Scientific Publications 2004
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J
2004. "Multidimensional Proteome Analysis of Human Mammary Epithelial Cells." Journal of Proteome Research 3(1):68-75. Abstract Recent multidimensional liquid chromatography MS/MS studies have contributed to the identification of large numbers of expressed proteins for numerous species. The present study couples size exclusion chromatography of intact proteins with strong cation exchange chromatography to detect tryptically digested peptides in the global protein mixture of human mammary epithelial cells (HMECs) based upon the use of very high resolution, reversed phase capillary LC–MS/MS. A total of >6,200 unique peptides were identified with high confidence covering 1,700 different proteins, out of which 93% were mapped to chromosomal locations providing an estimated 4.4% coverage of the annotated human genome based upon the National Center for Biotechnology Information (NCBI). This database provides a baseline for comparison against variations in other genetically and environmentally perturbed systems. Proteins identified were categorized based upon intracellular location and biological process with the identification of numerous receptors, regulatory proteins, and extracellular proteins, demonstrating the usefulness of this application in the global analysis of human cells for future comparative studies.
2004. "First-principles study of noncommutative band offsets at [alpha]-Cr2O3/[alpha]-Fe2O3(0001) interfaces." Physical Review. B, Condensed Matter and Materials Physics 69(20):205106. Abstract Using first-principles density functional theory, we have modeled the atomic, electronic and magnetic structure of epitaxial interfaces between alpha-hematite and alpha-chromia (corundum structure) in the hexagonal (0001) basal plane. Our model was a superlattice with a period of about 27.5Å, corresponding to the shortest-period superlattice considered in a recent series of experiments (Chambers et al., Phys. Rev. B 61, 13223 (2000)). Two different epitaxial interface structures were studied: (i) an oxygen plane separating an Fe double layer from a Cr double layer, or (ii) a metal double layer split between Fe and Cr. We found that these two structures are close in total energy but have distinct spin structure and different valence band offsets (chromia above hematite by 0.4 and 0.6 eV for (i) and (ii) respectively), possibly explaining the experimental non-commutative band offset seen in this system (0.3±0.1 eV for hematite grown atop chromia, and 0.7±0.1 eV for the reverse).
2004. "Protein Immobilization on Carbon Nanotubes Via a Two-StepProcess of Diimide-Activated Amidation." Journal of Materials Chemistry 14:37-39. Abstract Carbon nanotubes exhibit interesting electrical, structural and mechanical properties that make them highly promising nanoscale building blocks for the construction of novel functional materials. Many potential applications have been proposed, such as conductive and high-strength composites, field emission displays, fuel cells, sensors, and hydrogen storage media.1,2 In addition, biosensors for detecting abnormalities3–5 and bio-fuel cells6 for embedded devices are among the most exciting applications. In order to create the synergy between the biomolecules and nanotubes required to realize these applications, biomolecules, such as proteins and DNAs, must be connected to the carbon nanotubes. This connection can be non-covalent interaction or covalent bonding. There have been several reports on the immobilization of biomolecules on carbon nanotubes,7–13 and most of them use non-covalent interaction. The best stability, accessibility and selectivity, however, will be achieved through covalent bonding because of its capability to control the location of the biomolecule, improve stability, accessibility and selectivity and reduce leaching. In the present study, we report the covalent bonding of proteins to nitrogen-doped multiwalled carbon nanotubes (CNx MWNTs) via a two-step process of diimide-activated amidation between the carboxylic acid groups on CNx MWNTs and the amine groups on proteins.
2004. "Direct Determination of Volume Changes in Ion-Beam-Irradiated SiC." Journal of Applied Physics 95(9):4687-4690. Abstract A single crystal 6H-SiC wafer was sequentially implanted in two areas at 873 and 295 K using 2.0 MeV Au₂⁺ ions under off-axis conditions. Identical Au profiles, as a function of atomic areal density, were produced at 873 and 295 K. The linear expansion in the amorphous state produced at 295 K was measured relative to the slightly damaged state produced at 873 K, using the Au profiles as references. The red-shift of the plasmon-loss peak was also used to directly measure the local density changes. Based on these measurements, the volume expansion of the amorphous state in 6H-SiC at 295 K is 11.51.9%, while that in the slightly damaged state at 873 is 0.9%.
2004. "Carbon Analysis using Energetic Ion Beams." Nuclear Instruments and Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms 222(3-4):538-546. Abstract Both Nuclear reaction analysis and non-Rutherford elastic scattering have been widely used for analysis of light elements in solids; these two ion-beam methods complement more traditional analysis by Rutherford backscattering spectrometry. In this study, the reaction/scattering cross-sections for 12C(p,p)12C, 12C(d,p)13C, and 12C(a,a)12C at an angle of 150 (degrees) are measured over relevant energy regions using thin films of carbon (5.8 ug/cm2) on silicate glass. The results are plotted and tabulated as a function of ion energy, with typical uncertainties of 4% for the cross section data. In addition, the angular distribution of the cross sections for the reaction 12C(d,p)13C at an ion energy of 0.94 MeV has also been determined from 100 (degrees) to 170 (degrees). An example for the application of this reaction to SiC is given.
2004. "Amorphization Processes in Au Ion Irradiated GaN at 150 - 300 K." Nuclear Instruments and Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms 218:427-432. Abstract Epitaxial single-crystal gallium nitride (GaN) films on sapphire were irradiated at temperatures between 150 and 300 K using 1.0 MeV Au₂⁺ ions over a range of fluences. The accumulation of disorder on the Ga sublattice has been investigated based on 2.0 MeV He+ RBS along the <0001>-axial channeling direction. In general, the degree of disorder in the irradiated GaN increases at low doses and saturates at intermediate doses; at higher doses, a rapid amorphization process occurs as a result of the ingrowth of surface defects. Results from this study indicate that there may be a dynamic recovery stage on the Ga sublattice in GaN between 250 and 300 K. High-resolution TEM studies show that the microstructure in the disorder saturation stage contains a dense network of planar defects (basal-plane dislocation loops and stacking faults), while the more highly disordered regime includes amorphous domains and small crystalline zones that are randomly oriented.
2004. "Thermal and Dynamic Responses of Ag Implants in Silicon Carbide ." Nuclear Instruments and Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms 219-220:642-646. Abstract A single crystal wafer of 6H-SiC was sequentially implanted in two different areas at 210 and 873 K, respectively, to the same fluence of 500 Ag₂⁺/nm₂. Rutherford backscattering spectrometry (RBS) has been used in a random orientation to profile the Ag implants and along the <0001>-axial channeling direction to determine the defect concentrations. Additional irradiation at 873 K with 5.4 MeV Si₂⁺ ions does not promote diffusion of the implants in either the crystalline or fully-amorphized SiC. There is no evidence of significant diffusion of the implanted Ag in crystalline SiC during thermal annealing at temperatures up to 1573 K. However, it appears that the Ag tends to diffuse toward the surface in amorphous SiC at 1573 K.
2004. "Temperature Dependence of Disorder Accumulation and Amorphization in Au-Ion Irradiated 6H-SiC." Physical Review. B, Condensed Matter 70(16):165208, 1-8. Abstract Disorder accumulation and amorphization in 6H-SiC single crystals irradiated with 2.0 MeV Au₂⁺ ions at temperatures ranging from 150 to 550 K have been investigated systematically based on 0.94 MeV D⁺ channeling analyses along the <0001> axis. Physical models have been applied to fit the experimental data and to interpret the temperature dependence of the disordering processes. Results show that defect-stimulated amorphization in Au₂⁺-irradiated 6H-SiC dominates the disordering processes at temperatures below 500 K, while formation of clusters becomes predominant above 500 K. Two distinctive dynamic recovery stages are observed over the temperature range from 150 to 550 K, resulting from the coupled processes of close-pair recombination and interstitial migration and annihilation on both sublattices. These two stages overlap very well with the previously observed thermal recovery stages. Based on the model fits, the critical temperature for amorphization in 6H-SiC under the Au₂⁺ ion irradiation conditions corresponds to 501 +- 10 K.
2004. "A Numerical Process Control Method for Circular-Tube Hydroforming Prediction." International Journal of Plasticity 20(6):1111-1137. Abstract This paper describes the development of a solution control method that tracks the stresses, strains and mechanical behavior of a tube during hydroforming to estimate the proper axial feed (end-feed) and internal pressure loads through time. The analysis uses the deformation theory of plasticity and Hill?s criterion to describe the plastic flow. Before yielding, the pressure and end-feed increments are estimated based on the initial tube geometry, elastic properties and yield stress. After yielding, the pressure increment is calculated based on the tube geometry at the previous solution increment and the current hoop stress increment. The end-feed increment is computed from the increment of the axial plastic strain. Limiting conditions such as column buckling (of long tubes), local axi-symmetric wrinkling of shorter tubes, and bursting due to localized wall thinning are considered. The process control method has been implemented in the Marc finite element code. Hydroforming simulations using this process control method were conducted to predict the load histories for controlled expansion of 6061-T4 aluminum tubes within a conical die shape and under free hydroforming conditions. The predicted loading paths were transferred to the hydroforming equipment to form the conical and free-formed tube shapes. The model predictions and experimental results are compared for deformed shape, strains and the extent of forming at rupture.
2004. "Effect of Gallium Nitride Template Layer Strain on the Growth of InxGa1-xN/GaN Multiple Quantum Well Light Emitting Diodes." Journal of Applied Physics 96(3):1381-1386. Abstract GaN template layer strain effects on the growth of InGaN/GaN light emitting diodes (LED) devices were investigated. Seven-period InGaN/GaN multiple quantum well structures (MQW) were deposited on 5µm and 15µm GaN template layers. It was found that the electroluminescence (EL) emission of the 15µm device was red-shifted by approximately 132meV. Triple-axis X-Ray Diffraction (TAXRD) and Cross-Sectional Transmission Electron Microscopy (XTEM) show that the 15µm template layer device was virtually unstrained while the 5µm layer experienced tensile strain. Dynamic Secondary Ion Mass Spectrometry (SIMS) depth profiles show that the 15µm template layer device had an average indium concentration of 11% higher than that of the 5µm template layer device even though the MQW structures were deposited during the same growth run. It was also found that the 15µm layer device had a higher average growth rate than the 5µm template layer device. This difference in indium concentration and growth rate was due to changes in thermodynamic limitations caused by strain differences in the template layers.
2004. "Semiactive Infrared Remote Sensing: A Practical Prototype and Field Comparison ." Applied Optics 43(3):638-650. Abstract A semiactive method of Fourier-transform (FTIR) remote sensing has been developed and field tested. The method replaces the sender telescope of an active technique with an extended, heated broadband source. The output of the extended source (a commercial griddle) is not collimated and thus facilitates alignment by having the detector optics simply point at the griddle. The present source fills the detector's field of view at 100 m and maintains a temperature ~80 K warmer than ambient. In field tests with live CO releases, the method was ~30 times less sensitive than active methods, but ~30 times more sensitive than passive methods, with far greater sensitivity in the midwave infrared.
