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  • 1
    Electronic Resource
    Electronic Resource
    Composition effects on structural and optical infrared properties of CuIn0.5Ga0.5Se2 (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 1776-1783 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dependence of structural parameters and force constants for Cu–Se, Ga–Se, and In–Se bonds on compositional deviations in CuIn0.5Ga0.5Se2 have been studied. The composition gradient along the ingot was obtained by a single fusion at 1150 °C of the components and subsequent slow cooling in a still ampoule placed in a vertical furnace. All along the sample, a single chalcopyrite phase is present and its composition along its length was found by energy dispersive analysis of x-ray measurements on slices. Unit cell parameters, anion displacement, and Cu occupation fraction in its sublattice were analyzed by x-ray powder diffraction and Rietveld refinement methods. The anion displacement found is a function of the Cu defect in its sublattice. The existence of associated defects, i.e., two Cu vacancies and one Ga in Cu site, [2V(Cu)+GaCu], is proposed to explain the Cu defect in its sublattice and the changes in lattice parameters. This leads to the existence of BIII vacancies (BIII=In+Ga), and interstitial Cu up to 8 at. % that also cause changes in the structural parameters. Infrared reflectance measurements led to the imaginary dielectric constant determination which, fitted to a Lorentz function, permitted to obtain atomic vibration modes. Using the model of Neumann for chalcopyrites, the values of force constants for Cu–Se, Ga–Se, and In–Se bonds were computed. These appear to increase when the occupation of each sublattice increases. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1303063
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  • 2
    Electronic Resource
    Electronic Resource
    Composition effects on the crystal structure of CuInSe2 (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 5610-5616 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By x-ray powder diffraction and the Rietveld refinement method, the atomic positions in CuInSe2 were determined for compositions close to stoichiometry. The Se position, x(Se), was found to be correlated to the Cu content. According to a model proposed by Jaffe and Zunger [Phys. Rev. B 29, 1882 (1984)], changes in x(Se) induce a variation in the optical band gap, Eg. This could explain the spread in energy gap, Eg, found by many authors for this compound. The increase in the lattice parameter, a, correlated with the difference between the energy dispersive analysis of x rays and x-ray diffraction determined Cu contents, suggests the presence of a fraction of Cu atoms as interstitials. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363611
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  • 3
    Electronic Resource
    Electronic Resource
    An approach to the energy gap determination from reflectance measurements (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 616-618 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method to obtain the band gap energy value from reflectance measurements has been developed for bulk materials with direct and indirect gaps. In an energy region around the gap value, the experimental reflectivity is fitted by two functions of the type R=A0+A1′(1/hν)2−A1′Eg×(1/hν)3 and R=A0+B[(hν−Eg)/(hν)]4, for direct and indirect transitions, respectively, in an energy range around the gap value. This implies that the absorption coefficient, α, shows a dependence with the energy α=(A/hν)(hν−Eg)m with m=1/2, 2 for direct and indirect gaps, respectively. The method has been checked in several materials of known energy gaps including Si and Ge. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366650
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  • 4
    Electronic Resource
    Electronic Resource
    Estimation of Tissue Construction Cost from Heat of Combustion and Organic Nitrogen Content (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 10 (1987), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. We present a method for estimating the construction costs of plant tissues from measurements of heat of combustion, ash content, and organic nitrogen content. The method predicts glucose equivalents, the amount of glucose required to provide carbon skeletons and reductant to synthesize a quantity of organic product. Glucose equivalents have previously been calculated from the elemental composition of tissue. We define construction cost as the amount of glucose required to provide carbon skeletons, reductant and ATP for synthesizing the organic compounds in a tissue via standard biochemical pathways. The fraction of the total construction cost of a compound or tissue (excluding costs of transporting compounds) that is reflected in its glucose equivalents is the biosynthetic efficiency (EB). This quantity varies between 0.84 and 0.95 for tissues with a wide range of compositions. Using the new method, total construction cost can be estimated to ± 6% of the value obtained from biochemical pathway analysis.Construction costs of leaves of three chaparral species were estimated using the proposed method and compared to previously published values, derived using different methods. Agreement among methods was generally good. Differences were probably due to a combination of inaccuracy in the estimated biosynthetic efficiency and technical difficulties with biochemical analysis, one of the older methods of determining construction cost.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/1365-3040.ep11604754
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  • 5
    Electronic Resource
    Electronic Resource
    Chemical composition and construction cost for roots of Mediterranean trees, shrub species and grassland communities (2002)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 25 (2002), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The construction cost of fine roots was studied in 23 woody species and two grassland communities, growing under natural conditions in southern Spain. Calculation of the energy (glucose) required for their synthesis was based on the quantification of chemical components present in tissues. Despite considerable differences in the chemical composition of the three life forms studied (trees, shrubs and herbaceous), detected differences in construction cost were non-significant (mean value: 1·64 ± 0·13 g glucose g−1). However, shrubs and herbaceous plants growing in more fertile habitats expended significantly less energy on root synthesis (1·58 ± 0·06 and 1·41 ± 0·05 g glucose g−1, respectively) than those growing in less fertile areas (1·80 ± 0·06 and 1·57 ± 0·1 g glucose g−1, respectively), because they contained smaller amounts of either waxes (shrubs) or lignins (herbaceous), both expensive to synthesize, and, proportionately, more cellulose; which is inexpensive to synthesize. Deciduous and evergreen tree species also differed mainly with regard to wax and cellulose contents, giving rise to a significantly higher construction cost in evergreens (1·57 ± 0·07 g glucose g−1 versus 1·78 ± 0·02 g glucose g−1). The differences observed in construction cost appeared to be due more to habitat-induced differences in chemical composition than to any intrinsic difference between the species studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2002.00848.x
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  • 6
    Electronic Resource
    Electronic Resource
    Root respiration and associated costs in deciduous and evergreen species of Quercus (2002)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 25 (2002), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Root construction and maintenance costs were estimated in four evergreen and three deciduous Quercus species that are typical in the landscape of southern Spain. The cost quantification was based on analysis of the growth–­respiration ratio. Values observed for both construction cost (ranging from 1·17 to 1·29 g glucose g−1 dry weight) and maintenance   cost   (ranging   from   6·22   to   11·71 mg glucose g−1 dry weight d−1) were generally lower than those reported in other studies. The results showed non-significant differences between deciduous and evergreen species. The lack of significant differences between species appeared to be due to the homogeneity of growth conditions. Hydroponic culture, with unrestricted nutrient and water supply, would lead to low tissue carbon content and low respiration rates, leading to the low costs observed. Furthermore, the fact that root organs are clearly importers of organic molecules inevitably entails some underestimation of the respiration associated with growth and, to a lesser extent, with maintenance respiration. This leads in turn to underestimation of the corresponding construction and maintenance costs. All this raises doubts as to the suitability of this method for studying root systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2002.00903.x
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  • 7
    Electronic Resource
    Electronic Resource
    Characterization of the conformers in poly(3,3-diethyl oxetane) by vibrational spectroscopy (1989)
    Springer
    Polymer bulletin 21 (1989), S. 85-88 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The monoclinic and orthorhombic conformers of Poly(3,3-Diethyl oxetane) can be obtained depending on crystallization temperature. However, if the crystallization of a given modification is unaccomplished, the other modification can be crystallized from the amorphous phase. The molecular vibrations in the region 700–800 cm−1, which are associated with the “breathing” mode, are highly dependent on the conformation of the polymer chain. This band is used to study the influence of the temperatures and times of crystallization on the structural modifications of this polymer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00700273
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  • 8
    Electronic Resource
    Electronic Resource
    Construction and maintenance costs of mediterranean-climate evergreen and deciduous leaves I. Growth and CO2 exchange analysis (1982)
    Springer
    Oecologia 53 (1982), S. 208-213 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Gas exchange and leaf growth analysis were used in conjunction to determine leaf-construction and maintenance costs in three co-occurring shrubs of the california chaparral, one evergreen, Heteromeles arbutifolia, and two drougth deciduous species, Lepechinia calycina, and Diplacus aurantiacus. The construction costs per unit of leaf weight were similar among the three species and very close to values reported for other evergreens but considerably higher than leaf construction costs for other deciduous or herbaceous plants. Maintenance costs per unit of leaf weight were significantly greater in one deciduous species, L. calycina, than in the evergreen. Maintenance costs for all species were in the range reported for herbaceous species and considerably above those reported for other evergreens.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00545665
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  • 9
    Electronic Resource
    Electronic Resource
    Compromises between water-use efficiency and nitrogen-use efficiency in five species of California evergreens (1983)
    Springer
    Oecologia 60 (1983), S. 384-389 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In five California evergreen trees and shrubs cooccurring in this study but most common in habitats of different moisture availability, leaf nitrogen was a major determinant of photosynthetic capacity. Within each species, stomatal conductance was highly correlated with photosynthetic capacity, resulting in little variation in the concentration of CO2 in the intercellular spaces. Among species, intercellular CO2 concentrations varied significantly. Under controlled conditions, the leaves that realized the highest photosynthesis per unit of leaf nitrogen tended to realize the lowest photosynthesis per unit of water transpired. The ratio of photosynthesis to transpiration, an instantaneous measure of intrinsic water-use efficiency, was highest in the species commonly found in the direst habitats and lowest in the species most common in the wettes habitats.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00376856
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  • 10
    Electronic Resource
    Electronic Resource
    Micro-Raman spectroscopy study of the process of microindentation in polymers (1992)
    Springer
    Journal of materials science 27 (1992), S. 2231-2236 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The residual deformation produced by Vickers microindentations in poly(3,3-dimethyl oxetane) (PDMO) was analysed by Raman microspectroscopy. Microstructural variations were observed as the Raman spectra were recorded at different positions along and out of the microindentation. A gradual distribution of the monoclinic and orthorhombic structures arises as the spectra were scanned from the centre to the edge of the impression area. This crystalline variation in PDMO, which reflects the degree of stress present on the surface of the sample, was utilized to obtain information on the distribution of pressure in and around the microindentation. In addition to the clear variation of pressure inside the permanently deformed region, no crystalline transformation was noted out of the impression area. Similar features were observed when the Raman spectra were recorded along one of the diagonals of the indentation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01117942
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