4,361 research outputs found
Solar X-ray spectrum reproduced in vacuum
Desired low energy X rays are produced by modifying commercial ion tubes and combining them with standard power supplies and control circuitry. These X rays have less deviation from the solar X ray spectrum in energy and intensity
Steady-state dynamics and effective temperatures of quantum criticality in an open system
We study the thermal and non-thermal steady state scaling functions and the
steady-state dynamics of a model of local quantum criticality. The model we
consider, i.e. the pseudogap Kondo model, allows us to study the concept of
effective temperatures near fully interacting as well as weak-coupling fixed
points. In the vicinity of each fixed point we establish the existence of an
effective temperature --different at each fixed point-- such that the
equilibrium fluctuation-dissipation theorem is recovered. Most notably,
steady-state scaling functions in terms of the effective temperatures coincide
with the equilibrium scaling functions. This result extends to higher
correlation functions as is explicitly demonstrated for the Kondo singlet
strength. The non-linear charge transport is also studied and analyzed in terms
of the effective temperature.Comment: 5 pages, 4 figures; Supplementary Material (7 pages, 1 figure
A Study of Meteoroid Impact Phenomena
Process of crater formation resulting from impact of hypervelocity projectile - meteoroid impac
Improving impact resistance of ceramic materials by energy absorbing surface layers
Energy absorbing surface layers were used to improve the impact resistance of silicon nitride and silicon carbide ceramics. Low elastic modulus materials were used. In some cases, the low elastic modulus was achieved using materials that form localized microcracks as a result of thermal expansion anisotropy, thermal expansion differences between phases, or phase transformations. In other cases, semi-vitreous or vitreous materials were used. Substantial improvements in impact resistance were observed at room and elevated temperatures
Spatially distributed water-balance and meteorological data from the Wolverton catchment, Sequoia National Park, California
Accurate water-balance measurements in the seasonal, snow-dominated Sierra Nevada are important for forest and downstream water management. However, few sites in the southern Sierra offer detailed records of the spatial and temporal patterns of snowpack and soil-water storage and the fluxes affecting them, i.e., precipitation as rain and snow, snowmelt, evapotranspiration, and runoff. To explore these stores and fluxes we instrumented the Wolverton basin (2180-2750 m) in Sequoia National Park with distributed, continuous sensors. This 2006-2016 record of snow depth, soil moisture and soil temperature, and meteorological data quantifies the hydrologic inputs and storage in a mostly undeveloped catchment. Clustered sensors record lateral differences with regards to aspect and canopy cover at approximately 2250 and 2625 m in elevation, where two meteorological stations are installed. Meteorological stations record air temperature, relative humidity, radiation, precipitation, wind speed and direction, and snow depth. Data are available at hourly intervals by water year (1 October-30 September) in non-proprietary formats from online data repositories (https://doi.org/10.6071/M3S94T)
Diagrammatic theory of the Anderson impurity model with finite Coulomb interaction
We have developed a self-consistent conserving pseudo particle approximation
for the Anderson impurity model with finite Coulomb interaction, derivable from
a Luttinger Ward functional. It contains an infinite series of skeleton
diagrams built out of fully renormalized Green's functions. The choice of
diagrams is motivated by the Schrieffer Wolff transformation which shows that
singly and doubly occupied states should appear in all bare diagrams
symmetrically. Our numerical results for are in excellent agreement with
the exact values known from the Bethe ansatz solution. The low energy physics
of non-Fermi liquid Anderson impurity systems is correctly described while the
present approximation fails to describe Fermi liquid systems, since some
important coherent spin flip and charge transfer processes are not yet
included. It is believed that CTMA (Conserving T-matrix approximation) diagrams
will recover also Fermi liquid behavior for Anderson models with finite Coulomb
interaction as they do for infinite Coulomb interaction.Comment: 4 pages, 2 figures, presented at the NATO Advanced Research Workshop
on "Size Dependent MAgnetic Scattering", Pecs, Hungary, May 28 - June 1, 200
Recent advances in malaria genomics and epigenomics
Malaria continues to impose a significant disease burden on low- and middle-income countries in the tropics. However, revolutionary progress over the last 3Â years in nucleic acid sequencing, reverse genetics, and post-genome analyses has generated step changes in our understanding of malaria parasite (Plasmodium spp.) biology and its interactions with its host and vector. Driven by the availability of vast amounts of genome sequence data from Plasmodium species strains, relevant human populations of different ethnicities, and mosquito vectors, researchers can consider any biological component of the malarial process in isolation or in the interactive setting that is infection. In particular, considerable progress has been made in the area of population genomics, with Plasmodium falciparum serving as a highly relevant model. Such studies have demonstrated that genome evolution under strong selective pressure can be detected. These data, combined with reverse genetics, have enabled the identification of the region of the P. falciparum genome that is under selective pressure and the confirmation of the functionality of the mutations in the kelch13 gene that accompany resistance to the major frontline antimalarial, artemisinin. Furthermore, the central role of epigenetic regulation of gene expression and antigenic variation and developmental fate in P. falciparum is becoming ever clearer. This review summarizes recent exciting discoveries that genome technologies have enabled in malaria research and highlights some of their applications to healthcare. The knowledge gained will help to develop surveillance approaches for the emergence or spread of drug resistance and to identify new targets for the development of antimalarial drugs and perhaps vaccines
Gravitational collapse of plasmas in General Relativity
We provide a covariant derivation of plasma physics coupled to gravitation by
utilizing the 3+1 formulation of general relativity, including a discussion of
the Lorentz force law. We then reduce the system to the spherically symmetric
case and show that all regions of the spacetime can be represented in a single
coordinate system, thus revoking the need for junction conditions. We further
show that the region exterior to the collapsing region is naturally described
by the charged Vaidya spacetime in non-null coordinates.Comment: Talk given at the Spanish Relativity Meeting, Tenerife, September
200
Forecasting Value-at-Risk with Time-Varying Variance, Skewness and Kurtosis in an Exponential Weighted Moving Average Framework
This paper provides an insight to the time-varying dynamics of the shape of
the distribution of financial return series by proposing an exponential
weighted moving average model that jointly estimates volatility, skewness and
kurtosis over time using a modified form of the Gram-Charlier density in which
skewness and kurtosis appear directly in the functional form of this density.
In this setting VaR can be described as a function of the time-varying higher
moments by applying the Cornish-Fisher expansion series of the first four
moments. An evaluation of the predictive performance of the proposed model in
the estimation of 1-day and 10-day VaR forecasts is performed in comparison
with the historical simulation, filtered historical simulation and GARCH model.
The adequacy of the VaR forecasts is evaluated under the unconditional,
independence and conditional likelihood ratio tests as well as Basel II
regulatory tests. The results presented have significant implications for risk
management, trading and hedging activities as well as in the pricing of equity
derivatives
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