Ion exchange properties of some new chelating resins from cresol urea formaldehyde

Terpolymers resins( o,m,p –C UF) synthesized by the condensation of o,m,p- Cresol and Urea with Formaldehyde in the presence of acid catalyst , FTIR- spectroscopy and thermogravimetric analysis were used to characterize the terpolymers. Chelating ion exchange properties of these polymers were studied for Fe 2+ , Cu 2+ and Zn 2+ ions. A batch equilibrium method was employed in the study of the selectivity of metal ion uptake . the study was carried out over a wide pH range and shaking time.The OUF and PUF terpolymers showed highest selectivity for ions being studied

Ion exchange properties of some new chelating resins from cresol urea formaldehyde

Terpolymers resins( o,m,

Methods for Temporal Analysis

The authors review sociological literature describing different perspectives and uses of studies of change in discrete (qualitative) and quantitative outcomes. They show that, contrary to many injunctions, temporal analysis is not always superior to cross-sectional analysis for studying change, particularly for two-wave panel measures. The main factor is whether confounding influences vary more over time than over measured outcomes. Modeling change processes and event history methods use more of the data and provide a better picture of change using temporal data

Organizational Mortality of Small Firms: The Effects of Entrepreneurial Age and Human Capital

This paper addresses the issue of internal determination of organizational outcomes. It is argued that in small and simply structured organizations a considerable proportion of the variance in organizational activities and outcomes is associated with individuals. In particular, the paper uses human capital theory to derive hypotheses about individual determinants of organizational mortality. These hypotheses are tested with event-history data of firm registrations and de-registrations in a West German region. The hypotheses are corroborated by the data, but the effects may nonetheless be due to processes linking individual characteristics with organizational performance other than those suggested by the human capital approach

Quality of Maximum Likelihood Estimates of Parameters in a Log-Linear Rate Model

The authors address four sources of indeterminacy in maximum likelihood estimation (MLE) for multivariate modeling of change using panel data: censoring, caused by changes that occur after the observation period ends; small sample size; interacting censoring with sample size; and collinearity among causal variables. They explore the issues with simulations and conclude that MLE estimates are generally efficient except when censoring is extreme, and efficiency is only slightly affected by collinearity among independent variables. Related publications include Tuma and Hannan (1979) and Tuma, Hannan, and Groeneveld (1979)

Crystal-clear neuronal computing

Induced progressive crystallization in chalcogenide-based materials can be used to closely mimic neuronal functions, opening new paths to neuromorphic computing

Alternative Estimation Procedures for Event-History Analysis: A Monte Carlo Study

The authors compare alternative procedures for estimating parameters of event-history models: ordinary least squares, Kaplan-Meier least squares, maximum likelihood, and partial likelihood. They report results of simulations comparing maximum likelihood and partial likelihood estimators for small samples in terms of several potential sources of error. A related paper is Tuma, Hannan, and Groeneveld (1979)

Dynamic coupling of fast channel gating with slow ATP-turnover underpins protein transport through the Sec translocon.

The Sec translocon is a highly conserved membrane assembly for polypeptide transport across, or into, lipid bilayers. In bacteria, secretion through the core channel complex-SecYEG in the inner membrane-is powered by the cytosolic ATPase SecA. Here, we use single-molecule fluorescence to interrogate the conformational state of SecYEG throughout the ATP hydrolysis cycle of SecA. We show that the SecYEG channel fluctuations between open and closed states are much faster (~20-fold during translocation) than ATP turnover, and that the nucleotide status of SecA modulates the rates of opening and closure. The SecY variant PrlA4, which exhibits faster transport but unaffected ATPase rates, increases the dwell time in the open state, facilitating pre-protein diffusion through the pore and thereby enhancing translocation efficiency. Thus, rapid SecYEG channel dynamics are allosterically coupled to SecA via modulation of the energy landscape, and play an integral part in protein transport. Loose coupling of ATP-turnover by SecA to the dynamic properties of SecYEG is compatible with a Brownian-rachet mechanism of translocation, rather than strict nucleotide-dependent interconversion between different static states of a power stroke

pH-induced molecular shedding drives the formation of amyloid fibril-derived oligomers

Amyloid disorders cause debilitating illnesses through the formation of toxic protein aggregates. The mechanisms of amyloid toxicity and the nature of species responsible for mediating cellular dysfunction remain unclear. Here, using β2-microglobulin (β2m) as a model system, we show that the disruption of membranes by amyloid fibrils is caused by the molecular shedding of membrane-active oligomers in a process that is dependent on pH. Using thioflavin T (ThT) fluorescence, NMR, EM and fluorescence correlation spectroscopy (FCS), we show that fibril disassembly at pH 6.4 results in the formation of nonnative spherical oligomers that disrupt synthetic membranes. By contrast, fibril dissociation at pH 7.4 results in the formation of nontoxic, native monomers. Chemical cross-linking or interaction with hsp70 increases the kinetic stability of fibrils and decreases their capacity to cause membrane disruption and cellular dysfunction. The results demonstrate how pH can modulate the deleterious effects of preformed amyloid aggregates and suggest why endocytic trafficking through acidic compartments may be a key factor in amyloid disease