4,593 research outputs found
A Physical Picture of Bispectrum Baryon Acoustic Oscillations in the Interferometric Basis
We present a picture of the matter bispectrum in a novel "interferometric"
basis designed to highlight interference of the baryon acoustic oscillations
(BAO) in the power spectra composing it. Triangles where constructive
interference amplifies BAO provide stronger cosmic distance constraints than
triangles with destructive interference. We show that the amplitude of the BAO
feature in the full cyclically summed bispectrum can be decomposed into simpler
contributions from single terms or pairs of terms in the perturbation theory
bispectrum, and that across large swathes of our parameter space the full BAO
amplitude is described well by the amplitude of BAO in a single term. The
dominant term is determined largely by the kernel of Eulerian
standard perturbation theory. We present a simple physical picture of the BAO
amplitude in each term; the BAO signal is strongest in triangle configurations
where two wavenumbers differ by a multiple of the BAO fundamental wavelength.Comment: 21 pages, 15 figure
Probing the Cluster Mass Distribution using Subaru Weak Lensing Data
We present results from a weak lensing analysis of the galaxy cluster A1689
(z=0.183) based on deep wide-field imaging data taken with Suprime-Cam on
Subaru telescope. A maximum entropy method has been used to reconstruct
directly the projected mass distribution of A1689 from combined lensing
distortion and magnification measurements of red background galaxies.The
resulting mass distribution is clearly concentrated around the cD galaxy, and
mass and light in the cluster are similarly distributed in terms of shape and
orientation. The azimuthally-averaged mass profile from the two-dimensional
reconstruction is in good agreement with the earlier results from the Subaru
one-dimensional analysis of the weak lensing data, supporting the assumption of
quasi-circular symmetry in the projected mass distribution of the cluster.Comment: To appear in Mod. Phys. Lett. A, 8pages, 5 figures, minor typo errors
corrected, Fig.5 modifie
Space charge and charge trapping characteristics of cross-linked polyethylene subjected to ac electric stresses
This paper reports on the result of space charge evolution in cross-linked polyethylene (XLPE) planar samples of approximately 220 ?m thick. The space charge measurement technique used in this study is the PEA method. There are two phases to this experiment. In the first phase, the samples were subjected to dc 30 kVdc/mm and ac (sinusoidal) electric stress level of 30 kVpk/mm at frequencies of 1 Hz, 10 Hz and 50 Hz ac. In addition, ac space charge under 30 kVrms/mm and 60 kVpk/mm electric stress at 50 Hz was also investigated. The volts off results showed that the amount of charge trapped in XLPE sample under dc electric stress is significantly bigger than samples under ac stress even when the applied ac stresses are substantially higher. The second phase of the experiment involves studying the dc space charge evolution in samples that were tested under ac stress during the first phase of the experiment. Ac ageing causes positive charge to become more dominant over negative charge. It was also discovered that ac ageing creates deeper traps, particularly for negative charge. This paper also gave a brief overview of the data processing methods used to analyse space charge under ac electric stress
59Co-NMR Knight Shift of Superconducting Three-Layer NaxCoO2.yH2O
The superconducting state of NaxCoO2.yH2O with three CoO2 layers in a unit
cell has been studied by 59Co-NMR. The Knight shift measured for a peak of the
NMR spectra corresponding to the external magnetic field H along one of the
principal directions within the CoO2 plane, exhibits a rapid decrease with
decreasing temperature T below the superconducting transition temperature Tc,
indicating that the spin susceptibility is suppressed in the superconducting
phase, at least, for this field direction. Because differences of the
superconducting properties are rather small between this three-layer
NaxCoO2.yH2O and previously reported NaxCoO2.yH2O with two CoO2 layers within a
unit cell, the present result of the Knight shift studies indicates that the
Cooper pairs of the former system are in the singlet state as in the latter,
for which the spin susceptibility is suppressed for both directions of H
parallel and perpendicular to the CoO2 plane.Comment: 5 page
BIPHASIC PATTERN OF THYMUS REGENERATION AFTER WHOLE-BODY IRRADIATION
Whole-body irradiation of mice with 300 or 400 R causes a precipitous fall in thymus weight, followed by an increase in the mitotic index and an almost complete restoration of thymus mass. This phase is followed by a secondary fall in thymus weight and gradual recovery. This secondary fall can be prevented by intravenous injection of bone marrow or shielding of the hind limbs during irradiation. The hypothesis is proposed that the thymus depends on the migration of cells from the bone marrow to the thymus for the maintenance of its cell population. Bone marrow cells with chromosome markers injected intravenously into normal or lightly irradiated (150 R) animals do not populate the host bone marrow to any significant degree. After whole-body irradiation with heavy doses (400 R), donor cells dominate the marrow. There may be a competition between dividing cells in the bone marrow which regulates proliferation of hemic cells. Bone marrow cells with marker chromosomes do not repopulate the thymus in irradiated animals until long after repopulating the bone marrow. It is possible that these cells have to pass through the marrow or the blood-marrow barrier to acquire characteristics needed for entering the thymus. After whole-body irradiation with 500 R or more, the first phase of regeneration of the thymus, represented by an increase in the mitotic index, does not occur to a significant degree. Apparently cells in the thymus capable of proliferation have been largely eliminated, and restoration of organ mass depends chiefly on seeding from other sources, probably the bone marrow. After whole-body irradiation with 200 R, only the first phase of thymus weight loss and regeneration takes place. Probably bone marrow injury is too small to interfere with the supply of cells repopulating the thymus
Requirements Quick Notes
A short introduction to requirements and their role in system development. Includes industry definition of requirements, overview of basic requirements process including numbering of requirements, ties to testing, and traceability. An introduction to requirements quality attributes (correct, unambiguous, etc.) Includes references to requirements process, numbering, and quality papers
The Lyman-alpha Forest at z~4: Keck HIRES Observations of Q 0000-26
This paper describes a study of the Lyman-alpha forest absorption clouds
along the quasar sightline Q0000-26 (zem=4.1). The spectrum was obtained with
the High Resolution Spectrometer on the 10m Keck telescope. We derive accurate
H I column density and Doppler width distributions for the clouds from Voigt
profile fitting. We also analyze simulated Lyman-alpha forest spectra of
matching characteristics in order to gauge the effects of line
blending/blanketing and noise in the data. The results are compared with
similar studies at lower redshifts in order to study any possible evolution in
the clouds' properties. We also estimate the mean intensity of the UV
background at z=4 from an analysis of the proximity effect.Comment: plain TeX containing 23 PS pages, 3 PS tables, and 9 PS figures, ApJ,
Dec 1, 1996 issue replacing an earlier version which contains an corrupted
table
Bispectrum as Baryon Acoustic Oscillation Interferometer
The galaxy bispectrum, measuring excess clustering of galaxy triplets, offers
a probe of dark energy via baryon acoustic oscillations (BAOs). However up to
now it has been severely underused due to the combinatorically explosive number
of triangles. Here we exploit interference in the bispectrum to identify
triangles that amplify BAOs. This approach reduces the computational cost of
estimating covariance matrices, offers an improvement in BAO constraints
equivalent to lengthening BOSS by 30%, and simplifies adding bispectrum BAO
information to future large-scale redshift survey analyses.Comment: 6 pages, 3 figures; revised to match published versio
Charge-fluctuation contribution to the Raman response in superconducting cuprates
We calculate the Raman response contribution due to collective modes, finding
a strong dependence on the photon polarizations and on the characteristic
wavevectors of the modes. We compare our results with recent Raman spectroscopy
experiments in underdoped cuprates, and
, where anomalous low-energy peaks are
observed, which soften upon lowering the temperature. We show that the specific
dependence on doping and on photon polarizations of these peaks is only
compatible with charge collective excitations at finite wavelength.Comment: 5 pages, 3 figure
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