Observations of the low Earth orbit radiation environment from Mir

Recent measurements of the high-energy charged particle environment with the Radiation Environment Monitor (REM) aboard the Russian Mir space station are presented. Ionizing dose rates in a silicon detector have been measured with two shieldings. The dose is mainly accumulated in two distinct areas, the South Atlantic Anomaly (SAA) and the region of closest approach to the magnetic poles. Whereas the radiation in the South Atlantic Anomaly varied little during 1995, large changes of the daily absorbed doses in the polar regions are observed. A comparison of REM doses with the NASA AP-8 and AE-8 radiation models revealed major differences. AP-8 tends to underestimate the average REM doses, whereas AE-8 overestimates REM doses, and rather describes the worst case.     

On orthogonal and symplectic matrix ensembles

The focus of this paper is on the probability,E (O;J), that a setJ consisting of a finite union of intervals contains no eigenvalues for the finiteN Gaussian Orthogonal (=1) and Gaussian Symplectic (=4) Ensembles and their respective scaling limits both in the bulk and at the edge of the spectrum. We show how these probabilities can be expressed in terms of quantities arising in the corresponding unitary (=2) ensembles. Our most explicit new results concern the distribution of the largest eigenvalue in each of these ensembles. In the edge scaling limit we show that these largest eigenvalue distributions are given in terms of a particular Painlevé II function.     

Enhancement of the cubic molecular hyperpolarizabilities of nickel benzendithiol by donor and acceptor groups

In this paper the enhancement of the values of the cubic molecular hyperpolarizability of the nickel benzendithiol system, resulting from the selective addition of acceptor and donor groups to the ligand structure, is presented. The polarization of the molecular electronic structure is calculated by the finite field method. Significant increases in the values of are obtained from bridging two p-nitroaniline molecules with the square planar nickel structure. These results show that structures with significant values of x ⁽²⁾ that are derived from the inclusion of donor and acceptor groups might also be included into the ligands of the nickel dithiolene complex to give rise to materials with enhanced values of x ⁽³⁾.     

Rapid sensitive speciation analysis of butyl- and phenyltin compounds in water by capillary gas chromatography atomic emission spectrometry (GC-AES) after in-situ ethylation and in-liner preconcentration

Summary A rapid, simple and sensitive method has been developed for the simultaneous determination of butyl- and phenyltin species in environmental waters. The ionic organotin compounds are ethylated in the aqueous phase using sodium tetraethylborate (NaBEt₄) and extracted with hexane. A 25 l aliquot of the extract is injected at a low temperature into a Tenax filled liner. After solvent venting the analytes are transferred onto the capillary column using programmed temperature vaporization (PTV) injection. Detection is done by means of a microwave induced plasma atomic emission detector (MIP AED). The method allows the determination of butyl- and phenyltin compounds in water samples down to the level of 0.1 ng/l (as Sn) while 50 ml of sample is sufficient for analysis. The accuracy of the method was confirmed by GC-AAS after chelation and Grignard derivatization.