Showing papers by "Xiang Zhang published in 1998"

Powder metal matrix composites: selection and processing

Abstract: There has been growing interest in the last decade in the development of metal matrix composites (MMCs) for the aerospace industry because of their attractive physical and mechanical properties and enhanced elevated temperature capabilities. However, some of the fabrication techniques (e.g. using powder metallurgy) for this new class of MMCs are hampered by (i) the poor distribution of the reinforcements, and (ii) the limited room temperature ductility of the composites and hence formability. This presentation reports work done to address the above two problems by (i) an analysis based on size difference of matrix and reinforcement particles, taking into account the processing parameters, and (ii) introducing a innovative way of extruding brittle composites to increase its formability.

Impact damage in composite aircraft structures-experimental testing and numerical simulation

Abstract: This paper describes a strategy for predicting internal damage in a laminated composite structure, when subjected to low-velocity impact. The aim was to obtain a better understanding of and cure for the notorious reduction in strength of aircraft compression panels when they suffered barely visible impact damage (BVID). A finite element model is presented which incorporates the non-linear behaviour due to gross deformation, interlaminar delamination and in-plane fibre and matrix failure. The strategy is validated by impact tests for a wide range of carbon/epoxy composite structures ranging from small stiff plates to realistic aircraft compression panels. It is demonstrated that the finite element model is capable of predicting impact damage in laminated composite structures and thus could be used as a design tool.

Carrier relaxation and recombination in an InGaN/GaN quantum well probed with time-resolved cathodoluminescence

Abstract: Spatially, spectrally, and temporally resolved cathodoluminescence (CL) techniques have been employed to examine the optical properties and kinetics of carrier relaxation for metalorganic chemical vapor deposition grown InGaN/GaN single quantum wells (QWs). Cathodoluminescence wavelength imaging of the QW sample revealed local band gap variations, indicating the presence of local In composition fluctuations and segregation during growth. A detailed time-resolved CL study shows that carriers generated in the boundary regions will diffuse toward and recombine at InN-rich centers, resulting in a strong lateral excitonic localization prior to radiative recombination.

Micro-stereolithography for MEMS

Abstract: Micro stereolithography (μSL) is a novel micro-manufacturing process which builds the truly 3D microstructures by solidifying the liquid monomer in a layer by layer fashion. In this work, an advanced micro stereolithography (μSL) apparatus is designed and developed which includes an Ar+ laser, the beam delivery system, computer-controlled precision x-y-z stages and CAD design tool, and in situ process monitoring systems. The 1.2 μm resolution of μSL fabrication has been achieved with this apparatus. The micro tubes with high aspect ratio of 16 and real 3D microchannels and micro cones arc fabricated on silicon substrate. For the first time, micro stereolithography of ceramic micro gears has been successfully demonstrated.

The effects of heating and annealing processes on the surface morphology and quality of double-sided YBa2Cu3O7−δ thin films

Abstract: A series of YBa 2 Cu 3 O 7− δ (YBCO) double-sided thin films were prepared by pulsed-laser deposition (PLD) and measured by XRD, SEM, AFM, electrical-transport and microwave surface resistance ( R s ) measurements. The results showed that the surface morphology of the first side of the film consisted of more troughs and big particles, while that of the second side of the film consisted of almost no troughs but small, bar-like oriented particles. The difference has been attributed to the heating and annealing processes during deposition. The improved substrate surface conditions for the deposition of the second side of the film led to better film quality in terms of the T c0 and R s values. Our results implied that a pre-annealing process of the substrates and a proper post-annealing process of the films after deposition would improve the film quality and reduce the difference between the two sides of the YBCO films fabricated by PLD.

[Determination of zinc, copper, iron and manganese contents in hair for MPA patients and healthy men].

Abstract: In this paper the contents of zinc, copper, iron and manganese in hair for MPA patients and 38 hair-healthy men have been determined by FAAS. The results show that the hair zinc and manganese levels in MPA patients are significantly lower than that in hair-healthy men. The hair copper level in MPA patients is significantly higher than that in hair-healthy men. There are statistic difference (P 0.05) in the iron level among the two gopups. This paper provides useful material for the research of the cause and treatment of the MPA.

[Expression of interleukin-8 and its receptor in acute promyelocytic leukemia under all-trans retinoic acid treatment].

Abstract: OBJECTIVE To evaluate the clinical significance of expression of interleukin-(IL-8) and its type A receptor(IL-8RA) in acute promyelocytic leukemia(APL) patients under all trans-retinoic acid(ATRA) induction. METHODS Serum IL-8 level of 18 APL patients were dynamically studied(ELISA). Fresh APL cells from 3 patients were cultured with ATRA(10(-6) mmol/L). Supernatant IL-8 level and IL-8RA expression on APL cells were measured by FACS. RESULTS In vitro, IL-8 concentrations decreased 72 hours after incubation, while IL-8RA increased. In vivo, IL-8 increased more rapidly and markedly than temperature and WBC counts did before retinoic acid syndrome(RA-S) occurred. Serum IL-6 and IL-8 levels significantly increased when the patients suffered infection, and IL-8 increased even before fever. Both IL-8 and D-dimer increased while DIC progressed. CONCLUSION ATRA inhibited IL-8 secretion of APL cells while increased the expression of IL-8RA. Monitoring serum IL-8 concentrations could predict the development of RA-S and infection. Increase of both IL-8 and D-dimer concentrations suggested DIC progression.

[10-Hydroxycamptothecin induces apoptosis in human T24 urinary bladder cancer cells].

Abstract: OBJECTIVE To study the emechanisms of 10-Hydroxycamptothecine (HPT) inhibiting human urinary bladder cancer. METHODS Using flow cytometry, electron microscopy and fluorescence microscopy, we studied the effects of HPT on human T24 urinary bladder cancer cells. RESULTS HPT at 0.005 mg/L inhibited T24 bladder cancer cells by preventing the cells from S phase to G2/M phase and did not induce apoptosis. The apoptotic cells were induced by HPT at the concentration of 0.01-0.10 mg/L. CONCLUSION HPT can inhibit human T24 urinary bladder cancer cells and induced apoptosis at some concentrations. The induction of apoptosis is a very important mechanism of 10-Hydroxycamptothecine to treat urinary bladder cancer cells.

Cathodoluminescence study of disordering of GaAs/AlGaAs quantum wells using an AlAs native oxide and thermal annealing technique

Abstract: GaAs/AlGaAs quantum wells (QWs), selectively disordered using an AlAs native oxide and thermal annealing technique, were studied using spectrally, spatially, and temporally resolved cathodoluminescence (CL). The spectral shift of the QW luminescence was determined as a function of annealing temperature in the oxide and nonoxide regions. Time-resolved CL was used to assess the impact of defects and the built-in field near the oxide/nonoxide transition region on the carrier lifetime. Spatially resolved CL spectroscopy was used to examine changes in the QW luminescence intensity near the transition region. The carrier lifetime was found to increase in the transition region, owing to the enhanced spatial separation of electrons and holes in this region. From CL images and line scans of three samples annealed at different temperatures, a partial dead region is found between oxide and nonoxide regions. Details of the native oxide formation are discussed.