Vish V. Subramaniam

Tribological properties of polished diamond films

Despite the rapid progress being made in the synthesis of diamond films and recent interest in polishing of diamond films, no systematic measurements of friction and wear on polished diamond films have been reported. In the present study, chemomechanical and laser polishing techniques are used, and friction and wear data on the chemomechanically polished diamond films are presented. With the chemomechanical polishing technique used in this study, the rms roughness of hot filament chemical vapor deposited diamond films can be reduced from about 657 to about 170 nm with rounding off of sharp asperities with no change in the diamond structure. The polished films exhibit coefficient of friction (∼0.1) and wear rates much lower than that of unpolished films. Friction and wear properties of the polished films are comparable to that of single‐crystal natural diamond. Based on this study, it is concluded that polished films are potential candidates for tribological applications.

Near-infrared fluorescence labeled anti-TAG-72 monoclonal antibodies for tumor imaging in colorectal cancer xenograft mice.

Anti-TAG-72 monoclonal antibodies target the tumor-associated glycoprotein (TAG)-72 in various solid tumors. This study evaluated the use of anti-TAG-72 monoclonal antibodies, both murine CC49 and humanized CC49 (HuCC49deltaCH2), for near-infrared fluorescent (NIR) tumor imaging in colorectal cancer xenograft models. The murine CC49 and HuCC49deltaCH2 were conjugated with Cy7 monofunctional N-hydroxysuccinimide ester (Cy7-NHS). Both in vitro and in vivo anti-TAG-72 antibody binding studies were performed. The in vitro study utilized the human colon adenocarcinoma cell line LS174T that was incubated with Cy7, antibody-Cy7 conjugates, or excessive murine CC49 followed by the antibody-Cy7 conjugates and was imaged by fluorescence microscopy. The in vivo study utilized xenograft mice, bearing LS174T subcutaneous tumor implants, that received tail vein injections of Cy7, murine CC49-Cy7, HuCC49deltaCH2-Cy7, or nonspecific IgG-Cy7 and were imaged by the Xenogen IVIS 100 system from 15 min to 288 h. The biodistribution of the fluorescence labeled antibodies was determined by imaging the dissected tissues. The in vitro study revealed that the antibody-Cy7 conjugates bound to LS174T cells and were blocked by excessive murine CC49. The in vivo study demonstrated that murine CC49 achieved a tumor/blood ratio of 15 at 96 h postinjection. In comparison, HuCC49deltaCH2-Cy7 cleared much faster than murine CC49-Cy7 from the xenograft mice, and HuCC49deltaCH2-Cy7 achieved a tumor/blood ratio of 12 at 18 h postinjection. In contrast, Cy7 and Cy7 labeled nonspecific IgG resulted in no demonstrable tumor accumulation. When mice were injected with excessive unlabeled murine CC49 at 6 h before the injection of murine CC49-Cy7 or HuCC49deltaCH2-Cy7, both the intensity and retention time of the fluorescence from the tumor were reduced. In summary, the Cy7 labeled murine CC49 and HuCC49deltaCH2 demonstrate tumor-targeting capabilities in living colorectal cancer xenograft mice and provide an alternative modality for tumor imaging.

Phenomenological Analysis of Shock-Wave Propagation in Weakly Ionized Plasmas

Shock propagation into weakly ionized gases shows several features differing markedly from conventional, nonionized-gas shock structure. Phenomenological analysis of general macroscopic features of the previously observed plasma shock effects allows only two possible interpretations: existence of an energy (momentum) flux toward the wave precursor or volumetric energy release (exothermic phase transition) in the upstream portion of the wave (precursor) followed by reverse transition in the downstream portion of the wave. It is shown that known microscopic mechanisms are not capable of producing such a flux or energy release: Typical processes involving electrons, ions, and excited species do not couple strongly to neutral atoms and molecules, and there is not enough energy stored in these species because of the low ionization fraction. The theoretical basis for phase transitions in low-density, weakly ionized plasmas also is unknown. Analysis of the steady two-wave system created by either of the two effects raises a question as to whether the observed plasma shocks are stable objects. Another question is whether there exists phase transition within the plasma shock. It also remains unclear to what extent twodimensional thermal inhomogeneity effects contribute to the observed phenomena. Answering these fundamental questions requires additional experimental studies of the problem. p D d E E/N F h j k

Supersonic Nonequilibrium Plasma Wind-Tunnel Measurements of Shock Modification and Flow Visualization

Experiments conducted in a new, small-scale, nonequilibrium plasma wind tunnel recently developed at Ohio State University are discussed. The facility provides a steady-state supersonic e ow of cold nonequilibrium plasma with well-characterized, near uniform, properties. The plasma is produced in aerodynamically stabilized highpressureglowdischargethatformstheplenumofthesupersonicnozzle.Thepossiblemodie cation ofthesupersonic e ow due to ionization is studied by measuring the angle of oblique shocks attached to the wedge located in the nozzle test section. The results do not show any detectable shock weakening or attenuation in weakly ionized nitrogen plasma, compared to the measurements in a nonionized gas e ow. Experiments in supersonic e owing nitrogen and helium afterglow also demonstrate a novel technique for high-density supersonic e ow visualization. It allows identifying all key features of the supersonic e ow, including shocks, boundary layers, e ow separation regions, andwakesby recording intensevisibleradiation of theweakly ionizedplasmas.Interpretation ofradiation intensitydistributionsinnonequilibriumsupersonice owingafterglowmayprovideinformationonkeymechanisms of energy storage and ultraviolet radiation in high-altitude rocket plumes. In addition, these e ow visualization experiments can be used for validation of multidimensional computer e ow codes used for internal e ow simulation.

Improvement of Human Keratinocyte Migration by a Redox Active Bioelectric Dressing

Exogenous application of an electric field can direct cell migration and improve wound healing; however clinical application of the therapy remains elusive due to lack of a suitable device and hence, limitations in understanding the molecular mechanisms. Here we report on a novel FDA approved redox-active Ag/Zn bioelectric dressing (BED) which generates electric fields. To develop a mechanistic understanding of how the BED may potentially influence wound re-epithelialization, we direct emphasis on understanding the influence of BED on human keratinocyte cell migration. Mapping of the electrical field generated by BED led to the observation that BED increases keratinocyte migration by three mechanisms: (i) generating hydrogen peroxide, known to be a potent driver of redox signaling, (ii) phosphorylation of redox-sensitive IGF1R directly implicated in cell migration, and (iii) reduction of protein thiols and increase in integrinαv expression, both of which are known to be drivers of cell migration. BED also increased keratinocyte mitochondrial membrane potential consistent with its ability to fuel an energy demanding migration process. Electric fields generated by a Ag/Zn BED can cross-talk with keratinocytes via redox-dependent processes improving keratinocyte migration, a critical event in wound re-epithelialization.

Diamond growth from a CO/CH4 mixture by laser excitation of CO: Laser excited chemical vapor deposition

We report for the first time, diamond growth from a mixture of 95% CO and 5% CH4 without gas phase hyperdilution of H2. Such a mixture has not been previously reported to yield diamond by any of the existing methods (hot‐filament chemical vapor deposition, plasma‐assisted chemical vapor deposition, or flame synthesis). In this paper we describe our observations of diamond growth at low pressures from vibrational excitation of CO in a CO/CH4 mixture by irradiation from a CO laser operating on its shorter wavelengths. We refer to this technique as laser excited chemical vapor deposition.

Synthesis of single-walled carbon nanotubes in vibrationally non-equilibrium carbon monoxide

Single-walled carbon nanotubes (SWNTs) are synthesized in a gas-phase non-equilibrium plasma process.The carbon producing CO disproportionation reaction is driven very efficiently in a flow reactor, in which extreme disequilibrium between the vibrational and translational mode of the carbon monoxide gas is maintained even at low translational temperatures by using a powerful and efficient carbon monoxide gas laser.In the presence of metal catalysts, the vibrationally excited CO reacts to form CO2 and structured carbon molecules, notably SWNTs.The individual tubes form ropes or flat ribbons and these are aligned parallel to each other into larger structures of SWNT material without any post-synthesis treatment. 2002 Published by Elsevier Science B.V.

Electron density and recombination rate measurements in CO-seeded optically pumped plasmas

Electron production rate and electron density in cold optically pumped CO–Ar and CO–N2 plasmas in the presence of small amounts of O2 and NO have been measured using a Thomson discharge probe and microwave attenuation. Nonequilibrium ionization in the plasmas is produced by an associative ionization mechanism in collisions of highly vibrationally excited CO molecules. It is shown that adding small amounts of O2 or NO (50–100 mTorr) to the baseline gas mixtures at P=100 torr results in an increase of the electron density by up to a factor of 20–40 (from ne<1010 cm−3 to ne=(1.5–3.0)×1011 cm−3). This occurs while the electron production rate either decreases (as in the presence of O2) or remains nearly constant within a factor of 2 (as in the presence of NO). It is also shown that the electron–ion recombination rates inferred from these measurements decrease by two to three orders of magnitude compared to their baseline values (with no additives in the cell), down to β≅1.5×10−8 cm3/s with 50–100 mTorr of oxy...

Numerical model of a transferred plasma arc

This article presents results of two-dimensional simulations for a transferred plasma arc. Calculations are performed for the internal plasma flow within the torch body, as well as the external plasma jet impinging on a surface. The governing equations describing the plasma flow are self-consistently coupled. These equations are the compressible Navier–Stokes equations for conservation of mass and momentum (in the radial and streamwise directions), conservation of energy, species continuity with finite-rate ionization and recombination kinetics, and the magnetic diffusion equation for the electromagnetics. The unsteady forms of these equations are time marched to steady state using the linearized block implicit method. This model does not employ any adjustable parameters, and therefore enables direct comparison with experiments. Model predictions are compared with experimental measurements of stagnation pressure distributions recorded on a water-cooled copper plate (workpiece), and indicate good agreement...

Friction and Wear Properties of Chemomechanically Polished Diamond Films

The role of surface roughness on the coefficient of friction and wear of polished CVD diamond films has been investigated. Diamond films grown on single crystal silicon (001) substrates by Hot Filament Chemical Vapor Deposition (HFCVD) process were polished by a chemomechanical process in which a diamond film was polished against another diamond film in the presence of a fused alkaline oxidizer at 320 o C. Friction and wear properties of these polished films were measured at elevated temperatures and in the presence of various gaseous environments