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  • Articles  (127)
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  • 1995-1999  (127)
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  • Articles  (127)
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  • 1
    Electronic Resource
    Electronic Resource
    Use of Kramers–Kronig transforms for the treatment of admittance spectroscopy data of p-n junctions containing traps (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7830-7836 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The use of Kramers–Kronig transforms is proposed for the treatment of admittance spectroscopy data of junctions when significant shunt conductance or series resistance is present. An algorithm has been implemented to calculate the transformations numerically and the validity of the method developed has been tested using simulated data. Two experimental systems, p-n junctions into InP made by ion implantation, and atomic-layer-epitaxy-grown CdS/CdTe heterojunctions, have been characterized using this procedure. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362391
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  • 2
    Electronic Resource
    Electronic Resource
    Metal–insulator transition in SrRuO3 induced by ion irradiation (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3375-3377 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the effect of He+ irradiation on the electrical resistivity and Curie temperature of ferromagnetic SrRuO3 thin films. An evolution from metallic to insulating behavior is observed when He+ ion fluence is increased, suggesting a metal–insulator transition. Damage by ion irradiation produces a strong decrease of the Curie temperature. On the other hand, no significant change in Tc (∼160 K) takes place in fresh samples grown at different substrate temperatures. We discuss the possible correlation between structural changes induced by irradiation, which reflect in an increase of the pseudocubic lattice parameter, and the observed depression of Tc.© 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122772
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  • 3
    Electronic Resource
    Electronic Resource
    Biochemical and phenotypical characterization of transgenic tomato plants overexpressing a basic peroxidase (1999)
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 106 (1999), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Tomato plants (Lycopersicon esculentum Mill. cv. Pera) were transformed via Agrobacterium tumefaciens with the binary vector pKYLX71 containing a tomato basic peroxidase (EC 1.11.1.7) gene, tpx1, under the control of the cauliflower mosaic virus (CaMV35S) promoter. Transgenic plants showed a 2–5-fold increase in the activity of the peroxidase ionically bound to the cell wall, whereas soluble peroxidase activity remained similar or even lower than wild-type plants. Isoelectric focusing showed the presence of a new isoperoxidase of pI ca 9 in the ionically bound extract. Western blot also showed the presence of a new band at 41 kDa that was absent in the wild-type extract. A 40–220% increment of lignin content of the leaf was found in transgenic plants. Shoot phenotype of transgenic plants was similar to wild type, although under stress, the plants appeared wilted and the new leaves had a reduced area and were thicker than wild-type or older transgenic leaves. The root system was underdeveloped in transgenic plants, but the rooting ability of the stem was not affected by the overexpression of peroxidase. Finally, the morphogenetic response of cotyledon and hypocotyl explants from transgenic plants was evaluated. In the case of cotyledons, the percentage of explants with shoot was not different from wild-type plants. For hypocotyl, one of the transgenic lines showed a 30% reduction in the percentage of shoot organogenesis. The results are discussed in relation to the role of tpx1 in lignin synthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.1999.106401.x
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  • 4
    Electronic Resource
    Electronic Resource
    Structural effects of the solvent composition in colloidal liquids (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 6025-6031 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper is concerned with the microstructure observed in colloidal dispersions of charged polymeric particles and their interaction potential at very low ionic strength. Both aspects are probed with the aid of new experimental data for nonaqueous media. The structure factor of ordered dispersions (with methanol–water and ethanol–water solvent mixtures) was determined using static light scattering. A different behavior (in the studied range of molar fraction) depending on the alcohol type is found. These results are analyzed assuming a Yukawa potential and applying integral equation theories (the Ornstein–Zernike equation and the HNC closure). The obtained effective charge is almost constant for methanol–water mixtures, whereas a decrease with the alcohol molar fraction is observed for ethanol–water. In order to account for these effects, a charge renormalization procedure is applied and discussed. The surface charge turns out to be an unsuitable input parameter for such an approach. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478505
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  • 5
    Electronic Resource
    Electronic Resource
    Sulphation of Rhizobium sp. NGR234 Nod factors is dependent on noeE, a new host-specificity gene (1997)
    Oxford UK : Blackwell Science Ltd
    Molecular microbiology 24 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Rhizobia secrete specific lipo-chitooligosaccharide signals (LCOs) called Nod factors that are required for infection and nodulation of legumes. In Rhizobium sp. NGR234, the reducing N-acetyl-d-glucosamine of LCOs is substituted at C6 with 2-O-methyl-l-fucose which can be acetylated or sulphated. We identified a flavonoid-inducible locus on the symbiotic plasmid pNGR234a that contains a new nodulation gene, noeEwhich is required for the sulphation of NGR234 Nod factors (NodNGR). noeE was identified by conjugation into the closely related Rhizobium fredii strain USDA257, which produces fucosylated but non-sulphated Nod factors (NodUSDA). R. fredii transconjugants producing sulphated LCOs acquire the capacity to nodulate Calopogonium caeruleum. Furthermore, mutation of noeE (NGRΔnoeE ) abolishes the production of sulphated LCOs and prevents nodulation of Pachyrhizus tuberosus. The sulphotransferase activity linked to NoeE is specific for fucose. In contrast, the sulphotransferase NodH of Rhizobium meliloti seems to be less specific than NoeE, because its introduction into NGRΔnoeE leads to the production of a mixture of LCOs that are sulphated on C6 of the reducing terminus and sulphated on the 2-O-methylfucose residue. Together, these findings show that noeE is a host-specificity gene which probably encodes a fucose-specific sulphotransferase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.3981777.x
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  • 6
    Electronic Resource
    Electronic Resource
    Plasmids from Halomonas eurihalina, a microorganism which produces an exopolysaccharide of biotechnological interest (1997)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 156 (1997), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The moderately halophilic bacterium Halomonas eurihalina strain F2-7, able to produce an exopolysaccharide, was found to contain two plasmids named pVE1 and pVE2, of 8.1 and 5.8 kb respectively. We found no evidence for the involvement of these plasmids in the expression of the mucoid phenotype. Restriction maps of both plasmids were constructed. Southern hybridization revealed similarities between them but excluded the existence of sequences homologous to other plasmids isolated from the Halomonas species. Neither pVE1 nor pVE2 displayed any homology with other plasmids isolated from moderate halophiles. The occurrence of similar plasmids in other strains of Halomonas eurihalina, isolated from hypersaline soils, has been detected. These small plasmids may be useful for the development of cloning vectors for moderately halophilic bacteria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1997.tb12736.x
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  • 7
    Electronic Resource
    Electronic Resource
    Community and pigment structure of Arctic cyanobacterial assemblages: the occurrence and distribution of UV-absorbing compounds (1999)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 28 (1999), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Three groups of cyanobacterial communities were widely distributed in the benthic environment of lakes, ponds and streams on Ellesmere Island and Cornwallis Island in the Canadian High Arctic: (1) sheets or spherical colonies of Nostoc (up to 20 mm diameter); (2) biofilms up to 7 mm thick, dominated almost exclusively by Oscillatoria; (3) microbial mats up to 8 mm thick containing several taxa, particularly Scytonema and Phormidium. The abundance of heterocystous genera (communities 1 and 3) implies that N2 fixation plays an important role in the nitrogen economy of these ecosystems. Most of the communities were rich in pigments absorbing in the UV-blue end of the spectrum, such as scytonemin and mycosporine-like amino acids. Spectroradiometric analyses of sections of the communities showed that short wavelength radiation did not reach the bottom layer where phycobiliprotein-rich cells were located. This lower community experienced low irradiance in the photosynthetically active radiation band (400–700 nm), restricted to the wavelengths of the yellow-red waveband (550–650 nm). The surface screening of high energy wavelengths may confer an adaptive advantage to these communities which grow under continuous light during the polar summer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6941.1999.tb00586.x
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  • 8
    Electronic Resource
    Electronic Resource
    Lexical Object Theory: Specification Level (1998)
    Springer
    Grammars 1 (1998), S. 57-84 
    Details
    ISSN: 1572-848X
    Keywords: computational representation and inference ; lexical object theory ; lexical object specification formalism ; unification-based grammar formalisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Linguistics and Literary Studies , Computer Science
    Notes: Abstract Unification has become a major paradigm in Mathematical and Computational Linguistics. The research done in this area may be classified in four main streams: feature structures as an adequate model for the description of linguistic phenomena, typed unification, representation of feature structures, and unification algorithms. This work proposes a new approach to unification-based Mathematical and Computational Linguistics: the Lexical Object Theory. The main design criteria are based on linguistic motivation, computational efficiency and formal soundness. The first part of the work outlines the main characteristics of the Lexical Object Theory, its comprehensive orientation, and its layered structure based on the separation of the following levels: specification, transformation, typification, representation and unification. The second part concentrates on the specification level of the Lexical Object Theory. The linguistic motivation of this model is presented, as well as a detailed description of the specification formalism, the computational model it is based on, and finally, the inference rules on lexical objects at the specification level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009978900499
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  • 9
    Electronic Resource
    Electronic Resource
    Short- and long-term effects of ammonium on photodependent nitrogen fixation in wetland rice fields of Spain (1997)
    Springer
    Biology and fertility of soils 24 (1997), S. 353-357 
    Details
    ISSN: 1432-0789
    Keywords: Key words Acetylene reduction assay ; Anabaena sp. ; Ammonium ; Cyanobacteria ; Nitrogen fixation ; Wetland rice fields ; Nitrogenase activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Short- and long-term experiments were conducted in the rice fields of Valencia, Spain, to determine the ecological significance of ammonium on nitrogen fixation. A significant inhibition of nitrogenase activity by ammonium, at concentrations higher than 0.5mM, was observed after 8h of incubation in short-term experiments done with a bloom of the N2-fixing cyanobacterium Anabaena sp. In a second set of short-term experiments for in situ assays of nitrogenase activity in the field, a significant correlation between nitrogenase activity and the number of N2-fixing cyanobacteria in soil was found. No significant inhibition of nitrogenase activity by ammonium at concentrations up to 2mM was observed in these assays after 24h of incubation. This lack of inhibition was probably due to the rapid decrease in ammonium content in the flood water. Only 5% of the ammonium initially added remained in the water 24h later. In the long-term experiments, nitrogenase activity was assayed in plots fertilized with 0, 70 and 140kgNha–1, over the cultivation cycle, for 5 years. A partial inhibition of nitrogenase activity by deep-placed N fertilizers was observed. Differences were only significant in 2 years. Mean results from 5 years only showed significant differences between plots fertilized with 0 and 140kgNha–1. The partial inhibition of nitrogenase activity by ammonium increased over the cultivation cycle. Inhibition was only significant in September, at the end of the cultivation cycle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050257
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  • 10
    Electronic Resource
    Electronic Resource
    Identification of Metabolic Bone Disease in Patients with Endogenous Hyperthyroidism: Role of Biological Markers of Bone Turnover (1997)
    Springer
    Calcified tissue international 61 (1997), S. 370-376 
    Details
    ISSN: 1432-0827
    Keywords: Key words: Hyperthyroidism — Bone mineral density — Dual X-ray absorptiometry — Bone turnover markers — Osteoporosis prediction.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. Active hyperthyroidism is associated with reduced bone mass. Nevertheless, not all patients show the same risk for developing osteoporosis. Our aim was to analyze some clinical and biochemical potential predictors of low bone mass in hyperthyroid patients. We studied 127 consecutive hyperthyroid patients (110 females, 17 males; aged 42 ± 16 years). Bone mineral density (BMD) was measured by dual X-ray absorptiometry (DXA) at lumbar spine (LS; L2–L4) and femoral neck (FN). Data were expressed as g/cm2 and T-score. Patients were placed into two groups based on recent WHO criteria: Group A, no osteoporosis (n = 98); and group B, lumbar or femoral osteoporosis (n = 29). Study protocol included evaluation of osteoporosis risk factors, anthropometrical variables, thyroid function, and bone turnover markers. Receiver-operating characteristic (ROC) plots for the precision of bone markers and multivariate analysis for the prediction of BMD and osteoporosis were performed. Group B showed greater age and proportion of menopausal females; lower weight, height, and calcium intake; longer duration of menopause; and greater levels of total and bone alkaline phosphatase and of urine hydroxyproline. No differences in thyroid function, osteocalcin, tartrate-resistant acid phosphatase, and type I collagen C-telopeptide (ICTP) were found. The best predictive model accounted for 46% and 62% of the variability of lumbar and femoral BMD respectively and correctly classified 89% of the osteoporotic hyperthyroid patients. No significant difference in ROC plots was observed. It is concluded that hyperthyroid patients with lumbar or femoral osteoporosis show a typical clinical and biochemical profile illustrating that the relationship between BMD and bone markers is better in high turnover states. Classical bone turnover markers show high performance in the evaluation of hyperthyroid bone disease.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002239900350
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