13,018 research outputs found
The L-amino acid oxidase of Neurospora
In 1944 one of us described a D-amino acid oxidase in extracts of Neurospora crassa (1). Except for slight activity against L-glutamate, no oxidation of L-amino acids was observed. Recently a means for inducing the formation of a soluble L-amino acid oxidase by the mold was reported by Bender, Krebs, and Horowitz (2). This is accomplished by reducing the biotin content of the basal medium (3) from the 5 γ per liter usually employed to 0.25 γ per liter. When cultured in such a medium, Neurospora produces an active L-amino acid oxidase which can be demonstrated both in extracts and in the medium. Reduction of the biotin level produces no effect on the D-amino acid oxidase, which is still found in extracts but not in the culture medium. The activity of the L-oxidase toward thirty-eight amino acids has been investigated by Bender and Krebs (4).
The initial purpose of the present investigation was to explore certain possibilities for a genetic study of the enzyme. Of special interest was the fact, cited by Bender et al. (a), that the oxidase could not be detected in all of the wild type strains tested. The question arose as to whether this is due to the genetic inability of certain strains to form the enzyme. In connection with the investigation of this problem a general survey of the properties of the enzyme was carried out, together with a preliminary study of the mechanism of the biotin effect and of the adaptive formation of the enzyme. The results of these studies are reported below.
Simultaneously with our investigation and independently of it, Dr. K. Burton (5), working in Professor Krebs’ laboratory, has carried out a study of the Neurospora L-amino acid oxidase. Where our respective studies overlap mutual confirmation was obtained in most essential points. We wish to thank Dr. Burton for permission to read his manuscript before publication
Vortex Glass is a Metal: Unified Theory of the Magnetic Field and Disorder-Tuned Bose Metals
We consider the disordered quantum rotor model in the presence of a magnetic
field. We analyze the transport properties in the vicinity of the multicritical
point between the superconductor, phase glass and paramagnetic phases. We find
that the magnetic field leaves metallic transport of bosons in the glassy phase
in tact. In the vicinity of the vicinity of the superconductivity-to-Bose metal
transition, the resistitivy turns on as with . This
functional form is in excellent agreement with the experimentally observed
turn-on of the resistivity in the metallic state in MoGe, namely , . The metallic state is also shown to presist in
three spatial dimensions. In addition, we also show that the metallic state
remains intact in the presence of Ohmic dissipation in spite of recent claims
to the contrary. As the phase glass in is identical to the vortex glass,
we conclude that the vortex glass is, in actuality, a metal rather than a
superconductor at T=0. Our analysis unifies the recent experiments on vortex
glass systems in which the linear resistivity remained non-zero below the
putative vortex glass transition and the experiments on thin films in which a
metallic phase has been observed to disrupt the direct transition from a
superconductor to an insulator.Comment: Published version with an appendix showing that the claim in
cond-mat/0510380 (and cond-mat/0606522) that Ohmic dissipation in the phase
glass leads to a superconducting state is false. A metal persists in this
case as wel
A difference boosting neural network for automated star-galaxy classification
In this paper we describe the use of a new artificial neural network, called
the difference boosting neural network (DBNN), for automated classification
problems in astronomical data analysis. We illustrate the capabilities of the
network by applying it to star galaxy classification using recently released,
deep imaging data. We have compared our results with classification made by the
widely used Source Extractor (SExtractor) package. We show that while the
performance of the DBNN in star-galaxy classification is comparable to that of
SExtractor, it has the advantage of significantly higher speed and flexibility
during training as well as classification.Comment: 9 pages, 1figure, 7 tables, accepted for publication in Astronomy and
Astrophysic
The Origin of the Young Stars in the Nucleus of M31
The triple nucleus of M31 consists of a population of old red stars in an
eccentric disk (P1 and P2) and another population of younger A stars in a
circular disk (P3) around M31's central supermassive black hole (SMBH). We
argue that P1 and P2 determine the maximal radial extent of the younger A star
population and provide the gas that fueled the starburst that generated P3. The
eccentric stellar disk creates an non-axisymmetric perturbation to the
potential. This perturbed potential drives gas into the inner parsec around the
SMBH, if the pattern speed of the eccentric stellar disk is . We show that stellar mass loss from P1 and P2 is
sufficient to create a gravitationally unstable gaseous disk of \sim
10^5\Msun every Gyrs, consistent with the 200 Myr age of P3. Similar
processes may act in other systems to produce very compact nuclear starbursts.Comment: 10 pages, 7 figures, accepted by ApJ, changes made from referee
suggestion
Saturation Spectroscopy of Iodine in Hollow-core Optical Fibre
We present high-resolution spectroscopy of Iodine vapour that is loaded and
trapped within the core of a hollow-core photonic crystal fibre (HC-PCF). We
compare the observed spectroscopic features to those seen in a conventional
iodine cell and show that the saturation characteristics differ significantly.
Despite the confined geometry it was still possible to obtain sub-Doppler
features with a spectral width of ~6 MHz with very high contrast. We provide a
simple theory which closely reproduces all the key observations of the
experiment.Comment: 12 pages, 7 figure
Vitamin D in Australia : issues and recommendations
BACKGROUND A significant number of Australians and people from specific groups within the community are suffering from vitamin D deficiency. It is no longer acceptable to assume that all people in Australia receive adequate vitamin D from casual exposure to sunlight.OBJECTIVE This article provides information on causes, consequences, treatment and prevention of vitamin D deficiency in Australia. DISCUSSION People at high risk of vitamin D deficiency include the elderly, those with skin conditions where avoidance of sunlight is required, dark skinned people (particularly women during pregnancy or if veiled) and patients with malabsorption, eg. coeliac disease. For most people, deficiency can be prevented by 5–15 minutes exposure of face and upper limbs to sunlight 4–6 times per week. If this is not possible then a vitamin D supplement of at least 400 IU* per day is recommended. In cases of established vitamin D deficiency, supplementation with 3000-5000 IU per day for at least 1 month is required to replete body stores. Increased availability of larger dose preparations of cholecalciferol would be a useful therapy in the case of severe deficiencies. * 40 IU (international units) = 1 µg<br /
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