Showing papers by "Xiang Zhang published in 1999"

Micro-stereolithography of polymeric and ceramic microstructures

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 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 microtubes with high aspect ratio of 16 and real 3D microchannels and microcones are fabricated on silicon substrate. For the first time, μSL of ceramic microgears has been successfully demonstrated.

Strong influence of SiO2 thin film on properties of GaN epilayers

Abstract: In this letter, we report strong degradation of photoluminescence (PL) performance of GaN epilayers due to SiO2 layers that were deposited on GaN surfaces by electron-beam evaporation. Secondary ion mass spectrometry measurements show that the oxygen concentration of GaN with SiO2 layers is one order of magnitude more than that of as-grown GaN. This fact indicates that oxygen can very easily replace nitrogen in GaN. It was also found that rapid thermal processing can recover and improve the optical quality of GaN with SiO2 layer. As a reference, SixNy was found to have little effect on PL performance of GaN.

MOCVD Growth and Characterization of GaN Films with Composite Intermediate Layer Buffer on Si Substrate

Abstract: GaN thin films have been grown on Si(001) substrate with specially designed composite intermediate layers (CIL) consisting of an ultrathin amorphous silicon layer and a GaN/AlxGa1—xN multilayered buffer by low pressure metal-organic chemical vapor deposition (MOCVD). The improved film quality has been obtained from adjusting the parameters and redesigning the buffer layer structures. These were verified from different materials characterization measurements. XRD patterns showed strong and narrow (0002) and (0004) peaks of wurtzite phase GaN, and no cubic or other phase features. Room temperature photoluminescence showed strong GaN near band edge emission at 3.42 eV with almost no deep defect emission features to be detected from the improved quality films. Raman scattering and infrared spectroscopy exhibited phonon and lattice vibration modes characteristic of wurtzite GaN with no modes related to cubic or other structural phase. Scanning electron microscopy reveals the polycrystalline structure with large grain sizes near 2 μm in these films.

Effect of OFQ injection into intracerebroventricular and preoptic area on blood pressure and heart rate in rats

Abstract: Orphanin FQ (OFQ) is a novel peptide comprised of an amino acid sequence very similar to that of dynorphin A. In the present investigation the effect of OFQ on cardiovascular activities was studied. Introcerebroventricular (icv) injection of OFQ at doses of 1 and 10 micrograms produced significant decrease in heart rate (HR) and mean arterial pressure (MAP). Icv pretreatment with naloxone could not prevent the hypotensive and bradycardial response produced by 1 microgram OFQ. Injection of 1 microgram OFQ preoptic area (POA) also caused a profound decrease of MAP and HR. These results indicate that OFQ can inhibit cardiovascular activities which are not mediated by mu, delta and kappa receptors. POA may be one of the target areas of these inhibitory effects.

Sensitizing effect of nonionic microemulsion on the derivative spectrophotometric determination of trace iron with sulfosalicylic acid

Abstract: The sensitizing effect of O/W microemulsion of Triton X-100/n-C5H11OH/n-C9H20/H2O as a medium on the derivative spectrophotometry of Fe-Sal was studied. The results show that the sensitivity of determination in O/W microemulsion was higher than that in micelle. The reagent Sal has higher distribution coefficient KD and constant K in microemulsion than in the micelle system and lower binding in O/W microemulsion than in the micelle system. This results also illustrate that O/W microemulsion has more solubilization for Sal than micelle does, so that O/W microemulsion has more sensitizing reaction than micelle does.

[Adenovirus-transferred antisense c-myc selectively induces tumor cell cycle arrest and apoptosis].

Abstract: OBJECTIVES To construct the recombinant adenovirus encoding antisense c-myc fragment and to investigate its effect on tumor cell proliferation and apoptosis. METHODS The shuttle plasmid encoding antisense c-myc was constructed by cloning c-myc cDNA fragment in the reverse direction into the pAdCMV. Then the plasmid pJM17 and the shuttle plasmid were co-transferred into 293 cells with liposome for homologous recombination to acquire recombinant adenovirus. The cell cycle, apoptosis, and the expression of related genes of the in vitro transferred human adenocarcinoma cell lines GLC-82 and SPC-A-1, as well as the human embryonic diploid lung cell line 2BS were studied. The effects on colony formation and treating effect on transplanted tumor in nude mice were also studied. RESULTS The recombinant adenovirus encoding antisense c-myc fragment was obtained with the titer of 3.3 x 10(10) pfu/ml. RT-PCR and Western blot showed that the expression of c-myc was reduced 3-5 days after infection. Simultaneously, obvious G1 arrest and apoptosis as well as the alteration of cyclin D1, bcl-2 and bax gene expression were observed in the infected tumor cells. The infected 2BS cells showed no such changes. The colony formation ability in vitro and the growth of the hetero-transplanted tumor in nude mice were also reduced. CONCLUSIONS The reduced expression of c-myc gene could induce human adenocarcinoma cells tumor-cell-specific G1 arrest and apoptosis, while it has no effect on normal cell.

[Function of B7/CD28 in anti-myeloma immunoreaction through activating T cells].

Abstract: Objective To explore the role of B7/CD28 molecule in priming the antimyeloma effect of T lymphocyte and the mechanism by which CD28 promoted the immunogenicity of myeloma cells. Methods Human B71 gene was transducted into XGs cells. CD28 agonist monoclonal antibody was primed. Primary allogeneic MLR, immunophenotypic analysis and quantitative measurement of IL2 were performed. Results XG cells were successfully transfected with B71 cDNA. The expressions of CD54,CD58, CD11a/CD18, CD40, CD40L, CD56, B72(CD86), HLA and HLA molecules were not affected by the transfection. The transduction of B7 gene dramatically increased the immunogenicity of tumor cells. In allo MLR, the B71 expressing XG cell could more effectively mediate the activation,proliferation and IL2 secretion of alloantigenic CD8+ T cells than XG cells did. Like B71 molecules, antiCD28 agonistic McAb could induce the MLR of alloT cell. Conclusion Human multiple myeloma cells failed to induce antitumor immunoreaction because of the weak expression of B7 molecules. The transfection of B71 or CD28 agonist antibody could stimulate and proliferate T lymphocytes and increase the immunogenicity of myeloma cells. CD28 agonist antibody might be promising for clinical application.

Micro-scale free surface rapid prototyping

Abstract: Summary form only given. IC-based micromachining processes used to fabricate MEMS devices have certain limitations. First, most of the IC-based micromachining processes cannot be used to fabricate complex 3D micro parts with high aspect ratios. Second, only a few semiconductors and other materials can be processed by the current IC-based micromachining for MEMS; Many other important engineering materials, such as smart ceramics and functional polymer cannot be easily incorporated into MEMS. A novel microfabrication process, constrain surface micro stereolithography, was introduced to fabricate high aspect ratio and complex 3D microstructures (Maruo et al., 1997). However, the constrained surface method used has generated many inherent problems such as layer sticking defects (Maruo and Kawata, 1997). A free surface micro stereolithography (/spl mu/SL) method is developed. Sophisticated 3D parts can be made by scanning a UV beam on the liquid monomer resin, curing the resin into solid polymer in a layer by layer fashion (1-10 /spl mu/m in thickness), and stacking together all layers with various contours. In contrast to conventional subtractive micromachining, the micro stereolithography is an additive process, which enables one to fabricate high aspect ratio microstructures with novel smart materials.

[GFAAS determination of trace lead in toothpaste using L'vov platform].

Abstract: Sensitivity in determining low melting point metals is highly improved by means of platform technique in graphite furnace AAS. In this paper we describe a method of determining trace lead in toothpaste by this technique. The method of making the platform and the selection of the platform coating were discussed and the results with and without the platform were compared. The optimum ashing temperature, atomization temperature and experimental conditions were investigated. The interference of large amount Al and Ca in the matrix on determination of trace lead can be minimized by using platform technique. The precision of about 0.9% and detection limit of about 15 ng obtained by this improved method are much better than those by methods without platform.

The Formation of In-Rich Regions at the Perphery of the Inverted Hexahonal Pits of InGaN Thin-Films Grown by Metalorganic Vapor Phase Epitaxy

Abstract: InGaN thin films were grown by low-pressure metalorganic-vapor-phase-epitaxy (MOVPE) and characterized by cathodoluminescence (CL) and scanning electron microscopy (SEM). SEM images showed that InGaN samples have inverted hexagonal pits which are formed by the In segregation on the (1011) surfaces. Room temperature CL at the wavelengths corresponding to the GaN band edge, the In-poor and In-rich regions showed that the In–rich regions formed at the periphery of the hexagonal pits.