A probabilistic approach to the problem of electron localization in disordered systems and sharpness of the mobility edge

By applying the theory of the asymptotic distribution of extremes and a certain stability criterion to the question of the domain of convergence in the probability sense, of the renormalized perturbation expansion (RPE) for the site self-energy in a cellularly disordered system, an expression has been obtained in closed form for the probability of nonconvergence of the RPE on the real-energy axis. Hence, the intrinsic mobility mu (E) as a function of the carrier energy E is deduced to be given by mu (E)= mu 0exp(-exp( mod E mod -Ec) Delta ), where Ec is a nominal 'mobility edge' and Delta is the width of the random site-energy distribution. Thus mobility falls off sharply but continuously for mod E mod >Ec, in contradistinction with the notion of an abrupt 'mobility edge' proposed by Cohen et al. and Mott. Also, the calculated electrical conductivity shows a temperature dependence in qualitative agreement with experiments on disordered semiconductors.

Crystal structure from packing studies: application to the triclinic structure of the cyclic hexapeptide cyclo-(gly-tyr-gly)2

The paper describes a novel method of finding the position and orientation of a relatively rigid molecule in the unit cell from criteria concerning allowed contact distances between atoms. On application to the crystal structure of a hexapeptide, C25H31N6O8.2H2O, it was possible to solve the structure from this starting point, by a series of SFLS refinements with an increasingly larger number of reflexions at successive stages. The packing analysis succeeded, even though the water molecules were not included to start with.

An algebraic approach to the restoration of images

Two different matrix algorithms are described for the restoration of blurred pictures. These are illustrated by numerical examples.

Application of ab initio molecular orbital calculations to the structural moieties of carbohydrates. 3

Ab initio RHF/4-31G level molecular orbital calculations have been carried out on dimethoxymethane as a model compound for the acetal moiety in methyl pyranosides. The calculations are consistent with the predictions of the anomeric effect and the exo-anomeric effect. They reproduce very successfully the differences in molecular geometry observed by x-ray and neutron diffraction of single crystals of the methyl cy-D- and methyl 0-D-pyranosides. Calculations carried out at the 6-3 1G* level for methanediol confirm the earlier calculations at the 4-31G level, with smaller energy differences between the four staggered conformations.

Ultraspherical polynomials approach to the study of third-order non-linear systems

In this study, the Krylov-Bogoliubov-Mitropolskii-Popov asymptotic method is used to determine the transient response of third-order non-linear systems. Instead of averaging the non-linear functions over a cycle, they are expanded in ultraspherical polynomials and the constant term is retained. The resulting equations are solved to obtain the approximate solution. A numerical example is considered and the approximate solution is compared with the digital solution. The results show that there is good agreement between the two values.

An analytical approach to the study of a class of bi-state social interaction processes

Sufficient conditions for obtaining an equivalent linear model to classes of non-linear, bi-state, social interaction processes are derived. These parametric constraints, when satisfied, permit analytical determination of the dynamics of the non-linear process of social interaction.

An appendix to the paper "approximation of the perturbation equations of a quasi-linear hyperbolic system in the neighborhood of a bicharacteristic"

The theory of Varley and Cumberbatch [l] giving the intensity of discontinuities in the normal derivatives of the dependent variables at a wave front can be deduced from the more general results of Prasad which give the complete history of a disturbance not only at the wave front but also within a short distance behind the wave front. In what follows we omit the index M in Eq. (2.25) of Prasad [2].

Application of molecular orbital theory to the interpretation of x-ray absorption spectra of platinum complexes

X-ray LIII-absorption edges of platinum in nine octahedral complexes have been recorded using a bent crystal spectrograph. The edge features of the discontinuities have been interpreted with the help of qualitative molecular orbital diagrams. A correlation between the energy separation of the first two absorption maxima and the spectrochemical series of the ligands has been arrived at.

Application of Laplace transform technique to the solution of certain third-order non-linear systems

A number of papers have appeared on the application of operational methods and in particular the Laplace transform to problems concerning non-linear systems of one kind or other. This, however, has met with only partial success in solving a class of non-linear problems as each approach has some limitations and drawbacks. In this study the approach of Baycura has been extended to certain third-order non-linear systems subjected to non-periodic excitations, as this approximate method combines the advantages of engineering accuracy with ease of application to such problems. Under non-periodic excitations the method provides a procedure for estimating quickly the maximum response amplitude, which is important from the point of view of a designer. Limitations of such a procedure are brought out and the method is illustrated by an example taken from a physical situation.

Mapping of assembled epitopic regions of human chorionic gonadotropin reveals proximity of CTP alpha to the determinant loop beta 93-100

Three overlapping assembled epitopes of beta hCG have been mapped using MAb probes and a single step solid phase radioimmunoassay. These epitopes have been shown to be at receptor binding region comprising of the loop region beta Cys93-Cys100. Importance of disulphide bonds in maintaining integrity of these epitopes is assessed. Two MAbs (INN 58 and INN 22) interact with the beta region as well as the alpha C-terminal peptide, while the other MAb INN 24 interacts with only the beta region. Cross-reactivity pattern with beta hCG and hLH as web as the reported crystal structure of hCG substantiates the epitope identification. The results demonstrate utility of MAbs as probes in investigations on three-dimensional structure of gonadatropins.

Involvement of Synthesis and Phosphorylation of Nuclear Protein Factors That Bind to the Positivecis-Acting Element in the Transcriptional Activation of the CYP2B1/B2 Gene by Phenobarbitonein Vivo

The synthesis and phosphorylation of protein factor(s) that bind to the positivecis-acting element (−69 to −98 nt) of the CYP2B1/B2 gene have been examinedin vivoin the rat. Treatment of rats with cycloheximide, a protein synthetic inhibitor, suppresses basal as well as phenobarbitone-induced levels of CYP2B1/B2 mRNA and its run-on transcription. Under these conditions, complex formation of the nuclear extract with the positive element is also inhibited, as judged by gel shift assays. Treatment of rats with 2-aminopurine, a general protein kinase inhibitor, blocks the phenobarbitone-mediated increase in CYP2B1/B2 mRNA, cell-free transcription of a minigene construct containing the positive element, pP450e179DNA, and binding of nuclear proteins to the positive element. Treatment of rats with okadaic acid, a protein phosphatase inhibitor, mimics the effects of phenobarbitone, but only partially. Thus, both phenobarbitone and okadaic acid individually enhance binding of the nuclear protein(s) to the positive element, cell-free transcription of the minigene construct, and phosphorylation of the not, vert, similar26- and 94-kDa proteins binding to the positive element. But unlike phenobarbitone, okadaic acid is not an inducer of CYP2B1/B2 mRNA or its run-on transcription. Thus, phenobarbitone-responsive positive element interactions constitute only a minimal requirement, and okadaic acid is perhaps not able to bring about the total requirement for activation of CYP2B1/B2 gene transcription that should include interaction between the minimal promoter and further upstream elements. An intriguing feature is the antagonistic effect of okadaic acid on phenobarbitone-mediated effects on CYP2B1/B2 mRNA levels, cell-free and run-on transcription, and nuclear protein binding to the positive element. The reason for this antagonism is not clear. It is concluded that phenobarbitone treatment enhancesin vivothe synthesis and phosphorylation of protein factors binding to the positive element and these constitute a minimal requirement for the transcriptional activation of the CYP2B1/B2 gene.

Hyperexpression of chicken riboflavin carrier protein: Antibodies to the recombinant protein curtail pregnancy in rodents

Chicken riboflavin carrier protein (RCP) is a phosphoglycoprotein present in the egg white and yolk of egg-laying animals and in the sera of laying hens and of estrogenized chicks. The RCP cDNA, encoding a protein of predictedMr27,000, has been cloned into a T7 polymerase-driven vector, and high-level expression was observed on induction with IPTG inEscherichia coli.The protein was largely localized in inclusion bodies when expressed at 37°C but was present in the cytosolic fraction when induced at 22°C. At 37°C, two major bands were detected in whole-cell lysates of the strain expressing the protein. N-terminal sequence analysis indicated that the two proteins represented translated products with and without the pelB leader sequence encoded in the pET20b vector, but both included an additional 10 amino acids generated during cloning procedures. The inclusion body obtained at 37°C, on extraction with detergent, led to preferential solubilization of the protein without the pelB signal sequence. The solubilized recombinant RCP was recognized by polyclonal antisera to native RCP but radioimmunoassay revealed quantitative differences in the epitopes exhibited by the recombinant protein. Thus, sequence-specific monoclonal antibodies to chicken RCP also cross-reacted with the recombinant protein with almost equal efficiency, but antibodies which recognize conformation-dependent epitopes showed relatively reduced cross-reactivity with the recombinant protein. Polyclonal antibodies to recombinant RCP were able to recognize both the native and the denatured RCP. Administration of recombinant RCP antisera to pregnant mice led to embryonic resorption leading to early pregnancy termination. These findings reveal that the recombinant protein will be useful for investigations related to the mechanism of pregnancy termination on immunoneutralization of RCP in mammals, as well as in unraveling folding properties of RCP in terms of its ligand binding and antigenetic determinants exposed at its surface.