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  • 1995-1999  (84)
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  • 1
    Electronic Resource
    Electronic Resource
    Coal mine workers' pneumoconiosis (1997)
    Springer
    Environmental geology 30 (1997), S. 72-80 
    Details
    ISSN: 1432-0495
    Keywords: Key words Coal mine workers' pneumoconiosis ; Coalification ; Macerals ; Organic compounds ; Phenols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The fibrogenic and cytotoxic potential of coal mine dust is independent of the amount of quartz and other inorganic parameters. Results of coal petrographical and organic geochemical investigations of coals and coal mine dust from the Ruhr and Ibbenbüren Region of Germany demonstrate variations of organic dust amount possibly influencing these noxious properties. Coal mine dust of high rank coals is characterized by a pronounced fibrogenic risk. This risk, independent of the quantity of quartz, is probably based on shape variations of different coal macerals. With increasing coalification of the corresponding seam, the vitrinite is enriched in its dust; however, lower concentrations have been determined for inertinite. Vitrinite shows constant shapes and sizes independent of the rank of coal. Inertinite particles with elongated to fibrous shapes tend to larger sizes with increasing coalification. Strikingly, coal mine dust from miners' lungs with high degrees of coal mine workers' pneumoconiosis (CWP) is enriched in inertinite. In contrast, high cytotoxicities in cell tests are known for coal mine dust from low coalified coals. High concentrations of phenolic compounds can be extracted by dichloromethane from low coalified coal mine dust. These compounds, which are characterized by a high water solubility and therefore high bioavailability, explain the high cytotoxicities of coal mine dust. Contamination of dust by diesel emissions in the coal mine can act as additionally supporting parameters for extended cytotoxicities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002540050134
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  • 2
    Electronic Resource
    Electronic Resource
    UV photostimulated desorption of ammonia from Cu(111) (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3414-3430 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Upon irradiation with 193 and 308 nm laser light photoinduced desorption of ammonia from Cu(111) was studied at three coverages less than one monolayer (ML). The linear power dependence of the desorption yield and angle-resolved translational energy distributions of desorbed molecules indicate that desorption occurs due to an electronic excitation rather than a thermal process. Polarization measurements indicate an excitation process which is mediated by hot substrate electrons. The isotope effect, i.e., the ratio of the cross sections for photostimulated desorption (at 193 nm) of NH3 and ND3, respectively, decreases from 4.1 ± 1.2 to 1.9 ± 0.5 when the coverage—with respect to the substrate atom density—was raised from ≈0.02 to ≈0.14 ML. The magnitude of this isotope effect suggests that the energy which is required to break the molecule–surface bond is acquired in an intramolecular coordinate during a short-lived electronic excitation. We propose that for high vibrational excitation on the ground-state potential energy surface (PES), efficient coupling of the inversion mode with the molecule–surface coordinate leads to desorption. In order to illustrate the suggested desorption mechanism at a semiquantitative level, we performed trajectory calculations on a two-dimensional model potential energy surface. The results predict that desorption occurs rapidly within a few vibrational periods of the umbrella mode (Tvib∼35 fs)—with comparable energy release into the translational and vibrational degrees of freedom. Ammonia is furthermore expected to desorb in an inverted geometry, i.e., with the hydrogen atoms pointing towards the surface as opposed to the adsorption geometry with the nitrogen end bound to the surface. Angular distributions of flux and mean translational energy are strongly peaked around the surface normal. Their width can be attributed to thermal motions parallel to the surface prior to excitation. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469215
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  • 3
    Electronic Resource
    Electronic Resource
    Electronic states of the C6H6/Cu{111} system: Energetics, femtosecond dynamics, and adsorption morphology (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 9155-9165 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two-photon-photoemission (2PPE) spectroscopy is employed to characterize electronic states of a bilayer C6H6/Cu{111} system at 85 K. The unoccupied benzene π* e2u state is observed with a binding energy of 4.6 eV above the Fermi level. This result agrees with inverse-photoemission (IPE) data and provides a case where the determination of the binding energy is identical for 2PPE and IPE. The π* e2u state is assigned in the 2PPE scheme as a final state which is the first observed final state in 2PPE of adsorbate-surface systems. The dependence of the electron dynamics on the morphology of an incomplete adsorption layer is also investigated. Two (n=1)-like image potential states A and B are observed which presumably originate from two different C6H6 adsorption geometries in the bilayer regime. The two image states A and B are characterized by electron effective masses of 1.1 and 1.9 me, binding energies of 3.30 and 3.45 eV above the Fermi level, and lifetimes of 40 and 20 fs, respectively. The dielectric continuum model and the Kronig–Penney model are employed to simulate the origin of (n=1)-like image states. The work function decreases from 4.9 eV at clean Cu{111} to 4.0 eV at bilayer coverage. The change of the work function and the observation of two image states suggest the redefining of the ratio of the numbers of benzene molecules in the first and the second layers of the bilayer regime to approximately 1:1 instead of 1:2, as previously reported. 2PPE is shown to be sensitive to the changes of morphologies, local work functions, and adsorbate-surface potentials during the layer formation. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477468
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of the negative thermal-expansion coefficient on the luminescence properties of (CdMnMg)Te (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 8704-8711 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In zinc-blende II–VI alloys the thermal-expansion coefficient for low temperatures is negative and becomes positive at higher temperatures. We investigated the luminescence properties of molecular-beam-epitaxy-grown (CdMnMg)Te layers in the temperature range from 2 up to 200 K and show that the anomalous temperature dependence of the lattice constant is reflected in the luminescence properties of the excitonic recombination and the internal transition of manganese (ITM). The temperature behavior of the ITM energy is nonmonotonic and the existence of a minimum in the photon energy (at the temperature TMn) can be correlated to the change of sign of the thermal-expansion coefficient. The decay constants of the ITM begins to decrease drastically at TMn, too. Considering a lattice constant dependent energy transfer rate to the infrared emitting state (1.2 eV) of the manganese ion the variation of the lifetimes can also be explained by the temperature dependence of the lattice constant. Furthermore, we have measured the ITM in bulk layers and observed a different dependence of the ITM properties on the temperature, demonstrating the influence of the growing conditions on the microscopic surrounding of the manganese ions. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362496
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  • 5
    Electronic Resource
    Electronic Resource
    Low-field magnetoresistance of La0.7Sr0.3MnO3 thin films with gradually changed texture (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 2218-2220 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A gradual change of the grain orientation with the substrate temperature (TS) during deposition has been observed for La0.7Sr0.3MnO3 films on Y-stabilized ZrO2(100) substrates. Epitaxial growth has been found around TS(approximate)800 °C. Both the low-field and the high-field magnetoresistance (MR) observed for the ferromagnetic state of these polycrystalline colossal MR manganite films were found to systematically depend on the degree of texture. The experimental results suggest a crucial role of a highly resistive region at the grain boundaries for this MR effect. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123806
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  • 6
    Electronic Resource
    Electronic Resource
    Solar cell efficiency and carrier multiplication in Si1−xGex alloys (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 4213-4221 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Crystalline Si1−xGex compounds offer the possibility for tuning the electronic energy band structure with the chemical composition of the alloy in order to adapt the material for devices utilizing the energy of solar photons at an optimum. We concentrate on the efficiency enhancement due to carrier multiplication by impact ionization. We calculate the internal quantum efficiency and the possible solar cell efficiency for this material system. The number of impact-generated charge carriers is obtained by a simulation of the competing carrier–carrier and carrier–photon scattering processes. These calculations show that the wave vector dependence of the scattering processes is unimportant for good agreement between theoretical and experimental quantum efficiencies in Si and Ge. Finally, we calculate solar cell efficiencies under the ideal assumption of unity collection efficiency and radiative recombination only. Impact ionization enhances the theoretical conversion efficiency by 0.5 percentage point; this improvement is curtailed by the strong phonon emission probability of hot carriers. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367177
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  • 7
    Electronic Resource
    Electronic Resource
    Magnetic behavior of the low-dimensional compounds Ba2Cu3O4Cl2 and Ba3Cu2O4Cl2 : The 7th joint MMM-intermag conference on magnetism and magnetic materials (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 7240-7242 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Orthorhombic Ba3Cu2O4Cl2 contains folded Cu2O4 chains along the crystallographic a direction with two different Cu sites. In single crystals of this compound the magnetization measured for a field applied parallel to the a axis shows a spin-flop transition at a threshold field of 2.6 T for temperatures below TN(approximate)20 K. Above TN a Curie–Weiss behavior is found with a paramagnetic moment of 2.0 μB per Cu atom. Parallel to the b or c axis the magnetization increases linearly with the field strength, and no metamagnetic transition was detected for these directions. It is concluded that Ba3Cu2O4Cl2 has localized magnetic moments which, at low temperatures, order antiferromagnetically parallel to the a axis. The bulklike magnetic behavior of this compound is probably caused by a strong coupling between the Cu2O4 chains. Tetragonal Ba2Cu3O4Cl2 is built up of Cu3O4 planes, also with two types of copper atoms (CuA,CuB). Its magnetization increases nearly linearly with the field. Below TNA=337 K single-crystalline Ba2Cu3O4Cl2 shows a spontaneous magnetization and ferromagnetic hysteresis for fields applied parallel to the tetragonal [100] or [110] directions. For T〈TNB(approximate)33 K, the coercive field is more than one order of magnitude larger compared to that measured in the temperature range TNB〈T〈TNA. The spontaneous magnetization observed in TNB〈T〈TNA may be attributed to weak ferromagnetism of the Dzyaloshinsky–Moriya type. The behavior of Ba2Cu3O4Cl2 at lower temperatures, T≤TNB, is not yet understood. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367613
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  • 8
    Electronic Resource
    Electronic Resource
    CCD photometry of 6 near-Earth asteroids (1995)
    Springer
    Earth, moon and planets 71 (1995), S. 177-187 
    Details
    ISSN: 1573-0794
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Photometric observations of 11 near-Earth asteroids were made within a regular NEA CCD photometric programme at Ondřejov Observatory in the first half of 1994. This paper shows obtained R lightcurves, V-R, R-I, and B-V color indices, and rotation preriods for 6 of them. Among the presented results, the most interesting are those for (4954) Eric, for which we obtained several high-quality lightcurves and which seems to indicate a surface heterogeneity, (1864) Daedalus, for which interesting comparison with older observations by Gehrelset al. (1971) can be made, and 1993 VW, for which the unusual color characteristics were observed. Two (1994 AW1 and 1994 GY) of the other three observed objects have fast rotations with periods of about 2.5 hours and relatively low amplitudes. Subsequent analysis of additional lightcurve data for 1994 AW1 has revealed a presence of two periods in its lightcurve (Pravecet al. 1995). The last object presented here is 1994 JF1, for which only lower limits on period and amplitude were determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00612955
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  • 9
    Electronic Resource
    Electronic Resource
    Copper speciation in aqueous solutions of fulvic acid and related molecular weight distributions (1999)
    Springer
    Fresenius' journal of analytical chemistry 363 (1999), S. 596-599 
    Details
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Potentiometric and fluorescence measurements of aqueous solutions of fulvic acid containing Cu(NO3)2 or Cu(ClO4)2, respectively, were carried out at 25 °C and pH 5.5 to determine naturally occurring Cu species. The fulvic acid used was isolated by XAD-8 from filtrated (0.3 μm) water of a peat bog in the Dachauer Moos near Munich. From the results an operational molecular weight of fulvic acid of about 750 g/ mol was estimated, which was confirmed by molecular weight distributions determined by high-performance size-exclusion chromatography (HPSEC), gel permeation chromatography (GPC) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Using this molecular weight and assuming that mainly 1:1 Cu-fulvic acid complexes are formed, a conditional stability constant of the Cu-fulvic acid complex of 105.9 could be calculated. These data are essential for the assessment of organic carrier-mediated migration of Cu as well as of the toxicological risk potential of Cu in aqueous environment and can be used as input parameters for geochemical modeling of the Cu species distribution in aqueous solutions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002160051256
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  • 10
    Electronic Resource
    Electronic Resource
    Minimal Surfaces of Least Total Curvature and Moduli Spaces of Plane Polygonal Arcs (1998)
    Springer
    Geometric and functional analysis 8 (1998), S. 1129-1170 
    Details
    ISSN: 1420-8970
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000390050125
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