"Cylindrical worlds" in biology: Does the aggregation strategy give a selective advantage?

Tree trunks and other cylindrical objects, where aggregated insects live, represent a very specific world for predator-prey interactions, which must differ from the situation on a 2D plane. In the present paper, in order to gain a better understanding of the specificity of predator-prey interaction in a cylindrical space, we applied a theoretical approach. Here we introduce a numerical model that allows us to test the effect of different interaction properties between predator and aggregated prey on the plane (2D) and on a cylinder (3D), taking into consideration different abilities of predators to visually detect the prey in these two types of space. The main aim was to test these interactions in an environment, which more realistically reproduces the conditions where aggregated insects usually live. We showed that the aggregation in conjunction with a specific environment may bring additional advantages for the prey. When one prey subgroup aggregates on the other side of the tree trunk and becomes invisible behind the horizon of events for the predator, the subgroup will survive with an extremely high probability. After all, the predator moving along one side of the tree will finally loose the major group completely.

Numerical simulation of the pattern formation of the springtail cuticle nanostructures.

Springtails (Collembola) are known to exhibit complex hierarchical nanostructures of their exoskeleton surface that repels water and other fluids with remarkable efficiency. These nanostructures were previously widely studied due to their structure, chemistry and fluid-repelling properties. These ultrastructural and chemical studies revealed the involvement of different components in different parts of the nanopattern, but the overall process of self-assembly into the complex rather regular structures observed remains unclear. Here, we model this process from a theoretical point of view partially using solutions related to the so-called Tammes problem. By using densities of three different reacting substances, we obtained a typical morphology that is highly similar to the ones observed on the cuticle of some springtail species. These results are important not only for our understanding of the formation of hierarchical nanoscale structures in nature, but also for the fabrication of novel surface coatings.

Effects of molecule anchoring and dispersion on nanoscopic friction under electrochemical control.

The application of electric fields is a promising strategy for in situ control of friction. While there have recently been many experimental studies on friction under the influence of electric fields, theoretical understanding is very limited. Recently, we introduced a simple theoretical model for friction under electrochemical conditions that focused on the interaction of a force microscope tip with adsorbed molecules whose orientation was dependent on the applied electric field. Here we focus on the effects of anchoring of the molecules on friction. We show that anchoring affects the intensity and width of the peak in the friction that occurs near a reorientation transition of adsorbed molecules, and explain this by comparing the strength of molecule-molecule and molecule-tip interactions. We derive a dispersion relation for phonons in the layer of adsorbed molecules and demonstrate that it can be used to understand important features of the frictional response.

[Thiotriazoline in the Treatment of Stable Angina Pectoris of II-III Functional Class].

Trimetazidine is a metabolic agent of proven efficacy in improving myocardial ischemia and angina. A comparative international multicenter randomized trial, assessed anti-anginal anti ischemic efficacy and safety of Trimetazidine (60 mg/d) and Thiotriazoline (600 mg/d) in symptomatic patients with chronic ischemic heart disease receiving the first line therapy. The study assessed the efficacy of the two drugs on total exercise duration, time to 1-mm ST segment depression, the number of angina attacks and nitroglycerin tablets consumed amount. Both drugs have demonstrated clinical efficacy equal for all primary and secondary endpoints.

[Thiotriazoline in the Treatment of Stable Angina IIIII Functional Class].

Trimetazidine is a metabolic agent of proven efficacy in improving myocardial ischemia and angina. A comparative international multicenter randomized trial, assessed anti-anginal anti ischemic efficacy and safety of Trimetazidine (60 mg/d) and Thiotriazoline (600 mg/d) in symptomatic patients with chronic ischemic heart disease receiving the first line therapy. The study assessed the efficacy of the two drugs on total exercise duration, time to 1-mm ST segment depression, the number of angina attacks and nitroglycerin tablets consumed amount. Both drugs have demonstrated clinical efficacy equal for all primary and secondary endpoints.

Nanoscopic friction under electrochemical control.

We propose a theoretical model of friction under electrochemical conditions focusing on the interaction of a force microscope tip with adsorbed polar molecules whose orientation depends on the applied electric field. We demonstrate that the dependence of friction force on the electric field is determined by the interplay of two channels of energy dissipation: (i) the rotation of dipoles and (ii) slips of the tip over potential barriers. We suggest a promising strategy to achieve a strong dependence of nanoscopic friction on the external field based on the competition between long-range electrostatic interactions and short-range chemical interactions between tip and adsorbed polar molecules.

Friction between a viscoelastic body and a rigid surface with random self-affine roughness.

In this Letter, we study the friction between a one-dimensional elastomer and a one-dimensional rigid body having a randomly rough surface. The elastomer is modeled as a simple Kelvin body and the surface as self-affine fractal having a Hurst exponent H in the range from 0 to 1. The resulting frictional force as a function of velocity always shows a typical structure: it first increases linearly, achieves a plateau and finally drops to another constant level. The coefficient of friction on the plateau depends only weakly on the normal force. At lower velocities, the coefficient of friction depends on two dimensionless combinations of normal force, sliding velocity, shear modulus, viscosity, rms roughness, rms surface gradient, the linear size of the system, and the Hurst exponent. We discuss the physical nature of different regions of the law of friction and suggest an analytical relation describing the coefficient of friction in a wide range of loading conditions. An important implication of the analytical result is the extension of the well-known "master curve procedure" to the dependencies on the normal force and the size of the system.

[Bubbles induced fluctuations of some properties of aqueous solutions].

A mathematical model of the air diffusion process through the water surface, taking into account the reverse flow of bubbles was proposed. The numerical solving gives self-oscillation of the dissolved air concentration. Spectral density of these oscillations has the 1/f-noise form, which explains the fluctuating nature of the observed properties of water and biological effects, which depend on the amount of dissolved air. A mechanism of spontaneous water luminescence observed after laser irradiation was suggested. The calculated luminescence self-oscillations have the form of a fractal with an infinite sequence of periods, which evolve in time and that is qualitatively consistent with the experiment.

[The influence of ezetimibe and simvaststin on platelet aggregation and protein c system in patients with coronary heart disease and hypercholesterolemia].

Therapy with ezetimib (10 mg daily for 2 weeks) caused a 24% reduction of plasma LDL cholesterol level (p < 0.05) and maximum ADP and collagen-induced platelet aggregation from 76.2 +/- 1.54 to 65.3 +/- 3.38% and from 71.5 +/- 3.98 to 53.6 +/- 5.24% (p < 0.05) respectively. Combination of ezetimibe and simvaststin did not produce an additional decrease in platelet aggregation.

[Endothelial dysfunction on initial stages of arterial hypertension among men of young age and it's connection with vascular risk factors].

Frequency of display endothelial dysfunction, arising on the initial stages of development arterial hypertension is investigated, depending on vascular risk factors. The main group was made by 86 men with arterial hypertension I-II stage, group of the control--practically healthy 50 men. Vasomotor endothelial function defined on a degree of vasodilatation a humeral artery in reply to reactive hyperemia. Damage signs of endothelial monolayer estimated by quantity of free circulating endothelial blue blood cells. It is established, that the simultaneous combination of functional or structural vascular infringements among persons with normal blood pressure was registered in 3 times less often in comparison to patients with an arterial hypertension (p<0,01). At the main group at a simultaneous combination inadequate vasodilatation and endotheliaemia occurrence risk factors in 1,5 times is higher, than at their isolated display (p>0,05).

Directed molecular transport in an oscillating channel with randomness.

Stability of directed transport and molecular separation in a symmetric channel is analyzed. The original mechanism is based on harmonic spatial oscillations of the channel, under which the system exhibits multiple regimes of a directed transport. The particles may be forced to move with different velocities and directions as the amplitude and/or frequency of the oscillations are adjusted to a proper resonance. The advantage of this mechanism in contrast to the ratchet systems is that the average particle velocity is larger than the velocity of the growing of the width of the particle spatial distribution. We have studied the stability of the directed transport with regard to random impacts to the channel parameters and oscillation frequency. Here we present the results of the simulations which show that the ability of the combined longitudinally and transversally vibrating randomized dynamic channel to perform directed molecular transport remains resilient to quite intensive random channel structure fluctuations (50-60%) and relatively strong random impacts to its oscillations (15-20%).

Reconstruction of potential from dynamic experiments.

In experimental studies of a surface by an underdamped mechanical surface force probe the "tip" can return repeatedly to the same points in space. This causes a problem in using the experimental data to extract information about the surface structure. We propose an approach which allows one to extract the mesoscopic surface structure from dynamic experiments with underdamped systems. The approach was tested on numerically generated random fractal potentials and is applied to extract potential relief from real experimental data.

Fractal Tomlinson model for mesoscopic friction: from microscopic velocity-dependent damping to macroscopic Coulomb friction.

A modified Tomlinson equation with fractal potential is studied. The effective potential is numerically generated and its mesoscopic structure is gradually adjusted to different scales by a number of Fourier modes. It is shown that with the change of scale the intensity of velocity-dependent damping in an effective Langevin equation can be gradually substituted by an equivalent constant "dry friction." For smooth macrosopic surfaces the effective equation completely reduces to the well known Coulomb law.

[Endothelial dysfunction and risk factors in coronary heart disease].

The subjects of the study were 64 patients with coronary heart disease, and 38 healthy individuals. In order to evaluate the degree of endothelial dysfunction (ED) reactive hyperemia test was performed; the degree of the relative increase of the brachial artery diameter, and the level of desquamated endothelial cells circulating in blood (CEC) were used as criteria of this dysfunction. Only in 6.5% of the controls signs of ED (endothelium-dependent vasodilatation (EDVD) less than 10% and the number of CEC being greater than 5 in the field of vision) was noted. In group II the signs of ED were registered in 40% of patients, in group III--in 59% of patients (p < 0.05). In patients with no standard risk factors or with only one of them, both tests revealed no signs of ED, while the presence of 4 or more risk factors lead to a 6-fold increase of the relative frequency of ED.

Tuning diffusion and friction in microscopic contacts by mechanical excitations.

We demonstrate that lateral vibrations of a substrate can dramatically increase surface diffusivity and mobility and reduce friction at the nanoscale. Dilatancy is shown to play an essential role in the dynamics of a nanometer-size tip which interacts with a vibrating surface. We find an abrupt dilatancy transition from the state with a small tip-surface separation to the state with a large separation as the vibration frequency increases. Atomic force microscopy experiments are suggested which can test the predicted effects.

[Effect of respiratory infections on the clinical course of coronary artery disease].

The subjects of the study were 64 patients with coronary artery disease (CAD), and 38 healthy controls. The study included determination of Chlamydia pneumonia (CLPN), Toxoplasma gondii (TG), Herpes simplex virus (HSV) 1, 2, Epstein-Barr virus (EBV), and antibodies to these microorganisms. Diagnostically significant elevation of the serum levels of IgG antibodies to CLPN, HSV 1, 2, or TG was associated with CAD progression, and seropositivity to several of the agents strongly correlated with CAD progression. Moreover, the risk of future coronary events increased depending on the level of total pathogen burden. These results suggest that intracellular infectious agents are involved in the development of atherosclerosis and CAD.

Actin-based motility: cooperative symmetry-breaking and phases of motion.

A microscopic model is proposed for the motility of a bead driven by the polymerization of actin filaments. The model exhibits a rich spectrum of behaviours similar to those observed in biomimetic experiments, which include spontaneous symmetry-breaking, various regimes of the bead's motion and correlations between the structure of the actin tail which propels the bead and the bead dynamics. The dependences of the dynamical properties (such as symmetry-breaking time, regimes of motion, mean velocity, and tail asymmetry) on the physical parameters (the bead radius and viscosity) agree well with the experimental observations. We find that most experimental observations can be reproduced taking into account only one type of filaments interacting with the bead: the detached filaments that push the bead. Our calculations suggest that the analysis of mean characteristics only (velocities, symmetry-breaking times, etc) does not always provide meaningful information about the mechanism of motility. The aim should be to obtain the corresponding distributions, which might be extremely broad and therefore not well represented by their mean only. Our findings suggest a simple coarse-grained description, which captures the main features obtained within the microscopic model.

Friction through dynamical formation and rupture of molecular bonds.

We introduce a model for friction in a system of two rigid plates connected by bonds (springs) and experiencing an external drive. The macroscopic frictional properties of the system are shown to be directly related to the rupture and formation dynamics of the microscopic bonds. Different regimes of motion are characterized by different rates of rupture and formation relative to the driving velocity. In particular, the stick-slip regime is shown to correspond to a cooperative rupture of the bonds. Moreover, the notion of static friction is shown to be dependent on the experimental conditions and time scales. The overall behavior can be described in terms of two Deborah numbers.