[en] The van der Pauw method for 2D samples of arbitrary shape with an isolated hole is considered. Correlations between extreme values of the resistances allow one to determine the specific resistivity of the sample and the dimensionless parameter related to the geometry of the isolated hole, known as the Riemann modulus. The parameter is invariant under conformal mappings. Experimental verification of the method is presented. (paper)

[en] A six-point generalization of the van der Pauw method is presented. The method is applicable for 2D homogeneous systems with an isolated hole. A single measurement performed on the contacts located arbitrarily on the sample edge allows us to determine the specific resistivity and a dimensionless parameter related to the hole, known as the Riemann modulus. The parameter is invariant under conformal mappings of the sample shape. The hole can be regarded as a high resistivity defect. Therefore, the method can be applied for the experimental determination of the sample inhomogeneity. (paper)

[en] We prove that if two conformal embeddings between Riemann surfaces with finite topology are homotopic, then they are isotopic through conformal embeddings. Furthermore, we show that the space of all conformal embeddings in a given homotopy class is homotopy equivalent to a point, a circle, a torus, or the unit tangent bundle of the codomain, depending on the induced homomorphism on fundamental groups. Quadratic differentials play a central role in the proof.

[en] Magnetized highly ionized sheet plasmas are created in steady state with sheet thickness of about the ion cyclotron diameter. The difference between the characters of slab and sheet plasmas are discussed and some ways of practical applications of the slab or the sheet plasmas are shown. (author)

No abstract available

[en] New methods of sheet stamping were developed: the gas forming with double-sided heating of a blank part and the gas molding with backpressure. In case of the first method the blank part is heated to the set temperature by means of a double-sided impact of combustion products of gas mixtures, after which, under the influence of gas pressure a stamping process is performed. In case of gas molding with backpressure, the blank part is heated to the set temperature by one-sided impact of the combustion products, while backpressure is created on the opposite side of the blank part by compressed air. In both methods the deformation takes place in the temperature range of warm or hot treatment due to the heating of a blank part. This allows one to form parts of complicated shape within one technological operation, which significantly reduces the cost of production. To implement these methods, original devices were designed and produced, which are new types of forging and stamping equipment. Using these devices, an experimental research on the stamping process was carried out and high-quality parts were obtained, which makes it possible to recommend the developed methods of stamping in the industrial production. Their application in small-scale production will allow one to reduce the cost price of stamped parts 2 or 3 times. (paper)

No abstract available

[en] The cylindrical plasma flow caused by dc discharge along a magnetic field is transformed into a sheet plasma flow (13 cm in width, 40 cm in length and about 3 mm in thickness) while electron components (up to 100 A) in the plasma flow are accelerated by a power supply of 80 V to 220 V. In the first experiment, the sheet plasma where an argon ion current density of 19 mA/cm² is extracted is produced under an argon gas pressure of 1.3 x 10^-1 Pa, an electron acceleration voltage V_A=100 V and an electron acceleration current I_A=50 A. In the second experiment, the sheet plasma is produced under an argon pressure of 5.3 Pa, V_A=100 V and I_A=100 A. In the third experiment, the sheet plasma is produced under a hydrogen gas pressure of 52 Pa, V_A=220 V and I_A=100 A. These electron acceleration sheet plasmas are very useful for large-area and high-speed plasma processes. It should be noted that the ordinary vacuum conductance of the electron acceleration anode slit is greatly reduced to 1/8 of the original value when an electron acceleration current of 100 A enters the acceleration anode region through the slit. (author)

[en] Let M be a compact Riemann surface, h(x) a positive smooth function on M, and φ(x) a smooth function on M which satisfies that ∫_Me^φdV_g = 1. In this paper, we consider the functional J(u) =₂¹∫_M|∇u|²e^φdV_g+8πc ∫_Mue^φdV_g-8πclog ∫_Mhe^u+φdV_g. We give a sufficient condition under which J achieves its minimum for c ≤ inf_xelementofMΦ(x). (author)

[en] Design of tube sheets and other perforated parts of pressure vessels is based on the concept of an equivalent material. Properties of such materials in elastic range are quite well understood and described. In view of the fact that the engineering structures are more often designed employing the theory of plasticity it is necessary to study the plastic properties of perforated materials. Due to the regular distribution of the holes a perforated material in the macroscale is anisotropic and a yield condition for such materials is a function of stresses and the angle defining the orientation of the stresses applied with respect to the principal axes of the perforation pattern. This work presents an experimental study of plasticity in the biaxial stress state for perforated materials with a square penetration pattern. Tests were carried out on tube specimens of mild steel St3S and subjected to axial load, internal pressure and torsion. (orig.)