A study of continuous-wave two-frequency NQR

A simple continuous-wave parallel to pulse version of a multifrequency nuclear quadrupole resonance (NQR) device was constructed and tested: two orthogonal radio-frequency (RF) fields were applied simultaneously at two suitable frequencies to a multilevel quadrupole probe (I⋝1). A modified superregenerative NQR oscillator-detector (SRO) was utilized. An additional coil and RF source were used to irradiate the sample at the second frequency. After tuning the SRO to a chosen NQR line, the signal proportional to the population difference of the corresponding pair of energy levels was monitored. When another suitable transition was saturated simultaneously, sharing one level with the monitored line, the corresponding population change was also reflected in the first signal intensity change. The phenomenon was examined for Sb nuclei in Sb₂S₃ powder at room temperature.     

MR measurement technique of rapidly switched gradient magnetic fields in MR tomography

Gradient eddy currents, induced in the surrounding conductive structures in a magnetic resonance (MR) magnet, are a major problem in MR imaging, in localized MR spectroscopy and in many other MR experiments. We present a comparison of three methods of measuring the gradient time characteristics and the time changes of basic magnetic fieldB ₀ after the gradient is switched off. The methods are based on the selective excitation of a thin layer of the sample and on acquiring the MR signal obtained after the end of the gradient pulse and on the computation of the instantaneous frequency of the signal. At this point, the time gradient characteristic is proportional to the instantaneous frequency of the MR signal, which has a small signal-to-noise ratio. We use the characteristics measured to set the pre-emphasis parameters in a 200 MHz/200 mm MR scanner. From the results obtained by measurement it follows that all methods are convenient for simple and quick characterization of magnetic field gradient in MR tomographic magnets.     

An Approximate Functional Equation for the Lerch Zeta Function

In this paper, we establish an approximate functional equation for the Lerch zeta function, which is a generalization of the Riemann zeta function and the Hurwitz zeta function.     

On pseudodynamics of internal degrees of freedom

The results concerning the study of the model formulated within the Grassmann algebra G₆ are presented. It is shown under what assumptions the model reproduces basic features of leptons as they follow from the model of the electroweak interactions. Orbital degrees of freedom are ignored throughout the paper.     

The Green-Kubo Formula and the Onsager Reciprocity Relations in Quantum Statistical Mechanics

We study linear response theory in the general framework of algebraic quantum statistical mechanics and prove the Green-Kubo formula and the Onsager reciprocity relations for heat fluxes generated by temperature differentials. Our derivation is axiomatic and the key assumptions concern ergodic properties of non-equilibrium steady states.     

A continuous linear right inverse of the representation operator and applications to the convolution operators

Rostov-na-Donu. Translated fromSibirskiî Matematicheskiî Zhurnal, Vol. 34, No. 1, pp. 70–84, January–February, 1993.     

Cyclic boronates in the mass spectrometry of ecdysteroids

For the structural elucidation of ecdysteroids a reaction with phenylboronic acid has been employed. This reaction takes place exclusively on the C20,C22 diol moiety, thus facilitating fast and easy detection of this moiety in the molecule od ecdysteroid. This derivatization also redirects fragmentation to C17/C20 bond cleavage with charge retention on both fragments enabling assessment of the structure both of the steroid nucleus and of the side-chain. Possible reaction of phenylboronic acid with the diol moiety of the glycosyl group of the glycoside od ecdysteroid, producing di-adduct, is demonstrated; participation of the 5β-hydroxy group of 5β,20-dihydroxyecdysone in the formation of such a di-adduct is discussed; and the role of theenol form of the 6-carbonyl group is proved.     

Low-energy photoluminescence of structures with GeSi/Si(001) self-assembled nanoislands

The photoluminescence spectra of structures with self-assembled GeSi/Si(001) islands are investigated as functions of the growth temperature. It is shown that the shift of the peak of photoluminescence from islands toward lower energies on decreasing the growth temperature is due to the suppression of Si diffusion into islands and an increase in the fraction of Ge in islands. A photoluminescence signal from the GeSi islands is found in the region of energies down to 0.6 eV, which is considerably smaller than the band-gap width in bulk Ge. The position of the peak of photoluminescence from islands is described well by the model of a real-space indirect optical transition with account of the real composition and elastic strains of the islands. Mono-and multilayer structures are obtained with self-assembled GeSi/Si(001) nanoislands exhibiting a photoluminescence signal in the region 1.3–2 μm at room temperature.