Photoelectric Emission from Interstellar Dust: Grain Charging and Gas Heating

We model the photoelectric emission from and charging of interstellar dust and obtain photoelectric gas heating efficiencies as a function of grain size and the relevant ambient conditions. Using realistic grain size distributions, we evaluate the net gas heating rate for various interstellar environments, and find less heating for dense regions characterized by R_V=5.5 than for diffuse regions with R_V=3.1. We provide fitting functions which reproduce our numerical results for photoelectric heating and recombination cooling for a wide range of interstellar conditions. In a separate paper we will examine the implications of these results for the thermal structure of the interstellar medium. Finally, we investigate the potential importance of photoelectric heating in H II regions, including the warm ionized medium. We find that photoelectric heating could be comparable to or exceed heating due to photoionization of H for high ratios of the radiation intensity to the gas density. We also find that photoelectric heating by dust can account for the observed variation of temperature with distance from the galactic midplane in the warm ionized medium.Comment: 50 pages, including 18 figures; corrected title and abstract field

Study of polytopic membrane protein topological organization as a function of membrane lipid composition.

A protocol is described using lipid mutants and thiol-specific chemical reagents to study lipid-dependent and host-specific membrane protein topogenesis by the substituted-cysteine accessibility method as applied to transmembrane domains (SCAM). SCAM is adapted to follow changes in membrane protein topology as a function of changes in membrane lipid composition. The strategy described can be adapted to any membrane system

Switching Transport through Nanopores with pH-Responsive Polymer Brushes for Controlled Ion Permeability

Several nanoporous platforms were functionalized with pH-responsive poly(methacrylic acid) (PMAA) brushes using surface-initiated atom transfer radical polymerization (SI-ATRP). The growth of the PMAA brush and its pH-responsive behavior from the nanoporous platforms were confirmed by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). The swelling behavior of the pH-responsive PMAA brushes grafted only from the nanopore walls was investigated by AFM in aqueous liquid environment with pH values of 4 and 8. AFM images displayed open nanopores at pH 4 and closed ones at pH 8, which rationalizes their use as gating platforms. Ion conductivity across the nanopores was investigated with current–voltage measurements at various pH values. Enhanced higher resistance across the nanopores was observed in a neutral polymer brush state (lower pH values) and lower resistance when the brush was charged (higher pH values). By adding a fluorescent dye in an environment of pH 4 or pH 8 at one side of the PMAA-brush functionalized nanopore array chips, diffusion across the nanopores was followed. These experiments displayed faster diffusion rates of the fluorescent molecules at pH 4 (PMAA neutral state, open pores) and slower diffusion at pH 8 (PMAA charged state, closed pores) showing the potential of this technology toward nanoscale valve applications

Anti-inflammatory agents and monoHER protect against DOX-induced cardiotoxicity and accumulation of CML in mice

Cardiac damage is the major limiting factor for the clinical use of doxorubicin (DOX). Preclinical studies indicate that inflammatory effects may be involved in DOX-induced cardiotoxicity. Nɛ-(carboxymethyl) lysine (CML) is suggested to be generated subsequent to oxidative stress, including inflammation. Therefore, the aim of this study was to investigate whether CML increased in the heart after DOX and whether anti-inflammatory agents reduced this effect in addition to their possible protection on DOX-induced cardiotoxicity. These effects were compared with those of the potential cardioprotector 7-monohydroxyethylrutoside (monoHER)

Wear, friction and sliding speed correlations on Langmuir-Blodgett-films observed by atomic force microscopy

The dependence of friction and wear on sliding parameters has been investigated with an atomic force microscope. Measurements have been performed on Langmuir-Blodgett monolayers. For the purpose of this study a special counterion polymer has been used to supply a facile insight into the friction and wear dependence on the scan velocity. With a minimum constant load in the order of 10(-8) N, wear has been observed to occur randomly at film defect sites but also on initially intact film areas. Wear is always accompanied by an increase of friction forces. A wearless friction dependence on the scan velocity could not be observed. The process of wear is discussed in terms of shear forces and adhesive contact forces. Whereas the plastic deformation at the film defect sites can be explained by shear forces, the wear process on initially defect free surfaces could be related to adhesive forces and quantified

Force Microscopy Study of Friction and Elastic Compliance of Phase-Separated Organic Thin Films

A correlation between friction and elasticity is drawn from measurements on organic thin films with a modified scanning force microscope (SFM). Local elastic compliance has been measured simultaneously with both topography and friction on the submicrometer scale on thin films of phase-separated mixtures of fluorocarbons and hydrocarbons. On the fluorocarbon domains, higher friction and lower Young`s modulus than on the hydrocarbon domains have been found. Variations in pH during sample preparation lead to differences in film formation, detected with the SFM as changes in topography, elasticity, and friction. On increasing pH, both the Young`s modulus and friction force are found to decrease. This unexpected result is discussed in terms of film formation and cohesive energy mechanisms