4,422 research outputs found
Bianchi Type III String Cosmological Models with Time Dependent Bulk Viscosity
Bianchi type III string cosmological models with bulk viscous fluid for
massive string are investigated. To get the determinate model of the universe,
we have assumed that the coefficient of bulk viscosity () is inversely
proportional to the expansion () in the model and expansion ()
in the model is proportional to the shear (). This leads to , and are constants. The behaviour of the model in presence
and absence of bulk viscosity, is discussed. The physical implications of the
models are also discussed in detail.Comment: 11 pages, no figur
Power-Gating Technique for Network-on-Chip Buffers
A new approach to reducing leakage power in network-on-chip buffers is presented. The non-uniformity of buffer utilisation is leveraged across the network and power-gating is applied to scarcely utilised buffers. Instead of turning-off the buffers completely, a buffer portion is kept turned-on. This design choice has a significant performance benefit because the buffer is always able to receive network packets. Design aspects and trade-offs in a 45 nm CMOS technology are discussed and results obtained over video application benchmarks are presented. It is shown that it is possible to reduce buffer leakage by 40% without performance penalt
Bianchi Type I Massive String Magnetized Barotropic Perfect Fluid Cosmological Model in General Relativity
Bianchi type I massive string cosmological model with magnetic field of
barotropic perfect fluid distribution through the techniques used by Latelier
and Stachel, is investigated. To get the deterministic model of the universe,
it is assumed that the universe is filled with barotropic perfect fluid
distribution. The magnetic field is due to electric current produced along
x-axis with infinite electrical conductivity. The behaviour of the model in
presence and absence of magnetic field together with other physical aspects is
further discussed.Comment: 10 pages, no figure. Chin. Phys. Lett., Vol. 24, No. 8 (2007), to
appea
High-Dimensional Stochastic Design Optimization by Adaptive-Sparse Polynomial Dimensional Decomposition
This paper presents a novel adaptive-sparse polynomial dimensional
decomposition (PDD) method for stochastic design optimization of complex
systems. The method entails an adaptive-sparse PDD approximation of a
high-dimensional stochastic response for statistical moment and reliability
analyses; a novel integration of the adaptive-sparse PDD approximation and
score functions for estimating the first-order design sensitivities of the
statistical moments and failure probability; and standard gradient-based
optimization algorithms. New analytical formulae are presented for the design
sensitivities that are simultaneously determined along with the moments or the
failure probability. Numerical results stemming from mathematical functions
indicate that the new method provides more computationally efficient design
solutions than the existing methods. Finally, stochastic shape optimization of
a jet engine bracket with 79 variables was performed, demonstrating the power
of the new method to tackle practical engineering problems.Comment: 18 pages, 2 figures, to appear in Sparse Grids and
Applications--Stuttgart 2014, Lecture Notes in Computational Science and
Engineering 109, edited by J. Garcke and D. Pfl\"{u}ger, Springer
International Publishing, 201
On Absorption by Circumstellar Dust, With the Progenitor of SN2012aw as a Case Study
We use the progenitor of SN2012aw to illustrate the consequences of modeling
circumstellar dust using Galactic (interstellar) extinction laws that (1)
ignore dust emission in the near-IR and beyond; (2) average over dust
compositions, and (3) mis-characterize the optical/UV absorption by assuming
that scattered photons are lost to the observer. The primary consequences for
the progenitor of SN2012aw are that both the luminosity and the absorption are
significantly over-estimated. In particular, the stellar luminosity is most
likely in the range 10^4.8 < L/Lsun < 10^5.0 and the star was not extremely
massive for a Type IIP progenitor, with M < 15Msun. Given the properties of the
circumstellar dust and the early X-ray/radio detections of SN2012aw, the star
was probably obscured by an on-going wind with Mdot ~ 10^-5.5 to 10^-5.0
Msun/year at the time of the explosion, roughly consistent with the expected
mass loss rates for a star of its temperature (T_* ~ 3600K) and luminosity. In
the spirit of Galactic extinction laws, we supply simple interpolation formulas
for circumstellar extinction by dusty graphitic and silicate shells as a
function of wavelength (>0.3 micron) and total (absorption plus scattering)
V-band optical depth (tau < 20). These do not include the contributions of dust
emission, but provide a simple, physical alternative to incorrectly using
interstellar extinction laws.Comment: Submitted to Ap
Triple-decker complexes incorporating three distinct deck architectures
The reactivity of the dilithioplumbole ([Li(thf)(μ,η-L)], L = 1,4-bis-tert-butyl-dimethylsilyl-2,3-bis-phenyl-plumbolyl) towards the reactive pnictogen precursors P, pentaphosphaferrocene, and pentaarsaferrocene ([Cp*Fe(η-E)] (Cp* = η-CMe, E = P, As)) is reported. The reaction with P afforded a phospholyl lithium complex, via lead-phosphorus exchange, while the reactions with [Cp*Fe(η-E)] yielded the first examples of Pb–Fe–Li heterotrimetallic triple-decker polypnictogenides with three different deck motifs
Lack of clustering in low-redshift 21-cm intensity maps cross-correlated with 2dF galaxy densities
We report results from 21-cm intensity maps acquired from the Parkes radio
telescope and cross-correlated with galaxy maps from the 2dF galaxy survey. The
data span the redshift range and cover approximately 1,300
square degrees over two long fields. Cross correlation is detected at a
significance of . The amplitude of the cross-power spectrum is low
relative to the expected dark matter power spectrum, assuming a neutral
hydrogen (HI) bias and mass density equal to measurements from the ALFALFA
survey. The decrement is pronounced and statistically significant at small
scales. At , the cross power spectrum is more
than a factor of 6 lower than expected, with a significance of .
This decrement indicates either a lack of clustering of neutral hydrogen (HI),
a small correlation coefficient between optical galaxies and HI, or some
combination of the two. Separating 2dF into red and blue galaxies, we find that
red galaxies are much more weakly correlated with HI on scales, suggesting that HI is more associated with blue
star-forming galaxies and tends to avoid red galaxies.Comment: 12 pages, 3 figures; fixed typo in meta-data title and paper author
Upper critical field, lower critical field and critical current density of FeTe0.60Se0.40 single crystal
The transport and magnetic studies are performed on high quality
FeTe0.60Se0.40 single crystals to determine the upper critical fields (Hc2),
lower critical field (Hc1) and the Critical current density (Jc). The value of
upper critical field Hc2 are very large, whereas the activation energy as
determined from the slope of the Arrhenius plots are was found to be lower than
that in the FeAs122 superconductor. The lower critical field was determined in
ab direction and c direction of the crystal, and was found to have a anisotropy
of 'gamma'{=(Hc1//c) / (Hc1//b)} ~ 4. The magnetic isotherms measured up to 12
Tesla shows the presence of fishtail behavior. The critical current densities
at 1.8K of the single crystal was found to almost same in both ab and c
direction as 1X105 Amp/cm2 in low field regime.Comment: 9 pages, 6 figure
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