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211.
Mycelia of Aspergillus oryzae display high enantioselectivity towards (R)-flurbiprofen and can be efficiently used in pure organic solvent for the resolution of (R,S)-flurbiprofen through esterification. The use of the lyophilized mycelia facilitates the separation process so that in one step the two enantiomers of flurbiprofen, which are both valuable for pharmaceutical applications, can be easily separated. The biotransformation can be carried out in different apolar solvents using different primary alcohols as nucleophiles under very mild conditions. 相似文献
212.
This article deals with empty spacetime and the question of its physical reality. By “empty spacetime” we mean a collection of bare spacetime points, the remains of ridding spacetime of all matter and fields. We ask whether these geometric objects—themselves intrinsic to the concept of field—might be observable through some physical test. By taking quantum-mechanical notions into account, we challenge the negative conclusion drawn from the diffeomorphism invariance postulate of general relativity, and we propose new foundational ideas regarding the possible observation—as well as conceptual overthrow—of this geometric ether. 相似文献
213.
Franco Carillo Giorgio Biasiol Diego Frustaglia Francesco Giazotto Lucia Sorba Fabio Beltram 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):53
Electron-phase modulation in magnetic and electric fields will be presented in In0.75Ga0.25As Aharonov–Bohm (AB) rings. The zero Schottky barrier of this material made it possible to nanofabricate devices with radii down to below 200 nm without carrier depletion. We shall present a fabrication scheme based on wet and dry etching that yielded excellent reproducibility, very high contrast of the oscillations and good electrical gating. The operation of these structures is compatible with closed-cycle refrigeration and suggests that this process can yield coherent electronic circuits that do not require cryogenic liquids. The InGaAs/AlInAs heterostructure was grown by MBE on a GaAs substrate [F. Capotondi, G. Biasiol, D. Ercolani, V. Grillo, E. Carlino, F. Romanato, L. Sorba, Thin Solid Films 484 (2005) 400], and in light of the large effective g-factor and the absence of the Schottky barrier is a material system of interest for the investigation of spin-related effects [W. Desrat, F. Giazotto, V. Pellegrini, F. Beltram, F. Capotondi, G. Biasiol, L. Sorba, D.K. Maude, Phys. Rev. B 69 (2004) 245324; W. Desrat, F. Giazotto, V. Pellegrini, M. Governale, F. Beltram, F. Capotondi, G. Biasiol, L. Sorba, Phys. Rev. B 71 (2005) 153314; J. Nitta, T. Akazaki, H. Takayanagi, T. Enoki, Phys. Rev. Lett. 78 (1997) 1335] and the realization of hybrid superconductor/semiconductor devices [Th. Schäpers, A. Kaluza, K. Neurohr, J. Malindretos, G. Crecelius, A. van der Hart, H. Hardtdegen, H. Lüth, Appl. Phys. Lett. 71 (1997) 3575]. 相似文献
214.
We analyze asymptotically a differential-difference equation, that arises in a Markov-modulated fluid model. Here, there are N identical sources that turn on and off , and when on they generate fluid at unit rate into a buffer, which processes the fluid at a rate c < N . In the steady-state limit, the joint probability distribution of the buffer content and the number of active sources satisfies a system of N + 1 ODEs, that can also be viewed as a differential-difference equation analogous to a backward/forward parabolic PDE. We use singular perturbation methods to analyze the problem for N →∞ , with appropriate scalings of the two state variables. In particular, the ray method and asymptotic matching are used. 相似文献
215.
The effect of a varying cosmological term and a dissipative bulk stress on the evolution of a homogeneous and isotropic universe is investigated. In the cases of interest neither analytical nor qualitative analysis is feasible and so we study these numerically only. Our work extends that of Calvão et al. to bulk stresses not considered in their analysis. 相似文献
216.
The behaviour of allylbutyltin dichloride in water, water–ethanol and water–hexane media, under either homogeneous or heterogeneous conditions, has been studied. 1,3-Diallyl-1,3-dibutyl-1,3-dichlorodistannoxane, butyltin di(hydroxy)chloride and butyltin trichloride arise from the solvolytic, acid–base and degradation processes. The degradation process involving the cleavage of the tin–carbon allyl bond has been interpreted to occur via an intramolecular reaction at the expense of the cation [Bu(CH2=CHCH2)Sn(OH)(H2O)n]+. The mechanistic pathway is ascribable to an internal interaction of the electrophilic cation with a bonded water molecule. This mechanistic proposal may be of some help with understanding of the chemical degradation of diorganotin derivatives in aquatic environments. 相似文献
217.
I. Tamayo J. Belana J. C. Caadas M. Mudarra J. A. Diego J. Sellars 《Journal of Polymer Science.Polymer Physics》2003,41(12):1412-1421
With thermally stimulated depolarization currents, we researched the relaxations of crosslinked polyethylene as it is used in medium‐voltage cable insulation. Through conventional polarization two heteropolar peaks stand up in the spectra, at 80 and 105 °C. As the sample is annealed, a homopolar peak is developed at about 99 °C. With window polarization, our results indicated that the 80 °C peak is a structured peak related to polar crosslinking subproducts and impurities. The 105 and 99 °C peaks are fitted to the general kinetic‐order model because the 105 °C peak is related to free‐charge detrapping at the crystalline phase, in the bulk and maybe at the amorphous‐crystal interphases, and the peak that is observed at 99 °C is due to injected charge. Annealing at high temperatures promotes the creation of traps in the material. Charge trapping at T < 70 °C seems to be related to the increased insulator resistivity with annealing time. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1412–1421, 2003 相似文献
218.
219.
Carmen R. Maldonado Miguel Quirs Juan M. Salas 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):o489-o491
The title compound, C5H5N5OS·H2O, crystallizes as the monohydrate. Disorder of the H atoms that participate in the hydrogen bonds implies that two different tautomers are present in the crystal structure, one of them with both acidic H atoms attached to the imidazole ring and the other with one acidic H atom on each ring. 相似文献
220.
Diego A. Murio 《Journal of Computational and Applied Mathematics》1982,8(2):111-119
An improperly-posed inverse heat conduction problem with radial symmetry is stabilized by reconstructing a mollified image of the unknowns. Strict error bounds are derived and after introducing certain inverse kernels, the numerical problem is solved with an absolute minimum of computation. 相似文献