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1.
An experimental study of the regimes of motion of spheres falling or ascending freely in a Newtonian fluid 总被引:1,自引:0,他引:1
This paper presents the results of an experimental investigation aimed at verifying some of the interesting conclusions of the numerical study by Jenny et al. concerning the instability and the transition of the motion of solid spheres falling or ascending freely in a Newtonian fluid. The phenomenon is governed by two dimensionsless parameters: the Galileo number G, and the ratio of the density of the spheres to that of the surrounding fluid ρs/ρ. Jenny et al. showed that the (G, ρs/ρ) parameter space may be divided into regions with distinct features of the trajectories followed eventually by the spheres after their release from rest. The characteristics of these ‘regimes of motion’ as described by Jenny et al., agree well with what was observed in our experiments. However, flow visualizations of the wakes of the spheres using a Schlieren optics technique raise doubts about another conclusion of Jenny et al., namely the absence of a bifid wake structure. 相似文献
2.
K. Schenk B. Drossel S. Clar F. Schwabl 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):177-185
We study finite-size effects in the self-organized critical forest-fire model by numerically evaluating the tree density and
the fire size distribution. The results show that this model does not display the finite-size scaling seen in conventional
critical systems. Rather, the system is composed of relatively homogeneous patches of different tree densities, leading to
two qualitatively different types of fires: those that span an entire patch and those that do not. As the system size becomes
smaller, the system contains less patches, and finally becomes homogeneous, with large density fluctuations in time.
Received 24 April 1999 and Received in final form 26 October 1999 相似文献
3.
A fabrication process for growth of GaN lateral polarity junctions consisting of Ga-polar and N-polar domains grown simultaneously side-by-side on c-plane sapphire was developed using the polarity control scheme. An ammonia-annealing step following deposition and patterning of a thin low-temperature AlN nucleation layer played a crucial role in avoiding mixed-polarity growth of the remaining AlN nucleation layer, as well as in nitriding the bare sapphire surface to facilitate growth of N-polar GaN. The achievement of both polar domains, free from inversion domains within a contiguous domain, led to Ga-polar domain exhibiting featureless morphology with highly resistive characteristics, while N-polar domains exhibited hexagonally faceted morphology and were highly conductive. 相似文献
4.
M.S. Zhang P. Zhang Z. Yin J. Liu 《Applied Physics A: Materials Science & Processing》1999,69(4):389-395
Barium sodium niobate (BSN) optical waveguide films were grown on potassium titanyl phosphate (KTP) substrate by pulsed laser
deposition (PLD). X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray pole spectroscopy, and X-ray photoelectron
spectroscopy (XPS) showed that the as-grown BSN films are epitaxially smooth, fine-particled and show small constituent deviation.
Both m lines of the waveguided TE and TM modes were recorded. Lattice match between the BSN(110) and both the KTP(001) and KTP(100)
planes is examined with mismatch less than 3%. Effective refractive indices as a function of incident wavelength and order
of the waveguided modes are studied. A phase matching relationship of k
(1)−2k
(0)=0 is established between the first-order and fundamental modes in the BSN/KTP waveguided system. Effective thicknesses for
TE and TM modes were obtained to be equal to 0.76 and 0.72 μm, respectively, larger than the thickness of the as-grown BSN
film of 0.60 μm. A constituent ratio of Ba:Na:Nb in the BSN film measured was equal to 2:0.82:5.14, slightly deviating from
the stoichiometric ratio of 2:1:5, which is attributed to higher relative asymptotic velocity for Nb species and higher evaporation
pressure for Na species. Finally, the main factors affecting quality of the as-grown BSN films are also discussed.
Received: 26 March 1999 / Accepted: 30 March 1999 / Published online: 19 August 1999 相似文献
5.
The shear-induced ordering of lamellar and gyroid structures of a nonionic surfactant C16E7/D2O system in a Couette shear cell ( 0.001 < < 10 s-1, : shear rate) has been investigated by using a small angle neutron scattering technique. In the lamellar phase, the steady
shear flow having > 0.01 s-1 suppresses undulation fluctuations of lamellae (Maxwell effect). This suppression of fluctuations brings two effects; 1)
shear-induced lamellae ordering toward a parallel orientation and 2) obstruction of a lamellar↦gyroid transition. It is quite
interesting to note that there is a characteristic shear rate range ( 0.01 < < 0.3 s-1), where both effects take place. We have also investigated the shear effects on the gyroid phase. Below the characteristic
shear rate range, the gyroid structure keeps three-dimensional network lattice, while above the characteristic shear rate
range, the gyroid structure transforms to the parallel orientation lamellae (shear-induced gyroid-lamellar transition). Thus
the shear flow having the characteristic shear rate plays very important roles in shear ordering phenomena.
Received 26 June 2000 and Received in final form 12 January 2001 相似文献
6.
Jacqueline Krim 《物理学进展》2013,62(3):155-323
This review provides an overview of recent advances that have been achieved in understanding the basic physics of friction and energy dissipation in molecularly thin adsorbed films and the associated impact on friction at microscopic and macroscopic length scales. Topics covered include a historical overview of the fundamental understanding of macroscopic friction, theoretical treatments of phononic and electronic energy dissipation mechanisms in thin films, and current experimental methods capable of probing such phenomena. Measurements performed on adsorbates sliding in unconfined geometries with the quartz crystal microbalance technique receive particular attention. The final sections review the experimental literature of how measurements of sliding friction in thin films reveal energy dissipation mechanisms and how the results can be linked to film-spreading behavior, lubrication, film phase transitions, superconductivity-dependent friction, and microelectromechanical systems applications. Materials systems reported on include adsorbed films comprised of helium, neon, argon, krypton, xenon, water, oxygen, nitrogen, carbon monoxide, ethane, ethanol, trifluoroethanol, methanol, cyclohexane, ethylene, pentanol, toluene, tricresylphosphate, t-butylphenyl phosphate, benzene, and iodobenzene. Substrates reported on include silver, gold, aluminum, copper, nickel, lead, silicon, graphite, graphene, fullerenes, C60, diamond, carbon, diamond-like carbon, and YBa2Cu3O7, and self-assembled monolayers consisting of tethered polymeric molecules. 相似文献
7.
L. Despont F. Clerc M. G. Garnier H. Berger L. Forró P. Aebi 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):421-426
Multiple scattering theory based on a
cluster model is used to simulate full hemispherical X-ray photoelectron
diffraction measurements on a 1T-TaS2(0001) surface. Key points to determine the surface termination are discussed. As the commonly applied single scattering simulations
do not give satisfying results, a multiple scattering approach has to be used to accurately simulate the full hemispherical
photoelectron diffraction patterns. Differences and similarities between calculations of Ta and S terminated surfaces are
presented along with experimental results at room temperature using both, the single and the multiple scattering approaches.
We find that the surface is S terminated and that the quantitative difference between the calculations for both terminations
permits to show the limits of the single scattering approach for solving surface termination problems. Moreover, by generalizing
the results obtained using the multiple scattering approach, we discuss the application of this method to other similar systems. 相似文献
8.
N. G. Fytas A. Malakis 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(1-2):39-43
The three-dimensional bimodal random-field Ising model is studied
via a new finite temperature numerical approach. The methods of
Wang-Landau sampling and broad histogram are implemented in a
unified algorithm by using the N-fold version of the Wang-Landau
algorithm. The simulations are performed in dominant energy
subspaces, determined by the recently developed critical minimum
energy subspace technique. The random-fields are obtained from a
bimodal distribution, that is we consider the discrete
(±Δ) case and the model is studied on cubic lattices with
sizes 4≤L ≤20. In order to extract information for the
relevant probability distributions of the specific heat and
susceptibility peaks, large samples of random-field realizations
are generated. The general aspects of the model's scaling behavior
are discussed and the process of averaging finite-size anomalies
in random systems is re-examined under the prism of the lack of
self-averaging of the specific heat and susceptibility of the
model. 相似文献
9.
G. E. Schröder-Turk A. Fogden S. T. Hyde 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(4):509-524
Balanced infinite periodic minimal surface families that contain the cubic Gyroid (G), Diamond (D) and Primitive (P) surfaces
are studied in terms of their global packing and local curvature properties. These properties are central to understanding
the formation of mesophases in amphiphile and copolymer molecular systems. The surfaces investigated are the tetragonal, rhombohedral
and hexagonal tD, tP, tG, rG, rPD and H surfaces. These non-cubic minimal surfaces furnish topology-preserving transformation
pathways between the three cubic surfaces. We introduce `packing (or global) homogeneity', defined as the standard deviation
Δd of the distribution of the channel diameter throughout the labyrinth, where the channel diameter d is determined from the
medial surface skeleton centered within the labyrinthine domains. Curvature homogeneity is defined similarly as the standard
deviation ΔK of the distribution of Gaussian curvature. All data are presented for distinct length normalisations: constant
surface-to-volume ratio, constant average Gaussian curvature and constant average channel diameter. We provide first and second
moments of the distribution of channel diameter for all members of these surfaces complementing curvature data from [A. Fogden,
S. Hyde, Eur. Phys. J. B 7, 91 (1999)]. The cubic G and D surfaces are deep local minima of Δd along the surface families (with G more homogeneous than
D), whereas the cubic P surface is an inflection point of Δd with adjacent, more homogeneous surface members. Both curvature
and packing homogeneity favour the tetragonal route between G and D (via tG and tD surfaces) in preference to the rhombohedral
route (via rG and rPD). 相似文献
10.
Copper thin films are deposited by thermal evaporation on unetched and etched monocrystalline silicon. The study by alpha particles backscattering (RBS) raises a strong diffusion of copper in silicon substrates with and without native suboxide layer. On the other hand, the X-rays diffraction shows the formation and the growth of Cu3Si and Cu4Si silicides. Whereas the scanning microscopy underlines large crystallites growth surrounded by black zones of silicon coming from the uncovered substrate, independently to the surface state of the substrate, after annealing at high temperature. The presence of native silicon suboxide at Cu/Si interface, influences in a drastic way the minimal temperature to which the interfacial reaction occurs. The oxygen impurities detected by microanalysis, after heat treatment under vacuum, are closely related to the growth of silicides crystallites. 相似文献