6,284 research outputs found
MOCASSIN: a fully three-dimensional Monte Carlo photoionization code
No full textThe study of photoionized environments is fundamental to many astrophysical problems. Up to the present most photoionization codes have numerically solved the equations of radiative transfer by making the extreme simplifying assumption of spherical symmetry. Unfortunately very few real astronomical nebulae satisfy this requirement. To remedy these shortcomings, a self-consistent, three-dimensional radiative transfer code has been developed using Monte Carlo techniques. The code, MOCASSIN, is designed to build realistic models of photoionized nebulae having arbitrary geometry and density distributions, with both the stellar and diffuse radiation fields treated self-consistently. In addition, the code is capable of treating one or more exciting stars located at non-central locations.The gaseous region is approximated by a cuboidal Cartesian grid composed of numerous cells. The physical conditions within each grid cell are determined by solving the thermal equilibrium and ionization balance equations. This requires a knowledge of the local primary and secondary radiation fields, which are calculated self-consistently by locally simulating the individual processes of ionization and recombination. The structure and the computational methods used in the MOCASSIN code are described in this paper.MOCASSIN has been benchmarked against established one-dimensional spherically symmetric codes for a number of standard cases, as defined by the Lexington/Meudon photoionization workshops: at Meudon in 1985 and at Lexington in 1995 and 2000. The results obtained for the benchmark cases are satisfactory and are presented in this paper. A performance analysis has also been carried out and is discussed here
The optimized string dynamic photovoltaic array
No full textThis paper presents a novel system for producing the optimum power output from photovoltaic arrays using dynamic cell reconfiguration. The proposed approach is the first in the literature that creates strings using individual sub-strings that have been characterized and categorized ensuring maximum power extraction for a given irradiance profile. This optimized and decentralized PV architecture can produce significantly more power than a static equivalent (by an average of 22.6%) and also outperforms the sophisticated alternative known as an irradiance equalized dynamic photovoltaic array (IEq-DPVA) by an average of 13.\% for the relevant tests carried out. The paper identifies the hardware requirements to produce such a system and it describes an algorithm that performs the optimized string reconfiguration strategy. Finally, a simulator programmed in MATLAB is used to compare the performance of the optimized string DPVA (OS-DPVA) against an irradiance equalized DPVA in a series of flexibility tests
Hyperfine splitting of [Al VI] 3.66 mu m and the Al isotopic ratio in NGC 6302
No full textThe core of planetary nebula NGC 6302 is filled with high-excitation photoionized gas at low expansion velocities. It represents a unique astrophysical situation in which to search for hyperfine structure (HFS) in coronal emission lines from highly ionized species. HFS is otherwise blended by thermal or velocity broadening. Spectra containing [Al vr] 3.66 mu m P-3(2) <- P-3(1), obtained with Phoenix on Gemini South at resolving powers of up to 75000, resolve the line into five hyperfine components separated by 20-60 km s(-1) as a result of the coupling of the I = 5/2 nuclear spin of Al-27 with the total electronic angular momentum J. The isotope Al-26 has a different nuclear spin of I = 5, and a different HFS, which allows us to place a 3 sigma upper limit on the Al-26/Al-27 abundance ratio of 1/33. We measure the HFS magnetic dipole coupling constants for [Al vr], and provide the first estimates of the electric quadrupole HFS coupling constants obtained through astronomical observations of an atomic transition
Atomic data from the IRON project - LI. Electron impact excitation of FeIX
No full textWe calculate collision strengths and thermally averaged collision strengths for electron excitation between the one hundred and forty energetically lowest levels of Fe8+. The scattering target is more elaborate than in any earlier work and large increases are found in the excitation rates among the levels of the 3s(2)3p(5)3d electron configuration due to resonance series that have not been considered previously. The implications for solar and stellar spectroscopy have been discussed elsewhere (Storey & Zeippen 2001). We correct some errors that were made in generating the figures given in that paper and present corrected versions
Dynamic nonlinear analyses for the 4-storey infilled R/C frame: study of a retrofitting solution
No full textA research project on assessment and retrofitting of R/C frame structures is currently being developed under the research programme of the ICONS TMR-research network. This paper presents and discusses the preliminary experimental results from a 4-storey bare frame representative of the common practice of 40~50 years ago in most south European countries and devotes special attention to the study of a retrofitting solution based on bracing and rubber dissipaters, which intends to increase stiffness and damping reducing consequently the earthquake deformation demands.O estudo aqui apresentado concentra-se numa solução de reforço de um pórtico utilizando contraventamentos (k-bracing) com perfis de aço em conjunto com elementos elastoméricos de dissipação. Os resultados das análises não lineares da estrutura com e sem alvenaria e com reforço são apresentados e discutidos. Na segunda parte da comunicação apresentam-se os resultados experimentais já disponíveis e discute-se o problema da modelação recorrendo aos resultados experimentais e comparando os resultados obtidos com diferentes tipos de modelos
At limits of life: multidisciplinary insights reveal environmental constraints on biotic diversity in continental Antarctica
No full textData source: Supporting information, http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0044578#s5Multitrophic communities that maintain the functionality of the extreme Antarctic terrestrial ecosystems, while the simplest of any natural community, are still challenging our knowledge about the limits to life on earth. In this study, we describe and interpret the linkage between the diversity of different trophic level communities to the geological morphology and soil geochemistry in the remote Transantarctic Mountains (Darwin Mountains, 80uS). We examined the distribution and diversity of biota (bacteria, cyanobacteria, lichens, algae, invertebrates) with respect to elevation, age of glacial drift sheets, and soil physicochemistry. Results showed an abiotic spatial gradient with respect to the diversity of the organisms across different trophic levels. More complex communities, in terms of trophic level diversity, were related to the weakly developed younger drifts (Hatherton and Britannia) with higher soil C/N ratio and lower total soluble salts content (thus lower conductivity). Our results indicate that an increase of ion concentration from younger to older drift regions drives a succession of complex to more simple communities, in terms of number of trophic levels and diversity within each group of organisms analysed. This study revealed that integrating diversity across multi-trophic levels of biotic communities with abiotic spatial heterogeneity and geological history is fundamental to understand environmental constraints influencing biological distribution in Antarctic soil ecosystems.Catarina Magalhães, Mark I. Stevens, S. Craig Cary, Becky A. Ball, Bryan C. Storey, Diana H. Wall, Roman Tűrk and Ulrike Ruprech
Post-war British working-class fiction with special reference to the novels of John Braine, Alan Sillitoe, Stan Barstow, David Storey and Barry Hines
No full textThis study is about British working-class fiction in the post-war period.
It covers various authors such as Robert Tressell, George Orwell, Walter Greenwood, Lewis Grassic Gibbon and DH Lawrence from the early twentieth century; writers traditionally classified as 'Angry Young Men' like John Osborne, Arnold Wesker, Shelagh Delaney, John Wain and
Kingsley Amis; and working-class novelists like John Braine, Stan Barstow, David Storey, Alan Sillitoe and Barry Hines from the 1950s and 1960s.
Some of the main issues dealt with in the course of this study are language, form, community, self/identity/autobiography, sexuality and relationship with bourgeois art. The major argument centres on two questions: representation of working-class life, and the
relationship between working-class literary tradition and dominant ideologies.
We will be arguing that while working-class fiction succeeded in challenging and rupturing bourgeois literary tradition, on the level of language and linguistic medium of expression for example, it utterly failed to break away from dominant, bourgeois modes of literary production in relation to form, for instance.
Our argument is situated within Marxist approaches to literature, a political and aesthetic position from which we attempt an analysis and an evaluation of this working-class literary tradition. These critical approaches provide us also with the theoretical tool to define the political perspective of this tradition, and to judge whether it was confined to a descriptive mode of representation or
located in a radical, political outlook
Correlates of constipation in people with Parkinson’s
No full textPurpose: To investigate clinical, demographic and dietary factors associated with constipation in a sample of community dwelling people with Parkinson’s disease, recruited through a specialist outpatient clinic. Partners/carers provided a convenience control group.Scope: Participants completed a baseline questionnaire (background information, diet and exercise, activities of daily living: mobility and manual dexterity, health-related quality of life (SF-12), stool frequency and characteristics, extent of concern due to constipation, laxative taking), and a four-week stool diary. The Rome criterion was used to determine constipation status. Multiple regression methods were used to explore the correlates of constipation. Baseline data were provided by 121 people with Parkinson’s, (54 controls), of whom 73% (25%) met the Rome criterion. Prospective diary data from 106 people with Parkinson’s (43 controls) showed lower proportions: 35% (7%) meeting the Rome criterion. Among all study subjects, i.e. Parkinson’s patients and controls taken together, the presence of constipation is predicted by having Parkinson’s disease (p = .003; odds ratio 4.80, 95% CI 1.64–14.04) and mobility score (p = .04; odds ratio 1.15, 95% CI 1.01–1.31), but not by dietary factors. Amongst people with Parkinson’s constipation is predicted by number of medications (p = .027). Laxative taking masks constipation, and is significantly associated with wearing protection against bowel incontinence (p = .009; odds ratio 4.80, 95% CI: 1.48–15.52).Conclusions: Constipation is disease-related, not a lifestyle factor. More research is needed on optimal management and laxative use.<br/
Treasure Vault for Railway Cars.
No full textPatent for a new and improved safe. This design consists in "a safety treasure-vault for express cars, &c., with the combination of the walls, floor, and roof of the vault constructed of bullet-proof steel plate riveted together at their corners, and the angle-irons to which the walls, floor, and roof are riveted, the bullet-proof steel-plate door, the parcel-delivery window, the combined desk-shelf and bullet-proof shutter, the said vault provided with a port-hole and the bullet-proof plug that stops the port-hole" (lines 21-31)
Hot-Carrier Stressing of NPN Polysilicon Emitter Bipolar Transistors Incorporating Fluorine
No full textThe effects of fluorine on the hot-carrier induced degradation in low-thermal-budget polysilicon emitter NPN bipolar transistors have been examined. Forward Gummel plots, base emitter (BE) diode characteristics, and stress currents were measured during reverse BE bias stress. Fluorinated devices behave similarly under stress to nonfluorinated devices retaining the initial improvement observed in the forward-bias base current, which is due to suppression of recombination in the BE junction depletion regions at the oxide/silicon interface. The benefits of fluorination and particularly the reduction in base current in fluorinated devices, appear to be robust - that is, there is no evidence that the defects passivated by fluorine are reactivated during stressing, or that fluorination introduces additional defects that are activated under stressing
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