2,256 research outputs found
Cosmic microwave background: polarization and temperature anisotropies from symmetric structures
I consider the case of anisotropies in the Cosmic Microwave Background (CMB)
from one single ordered perturbation source, or seed, existing well before
decoupling between matter and radiation. Such structures could have been left
by high energy symmetries breaking in the early universe.
I focus on the cases of spherical and cylindrical symmetry of the seed. I
give general analytic expressions for the polarization and temperature linear
perturbations, factoring out of the Fourier integral the dependence on the
photon propagation direction and on the geometric coordinates describing the
seed. I show how the CMB perturbations manifestly reflect the symmetries of
their seeds. CMB anisotropies are obtained with a line of sight integration.
This treatment highlights the undulatory properties of the CMB. I show with
numerical examples how the polarization and temperature perturbations propagate
beyond the size of their seeds, reaching the CMB sound horizon at the time
considered. Just like the waves from a pebble thrown in a pond, CMB anisotropy
from a seed intersecting the last scattering surface appears as a series of
temperature and polarization waves surrounding the seed, extending on the scale
of the CMB sound horizon at decoupling, roughly in the sky. Each wave
is characterized by its own value of the CMB perturbation, with the same mean
amplitude of the signal coming from the seed interior.
These waves could allow to distinguish relics from high energy processes of
the early universe from point-like astrophysical sources, because of their
angular extension and amplitude. Also, the marked analogy between polarization
and temperature signals offers cross correlation possibilities for the future
Planck Surveyor observations.Comment: 21 pages, seven postscript figures, final version accepted for
publication in Phys.Rev.
On the degree of scale invariance of inflationary perturbations
Many, if not most, inflationary models predict the power-law index of the
spectrum of density perturbations is close to one, though not precisely equal
to one, |n-1| \sim O(0.1), implying that the spectrum of density perturbations
is nearly, but not exactly, scale invariant. Some models allow n to be
significantly less than one (n \sim 0.7); a spectral index significantly
greater than one is more difficult to achieve. We show that n \approx 1 is a
consequence of the slow-roll conditions for inflation and ``naturalness,'' and
thus is a generic prediction of inflation. We discuss what is required to
deviate significantly from scale invariance, and then show, by explicit
construction, the existence of smooth potentials that satisfy all the
conditions for successful inflation and give as large as 2.Comment: 7 pages, 2 figures, submitted to Phys. Rev.
Preparation and ferroelectric properties of (124)-oriented SrBi4Ti4O15 ferroelectric thin film on (110)-oriented LaNiO3 electrode
A (124)-oriented SrBi4Ti4O15 (SBTi) ferroelectric thin film with high volume
fraction of {\alpha}SBTi(124)=97% was obtained using a metal organic
decomposition process on SiO2/Si substrate coated by (110)-oriented LaNiO3
(LNO) thin film. The remanent polarization and coercive field for
(124)-oriented SBTi film are 12.1 {\mu}C/cm2 and 74 kV/cm, respectively. No
evident fatigue of (124)-oriented SBTi thin film can be observed after
1{\times}10e9 switching cycles. Besides, the (124)-oriented SBTi film can be
uniformly polarized over large areas using a piezoelectric-mode atomic force
microscope. Considering that the annealing temperature was 650{\deg}C and the
thickness of each deposited layer was merely 30 nm, a long-range epitaxial
relationship between SBTi(124) and LNO(110) facets was proposed. The epitaxial
relationship was demonstrated based on the crystal structures of SBTi and LNO.Comment: 11 pages, 4 figures, published in Journal of Materials Science:
Materials in Electronics (JMSE), 19 (2008), 1031-103
The Tensor to Scalar Ratio of Phantom Dark Energy Models
We investigate the anisotropies in the cosmic microwave background in a class
of models which possess a positive cosmic energy density but negative pressure,
with a constant equation of state w = p/rho < -1. We calculate the temperature
and polarization anisotropy spectra for both scalar and tensor perturbations by
modifying the publicly available code CMBfast. For a constant initial curvature
perturbation or tensor normalization, we have calculated the final anisotropy
spectra as a function of the dark energy density and equation of state w and of
the scalar and tensor spectral indices. This allows us to calculate the
dependence of the tensor-to-scalar ratio on w in a model with phantom dark
energy, which may be important for interpreting any future detection of
long-wavelength gravitational waves.Comment: 5 pages, 4 figure
Decline and Fall of the Standard Model?
Motivations for physics beyond the Standard Model are reviewed, with
particular emphasis on supersymmetry at the TeV scale. Constraints on the
minimal supersymmetric extension of the Standard Model with universal soft
supersymmetry-breaking terms (CMSSM) are discussed. These are also combined
with the supersymmetric interpretation of the anomalous magnetic moment of the
muon. The prospects for observing supersymmetry at accelerators are reviewed
using benchmark scenarios to focus the discussion. Prospects for other
experiments are discussed, including the detection of cold dark matter, mu -> e
gamma and related processes, as well as proton decay.Comment: Invited talk at 20th International Symposium on Lepton and Photon
Interactions at High Energies, Rome, 2001, 16 pages LaTeX, 13 eps figures,
uses special .cls file (included
Polarization-dependent x-ray-absorption spectroscopy of RNi2B2C (R= Er to Lu):reduced Ni-3d occupancy in YbNi2B2C
Gait-based gender classification using persistent homology
In this paper, a topological approach for gait-based gender recognition is presented. First, a stack of human silhouettes, extracted by background subtraction and thresholding, were glued through their gravity centers, forming a 3D digital image I. Second, different filters (i.e. particular orders of the simplices) are applied on ∂ K(I) (a simplicial complex obtained from I) which capture relations among the parts of the human body when walking. Finally, a topological signature is extracted from the persistence diagram according to each filter. The measure cosine is used to give a similarity value between topological signatures. The novelty of the paper is a notion of robustness of the provided method (which is also valid for gait recognition). Three experiments are performed using all human-camera view angles provided in CASIA-B database. The first one evaluates the named topological signature obtaining 98.3% (lateral view) of correct classification rates, for gender identification. The second one shows results for different human-camera distances according to training and test (i.e. training with a human-camera distance and test with a different one). The third one shows that upper body is more discriminative than lower body
Low Mach number effect in simulation of high Mach number flow
In this note, we relate the two well-known difficulties of Godunov schemes:
the carbuncle phenomena in simulating high Mach number flow, and the inaccurate
pressure profile in simulating low Mach number flow. We introduced two simple
low-Mach-number modifications for the classical Roe flux to decrease the
difference between the acoustic and advection contributions of the numerical
dissipation. While the first modification increases the local numerical
dissipation, the second decreases it. The numerical tests on the double-Mach
reflection problem show that both modifications eliminate the kinked Mach stem
suffered by the original flux. These results suggest that, other than
insufficient numerical dissipation near the shock front, the carbuncle
phenomena is strongly relevant to the non-comparable acoustic and advection
contributions of the numerical dissipation produced by Godunov schemes due to
the low Mach number effect.Comment: 9 pages, 1 figur
Vibration Cycling Did Not Affect Energy Demands Compared to Normal Cycling During Maximal Graded Test
The aim of this study was to compare the physiological responses between a vibration induced cycling step protocol (Vib) and normal cycling (without vibration, no-Vib). Eighteen moderate trained males (age 24.1 ± 4.3 years; weight 76.5 ± 10.5 kg; height 178.0 ± 6.4 cm) have participated in this study. They randomly performed two gradual maximal exercise tests on two separate days using a new bike that automatically induces vibration cycling and the Corival cycle ergometer. The choice of two different bikes was made because of the impossibility to recreate the same power output without altering the cycling cadence on the vibration Bike. Both protocols were matched for power output and cycling cadence incrementations. Oxygen uptake (VO2), carbon dioxide production (VCO2), ventilation (VE), heart rate (HR), blood lactate and rating of perceived exertion (RPE) during each stage were continuously recorded. No statistical differences were founded for all variables when comparing the Vib to no-Vib trials, except a higher ventilation during the vibration trial at submaximal levels. The results of this study do not confirm those of previous studies stated that Vib increased metabolic demands during cycling exercise. Added vibration stimulus to an incremental cycling protocol does not affect physiological parameters.We would like to thank all the participants who took part in this investigation. A particular thank to Mr. Emanuele Gariffo who has substantially helped in the data collection. Also, our thank goes to the Sport Science Department at Greenwich University, London, United Kingdom, that logistically supported the study together with K. C. Wong Magna Fund at Ningbo University for their continuing encouragement
Finite-temperature scalar fields and the cosmological constant in an Einstein universe
We study the back reaction effect of massless minimally coupled scalar field
at finite temperatures in the background of Einstein universe. Substituting for
the vacuum expectation value of the components of the energy-momentum tensor on
the RHS of the Einstein equation, we deduce a relationship between the radius
of the universe and its temperature. This relationship exhibit a maximum
temperature, below the Planck scale, at which the system changes its behaviour
drastically. The results are compared with the case of a conformally coupled
field. An investigation into the values of the cosmological constant exhibit a
remarkable difference between the conformally coupled case and the minimally
coupled one.Comment: 7 pages, 2 figure
- …