10,070 research outputs found
On the Initial Stages of the Densification and Lithification of Sediments
Peer reviewedPostprin
Structure and thermodynamics of colloid-polymer mixtures: a macromolecular approach
The change of the structure of concentrated colloidal suspensions upon
addition of non-adsorbing polymer is studied within a two-component,
Ornstein-Zernicke based liquid state approach. The polymers' conformational
degrees of freedom are considered and excluded volume is enforced at the
segment level. The polymer correlation hole, depletion layer, and excess
chemical potentials are described in agreement with polymer physics theory in
contrast to models treating the macromolecules as effective spheres. Known
depletion attraction effects are recovered for low particle density, while at
higher densities novel many-body effects emerge which become dominant for large
polymers.Comment: 7 pages, 4 figures; to be published in Europhys. Let
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.
Superthermal electron processes in the upper atmosphere of Uranus: Aurora and electroglow
Strong ultraviolet emissions from the upper atmosphere of Uranus suggest that both auroral and electroglow phenomena are of significant aeronomical consequences in the structure of the upper atmosphere. Combined modeling and data analysis were performed to determine the effect of electroglow and auroral phenomena on the global heat and atomic hydrogen budgets in the Uranus upper atmosphere. The results indicate that the auroral and electroglow heat sources are not adequate to explain the high exospheric temperature observed at Uranus, but that the atomic hydrogen supplied by these processes is more than sufficient to explain the observations. The various superthermal electron distributions modeled have significantly different efficiencies for the various processes such as UV emission, heating, ionization, and atomic hydrogen production, and produce quite different H2 band spectra. However, additional information on the UV spectra and global parameters is needed before modeling can be used to distinguish between the possible mechanisms for electroglow
Estimation of near-surface attenuation in bedrock for analysis of intraplate seismic hazard
The significance of near-surface attenuation in bedrock, as distinct from attenuation in unconsolidated soft soil sediments, has been identified. The k parameter, which characterizes the extent of this attenuation mechanism, is generally difficult to measure, particularly in regions of low and moderate seismicity. Empirical correlation of k with the near-surface shear wave velocity parameter in rock has been developed using global information obtained from limited independent studies. The influence of shaking intensity on the value of k has been found to be negligible in conditions that are consistent with the average seismicity of Australia (as also for other intraplate regions). Thus, adjustment in the value of k to account for variations in earthquake magnitude, or the intensity of ground shaking, has not been recommended for intraplate conditions. In parallel with the empirical correlations, values of k have also been obtained from calibration analyses employing stochastic simulations of the seismological model, along with onedimensional non-linear shear wave analyses of the rock layers. Good agreement in the values of k obtained from the different approaches has been demonstrated. The correlation of k with the near-surface shear wave velocity of rock, as recommended in this paper, has thereby been reaffirmed
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&
Thermodynamic equilibrium and its stability for Microcanonical systems described by the Sharma-Taneja-Mittal entropy
It is generally assumed that the thermodynamic stability of equilibrium state
is reflected by the concavity of entropy. We inquire, in the microcanonical
picture, on the validity of this statement for systems described by the
bi-parametric entropy of Sharma-Taneja-Mittal. We analyze
the ``composability'' rule for two statistically independent systems, A and B,
described by the entropy with the same set of the deformed
parameters. It is shown that, in spite of the concavity of the entropy, the
``composability'' rule modifies the thermodynamic stability conditions of the
equilibrium state. Depending on the values assumed by the deformed parameters,
when the relation holds (super-additive systems), the concavity
conditions does imply the thermodynamics stability. Otherwise, when the
relation holds (sub-additive systems), the concavity
conditions does not imply the thermodynamical stability of the equilibrium
state.Comment: 13 pages, two columns, 1 figure, RevTex4, version accepted on PR
COP 26: Pavilion Proposals
There is considerable interest in having a Peatland Pavilion at the up-coming UNFCCC COP26 to be held in Glasgow in November 2021. The purpose of the pavilion would be to provide a focus for discussions about the increasingly recognised importance of peatlands and their role as major global stores of soil carbon but also, in their damaged state, as large sources of carbon emissions. UEL Architecture Masters students were set the task of developing potential designs for such a pavilion with the requirement that it incorporate an installation designed by the artist and UEL lecturer Michael Pinsky. The architectural concept drawn up by Hussein Ail Kassim and Mohammed Patel offers some thought-provoking ideas for such a Peatland Pavilion and thus opens up the debate about what form, both conceptually and architecturally, such a pavilion might take. It is worth highlighting that the themes of the different environment domes envisaged by Hussein and Mohammed can each be related to particular aspects of importance to peatlands
Segue Between Favorable and Unfavorable Solvation
Solvation of small and large clusters are studied by simulation, considering
a range of solvent-solute attractive energy strengths. Over a wide range of
conditions, both for solvation in the Lennard-Jones liquid and in the SPC model
of water, it is shown that the mean solvent density varies linearly with
changes in solvent-solute adhesion or attractive energy strength. This behavior
is understood from the perspective of Weeks' theory of solvation [Ann. Rev.
Phys. Chem. 2002, 53, 533] and supports theories based upon that perspective.Comment: 8 pages, 7 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
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