113 research outputs found
Subluminous B Stars and Progenitors of Helium Core White Dwarfs
Subluminous B (sdB) stars can result from stable Roche lobe overflow or common envelope ejection in close binary systems. The companions are either low mass main sequence stars or white dwarfs. We discuss mass determinations for sdB stars from such systems and report the discovery of the bright nearby sdB star, HD 188112, to be a close binary system of unusually low mass (0.23 solar masses). From the mass function it is evident that the companion is a massive compact object of at least 0.72 solar masses. The mass of the sdB HD 188112 is too low for the star to evolve into a C/O white dwarf, but it probably is a progenitor for a helium core white dwarf
Neonatal mortality in a referral hospital in Cameroon over a seven year period: trends, associated factors and causes.
Background: The fourth Millennium Development Goals targets reduction of the mortality rate of under-fives by 2/3 by the year 2015. This reduction starts with that of neonatal mortality representing 40% of childhood mortality. In Cameroon neonatal mortality was 31% in 2011.Objectives: We assessed the trends, associated factors and causes of neonatal deaths at the Yaounde Gynaeco-Obstetric and Pediatric Hospital.Methods: The study was a retrospective chart review. Data was collected from the hospital records, and included both maternal and neonatal variables from 1st January 2004 to 31st December 2010.Results: The neonatal mortality was 10%. Out-borns represented 49.3% of the deceased neonates with 11.3% born at home. The neonatal mortality rate followed a downward trend dropping from 12.4% in 2004 to 7.2% in 2010. The major causes of deaths were: neonatal sepsis (37.85%), prematurity (31.26%), birth asphyxia (16%), and congenital malformations (10.54%). Most (74.2%) of the deaths occurred within the first week with 35% occurring within 24hours of life. Mortality was higher in neonates with birth weight less than 2500g and a gestational age of less than 37 weeks. In the mothers, it was high in single parenthood , primiparous and in housewives and students..Conclusion: There has been a steady decline of neonatal mortality since 2004. Neonatal sepsis, prematurity, birth asphyxia and congenital malformations were the major causes of neonatal deaths. Neonatal sepsis remained constant although at lower rates over the study period.Key words: mortality, neonates, referral hospital, Cameroo
The contributions of diverse sense organs in the control of leg movement by a walking insect
Cruse H, Dean J, Suilmann M. The contributions of diverse sense organs in the control of leg movement by a walking insect. Journal of Comparative Physiology, A. 1984;154(5):695-705
The impact of low erythrocyte density in human blood on the fitness and energetic reserves of the African malaria vector Anopheles gambiae
Background
Anaemia is a common health problem in the developing world. This condition is characterized by a reduction in erythrocyte density, primarily from malnutrition and/or
infectious diseases such as malaria. As red blood cells are the primary source of protein for haematophagous mosquitoes, any reduction could impede the ability of mosquito vectors to transmit malaria by influencing their fitness or that of the parasites they transmit. The aim of this study was to determine the impact of differences in the density of red blood cells in human blood on malaria vector (Anopheles gambiae sensu stricto) fitness. The hypotheses tested are that mosquito vector energetic reserves and fitness are negatively influenced by reductions in the red cell density of host human blood meals commensurate with those expected from severe anaemia.
Methods
Mosquitoes (An. gambiae s.s.) were offered blood meals of different packed cell volume(PCV) of human blood consistent with those arising from severe anaemia (15%) and normalPCV (50%). Associations between mosquito energetic reserves (lipid, glucose and glycogen)and fitness measures (reproduction and survival) and blood meal PCV were investigated.
Results
The amount of protein that malaria vectors acquired from blood feeding (indexed by
haematin excretion) was significantly reduced at low blood PCV. However, mosquitoes
feeding on blood of low PCV had the same oviposition rates as those feeding on blood of normal PCV, and showed an increase in egg production of around 15%. The long-term survival of An. gambiae s.s was reduced after feeding on low PCV blood, but PCV had no significant impact on the proportion of mosquitoes surviving through the minimal period required to develop and transmit malaria parasites (estimated as 14 days post-blood feeding). The impact of blood PCV on the energetic reserves of mosquitoes was relatively minor.
Conclusions
These results suggest that feeding on human hosts whose PCV has been depleted due to severe anaemia does not significantly reduce the fitness or transmission potential of malaria vectors, and indicates that mosquitoes may be able exploit resources for reproduction more
efficiently from blood of low rather than normal PCV
Ages for exoplanet host stars
Age is an important characteristic of a planetary system, but also one that
is difficult to determine. Assuming that the host star and the planets are
formed at the same time, the challenge is to determine the stellar age.
Asteroseismology provides precise age determination, but in many cases the
required detailed pulsation observations are not available. Here we concentrate
on other techniques, which may have broader applicability but also serious
limitations. Further development of this area requires improvements in our
understanding of the evolution of stars and their age-dependent
characteristics, combined with observations that allow reliable calibration of
the various techniques.Comment: To appear in "Handbook of Exoplanets", eds. Deeg, H.J. & Belmonte,
J.A, Springer (2018
An ultraviolet-optical flare from the tidal disruption of a helium-rich stellar core
The flare of radiation from the tidal disruption and accretion of a star can
be used as a marker for supermassive black holes that otherwise lie dormant and
undetected in the centres of distant galaxies. Previous candidate flares have
had declining light curves in good agreement with expectations, but with poor
constraints on the time of disruption and the type of star disrupted, because
the rising emission was not observed. Recently, two `relativistic' candidate
tidal disruption events were discovered, each of whose extreme X-ray luminosity
and synchrotron radio emission were interpreted as the onset of emission from a
relativistic jet. Here we report the discovery of a luminous
ultraviolet-optical flare from the nuclear region of an inactive galaxy at a
redshift of 0.1696. The observed continuum is cooler than expected for a simple
accreting debris disk, but the well-sampled rise and decline of its light curve
follows the predicted mass accretion rate, and can be modelled to determine the
time of disruption to an accuracy of two days. The black hole has a mass of
about 2 million solar masses, modulo a factor dependent on the mass and radius
of the star disrupted. On the basis of the spectroscopic signature of ionized
helium from the unbound debris, we determine that the disrupted star was a
helium-rich stellar core.Comment: To appear in Nature on May 10, 201
Perspective from a Younger Generation -- The Astro-Spectroscopy of Gisbert Winnewisser
Gisbert Winnewisser's astronomical career was practically coextensive with
the whole development of molecular radio astronomy. Here I would like to pick
out a few of his many contributions, which I, personally, find particularly
interesting and put them in the context of newer results.Comment: 14 pages. (Co)authored by members of the MPIfR (Sub)millimeter
Astronomy Group. To appear in the Proceedings of the 4th
Cologne-Bonn-Zermatt-Symposium "The Dense Interstellar Medium in Galaxies"
eds. S. Pfalzner, C. Kramer, C. Straubmeier, & A. Heithausen (Springer:
Berlin
The stellar and sub-stellar IMF of simple and composite populations
The current knowledge on the stellar IMF is documented. It appears to become
top-heavy when the star-formation rate density surpasses about 0.1Msun/(yr
pc^3) on a pc scale and it may become increasingly bottom-heavy with increasing
metallicity and in increasingly massive early-type galaxies. It declines quite
steeply below about 0.07Msun with brown dwarfs (BDs) and very low mass stars
having their own IMF. The most massive star of mass mmax formed in an embedded
cluster with stellar mass Mecl correlates strongly with Mecl being a result of
gravitation-driven but resource-limited growth and fragmentation induced
starvation. There is no convincing evidence whatsoever that massive stars do
form in isolation. Various methods of discretising a stellar population are
introduced: optimal sampling leads to a mass distribution that perfectly
represents the exact form of the desired IMF and the mmax-to-Mecl relation,
while random sampling results in statistical variations of the shape of the
IMF. The observed mmax-to-Mecl correlation and the small spread of IMF
power-law indices together suggest that optimally sampling the IMF may be the
more realistic description of star formation than random sampling from a
universal IMF with a constant upper mass limit. Composite populations on galaxy
scales, which are formed from many pc scale star formation events, need to be
described by the integrated galactic IMF. This IGIMF varies systematically from
top-light to top-heavy in dependence of galaxy type and star formation rate,
with dramatic implications for theories of galaxy formation and evolution.Comment: 167 pages, 37 figures, 3 tables, published in Stellar Systems and
Galactic Structure, Vol.5, Springer. This revised version is consistent with
the published version and includes additional references and minor additions
to the text as well as a recomputed Table 1. ISBN 978-90-481-8817-
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
Low and seasonal malaria transmission in the middle Senegal River basin: identification and characteristics of Anopheles vectors
<p>Abstract</p> <p>Background</p> <p>During the last decades two dams were constructed along the Senegal River. These intensified the practice of agriculture along the river valley basin. We conducted a study to assess malaria vector diversity, dynamics and malaria transmission in the area.</p> <p>Methods</p> <p>A cross-sectional entomological study was performed in September 2008 in 20 villages of the middle Senegal River valley to evaluate the variations of <it>Anopheles </it>density according to local environment. A longitudinal study was performed, from October 2008 to January 2010, in 5 selected villages, to study seasonal variations of malaria transmission.</p> <p>Results</p> <p>Among malaria vectors, 72.34% of specimens collected were <it>An. arabiensis</it>, 5.28% <it>An. gambiae </it>of the S molecular form, 3.26% M form, 12.90% <it>An. pharoensis</it>, 4.70% <it>An. ziemanni</it>, 1.48% <it>An. funestus </it>and 0.04% <it>An. wellcomei</it>. <it>Anopheles </it>density varied according to village location. It ranged from 0 to 21.4 <it>Anopheles</it>/room/day and was significantly correlated with the distance to the nearest ditch water but not to the river.</p> <p>Seasonal variations of <it>Anopheles </it>density and variety were observed with higher human biting rates during the rainy season (8.28 and 7.55 <it>Anopheles </it>bite/man/night in October 2008 and 2009 respectively). Transmission was low and limited to the rainy season (0.05 and 0.06 infected bite/man/night in October 2008 and 2009 respectively). During the rainy season, the endophagous rate was lower, the anthropophagic rate higher and L1014F kdr frequency higher.</p> <p>Conclusions</p> <p>Malaria vectors are present at low-moderate density in the middle Senegal River basin with <it>An. arabiensis </it>as the predominant species. Other potential vectors are <it>An. gambiae </it>M and S form and <it>An. funestus</it>. Nonetheless, malaria transmission was extremely low and seasonal.</p
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