Efficient Excitation of Hybrid Modes in a THz Clinotron

Journal of Infrared, Millimeter, and Terahertz Waves - Various regimes of hybrid, bulk-surface, modes being excited in the clinotron oscillator with a sheet electron beam and nonuniform grating...     

Wear Resistance of Carbide and Boride Coatings on U8A Steel

Wear resistance measurements have been made with U8A steel bearing protective coatings based on the carbides of titanium, vanadium, and chromium or iron borides, for various forms of wear. The carbide and boride coatings raise the wear resistance considerably (by factors of 6-30 in accordance with the type of wear). Measurements have been made on the microhardness, microbrittleness, and adhesion of the coating to the substrate, which are effective characteristics that quite fully reflect the effects of the microhardness and state of stress, structure, and defectiveness on the wear resistance.     

Multiple Testing Correction in Medical Image Analysis

We present a novel method for correcting the significance level of hypothesis testing that requires multiple comparisons. It is based on the spectral graph theory, in which the variables are seen as the vertices of a complete undirected graph and the correlation matrix as the adjacency matrix that weights its edges. The method increases the statistical power of the analysis by refuting the assumption of independence among variables, while keeping the probability of false positives low. By computing the eigenvalues of the correlation matrix, it is possible to obtain valuable information about the dependence levels among the variables of the problem, so that the effective number of independent variables can be estimated. The method is compared to other available models and its effectiveness illustrated in case studies involving high-dimensional sets of variables.     

Superconductivity in W-containing diamond-like nanocomposite films

Superconductivity in a tungsten-containing carbon-oxide film was reported. The film with 500 nm thickness was deposited onto polycrystalline silicon oxides using chemical vapor deposition and the co-sputtering of a tungsten metal target. The bonding state of the carbon atoms and the macroscopic and microscopic crystal structure of the film were investigated by Raman spectroscopy, X-ray diffraction and transmission electron microscopy measurements. From the experimental results, we determined that this film essentially had an amorphous structure. The temperature dependence on resistivity was measured in the temperature range of 2–300 K. Resistive superconducting transition was observed at 3.8 K. The dc magnetizations were measured in the temperature range of 1.8–6.5 K. The diamagnetism resulting from a superconductive state was observed below 3.75 K, which is consistent with a resistive superconducting transition. It is thought that the finite sized clusters of the different superconductive transition temperatures cooperatively produce a macroscopic superconducting phenomenon.     

Crack propagation in ceramic composites with layered granular structure

Fracture experiments under conditions of subcritical crack extension were performed with double torsion and single-edge notched bend specimens of different alumina-based ceramic composites having layered granular structure. It is shown that it is possible to increase significantly the work-of-fracture as a result of layered granular structure organization. The pecularities of structure influence on the crack propagation kinetics were investigated, and the possibilities of acceleration and deceleration of subcritical crack growth are reported.     

Ceramic composite materials

Conclusion The concept of developing new materials with prescribed properties based on ideas about "building" structures may be realized in creating ceramic composite materials. Creation of heterogeneous composite structures is the main path for achieving high crack resistance (a parameter which mainly governs the operating reliability of structural articles). These structures make it possible to realize energy-consuming processes of the dissipation of work for failure from external forces. The level of properties achieved (crack resistance above 300 N/mm^3/2, strength above 500 N/mm²), and the high permissible operating temperatures make ceramic composite materials irreplaceable for a number of fields of technology. However, the main problems connected with the development of ceramic composites remain unresolved. These are problems for achieving the optimum structure and composition of the interface for components, thermal stability of reinforcing elements, the production cost of both fibers and composite materials, and obtaining highly compact matrices in composite materials reinforced with continuous fibers.Scientific Production Association of the Institute of Aviation Materials. Interbranch Scientific Research Center of Technical Ceramics. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 36–40, February, 1992.