Calculation of some N and C nuclear shielding parameters for some ureas and thioureas

Molecular orbital calculations using CNDO/S parameters are employed to determine bond-orders, charge-densities and the shielding of the ¹⁵N and ¹³C nuclei of a series of ureas and thioureas. For the sterically uncrowded molecules a linear relationship is noticed between the ¹⁵N chemical shifts and C---N bond-orders. When steric crowding occurs this simple relationship is no longer applicable.     

两种固体席夫碱15N化学屏蔽研究中的分子内氢键作用

应用量子化学基本原理,对两种固体化合物席夫碱类的¹⁵N化学位移的分子内氢键效应进行了研究.为简化计算,本文在计算过程中采用一种简化模型.其分子几何结构参数采用优化值.本文结果表明:理论值成功地再现了两种固体化合物的¹⁵N化学屏蔽值,证实了¹⁵N在分子内氢键形成过程中的屏蔽行为.本文证实当有分子内氢键形成时(大约为0.2nm),¹⁵N化学位移向高频区大约移动50ppm.本文结果对理论上定量估计氢键强度可能会有重要作用.     

Positive Solutions of Nonlocal Boundary Value Problems: A Unified Approach

We give a unified approach for studying the existence of multiplepositive solutions of nonlinear differential equations of theform where g, f are non-negativefunctions, subject to various nonlocal boundary conditions.We study these problems via new results for a perturbed integralequation, in the space C[0, 1], of the form where [u], ß[u] are linear functionalsgiven by Stieltjes integrals but are not assumed to be positivefor all positive u. This means we actually cover many more differentialequations than the simple equation written above. Previous resultshave studied positive functionals only, but even for positivefunctionals our methods give improvements on previous work.The well-known m-point boundary value problems are special casesand we obtain sharp conditions on the coefficients, which allowssome of them to have opposite signs. We also use some optimalassumptions on the nonlinear term.     

Parallel analysis of v-Src mutant protein function using reverse transfection cell arrays

The conversion of the genomic information produced by the recent sequencing projects into a comprehensive understanding of the human proteome has yet to occur. A new technology that represents a potential bridge between genomics and proteomics is reverse transfection. Reverse transfection cell microarrays are produced by overlaying cDNA arrays with mammalian cells, generating localized clusters of transfected cells with each cluster overexpressing a unique protein. This miniaturized cell-based microarray format affords parallel functional analysis of thousands of cDNA constructs in a high throughput format. In this report we document the development of a co-transfection methodology for reverse transfection applications. The demonstrated high co-transfection efficiency with a "marker" plasmid encoding for GFP enables the identification of transfected cells and eliminates the need for epitope-tagged constructs in cell-based high throughput screening applications using reverse transfection. This co-transfection method was used to study in parallel the structure/function of multiple versions of the v-Src protein using automated fluorescence microscopy. The wild-type v-Src protein and four mutants having insertions or deletions in the SH2 or SH3 domains displayed high levels of tyrosine kinase activity in HEK293T cells. Three other mutated v-Src proteins, including a kinase-dead version, were shown to be defective for tyrosine kinase activity. This reverse co-transfection approach is applicable for high throughput screening of both cDNA libraries and positional scanning recombinant protein libraries.     

Successful screening of large encoded combinatorial libraries leading to the discovery of novel p38 MAP kinase inhibitors

Screening of more than 2 million compounds comprising 41 distinct encoded combinatorial libraries revealed a novel structural class of p38 mitogen-activated protein (MAP) kinase inhibitors. The methodology used for screening large encoded combinatorial libraries combined with the statistical interpretation of screening results is described. A strong preference for a particular triaminotriazine aniline amide was discovered based on biological activity observed in the screening campaign. Additional screening of a focused follow-up combinatorial library yielded data expanding the unique combinatorial SAR and emphasizing an extraordinary preference for this particular building block and structural class. The preference is further highlighted when the p38 inhibitor data set is compared to data obtained for a panel of other kinases.     

Ytterbium-doped Y2O3 nanoparticle silica optical fibers for high power fiber lasers with suppressed photodarkening

We report efficient laser demonstration and spectroscopic characteristics of a Yb-doped Y₂O₃ (or Y₃Al₅O₁₂) nanoparticle silica fiber developed by conventional fiber fabrication technique. The spectroscopy study evidences modification in the environment of Yb ions by the Y₂O₃ nanoparticles. As a result, photodarkening induced loss is reduced by 20 times relative to Yb-doped aluminosilicate fibers. The fiber is suitable for power scaling with good laser slope efficiency of 79%.     

High-resolution X-ray photoelectron spectroscopy of chlorine-terminated GaAs(111)A surfaces

Oxide-terminated and Cl-terminated GaAs(111)A surfaces have been characterized in the As and Ga 3d regions by high-resolution, soft X-ray photoelectron spectroscopy. The Cl-terminated surface, formed by treatment with 6 M HCl(aq), showed no detectable As oxides or As(0) in the As 3d region. The Ga 3d spectrum of the Cl-terminated surface showed a broad, intense signal at 19.4 eV and a smaller signal at 21.7 eV. The Ga 3d peaks were fitted using three species, one representing bulk GaAs and the others representing two chemical species on the surface. The large peak was well-fitted by the bulk GaAs emission and by a second doublet, assigned to surface Ga atoms bonded to Cl, that was shifted by 0.34 eV from the bulk GaAs 3d emission. The smaller peak, shifted by 2.3 eV in binding energy relative to the bulk GaAs Ga 3d signal, is assigned to Ga(OH)3. The data confirm that wet chemical etching allows for the formation of well-defined, Cl-terminated GaAs(111)A surfaces free of detectable elemental As, that can provide a starting point for further functionalization of GaAs.     

Axisymmetric jets impinging on porous walls

The flow of axisymmetric turbulent jets impinging on porous walls has been studied experimentally. It is shown how the overall flow structure depends on the porosity of the surface. For high porosities (open area ratios, β, in excess of around 40% say) the porous wall, or screen, leads to a sudden increase in jet width and decrease in mean and fluctuating velocities, a direct consequence of the momentum flux extracted because of the screen drag. Lower porosities can lead to the appearance of radial wall jets on the upstream side of the screen but, in contrast to the corresponding case of planar jet impingement (Cant et al. in Exp Fluids 32:16–26, 2002), such wall jets never occur on the downstream side. The axial downstream velocities thus remain positive for all porosities. Jet growth rates for are initially increased by the screen, but once β≤0.4 momentum extraction by the screen is virtually complete, so that velocities become very small. Again, unlike in the corresponding planar case (for β≈0.4), recirculating regions upstream of the screen never occur. A simple argument is suggested to explain the fundamental differences in flow behaviour between planar and axisymmetric jet impingement onto porous screens and it is concluded that in the latter case the effects of the screen are generally more benign and unsurprising. Nonetheless, these axisymmetric flows, like the corresponding planar ones, provide a serious challenge for computational modelling.     

Positive current correlations associated with super-Poissonian shot noise

We report on shot noise cross spectrum measurements in a beam splitter configuration. Electrons tunneling through potential barriers are incident on a beam splitter and scattered into two separate channels. Such a partition process introduces correlations between the fluctuations of the two currents. Our work has confirmed that the generally expected negative correlations resulted from sub-Poissonian electron sources. More interestingly, positive cross correlations associated with barriers exhibiting super-Poissonian shot noise have also been observed. We have found that both positive and negative correlations can be related to the noise properties of the electron source.