153,361 research outputs found
New operational modes for the Ta2O5-based electrolyte conductance cell
Based on the recently presented conductance cell, two specific operational modes are proposed. In the oscillator mode, the conductivity of the electrolyte determines the frequency of an oscillator, experimentally obtaining a shift from 10 to 27 kHz for a KCl concentration range from 0.5 to 100 mM. In the pole mode, an inductor is placed in series with the cell, giving the real electrolyte resistance at the resonance frequency of the circuit, resulting in a linear relation between the log of the output voltage from 4 to 1000 mV as a function of the log of the KCl concentration, ranging from 0.2 to 100 mM
Compression properties of polymeric syntactic foam composites under cyclic loading
Syntactic foams are composite materials frequently used in applications
requiring the properties of low density and high damage tolerance. In the
present work, polymer-based syntactic foams were studied under cyclic
compression in order to investigate their compressibility, recoverability,
energy dissipation and damage tolerance. These syntactic foams were
manufactured by adding hollow polymer microspheres of various sizes and wall
thicknesses into a polyurethane matrix. The associated loading and unloading
curves during cyclic testing were recorded, revealing the viscoelastic nature
of the materials. SEM images of the samples were obtained in order to study
potential damage mechanisms during compression. It was observed that these
syntactic foams exhibit high elastic recovery and energy dissipation over a
wide range of compressional strains and the addition of polymer microspheres
mitigate the damage under compressional loading.Comment: 25 pages, 13 figure
NGC1333/IRAS4: A multiple star formation laboratory
We present SCUBA observations of the protomultiple system NGC1333/IRAS4 at
450um and 850um. The 850um map shows significant extended emission which is
most probably a remnant of the initial cloud core. At 450um, the component 4A
is seen to have an elongated shape suggestive of a disk. Also we confirm that
in addition to the 4A and 4B system, there exists another component 4C, which
appears to lie out of the plane of the system and of the extended emission.
Deconvolution of the beam reveals a binary companion to IRAS4B. Simple
considerations of binary dynamics suggest that this triple 4A-4BI-4BII system
is unstable and will probably not survive in its current form. Thus IRAS4
provides evidence that systems can evolve from higher to lower multiplicity as
they move towards the main sequence. We construct a map of spectral index from
the two wavelengths, and comment on the implications of this for dust evolution
and temperature differences across the map. There is evidence that in the
region of component 4A the dust has evolved, probably by coagulating into
larger or more complex grains. Furthermore, there is evidence from the spectral
index maps that dust from this object is being entrained in its associated
outflow.Comment: 10 pages, 10 figures. To appear in MNRAS. Uses mn.sty. Also available
at http://www.astro.phys.ethz.ch/papers/smith/smith_p_m.htm
Variable-camber systems integration and operational performance of the AFTI/F-111 mission adaptive wing
The advanced fighter technology integration, the AFTI/F-111 aircraft, is a preproduction F-111A testbed research airplane that was fitted with a smooth variable-camber mission adaptive wing. The camber was positioned and controlled by flexing the upper skins through rotary actuators and linkages driven by power drive units. The wing camber and control system are described. The measured servoactuator frequency responses are presented along with analytical predictions derived from the integrated characteristics of the control elements. A mission adaptive wing system chronology is used to illustrate and assess the reliability and dependability of the servoactuator system during 1524 hours of ground tests and 145 hours of flight testing
Discrepancies in Determinations of the Ginzburg-Landau Parameter
Long-standing discrepancies within determinations of the Ginzburg-Landau
parameter from supercritical field measurements on superconducting
microspheres are reexamined. The discrepancy in tin is shown to result from
differing methods of analyses, whereas the discrepancy in indium is a
consequence of significantly differing experimental results. The reanalyses
however confirms the lower determinations to within experimental
uncertainties.Comment: submitted to Phys. Rev.
Effects of lattice mismatch on interfacial structures of liquid and solidified Al in contact with hetero-phase substrates: MD simulations
Published under licence in IOP Conference Series: Material Science and Engineering by IOP Publishing Ltd. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.In this study, the effects of the misfit on in-plane structures of liquid Al and interfacial structure of solidified Al in contact with the heterophase substrates have been investigated, using molecular dynamics (MD) simulations. The MD simulations were conducted for Al/fcc (111) substrates with varied misfits. The order parameter and atomic arrangement indicated that the in-plane ordering of the liquid at the interface decreases significantly with an increase of the misfit, i.e., solid-like for small misfit and liquid-like for large misfit. Further, our MD simulation results revealed that a perfect orientation relationship forms at the interface between the substrate and the solidified Al for a misfit of less than -3% and the boundary is coherent. With an increase in the misfit, Shockley partial and extended dislocations form at the interface, and the boundary becomes a semi-coherent or low-angle twist boundary.EPSR
Coherent Imaging Spectroscopy of a Quantum Many-Body Spin System
Quantum simulators, in which well controlled quantum systems are used to
reproduce the dynamics of less understood ones, have the potential to explore
physics that is inaccessible to modeling with classical computers. However,
checking the results of such simulations will also become classically
intractable as system sizes increase. In this work, we introduce and implement
a coherent imaging spectroscopic technique to validate a quantum simulation,
much as magnetic resonance imaging exposes structure in condensed matter. We
use this method to determine the energy levels and interaction strengths of a
fully-connected quantum many-body system. Additionally, we directly measure the
size of the critical energy gap near a quantum phase transition. We expect this
general technique to become an important verification tool for quantum
simulators once experiments advance beyond proof-of-principle demonstrations
and exceed the resources of conventional computers
Mid-infrared Imaging of a Circumstellar Disk Around HR 4796: Mapping the Debris of Planetary Formation
We report the discovery of a circumstellar disk around the young A0 star, HR
4796, in thermal infrared imaging carried out at the W.M. Keck Observatory. By
fitting a model of the emission from a flat dusty disk to an image at
lambda=20.8 microns, we derive a disk inclination, i = 72 +6/-9 deg from face
on, with the long axis of emission at PA 28 +/-6 deg. The intensity of emission
does not decrease with radius as expected for circumstellar disks but increases
outward from the star, peaking near both ends of the elongated structure. We
simulate this appearance by varying the inner radius in our model and find an
inner hole in the disk with radius R_in = 55+/-15 AU. This value corresponds to
the radial distance of our own Kuiper belt and may suggest a source of dust in
the collision of cometesimals. By contrast with the appearance at 20.8 microns,
excess emission at lambda = 12.5 microns is faint and concentrated at the
stellar position. Similar emission is also detected at 20.8 microns in residual
subtraction of the best-fit model from the image. The intensity and ratio of
flux densities at the two wavelengths could be accounted for by a tenuous dust
component that is confined within a few AU of the star with mean temperature of
a few hundred degrees K, similar to that of zodiacal dust in our own solar
system. The morphology of dust emission from HR 4796 (age 10 Myr) suggests that
its disk is in a transitional planet-forming stage, between that of massive
gaseous proto-stellar disks and more tenuous debris disks such as the one
detected around Vega.Comment: 9 pages, 4 figures as LaTex manuscript and postscript files in
gzipped tar file. Accepted for publication in Astrophysical Journal Letters.
http://upenn5.hep.upenn.edu/~davidk/hr4796.htm
Random Topologies and the emergence of cooperation: the role of short-cuts
We study in detail the role of short-cuts in promoting the emergence of
cooperation in a network of agents playing the Prisoner's Dilemma Game (PDG).
We introduce a model whose topology interpolates between the one-dimensional
euclidean lattice (a ring) and the complete graph by changing the value of one
parameter (the probability p to add a link between two nodes not already
connected in the euclidean configuration). We show that there is a region of
values of p in which cooperation is largely enhanced, whilst for smaller values
of p only a few cooperators are present in the final state, and for p
\rightarrow 1- cooperation is totally suppressed. We present analytical
arguments that provide a very plausible interpretation of the simulation
results, thus unveiling the mechanism by which short-cuts contribute to promote
(or suppress) cooperation
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