Search Results - (Author, Cooperation:M. E. Katz)

2011-05-28

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

1572-946X

Springer Online Journal Archives 1860-2000

Physics

Abstract Cosmic-ray (CR) fluctuations in both the drift and diffusion approximations are investigated and the results compared with experimental data. Kinetic equation is used to obtain equations for the second moment of the CR distribution function (the correlation function of the distribution function fluctuations) in both approximations. An application of these approximations to the correlation function equation gives the relations between the CR power spectra and random magnetic fields in interplanetary space. Different magneto-turbulence models are taken in consideration and the relations between the spectral indices are obtained in various frequency intervals. The theoretical results are compared with experimental data obtained by the network of neutron monitors. The CR power spectra observed at the ground level during the years 1978–1981 has been calculated. The investigated frequency range of 3×10−8 to 10−4 Hz consists of two parts, with a ‘transient’ region of 10−6 to 10−5 Hz. Together with the ‘background’ CR fluctuations the contribution of both the periodic and aperiodic phenomena is observed.

Electronic Resource

1572-946X

Springer Online Journal Archives 1860-2000

Physics

Abstract A consistent theory of energy exchange between high-energy charged cosmic-ray particles and the random inhomogeneities of a magnetic field frozen in the moving solar wind plasma is developed. It is shown that the mode of the particle energy variations at a given law of plasma velocity variation in space is determined by the specific form of the particle distribution function. The equation for the density of cosmic-ray energy is obtained. Consideration is given to the generation of a charged particle energy spectrum in the course of multiple scatterings by the random inhomogeneities of the magnetic field.

Electronic Resource

1432-1998

Springer Online Journal Archives 1860-2000

Medicine

Abstract A young infants is presented with a mass partially obstructing the distal stomach. Sonography demonstrated the superficial origin of the lobulated lesion which proved to be focal foveolar hyperplasia, the most common cause of a gastric polypoid mass in adults but rare in children.

Electronic Resource

1432-1998

Springer Online Journal Archives 1860-2000

Medicine

Abstract A young infant with vomiting associated with a gastric polyp is presented. The polyp proved to be focal foveolar hyperplasia. These non-neoplastic polyps of unknown etiology are usually found in adults.

Electronic Resource

1572-9486

Springer Online Journal Archives 1860-2000

Physics

Electronic Resource

1432-1998

Springer Online Journal Archives 1860-2000

Medicine

Abstract A detailed survey of intussusception reduction practices at the International Pediatric Radiology '91 meeting in Stockholm yielded 78 responses from radiologists representing 21 countries on six continents. Results indicate a striking lack of concensus on basic technical issues such as the type of contrast material or reducing agent, the pressure limits for reduction, the use of balloontip tubes, the role of sedation, manipulation of the abdomen during reduction, and duration of symptoms beyond which reduction would not be attempted. For example, while gas reduction has been strongly promoted in the literature during the late 1980's, only 34.7% of the respondants indicated that this was their principle choice of reducing agent. Among technique choices which produced significant correlations with outcome, it is noteworthy that pooled data suggest an eightfold increase in perforations among those using gas rather than liquid for reduction. Also, although 53.8% of respondants use parenteral sedation at least part of the time, those who reported using it regularly had significantly lower success rates than all other radiologists. This study provides a current sampling of international opinion in a subject of importance to all pediatric radiologists; and by linking the responses with reported outcomes suggests opportunities for further investigation.

Electronic Resource

1572-946X

Springer Online Journal Archives 1860-2000

Physics

Abstract A drift kinetic theory of cosmic-ray (CR) propagation in inhomogeneous random large-scale magnetic fields (MF) is considered. An averaging of the drift kinetic equation for CR particles distribution was performed in the statistical ensemble of MF realization, whereby the curvature radius of randomly wandering MF is much larger than gyro-radiusR H of CR particles. Collisions of CR particles on the small-scale MF inhomogeneities with the characteristics scalel O ≪R H is not taken into account. It is proved that this random MF raises non-zero pitch-angle diffusion of the CR particles, which is very strong for particles with zero pitch angle. The transport equation is derived for a case of weak inhomogeneity of the random MF in the direction of MF mean value. In this case additional convection of particles in the direction of energy density gradient of random MF variables.

Electronic Resource

1572-946X

Springer Online Journal Archives 1860-2000

Physics

Abstract The influence of compressibility of media on both the statistical acceleration and the turbulent diffusion of cosmic-ray particles is investigated. The averaging over an ensemble of random velocity fields of the medium was performed in the kinetic equation. The kinetic coefficients, which are responsible for the particle acceleration, were obtained in the cases of weak and strong scattering due inhomogeneous magnetic fields.

Electronic Resource

1617-4623

Key words Gene regulation ; prtA ; Carbon catabolite repression ; pH regulation

Springer Online Journal Archives 1860-2000

Biology

Abstract  The extracellular proteases of Aspergillus nidulans are known to be regulated by carbon, nitrogen and sulphur metabolite repression. In this study, a mutant with reduced levels of extracellular protease was isolated by screening for loss of halo production on milk plates. Genetic analysis of the mutant showed that it contains a single, recessive mutation, in a gene which we have designated xprE, located on chromosme VI. The xprE1 mutation affected the production of extracellular proteases in response to carbon, nitrogen and, to a lesser extent, sulphur limitation. Three reversion mutations, xprF1, xprF2 and xprG1, which suppress xprE1, were characterised. Both xprF and xprG map to chromosome VII but the two genes are unlinked. The xprF1, xprF2 and xprG1 mutants showed high levels of milk-clearing activity on medium containing milk as a carbon source but reduced growth on a number of nitrogen sources. Evidence is presented that the xprE1 and xprG1 mutations alter expression of more than one protease and affect levels of alkaline protease gene mRNA.

Electronic Resource

1573-8515

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Electronic Resource

1617-4623

Key words Acetate metabolism  ;  facB  ;  Zn(II)2Cys6 (C6 zinc) binuclear cluster  ;  Aspergillus  ;  Gene regulation

Springer Online Journal Archives 1860-2000

Biology

Abstract Genetic studies have indicated that the facB gene of Aspergillus nidulans is a major regulatory gene involved in acetamide and acetate utilisation. Sequencing of the facB gene revealed that it encodes a protein that contains an N-terminal GAL4-like Zn(II)2Cys6 (or C6 zinc) binuclear cluster for DNA binding, leucine zipper-like heptad repeat motifs and central and C-terminal acidic α-helical regions, consistent with a function as a DNA-binding transcriptional activator. The Zn(II)2Cys6 cluster shows strong similarity with those of the Saccharomyces cerevisiae carbon metabolism regulatory proteins CAT8 and SIP4. A significant level of similarity with CAT8 is found throughout the length of the protein, suggesting at least partial functional homology. The facB genes of Aspergillus oryzae and Aspergillus niger were also sequenced and found to be highly conserved. Deletion of the facB gene confirmed that it is required for growth on acetate as a sole carbon source. Functional dissection using deletion and fusion constructs and in vitro mutagenesis indicated that the Zn(II)2Cys6 cluster and the C-terminal end of the protein are required for function.

Electronic Resource

1572-9672

Springer Online Journal Archives 1860-2000

Physics

Abstract This work gives a systematic description of the statistical theory of the propagation of cosmic ray charged particles through random electromagnetic fields in space. A kinetic equation is derived for the cosmic ray distribution function averaged over the statistical ensemble corresponding to a random field. Transition to the diffusion approximation is considered, and the problems of the scattering and acceleration of charged particles are analyzed. The theory of fluctuation effects in cosmic rays is briefly discussed.

Electronic Resource

1572-946X

Springer Online Journal Archives 1860-2000

Physics

Abstract The kinetic equation describing cosmic-ray propagation in interplanetary space has been used to construct a consistent theory of cosmic-ray anisotropy including the second spherical harmonic of particle angular distribution. The amplitude and phase of semi-diurnal cosmic-ray variation have been calculated. Expressions describing the relationships of the semi-diurnal variation parameters to helio-latitude distribution of cosmic rays have been derived. The results obtained are compared with observational data.

Electronic Resource