Rapid syntheses of oligo(p-phenyleneethynylene)s via iterative convergent approach

A general and controlled bidirectional growth strategy enable a very rapid and efficient construction of oligo(phenyleneethynylene)s possessing functional groups such as methylthio and thioacetate groups at both ends. The strategy employs only one reaction type with good to moderate yields to grow the conjugated chains. The synthesis is efficient and can give 23 benzene rings and 22 carbon-carbon triple bonds in the conjugated chains. The compounds are fully characterized by ¹H and ¹³C NMR and UV/vis and fluorescence spectroscopy.     

Ultrasonic investigation of amorphous carbon in various frequencies at low temperatures from 2.1 to 300 K

Using pulse echo overlap measurement, the elastic behavior of amorphous carbon has been studied at ambient and low temperatures. The smaller ratio B/G of the bulk modulus to shear modulus and smaller Poisson's ratio σ at room temperature indicate that there is an intrinsic stiffening of transverse acoustic phonons in the amorphous carbon. The acoustic velocity and attenuation for longitudinal modes have been measured between 2.1 and 300 K at three frequencies of 7, 21 and 35 MHz, respectively. Their frequency and temperature dependence are observed. The elastic constant C₁₁ increases with decreasing temperature and show enhanced stiffening at low temperatures. In the 130-220 K region, the abnormal change and effect of longitudinal velocity and attenuation with temperature and frequency, and a phase transition associated with structure relaxations are discussed.     

Hybrid inorganic/organic interpenetrating polymer networks based on zeolite 13x and polystyrene

A hybrid inorganic/organic interpenetrating polymer network (IPN) of a three-dimensional network structure zeolite crystal (13X, powder) and crosslinked or linear polystyrene (PS) was prepared and characterized by differential scanning calorimetry (DSC), solid-state¹³C-NMR, and scanning electron microscopy (SEM). The size and shape of the crystalline zeolite particles were revealed on SEM micrographs in both the pure zeolite and the IPNs. Solubility tests and the results of DSC with solid-state ¹³C-NMR confirm that some organic PS chains are incorporated within the internal three-dimensional channels of the zeolite particles. We speculate that the internal PS chains may adopt an extended “one-dimensional” conformation and exhibit no bulk polymer glass transition. These novel hybrid inorganic/organic IPNs are a new kind of IPN structure. © 1995 John Wiley & Sons, Inc.     

A globally convergent algorithm for the Euclidean multiplicity location problem

The Euclidean single facility location problem (ESFL) and the Euclidean multiplicity location problem (EMFL) are two special nonsmooth convex programming problems which have attracted a large literature. For the ESFL problem, there are algorithms which converge both globally and quadratically. For the EMFL problem, there are some quadratically convergent algorithms, but for global convergence, they all need nontrivial assumptions on the problem.In this paper, we present an algorithm for EMFL. With no assumption on the problem, it is proved that from any initial point, this algorithm generates a sequence of points which converges to the closed convex set of optimal solutions of EMFL.This research is supported in part by the Air Force Office of Scientific Research Grant AFOSR-87-0127, the National Science Foundation Grant DCR-8420935 and University of Minnesota Graduate School Doctoral Dissertation Fellowship awarded to G.L. Xue.     

A global optimization design for quasi-optics power combiner of 3mm wave solid-state sources

This paper describes a global optimization design for quasi-optics power combiner of solid-state millimeter-wave sources. The operating frequency is about 100 GHz and the oscillating sources are GaAs Gunn diodes. The source-array plane is a matrix consisting of NxN (N=3,5, ..., 2k+1, where k is positive integer) diodes. The radio frequency power of the combiner is from threefold to sevenfold larger than the sum total of the single diodes power. The global optimums of the array and the location in the cuvity of the suorce-array plane will be given by a global optimizition method.     

利用KTP晶体实现1.08μmNd：YAP激光器锁模

本文描述了利用ＫＴＰ晶体和腔的基波输出镜构成非线性镜实现１．０８μｍＮｄ：ＹＡＰ激光器的被动锁模。实验表明，这种新的锁模技术比用染料作可饱和吸收体的被动锁模技术有很多突出的优点，具有很大的发展潜力。实验测得锁模时基波１．０８μｍ输出２．４ｍＪ，二次谐波０．５４μｍ输出０．５ｍＪ（同样条件下的静态输出为２．５ｍＪ），基波脉冲的平均脉宽为４０ｐｓ。     

Microscopically structural studies of lithium niobate powders

On the basis of the crystallographic characteristics of lithium niobate (LN) crystals, Law of Bravais and Pauling's third rule (i.e. Polyhedral Sharing Rule) are employed with the aim to find the relationship between the crystal structure and morphological faces of LN powders. In order to validate our analytical results, we have successfully synthesized LN powders and measured the corresponding X-ray powder diffraction. Our results show that the structural analysis is consistent with the experimental data and is helpful and effective for us to control the single-crystal growth and to design superstructures at the specific plane, starting from the viewpoint of the microscopic behaviors of constituent chemical bonds and polyhedra in the crystallographic frame.     

Wavelet and harmonic filtering for distortion-invariant volume holographic correlation

The wavelet and harmonic filtering method suggested by Zalevsky and Ouzieli is introduced in this paper and adopted in our volume holographic image recognition system. This composite filter combines several scaled versions of the cascaded wavelet and harmonic filter, obtaining high discrimination ability and wide dynamic range of rotation and scale deformations. Optical experiments are conducted to demonstrate the validity and practicability of the algorithm. To the best of our knowledge, this is the first report of using this algorithm in a volume holographic system. Moreover, the separate correlation approach proposed in this paper greatly simplifies the manufacturing process and reduces the cost of the system.     

Reaction Mechanism Investigation Using Vibrational Mode Analysis for the Multichannel Reaction of CH_3O+CO

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