Relationship of sidechain hydrophobicity and alpha-helical propensity on the stability of the single-stranded amphipathic alpha-helix

The aim of the present investigation is to determine the effect of alpha-helical propensity and sidechain hydrophobicity on the stability of amphipathic alpha-helices. Accordingly, a series of 18-residue amphipathic alpha-helical peptides has been synthesized as a model system where all 20 amino acid residues were substituted on the hydrophobic face of the amphipathic alpha-helix. In these experiments, all three parameters (sidechain hydrophobicity, alpha-helical propensity and helix stability) were measured on the same set of peptide analogues. For these peptide analogues that differ by only one amino acid residue, there was a 0.96 kcal/mole difference in alpha-helical propensity between the most (Ala) and the least (Gly) alpha-helical analogue, a 12.1-minute difference between the most (Phe) and the least (Asp) retentive analogue on the reversed-phase column, and a 32.3 degrees C difference in melting temperatures between the most (Leu) and the least (Asp) stable analogue. The results show that the hydrophobicity and alpha-helical propensity of an amino acid sidechain are not correlated with each other, but each contributes to the stability of the amphipathic alpha-helix. More importantly, the combined effects of alpha-helical propensity and sidechain hydrophobicity at a ratio of about 2:1 had optimal correlation with alpha-helix stability. These results suggest that both alpha-helical propensity and sidechain hydrophobicity should be taken into consideration in the design of alpha-helical proteins with the desired stability.     

Dielectric properties of standard and modified electrical grade phenol-formaldehyde resin-paper laminates

The dielectric properties of phenol-formaldehyde cellulose laminates show four loss processes. There is a very low frequency polarization, the amplitude of which varies as an inverse function of charging voltage and which requires long charging times. This is ascribed to the formation of space charge at the resin-electrode interface. A low frequency internal process which is very dependent on absorbed moisture is ascribed to Maxwell-Wagner-Sillars interfacial polarization of the resin/wet cellulose boundary. A.c. conduction (again dependent on water absorption) is evident below about 1 MHz, and at the highest frequencies a further relaxation exists which is ascribed to dipole orientation of hydroxyl groups.

The dielectric properties are much improved by addition of small (less than 10⁻³ mol/kg) quantities of agents capable of oxidizing hydroxyl groups. In the case of the high frequency process this arises directly by reduction of hydroxyl content. However, the effect on a.c. conduction and the low frequency processes arises through a primary reduction of mositure absorption as the hydrophilic character of the resin and cellulose surface is diminished.     

Caries prevention--based on evidence? Or an act of faith?

The era of evidence-based healthcare requires that dentists' actions are supported by scientific proof of effectiveness. In this paper, evidence regarding the impact of strategies for caries prevention is derived from epidemiology and from a systematic review of research papers.     

Maximum likelihood parameter estimation of superimposed chirpsusing Monte Carlo importance sampling

We address the problem of parameter estimation of superimposed chirp signals in noise. The approach used here is a computationally modest implementation of a maximum likelihood (ML) technique. The ML technique for estimating the complex amplitudes, chirping rates, and frequencies reduces to a separable optimization problem where the chirping rates and frequencies are determined by maximizing a compressed likelihood function that is a function of only the chirping rates and frequencies. Since the compressed likelihood function is multidimensional, its maximization via a grid search is impractical. We propose a noniterative maximization of the compressed likelihood function using importance sampling. Simulation results are presented for a scenario involving closely spaced parameters for the individual signals     

External sources of individual differences? A cross-linguistic analysis of the phonetics of mothers' speech to 1-yr-old children.

Wide individual differences in early word production characterize children learning the same language, but the role of specific adult input in this interchild variability is unknown. Sampling the speech of American, French, and Swedish mothers (5 in each language group) to their 1-yr-old children, this study analyzed the distribution of consonantal categories, word length, and final consonants in running speech, content words, initial consonant of content words, and target words (adult models of words attempted by the children) as well as the children's own early words (from age 9 mo to about 18 mo). Variability is greater in child words than adult speech, and individual mother–child dyads show no evidence of specific maternal influence on the phonetics of the child's speech. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Origin of nonradiative recombination centers in AlGaInP grown by metalorganic vapor phase epitaxy

We report the first concrete evidence that oxygen causes nonradiative deep levels in (Al_x Ga_1–x)_0.5In_0.5P grown by metalorganic vapor phase epitaxy. We doped AlGaInP with O₂ and investigated the oxygen and deep level concentrations by secondary ion mass spectroscopy and isothermal capacitance transient spectroscopy. We confirmed that oxygen causes the D3 (thermal activation energy: E_T ? 1.0 e V for x = 0.7, nonradiative recombination center) and D2 (E_T ? 0.46 e V) levels, which we previously found in undoped AlGaInP. We demonstrate that the oxygen and nonradiative deep level concentrations are significantly reduced at higher growth temperatures, higher PH3 partial pressures, and substrate offset from (100) toward [011].     

A rely and guarantee method for timed CSP: a specification anddesign of a telephone exchange

A rely and guarantee method for timed communicating sequential processes (TCPSs), by which the behavior of a component belonging to a composite system is specified in terms of what it guarantees to its neighbors and what it relies on from them, is described. The method is illustrated using an overview of the specification of a plain old telephone service together with part of a design that provably satisfies this specification. The specification and design deal with safety, liveness, and troublesome race conditions     

Confirmation of Rb gene defects in B-CLL clones and evidence for variable predominance of the Rb defective cells within the CLL clone

In 70 B-CLL patients, deletion or translocation, at or near the retinoblastoma (Rb) site, was detected in 20 by cytogenetic analysis. Purified B cell clones from 13 of these B-CLL patients were isolated and studied for Rb gene status, Rb mRNA and the Rb protein product. Southern blot analysis of the Rb site detected internal deletions (N = 1) or a single allele loss (N = 2) in five patients. Northern blots detected reduced Rb mRNA in four patients. Immunoblot of whole cell lysate revealed reduced levels of unphosphorylated Rb protein in six CLL patients. No CLL B cell clone contained phosphorylated Rb species. These molecular studies have confirmed the cytogenetic alteration of 13q12-14 sites in B-CLL cells. In addition, cytogenetic and molecular biologic analysis suggest heterogeneity in the B cell clone for Rb gene abnormality. B-CLL patients with abnormalities in both cytogenetic and Rb DNA/RNA analysis will have a dominance of B cells with an Rb abnormality (N = 5). In patients whose Rb defective CLL cells constitute only a minor subpopulation of the total B cell clone, only cytogenetic defects would likely be detected (N = 7).     

Strategic planning of information systems at the corporate level

Strategic issues related to information systems are subject to conflicting trends. One is the more rapid change in environmental factors; the other is the growing complexity of requests that reduce the rate of response. This study examines the basis for concern about current issues. The factors are reviewed in the light of recently published material. Three organizational structures for information system planning are compared in terms of their ability to meet different organizational requirements. Techniques which have been used successfully in the definition of strategic issues and analysis of environmental factors are presented. The object is to aid the integration of information system strategies into the overall strategy of an enterprise.