A Study of Thermal Behaviour of HTS Devices at Alternating Current

The paper presents a study on thermal behavior of a coil made of a high-temperature supercon-ducting tape representing operation of a superconducting device (for example, a transformer). Based on the results of a physical experiment, a mathematical model of superconducting coil op-eration under short circuit conditions at the load side was developed. Regimes of overheating by variable short circuit currents were investigated. In this case, short circuit current amplitudes ex-ceeded a critical current of a superconductor, and coil parameters (e.g. an average nonlinearity parameter of a current-voltage characteristic, a superconductor length, and others) were varied. Permissible overheating for a coil with the possibility of its return into the superconducting state after emergency conditions in a dead-time period of automatic reclosing was considered. A crite-rion for return of a superconducting device into the superconducting state within a dead-time period of automatic reclosing has been obtained

RECURRENCE IN PUBLIC PROCESSES

This article is devoted to the analysis of periodical social progress in Russia and other market economies. This is determined through starting points of economic cycles following the results of changing the productive forces using versions of the Kondratjev`s cycle

Raske ja sügava puudega laste hooldamine kodus: probleemid ja teenuste vajalikkus ning kättesaadavus Pärnumaa näitel

http://www.ester.ee/record=b4430536~S1*es

Singlet-ground-state paramagnetic centers in CuO2 layers as seen from Tm169 NMR in TmBa2Cu3O6+x superconductors

The Tm169 nuclear spin-lattice relaxation in oxygen-deficient TmBa2Cu3O6+x compounds, as quenched and room-temperature annealed, has been measured at low temperatures. The results are consistent with the existence of paramagnetic centers in the CuO2 double layer, which have a nonmagnetic (singlet) ground state separated from an excited magnetic state by an energy gap of the order of 1 K. © 1995 The American Physical Society

Stripe motion in CuO2 planes of Y1-xPrxBa2Cu3O7 as observed from the Cu(2) quadrupole resonance

The NQR spectra of copper in the compounds YBa2Cu3O7, TmBa2Cu3O7, and Y0.9Pr0.1Ba2Cu3O7 at temperatures of 4.2-200 K are investigated by a pulsed NQR technique at frequencies of 28-33 MHz. Quantitative analysis of the spectra shows that the shape of the "plane" Cu(2) spectra is well described by using a model of 1D correlations of the charge and spin distribution in the CuO2 planes (stripe correlations). In the undoped superconductors the charge-spin stripe structure moves fast in the CuO2 planes, but doping the YBa2Cu3O7 lattice with praseodymium slows this motion down. © 1997 American Institute of Physics

Use of nuclear spin noise spectroscopy to monitor slow magnetization buildup at millikelvin temperatures

At ultralow temperatures, longitudinal nuclear magnetic relaxation times become exceedingly long and spectral lines are very broad. These facts pose particular challenges for the measurement of NMR spectra and spin relaxation phenomena. Nuclear spin noise spectroscopy is used to monitor proton spin polarization buildup to thermal equilibrium of a mixture of glycerol, water, and copper oxide nanoparticles at 17.5 mK in a static magnetic field of 2.5 T. Relaxation times determined in such a way are essentially free from perturbations caused by excitation radiofrequency pulses, radiation damping, and insufficient excitation bandwidth. The experimental spin-lattice relaxation times determined on resonance by saturation recovery with spin noise detection are consistently longer than those determined by using pulse excitation. These longer values are in better accordance with the expected field dependence trend than those obtained by on-resonance experiments with pulsed excitation

Cu(2) nuclear resonance evidence for an original magnetic phase in aged 60K-superconductors RBa2Cu3O6+x (R=Tm,Y)

It is widely believed that the long-range antiferromagnetic order in the RBa2Cu3O6+x compounds (R=Y and rare earths except of Ce, Pr, Tb) is totally suppressed for the oxygen index x>0.4 (AFM insulator-metal transition). We present the results of the copper NQR/NMR studies of aged RBa2Cu3O6+x (R=Tm,Y) samples showing that a magnetic order can still be present at oxygen contents x up to at least 0.7 and at temperatures as high as 77K.Comment: 7 pages, 6 figures. Submitted to Phys.Rev.

Cu(2) nuclear resonance evidence for a magnetic phase in aged 60-K superconductors RBa2Cu3O6+x (R = Tm, Y)

It is widely believed that the long-range antiferromagnetic order in the RBa2Cu3O6+x compounds (R = Y and rare earths except for Ce, Pr, Tb) is totally suppressed for the oxygen index x ≥ 0.4 (antiferromagnetic insulator-metal transition). We present the results of the copper nuclear quadrupole resonance/NMR studies of aged RBa2Cu3O6+x (R = Tm, Y) samples showing that a magnetic order can still be present at oxygen contents x up to at least 0.7 and at temperatures as high as 77 K

Intrinsic paramagnetic centers in 1-2-3 superconductors

The169Tm "enhanced" NMR in TmBa2Cu3O6+x (x=0.5, 0.6) at temperatures below 4.2K and the63Cu(1) NQR in YBa2Cu3O6.5 at temperatures above 4.2K are used to study properties of intrinsic paramagnetic centers incorporated into superconducting materials. The spin-lattice relaxation of thulium and copper nuclei reveals three types of paramagnetic centers to be present in oxygen-deficient 1-2-3 superconductors, those are (1) two-level ones with a spin S=1/2, localized outside CuO2 bilayers, (2) singlet-ground-state paramagnetic centers with an integer spin S≥1 in CuO2 bilayers, and (3) exchange copper-oxygen clusters with a half-integer spin S≥5/2, localized in a nearest neighborhood of CuOx basal plane at boundaries of superconducting OrthoII microdomains. © 1995 Plenum Publishing Corporation