48,626 research outputs found
Transport in ultradilute solutions of He in superfluid He
We calculate the effect of a heat current on transporting He dissolved in
superfluid He at ultralow concentration, as will be utilized in a proposed
experimental search for the electric dipole moment of the neutron (nEDM). In
this experiment, a phonon wind will generated to drive (partly depolarized)
He down a long pipe. In the regime of He concentrations and temperatures K, the phonons comprising the heat current
are kept in a flowing local equilibrium by small angle phonon-phonon
scattering, while they transfer momentum to the walls via the He first
viscosity. On the other hand, the phonon wind drives the He out of local
equilibrium via phonon-He scattering. For temperatures below K, both
the phonon and He mean free paths can reach the centimeter scale, and we
calculate the effects on the transport coefficients. We derive the relevant
transport coefficients, the phonon thermal conductivity and the He
diffusion constants from the Boltzmann equation. We calculate the effect of
scattering from the walls of the pipe and show that it may be characterized by
the average distance from points inside the pipe to the walls. The temporal
evolution of the spatial distribution of the He atoms is determined by the
time dependent He diffusion equation, which describes the competition
between advection by the phonon wind and He diffusion. As a consequence of
the thermal diffusivity being small compared with the He diffusivity, the
scale height of the final He distribution is much smaller than that of the
temperature gradient. We present exact solutions of the time dependent
temperature and He distributions in terms of a complete set of normal
modes.Comment: NORDITA PREPRINT 2015-37, 9 pages, 6 figure
Transport in very dilute solutions of He in superfluid He
Motivated by a proposed experimental search for the electric dipole moment of
the neutron (nEDM) utilizing neutron-He capture in a dilute solution of
He in superfluid He, we derive the transport properties of dilute
solutions in the regime where the He are classically distributed and rapid
He-He scatterings keep the He in equilibrium. Our microscopic
framework takes into account phonon-phonon, phonon-He, and He-He
scatterings. We then apply these calculations to measurements by Rosenbaum et
al. [J.Low Temp.Phys. {\bf 16}, 131 (1974)] and by Lamoreaux et al.
[Europhys.Lett. {\bf 58}, 718 (2002)] of dilute solutions in the presence of a
heat flow. We find satisfactory agreement of theory with the data, serving to
confirm our understanding of the microscopics of the helium in the future nEDM
experiment.Comment: 10 pages, 5 figures, v
Low Temperature Transport Properties of Very Dilute Classical Solutions of He in Superfluid He
We report microscopic calculations of the thermal conductivity, diffusion
constant and thermal diffusion constant for classical solutions of He in
superfluid He at temperatures T \la 0.6~K, where phonons are the dominant
excitations of the He. We focus on solutions with He concentrations
\la \,10^{-3}, for which the main scattering mechanisms are phonon-phonon
scattering via 3-phonon Landau and Beliaev processes, which maintain the
phonons in a drifting equilibrium distribution, and the slower process of
He-phonon scattering, which is crucial for determining the He
distribution function in transport. We use the fact that the relative changes
in the energy and momentum of a He atom in a collision with a phonon are
small to derive a Fokker-Planck equation for the He distribution function,
which we show has an analytical solution in terms of Sonine polynomials. We
also calculate the corrections to the Fokker-Planck results for the transport
coefficients.Comment: 29 pages, 2 figure
The Infrared Nucleus of the Wolf-Rayet Galaxy Henize 2-10
We have obtained near-infrared images and mid-infrared spectra of the
starburst core of the dwarf Wolf-Rayet galaxy He 2-10. We find that the
infrared continuum and emission lines are concentrated in a flattened ellipse
3-4'' or 150 pc across which may show where a recent accretion event has
triggered intense star formation. The ionizing radiation from this cluster has
an effective temperature of 40,000 K, corresponding to stars, and
the starburst is years old.Comment: 17 pages Latex, 7 postscript figures, 1 postscript table, accepted to
A
Phase II of the ASCE Benchmark Study on SHM
The task group on structural health monitoring of the Dynamic Committee of ASCE was formed in
1999 at the 12
th
Engineering Mechanics Conference. The task group has designed a number of analytical
studies on a benchmark structure and there are plans to follow these with an experimental program. The
first phase of the analytical studies was completed in 2001. The second phase, initiated in the summer of
2001, was formulated in the light of the experience gained on phase I and focuses on increasing realism in
the simulation of the discrepancies between the actual structure and the mathematical model used in the
analysis. This paper describes the rational that lead the SHM task group to the definition of phase II and
presents the details of the cases that are being considered
Parity-Violating Electron Scattering and Neucleon Structure
The measurement of parity violation in the helicity dependence of
electron-nucleon scattering provides unique information about the basic quark
structure of the nucleons. In this review, the general formalism of
parity-violating electron scattering is presented, with emphasis on elastic
electron-nucleon scattering. The physics issues addressed by such experiments
is discussed, and the major goals of the presently envisioned experimental
program are identified. %General aspects of the experimental technique are
reviewed and A summary of results from a recent series of experiments is
presented and the future prospects of this program are also discussed.Comment: 45 pages, 9 figure
A Descriptive Study of the Population Dynamics of Adult \u3ci\u3eDiabrotica Virgifera Virgifera\u3c/i\u3e (Coleoptera: Chrysomelidae) in Artificially Infested Corn Fields
The influence of corn plant phenology on the dynamics of adult western corn rootworm, Diabrotica virgifera virgifera, populations was studied during 1988 and 1989 in com fields artificially infested with eggs. Fifty percent of adult emergence from the soil occurred by day 194 in 1988 and day 203 in 1989. In both years, adult emergence was synchronized with corn flowering, eggs were recovered in soil samples approximately four days after reproductive females were first observed in the population, and oviposition was essentially complete about 25 days after it began. The number of reproductive female beetle-days accumulating per m2 was similar in both years. Approximately two times as many eggs were laid in 1988 (1239 eggs 1m2) as in 1989 (590 eggs 1m2). The difference in egg density may have been caused by differences among years in the temporal synchrony of reproductive beetles with flowering corn. Daily survival rates of adults were high while corn was flowering; exhibited a gradual decline during grain filling; and decreased rapidly during the grain drying stage
Comment on Photothermal radiometry parametric identifiability theory for reliable and unique nondestructive coating thickness and thermophysical measurements, J. Appl. Phys. 121(9), 095101 (2017)
A recent paper [X. Guo, A. Mandelis, J. Tolev and K. Tang, J. Appl. Phys.,
121, 095101 (2017)] intends to demonstrate that from the photothermal
radiometry signal obtained on a coated opaque sample in 1D transfer, one should
be able to identify separately the following three parameters of the coating:
thermal diffusivity, thermal conductivity and thickness. In this comment, it is
shown that the three parameters are correlated in the considered experimental
arrangement, the identifiability criterion is in error and the thickness
inferred therefrom is not trustable.Comment: 3 page
Hybrid Atom--Photon Quantum Gate in a Superconducting Microwave Resonator
We propose a novel hybrid quantum gate between an atom and a microwave photon
in a superconducting coplanar waveguide cavity by exploiting the strong
resonant microwave coupling between adjacent Rydberg states. Using
experimentally achievable parameters gate fidelities are possible on
sub-s timescales for waveguide temperatures below 40 mK. This provides a
mechanism for generating entanglement between two disparate quantum systems and
represents an important step in the creation of a hybrid quantum interface
applicable for both quantum simulation and quantum information processing.Comment: 4 pages, 4 figure
Simulation of an 1857-like Mw 7.9 San Andreas Fault Earthquake and the Response of Tall Steel Moment Frame Buildings in Southern California â A Prototype Study
In 1857, an earthquake of magnitude 7.9 occurred on the San Andreas fault, starting at Parkfield and rupturing
in a southeasterly direction for more than 360 km. Such a unilateral rupture produces significant directivity
toward the San Fernando and Los Angeles basins. The strong shaking in the basins due to this earthquake
would have had significant long-period content (2-8 s), and the objective of this study is to quantify the impact
of such an earthquake on two 18-story steel moment frame building models, hypothetically located at 636 sites
on a 3.5 km grid in southern California. End-to-end simulations include modeling the source and rupture of a
fault at one end, numerically propagating the seismic waves through the earth structure, simulating the damage
to engineered structures and estimating the economic impact at the other end using high-performance computing.
In this prototype study, we use an inferred finite source model of the magnitude 7.9, 2002 Denali fault
earthquake in Alaska, and map it onto the San Andreas fault with the rupture originating at Parkfield and
propagating southward over a distance of 290 km. Using the spectral element seismic wave propagation code,
SPECFEM3D, we simulate an 1857-like earthquake on the San Andreas fault and compute ground motions at
the 636 analysis sites. Using the nonlinear structural analysis program, FRAME3D, we subsequently analyze
3-D structural models of an existing tall steel building designed using the 1982 Uniform Building Code (UBC),
as well as one designed according to the 1997 UBC, subjected to the computed ground motion at each of these
sites. We summarize the performance of these structural models on contour maps of peak interstory drift.
We then perform an economic loss analysis for the two buildings at each site, using the Matlab Damage and
Loss Analysis (MDLA) toolbox developed to implement the PEER loss-estimation methodology. The toolbox
includes damage prediction and repair cost estimation for structural and non-structural components and allows
for the computation of the mean and variance of building repair costs conditional on engineering demand
parameters (i.e. inter-story drift ratios and peak floor accelerations). Here, we modify it to treat steel-frame
high-rises, including aspects such as mechanical, electrical and plumbing systems, traction elevators, and the
possibility of irreparable structural damage. We then generate contour plots of conditional mean losses for the
San Fernando and the Los Angeles basins for the pre-Northridge and modern code-designed buildings, allowing
for comparison of the economic effects of the updated code for the scenario event. In principle, by simulating
multiple seismic events, consistent with the probabilistic seismic hazard for a building site, the same basic
approach could be used to quantify the uncertain losses from future earthquakes
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