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21.
We present measurements of Eulerian longitudinal velocity autocorrelations in homogeneous, isotropic, high-intensity (~9%) free-stream turbulence behind an active grid. Spatial correlations are measured using particle image velocimetry as well as with two-point hot-wire anemometry (HWA), while temporal correlations are measured using HWA. The temporal correlations are transformed into spatial correlations by using Taylor's ‘frozen’ hypothesis with both the mean as well as instantaneous velocities. A model relating Eulerian spatial and temporal autocorrelations is also used for this purpose. The differences from the measured spatial correlation resulting from the use of Taylor's hypothesis on the temporal correlation is quantified; even at this moderately high level of turbulent intensity, the result from the use of the instantaneous velocity as convection velocity is practically indistinguishable from that obtained using the mean velocity. Use of the model produces a good agreement between the estimates of the spatial correlation function. A relation between Eulerian spatial and temporal integral scales is also derived. 相似文献
22.
23.
Roger Penrose 《Journal of statistical physics》1994,77(1-2):217-221
The second law of thermodynamics has two distinct aspects to its foundations. The first concerns the question of why entropy goes up in the future, and the second, of why it goes down in the past. Statistical physicists tend to be more concerned with the first question and with careful considerations of definition and mathematical detail. The second question is of quite a different nature; it leads into areas of cosmology and quantum gravity, where the mathematical and physical issues are ill understood. 相似文献
24.
We analyze the role and influence of a tradition of research linked to the concept of
primary matter
in nineteenth-century studies on the nature of the elements.The suggestion of William Prout
(1785-1850) in 1816 that the atomic weights of pure chemical elements are whole numbers and
multiples of the atomic weight of hydrogen, taken as unity, was met with serious confutations,which
in turn prompted several attempts to save Prouts hypothesis.We discuss these attempts in detail
and the objections raised against them, for instance by Dmitry Ivanovich Mendeleev (1834-1907).
We pay particular attention to the use of spectroscopy as a method for proving the existence of
elementary forms of matter inside atoms. Leaders in this field of research were two English scientists,
the astrophysicist Norman Lockyer (1836-1920) and the chemist William Crookes (1832-
1919). Both of their approaches involved the idea of primary matter. However, while Crookess
approach proved to be incorrect, Lockyers ideas survived for several years and supported the discovery
of the electron by J.J.Thomson (1856-1940). 相似文献
25.
本文先介绍用不确定关系粗略计算一维线性谐振子零点能,然后再结合普朗克量子假设给出谐振子能级公式. 相似文献
26.
We propose a degree of market efficiency in terms of entropy concepts. The relative efficiency for the US stock market varies over time from 1929 to 2012, with a slight decline in the past 10 years. 相似文献
27.
QingLe Pang 《Applied mathematics and computation》2010,217(5):2015-2023
By means of an extended homogeneous balance method and a variable separation hypothesis, a broad general variable separation solution with three specific arbitrary functions of the nonlinear (2+1)-dimensional Broer-Kaup (BK) equations was derived. Based on the derived solution, a number of abundant oscillating solitons, such as dromion, multi-dromion, solitoff, ring, multi-lump and so on, have been revealed in this study by selecting appropriate functions of the general variable separation solution. 相似文献
28.
A. V. Karasev 《Mathematical Notes》1999,66(5):550-555
Under the assumption of the continuum hypothesis, a differentiable 4-manifoldM of dimension dimM=∞ and cohomological dimension cA—dimM=4 is constructed. The spaceM is perfectly normal and hereditarily separable. Translated fromMatematicheskie Zametki, Vol. 66, No. 5, pp. 664–670, November, 1999. 相似文献
29.
We investigate properties of square-Gaussian stochastic processes. These processes are formed by quadratic forms of Gaussian processes or by limits in the mean square of quadratic forms of Gaussian processes. Special classes of these processes are determined and investigated. For processes from these classes estimates of large deviation probability are obtained. These estimates we use to estimate the probability that Gaussian vector-valued process leave some region on some interval of time. We construct asymptotic confidence regions for estimates of covariance functions of vector-valued Gaussian processes. Criterion of hypothesis testing on covariance functions of these processes is constructed. 相似文献
30.