On the geometry of the set of symmetric matrices with repeated eigenvalues

We investigate some geometric properties of the real algebraic variety \u394 of symmetric matrices with repeated eigenvalues. We explicitly compute the volume of its intersection with the sphere and prove a Eckart\u2013Young\u2013Mirsky-type theorem for the distance function from a generic matrix to points in \u394. We exhibit connections of our study to real algebraic geometry (computing the Euclidean distance degree of \u394) and random matrix theory

HTS Bi-2212 thick films for 3D waveguide structures

This paper presents results of development of high temperature superconducting (HTS) thick films for microwave components. Low cost thick film HTS technology was developed opening the possibility to implement 3-D superconducting structures of complex geometries covering variety of configurations typically used for waveguide microwave filters, diplexers, transitions and other components. Theoretical and practical aspects of this technique discussed including application of rigorous modeling approach, impact of tooling and machining tolerances to design specifications and production. Advantages and limitations are summarized. Practical example of 38 GHz waveguide filter presented, proving efficient application of the HTS technology developed for microwave components up to mm-wave frequency band

Sintering and densification mechanisms of Y2BaCuO5 pellets

The sintering and densification of YBaCuO (Y-211) pellets made from powders with different characteristics have been investigated in the temperature range 1000-1140°C. A pellet made from powder containing Ba-rich secondary phases shows very early liquid-assisted sintering and densification and clear evidence of exaggerated grain growth. The melting of BaCuO and YBaCuO (Y-123) secondary phases increases the rate of densification of Y-211 pellets made from other powders at temperatures above 1025-1030°C. All the liquid produced by the melting of the latter phases recrystallizes as intergranular layers of Y-123. These intergranular layers account for the darker appearance and for measurable electrical conductivities at room temperature of the pellets sintered at the higher temperatures. The development of exaggerated grain growth within a uniform fine-grained matrix opens the possibility of using controlled secondary recrystallization to obtain large single domains of Y-211, provided that the trapping of porosity can be avoided or minimized

Liquidus temperatures in calcium ferrite slags equilibrated with molten copper

Experimental laboratory methods have been developed that enable phase-equilibria studies to be carried out on slags in the system Ca-Cu-Fe-O in equilibrium with metallic copper. These techniques involve equilibration at temperature, rapid quenching, and chemical analysis of the phases using electron-probe X-ray microanalysis (EPMA). Equilibration experiments have been carried out in the temperature range of 1150 °C to 1250 °C (1423 to 1523 K) and in the composition range of 4 to 80 wt pct “Cu2O,” 0 to 25 wt pct CaO, and 20 to 75 wt pct “Fe2O3” in equilibrium with metallic copper. Liquidus and solidus data are reported for the primary-phase fields of spinel (magnetite) and dicalcium ferrite. The resulting data have been used to construct liquidus isotherms of the CaO-“Cu2O”-“Fe2O3” system at metallic copper saturation

Effects of Al2O3, CaO and Cr2O3 on liquidus temperatures of Fe-Mg-Si-O slags

Experimental studies have been carried out to determine phase equilibria in the Fe-Mg-Si-Al- Ca-Cr-O system in air and in reducing atmospheres. The univariant lines between spinel and tridymite primary phase fields, and between the pyroxene and tridymite primary phase fields in the Fe-Mg-Si-O system with and without CaO, Al2O3 and Cr2O3 addition have been determined. The measurements demonstrate clearly that the presence of Al2O3 and CaO in the system lowers the liquidus in the silica primary phase field. The study also confirms that lowering the oxygen potential in the system lowers the liquidus temperatures for Fe-Mg-Si-Al-Cr-Ca-O slags

QUALITY ASSESSMENT OF A USER INTERFACE BASED ON THE MENTAL TIME OF PERFORMING THE USER TASKS OF THE SUBJECT AREA

The overall development of information systems and their increasingly significant impact on all areas of the society expressed in such terms as "information society", etc., determines the increasing importance of user interfaces. Moreover, the quality and adequacy of the interface to the tasks of the subject area becomes the determining parameter when choosing a specific organization software product for computer support of the organization. The study of user interfaces involved with the 70s of the last century. Some methods of interface quality research, in particular, the GOMS method is used to date. However, the use of advanced training technology for mass professional users of information systems for the study of interfaces allows to effectively evaluate the interface in the learning process without using the GOMS method. This article is devoted to this issue. The article deals with the method of quantitative evaluation of the quality of the user interface in the form of such characteristics as errors and mental time of the tasks of the subject area. The structure of time of performing tasks of the subject area is analyzed. Mental time is allocated as the characteristic that chiefly determines the usability of the user interface. Mental time is based on the total time of the step, the calculation time at this step, and the mechanical time required for a person to perform an action that causes the step to be performed. It is shown that the use of anticipated training technology of mass professional user can significantly simplify the allocation of mental time by eliminating the time of the task computer. In the structure of time, the mechanical time required for a person to perform an action that causes the step to be performed is essential. In the GOMS method some standard numerical characteristics are used to estimate mechanical time. However, a hypothesis is put forward, and it is experimentally shown that a statistically significant minimum time for performing actions can be used as mechanical time. This hypothesis was experimentally confirmed. The method and results of this experiment are presented in the article. Developed on this basis, the methodology for assessing the quality of the interface can be used when retraining users in the process of transition of organizations to domestic software in order to evaluate the interfaces

Influence of magnesium oxide nanoparticles embedded in Bi-2212/Ag tapes on their superconducting properties

No Full Tex

Bi-2223 precursor billets for PIT wire production

High temperature superconductor precursor billets (feed rods) have been developed for loading into silver tubes. The billets are loaded prior to rolling or drawing operations in PIT wire manufacture. Investigations have shown that wires and tapes prepared from feed rod loaded tubes show enhanced uniformity of electrical transport properties when compared with conventional powder packing, especially in wires drawn to long lengths, Analysis on production feed rods have shown carbon content to be as low as 110 ppm