1,849 research outputs found
Phonon anomalies due to strong electronic correlations in layered organic metals
We show how the coupling between the phonons and electrons in a strongly
correlated metal can result in phonon frequencies which have a non-monotonic
temperature dependence. Dynamical mean-field theory is used to study the
Hubbard-Holstein model that describes the \kappa-(BEDT-TTF)_2 X family of
superconducting molecular crystals. The crossover with increasing temperature
from a Fermi liquid to a bad metal produces phonon anomalies that are
consistent with recent Raman scattering and acoustic experiments.Comment: 6 pages, 3 eps figure
A Comprehensive Comparative Test of Seven Widely-Used Spectral Synthesis Models Against Multi-Band Photometry of Young Massive Star Clusters
We test the predictions of spectral synthesis models based on seven different
massive-star prescriptions against Legacy ExtraGalactic UV Survey (LEGUS)
observations of eight young massive clusters in two local galaxies, NGC 1566
and NGC 5253, chosen because predictions of all seven models are available at
the published galactic metallicities. The high angular resolution, extensive
cluster inventory and full near-ultraviolet to near-infrared photometric
coverage make the LEGUS dataset excellent for this study. We account for both
stellar and nebular emission in the models and try two different prescriptions
for attenuation by dust. From Bayesian fits of model libraries to the
observations, we find remarkably low dispersion in the median E(B-V) (~0.03
mag), stellar masses (~10^4 M_\odot) and ages (~1 Myr) derived for individual
clusters using different models, although maximum discrepancies in these
quantities can reach 0.09 mag and factors of 2.8 and 2.5, respectively. This is
for ranges in median properties of 0.05-0.54 mag, 1.8-10x10^4 M_\odot and
1.6-40 Myr spanned by the clusters in our sample. In terms of best fit, the
observations are slightly better reproduced by models with interacting binaries
and least well reproduced by models with single rotating stars. Our study
provides a first quantitative estimate of the accuracies and uncertainties of
the most recent spectral synthesis models of young stellar populations,
demonstrates the good progress of models in fitting high-quality observations,
and highlights the needs for a larger cluster sample and more extensive tests
of the model parameter space.Comment: Accepted for publication in MNRAS (14 Jan. 2016). 30 pages, 16
figures, 9 table
The origin of the phase separation in partially deuterated -(ET)Cu[N(CN)]Br studied by infrared magneto-optical imaging spectroscopy
The direct observation of the phase separation between the metallic and
insulating states of 75 %-deuterated -(ET)Cu[N(CN)]Br ()
using infrared magneto-optical imaging spectroscopy is reported, as well as the
associated temperature, cooling rate, and magnetic field dependencies of the
separation. The distribution of the center of spectral weight () of
did not change under any of the conditions in which data were taken and
was wider than that of the non-deuterated material. This result indicates that
the inhomogenity of the sample itself is important as part of the origin of the
metal - insulator phase separation.Comment: 4 pages, 3 figures, accepted for publication in Solid State Commu
Comprehensive multi-wavelength modelling of the afterglow of GRB050525A
The Swift era has posed a challenge to the standard blast-wave model of Gamma
Ray Burst (GRB) afterglows. The key observational features expected within the
model are rarely observed, such as the achromatic steepening (`jet-break') of
the light curves. The observed afterglow light curves showcase additional
complex features requiring modifications within the standard model. Here we
present optical/NIR observations, millimeter upper limits and comprehensive
broadband modelling of the afterglow of the bright GRB 0505025A, detected by
Swift. This afterglow cannot be explained by the simplistic form of the
standard blast-wave model. We attempt modelling the multi-wavelength light
curves using (i) a forward-reverse shock model, (ii) a two-component outflow
model and (iii) blast-wave model with a wind termination shock. The
forward-reverse shock model cannot explain the evolution of the afterglow. The
two component model is able to explain the average behaviour of the afterglow
very well but cannot reproduce the fluctuations in the early X-ray light curve.
The wind termination shock model reproduces the early light curves well but
deviates from the global behaviour of the late-time afterglow.Comment: 20 pages, 6 figures, accepted for publication in MNRA
Electronic correlation in the infrared optical properties of the quasi two dimensional -type BEDT-TTF dimer system
The polarized optical reflectance spectra of the quasi two dimensional
organic correlated electron system -(BEDT-TTF)Cu[N(CN)],
Br and Cl are measured in the infrared region. The former shows the
superconductivity at 11.6 K and the latter does the
antiferromagnetic insulator transition at 28 K. Both the
specific molecular vibration mode of the BEDT-TTF molecule and
the optical conductivity hump in the mid-infrared region change correlatively
at 38 K of -(BEDT-TTF)Cu[N(CN)]Br, although
no indication of but the insulating behaviour below 50-60 K are found in -(BEDT-TTF)Cu[N(CN)]Cl. The
results suggest that the electron-molecular vibration coupling on the
mode becomes weak due to the enhancement of the itinerant
nature of the carriers on the dimer of the BEDT-TTF molecules below ,
while it does strong below because of the localized carriers on
the dimer. These changes are in agreement with the reduction and the
enhancement of the mid-infrared conductivity hump below and , respectively, which originates from the transitions between the upper
and lower Mott-Hubbard bands. The present observations demonstrate that two
different metallic states of -(BEDT-TTF)Cu[N(CN)]Br are
regarded as {\it a correlated good metal} below including the
superconducting state and {\it a half filling bad metal} above . In
contrast the insulating state of -(BEDT-TTF)Cu[N(CN)]Cl
below is the Mott insulator.Comment: 8 pages, 7 figure
Strangers in the night: nightlife studies and new urban tourism
This paper draws together recent scholarship from the study of urban tourism and nightlife. Though studies of urban tourism do not always specifically address nightlife, and likewise studies of the night and nightlife do not always examine tourism, both bodies of research overlap in important ways. Concerns about commercialisation, gentrification, displacement, and urban change are to be found in both bodies of research. However, while the study of urban tourism typically recognises the erasure of the host / guest binary and seeks to destabilise the notion of who is a tourist or stranger, studies of nightlife often rest on a much clearer distinction between who belongs and who does not. An argument proposed here is that while the host / guest, tourist / non-tourist binary is perhaps reconfiguring, the night and nightlife spaces reinstate these binaries in various ways. This paper thinks through debates about tourists and residents in the night, focusing in particular on questions of belonging, place identification and gentrification through night-time uses
Comparison of Experimental vs Theoretical Abundances of ÂčÂłCHâD and ÂčÂČCHâDâ for Isotopically Equilibrated Systems from 1 to 500 °C
Methane is produced and consumed via numerous microbial and chemical reactions in atmospheric, hydrothermal, and magmatic reactions. The stable isotopic composition of methane has been used extensively for decades to constrain the source of methane in the environment. A recently introduced isotopic parameter used to study the formation temperature and formational conditions of methane is the measurement of molecules of methane with multiple rare, heavy isotopes (âclumpedâ) such as ÂčÂłCHâD and ÂčÂČCHâDâ. In order to place methane clumped-isotope measurements into a thermodynamic reference frame that allows calculations of clumped-isotope based temperatures (geothermometry) and comparison between laboratories, all past studies have calibrated their measurements using a combination of experiment and theory based on the temperature dependence of clumped isotopologue distributions for isotopically equilibrated systems. These have previously been performed at relatively high temperatures (>150ËC). Given that many natural occurrences of methane form below these temperatures, previous calibrations require extrapolation when calculating clumped-isotope based temperatures outside of this calibration range. We provide a new experimental calibration of the relative equilibrium abundances of ÂčÂłCHâD and ÂčÂČCHâDâ from 1â500ËC using a combination of Îł-AlâOâ and Ni-based catalysts and compare them to new theoretical computations using Path Integral Monte Carlo (PIMC) methods and find 1:1 agreement (within ± 1 standard error) for the observed temperature dependence of clumping between experiment and theory over this range. This demonstrates that measurements, experiments, and theory agree from 1â500°C providing confidence in the overall approaches. Polynomial fits to PIMC computations, which are considered the most rigorous theoretical approach available, are given as follows (valid T â„ 270 K): âÂčÂłCHâDâ
1000Ăln(KÂčÂłCHâD)= 1.47348Ă10Âčâč/Tâ· - 2.08648Ă10Âčâ·/Tⶠ+ 1.19810Ă10Âčâ”/Tâ” - 3.54757Ă10ÂčÂČ/T⎠+5.54476Ă10âč/TÂł â 3.49294Ă10â¶/TÂČ + 8.89370Ă10â/T âÂčÂČCHâDââ
1000Ăln(8/3ĂKÂčÂČCHâDâ)= -9.67634Ă10Âčâ”/Tⶠ+ 1.71917Ă10ÂčâŽ/Tâ” - 1.24819Ă10ÂčÂČ/T⎠+ 4.30283Ă10âč/T3 -4.48660Ă10â¶/TÂČ + 1.86258Ă10Âł/T. We additionally compare PIMC computations to those performed utilizing traditional approaches that are the basis of most previous calibrations (Bigeleisen, Mayer, and Urey model, BMU) and discuss the potential sources of error in the BMU model relative to PIMC computations
Paedophiles in the community: inter-agency conflict, news leaks and the local press
This article explores the leaking of confidential information about secret Home Office plans to house convicted paedophiles within a local community (albeit inside a prison). It argues that a politics of paedophilia has emerged in which inter-agency consensus on the issue of âwhat to doâ with high-profile sex offenders has broken down. Accordingly, the article situates newspaper âoutingâ of paedophiles in the community in relation to vigilante journalism and leaked information from official agencies. The article then presents research findings from a case study of news events set in train following a whistle-blowing reaction by Prison Officersâ Association officials to Home Office plans. Drawing from a corpus of 10 interviews with journalists and key protagonists in the story, the article discusses both the dynamics of whistle blowing about paedophiles and also what happens after the whistle has blown
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