10 dB gain–, 15 GHz-Bandwidth amplifier has been designed andfabricated in InP-HBT technology. Operation of the amplifier was achieved at1.7 V at total current consumption of 40 mA. The amplifier designed to havea Bessel-transfer-function has almost constant group delay up to 30 GHz.Pulse- and eye-diagram- measurements have been performed to verify largesignal operation. At 3.3 V, 24 dB gain and 10 GHz bandwidth was achieved.The 1dB compression point at 1.7 V supply voltage is measured at –10dBm output power. 相似文献
Intraelemental relative photoelectron line intensities for 20 pure elements obtained under ultrahigh vacuum (5·10?9 torr) and high resolution with cleaned surfaces are presented. Theoretical and experimental aspects of relative photoelectron line intensities as well as other characteristics of significance to quantitative analysis are discussed. Experimental data are related to theoretical results and compared with other recent work. 相似文献
Transition moment directions for the double-bond region vibrations of uracil, thymine and cytosine are calculated using the fixed partial charge model approximation. The coupling between the two carbonyl bonds and the carbon—carbon double bond in uracil and thymine is sensitive to the choice of the corresponding stretching force constants. The transition moment directions are correspondingly changed, thus, in principle, enabling the quantitative determination of coupling between the vibrations from linear dichroism measurements. 相似文献
The aim of X-ray tomography is to reconstruct an unknown physical body from a collection of projection images. When the projection images are only available from a limited angle of view, the reconstruction problem is a severely ill-posed inverse problem. Statistical inversion allows stable solution of the limited-angle tomography problem by complementing the measurement data by a priori information. In this work, the unknown attenuation distribution inside the body is represented as a wavelet expansion, and a Besov space prior distribution together with positivity constraint is used. The wavelet expansion is thresholded before reconstruction to reduce the dimension of the computational problem. Feasibility of the method is demonstrated by numerical examples using in vitro data from mammography and dental radiology. 相似文献
The paper describes the changes that are being made in the mathematics teachers' subject studies in the Department of Mathematics at the University of Joensuu, in order to provide our mathematics students both with a sufficiently deep knowledge of mathematics and science, and with present-day expertise in their profession as teachers. While the formal structure of the mathematics curriculum remains structured and taught as courses with mostly traditional names like algebra, analysis, and linear algebra, there are also totally new ‘professionally oriented’ courses. Some of the old courses—with rather traditional and rigorous contents—have been changed in a more student-driven direction. In these ‘pedagogically oriented’ courses students are encouraged, and even forced, to study co-operatively in social interaction, for example to negotiate how to solve a problem decently, or how to build a formal definition for a concept with certain wanted attributes. As an ultimate example of a pedagogical experiment we describe in more detail an abstract algebra course, where co-operative learning is combined with intensive programming in a mathematically oriented computer environment. 相似文献
We provide a detailed investigation of the second-order nonlinear optical and structural properties of Langmuir-Blodgett (LB) films of nonracemic thiohelicenebisquinone (THBQ). We prepare both X- and Y-type films of different thicknesses and characterize them using optical second-harmonic generation and atomic-force microscopy (AFM). We find that the overall nonlinear properties of the samples are essentially independent of the film thickness and the deposition type and arise from susceptibility tensor components associated with chirality. Both X- and Y-type films can be described by D2 symmetry, which is a higher symmetry than the previously assumed C2 of LB films of THBQ and a similar helicenebisquinone (HBQ). However, the two types of films are shown to differ significantly with respect to the orientation of the in-plane axis. For Y type, the axis follows the direction of vertical sample deposition, but for X type, the direction of the axis varies randomly and significantly between different samples. The Y-type samples are therefore more ordered than the X-type samples. This was confirmed by AFM measurements in which the Y type exhibits uniform ordering into columnar structures. Similar structures in X type, on the other hand, are shorter and more randomly oriented, like those earlier observed for racemic samples of HBQ [Verbiest, T., et al. Science 1998, 282, 913]. The common nonlinear properties and different high-level ordering observed here for two different types of nonracemic samples reinforces that the nonlinearity of THBQ (and probably HBQ, as well) originates from the low-level columnar aggregation of the molecules with the higher-level structures playing a lesser role. In addition, within the columns, the molecules likely assume fairly random azimuthal orientations so that the columns themselves exhibit approximate Dinfinity symmetry. 相似文献
We study the spectral properties of two kinds of derivatives of the carbon fullerene C(60), small fullerenes and Si-heterofullerenes, by ab initio calculations. The principal method of study is the time-dependent density-functional theory in its full time-propagation form. C(20), C(28), C(32), C(36), and C(50), the most stable small fullerenes in the range of C(20)-C(50), are found to have characteristic features in their optical absorption spectra, originating from the geometry of the molecules in question. The comparison of measured and calculated absorption spectra is found to be a useful tool in differentiating between different, almost isoenergetic ground state structure candidates of small fullerenes. Substitutionally doped fullerenes are of interest due to their enhanced chemical reactivity. It is suggested that the doping degree can be obtained by studying the absorption spectra. For example, it is observed that the spectra gradually change when doping C(60) up to C(48)Si(12) so that absorption in the visible and near infrared regions increases. 相似文献
A series of tridentate P, N, P ligands comprising a central pyridine unit and two pendent diarylphosphane moieties (2, 6‐bis(CH2PAr2)pyridine; Ar = phenyl ( 1 ), 2‐methylphenyl ( 2 ), 2, 4, 6‐trimethylphenyl ( 3 )) as well as the corresponding iron ( 1‐FeCl2 , 2‐FeCl2 , 3‐FeCl2 ) and cobalt ( 1‐CoCl2 , 2‐CoCl2 , 3‐CoCl2 ) complexes were synthesized and characterized. An X‐ray structure analysis of 2‐CoCl2 and 3‐CoCl2 exhibited a trigonal‐bipyramidal coordination geometry at the metal center, the two chlorine atoms and the nitrogen occupying the equatorial and the phosphane units the apical positions. IR analysis indicated, that in all complexes the pyridine unit is coordinated to the metal center. The cobalt compounds were applied as catalyst precursors for the polymerization of ethene after activation with MAO. 相似文献
Currently, developing a stable nanocarrier with high cellular internalization and low toxicity is a key bottleneck in nanomedicine. Here, we have developed a successful method to covalently conjugate poly(methyl vinyl ether‐co‐maleic acid) (PMVE‐MA) copolymer on the surface of (3‐aminopropyl)triethoxysilane‐functionalized thermally carbonized porous silicon nanoparticles (APSTCPSi NPs), forming a surface negatively charged nanovehicle with unique properties. This polymer conjugated NPs could modify surface smoothness, charge, and hydrophilicity of the developed NPs, leading to considerable improvement in the colloidal and plasma stabilities via enhanced suspensibility and charge repulsion. Furthermore, despite the surface negative charge of the polymer‐conjugated NPs, the cellular internalization was increased in both MDA‐MB‐231 and MCF‐7 breast cancer cells. These results provide a proof‐of‐concept evidence that such polymer‐based PSi nanocomposite can be extensively used as a promising candidate for intracellular drug delivery.