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  • 1
    Electronic Resource
    Electronic Resource
    Cryogenic preservation of isolated rat Islets of Langerhans: Effect of cooling and warming rates (1979)
    Springer
    Diabetologia 16 (1979), S. 195-199 
    Details
    ISSN: 1432-0428
    Keywords: Cryobiology ; freezing ; low-temperature ; diabetes ; rat ; Islets of Langerhans ; dimethyl sulfoxide (DMSO) ; storage ; survival ; insulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Isolated rat Islets of Langerhans have been frozen to and stored at −196°. After thawing, these islets were capable of secreting near normal levels of insulin in response to graded glucose challenge. Maximal retention of functional viability as measured by the ability of the islets to secrete insulin in response to a glucose challenge was obtained after freezing islets at a cooling rate of approximately 75° per minute in the presence of 1.0 mol/l dimethyl sulfoxol followed by warming at rates of 〉 3.5° /minute. The critical freezing parameters include the time and temperature of exposure to dimethyl sulfoxide, the rate of cooling, the temperature of the post-thaw dilution from the freezing medium and the presence of serum in the dilution medium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01219798
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  • 2
    Electronic Resource
    Electronic Resource
    Biological weighting of ultraviolet (280–400 nm) induced mortality in marine zooplankton and fish. I. Atlantic cod (Gadus morhua) eggs (1999)
    Springer
    Marine biology 134 (1999), S. 269-284 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In the Gulf of St. Lawrence, Canada, productivity-determining biophysical interactions occur in the upper 0 to 30 m of the water column. The eggs and larvae of several commercially important marine invertebrates and fishes (e.g. Gadus morhua L.) are found in this layer. Measurements of the diffuse attenuation coefficients for ultraviolet-B radiation (280 to 320 nm, UV-B) at various locations in this geographic region indicated maximum 10% depths (the depth to which 10% of the surface energy penetrates at a given wavelength) of 3 to 4 m at a wavelength of 310 nm. This represents a significant percentage of the summer mixed-layer water column: organisms residing in this layer are exposed to UV-B radiation. Laboratory experiments using a Xenon-arc-lamp based solar simulator revealed that cod embryos exposed to UV-B exhibited high wavelength-dependent mortality. The strongest effects occurred under exposures to wavelengths below 312 nm. This susceptibility was also dependent upon developmental stage; mortality was particularly high during gastrulation. At the shorter wavelengths (〈305 nm) UV-B-induced mortality was strongly dose-dependent, and not significantly influenced by dose-rate. The biological weighting function (BWF) derived for UV-B-induced mortality in cod eggs is similar to that reported for naked DNA – suggesting that the mortality is a direct result of DNA damage. There was no evidence of a detrimental effect of ultraviolet-A radiation (320 to 400 nm). Calculations based upon the BWF indicate that, under current noon surface irradiance, 50% of cod eggs located at or very near (within 10 cm) the ocean surface will be dead after 42 h of exposure. Under solar spectral irradiance simulating a 20% decrease in ozone layer thickness, this time drops to 32 h. These are first-order estimates based upon surface irradiance taken at a time of day during which the values would be maximal. Nonetheless, they illustrate the relative changes in UV-B impacts that will result from ozone layer depletions expected over the coming decades. It is also important to point out that variability in cloud cover, water quality, and vertical distribution and displacement of cod eggs and larvae within the mixed layer, can all have a greater effect on the flux of UV-B radiation to which fish eggs are exposed than will ozone layer depletion at these latitudes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050545
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  • 3
    Electronic Resource
    Electronic Resource
    Biological weighting of ultraviolet (280–400 nm) induced mortality in marine zooplankton and fish. II. Calanus finmarchicus (Copepoda) eggs (1999)
    Springer
    Marine biology 134 (1999), S. 285-293 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The copepod Calanus finmarchicus Gunnerus is a key component of the planktonic food web in the Gulf of St. Lawrence, Canada. In this region, productivity-determining biophysical interactions occur in the upper 0 to 30 m of the water column. The eggs and nauplii of C. finmarchicus are found in this layer. Measurements of the diffuse attenuation coefficients for solar ultraviolet-B radiation (280 to 320 nm, UV-B) at various locations in this region indicated maximum 10% depths (the depth to which 10% of the surface energy penetrates) of 3 to 4 m at a wavelength of 310 nm. This represents a significant percentage of the summer mixed-layer water column: organisms residing in this layer are exposed to UV-B radiation. Laboratory experiments using a Xenon-arc-lamp based solar simulator revealed that C. finmarchicus embryos exposed to UV-B exhibited high wavelength-dependent mortality. The strongest effects occurred under exposures to wavelengths below 312 nm. A significant percentage of nauplii hatched from eggs exposed to these wavelengths exhibited malformations indicative of errors in pattern formation during embryogenesis. At the shorter wavelengths (〈305 nm), UV-B-induced mortality was strongly dependent on cumulative exposure. The biological weighting function (BWF) derived for UV-B-induced mortality in C. finmarchicus eggs is similar to that reported for naked DNA. This suggests that the UV-B-induced mortality effect on C. finmarchicus embryos is a direct result of DNA damage. There was no evidence of a detrimental effect of ultraviolet-A radiation (320 to 400 nm). Calculations based upon the BWF indicate that, under current noon surface irradiance, 50% of C. finmarchicus eggs located at or very near (within 10 cm) the ocean surface will be dead after 2.5 h of exposure. Under solar spectral irradiance simulating a 20% decrease in ozone layer thickness, this time drops to 2.2 h. These are first-order estimates based upon irradiance taken at a time of day during which the values would be maximal. Nonetheless, they illustrate the relative changes in UV-B effects that will result from ozone layer depletions expected over the coming decades. It is also important to point out that variability in cloud cover, water quality, and vertical distribution and displacement within the mixed layer, can all have a greater effect on the flux of UV-B radiation to which C. finmarchicus eggs are exposed than will ozone layer depletion at these latitudes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050546
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  • 4
    Electronic Resource
    Electronic Resource
    Evidence for an electrogenic ion transport pump in cells of higher plants (1970)
    Springer
    The journal of membrane biology 3 (1970), S. 210-222 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Cyanide (CN) and dinitrophenol (DNP) rapidly depolarize the cells of oat coleoptiles (Avena sativa L., cultivar Victory) and of pea epicotyls (Pisum sativum L., cultivar Alaska); the effect is reversible. This indicates that electrogenesis is metabolic in origin, and, since active transport is blocked in the presence of CN and DNP, perhaps caused by interference with ATP synthesis, that development of cell potential may be associated with active ion transport. Additional evidence for an electrogenic pump is as follows. (1) Cell electropotentials are higher than can be accounted for by ionic diffusion. (2) Inhibition of potential, respiration, andactive ion transport is nearly maximal, but a potential of −40 to −80 mV remains. This is probably a passive diffusion potential since, under these conditions, a fairly close fit to the Goldman constant-field equation is found in oat coleoptile cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868016
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  • 5
    Electronic Resource
    Electronic Resource
    Chemical vapor deposition and characterization of 6H-SiC thin films on off-axis 6H-SiC substrates (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 2672-2679 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-quality, monocrystalline 6H-SiC thin films have been epitaxially grown on 6H-SiC {0001} substrates which were prepared 3° off-axis from 〈0001〉 towards 〈112¯0〉 at 1773 K via chemical vapor deposition (CVD). Essentially, no defects were generated from the epilayer/substrate interface as determined by cross-sectional transmission electron microscopy (XTEM). Double positioning boundaries which were observed in β-SiC grown on 6H-SiC substrates were eliminated as confirmed by plan-view TEM. A strong dependence of the surface morphology of the as-grown thin films on the tilting orientation of the substrates was observed and reasons for this phenomenon are discussed. The unintentionally doped 6H-SiC thin films always exhibit n-type conduction with a carrier concentration on the order of 1016 cm−3. Au-6H-SiC Schottky barrier diodes were fabricated on the CVD 6H-SiC thin films and it was found that the leakage current at a reverse bias of 55 V was only 3.2×10−5 A/cm2. This is compared to SiC films grown on other substrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341608
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  • 6
    Electronic Resource
    Electronic Resource
    Metal Schottky barrier contacts to alpha 6H-SiC (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4757-4760 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Formation of Schottky barrier contacts to n-type 6H-SiC for a number of metals chosen to include a variety of physical and chemical properties has been investigated. The metals (Pd, Au, Ag, Tb, Er, Mn, Al, and Mg) were deposited onto room temperature surfaces terminated with a submonolayer coverage of oxygen. The metal/6H-SiC interface chemistry and Schottky barrier height φB during contact formation were obtained with x-ray photoemission spectroscopy; the electrical properties of subsequently formed thick contacts were characterized by current-voltage and capacitance-voltage techniques. The øB values for these metals extend over a wide 1.3 eV range. To a varying degree φB depends on the 6H-SiC crystal face (Si vs C). Mg and Al (Si face of latter) have φB=0.3 eV, a value which is suitable for nonalloyed ohmic contacts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352086
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  • 7
    Electronic Resource
    Electronic Resource
    Optical activation of Be implanted into GaN (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1622-1624 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single crystalline (0001) gallium nitride layers were implanted with beryllium. Photoluminescence (PL) measurements were subsequently performed as a function of implantation dose and annealing temperature. One new line in the PL spectra at 3.35 eV provided strong evidence for the presence of optically active Be acceptors and has been assigned to band–acceptor (eA) recombinations. The determined ionization energy of 150±10 meV confirmed that isolated Be has the most shallow acceptor level in GaN. Co-implantation of nitrogen did not enhance the activation of the Be acceptors. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122225
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  • 8
    Electronic Resource
    Electronic Resource
    Trends in residual stress for GaN/AlN/6H–SiC heterostructures (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2808-2810 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We discuss trends in residual stress as a function of film thickness, growth temperature, and substrate orientation for GaN/AlN/6H–SiC heterostructures. Films are mostly compressive for samples less than about 0.7 μm thick, are tensile up to about 2 μm, then abruptly become less tensile with stress values near 1 kbar thereafter. We interpret this as a successive relief of lattice mismatch and thermal stresses culminating in a catastrophic relief by unknown mechanisms at moderate thicknesses. These data indicate that relaxation processes in these heterostructures are not as well understood as previously supposed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122597
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  • 9
    Electronic Resource
    Electronic Resource
    Determination of ionization energies of the nitrogen donors in 6H-SiC by admittance spectroscopy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1956-1958 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nitrogen donor levels have been studied by admittance spectroscopy between 20 and 200 K in Schottky barriers made on lightly n-type epitaxial 6H-SiC layers. Measurements at different frequencies yield different freezeout temperatures which in turn are used to determine the donor level energies. Two electron traps at Ec−0.082 eV and at Ec−0.140 eV were detected. These levels are associated with nitrogen, respectively, at the hexagonal sites for the former and at the cubic sites for the latter level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357655
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  • 10
    Electronic Resource
    Electronic Resource
    High-temperature depletion-mode metal-oxide-semiconductor field-effect transistors in beta-SiC thin films (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 2028-2030 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Depletion-mode n-channel metal-oxide-semiconductor field-effect transistors were fabricated on n-type β-SiC (111) thin films epitaxially grown by chemical vapor deposition on the Si (0001) face of 6H α-SiC single crystals. The gate oxide was thermally grown on the SiC; the source and drain were doped n+ by N+ ion implantation at 823 K. Stable saturation and low subthreshold current were achieved at drain voltages exceeding 25 V. Transconductances as high as 11.9 mS/mm were achieved. Stable transistor action was observed at temperatures as high as 923 K, the highest temperature reported to date for a transistor in any material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.98282
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