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排序方式: 共有119条查询结果,搜索用时 15 毫秒
51.
We consider the linearized compressible Navier-Stokes equation near a parallel flow in a cylindrical domain restricting our
study to perturbations periodic in the generatrix direction. For any parameter values, we show that the initial value linear
evolution problem is solved by the direct sum of a (strictly) contraction semi-group and an analytic semi-group. Any unbounded
in time solution of this linear problem comes from isolated eigenvalues with finite multiplicities, which have non negative
real part, and whose imaginary part is bounded. In addition, we precise the structure of the spectrum of the generator of
the semi-group, locating the essential spectrum stricly on the left side of the complex plane.
Sunto Si linearizzano le equazioni di Navier-Stokes comprimibili attorno ad un moto lineare in un cilindro. Senza imporre restrizioni sul moto di base, si studia il problema lineare per perturbazioni periodiche nella direzione della generatrice del cilindro. Si prova che il problema di evoluzione lineare è dato dalla somma diretta di un semigruppo di stretta contrazione ed un semigruppo analitico. Ogni soluzione temporalmente non limitata deriva da autovalori isolati di molteplicità finita, aventi parte reale positiva e parte immaginaria limitata. Si studia anche la struttura dello spettro del generatore del semigruppo, costituito nel lato destro del piano complesso da autovalori di molteplicità finita, e nel lato sinistro di autovalori e da uno spettro essenziale situato su di una retta parallela all’asse immaginario.相似文献
52.
The first direct measurement of the atomic dipole phase in high-order harmonic generation obtained by an interferometric technique in the extreme ultraviolet (XUV) is reported. The effects associated with both the main quantum paths involved in the emission of a given plateau harmonic are investigated and compared with the expectations of the semi-classical model, which offers a very simple physical picture for the understanding of the involved electronic dynamics. 相似文献
53.
Nicolaou KC Lizos DE Kim DW Schlawe D de Noronha RG Longbottom DA Rodriquez M Bucci M Cirino G 《Journal of the American Chemical Society》2006,128(13):4460-4470
The marine-derived halipeptins A (1a) and D (1d) and their analogues 3a, 3d and 4a, 4d were synthesized starting from building blocks 10, 13, 14a or 14d, 15, and 16. The first strategy for assembling the building blocks, involving a macrolactamization reaction to form the 16-membered ring hydroxy thioamide 52d as a precursor, furnished the epi-isoleucine analogue (4d) of halipeptin D, whereas a second approach involving thiazoline formation prior to macrolactamization led to a mixture of halipeptins A (1a) and D (1d) and their analogues 3a, 3d (epimers at the indicated site) and 4a, 4d (epimers at the indicated site). The same route starting with D-Ala resulted in the exclusive formation of the epimeric halipeptin D analogue 3d. The synthesized halipeptins, together with the previously constructed oxazoline analogues 5d and 6d, were subjected to biological evaluation revealing anti-inflammatory properties for 1a, 1d, and 6d while being noncytotoxic against human colon cancer cells (HCT-116). 相似文献
54.
Giovanni De Filpo Roberta Cassano Luana Tortora Fiore P. Nicoletta Giuseppe Chidichimo 《Liquid crystals》2008,35(1):45-48
Polymer-dispersed liquid crystal (PDLC) films operating in reverse mode are transparent electro-optical devices, which can be turned into an opaque state by application of a suitable electric field. The effect was investigated of different UV powers, used during the polymerization process, on the electro-optical and morphology properties of PDLCs, working in reverse mode operation. Films were obtained by UV polymerization of mixtures of a low molecular weight nematic liquid crystal and a photopolymerizable liquid crystal monomer, homeotropically aligned by rough conductive surfaces. The electro-optical and morphology properties of samples were related to the polymerization conditions. Samples polymerized by lower UV powers exhibited “polymer ball” morphology and an electro-optical response due to the liquid crystal director reorientation, whereas samples obtained at higher UV powers showed a “Swiss cheese” morphology and an electro-optical response due to dynamic scattering. In addition, we observed by conductivity and IR measurements that UV exposure induces a degradation of the nematic liquid crystal. 相似文献
55.
Stefanelli M Nardis S Tortora L Fronczek FR Smith KM Licoccia S Paolesse R 《Chemical communications (Cambridge, England)》2011,47(14):4255-4257
Mono- and di-substituted β-nitro derivatives have been obtained from the reaction of ttcorrFeCl with sodium nitrite in refluxing DMF. This result is unprecedented for iron corrolates and further evidences the non-innocent character of the corrole ligand. 相似文献
56.
57.
Mariarosaria Rizzardi 《Numerical Algorithms》2018,77(4):955-982
For several applications, it is important to know the location of the singularities of a complex function: just for example, the rightmost singularity of a Laplace Transform is related to the exponential order of its inverse function. We discuss a numerical method to approximate, within an input accuracy tolerance, a finite sequence of Laurent coefficients of a function by means of the Discrete Fourier Transform (DFT) of its samples along an input circle. The circle may also enclose some singularities, since the method works with the Laurent expansion. The DFT is computed by the FFT algorithm so that, from a computational point of view, the efficiency is guaranteed. The function samples may be obtained by solving a numerical problem such as, for example, a differential problem. We derive, as consequences of the method, some new outcomes able to detect those singularities which are close to the circle and to discover if the singularities are all external or internal to the circle so that the Laurent expansion reduces to its regular or singular part, respectively. Other singularities may be located by means of a repeated application of the method, as well as an analytic continuation. Some examples and results, obtained by a first implementation, are reported. 相似文献
58.
D. Fong M. Heller A.M. Shapiro M. Widgoff F. Bruyant D. Bogert M. Johnson R. Burnstein C. Fu D. Petersen M. Robertson H. Rubin R. Sard A. Snyder J. Tortora D. Alyea C.-Y. Chien P. Lucas H.D. Taft 《Physics letters. [Part B]》1975,60(1):124-128
We present data on inclusive and semi-inclusive ?0 production in 147 GeV/c π?p interactions. We find a total cross section of 7.3 ± 1.3 mb. Most of this cross section is found in the lower topology events (? 10 prongs), and in the central and forward rapidity regions. The PT2 dependence of ?0 production, 〈:n>?0 per event, and the ?0/π+ ratios are also discussed. 相似文献
59.
D. Fong M. Heller A. Shapiro M. Widgoff F. Bruyant D. Bogert M. Johnson R. Burnstein C. Fu D. Petersen M. Robertson H. Rubin R. Sard A. Snyder J. Tortora D. Alyea C.-Y. Chien P. Lucas T. Watts 《Nuclear Physics B》1976,104(1):32-51
An SU(3) gauge-field non-topological soliton in three space-dimensions is discussed. Let N be the largest among the magnitudes of eigenvalues of the matrix Σ18λaQa, where the Qa's are the eight conserved charges in the classical SU(3) gauge theory, and the λa's the usual 3 × 3 Gell-Mann matrices. We show that stable solitons exist if N > a critical value NS, and if the ratio between the mass of the SU(3) gauge field and that of a relevant spin-0 field is >√6. Our trial function analysis suggests that, for large N, states with dets (Σ18λaQa) ≠ 0 are unstable against fission. 相似文献
60.