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  • 1
    Electronic Resource
    Electronic Resource
    Epitaxial surface-emitting laser on a lattice-mismatched substrate (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2057-2059 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have demonstrated continuous-wave, room-temperature, photopumped operation of a vertical-cavity surface-emitting laser having a 0.8% lattice mismatch with its GaAs substrate. Such mismatch provides flexibility in designing resonators with new lasing wavelengths. The laser resonator comprises lattice-matched In0.12Ga0.88As and In0.10Al0.90As quarter-wave layers for mirrors and a strained-layer superlattice of In0.23Ga0.77As/Al0.35Ga0.65As for an active region. The structure lases in the range 1.05–1.10 μm under continuous-wave photoexcitation in the wavelength range 900–950 nm. The differential power efficiency is as high as 68% and the threshold is 2 kW/cm2 (1.8 kA/cm2 injection current-density equivalent). Dislocation line densities observed by photoluminescence microscopy are about 6×102/cm in both the active region and the uppermost mirror layers. The lines predominate along one 〈110〉 direction along which the laser light is preferentially polarized. These observations suggest a way of polarizing surface-emitting lasers by intentional patterning of grating lines on the wafer surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107088
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  • 2
    Electronic Resource
    Electronic Resource
    Optical properties of fractal quantum wells (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 1736-1738 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the growth of new fractal quantum-well structures and the first studies of their optical properties. In these (Al,Ga)As structures the composition is varied in a fractal sequence between layers to create a highly branched, self-similar distribution of quantum wells. Experimentally, we studied optical absorption, luminescence and excitation spectra, and electron-hole recombination dynamics. We computed the electron and hole wave functions and transition energies and found good agreement with experiment. The optical and transport properties are strikingly different from those in single or periodic quantum wells. First, the band-edge absorption slope (change in optical density per unit energy) can be controlled over wide limits simply by modifying the sequence. Second, the transport of carriers across the quantum-well layers can be adjusted to control the carrier relaxation rate and energy distribution within the quantum wells. These results suggest possible applications of these new materials for several new devices including broadband emitters, solar cells, electro-optical, and nonlinear optical devices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109590
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  • 3
    Electronic Resource
    Electronic Resource
    The Application of Water-Quality Standards to UK Bathing Waters (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Water and environment journal 4 (1990), S. 0 
    Details
    ISSN: 1747-6593
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Data for 425 sampling locations in England and Wales, covering the 1987 bathing season, were analysed against a range of six water-quality standards used by European and North American agencies. The following order of relative stringency was established: EEC guide level 〉 US Environmental Protection Agency† 〉 Toronto†〉 Canadian Federal† 〉 Modified EEC standard 〉 EEC imperative level†.All European Community (EC) countries, at present abiding by the‘imperative’bacteriological standards of the bathing waters Directive, would experience a significant increase in non-compliance for the faecal coliform parameter if standards were altered from the current EEC imperative criteria to any of the existing alternative beach management standards.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1747-6593.1990.tb01451.x
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  • 4
    Electronic Resource
    Electronic Resource
    Response of small birch plants (Betula pendula Roth.) to elevated CO2 and nitrogen supply (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 16 (1993), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Small birch plants were grown for up to 80 d in a climate chamber at varied relative addition rates of nitrogen in culture solution, and at ambient (350 μmol mol-1) or elevated (700 μmol mol-1) concentrations of CO2. The relative addition rate of nitrogen controlled relative growth rate accurately and independently of CO2 concentration at sub-optimum levels. During free access to nutrients, relative growth rate was higher at elevated CO2. Higher values of relative growth rate and net assimilation rate were associated with higher values of plant N-concentration. At all N-supply rates, elevated CO2 resulted in higher values of net assimilation rate, whereas leaf weight ratio was independent of CO2. Specific leaf area (and leaf area ratio) was less at higher CO2 and at lower rates of N-supply. Lower values of specific leaf area were partly because of starch accumulation. Nitrogen productivity (growth rate per unit plant nitrogen) was higher at elevated CO2. At sub-optimal N-supply, the higher net assimilation rate at elevated CO2 was offset by a lower leaf area ratio. Carbon dioxide did not affect root/shoot ratio, but a higher fraction of plant dry weight was found in roots at lower N-supply. In the treatment with lowest N-supply, five times as much root length was produced per amount of plant nitrogen in comparison with optimum plants. The specific fine root length at all N-supplies was greater at elevated CO2. These responses of the root system to lower N-supply and elevated CO2 may have a considerable bearing on the acquisition of nutrients in depleted soils at elevated CO2. The advantage of maintaining steady-state nutrition in small plants while investigating the effects of elevated CO2 on growth is emphasized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1996.tb02069.x
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of elevated carbon dioxide concentration on photosynthesis and growth of small birch plants (Betula pendula Roth.) at optimal nutrition (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 15 (1992), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Small birch plants (Betula pendula Roth.) were grown from seed for periods of up to 70d in a climate chamber at optimal nutrition and at present (350 μmol mol−1) or elevated (700 μmol mol−1) concentrations of atmospheric CO2. Nutrients were sprayed over the roots in Ingestad-type units. Relative growth rate and net assimilation rate were slightly higher at elevated CO2, whereas leaf area ratio was slightly lower. Smaller leaf area ratio was associated with lower values of specific leaf area. Leaves grown at elevated CO2 had higher starch concentrations (dry weight basis) than leaves grown at present levels of CO2. Biomass allocation showed no change with CO2, and no large effects on stem height, number of side shoots and number of leaves were found. However, the specific root length of fine roots was higher at elevated CO2. No large difference in the response of carbon assimilation to intercellular CO2 concentration (A/Ci curves) were found between CO2 treatments. When measured at the growth environments, the rates of photosynthesis were higher in plants grown at elevated CO2 than in plants grown at present CO2. Water use efficiency of single leaves was higher in the elevated treatment. This was mainly attributable to higher carbon assimilation rate at elevated CO2. The difference in water use efficiency diminished with leaf age. The small treatment difference in relative growth rate was maintained throughout the experiment, which meant that the difference in plant size became progressively greater. Thus, where plant nutrition is sufficient to maintain maximum growth, small birch plants may potentially increase in size more rapidly at elevated CO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1992.tb01023.x
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  • 6
    Electronic Resource
    Electronic Resource
    An evaluation of techniques for measuring yield turgor in excised Salix leaves (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 15 (1992), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. The use of three techniques for determining yield turgor in excised Salix leaves was investigated. These were the osmotic-solutions technique, the psychrometer technique, and the pressure-chamber technique. The application of the osmotic-solutions technique to a range of leaf types was discussed and the appropriate corrections for volume changes and the contribution of apoplastic water were detailed. It was concluded that the osmotic-solutions technique is not satisfactory for use with slowly growing and/or very elastic leaves. The psychrometer and pressure-chamber techniques were both simple compared with the osmotic-solutions technique, and gave values for yield turgor in the range of 0·3–0·5 MPa. A disadvantage of the psychrometer technique for field applications is that it requires one psychrometer chamber per sample. The pressure-chamber technique was modified for use as a field technique where multiple sampling could be easily and inexpensively achieved. Particular care was required with this technique to prevent water loss from the leaf during stress relaxation, but simple and effective procedures for doing so were found. The modified pressure-chamber technique described here, is recommended as the preferred technique for measuring the yield turgor of leaves in experiments where many simultaneous estimates of yield turgor are to be made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1992.tb01463.x
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  • 7
    Electronic Resource
    Electronic Resource
    The Occurrence of Coliform Bacteria in the Surface Soils of Two Catchment Areas in the Yorkshire Dales (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Water and environment journal 5 (1991), S. 0 
    Details
    ISSN: 1747-6593
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: The levels of total coliform and Escherichia coli bacteria were determined within the surface soils of two upland catchments in North Yorkshire. The results indicated that enteric bacteria can survive for a sufficient period outside parent faecal material to provide a semi-permanent land store that might then be capable of contaminating upland waters following transport by hydrological processes. Significant differences in bacterial counts were found between broadly wet and dry soil moisture/vegetation zones in both catchments. This was explained by the more favourable survival conditions found where the soil moisture content was high enough to prevent the rapid desiccation and death of enteric bacteria. Significant differences were also found between the counts of total coliform and Escherichia coli bacteria in surface soils. It was concluded that the use of the total coliform group alone, as an indicator of the degree of sanitary bacterial contamination of soils, may over-estimate the true extent of contamination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1747-6593.1991.tb00661.x
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  • 8
    Electronic Resource
    Electronic Resource
    Pustular psoriasis in childhood (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Clinical and experimental dermatology 18 (1993), S. 0 
    Details
    ISSN: 1365-2230
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Recurrent annular pustular psoriasis over the trunk of an 11-year-old boy followed infantile psoriasis in the napkin area. Etretinate therapy induced a partial remission. The difficulty in distinguishing between annular pustular psoriasis and subcorneal pustular dermatosis of Sneddon and Wilkinson is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2230.1993.tb00985.x
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  • 9
    Electronic Resource
    Electronic Resource
    Dependence of amino acid composition upon nitrogen availability in birch (Betula pendula) (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 80 (1990), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Small birch plants (Betula pendula Roth.) were grown at different rates of exponentially increasing nitrogen supply. This resulted in plants with different relative growth rates and different internal nitrogen concentrations. Within a nitrogen treatment, both of these variables remained constant with time.Free amino acids were measured in leaves and roots of the seedlings at two different harvests. At greater nitrogen supply, higher concentrations of total amino acid nitrogen were found in roots and leaves. The ratio of amino acid nitrogen to total nitrogen was low albeit greater at higher nitrogen supply. Higher concentrations of amino acid nitrogen were mainly due to high concentrations of citrulline, glutamine, γ-aminobuitric acid and arginine.Greater leaf concentrations of amino acid nitrogen at higher nitrogen supply may be related lo increased concentrations in the xylem sap and/or may be indicative of small excesses of nitrogen with respect to current nitrogen usage in protein synthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1990.tb05671.x
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  • 10
    Electronic Resource
    Electronic Resource
    Net assimilation rate and shoot area development in birch (Betula pendula Roth.) at different steady-state values of nutrition and photon flux density (1992)
    Springer
    Trees 6 (1992), S. 1-6 
    Details
    ISSN: 1432-2285
    Keywords: Nitrogen ; Photon flux density ; Growth ; Betula
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Small birch plants (Betula pendula Roth.) were grown in a climate chamber at different, exponentially increasing rates of nitrogen supply and at different photon flux densities. This resulted in treatments with relative growth rate equal to the relative rate of increase in nitrogen supply and with different equilibrium values of plant nitrogen concentration. Nitrogen productivity (rate of dry matter increase per plant nitrogen) was largely independent of nitrogen supply and was greater at higher photon flux density. Leaf weight ratio, average specific leaf area (and thus leaf area ratio) were all greater at better nitrogen supply and at lower values of photon flux density. The dependencies were such that the ratio of total projected leaf area to plant nitrogen at a given photon flux density was similar at all rates of nitrogen supply. The ratio was greater at lower values of photon flux density. At a given value of photon flux density, net assimilation rate and net photosynthetic rate per shoot area (measured at the growth climate) were only slightly greater at better rates of nitrogen supply. Values were greater at higher photon flux densities. Acclimation of the total leaf area to plant nitrogen ratio and of net assimilation rate was such that nitrogen productivity was largely saturated with respect to photon flux density at values greater than 230 μmol m-2 s-1. At higher photon flux densities, any potential gain in nitrogen productivity associated with higher net assimilation rates was apparently offset by lower ratios of total leaf area to plant nitrogen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00224491
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