Chen, I-Wei
Email Address
ORCID
Disciplines
relationships.isProjectOf
relationships.isOrgUnitOf
Position
Introduction
Research Interests
Collection
34 results
Search Results
Now showing 1 - 10 of 34
Publication Effect of Seeding on the Microstructure and Mechanical Properties of alpha-SiAlON: I, Y-SiAlON(2002-05-01) Shuba, Roman; Zenotchkine, Misha; Chen, I-Wei; Kim, Joo-SunThe effect of seeding on the microstructure and mechanical properties of single-phase Y-α-SiAlON ceramics with elongated grains has been studied. Seeds of the intended α-SiAlON compositions but with different size, shape, and number of grains have been compared for their effects. The microstructure, resistance (R-curve) behavior, and Weibull modulus are strongly correlated to the number density of the seeds. The highest fracture toughness reached is ~12 MPa∙m1/2 and can be obtained with as little as 1% seeding. The thermodynamic stability of seeds has been examined and is attributed to their chemical composition.Publication Formation of beta-Silicon Nitride Crystals from (Si,Al,Mg,Y)(O,N) Liquid: II, Population Dynamics and Coarsening Kinetics(2003-09-01) Wang, Lingling; Tien, Tseng-Ying; Chen, I-WeiPrecipitation, growth, and coarsening of Si3N4 crystals in (Si,Al,Mg,Y)(O,N) liquids at 1680oC has been studied. Contrary to the common observation in kinetics, coarsening rates of crystals in length and width are found to accelerate when the total volume of crystals remains little changed. This is attributed to the concomitant β-Si3N4 to β′-SiAlON transformation, which introduces an additional driving force for crystal dissolution and reprecipitation. As a result of the additional driving force, which has a nonmonotonic size dependence, the normalized size distribution is expected to evolve with time, initially broadening, then shifting skewing as the transformation passes the midpoint, and finally converging to a sharp distribution as the transformation completes. These evolutions have been observed in all the compositions studied.Publication Nanoscale Engineering for Biomaterial Surfaces(2007-02-01) Lipski, Anna Marie; Jaquiery, Claude; Choi, Hoon; Eberli, Daniel; Stevens, Molly; Martin, Ivan; Chen, I-Wei; Shastri, V. PrasadPublication Biomedical nanoparticle carriers with combined thermal and magnetic responses(2008-10-01) Liu, Ting-Yu; Hu, Shang-Hsiu; Liu, Dean-Mo; Chen, San-Yuan; Chen, I-WeiSeveral biocompatible polymers are capable of large responses to small temperature changes around 37ºC. In water, their responses include shrinkage and swelling as well as transitions in wettability. These properties have been harnessed for biomedical applications such as tissue engineering scaffolds and drug delivery carriers. A soft material/hard material hybrid in which a magnetic metal or oxide is embedded in a temperature-responsive polymer matrix can combine the thermal sensitivity with magnetic signatures. Importantly, nanosizing such construct brings about new desirable features of extremely fast thermal response time, small magnetic hysteresis and enhanced magnetic susceptibility. Remote magnetic maneuvering and heating of the hybrid nanocolloids makes possible such applications as high-throughput enzyme separation and cell screening. Robust drug release on demand may also be obtained using these colloids and nanoparticle-derived thin film devices of combined thermal magnetic sensitivity.Publication Biphosphonate-Mediated Gene Vector Delivery from the Metal Surfaces of Stents(2006-01-01) Fishbein, Ilia; Alferiev, Ivan S; Nyanguile, Origene; Vohs, John M; Gaster, Richard; Wong, Gordon Sek-Yin; Chen, I-Wei; Felderman, Howard; Choi, Hoon; Wilensky, Robert L; Levy, Robert JThe clinical use of metallic expandable intravascular stents has resulted in imporved therapeutic outcomes for coronary artery disease. However, arterial reobstruction after stenting, in-stent restenosis, remains an important problem. Gene therapy to treat in-stent restenosis by using gene vector delivery from the metallic stent surfaces has never been demonstrated. The present studies investigated the hypothesis that metal-biphosphonate binding can enable site-specific gene vector delivery from metal surfaces. Polyallylamine biphosphonate (PAA-BP) was synthesized by using Michael addition methodology. Exposure to aqueous solutions of PAA-BP resulted in the formation of a monomolecular biphosphonate later on metal alloy surfaces (steel, nitinol, and cobalt-chromium), as demonstrated by x-ray photoelectron spectroscopy. Surface-bound PAA-BP enabled adenoviral (Ad) tethering due to covalent thiol-binding of either anti-Ad antibody or a recombinant Ad-receptor protein, D1. In arterial smooth muscle cell cultures, alloy samples configured with surface-tethered Ad were demonstrated to achieve site-specific transduction with a reporter gene, (GFP). Rat carotid stent angioplasties using metal stents exposed to aqueous PAA-BP and derivatized with anti-knob antibody or D1 resulted in extensive localized Ad-GFP expression in the arterial wall. In a separate study with a model therapeutic vector, Ad-inducible nitric oxide synthase (iNOS) attached to the biphosphonate-treated metal stent surface via D1, significant inhibition of restenosis was demonstrated (neointimal/media ration 1.68 ± 0.27 and 3.4 ± 0.35; Ad-iNOS vs. control, P < 0.01). Is is concluded that effective gene vector delivery from metallic stent surfaces can be achieved using this approach.Publication Paraffin-Based Process for Producing Layered Composites with Cellular Microstructures(2002-04-01) Dakskobler, Aleš; Kosmac, Tomaz; Chen, I-WeiA paraffin-based process that results in high-strength bimaterial ceramic layered composites is reported. The process facilitates rolling, folding, and shape retention at room temperature and allows the transition from a laminar to a cellular microstructure during deformation. The strength of sintered alumina/zirconia/alumina composites reached 700 MPa, higher than that of conventional zirconia-toughened alumina composites containing dispersed particles.Publication Elimination of Grain Boundary Glass in α-Sialon by Adding Aluminium(2005-10-19) Shuba, Roman; Chen, I-WeiThe elimination of residual glass in hot-pressed Y-α-SiAlON was demonstrated by varying the nitride composition. This was readily achieved by adding excess aluminium nitride (AlN), while the addition of excess Si3N4 had little effect. The amount of excess AlN required for this purpose increased with increasing Al and O content in α-SiAlON, and was higher if α-SiAlON contained larger interstitial cations. These results were explained by the thermodynamics of α-SiAlON precipitation. The elimination of liquid also led to suppressed grain growth, refined microstructure, and improved oxidation resistance. Grain coarsening by post-sintering annealing was required to obtain high fracture toughness.Publication Strained relaxation in buried SrRuO3 layer in (Ca1-xSrx) (Zr1-xRux)O3/SrRuO3/SrTiO3 System(2006-07-18) Kim, Soo Gil; Wang, Yudi; Chen, I-WeiA novel relaxation phenomenon occurs in buried SrRuO3 layers in strained (Ca1-xSrx) (Zr1-xRux)O3/SrRuO3/SrTiO3 (001) thin film system. The lightly strained SrRuO3 buried layer is initially clamped by the SrTiO3 substrate. After a heavily strained (Ca1-xSrx) (Zr1-xRux)O3 overlayer is deposited, localized strain relaxation develops in the buried layer. This is manifested by a crosshatch pattern of 〈100〉 corrugations on the surface, due to the slip of 〈100〉 {100} threading dislocations. The phenomenon can be controlled by tuning the growth kinetics and strain energy of the overlayer.Publication Electron localization and magnetism in SrRuO3 with non-magnetic cation substitution(2011-01-02) Tong, W.; Huang, F Q; Chen, I-WeiThe destruction of the ferromagnetism of alloyed SrRuO3 can be caused by electron localization at the substitution sites. Among all the non-magnetic cations that enter the B site, Zr4+ is the least disruptive to conductivity and ferromagnetism. This is because Zr4+ does not cause any charge disorder, and its empty d electron states which are poorly matched in energy with the Ru t2g4 states cause the least resonance scattering of Ru’s d electrons. Conducting Sr(Ru, Zr)O3 may be used as an electrode for perovskite-based thin film devices, while its insulating counterpart provides unprecedented magnetoresistance, seldom seen in other non-manganite and non-cobaltite perovskites. (Some figures in this article are in colour only in the electronic version)Publication Magnetic impurities in conducting oxides. II. (Sr1-xLax)(Ru1-xCox)O3 system(2004-09-20) Mamchik, Alexander; Dmowski, Wotjek; Egami, Takeshi; Chen, I-WeiThe perovskite solid solution between ferromagnetic SrRuO3 and antiferromagnetic LaCoO3 is studied and its structural, electronic,and magnetic properties are compared with (Sr1-xLax)(Ru1-xFex)O3. The lower 3d energy levels of Co3+ cause a local charge transfer from 4d Ru4+, a reaction that has the novel feature of being sensitive to the local atomic structure such as cation order. Despite such a complication, Co, like Fe, spin-polarizes the itinerant electrons in SrRuO3 to form a large local magnetic moment that is switchable at high fields. In the spin glass regime when Anderson localization dominates, a large negative magnetoresistance emerges as a result of spin polarization of mobile electronic carriers that occupy states beyond the mobility edge. A phenomenological model predicting an inverse relation between magnetoresistance and saturation magnetization is proposed to explain the composition dependence of magnetoresistance for both (Sr1-xLax)(Ru1-xCOx)O3 and (Sr1-xLax)(Ru1-xFex)O3 systems.