628 research outputs found
Helioseismic Holography of an Artificial Submerged Sound Speed Perturbation and Implications for the Detection of Pre-Emergence Signatures of Active Regions
We use a publicly available numerical wave-propagation simulation of Hartlep
et al. 2011 to test the ability of helioseismic holography to detect signatures
of a compact, fully submerged, 5% sound-speed perturbation placed at a depth of
50 Mm within a solar model. We find that helioseismic holography as employed in
a nominal "lateral-vantage" or "deep-focus" geometry employing quadrants of an
annular pupil is capable of detecting and characterizing the perturbation. A
number of tests of the methodology, including the use of a plane-parallel
approximation, the definition of travel-time shifts, the use of different
phase-speed filters, and changes to the pupils, are also performed. It is found
that travel-time shifts made using Gabor-wavelet fitting are essentially
identical to those derived from the phase of the Fourier transform of the
cross-covariance functions. The errors in travel-time shifts caused by the
plane-parallel approximation can be minimized to less than a second for the
depths and fields of view considered here. Based on the measured strength of
the mean travel-time signal of the perturbation, no substantial improvement in
sensitivity is produced by varying the analysis procedure from the nominal
methodology in conformance with expectations. The measured travel-time shifts
are essentially unchanged by varying the profile of the phase-speed filter or
omitting the filter entirely. The method remains maximally sensitive when
applied with pupils that are wide quadrants, as opposed to narrower quadrants
or with pupils composed of smaller arcs. We discuss the significance of these
results for the recent controversy regarding suspected pre-emergence signatures
of active regions
Non-equilibrium entangled steady state of two independent two-level systems
We determine and study the steady state of two independent two-level systems
weakly coupled to a stationary non-equilibrium environment. Whereas this
bipartite state is necessarily uncorrelated if the splitting energies of the
two-level systems are different from each other, it can be entangled if they
are equal. For identical two-level systems interacting with two bosonic heat
baths at different temperatures, we discuss the influence of the baths
temperatures and coupling parameters on their entanglement. Geometric
properties, such as the baths dimensionalities and the distance between the
two-level systems, are relevant. A regime is found where the steady state is a
statistical mixture of the product ground state and of the entangled singlet
state with respective weights 2/3 and 1/3
Treatment of electrical status epilepticus in sleep : A pooled analysis of 575 cases
OBJECTIVE: Epileptic encephalopathy with electrical status epilepticus in sleep (ESES) is a pediatric epilepsy syndrome with sleep-induced epileptic discharges and acquired impairment of cognition or behavior. Treatment of ESES is assumed to improve cognitive outcome. The aim of this study is to create an overview of the current evidence for different treatment regimens in children with ESES syndrome. METHODS: A literature search using PubMed and Embase was performed. Articles were selected that contain original treatment data of patients with ESES syndrome. Authors were contacted for additional information. Individual patient data were collected, coded, and analyzed using logistic regression analysis. The three predefined main outcome measures were improvement in cognitive function, electroencephalography (EEG) pattern, and any improvement (cognition or EEG). RESULTS: The literature search yielded 1,766 articles. After applying inclusion and exclusion criteria, 112 articles and 950 treatments in 575 patients could be analyzed. Antiepileptic drugs (AEDs, n = 495) were associated with improvement (i.e., cognition or EEG) in 49% of patients, benzodiazepines (n = 171) in 68%, and steroids (n = 166) in 81%. Surgery (n = 62) resulted in improvement in 90% of patients. In a subgroup analysis of patients who were consecutively reported (585 treatments in 282 patients), we found improvement in a smaller proportion treated with AEDs (34%), benzodiazepines (59%), and steroids (75%), whereas the improvement percentage after surgery was preserved (93%). Possible predictors of improved outcome were treatment category, normal development before ESES onset, and the absence of structural abnormalities. SIGNIFICANCE: Although most included studies were small and retrospective and their heterogeneity allowed analysis of only qualitative outcome data, this pooled analysis suggests superior efficacy of steroids and surgery in encephalopathy with ESES
A Planck-scale axion and SU(2) Yang-Mills dynamics: Present acceleration and the fate of the photon
From the time of CMB decoupling onwards we investigate cosmological evolution
subject to a strongly interacting SU(2) gauge theory of Yang-Mills scale
eV (masquerading as the factor of the SM at
present). The viability of this postulate is discussed in view of cosmological
and (astro)particle physics bounds. The gauge theory is coupled to a spatially
homogeneous and ultra-light (Planck-scale) axion field. As first pointed out by
Frieman et al., such an axion is a viable candidate for quintessence, i.e.
dynamical dark energy, being associated with today's cosmological acceleration.
A prediction of an upper limit for the duration of the
epoch stretching from the present to the point where the photon starts to be
Meissner massive is obtained: billion years.Comment: v3: consequences of an error in evolution equation for coupling
rectified, only a minimal change in physics results, two refs. adde
On the SigmaN cusp in the pp -> pK+Lambda reaction
Measurements of the reaction at = 2.28 GeV have
been carried out at COSY-TOF. In addition to the FSI and
resonance excitation effects a pronounced narrow structure is observed in the
Dalitz plot and in its projection on the -invariant mass. The
structure appears at the N threshold and is interpreted as
N cusp effect. The observed width of 20 MeV/ is substantially
broader than anticipated from previous inclusive measurements. Angular
distributions of this cusp structure are shown to be dissimilar to those in the
residual channel, but similar to those observed in the
channel
Coherent QCD phenomena in the Coherent Pion-Nucleon and Pion-Nucleus Production of Two Jets at High Relative Momenta
We use QCD to compute the cross section for coherent production of a di-jet
(treated as a moving at high relative transverse momentum,). In the target rest frame,the space-time evolution of this reaction is
dominated by the process in which the high component of
the pion wave function is formed before reaching the target. It then interacts
through two gluon exchange. In the approximation of keeping the leading order
in powers of and all orders in
the amplitudes for other processes are
shown to be smaller at least by a power of . The resulting dominant
amplitude is proportional to ( is the fraction
light-cone(+)momentum carried by the quark in the final state) times the skewed
gluon distribution of the target. For the pion scattering by a nuclear target,
this means that at fixed (but ) the nuclear process in which there is only a single interaction is the
most important one to contribute to the reaction. Thus in this limit color
transparency phenomena should occur.These findings are in accord with E971
experiment at FNAL. We also re-examine a potentially important nuclear multiple
scattering correction which is positive and . The
meaning of the signal obtained from the experimental measurement of pion
diffraction into two jets is also critically examined and significant
corrections are identified.We show also that for values of achieved
at fixed target energies, di-jet production by the e.m. field of the nucleus
leads to an insignificant correction which gets more important as
increases.Comment: 23 pages, 9 figure
Optimal Flying Wings: A Numerical Optimization Study
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97067/1/AIAA2012-1758.pd
Dynamical mean-field approach to materials with strong electronic correlations
We review recent results on the properties of materials with correlated
electrons obtained within the LDA+DMFT approach, a combination of a
conventional band structure approach based on the local density approximation
(LDA) and the dynamical mean-field theory (DMFT). The application to four
outstanding problems in this field is discussed: (i) we compute the full
valence band structure of the charge-transfer insulator NiO by explicitly
including the p-d hybridization, (ii) we explain the origin for the
simultaneously occuring metal-insulator transition and collapse of the magnetic
moment in MnO and Fe2O3, (iii) we describe a novel GGA+DMFT scheme in terms of
plane-wave pseudopotentials which allows us to compute the orbital order and
cooperative Jahn-Teller distortion in KCuF3 and LaMnO3, and (iv) we provide a
general explanation for the appearance of kinks in the effective dispersion of
correlated electrons in systems with a pronounced three-peak spectral function
without having to resort to the coupling of electrons to bosonic excitations.
These results provide a considerable progress in the fully microscopic
investigations of correlated electron materials.Comment: 24 pages, 14 figures, final version, submitted to Eur. Phys. J. for
publication in the Special Topics volume "Cooperative Phenomena in Solids:
Metal-Insulator Transitions and Ordering of Microscopic Degrees of Freedom
Kaon induced Lambda(1405) production on a deuteron target at DAFNE
The K^- induced production of Lambda(1405) in the K^- d to pi Sigma n
reaction is investigated having in mind the conditions of the DAFNE facility at
Frascati where kaons are obtained from the decay of slow moving phi mesons. We
find that the K^- d to Lambda(1405) n process favors the production of
Lambda(1405) initiated by the K^- p channel, which gives largest weight to the
higher mass Lambda(1405) appearing at 1420 MeV in chiral theories. We find that
the fastest kaons from the decay of the phi are well suited to see this
resonance, particularly if one selects forward going neutrons in the center of
mass, which reduce the contribution of single scattering and make the double
scattering dominate where the signal of the resonance appears clearer.Comment: 6pages, 7 figure
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