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Abstract: A significant difference in the growth mechanism of spatially closed structures of gallium nitride during selective growth in submicron windows with and without penetration into the GaN sublayer was demonstrated. The mechanisms of generation and development of dislocations, their role in the formation of self-organizing coaxial structures were modeled.

A new effect of the n-and p-type doping of the Si(100) substrate with a SiC film on the growth mechanism and structure of AlN and GaN epitaxial layers has been revealed. It has been experimentally shown that the mechanism of AlN and GaN layer growth on the surface of a SiC layer synthesized by substituting atoms on n- and p-Si substrates is fundamentally different. It has been found that semipolar AlN and GaN layers on the SiC/Si(100) surface grow in the epitaxial and polycrystalline structures on p-Si and n-Si substrates, respectively. A new method for synthesizing epitaxial semipolar AlN and GaN layers by chloride–hydride epitaxy on silicon substrates has been proposed.

The spectra of the fourth and fifth CH stretching overtones of cyclohexene and cyclopentene molecules and of some of their selectively deuterated derivatives have been measured by dye laser intracavity spectroscopy with photoacoustic detection. The intramolecular relaxation of the vibrational energy occurs principally through Fermi resonances with CH2bending combinations in cyclohexene and through a coupling between the stretching and the ring puckering motions in cyclopentene.

This paper presents an express technique for determining the diffusion coefficients of chromium in ZnSe, using a Tm:YLF laser that emits at 1.908 ?m. The diffusion coefficients of chromium in ZnSe obtained by deposition from the vapor phase are determined to be D=(9.5±0.6)×10^?9??cm^2/s and D=(1.0±0.1)×10^?9??cm^2/s at 1100°C and 900°C, respectively. The absorption cross section of Cr^2+ ions in zinc selenide at 1.908 ?m was 4.6×10^?19??cm^2.

Abstract: A study was made of GaN crystals grown by HVPE and MOCVD. Thulium was introduced by diffusion. It is shown that the Tm rare-earth ion acts as an acceptor in a GaN semiconductor matrix if the undoped crystal contains deep-level defects. Intracenter f-f transitions characteristic of Tm were observed in the short-and long-wavelength spectral regions. The short-wavelength emission intensity is higher in crystals obtained by MOCVD.

Abstract: Doping of GaN crystals prepared by various methods (HVPE and MOCVD) with various degrees of perfection of the mosaic structure, using rare-earth (RE) ions has been studied. An analysis of the shape of the photoluminescence spectra obtained before and after the doping showed that, as the defect concentration decreases, the intracenter f-f transitions characteristic of RE ions, at 1.54 and 0.54 m in Er3+ and 0.72 m in Sm2+, become observable. The intracenter f-f transitions of RE ions are seen, as a rule, in epitaxial layers with well-aggregated and relaxed domains and are absent in the case of a mosaic structure containing domains in the near-surface part of the epitaxial layer that are not fully coalesced. RE doping of the crystals under study was observed to initiate defect gettering.

Abstract: A study of the variation of photoluminescence spectra of bulk Eu-doped GaN samples revealed that the dopant can reside in the crystal in various charge states depending on the total defect concentration in the starting semiconductor host matrix. In crystals with the lowest concentration of shallow-level defects, the ion can exist only in one charge state, Eu3+. At higher concentrations of such defects, Eu can be observed in two charge states, Eu2+ and Eu3+. A rare-earth impurity was found to act as a getter of defects in the starting GaN matrix.

The anisotropy of the dielectric permittivity and spontaneous polarization for pure and α-alanine doped diglycine nitrate has been studied. The actual polar direction is considered to be the normal direction to the 60°X-cut. The deviation of the spontaneous polarization vector in the mirror plane m for the ferroelectric phase has not been observed. The mechanism of partial substitution of alanine for glycine in this crystal is shown to be the same as in triglycine sulfate.

The behaviour of some elastic constants of diglycine nitrate across the ferroelectric phase transition were measured with Brillouin scattering. The results were compared with low frequency behaviour of one elastic constant. Results were analysed in the framework of Landau free energy expansion. Discrepancy was found between the relaxation time for the spontaneous polarization from dielectric measurements and our results.

We wanted to determine whether there is a correlation between the quantitative character, the penetrance of the loss of humeral bristles in scute lines, and the distribution of transposable genetic elements in their genomes. We derived 18 isogenic lines with penetrance ranging between 2.8% and 92.0% from six mutant lines. The localization of the transposable elements (TEs) P, mdg1, Dm412, copia, gypsy and B104 was determined in all isogenic derivatives by in situ hybridization. The total number of the TE sites over all lines was 180. A comparison of the distribution of the TEs in the isogenic lines revealed the location of sites typical of lines with similar penetrance, no matter which parental line was involved. The results obtained suggest that such typical sites appear to tag the genome regions where the polygenes affecting the character in question are most likely to be found.

The functional expression of 12 scute alleles in homozygotes and compounds of Drosophila melanogaster at 14°, 22°, 30°C is analysed. Based on the data obtained, linear maps for bristles and mutations are built. The basic features of the maps, clustering and polarity, are invariable with respect to temperature, scute gene dosage and cross direction. In addition local dominance of the norm over bristle reduction was produced by the scute mutation; different types of complementation reactions were established for each bristle. The gene scute is treated as an operon-like system, composed of 3–4 cistrons with each controlling the formation of bristles on a particular region of the fly's body. This model argues well with the structure of maps constructed and implies a post-translational level of initial events of bristle-formation process.

In accordance with the hypercycle theory of M. Eigen and P. Schuster [(1979) Hypercycle: A Principle of Natural Self-Organization (Springer, New York)], the ancestors of modern tRNAs appear to have emerged via the shortest possible way, both complementary strands of a short symmetrical double helix serving as pre-tRNAs with complementary anticodons. This conclusion is based upon results of comparative sequence analysis of the 17-base-long anticodon loop and stem of tRNAs totaling 896 and especially of 22 pairs of consensus tRNAs with complementary or quasi-complementary anticodons. With regard to the anticodon loop and stem of pairs of consensus tRNAs, complementary distances were considerably less than direct distances--i.e., antiparallel pairing invariably yielded fewer mismatches than direct pairing. Furthermore, the smallest complementary distance was detected when two antiparallel sequences formed irregular G-U bonds in their anticodon triplets. The above implies that pre-tRNAs in peribiotic times were long hairpin structures having 73 bases or more, the middle base of an anticodon being the center of symmetry. Accordingly, each pair of pre-tRNAs with complementary anticodons should have been almost identical with each other except for their three central bases. The above situation appears to have dictated the early establishment of direct links between anticodons and the type of amino acids with which tRNAs are to be charged. This direct link is still maintained between modern aminoacyl-tRNA synthetases and anticodons. Replication of the double helices concertedly generated new codons for the same pair of amino acids. Thus, occurrence of synonymous as well as certain "palindromic" features of the genetic code table might have been determined by this mechanism.

The I4N and 170 quadrupole couplings in diglycine nitrate have been determined by proton- 14N and proton-170 double resonance. The O─H──O bonded proton is moving between two off-centre sites in the H─bond above TC and is frozen out in an off-centre site below TC. The results show that the basic phase transition mechanism is a biasing of the flipping of the ─NH3 groups around the C─N bondbetween two equilibrium orientations separated by ∼ 60° connected with a corresponding rotation of the NO3-; ions, an exchange of the ionic character of the two glycine molecules and a transfer of the O─H──O bonded proton.

A total of 1268 available (excluding mitochondrial) tRNA sequences was used to reconstruct the common consensus image of their acceptor domains. Its structure appeared as a 11-bp-long double-stranded palindrome with complementary triplets in the center, each flanked by the 3'-ACCD and NGGU-5' motifs on each strand (D, base determinator). The palindrome readily extends up to the modern tRNA-like cloverleaf passing through an intermediate hairpin having in the center the single-stranded triplet, in supplement to its double-stranded precursor. The latter might represent an original anticodon-codon pair mapped at 1-2-3 positions of the present-day tRNA acceptors. This conclusion is supported by the striking correlation: in pairs of consensus tRNAs with complementary anticodons, their bases at the 2nd position of the acceptor stem were also complementary. Accordingly, inverse complementarity was also evident at the 71st position of the acceptor stem. With a single exception (tRNA(Phe)-tRNA(Glu) pair), the parallelism is especially impressive for the pairs of tRNAs recognized by aminoacyl-tRNA synthetases (aaRS) from the opposite classes. The above complementarity still doubly presented at the key central position of real single-stranded anticodons and their hypothetical double-stranded precursors is consistent with our previous data pointing to the double-strand use of ancient RNAs in the origin of the main actors in translation- tRNAs with complementary anticodons and the two classes of aaRS.

The synthesis has been performed of ten tetrapeptides of the general formula Dnp-Gly-Gly-X-Arg-OH, where X = Val, Phe, Abu, Asp (OBut), Asp, Met, D-Phe, Ser, Thr, or Trp. The synthesis was carried out with Dnp-Gly-Gly-ONp, activated esters of protected amino acids, and arginine with an unprotected carboxy group. The coefficients of molar extinction of the tetrapeptides at 660 nm are given. It has been shown that the peptides can be used to determine the activities of neutral and alkaline proteinases from various sources, the peptides with X = Phe, Met, and Abu exhibiting the highest sensitivity to enzymatic hydrolysis.

The article shows the necessity and the prospects of high-tech activities development in the GCC countries (Oman, Qatar, Kuwait, Bahrain, Saudi Arabia and the United Arab Emirates) on the example of Bahrain. It explores the role of high-tech industries in the world and in the region, in particular, the high and growing importance of aerospace activities in Bahrain and other GCC countries and substantiates the view, concerning the possibility to enhance cooperation in this area between Bahrain and Russia.

The characteristics of a room-temperature laser based on a polycrystalline Fe2+:ZnSe sample pumped by a non-chain HF laser are studied. The laser energy is E=175 mJ at the efficiencies with respect to the incident and absorbed pump energy ep [?] 22% and habs [?] 29%, respectively.