共查询到20条相似文献,搜索用时 31 毫秒
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《Journal of computational physics》2008,227(2):1372-1386
We combine the finite element method with the Eulerian–Lagrangian Localized Adjoint Method (ELLAM) to solve the convection–diffusion equations that describe the kinematics of magnetohydrodynamic flows, i.e., the advection and diffusion of a magnetic field. Simulations of three two-dimensional test problems are presented and in each case we analyze the energy of the magnetic field as it evolves towards its equilibrium state. Our numerical results highlight the accuracy and efficiency of the ELLAM approach for convection-dominated problems. 相似文献
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O. S. Greger S. V. Krivokhizha E. S. Lapteva L. L. Chaikov 《Bulletin of the Lebedev Physics Institute》2010,37(9):263-267
A decrease in the characteristic correlation time of light scattered by silicon particles in transformer oil and an increase
in their effective diffusion coefficient when the particle suspension in oil is exposed to a dc electric field were experimentally
shown. The current in the suspension did not exceed 100 nA and its temperature was unchanged. It was also shown that the shape
of the correlation function of light scattered by particles changes, i.e., a Gaussian factor appears in it. The dependences
of the exponential and Gaussian components on the electrode voltage are presented. 相似文献
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J B Caban T S Moerland S J Gibbs L McFadden B R Locke 《Magnetic resonance imaging》1999,17(8):1183-1191
Magnetic resonance microscopy of skin from hairless rats under the influence of electrical fields was conducted for two cases: 1) low voltage constant electrical fields and 2) high-voltage short pulse, electrical fields. Under conditions of the low voltage and low current iontophoresis, i.e., 0 to 20 V, and 0 to 0.5 mA/cm2, it was found that the skin structure, as observed by magnetic resonance microscopy, did not significantly change until 20 Volts were applied across the 0.1 cm thick skin. Under these conditions, the viable epidermis appeared to swell, and this result corresponded to observations from scanning electron microscopy and other research from the literature. High voltage electrical fields, i.e., 220 V 1 ms pulses repeated once per second, appeared to hydrate the stratum corneum as is consistent with published literature on electroporation. In the case of iontophoresis, water self-diffusion coefficients in the epidermis and hair follicle regions at all voltages were affected by the electrical field. Statistical analysis at the 95% confidence level for the comparison of the average differences between diffusion coefficients with the electrical field on and with the electrical field off for pair matched pixels for the viable epidermis show that for 5 V (p = 0.00377), 10 V (p = 0.0108), 20 V (p = 0.0219) regimes there are statistically significant (p < or = 0.05) changes due to the applied electric field. The same analysis for the hair follicle region at 5 V (p = 6.89 x 10(-7)), 10 V (p = 1.42 x 10(-5)), 20 V (p = 3.23 x 10(-3)) also show statistically significant changes (p < or = 0.05). When the electroporation pulse was applied, the water diffusion coefficients increased by about 30% to 6.6 x 10(-6) cm2/s +/- 2.4 x 10(-7) cm2/s and 8.3 x 10(-6) cm2/s +/- 3.7 x 10(-7) cm2/s, for the epidermis and hair follicle regions, respectively. Significant differences were noted between diffusion coefficients in the viable epidermis and the hair follicles for all cases. 相似文献
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The intensity of light dynamic scattering by a nematic liquid crystal with negative dielectric anisotropy (ZhK-440) as a function of the constant electric field strength has been studied under different interfacial conditions. It has been shown that potential barriers that arise at the interfaces not only influence the scattering intensity, but may also radically change the form of the dependence; i.e., the curves of optical transmission in the direction of the incident beam may have a minimum under certain field strengths. At higher strengths, the cells become totally transparent again. This anomalous behavior of the transmission curve is associated with the fact that the conductivity of the cells drops below a critical value with growing field strength, as the resistance of the space charge region at the inversely biased junction of the extraction electrode rises. In addition, it has been shown that the high resistance of the cells at low voltages may be attributed not only to a low concentration of impurities in the liquid crystal, but also to a low emissivity of the injecting electrode and a weak electron affinity of the extraction electrode. 相似文献
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We propose a model for growing fractal networks based on the mechanisms learned from the diffusion-limited aggregation (DLA) model in fractal geometries in the viewpoint of network. By studying the DLA network, our model introduces multiplicative growth, aging and geographical preferential attachment mechanisms, whereby featuring topological self-similar property and hierarchical modularity. According to the results of theoretical analysis and simulation, the degree distribution of the proposed model shows a mixed degree distribution (i.e., exponential and algebraic degree distribution) and the fractal dimension and clustering coefficient can be tuned by changing the values of parameters. 相似文献
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We consider a conformal theory of fractal growth patterns in two dimensions, including diffusion limited aggregation (DLA) as a particular case. In this theory the fractal dimension of the asymptotic cluster manifests itself as a dynamical exponent observable already at very early growth stages. Using a renormalization relation we show from early stage dynamics that the dimension D of DLA can be estimated, 1.69相似文献
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K J Cole R A Konopacki J H Abbs 《The Journal of the Acoustical Society of America》1983,74(5):1362-1366
A miniature recessed (i.e., cup) surface EMG electrode intended for use in the perioral region during speech has been constructed and tested. In addition to its small size and low mass, a custom acrylic electrode housing features an extruded design to yield secure attachment to the skin with skin cement rather than with conventional double adhesive collars. A durable, commercially manufactured disk of homogeneous silver and silver chloride was utilized to optimize bioelectric characteristics and durability. In relation to the commonly used fine-wire intramuscular electrode composed of platinum-iridium, this surface electrode demonstrates comparable bioelectric performance in perioral applications including low, stable, and well-matched skin-electrode impedance, a low noise floor, a surprisingly wide bandwidth, and good signal-to-noise ratios. 相似文献
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This paper deals with computer simulation of plasma erosion opening switch (PEOS) operation in the context of short-pulse high-power ion beam (HPIB) generation in microsecond store systems. The scaling of PEOS parameters and ion diode characteristics with various operating conditions was determined. The simulations showed the best PEOS characteristics for a hydrogen plasma (i.e., the lowest mass) with a high flow velocity and low density, although for some applications a plasma with A/Z > 1 may be preferable. It was shown that the efficiency of HPIB generation in the diode depends on its location relative to the PEOS, the time delay of anode plasma formation, the use of a spiral electrode in the PEOS region, and the use of an arrangement involving an ion return current bypass through the PEOS region. The optimization of the PEOS and ion diode with coaxial configurations and 100 kJ stored in the 600-kV Marx yielded a 16-percent overall efficiency HPIB generation in the diode, with a diode voltage and power of 4.2 MV and 0.42 TW, respectively. 相似文献
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Q. Wang D.S. Shang Z.H. Wu L.D. Chen X.M. Li 《Applied Physics A: Materials Science & Processing》2007,86(3):357-360
“Negative” electric-pulse-induced reversible resistance (EPIR) switching phenomenon was found in In/PCMO/Pt sandwich, in which
the high resistance can be written with positive voltage pulses, and the low resistance can be reset using negative voltage
pulses (the positive voltage direction is defined as going from the top electrode to the bottom electrode). This is just the
opposite from the “positive” EPIR effect in Ag/PCMO/Pt sandwich, in which the high resistance can be written only with negative
voltage pulses, and the low resistance can be reset using positive voltage pulses. The I–V hysteresis curves of In/PCMO/Pt
and Ag/PCMO/Pt sandwiches also show opposite directions, i.e., counterclockwise and clockwise under a negative voltage region
for indium and Ag electrode systems, respectively. C–V characteristics show that the barrier does not exist in Ag/PCMO/Pt
sandwich, while In/PCMO/Pt sandwich exhibits an obvious Schottky-like barrier. We suggest that in the negative EPIR behavior
in In/PCMO/Pt structure, the resistance states are mainly controlled changing the Schottky-like barrier at the interface with
the weak effect of carrier trapping process, while the positive EPIR behavior in Ag/PCMO/Pt sandwich mainly depends on the
carrier trapping process at the interface.
PACS 72.80.-r; 73.40.-C; 75.70.-i 相似文献
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One of the main consequences of chaos is that transport is enhanced with respect to the fluid at rest, where only molecular
diffusion is present. Considering long times and spatial scales much larger than the length scale of the velocity field, particles
typically diffuse with a diffusion constant, usually much bigger than the molecular one. Nevertheless there are some important
physical systems in which the particle motion is not a normal diffusive process: in such a case one speaks of anomalous diffusion.
In this paper, anomalous diffusion is experimentally studied in an oscillating two-dimensional vortex system. In particular,
scalar enhanced diffusion due to the synchronization between different characteristic frequencies of the investigated flow
(i.e., resonance) is investigated. The flow has been generated by applying an electromagnetic forcing on a thin layer of an
electrolyte solution and measurements are made through image analysis. In particular, by using the Feature Tracking (FT) technique,
we are able to obtain a large amount of Lagrangian data (i.e., the seeding density can be very high and trajectories can be
followed for large time intervals) and transport can be characterized by analyzing the growth of the variance of particle
displacements versus time and the dependence of the diffusion coefficient on the flow characteristic frequencies. 相似文献
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Spatial parameters of the X-ray radiation produced by a high-voltage nanosecond discharge evolving in air under atmospheric
pressure in the rod (cathode)-plane electrode system with a 10-cm electrode spacing are studied experimentally. A ∼170-ns
voltage pulse with an amplitude of ∼200 kV and 10-ns rise time is applied to the cathode. The photoelectronic method is used
to study, under the same conditions, the integrated (over the gap) characteristics of the radiation, in particular, the duration
of its generation. It is found that, when the size of the X-ray source is not smaller than that of the discharge region of
diffusive luminescence, radiation from the cathode region of the gap is primarily observed (i.e., from the region where the
electric field distribution is sharply inhomogeneous). The X-ray generation is usually observed after the bridging of the
discharge gap, the X-ray pulse having a rise time of ∼3 ns, a duration of ∼10 ns, and an effective radiation energy of ∼6
keV. 相似文献
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Yun GS Lee W Choi MJ Lee J Park HK Tobias B Domier CW Luhmann NC Donné AJ Lee JH;KSTAR Team 《Physical review letters》2011,107(4):045004
The filamentary nature and dynamics of edge-localized modes (ELMs) in the KSTAR high-confinement mode plasmas have been visualized in 2D via electron cyclotron emission imaging. The ELM filaments rotating with a net poloidal velocity are observed to evolve in three distinctive stages: initial linear growth, interim quasisteady state, and final crash. The crash is initiated by a narrow fingerlike perturbation growing radially from a poloidally elongated filament. The filament bursts through this finger, leading to fast and collective heat convection from the edge region into the scrape-off layer, i.e., ELM crash. 相似文献
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利用耦合理论推导了通过外腔反馈实现锁相运行的激光二极管列阵所满足的本征值方程。在忽略非相邻单元间耦合的串联运行方式下,解析求解了包括端面反射的列阵方程的本征值。求出了各阶超模的近场分布,并得到了考虑单个发光单元影响时的远场分布,具体为:当列阵运行于基超模时,近场各个单元间的光场同相,在远场中心位置出现光强主极大;而在其它高阶模式,近场各个单元间光场不同相,远场光强主极大出现在中心位置两侧;远场总体受到单个发光单元近场分布函数的调制。 相似文献
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H.M. Deylami N. Amanifard F. Dolati R. Kouhikamali K. Mostajiri 《Journal of Electrostatics》2013,71(4):656-665
Forced convection heat transfer enhancement with electrohydrodynamic (EHD) technique of turbulent flow inside a smooth channel has been numerically investigated. A two dimensional numerical approach has been chosen to evaluate the local and average heat transfer coefficient. In addition, the swirling flow pattern in the presence of an electric field has been studied. To achieve higher enhancement while using multiple electrodes, variety of electrode arrangements have been examined for specified values of Reynolds number, applied voltage, and wire radius. The results demonstrate that different electrode arrangements cause significant improvement of the heat transfer coefficient. 相似文献
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Yunjung Kim Gook-Hee HanSewhan Jin Eun-Ha ChoiHan Sup Uhm Guangsup Cho 《Current Applied Physics》2014,14(12):1718-1726
The propagation of plasma jets with argon gas is characterized in terms of two factors, the effect of electric field distribution along the tube and the effect of voltage polarity, from the observed results of optical signals along the entire column of plasma. The optical signal of plasma propagates from the high electric-field region of high-voltage electrode toward the low field region of the open air-space, regardless of the polarity of the voltage. The optical intensity and the propagation velocity are higher for the positive voltage than for the negative voltage. Moreover, the length of plasma plume exited from the end of the glass tube into the open air is shorter for the negative voltage. When the optical intensity is strong enough, a secondary peak signal follows the primary peak. In the plasma column on the inside of the glass tube, the optical intensity and the propagation velocity depend on the strength of the electric field; they are both high at the high-field region of voltage terminal and decay toward the end of the tube. The velocity is as fast as 104 m/s at the high-field region and slows down to 103 m/s at the low-field region of the glass-tube end. However, the plasma accelerates drastically to be (104–105) m/s after exiting the glass tube toward open air, even though the electric field is a quite low and thus the optical signal decays low before fading out. The experimental observations present in this report are explained with the propagation of the plasma diffusion waves. 相似文献
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《中国科学:物理学 力学 天文学(英文版)》2019,(12)
Dissolutive wetting, i.e., droplet wetting on dissolvable surfaces, is essential for various natural phenomena and industrial applications such as the formation of sinkholes, enhancing shale gas recovery, drug design, MEMS, and so on. It is difficult to predict the evolution of concentration field and solid-liquid interface owing to the coupled effects of wetting, diffusion, and convection. This study makes substantial progress by proposing a new theory based on Onsager's variational principle and finding two modes of solute transport, i.e., shifting and lifting modes. Furthermore, we investigate the influence of wetting and dissolution coupling on the interface shape using a phase diagram. Using our theory, we can predict and inversely predict the interface evolution. 相似文献