Calibration measurements of the characteristics of tracks from superheavy nuclei in olivine crystals from meteorites

To identify the charge of detected cosmic ray nuclei, it is necessary that the dynamic and geometric parameters of tracks (the etching rate of a nuclear track, as well as the length and the diameter of the track channel) be determined with a high accuracy. Results of the experimental investigations of tracks produced in olivine crystals from the Marjalahti pallasite by accelerated Xe and U nuclei are presented. These investigations were performed as part of the Olimpiya project. It is shown that the etching rate and the fully etched track length are independent of the track orientation relative to the crystallographic symmetry axes of each olivine crystal under investigation.     

Photoluminescence of erbium ions in heterostructures with silicon nanocrystals

Photoluminescence properties of erbium-doped silicon dioxide layers containing silicon nanocrystals with 1.5–4.5 nm average size are investigated. It is found that the intensity and mean lifetime of the Er³⁺-ion photoluminescence depend on the nanocrystal size, optical pump intensity, and temperature. The results obtained are explained both by the effect of the local environment on Er³⁺ ions and by the manifestation of nonradiative deexcitation of ions caused by the transfer of energy back into the solid-state matrix and the Auger processes.     

Charge carrier transport in a structure with silicon nanocrystals embedded into oxide matrix

Current-voltage characteristics of Al/SiO₂/c-Si structures with silicon nanocrystals (nc-Si) in the oxide layer are studied in a wide temperature range. The analysis based on the experimental data has shown that thermostimulated tunneling via electron states in nc-Si is a most probable mechanism of charge carrier transport in these structures.     

4-fluorophenylglycine as a label for 19F NMR structure analysis of membrane-associated peptides

The non-natural amino acid 4-fluorophenylglycine (4F-Phg) was incorporated into several representative membrane-associated peptides for dual purpose. The (19)F-substituted ring is directly attached to the peptide backbone, so it not only provides a well-defined label for highly sensitive (19)F NMR studies but, in addition, the D and L enantiomers of the stiff side chain may serve as reporter groups on the transient peptide conformation during the biological function. Besides peptide synthesis, which is accompanied by racemisation of 4F-Phg, we also describe separation of the epimers by HPLC and removal of trifluoroacetic acid. As a first example, 18 different analogues of the fusogenic peptide "B18" were prepared and tested for induction of vesicle fusion; the results confirmed that hydrophobic sites tolerated 4F-Phg labelling. Similar fusion activities within each pair of epimers suggest that the peptide is less structured in the fusogenic transition state than in the helical ground state. In a second example, five doubly labelled analogues of the antimicrobial peptide gramicidin S were compared by using bacterial growth inhibition assays. This cyclic beta-sheet peptide could accommodate both L and D substituents on its hydrophobic face. As a third example, we tested six analogues of the antimicrobial peptide PGLa. The presence of d-4F-Phg reduced the biological activity of the peptide by interfering with its amphiphilic alpha-helical fold. Finally, to illustrate the numerous uses of l-4F-Phg in (19)F NMR spectroscopy, we characterised the interaction of labelled PGLa with uncharged and negatively charged membranes. Observing the signal of the free peptide in an aqueous suspension of unilamellar vesicles, we found a linear saturation behaviour that was dominated by electrostatic attraction of the cationic PGLa. Once the peptide is bound to the membrane, however, solid-state (19)F NMR spectroscopy of macroscopically oriented samples revealed that the charge density has virtually no further influence on the structure, alignment or mobility of the peptide.     

A study of the local electronic and atomic structure in <Emphasis Type="Italic">a</Emphasis>-Si<Subscript>x</Subscript>C<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> amorphous alloys using ultrasoft X-ray emission spectroscopy

X-ray spectroscopy has been used to obtain data on the local electronic and atomic structure of a-Si_xC_1?x:H(Er) alloys produced by plasma-enhanced chemical vapor deposition (PECVD) with various relative amounts of silane and methane in the gas mixture (x=0.3–0.9). It is shown that the alloys contain silicon and carbon atoms in different coordination environments. Silicon is observed as elementary amorphous silicon and silicon carbide, and the relative amounts of these phases in the films depend on the composition of the gas mixture. Carbon atoms can form bonds with silicon in a coordination close to that found in crystalline silicon carbide, with a noticeable amount of C-H bonds also appearing. In addition, carbon can form an elementary carbon phase with various coordination numbers characteristic of graphite and diamond in the film.     

Effect of dissipation of mechanical energy on hysteresis combustion

Combustion, Explosion, and Shock Waves -     

Specific features of electrical transport in anisotropically nanostructured silicon

Electrical transport in layers of porous silicon obtained by electrochemical etching of (110)-oriented single-crystal silicon wafers of p type was studied. It was found that the lateral conductivity and photoconductivity of the layers along the \([1\bar 10]\) crystallographic axis substantially exceed those along the [001] axis. The results obtained are explained in terms of the effective-medium model, which takes into account the presence of potential barriers at boundaries of anisotropically shaped silicon nanocrystals. The exponential dependence of the conductivity of porous silicon on the square root of the applied voltage is interpreted in terms of the Poole-Frenkel effect.     

Silicon network in a-Si:H films containing ordered inclusions

a-Si:H films with inclusions of (SiH₂)_n clusters or Si nanocrystals have been grown by magnetron-assisted SiH₄ decomposition (dc-MASD). The films were characterized by the microstructural parameter R=0.7–1.0. Ultrasoft X-ray emission spectroscopy was applied to establish the effect of these inclusions on the increasing ordering of Si network. It is shown that, irrespective of the nature of the inclusions, their effect is strongest for films of intrinsic material deposited at high temperatures (up to 400°C).     

Management of distributed knowledge encapsulated in embedded devices

Embedded electronic devices are now to be found everywhere. In general, they can be used to collect different sorts of data (e.g. on temperature, humidity, illumination and locations). In some specific domains, such as industrial automation, embedded devices are used for process control. The devices may have a programme that can respond immediately to environmental changes perceived through sensors. In the control of large sites, where there are many devices, higher level decisions are made or processed in dedicated computers far away from the sources (devices) where the initial data are collected. This article shows how it is possible to manage portions of distributed knowledge, hosted in embedded devices, making it possible for each embedded device to hold and manage its piece of knowledge. In addition, presented approach allows keeping locus of control at the embedded device level, where the embedded device can make decisions knowing the status of the rest of the world, device contributions and their effects in the overall distributed system knowledge base.