| 1. |
- Larsson, Jenny, 1974-, et al.
(författare)
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Anti-inflammatory effects of a titanium-peroxy gel: role of oxygen metabolites and apoptosis.
- 2004
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Ingår i: Journal of biomedical materials research. Part A. - : Wiley. - 1549-3296 .- 0021-9304 .- 1097-4636. ; 68:3, s. 448-57
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Tidskriftsartikel (refereegranskat)abstract
- Polymorphonuclear neutrophils (PMN) are among the first inflammatory cells to arrive at an implant interface, where they encounter with the foreign material and may produce reactive oxygen species (ROS). During the interaction between titanium and ROS, titanium-peroxy (Ti-peroxy) compounds may be formed. We used a Ti-peroxy gel, made from titanium and hydrogen peroxide, to study the effects of Ti-peroxy compounds on PMN. In the absence of serum, the Ti-peroxy gel decreased the oxidative response of PMN to yeast and PMA and reduced PMN apoptosis without inducing necrosis. These effects could not be ascribed to the release of hydrogen peroxide from the Ti-peroxy gel, because a steady-state hydrogen peroxide producing system failed to mimic the effects of the gel. The effects were similarly unaffected when PMN were preincubated with beta(2)-integrin antibodies, questioning the involvement of adhesion molecules. Nevertheless, when a filter was used to separate the Ti-peroxy gel from the cells, the gel effect on PMN life span was abolished, pointing to a contact-dependent mechanism. In the presence of serum, the Ti-peroxy gel had no effect on the PMN oxidative response and life span, but appeared rather inert. In summary, this study demonstrates that the Ti-peroxy gel has potentially anti-inflammatory properties through a combined peroxide and physical contact effect, supporting the notion that interactions between titanium and inflammatory cells are responsible for the good performance of titanium in vivo.
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| 2. |
- Ahuja, Rajeev, et al.
(författare)
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Electronic and optical properties of lead iodide
- 2002
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 92:12, s. 7219-7224
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Tidskriftsartikel (refereegranskat)abstract
- The electronic properties and the optical absorption of lead iodide (PbI2) have been investigated experimentally by means of optical absorption and spectroscopic ellipsometry, and theoretically by a full-potential linear muffin-tin-orbital method. PbI2 has been recognized as a very promising detector material with a large technological applicability. Its band-gap energy as a function of temperature has also been measured by optical absorption. The temperature dependence has been fitted by two different relations, and a discussion of these fittings is given.
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| 3. |
- Ahuja, Rajeev, et al.
(författare)
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Optical properties of 4H-SiC
- 2002
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:4, s. 2099-2103
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Tidskriftsartikel (refereegranskat)abstract
- The optical band gap energy and the dielectric functions of n-type 4H-SiC have been investigated experimentally by transmission spectroscopy and spectroscopic ellipsometry and theoretically by an ab initio full-potential linear muffin-tin-orbital method. We present the real and imaginary parts of the dielectric functions, resolved into the transverse and longitudinal photon moment a, and we show that the anisotropy is small in 4H-SiC. The measurements and the calculations fall closely together in a wide range of energies.
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| 4. |
- Ahuja, Rajeev, et al.
(författare)
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Optical properties of SiGe alloys
- 2003
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 93:7, s. 3832-3836
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Tidskriftsartikel (refereegranskat)abstract
- The optical properties of Si1-xGex have been investigated theoretically using a full-potential linear muffin-tin-orbital method. We present the density-of-states as well as the real and imaginary parts of the dielectric function. The calculated dielectric function was found to be in good agreement with the spectroscopic ellipsometry measurements by J. Bahng , J. Phys.: Condens. Matter 13, 777 (2001), and we obtained a static dielectric constant of epsilon(0)=12.19+2.45x in the Si rich regime (xless than or equal to0.5).
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| 5. |
- Araujo, C. M., et al.
(författare)
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Electrical resistivity, MNM transition and band-gap narrowing of cubic GaN : Si
- 2002
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Ingår i: Microelectronics Journal. - 0026-2692. ; 33:4, s. 365-369
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Tidskriftsartikel (refereegranskat)abstract
- The electrical resistivity of the Si-donor cubic GaN is investigated theoretically at low temperature. The critical impurity concentration, N-c, for the metal-nonmetal transition is estimated in three different ways: from using the generalized Drude approach (GDA) for the resistivity; from the vanishing of the chemical potential calculated using the dielectric function model with a Lorentz-Lorenz correction; from finding the crossing point between the energy in the insulating and metallic states. The bandgap narrowing (BGN) has been determined theoretically and experimentally above the MNM transition, The experimental data have been obtained with photoluminescence measurements. Theoretical and experimental results are in rough agreement in the range of impurity concentration of interest.
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| 6. |
- Araujo, C. M., et al.
(författare)
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Spin-dependent conductance in nonmagnetic InGaAs asymmetric double barrier devices
- 2004
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Ingår i: Brazilian journal of physics. - 0103-9733 .- 1678-4448. ; 34:2B, s. 632-634
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Tidskriftsartikel (refereegranskat)abstract
- The spin dependence of the conductance of an asymmetric double-barrier InGaAs device is studied within the multiband k(.)p and envelope function approximations. The spin-dependent transmission probability for electrons across the structure is obtained using transfer matrices and the low bias conductance per unit area is calculated as a function of the Fermi energy (or doping) in the contacts. The possibility to obtain spin polarized currents in such devices is demonstrated, however, the resulting degree of polarization is rather small (a few percent) in the specific InGaAs structures considered here.
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| 7. |
- Bertilsson, Kent, et al.
(författare)
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The Effect of Different Transport Models in Simulation of High Frequency 4H-SiC and 6H-SiC Vertical MESFETs
- 2001
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Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 45:5, s. 645-653
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Tidskriftsartikel (refereegranskat)abstract
- A full band Monte Carlo (MC) study of the high frequency performance of a 4H-SiC Short channel vertical MESFET is presented. The MC model used is based on data from a full potential band structure calculation using the local density approximation to the density functional theory. The MC results have been compared with simulations using state of the art drift-diffusion and hydrodynamic transport models. Transport parameters such as mobility, saturation velocity and energy relaxation time are extracted from MC simulations
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| 8. |
- da Silva, A. F., et al.
(författare)
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Critical concentration for the doping-induced metal-nonmetal transition in cubic and hexagonal GaN
- 2002
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 92:5, s. 2550-2555
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Tidskriftsartikel (refereegranskat)abstract
- The critical concentration for the metal-nonmetal transition has been calculated for n-type and p-type GaN. Both cubic and hexagonal structures of GaN have been considered. Three different computational methods have been utilized: the first is the original Mott model, the second is an extended Mott-Hubbard model, and the third method is based on total energy of the metallic and the nonmetallic phases. All three methods show a similar value of the critical concentration, about 10(18) and 10(20) cm(-3) for n-type and p-type doped materials, respectively.
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| 9. |
- da Silva, A. F., et al.
(författare)
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Electrical resistivity of acceptor carbon in GaAs
- 2004
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 95:5, s. 2532-2535
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Tidskriftsartikel (refereegranskat)abstract
- The electrical resistivity was investigated from room temperature down to 1.7 K for the shallow acceptor carbon in GaAs prepared by ion implantation with impurity concentrations between 10(17) and 10(19) cm(-3). Good agreement was obtained between the measured resistivities and resistivities calculated by a generalized Drude approach at similar temperatures and doping concentrations. The critical impurity concentration for the metal-nonmetal transition was found to be about 10(18) cm(-3).
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| 10. |
- da Silva, A. F., et al.
(författare)
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Influence of Si doping on optical properties of wurtzite GaN
- 2001
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 13:40, s. 8891-8899
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Tidskriftsartikel (refereegranskat)abstract
- The band gap shift (BGS) of Si-doped wurtzite GaN for impurity concentrations spanning the insulating to the metallic regimes has been investigated at low temperature. The critical impurity concentration for the metal-non-metal transition is estimated from the generalized Drude approach for the resistivity to be about 1.0 x 10(18) cm(-3). The calculations for the BGS were carried out within a framework of the random phase approximation, taking into account the electron-electron, electron-optical phonon, and electron-ion interactions. In the wake of very recent photoluminescence measurements, we have shown and discussed the possible transitions involved in the experimental results.
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