X光机数字图像增强器的关键技术研究

X光机数字图像增强器是X射线成像系统中的重要一环,而目前常用的X光机数字图像增强器往往存在瑕疵点、信噪比过低等问题。针对噪声问题,提出了一种动态降噪算法,改善了运动环境下的降噪质量。同时,对存在瑕疵点的这一现象,提出了一种检测与校正的算法。最后在自行设计的X光机数字图像增强器样机上将以上两种算法成功实现。     

Optimized second-harmonic generation in quantum cascade lasers

Optimized second-harmonic generation (SHG) in quantum cascade (QC) lasers with specially designed active regions is reported. Nonlinear optical cascades of resonantly coupled intersubband transitions with giant second-order nonlinearities were integrated with each QC-laser active region. QC lasers with three-coupled quantum-well (QW) active regions showed up to 2 /spl mu/W of SHG light at 3.75 /spl mu/m wavelength at a fundamental peak power and wavelength of 1 W and 7.5 /spl mu/m, respectively. These lasers resulted in an external linear-to-nonlinear conversion efficiency of up to 1 /spl mu/W/W/sup 2/. An improved 2-QW active region design at fundamental and SHG wavelengths of 9.1 and 4.55 /spl mu/m, respectively, resulted in a 100-fold improved external linear-to-nonlinear power conversion efficiency, i.e. up to 100 /spl mu/W/W/sup 2/. Full theoretical treatment of nonlinear light generation in QC lasers is given, and excellent agreement with the experimental results is obtained. For the best structure, a second-order nonlinear susceptibility of 4.7/spl times/10/sup -5/ esu (2/spl times/10/sup 4/pm/V) is calculated, about two orders of magnitude above conventional nonlinear optical materials and bulk III-V semiconductors.     

SBS Suppression Using a Multichannel Tunable Laser with Data-Encoding Capability

We demonstrate stimulated Brillouin scattering (SBS) using a new laser transmitter. The device uses an integrated FM modulator for both SBS suppression and channel tuning, and an integrated AM modulator for data encoding. We measure thresholds of 25 dBm on four separate wavelength division multiplexing channels. The required modulation signal is very small, 95 mVpp, and the residual AM is only 1 %.     

Experimental, Theoretical and Biological Activity Study on the Acyl-Substituted Benzo-18-crown-6, Dibenzo-18-crown-6 and Dibenzo-24-crown-8

Hexadecanoyl, dihexadecanoyl, dioctadecaneoyl, di-10-undecenoyl, and dicis-9-octadecenoyl derivatives of benzo[18]crown-6, dibenzo[18]crown-6 and dibenzo[24]-8 were synthesized by the condensation of carboxylic acids (palmitic, stearic, oleic and undecenoic acid) with benzo and dibenzo crown ethers in the presence of zinc chloride. The extraction equilibrium constants of such macrocyclic ethers with long side chains were estimated using chloroform/water and dichloromethane/water membranes transfer of Na-PAR (4-(2-pyridylazo)-resorcinol mono sodium monohydrate) with UV–Vis spectroscopy. It was found that they were in the range of 10.88–11.71 in dichloromethane and 8.04–11.77 in chloroform. These results actually show that the Na+ binding effect of macrocyclic ethers depends on the type and the length of side chains. The geometrical properties of the molecules were studied employing semi-empirical calculations by simulated annealing technique. The frontier molecular orbital energies and dipole moments were also examined. The biological activity results showed that the synthesized crown ethers have no activity against the studied microorganisms.     

FEATURES OF BIOECONOMICS MODELS FOR THE OPTIMAL MANAGEMENT OF A FISHERY EXPLOITED BY TWO DIFFERENT FLEETS

ABSTRACT. After the extension of the Exclusive Economic Zone, in 1977, to 200 miles, most fish stocks came under jurisdiction of the adjacent coastal states. This development opened prospects of effective management of the open sea fisheries. Coastal states have the right to plan out the operation of so-called by Clarke and Munro “distant water fishing nations” from their Exclusive Economic Zone. Under some arrangements, a foreign fleet is allowed to harvest the resource in the Exclusive Economic Zone area. Clarke and Munro, in [1987] and [1991], focus on the issue of optimum terms and conditions of access and, in doing so, built a multiobjective model. The main goal of the present work is the development of a more general model including more variables and parameters related to the presence of a domestic fleet as well as a distant water fishing nation. The main difficulty resides in sharing the harvesting between the two fleets. The study responds to the realistic problemof coastal states who own enough resource stocks to allow harvesting by several kinds of fleets. Two optimal scenarios are developed, in each of them a solution is given.     

Superconductivity and magnetic order in the pseudoternary system Ho1−xEuxMo6S8

Ac susceptibility, resistance and magnetization experiments on the pseudoternary system, Ho_1?xEu_xMo₆S₈ confirm that there exist three distinct domains of concentration between x=0 and 1 with respect to the interplay of superconductivity and magnetism.     

Epitaxially stabilized GexSn1−x diamond cubic alloys

We have investigated the stabilization of Ge_xSn_1-x on (001) InSb substrates, as well as InSb coated GaAs substrates. We find that alloys up to ≈1500Å can be stabilized when 0 <x < 0.13. Single crystal, twinned material has been grown forx = 0.16, but only for thicknesses up to 500Å. Forx < 0.13, reflection high energy electron diffraction (RHEED) patterns reveal four stages of growth: quasi-two-dimensional growth, threedimensional growth, twinned growth, and finally phase separated growth. Ion channeling (001) results support the RHEED data, showing that film quality degrades with increasing thickness. Double and triple crystal x-ray diffraction results indicate that 1200Å-thick Ge_xSn_1-x films have excellent crystallinity forx < 0.10. Forx > 0.10, we observe partial phase separation into coherent α-Sn and α-GeSn. The films are stable in the temperature range of 125-130° C, depending on Ge concentration. We present a thermodynamic model which exhibits the trends observed in the growth and stability of epitaxially stabilized Ge_xSn_1-x alloys. Electrical and optical measurements show consistently high carrier concentrations (10²¹ cm^-3) and low carrier mobility (<1000 cm²/ Vsec) for the alloys.     

The mirror of television: a comparison of black and white adolescents' body image

Research has shown differences in the extent of eating-disordered attitudes and behaviors between African American and European American women. However, the extent to which those differences are a result of differences in cognitive processing and exposure of mediated images remains untested. This study tests that notion through the framework of social comparison theory. The sample consists of 145 White and 33 Black females from 2 high schools in 2 medium-sized Midwestern cities. Results indicate that African American girls do respond differently to and are differently affected by thin images than European American girls. However, there are also some similarities between the adolescents that foreshadow a narrowing of the ethnic gap in the development of eating disorders.     

Majority-minority influence: identifying argumentative patterns and predicting argument-outcome links

In this paper, the authors investigate the argument activities of majority and minority faction in small group decision-making situations. We begin by identifying patterns of argument that characterize majority and minority communication in 34 discussions and then test several subgroup-outcome and argument-outcome links. Results indicate that winning and losing subgroups argue differently (as do minority and majority subgroups overall) and that consistency in argument is a strong predictor of subgroup success. Both theoretical and practical implications for subgroup influence in group decision making accrue from these findings.     

How experimental design can improve the validation process. Studies in pharmaceutical analysis

A critical discussion about the possibility of improving the method validation process by means of experimental design is presented. The reported multivariate strategies concern the evaluation of the performance parameters robustness and intermediate precision, and the optimisation of bias and repeatability. In particular, accuracy and precision improvement constitutes a special subset of experimental design in which the bias and the relative standard deviation of the assay are optimised. D-optimal design was used in order to plan experiments for this aim. The analytical methods considered were capillary electrophoresis, HPLC, adsorptive stripping voltammetry and differential pulse polarography. All methods were applied to real pharmaceutical analysis problems.