共查询到20条相似文献,搜索用时 15 毫秒
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Bolivar AO 《Physical review letters》2005,94(2):026807
In the large damping limit we derive a Fokker-Planck equation in configuration space (the so-called Smoluchowski equation) describing a Brownian particle immersed into a thermal environment and subjected to a nonlinear external force. We quantize this stochastic system and survey the problem of escape over a double-well potential barrier. Our finding is that the quantum Kramers rate does not depend on the friction coefficient at low temperatures; i.e., we predict a superfluidity phenomenon in overdamped open systems. Moreover, at zero temperature we show that the quantum escape rate does not vanish in the strong friction regime. This result, therefore, is in contrast with the work by Ankerhold et al. [Phys. Rev. Lett. 87, 086802 (2001)]] in which no quantum tunneling is predicted at zero temperature. 相似文献
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The internal friction of deuterium-doped vanadium has been investigated in the temperature range from 65 to 350 K. At low
deuterium concentrations (≦0.18 at.−%) a relaxation effect has been observed near 90 K; its activation energy and its limiting
relaxation tiem are 0.17 eV and 2×10−12 sec, respectively. A second internal friction peak (precipitation peak) appears in more heavily doped samples; the position
of this second peak shifts to higher temperatures as the deuterium content is increased. Possible mechanisms for the two peaks
are discussed. The phase diagram of the vanadium-deuterium system at low temperatures has been deduced from the correlation
between the deuterium concentration and the position of the precipitation peak. 相似文献
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The influence of additions of interstitial oxygen and nitrogen on the internal friction spetrum of the niobium-1 at-% titanium
alloy was studied. The nature of the various observed relaxation processes introduced by the presence of substitutional titanium
is discussed. A thermodynamic analysis was carried out for two pronounced interaction peaks attributed to the stress-induced
reorientation of single oxygen or nitrogen atoms around single titanium atoms and the respective binding energies were estimated.
It was also found that, over the range of oxygen concentration studied, interstitial oxygen is completely removed from random
migration by substitutional titanium atoms acting as trapping centres, whilst nitrogen population is always partitioned between
mobile and trapped atoms even at very low relative nitrogen concentrationsC
N/C
Ti. A possible reason for the different behavior of oxygen and nitrogen is suggested. 相似文献
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Positron Lifetime measurements reveal that neutron irradiation at 350 and 400°C can produce sub-electron microscopic voids in Mo. The results show that the lifetime in voids reaches a saturation value with increasing void size to a dimension less than 20 Å. It is suggested that the difference among known data for τ2 ? 450 ps can be attributed to differences in the metal-void interface and gaseous conditions within the void. 相似文献
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V. M. Lebedev V. T. Lebedev S. P. Orlov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2012,6(5):718-721
The supra-atomic structure of single crystals of synthetic quartz with a dislocation density of 54 cm?2 in their initial state and after irradiation in a VVR-M reactor by fast neutrons with the energy, E n > 0.1 MeV, at fluences of 2.3 × 1019 and 4.5 × 1019 N/cm2, has been studied by the method of small-angle thermal neutron scattering. It has been established that fast neutrons create point, linear, and bulk defects throughout the entire material. It has been shown that extended defects have a significant integral length per volume unit equal to ??3 × 1011 cm/cm3, and can form a consolidated network in the sample with a cell size of ??30 nm, through the channels of which the migration of impurity atoms and molecules is possible. 相似文献
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The effects of deuteride precipitation from Ta-D solid solution was investigated by vibration frequency and internal friction measurements in the temperature range (80–300) K. Initiation of deuteride precipitation is indicated by the inflexion of the frequency curve, whereas the onset of the dislocation-loops formation around the deuteride particles is correlated with the internal friction growth (precipitation peak). The dislocation interstitial drag model which seems to better account for the precipitation peak, is discussed. The phase diagram of the Ta-D system was determined in the range of (0.2–7.5) at.~%. 相似文献
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V. I. Grafutin A. G. Zaluzhnyi S. P. Timoshenkov O. M. Britkov O. V. Ilyukhina G. G. Myasishcheva E. P. Prokop’ev Yu. V. Funtikov 《Journal of Experimental and Theoretical Physics》2008,106(4):625-634
The influence of proton bombardment and metal atom impurities on the structure of quartz single crystals has been studied. The related defects have been studied using positron annihilation spectroscopy (angular correlation of positron-annihilation photons), acoustic absorption, and optical absorption measurements. It is shown that the presence of a narrow component f in the angular distribution of annihilation photons (ADAP), which is related to the formation of parapositronium, determines a high sensitivity of this method with respect to features of the crystal structure of quartz. It is established that the defectness of the structure of irradiated quartz crystals can be characterized by the ratio f/f 0 of the relative intensities of narrow components in the ADAP curves measured before (f 0) and after (f) irradiation. Any process leading to a decrease in the probability of positronium formation (e.g., positron loss as a result of the trapping on defects and the interaction with impurity atoms and lattice distortions) decreases the intensity of the narrow component. Based on the ADAP data, estimates of the radii and concentrations of nanodefects in quartz have been obtained and their variation upon annealing at temperatures up to T = 873 K has been studied. 相似文献
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P. I. Arseev N. S. Maslova S. I. Oreshkin V. I. Panov S. V. Savinov 《JETP Letters》2000,72(11):565-568
Interaction of two localized impurity states of Si atoms at a GaAs surface was studied by scanning tunneling microscopy and spectroscopy. The effects of a twofold “switching” on and off of the states of each of the interacting atoms, the tunneling-interaction-induced mutual level pulling of these states, and the level stabilization near E F were observed. These effects are explained in terms of the extended Anderson model. 相似文献
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Co islands grown on Cu(111) with a stacking fault at the interface present a conductance in the empty electronic states larger than the Co islands that follow the stacking sequence of the Cu substrate. Electrons can be more easily injected into these faulted interfaces, providing a way to enhance transmission in future spintronic devices. The electronic states associated with the stacking fault are visualized by tunneling spectroscopy, and its origin is identified by band structure calculations. 相似文献
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A. Puškár 《Ultrasonics》1982,20(3):118-122
A new interpretation of some characteristics of material push-pull loaded at a frequency of 23 kHz can be evaluated by measuring the internal friction and elasticity modulus defect at different strain amplitudes. It is possible to obtain interesting relations describing the material's cyclic microplasticity response. The paper presents some basic relationships between the ‘plastic’ internal friction, elasticity modulus defect, hysteresis loop area, plastic strain amplitude and the cyclic deformation hardening coefficient, for low carbon steel with different grain sizes. 相似文献
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G. Dlubek R. Krause O. Brümmer J. Tittes 《Applied Physics A: Materials Science & Processing》1987,42(2):125-127
Positron-lifetime measurements have been used to study the annealing of vacancies in neutron-irradiated GaAs. The vacancies which are interpreted as defects in the Ga sublattice disappear in a single annealing stage (at 500°C in GaAs doped with Si or Zn, and at 600°C in Cr-doped GaAs). 相似文献
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V. M. Arzhavitin N. N. Efimova M. B. Ustimenkova V. A. Finkel’ 《Physics of the Solid State》2001,43(11):2121-2125
The results of high-temperature (20≤T≤800°C) relaxation and magnetic investigations of ferrite Li0.5Fe2.5O4 in various structural states are given. Anomalies of internal friction caused by the occurrence of ferrimagnetic and structural (ordering type) second-order phase transitions and by vibrations of domain walls of ferrimagnetic and antiphase domains were revealed. It is shown that the 1: 3 ordering of Fe3+ and Li+ ions in the octahedral sublattice of the spinel leads to a decrease in the Curie temperature, a change in the character of the temperature dependence of the low-field magnetization, and a narrowing of the temperature range of the structural phase transition, as well to a substantial weakening of dissipation processes connected with vibrations of ferrimagnetic domain walls in the field of elastic stresses. 相似文献