156 research outputs found
Surface Tension between Kaon Condensate and Normal Nuclear Matter Phase
We calculate for the first time the surface tension and curvature coefficient
of a first order phase transition between two possible phases of cold nuclear
matter, a normal nuclear matter phase in equilibrium with a kaon condensed
phase, at densities a few times the saturation density. We find the surface
tension is proportional to the difference in energy density between the two
phases squared. Furthermore, we show the consequences for the geometrical
structures of the mixed phase region in a neutron star.Comment: 7 pages, 5 figures (Latex
Evaluation of 976 nm Multimode Single Emitter Laser Diodes for Efficient Pumping of 100 W+ Yb-doped Fiber Laser
Experimental evaluation of spectral and power-current (P-I) characteristics of fiber coupled single emitter multimode laser diodes used for development of efficient pumping assembly is reported. Fiber coupled laser diodes emitting around 976 nm are best suited for pumping Yb-doped fiber lasers because of excellent coupling efficiency and reduced thermal load. We have experimentally investigated emission spectrum of fiber coupled multimode laser diodes at different temperatures and drive currents. It is found that peak emission wavelength shifts towards the longer wavelength with increase in temperature and drive current. P-I characteristics of fiber coupled laser diodes have been obtained and presented for drive current from 0.4 A to 11.5 A. Based on experiment, we have constructed spectrally matched laser diode assembly for efficient pumping of 100 W fiber laser. It requires very precise control of temperature and drive current to maintain the emission spectrum. Total 162 W power is pumped in to the Yb-doped fiber laser cavity through multi-mode pump combiners and we have obtained 110 W fiber laser output power @1070 nm. The achieved optical-to-optical efficiency is 68 per cent
Stability of the lattice formed in first-order phase transitions to matter containing strangeness in protoneutron stars
Well into the deleptonization phase of a core collapse supernova, a
first-order phase transition to matter with macroscopic strangeness content is
assumed to occur and lead to a structured lattice defined by negatively charged
strange droplets. The lattice is shown to crystallize for expected droplet
charges and separations at temperatures typically obtained during the
protoneutronstar evolution. The melting curve of the lattice for small
spherical droplets is presented. The one-component plasma model proves to be an
adequate description for the lattice in its solid phase with deformation modes
freezing out around the melting temperature. The mechanical stability against
shear stresses is such that velocities predicted for convective phenomena and
differential rotation during the Kelvin-Helmholtz cooling phase might prevent
the crystallization of the phase transition lattice. A solid lattice might be
fractured by transient convection, which could result in anisotropic neutrino
transport. The melting curve of the lattice is relevant for the mechanical
evolution of the protoneutronstar and therefore should be included in future
hydrodynamics simulations.Comment: accepted for publication in Physical Review
Warm stellar matter with deconfinement: application to compact stars
We investigate the properties of mixed stars formed by hadronic and quark
matter in -equilibrium described by appropriate equations of state (EOS)
in the framework of relativistic mean-field theory. We use the non- linear
Walecka model for the hadron matter and the MIT Bag and the Nambu-Jona-Lasinio
models for the quark matter. The phase transition to a deconfined quark phase
is investigated. In particular, we study the dependence of the onset of a mixed
phase and a pure quark phase on the hyperon couplings, quark model and
properties of the hadronic model. We calculate the strangeness fraction with
baryonic density for the different EOS. With the NJL model the strangeness
content in the mixed phase decreases. The calculations were performed for T=0
and for finite temperatures in order to describe neutron and proto-neutron
stars. The star properties are discussed. Both the Bag model and the NJL model
predict a mixed phase in the interior of the star. Maximum allowed masses for
proto-neutron stars are larger for the NJL model ( M)
than for the Bag model ( M).Comment: RevTeX,14 figures, accepted to publication in Physical Review
Techniques for efficiently implementing totally self-checking checkers in MOS technology
This paper presents some new techniques for reducing the transistor count oof MOS implementations of totally self-checking (TSC) checkers. The techniques are (1) transfer of fanouts, (2) removal of inverters and (3) use of multi-level realizations of functions. These techniques also increase the speed of the circuit and may reduce the number of required tests. Their effectiveness has been demonstrated by applying them to m-out-of-n and Berger code checkers. Impressive reductions of up to 90% in the transistor count in some cases have been obtained for the MOS implementation of these checkers. This directly translates into saving of chip area.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26970/1/0000537.pd
SL(2,Z) symmetries, Supermembranes and Symplectic Torus Bundles
We give the explicit formulation of the 11D supermembrane as a symplectic
torus bundle with non trivial monodromy and non vanishing Euler class. This
construction allows a classification of all supermembranes showing explicitly
the discrete SL(2,Z) symmetries associated to dualities. It hints as the origin
in M-theory of the gauging of the effective theories associated to string
theories.Comment: 13 pages, Late
Scintillation Counters for the D0 Muon Upgrade
We present the results of an upgrade to the D0 muon system. Scintillating
counters have been added to the existing central D0 muon system to provide
rejection for cosmic ray muons and out-of-time background, and to provide
additional fast timing information for muons in an upgraded Tevatron.
Performance and results from the 1994-1996 Tevatron run are presented.Comment: 30 pages, 25 postscript figure
Magnetism in Dense Quark Matter
We review the mechanisms via which an external magnetic field can affect the
ground state of cold and dense quark matter. In the absence of a magnetic
field, at asymptotically high densities, cold quark matter is in the
Color-Flavor-Locked (CFL) phase of color superconductivity characterized by
three scales: the superconducting gap, the gluon Meissner mass, and the
baryonic chemical potential. When an applied magnetic field becomes comparable
with each of these scales, new phases and/or condensates may emerge. They
include the magnetic CFL (MCFL) phase that becomes relevant for fields of the
order of the gap scale; the paramagnetic CFL, important when the field is of
the order of the Meissner mass, and a spin-one condensate associated to the
magnetic moment of the Cooper pairs, significant at fields of the order of the
chemical potential. We discuss the equation of state (EoS) of MCFL matter for a
large range of field values and consider possible applications of the magnetic
effects on dense quark matter to the astrophysics of compact stars.Comment: To appear in Lect. Notes Phys. "Strongly interacting matter in
magnetic fields" (Springer), edited by D. Kharzeev, K. Landsteiner, A.
Schmitt, H.-U. Ye
A dc-link voltage stability analysis technique for hybrid five-phase open-end winding drives
This paper studies the dc-link voltage stability for a hybrid five-phase open-end winding (OeW) drive operating under carrier based (CB) pulse-width modulation (PWM). The drive consists of a five-phase induction machine, supplied using one three-level and one two-level voltage source inverter (VSI). This configuration is analysed for the case of isolated dc-link rails, while dc-link voltage ratio is considered as an additional degree of freedom. It is demonstrated that different dc-link voltage ratios lead to the different overall number of voltage levels across stator windings. Modulation strategies are investigated and their performances are analysed from the dc-link voltages stability point of view. An analytical method for dc-link voltage stability analysis is presented. Results show that the four-level configuration always leads to stable dc-link voltages, regardless of the modulation strategy. On the other hand, if six-level configuration is combined with modulation strategies that lead to an optimal harmonic performance, not all dc-link capacitor voltages will be in balance depending on the operating conditions
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