Binding Reactions at Finite Systems

A perpetual yearn exists among computational scientists to scale-down the size of physical systems, a desire shared as well with experimentalists able to track single molecules. A question then arises whether averages observed at small systems are the same as those observed at large, or macroscopic, systems. Utilizing statistical-mechanics formulations in ensembles in which the total numbers of particles are fixed, we demonstrate that system's properties of binding reactions are not homogeneous functions. That means averages of intensive properties, such as the concentration of the bound-state, at finite-systems are different than those at large-systems. The discrepancy increases with decreasing numbers of particles, temperature, and volume. As perplexing as it may sound, despite these variations in average quantities, extracting the equilibrium constant from systems of different sizes does yield the same value. The reason is that correlations in reactants' concentrations are ought be accounted for in the expression of the equilibrium constant, being negligible at large-scale but significant at small-scale. Similar arguments pertain to the calculations of the reaction rate-constants, more specifically, the bimolecular rate of the forward reaction is related to the average of the product (and not to the product of the averages) of the reactants' concentrations. Furthermore, we derive relations aiming to predict the composition of the system only from the value of the equilibrium constant. All predictions are validated by Monte-Carlo and molecular dynamics simulations. An important significance of these findings is that the expression of the equilibrium constant at finite systems is not dictated solely by the chemical equation but requires knowledge of the elementary processes involved.

Nanosecond breakdown in a pulsed open discharge

The paper presents the results of studies of open discharge breakdown characteristics at nanosecond supply pulse in helium, neon, argon working medium in a wide pressure range. It is shown that the open discharge exists in the range of p He = 20–100 Torr, pNe = 1.5–25 Torr, p Ar = 0.5–3.7 Torr with used experimental conditions. With increasing pressure, the role of separate elementary processes increases which can lead to a change of the discharge form to a presumably avalanche or streamer discharge. However, in this case, due to the photoemissive nature of the open discharge initiation, the similarity law Ep = f(pι) does not coincide with that for a nanosecond avalanche discharge.

Energy Consumption Evaluation of Active Tillage Machines Using Dynamic Modelling

Soil tillage is a very energy-intensive operation. A general expectation is to reduce energy consumption and reduce soil compaction with as few turns and interventions as possible. Thus, more and more attention is being paid to the use of active tillage machines. The aim of the present work is to test a new approach to optimize PTO-driven tilling machine operations regarding energy consumption. A real, active tillage machine, the MSS-140 type spading machine, was investigated in the Matlab® Simscape™ environment. The solid model of the spading machine was built using actual dimensions. The work done by a single spade is broken down into elementary processes. The acting forces on the implement, in each elementary process for different advancing speeds, were modelled and calculated. The model is suitable for illustrating the dynamics of loads and for calculating the mechanical work. The model was also tested in comparison with real fuel consumption. The consumed fuel quantity was measured and the energy requirement for the model calculated at three advancing speeds. A comparison between the measured and calculated energy consumption values was made: the calculated results are similar to the measured values; the mean difference is 9.91%, with a standard deviation 3.3%.

PLASMA NEW SELECTIVE PROPERTIES FOR EFFICIENT USE IN ELECTRONICS AND TELECOMMUNICATIONS

In terms of active and passive electronic counteraction, detection of geophysical phenomena of artificial andnatural origin is becoming increasingly important. Discovering new properties of plasma enables to improve the informationcomponent of radio signals more effectively and use the obtained properties in related fields. Elementary processes in thelongitudinal and transverse directions of the discharge, depending on natural and artificial conditions, under different typesof gaseous medium used; at different gas pressures and different pulse-periodic application of an electric field is studied inthe article. The difference of discharge properties in inert and molecular gases with different designs and electrodes of thelaboratory device is shown. It is established that the change of functional purpose between the cathodes and the anodes doesnot change the shape of the discharge. The presence of ambipolar diffusion of charge carriers acting on a large area of plasmawas determined. Partial charge carrier homogeneity has been established, which is observed only along the plasma surface,and homogeneity is violated in the perpendicular direction. The difference in energy input in the discharge, depending on thedesign of the electrodes other things being equal is determined. The identified properties of plasma enable them to be usedmore effectively for practical implementation in the field of electronics and telecommunications and other industries.

Focal seizures are organized by feedback between neural activity and ion concentration changes

Human and animal EEG data demonstrate that focal seizures start with low-voltage fast activity, evolve into rhythmic burst discharges and are followed by a period of suppressed background activity. This suggests that processes with dynamics in the range of tens of seconds govern focal seizure evolution. We investigate the processes associated with seizure dynamics by complementing the Hodgkin-Huxley mathematical model with the physical laws that dictate ion movement and maintain ionic gradients. We show that the disturbance of K+and Cl−homeostasis by the fast discharge of inhibitory interneurons is sufficient to initiate seizures, which are maintained by positive feedback between ion concentration changes and neuronal activity. Gradual Na+accumulation increases the rate of the Na+/K+-pump, creating negative feedback which slows down and terminates ictal discharges and contributes to the postictal state. Our results emphasize ionic dynamics as elementary processes behind seizure generation and indicate targets for new therapeutic strategies.