Search Results - (Author, Cooperation:G. Fuchs)

2011-10-11

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Biocatalysis ; Catalytic Domain ; Crystallography, X-Ray ; Dihydroxyacetone Phosphate/metabolism ; Fructose-Bisphosphate Aldolase/*chemistry/*metabolism ; Fructosediphosphates/metabolism ; Fructosephosphates/metabolism ; Glyceraldehyde 3-Phosphate/metabolism ; Magnesium/metabolism ; Models, Molecular ; Phosphoric Monoester Hydrolases/*chemistry/*metabolism ; Protein Conformation ; Schiff Bases/chemistry ; Temperature ; Thermoproteus/*enzymology

2012-03-09

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Biocatalysis ; Epoxy Compounds/chemistry/*metabolism/*toxicity ; Iron/metabolism ; Molecular Sequence Data ; Multienzyme Complexes/chemistry/genetics/metabolism ; Oxygen/*chemistry/*metabolism ; Oxygenases/chemistry/genetics/*metabolism ; Phenylacetates/metabolism ; Pseudomonas/*enzymology/genetics ; Thiolester Hydrolases/metabolism

1089-7550

AIP Digital Archive

Physics

Au islands deposited on Al2O3 films were irradiated with a pulsed laser beam. The result is the formation of depleted zones and chains of aggregates at the edge of the irradiated area. The fractal analysis of these Au cluster chains formed after irradiation gives a dimension of 1.50–1.55 consistent with the process of cluster-cluster aggregation which occurs under diffusion limited conditions.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Quantum-well lasers can achieve a low spectral linewidth because of their high differential gain, leading to a lower linewidth enhancement factor α than for bulk lasers. The differential refractive index and the gain of InGaAs separate confinement multi-quantum-well lasers with two different quaternary barrier layers, have been determined from the spontaneous emission spectra below threshold. The measured value of the α factor is about 2.8 up to 3.5 at the gain maximum for both laser structures. The refractive index and the gain spectra are connected via the Kramers–Kronig relation. Therefore, the differential refractive index and the α factor have been deduced from calculated gain spectra with an additional contribution of the intraband transitions of the free carriers.

Electronic Resource

1089-7674

AIP Digital Archive

Physics

An overview is given of recent advances toward the realization of high density, high confinement plasmas with radiating mantles in limiter and divertor tokamaks worldwide. Radiatively improved mode discharges on the Torus Experiment for Technology Oriented Research 94 (TEXTOR-94) [Proceedings of the 16th IEEE Symposium on Fusion Engineering, 1995 (Institute for Electrical and Electronics Engineers, Piscataway, NJ, 1995), p. 470] have recently been obtained at trans-Greenwald densities (up to n¯/nGW=1.4) with high confinement mode free of edge localized modes (ELM-free H-mode) confinement quality. Experiments in DIII-D [J. Luxon et al., Proceedings of the 11th IAEA Conference on Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Association, Vienna, 1987), Vol. 1, p. 159] divertor plasmas with a low confinement mode edge have confirmed the dramatic changes in confinement observed with impurity seeding on TEXTOR-94. Recent experiment with impurity seeding on the Joint European Torus [Rebut et al., Fusion Eng. Des. 22, 7 (1993)], and the Japanese Atomic Energy Research Institute Tokamak 60 Upgrade [Horiike et al., Fusion Eng. Des. 16, 285 (1991); Hosogane et al., Proceedings of the 16th IAEA Conference on Plasma Physics and Controlled Nuclear Fusion Research Montreal, 1987 (International Atomic Energy Association, Vienna, 1987), Vol. 3, p. 555] have extended high confinement in ELMy H-mode plasmas to higher densities. Finally, recent progress in the physical understanding of radiating mantle plasmas is summarized. © 2001 American Institute of Physics.

Electronic Resource

1089-7674

AIP Digital Archive

Physics

An overview of the results obtained so far for the radiative I-mode regime on the upgraded Torus Experiment for Technology Oriented Research (TEXTOR-94) [Proceedings of the 16th IEEE Symposium on Fusion Engineering (Institute of Electrical and Electronics Engineers, Piscataway, NJ, 1995), Vol. 1, p. 470] is given. This regime is obtained under quasistationary conditions with edge neon seeding in a pumped limiter tokamak with circular cross section. It combines high confinement and high β (up to a normalized beta, βn=2) with low edge q values (down to qa=2.8) and high density even above the Greenwald limit together with dominant edge radiative heat exhaust, and therefore shows promise for the future of fusion research. Bulk and edge properties of these discharges are described, and a detailed account is given of the energy and particle confinement and their scaling. Energy confinement scales linearly with density as for the nonsaturated Ohmic Neo-Alcator scaling, but the usual degradation with total power remains. No deleterious effects of the neon seeding on fusion reactivity and plasma stability have been observed. © 1997 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Single crystals of lithium niobate (LiNbO3) with y-cut orientation were irradiated at GANIL with 5.17 MeV/amu 155Gd ions at a fluence ranging from 1.5×1011 to 6.0×1011 ions cm−2. After irradiation the samples were implanted with europium ions of 70 keV energy at a fixed fluence of 5×1016 ions cm−2. Both irradiations and implantations were performed at room temperature. Thermal treatments in air, in the range 300–1100 °C, were applied to investigate the influence of the preirradiation damage on the thermal evolution of Eu implanted LiNbO3 crystals. Transmission electron microscopy micrographs exhibit the amorphous track formed by high-energy irradiations. Rutherford backscattering spectrometry results show that these amorphous tracks enhance the europium diffusion in depth of the LiNbO3. A diffusion coefficient and an activation energy were estimated to be about 4.2×10−15 cm2 s−1 and 0.42 eV, respectively. © 1995 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We report on nonlinear optical absorption in InGaAs/InGaAsP separate confinement multiple-quantum-well (SCMQW) structures based on charge-carrier induced band bending. Carrier induced localization and related changes in absorption strength due to spatial separation of electrons and holes are utilized to design SCMQW structures with a new type of optical nonlinearity. Experimentally, we observe strong changes in optical absorption with increasing excitation power. Compared to exciton bleaching, the new nonlinearity dominates at low carrier densities.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Ag-sheathed powder-in-tube wires on the basis of the high Tc superconductor YBa2Cu3Ox are produced by a drawing process. After cold working, the wires are not superconducting. By heat treatment at temperatures 〉900 °C, lattice defects are healed and the contact between the grains is improved. After this heat treatment the wires are slowly cooled in an O2 atmosphere in order to adjust the optimum O2 stoichiometry. The annealing temperature has a strong influence on the attainable critical current density. By annealing a wire with 420 ppm carbon content at 950 °C, jc values of 5020 A/cm2 at 4.2 K and 1130 A/cm2 at 77 K were achieved. Drastically reduced critical current densities in wires with high carbon content demonstrate the importance of a low carbon content for achieving high critical current densities in YBa2Cu3Ox .

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report the determination of Auger recombination coefficients in bulk and quantum well InGaAs by time-resolved luminescence measurements. In bulk InGaAs the coefficient is C=3.2×10−28 cm6/s and has the temperature dependence of the valence-band Auger effect involving the split-off valence band. In 11 nm quantum well InGaAs we find C=0.9×10−28 cm6/s, independent of temperature. The Auger coefficient decreases slightly with decreasing well width.

Electronic Resource

1468-2494

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

The penetration of chemical reagents through human hair after bleaching has been spatially characterized using infrared microspectroscopy (IMS) with a synchrotron source. Chemical imaging of hair cross sections before and after bleaching was achieved with high contrast, using the peptide and lipid mid-infrared vibrational bands which are characteristic of hair. The ability to make images using functional groups as a contrast mechanism can be applied to studies of other chemical groups, if present, in the structure of the hair. As an example we show how the penetration of an organic active reagent in the hair structure can be quantified with a spatial resolution of few microns.These results demonstrate that synchrotron IMS is a powerful tool for characterizing chemical interactions of hair samples with specific cosmetic materials.〈section xml:id="abs1-2"〉〈title type="main"〉RésuméLa pénétration d'une molécule organique à l'intérieur de cheveux décolorés a été spatialement caractérisée par microspectroscopie infrarouge en utilisant une source de rayonnement synchrotron. Les images en contraste chimique de coupes microtomiques transversales de cheveux ont été obtenues avec un excellent contraste, en utilisant les bandes infrarouges des groupements peptides et lipidiques qui sont caractéristiques de sa structure. La possibilité d'obtenir des images en utilisant les différents groupements fonctionnels présents dans les spectres infrarouges permet d'étudier la répartition d'autres molécules chimiques si elles sont présentes en concentration suffisante dans la structure du cheveu. Cette caractéristique a été utilisée ici pour étudier la pénétration d'une molécule organique à travers la structure du cheveu avec une résolution latérale de quelques microns. Ces résultats démontrent la faisabilité de la microspectroscopie infrarouge par rayonnement synchrotron pour étudier spatialement les interactions entre le cheveu et des produits cosmétiques.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have determined the differential gain, nonlinear gain factor, spontaneous emission factor, and the K factor for InGaAs separate confinement multiquantum well lasers with InGaAsP and InGaAlAs barriers using a new parasitic-free modulation technique. We find that the nonlinear gain factor ε is more than four times, and the K factor more than two times lower for lasers with InGaAlAs barriers than for those with InGaAsP barriers. This strongly suggests that InGaAs/InGaAlAs lasers are more suitable for high bandwidth applications.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The crucial problem in controlling and filtering the size of free neutral clusters generated by a cluster source is studied in the particular case of the Sattler source type. The present work shows that a velocity selector can be used to control the size of neutral clusters produced in the low-energy cluster beam deposition system. This velocity selector is also used to measure the kinetic energy of free Bi clusters. The experimental results obtained for Bi clusters are compared with previous theoretical predictions.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report the determination of the Auger recombination coefficient in strained and unstrained InGaAs/InGaAsP/InP separate-confinement multiple quantum-well laser structures. For a temperature of 300 K and a well width of 100 A(ring), we find an Auger coefficient of C=1.0×10−28 cm6 s−1, independent of strain and only weakly dependent on temperature. These properties of the Auger coefficient indicate the dominance of phonon-assisted Auger recombination. Our model calculations based on a six-band kp theory explain the experimentally found dependency on temperature and strain. The consequences on laser performance are discussed.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We present a model for quantum-well lasers which for the first time provides an explanation for the increased damping of the relaxation resonance observed in these lasers. Slow transport of holes between the individual wells is shown to lead to a strongly inhomogeneous carrier distribution and to increased damping as well as to RC-like contributions to the modulation response. The model quantitatively explains the differences observed between lasers of varying structure and lasers made from different material systems.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report the direct determination of absorption losses in unstrained InGaAs/InGaAsP and InGaAs/InGaAlAs and strained InGaAs/InGaAsP layer multiple quantum well (MQW) laser structures. In the case of the unstrained structures we find a strong dependence of the absorption on carrier density indicating the presence of an intrinsic optical loss mechanism, the intervalence band absorption (IVBA). In the strained layer InGaAs/InGaAsP structures, IVBA is completely switched off. Our results explain the superiority of strained layer InGaAs MQW lasers.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Bulk melt textured YBa2Cu3O7−δ samples with single grains of about 24 mm diameter were obtained by use of SmBa2Cu3O7−x seed crystals. The maximum trapped field B0 in the gap between two samples was investigated as function of temperature. B0 increased from 1 T at 77 K to 8.5 T at 51.5 K, which is the highest trapped field achieved in nonirradiated samples. At low temperatures, cracking of the samples was observed under magnetic pressure. In this temperature range, the trapped field is limited by the mechanical strength of the samples, for which a value of 25 MPa was estimated. © 1997 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

High-quality binary (Nd0.33Sm0.67)Ba2Cu3O7−δ monodomain superconductors were fabricated by the combination of a compositional-controlled melt-processing technique in air and postannealing in Ar. Critical current densities over the whole field range were observed strongly dependent on Ar postannealing while holding superconducting transition temperatures as high as 96 K. The suppressed chemical variation between the rare-earth element (RE: Nd, Sm) and Ba associated with disperse RE2BaCuOy (RE211) precipitate due to the decomposition occurring in Ar postannealing was attributed to the modified flux pinning. This makes Ar postannealing promising to process superconductors with desired properties for various applications. © 1999 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

High density nanocrystalline MgB2 bulk superconductors with distinctly improved pinning were prepared by mechanical alloying of Mg and B powders at ambient temperatures followed by hot pressing. The nanocrystalline samples reveal high jc=105 A/cm2 at 20 K and 1 T together with an irreversibility line strongly shifted towards higher fields resulting in Hirr(T)∼0.8 Hc2(T), whereas typically Hirr(T)∼0.5 Hc2(T) is observed for untextured bulk samples. These values exceed those of all other reported bulk samples and are in the range of values for thin films. The improved pinning of this material, which mainly consists of spherical grains about 40–100 nm in size, is attributed to the large number of grain boundaries in the nanocrystalline state. © 2002 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Improved trapped fields are reported for bulk melt-textured YBa2Cu3O7−δ (YBCO) material in the temperature range between 20 and 50 K. Trapped fields up to 12.2 T were obtained at 22 K on the surface of single YBCO disks (with Ag and Zn additions). In YBCO minimagnets, maximum trapped fields of 16 T (at 24 K) and of 11,2 T (at 47 K) were achieved using (Zn+Ag) and Zn additions, respectively. In all cases, the YBCO disks were encapsulated in steel tubes in order to reinforce the material against the large tensile stress acting during the magnetizing process and to avoid cracking. We observed cracking not only during the magnetizing process, but also as a consequence of flux jumps due to thermomagnetic instabilities in the temperature range betweeen 20 and 30 K. © 2001 American Institute of Physics.

Electronic Resource