2,701 research outputs found
Phonon sidebands of localized excitons in molecular crystals with methyl torsions: Hexamethylbenzene
Fluorescence and phosphorescence phonon sidebands of isotopic mixed hexamethylbenzene crystals at 2°K are presented. The external phonons can be observed separately from the semiâinternal (methyl torsion) ones. The nature of the electronic or vibronic state has observable but not drastic effects on the excitonâphonon coupling function. Likewise, the exciton delocalization is of minor importance to the excitonâphonon function in hexamethylbenzene. The coupling between external and internal vibrations is also weak in this system. The excitonâphonon coupling appears comparable for the optical and acoustic phonons in hexamethylbenzene. The phonon sidebands give some of the phonon singularities of the lowâtemperature crystal.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70173/2/JCPSA6-60-6-2365-1.pd
Spin resonance in the superconducting state of LiFeODFeSe observed by neutron spectroscopy
We have performed inelastic neutron scattering measurements on a powder
sample of the superconductor lithium iron selenide hydroxide
LiFeODFeSe (, \,K). The spectrum shows an enhanced intensity below over an
energy range , where is the
superconducting gap, with maxima at the wave vectors \,\AA and \,\AA. The behavior of this
feature is consistent with the spin resonance mode found in other
unconventional superconductors, and strongly resembles the spin resonance
observed in the spectrum of the molecular-intercalated iron selenide,
Li(ND)(ND)FeSe. The signal can
be described with a characteristic two-dimensional wave vector
in the Brillouin zone of the iron square lattice, consistent with the nesting
vector between electron Fermi sheets
Renormalisation-theoretic analysis of non-equilibrium phase transitions II: The effect of perturbations on rate coefficients in the Becker-Doring equations
We study in detail the application of renormalisation theory to models of
cluster aggregation and fragmentation of relevance to nucleation and growth
processes. In particular, we investigate the Becker-Doring (BD) equations,
originally formulated to describe and analyse non-equilibrium phase
transitions, but more recently generalised to describe a wide range of
physicochemical problems. We consider here rate coefficients which depend on
the cluster size in a power-law fashion, but now perturbed by small amplitude
random noise. Power-law rate coefficients arise naturally in the theory of
surface-controlled nucleation and growth processes. The noisy perturbations on
these rates reflect the effect of microscopic variations in such mean-field
coefficients, thermal fluctuations and/or experimental uncertainties. In the
present paper we generalise our earlier work that identified the nine classes
into which all dynamical behaviour must fall by investigating how random
perturbations of the rate coefficients influence the steady-state and kinetic
behaviour of the coarse-grained, renormalised system. We are hence able to
confirm the existence of a set of up to nine universality classes for such BD
systems.Comment: 30 pages, to appear in J Phys A Math Ge
Renormalisation-theoretic analysis of non-equilibrium phase transitions I: The Becker-Doring equations with power law rate coefficients
We study in detail the application of renormalisation theory to models of
cluster aggregation and fragmentation of relevance to nucleation and growth
processes. We investigate the Becker-Dorging equations, originally formulated
to describe and analyse non-equilibrium phase transitions, and more recently
generalised to describe a wide range of physicochemical problems. In the
present paper we analyse how the systematic coarse-graining renormalisation of
the \BD system of equations affects the aggregation and fragmentation rate
coefficients. We consider the case of power-law size-dependent cluster rate
coefficients which we show lead to only three classes of system that require
analysis: coagulation-dominated systems, fragmentation-dominated systems and
those where coagulation and fragmentation are exactly balanced. We analyse the
late-time asymptotics associated with each class.Comment: 18 pages, to appear in J Phys A Math Ge
Calculation of the crystal-melt interfacial free energy of succinonitrile from molecular simulation
This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/124/4/10.1063/1.2149859
Climate forcing of unprecedented intense-hurricane activity in the last 2000 years
© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Earth's Future 3 (2015): 49â65, doi:10.1002/2014EF000274.How climate controls hurricane variability has critical implications for society is not well understood. In part, our understanding is hampered by the short and incomplete observational hurricane record. Here we present a synthesis of intense-hurricane activity from the western North Atlantic over the past two millennia, which is supported by a new, exceptionally well-resolved record from Salt Pond, Massachusetts (USA). At Salt Pond, three coarse grained event beds deposited in the historical interval are consistent with severe hurricanes in 1991 (Bob), 1675, and 1635 C.E., and provide modern analogs for 32 other prehistoric event beds. Two intervals of heightened frequency of event bed deposition between 1400 and 1675 C.E. (10 events) and 150 and 1150 C.E. (23 events), represent the local expression of coherent regional patterns in intense-hurricaneâinduced event beds. Our synthesis indicates that much of the western North Atlantic appears to have been active between 250 and 1150 C.E., with high levels of activity persisting in the Caribbean and Gulf of Mexico until 1400 C.E. This interval was one with relatively warm sea surface temperatures (SSTs) in the main development region (MDR). A shift in activity to the North American east coast occurred ca. 1400 C.E., with more frequent severe hurricane strikes recorded from The Bahamas to New England between 1400 and 1675 C.E. A warm SST anomaly along the western North Atlantic, rather than within the MDR, likely contributed to the later active interval being restricted to the east coast.Funding was provided by US National Science Foundation (awards 0903020 and 1356708), the Risk Prediction Initiative at the Bermuda Institute for Ocean Sciences (BIOS), US Department of Energy National Institute for Climate Change Research, National Oceanic and Atmospheric Administration (award NA11OAR431010), and the Dalio Explore Fund
Confirmed Angiosarcoma: Prognostic Factors and Outcome in 50 Prospectively Followed Patients
Purpose. Angiosarcoma is a rare tumor with endothelial cell
differentiation that may arise in any anatomic location.The purpose of this report was to
identify prognostic factors on outcome in a group of prospectively followed patients with
confirmed angiosarcoma
Renormalization Group Theory for Global Asymptotic Analysis
We show with several examples that renormalization group (RG) theory can be
used to understand singular and reductive perturbation methods in a unified
fashion. Amplitude equations describing slow motion dynamics in nonequilibrium
phenomena are RG equations. The renormalized perturbation approach may be
simpler to use than other approaches, because it does not require the use of
asymptotic matching, and yields practically superior approximations.Comment: 13 pages, plain tex + uiucmac.tex (available from babbage.sissa.it),
one PostScript figure appended at end. Or (easier) get compressed postscript
file by anon ftp from gijoe.mrl.uiuc.edu (128.174.119.153), file
/pub/rg_sing_prl.ps.
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