Droplet-like heterogeneity of aqueous tetrahydrofuran solutions at the submicrometer scale.

A droplet formation in aqueous solutions of tetrahydrofuran (THF) has been experimentally detected at the submicrometer scale using two independent laser diagnostic techniques (dynamic light scattering and laser phase microscopy) and described in terms of THF-water intermolecular hydrogen bonding. It is shown that the nanodroplets have a mean size of 300 nm, their refractive index is higher than that of the ambient liquid, and they are highly enriched with THF molecules. The maximum of light scattering intensity falls within the THF concentration range 2-8 mol. %, which corresponds to the volume number density of the nanodroplets ∼1010-1011 cm-3. A theoretical explanation of forming the nanodroplets with a high content of THF, which is based on a model of dichotomous noise being applied to the so-termed "twinkling" hydrogen bonds and involves spinodal decomposition in the unstable region enclosed within the dichotomous binodal, is proposed. The parameters of hydrogen bonds in the molecular system "water-THF" were found, and the phase diagram of the solution with allowance for cross-linking hydrogen bonds was constructed.

[Electroimpedance Methods of Investigation of Cardiac Activity].

AIM: of the present work was assessment of possibility to use modern electroimpedace methods for the study of activity of the heart. Electroimpemdace methods of measurement for many years remained in the shadow of other diagnostic methods because of low accuracy in evaluation of various parameters. At present, there are technologies of measurement which allow to carry out electroimpedance investigations of cardiac activity dynamically and with acceptable accuracy. In this article, we present methods of electroimpedace measurements created in Institute of Biomedical Equipment of N.E. Bauman Technical University. These methods allow to assess dynamics of movement of ventricles of the heart, to evaluate volume parameters of cardiac activity and all temporal phases of activity of cardiac chambers. We also present data of studies on healthy volunteers and patients of cardiological profile. It has been shown that patients with atrial fibrillation have substantially increased duration of electrical and mechanical activity of atria and ventricles as well as lowed ejection fraction compared with other participants of experiments.

[Modeling of steady-state and relaxation elastic properties of the papillary muscle at rest].

The biomechanical modeling of a papillary muscle preparation as an adequate object for studying the properties of the myocardial tissue under uniaxial stretching has been performed. The steady-state and relaxation tests of the papillary muscle of laboratory animals (rabbit and rat) have been conducted in normal conditions and after the maceration of intracellular structures with high ionic strength solution. It has been shown that the main contribution to the viscoelastic properties in the initial range of physiological deformations is made by the connective tissue skeleton, whereas under large physiological deformations, by intracellular structures.

[Viscoelastic properties of isolated papillary muscle: contributions of connective tissue skeleton and intracellular matrix].

Peculiarities of viscoelastic behavior of rabbit papillary muscle in passive state are studied by transversal versus longitudinal deformation curves, stress-strain and hysteresis curves, and stress relaxation curves under ramp stretching. The papillary muscle was chosen because of mostly longitudinal orientation of fibers and its elongated shape, which both make it as an appropriate model for uniaxial tests. The problem of evaluation of connective tissue protein structures and intracellular matrix contribution into the properties under consideration is solved by using the maceration method to remove intracellular structures. The different contribution of intracellular and extracellular protein features into total properties of a papillary muscle leads to nonlinearity of myocardial viscoelastic properties, such as the increase of differential elastic module and relaxation time with deformation.