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  • 1
    Electronic Resource
    Electronic Resource
    Influence of irradiation conditions on plasma evolution in laser-surface interaction (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3071-3079 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The plasma plume induced by pulsed CO2 laser irradiation of a Ti target at power densities up to 4×108 W cm−2 was studied by emission spectroscopy. Time- and space-resolved measurements were performed by varying laser intensity, laser temporal pulse shape, ambient gas pressure, and the nature of the ambient gas. Experimental results are discussed by comparison with usual models. We show that shock wave and plasma propagation depend critically on the ratio Ivap/Ii, Ivap being the intensity threshold for surface vaporization and Ii the plasma ignition threshold of the ambient gas. Spectroscopic diagnostics of the helium breakdown plasma show maximum values of electron temperature and electron density in the order of kTe∼10 eV and ne=1018 cm−3, respectively. The plasma cannot be described by local thermodynamic equilibrium modeling. Nevertheless, excited metal atoms appear to be in equilibrium with electrons, hence, they can be used like a probe to measure the electron temperature. In order to get information on the role of the plasma in the laser-surface interaction, Ti surfaces were investigated by microscopy after irradiation. Thus an enhanced momentum transfer from the plasma to the target due to the recoil pressure of the breakdown plasma could be evidenced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354594
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  • 2
    Electronic Resource
    Electronic Resource
    Multistage plasma initiation process by pulsed CO2 laser irradiation of a Ti sample in an ambient gas (He, Ar, or N2) (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 1091-1099 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: New experimental results are reported on plasma initiation in front of a titanium sample irradiated by ir (λ=10.6 μm) laser pulses in an ambient gas (He, Ar, and N2) at pressures ranging from several Torr up to the atmosphere. The plasma is studied by space- and time-resolved emission spectroscopy, while sample vaporization is probed by laser-induced fluorescence spectroscopy. Threshold laser intensities leading to the formation of a plasma in the vapor and in the ambient gases are determined. Experimental results support the model of a vaporization mechanism for the plasma initiation (vaporization-initiated plasma breakdown). The plasma initiation is described by simple numerical criteria based on a two-stage process. Theoretical predictions are found to be in a reasonable agreement with the experiment. This study provides also a clear explanation of the influence of the ambient gas on the laser beam-metal surface energy transfer. Laser irradiation always causes an important vaporization when performed in He, while in the case of Ar or N2, the interaction is reduced in heating and vaporization of some surface defects and impurities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353271
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  • 3
    Electronic Resource
    Electronic Resource
    Investigation by laser-induced fluorescence of surface vaporization during the pulsed CO2 laser irradiation of a titanium sample in an ambient gas (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5629-5634 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This work deals with the study of laser-induced surface vaporization in the presence of an ambient gas, in the conditions where a plasma develops at the gas-material interface. In the experiment, a pulsed CO2 laser is focused onto a titanium target in a cell containing He, Ar, or N2 from a few tenths of Torr up to atmospheric pressure. The temporal and spatial distributions of Ti atoms vaporized from the surface are measured by laser-induced fluorescence spectroscopy. Strong evaporation is observed in helium up to several hundred Torr. In this gas, the Ti atom plume expands according to the propagation of a blast-wave. On the contrary, a very small quantity of material is vaporized in the presence of Ar or N2, because a highly absorbing breakdown plasma develops in this case, as soon as the surface vaporization threshold is reached, shielding the target from subsequent laser heating. These results corroborate our previous analysis based on the spectroscopic observation of the plasma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350494
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  • 4
    Electronic Resource
    Electronic Resource
    Study of initial dust formation in an Ar-SiH4 discharge by laser induced particle explosive evaporation (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 148-153 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The initial step of particulate growth in a dust forming low pressure radio-frequency discharge has been studied in situ by laser induced particle explosive evaporation (LIPEE). With respect to the conventional light scattering, this method has been found much more efficient to observe small nanometer size particles, especially in the case of UV excimer laser radiation. Experimental results interpreted by a simple model of laser-particle interaction show that the intensity of LIPEE continuum emission depends on the particle radius roughly as r4. This interaction is essentially different from Rayleigh scattering, as the latter varies as r6. A study of time evolution of powder formation by LIPEE emission reveals the initial formation of nanometer size crystallites and the coalescence process leading to larger scale particles. It could be demonstrated that the critical step of dust formation is the initial clustering process leading to nanometer scale crystallites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357120
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  • 5
    Electronic Resource
    Electronic Resource
    Direct carbide synthesis by multipulse excimer laser treatment of Ti samples in ambient CH4 gas at superatmospheric pressure (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5286-5294 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Successful carbidation of Ti in a layer forming on the surface of a Ti sample submitted to multipulse excimer (λ=308 nm) laser treatment in CH4 at a slightly superatmospheric pressure is reported. The layer is only surface contaminated with oxygen while its main part consists of fcc TiC. The layer apparently ends with a tail of carbides with low C content, extending deeper into the sample's bulk. The characteristics of the synthesized layer are suggested to be related to the peculiarities of the chemical synthesis which are enhanced by gas propulsion into a melted layer under the recoil action of a plasma evolving in front of the sample. A cavitation mechanism inside the melted surface layer in order to account for plasma initiation is proposed. This mechanism also facilitates the strong substance propulsion into the sample's bulk.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355729
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  • 6
    Electronic Resource
    Electronic Resource
    Deposition of high quality TiN films by excimer laser ablation in reactive gas (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 5781-5789 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new laser method is proposed for the deposition of high purity, hard fcc TiN layers of unlimited thickness. The film thickness can be very finely controlled mainly through the intermediary of the number of applied laser pulses as the deposition rate is of only 0.02–0.05 nm/pulse. The ablation is promoted from a Ti target by high intensity multipulse excimer laser irradiation in a low pressure N2 ambient gas while the forming compound is collected on a Si single-crystalline wafer. The best results have been obtained for an ambient pressure of p=10–30 mTorr and a distance between the target and support of d=10 mm. It is shown that the formation of a liquid phase within the irradiated zone, maintained even after the end of a laser pulse, is the most important requisite for TiN formation. TiN is then ablated as a stoichio- metric phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354198
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  • 7
    Electronic Resource
    Electronic Resource
    Spinal cord injury-induced lesional expression of the repulsive guidance molecule (RGM) (2005)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 21 (2005), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The repulsive guidance molecule (RGM) is involved in the formation of the central nervous system (CNS) during development by modulating guidance of growing axons. However, a role of RGM in CNS injury remains to be established. We studied the expression of RGM in the spinal cord of rats with spinal cord injury (SCI). After SCI, RGM+ cells accumulated in lesions and peri-lesional areas. During the first days after SCI, RGM expression was confined to neurons, ballooned neurite fibers/retraction bulbs, smooth muscle/endothelial cells, and to leucocytes infiltrating the lesion. Lesional RGM expression was frequently confined to hypertrophic β-APP+ and RhoA+ neurites/retraction bulbs. With maturation of the lesion, we observed RGM expression by components of the developing scar tissue (cicatrix), such as fibroblastoid cells, reactive astrocytes and in addition a pronounced extracellular RGM deposition resembling neo-laminae. Frequent RGM+, RhoA+ coexpression by lesional retraction bulbs represent first preliminary evidence of RGM to exert growth inhibitory effects by the second messenger system RhoA. To date, RGM is one of the most potent axonal growth inhibitors identified and present in axonal growth impediments (i) oligodendrocytes; (ii) the plexus choroideus and (iii) components of the developing scar.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-9568.2005.03962.x
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  • 8
    Electronic Resource
    Electronic Resource
    Partial purification of the rat erythrocyte receptor for the channel-forming toxin aerolysin and reconstitution into planar lipid bilayers (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 14 (1994), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The cytolytic toxin aerolysin binds to a receptor on the surface of eukaryotic cells. Murine erythrocytes are among the most sensitive to the toxin. Here we describe the detergent solubilization and partial purification of the receptor from rat erythrocytes. We show that it can be successfully incorporated into planar lipid bilayers, greatly decreasing the concentration of aerolysin required to form channels. Exploiting the ability of the receptor to bind aerolysin after SDS electrophoresis and blotting, we obtain evidence that it is a 47 kDa glycoprotein that is sensitive to proteases and N-glycosidase. It may correspond to CHIP28, the water channel of the human erythrocyte.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1994.tb01341.x
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  • 9
    Electronic Resource
    Electronic Resource
    Cell-type specific response of peripheral blood lymphocytes to methotrexate in the treatment of rheumatoid arthritis (1994)
    Springer
    Journal of molecular medicine 72 (1994), S. 535-540 
    Details
    ISSN: 1432-1440
    Keywords: Lymphocyte subsets ; Disease-modifying antirheumatic drugs ; Flow cytometry ; Immunosuppression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The mode of action of methotrexate in the treatment of rheumatoid arthritis is still questionable. Although in vitro results suggest an immunosuppressive effect of methotrexate, several clinical studies have failed to confirm these effects in patients treated with oral low-dose methotrexate. With respect to the highly variable bioavailability of methotrexate, we investigated the effects of an intravenous administration of 15 mg methotrexate per week on peripheral blood lymphocyte subsets in eight patients with rheumatoid arthritis. Methotrexate after 12 weeks significantly (P〈0.01) reduced total peripheral blood lymphocytes and led to a pronounced redistribution of lymphocyte subsets with a preferred reductive effect on B-lymphocytes (P〈0.005) and T-lymphocytes (P〈0.05). Natural killer cells and killer cell-like T cells, on the other hand, were unaffected by the treatment. Our results suggest a cell-type specific effect of intravenously administered low-dose methotrexate on peripheral blood lymphocytes. This effect, in our opinion, may contribute to the mode of action of methotrexate as an immunosuppressive drug in the treatment of rheumatoid arthritis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00207484
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  • 10
    Electronic Resource
    Electronic Resource
    Spectroscopic observation of the plasma produced by a CO2 laser beam interacting with titanium target under helium and/or argon atmosphere (1992)
    Springer
    Applied physics 55 (1992), S. 340-346 
    Details
    ISSN: 1432-0630
    Keywords: 52.50.Jm ; 52.70.Kz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract In many laser applications such as drilling, welding and cutting, the role of the plasma in the transfer of energy between the laser beam and the metal surface appears to be rather important. It depends on several parameters such as laser wavelength, irradiation time and deposited energy but especially on the buffer gas nature. In this work the plasma is initiated by a TEA-CO2 laser beam perpendicularly focussed onto a Ti target (100 MW/cm2), in a cell containing He, Ar or a He-Ar mixture as buffer gas. The plasma is studied by time and space resolved spectroscopic diagnostics. The results show that helium allows target erosion whereas a highly absorbing breakdown plasma develops in argon shielding the target from the subsequent laser heating. With only 20% Ar in He, a strong quenching of the He plasma by Ar occurs, and the Ar plasma effect is dominant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00324082
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