1,151 research outputs found
The development of a power spectral density processor for C and L band airborne radar scatterometer sensor systems
A real-time signal processor was developed for the NASA/JSC L-and C-band airborne radar scatterometer sensor systems. The purpose of the effort was to reduce ground data processing costs. Conversion of two quadrature channels of data (like and cross polarized) was made to obtain Power Spectral Density (PSD) values. A chirp-z transform (CZT) approach was used to filter the Doppler return signal and improved high frequency and angular resolution was realized. The processors have been tested with record signals and excellent results were obtained. CZT filtering can be readily applied to scatterometers operating at other wavelengths by altering the sample frequency. The design of the hardware and software and the results of the performance tests are described in detail
Solid molecular hydrogen: The Broken Symmetry Phase
By performing constant-pressure variable-cell ab initio molecular dynamics
simulations we find a quadrupolar orthorhombic structure, of symmetry,
for the broken symmetry phase (phase II) of solid H2 at T=0 and P =110 - 150
GPa. We present results for the equation of state, lattice parameters and
vibronic frequencies, in very good agreement with experimental observations.
Anharmonic quantum corrections to the vibrational frequencies are estimated
using available data on H2 and D2. We assign the observed modes to specific
symmetry representations.Comment: 5 pages (twocolumn), 4 Postscript figures. To appear in Phys. Rev.
Let
Classical and quantum: a conflict of interest
We highlight three conflicts between quantum theory and classical general
relativity, which make it implausible that a quantum theory of gravity can be
arrived at by quantising classical gravity. These conflicts are: quantum
nonlocality and space-time structure; the problem of time in quantum theory;
and the quantum measurement problem. We explain how these three aspects bear on
each other, and how they point towards an underlying noncommutative geometry of
space-time.Comment: 15 pages. Published in `Gravity and the quantum' [Essays in honour of
Thanu Padmanabhan on the occasion of his sixtieth birthday] Eds. Jasjeet
Singh Bagla and Sunu Engineer (Springer, 2017
Microwave background anisotropies in quasiopen inflation
Quasiopenness seems to be generic to multi-field models of single-bubble open
inflation. Instead of producing infinite open universes, these models actually
produce an ensemble of very large but finite inflating islands. In this paper
we study the possible constraints from CMB anisotropies on existing models of
open inflation. The effect of supercurvature anisotropies combined with the
quasiopenness of the inflating regions make some models incompatible with
observations, and severely reduces the parameter space of others. Supernatural
open inflation and the uncoupled two-field model seem to be ruled out due to
these constraints for values of . Others, such as the
open hybrid inflation model with suitable parameters for the slow roll
potential can be made compatible with observations.Comment: 19 pages, ReVTeX, 10 figures inserted with eps
Evolution of the Scale Factor with a Variable Cosmological Term
Evolution of the scale factor a(t) in Friedmann models (those with zero
pressure and a constant cosmological term Lambda) is well understood, and
elegantly summarized in the review of Felten and Isaacman [Rev. Mod. Phys. 58,
689 (1986)]. Developments in particle physics and inflationary theory, however,
increasingly indicate that Lambda ought to be treated as a dynamical quantity.
We revisit the evolution of the scale factor with a variable Lambda-term, and
also generalize the treatment to include nonzero pressure. New solutions are
obtained and evaluated using a variety of observational criteria. Existing
arguments for the inevitability of a big bang (ie., an initial state with a=0)
are substantially weakened, and can be evaded in some cases with Lambda_0 (the
present value of Lambda) well below current experimental limits.Comment: 29 pages, 12 figures (not included), LaTeX, uses Phys Rev D style
files (revtex.cls, revtex.sty, aps.sty, aps10.sty, prabib.sty). To appear in
Phys Rev
Electronic States and Magnetic Propertis of Edge-sharing Cu-O Chains
The electronic states and magnetic properties for the copper oxides
containing edge-sharing Cu-O chains such as LiCuO,
LaCaCuO and CuGeO are systematically studied. The
optical conductivity and the temperature dependence of the
magnetic susceptibility for single crystalline samples LiCuO
are measured as a reference system and analyzed by using the exact
diagonalization method for small Cu-O clusters. It is shown that the spectral
distribution of is different between edge-sharing and
corner-sharing Cu-O-Cu bonds. The charge transfer gap in edge-sharing chains is
larger than that of high- cuprates. The exchange interaction between
nearest-neighbor copper ions in edge-sharing chains depends sensitively
on the Cu-O-Cu bond angles. In addition to , the exchange interaction
between next-nearest-neighbor copper ions has sufficient contribution to
the magnetic properties. We calculate and for all the copper oxides
containing edge-sharing Cu-O chains and discuss the magnetic properties.Comment: 10 pages,RevTeX,8 postscript figures. Accepted for publication in
Phys. Rev.
Open Hybrid Inflation
We propose an open hybrid inflation scenario that produces an open universe
with a `tilted' n>1 spectrum of metric perturbations. The model contains a
symmetry breaking field that tunnels to its true vacuum, producing a single
bubble inside which hybrid inflation drives the universe to almost flatness. In
order to obtain density perturbations with n > 1 we use the recently proposed
new version of hybrid inflation scenario called tilted hybrid inflation. In
this scenario, unlike in the previously known versions of hybrid inflation, a
considerable tilt of the spectrum can be obtained without fine-tuning. The
stage of inflation in this model is rather short, which allows us to obtain an
inflationary universe with Omega < 1 in a more natural way. We study the
separate contribution of scalar perturbations coming from the continuum
subcurvature modes, the discrete supercurvature mode and the bubble wall mode
to the angular power spectrum of temperature fluctuations in open inflation. We
derive bounds on the parameters of the model so that the predicted spectrum is
compatible with the observed anisotropy of the microwave background.Comment: 9 pages, 6 figures, ReVTe
Evidence for the h_b(1P) meson in the decay Upsilon(3S) --> pi0 h_b(1P)
Using a sample of 122 million Upsilon(3S) events recorded with the BaBar
detector at the PEP-II asymmetric-energy e+e- collider at SLAC, we search for
the spin-singlet partner of the P-wave chi_{bJ}(1P) states in the
sequential decay Upsilon(3S) --> pi0 h_b(1P), h_b(1P) --> gamma eta_b(1S). We
observe an excess of events above background in the distribution of the recoil
mass against the pi0 at mass 9902 +/- 4(stat.) +/- 2(syst.) MeV/c^2. The width
of the observed signal is consistent with experimental resolution, and its
significance is 3.1sigma, including systematic uncertainties. We obtain the
value (4.3 +/- 1.1(stat.) +/- 0.9(syst.)) x 10^{-4} for the product branching
fraction BF(Upsilon(3S)-->pi0 h_b) x BF(h_b-->gamma eta_b).Comment: 8 pages, 4 postscript figures, submitted to Phys. Rev. D (Rapid
Communications
Planck 2013 results. XXII. Constraints on inflation
We analyse the implications of the Planck data for cosmic inflation. The Planck nominal mission temperature anisotropy measurements, combined with the WMAP large-angle polarization, constrain the scalar spectral index to be ns = 0:9603 _ 0:0073, ruling out exact scale invariance at over 5_: Planck establishes an upper bound on the tensor-to-scalar ratio of r < 0:11 (95% CL). The Planck data thus shrink the space of allowed standard inflationary models, preferring potentials with V00 < 0. Exponential potential models, the simplest hybrid inflationary models, and monomial potential models of degree n _ 2 do not provide a good fit to the data. Planck does not find statistically significant running of the scalar spectral index, obtaining dns=dln k = 0:0134 _ 0:0090. We verify these conclusions through a numerical analysis, which makes no slowroll approximation, and carry out a Bayesian parameter estimation and model-selection analysis for a number of inflationary models including monomial, natural, and hilltop potentials. For each model, we present the Planck constraints on the parameters of the potential and explore several possibilities for the post-inflationary entropy generation epoch, thus obtaining nontrivial data-driven constraints. We also present a direct reconstruction of the observable range of the inflaton potential. Unless a quartic term is allowed in the potential, we find results consistent with second-order slow-roll predictions. We also investigate whether the primordial power spectrum contains any features. We find that models with a parameterized oscillatory feature improve the fit by __2 e_ _ 10; however, Bayesian evidence does not prefer these models. We constrain several single-field inflation models with generalized Lagrangians by combining power spectrum data with Planck bounds on fNL. Planck constrains with unprecedented accuracy the amplitude and possible correlation (with the adiabatic mode) of non-decaying isocurvature fluctuations. The fractional primordial contributions of cold dark matter (CDM) isocurvature modes of the types expected in the curvaton and axion scenarios have upper bounds of 0.25% and 3.9% (95% CL), respectively. In models with arbitrarily correlated CDM or neutrino isocurvature modes, an anticorrelated isocurvature component can improve the _2 e_ by approximately 4 as a result of slightly lowering the theoretical prediction for the ` <_ 40 multipoles relative to the higher multipoles. Nonetheless, the data are consistent with adiabatic initial conditions
Open inflation models and gravitational wave anisotropies in the CMB
We study the large scale power spectrum of gravitational wave perturbations
of the microwave background in the context of single-bubble open inflation
models. We compute the ratio of tensor to scalar contributions to the CMB
anisotropies as a function of , the spectral index and the
tunneling parameter . We find that gravitational wave anisotropies
can be very large at small values of this tunneling parameter. We also consider
the contribution of supercurvature and bubble wall modes and find constraints
on the parameters of open inflation models from the observed temperature
anisotropies of the CMB. We show that the induced gravity and open hybrid
scenarios are compatible with present observations for a reasonable range of
parameters.Comment: Revised version accepted in Physical Review
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