共查询到20条相似文献,搜索用时 0 毫秒
1.
I. V. Kalinin E. Kats M. Koza V. V. Lauter H. Lauter A. V. Puchkov 《JETP Letters》2008,87(11):645-648
Evidence of a superfluid liquid phase present in polycrystalline helium at a temperature of 0.2 K and a pressure of 51 bar has been obtained by means of inelastic neutron scattering. The superfluid component is absent at a temperature of 0.6 K and the same pressure. Thus, a “solid helium-superfluid helium” phase transition has been discovered. The sample of solid helium in a porous medium (silica aerogel) has been prepared with the use of a capillary blocking technique. The shape of the structure factor of the superfluid phase indicates the presence of clusters or the effects of a restricted geometry. The results may be used to explain the nonclassical rotational inertia phenomenon in solid helium (often referred to as supersolidity, Nature, 2004). 相似文献
2.
F. Zappa S. Denifl I. Mähr J. Lecointre F. Rondino Olof Echt T. D. Märk P. Scheier 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):117-120
Embedding molecules in helium clusters has become a
powerful technique for the preparation of cold targets for spectroscopy
experiments, as well as for the assembly of complex, fragile molecular
species. We have recently developed a helium cluster source and a pick-up cell
to produce neutral beams of doped helium droplets, to be used as targets in
studies on electron collisions with molecules of biological relevance. In
the present work we present the results of a series of experiments on
electron-impact ionization of helium clusters doped with thymine and
1-methylthymine, where several interesting phenomena were observed, i.e.,
(i) electron impact ionization of molecular clusters inside the helium
droplets leads predominantly to protonated clusters; (ii) the appearance
energies are close to the ionization threshold of the helium atom but
ionization efficiency curves in addition extend down by several eV; (iii)
ionized molecular clusters can undergo metastable decay via the loss of one
neutral monomer. 相似文献
3.
4.
5.
V.B. Efimov A.N. Ganshin G.V. Kolmakov P.V.E. McClintock L.P. Mezhov-Deglin 《The European physical journal. Special topics》2010,185(1):181-193
Rogue waves have been observed in superfluid helium. The experimental system consists of high intensity second sound (temperature-entropy)
waves within a resonant cavity. Under steady state conditions, with a constant oscillatory driving force at the resonant frequency,
the waves are turbulent and there are fluxes of energy towards both high and low frequencies. Rogue waves appear under the
nonequilibrium conditions that prevail shortly after the drive has been switched on, prior to establishment of the steady
state. The experiment is described briefly, relevant results are presented and discussed theoretically in terms of nonlinear
wave interactions, and possible connections to rogue waves on the ocean are considered. 相似文献
6.
B. Tabbert M. Beau H. Günther W. Häußler C. Hönninger K. Meyer B. Plagemann G. zu Putlitz 《Zeitschrift für Physik B Condensed Matter》1995,97(3):425-432
Optical spectra of atomic impurities in liquid helium have been investigated. Comparison is made between the wavelength of the free atomic and ionic lines and those in the liquid helium matrix. Simultaneously, the line width and a possible asymmetry is recorded. Presence and absence of radiative transitions depend on the species of the atom implanted in the quantum fluid. The absence of any optical transitions from states lying as low as 1,8 eV below the ionization limit will be explained in this paper. 相似文献
7.
M. Beau H. Günther G. zu Putlitz B. Tabbert 《Zeitschrift für Physik B Condensed Matter》1996,101(2):253-262
Optical spectra, level population and nonradiative deexcitation processes of atomic impurities in liquid helium have been investigated. The recombination of electrons and positive metal ions are described by the tunneling model. This model explains the population gap of 1.8 eV below the ionisation limit which was observed for several neutral defect atoms in liquid helium. In the framework of a pseudopotential theory excited singlet levels of Ba, Ca and Na atoms are recalculated and compared to experimental data. Non-spherical atomic defects for excited p-states are treated also. Quadrupole vibrations of these distorted defect structures are assumed to be responsible for inducing multiphonon transitions between excited atomic states. 相似文献
8.
W. Schott J.M. Pendlebury I. Altarev S. Gröger E. Gutsmiedl F.J. Hartmann S. Paul G. Petzoldt P. Schmidt-Wellenburg U. Trinks 《The European Physical Journal A - Hadrons and Nuclei》2003,16(4):599-601
Ultra-cold neutrons (UCN) are produced in superfluid helium by single- and multi-phonon excitation. The UCN production rate
density R
II via multiphonons can be larger than that by one-phonon excitation R
I being due to the dependence of the incident neutron spectral flux density dφ/dλ on the wavelength λ.
Received: 28 March 2002 / Accepted: 19 December 2002 / Published online: 11 March 2003
RID="a"
ID="a"e-mail: wschott@e18.physik.tu-muenchen.de
RID="b"
ID="b"On leave of absence from PNPI, Gatchina, Russia
Communicated by T. Walcher 相似文献
9.
R. Owczarek 《International Journal of Theoretical Physics》1991,30(12):1605-1612
Some aspects of classical field-theoretic phenomenology of superfluid helium are presented. 相似文献
10.
H. Lambaré P. Roche S. Balibar H.J. Maris O.A. Andreeva C. Guthmann K.O. Keshishev E. Rolley 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):381-391
We have studied the nucleation of bubbles in pure superfluid helium-4 at temperatures down to 65 mK. We have found that the
nucleation is a stochastic process, and that at temperatures below 600 mK the nucleation rate is independent of temperature.
These results are consistent with the assumption that the nucleation takes place via quantum tunneling.
Received: 15 November 1997 / Received in final form: 19 December 1997 / Accepted: 22 January 1998 相似文献
11.
12.
13.
The Fulde-Ferrell state in a superfluid3He-4HeII solution is investigated. Starting from its broken symmetry, a relative translation-gauge symmetry, the linearized hydrodynamic equations to lowest order in wave number are presented. To this order, the superfluid current perpendicular to the preferred direction vanishes identically; at the same time, supercurrents generated by a uniform change in temperature or density become possible. The Goldstone mode of the Fulde-Ferrell state is shown to be a propagating spin-temperature-shear wave. 相似文献
14.
Nils Brenning 《Journal of Quantitative Spectroscopy & Radiative Transfer》1980,24(4):293-318
Methods of measuring the electron temperature in low-density plasmas by He spectroscopy are examined. These utilize either the relative intensities of singlet and triplet lines or the absolute intensities of single lines. Calculations from measured and theoretical data show that both methods are seriously influenced by secondary processes, the most important of which are excitation from the metastable levels 21S and 23S, and excitation transfer in electron-atom collisions combined with imprisonment of resonance radiation. The calculations give parameter limits for the validity of different methods and combinations of lines. Due to the secondary processes, the determination of Te from relative line intensities is restricted to low-density, short-duration plasmas (typically ne < 2 × 1016 m-3, tex < 5 × 10-6 s) or to even lower densities that depend on the apparatus dimensions (typically ne < 3 × 1015 m-3, L ≈ 0.1 m). For the determination of Te from absolute line intensities, the situation is more favourable and, with a suitable choice of lines, typical restrictions on ne and tex are ne < 5 × 1017 m-3, tex < 10-5 s or ne < 1017 m-3, L ≈ 0.1 m for electron temperatures above 10 eV. For temperatures below 10 eV and degrees of imprisonment below 7% measurements are possible for electron densities up to 1019–1020 m-3, without any limits on tex or L. 相似文献
15.
Mubarak Ahmad 《Czechoslovak Journal of Physics》1975,25(10):1127-1138
The close structural similarity between the commutation relations of harmonic oscillator operators and the operators for Bose fields is exploited to study the excitation spectrum in superfluid helium 4. By applying ‘broken symmetry’ condition it is shown how the creation of phonon gives rise to superfluid behaviour of liquid He 4. The energy gap needed for roton excitation is derived. 相似文献
16.
We report new measurements of mixing of passive temperature field in a turbulent flow. The use of low temperature helium gas allows us to span a range of microscale Reynolds number, R(lambda), from 100 to 650. The exponents xi(n) of the temperature structure functions approximately r(xi(n)) are shown to saturate to xi(infinity) approximately 1.45+/-0.1 for the highest orders, n approximately 10. This saturation is a signature of statistics dominated by frontlike structures, the cliffs. Statistics of the cliffs' characteristics are performed, particularly their widths are shown to scale as the Kolmogorov length scale. 相似文献
17.
Sethumadhavan B Yao W Huang YH Lanou RE Maris HJ Seidel GM 《Physical review letters》2006,97(1):015301
Electrical breakdown of partially filled helium cells below 0.5 K is shown to be the result of Penning ionization of metastable triplet helium excimers bound to the surface of the liquid. 相似文献
18.
19.
I. V. Kalinin E. I. Kats M. Koza V. V. Lauter H. Lauter A. V. Puchkov 《Journal of Experimental and Theoretical Physics》2010,111(2):215-219
The results of recent neutron scattering studies of solid helium in silica aerogel are discussed. Previously I.V. Kalinin
et al., Pis’ma Zh. éksp. Teor. Fiz. 87 (1), 743 (2008) [JETP Lett. 87 (1), 645 (2008)], we detected the existence of a superfluid phase in solid helium at a temperature below 0.6 K and a pressure
of 51 bar, although, according to the phase diagram, helium should be in the solid state under these conditions. This work
is a continuation of the above studies whose main goal was to examine the detected phenomenon and to establish basic parameters
of the existence of a superfluid phase. We have determined the temperature of the superfluid transition from solid to superfluid
helium, T
C = 1.3 K, by analyzing experimental data. The superfluid phase excitation parameters (lifetime, intensity, and energy) have
a temperature dependence similar to that of bulk helium. The superfluid phase coexists with the solid phase in the entire
measured temperature range from T = 0.05 K to T
C and is a nonequilibrium one and disappears at T
C. 相似文献
20.
The thermodynamic properties of anisotropic quasiparticle systems of He II are considered for all degrees of anisotropy. It is shown that the thermodynamic functions of a strongly anisotropic phonon-roton system are mainly determined by rotons at all temperatures. Analytical expressions for the roton thermodynamic functions are obtained for all degrees of anisotropy. The maximum anisotropy is limited by the criterion for thermodynamic stability, which is here derived for the whole temperature range. 相似文献