14,480 research outputs found
Physiological Aspects of Genetics
A considerable amount of evidence indicates that desoxyribonucleic acid is capable of duplicating itself, a property also possessed by genes. (By a self-duplicating material, we mean one which plays some essential role in its own production.) Watson & Crick (1) have proposed a new structure for desoxyribonucleic acid which not only takes into account the existing analytical and x-ray diffraction data but also seems capable of explaining the mechanism of duplication. Their model consists of two helical chains coiled around the same axis, the purine and pyrimidine bases on the inside, the phosphate groups on the outside. The chains are held together by hydrogen bonds between the bases, the adenine residues of either chain being bonded specifically to thymine in the other, and similarly guanine to cytosine. The sequence of bases along one chain is not restricted, but once fixed the sequence along the other chain is determined. This complementarity, which is the most novel feature of the structure, suggests that duplication takes place by separation of the two chains, followed by the synthesis of its complement alongside each chain. The model is supported by recent x-ray diffraction studies (2, 3)
The Spatial Correlation of Bent-Tail Galaxies and Galaxy Clusters
We have completed a deep radio continuum survey covering 86 square degrees of
the Spitzer-South Pole Telescope deep field to test whether bent-tail galaxies
are associated with galaxy clusters. We present a new catalogue of 22 bent-tail
galaxies and a further 24 candidate bent-tail galaxies. Surprisingly, of the 8
bent-tail galaxies with photometric redshifts, only two are associated with
known clusters. While the absence of bent-tail sources in known clusters may be
explained by effects such as sensitivity, the absence of known clusters
associated with most bent-tail galaxies casts doubt upon current models of
bent-tail galaxies.Comment: Accepted by MNRA
Nuclear Structure Physics in Coherent Elastic Neutrino-Nucleus Scattering
The prospects of extracting new physics signals in a coherent elastic
neutrino-nucleus scattering (CENS) process are limited by the precision
with which the underlying nuclear structure physics, embedded in the weak
nuclear form factor, is known. We present microscopic nuclear structure physics
calculations of charge and weak nuclear form factors and CENS cross
sections on C, O, Ar, Fe and Pb nuclei. We
obtain the proton and neutron densities, and charge and weak form factors by
solving Hartree-Fock equations with a Skyrme (SkE2) nuclear potential. We
validate our approach by comparing Pb and Ar charge form factor
predictions with elastic electron scattering data. In view of the worldwide
interest in liquid-argon based neutrino and dark matter experiments, we pay
special attention to the Ar nucleus and make predictions for the
Ar weak form factor and the CENS cross sections. Furthermore, we
attempt to gauge the level of theoretical uncertainty pertaining to the
description of the Ar form factor and CENS cross sections by
comparing relative differences between recent microscopic nuclear theory and
widely-used phenomenological form factor predictions. Future precision
measurements of CENS will potentially help in constraining these nuclear
structure details that will in turn improve prospects of extracting new
physics.Comment: 12 pages, 14 figure
The psychophysics of absolute threshold and signal duration: A probabilistic approach
The absolute threshold for a tone depends on its duration; longer tones have lower thresholds. This effect has traditionally been explained in terms of ?temporal integration? involving the summation of energy or perceptual information over time. An alternative probabilistic explanation of the process is formulated in terms of simple equations that predict not only the time=duration dependence but also the shape of the psychometric function at absolute threshold. It also predicts a tight relationship between these two functions. Measurements made using listeners with either normal or impaired hearing show that the probabilistic equations adequately fit observed threshold-duration functions and psychometric functions. The mathematical formulation implies that absolute threshold can be construed as a two-valued function: (a) gain and (b) sensory threshold, and both parameters can be estimated from threshold-duration data. Sensorineural hearing impairment is sometimes associated with a smaller threshold=duration effect and sometimes with steeper psychometric functions. The equations explain why these two effects are expected to be linked. The probabilistic approach has the potential to discriminate between hearing deficits involving gain reduction and those resulting from a raised sensory threshold
Semi-Empirical Bound on the Chlorinr-37 Solar Neutrino Experiment
The Kamiokande measurement of energetic Boron-8 neutrinos from the sun is
used to set a lower bound on the contribution of the same neutrinos to the
signal in the \Chlorine\ experiment. Implications for Beryllium-7 neutrinos are
discussed.Comment: Latex, 6 pages + 1 postscript figure (included). UTAPHY-HEP-
Staging superstructures in high- Sr/O co-doped LaSrCuO
We present high energy X-ray diffraction studies on the structural phases of
an optimal high- superconductor LaSrCuO tailored by
co-hole-doping. This is specifically done by varying the content of two very
different chemical species, Sr and O, respectively, in order to study the
influence of each. A superstructure known as staging is observed in all
samples, with the staging number increasing for higher Sr dopings . We
find that the staging phases emerge abruptly with temperature, and can be
described as a second order phase transition with transition temperatures
slightly depending on the Sr doping. The Sr appears to correlate the
interstitial oxygen in a way that stabilises the reproducibility of the staging
phase both in terms of staging period and volume fraction in a specific sample.
The structural details as investigated in this letter appear to have no direct
bearing on the electronic phase separation previously observed in the same
samples. This provides new evidence that the electronic phase separation is
determined by the overall hole concentration rather than specific Sr/O content
and concommittant structural details.Comment: 8 pages, incl. 4 figure
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