Photon number measurement using heterodyne method for a detector's quantum efficiency determination based on spontaneous parametric down-conversion.

Active development of quantum informational components such as quantum computers and quantum key distribution systems requires parameter characterization of single photon detectors. A key property of the single photon detectors is detection efficiency. One of the methods of the detection efficiency measurement, as listed in the international standard ETSI, is the reference-free twin-photon-based Klyshko method. The signal-to-noise ratio (SNR) of this method depends on the combination of the pump wavelength, the nonlinear crystal's axis angle, and the type of detector's sensitive element. When the combination is difficult, one has to deal with the low SNR of the detector counts measurement. To gain the high SNR, one has to average the long record complicated with the "random telegraph signal" noise. This type of noise exhibits high spectral density at a zero frequency, where simple averaging works. The heterodyne based method we have proposed is to perform averaging at the higher frequency of the modulation introduced to the standard Klyshko measurement scheme. The method was numerically simulated and experimentally tested. The 14 times improvement in SNR for the proposed method relative to the simple averaging was demonstrated by the numerical simulation and confirmed experimentally.

Orientational dependencies of dynamics and relaxation of multiple quantum NMR coherences in one-dimensional systems.

Dynamics and relaxation, or decoherence, of multiple quantum (MQ) coherences are investigated experimentally and theoretically for different orientations of a single crystal of fluorapatite with respect to the external magnetic field. Dynamics of MQ coherences is studied as a function of the preparation period of the MQ NMR experiment. Their relaxation, or decoherence, during the evolution period is also investigated. Universal curves for dynamics and relaxation are obtained and describe the experimental data for different orientations of the investigated sample. Those curves prove the dipolar nature of the observed relaxation process. The contribution of the heteronuclear interactions to the dipolar relaxation is also investigated. The source of discrepancies between experimental data and theoretical results in the experiments with a large angle between the nuclear spin chains and the external magnetic field are discussed.

A high frequency resonance gravity gradiometer.

A new setup OGRAN--the large scale opto-acoustical gravitational detector is described. As distinguished from known gravitational bar detectors it uses the optical interferometrical readout for registering weak variations of gravity gradient at the kilohetz frequency region. At room temperature, its sensitivity is limited only by the bar Brownian noise at the bandwidth close to 100 Hz. It is destined for a search for rare events--gravitational pulses coincident with signals of neutrino scintillator (BUST) in the deep underground of Baksan Neutrino Observatory of INR RAS.

[The role of hypoxia-inducible factor family (HIF) proteins in the regulation of cells physiologic responses to hypoxia].

The review is devoted to the role of hypoxia-inducible factors (HIF) in the regulation of oxygen-dependent gene signalling. Structural features of HIF alpha and beta subunits as well as involvement of hydroxylation in the regulation of HIF stability and activity are described. Special attention is given to the role of phosphorylation and other post-translational modifications in the regulation of HIF expression and activity. The survey considers the involvement of hormones, cytokines and growth factors in HIF stimulation under normoxia. HIF target genes and promotor/enhancer sequences, responsible for oxygen-dependent gene regulation, are also described.

Stray field nuclear magnetic resonance of soil water: development of a new, large probe and preliminary results.

Development, characterization, and preliminary results of a recent technique capable of local measurements of pore-size distribution by a spatially resolved low resolution nuclear magnetic resonance (NMR) technique are described. Potential environmental uses include studying the change in pore-size distribution caused by surface compaction, which influences surface runoff, and obtaining information on the physical state of non-aqueous compounds in porous materials, which should aid the selection of appropriate soil remediation methods. Stray field (STRAFI) imaging is an NMR technique that allows distortion-free imaging of materials with short NMR relaxation times. The sample is placed in the strong axial fringe field gradient of a superconducting NMR magnet. We report on a new, unique, large 5-cm-diameter STRAFI probe, and its use for three preliminary test cases: water in ceramics of known pore size, paraffin wax and oil in sandstone rock, and water in soil at different matric potentials. The imaging is confined to one dimension with a spatial resolution of the order of 100 microm for protons. The optimum position for imaging occurs at 2.62 T and a gradient of 12.1 T/m. Water relaxation decay curves can be measured at any position in the 8-cm-long sample. These curves are decomposed into a series of terms each corresponding to a different pore size. Preliminary results show continuum fits to decay curves for a soil drained to three different matric potentials. Such information will be useful for interpreting water retention curves and will lead to understanding of the behavior of fluids in the vadose zone.

Hahn-echoes from 14N in solids by the stray-field method: prospects for imaging using Long Echo-Train Summation.

We have observed Hahn-echoes resulting from Powles-Mansfield pulse-sequences for a variety of nitrogen containing solids which exhibit a range of 14N electric quadrupole coupling constants (Cq) from 0 to 4.9 MHz. Long echo-decays were frequently obtained which allowed the collection of many echoes in one echo-train, so that the method of Long Echo-Train Summation (LETS), could be used to accumulate signal. A one-dimensional STRAFI-profile is shown for solid ammonium nitrate. The spatial resolution is discussed as a function of Cq.

[Recording of high resolution 31P NMR spectra from the surface of a living object]. / Registratsiia spektrov IaMR P vysokogo razresheniia s poverkhnosti zhivogo ob"ekta.

A surface coil probehead was worked out for the superconducting 50 mm bore magnet of NMR a high resolution NMR spectrometer with the field strength 8,46 T (145.78 MHz for 31P nuclei) with a 50 mm slot. The requirements were analysed for the surface R.F. coil to obtain the greatest possible single/noise ratio at fixed space selectivity. Real penetration depth of the radio-frequency field into the specimen was estimated. Spectra of liver and abdominal muscle of anesthetized mouse were obtained. The probehead may be applied to obtain high resolution 31P spectra in vivo studies of animal organs.