2,585 research outputs found
A novel modular stator hybrid-excited doubly salient synchronous machine with stator slot permanent magnets
This paper presents a novel modular stator hybrid-excited synchronous machine with stator slot permanent magnets (PMs). By regulating the field current, the magnetic field, and consequently the back electromotive force, as well as the average torque can be controlled. The existence of stator slot PMs alleviates the magnetic saturation and improves the flux regulation ratio. The frozen permeability method is employed to investigate the torque contributions by different magnetic sources. Possible stator and rotor pole combinations are illustrated, and the corresponding electromagnetic performances are evaluated with the finite-element method. It is revealed that 12-stator pole machines with 11- and 13-rotor poles exhibit superior average torque and lower torque ripple due to even-order harmonics elimination. Finally, a prototype with modular stator segments is manufactured to validate the analyses and simulations
Quantum Tunneling, Blackbody Spectrum and Non-Logarithmic Entropy Correction for Lovelock Black Holes
We show, using the tunneling method, that Lovelock black holes Hawking
radiate with a perfect blackbody spectrum. This is a new result. Within the
semiclassical (WKB) approximation the temperature of the spectrum is given by
the semiclassical Hawking temperature. Beyond the semiclassical approximation
the thermal nature of the spectrum does not change but the temperature
undergoes some higher order corrections. This is true for both black hole
(event) and cosmological horizons. Using the first law of thermodynamics the
black hole entropy is calculated. Specifically the -dimensional static,
chargeless black hole solutions which are spherically symmetric and
asymptotically flat, AdS or dS are considered. The interesting property of
these black holes is that their semiclassical entropy does not obey the
Bekenstein-Hawking area law. It is found that the leading correction to the
semiclassical entropy for these black holes is not logarithmic and next to
leading correction is also not inverse of horizon area. This is in contrast to
the black holes in Einstein gravity. The modified result is due to the presence
of Gauss-Bonnet term in the Lovelock Lagrangian. For the limit where the
coupling constant of the Gauss-Bonnet term vanishes one recovers the known
correctional terms as expected in Einstein gravity. Finally we relate the
coefficient of the leading (non-logarithmic) correction with the trace anomaly
of the stress tensor.Comment: minor modifications, two new references added, LaTeX, JHEP style, 34
pages, no figures, to appear in JHE
Pulse-shape discrimination with PbWO crystal scintillators
The light output, ratio, and pulse shape have been
investigated at C with PbWO crystal scintillators undoped, and
doped by F, Eu, Mo, Gd and S. The fast s and middle s components of scintillation decay were observed for all the samples. Slow
components of scintillation signal with the decay times s and s with the total intensity up to have been recognized for
several samples doped by Molybdenum. We found some indications of a pulse-shape
discrimination between particles and quanta with PbWO (Mo
doped) crystal scintillators.Comment: 12 pages, 5 figures, submitted to NIM
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On the unsteady-motion theory of magnetic forces for maglev
Motion-dependent magnetic forces are the key elements in the study of magnetically levitated vehicle (maglev) system dynamics. This paper presents an experimental and analytical study that will enhance their understanding of the role of unsteady-motion-dependent magnetic forces and demonstrate an experimental technique that can be used to measure those unsteady magnetic forces directly. The experimental technique provides a useful tool to measure motion-dependent magnetic forces for the prediction and control of maglev systems
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Vibration and stability of two tubes in crossflow
Two tubes in tandem and normal to flow were studied on the basis of the unsteady-flow theory. Motion-dependent fluid forces were measured in a water channel, and the pitch-to-diameter ratio was 1.35. From the measured fluid forces, fluid damping and stiffness were calculated as a function of reduced flow velocity and several Reynolds numbers. Once the fluid-damping and fluid-stiffness coefficients are known, coupled vibration and stability of the two tubes in crossflow can be predicted
Evidence for particle-hole excitations in the triaxial strongly-deformed well of ^{163}Tm
Two interacting, strongly-deformed triaxial (TSD) bands have been identified
in the Z = 69 nucleus ^{163}Tm. This is the first time that interacting TSD
bands have been observed in an element other than the Z = 71 Lu nuclei, where
wobbling bands have been previously identified. The observed TSD bands in
^{163}Tm appear to be associated with particle-hole excitations, rather than
wobbling. Tilted-Axis Cranking (TAC) calculations reproduce all experimental
observables of these bands reasonably well and also provide an explanation for
the presence of wobbling bands in the Lu nuclei, and their absence in the Tm
isotopes.Comment: 13 pages, 7 figure
Black hole collision with a scalar particle in four, five and seven dimensional anti-de Sitter spacetimes: ringing and radiation
In this work we compute the spectra, waveforms and total scalar energy
radiated during the radial infall of a small test particle coupled to a scalar
field into a -dimensional Schwarzschild-anti-de Sitter black hole. We focus
on and 7, extending the analysis we have done for . For small
black holes, the spectra peaks strongly at a frequency , which
is the lowest pure anti-de Sitter (AdS) mode. The waveform vanishes
exponentially as , and this exponential decay is governed
entirely by the lowest quasinormal frequency. This collision process is
interesting from the point of view of the dynamics itself in relation to the
possibility of manufacturing black holes at LHC within the brane world
scenario, and from the point of view of the AdS/CFT conjecture, since the
scalar field can represent the string theory dilaton, and 4, 5, 7 are
dimensions of interest for the AdS/CFT correspondence.Comment: 16 pages, 13 figures. Published versio
Global Phase Diagram of the Kondo Lattice: From Heavy Fermion Metals to Kondo Insulators
We discuss the general theoretical arguments advanced earlier for the T=0
global phase diagram of antiferromagnetic Kondo lattice systems, distinguishing
between the established and the conjectured. In addition to the well-known
phase of a paramagnetic metal with a "large" Fermi surface (P_L), there is also
an antiferromagnetic phase with a "small" Fermi surface (AF_S). We provide the
details of the derivation of a quantum non-linear sigma-model (QNLsM)
representation of the Kondo lattice Hamiltonian, which leads to an effective
field theory containing both low-energy fermions in the vicinity of a Fermi
surface and low-energy bosons near zero momentum. An asymptotically exact
analysis of this effective field theory is made possible through the
development of a renormalization group procedure for mixed fermion-boson
systems. Considerations on how to connect the AF_S and P_L phases lead to a
global phase diagram, which not only puts into perspective the theory of local
quantum criticality for antiferromagnetic heavy fermion metals, but also
provides the basis to understand the surprising recent experiments in
chemically-doped as well as pressurized YbRh2Si2. We point out that the AF_S
phase still occurs for the case of an equal number of spin-1/2 local moments
and conduction electrons. This observation raises the prospect for a global
phase diagram of heavy fermion systems in the Kondo-insulator regime. Finally,
we discuss the connection between the Kondo breakdown physics discussed here
for the Kondo lattice systems and the non-Fermi liquid behavior recently
studied from a holographic perspective.Comment: (v3) leftover typos corrected. (v2) Published version. 32 pages, 4
figures. Section 7, on the connection between the Kondo lattice systems and
the holographic models of non-Fermi liquid, is expanded. (v1) special issue
of JLTP on quantum criticalit
History effects and pinning regimes in solid vortex matter
We propose a phenomenological model that accounts for the history effects
observed in ac susceptibility measurements in YBa2Cu3O7 single crystals [Phys.
Rev. Lett. 84, 4200 (2000) and Phys. Rev. Lett. 86, 504 (2001)]. Central to the
model is the assumption that the penetrating ac magnetic field modifies the
vortex lattice mobility, trapping different robust dynamical states in
different regions of the sample. We discuss in detail on the response of the
superconductor to an ac magnetic field when the vortex lattice mobility is not
uniform inside the sample. We begin with an analytical description for a simple
geometry (slab) and then we perform numerical calculations for a strip in a
transverse magnetic field which include relaxation effects. In calculations,
the vortex system is assumed to coexist in different pinning regimes. The
vortex behavior in the regions where the induced current density j has been
always below a given threshold (j_c^>) is described by an elastic Campbell-like
regime (or a critical state regime with local high critical current density,
j_c^>). When the VS is shaken by symmetrical (e.g. sinusoidal) ac fields, the
critical current density is modified to j_c^) at
regions where vortices have been forced to oscillate by a current density
larger than j_c^>. Experimentally, an initial state with high critical current
density (j_c^>) can be obtained by zero field cooling, field cooling (with no
applied ac field) or by shaking the vortex lattice with an asymmetrical (e.g.
sawtooth) field. We compare our calculations with experimental ac
susceptibility results in YBa2Cu3O7 single crystals.Comment: 11 pages, 7 figures. To be published in PR
Higgs-Boson Production Induced by Bottom Quarks
Bottom quark-induced processes are responsible for a large fraction of the
LHC discovery potential, in particular for supersymmetric Higgs bosons.
Recently, the discrepancy between exclusive and inclusive Higgs boson
production rates has been linked to the choice of an appropriate bottom
factorization scale. We investigate the process kinematics at hadron colliders
and show that it leads to a considerable decrease in the bottom factorization
scale. This effect is the missing piece needed to understand the corresponding
higher order results. Our results hold generally for charged and for neutral
Higgs boson production at the LHC as well as at the Tevatron. The situation is
different for single top quark production, where we find no sizeable
suppression of the factorization scale. Turning the argument around, we can
specify how large the collinear logarithms are, which can be resummed using the
bottom parton picture.Comment: 18 page
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