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41.
The characteristics of ion beam extraction and focused to a volume as small as possible were investigated with the aid of computer code SIMION 3D version 7. This has been used to evaluate the extraction characteristics (accel-decel system) to generate an ion beam with low beam emittance and high brightness. The simulation process can provide a good study for optimizing the extraction and focusing system of the ion beam without any losses and transported to the required target. Also, a study of a simulation model for the extraction system of the ion source was used to describe the possible plasma boundary curvatures during the ion extraction that may be affected by the change in an extraction potential with a constant plasma density meniscus. 相似文献
42.
In this paper we propose a variant of the random coordinate descent method for solving linearly constrained convex optimization problems with composite objective functions. If the smooth part of the objective function has Lipschitz continuous gradient, then we prove that our method obtains an ?-optimal solution in $\mathcal{O}(n^{2}/\epsilon)$ iterations, where n is the number of blocks. For the class of problems with cheap coordinate derivatives we show that the new method is faster than methods based on full-gradient information. Analysis for the rate of convergence in probability is also provided. For strongly convex functions our method converges linearly. Extensive numerical tests confirm that on very large problems, our method is much more numerically efficient than methods based on full gradient information. 相似文献
43.
Christian P. Marocco Erik V. Davis Julie E. Finnell Phung-Hoang Nguyen Scott C. Mateer Ion Ghiviriga Clifford W. Padgett Brent D. Feske 《Tetrahedron: Asymmetry》2011,22(18-19):1784-1789
Fosfomycin is a gram positive and gram negative antibiotic that contains an asymmetric epoxide. An enzyme library was screened for its ability to reduce dimethyl(1-chloro-2-oxopropyl)phosphonate to the corresponding asymmetric chlorohydrin. Homology models were built in MOE, which were shown to accurately model the enzyme–substrate complex displaying the stereoselectivity that we observed. Two enzymes, YDR368w and YHR104w, were chosen for the scale up and synthesis of fosfomycin and its trans-(1S,2S)-diastereomer. 相似文献
44.
Ion Grosu Lo?c Toupet Gerard Plé Sorin Mager Eugen Mesaros Andreea Varga Elena Bogdan 《Monatshefte für Chemie / Chemical Monthly》2000,54(5):277-286
The synthesis and stereochemistry of new dibrominated spiro-1,3-dioxane derivatives are reported. Investigations by means
of NMR methods and single crystal X-ray diffraction for two compounds revealed the high regio- and diastereoselectivity of
the bromination reaction of some new spiro-1,3-dioxanes and the asymmetric induction of the chiral carbon atom located in
the spiro skeleton. 相似文献
45.
46.
We determine the rank generating function, the zeta polynomial and the M?bius function for the poset NC
(B)
(p, q) of annular non-crossing partitions of type B, where p and q are two positive integers. We give an alternative treatment of some of these results in the case q = 1, for which this poset is a lattice. We also consider the general case of multiannular noncrossing partitions of type
B, and prove that this reduces to the cases of non-crossing partitions of type B in the annulus and the disc. 相似文献
47.
Claudia Lar Gheorghe-Doru Roiban Romina Mariana Crăsneanu Ilişca Mihalca Elena Bogdan Anamaria Terec Ion Grosu 《Central European Journal of Chemistry》2011,9(2):218-223
The synthesis and photophysical properties of several 6,6″ symmetrically substituted 4′-aryl-2,2′:6′,2″-terpyridine derivatives
are reported herein. The UV-Vis spectra in acetonitrile as well as in dichloromethane show two intense bands in the UV areas
252–262 nm and 275–290 nm while the fluorescence emission spectra are only slightly influenced by chemical derivatization. 相似文献
48.
Vitalie Stavila Ion Bulimestru Aurelian Gulea Adam C. Colson Kenton H. Whitmire 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(3):m65-m68
The title complexes, hexaaquacobalt(II) bis(μ‐pyridine‐2,6‐dicarboxylato)bis[(pyridine‐2,6‐dicarboxylato)bismuthate(III)] dihydrate, [Co(H2O)6][Bi2(C7H4NO4)4]·2H2O, (I), and hexaaquanickel(II) bis(μ‐pyridine‐2,6‐dicarboxylato)bis[(pyridine‐2,6‐dicarboxylato)bismuthate(III)] dihydrate, [Ni(H2O)6][Bi2(C7H4NO4)4]·2H2O, (II), are isomorphous and crystallize in the triclinic space group P. The transition metal ions are located on the inversion centre and adopt slightly distorted MO6 (M = Co or Ni) octahedral geometries. Two [Bi(pydc)2]− units (pydc is pyridine‐2,6‐dicarboxylate) are linked via bridging carboxylate groups into centrosymmetric [Bi2(pydc)4]2− dianions. The crystal packing reveals that the [M(H2O)6]2+ cations, [Bi2(pydc)4]2− anions and solvent water molecules form multiple hydrogen bonds to generate a supramolecular three‐dimensional network. The formation of secondary Bi...O bonds between adjacent [Bi2(pydc)4]2− dimers provides an additional supramolecular synthon that directs and facilitates the crystal packing of both (I) and (II). 相似文献
49.
Wolfgang Muessel Helmut Strobel Maxime Joos Eike Nicklas Ion Stroescu Jiří Tomkovič David B. Hume Markus K. Oberthaler 《Applied physics. B, Lasers and optics》2013,113(1):69-73
We report on the optimization of high-intensity absorption imaging for small Bose–Einstein condensates. The imaging calibration exploits the linear scaling of the quantum projection noise with the mean number of atoms for a coherent spin state. After optimization for atomic clouds containing up to 300 atoms, we find an atom number resolution of $\varDelta_{\rm det}= 3.7$ atoms, mainly limited by photon shot noise and radiation pressure. 相似文献
50.
The process of drying a paint made of a dispersion of a polymer in a solvent is experimentally and theoretically studied at various constant temperatures. The diffusion of the solvent through the paint and evaporation from the surface is considered, as well as the subsequent shrinkage. From measurements made at the beginning and at the end of the drying operation on the kinetics of drying, the diffusivity is found to largely depend on the solvent concentration. An exponential relationship of the diffusivity versus the concentration is thus found and successfully tested for the whole process of drying, the diffusivity increasing with the solvent concentration. 相似文献