16,707 research outputs found
Using Lyman-alpha to detect galaxies that leak Lyman continuum
We propose to infer ionising continuum leaking properties of galaxies by
looking at their Lyman-alpha line profiles. We carry out Lyman-alpha radiation
transfer calculations in two models of HII regions which are porous to ionising
continuum escape: 1) the so-called "density bounded" media, in which massive
stars produce enough ionising photons to keep the surrounding interstellar
medium transparent to the ionising continuum, i.e almost totally ionised, and
2) "riddled ionisation-bounded" media, surrounded by neutral interstellar
medium, but with holes, i.e. with a covering factor lower than unity. The
Lyman-alpha spectra emergent from these configurations have distinctive
features: 1) a "classical" asymmetric redshifted profile in the first case, but
with a small shift of the maximum of the profile compare to the systemic
redshift (Vpeak < 150 km/s); 2) a main peak at the systemic redshift in the
second case (Vpeak = 0 km/s), with, as a consequence, a non-zero Lyman-alpha
flux bluewards the systemic redshift. Assuming that in a galaxy leaking
ionising photons, the Lyman-alpha component emerging from the leaking star
cluster(s) dominates the total Lyman-alpha spectrum, the Lyman-alpha shape may
be used as a pre-selection tool to detect Lyman continuum (LyC) leaking
galaxies, in objects with well determined systemic redshift, and high spectral
resolution Lyman-alpha spectra (R >= 4000). The examination of a sample of 10
local starbursts with high resolution HST-COS Lyman-alpha spectra and known in
the literature as LyC leakers or leaking candidates, corroborates our
predictions. Observations of Lyman-alpha profiles at high resolution should
show definite signatures revealing the escape of Lyman continuum photons from
star-forming galaxies.Comment: A&A in pres
Sexual behaviour and HIV/sexually transmitted infection risk behaviours in the general population of Slovenia, a low HIV prevalence country in central Europe.
OBJECTIVES: To describe sexual and HIV/sexually transmitted infection (STI) risk behaviours in Slovenia. METHODS: A nationally representative cross-sectional survey of the general population aged 18-49 years in 1999-2001 was conducted. The data were collected by face-to-face interviews and anonymous self-administered questionnaires. Statistical methods for complex survey data were used. RESULTS: 849 men and 903 women were interviewed. In the past 5 years, both men and women reported a median of one heterosexual partner (means 3.2, 1.5, respectively), concurrent heterosexual partnerships were reported by 24.4% of men and 8.2% of women, heterosexual sex with non-Slovenian partners by 12.6% of men and 12.2% of women, forced sex by 4.8% of women, paid heterosexual sex by 2.6% of men, sex with another man by 0.6% of men and heterosexual sex with an injecting drug user by 1.2% of men and 1.3% of women. In the past year, 22.7% of men and 9.5% of women reported forming at least one new heterosexual partnership. The mean numbers of episodes of heterosexual sex in the previous 4 weeks were 6.1 for men and 6.0 for women. Consistent and inconsistent condom use was reported more frequently among men reporting multiple female partners and those not married or cohabiting. CONCLUSIONS: Recent patterns of reported sexual behaviour are consistent with a low risk of HIV and STI transmission in Slovenia. The results will inform Slovenian sexual health policies including HIV/STI prevention, and are particularly valuable because population-based data on HIV/STI risk behaviour have not previously been available in low HIV prevalence countries of central Europe
The fate of ethane in Titan's hydrocarbon lakes and seas
Ethane is expected to be the dominant photochemical product on Titan's
surface and, in the absence of a process that sequesters it from exposed
surface reservoirs, a major constituent of its lakes and seas. Absorption of
Cassini's 2.2 cm radar by Ligeia Mare however suggests that this north polar
sea is dominated by methane. In order to explain this apparent ethane
deficiency, we explore the possibility that Ligeia Mare is the visible part of
an alkanofer that interacted with an underlying clathrate layer and investigate
the influence of this interaction on an assumed initial ethane-methane mixture
in the liquid phase. We find that progressive liquid entrapment in clathrate
allows the surface liquid reservoir to become methane-dominated for any initial
ethane mole fraction below 0.75. If interactions between alkanofers and
clathrates are common on Titan, this should lead to the emergence of many
methane-dominated seas or lakes.Comment: Accepted for publication in Icaru
A Search for Intrinsic Polarization in O Stars with Variable Winds
New observations of 9 of the brightest northern O stars have been made with
the Breger polarimeter on the 0.9~m telescope at McDonald Observatory and the
AnyPol polarimeter on the 0.4~m telescope at Limber Observatory, using the
Johnson-Cousins UBVRI broadband filter system. Comparison with earlier
measurements shows no clearly defined long-term polarization variability. For
all 9 stars the wavelength dependence of the degree of polarization in the
optical range can be fit by a normal interstellar polarization law. The
polarization position angles are practically constant with wavelength and are
consistent with those of neighboring stars. Thus the simplest conclusion is
that the polarization of all the program stars is primarily interstellar.
The O stars chosen for this study are generally known from ultraviolet and
optical spectroscopy to have substantial mass loss rates and variable winds, as
well as occasional circumstellar emission. Their lack of intrinsic polarization
in comparison with the similar Be stars may be explained by the dominance of
radiation as a wind driving force due to higher luminosity, which results in
lower density and less rotational flattening in the electron scattering inner
envelopes where the polarization is produced. However, time series of
polarization measurements taken simultaneously with H-alpha and UV spectroscopy
during several coordinated multiwavelength campaigns suggest two cases of
possible small-amplitude, periodic short-term polarization variability, and
therefore intrinsic polarization, which may be correlated with the more widely
recognized spectroscopic variations.Comment: LaTeX2e, 22 pages including 11 tables; 12 separate gif figures; uses
aastex.cls preprint package; accepted by The Astronomical Journa
IMPACTS OF LIBERALIZING THE JAPANESE PORK MARKET
The Japanese pork market is protected by a complex set of restrictions, including a variable levy and an import tariff. The combination of these policies distorts the quantity, price, and form of Japanese pork imports. An important issue relevant to the liberalization of the Japanese pork market is the accurate measurement of the price wedge between Japanese and world pork prices. The analysis indicates that the tariff equivalent of the price wedge over the 1986-88 period was 44%. If the tariff equivalent of the price wedge is reduced over a ten-year period, Japanese pork imports are projected to increase by over 39% initially and by over 215% compared to baseline projections by the year 2000. Producer welfare can be maintained by a deficiency payment scheme. A less costly alternative is an industry buffer scheme, which maintains the level of the pork industry for two years and then implements a declining deficiency payment scheme that limits the decrease in production levels to 5% per year.International Relations/Trade,
Japanese Beef Policy and GATT Negotiations: An Analysis of Reducing Assistance to Beef Producers
International Development, Livestock Production/Industries,
The Professional Corporation: An Overview
The purpose of this comment is to provide a newly formed, moderate-sized legal firm or the beginning legal individual practitioner with a broad overview of the benefits and problems that a professional corporation [hereinafter PC] offers when compared to a partnership or individual proprietorship structure. The emphasis here will be on the availability of in-depth material in the field along with the governing Internal Revenue Code and Treasury Regulations sections
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