5,582 research outputs found
Application of Radon Transform to Wavefield Filtering, Reconstruction, and Imaging of Dispersive Energies in Quantitative Bone Ultrasound
Multichannel ultrasonic axial-transmission data are multimodal by nature. Multichannel analysis of dispersive ultrasonic energies requires a reliable mapping of the data from the time– distance (t-x) domain to the frequency–wavenumber (f-k) or frequency–phase velocity (f-c) domain. The mapping is usually performed with the classical 2-D Fourier transform (FT) from t- x plane to f-k plane or to f-c plane with a subsequent substitution and interpolation via c=ω/k. The extracted dispersion trajectories of the guided modes lack the resolution in the transformed domain to discriminate wave modes. The resolving power associated with the FT is closely linked to the aperture of the recorded data. In this presentation, we present a linear high- resolution Radon transform (RT) algorithm [1 & 2] to filter and reconstruct wavefields, and to image the dispersive energies of the recorded wavefields through long bones. The RT is posed as an inverse problem, which allows implementation of the regularization strategy to enhance the focusing power. The simulated, ex-vivo, and in-vivo data will be used to illustrate the advantages and robustness of the high-resolution RT algorithm. The method accommodates unevenly spaced records, effectively attenuates noise, enhances the signal-to-noise ratio, improves the coherency of the guided wave modes, and reconstructs the missing records. The dispersive energies are well focused and the trajectories are much better resolved. The proposed transform presents a powerful signal enhancement and imaging tool to process ultrasonic wavefields and extract dispersive guided wave energies under limited aperture
Latency and time-dependent exposure in a case-control study
Detailed historical data are elicited often from subjects in retrospective studies, yielding time-dependent measures of exposures. Investigation of a hypothesized period of latency can be made by examining disease/exposure relationships in multiple time windows, either along the age or time-before diagnosis axes. We suggest splitting the data into many time intervals and separately fitting regression models tothe available data in each interval. Covariances between estimated coefficients from different intervals are empirically estimated, and used for assessing variability of specified functions of the time-specific coefficients. Alternative methods of interval formation and their consequences are discussed. We apply these methods to a French case-control study of oral contraceptive use and cervical cancer incidence, and compare the results to those of standard analyses.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29651/1/0000740.pd
A unified Witten-Reshetikhin-Turaev invariant for integral homology spheres
We construct an invariant J_M of integral homology spheres M with values in a
completion \hat{Z[q]} of the polynomial ring Z[q] such that the evaluation at
each root of unity \zeta gives the the SU(2) Witten-Reshetikhin-Turaev
invariant \tau_\zeta(M) of M at \zeta. Thus J_M unifies all the SU(2)
Witten-Reshetikhin-Turaev invariants of M. As a consequence, \tau_\zeta(M) is
an algebraic integer. Moreover, it follows that \tau_\zeta(M) as a function on
\zeta behaves like an ``analytic function'' defined on the set of roots of
unity. That is, the \tau_\zeta(M) for all roots of unity are determined by a
"Taylor expansion" at any root of unity, and also by the values at infinitely
many roots of unity of prime power orders. In particular, \tau_\zeta(M) for all
roots of unity are determined by the Ohtsuki series, which can be regarded as
the Taylor expansion at q=1.Comment: 66 pages, 8 figure
Periastron Advance in Spinning Black Hole Binaries: Gravitational Self-Force from Numerical Relativity
We study the general relativistic periastron advance in spinning black hole
binaries on quasi-circular orbits, with spins aligned or anti-aligned with the
orbital angular momentum, using numerical-relativity simulations, the
post-Newtonian approximation, and black hole perturbation theory. By imposing a
symmetry by exchange of the bodies' labels, we devise an improved version of
the perturbative result, and use it as the leading term of a new type of
expansion in powers of the symmetric mass ratio. This allows us to measure, for
the first time, the gravitational self-force effect on the periastron advance
of a non-spinning particle orbiting a Kerr black hole of mass M and spin S =
-0.5 M^2, down to separations of order 9M. Comparing the predictions of our
improved perturbative expansion with the exact results from numerical
simulations of equal-mass and equal-spin binaries, we find a remarkable
agreement over a wide range of spins and orbital separations.Comment: 18 pages, 12 figures; matches version to appear in Phys. Rev.
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Configuration and performance of fuel cell-combined cycle options
The natural gas, indirect-fired, carbonate fuel-cell-bottomed, combined cycle (NG-IFCFC) and the topping natural-gas/solid-oxide fuel-cell combined cycle (NG-SOFCCC) are introduced as novel power-plant systems for the distributed power and on-site markets in the 20-200 mega-watt (MW) size range. The novel NG-IFCFC power-plant system configures the ambient pressure molten-carbonate fuel cell (MCFC) with a gas turbine, air compressor, combustor, and ceramic heat exchanger: The topping solid-oxide fuel-cell (SOFC) combined cycle is not new. The purpose of combining a gas turbine with a fuel cell was to inject pressurized air into a high-pressure fuel cell and to reduce the size, and thereby, to reduce the cost of the fuel cell. Today, the SOFC remains pressurized, but excess chemical energy is combusted and the thermal energy is utilized by the Carnot cycle heat engine to complete the system. ASPEN performance results indicate efficiencies and heat rates for the NG-IFCFC or NG-SOFCCC are better than conventional fuel cell or gas turbine steam-bottomed cycles, but with smaller and less expensive components. Fuel cell and gas turbine systems should not be viewed as competitors, but as an opportunity to expand to markets where neither gas turbines nor fuel cells alone would be commercially viable. Non-attainment areas are the most likely markets
Post-starburst galaxies: more than just an interesting curiosity
From the VIMOS VLT DEEP Survey (VVDS) we select a sample of 16 galaxies with
spectra which identify them as having recently undergone a strong starburst and
subsequent fast quenching of star formation. These post-starburst galaxies lie
in the redshift range 0.510^9.75Msun. They have a number
density of 1x10^-4 per Mpc^3, almost two orders of magnitude sparser than the
full galaxy population with the same mass limit. We compare with simulations to
show that the galaxies are consistent with being the descendants of gas rich
major mergers. Starburst mass fractions must be larger than ~5-10% and decay
times shorter than ~10^8 years for post-starburst spectral signatures to be
observed in the simulations. We find that the presence of black hole feedback
does not greatly affect the evolution of the simulated merger remnants through
the post-starburst phase. The multiwavelength spectral energy distributions of
the post-starburst galaxies show that 5/16 have completely ceased the formation
of new stars. These 5 galaxies correspond to a mass flux entering the
red-sequence of rhodot(A->Q, PSB) = 0.0038Msun/Mpc^3/yr, assuming the defining
spectroscopic features are detectable for 0.35Gyr. If the galaxies subsequently
remain on the red sequence, this accounts for 38(+4/-11)% of the growth rate of
the red sequence. Finally, we compare our high redshift results with a sample
of galaxies with 0.05<z<0.1 observed in the SDSS and UKIDSS surveys. We find a
very strong redshift evolution: the mass density of strong post-starburst
galaxies is 230 times lower at z~0.07 than at z~0.7.Comment: 18 pages, 12 figures, to match version accepted to MNRAS. Minor
reordering of text in places and Sec 2.2 on SPH simulation comparisons
expande
Eosinophils Are Important for Protection, Immunoregulation and Pathology during Infection with Nematode Microfilariae
Eosinophil responses typify both allergic and parasitic helminth disease. In helminthic disease, the role of eosinophils can be both protective in immune responses and destructive in pathological responses. To investigate whether eosinophils are involved in both protection and pathology during filarial nematode infection, we explored the role of eosinophils and their granule proteins, eosinophil peroxidase (EPO) and major basic protein-1 (MBP-1), during infection with Brugia malayi microfilariae. Using eosinophil-deficient mice (PHIL), we further clarify the role of eosinophils in clearance of microfilariae during primary, but not challenge infection in vivo. Deletion of EPO or MBP-1 alone was insufficient to abrogate parasite clearance suggesting that either these molecules are redundant or eosinophils act indirectly in parasite clearance via augmentation of other protective responses. Absence of eosinophils increased mast cell recruitment, but not other cell types, into the broncho-alveolar lavage fluid during challenge infection. In addition absence of eosinophils or EPO alone, augmented parasite-induced IgE responses, as measured by ELISA, demonstrating that eosinophils are involved in regulation of IgE. Whole body plethysmography indicated that nematode-induced changes in airway physiology were reduced in challenge infection in the absence of eosinophils and also during primary infection in the absence of EPO alone. However lack of eosinophils or MBP-1 actually increased goblet cell mucus production. We did not find any major differences in cytokine responses in the absence of eosinophils, EPO or MBP-1. These results reveal that eosinophils actively participate in regulation of IgE and goblet cell mucus production via granule secretion during nematode-induced pathology and highlight their importance both as effector cells, as damage-inducing cells and as supervisory cells that shape both innate and adaptive immunity
Spectral Energy Distributions of Hard X-ray selected AGNs in the XMDS Survey
We present the spectral energy distributions (SEDs) of a hard X-ray selected
sample. The sample contains 136 sources with F(2-10 keV)>10^-14 erg/cm^2/s and
132 are AGNs. The sources are detected in a 1 square degree area of the
XMM-Newton-Medium Deep Survey where optical data from the VVDS, CFHTLS surveys,
and infrared data from the SWIRE survey are available. Based on a SED fitting
technique we derive photometric redshifts with sigma(1+z)=0.11 and 6% of
outliers and identify AGN signatures in 83% of the objects. This fraction is
higher than derived when a spectroscopic classification is available. The
remaining 17+9-6% of AGNs shows star-forming galaxy SEDs (SF class). The
sources with AGN signatures are divided in two classes, AGN1 (33+6-1%) and AGN2
(50+6-11). The AGN1 and AGN2 classes include sources whose SEDs are fitted by
type 1 and type 2 AGN templates, respectively. On average, AGN1s show soft
X-ray spectra, consistent with being unabsorbed, while AGN2s and SFs show hard
X-ray spectra, consistent with being absorbed. The analysis of the average SEDs
as a function of X-ray luminosity shows a reddening of the IR SEDs, consistent
with a decreasing contribution from the host galaxy at higher luminosities. The
AGNs in the SF classes are likely obscured in the mid-infrared, as suggested by
their low L(3-20micron)/Lcorr(0.5-10 keV) ratios. We confirm the previously
found correlation for AGNs between the radio luminosity and the X-ray and the
mid-infrared luminosities. The X-ray-radio correlation can be used to identify
heavily absorbed AGNs. However, the estimated radio fluxes for the missing AGN
population responsible for the bulk of the background at E>10 keV are too faint
to be detected even in the deepest current radio surveys.Comment: Accepted for publication in Ap
Electromagnetic characterization of soil-litter media – Application to the simulation of the microwave emissivity of the ground surface in forests
In order to improve our knowledge of the emitted signal of forests at L-band (1.4 GHz) we focused this study on permittivity measurements of heterogenic natural media such as soil or litter consisting of plant debris and organic matter. This study was done in the context of the upcoming SMOS (Soil Moisture and Ocean Salinity) satellite mission that will attempt to map surface soil moisture from L-band (1.4 GHz) passive microwave measurements. In the field of passive microwaves, very little information exists about the behaviour of the L-band signal of forests especially when litter is included in the soil-vegetation system. To date very few analyses have investigated the dielectric behaviour of the litter layer and its influence on the microwave emission of forests is generally neglected. © 2008 EDP Sciences
Decomposing Star Formation and Active Galactic Nucleus with Spitzer Mid-Infrared Spectra: Luminosity Functions and Co-Evolution
We present Spitzer 7-38um spectra for a 24um flux limited sample of galaxies
at z~0.7 in the COSMOS field. The detailed high-quality spectra allow us to
cleanly separate star formation (SF) and active galactic nucleus (AGN) in
individual galaxies. We first decompose mid-infrared Luminosity Functions
(LFs). We find that the SF 8um and 15um LFs are well described by Schechter
functions. AGNs dominate the space density at high luminosities, which leads to
the shallow bright-end slope of the overall mid-infrared LFs. The total
infrared (8-1000um) LF from 70um selected galaxies shows a shallower bright-end
slope than the bolometrically corrected SF 15um LF, owing to the intrinsic
dispersion in the mid-to-far-infrared spectral energy distributions. We then
study the contemporary growth of galaxies and their supermassive black holes
(BHs). Seven of the 31 Luminous Infrared Galaxies with Spitzer spectra host
luminous AGNs, implying an AGN duty cycle of 23+/-9%. The time-averaged ratio
of BH accretion rate and SF rate matches the local M_BH-M_bulge relation and
the M_BH-M_host relation at z ~ 1. These results favor co-evolution scenarios
in which BH growth and intense SF happen in the same event but the former spans
a shorter lifetime than the latter. Finally, we compare our mid-infrared
spectroscopic selection with other AGN identification methods and discuss
candidate Compton-thick AGNs in the sample. While only half of the mid-infrared
spectroscopically selected AGNs are detected in X-ray, ~90% of them can be
identified with their near-infrared spectral indices.Comment: ApJ Accepted. emulateapj style. 16 pages, 9 figures, 4 table
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