293 research outputs found
The low-frequency response in the surface superconducting state of ZrB single crystal}
The large nonlinear response of a single crystal ZrB to an ac field
(frequency 40 - 2500 Hz) for has been observed. Direct
measurements of the ac wave form and the exact numerical solution of the
Ginzburg-Landau equations, as well as phenomenological relaxation equation,
permit the study of the surface superconducting states dynamics. It is shown,
that the low frequency response is defined by transitions between the
metastable superconducting states under the action of an ac field. The
relaxation rate which determines such transitions dynamics, is found.Comment: 7 pages, 11 figure
Theory of flux cutting and flux transport at the critical current of a type-II superconducting cylindrical wire
I introduce a critical-state theory incorporating both flux cutting and flux
transport to calculate the magnetic-field and current-density distributions
inside a type-II superconducting cylinder at its critical current in a
longitudinal applied magnetic field. The theory is an extension of the elliptic
critical-state model introduced by Romero-Salazar and Perez-Rodriguez. The
vortex dynamics depend in detail upon two nonlinear effective resistivities for
flux cutting (\rho_\parallel) and flux flow (\rho_\perp), and their ratio r =
\rho_\parallel/\rho_\perp. When r < 1, the low relative efficiency of flux
cutting in reducing the magnitude of the internal magnetic-flux density leads
to a paramagnetic longitudinal magnetic moment. As a model for understanding
the experimentally observed interrelationship between the critical currents for
flux cutting and depinning, I calculate the forces on a helical vortex arc
stretched between two pinning centers when the vortex is subjected to a current
density of arbitrary angle \phi. Simultaneous initiation of flux cutting and
flux transport occurs at the critical current density J_c(\phi) that makes the
vortex arc unstable.Comment: 14 pages, 13 figure
Hamiltonian dynamics of extended objects
We consider a relativistic extended object described by a reparametrization
invariant local action that depends on the extrinsic curvature of the
worldvolume swept out by the object as it evolves. We provide a Hamiltonian
formulation of the dynamics of such higher derivative models which is motivated
by the ADM formulation of general relativity. The canonical momenta are
identified by looking at boundary behavior under small deformations of the
action; the relationship between the momentum conjugate to the embedding
functions and the conserved momentum density is established. The canonical
Hamiltonian is constructed explicitly; the constraints on the phase space, both
primary and secondary, are identified and the role they play in the theory
described. The multipliers implementing the primary constraints are identified
in terms of the ADM lapse and shift variables and Hamilton's equations shown to
be consistent with the Euler-Lagrange equations.Comment: 24 pages, late
Nucleation of Brane Universes
The creation of brane universes induced by a totally antisymmetric tensor
living in a fixed background spacetime is presented, where a term involving the
intrinsic curvature of the brane is considered. A canonical quantum mechanical
approach employing Wheeler-DeWitt equation is done. The probability nucleation
for the brane is calculated taking into account both an instanton method and a
WKB approximation. Some cosmological implications arose from the model are
presented.Comment: 19 pages, 2 figure
Black Holes in Higher-Dimensional Gravity
These lectures review some of the recent progress in uncovering the phase
structure of black hole solutions in higher-dimensional vacuum Einstein
gravity. The two classes on which we focus are Kaluza-Klein black holes, i.e.
static solutions with an event horizon in asymptotically flat spaces with
compact directions, and stationary solutions with an event horizon in
asymptotically flat space. Highlights include the recently constructed
multi-black hole configurations on the cylinder and thin rotating black rings
in dimensions higher than five. The phase diagram that is emerging for each of
the two classes will be discussed, including an intriguing connection that
relates the phase structure of Kaluza-Klein black holes with that of
asymptotically flat rotating black holes.Comment: latex, 49 pages, 5 figures. Lectures to appear in the proceedings of
the Fourth Aegean Summer School, Mytiline, Lesvos, Greece, September 17-22,
200
Spina bifida-predisposing heterozygous mutations in Planar Cell Polarity genes and Zic2 reduce bone mass in young mice
Fractures are a common comorbidity in children with the neural tube defect (NTD) spina bifida. Mutations in the Wnt/planar cell polarity (PCP) pathway contribute to NTDs in humans and mice, but whether this pathway independently determines bone mass is poorly understood. Here, we first confirmed that core Wnt/PCP components are expressed in osteoblasts and osteoclasts in vitro. In vivo, we performed detailed µCT comparisons of bone structure in tibiae from young male mice heterozygous for NTD-associated mutations versus WT littermates. PCP signalling disruption caused by Vangl2 (Vangl2Lp/+) or Celsr1 (Celsr1Crsh/+) mutations significantly reduced trabecular bone mass and distal tibial cortical thickness. NTD-associated mutations in non-PCP transcription factors were also investigated. Pax3 mutation (Pax3Sp2H/+) had minimal effects on bone mass. Zic2 mutation (Zic2Ku/+) significantly altered the position of the tibia/fibula junction and diminished cortical bone in the proximal tibia. Beyond these genes, we bioinformatically documented the known extent of shared genetic networks between NTDs and bone properties. 46 genes involved in neural tube closure are annotated with bone-related ontologies. These findings document shared genetic networks between spina bifida risk and bone structure, including PCP components and Zic2. Genetic variants which predispose to spina bifida may therefore independently diminish bone mass
Построение и обучение радиально-базисных нейросетей для приема телеграфно-кодовых конструкций
The use of neural network classification algorithms for solving the problem of receiving telegram-code structures is considered. The article provides comparison of the neural network classifiers analyzing the normalized input signal as well as the signal after the binary conversion. Various measures of the code distance in the space of informative features are considered. Recognition comparative results for the selected pair of symbols are given. On the basis of these results the code distance is determined, which ensures the minimum recognition error probability. The results obtained in the developed neural network classifier are compared with those obtained in correlation receivers operating in the signal time and frequency domains. The advantage of neural network algorithm is shown. The structure implementing the developed neural network classifier is provided. It is shown that the procedure for the classifier developing, k \ including selection of information signs and their amount, as well as code distance, is not of general nature and is to be performed for each set of recognizable symbols. It is stated that to generalize the received alphanumeric blocks it is necessary to use the second decision contour where current information on the reception and information on the duration of the observed symbol is supplied, which is the subject of further research.Рассмотрено использование алгоритмов нейросетевой классификации для решения задачи приема телеграфно-кодовых конструкций, оценена эффективность их применения. Обоснована структура предлагаемой нейросети-классификатора и получены ее параметры. В одинаковых условиях проведено экспериментальное сравнение эффективности применения разработанного метода и классических методов оптимального приема детерминированных сигналов, основанных на корреляционном подходе.
Demonstration of Fuel Hot-Spot Pressure in Excess of 50 Gbar for Direct-Drive, Layered Deuterium-Tritium Implosions on OMEGA
A record fuel hot-spot pressure P[subscript hs] = 56±7 Gbar was inferred from x-ray and nuclear diagnostics for direct-drive inertial confinement fusion cryogenic, layered deuterium–tritium implosions on the 60-beam, 30-kJ, 351-nm OMEGA Laser System. When hydrodynamically scaled to the energy of the National Ignition Facility, these implosions achieved a Lawson parameter ∼60% of the value required for ignition [A. Bose et al., Phys. Rev. E 93, LM15119ER (2016)], similar to indirect-drive implosions [R. Betti et al., Phys. Rev. Lett. 114, 255003 (2015)], and nearly half of the direct-drive ignition-threshold pressure. Relative to symmetric, one-dimensional simulations, the inferred hot-spot pressure is approximately 40% lower. Three-dimensional simulations suggest that low-mode distortion of the hot spot seeded by laser-drive nonuniformity and target-positioning error reduces target performance.United States. Department of Energy (DE-NA0001944
Parent-of-origin-specific allelic associations among 106 genomic loci for age at menarche.
Age at menarche is a marker of timing of puberty in females. It varies widely between individuals, is a heritable trait and is associated with risks for obesity, type 2 diabetes, cardiovascular disease, breast cancer and all-cause mortality. Studies of rare human disorders of puberty and animal models point to a complex hypothalamic-pituitary-hormonal regulation, but the mechanisms that determine pubertal timing and underlie its links to disease risk remain unclear. Here, using genome-wide and custom-genotyping arrays in up to 182,416 women of European descent from 57 studies, we found robust evidence (P < 5 × 10(-8)) for 123 signals at 106 genomic loci associated with age at menarche. Many loci were associated with other pubertal traits in both sexes, and there was substantial overlap with genes implicated in body mass index and various diseases, including rare disorders of puberty. Menarche signals were enriched in imprinted regions, with three loci (DLK1-WDR25, MKRN3-MAGEL2 and KCNK9) demonstrating parent-of-origin-specific associations concordant with known parental expression patterns. Pathway analyses implicated nuclear hormone receptors, particularly retinoic acid and γ-aminobutyric acid-B2 receptor signalling, among novel mechanisms that regulate pubertal timing in humans. Our findings suggest a genetic architecture involving at least hundreds of common variants in the coordinated timing of the pubertal transition
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