4,279 research outputs found
Critical theories for the pseudogap Kondo problem
We discuss quantum phase transitions in the pseudogap Kondo problem, which
describes a magnetic moment coupled to conduction electrons with a power-law
density of states, rho(omega) ~ |omega|^r. We show that different perturbative
expansions, together with renormalization group techniques, provide effective
low-energy field theories for the relevant critical fixed points. In
particular, we review expansions near the lower-critical and upper-critical
dimensions of the problem, being r=0 and r=1, respectively.Comment: 2 pages, 1 fig, submitted to SCES04 proceeding
Affirmative action through extra prizes
Some affirmative action policies establish that a set of disadvantaged competitors has access to an extra prize. We analyse the effects of creating an extra prize by reducing the prize in the main competition. Contestants differ in ability and agents with relatively low ability belong to a disadvantaged minority. All contestants compete for the main prize, but only disadvantaged agents can win the extra prize. We show that an extra prize is a powerful tool to ensure participation of disadvantaged agents. Moreover, for intermediate levels of the disadvantage of the minority, introducing an extra prize increases total equilibrium effort compared to a standard contest. Thus, even a contest designer not interested in affirmative action might establish an extra prize in order to enhance competition
A distinct magnetic property of the inner penumbral boundary III. Analysis of simulated sunspots
The analyses of sunspot observations revealed a fundamental magnetic property
of the umbral boundary, the invariance of the vertical component of the
magnetic field. We aim to analyse the magnetic properties of the umbra-penumbra
boundary in simulated sunspots and thus assess their similarity to observed
sunspots. Also, we aim to investigate the role of plasma and the ratio
of kinetic to magnetic energy in simulated sunspots on the convective motions.
We use a set of non-grey simulation runs of sunspots with the MURaM code. These
data are used to synthesise the Stokes profiles that are then degraded to the
Hinode spectropolarimeter-like observations. Then, the data are treated like
real Hinode observations of a sunspot and magnetic properties at the umbral
boundaries are determined. Simulations with potential field extrapolation
produce a realistic magnetic field configuration on their umbral boundaries.
Two simulations with potential field upper boundary, but different subsurface
magnetic field structures, differ significantly in the extent of their
penumbrae. Increasing the penumbra width by forcing more horizontal magnetic
fields at the upper boundary results in magnetic properties that are not
consistent with observations. This implies that the size of the penumbra is
given by the subsurface structure of the magnetic field. None of the sunspot
simulations is consistent with observed properties of the magnetic field and
direction of the Evershed flow at the same time. Strong outward directed
Evershed flows are only found in setups with artificially enhanced horizontal
component of the magnetic field at the top boundary that are not consistent
with the observed magnetic field properties at the UP boundary. We want to
stress out that the `photospheric' boundary of simulated sunspots is defined by
a magnetic field strength of equipartition field value
Sediment provenance indicated by magnetic susceptibility and inorganic geochemistry in the Baker-Martínez fjord system (Chile, 48°S)
Patagonian fjord sediments are increasingly used as high-resolution archives of past climate and environmental change, including variations in glacier mass balance, flood frequency, and seismic activity. To accurately interpret these proxy records, it is crucial to comprehend modern day sedimentation processes and determine the provenance of the sediments. With this in mind, the main objective of this study is to identify parameters that can be used to reconstruct sediment provenance in the fjords of Chilean Patagonia. We focus on the Baker-Martínez fjord system, which is located between the Northern and Southern Patagonian Icefields and seems particularly sensitive to climate change. This fjord system connects the terrestrial ecosystems of Patagonia with the SE Pacific Ocean, and most of its sediment originates from glacier-fed rivers draining either the Patagonian Batholith (PB; Baker and Huemules rivers) to the north, or the Eastern Andes Metamorphic Complex (EAMC; Bravo and Pascua rivers) to the south. Eighteen surface sediment samples from across the Baker-Martínez fjord system and 44 suspended sediment samples from two sequential (Baker fjord) and one continuous (Steffen fjord) sediment trap were investigated. In addition, we analyzed suspended sediment samples collected at the mouths of the four main rivers that drain the PB and EAMC to define end-members. We focus on mass-specific magnetic susceptibility (MS) and inorganic geochemistry, which seem to be particularly promising in this fjord system dominated by lithogenic sediments (97–85 wt%). Our results indicate that sediments derived from the PB are characterized by high MS, Ti/Al, and Fe/Al values, reflecting the granodioritic nature of the batholith (rich in pyroxene and amphibole). In contrast, sediments from the southern EAMC-derived rivers have significantly lower MS, Ti/Al, and Fe/Al values. The sediment trap results reveal MS values that increase with increasing Baker river discharge, either during the summer melt season, or during high precipitation events (rain-on-snow) in winter. Likewise, the MS, Ti/Al and Fe/Al values of the fjord surface sediments are also directly related to sediment provenance. In fjords fed by only one river (e.g., Martínez channel), however, the MS is significantly correlated with mean grain size (r = 0.90; p < 0.01) and with the proportion of lithogenic particles (r = 0.73; p < 0.05). The latter observation means that future research is needed to correct the MS and geochemical data for grain-size before using them as quantitative provenance indicators. This study suggests that, after grain-size correction, MS and inorganic geochemistry (Ti/Al and Fe/Al) can be used to reconstruct sediment provenance within the Baker-Martínez fjord system. Ultimately, applying these provenance indicators to long sediment cores from the same fjord system will allow us to reconstruct variations in the behavior of outlet glaciers from both icefields independently
Systematic Review of Physical Activity Trajectories and Mortality in Patients With Coronary Artery Disease.
BACKGROUND
The role of lifestyle physical activity (PA) trajectories in the mortality risk of patients with coronary heart disease (CHD) remains unclear.
OBJECTIVES
The purpose of this study was to determine the association of longitudinal PA trajectories with all-cause and cardiovascular disease (CVD) mortality in patients with CHD.
METHODS
Longitudinal cohorts reporting the association of PA trajectories with mortality in patients with CHD were identified in April 2021 by searching 5 databases without language restrictions. Published HRs and 95% CIs were pooled using random effects models and bias assessed by Egger regression.
RESULTS
A total of 9 prospective cohorts included 33,576 patients. The mean age was 62.5 years. The maximum follow-up was 15.7 years. All of the studies assessed PA through validated questionnaires, and mortality was well documented. Changes in PA defined 4 nominal PA trajectories. Compared with always-inactive patients, the risk of all-cause mortality was 50% lower in those who remained active (HR: 0.50; 95% CI: 0.39-0.63); 45% lower in those who were inactive but became active (HR: 0.55; 95% CI: 0.44-0.7); and 20% lower in those who were active but became inactive (HR: 0.80; 95% CI: 0.64-0.99). Similar results were observed for CVD mortality, except for the category of decreased activity (HR: 0.91; 95% CI: 0.67-1.24). The overall risk of bias was low. No evidence of publication bias was found. Multiple sensitivity analyses provided consistent results.
CONCLUSIONS
This study illustrates how patients with CHD may benefit by preserving or adopting an active lifestyle. The observation that the benefits of past activity can be weakened or lost if PA is not maintained may be confounded by disease progression
Exposure source for skin sensitizing hydroperoxides of limonene and linalool remains elusive: an analytical market surveillance
International audienc
Thickness-Dependent Differential Reflectance Spectra of Monolayer and Few-Layer MoS2, MoSe2, WS2 and WSe2
The research field of two dimensional (2D) materials strongly relies on
optical microscopy characterization tools to identify atomically thin materials
and to determine their number of layers. Moreover, optical microscopy-based
techniques opened the door to study the optical properties of these
nanomaterials. We presented a comprehensive study of the differential
reflectance spectra of 2D semiconducting transition metal dichalcogenides
(TMDCs), MoS2, MoSe2, WS2, and WSe2, with thickness ranging from one layer up
to six layers. We analyzed the thickness-dependent energy of the different
excitonic features, indicating the change in the band structure of the
different TMDC materials with the number of layers. Our work provided a route
to employ differential reflectance spectroscopy for determining the number of
layers of MoS2, MoSe2, WS2, and WSe2.Comment: Main text (3 Figures) and Supp. Info. (23 Figures
METHODOLOGY FOR ESTIMATING BIOMASS ENERGY POTENTIAL AND ITS APPLICATION TO COLOMBIA
This paper presents a methodology to estimate the biomass energy potential and its associated uncertainty at a country level when quality and availability of data are limited. The current biomass energy potential in Colombia is assessed following the proposed methodology and results are compared to existing assessment studies.
The proposed methodology is a bottom-up resource-focused approach with statistical analysis that uses a Monte Carlo algorithm to stochastically estimate the theoretical and the technical biomass energy potential. The paper also includes a proposed approach to quantify uncertainty combining a probabilistic propagation of uncertainty, a sensitivity analysis and a set of disaggregated sub-models to estimate reliability of predictions and reduce the associated uncertainty. Results predict a theoretical energy potential of 0.744 EJ and a technical potential of 0.059 EJ in 2010, which might account for 1.2% of the annual primary energy production (4.93 EJ)
Scaling stellar jets to the laboratory: the power of simulations
Advances in laser and Z-pinch technology, coupled with the development of
plasma diagnostics and the availability of high-performance computers, have
recently stimulated the growth of high-energy density laboratory astrophysics.
In particular a number of experiments have been designed to study radiative
shocks and jets with the aim of shedding new light on physical processes linked
to the ejection and accretion of mass by newly born stars.
Although general scaling laws are a powerful tools to link laboratory
experiments with astrophysical plasmas, the phenomena modelled are often too
complicated for simple scaling to remain relevant. Nevertheless, the
experiments can still give important insights into the physics of astrophysical
systems and can be used to provide the basic experimental validation of
numerical simulations in regimes of interest to astrophysics.
We will illustrate the possible links between laboratory experiments,
numerical simulations and astrophysics in the context of stellar jets. First we
will discuss the propagation of stellar jets in a cross-moving interstellar
medium and the scaling to Z-pinch produced jets. Our second example focuses on
slab-jets produced at the PALS (Prague Asterix Laser System) laser installation
and their practical applications to astrophysics. Finally, we illustrate the
limitations of scaling for radiative shocks, which are found at the head of the
most rapid stellar jets.Comment: 30 pages, 9 figure
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