19,828 research outputs found
The Scatter in the Relationship between Redshift and the Radio-to-Submm Spectral Index
We derive the scatter in the relationship between redshift and radio-to-submm
spectral index, alpha^{350}_{1.4}, using the observed spectral energy
distributions of 17 low redshift star forming galaxies. A mean galaxy model is
derived, along with the rms scatter in alpha^{350}_{1.4}. The scatter is
roughly constant with redshift. Constant rms scatter, combined with the
flattening of the mean alpha^{350}_{1.4} -- z relationship with increasing
redshift, leads to increasing uncertainty for redshift estimates at high
redshifts. Normalizing by the dust temperature in the manner proposed by Blain
decreases the scatter in alpha^{350}_{1.4} for most of the sample, but does not
remove outliers, and free-free absorption at rest frequencies above 1.4 GHz is
not likely to be a dominant cause for scatter in the alpha^{350}_{1.4} -- z
relationship. We re-derive the cumulative redshift distribution of the 14 field
galaxies in a recent submm and radio source sample of Smail et al.. The most
likely median redshift for the distribution is 2.7, with a conservative lower
limit of z = 2, as was also found by Smail et al. based on the original
alpha^{350}_{1.4} -- z models. The normalization and shape of the redshift
distribution for the faint submm sources are consistent with those expected for
forming elliptical galaxies.Comment: Added Erratum, standard AAS LATEX forma
Effect of Wave Types on Ultrasonic Texture Identification
The use of ultrasonic techniques to measure the material anisotropy of rolled metal sheets has been demonstrated in many studies. Electromagnetic acoustic transducer (EMAT) and laser ultrasonic (LU) methods have been favored since both are noncontact in nature and therefore potential candidates forin-situ process monitoring and control in rolling mills. Both techniques have the ability of generating various ultrasonic wave types. EMAT systems are usually based on the excitation of Lamb or SH (horizontally polarized shear) waves and are typically designed to generate narrow band waves with known wave types. LU, on the other hand, is characterized by the simultaneous generation of multiple wave types and modes, the specifics of which are dependent upon the properties of the generation laser pulse(s) (duration, temporal and spatial shape, power) and the boundary conditions of the specimen. In general wave propagation velocities are measured and then used to calculate the texture coefficients W400, W420 and W440 [1, 2]
Higher Derivative Operators as Counterterms in Orbifold Compactifications
In the context of 5D N=1 supersymmetric models compactified on S_1/Z_2 or
S_1/(Z_2 x Z_2') orbifolds and with brane-localised superpotential, higher
derivative operators are generated radiatively as one-loop counterterms to the
mass of the (brane or zero mode of the bulk) scalar field. It is shown that the
presence of such operators which are brane-localised is not related to the
mechanism of supersymmetry breaking considered (F-term, discrete or continuous
Scherk-Schwarz breaking) and initial supersymmetry does not protect against the
dynamical generation of such operators. Since in many realistic models the
scalar field is commonly regarded as the Higgs field, and the higher derivative
operators seem a generic presence in orbifold compactifications, we stress the
importance of these operators for solving the hierarchy problem.Comment: Contribution to the Conference "Supersymmetry 2005", Durham; 13
pages, LaTe
SDSS J075101.42+291419.1: A Super-Eddington Accreting Quasar with Extreme X-ray Variability
We report the discovery of extreme X-ray variability in a type 1 quasar: SDSS
J. It has a black hole mass of
measured from reverberation mapping (RM), and the black hole is accreting with
a super-Eddington accretion rate. Its XMM-Newton observation in 2015 May
reveals a flux drop by a factor of with respect to the Swift
observation in 2013 May when it showed a typical level of X-ray emission
relative to its UV/optical emission. The lack of correlated UV variability
results in a steep X-ray-to-optical power-law slope () of
-1.97 in the low X-ray flux state, corresponding to an X-ray weakness factor of
36.2 at rest-frame 2 keV relative to its UV/optical luminosity. The mild
UV/optical continuum and emission-line variability also suggest that the
accretion rate did not change significantly. A single power-law model modified
by Galactic absorption describes well the keV spectra of the X-ray
observations in general. The spectral fitting reveals steep spectral shapes
with . We search for active galactic nuclei (AGNs) with such
extreme X-ray variability in the literature and find that most of them are
narrow-line Seyfert 1 galaxies and quasars with high accretion rates. The
fraction of extremely X-ray variable objects among super-Eddington accreting
AGNs is estimated to be . We discuss two possible scenarios,
disk reflection and partial covering absorption, to explain the extreme X-ray
variability of SDSS J. We propose a possible origin for the
partial covering absorber, which is the thick inner accretion disk and its
associated outflow in AGNs with high accretion rates.Comment: 15 pages, 9 figures, accepted for publication in Ap
Electronic structure of YbB: Is it a Topological Insulator or not?
To resolve the controversial issue of the topological nature of the
electronic structure of YbB, we have made a combined study using density
functional theory (DFT) and angle resolved photoemission spectroscopy (ARPES).
Accurate determination of the low energy band topology in DFT requires the use
of modified Becke-Johnson exchange potential incorporating the spin-orbit
coupling and the on-site Coulomb interaction of Yb electrons as large
as 7 eV. We have double-checked the DFT result with the more precise GW band
calculation. ARPES is done with the non-polar (110) surface termination to
avoid band bending and quantum well confinement that have confused ARPES
spectra taken on the polar (001) surface termination. Thereby we show
definitively that YbB has a topologically trivial B 2-Yb 5
semiconductor band gap, and hence is a non-Kondo non-topological insulator
(TI). In agreement with theory, ARPES shows pure divalency for Yb and a -
band gap of 0.3 eV, which clearly rules out both of the previous scenarios of
- band inversion Kondo TI and - band inversion non-Kondo TI. We
have also examined the pressure-dependent electronic structure of YbB,
and found that the high pressure phase is not a Kondo TI but a
\emph{p}-\emph{d} overlap semimetal.Comment: The main text is 6 pages with 4 figures, and the supplementary
information contains 6 figures. 11 pages, 10 figures in total To be appeared
in Phys. Rev. Lett. (Online publication is around March 16 if no delays.
Hyperglycemia and Hyperlipidemia Act Synergistically to Induce Renal Disease in LDL Receptor-Deficient BALB Mice
Diabetic nephropathy is the leading cause of end-stage renal disease in Western countries, but only a portion of diabetic patients develop diabetic nephropathy. Dyslipidemia represents an important aspect of the metabolic imbalance in diabetic patients. In this study, we addressed the impact of combined hyperlipidemia and hyperglycemia on renal pathology. Kidneys from wildtype (WT) or LDL receptor-deficient BALB/cBy mice (BALB. LDLR -/-) were examined at 22 weeks of age. Diabetes was induced by administration of streptozotocin and mice were randomly assigned to either standard chow or Western diet. Chow fed BALB. LDLR -/- mice did not demonstrate renal abnormalities, whereas BALB. LDLR -/- mice fed a Western diet showed occasional glomerular and tubulointerstitial foam cells. Diabetic WT mice had modestly increased glomerular cellularity and extracellular matrix. Hyperlipidemic and diabetic BALB. LDLR -/- mice exhibited an increase in glomerular cellularity and extracellular matrix, accumulation of glomerular and tubulointerstitial foam cells and mesangial lipid deposits. The tubular epithelium demonstrated pronounced lipid induced tubular degeneration with increased tubular epithelial cell turnover. Hyperlipidemia and hyperglycemia seem to act synergistically in inducing renal injury in the BALB. LDLR-/- mouse. This model of diabetic nephropathy is unique in its development of tubular lesions and may represent a good model for hyperlipidemia-exacerbated diabetic nephropathy. Copyright (C) 2004 S. Karger AG, Basel
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