2,979 research outputs found
Discovery of low mass objects in Taurus
In infrared (2.2 micron, K-band) search of small regions (25 in square) near 26 members of the Taurus star-forming association has revealed 20 dim (K = 13-16 mag) stellar objects near 13 of them. Of these 20 objects, 9 are exceptionally red. It is argued that these 9 are probably also Taurus members. From the luminosities (0.4 to 4 times 10 the -3 power luminosity) and ages (estimated at 10(exp 6) years), masses can be determined by reference to theoretical low-mass cooling curves. The masses are in the range 0.005 to 0.015 solar mass, i.e., low-mass brown dwarfs. Proper motion studies of 7 of the objects visible on the POSS plates conducted by Burton Jones establish that 4 are highly probable Taurus members while 1 is a possible member
Chemical abundances in spiral and irregular galaxies. O and N abundances derived from global emission--line spectra
The validity of oxygen and nitrogen abundances derived from the global
emission-line spectra of galaxies via the P-method has been investigated using
a collection of published spectra of individual HII regions in irregular and
spiral galaxies. The conclusions of Kobulnicky, Kennicutt & Pizagno (1999) that
global emission-line spectra can reliably indicate the chemical properties of
galaxies has been confirmed. It has been shown that the comparison of the
global spectrum of a galaxy with a collection of spectra of individual HII
regions can be used to distinguish high and low metallicity objects and to
estimate accurate chemical abundances in a galaxy. The oxygen and nitrogen
abundances in samples of UV-selected and normal nearby galaxies have been
determined. It has been found that the UV-selected galaxies occupy the same
area in the N/O -- O/H diagram as individual HII regions in nearby galaxies.
Finally, we show that intermediate-redshift galaxies systematically deviate
from the metallicity -- luminosity trend of local galaxies.Comment: 15 pages, 17 figures, accepted for publication in Astronomy and
Astrophysic
Conceptual design study for an advanced cab and visual system, volume 2
The performance, design, construction and testing requirements are defined for developing an advanced cab and visual system. The rotorcraft system integration simulator is composed of the advanced cab and visual system and the rotorcraft system motion generator, and is part of an existing simulation facility. User's applications for the simulator include rotorcraft design development, product improvement, threat assessment, and accident investigation
Electronic response of aligned multishell carbon nanotubes
We report calculations of the effective electronic response of aligned
multishell carbon nanotubes. A local graphite-like dielectric tensor is
assigned to every point of the multishell tubules, and the effective transverse
dielectric function of the composite is computed by solving Maxwell's
equations. Calculations of both real and imaginary parts of the effective
dielectric function are presented, for various values of the filling fraction
and the ratio of the internal and external radii of hollow tubules. Our full
calculations indicate that the experimentally measured macroscopic dielectric
function of carbon nanotube materials is the result of a strong electromagnetic
coupling between the tubes, which cannot be accounted for with the use of
simplified effective medium theories. The presence of surface plasmons is
investigated, and both optical absorption cross sections and energy-loss
spectra of aligned tubules are calculated.Comment: 4 pages, 4 figures, to appear in Phys. Rev.
High Carbon in I Zwicky 18: New Results from Hubble Space Telescope Spectroscopy
We present new measurements of the gas-phase C/O abundance ratio in both the
NW and SE components of the extremely metal-poor dwarf irregular galaxy I Zw
18, based on ultraviolet spectroscopy of the two H II regions using the Faint
Object Spectrograph on the Hubble Space Telescope. We determine values of log
C/O = -0.63 +/- 0.10 for the NW component and log C/O = -0.56 +/- 0.09 for the
SE component. In comparison, log C/O = -0.37 in the sun, while log C/O = -0.85
+/- 0.07 in the three most metal-poor irregular galaxies measured by Garnett et
al. (1995a). Our measurements show that C/O in I Zw 18 is significantly higher
than in other comparably metal-poor irregular galaxies, and above predictions
for the expected C/O from massive star nucleosynthesis. These results suggest
that carbon in I Zw 18 has been enhanced by an earlier population of lower-mass
carbon producing stars; this idea is supported by stellar photometry of I Zw 18
and its companion, which demonstrate that the current bursts of massive stars
were not the first. Despite its very low metallicity, it is likely that I Zw 18
is not a ``primeval'' galaxy.Comment: 14 pages including 4 figures; uses aaspp4.sty. Accepted for
publication in ApJ. Postscript version also available by e-mail request to
author at [email protected]
Radiocarbon dating of methane and carbon dioxide evaded from a temperate peatland stream
Streams draining peatlands export large quantities of carbon in different chemical forms and
are an important part of the carbon cycle. Radiocarbon (14C) analysis/dating provides unique
information on the source and rate that carbon is cycled through ecosystems, as has recently
been demonstrated at the air-water interface through analysis of carbon dioxide (CO2) lost
from peatland streams by evasion (degassing). Peatland streams also have the potential to
release large amounts of methane (CH4) and, though 14C analysis of CH4 emitted by ebullition
(bubbling) has been previously reported, diffusive emissions have not. We describe methods
that enable the 14C analysis of CH4 evaded from peatland streams. Using these methods, we
investigated the 14C age and stable carbon isotope composition of both CH4 and CO2 evaded
from a small peatland stream draining a temperate raised mire. Methane was aged between
1617-1987 years BP, and was much older than CO2 which had an age range of 303-521 years
BP. Isotope mass balance modelling of the results indicated that the CO2 and CH4 evaded
from the stream were derived from different source areas, with most evaded CO2 originating
from younger layers located nearer the peat surface compared to CH4. The study demonstrates
the insight that can be gained into peatland carbon cycling from a methodological
development which enables dual isotope (14C and 13C) analysis of both CH4 and CO2 collected
at the same time and in the same way
Association of the Covid-19 lockdown with smoking, drinking, and attempts to quit in England: an analysis of 2019-2020 data
Aim: To examine changes in smoking, drinking and quitting/reduction behaviour following the COVIDâ19 lockdown in
England. Design/setting: Monthly crossâsectional surveys representative of the adult population in England,
aggregated before (April 2019âFebruary 2020) versus after (April 2020) lockdown. Participants: A total of 20 558
adults (â„ 16 years). Measurements: The independent variable was the timing of the COVIDâ19 lockdown (before versus
after March 2020). Dependent variables were: prevalence of smoking and highârisk drinking, pastâyear cessation and quit
attempts (among pastâyear smokers), pastâyear attempts to reduce alcohol consumption (among highârisk drinkers) and
use of evidenceâbased (e.g. prescription medication/faceâtoâface behavioural support) and remote support [telephone
support/websites/applications (apps)] for smoking cessation and alcohol reduction (among smokers/highârisk drinkers
who made a quit/reduction attempt). Covariates included age, sex, social grade, region and level of nicotine and alcohol
dependence (as relevant). Findings: The COVIDâ19 lockdown was not associated with a significant change in smoking
prevalence [17.0% (after) versus 15.9% (before), odds ratio (OR) = 1.09, 95% CI = 0.95â1.24], but was associated with
increases in quit attempts [39.6 versus 29.1%, adjusted odds ratio (ORadj) = 1.56, 95% CI = 1.23â1.98], quit success
(21.3 versus 13.9%, ORadj = 2.01, 95% CI = 1.22â3.33) and cessation (8.8 versus 4.1%, ORadj = 2.63, 95%
CI = 1.69â4.09) among pastâyear smokers. Among smokers who tried to quit, there was no significant change in use
of evidenceâbased support (50.0 versus 51.5%, ORadj = 1.10, 95% CI = 0.72â1.68) but use of remote support increased
(10.9 versus 2.7%, ORadj = 3.59, 95% CI = 1.56â8.23). Lockdown was associated with increases in highârisk drinking
(38.3 versus 25.1%, OR = 1.85, CI = 1.67â2.06), but also alcohol reduction attempts by highârisk drinkers (28.5 versus
15.3%, ORadj = 2.16, 95% CI = 1.77â2.64). Among highârisk drinkers who made a reduction attempt, use of
evidenceâbased support decreased (1.2 versus 4.0%, ORadj = 0.23, 95% CI = 0.05â0.97) and there was no significant
change in use of remote support (6.9 versus 6.1%, ORadj = 1.32, 95% CI = 0.64â2.75). Conclusions: Following the
March 2020 COVIDâ19 lockdown, smokers and highârisk drinkers in England were more likely than before lockdown to
report trying to quit smoking or reduce alcohol consumption and rates of smoking cessation and use of remote cessation
support were higher. However, highârisk drinking prevalence increased postâlockdown and use of evidenceâbased support
for alcohol reduction by highârisk drinkers decreased with no compensatory increase in use of remote support
Very Low Affinity B Cells Form Germinal Centers, Become Memory B Cells, and Participate in Secondary Immune Responses When Higher Affinity Competition Is Reduced
To understand the relationship between the affinity of the B cell antigen receptor (BCR) and the immune response to antigen, two lines of immunoglobulin H chain transgenic (Tg) mice were created. H50GÎŒa and T1(V23)ÎŒa mice express ÎŒ H chain transgenes that associate with the λ1 L chains to bind the (4-hydroxy-3-nitrophenyl)acetyl hapten with association constants (Kas) of only 1.2 Ă 105 Mâ1 and 3 Ă 104 Mâ1, respectively. Both lines mounted substantial antibody-forming cell (AFC) and germinal center (GC) responses. H50GÎŒa Tg mice also generated memory B cells. T1(V23)ÎŒa B cells formed AFC and GCs, but were largely replaced in late GCs by antigen-specific cells that express endogenous BCRs. Thus, B lymphocytes carrying BCRs with affinities previously thought to be irrelevant in specific immune responses are in fact capable of complete T cellâdependent immune responses when relieved of substantial competition from other B cells. The failure to observe such B cells normally in late primary responses and in memory B cell populations is the result of competition, rather than an intrinsic inability of low affinity B cells
The expert-public interface in municipal waste management decision making: exploring opinions from stakeholder groups
Local authorities need to find more effective ways to engage communities because public
participation in collection schemes and acceptance of municipal waste facilities are integral
to delivering effective waste strategies. The technical expertise politicians relied on in the
past, to produce cost-effective and environmentally sound solutions, no longer provides
sufficient justification to approve waste facilities. A new conceptualization of the relationship
between science and politics, whereby there is some balance in the use of expert and local
knowledge, is required to legitimize waste policy decisions. This paper aims to develop a
better understanding of what happens at the interface between âexpertâ and âpublicâ in
municipal waste management decision making. It establishes opinions on the extent to which
public values and preferences may be considered in practice in order to avoid or resolve
controversial issues by gaining public consent
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