32,720 research outputs found
Revisiting He-like X-ray Emission Line Plasma Diagnostics
A complete model of helium-like line and continuum emission has been
incorporated into the plasma simulation code Cloudy. All elements between He
and Zn are treated, any number of levels can be considered, and radiative and
collisional processes are included. This includes photoionization from all
levels, line transfer including continuum pumping and destruction by background
opacities, scattering, and collisional processes. The model is calculated
self-consistently along with the ionization and thermal structure of the
surrounding nebula. The result is a complete line and continuum spectrum of the
plasma. Here we focus on the ions of the He I sequence and reconsider the
standard helium-like X-ray diagnostics. We first consider semi-analytical
predictions and compare these with previous work in the low-density,
optically-thin limit. We then perform numerical calculations of helium-like
X-ray emission (such as is observed in some regions of Seyferts) and predict
line ratios as a function of ionizing flux, hydrogen density, and column
density. In particular, we demonstrate that, in photoionized plasmas, the
-ratio, a density indicator in a collisional plasma, depends on the
ionization fraction and is strongly affected by optical depth for large column
densities. We also introduce the notion that the -ratio is a measure of the
incident continuum at UV wavelengths. The -ratio, which is
temperature-sensitive in a collisional plasma, is also discussed, and shown to
be strongly affected by continuum pumping and optical depth as well. These
distinguish a photoionized plasma from the more commonly studied collisional
case.Comment: 28 pages, 7 figures, accepted to Ap
Immunofluorescent Examination of Biopsies from Long-Term Renal Allografts
Immunofluorescent examination of open renal biopsies revealed clear-cut glomerular localization of immunoglobulins not related clearly to the quality of donor-recipient histocompatibility in 19 of 34 renal allografts. The biopsies were obtained 18 to 31 months after transplantations primarily from related donors with a variable quality of histocompatibility match. IgG was the predominant immunoglobulin class fixed in 13 biopsies, and IgM in six. The pattern of immunoglobulin deposition was linear, connoting anti-GBM antibody in four of the 19; it was granular and discontinuous, connoting antigen–antibodycomplex deposits, in 13. An immune process may affect glomeruli of renal allografts by mechanisms comparable to those that cause glomerulonephritis in native kidneys. The transplant glomerulonephritis may represent a persistence of the same disease that originally destroyed the host kidneys or the consequence of a new humoral antibody response to allograft antigens. © 1970, Massachusetts Medical Society. All rights reserved
Accounting for Seismic Risk in Financial Analysis of Property Investment
A methodology is presented for making property investment decisions using loss
analysis and the principles of decision analysis. It proposes that the investor choose among
competing investment alternatives on the basis of the certainty equivalent of their net asset value
which depends on the uncertain discounted future net income, uncertain discounted future
earthquake losses, initial equity and the investor’s risk tolerance. The earthquake losses are
modelled using a seismic vulnerability function, the site seismic hazard function, and an
assumption that strong shaking at a site follows a Poisson process. A building-specific
vulnerability approach, called assembly-based vulnerability, or ABV, is used. ABV involves a
simulation approach that includes dynamic structural analyses and damage analyses using
fragility functions and probability distributions on unit repair costs and downtimes for all
vulnerable structural and nonstructural components in a building. The methodology is
demonstrated using some results from a seven-storey reinforced-concrete hotel in Los Angeles
Sheffield University CLEF 2000 submission - bilingual track: German to English
We investigated dictionary based cross language information
retrieval using lexical triangulation. Lexical triangulation combines the results
of different transitive translations. Transitive translation uses a pivot language
to translate between two languages when no direct translation resource is
available. We took German queries and translated then via Spanish, or Dutch
into English. We compared the results of retrieval experiments using these
queries, with other versions created by combining the transitive translations or
created by direct translation. Direct dictionary translation of a query introduces
considerable ambiguity that damages retrieval, an average precision 79% below
monolingual in this research. Transitive translation introduces more ambiguity,
giving results worse than 88% below direct translation. We have shown that
lexical triangulation between two transitive translations can eliminate much of
the additional ambiguity introduced by transitive translation
Improved He I Emissivities in the Case B Approximation
We update our prior work on the case B collisional-recombination spectrum of
He I to incorporate \textit{ab initio} photoionisation cross-sections. This
large set of accurate, self-consistent cross-sections represents a significant
improvement in He I emissivity calculations because it largely obviates the
piecemeal nature that has marked all modern works. A second, more recent set of
\textit{ab initio} cross-sections is also available, but we show that those are
less consistent with bound-bound transition probabilities than our adopted set.
We compare our new effective recombination coefficients with our prior work and
our new emissivities with those by other researchers, and we conclude with
brief remarks on the effects of the present work on the He I error budget. Our
calculations cover temperatures K and densities cm. Full results are available online.Comment: Accepted to MNRAS Letters; 4 pages, 4 figures, 2 tables, 1
supplemental fil
Few-fermion systems in one dimension: Ground- and excited-state energies and contacts
Using the lattice Monte Carlo method, we compute the energy and Tan's contact
in the ground state as well as the first excited state of few- to many-fermion
systems in a one-dimensional periodic box. We focus on unpolarized systems of
N=4,6,...,12 particles, with a zero-range interaction, and a wide range of
attractive couplings. In addition, we provide extrapolations to the
infinite-volume and thermodynamic limits.Comment: 8 pages, 12 figures; published versio
Stimulation of hepatic regeneration after partial hepatectomy by infusion of a cytosol extract from regenerating dog liver
A cytosol liver extract was prepared from adult dog livers and from liver remnants that had been regenerating for one, two and three days after 72 per cent partial hepatectomy. Given intraportally, the most active of these cytosols did not stimulate proliferation in the livers of normal dogs. However, infused during a six hour period into the portal vein of test group dogs, the cytosol from 48 and, especially, 72 hour regenerating livers augmented the regeneration response ordinarily produced by 44 per cent partial hepatectomy. The effect was delayed. It became identifiable 48 hours after infusion and reached a peak at 72 hours. Neither augmentation nor significant inhibition of the normal regeneration response was produced by cytosol from normal liver and 24 hour regenerating liver or by a six hour infusion of insulin. The amplification effect of active cytosol was equivocal when the infusions were given intraperitoneally and was not demonstrable at all by the intravenous route. In these investigations, it is confirmed that there are growth control factors in regenerating liver but the nature or physiologic significance of the factor or factors has not been clarified
Severity of disease and risk of malignant change in hereditary multiple exostoses. A genotype-phenotype study
We performed a prospective genotype-phenotype study using molecular screening and clinical assessment to compare the severity of disease and the risk of sarcoma in 172 individuals (78 families) with hereditary multiple exostoses. We calculated the severity of disease including stature, number of exostoses, number of surgical procedures that were necessary, deformity and functional parameters and used molecular techniques to identify the genetic mutations in affected individuals. Each arm of the genotype-phenotype study was blind to the outcome of the other. Mutations EXT1 and EXT2 were almost equally common, and were identified in 83% of individuals. Non-parametric statistical tests were used. There was a wide variation in the severity of disease. Children under ten years of age had fewer exostoses, consistent with the known age-related penetrance of this condition. The severity of the disease did not differ significantly with gender and was very variable within any given family. The sites of mutation affected the severity of disease with patients with EXT1 mutations having a significantly worse condition than those with EXT2 mutations in three of five parameters of severity (stature, deformity and functional parameters). A single sarcoma developed in an EXT2 mutation carrier, compared with seven in EXT1 mutation carriers. There was no evidence that sarcomas arose more commonly in families in whom the disease was more severe. The sarcoma risk in EXT1 carriers is similar to the risk of breast cancer in an older population subjected to breast-screening, suggesting that a role for regular screening in patients with hereditary multiple exostoses is justifiable. ©2004 British Editorial Society of Bone and Joint Surgery
Lighting as a Circadian Rhythm-Entraining and Alertness-Enhancing Stimulus in the Submarine Environment
The human brain can only accommodate a circadian rhythm that closely follows 24 hours. Thus, for a work schedule to meet the brain’s hard-wired requirement, it must employ a 24 hour-based program. However, the 6 hours on, 12 hours off (6/12) submarine watchstanding schedule creates an 18-hour “day” that Submariners must follow. Clearly, the 6/12 schedule categorically fails to meet the brain’s operational design, and no schedule other than one tuned to the brain’s 24 hour rhythm can optimize performance. Providing Submariners with a 24 hour-based watchstanding schedule—combined with effective circadian entrainment techniques using carefully-timed exposure to light—would allow crewmembers to work at the peak of their daily performance cycle and acquire more restorative sleep. In the submarine environment, where access to natural light is absent, electric lighting can play an important role in actively entraining—and closely maintaining—circadian regulation. Another area that is likely to have particular importance in the submarine environment is the potential effect of light to help restore or maintain alertness
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