应变纤锌矿ZnO/MgxZn1-xO量子点中离子施主束缚激子的光学性质

Within the framework of the effective-mass approximation and the dipole approximation, considering the three-dimensional confinement of the electron and hole and the strong built-in electric field(BEF) in strained wurtzite Zn O/Mg0:25Zn0:75O quantum dots(QDs), the optical properties of ionized donor-bound excitons(D+, X)are investigated theoretically using a variational method. The computations are performed in the case of finite band offset. Numerical results indicate that the optical properties of(D+, X) complexes sensitively depend on the donor position, the QD size and the BEF. The binding energy of(D+, X) complexes is larger when the donor is located in the vicinity of the left interface of the QDs, and it decreases with increasing QD size. The oscillator strength reduces with an increase in the dot height and increases with an increase in the dot radius. Furthermore, when the QD size decreases, the absorption peak intensity shows a marked increment, and the absorption coefficient peak has a blueshift. The strong BEF causes a redshift of the absorption coefficient peak and causes the absorption peak intensity to decrease remarkably. The physical reasons for these relationships have been analyzed in depth.     

Excited-state absorption of meso-tetrasulfonatophenyl porphyrin: Effects of pH and micelles

The influence of the environment on the excited state transitions of meso-tetrakis(p-sulfonatophenyl) porphyrin (TPPS) is reported. TPPS was investigated in protonated and non-protonated forms, and in the presence of the cationic cetyltrimethylammonium bromide (CTAB) micelles. The singlet excited-state absorption spectra were measured by using the white-light continuum Z-scan technique and the triplet–triplet absorption spectra were acquired employing an association of laser flash photolysis and Z-scan techniques. Our results show that the perseveration of the molecular symmetry, upon excitation, depends on the state of multiplicity of the molecules, as well as on the environment and structural characteristics of the porphyrin. Additionally, it was observed that for excited molecules, the ring distortion caused by the protonation of porphyrin ring has great influence on the changes observed for the symmetry and vibronic structure. The results clearly show that the porphyrin investigated is a promising candidate for optical limiting applications for all investigated environments.     

In vitro evaluation and in vivo performance of lyophilized gliclazide

Enhancement of the dissolution rate of the poorly water-soluble hypoglycemic agent, gliclazide, by the aid of lyophilization was investigated. Mannitol, sodium lauryl sulfate (SLS) and polyvinyl pyrrolidone (PVP-k-30) were employed in different weight ratios (43%, 56% and 64% w/w, respectively) as water-soluble excipients in the formulation. Lyophilized systems were found to exhibit extremely higher in vitro dissolution rate compared to the unprocessed drug powder. Solid state characterization of the lyophilized systems using X-ray powder diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry techniques revealed that dissolution enhancement was attributable to transformation of gliclazide from the crystalline to an amorphous state in the solid dispersion formed during the lyophilization process. The gastrointestinal absorption and hypoglycemic effect of the lyophilized gliclazide/SLS system were investigated following oral administration to Albino rabbits. C_max and area under the plasma concentration–time curve of gliclazide (AUC_0–12) after administration of the lyophilized formulations were significantly higher than those obtained after administration of the unprocessed gliclazide.     

Non-resonant RF and microwave response: A novel technique for the characterization of superconducting materials

When examined using continuous wave electron paramagnetic resonance and nuclear magnetic resonance spectrometers, the highT _c superconductors give rise to intense, low field, ‘non-resonant’ absorption signals in the superconducting state. This phenomenon can be used as a highly sensitive, contactless technique for the detection and characterization of superconductivity even in samples containing only minute amounts of the superconducting phase. Further, it can also be applied to the determination of material parameters of interest such asJ _c andH _c2 in addition to being a powerful way of distinguishing between weak-link superconductivity and bulk superconductivity. The details of these aspects are discussed.     

液晶光阀光电导层光吸收系数的研究

用化学气相沉积法制备了液晶光阀中光电导层———非晶硅薄膜,从实验中得出最佳制备工艺的参数取值。给出了用包络线法测量非晶硅薄膜光吸收系数的原理,测量了样品的光吸收系数随波长的变化规律。得到样品在最佳工艺条件下的光吸收系数高于1×103cm-1。     

地震数据采集系统中频谱均衡滤波器的理论设计

地层的高频吸收衰减效应是导致地震勘探分辨率不高的主要原因，在高分辨率野外地震数据系统中，频谱均衡滤波器所设置的重要部件。文章以频谱均衡滤波器的原理和地层吸收衰减特性为基础，用计算机模拟的方法研究地层吸收衰减使分辨率降低的程度和频谱均衡滤波器对分辨率的补偿效果，给出了较好的频谱均衡滤波器的设计方案。     

单轴-平面W型复合锶铁氧体的制备及其吸波特性研究

用草酸盐共沉淀和微量掺杂法研制六角晶系W型Ni,Zn,Co,Al多元复合锶铁氧体，通过调节Ni2W同Co2W的摩尔比例，可使该种铁氧体易磁化方向从C单轴型向垂于C轴的平面型转化，控制置换锶铁氧体中部分Fe3 的微量掺杂Al3 ，可以调整4πMs值，提高磁晶各向异性场，测试分析了5种不同含Co量的W型复合锶铁氧体粉料涂层的吸波特性，发现其自然共振吸收峰随Co含量增加向低频方向偏移，最高吸收峰可达32．8dB，是适用于电子隐形技术的高品位的微波吸收剂。     

Effect of bismuth replacement at barium site in Y-Ba-Cu-O system

X-ray diffraction, electron paramagnetic resonance, microwave absorption and resistivity measurements were carried out on YBa_2−x Bi _x Cu₃O₇ (0≤x≤0·5) superconductors in order to study the effect of bismuth on the structural and superconducting properties. A decrease in sintering temperature increased the amount of impurity phase. Transition from an orthorhombic (superconducting) phase to tetragonal structure produced no significant change in EPR zero-field signal at liquid nitrogen temperature (LNT). The non-resonance signal height decreased on higher concentration of bismuth. Sintered YBa_2−x Bi _x Cu₃O₇ superconductor had a strong EPR zero-field signal at LNT. We have evaluated particle size from XRD and EPR studies. The average particle size was about 0·4μm.     

Al,Ga取代Bi：DyIG薄膜的磁和磁光特性的研究

本文报道用热分解法在玻璃衬底上制备了Ａｌ和Ｇａ取代的Ｂｉ：ＤＹＩＧ薄膜，对其磁和磁光特性做了详细研究．Ａｌ和Ｇａ取代的薄膜均可获得好的矩形比和高的矫顽力．对于Ｂｉ１．２Ｄｙ１．８Ｆｅ５－ｘＭＸＯ１２（Ｍ＝Ａ１，ＧＺ）薄膜，Ａ１和Ｇ２的最佳替代成份分别为１．０和Ｇ．７；最佳晶化温度分别为７００ｏ℃和６７５℃．在波长５１０ｎｍ附近，法拉第旋转角可达８°／ｕｍ左右．光学吸收和品质因子的研究结果表明，Ａｌ和Ｇａ取代能够影响光学吸收和品质因子，其中Ｇａ取代对光学吸收和品质因子的影响较大．     

Quasi-static and dynamic crushing behaviors of aluminum and steel tubes with a cutout

Tubular members are commonly used as an energy absorber in engineering structures and many such members have a cutout. In this study, the crushing behaviors of tubes with a cutout are characterized and the effects of cutout on the energy absorption capabilities of these tubes are quantified. Systematic parametric studies were carried out to study the effect of material properties, including yield and ultimate strength of material, strain rate effect, location of cutout, tube length and impact speed on the crushing behaviors and energy absorption capacity of aluminum and steel tubes. First, a numerical model was constructed with a commercial explicit finite element code. It will be first proven that the numerical simulation can produce sufficiently accurate results in an economic manner. Subsequently, the crushing behavior of aluminum and steel tubes with a cutout was experimentally characterized and their energy absorption capacity was evaluated in terms of mean crushing force, peak crushing force and specific energy absorption (SEA). Tubes of various lengths with a cutout located at different locations, subject to both quasi-static and dynamic impact loadings were considered. For steel tubes, the numerical simulation investigated the influence of the strain rate effect and variation in strain hardening ratio of the material. Empirical equations describing the mean and peak crushing forces of aluminum and steel tubes with a cutout were developed using linear and nonlinear regression methods applied to the results obtained from the numerical and experimental studies.