Local structure studies of materials using pair distribution function analysis
NASA Astrophysics Data System (ADS)
Peterson, Joseph W.
A collection of pair distribution function studies on various materials is presented in this dissertation. In each case, local structure information of interest pushes the current limits of what these studies can accomplish. The goal is to provide insight into the individual material behaviors as well as to investigate ways to expand the current limits of PDF analysis. Where possible, I provide a framework for how PDF analysis might be applied to a wider set of material phenomena. Throughout the dissertation, I discuss 0 the capabilities of the PDF method to provide information pertaining to a material's structure and properties, ii) current limitations in the conventional approach to PDF analysis, iii) possible solutions to overcome certain limitations in PDF analysis, and iv) suggestions for future work to expand and improve the capabilities PDF analysis.
Algorithm for systematic peak extraction from atomic pair distribution functions.
Granlund, L; Billinge, S J L; Duxbury, P M
2015-07-01
The study presents an algorithm, ParSCAPE, for model-independent extraction of peak positions and intensities from atomic pair distribution functions (PDFs). It provides a statistically motivated method for determining parsimony of extracted peak models using the information-theoretic Akaike information criterion (AIC) applied to plausible models generated within an iterative framework of clustering and chi-square fitting. All parameters the algorithm uses are in principle known or estimable from experiment, though careful judgment must be applied when estimating the PDF baseline of nanostructured materials. ParSCAPE has been implemented in the Python program SrMise. Algorithm performance is examined on synchrotron X-ray PDFs of 16 bulk crystals and two nanoparticles using AIC-based multimodeling techniques, and particularly the impact of experimental uncertainties on extracted models. It is quite resistant to misidentification of spurious peaks coming from noise and termination effects, even in the absence of a constraining structural model. Structure solution from automatically extracted peaks using the Liga algorithm is demonstrated for 14 crystals and for C60. Special attention is given to the information content of the PDF, theory and practice of the AIC, as well as the algorithm's limitations. PMID:26131896
Temperature effects on atomic pair distribution functions of melts
NASA Astrophysics Data System (ADS)
Ding, J.; Xu, M.; Guan, P. F.; Deng, S. W.; Cheng, Y. Q.; Ma, E.
2014-02-01
Using molecular dynamics simulations, we investigate the temperature-dependent evolution of the first peak position/shape in pair distribution functions of liquids. For metallic liquids, the peak skews towards the left (shorter distance side) with increasing temperature, similar to the previously reported anomalous peak shift. Making use of constant-volume simulations in the absence of thermal expansion and change in inherent structure, we demonstrate that the apparent shift of the peak maximum can be a result of the asymmetric shape of the peak, as the asymmetry increases with temperature-induced spreading of neighboring atoms to shorter and longer distances due to the anharmonic nature of the interatomic interaction potential. These findings shed light on the first-shell expansion/contraction paradox for metallic liquids, aside from possible changes in local topological or chemical short-range ordering. The melts of covalent materials are found to exhibit an opposite trend of peak shift, which is attributed to an effect of the directionality of the interatomic bonds.
Temperature effects on atomic pair distribution functions of melts
Ding, J. Ma, E.; Xu, M.; Guan, P. F.; Deng, S. W.; Cheng, Y. Q.
2014-02-14
Using molecular dynamics simulations, we investigate the temperature-dependent evolution of the first peak position/shape in pair distribution functions of liquids. For metallic liquids, the peak skews towards the left (shorter distance side) with increasing temperature, similar to the previously reported anomalous peak shift. Making use of constant-volume simulations in the absence of thermal expansion and change in inherent structure, we demonstrate that the apparent shift of the peak maximum can be a result of the asymmetric shape of the peak, as the asymmetry increases with temperature-induced spreading of neighboring atoms to shorter and longer distances due to the anharmonic nature of the interatomic interaction potential. These findings shed light on the first-shell expansion/contraction paradox for metallic liquids, aside from possible changes in local topological or chemical short-range ordering. The melts of covalent materials are found to exhibit an opposite trend of peak shift, which is attributed to an effect of the directionality of the interatomic bonds.
Pair distribution function study on compression of liquid gallium
Luo, Shengnian; Yu, Tony; Chen, Jiuhua; Ehm, Lars; Guo, Quanzhong; Parise, John
2008-01-01
Integrating a hydrothermal diamond anvil cell (HDAC) and focused high energy x-ray beam from the superconductor wiggler X17 beamline at the National Synchrotron Light Source (NSLS) at the Brookhaven National Laboratory (BNL), we have successfully collected high quality total x-ray scattering data of liquid gallium. The experiments were conducted at a pressure range from 0.1GPa up to 2GPa at ambient temperature. For the first time, pair distribution functions (PDF) for liquid gallium at high pressure were derived up to 10 {angstrom}. Liquid gallium structure has been studied by x-ray absorption (Di Cicco & Filipponi, 1993; Wei et al., 2000; Comez et al., 2001), x-ray diffraction studies (Waseda & Suzuki, 1972), and molecular dynamics simulation (Tsay, 1993; Hui et al., 2002). These previous reports have focused on the 1st nearest neighbor structure, which tells us little about the atomic arrangement outside the first shell in non- crystalline materials. This study focuses on the structure of liquid gallium and the atomic structure change due to compression. The PDF results show that the observed atomic distance of the first nearest neighbor at 2.78 {angstrom} (first G(r) peak and its shoulder at the higher Q position) is consistent with previous studies by x-ray absorption (2.76 {angstrom}, Comez et al., 2001). We have also observed that the first nearest neighbor peak position did not change with pressure increasing, while the farther peaks positions in the intermediate distance range decreased with pressure increasing. This leads to a conclusion of the possible existence of 'locally rigid units' in the liquid. With the addition of reverse Monte Carlo modeling, we have observed that the coordination number in the local rigit unit increases with pressure. The bulk modulus of liquid gallium derived from the volume compression curve at ambient temperature (300K) is 12.1(6) GPa.
Atom Pair Distribution Functions of Liquid Water at 25circC from Neutron Diffraction
NASA Astrophysics Data System (ADS)
Narten, A. H.; Thiessen, W. E.; Blum, L.
1982-09-01
The structure of liquid water is described by three atom pair distribution functions gOO(r), gOH(r), and gHH(r). These functions have now been derived from neutron diffraction data on four mixtures of light and heavy water. They will provide a crucial and sensitive test for proposed models of liquid water.
Uncovering the intrinsic geometry from the atomic pair distribution function of nanomaterials
NASA Astrophysics Data System (ADS)
Lei, Ming; de Graff, Adam M. R.; Thorpe, M. F.; Wells, Stephen A.; Sartbaeva, Asel
2009-07-01
Atomic pair distribution functions are useful because they have an easy intuitive interpretation and can be obtained both experimentally and from computer-generated structure models. For bulk materials, atomic pair distribution functions are solely determined by the intrinsic atomic geometry, i.e., how atoms are positioned with respect to one another. For a nanomaterial, however, the atomic pair distribution function also depends on the shape and size of the nanomaterial. A modified form of the radial distribution function is discussed that decouples shape and size effects from intrinsic effects so that nanomaterials of any shape and size, sharing a common atomic geometry, map onto a universal curve, by using a form factor. Mapping onto this universal curve allows differences in the intrinsic atomic geometry of nanomaterials of various shapes and sizes to be directly compared. This approach is demonstrated on nanoscale amorphous and crystalline silica models. It is shown how form factors can be computed for arbitrary shapes and this is illustrated for tetrahedral nanoparticles of vitreous silica.
Mohideen, M Infas; Allan, Phoebe K; Chapman, Karena W; Hriljac, Joseph A; Morris, Russell E
2014-07-21
Nanoparticles of a copper-based layered coordination polymer, STAM-2, have been prepared via an ultrasound mediated transformation from a layered metal-organic framework, STAM-1. The structure of the material was then solved using pair distribution function analysis to identify the structural units present and the final structural model refined against the pair distribution function data. PMID:24310447
Finite Size Effects on the Real-Space Pair Distribution Function of Nanoparticles
Gilbert, Benjamin
2008-10-01
The pair distribution function (PDF) method is a powerful approach for the analysis of the structure of nanoparticles. An important approximation used in nanoparticle PDF simulations is the incorporation of a form factor describing nanoparticle size and shape. The precise effect of the form factor on the PDF is determined by both particle shape and structure if these characteristics are both anisotropic and correlated. The correct incorporation of finite size effects is important for distinguishing and quantifying the structural consequences of small particle size in nanomaterials.
Abeykoon, A. M. Milinda; Hu, Hefei; Wu, Lijun; Zhu, Yimei; Billinge, Simon J. L.
2015-01-30
Different protocols for calibrating electron pair distribution function (ePDF) measurements are explored and described for quantitative studies on nanomaterials. It is found that the most accurate approach to determine the camera length is to use a standard calibration sample of Au nanoparticles from the National Institute of Standards and Technology. Different protocols for data collection are also explored, as are possible operational errors, to find the best approaches for accurate data collection for quantitative ePDF studies.
Directional pair distribution function for diffraction line profile analysis of atomistic models
Leonardi, Alberto; Leoni, Matteo; Scardi, Paolo
2013-01-01
The concept of the directional pair distribution function is proposed to describe line broadening effects in powder patterns calculated from atomistic models of nano-polycrystalline microstructures. The approach provides at the same time a description of the size effect for domains of any shape and a detailed explanation of the strain effect caused by the local atomic displacement. The latter is discussed in terms of different strain types, also accounting for strain field anisotropy and grain boundary effects. The results can in addition be directly read in terms of traditional line profile analysis, such as that based on the Warren–Averbach method. PMID:23396818
Local Atomic Structure of Semiconductor Alloys Using Pair Distribution Function Analysis
Billinge, S.J.L.; Thorpe, M.F.
2002-06-24
We have been taking advantage of recent experimental developments, which involve utilizing diffraction data from x-rays or neutrons out to very large wave-vectors, to obtain a detailed structural characterization of semiconductor alloys. This approach allows an accurate Pair Distribution Function (PDF) to be obtained to 20A and beyond and reveals the local structure of the alloy directly. These data can be modeled explicitly to learn about local correlations and short-range order in materials. We are combining theory, modeling and experiments to study a range of materials from semiconductors to thermoelectrics and proton conductors.
Abeykoon M.; Billinge S.; Malliakas, C.D.; Juhas, P.; Bozin, E.S.; Kanatzidis, M.G.
2012-05-01
Quantitatively reliable atomic pair distribution functions (PDFs) have been obtained from nanomaterials in a straightforward way from a standard laboratory transmission electron microscope (TEM). The approach looks very promising for making electron derived PDFs (ePDFs) a routine step in the characterization of nanomaterials because of the ubiquity of such TEMs in chemistry and materials laboratories. No special attachments such as energy filters were required on the microscope. The methodology for obtaining the ePDFs is described as well as some opportunities and limitations of the method.
Li, Wei; Harrington, Richard; Tang, Yuanzhi; Kubicki, James D.; Aryanpour, Masoud; Reeder, Richard J.; Parise, John B.; Phillips, Brian L.
2012-03-15
Structural information is important for understanding surface adsorption mechanisms of contaminants on metal (hydr)oxides. In this work, a novel technique was employed to study the interfacial structure of arsenate oxyanions adsorbed on {gamma}-alumina nanoparticles, namely, differential pair distribution function (d-PDF) analysis of synchrotron X-ray total scattering. The d-PDF is the difference of properly normalized PDFs obtained for samples with and without arsenate adsorbed, otherwise identically prepared. The real space pattern contains information on atomic pair correlations between adsorbed arsenate and the atoms on {gamma}-alumina surface (Al, O, etc.). PDF results on the arsenate adsorption sample on {gamma}-alumina prepared at 1 mM As concentration and pH 5 revealed two peaks at 1.66 {angstrom} and 3.09 {angstrom}, corresponding to As-O and As-Al atomic pair correlations. This observation is consistent with those measured by extended X-ray absorption fine structure (EXAFS) spectroscopy, which suggests a first shell of As-O at 1.69 {+-} 0.01 {angstrom} with a coordination number of 4 and a second shell of As-Al at 3.13 {+-} 0.04 {angstrom} with a coordination number of 2. These results are in agreement with a bidentate binuclear coordination environment to the octahedral Al of {gamma}-alumina as predicted by density functional theory (DFT) calculation.
Novel trends in pair distribution function approaches on bulk systems with nanoscale heterogeneities
Emil S. Bozin; Billinge, Simon J. L.
2016-07-29
Novel materials for high performance applications increasingly exhibit structural order on the nanometer length scale; a domain where crystallography, the basis of Rietveld refinement, fails [1]. In such instances the total scattering approach, which treats Bragg and diffuse scattering on an equal basis, is a powerful approach. In recent years, the analysis of the total scattering data became an invaluable tool and the gold standard for studying nanocrystalline, nanoporous, and disordered crystalline materials. The data may be analyzed in reciprocal space directly, or Fourier transformed to the real-space atomic pair distribution function (PDF) and this intuitive function examined for localmore » structural information. Here we give a number of illustrative examples, for convenience picked from our own work, of recent developments and applications of total scattering and PDF analysis to novel complex materials. There are many other wonderful examples from the work of others.« less
The total scattering atomic pair distribution function: New methodology for nanostructure analysis
NASA Astrophysics Data System (ADS)
Masadeh, Ahmad
The conventional xray diffration (XRD) methods probe for the presence of long-range order (periodic structure) which are reflected in the Bragg peaks. Local structural deviations or disorder mainly affect the diffuse scattering intensity. In order to obtain structural information about both long-range order and local structure disorder, a technique that takes in account both Bragg and diffuse scattering need to be employed, such as the atomic pair distribution function (PDF) technique. This work introduces a PDF based methodology to quantitatively investigate nanostructure materials in general. The introduced methodology can be applied to extract quantitatively structural information about structure, crystallinity level, core/shell size, nanoparticle size, and inhomogeneous internal strain in the measured nanoparticles. This method is generally applicable to the characterization of the nano-scale solid, many of which may exhibit complex disorder and strain
NASA Astrophysics Data System (ADS)
Dimasi, Elaine; Jeffryes, Clayton; Rorrer, Gregory; Belton, David; Perry, Carole
2007-03-01
Biomineralization is a process by which living organisms create composite organic/mineral tissues which have hierarchical structures on micron and submicron scales. Fine control over mineral phase and morphology make biomineralization an important inspiration for materials science. It is often not appreciated that even amorphous minerals such as silica can exhibit hierarchical structure and special properties. One difficulty is that the molecular structures of amorphous phases can be hard to elucidate. We are exploring the use of pair distribution function measurements from synchrotron x-ray scattering to study silica structures, comparing both synthetic organic-modifed silicas and germanium-containing biosilica from diatoms. The raw scattering patterns show clear differences. We will discuss how these data can be scrutinized to determine what differences may be created at the molecular level by different silicification processes.
Gorelik, Tatiana E; Schmidt, Martin U; Kolb, Ute; Billinge, Simon J L
2015-04-01
This paper shows that pair-distribution function (PDF) analyses can be carried out on organic and organometallic compounds from powder electron diffraction data. Different experimental setups are demonstrated, including selected area electron diffraction and nanodiffraction in transmission electron microscopy or nanodiffraction in scanning transmission electron microscopy modes. The methods were demonstrated on organometallic complexes (chlorinated and unchlorinated copper phthalocyanine) and on purely organic compounds (quinacridone). The PDF curves from powder electron diffraction data, called ePDF, are in good agreement with PDF curves determined from X-ray powder data demonstrating that the problems of obtaining kinematical scattering data and avoiding beam damage of the sample are possible to resolve. PMID:25510245
Gorelik, Tatiana E.; Billinge, Simon J. L.; Schmidt, Martin U.; Kolb, Ute
2015-04-01
This paper shows for the first time that pair-distribution function analyses can be carried out on organic and organo-metallic compounds from powder electron diffraction data. Different experimental setups are demonstrated, including selected area electron diffraction (SAED) and nanodiffraction in transmission electron microscopy (TEM) or nanodiffraction in scanning transmission electron microscopy (STEM) modes. The methods were demonstrated on organo-metallic complexes (chlorinated and unchlorinated copper-phthalocyanine) and on purely organic compounds (quinacridone). The PDF curves from powder electron diffraction data, called ePDF, are in good agreement with PDF curves determined from X-ray powder data demonstrating that the problems of obtaining kinematical scattering data and avoiding beam-damage of the sample are possible to resolve.
Gorelik, Tatiana E.; Billinge, Simon J. L.; Schmidt, Martin U.; Kolb, Ute
2015-04-01
This paper shows for the first time that pair-distribution function analyses can be carried out on organic and organo-metallic compounds from powder electron diffraction data. Different experimental setups are demonstrated, including selected area electron diffraction (SAED) and nanodiffraction in transmission electron microscopy (TEM) or nanodiffraction in scanning transmission electron microscopy (STEM) modes. The methods were demonstrated on organo-metallic complexes (chlorinated and unchlorinated copper-phthalocyanine) and on purely organic compounds (quinacridone). The PDF curves from powder electron diffraction data, called ePDF, are in good agreement with PDF curves determined from X-ray powder data demonstrating that the problems of obtaining kinematical scattering datamore » and avoiding beam-damage of the sample are possible to resolve.« less
NASA Astrophysics Data System (ADS)
Liu, Shubin
1996-12-01
It has been shown previously that under certain circumstances the correlation energy density functional Ec[ρ] and its kinetic Tc[ρ] and potential Vc[ρ] components can be expanded in terms of homogeneous functionals An[ρ], with n=1,2,3,..., and where An[ρ] is homogeneous of degree (1-n) with respect to coordinate scaling. In this paper, we extend the analysis to expand similarly the pair distribution function gxc([ρ]r1,r2) and the second-order density matrix ρ2(r1,r2). It is found that both of them can be expanded under certain circumstances in terms of functionals an([ρ]r1,r2), with n=1,2,3,..., that are homogeneous of degree -n in coordinate scaling. The An[ρ] are explicitly obtained in terms of the an([ρ]r1,r2).
Prill, Dragica; Juhas, Pavol; Billinge, Simon J. L.; Schmidt, Martin U.
2016-01-01
In this study, a method towards the solution and refinement of organic crystal structures by fitting to the atomic pair distribution function (PDF) is developed. Approximate lattice parameters and molecular geometry must be given as input. The molecule is generally treated as a rigid body. The positions and orientations of the molecules inside the unit cell are optimized starting from random values. The PDF is obtained from carefully measured X-ray powder diffraction data. The method resembles `real-space' methods for structure solution from powder data, but works with PDF data instead of the diffraction pattern itself. As such it may bemore » used in situations where the organic compounds are not long-range-ordered, are poorly crystalline, or nanocrystalline. The procedure was applied to solve and refine the crystal structures of quinacridone (β phase), naphthalene and allopurinol. In the case of allopurinol it was even possible to successfully solve and refine the structure in P1 with four independent molecules. As an example of a flexible molecule, the crystal structure of paracetamol was refined using restraints for bond lengths, bond angles and selected torsion angles. In all cases, the resulting structures are in excellent agreement with structures from single-crystal data.« less
Total Scattering and Pair Distribution Function Analysis in Modelling Disorder in PZN
Whitfield, Ross E.; Goossens, Darren J; Welberry, T. R.
2016-01-01
The ability of the pair distribution function (PDF) analysis of total scattering (TS) from a powder to determine the local ordering in ferroelectric PZN (PbZn1/3Nb2/3O3) has been explored by comparison with a model established using single-crystal diffuse scattering (SCDS). While X-ray PDF analysis is discussed, the focus is on neutron diffraction results because of the greater extent of the data and the sensitivity of the neutron to oxygen atoms, the behaviour of which is important in PZN. The PDF was shown to be sensitive to many effects not apparent in the average crystal structure, including variations in the B-site—O separationmore » distances and the fact that (110) Pb2+ displacements are most likely. A qualitative comparison between SCDS and the PDF shows that some features apparent in SCDS were not apparent in the PDF. These tended to pertain to short-range correlations in the structure, rather than to interatomic separations. For example, in SCDS the short-range alternation of the B-site cations was quite apparent in diffuse scattering at (½ ½ ½), whereas it was not apparent in the PDF.« less
Burnell, Victoria A.; Readman, Jennifer E.; Tang, Chiu C; Parker, Julia E.; Thompson, Stephen P.; Hriljac, Joseph A.
2010-07-24
Crystalline metal (IV) phosphates with variable zirconium-to-titanium molar ratios of general formula (Ti_{1-x}Zr_{x})(HPO_{4})_{2} • H_{2}O have been prepared by precipitation of soluble salts of the metals with phosphoric acid and heating the amorphous solids in 12 M H_{3}PO_{4} in an autoclave. The new materials are structurally characterised by Rietveld analysis of synchrotron X-ray powder diffraction data and pair distribution function (PDF) analysis of high energy synchrotron X-ray total scattering data. A broad range of zirconium-titanium phosphate solid solutions were formed showing isomorphous substitution of titanium by zirconium in the α-titanium phosphate lattice and vice versa for titanium substitution into the α-zirconium phosphate lattice. In both cases the solubility is partial with the coexistence of two substituted phases observed in samples with nominal compositions between the solubility limits.
Prill, Dragica; Juhás, Pavol; Billinge, Simon J L; Schmidt, Martin U
2016-01-01
A method towards the solution and refinement of organic crystal structures by fitting to the atomic pair distribution function (PDF) is developed. Approximate lattice parameters and molecular geometry must be given as input. The molecule is generally treated as a rigid body. The positions and orientations of the molecules inside the unit cell are optimized starting from random values. The PDF is obtained from carefully measured X-ray powder diffraction data. The method resembles `real-space' methods for structure solution from powder data, but works with PDF data instead of the diffraction pattern itself. As such it may be used in situations where the organic compounds are not long-range-ordered, are poorly crystalline, or nanocrystalline. The procedure was applied to solve and refine the crystal structures of quinacridone (β phase), naphthalene and allopurinol. In the case of allopurinol it was even possible to successfully solve and refine the structure in P1 with four independent molecules. As an example of a flexible molecule, the crystal structure of paracetamol was refined using restraints for bond lengths, bond angles and selected torsion angles. In all cases, the resulting structures are in excellent agreement with structures from single-crystal data. PMID:26697868
X-ray Pair Distribution Function Analysis of Potassium Based Geopolymer
Bell, J.; Sarin, P; Driemeyer, P; Haggerty, R; Chupas, P; Kriven, W
2008-01-01
The atomic structure of geopolymers is often described as amorphous with a local structure that is equivalent to that of crystalline zeolites. However, this structural relationship has never been quantified beyond a first-nearest-neighbor bonding environment. In this study, the short to medium range (1 nm) structural order of metakaolin-based KAlSi{sub 2}O{sub 6}{center_dot}5.5H{sub 2}O geopolymer was quantified and compared to zeolitic tetragonal leucite (KAlSi2O6) using the X-ray atomic pair distribution function technique. Unheated KAlSi{sub 2}O{sub 6}{center_dot}5.5H{sub 2}O was found to be structurally similar to leucite out to a length of 8 {angstrom}, but had increased medium range disorder over the 4.5 {angstrom} < r < 8 {angstrom} range. On heating to >300 C, changes in the short to medium range structure were observed due to dehydration and removal of chemically bound water. Crystallization of leucite occurred in samples heated beyond 1050 C. Refinements of a leucite model against the PDF data for geopolymer heated to 1100 C for 24 h yielded a good fit.
Prill, Dragica; Juhas, Pavol; Billinge, Simon J. L.; Schmidt, Martin U.
2016-01-01
In this study, a method towards the solution and refinement of organic crystal structures by fitting to the atomic pair distribution function (PDF) is developed. Approximate lattice parameters and molecular geometry must be given as input. The molecule is generally treated as a rigid body. The positions and orientations of the molecules inside the unit cell are optimized starting from random values. The PDF is obtained from carefully measured X-ray powder diffraction data. The method resembles `real-space' methods for structure solution from powder data, but works with PDF data instead of the diffraction pattern itself. As such it may be used in situations where the organic compounds are not long-range-ordered, are poorly crystalline, or nanocrystalline. The procedure was applied to solve and refine the crystal structures of quinacridone (β phase), naphthalene and allopurinol. In the case of allopurinol it was even possible to successfully solve and refine the structure in P1 with four independent molecules. As an example of a flexible molecule, the crystal structure of paracetamol was refined using restraints for bond lengths, bond angles and selected torsion angles. In all cases, the resulting structures are in excellent agreement with structures from single-crystal data.
Total Scattering and Pair Distribution Function Analysis in Modelling Disorder in PZN
Whitfield, Ross E.; Goossens, Darren J; Welberry, T. R.
2016-01-01
The ability of the pair distribution function (PDF) analysis of total scattering (TS) from a powder to determine the local ordering in ferroelectric PZN (PbZn_{1/3}Nb_{2/3}O_{3}) has been explored by comparison with a model established using single-crystal diffuse scattering (SCDS). While X-ray PDF analysis is discussed, the focus is on neutron diffraction results because of the greater extent of the data and the sensitivity of the neutron to oxygen atoms, the behaviour of which is important in PZN. The PDF was shown to be sensitive to many effects not apparent in the average crystal structure, including variations in the B-site—O separation distances and the fact that (110) Pb^{2+} displacements are most likely. A qualitative comparison between SCDS and the PDF shows that some features apparent in SCDS were not apparent in the PDF. These tended to pertain to short-range correlations in the structure, rather than to interatomic separations. For example, in SCDS the short-range alternation of the B-site cations was quite apparent in diffuse scattering at (½ ½ ½), whereas it was not apparent in the PDF.
Atomic Structure of a Cesium Aluminosilicate Geopolymer: A Pair Distribution Function Study
Bell, J.; Sarin, P; Provis, J; Haggerty, R; Driemeyer, P; Chupas, P; van Deventer, J; Kriven, W
2008-01-01
The atomic pair distribution function (PDF) method was used to study the structure of cesium aluminosilicate geopolymer. The geopolymer was prepared by reacting metakaolin with cesium silicate solution followed by curing at 50C for 24 h in a sealed container. Heating of Cs-geopolymer above 1000C resulted in formation of crystalline pollucite (CsAlSi{sub 2}O{sub 6}). PDF refinement of the pollucite phase formed displayed an excellent fit over the 10-30 {angstrom} range when compared with a cubic pollucite model. A poorer fit was attained from 1-10 {angstrom} due to an additional amorphous phase present in the heated geopolymer. On the basis of PDF analysis, unheated Cs-geopolymer displayed structural ordering similar to pollucite up to a length scale of 9 {angstrom}, despite some differences. Our results suggest that hydrated Cs{sup +} ions were an integral part of the Cs-geopolymer structure and that most of the water present was not associated with Al-OH or Si-OH bonds.
High pressure pair distribution function studies of Green River oil shale.
Chapman, K. W.; Chupas, P. J.; Locke, D. R.; Winans, R. E.; Pugmire, R. J.; Univ. of Utah
2008-01-01
The compression behavior of a silicate-rich oil shale from the Green River formation in the pressure range 0.0-2.4 GPa was studied using in situ high pressure X-ray pair distribution function (PDF) measurements for the sample contained within a Paris-Edinburgh cell. The real-space local structural information in the PDF, G(r), was used to evaluate the compressibility of the oil shale. Specifically, the pressure-induced reduction in the medium- to long-range atom distances ({approx}6-20 {angstrom}) yielded an average sample compressibility corresponding to a bulk modulus of ca. 61-67 GPa. A structural model consisting of a three phase mixture of the principal crystalline oil shale components (quartz, albite and Illite) provided a good fit to the ambient pressure PDF data (R {approx} 30.7%). Indeed the features in the PDF beyond {approx} {angstrom}, were similarly well fit by a single phase model of the highest symmetry, highly crystalline quartz component. The factors influencing the observed compression behavior are discussed.
White, Claire E; Provis, John L; Bloomer, Breaunnah; Henson, Neil J; Page, Katharine
2013-06-14
With the ever-increasing environmentally-driven demand for technologically advanced structural materials, geopolymer cement is fast becoming a viable alternative to traditional cements due to its proven engineering characteristics and the reduction in CO2 emitted during manufacturing (as much as 80% less CO2 emitted in manufacture, compared to ordinary Portland cement). Nevertheless, much remains unknown regarding the kinetics of reaction responsible for nanostructural evolution during the geopolymerisation process. Here, in situ X-ray total scattering measurements and pair distribution function (PDF) analysis are used to quantify the extent of reaction as a function of time for alkali-activated metakaolin/slag geopolymer binders, including the impact of various activators (alkali hydroxide/silicate) on the kinetics of the geopolymerisation reaction. Quantifying the reaction process in situ from X-ray PDF data collected during the initial ten hours can provide an estimate of the total reaction extent, but when combined with data obtained at longer times (128 days here) enables more accurate determination of the overall rate of reaction. To further assess the initial stages of the geopolymerisation reaction process, a pseudo-single step first order rate equation is fitted to the extent of reaction data, which reveals important mechanistic information regarding the role of free silica in the activators in the evolution of the binder systems. Hence, it is shown that in situ X-ray PDF analysis is an ideal experimental local structure tool to probe the reaction kinetics of complex reacting systems involving transitions between disordered/amorphous phases, of which geopolymerisation is an important example. PMID:23450172
NASA Astrophysics Data System (ADS)
Key, Baris
The universally used negative electrode material in a LIB is carbon, because of its moderate capacity (372 mAhg-1 for graphite), cyclability and high rate capability. However, new, low cost, safe electrode materials with higher capacities are still urgently required for both portable and transportation applications. Silicon anodes are particularly attractive alternatives to carbon with extremely high gravimetric energy densities (3572 mAhg-1). Compared to graphite, silicon has a massive volumetric capacity of 8322 mAhcm-3 (calculated based on the original volume of silicon) which is approximately ten times that graphite. At room temperature, upon electrochemical lithiation, silicon undergoes a crystalline to amorphous phase transition forming a lithiated amorphous silicide phase. Unfortunately, due to the amorphous nature of the lithiated silicides, it is not possible to monitor all the structural changes that occur during lithium insertion/removal with conventional methods such as diffraction. The short range order of the amorphous materials remains unknown, preventing attempts to optimize performance based on electrochemical-structure correlations. In this work, a combination of local structure probes, ex-situ 7Li nuclear magnetic resonance (NMR) studies and pair distribution function (PDF) analysis of X-ray data was applied to investigate the changes in short range order that occur during the initial charge and discharge cycles. The distinct electrochemical profiles observed subsequent to the 1 st discharge have been shown to be associated with the formation of distinct amorphous lithiated silicide structures. A (de)lithiation model consisting of four different mechanisms, each being valid for regions of the charge or discharge process is proposed to explain the hysteresis and the steps in the electrochemical profile observed during lithiation and delithiation of Si. A spontaneous reaction of the fully lithiated lithium silicide with the electrolyte is directly
Pair distribution function analysis of La(Fe{sub 1−x}Ru{sub x})AsO compounds
Martinelli, A.; Palenzona, A.; Ferdeghini, C.; Mazzani, M.; Bonfa', P.; Allodi, G.
2014-12-15
The local structures of La(Fe{sub 1−x}Ru{sub x})AsO (0.00≤x≤0.80) compounds were investigated by means of pair distribution function analysis at room temperature; as a result, no phase separation or clustering takes place. Local distortions are no longer correlated beyond ∼15 Å for both pure and substituted samples, indicating that the presence of Ru atoms does not determine a notable variation in the length scale of the local distortion. Different types of short range correlation between Fe and Ru atoms do not produce significant changes in the pair distribution function. - Graphical abstract: Fe–As and Ru–As bond length distributions as obtained by pair distribution function analysis of La(Fe{sub 0.70}Ru{sub 0.30})AsO; As atoms (purple spheres) undergo a random shifting around their crystallographic positions (red spheres: Fe/Ru atoms). - Highlights: • No phase separation or clustering takes place in La(Fe{sub 1−x}Ru{sub x})AsO solid solutions. • Local distortions are no longer correlated beyond ∼15 Å. • Ru displays a tendency towards local enrichment in the transition metal sublattice.
Fry-Petit, A. M. E-mail: afry@fullerton.edu; Sheckelton, J. P.; McQueen, T. M. E-mail: afry@fullerton.edu; Rebola, A. F.; Fennie, C. J.; Mourigal, M.; Valentine, M.; Drichko, N.
2015-09-28
For over a century, vibrational spectroscopy has enhanced the study of materials. Yet, assignment of particular molecular motions to vibrational excitations has relied on indirect methods. Here, we demonstrate that applying group theoretical methods to the dynamic pair distribution function analysis of neutron scattering data provides direct access to the individual atomic displacements responsible for these excitations. Applied to the molecule-based frustrated magnet with a potential magnetic valence-bond state, LiZn{sub 2}Mo{sub 3}O{sub 8}, this approach allows direct assignment of the constrained rotational mode of Mo{sub 3}O{sub 13} clusters and internal modes of MoO{sub 6} polyhedra. We anticipate that coupling this well known data analysis technique with dynamic pair distribution function analysis will have broad application in connecting structural dynamics to physical properties in a wide range of molecular and solid state systems.
Fry-Petit, A M; Rebola, A F; Mourigal, M; Valentine, M; Drichko, N; Sheckelton, J P; Fennie, C J; McQueen, T M
2015-09-28
For over a century, vibrational spectroscopy has enhanced the study of materials. Yet, assignment of particular molecular motions to vibrational excitations has relied on indirect methods. Here, we demonstrate that applying group theoretical methods to the dynamic pair distribution function analysis of neutron scattering data provides direct access to the individual atomic displacements responsible for these excitations. Applied to the molecule-based frustrated magnet with a potential magnetic valence-bond state, LiZn2Mo3O8, this approach allows direct assignment of the constrained rotational mode of Mo3O13 clusters and internal modes of MoO6 polyhedra. We anticipate that coupling this well known data analysis technique with dynamic pair distribution function analysis will have broad application in connecting structural dynamics to physical properties in a wide range of molecular and solid state systems. PMID:26429001
Abeykoon, A. M. Milinda; Hu, Hefei; Wu, Lijun; Zhu, Yimei; Billinge, Simon J. L.
2015-02-01
We explore and describe different protocols for calibrating electron pair distribution function (ePDF) measurements for quantitative studies on nano-materials. We find the most accurate approach to determine the camera-length is to use a standard calibration sample of Au nanoparticles from National Institute of Standards and Technology. Different protocols for data collection are also explored, as are possible operational errors, to find the best approaches for accurate data collection for quantitative ePDF studies.
Billinge, S.; Farrowa, C.L.
2009-05-01
The relationship between the equations used in the atomic pair distribution function (PDF) method and those commonly used in small-angle-scattering (SAS) analyses is explicitly shown. The origin of the sloping baseline, -4{pi}r{rho}{sub 0}, in PDFs of bulk materials is identified as originating from the SAS intensity that is neglected in PDF measurements. The nonlinear baseline in nanoparticles has the same origin, and contains information about the shape and size of the nanoparticles.
Nyquist-Shannon sampling theorem applied to refinements of the atomic pair distribution function
Farrow, Christopher L.; Shaw, Margaret; Kim, Hyunjeong; Juhás, Pavol; Billinge, Simon J.L.
2011-12-07
We have systematically studied the optimal real-space sampling of atomic pair distribution (PDF) data by comparing refinement results from oversampled and resampled data. Based on nickel and a complex perovskite system, we show that not only is the optimal sampling bounded by the Nyquist interval described by the Nyquist-Shannon (NS) sampling theorem as expected, but near this sampling interval, the data points in the PDF are minimally correlated, which results in more reliable uncertainty estimates in the modeling. Surprisingly, we find that PDF refinements quickly become unstable for data on coarser grids. Although the Nyquist-Shannon sampling theorem is well known, it has not been applied to PDF refinements, despite the growing popularity of the PDF method and its adoption in a growing number of communities. Here, we give explicit expressions for the application of NS sampling theorem to the PDF case, and establish through modeling that it is working in practice, which lays the groundwork for this to become more widely adopted. This has implications for the speed and complexity of possible refinements that can be carried out many times faster than currently with no loss of information, and it establishes a theoretically sound limit on the amount of information contained in the PDF that will prevent over-parametrization during modeling.
Olds, Daniel; Wang, Hsiu -Wen; Page, Katharine
2015-01-01
This study discusses the potential problems and currently available solutions in modeling powder-diffraction-based pair distribution function (PDF) data from systems where morphological feature information content includes distances in the nanometre length scale, such as finite nanoparticles, nanoporous networks and nanoscale precipitates in bulk materials. The implications of an experimental finite minimumQvalue are reviewed by simulation, which also demonstrates the advantages of combining PDF data with small-angle scattering data. A simple Fortran90 code, DShaper, is introduced, which may be incorporated into PDF data fitting routines in order to approximate the so-called `shape function' for any atomistic model.
Pair distribution function (PDF) analysis of mesoporous α-Fe2O3 and Cr2O3.
Hill, Adrian H; Allieta, Mattia
2013-06-14
We have measured atomic pair distribution functions of novel mesoporous metal oxides, α-Fe2O3 and Cr2O3. These have an ordered pore mosaic as well as crystalline structure within the pore walls, making them an interesting class of materials to characterise. Comparison of "bulk" and mesoporous data sets has allowed an estimate of long range structural coherence to be derived; ≈125 Å and ≈290 Å for α-Fe2O3 and Cr2O3 respectively. Further "box-car" analysis has shown that above ≈40 Å both mesoporous samples deviate greatly from their bulk counterparts. This is attributed to the pores of the mesoporous structure creating voids in the pair-correlations, disrupting long range order. PMID:23619834
NASA Astrophysics Data System (ADS)
Saveliev, V. L.
2011-05-01
Pair collisions is the main interaction process in the Boltzmann gas dynamics. By making use of exactly the same physical assumptions as was used by Ludwig Boltzmann we write the kinetic equation for two-particle distribution function of molecules in the gas mixtures. Instead of the collision integral, there are the linear scattering operator and the chaos projector in the right part of this equation. Because the scattering operator is more simple then Boltzmann collision integral this equation opens new opportunities for mathematical description of the Boltzmann gas dynamics.
Olds, Daniel; Wang, Hsiu -Wen; Page, Katharine L.
2015-09-04
In this work we discuss the potential problems and currently available solutions in modeling powder-diffraction based pair-distribution function (PDF) data from systems where morphological feature information content includes distances in the nanometer length scale, such as finite nanoparticles, nanoporous networks, and nanoscale precipitates in bulk materials. The implications of an experimental finite minimum Q-value are addressed by simulation, which also demonstrates the advantages of combining PDF data with small angle scattering data (SAS). In addition, we introduce a simple Fortran90 code, DShaper, which may be incorporated into PDF data fitting routines in order to approximate the so-called shape-function for anymore » atomistic model.« less
Olds, Daniel; Wang, Hsiu -Wen; Page, Katharine L.
2015-09-04
In this work we discuss the potential problems and currently available solutions in modeling powder-diffraction based pair-distribution function (PDF) data from systems where morphological feature information content includes distances in the nanometer length scale, such as finite nanoparticles, nanoporous networks, and nanoscale precipitates in bulk materials. The implications of an experimental finite minimum Q-value are addressed by simulation, which also demonstrates the advantages of combining PDF data with small angle scattering data (SAS). We introduce a simple Fortran90 code, DShaper, which may be incorporated into PDF data fitting routines in order to approximate the so-called shape-function for any atomistic model.
Wesolowski, David J.; Wang, Hsiu -Wen; Page, Katharine L.; Naguib, Michael; Gogotsi, Yury
2015-12-08
MXenes are a recently discovered family of two-dimensional (2D) early transition metal carbides and carbonitrides, which have already shown many attractive properties and a great promise in energy storage and many other applications. However, a complex surface chemistry and small coherence length has been an obstacle in some applications of MXenes, also limiting accuracy of predictions of their properties. In this study, we describe and benchmark a novel way of modeling layered materials with real interfaces (diverse surface functional groups and stacking order between the adjacent monolayers) against experimental data. The structures of three kinds of Ti3C2Tx MXenes (T standsmore » for surface terminating species, including O, OH, and F) produced under different synthesis conditions were resolved for the first time using atomic pair distribution function obtained by high-quality neutron total scattering. The true nature of the material can be easily captured with the sensitivity of neutron scattering to the surface species of interest and the detailed third-generation structure model we present. The modeling approach leads to new understanding of MXene structural properties and can replace the currently used idealized models in predictions of a variety of physical, chemical and functional properties of Ti3C2-based MXenes. Furthermore, the developed models can be employed to guide the design of new MXene materials with selected surface termination and controlled contact angle, catalytic, optical, electrochemical and other properties. We suggest that the multi-level structural modeling should form the basis for a generalized methodology on modeling diffraction and pair distribution function data for 2D and layered materials.« less
NASA Astrophysics Data System (ADS)
Gori-Giorgi, Paola; Perdew, John P.
2002-10-01
We construct analytic formulas that represent the coupling-constant-averaged pair distribution function gxc(rs,ζ,kFu) of a three-dimensional nonrelativistic ground-state electron gas constrained to a uniform density with density parameter rs=(9π/4)1/3/kF and relative spin polarization ζ over the whole range 0
Yang, Xiaohao; Masadeh, Ahmad S; McBride, James R; Božin, Emil S; Rosenthal, Sandra J; Billinge, Simon J L
2013-06-14
The atomic pair distribution function (PDF) analysis of X-ray powder diffraction data has been used to study the structure of small and ultra-small CdSe nanoparticles. A method is described that uses a wurtzite and zinc-blende mixed phase model to account for stacking faults in CdSe particles. The mixed-phase model successfully describes the structure of nanoparticles larger than 2 nm yielding a stacking fault density of about 30%. However, for ultrasmall nanoparticles smaller than 2 nm, the models cannot fit the experimental PDF showing that the structure is significantly modified from that of larger particles and the bulk. The observation of a significant change in the average structure at ultra-small size is likely to explain the unusual properties of the ultrasmall particles such as their white light emitting ability. PMID:23525376
NASA Astrophysics Data System (ADS)
Odinokov, A. V.; Basilevsky, M. V.; Nikitina, E. A.
2011-10-01
The computations of the association constants Kass were performed at the microscopic level for the ion pair Cy+I- composed of the complex cyanine dye cation Cy+ coupled to the negative iodine counterion. The wide array of Kass values is arranged by a variation of the composition of the binary solvent mixtures toluene/dimethylsulfoxide with the accompanying change of the solvent polarity. The potentials of mean force (PMFs) are calculated for a set of interionic separations R in the Cy+I- by a methodology which combines the quantum-chemical techniques for the treatment of the electronic structure of the Cy+I- system with the recent dielectric continuum approach which accounts for the solvation effects. For a given solute/solvent system the probability function P(R), which describes the distribution of interionic separations, is constructed in terms of the PMFs and implemented for the evaluation of the Kass.
Harrington, R.; Hausner, D. B.; Bhandari, N.; Strongin, D. R.; Chapman, K. W.; Chupas, P. J.; Middlemiss, D. S.; Grey, C. P.; Parise, J. B.; X-Ray Science Division; Stony Brook Univ.; Temple Univ.
2010-01-01
Differential pair distribution function (d-PDF) analysis of high energy powder X-ray diffraction data was carried out on 2-line ferrihydrite nanoparticles with arsenate oxyanions adsorbed on the surface to investigate the binding mechanism. In this analysis, a PDF of ferrihydrite is subtracted from a PDF of ferrihydrite with arsenate sorbed on the surface, leaving only correlations from within the surface layer and between the surface and the particle. As-O and As-Fe correlations were observed at 1.68 and 3.29 {angstrom}, respectively, in good agreement with previously published EXAFS data, confirming a bidentate binuclear binding mechanism. Further peaks are observed in the d-PDF which are not present in EXAFS, corresponding to correlations between As and O in the particle and As-2nd Fe.
Zhu, Mengqiang; Farrow, Christopher L.; Post, Jeffrey E.; Livi, Kenneth J.T.; Billinge, Simon J.L.; Ginder-Vogel, Matthew; Sparks, Donald L.
2012-03-15
Manganese (Mn) oxides are among the most reactive natural minerals and play an important role in elemental cycling in oceanic and terrestrial environments. A large portion of naturally-occurring Mn oxides tend to be poorly-crystalline and/or nanocrystalline, with not fully resolved crystal structures. In this study, the crystal structures of their synthetic analogs including acid birnessite (AcidBir), {delta}-MnO{sub 2}, polymeric MnO{sub 2} (PolyMnO{sub 2}) and a bacteriogenic Mn oxide (BioMnO{sub x}), have been revealed using atomic pair distribution function (PDF) analysis. Results unambiguously verify that these Mn oxides are layered materials. The best models that accurately allow simulation of pair distribution functions (PDFs) belong to the monoclinic C12/m1 space group with a disk-like shape. The single MnO{sub 6} layers in the average structures deviate significantly from hexagonal symmetry, in contrast to the results of previous studies based on X-ray diffraction analysis in reciprocal space. Manganese occupancies in MnO{sub 6} layers are estimated to be 0.936, 0.847, 0.930 and 0.935, for AcidBir, BioMnOx, {delta}-MnO{sub 2} and PolyMnO{sub 2}, respectively; however, occupancies of interlayer cations and water molecules cannot be accurately determined using the models in this study. The coherent scattering domains (CSDs) of PolyMnO{sub 2}, {delta}-MnO{sub 2} and BioMnO{sub x} are at the nanometer scale, comprising one to three MnO{sub 6} layers stacked with a high disorder in the crystallographic c-axis direction. Overall, the results of this study advance our understanding of the mineralogy of Mn oxide minerals in the environment.
Billinge S. J.; Zhu, M.; Farrow, C.L.; Post, J.E.; Livi, K.J.T.; Ginder-Vogel, M.; Sparks, D.L.
2012-03-15
Manganese (Mn) oxides are among the most reactive natural minerals and play an important role in elemental cycling in oceanic and terrestrial environments. A large portion of naturally-occurring Mn oxides tend to be poorly-crystalline and/or nanocrystalline, with not fully resolved crystal structures. In this study, the crystal structures of their synthetic analogs including acid birnessite (AcidBir), {delta}-MnO{sub 2}, polymeric MnO{sub 2} (PolyMnO{sub 2}) and a bacteriogenic Mn oxide (BioMnO{sub x}), have been revealed using atomic pair distribution function (PDF) analysis. Results unambiguously verify that these Mn oxides are layered materials. The best models that accurately allow simulation of pair distribution functions (PDFs) belong to the monoclinic C12/m1 space group with a disk-like shape. The single MnO{sub 6} layers in the average structures deviate significantly from hexagonal symmetry, in contrast to the results of previous studies based on X-ray diffraction analysis in reciprocal space. Manganese occupancies in MnO{sub 6} layers are estimated to be 0.936, 0.847, 0.930 and 0.935, for AcidBir, BioMnO{sub x}, {delta}-MnO{sub 2} and PolyMnO{sub 2}, respectively; however, occupancies of interlayer cations and water molecules cannot be accurately determined using the models in this study. The coherent scattering domains (CSDs) of PolyMnO{sub 2}, {delta}-MnO{sub 2} and BioMnO{sub x} are at the nanometer scale, comprising one to three MnO{sub 6} layers stacked with a high disorder in the crystallographic c-axis direction. Overall, the results of this study advance our understanding of the mineralogy of Mn oxide minerals in the environment.
Benjamin A. Frandsen; Brunelli, Michela; Page, Katharine; Uemura, Yasutomo J.; Staunton, Julie B.; Billinge, Simon J. L.
2016-05-11
Here, we present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ~1 nm length scale that differ substantially from the low-temperature long-range spin arrangement. Ab initio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominatedmore » by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. Furthermore, the Anderson superexchange model for MnO is thus verified by experimentation and confirmed by ab initio theory.« less
NASA Astrophysics Data System (ADS)
Frandsen, Benjamin A.; Brunelli, Michela; Page, Katharine; Uemura, Yasutomo J.; Staunton, Julie B.; Billinge, Simon J. L.
2016-05-01
We present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ˜1 nm length scale that differ substantially from the low-temperature long-range spin arrangement. Ab initio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominated by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. The Anderson superexchange model for MnO is thus verified by experimentation and confirmed by ab initio theory.
NASA Astrophysics Data System (ADS)
Frandsen, Benjamin; Page, Katharine; Brunelli, Michela; Staunton, Julie; Billinge, Simon
Short-range magnetic correlations are known to exist in a variety of strongly correlated electron systems, but our understanding of the role they play is challenged by the difficulty of experimentally probing such correlations. Magnetic pair distribution function (mPDF) analysis is a newly developed neutron total scattering method that can reveal short-range magnetic correlations directly in real space, and may therefore help ameliorate this difficulty. We present temperature-dependent mPDF measurements of the short-range magnetic correlations in the paramagnetic phase of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. We observe significant correlations on a ~1 nm length scale that differ substantially from the low-temperature long-range-ordered spin arrangement. With no free parameters, ab initio calculations using the self-interaction-corrected local spin density approximation of density functional theory quantitatively reproduce the magnetic correlations to a high degree of accuracy. These results yield valuable insight into the magnetic exchange in MnO and showcase the utility of the mPDF technique for studying magnetic properties of strongly correlated electron systems.
Frandsen, Benjamin A; Brunelli, Michela; Page, Katharine; Uemura, Yasutomo J; Staunton, Julie B; Billinge, Simon J L
2016-05-13
We present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ∼1 nm length scale that differ substantially from the low-temperature long-range spin arrangement. Ab initio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominated by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. The Anderson superexchange model for MnO is thus verified by experimentation and confirmed by ab initio theory. PMID:27232042
Frandsen, Benjamin A; Billinge, Simon J L
2015-05-01
An experimental determination of the magnetic pair distribution function (mPDF) defined in an earlier paper [Frandsen et al. (2014). Acta Cryst. A70, 3-11] is presented for the first time. The mPDF was determined from neutron powder diffraction data from a reactor and a neutron time-of-flight total scattering source on a powder sample of the antiferromagnetic oxide MnO. A description of the data treatment that allowed the measured mPDF to be extracted and then modelled is provided and utilized to investigate the low-temperature structure of MnO. Atomic and magnetic co-refinements support the scenario of a locally monoclinic ground-state atomic structure, despite the average structure being rhombohedral, with the mPDF analysis successfully recovering the known antiferromagnetic spin configuration. The total scattering data suggest a preference for the spin axis to lie along the pseudocubic [10{\\overline 1}] direction. Finally, r-dependent PDF refinements indicate that the local monoclinic structure tends toward the average rhombohedral R{\\overline 3}m symmetry over a length scale of approximately 100 Å. PMID:25921501
Dambournet, Damien; Chapman, Karena W; Koudriachova, Marina V; Chupas, Peter J; Belharouak, Ilias; Amine, Khalil
2011-07-01
X-ray pair distribution function (PDF) methods and first-principles calculations have been combined to probe the structure of electrochemically lithiated TiO(2) Brookite. Traditional powder diffraction studies suggest that Brookite amorphizes upon lithium insertion, with the Bragg reflections disappearing. However, PDF analysis indicates that the TiO(2) framework connectivity is maintained throughout lithium intercalation, with expansions along the a and b axes. The Li(+) ions within the framework are poorly observed in the X-ray PDF, which is dominated by contributions from the more strongly scattering Ti and O atoms. First-principles calculations were used to identify energetically favorable Li(+) sites within the Brookite lattice and to develop a complete structural model of the lithiated material. This model replicates the local structure and decreased intermediate range order observed in the PDF data. The analysis suggests that local structural distortions of the TiO(2) lattice accommodate lithium in five-coordinate sites. This structural model is consistent with the observed electrochemical behavior. PMID:21627151
Dambournet, D.; Chapman, K. W.; Koudriachova, M. V.; Chupas, P. J.; Belharouak, I.; Amine, K.
2011-07-04
X-ray pair distribution function (PDF) methods and first-principles calculations have been combined to probe the structure of electrochemically lithiated TiO{sub 2} Brookite. Traditional powder diffraction studies suggest that Brookite amorphizes upon lithium insertion, with the Bragg reflections disappearing. However, PDF analysis indicates that the TiO{sub 2} framework connectivity is maintained throughout lithium intercalation, with expansions along the a and b axes. The Li{sup +} ions within the framework are poorly observed in the X-ray PDF, which is dominated by contributions from the more strongly scattering Ti and O atoms. First-principles calculations were used to identify energetically favorable Li{sup +} sites within the Brookite lattice and to develop a complete structural model of the lithiated material. This model replicates the local structure and decreased intermediate range order observed in the PDF data. The analysis suggests that local structural distortions of the TiO{sub 2} lattice accommodate lithium in five-coordinate sites. This structural model is consistent with the observed electrochemical behavior.
Cho, Hyung Min; Chu, Jhih-Wei
2009-10-01
We develop a new method to invert the target profiles of radial distribution functions (RDFs) to the pair forces between particles. The target profiles of RDFs can be obtained from all-atom molecular dynamics (MD) simulations or experiments and the inverted pair forces can be used in molecular simulations at a coarse-grained (CG) scale. Our method is based on a variational principle that determines the mean forces between CG sites after integrating out the unwanted degrees of freedom. The solution of this variational principle has been shown to correspond to the Yvon-Born-Green (YBG) equation [Noid et al., J. Phys. Chem. B 111, 4116 (2007)]. To invert RDFs, we solve the YBG equation iteratively by running a CG MD simulation at each step of iteration. A novelty of the iterative-YBG method is that during iteration, CG forces are updated according to the YBG equation without imposing any approximation as is required by other methods. As a result, only three to ten iterations are required to achieve convergence for all cases tested in this work. Furthermore, we show that not only are the target RDFs reproduced by the iterative solution; the profiles of the three-body correlation function in the YBG equation computed from all-atom and CG simulations also have a better agreement. The iterative-YBG method is applied to compute the CG forces of four molecular liquids to illustrate its efficiency and robustness: water, ethane, ethanol, and a water/methanol mixture. Using the resulting CG forces, all of the target RDFs observed in all-atom MD simulations are reproduced. We also show that the iterative-YBG method can be applied with a virial constraint to expand the representability of a CG force field. The iterative-YBG method thus provides a general and robust framework for computing CG forces from RDFs and could be systematically generalized to go beyond pairwise forces and to include higher-body interactions in a CG force field by applying the aforementioned variational
Morandeau, Antoine E.; White, Claire E.
2015-04-21
Calcium–silicate–hydrate (C–S–H) gel is the main binder component in hydrated ordinary Portland cement (OPC) paste, and is known to play a crucial role in the carbonation of cementitious materials, especially for more sustainable alternatives containing supplementary cementitious materials. However, the exact atomic structural changes that occur during carbonation of C–S–H gel remain unknown. Here, we investigate the local atomic structural changes that occur during carbonation of a synthetic calcium–silicate–hydrate gel exposed to pure CO₂ vapour, using in situ X-ray total scattering measurements and subsequent pair distribution function (PDF) analysis. By analysing both the reciprocal and real-space scattering data as the C–S–H carbonation reaction progresses, all phases present during the reaction (crystalline and non-crystalline) have been identified and quantified, with the results revealing the emergence of several polymorphs of crystalline calcium carbonate (vaterite and calcite) in addition to the decalcified C–S–H gel. Furthermore, the results point toward residual calcium being present in the amorphous decalcified gel, potentially in the form of an amorphous calcium carbonate phase. As a result of the quantification process, the reaction kinetics for the evolution of the individual phases have been obtained, revealing new information on the rate of growth/dissolution for each phase associated with C–S–H gel carbonation. Moreover, the investigation reveals that the use of real space diffraction data in the form of PDFs enables more accurate determination of the phases that develop during complex reaction processes such as C–S–H gel carbonation in comparison to the conventional reciprocal space Rietveld analysis approach.
NASA Astrophysics Data System (ADS)
Rademacher, N.; Bayarjargal, L.; Morgenroth, W.; Bauer, J. D.; Milman, V.; Winkler, B.
2015-05-01
The decomposition of SF6 in the presence of glassy carbon was induced in laser heated diamond anvil cells at 10-11 GPa and 2000-2500 K. The reaction products were characterised by synchrotron X-ray diffraction, including high pressure pair distribution function analysis, and micro-Raman spectroscopy combined with atomistic model calculations. The decomposition leads to elemental amorphous helical sulfur and crystalline CF4-III. Two different sulfur phases, namely helical Sμ and crystalline α-S8, were observed after recovering the laser heated samples of different experiments at ambient conditions.
Terban, Maxwell W; Johnson, Matthew; Di Michiel, Marco; Billinge, Simon J L
2015-03-12
Difference atomic pair distribution function methods have been applied to detect and characterize nanoparticles suspended in a solvent at very dilute concentrations. We specifically consider nanoparticles of a pharmaceutical compound in aqueous solution using X-ray PDF methods, a challenging case due to the low atomic number of the nanoparticle species. The nanoparticles were unambiguously detected at the level of 0.25 wt%. Even at these low concentrations the signals were highly reproducible, allowing for reliable detection and quantitative analysis of the nanoparticle structure. PMID:25732228
NASA Astrophysics Data System (ADS)
Baldini, M.; Postorino, P.; Malavasi, L.; Marini, C.; Chapman, K. W.; Mao, Ho-kwang
2016-06-01
The evolution of the local structure of VO2 was investigated across the pressure-induced insulator to metal transition (IMT) by means of pair distribution function measurements. The pressure behavior of the V-V and V-O bond lengths have been determined. The data demonstrated that the pressure-driven IMT is not activated by the suppression of the Peierls-type distortion. A clear octahedra symmetrization is observed in the metallic phase, suggesting a link between structural degree of freedom and the metallization process.
Olds, Daniel; Wang, Hsiu-Wen; Page, Katharine
2015-10-13
This article discusses the potential problems and currently available solutions in modeling powder-diffraction-based pair distribution function (PDF) data from systems where morphological feature information content includes distances in the nanometre length scale, such as finite nanoparticles, nanoporous networks and nanoscale precipitates in bulk materials. The implications of an experimental finite minimum
Olds, Daniel; Wang, Hsiu -Wen; Page, Katharine
2015-01-01
This study discusses the potential problems and currently available solutions in modeling powder-diffraction-based pair distribution function (PDF) data from systems where morphological feature information content includes distances in the nanometre length scale, such as finite nanoparticles, nanoporous networks and nanoscale precipitates in bulk materials. The implications of an experimental finite minimumQvalue are reviewed by simulation, which also demonstrates the advantages of combining PDF data with small-angle scattering data. A simple Fortran90 code, DShaper, is introduced, which may be incorporated into PDF data fitting routines in order to approximate the so-called `shape function' for any atomistic model.
Distributed processing; distributed functions?
Fox, Peter T.; Friston, Karl J.
2016-01-01
After more than twenty years busily mapping the human brain, what have we learned from neuroimaging? This review (coda) considers this question from the point of view of structure–function relationships and the two cornerstones of functional neuroimaging; functional segregation and integration. Despite remarkable advances and insights into the brain’s functional architecture, the earliest and simplest challenge in human brain mapping remains unresolved: We do not have a principled way to map brain function onto its structure in a way that speaks directly to cognitive neuroscience. Having said this, there are distinct clues about how this might be done: First, there is a growing appreciation of the role of functional integration in the distributed nature of neuronal processing. Second, there is an emerging interest in data-driven cognitive ontologies, i.e., that are internally consistent with functional anatomy. We will focus this review on the growing momentum in the fields of functional connectivity and distributed brain responses and consider this in the light of meta-analyses that use very large data sets to disclose large-scale structure–function mappings in the human brain. PMID:22245638
Filippov, Alexander E; Popov, Valentin L; Gorb, Stanislav N
2015-02-01
Microstructures responsible for temporary arresting of contacting surfaces are widely distributed on surfaces in different organisms. Recent morphological studies show that these structures have different density of outgrowths and not ideal distribution pattern on both complementary parts of the contact. One can suggest that this difference is optimized by natural selection to get stronger mechanical arrest within the system. In this paper, we simulate such a system numerically, both in the frames of continuous contact and discrete dynamical models to prove this hypothesis and elucidate other aspects of optimization of such mechanical adhesive systems. PMID:25533090
NASA Astrophysics Data System (ADS)
Takada, Yasutami
2006-03-01
It is a well-known fact that the electronic compressibility κ diverges in the 3D electron gas as the density parameter rs approaches 5.25. A recent investigation clarifies that this divergence is due to the excitonic effect in the electron-hole pair excitation, in particular, to its zero-energy excitation [1]. For rs>5.25, κ becomes negative, leading to the negative static dielectric function ɛ(q,0) for at least small q owing to the compressibility sum rule. Then we can expect that two positive test charges do not repel but attract to each other in such a system. Keeping this situation in mind, we have calculated the ion-pair distribution function g(R) in the expanded Rb liquid metal by using the Monte Carlo method and found interesting features in g(R) characteristic to the negative ɛ(q,0) [2]. Such features have been observed by the recent measurement of g(R) in the supercritical fluid Rb metal with continuously increasing rs from 5.25 [3]. This confirms the situation of κ<0 in the low-density 3D electron gas for the first time. [1] YT, J. Superconductivity 18, No.3 (2005). [2] H. Maebashi and YT, to be submitted. [3] K. Matsuda and K. Tamura, private communication.
Booth, C H; Bauer, E D; Bozin, E S; Billinge, S J L; Walter, M D
2010-07-20
The Cp{sup *}{sub 2} Yb(L) class of compounds, where Cp{sup *}=pentamethylcyclopentadienyl = C{sub 5}Me{sub 5} and L is either a 1,4-diazabutadiene or bipy = 2,2'bipyridine related ligand, have provided excellent analogies to the Kondo state on the nanoscale. Cp{sup *}{sub 2} Yb(4,4'-Me{sub 2}-bipy) furthers this analogy by demonstrating a valence transition as the sample is cooled below 200 K. Here, pair-distribution function (PDF) analysis of x-ray powder diffraction data demonstrate that the Cp{sup *}{sub 2}Yb(4,4'Me{sub 2}-bipy) molecule is virtually unchanged through the valence transition. However, the molecule’s stacking arrangement is altered through the valence transition.
Skinner, Lawrie B.; Huang, Congcong; Schlesinger, Daniel; Pettersson, Lars G. M.; Nilsson, Anders; Benmore, Chris J.
2013-02-21
Four recent x-ray diffraction measurements of ambient liquid water are reviewed here. Each of these measurements represents a significant development of the x-ray diffraction technique applied to the study of liquid water. Sources of uncertainty from statistical noise, Q-range, Compton scattering, and self-scattering are discussed. The oxygen-hydrogen contribution to the measured x-ray scattering pattern was subtracted using literature data to yield an experimental determination, with error bars, of the oxygen-oxygen pair-distribution function, g{sub OO}(r), which essentially describes the distribution of molecular centers. The extended Q-range and low statistical noise of these measurements has significantly reduced truncation effects and related errors in the g{sub OO}(r) functions obtained. From these measurements and error analysis, the position and height of the nearest neighbor maximum in g{sub OO}(r) were found to be 2.80(1) A and 2.57(5) respectively. Numerical data for the coherent differential x-ray scattering cross-section I{sub X}(Q), the oxygen-oxygen structure factor S{sub OO}(Q), and the derived g{sub OO}(r) are provided as benchmarks for calibrating force-fields for water.
Whitfield, Ross E.; Goossens, Darren J.; Welberry, T. Richard
2016-01-01
The ability of the pair distribution function (PDF) analysis of total scattering (TS) from a powder to determine the local ordering in ferroelectric PZN (PbZn1/3Nb2/3O3) has been explored by comparison with a model established using single-crystal diffuse scattering (SCDS). While X-ray PDF analysis is discussed, the focus is on neutron diffraction results because of the greater extent of the data and the sensitivity of the neutron to oxygen atoms, the behaviour of which is important in PZN. The PDF was shown to be sensitive to many effects not apparent in the average crystal structure, including variations in the B-site—O separation distances and the fact that 〈110〉 Pb2+ displacements are most likely. A qualitative comparison between SCDS and the PDF shows that some features apparent in SCDS were not apparent in the PDF. These tended to pertain to short-range correlations in the structure, rather than to interatomic separations. For example, in SCDS the short-range alternation of the B-site cations was quite apparent in diffuse scattering at (½ ½ ½), whereas it was not apparent in the PDF. PMID:26870378
NASA Astrophysics Data System (ADS)
Hong, Xinguo; Ehm, Lars; Zhong, Zhong; Ghose, Sanjit; Duffy, Thomas S.; Weidner, Donald J.
2016-02-01
We report development of micro-focusing optics for high-energy x-rays by combining a sagittally bent Laue crystal monchromator with Kirkpatrick-Baez (K-B) X-ray focusing mirrors. The optical system is able to provide a clean, high-flux X-ray beam suitable for pair distribution function (PDF) measurements at high pressure using a diamond anvil cell (DAC). A focused beam of moderate size (10-15 μm) has been achieved at energies of 66 and 81 keV. PDF data for nanocrystalline platinum (n-Pt) were collected at 12.5 GPa with a single 5 s X-ray exposure, showing that the in-situ compression, decompression, and relaxation behavior of samples in the DAC can be investigated with this technique. PDFs of n-Pt and nano Au (n-Au) under quasi-hydrostatic loading to as high as 71 GPa indicate the existence of substantial reduction of grain or domain size for Pt and Au nanoparticles at pressures below 10 GPa. The coupling of sagittally bent Laue crystals with K-B mirrors provides a useful means to focus high-energy synchrotron X-rays from a bending magnet or wiggler source.
Hong, Xinguo; Ehm, Lars; Zhong, Zhong; Ghose, Sanjit; Duffy, Thomas S.; Weidner, Donald J.
2016-02-23
We report development of micro-focusing optics for high-energy x-rays by combining a sagittally bent Laue crystal monchromator with Kirkpatrick-Baez (K–B) X-ray focusing mirrors. The optical system is able to provide a clean, high-flux X-ray beam suitable for pair distribution function (PDF) measurements at high pressure using a diamond anvil cell (DAC). A focused beam of moderate size (10–15 μm) has been achieved at energies of 66 and 81keV. PDF data for nanocrystalline platinum (n-Pt) were collected at 12.5 GPa with a single 5 s X-ray exposure, showing that the in-situ compression, decompression, and relaxation behavior of samples in the DACmore » can be investigated with this technique. PDFs of n-Pt and nano Au (n-Au) under quasi-hydrostatic loading to as high as 71GPa indicate the existence of substantial reduction of grain or domain size for Pt and Au nanoparticles at pressures below 10 GPa. In conclusion, the coupling of sagittally bent Laue crystals with K–B mirrors provides a useful means to focus high-energy synchrotron X-rays from a bending magnet or wiggler source.« less
Allan, P. K.; Chapman, K. W.; Chupas, P. J.; Hriljac, J. A.; Renouf, C. L.; Lucas, T. C. A.; Morris, R. E.
2012-01-01
Flexible metal-organic frameworks (MOFs) are materials of great current interest. A small class of MOFs show flexibility driven by reversible bonding rearrangements that lead directly to unusual properties. Cu-SIP-3 is a MOF based on the 5-sulfoisophthalate ligand, where the strong copper-carboxylate bonds ensure that the three-dimensional integrity of the structure is retained while allowing bonding changes to occur at the more weakly bonding sulfonate group leading to unusual properties such as the ultra-selective adsorption of only certain gases. While the integrity of the framework remains intact during bonding changes, crystalline order is not retained at all times during the transformations. X-Ray diffraction reveals that highly crystalline single crystals lose order during the transformation before regaining crystallinity once it is complete. Here we show how X-ray pair distribution function analysis can be used to reveal the mechanism of the transformations in Cu-SIP-3, identifying the sequence of atomic displacements that occur in the disordered phase. A similar approach reveals the underlying mechanism of Cu-SIP-3's ultra-selective gas adsorption.
Hong, Xinguo; Ehm, Lars; Zhong, Zhong; Ghose, Sanjit; Duffy, Thomas S; Weidner, Donald J
2016-01-01
We report development of micro-focusing optics for high-energy x-rays by combining a sagittally bent Laue crystal monchromator with Kirkpatrick-Baez (K-B) X-ray focusing mirrors. The optical system is able to provide a clean, high-flux X-ray beam suitable for pair distribution function (PDF) measurements at high pressure using a diamond anvil cell (DAC). A focused beam of moderate size (10-15 μm) has been achieved at energies of 66 and 81 keV. PDF data for nanocrystalline platinum (n-Pt) were collected at 12.5 GPa with a single 5 s X-ray exposure, showing that the in-situ compression, decompression, and relaxation behavior of samples in the DAC can be investigated with this technique. PDFs of n-Pt and nano Au (n-Au) under quasi-hydrostatic loading to as high as 71 GPa indicate the existence of substantial reduction of grain or domain size for Pt and Au nanoparticles at pressures below 10 GPa. The coupling of sagittally bent Laue crystals with K-B mirrors provides a useful means to focus high-energy synchrotron X-rays from a bending magnet or wiggler source. PMID:26902122
Hong, Xinguo; Ehm, Lars; Zhong, Zhong; Ghose, Sanjit; Duffy, Thomas S.; Weidner, Donald J.
2016-01-01
We report development of micro-focusing optics for high-energy x-rays by combining a sagittally bent Laue crystal monchromator with Kirkpatrick-Baez (K–B) X-ray focusing mirrors. The optical system is able to provide a clean, high-flux X-ray beam suitable for pair distribution function (PDF) measurements at high pressure using a diamond anvil cell (DAC). A focused beam of moderate size (10–15 μm) has been achieved at energies of 66 and 81 keV. PDF data for nanocrystalline platinum (n-Pt) were collected at 12.5 GPa with a single 5 s X-ray exposure, showing that the in-situ compression, decompression, and relaxation behavior of samples in the DAC can be investigated with this technique. PDFs of n-Pt and nano Au (n-Au) under quasi-hydrostatic loading to as high as 71 GPa indicate the existence of substantial reduction of grain or domain size for Pt and Au nanoparticles at pressures below 10 GPa. The coupling of sagittally bent Laue crystals with K–B mirrors provides a useful means to focus high-energy synchrotron X-rays from a bending magnet or wiggler source. PMID:26902122
NASA Technical Reports Server (NTRS)
Achilles, C. N.; Bish, D. L.; Rampe, E. B.; Morris, R. V.
2015-01-01
Soils on Mars have been analyzed by the Mars Exploration Rovers (MER) and most recently by the Mars Science Laboratory (MSL) rover. Chemical analyses from a majority of soil samples suggest that there is a relatively uniform global soil composition across much of the planet. A soil site, Rocknest, was sampled by the MSL science payload including the CheMin X-ray diffractometer and the Alpha Particle X-ray Spectrometer (APXS). Che- Min X-ray diffraction (XRD) data revealed crystalline phases and a broad, elevated background, indicating the presence of amorphous or poorly ordered materials (Fig 1). Based on the chemical composition of the bulk soil measured by APXS and the composition of crystalline phases derived from unit-cell parameters determined with CheMin data, the percentages of crystalline and amorphous phases were calculated at 51% and 49%, respectively. Attempts to model the amorphous contribution to CheMin XRD patterns were made using amorphous standards and full-pattern fitting methods and show that the broad, elevated background region can be fitted by basaltic glass, allophane, and palagonite. However, the modeling shows only that these phases have scattering patterns similar to that for the soil, not that they represent unique solutions. Here, we use pair distribution function (PDF) analysis to determine the short-range order of amorphous analogs in martian soils and better constrain the amorphous material detected by CheMin.
Locke, D. R.; Chupas, P. J.; Chapman, K. W.; Pugmire, R. J.; Winans, R. E.; Univ. of Utah
2008-01-01
The compression behavior of a silicate-rich oil shale from the Green River formation in the pressure range 0.0-2.4 GPa was studied using in situ high pressure X-ray pair distribution function (PDF) measurements for the sample contained within a Paris-Edinburgh cell. The real-space local structural information in the PDF, G(r), was used to evaluate the compressibility of the oil shale. Specifically, the pressure-induced reduction in the medium- to long-range atom distances (6-20 {angstrom}) yielded an average sample compressibility corresponding to a bulk modulus of ca. 61-67 GPa. A structural model consisting of a three phase mixture of the principal crystalline oil shale components (quartz, albite and Illite) provided a good fit to the ambient pressure PDF data (R 30.7%). Indeed the features in the PDF beyond 6 {angstrom}, were similarly well fit by a single phase model of the highest symmetry, highly crystalline quartz component.
A linked electron pair functional.
Knowles, Peter J; Cooper, Bridgette
2010-12-14
A modification of the variational configuration interaction functional in the first-order interacting space for molecular electronic structure is presented. The modified functional is a fully linked expression that by construction is extensive and invariant to transformations of the underlying orbital basis and is exact for an ensemble of separated two-electron subsystems. In addition, an approximation to variational coupled cluster is generated through truncation of the exponential cluster operator. When combined, these methods demonstrate accuracy that exceeds that of the standard coupled-cluster method, in particular in situations where the reference Slater determinant is not a good approximation. PMID:21171682
Bridges, F.; Downward, L.; Jiang, Y.; O'Brien, T.
2009-06-04
In many systems there is a significant coupling between the local structure and other properties of the system such as magnetism, electrical and thermal transport, metal/insulator transitions etc. In such materials, a detailed temperature-dependent study of the width of the Pair Distribution Function (PDF), {sigma}, can separate different contributions and provide a connection between the observed macroscopic observations and the underlying atomic interactions that produce them. The usual model for simple systems is that the T-dependence of {sigma}{sup 2} is described by an Einstein or Correlated Debye model, with one characteristic temperature for the system; in such models {sigma}{sup 2}(T) increases smoothly with T and has a slowly increasing slope. However that is not always the case: in structures with large unit cells containing several types of atoms, some atoms in the crystal can have a low Einstein temperature while others have a very high correlated Debye temperature as observed in a number of thermoelectric systems (skutterudites and clathrates). In others systems such as the negative thermal expansion material ZrW{sub 2}O{sub 8}, the same atom cam be involved in both low and high temperature Einstein modes. Vibrations of atoms (or molecular unit) described by a low Einstein temperature often control/determine the lattice properties. In other systems there are deviations from the T-dependence expected for either the Einstein or correlated Debye models -- such as a small increase in {sigma}{sup 2} at low temperatures for the Ru-Ru pair in PrRu{sub 4}Sb{sub 12} which has a metal/insulator transition near 60K, or a very sharp step in {sigma}{sup 2}(T) observed in the bilayer colossal magnetoresistance system La{sub 2-2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7} at the ferromagnetic transition. We discuss broadening of the PDF in more complex systems, show some simulations and then present several recent examples.
Kwon, Gihan; Kokhan, Oleksandr; Han, Ali; Chapman, Karena W.; Chupas, Peter J.; Du, Pingwu; Tiede, David M.
2015-12-01
Amorphous thin film oxygen evolving catalysts, OECs, of first-row transition metals show promise to serve as self-assembling photoanode materials in solar-driven, photoelectrochemical `artificial leaf' devices. This report demonstrates the ability to use high-energy X-ray scattering and atomic pair distribution function analysis, PDF, to resolve structure in amorphous metal oxide catalyst films. The analysis is applied here to resolve domain structure differences induced by oxyanion substitution during the electrochemical assembly of amorphous cobalt oxide catalyst films, Co-OEC. PDF patterns for Co-OEC films formed using phosphate, Pi, methylphosphate, MPi, and borate, Bi, electrolyte buffers show that the resulting domains vary in sizemore » following the sequence Pi < MPi < Bi. The increases in domain size for CoMPi and CoBi were found to be correlated with increases in the contributions from bilayer and trilayer stacked domains having structures intermediate between those of the LiCoOO and CoO(OH) mineral forms. The lattice structures and offset stacking of adjacent layers in the partially stacked CoMPi and CoBi domains were best matched to those in the LiCoOO layered structure. The results demonstrate the ability of PDF analysis to elucidate features of domain size, structure, defect content and mesoscale organization for amorphous metal oxide catalysts that are not readily accessed by other X-ray techniques. Finally, PDF structure analysis is shown to provide a way to characterize domain structures in different forms of amorphous oxide catalysts, and hence provide an opportunity to investigate correlations between domain structure and catalytic activity.« less
Kwon, Gihan; Kokhan, Oleksandr; Han, Ali; Chapman, Karena W.; Chupas, Peter J.; Du, Pingwu; Tiede, David M.
2015-12-01
Amorphous thin film oxygen evolving catalysts, OECs, of first-row transition metals show promise to serve as self-assembling photoanode materials in solar-driven, photoelectrochemical `artificial leaf' devices. This report demonstrates the ability to use high-energy X-ray scattering and atomic pair distribution function analysis, PDF, to resolve structure in amorphous metal oxide catalyst films. The analysis is applied here to resolve domain structure differences induced by oxyanion substitution during the electrochemical assembly of amorphous cobalt oxide catalyst films, Co-OEC. PDF patterns for Co-OEC films formed using phosphate, Pi, methylphosphate, MPi, and borate, Bi, electrolyte buffers show that the resulting domains vary in size following the sequence Pi < MPi < Bi. The increases in domain size for CoMPi and CoBi were found to be correlated with increases in the contributions from bilayer and trilayer stacked domains having structures intermediate between those of the LiCoOO and CoO(OH) mineral forms. The lattice structures and offset stacking of adjacent layers in the partially stacked CoMPi and CoBi domains were best matched to those in the LiCoOO layered structure. The results demonstrate the ability of PDF analysis to elucidate features of domain size, structure, defect content and mesoscale organization for amorphous metal oxide catalysts that are not readily accessed by other X-ray techniques. Finally, PDF structure analysis is shown to provide a way to characterize domain structures in different forms of amorphous oxide catalysts, and hence provide an opportunity to investigate correlations between domain structure and catalytic activity.
Kwon, Gihan; Kokhan, Oleksandr; Han, Ali; Chapman, Karena W.; Chupas, Peter J.; Du, Pingwu; Tiede, David M.
2015-01-01
Amorphous thin film oxygen evolving catalysts, OECs, of first-row transition metals show promise to serve as self-assembling photoanode materials in solar-driven, photoelectrochemical ‘artificial leaf’ devices. This report demonstrates the ability to use high-energy X-ray scattering and atomic pair distribution function analysis, PDF, to resolve structure in amorphous metal oxide catalyst films. The analysis is applied here to resolve domain structure differences induced by oxyanion substitution during the electrochemical assembly of amorphous cobalt oxide catalyst films, Co-OEC. PDF patterns for Co-OEC films formed using phosphate, Pi, methylphosphate, MPi, and borate, Bi, electrolyte buffers show that the resulting domains vary in size following the sequence Pi < MPi < Bi. The increases in domain size for CoMPi and CoBi were found to be correlated with increases in the contributions from bilayer and trilayer stacked domains having structures intermediate between those of the LiCoOO and CoO(OH) mineral forms. The lattice structures and offset stacking of adjacent layers in the partially stacked CoMPi and CoBi domains were best matched to those in the LiCoOO layered structure. The results demonstrate the ability of PDF analysis to elucidate features of domain size, structure, defect content and mesoscale organization for amorphous metal oxide catalysts that are not readily accessed by other X-ray techniques. PDF structure analysis is shown to provide a way to characterize domain structures in different forms of amorphous oxide catalysts, and hence provide an opportunity to investigate correlations between domain structure and catalytic activity. PMID:26634728
Jensen, Kirsten M Ø; Blichfeld, Anders B; Bauers, Sage R; Wood, Suzannah R; Dooryhée, Eric; Johnson, David C; Iversen, Bo B; Billinge, Simon J L
2015-09-01
By means of normal-incidence, high-flux and high-energy X-rays, total scattering data for pair distribution function (PDF) analysis have been obtained from thin films (tf), suitable for local structure analysis. By using amorphous substrates as support for the films, the standard Rapid Acquisition PDF setup can be applied and the scattering signal from the film can be isolated from the total scattering data through subtraction of an independently measured background signal. No angular corrections to the data are needed, as would be the case for grazing incidence measurements. The 'tfPDF' method is illustrated through studies of as-deposited (i.e. amorphous) and crystalline FeSb3 films, where the local structure analysis gives insight into the stabilization of the metastable skutterudite FeSb3 phase. The films were prepared by depositing ultra-thin alternating layers of Fe and Sb, which interdiffuse and after annealing crystallize to form the FeSb3 structure. The tfPDF data show that the amorphous precursor phase consists of corner-sharing FeSb6 octahedra with motifs highly resembling the local structure in crystalline FeSb3. Analysis of the amorphous structure allows the prediction of whether the final crystalline product will form the FeSb3 phase with or without excess Sb present. The study thus illustrates how analysis of the local structure in amorphous precursor films can help to understand crystallization processes of metastable phases and opens for a range of new local structure studies of thin films. PMID:26306190
Jensen, K. M.Ø.; Blichfeld, A. B.; Bauers, S. R.; Wood, S. R.; Dooryhee, E.; Johnson, D. C.; Iversen, B. B.; Billinge, S.
2015-07-05
By means of normal incidence, high flux and high energy x-rays, we have obtained total scattering data for Pair Distribution Function (PDF) analysis from thin films (tf), suitable for local structure analysis. By using amorphous substrates as support for the films, the standard Rapid Acquisition PDF setup can be applied and the scattering signal from the film can be isolated from the total scattering data through subtraction of an independently measured background signal. No angular corrections to the data are needed, as would be the case for grazing incidence measurements. We illustrate the ‘tfPDF’ method through studies of as depositedmore » (i.e. amorphous) and crystalline FeSb3 films, where the local structure analysis gives insight into the stabilization of the metastable skutterudite FeSb3 phase. The films were prepared by depositing ultra-thin alternating layers of Fe and Sb, which interdiffuse and after annealing crystallize to form the FeSb3 structure. The tfPDF data show that the amorphous precursor phase consists of corner-sharing FeSb6 octahedra with motifs highly resembling the local structure in crystalline FeSb3. Analysis of the amorphous structure allows predicting whether the final crystalline product will form the FeSb3 phase with or without excess Sb present. The study thus illustrates how analysis of the local structure in amorphous precursor films can help to understand crystallization processes of metastable phases and opens for a range of new local structure studies of thin films.« less
Jensen, K. M.Ø.; Blichfeld, A. B.; Bauers, S. R.; Wood, S. R.; Dooryhee, E.; Johnson, D. C.; Iversen, B. B.; Billinge, S.
2015-07-05
By means of normal incidence, high flux and high energy x-rays, we have obtained total scattering data for Pair Distribution Function (PDF) analysis from thin films (tf), suitable for local structure analysis. By using amorphous substrates as support for the films, the standard Rapid Acquisition PDF setup can be applied and the scattering signal from the film can be isolated from the total scattering data through subtraction of an independently measured background signal. No angular corrections to the data are needed, as would be the case for grazing incidence measurements. We illustrate the ‘tfPDF’ method through studies of as deposited (i.e. amorphous) and crystalline FeSb_{3} films, where the local structure analysis gives insight into the stabilization of the metastable skutterudite FeSb_{3} phase. The films were prepared by depositing ultra-thin alternating layers of Fe and Sb, which interdiffuse and after annealing crystallize to form the FeSb_{3} structure. The tfPDF data show that the amorphous precursor phase consists of corner-sharing FeSb_{6} octahedra with motifs highly resembling the local structure in crystalline FeSb_{3}. Analysis of the amorphous structure allows predicting whether the final crystalline product will form the FeSb_{3} phase with or without excess Sb present. The study thus illustrates how analysis of the local structure in amorphous precursor films can help to understand crystallization processes of metastable phases and opens for a range of new local structure studies of thin films.
Jensen, Kirsten M. Ø.; Blichfeld, Anders B.; Bauers, Sage R.; Wood, Suzannah R.; Dooryhée, Eric; Johnson, David C.; Iversen, Bo B.; Billinge, Simon J. L.
2015-01-01
By means of normal-incidence, high-flux and high-energy X-rays, total scattering data for pair distribution function (PDF) analysis have been obtained from thin films (tf), suitable for local structure analysis. By using amorphous substrates as support for the films, the standard Rapid Acquisition PDF setup can be applied and the scattering signal from the film can be isolated from the total scattering data through subtraction of an independently measured background signal. No angular corrections to the data are needed, as would be the case for grazing incidence measurements. The ‘tfPDF’ method is illustrated through studies of as-deposited (i.e. amorphous) and crystalline FeSb3 films, where the local structure analysis gives insight into the stabilization of the metastable skutterudite FeSb3 phase. The films were prepared by depositing ultra-thin alternating layers of Fe and Sb, which interdiffuse and after annealing crystallize to form the FeSb3 structure. The tfPDF data show that the amorphous precursor phase consists of corner-sharing FeSb6 octahedra with motifs highly resembling the local structure in crystalline FeSb3. Analysis of the amorphous structure allows the prediction of whether the final crystalline product will form the FeSb3 phase with or without excess Sb present. The study thus illustrates how analysis of the local structure in amorphous precursor films can help to understand crystallization processes of metastable phases and opens for a range of new local structure studies of thin films. PMID:26306190
Allan, Phoebe K; Griffin, John M; Darwiche, Ali; Borkiewicz, Olaf J; Wiaderek, Kamila M; Chapman, Karena W; Morris, Andrew J; Chupas, Peter J; Monconduit, Laure; Grey, Clare P
2016-02-24
Operando pair distribution function (PDF) analysis and ex situ (23)Na magic-angle spinning solid-state nuclear magnetic resonance (MAS ssNMR) spectroscopy are used to gain insight into the alloying mechanism of high-capacity antimony anodes for sodium-ion batteries. Subtraction of the PDF of crystalline NaxSb phases from the total PDF, an approach constrained by chemical phase information gained from (23)Na ssNMR in reference to relevant model compounds, identifies two previously uncharacterized intermediate species formed electrochemically; a-Na(3-x)Sb (x ≈ 0.4-0.5), a structure locally similar to crystalline Na3Sb (c-Na3Sb) but with significant numbers of sodium vacancies and a limited correlation length, and a-Na(1.7)Sb, a highly amorphous structure featuring some Sb-Sb bonding. The first sodiation breaks down the crystalline antimony to form first a-Na(3-x)Sb and, finally, crystalline Na3Sb. Desodiation results in the formation of an electrode formed of a composite of crystalline and amorphous antimony networks. We link the different reactivity of these networks to a series of sequential sodiation reactions manifesting as a cascade of processes observed in the electrochemical profile of subsequent cycles. The amorphous network reacts at higher voltages reforming a-Na(1.7)Sb, then a-Na(3-x)Sb, whereas lower potentials are required for the sodiation of crystalline antimony, which reacts to form a-Na(3-x)Sb without the formation of a-Na(1.7)Sb. a-Na(3-x)Sb is converted to crystalline Na3Sb at the end of the second discharge. We find no evidence of formation of NaSb. Variable temperature (23)Na NMR experiments reveal significant sodium mobility within c-Na3Sb; this is a possible contributing factor to the excellent rate performance of Sb anodes. PMID:26824406
NASA Astrophysics Data System (ADS)
Davis, Timur D.
2011-12-01
In the development of new medicinal products, poor oral bioavailability, due to the low solubilities of many active pharmaceutical ingredients (APIs), is increasingly a barrier for treatments to be administered using tablet or capsule formulations and one of the main challenges facing the pharmaceutical industry. Non-crystalline phases such as the amorphous and nanostructured states can confer increased solubility to a drug, and therefore, have recently garnered a lot of interest from pharmaceutical researchers. However, little is known about local ordering in non-crystalline pharmaceuticals due to the lack of reliable experimental probes, hindering the clinical application of these compounds. The powerful tools of crystallography begin to lose their potency for structures on the nanoscale; conventional X-ray powder diffraction (XRPD) patterns become broad and featureless in these cases and are not useful for differentiating between different local molecular packing arrangements. In this thesis, we introduce the use of high energy X-rays coupled with total scattering pair distribution function (TSPDF) and fingerprinting analysis to investigate the local structures of non-crystalline pharmaceutical compounds. The high energy X-rays allow us to experimentally collect diffuse scattering intensities, which contain information about a sample's local ordering, in addition to the Bragg scattering available in conventional XRPD experiments, while the TSPDF allows us to view the intra- and inter-molecular correlations in real space. The goal of this study was to address some fundamental problems involving fingerprinting non-crystalline APIs using TSPDF in order to lay the groundwork for the proper use of the technique by the pharmaceutical community. We achieved this by developing the methodology as well as the exploring the scientific implications. On the methodology side, we introduced PDFGetX3, a new software program for calculating TSPDFs that simplifies the procedure
2016-01-01
Operando pair distribution function (PDF) analysis and ex situ 23Na magic-angle spinning solid-state nuclear magnetic resonance (MAS ssNMR) spectroscopy are used to gain insight into the alloying mechanism of high-capacity antimony anodes for sodium-ion batteries. Subtraction of the PDF of crystalline NaxSb phases from the total PDF, an approach constrained by chemical phase information gained from 23Na ssNMR in reference to relevant model compounds, identifies two previously uncharacterized intermediate species formed electrochemically; a-Na3–xSb (x ≈ 0.4–0.5), a structure locally similar to crystalline Na3Sb (c-Na3Sb) but with significant numbers of sodium vacancies and a limited correlation length, and a-Na1.7Sb, a highly amorphous structure featuring some Sb–Sb bonding. The first sodiation breaks down the crystalline antimony to form first a-Na3–xSb and, finally, crystalline Na3Sb. Desodiation results in the formation of an electrode formed of a composite of crystalline and amorphous antimony networks. We link the different reactivity of these networks to a series of sequential sodiation reactions manifesting as a cascade of processes observed in the electrochemical profile of subsequent cycles. The amorphous network reacts at higher voltages reforming a-Na1.7Sb, then a-Na3–xSb, whereas lower potentials are required for the sodiation of crystalline antimony, which reacts to form a-Na3–xSb without the formation of a-Na1.7Sb. a-Na3–xSb is converted to crystalline Na3Sb at the end of the second discharge. We find no evidence of formation of NaSb. Variable temperature 23Na NMR experiments reveal significant sodium mobility within c-Na3Sb; this is a possible contributing factor to the excellent rate performance of Sb anodes. PMID:26824406
NASA Astrophysics Data System (ADS)
Shi, Chenyang
Structure and dynamics lie at the heart of the materials science. A detailed knowledge of both subjects would be foundational in understanding the materials' properties and predicting their potential applications. However, the task becomes increasingly dicult as the particle size is reduced to the nanometer scale. For nanostructured materials their laboratory x-ray scattering patterns are overlapped and broadened, making structure determination impossible. Atomic pair distribution function technique based on either synchrotron x-ray or neutron scattering data is known as the tool of choice for probing local structures. However, to solve the "structure problem" in low-dimensional materials with PDF is still challenging. For example for 2D materials of interest in this thesis the crystallographic modeling approach often yields unphysical thermal factors along stacking direction where new chemical intuitions about their actual structures and new modeling methodology/program are needed. Beyond this, lattice dynamical investigations on nanosized particles are extremely dicult. Laboratory tools such as Raman and infra-red only probe phonons at Brillouin zone center. Although in literature there are a great number of theoretical studies of their vibrational properties based on either empirical force elds or density functional theory, various approximations made in theories make the theoretical predictions less reliable. Also, there lacks the direct experiment result to validate the theory against. In this thesis, we studied the structure and dynamics of a wide variety of technologically relevant low-dimensional materials through synchrotron based x-ray PDF and high energy resolution inelastic x-ray scattering (HERIX) techniques. By collecting PDF data and employing advanced modeling program such as DiPy-CMI, we successfully determined the atomic structures of (i) emerging Ti3C2, Nb4C3 MXenes (transition metal carbides and/or nitrides) that are promising for energy storage
Pair correlation function integrals: Computation and use
NASA Astrophysics Data System (ADS)
Wedberg, Rasmus; O'Connell, John P.; Peters, Günther H.; Abildskov, Jens
2011-08-01
We describe a method for extending radial distribution functions obtained from molecular simulations of pure and mixed molecular fluids to arbitrary distances. The method allows total correlation function integrals to be reliably calculated from simulations of relatively small systems. The long-distance behavior of radial distribution functions is determined by requiring that the corresponding direct correlation functions follow certain approximations at long distances. We have briefly described the method and tested its performance in previous communications [R. Wedberg, J. P. O'Connell, G. H. Peters, and J. Abildskov, Mol. Simul. 36, 1243 (2010);, 10.1080/08927020903536366 Fluid Phase Equilib. 302, 32 (2011)], 10.1016/j.fluid.2010.10.004, but describe here its theoretical basis more thoroughly and derive long-distance approximations for the direct correlation functions. We describe the numerical implementation of the method in detail, and report numerical tests complementing previous results. Pure molecular fluids are here studied in the isothermal-isobaric ensemble with isothermal compressibilities evaluated from the total correlation function integrals and compared with values derived from volume fluctuations. For systems where the radial distribution function has structure beyond the sampling limit imposed by the system size, the integration is more reliable, and usually more accurate, than simple integral truncation.
Wesolowski, David J.; Wang, Hsiu -Wen; Page, Katharine L.; Naguib, Michael; Gogotsi, Yury
2015-12-08
MXenes are a recently discovered family of two-dimensional (2D) early transition metal carbides and carbonitrides, which have already shown many attractive properties and a great promise in energy storage and many other applications. However, a complex surface chemistry and small coherence length has been an obstacle in some applications of MXenes, also limiting accuracy of predictions of their properties. In this study, we describe and benchmark a novel way of modeling layered materials with real interfaces (diverse surface functional groups and stacking order between the adjacent monolayers) against experimental data. The structures of three kinds of Ti_{3}C_{2}T_{x} MXenes (T stands for surface terminating species, including O, OH, and F) produced under different synthesis conditions were resolved for the first time using atomic pair distribution function obtained by high-quality neutron total scattering. The true nature of the material can be easily captured with the sensitivity of neutron scattering to the surface species of interest and the detailed third-generation structure model we present. The modeling approach leads to new understanding of MXene structural properties and can replace the currently used idealized models in predictions of a variety of physical, chemical and functional properties of Ti_{3}C_{2}-based MXenes. Furthermore, the developed models can be employed to guide the design of new MXene materials with selected surface termination and controlled contact angle, catalytic, optical, electrochemical and other properties. We suggest that the multi-level structural modeling should form the basis for a generalized methodology on modeling diffraction and pair distribution function data for 2D and layered materials.
Multi-user distribution of polarization entangled photon pairs
NASA Astrophysics Data System (ADS)
Trapateau, J.; Ghalbouni, J.; Orieux, A.; Diamanti, E.; Zaquine, I.
2015-10-01
We experimentally demonstrate multi-user distribution of polarization entanglement using commercial telecom wavelength division demultiplexers. The entangled photon pairs are generated from a broadband source based on spontaneous parametric down conversion in a periodically poled lithium niobate crystal using a double path setup employing a Michelson interferometer and active phase stabilisation. We test and compare demultiplexers based on various technologies and analyze the effect of their characteristics, such as losses and polarization dependence, on the quality of the distributed entanglement for three channel pairs of each demultiplexer. In all cases, we obtain a Bell inequality violation, whose value depends on the demultiplexer features. This demonstrates that entanglement can be distributed to at least three user pairs of a network from a single source. Additionally, we verify for the best demultiplexer that the violation is maintained when the pairs are distributed over a total channel attenuation corresponding to 20 km of optical fiber. These techniques are therefore suitable for resource-efficient practical implementations of entanglement-based quantum key distribution and other quantum communication network applications.
Multi-user distribution of polarization entangled photon pairs
Trapateau, J.; Orieux, A.; Diamanti, E.; Zaquine, I.; Ghalbouni, J.
2015-10-14
We experimentally demonstrate multi-user distribution of polarization entanglement using commercial telecom wavelength division demultiplexers. The entangled photon pairs are generated from a broadband source based on spontaneous parametric down conversion in a periodically poled lithium niobate crystal using a double path setup employing a Michelson interferometer and active phase stabilisation. We test and compare demultiplexers based on various technologies and analyze the effect of their characteristics, such as losses and polarization dependence, on the quality of the distributed entanglement for three channel pairs of each demultiplexer. In all cases, we obtain a Bell inequality violation, whose value depends on the demultiplexer features. This demonstrates that entanglement can be distributed to at least three user pairs of a network from a single source. Additionally, we verify for the best demultiplexer that the violation is maintained when the pairs are distributed over a total channel attenuation corresponding to 20 km of optical fiber. These techniques are therefore suitable for resource-efficient practical implementations of entanglement-based quantum key distribution and other quantum communication network applications.
Božin, E S; Masadeh, A S; Hor, Y S; Mitchell, J F; Billinge, S J L
2011-01-28
The evolution of the short-range structural signature of the Ir4+ dimer state in CuIr2S4 thiospinel has been studied across the metal-insulator phase transitions as the metallic state is induced by temperature, Cr doping, and x-ray fluence. An atomic pair distribution function (PDF) approach reveals that there are no local dimers that survive into the metallic phase when this is invoked by temperature and doping. The PDF shows Ir4+ dimers when they exist, regardless of whether or not they are long-range ordered. At 100 K, exposure to a 98 keV x-ray beam melts the long-range dimer order within a few seconds, though the local dimers remain intact. This shows that the metallic state accessed on warming and doping is qualitatively different from the state obtained under x-ray irradiation. PMID:21405330
Distributed wireless quantum communication networks with partially entangled pairs
NASA Astrophysics Data System (ADS)
Yu, Xu-Tao; Zhang, Zai-Chen; Xu, Jin
2014-01-01
Wireless quantum communication networks transfer quantum state by teleportation. Existing research focuses on maximal entangled pairs. In this paper, we analyse the distributed wireless quantum communication networks with partially entangled pairs. A quantum routing scheme with multi-hop teleportation is proposed. With the proposed scheme, is not necessary for the quantum path to be consistent with the classical path. The quantum path and its associated classical path are established in a distributed way. Direct multi-hop teleportation is conducted on the selected path to transfer a quantum state from the source to the destination. Based on the feature of multi-hop teleportation using partially entangled pairs, if the node number of the quantum path is even, the destination node will add another teleportation at itself. We simulated the performance of distributed wireless quantum communication networks with a partially entangled state. The probability of transferring the quantum state successfully is statistically analyzed. Our work shows that multi-hop teleportation on distributed wireless quantum networks with partially entangled pairs is feasible.
Wong, Stanislaus; Papaefthymiou, Georgia C.; Lewis, Crystal S.; Han, Jinkyu; Zhang, Cheng; Li, Qiang; Shi, Chenyang; Abeykoon, A. M.Milinda; Billinge, Simon J.L.; Stach, Eric; et al
2015-05-06
The magnetic spinel ferrites, MFe₂O₄ (wherein 'M' = a divalent metal ion such as but not limited to Mn, Co, Zn, and Ni), represent a unique class of magnetic materials in which the rational introduction of different 'M's can yield correspondingly unique and interesting magnetic behaviors. Herein we present a generalized hydrothermal method for the synthesis of single-crystalline ferrite nanoparticles with 'M' = Mg, Fe, Co, Ni, Cu, and Zn, respectively, which can be systematically and efficaciously produced simply by changing the metal precursor. Our protocol can moreover lead to reproducible size control by judicious selection of various surfactants. Asmore » such, we have probed the effects of both (i) size and (ii) chemical composition upon the magnetic properties of these nanomaterials using complementary magnetometry and Mössbauer spectroscopy techniques. The structure of the samples was confirmed by atomic PDF analysis of X-ray and electron powder diffraction data as a function of particle size. These materials retain the bulk spinel structure to the smallest size (i.e., 3 nm). In addition, we have explored the catalytic potential of our ferrites as both (a) magnetically recoverable photocatalysts and (b) biological catalysts, and noted that many of our as-prepared ferrite systems evinced intrinsically higher activities as compared with their iron oxide analogues.« less
Wong, Stanislaus; Papaefthymiou, Georgia C.; Lewis, Crystal S.; Han, Jinkyu; Zhang, Cheng; Li, Qiang; Shi, Chenyang; Abeykoon, A. M.Milinda; Billinge, Simon J.L.; Stach, Eric; Thomas, Justin; Guerrero, Kevin; Munayco, Pablo; Munayco, Jimmy; Scorzelli, Rosa B.; Burnham, Philip; Viescas, Arthur J; Tiano, Amanda L.
2015-05-06
The magnetic spinel ferrites, MFe₂O₄ (wherein 'M' = a divalent metal ion such as but not limited to Mn, Co, Zn, and Ni), represent a unique class of magnetic materials in which the rational introduction of different 'M's can yield correspondingly unique and interesting magnetic behaviors. Herein we present a generalized hydrothermal method for the synthesis of single-crystalline ferrite nanoparticles with 'M' = Mg, Fe, Co, Ni, Cu, and Zn, respectively, which can be systematically and efficaciously produced simply by changing the metal precursor. Our protocol can moreover lead to reproducible size control by judicious selection of various surfactants. As such, we have probed the effects of both (i) size and (ii) chemical composition upon the magnetic properties of these nanomaterials using complementary magnetometry and Mössbauer spectroscopy techniques. The structure of the samples was confirmed by atomic PDF analysis of X-ray and electron powder diffraction data as a function of particle size. These materials retain the bulk spinel structure to the smallest size (i.e., 3 nm). In addition, we have explored the catalytic potential of our ferrites as both (a) magnetically recoverable photocatalysts and (b) biological catalysts, and noted that many of our as-prepared ferrite systems evinced intrinsically higher activities as compared with their iron oxide analogues.
Distance distributions of photogenerated charge pairs in organic photovoltaic cells.
Barker, Alex J; Chen, Kai; Hodgkiss, Justin M
2014-08-27
Strong Coulomb interactions in organic photovoltaic cells dictate that charges must separate over relatively long distances in order to circumvent geminate recombination and produce photocurrent. In this article, we measure the distance distributions of thermalized charge pairs by accessing a regime at low temperature where charge pairs are frozen out following the primary charge separation step and recombine monomolecularly via tunneling. The exponential attenuation of tunneling rate with distance provides a sensitive probe of the distance distribution of primary charge pairs, reminiscent of electron transfer studies in proteins. By fitting recombination dynamics to distributions of recombination rates, we identified populations of charge-transfer states and well-separated charge pairs. For the wide range of materials we studied, the yield of separated charges in the tunneling regime is strongly correlated with the yield of free charges measured via their intensity-dependent bimolecular recombination dynamics at room temperature. We therefore conclude that populations of free charges are established via long-range charge separation within the thermalization time scale, thus invoking early branching between free and bound charges across an energetic barrier. Subject to assumed values of the electron tunneling attenuation constant, we estimate critical charge separation distances of ∼3-4 nm in all materials. In some blends, large fullerene crystals can enhance charge separation yields; however, the important role of the polymers is also highlighted in blends that achieved significant charge separation with minimal fullerene concentration. We expect that our approach of isolating the intrinsic properties of primary charge pairs will be of considerable value in guiding new material development and testing the validity of proposed mechanisms for long-range charge separation. PMID:25102389
Nguyen-Phan, Thuy-Duong; Liu, Zongyuan; Luo, Si; Gamalski, Andrew D.; Vovchok, Dimitry; Xu, Wenqian; Stach, Eric A.; Polyansky, Dmitry E.; Fujita, Etsuko; Rodriguez, José A.; et al
2016-02-18
The functionalization of graphene oxide (GO) and graphene by TiO2 and other metal oxides has attracted considerable attention due to numerous promising applications in catalysis, energy conversion, and storage. We propose hydrogenation of this class of materials as a promising way to tune catalytic properties by altering the structural and chemical transformations that occur upon H incorporation. We also investigate the structural changes that occur during the hydrogenation process using in situ powder X-ray diffraction and pair distribution function analysis of GO–TiO2 and TiO2 under H2 reduction. Sequential Rietveld refinement was employed to gain insight into the evolution of crystalmore » growth of TiO2 nanoparticles in the presence of two-dimensional (2D) GO nanosheets. GO sheets not only significantly retarded the nucleation and growth of rutile impurities, stabilizing the anatase structure, but was also partially reduced to hydrogenated graphene by the introduction of atomic hydrogen into the honeycomb lattice. We discuss the hydrogenation processes and the resulting composite structure that occurs during the incorporation of atomic H and the dynamic structural transformations that leads to a highly active photocatalyst.« less
Pairing Nambu-Goldstone Modes within Nuclear Density Functional Theory.
Hinohara, Nobuo; Nazarewicz, Witold
2016-04-15
We show that the Nambu-Goldstone formalism of the broken gauge symmetry in the presence of the T=1 pairing condensate offers a quantitative description of the binding-energy differences of open-shell superfluid nuclei. We conclude that the pairing-rotational moments of inertia are excellent pairing indicators, which are free from ambiguities attributed to odd-mass systems. We offer a new, unified interpretation of the binding-energy differences traditionally viewed in the shell model picture as signatures of the valence nucleon properties. We present the first systematic analysis of the off-diagonal pairing-rotational moments of inertia and demonstrate the mixing of the neutron and proton pairing-rotational modes in the ground states of even-even nuclei. Finally, we discuss the importance of mass measurements of neutron-rich nuclei for constraining the pairing energy density functional. PMID:27127964
Pairing Nambu-Goldstone Modes within Nuclear Density Functional Theory
NASA Astrophysics Data System (ADS)
Hinohara, Nobuo; Nazarewicz, Witold
2016-04-01
We show that the Nambu-Goldstone formalism of the broken gauge symmetry in the presence of the T =1 pairing condensate offers a quantitative description of the binding-energy differences of open-shell superfluid nuclei. We conclude that the pairing-rotational moments of inertia are excellent pairing indicators, which are free from ambiguities attributed to odd-mass systems. We offer a new, unified interpretation of the binding-energy differences traditionally viewed in the shell model picture as signatures of the valence nucleon properties. We present the first systematic analysis of the off-diagonal pairing-rotational moments of inertia and demonstrate the mixing of the neutron and proton pairing-rotational modes in the ground states of even-even nuclei. Finally, we discuss the importance of mass measurements of neutron-rich nuclei for constraining the pairing energy density functional.
NASA Astrophysics Data System (ADS)
Petkov, V.; Shastri, S. D.
2010-04-01
We demonstrate how high-energy resonant x-ray diffraction (XRD) and differential atomic-pair-distribution function (PDF) analysis can be used to characterize the atomic ordering in materials of limited structural coherence with both excellent spatial resolution and element specificity. First we prove that this experimental approach is feasible by probing the K -absorption edge of Au(˜81keV) atoms in chemically ordered and disordered bulk Cu3Au alloys. The resulting Au-differential PDFs show very clearly the different ways Au atoms are known to occupy the sites of otherwise identical cubic lattices of those materials. Next we apply it to a more complex material: PtPd alloy and core-shell nanosized (˜2-4nm) particles by probing the K -absorption edge of Pt(˜78keV) . The resulting Pt-differential atomic PDFs reveal how exactly the atomic ordering of catalytically active Pt atoms is affected by the nanoparticles’ design, thus providing a firm structural basis for understanding their properties. The work is a step forward in expanding the limits of applicability of nontraditional XRD to the rapidly growing field of materials of unusual structural complexity.
Petkov, Valeri; Parvanov, Vencislav; Trikalitis, Pantelis; Malliakas, Christos; Vogt, Tom; Kanatzidis, Mercouri G
2005-06-22
The three-dimensional structures of emeraldine base polyaniline (PANI) and (polyaniline)(0.5)V(2)O(5) x 1.0 H(2)O have been determined by total X-ray scattering experiments. Atomic pair distribution functions (PDF) were measured to obtain experimental observables against which structural models were tested and refined. The PDF approach is necessary because of the limited structural coherence in these nanostructured materials. Polyaniline possesses a well-defined local atomic arrangement that can be described in terms of an 84-atom orthorhombic unit cell. The nanocomposite (PANI)(0.5)V(2)O(5) x 1.0 H(2)O too is locally well ordered and may be described in terms of a small number of structure-sensible parameters. The PDF approach allows the construction of structure models of PANI and (PANI)(0.5)V(2)O(5) x 1.0 H(2)O on the basis of which important materials' properties can be explained predicted and possibly improved. PMID:15954787
Im, Won Bin; Page, Katharine; DenBaars, Steven P.; Seshadri, Ram
2011-08-04
The compound LaSr{sub 2}AlO{sub 5} was recently introduced as a competitive Ce{sup 3+} host material for blue-pumped yellow phosphors for use in white light emitting diodes. A crucial feature of the crystal structure of LaSr{sub 2}AlO{sub 5} is that La, which is the host site for Ce{sup 3+}, is located in the 8h positions of the I4/mcm crystal structure, a site equally shared with Sr. While the average crystal structure of LaSr{sub 2}AlO{sub 5} as revealed by Rietveld analysis of laboratory and synchrotron X-ray diffraction data suggests nothing untoward, maximum entropy method analysis of the synchrotron X-ray data reveals the existence of conspicuous non-sphericity of the electron density. Pair distribution function analysis of the data suggests that despite their occupying the same crystallographic site, La and Sr possess distinct coordination environments, and the environment around La is more compact and regular than the environment suggested by the Rietveld refinement of the average structure. The absorption and emission from Ce{sup 3+} centers is controlled by the local coordination and symmetry, and the use of powerful new tools in unraveling details of these strengthens the rational search for new phosphors for solid state white lighting.
Petkov, V.; Shastri, S. D.; X-Ray Science Division; Central Michigan Univ.
2010-01-01
We demonstrate how high-energy resonant x-ray diffraction (XRD) and differential atomic-pair-distribution function (PDF) analysis can be used to characterize the atomic ordering in materials of limited structural coherence with both excellent spatial resolution and element specificity. First we prove that this experimental approach is feasible by probing the K-absorption edge of Au({approx}81 keV) atoms in chemically ordered and disordered bulk Cu3Au alloys. The resulting Au-differential PDFs show very clearly the different ways Au atoms are known to occupy the sites of otherwise identical cubic lattices of those materials. Next we apply it to a more complex material: PtPd alloy and core-shell nanosized ({approx}2-4 nm) particles by probing the K-absorption edge of Pt({approx}78 keV). The resulting Pt-differential atomic PDFs reveal how exactly the atomic ordering of catalytically active Pt atoms is affected by the nanoparticles design, thus providing a firm structural basis for understanding their properties. The work is a step forward in expanding the limits of applicability of nontraditional XRD to the rapidly growing field of materials of unusual structural complexity.
Synergy between pair coupled cluster doubles and pair density functional theory
Garza, Alejandro J.; Bulik, Ireneusz W.; Henderson, Thomas M.; Scuseria, Gustavo E.
2015-01-28
Pair coupled cluster doubles (pCCD) has been recently studied as a method capable of accounting for static correlation with low polynomial cost. We present three combinations of pCCD with Kohn–Sham functionals of the density and on-top pair density (the probability of finding two electrons on top of each other) to add dynamic correlation to pCCD without double counting. With a negligible increase in computational cost, these pCCD+DFT blends greatly improve upon pCCD in the description of typical problems where static and dynamic correlations are both important. We argue that—as a black-box method with low scaling, size-extensivity, size-consistency, and a simple quasidiagonal two-particle density matrix—pCCD is an excellent match for pair density functionals in this type of fusion of multireference wavefunctions with DFT.
Nucleon and nucleon-pair momentum distributions in A≤12 nuclei
Wiringa, Robert B.; Schiavilla, Rocco; Pieper, Steven C.; Carlson, Joseph A.
2014-02-10
We report variational Monte Carlo calculations of single-nucleon momentum distributions for A≤12 nuclei and nucleon-pair and nucleon-cluster momentum distributions for A≤8. The wave functions have been generated for a Hamiltonian containing the Argonne ν18 two-nucleon and Urbana X three-nucleon potentials. The single-nucleon and nucleon-pair momentum distributions exhibit universal features attributable to the one-pion-exchange tensor interaction The single-nucleon distributions are broken down into proton and neutron components and spin-up and spin-down components where appropriate. The nucleon-pair momentum distributions are given separately for pp and pn pairs. The nucleon-cluster momentum distributions include dp in 3He, tp and dd in S4He, αd inmore » 6Li,αt in 7Li, and αα in 8Be. Detailed tables are provided on-line for download.« less
Nucleon and nucleon-pair momentum distributions in A≤12 nuclei
Wiringa, Robert B.; Schiavilla, Rocco; Pieper, Steven C.; Carlson, Joseph A.
2014-02-10
We report variational Monte Carlo calculations of single-nucleon momentum distributions for A≤12 nuclei and nucleon-pair and nucleon-cluster momentum distributions for A≤8. The wave functions have been generated for a Hamiltonian containing the Argonne ν_{18} two-nucleon and Urbana X three-nucleon potentials. The single-nucleon and nucleon-pair momentum distributions exhibit universal features attributable to the one-pion-exchange tensor interaction The single-nucleon distributions are broken down into proton and neutron components and spin-up and spin-down components where appropriate. The nucleon-pair momentum distributions are given separately for pp and pn pairs. The nucleon-cluster momentum distributions include dp in ^{3}He, tp and dd in S^{4}He, αd in ^{6}Li,αt in ^{7}Li, and αα in ^{8}Be. Detailed tables are provided on-line for download.
Zeng,D.; Cabana, J.; Breger, J.; Yoon, W.; Grey, C.
2007-01-01
Several members of the compositional series Li[NixMnxCo(1-2x)]O2 (0.01 = x = 1/3) were synthesized and characterized. X-ray diffraction results confirm the presence of the layered a-NaFeO2-type structure, while X-ray absorption near-edge spectroscopy experiments verify the presence of Ni2+, Mn4+, and Co3+. Their local environment and short-range ordering were investigated by using a combination of 6Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and neutron pair distribution function (PDF) analysis, associated with reverse Monte Carlo (RMC) calculations. The 6Li MAS NMR spectra of compounds with low Ni/Mn contents (x = 0.10) show several well-resolved resonances, which start to merge when the amount of Ni and Mn increases, finally forming a broad resonance at high Ni/Mn contents. Analysis of the 6Li MAS NMR 6Li[Ni0.02Mn0.02Co0.96]O2 spectrum, is consistent with the formation of Ni2+ and Mn4+ clusters within the transition-metal layers, even at these low-doping levels. The oxidation state of Ni in this high Co content sample strongly depends upon the Li/transition metal ratio of the starting materials. Neutron PDF analysis of the highest Ni/Mn content sample Li[Ni1/3Mn1/3Co1/3]O2 shows a tendency for Ni cations to be close to Mn cations in the first coordination shell; however, the Co3+ ions are randomly distributed. Analysis of the intensity of the 'LiCoO2' resonance, arising from Li surrounded by Co3+ in its first two cation coordination shells, for the whole series provides further evidence for a nonrandom distribution of the transition-metal cations. The presence of the insulator-to-metal transition seen in the electrochemical profiles of these materials upon charging correlates strongly with the concentration of the 'LiCoO2' resonance.
Nuclear Parton Distribution Functions
I. Schienbein, J.Y. Yu, C. Keppel, J.G. Morfin, F. Olness, J.F. Owens
2009-06-01
We study nuclear effects of charged current deep inelastic neutrino-iron scattering in the framework of a {chi}{sup 2} analysis of parton distribution functions (PDFs). We extract a set of iron PDFs which are used to compute x{sub Bj}-dependent and Q{sup 2}-dependent nuclear correction factors for iron structure functions which are required in global analyses of free nucleon PDFs. We compare our results with nuclear correction factors from neutrino-nucleus scattering models and correction factors for charged-lepton--iron scattering. We find that, except for very high x{sub Bj}, our correction factors differ in both shape and magnitude from the correction factors of the models and charged-lepton scattering.
An efficient algorithm for generating random number pairs drawn from a bivariate normal distribution
NASA Technical Reports Server (NTRS)
Campbell, C. W.
1983-01-01
An efficient algorithm for generating random number pairs from a bivariate normal distribution was developed. Any desired value of the two means, two standard deviations, and correlation coefficient can be selected. Theoretically the technique is exact and in practice its accuracy is limited only by the quality of the uniform distribution random number generator, inaccuracies in computer function evaluation, and arithmetic. A FORTRAN routine was written to check the algorithm and good accuracy was obtained. Some small errors in the correlation coefficient were observed to vary in a surprisingly regular manner. A simple model was developed which explained the qualities aspects of the errors.
Mao, James X; Lee, Anita S; Kitchin, John R; Nulwala, Hunaid B; Luebke, David R; Damodaran, Krishnan
2013-04-24
Density Functional Theory is used to investigate a weakly coordinating room-temperature ionic liquid, 1-ethyl-3-methyl imidazolium tetracyanoborate ([Emim]{sup +}[TCB]{sup -}). Four locally stable conformers of the ion pair were located. Atoms-in-molecules (AIM) and electron density analysis indicated the existence of several hydrogen bonds. Further investigation through the Natural Bond Orbital (NBO) and Natural Energy Decomposition Analysis (NEDA) calculations provided insight into the origin of interactions in the [Emim]{sup +}[TCB]{sup -} ion pair. Strength of molecular interactions in the ionic liquid was correlated with frequency shifts of the characteristic vibrations of the ion pair. Harmonic vibrations of the ion pair were also compared with the experimental Raman and Infrared spectra. Vibrational frequencies were assigned by visualizing displacements of atoms around their equilibrium positions and through Potential Energy Distribution (PED) analysis.
Cluster pair correlation function of simple fluids: energetic connectivity criteria.
Pugnaloni, Luis A; Zarragoicoechea, Guillermo J; Vericat, Fernando
2006-11-21
We consider the clustering of Lennard-Jones particles by using an energetic connectivity criterion proposed long ago by Hill [J. Chem. Phys. 32, 617 (1955)] for the bond between pairs of particles. The criterion establishes that two particles are bonded (directly connected) if their relative kinetic energy is less than minus their relative potential energy. Thus, in general, it depends on the direction as well as on the magnitude of the velocities and positions of the particles. An integral equation for the pair connectedness function, proposed by two of the authors [Phys. Rev. E 61, R6067 (2000)], is solved for this criterion and the results are compared with those obtained from molecular dynamics simulations and from a connectedness Percus-Yevick-type integral equation for a velocity-averaged version of Hill's energetic criterion. PMID:17129128
The partial pair correlation functions of dense supercritical water
NASA Astrophysics Data System (ADS)
Tassaing, T.; Bellissent-Funel, M.-C.; Guillot, B.; Guissani, Y.
1998-05-01
Neutron diffraction measurements of heavy water and of two isotopic H2O/D2O mixtures at supercritical state (T = 380 °C and ρD2O = 0.73 g/cm3) are presented. In combining the set of neutron diffraction data with previous X-rays measurements of Yamanaka et al. (J. Chem. Phys., 101 (1994) 9830), it has been possible by using a Monte Carlo method to reach the partial pair correlation functions gOH(r), gHH(r) and gOO(r). The results are compared with molecular-dynamics simulations using the SPCE pair potential for water. These new results confirm that hydrogen bonding is still present in dense supercritical water.
Hyperdimensional analysis of amino acid pair distributions in proteins.
Henriksen, Svend B; Mortensen, Rasmus J; Geertz-Hansen, Henrik M; Neves-Petersen, Maria Teresa; Arnason, Omar; Söring, Jón; Petersen, Steffen B
2011-01-01
Our manuscript presents a novel approach to protein structure analyses. We have organized an 8-dimensional data cube with protein 3D-structural information from 8706 high-resolution non-redundant protein-chains with the aim of identifying packing rules at the amino acid pair level. The cube contains information about amino acid type, solvent accessibility, spatial and sequence distance, secondary structure and sequence length. We are able to pose structural queries to the data cube using program ProPack. The response is a 1, 2 or 3D graph. Whereas the response is of a statistical nature, the user can obtain an instant list of all PDB-structures where such pair is found. The user may select a particular structure, which is displayed highlighting the pair in question. The user may pose millions of different queries and for each one he will receive the answer in a few seconds. In order to demonstrate the capabilities of the data cube as well as the programs, we have selected well known structural features, disulphide bridges and salt bridges, where we illustrate how the queries are posed, and how answers are given. Motifs involving cysteines such as disulphide bridges, zinc-fingers and iron-sulfur clusters are clearly identified and differentiated. ProPack also reveals that whereas pairs of Lys residues virtually never appear in close spatial proximity, pairs of Arg are abundant and appear at close spatial distance, contrasting the belief that electrostatic repulsion would prevent this juxtaposition and that Arg-Lys is perceived as a conservative mutation. The presented programs can find and visualize novel packing preferences in proteins structures allowing the user to unravel correlations between pairs of amino acids. The new tools allow the user to view statistical information and visualize instantly the structures that underpin the statistical information, which is far from trivial with most other SW tools for protein structure analysis. PMID:22174733
Distribution functions of probabilistic automata
NASA Technical Reports Server (NTRS)
Vatan, F.
2001-01-01
Each probabilistic automaton M over an alphabet A defines a probability measure Prob sub(M) on the set of all finite and infinite words over A. We can identify a k letter alphabet A with the set {0, 1,..., k-1}, and, hence, we can consider every finite or infinite word w over A as a radix k expansion of a real number X(w) in the interval [0, 1]. This makes X(w) a random variable and the distribution function of M is defined as usual: F(x) := Prob sub(M) { w: X(w) < x }. Utilizing the fixed-point semantics (denotational semantics), extended to probabilistic computations, we investigate the distribution functions of probabilistic automata in detail. Automata with continuous distribution functions are characterized. By a new, and much more easier method, it is shown that the distribution function F(x) is an analytic function if it is a polynomial. Finally, answering a question posed by D. Knuth and A. Yao, we show that a polynomial distribution function F(x) on [0, 1] can be generated by a prob abilistic automaton iff all the roots of F'(x) = 0 in this interval, if any, are rational numbers. For this, we define two dynamical systems on the set of polynomial distributions and study attracting fixed points of random composition of these two systems.
Valence quark spin distribution functions
Nathan Isgur
1998-09-01
The hyperfine interactions of the constituent quark model provide a natural explanation for many nucleon properties, including the {Delta} - N splitting, the charge radius of the neutron, and the observation that the proton's quark distribution function ratio d(x)/u(x) {r_arrow} 0 as x {r_arrow} 1. The hyperfine-perturbed quark model also makes predictions for the nucleon spin-dependent distribution functions. Precision measurements of the resulting asymmetries A{sub 1}{sup p}(x) and A{sub 1}{sup n}(x) in the valence region can test this model and thereby the hypothesis that the valence quark spin distributions are ''normal''.
Distributed Pair Programming Using Collaboration Scripts: An Educational System and Initial Results
ERIC Educational Resources Information Center
Tsompanoudi, Despina; Satratzemi, Maya; Xinogalos, Stelios
2015-01-01
Since pair programming appeared in the literature as an effective method of teaching computer programming, many systems were developed to cover the application of pair programming over distance. Today's systems serve personal, professional and educational purposes allowing distributed teams to work together on the same programming project. The…
Kinematic distributions for electron pair production by muons
NASA Technical Reports Server (NTRS)
Linsker, R.
1972-01-01
Cross sections and kinematic distributions for the trident production process plus or negative muon plus charge yields plus or minus muon plus electron plus positron plus charge (with charge = dipion moment and Fe) are given for beam energies of 100 to 300 GeV at fixed (electron positron) masses from 5 to 15 GeV. This process is interesting as a test of quantum electrodynamics at high energies, and in particular as a test of the form of the photon propagator at large timelike (four-momentum) squared. For this purpose, it is desirable to impose kinematic cuts that favor those Bethe-Heitler graphs which contain a timelike photon propagator. It is found that there are substantial differences between the kinematic distributions for the full Bethe-Heitler matrix element and the distributions for the two timelike-photon graphs alone; these differences can be exploited in the selection of appropriate kinematic cuts.
Structure functions and parton distributions
Martin, A.D.; Stirling, W.J.; Roberts, R.G.
1995-07-01
The MRS parton distribution analysis is described. The latest sets are shown to give an excellent description of a wide range of deep-inelastic and other hard scattering data. Two important theoretical issues-the behavior of the distributions at small x and the flavor structure of the quark sea-are discussed in detail. A comparison with the new structure function data from HERA is made, and the outlook for the future is discussed.
Modeling the Pauli potential in the pair density functional theory.
Amovilli, C; Nagy, A
2008-11-28
In the ground state the pair density can be determined by solving a single auxiliary equation of a two-particle problem. A novel method for determining the Pauli potential entering this equation is presented and, starting from a reliable description of the pair density, an analytical expression is derived for atomic systems. Test calculations are presented for Be and isoelectronic C(2+) and O(4+) ions. PMID:19045853
Yield, variance and spatial distribution of electron-hole pairs in CsI
Gao, Fei; Xie, Y.; Kerisit, S.; Campbell, L. W.; Weber, William J
2011-01-01
A Monte Carlo method previously developed has been applied to simulate the interaction of photons with CsI over the energy range from 50 eV to ~ 1 MeV and the subsequent electron cascades, as well as various quantum mechanical processes. The MC model has been employed to investigate the creation and nano-scale spatial distribution of electron-hole pairs and to calculate important intrinsic properties, including the W value, which is the mean energy required to produce an electron-hole pair, and the Fano factor. At energies lower than 10 keV, W generally decreases with increasing photon energy from 19 to 15 eV, whereas it saturates to 15 eV for higher energies. However, W exhibits a sawtooth variation, and discontinuities at the shell edges that follow the photoionization cross sections. The Fano factor, F, generally increases with increasing energy, and has a value of 0.28 at energies higher than 10 keV. The decrease of W value up to 10 keV may account for the initial rise in relative light yield with incident energy, as observed in experiments in CsI, and this suggests that the nonlinearity at low energy range may be associated with intrinsic properties of materials. Also, the spatial distribution of e-h pairs shows that the e-h pairs are primarily distributed along fast electron tracks in CsI, but the density of electron-hole pairs is low. A significant number of electron-hole pairs are produced through the different ionization channels of core shells and corresponding relaxation processes, which may provide an explanation why the Fano factor in CsI is larger than that in Si or Ge. The spatial distribution and density of thermalized electron-hole pairs along the primary and secondary tracks are important for large scale simulations of electron-hole pair transport.
Moriya, Maki; Miyahara, Masahiko; Hokazono, Mana; Sasaki, Hirokazu; Nemoto, Atsushi; Katayama, Shingo; Akimoto, Yuji; Hirano, Shin-ichi; Ren, Yang
2014-10-01
The stable cycling performance with a high discharge capacity of similar to 190 mAh g(-1) in a carbon-hybridized Li2MnSiO4 nanostructured powder has prompted an experimental investigation of the charged/discharged structures using synchrotron-based and laboratory-based X-rays and atomic-pair distributionfunction (PDF) analyses. A novel method of in-situ spray pyrolysis of a precursor solution with glucose as a carbon source enabled the successful synthesis of the carbon-hybridized Li2(M)nSiO(4) nanoparticles. The XRD patters of the discharged (lithiated) samples exhibit a long-range ordered structure characteristic of the (beta) Li2MnSiO4 crystalline phase (space group Pmn2(1)) which dissipates in the charged (delithiated) samples. However, upon discharging the long-range ordered structure recovers in each cycle. The disordered structure, according to the PDF analysis, is mainly due to local distortions of the MnO4 tetrahedra which show a mean Mn-O nearest neighbor distance shorter than that of the long-range ordered phase. These results corroborate the notion of the smaller Mn3+/Mn4+ ionic radii in the Li extracted phase versus the larger Mn2+ ionic radius in Li inserted phase. Thus Li extraction/insertion drives the fluctuation between the disordered and the long-range ordered structures. (C) 2014 Elsevier B.V. All rights reserved.
Yield, variance and spatial distribution of electron–hole pairs in CsI
Gao, Fei; Xie, YuLong; Kerisit, Sebastien N.; Campbell, Luke W.; Weber, William J.
2011-10-01
A Monte Carlo (MC) method previously developed has been applied to simulate the interaction of photons, with energies ranging from 50 eV to ~ 1 MeV, with CsI and the subsequent electron cascades. The MC model has been employed to compute nano-scale spatial distributions of electron-hole pairs and important intrinsic properties, including W, the mean energy per electron-hole pair, and the Fano factor, F. W exhibits discontinuities at the shell edges that follow the photoionization cross sections and decreases with increasing photon energy (from ~19 to 15 eV), with an asymptotic value of 15.2 eV at high energy. This decrease may contribute the initial rise in relative light yield with incident energy observed experimentally for CsI, thus suggesting that nonlinearity may be associated with intrinsic properties of the material at low energies. F is calculated to increase with increasing energy and has an asymptotic value of 0.28. A significant number of electron-hole pairs are produced through the different ionization channels of core shells and corresponding relaxation processes, which may explain why F is larger for CsI than for Si or Ge. Finally, the calculated spatial distributions show that the electron-hole pairs are primarily distributed along fast electron tracks. These spatial distributions constitute important input for large-scale simulations of electron-hole pair transport.
The counterbalance theory for evolution and function of paired receptors.
Barclay, A Neil; Hatherley, Deborah
2008-11-14
Paired receptors are families of membrane proteins containing similar extracellular regions but differing in their potential for signaling with one type able to give inhibitory signals and the other activating. Inhibitory receptors could be good targets for pathogens to restrict immune responses against them. Here we suggest that activating members may have evolved to counterbalance pathogens utilizing the inhibitory pathway. Thus, if a pathogen utilizes any part of the inhibitory receptor to downregulate responses against itself, it may, because of similarities in structure, also bind the activating receptor and give an opposing signal. We evaluate recent structural data on SIRPalpha (signal regulatory protein) and LILRB1 (leukocyte immunoglobulin-like receptor subfamily B member 1) showing evidence of pathogen pressure in nonligand-binding regions of these receptors together with data on pathogen binding to PIRs (paired Ig-like receptors) to provide support for this theory. PMID:19006692
Unbiased estimators for spatial distribution functions of classical fluids.
Adib, Artur B; Jarzynski, Christopher
2005-01-01
We use a statistical-mechanical identity closely related to the familiar virial theorem, to derive unbiased estimators for spatial distribution functions of classical fluids. In particular, we obtain estimators for both the fluid density rho(r) in the vicinity of a fixed solute and the pair correlation g(r) of a homogeneous classical fluid. We illustrate the utility of our estimators with numerical examples, which reveal advantages over traditional histogram-based methods of computing such distributions. PMID:15638649
Familial Clustering of Executive Functioning in Affected Sibling Pair Families with ADHD
ERIC Educational Resources Information Center
Slaats-Willemse, Dorine; Swaab-Barneveld, Hanna; De Sonneville, Leo; Buitelaar, Jan
2005-01-01
Objective: To investigate familial clustering of executive functioning (i.e., response inhibition, fine visuomotor functioning, and attentional control) in attention-deficit/hyperactivity disorder (ADHD)-affected sibling pairs. Method: Fifty-two affected sibling pairs aged 6 to 18 years and diagnosed with ADHD according to DSM-IV performed the…
Variational derivation of equation for generalized pair correlation function
NASA Technical Reports Server (NTRS)
Malik, F. Bary
1992-01-01
The wavefunction of a system is explicitly written down in a fully anti-symmetric way between a fermion pair and a medium, and the equations for each one of them are derived from the variation of total energy for bound systems and by forming appropriate scalar products for continuum states. High-energy particles, such as protons, electrons, and nuclei impinging upon spacecraft, produce secondary radiations. In order to protect the internal environment of spacecraft from these radiations, their intensities are determined in many instances theoretically, and an appropriate program has been developed in the High Energy Science Branch. The purpose of this research is to investigate the problem of indistinguishability of an incident projectile with one of the same in a target.
Hoyer, Chad E; Gagliardi, Laura; Truhlar, Donald G
2015-11-01
Time-dependent Kohn-Sham density functional theory (TD-KS-DFT) is useful for calculating electronic excitation spectra of large systems, but the low-energy spectra are often complicated by artificially lowered higher-energy states. This affects even the lowest energy excited states. Here, by calculating the lowest energy spin-conserving excited state for atoms from H to K and for formaldehyde, we show that this problem does not occur in multiconfiguration pair-density functional theory (MC-PDFT). We use the tPBE on-top density functional, which is a translation of the PBE exchange-correlation functional. We compare to a robust multireference method, namely, complete active space second-order perturbation theory (CASPT2), and to TD-KS-DFT with two popular exchange-correlation functionals, PBE and PBE0. We find for atoms that the mean unsigned error (MUE) of MC-PDFT with the tPBE functional improves from 0.42 to 0.40 eV with a double set of diffuse functions, whereas the MUEs for PBE and PBE0 drastically increase from 0.74 to 2.49 eV and from 0.45 to 1.47 eV, respectively. PMID:26722961
NASA Astrophysics Data System (ADS)
Petkov, Valeri; Prasai, Binay; Shan, Shiyao; Ren, Yang; Wu, Jinfang; Cronk, Hannah; Luo, Jin; Zhong, Chuan-Jian
2016-05-01
Here we present the results from a study aimed at clarifying the relationship between the atomic structure and activity of nanocatalysts for chemical reactions driving fuel cells, such as the oxygen reduction reaction (ORR). In particular, using in operando high-energy X-ray diffraction (HE-XRD) we tracked the evolution of the atomic structure and activity of noble metal-transition metal (NM-TM) nanocatalysts for ORR as they function at the cathode of a fully operational proton exchange membrane fuel cell (PEMFC). Experimental HE-XRD data were analysed in terms of atomic pair distribution functions (PDFs) and compared to the current output of the PEMFC, which was also recorded during the experiments. The comparison revealed that under actual operating conditions, NM-TM nanocatalysts can undergo structural changes that differ significantly in both length-scale and dynamics and so can suffer losses in their ORR activity that differ significantly in both character and magnitude. Therefore we argue that strategies for reducing ORR activity losses should implement steps for achieving control not only over the length but also over the time-scale of the structural changes of NM-TM NPs that indeed occur during PEMFC operation. Moreover, we demonstrate how such a control can be achieved and thereby the performance of PEMFCs improved considerably. Last but not least, we argue that the unique capabilities of in operando HE-XRD coupled to atomic PDF analysis to characterize active nanocatalysts inside operating fuel cells both in a time-resolved manner and with atomic level resolution, i.e. in 4D, can serve well the ongoing search for nanocatalysts that deliver more with less platinum.Here we present the results from a study aimed at clarifying the relationship between the atomic structure and activity of nanocatalysts for chemical reactions driving fuel cells, such as the oxygen reduction reaction (ORR). In particular, using in operando high-energy X-ray diffraction (HE
Petkov, Valeri; Prasai, Binay; Shan, Shiyao; Ren, Yang; Wu, Jinfang; Cronk, Hannah; Luo, Jin; Zhong, Chuan-Jian
2016-05-19
Here we present the results from a study aimed at clarifying the relationship between the atomic structure and activity of nanocatalysts for chemical reactions driving fuel cells, such as the oxygen reduction reaction (ORR). In particular, using in operando high-energy X-ray diffraction (HE-XRD) we tracked the evolution of the atomic structure and activity of noble metal-transition metal (NM-TM) nanocatalysts for ORR as they function at the cathode of a fully operational proton exchange membrane fuel cell (PEMFC). Experimental HE-XRD data were analysed in terms of atomic pair distribution functions (PDFs) and compared to the current output of the PEMFC, which was also recorded during the experiments. The comparison revealed that under actual operating conditions, NM-TM nanocatalysts can undergo structural changes that differ significantly in both length-scale and dynamics and so can suffer losses in their ORR activity that differ significantly in both character and magnitude. Therefore we argue that strategies for reducing ORR activity losses should implement steps for achieving control not only over the length but also over the time-scale of the structural changes of NM-TM NPs that indeed occur during PEMFC operation. Moreover, we demonstrate how such a control can be achieved and thereby the performance of PEMFCs improved considerably. Last but not least, we argue that the unique capabilities of in operando HE-XRD coupled to atomic PDF analysis to characterize active nanocatalysts inside operating fuel cells both in a time-resolved manner and with atomic level resolution, i.e. in 4D, can serve well the ongoing search for nanocatalysts that deliver more with less platinum. PMID:27160891
Function transfer in human operant experiments: the role of stimulus pairings.
Tonneau, François; González, Carmen
2004-01-01
Although function transfer often has been studied in complex operant procedures (such as matching to sample), whether operant reinforcement actually produces function transfer in such settings has not been established. The present experiments, with high school students as subjects, suggest that stimulus pairings can promote function transfer in conditions that closely approximate those of matching to sample. In Experiment 1, the subjects showed transfer of operant responding from three geometric figures (C1, C2, C3) to three colored shapes (B1, B2, B3) when the latter were paired with the former. Experiment 2 involved two groups of subjects. In the matching group, subjects matched the colored shapes with the geometric figures; in the yoked group, the shapes were merely paired with the geometric figures, and the schedule of stimulus pairing was yoked to the performance of the subjects in the matching group. Both groups of subjects showed function transfer. Experiment 3 documented function transfer from C stimuli to B stimuli through indirect stimulus pairings (A-B, A-C). In Experiment 4, function transfer was obtained even though the subjects vocalized continuously during the pairing trials, presumably preventing covert verbalization that might mediate transfer effects. Our results are consistent with a Pavlovian account and raise difficulties for current operant theories of function transfer. PMID:15357508
The Differential cross section distribution of Drell-Yan dielectron pairs in the z boson mass region
Han, Jiyeon; /Rochester U.
2008-11-01
We report on a measurement of the rapidity distribution, d{sigma}/dy, for Z=Drell-Yan {yields} ee events produced in p{bar p} collisions at {radical}s = 1.96 TeV. The data sample consists of 2.13 fb{sup -1} corresponding to about 160,000 Z/Drell-Yan {yields} ee candidates in the Z boson mass region collected by the Collider Detector at Fermilab. The d{sigma}/dy distribution, which is measured over the full kinematic range for e{sup +}e{sup -} pairs in the invariant mass range 66 < M{sub ee} < 116 GeV/c{sup 2}, is compared with theory predictions. There is good agreement between the data and predictions of Quantum Chromodynamics in Next to Leading Order with the CTEQ6.1M Parton Distribution Functions.
Sweet complementarity: the functional pairing of glycans with lectins.
Gabius, H-J; Manning, J C; Kopitz, J; André, S; Kaltner, H
2016-05-01
Carbohydrates establish the third alphabet of life. As part of cellular glycoconjugates, the glycans generate a multitude of signals in a minimum of space. The presence of distinct glycotopes and the glycome diversity are mapped by sugar receptors (antibodies and lectins). Endogenous (tissue) lectins can read the sugar-encoded information and translate it into functional aspects of cell sociology. Illustrated by instructive examples, each glycan has its own ligand properties. Lectins with different folds can converge to target the same epitope, while intrafamily diversification enables functional cooperation and antagonism. The emerging evidence for the concept of a network calls for a detailed fingerprinting. Due to the high degree of plasticity and dynamics of the display of genes for lectins the validity of extrapolations between different organisms of the phylogenetic tree yet is inevitably limited. PMID:26956894
Function Transfer in Human Operant Experiments: The Role of Stimulus Pairings
ERIC Educational Resources Information Center
Tonneau, Francois; Gonzalez, Carmen
2004-01-01
Although function transfer often has been studied in complex operant procedures (such as matching to sample), whether operant reinforcement actually produces function transfer in such settings has not been established. The present experiments, with high school students as subjects, suggest that stimulus pairings can promote function transfer in…
Symmetric time warping, Boltzmann pair probabilities and functional genomics.
Clote, Peter; Straubhaar, Jürg
2006-07-01
Given two time series, possibly of different lengths, time warping is a method to construct an optimal alignment obtained by stretching or contracting time intervals. Unlike pairwise alignment of amino acid sequences, classical time warping, originally introduced for speech recognition, is not symmetric in the sense that the time warping distance between two time series is not necessarily equal to the time warping distance of the reversal of the time series. Here we design a new symmetric version of time warping, and present a formal proof of symmetry for our algorithm as well as for one of the variants of Aach and Church [1]. We additionally design quadratic time dynamic programming algorithms to compute both the forward and backward Boltzmann partition functions for symmetric time warping, and hence compute the Boltzmann probability that any two time series points are aligned. In the future, with the availability of increasingly long and accurate time series gene expression data, our algorithm can provide a sense of biological significance for aligned time points - e.g. our algorithm could be used to provide evidence that expression values of two genes have higher Boltzmann probability (say) in the G1 and S phase than in G2 and M phases. Algorithms, source code and web interface, developed by the first author, are made publicly available via the Boltzmann Time Warping web server at bioinformatics.bc.edu/clotelab/. PMID:16791652
NASA Astrophysics Data System (ADS)
Saito, Ikumi; Mizutani, Koichi; Wakatsuki, Naoto; Kawabe, Satoshi
2009-07-01
It is important to maintain an adequate indoor temperature for comfortable working conditions, improvement of the rate of production of farm goods grown in greenhouses, and for saving energy. Thus, it is necessary to measure the temperature distribution to realize efficient air-conditioning systems. However, we have to use many conventional instruments to measure the temperature distribution. We proposed a measurement system for vertical temperature distribution using a single pair of loudspeaker (SP) and microphone (MIC), and acoustic reflectors. This system consists of SP, MIC, and multiple acoustic reflectors, and it can be used to determine the temperature distribution from the mean temperature of the area bounded by two reflectors. In experiments, the vertical temperature distribution was measured using five sound probes in a large facility every 20 s for 24 h. From the results of this experiment, it was verified that this system can be used to measure the vertical temperature distribution from the mean temperature of each area bounded by two reflectors. This system could be used to measure the change in the temperature distribution over time. We constructed a simple system to measure the vertical temperature distribution.
Trelles-Sticken, Edgar; Dresser, Michael E.; Scherthan, Harry
2000-01-01
We have investigated the requirements for NDJ1 in meiotic telomere redistribution and clustering in synchronized cultures of Saccharomyces cerevisiae. On induction of wild-type meiosis, telomeres disperse from premeiotic aggregates over the nuclear periphery, and then cluster near the spindle pole body (bouquet arrangement) before dispersing again. In ndj1Δ meiocytes, telomeres are scattered throughout the nucleus and fail to form perinuclear meiosis-specific distribution patterns, suggesting that Ndj1p may function to tether meiotic telomeres to the nuclear periphery. Since ndj1Δ meiocytes fail to cluster their telomeres at any prophase stage, Ndj1p is the first protein shown to be required for bouquet formation in a synaptic organism. Analysis of homologue pairing by two-color fluorescence in situ hybridization with cosmid probes to regions on III, IX, and XI revealed that disruption of bouquet formation is associated with a significant delay (>2 h) of homologue pairing. An increased and persistent fraction of ndj1Δ meiocytes with Zip1p polycomplexes suggests that chromosome polarization is important for synapsis progression. Thus, our observations support the hypothesis that meiotic telomere clustering contributes to efficient homologue alignment and synaptic pairing. Under naturally occurring conditions, bouquet formation may allow for rapid sporulation and confer a selective advantage. PMID:11018056
NASA Astrophysics Data System (ADS)
Shabram, Megan; Jontof-Hutter, Daniel; Ford, Eric B.
2015-12-01
We characterize the mass-radius-eccentricity distribution of transiting planets near first-order mean motion resonances using Transit Timing Variation (TTV) observations from NASA's Kepler mission. Kepler's precise measurements of transit times (Mazeh et al. 2014; Rowe et al. 2015) constrain the planet-star mass ratio, eccentricity and pericenter directions for hundreds of planets. Strongly-interacting planetary systems allow TTVs to provide precise measurements of masses and orbital eccentricities separately (e.g., Kepler-36, Carter et al. 2012). In addition to these precisely characterized planetary systems, there are several systems harboring at least two planets near a mean motion resonance (MMR) for which TTVs provide a joint constraint on planet masses, eccentricities and pericenter directions (Hadden et al. 2015). Unfortunately, a near degeneracy between these parameters leads to a posterior probability density with highly correlated uncertainties. Nevertheless, the population encodes valuable information about the distribution of planet masses, orbital eccentricities and the planet mass-radius relationship. We characterize the distribution of masses and eccentricities for near-resonant transiting planets by combining a hierarchical Bayesian model with an analytic model for the TTV signatures of near-resonant planet pairs (Lithwick & Wu 2012). By developing a rigorous statistical framework for analyzing the TTV signatures of a population of planetary systems, we significantly improve upon previous analyses. For example, our analysis includes transit timing measurements of near-resonant transiting planet pairs regardless of whether there is a significant detection of TTVs, thereby avoiding biases due to only including TTV detections.
Linear Response Calculation using Canonical-basis TDHFB with a schematic pairing functional
Ebata, S.; Nakatsukasa, T.; Inakura, T.; Hashimoto, Y.; Yabana, K.
2010-08-12
We derive the Canonical-basis Time-Dependent Hartree-Fock-Bogoliubov (CbTDHFB) equations using time-dependent variational principle with a special pairing energy functional. We obtain the isoscalar quadrupole strength functions for Neon isotopes with small-amplitude CbTDHFB calculation in the three-dimensional coordinate-space representation.
Angular distribution of positrons in coherent pair production in deformed crystals
NASA Astrophysics Data System (ADS)
Parazian, V. V.
2009-05-01
We investigate the angular distribution of positrons in the coherent process electron-positron pair creation process by high-energy photons in a periodically deformed single crystal with a complex base. The formula for the corresponding differential cross section is derived for an arbitrary deformation field. The case is considered in detail when the photon enters into the crystal at small angles with respect to a crystallographic axis. The results of the numerical calculations are presented for SiO2 and diamond single crystals and Moliere parameterization of the screened atomic potentials in the case of the deformation field generated by an acoustic wave of S-type.
d sigma/dy Distribution of Drell-Yan Dielectron Pairs
Han, Jiyeon; Bodek, A.; Sakumoto, W.; Chung, Y.; /Rochester U.
2007-11-01
The authors report on the measurement of the rapidity distribution, d{sigma}/dY, over the full kinematic range for e{sup +}e{sup -} pairs produced in p{bar p} collisions at {radical}s = 1.96 TeV in the Z boson region of 66 < M{sub ee} < 116 GeV/c{sup 2}. The data sample consists of 1.1 fb{sup -1} of p{bar p} collisions at {radical}s = 1.96 TeV taken by the Collider Detector at Fermilab (CDF). The d{sigma}/dy is compared with the NLO theory prediction.
A Photographic View of Cumulative Distribution Functions
ERIC Educational Resources Information Center
Jernigan, Robert W.
2008-01-01
This article shows a concrete and easy recognizable view of a cumulative distribution function(cdf). Photograph views of the search tabs on dictionaries are used to increase students' understanding and facility with the concept of a cumulative distribution function. Projects for student investigations are also given. This motivation and view helps…
Wigner distribution function in nonlinear optics.
Dragoman, D
1996-07-20
Transformation laws for the Wigner distribution function, the radiant intensity, the radiant emittance, and the first- and second-order moments of the Wigner distribution function through an inhomogeneous, Kerr-type medium have been derived as well as for the beam quality factor and the kurtosis parameter. It is shown that the inhomogeneous Kerr-type medium can be approximated from the Wigner-distribution-function transformation-law point of view with a symplectic ABCD matrix with elements depending on the field distribution. PMID:21102821
The parton distribution function library
Plothow-Besch, H.
1995-07-01
This article describes an integrated package of Parton Density Functions called PDFLIB which has been added to the CERN Program Library Pool W999 and is labelled as W5051. In this package all the different sets of parton density functions of the Nucleon, Pion and the Photon which are available today have been put together. All these sets have been combined in a consistent way such that they all have similar calling sequences and no external data files have to be read in anymore. A default set has been prepared, although those preferring their own set or wanting to test a new one may do so within the package. The package also offers a program to calculate the strong coupling constant {alpha}, to first or second order. The correct {Lambda}{sub QCD} associated to the selected set of structure functions and the number of allowed flavours with respect to the given Q{sup 2} is automatically used in the calculation. The selection of sets, the program parameters as well as the possibilities to modify the defaults and to control errors occurred during execution are described.
Synthesis and characterization of bifunctional surfaces with tunable functional group pairs
NASA Astrophysics Data System (ADS)
Galloway, John M.; Kung, Mayfair; Kung, Harold H.
2016-06-01
Grafting of pairs of functional groups onto a silica surface was demonstrated by tethering both terminals of an organochlorosilane precursor molecule, Cl2(CH3)Si(CH2)4(CO)(OSi(i-Pr)2)(CH2)2Si(CH3)Cl2, that possess a cleavable silyl ester bond, onto a silica surface. Hydrolytic cleavage of the silyl ester bond of the grafted molecule resulted in the generation of organized pairs of carboxylic acid and organosilanol groups. This organosilanol moiety was easily transformed into other functional groups through condensation reactions to form, together with the neighboring acid group, pairs such as carboxylic acid/secondary amine, carboxylic acid/pyridine, and carboxylic acid/phosphine. In the case of carboxylic acid/amine pairing, there was evidence of the formation of amide. A sample grafted with amine-carboxylic acid pairs was three times more active (per free amine) than a sample without such pairs for the nitroaldol condensation of 4-nitrobenzaldehyde and nitromethane.
NASA Astrophysics Data System (ADS)
Bandyopadhyay, Arkamita; Pati, Swapan K.
2015-03-01
Density functional theory calculations have been performed on three charge transfer donor-acceptor (D-A) molecular pairs, i.e. naphthalene-diamine (Naph) and tetrathiafulvalene (TTF) molecules as electron donors and benzene-diimide (Diimide) and tetracyanoquinodimethane (TCNQ) as electron acceptors. Structural, charge transfer and optical properties of the systems have been studied. The D-A pairs then has been considered inside a macrocycle (cucurbit[8]uril) cavity and Naph-Diimide and TTF-Diimide pairs have been shown to exhibit changes in their structures and orientations, TTF-TCNQ pair does not show any significant structural change. Our work suggests that these changes in structures or orientations are result of electronic repulsion between the keto group oxygen atoms and it can lead to tuning of charge transfer and optical properties of the systems.
Separation of photo-induced radical pair in cryptochrome to a functionally critical distance
NASA Astrophysics Data System (ADS)
Solov'yov, Ilia A.; Domratcheva, Tatiana; Schulten, Klaus
2014-01-01
Cryptochrome is a blue light receptor that acts as a sensor for the geomagnetic field and assists many animals in long-range navigation. The magnetoreceptor function arises from light-induced formation of a radical pair through electron transfer between a flavin cofactor (FAD) and a triad of tryptophan residues. Here, this electron transfer is investigated by quantum chemical and classical molecular dynamics calculations. The results reveal how sequential electron transfer, assisted by rearrangement of polar side groups in the cryptochrome interior, can yield a FAD-Trp radical pair state with the FAD and Trp partners separated beyond a critical distance. The large radical pair separation reached establishes cryptochrome's sensitivity to the geomagnetic field through weakening of distance-dependent exchange and dipole-dipole interactions. It is estimated that the key secondary electron transfer step can overcome in speed both recombination (electron back-transfer) and proton transfer involving the radical pair reached after primary electron transfer.
Measurement device-independent quantum key distribution with heralded pair coherent state
NASA Astrophysics Data System (ADS)
Chen, Dong; Shang-Hong, Zhao; Lei, Shi
2016-07-01
The original measurement device-independent quantum key distribution is reviewed, and a modified protocol using heralded pair coherent state (HPCS) is proposed to overcome the quantum bit error rate associated with the dark count rate of the detectors in long-distance quantum key distribution. Our simulation indicates that the secure transmission distance can be improved evidently with HPCS owing to the lower probability of vacuum events when compared with weak coherent source scenario, while the secure key rate can be increased with HPCS due to the higher probability of single-photon events when compared with heralded single-photon source scenario. Furthermore, we apply the finite key analysis to the decoy state MDI-QKD with HPCS and obtain a practical key rate.
Plasma Dispersion Function for the Kappa Distribution
NASA Technical Reports Server (NTRS)
Podesta, John J.
2004-01-01
The plasma dispersion function is computed for a homogeneous isotropic plasma in which the particle velocities are distributed according to a Kappa distribution. An ordinary differential equation is derived for the plasma dispersion function and it is shown that the solution can be written in terms of Gauss' hypergeometric function. Using the extensive theory of the hypergeometric function, various mathematical properties of the plasma dispersion function are derived including symmetry relations, series expansions, integral representations, and closed form expressions for integer and half-integer values of K.
Particulate distribution function evolution for ejecta transport
Hammerberg, James Edward; Plohr, Bradley J
2010-01-01
The time evolution of the ejecta distribution function in a gas is discussed in the context of the recent experiments of W. Buttler and M. Zellner for well characterized Sn surfaces. Evolution equations are derived for the particulate distribution function when the dominant gas-particle interaction in is particulate drag. In the approximation of separability of the distribution function in velocity and size, the solution for the time dependent distribution function is a Fredholm integral equation of the first kind whose kernel is expressible in terms of the vacuum time dependent velocity distribution function measured with piezo probes or Asay foils. The solution of this equation in principle gives the size distribution function. We discuss the solution of this equation and the results of the Buttler - Zellner experiments. These suggest that correlations in velocity and size are necessary for a complete description of the transport dala. The solutions presented also represent an analytic test problem for the calculated distribution function in ejecta transport implementations.
An unnatural base pair system for efficient PCR amplification and functionalization of DNA molecules
Kimoto, Michiko; Kawai, Rie; Mitsui, Tsuneo; Yokoyama, Shigeyuki; Hirao, Ichiro
2009-01-01
Toward the expansion of the genetic alphabet, we present an unnatural base pair system for efficient PCR amplification, enabling the site-specific incorporation of extra functional components into DNA. This system can be applied to conventional PCR protocols employing DNA templates containing unnatural bases, natural and unnatural base triphosphates, and a 3′→5′ exonuclease-proficient DNA polymerase. For highly faithful and efficient PCR amplification involving the unnatural base pairing, we identified the natural-base sequences surrounding the unnatural bases in DNA templates by an in vitro selection technique, using a DNA library containing the unnatural base. The system facilitates the site-specific incorporation of a variety of modified unnatural bases, linked with functional groups of interest, into amplified DNA. DNA fragments (0.15 amol) containing the unnatural base pair can be amplified 107-fold by 30 cycles of PCR, with <1% total mutation rate of the unnatural base pair site. Using the system, we demonstrated efficient PCR amplification and functionalization of DNA fragments for the extremely sensitive detection of zeptomol-scale target DNA molecules from mixtures with excess amounts (pmol scale) of foreign DNA species. This unnatural base pair system will be applicable to a wide range of DNA/RNA-based technologies. PMID:19073696
Fog droplet distribution functions for lidar
Mallow, J.V.
1982-04-15
The interpretation of lidar data on fog has been limited by two obstacles: approximations in the form of the Mie scattering cross sections for water droplets, and droplet size distribution functions whose relationship to the experiment has not been clear. This paper develops a method for generating distribution functions from experimental data. These functions are then used with newly available Mie cross sections to obtain backscattering and extinction coefficients for singly scattered ruby laser pulses in fog. The results show what experimental lidar accuracies are needed to uniquely determine fog droplet size distribution.
Description of pairing correlation in many-body finite systems with density functional theory
NASA Astrophysics Data System (ADS)
Hupin, Guillaume; Lacroix, Denis
2011-02-01
Different steps leading to the new functional for pairing based on natural orbitals and occupancies proposed earlier [D. Lacroix and G. Hupin, Phys. Rev. BPLRBAQ1098-012110.1103/PhysRevB.82.144509 82, 144509 (2010)] are carefully analyzed. Properties of quasiparticle states projected onto good particle numbers are first reviewed. These properties are used to (i) prove the existence of such a functional, (ii) provide an explicit functional through a 1/N expansion starting from the BCS approach, and (iii) give a compact form of the functional summing up all orders in the expansion. The functional is benchmarked in the case of the picket-fence pairing Hamiltonian where even and odd systems are studied, using the blocking technique, at various particle numbers and coupling strengths, with uniform and random single-particle level spacing. In all cases, very good agreement is found, with a deviation of <1% compared to the exact energy.
NASA Astrophysics Data System (ADS)
Wiktor, Julia; Jomard, Gérald; Torrent, Marc; Barthe, Marie-France; Bertolus, Marjorie
2016-05-01
We performed calculations of momentum distributions of annihilating electron-positron pairs in various fully relaxed vacancy defects in SiC. We used self-consistent two-component density functional theory schemes to find the electronic and positronic densities and wave functions in the considered systems. Using the one-dimensional momentum distributions (Doppler-broadened annihilation radiation line shapes) we calculated the line-shape parameters S and W . We emphasize the effect of the experimental resolution and the choice of the integration ranges for the S and W parameters on the distributions of the points corresponding to different defects in the S (W ) plot. We performed calculation for two polytypes of SiC, 3 C , and 6 H and showed that for silicon vacancies and clusters containing this defect there were no significant differences between the Doppler spectra. The results of the Doppler spectra calculations were compared with experimental data obtained for n -type 6 H -SiC samples irradiated with 4-MeV Au ions. We observed a good general agreement between the measured and calculated points.
The uniqueness theorems of meromorphic functions sharing three values and one pair of values
NASA Astrophysics Data System (ADS)
Li, Xiao-Min; Yi, Hong-Xun
2008-03-01
In this paper, we deal with a uniqueness theorem of two meromorphic functions that have three weighted sharing values and one pair of values. The results in this paper improve those given by G.G. Gundersen, G. Brosch, T.C. Alzahary, T.C. Alzahary and H.X. Yi, I. Lahiri and P. Sahoo, and other authors.
Transversity distribution functions in the valon model
NASA Astrophysics Data System (ADS)
Alizadeh Yazdi, Z.; Taghavi-Shahri, F.; Arash, F.; Zomorrodian, M. E.
2014-05-01
We use the valon model to calculate the transversity distribution functions inside the nucleon. Transversity distributions indicate the probability to find partons with spin aligned (antialigned) to the transversely polarized nucleon. The results are in good agreement with all available experimental data and also global fits.
Extracting the kaon Collins function from e+e- hadron pair production data
NASA Astrophysics Data System (ADS)
Anselmino, M.; Boglione, M.; D'Alesio, U.; Hernandez, J. O. Gonzalez; Melis, S.; Murgia, F.; Prokudin, A.
2016-02-01
The latest data released by the BABAR Collaboration on azimuthal correlations measured for pion-kaon and kaon-kaon pairs produced in e+e- annihilations allow, for the first time, a direct extraction of the kaon Collins functions. These functions are then used to compute the kaon Collins asymmetries in semi-inclusive deep inelastic scattering processes, which result in good agreement with the measurements performed by the HERMES and COMPASS collaborations.
Generating functions for generalized binomial distributions
NASA Astrophysics Data System (ADS)
Bergeron, H.; Curado, E. M. F.; Gazeau, J. P.; Rodrigues, Ligia M. C. S.
2012-10-01
In a recent article generalization of the binomial distribution associated with a sequence of positive numbers was examined. The analysis of the nonnegativeness of the formal probability distributions was a key point to allow to give them a statistical interpretation in terms of probabilities. In this article we present an approach based on generating functions that solves the previous difficulties. Our main theorem makes explicit the conditions under which those formal probability distributions are always non-negative. Therefore, the constraints of non-negativeness are automatically fulfilled giving a complete characterization in terms of generating functions. A large number of analytical examples becomes available.
NASA Astrophysics Data System (ADS)
Henderson, D.; Plischke, M.
1987-04-01
Starting from well-known relations for the derivatives of the radial distribution functions of a mixture of fluids, and allowing the diameter of one particle to become exceedingly large, three sum rules for a fluid with density inhomogeneities are obtained. None of these sum rules are new. However, the relation between the Lovett-Mou-Buff-Wertheim and the Born-Green hierarchy of equations seems not well known. The accuracy of a recent parametrization of the pair correlation of hard spheres near a hard wall and of the solutions of the Percus-Yevick and hypernetted-chain equation for this same function are examined by determination of how well these functions satisfy these sum rules and the accuracy of their surface tension, calculated from the sum rule of Triezenberg and Zwanzig. Generally speaking, the Percus-Yevick theory gives the best results and the hypernetted-chain approximation gives the worst results with the parametrization being intermediate.
Measurement-device-independent quantum key distribution with pairs of vector vortex beams
NASA Astrophysics Data System (ADS)
Chen, Dong; Zhao, Shang-Hong; Shi, Lei; Liu, Yun
2016-03-01
The vector vortex (VV) beam, originally introduced to exhibit a form of single-particle quantum entanglement between different degrees of freedom, has specific applications for quantum-information protocols. In this paper, by combining measurement-device-independent quantum key distribution (MDIQKD) with a spontaneous parametric-downconversion source (SPDCS), we present a modified MDIQKD scheme with pairs of VV beams, which shows a structure of hybrid entangled entanglement corresponding to intrasystem entanglement and intersystem entanglement. The former entanglement, which is entangled between polarization and orbit angular momentum within each VV beam, is adopted to overcome the polarization misalignment associated with random rotations in quantum key distribution. The latter entanglement, which is entangled between the two VV beams, is used to perform the MDIQKD protocol with SPDCS to inherit the merit of the heralded process. The numerical simulations show that our modified scheme has apparent advances both in transmission distance and key-generation rate compared to the original MDIQKD. Furthermore, our modified protocol only needs to insert q plates in a practical experiment.
Pair-flowered cymes in the Lamiales: structure, distribution and origin
Weber, Anton
2013-01-01
Background and Aims In the Lamiales, indeterminate thyrses (made up of axillary cymes) represent a significant inflorescence type. However, it has been largely overlooked that there occur two types of cymes: (1) ordinary cymes, and (2) ‘pair-flowered cymes’ (PFCs), with a flower pair (terminal and front flower) topping each cyme unit. PFCs are unique to the Lamiales and their distribution, origin and phylogeny are not well understood. Methods The Lamiales are screened as to the occurrence of PFCs, ordinary cymes and single flowers (constituting racemic inflorescences). Key Results PFCs are shown to exhibit a considerable morphological and developmental diversity and are documented to occur in four neighbouring taxa of Lamiales: Calceolariaceae, Sanango, Gesneriaceae and Plantaginaceae. They are omnipresent in the Calceolariaceae and almost so in the Gesneriaceae. In the Plantaginaceae, PFCs are restricted to the small sister tribes Russelieae and Cheloneae (while the large remainder has single flowers in the leaf/bract axils; ordinary cymes do not occur). Regarding the origin of PFCs, the inflorescences of the genus Peltanthera (unplaced as to family; sister to Calceolariaceae, Sanango and Gesneriaceae in most molecular phylogenies) support the idea that PFCs have originated from paniculate systems, with the front-flowers representing remnant flowers. Conclusions From the exclusive occurrence of PFCs in the Lamiales and the proximity of the respective taxa in molecular phylogenies it may be expected that PFCs have originated once, representing a synapomorphy for this group of taxa and fading out within the Plantaginaceae. However, molecular evidence is ambiguous. Depending on the position of Peltanthera (depending in turn on the kind and number of genes and taxa analysed) a single, a double (the most probable scenario) or a triple origin appears conceivable. PMID:23884395
NASA Astrophysics Data System (ADS)
Afanasjev, A. V.; Abdurazakov, O.
2013-07-01
The cranked relativistic Hartree-Bogoliubov theory has been applied for a systematic study of pairing and rotational properties of actinides and light superheavy nuclei. Pairing correlations are taken into account by the Brink-Booker part of finite-range Gogny D1S force. For the first time, in the covariant density functional theory (CDFT) framework, the pairing properties of deformed nuclei are studied via the quantities (such as three-point Δ(3) indicators) related to odd-even mass staggerings. The investigation of the moments of inertia at low spin and the Δ(3) indicators shows the need for an attenuation of the strength of the Brink-Booker part of the Gogny D1S force in pairing channel. The investigation of rotational properties of even-even and odd-mass nuclei at normal deformation, performed in the density functional theory framework in such a systematic way for the first time, reveals that in the majority of the cases the experimental data are well described. These include the evolution of the moments of inertia with spin, band crossings in the A≥242 nuclei, the impact of the particle in specific orbital on the moments of inertia in odd-mass nuclei. The analysis of the discrepancies between theory and experiment in the band crossing region of A≤240 nuclei suggests the stabilization of octupole deformation at high spin, not included in the present calculations. The evolution of pairing with deformation, which is important for the fission barriers, has been investigated via the analysis of the moments of inertia in the superdeformed minimum. The dependence of the results on the CDFT parametrization has been studied by comparing the results of the calculations obtained with the NL1 and NL3* parametrizations.
Carlson, Rebecca K; Li Manni, Giovanni; Sonnenberger, Andrew L; Truhlar, Donald G; Gagliardi, Laura
2015-01-13
Kohn-Sham density functional theory, resting on the representation of the electronic density and kinetic energy by a single Slater determinant, has revolutionized chemistry, but for open-shell systems, the Kohn-Sham Slater determinant has the wrong symmetry properties as compared to an accurate wave function. We have recently proposed a theory, called multiconfiguration pair-density functional theory (MC-PDFT), in which the electronic kinetic energy and classical Coulomb energy are calculated from a multiconfiguration wave function with the correct symmetry properties, and the rest of the energy is calculated from a density functional, called the on-top density functional, that depends on the density and the on-top pair density calculated from this wave function. We also proposed a simple way to approximate the on-top density functional by translation of Kohn-Sham exchange-correlation functionals. The method is much less expensive than other post-SCF methods for calculating the dynamical correlation energy starting with a multiconfiguration self-consistent-field wave function as the reference wave function, and initial tests of the theory were quite encouraging. Here, we provide a broader test of the theory by applying it to bond energies of main-group molecules and transition metal complexes, barrier heights and reaction energies for diverse chemical reactions, proton affinities, and the water dimerization energy. Averaged over 56 data points, the mean unsigned error is 3.2 kcal/mol for MC-PDFT, as compared to 6.9 kcal/mol for Kohn-Sham theory with a comparable density functional. MC-PDFT is more accurate on average than complete active space second-order perturbation theory (CASPT2) for main-group small-molecule bond energies, alkyl bond dissociation energies, transition-metal-ligand bond energies, proton affinities, and the water dimerization energy. PMID:26574206
Electron energy-distribution functions in gases
Pitchford, L.C.
1981-01-01
Numerical calculation of the electron energy distribution functions in the regime of drift tube experiments is discussed. The discussion is limited to constant applied fields and values of E/N (ratio of electric field strength to neutral density) low enough that electron growth due to ionization can be neglected. (GHT)
Calculation of the Poisson cumulative distribution function
NASA Technical Reports Server (NTRS)
Bowerman, Paul N.; Nolty, Robert G.; Scheuer, Ernest M.
1990-01-01
A method for calculating the Poisson cdf (cumulative distribution function) is presented. The method avoids computer underflow and overflow during the process. The computer program uses this technique to calculate the Poisson cdf for arbitrary inputs. An algorithm that determines the Poisson parameter required to yield a specified value of the cdf is presented.
Probability distribution functions in turbulent convection
NASA Technical Reports Server (NTRS)
Balachandar, S.; Sirovich, L.
1991-01-01
Results of an extensive investigation of probability distribution functions (pdfs) for Rayleigh-Benard convection, in hard turbulence regime, are presented. It is shown that the pdfs exhibit a high degree of internal universality. In certain cases this universality is established within two Kolmogorov scales of a boundary. A discussion of the factors leading to the universality is presented.
Weibel instability with semirelativistic Maxwellian distribution function
Zaheer, S.; Murtaza, G.
2007-07-15
A macroscopic description of the linear Weibel instability, based on semirelativistic distribution in an unmagnetized plasma is presented. In particular, analytical expressions are derived for the real and imaginary parts of the dielectric constant for the Maxwellian and semirelativistic Maxwellian distribution functions under the conditions of {xi}=({omega}/k{sub parallel}{theta}{sub parallel})>>1 and <<1. The real frequency and the growth rate of the instability for the semirelativistic case now depends upon the factor {chi} generated from the relativistic term in the distribution function. The presence of {chi} which is always greater than unity favors the Weibel instability to occur even for the small anisotropy of temperature. As we increase the value of {chi} large enough that it dominates over other terms, the damping changes into growth. In the limiting case, i.e., {chi}=1, the results approach the Maxwellian situation.
NASA Technical Reports Server (NTRS)
Chong, D. P.; Langhoff, S. R.
1986-01-01
A modified coupled pair functional (CPF) method is presented for the configuration interaction problem that dramatically improves properties for cases where the Hartree-Fock reference configuration is not a good zeroth-order wave function description. It is shown that the tendency for CPF to overestimate the effect of higher excitations arises from the choice of the geometric mean for the partial normalization denominator. The modified method is demonstrated for ground state dipole moment calculations of the NiH, CuH, and ZnH transition metal hydrides, and compared to singles-plus-doubles configuration interaction and the Ahlrichs et al. (1984) CPF method.
Hietanen, A.
1971-01-01
Distribution of major and minor elements has been determined for five hornblende-biotite pairs from hornblende-biotite quartz diorite and monzotonalite and for a clinopyroxene-orthopyroxene pair from pyroxene diorite collected from the border zones and centers of zoned plutons in the northern Sierra Nevada, California. The distribution coefficients Kd [Mg/Fe] for biotite/hornblende are of the same magnitude (0.61-0.67) for both the mafic border zone and the silicic center. For comparison, KD [Mg/Fe] values for biotite/hornblende from plutonic rocks of the central Sierra Nevada and the southern California batholith were calculated from data published by others. Rocks of the oldest age group (ca. 150 m.y.) in the central Sierra Nevada have an average distribution coefficient, KD, of 0.64, close to the average KD in the study area, where K-Ar dates are 143 to 129 m.y. The intermediate age group has an average KD=0.81, and the youngest group has KD=0.77. KD [Mg/Fe] for biotite/hornblende from the southern California batholith is 0.83, close to the average of the intermediate age group in the central Sierra Nevada. The calculated difference in pressure of crystallization between rocks of the Feather River area and the southern California batholith is 1 kb; the rocks of the Feather River area being crystallized at a higher pressure. This is in good agreement with the low-pressure contact metamorphism in the south (pyroxene hornfels facies), as compared with a medium-pressure metamorphism around the northern plutons, where andalusitesillimanite-cordierite and andalusite-staurolite subfacies of the amphibolite facies indicate pressures of about 4 kb. Trace elements Cr, V, Ni, Co, Ga are distributed equally between biotite and hornblende, whereas Ba and possibly Cu are concentrated in biotite and Sr and Sc and possibly Zr in hornblende. ?? 1971 Springer-Verlag.
Recent progress on nuclear parton distribution functions
NASA Astrophysics Data System (ADS)
Hirai, M.; Kumano, S.; Saito, K.
2011-09-01
We report current status of global analyses on nuclear parton distribution functions (NPDFs). The optimum NPDFs are determined by analyzing high-energy nuclear reaction data. Due to limited experimental measurements, antiquark modifications have large uncertainties at x > 0.2 and gluon modifications cannot be determined. A nuclear modification difference between u and d quark distributions could be an origin of the long-standing NuTeV sin2θw anomaly. There is also an issue of nuclear modification differences between the structure functions of charged-lepton and neutrino reactions. Next, nuclear clustering effects are discussed in structure functions F2A as a possible explanation for an anomalous result in the 9Be nucleus at the Thomas Jefferson National Accelerator Facility (JLab). Last, tensor-polarized quark and antiquark distribution functions are extracted from HERMES data on the polarized structure function b1 of the deuteron, and they could be used for testing theoretical models and for proposing future experiments, for example, the one at JLab. Such measurements could open a new field of spin physics in spin-one hadrons.
Wigner distribution function for finite signals
NASA Astrophysics Data System (ADS)
Wolf, Kurt B.; Atakishiyev, Natig M.; Chumakov, Sergey M.
1997-07-01
We construct a bilinear form with the properties of the Wigner distribution function for a model of finite optics: the multimodal linear waveguide. This is a guide that can carry a finite number of oscillator modes, and sends/reads the data by an equal number of sensors. The Wigner distribution function is a function of the classical observables of position and momentum, as well as the mode content; it provides a visual image corresponding to the (`musical') score of the signal. The dynamical group for this model is SU(2) and the wavefunctions span the space of a finite-dimensional irreducible representation of this group. Phase space is a sphere and the linear optical transformations are: translations along the waveguide, refractive wedges and inclined slabs, which correspond to rotations around the 3-, 1-, and 2-axes, respectively. Coherent and Schrodinger cat states are readily identified.
Metal-ligand multiple bonds as frustrated Lewis pairs for C-H functionalization.
Whited, Matthew T
2012-01-01
The concept of frustrated Lewis pairs (FLPs) has received considerable attention of late, and numerous reports have demonstrated the power of non- or weakly interacting Lewis acid-base pairs for the cooperative activation of small molecules. Although most studies have focused on the use of organic or main-group FLPs that utilize steric encumbrance to prevent adduct formation, a related strategy can be envisioned for both organic and inorganic complexes, in which "electronic frustration" engenders reactivity consistent with both nucleophilic (basic) and electrophilic (acidic) character. Here we propose that such a description is consistent with the behavior of many coordinatively unsaturated transition-metal species featuring metal-ligand multiple bonds, and we further demonstrate that the resultant reactivity may be a powerful tool for the functionalization of C-H and E-H bonds. PMID:23209486
Molecular Interactions in 1-Ethyl-3-methylimidazolium Acetate Ion Pair: A Density Functional Study
NASA Astrophysics Data System (ADS)
Dhumal, Nilesh R.; Kim, Hyung J.; Kiefer, Johannes
2009-08-01
The density functional method is used to obtain the molecular structure, electron density topography, and vibrational frequencies of the ion pair 1-ethyl-3-methylimidazolium acetate. Different conformers are simulated on the basis of molecular interactions between the 1-ethyl-3-methylimidazolium cation and acetate anion. The lowest energy conformers exhibit strong C-H···O interionic interactions compared with other conformers. Characteristic vibrational frequencies of the ion pair and their shifts with respect to free ions are analyzed via the natural bond orbitals and difference electron density maps coupled with molecular electron density topology. Theoretically scaled vibrational frequencies are also compared with the spontaneous Raman scattering and attenuated total reflection infrared absorption measurements.
Fiedler, Klaus
2016-02-01
Drawing on illustrative examples of the functional and cognitive psychology in contemporary research, the present article emphasizes the primacy of functional relationships, which provide the fundament for all attempts to uncover invisible cognitive processes. Cognitive research is not only inherently more difficult and much more ambitious than functional research. It also suffers from several home-made problems, such as unwarranted inferences from model fitting, the mediation-analysis cult and the failure to take environmental influences into account. However, despite the primacy of functional psychology and the problems associated with the ambitious goals of cognitive research, the two partners in this unequal pair are firmly connected and jointly responsible for the most impressive examples of progress in behavioural science. PMID:25921294
Representations and uses of light distribution functions
NASA Astrophysics Data System (ADS)
Lalonde, Paul Albert
1998-11-01
At their lowest level, all rendering algorithms depend on models of local illumination to define the interplay of light with the surfaces being rendered. These models depend both on the representations of light scattering at a surface due to reflection and to an equal extent on the representation of light sources and light fields. Both emission and reflection have in common that they describe how light leaves a surface as a function of direction. Reflection also depends on an incident light direction. Emission can depend on the position on the light source We call the functions representing emission and reflection light distribution functions (LDF's). There are some difficulties to using measured light distribution functions. The data sets are very large-the size of the data grows with the fourth power of the sampling resolution. For example, a bidirectional reflectance distribution function (BRDF) sampled at five degrees angular resolution, which is arguably insufficient to capture highlights and other high frequency effects in the reflection, can easily require one and a half million samples. Once acquired this data requires some form of interpolation to use them. Any compression method used must be efficient, both in space and in the time required to evaluate the function at a point or over a range of points. This dissertation examines a wavelet representation of light distribution functions that addresses these issues. A data structure is presented that allows efficient reconstruction of LDFs for a given set of parameters, making the wavelet representation feasible for rendering tasks. Texture mapping methods that take advantage of our LDF representations are examined, as well as techniques for filtering LDFs, and methods for using wavelet compressed bidirection reflectance distribution functions (BRDFs) and light sources with Monte Carlo path tracing algorithms. The wavelet representation effectively compresses BRDF and emission data while inducing only a
TRANSVERSE POLARIZATION DISTRIBUTION AND FRAGMENTATION FUNCTIONS
BOER,D.
2000-04-11
The authors discuss transverse polarization distribution and fragmentation functions, in particular, T-odd functions with transverse momentum dependence, which might be relevant for the description of single transverse spin asymmetries. The role of intrinsic transverse momentum in the expansion in inverse powers of the hard scale is elaborated upon. The sin {phi} single spin asymmetry in the process e {rvec p} {r_arrow} e{prime} {pi}{sup +} X as recently reported by the HERMES Collaboration is investigated, in particular, by using the bag model.
Functional neuroimaging study in identical twin pairs discordant for regular cigarette smoking.
Lessov-Schlaggar, Christina N; Lepore, Rebecca L; Kristjansson, Sean D; Schlaggar, Bradley L; Barnes, Kelly Anne; Petersen, Steven E; Madden, Pamela A F; Heath, Andrew C; Barch, Deanna M
2013-01-01
Despite the tremendous public health and financial burden of cigarette smoking, relatively little is understood about brain mechanisms that subserve smoking behavior. This study investigated the effect of lifetime regular smoking on brain processing in a reward guessing task using functional magnetic resonance imaging and a co-twin control study design in monozygotic (MZ) twin pairs that maximally controls for genetic and family background factors. Young adult (24-34 years) MZ female twin pairs (n = 15 pairs), discordant for regular smoking defined using Centers for Disease Control criteria as having smoked ≥100 cigarettes in their lifetime, were recruited from an ongoing genetic epidemiological longitudinal study of substance use and psychopathology. We applied hypothesis-driven region of interest (ROI) and whole-brain analyses to investigate the effect of regular smoking on reward processing. Reduced response to reward and punishment in regular compared with never-regular smokers was seen in hypothesis-driven ROI analysis of bilateral ventral striatum. Whole-brain analysis identified bilateral reward-processing regions that showed activation differences in response to winning or losing money but no effect of regular smoking; and frontal/parietal regions, predominantly in the right hemisphere, that showed robust effect of regular smoking but no effect of winning or losing money. Altogether, using a study design that maximally controls for group differences, we found that regular smoking had modest effects on striatal reward processing regions but robust effects on cognitive control/attentional systems. PMID:22340136
S-pairing in neutron matter: I. Correlated basis function theory
NASA Astrophysics Data System (ADS)
Fabrocini, Adelchi; Fantoni, Stefano; Illarionov, Alexey Yu.; Schmidt, Kevin E.
2008-05-01
S-wave pairing in neutron matter is studied within an extension of correlated basis function (CBF) theory to include the strong, short range spatial correlations due to realistic nuclear forces and the pairing correlations of the Bardeen, Cooper and Schrieffer (BCS) approach. The correlation operator contains central as well as tensor components. The correlated BCS scheme of [S. Fantoni, Nucl. Phys. A 363 (1981) 381], developed for simple scalar correlations, is generalized to this more realistic case. The energy of the correlated pair condensed phase of neutron matter is evaluated at the two-body order of the cluster expansion, but considering the one-body density and the corresponding energy vertex corrections at the first order of the Power Series expansion. Based on these approximations, we have derived a system of Euler equations for the correlation factors and for the BCS amplitudes, resulting in correlated nonlinear gap equations, formally close to the standard BCS ones. These equations have been solved for the momentum independent part of several realistic potentials (Reid, Argonne v and Argonne v) to stress the role of the tensor correlations and of the many-body effects. Simple Jastrow correlations and/or the lack of the density corrections enhance the gap with respect to uncorrelated BCS, whereas it is reduced according to the strength of the tensor interaction and following the inclusion of many-body contributions.
Selected topics on parton distribution functions
Hirai, M.; Saito, K.; Kawamura, H.; Kumano, S.
2011-12-14
We report recent studies on structure functions of the nucleon and nuclei. First, clustering effects are investigated in the structure function F{sub 2} of {sup 9}Be for explaining an unusual nuclear correction found in a JLab experiment. We propose that high densities created by formation of clustering structure like 2{alpha}+neutron in {sup 9}Be is the origin of the unexpected JLab result by using the antisymmetrized molecular dynamics (AMD). There is an approved proposal at JLab to investigate the structure functions of light nuclei including the cluster structure, so that much details will become clear in a few years. Second, tensor-polarized quark and antiquark distributions are obtained by analyzing HERMES measurements on the structure function b{sub 1} for the deuteron. The result suggests a finite tensor polarization for antiquark distributions, which is an interesting topic for further theoretical and experimental investigations. An experimental proposal exists at JLab for measuring b{sub 1} of the deuteron as a new tensor-structure study in 2010's. Furthermore, the antiquark tensor polarization could be measured by polarized deuteron Drell-Yan processes at hadron facilities such as J-PARC and GSI-FAIR. Third, the recent CDF dijet anomaly is investigated within the standard model by considering possible modifications of the strange-quark distribution. We find that the shape of a dijet-mass spectrum changes depending on the strange-quark distribution. It indicates that the CDF excess could be partially explained as a PDF effect, particularly by the strangeness in the nucleon, within the standard model if the excess at m{sub jj}{approx_equal}140 GeV is not a sharp peak.
Nuclear parton distribution functions and their uncertainties
Hirai, M.; Kumano, S.; Nagai, T.-H.
2004-10-01
We analyze experimental data of nuclear structure-function ratios F{sub 2}{sup A}/F{sub 2}{sup A{sup '}} and Drell-Yan cross section ratios for obtaining optimum parton distribution functions (PDFs) in nuclei. Then, uncertainties of the nuclear PDFs are estimated by the Hessian method. Valence-quark distributions are determined by the F{sub 2} data at large x; however, the small-x part is not obvious from the data. On the other hand, the antiquark distributions are determined well at x{approx}0.01 from the F{sub 2} data and at x{approx}0.1 by the Drell-Yan data; however, the large-x behavior is not clear. Gluon distributions cannot be fixed by the present data and they have large uncertainties in the whole x region. Parametrization results are shown in comparison with the data. We provide a useful code for calculating nuclear PDFs at given x and Q{sup 2}.
Electron distribution functions in electric field environments
NASA Technical Reports Server (NTRS)
Rudolph, Terence H.
1991-01-01
The amount of current carried by an electric discharge in its early stages of growth is strongly dependent on its geometrical shape. Discharges with a large number of branches, each funnelling current to a common stem, tend to carry more current than those with fewer branches. The fractal character of typical discharges was simulated using stochastic models based on solutions of the Laplace equation. Extension of these models requires the use of electron distribution functions to describe the behavior of electrons in the undisturbed medium ahead of the discharge. These electrons, interacting with the electric field, determine the propagation of branches in the discharge and the way in which further branching occurs. The first phase in the extension of the referenced models , the calculation of simple electron distribution functions in an air/electric field medium, is discussed. Two techniques are investigated: (1) the solution of the Boltzmann equation in homogeneous, steady state environments, and (2) the use of Monte Carlo simulations. Distribution functions calculated from both techniques are illustrated. Advantages and disadvantages of each technique are discussed.
NASA Astrophysics Data System (ADS)
Kumar, Krishan; Garg, Vinayak; Moudgil, R. K.
2013-06-01
We report a theoretical study on the spin-resolved pair-correlation functions gσσ'(r) of a two-dimensional electron gas having arbitrary spin polarization ζ by including the dynamics of exchange-correlations within the dynamical self-consistent mean-field theory of Hasegawa and Shimizu. The calculated g↑↑(r), g↓↓(r) and g↑↓(r) exhibit a nice agreement with the recent quantum Monte Carlo simulation data of Gori-Giorgi et al. However, the agreement for the minority spin correlation function g↓↓(r) decreases with increase in ζ and/or decrease in electron density. Nevertheless, the spin-summed correlation function remains close to the simulation data.
Datta, Rhea R.; Cruickshank, Tami; Kumar, Justin P.
2011-01-01
The retinal determination (RD) network in Drosophila comprises fourteen known nuclear proteins that include DNA binding proteins, transcriptional co-activators, kinases and phosphatases. The composition of the network varies considerably throughout the animal kingdom, with the network in several basal insects having fewer members and with vertebrates having potentially significantly higher numbers of retinal determination genes. One important contributing factor for the variation in gene number within the network is gene duplication. For example, ten members of the RD network in Drosophila are derived from duplication events. Here we present an analysis of the coding regions of the five pairs of duplicate genes from within the retinal determination network of several different Drosophila species. We demonstrate that there is differential selection across the coding regions of all RD genes. Additionally, some of the most significant differences in ratios of non-silent to silent site substitutions (dN/dS) between paralog pairs are found within regions that have no ascribed function. Previous structure/function analyses of several duplicate genes have identified areas within one gene that contain novel activities when compared to its paralog. The evolutionary analysis presented here identifies these same areas in the paralogs as being under high levels of relaxed selection. We suggest that sequence divergence between paralogs and selection signatures can be used as a reasonable predictor of functional changes in rapidly evolving motifs. PMID:21210943
Comparing Functional Analysis and Paired-choice Assessment Results in Classroom Settings
Berg, Wendy K; Wacker, David P; Cigrand, Karla; Merkle, Steve; Wade, Jeanie; Henry, Kim; Wang, Yu-Chia
2007-01-01
The results of a functional analysis of problem behavior and a paired-choice assessment were compared to determine whether the same social reinforcers were identified for problem behavior and an appropriate response (time allocation). The two assessments were conducted in classroom settings with 4 adolescents with mental retardation who engaged in severe problem behavior. Each student's classroom teacher served as the therapist for all phases of assessment. The two assessment procedures identified the same social reinforcers for problem and appropriate behavior for 3 of 4 participants. PMID:17970268
Functional connectivity of paired default mode network subregions in primary insomnia
Nie, Xiao; Shao, Yi; Liu, Si-yu; Li, Hai-jun; Wan, Ai-lan; Nie, Si; Peng, De-chang; Dai, Xi-jian
2015-01-01
Objective The aim of this study is to explore the resting-state functional connectivity (FC) differences between the paired default mode network (DMN) subregions in patients with primary insomnia (PIs). Methods Forty-two PIs and forty-two age- and sex-matched good sleepers (GSs) were recruited. All subjects underwent the resting-state functional magnetic resonance imaging scans. The seed-based region-to-region FC method was used to evaluate the abnormal connectivity within the DMN subregions between the PIs and the GSs. Pearson correlation analysis was used to investigate the relationships between the abnormal FC strength within the paired DMN subregions and the clinical features in PIs. Results Compared with the GSs, the PIs showed higher Pittsburgh Sleep Quality Index score, Hamilton Anxiety Rating Scale score, Hamilton Depression Rating Scale score, Self-Rating Depression Scale score, Self Rating Anxiety Scale score, Self-Rating Scale of Sleep score, and Profile of Mood States score (P<0.001). Compared with the GSs, the PIs showed significant decreased region-to-region FC between the medial prefrontal cortex and the right medial temporal lobe (t=−2.275, P=0.026), and between the left medial temporal lobe and the left inferior parietal cortices (t=−3.32, P=0.001). The abnormal FC strengths between the DMN subregions did not correlate with the clinical features. Conclusion PIs showed disrupted FC within the DMN subregions. PMID:26719693
Estimation and optimization of loss-of-pair uncertainties based on PIV correlation functions
NASA Astrophysics Data System (ADS)
Scharnowski, Sven; Kähler, Christian J.
2016-02-01
The uncertainty quantification of particle image velocimetry (PIV) measurements is still an open problem, and to date, no consensus exists about the best suited approach. When the spatial resolution is not appropriate, the largest uncertainties are usually caused by flow gradients. But also the amount of loss-of-pairs due to out-of-plane flow motion and insufficient light-sheet overlap causes strong uncertainties in real experiments. In this paper, we show how the amount of loss-of-pairs can be quantified using the volume of the correlation function normalized by the volume of the autocorrelation function. The findings are an important step toward a reliable uncertainty estimation of instantaneous planar velocity fields computed from PIV and stereo-PIV data. Another important consequence of the analysis is that the results allow for the optimization of PIV and stereo-PIV setups in view of minimizing the total error. In particular, it is shown that the best results (concerning the relative uncertainty) can be achieved if the out-of-plane loss-of-correlation is smaller than one ( F o ). The only exception is the case where the out-of-plane motion is exactly zero. The predictions are confirmed experimentally in the last part of the paper.
NASA Astrophysics Data System (ADS)
Prüstel, Thorsten; Meier-Schellersheim, Martin
2012-08-01
We derive an exact Green's function of the diffusion equation for a pair of disk-shaped interacting particles in two dimensions subject to a backreaction boundary condition. Furthermore, we use the obtained function to calculate exact expressions for the survival probability and the time-dependent rate coefficient for the initially unbound pair and the survival probability of the bound state. The derived expressions will be of particular utility for the description of reversible membrane-bound reactions in cell biology.
Spaceflight alters immune cell function and distribution
NASA Technical Reports Server (NTRS)
Sonnenfeld, Gerald; Mandel, Adrian D.; Konstantinova, Irina V.; Berry, Wallace D.; Taylor, Gerald R.; Lesniak, A. T.; Fuchs, Boris B.; Rakhmilevich, Alexander L.
1992-01-01
Experiments are described which were performed onboard Cosmos 2044 to determine spaceflight effects on immunologically important cell function and distribution. Results indicate that bone marrow cells from flown and suspended rats exhibited a decreased response to a granulocyte/monocyte colony-stimulating factor compared with the bone marrow cells from control rats. Bone marrow cells showed an increase in the percentage of cells expressing markers for helper T-cells in the myelogenous population and increased percentages of anti-asialo granulocyte/monocyte-1-bearing interleulin-2 receptor bearing pan T- and helper T-cells in the lymphocytic population.
NASA Astrophysics Data System (ADS)
Matsumoto, M.; Inotani, D.; Ohashi, Y.
2016-05-01
We investigate strong-coupling properties of a two-dimensional ultracold Fermi gas in the normal state. Including pairing fluctuations within the framework of a T-matrix approximation, we calculate the distribution function n({\\varvec{Q}}) of Cooper pairs in terms of the center of mass momentum {\\varvec{Q}}. In the strong-coupling regime, n({\\varvec{Q}}=0) is shown to exhibit a remarkable increase with decreasing the temperature in the low temperature region, which agrees well with the recent experiment on a two-dimensional ^6Li Fermi gas (Ries et al. in Phys Rev Lett 114:230401, 2015). Our result indicates that the observed remarkable increase of the number of Cooper pairs with zero center of mass momentum can be explained without assuming the Berezinskii-Kosterlitz-Thouless (BKT) transition, when one properly includes pairing fluctuations that are enhanced by the low-dimensionality of the system. Since the BKT transition is a crucial topic in two-dimensional Fermi systems, our results would be useful for the study toward the realization of this quasi-long-range order in an ultracold Fermi gas.
Forsberg, Zarah; Mackenzie, Alasdair K.; Sørlie, Morten; Røhr, Åsmund K.; Helland, Ronny; Arvai, Andrew S.; Vaaje-Kolstad, Gustav; Eijsink, Vincent G. H.
2014-01-01
For decades, the enzymatic conversion of cellulose was thought to rely on the synergistic action of hydrolytic enzymes, but recent work has shown that lytic polysaccharide monooxygenases (LPMOs) are important contributors to this process. We describe the structural and functional characterization of two functionally coupled cellulose-active LPMOs belonging to auxiliary activity family 10 (AA10) that commonly occur in cellulolytic bacteria. One of these LPMOs cleaves glycosidic bonds by oxidation of the C1 carbon, whereas the other can oxidize both C1 and C4. We thus demonstrate that C4 oxidation is not confined to fungal AA9-type LPMOs. X-ray crystallographic structures were obtained for the enzyme pair from Streptomyces coelicolor, solved at 1.3 Å (ScLPMO10B) and 1.5 Å (CelS2 or ScLPMO10C) resolution. Structural comparisons revealed differences in active site architecture that could relate to the ability to oxidize C4 (and that also seem to apply to AA9-type LPMOs). Despite variation in active site architecture, the two enzymes exhibited similar affinities for Cu2+ (12–31 nM), redox potentials (242 and 251 mV), and electron paramagnetic resonance spectra, with only the latter clearly different from those of chitin-active AA10-type LPMOs. We conclude that substrate specificity depends not on copper site architecture, but rather on variation in substrate binding and orientation. During cellulose degradation, the members of this LPMO pair act in synergy, indicating different functional roles and providing a rationale for the abundance of these enzymes in biomass-degrading organisms. PMID:24912171
Forsberg, Zarah; Mackenzie, Alasdair K; Sørlie, Morten; Røhr, Åsmund K; Helland, Ronny; Arvai, Andrew S; Vaaje-Kolstad, Gustav; Eijsink, Vincent G H
2014-06-10
For decades, the enzymatic conversion of cellulose was thought to rely on the synergistic action of hydrolytic enzymes, but recent work has shown that lytic polysaccharide monooxygenases (LPMOs) are important contributors to this process. We describe the structural and functional characterization of two functionally coupled cellulose-active LPMOs belonging to auxiliary activity family 10 (AA10) that commonly occur in cellulolytic bacteria. One of these LPMOs cleaves glycosidic bonds by oxidation of the C1 carbon, whereas the other can oxidize both C1 and C4. We thus demonstrate that C4 oxidation is not confined to fungal AA9-type LPMOs. X-ray crystallographic structures were obtained for the enzyme pair from Streptomyces coelicolor, solved at 1.3 Å (ScLPMO10B) and 1.5 Å (CelS2 or ScLPMO10C) resolution. Structural comparisons revealed differences in active site architecture that could relate to the ability to oxidize C4 (and that also seem to apply to AA9-type LPMOs). Despite variation in active site architecture, the two enzymes exhibited similar affinities for Cu(2+) (12-31 nM), redox potentials (242 and 251 mV), and electron paramagnetic resonance spectra, with only the latter clearly different from those of chitin-active AA10-type LPMOs. We conclude that substrate specificity depends not on copper site architecture, but rather on variation in substrate binding and orientation. During cellulose degradation, the members of this LPMO pair act in synergy, indicating different functional roles and providing a rationale for the abundance of these enzymes in biomass-degrading organisms. PMID:24912171
Threshold resummation and the determination of parton distribution functions
NASA Astrophysics Data System (ADS)
Westmark, David
Precise knowledge of parton distribution functions (PDFs) is necessary to the accurate calculation of QCD observables initiated by hadrons. The deep inelastic scattering (DIS) and lepton pair production (LPP) processes are primary sources of information on PDFs. Recent global fits for PDFs have used DIS data from the large Bjorken x, moderate Q 2 region. It is known that there are large logarithms in this kinematic region that can be resummed using threshold resummation techniques. The purpose of this study is to investigate the effects of simultaneously including DIS and LPP threshold resummation in the determinations of PDFs. The analysis includes a study of the effects of the choice of resummation prescription and of current resummation methods used in the LPP rapidity and x F distributions. It is demonstrated theoretically and phenomenologically that the current resummation methods for such distributions are approximations that lose accuracy at high rapidities or xF. The unapproximated resummation formalism is extended to the MS scheme in the minimal and Borel prescriptions and used in conjunction with resummation in DIS to perform a global fit. The resultant PDF sets that correspond to two choices of resummation prescription are analyzed to determine the effect of threshold resummation on PDF fits and its theoretical uncertainties.
Zia, Roseanna N; Swan, James W; Su, Yu
2015-12-14
The formulation of detailed models for the dynamics of condensed soft matter including colloidal suspensions and other complex fluids requires accurate description of the physical forces between microstructural constituents. In dilute suspensions, pair-level interactions are sufficient to capture hydrodynamic, interparticle, and thermodynamic forces. In dense suspensions, many-body interactions must be considered. Prior analytical approaches to capturing such interactions such as mean-field approaches replace detailed interactions with averaged approximations. However, long-range coupling and effects of concentration on local structure, which may play an important role in, e.g., phase transitions, are smeared out in such approaches. An alternative to such approximations is the detailed modeling of hydrodynamic interactions utilizing precise couplings between moments of the hydrodynamic traction on a suspended particle and the motion of that or other suspended particles. For two isolated spheres, a set of these functions was calculated by Jeffrey and Onishi [J. Fluid Mech. 139, 261-290 (1984)] and Jeffrey [J. Phys. Fluids 4, 16-29 (1992)]. Along with pioneering work by Batchelor, these are the touchstone for low-Reynolds-number hydrodynamic interactions and have been applied directly in the solution of many important problems related to the dynamics of dilute colloidal dispersions [G. K. Batchelor and J. T. Green, J. Fluid Mech. 56, 375-400 (1972) and G. K. Batchelor, J. Fluid Mech. 74, 1-29 (1976)]. Toward extension of these functions to concentrated systems, here we present a new stochastic sampling technique to rapidly calculate an analogous set of mobility functions describing the hydrodynamic interactions between two hard spheres immersed in a suspension of arbitrary concentration, utilizing accelerated Stokesian dynamics simulations. These mobility functions provide precise, radially dependent couplings of hydrodynamic force and torque to particle translation
Zia, Roseanna N. Su, Yu; Swan, James W.
2015-12-14
The formulation of detailed models for the dynamics of condensed soft matter including colloidal suspensions and other complex fluids requires accurate description of the physical forces between microstructural constituents. In dilute suspensions, pair-level interactions are sufficient to capture hydrodynamic, interparticle, and thermodynamic forces. In dense suspensions, many-body interactions must be considered. Prior analytical approaches to capturing such interactions such as mean-field approaches replace detailed interactions with averaged approximations. However, long-range coupling and effects of concentration on local structure, which may play an important role in, e.g., phase transitions, are smeared out in such approaches. An alternative to such approximations is the detailed modeling of hydrodynamic interactions utilizing precise couplings between moments of the hydrodynamic traction on a suspended particle and the motion of that or other suspended particles. For two isolated spheres, a set of these functions was calculated by Jeffrey and Onishi [J. Fluid Mech. 139, 261–290 (1984)] and Jeffrey [J. Phys. Fluids 4, 16–29 (1992)]. Along with pioneering work by Batchelor, these are the touchstone for low-Reynolds-number hydrodynamic interactions and have been applied directly in the solution of many important problems related to the dynamics of dilute colloidal dispersions [G. K. Batchelor and J. T. Green, J. Fluid Mech. 56, 375–400 (1972) and G. K. Batchelor, J. Fluid Mech. 74, 1–29 (1976)]. Toward extension of these functions to concentrated systems, here we present a new stochastic sampling technique to rapidly calculate an analogous set of mobility functions describing the hydrodynamic interactions between two hard spheres immersed in a suspension of arbitrary concentration, utilizing accelerated Stokesian dynamics simulations. These mobility functions provide precise, radially dependent couplings of hydrodynamic force and torque to particle
NASA Astrophysics Data System (ADS)
Zia, Roseanna N.; Swan, James W.; Su, Yu
2015-12-01
The formulation of detailed models for the dynamics of condensed soft matter including colloidal suspensions and other complex fluids requires accurate description of the physical forces between microstructural constituents. In dilute suspensions, pair-level interactions are sufficient to capture hydrodynamic, interparticle, and thermodynamic forces. In dense suspensions, many-body interactions must be considered. Prior analytical approaches to capturing such interactions such as mean-field approaches replace detailed interactions with averaged approximations. However, long-range coupling and effects of concentration on local structure, which may play an important role in, e.g., phase transitions, are smeared out in such approaches. An alternative to such approximations is the detailed modeling of hydrodynamic interactions utilizing precise couplings between moments of the hydrodynamic traction on a suspended particle and the motion of that or other suspended particles. For two isolated spheres, a set of these functions was calculated by Jeffrey and Onishi [J. Fluid Mech. 139, 261-290 (1984)] and Jeffrey [J. Phys. Fluids 4, 16-29 (1992)]. Along with pioneering work by Batchelor, these are the touchstone for low-Reynolds-number hydrodynamic interactions and have been applied directly in the solution of many important problems related to the dynamics of dilute colloidal dispersions [G. K. Batchelor and J. T. Green, J. Fluid Mech. 56, 375-400 (1972) and G. K. Batchelor, J. Fluid Mech. 74, 1-29 (1976)]. Toward extension of these functions to concentrated systems, here we present a new stochastic sampling technique to rapidly calculate an analogous set of mobility functions describing the hydrodynamic interactions between two hard spheres immersed in a suspension of arbitrary concentration, utilizing accelerated Stokesian dynamics simulations. These mobility functions provide precise, radially dependent couplings of hydrodynamic force and torque to particle translation
Garza, Alejandro J; Sousa Alencar, Ana G; Scuseria, Gustavo E
2015-12-28
Singlet-paired coupled cluster doubles (CCD0) is a simplification of CCD that relinquishes a fraction of dynamic correlation in order to be able to describe static correlation. Combinations of CCD0 with density functionals that recover specifically the dynamic correlation missing in the former have also been developed recently. Here, we assess the accuracy of CCD0 and CCD0+DFT (and variants of these using Brueckner orbitals) as compared to well-established quantum chemical methods for describing ground-state properties of singlet actinide molecules. The f(0) actinyl series (UO2(2+), NpO2(3+), PuO2(4+)), the isoelectronic NUN, and thorium (ThO, ThO(2+)) and nobelium (NoO, NoO2) oxides are studied. PMID:26723650
Recognition Memory for Pairs of Words as a Function of Associative Context.
ERIC Educational Resources Information Center
Underwood, Benton J.
The purpose of these studies was to test a theory of associative context (defined as the association between two words in a pair) on recognition memory. The theory states that culturally associated words in a pair and nonassociated words in a pair differ after a single study trial in terms of their frequency representation in memory. Two…
Properties of the cosmological density distribution function
NASA Astrophysics Data System (ADS)
Bernardeau, Francis; Kofman, Lev
1995-04-01
The properties of the probability distribution function (PDF) of the cosmological continuous density field are studied. We focus our analysis on the quasi-linear regime where various calculations, based on dynamically motivated methods, have been presented: either by using the Zel'dovich approximation (ZA) or by using the perturbation theory to evaluate the behavior of the moments of the distribution function. We show how these two approaches are related to each other and that they can be used in a complementary way. For that respect, the one-dimensional dynamics, where the ZA is exact solution, has first been used as a testing ground. In particular, we show that, when the density PDF obtained with the ZA is regularized, its various moments exhibit the behavior expected by the perturbation theory applied to the ZA. We show that ZA approach can be used for arbitrary initial conditions (not only Gaussian) and that the nonlinear evolution of the moments can be obtained. The perturbation theory can be used for the exact dynamics. We take into account the final filtering of the density field both for ZA and perturbation theory. Applying these techniques, we got the generating function of the moments for the one-dimensional dynamics, the three-dimensional ZA, with and without smoothing effects. We also suggest methods to build PDFs. One is based on the Laplace inverse transform of the moment generating function. The other, the Edgeworth expansion, is obtained when the previous generating function is truncated at a given order and allows evaluation of the PDF out of limited number of moments. It provides insight on the relationship between the moments and the shape of the density PDF. In particular, it provides an alternative method to evaluate the skewness and kurtosis by measuring the PDF around its maximum. Eventually, results obtained from a numerical simulation with cold dark matter initial conditions have been used to validate the accuracy of the considered
Distribution function approach to redshift space distortions
Seljak, Uroš; McDonald, Patrick E-mail: pvmcdonald@lbl.gov
2011-11-01
We develop a phase space distribution function approach to redshift space distortions (RSD), in which the redshift space density can be written as a sum over velocity moments of the distribution function. These moments are density weighted and have well defined physical interpretation: their lowest orders are density, momentum density, and stress energy density. The series expansion is convergent if kμu/aH < 1, where k is the wavevector, H the Hubble parameter, u the typical gravitational velocity and μ = cos θ, with θ being the angle between the Fourier mode and the line of sight. We perform an expansion of these velocity moments into helicity modes, which are eigenmodes under rotation around the axis of Fourier mode direction, generalizing the scalar, vector, tensor decomposition of perturbations to an arbitrary order. We show that only equal helicity moments correlate and derive the angular dependence of the individual contributions to the redshift space power spectrum. We show that the dominant term of μ{sup 2} dependence on large scales is the cross-correlation between the density and scalar part of momentum density, which can be related to the time derivative of the matter power spectrum. Additional terms contributing to μ{sup 2} and dominating on small scales are the vector part of momentum density-momentum density correlations, the energy density-density correlations, and the scalar part of anisotropic stress density-density correlations. The second term is what is usually associated with the small scale Fingers-of-God damping and always suppresses power, but the first term comes with the opposite sign and always adds power. Similarly, we identify 7 terms contributing to μ{sup 4} dependence. Some of the advantages of the distribution function approach are that the series expansion converges on large scales and remains valid in multi-stream situations. We finish with a brief discussion of implications for RSD in galaxies relative to dark matter
Audio feature extraction using probability distribution function
NASA Astrophysics Data System (ADS)
Suhaib, A.; Wan, Khairunizam; Aziz, Azri A.; Hazry, D.; Razlan, Zuradzman M.; Shahriman A., B.
2015-05-01
Voice recognition has been one of the popular applications in robotic field. It is also known to be recently used for biometric and multimedia information retrieval system. This technology is attained from successive research on audio feature extraction analysis. Probability Distribution Function (PDF) is a statistical method which is usually used as one of the processes in complex feature extraction methods such as GMM and PCA. In this paper, a new method for audio feature extraction is proposed which is by using only PDF as a feature extraction method itself for speech analysis purpose. Certain pre-processing techniques are performed in prior to the proposed feature extraction method. Subsequently, the PDF result values for each frame of sampled voice signals obtained from certain numbers of individuals are plotted. From the experimental results obtained, it can be seen visually from the plotted data that each individuals' voice has comparable PDF values and shapes.
Pion valence-quark parton distribution function
NASA Astrophysics Data System (ADS)
Chang, Lei; Thomas, Anthony W.
2015-10-01
Within the Dyson-Schwinger equation formulation of QCD, a rainbow ladder truncation is used to calculate the pion valence-quark distribution function (PDF). The gap equation is renormalized at a typical hadronic scale, of order 0.5 GeV, which is also set as the default initial scale for the pion PDF. We implement a corrected leading-order expression for the PDF which ensures that the valence-quarks carry all of the pion's light-front momentum at the initial scale. The scaling behavior of the pion PDF at a typical partonic scale of order 5.2 GeV is found to be (1 - x) ν, with ν ≃ 1.6, as x approaches one.
Nuclear modifications of Parton Distribution Functions
NASA Astrophysics Data System (ADS)
Adeluyi, Adeola Adeleke
This dissertation addresses a central question of modern nuclear physics: how does the behavior of fundamental degrees of freedom (quarks and gluons) change in the nuclear environment? This is an important aspect of experimental studies at current facilities such as the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory and the Continuous Electron Beam Accelerator Facility (CEBAF) at the Thomas Jefferson National Laboratory (JLAB). It is also highly relevant to planned experimental efforts at the Large Hadron Collider (LHC) and the future Electron Ion Collider (EIC). All these facilities probe matter via collisions involving nuclei; thus complications arise due to the presence of the attendant nuclear medium. Theoretical efforts to understand and interpret experimental results from such collisions are therefore largely dependent on the resolution of this question. The development of nuclear physics demonstrates that theoretical description is most efficient in terms of the effective degrees of freedom relevant to the scale (energy) being probed. Thus at low energies, nuclei are described as bound states of protons and neutrons (nucleons). At higher energies, the nucleons are no longer elementary, but are revealed to possess an underlying substructure: they are made up of quarks and gluons, collectively termed partons. The mometum distributions of these partons in the nucleon are referred to as Parton Distribution Functions (PDFs). Parton distributions can be determined from experimental measurements of structure functions. The ratio of nuclear structure functions to nucleon structure functions (generically referred to as nuclear ratio) is a measure of the nuclear modifications of the free nucleon PDFs. Thus a study of the nuclear ratio suffices to gain an understanding of nuclear modifications. In this dissertation we aim to describe theoretically nuclear modifications in a restricted region where the nuclear ratio is less than unity, the so
Linear dispersion properties of ring velocity distribution functions
Vandas, Marek
2015-06-15
Linear properties of ring velocity distribution functions are investigated. The dispersion tensor in a form similar to the case of a Maxwellian distribution function, but for a general distribution function separable in velocities, is presented. Analytical forms of the dispersion tensor are derived for two cases of ring velocity distribution functions: one obtained from physical arguments and one for the usual, ad hoc ring distribution. The analytical expressions involve generalized hypergeometric, Kampé de Fériet functions of two arguments. For a set of plasma parameters, the two ring distribution functions are compared. At the parallel propagation with respect to the ambient magnetic field, the two ring distributions give the same results identical to the corresponding bi-Maxwellian distribution. At oblique propagation, the two ring distributions give similar results only for strong instabilities, whereas for weak growth rates their predictions are significantly different; the two ring distributions have different marginal stability conditions.
Pretzelosity distribution function h(1T)**perpendicular
Avagyan, Harutyun; V. Efremov, A.; Schweitzer, Peter; Yuan, Feng
2009-01-01
The 'pretzelosity' distribution is discussed. Theoretical properties, model results, and perspectives to access experimental information on this leading twist, transverse momentum dependent parton distribution function are reviewed. Its relation to helicity and transversity distributions is highlighted.
Measurements of Correlated Pair Momentum Distributions in {sup 3}He(e,e{prime}pp)n with CLAS
Rustam Niyazov
2003-05-01
We have measured the {sup 3}He(e,e{prime}pp)n reaction at 2.2 and 4.4 GeV over a wide kinematic range. The kinetic energy distribution for ''fast'' nucleons (p > 250 MeV/c) peaks where two nucleons each have 20% or less and the third or ''leading'' nucleon carries most of the transferred energy. These fast nucleon pairs (both pp and pn) are back-to-back and carry very little momentum along {rvec q}, indicating that they are spectators. Experimental and theoretical evidence indicates that we have measured NN correlations in {sup 3}He(e,e{prime}pp)n by striking the third nucleon and detecting the spectator correlated pair.
Feldmann, Andreas; Kehr, Gerald; Daniliuc, Constantin G; Mück-Lichtenfeld, Christian; Erker, Gerhard
2015-08-24
The vicinal P/B frustrated Lewis pair (FLP) Mes2PCH2CH2B(C6F5)2 undergoes 1,1-carboboration reactions with the Me3Si-substituted enynes to give ring-enlarged functionalized C3-bridged P/B FLPs. These serve as active FLPs in the activation of dihydrogen to give the respective zwitterionic [P]H(+)/[B]H(-) products. One such product shows activity as a metal-free catalyst for the hydrogenation of enamines or a bulky imine. The ring-enlarged FLPs contain dienylborane functionalities that undergo "bora-Nazarov"-type ring-closing rearrangements upon photolysis. A DFT study had shown that the dienylborane cyclization of such systems itself is endothermic, but a subsequent C6F5 migration is very favorable. Furthermore, substituted 2,5-dihydroborole products are derived from cyclization and C6F5 migration from the photolysis reaction. In the case of the six-membered annulation product, a subsequent stereoisomerization reaction takes place and the resultant compound undergoes a P/B FLP 1,2-addition reaction with a terminal alkyne with rearrangement. PMID:26284948
Kimsey, Isaac; Al-Hashimi, Hashim M.
2014-01-01
There are a growing number of studies reporting the observation of purine-pyrimidine base-pairs that are seldom observed in unmodified nucleic acids because they entail the loss of energetically favorable interactions or require energetically costly base ionization or tautomerization. These high energy purine-pyrimidine base-pairs include G•C+ and A•T Hoogsteen base-pairs, which entail ~180° rotation of the purine base in a Watson-Crick base-pair, protonation of cytosine N3, and constriction of the C1′–C1′ distance by ~2.5 Å. Other high energy pure-pyrimidine base-pairs include G•T, G•U, and A•C mispairs that adopt Watson-Crick like geometry through either base ionization or tautomerization. Although difficult to detect and characterize using biophysical methods, high energy purine-pyrimidine base-pairs appear to be more common than once thought. They further expand the structural and functional diversity of canonical and noncanonical nucleic acid base-pairs. PMID:24721455
NASA Astrophysics Data System (ADS)
Pietinen, Sami; Tenhunen, Vesa; Tukiainen, Markku
Several methods and techniques have surfaced to address the ongoing concerns of quality and productivity of software development. Among these is the Pair Programming (PP) method, which has gained a lot off attention through being an essential part of an agile software development methodology called the eXtreme Programming (XP). In this paper, we present the results of two controlled case studies that investigate the possible productivity improvement through the incorporation of PP over solo programming. The main focus is on implementation task, more specifically in programming, although PP is suitable for other tasks too. Our results show that very high level of PP use might be difficult to achieve in a very tightly scheduled software development project, but some of the benefits can be seen to come true even with proportional use of PP. In our case, PP added the additional effort of 13% over solo programming.
Tests of structure functions using lepton pairs: W-charge asymmetry at CDF
NASA Astrophysics Data System (ADS)
Sakumoto, W. K.
1994-09-01
Large asymmetry of W-bosons produced in p(bar-p) collisions has been measured using 19 039 W yields e nu and W yields mu nu decays recorded by the CDF detector during the 1992-1993 Tevatron collider run. The asymmetry is sensitive to the slope of the proton's d/u quark distribution ratio down to x less than 0.01 at Q(exp 2) approximately M(sub w)(exp 2), where nonperturbative QCD effects are minimal. Of recent parton distribution functions, those of Martin, Roberts, and Stirling are favored over those of the CTEQ collaboration. This difference is seen even though both sets agree, at the level of the nuclear shadowing corrections, with the recent NMC measurements of F(sub 2)(sup mu n)/F(sub 2)(sup mu p).
Tests of structure functions using lepton pairs: W-charge asymmetry at CDF
Sakumoto, W.K.; CDF Collaboration
1994-09-01
Large asymmetry of W-bosons produced in p{bar p} collisions has been measured using 19 039 W {yields} e{nu} and W {yields} {mu}{nu} decays recorded by the CDF detector during the 1992--1993 Tevatron collider run. The asymmetry is sensitive to the slope of the proton`s d/u quark distribution ratio down to x < 0.01 at Q{sup 2} {approx} M{sub w}{sup 2}, where nonperturbative QCD effects are minimal. Of recent parton distribution functions, those of Martin, Roberts and Stirling are favored over those of the CTEQ collaboration. This difference is seen even though both sets agree, at the leval of the nuclear shadowing corrections, with the recent NMC measurements of F{sub 2}{sup mu}n/F{sub 2}{sup mu}p.
Shin, Jae Yen; Lopez-Garrido, Javier; Lee, Sang-Hyuk; Diaz-Celis, Cesar; Fleming, Tinya; Bustamante, Carlos; Pogliano, Kit
2015-05-07
SpoIIIE is a membrane-anchored DNA translocase that localizes to the septal midpoint to mediate chromosome translocation and membrane fission during Bacillus subtilis sporulation. Here we use cell-specific protein degradation and quantitative photoactivated localization microscopy in strains with a thick sporulation septum to investigate the architecture and function of the SpoIIIE DNA translocation complex in vivo. We were able to visualize SpoIIIE complexes with approximately equal numbers of molecules in the mother cell and the forespore. Cell-specific protein degradation showed that only the mother cell complex is required to translocate DNA into the forespore, whereas degradation in either cell reversesmore » membrane fission. Our data suggest that SpoIIIE assembles a coaxially paired channel for each chromosome arm comprised of one hexamer in each cell to maintain membrane fission during DNA translocation. We show that SpoIIIE can operate, in principle, as a bi-directional motor that exports DNA.« less
Soft and collinear factorization and transverse momentum dependent parton distribution functions
NASA Astrophysics Data System (ADS)
Echevarría, Miguel G.; Idilbi, Ahmad; Scimemi, Ignazio
2013-11-01
In this work we consider how a parton distribution function, with an explicit transverse momentum dependence can be properly defined in a regularization-scheme independent manner. We argue that by considering a factorized form of the transverse momentum dependent spectrum for the production of a heavy lepton pair in Drell-Yan reaction, one should first split the relevant soft function into two boost invariant contributions. When those soft contributions are added to the pure collinear contributions, well-defined hadronic matrix elements emerge, i.e., the transverse momentum dependent distributions. We also perform a comparison with Collins' definition.
Functional model for the [Fe] hydrogenase inspired by the frustrated Lewis pair concept.
Kalz, Kai F; Brinkmeier, Alexander; Dechert, Sebastian; Mata, Ricardo A; Meyer, Franc
2014-11-26
[Fe] hydrogenase (Hmd) catalyzes the heterolytic splitting of H2 by using, in its active site, a unique organometallic iron-guanylylpyridinol (FeGP) cofactor and, as a hydride acceptor, the substrate methenyltetrahydromethanopterin (methenyl-H4MPT(+)). The combination FeGP/methenyl-H4MPT(+) and its reactivity bear resemblance to the concept of frustrated Lewis pairs (FLPs), some of which have been shown to heterolytically activate H2. The present work exploits this interpretation of Hmd reactivity by using the combination of Lewis basic ruthenium metalates, namely K[CpRu(CO)2] (KRp) and a related polymeric Cp/Ru/CO compound (Rs), with the new imidazolinium salt 1,3-bis(2,6-difluorophenyl)-2-(4-tolyl)imidazolinium bromide ([(Tol)Im(F4)](+)Br(-)) that was designed to emulate the hydride acceptor properties of methenyl-H4MPT(+). Solid-state structures of [(Tol)Im(F4)](+)Br(-) and the corresponding imidazolidine H(Tol)Im(F4) reveal that the heterocycle undergoes similar structural changes as in the biological substrate. DFT calculations indicate that heterolytic splitting of dihydrogen by the FLP Rp(-)/[(Tol)Im(F4)](+) is exothermic, but the formation of the initial Lewis pair should be unfavorable in polar solvents. Consequently the combination Rp(-)/[(Tol)Im(F4)](+) does not react with H2 but leads instead to side products from nucleophilic substitution (k = 4 × 10(-2) L mol (-1) s(-1) at room temperature). In contrast, the heterogeneous combination Rs/[(Tol)Im(F4)](+) does split H2 heterolytically to give H(Tol)Im(F4) and HRuCp(CO)2 (HRp) or D(Tol)Im(F4) and DRp when using D2. The reaction has been followed by (1)H/(2)H and (19)F NMR spectroscopy as well as by IR spectroscopy and reaches 96% conversion after 1 d. Formation of H(Tol)Im(F4) under these conditions demonstrates that superelectrophilic activation by protonation, which has been proposed for methenyl-H4MPT(+) to increase its carbocationic character, is not necessarily required for an imidazolinium ion to
Huang, Lin; Wang, Jia; Lilley, David M J
2016-06-20
k-turns are commonly-occurring motifs that introduce sharp kinks into duplex RNA, thereby facilitating tertiary contacts. Both the folding and conformation of k-turns are determined by their local sequence. k-turns fall into two conformational classes, called N3 and N1, that differ in the pattern of hydrogen bonding in the core. We show here that this is determined by the basepair adjacent to the critical G•A pairs. We determined crystal structures of a series of Kt-7 variants in which this 3b,3n position has been systematically varied, showing that this leads to a switch in the conformation. We have previously shown that the 3b,3n position also determines the folding characteristics of the k-turn, i.e. whether or not the k-turn can fold in the presence of metal ions alone. We have analyzed the distribution of 3b,3n sequences from four classes of k-turns from ribosomes, riboswitches and U4 snRNA, finding a strong conservation of properties for a given k-turn type. We thus demonstrate a strong association between biological function, 3b,3n sequence and k-turn folding and conformation. This has strong predictive power, and can be applied to the modeling of large RNA architectures. PMID:27016741
Huang, Lin; Wang, Jia; Lilley, David M. J.
2016-01-01
k-turns are commonly-occurring motifs that introduce sharp kinks into duplex RNA, thereby facilitating tertiary contacts. Both the folding and conformation of k-turns are determined by their local sequence. k-turns fall into two conformational classes, called N3 and N1, that differ in the pattern of hydrogen bonding in the core. We show here that this is determined by the basepair adjacent to the critical G•A pairs. We determined crystal structures of a series of Kt-7 variants in which this 3b,3n position has been systematically varied, showing that this leads to a switch in the conformation. We have previously shown that the 3b,3n position also determines the folding characteristics of the k-turn, i.e. whether or not the k-turn can fold in the presence of metal ions alone. We have analyzed the distribution of 3b,3n sequences from four classes of k-turns from ribosomes, riboswitches and U4 snRNA, finding a strong conservation of properties for a given k-turn type. We thus demonstrate a strong association between biological function, 3b,3n sequence and k-turn folding and conformation. This has strong predictive power, and can be applied to the modeling of large RNA architectures. PMID:27016741
Measurement-device-independent quantum key distribution with heralded pair coherent state
NASA Astrophysics Data System (ADS)
Wang, Xiang; Wang, Yang; Chen, Rui-Ke; Zhou, Chun; Li, Hong-Wei; Bao, Wan-Su
2016-06-01
Measurement-device-independent QKD (MDI-QKD) can solve security loophole problems brought by imperfections of detectors and provide enhanced practical security compared to traditional QKD. We propose an active-passive-combined decoy state MDI-QKD protocol with heralded pair coherent state (HPCS) source. By calculating the lower bound of the single-photon counting rate and the upper bound of the single-photon error rate, we present formulas of the secure key rate in our protocol. Based on the linear lossy channel model, we present calculation methods of estimating the overall gain and quantum bit error rate for HPCS source with full phase randomization. We numerically compare secure key rates for different decoy MDI-QKD protocol with different sources. The result shows that the active-passive-combined decoy state MDI-QKD protocol with HPCS source has certain superiority in the secure key rate. It can provide an important theoretical reference for practical implementations of MDI-QKD.
Ploetz, Elizabeth A.; Smith, Paul E.
2015-03-07
Kirkwood-Buff or Fluctuation Solution Theory can be used to provide experimental pair fluctuations, and/or integrals over the pair distribution functions, from experimental thermodynamic data on liquid mixtures. Here, this type of approach is used to provide triplet and quadruplet fluctuations, and the corresponding integrals over the triplet and quadruplet distribution functions, in a purely thermodynamic manner that avoids the use of structure factors. The approach is then applied to binary mixtures of water + methanol and benzene + methanol over the full composition range under ambient conditions. The observed correlations between the different species vary significantly with composition. The magnitude of the fluctuations and integrals appears to increase as the number of the most polar molecule involved in the fluctuation or integral also increases. A simple physical picture of the fluctuations is provided to help rationalize some of these variations.
NASA Astrophysics Data System (ADS)
Singh, Ram Chandra; Ram, Jokhan
2006-09-01
A closure for the pair-correlation functions of molecular fluids is described in which the hypernetted-chain and the Percus-Yevick approximations are “mixed” as a function of interparticle separation. An adjustable parameter α in the mixing function is used to enforce thermodynamic consistency, by which it is meant that identical results are obtained when the equations of state are calculated via the virial and compressibility routes, respectively. The mixed integral equation for the pair-correlation functions has been solved for two model fluids: (i) a fluid of the hard Gaussian overlap model, and (ii) a fluid the molecules of which interact via a modified Gay-Berne model potential. For the modified Gay-Berne fluid we have slightly modified the original Gay-Berne potential to study the effect of attraction on hard core systems. The pair-correlation functions of the isotropic phase which enter in the density-functional theory as input informations have been calculated from the integral equation theories for these model fluids. We have used two different versions of the density-functional theory known as the second order and modified weighted-density-functional theory to locate the isotropic-nematic (I-N) transitions and calculate the values of transition parameters for the hard Gaussian overlap and modified Gay-Berne model fluids. We have compared our results with those of computer simulations wherever they are available. We find that the density-functional theory is good to study the I-N transition in molecular fluids if the values of the pair-correlation functions in the isotropic phase are accurately known.
Bright integrated photon-pair source for practical passive decoy-state quantum key distribution
NASA Astrophysics Data System (ADS)
Krapick, S.; Stefszky, M. S.; Jachura, M.; Brecht, B.; Avenhaus, M.; Silberhorn, C.
2014-01-01
We report on a bright, nondegenerate type-I parametric down-conversion source, which is well suited for passive decoy-state quantum key distribution. We show the photon-number-resolved analysis over a broad range of pump powers and we prove heralded higher-order n-photon states up to n =4. The inferred photon click statistics exhibit excellent agreements to the theoretical predictions. From our measurement results we conclude that our source meets the requirements to avert photon-number-splitting attacks.
Dzuba, Sergei A
2016-08-01
Pulsed double electron-electron resonance technique (DEER, or PELDOR) is applied to study conformations and aggregation of peptides, proteins, nucleic acids, and other macromolecules. For a pair of spin labels, experimental data allows for the determination of their distance distribution function, P(r). P(r) is derived as a solution of a first-kind Fredholm integral equation, which is an ill-posed problem. Here, we suggest regularization by increasing the distance discretization length to its upper limit where numerical integration still provides agreement with experiment. This upper limit is found to be well above the lower limit for which the solution instability appears because of the ill-posed nature of the problem. For solving the integral equation, Monte Carlo trials of P(r) functions are employed; this method has an obvious advantage of the fulfillment of the non-negativity constraint for P(r). The regularization by the increasing of distance discretization length for the case of overlapping broad and narrow distributions may be employed selectively, with this length being different for different distance ranges. The approach is checked for model distance distributions and for experimental data taken from literature for doubly spin-labeled DNA and peptide antibiotics. PMID:27289419
NASA Astrophysics Data System (ADS)
Dzuba, Sergei A.
2016-08-01
Pulsed double electron-electron resonance technique (DEER, or PELDOR) is applied to study conformations and aggregation of peptides, proteins, nucleic acids, and other macromolecules. For a pair of spin labels, experimental data allows for the determination of their distance distribution function, P(r). P(r) is derived as a solution of a first-kind Fredholm integral equation, which is an ill-posed problem. Here, we suggest regularization by increasing the distance discretization length to its upper limit where numerical integration still provides agreement with experiment. This upper limit is found to be well above the lower limit for which the solution instability appears because of the ill-posed nature of the problem. For solving the integral equation, Monte Carlo trials of P(r) functions are employed; this method has an obvious advantage of the fulfillment of the non-negativity constraint for P(r). The regularization by the increasing of distance discretization length for the case of overlapping broad and narrow distributions may be employed selectively, with this length being different for different distance ranges. The approach is checked for model distance distributions and for experimental data taken from literature for doubly spin-labeled DNA and peptide antibiotics.
Detection of prokaryotic promoters from the genomic distribution of hexanucleotide pairs
Jacques, Pierre-Étienne; Rodrigue, Sébastien; Gaudreau, Luc; Goulet, Jean; Brzezinski, Ryszard
2006-01-01
Background In bacteria, sigma factors and other transcriptional regulatory proteins recognize DNA patterns upstream of their target genes and interact with RNA polymerase to control transcription. As a consequence of evolution, DNA sequences recognized by transcription factors are thought to be enriched in intergenic regions (IRs) and depleted from coding regions of prokaryotic genomes. Results In this work, we report that genomic distribution of transcription factors binding sites is biased towards IRs, and that this bias is conserved amongst bacterial species. We further take advantage of this observation to develop an algorithm that can efficiently identify promoter boxes by a distribution-dependent approach rather than a direct sequence comparison approach. This strategy, which can easily be combined with other methodologies, allowed the identification of promoter sequences in ten species and can be used with any annotated bacterial genome, with results that rival with current methodologies. Experimental validations of predicted promoters also support our approach. Conclusion Considering that complete genomic sequences of over 1000 bacteria will soon be available and that little transcriptional information is available for most of them, our algorithm constitutes a promising tool for the prediction of promoter sequences. Importantly, our methodology could also be adapted to identify DNA sequences recognized by other regulatory proteins. PMID:17014715
Efremov, A. V.; Teryaev, O. V.; Schweitzer, P.; Zavada, P.
2011-03-01
We derive relations between transverse momentum dependent distribution functions and the usual parton distribution functions in the 3D covariant parton model, which follow from Lorentz invariance and the assumption of a rotationally symmetric distribution of parton momenta in the nucleon rest frame. Using the known parton distribution functions f{sub 1}{sup a}(x) and g{sub 1}{sup a}(x) as input we predict the x- and p{sub T}-dependence of all twist-2 T-even transverse momentum dependent distribution functions.
Ackermann, M.; Ajello, M.; Allafort, A.; Bechtol, K.; Bloom, E. D.; Borgland, A. W.; Bottacini, E.; Buehler, R.; Asano, K.; Atwood, W. B.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Ballet, J.; Bastieri, D.; Bonamente, E.; Brandt, T. J.; Brigida, M.; Bruel, P. E-mail: mar0@uw.edu [Laboratoire Leprince-Ringuet, Ecole polytechnique, CNRS and others
2013-03-01
The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to detect photons with energies from Almost-Equal-To 20 MeV to >300 GeV. The pre-launch response functions of the LAT were determined through extensive Monte Carlo simulations and beam tests. The point-spread function (PSF) characterizing the angular distribution of reconstructed photons as a function of energy and geometry in the detector is determined here from two years of on-orbit data by examining the distributions of {gamma} rays from pulsars and active galactic nuclei (AGNs). Above 3 GeV, the PSF is found to be broader than the pre-launch PSF. We checked for dependence of the PSF on the class of {gamma}-ray source and observation epoch and found none. We also investigated several possible spatial models for pair-halo emission around BL Lac AGNs. We found no evidence for a component with spatial extension larger than the PSF and set upper limits on the amplitude of halo emission in stacked images of low- and high-redshift BL Lac AGNs and the TeV blazars 1ES0229+200 and 1ES0347-121.
NASA Astrophysics Data System (ADS)
Yu, Z.; Baym, G.
2006-06-01
The spin response functions measured in multicomponent fermion gases by means of rf transitions between hyperfine states are strongly constrained by the symmetry of the interatomic interactions. Such constraints are reflected in the spin f -sum rule that the response functions must obey. In particular, only if the effective interactions are not fully invariant in SU(2) spin space, are the response functions sensitive to mean field and pairing effects. We demonstrate, via a self-consistent calculation of the spin-spin correlation function within the framework of Hartree-Fock-BCS theory, how one can derive a correlation function explicitly obeying the f -sum rule. By contrast, simple one-loop approximations to the spin response functions do not satisfy the sum rule, except in special cases. As we show, the emergence of a second peak at higher frequency in the rf spectrum, as observed in a recent experiment in trapped Li6 , can be understood as the contribution from the paired fermions, with a shift of the peak from the normal particle response proportional to the square of the BCS pairing gap.
Quantum key distribution using a series of quantum correlated photon pairs
Inoue, Kyo
2005-03-01
The differential-phase-shift quantum key distribution (DPS-QKD) is a recently proposed QKD scheme in which a pulse train is transmitted through a quantum channel. This paper extends the ideal of the DPS-QKD to entanglement-based systems. Two schemes are presented. In one, an entanglement source sends pulse trains of signal and idler to two parties (Alice and Bob), respectively, who phase-modulate the incoming pulses and receive them after one-bit delay interferometers. In the other, two entanglement sources are prepared, one between Alice and a repeating node (Charlie) and one between Charlie and Bob, which send signal and idler pulse trains to Alice and Bob and Charlie, respectively. These schemes offer a longer distance between Alice and Bob than the conventional DPS-QKD.
Extractions of polarized and unpolarized parton distribution functions
Jimenez-Delgado, Pedro
2014-01-01
An overview of our ongoing extractions of parton distribution functions of the nucleon is given. First JAM results on the determination of spin-dependent parton distribution functions from world data on polarized deep-inelastic scattering are presented first, and followed by a short report on the status of the JR unpolarized parton distributions. Different aspects of PDF analysis are briefly discussed, including effects of the nuclear structure of targets, target-mass corrections and higher twist contributions to the structure functions.
NASA Astrophysics Data System (ADS)
Yuan, Jing; Hu, Jiangping
2016-03-01
Pairing symmetries of iron-based superconductors are investigated systematically in a five-orbital model within the different regions of interaction parameters by functional renormalization group (FRG). Even for a fixed Fermi surface with both hole and electron pockets, it is found that depending on interaction parameters, a variety of pairing symmetries, including two types of d-wave and two types of s-wave pairing symmetries, can emerge. Only the dx^2-y^2 - and the s±-waves are robustly supported by the nearest-neighbor (NN) intra-orbital J 1 and the next-nearest-neighbor (NNN) intra-orbital J 2 antiferromagnetic (AFM) exchange couplings, respectively. This study suggests that the accurate initial input of the interaction parameters is essential to make FRG a useful method to determine the leading channel of superconducting instability.
Self-Energy Correction to Momentum-Density Distribution of Positron-Electron Pairs
NASA Astrophysics Data System (ADS)
Tang, Z.; Nagai, Y.; Inoue, K.; Toyama, T.; Chiba, T.; Saito, M.; Hasegawa, M.
2005-03-01
Positron two-dimensional angular correlation of annihilation radiation (2D ACAR), i.e., the 2D projection of the electron momentum densities sampled by positron, in Si is employed to verify the prediction of the density functional theory within the local-density approximation (LDA). Carefully conducted test shows that the LDA introduces small but definite discrepancies to the 2D-ACAR anisotropies. Self-energy calculation using the GW method indicates that density-fluctuation contributes anisotropic momentum-density correction and thus improves the agreement between theory and experiment. These results provide valuable annotations to the arguments concerning the accuracy and validity of the LDA and GW schemes.
The function of one-word mediators in the recall of word pairs.
Bellezza, F S; Poplawsky, A J
1974-05-01
The problem of demonstrating that natural language mediators play a role in learning and are not epiphenomena resulting from learning is an important problem in cognitive learning theories. Using a cued-recall and a free-recall learning task, Ss were requested to add a one-word mediator to some of the pairs of concrete nouns presented, The mediated pairs were learned better than the control pairs in both tasks. Both words were recalled only when the mediator was also recalled. Also, one-word mediators were the most effective recall cues and were the best recalled words in free recall. A two-stage learning model adequately described the data. However, a counterargument can be made which considers the mediator to be a high associate of one of the words presented and actually has no direct link to the other presented word. A possible experimental resolution of the problem is discussed. PMID:21274772
Klusek-Gawenda, M.; Szczurek, A.
2010-07-15
The cross sections for exclusive muon-pair production in nucleus-nucleus collisions are calculated and several differential distributions are shown. Realistic (Fourier transform of charge density) charge form factors of nuclei are used and the corresponding results are compared with the cross sections calculated with monopole form factor often used in the literature and discussed recently in the context of higher-order QED corrections. Absorption effects are discussed and quantified. The cross sections obtained with realistic form factors are significantly smaller than those obtained with the monopole form factor. The effect is bigger for large muon rapidities and/or large muon transverse momenta. The predictions for the STAR and PHENIX collaboration measurements at RHIC as well as the ALICE and CMS collaborations at LHC are presented.
Parametric Probability Distribution Functions for Axon Diameters of Corpus Callosum
Sepehrband, Farshid; Alexander, Daniel C.; Clark, Kristi A.; Kurniawan, Nyoman D.; Yang, Zhengyi; Reutens, David C.
2016-01-01
Axon diameter is an important neuroanatomical characteristic of the nervous system that alters in the course of neurological disorders such as multiple sclerosis. Axon diameters vary, even within a fiber bundle, and are not normally distributed. An accurate distribution function is therefore beneficial, either to describe axon diameters that are obtained from a direct measurement technique (e.g., microscopy), or to infer them indirectly (e.g., using diffusion-weighted MRI). The gamma distribution is a common choice for this purpose (particularly for the inferential approach) because it resembles the distribution profile of measured axon diameters which has been consistently shown to be non-negative and right-skewed. In this study we compared a wide range of parametric probability distribution functions against empirical data obtained from electron microscopy images. We observed that the gamma distribution fails to accurately describe the main characteristics of the axon diameter distribution, such as location and scale of the mode and the profile of distribution tails. We also found that the generalized extreme value distribution consistently fitted the measured distribution better than other distribution functions. This suggests that there may be distinct subpopulations of axons in the corpus callosum, each with their own distribution profiles. In addition, we observed that several other distributions outperformed the gamma distribution, yet had the same number of unknown parameters; these were the inverse Gaussian, log normal, log logistic and Birnbaum-Saunders distributions. PMID:27303273
Cooper, Fred M; Mihaila, Bogdan; Dawson, John F
2008-01-01
Recently the transverse distribution of particle production from strong constant chromo-electric fields has been explicitly calculated in Ref. 1 for soft-gluon production and in Ref. 2 for quark (antiquark) production. This particle production method, originally discussed by Heisenberg and Euler, Schwinger and Weisskopf, has a long history as a model of the production of the quark gluon plasma following a relativistic heavy ion collision. The physical picture considered here is that of two relativistic heavy nuclei colliding and leaving behind a semi-classical gluon field which then non-perturbatively produces gluon and quark-antiquark pairs via the Schwinger mechanism. At high energy large hadron colliders, such as RHIC (Au-Au collisions at {radical}{ovr s} = 200 GeV) and LHC (Pb-Pb collisions at {radical}{ovr s} = 5.5 TeV), about half the total center-of-mass energy, E{sub cm}, goes into the production of a semi-classical gluon field, which can be thought to be initially in a Lorentz contracted disc. The gluon field in SU(3) is described by two Casimir invariants, the first one, C{sub 1} = E{sup a}E{sup a}, being related to the energy density of the initial field, where the second one, C{sub 2} = [d{sub abc}E{sup a}E{sup b}E{sup c}]{sup 2}, is related to the SU(3) color hypercharge left behind by the leading particles. So the question we want to study in this short note is how sensitive the transverse distribution is to this second Casimir invariant C{sub 2}. We have considered the dependence of the pair production rate of quarks and gluons from a strong chromo-electric field and have discovered that the effect of the second Casimir invariant of SU(3), which was not present in the electric field problem, effects the distribution by less than 15%. This event by event dependence of the transverse momentum distribution of jets on C{sub 2} may be something of interest at heavy ion colliders.
Optimal Reward Functions in Distributed Reinforcement Learning
NASA Technical Reports Server (NTRS)
Wolpert, David H.; Tumer, Kagan
2000-01-01
We consider the design of multi-agent systems so as to optimize an overall world utility function when (1) those systems lack centralized communication and control, and (2) each agents runs a distinct Reinforcement Learning (RL) algorithm. A crucial issue in such design problems is to initialize/update each agent's private utility function, so as to induce best possible world utility. Traditional 'team game' solutions to this problem sidestep this issue and simply assign to each agent the world utility as its private utility function. In previous work we used the 'Collective Intelligence' framework to derive a better choice of private utility functions, one that results in world utility performance up to orders of magnitude superior to that ensuing from use of the team game utility. In this paper we extend these results. We derive the general class of private utility functions that both are easy for the individual agents to learn and that, if learned well, result in high world utility. We demonstrate experimentally that using these new utility functions can result in significantly improved performance over that of our previously proposed utility, over and above that previous utility's superiority to the conventional team game utility.
A new family of distribution functions for spherical galaxies
NASA Astrophysics Data System (ADS)
Gerhard, Ortwin E.
1991-06-01
The present study describes a new family of anisotropic distribution functions for stellar systems designed to keep control of the orbit distribution at fixed energy. These are quasi-separable functions of energy and angular momentum, and they are specified in terms of a circularity function h(x) which fixes the distribution of orbits on the potential's energy surfaces outside some anisotropy radius. Detailed results are presented for a particular set of radially anisotropic circularity functions h-alpha(x). In the scale-free logarithmic potential, exact analytic solutions are shown to exist for all scale-free circularity functions. Intrinsic and projected velocity dispersions are calculated and the expected properties are presented in extensive tables and graphs. Several applications of the quasi-separable distribution functions are discussed. They include the effects of anisotropy or a dark halo on line-broadening functions, the radial orbit instability in anisotropic spherical systems, and violent relaxation in spherical collapse.
NASA Technical Reports Server (NTRS)
Witherow, William K. (Inventor)
1988-01-01
A Lambertian reference standard for uniformly scattering a beam of light is constructed of a plate having a planar surface with a layer of glue disposed on the surface. An evenly packed layer of monodisperse spheres is set in the layer, and when the standard is used for bi-directional (BRDF) measurements, the spheres are coated with a layer of highly relective substance, such as gold or silver. When the standard is used for bi-directional transmittance distribution function (BTDF) measurements, the spheres are of a transparent material and are provided with a roughened surface, as by acid etching. In this case, the layer of glue is an optical cement, and the plate is of glass, with the spheres, the layer, and the plate all possessing a similar refractive index.
Self-Organizing Maps and Parton Distribution Functions
K. Holcomb, Simonetta Liuti, D. Z. Perry
2011-05-01
We present a new method to extract parton distribution functions from high energy experimental data based on a specific type of neural networks, the Self-Organizing Maps. We illustrate the features of our new procedure that are particularly useful for an anaysis directed at extracting generalized parton distributions from data. We show quantitative results of our initial analysis of the parton distribution functions from inclusive deep inelastic scattering.
Messenger RNA modifications: Form, distribution, and function.
Gilbert, Wendy V; Bell, Tristan A; Schaening, Cassandra
2016-06-17
RNA contains more than 100 distinct modifications that promote the functions of stable noncoding RNAs in translation and splicing. Recent technical advances have revealed widespread and sparse modification of messenger RNAs with N(6)-methyladenosine (m(6)A), 5-methylcytosine (m(5)C), and pseudouridine (Ψ). Here we discuss the rapidly evolving understanding of the location, regulation, and function of these dynamic mRNA marks, collectively termed the epitranscriptome. We highlight differences among modifications and between species that could instruct ongoing efforts to understand how specific mRNA target sites are selected and how their modification is regulated. Diverse molecular consequences of individual m(6)A modifications are beginning to be revealed, but the effects of m(5)C and Ψ remain largely unknown. Future work linking molecular effects to organismal phenotypes will broaden our understanding of mRNA modifications as cell and developmental regulators. PMID:27313037
Finding of a highly efficient ZFN pair for Aqpep gene functioning in murine zygotes
FUJII, Wataru; ONUMA, Asuka; YOSHIOKA, Shin; NAGASHIMA, Keisuke; SUGIURA, Koji; NAITO, Kunihiko
2015-01-01
The generation efficiencies of mutation-induced mice when using engineered zinc-finger nucleases (ZFNs) have been generally 10 to 20% of obtained pups in previous studies. The discovery of high-affinity DNA-binding modules can contribute to the generation of various kinds of novel artificial chromatin-targeting tools, such as zinc-finger acetyltransferases, zinc-finger histone kinases and so on, as well as improvement of reported zinc-finger recombinases and zinc-finger methyltransferases. Here, we report a novel ZFN pair that has a highly efficient mutation-induction ability in murine zygotes. The ZFN pair induced mutations in all obtained mice in the target locus, exon 17 of aminopeptidase Q gene, and almost all of the pups had biallelic mutations. This high efficiency was also shown in the plasmid DNA transfected in a cultured human cell line. The induced mutations were inherited normally in the next generation. The zinc-finger modules of this ZFN pair are expected to contribute to the development of novel ZF-attached chromatin-targeting tools. PMID:26460691
Rationalisation of distribution functions for models of nanoparticle magnetism
NASA Astrophysics Data System (ADS)
El-Hilo, M.; Chantrell, R. W.
2012-08-01
A formalism is presented which reconciles the use of different distribution functions of particle diameter in analytical models of the magnetic properties of nanoparticle systems. For the lognormal distribution a transformation is derived which shows that a distribution of volume fraction transforms into a lognormal distribution of particle number albeit with a modified median diameter. This transformation resolves an apparent discrepancy reported in Tournus and Tamion [Journal of Magnetism and Magnetic Materials 323 (2011) 1118].
Distributed implementation of functional program evaluation
Fasel, J.H.; Douglass, R.J.; Michelsen, R.; Hudak, P.
1985-01-01
In this paper, we explore the potential of the functional model, particularly as it pertains to architecture. In Section 2, we describe the graph-reduction operational model of computation and its relation to AI problems. In Section 3, we discuss a class of architectures that implement graph reduction and a prototype implementation in this class being developed at Los Alamos. Finally, we speculate on the applicability of graph reduction to some other classes of architecture.
Computer routines for probability distributions, random numbers, and related functions
Kirby, W.
1983-01-01
Use of previously coded and tested subroutines simplifies and speeds up program development and testing. This report presents routines that can be used to calculate various probability distributions and other functions of importance in statistical hydrology. The routines are designed as general-purpose Fortran subroutines and functions to be called from user-written main progress. The probability distributions provided include the beta, chi-square, gamma, Gaussian (normal), Pearson Type III (tables and approximation), and Weibull. Also provided are the distributions of the Grubbs-Beck outlier test, Kolmogorov 's and Smirnov 's D, Student 's t, noncentral t (approximate), and Snedecor F. Other mathematical functions include the Bessel function, I sub o, gamma and log-gamma functions, error functions, and exponential integral. Auxiliary services include sorting and printer-plotting. Random number generators for uniform and normal numbers are provided and may be used with some of the above routines to generate numbers from other distributions. (USGS)
Computer routines for probability distributions, random numbers, and related functions
Kirby, W.H.
1980-01-01
Use of previously codes and tested subroutines simplifies and speeds up program development and testing. This report presents routines that can be used to calculate various probability distributions and other functions of importance in statistical hydrology. The routines are designed as general-purpose Fortran subroutines and functions to be called from user-written main programs. The probability distributions provided include the beta, chisquare, gamma, Gaussian (normal), Pearson Type III (tables and approximation), and Weibull. Also provided are the distributions of the Grubbs-Beck outlier test, Kolmogorov 's and Smirnov 's D, Student 's t, noncentral t (approximate), and Snedecor F tests. Other mathematical functions include the Bessel function I (subzero), gamma and log-gamma functions, error functions and exponential integral. Auxiliary services include sorting and printer plotting. Random number generators for uniform and normal numbers are provided and may be used with some of the above routines to generate numbers from other distributions. (USGS)
An Orientation Distribution Function for Trabecular Bone
Lawrence Livermore National Laboratory
2004-10-08
We describe a new method for quantifying the orientation of trabecular bone from three-dimensional images. Trabecular lattices from five human vertebrae were decomposed into individual trabecular elements, and the orientation, mass, and thickness of each element were recorded. Continuous functions that described the total mass (M({var_phi},{theta})) and mean thickness ({tau}({var_phi},{theta})) of all trabeculae as a function of orientation were derived. The results were compared with experimental measurements of the elastic modulus in the three principal anatomic directions. A power law scaling relationship between the anisotropies in mass and elastic modulus was observed; the scaling exponent was 1.41 (R{sup 2} = 0.88). As expected, the preponderance of trabecular mass was oriented along the cranial-caudal direction; on average, there was 3.4 times more mass oriented vertically than horizontally. Moreover, the vertical trabeculae were 30% thicker, on average, than the horizontal trabeculae. The vertical trabecular thickness was inversely related to the connectivity (R{sup 2} = 0.70; p = 0.07), suggesting a possible organization into either few, thick trabeculae or many thin trabeculae. The method, which accounts for the mechanical connectedness of the lattice, provides a rapid way to both visualize and quantify the three-dimensional organization of trabecular bone.
A.V. Efremov, P. Schweitzer, O.V. Teryaev, P. Zavada
2011-03-01
We derive relations between transverse momentum dependent distribution functions (TMDs) and the usual parton distribution functions (PDFs) in the 3D covariant parton model, which follow from Lorentz invariance and the assumption of a rotationally symmetric distribution of parton momenta in the nucleon rest frame. Using the known PDFs f_1(x) and g_1(x) as input we predict the x- and pT-dependence of all twist-2 T-even TMDs.
Dijksterhuis, Jacomijn P; Baljinnyam, Bolormaa; Stanger, Karen; Sercan, Hakki O; Ji, Yun; Andres, Osler; Rubin, Jeffrey S; Hannoush, Rami N; Schulte, Gunnar
2015-03-13
The seven-transmembrane-spanning receptors of the FZD1-10 class are bound and activated by the WNT family of lipoglycoproteins, thereby inducing a complex network of signaling pathways. However, the specificity of the interaction between mammalian WNT and FZD proteins and the subsequent signaling cascade downstream of the different WNT-FZD pairs have not been systematically addressed to date. In this study, we determined the binding affinities of various WNTs for different members of the FZD family by using bio-layer interferometry and characterized their functional selectivity in a cell system. Using purified WNTs, we show that different FZD cysteine-rich domains prefer to bind to distinct WNTs with fast on-rates and slow off-rates. In a 32D cell-based system engineered to overexpress FZD2, FZD4, or FZD5, we found that WNT-3A (but not WNT-4, -5A, or -9B) activated the WNT-β-catenin pathway through FZD2/4/5 as measured by phosphorylation of LRP6 and β-catenin stabilization. Surprisingly, different WNT-FZD pairs showed differential effects on phosphorylation of DVL2 and DVL3, revealing a previously unappreciated DVL isoform selectivity by different WNT-FZD pairs in 32D cells. In summary, we present extensive mapping of WNT-FZD cysteine-rich domain interactions complemented by analysis of WNT-FZD pair functionality in a unique cell system expressing individual FZD isoforms. Differential WNT-FZD binding and selective functional readouts suggest that endogenous WNT ligands evolved with an intrinsic natural bias toward different downstream signaling pathways, a phenomenon that could be of great importance in the design of FZD-targeting drugs. PMID:25605717
Dijksterhuis, Jacomijn P.; Baljinnyam, Bolormaa; Stanger, Karen; Sercan, Hakki O.; Ji, Yun; Andres, Osler; Rubin, Jeffrey S.; Hannoush, Rami N.; Schulte, Gunnar
2015-01-01
The seven-transmembrane-spanning receptors of the FZD1–10 class are bound and activated by the WNT family of lipoglycoproteins, thereby inducing a complex network of signaling pathways. However, the specificity of the interaction between mammalian WNT and FZD proteins and the subsequent signaling cascade downstream of the different WNT-FZD pairs have not been systematically addressed to date. In this study, we determined the binding affinities of various WNTs for different members of the FZD family by using bio-layer interferometry and characterized their functional selectivity in a cell system. Using purified WNTs, we show that different FZD cysteine-rich domains prefer to bind to distinct WNTs with fast on-rates and slow off-rates. In a 32D cell-based system engineered to overexpress FZD2, FZD4, or FZD5, we found that WNT-3A (but not WNT-4, -5A, or -9B) activated the WNT-β-catenin pathway through FZD2/4/5 as measured by phosphorylation of LRP6 and β-catenin stabilization. Surprisingly, different WNT-FZD pairs showed differential effects on phosphorylation of DVL2 and DVL3, revealing a previously unappreciated DVL isoform selectivity by different WNT-FZD pairs in 32D cells. In summary, we present extensive mapping of WNT-FZD cysteine-rich domain interactions complemented by analysis of WNT-FZD pair functionality in a unique cell system expressing individual FZD isoforms. Differential WNT-FZD binding and selective functional readouts suggest that endogenous WNT ligands evolved with an intrinsic natural bias toward different downstream signaling pathways, a phenomenon that could be of great importance in the design of FZD-targeting drugs. PMID:25605717
Ronkainen, Paula H A; Kovanen, Vuokko; Alén, Markku; Pöllänen, Eija; Palonen, Eeva-Maija; Ankarberg-Lindgren, Carina; Hämäläinen, Esa; Turpeinen, Ursula; Kujala, Urho M; Puolakka, Jukka; Kaprio, Jaakko; Sipilä, Sarianna
2009-07-01
We investigated whether long-term hormone replacement therapy (HRT) is associated with mobility and lower limb muscle performance and composition in postmenopausal women. Fifteen 54- to 62-yr-old monozygotic female twin pairs discordant for HRT were recruited from the Finnish Twin Cohort. Habitual (HWS) and maximal (MWS) walking speeds over 10 m, thigh muscle composition, lower body muscle power assessed as vertical jumping height, and maximal isometric hand grip and knee extension strengths were measured. Intrapair differences (IPD%) with 95% confidence intervals (CI) were calculated. The mean duration of HRT use was 6.9 +/- 4.1 yr. MWS was on average 7% (0.9 to 13.1%, P = 0.019) and muscle power 16% (-0.8 to 32.8%, P = 0.023) greater in HRT users than in their cotwins. Thigh muscle cross-sectional area tended to be larger (IPD% = 6%, 95% CI: -0.07 to 12.1%, P = 0.065), relative muscle area greater (IPD% = 8%, CI: 0.8 to 15.0%, P = 0.047), and relative fat area smaller (IPD% = -5%, CI: -11.3 to 1.2%, P = 0.047) in HRT users than in their sisters. There were no significant differences in maximal isometric strengths or HWS between users and nonusers. Subgroup analyses revealed that estrogen-containing therapies (11 pairs) significantly decreased total body and thigh fat content, whereas tibolone (4 pairs) tended to increase muscle cross-sectional area. This study showed that long-term HRT was associated with better mobility, greater muscle power, and favorable body and muscle composition among 54- to 62-yr-old women. The results indicate that HRT is a potential agent in preventing muscle weakness and mobility limitation in older women. PMID:19246654
Halder, Antarip; Bhattacharya, Sohini; Datta, Ayan; Bhattacharyya, Dhananjay; Mitra, Abhijit
2015-10-21
The roles of protonated nucleobases in stabilizing different structural motifs and in facilitating catalytic functions of RNA are well known. Among different polar sites of all the nucleobases, N7 of guanine has the highest protonation propensity at physiological pH. However, unlike other easily protonable sites such as N1 and N3 of adenine or N3 of cytosine, N7 protonation of guanine does not lead to the stabilization of base pairs involving its protonated Hoogsteen edge. It also does not facilitate its participation in any acid-base catalysis process. To explore the possible roles of N7 protonated guanine, we have studied its base pairing potentials involving WatsonCrick and sugar edges, which undergo major charge redistribution upon N7 protonation. We have carried out quantum chemical geometry optimization at the M05-2X/6-311G+(2d,2p) level, followed by interaction energy calculation at the MP2/aug-cc-pVDZ level, along with the analysis of the context of occurrence for selected base pairs involving the sugar edge or the WatsonCrick edge of guanine within a non-redundant set of 167 RNA crystal structures. Our results suggest that, four base pairs - G:C W:W trans, G:rC W:S cis, G:G W:H cis and G:G S:H trans may involve N7 protonated guanine. These base pairs deviate significantly from their respective experimental geometries upon QM optimization, but they retain their experimental geometries if guanine N7 protonation is considered during optimization. Our study also reveals the role of guanine N7 protonation (i) in stabilizing important RNA structural motifs, (ii) in providing a framework for designing pH driven molecular motors and (iii) in providing an alternative strategy to mimic the effect of post-transcriptional changes. PMID:26382322
Mapping distributed brain function and networks with diffuse optical tomography
Eggebrecht, Adam T.; Ferradal, Silvina L.; Robichaux-Viehoever, Amy; Hassanpour, Mahlega S.; Dehghani, Hamid; Snyder, Abraham Z.; Hershey, Tamara; Culver, Joseph P.
2014-01-01
Mapping of human brain function has revolutionized systems neuroscience. However, traditional functional neuroimaging by positron emission tomography or functional magnetic resonance imaging cannot be used when applications require portability, or are contraindicated because of ionizing radiation (positron emission tomography) or implanted metal (functional magnetic resonance imaging). Optical neuroimaging offers a non-invasive alternative that is radiation free and compatible with implanted metal and electronic devices (for example, pacemakers). However, optical imaging technology has heretofore lacked the combination of spatial resolution and wide field of view sufficient to map distributed brain functions. Here, we present a high-density diffuse optical tomography imaging array that can map higher-order, distributed brain function. The system was tested by imaging four hierarchical language tasks and multiple resting-state networks including the dorsal attention and default mode networks. Finally, we imaged brain function in patients with Parkinson’s disease and implanted deep brain stimulators that preclude functional magnetic resonance imaging. PMID:25083161
Mapping distributed brain function and networks with diffuse optical tomography
NASA Astrophysics Data System (ADS)
Eggebrecht, Adam T.; Ferradal, Silvina L.; Robichaux-Viehoever, Amy; Hassanpour, Mahlega S.; Dehghani, Hamid; Snyder, Abraham Z.; Hershey, Tamara; Culver, Joseph P.
2014-06-01
Mapping of human brain function has revolutionized systems neuroscience. However, traditional functional neuroimaging by positron emission tomography or functional magnetic resonance imaging cannot be used when applications require portability, or are contraindicated because of ionizing radiation (positron emission tomography) or implanted metal (functional magnetic resonance imaging). Optical neuroimaging offers a non-invasive alternative that is radiation free and compatible with implanted metal and electronic devices (for example, pacemakers). However, optical imaging technology has heretofore lacked the combination of spatial resolution and wide field of view sufficient to map distributed brain functions. Here, we present a high-density diffuse optical tomography imaging array that can map higher-order, distributed brain function. The system was tested by imaging four hierarchical language tasks and multiple resting-state networks including the dorsal attention and default mode networks. Finally, we imaged brain function in patients with Parkinson's disease and implanted deep brain stimulators that preclude functional magnetic resonance imaging.
Paired-end genomic signature tags: a method for the functional analysis of genomes and epigenomes.
Dunn, John J; McCorkle, Sean R; Everett, Logan; Anderson, Carl W
2007-01-01
Because paired-end genomic signature tags are sequenced-based, they have the potential to become an alternate tool to tiled microarray hybridization as a method for genome-wide localization of transcription factors and other sequence-specific DNA binding proteins. As outlined here the method also can be used for global analysis of DNA methylation. One advantage of this approach is the ability to easily switch between different genome types without having to fabricate a new microarray for each and every DNA type. However, the method does have some disadvantages. Among the most rate-limiting steps of our PE-GST protocol are the need to concatemerize the diTAGs, size fractionate them and then clone them prior to sequencing. This is usually followed by additional steps to amplify and size select for long (> or = 500) concatemer inserts prior to sequencing. These time-consuming steps are important for standard DNA sequencing as they increase efficiency approximately 20-30-fold since each amplified concatemer can now provide information on multiple tags; the limitation on data acqui- sition is read length during sequencing. However, the development of new sequencing methods such as Life Sciences' 454 new nanotechnology-based sequencing instrument (41) could increase tag sequencing efficiency by several orders of magnitude (> or = 100,000 diTAG reads/run), which is sufficient to provide in-depth global analysis of all ChIP PE-GSTs in a single run. This is because the lengths of our paired-end diTAGs (approximately 60 bp) fall well within the region of high accuracy for read lengths on this instrument. In principle, sequence analysis of diTAGs could begin as soon as they are generated, thereby completely bypassing the need for the concatemerization, sizing, downstream cloning steps and sequencing template purification. In addition, our protocol places any one of several unique four-base long nucleotide sequences, such as GATC, between each and every diTAG pair, which could
Huettl, Rosa-Eva; Eckstein, Simone; Stahl, Tessa; Petricca, Stefania; Ninkovic, Jovica; Götz, Magdalena; Huber, Andrea B
2016-05-01
During development of the CNS, stem and progenitor cell proliferation, cell fate designation, and patterning decisions are tightly regulated by interdependent networks of key transcriptional regulators. In a genetic approach we analyzed divergent functionality of the PAI and RED sub-domains of the Pax6 Paired domain (PD) during progenitor zone formation, motor and interneuron development, and peripheral connectivity at distinct levels within the neural tube: within the hindbrain, mutation of the PAI sub-domain severely affected patterning of the p3 and pMN domains and establishment of the corresponding motor neurons. Exit point designation of hypoglossal axons was disturbed in embryos harboring either mutations in the PD sub-domains or containing a functional Pax6 Null allele. At brachial spinal levels, we propose a selective involvement of the PAI sub-domain during patterning of ventral p2 and pMN domains, critically disturbing generation of specific motor neuron subtypes and increasing V2 interneuron numbers. Our findings present a novel aspect of how Pax6 not only utilizes its modular structure to perform distinct functions via its paired and homeodomain. Individual sub-domains can exert distinct functions, generating a new level of complexity for transcriptional regulation by one single transcription factor not only in dorso-ventral, but also rostro-caudal neural tube patterning. PMID:26187199
A thermal distribution function for relativistic magnetically insulated electron flows
Desjarlais, M.P.; Sudan, R.N.
1986-05-01
A distribution function is presented that may be used to study the effects of finite temperature on the equilibrium and stability properties of magnetically insulated electron flows. This distribution function has the useful property that it generates the thoroughly studied class of constant Q = ..omega../sup 2//sub p//..cap omega../sup 2/ equilibria in its zero-temperature limit. Analytic solutions are given for the general, constant Q, zero-temperature equilibria.
NASA Astrophysics Data System (ADS)
Hu, Li-Yun; Fan, Hong-Yi
2009-12-01
We calculate Wigner function, tomogram of the pair coherent state by using its Schmidt decomposition in the coherent state representation. It turns out that the Wigner function can be seen as the quantum entanglement (QE) between two two-variable Hermite polynomials (TVHP) and the tomogram is further simplified as QE of two single-variable Hermite polynomials. The Husimi function of pair coherent state is also calculated.
Generalised partition functions: inferences on phase space distributions
NASA Astrophysics Data System (ADS)
Treumann, Rudolf A.; Baumjohann, Wolfgang
2016-06-01
It is demonstrated that the statistical mechanical partition function can be used to construct various different forms of phase space distributions. This indicates that its structure is not restricted to the Gibbs-Boltzmann factor prescription which is based on counting statistics. With the widely used replacement of the Boltzmann factor by a generalised Lorentzian (also known as the q-deformed exponential function, where κ = 1/|q - 1|, with κ, q ∈ R) both the kappa-Bose and kappa-Fermi partition functions are obtained in quite a straightforward way, from which the conventional Bose and Fermi distributions follow for κ → ∞. For κ ≠ ∞ these are subject to the restrictions that they can be used only at temperatures far from zero. They thus, as shown earlier, have little value for quantum physics. This is reasonable, because physical κ systems imply strong correlations which are absent at zero temperature where apart from stochastics all dynamical interactions are frozen. In the classical large temperature limit one obtains physically reasonable κ distributions which depend on energy respectively momentum as well as on chemical potential. Looking for other functional dependencies, we examine Bessel functions whether they can be used for obtaining valid distributions. Again and for the same reason, no Fermi and Bose distributions exist in the low temperature limit. However, a classical Bessel-Boltzmann distribution can be constructed which is a Bessel-modified Lorentzian distribution. Whether it makes any physical sense remains an open question. This is not investigated here. The choice of Bessel functions is motivated solely by their convergence properties and not by reference to any physical demands. This result suggests that the Gibbs-Boltzmann partition function is fundamental not only to Gibbs-Boltzmann but also to a large class of generalised Lorentzian distributions as well as to the corresponding nonextensive statistical mechanics.
Aaltonen, T
2011-04-28
We report a study of the invariant mass distribution of jet pairs produced in association with a W boson using data collected with the CDF detector which correspond to an integrated luminosity of 4.3 fb-1. The observed distribution has an excess in the 120-160 GeV/c2 mass range which is not described by current theoretical predictions within the statistical and systematic uncertainties. In this letter we report studies of the properties of this excess.
New insight on the Sivers transverse momentum dependent distribution function
M. Anselmino, M. Boglione, U. D'Alesio, S. Melis, F. Murgia, A. Prokudin
2011-05-01
Polarised Semi-Inclusive Deep Inelastic Scattering (SIDIS) processes allow to study Transverse Momentum Dependent partonic distributions (TMDs), which reveal a non trivial three dimensional internal structure of the hadrons in momentum space. One of the most representative of the TMDs is the so-called Sivers function that describes the distribution of unpolarized quarks inside a transversely polarized proton. We present a novel extraction of the Sivers distribution functions from the most recent experimental data of HERMES and COMPASS experiments. Using suitable parametrizations, within the TMD factorization scheme, and a simple fitting strategy, we also perform a preliminary exploration of the role of the proton sea quarks.
Pion and kaon valence-quark parton distribution functions
NASA Astrophysics Data System (ADS)
Nguyen, Trang; Bashir, Adnan; Roberts, Craig D.; Tandy, Peter C.
2011-06-01
A rainbow-ladder truncation of QCD’s Dyson-Schwinger equations, constrained by existing applications to hadron physics, is employed to compute the valence-quark parton distribution functions of the pion and kaon. Comparison is made to π-N Drell-Yan data for the pion’s u-quark distribution and to Drell-Yan data for the ratio uK(x)/uπ(x): the environmental influence of this quantity is a parameter-free prediction, which agrees well with existing data. Our analysis unifies the computation of distribution functions with that of numerous other properties of pseudoscalar mesons.
Pion and kaon valence-quark parton distribution functions.
Nguyen, T.; Bashir, A.; Roberts, C. D.; Tandy, P. C.
2011-06-16
A rainbow-ladder truncation of QCD's Dyson-Schwinger equations, constrained by existing applications to hadron physics, is employed to compute the valence-quark parton distribution functions of the pion and kaon. Comparison is made to {pi}-N Drell-Yan data for the pion's u-quark distribution and to Drell-Yan data for the ratio u{sub K}(x)/u{sub {pi}}(x): the environmental influence of this quantity is a parameter-free prediction, which agrees well with existing data. Our analysis unifies the computation of distribution functions with that of numerous other properties of pseudoscalar mesons.
Pion and kaon valence-quark parton distribution functions
Nguyen, Trang; Bashir, Adnan; Roberts, Craig D.; Tandy, Peter C.
2011-06-15
A rainbow-ladder truncation of QCD's Dyson-Schwinger equations, constrained by existing applications to hadron physics, is employed to compute the valence-quark parton distribution functions of the pion and kaon. Comparison is made to {pi}-N Drell-Yan data for the pion's u-quark distribution and to Drell-Yan data for the ratio u{sub K}(x)/u{sub {pi}}(x): the environmental influence of this quantity is a parameter-free prediction, which agrees well with existing data. Our analysis unifies the computation of distribution functions with that of numerous other properties of pseudoscalar mesons.
The electron distribution function upstream from the earth's bow shock
NASA Technical Reports Server (NTRS)
Cairns, Iver H.
1987-01-01
A general analytic theory for the distribution function of particles backstreaming from an arbitrary shock in a magnetized plasma is presented. Particle motions are shown to be restricted to two-dimensional planes. A general form for the source term describing upstreaming particles accelerated at the shock is presented along with explicit source terms for planar and parabolic shocks. The origin and form of the escape velocity cutoff for a shock in a magnetized plasma are discussed. The distribution function upstream of a finite planar shock and a parabolic shock in two dimensions is calculated, and an analytic approximation of the cutoff velocity at points in the upstream region is derived. The theory is then applied to the earth's bow shock, calculating distribution functions and the nature and spatial variation of the cutoff velocity. The theory for the particle distribution upstream of the bow shock is compared with the model of Filbert and Kellogg (1979).
Baeck, Annelies; Wagemans, Johan; Op de Beeck, Hans P
2013-04-15
Natural scenes typically contain multiple visual objects, often in interaction, such as when a bottle is used to fill a glass. Previous studies disagree about the representation of multiple objects and the role of object position herein, nor did they pinpoint the effect of potential interactions between the objects. In an fMRI study, we presented four single objects in two different positions and object pairs consisting of all possible combinations of the single objects. Objects pairs could form either a meaningful action configuration in which they interact with each other or a non-meaningful configuration. We found that for single objects and object pairs both identity and position were represented in multi-voxel activity patterns in LOC. The response patterns of object pairs were best predicted by a weighted average of the response patterns of the constituent objects, with the strongest single-object response (the max response) weighted more than the min response. The difference in weight between the max and the min object was larger for familiar action pairs than for other pairs when participants attended to the configuration. A weighted average thus relates the response patterns of object pairs to the response patterns of single objects, even when the objects interact. PMID:23266747
Lee, Choong-Hee; Ryu, Jungwon; Lee, Sang-Hun; Kim, Hakjin; Lee, Inah
2016-08-01
The hippocampus plays critical roles in both object-based event memory and spatial navigation, but it is largely unknown whether the left and right hippocampi play functionally equivalent roles in these cognitive domains. To examine the hemispheric symmetry of human hippocampal functions, we used an fMRI scanner to measure BOLD activity while subjects performed tasks requiring both object-based event memory and spatial navigation in a virtual environment. Specifically, the subjects were required to form object-place paired associate memory after visiting four buildings containing discrete objects in a virtual plus maze. The four buildings were visually identical, and the subjects used distal visual cues (i.e., scenes) to differentiate the buildings. During testing, the subjects were required to identify one of the buildings when cued with a previously associated object, and when shifted to a random place, the subject was expected to navigate to the previously chosen building. We observed that the BOLD activity foci changed from the left hippocampus to the right hippocampus as task demand changed from identifying a previously seen object (object-cueing period) to searching for its paired-associate place (object-cued place recognition period). Furthermore, the efficient retrieval of object-place paired associate memory (object-cued place recognition period) was correlated with the BOLD response of the left hippocampus, whereas the efficient retrieval of relatively pure spatial memory (spatial memory period) was correlated with the right hippocampal BOLD response. These findings suggest that the left and right hippocampi in humans might process qualitatively different information for remembering episodic events in space. © 2016 The Authors Hippocampus Published by Wiley Periodicals, Inc. PMID:27009679
Kappa distribution and Probability Density Functions in Solar Wind
NASA Astrophysics Data System (ADS)
Jurac, S.
2004-12-01
A signature of a statistical intermittency is the presence of large deviations from the average value: this increased probability of finding extreme deviations is characterized by Probability Density Functions (PDFs) which exhibit non Gaussian power-law tails. Such power-law distributions were observed over decades in biology, chemistry, finance and other fields. Known examples include heartbeat histograms, price distribution, turbulent fluid flow and many other non-equilibrium systems. It is shown that the Kappa distribution represents a good description of PDFs observed in Solar wind. The asymmetric fluctuations in variance over time observed in solar wind PDFs are Gamma distributed. It is shown that, by assuming such a distribution of variance, the Kappa distribution can be analitically derived.
Analyzing Distributed Functions in an Integrated Hazard Analysis
NASA Technical Reports Server (NTRS)
Morris, A. Terry; Massie, Michael J.
2010-01-01
Large scale integration of today's aerospace systems is achievable through the use of distributed systems. Validating the safety of distributed systems is significantly more difficult as compared to centralized systems because of the complexity of the interactions between simultaneously active components. Integrated hazard analysis (IHA), a process used to identify unacceptable risks and to provide a means of controlling them, can be applied to either centralized or distributed systems. IHA, though, must be tailored to fit the particular system being analyzed. Distributed systems, for instance, must be analyzed for hazards in terms of the functions that rely on them. This paper will describe systems-oriented IHA techniques (as opposed to traditional failure-event or reliability techniques) that should be employed for distributed systems in aerospace environments. Special considerations will be addressed when dealing with specific distributed systems such as active thermal control, electrical power, command and data handling, and software systems (including the interaction with fault management systems). Because of the significance of second-order effects in large scale distributed systems, the paper will also describe how to analyze secondary functions to secondary functions through the use of channelization.
Global NLO Analysis of Nuclear Parton Distribution Functions
Hirai, M.; Kumano, S.; Nagai, T.-H.
2008-02-21
Nuclear parton distribution functions (NPDFs) are determined by a global analysis of experimental measurements on structure-function ratios F{sub 2}{sup A}/F{sub 2}{sup A{sup '}} and Drell-Yan cross section ratios {sigma}{sub DY}{sup A}/{sigma}{sub DY}{sup A{sup '}}, and their uncertainties are estimated by the Hessian method. The NPDFs are obtained in both leading order (LO) and next-to-leading order (NLO) of {alpha}{sub s}. As a result, valence-quark distributions are relatively well determined, whereas antiquark distributions at x>0.2 and gluon distributions in the whole x region have large uncertainties. The NLO uncertainties are slightly smaller than the LO ones; however, such a NLO improvement is not as significant as the nucleonic case.
Polyakov, Evgeny A; Vorontsov-Velyaminov, Pavel N
2014-08-28
Properties of ferrofluid bilayer (modeled as a system of two planar layers separated by a distance h and each layer carrying a soft sphere dipolar liquid) are calculated in the framework of inhomogeneous Ornstein-Zernike equations with reference hypernetted chain closure (RHNC). The bridge functions are taken from a soft sphere (1/r(12)) reference system in the pressure-consistent closure approximation. In order to make the RHNC problem tractable, the angular dependence of the correlation functions is expanded into special orthogonal polynomials according to Lado. The resulting equations are solved using the Newton-GRMES algorithm as implemented in the public-domain solver NITSOL. Orientational densities and pair distribution functions of dipoles are compared with Monte Carlo simulation results. A numerical algorithm for the Fourier-Hankel transform of any positive integer order on a uniform grid is presented. PMID:25173007
Directional velocity analyzer for measuring electron distribution functions in plasmas
NASA Technical Reports Server (NTRS)
Stenzel, R. L.; Gekelman, W.; Wild, N.; Urrutia, J. M.; Whelan, D.
1983-01-01
A directional velocity analyzer has been developed for measuring electron distribution functions in plasmas. It contains a collimating aperture which selects particles from a narrow cone in velocity space and a retarding potential analyzer. The distribution function f(v, theta, phi) is obtained from a large number of analyzer traces taken at different angles theta, phi. In addition, the small analyzer can be moved in space and the measurements are time resolved so as to obtain the complete phase space information f(v,r,t). The large data flow of this seven-variable function is processed with a high-speed digital data-acquisition system. The new electron velocity analyzer is applicable over a wide parameter range in electron energies and densities. Various cases of anisotropic distributions such as beams, shells, tails, and drifts have been successfully investigated.
Nonclassicality indicator for the real phase-space distribution functions
Sadeghi, Parvin; Khademi, Siamak; Nasiri, Sadollah
2010-07-15
Benedict et al. and Kenfack et al. advocated nonclassicality indicators based on the measurement of negativity of the Wigner distribution functions. These indicators have some applications in quantum mechanics and quantum optics. In this paper we define a nonclassicality indicator in terms of the interference in phase space, which is applicable to some real distribution functions including those of Wigner. As a special case one may reproduce the previous results using our indicator for the Wigner distribution functions. This indicator is examined for cases of the Schroedinger cat state and the thermal states and the results are compared with those obtained by previous methods. It seems that the physical behavior of nonclassicality indicators originates in the uncertainty principle. This is shown by an onto correspondence between these indicators and the uncertainty principle.
Weibel instability with non-Maxwellian distribution functions
Zaheer, S.; Murtaza, G.
2007-02-15
The Weibel instability in an unmagnetized plasma is investigated for non-Maxwellian distribution functions. In particular, analytical expressions are derived for the real and imaginary parts of the dielectric constant for the Maxwellian, kappa ({kappa}), and (r,q) distribution functions under the conditions of {xi}={omega}/k{sub parallel}{theta}{sub parallel}>>1 and <<1. The real frequency and the growth rate of the instability now depend upon the values of the spectral indices of the distribution functions. In general, the growth rate is suppressed for small values of {kappa} and q (keeping r fixed) and for negative values of r (keeping q fixed) instability transforms into damping. In the limiting cases (i) {kappa}{yields}{infinity} and (ii) r=0, q{yields}{infinity}, the results approach to the Maxwellian situation.
Measured quantum probability distribution functions for Brownian motion
Ford, G. W.; O'Connell, R. F.
2007-10-15
The quantum analog of the joint probability distributions describing a classical stochastic process is introduced. A prescription is given for constructing the quantum distribution associated with a sequence of measurements. For the case of quantum Brownian motion this prescription is illustrated with a number of explicit examples. In particular, it is shown how the prescription can be extended in the form of a general formula for the Wigner function of a Brownian particle entangled with a heat bath.
Asymptotic decay of the pair correlation function in molecular fluids: Application to hard rods
NASA Astrophysics Data System (ADS)
Savenko, S. V.; Dijkstra, Marjolein
2005-08-01
We investigate the asymptotic decay of the total correlation function h(1,2) in molecular fluids. To this end, we expand the angular dependence of h(1,2) and the direct correlation function c(1,2) in the Ornstein-Zernike equation in a complete set of rotational invariants. We show that all the harmonic expansion coefficients hl1l2l(r) are governed by a common exponential decay length and a common wavelength of oscillations in the isotropic phase. We determine the asymptotic decay of the total correlation functions by investigating the pole structure of the reciprocal ( q -space) harmonic expansion coefficients hl1l2l(q) . The expansion coefficients in laboratory frame of reference hl1l2l(r) are calculated in computer simulations for an isotropic fluid of hard spherocylinders. We find that the asymptotic decay of h(1,2) is exponentially damped oscillatory for hard spherocylinders with a length-to-diameter ratio L/D⩽10 for all statepoints in the isotropic fluid phase. We compare our results on the pole structure using different theoretical Ansätze for c(1,2) for hard ellipsoids. The theoretical results show that the asymptotic decay of h(1,2) is exponentially damped oscillatory for all elongations of the ellipsoids.
Shimizu, Eisuke; Tokuyama, Yuki; Okutsu, Naoko; Nomura, Kazuya; Danilov, Victor I; Kurita, Noriyuki
2015-01-01
Recently, the influence of radiation on human body has been recognized as a serious problem. In particular, highly reactive hydroxyl radicals *OH produced by the radiation react with DNA, resulting in a great damage on its structure and electronic properties. It is thus important to investigate the reaction mechanism of *OH to DNA for elucidating the initial damage in DNA induced by the radiation. In the present study, we search for transition states (TS) of the reaction between G-C/A-T base-pair and [Formula: see text] in vacuum and in water, by the density functional theory (DFT) calculations. At first, we obtain the stable structures for the dehydrogenated G-C and A-T, in which the hydrogen atom of NH2 group of G or A base is abstracted by [Formula: see text]. From the structures of the dehydrogenated as well as the natural base-pairs, the TS between these structures is searched for and the activation free energy (AFE) is estimated for the reaction. In vacuum, AFEs for the G-C and A-T are almost the same each other, while the stabilization energy by the reaction for G-C is about 4.9 kcal/mol larger than that for A-T, indicating that the population of the dehydrogenated G-C is remarkably larger than that of the dehydrogenated A-T in vacuum. On the other hand, in water approximated by the continuum solvation model, the AFE for A-T is 2.6 kcal/mol smaller than that for G-C, indicating that the reaction dehydrogenated by [Formula: see text] occurs more frequently for the solvated A-T base-pair than G-C. PMID:24460544
Lone-pair distribution and plumbite network formation in high lead silicate glass, 80PbO·20SiO2.
Alderman, Oliver L G; Hannon, Alex C; Holland, Diane; Feller, Steve; Lehr, Gloria; Vitale, Adam J; Hoppe, Uwe; Zimmerman, Martin v; Watenphul, Anke
2013-06-14
For the first time a detailed structural model has been determined which shows how the lone-pairs of electrons are arranged relative to each other in a glass network containing lone-pair cations. High energy X-ray and neutron diffraction patterns of a very high lead content silicate glass (80PbO·20SiO2) have been used to build three-dimensional models using empirical potential structure refinement. Coordination number and bond angle distributions reveal structural similarity to crystalline Pb11Si3O17 and α- and β-PbO, and therefore strong evidence for a plumbite glass network built from pyramidal [PbO(m)] polyhedra (m ~ 3-4), with stereochemically active lone-pairs, although with greater disorder in the first coordination shell of lead compared to the first coordination shell of silicon. The oxygen atoms are coordinated predominantly to four cations. Explicit introduction of lone-pair entities into some models leads to modification of the local Pb environment, whilst still allowing for reproduction of the measured diffraction patterns, thus demonstrating the non-uniqueness of the solutions. Nonetheless, the models share many features with crystalline Pb11Si3O17, including the O-Pb-O bond angle distribution, which is more highly structured than reported for lower Pb content glasses using reverse Monte Carlo techniques. The lone-pair separation of 2.85 Å in the model glasses compares favourably with that estimated in α-PbO as 2.88 Å, and these lone-pairs organise to create voids in the glass, just as they create channels in Pb11Si3O17 and interlayer spaces in the PbO polymorphs. PMID:23657606
Electron distribution function in a plasma generated by fission fragments
NASA Technical Reports Server (NTRS)
Hassan, H. A.; Deese, J. E.
1976-01-01
A Boltzmann equation formulation is presented for the determination of the electron distribution function in a plasma generated by fission fragments. The formulation takes into consideration ambipolar diffusion, elastic and inelastic collisions, recombination and ionization, and allows for the fact that the primary electrons are not monoenergetic. Calculations for He in a tube coated with fissionable material shows that, over a wide pressure and neutron flux range, the distribution function is non-Maxwellian, but the electrons are essentially thermal. Moreover, about a third of the energy of the primary electrons is transferred into the inelastic levels of He. This fraction of energy transfer is almost independent of pressure and neutron flux.
Functional implication of archaeal homologues of human RNase P protein pair Pop5 and Rpp30.
Hamasaki, Masato; Hazeyama, Kohsuke; Iwasaki, Fumihiko; Ueda, Toshifumi; Nakashima, Takashi; Kakuta, Yoshimitsu; Kimura, Makoto
2016-01-01
PhoPop5 and PhoRpp30 in the hyperthermophilic archaeon Pyrococcus horikoshii, homologues of human ribonuclease P (RNase P) proteins hPop5 and Rpp30, respectively, fold into a heterotetramer [PhoRpp30-(PhoPop5)2-PhoRpp30], which plays a crucial role in the activation of RNase P RNA (PhopRNA). Here, we examined the functional implication of PhoPop5 and PhoRpp30 in the tetramer. Surface plasmon resonance (SPR) analysis revealed that the tetramer strongly interacts with an oligonucleotide including the nucleotide sequence of a stem-loop SL3 in PhopRNA. In contrast, PhoPop5 had markedly reduced affinity to SL3, whereas PhoRpp30 had little affinity to SL3. SPR studies of PhoPop5 mutants further revealed that the C-terminal helix (α4) in PhoPop5 functions as a molecular recognition element for SL3. Moreover, gel filtration indicated that PhoRpp30 exists as a monomer, whereas PhoPop5 is an oligomer in solution, suggesting that PhoRpp30 assists PhoPop5 in attaining a functionally active conformation by shielding hydrophobic surfaces of PhoPop5. These results, together with available data, allow us to generate a structural and mechanistic model for the PhopRNA activation by PhoPop5 and PhoRpp30, in which the two C-terminal helices (α4) of PhoPop5 in the tetramer whose formation is assisted by PhoRpp30 act as binding elements and bridge SL3 and SL16 in PhopRNA. PMID:26152732
NASA Astrophysics Data System (ADS)
Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Aben, R.; Abolins, M.; AbouZeid, O. S.; Abramowicz, H.; Abreu, H.; Abreu, R.; Abulaiti, Y.; Acharya, B. S.; Adamczyk, L.; Adams, D. L.; Adelman, J.; Adomeit, S.; Adye, T.; Affolder, A. A.; Agatonovic-Jovin, T.; Agricola, J.; Aguilar-Saavedra, J. A.; Ahlen, S. P.; Ahmadov, F.; Aielli, G.; Akerstedt, H.; Åkesson, T. P. A.; Akimov, A. V.; Alberghi, G. L.; Albert, J.; Albrand, S.; Alconada Verzini, M. J.; Aleksa, M.; Aleksandrov, I. N.; Alexa, C.; Alexander, G.; Alexopoulos, T.; Alhroob, M.; Alimonti, G.; Alio, L.; Alison, J.; Alkire, S. P.; Allbrooke, B. M. M.; Allport, P. P.; Aloisio, A.; Alonso, A.; Alonso, F.; Alpigiani, C.; Altheimer, A.; Alvarez Gonzalez, B.; Álvarez Piqueras, D.; Alviggi, M. G.; Amadio, B. T.; Amako, K.; Amaral Coutinho, Y.; Amelung, C.; Amidei, D.; Amor Dos Santos, S. P.; Amorim, A.; Amoroso, S.; Amram, N.; Amundsen, G.; Anastopoulos, C.; Ancu, L. S.; Andari, N.; Andeen, T.; Anders, C. F.; Anders, G.; Anders, J. K.; Anderson, K. J.; Andreazza, A.; Andrei, V.; Angelidakis, S.; Angelozzi, I.; Anger, P.; Angerami, A.; Anghinolfi, F.; Anisenkov, A. V.; Anjos, N.; Annovi, A.; Antonelli, M.; Antonov, A.; Antos, J.; Anulli, F.; Aoki, M.; Aperio Bella, L.; Arabidze, G.; Arai, Y.; Araque, J. P.; Arce, A. T. H.; Arduh, F. A.; Arguin, J.-F.; Argyropoulos, S.; Arik, M.; Armbruster, A. J.; Arnaez, O.; Arnold, H.; Arratia, M.; Arslan, O.; Artamonov, A.; Artoni, G.; Artz, S.; Asai, S.; Asbah, N.; Ashkenazi, A.; Åsman, B.; Asquith, L.; Assamagan, K.; Astalos, R.; Atkinson, M.; Atlay, N. B.; Augsten, K.; Aurousseau, M.; Avolio, G.; Axen, B.; Ayoub, M. K.; Azuelos, G.; Baak, M. A.; Baas, A. E.; Baca, M. J.; Bacci, C.; Bachacou, H.; Bachas, K.; Backes, M.; Backhaus, M.; Bagiacchi, P.; Bagnaia, P.; Bai, Y.; Bain, T.; Baines, J. T.; Baker, O. K.; Baldin, E. M.; Balek, P.; Balestri, T.; Balli, F.; Balunas, W. K.; Banas, E.; Banerjee, Sw.; Bannoura, A. A. E.; Barak, L.; Barberio, E. L.; Barberis, D.; Barbero, M.; Barillari, T.; Barisonzi, M.; Barklow, T.; Barlow, N.; Barnes, S. L.; Barnett, B. M.; Barnett, R. M.; Barnovska, Z.; Baroncelli, A.; Barone, G.; Barr, A. J.; Barreiro, F.; Barreiro Guimarães da Costa, J.; Bartoldus, R.; Barton, A. E.; Bartos, P.; Basalaev, A.; Bassalat, A.; Basye, A.; Bates, R. L.; Batista, S. J.; Batley, J. R.; Battaglia, M.; Bauce, M.; Bauer, F.; Bawa, H. S.; Beacham, J. B.; Beattie, M. D.; Beau, T.; Beauchemin, P. H.; Beccherle, R.; Bechtle, P.; Beck, H. P.; Becker, K.; Becker, M.; Beckingham, M.; Becot, C.; Beddall, A. J.; Beddall, A.; Bednyakov, V. A.; Bee, C. P.; Beemster, L. J.; Beermann, T. A.; Begel, M.; Behr, J. K.; Belanger-Champagne, C.; Bell, W. H.; Bella, G.; Bellagamba, L.; Bellerive, A.; Bellomo, M.; Belotskiy, K.; Beltramello, O.; Benary, O.; Benchekroun, D.; Bender, M.; Bendtz, K.; Benekos, N.; Benhammou, Y.; Benhar Noccioli, E.; Benitez Garcia, J. A.; Benjamin, D. P.; Bensinger, J. R.; Bentvelsen, S.; Beresford, L.; Beretta, M.; Berge, D.; Bergeaas Kuutmann, E.; Berger, N.; Berghaus, F.; Beringer, J.; Bernard, C.; Bernard, N. R.; Bernius, C.; Bernlochner, F. U.; Berry, T.; Berta, P.; Bertella, C.; Bertoli, G.; Bertolucci, F.; Bertsche, C.; Bertsche, D.; Besana, M. I.; Besjes, G. J.; Bessidskaia Bylund, O.; Bessner, M.; Besson, N.; Betancourt, C.; Bethke, S.; Bevan, A. J.; Bhimji, W.; Bianchi, R. M.; Bianchini, L.; Bianco, M.; Biebel, O.; Biedermann, D.; Biesuz, N. V.; Biglietti, M.; Bilbao De Mendizabal, J.; Bilokon, H.; Bindi, M.; Binet, S.; Bingul, A.; Bini, C.; Biondi, S.; Bjergaard, D. M.; Black, C. W.; Black, J. E.; Black, K. M.; Blackburn, D.; Blair, R. E.; Blanchard, J.-B.; Blanco, J. E.; Blazek, T.; Bloch, I.; Blocker, C.; Blum, W.; Blumenschein, U.; Blunier, S.; Bobbink, G. J.; Bobrovnikov, V. S.; Bocchetta, S. S.; Bocci, A.; Bock, C.; Boehler, M.; Bogaerts, J. A.; Bogavac, D.; Bogdanchikov, A. G.; Bohm, C.; Boisvert, V.; Bold, T.; Boldea, V.; Boldyrev, A. S.; Bomben, M.; Bona, M.; Boonekamp, M.; Borisov, A.; Borissov, G.; Borroni, S.; Bortfeldt, J.; Bortolotto, V.; Bos, K.; Boscherini, D.; Bosman, M.; Boudreau, J.; Bouffard, J.; Bouhova-Thacker, E. V.; Boumediene, D.; Bourdarios, C.; Bousson, N.; Boutle, S. K.; Boveia, A.; Boyd, J.; Boyko, I. R.; Bozic, I.; Bracinik, J.; Brandt, A.; Brandt, G.; Brandt, O.; Bratzler, U.; Brau, B.; Brau, J. E.; Braun, H. M.; Breaden Madden, W. D.; Brendlinger, K.; Brennan, A. J.; Brenner, L.; Brenner, R.; Bressler, S.; Bristow, T. M.; Britton, D.; Britzger, D.; Brochu, F. M.; Brock, I.; Brock, R.; Bronner, J.; Brooijmans, G.; Brooks, T.; Brooks, W. K.; Brosamer, J.; Brost, E.; Bruckman de Renstrom, P. A.; Bruncko, D.; Bruneliere, R.; Bruni, A.; Bruni, G.; Bruschi, M.; Bruscino, N.; Bryngemark, L.; Buanes, T.; Buat, Q.; Buchholz, P.
2016-05-01
Distributions of transverse momentum p_T^{ℓ ℓ } and the related angular variable φ ^*_η of DrellΓÇôYan lepton pairs are measured in 20.3┬áfb^{-1} of protonΓÇôproton collisions at √{s}=8┬áTeV with the ATLAS detector at the LHC. Measurements in electron-pair and muon-pair final states are corrected for detector effects and combined. Compared to previous measurements in protonΓÇôproton collisions at √{s}=7┬áTeV, these new measurements benefit from a larger data sample and improved control of systematic uncertainties. Measurements are performed in bins of lepton-pair mass above, around and below the Z-boson mass peak. The data are compared to predictions from perturbative and resummed QCD calculations. For values of φ ^*_η < 1 the predictions from the Monte Carlo generator ResBos are generally consistent with the data within the theoretical uncertainties. However, at larger values of φ ^*_η this is not the case. Monte Carlo generators based on the parton-shower approach are unable to describe the data over the full range of p_T^{ℓ ℓ } while the fixed-order prediction of Dynnlo falls below the data at high values of p_T^{ℓ ℓ }. ResBos and the parton-shower Monte Carlo generators provide a much better description of the evolution of the φ ^*_η and p_T^{ℓ ℓ } distributions as a function of lepton-pair mass and rapidity than the basic shape of the data.
Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Aben, R.; Abolins, M.; AbouZeid, O. S.; Abramowicz, H.; Abreu, H.; Abreu, R.; et al
2016-05-23
Distributions of transverse momentum pTℓℓ and the related angular variablemore » $$\\phi ^*_{\\eta }$$ of Drell-Yan lepton pairs are measured in 20.3 fb–1 of proton-proton collisions at √s=8 TeV with the ATLAS detector at the LHC. Measurements in electron-pair and muon-pair final states are corrected for detector effects and combined. Compared to previous measurements in protonΓÇôproton collisions at √s=7 TeV these new measurements benefit from a larger data sample and improved control of systematic uncertainties. Measurements are performed in bins of lepton-pair mass above, around and below the Z -boson mass peak. The data are compared to predictions from perturbative and resummed QCD calculations. For values of $$\\phi ^*_{\\eta }$$<1 the predictions from the Monte Carlo generator ResBos are generally consistent with the data within the theoretical uncertainties. However, at larger values of $$\\phi ^*_{\\eta }$$ this is not the case. Monte Carlo generators based on the parton-shower approach are unable to describe the data over the full range of pTℓℓ while the fixed-order prediction of Dynnlo falls below the data at high values of pTℓℓ. Here, ResBos and the parton-shower Monte Carlo generators provide a much better description of the evolution of the $$\\phi ^*_{\\eta }$$ and pTℓℓ distributions as a function of lepton-pair mass and rapidity than the basic shape of the data.« less
Two-integral distribution functions for axisymmetric galaxies
NASA Technical Reports Server (NTRS)
Hunter, C.; Qian, Edward
1993-01-01
The new method presented for finding distribution functions, which depend only on the classical integrals of energy and angular momentum for stellar systems with known axisymmetric densities, is the analog for the axisymmetric case of Eddington's classical solution for the isotropic distribution function, depending only on energy, of a known spherical density. It is required that density be expressed as a function of the potential and of a radial coordinate. Our solution is also an integral which is derived directly from the density, and hence can be used with complicated densities. A numerical quadrature is generally required to evaluate this solution, but contour integrals can be computed accurately by numerical quadrature; this is preferable to an explicit evaluation if the latter is an infinite series, such as is obtained using Fricke's method. We give several examples, including some for which our distribution functions are new. Our method can be extended simply to the related problems of finding anisotropic distribution functions for spherical or disk systems.
Li, Hao; Huang, Yue; Yu, Yue; Li, Tianqi; Li, Genxi; Anzai, Jun-ichi
2016-01-01
Diseases such as cancer arise from systematical reconfiguration of interactions of exceedingly large numbers of proteins in cell signaling. The study of such complicated molecular mechanisms requires multiplexed detection of the inter-connected activities of several proteins in a disease-associated context. However, the existing methods are generally not well-equipped for this kind of application. Here a method for analyzing functionally linked protein activities is developed based on enzyme controlled pairing between complementary peptide helix strands, which simultaneously enables elaborate regulation of catalytic activity of the paired peptides. This method has been used to detect three different types of protein modification enzymes that participate in the modification of extracellular matrix and the formation of invasion front in tumour. In detecting breast cancer tissue samples using this method, up-regulated activity can be observed for two of the assessed enzymes, while the third enzyme is found to have a subtle fluctuation of activity. These results may point to the application of this method in evaluating prometastatic activities of proteins in tumour. PMID:27140831
On the anisotropy of the He+ velocity distribution function
NASA Astrophysics Data System (ADS)
Drews, Christian; Berger, Lars; Taut, Andreas; Peleikis, Thies; Wimmer-Schweingruber, Robert F.
2016-03-01
Shortly after their ionization, PickUp Ions (PUIs) develop a highly anisotropic toroidal Velocity Distribution Function (VDF) due to their interaction with the magnetized solar wind plasma. In this study we present a method to quantify the anisotropic state of pickup ion velocity distribution functions via in-situ PUI observations. The ratio R(wsw) = f (wsw)⊥/f (wsw)|| is obtained by sorting the observed PUI velocity spectra, f (wsw), into two different magnetic regimes, one magnetic field orientation, Φ⊥, in which the PUI torus distribution lies inside the instrument's field of view (Φ⊥), and one in which the torus distribution lies exclusively outside the instrument's aperture (Φ‖). Because R(wsw) is a measure of the relative flux increase induced by PUIs that are distributed anisotropically compared to PUIs distributed isotropically in phase space, we can quantify the anisotropy of the pickup ion VDF via this approach. The method is then applied to the example of He+ observation by STEREO PLASTIC in an energy range between 0.2 < wsw < 2.7
Hinde, Elizabeth; Digman, Michelle A.; Hahn, Klaus M.; Gratton, Enrico
2013-01-01
Here we present a fluctuation-based approach to biosensor Förster resonance energy transfer (FRET) detection that can measure the molecular flow and signaling activity of proteins in live cells. By simultaneous use of the phasor approach to fluorescence lifetime imaging microscopy (FLIM) and cross–pair correlation function (pCF) analysis along a line scanned in milliseconds, we detect the spatial localization of Rho GTPase activity (biosensor FRET signal) as well as the diffusive route adopted by this active population. In particular we find, for Rac1 and RhoA, distinct gradients of activation (FLIM-FRET) and a molecular flow pattern (pCF analysis) that explains the observed polarized GTPase activity. This multiplexed approach to biosensor FRET detection serves as a unique tool for dissection of the mechanism(s) by which key signaling proteins are spatially and temporally coordinated. PMID:23248275
NASA Astrophysics Data System (ADS)
Brandt, Benedikt B.; Yannouleas, Consatntine; Landman, Uzi
We report on exact benchmark configuration-interaction computational solutions of the many-body Hamiltonian, uncovering the spectral evolution, wave function anatomy, and entanglement properties of a few interacting ultracold fermions in the entire parameter range, including crossover from an single-well to a double-well confinement and a controllable energy imbalance between the wells. According to recent experiments, the two wells are taken as quasi-one-dimensional and both the linear and parrallel configurations of them are considered. We demonstrate attractive pairing and formation of repulsive, highly correlated, ultracold Wigner molecules, associated with the emergence of Heisenberg spin chains. For two fermions, the entanglement measure of the von-Neumann entropy is used as a diagnostic tool for identifying maximally entangled two-qubit Bell states. Supported by the Air Force Office of Scientific Research.
The Functional Distribution of Setswana and English in Botswana
ERIC Educational Resources Information Center
Bagwasi, Mompoloki M.
2003-01-01
In multilingual societies such as Botswana, language use is an extremely complex matter, further compounded by the fact that the languages involved are themselves dynamic phenomena that often elude the planned outcomes of policies which try to shape and constrain them. The paper describes the functional distribution of the national language…
Numerical Loading of a Maxwellian Probability Distribution Function
J. L. V. Lewandowski
2003-03-24
A renormalization procedure for the numerical loading of a Maxwellian probability distribution function (PDF) is formulated. The procedure, which involves the solution of three coupled nonlinear equations, yields a numerically loaded PDF with improved properties for higher velocity moments. This method is particularly useful for low-noise particle-in-cell simulations with electron dynamics.
Diaphony, a measure of uniform distribution, and the Patterson function.
Hornfeck, Wolfgang; Kuhn, Philipp
2015-07-01
This paper reviews the number-theoretic concept of diaphony, a measure of uniform distribution for number sequences and point sets based on a Fourier theory approach, and its relation to crystallographic concepts like the largest interplanar spacing of a lattice, the structure-factor equation and the Patterson function. PMID:26131895
Photoelectron distribution function over the illuminated part of the Moon
NASA Astrophysics Data System (ADS)
Popel, Sergey I.; Golub', Anatoly; Zelenyi, Lev
2014-09-01
Photoelectron distribution functions in the near-surface layer over the lunar surface are obtained on the basis of the kinetic approach. The results are shown to depend strongly on the quantum yield of lunar regolith. It is demonstrated that photoelectrons with energies of about both 1 eV and 0.1 eV should be observed in the corresponding measurements.
A TWACS system alarm function for distribution automation
Mak, S.T.; Radford, D. )
1994-04-01
A new application designated as the System Alarm Function'' is made possible by using the Unsolicited Inbound'' capability recently developed for the Two Way Automatic Communication System (TWACS) System-10, which is already used by several electric utilities in the USA for demand side management, remote metering and distribution automation is reviewed here. The UNSOLICITED INBOUND'' algorithm development, the operational issues that are pertinent to the understanding of collisions between multiple alarms and the effects on the alarm response time'' are discussed in detail. This master-to-master relationship between remote transponders in the distribution network and the central control computer opens the door to multiple functional capabilities in the area of distribution automation and remote monitoring.
Biswas, Anindya; Das, Tapan Kumar; Chakrabarti, Barnali
2010-09-14
We study the ground state pair-correlation properties of a weakly interacting trapped Bose gas in three dimensions by using a correlated many-body method. The use of the van der Waals interaction potential and an external trapping potential shows realistic features. We also test the validity of shape-independent approximation in the calculation of correlation properties.
Johnson SB as general functional form for raindrop size distribution
NASA Astrophysics Data System (ADS)
Cugerone, Katia; De Michele, Carlo
2015-08-01
Drop size distribution represents the statistical synthesis of rainfall dynamics at particle size scale. Gamma and Lognormal distributions have been widely used in the literature to approximate the drop diameter variability, contrarily to the natural upper boundary of the variable, with almost always site-specific studies and without the support of statistical goodness-of-fit tests. In this work, we present an extensive statistical investigation of raindrop size distribution based on eight data sets, well distributed on the Earth's surface, which have been analyzed by using skewness-kurtosis plane, AIC and BIC indices and Kolmogorov-Smirnov test. Here for the first time, the Johnson SB is proposed as general functional form to describe the drop diameter variability specifically at 1 min time scale. Additional analyses demonstrate that the model is well suitable even for larger time intervals (≥1 min).
Analytic scaling function for island-size distributions.
Dubrovskii, V G; Sibirev, N V
2015-04-01
We obtain an explicit solution for the island-size distribution described by the rate equations for irreversible growth with the simplified capture rates of the form σ(s)(Θ)∝Θ(p)(a+s-1) for all s≥1, where s is the size and Θ is the time-dependent coverage. The intrinsic property of this solution is its scaling form in the continuum limit. The analytic scaling function depends on the two parameters a and p and is capable of describing very dissimilar distribution shapes, both monomodal and monotonically decreasing. The obtained results suggest that the scaling features of the size distributions are closely related to the size linearity of the capture rates. A simple analytic scaling is obtained rigorously here and helps to gain a better theoretical understanding of possible origins of the scaling behavior of the island-size distributions. PMID:25974509
Valence-quark distribution functions in the kaon and pion
NASA Astrophysics Data System (ADS)
Chen, Chen; Chang, Lei; Roberts, Craig D.; Wan, Shaolong; Zong, Hong-Shi
2016-04-01
We describe expressions for pion and kaon dressed-quark distribution functions that incorporate contributions from gluons which bind quarks into these mesons and hence overcome a flaw of the commonly used handbag approximation. The distributions therewith obtained are purely valence in character, ensuring that dressed quarks carry all the meson's momentum at a characteristic hadronic scale and vanish as (1 -x )2 when Bjorken-x →1 . Comparing such distributions within the pion and kaon, it is apparent that the size of S U (3 ) -flavor symmetry breaking in meson parton distribution functions is modulated by the flavor dependence of dynamical chiral symmetry breaking. Corrections to these leading-order formulas may be divided into two classes, responsible for shifting dressed-quark momentum into glue and sea quarks. Working with available empirical information, we build an algebraic framework that is capable of expressing the principal impact of both classes of corrections. This enables a realistic comparison with experiment which allows us to identify and highlight basic features of measurable pion and kaon valence-quark distributions. We find that whereas roughly two thirds of the pion's light-front momentum is carried by valence dressed quarks at a characteristic hadronic scale; this fraction rises to 95% in the kaon; evolving distributions with these features to a scale typical of available Drell-Yan data produces a kaon-to-pion ratio of u -quark distributions that is in agreement with the single existing data set, and predicts a u -quark distribution within the pion that agrees with a modern reappraisal of π N Drell-Yan data. Precise new data are essential in order to validate this reappraisal and because a single modest-quality measurement of the kaon-to-pion ratio cannot be considered definitive.
Aaltonen, T
2011-04-28
We report a study of the invariant mass distribution of jet pairs produced in association with a W boson using data collected with the CDF detector which correspond to an integrated luminosity of 4.3 fb^{-1}. The observed distribution has an excess in the 120-160 GeV/c^{2} mass range which is not described by current theoretical predictions within the statistical and systematic uncertainties. In this letter we report studies of the properties of this excess.
NASA Astrophysics Data System (ADS)
Harnisch, Bernd; Weigel, Thomas
1994-09-01
The calculation of the BRDF (Bi-Directional-Reflection-Distribution-Function) from profile measurements was performed theoretically and verified by measurements on a BK7 sample. The assumptions on the surface topography and approximations done are highlighted.
Variations of electron distribution functions in the solar wind
NASA Technical Reports Server (NTRS)
Pilipp, W. G.; Muehlhaeuser, K.-H.; Miggenrieder, H.; Rosenbauer, H.; Schwenn, R.
1987-01-01
Variations of electron distribution functions in the solar wind have been investigated using the electron data observed aboard Helios 2 during the first four months of its mission in 1976 in the distance range between 0.3 and 1 AU. In particular, variations across the sector structure of the interplanetary magnetic field and across the plasma stream structures have been studied. It has been found that there is a strong correlation between the electron properties and the sector structure of the magnetic field. Within the interior of magnetic sectors the electron distribution functions are extremely anisotropic and skewed with respect to the magnetic field direction at high particle energies. Toward sector boundaries the electron distribution functions become less anisotropic and less skewed. Right at sector boundaries the electrons are relatively cool, and their distributions are nearly isotropic often showing a slight bidirectional anisotropy. These observations have been interpreted to indicate that scattering of electrons with energies above 100 eV is weak within the interior of magnetic sectors but anomalous scattering increases drastically toward sector boundaries for all energies in the halo regime up to several hundred eV. There is evidence for closed magnetic field structures, probably occurring frequently in the solar wind, where the magnetic field lines should usually be connected to the sun outside sector boundaries but may or may not be disconnected from the sun at sector boundaries.
Magnetospheric electron-velocity-distribution function information from wave observations
NASA Astrophysics Data System (ADS)
Benson, Robert F.; ViñAs, Adolfo F.; Osherovich, Vladimir A.; Fainberg, Joseph; Purser, Carola M.; Adrian, Mark L.; Galkin, Ivan A.; Reinisch, Bodo W.
2013-08-01
The electron-velocity-distribution function was determined to be highly non-Maxwellian and more appropriate to a kappa distribution, with κ ≈ 2.0, near magnetic midnight in the low-latitude magnetosphere just outside a stable plasmasphere during extremely quiet geomagnetic conditions. The kappa results were based on sounder-stimulated Qn plasma resonances using the Radio Plasma Imager (RPI) on the IMAGE satellite; the state of the plasmasphere was determined from IMAGE/EUV observations. The Qn resonances correspond to the maximum frequencies of Bernstein-mode waves that are observed between the harmonics of the electron cyclotron frequency in the frequency domain above the upper-hybrid frequency. Here we present the results of a parametric investigation that included suprathermal electrons in the electron-velocity-distribution function used in the plasma-wave dispersion equation to calculate the Qn frequencies for a range of kappa and fpe/fce values for Qn resonances from Q1 to Q9. The Qn frequencies were also calculated using a Maxwellian distribution, and they were found to be greater than those calculated using a kappa distribution with the frequency differences increasing with increasing n for a fixed κ and with decreasing κ for a fixed n. The calculated fQn values have been incorporated into the RPI BinBrowser software providing a powerful tool for rapidly obtaining information on the nature of the magnetospheric electron-velocity-distribution function and the electron number density Ne. This capability enabled accurate (within a few percent) in situ Ne determinations to be made along the outbound orbital track as IMAGE moved away from the plasmapause. The extremely quiet geomagnetic conditions allowed IMAGE/EUV-extracted counts to be compared with the RPI-determined orbital-track Ne profile. The comparisons revealed remarkably similar Ne structures.
Magnetospheric Electron-Velocity-Distribution Function Information from Wave Observations
NASA Astrophysics Data System (ADS)
Benson, R. F.; Vinas, A. F.; Osherovich, V. A.; Fainberg, J.; Purser, C. M.; Adrian, M. L.; Galkin, I. A.; Reinisch, B. W.
2013-12-01
The electron-velocity-distribution function was determined to be highly non-Maxwellian and more appropriate to a kappa distribution, with κ ≈ 2.0, near magnetic midnight in the low-latitude magnetosphere just outside a stable plasmasphere during extremely quiet geomagnetic conditions. The kappa results were based on sounder-stimulated Qn plasma resonances using the Radio Plasma Imager (RPI) on the IMAGE satellite; the state of the plasmasphere was determined from IMAGE/EUV observations. The Qn resonances correspond to the maximum frequencies of Bernstein-mode waves that are observed between the harmonics of the electron cyclotron frequency in the frequency domain above the upper-hybrid frequency. Here we present the results of a parametric investigation that included suprathermal electrons in the electron-velocity-distribution function used in the plasma-wave dispersion equation to calculate the Qn frequencies for a range of kappa and fpe/fce values for Qn resonances from Q1 to Q9. The Qn frequencies were also calculated using a Maxwellian distribution and they were found to be greater than those calculated using a kappa distribution with the frequency differences increasing with increasing n for a fixed κ and with decreasing κ for a fixed n. The calculated fQn values have been incorporated into the RPI BinBrowser software providing a powerful tool for rapidly obtaining information on the nature of the magnetospheric electron-velocity-distribution function and the electron number density Ne. This capability enabled accurate (within a few percent) in-situ Ne determinations to be made along the outbound orbital track as IMAGE moved away from the plasmapause. The extremely quiet geomagnetic conditions allowed IMAGE/EUV-extracted counts to be compared with the RPI-determined orbital-track Ne profile. The comparisons revealed remarkably similar Ne structures.
Transverse momentum dependent distribution functions in the bag model
Harut A. Avakian; Efremov, A. V.; Schweitzer, P.; Yuan, F.
2010-04-01
Leading and subleading twist transverse momentum dependent parton distribution functions (TMDs) are studied in a quark model framework provided by the bag model. A complete set of relations among different TMDs is derived, and the question is discussed how model-(in)dependent such relations are. A connection of the pretzelosity distribution and quark orbital angular momentum is derived. Numerical results are presented, and applications for phenomenology discussed. In particular, it is shown that in the valence-x region the bag model supports a Gaussian Ansatz for the transverse momentum dependence of TMDs.
Transverse momentum dependent distribution functions in the bag model
Avakian, H.; Efremov, A. V.; Schweitzer, P.; Yuan, F.
2010-04-01
Leading and subleading-twist transverse momentum dependent parton distribution functions (TMDs) are studied in a quark-model framework provided by the bag model. A complete set of relations among different TMDs is derived, and the question is discussed how model (in)dependent such relations are. A connection of the pretzelosity distribution and quark orbital angular momentum is derived. Numerical results are presented, and applications for phenomenology are discussed. In particular, it is shown that in the valence-x region the bag model supports a Gaussian Ansatz for the transverse momentum dependence of TMDs.
The transverse momentum dependent distribution functions in the bag model
Avakian, Harut; Efremov, Anatoly; Schweitzer, Peter; Yuan, Feng
2010-01-29
Leading and subleading twist transverse momentum dependent parton distribution functions (TMDs) are studied in a quark model framework provided by the bag model. A complete set of relations among different TMDs is derived, and the question is discussed how model-(in)dependent such relations are. A connection of the pretzelosity distribution and quark orbital angular momentum is derived. Numerical results are presented, and applications for phenomenology discussed. In particular, it is shown that in the valence-x region the bag model supports a Gaussian Ansatz for the transverse momentum dependence of TMDs.
Sim, Joo Yong; Moeller, Jens; Hart, Kevin C.; Ramallo, Diego; Vogel, Viola; Dunn, Alex R.; Nelson, W. James; Pruitt, Beth L.
2015-01-01
Mechanical linkage between cell–cell and cell–extracellular matrix (ECM) adhesions regulates cell shape changes during embryonic development and tissue homoeostasis. We examined how the force balance between cell–cell and cell–ECM adhesions changes with cell spread area and aspect ratio in pairs of MDCK cells. We used ECM micropatterning to drive different cytoskeleton strain energy states and cell-generated traction forces and used a Förster resonance energy transfer tension biosensor to ask whether changes in forces across cell–cell junctions correlated with E-cadherin molecular tension. We found that continuous peripheral ECM adhesions resulted in increased cell–cell and cell–ECM forces with increasing spread area. In contrast, confining ECM adhesions to the distal ends of cell–cell pairs resulted in shorter junction lengths and constant cell–cell forces. Of interest, each cell within a cell pair generated higher strain energies than isolated single cells of the same spread area. Surprisingly, E-cadherin molecular tension remained constant regardless of changes in cell–cell forces and was evenly distributed along cell–cell junctions independent of cell spread area and total traction forces. Taken together, our results showed that cell pairs maintained constant E-cadherin molecular tension and regulated total forces relative to cell spread area and shape but independently of total focal adhesion area. PMID:25971797
NASA Astrophysics Data System (ADS)
Julie, Hongki; Pasaribu, Udjianna S.; Pancoro, Adi
2015-12-01
This paper will allow Markov Chain's application in genome shared identical by descent by two individual at full sibs model. The full sibs model was a continuous time Markov Chain with three state. In the full sibs model, we look for the cumulative distribution function of the number of sub segment which have 2 IBD haplotypes from a segment of the chromosome which the length is t Morgan and the cumulative distribution function of the number of sub segment which have at least 1 IBD haplotypes from a segment of the chromosome which the length is t Morgan. This cumulative distribution function will be developed by the moment generating function.
Ma, Ge; Pan, Ping-Ying; Eisenstein, Samuel; Divino, Celia M; Lowell, Clifford A; Takai, Toshiyuki; Chen, Shu-Hsia
2011-03-25
Myeloid-derived suppressor cells (MDSCs) bear characteristics of precursors for both M1 and M2 macrophages. The molecular mechanism underlying the differentiation into M1 and M2 macrophages and the relationship of this differentiation to antitumor responses remains largely undefined. Herein, we investigate the potential function of paired immunoglobulin-like receptor B (PIR-B), also known as leukocyte immunoglobulin-like receptor subfamily B member 3 (LILRB3) in MDSC differentiation, and its role in tumor-induced immunity. Our studies indicated that MDSCs genetically ablated for PIR-B (Lilrb3(-/-)) underwent a specific transition to M1-like cells when entering the periphery from bone marrow, resulting in decreased suppressive function, regulatory T cell activation activity, primary tumor growth, and lung metastases. Activation of Toll-like receptor (TLR), signal transducers, and activators of transcription 1 (STAT1), and nuclear factor-kappa B (NF-κB) signaling in Lilrb3(-/-) MDSC promoted the acquisition of M1 phenotype. Inhibition of the PIR-B signaling pathway promoted MDSC differentiation into M1 macrophages. PMID:21376641
Hwang, Candy S.; Xu, Liang; Wang, Wei; Ulrich, Sébastien; Zhang, Lu; Chong, Jenny; Shin, Ji Hyun; Huang, Xuhui; Kool, Eric T.; McKenna, Charles E.; Wang, Dong
2016-01-01
RNA polymerase II (pol II) utilizes a complex interaction network to select and incorporate correct nucleoside triphosphate (NTP) substrates with high efficiency and fidelity. Our previous ‘synthetic nucleic acid substitution’ strategy has been successfully applied in dissecting the function of nucleic acid moieties in pol II transcription. However, how the triphosphate moiety of substrate influences the rate of P-O bond cleavage and formation during nucleotide incorporation is still unclear. Here, by employing β,γ-bridging atom-‘substituted’ NTPs, we elucidate how the methylene substitution in the pyrophosphate leaving group affects cognate and non-cognate nucleotide incorporation. Intriguingly, the effect of the β,γ-methylene substitution on the non-cognate UTP/dT scaffold (∼3-fold decrease in kpol) is significantly different from that of the cognate ATP/dT scaffold (∼130-fold decrease in kpol). Removal of the wobble hydrogen bonds in U:dT recovers a strong response to methylene substitution of UTP. Our kinetic and modeling studies are consistent with a unique altered transition state for bond formation and cleavage for UTP/dT incorporation compared with ATP/dT incorporation. Collectively, our data reveals the functional interplay between NTP triphosphate moiety and base pair hydrogen bonding recognition during nucleotide incorporation. PMID:27060150
Transverse momentum-dependent parton distribution functions in lattice QCD
Engelhardt, Michael G.; Musch, Bernhard U.; Haegler, Philipp G.; Negele, John W.; Schaefer, Andreas
2013-08-01
A fundamental structural property of the nucleon is the distribution of quark momenta, both parallel as well as perpendicular to its propagation. Experimentally, this information is accessible via selected processes such as semi-inclusive deep inelastic scattering (SIDIS) and the Drell-Yan process (DY), which can be parametrized in terms of transversemomentum-dependent parton distributions (TMDs). On the other hand, these distribution functions can be extracted from nucleon matrix elements of a certain class of bilocal quark operators in which the quarks are connected by a staple-shaped Wilson line serving to incorporate initial state (DY) or final state (SIDIS) interactions. A scheme for evaluating such matrix elements within lattice QCD is developed. This requires casting the calculation in a particular Lorentz frame, which is facilitated by a parametrization of the matrix elements in terms of invariant amplitudes. Exploratory results are presented for the time-reversal odd Sivers and Boer-Mulders transverse momentum shifts.
Oblique propagation, wave particle interaction and particle distribution function
NASA Astrophysics Data System (ADS)
Osmane, Adnane; Hamza, A. M.; Meziane, Karim
Recent results from the Cluster mission have stimulated theoretical investigations and simulations to explain ion distribution functions observed in the quasi-perp bow shock. High-time resolution observations have revealed distributions of gyrating ions that are gyrophase-bunched. When not produced at the shock, such distributions are believed to be resulting from interactions between field-aligned beams and low frequency beamdriven waves . The Conventional models used to account for such distributions assume that the waves are purely transverse, and that they propagate parallel to the ambient magnetic eld. However observations indicate that these waves are propagating obliquely with respect to the ambient magnetic eld [Meziane et al., 2001]. A theoretical investigation of the non-relativistic wave-particle interaction in a background magnetic eld with the electromagnetic wave propagating obliquely has been addressed previously, resulting in a dynamical system describing the wave interaction with a single ion in the absence of dissipation mechanisms. [Hamza et al., 2005] This dynamical system has been numerically integrated to construct the ion distribution functions by seeding the particles with di erent initial conditions. We compute the particle orbits and simulate the time evolution of the distribution functions based on Liouville's theorem of phase space density conservation. It will be shown that the trapping which is due to the oblique propagation of the wave, gives an explanation for gyrophase-bunching and unstable distributions in velocity space which could trigger instabilities such as firehose and mirror. Therefore this exercise provide insights on the particle dynamics and onset of waves away from the shock. Meziane, K., C. Mazelle, R.P. Lin, D. LeQueau, D.E. Larson, G.K. Parks, R.P. Lepping (2001), Three dimensional observations of gyrating ions distributions far upstream from the Earth's bow shock and their association with low-frequency waves, J
Probabilistic Q-function distributions in fermionic phase-space
NASA Astrophysics Data System (ADS)
Rosales-Zárate, Laura E. C.; Drummond, P. D.
2015-03-01
We obtain a positive probability distribution or Q-function for an arbitrary fermionic many-body system. This is different to previous Q-function proposals, which were either restricted to a subspace of the overall Hilbert space, or used Grassmann methods that do not give probabilities. The fermionic Q-function obtained here is constructed using normally ordered Gaussian operators, which include both non-interacting thermal density matrices and BCS states. We prove that the Q-function exists for any density matrix, is real and positive, and has moments that correspond to Fermi operator moments. It is defined on a finite symmetric phase-space equivalent to the space of real, antisymmetric matrices. This has the natural SO(2M) symmetry expected for Majorana fermion operators. We show that there is a physical interpretation of the Q-function: it is the relative probability for observing a given Gaussian density matrix. The distribution has a uniform probability across the space at infinite temperature, while for pure states it has a maximum value on the phase-space boundary. The advantage of probabilistic representations is that they can be used for computational sampling without a sign problem.
Hyaluronan and synovial joint: function, distribution and healing
2013-01-01
Synovial fluid is a viscous solution found in the cavities of synovial joints. The principal role of synovial fluid is to reduce friction between the articular cartilages of synovial joints during movement. The presence of high molar mass hyaluronan (HA) in this fluid gives it the required viscosity for its function as lubricant solution. Inflammation oxidation stress enhances normal degradation of hyaluronan causing several diseases related to joints. This review describes hyaluronan properties and distribution, applications and its function in synovial joints, with short review for using thiol compounds as antioxidants preventing HA degradations under inflammation conditions. PMID:24678248
Ploetz, Elizabeth A.; Karunaweera, Sadish; Smith, Paul E.
2015-01-28
Fluctuation solution theory has provided an alternative view of many liquid mixture properties in terms of particle number fluctuations. The particle number fluctuations can also be related to integrals of the corresponding two body distribution functions between molecular pairs in order to provide a more physical picture of solution behavior and molecule affinities. Here, we extend this type of approach to provide expressions for higher order triplet and quadruplet fluctuations, and thereby integrals over the corresponding distribution functions, all of which can be obtained from available experimental thermodynamic data. The fluctuations and integrals are then determined using the International Association for the Properties of Water and Steam Formulation 1995 (IAPWS-95) equation of state for the liquid phase of pure water. The results indicate small, but significant, deviations from a Gaussian distribution for the molecules in this system. The pressure and temperature dependence of the fluctuations and integrals, as well as the limiting behavior as one approaches both the triple point and the critical point, are also examined.
Ploetz, Elizabeth A; Karunaweera, Sadish; Smith, Paul E
2015-01-28
Fluctuation solution theory has provided an alternative view of many liquid mixture properties in terms of particle number fluctuations. The particle number fluctuations can also be related to integrals of the corresponding two body distribution functions between molecular pairs in order to provide a more physical picture of solution behavior and molecule affinities. Here, we extend this type of approach to provide expressions for higher order triplet and quadruplet fluctuations, and thereby integrals over the corresponding distribution functions, all of which can be obtained from available experimental thermodynamic data. The fluctuations and integrals are then determined using the International Association for the Properties of Water and Steam Formulation 1995 (IAPWS-95) equation of state for the liquid phase of pure water. The results indicate small, but significant, deviations from a Gaussian distribution for the molecules in this system. The pressure and temperature dependence of the fluctuations and integrals, as well as the limiting behavior as one approaches both the triple point and the critical point, are also examined. PMID:25637990
Karunaweera, Sadish
2015-01-01
Fluctuation solution theory has provided an alternative view of many liquid mixture properties in terms of particle number fluctuations. The particle number fluctuations can also be related to integrals of the corresponding two body distribution functions between molecular pairs in order to provide a more physical picture of solution behavior and molecule affinities. Here, we extend this type of approach to provide expressions for higher order triplet and quadruplet fluctuations, and thereby integrals over the corresponding distribution functions, all of which can be obtained from available experimental thermodynamic data. The fluctuations and integrals are then determined using the International Association for the Properties of Water and Steam Formulation 1995 (IAPWS-95) equation of state for the liquid phase of pure water. The results indicate small, but significant, deviations from a Gaussian distribution for the molecules in this system. The pressure and temperature dependence of the fluctuations and integrals, as well as the limiting behavior as one approaches both the triple point and the critical point, are also examined. PMID:25637990
Work function distribution for W Ir mixed metal matrix cathodes
NASA Astrophysics Data System (ADS)
Santhosh Kumar, K.; Durga Devi, P.; Ravi, M.; Bhat, K. S.
2006-06-01
Mixed metal matrix cathodes have inherent non-uniformity and patchiness of emission due to the presence of two-alloy phase structure on the surface. I- V characteristics of cathode studied in a close spaced diode configuration is one of the easy and cost effective methods to estimate the variation of work function on the cathode surface. Tungsten iridium mixed metal matrix dispenser cathodes of Ø1.4 mm (80 wt.% W-20 wt.% Ir) have been fabricated in the laboratory and their I- V characteristics have been investigated in diode configuration. In this paper the model suggested by Tonnerre et al. has been used to find out the work function distribution of W-Ir cathodes from I- V characteristics. An attempt has been made to correlate the microstructure with the work function values.
Bork, Nicolai; Bonanos, Nikolaos; Rossmeisl, Jan; Vegge, Tejs
2011-09-01
A density functional theory investigation of the thermodynamic and kinetic properties of hydrogen-hydrogen defect interactions in the cubic SrTiO(3) perovskite is presented. We find a net attraction between two hydrogen atoms with an optimal separation of ∼2.3 Å. The energy gain is ca. 0.33 eV compared to two non-interacting H defects. The main cause of the net attractive potential is elastic defect interactions through lattice deformation. Two possible diffusion paths for the hydrogen defect pair are investigated and are both determined to be faster than the corresponding diffusion path for single hydrogen atoms. Finally, we set up a simple model to determine the contribution from the double hydrogen defect to the total hydrogen flux, and find the double defect to be the main diffusing species at temperatures below ca. 400 °C. Post submission infrared absorption experiments show excellent agreement with the proposed properties of the double hydrogen defect. PMID:21769355
Improving Project Management with Simulation and Completion Distribution Functions
NASA Technical Reports Server (NTRS)
Cates, Grant R.
2004-01-01
Despite the critical importance of project completion timeliness, management practices in place today remain inadequate for addressing the persistent problem of project completion tardiness. A major culprit in late projects is uncertainty, which most, if not all, projects are inherently subject to. This uncertainty resides in the estimates for activity durations, the occurrence of unplanned and unforeseen events, and the availability of critical resources. In response to this problem, this research developed a comprehensive simulation based methodology for conducting quantitative project completion time risk analysis. It is called the Project Assessment by Simulation Technique (PAST). This new tool enables project stakeholders to visualize uncertainty or risk, i.e. the likelihood of their project completing late and the magnitude of the lateness, by providing them with a completion time distribution function of their projects. Discrete event simulation is used within PAST to determine the completion distribution function for the project of interest. The simulation is populated with both deterministic and stochastic elements. The deterministic inputs include planned project activities, precedence requirements, and resource requirements. The stochastic inputs include activity duration growth distributions, probabilities for events that can impact the project, and other dynamic constraints that may be placed upon project activities and milestones. These stochastic inputs are based upon past data from similar projects. The time for an entity to complete the simulation network, subject to both the deterministic and stochastic factors, represents the time to complete the project. Repeating the simulation hundreds or thousands of times allows one to create the project completion distribution function. The Project Assessment by Simulation Technique was demonstrated to be effective for the on-going NASA project to assemble the International Space Station. Approximately $500
Chasman, R.R.
1996-12-31
In this contribution, the author mentions some features of pairing forces that are unique to nuclei and cover some areas of major interest in nuclear structure research, that involve pairing. At the level of most nuclear structure studies, nuclei are treated as consisting of two kinds of fermions (protons and neutrons) in a valence space with rather few levels. These features give rise to unique aspects of pairing forces in nuclei: (1) n-p pairing in T = 0 as well as the usual T = 1 pairing that is characteristic of like fermions; (2) a need to correct pairing calculations for the (1/N) effects that can typically be neglected in superconducting solids. An issue of current concern is the nature of the pairing interaction: several recent studies suggest a need for a density dependent form of the pairing interaction. There is a good deal of feedback between the questions of accurate calculations of pairing interactions and the form and magnitude of the pairing interaction. Finally, the authors discuss some many-body wave functions that are a generalization of the BCS wave function form, and apply them to a calculation of energy level spacings in superdeformed rotational bands.
Kim, Sangtae; Mischerikow, Nikolai; Bandeira, Nuno; Navarro, J. Daniel; Wich, Louis; Mohammed, Shabaz; Heck, Albert J. R.; Pevzner, Pavel A.
2010-01-01
Recent emergence of new mass spectrometry techniques (e.g. electron transfer dissociation, ETD) and improved availability of additional proteases (e.g. Lys-N) for protein digestion in high-throughput experiments raised the challenge of designing new algorithms for interpreting the resulting new types of tandem mass (MS/MS) spectra. Traditional MS/MS database search algorithms such as SEQUEST and Mascot were originally designed for collision induced dissociation (CID) of tryptic peptides and are largely based on expert knowledge about fragmentation of tryptic peptides (rather than machine learning techniques) to design CID-specific scoring functions. As a result, the performance of these algorithms is suboptimal for new mass spectrometry technologies or nontryptic peptides. We recently proposed the generating function approach (MS-GF) for CID spectra of tryptic peptides. In this study, we extend MS-GF to automatically derive scoring parameters from a set of annotated MS/MS spectra of any type (e.g. CID, ETD, etc.), and present a new database search tool MS-GFDB based on MS-GF. We show that MS-GFDB outperforms Mascot for ETD spectra or peptides digested with Lys-N. For example, in the case of ETD spectra, the number of tryptic and Lys-N peptides identified by MS-GFDB increased by a factor of 2.7 and 2.6 as compared with Mascot. Moreover, even following a decade of Mascot developments for analyzing CID spectra of tryptic peptides, MS-GFDB (that is not particularly tailored for CID spectra or tryptic peptides) resulted in 28% increase over Mascot in the number of peptide identifications. Finally, we propose a statistical framework for analyzing multiple spectra from the same precursor (e.g. CID/ETD spectral pairs) and assigning p values to peptide-spectrum-spectrum matches. PMID:20829449
Boetker, Johan P; Koradia, Vishal; Rades, Thomas; Rantanen, Jukka; Savolainen, Marja
2012-01-01
Amlodipine besilate, a calcium channel antagonist, exists in several solid forms. Processing of anhydrate and dihydrate forms of this drug may lead to solid state changes, and is therefore the focus of this study. Milling was performed for the anhydrate form, whereas the dihydrate form was subjected to quench cooling thereby creating an amorphous form of the drug from both starting materials. The milled and quench cooled samples were, together with the crystalline starting materials, analyzed with X-ray powder diffraction (XRPD), Raman spectroscopy and atomic pair-wise distribution function (PDF) analysis of the XRPD pattern. When compared to XRPD and Raman spectroscopy, the PDF analysis was superior in displaying the difference between the amorphous samples prepared by milling and quench cooling approaches of the two starting materials. PMID:24300182
Adler, S S; Afanasiev, S; Aidala, C; Ajitanand, N N; Akiba, Y; Alexander, J; Amirikas, R; Aphecetche, L; Aronson, S H; Averbeck, R; Awes, T C; Azmoun, R; Babintsev, V; Baldisseri, A; Barish, K N; Barnes, P D; Bassalleck, B; Bathe, S; Batsouli, S; Baublis, V; Bazilevsky, A; Belikov, S; Berdnikov, Y; Bhagavatula, S; Boissevain, J G; Borel, H; Borenstein, S; Brooks, M L; Brown, D S; Bruner, N; Bucher, D; Buesching, H; Bumazhnov, V; Bunce, G; Burward-Hoy, J M; Butsyk, S; Camard, X; Chai, J-S; Chand, P; Chang, W C; Chernichenko, S; Chi, C Y; Chiba, J; Chiu, M; Choi, I J; Choi, J; Choudhury, R K; Chujo, T; Cianciolo, V; Cobigo, Y; Cole, B A; Constantin, P; d'Enterria, D; David, G; Delagrange, H; Denisov, A; Deshpande, A; Desmond, E J; Devismes, A; Dietzsch, O; Drapier, O; Drees, A; du Rietz, R; Durum, A; Dutta, D; Efremenko, Y V; El Chenawi, K; Enokizono, A; En'yo, H; Esumi, S; Ewell, L; Fields, D E; Fleuret, F; Fokin, S L; Fox, B D; Fraenkel, Z; Frantz, J E; Franz, A; Frawley, A D; Fung, S-Y; Garpman, S; Ghosh, T K; Glenn, A; Gogiberidze, G; Gonin, M; Gosset, J; Goto, Y; Granier de Cassagnac, R; Grau, N; Greene, S V; Grosse Perdekamp, M; Guryn, W; Gustafsson, H-A; Hachiya, T; Haggerty, J S; Hamagaki, H; Hansen, A G; Hartouni, E P; Harvey, M; Hayano, R; Hayashi, N; He, X; Heffner, M; Hemmick, T K; Heuser, J M; Hibino, M; Hill, J C; Holzmann, W; Homma, K; Hong, B; Hoover, A; Ichihara, T; Ikonnikov, V V; Imai, K; Isenhower, D; Ishihara, M; Issah, M; Isupov, A; Jacak, B V; Jang, W Y; Jeong, Y; Jia, J; Jinnouchi, O; Johnson, B M; Johnson, S C; Joo, K S; Jouan, D; Kametani, S; Kamihara, N; Kang, J H; Kapoor, S S; Katou, K; Kelly, S; Khachaturov, B; Khanzadeev, A; Kikuchi, J; Kim, D H; Kim, D J; Kim, D W; Kim, E; Kim, G-B; Kim, H J; Kistenev, E; Kiyomichi, A; Kiyoyama, K; Klein-Boesing, C; Kobayashi, H; Kochenda, L; Kochetkov, V; Koehler, D; Kohama, T; Kopytine, M; Kotchetkov, D; Kozlov, A; Kroon, P J; Kuberg, C H; Kurita, K; Kuroki, Y; Kweon, M J; Kwon, Y; Kyle, G S; Lacey, R; Ladygin, V; Lajoie, J G; Lebedev, A; Leckey, S; Lee, D M; Lee, S; Leitch, M J; Li, X H; Lim, H; Litvinenko, A; Liu, M X; Liu, Y; Maguire, C F; Makdisi, Y I; Malakhov, A; Manko, V I; Mao, Y; Martinez, G; Marx, M D; Masui, H; Matathias, F; Matsumoto, T; McGaughey, P L; Melnikov, E; Messer, F; Miake, Y; Milan, J; Miller, T E; Milov, A; Mioduszewski, S; Mischke, R E; Mishra, G C; Mitchell, J T; Mohanty, A K; Morrison, D P; Moss, J M; Mühlbacher, F; Mukhopadhyay, D; Muniruzzaman, M; Murata, J; Nagamiya, S; Nagle, J L; Nakamura, T; Nandi, B K; Nara, M; Newby, J; Nilsson, P; Nyanin, A S; Nystrand, J; O'Brien, E; Ogilvie, C A; Ohnishi, H; Ojha, I D; Okada, K; Ono, M; Onuchin, V; Oskarsson, A; Otterlund, I; Oyama, K; Ozawa, K; Pal, D; Palounek, A P T; Pantuev, V; Papavassiliou, V; Park, J; Parmar, A; Pate, S F; Peitzmann, T; Peng, J-C; Peresedov, V; Pinkenburg, C; Pisani, R P; Plasil, F; Purschke, M L; Purwar, A K; Rak, J; Ravinovich, I; Read, K F; Reuter, M; Reygers, K; Riabov, V; Riabov, Y; Roche, G; Romana, A; Rosati, M; Rosnet, P; Ryu, S S; Sadler, M E; Saito, N; Sakaguchi, T; Sakai, M; Sakai, S; Samsonov, V; Sanfratello, L; Santo, R; Sato, H D; Sato, S; Sawada, S; Schutz, Y; Semenov, V; Seto, R; Shaw, M R; Shea, T K; Shibata, T-A; Shigaki, K; Shiina, T; Silva, C L; Silvermyr, D; Sim, K S; Singh, C P; Singh, V; Sivertz, M; Soldatov, A; Soltz, R A; Sondheim, W E; Sorensen, S P; Sourikova, I V; Staley, F; Stankus, P W; Stenlund, E; Stepanov, M; Ster, A; Stoll, S P; Sugitate, T; Sullivan, J P; Takagui, E M; Taketani, A; Tamai, M; Tanaka, K H; Tanaka, Y; Tanida, K; Tannenbaum, M J; Tarján, P; Tepe, J D; Thomas, T L; Tojo, J; Torii, H; Towell, R S; Tserruya, I; Tsuruoka, H; Tuli, S K; Tydesjö, H; Tyurin, N; van Hecke, H W; Velkovska, J; Velkovsky, M; Veszprémi, V; Villatte, L; Vinogradov, A A; Volkov, M A; Vznuzdaev, E; Wang, X R; Watanabe, Y; White, S N; Wohn, F K; Woody, C L; Xie, W; Yang, Y; Yanovich, A; Yokkaichi, S; Young, G R; Yushmanov, I E; Zajc, W A; Zhang, C; Zhou, S; Zhou, S J; Zolin, L
2006-08-01
Azimuthal correlations of jet-induced high-p(T) charged hadron pairs are studied at midrapidity in Au+Au collisions at sqrt[s(NN)]=200 GeV. The distribution of jet-associated partner hadrons (1.0
NASA Astrophysics Data System (ADS)
Andrew, Keith; Smailhodzic, A.; Carini, M.; Barnaby, D.
2010-01-01
We use data from the Sloan Digital Sky Survey, the DEEP2 and 2dF Galaxy Redshift surveys and numerical runs of the Gadget II code to analyze the distribution of cosmological voids in the universe similar to the model proposed by Mekjian.1. The Void Probability Function focuses on a scaling model inspired from percolation theory that gives an analytical form for the distribution function. For large redshifts the early universe was smooth and the probability function has a simple mathematical form that mimics the two point correlation results leading to a generalized power law. As various large scale galactic structures emerge in a given simulation a number of relatively empty regions are isolated and characterized as voids based upon number counts in the associated volume. The number density of these regions is such that the universe has a large scale “sponge-like” appearance with voids of all scales permeating the field of observation. For these data sets we examine the range of critical void probability function parameters that give rise to the best fit to the numerical and observational data. Several expressions for the probability distribution differ at the long end tail of the distribution which is sensitive to the Levy index of the distribution. Almost all of the distributions can be expressed as special cases of the Fox H function which has an asymptotic form whose tail depends upon the Levy index. We analyze the Levy index expressions and link them to the Fox H function parameters and to an anomalous diffusion equation that gives rise to the observed LSS void pattern. We wish to thank the Kentucky Space Grant Consortium for providing the NASA grant funding this research 1. Aram Z. Mekjian , Generalized statistical models of voids and hierarchical structure in cosmology, The Astrophysical Journal, 655: 1-10, 2007, arXiv:0712.1217
Illuminating the 1/x Moment of Parton Distribution Functions
Brodsky, Stanley J.; Llanes-Estrada, Felipe J.; Szczepaniak, Adam P.; /Indiana U.
2007-10-15
The Weisberger relation, an exact statement of the parton model, elegantly relates a high-energy physics observable, the 1/x moment of parton distribution functions, to a nonperturbative low-energy observable: the dependence of the nucleon mass on the value of the quark mass or its corresponding quark condensate. We show that contemporary fits to nucleon structure functions fail to determine this 1/x moment; however, deeply virtual Compton scattering can be described in terms of a novel F1/x(t) form factor which illuminates this physics. An analysis of exclusive photon-induced processes in terms of the parton-nucleon scattering amplitude with Regge behavior reveals a failure of the high Q2 factorization of exclusive processes at low t in terms of the Generalized Parton-Distribution Functions which has been widely believed to hold in the past. We emphasize the need for more data for the DVCS process at large t in future or upgraded facilities.
Big bang nucleosynthesis with independent neutrino distribution functions
Smith, Christel J.; Fuller, George M.; Smith, Michael S.
2009-05-15
We have performed new big bang nucleosynthesis calculations, which employ arbitrarily specified, time-dependent neutrino and antineutrino distribution functions for each of up to four neutrino flavors. We self-consistently couple these distributions to the thermodynamics, the expansion rate, and scale factor-time/temperature relationship, as well as to all relevant weak, electromagnetic, and strong nuclear reaction processes in the early Universe. With this approach, we can treat any scenario in which neutrino or antineutrino spectral distortion might arise. These scenarios might include, for example, decaying particles, active-sterile neutrino oscillations, and active-active neutrino oscillations in the presence of significant lepton numbers. Our calculations allow lepton numbers and sterile neutrinos to be constrained with observationally determined primordial helium and deuterium abundances. We have modified a standard big bang nucleosynthesis code to perform these calculations and have made it available to the community.
Reliable distribution networks design with nonlinear fortification function
NASA Astrophysics Data System (ADS)
Li, Qingwei; Savachkin, Alex
2016-03-01
Distribution networks have been facing an increased exposure to the risk of unpredicted disruptions causing significant economic losses. The current literature features a limited number of studies considering fortification of network facilities. In this paper, we develop a reliable uncapacitated fixed-charge location model with fortification to support the design of distribution networks. The model considers heterogeneous facility failure probabilities, one layer of supplier backup, and facility fortification within a finite budget. Facility reliability improvement is modelled as a nonlinear function of fortification investment. The problem is formulated as a nonlinear mixed integer programming model proven to be ?-hard. A Lagrangian relaxation-based heuristic algorithm is developed and its computational efficiency for solving large-scale problems is demonstrated.
Probability Distribution Function Evolution for Binary Alloy Solidification
Steinzig, M.L.; Harlow, F.H.
1999-02-26
The thermally controlled solidification of a binary alloy, nucleated at isolated sites, is described by the evolution of a probability distribution function, whose variables include grain size and distance to nearest neighbor, together with descriptors of shape, orientation, and such material properties as orientation of nonisotropic elastic modulus and coefficient of thermal expansion. The relevant Liouville equation is described and coupled with global equations for energy and solute transport. Applications are discussed for problems concerning nucleation and impingement and the consequences for final size and size distribution. The goal of this analysis is to characterize the grain structure of the solidified casting and to enable the description of its probable response to thermal treatment, machining, and the imposition of mechanical insults.
Sadhu, Biswajit; Sundararajan, Mahesh; Velmurugan, Gunasekaran; Venuvanalingam, Ponnambalam
2015-09-21
Designing new and innovative receptors for the selective binding of radionuclides is central to nuclear waste management processes. Recently, a new multi-topic ion-pair receptor was reported which binds a variety of cesium salts. Due to the large size of the receptor, quantum chemical calculations on the full ion-pair receptors are restricted, thus the binding mechanisms are not well understood at the molecular level. We have assessed the binding strengths of various cesium salts to the recently synthesized multi-topic ion-pair receptor molecule using density functional theory based calculations. Our calculations predict that the binding of cesium salts to the receptor predominantly occurs via the cooperative binding mechanism. Cesium and the anion synergistically assist each other to bind favorably inside the receptor. Energy decomposition analysis on the ion-pair complexes shows that the Cs salts are bound to the receptor mainly through electrostatic interactions with small contribution from covalent interactions for large ionic radius anions. Further, QTAIM analysis characterizes the importance of different inter-molecular interactions between the ions and the receptor inside the ion-pair complexes. The role of the crystallographic solvent molecule contributes significantly by ~10 kcal mol(-1) to the overall binding affinities which is quite significant. Further, unlike the recent molecular mechanics (MM) calculations, our calculated binding affinity trends for various Cs ion-pair complexes (CsF, CsCl and CsNO3) are now in excellent agreement with the experimental binding affinity trends. PMID:26227949
Comparison of the bidirectional reflectance distribution function of various surfaces
NASA Technical Reports Server (NTRS)
Fernandez, Rene; Seasholtz, Richard G.; Oberle, Lawrence G.; Kadambi, Jaikrishnan R.
1988-01-01
Described is the development and use of a system to measure the Bidirectional Reflectance Distribution Function (BRDF) of various surfaces. The BRDF measurements are used in the analysis and design of optical measurement systems, such as laser anemometers. An argon ion laser (514 nm) is the light source. Preliminary results are presented for eight samples: two glossy black paints, two flat black paints, black glass, sand blasted aluminum, unworked aluminum, and a white paint. A BaSO4 white reflectance standard was used as the reference sample throughout the tests. The reflectance characteristics of these surfaces are compared.
Transverse Momentum Dependent (TMD) Parton Distribution Functions: Status and Prospects
NASA Astrophysics Data System (ADS)
Angeles-Martinez, R.; Bacchetta, A.; Balitsky, I. I.; Boer, D.; Boglione, M.; Boussarie, R.; Ceccopieri, F. A.; Cherednikov, I. O.; Connor, P.; Echevarria, M. G.; Ferrera, G.; Grados Luyando, J.; Hautmann, F.; Jung, H.; Kasemets, T.; Kutak, K.; Lansberg, J. P.; Lelek, A.; Lykasov, G.; Madrigal Martinez, J. D.; Mulders, P. J.; Nocera, E. R.; Petreska, E.; Pisano, C.; Plačakytė, R.; Radescu, V.; Radici, M.; Schnell, G.; Scimemi, I.; Signori, A.; Szymanowski, L.; Taheri Monfared, S.; Van der Veken, F. F.; van Haevermaet, H. J.; Van Mechelen, P.; Vladimirov, A. A.; Wallon, S.
We provide a concise overview on transverse momentum dependent (TMD) parton distribution functions, their application to topical issues in high-energy physics phenomenology, and their theoretical connections with QCD resummation, evolution and factorization theorems. We illustrate the use of TMDs via examples of multi-scale problems in hadronic collisions. These include transverse momentum q_T spectra of Higgs and vector bosons for low q_T, and azimuthal correlations in the production of multiple jets associated with heavy bosons at large jet masses. We discuss computational tools for TMDs, and present an application of a new tool, TMDlib, to parton density fits and parameterizations.
Are there approximate relations among transverse momentum dependent distribution functions?
Harutyun AVAKIAN; Anatoli Efremov; Klaus Goeke; Andreas Metz; Peter Schweitzer; Tobias Teckentrup
2007-10-11
Certain {\\sl exact} relations among transverse momentum dependent parton distribution functions due to QCD equations of motion turn into {\\sl approximate} ones upon the neglect of pure twist-3 terms. On the basis of available data from HERMES we test the practical usefulness of one such ``Wandzura-Wilczek-type approximation'', namely of that connecting $h_{1L}^{\\perp(1)a}(x)$ to $h_L^a(x)$, and discuss how it can be further tested by future CLAS and COMPASS data.
Momentum distribution function of the electron gas at metallic densities
NASA Astrophysics Data System (ADS)
Takada, Yasutami; Yasuhara, H.
1991-10-01
The momentum distribution function n(k) of the electron gas is calculated in the effective-potential-expansion method at metallic densities. The recently established self-consistency relation between n(k) and the correlation energy [Y. Takada and T. Kita, J. Phys. Soc. Jpn. 60, 25 (1991)] is employed to check the accuracy of our results. This check shows that the effective-potential-expansion method provides probably the exact and at least more accurate results of n(k) than all the other methods that have given n(k) thus far.
Transfer function modeling of damping mechanisms in distributed parameter models
NASA Technical Reports Server (NTRS)
Slater, J. C.; Inman, D. J.
1994-01-01
This work formulates a method for the modeling of material damping characteristics in distributed parameter models which may be easily applied to models such as rod, plate, and beam equations. The general linear boundary value vibration equation is modified to incorporate hysteresis effects represented by complex stiffness using the transfer function approach proposed by Golla and Hughes. The governing characteristic equations are decoupled through separation of variables yielding solutions similar to those of undamped classical theory, allowing solution of the steady state as well as transient response. Example problems and solutions are provided demonstrating the similarity of the solutions to those of the classical theories and transient responses of nonviscous systems.
Are there approximate relations among transverse momentum dependent distribution functions?
Avakian, H.; Efremov, A. V.; Goeke, K.; Schweitzer, P.; Teckentrup, T.; Metz, A.
2008-01-01
Certain exact relations among transverse momentum dependent parton distribution functions due to QCD equations of motion turn into approximate ones upon the neglect of pure twist-3 terms. On the basis of available data from HERMES, we test the practical usefulness of one such 'Wandzura-Wilczek-type approximation', namely, of that connecting h{sub 1L}{sup perpendicular}({sup 1a})(x) to h{sub L}{sup a}(x), and discuss how it can be further tested by future CLAS and COMPASS data.
Transverse momentum dependent (TMD) parton distribution functions: Status and prospects*
Angeles-Martinez, R.; Bacchetta, A.; Balitsky, Ian I.; Boer, D.; Boglione, M.; Boussarie, R.; Ceccopieri, F. A.; Cherednikov, I. O.; Connor, P.; Echevarria, M. G.; et al
2015-01-01
In this study, we review transverse momentum dependent (TMD) parton distribution functions, their application to topical issues in high-energy physics phenomenology, and their theoretical connections with QCD resummation, evolution and factorization theorems. We illustrate the use of TMDs via examples of multi-scale problems in hadronic collisions. These include transverse momentum qT spectra of Higgs and vector bosons for low qT, and azimuthal correlations in the production of multiple jets associated with heavy bosons at large jet masses. We discuss computational tools for TMDs, and present the application of a new tool, TMDLIB, to parton density fits and parameterizations.
Multi-pair states in electron-positron pair creation
NASA Astrophysics Data System (ADS)
Wöllert, Anton; Bauke, Heiko; Keitel, Christoph H.
2016-09-01
Ultra strong electromagnetic fields can lead to spontaneous creation of single or multiple electron-positron pairs. A quantum field theoretical treatment of the pair creation process combined with numerical methods provides a description of the fermionic quantum field state, from which all observables of the multiple electron-positron pairs can be inferred. This allows to study the complex multi-particle dynamics of electron-positron pair creation in-depth, including multi-pair statistics as well as momentum distributions and spin. To illustrate the potential benefit of this approach, it is applied to the intermediate regime of pair creation between nonperturbative Schwinger pair creation and perturbative multiphoton pair creation where the creation of multi-pair states becomes nonnegligible but cascades do not yet set in. Furthermore, it is demonstrated how spin and helicity of the created electrons and positrons are affected by the polarization of the counterpropagating laser fields, which induce the creation of electron-positron pairs.
Probability distribution function for reorientations in Maier-Saupe potential
NASA Astrophysics Data System (ADS)
Sitnitsky, A. E.
2016-06-01
Exact analytic solution for the probability distribution function of the non-inertial rotational diffusion equation, i.e., of the Smoluchowski one, in a symmetric Maier-Saupe uniaxial potential of mean torque is obtained via the confluent Heun's function. Both the ordinary Maier-Saupe potential and the double-well one with variable barrier width are considered. Thus, the present article substantially extends the scope of the potentials amenable to the treatment by reducing Smoluchowski equation to the confluent Heun's one. The solution is uniformly valid for any barrier height. We use it for the calculation of the mean first passage time. Also the higher eigenvalues for the relaxation decay modes in the case of ordinary Maier-Saupe potential are calculated. The results obtained are in full agreement with those of the approach developed by Coffey, Kalmykov, Déjardin and their coauthors in the whole range of barrier heights.
A DERIVATION OF (HALF) THE DARK MATTER DISTRIBUTION FUNCTION
Hansen, Steen H.; Sparre, Martin E-mail: sparre@dark-cosmology.dk
2012-09-01
All dark matter structures appear to follow a set of universalities, such as phase-space density or velocity anisotropy profiles; however, the origin of these universalities remains a mystery. Any equilibrated dark matter structure can be fully described by two functions, namely the radial and tangential velocity distribution functions (VDFs), and once these two are understood we will understand all the observed universalities. Here, we demonstrate that if we know the radial VDF then we can derive and understand the tangential VDF. This is based on simple dynamical arguments about properties of collisionless systems. We use a range of controlled numerical simulations to demonstrate the accuracy of this result. We therefore boil the question of the dark matter structural properties down to understanding the radial VDF.
Functional platform for controlled subcellular distribution of carbon nanotubes.
Serag, Maged F; Kaji, Noritada; Venturelli, Enrica; Okamoto, Yukihiro; Terasaka, Kazuyoshi; Tokeshi, Manabu; Mizukami, Hajime; Braeckmans, Kevin; Bianco, Alberto; Baba, Yoshinobu
2011-11-22
As nanoparticles can cross different cellular barriers and access different tissues, control of their uptake and cellular fate presents a functional approach that will be broadly applicable to nanoscale technologies in cell biology. Here we show that the trafficking of single-walled carbon nanotubes (SWCNTs) through various subcellular membranes of the plant cell is facilitated or inhibited by attaching a suitable functional tag and controlling medium components. This enables a unique control over the uptake and the subcellular distribution of SWCNTs and provides a key strategy to promote their cellular elimination to minimize toxicity. Our results also demonstrate that SWCNTs are involved in a carrier-mediated transport (CMT) inside cells; this is a phenomenon that scientists could use to obtain novel molecular insights into CMT, with the potential translation to advances in subcellular nanobiology. PMID:21981659
Memory intensive functional architecture for distributed computer control systems
Dimmler, D.G.
1983-10-01
A memory-intensive functional architectue for distributed data-acquisition, monitoring, and control systems with large numbers of nodes has been conceptually developed and applied in several large-scale and some smaller systems. This discussion concentrates on: (1) the basic architecture; (2) recent expansions of the architecture which now become feasible in view of the rapidly developing component technologies in microprocessors and functional large-scale integration circuits; and (3) implementation of some key hardware and software structures and one system implementation which is a system for performing control and data acquisition of a neutron spectrometer at the Brookhaven High Flux Beam Reactor. The spectrometer is equipped with a large-area position-sensitive neutron detector.
High Resolution Radial Distribution Function of Pure Amorphous Silicon
Laaziri, K.; Roorda, S.; Chicoine, M.; Kycia, S.; Robertson, J.L.; Wang, J.; Moss, S.C.
1999-04-01
The structure factor S(Q) of high purity amorphous Si membranes prepared by ion implantation was measured over an extended Q range (0.03{endash}55 {Angstrom} {sup {minus}1} ). Calculation of the first neighbor shell coordination (C{sub 1} ) as a function of maximum Q indicates that measurement of S(Q) out to at least 40 {Angstrom}{sup {minus}1} is required to reliably determine the radial distribution function (RDF). A 2{percent} change in C{sub 1} and subtle changes in the rest of the RDF were observed upon annealing, consistent with point defect removal. After annealing at 600thinsp{degree}C, C{sub 1}=3.88 , which would explain why amorphous Si is less dense than crystalline Si. {copyright} {ital 1999} {ital The American Physical Society}
NASA Astrophysics Data System (ADS)
Arneodo, M.; Arvidson, A.; Aubert, J. J.; Badelek, B.; Beaufays, J.; Bee, C. P.; Benchouk, C.; Berghoff, G.; Bird, I. G.; Blum, D.; Böhm, E.; De Bouard, X.; Brasse, F. W.; Braun, H.; Broll, C.; Brown, S. C.; Brück, H.; Calen, H.; Chima, J. S.; Ciborowski, J.; Clifft, R.; Coignet, G.; Combley, F.; Coughlan, J.; D'Agostini, G.; Dahlgren, S.; Dengler, F.; Derado, I.; Dreyer, T.; Drees, J.; Düren, M.; Eckardt, V.; Edwards, A.; Edwards, M.; Ernst, T.; Eszes, G.; Favier, J.; Ferrero, M. I.; Figiel, J.; Flauger, W.; Foster, J.; Gabathuler, E.; Gajewski, J.; Gamet, R.; Gayler, J.; Geddes, N.; Grafström, P.; Grard, F.; Haas, J.; Hagberg, E.; Hasert, F. J.; Hayman, P.; Heusse, P.; Jaffre, M.; Jacholkowska, A.; Janata, F.; Jancso, G.; Johnson, A. S.; Kabuss, E. M.; Kellner, G.; Korbel, V.; Krüger, A.; Krüger, J.; Kullander, S.; Landgraf, U.; Lanske, D.; Loken, J.; Long, K.; Maire, M.; Malecki, P.; Manz, A.; Maselli, S.; Mohr, W.; Montanet, F.; Montgomery, H. E.; Nagy, E.; Nassalski, J.; Norton, P. R.; Oakham, F. G.; Osborne, A. M.; Pascaud, C.; Pawlik, B.; Payre, P.; Peroni, C.; Peschel, H.; Pessard, H.; Pettingale, J.; Pietrzyk, B.; Poensgen, B.; Pötsch, M.; Renton, P.; Ribarics, P.; Rith, K.; Rondio, E.; Sandacz, A.; Scheer, M.; Schlagböhmer, A.; Schiemann, H.; Schmitz, N.; Schneegans, M.; Scholz, M.; Schouten, M.; Schröder, T.; Schultze, K.; Sloan, T.; Stier, H. E.; Studt, M.; Taylor, G. N.; Thenard, J. M.; Thompson, J. C.; De la Torre, A.; Toth, J.; Urban, L.; Urban, L.; Wallucks, W.; Whalley, M.; Wheeler, S.; Williams, W. S. C.; Wimpenny, S. J.; Windmolders, R.; Wolf, G.; European Muon Collaboration
1989-07-01
A new determination of the u valence quark distribution function in the proton is obtained from the analysis of identified charged pions, kaons, protons and antiprotons produced in muon-proton and muon-deuteron scattering. The comparison with results obtained in inclusive deep inelastic lepton-nucleon scattering provides a further test of the quark-parton model. The u quark fragmentation functions into positive and negative pions, kaons, protons and antiprotons are also measured.
Technology Transfer Automated Retrieval System (TEKTRAN)
GPS collars were used to describe the daily distribution patterns of cows and their calves from 18 to 60 days postpartum on pinyon juniper-shortgrass rangeland in central New Mexico. Eighteen, 3 year old cows and their calves were fitted weekly with GPS collars for seven consecutive weeks. Twenty da...
A pseudo zeta function and the distribution of primes.
Chernoff, P R
2000-07-01
The Riemann zeta function is given by: [equation, see published text]. Zeta(s) may be analytically continued to the entire s-plane, except for a simple pole at s = 0. Of great interest are the complex zeros of zeta(s). The Riemann hypothesis states that the complex zeros all have real part 1/2. According to the prime number theorem, pn approximately n logn, where pn is the nth prime. Suppose that pn were exactly nlogn. In other words, in the Euler product above, replace the nth prime by nlogn. In this way, we define a pseudo zeta function C(s) for Re s > 1. One can show that C(s) may be analytically continued at least into the half-plane Re s > 0 except for an isolated singularity (presumably a simple pole) at s = 0. It may be shown that the pseudo zeta function C(s) has no complex zeros whatsoever. This means that the complex zeros of the zeta function are associated with the irregularity of the distribution of the primes. PMID:10884402
Multivesicular Bodies in Neurons: Distribution, Protein Content, and Trafficking Functions
VON BARTHELD, CHRISTOPHER S.; ALTICK, AMY L.
2011-01-01
Summary Multivesicular bodies (MVBs) are intracellular endosomal organelles characterized by multiple internal vesicles that are enclosed within a single outer membrane. MVBs were initially regarded as purely prelysosomal structures along the degradative endosomal pathway of internalized proteins. MVBs are now known to be involved in numerous endocytic and trafficking functions, including protein sorting, recycling, transport, storage, and release. This review of neuronal MVBs summarizes their research history, morphology, distribution, accumulation of cargo and constitutive proteins, transport, and theories of functions of MVBs in neurons and glia. Due to their complex morphologies, neurons have expanded trafficking and signaling needs, beyond those of “geometrically simpler” cells, but it is not known whether neuronal MVBs perform additional transport and signaling functions. This review examines the concept of compartment-specific MVB functions in endosomal protein trafficking and signaling within synapses, axons, dendrites and cell bodies. We critically evaluate reports of the accumulation of neuronal MVBs based on evidence of stress-induced MVB formation. Furthermore, we discuss potential functions of neuronal and glial MVBs in development, in dystrophic neuritic syndromes, injury, disease, and aging. MVBs may play a role in Alzheimer’s, Huntington’s, and Niemann-Pick diseases, some types of frontotemporal dementia, prion and virus trafficking, as well as in adaptive responses of neurons to trauma and toxin or drug exposure. Functions of MVBs in neurons have been much neglected, and major gaps in knowledge currently exist. Developing truly MVB-specific markers would help to elucidate the roles of neuronal MVBs in intra- and intercellular signaling of normal and diseased neurons. PMID:21216273
Universal functional form of 1-minute raindrop size distribution?
NASA Astrophysics Data System (ADS)
Cugerone, Katia; De Michele, Carlo
2015-04-01
Rainfall remains one of the poorly quantified phenomena of the hydrological cycle, despite its fundamental role. No universal laws describing the rainfall behavior are available in literature. This is probably due to the continuous description of rainfall, which is a discrete phenomenon, made by drops. From the statistical point of view, the rainfall variability at particle size scale, is described by the drop size distribution (DSD). With this term, it is generally indicated as the concentration of raindrops per unit volume and diameter, as the probability density function of drop diameter at the ground, according to the specific problem of interest. Raindrops represent the water exchange, under liquid form, between atmosphere and earth surface, and the number of drops and their size have impacts in a wide range of hydrologic, meteorologic, and ecologic phenomena. DSD is used, for example, to measure the multiwavelength rain attenuation for terrestrial and satellite systems, it is an important input for the evaluation of the below cloud scavenging coefficient of the aerosol by precipitation, and is of primary importance to make estimates of rainfall rate through radars. In literature, many distributions have been used to this aim (Gamma and Lognormal above all), without statistical supports and with site-specific studies. Here, we present an extensive investigation of raindrop size distribution based on 18 datasets, consisting in 1-minute disdrometer data, sampled using Joss-Waldvogel or Thies instrument in different locations on Earth's surface. The aim is to understand if an universal functional form of 1-minute drop diameter variability exists. The study consists of three main steps: analysis of the high order moments, selection of the model through the AIC index and test of the model with the use of goodness-of-fit tests.
Khabiboulline, Emil T.; Steinhardt, Charles L.; Silverman, John D.; Ellison, Sara L.; Mendel, J. Trevor; Patton, David R.
2014-11-01
We study how active galactic nucleus (AGN) activity changes across environments from galaxy pairs to clusters using 143,843 galaxies with z < 0.2 from the Sloan Digital Sky Survey. Using a refined technique, we apply a continuous measure of AGN activity, characteristic of the ionization state of the narrow-line emitting gas. Changes in key emission-line ratios ([N II] λ6548/Hα, [O III] λ5007/Hβ) between different samples allow us to disentangle different environmental effects while removing contamination. We confirm that galaxy interactions enhance AGN activity. However, conditions in the central regions of clusters are inhospitable for AGN activity even if galaxies are in pairs. These results can be explained through models of gas dynamics in which pair interactions stimulate the transfer of gas to the nucleus and clusters suppress gas availability for accretion onto the central black hole.
NASA Astrophysics Data System (ADS)
Khabiboulline, Emil T.; Steinhardt, Charles L.; Silverman, John D.; Ellison, Sara L.; Mendel, J. Trevor; Patton, David R.
2014-11-01
We study how active galactic nucleus (AGN) activity changes across environments from galaxy pairs to clusters using 143,843 galaxies with z < 0.2 from the Sloan Digital Sky Survey. Using a refined technique, we apply a continuous measure of AGN activity, characteristic of the ionization state of the narrow-line emitting gas. Changes in key emission-line ratios ([N II] λ6548/Hα, [O III] λ5007/Hβ) between different samples allow us to disentangle different environmental effects while removing contamination. We confirm that galaxy interactions enhance AGN activity. However, conditions in the central regions of clusters are inhospitable for AGN activity even if galaxies are in pairs. These results can be explained through models of gas dynamics in which pair interactions stimulate the transfer of gas to the nucleus and clusters suppress gas availability for accretion onto the central black hole.
ERIC Educational Resources Information Center
Miller, Pat
2005-01-01
Cold February weather and pancakes are a traditional pairing. Pancake Day began as a way to eat up the foods that were abstained from in Lent--traditionally meat, fat, eggs and dairy products. The best-known pancake event is The Pancake Day Race in Buckinghamshire, England, which has been run since 1445. This column describes pairs of books that…
Structure, stability and function of 5-chlorouracil modified A:U and G:U base pairs
Patra, Amritraj; Harp, Joel; Pallan, Pradeep S.; Zhao, Linlin; Abramov, Mikhail; Herdewijn, Piet; Egli, Martin
2012-12-28
The thymine analog 5-chlorouridine, first reported in the 1950s as anti-tumor agent, is known as an effective mutagen, clastogen and toxicant as well as an effective inducer of sister-chromatid exchange. Recently, the first microorganism with a chemically different genome was reported; the selected Escherichia coli strain relies on the four building blocks 5-chloro-2'-deoxyuridine (ClU), A, C and G instead of the standard T, A, C, G alphabet [Marlière,P., Patrouix,J., Döring,V., Herdewijn,P., Tricot,S., Cruveiller,S., Bouzon,M. and Mutzel,R. (2011) Chemical evolution of a bacterium’s genome. Angew. Chem. Int. Ed., 50, 7109–7114]. The residual fraction of T in the DNA of adapted bacteria was <2% and the switch from T to ClU was accompanied by a massive number of mutations, including >1500 A to G or G to A transitions in a culture. The former is most likely due to wobble base pairing between ClU and G, which may be more common for ClU than T. To identify potential changes in the geometries of base pairs and duplexes as a result of replacement of T by ClU, we determined four crystal structures of a B-form DNA dodecamer duplex containing ClU:A or ClU:G base pairs. The structures reveal nearly identical geometries of these pairs compared with T:A or T:G, respectively, and no consequences for stability and cleavage by an endonuclease (EcoRI). The lack of significant changes in the geometry of ClU:A and ClU:G base pairs relative to the corresponding native pairs is consistent with the sustained unlimited self-reproduction of E. coli strains with virtually complete T→ClU genome substitution.
Transverse momentum dependent (TMD) parton distribution functions: Status and prospects*
Angeles-Martinez, R.; Bacchetta, A.; Balitsky, Ian I.; Boer, D.; Boglione, M.; Boussarie, R.; Ceccopieri, F. A.; Cherednikov, I. O.; Connor, P.; Echevarria, M. G.; Ferrera, G.; Grados Luyando, J.; Hautmann, F.; Jung, H.; Kasemets, T.; Kutak, K.; Lansberg, J. P.; Lykasov, G.; Madrigal Martinez, J. D.; Mulders, P. J.; Nocera, E. R.; Petreska, E.; Pisano, C.; Placakyte, R.; Radescu, V.; Radici, M.; Schnell, G.; Signori, A.; Szymanowski, L.; Taheri Monfared, S.; Van der Veken, F. F.; van Haevermaet, H. J.; Van Mechelen, P.; Vladimirov, A. A.; Wallon, S.
2015-01-01
In this study, we review transverse momentum dependent (TMD) parton distribution functions, their application to topical issues in high-energy physics phenomenology, and their theoretical connections with QCD resummation, evolution and factorization theorems. We illustrate the use of TMDs via examples of multi-scale problems in hadronic collisions. These include transverse momentum q_{T} spectra of Higgs and vector bosons for low q_{T}, and azimuthal correlations in the production of multiple jets associated with heavy bosons at large jet masses. We discuss computational tools for TMDs, and present the application of a new tool, TMD_{LIB}, to parton density fits and parameterizations.
Anomalous Skin Effect for Anisotropic Electron Velocity Distribution Function
Igor Kaganovich; Edward Startsev; Gennady Shvets
2004-02-19
The anomalous skin effect in a plasma with a highly anisotropic electron velocity distribution function (EVDF) is very different from skin effect in a plasma with the isotropic EVDF. An analytical solution was derived for the electric field penetrated into plasma with the EVDF described as a Maxwellian with two temperatures Tx >> Tz, where x is the direction along the plasma boundary and z is the direction perpendicular to the plasma boundary. The skin layer was found to consist of two distinctive regions of width of order nTx/w and nTz/w, where nTx,z/w = (Tx,z/m)1/2 is the thermal electron velocity and w is the incident wave frequency.
Probabilistic downscaling approaches: Application to wind cumulative distribution functions
NASA Astrophysics Data System (ADS)
Michelangeli, P.-A.; Vrac, M.; Loukos, H.
2009-06-01
A statistical method is developed to generate local cumulative distribution functions (CDFs) of surface climate variables from large-scale fields. Contrary to most downscaling methods producing continuous time series, our “probabilistic downscaling methods” (PDMs), named “CDF-transform”, is designed to deal with and provide local-scale CDFs through a transformation applied to large-scale CDFs. First, our PDM is compared to a reference method (Quantile-matching), and validated on a historical time period by downscaling CDFs of wind intensity anomalies over France, for reanalyses and simulations from a general circulation model (GCM). Then, CDF-transform is applied to GCM output fields to project changes in wind intensity anomalies for the 21st century under A2 scenario. Results show a decrease in wind anomalies for most weather stations, ranging from less than 1% (in the South) to nearly 9% (in the North), with a maximum in the Brittany region.
Ion distribution function in a plasma with uniform electric field
Lampe, M.; Joyce, G.; Roecker, T. B.; Zhdanov, S. K.; Ivlev, A. V.; Morfill, G. E.
2012-11-15
For a homogeneous partially ionized plasma subject to a uniform electric field E, several methods and models are used to calculate the distribution function f(v) for ions subject to charge-exchange collisions. The exact solution for f(v), based on the energy-dependent cross section for Ar, is obtained by Monte Carlo (MC) simulation. This is compared to the MC results for f(v), based on either a constant cross section {sigma} or a constant collision frequency {nu}. The constant-{sigma} model is found to accurately represent f(v) for any value of E, whereas the constant-{nu} results are qualitatively incorrect for large fields. Under the constant-{sigma} assumption, a simple, easily solvable ordinary differential equation is obtained which reproduces the MC results with good accuracy.
Rotation angle system of bidirectional reflectance distribution function measurement device
NASA Astrophysics Data System (ADS)
Wu, Houping; Feng, Guojin; Zheng, Chundi; Li, Ping; Wang, Yu
2015-10-01
This article described the rotation angle system of the bidirectional reflectance distribution function (BRDF) measurement device. A high-precision multidimensional angle platform device is built. The rotation angle system uses two scanning rotational mechanical arms and a two-dimensional coaxial turntable mechanical structure, each rotational axis are driven by high-power motor and completed closed-loop control with high-precision encoder. Rotation of the motors can be automatically measured in accordance with point by the control software. The detecting arm can be rotated to measure any point in hemisphere space, the rotary range of light arm is +/- 90 °, the rotary range of sample stage is 360 ° and the angular resolution is 0.01°. The rotation angle system meets the absolute positioning hemisphere space requirements of BRDF device. The experimental result shows that the rotation angle system met the high-precision positioning requirements for the BRDF absolute measurement.
Solute-Solvent Energetics Based on Proximal Distribution Functions.
Ou, Shu-Ching; Pettitt, B Montgomery
2016-08-25
We consider the hydration structure and thermodynamic energetics of solutes in aqueous solution. On the basis of the dominant local correlation between the solvent and the chemical nature of the solute atoms, proximal distribution functions (pDF) can be used to quantitatively estimate the hydration pattern of the macromolecules. We extended this technique to study the solute-solvent energetics including the van der Waals terms representing excluded volume and tested the method with butane and propanol. Our results indicate that the pDF-reconstruction algorithm can reproduce van der Waals solute-solvent interaction energies to useful kilocalorie per mole accuracy. We subsequently computed polyalanine-water interaction energies for a variety of conformers, which also showed agreement with the simulated values. PMID:27095487
Constitutive relations associated with the Mott-Smith distribution function
Nathenson, M.; Baganoff, D.
1973-01-01
It is shown that the distribution function assumed by Mott-Smith determines a unique relation between heat flux, stress, and fluid velocity given by q = (3/2)??u, i.e., it provides a constitutive relation for heat flux, and it also determines a simple expression for this ratio of third-order central moments Q = . These expressions allow the equation of transfer for c x2 to be cast in a form that yields a nonlinear constitutive relation for stress. The results obtained from the Mott-Smith ansatz are compared with the theory of Baganoff and Nathenson and results from a numerical solution of the Boltzmann equation for shock-wave structure obtained by Hicks and Yen.
Distribution Function in the Center of the Dark Matter Halo
NASA Astrophysics Data System (ADS)
Ma, Ding; He, Ping
N-body simulations of dark matter halos show that the density profiles of the halos behave as ρ(r) ∝ r-α(r), where the density logarithmic slope α ≃ 1-1.5 in the center and α ≃ 3-4 in the outer parts of the halos. However, some observations are not in agreement with simulations in the very central region of the halos. The simulations also show that the velocity dispersion anisotropy parameter β ≈ 0 in the inner part of the halo and the so-called pseudo-phase-space density ρ/σ3 behaves as a power law in radius r. With these results in mind, we study the distribution function and the pseudo-phase-space density ρ/σ3 of the center of dark matter halos and find that they are closely related.
Surface contamination monitoring by the measurement of scattering distribution functions
NASA Astrophysics Data System (ADS)
Carosso, Paola A.; Pugel, Nancy J.
1987-06-01
This paper describes the use of Bidirectional Scattering Distribution Functions (BSDF) to quantify surface degradation, thus providing an effective method for contamination monitoring. This approach to contamination monitoring is based on the use of witness surfaces (mirrors or glass slides) located next to the critical surfaces. Contaminant accretion can be monitored during all phases of spacecraft fabrication, assembly, and testing. The method can be applied in other areas of contamination control such as monitoring of clean room environments. The BSDF can also prove extremely useful in establishing contamination control requirements and acceptability criteria. This paper describes the apparatus adopted to perform BSDF measurements and discusses some practical aspects of data collection. The results obtained in contamination monitoring programs performed at the NASA Goddard Space Flight Center are presented. Some possible new applications of this monitoring technique are also addressed.
The Earthquake Frequency-Magnitude Distribution Functional Shape
NASA Astrophysics Data System (ADS)
Mignan, A.
2012-04-01
Knowledge of the completeness magnitude Mc, magnitude above which all earthquakes are detected, is a prerequisite to most seismicity analyses. Although computation of Mc is done routinely, different techniques often result in different values. Since an incorrect estimate can lead to under-sampling or worse to an erroneous estimate of the parameters of the Gutenberg-Richter (G-R) law, a better assessment of the deviation from the G-R law and thus of the earthquake detectability is of paramount importance to correctly estimate Mc. This is especially true for refined mapping of seismicity parameters such as in earthquake forecast models. The capacity of a seismic network to detect small earthquakes can be evaluated by investigating the functional shape of the earthquake Frequency-Magnitude Distribution (FMD). The non-cumulative FMD takes the form N(m) ∝ exp(-βm)q(m) where N(m) is the number of events of magnitude m, exp(-βm) the G-R law and q(m) a probability function. q(m) is commonly defined as the cumulative Normal distribution to describe the gradual curvature often observed in bulk FMDs. Recent results however show that this gradual curvature is potentially due to spatial heterogeneities in Mc, meaning that the functional shape of the elemental (local) FMD still has to be described. Based on preliminary observations, we propose an exponential detection function of the form q(m) = exp(κ(m-Mc)) for m < Mc and q(m) = 1 for m ≥ Mc, which leads to an FMD of angular shape. The two FMD models (gradually curved and angular) are compared in Southern California and Nevada. We show that the angular shaped FMD model better describes the elemental FMD and that the sum of elemental FMDs with different Mc(x,y) leads to the gradually curved FMD at the regional scale. We show that the proposed model (1) provides more robust estimates of Mc, (2) better estimates local b-values, and (3) gives an insight into earthquake detectability properties by using seismicity as a proxy
Polarized reflectance and transmittance distribution functions of the ocean surface.
Hieronymi, Martin
2016-07-11
Two aspects of ocean modelling are treated: representation of ocean waves considering all size-classes of waves and tracing of light-interactions at the wavy sea surface. Nonlinear wave profiles are realized accounting for a wide range of climatologically relevant sea states and wind speeds. Polarized ray tracing is used to investigate air-incident and whitecap-free reflectance and transmittance distributions with high angular resolution subject to sea-characterizing parameters, such as significant wave height, peak wave period, wind speed, and surface roughness. Wave-shadowing effects of incident and multiple reflected rays are fully considered. Their influence mostly starts with incidence angles greater than 60°, i.e., when the sun is near the horizon, and is especially pronounced for steep sea states. The net effect of multiple reflections is a redistribution of reflectance and transmittance fractions in their respective hemispheres and a slight increase of the net transmission of light into the sea. Revised reflectance and transmittance distribution functions, RDF and TDF, are provided depending on surface roughness in terms of the mean-square slope; reference is made to other sea state parameters. In comparison with the slope statistics approach, uncertainties related to sun near the horizon are reduced and on average this study yields somewhat higher reflectance values with some variability related to the sea state. By means of provided data, irradiance and radiance reflectances can be computed using desired sky radiance distributions, e.g., clear sky, overcast or partly cloudy sky, as well as wind or sea state information including wave propagation direction. PMID:27410893
LUMINOUS SATELLITES. II. SPATIAL DISTRIBUTION, LUMINOSITY FUNCTION, AND COSMIC EVOLUTION
Nierenberg, A. M.; Treu, T.; Auger, M. W.; Marshall, P. J.; Fassnacht, C. D.; Busha, Michael T.
2012-06-20
We infer the normalization and the radial and angular distributions of the number density of satellites of massive galaxies (log{sub 10}[M*{sub h}/M{sub Sun }] > 10.5) between redshifts 0.1 and 0.8 as a function of host stellar mass, redshift, morphology, and satellite luminosity. Exploiting the depth and resolution of the COSMOS Hubble Space Telescope images, we detect satellites up to 8 mag fainter than the host galaxies and as close as 0.3 (1.4) arcsec (kpc). Describing the number density profile of satellite galaxies to be a projected power law such that P(R){proportional_to}R{sup {gamma}{sub p}}, we find {gamma}{sub p} = -1.1 {+-} 0.3. We find no dependency of {gamma}{sub p} on host stellar mass, redshift, morphology, or satellite luminosity. Satellites of early-type hosts have angular distributions that are more flattened than the host light profile and are aligned with its major axis. No significant average alignment is detected for satellites of late-type hosts. The number of satellites within a fixed magnitude contrast from a host galaxy is dependent on its stellar mass, with more massive galaxies hosting significantly more satellites. Furthermore, high-mass late-type hosts have significantly fewer satellites than early-type galaxies of the same stellar mass, possibly indicating that they reside in more massive halos. No significant evolution in the number of satellites per host is detected. The cumulative luminosity function of satellites is qualitatively in good agreement with that predicted using SubHalo Abundance Matching techniques. However, there are significant residual discrepancies in the absolute normalization, suggesting that properties other than the host galaxy luminosity or stellar mass determine the number of satellites.
Nagy, A; Amovilli, C
2008-03-21
In the ground state, the pair density n can be determined by solving a single auxiliary equation of a two-particle problem. Electron-electron cusp condition and asymptotic behavior for the Pauli potential of the effective potential of the two-particle equation are presented. PMID:18361562
Distributed Evaluation Functions for Fault Tolerant Multi-Rover Systems
NASA Technical Reports Server (NTRS)
Agogino, Adrian; Turner, Kagan
2005-01-01
The ability to evolve fault tolerant control strategies for large collections of agents is critical to the successful application of evolutionary strategies to domains where failures are common. Furthermore, while evolutionary algorithms have been highly successful in discovering single-agent control strategies, extending such algorithms to multiagent domains has proven to be difficult. In this paper we present a method for shaping evaluation functions for agents that provide control strategies that both are tolerant to different types of failures and lead to coordinated behavior in a multi-agent setting. This method neither relies of a centralized strategy (susceptible to single point of failures) nor a distributed strategy where each agent uses a system wide evaluation function (severe credit assignment problem). In a multi-rover problem, we show that agents using our agent-specific evaluation perform up to 500% better than agents using the system evaluation. In addition we show that agents are still able to maintain a high level of performance when up to 60% of the agents fail due to actuator, communication or controller faults.
PROBABILITY DISTRIBUTION FUNCTIONS OF COSMOLOGICAL LENSING: CONVERGENCE, SHEAR, AND MAGNIFICATION
Takahashi, Ryuichi; Oguri, Masamune; Sato, Masanori; Hamana, Takashi
2011-11-20
We perform high-resolution ray-tracing simulations to investigate probability distribution functions (PDFs) of lensing convergence, shear, and magnification on distant sources up to the redshift of z{sub s} = 20. We pay particular attention to the shot noise effect in N-body simulations by explicitly showing how it affects the variance of the convergence. We show that the convergence and magnification PDFs are closely related to each other via the approximate relation {mu} = (1 - {kappa}){sup -2}, which can reproduce the behavior of PDFs surprisingly well up to the high magnification tail. The mean convergence measured in the source plane is found to be systematically negative, rather than zero as often assumed, and is correlated with the convergence variance. We provide simple analytical formulae for the PDFs, which reproduce simulated PDFs reasonably well for a wide range of redshifts and smoothing sizes. As explicit applications of our ray-tracing simulations, we examine the strong-lensing probability and the magnification effects on the luminosity functions of distant galaxies and quasars.
Hydroxyl functionalized thermosensitive microgels with quadratic crosslinking density distribution.
Elmas, Begum; Tuncel, Murvet; Senel, Serap; Patir, S; Tuncel, Ali
2007-09-01
N-isopropylacrylamide (NIPA) based uniform thermosensitive microgels were synthesized by dispersion polymerization by using relatively hydrophilic crosslinking agents with hydroxyl functionality. Glycerol dimethacrylate (GDMA), pentaerythritol triacrylate (PETA) and pentaerythritol propoxylate triacrylate (PEPTA) were used as crosslinking agents with different hydrophilicities. A protocol was first proposed to determine the crosslinking density distribution in the thermosensitive microgel particles by confocal laser scanning microscopy (CLSM). The microgels were fluorescently labeled by using hydroxyl group of the crosslinking agent. The CLSM observations performed with the microgels synthesized by three different crosslinking agents showed that the crosslinking density exhibited a quadratic decrease with the increasing radial distance in the spherical microgel particles. This structure led to the formation of more loose gel structure on the particle surface with respect to the center. Then the use of hydrophilic crosslinking agents in the dispersion polymerization of NIPA made possible the synthesis of thermosensitive microgels carrying long, flexible and chemically derivatizable (i.e., hydroxyl functionalized) fringes on the surface by a single-stage dispersion polymerization. The microgels with all crosslinking agents exhibited volume phase transition with the increasing temperature. The microgel obtained by the most hydrophilic crosslinking agent, GDMA exhibited higher hydrodynamic diameters in the fully swollen form at low temperatures than those obtained by PETA and PEPTA. Higher hydrodynamic size decrease from fully swollen form to the fully shrunken form was also observed with the same microgel. PMID:17532327
Application of Wigner distribution function for analysis of radio occultations
NASA Astrophysics Data System (ADS)
Gorbunov, M. E.; Lauritsen, K. B.; Leroy, S. S.
2010-12-01
We present the Wigner distribution function (WDF) as an alternative to radio holographic (RH) analysis in the interpretation of radio occultation (RO) observations of the Earth's atmosphere. RH analysis is widely used in RO retrieval to isolate signal from noise and to identify atmospheric multipath. The same task is performed by WDF which also maps a 1-D wave function to 2-D time-frequency phase space and which has maxima located at the ray manifold. Unlike the standard RH technique based on the spectrum analysis in small sliding apertures, WDF is given by a global integral transform, which allows for a higher resolution. We present a tomographic derivation of the WDF and discuss its properties. Examples of analysis of simulations and COSMIC RO data show that WDF allows for a much sharper localization of the details of bending angle profiles as compared to the standard RH analysis in sliding apertures. Both WDF and RH allow for identification of multivalued bending angle profiles arising in the presence of strong horizontal gradients and may introduce a negative bias into bending angle retrieval.
Ion energy distribution functions in a supersonic plasma jet
NASA Astrophysics Data System (ADS)
Caldirola, S.; Roman, H. E.; Riccardi, C.
2014-11-01
Starting from experimental measurements of ion energy distribution functions (IEDFs) in a low pressure supersonic plasma jet, we propose a model to simulate them numerically from first principles calculations. Experimentally we acquired IEDFs with a quadrupole mass spectrometer (QMS) collecting the argon ions produced from a inductively coupled plasma (ICP) and driven into a supersonic free gas expansion. From the discussion of these results and the physics of our system we developed a simulation code. Integrating the equations of motion the code evolves the trajectory of a single ion across the jet. Ar+- Ar collisions are modelled with a 12-4 Lennard-Jones potential which considers induced dipole interactions. IEDFs were simulated at different positions along the jet and compared with the experimental data showing good agreement. We have also implemented a charge transfer mechanism in which the ion releases its charge to a neutral atom which can take place at sufficiently close distances and is a function of the impact energy.
The mass distribution function of planets in the Galaxy
NASA Astrophysics Data System (ADS)
Malhotra, Renu
2016-05-01
I will describe some deductions about the planet mass function from the observational data of exoplanets and theoretical considerations of dynamical stability of planetary systems. The Kepler mission has carried out a systematic survey for planets in the Galaxy, and obtained data on several hundred exo-planetary systems. Analysis of these data indicates that planetary orbital separations have an approximately log-normal distribution. Taken together with plausible ansatzs for the dynamical stability of multi-planet systems, it appears that the planet mass function is peaked in logarithm of mass, with the most probable value of log m/M_Earth ∼ (0.6 ‑ 1.0). A modest extrapolation finds that Earth mass planets are about ~1000 times more common than Jupiter mass planets, and that the most common planets in the Galaxy may be of lunar-to-Mars mass.This research was supported by NSF (grant AST-1312498) and NASA (grant NNX14AG93G).
A Riemannian framework for orientation distribution function computing.
Cheng, Jian; Ghosh, Aurobrata; Jiang, Tianzi; Deriche, Rachid
2009-01-01
Compared with Diffusion Tensor Imaging (DTI), High Angular Resolution Imaging (HARDI) can better explore the complex microstructure of white matter. Orientation Distribution Function (ODF) is used to describe the probability of the fiber direction. Fisher information metric has been constructed for probability density family in Information Geometry theory and it has been successfully applied for tensor computing in DTI. In this paper, we present a state of the art Riemannian framework for ODF computing based on Information Geometry and sparse representation of orthonormal bases. In this Riemannian framework, the exponential map, logarithmic map and geodesic have closed forms. And the weighted Frechet mean exists uniquely on this manifold. We also propose a novel scalar measurement, named Geometric Anisotropy (GA), which is the Riemannian geodesic distance between the ODF and the isotropic ODF. The Renyi entropy H1/2 of the ODF can be computed from the GA. Moreover, we present an Affine-Euclidean framework and a Log-Euclidean framework so that we can work in an Euclidean space. As an application, Lagrange interpolation on ODF field is proposed based on weighted Frechet mean. We validate our methods on synthetic and real data experiments. Compared with existing Riemannian frameworks on ODF, our framework is model-free. The estimation of the parameters, i.e. Riemannian coordinates, is robust and linear. Moreover it should be noted that our theoretical results can be used for any probability density function (PDF) under an orthonormal basis representation. PMID:20426075
On the electron equilibrium distribution function in the kinetic theory of electron cyclotron maser
NASA Astrophysics Data System (ADS)
Shenggang, Liu
1981-11-01
The problems concerning the specification of electron equilibrium distribution function for the kinetic theory of ECRM are investigated in this paper. After detailed analysis of the published equilibium distribution functions, several conclusion have been achieved.
Bobrowski, Adam; Kimmel, Marek
2004-12-01
This is a continuation of the series of articles (C.R. Rao, D.N. Shanbhag (Eds.), Handbook of Statistics 19: Stochastic Processes: Theory and Methods, Elsevier Science, Amsterdam, 2001 (Chapter 8); Math. Biosci. 175 (2002) 83; Math. Meth. Appl. Sci. 26 (2003) 1587; Adv. Appl. Probab. 36 (2004) 57) devoted to a study of the interplay between two of the main forces of population genetics, mutations and drift, in the Fisher-Wright model. We provide discrete-time versions of theorems describing asymptotic behavior of joint distributions of characteristics of a pair of individuals in this model; their continuous-time counterparts were presented in the previous papers. Furthermore, we show that imbalance index, introduced in Kimmel et al. (Genetics 148 (1998) 1921) and King et al. (Mol. Biol. Evol. 17(12) (2000) 1895) in the context of continuous-time models, may also be used in discrete-time models to detect past population growth. PMID:15560913
Conductance Distributions for Empirical Orthogonal Function Analysis and Optimal Interpolation
NASA Astrophysics Data System (ADS)
Knipp, Delores; McGranaghan, Ryan; Matsuo, Tomoko
2016-04-01
We show the first characterizations of the primary modes of ionospheric Hall and Pedersen conductance variability as empirical orthogonal functions (EOFs). These are derived from six satellite years of Defense Meteorological Satellite Program (DMSP) particle data acquired during the rise of solar cycles 22 and 24. The 60 million DMSP spectra were each processed through the Global Airlglow Model. This is the first large-scale analysis of ionospheric conductances completely free of assumption of the incident electron energy spectra. We show that the mean patterns and first four EOFs capture ˜50.1 and 52.9% of the total Pedersen and Hall conductance variabilities, respectively. The mean patterns and first EOFs are consistent with typical diffuse auroral oval structures and quiet time strengthening/weakening of the mean pattern. The second and third EOFs show major disturbance features of magnetosphere-ionosphere (MI) interactions: geomagnetically induced auroral zone expansion in EOF2 and the auroral substorm current wedge in EOF3. The fourth EOFs suggest diminished conductance associated with ionospheric substorm recovery mode. These EOFs are then used in a new optimal interpolation (OI) technique to estimate complete high-latitude ionospheric conductance distributions. The technique combines particle precipitation-based calculations of ionospheric conductances and their errors with a background model and its error covariance (estimated by EOF analysis) to infer complete distributions of the high-latitude ionospheric conductances for a week in late 2011. The OI technique captures: 1) smaller-scaler ionospheric conductance features associated with discrete precipitation and 2) brings ground- and space-based data into closer agreement. We show quantitatively and qualitatively that this new technique provides better ionospheric conductance specification than past statistical models, especially during heightened geomagnetic activity.
Quasar Spectral Energy Distributions As A Function Of Physical Property
NASA Astrophysics Data System (ADS)
Townsend, Shonda; Ganguly, R.; Stark, M. A.; Derseweh, J. A.; Richmond, J. M.
2012-05-01
Galaxy evolution models have shown that quasars are a crucial ingredient in the evolution of massive galaxies. Outflows play a key role in the story of quasars and their host galaxies, by helping regulate the accretion process, the star-formation rate and mass of the host galaxy (i.e., feedback). The prescription for modeling outflows as a contributor to feedback requires knowledge of the outflow velocity, geometry, and column density. In particular, we need to understand how these depend on physical parameters and how much is determined stochastically (and with what distribution). In turn, models of outflows have shown particular sensitivity to the shape of the spectral energy distribution (SED), depending on the UV luminosity to transfer momentum to the gas, the X-ray luminosity to regulate how efficiently that transfer can be, etc. To investigate how SED changes with physical properties, we follow up on Richards et al. (2006), who constructed SEDs with varying luminosity. Here, we construct SEDs as a function of redshift, and physical property (black hole mass, bolometric luminosity, Eddington ratio) for volume limited samples drawn from the Sloan Digital Sky Survey, with photometry supplemented from 2MASS, WISE, GALEX, ROSAT, and Chandra. To estimate black hole masses, we adopt the scaling relations from Greene & Ho (2005) based on the H-alpha emission line FWHM. This requires redshifts less than 0.4. To construct volume-limited subsamples, we begin by adopting g=19.8 as a nominal limiting magnitude over which we are guaranteed to detect z<0.4 quasars. At redshift 0.4, we are complete down to Mg=-21.8, which yields 3300 objects from Data Release 7. At z=0.1, we are complete down to Mg=-18.5. This material is based upon work supported by the National Aeronautics and Space Administration under Grant No. 09-ADP09-0016 issued through the Astrophysics Data Analysis Program.
ALPHA ENHANCEMENT AND THE METALLICITY DISTRIBUTION FUNCTION OF PLAUT'S WINDOW
Johnson, Christian I.; Michael Rich, R.; Fulbright, Jon P.; Valenti, Elena; McWilliam, Andrew E-mail: rmr@astro.ucla.edu E-mail: evalenti@eso.org
2011-05-10
We present Fe, Si, and Ca abundances for 61 giants in Plaut's window (l = -1{sup 0}, b = -8.{sup 0}5) and Fe abundances for an additional 31 giants in a second, nearby field (l = 0{sup 0}, b = -8{sup 0}) derived from high-resolution (R {approx} 25,000) spectra obtained with the Blanco 4 m telescope and Hydra multifiber spectrograph. The median metallicity of red giant branch (RGB) stars in the Plaut's field is {approx}0.4 dex lower than those in Baade's window, and confirms the presence of an iron abundance gradient along the bulge minor axis. The full metallicity range of our (biased) RGB sample spans -1.5 < [Fe/H] < +0.3, which is similar to that found in other bulge fields. We also derive a photometric metallicity distribution function for RGB stars in the (l = -1{sup 0}, b = -8{sup 0}.5) field and find very good agreement with the spectroscopic metallicity distribution. The radial velocity (RV) and dispersion data for the bulge RGB stars are in agreement with previous results of the Bulge Radial Velocity Assay survey, and we find evidence for a decreasing velocity dispersion with increasing [Fe/H]. The [{alpha}/Fe] enhancement in Plaut field stars is nearly identical to that observed in Baade's window, and suggests that an [{alpha}/Fe] gradient does not exist between b = -4{sup 0} and -8{sup 0}. Additionally, a subset of our sample (23 stars) appears to be foreground red clump stars that are very metal rich, exhibit small metallicity and RV dispersions, and are enhanced in {alpha} elements. While these stars likely belong to the Galactic inner disk population, they exhibit [{alpha}/Fe] ratios that are enhanced above the thin and thick disk.
Coarse graining the distribution function of cold dark matter - II
NASA Astrophysics Data System (ADS)
Henriksen, R. N.
2004-12-01
We study analytically the coarse- and fine-grained distribution function (DF) established by the self-similar infall of collisionless matter. We find this function explicitly for isotropic and spherically symmetric systems in terms of cosmological initial conditions. The coarse-grained function is structureless and steady but the familiar phase-space sheet substructure is recovered in the fine-grained limit. By breaking the self-similarity of the halo infall we are able to argue for a central density flattening. In addition there will be an edge steepening. The best-fitting analytic density function is likely to be provided by a high-order polytrope fit smoothly to an outer power law of index -3 for isolated systems. There may be a transition to a -4 power law in the outer regions of tidally truncated systems. As we find that the central flattening is progressive in time, dynamically young systems such as galaxy clusters may well possess a Navarro, Frenk and White type density profile, while primordial dwarf galaxies, for example, are expected to have cores. This progressive flattening is expected to end either in the non-singular isothermal sphere, or in the non-singular metastable polytropic cores; as the DFs associated with each of these arise naturally in the bulk halo during the infall. We suggest, based on previous studies of the evolution of de-stabilized polytropes, that a collisionless system may pass through a family of polytropes of increasing order, finally approaching the limit of the non-singular isothermal sphere, if the `violent' collective relaxation is frequently re-excited by `merger' events. Thus central dominant (cD) galaxies, and indeed all bright galaxies that have grown in this fashion, should be in polytropic states. Our results suggest that no physics beyond that of wave-particle scattering is necessary to explain the nature of dark matter density profiles. However, this may be assisted by the scattering of particles from the centre of the
Rosenberg, Miriam I; Brent, Ava E; Payre, François; Desplan, Claude
2014-01-01
Embryonic anterior–posterior patterning is well understood in Drosophila, which uses ‘long germ’ embryogenesis, in which all segments are patterned before cellularization. In contrast, most insects use ‘short germ’ embryogenesis, wherein only head and thorax are patterned in a syncytial environment while the remainder of the embryo is generated after cellularization. We use the wasp Nasonia (Nv) to address how the transition from short to long germ embryogenesis occurred. Maternal and gap gene expression in Nasonia suggest long germ embryogenesis. However, the Nasonia pair-rule genes even-skipped, odd-skipped, runt and hairy are all expressed as early blastoderm pair-rule stripes and late-forming posterior stripes. Knockdown of Nv eve, odd or h causes loss of alternate segments at the anterior and complete loss of abdominal segments. We propose that Nasonia uses a mixed mode of segmentation wherein pair-rule genes pattern the embryo in a manner resembling Drosophila at the anterior and ancestral Tribolium at the posterior. DOI: http://dx.doi.org/10.7554/eLife.01440.001 PMID:24599282
Controlling the Electron Energy Distribution Function Using an Anode
NASA Astrophysics Data System (ADS)
Baalrud, Scott D.; Barnat, Edward V.; Hopkins, Mathew M.
2014-10-01
Positively biased electrodes inserted into plasmas influence the electron energy distribution function (EEDF) by providing a sink for low energy electrons that would otherwise be trapped by ion sheaths at the chamber walls. We develop a model for the EEDF in a hot filament generated discharge in the presence of positively biased electrodes of various surface areas, and compare the model results with experimental Langmuir probe measurements and particle-in-cell simulations. In the absence of an anode, the EEDF is characterized by a cool trapped population at energies below the sheath energy, and a comparatively warm tail population associated with the filament primaries. Anodes that are small enough to collect a negligible fraction of the electrons exiting the plasma have little affect on the EEDF, but as the anode area approaches √{me /mi }Aw , where Aw is the chamber wall area, the anode collects most of the electrons leaving the plasma. This drastically reduces the density of the otherwise trapped population, causing an effective heating of the electrons and a corresponding density decrease. A global model is developed based on the EEDF model and current balance, which shows the interconnected nature of the electron temperature, density and the plasma potential. This work was supported by the Office of Fusion Energy Science at the U.S. Department of Energy under Contract DE-AC04-94SL85000, and by the University of Iowa Old Gold Program.
First principles simulations of fluid water: The radial distribution functions
NASA Astrophysics Data System (ADS)
Ortega, José; Lewis, James P.; Sankey, Otto F.
1997-03-01
We apply a recently developed first principles but simplified molecular dynamics method to the simulation of water at different conditions. The computational simplicity of this method allows its application to systems containing a significant number of molecules, yet still taking explicitly into account the quantum electronic structure of the system. In the present work we simulate a system of 216 H2O molecules with periodic boundary conditions at two different densities (ρ=1.0 g/cm3 and ρ=0.72 g/cm3 and temperatures ranging from ˜300 K to ˜580 K. The effect of density and temperature on the structure of water is analyzed by means of the partial radial distribution functions gOO, gOH and gHH . We find an important reduction of the hydrogen-bond peak for water at the supercritical conditions ρ= 0.72 g/cm3, T=580 K, in good agreement with recent experimental results.
The distribution function of the Galaxy's dark halo
NASA Astrophysics Data System (ADS)
Binney, J.; Piffl, T.
2015-12-01
Starting from the hypothesis that the Galaxy's dark halo responded adiabatically to the infall of baryons, we have constructed a self-consistent dynamical model of the Galaxy that satisfies a large number of observations, including measurements of gas terminal velocities and masers, the kinematics of 180 000 giant stars from the RAVE (RAdial Velocity Experiment) survey and star-count data from the Sloan Digital Sky Survey. The stellar disc and the dark halo are both specified by distribution functions of the action integrals. The model is obtained by extending the work of Piffl et al. from the construction of a single model to a systematic search of model space. Whereas the model of Piffl et al. violated constraints on the terminal-velocity curve, our model respects these constraints by adopting a long scalelength Rd = 3.66 kpc for the thin and thick discs. The model is, however, inconsistent with the measured optical depth for microlensing of bulge stars because it attributes too large a fraction of the density at R ≲ 3 kpc to dark matter rather than stars. Moreover, it now seems likely that the thick disc's scalelength is significantly shorter than the model implies. Shortening this scalelength would cause the constraints from the rotation curve to be violated anew. We conclude that we can now rule out adiabatic compression of our Galaxy's dark halo.
ERIC Educational Resources Information Center
Balasooriya, Uditha; Li, Jackie; Low, Chan Kee
2012-01-01
For any density function (or probability function), there always corresponds a "cumulative distribution function" (cdf). It is a well-known mathematical fact that the cdf is more general than the density function, in the sense that for a given distribution the former may exist without the existence of the latter. Nevertheless, while the density…
NASA Astrophysics Data System (ADS)
Takeuchi, Tsutomu T.
2010-08-01
We provide an analytic method to construct a bivariate distribution function (DF) with given marginal distributions and correlation coefficient. We introduce a convenient mathematical tool, called a copula, to connect two DFs with any prescribed dependence structure. If the correlation of two variables is weak (Pearson's correlation coefficient |ρ| < 1/3), the Farlie-Gumbel-Morgenstern (FGM) copula provides an intuitive and natural way to construct such a bivariate DF. When the linear correlation is stronger, the FGM copula cannot work anymore. In this case, we propose using a Gaussian copula, which connects two given marginals and is directly related to the linear correlation coefficient between two variables. Using the copulas, we construct the bivariate luminosity function (BLF) and discuss its statistical properties. We focus especially on the far-infrared-far-ulatraviolet (FUV-FIR) BLF, since these two wavelength regions are related to star-formation (SF) activity. Though both the FUV and FIR are related to SF activity, the univariate LFs have a very different functional form: the former is well described by the Schechter function whilst the latter has a much more extended power-law-like luminous end. We construct the FUV-FIR BLFs using the FGM and Gaussian copulas with different strengths of correlation, and examine their statistical properties. We then discuss some further possible applications of the BLF: the problem of a multiband flux-limited sample selection, the construction of the star-formation rate (SFR) function, and the construction of the stellar mass of galaxies (M*)-specific SFR (SFR/M*) relation. The copulas turn out to be a very useful tool to investigate all these issues, especially for including complicated selection effects.
NASA Technical Reports Server (NTRS)
MacKenzie, Anne I.; Rao, Sadasiva M.; Baginski, Michael E.
2007-01-01
A pair of basis functions is presented for the surface integral, method of moment solution of scattering by arbitrarily-shaped, three-dimensional dielectric bodies. Equivalent surface currents are represented by orthogonal unit pulse vectors in conjunction with triangular patch modeling. The electric field integral equation is employed with closed geometries for dielectric bodies; the method may also be applied to conductors. Radar cross section results are shown for dielectric bodies having canonical spherical, cylindrical, and cubic shapes. Pulse basis function results are compared to results by other methods.
ERIC Educational Resources Information Center
Monsour, Florence
2000-01-01
Mentoring programs that pair experienced and first-time teachers are gaining prominence in supporting, developing, and retaining new teachers. The successful Beginning Teacher Assistance program at University of Wisconsin-River Falls was designed to give new K-12 teachers the opportunity for yearlong, structured support from mentor teachers. (MLH)
NASA Technical Reports Server (NTRS)
Pilipp, W. G.; Muehlhaeuser, K.-H.; Miggenrieder, H.; Montgomery, M. D.; Rosenbauer, H.
1987-01-01
The details of the shapes of three typical electron distribution functions observed by the Helios 1 and 2 probes in the solar wind between 0.3 AU and 1 AU are analyzed and compared with theoretical predictions. These are (1) a distribution function with a narrow 'strahl' (narrow beam), which is extremely anisotropic and skewed with respect to the magnetic field direction at particle energies above 100 eV; (2) a distribution function with a broad 'strahl', less anisotropic and skewed; and (3) a nearly isotropic distribution function. For each distribution function, a sudden change in the slope was discerned, separating the 'core' at lower energies from the 'halo' at higher energies. The most obvious differences of the analyzed electron distribution functions were observed at energies above 50-100 eV. The possible origins for the observed features of the distribution functions are discussed.
Mars: New Determination of Impact Crater Production Function Size Distribution
NASA Astrophysics Data System (ADS)
Hartmann, William K.
2006-12-01
Several authors have questioned our knowledge of Martian impact crater production function size-frequency distribution (PFSFD), especially at small diameters D. Plescia (2005) questioned whether any area of Mars shows size distributions used for estimating crater retention ages on Mars. McEwen et al. (2005) and McEwen and Bierhaus (2006) suggested existing PFSFD’s are hopelessly confused by the presence of secondaries, and that my isochrons give primary crater densities off by factors of several thousand at small D. In 2005, I addressed some of these concerns, noting my curves do not estimate primary crater densities per se, but show total numbers of primaries + semi-randomly “distant secondaries” (negating many McEwen et al. critiques). In 2006 I have conducted new crater counts on a PFSFD test area suggested by Ken Tanaka. This area shows young lava flows of similar crater density, west of Olympus Mons (around 30 deg N, 100 deg W). Multiple crater counts were made on several adjacent Odyssey THEMIS images and MGS MOC images, giving the SFD over a range of 11m
NASA Astrophysics Data System (ADS)
Hainline, Kevin N.; Hickox, Ryan C.; Chen, Chien-Ting; Carroll, Christopher M.; Jones, Mackenzie L.; Zervos, Alexandros S.; Goulding, Andrew D.
2016-05-01
We explore the gas ionization and kinematics, as well as the optical-IR spectral energy distributions for UGC 11185, a nearby pair of merging galaxies hosting obscured active galactic nuclei (AGNs), also known as SDSS J181611.72+423941.6 and J181609.37+423923.0 (J1816NE and J1816SW, z ≈ 0.04). Due to the wide separation between these interacting galaxies (∼23 kpc), observations of these objects provide a rare glimpse of the concurrent growth of supermassive black holes at an early merger stage. We use BPT line diagnostics to show that the full extent of the narrow-line emission in both galaxies is photoionized by an AGN, and confirm the existence of a 10 kpc-scale ionization cone in J1816NE, while in J1816SW the AGN narrow-line region is much more compact (1–2 kpc) and relatively undisturbed. Our observations also reveal the presence of ionized gas that nearly spans the entire distance between the galaxies, which is likely in a merger-induced tidal stream. In addition, we carry out a spectral analysis of the X-ray emission using data from XMM-Newton. These galaxies represent a useful pair to explore how the [O iii] luminosity of an AGN is dependent on the size of the region used to explore the extended emission. Given the growing evidence for AGN “flickering” over short timescales, we speculate that the appearances and impacts of these AGNs may change multiple times over the course of the galaxy merger, which is especially important given that these objects are likely the progenitors of the types of systems commonly classified as “dual AGNs.”
Sevelinges, Yannick; Mouly, Anne-Marie; Raineki, Charlis; Moriceau, Stéphanie; Forest, Christina; Sullivan, Regina M.
2010-01-01
Maltreatment from the caregiver induces vulnerability to later life psychopathologies, yet attraction and comfort is sometimes provided by cues associated with early life maltreatment. We used a rat model of early life maltreatment with odor-0.5mA shock conditioning to produce depressive-like behaviors and questioned whether stimuli associated with maltreatment would restore emotional neurobehavioral function to control levels. Pups received daily novel odor-0.5mA shock conditioning from postnatal day 8 to 12. This procedure produces a new maternal odor that controls pups' attachment behaviors. In adulthood, either with or without the infant odor, animals received a Forced Swim Test, Sucrose Preference Test or assessment of amygdala and olfactory system functioning using field potential signal evoked by olfactory bulb paired-pulse electrical stimulation. Following neonatal odor-shock pairings, but not unpaired controls, adults without the odor present showed increased depression-like behavior in the Forced Swim Test and Sucrose Preference Test and a deficit in paired-pulse inhibition in amygdala and piriform (olfactory) cortex. All effects were brought to control levels when the infant conditioned odor was presented during behavioral and neural tests. The ability of cues associated with early life maltreatment to normalize behavior and amygdala activity suggests these cues provide adaptive value in adulthood. PMID:21037982
Nongyrotropic electron velocity distribution functions near the lunar surface
NASA Astrophysics Data System (ADS)
Harada, Yuki; Machida, Shinobu; Saito, Yoshifumi; Yokota, Shoichiro; Asamura, Kazushi; Nishino, Masaki N.; Tsunakawa, Hideo; Shibuya, Hidetoshi; Takahashi, Futoshi; Matsushima, Masaki; Shimizu, Hisayoshi
2012-07-01
We have analyzed nongyrotropic electron velocity distribution functions (VDFs) obtained near the lunar surface. Electron VDFs, measured at ˜10-100 km altitude by Kaguya in both the solar wind and the Earth's magnetosphere, exhibit nongyrotropic empty regions associated with the ‘gyroloss’ effect; i.e., electron absorption by the lunar surface combined with electron gyromotion. Particle-trace calculations allow us to derive theoretical forbidden regions in the electron VDFs, thereby taking into account the modifications due to nonuniform magnetic fields caused by diamagnetic-current systems, lunar-surface charging, and electric fields perpendicular to the magnetic field. Comparison between the observed empty regions with the theoretically derived forbidden regions suggests that various components modify the characteristics of the nongyrotropic electron VDFs depending on the ambient-plasma conditions. On the lunar nightside in the magnetotail lobes, negative surface potentials slightly reduce the size of the forbidden regions, but there are no distinct effects of either the diamagnetic current or perpendicular electric fields. On the dayside in the solar wind, the observations suggest the presence of either the diamagnetic-current or solar wind convection electric field effects, or both. In the terrestrial plasma sheet, all three mechanisms can substantially modify the characteristics of the forbidden regions. The observations imply the presence of a local electric field of at least 5 mV/m although the mechanism responsible for production of such a strong electric field is unknown. Analysis of nongyrotropic VDFs associated with the gyroloss effect near solid surfaces can promote a better understanding of the near-surface plasma environment and of plasma-solid-surface interactions.
Spaceflight effects on T lymphocyte distribution, function and gene expression
Gridley, Daila S.; Slater, James M.; Luo-Owen, Xian; Rizvi, Asma; Chapes, Stephen K.; Stodieck, Louis S.; Ferguson, Virginia L.; Pecaut, Michael J.
2009-01-01
The immune system is highly sensitive to stressors present during spaceflight. The major emphasis of this study was on the T lymphocytes in C57BL/6NTac mice after return from a 13-day space shuttle mission (STS-118). Spleens and thymuses from flight animals (FLT) and ground controls similarly housed in animal enclosure modules (AEM) were evaluated within 3–6 h after landing. Phytohemagglutinin-induced splenocyte DNA synthesis was significantly reduced in FLT mice when based on both counts per minute and stimulation indexes (P < 0.05). Flow cytometry showed that CD3+ T and CD19+ B cell counts were low in spleens from the FLT group, whereas the number of NK1.1+ natural killer (NK) cells was increased (P < 0.01 for all three populations vs. AEM). The numerical changes resulted in a low percentage of T cells and high percentage of NK cells in FLT animals (P < 0.05). After activation of spleen cells with anti-CD3 monoclonal antibody, interleukin-2 (IL-2) was decreased, but IL-10, interferon-γ, and macrophage inflammatory protein-1α were increased in FLT mice (P < 0.05). Analysis of cancer-related genes in the thymus showed that the expression of 30 of 84 genes was significantly affected by flight (P < 0.05). Genes that differed from AEM controls by at least 1.5-fold were Birc5, Figf, Grb2, and Tert (upregulated) and Fos, Ifnb1, Itgb3, Mmp9, Myc, Pdgfb, S100a4, Thbs, and Tnf (downregulated). Collectively, the data show that T cell distribution, function, and gene expression are significantly modified shortly after return from the spaceflight environment. PMID:18988762
Sparse Solution of Fiber Orientation Distribution Function by Diffusion Decomposition
Yeh, Fang-Cheng; Tseng, Wen-Yih Isaac
2013-01-01
Fiber orientation is the key information in diffusion tractography. Several deconvolution methods have been proposed to obtain fiber orientations by estimating a fiber orientation distribution function (ODF). However, the L2 regularization used in deconvolution often leads to false fibers that compromise the specificity of the results. To address this problem, we propose a method called diffusion decomposition, which obtains a sparse solution of fiber ODF by decomposing the diffusion ODF obtained from q-ball imaging (QBI), diffusion spectrum imaging (DSI), or generalized q-sampling imaging (GQI). A simulation study, a phantom study, and an in-vivo study were conducted to examine the performance of diffusion decomposition. The simulation study showed that diffusion decomposition was more accurate than both constrained spherical deconvolution and ball-and-sticks model. The phantom study showed that the angular error of diffusion decomposition was significantly lower than those of constrained spherical deconvolution at 30° crossing and ball-and-sticks model at 60° crossing. The in-vivo study showed that diffusion decomposition can be applied to QBI, DSI, or GQI, and the resolved fiber orientations were consistent regardless of the diffusion sampling schemes and diffusion reconstruction methods. The performance of diffusion decomposition was further demonstrated by resolving crossing fibers on a 30-direction QBI dataset and a 40-direction DSI dataset. In conclusion, diffusion decomposition can improve angular resolution and resolve crossing fibers in datasets with low SNR and substantially reduced number of diffusion encoding directions. These advantages may be valuable for human connectome studies and clinical research. PMID:24146772
Predictions of Geospace Drivers By the Probability Distribution Function Model
NASA Astrophysics Data System (ADS)
Bussy-Virat, C.; Ridley, A. J.
2014-12-01
Geospace drivers like the solar wind speed, interplanetary magnetic field (IMF), and solar irradiance have a strong influence on the density of the thermosphere and the near-Earth space environment. This has important consequences on the drag on satellites that are in low orbit and therefore on their position. One of the basic problems with space weather prediction is that these drivers can only be measured about one hour before they affect the environment. In order to allow for adequate planning for some members of the commercial, military, or civilian communities, reliable long-term space weather forecasts are needed. The study presents a model for predicting geospace drivers up to five days in advance. This model uses the same general technique to predict the solar wind speed, the three components of the IMF, and the solar irradiance F10.7. For instance, it uses Probability distribution functions (PDFs) to relate the current solar wind speed and slope to the future solar wind speed, as well as the solar wind speed to the solar wind speed one solar rotation in the future. The PDF Model has been compared to other models for predictions of the speed. It has been found that it is better than using the current solar wind speed (i.e., persistence), and better than the Wang-Sheeley-Arge Model for prediction horizons of 24 hours. Once the drivers are predicted, and the uncertainty on the drivers are specified, the density in the thermosphere can be derived using various models of the thermosphere, such as the Global Ionosphere Thermosphere Model. In addition, uncertainties on the densities can be estimated, based on ensembles of simulations. From the density and uncertainty predictions, satellite positions, as well as the uncertainty in those positions can be estimated. These can assist operators in determining the probability of collisions between objects in low Earth orbit.
"Distribution and functional identification of complex class 1 integrons".
Quiroga, María Paula; Arduino, Sonia Marina; Merkier, Andrea Karina; Quiroga, Cecilia; Petroni, Alejandro; Roy, Paul H; Centrón, Daniela
2013-10-01
The emergence of extended-spectrum β-lactamases and plasmid-mediated resistance to quinolones has been previously found to be associated with the dissemination of complex class 1 integrons in Argentina. In this study, we analyzed their distribution through time and evaluated the functionality of the Orf513 protein, which is the putative recombinase of the ISCR1 mobile element. We investigated the presence of the orf513, blaCTX-M-2, dfrA3b, qnrB10 and blaDHA-1 genes by PCR and DNA sequencing as well as their linkage to class 1 integrons in 451 non-epidemiologically related nosocomial strains resistant to at least one expanded-spectrum cephalosporin and to one aminoglycoside, isolated between 1989 and 2010 from 7 hospitals from Buenos Aires City. The epidemiology of complex class 1 integrons was found to be notably different among fermenting (94/171) and non-fermenting clinical bacilli isolates (1/280). The ISCR1::qnrB10 positive isolates were found since 1993, confirming its presence in clinical isolates more than a decade before its first description. As expected, In35::ISCR1::blaCTX-M-2 was the most common complex class 1 integron among Enterobacteriaceae isolates, particularly in Proteus mirabilis. Experimental analysis corroborated the activity of the Orf513 protein, which was found to bind specific DNA sequences containing the previously suggested oriIS region. These findings showed the high dispersion and maintenance of complex class 1 integrons across time in our nosocomial isolates. The contribution of the ISCR1 mobile element to multidrug resistant phenotypes is significant due to its sustained association to class 1 integrons. PMID:23838285
Functional interplay between SA1 and TRF1 in telomeric DNA binding and DNA-DNA pairing.
Lin, Jiangguo; Countryman, Preston; Chen, Haijiang; Pan, Hai; Fan, Yanlin; Jiang, Yunyun; Kaur, Parminder; Miao, Wang; Gurgel, Gisele; You, Changjiang; Piehler, Jacob; Kad, Neil M; Riehn, Robert; Opresko, Patricia L; Smith, Susan; Tao, Yizhi Jane; Wang, Hong
2016-07-27
Proper chromosome alignment and segregation during mitosis depend on cohesion between sister chromatids. Cohesion is thought to occur through the entrapment of DNA within the tripartite ring (Smc1, Smc3 and Rad21) with enforcement from a fourth subunit (SA1/SA2). Surprisingly, cohesin rings do not play a major role in sister telomere cohesion. Instead, this role is replaced by SA1 and telomere binding proteins (TRF1 and TIN2). Neither the DNA binding property of SA1 nor this unique telomere cohesion mechanism is understood. Here, using single-molecule fluorescence imaging, we discover that SA1 displays two-state binding on DNA: searching by one-dimensional (1D) free diffusion versus recognition through subdiffusive sliding at telomeric regions. The AT-hook motif in SA1 plays dual roles in modulating non-specific DNA binding and subdiffusive dynamics over telomeric regions. TRF1 tethers SA1 within telomeric regions that SA1 transiently interacts with. SA1 and TRF1 together form longer DNA-DNA pairing tracts than with TRF1 alone, as revealed by atomic force microscopy imaging. These results suggest that at telomeres cohesion relies on the molecular interplay between TRF1 and SA1 to promote DNA-DNA pairing, while along chromosomal arms the core cohesin assembly might also depend on SA1 1D diffusion on DNA and sequence-specific DNA binding. PMID:27298259
Required distribution of noise sources for Green's function recovery in diffusive fields
NASA Astrophysics Data System (ADS)
Shamsalsadati, S.; Weiss, C. J.
2011-12-01
In the most general sense, noise is the part of the signal of little or no interest, due to a multitude of reasons such as operator error, imperfect instrumentation, experiment design, or inescapable background interference. Considering the latter, it has been shown that Green's function can be extracted from cross-correlation of the ambient, diffusive wavefields arising from background random noise sources. Pore pressure and low-frequency electromagnetic induction are two such examples of diffusive fields. In theory, applying Green's function method in geophysical exploration requires infinity of volumetrically distributed sources; however, in the real world the number of noise sources in an area is limited, and furthermore, unevenly distributed in time, space and spectral content. Hence, quantification of the requisite noise sources that enable us to calculate Green's function acceptably well remains an open research question. The purpose of this study is to find the area of noise sources that contribute most to the Green's function estimation in diffusive systems. We call such a region the Volume of Relevance (VoR). Our analysis builds upon recent work in 1D homogeneous system where it was shown that sources located between two receivers positions are the most important ones for the purpose of Green's function recovery. Our results confirm the previous finding but we also examine the effect of heterogeneity, dimensionality and receiver location in both 1D and 2D at a fixed frequency. We demonstrate that for receivers located symmetrically across an interface between regions of contrasting diffusivity, the VoR rapidly shifts from one side of the interface to the other, and back again, as receiver separation increases. We also demonstrate that where the receiver pair is located on the interface itself, the shifting is less rapid, and for moderate to high diffusivity contrasts, the VoR remains entirely on the more diffusive side. In addition, because classical
Maddoux, John A; Liu, Fuqin; Symes, Lene; McFarlane, Judith; Paulson, Rene; Binder, Brenda K; Fredland, Nina; Nava, Angeles; Gilroy, Heidi
2016-04-01
Partner violence is associated with numerous negative consequences for victims, especially poor mental health. Children who are exposed to partner violence are more likely to have behavior problems. Nevertheless, research on the relationship between severity of abuse, maternal mental health functioning following partner violence, and child behavior problems is limited. We explored the direct and indirect effects on the child's behavioral functioning of severity of maternal abuse and maternal mental health functioning following abuse. A sample of 300 mothers was recruited when they sought assistance for abuse for the first time at shelters for abused women or at the district attorney's office. Severity of abuse, mothers' mental health functioning, and child behavioral functioning were measured by maternal self-report at entry into the study and 4 months later. In SEM analysis, at both entry and 4 months, severity of abuse had a direct effect on maternal mental health functioning, which in turn had a direct effect on child behavioral functioning. The path from severity of abuse to child behavioral functioning also was significant but became non- significant once maternal mental health functioning was added to the equation, indicating that the path from severity of abuse to child behavioral functioning was indirect and occurred as a result of the mother's mental health functioning, which remained directly linked to child behavioral problems. Intergenerational interventions are needed to address both maternal mental health and child behavioral functioning when a mother reports partner violence and is experiencing mental health problems. PMID:26694769
NASA Astrophysics Data System (ADS)
Simões Júnior, F. J. R.; Alves, M. V.; Rizzato, F. B.
2005-12-01
Results from plasma wave experiments in spacecrafts give support to nonlinear interactions involving Langmuir, electromagnetic, and ion-acoustic waves in association with type III solar radio bursts. Starting from a general form of Zakharov equation (Zakharov, V.E., 1985. Collapse and self-focusing of Langmuir waves. Hand-book of Plasma Physics Cap.2, 81 121) the equations for electric fields and density fluctuations (density gratings) induced by a pair of counterpropagating Langmuir waves are obtained. We consider the coupling of four triplets. Each two triplets have in common the Langmuir pump wave (forward or backward wave) and a pair of independent density gratings. We numerically solve the dispersion relation for the system, extending the work of (Alves, M.V., Chian, A.C.L., Moraes, M.A.E., Abalde, J.R., Rizzato, F.B., 2002. A theory of the fundamental plasma emission of type- III solar radio bursts. Astronomy and Astrophysics 390, 351 357). The ratio of anti-Stokes (AS) (ω0+ω) to Stokes (S) (ω0-ω) electromagnetic mode amplitudes is obtained as a function of the pump wave frequency, wave number, and energy. We notice that the simultaneous excitation of AS and S distinguishable modes, i.e., with Re{ω}=ω≠0, only occurs when the ratio between the pump wave amplitudes, r is ≠1 and the pump wave vector k0 is <(13)W01/2, W0 being the forward pump wave energy. We also observe that the S mode always receives more energy.
Stagg, A J; Harding, B; Hughes, R A; Keat, A; Knight, S C
1991-01-01
Dendritic cells (DC), potent antigen-presenting cells, are known to be increased in numbers in inflammatory lesions in rheumatoid arthritis and juvenile chronic arthritis. In this study, patients with seronegative arthritis were studied; the distribution and functional properties of DC enriched low density cells (LDC) from peripheral blood (PB) and synovial fluid (SF) were compared. The composition of LDC from both sources was similar, comprising approximately 30% DC, 60% monocytes with few T lymphocytes. SF was significantly enriched for LDC compared with paired peripheral blood (P less than 0.0001) or peripheral blood from healthy controls (P less than 0.001). In contrast, patient PB contained fewer LDC (P less than 0.05) overall than healthy controls. LDC from both sources were potent simulators of allogeneic PB T cells in a mixed leucocyte reaction (MLR), but in four out of 10 patients SF LDC were significantly more stimulatory. In autologous MLRs (AMLRs) SF T cells were not stimulated by either LDC population. This anergy of T cells was confined to the joint as patient PB T cells showed an AMLR response to PB LDC which was similar to that seen in cells from healthy controls. PB T cells also responded to SF LDC; in a minority of patients SF LDC caused significantly greater stimulation in AMLR than PB LDC and the possibility is discussed that this may represent presentation of antigen acquired in vivo. PMID:1826647
Qaisar, Rizwan; Renaud, Guillaume; Hedstrom, Yvette; Pöllänen, Eija; Ronkainen, Paula; Kaprio, Jaakko; Alen, Markku; Sipilä, Sarianna; Artemenko, Konstantin; Bergquist, Jonas; Kovanen, Vuokko; Larsson, Lars
2013-01-01
Ageing is associated with a decline in muscle mass and strength leading to increased physical dependency in old age. Postmenopausal women experience a greater decline than men of similar age in parallel with the decrease in female sex steroid hormone production. We recruited six monozygous female twin pairs (55–59 years old) where only one twin pair was on hormone replacement therapy (HRT use = 7.8 ± 4.3 years) to investigate the association of HRT with the cytoplasmic volume supported by individual myonuclei (myonuclear domain (MND) size,) together with specific force at the single fibre level. HRT use was associated with a significantly smaller (∼27%; P < 0.05) mean MND size in muscle fibres expressing the type I but not the IIa myosin heavy chain (MyHC) isoform. In comparison to non-users, higher specific force was recorded in HRT users both in muscle fibres expressing type I (∼27%; P < 0.05) and type IIa (∼23%; P < 0.05) MyHC isoforms. These differences were fibre-type dependent, i.e. the higher specific force in fast-twitch muscle fibres was primarily caused by higher force per cross-bridge while slow-twitch fibres relied on both a higher number and force per cross-bridge. HRT use had no effect on fibre cross-sectional area (CSA), velocity of unloaded shortening (V0) and relative proportion of MyHC isoforms. In conclusion, HRT appears to have significant positive effects on both regulation of muscle contraction and myonuclei organization in postmenopausal women. PMID:23459759
Metallicity Distribution Functions of Four Local Group Dwarf Galaxies
NASA Astrophysics Data System (ADS)
Ross, Teresa L.; Holtzman, Jon; Saha, Abhijit; Anthony-Twarog, Barbara J.
2015-06-01
We present stellar metallicities in Leo I, Leo II, IC 1613, and Phoenix dwarf galaxies derived from medium (F390M) and broad (F555W, F814W) band photometry using the Wide Field Camera 3 instrument on board the Hubble Space Telescope. We measured metallicity distribution functions (MDFs) in two ways, (1) matching stars to isochrones in color-color diagrams and (2) solving for the best linear combination of synthetic populations to match the observed color-color diagram. The synthetic technique reduces the effect of photometric scatter and produces MDFs 30%-50% narrower than the MDFs produced from individually matched stars. We fit the synthetic and individual MDFs to analytical chemical evolution models (CEMs) to quantify the enrichment and the effect of gas flows within the galaxies. Additionally, we measure stellar metallicity gradients in Leo I and II. For IC 1613 and Phoenix our data do not have the radial extent to confirm a metallicity gradient for either galaxy. We find the MDF of Leo I (dwarf spheroidal) to be very peaked with a steep metal-rich cutoff and an extended metal-poor tail, while Leo II (dwarf spheroidal), Phoenix (dwarf transition), and IC 1613 (dwarf irregular) have wider, less peaked MDFs than Leo I. A simple CEM is not the best fit for any of our galaxies; therefore we also fit the “Best Accretion Model” of Lynden-Bell. For Leo II, IC 1613, and Phoenix we find similar accretion parameters for the CEM even though they all have different effective yields, masses, star formation histories, and morphologies. We suggest that the dynamical history of a galaxy is reflected in the MDF, where broad MDFs are seen in galaxies that have chemically evolved in relative isolation and narrowly peaked MDFs are seen in galaxies that have experienced more complicated dynamical interactions concurrent with their chemical evolution. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is
Degradation nonuniformity in the solar diffuser bidirectional reflectance distribution function.
Sun, Junqiang; Chu, Mike; Wang, Menghua
2016-08-01
The assumption of angular dependence stability of the solar diffuser (SD) throughout degradation is critical to the on-orbit calibration of the reflective solar bands (RSBs) in many satellite sensors. Recent evidence has pointed to the contrary, and in this work, we present a thorough investigative effort into the angular dependence of the SD degradation for the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (SNPP) satellite and for the twin Moderate-resolution Imaging Spectroradiometer (MODIS) onboard Terra and Aqua spacecrafts. One common key step in the RSB calibration is the use of the SD degradation performance measured by an accompanying solar diffuser stability monitor (SDSM) as a valid substitute for the SD degradation factor in the direction of the RSB view. If SD degradations between these two respective directions do not maintain the same relative relationship over time, then the unmitigated use of the SDSM-measured SD degradation factor in the RSB calibration calculation will generate bias, and consequently, long-term drift in derived science products. We exploit the available history of the on-orbit calibration events to examine the response of the SDSM and the RSB detectors to the incident illumination reflecting off SD versus solar declination angle and show that the angular dependency, particularly at short wavelengths, evolves with respect to time. The generalized and the decisive conclusion is that the bidirectional reflectance distribution function (BRDF) of the SD degrades nonuniformly with respect to both incident and outgoing directions. Thus, the SDSM-based measurements provide SD degradation factors that are biased relative to the RSB view direction with respect to the SD. The analysis also reveals additional interesting phenomena, for example, the sharp behavioral change in the evolving angular dependence observed in Terra MODIS and SNPP VIIRS. For SNPP VIIRS the mitigation for this
McMenamin, Paul G
2007-01-01
the CNS of a few other classes of non‐mammalian vertebrates, suggest that retinal vascularisation may have evolved independently in marsupial and eutherian mammals and that the former may have evolved from a common primitive mammal‐like reptilian ancestor which possessed paired vasculature in the CNS. Eutherian mammals may have evolved from an ancestor with anastomotic networks in the CNS or this pattern may have evolved later in eutherian mammal evolutionary radiation. The possible functional and physiological significance of the paired vessels is discussed. PMID:17475712
Knight, S J L; Yau, C; Clifford, R; Timbs, A T; Sadighi Akha, E; Dréau, H M; Burns, A; Ciria, C; Oscier, D G; Pettitt, A R; Dutton, S; Holmes, C C; Taylor, J; Cazier, J-B; Schuh, A
2012-01-01
Genome-wide array approaches and sequencing analyses are powerful tools for identifying genetic aberrations in cancers, including leukemias and lymphomas. However, the clinical and biological significance of such aberrations and their subclonal distribution are poorly understood. Here, we present the first genome-wide array based study of pre-treatment and relapse samples from patients with B-cell chronic lymphocytic leukemia (B-CLL) that uses the computational statistical tool OncoSNP. We show that quantification of the proportion of copy number alterations (CNAs) and copy neutral loss of heterozygosity regions (cnLOHs) in each sample is feasible. Furthermore, we (i) reveal complex changes in the subclonal architecture of paired samples at relapse compared with pre-treatment, (ii) provide evidence supporting an association between increased genomic complexity and poor clinical outcome (iii) report previously undefined, recurrent CNA/cnLOH regions that expand or newly occur at relapse and therefore might harbor candidate driver genes of relapse and/or chemotherapy resistance. Our findings are likely to impact on future therapeutic strategies aimed towards selecting effective and individually tailored targeted therapies. PMID:22258401
Nosenko, Yevgeniy; Riehn, Christoph; Niedner-Schatteburg, Gereon
2016-03-16
Metal base pairs of Ag(I) cations and 1-methylthymine (1MT) or deprotonated 1-methylthymine (1MT-H) are produced and analyzed by electrospray ionization mass spectrometry (ESI-MS). Mass-selected ions of type [Ag2(1MT)(1MT-H)](+) and [Ag3(1MT-H)2](+) are interrogated by infrared multiple-photon dissociation (IRMPD) in an ion trap in the range of 1200-3700 cm(-1). Supporting spectroscopic data were obtained from the investigation of the analogous 2'-deoxy-thymidine complexes which exhibit advantageously high fragment yields. By comparison with calculated linear IR spectra (obtained by density functional theory, DFT) we assign the structures and the possible isomeric forms of these metal base pairs and their dependence on the number of mediating Ag(I) ions. Based on the observed Ag(+)/1MT complexes and related polarizable continuum model DFT calculations we describe the probable formation pathways in aqueous solution. The present findings pave the way for subsequent UV investigations of the multi-metal mediated base pairs. PMID:26940234
Distributed representations in memory: Insights from functional brain imaging
Rissman, Jesse; Wagner, Anthony D.
2015-01-01
Forging new memories for facts and events, holding critical details in mind on a moment-to-moment basis, and retrieving knowledge in the service of current goals all depend on a complex interplay between neural ensembles throughout the brain. Over the past decade, researchers have increasingly leveraged powerful analytical tools (e.g., multi-voxel pattern analysis) to decode the information represented within distributed fMRI activity patterns. In this review, we discuss how these methods can sensitively index neural representations of perceptual and semantic content, and how leverage on the engagement of distributed representations provides unique insights into distinct aspects of memory-guided behavior. We emphasize that, in addition to characterizing the contents of memories, analyses of distributed patterns shed light on the processes that influence how information is encoded, maintained, or retrieved, and thus inform memory theory. We conclude by highlighting open questions about memory that can be addressed through distributed pattern analyses. PMID:21943171
NASA Astrophysics Data System (ADS)
Guelfucci, J. P.; Fitte-Rey, J.; Casanovas, J.; Baird, J. K.
1997-06-01
A semi-empirical method is tested to determine the spatial distribution function of the thermalized photoelectrons, created by vacuum ultraviolet (VUV) or γ irradiations of some liquid alkanes. It seems that modified exponentials must be associated to the thermalization process on VUV irradiation. A Gaussian distribution function could be used for high-energy irradiation. The partial inadequacy of the method in the case of high-energy irradiation can be imputed to the existence of multiple ion pair recombinations.
Performance Analysis of Two-Way OFDM Relay Systems with Ordered Subcarrier Pairing
NASA Astrophysics Data System (ADS)
Yang, Wendong; Wang, Kaihua; Cai, Yueming; Yang, Weiwei; Tu, Jia
2014-05-01
In this paper, we first prove the optimality of ordered subcarrier pairing (OSP) in two-way orthogonal frequency division multiplexing (OFDM) relay systems. The probability distribution function (PDF) and the cumulative distribution function (CDF) of the signal-to-noise ratio (SNR) is then derived for each subcarrier pair of the two-way links over Rayleigh fading channels. Furthermore, we analyze the performance of the systems including outage probability, symbol error rate (SER) and capacity. Monte Carlo simulations validate our analysis.
Model Etch Profiles for Ion Energy Distribution Functions in an Inductively Coupled Plasma Reactor
Abraham-Shrauner, B.; Chen, W.; Woodworth, J.R.
1998-12-14
Rectangular trench profiles are modeled with analytic etch rates determined from measured ion distribution functions. The pattern transfer step for this plasma etch is for trilayer lithography. Argon and chlorine angular ion energy distribution functions measured by a spherical collector ring analyzer are fit to a sum of drifting Maxwellian velocity distribution functions with anisotropic temperatures. The fit of the model ion distribution functions by a simulated annealing optimization procedure converges adequately for only two drifting Maxwellians. The etch rates are proportional to analytic expressions for the ion energy flux. Numerical computation of the etch profiles by integration of the characteristic equations for profile points and connection of the profiles points is efficient.
Transition in the Equilibrium Distribution Function of Relativistic Particles
Mendoza, M.; Araújo, N. A. M.; Succi, S.; Herrmann, H. J.
2012-01-01
We analyze a transition from single peaked to bimodal velocity distribution in a relativistic fluid under increasing temperature, in contrast with a non-relativistic gas, where only a monotonic broadening of the bell-shaped distribution is observed. Such transition results from the interplay between the raise in thermal energy and the constraint of maximum velocity imposed by the speed of light. We study the Bose-Einstein, the Fermi-Dirac, and the Maxwell-Jüttner distributions, and show that they all exhibit the same qualitative behavior. We characterize the nature of the transition in the framework of critical phenomena and show that it is either continuous or discontinuous, depending on the group velocity. We analyze the transition in one, two, and three dimensions, with special emphasis on twodimensions, for which a possible experiment in graphene, based on the measurement of the Johnson-Nyquist noise, is proposed. PMID:22937220
Transition in the Equilibrium Distribution Function of Relativistic Particles
NASA Astrophysics Data System (ADS)
Mendoza, M.; Araújo, N. A. M.; Succi, S.; Herrmann, H. J.
2012-08-01
We analyze a transition from single peaked to bimodal velocity distribution in a relativistic fluid under increasing temperature, in contrast with a non-relativistic gas, where only a monotonic broadening of the bell-shaped distribution is observed. Such transition results from the interplay between the raise in thermal energy and the constraint of maximum velocity imposed by the speed of light. We study the Bose-Einstein, the Fermi-Dirac, and the Maxwell-Jüttner distributions, and show that they all exhibit the same qualitative behavior. We characterize the nature of the transition in the framework of critical phenomena and show that it is either continuous or discontinuous, depending on the group velocity. We analyze the transition in one, two, and three dimensions, with special emphasis on twodimensions, for which a possible experiment in graphene, based on the measurement of the Johnson-Nyquist noise, is proposed.
Renormdynamics, multiparticle production, negative binomial distribution, and Riemann zeta function
NASA Astrophysics Data System (ADS)
Makhaldiani, N. V.
2013-09-01
After short introduction, we consider different aspects of the renormdynamics. Then scaling functions of the multiparticle production processes and corresponding stochastic dynamics are considered. Nonperturbative quasi-particle dynamics is considered on the base of the toy QCD- O( N)-sigma model. Last section concerns to the NBD-Riemann zeta function connection.
NASA Astrophysics Data System (ADS)
Nazaryan, T. A.; Petrosian, A. R.; Hakobyan, A. A.; Adibekyan, V. Zh.; Kunth, D.; Mamon, G. A.; Turatto, M.; Aramyan, L. S.
2014-07-01
We investigate the influence of close neighbor galaxies on the properties of supernovae (SNe) and their host galaxies using 56 SNe located in pairs of galaxies with different levels of star formation (SF) and nuclear activity. The mean distance of type II SNe from nuclei of hosts is greater by about a factor of 2 than that of type Ibc SNe. The distributions and mean distances of SNe are consistent with previous results compiled with the larger sample. For the first time it is shown that SNe Ibc are located in pairs with significantly smaller difference of radial velocities between components than pairs containing SNe Ia and II. We consider this as a result of higher star formation rate (SFR) of these closer systems of galaxies.
Data synthesis and display programs for wave distribution function analysis
NASA Technical Reports Server (NTRS)
Storey, L. R. O.; Yeh, K. J.
1992-01-01
At the National Space Science Data Center (NSSDC) software was written to synthesize and display artificial data for use in developing the methodology of wave distribution analysis. The software comprises two separate interactive programs, one for data synthesis and the other for data display.
Distributed Learning Environment: Major Functions, Implementation, and Continuous Improvement.
ERIC Educational Resources Information Center
Converso, Judith A.; Schaffer, Scott P.; Guerra, Ingrid J.
The content of this paper is based on a development plan currently in design for the U.S. Navy in conjunction with the Learning Systems Institute at Florida State University. Leading research (literature review) references and case study ("best practice") references are presented as supporting evidence for the results-oriented distributed learning…
On, Jason S.W.; Duan, Cumming; Chow, Billy K.C.; Lee, Leo T.O.
2015-01-01
Several hypotheses have been proposed regarding the origin and evolution of the secretin family of peptides and receptors. However, identification of homologous ligand–receptor pairs in invertebrates and vertebrates is difficult because of the low levels of sequence identity between orthologs of distant species. In this study, five receptors structurally related to the vertebrate class B1 G protein-coupled receptor (GPCR) family were characterized from amphioxus (Branchiostoma floridae). Phylogenetic analysis showed that they clustered with vertebrate parathyroid hormone receptors (PTHR) and pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon receptors. These PTHR-like receptors shared synteny with several PTH and PACAP/glucagon receptors identified in spotted gar, Xenopus, and human, indicating that amphioxus preserves the ancestral chordate genomic organization of these receptor subfamilies. According to recent data by Mirabeau and Joly, amphioxus also expresses putative peptide ligands including homologs of PTH (bfPTH1 and 2) and PACAP/GLUC-like peptides (bfPACAP/GLUCs) that may interact with these receptors. Functional analyses showed that bfPTH1 and bfPTH2 activated one of the amphioxus receptors (bf98C) whereas bfPACAP/GLUCs strongly interacted with bf95. In summary, our data confirm the presence of PTH and PACAP/GLUC ligand–receptor pairs in amphioxus, demonstrating that functional homologs of vertebrate PTH and PACAP/glucagon GPCR subfamilies arose before the cephalochordate divergence from the ancestor of tunicates and vertebrates. PMID:25841489
On, Jason S W; Duan, Cumming; Chow, Billy K C; Lee, Leo T O
2015-08-01
Several hypotheses have been proposed regarding the origin and evolution of the secretin family of peptides and receptors. However, identification of homologous ligand-receptor pairs in invertebrates and vertebrates is difficult because of the low levels of sequence identity between orthologs of distant species. In this study, five receptors structurally related to the vertebrate class B1 G protein-coupled receptor (GPCR) family were characterized from amphioxus (Branchiostoma floridae). Phylogenetic analysis showed that they clustered with vertebrate parathyroid hormone receptors (PTHR) and pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon receptors. These PTHR-like receptors shared synteny with several PTH and PACAP/glucagon receptors identified in spotted gar, Xenopus, and human, indicating that amphioxus preserves the ancestral chordate genomic organization of these receptor subfamilies. According to recent data by Mirabeau and Joly, amphioxus also expresses putative peptide ligands including homologs of PTH (bfPTH1 and 2) and PACAP/GLUC-like peptides (bfPACAP/GLUCs) that may interact with these receptors. Functional analyses showed that bfPTH1 and bfPTH2 activated one of the amphioxus receptors (bf98C) whereas bfPACAP/GLUCs strongly interacted with bf95. In summary, our data confirm the presence of PTH and PACAP/GLUC ligand-receptor pairs in amphioxus, demonstrating that functional homologs of vertebrate PTH and PACAP/glucagon GPCR subfamilies arose before the cephalochordate divergence from the ancestor of tunicates and vertebrates. PMID:25841489
Lux, Renate; Riep, Birgit; Kikhney, Judith; Friedmann, Anton; Wolinsky, Lawrence E.; Göbel, Ulf B.; Daims, Holger; Moter, Annette
2012-01-01
The polymicrobial nature of periodontal diseases is reflected by the diversity of phylotypes detected in subgingival plaque and the finding that consortia of suspected pathogens rather than single species are associated with disease development. A number of these microorganisms have been demonstrated in vitro to interact and enhance biofilm integration, survival or even pathogenic features. To examine the in vivo relevance of these proposed interactions, we extended the spatial arrangement analysis tool of the software daime (digital image analysis in microbial ecology). This modification enabled the quantitative analysis of microbial co-localization in images of subgingival biofilm species, where the biomass was confined to fractions of the whole-image area, a situation common for medical samples. Selected representatives of the disease-associated red and orange complexes that were previously suggested to interact with each other in vitro (Tannerella forsythia with Fusobacterium nucleatum and Porphyromonas gingivalis with Prevotella intermedia) were chosen for analysis and labeled with specific fluorescent probes via fluorescence in situ hybridization. Pair cross-correlation analysis of in vivo grown biofilms revealed tight clustering of F. nucleatum/periodonticum and T. forsythia at short distances (up to 6 µm) with a pronounced peak at 1.5 µm. While these results confirmed previous in vitro observations for F. nucleatum and T. forsythia, random spatial distribution was detected between P. gingivalis and P. intermedia in the in vivo samples. In conclusion, we successfully employed spatial arrangement analysis on the single cell level in clinically relevant medical samples and demonstrated the utility of this approach for the in vivo validation of in vitro observations by analyzing statistically relevant numbers of different patients. More importantly, the culture-independent nature of this approach enables similar quantitative analyses for
The distribution of the short-return function
NASA Astrophysics Data System (ADS)
Abadi, Miguel; Lambert, Rodrigo
2013-05-01
We consider the first return of a sequence x_{0}^{n-1} to itself T_n(x_{0}^{n-1}) . It is known that Tn/n converges to 1 almost surely for ergodic processes with positive entropy. Large deviations are also known. We study the fluctuations of Tn. For product measures over a countable alphabet we prove the convergence in distribution of Tn, properly re-scaled, to a non-degenerated, non-parametric, distribution. We also show that the re-scaled factors behave as follows: expectation of Tn is about n minus a positive constant and the variance is about a constant. As an application, we compute bounds and limiting values of the proportion of self-avoiding sequences. We illustrate with some examples.
NASA Technical Reports Server (NTRS)
Grzanka, E.; Stelmakh, S.; Gierlotka, S.; Zhao, Y.; Palosz, B.; Palosz, W.
2003-01-01
Key properties of nanocrystals are determined by their real atomic structure, therefore a reasonable understanding and meaningful interpretation of their properties requires a realistic model of the structure. In this paper we present an evidence of a complex response of the lattice distances to external pressure indicating a presence of a complex structure of Sic nanopowders. The experiments were performed on nanocrystalline Sic subjected to hydrostatic or isostatic pressure using synchrotron and neutron powder diffraction. Elastic properties of the samples were examined based on X-ray diffraction data using a Diamond Anvil Cell (DAC) in HASYLAB at DESY. The dependence'of the lattice parameters and of the Bragg reflections width with pressure exhibits a ha1 nature of the properties (compressibilities) of the powders and indicates a complex structure of the grains. We interpreted tws behaviour as originating from different elastic properties of the grain interior and surface. Analysis of the dependence of individual interatomic distances on pressure was based on in-situ neutron diffraction measurements done with HbD diffractometer at LANSCE in Los Alamos National Laboratory with the Paris-Edinburgh cell under pressures up to 8 GPa (Qmax = 26/A). Interatomic distances were obtained by PDF analysis using the PDFgetN program. We have found that the interatomic distances undergo a complex, non-monotonic changes. Even under substantial pressures a considerable relaxation of the lattice may take place: some interatomic distances increase with an increase in pressure. We relate this phenomenon to: (1), changes of the microstructure of the densified material, in particular breaking of its fractal chain structure and, (2), its complex structure resembling that of a material composed of two phases, each with its distinct elastic properties.
NASA Astrophysics Data System (ADS)
Billinge, Simon J. L.
2008-07-01
Emerging materials of scientific and technological interest are generally complex and often nanostructured: they have atomic orderings that extend on nanometer length-scales. These can be discrete nanoparticles; bulk crystals with nanoscale chemical or displacive order within them; mesoporous materials that are bulk materials containing nanoscale holes; and nanocomposites that are intimate heterogeneous mixtures of nano-sized constituents. As always, a quantitative knowledge of the atomic structure within these materials is a prerequisite to understanding and engineering their properties. Traditional crystallographic methods for obtaining this information break down at the nanoscale, sometimes referred to as “the nanostructure problem”. We describe here some emerging methods for studying nanoscale structure. We present some examples of recent successes. Finally, we discuss future directions and opportunities and draw attention to limitations and potential problems.
2015-01-01
An efficient new molecular orbital (MO) basis algorithm is reported implementing the pair atomic resolution of the identity approximation (PARI) to evaluate the exact exchange contribution (K) to self-consistent field methods, such as hybrid and range-separated hybrid density functionals. The PARI approximation, in which atomic orbital (AO) basis function pairs are expanded using auxiliary basis functions centered only on their two respective atoms, was recently investigated by Merlot et al. [J. Comput. Chem.2013, 34, 1486]. Our algorithm is significantly faster than quartic scaling RI-K, with an asymptotic exchange speedup for hybrid functionals of (1 + X/N), where N and X are the AO and auxiliary basis dimensions. The asymptotic speedup is 2 + 2X/N for range separated hybrids such as CAM-B3LYP, ωB97X-D, and ωB97X-V which include short- and long-range exact exchange. The observed speedup for exchange in ωB97X-V for a C68 graphene fragment in the cc-pVTZ basis is 3.4 relative to RI-K. Like conventional RI-K, our method greatly outperforms conventional integral evaluation in large basis sets; a speedup of 19 is obtained in the cc-pVQZ basis on a C54 graphene fragment. Negligible loss of accuracy relative to exact integral evaluation is demonstrated on databases of bonded and nonbonded interactions. We also demonstrate both analytically and numerically that the PARI-K approximation is variationally stable. PMID:25691831
Theodorakis, Panagiotis E; Dellago, Christoph; Kahl, Gerhard
2013-01-14
We discuss a coarse-grained model recently proposed by Starr and Sciortino [J. Phys.: Condens. Matter 18, L347 (2006)] for spherical particles functionalized with short single DNA strands. The model incorporates two key aspects of DNA hybridization, i.e., the specificity of binding between DNA bases and the strong directionality of hydrogen bonds. Here, we calculate the effective potential between two DNA-functionalized particles of equal size using a parallel replica protocol. We find that the transition from bonded to unbonded configurations takes place at considerably lower temperatures compared to those that were originally predicted using standard simulations in the canonical ensemble. We put particular focus on DNA-decorations of tetrahedral and octahedral symmetry, as they are promising candidates for the self-assembly into a single-component diamond structure. Increasing colloid size hinders hybridization of the DNA strands, in agreement with experimental findings. PMID:23320725
Fluctuations of the one-body distribution function
Bonasera, A.; Gulminelli, F.; Schuck, P. Laboratorio Nazionale del Sud, via A. Doria, 95125 Catania Dipartimento di Fisica and Istituto Nazionale di Fisica Nucleare, via Celoria 16, 20133 Milano Institute des Sciences Nucleaires, F-38026 Grenoble CEDEX )
1992-10-01
A general method to evaluate fluctuations of the semiclassical one-body Wigner function is presented both in the equilibrium and nonequilibrium framework. The model is valid far away from critical points, where the Boltzmann-Nordheim-Vlasov equation represents a good approximation of the average Wigner function. A first application of the model in momentum space is shown in comparison with different analytical results. An extension to realistic phase space calculations of heavy ion collisions is straightforward and numerically feasible. In this case, together with fluctations coming from the scattering processes, mean field fluctuations are automatically included. The role of Landau damping is discussed.
A model distribution function for relativistic bi-Maxwellian with drift
Naito, O.
2013-04-15
A model distribution function for relativistic bi-Maxwellian with drift is proposed, based on the maximum entropy principle and the relativistic canonical transformation. Since the obtained expression is compatible with the existing distribution functions and has a relatively simple form as well as smoothness, it might serve as a useful tool in the research fields of space or high temperature fusion plasmas.
NASA Astrophysics Data System (ADS)
Devianto, Dodi
2016-02-01
It is constructed convolution of generated random variable from independent and identically exponential distribution with stabilizer constant. The characteristic function of this distribution is obtained by using Laplace-Stieltjes transform. The uniform continuity property of characteristic function from this convolution is obtained by using analytical methods as basic properties.
THE INITIAL MASS FUNCTION MODELED BY A LEFT TRUNCATED BETA DISTRIBUTION
Zaninetti, Lorenzo
2013-03-10
The initial mass function for stars is usually fitted by three straight lines, which means it has seven parameters. The presence of brown dwarfs (BDs) increases the number of straight lines to four and the number of parameters to nine. Another common fitting function is the lognormal distribution, which is characterized by two parameters. This paper is devoted to demonstrating the advantage of introducing a left truncated beta probability density function, which is characterized by four parameters. The constant of normalization, the mean, the mode, and the distribution function are calculated for the left truncated beta distribution. The normal beta distribution that results from convolving independent normally distributed and beta distributed components is also derived. The chi-square test and the Kolmogorov-Smirnov test are performed on a first sample of stars and BDs that belongs to the massive young cluster NGC 6611, and on a second sample that represents the masses of the stars of the cluster NGC 2362.
NASA Technical Reports Server (NTRS)
Mcclelland, J.; Silk, J.
1979-01-01
The evolution of the two-point correlation function for the large-scale distribution of galaxies in an expanding universe is studied on the assumption that the perturbation densities lie in a Gaussian distribution centered on any given mass scale. The perturbations are evolved according to the Friedmann equation, and the correlation function for the resulting distribution of perturbations at the present epoch is calculated. It is found that: (1) the computed correlation function gives a satisfactory fit to the observed function in cosmological models with a density parameter (Omega) of approximately unity, provided that a certain free parameter is suitably adjusted; (2) the power-law slope in the nonlinear regime reflects the initial fluctuation spectrum, provided that the density profile of individual perturbations declines more rapidly than the -2.4 power of distance; and (3) both positive and negative contributions to the correlation function are predicted for cosmological models with Omega less than unity.
NASA Astrophysics Data System (ADS)
Francisco, E.; Pendás, A. Martín; Blanco, M. A.
2008-04-01
Given an N-electron molecule and an exhaustive partition of the real space ( R) into m arbitrary regions Ω,Ω,…,Ω ( ⋃i=1mΩ=R), the edf program computes all the probabilities P(n,n,…,n) of having exactly n electrons in Ω, n electrons in Ω,…, and n electrons ( n+n+⋯+n=N) in Ω. Each Ω may correspond to a single basin (atomic domain) or several such basins (functional group). In the later case, each atomic domain must belong to a single Ω. The program can manage both single- and multi-determinant wave functions which are read in from an aimpac-like wave function description ( .wfn) file (T.A. Keith et al., The AIMPAC95 programs, http://www.chemistry.mcmaster.ca/aimpac, 1995). For multi-determinantal wave functions a generalization of the original .wfn file has been introduced. The new format is completely backwards compatible, adding to the previous structure a description of the configuration interaction (CI) coefficients and the determinants of correlated wave functions. Besides the .wfn file, edf only needs the overlap integrals over all the atomic domains between the molecular orbitals (MO). After the P(n,n,…,n) probabilities are computed, edf obtains from them several magnitudes relevant to chemical bonding theory, such as average electronic populations and localization/delocalization indices. Regarding spin, edf may be used in two ways: with or without a splitting of the P(n,n,…,n) probabilities into α and β spin components. Program summaryProgram title: edf Catalogue identifier: AEAJ_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEAJ_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 5387 No. of bytes in distributed program, including test data, etc.: 52 381 Distribution format: tar.gz Programming language: Fortran 77 Computer
Characterizing short-term stability for Boolean networks over any distribution of transfer functions
NASA Astrophysics Data System (ADS)
Seshadhri, C.; Smith, Andrew M.; Vorobeychik, Yevgeniy; Mayo, Jackson R.; Armstrong, Robert C.
2016-07-01
We present a characterization of short-term stability of Kauffman's N K (random) Boolean networks under arbitrary distributions of transfer functions. Given such a Boolean network where each transfer function is drawn from the same distribution, we present a formula that determines whether short-term chaos (damage spreading) will happen. Our main technical tool which enables the formal proof of this formula is the Fourier analysis of Boolean functions, which describes such functions as multilinear polynomials over the inputs. Numerical simulations on mixtures of threshold functions and nested canalyzing functions demonstrate the formula's correctness.
Seshadhri, C; Smith, Andrew M; Vorobeychik, Yevgeniy; Mayo, Jackson R; Armstrong, Robert C
2016-07-01
We present a characterization of short-term stability of Kauffman's NK (random) Boolean networks under arbitrary distributions of transfer functions. Given such a Boolean network where each transfer function is drawn from the same distribution, we present a formula that determines whether short-term chaos (damage spreading) will happen. Our main technical tool which enables the formal proof of this formula is the Fourier analysis of Boolean functions, which describes such functions as multilinear polynomials over the inputs. Numerical simulations on mixtures of threshold functions and nested canalyzing functions demonstrate the formula's correctness. PMID:27575142
Nilsson, Henrik; Karlgren, Silja; Blomqvist, Lennart; Jonas, Eduard
2015-01-01
Background Previous studies have shown that liver function is inhomogeneously distributed in diseased livers, and this uneven distribution cannot be compensated for if a global liver function test is used for the prediction of post-operative remnant liver function. Dynamic Gd-EOB-DTPA-enhanced magnetic resonance imaging (MRI) can assess segmental liver function, thus offering the possibility to overcome this problem. Methods In 10 patients with liver cirrhosis and 10 normal volunteers, the contribution of individual liver segments to total liver function and volume was calculated using dynamic Gd-EOB-DTPA-enhanced MRI. Remnant liver function predictions using a segmental method and global assessment were compared for a simulated left hemihepatectomy. For the prediction based on segmental functional MRI assessment, the estimated function of the remnant liver segments was added. Results Global liver function assessment overestimated the remnant liver function in 9 out of 10 patients by as much as 9.3% [median −3.5% (−9.3–3.5%)]. In the normal volunteers there was a slight underestimation of remnant function in 9 out of 10 cases [median 1.07% (−0.7–2.5%)]. Discussion The present study underlines the necessity of a segmental liver function test able to compensate for the non-homogeneous nature of liver function, if the prediction of post-operative remnant liver function is to be improved. PMID:25297934
Multi-level methods and approximating distribution functions
NASA Astrophysics Data System (ADS)
Wilson, D.; Baker, R. E.
2016-07-01
Biochemical reaction networks are often modelled using discrete-state, continuous-time Markov chains. System statistics of these Markov chains usually cannot be calculated analytically and therefore estimates must be generated via simulation techniques. There is a well documented class of simulation techniques known as exact stochastic simulation algorithms, an example of which is Gillespie's direct method. These algorithms often come with high computational costs, therefore approximate stochastic simulation algorithms such as the tau-leap method are used. However, in order to minimise the bias in the estimates generated using them, a relatively small value of tau is needed, rendering the computational costs comparable to Gillespie's direct method. The multi-level Monte Carlo method (Anderson and Higham, Multiscale Model. Simul. 10:146-179, 2012) provides a reduction in computational costs whilst minimising or even eliminating the bias in the estimates of system statistics. This is achieved by first crudely approximating required statistics with many sample paths of low accuracy. Then correction terms are added until a required level of accuracy is reached. Recent literature has primarily focussed on implementing the multi-level method efficiently to estimate a single system statistic. However, it is clearly also of interest to be able to approximate entire probability distributions of species counts. We present two novel methods that combine known techniques for distribution reconstruction with the multi-level method. We demonstrate the potential of our methods using a number of examples.
SIR model with general distribution function in the infectious period
NASA Astrophysics Data System (ADS)
Gomes, Marcelo F. C.; Gonçalves, Sebastián
2009-08-01
The Susceptible-Infected-Removed or SIR model, as it was formulated by Kermack and McKendrick, is the key model for epidemic dynamics. Most applications of such a basic scheme use a constant rate for the removal term. However, that assumption corresponds to the rather unrealistic exponential distribution of infectious times. On the other hand, recent approaches, like numerical simulations, frequently assume a fixed and uniform duration for the infectious state-which is unrealistic too. The extreme assumptions in those different schemes are a hurdle that can frustrate any intention of drawing comparison between results from them. In the present contribution we study the delay equations for the SIR model, comparing the solutions for many typical cases with the simulation counterpart and with the standard SIR model. Using delay equations, where each infected individual is removed at a specific time after being infected, the dynamics for the infected and susceptible agree almost exactly with the numerical implementation. Even in the general case of distributed infective periods, the agreement is excellent.
Stone, John E.; Kohlmeyer, Axel
2011-01-01
The calculation of radial distribution functions (RDFs) from molecular dynamics trajectory data is a common and computationally expensive analysis task. The rate limiting step in the calculation of the RDF is building a histogram of the distance between atom pairs in each trajectory frame. Here we present an implementation of this histogramming scheme for multiple graphics processing units (GPUs). The algorithm features a tiling scheme to maximize the reuse of data at the fastest levels of the GPU’s memory hierarchy and dynamic load balancing to allow high performance on heterogeneous configurations of GPUs. Several versions of the RDF algorithm are presented, utilizing the specific hardware features found on different generations of GPUs. We take advantage of larger shared memory and atomic memory operations available on state-of-the-art GPUs to accelerate the code significantly. The use of atomic memory operations allows the fast, limited-capacity on-chip memory to be used much more efficiently, resulting in a fivefold increase in performance compared to the version of the algorithm without atomic operations. The ultimate version of the algorithm running in parallel on four NVIDIA GeForce GTX 480 (Fermi) GPUs was found to be 92 times faster than a multithreaded implementation running on an Intel Xeon 5550 CPU. On this multi-GPU hardware, the RDF between two selections of 1,000,000 atoms each can be calculated in 26.9 seconds per frame. The multi-GPU RDF algorithms described here are implemented in VMD, a widely used and freely available software package for molecular dynamics visualization and analysis. PMID:21547007
Levine, Benjamin G; Stone, John E; Kohlmeyer, Axel
2011-05-01
The calculation of radial distribution functions (RDFs) from molecular dynamics trajectory data is a common and computationally expensive analysis task. The rate limiting step in the calculation of the RDF is building a histogram of the distance between atom pairs in each trajectory frame. Here we present an implementation of this histogramming scheme for multiple graphics processing units (GPUs). The algorithm features a tiling scheme to maximize the reuse of data at the fastest levels of the GPU's memory hierarchy and dynamic load balancing to allow high performance on heterogeneous configurations of GPUs. Several versions of the RDF algorithm are presented, utilizing the specific hardware features found on different generations of GPUs. We take advantage of larger shared memory and atomic memory operations available on state-of-the-art GPUs to accelerate the code significantly. The use of atomic memory operations allows the fast, limited-capacity on-chip memory to be used much more efficiently, resulting in a fivefold increase in performance compared to the version of the algorithm without atomic operations. The ultimate version of the algorithm running in parallel on four NVIDIA GeForce GTX 480 (Fermi) GPUs was found to be 92 times faster than a multithreaded implementation running on an Intel Xeon 5550 CPU. On this multi-GPU hardware, the RDF between two selections of 1,000,000 atoms each can be calculated in 26.9 seconds per frame. The multi-GPU RDF algorithms described here are implemented in VMD, a widely used and freely available software package for molecular dynamics visualization and analysis. PMID:21547007
Levine, Benjamin G.; Stone, John E.; Kohlmeyer, Axel
2011-05-01
The calculation of radial distribution functions (RDFs) from molecular dynamics trajectory data is a common and computationally expensive analysis task. The rate limiting step in the calculation of the RDF is building a histogram of the distance between atom pairs in each trajectory frame. Here we present an implementation of this histogramming scheme for multiple graphics processing units (GPUs). The algorithm features a tiling scheme to maximize the reuse of data at the fastest levels of the GPU's memory hierarchy and dynamic load balancing to allow high performance on heterogeneous configurations of GPUs. Several versions of the RDF algorithm are presented, utilizing the specific hardware features found on different generations of GPUs. We take advantage of larger shared memory and atomic memory operations available on state-of-the-art GPUs to accelerate the code significantly. The use of atomic memory operations allows the fast, limited-capacity on-chip memory to be used much more efficiently, resulting in a fivefold increase in performance compared to the version of the algorithm without atomic operations. The ultimate version of the algorithm running in parallel on four NVIDIA GeForce GTX 480 (Fermi) GPUs was found to be 92 times faster than a multithreaded implementation running on an Intel Xeon 5550 CPU. On this multi-GPU hardware, the RDF between two selections of 1,000,000 atoms each can be calculated in 26.9 s per frame. The multi-GPU RDF algorithms described here are implemented in VMD, a widely used and freely available software package for molecular dynamics visualization and analysis.
NASA Astrophysics Data System (ADS)
Heidrich-Meisner, Fabian; Bolech, Carlos; Langer, Stephan; McCulloch, Ian; Orso, Giuliano; Rigol, Marcos
2013-03-01
We study the sudden expansion of a spin-imbalanced Fermi gas in an optical lattice after quenching the trapping potential to zero, described by the attractive Hubbard model. Using time-dependent density matrix renormalization group simulations we demonstrate that the momentum distribution functions (MDFs) of majority and minority fermions become stationary after surprisingly short expansion times. We explain this via a quantum distillation mechanism that results in a spatial separation of excess fermions and pairs, causing Fulde-Ferrell-Larkin-Ovchinnikov correlations to disappear rapidly. We further argue that the asymptotic form of the MDFs is determined by the integrals of motion of this integrable quantum system, namely the rapidities from the Bethe ansatz solution. We discuss the relevance of our results for the observation of Fulde-Ferrell-Larkin-Ovchinnikov correlations in 1D systems, related to recent experiments from Rice University.
Distributing functionality in the Drift Scan Camera System
Nicinski, T.; Constanta-Fanourakis, P.; MacKinnon, B.; Petravick, D.; Pluquet, C.; Rechenmacher, R.; Sergey, G.
1993-11-01
The Drift Scan Camera (DSC) System acquires image data from a CCD camera. The DSC is divided physically into two subsystems which are tightly coupled to each other. Functionality is split between these two subsystems: the front-end performs data acquisition while the host subsystem performs near real-time data analysis and control. Yet, through the use of backplane-based Remote Procedure Calls, the feel of one coherent system is preserved. Observers can control data acquisition, archiving to tape, and other functions from the host, but, the front-end can accept these same commands and operate independently. The DSC meets the needs for such robustness and cost-effective computing.
Transverse momentum-dependent parton distribution functions from lattice QCD
Michael Engelhardt, Philipp Haegler, Bernhard Musch, John Negele, Andreas Schaefer
2012-12-01
Transverse momentum-dependent parton distributions (TMDs) relevant for semi-inclusive deep inelastic scattering (SIDIS) and the Drell-Yan process can be defined in terms of matrix elements of a quark bilocal operator containing a staple-shaped Wilson connection. Starting from such a definition, a scheme to determine TMDs in lattice QCD is developed and explored. Parametrizing the aforementioned matrix elements in terms of invariant amplitudes permits a simple transformation of the problem to a Lorentz frame suited for the lattice calculation. Results for the Sivers and Boer-Mulders transverse momentum shifts are obtained using ensembles at the pion masses 369MeV and 518MeV, focusing in particular on the dependence of these shifts on the staple extent and a Collins-Soper-type evolution parameter quantifying proximity of the staples to the light cone.
Distributed Language: Biomechanics, Functions, and the Origins of Talk
NASA Astrophysics Data System (ADS)
Cowley, Stephen J.
Emphasizing that word-forms are culturally selected, the paper takes a distributed view of language. This is used to frame evidence that, in ontogenesis, language emerges under dual control by adult and child. Since parties gear to each other's biomechanics, norm-based behaviour prompts affective processes that drive prepared learning. This, it is argued, explains early stages in learning to talk. Next, this approach to external symbol grounding (ESG) is contrasted with ones where a similar problem is treated as internal to the agent. Then, turning to synthetic models, I indicate how the ESG can be used to model either populations of agents or dyads who, using complex signals, transform each other's agency.
NASA Astrophysics Data System (ADS)
Guo, Jia; Wang, Changchun; Mao, Weiyong; Yang, Wuli; Liu, Changjia; Chen, Jiyao
2008-08-01
In this paper, we present a facile and robust approach to synthesize multifunctional organic/inorganic composite microspheres with chitosan-poly(methacrylic acid) (CS-PMAA) shells and cadmium tellurium/iron oxide nanoparticle cores. Due to the strong electrostatic interaction between the negatively charged nanoparticles and the protonated CS polymers, the CS/nanoparticle complexes were utilized as templates for the subsequent polymerization of methacrylic acid. The resulting composite microspheres with luminescence and magnetic properties have regular morphologies and narrow size distributions. In contrast to previous reports, this route was based on a one-pot strategy without the aid of surfactants, organic solvent, or polymerizable ligands in aqueous solution. The encapsulated CdTe semiconductor nanocrystals inside the microspheres exhibited strong and stable photoluminescence properties in the pH range 5.0-11.0. When the pH was adjusted below 4, the photoluminescence decreased sharply and even quenched completely. However, the weakened fluorescence emission could be recovered to some degree upon an increase of pH above 5. Additionally, when both Fe3O4 and CdTe nanoparticles were encapsulated within CS-PMAA microspheres, the magnetic content of the microspheres could be efficiently controlled by tuning the feeding molar ratio of MAA monomers and glucosamine units of CS. From the preliminary attempts, it was found that the multifunctional microspheres as imaging agents could improve the rate and extent of cellular uptake under short-term exposure to an applied magnetic field, and so exhibit a great potential as bioactive molecule carriers.
The Drosophila mojavensis Bari3 transposon: distribution and functional characterization
2014-01-01
Background Bari-like transposons belong to the Tc1-mariner superfamily, and they have been identified in several genomes of the Drosophila genus. This transposon’s family has been used as paradigm to investigate the complex dynamics underlying the persistence and structural evolution of transposable elements (TEs) within a genome. Three structural Bari variants have been identified so far and can be distinguished based on the organization of their terminal inverted repeats. Bari3 is the last discovered member of this family identified in Drosophila mojavensis, a recently emerged species of the Repleta group of the genus Drosophila. Results We studied the insertion pattern of Bari3 in different D. mojavensis populations and found evidence of recent transposition activity. Analysis of the transposase domains unveiled the presence of a functional nuclear localization signal, as well as a functional binding domain. Using luciferase-based assays, we investigated the promoter activity of Bari3 as well as the interaction of its transposase with its left terminus. The results suggest that Bari3 is transposition-competent. Finally we demonstrated transposase transcript processing when the transposase gene is overexpressed in vivo and in vitro. Conclusions Bari3 displays very similar structural and functional features with its close relative, Bari1. Our results strongly suggest that Bari3 is an independent element that has generated genomic diversity in D. mojavensis. It can autonomously transcribe its transposase gene, which in turn can localize in the nucleus and bind the terminal inverted repeats of the transposon. Nevertheless, the identification of an unpredicted spliced form of the Bari3 transposase transcript allows us to hypothesize a control mechanism of its mobility based on mRNA processing. These results will aid the studies on the Bari family of transposons, which is intriguing for its widespread diffusion in Drosophilids coupled with a structural diversity
He, Susu; Hickman, Alison B; Dyda, Fred; Johnson, Neil P; Chandler, Michael; Ton-Hoang, Bao
2011-10-01
Single-stranded (ss) transposition, a recently identified mechanism adopted by members of the widespread IS200/IS605 family of insertion sequences (IS), is catalysed by the transposase, TnpA. The transposase of IS608, recognizes subterminal imperfect palindromes (IP) at both IS ends and cleaves at sites located at some distance. The cleavage sites, C, are not recognized directly by the protein but by short sequences 5' to the foot of each IP, guide (G) sequences, using a network of canonical ('Watson-Crick') base interactions. In addition a set of non-canonical base interactions similar to those found in RNA structures are also involved. We have reconstituted a biologically relevant complex, the transpososome, including both left and right ends and TnpA, which catalyses excision of a ss DNA circle intermediate. We provide a detailed picture of the way in which the IS608 transpososome is assembled and demonstrate that both C and G sequences are essential for forming a robust transpososome detectable by EMSA. We also address several questions central to the organization and function of the ss transpososome and demonstrate the essential role of non-canonical base interactions in the IS608 ends for its stability by using point mutations which destroy individual non-canonical base interactions. PMID:21745812
Salk, S.H.S.; Lee, S.S.
1999-11-01
Based on the U(1) and SU(2) slave-boson approaches to the t-J Hamiltonian, the authors evaluate the one electron spectral functions for the hole doped high {Tc} cuprates for comparison with the angle resolved photoemission spectroscopy (ARPES) data. They find that the observed quasiparticle peak in the superconducting state is correlated with the hump which exists in the normal state. They find that the spectral weight of the quasiparticle peak increases as doping rate increases, which is consistent with observation. As a consequence of the phase fluctuation effects of the spinon and holon pairing order parameters the spectral weight of the predicted peak obtained from the SU(2) theory is found to be smaller than the one predicted from U(1) mean field theory.
Sargisson, Rebecca J; White, K Geoffrey
2003-01-01
Forgetting functions with 18 delay intervals were generated for delayed matching-to-sample performance in pigeons. Delay interval variation was achieved by arranging five different sets of five delays across daily sessions. In different conditions, the delays were distributed in arithmetic or logarithmic series. There was no convincing evidence for different effects on discriminability of the distributions of different delays. The mean data were better fitted by some mathematical functions than by others, but the best-fitting functions depended on the distribution of delays. In further conditions with a fixed set of five delays, discriminability was higher with a logarithmic distribution of delays than with an arithmetic distribution. This result is consistent with the treatment of the forgetting function in terms of generalization decrement. PMID:14964709
Extrahypophysial distribution of corticotropin as a function of brain size.
Moldow, R; Yalow, R S
1978-01-01
Determination by radioimmunoassay of corticotropin in the brains of rats, rabbits, dogs, monkeys, and human beings reveals that the dimensions within which the hormone is found is about the same for each of these species but that the anatomical regions in which the hormone is found depends on brain size. Corticotropin is widely distributed in the brain of rats but is found only in the hypothalamic region of the primate brain. The patterns of immunoreactivity observed after Sephadex gel filtration confirm that the molecular forms of corticotropin found in extrahypophysial regions are similar to those in the pituitary of each species. These findings suggest that the mammalian pituitary is the sole site of synthesis of the hormone. The observation of persistence of corticotropin in the brains of commerically hypophysectomized rats has been interpreted by others as suggesting diencephalic as well as pituitary origin for this peptide. However, our studies demonstrate that 8 weeks after hypophysectomy the rats we have received from commerical sources manifest stress-stimulated plasma corticotropin concentrations about 80% of that found in intact rats in spite of the fact that residual pituitary tissue was not found by visual inspection of the sella. Scrapings from the sella revealed a corticotropin content up to 5% that of the average rat pituitary. Images PMID:204943
Garbage collection for functional languages in a distributed system
Eckart, J.D.
1987-01-01
Garbage collection is a helpful facility provided by many applicative languages such as Prolog, SISAL, FP, and Lisp. While these, and other, languages provide easy recognition of actions that may be executed in parallel, the garbage-collection algorithms used for single-machine environments become significantly more inefficient in multi-machine environments. Thus, in order to make effective use of these languages, more-efficient algorithms for collecting inter-machine structures is needed. Reference marking is the algorithm developed to meet these needs. It takes advantage of the semantics of applicative languages allowing each parallel action to be responsible for collecting any discarded structures it was responsible for creating. Simulation results comparing the performance of reference marking with other distributed garbage-collection algorithms are given. A variety of problem types and sizes are examined to determine the effects of particular styles of computation on each of the garbage-collection algorithms. The results gathered demonstrate the usefulness of the reference-marking algorithm in both uni- and multi-machine systems.
Lone pairs: an electrostatic viewpoint.
Kumar, Anmol; Gadre, Shridhar R; Mohan, Neetha; Suresh, Cherumuttathu H
2014-01-16
A clear-cut definition of lone pairs has been offered in terms of characteristics of minima in molecular electrostatic potential (MESP). The largest eigenvalue and corresponding eigenvector of the Hessian at the minima are shown to distinguish lone pair regions from the other types of electron localization (such as π bonds). A comparative study of lone pairs as depicted by various other scalar fields such as the Laplacian of electron density and electron localization function is made. Further, an attempt has been made to generalize the definition of lone pairs to the case of cations. PMID:24372481
Computation of Multimodal Size-Velocity-Temperature Spray Distribution Functions
NASA Astrophysics Data System (ADS)
Archambault, Mark R.
2002-09-01
An alternative approach to modeling spray flows-one which does not involve simulation or stochastic integration is to directly compute the evolution of the probability density function (PDF) describing the drops. The purpose of this paper is to continue exploring an alternative method of solving the spray flow problem. The approach is to derive and solve a set of Eulerian moment transport equations for the quantities of interest in the spray, coupled with the appropriate gas-phase (Eulerian) equations. A second purpose is to continue to explore how a maximum-entropy criterion may be used to provide closure for such a moment-based model. The hope is to further develop an Eulerian-Eulerian model that will permit one to solve for detailed droplet statistics directly without the use of stochastic integration or post-averaging of simulations.
NASA Astrophysics Data System (ADS)
Ahmad, Farooq; Malik, Manzoor A.; Mir, Hameeda
2014-02-01
We evaluate a distribution function for the system of galaxies clustering gravitationally in an expanding universe on the basis of statistical mechanics. We extend our previous work to incorporate the effect of any ratio of gravitational potential to kinetic energies. We determine the cosmological many-body partition function inclusive of higher order terms and calculate all thermodynamic quantities and the distribution function from it. We find that our new results are consistent with the previous ones, particularly in the large bar{N} (average number of galaxies) limit. We also investigate the effect on clustering parameter b and find our new results in very good agreement with the previous ones in the small b limit. We find that for large b, the departure from the original distribution function is greater. We also observe that the effect of softening on the distribution function is consistent with our previous work.
Liu, Fuli; Hu, Zimin; Liu, Wenhui; Li, Jingjing; Wang, Wenjun; Liang, Zhourui; Wang, Feijiu; Sun, Xiutao
2016-01-01
Using transcriptome data to mine microsatellite and develop markers has growingly become prevalent. However, characterizing the possible function of microsatellite is relatively rare. In this study, we explored microsatellites in the transcriptome of the brown alga Sargassum thunbergii and characterized the frequencies, distribution, function and evolution, and developed primers to validate these microsatellites. Our results showed that Tri-nucleotide is the most abundant, followed by di- and mono-nucleotide. The length of microsatellite was significantly affected by the repeat motif size. The density of microsatellite in the CDS region is significantly lower than that in the UTR region. The annotation of the transcripts containing microsatellite showed that 573 transcripts have GO terms and can be categorized into 42 groups. Pathways enrichment showed that microsatellites were significantly overrepresented in the genes involved in pathways such as Ubiquitin mediated proteolysis, RNA degradation, Spliceosome, etc. Primers flanking 961 microsatellite loci were designed, and among the 30 pairs of primer selected randomly for availability test, 23 were proved to be efficient. These findings provided new insight into the function and evolution of microsatellite in transcriptome, and the identified microsatellite loci within the annotated gene will be useful for developing functional markers in S. thunbergii. PMID:26732855
Liu, Fuli; Hu, Zimin; Liu, Wenhui; Li, Jingjing; Wang, Wenjun; Liang, Zhourui; Wang, Feijiu; Sun, Xiutao
2016-01-01
Using transcriptome data to mine microsatellite and develop markers has growingly become prevalent. However, characterizing the possible function of microsatellite is relatively rare. In this study, we explored microsatellites in the transcriptome of the brown alga Sargassum thunbergii and characterized the frequencies, distribution, function and evolution, and developed primers to validate these microsatellites. Our results showed that Tri-nucleotide is the most abundant, followed by di- and mono-nucleotide. The length of microsatellite was significantly affected by the repeat motif size. The density of microsatellite in the CDS region is significantly lower than that in the UTR region. The annotation of the transcripts containing microsatellite showed that 573 transcripts have GO terms and can be categorized into 42 groups. Pathways enrichment showed that microsatellites were significantly overrepresented in the genes involved in pathways such as Ubiquitin mediated proteolysis, RNA degradation, Spliceosome, etc. Primers flanking 961 microsatellite loci were designed, and among the 30 pairs of primer selected randomly for availability test, 23 were proved to be efficient. These findings provided new insight into the function and evolution of microsatellite in transcriptome, and the identified microsatellite loci within the annotated gene will be useful for developing functional markers in S. thunbergii. PMID:26732855
Ono, M; Yuasa, T; Ra, C; Takai, T
1999-10-15
Paired Ig-like receptors (PIR) are polymorphic type I transmembrane proteins belonging to an Ig superfamily encoded by multiple isotypic genes. They are expressed on immune cells such as mast cells, macrophages, and B lymphocytes. Two subtypes of PIR have been classified according to the difference in the primary structure of the PIR transmembrane and cytoplasmic regions. These subtypes are designated as PIR-A and PIR-B. In this study, the transmembrane and cytoplasmic regions of the PIR-A subtype were shown to mediate activation signal events such as cytoplasmic calcium mobilization, protein tyrosine phosphorylations, and degranulation in rat mast cell line RBL-2H3. The association of the Fc receptor gamma and beta subunits with PIR-A was shown to be responsible for PIR-A function but not required for membrane expression of PIR-A on COS-7 cells. We further revealed the role of two charged amino acid residues in the transmembrane region, namely arginine and glutamic acid, in PIR-A function and its association with the above subunits. In contrast to the inhibitory nature of the PIR-B subtype, present findings reveal that PIR-A potentially acts as a stimulatory receptor in mast cells, suggesting a mechanism for regulation of mast cell functions by the PIR family. PMID:10514523
NASA Technical Reports Server (NTRS)
Deese, J. E.; Hassan, H. A.
1979-01-01
The role played by fission fragments and electron distribution functions in nuclear pumped lasers is considered and procedures for their calculations are outlined. The calculations are illustrated for a He-3/Xe mixture where fission is provided by the He-3(n,p)H-3 reaction. Because the dominant ion in the system depends on the Xe fraction, the distribution functions cannot be determined without the simultaneous consideration of a detailed kinetic model. As is the case for wall sources of fission fragments, the resulting plasmas are essentially thermal but the electron distribution functions are non-Maxwellian.
Landau damping in space plasmas with generalized (r,q) distribution function
Qureshi, M.N.S.; Shi, J.K.; Ma, S.Z.
2005-12-15
Space plasmas possessing non-Maxwellian particle distribution functions with an enhanced high-energy tail and shoulder in the profile of distribution function take an important role to the wave particle interaction. In the present paper Landau damping of electron plasma (Langmuir) waves and ion-acoustic waves in a hot, isotropic, unmagnetized plasma is studied with the generalized (r,q) distribution function. The results show that for the Langmuir oscillations Landau damping becomes severe as the spectral index r or q reduces. However, for the ion-acoustic waves Landau damping is more sensitive to the ion temperature than the spectral indices.
Spectral analysis of pair-correlation bandwidth: application to cell biology images
Binder, Benjamin J.; Simpson, Matthew J.
2015-01-01
Images from cell biology experiments often indicate the presence of cell clustering, which can provide insight into the mechanisms driving the collective cell behaviour. Pair-correlation functions provide quantitative information about the presence, or absence, of clustering in a spatial distribution of cells. This is because the pair-correlation function describes the ratio of the abundance of pairs of cells, separated by a particular distance, relative to a randomly distributed reference population. Pair-correlation functions are often presented as a kernel density estimate where the frequency of pairs of objects are grouped using a particular bandwidth (or bin width), Δ>0. The choice of bandwidth has a dramatic impact: choosing Δ too large produces a pair-correlation function that contains insufficient information, whereas choosing Δ too small produces a pair-correlation signal dominated by fluctuations. Presently, there is little guidance available regarding how to make an objective choice of Δ. We present a new technique to choose Δ by analysing the power spectrum of the discrete Fourier transform of the pair-correlation function. Using synthetic simulation data, we confirm that our approach allows us to objectively choose Δ such that the appropriately binned pair-correlation function captures known features in uniform and clustered synthetic images. We also apply our technique to images from two different cell biology assays. The first assay corresponds to an approximately uniform distribution of cells, while the second assay involves a time series of images of a cell population which forms aggregates over time. The appropriately binned pair-correlation function allows us to make quantitative inferences about the average aggregate size, as well as quantifying how the average aggregate size changes with time. PMID:26064605
NASA Astrophysics Data System (ADS)
Shirbisheh, Vahid
2012-06-01
As the first step towards developing noncommutative geometry over Hecke C ∗-algebras, we study property (RD) (Rapid Decay) for Hecke pairs. When the subgroup H in a Hecke pair ( G, H) is finite, we show that the Hecke pair ( G, H) has (RD) if and only if G has (RD). This provides us with a family of examples of Hecke pairs with property (RD). We also adapt Paul Jolissant's works in Jolissaint (J K-Theory 2:723-735, 1989; Trans Amer Math Soc 317(1):167-196, 1990) to the setting of Hecke C ∗-algebras and show that when a Hecke pair ( G, H) has property (RD), the algebra of rapidly decreasing functions on the set of double cosets is closed under holomorphic functional calculus of the associated (reduced) Hecke C ∗-algebra. Hence they have the same K 0-groups.
Gopal, A; Samant, S S
2008-01-01
The measurement of the modulation transfer function (MTF) of an imaging device is a common requirement in evaluating radiographic detector performance. Such measurements are considered mandatory in detector development research, and may also be carried out as part of routine quality assurance (QA) checks of image quality. Traditionally, MTF measurement has been performed by imaging either a narrow slit or a sharp edge in order to generate a line spread function, whose Fourier transform provides the MTF on a near-continuous frequency domain. Much less commonly employed is the method of square-wave line-pair modulations, in which the modulation response to bar resolution targets contained in a bar pattern is used to estimate the MTF at discrete spatial frequencies. While the slit and edge methods offer advantages of accuracy and a well-know standardized protocol for measurement based on several decades of development, their major limitation is the difficult and time-consuming experimental setup that is necessary to ensure accurate measurements. On the other hand, the bar pattern offers the advantage of a quick, simple, and easy measurement without the need for a complex experimental setup, with the main disadvantages of the technique being a pseudo-normalization that may lead to an overestimated MTF, and corrections for removing higher-order frequency harmonics that require interpolating between discrete spatial frequencies. Therefore, bar patterns are traditionally used for qualitative imaging applications like detector QA in terms of relative and arbitrarily defined spatial resolution metrics, while slit and edge methods are preferred for quantitative MTF measurements. Compared to diagnostic x rays, MTF measurements using megavoltage x rays are further complicated by low x-ray attenuation and excessive Compton scattering. In this work, a method to measure the MTF of megavoltage x-ray detectors based on imaging square-wave line pairs with improved near
Gopal, A.; Samant, S. S.
2008-01-15
The measurement of the modulation transfer function (MTF) of an imaging device is a common requirement in evaluating radiographic detector performance. Such measurements are considered mandatory in detector development research, and may also be carried out as part of routine quality assurance (QA) checks of image quality. Traditionally, MTF measurement has been performed by imaging either a narrow slit or a sharp edge in order to generate a line spread function, whose Fourier transform provides the MTF on a near-continuous frequency domain. Much less commonly employed is the method of square-wave line-pair modulations, in which the modulation response to bar resolution targets contained in a bar pattern is used to estimate the MTF at discrete spatial frequencies. While the slit and edge methods offer advantages of accuracy and a well-known standardized protocol for measurement based on several decades of development, their major limitation is the difficult and time-consuming experimental setup that is necessary to ensure accurate measurements. On the other hand, the bar pattern offers the advantage of a quick, simple, and easy measurement without the need for a complex experimental setup, with the main disadvantages of the technique being a pseudo-normalization that may lead to an overestimated MTF, and corrections for removing higher-order frequency harmonics that require interpolating between discrete spatial frequencies. Therefore, bar patterns are traditionally used for qualitative imaging applications like detector QA in terms of relative and arbitrarily defined spatial resolution metrics, while slit and edge methods are preferred for quantitative MTF measurements. Compared to diagnostic x rays, MTF measurements using megavoltage x rays are further complicated by low x-ray attenuation and excessive Compton scattering. In this work, a method to measure the MTF of megavoltage x-ray detectors based on imaging square-wave line pairs with improved near
Low-energy ion distribution functions on a magnetically quiet day at geostationary altitude /L = 7/
NASA Technical Reports Server (NTRS)
Singh, N.; Raitt, W. J.; Yasuhara, F.
1982-01-01
Ion energy and pitch angle distribution functions are examined for a magnetically quiet day using averaged data from ATS 6. For both field-aligned and perpendicular fluxes, the populations have a mixture of characteristic energies, and the distribution functions can be fairly well approximated by Maxwellian distributions over three different energy bands in the range 3-600 eV. Pitch angle distributions varying with local time, and energy distributions are used to compute total ion density. Pitch angle scattering mechanisms responsible for the observed transformation of pitch angle distribution are examined, and it is found that a magnetic noise of a certain power spectral density belonging to the electromagnetic ion cyclotron mode near the ion cyclotron frequency can be effective in trapping the field aligned fluxes by pitch angle scattering.
The U.S. Environmental Protection Agency's Environmental Monitoring and Assessment Program (EMAP) employs the cumulative distribution function (cdf) to measure the status of quantitative variables for resources of interest. The ability to compare cdf's for a resource from, say,...
Numerical solution of distributed order fractional differential equations by hybrid functions
NASA Astrophysics Data System (ADS)
Mashayekhi, S.; Razzaghi, M.
2016-06-01
In this paper, a new numerical method for solving the distributed fractional differential equations is presented. The method is based upon hybrid functions approximation. The properties of hybrid functions consisting of block-pulse functions and Bernoulli polynomials are presented. The Riemann-Liouville fractional integral operator for hybrid functions is introduced. This operator is then utilized to reduce the solution of the distributed fractional differential equations to a system of algebraic equations. Illustrative examples are included to demonstrate the validity and applicability of the technique.
Functional Stereology for 3D Particle Size Distributions from 2D Observations: a Practical Approach
NASA Astrophysics Data System (ADS)
Proussevitch, A. A.; Sahagian, D. L.; Jutzeler, M.
2010-12-01
Functional stereology applies known deconvolution techniques to obtain 3D size distributions from 2D cross-section data based on an assumption that both 2D and 3D statistics have known distribution functions with unknown parameters. A new stereological approach enables us to solve this problem by utilizing function minimization to find parameters of the distribution functions. There is no limit to continuous distribution function types that could be used, such as Gaussian, Logistic, Weibull, Gamma, and others. As compared to previously known 2D to 3D conversion methods (e.g. Sahagian and Proussevitch, 1998), functional stereology has much greater practical application to non-spherical particles/objects because it is free of uncontrollable error propagation for all particles shapes. The new practical method of functional stereology has been implemented in Stereonet software adapted for both a) direct logarithmic scales of particle/voids volumes, and b) Phi units of linear dimensions (-log2 of size). Applications of the method include distribution of voids/bubbles in all types of volcanic rocks, pore networks in sedimentary rocks, mineral and grain sizes, volcanic clasts, breccia, and texture features of a wide range of rock formations. Such applications demonstrate utility of this functional stereology approach.
Modeling free molecular plume flow and impingement by an ellipsoidal distribution function
NASA Astrophysics Data System (ADS)
Legge, Hubert
Modeling frozen plume flow is outlined using a freezing surface and an ellipsoidal distribution function beyond a freezing surface. Formulas are given for the number flux, pressure, shear stress, and heat-transfer on a surface element in free molecular flow with an ellipsoidal distribution function. To demonstrate the accuracy of the modeling, the method is applied to the totally frozen Knudsen effusion, for which the flow quantities are given. For the given example, the accuracy is better than 2.5 percent.
The probability distribution function for the sum of squares of independent random variables
NASA Astrophysics Data System (ADS)
Fateev, Yury; Dmitriev, Dmitry; Tyapkin, Valery; Kremez, Nikolai; Shaidurov, Vladimir
2016-08-01
In the present paper, the probability distribution function is derived for the sum of squares of random variables for nonzero expectations. This distribution function enables one to develop an efficient one-step algorithm for phase ambiguity resolution when determining the spatial orientation from signals of satellite radio-navigation systems. Threshold values for rejecting false solutions and statistical properties of the algorithm are obtained.
Energy distribution functions of kilovolt ions in a modified Penning discharge
NASA Technical Reports Server (NTRS)
Roth, J. R.
1972-01-01
The distribution function of ion energy parallel to the magnetic field of a Penning discharge was measured with a retarding potential energy analyzer. Simultaneous measurements of the ion energy distribution function perpendicular to the magnetic field were made with a charge-exchange neutral detector. The ion energy distribution functions are approximately Maxwellian, and their kinetic temperatures are equal within experimental error. This suggests that turbulent processes previously observed Maxwellianize the velocity distribution along a radius in velocity space, and result in an isotropic energy distribution. The kinetic temperatures are on the order of kilovolts, and the tails of the ion energy distribution functions are Maxwellian up to a factor of 7 e-folds in energy. When the distributions depart from Maxwellian, they are enhanced above the Maxwellian tail. Above densities of about 10 to the 10th power particles/cc, this enhancement appears to be the result of a second, higher temperature Maxwellian distribution. At these high particle energies, only the ions perpendicular to the magnetic field lines were investigated.
Efremov, A. V.; Teryaev, O. V.; Schweitzer, P.; Zavada, P.
2009-07-01
Transverse parton momentum dependent distribution functions (TMDs) of the nucleon are studied in a covariant model, which describes the intrinsic motion of partons in terms of a covariant momentum distribution. The consistency of the approach is demonstrated, and model relations among TMDs are studied. As a by-product it is shown how the approach allows to formulate the nonrelativistic limit.
What probability distribution functions tell us about the processes of star formation
NASA Astrophysics Data System (ADS)
Schneider, N.; Ossenkopf, V.; Klessen, R. S.; Csengeri, T.; Girichidis, P.; Federrath, C.; Tremblin, P.; Bontemps, S.; Peretto, N.; Simon, R.
2016-05-01
Probability distribution functions of column density (N-PDFs) are used to evaluate the relative importance of gravity, turbulence, magnetic fields, geometry, and radiative feedback governing the cloud's density structure and star-formation activity. These proce- sses influence the N-PDF and thus determine their shape, ranging from a purely lognormal distribution to one with power-law tail(s).
Shagayda, Andrey
2012-08-15
Analytical studies and numerical simulations show that the electron velocity distribution function in a Hall thruster discharge with crossed electric and magnetic fields is not Maxwellian. This is due to the fact that the mean free path between collisions is greater than both the Larmor radius and the characteristic dimensions of the discharge channel. However in numerical models of Hall thrusters, a hydrodynamic approach is often used to describe the electron dynamics, because discharge simulation in a fully kinetic approach requires large computing resources and is time consuming. A more accurate modeling of the electron flow in the hydrodynamic approximation requires taking into account the non-Maxwellian character of the distribution function and finding its moments, an approach that reflects the properties of electrons drifting in crossed electric and magnetic fields better than the commonly used Euler or Navier-Stokes approximations. In the present paper, an expression for the electron velocity distribution function in rarefied spatially homogeneous stationary plasma with crossed electric and magnetic fields and predominance of collisions with heavy particles is derived in the relaxation approximation. The main moments of the distribution function including longitudinal and transversal temperatures, the components of the viscous stress tensor, and of the heat flux vector are calculated. Distinctive features of the hydrodynamic description of electrons with a strongly non-equilibrium distribution function and the prospects for further development of the proposed approach for calculating the distribution function in spatially inhomogeneous plasma are discussed.
SEP distribution function and probability of the maximum magnitudes of events
NASA Astrophysics Data System (ADS)
Nymmik, Rikho
Based on the current knowledge the magnitude of specific anticipated SEP event is a random variable taken from large array of expected values. This set of expected values can be determined in terms of the distribution function. Form of the distribution function of SЕР events is usually determined from the data of continuous satellite measurement. Sometimes but without much effect indirect evidences, such as isotopes of samples of lunar rocks, data on the density of radioactive isotopes in the annual rings of ancient trees are used to determine the SEPE distribution function. The most successful was the attempt to describe the distribution function for 21-23 solar cycles by power-low function with exponential cutoff in the area of large events. Significant addition to the available information are relatively new data (McCracken et al., JGR 106(A10), 21585-21498, 2001) on the radioactive isotopes in the Greenland ice, which gives the additional information about the extreme SEP events since 1561. However, the lack of information about full set of events (mainly on small events) does not allow to use these data directly to determine the distribution function. However, using correlation between the number of sunspots and the corresponding mean number of SEP events, one can determine the distribution function since 1561 based on Greenland data. Surprisingly, the parameter values of this function coincide with those calculated from satellite data. Analysis of the obtained parameters of the distribution function shows that the maximum fluence of protons with energies above 30 MeV does not exceed 1011 cm-2 protons with about 10-11 midget probability.
Herculano-Houzel, Suzana; Watson, Charles; Paxinos, George
2013-01-01
How are neurons distributed along the cortical surface and across functional areas? Here we use the isotropic fractionator (Herculano-Houzel and Lent, 2005) to analyze the distribution of neurons across the entire isocortex of the mouse, divided into 18 functional areas defined anatomically. We find that the number of neurons underneath a surface area (the N/A ratio) varies 4.5-fold across functional areas and neuronal density varies 3.2-fold. The face area of S1 contains the most neurons, followed by motor cortex and the primary visual cortex. Remarkably, while the distribution of neurons across functional areas does not accompany the distribution of surface area, it mirrors closely the distribution of cortical volumes—with the exception of the visual areas, which hold more neurons than expected for their volume. Across the non-visual cortex, the volume of individual functional areas is a shared linear function of their number of neurons, while in the visual areas, neuronal densities are much higher than in all other areas. In contrast, the 18 functional areas cluster into three different zones according to the relationship between the N/A ratio and cortical thickness and neuronal density: these three clusters can be called visual, sensory, and, possibly, associative. These findings are remarkably similar to those in the human cerebral cortex (Ribeiro et al., 2013) and suggest that, like the human cerebral cortex, the mouse cerebral cortex comprises two zones that differ in how neurons form the cortical volume, and three zones that differ in how neurons are distributed underneath the cortical surface, possibly in relation to local differences in connectivity through the white matter. Our results suggest that beyond the developmental divide into visual and non-visual cortex, functional areas initially share a common distribution of neurons along the parenchyma that become delimited into functional areas according to the pattern of connectivity established later
Felten, T.; Schlickeiser, R.
2013-10-15
Using the general expressions for the magnetic fluctuation spectrum from uncorrelated plasma particles, it is shown that an isotropic, unmagnetized plasma with arbitrary momentum distribution function spontaneously emits an aperiodic, collective, transverse, damped mode. The collective mode with the dispersion relation γ(k) provides the strongest contribution to the magnetic field fluctuation spectrum. Its existence has been proven before for Maxwellian and Lorentzian plasma distribution functions. Here it is demonstrated that this collective aperiodic mode exists in any isotropic unmagnetized, irrespective of the explicit form of the momentum distribution of plasma particles.
Rovó, Alicia; Daikeler, Thomas; Halter, Jörg; Heim, Dominik; Tsakiris, Dimitrios A.; Stern, Martin; Waltimo, Tuomas; Studt, Jan Dirk; Tyndall, Alan; Gratwohl, Alois; Tichelli, André
2011-01-01
Background Hematopoietic stem cell transplantation has become an established procedure worldwide. Severe early and late complications are well described. Little is known about more subtle changes in general health status of very long-term survivors. The study objective was to assess health status of very long-term survivors in comparison with their respective human leukocyte antigen-identical sibling donors. Design and Methods Case matched comparison in a cross-sectional cohort was performed in a tertiary university hospital and referral center for hematopoietic stem cell transplantation. Forty-four pairs of recipients and their respective donors with a very long-term (17.5 years median; 11–26 years range) follow up after allogeneic hematopoietic stem cell transplantation were included. A comparative clinical evaluation and examination of routine clinical chemistry tests was carried out. Results Recipients more frequently had a lower Karnofsky score (P=0.05), hypertension (P=0.015) and dyslipidemia (P=0.002) but were less likely to be smokers (P=0.016). Recipients showed systematically lower glomerular filtration rates (P<0.0001), higher liver function tests (P=0.0004 for Aspartat-Amino-Transferase) and reduced thyroid function (P=0.002) despite normal or near normal values, and independent of presence or absence of chronic graft-versus-host disease. Indicators of inflammation were more frequent in recipients (9 of 44) with ongoing chronic graft-versus-host disease as measured by higher C-reactive protein (P=0.001) and higher von Willebrand factor (P=0.002). Conclusions Clinically very long-term survivors after an allogeneic hematopoietic stem cell transplantation present more frequently with cardiovascular risk factors and with subtle signs of altered organ function compared to their sibling donors. Even minimal ongoing chronic graft-versus-host disease remains associated with elevated laboratory indicators of inflammation. The clinical significance of these
NASA Astrophysics Data System (ADS)
Ortiz, G.; Ballone, P.
1994-07-01
The properties of the three-dimensional uniform electron gas in the Fermi liquid regime are analyzed using variational Monte Carlo (VMC) and fixed-node diffusion Monte Carlo methods. Our study extends those of Ceperley [Phys. Rev. B 18, 3126 (1978)] and Ceperley and Alder [Phys. Rev. Lett. 45, 566 (1980)] to larger system sizes with improved statistics and, more importantly, to partial spin polarization. The density range 0.8<=rs<=10, which is the most relevant for density functional computations, is studied in detail. We analyze the size dependence of the simulation results and present an extended set of correlation energies extrapolated to the thermodynamic limit. Using the VMC method we analyze the spin dependence of the correlation energy, and we compare our results to several interpolation formulas used in density functional calculations. We summarize our results by a simple interpolation formula. In addition, we present results for the radial distribution function, the structure factor, the momentum distribution, and triplet correlation functions, and we discuss the comparison with many-body semianalytic theories.
NASA Technical Reports Server (NTRS)
Gurgiolo, Chris; Vinas, Adolfo F.
2009-01-01
This paper presents a spherical harmonic analysis of the plasma velocity distribution function using high-angular, energy, and time resolution Cluster data obtained from the PEACE spectrometer instrument to demonstrate how this analysis models the particle distribution function and its moments and anisotropies. The results show that spherical harmonic analysis produced a robust physical representation model of the velocity distribution function, resolving the main features of the measured distributions. From the spherical harmonic analysis, a minimum set of nine spectral coefficients was obtained from which the moment (up to the heat flux), anisotropy, and asymmetry calculations of the velocity distribution function were obtained. The spherical harmonic method provides a potentially effective "compression" technique that can be easily carried out onboard a spacecraft to determine the moments and anisotropies of the particle velocity distribution function for any species. These calculations were implemented using three different approaches, namely, the standard traditional integration, the spherical harmonic (SPH) spectral coefficients integration, and the singular value decomposition (SVD) on the spherical harmonic methods. A comparison among the various methods shows that both SPH and SVD approaches provide remarkable agreement with the standard moment integration method.
Effects of the Electron Energy Distribution Function on Modeled X-ray Spectra
Shlyaptseva, A S; Hansen, S B
2004-02-19
This paper presents the results of a broad investigation into the effects of the electron energy distribution function on the predictions of non-LTE collisional-radiative atomic kinetics models. The effects of non-Maxwellian and suprathermal (''hot'') electron distributions on collisional rates (including three-body recombination) are studied. It is shown that most collisional rates are fairly insensitive to the functional form and characteristic energy of the electron distribution function as long as the characteristic energy is larger than the threshold energy for the collisional process. Collisional excitation and ionization rates, however, are highly sensitive to the fraction of hot electrons. This permits the development of robust spectroscopic diagnostics that can be used to characterize the electron density, bulk electron temperature, and hot electron fraction of plasmas with non-equilibrium electron distribution functions (EDFs). Hot electrons are shown to increase and spread out plasma charge state distributions, amplify the intensities of emission lines fed by direct collisional excitation and radiative cascades, and alter the structure of satellite features in both K- and L-shell spectra. The characteristic energy, functional form, and spatial properties of hot electron distributions in plasmas are open to characterization through their effects on high-energy continuum and line emission and on the polarization of spectral lines.
A note on the probability distribution function of the surface electromyogram signal☆
Nazarpour, Kianoush; Al-Timemy, Ali H.; Bugmann, Guido; Jackson, Andrew
2013-01-01
The probability density function (PDF) of the surface electromyogram (EMG) signals has been modelled with Gaussian and Laplacian distribution functions. However, a general consensus upon the PDF of the EMG signals is yet to be reached, because not only are there several biological factors that can influence this distribution function, but also different analysis techniques can lead to contradicting results. Here, we recorded the EMG signal at different isometric muscle contraction levels and characterised the probability distribution of the surface EMG signal with two statistical measures: bicoherence and kurtosis. Bicoherence analysis did not help to infer the PDF of measured EMG signals. In contrast, with kurtosis analysis we demonstrated that the EMG PDF at isometric, non-fatiguing, low contraction levels is super-Gaussian. Moreover, kurtosis analysis showed that as the contraction force increases the surface EMG PDF tends to a Gaussian distribution. PMID:23047056
Pruess, K.; Karasaki, K.
1982-01-01
After a brief review of the multiple interacting continua method, the concept of a proximity function is introduced as the central geometrical quantity which defines the matrix-fracture interaction. Subsequently, proximity functions are considered for regular and irregular fracture distributions, using Monte Carlo integration techniques. (MHR)
NASA Astrophysics Data System (ADS)
Parry, A. O.; Rascón, C.; Willis, G.; Evans, R.
2014-09-01
We study the density-density correlation function G(r, r‧) in the interfacial region of a fluid (or Ising-like magnet) with short-ranged interactions using square gradient density functional theory. Adopting a simple double parabola approximation for the bulk free-energy density, we first show that the parallel Fourier transform G(z, z‧ q) and local structure factor S(z q) separate into bulk and excess contributions. We attempt to account for both contributions by deriving an interfacial Hamiltonian, characterised by a wavevector dependent surface tension σ(q), and then reconstructing density correlations from correlations in the interface position. We show that the standard crossing criterion identification of the interface, as a surface of fixed density (or magnetization), does not explain the separation of G(z, z‧ q) and the form of the excess contribution. We propose an alternative definition of the interface position based on the properties of correlations between points that ‘float’ with the surface and show that this describes the full q and z dependence of the excess contributions to both G and S. However, neither the ‘crossing-criterion’ nor the new ‘floating interface’ definition of σ(q) are quantities directly measurable from the total structure factor Stot(q) which contains additional q dependence arising from the non-local relation between fluctuations in the interfacial position and local density. Since it is the total structure factor that is measured experimentally or in simulations, our results have repercussions for earlier attempts to extract and interpret σ(q).
Chord-length and free-path distribution functions for many-body systems
Lu, B. ); Torquato, S. )
1993-04-15
We study fundamental morphological descriptors of disordered media (e.g., heterogeneous materials, liquids, and amorphous solids): [ital the] [ital chord]-[ital length] [ital distribution] [ital function] [ital p]([ital z]) and the [ital free]-[ital path] [ital distribution] [ital function] [ital p]([ital z],[ital a]). For concreteness, we will speak in the language of heterogeneous materials composed of two different materials or phases.'' The probability density function [ital p]([ital z]) describes the distribution of chord lengths in the sample and is of great interest in stereology. For example, the first moment of [ital p]([ital z]) is the mean intercept length'' or mean chord length.'' The chord-length distribution function is of importance in transport phenomena and problems involving discrete free paths'' of point particles (e.g., Knudsen diffusion and radiative transport). The free-path distribution function [ital p]([ital z],[ital a]) takes into account the finite size of a simple particle of radius [ital a] undergoing discrete free-path motion in the heterogeneous material and we show that it is actually the chord-length distribution function for the system in which the pore space'' is the space available to a finite-sized particle of radius [ital a]. Thus it is shown that [ital p]([ital z])=[ital p]([ital z],0). We demonstrate that the functions [ital p]([ital z]) and [ital p]([ital z],[ital a]) are related to another fundamentally important morphological descriptor of disordered media, namely, the so-called lineal-path function [ital L]([ital z]) studied by us in previous work [Phys. Rev. A [bold 45], 922 (1992)]. The lineal path function gives the probability of finding a line segment of length [ital z] wholly in one of the phases'' when randomly thrown into the sample.
DE-1 observations of hole electron distribution functions and the cyclotron maser resonance
NASA Technical Reports Server (NTRS)
Lin, C. S.; Burch, J. L.; Gurgiolo, C.; Wu, C. S.
1986-01-01
The hole electron distribution functions observed by the DE-1 satellite within inverted-V events at altitudes of between 9000 km and 15,000 km are examined as a possible free energy source for exciting Z-mode radiation through cyclotron maser resonance. In the DE-1 observations the hole distribution function had center velocities varying between 8000 km/s and 20,000 km/s, with the radii varying between 2000 km/s and 10,000 km/s. The observed distribution function is fitted by an exponential function around the center of the hole, and is used to calculate growth rates of Z-mode radiation. Growth rates as high as 0.001 of the electron gyrofrequency are obtained. It is also shown that the observed hole distribution functions can excite Z-mode radiation at wave frequencies slightly above the gyrofrequency, and wave propagation angles slightly below 90 deg in the source region. The results suggest that the hole distribution function could provide additional amplification for Z-mode waves in the auroral zone.
NASA Technical Reports Server (NTRS)
Convery, P. D.; Schriver, D.; Ashour-Abdalla, M.; Richard, R. L.
2002-01-01
Nongyrotropic plasma distribution functions can be formed in regions of space where guiding center motion breaks down as a result of strongly curved and weak ambient magnetic fields. Such are the conditions near the current sheet in the Earth's middle and distant magnetotail, where observations of nongyrotropic ion distributions have been made. Here a systematic parameter study of nongyrotropic proton distributions using electromagnetic hybrid simulations is made. We model the observed nongyrotropic distributions by removing a number of arc length segments from a cold ring distribution and find significant differences with the results of simulations that initially have a gyrotropic ring distribution. Model nongyrotropic distributions with initially small perpendicular thermalization produce growing fluctuations that diffuse the ions into a stable Maxwellian-like distribution within a few proton gyro periods. The growing waves produced by nongyrotropic distributions are similar to the electromagnetic proton cyclotron waves produced by a gyrotropic proton ring distribution in that they propagate parallel to the background magnetic field and occur at frequencies on the order of the proton gyrofrequency, The maximum energy of the fluctuating magnetic field increases as the initial proton distribution is made more nongyrotropic, that is, more highly bunched in perpendicular velocity space. This increase can be as much as twice the energy produced in the gyrotropic case.
Note: On the universality of proximal radial distribution functions of proteins
NASA Astrophysics Data System (ADS)
Lin, Bin; Pettitt, B. Montgomery
2011-03-01
Protein hydration is important to protein structure and function. Molecular distribution functions have been an invaluable tool to study protein hydration. Proximal radial distribution functions (pRDFs) have been postulated as being transferable across proteins based on evidence collected from two proteins [V. A. Makarov, B. K. Andrews, and B. M. Pettitt, Biopolymers 45(7), 469 (1998)]. Here we selected nine proteins with different sizes as well as different secondary topologies. We show that pRDFs are universal for proteins with compact structures. We further compare these pRDFs with those calculated from polyglycines that have no defined structures to consider the extent of the validity of this approach.
Note: On the Universality of Proximal Radial Distribution Functions of Proteins
Lin, Bin; Pettitt, Bernard M.
2011-03-10
Protein hydration is important to protein structure and function. Molecular distribution functions have been an invaluable tool to study protein hydration. Proximal radial distribution functions (pRDFs) have been postulated as being transferable across proteins based on evidence collected from two proteins [V. A. Makarov, B. K. Andrews, and B. M. Pettitt, Biopolymers 45(7), 469 (1998)]. Here we selected nine proteins with different sizes as well as different secondary topologies. We show that pRDFs are universal for proteins with compact structures. We further compare these pRDFs with those calculated from polyglycines that have no defined structures to consider the extent of the validity of this approach.
The MLP distribution: a modified lognormal power-law model for the stellar initial mass function
NASA Astrophysics Data System (ADS)
Basu, Shantanu; Gil, M.; Auddy, Sayantan
2015-05-01
This work explores the mathematical properties of a distribution introduced by Basu & Jones (2004), and applies it to model the stellar initial mass function (IMF). The distribution arises simply from an initial lognormal distribution, requiring that each object in it subsequently undergoes exponential growth but with an exponential distribution of growth lifetimes. This leads to a modified lognormal with a power-law (MLP) distribution, which can in fact be applied to a wide range of fields where distributions are observed to have a lognormal-like body and a power-law tail. We derive important properties of the MLP distribution, like the cumulative distribution, the mean, variance, arbitrary raw moments, and a random number generator. These analytic properties of the distribution can be used to facilitate application to modelling the IMF. We demonstrate how the MLP function provides an excellent fit to the IMF compiled by Chabrier and how this fit can be used to quickly identify quantities like the mean, median, and mode, as well as number and mass fractions in different mass intervals.
Puri, Nidhi; Manoharlal, Raman; Sharma, Monika; Sanglard, Dominique; Prasad, Rajendra
2011-01-07
Research highlights: {yields} First report to demonstrate an in vivo expression system of an ABC multidrug transporter CgCdr1p of C. glabrata. {yields} First report on the structure and functional characterization of CgCdr1p. {yields} Functional conservation of divergent but typical residues of CgCdr1p. {yields} CgCdr1p elicits promiscuity towards substrates and has a large drug binding pocket with overlapping specificities. -- Abstract: We have taken advantage of the natural milieu of matched pair of azole sensitive (AS) and azole resistant (AR) clinical isolates of Candida glabrata for expressing its major ABC multidrug transporter, CgCdr1p for structure and functional analysis. This was accomplished by tagging a green fluorescent protein (GFP) downstream of ORF of CgCDR1 and integrating the resultant fusion protein at its native chromosomal locus in AS and AR backgrounds. The characterization confirmed that in comparison to AS isolate, CgCdr1p-GFP was over-expressed in AR isolates due to its hyperactive native promoter and the GFP tag did not affect its functionality in either construct. We observed that in addition to Rhodamine 6 G (R6G) and Fluconazole (FLC), a recently identified fluorescent substrate of multidrug transporters Nile Red (NR) could also be expelled by CgCdr1p. Competition assays with these substrates revealed the presence of overlapping multiple drug binding sites in CgCdr1p. Point mutations employing site directed mutagenesis confirmed that the role played by unique amino acid residues critical to ATP catalysis and localization of ABC drug transporter proteins are well conserved in C. glabrata as in other yeasts. This study demonstrates a first in vivo novel system where over-expression of GFP tagged MDR transporter protein can be driven by its own hyperactive promoter of AR isolates. Taken together, this in vivo system can be exploited for the structure and functional analysis of CgCdr1p and similar proteins wherein the arte-factual concerns
NASA Astrophysics Data System (ADS)
Brandt, Benedikt B.; Yannouleas, Constantine; Landman, Uzi
2015-10-01
"Bottom-up" approaches to the many-body physics of fermions have demonstrated recently precise number and site-resolved preparations with tunability of interparticle interactions in single-well, SW, and double-well, DW, nano-scale confinements created by manipulating ultracold fermionic atoms with optical tweezers. These experiments emulate an analogue-simulator mapping onto the requisite microscopic hamiltonian, approaching realization of Feynman's vision of quantum simulators that "will do exactly the same as nature". Here we report on exact benchmark configuration-interaction computational microscopy solutions of the hamiltonian, uncovering the spectral evolution, wave-function anatomy, and entanglement properties of the interacting fermions in the entire parameter range, including crossover from a SW to a DW confinement and a controllable energy imbalance between the wells. We demonstrate attractive pairing and formation of repulsive, highly-correlated, ultracold Wigner molecules, well-described in the natural orbital representation. The agreement with the measurements affirms the henceforth gained deep insights into ultracold molecules and opens access to the size-dependent evolution of nano-clustered and condensed-matter phases and ultracold-atoms quantum information.
Chan, L.P. ); Harshman, D.R. ); Lynn, K.G. ); Massidda, S. , PHB Ecublens, CH-105 Lausanne ); Mitzi, D.B. )
1991-09-02
We report the first measurement of the positron-electron momentum density in superconducting single-crystal Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} ({ital T}{sub {ital c}}{approx}90 K). The observed anisotropy exhibits a twofold (rather than fourfold) symmetry, which is attributed to the superlattice modulation along the {ital b} axis of the BiO{sub 2} layers. Subtraction of the superlattice contribution also reveals a pair momentum distribution consistent with the CuO{sub 2} and BiO{sub 2} Fermi surfaces, and in reasonable agreement with the theoretical pair momentum density derived from band theory.
Observations of the directional distribution of the wind energy input function over swell waves
NASA Astrophysics Data System (ADS)
Shabani, Behnam; Babanin, Alex V.; Baldock, Tom E.
2016-02-01
Field measurements of wind stress over shallow water swell traveling in different directions relative to the wind are presented. The directional distribution of the measured stresses is used to confirm the previously proposed but unverified directional distribution of the wind energy input function. The observed wind energy input function is found to follow a much narrower distribution (β∝cos3.6θ) than the Plant (1982) cosine distribution. The observation of negative stress angles at large wind-wave angles, however, indicates that the onset of negative wind shearing occurs at about θ≈ 50°, and supports the use of the Snyder et al. (1981) directional distribution. Taking into account the reverse momentum transfer from swell to the wind, Snyder's proposed parameterization is found to perform exceptionally well in explaining the observed narrow directional distribution of the wind energy input function, and predicting the wind drag coefficients. The empirical coefficient (ɛ) in Snyder's parameterization is hypothesised to be a function of the wave shape parameter, with ɛ value increasing as the wave shape changes between sinusoidal, sawtooth, and sharp-crested shoaling waves.
Tensor-polarized quark and antiquark distribution functions in a spin-one hadron
NASA Astrophysics Data System (ADS)
Kumano, S.
2010-07-01
It is becoming crucial to understand orbital-angular-momentum contributions for clarifying the nucleon-spin issue in the parton level. Twist-two structure functions b1 and b2 for spin-one hadrons could probe orbital-angular-momentum effects, which reflect a different aspect from current studies for the spin-1/2 nucleon. The structure functions b1 and b2 are described by tensor-polarized quark and antiquark distributions δTq and δTq¯. Using HERMES data on the b1 structure function for the deuteron, we made an analysis of extracting the distributions δTq and δTq¯ in a simple x-dependent functional form. Optimum distributions are proposed for the tensor-polarized valence and antiquark distribution functions from the analysis. A finite tensor polarization is obtained for antiquarks if we impose a constraint that the first moments of tensor-polarized valence-quark distributions vanish.
Tensor-polarized quark and antiquark distribution functions in a spin-one hadron
Kumano, S.
2010-07-01
It is becoming crucial to understand orbital-angular-momentum contributions for clarifying the nucleon-spin issue in the parton level. Twist-two structure functions b{sub 1} and b{sub 2} for spin-one hadrons could probe orbital-angular-momentum effects, which reflect a different aspect from current studies for the spin-1/2 nucleon. The structure functions b{sub 1} and b{sub 2} are described by tensor-polarized quark and antiquark distributions {delta}{sub T}q and {delta}{sub T}q. Using HERMES data on the b{sub 1} structure function for the deuteron, we made an analysis of extracting the distributions {delta}{sub T}q and {delta}{sub T}q in a simple x-dependent functional form. Optimum distributions are proposed for the tensor-polarized valence and antiquark distribution functions from the analysis. A finite tensor polarization is obtained for antiquarks if we impose a constraint that the first moments of tensor-polarized valence-quark distributions vanish.
NASA Technical Reports Server (NTRS)
Pilipp, W. G.; Muehlhaeuser, K.-H.; Miggenrieder, H.; Montgomery, M. D.; Rosenbauer, H.
1987-01-01
Electron distribution functions with unusual features, which have been observed on rare occasions in the solar wind by the Helios probes, are presented. Two examples show a strong symmetric bidirectional anisotropy in the energy regime of the halo up to particle energies of 800 eV (double-strahl distributions). Another example shows an unusually strong bidirectional anisotropy in the energy regime of the core (below 150 eV). The infrequently observed double-strahl distributions provide evidence that magnetic field loops can exist in the solar wind where electrons are trapped. In addition, they provide evidence that in the case of electrons trapped in closed magnetic field structures the break in the energy spectrum separating the core from the halo is produced only by collisions. On the other hand, the class of distribution functions with strongly anisotropic cores indicates that in the case of 'open' magnetic field lines the break between core and halo is largely determined both by the interplanetary electrostatic potential and by collisions.
Pairing Properties of Superheavy Nuclei
Staszczak, A.; Dobaczewski, J.; Nazarewicz, Witold
2007-01-01
Pairing properties of even-even superheavy N=184 isotones are studied within the Skyrme-Hartree-Fock+BCS approach. In the particle-hole channel we take the Skyrme energy density functional SLy4, while in the particle-particle channel we employ the seniority pairing force and zero-range delta-interactions with different forms of density dependence. We conclude that the calculated static fission trajectories weakly depend on the specific form of the delta-pairing interaction. We also investigate the impact of triaxiality on the inner fission barrier and find a rather strong Z dependence of the effect.
Normalized ion distribution function in expanding sheaths of 2D grid electrodes
NASA Astrophysics Data System (ADS)
Yi, Changho; Namkung, Won; Cho, Moohyun
2016-04-01
Ion distributions in expanding collisionless sheaths of two-dimensional (2D) grid electrodes were studied by using XOOPIC (particle-in-cell) simulations when short pulses of negative high-voltage were applied to electrodes immersed in plasmas. 2D grid electrodes consist of a periodic array of cylindrical electrodes, and the opening ratio of the grid electrodes is defined by the ratio of the spacing between cylindrical electrodes to the periodic length of the grid electrodes. In this paper, we introduce a normalized ion distribution function in normalized coordinates, and it is shown by simulation that the normalized ion distribution function depends only on the opening ratio of the grid electrodes. When the opening ratio of the grid electrodes is fixed, the ion distribution in expanding sheaths can be easily found in various conditions using only a single run of a PIC simulation, and the computation time can be significantly reduced.
Fitness function distributions over generalized search neighborhoods in the q-ary hypercube.
Sutton, Andrew M; Chicano, Francisco; Whitley, L Darrell
2013-01-01
The frequency distribution of a fitness function over regions of its domain is an important quantity for understanding the behavior of algorithms that employ randomized sampling to search the function. In general, exactly characterizing this distribution is at least as hard as the search problem, since the solutions typically live in the tails of the distribution. However, in some cases it is possible to efficiently retrieve a collection of quantities (called moments) that describe the distribution. In this paper, we consider functions of bounded epistasis that are defined over length-n strings from a finite alphabet of cardinality q. Many problems in combinatorial optimization can be specified as search problems over functions of this type. Employing Fourier analysis of functions over finite groups, we derive an efficient method for computing the exact moments of the frequency distribution of fitness functions over Hamming regions of the q-ary hypercube. We then use this approach to derive equations that describe the expected fitness of the offspring of any point undergoing uniform mutation. The results we present provide insight into the statistical structure of the fitness function for a number of combinatorial problems. For the graph coloring problem, we apply our results to efficiently compute the average number of constraint violations that lie within a certain number of steps of any coloring. We derive an expression for the mutation rate that maximizes the expected fitness of an offspring at each fitness level. We also apply the results to the slightly more complex frequency assignment problem, a relevant application in the domain of the telecommunications industry. As with the graph coloring problem, we provide formulas for the average value of the fitness function in Hamming regions around a solution and the expectation-optimal mutation rate. PMID:23163780
Dust heating by Alfvén waves using non-Maxwellian distribution function
Zubia, K.; Shah, H. A.; Yoon, P. H.
2015-08-15
Quasilinear theory is employed in order to evaluate the resonant heating rate by Alfvén waves, of multiple species dust particles in a hot, collisionless, and magnetized plasma, with the underlying assumption that the dust velocity distribution function can be modeled by a generalized (r, q) distribution function. The kinetic linear dispersion relation for the electromagnetic dust cyclotron Alfvén waves is derived, and the dependence of the heating rate on the magnetic field, mass, and density of the dust species is subsequently investigated. The heating rate and its dependence on the spectral indices r and q of the distribution function are also investigated. It is found that the heating is sensitive to negative value of spectral index r.
NASA Astrophysics Data System (ADS)
de Vega, H. J.; Sanchez, N. G.
2016-05-01
We find the distribution function f(E) for dark matter (DM) halos in galaxies and the corresponding equation of state from the (empirical) DM density profiles derived from observations. We solve for DM in galaxies the analogous of the Eddington equation originally used for the gas of stars in globular clusters. The observed density profiles are a good realistic starting point and the distribution functions derived from them are realistic. We do not make any assumption about the DM nature, the methods developed here apply to any DM kind, though all results are consistent with warm dark matter (WDM). With these methods we find: (i) Cored density profiles behaving quadratically for small distances ρ(r)= r → 0ρ(0) ‑ Kr2 produce distribution functions which are finite and positive at the halo center while cusped density profiles always produce divergent distribution functions at the center. (ii) Cored density profiles produce approximate thermal Boltzmann distribution functions for r ≲ 3rh where rh is the halo radius. (iii) Analytic expressions for the dispersion velocity and the pressure are derived yielding at each halo point an ideal DM gas equation of state with local temperature T(r) ≡ mv2(r)/3. T(r) turns out to be constant in the same region where the distribution function is thermal and exhibits the same temperature within the percent. The self-gravitating DM gas can thermalize despite being collisionless because it is an ergodic system. (iv) The DM halo can be consistently considered at local thermal equilibrium with: (a) a constant temperature T(r) = T0 for r ≲ 3rh, (b) a space dependent temperature T(r) for 3rh < r ≲ Rvirial, which slowly decreases with r. That is, the DM halo is realistically a collisionless self-gravitating thermal gas for r ≲ Rvirial. (v) T(r) outside the halo radius nicely follows the decrease of the circular velocity squared.
Electron Velocity Distribution Function in Magnetic Clouds in the Solar Wind
NASA Technical Reports Server (NTRS)
Nieves-Chinchil, Teresa; Vinas, Adolfo F.; Bale, Stuart D.
2006-01-01
We present a study of the kinetic properties of the electron velocity distribution functions within magnetic clouds, since they are the dominant thermal component. The study is based on high time resolution data from the GSFC WIND/SWE electron spectrometer and the Berkeley 3DP electron plasma instruments. Recent studies on magnetic clouds have shown observational evidence of anti-correlation between the total electron density and electron temperature, which suggest a polytrope law P(sub e) = alpha(Nu(sub e) (sup gamma)) for electrons with the constant gamma approximates 0.5 < 1. This anti-correlation and small polytropic gamma-values is interpreted in the context of the presence of highly non-Maxwellian electron distributions (i.e. non-thermal) within magnetic clouds. These works suggested that the non-thermal electrons can contribute as much as 50% of the total electron pressure within magnetic clouds. We have revisited some of the magnetic cloud events previously studied and attempted to quantify the nature of the non-thermal electrons by modeling the electron velocity distribution function using a kappa distribution function to characterize the kinetic non-thermal effects. If non-thermal tail effects are the source for the anti-correlation between the moment electron temperature and density and if the kappa distribution is a reasonable representative model of non-thermal effects, then the electron velocity distribution within magnetic clouds should show indication for small K-values when gamma < 1.
Formation of Kappa Distribution Functions and Eddy Diffusion in the Magnetosphere of the Earth
NASA Astrophysics Data System (ADS)
Antonova, Elizaveta; Stepanova, Marina; Kirpichev, Igor; Vovchenko, Vadim; Ovchinnikov, Ilyav
2016-07-01
One of the main features of collisionless magnetospheric plasma is the comparatively quick relaxation of distribution functions to kappa distributions. The form of the kappa distribution consists of a Maxwellian core at low energies and a power law spectrum at high energies. Kappa functions describe particle distributions for the systems that are in stationary state but out of thermal equilibrium. Simultaneous determination of the parameters of kappa distributions in different magnetospheric regions is important for understanding the role of different processes of particle acceleration and relaxation of kappa distribution functions to the Maxwellian ones. We analyze the applicability of kappa approximation for different magnetocpheric regions using the data of the Time History of Events and Macroscale Interactions during Substorms spacecraft (THEMIS) mission. We selected events when at least four satellites of THEMIS mission were aligned along the tail between approximately 7 and 30Re. It was found that for the majority of events the values of power index is increased tailwards. We consider such feature as the result of the existence of the inner magnetosphere sources of particle acceleration. We analyze the role of regular bulk transport and the turbulent transport by eddies of different scale in the formation of observed dependences.
Schroeder, J. W. R. Skiff, F.; Howes, G. G.; Kletzing, C. A.; Carter, T. A.; Dorfman, S.
2015-12-10
Wave propagation can be an accurate method for determining material properties. High frequency whistler mode waves (0.7 < ω/|Ω{sub ce}| < 1) in an overdense plasma (ω{sub pe} > |Ω{sub ce}|) are damped primarily by Doppler-shifted electron cyclotron resonance. A kinetic description of whistler mode propagation parallel to the background magnetic field shows that damping is proportional to the parallel electron distribution function. This property enables an experimental determination of the parallel electron distribution function using a measurement of whistler mode wave absorption. The whistler mode wave absorption diagnostic uses this technique on UCLA’s Large Plasma Device (LaPD) to measure the distribution of high energy electrons (5 − 10v{sub te}) with 0.1% precision. The accuracy is limited by systematic effects that need to be considered carefully. Ongoing research uses this diagnostic to investigate the effect of inertial Alfvén waves on the electron distribution function. Results presented here verify experimentally the linear effects of inertial Alfvén waves on the reduced electron distribution function, a necessary step before nonlinear physics can be tested. Ongoing experiments with the whistler mode wave absorption diagnostic are making progress toward the first direct detection of electrons nonlinearly accelerated by inertial Alfvén waves, a process believed to play an important role in auroral generation.
NASA Astrophysics Data System (ADS)
Cheng, Hong; Zou, Xue-Yong; Zhang, Chun-Lai
2006-11-01
Saltating sand grains are the primary component of airborne sand and account for 75% of all transport flux of sand grains. Although they have been widely studied, the microscopic and macroscopic aspects of blown sand physics have not been united, and this has slowed development of this field. The main reason for this is that the bridge (probability distribution functions for initial liftoff velocities of saltating sand grains) between the macroscopic and microscopic research has not been satisfactorily solved because it is difficult to measure the initial liftoff parameters of saltating sand grains and because the underlying theory is lacking. In this paper, we combined theoretical analyses with wind tunnel experiment data to describe the liftoff parameters of saltating sand grains (the horizontal, vertical, and resultant liftoff velocities and angles). On the basis of these data, the liftoff angles follow a LogNorm4 distribution function, whereas the horizontal, vertical, and resultant liftoff velocities follow a Gamma distribution function. We also demonstrated that it is feasible to colligate initial liftoff velocities of saltating sand grains obtained under different frictional wind velocities by different scholars in wind tunnel experiments and comprehensively analyze their distributions. Therefore the distribution functions of initial liftoff velocities of saltating sand grains presented in this paper do a good job of reflecting the underlying physics.