4,829 research outputs found
Snake Hybridization: A Case for Intrabaraminic Diversity
Snakes have rarely been examined as examples of intrabaraminic variation due to the relative obscurity of knowledge regarding the subject of these secretive animals as well as the relative newness of the breeding of snakes. North American species of snakes of the genera Lampropeltis, Pituophis, and Elaphe, while classified in separate genera may actually be more closely related than evolutionary biology predicts.
This study examined intergeneric and interspecific hybridization of several species of colubrid snakes through the use of both natural breeding methods and scent disguise to fool the different species to interbreed. Eleven different species of three different genera were used in this experiment. Results of the crosses were as expected to resemble midpoints of color and pattern between the parental species. Banding patterns appeared to be dominant over blotches and stripes. The most interesting finding was that the amelanistic varieties of the California kingsnake, L.g.californiae, and the corn snake, E.g.guttata are apparently allelic forms of amelanism regardless of the fact that these snakes are members of different genera. When the two genera were crossed this albinism appeared in the F1 generation. All types of the hybrids produced were viable and fertile. As such, they are most likely examples of intrabaraminic diversity of created “kinds” rather than evolutionary speciation. This paper adds viability, homologous genes, and pigment variations to the list of character space criteria for recognizing baramins
Latitudinal Shear Instabilities during Type I X-ray Bursts
Coherent oscillations have been observed during Type I X-ray bursts from 14
accreting neutron stars in low mass X-ray binaries, providing important
information about their spin frequencies. However, the origin of the brightness
asymmetry on the neutron star surface producing these oscillations is still not
understood. We study the stability of a zonal shearing flow on the neutron star
surface using a shallow water model. We show that differential rotation of >2%
between pole and equator, with the equator spinning faster than the poles, is
unstable to hydrodynamic shear instabilities. The unstable eigenmodes have
properties well-matched to burst oscillations: low azimuthal wavenumber m, wave
speeds 1 or 2% below the equatorial spin rate, and e-folding times close to a
second. Instability is related to low frequency buoyantly driven r-modes that
have a mode frequency within the range of rotation frequencies in the
differentially rotating shell. We discuss the implications for burst
oscillations. Growth of shear instabilities may explain the brightness
asymmetry in the tail of X-ray bursts, although some fine tuning of the level
of differential rotation and a spin frequency near 300 Hz are required in order
for the fastest growing mode to have m=1. If shear instabilities are to operate
during a burst, temperature contrasts of 30% across the star must be created
during ignition and spreading of the flash.Comment: To appear in ApJ (12 pages, 11 figures
Interactive manipulation of microparticles in an octagonal sonotweezer
An ultrasonic device for micro-patterning and precision manipulation of micrometre-scale particles is demonstrated. The device is formed using eight piezoelectric transducers shaped into an octagonal cavity. By exciting combinations of transducers simultaneously, with a controlled phase delay between them, different acoustic landscapes can be created, patterning micro-particles into lines, squares, and more complex shapes. When operated with all eight transducers the device can, with appropriate phase control, manipulate the two dimensional acoustic pressure gradient; it thus has the ability to position and translate a single tweezing zone to different locations on a surface in a precise and programmable manner
Polar kicks and the spin period - eccentricity relation in double neutron stars
We present results of a population synthesis study aimed at examining the
role of spin-kick alignment in producing a correlation between the spin period
of the first-born neutron star and the orbital eccentricity of observed double
neutron star binaries in the Galactic disk. We find spin-kick alignment to be
compatible with the observed correlation, but not to alleviate the requirements
for low kick velocities suggested in previous population synthesis studies. Our
results furthermore suggest low- and high-eccentricity systems may form through
two distinct formation channels distinguished by the presence or absence of a
stable mass transfer phase before the formation of the second neutron star. The
presence of highly eccentric systems in the observed sample of double neutron
stars may furthermore support the notion that neutron stars accrete matter when
moving through the envelope of a giant companion.Comment: To appear in the proceedings of "40 Years of Pulsars: Millisecond
Pulsars, Magnetars, and More", August 12-17, 2007, McGill University,
Montreal, Canad
A Mixed Solar Core, Solar Neutrinos and Helioseismology
We consider a wide class of solar models with mixed core.
Most of these models can be excluded as the predicted sound speed profile is
in sharp disagreement with helioseismic constraints. All the remaining models
predict Be and/or B neutrino fluxes at least as large as those of SSMs.
In conclusion, helioseismology shows that a mixed solar core cannot account for
the neutrino deficit implied by the current solar neutrino experiments.Comment: 6 pages, RevTeX, plus 5 postscript figure
Space cowboys odyssey: beyond the Gould Belt
We present our new advanced model for population synthesis of close-by
cooling NSs. Detailed treatment of the initial spatial distribution of NS
progenitors and a detailed ISM structure up to 3 kpc give us an opportunity to
discuss the strategy to look for new isolated cooling NSs. Our main results in
this respect are the following: new candidates are expected to be identified
behind the Gould Belt, in directions to rich OB associations, in particular in
the Cygnus-Cepheus region; new candidates, on average, are expected to be
hotter than the known population of cooling NS. Besides the usual approach
(looking for soft X-ray sources), the search in 'empty' -ray error
boxes or among run-away OB stars may yield new X-ray thermally emitting NS
candidates.Comment: 3 pages, 2 figures, proceedings of the conference "40 Years of
Pulsars ", 12-17 August 2007, Montreal, Canad
Low Frequency Observations of Millisecond Pulsars with the WSRT
With LOFAR beginning operation in 2008 there is huge potential for studying
pulsars with high signal to noise at low frequencies. We present results of
observations made with the Westerbork Synthesis Radio Telescope to revisit,
with modern technology, this frequency range. Coherently dedispersed profiles
of millisecond pulsars obtained simultaneously between 115-175 MHz are
presented. We consider the detections and non-detections of 14 MSPs in light of
previous observations and the fluxes, dispersion measures and spectral indices
of these pulsars. The excellent prospects for LOFAR finding new MSPs and
studying the existing systems are then discussed in light of these results.Comment: 5 pages, 5 figures, To appear in the proceedings of "40 Years of
Pulsars: Millisecond Pulsars, Magnetars, and More", August 12-17, 2007,
McGill University, Montreal, Canad
Haplotype analysis of the PPARgamma Pro12Ala and C1431T variants reveals opposing associations with body weight.
BACKGROUND: Variation at the PPARG locus may influence susceptibility to type 2 diabetes and related traits. The Pro12Ala polymorphism may modulate receptor activity and is associated with protection from type 2 diabetes. However, there have been inconsistent reports of its association with obesity. The silent C1431T polymorphism has not been as extensively studied, but the rare T allele has also been inconsistently linked to increases in weight. Both rare alleles are in linkage disequilibrium and the independent associations of these two polymorphisms have not been addressed. RESULTS: We have genotyped a large population with type 2 diabetes (n = 1107), two populations of non-diabetics from Glasgow (n = 186) and Dundee (n = 254) and also a healthy group undergoing physical training (n = 148) and investigated the association of genotype with body mass index. This analysis has demonstrated that the Ala12 and T1431 alleles are present together in approximately 70% of the carriers. By considering the other 30% of individuals with haplotypes that only carry one of these polymorphisms, we have demonstrated that the Ala12 allele is consistently associated with a lower BMI, whilst the T1431 allele is consistently associated with higher BMI. CONCLUSION: This study has therefore revealed an opposing interaction of these polymorphisms, which may help to explain previous inconsistencies in the association of PPARG polymorphisms and body weight
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