8,299 research outputs found
An exact equilibrium reduced density matrix formulation I: The influence of noise, disorder, and temperature on localization in excitonic systems
An exact method to compute the entire equilibrium reduced density matrix for
systems characterized by a system-bath Hamiltonian is presented. The approach
is based upon a stochastic unraveling of the influence functional that appears
in the imaginary time path integral formalism of quantum statistical mechanics.
This method is then applied to study the effects of thermal noise, static
disorder, and temperature on the coherence length in excitonic systems. As
representative examples of biased and unbiased systems, attention is focused on
the well-characterized light harvesting complexes of FMO and LH2, respectively.
Due to the bias, FMO is completely localized in the site basis at low
temperatures, whereas LH2 is completely delocalized. In the latter, the
presence of static disorder leads to a plateau in the coherence length at low
temperature that becomes increasingly pronounced with increasing strength of
the disorder. The introduction of noise, however, precludes this effect. In
biased systems, it is shown that the environment may increase the coherence
length, but only decrease that of unbiased systems. Finally it is emphasized
that for typical values of the environmental parameters in light harvesting
systems, the system and bath are entangled at equilibrium in the single
excitation manifold. That is, the density matrix cannot be described as a
product state as is often assumed, even at room temperature. The reduced
density matrix of LH2 is shown to be in precise agreement with the steady state
limit of previous exact quantum dynamics calculations.Comment: 37 pages, 12 figures. To appear in Phys. Rev.
Derivation of Boltzmann Principle
We present a derivation of Boltzmann principle
based on classical mechanical models of thermodynamics. The argument is based
on the heat theorem and can be traced back to the second half of the nineteenth
century with the works of Helmholtz and Boltzmann. Despite its simplicity, this
argument has remained almost unknown. We present it in a modern, self-contained
and accessible form. The approach constitutes an important link between
classical mechanics and statistical mechanics
VLBA imaging of the 3mm SiO maser emission in the disk-wind from the massive protostellar system Orion Source I
We present the first images of the 28SiO v=1, J=2-1 maser emission around the
closest known massive young stellar object Orion Source I observed at 86 GHz
(3mm) with the VLBA. These images have high spatial (~0.3 mas) and spectral
(~0.054 km/s) resolutions. We find that the 3mm masers lie in an X-shaped locus
consisting of four arms, with blue-shifted emission in the south and east arms
and red-shifted emission in the north and west arms. Comparisons with previous
images of the 28SiO v=1,2, J=1-0 transitions at 7mm (observed in 2001-2002)
show that the bulk of the J=2-1 transition emission follows the streamlines of
the J=1-0 emission and exhibits an overall velocity gradient consistent with
the gradient at 7mm. While there is spatial overlap between the 3mm and 7mm
transitions, the 3mm emission, on average, lies at larger projected distances
from Source I (~44 AU compared with ~35 AU for 7mm). The spatial overlap
between the v=1, J=1-0 and J=2-1 transitions is suggestive of a range of
temperatures and densities where physical conditions are favorable for both
transitions of a same vibrational state. However, the observed spatial offset
between the bulk of emission at 3mm and 7mm possibly indicates different ranges
of temperatures and densities for optimal excitation of the masers. We discuss
different maser pumping models that may explain the observed offset. We
interpret the 3mm and 7mm masers as being part of a single wide-angle outflow
arising from the surface of an edge-on disk rotating about a
northeast-southwest axis, with a continuous velocity gradient indicative of
differential rotation consistent with a Keplerian profile in a high-mass
proto-binary.Comment: 11 pages, 12 figures; accepted for publication in A&
Origin of entropy convergence in hydrophobic hydration and protein folding
An information theory model is used to construct a molecular explanation why
hydrophobic solvation entropies measured in calorimetry of protein unfolding
converge at a common temperature. The entropy convergence follows from the weak
temperature dependence of occupancy fluctuations for molecular-scale volumes in
water. The macroscopic expression of the contrasting entropic behavior between
water and common organic solvents is the relative temperature insensitivity of
the water isothermal compressibility. The information theory model provides a
quantitative description of small molecule hydration and predicts a negative
entropy at convergence. Interpretations of entropic contributions to protein
folding should account for this result.Comment: Phys. Rev. Letts. (in press 1996), 3 pages, 3 figure
DE 1 RIMS operational characteristics
The Retarding Ion Mass Spectrometer (RIMS) on the Dynamics Explorer 1 spacecraft observes both the thermal and superthermal (50 eV) ions of the ionosphere and inner magnetosphere. It is capable of measuring the detailed species distribution function of these ions in many cases. It was equipped with an integral electrometer to permit in-flight calibration of the detector sensitivities and variations thereof. A guide to understanding the RIMS data set is given. The reduction process from count rates to physical quantities is discussed in some detail. The procedure used to establish in-flight calibration is described, and results of a comparison with densities from plasma wave measurements are provided. Finally, a discussion is provided of various anomalies in the data set, including changes of channeltron efficiency with time, spin modulation of the axial sensor heads, apparent potential differences between the sensor heads, and failures of the radial head retarding potential sweep and of the -Z axial head aperture plane bias. Studies of the RIMS data set should be conducted only with a thorough awareness of the material presented here, or in collaboration with one of the scientists actively involved with RIMS data analysis
Implementation of the Hierarchical Reference Theory for simple one-component fluids
Combining renormalization group theoretical ideas with the integral equation
approach to fluid structure and thermodynamics, the Hierarchical Reference
Theory is known to be successful even in the vicinity of the critical point and
for sub-critical temperatures. We here present a software package independent
of earlier programs for the application of this theory to simple fluids
composed of particles interacting via spherically symmetrical pair potentials,
restricting ourselves to hard sphere reference systems. Using the hard-core
Yukawa potential with z=1.8/sigma for illustration, we discuss our
implementation and the results it yields, paying special attention to the core
condition and emphasizing the decoupling assumption's role.Comment: RevTeX, 16 pages, 2 figures. Minor changes, published versio
Experiencing Audio Recorded Research (EARR): Giving Voice to Qualitative Poster Presentations
Qualitative research emphasizes and honors the words of participants in an effort to generate meaning and knowledge, yet participants’ voices are rarely heard beyond data collection and analysis. We explore the potential to share participants\u27 voices when disseminating research through audio - enhanced poster presentations. Technological advancements in multimedia could revolutionize poster presentations, especially for qualitative research. We describe the history of audio guides and how they can be applied to the dissemination of qualitative research. We also introduce the Experiencing Audio Recorded Research (EARR) Model to facilitate designing a multisensory approach to qualitative data dissemination through integrating audio technology into presentations
1861-10-04 L.H. Chandler recommends Samuel Lovejoy for a position as hospital steward
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