11,768 research outputs found
New results on alpha_s and optimized scales
A summary of the latest alpha_s results at LEP1 and LEP2 from event-shape
predictions at Order(alpha2_s) + NLLA is presented. Later these are compared to
measurements obtained using the Experimentally Optimized Scale method. Finally
the alpha_s measurement from the 4-jet rate is discussed.Comment: 6 pages, 4 figures, talk presented at the 30th ISMD, Hungary, October
200
Thermal X-ray emission from shocked ejecta in Type Ia Supernova Remnants. Prospects for explosion mechanism identification
The explosion mechanism behind Type Ia supernovae is a matter of continuing
debate. The diverse attempts to identify or at least constrain the physical
processes involved in the explosion have been only partially successful so far.
In this paper we propose to use the thermal X-ray emission from young supernova
remnants originated in Type Ia events to extract relevant information
concerning the explosions themselves. We have produced a grid of thermonuclear
supernova models representative of the paradigms currently under debate: pure
deflagrations, delayed detonations, pulsating delayed detonations and
sub-Chandrasekhar explosions, using their density and chemical composition
profiles to simulate the interaction with the surrounding ambient medium and
the ensuing plasma heating, non-equilibrium ionization and thermal X-ray
emission of the ejecta. Key observational parameters such as electron
temperatures, emission measures and ionization time scales are presented and
discussed. We find that not only is it possible to identify the explosion
mechanism from the spectra of young Type Ia Supernova Remnants, it is in fact
necessary to take the detailed ejecta structure into account if such spectra
are to be modeled in a self-consistent way. Neither element line flux ratios
nor element emission measures are good estimates of the true ratios of ejected
masses, with differences of as much as two or three orders of magnitude for a
given model. Comparison with observations of the Tycho SNR suggests a delayed
detonation as the most probable explosion mechanism. Line strengths, line
ratios, and the centroid of the Fe Kalpha line are reasonably well reproduced
by a model of this kind.Comment: 11 pages, 8 figures (5 of them color), accepted for publication by
the Ap
Isotopic overabundances and the energetic particle model of solar flares
According to the energetic particle model of solar flares particles are efficiently accelerated in the magnetic field loop of an active region (AR) by hydromagnetic turbulence. It is demonstrated that the isotopic overabundances observed in some flares are not a consequence of the flare itself but are characteristic of the plasma in the AR. Only when a flare releases the plasma into the interplanetary space it is possible to observe this anomalous composition at spacecraft locations
Multi-vortex dynamics in junctions of charge density waves
Ground state reconstruction by creation of topological defects in junctions
of CDWs is a convenient playground for modern efforts of field-effect
transformations in strongly correlated materials with spontaneous symmetry
breakings. Being transient, this effect contributes also to another new science
of pump-induced phase transitions. We present a dynamical model for behavior of
the CDW in restricted geometries of junctions under an applied voltage or a
passing current. The model takes into account multiple interacting fields: the
amplitude and the phase of the CDW complex order parameter, distributions of
the electric field, the density and the current of various normal carriers. A
particular challenge was to monitor the local conservation of the condensed and
the normal charge densities. That was done easily invoking the chiral
invariance and the associated anomaly, but prize is an unconventional
Ginsburg-Landau type theory which is not analytic with respect to the order
parameter. The numerical modeling poses unusual difficulties but still can
demonstrate that vortices are nucleated at the junction boundary when the
voltage across, or the current through, exceed a threshold.Comment: To be published in proceedings of the conference SUPERSTRIPES-2014,
A. Bianconi ed., J. Supercond. Nov. Mag., (2015
Removing batch effects for prediction problems with frozen surrogate variable analysis
Batch effects are responsible for the failure of promising genomic prognos-
tic signatures, major ambiguities in published genomic results, and retractions
of widely-publicized findings. Batch effect corrections have been developed to
re- move these artifacts, but they are designed to be used in population
studies. But genomic technologies are beginning to be used in clinical
applications where sam- ples are analyzed one at a time for diagnostic,
prognostic, and predictive applica- tions. There are currently no batch
correction methods that have been developed specifically for prediction. In
this paper, we propose an new method called frozen surrogate variable analysis
(fSVA) that borrows strength from a training set for individual sample batch
correction. We show that fSVA improves prediction ac- curacy in simulations and
in public genomic studies. fSVA is available as part of the sva Bioconductor
package
Quantum Mechanical Corrections to the Schwarzschild Black Hole Metric
Motivated by quantum mechanical corrections to the Newtonian potential, which
can be translated into an -correction to the component of the
Schwarzschild metric, we construct a quantum mechanically corrected metric
assuming . We show how the Bekenstein black hole entropy
receives its logarithmic contribution provided the quantum mechanical
corrections to the metric are negative. In this case the standard horizon at
the Schwarzschild radius increases by small terms proportional to
and a remnant of the order of Planck mass emerges. We contrast these results
with a positive correction to the metric which, apart from a corrected
Schwarzschild horizon, leads to a new purely quantum mechanical horizon.Comment: 14 pages Latex, enlarged version as compared to the published on
Semidefinite Programming Approach for the Quadratic Assignment Problem with a Sparse Graph
The matching problem between two adjacency matrices can be formulated as the
NP-hard quadratic assignment problem (QAP). Previous work on semidefinite
programming (SDP) relaxations to the QAP have produced solutions that are often
tight in practice, but such SDPs typically scale badly, involving matrix
variables of dimension where n is the number of nodes. To achieve a speed
up, we propose a further relaxation of the SDP involving a number of positive
semidefinite matrices of dimension no greater than the number
of edges in one of the graphs. The relaxation can be further strengthened by
considering cliques in the graph, instead of edges. The dual problem of this
novel relaxation has a natural three-block structure that can be solved via a
convergent Augmented Direction Method of Multipliers (ADMM) in a distributed
manner, where the most expensive step per iteration is computing the
eigendecomposition of matrices of dimension . The new SDP
relaxation produces strong bounds on quadratic assignment problems where one of
the graphs is sparse with reduced computational complexity and running times,
and can be used in the context of nuclear magnetic resonance spectroscopy (NMR)
to tackle the assignment problem.Comment: 31 page
- âŠ