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101.
The flow over drag reducing riblets is examined computationally using a time-dependent model of the viscous wall region. The flow at the upper bound of the computational domain (y +?40) is described using a streamwise eddy model consisting of two scales. A control-volume finite-element method utilizing triangular meshes is used to exactly fit the riblet cross-sectional geometry. Observations of the transient flow conditions suggest that the riblets limit the lateral spread of fluid inrushes towards the wall and retain low momentum fluid in the riblet valleys effectively isolating much of the wall from such inrushes. The generation of intermittent secondary vortices within the riblet valleys also occurs; however, these appear to be quite weak and fairly short-lived. 相似文献
102.
A simple iterative procedure is illustrated here to overcome two problems frequently encountered in hot-wire anemometry: (1) the calibration of hot wires at low velocity and (2) to account for the wall-proximity correction in the actual measurements. The low-velocity calibration method used an iterative correction procedure based on laminar pipe velocity profiles. It is shown that the use of this approach, together with a simple wall proximity correction procedure, provides a simple and accurate calibration of both single and cross hot wires, and gives reliable measurements. 相似文献
103.
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106.
Lewis CA Chiu A Kubryk M Balsells J Pollard D Esser CK Murry J Reamer RA Hansen KB Miller SJ 《Journal of the American Chemical Society》2006,128(51):16454-16455
The chirality of biological receptors often requires syntheses of therapeutic compounds in single enantiomer form. The field of asymmetric catalysis addresses enantioselective synthesis with chiral catalysts. Chemical differentiation of sites within molecules that are separated in space by long distances presents special challenges to chiral catalysts. As the distance between enantiotopic sites increases within a substrate, so too may the requirements for size and complexity for the catalyst. The extreme of catalyst complexity could be defined by macromolecular enzymes and their amazing capacity to effect stereospecific reactions over long distances between reactive sites and enzyme-substrate contacts. We report here a synthetic, miniaturized enzyme mimic that catalyzes a desymmetrization reaction over a very long distance. 相似文献
107.
RM. Murugappan M. Karthikeyan A. Aravinth MR. Alamelu 《Applied biochemistry and biotechnology》2012,168(8):2170-2183
In the present study, siderophore produced by the marine yeast Aureobasidium pullulans was characterized as hydroxamate by chemical and bioassays. The hydroxamate assignment was supported by the appearance of peaks at 1,647.21?C1,625.99?cm?1 and at 1,435.04?cm?1 in the infrared spectrum. The purified siderophore exhibited specific growth-promoting activity under iron-limited conditions for siderophore auxotrophic probiotic bacteria. Cross-utilization of siderophore indicates a symbiotic relationship between the yeast A. pullulans and the selected probiotic bacterial strains. Statistical optimization of medium components for improved siderophore production in A. pullulans was depicted by response surface methodology. The shift in UV?CVis spectroscopy indicates the photoreactive property and subsequent oxidative cleavage of purified siderophore on exposure to sunlight. 相似文献
108.
The interpretations of transport properties of concentrated aqueous solutions by the physics of glass-forming liquids approach recently applied to normal pressure measurements is extended by analysis of the pressure dependence of the electrical conductance of Ca(NO3)2 and MgCl2 solutions. The conductance of these solutions has been determined to 3 kbar over the temperature range 20–100°C for compositions 9–20 mole% Ca(NO3)2 (5.6–13.9 m) and 80–200°C for MgCl2 solutions of composition 12.4 and 14.2% MgCl2. Using high-pressure-data determination of the glass-transition temperature to eliminate one adjustable parameter, it is found that the pressure dependence of the conductance of these solutions can be adequately described by ascribing all the pressure dependences to a single parameter, the ideal glass temperature To(P) of the Vogel-Tammann-Fulcher (VTF) equation known to describe temperature dependences of transport in viscous liquids. The results are discussed in terms of the Adam-Gibbs entropy theory and the Angell-Rao bond lattice model. The latter relates the pressure dependence of conductance to the volume change involved in configurational excitations of the liquid quasi-lattice, for which a mean volume increment of 1.6 cm3/mole is obtained. 相似文献
109.
This paper describes the incorporation of a pulsed ruby laser into an electronic speckle pattern interferometer. A technique is described for observing vibrational and transient events with a double pulsed laser and some typical results are given. Results of the application of the interferometer to non-destructive testing are included. 相似文献
110.
David Pollard 《Probability Theory and Related Fields》1981,57(2):181-195
Summary The empirical measure P
n
for iid sampling on a distribution P is formed by placing mass n
–1 at each of the first n observations. Generalizations of the classical Glivenko-Cantelli theorem for empirical measures have been proved by Vapnik and ervonenkis using combinatorial methods. They found simple conditions on a class C to ensure that sup {|P
n
(C) – P(C)|: C C} converges in probability to zero. They used a randomization device that reduced the problem to finding exponential bounds on the tails of a hypergeometric distribution. In this paper an alternative randomization is proposed. The role of the hypergeometric distribution is thereby taken over by the binomial distribution, for which the elementary Bernstein inequalities provide exponential boundson the tails. This leads to easier proofs of both the basic results of Vapnik-ervonenkis and the extensions due to Steele. A similar simplification is made in the proof of Dudley's central limit theorem forn
1/2(P P
n
–P)— a result that generalizes Donsker's functional central limit theorem for empirical distribution functions.This research was supported in part by the Air Force Office of Scientific Research, Contract No. F49620-79-C-0164 相似文献