tissue-scale diffusivity. We then asked how this diffusion-based framework functions in establishing a signaling gradient of endogenous molecules. ANGUSTIFOLIA3 (AN3) is a transcriptional co-activator, and as we have shown here, it forms a long-range signaling gradient along the leaf proximal-to-distal axis to determine a cell-proliferation domain. By genetically engineering AN3 mobility, we assessed each contribution of cell-to-cell movement and tissue growth to the distribution of the AN3 gradient. We constructed a diffusion-based theoretical model using these quantitative data to analyze the AN3 gradient formation and demonstrated that it could be achieved solely by the diffusive molecular transport in a growing tissue. Our results indicate that the spatially different tissue-scale diffusivity is a core mechanism for AN3 gradient formation. This provides evidence that the pure diffusion process establishes the formation of the long-range signaling

  10. Dual fuel gradients in uranium silicide plates

    SciTech Connect

    Pace, B.W.

    1997-08-01

    Babcock & Wilcox has been able to achieve dual gradient plates with good repeatability in small lots of U{sub 3}Si{sub 2} plates. Improvements in homogeneity and other processing parameters and techniques have allowed the development of contoured fuel within the cladding. The most difficult obstacles to overcome have been the ability to evaluate the bidirectional fuel loadings in comparison to the perfect loading model and the different methods of instilling the gradients in the early compact stage. The overriding conclusion is that to control the contour of the fuel, a known relationship between the compact, the frames and final coremore » gradient must exist. Therefore, further development in the creation and control of dual gradients in fuel plates will involve arriving at a plausible gradient requirement and building the correct model between the compact configuration and the final contoured loading requirements.« less

  11. Approximate error conjugation gradient minimization methods

    DOEpatents

    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.

  12. Temperature Gradient-Induced Instability of Perovskite via Ion Transport.

    PubMed

    Wang, Xinwei; Liu, Hong; Zhou, Feng; Dahan, Jeremy; Wang, Xin; Li, Zhengping; Shen, Wenzhong

    2018-01-10

    Perovskite has been known as a promising novel material for photovoltaics and other fields because of its excellent opto-electric properties and convenient fabrication. However, its stability has been a widely known haunting factor that has severely deteriorated its application in reality. In this work, it has been discovered for the first time that perovskite can become significantly chemically unstable with the existence of a temperature gradient in the system, even at temperature far below its thermal decomposition condition. A study of the detailed mechanism has revealed that the existence of a temperature gradient could induce a mass transport process of extrinsic ionic species into the perovskite layer, which enhances its decomposition process. Moreover, this instability could be effectively suppressed with a reduced temperature gradient by simple structural modification of the device. Further experiments have proved the existence of this phenomenon in different perovskites with various mainstream substrates, indicating the universality of this phenomenon in many previous studies and future research. Hopefully, this work may bring deeper understanding of its formation mechanisms and facilitate the general development of perovskite toward its real application.

  13. Intramyocardial pressure gradients in working and nonworking isolated cat hearts.

    PubMed

    Mihailescu, L S; Abel, F L

    1994-03-01

    This study presents an improved method for the measurement of intramyocardial pressure (IMP) using the servo-nulling mechanism. Glass micropipettes (20-24 microns OD) were used as transducers, coated to increase their mechanical resistance to breakage, and placed inside the left ventricular wall with a micropipette holder and manipulator. IMP was measured at the base of the left ventricle in working and nonworking isolated cat hearts that were perfused with Krebs-Henseleit buffer. In working hearts a transmural gradient of systolic IMP oriented from endocardium toward the epicardium was found; the endocardial values for systolic IMP were slightly higher than systolic left ventricular pressure (LVP), by 11-18%. Increases in afterload induced increases in IMP, without changing the systolic IMP-to-LVP ratio. In nonworking hearts with drained left ventricles, the systolic transmural gradient for IMP described for working hearts persisted, but at lower values, and was directly dependent on coronary perfusion pressure. Systolic IMP-to-LVP ratios were always > 1. The diastolic IMP of both working and nonworking hearts exhibited irregular transmural gradients. Our results support the view that generated systolic IMP is largely independent of LVP development.

  14. Rolling motion of an elastic cylinder induced by elastic strain gradients

    NASA Astrophysics Data System (ADS)

    Chen, Lei; Chen, Shaohua

    2014-10-01

    Recent experiment shows that an elastic strain gradient field can be utilized to transport spherical particles on a stretchable substrate by rolling, inspired by which a generalized plane-strain Johnson-Kendall-Roberts model is developed in this paper in order to verify possible rolling of an elastic cylinder adhering on an elastic substrate subject to a strain gradient. With the help of contact mechanics, closed form solutions of interface tractions, stress intensity factors, and corresponding energy release rates in the plane-strain contact model are obtained, based on which a possible rolling motion of an elastic cylinder induced by strain gradients is found and the criterion for the initiation of rolling is established. The theoretical prediction is consistent well with the existing experimental observation. The result should be helpful for understanding biological transport mechanisms through muscle contractions and the design of transport systems with strain gradient.

  15. Learning-Related Shifts in Generalization Gradients for Complex Sounds

    PubMed Central

    Wisniewski, Matthew G.; Church, Barbara A.; Mercado, Eduardo

    2010-01-01

    Learning to discriminate stimuli can alter how one distinguishes related stimuli. For instance, training an individual to differentiate between two stimuli along a single dimension can alter how that individual generalizes learned responses. In this study, we examined the persistence of shifts in generalization gradients after training with sounds. University students were trained to differentiate two sounds that varied along a complex acoustic dimension. Students subsequently were tested on their ability to recognize a sound they experienced during training when it was presented among several novel sounds varying along this same dimension. Peak shift was observed in Experiment 1 when generalization tests immediately followed training, and in Experiment 2 when tests were delayed by 24 hours. These findings further support the universality of generalization processes across species, modalities, and levels of stimulus complexity. They also raise new questions about the mechanisms underlying learning-related shifts in generalization gradients. PMID:19815929

  16. Advances in high gradient normal conducting accelerator structures

    SciTech Connect

    Simakov, Evgenya Ivanovna; Dolgashev, Valery A.; Tantawi, Sami G.

    Here, this paper reviews the current state-of-the-art in understanding the phenomena of ultra-high vacuum radio-frequency (rf) breakdown in accelerating structures and the efforts to improve stable operation of the structures at accelerating gradients above 100 MV/m. Numerous studies have been conducted recently with the goal of understanding the dependence of the achievable accelerating gradients and breakdown rates on the frequency of operations, the geometry of the structure, material and method of fabrication, and operational temperature. Tests have been conducted with single standing wave accelerator cells as well as with the multi-cell traveling wave structures. Notable theoretical effort was directed atmore » understanding the physical mechanisms of the rf breakdown and its statistical behavior. Finally, the achievements presented in this paper are the result of the large continuous self-sustaining collaboration of multiple research institutions in the United States and worldwide.« less

  17. Ecological and evolutionary drivers of the elevational gradient of diversity.

    PubMed

    Laiolo, Paola; Pato, Joaquina; Obeso, José Ramón

    2018-05-02

    Ecological, evolutionary, spatial and neutral theories make distinct predictions and provide distinct explanations for the mechanisms that control the relationship between diversity and the environment. Here, we test predictions of the elevational diversity gradient focusing on Iberian bumblebees, grasshoppers and birds. Processes mediated by local abundance and regional diversity concur in explaining local diversity patterns along elevation. Effects expressed through variation in abundance were similar among taxa and point to the overriding role of a physical factor, temperature. This determines how energy is distributed among individuals and ultimately how the resulting pattern of abundance affects species incidence. Effects expressed through variation in regional species pools depended instead on taxon-specific evolutionary history, and lead to diverging responses under similar environmental pressures. Local filters and regional variation also explain functional diversity gradients, in line with results from species richness that indicate an (local) ecological and (regional) historical unfolding of diversity-elevation relationships. © 2018 John Wiley & Sons Ltd/CNRS.

  18. Gravitation is a Gradient in the Velocity of Light

    NASA Astrophysics Data System (ADS)

    Froedge, Dt

    2017-01-01

    It is well known that a photon moving in a gravitational field has a trajectory that can be defined by Fermat's principle with a variable speed of light and no other gravitational influence. If it can be shown that a particle composed of speed of light sub-particles has the same acceleration in a variable index of refraction as a particle in a gravitational field, then there is no need to ascribe any other mechanism to gravitation than a gradient in c. This makes gravitation an electromagnetic phenomenon, and if QFT can illustrate a gradient in c can be produced by the internal motion of lightspeed sub-particles then the unification of QM and gravitation becomes more straightforward. http://www.arxdtf.org/css/GravAPS.pdf.

  19. Effects of Spatial Gradients on Electron Runaway Acceleration

    NASA Technical Reports Server (NTRS)

    MacNeice, Peter; Ljepojevic, N. N.

    1996-01-01

    The runaway process is known to accelerate electrons in many laboratory plasmas and has been suggested as an acceleration mechanism in some astrophysical plasmas, including solar flares. Current calculations of the electron velocity distributions resulting from the runaway process are greatly restricted because they impose spatial homogeneity on the distribution. We have computed runaway distributions which include consistent development of spatial gradients in the energetic tail. Our solution for the electron velocity distribution is presented as a function of distance along a finite length acceleration region, and is compared with the equivalent distribution for the infinitely long homogenous system (i.e., no spatial gradients), as considered in the existing literature. All these results are for the weak field regime. We also discuss the severe restrictiveness of this weak field assumption.

  20. Recent identification of an ERK signal gradient governing planarian regeneration.

    PubMed

    Agata, Kiyokazu; Tasaki, Junichi; Nakajima, Elizabeth; Umesono, Yoshihiko

    2014-06-01

    Planarians have strong regenerative abilities derived from their adult pluripotent stem cell (neoblast) system. However, the molecular mechanisms involved in planarian regeneration have long remained a mystery. In particular, no anterior-specifying factor(s) could be found, although Wnt family proteins had been successfully identified as posterior-specifying factors during planarian regeneration (Gurley et al., 2008; Petersen and Reddien, 2008). A recent textbook of developmental biology therefore proposes a Wnt antagonist as a putative anterior factor (Gilbert, 2013). That is, planarian regeneration was supposed to be explained by a single decreasing gradient of the β-catenin signal from tail to head. However, recently we succeeded in demonstrating that in fact the extracellular-signal regulated kinases (ERK) form a decreasing gradient from head to tail to direct the reorganization of planarian body regionality after amputation (Umesono et al., 2013). Copyright © 2014 Elsevier GmbH. All rights reserved.

  1. Advances in high gradient normal conducting accelerator structures

    DOE PAGES

    Simakov, Evgenya Ivanovna; Dolgashev, Valery A.; Tantawi, Sami G.

    2018-03-09

    Here, this paper reviews the current state-of-the-art in understanding the phenomena of ultra-high vacuum radio-frequency (rf) breakdown in accelerating structures and the efforts to improve stable operation of the structures at accelerating gradients above 100 MV/m. Numerous studies have been conducted recently with the goal of understanding the dependence of the achievable accelerating gradients and breakdown rates on the frequency of operations, the geometry of the structure, material and method of fabrication, and operational temperature. Tests have been conducted with single standing wave accelerator cells as well as with the multi-cell traveling wave structures. Notable theoretical effort was directed atmore » understanding the physical mechanisms of the rf breakdown and its statistical behavior. Finally, the achievements presented in this paper are the result of the large continuous self-sustaining collaboration of multiple research institutions in the United States and worldwide.« less

  2. Developing Gradient Metal Alloys through Radial Deposition Additive Manufacturing

    PubMed Central

    Hofmann, Douglas C.; Roberts, Scott; Otis, Richard; Kolodziejska, Joanna; Dillon, R. Peter; Suh, Jong-ook; Shapiro, Andrew A.; Liu, Zi-Kui; Borgonia, John-Paul

    2014-01-01

    Interest in additive manufacturing (AM) has dramatically expanded in the last several years, owing to the paradigm shift that the process provides over conventional manufacturing. Although the vast majority of recent work in AM has focused on three-dimensional printing in polymers, AM techniques for fabricating metal alloys have been available for more than a decade. Here, laser deposition (LD) is used to fabricate multifunctional metal alloys that have a strategically graded composition to alter their mechanical and physical properties. Using the technique in combination with rotational deposition enables fabrication of compositional gradients radially from the center of a sample. A roadmap for developing gradient alloys is presented that uses multi-component phase diagrams as maps for composition selection so as to avoid unwanted phases. Practical applications for the new technology are demonstrated in low-coefficient of thermal expansion radially graded metal inserts for carbon-fiber spacecraft panels. PMID:24942329

  3. Gradient pre-emphasis to counteract first-order concomitant fields on asymmetric MRI gradient systems.

    PubMed

    Tao, Shengzhen; Weavers, Paul T; Trzasko, Joshua D; Shu, Yunhong; Huston, John; Lee, Seung-Kyun; Frigo, Louis M; Bernstein, Matt A

    2017-06-01

    To develop a gradient pre-emphasis scheme that prospectively counteracts the effects of the first-order concomitant fields for any arbitrary gradient waveform played on asymmetric gradient systems, and to demonstrate the effectiveness of this approach using a real-time implementation on a compact gradient system. After reviewing the first-order concomitant fields that are present on asymmetric gradients, we developed a generalized gradient pre-emphasis model assuming arbitrary gradient waveforms to counteract their effects. A numerically straightforward, easily implemented approximate solution to this pre-emphasis problem was derived that was compatible with the current hardware infrastructure of conventional MRI scanners for eddy current compensation. The proposed method was implemented on the gradient driver subsystem, and its real-time use was tested using a series of phantom and in vivo data acquired from two-dimensional Cartesian phase-difference, echo-planar imaging, and spiral acquisitions. The phantom and in vivo results demonstrated that unless accounted for, first-order concomitant fields introduce considerable phase estimation error into the measured data and result in images with spatially dependent blurring/distortion. The resulting artifacts were effectively prevented using the proposed gradient pre-emphasis. We have developed an efficient and effective gradient pre-emphasis framework to counteract the effects of first-order concomitant fields of asymmetric gradient systems. Magn Reson Med 77:2250-2262, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  4. Gradient Pre-Emphasis to Counteract First-Order Concomitant Fields on Asymmetric MRI Gradient Systems

    PubMed Central

    Tao, Shengzhen; Weavers, Paul T.; Trzasko, Joshua D.; Shu, Yunhong; Huston, John; Lee, Seung-Kyun; Frigo, Louis M.; Bernstein, Matt A.

    2016-01-01

    PURPOSE To develop a gradient pre-emphasis scheme that prospectively counteracts the effects of the first-order concomitant fields for any arbitrary gradient waveform played on asymmetric gradient systems, and to demonstrate the effectiveness of this approach using a real-time implementation on a compact gradient system. METHODS After reviewing the first-order concomitant fields that are present on asymmetric gradients, a generalized gradient pre-emphasis model assuming arbitrary gradient waveforms is developed to counteract their effects. A numerically straightforward, simple to implement approximate solution to this pre-emphasis problem is derived, which is compatible with the current hardware infrastructure used on conventional MRI scanners for eddy current compensation. The proposed method was implemented on the gradient driver sub-system, and its real-time use was tested using a series of phantom and in vivo data acquired from 2D Cartesian phase-difference, echo-planar imaging (EPI) and spiral acquisitions. RESULTS The phantom and in vivo results demonstrate that unless accounted for, first-order concomitant fields introduce considerable phase estimation error into the measured data and result in images exhibiting spatially dependent blurring/distortion. The resulting artifacts are effectively prevented using the proposed gradient pre-emphasis. CONCLUSION An efficient and effective gradient pre-emphasis framework is developed to counteract the effects of first-order concomitant fields of asymmetric gradient systems. PMID:27373901

  5. Pure phase encode magnetic field gradient monitor.

    PubMed

    Han, Hui; MacGregor, Rodney P; Balcom, Bruce J

    2009-12-01

    Numerous methods have been developed to measure MRI gradient waveforms and k-space trajectories. The most promising new strategy appears to be magnetic field monitoring with RF microprobes. Multiple RF microprobes may record the magnetic field evolution associated with a wide variety of imaging pulse sequences. The method involves exciting one or more test samples and measuring the time evolution of magnetization through the FIDs. Two critical problems remain. The gradient waveform duration is limited by the sample T(2)*, while the k-space maxima are limited by gradient dephasing. The method presented is based on pure phase encode FIDs and solves the above two problems in addition to permitting high strength gradient measurement. A small doped water phantom (1-3 mm droplet, T(1), T(2), T(2)* < 100 micros) within a microprobe is excited by a series of closely spaced broadband RF pulses each followed by FID single point acquisition. Two trial gradient waveforms have been chosen to illustrate the technique, neither of which could be measured by the conventional RF microprobe measurement. The first is an extended duration gradient waveform while the other illustrates the new method's ability to measure gradient waveforms with large net area and/or high amplitude. The new method is a point monitor with simple implementation and low cost hardware requirements.

  6. Satellite gravity gradient grids for geophysics

    PubMed Central

    Bouman, Johannes; Ebbing, Jörg; Fuchs, Martin; Sebera, Josef; Lieb, Verena; Szwillus, Wolfgang; Haagmans, Roger; Novak, Pavel

    2016-01-01

    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. PMID:26864314

  7. Gradient-based multiresolution image fusion.

    PubMed

    Petrović, Valdimir S; Xydeas, Costas S

    2004-02-01

    A novel approach to multiresolution signal-level image fusion is presented for accurately transferring visual information from any number of input image signals, into a single fused image without loss of information or the introduction of distortion. The proposed system uses a "fuse-then-decompose" technique realized through a novel, fusion/decomposition system architecture. In particular, information fusion is performed on a multiresolution gradient map representation domain of image signal information. At each resolution, input images are represented as gradient maps and combined to produce new, fused gradient maps. Fused gradient map signals are processed, using gradient filters derived from high-pass quadrature mirror filters to yield a fused multiresolution pyramid representation. The fused output image is obtained by applying, on the fused pyramid, a reconstruction process that is analogous to that of conventional discrete wavelet transform. This new gradient fusion significantly reduces the amount of distortion artefacts and the loss of contrast information usually observed in fused images obtained from conventional multiresolution fusion schemes. This is because fusion in the gradient map domain significantly improves the reliability of the feature selection and information fusion processes. Fusion performance is evaluated through informal visual inspection and subjective psychometric preference tests, as well as objective fusion performance measurements. Results clearly demonstrate the superiority of this new approach when compared to conventional fusion systems.

  8. Speciation gradients and the distribution of biodiversity.

    PubMed

    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.

  9. Evolutionary origin of the latitudinal diversity gradient in liverworts.

    PubMed

    Laenen, Benjamin; Patiño, Jairo; Hagborg, Anders; Désamoré, Aurélie; Wang, Jian; Jonathan Shaw, A; Goffinet, Bernard; Vanderpoorten, Alain

    2018-06-08

    A latitudinal diversity gradient towards the tropics appears as one most recurrent patterns in ecology, but the mechanisms underlying this pattern remain an area of controversy. In angiosperms, the tropical conservatism hypothesis proposes that most groups originated in the tropics and are adapted to a tropical climatic regime, and that relatively few species have evolved physiological adaptations to cold, dry or unpredictable climates. This mechanism is, however, unlikely to apply across land plants, and in particular, to liverworts, a group of about 7500 species, whose ability to withstand cold much better than their tracheophyte counterparts is at odds with the tropical conservatism hypothesis. Molecular dating, diversification rate analyses and ancestral area reconstructions were employed to explore the evolutionary mechanisms that account for the latitudinal diversity gradient in liverworts. As opposed to angiosperms, tropical liverwort genera are not older than their extra-tropical counterparts (median stem age of tropical and extra-tropical liverwort genera of 24.35±39.65 Ma and 39.57±49.07 Ma, respectively), weakening the 'time for speciation hypothesis'. Models of ancestral area reconstructions with equal migration rates between tropical and extra-tropical regions outperformed models with asymmetrical migration rates in either direction. The symmetry and intensity of migrations between tropical and extra-tropical regions suggested by the lack of resolution in ancestral area reconstructions towards the deepest nodes are at odds with the tropical niche conservatism hypothesis. In turn, tropical genera exhibited significantly higher net diversification rates than extra-tropical ones, suggesting that the observed latitudinal diversity gradient results from either higher extinction rates in extra-tropical lineages or higher speciation rates in the tropics. We discuss a series of experiments to help deciphering the underlying evolutionary mechanisms. Copyright

  10. Multiscale design and synthesis of biomimetic gradient protein/biosilica composites for interfacial tissue engineering.

    PubMed

    Guo, Jin; Li, Chunmei; Ling, Shengjie; Huang, Wenwen; Chen, Ying; Kaplan, David L

    2017-11-01

    Continuous gradients present at tissue interfaces such as osteochondral systems, reflect complex tissue functions and involve changes in extracellular matrix compositions, cell types and mechanical properties. New and versatile biomaterial strategies are needed to create suitable biomimetic engineered grafts for interfacial tissue engineering. Silk protein-based composites, coupled with selective peptides with mineralization domains, were utilized to mimic the soft-to-hard transition in osteochondral interfaces. The gradient composites supported tunable mineralization and mechanical properties corresponding to the spatial concentration gradient of the mineralization domains (R5 peptide). The composite system exhibited continuous transitions in terms of composition, structure and mechanical properties, as well as cytocompatibility and biodegradability. The gradient silicified silk/R5 composites promoted and regulated osteogenic differentiation of human mesenchymal stem cells in an osteoinductive environment in vitro. The cells differentiated along the composites in a manner consistent with the R5-gradient profile. This novel biomimetic gradient biomaterial design offers a useful approach to meet a broad range of needs in regenerative medicine. Copyright © 2017 Elsevier Ltd. All rights reserved.

  11. SW New Mexico BHT geothermal gradient calculations

    DOE Data Explorer

    Shari Kelley

    2015-07-24

    This file contains a compilation of BHT data from oil wells in southwestern New Mexico. Surface temperature is calculated using the collar elevation. An estimate of geothermal gradient is calculated using the estimated surface temperature and the uncorrected BHT data.

  12. Improving GOCE cross-track gravity gradients

    NASA Astrophysics Data System (ADS)

    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.

  13. Stability of gradient semigroups under perturbations

    NASA Astrophysics Data System (ADS)

    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).

  14. Intratumoral oxygen gradients mediate sarcoma cell invasion

    PubMed Central

    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

  15. Panel flutter optimization by gradient projection

    NASA Technical Reports Server (NTRS)

    Pierson, B. L.

    1975-01-01

    A gradient projection optimal control algorithm incorporating conjugate gradient directions of search is described and applied to several minimum weight panel design problems subject to a flutter speed constraint. New numerical solutions are obtained for both simply-supported and clamped homogeneous panels of infinite span for various levels of inplane loading and minimum thickness. The minimum thickness inequality constraint is enforced by a simple transformation of variables.

  16. Intratumoral oxygen gradients mediate sarcoma cell invasion.

    PubMed

    Lewis, Daniel M; Park, Kyung Min; Tang, Vitor; Xu, Yu; Pak, Koreana; Eisinger-Mathason, T S Karin; Simon, M Celeste; Gerecht, Sharon

    2016-08-16

    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 mm(3)) 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.

  17. Magnetoelectrets prepared by using temperature gradient method

    NASA Astrophysics Data System (ADS)

    Ojha, Pragya; Qureshi, M. S.; Malik, M. M.

    2015-05-01

    A novel Temperature Gradient method for preparation of magnetoelectret is proposed. Non uniform magnetic field and temperature gradient are expected to be the main cause for the formation of magnetoelectrets (MEs). Being bad conductors of heat, during their formation, there is a possibility for the existence of a temperature gradient along the dielectric electrode interface. In this condition, the motion of, molecules and charge carriers are dependent on Temperature Gradient in a preferred direction. To increase this temperature gradient on both sides of the sample novel method for the preparation of MEs is developed for the first time. For this method the special sample holders are designed in our laboratory. MEs are prepared in such a way that one surface is cooled and the other is heated, during the process. With the help of XRD analysis using Type-E orientation pattern and surface charge studies on magnetoelectrets, the two main causes Non uniform magnetic field and temperature gradient for the formation of magnetoelectrets (MEs), are authenticated experimentally.

  18. Analysis of bacterial migration. 2: Studies with multiple attractant gradients

    SciTech Connect

    Strauss, I.; Frymier, P.D.; Hahn, C.M.

    1995-02-01

    Many motile bacteria exhibit chemotaxis, the ability to bias their random motion toward or away from increasing concentrations of chemical substances which benefit or inhibit their survival, respectively. Since bacteria encounter numerous chemical concentration gradients simultaneously in natural surroundings, it is necessary to know quantitatively how a bacterial population responds in the presence of more than one chemical stimulus to develop predictive mathematical models describing bacterial migration in natural systems. This work evaluates three hypothetical models describing the integration of chemical signals from multiple stimuli: high sensitivity, maximum signal, and simple additivity. An expression for the tumbling probability for individualmore » stimuli is modified according to the proposed models and incorporated into the cell balance equation for a 1-D attractant gradient. Random motility and chemotactic sensitivity coefficients, required input parameters for the model, are measured for single stimulus responses. Theoretical predictions with the three signal integration models are compared to the net chemotactic response of Escherichia coli to co- and antidirectional gradients of D-fucose and [alpha]-methylaspartate in the stopped-flow diffusion chamber assay. Results eliminate the high-sensitivity model and favor the simple additivity over the maximum signal. None of the simple models, however, accurately predict the observed behavior, suggesting a more complex model with more steps in the signal processing mechanism is required to predict responses to multiple stimuli.« less

  19. ROBUSTNESS OF SIGNALING GRADIENT IN DROSOPHILA WING IMAGINAL DISC

    PubMed Central

    Lei, Jinzhi; Wan, Frederic Y. M.; Lander, Arthur D.; Nie, Qing

    2012-01-01

    Quasi-stable gradients of signaling protein molecules (known as morphogens or ligands) bound to cell receptors are known to be responsible for differential cell signaling and gene expressions. From these follow different stable cell fates and visually patterned tissues in biological development. Recent studies have shown that the relevant basic biological processes yield gradients that are sensitive to small changes in system characteristics (such as expression level of morphogens or receptors) or environmental conditions (such as temperature changes). Additional biological activities must play an important role in the high level of robustness observed in embryonic patterning for example. It is natural to attribute observed robustness to various type of feedback control mechanisms. However, our own simulation studies have shown that feedback control is neither necessary nor sufficient for robustness of the morphogen decapentaplegic (Dpp) gradient in wing imaginal disc of Drosophilas. Furthermore, robustness can be achieved by substantial binding of the signaling morphogen Dpp with nonsignaling cell surface bound molecules (such as heparan sulfate proteoglygans) and degrading the resulting complexes at a sufficiently rapid rate. The present work provides a theoretical basis for the results of our numerical simulation studies. PMID:24098092

  20. Simple Microfluidic Device For Studying Chemotaxis In Response To Dual Gradients

    PubMed Central

    Moussavi-Haramic, S. F.; Pezzi, H. M.; Huttenlocher, A.; Beebe, D. J.

    2016-01-01

    Chemotaxis is a fundamental biological process where complex chemotactic gradients are integrated and prioritized to guide cell migration toward specific locations. To understand the mechanisms of gradient dependent cell migration, it is important to develop in vitro models that recapitulate key attributes of the chemotactic cues present in vivo. Current in vitro tools for studying cell migration are not amenable to easily study the response of neutrophils to dual gradients. Many of these systems require external pumps and complex setups to establish and maintain the gradients. Here we report a simple yet innovative microfluidic device for studying cell migration in the presence of dual chemotactic gradients through a 3-dimensional substrate. The device is tested and validated by studying the migration of the neutrophil-like cell line PLB-985 to gradients of fMLP. Furthermore, the device is expanded and used with heparinised whole blood, whereupon neutrophils were observed to migrate from whole blood towards gradients of fMLP eliminating the need for any neutrophil purification or capture steps. PMID:25893484

  1. Thermoelectrically cooled temperature-gradient apparatus for comparative cell and virus temperature studies.

    PubMed

    Clark, H F; Kaminski, F; Karzon, D T

    1970-05-01

    Establishment of a near-linear temperature gradient in an incubator has been accomplished by the application of heat to one terminus of a conducting body, normally a metal bar, and the removal of heat from the other terminus of the conducting body. Such incubators have been complex and unwieldy because of the need for mechanical refrigeration. We have described a simplified temperature gradient incubator which uses thermoelectric module cooling coupled with electric heating. Along the gradient, 20 stations in two parallel rows of 10, each accommodating a 30-ml plastic cell culture flask, were continually monitored by an electronic thermometer, and the temperatures were recorded. By manipulation of two simple potentiometer controls, any temperature gradient between 0 and 50 C could be obtained. Minor deviations which occurred between theoretically perfect and obtained temperature gradients were reproducible and readily measured. The gradient incubator was particularly applicable to (i) simultaneously studying a given biological activity over the entire temperature range supporting the growth of a given cell, virus, or microorganism, or (ii) precisely defining the upper or lower temperature limits of a biological system by 10-point determinations. Preliminary experiments have demonstrated the usefulness of the apparatus in characterizing the temperature limits for growth in vitro of cells of reptilian cell lines. The gradient incubator was also successfully utilized for the characterization of the effect of temperature on the efficiency of plating of amphibian viruses and possible temperature variants of those viruses.

  2. Full magnetic gradient tensor from triaxial aeromagnetic gradient measurements: Calculation and application

    NASA Astrophysics Data System (ADS)

    Luo, Yao; Wu, Mei-Ping; Wang, Ping; Duan, Shu-Ling; Liu, Hao-Jun; Wang, Jin-Long; An, Zhan-Feng

    2015-09-01

    The full magnetic gradient tensor (MGT) refers to the spatial change rate of the three field components of the geomagnetic field vector along three mutually orthogonal axes. The tensor is of use to geological mapping, resources exploration, magnetic navigation, and others. However, it is very difficult to measure the full magnetic tensor gradient using existing engineering technology. We present a method to use triaxial aeromagnetic gradient measurements for deriving the full MGT. The method uses the triaxial gradient data and makes full use of the variation of the magnetic anomaly modulus in three dimensions to obtain a self-consistent magnetic tensor gradient. Numerical simulations show that the full MGT data obtained with the proposed method are of high precision and satisfy the requirements of data processing. We selected triaxial aeromagnetic gradient data from the Hebei Province for calculating the full MGT. Data processing shows that using triaxial tensor gradient data allows to take advantage of the spatial rate of change of the total field in three dimensions and suppresses part of the independent noise in the aeromagnetic gradient. The calculated tensor components have improved resolution, and the transformed full tensor gradient satisfies the requirement of geological mapping and interpretation.

  3. Murine intracochlear drug delivery: reducing concentration gradients within the cochlea.

    PubMed

    Borkholder, David A; Zhu, Xiaoxia; Hyatt, Brad T; Archilla, Alfredo S; Livingston, William J; Frisina, Robert D

    2010-09-01

    Direct delivery of compounds to the mammalian inner ear is most commonly achieved by absorption or direct injection through the round window membrane (RWM), or infusion through a basal turn cochleostomy. These methods provide direct access to cochlear structures, but with a strong basal-to-apical concentration gradient consistent with a diffusion-driven distribution. This gradient limits the efficacy of therapeutic approaches for apical structures, and puts constraints on practical therapeutic dose ranges. A surgical approach involving both a basal turn cochleostomy and a posterior semicircular canal canalostomy provides opportunities for facilitated perfusion of cochlear structures to reduce concentration gradients. Infusion of fixed volumes of artificial perilymph (AP) and sodium salicylate were used to evaluate two surgical approaches in the mouse: cochleostomy-only (CO), or cochleostomy-plus-canalostomy (C+C). Cochlear function was evaluated via closed-system distortion product otoacoustic emissions (DPOAE) threshold level measurements from 8 to 49 kHz. AP infusion confirmed no surgical impact to auditory function, while shifts in DPOAE thresholds were measured during infusion of salicylate and AP (washout). Frequency dependent shifts were compared for the CO and C+C approaches. Computer simulations modeling diffusion, volume flow, interscala transport, and clearance mechanisms provided estimates of drug concentration as a function of cochlear position. Simulated concentration profiles were compared to frequency-dependent shifts in measured auditory responses using a cochlear tonotopic map. The impact of flow rate on frequency dependent DPOAE threshold shifts was also evaluated for both surgical approaches. Both the C+C approach and a flow rate increase were found to provide enhanced response for lower frequencies, with evidence suggesting the C+C approach reduces concentration gradients within the cochlea. Copyright (c) 2010 Elsevier B.V. All rights reserved.

  4. Murine Intracochlear Drug Delivery: Reducing Concentration Gradients within the Cochlea

    PubMed Central

    Borkholder, David A.; Zhu, Xiaoxia; Hyatt, Brad T.; Archilla, Alfredo S.; Livingston, William J.; Frisina, Robert D.

    2010-01-01

    Direct delivery of compounds to the mammalian inner ear is most commonly achieved by absorption or direct injection through the round window membrane (RWM), or infusion through a basal turn cochleostomy. These methods provide direct access to cochlear structures, but with a strong basal-to-apical concentration gradient consistent with a diffusion-driven distribution. This gradient limits the efficacy of therapeutic approaches for apical structures, and puts constraints on practical therapeutic dose ranges. A surgical approach involving both a basal turn cochleostomy and a posterior semicircular canal canalostomy provides opportunities for facilitated perfusion of cochlear structures to reduce concentration gradients. Infusion of fixed volumes of artificial perilymph (AP) and sodium salicylate were used to evaluate two surgical approaches in the mouse: cochleostomy-only (CO), or cochleostomy-plus-canalostomy (C+C). Cochlear function was evaluated via closed-system distortion product otoacoustic emissions (DPOAE) threshold level measurements from 8-49 kHz. AP infusion confirmed no surgical impact to auditory function, while shifts in DPOAE thresholds were measured during infusion of salicylate and AP (washout). Frequency dependent shifts were compared for the CO and C+C approaches. Computer simulations modeling diffusion, volume flow, interscala transport, and clearance mechanisms provided estimates of drug concentration as a function of cochlear position. Simulated concentration profiles were compared to frequency-dependent shifts in measured auditory responses using a cochlear tonotopic map. The impact of flow rate on frequency dependent DPOAE threshold shifts was also evaluated for both surgical approaches. Both the C+C approach and a flow rate increase were found to provide enhanced response for lower frequencies, with evidence suggesting the C+C approach reduces concentration gradients within the cochlea. PMID:20451593

  5. On Localized Vapor Pressure Gradients Governing Condensation and Frost Phenomena.

    PubMed

    Nath, Saurabh; Boreyko, Jonathan B

    2016-08-23

    Interdroplet vapor pressure gradients are the driving mechanism for several phase-change phenomena such as condensation dry zones, interdroplet ice bridging, dry zones around ice, and frost halos. Despite the fundamental nature of the underlying pressure gradients, the majority of studies on these emerging phenomena have been primarily empirical. Using classical nucleation theory and Becker-Döring embryo formation kinetics, here we calculate the pressure field for all possible modes of condensation and desublimation in order to gain fundamental insight into how pressure gradients govern the behavior of dry zones, condensation frosting, and frost halos. Our findings reveal that in a variety of phase-change systems the thermodynamically favorable mode of nucleation can switch between condensation and desublimation depending upon the temperature and wettability of the surface. The calculated pressure field is used to model the length of a dry zone around liquid or ice droplets over a broad parameter space. The long-standing question of whether the vapor pressure at the interface of growing frost is saturated or supersaturated is resolved by considering the kinetics of interdroplet ice bridging. Finally, on the basis of theoretical calculations, we propose that there exists a new mode of frost halo that is yet to be experimentally observed; a bimodal phase map is developed, demonstrating its dependence on the temperature and wettability of the underlying substrate. We hope that the model and predictions contained herein will assist future efforts to exploit localized vapor pressure gradients for the design of spatially controlled or antifrosting phase-change systems.

  6. Protein gradients in single cells induced by their coupling to "morphogen"-like diffusion

    NASA Astrophysics Data System (ADS)

    Nandi, Saroj Kumar; Safran, Sam A.

    2018-05-01

    One of the many ways cells transmit information within their volume is through steady spatial gradients of different proteins. However, the mechanism through which proteins without any sources or sinks form such single-cell gradients is not yet fully understood. One of the models for such gradient formation, based on differential diffusion, is limited to proteins with large ratios of their diffusion constants or to specific protein-large molecule interactions. We introduce a novel mechanism for gradient formation via the coupling of the proteins within a single cell with a molecule, that we call a "pronogen," whose action is similar to that of morphogens in multi-cell assemblies; the pronogen is produced with a fixed flux at one side of the cell. This coupling results in an effectively non-linear diffusion degradation model for the pronogen dynamics within the cell, which leads to a steady-state gradient of the protein concentration. We use stability analysis to show that these gradients are linearly stable with respect to perturbations.

  7. Biological amine transport in chromaffin ghosts. Coupling to the transmembrane proton and potential gradients.

    PubMed

    Johnson, R G; Pfister, D; Carty, S E; Scarpa, A

    1979-11-10

    The effect of the transmembrane proton gradient (delta pH) and potential gradient (delta psi) upon the rate and extent of amine accumulation was investigated in chromaffin ghosts. The chromaffin ghosts were formed by hypo-osmotic lysis of isolated bovine chromaffin granules and extensive dialysis in order to remove intragranular binding components and dissipate the endogenous electrochemical gradients. Upon ATP addition to suspensions of chromaffin ghosts, a transmembrane proton gradient alone, a transmembrane gradient alone, or both, could be established, depending upon the compositions of the media in which the ghosts were formed and resuspended. When chloride was present in the medium, addition of ATP resulted in the generation of a transmembrane proton gradient, acidic inside of 1 pH unit (measured by [14C]methylamine distribution), and no transmembrane potential (measured by [14C]-thiocyanate distribution). When ATP was added to chromaffin ghosts suspended in a medium in which chloride was substituted by isethionate, a transmembrane potential, inside positive, of 45 mV and no transmembrane proton gradient, was measured. In each medium, the addition of agents known to affect proton or potential gradients, respectively, exerted a predictable mechanism of action. Accumulation of [14C]epinephrine or [14C]5-hydroxytryptamine was over 1 order of magnitude greater in the presence of the transmembrane proton gradient or the transmembrane potential than in the absence of any gradient and, moreover, was related to the magnitude of the proton or potential gradient in a dose-dependent manner. When ghosts were added to a medium containing chloride and isethionate, both a delta pH and delta psi could be generated upon addition of ATP. In this preparation, the maximal rate of amine accumulation was observed. The results indicate that amine accumulation into chromaffin ghosts can occur in the presence of either a transmembrane proton gradient, or a transmembrane potential

  8. Microsphere-based gradient implants for osteochondral regeneration: a long-term study in sheep

    PubMed Central

    Mohan, Neethu; Gupta, Vineet; Sridharan, Banu Priya; Mellott, Adam J; Easley, Jeremiah T; Palmer, Ross H; Galbraith, Richard A; Key, Vincent H; Berkland, Cory J; Detamore, Michael S

    2015-01-01

    Background: The microfracture technique for cartilage repair has limited ability to regenerate hyaline cartilage. Aim: The current study made a direct comparison between microfracture and an osteochondral approach with microsphere-based gradient plugs. Materials & methods: The PLGA-based scaffolds had opposing gradients of chondroitin sulfate and β-tricalcium phosphate. A 1-year repair study in sheep was conducted. Results: The repair tissues in the microfracture were mostly fibrous and had scattered fissures with degenerative changes. Cartilage regenerated with the gradient plugs had equal or superior mechanical properties; had lacunated cells and stable matrix as in hyaline cartilage. Conclusion: This first report of gradient scaffolds in a long-term, large animal, osteochondral defect demonstrated potential for equal or better cartilage repair than microfracture. PMID:26418471

  9. Bauschinger Effect and Back Stress in Gradient Cu-Ge Alloy

    NASA Astrophysics Data System (ADS)

    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.

  10. Performance optimization in electric field gradient focusing.

    PubMed

    Sun, Xuefei; Farnsworth, Paul B; Tolley, H Dennis; Warnick, Karl F; Woolley, Adam T; Lee, Milton L

    2009-01-02

    Electric field gradient focusing (EFGF) is a technique used to simultaneously separate and concentrate biomacromolecules, such as proteins, based on the opposing forces of an electric field gradient and a hydrodynamic flow. Recently, we reported EFGF devices fabricated completely from copolymers functionalized with poly(ethylene glycol), which display excellent resistance to protein adsorption. However, the previous devices did not provide the predicted linear electric field gradient and stable current. To improve performance, Tris-HCl buffer that was previously doped in the hydrogel was replaced with a phosphate buffer containing a salt (i.e., potassium chloride, KCl) with high mobility ions. The new devices exhibited stable current, good reproducibility, and a linear electric field distribution in agreement with the shaped gradient region design due to improved ion transport in the hydrogel. The field gradient was calculated based on theory to be approximately 5.76 V/cm(2) for R-phycoerythrin when the applied voltage was 500 V. The effect of EFGF separation channel dimensions was also investigated; a narrower focused band was achieved in a smaller diameter channel. The relationship between the bandwidth and channel diameter is consistent with theory. Three model proteins were resolved in an EFGF channel of this design. The improved device demonstrated 14,000-fold concentration of a protein sample (from 2 ng/mL to 27 microg/mL).

  11. Income inequality and socioeconomic gradients in mortality.

    PubMed

    Wilkinson, Richard G; Pickett, Kate E

    2008-04-01

    We investigated whether the processes underlying the association between income inequality and population health are related to those responsible for the socioeconomic gradient in health and whether health disparities are smaller when income differences are narrower. We used multilevel models in a regression analysis of 10 age- and cause-specific US county mortality rates on county median household incomes and on state income inequality. We assessed whether mortality rates more closely related to county income were also more closely related to state income inequality. We also compared mortality gradients in more- and less-equal states. Mortality rates more strongly associated with county income were more strongly associated with state income inequality: across all mortality rates, r= -0.81; P=.004. The effect of state income inequality on the socioeconomic gradient in health varied by cause of death, but greater equality usually benefited both wealthier and poorer counties. Although mortality rates with steep socioeconomic gradients were more sensitive to income distribution than were rates with flatter gradients, narrower income differences benefit people in both wealthy and poor areas and may, paradoxically, do little to reduce health disparities.

  12. Jupiter's evolution with primordial composition gradients

    NASA Astrophysics Data System (ADS)

    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

  13. Importance of Ionospheric Gradients for error Correction

    NASA Astrophysics Data System (ADS)

    Ravula, Ramprasad

    Importance of Ionospheric Gradients for error Correction R. Ram Prasad1, P.Nagasekhar2 1Sai Spurthi Institute of Technology-JNTU Hyderabad,2Sai Spurthi Institute of Technology-JNTU Hyderabad Email ID:rams.ravula@gmail.com In India, Indian Space Research Organization (ISRO) has established with an objective to develop space technology and its application to various national tasks. To cater to the needs of civil aviation applications, GPS Aided Geo Augmented Navigation (GAGAN) system is being jointly implemented along with Airports Authority of India (AAI) over the Indian region. The most predominant parameter affecting the navigation accuracy of GAGAN is ionospheric delay which is a function of total number of electrons present in one square meter cylindrical cross sectional area in the line of site direction between the satellite and the user on the earth i.e. Total Electron Content (TEC).The irregular distribution of electron densities i.e. rate of TEC variation, causes Ionospheric gradients such as spatial gradients (Expressed in TECu/km) and temporal gradients (Expressed in TECu /minute). Among the satellite signals arriving to the earth in multiple directions, the signals which suffer from severe ionospheric gradients can be estimated i.e. Rate of TEC Index (ROTI) and Rate of TEC (ROT). These aspects which contribute to errors can be treated for improving GAGAN positional accuracy.

  14. Quantification of the effect of temperature gradients in soils on subsurface radon signal

    NASA Astrophysics Data System (ADS)

    Haquin, Gustavo; Ilzycer, Danielle; Kamai, Tamir; Zafrir, Hovav; Weisbrod, Noam

    2017-04-01

    Temperature gradients that develop in soils due to atmospheric temperature cycles are factors of primary importance in determining the rates and directions of subsurface gas flow. Models including mechanisms of thermal convection and thermal diffusion partially explain the impact of temperature gradients on subsurface radon transport. However, the overall impact of temperature gradients on subsurface radon transport is still not well understood. A laboratory setup was designed and built to experimentally investigate the influence of temperature gradients on radon transport under well controlled conditions. A 60 cm diameter and 120 cm tall column was thermally insulated except from the atmosphere-soil interface, such that it was constructed to simulate field conditions where temperature gradients in soils are developed following atmospheric temperature cycles. The column was filled with fine grinded phosphate rock which provided the porous media with radon source. Radon in soil-air was continuously monitored using NaI gamma detectors positioned at different heights along the column. Soil temperature, differential pressure, and relative humidity were monitored along the column. Experiments based on steep and gradual stepwise changes in ambient temperature were conducted. Absolute changes on radon levels in the order of 10-30% were measured at temperature gradients of up to ±20oC/m. Results showed a non-linear correlation between the temperature gradient and the subsurface radon concentration. An asymmetric relationship between the radon concentration and the temperature gradients for ΔT>0 and ΔT<0 was also observed. Laboratory simulations of the time- and depth-dependent temperature wave functions with frequencies ranged from a daily cycle to few days were performed. In response to the harmonic temperature behaviour radon oscillations at similar frequencies were detected correspondingly. In this work a quantitative relationship between radon and temperature

  15. Stabilization of electron-scale turbulence by electron density gradient in national spherical torus experiment

    SciTech Connect

    Ruiz Ruiz, J.; White, A. E.; Ren, Y.

    2015-12-15

    Theory and experiments have shown that electron temperature gradient (ETG) turbulence on the electron gyro-scale, k{sub ⊥}ρ{sub e} ≲ 1, can be responsible for anomalous electron thermal transport in NSTX. Electron scale (high-k) turbulence is diagnosed in NSTX with a high-k microwave scattering system [D. R. Smith et al., Rev. Sci. Instrum. 79, 123501 (2008)]. Here we report on stabilization effects of the electron density gradient on electron-scale density fluctuations in a set of neutral beam injection heated H-mode plasmas. We found that the absence of high-k density fluctuations from measurements is correlated with large equilibrium density gradient, which ismore » shown to be consistent with linear stabilization of ETG modes due to the density gradient using the analytical ETG linear threshold in F. Jenko et al. [Phys. Plasmas 8, 4096 (2001)] and linear gyrokinetic simulations with GS2 [M. Kotschenreuther et al., Comput. Phys. Commun. 88, 128 (1995)]. We also found that the observed power of electron-scale turbulence (when it exists) is anti-correlated with the equilibrium density gradient, suggesting density gradient as a nonlinear stabilizing mechanism. Higher density gradients give rise to lower values of the plasma frame frequency, calculated based on the Doppler shift of the measured density fluctuations. Linear gyrokinetic simulations show that higher values of the electron density gradient reduce the value of the real frequency, in agreement with experimental observation. Nonlinear electron-scale gyrokinetic simulations show that high electron density gradient reduces electron heat flux and stiffness, and increases the ETG nonlinear threshold, consistent with experimental observations.« less

  16. Strategies and applications for incorporating physical and chemical signal gradients in tissue engineering.

    PubMed

    Singh, Milind; Berkland, Cory; Detamore, Michael S

    2008-12-01

    From embryonic development to wound repair, concentration gradients of bioactive signaling molecules guide tissue formation and regeneration. Moreover, gradients in cellular and extracellular architecture as well as in mechanical properties are readily apparent in native tissues. Perhaps tissue engineers can take a cue from nature in attempting to regenerate tissues by incorporating gradients into engineering design strategies. Indeed, gradient-based approaches are an emerging trend in tissue engineering, standing in contrast to traditional approaches of homogeneous delivery of cells and/or growth factors using isotropic scaffolds. Gradients in tissue engineering lie at the intersection of three major paradigms in the field-biomimetic, interfacial, and functional tissue engineering-by combining physical (via biomaterial design) and chemical (with growth/differentiation factors and cell adhesion molecules) signal delivery to achieve a continuous transition in both structure and function. This review consolidates several key methodologies to generate gradients, some of which have never been employed in a tissue engineering application, and discusses strategies for incorporating these methods into tissue engineering and implant design. A key finding of this review was that two-dimensional physicochemical gradient substrates, which serve as excellent high-throughput screening tools for optimizing desired biomaterial properties, can be enhanced in the future by transitioning from two dimensions to three dimensions, which would enable studies of cell-protein-biomaterial interactions in a more native tissue-like environment. In addition, biomimetic tissue regeneration via combined delivery of graded physical and chemical signals appears to be a promising strategy for the regeneration of heterogeneous tissues and tissue interfaces. In the future, in vivo applications will shed more light on the performance of gradient-based mechanical integrity and signal delivery

  17. Strategies and Applications for Incorporating Physical and Chemical Signal Gradients in Tissue Engineering

    PubMed Central

    Singh, Milind; Berkland, Cory

    2008-01-01

    From embryonic development to wound repair, concentration gradients of bioactive signaling molecules guide tissue formation and regeneration. Moreover, gradients in cellular and extracellular architecture as well as in mechanical properties are readily apparent in native tissues. Perhaps tissue engineers can take a cue from nature in attempting to regenerate tissues by incorporating gradients into engineering design strategies. Indeed, gradient-based approaches are an emerging trend in tissue engineering, standing in contrast to traditional approaches of homogeneous delivery of cells and/or growth factors using isotropic scaffolds. Gradients in tissue engineering lie at the intersection of three major paradigms in the field—biomimetic, interfacial, and functional tissue engineering—by combining physical (via biomaterial design) and chemical (with growth/differentiation factors and cell adhesion molecules) signal delivery to achieve a continuous transition in both structure and function. This review consolidates several key methodologies to generate gradients, some of which have never been employed in a tissue engineering application, and discusses strategies for incorporating these methods into tissue engineering and implant design. A key finding of this review was that two-dimensional physicochemical gradient substrates, which serve as excellent high-throughput screening tools for optimizing desired biomaterial properties, can be enhanced in the future by transitioning from two dimensions to three dimensions, which would enable studies of cell–protein–biomaterial interactions in a more native tissue–like environment. In addition, biomimetic tissue regeneration via combined delivery of graded physical and chemical signals appears to be a promising strategy for the regeneration of heterogeneous tissues and tissue interfaces. In the future, in vivo applications will shed more light on the performance of gradient-based mechanical integrity and signal

  18. Evidence of counter-gradient growth in western pond turtles (Actinemys marmorata) across thermal gradients

    Treesearch

    Melissa L. Snover; Michael J. Adams; Donald T. Ashton; Jamie B. Bettaso; Hartwell H. Welsh

    2015-01-01

    Summary1. 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...

  19. Model of separation performance of bilinear gradients in scanning format counter-flow gradient electrofocusing techniques.

    PubMed

    Shameli, Seyed Mostafa; Glawdel, Tomasz; Ren, Carolyn L

    2015-03-01

    Counter-flow gradient electrofocusing allows the simultaneous concentration and separation of analytes by generating a gradient in the total velocity of each analyte that is the sum of its electrophoretic velocity and the bulk counter-flow velocity. In the scanning format, the bulk counter-flow velocity is varying with time so that a number of analytes with large differences in electrophoretic mobility can be sequentially focused and passed by a single detection point. Studies have shown that nonlinear (such as a bilinear) velocity gradients along the separation channel can improve both peak capacity and separation resolution simultaneously, which cannot be realized by using a single linear gradient. Developing an effective separation system based on the scanning counter-flow nonlinear gradient electrofocusing technique usually requires extensive experimental and numerical efforts, which can be reduced significantly with the help of analytical models for design optimization and guiding experimental studies. Therefore, this study focuses on developing an analytical model to evaluate the separation performance of scanning counter-flow bilinear gradient electrofocusing methods. In particular, this model allows a bilinear gradient and a scanning rate to be optimized for the desired separation performance. The results based on this model indicate that any bilinear gradient provides a higher separation resolution (up to 100%) compared to the linear case. This model is validated by numerical studies. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Momentum-weighted conjugate gradient descent algorithm for gradient coil optimization.

    PubMed

    Lu, Hanbing; Jesmanowicz, Andrzej; Li, Shi-Jiang; Hyde, James S

    2004-01-01

    MRI gradient coil design is a type of nonlinear constrained optimization. A practical problem in transverse gradient coil design using the conjugate gradient descent (CGD) method is that wire elements move at different rates along orthogonal directions (r, phi, z), and tend to cross, breaking the constraints. A momentum-weighted conjugate gradient descent (MW-CGD) method is presented to overcome this problem. This method takes advantage of the efficiency of the CGD method combined with momentum weighting, which is also an intrinsic property of the Levenberg-Marquardt algorithm, to adjust step sizes along the three orthogonal directions. A water-cooled, 12.8 cm inner diameter, three axis torque-balanced gradient coil for rat imaging was developed based on this method, with an efficiency of 2.13, 2.08, and 4.12 mT.m(-1).A(-1) along X, Y, and Z, respectively. Experimental data demonstrate that this method can improve efficiency by 40% and field uniformity by 27%. This method has also been applied to the design of a gradient coil for the human brain, employing remote current return paths. The benefits of this design include improved gradient field uniformity and efficiency, with a shorter length than gradient coil designs using coaxial return paths. Copyright 2003 Wiley-Liss, Inc.

  1. Gradient Pattern Analysis Applied to Galaxy Morphology

    NASA Astrophysics Data System (ADS)

    Rosa, R. R.; de Carvalho, R. R.; Sautter, R. A.; Barchi, P. H.; Stalder, D. H.; Moura, T. C.; Rembold, S. B.; Morell, D. R. F.; Ferreira, N. C.

    2018-04-01

    Gradient pattern analysis (GPA) is a well-established technique for measuring gradient bilateral asymmetries of a square numerical lattice. This paper introduces an improved version of GPA designed for galaxy morphometry. We show the performance of the new method on a selected sample of 54,896 objects from the SDSS-DR7 in common with Galaxy Zoo 1 catalog. The results suggest that the second gradient moment, G2, has the potential to dramatically improve over more conventional morphometric parameters. It separates early from late type galaxies better (˜90%) than the CAS system (C ˜ 79%, A ˜ 50%, S ˜ 43%) and a benchmark test shows that it is applicable to hundreds of thousands of galaxies using typical processing systems.

  2. Gradient pattern analysis applied to galaxy morphology

    NASA Astrophysics Data System (ADS)

    Rosa, R. R.; de Carvalho, R. R.; Sautter, R. A.; Barchi, P. H.; Stalder, D. H.; Moura, T. C.; Rembold, S. B.; Morell, D. R. F.; Ferreira, N. C.

    2018-06-01

    Gradient pattern analysis (GPA) is a well-established technique for measuring gradient bilateral asymmetries of a square numerical lattice. This paper introduces an improved version of GPA designed for galaxy morphometry. We show the performance of the new method on a selected sample of 54 896 objects from the SDSS-DR7 in common with Galaxy Zoo 1 catalogue. The results suggest that the second gradient moment, G2, has the potential to dramatically improve over more conventional morphometric parameters. It separates early- from late-type galaxies better (˜ 90 per cent) than the CAS system (C˜ 79 per cent, A˜ 50 per cent, S˜ 43 per cent) and a benchmark test shows that it is applicable to hundreds of thousands of galaxies using typical processing systems.

  3. Sound beam manipulation based on temperature gradients

    SciTech Connect

    Qian, Feng; School of Physics & Electronic Engineering, Changshu Institute of Technology, Changshu 215500; Quan, Li

    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 tomore » fields such as noise control or acoustic cloaking.« less

  4. Transverse gradient in Apple-type undulators

    PubMed Central

    Calvi, M.; Camenzuli, C.; Prat, E.; Schmidt, Th.

    2017-01-01

    Apple-type undulators are globally recognized as the most flexible devices for the production of variable polarized light in the soft X-ray regime, both at synchrotron and free-electron laser facilities. Recently, the implementation of transverse gradient undulators has been proposed to enhance the performance of new generation light sources. In this paper it is demonstrated that Apple undulators do not only generate linear and elliptical polarized light but also variable transverse gradient under certain conditions. A general theoretical framework is introduced to evaluate the K-value and its transverse gradient for an Apple undulator, and formulas for all regular operational modes and different Apple types (including the most recent Delta type and Apple X) are calculated and critically discussed. PMID:28452751

  5. Metamaterials with gradient negative index of refraction.

    PubMed

    Pinchuk, Anatoliy O; Schatz, George C

    2007-10-01

    We propose a new metamaterial with a gradient negative index of refraction, which can focus a collimated beam of light coming from a distant object. A slab of the negative refractive index metamaterial has a focal length that can be tuned by changing the gradient of the negative refractive index. A thin metal film pierced with holes of appropriate size or spacing between them can be used as a metamaterial with the gradient negative index of refraction. We use finite-difference time-domain calculations to show the focusing of a plane electromagnetic wave passing through a system of equidistantly spaced holes in a metal slab with decreasing diameters toward the edges of the slab.

  6. Water potential gradient in a tall sequoiadendron.

    PubMed

    Tobiessen, P

    1971-09-01

    With an elevator installed in a 90-meter tall Sequoiadendron to collect the samples, xylem pressure potential measurements were made approximately every 15 meters along 60 meters of the tree's height. The measured gradient was about -0.8 bar per 10 meters of height, i.e., less than the hydrostatic gradient. Correction of the xylem pressure potential data by calibration against a thermocouple psychrometer confirmed this result. Similar gradients are described in the literature in tall conifers at times of low transpiration, although a different sampling technique was used. If the data in the present study and those supporting it are typical, they imply a re-evaluation of either the use of the pressure chamber to estimate water potential or the present theories describing water transport in tall trees.

  7. Water Potential Gradient in a Tall Sequoiadendron

    PubMed Central

    Tobiessen, Peter; Rundel, Philip W.; Stecker, R. E.

    1971-01-01

    With an elevator installed in a 90-meter tall Sequoiadendron to collect the samples, xylem pressure potential measurements were made approximately every 15 meters along 60 meters of the tree's height. The measured gradient was about −0.8 bar per 10 meters of height, i.e., less than the hydrostatic gradient. Correction of the xylem pressure potential data by calibration against a thermocouple psychrometer confirmed this result. Similar gradients are described in the literature in tall conifers at times of low transpiration, although a different sampling technique was used. If the data in the present study and those supporting it are typical, they imply a re-evaluation of either the use of the pressure chamber to estimate water potential or the present theories describing water transport in tall trees. PMID:16657786

  8. Efficient gradient calibration based on diffusion MRI.

    PubMed

    Teh, Irvin; Maguire, Mahon L; Schneider, Jürgen E

    2017-01-01

    To propose a method for calibrating gradient systems and correcting gradient nonlinearities based on diffusion MRI measurements. The gradient scaling in x, y, and z were first offset by up to 5% from precalibrated values to simulate a poorly calibrated system. Diffusion MRI data were acquired in a phantom filled with cyclooctane, and corrections for gradient scaling errors and nonlinearity were determined. The calibration was assessed with diffusion tensor imaging and independently validated with high resolution anatomical MRI of a second structured phantom. The errors in apparent diffusion coefficients along orthogonal axes ranged from -9.2% ± 0.4% to + 8.8% ± 0.7% before calibration and -0.5% ± 0.4% to + 0.8% ± 0.3% after calibration. Concurrently, fractional anisotropy decreased from 0.14 ± 0.03 to 0.03 ± 0.01. Errors in geometric measurements in x, y and z ranged from -5.5% to + 4.5% precalibration and were likewise reduced to -0.97% to + 0.23% postcalibration. Image distortions from gradient nonlinearity were markedly reduced. Periodic gradient calibration is an integral part of quality assurance in MRI. The proposed approach is both accurate and efficient, can be setup with readily available materials, and improves accuracy in both anatomical and diffusion MRI to within ±1%. Magn Reson Med 77:170-179, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. © 2016 Wiley Periodicals, Inc.

  9. Efficient gradient calibration based on diffusion MRI

    PubMed Central

    Teh, Irvin; Maguire, Mahon L.

    2016-01-01

    Purpose To propose a method for calibrating gradient systems and correcting gradient nonlinearities based on diffusion MRI measurements. Methods The gradient scaling in x, y, and z were first offset by up to 5% from precalibrated values to simulate a poorly calibrated system. Diffusion MRI data were acquired in a phantom filled with cyclooctane, and corrections for gradient scaling errors and nonlinearity were determined. The calibration was assessed with diffusion tensor imaging and independently validated with high resolution anatomical MRI of a second structured phantom. Results The errors in apparent diffusion coefficients along orthogonal axes ranged from −9.2% ± 0.4% to + 8.8% ± 0.7% before calibration and −0.5% ± 0.4% to + 0.8% ± 0.3% after calibration. Concurrently, fractional anisotropy decreased from 0.14 ± 0.03 to 0.03 ± 0.01. Errors in geometric measurements in x, y and z ranged from −5.5% to + 4.5% precalibration and were likewise reduced to −0.97% to + 0.23% postcalibration. Image distortions from gradient nonlinearity were markedly reduced. Conclusion Periodic gradient calibration is an integral part of quality assurance in MRI. The proposed approach is both accurate and efficient, can be setup with readily available materials, and improves accuracy in both anatomical and diffusion MRI to within ±1%. Magn Reson Med 77:170–179, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. PMID:26749277

  10. Review of new shapes for higher gradients

    NASA Astrophysics Data System (ADS)

    Geng, R. L.

    2006-07-01

    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 Eacc has been increased from a few MV/m to ∼42 MV/m in SRF niobium cavities. The corresponding peak RF magnetic field Hpk on the niobium cavity surface is approaching the intrinsic RF critical magnetic field Hcrit,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 Hpk/ Eacc has been recently proposed. For a reduced Hpk/ Eacc, a higher ultimate Eacc is sustained when Hpk finally strikes Hcrit,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.

  11. Improved incorporation of strain gradient elasticity in the flexoelectricity based energy harvesting from nanobeams

    NASA Astrophysics Data System (ADS)

    Zhou, Yarong; Yang, Xu; Pan, Dongmei; Wang, Binglei

    2018-04-01

    Flexoelectricity, the coupling of strain gradient and polarization, exists in all the dielectric materials and numerous models have been proposed to study this mechanism. However, the contribution of strain gradient elasticity has typically been underestimated. In this work, inspired by the one-length scale parameter model developed by Deng et al. [19], we incorporate three length-scale parameters to carefully capture the contribution of the purely mechanical strain gradients on flexoelectricity. This three-parameter model is more flexible and could be applied to investigate the flexoelectricity in a wide range of complicated deformations. Accordingly, we carry out our analysis by studying a dielectric nanobeam under different boundary conditions. We show that the strain gradient elasticity and flexoelectricity have apparent size effects and significant influence on the electromechanical response. In particular, the strain gradient effects could significantly reduce the energy efficiency, indicating their importance and necessity. This work may be helpful in understanding the mechanism of flexoelectricity at the nanoscale and sheds light on the flexoelectricity energy harvesting.

  12. High pressure liquid chromatographic gradient mixer

    DOEpatents

    Daughton, Christian G.; Sakaji, Richard H.

    1985-01-01

    A gradient mixer which effects the continuous mixing of any two miscible solvents without excessive decay or dispersion of the resultant isocratic effluent or of a linear or exponential gradient. The two solvents are fed under low or high pressure by means of two high performance liquid chromatographic pumps. The mixer comprises a series of ultra-low dead volume stainless steel tubes and low dead volume chambers. The two solvent streams impinge head-on at high fluxes. This initial nonhomogeneous mixture is then passed through a chamber packed with spirally-wound wires which cause turbulent mixing thereby homogenizing the mixture with minimum "band-broadening".

  13. High-pressure liquid chromatographic gradient mixer

    DOEpatents

    Daughton, C.G.; Sakaji, R.H.

    1982-09-08

    A gradient mixer effects the continuous mixing of any two miscible solvents without excessive decay or dispersion of the resultant isocratic effluent or of a linear or exponential gradient. The two solvents are fed under low or high pressure by means of two high performance liquid chromatographic pumps. The mixer comprises a series of ultra-low dead volume stainless steel tubes and low dead volume chambers. The two solvent streams impinge head-on at high fluxes. This initial nonhomogeneous mixture is then passed through a chamber packed with spirally-wound wires which cause turbulent mixing thereby homogenizing the mixture with minimum band-broadening.

  14. The effect of density gradients on hydrometers

    NASA Astrophysics Data System (ADS)

    Heinonen, Martti; Sillanpää, Sampo

    2003-05-01

    Hydrometers are simple but effective instruments for measuring the density of liquids. In this work, we studied the effect of non-uniform density of liquid on a hydrometer reading. The effect induced by vertical temperature gradients was investigated theoretically and experimentally. A method for compensating for the effect mathematically was developed and tested with experimental data obtained with the MIKES hydrometer calibration system. In the tests, the method was found reliable. However, the reliability depends on the available information on the hydrometer dimensions and density gradients.

  15. Magnetic field of longitudinal gradient bend

    NASA Astrophysics Data System (ADS)

    Aiba, Masamitsu; Böge, Michael; Ehrlichman, Michael; Streun, Andreas

    2018-06-01

    The longitudinal gradient bend is an effective method for reducing the natural emittance in light sources. It is, however, not a common element. We have analyzed its magnetic field and derived a set of formulae. Based on the derivation, we discuss how to model the longitudinal gradient bend in accelerator codes that are used for designing electron storage rings. Strengths of multipole components can also be evaluated from the formulae, and we investigate the impact of higher order multipole components in a very low emittance lattice.

  16. Gradient Learning Algorithms for Ontology Computing

    PubMed Central

    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

  17. Apparent Brecciation Gradient, Mount Desert Island, Maine

    NASA Astrophysics Data System (ADS)

    Hawkins, A. T.; Johnson, S. E.

    2004-05-01

    Mount Desert Island, Maine, comprises a shallow level, Siluro-Devonian igneous complex surrounded by a distinctive breccia zone ("shatter zone" of Gilman and Chapman, 1988). The zone is very well exposed on the southern and eastern shores of the island and provides a unique opportunity to examine subvolcanic processes. The breccia of the Shatter Zone shows wide variation in percent matrix and clast, and may represent a spatial and temporal gradient in breccia formation due to a single eruptive or other catastrophic volcanic event. The shatter zone was divided into five developmental stages based on the extent of brecciation: Bar Harbor Formation, Sols Cliffs breccia, Seeley Road breccia, Dubois breccia, and Great Head breccia. A digital camera was employed to capture scale images of representative outcrops using a 0.5 m square Plexiglas frame. Individual images were joined in Adobe Photoshop to create a composite image of each outcrop. The composite photo was then exported to Adobe Illustrator, which was used to outline the clasts and produce a digital map of the outcrop for analysis. The fractal dimension (Fd) of each clast was calculated using NIH Image and a Euclidean distance mapping method described by Bérubé and Jébrak (1999) to quantify the morphology of the fragments, or the complexity of the outline. The more complex the fragment outline, the higher the fractal dimension, indicating that the fragment is less "mature" or has had less exposure to erosional processes, such as the injection of an igneous matrix. Sols Cliffs breccia has an average Fd of 1.125, whereas Great Head breccia has an average Fd of 1.040, with the stages between having intermediate values. The more complex clasts of the Sols Cliffs breccia with a small amount (26.38%) of matrix material suggests that it is the first stage in a sequence of brecciation ending at the more mature, matrix-supported (71.37%) breccia of Great Head. The results of this study will be used to guide isotopic

  18. Finite gradient elasticity and plasticity: a constitutive thermodynamical framework

    NASA Astrophysics Data System (ADS)

    Bertram, Albrecht

    2016-05-01

    In Bertram (Continuum Mech Thermodyn. doi: 10.1007/s00161-014-0387-0 , 2015), a mechanical framework for finite gradient elasticity and plasticity has been given. In the present paper, this is extended to thermodynamics. The mechanical theory is only briefly repeated here. A format for a rather general constitutive theory including all thermodynamic fields is given in a Euclidian invariant setting. The plasticity theory is rate-independent and unconstrained. The Clausius-Duhem inequality is exploited to find necessary and sufficient conditions for thermodynamic consistency. The residual dissipation inequality restricts the flow and hardening rules in combination with the yield criterion.

  19. On the relation between phase-field crack approximation and gradient damage modelling

    NASA Astrophysics Data System (ADS)

    Steinke, Christian; Zreid, Imadeddin; Kaliske, Michael

    2017-05-01

    The finite element implementation of a gradient enhanced microplane damage model is compared to a phase-field model for brittle fracture. Phase-field models and implicit gradient damage models share many similarities despite being conceived from very different standpoints. In both approaches, an additional differential equation and a length scale are introduced. However, while the phase-field method is formulated starting from the description of a crack in fracture mechanics, the gradient method starts from a continuum mechanics point of view. At first, the scope of application for both models is discussed to point out intersections. Then, the analysis of the employed mathematical methods and their rigorous comparison are presented. Finally, numerical examples are introduced to illustrate the findings of the comparison which are summarized in a conclusion at the end of the paper.

  20. Large Airborne Full Tensor Gradient Data Inversion Based on a Non-Monotone Gradient Method

    NASA Astrophysics Data System (ADS)

    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.

  1. The lateral variation of P n velocity gradient under Eurasia

    SciTech Connect

    Yang, Xiaoning

    We report that mantle lid P wave velocity gradient, or P n velocity gradient, reflects the depth and lateral variations of thermal and rheological state of the uppermost mantle. Mapping the P n velocity gradient and its lateral variation helps us gain insight into the temperature, composition, and dynamics of the uppermost mantle. In addition, because P n velocity gradient has profound influence on P n propagation behavior, an accurate mapping of P n velocity gradient also improves the modeling and prediction of P n travel times and amplitudes. In this study, I used measured P n travel times tomore » derive path-specific P n velocity gradients. I then inverted these velocity gradients for two-dimensional (2-D) P n velocity-gradient models for Eurasia based on the assumption that a path-specific Pn velocity gradient is the mean of laterally varying P n velocity gradients along the P n path. Result from a Monte Carlo simulation indicates that the assumption is appropriate. The 2-D velocity-gradient models show that most of Eurasia has positive velocity gradients. High velocity gradients exist mainly in tectonically active regions. Most tectonically stable regions show low and more uniform velocity gradients. In conclusion, strong velocity-gradient variations occur largely along convergent plate boundaries, particularly under overriding plates.« less

  2. The lateral variation of P n velocity gradient under Eurasia

    DOE PAGES

    Yang, Xiaoning

    2017-05-03

    We report that mantle lid P wave velocity gradient, or P n velocity gradient, reflects the depth and lateral variations of thermal and rheological state of the uppermost mantle. Mapping the P n velocity gradient and its lateral variation helps us gain insight into the temperature, composition, and dynamics of the uppermost mantle. In addition, because P n velocity gradient has profound influence on P n propagation behavior, an accurate mapping of P n velocity gradient also improves the modeling and prediction of P n travel times and amplitudes. In this study, I used measured P n travel times tomore » derive path-specific P n velocity gradients. I then inverted these velocity gradients for two-dimensional (2-D) P n velocity-gradient models for Eurasia based on the assumption that a path-specific Pn velocity gradient is the mean of laterally varying P n velocity gradients along the P n path. Result from a Monte Carlo simulation indicates that the assumption is appropriate. The 2-D velocity-gradient models show that most of Eurasia has positive velocity gradients. High velocity gradients exist mainly in tectonically active regions. Most tectonically stable regions show low and more uniform velocity gradients. In conclusion, strong velocity-gradient variations occur largely along convergent plate boundaries, particularly under overriding plates.« less

  3. HOT PRESSING WITH A TEMPERATURE GRADIENT

    DOEpatents

    Hausner, H.H.

    1958-05-20

    A method is described for producing powder metal compacts with a high length to width ratio, which are of substantially uniform density. The process consists in arranging a heating coil around the die and providing a temperature gradient along the length of the die with the highest temperature at the point of the compact farthest away from the ram or plunger.

  4. Magnetic Control of Concentration Gradient in Microgravity

    NASA Technical Reports Server (NTRS)

    Leslie, Fred; Ramachandran, Narayanan

    2005-01-01

    A report describes a technique for rapidly establishing a fluid-concentration gradient that can serve as an initial condition for an experiment on solutal instabilities associated with crystal growth in microgravity. The technique involves exploitation of the slight attractive or repulsive forces exerted on most fluids by a magnetic-field gradient. Although small, these forces can dominate in microgravity and therefore can be used to hold fluids in position in preparation for an experiment. The magnetic field is applied to a test cell, while a fluid mixture containing a concentration gradient is prepared by introducing an undiluted solution into a diluting solution in a mixing chamber. The test cell is then filled with the fluid mixture. Given the magnetic susceptibilities of the undiluted and diluting solutions, the magnetic-field gradient must be large enough that the magnetic force exceeds both (1) forces associated with the flow of the fluid mixture during filling of the test cell and (2) forces imposed by any residual gravitation and fluctuations thereof. Once the test cell has been filled with the fluid mixture, the magnetic field is switched off so that the experiment can proceed, starting from the proper initial conditions.

  5. Minimum maximum temperature gradient coil design.

    PubMed

    While, Peter T; Poole, Michael S; Forbes, Larry K; Crozier, Stuart

    2013-08-01

    Ohmic heating is a serious problem in gradient coil operation. A method is presented for redesigning cylindrical gradient coils to operate at minimum peak temperature, while maintaining field homogeneity and coil performance. To generate these minimaxT coil windings, an existing analytic method for simulating the spatial temperature distribution of single layer gradient coils is combined with a minimax optimization routine based on sequential quadratic programming. Simulations are provided for symmetric and asymmetric gradient coils that show considerable improvements in reducing maximum temperature over existing methods. The winding patterns of the minimaxT coils were found to be heavily dependent on the assumed thermal material properties and generally display an interesting "fish-eye" spreading of windings in the dense regions of the coil. Small prototype coils were constructed and tested for experimental validation and these demonstrate that with a reasonable estimate of material properties, thermal performance can be improved considerably with negligible change to the field error or standard figures of merit. © 2012 Wiley Periodicals, Inc.

  6. A progressive gradient moment nulling design technique.

    PubMed

    Pipe, J G; Chenevert, T L

    1991-05-01

    A method is presented for designing motion-compensated gradients in a progressive manner. The method is easily applicable to many types of waveforms, and can compensate for any order of motion. It can be implemented graphically or numerically. Underlying theory and examples of its application are provided.

  7. Multi-gradient drilling method and system

    DOEpatents

    Maurer, William C.; Medley, Jr., George H.; McDonald, William J.

    2003-01-01

    A multi-gradient system for drilling a well bore from a surface location into a seabed includes an injector for injecting buoyant substantially incompressible articles into a column of drilling fluid associated with the well bore. Preferably, the substantially incompressible articles comprises hollow substantially spherical bodies.

  8. 40 CFR 230.25 - Salinity gradients.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... entrance to an estuary or river mouth that significantly restricts the movement of the salt water into and... estuary. The downstream migration of the salinity gradient can occur, displacing the maximum sedimentation... estuary below that which is considered normal can affect the location and type of mixing thereby changing...

  9. 40 CFR 230.25 - Salinity gradients.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... entrance to an estuary or river mouth that significantly restricts the movement of the salt water into and... estuary. The downstream migration of the salinity gradient can occur, displacing the maximum sedimentation... estuary below that which is considered normal can affect the location and type of mixing thereby changing...

  10. 40 CFR 230.25 - Salinity gradients.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... entrance to an estuary or river mouth that significantly restricts the movement of the salt water into and... estuary. The downstream migration of the salinity gradient can occur, displacing the maximum sedimentation... estuary below that which is considered normal can affect the location and type of mixing thereby changing...

  11. 40 CFR 230.25 - Salinity gradients.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... entrance to an estuary or river mouth that significantly restricts the movement of the salt water into and... estuary. The downstream migration of the salinity gradient can occur, displacing the maximum sedimentation... estuary below that which is considered normal can affect the location and type of mixing thereby changing...

  12. Ocean thermal gradient hydraulic power plant.

    PubMed

    Beck, E J

    1975-07-25

    Solar energy stored in the oceans may be used to generate power by exploiting ploiting thermal gradients. A proposed open-cycle system uses low-pressure steam to elevate vate water, which is then run through a hydraulic turbine to generate power. The device is analogous to an air lift pump.

  13. Density Gradient Columns for Chemical Displays.

    ERIC Educational Resources Information Center

    Guenther, William B.

    1986-01-01

    Procedures for preparing density gradient columns for chemical displays are presented. They include displays illustrating acid-base reactions, metal ion equilibria, and liquid density. The lifetime of these metastable displays is surprising, some lasting for months in display cabinets. (JN)

  14. Conjugate Gradient Algorithms For Manipulator Simulation

    NASA Technical Reports Server (NTRS)

    Fijany, Amir; Scheid, Robert E.

    1991-01-01

    Report discusses applicability of conjugate-gradient algorithms to computation of forward dynamics of robotic manipulators. Rapid computation of forward dynamics essential to teleoperation and other advanced robotic applications. Part of continuing effort to find algorithms meeting requirements for increased computational efficiency and speed. Method used for iterative solution of systems of linear equations.

  15. Gradient Space under Orthography and Perspective

    DTIC Science & Technology

    1982-05-24

    surfaceorientation to image geometry [8, 9, 10, 13, 15]. The descriptions of important gradient space properties, however, have been scattered throughout...Kanade, T. A Theory of Origami World. Artificial Intelligence 13:279-311, 1980. *[8] Kanade, T. and Kender, J. Mapping Image Properies into Shape

  16. Annular beam with segmented phase gradients

    SciTech Connect

    Cheng, Shubo; Wu, Liang; Tao, Shaohua, E-mail: eshtao@csu.edu.cn

    2016-08-15

    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 owingmore » 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.« less

  17. Analysis of magnetic gradients to study gravitropism.

    PubMed

    Hasenstein, Karl H; John, Susan; Scherp, Peter; Povinelli, Daniel; Mopper, Susan

    2013-01-01

    Gravitropism typically is generated by dense particles that respond to gravity. Experimental stimulation by high-gradient magnetic fields provides a new approach to selectively manipulate the gravisensing system. The movement of corn, wheat, and potato starch grains in suspension was examined with videomicroscopy during parabolic flights that generated 20 to 25 s of weightlessness. During weightlessness, a magnetic gradient was generated by inserting a wedge into a uniform, external magnetic field that caused repulsion of starch grains. The resultant velocity of movement was compared with the velocity of sedimentation under 1 g conditions. The high-gradient magnetic fields repelled the starch grains and generated a force of at least 0.6 g. Different wedge shapes significantly affected starch velocity and directionality of movement. Magnetic gradients are able to move diamagnetic compounds under weightless or microgravity conditions and serve as directional stimulus during seed germination in low-gravity environments. Further work can determine whether gravity sensing is based on force or contact between amyloplasts and statocyte membrane system.

  18. A latitudinal phylogeographic diversity gradient in birds

    PubMed Central

    Seeholzer, Glenn F.; Harvey, Michael G.; Cuervo, Andrés M.; Brumfield, Robb T.

    2017-01-01

    High tropical species diversity is often attributed to evolutionary dynamics over long timescales. It is possible, however, that latitudinal variation in diversification begins when divergence occurs within species. Phylogeographic data capture this initial stage of diversification in which populations become geographically isolated and begin to differentiate genetically. There is limited understanding of the broader implications of intraspecific diversification because comparative analyses have focused on species inhabiting and evolving in restricted regions and environments. Here, we scale comparative phylogeography up to the hemisphere level and examine whether the processes driving latitudinal differences in species diversity are also evident within species. We collected genetic data for 210 New World bird species distributed across a broad latitudinal gradient and estimated a suite of metrics characterizing phylogeographic history. We found that lower latitude species had, on average, greater phylogeographic diversity than higher latitude species and that intraspecific diversity showed evidence of greater persistence in the tropics. Factors associated with species ecologies, life histories, and habitats explained little of the variation in phylogeographic structure across the latitudinal gradient. Our results suggest that the latitudinal gradient in species richness originates, at least partly, from population-level processes within species and are consistent with hypotheses implicating age and environmental stability in the formation of diversity gradients. Comparative phylogeographic analyses scaled up to large geographic regions and hundreds of species can show connections between population-level processes and broad-scale species-richness patterns. PMID:28406905

  19. Examining the Education Gradient in Chronic Illness

    ERIC Educational Resources Information Center

    Chatterji, Pinka; Joo, Heesoo; Lahiri, Kajal

    2015-01-01

    We examine the education gradient in diabetes, hypertension, and high cholesterol. We take into account diagnosed as well as undiagnosed cases and use methods accounting for the possibility of unmeasured factors that are correlated with education and drive both the likelihood of having illness and the propensity to be diagnosed. Data come from the…

  20. Integral Field Spectroscopy Surveys: Oxygen Abundance Gradients

    NASA Astrophysics Data System (ADS)

    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 (r<0.5re) and a flattennig in the outer regions. For lower masses (>109.5M⊙) 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.

  1. Controlling Thermal Gradients During Silicon Web Growth

    NASA Technical Reports Server (NTRS)

    Duncan, C. S.; Mchugh, J. P.; Skutch, M. E.; Piotrowski, P. A.

    1983-01-01

    Strategically placed slot helps to control critical thermal gradients in crucible for silicon web growth. Slot thermally isolates feed region of crucible from growth region; region where pellets are added stays hot. Heat absorbed by pellets during melting causes thermal unbalance than upsets growth conditions.

  2. Plasma membrane H⁺ -ATPase regulation is required for auxin gradient formation preceding phototropic growth.

    PubMed

    Hohm, Tim; Demarsy, Emilie; Quan, Clément; Allenbach Petrolati, Laure; Preuten, Tobias; Vernoux, Teva; Bergmann, Sven; Fankhauser, Christian

    2014-09-26

    Phototropism is a growth response allowing plants to align their photosynthetic organs toward incoming light and thereby to optimize photosynthetic activity. Formation of a lateral gradient of the phytohormone auxin is a key step to trigger asymmetric growth of the shoot leading to phototropic reorientation. To identify important regulators of auxin gradient formation, we developed an auxin flux model that enabled us to test in silico the impact of different morphological and biophysical parameters on gradient formation, including the contribution of the extracellular space (cell wall) or apoplast. Our model indicates that cell size, cell distributions, and apoplast thickness are all important factors affecting gradient formation. Among all tested variables, regulation of apoplastic pH was the most important to enable the formation of a lateral auxin gradient. To test this prediction, we interfered with the activity of plasma membrane H⁺ -ATPases that are required to control apoplastic pH. Our results show that H⁺ -ATPases are indeed important for the establishment of a lateral auxin gradient and phototropism. Moreover, we show that during phototropism, H⁺ -ATPase activity is regulated by the phototropin photoreceptors, providing a mechanism by which light influences apoplastic pH. © 2014 The Authors. Published under the terms of the CC BY 4.0 license.

  3. Plasma membrane H+-ATPase regulation is required for auxin gradient formation preceding phototropic growth

    PubMed Central

    Hohm, Tim; Demarsy, Emilie; Quan, Clément; Allenbach Petrolati, Laure; Preuten, Tobias; Vernoux, Teva; Bergmann, Sven; Fankhauser, Christian

    2014-01-01

    Phototropism is a growth response allowing plants to align their photosynthetic organs toward incoming light and thereby to optimize photosynthetic activity. Formation of a lateral gradient of the phytohormone auxin is a key step to trigger asymmetric growth of the shoot leading to phototropic reorientation. To identify important regulators of auxin gradient formation, we developed an auxin flux model that enabled us to test in silico the impact of different morphological and biophysical parameters on gradient formation, including the contribution of the extracellular space (cell wall) or apoplast. Our model indicates that cell size, cell distributions, and apoplast thickness are all important factors affecting gradient formation. Among all tested variables, regulation of apoplastic pH was the most important to enable the formation of a lateral auxin gradient. To test this prediction, we interfered with the activity of plasma membrane H+-ATPases that are required to control apoplastic pH. Our results show that H+-ATPases are indeed important for the establishment of a lateral auxin gradient and phototropism. Moreover, we show that during phototropism, H+-ATPase activity is regulated by the phototropin photoreceptors, providing a mechanism by which light influences apoplastic pH. PMID:25261457

  4. A review of gradient stiffness hydrogels used in tissue engineering and regenerative medicine.

    PubMed

    Xia, Tingting; Liu, Wanqian; Yang, Li

    2017-06-01

    Substrate stiffness is known to impact characteristics including cell differentiation, proliferation, migration and apoptosis. Hydrogels are polymeric materials distinguished by high water content and diverse physical properties. Gradient stiffness hydrogels are designed by the need to develop biologically friendly materials as extracellular matrix (ECM) alternatives to replace the separated and narrow-ranged hydrogel substrates. Important new discoveries in cell behaviors have been realized with model gradient stiffness hydrogel systems from the two-dimensional (2D) to three-dimensional (3D) scale. Basic and clinical applications for gradient stiffness hydrogels in tissue engineering and regenerative medicine continue to drive the development of stiffness and structure varied hydrogels. Given the importance of gradient stiffness hydrogels in basic research and biomedical applications, there is a clear need for systems for gradient stiffness hydrogel design strategies and their applications. This review will highlight past work in the field of gradient stiffness hydrogels fabrication methods, mechanical property test, applications as well as areas for future study. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1799-1812, 2017. © 2017 Wiley Periodicals, Inc.

  5. Design and Performance of Property Gradient Ternary Nitride Coating Based on Process Control.

    PubMed

    Yan, Pei; Chen, Kaijie; Wang, Yubin; Zhou, Han; Peng, Zeyu; Jiao, Li; Wang, Xibin

    2018-05-09

    Surface coating is an effective approach to improve cutting tool performance, and multiple or gradient coating structures have become a common development strategy. However, composition mutations at the interfaces decrease the performance of multi-layered coatings. The key mitigation technique has been to reduce the interface effect at the boundaries. This study proposes a structure design method for property-component gradient coatings based on process control. The method produces coatings with high internal cohesion and high external hardness, which could reduce the composition and performance mutations at the interface. A ZrTiN property gradient ternary nitride coating was deposited on cemented carbide by multi-arc ion plating with separated Ti and Zr targets. The mechanical properties, friction behaviors, and cutting performances were systematically investigated, compared with a single-layer coating. The results indicated that the gradient coating had better friction and wear performance with lower wear rate and higher resistance to peeling off during sliding friction. The gradient coating had better wear and damage resistance in cutting processes, with lower machined surface roughness Ra. Gradient-structured coatings could effectively inhibit micro crack initiation and growth under alternating force and temperature load. This method could be extended to similar ternary nitride coatings.

  6. The temporal distribution of directional gradients under selection for an optimum.

    PubMed

    Chevin, Luis-Miguel; Haller, Benjamin C

    2014-12-01

    Temporal variation in phenotypic selection is often attributed to environmental change causing movements of the adaptive surface relating traits to fitness, but this connection is rarely established empirically. Fluctuating phenotypic selection can be measured by the variance and autocorrelation of directional selection gradients through time. However, the dynamics of these gradients depend not only on environmental changes altering the fitness surface, but also on evolution of the phenotypic distribution. Therefore, it is unclear to what extent variability in selection gradients can inform us about the underlying drivers of their fluctuations. To investigate this question, we derive the temporal distribution of directional gradients under selection for a phenotypic optimum that is either constant or fluctuates randomly in various ways in a finite population. Our analytical results, combined with population- and individual-based simulations, show that although some characteristic patterns can be distinguished, very different types of change in the optimum (including a constant optimum) can generate similar temporal distributions of selection gradients, making it difficult to infer the processes underlying apparent fluctuating selection. Analyzing changes in phenotype distributions together with changes in selection gradients should prove more useful for inferring the mechanisms underlying estimated fluctuating selection. © 2014 The Author(s). Evolution © 2014 The Society for the Study of Evolution.

  7. Probing of molecular replication and accumulation in shallow heat gradients through numerical simulations.

    PubMed

    Keil, Lorenz; Hartmann, Michael; Lanzmich, Simon; Braun, Dieter

    2016-07-27

    How can living matter arise from dead matter? All known living systems are built around information stored in RNA and DNA. To protect this information against molecular degradation and diffusion, the second law of thermodynamics imposes the need for a non-equilibrium driving force. Following a series of successful experiments using thermal gradients, we have shown that heat gradients across sub-millimetre pores can drive accumulation, replication, and selection of ever longer molecules, implementing all the necessary parts for Darwinian evolution. For these lab experiments to proceed with ample speed, however, the temperature gradients have to be quite steep, reaching up to 30 K per 100 μm. Here we use computer simulations based on experimental data to show that 2000-fold shallower temperature gradients - down to 100 K over one metre - can still drive the accumulation of protobiomolecules. This finding opens the door for various environments to potentially host the origins of life: volcanic, water-vapour, or hydrothermal settings. Following the trajectories of single molecules in simulation, we also find that they are subjected to frequent temperature oscillations inside these pores, facilitating e.g. template-directed replication mechanisms. The tilting of the pore configuration is the central strategy to achieve replication in a shallow temperature gradient. Our results suggest that shallow thermal gradients across porous rocks could have facilitated the formation of evolutionary machines, significantly increasing the number of potential sites for the origin of life on young rocky planets.

  8. Gradient zone-boundary control in salt-gradient solar ponds

    DOEpatents

    Hull, J.R.

    1982-09-29

    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 sizeable fraction of the membrane area to allow sufficient salt diffusion while preventing turbulent entrainment into the gradient zone.

  9. Shadowgraph Study of Gradient Driven Fluctuations

    NASA Technical Reports Server (NTRS)

    Cannell, David; Nikolaenko, Gennady; Giglio, Marzio; Vailati, Alberto; Croccolo, Fabrizio; Meyer, William

    2002-01-01

    A fluid or fluid mixture, subjected to a vertical temperature and/or concentration gradient in a gravitational field, exhibits greatly enhanced light scattering at small angles. This effect is caused by coupling between the vertical velocity fluctuations due to thermal energy and the vertically varying refractive index. Physically, small upward or downward moving regions will be displaced into fluid having a refractive index different from that of the moving region, thus giving rise to the enhanced scattering. The scattered intensity is predicted to vary with scattering wave vector q, as q(sup -4), for sufficiently large q, but the divergence is quenched by gravity at small q. In the absence of gravity, the long wavelength fluctuations responsible for the enhanced scattering are predicted to grow until limited by the sample dimensions. It is thus of interest to measure the mean-squared amplitude of such fluctuations in the microgravity environment for comparison with existing theory and ground based measurements. The relevant wave vectors are extremely small, making traditional low-angle light scattering difficult or impossible because of stray elastically scattered light generated by optical surfaces. An alternative technique is offered by the shadowgraph method, which is normally used to visualize fluid flows, but which can also serve as a quantitative tool to measure fluctuations. A somewhat novel shadowgraph apparatus and the necessary data analysis methods will be described. The apparatus uses a spatially coherent, but temporally incoherent, light source consisting of a super-luminescent diode coupled to a single-mode optical fiber in order to achieve extremely high spatial resolution, while avoiding effects caused by interference of light reflected from the various optical surfaces that are present when using laser sources. Results obtained for a critical mixture of aniline and cyclohexane subjected to a vertical temperature gradient will be presented. The

  10. Stellar population gradients in galaxy discs from the CALIFA survey. The influence of bars

    NASA Astrophysics Data System (ADS)

    Sánchez-Blázquez, P.; Rosales-Ortega, F. F.; Méndez-Abreu, J.; Pérez, I.; Sánchez, S. F.; Zibetti, S.; Aguerri, J. A. L.; Bland-Hawthorn, J.; Catalán-Torrecilla, C.; Cid Fernandes, R.; de Amorim, A.; de Lorenzo-Caceres, A.; Falcón-Barroso, J.; Galazzi, A.; García Benito, R.; Gil de Paz, A.; González Delgado, R.; Husemann, B.; Iglesias-Páramo, Jorge; Jungwiert, B.; Marino, R. A.; Márquez, I.; Mast, D.; Mendoza, M. A.; Mollá, M.; Papaderos, P.; Ruiz-Lara, T.; van de Ven, G.; Walcher, C. J.; Wisotzki, L.

    2014-10-01

    While studies of gas-phase metallicity gradients in disc galaxies are common, very little has been done towards the acquisition of stellar abundance gradients in the same regions. We present here a comparative study of the stellar metallicity and age distributions in a sample of 62 nearly face-on, spiral galaxies with and without bars, using data from the CALIFA survey. We measure the slopes of the gradients and study their relation with other properties of the galaxies. We find that the mean stellar age and metallicity gradients in the disc are shallow and negative. Furthermore, when normalized to the effective radius of the disc, the slope of the stellar population gradients does not correlate with the mass or with the morphological type of the galaxies. In contrast to this, the values of both age and metallicity at ~2.5 scale lengths correlate with the central velocity dispersion in a similar manner to the central values of the bulges, although bulges show, on average, older ages and higher metallicities than the discs. One of the goals of the present paper is to test the theoretical prediction that non-linear coupling between the bar and the spiral arms is an efficient mechanism for producing radial migrations across significant distances within discs. The process of radial migration should flatten the stellar metallicity gradient with time and, therefore, we would expect flatter stellar metallicity gradients in barred galaxies. However, we do not find any difference in the metallicity or age gradients between galaxies with and without bars. We discuss possible scenarios that can lead to this lack of difference. Tables 1-3 and Appendices are available in electronic form at http://www.aanda.org

  11. Perspectives in flow-based microfluidic gradient generators for characterizing bacterial chemotaxis

    PubMed Central

    Wolfram, Christopher J.; Rubloff, Gary W.; Luo, Xiaolong

    2016-01-01

    Chemotaxis is a phenomenon which enables cells to sense concentrations of certain chemical species in their microenvironment and move towards chemically favorable regions. Recent advances in microbiology have engineered the chemotactic properties of bacteria to perform novel functions, but traditional methods of characterizing chemotaxis do not fully capture the associated cell motion, making it difficult to infer mechanisms that link the motion to the microbiology which induces it. Microfluidics offers a potential solution in the form of gradient generators. Many of the gradient generators studied to date for this application are flow-based, where a chemical species diffuses across the laminar flow interface between two solutions moving through a microchannel. Despite significant research efforts, flow-based gradient generators have achieved mixed success at accurately capturing the highly subtle chemotactic responses exhibited by bacteria. Here we present an analysis encompassing previously published versions of flow-based gradient generators, the theories that govern their gradient-generating properties, and new, more practical considerations that result from experimental factors. We conclude that flow-based gradient generators present a challenge inherent to their design in that the residence time and gradient decay must be finely balanced, and that this significantly narrows the window for reliable observation and quantification of chemotactic motion. This challenge is compounded by the effects of shear on an ellipsoidal bacterium that causes it to preferentially align with the direction of flow and subsequently suppresses the cross-flow chemotactic response. These problems suggest that a static, non-flowing gradient generator may be a more suitable platform for chemotaxis studies in the long run, despite posing greater difficulties in design and fabrication. PMID:27917249

  12. Perspectives in flow-based microfluidic gradient generators for characterizing bacterial chemotaxis.

    PubMed

    Wolfram, Christopher J; Rubloff, Gary W; Luo, Xiaolong

    2016-11-01

    Chemotaxis is a phenomenon which enables cells to sense concentrations of certain chemical species in their microenvironment and move towards chemically favorable regions. Recent advances in microbiology have engineered the chemotactic properties of bacteria to perform novel functions, but traditional methods of characterizing chemotaxis do not fully capture the associated cell motion, making it difficult to infer mechanisms that link the motion to the microbiology which induces it. Microfluidics offers a potential solution in the form of gradient generators. Many of the gradient generators studied to date for this application are flow-based, where a chemical species diffuses across the laminar flow interface between two solutions moving through a microchannel. Despite significant research efforts, flow-based gradient generators have achieved mixed success at accurately capturing the highly subtle chemotactic responses exhibited by bacteria. Here we present an analysis encompassing previously published versions of flow-based gradient generators, the theories that govern their gradient-generating properties, and new, more practical considerations that result from experimental factors. We conclude that flow-based gradient generators present a challenge inherent to their design in that the residence time and gradient decay must be finely balanced, and that this significantly narrows the window for reliable observation and quantification of chemotactic motion. This challenge is compounded by the effects of shear on an ellipsoidal bacterium that causes it to preferentially align with the direction of flow and subsequently suppresses the cross-flow chemotactic response. These problems suggest that a static, non-flowing gradient generator may be a more suitable platform for chemotaxis studies in the long run, despite posing greater difficulties in design and fabrication.

  13. On the impact of adverse pressure gradient on the supersonic turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Wang, Qian-Cheng; Wang, Zhen-Guo; Zhao, Yu-Xin

    2016-11-01

    By employing the particle image velocimetry, the mean and turbulent characteristics of a Mach 2.95 turbulent boundary layer are experimentally investigated without the impact of curvature. The physical mechanism with which the streamwise adverse pressure gradient affects the supersonic boundary layer is revealed. The data are compared to that of the concave boundary layer with similar streamwise distributions of wall static pressure to clarify the separate impacts of the adverse pressure gradient and the concave curvature. The logarithmic law is observed to be well preserved for both of the cases. The dip below the logarithmic law is not observed in present investigation. Theoretical analysis indicates that it could be the result of compromise between the opposite impacts of the compression wave and the increased turbulent intensity. Compared to the zero pressure gradient boundary layer, the principal strain rate and the turbulent intensities are increased by the adverse pressure gradient. The shear layer formed due the hairpin packets could be sharpened by the compression wave, which leads to higher principal strain rate and the associated turbulent level. Due to the additional impact of the centrifugal instability brought by the concave wall, even higher turbulent intensities than that of the adverse pressure gradient case are introduced. The existence of velocity modes within the zero pressure gradient boundary layer suggests that the large scale motions are statistically well organized. The generation of new velocity modes due to the adverse pressure gradient indicates that the turbulent structure is changed by the adverse pressure gradient, through which more turbulence production that cannot be effectively predicted by the Reynolds-stress transport equations could be brought.

  14. Lateral transport of solutes in microfluidic channels using electrochemically generated gradients in redox-active surfactants.

    PubMed

    Liu, Xiaoyang; Abbott, Nicholas L

    2011-04-15

    We report principles for a continuous flow process that can separate solutes based on a driving force for selective transport that is generated by a lateral concentration gradient of a redox-active surfactant across a microfluidic channel. Microfluidic channels fabricated with gold electrodes lining each vertical wall were used to electrochemically generate concentration gradients of the redox-active surfactant 11-ferrocenylundecyl-trimethylammonium bromide (FTMA) in a direction perpendicular to the flow. The interactions of three solutes (a hydrophobic dye, 1-phenylazo-2-naphthylamine (yellow AB), an amphiphilic molecule, 2-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-pentanoyl)-1-hexadecanoyl-sn-glycero-3-phosphocholine (BODIPY C(5)-HPC), and an organic salt, 1-methylpyridinium-3-sulfonate (MPS)) with the lateral gradients in surfactant/micelle concentration were shown to drive the formation of solute-specific concentration gradients. Two distinct physical mechanisms were identified to lead to the solute concentration gradients: solubilization of solutes by micelles and differential adsorption of the solutes onto the walls of the microchannels in the presence of the surfactant concentration gradient. These two mechanisms were used to demonstrate delipidation of a mixture of BODIPY C(5)-HPC (lipid) and MPS and purification of BODIPY C(5)-HPC from a mixture of BODIPY C(5)-HPC and yellow AB. Overall, the results of this study demonstrate that lateral concentration gradients of redox-active surfactants formed within microfluidic channels can be used to transport solutes across the microfluidic channels in a solute-dependent manner. The approach employs electrical potentials (<1 V) that are sufficiently small to avoid electrolysis of water, can be performed in solutions having high ionic strength (>0.1M), and offers the basis of continuous processes for the purification or separation of solutes in microscale systems. © 2011 American Chemical Society

  15. Bending efficiency through property gradients in bamboo, palm, and wood-based composites.

    PubMed

    Wegst, Ulrike G K

    2011-07-01

    Nature, to a greater extent than engineering, takes advantage of hierarchical structures. These allow for optimization at each structural level to achieve mechanical efficiency, meaning mechanical performance per unit mass. Palms and bamboos do this exceptionally well; both are fibre-reinforced cellular materials in which the fibres are aligned parallel to the stem or culm, respectively. The distribution of these fibres is, however, not uniform: there is a density and modulus gradient across the section. This property gradient increases the flexural rigidity of the plants per unit mass, mass being a measure of metabolic investment made into an organism's construction. An analytical model is presented with which a 'gradient shape factor' can be calculated that describes by how much a plant's bending efficiency is increased through gradient structures. Combining the 'gradient shape factor' with a 'microstructural shape factor' that captures the efficiency gained through the cellular nature of the fibre composite's matrix, and a 'macroscopical shape factor' with which the tubular shape of bamboo can be described, for example, it is possible to explore how much each of these three structural levels of the hierarchy contributes to the overall bending performance of the stem or culm. In analogy, the bending efficiency of the commonly used wood-based composite medium-density fibreboard can be analysed; its property gradient is due to its manufacture by hot pressing. A few other engineered materials exist that emulate property gradients; new manufacturing routes to prepare them are currently being explored. It appears worthwhile to pursue these further. Copyright © 2011. Published by Elsevier Ltd.

  16. Aligned coaxial tungsten oxide-carbon nanotube sheet: a flexible and gradient electrochromic film.

    PubMed

    Yao, Zhaojun; Di, Jiangtao; Yong, Zhenzhong; Zhao, Zhigang; Li, Qingwen

    2012-08-25

    We develop a simple dry wrapping method to fabricate a tungsten oxide (WO(3))/carbon nanotube (CNT) cable, in which WO(3) layers act as an electrochromic component while aligned CNTs as the core provide mechanical support and an anisotropic, continuous electron transport pathway. Interestingly, the resultant cable material exhibits an obvious gradient electrochromic phenomenon.

  17. Gradient structure-induced temperature responsiveness in styrene/methyl methacrylate gradient copolymers micelles.

    PubMed

    Zheng, Chao; Huang, Haiying; He, Tianbai

    2014-02-01

    In this work, micelles are formed by gradient copolymer of styrene and methyl methacrylate in acetone-water mixture and their temperature responsiveness is investigated in a narrow range near room temperature. Three different kinds of structural transitions could be induced by temperature: unimers to micelle transition, shrinkage/stretching of micelles, and morphological transition from spherical micelles to vesicles. In addition, a model analysis on the interface of gradient copolymer micelle is made to better understand these phenomena. It is found that both position and composition of the interface could alter in response to the change in temperature. According to the experiments and model analysis, it is proposed that temperature responsiveness might be an intrinsic and universal property of gradient copolymer micelles, which only originates from the gradient structure. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Evidence of counter-gradient growth in western pond turtles (Actinemys marmorata) across thermal gradients

    USGS Publications Warehouse

    Snover, Melissa; Adams, Michael J.; Ashton, Donald T.; Bettaso, Jamie B.; Welsh, Hartwell H.

    2015-01-01

    Given the importance of size and age at reproductive maturity to population dynamics, this information on counter-gradient growth will improve our ability to understand and predict the consequences of dam operations for downstream turtle populations.

  19. Gradient parameter and axial and field rays in the gradient-index crystalline lens model

    NASA Astrophysics Data System (ADS)

    Pérez, M. V.; Bao, C.; Flores-Arias, M. T.; Rama, M. A.; Gómez-Reino, C.

    2003-09-01

    Gradient-index models of the human lens have received wide attention in optometry and vision sciences for considering how changes in the refractive index profile with age and accommodation may affect refractive power. This paper uses the continuous asymmetric bi-elliptical model to determine gradient parameter and axial and field rays of the human lens in order to study the paraxial propagation of light through the crystalline lens of the eye.

  20. Gradient waveform pre-emphasis based on the gradient system transfer function.

    PubMed

    Stich, Manuel; Wech, Tobias; Slawig, Anne; Ringler, Ralf; Dewdney, Andrew; Greiser, Andreas; Ruyters, Gudrun; Bley, Thorsten A; Köstler, Herbert

    2018-02-25

    The gradient system transfer function (GSTF) has been used to describe the distorted k-space trajectory for image reconstruction. The purpose of this work was to use the GSTF to determine the pre-emphasis for an undistorted gradient output and intended k-space trajectory. The GSTF of the MR system was determined using only standard MR hardware without special equipment such as field probes or a field camera. The GSTF was used for trajectory prediction in image reconstruction and for a gradient waveform pre-emphasis. As test sequences, a gradient-echo sequence with phase-encoding gradient modulation and a gradient-echo sequence with a spiral read-out trajectory were implemented and subsequently applied on a structural phantom and in vivo head measurements. Image artifacts were successfully suppressed by applying the GSTF-based pre-emphasis. Equivalent results are achieved with images acquired using GSTF-based post-correction of the trajectory as a part of image reconstruction. In contrast, the pre-emphasis approach allows reconstruction using the initially intended trajectory. The artifact suppression shown for two sequences demonstrates that the GSTF can serve for a novel pre-emphasis. A pre-emphasis based on the GSTF information can be applied to any arbitrary sequence type. © 2018 International Society for Magnetic Resonance in Medicine.

  1. Effects of Gradient Coil Noise and Gradient Coil Replacement on the Reproducibility of Resting State Networks.

    PubMed

    Bagarinao, Epifanio; Tsuzuki, Erina; Yoshida, Yukina; Ozawa, Yohei; Kuzuya, Maki; Otani, Takashi; Koyama, Shuji; Isoda, Haruo; Watanabe, Hirohisa; Maesawa, Satoshi; Naganawa, Shinji; Sobue, Gen

    2018-01-01

    The stability of the MRI scanner throughout a given study is critical in minimizing hardware-induced variability in the acquired imaging data set. However, MRI scanners do malfunction at times, which could generate image artifacts and would require the replacement of a major component such as its gradient coil. In this article, we examined the effect of low intensity, randomly occurring hardware-related noise due to a faulty gradient coil on brain morphometric measures derived from T1-weighted images and resting state networks (RSNs) constructed from resting state functional MRI. We also introduced a method to detect and minimize the effect of the noise associated with a faulty gradient coil. Finally, we assessed the reproducibility of these morphometric measures and RSNs before and after gradient coil replacement. Our results showed that gradient coil noise, even at relatively low intensities, could introduce a large number of voxels exhibiting spurious significant connectivity changes in several RSNs. However, censoring the affected volumes during the analysis could minimize, if not completely eliminate, these spurious connectivity changes and could lead to reproducible RSNs even after gradient coil replacement.

  2. Effects of Gradient Coil Noise and Gradient Coil Replacement on the Reproducibility of Resting State Networks

    PubMed Central

    Bagarinao, Epifanio; Tsuzuki, Erina; Yoshida, Yukina; Ozawa, Yohei; Kuzuya, Maki; Otani, Takashi; Koyama, Shuji; Isoda, Haruo; Watanabe, Hirohisa; Maesawa, Satoshi; Naganawa, Shinji; Sobue, Gen

    2018-01-01

    The stability of the MRI scanner throughout a given study is critical in minimizing hardware-induced variability in the acquired imaging data set. However, MRI scanners do malfunction at times, which could generate image artifacts and would require the replacement of a major component such as its gradient coil. In this article, we examined the effect of low intensity, randomly occurring hardware-related noise due to a faulty gradient coil on brain morphometric measures derived from T1-weighted images and resting state networks (RSNs) constructed from resting state functional MRI. We also introduced a method to detect and minimize the effect of the noise associated with a faulty gradient coil. Finally, we assessed the reproducibility of these morphometric measures and RSNs before and after gradient coil replacement. Our results showed that gradient coil noise, even at relatively low intensities, could introduce a large number of voxels exhibiting spurious significant connectivity changes in several RSNs. However, censoring the affected volumes during the analysis could minimize, if not completely eliminate, these spurious connectivity changes and could lead to reproducible RSNs even after gradient coil replacement. PMID:29725294

  3. Cosmic ray intensity gradients in the solar system

    NASA Technical Reports Server (NTRS)

    Mckibben, R. B.

    1975-01-01

    Recent progress in the determination of cosmic-ray intensity gradients is reviewed. Direct satellite measurements of the integral gradient are described together with various types of indirect measurements, including measurements of the Ar-37/Ar-39 ratio in samples from the Lost City meteorite, studies of anisotropies in neutron-monitor counting rates, and analysis of the sidereal diurnal anisotropy observed at a single point on earth. Nucleonic radial gradients and electron gradients measured by satellites in differential energy windows are discussed, and theoretical studies of the physical processes involved in these gradients are summarized. Observations of intensity gradients in heliographic latitude are reported.

  4. Propulsion of Active Colloids by Self-Induced Field Gradients.

    PubMed

    Boymelgreen, Alicia; Yossifon, Gilad; Miloh, Touvia

    2016-09-20

    Previously, metallodielectric Janus particles have been shown to travel with their dielectric hemisphere forward under low frequency applied electric fields as a result of asymmetric induced-charge electroosmotic flow. Here, it is demonstrated that at high frequencies, well beyond the charge relaxation time of the electric double layer induced around the particle, rather than the velocity decaying to zero, the Janus particles reverse direction, traveling with their metallic hemisphere forward. It is proposed that such motion is the result of a surface force, arising from localized nonuniform electric field gradients, induced by the dual symmetry-breaking of an asymmetric particle adjacent to a wall, which act on the induced dipole of the particle to drive net motion even in a uniform AC field. Although the field is external, since the driving gradient is induced on the particle level, it may be considered an active colloid. We have thus termed this propulsion mechanism "self-dielectrophoresis", to distinguish from traditional dielectrophoresis where the driving nonuniform field is externally fixed and the particle direction is restricted. It is demonstrated theoretically and experimentally that the critical frequency at which the particle reverses direction can be characterized by a nondimensional parameter which is a function of electrolyte concentration and particle size.

  5. Vascular and Immunobiology of the Circulatory Sphingosine 1-Phosphate Gradient

    PubMed Central

    Yanagida, Keisuke; Hla, Timothy

    2017-01-01

    Vertebrates are endowed with a closed circulatory system, the evolution of which required novel structural and regulatory changes. Furthermore, immune cell trafficking paradigms adapted to the barriers imposed by the closed circulatory system. How did such changes occur mechanistically? We propose that spatial compartmentalization of the lipid mediator sphingosine 1-phosphate (S1P) may be one such mechanism. In vertebrates, S1P is spatially compartmentalized in the blood and lymphatic circulation, thus comprising a sharp S1P gradient across the endothelial barrier. Circulatory S1P has critical roles in maturation and homeostasis of the vascular system as well as in immune cell trafficking. Physiological functions of S1P are tightly linked to shear stress, the key biophysical stimulus from blood flow. Thus, circulatory S1P confinement could be a primordial strategy of vertebrates in the development of a closed circulatory system. This review discusses the cellular and molecular basis of the S1P gradients and aims to interpret its physiological significance as a key feature of the closed circulatory system. PMID:27813829

  6. A homogenized localizing gradient damage model with micro inertia effect

    NASA Astrophysics Data System (ADS)

    Wang, Zhao; Poh, Leong Hien

    2018-07-01

    The conventional gradient enhancement regularizes structural responses during material failure. However, it induces a spurious damage growth phenomenon, which is shown here to persist in dynamics. Similar issues were reported with the integral averaging approach. Consequently, the conventional nonlocal enhancement cannot adequately describe the dynamic fracture of quasi-brittle materials, particularly in the high strain rate regime, where a diffused damage profile precludes the development of closely spaced macrocracks. To this end, a homogenization theory is proposed to translate the micro processes onto the macro scale. Starting with simple elementary models at the micro scale to describe the fracture mechanisms, an additional kinematic field is introduced to capture the variations in deformation and velocity within a unit cell. An energetic equivalence between micro and macro is next imposed to ensure consistency at the two scales. The ensuing homogenized microforce balance resembles closely the conventional gradient expression, albeit with an interaction domain that decreases with damage, complemented by a micro inertia effect. Considering a direct single pressure bar example, the homogenized model is shown to resolve the non-physical responses obtained with conventional nonlocal enhancement. The predictive capability of the homogenized model is furthermore demonstrated by considering the spall tests of concrete, with good predictions on failure characteristics such as fragmentation profiles and dynamic tensile strengths, at three different loading rates.

  7. Adaptation to implied tilt: extensive spatial extrapolation of orientation gradients

    PubMed Central

    Roach, Neil W.; Webb, Ben S.

    2013-01-01

    To extract the global structure of an image, the visual system must integrate local orientation estimates across space. Progress is being made toward understanding this integration process, but very little is known about whether the presence of structure exerts a reciprocal influence on local orientation coding. We have previously shown that adaptation to patterns containing circular or radial structure induces tilt-aftereffects (TAEs), even in locations where the adapting pattern was occluded. These spatially “remote” TAEs have novel tuning properties and behave in a manner consistent with adaptation to the local orientation implied by the circular structure (but not physically present) at a given test location. Here, by manipulating the spatial distribution of local elements in noisy circular textures, we demonstrate that remote TAEs are driven by the extrapolation of orientation structure over remarkably large regions of visual space (more than 20°). We further show that these effects are not specific to adapting stimuli with polar orientation structure, but require a gradient of orientation change across space. Our results suggest that mechanisms of visual adaptation exploit orientation gradients to predict the local pattern content of unfilled regions of space. PMID:23882243

  8. A cdk1 gradient guides surface contraction waves in oocytes.

    PubMed

    Bischof, Johanna; Brand, Christoph A; Somogyi, Kálmán; Májer, Imre; Thome, Sarah; Mori, Masashi; Schwarz, Ulrich S; Lénárt, Péter

    2017-10-11

    Surface contraction waves (SCWs) in oocytes and embryos lead to large-scale shape changes coupled to cell cycle transitions and are spatially coordinated with the cell axis. Here, we show that SCWs in the starfish oocyte are generated by a traveling band of myosin II-driven cortical contractility. At the front of the band, contractility is activated by removal of cdk1 inhibition of the RhoA/RhoA kinase/myosin II signaling module, while at the rear, contractility is switched off by negative feedback originating downstream of RhoA kinase. The SCW's directionality and speed are controlled by a spatiotemporal gradient of cdk1-cyclinB. This gradient is formed by the release of cdk1-cyclinB from the asymmetrically located nucleus, and progressive degradation of cyclinB. By combining quantitative imaging, biochemical and mechanical perturbations with mathematical modeling, we demonstrate that the SCWs result from the spatiotemporal integration of two conserved regulatory modules, cdk1-cyclinB for cell cycle regulation and RhoA/Rok/NMYII for actomyosin contractility.Surface contraction waves (SCWs) are prominent shape changes coupled to cell cycle transitions in oocytes. Here the authors show that SCWs are patterned by the spatiotemporal integration of two conserved modules, cdk1-cyclinB for cell cycle regulation and RhoA/Rok/NMYII for actomyosin contractility.

  9. Abnormal center-periphery gradient in spatial attention in simultanagnosia.

    PubMed

    Balslev, Daniela; Odoj, Bartholomaeus; Rennig, Johannes; Karnath, Hans-Otto

    2014-12-01

    Patients suffering from simultanagnosia cannot perceive more than one object at a time. The underlying mechanism is incompletely understood. One hypothesis is that simultanagnosia reflects "tunnel vision," a constricted attention window around gaze, which precludes the grouping of individual objects. Although this idea has a long history in neuropsychology, the question whether the patients indeed have an abnormal attention gradient around the gaze has so far not been addressed. Here we tested this hypothesis in two simultanagnosia patients with bilateral parieto-occipital lesions and two control groups, with and without brain damage. We assessed the participants' ability to discriminate letters presented briefly at fixation with and without a peripheral distractor or in the visual periphery, with or without a foveal distractor. A constricted span of attention around gaze would predict an increased susceptibility to foveated versus peripheral distractors. Contrary to this prediction and unlike both control groups, the patients' ability to discriminate the target decreased more in the presence of peripheral compared with foveated distractors. Thus, the attentional spotlight in simultanagnosia does not fall on foveated objects as previously assumed, but rather abnormally highlights the periphery. Furthermore, we found the same center-periphery gradient in the patients' ability to recognize multiple objects. They detected multiple, but not single objects more accurately in the periphery than at fixation. These results suggest that an abnormal allocation of attention around the gaze can disrupt the grouping of individual objects into an integrated visual scene.

  10. Solvent coarsening around colloids driven by temperature gradients

    NASA Astrophysics Data System (ADS)

    Roy, Sutapa; Dietrich, Siegfried; Maciolek, Anna

    2018-04-01

    Using mesoscopic numerical simulations and analytical theory, we investigate the coarsening of the solvent structure around a colloidal particle emerging after a temperature quench of the colloid surface. Qualitative differences in the coarsening mechanisms are found, depending on the composition of the binary liquid mixture forming the solvent and on the adsorption preferences of the colloid. For an adsorptionwise neutral colloid, the phase next to its surface alternates as a function of time. This behavior sets in on the scale of the relaxation time of the solvent and is absent for colloids with strong adsorption preferences. A Janus colloid, with a small temperature difference between its two hemispheres, reveals an asymmetric structure formation and surface enrichment around it, even if the solvent is within its one-phase region and if the temperature of the colloid is above the critical demixing temperature Tc of the solvent. Our phenomenological model turns out to capture recent experimental findings according to which, upon laser illumination of a Janus colloid and due to the ensuing temperature gradient between its two hemispheres, the surrounding binary liquid mixture develops a concentration gradient.

  11. Automated apparatus for producing gradient gels

    DOEpatents

    Anderson, N.L.

    1983-11-10

    Apparatus for producing a gradient gel which serves as a standard medium for a two-dimensional analysis of proteins, the gel having a density gradient along its height formed by a variation in gel composition, with the apparatus including first and second pumping means each including a plurality of pumps on a common shaft and driven by a stepping motor capable of providing small incremental changes in pump outputs for the gel ingredients, the motors being controlled, by digital signals from a digital computer, a hollow form or cassette for receiving the gel composition, means for transferring the gel composition including a filler tube extending near the bottom of the cassette, adjustable horizontal and vertical arms for automatically removing and relocating the filler tube in the next cassette, and a digital computer programmed to automatically control the stepping motors, arm movements, and associated sensing operations involving the filling operation.

  12. Automated apparatus for producing gradient gels

    DOEpatents

    Anderson, Norman L.

    1986-01-01

    Apparatus for producing a gradient gel which serves as a standard medium for a two-dimensional analysis of proteins, the gel having a density gradient along its height formed by a variation in gel composition, with the apparatus including first and second pumping means each including a plurality of pumps on a common shaft and driven by a stepping motor capable of providing small incremental changes in pump outputs for the gel ingredients, the motors being controlled, by digital signals from a digital computer, a hollow form or cassette for receiving the gel composition, means for transferring the gel composition including a filler tube extending near the bottom of the cassette, adjustable horizontal and vertical arms for automatically removing and relocating the filler tube in the next cassette, and a digital computer programmed to automatically control the stepping motors, arm movements, and associated sensing operations involving the filling operation.

  13. A mesh gradient technique for numerical optimization

    NASA Technical Reports Server (NTRS)

    Willis, E. A., Jr.

    1973-01-01

    A class of successive-improvement optimization methods in which directions of descent are defined in the state space along each trial trajectory are considered. The given problem is first decomposed into two discrete levels by imposing mesh points. Level 1 consists of running optimal subarcs between each successive pair of mesh points. For normal systems, these optimal two-point boundary value problems can be solved by following a routine prescription if the mesh spacing is sufficiently close. A spacing criterion is given. Under appropriate conditions, the criterion value depends only on the coordinates of the mesh points, and its gradient with respect to those coordinates may be defined by interpreting the adjoint variables as partial derivatives of the criterion value function. In level 2, the gradient data is used to generate improvement steps or search directions in the state space which satisfy the boundary values and constraints of the given problem.

  14. Sequential pattern formation governed by signaling gradients

    NASA Astrophysics Data System (ADS)

    Jörg, David J.; Oates, Andrew C.; Jülicher, Frank

    2016-10-01

    Rhythmic and sequential segmentation of the embryonic body plan is a vital developmental patterning process in all vertebrate species. However, a theoretical framework capturing the emergence of dynamic patterns of gene expression from the interplay of cell oscillations with tissue elongation and shortening and with signaling gradients, is still missing. Here we show that a set of coupled genetic oscillators in an elongating tissue that is regulated by diffusing and advected signaling molecules can account for segmentation as a self-organized patterning process. This system can form a finite number of segments and the dynamics of segmentation and the total number of segments formed depend strongly on kinetic parameters describing tissue elongation and signaling molecules. The model accounts for existing experimental perturbations to signaling gradients, and makes testable predictions about novel perturbations. The variety of different patterns formed in our model can account for the variability of segmentation between different animal species.

  15. Entanglement-Gradient Routing for Quantum Networks.

    PubMed

    Gyongyosi, Laszlo; Imre, Sandor

    2017-10-27

    We define the entanglement-gradient routing scheme for quantum repeater networks. The routing framework fuses the fundamentals of swarm intelligence and quantum Shannon theory. Swarm intelligence provides nature-inspired solutions for problem solving. Motivated by models of social insect behavior, the routing is performed using parallel threads to determine the shortest path via the entanglement gradient coefficient, which describes the feasibility of the entangled links and paths of the network. The routing metrics are derived from the characteristics of entanglement transmission and relevant measures of entanglement distribution in quantum networks. The method allows a moderate complexity decentralized routing in quantum repeater networks. The results can be applied in experimental quantum networking, future quantum Internet, and long-distance quantum communications.

  16. Spatial transposition gradients in visual working memory.

    PubMed

    Rerko, Laura; Oberauer, Klaus; Lin, Hsuan-Yu

    2014-01-01

    In list memory, access to individual items reflects limits of temporal distinctiveness. This is reflected in the finding that neighbouring list items tend to be confused most often. This article investigates the analogous effect of spatial proximity in a visual working-memory task. Items were presented in different locations varying in spatial distance. A retro-cue indicated the location of the item relevant for the subsequent memory test. In two recognition experiments, probes matching spatially close neighbours of the relevant item led to more false alarms than probes matching distant neighbours or non-neighbouring memory items. In two probed-recall experiments, one with simultaneous, the other with sequential memory item presentation, items closer to the cued location were more frequently chosen for recall than more distant items. These results reflect a spatial transposition gradient analogous to the temporal transposition gradient in serial recall and challenge fixed-capacity models of visual working memory (WM).

  17. Degraded character recognition based on gradient pattern

    NASA Astrophysics Data System (ADS)

    Babu, D. R. Ramesh; Ravishankar, M.; Kumar, Manish; Wadera, Kevin; Raj, Aakash

    2010-02-01

    Degraded character recognition is a challenging problem in the field of Optical Character Recognition (OCR). The performance of an optical character recognition depends upon printed quality of the input documents. Many OCRs have been designed which correctly identifies the fine printed documents. But, very few reported work has been found on the recognition of the degraded documents. The efficiency of the OCRs system decreases if the input image is degraded. In this paper, a novel approach based on gradient pattern for recognizing degraded printed character is proposed. The approach makes use of gradient pattern of an individual character for recognition. Experiments were conducted on character image that is either digitally written or a degraded character extracted from historical documents and the results are found to be satisfactory.

  18. Ecological gradients within a Pennsylvanian mire forest

    USGS Publications Warehouse

    DiMichele, W.A.; Falcon-Lang, H. J.; Nelson, W.J.; Elrick, S.D.; Ames, P.R.

    2007-01-01

    Pennsylvanian coals represent remains of the earliest peat-forming rain forests, but there is no current consensus on forest ecology. Localized studies of fossil forests suggest intermixture of taxa (heterogeneity), while, in contrast, coal ball and palynological analyses imply the existence of pronounced ecological gradients. Here, we report the discovery of a spectacular fossil forest preserved over ???1000 ha on top of the Pennsylvanian (Desmoinesian) Herrin (No. 6) Coal of Illinois, United States. The forest was abruptly drowned when fault movement dropped a segment of coastal mire below sea level. In the largest study of its kind to date, forest composition is statistically analyzed within a well-constrained paleogeographic context. Findings resolve apparent conflicts in models of Pennsylvanian mire ecology by confirming the existence of forest heterogeneity at the local scale, while additionally demonstrating the emergence of ecological gradients at landscape scale. ?? 2007 The Geological Society of America.

  19. Opinion Formation Models on a Gradient

    PubMed Central

    Gastner, Michael T.; Markou, Nikolitsa; Pruessner, Gunnar; Draief, Moez

    2014-01-01

    Statistical physicists have become interested in models of collective social behavior such as opinion formation, where individuals change their inherently preferred opinion if their friends disagree. Real preferences often depend on regional cultural differences, which we model here as a spatial gradient g in the initial opinion. The gradient does not only add reality to the model. It can also reveal that opinion clusters in two dimensions are typically in the standard (i.e., independent) percolation universality class, thus settling a recent controversy about a non-consensus model. However, using analytical and numerical tools, we also present a model where the width of the transition between opinions scales , not as in independent percolation, and the cluster size distribution is consistent with first-order percolation. PMID:25474528

  20. Discontinuity of cortical gradients reflects sensory impairment

    PubMed Central

    Saadon-Grosman, Noam; Tal, Zohar; Itshayek, Eyal; Amedi, Amir; Arzy, Shahar

    2015-01-01

    Topographic maps and their continuity constitute a fundamental principle of brain organization. In the somatosensory system, whole-body sensory impairment may be reflected either in cortical signal reduction or disorganization of the somatotopic map, such as disturbed continuity. Here we investigated the role of continuity in pathological states. We studied whole-body cortical representations in response to continuous sensory stimulation under functional MRI (fMRI) in two unique patient populations—patients with cervical sensory Brown-Séquard syndrome (injury to one side of the spinal cord) and patients before and after surgical repair of cervical disk protrusion—enabling us to compare whole-body representations in the same study subjects. We quantified the spatial gradient of cortical activation and evaluated the divergence from a continuous pattern. Gradient continuity was found to be disturbed at the primary somatosensory cortex (S1) and the supplementary motor area (SMA), in both patient populations: contralateral to the disturbed body side in the Brown-Séquard group and before repair in the surgical group, which was further improved after intervention. Results corresponding to the nondisturbed body side and after surgical repair were comparable with control subjects. No difference was found in the fMRI signal power between the different conditions in the two groups, as well as with respect to control subjects. These results suggest that decreased sensation in our patients is related to gradient discontinuity rather than signal reduction. Gradient continuity may be crucial for somatotopic and other topographical organization, and its disruption may characterize pathological processing. PMID:26655739

  1. Designing optimal nanofocusing with a gradient hyperlens

    NASA Astrophysics Data System (ADS)

    Shen, Lian; Prokopeva, Ludmila J.; Chen, Hongsheng; Kildishev, Alexander V.

    2017-11-01

    We report the design of a high-throughput gradient hyperbolic lenslet built with real-life materials and capable of focusing a beam into a deep sub-wavelength spot of λ/23. This efficient design is achieved through high-order transformation optics and circular effective-medium theory (CEMT), which are used to engineer the radially varying anisotropic artificial material based on the thin alternating cylindrical metal and dielectric layers. The radial gradient of the effective anisotropic optical constants allows for matching the impedances at the input and output interfaces, drastically improving the throughput of the lenslet. However, it is the use of the zeroth-order CEMT that enables the practical realization of a gradient hyperlens with realistic materials. To illustrate the importance of using the CEMT versus the conventional planar effective-medium theory (PEMT) for cylindrical anisotropic systems, such as our hyperlens, both the CEMT and PEMT are adopted to design gradient hyperlenses with the same materials and order of elemental layers. The CEMT- and PEMT-based designs show similar performance if the number of metal-dielectric binary layers is sufficiently large (9+ pairs) and if the layers are sufficiently thin. However, for the manufacturable lenses with realistic numbers of layers (e.g. five pairs) and thicknesses, the performance of the CEMT design continues to be practical, whereas the PEMT-based design stops working altogether. The accurate design of transformation optics-based layered cylindrical devices enabled by CEMT allow for a new class of robustly manufacturable nanophotonic systems, even with relatively thick layers of real-life materials.

  2. Exploration of very high gradient cavities

    SciTech Connect

    Eremeev, Grigory

    2011-07-01

    Several of the 9-cell ILC cavities processed at Jlab within ongoing ILC R&D program have shown interesting behavior at high fields, such as mode mixing and sudden field emission turn-on during quench. Equipped with thermometry and oscillating superleak transducer (OST) system for quench detection, we couple our RF measurements with local dissipation measurements. In this contribution we report on our findings with high gradient SRF cavities.

  3. M-step preconditioned conjugate gradient methods

    NASA Technical Reports Server (NTRS)

    Adams, L.

    1983-01-01

    Preconditioned conjugate gradient methods for solving sparse symmetric and positive finite systems of linear equations are described. Necessary and sufficient conditions are given for when these preconditioners can be used and an analysis of their effectiveness is given. Efficient computer implementations of these methods are discussed and results on the CYBER 203 and the Finite Element Machine under construction at NASA Langley Research Center are included.

  4. Velocity Gradient Power Functional for Brownian Dynamics.

    PubMed

    de Las Heras, Daniel; Schmidt, Matthias

    2018-01-12

    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.

  5. Conjugate gradient optimization programs for shuttle reentry

    NASA Technical Reports Server (NTRS)

    Powers, W. F.; Jacobson, R. A.; Leonard, D. A.

    1972-01-01

    Two computer programs for shuttle reentry trajectory optimization are listed and described. Both programs use the conjugate gradient method as the optimization procedure. The Phase 1 Program is developed in cartesian coordinates for a rotating spherical earth, and crossrange, downrange, maximum deceleration, total heating, and terminal speed, altitude, and flight path angle are included in the performance index. The programs make extensive use of subroutines so that they may be easily adapted to other atmospheric trajectory optimization problems.

  6. Generalized gradient algorithm for trajectory optimization

    NASA Technical Reports Server (NTRS)

    Zhao, Yiyuan; Bryson, A. E.; Slattery, R.

    1990-01-01

    The generalized gradient algorithm presented and verified as a basis for the solution of trajectory optimization problems improves the performance index while reducing path equality constraints, and terminal equality constraints. The algorithm is conveniently divided into two phases, of which the first, 'feasibility' phase yields a solution satisfying both path and terminal constraints, while the second, 'optimization' phase uses the results of the first phase as initial guesses.

  7. Velocity Gradient Power Functional for Brownian Dynamics

    NASA Astrophysics Data System (ADS)

    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.

  8. Metallicity Gradients in the Intracluster Gas of Abell 496

    NASA Astrophysics Data System (ADS)

    Dupke, Renato A.; White, Raymond E., III

    2000-07-01

    Analysis of spatially resolved ASCA spectra of the intracluster gas in Abell 496 confirms there are mild metal abundance enhancements near the center, as previously found in a joint analysis of spectra from Ginga Large Area Counter and Einstein solid state spectrometer. Simultaneous analysis of spectra from all ASCA instruments (SIS+GIS) shows that the iron abundance is 0.36+/-0.03 solar 3'-12' from the center of the cluster and rises ~50% to 0.53+/-0.04 solar within the central 2'. The F-test shows that this abundance gradient is significant at the more than 99.99% level. Nickel and sulfur abundances are also centrally enhanced. We use a variety of elemental abundance ratios to assess the relative contribution of Type Ia supernovae (SNe Ia) and Type II supernovae (SNe II) to the metal enrichment of the intracluster gas. We find spatial gradients in several abundance ratios, indicating that the fraction of iron from SNe Ia increases toward the cluster center, with SNe Ia accounting for ~50% of the iron mass 3'-12' from the center and ~70% within 2'. The increased proportion of SN Ia ejecta at the center is such that the central iron abundance enhancement can be attributed wholly to SNe Ia; we find no significant gradient in SN II ejecta. These spatial gradients in the proportion of SN Ia/II ejecta imply that the dominant metal enrichment mechanism near the center is different than in the outer parts of the cluster. We show that the central abundance enhancement is unlikely to be due to ram pressure stripping of gas from cluster galaxies or to secularly accumulated stellar mass loss within the central cD. We suggest that the additional SN Ia ejecta near the center is the vestige of a secondary SN Ia-driven wind from the cD (following a more energetic protogalactic SN II-driven wind phase), which was partially smothered in the cD due to its location at the cluster center.

  9. Calibration of a rotating accelerometer gravity gradiometer using centrifugal gradients

    NASA Astrophysics Data System (ADS)

    Yu, Mingbiao; Cai, Tijing

    2018-05-01

    The purpose of this study is to calibrate scale factors and equivalent zero biases of a rotating accelerometer gravity gradiometer (RAGG). We calibrate scale factors by determining the relationship between the centrifugal gradient excitation and RAGG response. Compared with calibration by changing the gravitational gradient excitation, this method does not need test masses and is easier to implement. The equivalent zero biases are superpositions of self-gradients and the intrinsic zero biases of the RAGG. A self-gradient is the gravitational gradient produced by surrounding masses, and it correlates well with the RAGG attitude angle. We propose a self-gradient model that includes self-gradients and the intrinsic zero biases of the RAGG. The self-gradient model is a function of the RAGG attitude, and it includes parameters related to surrounding masses. The calibration of equivalent zero biases determines the parameters of the self-gradient model. We provide detailed procedures and mathematical formulations for calibrating scale factors and parameters in the self-gradient model. A RAGG physical simulation system substitutes for the actual RAGG in the calibration and validation experiments. Four point masses simulate four types of surrounding masses producing self-gradients. Validation experiments show that the self-gradients predicted by the self-gradient model are consistent with those from the outputs of the RAGG physical simulation system, suggesting that the presented calibration method is valid.

  10. Gradient Dynamics and Entropy Production Maximization

    NASA Astrophysics Data System (ADS)

    Janečka, Adam; Pavelka, Michal

    2018-01-01

    We compare two methods for modeling dissipative processes, namely gradient dynamics and entropy production maximization. Both methods require similar physical inputs-how energy (or entropy) is stored and how it is dissipated. Gradient dynamics describes irreversible evolution by means of dissipation potential and entropy, it automatically satisfies Onsager reciprocal relations as well as their nonlinear generalization (Maxwell-Onsager relations), and it has statistical interpretation. Entropy production maximization is based on knowledge of free energy (or another thermodynamic potential) and entropy production. It also leads to the linear Onsager reciprocal relations and it has proven successful in thermodynamics of complex materials. Both methods are thermodynamically sound as they ensure approach to equilibrium, and we compare them and discuss their advantages and shortcomings. In particular, conditions under which the two approaches coincide and are capable of providing the same constitutive relations are identified. Besides, a commonly used but not often mentioned step in the entropy production maximization is pinpointed and the condition of incompressibility is incorporated into gradient dynamics.

  11. Lateral weathering gradients in glaciated catchments

    NASA Astrophysics Data System (ADS)

    McGuire, K. J.; Bailey, S. W.; Ross, D. S.; Strahm, B. D.; Schreiber, M. E.

    2016-12-01

    Mineral dissolution and the distribution of weathering products are fundamental processes that drive development and habitability of the Earth's critical zone; yet, the spatial configuration of these processes in some systems is not well understood. Feedbacks between hydrologic flows and weathering fluxes are necessary to understanding how the critical zone develops. In upland glaciated catchments of the northeastern USA, primary mineral dissolution and the distribution of weathering products are spatially distinct and predictable over short distances. Hillslopes, where shallow soils force lateral hydrologic fluxes through accumulated organic matter, produce downslope gradients in mineral depletion, weathering product accumulation, soil development, and solute chemistry. We propose that linked gradients in hydrologic flow paths, soil depth, and vegetation lead to predictable differences in the location and extent of mineral dissolution in regolith (soil, subsoil, and rock fragments) and bedrock, and that headwater catchments within the upland glaciated northeast show a common architecture across hillslopes as a result. Examples of these patterns and processes will be illustrated using observations from the Hubbard Brook Experimental Forest in New Hampshire where laterally distinct soils with strong morphological and biogeochemical gradients have been documented. Patterns in mineral depletion and product accumulation are essential in predicting how ecosystems will respond to stresses, disturbance, and management.

  12. Crosswind Shear Gradient Affect on Wake Vortices

    NASA Technical Reports Server (NTRS)

    Proctor, Fred H.; Ahmad, Nashat N.

    2011-01-01

    Parametric simulations with a Large Eddy Simulation (LES) model are used to explore the influence of crosswind shear on aircraft wake vortices. Previous studies based on field measurements, laboratory experiments, as well as LES, have shown that the vertical gradient of crosswind shear, i.e. the second vertical derivative of the environmental crosswind, can influence wake vortex transport. The presence of nonlinear vertical shear of the crosswind velocity can reduce the descent rate, causing a wake vortex pair to tilt and change in its lateral separation. The LES parametric studies confirm that the vertical gradient of crosswind shear does influence vortex trajectories. The parametric results also show that vortex decay from the effects of shear are complex since the crosswind shear, along with the vertical gradient of crosswind shear, can affect whether the lateral separation between wake vortices is increased or decreased. If the separation is decreased, the vortex linking time is decreased, and a more rapid decay of wake vortex circulation occurs. If the separation is increased, the time to link is increased, and at least one of the vortices of the vortex pair may have a longer life time than in the case without shear. In some cases, the wake vortices may never link.

  13. Diffusiophoresis in one-dimensional solute gradients

    SciTech Connect

    Ault, Jesse T.; Warren, Patrick B.; Shin, Sangwoo

    Here, the diffusiophoretic motion of suspended colloidal particles under one-dimensional solute gradients is solved using numerical and analytical techniques. Similarity solutions are developed for the injection and withdrawal dynamics of particles into semi-infinite pores. Furthermore, a method of characteristics formulation of the diffusion-free particle transport model is presented and integrated to realize particle trajectories. Analytical solutions are presented for the limit of small particle diffusiophoretic mobility Γ p relative to the solute diffusivity D s for particle motions in both semi-infinite and finite domains. Results confirm the build up of local maxima and minima in the propagating particle front dynamics.more » The method of characteristics is shown to successfully predict particle motions and the position of the particle front, although it fails to accurately predict suspended particle concentrations in the vicinity of sharp gradients, such as at the particle front peak seen in some injection cases, where particle diffusion inevitably plays an important role. Results inform the design of applications in which the use of applied solute gradients can greatly enhance particle injection into and withdrawal from pores.« less

  14. Comparing species interaction networks along environmental gradients.

    PubMed

    Pellissier, Loïc; Albouy, Camille; Bascompte, Jordi; Farwig, Nina; Graham, Catherine; Loreau, Michel; Maglianesi, Maria Alejandra; Melián, Carlos J; Pitteloud, Camille; Roslin, Tomas; Rohr, Rudolf; Saavedra, Serguei; Thuiller, Wilfried; Woodward, Guy; Zimmermann, Niklaus E; Gravel, Dominique

    2018-05-01

    Knowledge of species composition and their interactions, in the form of interaction networks, is required to understand processes shaping their distribution over time and space. As such, comparing ecological networks along environmental gradients represents a promising new research avenue to understand the organization of life. Variation in the position and intensity of links within networks along environmental gradients may be driven by turnover in species composition, by variation in species abundances and by abiotic influences on species interactions. While investigating changes in species composition has a long tradition, so far only a limited number of studies have examined changes in species interactions between networks, often with differing approaches. Here, we review studies investigating variation in network structures along environmental gradients, highlighting how methodological decisions about standardization can influence their conclusions. Due to their complexity, variation among ecological networks is frequently studied using properties that summarize the distribution or topology of interactions such as number of links, connectance, or modularity. These properties can either be compared directly or using a procedure of standardization. While measures of network structure can be directly related to changes along environmental gradients, standardization is frequently used to facilitate interpretation of variation in network properties by controlling for some co-variables, or via null models. Null models allow comparing the deviation of empirical networks from random expectations and are expected to provide a more mechanistic understanding of the factors shaping ecological networks when they are coupled with functional traits. As an illustration, we compare approaches to quantify the role of trait matching in driving the structure of plant-hummingbird mutualistic networks, i.e. a direct comparison, standardized by null models and hypothesis

  15. Gradient flows without blow-up for Lefschetz thimbles

    DOE PAGES

    Tanizaki, Yuya; Nishimura, Hiromichi; Verbaarschot, Jacobus J. M.

    2017-10-16

    We propose new gradient flows that define Lefschetz thimbles and do not blow up in a finite flow time. Here, we study analytic properties of these gradient flows, and confirm them by numerical tests in simple examples.

  16. Metabolic gradients: a new system for old questions.

    PubMed

    Blackstone, Neil W

    2008-04-22

    Metabolic gradients are likely to be crucial to normal and abnormal development of cells and tissues. As shown by a new study, a Xenopus egg model system has great promise to illuminate quantitative measures of metabolic gradients in living cytoplasm.

  17. Biodiversity effects on ecosystem functioning change along environmental stress gradients.

    PubMed

    Steudel, Bastian; Hector, Andy; Friedl, Thomas; Löfke, Christian; Lorenz, Maike; Wesche, Moritz; Kessler, Michael; Gessner, Mark

    2012-12-01

    Positive relationship between biodiversity and ecosystem functioning has been observed in many studies, but how this relationship is affected by environmental stress is largely unknown. To explore this influence, we measured the biomass of microalgae grown in microcosms along two stress gradients, heat and salinity, and compared our results with 13 published case studies that measured biodiversity-ecosystem functioning relationships under varying environmental conditions. We found that positive effects of biodiversity on ecosystem functioning decreased with increasing stress intensity in absolute terms. However, in relative terms, increasing stress had a stronger negative effect on low-diversity communities. This shows that more diverse biotic communities are functionally less susceptible to environmental stress, emphasises the need to maintain high levels of biodiversity as an insurance against impacts of changing environmental conditions and sets the stage for exploring the mechanisms underlying biodiversity effects in stressed ecosystems. © 2012 Blackwell Publishing Ltd/CNRS.

  18. Diffusion and surface alloying of gradient nanostructured metals

    PubMed Central

    Lu, Ke

    2017-01-01

    Gradient nanostructures (GNSs) have been optimized in recent years for desired performance. The diffusion behavior in GNS metals is crucial for understanding the diffusion mechanism and relative characteristics of different interfaces that provide fundamental understanding for advancing the traditional surface alloying processes. In this paper, atomic diffusion, reactive diffusion, and surface alloying processes are reviewed for various metals with a preformed GNS surface layer. We emphasize the promoted atomic diffusion and reactive diffusion in the GNS surface layer that are related to a higher interfacial energy state with respect to those in relaxed coarse-grained samples. Accordingly, different surface alloying processes, such as nitriding and chromizing, have been modified significantly, and some diffusion-related properties have been enhanced. Finally, the perspectives on current research in this field are discussed. PMID:28382244

  19. Surface modification and its role in the preparation of FeSi gradient alloys with good magnetic property and ductility

    NASA Astrophysics Data System (ADS)

    Yu, Haiyuan; Bi, Xiaofang

    2018-04-01

    Realization of the effective Si penetration at a lower processing temperature is a challenge, but of significance in reducing the strict requirements for the equipment and realizing cost-cutting in production. In this work, we have modified the surface microstructure of Fe-3 wt%Si alloy by using surface mechanical attrition treatment. The modified surface microstructure is characteristic of nanocrystalline, which is found to significantly enhance the efficiency of subsequent Si penetration into the alloy, and successively leading to the decrease of penetration temperature up to 200 °C. As a consequence, the Si gradient distribution across thickness can be readily controlled by changing penetration time, and FeSi alloys with various gradients are prepared by chemical vapor deposition along with subsequent annealing process. The dependence of magnetic and mechanical properties on Si gradient for demonstrates that the increase of Si gradient reduces core losses, especially at higher frequencies, and meanwhile improves ductility of FeSi alloys as well. The mechanism underlying the effect of Si gradient is clarified by combining magnetostriction measurement and domain structure observations. This work provides a facile and effective way for achieving gradient FeSi alloys with good magnetic property and ductility.

  20. OPTICAL-NEAR-INFRARED COLOR GRADIENTS AND MERGING HISTORY OF ELLIPTICAL GALAXIES

    SciTech Connect

    Kim, Duho; Im, Myungshin

    2013-04-01

    metallicity gradients changes as a result of major dry merging, the mean metallicity gradient should flatten by 40% and its scatter becomes smaller by 80% per a mass-doubling scale if ellipticals evolve only through major dry merger. Our result, although limited by a number statistics at the massive end, is consistent with the picture that major dry merging is an important mechanism for the evolution for ellipticals at M > 10{sup 11.4} M{sub Sun }, but is less important at the lower mass range.« less

  1. Optical-Near-infrared Color Gradients and Merging History of Elliptical Galaxies

    NASA Astrophysics Data System (ADS)

    Kim, Duho; Im, Myungshin

    2013-04-01

    changes as a result of major dry merging, the mean metallicity gradient should flatten by 40% and its scatter becomes smaller by 80% per a mass-doubling scale if ellipticals evolve only through major dry merger. Our result, although limited by a number statistics at the massive end, is consistent with the picture that major dry merging is an important mechanism for the evolution for ellipticals at M > 1011.4 M ⊙, but is less important at the lower mass range.

  2. Homeostasis of the Intraparenchymal-Blood Glutamate Concentration Gradient: Maintenance, Imbalance, and Regulation

    PubMed Central

    Bai, Wei; Zhou, Yuan-Guo

    2017-01-01

    It is widely accepted that glutamate is the most important excitatory neurotransmitter in the central nervous system (CNS). However, there is also a large amount of glutamate in the blood. Generally, the concentration gradient of glutamate between intraparenchymal and blood environments is stable. However, this gradient is dramatically disrupted under a variety of pathological conditions, resulting in an amplifying cascade that causes a series of pathological reactions in the CNS and peripheral organs. This eventually seriously worsens a patient’s prognosis. These two “isolated” systems are rarely considered as a whole even though they mutually influence each other. In this review, we summarize what is currently known regarding the maintenance, imbalance and regulatory mechanisms that control the intraparenchymal-blood glutamate concentration gradient, discuss the interrelationships between these systems and further explore their significance in clinical practice. PMID:29259540

  3. Surface Profile and Stress Field Evaluation using Digital Gradient Sensing Method

    DOE PAGES

    Miao, C.; Sundaram, B. M.; Huang, L.; ...

    2016-08-09

    Shape and surface topography evaluation from measured orthogonal slope/gradient data is of considerable engineering significance since many full-field optical sensors and interferometers readily output accurate data of that kind. This has applications ranging from metrology of optical and electronic elements (lenses, silicon wafers, thin film coatings), surface profile estimation, wave front and shape reconstruction, to name a few. In this context, a new methodology for surface profile and stress field determination based on a recently introduced non-contact, full-field optical method called digital gradient sensing (DGS) capable of measuring small angular deflections of light rays coupled with a robust finite-difference-based least-squaresmore » integration (HFLI) scheme in the Southwell configuration is advanced here. The method is demonstrated by evaluating (a) surface profiles of mechanically warped silicon wafers and (b) stress gradients near growing cracks in planar phase objects.« less

  4. Three-dimensional Macroscopic Scaffolds With a Gradient in Stiffness for Functional Regeneration of Interfacial Tissues

    PubMed Central

    Singh, Milind; Dormer, Nathan; Salash, Jean R.; Christian, Jordan M.; Moore, David S.; Berkland, Cory; Detamore, Michael S.

    2010-01-01

    A novel approach has been demonstrated to construct biocompatible, macroporous 3-D tissue engineering scaffolds containing a continuous macroscopic gradient in composition that yields a stiffness gradient along the axis of the scaffold. Polymeric microspheres, made of poly(d,l-lactic-co-glycolic acid) (PLGA), and composite microspheres encapsulating a higher stiffness nano-phase material (PLGA encapsulating CaCO3 or TiO2 nanoparticles) were used for the construction of microsphere-based scaffolds. Using controlled infusion of polymeric and composite microspheres, gradient scaffolds displaying an anisotropic macroscopic distribution of CaCO3/TiO2 were fabricated via an ethanol sintering technique. The controllable mechanical characteristics and biocompatible nature of these scaffolds warrants further investigation for interfacial tissue engineering applications. PMID:20336753

  5. Dynamic creation and evolution of gradient nanostructure in single-crystal metallic microcubes.

    PubMed

    Thevamaran, Ramathasan; Lawal, Olawale; Yazdi, Sadegh; Jeon, Seog-Jin; Lee, Jae-Hwang; Thomas, Edwin L

    2016-10-21

    We demonstrate the dynamic creation and subsequent static evolution of extreme gradient nanograined structures in initially near-defect-free single-crystal silver microcubes. Extreme nanostructural transformations are imposed by high strain rates, strain gradients, and recrystallization in high-velocity impacts of the microcubes against an impenetrable substrate. We synthesized the silver microcubes in a bottom-up seed-growth process and use an advanced laser-induced projectile impact testing apparatus to selectively launch them at supersonic velocities (~400 meters per second). Our study provides new insights into the fundamental deformation mechanisms and the effects of crystal and sample-shape symmetries resulting from high-velocity impacts. The nanostructural transformations produced in our experiments show promising pathways to developing gradient nanograined metals for engineering applications requiring both high strength and high toughness-for example, in structural components of aircraft and spacecraft. Copyright © 2016, American Association for the Advancement of Science.

  6. Concentration gradient induced morphology evolution of silica nanostructure growth on photoresist-derived carbon micropatterns

    NASA Astrophysics Data System (ADS)

    Liu, Dan; Shi, Tielin; Xi, Shuang; Lai, Wuxing; Liu, Shiyuan; Li, Xiaoping; Tang, Zirong

    2012-09-01

    The evolution of silica nanostructure morphology induced by local Si vapor source concentration gradient has been investigated by a smart design of experiments. Silica nanostructure or their assemblies with different morphologies are obtained on photoresist-derived three-dimensional carbon microelectrode array. At a temperature of 1,000°C, rope-, feather-, and octopus-like nanowire assemblies can be obtained along with the Si vapor source concentration gradient flow. While at 950°C, stringlike assemblies, bamboo-like nanostructures with large joints, and hollow structures with smaller sizes can be obtained along with the Si vapor source concentration gradient flow. Both vapor-liquid-solid and vapor-quasiliquid-solid growth mechanisms have been applied to explain the diverse morphologies involving branching, connecting, and batch growth behaviors. The present approach offers a potential method for precise design and controlled synthesis of nanostructures with different features.

  7. Dynamic creation and evolution of gradient nanostructure in single-crystal metallic microcubes

    NASA Astrophysics Data System (ADS)

    Thevamaran, Ramathasan; Lawal, Olawale; Yazdi, Sadegh; Jeon, Seog-Jin; Lee, Jae-Hwang; Thomas, Edwin L.

    2016-10-01

    We demonstrate the dynamic creation and subsequent static evolution of extreme gradient nanograined structures in initially near-defect-free single-crystal silver microcubes. Extreme nanostructural transformations are imposed by high strain rates, strain gradients, and recrystallization in high-velocity impacts of the microcubes against an impenetrable substrate. We synthesized the silver microcubes in a bottom-up seed-growth process and use an advanced laser-induced projectile impact testing apparatus to selectively launch them at supersonic velocities (~400 meters per second). Our study provides new insights into the fundamental deformation mechanisms and the effects of crystal and sample-shape symmetries resulting from high-velocity impacts. The nanostructural transformations produced in our experiments show promising pathways to developing gradient nanograined metals for engineering applications requiring both high strength and high toughness—for example, in structural components of aircraft and spacecraft.

  8. The Role of Nonlinear Gradients in Parallel Imaging: A k-Space Based Analysis.

    PubMed

    Galiana, Gigi; Stockmann, Jason P; Tam, Leo; Peters, Dana; Tagare, Hemant; Constable, R Todd

    2012-09-01

    Sequences that encode the spatial information of an object using nonlinear gradient fields are a new frontier in MRI, with potential to provide lower peripheral nerve stimulation, windowed fields of view, tailored spatially-varying resolution, curved slices that mirror physiological geometry, and, most importantly, very fast parallel imaging with multichannel coils. The acceleration for multichannel images is generally explained by the fact that curvilinear gradient isocontours better complement the azimuthal spatial encoding provided by typical receiver arrays. However, the details of this complementarity have been more difficult to specify. We present a simple and intuitive framework for describing the mechanics of image formation with nonlinear gradients, and we use this framework to review some the main classes of nonlinear encoding schemes.

  9. Lateral shearing optical gradient force in coupled nanobeam photonic crystal cavities

    SciTech Connect

    Du, Han; Zhang, Xingwang; Chau, Fook Siong

    2016-04-25

    We report the experimental observation of lateral shearing optical gradient forces in nanoelectromechanical systems (NEMS) controlled dual-coupled photonic crystal (PhC) nanobeam cavities. With an on-chip integrated NEMS actuator, the coupled cavities can be mechanically reconfigured in the lateral direction while maintaining a constant coupling gap. Shearing optical gradient forces are generated when the two cavity centers are laterally displaced. In our experiments, positive and negative lateral shearing optical forces of 0.42 nN and 0.29 nN are observed with different pumping modes. This study may broaden the potential applications of the optical gradient force in nanophotonic devices and benefit the futuremore » nanooptoelectromechanical systems.« less

  10. Quantifying Dynamic Changes in Plantar Pressure Gradient in Diabetics with Peripheral Neuropathy.

    PubMed

    Lung, Chi-Wen; Hsiao-Wecksler, Elizabeth T; Burns, Stephanie; Lin, Fang; Jan, Yih-Kuen

    2016-01-01

    Diabetic foot ulcers remain one of the most serious complications of diabetes. Peak plantar pressure (PPP) and peak pressure gradient (PPG) during walking have been shown to be associated with the development of diabetic foot ulcers. To gain further insight into the mechanical etiology of diabetic foot ulcers, examination of the pressure gradient angle (PGA) has been recently proposed. The PGA quantifies directional variation or orientation of the pressure gradient during walking and provides a measure of whether pressure gradient patterns are concentrated or dispersed along the plantar surface. We hypothesized that diabetics at risk of foot ulceration would have smaller PGA in key plantar regions, suggesting less movement of the pressure gradient over time. A total of 27 participants were studied, including 19 diabetics with peripheral neuropathy and 8 non-diabetic control subjects. A foot pressure measurement system was used to measure plantar pressures during walking. PPP, PPG, and PGA were calculated for four foot regions - first toe (T1), first metatarsal head (M1), second metatarsal head (M2), and heel (HL). Consistent with prior studies, PPP and PPG were significantly larger in the diabetic group compared with non-diabetic controls in the T1 and M1 regions, but not M2 or HL. For example, PPP was 165% (P = 0.02) and PPG was 214% (P < 0.001) larger in T1. PGA was found to be significantly smaller in the diabetic group in T1 (46%, P = 0.04), suggesting a more concentrated pressure gradient pattern under the toe. The proposed PGA may improve our understanding of the role of pressure gradient on the risk of diabetic foot ulcers.

  11. Apparatus for investigating the reactions of soft-bodied invertebrates to controlled humidity gradients

    PubMed Central

    Russell, Joshua; Pierce-Shimomura, Jonathan T.

    2015-01-01

    Background While many studies have assayed behavioral responses of animals to chemical, temperature and light gradients, fewer studies have assayed how animals respond to humidity gradients. Our novel humidity chamber has allowed us to study the neuromolecular basis of humidity sensation in the nematode Caenorhabditis elegans (Russell et al. 2014). New Method We describe an easy-to-construct, low-cost humidity chamber to assay the behavior of small animals, including soft-bodied invertebrates, in controlled humidity gradients. Results We show that our humidity-chamber design is amenable to soft-bodied invertebrates and can produce reliable gradients ranging 0.3–8% RH/cm across a 9-cm long x 7.5-cm wide gel-covered arena. Comparison with Existing Method(s) Previous humidity chambers relied on circulating dry and moist air to produce a steep humidity gradient in a small arena (e.g. Sayeed & Benzer, 1996). To remove the confound of moving air that may elicit mechanical responses independent of humidity responses, our chamber controlled the humidity gradient using reservoirs of hygroscopic materials. Additionally, to better observe the behavioral mechanisms for humidity responses, our chamber provided a larger arena. Although similar chambers have been described previously, these approaches were not suitable for soft-bodied invertebrates or for easy imaging of behavior because they required that animals move across wire or fabric mesh. Conclusion The general applicability of our humidity chamber overcomes limitations of previous designs and opens the door to observe the behavioral responses of soft-bodied invertebrates, including genetically powerful C. elegans and Drosophila larvae. PMID:25176025

  12. Efficient approach to obtain free energy gradient using QM/MM MD simulation

    SciTech Connect

    Asada, Toshio; Koseki, Shiro; The Research Institute for Molecular Electronic Devices

    2015-12-31

    The efficient computational approach denoted as charge and atom dipole response kernel (CDRK) model to consider polarization effects of the quantum mechanical (QM) region is described using the charge response and the atom dipole response kernels for free energy gradient (FEG) calculations in the quantum mechanical/molecular mechanical (QM/MM) method. CDRK model can reasonably reproduce energies and also energy gradients of QM and MM atoms obtained by expensive QM/MM calculations in a drastically reduced computational time. This model is applied on the acylation reaction in hydrated trypsin-BPTI complex to optimize the reaction path on the free energy surface by means ofmore » FEG and the nudged elastic band (NEB) method.« less

  13. Controlling the Accumulation of Water at Oil-Solid Interfaces with Gradient Coating.

    PubMed

    Li, Yan; Yang, Qiaomu; Mei, Ran Andy; Cai, Meirong; Heng, Jerry Y Y; Yang, Zhongqiang

    2017-07-13

    In this work, we demonstrate a strategy to control the accumulation of water in the oil-solid interface using a gradient coating. Gradient chemistry on glass surface is created by vapor diffusion of organosilanes, leading to a range of contact angles from 110 to 20°. Hexadecane is placed on the gradient substrate as an oil layer, forming a "water/hexadecane/gradient solid substrate" sandwich structure. During incubation, water molecules spontaneously migrate through the micrometer-thick oil layer and result in the formation of micrometer-sized water droplets at the oil-solid interface. It turns out that water droplets at more hydrophobic regions tend to be closer to a regular spherical shape, which is attributed to their higher contact angle with the hydrophobic substrate. However, along the gradient from hydrophobic to hydrophilic, the water droplets gradually form more irregular shapes, as hydrophilic surfaces pin the edges of droplets to form a distorted morphology. It indicates that more hydrophilic surfaces containing more Si-OH groups lead to a higher electrostatic interaction with water and a higher growth rate of interfacial water droplets. This work provides further insights into the mechanism of spontaneous water accumulation at oil-solid interfaces and assists in the rational design for controlling such interfacial phenomenon.

  14. Tuning the Voices of a Choir: Detecting Ecological Gradients in Time-Series Populations.

    PubMed

    Buras, Allan; van der Maaten-Theunissen, Marieke; van der Maaten, Ernst; Ahlgrimm, Svenja; Hermann, Philipp; Simard, Sonia; Heinrich, Ingo; Helle, Gerd; Unterseher, Martin; Schnittler, Martin; Eusemann, Pascal; Wilmking, Martin

    2016-01-01

    This paper introduces a new approach-the Principal Component Gradient Analysis (PCGA)-to detect ecological gradients in time-series populations, i.e. several time-series originating from different individuals of a population. Detection of ecological gradients is of particular importance when dealing with time-series from heterogeneous populations which express differing trends. PCGA makes use of polar coordinates of loadings from the first two axes obtained by principal component analysis (PCA) to define groups of similar trends. Based on the mean inter-series correlation (rbar) the gain of increasing a common underlying signal by PCGA groups is quantified using Monte Carlo Simulations. In terms of validation PCGA is compared to three other existing approaches. Focusing on dendrochronological examples, PCGA is shown to correctly determine population gradients and in particular cases to be advantageous over other considered methods. Furthermore, PCGA groups in each example allowed for enhancing the strength of a common underlying signal and comparably well as hierarchical cluster analysis. Our results indicate that PCGA potentially allows for a better understanding of mechanisms causing time-series population gradients as well as objectively enhancing the performance of climate transfer functions in dendroclimatology. While our examples highlight the relevance of PCGA to the field of dendrochronology, we believe that also other disciplines working with data of comparable structure may benefit from PCGA.

  15. Tuning the Voices of a Choir: Detecting Ecological Gradients in Time-Series Populations

    PubMed Central

    Buras, Allan; van der Maaten-Theunissen, Marieke; van der Maaten, Ernst; Ahlgrimm, Svenja; Hermann, Philipp; Simard, Sonia; Heinrich, Ingo; Helle, Gerd; Unterseher, Martin; Schnittler, Martin; Eusemann, Pascal; Wilmking, Martin

    2016-01-01

    This paper introduces a new approach–the Principal Component Gradient Analysis (PCGA)–to detect ecological gradients in time-series populations, i.e. several time-series originating from different individuals of a population. Detection of ecological gradients is of particular importance when dealing with time-series from heterogeneous populations which express differing trends. PCGA makes use of polar coordinates of loadings from the first two axes obtained by principal component analysis (PCA) to define groups of similar trends. Based on the mean inter-series correlation (rbar) the gain of increasing a common underlying signal by PCGA groups is quantified using Monte Carlo Simulations. In terms of validation PCGA is compared to three other existing approaches. Focusing on dendrochronological examples, PCGA is shown to correctly determine population gradients and in particular cases to be advantageous over other considered methods. Furthermore, PCGA groups in each example allowed for enhancing the strength of a common underlying signal and comparably well as hierarchical cluster analysis. Our results indicate that PCGA potentially allows for a better understanding of mechanisms causing time-series population gradients as well as objectively enhancing the performance of climate transfer functions in dendroclimatology. While our examples highlight the relevance of PCGA to the field of dendrochronology, we believe that also other disciplines working with data of comparable structure may benefit from PCGA. PMID:27467508

  16. Engineering Enriched Microenvironments with Gradients of Platelet Lysate in Hydrogel Fibers.

    PubMed

    Santo, Vítor E; Babo, Pedro; Amador, Miguel; Correia, Cláudia; Cunha, Bárbara; Coutinho, Daniela F; Neves, Nuno M; Mano, João F; Reis, Rui L; Gomes, Manuela E

    2016-06-13

    Gradients of physical and chemical cues are characteristic of specific tissue microenvironments and contribute toward morphogenesis and tissue regeneration upon injury. Recent advances on microfluidics and hydrogel manipulation raised the possibility of generating biomimetic biomaterials enriched with bioactive factors and encapsulating cells following designs specifically tailored for a target application. The novelty of this work relies on the combination of methacrylated gellan gum (MeGG) with platelet lysate (PL), aiming to generate novel advanced 3D PL-enriched photo-cross-linkable hydrogels and overcoming the lack of adhesion sites provided by the native MeGG hydrogels. This combination takes advantage of the availability, enriched growth factor composition, and potential autologous application of PL while simultaneously preserving the ability provided by MeGG to tailor mechanical properties, protein release kinetics, and shape of the construct according to the desired goal. Incorporation of PL in the hydrogels significantly improved cellular adhesion and viability in the constructs. The use of microfluidic tools allowed the design of a fiber-like hydrogel incorporating a gradient of PL along the length of the fiber. These spatial protein gradients led to the viability and cell number gradients caused by maintenance of human umbilical vein endothelial cells (HUVECs) survival in the fibers toward the PL-enriched sections in comparison with the nonloaded MeGG sections of the fibers. Altogether, we propose a proof of concept strategy to design a PL gradient biomaterial with potential in tissue engineering approaches and analysis of cell-microenvironment interactions.

  17. Gradient twinned 304 stainless steels for high strength and high ductility

    DOE PAGES

    Chen, Aiying; Liu, Jiabin; Wang, Hongtao; ...

    2016-04-23

    Gradient materials often have attractive mechanical properties that outperform uniform microstructure counterparts. It remains a difficult task to investigate and compare the performance of various gradient microstructures due to the difficulty of fabrication, the wide range of length scales involved, and their respective volume percentage variations. We have investigated four types of gradient microstructures in 304 stainless steels that utilize submicrotwins, nanotwins, nanocrystalline-, ultrafine- and coarse-grains as building blocks. Tensile tests reveal that the gradient microstructure consisting of submicrotwins and nanotwins has a persistent and stable work hardening rate and yields an impressive combination of high strength and high ductility,more » leading to a toughness that is nearly 50% higher than that of the coarse-grained counterpart. Ex- and in-situ transmission electron microscopy indicates that nanoscale and submicroscale twins help to suppress and limit martensitic phase transformation via the confinement of martensite within the twin lamellar. Twinning and detwinning remain active during tensile deformation and contribute to the work hardening behavior. We discuss the advantageous properties of using submicrotwins as the main load carrier and nanotwins as the strengthening layers over those coarse and nanocrystalline grains. Furthermore, our work uncovers a new gradient design strategy to help metals and alloys achieve high strength and high ductility.« less

  18. Topography- and management-mediated resource gradients maintain rare and common plant diversity around paddy terraces.

    PubMed

    Uematsu, Yuta; Ushimaru, Atushi

    2013-09-01

    Examining the causes of interspecific differences in susceptibility to bidirectional land-use changes (land abandonment and use-intensification) is important for understanding the mechanisms of global biodiversity loss in agricultural landscapes. We tested the hypothesis that rare (endangered) plant species prefer wet and oligotrophic areas within topography- and management-mediated resource (soil water content, nutrient, and aboveground biomass) gradients, making them more susceptible to both abandonment and use-intensification of agricultural lands. We demonstrated that topography and management practices generated resource gradients in seminatural grasslands around traditional paddy terraces. Terraced topography and management practices produced a soil moisture gradient within levees and a nutrient gradient within paddy terraces. Both total and rare species diversity increased with soil water content. Total species diversity increased in more eutrophied areas with low aboveground biomass, whereas rare species diversity was high under oligotrophic conditions. Rare and common species were differentially distributed along the human-induced nutrient gradient, with rare species preferring wet, nutrient-poor environments in the agricultural landscapes studied. We suggest that conservation efforts should concentrate on wet, nutrient-poor areas within such landscapes, which can be located easily using land-use and topography maps. This strategy would reduce the costs of finding and conserving rare grassland species in a given agricultural landscape.

  19. A gradient in the duration of the G1 phase in the murine neocortical proliferative epithelium

    NASA Technical Reports Server (NTRS)

    Miyama, S.; Takahashi, T.; Nowakowski, R. S.; Caviness, V. S. Jr

    1997-01-01

    Neuronogenesis in the neocortical pseudostratified ventricular epithelium (PVE) is initiated rostrolaterally and progresses caudo-medially as development progresses. Here we have measured the cytokinetic parameters and the fractional neuronal output parameter, Q, of laterally located early-maturing regions over the principal embryonic days (E12-E15) of neocortical neuronogenesis in the mouse. These measures are compared with ones previously made of a medial, late-maturing portion of the PVE. Laterally, as medially, the duration of the neuronogenetic interval is 6 days and comprises 11 integer cell cycles. Also, in both lateral and medial areas the length of G1 phase (TG1) increases nearly 4-fold and is the only cell cycle parameter to change. Q progresses essentially identically laterally and medially with respect to the succession of integer cell cycles. Most importantly, from E12 to E13 there is a steeply declining lateral to medial gradient in TG1. The gradient is due both to the lateral to medial graded stage of neuronogenesis and to the stepwise increase in TG1 with each integer cycle during the neuronogenetic interval. To our knowledge this gradient in TG1 of the cerebral PVE is the first cell biological gradient to be demonstrated experimentally in such an extensive proliferative epithelial sheet. We suggest that this gradient in TG1 is the cellular mechanism for positionally encoding a protomap of the neocortex within the PVE.

  20. Flow perfusion culture of MC3T3-E1 osteogenic cells on gradient calcium polyphosphate scaffolds with different pore sizes.

    PubMed

    Chen, Liang; Song, Wei; Markel, David C; Shi, Tong; Muzik, Otto; Matthew, Howard; Ren, Weiping

    2016-02-01

    Calcium polyphosphate is a biodegradable bone substitute. It remains a challenge to prepare porous calcium polyphosphate with desired gradient porous structures. In this study, a modified one-step gravity sintering method was used to prepare calcium polyphosphate scaffolds with desired-gradient-pore-size distribution. The differences of porous structure, mechanical strength, and degradation rate between gradient and homogenous calcium polyphosphate scaffolds were evaluated by micro-computed tomography, scanning electron microscopy, and mechanical testing. Preosteoblastic MC3T3-E1 cells were seeded onto gradient and homogenous calcium polyphosphate scaffolds and cultured in a flow perfusion bioreactor. The distribution, proliferation, and differentiation of the MC3T3-E1 cells were compared to that of homogenous calcium polyphosphate scaffolds. Though no significant difference of cell proliferation was found between the gradient and the homogenous calcium polyphosphate scaffolds, a much higher cell differentiation and mineralization were observed in the gradient calcium polyphosphate scaffolds than that of the homogenous calcium polyphosphate scaffolds, as manifested by increased alkaline phosphatase activity (p < 0.05). The improved distribution and differentiation of cultured cells within gradient scaffolds were further supported by both (18)F-fluorine micro-positron emission tomography scanning and in vitro tetracycline labeling. We conclude that the calcium polyphosphate scaffold with gradient pore sizes enhances osteogenic cell differentiation as well as mineralization. The in vivo performance of gradient calcium polyphosphate scaffolds warrants further investigation in animal bone defect models. © The Author(s) 2015.

  1. Biogeochemistry of a temperate forest nitrogen gradient

    USGS Publications Warehouse

    Perakis, Steven S.; Sinkhorn, Emily R.

    2011-01-01

    Wide natural gradients of soil nitrogen (N) can be used to examine fundamental relationships between plant–soil–microbial N cycling and hydrologic N loss, and to test N-saturation theory as a general framework for understanding ecosystem N dynamics. We characterized plant production, N uptake and return in litterfall, soil gross and net N mineralization rates, and hydrologic N losses of nine Douglas-fir (Pseudotsuga menziesii) forests across a wide soil N gradient in the Oregon Coast Range (USA). Surface mineral soil N (0–10 cm) ranged nearly three-fold from 0.29% to 0.78% N, and in contrast to predictions of N-saturation theory, was linearly related to 10-fold variation in net N mineralization, from 8 to 82 kg N·ha−1·yr−1. Net N mineralization was unrelated to soil C:N, soil texture, precipitation, and temperature differences among sites. Net nitrification was negatively related to soil pH, and accounted for −1·yr−1. Aboveground net primary production per unit net N mineralization varied inversely with soil N, suggesting progressive saturation of plant N demands at high soil N. Hydrologic N losses were dominated by dissolved organic N at low-N sites, with increased nitrate loss causing a shift to dominance by nitrate at high-N sites, particularly where net nitrification exceeded plant N demands. With the exception of N mineralization patterns, our results broadly support the application of the N-saturation model developed from studies of anthropogenic N deposition to understand N cycling and saturation of plant and microbial sinks along natural soil N gradients. This convergence of behavior in unpolluted and polluted forest N cycles suggests that where future reductions in deposition to polluted sites do occur, symptoms of N saturation are most likely to persist where soil N content remains elevated.

  2. A motor-driven syringe-type gradient maker for forming immobilized pH gradient gels.

    PubMed

    Fawcett, J S; Sullivan, J V; Chidakel, B E; Chrambach, A

    1988-05-01

    A motor driven gradient maker based on the commercial model (Jule Inc., Trumbull, CT) was designed for immobilized pH gradient gels to provide small volumes, rapid stirring and delivery, strict volume and temperature control and air exclusion. The device was constructed and by a convenient procedure yields highly reproducible gradients either in solution or on polyacrylamide gels.

  3. Impact of Ozone Gradient on Grapevine Leaves

    NASA Astrophysics Data System (ADS)

    Alebic-Juretic, Ana; Bokan-Vucelic, Itana; Mifka, Boris; Zatezalo, Marija; Zubak, Velimir

    2017-04-01

    Due to complex orography and air mass circulation, the Rijeka Bay area is characterized by O3 gradient, with concentrations risen with the altitude (1). Therefore AOT40 values were often exceeded and should result in harmful effects on vegetation. Based on previous controlled experiments (2), we examined the possible effect of atmospheric ozone on grape leaves under natural O3 gradient. Grapevine leaves (2-5) were collected from May to September 2016 at two sampling points in the proximity of two AQM stations: Site 1 in the city centre (20m asl) and Site 2 (186m asl) in the suburban settlement. Subsequent to weighing and determination of surface area, the leaves (0,5 g) were extracted in 95% ethanol and analysed on chlorophyl a (Chla), chlorophyl b (Chlb) and carotene (Car) content by UV-VIS spectrometry on 3 wavelengths (664, 649, 470 nm) (3) In summer 2016 O3 gradient was not that pronounced as usual (1), but stil the concentrations differed by approx. 20%, exceeding national AOT40 value at both sites (22.360 and 28.061 μg m-3 h, respectively, at Sites 1 and 2). The concentrations of other pollutants were bellow limit values (LV). The Cha and Chb in a sample leaves collected at the end of May at Site 2 are equal to that with filtered O3 in control experiment (2), i.e. without damage caused by ozone, while the Car content is lower approx. 50% and is kept at the same level. The con-centrations of pigments obtained in July prooved the possible damage by O3, while in subsequent months could speed up natural ageing. This is the first evidence of O3 damage on plants in the Rijeka Bay area, in spite of weaker O3 gradient and lacking visible signs of damage. Preliminary results indicate the need for more frequent sampling, particularly in the period included in AOT40 (May-July). References: 1. Alebić-Juretić A (2012) Int J Remote Sensing, 33(2): 335-345 2. Britvec M, Reichenauer T, Soja G., Ljubešić N, Pećina M (2001) Biologia (Bratislava),56/4: 417-424 3. Sumanata

  4. Stereo vision with distance and gradient recognition

    NASA Astrophysics Data System (ADS)

    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.

  5. Broadband mode conversion via gradient index metamaterials

    PubMed Central

    Wang, HaiXiao; Xu, YaDong; Genevet, Patrice; Jiang, Jian-Hua; Chen, HuanYang

    2016-01-01

    We propose a design for broadband waveguide mode conversion based on gradient index metamaterials (GIMs). Numerical simulations demonstrate that the zeroth order of transverse magnetic mode or the first order of transverse electric mode (TM0/TE1) can be converted into the first order of transverse magnetic mode or the second order of transverse electric mode (TM1/TE2) for a broadband of frequencies. As an application, an asymmetric propagation is achieved by integrating zero index metamaterials inside the GIM waveguide. PMID:27098456

  6. Drift and separation in collisionality gradients

    DOE PAGES

    Ochs, I. E.; Rax, J. M.; Gueroult, R.; ...

    2017-07-20

    Here we identify a single-particle drift resulting from collisional interactions with a background species, in the presence of a collisionality gradient and background net flow. We also analyze this drift in different limits, showing how it reduces to the well known impurity pinch for high-Zi impurities. We find that in the low-temperature, singly ionized limit, the magnitude of the drift becomes mass-dependent and energy-dependent. Furthermore, by solving for the resulting diffusion-advection motion, we propose a mass-separation scheme that takes advantage of this drift, and analyze the separative capability as a function of collisionally dissipated energy.

  7. Drift and separation in collisionality gradients

    SciTech Connect

    Ochs, I. E.; Rax, J. M.; Gueroult, R.

    Here we identify a single-particle drift resulting from collisional interactions with a background species, in the presence of a collisionality gradient and background net flow. We also analyze this drift in different limits, showing how it reduces to the well known impurity pinch for high-Zi impurities. We find that in the low-temperature, singly ionized limit, the magnitude of the drift becomes mass-dependent and energy-dependent. Furthermore, by solving for the resulting diffusion-advection motion, we propose a mass-separation scheme that takes advantage of this drift, and analyze the separative capability as a function of collisionally dissipated energy.

  8. Gradient nonlinearity calibration and correction for a compact, asymmetric magnetic resonance imaging gradient system.

    PubMed

    Tao, S; Trzasko, J D; Gunter, J L; Weavers, P T; Shu, Y; Huston, J; Lee, S K; Tan, E T; Bernstein, M A

    2017-01-21

    Due to engineering limitations, the spatial encoding gradient fields in conventional magnetic resonance imaging cannot be perfectly linear and always contain higher-order, nonlinear components. If ignored during image reconstruction, gradient nonlinearity (GNL) manifests as image geometric distortion. Given an estimate of the GNL field, this distortion can be corrected to a degree proportional to the accuracy of the field estimate. The GNL of a gradient system is typically characterized using a spherical harmonic polynomial model with model coefficients obtained from electromagnetic simulation. Conventional whole-body gradient systems are symmetric in design; typically, only odd-order terms up to the 5th-order are required for GNL modeling. Recently, a high-performance, asymmetric gradient system was developed, which exhibits more complex GNL that requires higher-order terms including both odd- and even-orders for accurate modeling. This work characterizes the GNL of this system using an iterative calibration method and a fiducial phantom used in ADNI (Alzheimer's Disease Neuroimaging Initiative). The phantom was scanned at different locations inside the 26 cm diameter-spherical-volume of this gradient, and the positions of fiducials in the phantom were estimated. An iterative calibration procedure was utilized to identify the model coefficients that minimize the mean-squared-error between the true fiducial positions and the positions estimated from images corrected using these coefficients. To examine the effect of higher-order and even-order terms, this calibration was performed using spherical harmonic polynomial of different orders up to the 10th-order including even- and odd-order terms, or odd-order only. The results showed that the model coefficients of this gradient can be successfully estimated. The residual root-mean-squared-error after correction using up to the 10th-order coefficients was reduced to 0.36 mm, yielding spatial accuracy comparable to

  9. Gradient nonlinearity calibration and correction for a compact, asymmetric magnetic resonance imaging gradient system

    PubMed Central

    Tao, S; Trzasko, J D; Gunter, J L; Weavers, P T; Shu, Y; Huston, J; Lee, S K; Tan, E T; Bernstein, M A

    2017-01-01

    Due to engineering limitations, the spatial encoding gradient fields in conventional magnetic resonance imaging cannot be perfectly linear and always contain higher-order, nonlinear components. If ignored during image reconstruction, gradient nonlinearity (GNL) manifests as image geometric distortion. Given an estimate of the GNL field, this distortion can be corrected to a degree proportional to the accuracy of the field estimate. The GNL of a gradient system is typically characterized using a spherical harmonic polynomial model with model coefficients obtained from electromagnetic simulation. Conventional whole-body gradient systems are symmetric in design; typically, only odd-order terms up to the 5th-order are required for GNL modeling. Recently, a high-performance, asymmetric gradient system was developed, which exhibits more complex GNL that requires higher-order terms including both odd- and even-orders for accurate modeling. This work characterizes the GNL of this system using an iterative calibration method and a fiducial phantom used in ADNI (Alzheimer’s Disease Neuroimaging Initiative). The phantom was scanned at different locations inside the 26-cm diameter-spherical-volume of this gradient, and the positions of fiducials in the phantom were estimated. An iterative calibration procedure was utilized to identify the model coefficients that minimize the mean-squared-error between the true fiducial positions and the positions estimated from images corrected using these coefficients. To examine the effect of higher-order and even-order terms, this calibration was performed using spherical harmonic polynomial of different orders up to the 10th-order including even- and odd-order terms, or odd-order only. The results showed that the model coefficients of this gradient can be successfully estimated. The residual root-mean-squared-error after correction using up to the 10th-order coefficients was reduced to 0.36 mm, yielding spatial accuracy comparable to

  10. Cell orientation gradients on an inverse opal substrate.

    PubMed

    Lu, Jie; Zou, Xin; Zhao, Ze; Mu, Zhongde; Zhao, Yuanjin; Gu, Zhongze

    2015-05-20

    The generation of cell gradients is critical for understanding many biological systems and realizing the unique functionality of many implanted biomaterials. However, most previous work can only control the gradient of cell density and this has no effect on the gradient of cell orientation, which has an important role in regulating the functions of many connecting tissues. Here, we report on a simple stretched inverse opal substrate for establishing desired cell orientation gradients. It was demonstrated that tendon fibroblasts on the stretched inverse opal gradient showed a corresponding alignment along with the elongation gradient of the substrate. This "random-to-aligned" cell gradient reproduces the insertion part of many connecting tissues, and thus, will have important applications in tissue engineering.

  11. Evaluation of gravitational gradients generated by Earth's crustal structures

    NASA Astrophysics Data System (ADS)

    Novák, Pavel; Tenzer, Robert; Eshagh, Mehdi; Bagherbandi, Mohammad

    2013-02-01

    Spectral formulas for the evaluation of gravitational gradients generated by upper Earth's mass components are presented in the manuscript. The spectral approach allows for numerical evaluation of global gravitational gradient fields that can be used to constrain gravitational gradients either synthesised from global gravitational models or directly measured by the spaceborne gradiometer on board of the GOCE satellite mission. Gravitational gradients generated by static atmospheric, topographic and continental ice masses are evaluated numerically based on available global models of Earth's topography, bathymetry and continental ice sheets. CRUST2.0 data are then applied for the numerical evaluation of gravitational gradients generated by mass density contrasts within soft and hard sediments, upper, middle and lower crust layers. Combined gravitational gradients are compared to disturbing gravitational gradients derived from a global gravitational model and an idealised Earth's model represented by the geocentric homogeneous biaxial ellipsoid GRS80. The methodology could be used for improved modelling of the Earth's inner structure.

  12. Development of a shear stress-free microfluidic gradient generator capable of quantitatively analyzing single-cell morphology.

    PubMed

    Barata, David; Spennati, Giulia; Correia, Cristina; Ribeiro, Nelson; Harink, Björn; van Blitterswijk, Clemens; Habibovic, Pamela; van Rijt, Sabine

    2017-09-07

    Microfluidics, the science of engineering fluid streams at the micrometer scale, offers unique tools for creating and controlling gradients of soluble compounds. Gradient generation can be used to recreate complex physiological microenvironments, but is also useful for screening purposes. For example, in a single experiment, adherent cells can be exposed to a range of concentrations of the compound of interest, enabling high-content analysis of cell behaviour and enhancing throughput. In this study, we present the development of a microfluidic screening platform where, by means of diffusion, gradients of soluble compounds can be generated and sustained. This platform enables the culture of adherent cells under shear stress-free conditions, and their exposure to a soluble compound in a concentration gradient-wise manner. The platform consists of five serial cell culture chambers, all coupled to two lateral fluid supply channels that are used for gradient generation through a source-sink mechanism. Furthermore, an additional inlet and outlet are used for cell seeding inside the chambers. Finite element modeling was used for the optimization of the design of the platform and for validation of the dynamics of gradient generation. Then, as a proof-of-concept, human osteosarcoma MG-63 cells were cultured inside the platform and exposed to a gradient of Cytochalasin D, an actin polymerization inhibitor. This set-up allowed us to analyze cell morphological changes over time, including cell area and eccentricity measurements, as a function of Cytochalasin D concentration by using fluorescence image-based cytometry.

  13. Asymmetric Uncertainty Expression for High Gradient Aerodynamics

    NASA Technical Reports Server (NTRS)

    Pinier, Jeremy T

    2012-01-01

    When the physics of the flow around an aircraft changes very abruptly either in time or space (e.g., flow separation/reattachment, boundary layer transition, unsteadiness, shocks, etc), the measurements that are performed in a simulated environment like a wind tunnel test or a computational simulation will most likely incorrectly predict the exact location of where (or when) the change in physics happens. There are many reasons for this, includ- ing the error introduced by simulating a real system at a smaller scale and at non-ideal conditions, or the error due to turbulence models in a computational simulation. The un- certainty analysis principles that have been developed and are being implemented today do not fully account for uncertainty in the knowledge of the location of abrupt physics changes or sharp gradients, leading to a potentially underestimated uncertainty in those areas. To address this problem, a new asymmetric aerodynamic uncertainty expression containing an extra term to account for a phase-uncertainty, the magnitude of which is emphasized in the high-gradient aerodynamic regions is proposed in this paper. Additionally, based on previous work, a method for dispersing aerodynamic data within asymmetric uncer- tainty bounds in a more realistic way has been developed for use within Monte Carlo-type analyses.

  14. Droplet microfluidics driven by gradients of confinement.

    PubMed

    Dangla, Rémi; Kayi, S Cagri; Baroud, Charles N

    2013-01-15

    The miniaturization of droplet manipulation methods has led to drops being proposed as microreactors in many applications of biology and chemistry. In parallel, microfluidic methods have been applied to generate monodisperse emulsions for applications in the pharmaceuticals, cosmetics, and food industries. To date, microfluidic droplet production has been dominated by a few designs that use hydrodynamic forces, resulting from the flowing fluids, to break drops at a junction. Here we present a platform for droplet generation and manipulation that does not depend on the fluid flows. Instead, we use devices that incorporate height variations to subject the immiscible interfaces to gradients of confinement. The resulting curvature imbalance along the interface causes the detachment of monodisperse droplets, without the need for a flow of the external phase. Once detached, the drops are self-propelled due to the gradient of surface energy. We show that the size of the drops is determined by the device geometry; it is insensitive to the physical fluid properties and depends very weakly on the flow rate of the dispersed phase. This allows us to propose a geometric theoretical model that predicts the dependence of droplet size on the geometric parameters, which is in agreement with experimental measurements. The approach presented here can be applied in a wide range of standard applications, while simplifying the device operations. We demonstrate examples for single-droplet operations and high-throughput generation of emulsions, all of which are performed in simple and inexpensive devices.

  15. Droplet microfluidics driven by gradients of confinement

    PubMed Central

    Dangla, Rémi; Kayi, S. Cagri; Baroud, Charles N.

    2013-01-01

    The miniaturization of droplet manipulation methods has led to drops being proposed as microreactors in many applications of biology and chemistry. In parallel, microfluidic methods have been applied to generate monodisperse emulsions for applications in the pharmaceuticals, cosmetics, and food industries. To date, microfluidic droplet production has been dominated by a few designs that use hydrodynamic forces, resulting from the flowing fluids, to break drops at a junction. Here we present a platform for droplet generation and manipulation that does not depend on the fluid flows. Instead, we use devices that incorporate height variations to subject the immiscible interfaces to gradients of confinement. The resulting curvature imbalance along the interface causes the detachment of monodisperse droplets, without the need for a flow of the external phase. Once detached, the drops are self-propelled due to the gradient of surface energy. We show that the size of the drops is determined by the device geometry; it is insensitive to the physical fluid properties and depends very weakly on the flow rate of the dispersed phase. This allows us to propose a geometric theoretical model that predicts the dependence of droplet size on the geometric parameters, which is in agreement with experimental measurements. The approach presented here can be applied in a wide range of standard applications, while simplifying the device operations. We demonstrate examples for single-droplet operations and high-throughput generation of emulsions, all of which are performed in simple and inexpensive devices. PMID:23284169

  16. Optimization of ceramic strength using elastic gradients

    PubMed Central

    Zhang, Yu; Ma, Li

    2009-01-01

    We present a new concept for strengthening ceamics by utilizing a graded structure with a low elastic modulus at both top and bottom surfaces sandwiching a high-modulus interior. Closed-form equations have been developed for stress analysis of simply supported graded sandwich beams subject to transverse center loads. Theory predicts that suitable modulus gradients at the ceramic surface can effectively reduce and spread the maximum bending stress from the surface into the interior. The magnitude of such stress dissipation is governed by the thickness ratio of the beam to the graded layers. We test our concept by infiltrating both top and bottom surfaces of a strong class of zirconia ceramic with an in-house prepared glass of similar coefficient of thermal expansion and Poisson’s ratio to zirconia, producing a controlled modulus gradient at the surface without significant long-range residual stresses. The resultant graded glass/zirconia/glass composite exhibits significantly higher load-bearing capacity than homogeneous zirconia. PMID:20161019

  17. Performance evaluation of matrix gradient coils.

    PubMed

    Jia, Feng; Schultz, Gerrit; Testud, Frederik; Welz, Anna Masako; Weber, Hans; Littin, Sebastian; Yu, Huijun; Hennig, Jürgen; Zaitsev, Maxim

    2016-02-01

    In this paper, we present a new performance measure of a matrix coil (also known as multi-coil) from the perspective of efficient, local, non-linear encoding without explicitly considering target encoding fields. An optimization problem based on a joint optimization for the non-linear encoding fields is formulated. Based on the derived objective function, a figure of merit of a matrix coil is defined, which is a generalization of a previously known resistive figure of merit for traditional gradient coils. A cylindrical matrix coil design with a high number of elements is used to illustrate the proposed performance measure. The results are analyzed to reveal novel features of matrix coil designs, which allowed us to optimize coil parameters, such as number of coil elements. A comparison to a scaled, existing multi-coil is also provided to demonstrate the use of the proposed performance parameter. The assessment of a matrix gradient coil profits from using a single performance parameter that takes the local encoding performance of the coil into account in relation to the dissipated power.

  18. Pressure gradient induced generation of microbubbles

    NASA Astrophysics Data System (ADS)

    Evangelio, Alvaro; Campo-Cortes, Francisco; Gordillo, Jose Manuel

    2015-11-01

    It is well known that the controlled production of monodisperse bubbles possesses uncountable applications in medicine, pharmacy and industry. Here we provide with a detailed physical description of the bubble formation processes taking place in a type of flow where the liquid pressure gradient can be straightforwardly controlled. In our experiments, a gas flow rate discharges through a cylindrical needle into a pressurized chamber. The pressure gradient created from the exit of the injection needle towards the entrance of a extraction duct promotes the stretching of the gas ligament downstream. In our analysis, which is supported by an exhaustive experimental study in which the liquid viscosity is varied by three orders of magnitude, different regimes can be distinguished depending mainly on the Reynolds number. Through our physical modeling, we provide closed expressions for both the bubbling frequencies and for the bubble diameters as well as the conditions under which a monodisperse generation is obtained in all regimes found. The excellent agreement between our expressions and the experimental data fully validates our physical modeling.

  19. The multigrid preconditioned conjugate gradient method

    NASA Technical Reports Server (NTRS)

    Tatebe, Osamu

    1993-01-01

    A multigrid preconditioned conjugate gradient method (MGCG method), which uses the multigrid method as a preconditioner of the PCG method, is proposed. The multigrid method has inherent high parallelism and improves convergence of long wavelength components, which is important in iterative methods. By using this method as a preconditioner of the PCG method, an efficient method with high parallelism and fast convergence is obtained. First, it is considered a necessary condition of the multigrid preconditioner in order to satisfy requirements of a preconditioner of the PCG method. Next numerical experiments show a behavior of the MGCG method and that the MGCG method is superior to both the ICCG method and the multigrid method in point of fast convergence and high parallelism. This fast convergence is understood in terms of the eigenvalue analysis of the preconditioned matrix. From this observation of the multigrid preconditioner, it is realized that the MGCG method converges in very few iterations and the multigrid preconditioner is a desirable preconditioner of the conjugate gradient method.

  20. Intergenerational and socioeconomic gradients of child obesity.

    PubMed

    Costa-Font, Joan; Gil, Joan

    2013-09-01

    Can the rise in obesity among children be attributed to the intergenerational transmission of parental influences? Does this trend affect the influence of parent's socioeconomic status on obesity? This paper documents evidence of an emerging social gradient of obesity in pre-school children resulting from a combination of both socio-economic status and less intensive childcare associated with maternal employment, when different forms of intergenerational transmission are controlled for. We also estimate and decompose income related inequalities in child obesity. We take advantage of a uniquely constructed dataset from Spain that contains records form 13,358 individuals for a time period (years 2003-2006) in which a significant spike in the growth of child obesity was observed. Our results suggest robust evidence of both socioeconomic and intergenerational gradients. Results are suggestive of a high income effect in child obesity, alongside evidence that income inequalities have doubled in just three years with a pure income effect accounting for as much as 72-66% of these income inequality estimates, even when intergenerational transmission is accounted for. Although, intergenerational transmission does not appear to be gender specific, when accounted for, mother's labour market participation only explains obesity among boys but not among girls. Hence, it appears income and parental influences are the central determinants of obesity among children. Copyright © 2013 Elsevier Ltd. All rights reserved.

  1. A theoretical investigation of symmetry-origin unidirectional energy gradient in light-harvesting dendrimers.

    PubMed

    Koda, Shin-ichi

    2016-03-21

    We theoretically investigate a possibility that the symmetry of the repetitively branched structure of light-harvesting dendrimers creates the energy gradient descending toward inner generations (layers of pigment molecules) of the dendrimers. In the first half of this paper, we define a model system using the Frenkel exciton Hamiltonian that focuses only on the topology of dendrimers and numerically show that excitation energy tends to gather at inner generations of the model system at a thermal equilibrium state. This indicates that an energy gradient is formed in the model system. In the last half, we attribute this result to the symmetry of the model system and propose two symmetry-origin mechanisms creating the energy gradient. The present analysis and proposition are based on the theory of the linear chain (LC) decomposition [S. Koda, J. Chem. Phys. 142, 204112 (2015)], which equivalently transforms the model system into a set of one-dimensional systems on the basis of the symmetry of dendrimers. In the picture of the LC decomposition, we find that energy gradient is formed both in each linear chain and among linear chains, and these two mechanisms explain the numerical results well.

  2. A theoretical investigation of symmetry-origin unidirectional energy gradient in light-harvesting dendrimers

    NASA Astrophysics Data System (ADS)

    Koda, Shin-ichi

    2016-03-01

    We theoretically investigate a possibility that the symmetry of the repetitively branched structure of light-harvesting dendrimers creates the energy gradient descending toward inner generations (layers of pigment molecules) of the dendrimers. In the first half of this paper, we define a model system using the Frenkel exciton Hamiltonian that focuses only on the topology of dendrimers and numerically show that excitation energy tends to gather at inner generations of the model system at a thermal equilibrium state. This indicates that an energy gradient is formed in the model system. In the last half, we attribute this result to the symmetry of the model system and propose two symmetry-origin mechanisms creating the energy gradient. The present analysis and proposition are based on the theory of the linear chain (LC) decomposition [S. Koda, J. Chem. Phys. 142, 204112 (2015)], which equivalently transforms the model system into a set of one-dimensional systems on the basis of the symmetry of dendrimers. In the picture of the LC decomposition, we find that energy gradient is formed both in each linear chain and among linear chains, and these two mechanisms explain the numerical results well.

  3. Modulation of monocytic leukemia cell function and survival by high gradient magnetic fields and mathematical modeling studies.

    PubMed

    Zablotskii, Vitalii; Syrovets, Tatiana; Schmidt, Zoe W; Dejneka, Alexandr; Simmet, Thomas

    2014-03-01

    The influence of spatially modulated high gradient magnetic fields on cellular functions of human THP-1 leukemia cells is studied. We demonstrate that arrays of high-gradient micrometer-sized magnets induce i) cell swelling, ii) prolonged increased ROS production, and iii) inhibit cell proliferation, and iv) elicit apoptosis of THP-1 monocytic leukemia cells in the absence of chemical or biological agents. Mathematical modeling indicates that mechanical stress exerted on the cells by high magnetic gradient forces is responsible for triggering cell swelling and formation of reactive oxygen species followed by apoptosis. We discuss physical aspects of controlling cell functions by focused magnetic gradient forces, i.e. by a noninvasive and nondestructive physical approach. Copyright © 2014 Elsevier Ltd. All rights reserved.

  4. Gradient Models in Molecular Biophysics: Progress, Challenges, Opportunities

    PubMed Central

    Bardhan, Jaydeep P.

    2014-01-01

    In the interest of developing a bridge between researchers modeling materials and those modeling biological molecules, we survey recent progress in developing nonlocal-dielectric continuum models for studying the behavior of proteins and nucleic acids. As in other areas of science, continuum models are essential tools when atomistic simulations (e.g. molecular dynamics) are too expensive. Because biological molecules are essentially all nanoscale systems, the standard continuum model, involving local dielectric response, has basically always been dubious at best. The advanced continuum theories discussed here aim to remedy these shortcomings by adding features such as nonlocal dielectric response, and nonlinearities resulting from dielectric saturation. We begin by describing the central role of electrostatic interactions in biology at the molecular scale, and motivate the development of computationally tractable continuum models using applications in science and engineering. For context, we highlight some of the most important challenges that remain and survey the diverse theoretical formalisms for their treatment, highlighting the rigorous statistical mechanics that support the use and improvement of continuum models. We then address the development and implementation of nonlocal dielectric models, an approach pioneered by Dogonadze, Kornyshev, and their collaborators almost forty years ago. The simplest of these models is just a scalar form of gradient elasticity, and here we use ideas from gradient-based modeling to extend the electrostatic model to include additional length scales. The paper concludes with a discussion of open questions for model development, highlighting the many opportunities for the materials community to leverage its physical, mathematical, and computational expertise to help solve one of the most challenging questions in molecular biology and biophysics. PMID:25505358

  5. Gradient Models in Molecular Biophysics: Progress, Challenges, Opportunities.

    PubMed

    Bardhan, Jaydeep P

    2013-12-01

    In the interest of developing a bridge between researchers modeling materials and those modeling biological molecules, we survey recent progress in developing nonlocal-dielectric continuum models for studying the behavior of proteins and nucleic acids. As in other areas of science, continuum models are essential tools when atomistic simulations (e.g. molecular dynamics) are too expensive. Because biological molecules are essentially all nanoscale systems, the standard continuum model, involving local dielectric response, has basically always been dubious at best. The advanced continuum theories discussed here aim to remedy these shortcomings by adding features such as nonlocal dielectric response, and nonlinearities resulting from dielectric saturation. We begin by describing the central role of electrostatic interactions in biology at the molecular scale, and motivate the development of computationally tractable continuum models using applications in science and engineering. For context, we highlight some of the most important challenges that remain and survey the diverse theoretical formalisms for their treatment, highlighting the rigorous statistical mechanics that support the use and improvement of continuum models. We then address the development and implementation of nonlocal dielectric models, an approach pioneered by Dogonadze, Kornyshev, and their collaborators almost forty years ago. The simplest of these models is just a scalar form of gradient elasticity, and here we use ideas from gradient-based modeling to extend the electrostatic model to include additional length scales. The paper concludes with a discussion of open questions for model development, highlighting the many opportunities for the materials community to leverage its physical, mathematical, and computational expertise to help solve one of the most challenging questions in molecular biology and biophysics.

  6. Sources of stress gradients in electrodeposited Ni MEMS.

    SciTech Connect

    Hearne, Sean Joseph; Floro, Jerrold Anthony; Dyck, Christopher William

    2004-06-01

    The ability of future integrated metal-semiconductor micro-systems such as RF MEMS to perform highly complex functions will depend on developing freestanding metal structures that offer improved conductivity and reflectivity over polysilicon structures. For example, metal-based RF MEMS technology could replace the bulky RF system presently used in communications, navigation, and avionics systems. However, stress gradients that induce warpage of active components have prevented the implementation of this technology. Figure 1, is an interference micrograph image of a series of cantilever beams fabricated from electrodeposited Ni. The curvature in the beams was the result of stress gradients intrinsic to the electrodepositionmore » process. To study the sources of the stress in electrodeposition of Ni we have incorporated a wafer curvature based stress sensor, the multibeam optical stress sensor, into an electrodeposition cell. We have determined that there are two regions of stress induced by electrodepositing Ni from a sulfamate-based bath (Fig 2). The stress evolution during the first region, 0-1000{angstrom}, was determined to be dependent only on the substrate material (Au vs. Cu), whereas the stress evolution during the second region, >1000{angstrom}, was highly dependent on the deposition conditions. In this region, the stress varied from +0.5 GPa to -0.5GPa, depending solely on the deposition rate. We examined four likely sources for the compressive intrinsic stress, i.e. reduction in tensile stress, and determined that only the adatom diffusion into grain boundaries model of Sheldon, et al. could account for the observed compressive stress. In the presentation, we shall discuss the compressive stress generation mechanisms considered and the ramifications of these results on fabrication of electrodeposited Ni for MEMS applications.« less

  7. Gradient models in molecular biophysics: progress, challenges, opportunities

    NASA Astrophysics Data System (ADS)

    Bardhan, Jaydeep P.

    2013-12-01

    In the interest of developing a bridge between researchers modeling materials and those modeling biological molecules, we survey recent progress in developing nonlocal-dielectric continuum models for studying the behavior of proteins and nucleic acids. As in other areas of science, continuum models are essential tools when atomistic simulations (e.g., molecular dynamics) are too expensive. Because biological molecules are essentially all nanoscale systems, the standard continuum model, involving local dielectric response, has basically always been dubious at best. The advanced continuum theories discussed here aim to remedy these shortcomings by adding nonlocal dielectric response. We begin by describing the central role of electrostatic interactions in biology at the molecular scale, and motivate the development of computationally tractable continuum models using applications in science and engineering. For context, we highlight some of the most important challenges that remain, and survey the diverse theoretical formalisms for their treatment, highlighting the rigorous statistical mechanics that support the use and improvement of continuum models. We then address the development and implementation of nonlocal dielectric models, an approach pioneered by Dogonadze, Kornyshev, and their collaborators almost 40 years ago. The simplest of these models is just a scalar form of gradient elasticity, and here we use ideas from gradient-based modeling to extend the electrostatic model to include additional length scales. The review concludes with a discussion of open questions for model development, highlighting the many opportunities for the materials community to leverage its physical, mathematical, and computational expertise to help solve one of the most challenging questions in molecular biology and biophysics.

  8. The orbital mechanics of flight mechanics

    NASA Technical Reports Server (NTRS)

    Dunning, R. S.

    1973-01-01

    A reference handbook on modern dynamic orbit theory is presented. Starting from the most basic inverse-square law, the law of gravity for a sphere is developed, and the motion of point masses under the influence of a sphere is considered. The reentry theory and the orbital theory are discussed along with the relative motion between two bodies in orbit about the same planet. Relative-motion equations, rectangular coordinates, and the mechanics of simple rigid bodies under the influence of a gravity gradient field are also discussed.

  9. B1 gradient coherence selection using a tapered stripline.

    PubMed

    van Meerten, S G J; Tijssen, K C H; van Bentum, P J M; Kentgens, A P M

    2018-01-01

    Pulsed-field gradients are common in modern liquid state NMR pulse sequences. They are often used instead of phase cycles for the selection of coherence pathways, thereby decreasing the time required for the NMR experiment. Soft off-resonance pulses with a B 1 gradient result in a spatial encoding similar to that created by pulsed-field (B 0 ) gradients. In this manuscript we show that pulse sequences with pulsed-field gradients can easily be converted to one which uses off-resonance B 1 field gradient (OFFBEAT) pulses. The advantage of B 1 gradient pulses for coherence selection is that the chemical shift evolution during the pulses is (partially) suppressed. Therefore no refocusing echos are required to correct for evolution during the gradient pulses. A tapered stripline is shown to be a convenient tool for creating a well-defined gradient in the B 1 field strength. B 1 gradient coherence selection using a tapered stripline is a simple and cheap alternative to B 0 pulsed-field gradients. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

  10. Neutrophil migration under spatially-varying chemoattractant gradient profiles.

    PubMed

    Halilovic, Iris; Wu, Jiandong; Alexander, Murray; Lin, Francis

    2015-01-01

    Chemotaxis plays an important role in biological processes such as cancer metastasis, embryogenesis, wound healing, and immune response. Neutrophils are the frontline defenders against invasion of foreign microorganisms into our bodies. To achieve this important immune function, a neutrophil can sense minute chemoattractant concentration differences across its cell body and effectively migrate toward the chemoattractant source. Furthermore, it has been demonstrated in various studies that neutrophils are highly sensitive to changes in the surrounding chemoattractant environments, suggesting the role of a chemotactic memory for processing the complex spatiotemporal chemical guiding signals. Using a microfluidic device, in the present study we characterized neutrophil migration under spatially varying profiles of interleukine-8 gradients, which consist of three spatially ordered regions of a shallow gradient, a steep gradient and a nearly saturated gradient. This design allowed us to examine how neutrophils migrate under different chemoattractant gradient profiles, and how the migratory response is affected when the cell moves from one gradient profile to another in a single experiment. Our results show robust neutrophil chemotaxis in the shallow and steep gradient, but not the saturated gradient. Furthermore, neutrophils display a transition from chemotaxis to flowtaxis when they migrate across the steep gradient interface, and the relative efficiency of this transition depends on the cell's chemotaxis history. Finally, some neutrophils were observed to adjust their morphology to different gradient profiles.

  11. Optimal Disturbances in Boundary Layers Subject to Streamwise Pressure Gradient

    NASA Technical Reports Server (NTRS)

    Tumin, Anatoli; Ashpis, David E.

    2003-01-01

    Laminar-turbulent transition in shear flows is still an enigma in the area of fluid mechanics. The conventional explanation of the phenomenon is based on the instability of the shear flow with respect to infinitesimal disturbances. The conventional hydrodynamic stability theory deals with the analysis of normal modes that might be unstable. The latter circumstance is accompanied by an exponential growth of the disturbances that might lead to laminar-turbulent transition. Nevertheless, in many cases, the transition scenario bypasses the exponential growth stage associated with the normal modes. This type of transition is called bypass transition. An understanding of the phenomenon has eluded us to this day. One possibility is that bypass transition is associated with so-called algebraic (non-modal) growth of disturbances in shear flows. In the present work, an analysis of the optimal disturbances/streamwise vortices associated with the transient growth mechanism is performed for boundary layers in the presence of a streamwise pressure gradient. The theory will provide the optimal spacing of the control elements in the spanwise direction and their placement in the streamwise direction.

  12. Food web complexity and stability across habitat connectivity gradients.

    PubMed

    LeCraw, Robin M; Kratina, Pavel; Srivastava, Diane S

    2014-12-01

    The effects of habitat connectivity on food webs have been studied both empirically and theoretically, yet the question of whether empirical results support theoretical predictions for any food web metric other than species richness has received little attention. Our synthesis brings together theory and empirical evidence for how habitat connectivity affects both food web stability and complexity. Food web stability is often predicted to be greatest at intermediate levels of connectivity, representing a compromise between the stabilizing effects of dispersal via rescue effects and prey switching, and the destabilizing effects of dispersal via regional synchronization of population dynamics. Empirical studies of food web stability generally support both this pattern and underlying mechanisms. Food chain length has been predicted to have both increasing and unimodal relationships with connectivity as a result of predators being constrained by the patch occupancy of their prey. Although both patterns have been documented empirically, the underlying mechanisms may differ from those predicted by models. In terms of other measures of food web complexity, habitat connectivity has been empirically found to generally increase link density but either reduce or have no effect on connectance, whereas a unimodal relationship is expected. In general, there is growing concordance between empirical patterns and theoretical predictions for some effects of habitat connectivity on food webs, but many predictions remain to be tested over a full connectivity gradient, and empirical metrics of complexity are rarely modeled. Closing these gaps will allow a deeper understanding of how natural and anthropogenic changes in connectivity can affect real food webs.

  13. Maternal Education Gradients in Infant Health in Four South American Countries.

    PubMed

    Wehby, George L; López-Camelo, Jorge S

    2017-11-01

    Objective We investigate gradients (i.e. differences) in infant health outcomes by maternal education in Argentina, Brazil, Chile, and Venezuela and explore channels related to father's education, household labor outcomes, and maternal health, fertility, and use of prenatal services and technology. Methods We employ secondary interview and birth record data similarly collected across a network of birth hospitals from the early 1980s through 2011 within the Latin American Collaborative Study of Congenital Anomalies (ECLAMC). Focusing on children without birth defects, we estimate gradients in several infant health outcomes including birth weight, gestational age, and hospital discharge status by maternal education using ordinary least squares regression models adjusting for several demographic factors. To explore channels, we add as covariates father's education, parental occupational activity, maternal health and fertility history, and use of prenatal services and technology and evaluate changes in the coefficient of maternal education. We use the same models for each country sample. Results We find important differences in gradients across countries. We find evidence for educational gradients in preterm birth in three countries but weaker evidence for gradients in fetal growth. The extent to which observed household and maternal factors explain these gradients based on changes in the regression coefficient of maternal education when controlling for these factors as covariates also varies between countries. In contrast, we generally find evidence across all countries that higher maternal education is associated with increased use of prenatal care services and technology. Conclusions Our findings suggest that differences in infant health by maternal education and their underlying mechanisms vary and are not necessarily generalizable across countries. However, the positive association between maternal education and use of prenatal services and technology is more

  14. Litterfall production along successional and altitudinal gradients of subtropical monsoon evergreen broadleaved forests in Guangdong, China

    USGS Publications Warehouse

    Zhou, G.; Guan, L.; Wei, X.; Zhang, Dongxiao; Zhang, Q.; Yan, J.; Wen, D.; Liu, J.; Liu, S.; Huang, Z.; Kong, G.; Mo, J.; Yu, Q.

    2007-01-01

    Evaluation of litterfall production is important for understanding nutrient cycling, forest growth, successional pathways, and interactions with environmental variables in forest ecosystems. Litterfall was intensively studied during the period of 1982-2001 in two subtropical monsoon vegetation gradients in the Dinghushan Biosphere Reserve, Guangdong Province, China. The two gradients include: (1) a successional gradient composed of pine forest (PF), mixed pine and broadleaved forest (MF) and monsoon evergreen broadleaved forest (BF), and (2) an altitudinal gradient composed of Baiyunci ravine rain forest (BRF), Qingyunci ravine rain forest (QRF), BF and mountainous evergreen broadleaved forest (MMF). Mean annual litterfall production was 356, 861 and 849 g m-2 for PF, MF and BF of the successional gradient, and 1016, 1061, 849 and 489 g m-2 for BRF, QRF, BF and MMF of the altitudinal gradient, respectively. As expected, mean annual litterfall of the pioneer forest PF was the lowest, but rapidly increased over the observation period while those in other forests were relatively stable, confirming that forest litterfall production is closely related to successional stages and growth patterns. Leaf proportions of total litterfall in PF, MF, BF, BRF, QRF and MMF were 76.4%, 68.4%, 56.8%, 55.7%, 57.6% and 69.2%, respectively, which were consistent with the results from studies in other evergreen broadleaved forests. Our analysis on litterfall monthly distributions indicated that litterfall production was much higher during the period of April to September compared to other months for all studied forest types. Although there were significant impacts of some climate variables (maximum and effective temperatures) on litterfall production in some of the studied forests, the mechanisms of how climate factors (temperature and rainfall) interactively affect litterfall await further study. ?? 2006 Springer Science+Business Media B.V.

  15. Constant field gradient planar coupled cavity structure

    DOEpatents

    Kang, Y.W.; Kustom, R.L.

    1999-07-27

    A cavity structure is disclosed having at least two opposing planar housing members spaced apart to accommodate the passage of a particle beam through the structure between the members. Each of the housing members have a plurality of serially aligned hollows defined therein, and also passages, formed in the members, which interconnect serially adjacent hollows to provide communication between the hollows. The opposing planar housing members are spaced and aligned such that the hollows in one member cooperate with corresponding hollows in the other member to form a plurality of resonant cavities aligned along the particle beam within the cavity structure. To facilitate the obtaining of a constant field gradient within the cavity structure, the passages are configured so as to be incrementally narrower in the direction of travel of the particle beam. In addition, the spacing distance between the opposing housing members is configured to be incrementally smaller in the direction of travel of the beam. 16 figs.

  16. Constant field gradient planar coupled cavity structure

    DOEpatents

    Kang, Yoon W.; Kustom, Robert L.

    1999-01-01

    A cavity structure having at least two opposing planar housing members spaced apart to accommodate the passage of a particle beam through the structure between the members. Each of the housing members have a plurality of serially aligned hollows defined therein, and also passages, formed in the members, which interconnect serially adjacent hollows to provide communication between the hollows. The opposing planar housing members are spaced and aligned such that the hollows in one member cooperate with corresponding hollows in the other member to form a plurality of resonant cavities aligned along the particle beam within the cavity structure. To facilitate the obtaining of a constant field gradient within the cavity structure, the passages are configured so as to be incrementally narrower in the direction of travel of the particle beam. In addition, the spacing distance between the opposing housing members is configured to be incrementally smaller in the direction of travel of the beam.

  17. Fractional calculus and morphogen gradient formation

    NASA Astrophysics Data System (ADS)

    Yuste, Santos Bravo; Abad, Enrique; Lindenberg, Katja

    2012-12-01

    Some microscopic models for reactive systems where the reaction kinetics is limited by subdiffusion are described by means of reaction-subdiffusion equations where fractional derivatives play a key role. In particular, we consider subdiffusive particles described by means of a Continuous Time Random Walk (CTRW) model subject to a linear (first-order) death process. The resulting fractional equation is employed to study the developmental biology key problem of morphogen gradient formation for the case in which the morphogens are subdiffusive. If the morphogen degradation rate (reactivity) is constant, we find exponentially decreasing stationary concentration profiles, which are similar to the profiles found when the morphogens diffuse normally. However, for the case in which the degradation rate decays exponentially with the distance to the morphogen source, we find that the morphogen profiles are qualitatively different from the profiles obtained when the morphogens diffuse normally.

  18. Quasi parton distributions and the gradient flow

    DOE PAGES

    Monahan, Christopher; Orginos, Kostas

    2017-03-22

    We propose a new approach to determining quasi parton distribution functions (PDFs) from lattice quantum chromodynamics. By incorporating the gradient flow, this method guarantees that the lattice quasi PDFs are finite in the continuum limit and evades the thorny, and as yet unresolved, issue of the renormalization of quasi PDFs on the lattice. In the limit that the flow time is much smaller than the length scale set by the nucleon momentum, the moments of the smeared quasi PDF are proportional to those of the lightfront PDF. Finally, we use this relation to derive evolution equations for the matching kernelmore » that relates the smeared quasi PDF and the light-front PDF.« less

  19. Quasi parton distributions and the gradient flow

    SciTech Connect

    Monahan, Christopher; Orginos, Kostas

    We propose a new approach to determining quasi parton distribution functions (PDFs) from lattice quantum chromodynamics. By incorporating the gradient flow, this method guarantees that the lattice quasi PDFs are finite in the continuum limit and evades the thorny, and as yet unresolved, issue of the renormalization of quasi PDFs on the lattice. In the limit that the flow time is much smaller than the length scale set by the nucleon momentum, the moments of the smeared quasi PDF are proportional to those of the lightfront PDF. Finally, we use this relation to derive evolution equations for the matching kernelmore » that relates the smeared quasi PDF and the light-front PDF.« less

  20. Magnon dark modes and gradient memory

    PubMed Central

    Zhang, Xufeng; Zou, Chang-Ling; Zhu, Na; Marquardt, Florian; Jiang, Liang; Tang, Hong X.

    2015-01-01

    Extensive efforts have been expended in developing hybrid quantum systems to overcome the short coherence time of superconducting circuits by introducing the naturally long-lived spin degree of freedom. Among all the possible materials, single-crystal yttrium iron garnet has shown up recently as a promising candidate for hybrid systems, and various highly coherent interactions, including strong and even ultrastrong coupling, have been demonstrated. One distinct advantage in these systems is that spins form well-defined magnon modes, which allows flexible and precise tuning. Here we demonstrate that by dissipation engineering, a non-Markovian interaction dynamics between the magnon and the microwave cavity photon can be achieved. Such a process enables us to build a magnon gradient memory to store information in the magnon dark modes, which decouple from the microwave cavity and thus preserve a long lifetime. Our findings provide a promising approach for developing long-lifetime, multimode quantum memories. PMID:26568130

  1. Magnon dark modes and gradient memory.

    PubMed

    Zhang, Xufeng; Zou, Chang-Ling; Zhu, Na; Marquardt, Florian; Jiang, Liang; Tang, Hong X

    2015-11-16

    Extensive efforts have been expended in developing hybrid quantum systems to overcome the short coherence time of superconducting circuits by introducing the naturally long-lived spin degree of freedom. Among all the possible materials, single-crystal yttrium iron garnet has shown up recently as a promising candidate for hybrid systems, and various highly coherent interactions, including strong and even ultrastrong coupling, have been demonstrated. One distinct advantage in these systems is that spins form well-defined magnon modes, which allows flexible and precise tuning. Here we demonstrate that by dissipation engineering, a non-Markovian interaction dynamics between the magnon and the microwave cavity photon can be achieved. Such a process enables us to build a magnon gradient memory to store information in the magnon dark modes, which decouple from the microwave cavity and thus preserve a long lifetime. Our findings provide a promising approach for developing long-lifetime, multimode quantum memories.

  2. Error analysis of stochastic gradient descent ranking.

    PubMed

    Chen, Hong; Tang, Yi; Li, Luoqing; Yuan, Yuan; Li, Xuelong; Tang, Yuanyan

    2013-06-01

    Ranking is always an important task in machine learning and information retrieval, e.g., collaborative filtering, recommender systems, drug discovery, etc. A kernel-based stochastic gradient descent algorithm with the least squares loss is proposed for ranking in this paper. The implementation of this algorithm is simple, and an expression of the solution is derived via a sampling operator and an integral operator. An explicit convergence rate for leaning a ranking function is given in terms of the suitable choices of the step size and the regularization parameter. The analysis technique used here is capacity independent and is novel in error analysis of ranking learning. Experimental results on real-world data have shown the effectiveness of the proposed algorithm in ranking tasks, which verifies the theoretical analysis in ranking error.

  3. Microfluidic quadrupole and floating concentration gradient.

    PubMed

    Qasaimeh, Mohammad A; Gervais, Thomas; Juncker, David

    2011-09-06

    The concept of fluidic multipoles, in analogy to electrostatics, has long been known as a particular class of solutions of the Navier-Stokes equation in potential flows; however, experimental observations of fluidic multipoles and of their characteristics have not been reported yet. Here we present a two-dimensional microfluidic quadrupole and a theoretical analysis consistent with the experimental observations. The microfluidic quadrupole was formed by simultaneously injecting and aspirating fluids from two pairs of opposing apertures in a narrow gap formed between a microfluidic probe and a substrate. A stagnation point was formed at the centre of the microfluidic quadrupole, and its position could be rapidly adjusted hydrodynamically. Following the injection of a solute through one of the poles, a stationary, tunable, and movable-that is, 'floating'-concentration gradient was formed at the stagnation point. Our results lay the foundation for future combined experimental and theoretical exploration of microfluidic planar multipoles including convective-diffusive phenomena.

  4. A fast, preconditioned conjugate gradient Toeplitz solver

    NASA Technical Reports Server (NTRS)

    Pan, Victor; Schrieber, Robert

    1989-01-01

    A simple factorization is given of an arbitrary hermitian, positive definite matrix in which the factors are well-conditioned, hermitian, and positive definite. In fact, given knowledge of the extreme eigenvalues of the original matrix A, an optimal improvement can be achieved, making the condition numbers of each of the two factors equal to the square root of the condition number of A. This technique is to applied to the solution of hermitian, positive definite Toeplitz systems. Large linear systems with hermitian, positive definite Toeplitz matrices arise in some signal processing applications. A stable fast algorithm is given for solving these systems that is based on the preconditioned conjugate gradient method. The algorithm exploits Toeplitz structure to reduce the cost of an iteration to O(n log n) by applying the fast Fourier Transform to compute matrix-vector products. Matrix factorization is used as a preconditioner.

  5. Molecular evolution and the latitudinal biodiversity gradient.

    PubMed

    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.

  6. Formulating viscous hydrodynamics for large velocity gradients

    SciTech Connect

    Pratt, Scott

    2008-02-15

    Viscous corrections to relativistic hydrodynamics, which are usually formulated for small velocity gradients, have recently been extended from Navier-Stokes formulations to a class of treatments based on Israel-Stewart equations. Israel-Stewart treatments, which treat the spatial components of the stress-energy tensor {tau}{sub ij} as dynamical objects, introduce new parameters, such as the relaxation times describing nonequilibrium behavior of the elements {tau}{sub ij}. By considering linear response theory and entropy constraints, we show how the additional parameters are related to fluctuations of {tau}{sub ij}. Furthermore, the Israel-Stewart parameters are analyzed for their ability to provide stable and physical solutions for sound waves.more » Finally, it is shown how these parameters, which are naturally described by correlation functions in real time, might be constrained by lattice calculations, which are based on path-integral formulations in imaginary time.« less

  7. High gradient lens for charged particle beam

    DOEpatents

    Chen, Yu-Jiuan

    2014-04-29

    Methods and devices enable shaping of a charged particle beam. A dynamically adjustable electric lens includes a series of alternating a series of alternating layers of insulators and conductors with a hollow center. The series of alternating layers when stacked together form a high gradient insulator (HGI) tube to allow propagation of the charged particle beam through the hollow center of the HGI tube. A plurality of transmission lines are connected to a plurality of sections of the HGI tube, and one or more voltage sources are provided to supply an adjustable voltage value to each transmission line of the plurality of transmission lines. By changing the voltage values supplied to each section of the HGI tube, any desired electric field can be established across the HGI tube. This way various functionalities including focusing, defocusing, acceleration, deceleration, intensity modulation and others can be effectuated on a time varying basis.

  8. Electron temperature gradient scale at collisionless shocks.

    PubMed

    Schwartz, Steven J; Henley, Edmund; Mitchell, Jeremy; Krasnoselskikh, Vladimir

    2011-11-18

    Shock waves are ubiquitous in space and astrophysics. They transform directed flow energy into thermal energy and accelerate energetic particles. The energy repartition is a multiscale process related to the spatial and temporal structure of the electromagnetic fields within the shock layer. While large scale features of ion heating are known, the electron heating and smaller scale fields remain poorly understood. We determine for the first time the scale of the electron temperature gradient via electron distributions measured in situ by the Cluster spacecraft. Half of the electron heating coincides with a narrow layer several electron inertial lengths (c/ω(pe)) thick. Consequently, the nonlinear steepening is limited by wave dispersion. The dc electric field must also vary over these small scales, strongly influencing the efficiency of shocks as cosmic ray accelerators.

  9. High-gradient compact linear accelerator

    DOEpatents

    Carder, B.M.

    1998-05-26

    A high-gradient linear accelerator comprises a solid-state stack in a vacuum of five sets of disc-shaped Blumlein modules each having a center hole through which particles are sequentially accelerated. Each Blumlein module is a sandwich of two outer conductive plates that bracket an inner conductive plate positioned between two dielectric plates with different thicknesses and dielectric constants. A third dielectric core in the shape of a hollow cylinder forms a casing down the series of center holes, and it has a dielectric constant different that the two dielectric plates that sandwich the inner conductive plate. In operation, all the inner conductive plates are charged to the same DC potential relative to the outer conductive plates. Next, all the inner conductive plates are simultaneously shorted to the outer conductive plates at the outer diameters. The signal short will propagate to the inner diameters at two different rates in each Blumlein module. A faster wave propagates quicker to the third dielectric core across the dielectric plates with the closer spacing and lower dielectric constant. When the faster wave reaches the inner extents of the outer and inner conductive plates, it reflects back outward and reverses the field in that segment of the dielectric core. All the field segments in the dielectric core are then in unipolar agreement until the slower wave finally propagates to the third dielectric core across the dielectric plates with the wider spacing and higher dielectric constant. During such unipolar agreement, particles in the core are accelerated with gradients that exceed twenty megavolts per meter. 10 figs.

  10. High-gradient compact linear accelerator

    DOEpatents

    Carder, Bruce M.

    1998-01-01

    A high-gradient linear accelerator comprises a solid-state stack in a vacuum of five sets of disc-shaped Blumlein modules each having a center hole through which particles are sequentially accelerated. Each Blumlein module is a sandwich of two outer conductive plates that bracket an inner conductive plate positioned between two dielectric plates with different thicknesses and dielectric constants. A third dielectric core in the shape of a hollow cylinder forms a casing down the series of center holes, and it has a dielectric constant different that the two dielectric plates that sandwich the inner conductive plate. In operation, all the inner conductive plates are charged to the same DC potential relative to the outer conductive plates. Next, all the inner conductive plates are simultaneously shorted to the outer conductive plates at the outer diameters. The signal short will propagate to the inner diameters at two different rates in each Blumlein module. A faster wave propagates quicker to the third dielectric core across the dielectric plates with the closer spacing and lower dielectric constant. When the faster wave reaches the inner extents of the outer and inner conductive plates, it reflects back outward and reverses the field in that segment of the dielectric core. All the field segments in the dielectric core are then in unipolar agreement until the slower wave finally propagates to the third dielectric core across the dielectric plates with the wider spacing and higher dielectric constant. During such unipolar agreement, particles in the core are accelerated with gradients that exceed twenty megavolts per meter.

  11. Seismic Velocity Gradients Across the Transition Zone

    NASA Astrophysics Data System (ADS)

    Escalante, C.; Cammarano, F.; de Koker, N.; Piazzoni, A.; Wang, Y.; Marone, F.; Dalton, C.; Romanowicz, B.

    2006-12-01

    One-D elastic velocity models derived from mineral physics do a notoriously poor job at predicting the velocity gradients in the upper mantle transition zone, as well as some other features of models derived from seismological data. During the 2006 CIDER summer program, we computed Vs and Vp velocity profiles in the upper mantle based on three different mineral physics approaches: two approaches based on the minimization of Gibbs Free Energy (Stixrude and Lithgow-Bertelloni, 2005; Piazzoni et al., 2006) and one obtained by using experimentally determined phase diagrams (Weidner and Wang, 1998). The profiles were compared by assuming a vertical temperature profile and two end-member compositional models, the pyrolite model of Ringwood (1979) and the piclogite model of Anderson and Bass (1984). The predicted seismic profiles, which are significantly different from each other, primarily due to different choices of properties of single minerals and their extrapolation with temperature, are tested against a global dataset of P and S travel times and spheroidal and toroidal normal mode eigenfrequencies. All the models derived using a potential temperature of 1600K predict seismic velocities that are too slow in the upper mantle, suggesting the need to use a colder geotherm. The velocity gradient in the transition zone is somewhat better for piclogite than for pyrolite, possibly indicating the need to increase Ca content. The presence of stagnant slabs in the transition zone is a possible explanation for the need for 1) colder temperature and 2) increased Ca content. Future improvements in seismic profiles obtained from mineral physics will arise from better knowledge of elastic properties of upper mantle constituents and aggregates at high temperature and pressure, a better understanding of differences between thermodynamic models, and possibly the effect of water through and on Q. High resolution seismic constraints on velocity jumps at 400 and 660 km also need to be

  12. Reaction Gradients Viewed Inside Single Photoactive Particles

    NASA Astrophysics Data System (ADS)

    Alpert, P.; Corral Arroyo, P.; Dou, J.; Kreiger, U.; Luo, B.; Peter, T.; Ammann, M.

    2017-12-01

    In terms of chemical selectivity and spatial resolution, a technique known as scanning transmission X-ray microscopy coupled to near-edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS) is unmatched and will remain so for years into the future. We present a recent development coupling STXM/NEXAFS to a custom-built photochemical environmental reactor in which aerosol particles reside allowing for in situ chemical imaging. A laboratory investigation of metal-organic complex photochemistry was conducted. Transition metals are of great importance to atmospheric chemistry and aerosol photochemical aging due to their ability to catalyze oxidation reactions. Aerosol particles composed of mixtures of citric acid and iron citrate were probed for their organic carbon composition and iron oxidation state under atmospherically relevant conditions. At 40% relative humidity, oxygen diffusion and reaction was severely limited. Fe was reoxidized in the first 200 nm of the particle surface leaving reduced iron in the core. Similar gradients were observed at 60% RH, however waiting approximately 2 hours in the dark resulted in a recovery of the initial Fe(III) concentration. We draw two main conclusions from our findings. Frist, the oxidation gradients must have been the result of anoxic conditions at the interior of aerosol particles. This was predicted using a newly developed model for molecular diffusion through multiple layers with a reaction framework describing the photochemical processing of the metal organic matrix. Second, the lifetime of organic radicals in an anoxic diffusion limited organic matrix must be considerably long ( hours) to completely reoxidize iron as they wait for molecular oxygen. Long radical lifetimes in viscous organic aerosol in turn, could create high radical concentrations or favor radical-radical reactions in particles typically not considered when oxygen is plentiful. Our results impact predictions of aerosol physiochemical properties, e

  13. Drop casting of stiffness gradients for chip integration into stretchable substrates

    NASA Astrophysics Data System (ADS)

    Naserifar, Naser; LeDuc, Philip R.; Fedder, Gary K.

    2017-04-01

    Stretchable electronics have demonstrated promise within unobtrusive wearable systems in areas such as health monitoring and medical therapy. One significant question is whether it is more advantageous to develop holistic stretchable electronics or to integrate mature CMOS into stretchable electronic substrates where the CMOS process is separated from the mechanical processing steps. A major limitation with integrating CMOS is the dissimilar interface between the soft stretchable and hard CMOS materials. To address this, we developed an approach to pattern an elastomeric polymer layer with spatially varying mechanical properties around CMOS electronics to create a controllable material stiffness gradient. Our experimental approach reveals that modifying the interfaces can increase the strain failure threshold up to 30% and subsequently decreases delamination. The stiffness gradient in the polymer layer provides a safe region for electronic chips to function under a substrate tensile strain up to 150%. These results will have impacts in diverse applications including skin sensors and wearable health monitoring systems.

  14. Design of a High Thermal Gradient Bridgman Furnace

    NASA Technical Reports Server (NTRS)

    LeCroy, J. E.; Popok, D. P.

    1994-01-01

    The Advanced Automated Directional Solidification Furnace (AADSF) is a Bridgman-Stockbarger microgravity processing facility, designed and manifested to first fly aboard the second United States Microgravity Payload (USMP-2) Space Shuttle mission. The AADSF was principally designed to produce high axial thermal gradients, and is particularly suitable for metals solidification experiments, including non-dilute alloys. To accommodate a wider range of experimental conditions, the AADSF is equipped with a reconfigurable gradient zone. The overall design of the AADSF and the relationship between gradient zone design and furnace performance are described. Parametric thermal analysis was performed and used to select gradient zone design features that fulfill the high thermal gradient requirements of the USMP-2 experiment. The thermal model and analytical procedure, and parametric results leading to the first flight gradient zone configuration, are presented. Performance for the USMP-2 flight experiment is also predicted, and analysis results are compared to test data.

  15. Modified conjugate gradient method for diagonalizing large matrices.

    PubMed

    Jie, Quanlin; Liu, Dunhuan

    2003-11-01

    We present an iterative method to diagonalize large matrices. The basic idea is the same as the conjugate gradient (CG) method, i.e, minimizing the Rayleigh quotient via its gradient and avoiding reintroducing errors to the directions of previous gradients. Each iteration step is to find lowest eigenvector of the matrix in a subspace spanned by the current trial vector and the corresponding gradient of the Rayleigh quotient, as well as some previous trial vectors. The gradient, together with the previous trial vectors, play a similar role as the conjugate gradient of the original CG algorithm. Our numeric tests indicate that this method converges significantly faster than the original CG method. And the computational cost of one iteration step is about the same as the original CG method. It is suitable for first principle calculations.

  16. Convection driven generation of long-range material gradients

    PubMed Central

    Du, Yanan; Hancock, Matthew J.; He, Jiankang; Villa-Uribe, Jose; Wang, Ben; Cropek, Donald M.; Khademhosseini, Ali

    2009-01-01

    Natural materials exhibit anisotropy with variations in soluble factors, cell distribution, and matrix properties. The ability to recreate the heterogeneity of the natural materials is a major challenge for investigating cell-material interactions and for developing biomimetic materials. Here we present a generic fluidic approach using convection and alternating flow to rapidly generate multi-centimeter gradients of biomolecules, polymers, beads and cells and cross-gradients of two species in a microchannel. Accompanying theoretical estimates and simulations of gradient growth provide design criteria over a range of material properties. A poly(ethyleneglycol) hydrogel gradient, a porous collagen gradient and a composite material with a hyaluronic acid/gelatin cross-gradient were generated with continuous variations in material properties and in their ability to regulate cellular response. This simple yet generic fluidic platform should prove useful for creating anisotropic biomimetic materials and high-throughput platforms for investigating cell-microenvironment interaction. PMID:20035990

  17. Preliminary map of temperature gradients in the conterminous United States

    SciTech Connect

    Guffanti, M.; Nathenson, M.

    1980-09-01

    Temperature gradients have been determined from temperature/depth measurements made in drill holes deeper than 600 m and used in the construction of a temperature-gradient map of the conterminous United States. The map displays temperature gradients (in /sup 0/C/km) that can be expected to exist regionally in a conductive thermal regime to a depth of 2 km. The major difference between this map and the AAPG-USGS temperature-gradient map is in the midcontinental region where the AAPG-USGS map does not demarcate a division between colder eastern and warmer western thermal regimes. A comparison with the heat-flow map of Sass et al. (1980)more » indicates that temperature gradients commonly reflect regional heat flow, and the gross east-west division of the United States on the basis of heat flow is also expressed by temperature gradient.« less

  18. Cell motility regulation on a stepped micro pillar array device (SMPAD) with a discrete stiffness gradient.

    PubMed

    Lee, Sujin; Hong, Juhee; Lee, Junghoon

    2016-02-28

    Our tissues consist of individual cells that respond to the elasticity of their environment, which varies between and within tissues. To better understand mechanically driven cell migration, it is necessary to manipulate the stiffness gradient across a substrate. Here, we have demonstrated a new variant of the microfabricated polymeric pillar array platform that can decouple the stiffness gradient from the ECM protein area. This goal is achieved via a "stepped" micro pillar array device (SMPAD) in which the contact area with the cell was kept constant while the diameter of the pillar bodies was altered to attain the proper mechanical stiffness. Using double-step SU-8 mold fabrication, the diameter of the top of every pillar was kept uniform, whereas that of the bottom was changed, to achieve the desired substrate rigidity. Fibronectin was immobilized on the pillar tops, providing a focal adhesion site for cells. C2C12, HeLa and NIH3T3 cells were cultured on the SMPAD, and the motion of the cells was observed by time-lapse microscopy. Using this simple platform, which produces a purely physical stimulus, we observed that various types of cell behavior are affected by the mechanical stimulus of the environment. We also demonstrated directed cell migration guided by a discrete rigidity gradient by varying stiffness. Interestingly, cell velocity was highest at the highest stiffness. Our approach enables the regulation of the mechanical properties of the polymeric pillar array device and eliminates the effects of the size of the contact area. This technique is a unique tool for studying cellular motion and behavior relative to various stiffness gradients in the environment.

  19. Free drainage of aqueous foams: Container shape effects on capillarity and vertical gradients

    NASA Astrophysics Data System (ADS)

    Saint-Jalmes, A.; Vera, M. U.; Durian, D. J.

    2000-06-01

    The standard drainage equation applies only to foam columns of constant cross-sectional area. Here, we generalize to include the effects of arbitrary container shape and develop an exact solution for an exponential, "Eiffel Tower", sample. This geometry largely eliminates vertical wetness gradients, and hence capillary effects, and should permit a clean test of dissipation mechanisms. Agreement with experiment is not achieved at late times, however, highlighting the importance of both boundary conditions and coarsening.

  20. Stream pH as an abiotic gradient influencing distributions of trout in Pennsylvania streams

    USGS Publications Warehouse

    Kocovsky, P.M.; Carline, R.F.

    2005-01-01

    Elevation and stream slope are abiotic gradients that limit upstream distributions of brook trout Salvelinus fontinalis and brown trout Salmo trutta in streams. We sought to determine whether another abiotic gradient, base-flow pH, may also affect distributions of these two species in eastern North America streams. We used historical data from the Pennsylvania Fish and Boat Commission's fisheries management database to explore the effects of reach elevation, slope, and base-flow pH on distributional limits to brook trout and brown trout in Pennsylvania streams in the Appalachian Plateaus and Ridge and Valley physiographic provinces. Discriminant function analysis (DFA) was used to calculate a canonical axis that separated allopatric brook trout populations from allopatric brown trout populations and allowed us to assess which of the three independent variables were important gradients along which communities graded from allopatric brook trout to allopatric brown trout. Canonical structure coefficients from DFA indicated that in both physiographic provinces, stream base-flow pH and slope were important factors in distributional limits; elevation was also an important factor in the Ridge and Valley Province but not the Appalachian Plateaus Province. Graphs of each variable against the proportion of brook trout in a community also identified apparent zones of allopatry for both species on the basis of pH and stream slope. We hypothesize that pH-mediated interspecific competition that favors brook trout in competition with brown trout at lower pH is the most plausible mechanism for segregation of these two species along pH gradients. Our discovery that trout distributions in Pennsylvania are related to stream base-flow pH has important implications for brook trout conservation in acidified regions. Carefully designed laboratory and field studies will be required to test our hypothesis and elucidate the mechanisms responsible for the partitioning of brook trout and

  1. High energy X-ray diffraction study of a dental ceramics–titanium functional gradient material prepared by field assisted sintering technique

    SciTech Connect

    Witte, K., E-mail: kerstin.witte@uni-rostock.de; Bodnar, W.; Schell, N.

    A functional gradient material with eleven layers composed of a dental ceramics and titanium was successfully consolidated using field assisted sintering technique in a two-step sintering process. High energy X-ray diffraction studies on the gradient were performed at High Energy Material Science beamline at Desy in Hamburg. Phase composition, crystal unit edges and lattice mismatch along the gradient were determined applying Rietveld refinement procedure. Phase analysis revealed that the main crystalline phase present in the gradient is α-Ti. Crystallinity increases stepwisely along the gradient with a decreasing increment between every next layer, following rather the weight fraction of titanium. Themore » crystal unit edge a of titanium remains approximately constant with a value of 2.9686(1) Å, while c is reduced with increasing amount of titanium. In the layer with pure titanium the crystal unit edge c is constant with a value of 4.7174(2) Å. The lattice mismatch leading to an internal stress was calculated over the whole gradient. It was found that the maximal internal stress in titanium embedded in the studied gradient is significantly smaller than its yield strength, which implies that the structure of titanium along the whole gradient is mechanically stable. - Highlights: • High energy XRD studies of dental ceramics–Ti gradient material consolidated by FAST. • Phase composition, crystallinity and lattice parameters are determined. • Crystallinity increases stepwisely along the gradient following weight fraction of Ti. • Lattice mismatch leading to internal stress is calculated over the whole gradient. • Internal stress in α-Ti embedded in the gradient is smaller than its yield strength.« less

  2. Directional solidification at ultra-high thermal gradient

    NASA Technical Reports Server (NTRS)

    Flemings, M. C.; Lee, D. S.; Neff, M. A.

    1980-01-01

    A high gradient controlled solidification (HGC) furnace was designed and operated at gradients up to 1800 C/cm to continuously produce aluminum alloys. Rubber '0' rings for the water cooling chamber were eliminated, while still maintaining water cooling directly onto the solidified metal. An HGC unit for high temperature ferrous alloys was also designed. Successful runs were made with cast iron, at thermal gradients up to 500 C/cm.

  3. Minimizing inner product data dependencies in conjugate gradient iteration

    NASA Technical Reports Server (NTRS)

    Vanrosendale, J.

    1983-01-01

    The amount of concurrency available in conjugate gradient iteration is limited by the summations required in the inner product computations. The inner product of two vectors of length N requires time c log(N), if N or more processors are available. This paper describes an algebraic restructuring of the conjugate gradient algorithm which minimizes data dependencies due to inner product calculations. After an initial start up, the new algorithm can perform a conjugate gradient iteration in time c*log(log(N)).

  4. Comparison of genetic algorithms with conjugate gradient methods

    NASA Technical Reports Server (NTRS)

    Bosworth, J. L.; Foo, N. Y.; Zeigler, B. P.

    1972-01-01

    Genetic algorithms for mathematical function optimization are modeled on search strategies employed in natural adaptation. Comparisons of genetic algorithms with conjugate gradient methods, which were made on an IBM 1800 digital computer, show that genetic algorithms display superior performance over gradient methods for functions which are poorly behaved mathematically, for multimodal functions, and for functions obscured by additive random noise. Genetic methods offer performance comparable to gradient methods for many of the standard functions.

  5. Archaea diversity in vegetation gradients from the Brazilian Cerrado.

    PubMed

    Araujo, Ademir Sergio Ferreira de; Mendes, Lucas Wiliam; Bezerra, Walderly Melgaço; Nunes, Luis Alfredo Pinheiro Leal; Lyra, Maria do Carmo Catanho Pereira de; Figueiredo, Marcia do Vale Barreto; Melo, Vania Maria Maciel

    2018-02-11

    We used 16S rRNA sequencing to assess the archaeal communities across a gradient of Cerrado. The archaeal communities differed across the gradient. Crenarcheota was the most abundant phyla, with Nitrosphaerales and NRPJ as the predominant classes. Euryachaeota was also found across the Cerrado gradient, including the classes Metanocellales and Methanomassiliicoccaceae. Copyright © 2018 Sociedade Brasileira de Microbiologia. Published by Elsevier Editora Ltda. All rights reserved.

  6. On the Convergence Analysis of the Optimized Gradient Method.

    PubMed

    Kim, Donghwan; Fessler, Jeffrey A

    2017-01-01

    This paper considers the problem of unconstrained minimization of smooth convex functions having Lipschitz continuous gradients with known Lipschitz constant. We recently proposed the optimized gradient method for this problem and showed that it has a worst-case convergence bound for the cost function decrease that is twice as small as that of Nesterov's fast gradient method, yet has a similarly efficient practical implementation. Drori showed recently that the optimized gradient method has optimal complexity for the cost function decrease over the general class of first-order methods. This optimality makes it important to study fully the convergence properties of the optimized gradient method. The previous worst-case convergence bound for the optimized gradient method was derived for only the last iterate of a secondary sequence. This paper provides an analytic convergence bound for the primary sequence generated by the optimized gradient method. We then discuss additional convergence properties of the optimized gradient method, including the interesting fact that the optimized gradient method has two types of worstcase functions: a piecewise affine-quadratic function and a quadratic function. These results help complete the theory of an optimal first-order method for smooth convex minimization.

  7. Gradient induced liquid motion on laser structured black Si surfaces

    NASA Astrophysics Data System (ADS)

    Paradisanos, I.; Fotakis, C.; Anastasiadis, S. H.; Stratakis, E.

    2015-09-01

    This letter reports on the femtosecond laser fabrication of gradient-wettability micro/nano-patterns on Si surfaces. The dynamics of directional droplet spreading on the surface tension gradients developed is systematically investigated and discussed. It is shown that microdroplets on the patterned surfaces spread at a maximum speed of 505 mm/s, which is the highest velocity demonstrated so far for liquid spreading on a surface tension gradient in ambient conditions. The application of the proposed laser patterning technique for the precise fabrication of surface tension gradients for open microfluidic systems, liquid management in fuel cells, and drug delivery is envisaged.

  8. Refined discrete and empirical horizontal gradients in VLBI analysis

    NASA Astrophysics Data System (ADS)

    Landskron, Daniel; Böhm, Johannes

    2018-02-01

    Missing or incorrect consideration of azimuthal asymmetry of troposphere delays is a considerable error source in space geodetic techniques such as Global Navigation Satellite Systems (GNSS) or Very Long Baseline Interferometry (VLBI). So-called horizontal troposphere gradients are generally utilized for modeling such azimuthal variations and are particularly required for observations at low elevation angles. Apart from estimating the gradients within the data analysis, which has become common practice in space geodetic techniques, there is also the possibility to determine the gradients beforehand from different data sources than the actual observations. Using ray-tracing through Numerical Weather Models (NWMs), we determined discrete gradient values referred to as GRAD for VLBI observations, based on the standard gradient model by Chen and Herring (J Geophys Res 102(B9):20489-20502, 1997. https://doi.org/10.1029/97JB01739) and also for new, higher-order gradient models. These gradients are produced on the same data basis as the Vienna Mapping Functions 3 (VMF3) (Landskron and Böhm in J Geod, 2017.https://doi.org/10.1007/s00190-017-1066-2), so they can also be regarded as the VMF3 gradients as they are fully consistent with each other. From VLBI analyses of the Vienna VLBI and Satellite Software (VieVS), it becomes evident that baseline length repeatabilities (BLRs) are improved on average by 5% when using a priori gradients GRAD instead of estimating the gradients. The reason for this improvement is that the gradient estimation yields poor results for VLBI sessions with a small number of observations, while the GRAD a priori gradients are unaffected from this. We also developed a new empirical gradient model applicable for any time and location on Earth, which is included in the Global Pressure and Temperature 3 (GPT3) model. Although being able to describe only the systematic component of azimuthal asymmetry and no short-term variations at all, even these

  9. [Diagnostic importance of the alveolar-arterial oxygen gradient].

    PubMed

    Weinans, Marije A E; Drost-de Klerck, Amanda M; ter Maaten, Jan C

    2012-01-01

    The alveolar-arterial (A-a) oxygen gradient is the difference between the partial pressure of oxygen in the alveoli and the partial pressure of arterial oxygen and can be elevated in the case of pulmonary disease. We describe a 41-year-old patient with pneumonia who presented with abdominal pain, in whom calculation of the A-a gradient could have led to earlier diagnosis. The A-a oxygen gradient is mainly of diagnostic importance and the presented nomogram allows easy and quick interpretation. This might lead to a more frequent use of the A-a oxygen gradient in the future.

  10. On the Convergence Analysis of the Optimized Gradient Method

    PubMed Central

    Kim, Donghwan; Fessler, Jeffrey A.

    2016-01-01

    This paper considers the problem of unconstrained minimization of smooth convex functions having Lipschitz continuous gradients with known Lipschitz constant. We recently proposed the optimized gradient method for this problem and showed that it has a worst-case convergence bound for the cost function decrease that is twice as small as that of Nesterov’s fast gradient method, yet has a similarly efficient practical implementation. Drori showed recently that the optimized gradient method has optimal complexity for the cost function decrease over the general class of first-order methods. This optimality makes it important to study fully the convergence properties of the optimized gradient method. The previous worst-case convergence bound for the optimized gradient method was derived for only the last iterate of a secondary sequence. This paper provides an analytic convergence bound for the primary sequence generated by the optimized gradient method. We then discuss additional convergence properties of the optimized gradient method, including the interesting fact that the optimized gradient method has two types of worstcase functions: a piecewise affine-quadratic function and a quadratic function. These results help complete the theory of an optimal first-order method for smooth convex minimization. PMID:28461707

  11. Observations of wave-induced pore pressure gradients and bed level response on a surf zone sandbar

    NASA Astrophysics Data System (ADS)

    Anderson, Dylan; Cox, Dan; Mieras, Ryan; Puleo, Jack A.; Hsu, Tian-Jian

    2017-06-01

    Horizontal and vertical pressure gradients may be important physical mechanisms contributing to onshore sediment transport beneath steep, near-breaking waves in the surf zone. A barred beach was constructed in a large-scale laboratory wave flume with a fixed profile containing a mobile sediment layer on the crest of the sandbar. Horizontal and vertical pore pressure gradients were obtained by finite differences of measurements from an array of pressure transducers buried within the upper several centimeters of the bed. Colocated observations of erosion depth were made during asymmetric wave trials with wave heights between 0.10 and 0.98 m, consistently resulting in onshore sheet flow sediment transport. The pore pressure gradient vector within the bed exhibited temporal rotations during each wave cycle, directed predominantly upward under the trough and then rapidly rotating onshore and downward as the wavefront passed. The magnitude of the pore pressure gradient during each phase of rotation was correlated with local wave steepness and relative depth. Momentary bed failures as deep as 20 grain diameters were coincident with sharp increases in the onshore-directed pore pressure gradients, but occurred at horizontal pressure gradients less than theoretical critical values for initiation of the motion for compact beds. An expression combining the effects of both horizontal and vertical pore pressure gradients with bed shear stress and soil stability is used to determine that failure of the bed is initiated at nonnegligible values of both forces.Plain Language SummaryThe pressure <span class="hlt">gradient</span> present within the seabed beneath breaking waves may be an important physical <span class="hlt">mechanism</span> transporting sediment. A large-scale laboratory was used to replicate realistic surfzone conditions in controlled tests, allowing for horizontal and vertical pressure <span class="hlt">gradient</span> magnitudes and the resulting sediment bed response to be observed with</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/883167','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/883167"><span>Pumpernickel Valley Geothermal Project Thermal <span class="hlt">Gradient</span> Wells</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Z. Adam Szybinski</p> <p>2006-01-01</p> <p>The Pumpernickel Valley geothermal project area is located near the eastern edge of the Sonoma Range and is positioned within the structurally complex Winnemucca fold and thrust belt of north-central Nevada. A series of approximately north-northeast-striking faults related to the Basin and Range tectonics are superimposed on the earlier structures within the project area, and are responsible for the final overall geometry and distribution of the pre-existing structural features on the property. Two of these faults, the Pumpernickel Valley fault and Edna Mountain fault, are range-bounding and display numerous characteristics typical of strike-slip fault systems. These characteristics, when combined withmore » geophysical data from Shore (2005), indicate the presence of a pull-apart basin, formed within the releasing bend of the Pumpernickel Valley – Edna Mountain fault system. A substantial body of evidence exists, in the form of available geothermal, geological and geophysical information, to suggest that the property and the pull-apart basin host a structurally controlled, extensive geothermal field. The most evident manifestations of the geothermal activity in the valley are two areas with hot springs, seepages, and wet ground/vegetation anomalies near the Pumpernickel Valley fault, which indicate that the fault focuses the fluid up-flow. There has not been any geothermal production from the Pumpernickel Valley area, but it was the focus of a limited exploration effort by Magma Power Company. In 1974, the company drilled one exploration/temperature <span class="hlt">gradient</span> borehole east of the Pumpernickel Valley fault and recorded a thermal <span class="hlt">gradient</span> of 160oC/km. The 1982 temperature data from five unrelated mineral exploration holes to the north of the Magma well indicated geothermal <span class="hlt">gradients</span> in a range from 66 to 249oC/km for wells west of the fault, and ~283oC/km in a well next to the fault. In 2005, Nevada Geothermal Power Company drilled four geothermal <span class="hlt">gradient</span> wells</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5841055','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5841055"><span>An abnormal periventricular magnetization transfer ratio <span class="hlt">gradient</span> occurs early in multiple sclerosis</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Brown, J William L; Pardini, Matteo; Brownlee, Wallace J; Fernando, Kryshani; Samson, Rebecca S; Prados Carrasco, Ferran; Ourselin, Sebastien; Gandini Wheeler-Kingshott, Claudia A M; Miller, David H; Chard, Declan T</p> <p>2017-01-01</p> <p> sclerosis. The magnetization transfer ratio <span class="hlt">gradient</span> was not significantly affected by the presence of brain lesions [T2 lesions (P = 0.918), periventricular T2 lesions (P = 0.580) or gadolinium-enhancing T1 lesions (P = 0.724)]. The magnetization transfer ratio <span class="hlt">gradient</span> also correlated with Expanded Disability Status Scale score 5 years later (Spearman r = 0.313, P = 0.027). An abnormal periventricular magnetization transfer ratio <span class="hlt">gradient</span> occurs early in multiple sclerosis, is clinically relevant, and may arise from one or more <span class="hlt">mechanisms</span> that are at least partly independent of lesion formation. PMID:28043954</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018AdWR..112...72B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018AdWR..112...72B"><span>Modeling chemical <span class="hlt">gradients</span> in sediments under losing and gaining flow conditions: The <span class="hlt">GRADIENT</span> code</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Boano, Fulvio; De Falco, Natalie; Arnon, Shai</p> <p>2018-02-01</p> <p>Interfaces between sediments and water bodies often represent biochemical hotspots for nutrient reactions and are characterized by steep concentration <span class="hlt">gradients</span> of different reactive solutes. Vertical profiles of these concentrations are routinely collected to obtain information on nutrient dynamics, and simple codes have been developed to analyze these profiles and determine the magnitude and distribution of reaction rates within sediments. However, existing publicly available codes do not consider the potential contribution of water flow in the sediments to nutrient transport, and their applications to field sites with significant water-borne nutrient fluxes may lead to large errors in the estimated reaction rates. To fill this gap, the present work presents <span class="hlt">GRADIENT</span>, a novel algorithm to evaluate distributions of reaction rates from observed concentration profiles. <span class="hlt">GRADIENT</span> is a Matlab code that extends a previously published framework to include the role of nutrient advection, and provides robust estimates of reaction rates in sediments with significant water flow. This work discusses the theoretical basis of the method and shows its performance by comparing the results to a series of synthetic data and to l