212Bi-212Po alpha source for the calibration and functional testing of silicon detectors: Preparation and characterisation.

Silicon detectors are widely used in space radiation dosimeter systems for measuring energetic charged particles. Calibration of such systems is usually performed with protons and heavier ions in high energy particle accelerators. For preliminary energy calibration and functional testing of silicon detectors, at any time during the development, an equipment producing a thin 212Bi-212Po alpha particle emitting source was designed and constructed. Our aim was to develop an alpha source with negligible self-shielding and short life-time in order to prevent the long-term contamination of the detectors with alpha particle emitting nuclides. In the present paper, a description of the method chosen, and the equipment developed are given. Estimates of the activity of the source produced was obtained from measurements with the RADTEL space radiation telescope under development in the Centre for Energy Research, Hungarian Academy of Sciences (MTA EK). It was also used to verify that the alpha particle emitting source is suitable for the preliminary calibration and functional testing of silicon detector systems.

Temperature of nonequilibrium steady-state systems

We determined the operational temperatures of nonequilibrium-molecular-dynamics (NEMD) systems by the recently developed thermometer [A. Baranyai, Phys. Rev. E 61, R3306 (2000)] and compared these values to the dynamic temperatures [H. H. Rough, Phys. Rev. Lett. 78, 772 (1997)] of the same systems. NEMD models use a synthetic thermostat, a numerical feedback procedure to remove the dissipative heat instantaneously. A consequence of this feedback is a splitting of the dynamic temperature. The kinetic part is different from the configurational part because the energy is removed through the momentum subspace of the system. In addition to this, these temperature values also vary with respect to the direction of the external perturbation. In the case of planar Couette flow and color flow, the isotropic operational temperatures of dense liquids are always closer to the configurational than to the kinetic temperatures. We show that the observed split and the pronounced directional dependence of the dynamic temperature is an artifact caused by the instantaneous feedback of NEMD models. Since relaxation of a preset difference between the kinetic and the configurational temperature is an order of magnitude faster than the relaxation of the heat flux vector, for models with realistic thermostas such a split must be very small. We argue that in real systems, even far from equilibrium, the operational temperature and both terms of the dynamic temperature must be practically identical and isotropic.

Numerical temperature measurement in far from equilibrium model systems

We used a spherical piece of a solid crystal as a thermometer to measure the temperature of far from equilibrium model fluids thermostatted by a numerical feedback mechanism. The thermometer, consisting of 135 or 321 small particles, was devised to behave like one of the fluid particles in order to maintain the homogeneity of the dissipative dynamical system. We found the temperature determined by the random velocities in the close-to-equilibrium thermometer to be substantially different from the kinetic temperature of the studied nonequilibrium molecular dynamics models. We discuss the implications of our results.

Towards a computational chemical potential for nonequilibrium steady-state systems.

We explore an approach to derive a computable chemical potential analog for thermostatted steady-state systems arbitrarily far from equilibrium. Although our method is not rigorous, it is based on theoretical and numerical evidence and exploits analogies with Widom's method widely used in computer simulations of equilibrium fluids. We obtain two formulas, one for steady states and one for the transient region. Despite being analogous to the equilibrium expression, the steady-state formula can only be used for approximate calculations. Possessing less obvious characteristics, we present representative calculations for the transient approach and discuss its numerical feasibility.

[Tests of biodegradation of cytostatics cyclophosphamide and ifosfamide using the Closed Bottle Test (OECD 301 D)]. / Prüfung des biologischen Abbaus der Zytostatika Cyclophosphamid und Ifosfamid mit dem Closed Bottle Test (OECD 301 D).

Hospital and communal waste water differ with respect to their content of specific chemical substances like disinfectants or medicaments. Some medicaments are metabolized poorly by patients after administration. Antineoplastic substances are supposed to be carcinogen, mutagen and fetotoxic and embryotoxic substances. At the present there is no information available about their behaviour in the environment. Therefore the biodegradation of ifosfamide and cyclophosphamide was investigated by using the Closed Bottle Test (OECD 301 D). Both the structural isomeric antineoplastics were not biodegraded at a concentration of 5 mg/l in the Closed Bottle Test within 28 days ("not readily biodegradable"). A prolongation of the test up to 57 days did not alter the result. Abiotic elimination was neglectible. Cyclophosphamide and ifosfamide were not found toxic against waste water microorganisms. Further investigations about the elimination of ifosfamide and cyclophosphamide in the process of waste water treatment are necessary to get more knowledge about the possible risk connected with these substances.