共查询到20条相似文献,搜索用时 46 毫秒
1.
J. L. Vinningland R. Toussaint M. Niebling E. G. Flekkøy K. J. Måløy 《The European physical journal. Special topics》2012,204(1):27-40
When submillimetric particles are confined in a fluid such that a compact cluster of particles lie above the clear fluid,
particles will detach from the lower boundary of the cluster and form an unstable separation front giving rise to growing
fingers of falling particles. We study this problem using both experiments and hybrid granular/fluid mechanics models. In
the case of particles from 50 to 500 microns in diameter falling in air, we study the horizontal density fluctuations at early
times: the amplitude of the density difference between two points at a certain horizontal distance grows as a power law of
time. This happens up to a saturation corresponding to a power law of the distance. The way in which the correlation length
builds up to this saturation also follows a power law of time. We show that these decompaction fronts in sedimentation problems
follow a Family-Vicsek scaling, characterize the dynamic and Hurst exponent of the lateral density fluctuations, respectively
z ∼ 1 and ζ ∼ 0.75, and show how the prefactors depend on the grain diameter. We also show from similar simulations with a
more viscous and incompressible fluid, that this feature is independent of the fluid compressibility or viscosity, ranging
from air to water/glycerol mixtures. 相似文献
2.
We ask the question whether it is possible to diagnose the existence of “Dragon-Kings” (DK), namely anomalous observations
compared to a power law background distribution of event sizes. We present two new statistical tests, the U-test and the DK-test,
aimed at identifying the existence of even a single anomalous event in the tail of the distribution of just a few tens of
observations. The DK-test in particular is derived such that the p-value of its statistic is independent of the exponent characterizing the null hypothesis, which can use an exponential or
power law distribution. We demonstrate how to apply these two tests on the distributions of cities and of agglomerations in
a number of countries. We find the following evidence for Dragon-Kings: London in the distribution of city sizes of Great
Britain; Moscow and St-Petersburg in the distribution of city sizes in the Russian Federation; and Paris in the distribution
of agglomeration sizes in France. True negatives are also reported, for instance the absence of Dragon-Kings in the distribution
of cities in Germany. 相似文献
3.
S. di Stasio 《Applied physics. B, Lasers and optics》2000,70(4):635-643
The possibility of inferring by a non-invasive experimental method the size of primary particles (spherules), which constitute the agglomerated soot generated in an ethylene–air diffusion flame, is investigated. In contrast to the
predictions from the Mie theory for isolated spheres, experimental evidence is provided here about the fact that the size
of spherules (some tens of nanometers), which stick together to form agglomerates (some hundreds of nanometers), can be recognized
from polarization ratio measurements. Validation of the proposed scattering technique is obtained by first performing standard
measurements of the primary particle size by SEM analysis of soot samples taken on quartz inserted directly in the flame along
the burner axis. Then, the polarization ratio P(θ)≡σHH/σVV of scattered light is measured at the same locations and for the same flame conditions for different polar scattering angles
θ. As major result, evidence is provided of a linear relationship existing between the primary sizes, obtained independently
by SEM analysis, and the measurements of the polarization ratio P(90°). Finally, a procedure is reported and applied to retrieve
the absolute spherule size from the direct observation of the transition between the power-law and Porod’s scattering regimes,
which correspond to the domains of long-range (fractal) and short-range (not fractal) interactions between primary particles,
respectively.
Received: 24 February 1999 / Final version: 6 December 1999 / Published online: 1 March 2000 相似文献
4.
Thermodynamically stable vortex—antivortex structures in a quasi-twodimensional superconductor in a tilted magnetic field
are predicted. For this geometry, both orbital and spin pair-breaking effects exist, with their relative strength depending
on the tilt angle θ. The spectrum of possible states contains the ordinary vortex state (for large θ) and the Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) state (for θ = 0) as limits. The quasi-classical equations are solved nearH
c2 for arbitrary θ and it is shown that stable states with co-existing vortices and antivortices exist in a small interval close
to θ= 0. The results are compared with recent predictions of antivortices in mesoscopic samples. 相似文献
5.
H-chitosan that exhibited solubility in THF was prepared by acyl modification of chitosan. Films of H-chitosan containing
LiCF3SO3 were prepared by the solution cast technique. The effect of salt concentration on the frequency-dependent dielectric properties
of H-chitosan: LiCF3SO3 complexes were investigated by impedance spectroscopy, in the temperature range from 243 to 373 K. The dielectric properties
and ac conductivity of the samples prepared have been analyzed. The dielectric constant increases sharply with temperature
in the low frequency region. At higher frequencies, the effect of temperature on the dielectric constant is negligible. The
values of dielectric constant were also found to increase with increasing conductivity of the samples. The imaginary part,
Mi of electrical modulus shows the formation of dispersion peak. Relaxation times for the ionic charge carriers were extracted
from the loss tangent maximum peak at various temperatures. The plot of relaxation times as a function of temperature shows
Arrhenius type behaviour. The ac conductivity was found to obey the universal power law and as the temperature increases,
the feature of σ(θ) α θn is more predominant. The temperature dependence of the power law exponent n is reasonably interpreted by the overlapping
large polaron tunneling (OLPT) model. 相似文献
6.
Z.F. Huang S. Solomon 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(4):601-607
We study by theoretical analysis and by direct numerical simulation the dynamics of a wide class of asynchronous stochastic
systems composed of many autocatalytic degrees of freedom. We describe the generic emergence of truncated power laws in the
size distribution of their individual elements. The exponents α of these power laws are time independent and depend only on
the way the elements with very small values are treated. These truncated power laws determine the collective time evolution
of the system. In particular the global stochastic fluctuations of the system differ from the normal Gaussian noise according
to the time and size scales at which these fluctuations are considered. We describe the ranges in which these fluctuations
are parameterized respectively by: the Lévy regime α < 2, the power law decay with large exponent ( α > 2), and the exponential
decay. Finally we relate these results to the large exponent power laws found in the actual behavior of the stock markets
and to the exponential cut-off detected in certain recent measurement.
Received 29 July 2000 and Received in final form 25 September 2000 相似文献
7.
Lorenzo Bertini Davide Gabrielli Joel L. Lebowitz 《Journal of statistical physics》2005,121(5-6):843-885
We investigate a one-dimensional chain of 2N harmonic oscillators in which neighboring sites have their energies redistributed randomly. The sites −N and N are in contact with thermal reservoirs at different temperature τ− and τ+. Kipnis et al. (J. Statist. Phys., 27:65–74 (1982).) proved that this model satisfies Fourier’s law and that in the hydrodynamical scaling limit, when N → ∞, the stationary state has a linear energy density profile
, u ∈[−1,1]. We derive the large deviation function S(θ(u)) for the probability of finding, in the stationary state, a profile θ(u) different from
. The function S(θ) has striking similarities to, but also large differences from, the corresponding one of the symmetric exclusion process.
Like the latter it is nonlocal and satisfies a variational equation. Unlike the latter it is not convex and the Gaussian normal
fluctuations are enhanced rather than suppressed compared to the local equilibrium state. We also briefly discuss more general
models and find the features common in these two and other models whose S(θ) is known. 相似文献
8.
Mikuláš Blažek 《Czechoslovak Journal of Physics》1997,47(6):589-601
In frame of the phenomena revealing multifractality, two inverse problems are formulated and their solution is outlined; namley,
(i) to what extent the indices characterizing scaling properties of dynamical fluctuations (specified by factorial moments)
are determined by means of power law indicesτ(q) which characterize scaling properties of the associated frequency moments, the later moments representing asymptotics (for
sufficiently large multiplicities) of the former ones, and (ii) to what extent the scaling indicesτ(q) are determined by their asymptotic properties (at large absolute value of the orderq ascribed to the associated frequency moments and taken at a finite and fixed energy). 相似文献
9.
RUAN Ying CAO Chongde & WEI Bingbo Department of Applied Physics Northwestern Polytechnical University Xi’an China 《中国科学G辑(英文版)》2004,47(6):717-728
~~Rapid growth of ternary eutectic un der high undercooling conditions1.Offerman, S.E., Dijk, N.H., Sietsma, J.et al., Grain nucleation and growth during phase transformations, Science, 2002, 298: 1003-1005.
2.Warren, J.A., Langer, J.S., Prediction of dendritic spacings in a directional-solidification experiment, Phys.Rev.E, 1993, 47: 2702-2712.
3.Cao, C.D., Wang, N., Wei, B., Containerless rapid solidification of undercooled Cu-Co peritectic alloys, Science in China, Ser.A, … 相似文献
10.
S. Jain P. Buckley 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(1-2):133-136
Persistence is studied in a financial context by mapping the time
evolution of the values of the shares quoted on the London Financial
Times Stock Exchange 100 index (FTSE 100) onto Ising spins.
By following the time dependence
of the spins, we find evidence for power law decay of the proportion
of shares that remain either above or below their 'starting'
values. As a result, we estimate a persistence exponent for the
underlying financial market to be θf∼0.5. 相似文献
11.
Xavier Gerbaux Armand Hadni M. Tazawa 《International Journal of Infrared and Millimeter Waves》1997,18(9):1611-1635
The different technical approaches are considered mostly to compare the accuracy attainable in microwaves to Far IR where
new resonant tchniques have been developped. It is possible to use the fringes of the observed spectra to get directly the
London penetration length. However in the present state of the Art there is more accuracy to use a two-fluid model with at
least one Mid-IR oscillator, and a strategy is possible to fit separately the different parameters. The different results
are reviewed and compared to the microwaves data. There is a good accordance, except perhaps for the power law-giving the
concentration of quasiparticles in the superconductive phase. For a thin film of YBCO devoid of grain-boundaries (no twins),
a θ4 law is found instead of a θ1.5 law for an ordinary film. It should be highly valuable that both microwaves and Far-IR data should be taken on the same sample.
presented at the 22nd International Conference on Infrared and Millimeter Waves, July 20–25, 1997, Wintergreen, Virginia 22958
USA. 相似文献
12.
V. Bellani C. Bocchi T. Ciabattoni S. Franchi P. Frigeri P. Galinetto M. Geddo F. Germini G. Guizzetti L. Nasi M. Patrini L. Seravalli G. Trevisi 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(3):217-222
This work deals with the strain relaxation mechanism in InGaAs metamorphic buffers (MBs) grown on GaAs substrates and overgrown
by InAs quantum dots (QD). The residual strain is measured by using Raman scattering and X-ray diffraction, both in Reciprocal
Space Map and in single ω-2θ scan modes (ω and θ being the incidence angles on the sample surface and on the scattering planes,
respectively). By relating the GaAs-like longitudinal optical phonon frequency ωLO of InGaAs MBs to the in-plane residual strain ε measured by means of photoreflectance (PR), the linear ε-vs.-ωLO working curve is obtained. The results of Raman and XRD measurements, as well as those obtained by PR, are in a very satisfactory
agreement. The respective advantages of the techniques are discussed. The measurements confirm that strain relaxation depends
on the thickness t of the buffer layer following a ~t-1/2 power law, that can be explained by an energy-balance model. 相似文献
13.
We explore a novel possibility for lowering the solar mixing angle (θ
12) from tri-bimaximal mixings, without sacrificing the predictions of maximal atmospheric mixing angle (θ
23 = 45°) and zero reactor angle (θ
13 = 0°) in the inverted and normal hierarchical neutrino mass models having 2–3 symmetry. This can be done through the identification
of a flavour twister term in the texture of neutrino mass matrix and the variation of such term leads to lowering of solar
mixing angle. For the observed ranges of Δm
212 and Δm
232, we calculate the predictions on tan2
θ
12 = 0.5, 0.45, 0.35 for different input values of the parameters in the neutrino mass matrix. We also observe a possible transition
from inverted hierarchical model having even CP parity (Type-IHA) to inverted hierarchical model having odd CP parity (Type-IHB)
in the first two mass eigenvalues, when there is a change in input values of parameters in the same mass matrix. The present
work differs from the conventional approaches for the deviations from tri-bimaximal mixing, where the 2–3 symmetry is broken,
leading to θ
23 ≠ 45° and θ
13 ≠ 0°.
相似文献
14.
A.E. Ball A. Braem L. Camilleri A. Catinaccio G. Chelkov F. Dydak A. Elagin P.K. Frandsen M. Gostkin A. Grant A. Guskov C. Joram Z. Krumshteyn H. Müller H. Postema M. Price T. Rovelli D. Schinzel J. Séguinot G. Valenti R. Voss J. Wotschack A. Zhemchugov 《The European Physical Journal C - Particles and Fields》2007,49(4):1117-1142
Today’s greatest challenge in accelerator-based neutrino physics is to measure the mixing angle θ13 which is known to be much smaller than the solar mixing angle θ12 and the atmospheric mixing angle θ23. A non-zero value of the angle θ13 is a prerequisite for observing CP violation in neutrino mixing. In this paper, we discuss a deep-sea neutrino experiment
with 1.5 Mt fiducial target mass in the Gulf of Taranto with the prime objective of measuring θ13. The detector is exposed to the CERN neutrino beam to Gran Sasso in off-axis geometry. Monochromatic muon neutrinos of ≈
800 MeV energy are the dominant beam component. Neutrinos are detected through quasi-elastic, charged-current reactions in
sea water; electrons and muons are detected in a large-surface, ring-imaging Cherenkov detector. The profile of the seabed
in the Gulf of Taranto allows for a moveable experiment at variable distances from CERN, starting at 1100 km. From the oscillatory
pattern of the disappearance of muon neutrinos, the experiment will measure sin2θ23 and especially Δm2
23 with high precision. The appearance of electron neutrinos will be observed with a sensitivity to P(νμ→νe) as small as 0.0035 (90% CL) and sin2θ13 as small as 0.0019 (90% CL; for a CP phase angle δ=0° and for normal neutrino mass hierarchy). 相似文献
15.
S. R. Hanna 《Il Nuovo Cimento C》1990,13(6):889-894
Summary At downwind distances of 400 m or less, the angular standard deviation, σθc, of the lateral distribution of pollutants released from a point source over a given time period is shown to equal the standard
deviation, σθ, of the wind direction fluctuations observed over the same time period. Data taken during light wind, stable conditions at
two field sites (Idaho Falls, ID, and Oak Ridge, TN) are used in this analysis. This relation is most reliable if the pollutant
concentration distribution is observed on a circle at constant distance from the source (i.e., on a polar coordinate system).
Paper presented at the GNFAO/EURASAP Meeting, Turin, September 1989.
To speed up publication, proofs were not sent to the author and were supervised by the Scientific Committee. 相似文献
16.
F. Schümann S. Zavatarelli L. Gialanella U. Greife M. Junker D. Rogalla C. Rolfs F. Strieder H.P. Trautvetter 《The European Physical Journal A - Hadrons and Nuclei》1998,2(4):337-342
Abstact: The elastic scattering cross sections, σ (E,θ), for the systems He+Ta and He+W have been measured at θlab=165° and E
lab=76.1 keV to 3.988 MeV using targets with a thickness of a few atomic layers. The results are smaller than the results given
by the Rutherford scattering law, σR(E,θ), due to the effects of electron screening and can be described by σ(E,θ)/σR(E,θ)=(1+Ue/E)−1, where U
e is an atomic screening potential energy. The deduced average value, U
e=28 ± 3 keV, is consistent with the Moliére- and Lenz-Jensen-models as well as electron binding energies.
Received: 25 May 1998 相似文献
17.
D. I. Bilenko A. A. Sagaidachnyi V. V. Galushka V. P. Polyanskaya 《Technical Physics》2010,55(10):1478-1483
The possibility of multiparametric determination of properties of structures from the data on the dependence of reflectances
R
p
and R
s
for polarized radiation and ratio R
p
/R
s
on the angle of incidence θ and from the angular dependence 1/R
p
(ΔR/Δθ) is investigated. The results of natural and computer experiments revealed a high sensitivity of the angular dependence
R
p
(θ) of the reflectance to the values of optical constants and thickness of layered structures. Quantitative results of multiparametric
measurements are verified by the independent method of spectral ellipsometry. The possibility of multiparametric determination
of the properties and thickness of nanometer dielectric, metallic, and semiconducting layers on various substrates and the
properties of substrates in such structures is established. 相似文献
18.
S. Roux J.F. Muzy A. Arneodo 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(2):301-322
Swirling turbulent flows display intermittent pressure drops associated with intense vorticity filaments. Using the wavelet
transform modulus maxima representation of pressure fluctuations, we propose a method of characterizing these pressure drop
events from their time-scale properties. This method allows us to discriminate fluctuations induced by just formed (young)
as well as by burst (old) filaments from background pressure fluctuations. The statistical characteristics of these filaments
(core size, waiting time) are analyzed in details and compared with previously reported experimental and numerical findings.
Their intermittent occurrence is found to be governed by a pure Poisson's law, the hallmark of independent events. Then we
apply the wavelet transform modulus maxima (WTMM) method to the background pressure fluctuations. This study reveals that,
once removed all the filaments, the “multifractal” nature of pressure fluctuations still persists. This is a clear indication
that the statistical contribution of the filaments is not important enough to account for the intermittency phenomenon in
turbulents flows.
Received 27 July 1998 and Received in final form 23 November 1998 相似文献
19.
V. N. Skokov V. P. Koverda A. V. Vinogradov A. V. Reshetnikov 《Thermophysics and Aeromechanics》2010,17(1):99-106
Experiments on water cavitation in ultrasonic field have been carried out. Low frequency fluctuations of the intensity of
laser beam run through the cavitation area have been studied. Experiments have proved presence of low-frequency random fluctuations
with frequency dependence of power spectra, S ∼ 1/f
α
where the exponent α ranged within 0.8 ≤ α ≤ 1.2. From experimental realizations, large-scale low frequency pulsations characterized by scale invariance, which duration
is distributed according to the power law, have been distinguished. The results are explained on the basis of mathematical
model for the rise of scale invariant fluctuations with 1/f
α
power spectrum in the system of two nonlinear stochastic differential equations describing interaction of heterogeneous phase
transitions. Distribution of extreme low frequency emissions obtained from numerical solutions to stochastic equations takes
the power series form. Correlations of dynamic scaling between critical indicators determining frequency dependence of pulsations
power spectra α and distribution functions of extreme low frequency pulsation amplitudes β have been determined. It is shown that both in the experiments on acoustic cavitation of water and in the theoretical model
of interacting phase transitions critical indicators are bound with the correlation α + β = 2. Spectra of fluctuation power are determined in the experiments simpler and more accurately than the function of extreme
amplitudes distribution. In case when only one frequency dependence of fluctuation capacity spectra is known correlations
between indicators serve to obtain information on the distribution of large scale emissions and to estimate critical amplitudes. 相似文献
20.
A. V. Dubrov V. D. Dubrov Y. N. Zavalov V. Y. Panchenko 《Applied physics. B, Lasers and optics》2011,105(3):537-543
The results of measurement of fluctuations of brightness temperature T in the region of exposure to laser radiation of a 3 mm-thick steel plate are presented. The local luminosity along the cut-front
was measured using two-color multichannel pyrometer. Cutting trials were carried out with CO2 laser (10.6 μm, 1200 W) and fiber laser (1.07 μm, 1800 W). Special attention was given to the frequency range of temperature
fluctuations above frequency of melt overflight, aiming on on-line monitoring applications. It is shown that local fluctuations
of T are related to local melt’s surface deformations due to unequal radiation absorption; thus the noise spectrum of T fluctuations reflects turbulent surface deformation, caused by gas jet and capillary waves. It is also shown that the thermo-capillary
effect with capillary-wave turbulence generation can be observed in case of exposure to 10.6 μm radiation with a laser intensity
of about 1 MW/cm2. The power law of “−7/6” describes the spectrum of the T fluctuation variance in this case of anomalous absorption of radiation, and the standard deviation of T is in excess of 10 K for a frequency of 14 kHz. There is no such effect in case of fiber-laser radiation applying, and the
source of the capillary waves is only forced low-frequency deformations of the melt surface. The standard deviation of T does not exceed 3 K on the frequency of 14 kHz, and above, and a power law of the spectrum fluctuation is described by about
“−3” in that range. 相似文献