Engineering topics

Qi, Wang

Publications and source records attributed to Qi, Wang.

9 records

DOE OSTI2013

Improving the homogeneity of alternating current-drive atmospheric pressure dielectric barrier discharges in helium with an additional low-amplitude radio frequency power source: A numerical study

It was proposed in this paper that the homogeneity of the atmospheric pressure discharge driven by an ac power source could be improved by applying an auxiliary low-amplitude rf power source. To verify the idea, a two-dimensional fluid model then was applied to study the atmospheric discharges in helium driven by ac power, low-amplitude rf power, and combined ac and low-amplitude rf power, respectively. Simulation results confirmed that an auxiliary rf power could improve the homogeneity of a discharge driven by an ac power source. It was further found that there existed a threshold voltage of the rf power source leading to the transition from inhomogeneous to homogeneous discharge. As the frequency of the rf power source increased from 2 to 22 MHz, the magnitude of the threshold voltage dropped first rapidly and then to a constant value. When the frequency was over 13.56 MHz, the magnitude of the threshold voltage was smaller than one-sixth of the ac voltage amplitude under the simulated discharge parameters.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2012

Identification and Characterization of a Small Inhibitory Peptide That Can Target DNA-PKcs Autophosphorylation and Increase Tumor Radiosensitivity

Purpose: The DNA protein kinase catalytic subunit (DNA-PKcs) is one of the critical elements involved in the DNA damage repair process. Inhibition of DNA-PKcs results in hypersensitivity to ionizing radiation (IR); therefore, this approach has been explored to develop molecular targeted radiosensitizers. Here, we aimed to develop small inhibitory peptides that could specifically target DNA-PKcs autophosphorylation, a critical step for the enzymatic activation of the kinase in response to IR. Methods and Materials: We generated several small fusion peptides consisting of 2 functional domains, 1 an internalization domain and the other a DNA-PKcs autophosphorylation inhibitory domain. We characterized the internalization, toxicity, and radiosensitization activities of the fusion peptides. Furthermore, we studied the mechanisms of the inhibitory peptides on DNA-PKcs autophosphorylation and DNA repair. Results: We found that among several peptides, the biotin-labeled peptide 3 (BTW3) peptide, which targets DNA-PKcs threonine 2647 autophosphorylation, can abrogate IR-induced DNA-PKcs activation and cause prolonged {gamma}-H2AX focus formation. We demonstrated that BTW3 exposure led to hypersensitivity to IR in DNA-PKcs-proficient cells but not in DNA-PKcs-deficient cells. Conclusions: The small inhibitory peptide BTW3 can specifically target DNA-PKcs autophosphorylation and enhance radiosensitivity; therefore, it can be further developed as a novel class of radiosensitizer.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2012

Photochemical deterioration of the organic/metal contacts in organic optoelectronic devices

We study the effect of exposure to light on a wide range of organic/metal contacts that are commonly used in organic optoelectronic devices and found that irradiation by light in the visible and UV range results in a gradual deterioration in their electrical properties. This photo-induced contact degradation reduces both charge injection (i.e., from the metal to the organic layer) and charge extraction (i.e., from the organic layer to the metal). X-ray photoelectron spectroscopy (XPS) measurements reveal detectable changes in the interface characteristics after irradiation, indicating that the photo-degradation is chemical in nature. Changes in XPS characteristics after irradiation suggests a possible reduction in bonds associated with organic-metal complexes. Measurements of interfacial adhesion strength using the four-point flexure technique reveal a decrease in organic/metal adhesion in irradiated samples, consistent with a decrease in metal-organic bond density. The results shed the light on a new material degradation mechanism that appears to have a wide presence in organic/metal interfaces in general, and which likely plays a key role in limiting the stability of various organic optoelectronic devices such as organic light emitting devices, organic solar cells, and organic photo-detectors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2012

Synthesis of graphene-based Pt nanoparticles by a one-step in situ plasma approach under mild conditions

Herein, a one-step in situ plasma approach to synthesize the highly dispersed Pt nanoparticles on graphene under mild conditions is reported. The graphene oxide (GO) was transformed into graphene and H{sub 2}PtCl{sub 6} was simultaneously transformed into Pt nanoparticles under argon plasma conditions. The synthesized graphene-based Pt nanoparticles were characterized by scanning electron microscopy, atomic force microscopy, x-ray diffraction, and Fourier transform infrared spectroscopy. The analysis showed that the Pt nanoparticles were deposited on graphene as a form of face-centered cubical structure and the oxygen groups on graphene oxide were partially removed. The results of x-ray photoelectron spectroscopy analysis further confirmed the results.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2012

Activation of water on the TiO{sub 2} (110) surface: The case of Ti adatoms

Using first-principles calculations we have studied the reactions of water over Ti adatoms on the (110) surface of rutile TiO{sub 2}. Our results provide fundamental insights into the microscopic mechanisms that drive this reaction at the atomic level and assess the possibility of using this system to activate the water dissociation reaction. In particular, we show that a single water molecule dissociates exothermically with a small energy barrier of 0.17 eV. After dissociation, both H{sup +} and OH{sup -} ions bind strongly to the Ti adatom, which serves as an effective reactive center on the TiO{sub 2} surface. Finally, clustering of Ti adatoms does not improve the redox activity of the system and results in a slightly higher energy barrier for water dissociation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2011

Numerical investigation of pulse-modulated atmospheric radio frequency discharges in helium under different duty cycles

Experiments observed that the pulse duty cycle has effects on the plasma homogeneity in pulse-modulated radio frequency (rf) discharges. In this paper, pulse-modulated rf (13.56 MHz) helium discharges are theoretically investigated using a two dimensional fluid model. With the pulse period being fixed to 15 {mu}s, it is found that when the pulse-on duration is over 4 {mu}s, i.e., the duty cycle is larger than approximately 27%, the discharge transits from an inhomogeneous to a homogeneous mode in every specific part of each pulse cycle under currently-used simulation parameters. More quantitative analysis shows that the discharge becomes more homogeneous as the duty cycle is increased but does not reach complete homogeneity. Possible reasons for the homogeneity improvement are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2011

Numerical investigation on operation mode influenced by external frequency in atmospheric pressure barrier discharge

The influence of external driving frequency on the discharge mode in the dielectric barrier discharge was investigated with a two-dimensional, self-consistent fluid model. The simulation results show that the helium discharge exhibits three operation modes: Townsend, homogeneous glow, and local glow discharges from the lower frequency (1 kHz) to the higher frequency (100 kHz) under discharge parameters specified in this work. The discharge operates in a Townsend mode when the driving frequency varies from 1 to about 7 kHz; while it exhibits homogenous glow characteristics in an approximate range from 7 to 65 kHz; when the external frequency exceeds 65 kHz, it turns into a local glow discharge. The effects of external driving frequency on the discharge mode were revealed and the physical reasons were discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2011

Tunable band gap near the Dirac point in nonlinear negative-zero-positive index metamaterial waveguide

We make theoretical investigations of the nonlinear guided modes near the Dirac point (DP) in nonlinear negative-zero-positive index metamaterial (NZPIM) waveguide. When the nonlinearity is self-focusing, an asymmetric forbidden band exists near the DP that can be modulated by the strength of the nonlinearity. However, the self-defocusing nonlinearity can completely eliminate the asymmetric band gap. We also study the nonlinear surface waves in such nonlinear NZPIM waveguide. These results may predict analogous phenomena in nonlinear graphene.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2011

Random errors in interferometry with the least-squares method

This investigation analyzes random errors in interferometric surface profilers using the least-squares method when random noises are present. Two types of random noise are considered here: intensity noise and position noise. Two formulas have been derived for estimating the standard deviations of the surface height measurements: one is for estimating the standard deviation when only intensity noise is present, and the other is for estimating the standard deviation when only position noise is present. Measurements on simulated noisy interferometric data have been performed, and standard deviations of the simulated measurements have been compared with those theoretically derived. The relationships have also been discussed between random error and the wavelength of the light source and between random error and the amplitude of the interference fringe.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗