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  • American Institute of Physics (AIP)  (12)
  • Blackwell Science Ltd  (4)
  • 2000-2004  (8)
  • 1995-1999  (8)
  • 1
    Electronic Resource
    Electronic Resource
    Lattice site location of ion-implanted 8Li in Silicon Carbide (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 1046-1052 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The lattice sites of ion-implanted Li atoms in 6H-, 4H-, and 3C-SiC were studied. Radioactive 8Li ions (t1/2=0.84 s) were implanted with 60 keV into the crystalline SiC samples, and the channeling and blocking effects of 1.6 MeV alpha particles emitted in the decay were measured to determine the Li lattice sites. The alpha emission channeling spectra measured along different crystallographic directions reveal that Li occupies mainly interstitial sites with tetrahedral symmetry, centered along the c-axis atom rows in the hexagonal lattices. In the cubic 3C-SiC structure, Li is located on tetrahedral interstitial sites as well. For 6H-SiC, the implantation temperature was varied between 200 and 823 K without observing significant changes in the emission channeling spectra. Thus, Li diffusion or Li defect interaction resulting in a lattice site change does not occur in this temperature regime. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1425442
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  • 2
    Electronic Resource
    Electronic Resource
    Ion beam deposition of fluorinated amorphous carbon (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 4237-4245 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the growth and the properties of (t)a-C:F films prepared by the deposition of mass separated 12C+ and 19F+ ions as a function of the F concentration. The films are always strongly F deficient due to the formation of volatile F2 and CFx molecules during the deposition process. A maximum F content of about 25 at. % is obtained for an ion charge ratio of C+:F+=1:1. The observed mechanical, optical, electrical, and structural properties as well as the thermal stability of the films are strongly influenced by the F content. A three step progression of the film structure is evident for increasing F concentration: the amorphous three-dimensional network of tetrahedrally bonded carbon atoms of pure carbon films (ta-C) with diamondlike properties is doped for very low F concentrations (ta-C:F). A further increase of the F content results first in transformation to a graphitelike amorphous structure (a-C:F) before the deposited films become porous and to a polymerlike one for the highest F content. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1404419
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  • 3
    Electronic Resource
    Electronic Resource
    Increased CNS uptake and enhanced antinociception of morphine-6-glucuronide in rats after inhibition of P-glycoprotein (2002)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 83 (2002), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Morphine-6-glucuronide (M6G) is a substrate of P-glycoprotein (P-gp), which forms an outward transporter at the blood–brain barrier. Inhibition of P-gp may therefore be expected to cause increased CNS uptake of M6G. We directly assessed the spinal concentrations of M6G and its antinociceptive effects in rats following pharmacological inhibition of P-gp. Spinal cord tissue concentrations of M6G were assessed by microdialysis with probes transversally implanted through the dorsal horns of the spinal cord at level L4. Ten rats received M6G intravenously (0.018 mg/kg loading dose plus 0.00115 mg/kg/min for an 8-h infusion), five of them together with PSC833 to inhibit P-gp (32-h infusion, starting 24 h before the addition of M6G). Antinociceptive effects were explored by means of formalin tests. After having obtained evidence for enhanced CNS uptake and antinociception of M6G in the presence of PSC833, additional behavioural experiments were performed in another 32 rats to assess the dose dependency of the antinociceptive effects of M6G either with or without PSC833 in comparison with both PSC833 alone and placebo. Inhibition of P-gp increased the M6G concentrations in the spinal cord approximately three-fold whereas the plasma concentrations were increased only by a factor of 1.4, which resulted in a more than doubled spinal cord/plasma concentration ratio (from 0.08 ± 0.03 for M6G alone to 0.17 ± 0.08 for M6G plus PSC833). Antinociceptive effects of M6G were significantly enhanced by inhibition of P-gp. Inhibition of P-gp alters the transport of M6G across the blood–brain barrier, resulting in enhanced spinal cord uptake and enhanced antinociception.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2002.01177.x
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of selective COX-1 and -2 inhibition on formalin-evoked nociceptive behaviour and prostaglandin E2 release in the spinal cord (2001)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 79 (2001), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Nociception evoked prostaglandin (PG) release in the spinal cord considerably contributes to the induction of hyperalgesia and allodynia. To evaluate the relative contribution of cyclooxygenase-1 (COX-1) and COX-2 in this process we assessed the effects of the selective COX-1 inhibitor SC560 and the selective COX-2 inhibitor celecoxib on formalin-evoked nociceptive behaviour and spinal PGE2 release. SC560 (10 and 20 mg/kg) significantly reduced the nociceptive response and completely abolished the formalin-evoked PGE2 raise. In contrast, celecoxib (10 and 20 mg/kg) was ineffective in both regards, i.e. the flinching behaviour was largely unaltered and the formalin-induced PGE2 raise as assessed using microdialysis was only slightly, not significantly reduced. This suggests that the formalin-evoked rapid PG release was primarily caused by COX-1 and was independent of COX-2. Mean free spinal cord concentrations of celecoxib during the formalin assay were 32.0 ± 4.5 nm, thus considerably higher than the reported IC50 for COX-2 (3–7 nm). Therefore, the lack of efficacy of celecoxib is most likely not to be a result of poor tissue distribution. COX-2 mRNA and protein expression in the spinal cord were not affected by microdialysis alone but the mRNA rapidly increased following formalin injection and reached a maximum at 2 h. COX-2 protein was unaltered up to 4 h after formalin injection. The time course of COX-2 up-regulation suggests that the formalin-induced nociceptive response precedes COX-2 protein de novo synthesis and may therefore be unresponsive to COX-2 inhibition. Considering the results obtained with the formalin model it may be hypothesized that the efficacy of celecoxib in early injury evoked pain may be less than that of unselective NSAIDs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2001.00613.x
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  • 5
    Electronic Resource
    Electronic Resource
    Ion implanted dopants in GaN and AlN: Lattice sites, annealing behavior, and defect recovery (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 2149-2157 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The recovery of structural defects in gallium nitride (GaN) and aluminum nitride (AlN) after implantation of 111In+ and 89Sr+ in the dose range (0.1–3) 1013 cm−2 and ion energies of 60–400 keV has been investigated as a function of annealing temperature with emission channeling (EC) and perturbed γγ angular correlation spectroscopy. The implanted In and Sr atoms occupied substitutional sites in heavily perturbed surroundings of point defects after room temperature implantation. No amorphization of the lattice structure was observed. The point defects could be partly removed after annealing to 1473 K for 10–30 min. Lattice site occupation of implanted light alkalis, 24Na+ in GaN and AlN as well as 8Li+ in AlN, were also determined by EC as a function of implantation and annealing temperature. These atoms occupied mainly interstitial sites at room temperature. Lithium diffusion and the occupation of substitutional sites was observed in GaN and AlN at implantation temperatures above 700 K. A lattice site change was also observed for sodium in AlN, but not in GaN after annealing to 1073 K for 10 min. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372154
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  • 6
    Electronic Resource
    Electronic Resource
    Lattice site location studies of ion implanted 8Li in GaN (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 3085-3089 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The lattice sites of ion implanted Li atoms in GaN were studied as a function of implantation temperature between room temperature and 770 K. We measured the channeling and blocking patterns of α-particles emitted in the radioactive decay of implanted 8Li ions to determine the Li lattice sites. Below 700 K Li atoms occupy mainly interstitial sites in the center of the c-axis hexagons at positions c/4 and 3c/4, where c is the lattice constant in c-axis direction. Around 700 K Li starts to diffuse and presumably interacts with vacancies created in the implantation process. This leads to the formation of substitutional Li above 700 K. An activation energy of about 1.7 eV for interstitial Li diffusion was determined. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368463
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  • 7
    Electronic Resource
    Electronic Resource
    Direct evidence of micropipe-related pure superscrew dislocations in SiC (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 353-355 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A set of powerful x-ray imaging techniques using white-beam synchrotron radiation have been developed and applied to clearly reveal and map micropipes in SiC crystals at a "magnified" level. The experimental results and the corresponding simulations demonstrate explicitly that the micropipes are pure superscrew dislocations (SSDs). Moreover, these techniques provide accurate descriptions of the detailed structure of the SSDs, including the spatial distribution of the strain fields, the magnitudes of the Burgers vectors, the dislocation senses, and the surface relaxation effects. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123069
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  • 8
    Electronic Resource
    Electronic Resource
    Photodissociation of NH2: Two-dimensional potential energy surfaces for the dissociation into NH and H (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 5558-5571 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Extensive multireference configuration interaction calculations were carried out in order to obtain complete two-dimensional (2D) potential energy surfaces for the amidogen (NH2) radical as functions of both N–H bond lengths keeping the bond angle fixed at its experimental ground state equilibrium value. The eight lowest-lying states (four of each symmetry, A′ and A″) were treated mainly for the purpose of using these surfaces in subsequent studies of the photodissociation dynamics. In analogy with the neighboring dihydrides CH2 and H2O the photodissociation of NH2 into NH+H (hydrogen abstraction) takes place preferentially after excitation of the first two Rydberg s states (3 2A′/2 2A1 and 2 2A″/2 2B1) found closely together at about 7.6 eV. The transition dipole moments connecting the ground state with these two states are large (0.44 a.u. and 0.66 a.u.) in the Franck–Condon region, but the behavior of the potentials in the dissociation channel is quite different. The 3 2A′/2 2A1 state is weakly repulsive whereas the 2 2A″/2 2B1 state is strongly repulsive. This will result in differences in the dissociation dynamics for the two states.The next higher state which should play a role in the NH2 photodissociation is the 4 2A″/3 2B1 Rydberg s state at 9.4 eV, because of its large transition dipole moment with the ground state (0.36 a.u.). Close to this state, many Rydberg p states were found. Due to the high density of states in the region above 9.0 eV, interactions of these states are expected and should lead to complicated dissociation dynamics. Contrary to CH2, the two low-lying valence states for NH2 are found at lower energies [2.2 eV (1 2A1) and 6.5 eV (1 2B2)], well separated from the first members of the Rydberg series. These states are less important for the photodissociation of NH2, compared with CH2, because the first state is bound and the transition to the other is dipole-forbidden in C2v symmetry. For H2O, the valence states are missing. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471796
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  • 9
    Electronic Resource
    Electronic Resource
    High resolution rotational analysis of the B 3Π–X 3Δ (1,0) band of titanium monoxide (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 4375-4381 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The B 3Π–X 3Δ (1,0) band of titanium monoxide has been studied at sub-Doppler resolution (0.002 cm−1) by crossing a beam of TiO molecules with a cw tunable laser beam and by collecting the laser-induced fluorescence. The rotational structure of 42 branches belonging to the 3Π–3Δ transition has been analyzed up to rotational quantum numbers equal to 94. Spectroscopic data have been reduced to a set of 24 molecular constants, using a case (a) effective Hamiltonian. The rotational, spin–orbit and Λ-doubling constants are discussed in terms of the leading configurations which give rise to the X 3Δ and B 3Π electronic states. It is shown that for the B state, existing ab initio calculations are not able to reproduce the second order spin–orbit effect and the Λ doubling effect. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469486
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  • 10
    Electronic Resource
    Electronic Resource
    Tunneling through the potential barrier of the B1Πu state of 7Li–7Li (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1926-1936 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A sub-Doppler experiment involving an effusive beam of lithium dimers and a continuous wave (cw) tunable dye laser is used to record the absorption spectrum of the B–X system. Predissociation due to tunneling through the potential barrier of the B state is studied in a small range of energy above the Li(2p)+Li(2s) dissociation limit by analyzing the shape of homogeneously broadened absorption lines and by measuring the fluorescence intensity of Li atoms. Experimental data are interpreted in the frame of a semiclassical dynamical model involving the shape of the potential barrier. Their accuracy should address an improvement of the potential shape through a full quantal dynamical model. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479461
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