80,583 research outputs found
Simultaneous spectral and reverberation modelling of relativistic reflection in Mrk 335
We present an X-ray spectral and timing model to investigate the broad and
variable iron line seen in the high flux state of Mrk 335. The model consists
of a variable X-ray source positioned along the rotation axis of the black hole
that illuminates the accretion disc producing a back-scattered, ionized
reflection spectrum. We compute time lags including full dilution effects and
perform simultaneous fitting of the 2-10 keV spectrum and the
frequency-dependent time lags of 2.5-4 vs. 4-6.5 keV bands. The best-fitting
parameters are consistent with a black hole mass of approximately 1.3 x 10^7
M_sun, disc inclination of 45 degrees and the photon index of the direct
continuum of 2.4. The iron abundance is 0.5 and the ionization parameter is
10^3 erg cm / s at the innermost part of the disc and decreases further out.
The X-ray source height is very small, approximately 2 r_g. Furthermore, we fit
the Fe L lags simultaneously with the 0.3-10 keV spectrum. The key parameters
are comparable to those previously obtained. We also report the differences
below 2 keV using the xillver and reflionx models which could affect the
interpretation of the soft excess. While simultaneously fitting spectroscopic
and timing data can break the degeneracy between the source height and the
black hole mass, we find that the measurements of the source height and the
central mass significantly depend on the ionization state of the disc and are
possibly model-dependent.Comment: 11 pages, 8 figures, accepted for publication in MNRA
Exact solution of lossy asymmetrical coupled dielectric slab waveguides
This paper gives an exact characteristic equation for asymmetrical coupled dielectric slab waveguides with losses in both the guiding and surrounding regions. For the lossless case the solution of a single transcendental equation is all that is required for the evaluation of the propagation constant
Higher diversity of Rhizobium leguminosarum biovar viciae populations in arable soils than in grass soils
The bacterial genetic diversity after long-term arable cultivation was compared with that under permanent grassland using replicated paired contrasts, Pea-nodulating Rhizobium leguminosarum populations were sampled from pairs of arable and grass sites at four locations in Yorkshire, United Kingdom, isolates were characterized using both chromosomal (16S-23S ribosomal DNA internal transcribed spacer PCR-restriction fragment length polymorphism) and plasmid (group-specific repC PCR amplification) markers. The diversities of chromosomal types, repC profiles, and combined genotypes were calculated using richness in types (adjusted to equal sample sizes by rarefaction), Shannon-Wiener index, and Simpson's index. The relative differences in diversity within each pair of sites were similar for all three diversity measures, Chromosomal types, repC profiles, and combined genotypes were each more diverse in arable soils than in grass soils at two of the four locations. The other comparisons showed no significant differences. We conclude that rhizobial diversity can be affected by differences between these two management regimens. Multiple regression analyses indicated that lower diversity was associated with high potential nitrogen and phosphate levels or with acidity
Characterization of a thermoplastic polyimidesulfone
The detailed characterization of an experimental thermoplastic polyimidesulfone adhesive based on 3,3 prime-diaminodiphenylsulfone and 3,3 prime,4,4 prime-benzophenone tetracarboxylic dianhydride was studied. Model compounds were also examined. Thermal cyclization of the amide-acid to the imide was studied by a variety of techniques including DSC, TGA, MS, in situ diffuse reflectance-FTIR, and flow mearsurement. Characterizations were continued during the processing of adhesive tapes and the fabrication, bonding, and testing of lap shear specimens. Results provide fundamental insights into the role of cure chemistry, and the effects of residual solvent and volatile produces on processing and performance. These insights and the resulting chemical models should lead to more efficient processing cycles for these and other related thermoplastic adhesive systems
Polyimides with pendant alkyl groups
The effect on selected polyimide properties when pendant alkyl groups were attached to the polymer backbone was investigated. A series of polymers were prepared using benzophenone tetracarboxylic acid dianhydride (BTDA) and seven different p-alkyl-m,p'-diaminobenzophenone monomers. The alkyl groups varied in length from C(1) (methyl) to C(9) (nonyl). The polyimide prepared from BTDA and m,p'-diaminobenzophenone was included as a control. All polymers were characterized by various chromatographic, spectroscopic, thermal, and mechanical techniques. Increasing the length of the pendant alkyl group resulted in a systematic decrease in glass transition temperature (Tg) for vacuum cured films. A 70 C decrease in Tg to 193 C was observed for the nonyl polymer compared to the Tg for the control. A corresponding systematic increase in Tg indicative of crosslinking, was observed for air cured films. Thermogravimetric analysis revealed a slight sacrifice in thermal stability with increasing alkyl length. No improvement in film toughness was observed
Initial success of native grasses is contingent on multiple interactions among exotic grass competition, temporal priority, rainfall and site effects.
Ecological communities are increasingly being recognized as the products of contemporary drivers and historical legacies that are both biotic and abiotic. In an attempt to unravel multiple layers of ecological contingency, we manipulated (i) competition with exotic annual grasses, (ii) the timing of this competition (temporal priority in arrival/seeding times) and (iii) watering (simulated rainfall) in a restoration-style planting of native perennial grasses. In addition, we replicated this experiment simultaneously at three sites in north-central California. Native perennial grasses had 73-99 % less cover when planted with exotic annuals than when planted alone, but this reduction was greatly ameliorated by planting the natives 2 weeks prior to the exotics. In a drought year, irrigation significantly reduced benefits of early planting so that these benefits resembled those observed in a non-drought year. There were significant differences across the three sites (site effects and interactions) in (i) overall native cover, (ii) the response of natives to competition, (iii) the strength of the temporal priority effect and (iv) the degree to which supplemental watering reduced priority effects. These results reveal the strong multi-layered contingency that underlies even relatively simple communities
X-ray time lags in AGN: inverse-Compton scattering and spherical corona model
We develop a physically motivated, spherical corona model to investigate the
frequency-dependent time lags in AGN. The model includes the effects of Compton
up-scattering between the disc UV photons and coronal electrons, and the
subsequent X-ray reverberation from the disc. The time lags are associated with
the time required for multiple scatterings to boost UV photons up to soft and
hard X-ray energies, and the light crossing time the photons take to reach the
observer. This model can reproduce not only low-frequency hard and
high-frequency soft lags, but also the clear bumps and wiggles in reverberation
profiles which should explain the wavy-residuals currently observed in some
AGN. Our model supports an anti-correlation between the optical depth and
coronal temperatures. In case of an optically thin corona, time delays due to
propagating fluctuations may be required to reproduce observed time lags. We
fit the model to the lag-frequency data of 1H0707-495, Ark 564, NGC 4051 and
IRAS 13224-3809 estimated using the minimal bias technique so that the observed
lags here are highest-possible quality. We find their corona size is ~7-15 r_g
having the constrained optical depth ~2-10. The coronal temperature is ~150-300
keV. Finally, we note that the reverberation wiggles may be signatures of
repeating scatters inside the corona that control the distribution of X-ray
sources.Comment: 15 pages, 10 figures, accepted for publication in MNRA
Free energies in the presence of electric and magnetic fields
We discuss different free energies for materials in static electric and
magnetic fields. We explain what the corresponding Hamiltonians are, and
describe which choice gives rise to which result for the free energy change,
dF, in the thermodynamic identity. We also discuss which Hamiltonian is the
most appropriate for calculations using statistical mechanics, as well as the
relationship between the various free energies and the "Landau function", which
has to be minimized to determine the equilibrium polarization or magnetization,
and is central to Landau's theory of second order phase transitions
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