1,268 research outputs found
Inbreeding Effects On Sperm Production in Clam Shrimp (Eulimnadia Texana)
Hypothesis: Inbreeding depression is manifest in lower sperm production. Organism: Freshwater crustaceans (clam shrimp - Eulimnadia texana), from the southwestern United States, which have high levels of inbreeding. Methods: Comparisons of semi-thin sections of the male gonad among selfed and outcrossed siblings from four families. Results: There was a twofold reduction in sperm production in inbred relative to outcrossed males. Inbreeding depression in males was higher than previous estimates from hermaphrodites. Conclusions: Inbreeding markedly reduces sperm production. The observed low levels of sperm production can explain both the low average outcrossing rates as well as the variation in these rates reported in previous studies of these crustaceans
The Pelvic Flexure Separates Distinct Microbial Communities in the Equine Hindgut
As hindgut fermenters, horses are especially dependent on the microbiota residing in their cecum and large intestines. Interactions between these microbial populations and the horse are critical for maintaining gut homeostasis, which supports proper digestion. The current project was motivated to determine if any features of the fecal microbiota are informative of the microbial communities from the cecum, ventral colon, or dorsal colon. Digesta from the cecum, ventral colon, dorsal colon and feces were collected from 6 yearling miniature horses. Microbial DNA was isolated and the microbiota from each sample was characterized by profiling the V4 region of the 16S rRNA. Principal coordinate analysis of the beta diversity results revealed significant (p = 0.0001; F = 5.2393) similarities between the microbial populations from cecal and ventral colon and the dorsal colon and fecal samples, however, there was little overlap between the proximal and distal ends of the hindgut. These distinct population structures observed in our results coincide with the pelvic flexure, which itself separates intestinal compartments with distinct roles in digestive physiology. An indicator species analysis confirmed the population differences, supported by the identification of several microbial families characteristic of the compartments upstream of the pelvic flexure that were not represented following it. Our data suggest that the fecal microbiota is not informative of the proximal hindgut but can provide insight into communities of the distal compartments. Further, our results suggest that the pelvic flexure might be an important anatomical landmark relative to the microbial communities in the equine large intestine
Receiver Function Constraints on Crustal Seismic Velocities and Partial Melting beneath the Red Sea Rift and Adjacent Regions, Afar Depression
The Afar Depression is an ideal locale for the investigation of crustal processes involved in the transition from continental rifting to oceanic spreading. To provide relatively high resolution images of the crust beneath the Red Sea rift (RSR) represented by the Tendaho graben in the Afar Depression, we deployed an array of 18 broadband seismic stations in 2010 and 2011. Stacking of about 2300 receiver functions from the 18 and several nearby stations along the ~200 km long array reveals an average crustal thickness of 22 ± 4 km, ranging from ~17 km near the RSR axis to 30 km within the overlap zone between the Red Sea and Gulf of Aden rifts. The resulting anomalously high Vp/Vs ratios decrease from 2.40 in the southwest to 1.85 within the overlap zone. We utilize theoretical Vp and melt fraction relationships to obtain an overall highly reduced average crustal Vp of ~5.1 km/s. The melt percentage is about 10% beneath the RSR while the overlap zone contains minor quantities of partial melt. The observed high Vp/Vs values beneath most of the study area indicate widespread partial melting beneath the southwest half of the profile, probably as a result of gradual eastward migration of the RSR axis. Our results also suggest that the current extensional strain in the lower crust beneath the region is diffuse, while the strain field in the upper crust is localized along narrow volcanic segments. These disparate styles of deformation imply a high degree of decoupling between the upper and lower crust
Hubble Space Telescope WFPC-2 Imaging of Cassiopeia A
The young SNR Cassiopeia A was imaged with WFPC-2 through four filters
selected to capture the complete velocity range of the remnant's main shell in
several important emission lines. Primary lines detected were [O III]
4959,5007, [N II] 6583, [S II] 6716,6731 + [O II] 7319,7330 + [O I] 6300,6364,
and [S III] 9069,9532. About 3/4th of the remnant's main shell was imaged in
all four filters. Considerable detail is observed in the reverse-shocked ejecta
with typical knot scale lengths of 0.2"-0.4" (1 - 2 x 10^16 cm). Both bright
and faint emission features appear highly clumped. Large differences in [S III]
and [O III] line intensities indicating chemical abundance differences are also
seen, particularly in knots located along the bright northern limb and near the
base of the northeast jet. A line of curved overlapping filament in the
remnant's northwestern rim appears to mark the location of the remnant's
reverse shock front in this region. Finger-like ejecta structures elsewhere
suggest cases where the reverse shock front is encountering the remnant's
clumped ejecta. Narrow-band [N II] images of the remnant's circumstellar knots
("QSFs") reveal them to be 0.1"-0.6" thick knots and filaments, often with
diffuse edges facing away from the center of expansion. Three color composite
images of the whole remnant and certain sections along with individual filter
enlargements of selected regions of the bright optical shell are presented and
discussed.Comment: 26 pages, 12 figures Accepted to the Astronomical Journa
A cross-sectional study of vascular risk factors in a rural South African population : data from the Southern African Stroke Prevention Initiative (SASPI)
Background: Rural sub-Saharan Africa is at an early stage of economic and health transition. It is
predicted that the 21st century will see a serious added economic burden from non-communicable disease
including vascular disease in low-income countries as they progress through the transition. The stage of
vascular disease in a population is thought to result from the prevalence of vascular risk factors. Already
hypertension and stroke are common in adults in sub-Saharan Africa. Using a multidisciplinary approach
we aimed to assess the prevalence of several vascular risk factors in Agincourt, a rural demographic
surveillance site in South Africa.
Methods: We performed a cross sectional random sample survey of adults aged over 35 in Agincourt
(population ≈ 70 000). Participants were visited at home by a trained nurse who administered a
questionnaire, carried out clinical measurements and took a blood sample. From this we assessed
participants' history of vascular risk, blood pressure using an OMRON 705 CP monitor, waist
circumference, body mass index (BMI), ankle brachial index (ABI), and total and HDL cholesterol.
Results: 402 people (24% men) participated. There was a high prevalence of smoking in men, but the
number of cigarettes smoked was small. There was a striking difference in mean BMI between men and
women (22.8 kg/m2 versus 27.2 kg/m2), but levels of blood pressure were very similar. 43% of participants
had a blood pressure greater than 140/90 or were on anti-hypertensive treatment and 37% of participants
identified with measured high blood pressure were on pharmacological treatment. 12% of participants had
an ABI of < 0.9, sugesting the presence of sub-clinical atheroma. 25.6% of participants had a total
cholesterol level > 5 mmol/l.
Conclusion: We found a high prevalence of hypertension, obesity in women, and a suggestion of
subclinical atheroma despite relatively favourable cholesterol levels in a rural South African population.
South Africa is facing the challenge of an emerging epidemic of vascular disease. Research to establish the
social determinates of these risk factors and interventions to reduce both individual and population risk
are required
Control of proton energy in ultra-high intensity laser-matter interaction
Recent breakthroughs in short pulse laser technology resulted in (i) generation of ultra-high intensity (2×1022 W/cm2) and (ii) ultra-high contrast (10−11) short pulses at the Hercules facility of the University of Michigan, which has created the possibility of exploring a new regime of ion acceleration – the regime of Directed Coulomb Explosion (DCE). In this regime of sufficiently high laser intensities and target thicknesses approaching the relativistic plasma skin depth it is possible to expel electrons from the target focal volume by the laser's ponderomotive force allowing for direct laser ion acceleration combined with a Coulomb explosion. That results in greater than 100 MeV protons with a quasi-monoenergetic energy spectrum. The utilization of beam shaping, namely, the use of flat-top beams, leads to more efficient proton acceleration due to the increase of the longitudinal field. According to the results of 2D PIC simulations a 500 TW laser pulse with a super-Gaussian beam profile interacting with 0.1 micron aluminium-hydrogen foil is able to produce monoenergetic protons with the energy up to 240 MeV.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85403/1/jpconf10_244_042025.pd
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