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1.
We calculate the loss induced in a single-mode rectangular optical waveguide by the presence of a second waveguide, perpendicular to the first, which crosses over the first waveguide at a variable distance d. Our calculation is applied to the analysis of several doped silica waveguides of practical importance for optical circuit design. 相似文献
2.
Polynuclear Complexes with Fe? As, Fe? Sb, and Fe? Bi Frameworks The anionic iron clusters Fe3(CO)112? and Fe4(CO)132? were reacted with compounds EX3 and with organic derivatives REX2 and R2EX of the elements arsenic, antimony, and bismuth. Commonly redox and cluster degradation reactions were observed. The new complexes [(CO)4Fe? AsMe2? Fe(CO)4]?, [HFe3(CO)9(mu;3-SbBut)]?, [Fe3(CO)10 (mu;3-Sb)]?, and [Fe3(CO)10(mu;3-Bi)]? were formed and isolated as their PPN salts. The Fe? As? Fe complex was identified by a structure determination, the other complexes were identified by their spectra. 相似文献
3.
A 6000-fold rate enhancement has been observed for the hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) in the presence of 0.2 mM Cu(i-Pr(3)[9]aneN(3))(2+) at pH 9.2 and 50 degrees C. In a direct comparison, the rate of hydrolysis of BNPP is accelerated at least 60-fold over the previously reported catalyst Cu([9]aneN(3))(2+). As observed for Cu([9]aneN(3))(2+), hydrolysis is selective for diesters over monoesters. Hydrolysis of BNPP by Cu(i-Pr(3)[9]aneN(3))(2+) is catalytic, exhibiting both rate enhancement and turnover. The reaction is inhibited by both p-nitrophenyl phosphate and inorganic phosphate. The reaction is first-order in substrate and half-order in metal complex, with a k(1.5) of 0.060 +/- 0.004 M(-1/2) s(-1) at 50 degrees C. The temperature dependence of the rate constant results in a calculated activation enthalpy (Delta H(++) of 51 +/- 2 kJ mol(-1) and activation entropy (Delta S(++)) of -110 +/- 6 J mol(-1) K(-1). The kinetic pK(a) of 7.8 +/- 0.2 is close to the thermodynamic pK(a) of 7.9 +/- 0.2, consistent with deprotonation of a coordinated water molecule in the active form of the catalyst. The active catalyst [Cu(i-Pr(3)[9]aneN(3))(OH)(OH(2))](+) is in equilibrium with an inactive dimer, and the formation constant for this dimer is between 216 and 1394 M(-1) at pH 9.2 and 50 degrees C. Temperature dependence of the dimer formation constant K(f) indicates an endothermic enthalpy of formation for the dimer of 27 +/- 3 kJ mol(-1). The time course of anaerobic DNA cleavage by Cu(i-Pr(3)[9]aneN(3))(2+) is presented over a wide range of concentrations at pH 7.8 at 50 degrees C. The concentration dependence of DNA cleavage by Cu([9]aneN(3))(2+) and Cu(i-Pr(3)[9]aneN(3))(2+) reveals a maximum cleavage efficiency at sub-micromolar concentrations of cleavage agent. DNA cleavage by Cu(i-Pr(3)[9]aneN(3))(2+) is twice as efficient at pH 7.8 as at pH 7.2. 相似文献
4.
Lorraine M. Deck Robert T. Paine Elizabeth R. BrightSabrina Ouizem Diane A. Dickie 《Tetrahedron letters》2014
Simple, aqueous-based syntheses of methylpyridine and methylpyridine N-oxide decorated 3,4-dihydro-2H-naphthoxazine and 2,3-dihydro-1H-naphthoxazine monomers, as well as thermally promoted syntheses of 3,4-dihydro-2H-benzoxazine monomers and bisoxazine methylpyridine derivatives of substituted 1,5-, 2,6-, and 2,7-dihydroxynaphthalenes are described. The crystal structures of two derivatives are presented. 相似文献
5.
Hemigossypol (3), a sesquiterpene natural product, was previously isolated from Gossypium barbadense and was shown to display improved anti-fungal activity compared to gossypol (1), the disesquiterpene dimer of hemigossypol (3). Gossypol exhibits multiple biological activities. In order to study whether hemigossypol and its derivatives retain the various bioactivities of gossypol, we developed a short and convenient synthetic scheme to synthesize hemigossypol. This is the first de novo synthesis of this natural product. In addition derivatives of hemigossypol with various 2,5-alkyl substituents were synthesized. Modification of the synthetic scheme also afforded the natural product hemigossylic lactone (4) and its 2,5-substituted derivatives. 相似文献
6.
Justin J Heynekamp Lucy A Hunsaker Thomas A Vander Jagt Lorraine M Deck David L Vander Jagt 《BMC chemical biology》2006,6(1):1-11
Background
Urokinase-type plasminogen activator (uPA) plays a major role in extracellular proteolytic events associated with tumor cell growth, migration and angiogenesis. Consequently, uPA is an attractive target for the development of small molecule active site inhibitors. Most of the recent drug development programs aimed at nonpeptidic inhibitors targeted at uPA have focused on arginino mimetics containing amidine or guanidine functional groups attached to aromatic or heterocyclic scaffolds. There is a general problem of limited bioavailability of these charged inhibitors. In the present study, uPA inhibitors were designed on an isocoumarin scaffold containing uncharged substituents. 相似文献7.
P. R. Spalart S. Deck M. L. Shur K. D. Squires M. Kh. Strelets A. Travin 《Theoretical and Computational Fluid Dynamics》2006,20(3):181-195
Detached-eddy simulation (DES) is well understood in thin boundary layers, with the turbulence model in its Reynolds-averaged Navier–Stokes (RANS) mode and flattened grid cells, and in regions of massive separation, with the turbulence model in its large-eddy simulation (LES) mode and grid cells close to isotropic. However its initial formulation, denoted DES97 from here on, can exhibit an incorrect behavior in thick boundary layers and shallow separation regions. This behavior begins when the grid spacing parallel to the wall Δ∥ becomes less than the boundary-layer thickness δ, either through grid refinement or boundary-layer thickening. The grid spacing is then fine enough for the DES length scale to follow the LES branch (and therefore lower the eddy viscosity below the RANS level), but resolved Reynolds stresses deriving from velocity fluctuations (“LES content”) have not replaced the modeled Reynolds stresses. LES content may be lacking because the resolution is not fine enough to fully support it, and/or because of delays in its generation by instabilities. The depleted stresses reduce the skin friction, which can lead to premature separation.For some research studies in small domains, Δ∥ is made much smaller than δ, and LES content is generated intentionally. However for natural DES applications in useful domains, it is preferable to over-ride the DES limiter and maintain RANS behavior in boundary layers, independent of Δ∥ relative to δ. For this purpose, a new version of the technique – referred to as DDES, for Delayed DES – is presented which is based on a simple modification to DES97, similar to one proposed by Menter and Kuntz for the shear–stress transport (SST) model, but applicable to other models. Tests in boundary layers, on a single and a multi-element airfoil, a cylinder, and a backward-facing step demonstrate that RANS function is indeed maintained in thick boundary layers, without preventing LES function after massive separation. The new formulation better fulfills the intent of DES. Two other issues are discussed: the use of DES as a wall model in LES of attached flows, in which the known log-layer mismatch is not resolved by DDES; and a correction that is helpful at low cell Reynolds numbers. 相似文献
8.
A discussion is given of the relation between the maximum functionaltheorem and Schwinger's variational principle, and it is shownthat the bound given by Schwinger's principle is better thanor the same as that given by the maximum functional theorem. 相似文献
9.
The critical temperatures of thin superconducting films of Pb in intimate contact with PbTe have been measured resistively. The films were formed by sequential deposition and by co-evaporation of Pb and PbTe. The results show a depression of the critical temperature. 相似文献
10.
G. T. Jones B. W. Kennedy R. P. Middleton S. W. O'Neale A. M. Cooper A. Grant H. Klein J. Mittendorfer D. R. O. Morrison A. Parker P. Schmid H. Wachsmuth F. Hamisi M. M. Mobayyen O. Villalobos-Baillie M. Aderholz L. Deck N. Schmitz W. Wittek G. Corrigan G. Myatt D. Radojicic M. Retter 《Zeitschrift fur Physik C Particles and Fields》1984,25(2):121-127
Data from a neutrino and antineutrino hydrogen experiment with BEBC are used to investigate transverse properties of the produced charged hadrons. Measurements are presented on average transverse momenta of charged pions as functions of Feynman-x and the hadronic mass, on the transverse momentum flow within an event and on jet-related quantities. The main features of the data are well described by the LUND model. The data favour a version of the model in which soft gluon effects are included and the primordial transverse momentum of the quarks in the proton is small. Effects from 1st order QCD (hard gluon emission) are negligible. 相似文献