1,009 research outputs found
V-T Theory of Self Dynamic Response in a Monatomic Liquid
A new theoretical model for self dynamic response is developed using
Vibration-Transit (V-T) theory, and is applied to liquid sodium at all
wavevectors q from the hydrodynamic regime to the free particle limit. In this
theory the zeroth-order Hamiltonian describes the vibrational motion in a
single random valley harmonically extended to infinity. This Hamiltonian is
tractable, is evaluated a priori for monatomic liquids, and the same
Hamiltonian (the same set of eigenvalues and eigenvectors) is used for
equilibrium and nonequlibrium theory. Here, for the self intermediate
scattering function Fself(q,t) we find the vibrational contribution is in near
perfect agreement with molecular dynamics (MD) through short and intermediate
times, at all q. This is direct confirmation that normal mode vibrational
correlations are present in the motion of the liquid state. The primary transit
effect is diffusive motion of the vibrational equilibrium positions, as the
liquid transits rapidly among random valleys. This motion is modeled as a
standard random walk, and the resulting theoretical Fself(q,t) is in excellent
agreement with MD results at all q and t. In the limit for q to infinity, the
theory automatically exhibits the correct approach to the free-particle limit.
Also in the limit for q to zero, the hydrodynamic limit emerges as well. In
contrast to the benchmark theories of generalized hydrodynamics and mode
coupling, the present theory is near a priori, while achieving modestly better
accuracy. Therefore, in our view, it constitutes an improvement over the
traditional theories.Comment: 16 pages, 11 figures, Journal Paper. Following referee's comments,
Section IID has been completely rewritten and a new Section IIE has been
adde
Sleep deprivation impairs and caffeine enhances my performance, but not always our performance: how acting in a group can change the effects of impairments and enhancements
What effects do factors that impair or enhance performance in individuals have when these individuals act in groups? We provide a framework, called the GIE ("Effects of Grouping on Impairments and Enhancementsâ) framework, for investigating this question. As prominent examples for individual-level impairments and enhancements, we discuss sleep deprivation and caffeine. Based on previous research, we derive hypotheses on how they influence performance in groups, specifically process gains and losses in motivation, individual capability, and coordination. We conclude that the effect an impairment or enhancement has on individual-level performance is not necessarily mirrored in group performance: grouping can help or hurt. We provide recommendations on how to estimate empirically the effects individual-level performance impairments and enhancements have in groups. By comparing sleep deprivation to stress and caffeine to pharmacological cognitive enhancement, we illustrate that we cannot readily generalize from group results on one impairment or enhancement to another, even if they have similar effects on individual-level performance
Microscopic dynamics in liquid metals: the experimental point of view
The experimental results relevant for the understanding of the microscopic
dynamics in liquid metals are reviewed, with special regards to the ones
achieved in the last two decades. Inelastic Neutron Scattering played a major
role since the development of neutron facilities in the sixties. The last ten
years, however, saw the development of third generation radiation sources,
which opened the possibility of performing Inelastic Scattering with X rays,
thus disclosing previously unaccessible energy-momentum regions. The purely
coherent response of X rays, moreover, combined with the mixed
coherent/incoherent response typical of neutron scattering, provides enormous
potentialities to disentangle aspects related to the collectivity of motion
from the single particle dynamics.
If the last twenty years saw major experimental developments, on the
theoretical side fresh ideas came up to the side of the most traditional and
established theories. Beside the raw experimental results, therefore, we review
models and theoretical approaches for the description of microscopic dynamics
over different length-scales, from the hydrodynamic region down to the single
particle regime, walking the perilous and sometimes uncharted path of the
generalized hydrodynamics extension. Approaches peculiar of conductive systems,
based on the ionic plasma theory, are also considered, as well as kinetic and
mode coupling theory applied to hard sphere systems, which turn out to mimic
with remarkable detail the atomic dynamics of liquid metals. Finally, cutting
edges issues and open problems, such as the ultimate origin of the anomalous
acoustic dispersion or the relevance of transport properties of a conductive
systems in ruling the ionic dynamic structure factor are discussed.Comment: 53 pages, 41 figures, to appear in "The Review of Modern Physics".
Tentatively scheduled for July issu
Characterization of Lifestyle in Spinocerebellar Ataxia Type 3 and Association with Disease Severity
BACKGROUND: Lifestyle could influence the course of hereditary ataxias, but representative data are missing. OBJECTIVE: The objective of this study was to characterize lifestyle in spinocerebellar ataxia type 3 (SCA3) and investigate possible associations with disease parameters. METHODS: In a prospective cohort study, data on smoking, alcohol consumption, physical activity, physiotherapy, and body mass index (BMI) were collected from 243 patients with SCA3 and 119 controls and tested for associations with age of onset, disease severity, and progression. RESULTS: Compared with controls, patients with SCA3 were less active and consumed less alcohol. Less physical activity and alcohol abstinence were associated with more severe disease, but not with progression rates or age of onset. Smoking, BMI, or physiotherapy did not correlate with disease parameters. CONCLUSION: Differences in lifestyle factors of patients with SCA3 and controls as well as associations of lifestyle factors with disease severity are likely driven by the influence of symptoms on behavior. No association between lifestyle and disease progression was detected. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society
Notes on the algebraic curves in (p,q) minimal string theory
Loop amplitudes in (p,q) minimal string theory are studied in terms of the
continuum string field theory based on the free fermion realization of the KP
hierarchy. We derive the Schwinger-Dyson equations for FZZT disk amplitudes
directly from the W_{1+\infty} constraints in the string field formulation and
give explicitly the algebraic curves of disk amplitudes for general
backgrounds. We further give annulus amplitudes of FZZT-FZZT, FZZT-ZZ and ZZ-ZZ
branes, generalizing our previous D-instanton calculus from the minimal unitary
series (p,p+1) to general (p,q) series. We also give a detailed explanation on
the equivalence between the Douglas equation and the string field theory based
on the KP hierarchy under the W_{1+\infty} constraints.Comment: 61 pages, 1 figure, section 2.5 and Appendix B added, references
added, final version to appear in JHE
Machine-learning of atomic-scale properties based on physical principles
We briefly summarize the kernel regression approach, as used recently in
materials modelling, to fitting functions, particularly potential energy
surfaces, and highlight how the linear algebra framework can be used to both
predict and train from linear functionals of the potential energy, such as the
total energy and atomic forces. We then give a detailed account of the Smooth
Overlap of Atomic Positions (SOAP) representation and kernel, showing how it
arises from an abstract representation of smooth atomic densities, and how it
is related to several popular density-based representations of atomic
structure. We also discuss recent generalisations that allow fine control of
correlations between different atomic species, prediction and fitting of
tensorial properties, and also how to construct structural kernels---applicable
to comparing entire molecules or periodic systems---that go beyond an additive
combination of local environments
The COSMOS-WIRCam near-infrared imaging survey: I: BzK selected passive and star forming galaxy candidates at z>1.4
(abridged) We present a new near-infrared survey covering the 2 deg sq COSMOS
field. Combining our survey with Subaru B and z images we construct a deep,
wide-field optical-infrared catalogue. At Ks<23 (AB magnitudes) our survey
completeness is greater than 90% and 70% for stars and galaxies respectively
and contains 143,466 galaxies and 13,254 stars. At z~2 our catalogues contain
3931 quiescent and 25,757 star-forming BzK-selected galaxies representing the
largest and most secure sample of these objects to date. Our counts of
quiescent galaxies turns over at Ks~22 an effect which we demonstrate cannot be
due to sample incompleteness. In our survey both the number of faint and bright
quiescent objects exceeds the predictions of a semi-analytic galaxy formation
model, indicating potentially the need for further refinements in the amount of
merging and AGN feedback at z~2 in these models. We measure the angular
correlation function for each sample and find that at small scales the
correlation function for passive BzK galaxies exceeds the clustering of dark
matter. We use 30-band photometric redshifts to derive the spatial correlation
length and the redshift distributions for each object class. At Ks<22 we find
r_0^{\gamma/1.8}=7.0 +/-0.5h^{-1} Mpc for the passive BzK candidates and
4.7+/-0.8h^{-1} Mpc for the star-forming BzK galaxies. Our pBzK galaxies have
an average photometric redshift of z_p~1.4, in approximate agreement with the
limited spectroscopic information currently available. The stacked Ks image
will be made publicly available from IRSA.Comment: Accepted for publication in Astrophysical Journal. 17 pages, 17
figures, minor revisions to match published version available at
http://adsabs.harvard.edu/abs/2010ApJ...708..202
Structural study of an amorphous NiZr2 alloy by anomalous wide angle X-ray scattering and Reverse Monte Carlo simulations
The local atomic structure of an amorphous NiZr2 alloy was investigated using
the anomalous wide-angle x-ray scattering (AWAXS), differential anomalous
scattering (DAS) and reverse Monte Carlo (RMC) simulations techniques. The
AWAXS measurements were performed at eight different incident photon energies,
including some close to the Ni and Zr K edges. From the measurements eight
total structure factor S(K,E) were derived. Using the AWAXS data four
differential structure factors DSFi(K,Em,En) were derived, two about the Ni and
Zr edges. The partial structure factors SNi-Ni(K), SNi-Zr(K) and SZr-Zr(K) were
estimated by using two different methods. First, the S(K,E) and DSFi(K,Em,En)
factors were combined and used in a matrix inversion process. Second, three
S(K,E) factors were used as input data in the RMC technique. The coordination
numbers and interatomic distances for the first neighbors extracted from the
partial structure factors obtained by these two methods show a good agreement.
By using the three-dimensional structure derived from the RMC simulations, the
bond-angle distributions were calculated and they suggest the presence of
distorted triangular-faced polyhedral units in the amorphous NiZr2 structure.
We have used the Warren chemical short-range order parameter to evaluate the
chemical short-range order for the amorphous NiZr2 alloy and for the NiZr2
compound. The calculated values show that the chemical short-range order found
in these two materials is similar to that found in a solid solution.Comment: Submitted to Phys. Rev. B, 8 figure
Elliptical Galaxies and Bulges of Disk Galaxies: Summary of Progress and Outstanding Issues
This is the summary chapter of a review book on galaxy bulges. Bulge
properties and formation histories are more varied than those of ellipticals. I
emphasize two advances: 1 - "Classical bulges" are observationally
indistinguishable from ellipticals, and like them, are thought to form by major
galaxy mergers. "Disky pseudobulges" are diskier and more actively star-forming
(except in S0s) than are ellipticals. Theys are products of the slow
("secular") evolution of galaxy disks: bars and other nonaxisymmetries move
disk gas toward the center, where it starbursts and builds relatively flat,
rapidly rotating components. This secular evolution is a new area of galaxy
evolution work that complements hierarchical clustering. 2 - Disks of
high-redshift galaxies are unstable to the formation of mass clumps that sink
to the center and merge - an alternative channel for the formation of classical
bulges. I review successes and unsolved problems in the formation of
bulges+ellipticals and their coevolution (or not) with supermassive black
holes. I present an observer's perspective on simulations of dark matter galaxy
formation including baryons. I review how our picture of the quenching of star
formation is becoming general and secure at redshifts z < 1. The biggest
challenge is to produce realistic bulges+ellipticals and disks that overlap
over a factor of 10**3 in mass but that differ from each other as observed over
that whole range. Second, how does hierarchical clustering make so many giant,
bulgeless galaxies in field but not cluster environments? I argue that we rely
too much on AGN and star-formation feedback to solve these challenges.Comment: 46 pages, 10 postscript figures, accepted for publication in Galactic
Bulges, ed. E. Laurikainen, R. F. Peletier, & D. A. Gadotti (New York:
Springer), in press (2015
Natural history, phenotypic spectrum, and discriminative features of multisystemic RFC1 disease
Objective To delineate the full phenotypic spectrum, discriminative features, piloting longitudinal progression data, and sample size calculations of replication factor complex subunit 1 (RFC1) repeat expansions, recently identified as causing cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS).
Methods Multimodal RFC1 repeat screening (PCR, Southern blot, whole-exome/genome sequencing?based approaches) combined with cross-sectional and longitudinal deep phenotyping in (1) cross-European cohort A (70 families) with ?2 features of CANVAS or ataxia with chronic cough (ACC) and (2) Turkish cohort B (105 families) with unselected late-onset ataxia.
Results Prevalence of RFC1 disease was 67% in cohort A, 14% in unselected cohort B, 68% in clinical CANVAS, and 100% in ACC. RFC1 disease was also identified in Western and Eastern Asian individuals and even by whole-exome sequencing. Visual compensation, sensory symptoms, and cough were strong positive discriminative predictors (>90%) against RFC1-negative patients. The phenotype across 70 RFC1-positive patients was mostly multisystemic (69%), including dysautonomia (62%) and bradykinesia (28%) (overlap with cerebellar-type multiple system atrophy [MSA-C]), postural instability (49%), slow vertical saccades (17%), and chorea or dystonia (11%). Ataxia progression was ?1.3 Scale for the Assessment and Rating of Ataxia points per year (32 cross-sectional, 17 longitudinal assessments, follow-up ?9 years [mean 3.1 years]) but also included early falls, variable nonlinear phases of MSA-C?like progression (SARA points 2.5?5.5 per year), and premature death. Treatment trials require 330 (1-year trial) and 132 (2-year trial) patients in total to detect 50% reduced progression.
Conclusions RFC1 disease is frequent and occurs across continents, with CANVAS and ACC as highly diagnostic phenotypes yet as variable, overlapping clusters along a continuous multisystemic disease spectrum, including MSA-C-overlap. Our natural history data help to inform future RFC1 treatment trials.
Classification of Evidence This study provides Class II evidence that RFC1 repeat expansions are associated with CANVAS and ACC.FUNDING: Study Funding This work was supported via the European Unionâs Horizon 2020 research and innovation program by the BMBF under the frame of the E-Rare-3 network PREPARE (01GM1607; to M. Synofzik,M.A., H.P., B.P.v.d.W.), by the DFG under the frame of EJP-RD network PROSPAX (No. 441409627; M. Synofzik, B.P.v.d.W., A.N.B.), and grant 779257 âSolve-RDâ (toM. Synofzik, B.P.v.d.W.). B.P.v.d.W. receives additional research support from ZonMW, Hersenstichting, Gossweiler Foundation, uniQure, and Radboud University Medical Centre. T.B.H. was supported by the DFG (No 418081722). A.T. receives funding from the University of Tšubingen, medical faculty, for the Clinician Scientist Program grant 439-0-0. A.C. thanks Medical Research Council, MR/T001712/1) and Fondazione CARIPLO (2019-1836) for grant support. L.S., T.K., B.P.v.d.W., and M. Synofzik are members of the European Reference Network for Rare Neurological Diseases, project 739510. A.N.B. is supported by the Suna and Inan Kirac Foundation and Koç University School of Medicine
- âŠ