共查询到20条相似文献,搜索用时 328 毫秒
1.
N. Mohapatra K. K. Iyer E. V. Sampathkumaran 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(4):451-454
We report a large entropy change (ΔS) below 300 K, peaking near T
C
= 220 K, due to isothermal change of magnetic field, for Gd4Co3, with a refrigeration capacity higher than that for, say, LaFe11.4Si1.6, ordering magnetically in the same temperature range. A noteworthy finding is that the isothermal magnetization is nonhysteretic
— an important criterion for magnetic refrigeration without loss. ΔS behavior is also compared with that of magnetoresistance. 相似文献
2.
Curvature and external electric field effects on the persistent current in chiral toroidal carbon nanotubes 总被引:1,自引:0,他引:1
N. Xu J. W. Ding H. B. Chen M. M. Ma 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(1):71-75
Taking into account the intrinsic curvature, we calculate the persistent currents (Ipcs) in chiral toroidal carbon nanotubes (TCNs) by developing the supercell approach. It is shown that in the presence of curvature,
the typical current (Ity) oscillates with the unit cell number (P) and tends to be zero, while it damps exponentially in the absence of curvature.
Due to the curvature effects, especially, a paramagnetism-diamagnetism transition is observed in chiral TCNs, depending on
the ring diameter and chirality. In addition, the effect of external electric field energy (Eef) on persistent current is also explored. It is shown that in the presence of electric field, Ity vary unmonotonously with Eef. A pronounced peak of Ity is obtained at high Eef region. By modulating the value of Eef, a paramagnetism-diamagnetism or diamagnetism- paramagnetism transition is observed. 相似文献
3.
R. Vladoiu M. Contulov A. Mandes G. Musa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(2):287-291
The M-effect (monochromatization-effect) is a powerful tool which can give high intensity monochromatic spectra with a certain
wavelength depending on the type of used gas mixtures to generate plasma state. The effect consists in the emission of a single
spectral line of plasmas ignited in certain gas mixtures. The main condition to obtain the M effect is the presence of an
electropositive and an electronegative gas mixture. For example, in the case of Ne+H2 monochrome radiation was obtained, the wavelength of Ne being 585.3 nm (1s2–2p5). In this paper we prove the general character of this effect, i.e. if the optical emission spectra reduced to nearly one
line can be observed also in other gas mixture discharges, for example in the case of one electronegative gas and two electropositive
gases. Different other mixtures, as Xe+Ne+H2 and Xe+Ar+H2 have been studied. In all these cases, the M-effect appeared without doubt. 相似文献
4.
The airborne transport of particles on a granular surface by the
saltation mechanism is studied through numerical simulation of
particles dragged by turbulent air flow. We calculate the
saturated flux qs and show that its dependence on the wind
strength u* is consistent with several empirical relations
obtained from experimental measurements. We propose and explain
a new relation for fluxes close to the threshold velocity ut,
namely, qs=a(u*-ut)α with α≈2. We
also obtain the distortion of the velocity profile of the wind due to the
drag of the particles and find a novel dynamical
scaling relation. We also obtain a new expression for the dependence of
the height of the saltation layer as function of the strength of the wind. 相似文献
5.
6.
K.?Koyasu M.?Niemietz W.?Westh?user G.?Gantef?r 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,53(1):59-62
The decay path of an Ag8(O2)- cluster photoexcited by a 3.1 eV photon is elucidated using time-resolved photoelectron spectroscopy. Photoabsorption results
in the formation of an excited state giving rise to a peak in the photoelectron spectra with well-resolved vibrational finestructure.
With a lifetime of about 100 fs this bound state decays into an anti-bonding state which dissociates into O2 and Ag8- on a timescale of 10 ps. In the photoelectron spectra, this corresponds to a broad maximum shifting gradually towards higher
binding energy while the O2 and Ag8- separate. Finally, the spectrum of bare Ag8- appears. This process is unique to small clusters, because on metal surfaces excited state lifetimes are too short to allow
for direct dissociation. 相似文献
7.
A. -B.M.A. Ibrahim J. Osman 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(2):193-198
In this paper we investigate the intrinsic optical bistability (IOB) in a
ferroelectric (FE) single layer using an alternative analysis. The FE
material is considered to have an intensity-dependent refractive index where
the third order nonlinear susceptibility χ(3) acts like Kerr
coefficient. The nonlinear response of the FE medium is modeled using the
Landau-Khalatnikov (LK) dynamical equation with the nonlinear anharmonic
potential obtained from the Landau-Devonshire free energy expressed in terms
of polarization. Within a single frequency approximation, the
electromagnetic wave equation is written in terms of the polarization P
rather than the electric field E as the dependent variable. With the
application of the nonlinear boundary conditions we have derived expressions
for both reflectance and transmittance as a function of the electric field
incident amplitude, polarization and other material parameters. The
formalism proves to be more suitable for FE materials since most of these
materials have highly linear and nonlinear coefficients especially when the
operating frequency is in the resonance region. The effects of thickness,
operating frequency and temperature on BaTiO3 single film are
investigated theoretically. The results presented here agree in principle
with the recent experimental observations of intrinsic OB in BaTiO3
monocrystal and other FE photorefractive materials. 相似文献
8.
Xi-Wen Hou Jing-Hua Chen Ming-Fang Wan Zhong-Qi Ma 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(1):37-41
The dynamical comparison of entanglement, measured by linear entropy and negativity, is carried out for initial pure separable
states in vibrations of H2O and SO2. It is shown that both measures of an initial state with local-mode character have the same period for H2O, while those of an initial state with normal-mode character are no longer identical in period. When the total quantum number
of the initial state is one, both measures rise and lower together with the period for H2O being larger than that for SO2. For a suitable state in H2O, both measures exhibit a beat phenomenon with a long period. 相似文献
9.
Ultrathin gate dielectrics for silicon nanodevices 总被引:1,自引:0,他引:1
M. Hirose W. Mizubayashi Khairurrijal M. Ikeda H. Murakami A. Kohno K. Shibahara S. Miyazaki 《Superlattices and Microstructures》2000,27(5-6)
This paper reviews recent progress in structural and electronic characterizations of ultrathin SiO2thermally grown on Si(100) surfaces and applications of such nanometer-thick gate oxides to advanced MOSFETs and quantum-dot MOS memory devices. Based on an accurate energy band profile determined for the n + -poly- Si/SiO2/Si(100) system, the measured tunnel current through ultrathin gate oxides has been quantitatively explained by theory. From the detailed analysis of MOSFET characteristics, the scaling limit of gate oxide thickness is found to be 0.8 nm. Novel MOSFETs with a silicon quantum-dot floating gate embedded in the gate oxide have indicated the multiple-step electron injection to the dot, being interpreted in terms of Coulombic interaction among charged dots. 相似文献
10.
I. Popov T. Kunze S. Gemming G. Seifert 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):439-446
The preferred adsorption sites and the propensity for a self-organised growth of the molybdenum sulfide cluster Mo6S8 on the Au(111) surface are investigated by density-functional band-structure calculations with pseudopotentials and a plane
wave basis set. The quasi-cubic cluster preferentially adsorbs via a face and remains structurally intact.
It experiences a strong, mostly non-ionic attraction to the surface
at several quasi-isoenergetic adsorption positions. A scan of the potential energy surface exhibits only small barriers between
adjacent strong adsorption sites. Hence, the cluster may move in a potential well with degenerate local energy minima at room
temperature. The analysis of the electronic structure reveals a negligible
electron transfer and S-Au hybridised states, which indicate that the cluster-surface
interaction is dominated by S-Au bonds, with minor contributions from
the Mo atom in the surface vicinity. All results indicate that Mo6S8 clusters
on the Au(111) surface can undergo a template-mediated self-assembly to an ordered inorganic monolayer, which is still redox
active and may be employed as surface-active agent in the integration of noble metal and ionic or biological components within
nano-devices.
Therefore, a classical potential model was developed on the basis of the DFT data,
which allows to study larger cluster assemblies on the Au(111). 相似文献
11.
I. Živković V. P.S. Awana H. Berger 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(4):423-431
We have performed an investigation of the nonlinear magnetic response in ruthenocuprates. A negative, diverging-like peak
at the main magnetic transition TN in RuSr2
RECu2O8 (RE = Gd, Y) indicates a possible canted antiferromagnetic order. Another well defined feature above TN points to a blocking of superparamagnetic particles through the T-3 dependence of the third harmonic at higher temperatures. Below TN a nondiverging peak appears, which is strongly affected by the addition of 10% of Cu ions in the RuO2 planes. In RuSr2
RE
2-xCexCu2O10 the main magnetic transition TM is accompanied by two characteristic temperatures in the third harmonic of the ac susceptibility, in agreement with recent
studies from μSR and M?ssbauer spectroscopy. We find that the spin-spin correlation temperature is the same in both families
of ruthenocuprates. 相似文献
12.
M. V. Kossov 《The European Physical Journal A - Hadrons and Nuclei》2008,36(3):289-293
The CHIPS (CHiral Invariant Phase Space) model is used for approximation of the Drell-Yan process in hadron-nucleon interactions.
It is proved that the Drell-Yan cross-section at low p
T
2 is a function of only x1 and x2 and does not evolve as a function of the squared mass of the lepton pair M2. The CHIPS model predicts that the Drell-Yan structure functions evolve as a function of p
T
2 . This p
T
2 evolution can be measured in experiments at RHIC and LHC. 相似文献
13.
An all-electron scalar relativistic calculation on AunH2S (n = 1-13) clusters has been performed by using density functional theory with the generalized gradient approximation at PW91 level. The small gold cluster would like to bond with sulfur in the same plane and the H2S molecule prefers to occupy the on-top and single fold coordination site in the cluster. The Aun structures and H2S molecule in all AunH2S clusters are only slightly perturbed and still maintain their structural integrity. After adsorption, the S-H, H-H bond-lengths and most Au-Au bond-lengths are elongated, only a few Au-Au bond-lengths far from H2S molecule are shortened. The reactivity enhancement of H2S molecule is obvious and the strong gold-sulfur bond is observed expectedly. The most favorable adsorption takes place in the case that the H2S molecule is adsorbed by an even-numbered Aun cluster and becomes AunH2S cluster with even number of valence electrons. It is believed that the strong scalar relativistic effect is favorable to H2S molecule adsorption onto small gold clusters and is also one of the important reasons for the strong gold-sulfur bond. 相似文献
14.
M. Bonura A. Agliolo Gallitto M. Li Vigni C. Ferdeghini C. Tarantini 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(2):165-177
We report on the microwave surface resistance of two
polycrystalline Mg11 B2 samples; one consists of
pristine material, the other has been irradiated at very high neutron
fluence. It has already been reported that in the strongly irradiated
sample the two gaps merge into a single value. The mw surface resistance
has been measured in the linear regime as a function of the temperature and the DC magnetic
field, at increasing and decreasing fields. The results obtained in the
strongly irradiated sample are quite well justified in the framework of a
generalized Coffey and Clem model, in which we take into account the field
distribution inside the sample due to the critical state. The results
obtained in the pristine sample show several anomalies, especially at low
temperatures, which cannot be justified in the framework of standard
models for the fluxon dynamics. Only at temperatures near Tc and for
magnetic fields greater than 0.5Hc2(T) the experimental data can quantitatively be
accounted for by the Coffey and Clem model, provided that the
upper-critical-field anisotropy is taken into due account. 相似文献
15.
When the processive motor protein kinesin walks along the biopolymer microtubule it can occasionally make a backward step.
Recent single molecule experiments on moving kinesin have revealed that the forward-to-backward step ratio decreases exponentially
with the load force. Carter and Cross (Nature 435, 308-312, 2005) found that this ratio tightly followed 802 × exp[−0.95F], where F is the load force in piconewtons. A straightforward analysis of a Brownian step leads to L/(2k
B
T) as the factor in front of the load force, where L is the 8 nm stepsize, k
B
is the Boltzmann constant, and T is the temperature. The factor L/(2k
B
T) does indeed equal 0.95 pN−1. The same analysis shows how the 802 prefactor derives from the power stroke energy G as exp[G/(2k
B
T)]. There are indications that the power stroke derives from the entropically driven coiling of the 30 amino acid neck linker
that connects the two kinesin heads. This idea is examined and consequences are deduced. 相似文献
16.
M. B. Das S. Karmakar 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(3):339-341
Lifetimes of eight levels belonging to the 5p46d configuration of
singly ionized xenon have been measured by high frequency deflection
technique with a delayed coincidence single photon counting arrangement. The
results have been compared with other experimental and theoretical values.
The lifetimes of the 6d 2F3/2 and 6d 4F3/2 levels have
been measured for the first time. 相似文献
17.
G. Pal Y. Pavlyukh H. C. Schneider W. Hübner 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(4):483-496
A novel approach for GW-based calculations of
quasiparticle properties for finite systems is presented, in which
the screened interaction is obtained directly from a linear response
calculation of the density-density correlation function. The
conserving nature of our results is shown by explicit evaluation of
the f-sum rule. As an application, energy renormalizations and
level broadenings are calculated for the closed-shell Na9
+ and
Na21
+ clusters, as well as for Na4. Pronounced
improvements of conserving approximations to RPA-level results are
obtained. 相似文献
18.
B. Molina J. R. Soto A. Calles 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,51(2):225-231
In this work we explored the competition between spin-orbit and Jahn-Teller effects as decisive influences in the ground states
of the Td Au20
±γ (γ=1,2,3). All our electronic calculations were based in the relativistic density functional theory in the zeroth-order regular
approximation (ZORA) to the Dirac equation. Calculations were done in both versions of ZORA: scalar relativistic and full-relativistic
including the spin-orbit interaction. We concluded that for the Au20
-3 ion is necessary to use a full-relativistic theory in order to predict a symmetry-lowering from tetrahedral. We predict a
trigonal C3v isomeric form for this trianion due to a Jahn-Teller distortion of its parent Td. For the rest of ions we found a tendency to conserve their pristine tetrahedral configurations. In these cases we found
one of both possibilities: a quenching of the vibronic interaction by spin-orbit coupling or simply a weak Jahn-Teller effect
which is not enough to distort appreciably the cluster. 相似文献
19.
Y. Qu S. L. Ban 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(3):321-329
Based on the dielectric continuum phonon model, uniaxialmodel and force balance equation the mobility of two dimensional electrongas in wurtzite AlxGa1-xN/GaN/AlxGa1-xN quantum wells isdiscussed theoretically within the temperature range dominated by opticalphonons. The dependences of the electron mobility on temperature, Al molarfraction and electron sheet density are presented including hydrostaticpressure effect. The built-in electric field is also taken into account. Itis found that under normal pressure the main contribution to the mobility isfrom the scattering of interface optical phonons in narrow (for well widthd < 12 Å) and wide (for d > 117 Å and d > 65 Å for finitelythick barriers and infinitely thick ones, respectively) wells, whereas thatis from the scattering of confined optical phonons in a well with anintermediate width. It is shown that the electron mobility decreases withincreasing Al molar fraction and temperature, whereas increases obviouslywith increasing electron sheet density. The theoretical calculated electronmobility is 978 cm2/V?s which is higher than an available experimentaldata 875 cm2/V?s when x equals to 0.58 at room temperature. Theresults under hydrostatic pressure considering the modification of strainindicate that the mobility increases slightly as hydrostatic pressureincreases from 0 to 10 GPa. 相似文献
20.
N. Kouvaris A. Provata 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(1):97-106
An ecosystem containing three interacting species is studied using both Mean Field approach and Kinetic Monte Carlo
simulations on a lattice substrate. The so called 3rd order LLV model involves birth, death and reaction
processes with 3rd order nonlinearities and feedbacks. At the mean field level this system exhibits conservative
oscillations; the analytic form of the constant of motion is presented. The stochastic simulations show that the
density oscillations disappear for sufficiently large lattices, while they are present locally, on small lattice
windows. Introduction of mixing via long range migration in the two reacting species changes this picture. For small
migration rates p, the behavior remains as with p = 0 and the system is divided into local asynchronous oscillators.
As p increases the system passes through a phase transition and exhibits a weak disorder limit cycle through a supercritical
Hopf-like bifurcation. The amplitude of the limit cycle depends on the rate p, on the range of migration
r and on the system kinetic rates k1, k2 and k3. 相似文献