48,915 research outputs found
Agegraphic Chaplygin gas model of dark energy
We establish a connection between the agegraphic models of dark energy and
Chaplygin gas energy density in non-flat universe. We reconstruct the potential
of the agegraphic scalar field as well as the dynamics of the scalar field
according to the evolution of the agegraphic dark energy. We also extend our
study to the interacting agegraphic generalized Chaplygin gas dark energy
model.Comment: 8 page
Interacting non-minimally coupled canonical, phantom and quintom models of holographic dark energy in non-flat universe
Motivated by our recent work \cite{set1}, we generalize this work to the
interacting non-flat case. Therefore in this paper we deal with canonical,
phantom and quintom models, with the various fields being non-minimally coupled
to gravity, within the framework of interacting holographic dark energy. We
employ the holographic model of interacting dark energy to obtain the equation
of state for the holographic energy density in non-flat (closed) universe
enclosed by the event horizon measured from the sphere of horizon named .Comment: 18 pages, 3 figures. Accepted for publication in IJMPD (2010
Observational constraints on patch inflation in noncommutative spacetime
We study constraints on a number of patch inflationary models in
noncommutative spacetime using a compilation of recent high-precision
observational data. In particular, the four-dimensional General Relativistic
(GR) case, the Randall-Sundrum (RS) and Gauss-Bonnet (GB) braneworld scenarios
are investigated by extending previous commutative analyses to the infrared
limit of a maximally symmetric realization of the stringy uncertainty
principle. The effect of spacetime noncommutativity modifies the standard
consistency relation between the tensor spectral index and the tensor-to-scalar
ratio. We perform likelihood analyses in terms of inflationary observables
using new consistency relations and confront them with large-field inflationary
models with potential V \propto \vp^p in two classes of noncommutative
scenarios. We find a number of interesting results: (i) the quartic potential
(p=4) is rescued from marginal rejection in the class 2 GR case, and (ii) steep
inflation driven by an exponential potential (p \to \infty) is allowed in the
class 1 RS case. Spacetime noncommutativity can lead to blue-tilted scalar and
tensor spectra even for monomial potentials, thus opening up a possibility to
explain the loss of power observed in the cosmic microwave background
anisotropies. We also explore patch inflation with a Dirac-Born-Infeld tachyon
field and explicitly show that the associated likelihood analysis is equivalent
to the one in the ordinary scalar field case by using horizon-flow parameters.
It turns out that tachyon inflation is compatible with observations in all
patch cosmologies even for large p.Comment: 16 pages, 11 figures; v2: updated references, minor corrections to
match the Phys. Rev. D versio
Close binary evolution I. The tidally induced shear mixing in rotating binaries
We study how tides in a binary system induce some specific internal shear
mixing, able to substantially modify the evolution of close binaries prior to
mass transfer. We construct numerical models accounting for tidal interactions,
meridional circulation, transport of angular momentum, shears and horizontal
turbulence and consider a variety of orbital periods and initial rotation
velocities. Depending on orbital periods and rotation velocities, tidal effects
may spin down (spin down Case) or spin up (spin up Case) the axial rotation. In
both cases, tides may induce a large internal differential rotation. The
resulting tidally induced shear mixing (TISM) is so efficient that the internal
distributions of angular velocity and chemical elements are greatly influenced.
The evolutionary tracks are modified, and in both cases of spin down and spin
up, large amounts of nitrogen can be transported to the stellar surfaces before
any binary mass transfer. Meridional circulation, when properly treated as an
advection, always tends to counteract the tidal interaction, tending to spin up
the surface when it is braked down and vice versa. As a consequence, the times
needed for the axial angular velocity to become equal to the orbital angular
velocity may be larger than given by typical synchronization timescales. Also,
due to meridional circulation some differential rotation remains in tidally
locked binary systems.Comment: 10 pages, 18 figures, Accepted for publication in Astronomy and
Astrophysic
A Novel Large Moment Antiferromagnetic Order in K0.8Fe1.6Se2 Superconductor
The discovery of cuprate high Tc superconductors has inspired searching for
unconventional su- perconductors in magnetic materials. A successful recipe has
been to suppress long-range order in a magnetic parent compound by doping or
high pressure to drive the material towards a quantum critical point, which is
replicated in recent discovery of iron-based high TC superconductors. The
long-range magnetic order coexisting with superconductivity has either a small
magnetic moment or low ordering temperature in all previously established
examples. Here we report an exception to this rule in the recently discovered
potassium iron selenide. The superconducting composition is identified as the
iron vacancy ordered K0.8Fe1.6Se2 with Tc above 30 K. A novel large moment 3.31
{\mu}B/Fe antiferromagnetic order which conforms to the tetragonal crystal
symmetry has the unprecedentedly high an ordering temperature TN = 559 K for a
bulk superconductor. Staggeredly polarized electronic density of states thus is
suspected, which would stimulate further investigation into superconductivity
in a strong spin-exchange field under new circumstance.Comment: 5 figures, 5 pages, and 2 tables in pdf which arXiv.com cannot tak
Thermomechanical Characterization And Modeling For TSV Structures
Continual scaling of devices and on-chip wiring has brought significant challenges for materials and processes beyond the 32-nm technology node in microelectronics. Recently, three-dimensional (3-D) integration with through-silicon vias (TSVs) has emerged as an effective solution to meet the future technology requirements. Among others, thermo-mechanical reliability is a key concern for the development of TSV structures used in die stacking as 3-D interconnects. This paper presents experimental measurements of the thermal stresses in TSV structures and analyses of interfacial reliability. The micro-Raman measurements were made to characterize the local distribution of the near-surface stresses in Si around TSVs. On the other hand, the precision wafer curvature technique was employed to measure the average stress and deformation in the TSV structures subject to thermal cycling. To understand the elastic and plastic behavior of TSVs, the microstructural evolution of the Cu vias was analyzed using focused ion beam (FIB) and electron backscattering diffraction (EBSD) techniques. Furthermore, the impact of thermal stresses on interfacial reliability of TSV structures was investigated by a shear-lag cohesive zone model that predicts the critical temperatures and critical via diameters.Microelectronics Research Cente
The Measure for the Multiverse and the Probability for Inflation
We investigate the measure problem in the framework of inflationary
cosmology. The measure of the history space is constructed and applied to
inflation models. Using this measure, it is shown that the probability for the
generalized single field slow roll inflation to last for e-folds is
suppressed by a factor , and the probability for the generalized
-field slow roll inflation is suppressed by a much larger factor
. Some non-inflationary models such as the cyclic model do not
suffer from this difficulty.Comment: 16 page
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