6,681 research outputs found
Simultaneous Brownian Motion of N Particles in a Temperature Gradient
A system of N Brownian particles suspended in a nonuniform heat bath is
treated as a thermodynamic system whith internal degrees of freedom, in this
case their velocities and coordinates. Applying the scheme of non-equilibrium
thermodynamics, one then easily obtains the Fokker-Planck equation for
simultaneous Brownian motion of N particles in a temperature gradient. This
equation accounts for couplings in the motion as a result of hydrodynamic
interactions between particles.Comment: 9 pages, RevTe
Multiscaling for Classical Nanosystems: Derivation of Smoluchowski and Fokker-Planck Equations
Using multiscale analysis and methods of statistical physics, we show that a
solution to the N-atom Liouville Equation can be decomposed via an expansion in
terms of a smallness parameter epsilon, wherein the long scale time behavior
depends upon a reduced probability density that is a function of slow-evolving
order parameters. This reduced probability density is shown to satisfy the
Smoluchowski equation up to order epsilon squared for a given range of initial
conditions. Furthermore, under the additional assumption that the nanoparticle
momentum evolves on a slow time scale, we show that this reduced probability
density satisfies a Fokker-Planck equation up to the same order in epsilon.
This approach applies to a broad range of problems in the nanosciences.Comment: 23 page
The two-body problem of ultra-cold atoms in a harmonic trap
We consider two bosonic atoms interacting with a short-range potential and
trapped in a spherically symmetric harmonic oscillator. The problem is exactly
solvable and is relevant for the study of ultra-cold atoms. We show that the
energy spectrum is universal, irrespective of the shape of the interaction
potential, provided its range is much smaller than the oscillator length.Comment: Final version accepted for publication in Am. Journ. Phy
Alien Registration- Shea, William P. (Houlton, Aroostook County)
https://digitalmaine.com/alien_docs/34899/thumbnail.jp
Monitoring the wetland landscape: white-faced ibis (Plegadis chihi) breeding habitat as a model assemblage
Wetlands structure landscape biodiversity by providing critical habitat to numerous fish and wildlife species. However, climate change, growing human populations, and shifting land use practices strain limited water supplies that sustain wetlands in the semi-arid western US. Conserving a wetland network with prominent value to wildlife is paramount to ensure future security of habitat and ecosystem processes. Here, I use white-faced ibis (Plegadis chihi; hereafter ‘ibis’) breeding colonies as a model system to identify and monitor a landscape-scale wetland network across the semi-arid western US. Ibis serve an important role in marking ecologically important wetland networks because they require a wide range of wetland habitats near colony locations for nesting and foraging. My analysis encompasses 153 breeding colonies in eight regions, derived from ecoregions, located on private and public lands. I evaluate long- term (1988-2020) patterns of wetland availability at ibis breeding colonies using surface water as a proxy for wetland flooding. Surface water trends are examined based on individual colony, region, ownership, hydrology (i.e. annual duration of wetland flooding), and wetland types (e.g. flood-irrigated agriculture, managed wetlands). To identify landscape drivers influencing flooding patterns, I link long-term trends to regional climate and anthropogenic factors. Analysis shows that approximately 60% of individual colony locations experienced wetland drying, and 5 of the 8 regions showed significant declines in wetland availability. Snow-water equivalent, daily minimum temperature, and irrigation were prevalent drivers of wetland trends. Publicly managed wildlife refuges, a central component to the colony network, were specifically impacted by patterns of wetland drying. These areas provide important over-water nesting locations in semi- permanent wetlands. Additionally, declines in flood-irrigated agriculture impacted adjacent ibis colonies through reduced foraging habitat. While underlying mechanisms influencing individual wetland sites are complex, pervasive drying of nesting and foraging habitat imperils the wetland network resiliency. Regional coordination and private-public partnerships are key to the long- term viability of a wetland network that benefits ibis and numerous other wetland-dependent species
Energy and Atomic Number Dependence of Electron Depth-Dose and Lateral-Dose Function
A review of available Depth-Dose functions determined both experimentally and by Monte-Carlo simulation in a variety of materials reveals that, although there is general agreement as to the shape of the function, there is considerable disagreement concerning quantitative measures such as the range of the incident electrons and the position of the maximum of the Depth-Dose curve relative to the range. This finding is contrary to the typical assumption that the shape of the Depth-Dose curve is not dependent on the beam energy and only slightly dependent on the target material
Low Frequency Radio Constraints on the Synchrotron Cosmic Web
We present a search for the synchrotron emission from the synchrotron cosmic
web by cross correlating 180MHz radio images from the Murchison Widefield Array
with tracers of large scale structure (LSS). We use two versions of the radio
image covering degrees with point sources brighter than
0.05 Jy subtracted, with and without filtering of Galactic emission. As tracers
of the LSS we use the Two-Micron-All-Sky-Survey (2MASS) and the Widefield
InfraRed Explorer (WISE) redshift catalogues to produce galaxy number density
maps. The cross correlation functions all show peak amplitudes at zero degrees,
decreasing with varying slopes towards zero correlation over a range of one
degree. The cross correlation signals include components from point source,
Galactic, and extragalactic diffuse emission. We use models of the diffuse
emission from smoothing the density maps with Gaussians of sizes 1-4 Mpc to
find limits on the cosmic web components. From these models we find surface
brightness 99.7 per cent upper limits in the range of 0.09-2.20 mJy beam
(average beam size of 2.6 arcmin), corresponding to 0.01-0.30 mJy
arcmin. Assuming equipartition between energy densities of cosmic rays
and the magnetic field, the flux density limits translate to magnetic field
strength limits of 0.03-1.98 G, depending heavily on the spectral index.
We conclude that for a 3 detection of 0.1 G magnetic field
strengths via cross correlations, image depths of sub-mJy to sub-Jy are
necessary. We include discussion on the treatment and effect of extragalactic
point sources and Galactic emission, and next steps for building on this work.Comment: 25 pages, 18 figures, 4 tables, accepted for publication in MNRA
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