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  • 1
    Electronic Resource
    Electronic Resource
    Energetics of dislocation dipoles in capped epitaxially strained layers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1598-1603 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Most device structures based on strained epitaxial layers are capped by a second, unstrained layer to increase the mechanical stability of the structure. In order to calculate the energies of these structures it is necessary to synthesize the total energy from the energies of the line defects they contain (interfacial dislocations and dislocation dipoles). The self energies and interaction energies of dislocations and dipoles are calculated and their behavior examined as a function of their spacing and the thicknesses of the strained and capping layers. The results confirm the observations that capped strained layers are more stable than uncapped ones (of the same strained layer thickness) and that capping layers do not need to be thicker than approximately three times the strained layer thickness. An expression is deduced for the total energy of finite, nonuniform arrays of dipoles in capped layers and, by analogy with a similar earlier expression for dislocations in uncapped layers, it is concluded that the effect of a nonuniformity in the dipole spacing will be to increase the energy of the system compared with that of a uniform array having the same average spacing. The results in this paper can be used to assess the stability of devices and their rate of degradation by strain relaxation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357739
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  • 2
    Electronic Resource
    Electronic Resource
    The energy of finite systems of misfit dislocations in epitaxial strained layers (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2242-2248 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Previous approaches to calculating the energy of a system of misfit dislocations in epitaxial strained layers have assumed that the system is infinite in the plane of the epitaxial interface and that the dislocations are uniformly spaced. Here a method is presented which is capable of dealing with finite systems of nonuniformly spaced dislocations of the type observed experimentally. The principle of the method is to explicitly account for the interactions between pairs of misfit dislocations. When the dislocations are infinite and uniformly spaced the present approach is shown to be equivalent to an earlier exact treatment. The present approach applied to finite systems of uniformly spaced dislocations shows that the energy per unit area converges to that of the infinite system very slowly; particularly when the spacing of the dislocations is less than the thickness of the epitaxial layer. Typically, systems must be larger than 30×30 dislocations for their energy per unit area to be within 10% of that of the infinite system. Similarly the infinite system will overestimate the energy of a 10×10 array by about 30%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351617
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  • 3
    Electronic Resource
    Electronic Resource
    Energy of arrays of nonperiodic interacting dislocations in semiconductor strained epilayers: Implications for strain relaxation (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 1773-1780 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interaction energy EirrI of arrays of dislocations with nonperiodic (or irregular) distribution is calculated. The calculations have been made for uniform-random and Gaussian distributions of dislocations. The method used is, however, general and can also be applied to any arbitrary or an observed distribution of dislocations. The results for several values of average spacing p¯ and standard deviation σ are given and are compared with the energy EI of periodic arrays with spacing p=p¯. The total energy EirrT of strained layers containing nonperiodic dislocation arrays is also calculated. The results for both 90° and 60° dislocations are given. For sufficiently large numbers of dislocations, EirrI is always larger than EI. The difference between the energies EirrI and EI increases rapidly as the standard deviation σ of the nonperiodic distribution increases. The equilibrium strain relaxation in thick layers and the strain relaxation on annealing the metastable layers are usually calculated by modeling the nonperiodic array as an equivalent periodic array with p=p¯. It is found that this procedure for the calculation of the strain relaxation is not valid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353213
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  • 4
    Electronic Resource
    Electronic Resource
    Diets and feeding selectivity among the epipelagic copepod community near South Georgia in summer (1994)
    Springer
    Polar biology 14 (1994), S. 551-560 
    Details
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract During the austral midsummers of 1989/1990 and 1990/1991, seven grazing experiments were undertaken near South Georgia. The copepods spanned 3 orders of magnitude in body mass, from young copepodids of small pseudocalanids to adult females of Rhincalanus gigas. Incubations were in natural sea-water and feeding rates were determined by microscope counts of food items (size range 7–1200 μm). Daily rations of the smallest copepods were up to 120% body carbon per day. These high rations contrast with values of less than 10% for large copepods (older copepodids of Calanoides acutus and R. gigas). All sizes of copepods could ingest the full size spectrum of measured particles. However, maximum filtration rates of small copepods were on cells 〈100 μm whereas the large grazers cleared the largest cells (usually long diatoms) at maximum rates. Motile, non-diatom taxa (mainly heterotrophic, aloricate dinoflagellates and ciliates) did not appear to have been eaten in preference to diatoms of similar size, but their abundance and high calorific value meant that they comprised a median of 43% of carbon intake across the experiments. These motile, mainly 〈50 μm cells were of a suitable size for ingestion by small copepods and consequently featured more prominently in their diets. The ability of small copepods to feed heavily on cells 〈50 μm, before, during or after blooms, may be important in their life cycles, leading to reduced competition with their larger relatives.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00238225
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  • 5
    Electronic Resource
    Electronic Resource
    Life cycles ofCalanoides acutus, Calanus simillimus andRhincalanus gigas (Copepoda: Calanoida) within the Scotia Sea (1991)
    Springer
    Marine biology 109 (1991), S. 79-91 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The life cycles and distribution of three dominant copepods,Calanoides acutus, Calanus simillimus andRhincalanus gigas were studied from the “Discovery” collections in the Scotia Sea earlier this century.C. simillimus is a sub-Antarctic species which mates in the top 250 m mainly in spring. The rapid development of the summer generation may allow a second mating period and a smaller second generation to appear in late summer.C. simillimus remains in the surface layers for a longer period thanCalanoides acutus orR. gigas, and its depth distribution is bimodal throughout the winter.R. gigas is most abundant in sub-Antarctic waters to the north of the Polar Front. It mates within the top 750 m later in spring, and development seems less synchronised than that of the other two species, with egg laying and the growth season being more protracted. Stages CIII and CIV are reached by the first autumn and further development resumes very early the following spring. It is not clear whether the majority then spawn or whether a further year may be needed to complete the life cycle. The predominantly Antarctic species,C. acutus mates below 750 m in middle to late winter and the summer generation develops rapidly to either CIV or CV. Its lifespan seems typically 1 yr, but some of the CVs which fail to moult and spawn in winter survive into their second summer, and their subsequent fate is uncertain. The cold-water speciesCalanus propinquus is comparatively rare in the Scotia Sea and aspects of its distribution and life cycle are briefly described for comparison. Regional variations in the timing of these events were apparent forC. simillimus and possiblyCalanoides acutus, but were not seen inR. gigas. Their geographic and vertical separation, together with their asynchronous life cycles support the concept of habitat-partitioning of these dominant herbivores.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01320234
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  • 6
    Electronic Resource
    Electronic Resource
    Diel vertical migration and feeding of copepods at an oceanic site near South Georgia (1992)
    Springer
    Marine biology 113 (1992), S. 583-593 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Twelve Longhurst Hardy Plankton Recorder (LHPR) profiles were taken over a 16 h period in January 1990, in order to study feeding of four copepod species at an Antarctic oceanic site near South Georgia. Vertical distributions of their life stages, as well as those of dominant competitors and predators, are described in relation to the feeding cycles of Calanoides acutus CV, Calanus simillimus CV, Calanus propinquus CV and Rhincalanus gigas CIII, CV and CVI♀. Comparisons with vertical ring-net catches, which were used for concomitant gutevacuation experiments, demonstrated the suitability of the LHPR for these fine-scale studies. Planktonic predators, with the exception of the diel migrant Themisto gaudichaudii, resided deeper than the herbivores. During the day and around midnight, when feeding rates were low, species and stages reached their maximum vertical separation. At these times, new generation copepodites of the four species lived progressively deeper and the overwintered generation (i.e., R. gigas Stages CIV, CV, CVI) were progressively shallower. During the afternoon or evening (depending on species), all stages older than CII, as well as Euphausia frigida and T. gaudichaudii, migrated upwards, to amass in the surface mixed layer. Feeding was restricted to darkness, although R. gigas commenced several hours before dusk. In detail their migration and feeding differed widely, with combinations of unimodal and apparent bimodal cycles. As a whole, the results suggest that (1) feeding could occur during sinking as well as during upward migrations, (2) upward migrations were not always associated with feeding increases, and (3) individuals appeared to descend after filling their guts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349702
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  • 7
    Electronic Resource
    Electronic Resource
    The gene responsible for familial hypocalciuric hypercalcemia maps to chromosome 3q in four unrelated families (1992)
    [s.l.] : Nature Publishing Group
    Nature genetics 1 (1992), S. 295-300 
    Details
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Familial hypocalciuric hypercalcemia (FHH) is an autosomal dominant syndrome of unknown aetiology characterized by lifelong elevation in serum calcium concentration and low urinary calcium excretion. These features suggest that the causal gene is important for maintenance of extracellular calcium ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/ng0792-295
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  • 8
    Electronic Resource
    Electronic Resource
    Structure of 4-bromo-13α-methyl-13aαH-tetrahydropseudocoptisin (1992)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 48 (1992), S. 931-932 
    Details
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108270191011666
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  • 9
    Electronic Resource
    Electronic Resource
    Feeding rates and diel vertical migration of copepods near South Georgia: comparison of shelf and oceanic sites (1992)
    Springer
    Marine biology 114 (1992), S. 49-56 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Seventeen Longhurst Hardy Plankton Recorder profiles were taken over a diel cycle in January 1990 to study the feeding of four major copepods over the South Georgia shelf. Ontogenetic changes in vertical migration were followed and feeding cycles determined by gut fluorometry for Calanoides acutus Stage CV, Calanus sinillimus CV and CVI♀, C. propinquus CV and Rhincalanus gigas CV and CVI♀. In common with a neighbouring oceanic site visited two weeks later and reported elsewhere, all four species had a diel cycle of feeding and migration. The vertical distributions of C. simillimus (all stages), R. gigas (nauplii) and Euphausia frigida (postlarvae) were similar at both sites, the night being spent within the chlorophyll maximum at 15 to 30 m. However, the biomass dominants, C. acutus and R. gigas, dwelt below the chlorophyll maximum, about 30 m deeper than their oceanic counterparts. Unlike the oceanic site, feeding at the shelf site was not restricted to darkness, but increased 6 to 10 h before nightfall and finished at dawn; the intervening period coincided with sinking and digestion. Daylight feeding may have been induced by the shorter night, lower light levels or greater food requirements at the shelf site, despite planktonic predators being over three times more abundant. Daily ration estimates for R. gigas at both sites were only ∼2% body carbon per day. These low values contrast with its smaller competirors, whose rations were in the range 5.6 to 27%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350855
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  • 10
    Electronic Resource
    Electronic Resource
    A segmented algorithm for simulated annealing (1992)
    Springer
    Statistics and computing 2 (1992), S. 221-230 
    Details
    ISSN: 1573-1375
    Keywords: D-optimality ; exact design ; generalized simulated annealing ; nonlinear optimization ; renewal process ; segmented algorithm ; simulated annealing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract The properties of a parameterized form of generalized simulated annealing for function minimization are investigated by studying the properties of repeated minimizations from random starting points. This leads to the comparison of distributions of function values and of numbers of function evaluations. Parameter values which yield searches repeatedly terminating close to the global minimum may require unacceptably many function evaluations. If computational resources are a constraint, the total number of function evaluations may be limited. A sensible strategy is then to restart at a random point any search which terminates, until the total allowable number of function evaluations has been exhausted. The response is now the minimum of the function values obtained. This strategy yields a surprisingly stable solution for the parameter values of the simulated annealing algorithm. The algorithm can be further improved by segmentation in which each search is limited to a maximum number of evaluations, perhaps no more than a fifth of the total available. The main tool for interpreting the distributions of function values is the boxplot. The application is to the optimum design of experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01889682
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