X-ray topographic study of quartz cavities with a triple electrode

AT-cut quartz cavities with a triple electrode have been studied. Their main advantage over cavities with an orthogonally directed electric field is that the triple electrode hinders excitation of vibrations on the first mechanical harmonic. A comparison of the parameters of different cavities shows that, in the case of their excitation on the first harmonic, the equivalent resistance of triple-electrode cavities is higher by a factor of 24, their equivalent inductance is higher by a factor of 3, and their Q factor is lower by a factor of 12 compared to the corresponding parameters of conventional cavities. When working on the third harmonic, the parameters of triple-electrode cavity are comparable with those of cavities with an orthogonally directed electric field. An X-ray topographic study of the vibrations of piezoelectric cells in triple-electrode cavities showed a pronounced vibration antinode on the third harmonic, located at the plate center, whereas the corresponding first-harmonic antinode is distorted and diffuse. The values of the Q factor of element vibrations on these harmonics differ by a factor of almost 8. Thus, the use of a triple electrode provides optimal conditions for cavity operation on the third harmonic. There is no need to use any other tools (e.g., introduce an additional resistor) to suppress the first harmonic.     

Variation of a Defect Structure of Lithium Tetraborate (Li2B4O7) in an External Electric Field

Physics of the Solid State - The variation of a defect structure of a lithium tetraborate single crystal under the influence of a high-strength external electric field applied along polar direction...     

Identification of Regions in Apomyoglobin that Form Intermolecular Interactions in Amyloid Aggregates Using High-Performance Mass Spectrometry

The formation of amyloid aggregates in human organs and tissues causes the development of incurable diseases. However, experimental studies of the mechanism of amyloid formation by proteins and the structural characteristics of amyloids are complicated because of the heterogeneity and high molecular weight of the aggregates. We used limited proteolysis and mass spectrometry for the identification of regions in the apomyoglobin polypeptide chain, which give rise to intermolecular interactions in amyloid structures. Tandem mass spectroscopy enabled the identification of regions in the myoglobin polypeptide chain, which form the core of amyloid structures. It was shown that the main structural elements for the formation of the core of amyloid fibrils in myoglobin were regions from 60 through 90 and from 97 through 124 amino acid residues. These regions coincide well with those theoretically predicted. This approach yielded important data on the structure of protein molecules in aggregates and on conformational rearrangements of apomyoglobin upon amyloid formation.     

Thermal and Magnetic Properties of Maghemite γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Synthesized by a Precursor Method

Low-dimension ferromagnetic maghemite γ-Fe₂O₃ was synthesized through a precursor route, using basic iron formate Fe(OH)(HCOO)₂ as a precursor. Conditions of formation of γ-Fe₂O₃ and the temperature range of its existence on heating in air were determined. The saturation magnetization of γ-Fe₂O₃ produced through heating the precursor at 350°C 57.5 (T = 4.2 K) and 43.8 emu/g (T = 300 K).     

Formation of unusual nonferroic domains in TeO2 single crystals under external electric field

The formation of unusual slowly relaxing domains under an external dc electric field has been revealed in paratellurite (TeO₂) crystals. These domains differ from those arising in ferroics (ferromagnets, ferroelectrics, ferroelastics, etc.). The effect is characterized by the existence of a threshold field strength (at which domains begin to be formed) and long equilibrium settling times (up to a few hours, depending on the electric field strength). A crystal returns to the initial single-domain state also after a few hours after the field is switched off. High-resolution triple-crystal X-ray diffractometry has revealed that domains retaining the paraelastic tetragonal phase rotate with respect to each other in space without changing their lattice parameter. The domain sizes are 2–4 mm, depending on the field strength. Currently, the exact mechanisms of domain formation are unclear. Possible reasons for the formation of these defects and an analogy of the observed effects with the behavior of liquid crystals under electric field are discussed.     

Existence of families without positive numerations

An example is constructed of a computable family of recursively enumerable sets which does not have computable positive numerations but does possess a computable minimal numeration.Translated from Matematicheskie Zametki, Vol. 13, No. 4, pp. 597–604, April, 1973.     

Iteration operators on a set of continuous functions of Baire space

Continuous functions on Baire space are considered. Iteration operators are defined on a set of continuous functions. The idea of a module of continuity of a function is introduced. The condition for the growth of module of continuity φ whose satisfaction guarantees that for any enumerable sequence of integration operators and any natural n there exists (n + 1) argument function with the module of continuity φ which cannot be obtained from n-argument functions with the module of continuity φ using any operator of this sequence is formulated. Examples of iteration operators are given.     

Low-temperature electron properties of Heusler alloys Fe<Subscript>2</Subscript>VAl and Fe<Subscript>2</Subscript>CrAl: Effect of annealing

We present the results of measurements of low-temperature heat capacity, as well as electrical and magnetic properties of Heusler alloys Fe₂VAl and Fe₂CrAl prepared in different ways using various heat treatment regimes. The density of states at the Fermi level is estimated. A contribution of ferromagnetic clusters in the low-temperature heat capacity of the Fe₂VAl alloy is detected. The change in the number and volume of clusters as a result of annealing of an alloy affects the behavior of their low-temperature heat capacity, resistivity, and magnetic properties.     

Magnetic Properties of Iron-Doped Bi2Se3, a Topological Insulator

Physics of the Solid State - We study the dc magnetization of a Bi1.94Fe0.06Se3 single crystal in the temperature range of 1.9&nbsp;to 400 K in applied magnetic fields up to 70 kOe for two...