Classification of certain pairs of operators (P, Q) satisfying [P, Q] = −i Id

In a separable Hilbert space a certain class of pairs of operators (P, Q) satisfying the Born-Heisenberg commutation relation [P, Q] = ?i Id on a dense domain Ω is investigated. This class is essentially defined by requiring Q bounded and self-adjoint, P symmetric and $\text{PΩ ? Ω, QΩ ? Ω}$. We show that Q is absolutely continuous and that P can be thought of as a first order differential operator. The class considered contains the pair “angle ?” and “angular momentum L_z.” It is expected that the methods of this paper can be applied to more general classes of operators (P, Q) including the Schrödinger case.     

Protein type effects on steady-state crossflow membrane ultrafiltration fluxes and protein transmission

The permeate fluxes and percent protein transmission were evaluated for steady-state crossflow ultrafiltration of two proteins of different composition: bovine serum albumin (BSA), containing fatty acid, and “fatty-acid-poor” BSA, from which most of the fatty acids had been removed (BSA/FAP). The influences of protein concentration up to 6.5 percent w/v, transmembrane pressure, ionic environment and membrane type (i.e. nominal molecular weight cut-off) were investigated. For both BSA and BSA/FAP, the fluxes and the protein transmission were dependent on the amount of salt present. The higher fatty acid content in the BSA apparently enhanced protein-protein interaction, resulting in a more cohesive and resistant fouling layer; permeate fluxes were lower with BSA/FAP than with BSA at otherwise corresponding operating conditions. A hysteresis behaviour of the flux (J)-transmembrane pressure (TMP) relationship was observed whenever the ultrafiltration unit was operated at a TMP less than some higher value to which the membrane previously had been exposed.     

Prussian Blue Modified Amperometric Hg2+ Ion Biosensor Based on Glucose Oxidase Inhibition

In this research a Hg²⁺ ion biosensor was developed by combining Prussian blue (PB) with glucose oxidase (GOx) – an enzyme that can be inhibited by Hg²⁺ ions. An application of PB in the design of Hg²⁺ ion biosensor enabled detecting changes in hydrogen peroxide reduction current at low operational potential of 0.2 vs Ag|AgCl,KCl_sat. The described Hg²⁺ ion biosensor exhibited wide linear range from 27 μM to 247 μM of Hg²⁺ and higher maximal detectable concentration of Hg²⁺ than other GOx inhibition-based biosensors, making it convenient for the analysis of samples with high concentration of Hg²⁺ ions.     

Ultraviolet radiation-induced limitation to epilithic microbial growth in arid deserts--dosimetric experiments in the hyperarid core of the Atacama Desert

Experiments were conducted during November 2003 in the dry core of the Atacama Desert, Yungay, Chile to test the hypothesis that UV radiation, in environments where liquid water is not available, and thus enzymatic repair of UV-induced damage is inhibited, can prevent epilithic colonization. Novel dosimeters made from the cryptoendolithic, desiccation and radiation-resistant cyanobacterium Chroococcidiopsis sp. isolated from the dry Negev desert, Israel, showed that monolayers of this organism were killed within one day. The diurnal profile of microbial loss of viability was investigated with dosimeters of Bacillus subtilis, which similarly showed cell death within one day. Soil grains obtained from south of Yungay where liquid water is more abundant and transported to the hyperarid core showed killing of indigenous vegetative organisms within one day. Gypsum and mineral grain coverings of 1mm were sufficient to prevent measurable UV-induced damage of Chroococcidiopsis and B. subtilis after 8d exposure. These results show that under extreme desiccation and an ambient UV flux the surface of rocks can potentially be rendered sterile, but that millimetre thick mineral coverings can protect organisms from UV-induced killing, consistent with the observed patterns of lithophytic colonization in the Atacama Desert. These data further show that UV radiation can be an important limiting factor in surface biological rock weathering in arid regions.     

Conductometric determination of the concentration of acid centers on functionalized materials

The potentialities of conductometric titration were investigated for the study of protolytically active groups using organosilicas with immobilized acid groups of different types as an example. The methods of conductometric and pH-metric titration were compared in determining the concentrations of these groups. It was found that pH metry was mainly applicable to the determination of strongly acid groups of organosilicas, whereas conductometric titration can be applied to the determination of all types of test materials. It was shown that conductometry is a promising method for estimating the energetic heterogeneity of the immobilized layer and the concentration of functional groups on the surface of organosilicas.     

Atomic concentration of hydrogen in tetra- and hexaamine heteroligand chromium(III) complexes with cyclic tetraamines

Based on the revealed dependence of the atomic concentration of hydrogen (N_H) on the composition and structure of tetra- and hexaamine heteroligand chromium(III) complexes with cyclic tetraamines, routes to new materials with high N_H for preparing effective composites for protection from neutron radiation were suggested.     

Behaviour of pure water and water mixture with benzene or chloroform adsorbed onto ordered mesoporous silicas

Structural characteristics of synthesized ordered mesoporous silicas MCM-41, MCM-48 and SBA-15 were studied using XRD, nitrogen adsorption and FTIR methods. Pure water and mixtures with water/benzene and water/chloroform-d adsorbed onto silicas were studied by ¹H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial liquids. Concentrated aqueous suspensions of MCM-48 and SBA-15 were studied by thermally stimulated depolarization current (TSDC) method. Benzene and chloroform-d can displace a portion of water to broad pores from the pore walls and from narrower pores, especially in the case of a large excess of an organic solvent. This process is accompanied by diminution of both interaction energy of water with an adsorbent surface and freezing temperature depression of adsorbed water. The effect of nonpolar benzene on pore water is much stronger than that of weakly polar chloroform-d. Modifications of the Gibbs-Thomson relation to describe the freezing point depression of mixtures of immiscible liquids confined in pores allow us to determine distribution functions of sizes of structures with unfrozen pore water and benzene. Former address: Pisarzhevskii Institute of Physical Chemistry, 31 Prospect Nauki, Kiev, Ukraine     

Crystal chemistry of the G-phases in the {Ti, Zr, Hf}-Ni-Si systems

Ternary compounds M₆Ni₁₆Si₇ (M=Ti, Zr, Hf) have been investigated by X-ray powder/single crystal and neutron powder diffraction. Compounds with Zr and Hf crystallize in the ordered Th₆Mn₂₃ type (Mg₆Cu₁₆Si₇-type, space group ), whereas Ti₆Ni_16.7Si₇ contains an additional Ni atom partially occupying the 24e site (M2 site, x=0.4637,0,0; occ.=0.119) inside a Ti octahedron; Ti atoms occupy a split position. Ti₆Ni_16.7Si₇ represents a new variant of the filled Th₆Mn₂₃ type structure. Ab initio calculations confirm the structural difference: additional Ni atoms favour the 24e site for Ti₆Ni_16.7Si₇, however, for the Zr and Hf-based compounds the unoccupied site renders an energetically lower ground state. Enthalpies of formation of Ti₆Ni₁₇Si₇, Zr₆Ni₁₆Si₇, and Hf₆Ni₁₆Si₇ were calculated to be −68.65, −74.78, and −78.59 kJ/(mol of atoms), respectively.     

Exposure of Arctic Field Scientists to Ultraviolet Radiation Evaluated Using Personal Dosimeters

During July 2000 we used an electronic personal dosimeter (X-2000) and a biological dosimeter (Deutsches Zentrum für Luft- und Raumfahrt: Biofilm) to characterize the UV radiation exposure of arctic field scientists involved in biological and geological fieldwork. These personnel were working at the Haughton impact structure on Devon Island (75 degrees N) in the Canadian High Arctic under a 24 h photoperiod. During a typical day of field activities under a clear sky, the total daily erythemally weighted exposure, as measured by electronic dosimetry, was up to 5.8 standard erythemal dose (SED). Overcast skies (typically 7-8 okta of stratus) reduced exposures by a mean of 54%. We estimate that during a month of field activity in July a typical field scientist at this latitude could potentially receive approximately 80 SED to the face. Because of body movements the upper body was exposed to a UV regimen that often changed on second-to-second time-scales as assessed by electronic dosimetry. Over a typical 10 min period on vehicle traverse, we found that erythemal exposure could vary to up to 87% of the mean exposure. Time-integrated exposures showed that the type of outdoor field activities in the treeless expanse of the polar desert had little effect on the exposure received. Although absolute exposure changed in accordance with the time of day, the exposure ratio (dose received over horizontal dose) did not vary much over the day. Under clear skies the mean exposure ratio was 0.35 +/- 0.12 for individual activities at different times of the day assessed using electronic dosimetry. Biological dosimetry showed that the occupation was important in determining daily exposures. In our study, scientists in the field received an approximately two-fold higher dose than individuals, such as medics and computer scientists, who spent the majority of their time in tents.     

Solid-Phase Substitution of Ammonia in Hexaamine Heteroligand Complexes of Chromium(III) with Cyclic Tetraamines

The solid-phase substitution of ammonia in heteroligand hexaamine complexes of chromium(III) with cyclic tetraamines was studied. The kinetic stability of these compounds, determined from the value of the activation energy, is lower than for other hexaamine compounds of chromium(III). This is due to the weakening of the Cr—NH₃ bonds and to the less close packing of the ions in the crystal lattice. For complexes with the trans structure the thermal stability increases in the series of tetraazamacrocyclic ligands teta < cyclam < TMC.