共查询到20条相似文献,搜索用时 31 毫秒
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U. Ernst J. Schuster F. Schreck A. Marte A. Kuhn G. Rempe 《Applied physics. B, Lasers and optics》1998,67(6):719-722
5 rubidium-87 atoms released from an Ioffe–Pritchard magnetic trap is investigated experimentally. The expansion dynamics depend
only on the trap frequencies, which are determined independently. The data are in good agreement with the expected expansion
of a condensate, and are clearly distinct from the behaviour of a classical gas in the hydrodynamic regime.
Received: 3 June 1998/Final version: 25 September 1998 相似文献
3.
C. Clanet E. Villermaux 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):529-536
We first introduce a simple and new method for the quantitative analysis of some nonlinear oscillating systems. It is shown
that if the dynamics of the system reduces to piecewise exponential growth and exponential damping phases, then the amplitude
and period of the motion can be computed with accuracy in the nonlinear regime without invoking linear stability arguments
or perturbative expansions. This method is then successfully applied to the delayed logistic application and to the Lotka-Volterra
prey-predator model. For both of these systems, we provide an accurate analytical expression for the period of the oscillations
in the nonlinear regime.
Received: 27 April 1998 / Received in final form: 25 June 1998 / Accepted: 29 June 1998 相似文献
4.
A. Wobst D. Weinmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):159-167
The curvatures of two-particle energy levels with respect to the enclosed magnetic flux in mesoscopic disordered rings are
investigated numerically. We find that the typical value of the curvatures is increased by interactions in the localised regime
and decreased in the metallic regime. This confirms a prediction by Akkermans and Pichard (Eur. Phys. J. B 1, 223 (1998)). The interaction-induced changes of the typical curvatures at different energies and disorder strengths exhibit
one-parameter scaling with a conductance-like single parameter. This suggests that interactions could influence the conductance
of mesoscopic systems similarly.
Received 24 August 1998 相似文献
5.
E. Roissé V. Couderc A. Barthélémy F. Louradour 《Applied physics. B, Lasers and optics》1999,69(2):89-91
We report the first diode-pumped solid-state laser operating in cw-mode-locked regime and simultaneously achieving intracavity
frequency-tripling. This laser provide UV picosecond pulses (λ=355 nm) of 10 ps duration with 0.5 mW average power at 150 MHz
repetition rate. A different set of adjustments gave rise to a Q-switched mode-locked regime. Trains of hundred UV pulses
of 60 ps duration and 4 W peak power were produced in this latter case at 50 kHz repetition rate.
Received: 12 October 1998 / Revised version: 12 December 1998 / Published online: 26 May 1999 相似文献
6.
M. Dumm M. Dressel M. Nicklas P. Lunkenheimer A. Loidl M. Weiden F. Steglich B. Assmann H. Homborg P. Fulde 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):317-322
The magnetic susceptibility, using dc and electron spin resonance (ESR) methods, the specific heat, and the infrared properties
of the one-dimensional molecular semiconductors lithium phthalocyanine (LiPc) and the iodinated compound LiPcI have been investigated
for temperatures K. LiPc has a half-filled conduction band and is expected to be an organic metal. However, due to the strong Coulomb repulsion
the system is a one-dimensional Mott-Hubbard insulator with a Hubbard gap of 0.75 eV as inferred from optical measurements.
The localized electrons along the molecular stacks behave like a S = 1/2 antiferromagnetic spin chain. The spin susceptibility, as determined by ESR experiments, and the magnetic contribution
to the heat capacity show a Bonner-Fisher type of behavior with an exchange constant K. LiPcI is an intrinsic narrow-gap semiconductor with an optical gap of 0.43 eV. In ESR experiments it is silent, indicating
that all the unpaired electrons have been removed from the macrocycle via doping with iodine.
Received: 16 June 1998 / Accepted: 14 July 1998 相似文献
7.
A.A. Zvyagin D.M. Apal'kov 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):565-569
We present a Bethe Ansatz based investigation of a one-dimensional (1D) Heisenberg spin chain in a real 3D crystal lattice.
We have shown that due to an influence of the lattice distortion on a crystalline field of ligands of magnetic ions, a Heisenberg
antiferromagnetic spin chain is unstable under the appearance of a magnetic anisotropy of the “easy-plane” type. The effects of an external magnetic
field and nonzero temperature onto such a phase transition are studied.
Received: 19 January 1998 / Revised: 16 March 1998 / Accepted: 17 March 1998 相似文献
8.
M.V. Moskalets 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(4):645-649
The effect of an electrostatic energy (in the geometrical capacitance approach) on a persistent current is considered. It
is shown that at high temperatures the current amplitude shows periodic dips as a function of the potential difference between
a ring and a reservoir. These dips correspond to a lift of the Coulomb blockade. In a minimum of a dips a current is periodic
in a magnetic flux with a period at any temperatures.
Received: 6 April 1998 / Revised: 5 June 1998 / Accepted: 21 July 1998 相似文献
9.
B.Z. Narymbetov N.D. Kushch L.V. Zorina S.S. Khasanov R.P. Shibaeva T.G. Togonidze A.E. Kovalev M.V. Kartsovnik L.I. Buravov E.B. Yagubskii E. Canadell A. Kobayashi H. Kobayashi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):179-185
The -(BETS)2C(CN)3 radical cation salt was prepared by electrocrystallization, and its crystal structure was determined by single crystal X-ray
diffraction. The electronic structure of -(BETS)2C(CN)3 was studied by means of the extended Hückel tight binding method. The electrical conductivity of this salt as a function
of temperature shows a metallic behaviour down to 1.3 K. Shubnikov-de Haas oscillations reveal both the classical and magnetic
breakdown orbits on the Fermi surface typical of the -type organic conductors. In addition, a low frequency oscillation (250 T) which is not predicted by the band structure calculations
has been found in the oscillation spectrum.
Received: 11 March 1998 / Revised: 9 June 1998 / Accepted: 11 June 1998 相似文献
10.
G. Peng J.-U. Sommer A. Blumen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):73-79
We investigate numerically, using the bond-fluctuation model, the adsorption of many random AB-copolymers with excluded volume
interactions at the interface between two solvents. We find two regimes, controlled by the total number of polymers. In the
first (dilute) regime, the copolymers near the interface extend parallel to it, while in the second regime they extend perpendicular
to it. The density at the interface and the density in the bulk depend differently on the total number of copolymers: In the
first regime the density at the interface increases more rapidly than in the bulk, whereas the opposite is true in the second
regime.
Received 4 March 1998 and Received in final form 22 September 1998 相似文献
11.
C. Wiele F. Haake K. Rzażewski 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(3):405-409
We solve the superradiant laser model in two limiting cases. First the stationary low-pumping regime is considered where a
first-order phase transition in the semiclassical solution occurs. This discontinuity is smeared out in the quantum regime.
Second, we solve the model in the non-stationary regime where we find a temporally periodic solution. For a certain parameter
range well-separated pulses may occur.
Received: 19 June 1998 / Accepted: 19 October 1998 相似文献
12.
D. Elefant G. Reiss C. Baier 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(1):45-53
On bulk layered single crystals (Bi0.25Sb0.75)2Te3 with a hole concentration cm-3 and a mobility cm2/Vs magnetoresistance and Hall effect investigations were performed in the temperature range T = 1.4 K ... 20 K in magnetic fields up to 18 T. For the magnetic field perpendicular to the layered structure giant Shubnikov-de
Haas oscillations are measured; the positions of the maxima are triplets in the reciprocally scaled magnetic field. From the
damping of the amplitudes with increasing temperature the cyclotron mass m
c
= 0.12m
0
is evaluated. Correlated with the SdH oscillations doublets of Hall effect plateaus (or kinks in low fields) are found. The
weak well known Shubnikov-de Haas oscillations from the generally accepted multivallied highest valence band can be detected
as a modulation on the giant oscillation. The high anisotropy of the SdH oscillations and their triplet structure in connection
with the layered crystal structure lead us to suggest that the effects are caused by hole carrier pairing (mediated by the
bipolaron mechanism) in quasi 2D sheets parallel to the crystal layer stacks. The measured Hall plateau resistances coincide
with the quantum Hall effect values considering the number of layer stacks and the valley degeneracy of the 3D hole carrier
reservoir. The ratio of spin splitting to Landau (cyclotron) splitting is observed to be .
Received: 12 September 1997 / Revised: 8 January 1998 / Accepted: 22 January 1998 相似文献
13.
G.N. Zhizhin E.V. Alieva L.A. Kuzik V.A. Yakovlev D.M. Shkrabo A.F.G. van der Meer M.J. van der Wiel 《Applied Physics A: Materials Science & Processing》1998,67(6):667-673
2 , BaF2, MgO, LiNbO3 were determined. The nonlinear spectroscopy applications of SEW–FEL techniques to studies of a second-harmonic generation
(SHG) on crystal surfaces in the regime of counterpropagating SEWs – the frequency dependence of efficiency and the influence
of a thin film deposition on a quartz surface – are described.
Received: 15 May 1998/Accepted: 25 August 1998 相似文献
14.
S. Bottin H. Chaté 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(1):143-155
We argue on general grounds that the transition to turbulence in plane Couette flow is best studied experimentally at a statistical
level. We present such a statistical analysis of experimental data guided by a parallel investigation of a simple coupled
map lattice model for spatiotemporal intermittency. We confirm that this generic type of spatiotemporal chaos is relevant
in the context of plane Couette flow, where the linear stability of the laminar regime at all Reynolds numbers insures the
necessary local subcriticality. Using large ensembles of similar experiments, we show the existence of a well-defined threshold
Reynolds number above which a unique, turbulent, intermittent attractor coexists with the laminar flow. Furthermore, our data
reveals that this transition to spatiotemporal intermittency is discontinuous, i.e. akin to a first-order phase transition.
Received: 10 April 1998 / Revised: 22 June 1998 / Accepted: 24 June 1998 相似文献
15.
1-x NdyLax-yMgxAl12-xO19) is a new material, tunable in the 1–1.1 μm band. We present the first results of pulsed laser emission of this crystal under
flashlamp pumping. We obtain a slope efficiency of 3.3% with a maximum average power of 40 W at 40 Hz in free-lasing regime.
Nd:Cr codoping of ASL is also tested, but with much lower efficiency.
Received: 12 June 1998/Revised version: 30 September 1998 相似文献
16.
M. Acharyya D. Stauffer 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):571-575
We have studied the nucleation in the nearest neighbour ferromagnetic Ising model, in different (d) dimensions, by extensive Monte-Carlo simulation using the heat-bath dynamics. The nucleation time () has been studied as a function of the magnetic field (h) for various system sizes in different dimensions (d=2,3,4). The logarithm of the nucleation time is found to be proportional to the power (-(d-1)) of the magnetic field (h) in d dimensions. The size dependent crossover from coalescence to nucleation regime is observed in all dimensions. The distribution
of metastable lifetimes are studied in both regions. The numerical results are compared and found to be consistent with the
classical theoretical predictions. In two dimensions, we have also studied the dynamical response to a sinusoidally oscillating
magnetic field. The reversal time is studied as a function of the inverse of the coercive field. The applicability of the
classical nucleation theory to study the hysteresis and coercivity has been discussed.
Received: 21 January 1998 / Accepted: 17 March 1998 相似文献
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A new method for extracting the hyperfine anomaly from experimental hyperfine structure constants is suggested. Instead of
independent high-precision measurements of the nuclear magnetic dipole moment, precise measurements of magnetic dipole hyperfine
interaction constants for two atomic states and a theoretical analysis can be used. This can lead to determination of hyperfine
anomaly for radioactive isotopes where the nuclear magnetic dipole moment is not known with high accuracy.
Received: 17 February 1998 相似文献
19.
E. Degroote P.L. Garcia-Ybarra 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):381-386
Flame spreading over liquid ethanol has been experimentally characterized for ethanol for subflash temperatures, in two different
channels. Three different spreading regimes have been observed. A uniform region (with flame velocities close to 10 cm/s)
appears for values of the initial surface liquid temperature above a critical value . For values an oscillatory regime occurs. For very low temperatures, , a new uniform regime appears with slow propagation velocities (close to 1 cm/s). The critical point has been described as a Hopf bifurcation, while resembles a homoclinic connection.
Received 16 October 1998 and Received in final form 23 June 1999 相似文献
20.
A. Dinia S. Zoll M. Gester D. Stoeffler J.P. Jay K. Ounadjela H.A.M. van den Berg H. Rakoto 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):203-214
The structural, magnetic and transport properties of Co/Rh sandwiches grown by ultra high vacuum evaporation and sputtering
have been studied. High-energy electron diffraction observations during the growth reveal that both Co and Rh layers have
been stabilised in the (111) fcc structure for the evaporated sandwiches. X-ray measurements performed on sputtered samples
show a predominant fcc polycrystalline structure of the stacks with a preferential (111) texture. Magnetisation and magnetoresistance
measurements show a very strong antiferromagnetic exchange coupling for thin Rh layers, reaching for 4.8? Rh, the strongest ever observed in exchange coupled systems. This value is in good agreement with the value of obtained by ab initio calculations for Co/Rh (hcp) superlattices. This is explained by the magnetic nature of the Co/Rh interfaces. Indeed, the
variation of the measured saturation magnetisation as a function of the Co layer thickness shows no evidence of Co moment
reduction for the Co atoms located at the interfaces, even for the very thin layers. The value of the preserved magnetic moments
of the cobalt atoms at the interfaces is confirmed by ab initio calculations for Co/Rh superlattices taking the intermixing into account.
Received: 18 February 1998 / Received in final form: 30 April 1998 /
Accepted: 29 May 1998 相似文献