H. Huber

Neutron star properties with relativistic equations of state

We study the properties of neutron stars adopting relativistic equations of state of neutron star matter, calculated in the framework of the relativistic Brueckner–Hartree–Fock approximation for electrically charge neutral neutron star matter in beta–equilibrium. For higher densities more baryons (hyperons etc.) are included by means of the relativistic Hartree– or Hartree–Fock approximation. The special features of the different approximations and compositions are discussed in detail. Besides standard neutron star properties special emphasis is put on the limiting periods of neutron stars, for which the Kepler criterion and gravitation–reaction instabilities are considered. Furthermore the cooling behaviour of neutron stars is investigated, too. For comparison we also give the outcome for some nonrelativistic equations of state.

Symmetric and asymmetric nuclear matter in the relativistic approach at finite temperatures

The properties of hot matter are studied in the frame of the relativistic Brueckner-Hartree-Fock theory. The equations are solved self-consistently in the full Dirac space. For the interaction we used the potentials given by Brockmann and Machleidt. The obtained critical temperatures are smaller than in most of the nonrelativistic investigations. We also calculated the thermodynamic properties of hot matter in the relativistic Hartree–Fock approximation, where the force parameters were adjusted to the outcome of the relativistic Brueckner–Hartree–Fock calculations at zero temperature. Here, one obtains higher critical temperatures, which are comparable with other relativistic calculations in the Hartree scheme.

Relativistic investigations of symmetric and asymmetric nuclear matter

Abstract In the framework of relativistic nuclear field theory the parameters of symmetric and asymmetric nuclear matter are calculated in the relativistic Brueckner-Hartree-Fock and Λ 00 approximation, respectively. The equations are solved self-consistently in the full Dirac space, so avoiding the ambiguities in the choice of the effective scattering amplitude. The results are compared with the standard method, where one only determines the scattering amplitude for positive energy spinors. Furthermore we tested the assumption of momentum independent self-energy. The results for asymmetric matter are in the structure similar to the outcome of the relativistic Hartree-Fock approximation, but differ from the nonrelativistic treatment. The agreement with the empirical values is quite satisfactory.

Compatibility of Neutron Star Masses and Hyperon Coupling Constants

Abstract It is shown that the modern equations of state for neutron star matter based on microscopic calculations of symmetric and asymmetric nuclear matter are compatible with the lower bound on the maximum neutron-star mass for a certain range of hyperon coupling constants, which are constrained by the binding energies of hyperons in symmetric nuclear matter. The hyperons are included by means of the relativistic Hartree-or Hartree-Fock approximation. The obtained couplings are also in satisfactory agreement with hypernuclei data in the relativistic Hartree scheme. Within the relativistic Hartree-Fock approximation, hypernuclei have not been investigated so far.

Relativisitic calculations of neutron star matter

Abstract The microscopic relativistic Brueckner-Hartree-Fock approximation is extended to the treatment of electrically charge neutral neutron star matter in generalized beta equilibrium. In the framework of this self-consistent many-body scheme, we calculate the equation of state, the asymmetry, and the hadron/lepton composition of such matter. For the one-boson-exchange potential we use the Brockmann-Machleidt potentials A and B . Furthermore we appraise the possibility of parametrizing the Brueckner-Hartree-Fock outcome in terms of the relativistic Hartree and Hartree-Fock approximations. Such parametrizations will be very helpful for future studies (e.g., equations of state of proto-neutron stars and supernovae), since much less numerical effort is needed to compute the equation of state within the latter two approximations.

Photometrische Bestimmung der Zytotoxizität von Chemikalien

ZusammenfassungEs werden zwei Testverfahren zur Bestimmung der Zytotoxizität von Chemikalien vorgestellt. Zum einen wird das ProtozoonTetrahymena pyriformis in Flüssigmedium, zum anderen das BakteriumPseudomonas aeruginosa in Mangelmedium 18–20 Stunden zusammen mit den Prüfsubstanzen in Mikrotitrationsplatten mit 96 Vertiefungen kultiviert. Testparameter ist jeweils die Proliferationshemmung bzw. die Anzahl der lebenden Zellen nach Expositionsende. Ein Maß dafür ist die Umwandlung eines Tetrazoliumsalzes zu unlöslichem, blauem Formazan, welches nach Solubilisierung mit einem Detergens und Isopropanol photometrisch gemessen wird. Die EC50-Werte (mol/l) im Ciliaten-(Pseudomonaden-)Test waren für: Cetyltrimethylammoniumbromid: 10−5,81 (10−5,08) Benzyldimethyldodecylammoniumchlorid: 10−4,68 (10−3,80) Dodecylbenzolsulfonsäure-Natriumsalz: 10−4,50 (10−4,14) Kaliumdichromat: 10−3,97 (10−5,11) Toluol-4-sulfonsäure-Natriumsalz: 10−2,71 (10−2,50) 4-Nitrophenol: 10−4,00 (10−3,64) Wegen der einfachen und schnellen Handhabung eignen sich die Verfahren für das Screening einer großen Anzahl von Proben.AbstractTwo test methods are presented to assess the cytotoxicity of chemicals. On one hand the protozoonTetrahymena pyriformis and on the other the bacteriumPseudomonas aeruginosa is cultured in defined media containing the test chemicals. Test parameter is the quantity of living cells surviving exposure. The conversion of the tetrazolium salt MTT into formazan is equivalent to cell viability. A mixture of detergent and isopropanol is used to dissolve the blue formazan which is not soluble in water, prior to photometric measurement. For cetyltrimethylammonium bromide, benzyldimethyldodecylammonium chloride, dodecylbenzenesulfonic acid sodium salt, potassium dichromate, 4-toluenesulfonic acid sodium salt, and 4-nitrophenol the EC50-values (mol/l) in theTetrahymena pyriformis- (Pseudomonas aeruginosa) test system were: 10−5,81 (10−5,08); 10−4,68) (10−3,80; 10−4,50 (10−4,14); 10−3,97 (10−5,11); 10−2,71 (10−2,50) and 10−4,00 (10−3,64). — With the assays described here it is possible to measure a large number of samples by quick and simple means.

The Relativistic Treatment of Symmetric and Asymmetric Nuclear Matter

In the last decades it was realized that certain features of the nuclear problem can only be described by going beyond the nonrelativistic approach. Relativistic treatments of the nuclear many-body problem have advantages in several respects, for instance1, 2: An extremely useful Dirac phenomenology in the description of nucleon- nucleus scattering3; the shift of the equilibrium density from the so-called “Coester band” towards the “experimental” value via a new saturation mechanism4, 5; the natural incorporation of the spin-orbit force1, 2and the successful description of finite nuclei6, 7, etc.