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  • Springer  (65)
  • American Institute of Physics (AIP)  (3)
  • Wiley-Blackwell  (3)
  • American Meteorological Society (AMS)
  • 1985-1989  (71)
Collection
Year
  • 1
    ISSN: 1432-1041
    Keywords: azathioprine ; 6-thiouric acid ; 6-mercaptopurine ; renal transplantation ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The immunosuppressive activity of azathioprine (AZA) is unpredictable and depends on the formation of intracellular thiopurine ribonucleotides. However, the quantification of these active thiopurines presents difficult analytical problems. It has recently been postulated that plasma concentrations of 6-thiouric acid (6-TU) and 6-mercaptopurine (6-MP), metabolites of AZA, may provide more readily measurable indices of the pharmacologic activity of AZA. In order to evaluate the utility of 6-TU and 6-MP plasma concentrations in monitoring AZA therapy, we studied their pharmacokinetics in 6 renal transplant patients, and their in vitro immunosuppressive potency in a mixed lymphocyte proliferation assay. A peak plasma 6-TU concentration of 710.7 ng/ml was observed at 3.8 h after oral dosing. Good correlation was observed between the elimination t1/2 of 6-TU and serum creatinine, and between AUC over 24 h and serum creatinine. However, we did not observe a second peak in plasma 6-TU concentration that could be attributed to the degradation of active AZA metabolites. 6-MP plasma concentrations in the patients were low (mean peak concentration 36.0 ng/ml) and rapidly disappeared within 8 h. In vitro immunosuppressive activity could not be demonstrated for 6-TU over a concentration range of 1.25 ng/ml to 0.25 mg/ml. We conclude that 6-TU is pharmacologically inert and is primarily eliminated by the kidneys. Our findings currently do not support the use of plasma concentrations of 6-TU or 6-MP to monitor AZA therapy. In order to optimize AZA therapy, analytical techniques that are technically feasible and that can directly quantify the active intracellular thiopurines are being explored.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 7184-7194 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a computer simulation of the real-time detection of ultrafast electronic decay dynamics in polyatomic molecules with femtosecond laser pulses. The intramolecular non-Born-Oppenheimer quantum dynamics is treated numerically exactly for a two-state three-mode vibronic coupling model representing the conically intersecting S1 and S2 excited states of pyrazine. The pump–probe signal is evaluated in lowest order perturbation theory with respect to the radiation–matter interaction by numerical integration over the pump and probe pulses. We discuss in some detail the dependence of the pump–probe signal on the properties of the laser pulses (frequencies and pulse durations). The calculations predict a dramatic (∼12 000 cm−1) and ultrafast (∼20 fs) red shift of the stimulated-emission signal as well as distinctive quantum beats in the pump–probe signal as a function of the delay time. Both effects are very pronounced and should therefore be relatively easily detectable experimentally. They are expected to be generic features of ultrafast internal-conversion processes in polyatomic molecules.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 1799-1806 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An accurate and efficient numerical scheme is presented for calculating electrical conditions inside wire-duct electrostatic precipitators. A Galerkin finite-element method with quadratic interpolation is employed in solving Poisson's equation to yield the electric potential solution. A backward difference method is utilized to compute the space-charge density from the continuity equation. The two methods are iteratively applied until convergence criteria for electric potential and current density are met. Computed potential and electric field values show good agreement with analytic solutions and experimental measurements. Comparisons between the present scheme and a finite-difference scheme show that the finite-element method offers distinct advantages in predicting the electrical characteristics of precipitators.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 34-36 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of oxygen precipitation and surface films (SiO2 vs Si3N4) on P diffusion at 1100 °C in Czochralski silicon have been studied. With a fast precipitation rate, P diffusion under both kinds of films is enhanced because of the supersaturation of Si interstitials caused by oxygen precipitation. The larger enhancement in P diffusion under Si3N4 than that under SiO2 covered with Si3N4 is attributed to the slower recombination velocity of interstitials at the Si3N4/Si interface. P diffusion in a denuded zone behaves like that in float-zone Si until the interstitials generated under that zone arrive at the interface.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Archiv der Mathematik 47 (1986), S. 408-409 
    ISSN: 1420-8938
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0983
    Keywords: Plant mitochondrial DNA ; Restriction enzyme analysis ; rRNA genes ; Tomato cell suspension cultures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mitochondrial DNA (mtDNA) from Lycopersicon esculentum was purified from cell suspension cultures. The DNA, isolated from mitochondria purified by two successive sucrose density gradients, was uncontaminated with nuclear DNA or DNA from proplastids. The total molecular weights of BamHI, BglI, and BglII fragments indicate a mitochondrial genome size of at least 270 kb. Cross hybridization between tomato mtDNA and cloned spinach plastid genes revealed some homology. In hybridization experiments using cloned mitochondrial rRNA genes and BamHI digested total mtDNA the presence of recombination repeats is demonstrated.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-1939
    Keywords: Allocation patterns ; Restionaceae ; Nitrogen ; Dry mass ; Fynbos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The annual growth pattern of male plants of the endemic, dioecious fynbos species, Thamnochortus punctatus, revealed sequential growth of the various below-and above-ground organs. Root and rhizome development were favoured in the wet winter months while culm elongation occurred in the warmer but drier spring to summer period. The reproductive phase of development followed in the hot dry summer and autumn. The asynchronous pattern of growth is suggested to enable the plant to maximize utilization of scarce resources within the confines of the environmental controls determined by the mediterranean-climate. Maximum root and rhizome activity in the rainy season enabled the plant to absorb and store nitrogen in mature culms for later above ground organ development. As the absorption of nitrogen from senscing material is essential for this pattern of organ development to assist in alleviating nutrient scarcity the high degree of nitrogen reabsorption, 35 to 70% for branches and culms respectively, shows the potential importance of asynchronous organ growth in overcoming nitrogen limitation of plant growth. Comparisons of dry mass and nitrogen allocation patterns indicate that developmental strategies employed by evergreen, perennial plants in climatically and edaphically constrained environments cannot be deduced from biomass allocation patterns alone as they do not appear to reflect strategies evolved to overcome nutrient limitation.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 81 (1989), S. 412-417 
    ISSN: 1432-1939
    Keywords: Myrmecochory ; Fynbos ; Regeneration ; Fire ; Nutrient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Leucospermum conocarpodendron (L.) Buek (Proteaceae) seedlings were excavated several months after a fire in Cape fynbos. Seedlings under burnt parental skeletons had short hypocotyls (mean 25 mm) indicating passive dispersal whereas seedlings in the open were more deeply buried (mean 48 mm) by ants. Soil nutrient concentrations at the site of germination were negatively related to depth of burial and distance from parent. Ant dispersal resulted in seedlings emerging in soils with lower nutrient concentrations than passively dispersed seeds. Tissue analysis supported the soil results with lower P content in seedlings from open (ant dispersed) sites. Seedling survival in the first year of establishment was also lower in open sites, but not significantly so. However seedlings were slightly taller in the open. The results of this study, the first on naturally occurring intraspecific variation in myrmecochory, strongly contradict current explanations for the high incidence of myrmecochory in nutrient poor environments.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 38 (1988), S. 1-1 
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
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