Epoxidation of styrene catalyzed by metal complexes of poly(vinylbenzyl)acetylacetonate

The epoxidation of styrene to styrene oxide at higher than 96% yield has been achieved by the catalysis by poly-(vinylbenzyl)acetylacetonate complexes of cobalt(II) or manganese(II) in the presence of isobutyraldehyde under an atmospheric pressure of molecular oxygen at room temperature. The kind of aldehyde and aldehyde/styrene molar ratio greatly influenced the reaction. The catalyst could be recycled, but after recycling for five times, the yield of styrene oxide decreased from 96.0% to 84.6%.     

Side-chain liquid crystalline polymers: The synthesis and characterization of poly[4-nitrothiophenyl-4-(ω-methacryloyl oxyalkyloxy)] benzoate

A new series of sulfur-containing side-chain liquid crystalline polymer is described. Mesomorphic side chains with methylene spacers of different lengths have been synthesized, and their structures were identified by nuclear magnetic resonance, infrared and mass spectrometry. The liquid crystalline nature of the polymers was characterized by microscopy and differential scanning calorimetry.     

The spectrum for rotational Steiner triple systems

We develop some recursive constructions for rotational Steiner triple systems with which the spectrum of a k-rotational Steiner triple system of order v is completely determined for each positive integer k. © 1996 John Wiley & Sons, Inc.     

Characterizing Plasma-exposed In0.52Al0.48As Surface Using Photoreflectance-, Raman-, and Photoluminescence Spectra Method

We have performed Photoreflectance (PR), Raman Scattering (RS), and Photoluminescence (PL) experiments to characterize the In_0.52Al_0.48As surface exposed to plasma by a gas mixture of CH₄/H₂/Ar, PR spectra indicate that RIE (plasma) causes defects such as nonradiative recombination centers, scattering centers, and defects leading to the decrease of signal intensity, broaden line width and red shift of the transitions by increasing the rf power. In the Raman scattering study, RIE causes defects against InAs-like and AlAs-like LO modes vibration. As the rf power increased, the maximum of two LO modes shifts towards lower frequency and the line shape becomes increasingly asymmetric. Also, the intensity degrades gradually by disorder and point defects with increasing rf power. The PL transition energies show a red-shift with increasing the rf power. In addition, the spectral feature broadens, and the intensity decreases with rf power higher than 200 w. The consistence of the PL, PR, and RS results indicate that these three methods can be used as sensitive probes to evaluate the near surface damage of the epilayer.     

Gettering Properties of Praseodymium in GaAs,In0.53Ga0.47As,and InP Grown by Liquid Phase Epitaxy

The incorporation of praseodymium (Pr) into GaAs, In_0.53Ga_0.47As, and InP during liquid-phase epitaxy were investigated by double crystal x-ray diffraction, Hall effect, low temperature photoluminescence (PL) measurements. The lattice mismatch slightly vary with Pr concentration in the growth melts. Examinations of the electrical property illustrate that the lower carriers concentrations and a higher mobilities are obtain from Pr-doped epilayers than undoped sample (In_0.53Ga_0.47As and InP). The PL spectra (15-K) show that the intensity of the impurity related peaks decreases and the near-band-to-band luminescence intensity increase. They also reveal that the impurities are gettered by Pr ions during LPE growth. Thus, for the purpose of purification, proper amount of Pr in the growth melts is suggested. No intra-4f-shell transition line is observed from the Pr-doped GaAs, In_0.53Ga_0.47As, and InP layers.     

Kinetic model of living radical polymerization

This work studies the kinetics of living radical polymerization by means of both the nonsteady state approach and the quasi-stationary state method. Expressions for the numberand weight-average degress of polymerization and the polydispersity index were derived. Numerical results show that the concentration of residual initiator seriously influences the polydispersity index of the resulting polymer. The calculated outcomes of the non-steady state approach are evidently different from those of the quasi-stationary state method when the magnitude of the rate constant of termination is comparable with that of the propagation rate constant, and the difference becomes negligible if the rate constant of the termination (k_t) is much larger than that of propagation (k_p). The polydispersity index of the resulting polymer increases with decreasing ratios of k_t to k_p or M_O to I_O (initial concentrations of monomer and initiator).     

冰盘管密度对蓄冷槽取冷特性影响的实验研究

通过构建高密度直接蒸发式冰盘管实验台,研究了不同冰盘管密度对取冷特性的影响。实验结果表明:随着蓄冷槽中冰盘管密度的增大,可使直接蒸发式蓄冰槽取冷水温进一步降低,取冷速率进一步提高,从而能更好地满足低温送风空调系统的要求及空调高峰负荷变化的需要。     

人造金刚石合成中黑色低磁金刚石的研究

 通过对合成金刚石的原材料和合成产物——石墨、Ni₇₀Mn₂₅Co₅触媒、普通人造金刚石、黑色人造金刚石、NiMnCoC熔体的磁化率测试,以及对黑色人造金刚石和普通人造金刚石破碎断面扫描电镜的对比分析,认为黑色人造金刚石形成低磁性的原因是由于合成过程中温度偏高、压力偏低,生长的金刚石质量差、裂纹多。晶体内夹杂了很多石墨与触媒包裹体,同时金刚石表面与金刚石晶体内的触媒包裹体之间形成贯穿性的裂纹。在金刚石化学提纯处理过程中,金刚石晶体内的铁磁性触媒包裹体杂质被通过裂纹进入的酸除去。因而在检测金刚石磁性时,黑色金刚石的磁性很小,呈弱磁性。     

一个关于肿瘤治疗的自由边界问题的数学分析

§1Introduction Avarietyofpartialdifferentialequationmodelsfortumorgrowthortherapyhave beendevelopedinthelastthreedecades[see2,3,16-18,21-26].Mostofthosemodelsare informoffreeboundaryproblems,andareverydiversified.Rigorousmathematical analysisofsuchfreeboundaryproblemshasdrawngreatinterest,andmanyinteresting resultshavebeenestablished[4-15].Inthispaperwedealwithamathematicalmodeldescribingtumorchemotherapy.In thismodelthetumorisviewedasdenselypacked,radially-symmetricsphereofradiusR(t)contain…     

四元数广义奇异值分解及其应用

This paper derives a theorem of generalized singular value decomposition of quaternion matrices(QGSVD),studies the solution of general quaternion matrix equation AXB-CYD=E,and obtains quaternionic Roth's theorem.This paper also suggestssufficient and necessary conditions for the existence and uniqueness of solutions and explicit forms of the solutions of the equation.