2,025 research outputs found
Molecular dynamics simulations of the evaporation of particle-laden droplets
We use molecular dynamics simulations to study the evaporation of
particle-laden droplets on a heated surface. The droplets are composed of a
Lennard-Jones fluid containing rigid particles which are spherical sections of
an atomic lattice, and heating is controlled through the temperature of an
atomistic substrate. We observe that sufficiently large (but still nano-sized)
particle-laden drops exhibit contact line pinning, measure the outward fluid
flow field which advects particle to the drop rim, and find that the structure
of the resulting aggregate varies with inter-particle interactions. In
addition, the profile of the evaporative fluid flux is measured with and
without particles present, and is also found to be in qualitative agreement
with earlier theory. The compatibility of simple nanoscale calculations and
micron-scale experiments indicates that molecular simulation may be used to
predict aggregate structure in evaporative growth processes
Shear flow pumping in open microfluidic systems
We propose to drive open microfluidic systems by shear in a covering fluid
layer, e.g., oil covering water-filled chemical channels. The advantages as
compared to other means of pumping are simpler forcing and prevention of
evaporation of volatile components. We calculate the expected throughput for
straight channels and show that devices can be built with off-the-shelf
technology. Molecular dynamics simulations suggest that this concept is
scalable down to the nanoscale.Comment: 4 pages, 4 figure, submitted to Phys. Rev. Let
Static Torsion Testing and Modeling of a Variable Thickness Hybrid Composite Bull Gear
Torsional strength of a variable thickness hybrid gear web was measured by performing static testing on the part in a large torsion test frame. The outer rim of the hybrid gear web was fixed to the bottom of the test frame and loading was applied to the web through a shaft. The test setup included the installation of digital image correlation (DIC) systems to obtain deformation and strain measurements from the surfaces of the hybrid gear web and the mechanical test equipment to ensure reliability of the test. The results indicated that the variable thickness hybrid gear web achieved approximately twice the torsional strength compared to that of previous hybrid gear designs. The DIC analysis showed significantly more straining of the loading shaft than the actual test article. Additionally, the results demonstrated the importance and affect that the metallic, lobed interlock features had on the principal strain and out-of-plane displacement fields. The analysis revealed that the fixed outer rim was in fact rotating and a rigid body motion compensation (RBMC) function was computed to determine the actual rotation of the hub and composite web relative to the outer rim. Modeling simulations were performed for the variable thickness hybrid gear web and correlated well with the RBMC rotational deformation seen in the DIC analysis. In addition to benchmarking the load capacity of the hybrid gear web, measuring its strength is useful information to define the parameters needed for dynamic, endurance, and other testing of the part
Harnessing post-translational modifications for next-generation HIV immunogens
The extensive post-translational modifications of the envelope spikes of the human immunodeficiency virus (HIV) present considerable challenges and opportunities for HIV vaccine design. These oligomeric glycoproteins typically have over 30 disulfide bonds and around a 100 N-linked glycosylation sites, and are functionally dependent on protease cleavage within the secretory system. The resulting mature structure adopts a compact fold with the vast majority of its surface obscured by a protective shield of glycans which can be targeted by broadly neutralizing antibodies (bnAbs). Despite the notorious heterogeneity of glycosylation, rare B-cell lineages can evolve to utilize and cope with viral glycan diversity, and these structures therefore present promising targets for vaccine design. The latest generation of recombinant envelope spike mimetics contains re-engineered post-translational modifications to present stable antigens to guide the development of bnAbs by vaccination
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An Analysis of How Students Take the Initiative in Keyboard-to-Keyboard Tutorial Dialogues in a Fixed Domain
By student initiatives we mean productions which the student could reasonably expect to modify the course of the tutorial dialog;ue. Asking a question is one kind of student initiative. This paper describes a system called CircSim-Tutor which we are building, the background of the project, the 28 hour-long tutoring sessions jmalyzed in this paper, and the analysis done. It compares our work to previous work, gives a classification of the student initiatives found and of the tutor's responses to them, and discusses some examples
Radial Temperature Profiles of X-Ray--Emitting Gas Within Clusters of Galaxies
Previous analyses of ASCA data of clusters of galaxies have found conflicting
results regarding the slope of the temperature profile of the hot X-ray gas
within clusters, mainly because of the large, energy-dependent point spread
function (PSF) of the ASCA mirrors. We present a summary of all ASCA-determined
cluster temperature profiles found in the literature, and find a discrepancy in
the radial temperature trend of clusters based on which PSF-correction routine
is used. This uncertainty in the cluster temperature profile in turn can lead
to large uncertainties in the amount of dark matter in clusters. In this study,
we have used ROSAT PSPC data to obtain independent relative temperature
profiles for 26 clusters, most of which have had their temperature profiles
determined by ASCA. Our aim is not to measure the actual temperature values of
the clusters, but to use X-ray color profiles to search for a hardening or
softening of the spectra with radius for comparison to ASCA-derived profiles.
The radial color profiles indicate that outside of the cooling flow region, the
temperature profiles of clusters are in general constant. Within 35% of the
virial radius, we find a temperature drop of 20% at 10 keV and 12% at 5 keV can
be ruled out at the 99% confidence level. A subsample of non-cooling flow
clusters shows that the condition of isothermality applies at very small radii
too, although cooling gas complicates this determination in the cooling flow
subsample. The colors predicted from the temperature profiles of a series of
hydrodynamical cluster simulations match the data very well, although they
cannot be used to discriminate among different cosmologies. An additional
result is that the color profiles show evidence for a central peak in
metallicity in low temperature clusters.Comment: 39 pages, 15 embedded Postscript figures, uses aaspp4.sty, accepted
for publication in Astrophysical Journa
Parallel TREE code for two-component ultracold plasma analysis
The TREE method has been widely used for long-range interaction {\it N}-body
problems. We have developed a parallel TREE code for two-component classical
plasmas with open boundary conditions and highly non-uniform charge
distributions. The program efficiently handles millions of particles evolved
over long relaxation times requiring millions of time steps. Appropriate domain
decomposition and dynamic data management were employed, and large-scale
parallel processing was achieved using an intermediate level of granularity of
domain decomposition and ghost TREE communication. Even though the
computational load is not fully distributed in fine grains, high parallel
efficiency was achieved for ultracold plasma systems of charged particles. As
an application, we performed simulations of an ultracold neutral plasma with a
half million particles and a half million time steps. For the long temporal
trajectories of relaxation between heavy ions and light electrons, large
configurations of ultracold plasmas can now be investigated, which was not
possible in past studies
Multipartite entanglement in the 1-D spin- Heisenberg Antiferromagnet
Multipartite entanglement refers to the simultaneous entanglement between
multiple subsystems of a many-body quantum system. While multipartite
entanglement can be difficult to quantify analytically, it is known that it can
be witnessed through the Quantum Fisher information (QFI), a quantity that can
also be related to dynamical Kubo response functions. In this work, we first
show that the finite temperature QFI can generally be expressed in terms of a
static structure factor of the system, plus a correction that vanishes as
. We argue that this implies that the static structure factor
witnesses multipartite entanglement near quantum critical points at
temperatures below a characteristic energy scale that is determined by
universal properties, up to a non-universal amplitude. Therefore, in systems
with a known static structure factor, we can deduce finite temperature scaling
of multipartite entanglement and low temperature entanglement depth without
knowledge of the full dynamical response function of the system. This is
particularly useful to study 1D quantum critical systems in which sub-power-law
divergences can dominate entanglement growth, where the conventional scaling
theory of the QFI breaks down. The 1D spin- antiferromagnetic
Heisenberg model is an important example of such a system, and we show that
multipartite entanglement in the Heisenberg chain diverges non-trivially as
. We verify these predictions with calculations of the
QFI using conformal field theory and matrix product state simulations. Finally
we discuss the implications of our results for experiments to probe
entanglement in quantum materials, comparing to neutron scattering data in
KCuF, a material well-described by the Heisenberg chain.Comment: 8 pages and 3 figures; 1 page and 1 figure of the appendix; typos
corrected; references adde
Report of the panel on geopotential fields: Gravity field, section 8
The objective of the Geopotential Panel was to develop a program of data acquisition and model development for the Earth's gravity and magnetic fields that meet the basic science requirements of the solid Earth and ocean studies. Presented here are the requirements for gravity information and models through the end of the century, the present status of our knowledge, data acquisition techniques, and an outline of a program to meet the requirements
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