共查询到20条相似文献,搜索用时 31 毫秒
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Results of a code describing magnetic-field penetration into a plasma with theta-pinch geometry is presented. Classical coilisional effects can describe the Alfven velocity scaling but fail to account for observed penetration times and neutral density scaling. 相似文献
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A linear algebra based deprivation is presented to demonstrate that linearly time scaling an entire gradient waveform by a factor "R" exponentially increases its sensitivity to time derivatives of position by R(i + 1), where i refers to the i-th derivative of position (e.g., i = 1 is velocity). Thus, time scaling will preserve zero valued refocussing moments associated with artifact reduction techniques designed for motion occurring between excitation and detection. Typically, gradient waveforms for artifact reduction techniques are derived for use only at specific echo times. The time scaling described here allows for simple modification of refocussing gradient waveforms for use at variable echo times. Motion sensitivity associated with non-zero moment gradient waveforms can be easily predicted and modified using this technique, with consideration for field of view, resolution, and bandwidth. A clinical example is presented showing the predicted changes in sensitivity to nonrefocussed derivatives of position as the imaging gradients are time scaled. Further, trade-offs and alternatives in sensitivity to motion, slice thickness, image bandwidth, field of view and resolution will be discussed in conjunction with time scaling. This technique will have applicability in many situations involving MRI of moving tissue and a clinical example in cardiac imaging is presented. 相似文献
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We introduce examples of three- and four-mode entangled Gaussian mixed states that are not detected by the scaling and Peres–Horodecki
separability criteria. The presented modification of the scaling criterion resolves this problem. Also it is shown that the
new criterion reproduces the main features of the scaling pictures for different cases of entangled states, while the previous
versions lead to completely different outcomes. This property of the presented scheme is evidence of its higher generality. 相似文献
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The scaling law for aerodynamic dipole type of sound from constrictions in low speed flow ducts by Nelson and Morfey is revisited. A summary of earlier published results using this scaling law is presented together with some new data. Based on this, an effort to find a general scaling law for the sound power for components with both distinct and non-distinct flow separation points are made. Special care is taken to apply the same scaling to all data based on the pressure drop. Results from both rectangular and circular ducts, duct flow velocities from 2 to 120 m/s and sound power measurements made both in ducts and in reverberation chambers are presented. The computed sound power represents the downstream source output in a reflection free duct. In particular for the low frequency plane wave range strong reflections from e.g. openings can affect the sound power output. This is handled by reformulating the Nelson and Morfey model in the form of an active acoustic 2-port. The pressure loss information needed for the semi-empirical scaling law can be gained from CFD simulations. A method using Reynold Average Navier Stokes (RANS) simulations is presented, where the required mesh quality is evaluated and estimation of the dipole source strength via the use of the pressure drop is compared to using the turbulent kinetic energy. 相似文献
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Summary The most general function with scaling properties, that is, with superposition properties along a given direction, is deduced
from the general solution of the partial differential equation that describes the scaling conditions. The time-temperature
superposition, which means a scaling behaviour with a translation path parallel to the abscissa, is discussed within the general
formalism presented and some examples are considered in detail.
The authors of this paper have agreed to not receive the proofs for correction. 相似文献
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Caballero JA Amaro JE Barbaro MB Donnelly TW Maieron C Udias JM 《Physical review letters》2005,95(25):252502
Superscaling of the quasielastic cross section in charged-current neutrino-nucleus reactions at energies of a few GeV is investigated within the framework of the relativistic impulse approximation. Several approaches are used to describe final-state interactions and comparisons are made with the plane-wave approximation. Superscaling is very successful in all cases. The scaling function obtained using a relativistic mean field for the final states shows an asymmetric shape with a long tail extending towards positive values of the scaling variable, in excellent agreement with the behavior presented by the experimental scaling function. 相似文献
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Li X 《The Journal of the Acoustical Society of America》2010,127(5):EL203-EL208
This paper is concerned with the ensemble statistics of the dynamic responses of a random system subjected to harmonic excitations. Random point process theory is employed to derive general scaling laws with the Gaussian orthogonal ensemble assumption about the system natural frequencies. A scaled model is built to simulate the high-frequency vibrations of the original system. Specific forms of the scaling laws are presented for a mass-loaded plate regarding the scaling factors for the structural parameters. The ensemble statistics predicted from the scaled model are compared favorably with those obtained from the original system. 相似文献
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A novel monolithic ring laser with high potential for power scaling, the disk nonplanar ring oscillator, is presented. We achieved power scaling by reducing the pump-light-induced aberrations. The basic idea of our approach is to attach a thin Nd:YAG disk to an undoped nonplanar YAG ring resonator while the other side of the disk is mounted on a heat sink. First promising experiments have demonstrated a single-frequency cw output power of 1.6 W at 1.06 microm with a slope efficiency of 45%. Power scaling to several watts seems to be possible. 相似文献
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《Heat Recovery Systems and CHP》1991,11(6):471-481
A procedure to diagnose cases of production decrease in geothermal wells is presented. Most commonly, a production decrease in geothermal wells is due to: surface pipeline scaling, mechanical damage in the wellbore, entrance of cooler fluids to the producing reservoir layer and reservoir and well pipeline scaling. The procedure, which is presented as a decision diagram, is based in chemical and well production data. It is able to identify the above mentioned causes for a given well. This procedure was successfully applied to 17 wells from the Cerro Prieto geothermal field. In addition, a silica deposition rate parameter, Rd, was designed. It can be used as a forecasting tool for well scaling. It is proposed that this parameter is important in deriving suitable production strategies to minimise the effect of silica scaling processes in the reservoir. 相似文献
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Extended de Gennes-Fisher (EdGF) local-functional method has been applied to the thermodynamic Casimir effect away from the critical point for systems in the Ising universality class confined between parallel plane plates with symmetric boundary conditions [denoted (ab)=(++)]. Results on the universal scaling functions of the Casimir force W++(y) (y is a temperature-dependent scaling variable) and Gibbs adsorption G[over ](y) are presented in spatial dimension d=3. Also, the mean-field form of the universal scaling function of the Gibbs adsorption G[over ](y) is derived within the local functional theory. Asymptotic behavior of W++(y) for large values of the scaling variable y is analyzed in general dimension d. 相似文献
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Hiroshi Furukawa 《物理学进展》2013,62(6):703-750
A review of the dynamics of phase separation is presented, which focuses on the scaling assumption of the problem. Conventional linear and nonlinear theories are briefly reviewed. The problems with these conventional theories, and how the scaling idea can be used to overcome them are discussed. The growth rates of the droplets, domains, or grains are discussed in terms of the scaling assumption, and experimental tests of the scaling assumption for growth laws and scattering intensities are reviewed. To explain singular properties of the structure function and growth rate, which are observed experimentally, a strong correlation among droplets or grains on phase separations is postulated. A nonconventional form of the scattering function and a nonconventional droplet growth rate are explained qualitatively. 相似文献
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J. Chalupa 《Solid State Communications》1981,38(6):511-513
Numerical calculations on the disordered quantum Heisenberg antiferromagnetic chain yield low-temperature behavior independent of the detailed form of the randomness. A simple scaling interpretation, which makes contact with earlier theoretical work, of these complicated calculations is presented. An analogy with a one-parameter scaling theory of localization is explored. 相似文献
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Lei -Han Tang 《Journal of statistical physics》1992,67(3-4):819-826
The steady-state height-height correlation function for the (1 + 1)-dimensional single-step model is calculated in a large-scale Monte Carlo simulation. Analysis of the data yields a universal ratio of scaling amplitudes which differs from the value obtained recently from a mode-coupling calculation. An empirical form for a universal scaling function is also presented. 相似文献
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基于矩孔光学傅里叶变换的匹配滤波器缩放比例标定方法研究 总被引:1,自引:1,他引:0
为了使待识别目标的傅里叶变换频谱与匹配滤波器频谱分布严格重合,提出了一种基于矩孔图像光学傅里叶变换的匹配滤波器缩放比例标定方法。针对范德卢格特型光学相关器,在分析场景空间光调制器傅里叶变换频谱分布的基础上,以矩孔图像的频谱间距作为基准标定匹配滤波器的缩放比例;并利用焦距为400mm的傅里叶透镜作为一个实例,计算出其匹配滤波器缩放比例为1.068,对标定结果进行了实验验证。结果表明,此方法适用于范德卢格特型光学相关器中匹配滤波器的缩放比例标定,能够有效提高相关峰的能量和信噪比。 相似文献
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感兴趣区域提升幅度确定及编码 总被引:7,自引:7,他引:0
基于小波变换的星载图像压缩中,感兴趣区域编码实现面临主要问题之一是如何确定小波域系数提升的幅度.提出了一种比特平面熵估计值计算模型及计算算法,能够有效逼近比特平面编码实际输出码率,同时提出了系数提升幅度的算法,从而解决了基于比特平面提升的感兴趣区域编码中系数提升幅度确定问题,可以保证感兴趣区域重建质量要求的前提下,背景和总体重建质量更好.该算法是根据图像内容和用户要求计算系数提升幅度,不需要进行人工干预,图像的复杂度不同,提升幅度也会不同.该算法适合感兴趣区域确定如干涉高光谱图像这类图像的编码.仿真结果表明,尽管不同图像具有不同的复杂度,本文算法都能够准确确定感兴趣区域系数的提升幅度,从而有效保证了总体编码效果更好. 相似文献