268 research outputs found
The Influence of Dust Formation Modelling on Na I and K I Line Profiles in Substellar Atmospheres
We aim to understand the correlation between cloud formation and alkali line
formation in substellar atmospheres.We perform line profile calculations for Na
I and K I based on the coupling of our kinetic model for the formation and
composition of dust grains with 1D radiative transfer calculations in
atmosphere models for brown dwarfs and giant gas planets. The Na I and K I line
profiles sensibly depend on the way clouds are treated in substellar atmosphere
simulations. The kinetic dust formation model results in the highest
pseudo-continuum compared to the limiting cases.Comment: 5 pages, Accepted for publication in MNRA
Anomalous Lattice Response at the Mott Transition in a Quasi-2D Organic Conductor
Discontinuous changes of the lattice parameters at the Mott metal-insulator
transition are detected by high-resolution dilatometry on deuterated crystals
of the layered organic conductor -(BEDT-TTF)Cu[N(CN)]Br.
The uniaxial expansivities uncover a striking and unexpected anisotropy,
notably a zero-effect along the in-plane c-axis along which the electronic
interactions are relatively strong. A huge thermal expansion anomaly is
observed near the end-point of the first-order transition line enabling to
explore the critical behavior with very high sensitivity. The analysis yields
critical fluctuations with an exponent 0.8 0.15
at odds with the novel criticality recently proposed for these materials
[Kagawa \textit{et al.}, Nature \textbf{436}, 534 (2005)]. Our data suggest an
intricate role of the lattice degrees of freedom in the Mott transition for the
present materials.Comment: 4 pages, 4 figure
Determining ethylene group disorder levels in -(BEDT-TTF)Cu[N(CN)]Br
We present a detailed structural investigation of the organic superconductor
-(BEDT-TTF)Cu[N(CN)]Br at temperatures from 9 to 300 K.
Anomalies in the dependence of the lattice parameters are associated with a
glass-like transition previously reported at = 77 K. From structure
refinements at 9, 100 and 300 K, the orthorhombic crystalline symmetry, space
group {\it Pnma}, is established at all temperatures. Further, we extract the
dependence of the occupation factor of the eclipsed conformation of the
terminal ethylene groups of the BEDT-TTF molecule. At 300 K, we find 67(2) %,
with an increase to 97(3) % at 9 K. We conclude that the glass-like transition
is not primarily caused by configurational freezing-out of the ethylene groups
Resistivity studies under hydrostatic pressure on a low-resistance variant of the quasi-2D organic superconductor kappa-(BEDT-TTF)2Cu[N(CN)2]Br: quest for intrinsic scattering contributions
Resistivity measurements have been performed on a low (LR)- and high
(HR)-resistance variant of the kappa-(BEDT-TTF)_2Cu[N(CN)_2]Br superconductor.
While the HR sample was synthesized following the standard procedure, the LR
crystal is a result of a somewhat modified synthesis route. According to their
residual resistivities and residual resistivity ratios, the LR crystal is of
distinctly superior quality. He-gas pressure was used to study the effect of
hydrostatic pressure on the different transport regimes for both variants. The
main results of these comparative investigations are (i) a significant part of
the inelastic-scattering contribution, which causes the anomalous rho(T)
maximum in standard HR crystals around 90 K, is sample dependent, i.e.
extrinsic in nature, (ii) the abrupt change in rho(T) at T* approx. 40 K from a
strongly temperature-dependent behavior at T > T* to an only weakly T-dependent
rho(T) at T < T* is unaffected by this scattering contribution and thus marks
an independent property, most likely a second-order phase transition, (iii)
both variants reveal a rho(T) proportional to AT^2 dependence at low
temperatures, i.e. for T_c < T < T_0, although with strongly sample-dependent
coefficients A and upper bounds for the T^2 behavior measured by T_0. The
latter result is inconsistent with the T^2 dependence originating from coherent
Fermi-liquid excitations.Comment: 8 pages, 6 figure
Quantifying trading behavior in financial markets using Google Trends
Crises in financial markets affect humans worldwide. Detailed market data on trading decisions reflect some of the complex human behavior that has led to these crises. We suggest that massive new data sources resulting from human interaction with the Internet may offer a new perspective on the behavior of market participants in periods of large market movements. By analyzing changes in Google query volumes for search terms related to finance, we find patterns that may be interpreted as âearly warning signsâ of stock market moves. Our results illustrate the potential that combining extensive behavioral data sets offers for a better understanding of collective human behavior
Electron-phonon renormalization of the absorption edge of the cuprous halides
Compared to most tetrahedral semiconductors, the temperature dependence of
the absorption edges of the cuprous halides (CuCl, CuBr, CuI) is very small.
CuCl and CuBr show a small increase of the gap with increasing
temperature, with a change in the slope of vs. at around 150 K: above
this temperature, the variation of with becomes even smaller. This
unusual behavior has been clarified for CuCl by measurements of the low
temperature gap vs. the isotopic masses of both constituents, yielding an
anomalous negative shift with increasing copper mass. Here we report the
isotope effects of Cu and Br on the gap of CuBr, and that of Cu on the gap of
CuI. The measured isotope effects allow us to understand the corresponding
temperature dependences, which we also report, to our knowledge for the first
time, in the case of CuI. These results enable us to develop a more
quantitative understanding of the phenomena mentioned for the three halides,
and to interpret other anomalies reported for the temperature dependence of the
absorption gap in copper and silver chalcogenides; similarities to the behavior
observed for the copper chalcopyrites are also pointed out.Comment: 14 pages, 5 figures, submitted to Phys. Rev.
A comparison of chemistry and dust cloud formation in ultracool dwarf model atmospheres
The atmospheres of substellar objects contain clouds of oxides, iron,
silicates, and other refractory condensates. Water clouds are expected in the
coolest objects. The opacity of these `dust' clouds strongly affects both the
atmospheric temperature-pressure profile and the emergent flux. Thus any
attempt to model the spectra of these atmospheres must incorporate a cloud
model. However the diversity of cloud models in atmospheric simulations is
large and it is not always clear how the underlying physics of the various
models compare. Likewise the observational consequences of different modeling
approaches can be masked by other model differences, making objective
comparisons challenging. In order to clarify the current state of the modeling
approaches, this paper compares five different cloud models in two sets of
tests. Test case 1 tests the dust cloud models for a prescribed L, L--T, and
T-dwarf atmospheric (temperature T, pressure p, convective velocity
vconv)-structures. Test case 2 compares complete model atmosphere results for
given (effective temperature Teff, surface gravity log g). All models agree on
the global cloud structure but differ in opacity-relevant details like grain
size, amount of dust, dust and gas-phase composition. Comparisons of synthetic
photometric fluxes translate into an modelling uncertainty in apparent
magnitudes for our L-dwarf (T-dwarf) test case of 0.25 < \Delta m < 0.875 (0.1
< \Delta m M 1.375) taking into account the 2MASS, the UKIRT WFCAM, the Spitzer
IRAC, and VLT VISIR filters with UKIRT WFCAM being the most challenging for the
models. (abr.)Comment: 22 pages, 17 figures, MNRAS 2008, accepted, (minor grammar/typo
corrections
Midline fascial plication under continuous digital transrectal control: which factors determine anatomic outcome?
Contains fulltext :
88897.pdf (publisher's version ) (Closed access)INTRODUCTION AND HYPOTHESIS: The aim of the study was to report anatomic and functional outcome of midline fascial plication under continuous digital transrectal control and to identify predictors of anatomic failure. METHODS: Prospective observational cohort. Anatomic success defined as POP-Q stage or= II underwent midline fascial plication under continuous digital transrectal control. Median follow-up was 14 months (12-35 months), and anatomic success was 80.3% (95% CI 75-86). Independent predictors of failure were posterior compartment POP stage >or= III [OR 8.7 (95% CI 2.7-28.1)] and prior colposuspension [OR 5.6 (95% CI 1.1-27.8)]. Sixty-three percent of patients bothered by obstructed defaecation experienced relief after surgery. CONCLUSIONS: Anatomic and functional outcomes were good. Risk factors for anatomic failure were initial size of posterior POP (stage >or= III) and prior colposuspension.1 juni 201
Crises and collective socio-economic phenomena: simple models and challenges
Financial and economic history is strewn with bubbles and crashes, booms and
busts, crises and upheavals of all sorts. Understanding the origin of these
events is arguably one of the most important problems in economic theory. In
this paper, we review recent efforts to include heterogeneities and
interactions in models of decision. We argue that the Random Field Ising model
(RFIM) indeed provides a unifying framework to account for many collective
socio-economic phenomena that lead to sudden ruptures and crises. We discuss
different models that can capture potentially destabilising self-referential
feedback loops, induced either by herding, i.e. reference to peers, or
trending, i.e. reference to the past, and account for some of the phenomenology
missing in the standard models. We discuss some empirically testable
predictions of these models, for example robust signatures of RFIM-like herding
effects, or the logarithmic decay of spatial correlations of voting patterns.
One of the most striking result, inspired by statistical physics methods, is
that Adam Smith's invisible hand can badly fail at solving simple coordination
problems. We also insist on the issue of time-scales, that can be extremely
long in some cases, and prevent socially optimal equilibria to be reached. As a
theoretical challenge, the study of so-called "detailed-balance" violating
decision rules is needed to decide whether conclusions based on current models
(that all assume detailed-balance) are indeed robust and generic.Comment: Review paper accepted for a special issue of J Stat Phys; several
minor improvements along reviewers' comment
Mass splittings of the baryon decuplet and antidecuplet with the second-order flavor symmetry breakings within a chiral soliton model
We revisit the mass splittings of SU(3) baryons, taking into account the
second-order effects of isospin and SU(3) flavor symmetry breakings within the
framework of a chiral soliton model. The masses of the baryon decuplet turn out
to be improved, compared to those with the first-order corrections. The mass of
the N^* as a member of the baryon antidecuplet is obtained as M_{n^*}=1687 MeV,
which is in agreement with the recent experimental data. The pion-nucleon sigma
term becomes \Sigma_{\pi N}=(50.5\pm 5.4) MeV.Comment: 9 pages. No figure. arXiv admin note: substantial text overlap with
arXiv:1010.379
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