Methodology for determining of the main characteristics of a refrigeration system with condensation heat removal by radiative cooling

To reduce the condensation pressure of the refrigerant in the summer, refrigeration system has been developed, in which, during periods of high air temperature, the heat of condensation is removed to the coolant, which was pre-cooled at night due to radiative cooling. A methodology has been developed for determining the main characteristics of the elements of the proposed system and calculating its daily energy consumption. The calculation shows that the proposed system with a nominal refrigerating capacity of 10 kW, using the R404a refrigerant, allows in the climate of the city of Shymkent to reduce the condensation temperature to +32.9°C, and daily energy consumption by 6.5% compared to an ordinary vapor compression refrigeration machine

Thermal Diffusion of a Two Layer System

In this paper thermal conductivity and thermal diffusivity of a two layer system is examined from the theoretical point of view. We use the one dimensional heat diffusion equation with the appropriate solution in each layer and boundary conditions at the interfaces to calculate the heat transport in this bounded system. We also consider the heat flux at the surface of the samle as boundary condition instead of using a fixed tempertaure. From this, we obtain an expression for the efective thermal diffusivity of the composite sample in terms of the thermal diffusivity of its constituent materials whithout any approximations.Comment: 16 pages, 1 figure, RevTeX v. 3.0 macro packag

Individual rules for trail pattern formation in Argentine ants (Linepithema humile)

We studied the formation of trail patterns by Argentine ants exploring an empty arena. Using a novel imaging and analysis technique we estimated pheromone concentrations at all spatial positions in the experimental arena and at different times. Then we derived the response function of individual ants to pheromone concentrations by looking at correlations between concentrations and changes in speed or direction of the ants. Ants were found to turn in response to local pheromone concentrations, while their speed was largely unaffected by these concentrations. Ants did not integrate pheromone concentrations over time, with the concentration of pheromone in a 1 cm radius in front of the ant determining the turning angle. The response to pheromone was found to follow a Weber's Law, such that the difference between quantities of pheromone on the two sides of the ant divided by their sum determines the magnitude of the turning angle. This proportional response is in apparent contradiction with the well-established non-linear choice function used in the literature to model the results of binary bridge experiments in ant colonies (Deneubourg et al. 1990). However, agent based simulations implementing the Weber's Law response function led to the formation of trails and reproduced results reported in the literature. We show analytically that a sigmoidal response, analogous to that in the classical Deneubourg model for collective decision making, can be derived from the individual Weber-type response to pheromone concentrations that we have established in our experiments when directional noise around the preferred direction of movement of the ants is assumed.Comment: final version, 9 figures, submitted to Plos Computational Biology (accepted

Effects of Crystal Structure and the On-Site Coulomb Interactions on the Electronic and Magnetic Structure of Pyrochlores A2A_2Mo2_2O7_7 (A= Y, Gd, and Nd)

Being motivated by recent experimental studies, we investigate magnetic structures of the Mo pyrochlores $A_2$Mo$_2$O$_7$ ($A$= Y, Nd, and Gd) and their impact on the electronic properties. The latter are closely related with the behavior of twelve Mo($t_{2g}$) bands, located near the Fermi level and well separated from the rest of the spectrum. We use a mean-field Hartree-Fock approach, which combines fine details of the electronic structure for these bands, extracted from the conventional calculations in the local-density approximation, the spin-orbit interaction, and the on-site Coulomb interactions amongst the Mo(4d) electrons, treated in the most general rotationally invariant form. The Coulomb repulsion U plays a very important role in the problem, and the semi-empirical value U$\sim$1.5-2.5 eV accounts simultaneously for the metal-insulator (M-I) transition, the ferromagnetic (FM) - spin-glass (SG) transition, and for the observed enhancement of the anomalous Hall effect (AHE). The M-I transition is mainly controlled by $U$. The magnetic structure at the metallic side is nearly collinear FM, due to the double exchange mechanism. The transition into the insulating state is accompanied by the large canting of spin and orbital magnetic moments. The sign of exchange interactions in the insulating state is controlled by the Mo-Mo distances. Smaller distances favor the antiferromagnetic coupling, which preludes the SG behavior in the frustrated pyrochlore lattice. Large AHE is expected in the nearly collinear FM state, near the point of M-I transition, and is related with the unquenched orbital magnetization at the Mo sites. We also predict large magneto-optical effect in the same FM compounds.Comment: 26 pages, 17 figures (low resolution is used for Figs. 6, 8, and 9, please contact directly if you need the originals), 1 tabl

Dynamic running test results of diesel train 630m of production А.S. PESA (Poland)

Purpose. Experimental definition of values of the dynamic parameters characterizing traffic safety of the rail autobus in tangent and curved track sections and switches, and conformity check to their demands of normative documents. Methodology. Test methods are based on comparison of experimentally determined dynamic qualities of the autobus with their admitted values. As the parameters defining traffic safety, the numerical value of which is resulted further, are used the following ones: the derailment stability coefficient; vertical dynamics coefficients in the first and second steps of spring suspension; the frame forces; smoothness of movement. Determination of the derailment stability coefficient is performed by a known technique. Vertical dynamics coefficients in the each step of spring suspension are defined as the relation of dynamic vertical bending flexures to magnitudes of their static values corresponding to the set occupancy of the autobus. Findings. Coefficient values of the vertical dynamics of train carriages in the first and second steps of spring suspension, as well as the value of frame forces and parameters of movement smoothness did not exceed the admissible standard values, and was higher than the minimum admissible value. Originality. Values of the parameters characterizing dynamic qualities of new type of the rail autobus are obtained, and possibility of its operation on the main ways of the railways of Ukraine is shown. Practical value. Admissible speeds of the rail autobus traffic on various railway track sections are defined