Giant magnetoresistance in quantum magnetic contacts

We present calculations of quantized conductance and magnetoresistance in nanosize point contacts between two ferromagnetic metals. When conductance is open for only one conduction electron spin-projection, the magnitude of magnetoresistance is limited by the rate of conduction electron spin-reversal processes. In the case when both spin-channels contribute to the conductance we analyze the influence of the point contact cross-section asymmetry on the giant megnetoresistance. Recent experiments on magnetoresistance of magnetic point contacts are discussed in the framework of the developed theory. © 2002 Elsevier Science B.V. All rights reserved

The current status of orbital experiments for UHECR studies

Two types of orbital detectors of extreme energy cosmic rays are being developed nowadays: (i) TUS and KLYPVE with reflecting optical systems (mirrors) and (ii) JEM-EUSO with high-transmittance Fresnel lenses. They will cover much larger areas than existing ground-based arrays and almost uniformly monitor the celestial sphere. The TUS detector is the pioneering mission developed in SINP MSU in cooperation with several Russian and foreign institutions. It has relatively small field of view (+/-4.5 deg), which corresponds to a ground area of 6.4x10^3 sq.km. The telescope consists of a Fresnel-type mirror-concentrator (~2 sq.m) and a photo receiver (a matrix of 16x16 photomultiplier tubes). It is to be deployed on the Lomonosov satellite, and is currently at the final stage of preflight tests. Recently, SINP MSU began the KLYPVE project to be installed on board of the Russian segment of the ISS. The optical system of this detector contains a larger primary mirror (10 sq.m), which allows decreasing the energy threshold. The total effective field of view will be at least +/-14 degrees to exceed the annual exposure of the existing ground-based experiments. Several configurations of the detector are being currently considered. Finally, JEM-EUSO is a wide field of view (+/-30 deg) detector. The optics is composed of two curved double-sided Fresnel lenses with 2.65 m external diameter, a precision diffractive middle lens and a pupil. The ultraviolet photons are focused onto the focal surface, which consists of nearly 5000 multi-anode photomultipliers. It is developed by a large international collaboration. All three orbital detectors have multi-purpose character due to continuous monitoring of various atmospheric phenomena. The present status of development of the TUS and KLYPVE missions is reported, and a brief comparison of the projects with JEM-EUSO is given.Comment: 18 pages; based on the rapporteur talk given by M.I. Panasyuk at ECRS-2014; v2: a few minor language issues fixed thanks to the editor; to be published in the proceeding

Spectroscopy and stimulated emission of Nd3+ in an acentric CsY2F7 host

The results of preliminary spectroscopic studies of new fluoride single-crystal CsY2F7 that is activated by Nd3+ ions are given. Direct evidence for the possibility of application of this ordered material as a laser host is given for the first time to our knowledge. Stimulated emission of Nd3+ ions on the main intermultiplet transition is obtained under both nonselective flash-lamp pumping conditions and continuous Ar ion laser pumping conditions. © 1992 Optical Society of America

Dynamic NMR study of cyclic derivatives of pyridoxine

Copyright © 2014 John Wiley & Sons, Ltd. A series of pyridoxine derivatives was investigated by 1H and 2D nuclear overhauser enhancement spectroscopy (NOESY) NMR. The free energies of activation for the pyridyl-oxygen rotation of the 2,4-dinitrophenyl ether of the seven-membered acetals of pyridoxine were measured by dynamic NMR. A conformational exchange between the chair and twist forms of the seven-membered acetal ring was confirmed by dynamic NMR and STO3G computations

Dynamic NMR study of cyclic derivatives of pyridoxine

A series of pyridoxine derivatives was investigated by 1H and 2D nuclear overhauser enhancement spectroscopy (NOESY) NMR. The free energies of activation for the pyridyl-oxygen rotation of the 2,4-dinitrophenyl ether of the seven-membered acetals of pyridoxine were measured by dynamic NMR. A conformational exchange between the chair and twist forms of the seven-membered acetal ring was confirmed by dynamic NMR and STO3G computations. © 2014 John Wiley & Sons, Ltd

¹H NMR Characterization of Two New Pyridoxine Derivatives

© 2016, Springer Science+Business Media New York.Two new pyridoxine derivatives were studied by dynamic 1H NMR spectroscopy. The complete 1H NMR data for two pyridoxine derivatives are presented. Assignment of the signals in the spectra was achieved using 1D and 2D COSY NMR experiments

Dynamic NMR study of dinitrophenyl derivatives of seven-membered cyclic ketals of pyridoxine

© 2015 John Wiley & Sons, Ltd. Two pyridoxine derivatives containing a dinitrophenyl moiety were investigated by 1H NMR spectroscopy. Conformational dynamics in solution were studied for each compound using dynamic NMR experiments. It was shown that both compounds studied are involved into two conformational exchange processes. The first process is a transformation of the seven-membered cycle conformation between the enantiomeric P-twist and M-twist forms, and the second is a rotation of the dinitrophenyl fragment of the molecules around the C-O bond. Energy barriers of both conformational transitions were determined

Spectral-kinetic and lasing characteristics of new Nd3+-activated laser hosts of the KF–YF3 system

The results of the investigation of two new laser hosts are reported. Stimulated emission from Nd3+ ions has been observed for the first time in the two ordered fluoride crystals of the KF–YF3 system: KYF4 (FYK) and K2YF5 (PYFK). The major luminescent and lasing characteristics of the crystals are presented. The stimulated emission spectrum features and application prospects of the new laser hosts are discussed. © 1990 Taylor & Francis Ltd

Stereodynamics of some pyridoxine derivatives

Copyright © 2016 John Wiley & Sons, Ltd.The conformational properties of three pyridoxine derivatives were studied by 1H dynamic NMR spectroscopy. Conformational exchange caused by a rotation of 2-nytrophenyl group around one single C–C bond, of 2,4-dinitrophenyl substituent around two single C–O bonds, and twist-twist transformations of the seven-membered ketal cycle was observed by NMR experiments at low temperatures. Meanwhile, the conformational exchange of the acetal ring remains fast in the NMR timescale even at 198 K. The energy barriers for all observed conformational exchange processes were determined by the lineshape analysis of dynamic NMR spectra. The activation barriers of the 2-nitrophenyl group rotation were almost the same for all studied compounds, about 40–41 kJ/mol. The energy barriers of the conformational exchange processes of the 2,4-nitrophenyl group and the ketal cycle increased significantly up to 10 kJ/mol in comparison with previously studied compounds with similar structure. Copyright © 2016 John Wiley & Sons, Ltd