2,004 research outputs found
Feeding habits of anophelines (Diptera: Culicidae) in 1971-78, with reference to the human blood index: a review
A synoptic view is given of the data amassed by WHO, with technical assistance from the Imperial College of Science and Technology, on the origins of blood-meals in Anopheles samples collected from 1971 to 1978. Attention is focused on the proportion of each sample found to contain human blood and on the problems of interpreting from this the human blood index or degree of biting-contact with man exhibited by vector populations. The difficulties of overcoming bias in sampling, which are formidable in unsprayed areas, are further compounded where the dwellings are treated with a slow-acting residual insecticide which knocks down many engorged mosquitoes before they can be collected from their daytime resting places. There is evidence to suggest that the host-selection patterns of those vectors which are ‘opportunistic' feeders may be heavily influenced, even from village to village or from month to month, by the changing availability of alternative hosts, particularly cattle. This suggests in turn that the possibilities of manipulating the degree of mosquito-man contact by encouraging deflection to animals (zooprophylaxis) or by measures to afford a degree of personal protection should not be under-estimated by malaria strategists. It may sometimes be found less difficult to reduce the vector's human blood index than it is to measure it, but in view of the epidemiological importance of this parameter, suggestions are put forward for improving entomological field practice in this area. They include a quantitative survey of the biotopes available to the mosquito population as diurnal shelters, a longitudinal survey of the densities of blood-fed females per biotope, and a survey of the numbers and the respective distribution of people and domestic animals available as hosts. The work-load entailed by such a thorough form of investigation, to be repeated where necessary at different seasons of the year, underlines the necessity to concentrate efforts on a small number of localities, carefully chosen for the malaria situations they represent and the vector populations they support. A large-scale blood-meal sampling programme, confined to these selected localities, is most likely in our estimation to yield information of value for controlling malaria vector
Chandra Observations of the Gravitationally Lensed System 2016+112
An observation of the gravitationally lensed system 2016+112 with the Chandra
X-ray Observatory has resolved a mystery regarding the proposed presence of a
dark matter object in the lens plane of this system. The Chandra ACIS
observation has clearly detected the lensed images of 2016+112 with positions
in good agreement with those reported in the optical and also detects 13
additional X-ray sources within a radius of 3.5 arcmin. Previous X-ray
observations in the direction of 2016+112 with the ROSAT HRI and ASCA SIS have
interpreted the X-ray data as arising from extended emission from a dark
cluster. However, the present Chandra observation can account for all the X-ray
emission as originating from the lensed images and additional point X-ray
sources in the field. Thus cluster parameters based on previous X-ray
observations are unreliable. We estimate an upper limit on the mass-to-light
ratio within a radius of 800 h_(50)^(-1) kpc of M/L_(V) < 190 h_(50)
(M/L_(V))_Sun. The lensed object is quite unusual, with reported narrow
emission lines in the optical that suggest it may be a type-2 quasar (Yamada
et. al. 1999). Our modeling of the X-ray spectrum of the lensed object implies
that the column density of an intrinsic absorber must lie between 3 and 85 x
10^22 cm^-2 (3 sigma confidence level). The 2-10 keV luminosity of the lensed
object, corrected for the lens magnification effect and using the above range
of intrinsic absorption, is 3 x 10^43 - 1.4 x 10^44 erg/s.Comment: 9 pages, includes 2 figures, Accepted for publication in ApJ
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Exploring Knowledge, Attitudes, and Sexual Behaviors among Young Adults in Rural Zacatecas, Mexico
According to The Joint United Nations Programme on HIV and AIDS report of regional
statistics for HIV/AIDS from 2001-2008, Latin America has the third highest prevalence of HIV/AIDS
among children and adults in the world with about 2 million infected in 2008. Among all of these
countries, Mexico has the second highest prevalence in Latin America. Another topic of public
health concern associated with the boom of the younger generations in Mexico is the potential
increase in unintended pregnancies. The objective of this study was to explore the factors
influencing knowledge, attitudes and beliefs regarding reproductive health, as well as sexual risk
behaviors among young adults in a rural community in Mexico. A mixed-methods investigation
was conducted, including 10 closed-ended questionnaires and 10 in-depth interviews with five
females and five males ranging from 18-28 years of age. Findings indicate that level of
education had little influence on awareness of contraceptive methods and depth of knowledge
increased only slightly with years of education. Religious affiliation was not related to
contraceptive preference and/or use, and pre-marital sex was less common among females. The
reasons influencing pre-marital sex were attributed to societal norms and familial pressures and
were independent of religious background
Constraining H0 from Chandra Observations of Q0957+561
We report the detection of the lens cluster of the gravitational lens (GL)
system Q0957+561 from a deep observation with the Advanced CCD Imaging
Spectrometer on-board the Chandra X-ray Observatory. Intracluster X-ray
emission is found to be centered 4.3 +/- 1.3 arcsec east and 3.5(-0.6,+1.3)
arcsec north of image B, nearer than previous estimates. Its spectrum can be
modeled well with a thermal plasma model consistent with the emission
originating from a cluster at a redshift of 0.36. Our best-fit estimates of the
cluster temperature of T_e = 2.09(-0.54,+0.83) keV (90 percent confidence) and
mass distribution of the cluster are used to derive the convergence parameter
kappa, the ratio of the cluster surface mass density to the critical density
required for lensing. We estimate the convergence parameter at the location of
the lensed images A and B to be kappa_A = 0.22(+0.14,-0.07) and kappa_B =
0.21(+0.12,-0.07), respectively (90 percent confidence levels). The observed
cluster center, mass distribution and convergence parameter kappa provide
additional constraints to lens models of this system. Our new results break a
mass-sheet degeneracy in GL models of this system and provide better
constraints of ~ 29 percent (90 percent confidence levels) on the Hubble
constant. We also present results from the detection of the most distant X-ray
jet (z = 1.41) detected to date. The jet extends approximately 8 arcsec NE of
image A and three knots are resolved along the X-ray jet with flux densities
decreasing with distance from the core. The observed radio and optical flux
densities of the knots are fitted well with a synchrotron model and the X-ray
emission is modeled well with inverse Compton scattering of Cosmic Microwave
Background photons by synchrotron-emitting electrons in the jet.Comment: 18 pages, includes 7 figures, Accepted for publication in Ap
Larval food quantity affects the capacity of adult mosquitoes to transmit human malaria
Adult traits of holometabolous insects are shaped by conditions experienced during larval development, which might impact interactions between adult insect hosts and parasites. However, the ecology of larval insects that vector disease remains poorly understood. Here, we used Anopheles stephensi mosquitoes and the human malaria parasite Plasmodium falciparum, to investigate whether larval conditions affect the capacity of adult mosquitoes to transmit malaria. We reared larvae in two groups; one group received a standard laboratory rearing diet, whereas the other received a reduced diet. Emerging adult females were then provided an infectious blood meal. We assessed mosquito longevity, parasite development rate and prevalence of infectious mosquitoes over time. Reduced larval food led to increased adult mortality and caused a delay in parasite development and a slowing in the rate at which parasites invaded the mosquito salivary glands, extending the time it took for mosquitoes to become infectious. Together, these effects increased transmission potential of mosquitoes in the high food regime by 260-330%. Such effects have not, to our knowledge, been shown previously for human malaria and highlight the importance of improving knowledge of larval ecology to better understand vector-borne disease transmission dynamics
Helical Jet in the Gravitationally Lensed Blazar PKS1830-211
Recent radio VLBI observations of the complex gravitationally lensed system
PKS1830-211 have thrown up some questions with regard to the processes occuring
at the heart of the blazar source at a redshift of 2.51, which is viewed almost
straight down the jet axis. This work links, by a model of a helical jet
tracked by ballistically ejected plasmons from a precessing nozzle,
observations on the scale of tens of microarcseconds to those on the scale of
milliarcseconds. An observed jet precession period of 1.08 years is inferred
from the model, translating to an intrinsic period of 30.8 years for a source
at redshift 2.51 and an assumed jet bulk velocity of 0.99 c. This fits well
with the picture of an active galactic nucleus hosting a binary black hole
system at its centre, with the jet emitted by one member of the system, and the
precession as being due to its orbital motion around its companion.Comment: Accepted for publication in the MNRA
First e-VLBI observations of GRS 1915+105
We present results from the first successful open call e-VLBI science run,
observing the X-ray binary GRS 1915+105. e-VLBI science allows the rapid
production of VLBI radio maps, within hours of an observation rather than
weeks, facilitating a decision for follow-up observations. A total of 6
telescopes observing at 5 GHz across the European VLBI Network (EVN) were
correlated in real time at the Joint Institute for VLBI in Europe (JIVE).
Constant data rates of 128 Mbps were transferred from each telescope, giving 4
TB of raw sampled data over the 12 hours of the whole experiment. Throughout
this, GRS 1915+105 was observed for a total of 5.5 hours, producing 2.8 GB of
visibilities of correlated data. A weak flare occurred during our observations,
and we detected a slightly resolved component of 2.7 x 1.2 milliarcsecond with
a position angle of 140 (+/-2) degrees. The peak brightness was 10.2 mJy per
beam, with a total integrated radio flux of 11.1 mJy.Comment: Accepted for publication in MNRAS 4 pages, 3 figure
Using Water Chemistry Data to Quantify Source Contribution to Stream Flow in a Coastal Plain Watershed
2010 S.C. Water Resources Conference - Science and Policy Challenges for a Sustainable Futur
A brain electrical activity electroencephalographic-based biomarker of functional impairment in traumatic brain injury: A multi-site validation trial
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