Showing papers by "Russian Academy of Sciences published in 1982"

Stability of proteins. Proteins which do not present a single cooperative system

Abstract: Publisher Summary The chapter discusses the protein stability with emphasis on compact globular proteins representing a single cooperative system. All the small compact globular proteins represent cooperative systems; they exhibit an extreme cooperativity that integrates the whole of their structure into a single structural unit. The large proteins, to which fibrillar proteins are also related, do not present single cooperative systems, but are subdivided into definite cooperative subsystems—structural blocks or domains. The advances in studying the stability of complicated proteins are connected with two methodical achievements: (1) the appearance of the precise scanning microcalorimetric technique, which affords reliable information on the heat capacity function of proteins in a broad temperature range; and (2) realization of the fact that the complicated heat effect of disruption of a complex macromolecular structure can be analyzed thermodynamically. The thermodynamic specificity of collagen has been considered. The volume of globular proteins does not increase at denaturation but decreases, as seen from their ability to denature under high pressure. The results of calorimetric studies are discussed, presenting the specific melting enthalpy of various protein structures—globular proteins, double-stranded coiled coils, and triplestranded coiled coils. The practical importance of thermodynamic studies of protein stability—that is, its importance not only for understanding the principles of organization of these molecules, but just for obtaining structural information on the domain level is emphasized.

Computation of wave fields in inhomogeneous media — Gaussian beam approach

Abstract: Summary. An asymptotic procedure for the computation of wave fields in two-dimensional laterally inhomogeneous media is proposed. It is based on the simulation of the wave field by a system of Gaussian beams. Each beam is continued independently through an arbitrary inhomogeneous structure. The complete wave field at a receiver is then obtained as an integral superposition of all Gaussian beams arriving in some neighbourhood of the receiver. The corresponding integral formula is valid even in various singular regions where the ray method fails (the vicinity of caustic, critical point, etc.). Numerical examples are given.

Polyhedral oligosilsesquioxanes and their homo derivatives

Abstract: A critical analysis of the present state of synthetic methods and mechanisms of the formation of polyhedral oligosilsesquioxanes and their homo derivatives is given. The data available on the structure, physico-chemical properties, reactivity, and application of the above compounds are summarized and systematized.

Erbium glass lasers and their applications

Abstract: In this paper results of experimental investigations into erbium glass lasers and their likely applications are discussed. Regularities of the inversion energy accumulation, also as channels of energy losses, are covered in detail. Different erbium lasers, both flashtube and neodymium laser-pumped, are compared. Parameters of some erbium laser glasses are presented, including the new LGS-E7, which requires a smaller pumping energy density (less than 100–200 J cm-2). Test data from experimental models are summarized.

Selection against harmful mutations in large sexual and asexual populations.

Abstract: Selection against harmful mutations in large populations is studied assuming that the rate of fitness decrease grows with every new mutation added to a genome. Under this reasonable assumption (Mayr, 1970) the average fitness of a sexual population, without linkage between the loci, is higher, and the average equilibrium number of harmful mutations per individual lower, than in an asexual population. If a gamete contains on the average one or more new mutations, the resulting advantage of sexual reproduction and recombination seems to be sufficient to counterbalance the double advantage of parthenogenesis. Moreover, selection against harmful mutations is probably the most powerful factor preventing linkage disequilibrium even with epistatic interaction between the loci.

Ubiquitous transposon-like repeats B1 and B2 of the mouse genome: B2 sequencing.

Abstract: Mouse genome contains two major families of short interspersed repeats in more than 10(5) copies scattered throughout the whole genome. They are referred to as B1 and B2 sequences since they were first isolated from the genome library by means of a dsRNA-B probe /1/. In this work, two copies of the B2 family were sequenced and compared with the previously sequenced B1 repeat /2/. A B2 ubiquitous repeat is ca. 190 bp long. The members of the family deviate in 3-5% of nucleotides from the consensus sequence. B2 contains regions of homology to the RNA polymerase III split promoter and to 4.5S snRNA I. Both B1 and B2 contain regions which resemble junctions between exons and introns. In contrast to B1, B2 does not contain apparent homologies to papova viral replication origins and a human Alu sequence. One side of the B2 repeat is represented by a very AT-rich sequence (ca. 30 bp long) followed with an oligo (dA) stretch 10-15 nucleotides long. This region of the repeat is the most variable one. The whole unit is flanked with 15-16 bp direct repeats different in sequenced copies of B2. The same is true of some copies of the B1 family. The properties of B1 and B2 repeats suggest that they may represent a novel class of transposon-like elements in eukaryotic genome. A possible role of B-type repeats in genome reorganization, DNA replication and pre-mRNA processing is discussed.

Interaction of afferent and efferent signals underlying joint position sense: empirical and theoretical approaches.

Abstract: A model of joint position sense is considered based on the concept that central motor commands are adequately expressed in terms of shifts of the so-called invariant length-tension characteristics for agonist and antagonist muscles The main points of this concept are discussed to clarify them and to prevent misunderstanding The basic idea of the model is that the efferent copy of the central motor commands plays the role of a reference frame for evaluation of afferent proprioceptive discharges An experiment with reproduction of constrained movements was performed in order to investigate the influence of voluntary flexor or extensor muscle tension on position sense in the elbow joint The results demonstrate adequate perception of joint position on the background of voluntary muscle tension and thus are quite consistent with the model The role of afferent and efferent signals in position sense is discussed with special reference to views expressed recently by different authors The interrelation between position sense and sense of effort is considered, based on a concept of senso-motor space

Diapause and biological rhythms in ticks

Abstract: Publisher Summary This chapter discusses the daily and seasonal rhythms in ticks and their regulation Ticks have a great diversity of biological rhythms that probably play a significant role in tick adaptation to seasonal and daily cycles as they do among insects Ticks display circadian rhythms in important activities, such as host seeking, feeding, detachment from the host, and laying eggs The detachment rhythm is particularly critical for ticks adapted to hosts with regular nesting habits Seasonal rhythms, regulated by diapause, are important for synchronizing tick activities with favorable climatic conditions The diapausing tick also has the advantage of being more resistant to unfavorable temperatures Regulation of daily and seasonal rhythms depends on the direct response of the tick to environmental conditions and also on an internal “physiological clock” Biological clocks are of great value to ticks, as they are to other animals, in the control of many aspects of their physiology and behavior, enabling the coordination of vital processes and their temporal organization As a result, ticks have the ability to show adaptive behavioral and physiological changes that appear to predict daily and seasonal changes in the environment and ensure survival

First-order phase transitions in large entropy lattice models

Abstract: We show the existence of a first-order phase transition in thev-dimensional Potts model forv≧2, when the number of states of a single spin is big enough. Low-temperature pure phases are proved to survive up to the critical temperature. Also the existence of a first-order transition in thev-dimensional Potts gauge model,v≧3, is obtained if the underlying gauge group is finite but large.

Multi-armed vortices in an active chemical medium

Abstract: An excellent example of self-organization in nonequilibrium systems1,2 is the origination of rotating spiral vortices. These vortices have been observed in a wide range of active media—in the morphogenesis processes of social amoeba Dictyostelium discoideum3,4, in cardiac muscle during some arrhythmias5 and in the Belousov–Zhabotinsky reaction6–9. All these vortices are simple spirals. The rotating structures of a higher order of symmetry such as multiarmed vortices have not previously been observed experimentally. We have obtained two-, three- and four-armed rotating spiral vortices in an active chemical medium. These structures were appreciably stable and we observed their rotation for more than half an hour, which was in striking contrast to unstable multiple vortices in many other physical systems (such as superfluid 4He or superconductors10,11).

On the Energy Spectrum of Dislocations in Silicon

Abstract: Using deep level transient spectroscopy (DLTS) the defects introduced into silicon by plastic deformation are investigated with respect to their capture and emission characteristics. In agreement with what has been found by electron spin resonance (EPR), kind and density of the detected localized states strongly change with deformation temperature and during anneal around 0.6 Tm (Tm melting temperature). While part of this effect can be certainly explained by anneal out of point defects, there must be a structural change in the core region of the dislocation, since the dislocation density remains unchanged during anneal. Die Defekte, die in Silizium durch plastische Verformung entstehen, wurden mit Hilfe einer Kapazitatsspektroskopie (DLTS) bezuglich ihrer Einfangs- und Emissionscharakteristik untersucht. In Ubereinstimmung mit den Ergebnissen der Elektronenspinresonanz (EPR) andern sich Art und Dichte der nachgewiesenen lokalisierten Zustande mit der Verformungstemperatur und wahrend des Ausheilens bei etwa 0,6 Tm (Tm Schmelztemperatur). Wahrend ein Teil dieses Effekts sicherlich auf das Ausheilen von Punktdefekten zuruckzufuhren ist, mus es auch eine strukturelle Anderung im Gebiet des Versetzungskernes geben, da die Versetzungsdichte durch die Gluhung nicht geandert wird.

The primary structure of E. coli RNA polymerase, Nucleotide sequence of the rpoC gene and amino acid sequence of the beta'-subunit.

Abstract: The primary structure of the E. coli rpoC gene (5321 base pairs) coding the beta'-subunit of RNA polymerase as well as its adjacent segment have been determined. The structure analysis of the peptides obtained by cleavage of the protein with cyanogen bromide and trypsin has confirmed the amino acid sequence of the beta'-subunit deduced from the nucleotide sequence analysis. The beta'-subunit of E. coli RNA polymerase contains 1407 amino acid residues. Its translation is initiated by codon GUG and terminated by codon TAA. It has been detected that the sequence following the terminating codon is strikingly homologous to known sequences of rho-independent terminators.

An exact solution to a certain non-linear random vibration problem

Abstract: A single-degree-of-freedom system with a special type of non-linear damping and both external and parametric white-noise excitations is considered. For the special case, when the intensities of coordinates and velocity modulation satisfy a certain condition an exact analytical solution is obtained to the corresponding stationary Fokker-Planck-Kolmogorov equation yielding an expression for joint probability density of coordinate and velocity. This solution is analyzed particularly in connection with stochastic stability problem for the corresponding linear system; certain implications are illustrated for the system, which is stable with respect to probability but unstable in the mean square. The solution obtained may be used to check different approximate methods for analysis of systems with randomly varying parameters.

CHAPTER VII – Differential Invariants

Abstract: Publisher Summary This chapter focuses on the theory and applications of differential invariants of Lie transformation groups, which can be infinite. It discusses the concepts of a differential invariant and special transformation of a differential equation, the so-called group stratification. The central theorem is about the finiteness of bases for differential invariants of arbitrary Lie groups. In the proposed variant Tresse's theorem is completely established in infinitesimal language by the means of invariant differential operators. An equation E is called automorphic relative to the given group G if all its solutions are situated on the orbit of one of them. In other words, from one given solution U, it is possible to find all solutions by applying to U the transformations of the group G. Classical problems of the construction and classification of automorphic systems provide excellent examples of the applications of the general theory, and these play an important role in the problems of invariant transformations for differential equations.