Altered protein synthesis in rat kidney cells exposed to semiconductor materials

It is thought that the extensive industrial use of arsenic, gallium and indium, which have applications as the materials for III–V semiconductors, will increase human exposure to these compounds in the near future. We have undertaken the development of new biological indicators for assessing exposure to these elements. Element-specific alterations in protein synthesis patterns were expected to occur following exposure to arsenic compounds. We examined alterations in protein synthesis in primary cultures of rat kidney proximal tubule epithelial cells by sodium arsenite, gallium chloride and indium chloride, utilizing two-dimensional gel electrophoresis. After incubation with the chemicals for 20 h, newly synthesized proteins were labeled with [³⁵S]methionine. A protein with a molecular weight (M_r) of 30 000 was markedly induced on exposure to 10 μM arsenite or 300 μM gallium chloride, and synthesis of proteins with M_r values of 85 000, 71 000, 65 000, 51 000, 38 000 and 28 000 were also increased by exposure to arsenite and gallium chloride. No significant changes were observed upon exposure to indium. Some of these increased proteins could be heat-shock proteins.     

Three-photon near-threshold photoionization dynamics of isooctane

The electron survival probability following three-photon (9.3 eV total) near-threshold photoionization of neat isooctane is measured with sub-50 fs time resolution. The measured dynamics are nonexponential in time and are well described by a diffusion-controlled electron-cation recombination model. Excitation-power-dependent studies indicate that the unperturbed three-photon threshold ionization is only observed for pump irradiance below 0.5 TW cm2. At excitation fields above this level, the signal is no longer cubic in the excitation irradiance, and the observed electron survival probability dramatically changes, decaying as a single exponential in time.     

Investigations of a new field in gas chromatography: capillary columns with a super-thick layer of stationary liquid phase

Basic characteristics (efficiency, selectivity, non-equilibrium) of capillary columns with a super-thick layer of stationary liquid phase are investigated. In contrast to traditionally used capillary columns with standard stationary phase thickness of 0.1-0.5 um, some new variables are now established. Firstly, the values of relative retention depend on carrier gas linear velocity. Secondly, the asymmetry of chromatographic peaks increased in accordance with the increase in carrier gas velocity. Thirdly, it was theoretically and experimentally shown that dependence of the height equivalent to a theoretical plate (HETP) on carrier gas velocity is linear. The above noted variables are evidences that the new type of GC is realized under these conditions. The use of capillary columns with super-thick layer of stationary liquid phase is practical when the following problems have to be solved: (1) Separation of highly volatile substances; (2) Preliminary concentration of trace compounds from strong diluted samples; (3) Improvements in measurement and accuracy due to the advantages of splitless injection into wide bore columns with super-thick films. Solutions to some analytical tasks while using super-thick stationary liquid phase are shown: (1) Large volume injection into capillary column with sample transfer speed up to 100 microL min(-1); (2) Isothermal splitless injection; (3) Separation of low boiling compounds; (4) Separation of polar substances (alcohols).     

High temperature gas chromatography: The development of new aluminum clad flexible fused silica glass capillary columns coated with thermostable nonpolar phases: Part 1

With the simultaneous development of blank aluminum clad flexible fused silica glass capillary tubing capable of withstanding temperatures up to 500°C, coincident with a series of special high temperature methyl polysiloxane polymers, it was possible to produce for the first time, long lived fused silica capillary columns containing thin films of thermostable stationary phases which could be maintained isothermally at 400425°C and temperature programmed to 425–440°C. The “bleed rate” here for a well conditioned column was 5 picoamperes or less. Under these circumstances, alkanes with carbon numbers in the C-90 to C-100 area were rapidly and efficiently eluted from these columns. By extrapolation here, one can easily detect certain compounds with boiling points in the 750°C range. Since this type of capillary column was found to possess certain favorable properties, it was thought that it will soon replace the packed column and will probably be more popular than the borosilicate capillary column for many high temperature applications. Moreover, evidence has now accumulated which leads us to further believe that the majority of analyses of “high molecular weight” compounds performed by Supercritical Fluid Chromatography (SFC), utilizing very narrow bore fused silica capillary columns at several hundred atmospheres, can be much more simply, much more rapidly, much more economically, and much more efficiently accomplished by gas chromatography utilizing this new generation of high temperature capillary columns.     

High temperature gas chromatography: The development of new aluminum clad flexible fused silica glass capillary columns coated with thermostable nonpolar phases: Part 2

Samples, representative of certain classes of “high molecular weight” and/or less volatile substances, were analyzed by gas chromatography utilizing a new generation of aluminum clad flexible fused silica glass capillary columns containing thin films of a methyl polysioxane stationary phase capable of being operated isothermally to 400–425°C and temperature programmed to 425–440°C. The results obtained here were compared with those described in the literature discussing the latest advances in Supercritical Fluid Chromatography (SFC) in the analysis of precisely the same types of samples. In all instances, the gas chromatographic method provided superior speed of analysis, superior column efficiency, and superior resolution of the component bands. This was due to fundamental factors, favoring the diffusivity of the solutes in both the gas and liquid phases in this process at these high temperatures. Under these circumstances, it is thought that the strength of SFC mainly lies in the analysis of thermally labile samples until the advocates of this technique make more definitive strides in the handling of still higher molecular weight substances well beyond the newly expanded range of gas chromatography.     

Simple Zeros of the Riemann Zeta-Function

Assuming the Riemann Hypothesis, Montgomery showed by meansof his pair correlation method that at least two-thirds of thezeros of Riemann's zeta-function are simple. Later he and Taylorimproved this to 67.25 percent and, more recently, Cheer andGoldston increased the percentage to 67.2753. Here we proveby a new method that if the Riemann and Generalized LindelöofHypotheses hold, then at least 70.3704 percent of the zerosare simple and at least 84.5679 percent are distinct. Our methoduses mean value estimates for various functions defined by Dirichletseries sampled at the zeros of the Riemann zeta-function. 1991Mathematics Subject Classification: 11M26.     

Existence and Uniqueness of Fixed Points for Markov Operators and Markov Processes

This paper concerns a Markov operator T on a space L₁, and aMarkov process P which defines a Markov operator on a spaceM of finite signed measures. For T, the paper presents necessaryand sufficient conditions for:

a the existence of invariant probabilitydensities (IPDs)

b the existence of strictly positive IPDs,and

c the existence and uniqueness of IPDs.

Similar resultson invariant probability measures for P are presented. The basicapproach is to pose a fixed-point problem as the problem ofsolving a certain linear equation in a suitable Banach space,and then obtain necessary and sufficient conditions for thisequation to have a solution. 1991 Mathematics Subject Classification:60J05, 47B65, 47N30.