Effect of ion flux on recrystallization and resistance lowering in phosphorus-implanted (0001)-oriented 4H-SiC

High-dose ion implantation of phosphorus into 4H-SiC (0001) has been investigated with three different ion fluxes ranging from 1.0 to 4.0 x 10(12) P(+)cm(-2.)s(-1) and keeping the implantation dose constant at 2.0 x 10(15) P(+)cm(-2). The implantations are performed at room temperature and subsequently annealed at 1500 degrees C. Photoluminescence and Raman scattering are employed to investigate the implantation-induced damages and the residual defects after annealing. The electrical properties of the implanted layer are evaluated by Hall effect measurements on the sample with a van der Pauw configuration. Based on these results, it is revealed that the damages and defects in implanted layers can be greatly reduced by decreasing the ion flux. Considering room temperature implantation and a relatively low annealing temperature of 1500 degrees C, a reasonably low sheet resistance of 106 Omega/square is obtained at ion flux of 1.0 x 10(12) P(+)cm(-2.)s(-1) with a donor concentration of 4.4 x 10(19)cm(-3).

PEGylated Phospholipid Membrane on Polymer Cushion and Its Interaction with Cholesterol

By employing poly(ethylene glycol) (PEG) shielding and a polymer cushion to achieve air stability of the lipid membrane, we have analyzed PEG influence on dried membranes and the interaction with cholesterol. Small unilamellar vesicles (SUVs) formed by the mixture of 1,2-dimyristoylphosphatidylcholine (DMPC) with different molar fraction of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(poly(ethylene glycol))-2000] (DSPE-PEG(2000)) adsorb and fuse into membranes on different polymer-modified silicon dioxide surfaces, including chitosan, poly(L-lysine) (PLL), and hyaluronic acid, Dried membranes arc further examined by ellipsometer and atomic force microscopy (AFM). Only chitosan can support a visible and uniform lipid array. The thickness of dry PEGylated lipid membrane is reduced gradually as the molar fraction of PEG increases. AFM scanning confirms the lipid membrane stacking for vesicles containing low PEG, and only a proper amount of PEG can maintain a single lipid hi lover; however, the air stability of the membrane will be destroyed if overloading. PEG. Cholesterol incorporation can greatly improve the structural stability of lipid membrane, especially for those containing high molar fraction of PEG. Different amounts of cholesterol influence the thickness and surface morphology of dried membrane.

Glucose-lowering activity of amino acid-N-phosphonic acid oxovanadium complexes and its interaction with DNA

Vanadium has well-documented lowering glucose properties both in vitro and in vivo. The design of new oxovanadium(IV) coordination compounds, intended for use as insulin-enhancing agents in the treatment of diabetes mellitus, can potentially benefit from a synergistic approach, in which the whole complex has more than an additive effect from its component parts. Biological testing with oxovanadium(IV) organic phosphonic acid, for insulin-enhancing potential included acute administration, by oral gavage in streptozotocin (STZ) diabetic rats. The complexes of oxovanadium(IV) amino acid-N-phosphonic acid exhibit higher lowering glucose activity in vivo. The interaction of the complexes of oxovanadium(IV) amino acid-N-phosphonic acid with DNA was investigated by agarose gel electrophoresis. The results indicated that these complexes have strong interaction with DNA.

Ion channel behavior of amphotericin B in sterol-free and cholesterol- or ergosterol-containing supported phosphatidylcholine bilayer model membranes investigated by electrochemistry and spectroscopy

Amphotericin B (AmB) is a popular drug frequently applied in the treatment of systemic fungal infections. In the presence of ruthenium (II) as the maker ion, the behavior of AmB to form ion channels in sterol-free and cholesterol- or ergosterol-containing supported phosphatidylcholine bilayer model membranes were studied by cyclic votammetry, AC impedance spectroscopy, and UV/visible absorbance spectroscopy. Different concentrations of AmB ranging from a molecularly dispersed to a highly aggregated state of the drug were investigated. In a fixed cholesterol or ergosterol content (5 mol %) in glassy carbon electrode-supported model membranes, our results showed that no matter what form of AmB, monomeric or aggregated, AmB could form ion channels in supported ergosterol-containing phosphatidylcholine bilayer model membranes. However, AmB could not form ion channels in its monomeric form in sterol-free and cholesterol-containing supported model membranes. On the one hand, when AmB is present as an aggregated state, it can form ion channels in cholesterol-containing supported model membranes; on the other hand, only when AmB is present as a relatively highly aggregated state can it form ion channels in sterol-free supported phosphatidylcholine bilayer model membranes. The results showed that the state of AmB played an important role in forming ion channels in sterol-free and cholesterol-containing supported phosphatidylcholine bilayer model membranes.

Interaction of scopolamine and cholesterol with sphingomyelin bilayers by FT-Raman spectroscopy

The interaction of scopolamine and cholesterol with sphingomyelin bilayers has been investigated by FT-Raman spectroscopy in head-group region (600-1000 cm(-1)), the C-C stretching (1000-1200 cm(-1)), CH2 deformation (1400-1500 cm(-1)) and the C-H stretching (2800-3000 cm(-1)) mode regions. The results indicate that scopolamine and cholesterol do not change the conformation of O-C-C-N+ backbone in the choline group of sphingomyelin bilayers, the polar headgroup is still extending parallel to the bilayer surface and O-C-C-N+ group is still in its gauche conformer. Scopolamine and cholesterol lower the order of the interface, the interchain, CH2 crystal lattices and the lateral chain-chain packing, and increase their fluidity.

Interaction of La3+ and cholesterol with dipalmitoylphosphatidylglycerol bilayers by FT-Raman spectroscopy

The interaction of La3+ and cholesterol with the negatively charged phospholipid dipalmitoylphosphatidylglycerol bilayers was studied by Fourier transform-Raman spectroscopy. La3+ was shown to increase interchain order and intermolecular ordering of the lipid lattice, cholesterol exhibited less of an effect, the La3+-DPPG-cholesterol complex was more ordered than cholesterol=DPPG nd less ordered than La3+-DPPG complexes, cholesterol modulates the order/disorder parameters of DPPG bilayers.

CHOLESTEROL SENSOR-BASED ON ELECTRODEPOSITION OF CATALYTIC PALLADIUM PARTICLES

A layer of palladium particles was electrodeposited on a glassy carbon electrode. The dispersed Pd particles resulted in a large decrease in overvoltage for the electrochemical oxidation of H2O2 down to +0.4 V vs. Ag/AgCl, based on which a new kind of cholesterol sensor was fabricated. Cholesterol oxidase was immobilized on the Pd-dispersed electrode by cross-linking with glutaraldehyde and a layer of poly(o-phenylenediamine) (PPD) film was electropolymerized on the enzyme layer. The sensor shows a linear response in the concentration range 0.05-4.50 mmol l-1 with a rapid response of less than 20 s. The polymer film can prevent interference from uric acid and ascorbic acid and also increases the thermal stability of the sensor. The sensor can be used for 200 assays without an obvious decrease in activity.

Dynamical symmetry of screened Coulomb potential and isotropic harmonic oscillator

It is shown that for the screened Coulomb potential and isotropic harmonic oscillator, there exists an infinite number of closed orbits for suitable angular momentum values. At the aphelion (perihelion) points of classical orbits, an extended Runge-Lenz vector for the screened Coulomb potential and an extended quadrupole tensor for the screened isotropic harmonic oscillator are still conserved. For the screened two-dimensional (2D) Coulomb potential and isotropic harmonic oscillator, the dynamical symmetries SO3 and SU(2) are still preserved at the aphelion (perihelion) points of classical orbits, respectively. For the screened 3D Coulomb potential, the dynamical symmetry SO4 is also preserved at the aphelion (perihelion) points of classical orbits. But for the screened 3D isotropic harmonic oscillator, the dynamical symmetry SU(2) is only preserved at the aphelion (perihelion) points of classical orbits in the eigencoordinate system. For the screened Coulomb potential and isotropic harmonic oscillator, only the energy (but not angular momentum) raising and lowering operators can be constructed from a factorization of the radial Schrodinger equation.

The Effect of the Thickness of Fe2 Al5 Phase Layer at Fe/Al Interface on the Mechanics Behavior of Hot Dip Aluminizing Coating

Hot Dip Aluminized Coatings with different thickness were prepared on Q235 steel in aluminum solutions with different temperature for certain time. Through tensile tests and in-situ SEM observations, the effect of the coating's microstructure on the tensile strength of the samples was studied. It was disclosed at certain aluminum solution temperature,transaction layers mainly composed of Fe2 Al5 phase got thicker with time prolonging, and this changed initial crack's extending direction from parallel with to vertical with stretching direction. The change in crack direction decreased tensile strength of samples, thus made the coating easy to break. It was concluded that the existence of thick Fe2 Al5 phase layer was the basic reason for the lowering of tensile strength of the coating.

IL-8-induced L-selectin shedding regulates its binding kinetics to PSGL-1

L-selectin plays a crucial role in inflammation cascade by initiating the tethering and rolling of leukocytes on endothelium wall. While many L-selectin molecules are rapidly shed from the cell surface upon activation, the remaining membrane-anchored L-selectin may still play an important role in regulating leukocyte rolling and adhesion with different binding kinetics. Here we developed an in vitro model to activate Jurkat cells via interlukin-8 (IL-8) and quantified the two-dimensional (2D) binding kinetics, using a micropipette aspiration assay, of membrane-anchored L-selectin to P-selectin glycoprotein ligand 1 (PSGL-1) ligand coupled onto human red blood cells (RBCs). The data indicated that L-selectin shedding reduced the amount of membrane-anchored L-selectin and lowered both its reverse and forward rates. These results suggested that the rolling dynamics of activated leukocytes was determined by two opposite impacts: reducing the surface presentation would enhance the rolling but lowering the kinetic rates would decrease the rolling. This finding provides a new insight into understanding how L-selectin shedding regulates leukocyte rolling and adhesion.

Some engineering issues of an FBG sensor with the dual gratings parallel matched interrogation method

The key issues of engineering application of the dual gratings parallel matched interrogation method are expanding the measurable range, improving the usability, and lowering the cost by adopting a compact and simple setup based on existing conditions and improving the precision of the data-processing scheme. A credible and effective data-processing scheme based on a novel divisional look-up table is proposed based on the advantages of other schemes. Any undetermined data is belonged to a certain section, which can be confirmed at first, then it can be looked up in the table to correspond to microstrain by the scheme. It not only solves inherent problems of the traditional one (double value and small measurable range) but also enhances the precision, which improves the performance of the system. From the experimental results, the measurable range of the system is 525 mu epsilon, and the precision is +/- 1 mu epsilon based on normal matched gratings. The system works in real time, which is competent for most engineering measurement requirements. (C) 2007 Elsevier GmbH. All rights reserved.

Enhancement of near-band-edge photoluminescence of ZnO thin films in sandwich configuration at room temperature

ZnO/ITO/ZnO sandwich structure films were fabricated. The effects of buffer layer on the structure and optical properties of ZnO films were investigated by x-ray diffraction (XRD), photoluminescence, optical transmittance, and absorption measurements. XRD spectra indicate that a buffer layer has the effects of lowering the grain orientation of ZnO films and increasing the residual stresses in the films. The near-band-edge emissions of ZnO films deposited on both single indium tin oxide (ITO) buffer and ITO/ZnO double buffers are significantly enhanced compared with that deposited on a bare substrate due to the quantum confinement effect. (C) 2006 American Institute of Physics.