Исследование процессов формирования пористых выплавляемых моделей, применяемых для изготовления высокоточного литья

Aerospace, manufacturing, and shipbuilding industries strive to enhance their competitiveness by optimizing material utilization and improving production processes. The investment casting process offers the capability to fabricate intricate and precise components using a diverse range of alloys. However, this method is not without its drawbacks, including high manufacturing costs and a significant rate of defective castings, which can reach up to 30 %. These defects primarily arise from the stresses imposed on the wax patterns and ceramic molds, leading to their distortion. To address this issue, efforts have been made to reduce stress by employing compacted wax powders for the production of investment patterns. However, stress relaxation in the wax patterns remains a concern as it can result in elastic deformation of the compacted material and subsequent alterations in the final product dimensions. To mitigate this issue, a series of tests were conducted with the objective of studying stress relaxation under constant compression strain, as described by the Kohlrausch equation. The obtained results provide valuable insights that enable the prediction of the ultimate dimensions of patterns created using different grades of wax.Конкурентоспособность современных предприятий машино-, судо- и авиастроения во многом определяется материало- и энергоэффективностью технологий, направленных на получение конструкций и узлов деталей ответственного назначения. Применение литья по выплавляемым моделям (ЛВМ) обеспечивает получение заготовок повышенной размерной и геометрической точности, сложной пространственной конфигурации из широкой номенклатуры сплавов. К недостаткам ЛВМ следует отнести многостадийность процесса и высокую стоимость конечного продукта, что предполагает недопустимость брака, доля которого может достигать 30 %. Брак в ЛВМ преимущественно вызван теплофизическими явлениями, сопровождающими ряд технологических операций и обусловливающими наличие напряжений в структуре воскообразных и керамических материалов, что определяет деформационные процессы в выплавляемых моделях и оболочковых формах. Для устранения негативного влияния теплофизического фактора и снижения напряжений в структурах промежуточных изделий процесса, выплавляемые модели формируют прессованием порошков воскообразных модельных композиций. При этом нерешенным остается вопрос релаксации напряжений в прессовках, приводящих к упругому отклику уплотненного материала и, как следствие, изменению размеров получаемого изделия. Поиск вариантов наиболее рационального режима формирования прессовки привел к необходимости проведения серии экспериментов, в результате которых предполагается достижение релаксации напряжений σ в условиях постоянной деформации сжатия, описываемого уравнением Кольрауша. Полученные в ходе эксперимента результаты позволят прогнозировать конечные размеры прессовок и сформировать математическую модель процесса, актуальную для широкой номенклатуры воскообразных модельных материалов, применяемых в ЛВМ

Quantal Two-Centre Coulomb Problem treated by means of the Phase-Integral Method I. General Theory

The present paper concerns the derivation of phase-integral quantization conditions for the two-centre Coulomb problem under the assumption that the two Coulomb centres are fixed. With this restriction we treat the general two-centre Coulomb problem according to the phase-integral method, in which one uses an {\it a priori} unspecified {\it base function}. We consider base functions containing three unspecified parameters $C, \tilde C$ and $\Lambda$. When the absolute value of the magnetic quantum number $m$ is not too small, it is most appropriate to choose $\Lambda=|m|\ne 0$. When, on the other hand, $|m|$ is sufficiently small, it is most appropriate to choose $\Lambda = 0$. Arbitrary-order phase-integral quantization conditions are obtained for these choices of $\Lambda$. The parameters $C$ and $\tilde C$ are determined from the requirement that the results of the first and the third order of the phase-integral approximation coincide, which makes the first-order approximation as good as possible. In order to make the paper to some extent self-contained, a short review of the phase-integral method is given in the Appendix.Comment: 23 pages, RevTeX, 4 EPS figures, submitted to J. Math. Phy

FEATURES MODIFYING VARIOUS TYPES OF IRON-CARBON ALLOYS

The article describes the features of the modification of cast iron, high chrome cast iron and steel. It is shown that the modification of cast iron complex modifier should be based on the thickness of the walls of castings, and for steel and high chrome cast iron, it is beneficial to the macro and microstructure. The data confirming the removal of transcrystallization and size reduction microand macrostructure of castings in various types of iron-carbon alloys. Experimentally proved that in the transition from columnar to equiaxed structure observed increase in the number of eutectic cells, which confirms the position that transcrystallization terminated as a result of nucleation and growth of equiaxed crystalsin the area of concentration supercoolin

Neutral and non-neutral collisionless plasma equilibria for twisted flux tubes: the Gold-Hoyle model in a background field

We calculate exact one-dimensional collisionless plasma equilibria for a continuum of flux tube models, for which the total magnetic field is made up of the “force-free” Gold-Hoyle magnetic flux tube embedded in a uniform and anti-parallel background magnetic field. For a sufficiently weak background magnetic field, the axial component of the total magnetic field reverses at some finite radius. The presence of the background magnetic field means that the total system is not exactly force-free, but by reducing its magnitude, the departure from force-free can be made as small as desired. The distribution function for each species is a function of the three constants of motion; namely, the Hamiltonian and the canonical momenta in the axial and azimuthal directions. Poisson's equation and Ampère's law are solved exactly, and the solution allows either electrically neutral or non-neutral configurations, depending on the values of the bulk ion and electron flows. These equilibria have possible applications in various solar, space, and astrophysical contexts, as well as in the laboratory

On integrable system on S2S^2 with the second integral quartic in the momenta

We consider integrable system on the sphere $S^2$ with an additional integral of fourth order in the momenta. At the special values of parameters this system coincides with the Kowalevski-Goryachev-Chaplygin system.Comment: LaTeX, 6 page

A New Nanoporous Material Based on Amorphous Silicon Dioxide

Processes for making nanoporous SiO2 layers on Si via the irradiation of thermally oxidized silicon wafers with fast ions followed by chemical treatment in a solution or vapor of hydrofluoric acid are presented. It is shown that the density, shape, diameter, and length to diameter ratio of channels etched in silicon dioxide can be controlled by varying the regimes of fast ion irradiation or chemical treatment of SiO2/Si structures. Track parameters calculated using the thermal spike model are compared with the chemical etching data

Красное смещение излучения точечного источника, движущегося в поле вращающейся черной дыры

The method of calculation of redshift of light from a point-like source that moves in the gravitational field of the Kerr black hole as a function of time of observation is developed. The widely presented in literature methods for solving the boundary problem are based on a numerical selection of parameters of geodesics. In contrast, the proposed method is based on approximate analytical expressions for isotropic geodesics in the Kerr metric. The proposed method is illustrated by the example of a model problem with parameters corresponding to real stars moving in the immediate vicinity of a supermassive black hole located in the Center of our Galaxy. The same example shows the efficiency and good accuracy of this method.Для точечного источника электромагнитного излучения, движущегося в гравитационном поле вращающейся черной дыры, описываемой метрикой Керра, разработан метод вычисления красного смещения как функции времени удаленного наблюдателя. В отличие от широко представленных в литературе способов, граничная задача для траектории луча решена не численным подбором параметров, а на основе приближенных аналитических выражений для изотропных геодезических в метрике Керра. Предложенный метод проиллюстрирован на примере модельной задачи с параметрами, соответствующими реальным звездам, движущимся в непосредственной близости сверхмассивной черной дыры, находящейся в центре нашей Галактики. На этом же примере показана эффективность и хорошая точность данного метода

Measurement of the Analyzing Power in p⃗d→(pp)n\vec{p}d \to (pp)n \\with a Fast Forward 1S0^1S_0--Diproton

A measurement of the analyzing power $A_y$ of the $\vec{p}d \to (pp) + n$ reaction was carried out at beam energies of 0.5 and 0.8 GeV by detection of a fast forward proton pair of small excitation energy $E_{pp} < 3$ MeV. The kinematically complete experiment made use of the ANKE spectrometer at the internal beam of COSY and a deuterium cluster--jet target. For the first time the $S$--wave dominance in the fast diproton is experimentally demonstrated in this reaction. While at $T_p=0.8$ GeV the measured analyzing power $A_y$ vanishes, it reaches almost unity at $T_p=0.5$ GeV for neutrons scattered at $\theta_n^{c.m.}=167^\circ$. The results are compared with a model taking into account one--nucleon exchange, single scattering and $\Delta$ (1232) excitation in the intermediate state. The model describes fairly well the unpolarized cross section obtained earlier by us and the analyzing power at 0.8 GeV, it fails to reproduce the angular dependence of $A_y$ at 0.5 GeV.Comment: 4 pages, 4 figures, 1 tabl

3^3He Structure and Mechanisms of p3p^3He Backward Elastic Scattering

The mechanism of $p^3$He backward elastic scattering is studied. It is found that the triangle diagrams with the subprocesses $pd\to ^3$He$\pi^0$, $pd^*\to ^3$He$\pi^0$ and $p(pp)\to^3$He$\pi^+$, where $d^*$ and $pp$ denote the singlet deuteron and diproton pair in the $^1S_0$ state, respectively, dominate in the cross section at 0.3-0.8 GeV, and their contribution is comparable with that for a sequential transfer of a $np$ pair at 1-1.5 GeV. The contribution of the $d^*+pp$, estimated on the basis of the spectator mechanism of the $p(NN)\to ^3$He$\pi$ reaction, increases the $p^3$He$\to ^3$He$p$ cross section by one order of magnitude as compared to the contribution of the deuteron alone. Effects of the initial and final states interaction are taken into account.Comment: 17 pages, Latex, 4 postscript figures, expanded version, accepted by Physical Review

The Ethnic 'Other' in Ukrainian History Textbooks: The Case of Russia and the Russians

This paper examines portrayals of Russia and the Russians in two generations of Ukrainian history textbooks. It observes that the textbooks are highly condemning of Ukraine's main ethnic other in the guise of foreign ruler: the tsarist authorities and the Soviet regime are always attributed dubious and malicious intentions even if there is appreciation for some of their policies. By contrast, the books, certainly those of the second generation, refrain from presenting highly biased accounts of the ethnic other as a national group (i.e. Russians). Instances where negative judgements do fall onto Russians are counterbalanced by excerpts criticizing ethnic Ukrainians or highlighting conflicting interests within the Ukrainian ethnic group. The negative appraisal of the ethnic other as foreign ruler is clearly instrumental for the nation-building project as it sustains a discourse legitimating the existence of Ukraine as independent state. However, recent trends in history education, the paper concludes, suggest that the importance of nurturing patriotism as a national policy objective is diminishing