Roughening of ion-eroded surfaces

Recent experimental studies focusing on the morphological properties of surfaces eroded by ion-bombardment report the observation of self-affine fractal surfaces, while others provide evidence about the development of a periodic ripple structure. To explain these discrepancies we derive a stochastic growth equation that describes the evolution of surfaces eroded by ion bombardment. The coefficients appearing in the equation can be calculated explicitly in terms of the physical parameters characterizing the sputtering process. Exploring the connection between the ion-sputtering problem and the Kardar-Parisi-Zhang and Kuramoto-Sivashinsky equations, we find that morphological transitions may take place when experimental parameters, such as the angle of incidence of the incoming ions or their average penetration depth, are varied. Furthermore, the discussed methods allow us to calculate analytically the ion-induced surface diffusion coefficient, that can be compared with experiments. Finally, we use numerical simulations of a one dimensional sputtering model to investigate certain aspects of the ripple formation and roughening.Comment: 20 pages, LaTeX, 5 ps figures, contribution to the 4th CTP Workshop on Statistical Physics "Dynamics of Fluctuating Interfaces and Related Phenomena", Seoul National University, Seoul, Korea, January 27-31, 199

A model of evolution with constant selective pressure for regulatory DNA sites

<p>Abstract</p> <p>Background</p> <p>Molecular evolution is usually described assuming a neutral or weakly non-neutral substitution model. Recently, new data have become available on evolution of sequence regions under a selective pressure, e.g. transcription factor binding sites. To reconstruct the evolutionary history of such sequences, one needs evolutionary models that take into account a substantial constant selective pressure.</p> <p>Results</p> <p>We present a simple evolutionary model with a single preferred (consensus) nucleotide and the neutral substitution model adopted for all other nucleotides. This evolutionary model has a rate matrix in which all substitutions that do not involve the consensus nucleotide occur with the same rate. The model has two time scales for achieving a stationary distribution; in the general case only one of the two rate parameters can be evaluated from the stationary distribution. In the middle-time zone, a counterintuitive behavior was observed for some parameter values, with a probability of conservation for a non-consensus nucleotide greater than that for the consensus nucleotide. Such an effect can be observed only in the case of weak preference for the consensus nucleotide, when the probability to observe the consensus nucleotide in the stationary distribution is less than 1/2. If the substitution rate is represented as a product of mutation and fixation, only the fixation can be calculated from the stationary distribution. The exhibited conservation of non-consensus nucleotides does not take place if the elements of mutation matrix are identical, and can be related to the reduced mutation rate between the non-consensus nucleotides. This bias can have no effect on the stationary distribution of nucleotide frequencies calculated over the ensemble of multiple alignments, e.g. transcription factor binding sites upstream of different sets of co-regulated orthologous genes.</p> <p>Conclusion</p> <p>The derived model can be used as a null model when analyzing the evolution of orthologous transcription factor binding sites. In particular, our findings show that a nucleotide preferred at some position of a multiple alignment of binding sites for some transcription factor in the same genome is not necessarily the most conserved nucleotide in an alignment of orthologous sites from different species. However, this effect can take place only in the case of a mutation matrix whose elements are not identical.</p

Study of the conditional flexibility effect of compressed chord on the overall stability of corrugated beams

In this paper, the calculation of cut corrugated beams loaded with uniformly distributed load in the plane of the wall, with a wall height of 333 and 500 mm (54 sizes), chord width from 160 to 400 mm and chord thickness from 6 to 30 mm for general stability in accordance with Building Codes (BC) 294.1325800.2017 is made. A geometric criterion has been defined which defines the boundaries of the load-carrying capacity of Russian corrugated beams between the flat bending form stability and the strength of the normal section under the action of the bending moment in the plane of the wall

Неотектоническое районирование трассы газопровода Починки – Грязовец МосковскоНижегородского региона

Based on the structural-geomorphological method, neotectonic zonation of the Pochinki-Gryazovets gas pipeline was carried out for the safety purposes. Taking into account the probable stress sources, the geodynamic conditions of block structures formation are considered. Studies made it possible to subdivide the pipeline area into two parts: southern and northern. The southern part of the gas pipeline is located within the block characterized by tensile stress conditions; the northern part of pipeline relates to the block affected by compressive stress. The boundary between these blocks is considered as a geodynamic active zone and poses the risk for the pipeline safety.На основе структурно-геоморфологического метода впервые проведено неотектоническое районирование газопроводной трассы Починки – Грязовец с целью безопасной эксплуатации. С учетом вероятных источников напряжений рассмотрены геодинамические условия формирования блоковых структур. Исследования позволили разделить протяженную трассу газопровода на две части: южную и северную. Южная часть трассы находится в пределах блока, подверженного влиянию напряжений растяжения, северная – в пределах блока, подверженного влиянию напряжений сжатия. Граница между этими блоками рассматривается в качестве геодинамически активной зоны и геоэкологически значимой для трубопроводной трассы

Engineering methodology for calculation of corrugated beams for bending and torsion. Flat bend form stability

An engineering design procedure for calculating bending with torsion in corrugated beams, including finding the critical load of general stability, implemented in the commonly used MS Excel spreadsheet and verified in the LIRA-SAPR software package, has been proposed. The method makes it possible to take into account the beams section variability and corrugation parameters, to estimate the loading eccentricity effect, availability of supporting ribs and reinforcements of the compressed chord from the bending plane. Calculation results of particular design solutions for corrugated beams with definition of critical loads at transverse bending are given. Results of test calculation of a bent channel beam with calculation of stress-strain state parameters and its verification with the LIRA-SAP software package are given

Text and metatext event in the gaze behavior of impulsive and reflective readers

The subject of experimental studies of the authors are the factors that determine the distribution attention while reading. The study analyzes the features of constructing an event in text and metatext fragments of plays as capable of impact on changes in the oculomotor behavior of readers, reflective and impulsiv

Самородная платина в хондрите

The article presents the first results of the study of native platinum extracted from chondrite. The native platinum forms microinclusions in carbonaceous matter andchromites, which are found in ordinary chondrite. Native platinum forms micrograins and aggregates of cubic microcrystals, most of which are free from impurities. The composition of platinum-containing chromites corresponds to terrestrial analogues of ultrabasic mantle rocks. Assumption about the magmatic origin of platinum-containing carbon is made.Приведены первые результаты изучения самородной платины, микровключения которой обнаружены в углеродистом веществе и хромитах из обыкновенного хондрита. Самородная платина образует мелкие зерна и сростки кубических микрокристаллов, большинство которых свободны от примесей. Определен состав содержащих платину хромшпинелидов и установлено, что он соответствует земным аналогам из ультраосновных пород мантийного происхождения. Сделано предположение о магматическом происхождении содержащего платину углерода

Tracing the Evolution of Temperature in Near Fermi Energy Heavy Ion Collisions

The kinetic energy variation of emitted light clusters has been employed as a clock to explore the time evolution of the temperature for thermalizing composite systems produced in the reactions of 26A, 35A and 47A MeV $^{64}$Zn with $^{58}$Ni, $^{92}$Mo and $^{197}$Au. For each system investigated, the double isotope ratio temperature curve exhibits a high maximum apparent temperature, in the range of 10-25 MeV, at high ejectile velocity. These maximum values increase with increasing projectile energy and decrease with increasing target mass. The time at which the maximum in the temperature curve is reached ranges from 80 to 130 fm/c after contact. For each different target, the subsequent cooling curves for all three projectile energies are quite similar. Temperatures comparable to those of limiting temperature systematics are reached 30 to 40 fm/c after the times corresponding to the maxima, at a time when AMD-V transport model calculations predict entry into the final evaporative or fragmentation stage of de-excitation of the hot composite systems. Evidence for the establishment of thermal and chemical equilibrium is discussed.Comment: 9 pages, 5 figure

A Ghoshal-like Test of Equilibration in Near-Fermi-Energy Heavy Ion Collisions

Calorimetric and coalescence techniques have been employed to probe equilibration for hot nuclei produced in heavy ion collisions of 35 to 55 MeV/u projectiles with medium mass targets. Entrance channel mass asymmetries and energies were selected in order that very hot composite nuclei of similar mass and excitation would remain after early stage pre-equilibrium particle emission. Inter-comparison of the properties and de-excitation patterns for these different systems provides evidence for the production of hot nuclei with decay patterns relatively independent of the specific entrance channel.Comment: 7 pages, 2 figure