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131.
A highly efficient, stereospecific synthesis of the epimeric pentenomycins is reported utilizing the stereospecific addition of OsO4 to substituted cyclopentenes. 相似文献
132.
H Narfi Stefansson Kevin W Eliceiri Charles F Thomas Amos Ron Ron DeVore Robert Sharpley John G White 《Microscopy and microanalysis》2005,11(1):9-17
The use of multifocal-plane, time-lapse recordings of living specimens has allowed investigators to visualize dynamic events both within ensembles of cells and individual cells. Recordings of such four-dimensional (4D) data from digital optical sectioning microscopy produce very large data sets. We describe a wavelet-based data compression algorithm that capitalizes on the inherent redunancies within multidimensional data to achieve higher compression levels than can be obtained from single images. The algorithm will permit remote users to roam through large 4D data sets using communication channels of modest bandwidth at high speed. This will allow animation to be used as a powerful aid to visualizing dynamic changes in three-dimensional structures. 相似文献
133.
It is well known that nonlinear approximation has an advantage over linear schemes in the sense that it provides comparable approximation rates to those of the linear schemes, but to a larger class of approximands. This was established for spline approximations and for wavelet approximations, and more recently by DeVore and Ron (in press) [2] for homogeneous radial basis function (surface spline) approximations. However, no such results are known for the Gaussian function, the preferred kernel in machine learning and several engineering problems. We introduce and analyze in this paper a new algorithm for approximating functions using translates of Gaussian functions with varying tension parameters. At heart it employs the strategy for nonlinear approximation of DeVore-Ron, but it selects kernels by a method that is not straightforward. The crux of the difficulty lies in the necessity to vary the tension parameter in the Gaussian function spatially according to local information about the approximand: error analysis of Gaussian approximation schemes with varying tension are, by and large, an elusive target for approximators. We show that our algorithm is suitably optimal in the sense that it provides approximation rates similar to other established nonlinear methodologies like spline and wavelet approximations. As expected and desired, the approximation rates can be as high as needed and are essentially saturated only by the smoothness of the approximand. 相似文献
134.
135.
Summary. We study here in detail the location of the real and complex zeros of the partial sums of and , which extends results of Szeg? (1924) and Kappert (1996).
Received November 9, 2000 / Published online August 17, 2001 相似文献
136.
In this paper, we characterize the space of almost periodic (AP) functions in one variable using either a Weyl–Heisenberg (WH) system or an affine system. Our observation is that the sought-for characterization of the AP space is valid if and only if the given WH (respectively,
affine) system is an L
2(ℝ)-frame. Moreover, the frame bounds of the system are also the sharpest bounds in our characterization. This draws an intriguing
and quite unexpected connection between L
2(ℝ) representations and AP-representations.
相似文献
137.
The Ramanujan Journal - We evaluate 35 different theta derivatives with rational characteristics using the method of Matsuda, in which the logarithmic derivatives at $$z=0$$ of the triple product... 相似文献
138.
As a result of environmental concern, there is an increasing interest in the development of biodegradable polymers for packaging with suitable properties, as an alternative to the synthetic petroleum‐based polymers. However, such biodegradable polymers are prevented for use in wide industrial and commercial packaging because of their limited gas and vapor barrier properties. This obstacle urges innovative strategies to achieve enhanced gas barrier properties using “bio‐layering” technologies. Whey protein isolate (WPI), a by‐product of the cheese industry, has quite promising properties for packaging purposes. It possesses good oxygen, aroma, and oil barrier properties; however, its permeability to water vapor is high. In this study, several WPI coatings were obtained, adding polyvinyl alcohol and pectin to improve the coated film properties; in addition, nanoclays were used to improve water vapor barrier properties. Comparison of neat poly (lactic acid) film versus poly (lactic acid) coated with WPI presented advantage of the later: improvement of about 90% in the oxygen barrier properties and about 27% in the water vapor barrier properties. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
139.
Foister S Taylor LL Feng JJ Chen WL Lin A Cheng FC Smith AB Hirschmann R 《Organic letters》2006,8(9):1799-1802
[structure: see text] Cyclic hexapeptides, incorporating a dipeptide unit in place of the disulfide bond found in urotensin, were prepared and screened at the human urotensin receptor. The bridging dipeptide unit was found to influence dramatically the affinity for the urotensin receptor. Alanyl-N-methylalanyl and alanylprolyl dipeptide bridges failed to afford active ligands, while the alanyl-alanyl unit yielded a ligand with submicromolar affinity for the urotensin receptor. Further development led to a hexapeptide agonist with nanomolar affinity (2.8 nM). 相似文献
140.
[structure: see text] A stereocontrolled total synthesis of (+)-nodulisporic acid F, the simplest member of a family of novel ectoparasiticidal agents, has been achieved. Highlights of the effective modular synthetic strategy include anionic union of a tricyclic lactone with o-toluidine via our 2-substituted indole synthetic protocol, an optimized C-ring construction protocol, and a late-stage installation of the alpha,beta-unsaturated carboxylic acid side chain via the B-alkyl Suzuki-Miyaura cross-coupling tactic. 相似文献