5,852 research outputs found
Dense gas and HII regions in the starburst galaxy NGC 253
The energetic activity in the nuclear barred region of NGC 253 is attributable to a burst of star formation. NGC 253 is in many ways a twin of the prototypical starburst galaxy M82; the strong non-thermal radio continuum, high far-infrared luminosity, and bright molecular emission of the central 1 Kpc parallel the morphology of the M82 starburst. Furthermore, the filamentary low ionization optical emission and extended x ray emission along the minor axis in NGC 253 is similar to a scaled down version of the well developed galactic bipolar wind in M82. The infrared luminosity of NGC 253, 3(exp 10) solar luminosity, is comparable to M82 but is emitted from a smaller region (Telesco and Harper 1980). This suggests that the NGC 253 starburst may be more intense and at an earlier evolutionary stage than M82. However, the presence of a non-stellar AGN in NGC 253 may complicate the comparison (Turner and Ho, 1985). Researchers used the Hat Creek millimeter interferometer to map emission from the J = 1 to 0 transitions of HCN and HCO(+) as well as 3 mm continuum emission, toward the nuclear region of NGC 253. The HCO(+) and continuum observations are sensitive to spatial scales from 6 to 45 seconds. The 2 minute field of view comfortably includes the entire starburst region (about 40 seconds; 650 pc). Because the longer baseline HCN observations are not yet complete, they are only sensitive to spatial scales from 15 to 45 seconds
First-principles calculations of magnetization relaxation in pure Fe, Co, and Ni with frozen thermal lattice disorder
The effect of the electron-phonon interaction on magnetization relaxation is
studied within the framework of first-principles scattering theory for Fe, Co,
and Ni by displacing atoms in the scattering region randomly with a thermal
distribution. This "frozen thermal lattice disorder" approach reproduces the
non-monotonic damping behaviour observed in ferromagnetic resonance
measurements and yields reasonable quantitative agreement between calculated
and experimental values. It can be readily applied to alloys and easily
extended by determining the atomic displacements from ab initio phonon spectra
Validity of effective material parameters for optical fishnet metamaterials
Although optical metamaterials that show artificial magnetism are mesoscopic
systems, they are frequently described in terms of effective material
parameters. But due to intrinsic nonlocal (or spatially dispersive) effects it
may be anticipated that this approach is usually only a crude approximation and
is physically meaningless. In order to study the limitations regarding the
assignment of effective material parameters, we present a technique to retrieve
the frequency-dependent elements of the effective permittivity and permeability
tensors for arbitrary angles of incidence and apply the method exemplarily to
the fishnet metamaterial. It turns out that for the fishnet metamaterial,
genuine effective material parameters can only be introduced if quite stringent
constraints are imposed on the wavelength/unit cell size ratio. Unfortunately
they are only met far away from the resonances that induce a magnetic response
required for many envisioned applications of such a fishnet metamaterial. Our
work clearly indicates that the mesoscopic nature and the related spatial
dispersion of contemporary optical metamaterials that show artificial magnetism
prohibits the meaningful introduction of conventional effective material
parameters
Vibrational spectra of t-butyl alcohol, t-butylamine and t-butyl alcohol + t-butylamine binary liquid mixtures
Raman and FT-IR absorption spectra of t-butyl alcohol and t-butylamine pure components have been recorded in the liquid state in the region of 400-4000 cm-1. The data obtained have been used to propose complete vibrational assignments for each of the liquid component and the structural features are discussed. Additionally, the Raman and infrared spectra of the binary liquid mixtures for the t-butyl alcohol/t-butylamine system have also been recorded. The variations in frequency shifts, intensities and line widths are discussed with a view to understanding the origin of such variations. KEY WORDS: Infrared and Raman spectra, Binary solution, t-Butanol, t-Butylamine Bull. Chem. Soc. Ethiop. 2003, 17(2), 211-218
Negative vaccine attitudes and intentions to vaccinate against Covid-19 in relation to smoking status: a population survey of UK adults
INTRODUCTION: We examined differences in negative attitudes towards vaccines in general, and intentions to vaccinate against Covid-19 specifically, by smoking status in a large sample of adults in the UK. METHOD: Data were from 29,148 adults participating in the Covid-19 Social Study in September-October 2020. Linear regression analyses examined associations between smoking status (current/former/never) and four types of general negative vaccine attitudes: mistrust of vaccine benefit, worries about unforeseen effects, concerns about commercial profiteering, and preference for natural immunity. Multinomial logistic regression examined associations between smoking status and uncertainty and unwillingness to be vaccinated for Covid-19. Covariates included sociodemographic characteristics and diagnosed health conditions. RESULTS: Relative to never and former smokers, current smokers reported significantly greater mistrust of vaccine benefit, were more worried about unforeseen future effects, had greater concerns about commercial profiteering, and had a stronger preference for natural immunity (Badjs 0.16-0.36, p<0.001). Current smokers were more likely to be uncertain (27.6% vs. 22.7% of never smokers: RRadj 1.43 [95%CI 1.31-1.56]; vs. 19.3% of former smokers: RRadj 1.55 [1.41-1.73]) or unwilling (21.5% vs. 11.6% of never smokers: RRadj 2.12 [1.91-2.34]; vs. 14.7% of former smokers: RRadj 1.53 [1.37-1.71]) to receive a Covid-19 vaccine. CONCLUSIONS: Current smokers hold more negative attitudes towards vaccines in general, and are more likely to be undecided or unwilling to vaccinate against Covid-19, compared with never and former smokers. With a disproportionately high number of smokers belonging to socially clustered and disadvantaged socioeconomic groups, lower vaccine uptake in this group could also exacerbate health inequalities. IMPLICATIONS: These results suggest that without intervention, smokers will be less likely than non-smokers to take up the offer of a Covid-19 vaccine when offered. Targeted policy action may be required to ensure low uptake of Covid-19 vaccination programmes does not compound health inequalities between smokers and non-smokers
Contact-less measurements of Shubnikov-de Haas oscillations in the magnetically ordered state of CeAgSb and SmAgSb single crystals
Shubnikov - de Haas oscillations were measured in single crystals of highly
metallic antiferromagnetic SmAgSb and ferromagnetic CeAgSb using a
tunnel diode resonator. Resistivity oscillations as a function of applied
magnetic field were observed via measurements of skin depth variation. The
effective resolution of p allows a detailed study
of the SdH spectra as a function of temperature. The effects of the Sm long -
range magnetic ordering as well as its electronic structure (-electrons) on
the Fermi surface topology is discussed
Single nucleotide polymorphisms for assessing genetic diversity in castor bean (Ricinus communis)
<p>Abstract</p> <p>Background</p> <p>Castor bean (<it>Ricinus communis</it>) is an agricultural crop and garden ornamental that is widely cultivated and has been introduced worldwide. Understanding population structure and the distribution of castor bean cultivars has been challenging because of limited genetic variability. We analyzed the population genetics of <it>R. communis </it>in a worldwide collection of plants from germplasm and from naturalized populations in Florida, U.S. To assess genetic diversity we conducted survey sequencing of the genomes of seven diverse cultivars and compared the data to a reference genome assembly of a widespread cultivar (Hale). We determined the population genetic structure of 676 samples using single nucleotide polymorphisms (SNPs) at 48 loci.</p> <p>Results</p> <p>Bayesian clustering indicated five main groups worldwide and a repeated pattern of mixed genotypes in most countries. High levels of population differentiation occurred between most populations but this structure was not geographically based. Most molecular variance occurred within populations (74%) followed by 22% among populations, and 4% among continents. Samples from naturalized populations in Florida indicated significant population structuring consistent with local demes. There was significant population differentiation for 56 of 78 comparisons in Florida (pairwise population ϕ<sub>PT </sub>values, <it>p </it>< 0.01).</p> <p>Conclusion</p> <p>Low levels of genetic diversity and mixing of genotypes have led to minimal geographic structuring of castor bean populations worldwide. Relatively few lineages occur and these are widely distributed. Our approach of determining population genetic structure using SNPs from genome-wide comparisons constitutes a framework for high-throughput analyses of genetic diversity in plants, particularly in species with limited genetic diversity.</p
A surface electrode point Paul trap
We present a model as well as experimental results for a surface electrode
radio-frequency Paul trap that has a circular electrode geometry well-suited
for trapping of single ions and two-dimensional planar ion crystals. The trap
design is compatible with microfabrication and offers a simple method by which
the height of the trapped ions above the surface may be changed \emph{in situ}.
We demonstrate trapping of single and few Sr+ ions over an ion height range of
200-1000 microns for several hours under Doppler laser cooling, and use these
to characterize the trap, finding good agreement with our model.Comment: 10 pages, 11 figures, 1 tabl
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