71,893 research outputs found
Different Melting Behavior in Pentane and Heptane Monolayers on Graphite; Molecular Dynamics Simulations
Molecular dynamics simulations are utilized to study the melting transition
in pentane (C5H12) and heptane (C7H16), physisorbed onto the basal plane of
graphite at near-monolayer coverages. Through use of the newest, optimized
version of the anisotropic united-atom model (AUA4) to simulate both systems at
two separate coverages, this study provides evidence that the melting
transition for pentane and heptane monolayers are significantly different.
Specifically, this study proposes a very rapid transition from the solid
crystalline rectangular-centered (RC) phase to a fluid phase in pentane
monolayers, whereas heptane monolayers exhibit a slower transition that
involves a more gradual loss of RC order in the solid-fluid phase transition.
Through a study of the melting behavior, encompassing variations where the
formation of gauche defects in the alkyl chains are eliminated, this study
proposes that this gradual melting behavior for heptane monolayers is a result
of less orientational mobility of the heptane molecules in the solid RC phase,
as compared to the pentane molecules. This idea is supported through a study of
a nonane monolayer, which gives the gradual melting signature that heptane
monolayers also seem to indicate. The results of this work are compared to
previous experiment over pentane and heptane monolayers, and are found to be in
good agreement
Recognition of viral glycoproteins by influenza A-specific cross- reactive cytolytic T lymphocytes
Two populations of cytolytic T lymphocytes (CTL) generated after influenza A virus infection can be distinguished into one with specificity for the sensitizing hemagglutinin type and a second with cross-reactivity for antigens induced by other type-A influenza viruses. The molecules carrying the antigenic determinants recognized by the cross-reactive CTL were studied. In L-929 cells abortively infected with fowl plague virus, matrix (M) protein synthesis is specifically inhibited, whereas the envelope glycoproteins, hemagglutinin and neuraminidase, are synthesized and incorporated into the plasma membrane. These target cells were lysed by cross-reactive CTL. The envelope proteins of type A/Victoria virus were separated from the other virion components and reconstituted into lipid vesicles that lacked M protein that subsequently were used to prepare artificial target cells. Target-cell formation with vesicles was achieved by addition of fusion-active Sendai virus. These artificial target cells were also susceptible to lysis by cross-reactive CTL. In contrast to previous observations that suggested that the M protein of influenza viruses is recognized by these effector cells, we present evidence that the antigencic determinants induced by the viral glycoproteins are recognized
On the use of internal state variables in thermoviscoplastic constitutive equations
The general theory of internal state variables are reviewed to apply it to inelastic metals in use in high temperature environments. In this process, certain constraints and clarifications will be made regarding internal state variables. It is shown that the Helmholtz free energy can be utilized to construct constitutive equations which are appropriate for metallic superalloys. Internal state variables are shown to represent locally averaged measures of dislocation arrangement, dislocation density, and intergranular fracture. The internal state variable model is demonstrated to be a suitable framework for comparison of several currently proposed models for metals and can therefore be used to exhibit history dependence, nonlinearity, and rate as well as temperature sensitivity
Collective motion of binary self-propelled particle mixtures
In this study, we investigate the phenomenon of collective motion in binary
mixtures of self-propelled particles. We consider two particle species, each of
which consisting of pointlike objects that propel with a velocity of constant
magnitude. Within each species, the particles try to achieve polar alignment of
their velocity vectors, whereas we analyze the cases of preferred polar,
antiparallel, as well as perpendicular alignment between particles of different
species. Our focus is on the effect that the interplay between the two species
has on the threshold densities for the onset of collective motion and on the
nature of the solutions above onset. For this purpose, we start from suitable
Langevin equations in the particle picture, from which we derive mean field
equations of the Fokker-Planck type and finally macroscopic continuum field
equations. We perform particle simulations of the Langevin equations, linear
stability analyses of the Fokker-Planck and macroscopic continuum equations,
and we numerically solve the Fokker-Planck equations. Both, spatially
homogeneous and inhomogeneous solutions are investigated, where the latter
correspond to stripe-like flocks of collectively moving particles. In general,
the interaction between the two species reduces the threshold density for the
onset of collective motion of each species. However, this interaction also
reduces the spatial organization in the stripe-like flocks. The most
interesting behavior is found for the case of preferred perpendicular alignment
between different species. There, a competition between polar and truly nematic
orientational ordering of the velocity vectors takes place within each particle
species. Finally, depending on the alignment rule for particles of different
species and within certain ranges of particle densities, identical and inverted
spatial density profiles can be found for the two particle species.Comment: 16 pages, 10 figure
Method and apparatus for aligning a laser beam projector Patent
Laser beam projector for continuous, precise alignment between target, laser generator, and astronomical telescope during trackin
Model of hard spheroplatelets near a hard wall
A system of hard spheroplatelets near an impenetrable wall is studied in the
low-density Onsager approximation. Spheroplatelets have optimal shape between
rods and plates, and the direct transition from the isotropic to biaxial
nematic phase is present. A simple local approximation for the one-particle
distribution function is used. Analytical results for the surface tension and
the entropy contributions are derived. The density and the order-parameter
profiles near the wall are calculated. The preferred orientation of the short
molecule axes is perpendicular to the wall. Biaxiality close to the wall can
appear only if the phase is biaxial in the bulk.Comment: 11 pages, 9 figures, revised version published in PR
Method of directing a laser beam with very high accuracy
System will collimate and direct an argon laser beam with high angular tracking accuracy at objects on the moons surface. It can be adapted to missile and satellite tracking
Effect of Image Forces on Polyelectrolyte Adsorption at a Charged Surface
The adsorption of flexible and highly charged polyelectrolytes onto
oppositely charged planar surfaces is investigated by means of Monte Carlo
simulations. The effect of image forces stemming from the dielectric
discontinuity at the substrate interface is considered. The influence, at fixed
polyelectrolyte volume fraction, of chain length and surface-charge density is
also considered. A detailed structural study, including monomer and fluid
charge distributions, is provided. It is demonstrated that image forces can
considerably reduce the degree of polyelectrolyte adsorption and concomitantly
inhibit the charge inversion of the substrate by polyelectrolytes.Comment: 19 pages - 7 eps figs - RevTex 4 - submitted for publicatio
Electron trapping optical data storage system and applications
A new technology developed at Optex Corporation out-performs all other existing data storage technologies. The Electron Trapping Optical Memory (ETOM) media stores 14 gigabytes of uncompressed data on a single, double-sided 130 mm disk with a data transfer rate of up to 120 megabits per second. The disk is removable, compact, lightweight, environmentally stable, and robust. Since the Write/Read/Erase (W/R/E) processes are carried out photonically, no heating of the recording media is required. Therefore, the storage media suffers no deleterious effects from repeated W/R/E cycling. This rewritable data storage technology has been developed for use as a basis for numerous data storage products. Industries that can benefit from the ETOM data storage technologies include: satellite data and information systems, broadcasting, video distribution, image processing and enhancement, and telecommunications. Products developed for these industries are well suited for the demanding store-and-forward buffer systems, data storage, and digital video systems needed for these applications
The Transition between Nonorthogonal Polarization Modes in PSR B2016+28 at 1404 MHz
Polarization observations of the radio emission from PSR B2016+28 at 1404 MHz
reveal properties that are consistent with two, very different, interpretations
of the pulsar's viewing geometry. The pulsar's average polarization properties
show a rapid change in position angle (PA) near the pulse center, suggesting
that the observer's sightline nearly intersects the star's magnetic pole. But
single pulse, polarization observations of the pulsar show nearly orthogonal
modes of polarization following relatively flat and parallel PA trajectories
across the pulse, suggesting that the sightline is far from the pole.
Additionally, PA histograms reveal a "modal connecting bridge", of unknown
origin, joining the modal PA trajectories over much of the pulse and following
the rapid PA change shown in the average data. The nonorthogonality of
polarization modes is incorporated in a statistical model of radio polarization
to account for the deviations from mode orthogonality that are observed in the
pulsar. The model is used to interpret the rapid PA change and modal connecting
bridge as a longitudinally-resolved transition between modes of nonorthogonal
polarization. Thus, the modal PA trajectories are argued to reflect the
pulsar's true viewing geometry. This interpretation is consistent with the
pulsar's morphological classification, preserves the Radhakrishnan & Cooke
model of pulsar radio emission, and avoids the complication that the modal
connecting bridge might be produced by some other emission mechanism. The
statistical model's ability to simulate the rich variety of polarization
properties observed in the emission lends additional support to the model's
applicability and its underlying assumption that the polarization modes occur
simultaneously.Comment: Accepted for publication in Ap
- …