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  • 1
    Electronic Resource
    Electronic Resource
    Periplasmic superoxide dismutases in Aquaspirillum magnetotacticum (1989)
    Springer
    Archives of microbiology 152 (1989), S. 342-346 
    Details
    ISSN: 1432-072X
    Keywords: Magnetic bacteria ; Periplasm ; Superoxide dismutase ; Peroxidase ; Microaerophiles ; O2 toxicity ; Aquaspirillum magnetotacticum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Aquaspirillum magnetotacticum MS-1 cells cultured microaerobically (dissolved O2 tension 1% of saturation), expressed proteins with superoxide dismutase (SOD) activity. The majority (roughly 95%) of total cell superoxide dismutase activity was located in the cell periplasm with little or no activity in the cell cytoplasm. Irontype SOD (FeSOD) contributed 88% of the total activity activity detected, although a manganese-type SOD (MnSOD) was present in the periplasm as well. Cells cultured at a higher dissolved O2 tension (10% of saturation) expressed increased activity of the MnSOD relative to that of the FeSOD.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00425171
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  • 2
    Electronic Resource
    Electronic Resource
    Polyakov string in variable dimensions (1991)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 32 (1991), S. 266-279 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A nonperturbative approach to Polyakov string theory in variable dimensions will be developed. The result leads to a reinterpretation of the critical dimension and an effective compactification of the theory. At each stage the variable dimension theory is based on Gaussian measures, so a discussion of Gaussian measures in linear topological vector spaces is included, detailing the sets of measure zero that arise when the inner product is degenerate. The dimension can be taken to ∞ and the limiting sum exists. The limit represents a correction to [Det Δ]−1/2, which arises as a naive limit. The analysis involves an interplay between zero modes and sets of measure zero with respect to the Gaussian measures. Target space isometries require the factoring out of equivalent configurations from the path integral, which necessitates a discussion of functional Haar measures. The inclusion of source terms is considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529130
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  • 3
    Electronic Resource
    Electronic Resource
    Implantation tailoring of electrically active dopant profiles in GaAs (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 1206-1210 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A common problem with fabricating n-type layers in semi-insulating GaAs by ion implantation is the variation in the net activation efficiency on the substrate side of the implanted dopant profile. We compare two methods for modifying these doping profile tails in order to achieve uniform activation properties of implanted layers over large wafer areas. The two methods are compensation of an n-type doping profile by a buried damage layer (oxygen or helium implants) or by coimplantation of an acceptor species (beryllium). Experimental results are shown both for n-only and n+-n profile modifications. The use of Be to form a buried p-type layer has several advantages over the damage-induced compensation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341886
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  • 4
    Electronic Resource
    Electronic Resource
    Ion implantation damage and annealing in InAs, GaSb, and GaP (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 629-636 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The characteristics of ion implantation induced damage in InAs, GaSb, and GaP, and its removal by rapid thermal annealing have been investigated by Rutherford backscattering and transmission electron microscopy. There is relatively poor regrowth of these materials if they were amorphized during the implantation, leaving significant densities of dislocation loops, microtwins, and in the case of GaSb, polycrystalline material. For implant doses below the amorphization threshold, rapid annealing produces good recovery of the lattice disorder, with backscattering yields similar to unimplanted material. The redistribution of the implanted acceptor Mg is quite marked in all three semiconductors, whereas the donor Si shows no measurable motion after annealing of InAs or GaP. In GaSb, however, where it appears to predominantly occupy the group III site, it shows redistribution similar to that of Mg.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341952
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  • 5
    Electronic Resource
    Electronic Resource
    Ion beam thinning and polishing of YBa2Cu3O7 films (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 1915-1917 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Successive ion beam milling at grazing angles of a 2400-A(ring)-thick, c-axis-oriented YBa2Cu3O7 film is shown to give smooth films which superconduct at thicknesses on the order of tens of angstroms. The thinning and polishing process is characterized at successive milling stages using resistance transitions, x-ray analysis, scanning electron microscopy, and Rutherford backscattering and channeling analysis of composition and surface quality. As thinning proceeds, scanning electron microscopy and diffraction features associated with a-axis texture are removed and crystalline quality, as measured by x rays and channeling, markedly improves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102331
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  • 6
    Electronic Resource
    Electronic Resource
    Electrical and structural properties of Si/CrSi2/Si heterostructures fabricated using ion implantation (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 1260-1262 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using high dose implantation of Cr+ into (111)-oriented Si, followed by annealing, we have created continuous, buried layers of CrSi2 in Si. The layers are stoichiometric and epitaxially aligned along one of the substrate 〈111〉 directions. Results of temperature-dependent resistivity and Hall measurements on the early layers show that they are p-type degenerate semiconductors consistent with data for bulk samples. More recent layers appear to be single crystal with [0001] parallel to [111] and are n type with lower carrier density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103334
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  • 7
    Electronic Resource
    Electronic Resource
    The Impact of Storage of Soils during Opencast Mining on the Microbial Community: A Strategist Theory Interpretation (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 1 (1993), S. 0 
    Details
    ISSN: 1526-100X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The microbial community in a soil stripped and stored during opencast coal mining was analyzed. There were significant effects of soil disturbance on the microbial community: in particular, there were large decreases in the total microbial biomass, as determined by ATP analysis, and numbers of fungal propagules as a result of the store construction process, but there was no significant effect on the numbers of bacteria. During the subsequent months of storage there was a flush in the numbers of bacteria, with gram-negative bacteria showing an increase of nearly 700% in comparison to the control. During this time there was a steady accumulation in the amount of ammonium in the deepest part of the soil store, indicating the onset of anaerobiosis. These changes may be interpreted in terms of lifestyle strategy theory (Grime 1979). The bacteria exhibit behavior typical of R-strategists, or ruderal species, taking advantage of the nutrients made available by the death of fungal biomass during store construction. Fungi respond as C-strategists, or competitors, and they are severely affected by store construction-and unable to persist deep in the anaerobic part of the store. In contrast, anaerobes, S-strategists or stresstolerators, are able to survive under the same conditions. These changes have serious implications for the restoration of systems using stored topsoil as a resource. The microbial population has been altered in terms of its size and composition. Many of the fungi required for adequate breakdown and incorporation of organic matter will be absent, and the soils will be generally poor in microbial biomass. This will lead to inadequate nutrient cycling and poor soil structural stability, two factors essential for the restoration of a self-sustaining ecosystem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1526-100X.1993.tb00014.x
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  • 8
    Electronic Resource
    Electronic Resource
    Formation of continuous CoSi2 layers by high Co dose implantation into Si(100) (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 1629-1634 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the mechanisms for formation of continuous CoSi2 layers by high dose (∼1017 cm−2) Co implantation into Si(100). For single dose implantations, a critical dose exists above which coalescence into a single layer occurs after a vacuum anneal at 1000 °C for 30 min, but below which disconnected, strongly {111} faceted precipitates form. Transmission electron microscopy and Rutherford backscattering suggest that the key condition for continuous layer coalescence to occur is the formation of a connected array of small silicide precipitates either as-implanted or during an intermediate 600 °C anneal. This postulate is supported by the observation that super-critical doses which are builtup by successive subcritical doses and 1000 °C anneals do not coalesce into single layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346643
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  • 9
    Electronic Resource
    Electronic Resource
    Reactive ion etching of GaAs with CCl2F2:O2: Etch rates, surface chemistry, and residual damage (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1281-1292 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The reactive ion etching of GaAs with a CCl2F2:O2 discharge was investigated as a function of gas flow rate (10–60 sccm), total pressure (2–50 mTorr), power density (0.25–1.31 W cm−2), gas composition (0%–70% O2), and etch time (1–64 min). The etch rate decreases with increasing gas flow rate, increases with increasing power density, and goes through a maximum at a gas composition of 75:25 CCl2F2:O2 under our conditions. After etching at low-power densities (0.56 W cm−2) and for high CCl2F2 ratios (19:1 to O2), carbon and chlorine could be detected in the GaAs to a depth of less than 15 A(ring) by x-ray photoelectron spectroscopy. Under these conditions there was a Ga deficiency to a depth of ∼100 A(ring), which we ascribe to surface roughening and the preferential vaporization of As2O3 over Ga2O3. At high-power densities (1.31 W cm−2) a polymeric layer several hundred angstroms thick containing CCl and CF bonds was observed on the GaAs surface. Etching under O2-rich conditions did not lead to any additional creation of surface oxides. Both ion channeling and electron microscopy detected a thin disordered layer on the GaAs after etching. Small (〈100 A(ring) diam) dislocation loops were present at a depth varying from ∼400 A(ring) for 0.56 W cm−2 (380-V self-bias) plasma power density to ∼2200 A(ring) for 1.31 W cm−2 (680-V self-bias). The disorder was stable against a 500 °C annealing treatment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343023
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  • 10
    Electronic Resource
    Electronic Resource
    Characterization of InP/GaAs/Si structures grown by atmospheric pressure metalorganic chemical vapor deposition (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1083-1088 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thickness dependence of material quality of InP-GaAs-Si structures grown by atmospheric pressure metalorganic chemical vapor deposition was investigated. The InP thickness was varied from 1–4 μm, and that of the GaAs from 0.1–4 μm. For a given thickness of InP, its ion channeling yield and x-ray peak width were essentially independent of the GaAs layer thickness. The InP x-ray peak widths were typically 400–440 arcsec for 4-μm-thick layers grown on GaAs. The GaAs x-ray widths in turn varied from 320–1000 arcsec for layer thicknesses from 0.1–4 μm. Cross-sectional transmission electron microscopy showed high defect densities at both the InP-GaAs and GaAs-Si interfaces. In 4-μm-thick InP layers the average threading dislocation density was in the range (3–8)×108 cm−2 with a stacking fault density within the range (0.4–2)×108 cm2. The He+ ion channeling yield near the InP surface was similar to that of bulk InP (χmin∼4%), but rose rapidly toward the InP-GaAs heterointerface where it was typically around 50% for 1-μm-thick InP layers. All samples showed room-temperature luminescence, while at 4.4 K, exciton-related transitions, whose intensity was a function of the InP thickness, were observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343043
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