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  • 1
    Electronic Resource
    Electronic Resource
    Development of a three-dimensional numerical model of grain boundaries in highly doped polycrystalline silicon and applications to solar cells (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 4271-4274 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed a three-dimensional numerical model of grain boundaries to simulate the electrical properties of polycrystalline silicon with doping densities larger than approximately 5×1017 cm−3. We show that three-dimensional effects play an important role in quantifying the minority-carrier properties of polycrystalline silicon. Our simulations reproduce the open-circuit voltage of a wide range of published experiments on thin-film silicon p-n junction solar cells, choosing a velocity parameter for recombination at the grain boundaries, S, in the order of 105–106 cm/s. The simulations indicate that, although S has been reduced by one order of magnitude over the last two decades, improvements in the open-circuit voltage have mainly been achieved by increasing the grain size. A few options are proposed to further reduce S. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1456962
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  • 2
    Electronic Resource
    Electronic Resource
    Rear surface passivation of high-efficiency silicon solar cells by a floating junction (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 3574-3586 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The passivated emitter, rear locally diffused (PERL) cells, fabricated in our laboratory, reach an efficiency of 24.0%, the highest value for any silicon-based solar cell under terrestrial illumination. In an attempt to improve the rear surface passivation, which is usually obtained by a thermally grown oxide, we add a floating (i.e., noncontacted) p–n junction at the rear surface, resulting in the passivated emitter, rear floating p–n junction (PERF) cell design. Although these cells exhibit record 1-sun open-circuit voltages of up to 720 mV, their efficiency is degraded by nonlinearities ("shoulders'') in the logarithmic I–V curves. In order to understand and manipulate such nonlinearities, this paper presents a detailed investigation of the internal operation of PERF cells by means of numerical modelling based on experimentally determined device parameters. From the model, we derive design rules for optimum cell performance and develop a generalized argumentation that is suitable to compare the passivation properties of different surface structures. For example, the oxidized rear surface of the PERL cell is treated as an electrostatically induced floating junction in this approach and analogies to the diffused floating p–n junction are drawn. Our simulations indicate that optimum rear surface passivation can be obtained in three different ways. (i) The floating junction of the PERF cell should be very lightly doped, resulting in a sheet resistivity of 5000 Ω/(D'Alembertian), and losses due to shunt leaking paths between the p–n junction and the rear metal contacts must be avoided. (ii) The rear surface of the PERL cell should be passivated by chemical vapor deposition of a silicon nitride film containing a larger positive interface charge density than exists in thermally grown oxides. (iii) An external gate can be added at the rear with low leakage currents and gate voltages of around 15 V. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363231
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  • 3
    Electronic Resource
    Electronic Resource
    Limiting loss mechanisms in 23% efficient silicon solar cells (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 3491-3504 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The "passivated emitter and rear locally diffused'' (PERL) silicon solar cell structure presently demonstrates the highest terrestrial performance of any silicon-based solar cell. This paper presents a detailed investigation of the limiting loss mechanisms in PERL cells exhibiting independently confirmed 1-sun efficiencies of up to 23.0%. Optical, resistive, and recombinative losses are all analyzed under the full range of solar cell operating conditions with the aid of two-dimensional (2D) device simulations. The analysis is based on measurements of the reflectance, quantum efficiency, dark and illuminated current–voltage (I–V) characteristics, and properties of the Si–SiO2 interfaces employed on these cells for surface passivation. Through the use of the 2D simulations, particular attention has been paid to the magnitudes of the spatially resolved recombination losses in these cells. It is shown that approximately 50% of the recombination losses at the 1-sun maximum power point occur in the base of the cells, followed by recombination losses at the rear and front oxidized surfaces (25% and 〈25%, respectively). The relatively low fill factors of PERL cells are principally a result of resistive losses; however, the recombination behavior in the base and at the rear surface also contributes. This work predicts that the efficiency of 23% PERL cells could be increased by about 0.7% absolute if ohmic losses were eliminated, a further 1.1% absolute if there were no reflection losses at the nonmetallized front surface regions, about 2.0% by introducing ideal light trapping and eliminating shading losses due to the front metallization, and by about 3.7% absolute if the device had no defect-related recombination losses. New design rules for future efficiency improvements, evident from this analysis, are also presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358643
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  • 4
    Electronic Resource
    Electronic Resource
    Assessment and parameterisation of Coulomb-enhanced Auger recombination coefficients in lowly injected crystalline silicon (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 4938-4944 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In traditional band-to-band Auger recombination theory, the low-injection carrier lifetime is an inverse quadratic function of the doping density. However, for doping densities below about 3 ×1018 cm−3, the low-injection Auger lifetimes measured in the past on silicon were significantly smaller than predicted by this theory. Recently, a new theory has been developed [A. Hangleiter and R. Häcker, Phys. Rev. Lett. 65, 215 (1990)] that attributes these deviations to Coulombic interactions between mobile charge carriers. This theory has been supported experimentally to a high degree of accuracy in n-type silicon; however, no satisfactory support for it has been found in p-type silicon for doping densities below 3×1017 cm−3. In this work, we investigate the most recent lifetime measurements of crystalline silicon and support experimentally the Coulomb-enhanced Auger theory in p-type silicon in the doping range down to 1×1016 cm−3. Based on the experimental data, we present an empirical parameterisation of the low-injection Auger lifetime. This parameterisation is valid in n- and p-type silicon with arbitrary doping concentrations and for temperatures between 70 and 400 K. We implement this parameterisation into a numerical device simulator to demonstrate how the new Auger limit influences the open-circuit voltage capability of silicon solar cells. Further, we briefly discuss why the Auger recombination rates are less enhanced under high-injection conditions than under low-injection conditions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366360
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  • 5
    Electronic Resource
    Electronic Resource
    Starch metabolism in developing strawberry (Fragaria × ananassa) fruits (2004)
    Oxford, UK; Malden, USA : Munksgaard International Publishers
    Physiologia plantarum 121 (2004), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Fruit starch reserves can be an important contributor to the sugar content of some ripe fruit, and despite the relatively high financial premiums (compared to other fruit) commanded by ripe strawberries, neither their starch or sugar biochemistry has been examined in detail. This study assessed the rate of starch biosynthesis and breakdown in developing strawberry and sought to determine the temporal changes in the activities of selected enzymes known to be involved in sucrose-starch interconversions. Scanning electron microscopy revealed that starch levels appeared greatest in immature strawberry (Fragaria×ananassa, cv. Elsanta) at 7 days postanthesis, as evidenced by a decrease in the number of cells containing starch granules as ripening progressed. Levels of key enzymes of starch and sugar metabolism estimated using Western blotting and enzyme activity analysis showed that activities did not correlate with antigen levels. In particular, enzyme activity recovery experiments indicated that losses were due to non-proteinaceous inhibitors, and in particular protein binding: highlighting the potential for misinterpretation of enzyme activity data gathered from ripening (strawberry) fruit tissue extracts. Consequently, in vitro experiments using [U-14C] glucose revealed that incorporation to starch is low (11%) at the earliest developmental stages when starch content is greatest. Starch synthesis rate then declines to non-detectable levels as fruit expand and ripen. These results show that starch accumulates extremely early in the fruit formation process and that starch degradation predominates during fruit growth and development. We estimate that breakdown of transient starch can contribute up to 3% of the sugar accumulated in ripe fruit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.0031-9317.2004.0338.x
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  • 6
    Electronic Resource
    Electronic Resource
    Identification, cloning and expression analysis of strawberry (Fragaria × ananassa) mitochondrial citrate synthase and mitochondrial malate dehydrogenase (2004)
    Oxford, UK; Malden, USA : Munksgaard International Publishers
    Physiologia plantarum 121 (2004), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Salt-extractable proteins from the cell walls of immature and ripe strawberry (Fragaria × ananassa Duch. cv. Elsanta) fruit were separated using two-dimensional polyacrylamide gel electrophoresis. Seven polypeptides (enzymes) were characterized from their N-terminal sequences: (1) glyceraldhyde-3-phosphate dehydrogenase (EC 1.2.1.12); (2) triose phosphate isomerase (TPI; EC 5.3.1.1); (3) mitochondrial malate dehydrogenase (mMDH; EC 1.1.1.37); (4) NADH glutamate dehydrogenase (EC 1.4.1.3); (5) chalcone synthase (ChS; EC 2.3.1.74); (6) mitochondrial citrate synthase (mCS; EC 4.1.3.7); and (7) UDP glucose:flavonoid 3-O-glucosyltransferase (UDPG:FGT; EC 2.4.1.91). The sequenced polypeptides identified only cytosolic proteins, two of which (ChS and UDPG:FGT) had already been identified as being up-regulated in ripening (strawberry) fruit and important contributors to ripe fruit character. Our focus was therefore diverted to the enzymes mMDH and mCS for further molecular characterization as potentially important determinants of fruit flavour via regulation of the sugar : acid balance. Citrate synthase (CS) and malate dehydrogenase (MDH) enzyme activities increased substantially during ripening, as did citrate and malate contents. The increase in CS activity is supported by western blot analysis. One strawberry mCS (Fa-mCS-I) and two mMDH (Fa-mMDH-I and -II) cDNAs were cloned that were 77, 82 and 53% identical (respectively) to sequences from other plant sources. Northern analysis showed that CS and MDH expression did not correlate with enzyme activities and these findings are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.0031-9317.2004.00302.x
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  • 7
    Electronic Resource
    Electronic Resource
    Double allergy to the same drug in the same patient (2003)
    Oxford, UK : Munksgaard International Publishers
    Allergy 58 (2003), S. 0 
    Details
    ISSN: 1398-9995
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1398-9995.2003.00056_4.x
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  • 8
    Electronic Resource
    Electronic Resource
    The role of ethylene and cell wall modifying enzymes in raspberry (Rubus idaeus) fruit ripening (1999)
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 105 (1999), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: This study focuses on four raspberry (Rubus idaeus) genotypes from two different genetic backgrounds: cvs Glen Prosen and Glen Clova, bred at the Scottish Crop Research Institute (SCRI) and genotypes bred at Horticulture Research International (HRI), East Malling (EM), EM 4997 and EM 5007. The ripe fruit of each genotype pair were characterised subjectively by raspberry breeders as relatively firm or soft, respectively. Different stages of fruit development from each genotype were used to quantify fruit firmness, rates of ethylene evolution and ripening rate. Penetrometry data confirmed suspected firmness differences. Firmness correlated with rates of ethylene evolution. Rates of ethylene production also correlated with receptacle size. Storage of green fruits in 20 μl l−1 ethylene reduced fruit firmness, enhanced respiration rate and colour (anthocyanin) development and stimulated the development of cell wall hydrolase activities. However, during natural ripening in the field, fruit respiration rate declined, which indicates a non-climacteric ripening pattern. In drupelets, the activities of polygalacturonase (PG), pectin methylesterase (PME), Cx-cellulase (Cx) and β-galactosidase (β-gal.) increased substantially as ripening progressed. More detailed studies with ripe fruit of cv. Glen Clova indicated major isoforms of PG at pIs 3.3, 8.6 and 10.1; of PME at pIs 7.2, 8.5, 8.7, 8.8; of Cx at pI 2.4; and of β-gal. at pIs 6.3 and 6.7.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.1999.105220.x
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  • 9
    Electronic Resource
    Electronic Resource
    Tree Adjoining Languages and Multipushdown Languages (2000)
    Springer
    Theory of computing systems 33 (2000), S. 257-293 
    Details
    ISSN: 1433-0490
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract. Many families of grammars have been studied to extend the power of context-free grammars, while retaining the attractive properties of context-free languages. Some of these formalisms have been proved equivalent to tree adjoining grammars ( tag ), introduced by computational linguists to model natural languages. Another family of grammars, multidepth grammars, introduced for describing the syntax of programming languages, generates a hierarchy of languages, called k -pushdown languages (k-pdl ), for k ≥ 1 . Multidepth grammars are simpler than some other formalisms and have a very natural accepting device, called multipushdown automaton. Here we study the relationship of k-pdl with tal , the class of languages generated by tag . We prove that 2-pdl ⊂ tal ⊂ 3-pdl . Moreover, tal can be characterized exactly as the smallest full super-AFL that includes 2-pdl .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002240010004
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  • 10
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    Unknown
    Torino-Roma, Roma-Torino: Schermaglie (1954)
    Roma : Periodicals Archive Online (PAO)
    Studi romani. 2:3 (1954:magg./giugno) 303 
    Details
    ISSN: 0039-2995
    Topics: Romance Studies
    URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:4211-1954-002-03-000006
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