Estimation and Optimization of the Principal H-Maser Parameters

The scale along the coordinate axes in the equations of motion hitherto used for an H-maser (in relative units) is shown to depend on Q as the quality factor for an H-maser. This hinders both analysis of the operation of the H-maser and optimization of its parameters. The modified equations of motion proposed here do not have that shortcoming. We determine the atomic flux into the bulb that gives the H-maser the best metrological characteristics.     

Technical risk involved in long-term operation of steam turbines

The scope of the paper is the assessment of the technical risk involved in long-term operation of power units. Detailed analyses have been conducted for steam turbine components. The sources and consequences of risk have been identified and the probability of turbine components failure calculated. The quantitative assessment of the risk has been made and possibilities of its reduction discussed.     

Combined-Stage Sintering Model

By focusing on the similarities between the three stages of sintering, a single equation is derived that quantifies sintering as a continuous process from beginning to end. The microstructure is characterized by two separate parameters representing geometry and scale. The dimensionless geometry parameter, denoted T, comprises five scaling factors that relate specific microstructural featuers (e.g., surface curvature) to the scale (grain diameter). Calculations of T from experimental data show (a) agreement with computer simulations of initial-stage sintering, (b) the effect of surface diffusion on T, and (c) changes in T with microstructural evolution during sintering. Application of the model to the design of firing schedules and the study of microstructural geometry effects on sintering is discussed.     

Effect of high-temperature heat treatment on the properties of sealant Viksint U-2-28

The dependence of the ultimate shear strength of a lithium aluminosilicate ceramic-to-metal adhesive joint with the sealant Viksint U-2-28 on the thermal history of the samples was studied. A temperature threshold for a change in the strength of the adhesive joint was established. Possible mechanisms for the appearance of this threshold in terms of a change in the contribution of different components of the sealant to its adhesion properties, depending on the thermal aging regimes, are discussed.     

Reaction of YBa2Cu3O7-δ Powder with NOx Gas in an Aerosol Reactor

Thermodynamic calculations predict, and experiments verify, that YBa₂Cu₃O₇-₈ (123) powder is unstable in the presence of NO_x-containing aerosol reactor exhaust gases at temperatures below about 600°C. Powders collected above the stability temperature are single-phase 123, while powders collected at lower temperature contain Ba(NO₃)₂ formed by reaction of the powder with NO_x, after exit from the hot zone.     

Iron, copper and manganese metabolism in young sportsmen on diets supplemented with vitamins and microelements

Young skiers and untrained schoolchildren were under observation. During autumn, they manifested an increase in trace elements in the blood, particularly iron and copper, whereas in spring and summer, a dramatic fall of these elements. Supplementation of the diets with vitamins did not produce any demonstrable beneficial effect on metabolism of trace elements. Intake of vitamins in conjunction with iron, copper and manganese was followed by a more pronounced increase, as compared with the "vitamin" and especially with the control groups, in hemoglobin, red cell count, ceruloplasmin activity and by the increment of trace elements in the blood in the presence of high retention of iron and manganese in the body.     

The effect of pore formation on the reflectance of aluminum alloy 1421 during laser pulse action

It is shown that the appearance of micropores leads to an increase in the reflectance of aluminum-based alloy 1421 irradiated by laser pulses. The waveform of a reflected signal bears information on the onset and duration of the pore-formation process in the near-surface material layer during the action of a laser pulse.     

Dry friction of pure aluminum against steel

The behavior of aluminum during dry friction against a steel disk is studied. It has been found that, in the course of dry friction, severe wear of the surfaces of both materials occurs. With an increase in the applied pressure, the wear intensity of the friction pair grows, while the coefficient of friction decreases. The examination of the structure of the subsurface layers of the aluminum specimens has shown that the deformation that occurs in these layers makes a substantial contribution to the wear of these specimens.