752 research outputs found
IMAPS Observations of Interstellar Neutral Argon and the Implications for Partially Ionized Gas
We use the absorption features from neutral argon at 1048 and 1066 A to
determine interstellar abundances or their lower limits toward nine early-type
stars. These features were observed with the Interstellar Medium Absorption
Profile Spectrograph (IMAPS) along sight lines with low reddening and low
fractional abundances of molecular hydrogen. We find that the interstellar Ar I
is below its solar and B-star abundance with respect to hydrogen toward zeta
Pup, gamma2 Vel and beta Cen A with (logarithmic) reduction factors
-0.37+/-0.09, -0.18+/-0.10, and -0.61+/-0.12 dex, respectively.
While Ar can condense onto the surfaces of dust grains in the interiors of
dense clouds, it is unlikely that argon atoms are depleted by this process in
the low-density lines of sight considered in this study. Instead, we propose
that the relatively large photoionization cross section of Ar makes it much
easier to hide in its ionized form than H. In regions that are about half
ionized, this effect can lower Ar I/H I by -0.11 to -0.96 dex, depending on the
energy of the photoionizing radiation and its intensity divided by the local
electron density. We apply this interpretation for the condition of the gas in
front of beta Cen A, which shows the largest deficiency of Ar. Also, we
determine the expected magnitudes of the differential ionizations for He, N, O,
Ne and Ar in the partly ionized, warm gas in the local cloud around our solar
system. For the local cloud and others that can be probed by UV studies, the
observed Ar I to H I ratio may be a good discriminant between two possible
alternatives, collisional ionization or photoionization, for explaining the
existence of partly ionized regions.Comment: 36 pages, 3 figure
An evaluation of edge effects in nutritional accessibility and availability measures: a simulation study
<p>Abstract</p> <p>Background</p> <p>This paper addresses the statistical use of accessibility and availability indices and the effect of study boundaries on these measures. The measures are evaluated via an extensive simulation based on cluster models for local outlet density. We define outlet to mean either food retail store (convenience store, supermarket, gas station) or restaurant (limited service or full service restaurants). We designed a simulation whereby a cluster outlet model is assumed in a large study window and an internal subset of that window is constructed. We performed simulations on various criteria including one scenario representing an urban area with 2000 outlets as well as a non-urban area simulated with only 300 outlets. A comparison is made between estimates obtained with the full study area and estimates using only the subset area. This allows the study of the effect of edge censoring on accessibility measures.</p> <p>Results</p> <p>The results suggest that considerable bias is found at the edges of study regions in particular for accessibility measures. Edge effects are smaller for availability measures (when not smoothed) and also for short range accessibility</p> <p>Conclusions</p> <p>It is recommended that any study utilizing these measures should correct for edge effects. The use of edge correction via guard areas is recommended and the avoidance of large range distance-based accessibility measures is also proposed.</p
Low dose effects of ethanol on suckling rats: Enzymes activity, histological alterations and growth parameters.
زمینه و هدف: غلظت های پایین اتانول می توانند از طریق جفت به جنین و از طریق شیر مادر به نوزاد تازه متولد شده منتقل شوند. این مطالعه با هدف بررسی اثرات دوزهای مختلف اتانول در طول دوره شیردهی بر تغییرات آنزیمی، بافتی و شاخص های رشد نوزادان شیرخوار در موش صحرایی انجام شد. روش بررسی: در این مطالعه تجربی، 21 سر موش صحرایی ماده بالغ نژاد ویستار به سه گروه شامل دو گروه تیمار و یک گروه شاهد تقسیم شدند. به گروه های تیمار از روز یک زایمان تا روز 24 شیردهی آب آشامیدنی به همراه اتانول با غلظت حجمی 2 و 4 درصد تجویز شد و گروه شاهد تنها به آب آشامیدنی دسترسی داشتند. از هر گروه، 9 سر نوزاد موش صحرایی 25 روزه انتخاب و فعالیت سرمی آنزیم های آلانین آمینوترانسفراز، گاماگلوتامیک ترانسفراز، آسپارتات آمینوترانسفراز، آلکالین فسفاتاز، لاکتات دهیدروژناز، کراتین فسفوکیناز، نیتروژن اوره خون و کراتینین اندازه گیری شدند. همچنین مطالعات آسیب شناسی بر روی بافت های مغز، کبد و کلیه انجام شد. داده ها به کمک آزمون های آماری آنالیزواریانس و تست دانت در نرم افزار SPSS تجزیه و تحلیل شدند. یافته ها: در گروه های تجربی میزان فعالیت سرمی آنزیم های آلانین آمینوترانسفراز، آسپارتات آمینوترانسفراز، نیتروژن اوره خون، کراتین فسفوکیناز و آلکالین فسفاتاز اختلاف معنی داری را نسبت به گروه شاهد نشان ندادند (05/0P). مطالعات هیستوپاتولوژیک آسیب های مختلفی را در بافت مغز، کبد و کلیه نوزادان در معرض اتانول 4 حجمی را نشان داد. نتیجه گیری: بر اساس نتایج این مطالعه، مصرف نوشیدنی های الکلی در دوران شیردهی می تواند ضایعات جبران ناپذیری بر روی نوزاد داشته باشد
UV Absorption Lines from High-Velocity Gas in the Vela Supernova Remnant: New insights from STIS Echelle Observations of HD72089
The star HD72089 is located behind the Vela supernova remnant and shows a
complex array of high and low velocity interstellar absorption features arising
from shocked clouds. A spectrum of this star was recorded over the wavelength
range 1196.4 to 1397.2 Angstroms at a resolving power lambda/Delta lambda =
110,000 and signal-to-noise ratio of 32 by STIS on the Hubble Space Telescope.
We have identified 7 narrow components of C I and have measured their relative
populations in excited fine-structure levels. Broader features at heliocentric
velocities ranging from -70 to +130 km/s are seen in C II, N I, O I, Si II, S
II and Ni II. In the high-velocity components, the unusually low abundances of
N I and O I, relative to S II and Si II, suggest that these elements may be
preferentially ionized to higher stages by radiation from hot gas immediately
behind the shock fronts.Comment: 11 pages, 2 figures, Latex. Submitted for the special HST ERO issue
of the Astrophysical Journal Letter
CareTrack Australia: assessing the appropriateness of adult healthcare: protocol for a retrospective medical record review
Introduction: In recent years in keeping with international best practice, clinical guidelines for common conditions have been developed, endorsed and disseminated by peak national and professional bodies. Yet evidence suggests that there remain considerable gaps between the care that is regarded as appropriate by such guidelines and the care received by patients. With an ageing population and increasing treatment options and expectations, healthcare is likely to become unaffordable unless more appropriate care is provided. This paper describes a study protocol that seeks to determine the percentage of healthcare encounters in which patients receive appropriate care for 22 common clinical conditions and the reasons why variations exist from the perspectives of both patients and providers. Methods/design: A random stratified sample of at least 1000 eligible participants will be recruited from a representative cross section of the adult Australian population. Participants' medical records from the years 2009 and 2010 will be audited to assess the appropriateness of the care received for 22 common clinical conditions by determining the percentage of healthcare encounters at which the care provided was concordant with a set of 522 indicators of care, developed for these conditions by a panel of 43 disease experts. The knowledge, attitudes and beliefs of participants and healthcare providers will be examined through interviews and questionnaires to understand the factors influencing variations in care.Tamara D Hunt, Shanthi A Ramanathan, Natalie A Hannaford, Peter D Hibbert, Jeffrey Braithwaite, Enrico Coiera, Richard O Day, Johanna I Westbrook, William B Runcima
Photoionization of the Be isoelectronic sequence: total cross sections
The photoionization of the four-electron beryllium-like isoelectronic series
from the neutral to Fe^{+22} has been studied for ground ^1S and metastable ^3P
initial states. The wave functions of the final-state (target) ions were built
using the CIV3 code. Both nonrelativistic LS-coupling R-matrix and relativistic
Breit-Pauli (BP) R-matrix methods were used to calculate the cross sections in
the photon-energy range between the first ionization threshold and the 1s^2
4f_{7/2} threshold for each ion. Our total cross sections compare well with
experiment which is available for Be, B^+, C^{+2}, N^{+3}, and O^{+4}. The
agreement between the present work and previous calculations is discussed in
detail. The importance of relativistic effects is seen by the comparison
between the LS and the BP results.Comment: 45 pages, 3 tables, 22 figure
Light Element Abundances From z=0 To z=5
Plausible ratios of deuterium to hydrogen D/H as a function of metallicity,
time, and redshift are investigated. Guided by the heavy element abundance
patterns observed locally in Galactic dwarf stars and at large redshift in
quasi-stellar object absorption line systems, empirical evolution of the
relative abundance ratios Li/D, B/D, N/D, O/D, and F/D for QSO absorption line
systems are given for the possible evolutionary patterns in D/H. Shortened
abstract.Comment: 30 pages including 8 figures, ApJ in pres
Theory and applications of atomic and ionic polarizabilities
Atomic polarization phenomena impinge upon a number of areas and processes in
physics. The dielectric constant and refractive index of any gas are examples
of macroscopic properties that are largely determined by the dipole
polarizability. When it comes to microscopic phenomena, the existence of
alkaline-earth anions and the recently discovered ability of positrons to bind
to many atoms are predominantly due to the polarization interaction. An
imperfect knowledge of atomic polarizabilities is presently looming as the
largest source of uncertainty in the new generation of optical frequency
standards. Accurate polarizabilities for the group I and II atoms and ions of
the periodic table have recently become available by a variety of techniques.
These include refined many-body perturbation theory and coupled-cluster
calculations sometimes combined with precise experimental data for selected
transitions, microwave spectroscopy of Rydberg atoms and ions, refractive index
measurements in microwave cavities, ab initio calculations of atomic structures
using explicitly correlated wave functions, interferometry with atom beams, and
velocity changes of laser cooled atoms induced by an electric field. This
review examines existing theoretical methods of determining atomic and ionic
polarizabilities, and discusses their relevance to various applications with
particular emphasis on cold-atom physics and the metrology of atomic frequency
standards.Comment: Review paper, 44 page
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