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  • Computational Chemistry and Molecular Modeling  (6)
  • sorghum  (4)
  • 1990-1994  (10)
  • 1
    Electronic Resource
    Electronic Resource
    Canopy management possibilities for arboreal Leucaena in mixed sorghum and livestock small farm production systems in semi-arid India (1990)
    Springer
    Agroforestry systems 10 (1990), S. 135-152 
    Details
    ISSN: 1572-9680
    Keywords: Leucaena leucocephala ; Sorghum bicolor ; semi-arid India ; agroforestry ; fodder ; fuelwood ; sorghum ; pollarding ; micro-climate ; biomass
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A major problem for small farmers in the semi-arid tropics is the chronic shortage of fodder for draft animals. Leucaena leucocephala has improved productivity in many places in India and in various cropping systems, usually as either a pure crop or in a hedgerow alley-cropping configuration. Mixed cropping with arboreal forms is seldom seen. For off-season fodder production, hedgerows have the disadvantage of being open to unmanaged browsing when unfenced (as is usual). Arboreal forms are generally far less vulnerable. In this paper, the components of production of sorghum and arboreal Leucaena are measured under different intensities of canopy lopping. The most productive management system of those examined was pollarding of the Leucaena at the time of under-sowing with sorghum. In a year with less than 50% of average seasonal rainfall, this system gave a yield of 4.6 tonnes/ha/yr fresh wt fodder and 3.8 tonnes/ha/yr dry wt. of fuel harvests, while increasing the standing crop of wood by 1.8 t/ha/yr and retaining a yield of sorghum grain equivalent to 46% of pure sorghum cropping; the LER of this system was 1.35. Cash values of the alternative management systems were estimated, including the discounted Net Present Value of the standing crop of timber. Maximum value was attained with unlopped pure crop Leucaena followed by pollarded Leucaena with sorghum; pure crop sorghum achieved a lower value. These results demonstrate both the high productivity of Leucaena/sorghum based systems, and the stability of production even in poor rainfall conditions. Pollarding transferred the high future value of Leucaena timber to the present value of sorghum grain and fuelwood.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00115362
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  • 2
    Electronic Resource
    Electronic Resource
    A tree/crop interface design and its use for evaluating the potential of hedgerow intercropping (1991)
    Springer
    Agroforestry systems 13 (1991), S. 143-158 
    Details
    ISSN: 1572-9680
    Keywords: Tree-crop interface ; row orientation ; hedgerow intercropping ; alley cropping ; Leucaena ; sorghum ; sunflower ; experimental design ; semi-arid tropics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The paper describes a tree/crop interface (TCI) experiment designed to investigate the effects of row orientation using Leucaena leucocephala Lam. Each TCI plot consisted of a regularly pruned Leucaena hedge in the middle and 12 crop rows on either side. Eight such plots were arranged at 45° around a sole Leucaena plot with rows oriented in four compass directions viz., North-South, East-West, Northeast-Southwest and Northwest-Southeast. Results of four years from 1984 to 1987 did not show any effect of row orientation, and similarly, no effect was seen on crop rows due to their location on the windward or leeward side of the hedge. The TCI effect was positive on the first crop row in the first year because Leucaena grew slowly, but depressed the yield of the first 4 to 6 crop rows(1.8 to 2.7 m from hedge) in subsequent years. The negative effect of Leucaena was noted more on sunflower in a relatively dry year than on sorghum in other years. Results from the TCI plots were used to estimate the yield of five hedgerow intercropping (HI) systems with varying alley widths (2.7 to 9.9 m). Comparison with sole stands of Leucaena and crops indicated that HI was more productive particularly at close alley widths. For example, hedges spaced at 2.7 m and 3.6 m averaged 37% and 25% higher productivity than the respective sole stands; but this advantage may be an overestimation of the real potential. The relevance of TCI experiments for studying agroforestry systems, their merits and limitations, especially of the design employed in this study are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00140238
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  • 3
    Electronic Resource
    Electronic Resource
    A study of the potential of hedgerow intercropping in semi-arid India using a two-way systematic design (1990)
    Springer
    Agroforestry systems 11 (1990), S. 243-258 
    Details
    ISSN: 1572-9680
    Keywords: Alley cropping ; fodder ; India ; intercrops ; Leucaena ; pigeonpea ; semi-arid tropics ; sorghum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The potential of hedgerow intecrropping with Leucaena leucocephala was explored on vertic Inceptisols over 4 years at ICRISAT Center, Patancheru, India. The study was conducted using a systematic layout involving different alley widths ranging from 1.35 to 4.95 m and with varying distances between hedge and crops. The alleys were cropped with alternate rows of sorghum and pigeonpea. Hedges composed double Leucaena hedgerows 60 cm apart were periodically harvested for fodder. Sole crops of all components and a sorghum/pigeonpea intercrop were included in all four replications of the study. Starting in the second year, Leucaena was progressively more competitive to annual crops, causing substantial yield reduction. Competition (primarily for moisture) was most severe in narrow alleys and was greatest on pigeonpea. The growth of Leucaena was not sufficient to compensate for reduced crop yields. Land equivalent ratios (LERs) calculated on the basis of grain yield of crops and Leucaena fodder yields showed that hedgerow intercropping (HI) was advantageous over sole crops only during the first two years using wide alleys, but disadvantegeous in the last two years. LERs calculated on the basis of total dry matter indicated only a small advantage for HI (13–17 percent) over sole crops in wider (〉4 m) alleys. Average returns per year from HI exceeded those of the most productive annual crop system (sorghum/pigeonpea intercropping) by 8 percent in 4.05 m alleys, and by 16 percent in 4.95 m alleys. Fodder production during the dry season was 40 percent of the annual total in these alley widths. Thus hedgerow intercropping at 4–5 m alley width is not very attractive for farmers in semi-arid India, which has 600–700 mm of annual rainfall. There is a need to examine the potential of HI in wider alleys. The merits and limitations of the systematic design are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00045902
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  • 4
    Electronic Resource
    Electronic Resource
    Spatial distribution of root activity and nitrogen fixation in sorghum/pigeonpea intercropping on an Indian Alfisol (1993)
    Springer
    Plant and soil 155-156 (1993), S. 341-344 
    Details
    ISSN: 1573-5036
    Keywords: intercropping ; nitrogen fixation ; nodulation ; pigeonpea ; root respiration ; sorghum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A medium-duration pigeonpea cultivar (ICP 1–6) and a hybrid sorghum (CSH 5) were grown on a shallow Alfisol in monocropping and intercropping systems. Using a monolith method, spatial distribution of nodulation, acetylene reduction activity (ARA) and root respiration were measured. The number, mass and ARA of nodules decreased exponentially with distance from the plant base except at the late reproductive stage. Nodulation and ARA tended to be higher in the intercrop than in the monocrop. Respiration rate of roots increased with distance from the plant base and reached a maximum value at about 20–30 cm. The rate was higher in pigeonpea than in sorghum and also higher in intercrop than in monocrop. This study suggests that pigeonpea roots are physiologically more active than sorghum roots, implying that pigeonpea may become a strong competitor for nutrients in the soil when intercropped. The nitrogen-fixing ability of pigeonpea may be enhanced by intercropping because the sorghum rapidly absorbed inorganic N which would otherwise inhibit N2 fixation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00025052
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  • 5
    Electronic Resource
    Electronic Resource
    Temperature dependence of hydrogen transfer reactions via tunneling at low temperatures (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 47 (1993), S. 437-448 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper, we present a symmetrical and adiabatic reaction path for hydrogen transfer from methane by methyl by an ab initio method using the 6-31G** basis set with the MP2 corrections for UHF/6-31G** optimized geometries. The theoretical barrier is fitted with the symmetric Eckart function. We, then, take thermal averages of the rate constant (k) considering the discrete nature of the C-H oscillators and the continuous character of the various low-frequency modes of the composite system. Finally, we present a linear relation between log k and temperature. It is shown that this relation gives a good description of the kinetic results of both thermal and photochemical H-transfer reactions in the region of low temperatures. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560470604
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  • 6
    Electronic Resource
    Electronic Resource
    Ab initio calculations on CO4 centers in silicon dioxide (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 446-453 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab initio SCF-MO Hartree-Fock calculations were performed using the STO-3G, 6-31G, and 6-31G* basis sets to model hypothetical substitutional carbon impurities in silicon dioxide. We utilized nine-atom clusters, [C(OH)4]qt, with charge number qt = 0 and + 1. The positions of the C and O atoms were varied to achieve minimum total energies, while the fixed protons served to simulate the rigid crystal surroundings. In the optimized configuration of the neutral cluster, the C—O bond lengths are appreciably longer than typical C—O bonds, indicating relatively weak bonds for a carbon impurity at a silicon site. For comparison, the relative positions of all nine atoms in the [C(OH)4]0 model were allowed to vary. This unconstrained model yielded more normal bond lengths and was lower in energy than the fixed-proton model by 6.80 eV with the 6-31G* basis set. The free-H model compared favorably with the x-ray diffraction data for an analogous orthocarbonate. Our results are in concert with the lack of reports of any substitutional carbon impurity in α-quartz. In the fixed-H models, the twofold local symmetry was found to be retained when qt is 0 but not when qt is + 1. For the latter ion, the unrestricted H-F calculations indicate that this paramagnetic center has its spin population almost entirely on one oxygen ion and is high in energy (5.31 eV with 6-31G) compared to the diamagnetic neutral one. Conclusions reached with the nine-atom clusters were confirmed by a series of calculations on the extended model [C(OSiH3)4]0.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120406
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  • 7
    Electronic Resource
    Electronic Resource
    A general approach for atom-type assignment and the interconversion of molecular structure files (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 209-214 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: In molecular modeling projects which require use of several different computer programs, one encounters problems in sharing data between programs. One difficult problem is the conversion of atom types from one program's definition to another. A second problem is the conversion of a polymer, such as a protein or polynucleotide molecule, from a “general” program, which understands molecules as a collection of atoms, to a “polymer” program, which understands molecules as a collection of molecular fragments stored in some library. We describe here a new method by which atom types are deduced from the environment of each atom. We use the Daylight Chemical Information Systems library of programs to deduce the atom types based only on the atomic symbol, connectivity and formal charge of each atom in the molecule. We also describe a method by which the polypeptide nature and sequence of a molecule can be deduced from minimal information about the atoms in the molecule. We have written a computer program which demonstrates this method. This program deduces atom types for AMBER, GRIN/GRID, CHARMm, and ALOGP. It will also produce input files for the AMBER/PREP fragment library preparation program.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120210
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  • 8
    Electronic Resource
    Electronic Resource
    Conformational analysis of HIV protease inhibitors. I. Rotation of the amide group adjacent to the P′1 decahydroisoquinoline ring system in ro 31-8959 and related systems (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 14 (1993), S. 1446-1453 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Pipecolic acid derivatives have proven to be effective P′1 groups in a series of highly potent inhibitors of the enzyme HIV protease. One such inhibitor, Ro 31-8959, contains the saturated bicyclic ring system decahydroisoquinoline (DIQ) in the P′1 position. The binding orientation of Ro 31-8959 is known from X-ray crystallography. However, the bound conformation of the S-hydroxy diastereomer has not been studied, and for this molecule there are at least two different possible binding conformations. Specifically, the N-alkyl substituents may be equatorial or axial and the 3-carboxamide may be rotated into several different orientations. To gain a better understanding of the relative energies of these various conformations, ab initio molecular orbital calculations have been carried out on a series of pipecolic acid and DIQ derivatives. The results indicate that the lowest-energy N-equatorial rotamer is always at least 3 kcal/mol more stable than the lowest-energy N-axial rotamer. The presence of the second ring, as in the DIQ system, considerably raises the equatorial-axial difference to nearly 7 kcal/mol. Also, the preferred rotation angle of the amide group is different for the N-equatorial and N-axial cases. When the molecular dynamics-averaged conformation of the bound S-hydroxy inhibitor is considered, the energy difference between the N-equatorial and N-axial conformers drops to 4-5 kcal/mol. The preferred amide rotations in these systems are compared to those found in proline-containing peptides. Finally, some observations are made with respect to the large conformational energy penalty necessary for binding Ro 31-8959. © John Wiley & Sons, Inc.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540141206
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  • 9
    Electronic Resource
    Electronic Resource
    On a proposed radiation-induced polaronic hole in silicon dioxide (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 254-265 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab-initio self-consistent-field molecular-orbital (SCF MO) Hartree-Fock (HF) calculations using the STO-3G, 6-31G, and 6-31G* basis sets, were performed to model quasi-tetrahedral silicon species in silicon dioxide. Mostly nine-atom clusters, [Si(OH)4]qt, with charge number qt = 0 or + 1, were studied. The positions of the Si and O atoms were varied to achieve minimum total energies, while the protons were held fixed in the O-(neighboring)Si direction to simulate the rigid crystal surroundings. The α-quartz-type local symmetry C2 was found to be retained for the neutral cluster, but not for the ionic one. The unrestricted HF calculations indicate that the latter paramagnetic centre, (qt = +1), has its spin population almost entirely on one short-bonded oxygen ion bonded weakly to its neighboring Si, and is quite high in energy (9.55 eV with 6-31G) compared to the diamagnetic centre (qt = 0). The ionization energy is much higher than the self-trapping potential of the polaronic hole, a fact which may account for the failure so far to observe a [SiO4]+1 center in quartz by means of continuous-wave electron paramagnetic resonance spectroscopy. Calculations on the [SiO4]+1 center agree well with ultraviolet spectra, and with the [hole portion of a] proposed radiation-induced exciton in quartz. The hole in [Si(OH)4]+1 can be shifted from a short-bonded to a long-bonded oxygen to give the excited state [Si(OH)4]es+1. Conclusions reached with the nine-atom clusters were confirmed by a series of calculations on the extended model [Si(OSiH3)4]qt. Comparisons with the known isoelectronic species [AlO4]0 were carried out.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120216
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  • 10
    Electronic Resource
    Electronic Resource
    Reversed stereochemical preference in binding of Ro 31-8959 to HIV-1 proteinase: A free energy perturbation analysis (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 15 (1994), S. 1241-1253 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ro 31-8959 is a highly potent inhibitor of HIV-1 proteinase in phase III clinical trials for treatment of AIDS. It is also the first subnanomolar inhibitor that demonstrated reversed stereochemical preference at the central hydroxyl group. Free energy perturbation calculations have been carried out to rationalize the preference for the R-diastereomer by consideration of two models of the (weaker) S-diastereomer. In the first model, the central hydroxyl group makes only one hydrogen bond with the active site aspartates, whereas the hydroxyl group in the second model makes at least three strong hydrogen bonds. Using the first model, the free energy difference in binding of Ro 31-8959 and its S-diastereomer is calculated to be 3.4 kcal/mol, which is in close agreement with the experimental value. Although the second model has a more favorable interaction with the active site aspartates compared to the first model, it has a higher energy N-axial conformation at the decahydroisoquinoline group in P1′. We show here that the two contributions cancel each other and the two models of S-diastereomer are predicted to have equivalent binding. The stereochemical preference in a hydroxyethylamine series of inhibitors appears to be affected by both intermolecular and intramolecular (conformational) energies. The binding data on the proline containing inhibitors are rationalized based on these results. © 1994 by John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540151106
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