The expressions for average products of three neighboring spins in the Ising model have been found on lattices with coordination numbers 3 and 4 as functions of temperature and spontaneous ...magnetization. These expressions are used to compare the exact solution for the Ising model on a square lattice and the solutions found by approximate methods. A method of improving approximate methods is proposed for applying, in particular, to the Bethe approximation and to a change in the critical index of the temperature dependence of the spontaneous magnetization.
In this letter, the design and measurement results of a millimeter-wave beam switching antenna are presented. Several antenna prototypes have been fabricated and measured in planar and conformal ...installations. The developed prototype consists of three antenna arrays of 16 patch elements in each array and it is operating at 61 GHz with linear polarization. A single-pole three-throw semiconductor switch is attached to the manufactured prototype using copper pillar attachment. The main beam direction of the convex antenna can be changed by switching between the antenna arrays in the prototype. Half sphere 3-D radiation pattern measurements have been performed. For the convex prototype, bent on the cylinder with radius 25 mm, beam switching with -32 ° / + 34 ° degrees is achieved.
We consider the calculation of the entropy of an Ising ferromagnet with nonmagnetic impurities distributed at random over the lattice sites or bonds. The Ising magnet on the Bethe lattice is ...analyzed. On such a lattice, the situations with a random nonmagnetic dilution over the sites and bonds are indistinguishable. For calculating the entropy, the magnetization determined in the pseudo-chaotic approximation is used. In this approximation, we obtain the entropy as a function of the temperature, the concentration of magnetic atoms, and the external magnetic field. It is found that in zero external field, the system is frustrated in the sense that the ground-state entropy differs from zero. The value of this entropy is determined for concentrations magnetic atoms below as well as above the percolation threshold.
The method of averaging over interaction fields has been analyzed as applied to the problems of statistical physics. This method has been theoretically justified as applied to a spin cluster. Based ...on the general relations obtained, approximate solutions for the bond-diluted Ising model are found. These approximate solutions are compared with the exact solution for a one-dimensional chain of bond-diluted Ising spins.
Natural Edge Bilayer Graphene Transistor Domaratskiy, I. K.; Kashchenko, M. A.; Semkin, V. A. ...
Russian microelectronics,
12/2023, Volume:
52, Issue:
Suppl 1
Journal Article
Peer reviewed
Application of transverse electric field enables band gap opening in bilayer graphene (BLG) up to hundreds of millielectronvolts. The latter fact may potentially resolve the problem of poor ON/OFF ...current ratio in carbon-based field effect transistors (FETs). Still, the experimentally observed off-state resistivity in BLG typically saturates at tens of kΩ even at cryogenic temperatures. Here, we show that resistance saturation can be attributed to electron conduction along the disordered edge of BLG exposed to chemical etching. To this end, we fabricate and characterize the FET with encapsulated BLG channel not exposed to any kind of etching. The resistivity of such natural edge transistor does not demonstrate any tendency to saturation with increasing the band gap, and reaches tens of MΩ at temperature
T
∼ 25 K. Our result point to the importance of preserving the natural edge structure in 2d transistors for achieving of large ON/OFF current ratios.
The paper describes a procedure of numerical simulation of operating fluid (water) discharge into the air environment through the hydraulic paths of a mixer composed of two low-flow coaxial swirl ...injectors. The method is based on a two-velocity model of a two-phase liquid flow and determining the interface interaction resistance coefficient versus the Reynolds number in the course of solution. The Reynolds number is calculated from the relative velocity of the liquid components forming the two-phase flow. The paper investigates variations in the mixer spray pattern versus two characteristic dimensions reckoned among the key parameters to calculate the coefficient of interface interaction resistance. Algorithms of calculating the coefficient of interface interaction resistance are proposed. The results of modeling liquid mixing and film flow breakdown within and beyond the mixer hydraulic paths for different values of the characteristic dimensions are presented. It is shown that we can achieve the conformity of the calculation results obtained by using the proposed method with the cold flow data by selecting the values of characteristic dimensions with reference to which interface interaction resistance coefficients are determined. Further works are projected.
We consider a one-dimensional Ising model (chain) with the the nearest-neighbor interaction and with a random nonmagnetic dilution. We find the exact free energy of such a chain as a function of the ...impurity concentration, temperature, and the external magnetic field. In the case of antiferromagnetic interaction in the chain, we find the specific magnetization, the mean value of the product of neighboring spins, and the entropy as functions of these parameters. We study the residual system entropy.
A comparative study of the effect of osteoplastic materials based on tricalcium and octacalcium phosphate on the repair of bone defects in the pineal gland of Wistar rats was carried out at follow-up ...periods of 30, 60, and 90 days. It was found that the material based on octacalcium phosphate demonstrates a statistically significant increase in new bone tissue and a satisfactory rate of biodegradation in comparison with xenogenic apatite and tricalcium phosphate in all groups of experimental animals.
In this paper, we study the influence of the radius of a cylindrical supporting structure on radiation properties of a conformal millimeter-wave antenna array. Bent antenna array structures on ...cylindrical surfaces may have important applications in future mobile devices. Small radii may be needed if the antenna is printed on the edges of mobile devices and in items which human beings are wearing, such as wrist watches, bracelets, and rings. The antenna under study consists of four linear series-fed arrays of four patch elements and is operating at 58.8 GHz with linear polarization. The antenna array is fabricated on polytetrafluoroethylene substrate with thickness of 127 µm due to its good plasticity properties, and low losses. Results for both planar and conformal antenna arrays show rather good agreement between simulation and measurements. The results show that conformal antenna structures allow achieving large angular coverage and may allow beam-steering implementations if switches are used to select between different arrays around a cylindrical supporting structure.
Modeling Close Packing of 3D Objects Stoyan, Y. G.; Semkin, V. V.; Chugay, A. M.
Cybernetics and systems analysis,
03/2016, Volume:
52, Issue:
2
Journal Article
Peer reviewed
The paper represents the concept of Φ-functions and quasi Φ-functions as an efficient tool for mathematical modeling of three-dimensional packing problems for convex geometrical objects with ...continuous translations and rotations. A mathematical model of close packing of convex geometrical objects is formulated and its basic properties are considered. A solution method is proposed, which includes the following stages: constructing initial points, computing local extrema, and passing from one local minimum to another. The solution approach is efficient to solve optimization packing problems. Numerical examples are given.
PDF
