8,470 research outputs found
Phase behavior of a fluid with competing attractive and repulsive interactions
Fluids in which the interparticle potential has a hard core, is attractive at
moderate separations, and repulsive at greater separations are known to exhibit
novel phase behavior, including stable inhomogeneous phases. Here we report a
joint simulation and theoretical study of such a fluid, focusing on the
relationship between the liquid-vapor transition line and any new phases. The
phase diagram is studied as a function of the amplitude of the attraction for a
certain fixed amplitude of the long ranged repulsion. We find that the effect
of the repulsion is to substitute the liquid-vapor critical point and a portion
of the associated liquid-vapor transition line, by two first order transitions.
One of these transitions separates the vapor from a fluid of spherical
liquidlike clusters; the other separates the liquid from a fluid of spherical
voids. At low temperature, the two transition lines intersect one another and a
vapor-liquid transition line at a triple point. While most integral equation
theories are unable to describe the new phase transitions, the Percus Yevick
approximation does succeed in capturing the vapor-cluster transition, as well
as aspects of the structure of the cluster fluid, in reasonable agreement with
the simulation results.Comment: 15 pages, 20 figure
Development of methodologies and procedures for identifying STS users and uses
A study was conducted to identify new uses and users of the new Space Transporation System (STS) within the domestic government sector. The study develops a series of analytical techniques and well-defined functions structured as an integrated planning process to assure efficient and meaningful use of the STS. The purpose of the study is to provide NASA with the following functions: (1) to realize efficient and economic use of the STS and other NASA capabilities, (2) to identify new users and uses of the STS, (3) to contribute to organized planning activities for both current and future programs, and (4) to air in analyzing uses of NASA's overall capabilities
Optimizing Performance through Stress and Induction Levels in Virtual Reality Using Autonomic Responses
Virtual reality (VR) is now a consumer technology, but individuals' experience with systems or different applications varies enormously. This means that most consumer applications need to consider how to train naive users in the application's operation. We examine three different ways of imparting on-boarding instructions to users: first-person audio guidance, second-person non-player character (NPC) diegetic guidance or written instruction. Our primary hypothesis is that the second-person condition will induce a higher stress level on the user, given the perceived presence of a supervising NPC. Our secondary hypothesis is that there is a correlation between stress and performance, meaning that participants with elevated stress levels within a certain margin will complete their tasks faster and more successfully. By extension, participants whose stress levels are either above or below this optimal margin will under-perform on the same tasks. The tasks in question are an interaction test (IT), designed to test participants' abilities to pick up and manipulate virtual objects, and a mental rotation test (MRT), designed to place them under cognitive load. During these tasks we measure the users' level of stress from their bio signals via a mobile wearable device that tracks their heart rate (HR), galvanic skin response (GSR) and body temperature in real-time. Statistical significance was not found in the stress or performance levels between the instruction conditions, but the secondary hypothesis was supported and a correlation was found between stress and performance levels across the conditions in both HR and GSR
A model colloidal fluid with competing interactions: bulk and interfacial properties
Using a simple mean-field density functional theory theory (DFT), we
investigate the structure and phase behaviour of a model colloidal fluid
composed of particles interacting via a pair potential which has a hard core of
diameter , is attractive Yukawa at intermediate separations and
repulsive Yukawa at large separations. We analyse the form of the asymptotic
decay of the bulk fluid correlation functions, comparing results from our DFT
with those from the self consistent Ornstein-Zernike approximation (SCOZA). In
both theories we find rich crossover behaviour, whereby the ultimate decay of
correlation functions changes from monotonic to long-wavelength damped
oscillatory decay on crossing certain lines in the phase diagram, or sometimes
from oscillatory to oscillatory with a longer wavelength. For some choices of
potential parameters we find, within the DFT, a -line at which the
fluid becomes unstable with respect to periodic density fluctuations. SCOZA
fails to yield solutions for state points near such a -line. The
propensity to clustering of particles, which is reflected by the presence of a
long wavelength , slowly decaying oscillatory pair correlation
function, and a structure factor that exhibits a very sharp maximum at small
but non zero wavenumbers, is enhanced in states near the -line. We
present density profiles for the planar liquid-gas interface and for fluids
adsorbed at a planar hard wall. The presence of a nearby -transition
gives rise to pronounced long-wavelength oscillations in the one-body densities
at both types of interface.Comment: 14 pages, 11 figure
Phase transitions in simple and not so simple binary fluids
Compared to pure fluids, binary mixtures display a very diverse phase
behavior, which depends sensitively on the parameters of the microscopic
potential. Here we investigate the phase diagrams of simple model mixtures by
use of a microscopic implementation of the renormalization group technique.
First, we consider a symmetric mixture with attractive interactions, possibly
relevant for describing fluids of molecules with internal degrees of freedom.
Despite the simplicity of the model, slightly tuning the strength of the
interactions between unlike species drastically changes the topology of the
phase boundary, forcing or inhibiting demixing, and brings about several
interesting features such as double critical points, tricritical points, and
coexistence domains enclosing `islands' of homogeneous, mixed fluid.
Homogeneous phase separation in mixtures can be driven also by purely repulsive
interactions. As an example, we consider a model of soft particles which has
been adopted to describe binary polymer solutions. This is shown to display
demixing (fluid-fluid) transition at sufficiently high density. The nature and
the physical properties of the corresponding phase transition are investigated.Comment: 6 pages + 3 figures, presented at the 5th EPS Liquid Matter
Conference, Konstanz, 14-18 September 200
Exceptionally strong magnetism in 4d perovskites RTcO3 (R=Ca,Sr,Ba)
The evolution of the magnetic ordering temperature of the 4d3 perovskites
RTcO3 (R=Ca,Sr,Ba) and its relation with its electronic and structural
properties has been studied by means of hybrid density functional theory and
Monte Carlo simulations. When compared to the most widely studied 3d
perovskites the large spatial extent of the 4d shells and their relatively
strong hybridization with oxygen weaken the tendency to form Jahn-Teller like
orbital ordering. This strengthens the superexchange interaction. The resulting
insulating G-type antiferromagnetic ground state is characterized by large
superexchange coupling constants (26-35 meV) and Neel temperatures (750-1200
K). These monotonically increase as a function of the R ionic radius due to the
progressive enhancement of the volume and the associated decrease of the
cooperative rotation of the TcO6 octahedra.Comment: 4 pages, 3 figure
Mapping the links between gender, status and genre in Shakespeare’s plays
The AHRC-funded Encyclopedia of Shakespeare’s Language (ESL) project has produced a resource allowing users to explore Shakespeare’s plays in a variety of (semi-automatic) ways, via a web-based corpus query processor interface (CQPweb) hosted by Lancaster University. It enables users, for example, to interrogate a corpus of Shakespeare’s plays using queries restricted by dramatic genre, gender and/or social status of characters, and to target and explore the language of the plays not only at the word level, but also at the grammatical and semantic levels (by querying part-of-speech or semantic categories). Using keyword techniques, we examine how female and male language varies in general, by social status (high or low), and by genre (comedy, history and tragedy). Among our findings, we note differences in the use of pronouns and references to male authority (female overuse of ‘I’ and ‘husband’; male overuse of ‘we’ and ‘king’). We also observe that high-status males in comedies (as opposed to histories and tragedies) are characterised by polite requests (‘please you’) and sharp-minded ‘wit’. Despite many similarities between female and male usage of gendered forms of language (‘woman’), male characters alone use terms such as ‘womanish’ in a disparaging way
Heritability of testosterone levels in 12-year-old twins and its relation to pubertal development
The aim of this study was to estimate the heritability of variation in testosterone levels in 12-year-old children, and to explore the overlap in genetic and environmental influences on circulating testosterone levels and androgen dependent pubertal development. Midday salivary testosterone samples were collected on two consecutive days in a sample of 183 unselected twin pairs. Androgen induced pubertal development was assessed using self report Tanner scales of pubic hair development (boys and girls) and genital development (boys). A significant contribution of genetic effects to the variance in testosterone levels was found.
Heritability was approximately 50% in both boys and girls. The remaining proportion of the variance in testosterone levels could be explained by non-shared environmental influences. The relatively high correlation between testosterone levels of opposite sex dizygotic twins suggests that sex differences in genes influencing variation in testosterone levels have not yet developed in pre- and early puberty. Variance in pubertal development was explained by a large genetic component, moderate shared environmental influences, and a small non-shared environmental effect. Testosterone levels correlated moderately (r = .31) with pubertal development; the covariance between testosterone levels and pubertal development was entirely accounted for by genetic influences
Reply to Comment on "Cosmic rays, carbon dioxide, and climate"
In our analysis [Rahmstorf et al., 2004], we arrived at two main conclusions: the data of Shaviv and Veizer [2003] do not show a significant correlation of cosmic ray flux (CRF) and climate, and the authors' estimate of climate sensitivity to CO2 based on a simple regression analysis is questionable. After careful consideration of Shaviv and Veizer's comment, we want to uphold and reaffirm these conclusions. Concerning the question of correlation, we pointed out that a correlation arose only after several adjustments to the data, including shifting one of the four CRF peaks and stretching the time scale. To calculate statistical significance, we first need to compute the number of independent data points in the CRF and temperature curves being correlated, accounting for their autocorrelation. A standard estimate [Quenouille, 1952] of the number of effective data points is
urn:x-wiley:00963941:media:eost14930:eost14930-math-0001
where N is the total number of data points and r1, r2 are the autocorrelations of the two series. For the curves of Shaviv and Veizer [2003], the result is NEFF = 4.8. This is consistent with the fact that these are smooth curves with four humps, and with the fact that for CRF the position of the four peaks is determined by four spiral arm crossings or four meteorite clusters, respectively; that is, by four independent data points. The number of points that enter the calculation of statistical significance of a linear correlation is (NEFF− 2), since any curves based on only two points show perfect correlation; at least three independent points are needed for a meaningful result
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