共查询到20条相似文献,搜索用时 687 毫秒
1.
2.
Summary Hall mobility, μH, and electrical conductivity, σ, of unhydrogenated amorphous-gallium-arsenide films, prepared by r.f. sputtering, have been
measured. Conductivity as a function of temperature shows a variable-range hopping mechanism atT<260 K, while at high temperature, conductivity and Hall mobility are both thermally activated. The results are interpreted
in terms of the presence of defect complexes due to an excess of Ga. The stoichiometry and the structure of the films are
used to explain the behaviour and the values of μH. The values of the activation energy of the conductivity seem in agreement with theoretical calculations on the position
of electronic states created by defect complexes in the mobility-gap of a-GaAs. 相似文献
3.
A. Martin O. Rossier A. Buguin P. Auroy F. Brochard-Wyart 《The European physical journal. E, Soft matter》2000,3(4):337-341
We study theoretically the behavior of nanoscopic liquid films L (thickness e) intercalated between a solid S and a rubber R (elastic modulus μ). Thickness modulations involve a healing length , which results from a competition between elastic and disjoining pressure. With van der Waals interactions, , where a is a molecular size and h0 the rubber capillary length ( , interfacial tension). If the Hamaker constant of the intercalated liquid is negative, the film dewets by amplification of
peristaltic fluctuations (“spinodal dewetting”). The typical size of the contacts is predicted to scale like for films of thicknesses . The rise time of the fastest mode, predicted to scale like , should be very sensitive to the film thickness.
Received 11 February 2000 and Received in final form 22 May 2000 相似文献
4.
N. Mordant J.-F. Pinton 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):343-352
We study experimentally the motion of a solid sphere settling under gravity in a fluid at rest. The particle velocity is measured
with a new acoustic method. Variations of the sphere size and density allow measurements at Reynolds numbers, based on limit
velocity, between 40 and 7 000. At all Reynolds numbers, our observations are consistent with the presence of a memory-dependent
force acting on the particle. At short times it has a t
-1/2 behaviour as predicted by the unsteady Stokes equations and as observed in numerical simulations. At long times, the decay
of the memory (Basset) force is better fitted by an exponential behaviour. Comparison of the dynamics of spheres of different
densities for the same Reynolds number show that the density is an important control parameter. Light spheres show transitory
oscillations at Re∼ 400, but reach a constant limit speed.
Received 12 April 2000 and Received in final form 13 July 2000 相似文献
5.
This paper presents the results of a rheological study of thermotropic nematic colloids aggregated into cellular structures.
Small sterically stabilised PMMA particles dispersed in a liquid crystal matrix densely pack on cell interfaces, but reversibly
mix with the matrix when the system is heated above . We obtain a remarkably high elastic modulus, , which is a nearly linear function of particle concentration. A characteristic yield stress is required to disrupt the continuity
of cellular structure and liquify the response. The colloid aggregation in a “poor nematic” MBBA has the same cellular morphology
as in the “good nematic” 5CB, but the elastic strength is at least an order of magnitude lower. These findings are supported
by theoretical arguments based on the high surface tension interfaces of a foam-like cellular system, taking into account
the local melting of nematic liquid and the depletion locking of packed particles on interfaces.
Received 13 March 2000 and Received in final form 6 June 2000 相似文献
6.
M. Hiane J. Ebothé 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(4):485-495
We show that the electrodeposition of Ni-Zn alloys at the lowest growth velocities, v < 0.5μm/s, exclusively proceeds from an abnormal co-deposition phenomenon. The growth process in this v region greatly depends on the initial [Co2+] concentration of the film deposition bath. A theoretical approach of this process including the role of the saturation surface
roughness of the alloy, , leads to an estimation of the transport properties of the ad-atoms involved during the deposit formation. Their surface
diffusion coefficient varying between 1.76×10-10 and 2.40×10-8 cm-2/s exhibits a minimal value, D
s = 2.10×10-10 cm-2/s located between v = 0.17 and 0.35μm/s. The spatial scaling analysis of the local roughness, σ, examined according to the power-law σ≈L
α reveals that the resulting roughness exponents concurs with the Kardar-Parisi-Zhang dynamics including the restricted surface
diffusion. Two main v regions leads to different fractal textural features of the alloy film surface. Below 0.10 μm/s, the roughness exponent obtained
is α≈ 0.6, depicting a limited ad-atom mobility. Over v = 0.30μm/s, this exponent stabilises at α≈ 0.82, indicating an increase of the surface diffusion.
Received 16 August 2000 and Received in final form 20 June 2001 相似文献
7.
E. Kogan M. Auslender M. Kaveh 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):373-376
Localization and dephasing of conduction electrons in a low carrier density ferromagnet due to scattering on magnetic fluctuations
is considered. We claim the existence of the “mobility edge”, which separates the states with fast diffusion and the states
with slow diffusion; the latter is determined by the dephasing time. When the “mobility edge” crosses the Fermi energy a large
and sharp change of conductivity is observed. The theory provides an explanation for the observed temperature dependence of
conductivity in ferromagnetic semiconductors and manganite pyrochlores.
Received 17 January 1999 and Received in final form 12 March 1999 相似文献
8.
Chengyou Liu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(1):45-48
The photorefractive effect (PR) of a novels σ-π alternating polymer having 2,2'-bipyridyl in the polymer backbone and their
ruthenium complexes has been investigated. The ruthenium complex was used as the charge generator, the σ-π alternating polymer
backbone as the charge transporting channel and second-order nonlinear (NLO) optical chromophore. The photorefractive properties
were demonstrated by two-beam coupling (2BC), degenerated four-wave mixing (DFWM) and field-induced orientation birefringence
at wavelength of 532 nm. This polymer shows a enhanced photorefractive effect due to the efficient photoinduced metal-to-ligand
charge transfer (MLCT) inside the ruthenium complex. A net optical gain of about 22 cm-1 and the diffraction efficiency about 10% were obtained at the external electric field of 30 V/μm.
Received 21 December 1999 and Received in final form 7 July 2001 相似文献
9.
10.
A.V. Okotrub L.G. Bulusheva A.I. Romanenko A.L. Chuvilin N.A. Rudina Y.V. Shubin N.F. Yudanov A.V. Gusel’nikov 《Applied Physics A: Materials Science & Processing》2001,72(4):481-486
A helium-pressure influence on the structure and properties of carbonaceous material from the inner part of a deposit forming
in an arc discharge has been studied. At the helium pressure of about 150 Torr and higher, the material was found to have
a layered texture, which is perpendicular to the deposit growth axis. Electron microscopy measurements showed that a sample
produced in He gas of 800 Torr consists of ∼80% carbon nanotubes having predominant orientation in the layers. Electric conductivity
along and perpendicular to the samples’ surface have been measured from 4.2 to 500 K. The samples synthesised at higher helium
pressures have significant anisotropy of conductivity, increasing with the carbon nanotubes content rise. X-ray fluorescence
spectra represented the angle dependence that is caused by the anisotropy of chemical bonding in the carbon nanotubes. The
valence π- and σ-bands for the carbonaceous material were separated.
Received: 26 November 1999 / Accepted: 20 April 2000 / Published online: 10 January 2001 相似文献
11.
A.Yu. Korchin 《The European Physical Journal A - Hadrons and Nuclei》2001,11(4):427-440
Magnetic moment and radius of the nucleon are calculated in a nonlocal extension of the chiral linear σ-model. Properties
of the nonlocal model under the vector and axial transformations are considered. The conserved electromagnetic and vector
currents, and partially conserved axial vector current are obtained. In the calculation of the nucleon electromagnetic vertex
the π- and σ-loop diagrams are included. Contribution from vector mesons is added in the vector meson dominance model with
a gauge-invariant photon-meson coupling. The nonlocality parameter associated with the πN interaction is fixed from the experimental magnetic moment of the neutron. Other parameters (nonlocality parameter for the
σN interaction and the mass of the σ-meson) are constrained by the magnetic moment of the proton. The calculated electric and
magnetic mean-square radii of the proton and neutron are in satisfactory agreement with experiment.
Received: 12 February 2001 / Accepted: 4 September 2001 相似文献
12.
XU MingTian 《中国科学:物理学 力学 天文学(英文版)》2015,(4):80-88
In this paper,based on the mean field dynamo theory,the influence of the electromagnetic boundary condition on the dynamo actions driven by the small scale turbulent flows in a cylindrical vessel is investigated by the integral equation approach.The numerical results show that the increase of the electrical conductivity or magnetic permeability of the walls of the cylindrical vessel can reduce the critical magnetic Reynolds number.Furthermore,the critical magnetic Reynolds number is more sensitive to the varying electrical conductivity of the end wall or magnetic permeability of the side wall.For the anisotropic dynamo which is the mean field model of the Karlsruhe experiment,when the relative electrical conductivity of the side wall or the relative magnetic permeability of the end wall is less than some critical value,the m=1(m is the azimuthal wave number)magnetic mode is the dominant mode,otherwise the m=0 mode predominates the excited magnetic field.Therefore,by changing the material of the walls of the cylindrical vessel,one can select the magnetic mode excited by the anisotropic dynamo. 相似文献
13.
V. Shankar V. Kumaran 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(4):607-622
The stability of wall modes in fluid flow through a flexible tube of radius R surrounded by a viscoelastic material in the region R < r < HR is analysed using a combination of asymptotic and numerical methods. The fluid is Newtonian, while the flexible wall is modelled
as an incompressible viscoelastic solid. In the limit of high Reynolds number (Re), the vorticity of the wall modes is confined to a region of thickness O(Re
-1/3) in the fluid near the wall of the tube. Previous numerical studies on the stability of Hagen-Poiseuille flow in a flexible
tube to axisymmetric disturbances have shown that the flow could be unstable in the limit of high Re, while previous high Reynolds number asymptotic analyses have revealed only stable modes. To resolve this discrepancy, the
present work re-examines the asymptotic analysis of wall modes in a flexible tube using a new set of scaling assumptions.
It is shown that wall modes in Hagen-Poiseuille flow in a flexible tube are indeed unstable in the limit of high Re in the scaling regime Re∼Σ3/4. Here Σ is a nondimensional parameter characterising the elasticity of the wall, and Σ≡ρGR
2/η2, where ρ and η are the density and viscosity of the fluid, and G is the shear modulus of the wall medium. The results from the present asymptotic analysis are in excellent agreement with
the previous numerical results. Importantly, the present work shows that the different types of unstable modes at high Reynolds
number reported in previous numerical studies are qualitatively the same: they all belong to the class of unstable wall modes
predicted in this paper.
Received 12 June 2000 and Received in final form 8 November 2000 相似文献
14.
P. Nozières 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):447-457
The so called exhaustion problem occurs when few electrons have to screen many spins in a metal with magnetic impurities.
A singlet Fermi liquid ground state is possible only if all impurities are “isotropized” in such a way as to suppress their
entropy. That takes a time and the corresponding energy limits the Fermi liquid range. The present note explores that issue of time and energy scales, and it concludes that is much smaller than the single impurity Kondo temperature. Similarly the relevant energy scale is proportional to the number
of electrons. Recent results on the Mott metal insulator transition in infinite dimension are reconsidered in the light of
these results: controversies in that respect are shown to reduce to a simple physical question, with no firm answer as to
now.
Received: 5 May 1998 / Received in final form and Accepted: 29 July 1998 相似文献
15.
L. Gialanella F. Strieder L. Campajola A. D'Onofrio U. Greife G. Gyurky G. Imbriani G. Oliviero A. Ordine V. Roca C. Rolfs M. Romano D. Rogalla C. Sabbarese E. Somorjai F. Terrasi H.P. Trautvetter 《The European Physical Journal A - Hadrons and Nuclei》2000,9(3):303-305
The absolute cross section σ (E) of the radiative capture reaction p(7Be,γ)8B at the center-of-mass energy E = 992 keV has been measured using a radioactive 7Be ion beam and a windowless gas target system filled with H2 gas. The 8B residual nuclides were detected with a recoil separator consisting of momentum and velocity filters and a ΔE-E detector
telescope. The 8B yield was observed concurrently with the 7Be + p elastic scattering yield, relating σ(E) to the Rutherford scattering cross section. The resulting value, σ(E) = 0.41
± 0.11 μb, leads to an S(E) factor at zero energy of S(0) = 16 ± 4 eV b, in fair agreement with recommended values.
Received: 8 February 2000 相似文献
16.
Simultaneous calculation of the dipole moment μj and the relaxation time τj of a certain number of non-spherical rigid aliphatic polar liquid molecules (j) in non-polar solvents (i) under 9.8 GHz electric
field is possible from real ε′ij and imaginary ε″ij parts of the complex relative permittivity ε*ij. The low frequency and infinite frequency permittivities ε0ij and ε∞ij measured by Purohitet al [1,2] and Srivastava and Srivastava [3] at 25, 35 and 30°C respectively are used to obtain static μs. The ratio of the individual slopes of imaginary σ″ij and real σ′ij parts of high frequency (hf) complex conductivity σ*ij with weight fractionsw
jatw
j → 0 and the slopes of σ″ij— σ′ij curves for differentw
js [4] are employed to obtain τjs. The former method is better in comparison to the existing one as it eliminates polar-polar interaction. The hf μjs in Coulomb metre (C m) when compared with static and reported μs indicate that μs s favour the monomer formations which combine to form dimers in the hf electric field. The comparison among μs shows that
a part of the molecule is rotating under X-band electric field [5]. The theoretical μtheos from available bond angles and bond moments of the substituent polar groups attached to the parent molecules differ from
the measured μjs and μs to establish the possible existence of mesomeric, inductive and electromeric effects in polar liquid molecules. 相似文献
17.
R.M. Thaokar V. Shankar V. Kumaran 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(4):533-550
The stability of linear shear flow of a Newtonian fluid past a flexible membrane is analysed in the limit of low Reynolds
number as well as in the intermediate Reynolds number regime for two different membrane models. The objective of this paper
is to demonstrate the importance of tangential motion in the membrane on the stability characteristics of the shear flow.
The first model assumes the wall to be a “spring-backed” plate membrane, and the displacement of the wall is phenomenologically
related in a linear manner to the change in the fluid stresses at the wall. In the second model, the membrane is assumed to
be a two-dimensional compressible viscoelastic sheet of infinitesimal thickness, in which the constitutive relation for the
shear stress contains an elastic part that depends on the local displacement field and a viscous component that depends on
the local velocity in the membrane. The stability characteristics of the laminar flow in the limit of low are crucially dependent on the tangential motion in the membrane wall. In both cases, the flow is stable in the low Reynolds number limit in the absence of tangential motion in the membrane. However, the presence of tangential
motion in the membrane destabilises the shear flow even in the absence of fluid inertia. In this case, the non-dimensional velocity (Λt) required for unstable fluctuations is proportional to the wavenumber k ( Λ
t∼k) in the plate membrane type of wall while it scales as k2 in the viscoelastic membrane type of wall ( Λ
t∼k
2) in the limit k→ 0. The results of the low Reynolds number analysis are extended numerically to the intermediate Reynolds number regime for
the case of a viscoelastic membrane. The numerical results show that for a given set of wall parameters, the flow is unstable
only in a finite range of Reynolds number, and it is stable in the limit of large Reynolds number.
Received 8 November 2000 and Received in final form 20 March 2001 相似文献
18.
Y. Malécot C. Auriault H. Kahalerras Y. Gagne O. Chanal B. Chabaud B. Castaing 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):549-561
The velocity increments statistic in various turbulent flows is analysed through the hypothesis that different scales are
linked by a multiplicative process, of which multiplier is infinitely divisible. This generalisation of the Kolmogorov-Obukhov
theory is compatible with the finite Reynolds number value of real flows, thus ensuring safe extrapolation to the infinite
Reynolds limit. It exhibits a estimator universally depending on the Reynolds number of the flow, with the same law either for Direct Numerical Simulations
or experiments, both for transverse and longitudinal increments. As an application of this result, the inverse dependence
is used to define an unbiased value for a Large Eddy Simulation from the resolved scales velocity statistics. However, the exact shape of the multiplicative
process, though independent of the Reynolds number for a given experimental setup, is found to depend significantly on this
setup and on the nature of the increment, longitudinal or transverse. The asymmetry of longitudinal velocity increments probability
density functions exhibits similarly a dependence with the experimental setup, but also systematically depends on the Reynolds
number.
Received 7 January 2000 and Received in final form 17 March 2000 相似文献
19.
Th. Cabioc'h S. Camelio L. Henrard Ph. Lambin 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(3):535-540
Concentric-shell fullerenes, also called carbon onions, produced by carbon ion implantation into silver thin films, and subsequently
deposited on a silica substrate, were studied by optical transmission spectroscopy in the wavelength range 0.2 - 1.2 μm. In
this interval, the strongest absorption is due to the π-plasmon of sp2-like carbon. The position of the plasmon absorption band clearly evolved from 265 nm at low fluence to 230 nm at high implantation
fluences. A simulation of the optical spectra based on dielectric models of the concentric-shell fullerenes layer allowed
us to identify the first peak as due to disordered graphite and the latter to the carbon onions. The concentration of residual
graphite and the filling fraction of the carbon onions produced at high fluences could be estimated by fitting the optical
spectra with computed transmittance curves.
Received 13 July 2000 相似文献
20.
E. Vitoratos S. Sakkopoulos Ch. Anestis J. Spiliotopoulos K. Govender D. S. Boyle P. O'Brien 《Ionics》2005,11(3-4):259-261
An experimental study of the temperature dependence of the d.c. conductivity σ as a function of temperature T in the range
from 80–360 K on nanocrystalline ZnO:Al films (Al3+ 2%) of thickness 500 nm prepared on glass microscope slides by a dip — coating method is presented. The electrical conductivity
σ, which at room temperature varied between 0.1 to 2.7 S/cm, increased almost linearly with T for all the samples. Measurements
of the Hall coefficient at room temperature and in a magnetic field of 1.2 T, gave RH=0.53 cm3C−1, from which a carrier concentration of n=1.18×1019 cm−3 and a carrier mobility of μ=1.40 cm2/Vs were deduced.
Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14–18, 2004. 相似文献