Results 1 - 10 of 11369
Results 1 - 10 of 11369. Search took: 0.042 seconds
|Sort by: date | relevance|
[en] The line intensities of 010101g-000011u transition of linear tetratomic molecule C2H2 at temperatures from 2 K to 5000 K were calculated with the theory of molecular spectra. The effecting of nuclear-spin and centrifugal distortion constants were calculated and discussed. The conclusions show that the nuclear-spin becomes important only at very low temperatures, below 10 K for C2H2, but its effecting increases rapidly as the temperature is lowered further. When the centrifugal distortion is considered, the effecting is significant even at moderate temperature, affecting the line intensities by 0.03% at 500 K and by 0.81% at 5000 K. The results are of significance for the accurate calculation of molecular line intensities at different temperatures. (authors)
[en] Low temperature specific heat of high-temperature superconducting cuprates as YBa2 Cu3 O6+x is considered at the assumption of the existence of double-well potential systems connected with non-central positions of the apex oxygen atoms O(A). The contribution of these systems to the specific heat has been calculated by standard thermodynamic approach using the numerically calculated energy spectrum. The experimentally observed linear term in the specific heat, related to double-well potential systems, is explained as a composition having two parts: one common to the normal and the superconducting state, and other 'intrinsic' part, inherent to the superconducting state only. Distribution function of these double-well potential systems is obtained by a keen fitting procedure. The presented results support the suggestion for the existence of double-well potential systems and give the possibility to explain the dependence of the specific heat linear term on the oxygen deficit. (author)
[en] A realization of the numerous phases predicted in systems with long-range repulsive interactions was recently found in Pb/Si(111). Surprisingly, these numerous phases can be grown at low temperatures ∼40 K over macroscopic distances. This unusual observation can be explained from theoretical calculations of the collective diffusion coefficient Dc in systems with long-range repulsive interactions. Instead of a gradual dependence of Dc on coverage, it was found that Dc has sharp maxima at low temperatures for every stable phase (i.e., for every rational value of the coverage θ=p/q) in agreement with the experiment
[en] Preliminary results of measurements performed on two bulk MgB2 cylinders intended for use as toroidal magnetic shields with a novel cryogenic current comparator are reported up to 37 K, showing an attenuation factor greater than 106 at 27 K, lowering by a factor of 10 at 34 K. (rapid communication)
[en] We have carried out a high magnetic field study on single crystalline stoichiometric , a material discussed in terms quantum criticality in itinerant ferromagnets, by means of high field resistivity experiments. Our experiments have been performed at the Laboratoire National des Champs Magnétiques Intenses in Toulouse, France. The resistivity of single crystalline , has been investigated in external fields up to 15.5 T aligned along the c-axis in the temperature range of 1.4–55 K. The main focus of our study lies on the method to extract TN from the magnetoresistivity measurements, because TN could not be easily observed in temperature dependent resistivity for stoichiometric .
[en] Complete text of publication follows. In the previous research of cryogenic complex (dusty) plasma we observed experimentally the possibility of the formation of dust structures in cryogenic environment at 4.2-77 K. It was revealed from the experiments, among others, that the dust structures with high concentration of dust particles can be formed, in which interparticle distance is comparable with particle size - so-called superdense dusty plasma structures. Such structures had exotic properties such as globular (spherical) form, free boundaries, etc. In the present work new results on the experimental investigations of spheroidizing - phenomenon of the transition of dust structures to compact globular shape at cryogenic temperatures - were presented. The experiments were made by means of recently developed techniques and new cryogenic facilities (optical helium cryostat). Possible nature of such phenomenon is discussed.
[en] Using one-photon excitation we studied photoluminescence of C60 saturated with molecular hydrogen over a temperature range 10 to 230 K. Saturation of samples was done at a pressure of 30 atm and at temperatures low enough (T < 250 C) to exclude chemical sorption. The samples were saturated during periods of varied duration τ to reach different occupancy levels. To check reliability of our luminescence results and interpretation, our spectra for pure C60 were compared with data known in the art, demonstrating good compatibility. The luminescence spectra were attributed according to the approach of Akimoto and Kan,no by separating total spectra in two components of different origin. The A-type spectra, which are associated with exciton transport to deep traps, above 70 K become prevail over the B-type emission. Until saturation times did not exceed a certain value (for one, 50 h for a saturation temperature of 200 C) the integrated intensity I as a function of the temperature T of luminescence measurements, I(T), remained at a constant level up to the orientational vitrification point of about 100 K and then went rather steeply down with increasing T. However, at longer τ the intensity I(T) persisted in constancy to higher T (the higher, the longer τ) and then dropped with increasing T. This finding made us to reexamine more closely the lattice parameter vs saturation time dependence for saturation temperatures 200 and 230 C. As a result, additional evidence allowed us to infer that after completion of the single-molecule filling of O-voids (specifically, after roughly 50 h for Tsat = 200 C) a slower process of double filling sets in. Double filling entails an anisotropic deformation of the octahedral cage, which modifies rotational dynamics stronger than single filling. Further, we argue that singlet exciton transport to traps (which is responsible for the A-type emission) can be crucially hampered by rotational jumps of one of the molecules over which a travelling exciton is spread. Such jumps break coherence and the exciton stops thereby increasing the probability of emissionless deactivation. If so, then the temperature, at which the rotational jumps occur sufficiently frequently, may be by inference considered the unfreezing point for the orientational glass state (essentially coinciding with the inverse critical point Tg where the rotational system freezes into the orientational glass). This treatment of Tg differs from that existing in the art according to which the glass state is destroyed owing to the increased density of phonon states. Keeping to our reasoning, we conclude that the orientational glass state does not disappear but, instead, is conserved almost unchanged under one-molecule feeling and persists to appreciably higher temperatures in the case of double filling, which affects exciton dynamics stronger.
[en] Passive nuclear track methodology (NTM) is applied to study charged particles products of the reaction 7Li+Pb at ~ 31 MeV. It is a contribution to the 8pLP Project (LNL-INFN-Italy) in where it is shown as an alternative approach to register charged particle from reaction fragments by PADC detection. The main advantage is that the passive system integrates data over the whole experiment and has its importance for low rate reaction processes. Reaction products as well as scattered beam particles are determined from track shape analysis. Some limitations are inherent to NTM since a priori knowledge is required to correlate track size distribution given by each type of particle emerging from the target. Results show that the passive technique gives useful information when applied in reaction data interpretation for a relatively large range of particle types
[en] α-TDAE-C60 is a purely organic soft ferromagnet with TC∼16 K. The mechanism of the ferromagnetism was recently proposed to be antiferro-orbital-ordering of Jahn-Teller distorted C60- (Mizoguchi et al., Phys. Rev. B 63 (2001) 040417(R)), which reproduces the pressure dependence of TC. Further, [2+2]-polymerized β-TDAE-C60 was found under pressure more than 9 kbar, where the spin on TDAE missing in α-phase revives. This paper reports on the effect of uniaxial strain to TC, an increase up to 17.5 K, and on the nature of the polymeric β-TDAE-C60
[en] We give a straightforward generalization of the Ginzburg-Landau theory for superconductors where the scalar phase field is replaced by an antisymmetric Kalb-Ramond field. While the standard properties of superconductors are recovered for temperatures not very far from the critical one, we predict that at very low temperatures, where quantum phase effects are expected to play a significant role, the presence of vortices destroys superconductivity. A physical scenario behind the model proposed, which can be directly tested by experiments, is envisaged