We present the results of simulations and experimental studies of a W-band surface-wave oscillator powered by a ribbon high-current relativistic electron beam produced by SINUKI accelerator (IAP RAS, ...Nizhny Novgorod, 1 kA / 650 keV / 17 ns). Planar geometry of the interaction space facilitates efficient mode selection over wide transverse coordinate by using open waveguide at fairly large oversize factor (the width of the waveguide is ~ 8 wavelengths). Stable oscillation regime is obtained at frequency of 75 GHz with a pulse duration of about 5 ns. The output power measured by the calorimetric method reaches 25 MW.
scanning electron microscopy was used to study of the initial stages of the formation of a semipolar GaN(11
2) layer during Metalorganic Chemical Vapor Deposition on Si(113) substrates, on the ...surface of which
U
-shaped grooves with element sizes
<
100 nm (NP-Si(113)) were formed. It was found that NP-Si(113) substrates with a buffer AlN layer stimulate the formation of islands faceted by the planes
m
-GaN,
c
‑GaN. It is shown that there is a predominant growth of the
m
-GaN facet in comparison with
c
-GaN. The experimental results correspond to the Gibbs-Curie-Wolff selection principle, but taking into account elastic stresses in the
c
-GaN plane.
Scanning electron microscopy is used for studies of the initial stages of the formation of semipolar AlN (10
1) and AlN (10
2) layers during metal–organic vapor-phase epitaxy on a Si (100) substrate ...with a surface, on which a V-shaped nanostructure, whose elements are <100 nm in dimensions, is formed (a NP-Si(100) substrate). It is shown that, in the initial stage of epitaxy on the NP-Si(100) substrate, nuclei of AlN crystals are formed and then, depending on the crystallographic orientation of the V walls, crystals faceted by AlN (10
1) or AlN (10
2) planes are formed, correspondingly, on Si (111) or Si (111) misoriented in the 110 direction by 7°.
If the table of the genetic code is rearranged to put complementary codons face-to-face, it becomes apparent that the code displays latent mirror symmetry with respect to two sterically different ...modes of tRNA recognition. These modes involve distinct classes of aminoacyl-tRNA synthetases (aaRSs I and II) with recognition from the minor or major groove sides of the acceptor stem, respectively. We analyze the anticodon pairs complementary to the face-to-face codon couplets. Taking into account the invariant nucleotides on either side (5' and 3'), we consider the risk of anticodon confusion and subsequent erroneous aminoacylation in the ancestral coding system. This logic leads to the conclusion that ribozymic precursors of tRNA synthetases had the same two complementary modes of tRNA aminoacylation. This surprising case of molecular mimicry (1) shows a key potential selective advantage arising from the partitioning of aaRSs into two classes, (2) is consistent with the hypothesis that the two aaRS classes were originally encoded by the complementary strands of the same primordial gene and (3) provides a 'missing link' between the classic genetic code, embodied in the anticodon, and the second, or RNA operational, code that is embodied mostly in the acceptor stem and is directly responsible for proper tRNA aminoacylation.
It is an almost consensus opinion that the major carcinogenic risk of tobacco smoke is in its direct mutagenic action on DNA of cancer-related genes. The key data supposedly linking smoke-induced ...mutations to lung cancer were obtained from the adduct spectrum of the p53 tumor suppressor gene. Results of our analysis of p53 mutations compiled from the International Agency for Research on Cancer p53 database (April 1999 update) and from the literature point to a different causative link. Our new analytical tests focused on complementary base substitutions and showed that it is strand-specific repair of primary lesions and site-specific selection of the resultant mutations that determine the lung cancer-specific hot spots of G:C to T:A transversions along the p53 gene and also their increased abundance in lung tissues as compared with smoke-inaccessible tissues. However, on each of the two strands of p53 DNA, our tests revealed no significant difference between smokers and nonsmokers, either in the frequency of different types of mutations or in the frequency of their occurrence along the p53 gene. Moreover, in both smokers and nonsmokers, there was the same frequency of lung tumors with silent p53 mutations. Accordingly, we offer here a selection-based explanation of why lung cancers with nonsilent p53 mutations are more common in smokers than in nonsmokers. We conclude that physiological stresses (not necessarily genotoxic) aggravated by smoking are the leading risk factor in the p53-associated etiology of lung cancer.
•Si3N4 deposition from SiH4 and NH3 in III-N MOVPE reactors is studied.•Si3N4 deposition rate rises with temperature up to 1050–1100 °C.•Under any studied conditions Si3N4 deposition rate is linear ...with SiH4 concentration.•The higher the pressure is, the faster the Si3N4 deposition is.•Under H2 ambient deposition rate rapidly rises with NH3 flow and then gradually falls.
Si3N4 deposition from silane and ammonia in a number of III-N MOVPE reactors of various sizes was studied in a wide range of reactor conditions. It was revealed that Si3N4 deposition rate depends on temperature, pressure, carrier gas type, and ammonia concentration. Deposition rate rises with temperature up to 1050–1100 °C in a manner typical for temperature-activated processes, but under any studied conditions, including the 800–850 °C range, it is strictly linear with SiH4 concentration indicating the absence of high-order parasitic reactions at high temperature and surface passivation at low temperature. For a low-volume reactor the higher the pressure is, the faster the deposition is both for N2 and H2 carrier gases. For large reactors the dependence is non-monotonic. At temperature above 900 °C using H2 as a carrier gas results in a higher Si3N4 deposition rate than when using N2. If nitrogen is used as a carrier gas, deposition rate gradually rises with ammonia concentration. If hydrogen is used, deposition rate rapidly rises with ammonia concentration and then gradually falls. If hydrogen-nitrogen mixture is used as a carrier gas, deposition rate changes in a linear manner with the mole fraction of hydrogen in the carrier gas.
Molecular epidemiologists usually consider the spectrum of p53 mutations found in human tumors to be a signature of the corresponding environmental carcinogen(s). In lung cancer, this signature is ...the spectrum of G → T transversions, presumably induced by polycyclic aromatic hydrocarbons (PAH) from cigarette smoke. What complicates the situation, however, is that in the
p53 gene the same codons are preferential targets for not only mutagenesis but also tumorigenic selection. In this review, we compare the G → T spectra induced by PAH
o-quinones and diol epoxides with those in lung cancer and show that the main “shaper” of the latter is selection, not mutagenesis. In addition, we propose the approach that allows to distinguish selection and mutagenesis components of the
p53 spectra and, therefore, to test the suspect carcinogens for their “in vivo” mutagenic involvement. Collectively, the reviewed basic premises, concepts and data are consistent with the increasing recognition of environmental cancer risk conditions as selecting rather than inducing tumorigenic mutations.
The epitaxial growth of AlN and GaN layers is investigated using metalorganic vapor-phase epitaxy on a Si(100) substrate, on the surface of which a V-shaped nanostructure with elements of sub-100-nm ...size (NP-Si(100) substrate) is formed. It is shown that a corrugated surface is formed from semipolar AlN(10
1) planes with opposite axes of symmetry
c
during the formation of a semipolar AlN layer at the initial stage of epitaxy. Then, during the growth of the GaN layer, the transition from the symmetric state of two semipolar AlN planes to an asymmetric state with a single orientation of the
c
axis of the semipolar GaN(10
1) layer occurs, and the
c
direction in the growing semipolar layer coincides with the direction of the flow of
ions to the silicon surface during the formation of a nanomask.
It has been studied the morphology of the surface of the semipolar gallium nitride layers synthesized on nano-pattemed Si(100) or Si(113) substrates with a
V
-shaped or
U
-shaped surface profile, ...respectively. The morphology of the surface of the semipolar layers indicates that the different height-to-width ratio of the GaN(11-22) and GaN(10-11) blocks is associated with a higher growth rate of the GAN(11-22) face than GaN(10-11) and with different growth rates of the semipolar and polar crystal faces during the nucleation of the layer on a nano-patterned substrate.
The activity of key enzymes of energy and carbohydrate metabolism (cytochrome
C
oxidase, lactate dehydrogenase, glucose-6-phosphate dehydrogenase, and aldolase) was studied in juveniles of the ...three-spined stickleback
Gasterosteus aculeatus
from different biotopes of the White Sea (Seldyanaya Bight, Sukhaya Salma Strait, and Kolyushkovaya Lagoon). Sticklebacks from different biotopes differ mainly in the level of anaerobic metabolism and the degree of use of carbohydrates in the processes of glycolysis and biosynthesis in organs. The obtained results testified to adaptive mechanisms of restructuring of metabolic pathways of energy metabolism depending on habitat conditions in different biotopes (temperature and food supply).
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