Hydrogen Bonding of Carboxylic Acids in Aqueous Solutions—UV Spectroscopy, Viscosity, and Molecular Simulation of Acetic Acid

The UV spectra of aqueous acetic acid solutions up to 2M were investigated. At these wavelengths, the carboxylic acids exhibit an absorption peak, attributed to the C=O group, which shifts when hydrogen bonds are formed.. The measured spectra were best fitted to several bands, either of Gaussian or Lorentzian shape, which can be explained as several types of structural units formed by hydrogen bonds established between acetic acid and water molecules and between acetic acid molecules themselves. Molecular dynamics simulation of these mixtures was also performed, confirming the occurrence of several types of hydrogen bonds and showing the presence of dimers at higher concentrations. The viscosity and density of these solutions were also measured at different concentrations and temperatures. These results give a more complete picture of the hydrogen bond network of the system.     

A Simple 1-D Physical Model for the Crawling Nematode Sperm Cell

We develop a one-dimensional physical model of the crawling movement of simple cells: The sperm of a nematode, Ascaris suum. The model is based on the assumptions that polymerization and bundling of the cytoskeletal filaments generate the force for extension at the front, and that energy stored in the gel formed from the filament bundles is subsequently used to produce the contraction that pulls the rear of the cell forward. The model combines the mechanics of protrusion and contraction with chemical control, and shows how their coupling generates stable rapid migration, so that the cell length and velocity regulate to constant values.     

A General Solution of the Problem of Elastic-Wave Scattering by a Plane Crack

Doklady Physics - The 3D problem of elastic-wave scattering by cracks in a homogeneous isotropic medium is considered. Using the method of Green’s function and specially introduced auxiliary...