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J Ortner

Publications and source records attributed to J Ortner.

14 recordsLinked to original sources
PubMed2001

Evolution of induced axial magnetization in a two-component magnetized plasma.

In this paper, the evolution of the induced axial magnetization due to the propagation of an electromagnetic (em) wave along the static background magnetic field in a two-component plasma has been investigated using the Block equation. The evolution process induces a strong magnetic anisotropy in the plasma medium, depending nonlinearly on the incident wave amplitude. This induced magnetic anisotropy can modify the dispersion relation of the incident em wave, which has been obtained in this paper. In the low frequency Alfven wave limit, this dispersion relation shows that the resulting phase velocity of the incident wave depends on the square of the incident wave amplitude and on the static background magnetic field of plasma. The analytical results are in well agreement with the numerically estimated values in solar corona and sunspots.

Journal Article↗
PubMed2001

Energy loss of a charged particle in a magnetized quantum plasma.

This paper investigates the stopping power of a weakly coupled magnetized plasma. The effect of the Larmor rotation of the heavy charged test particle is carefully analyzed. The dielectric formalism is employed to obtain a general expression for the stopping power. A quantum mechanical form of the random-phase approximation dielectric function is used so that an arbitrary cutoff procedure is not required. Simple analytical expressions for the stopping power have been found for the cases of high and low projectile velocity of the test particle. The dependence of the stopping power on the angle of incidence is studied. A comparison with numerical solutions is given. It is found that in general a magnetic field reduces the stopping power of the plasma at high velocities, while it increases the stopping power at low velocities.

Journal Article↗
PubMed2001

Stopping power of strongly coupled electronic plasmas: sum rules and asymptotic forms.

The stopping power of coupled electronic plasmas is investigated. Within the dielectric formalism and employing the method of frequency moments for the dielectric function we obtain a general formula describing the linear stopping power of a coupled plasma. Analytical results for the low- and high-projectile-velocity asymptotic forms are obtained. A sum rule for the plasma heavy ions linear stopping power projectile velocity distribution is established to be related to the dielectric permeability "negative" frequency moment. This permits for a simple interpretation of stopping power data.

Journal Article↗
PubMed2000

Simultaneous detection of different glycosidase activities by 19F NMR spectroscopy.

A fast method for the simultaneous detection of different glycosidolytic activities in commercially available enzyme preparations and crude culture filtrates was found in using, as substrate, a mixture of different glycosyl fluorides and 19F NMR spectroscopy as a screening technique. Accompanying studies regarding the hydrolytic stability of these fluorides in various buffer systems, as well as conditions of their long-term storage, were carried out. A simple procedure for the preparation of beta-D-mannopyranosyl fluoride in gram quantities is given.

Fluorine↗
PubMed2000

Transglycosylation reactions with a crude culture filtrate from Thermoascus aurantiacus.

Some characteristics of regioselectivity and acceptor tolerance in transglycosylation reactions, catalysed by a crude culture filtrate from Thermoascus aurantiacus, were examined by employing methanol and monosaccharides as acceptors. When beta-D-mannopyranosyl fluoride was employed as the donor, the anomeric configuration of the newly formed bond was found to depend on the structure of the acceptor used.

Ascomycota↗
PubMed2000

Synthesis of deoxyfluoro sugars from carbohydrate precursors.

Results obtained over the past decade concerning the introduction of the fluorine atom into carbohydrate molecules, either by nucleophilic substitution or electrophilic addition reactions, are summarised. The first section mainly deals with the triflate/fluoride tandem sequence and the DAST-reaction. In the discussion, emphasis is given to the dependency of the reaction course on the stereochemical and protecting group features. Possible reaction pathways are direct substitution (with inversion or retention of configuration), rearrangement (combined with substitution and inversion of configuration at both of the centres involved) and elimination. Based on the assumption of cyclic transition states or transient intermediates (formed through participation of neighbouring groups), far-reaching mechanistic generalisations were made. On this basis, isolated examples from the literature, which are not in accordance with these generalisations, are specifically brought to attention. Results from the recently introduced reaction of safe and easy to handle N-F fluorinating agents with glycals are also reported. This approach allows the simple and stereoselective access to a series of 2-deoxy-2-fluoro aldopyranoses, as well as the synthesis of various C-1-substituted derivatives by an easy one-pot reaction. However, the same method applied to furanoid glycals is rather poor with respect to stereoselectivity. Finally, considerations on the importance of fluorine-specific reactions of the S(N)-type in related fields of organic synthesis are made.

Carbohydrates↗
PubMed2000

Systematic study of parameters influencing the action of Rose Bengal with visible light on bacterial cells: comparison between the biological effect and singlet-oxygen production.

As part of a project to study different methods for the disinfection of effluent water, the inactivation of different microorganisms (Escherichia coli, Deinococcus radiodurans and spores of Bacillus subtilis) using a combination of a photosensitizer (Rose Bengal) with simulated sunlight and oxygen was determined under various environmental conditions (temperature, pH index). In parallel, the singlet-oxygen (1O2) production was also measured under the same conditions. Whereas the vegetative cells could be inactivated much more efficiently at increased temperature and altered index of pH, the production of 1O2 remained essentially the same under these alterations. Additionally, the relations among the sensitivities of different cell types to be killed by our photodynamic treatments (PDT) were opposite to those found after exposure to ionizing radiation. The results of photodynamic experiments do not reflect the cells' capacity to repair DNA strand breaks. Spores of B. subtilis, as a nonvegetative system, could not be inactivated by illuminations up to 100 J cm-2. Together, these findings indicate that DNA is not the primary target, the inactivation of which leads to the killing of our test organisms. Instead, the cellular envelope appears to be the component being assaulted by our PDT.

Bacteria↗
PubMed1999

Equation of states for classical Coulomb systems: use of the Hubbard-Schofield approach.

An effective method based on the Hubbard-Schofield approach [Phys. Lett. A 40, 245 (1972)] is developed to calculate the free energy of classical Coulomb systems. This method significantly simplifies the derivation of the cluster expansion. A diagrammatic representation of the cluster integrals is proposed. Simple rules providing the leading order in density n of each diagrammatic contribution are found. We calculate the n(3) contribution and recover the results at the order n(5/2) obtained by the traditional method of resummation of diverging Mayer bonds.

Journal Article↗
PubMed1992

[The status of afebrile infantile convulsions within the epilepsy spectrum--a follow-up of 55 patients].

In an earlier study we observed 411 patients with cerebral convulsions, 118 of whom had the first convulsion during the 1 year of life. Among these 118 children we found 76 with afebrile convulsions. In this study we present the development and outcome in 55 patients with afebrile convulsions in the 1 year of life which could be observed for some years, most of them up to the present. In 25 infants the fits started in the newborn period, and in 30 infants after the 1 month; they were divided into groups with and without risk factors in the history. Benign neonatal convulsions were found in about one-third of children, with a good prognosis. These convulsions are divided into a dominantly inherited but rarely observed form and idiopathic benign neonatal convulsions. In contrast, among the newborns with risk factors in the history we found only half with a positive development. The results in the 30 infants with convulsions after the 1 month were similar with respect to risk factors in the history of risks. The 15 infants without risks had a good prognosis. Only 3 patients had oligoepilepsy. However, in the 15 patients with risks only 3 developed normally, 6 had no fits, but were neurologically or mentally handicapped, and 7 had fits and disability. We believe that afebrile convulsions without risk factors after the 1 month could be considered a late manifestation of benign newborn convulsions.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain Damage, Chronic↗
PubMedDate not supplied

Spacelab concept and its utilization for science.

The first part of the paper is devoted to the presentation of the Spacelab concepts, for which detailed design studies are at present being carried out by ESRO. The second part concentrates on the utilization of the Spacelab for the various fields of science, namely: (1) Atmospheric and space plasma physics, (2) Astronomy and astrophysics, (3) Material science and (4) Life sciences. The advantages of using the Spacelab for observations in these fields as compared to conventional automated satellites are highlighted.

Astronomy↗