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  • 1985-1989  (12)
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Year
  • 1
    ISSN: 1432-2048
    Keywords: Arachis ; Cell culture ; Enzyme induction (cell culture) ; Phenylalanine ammonia-lyase ; Phytoalexin ; Stilbene synthase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A peanut (Arachis hypogaea L.) cell-suspension culture susceptible to selective induction of stilbene formation was established. The principles of defense responses of the whole plant were found to be retained in the artificial system. The suspension culture was characterized by its growth curve and by various biochemical parameters. In the stationary phase, reached 8 d after transfer to a new medium, the formation of stilbenes and stilbene synthase could be induced without altering the levels of other enzymes. Eighteen hours after applying an artificial elicitor (ultraviolet-C light) or 4 h after eliciting with a crude preparation of Phytophthora cambivora cell walls, phenylalanineammonia-lyase activity was increased eightfold and stilbene-synthase activity 20-fold. The activity of phenylalanine ammonia-lyase reached its peak at a slightly different time from that of stilbene synthase. The main products of L-phenylalanine metabolism in the induced cells were resveratrol, 3,3′,5-trihydroxy-4′-methoxystilbene and isopentenylresveratrol. Likewise, feruloyl-CoA reductase, as a parameter of lignin formation, was enhanced following induction, albeit with a different time course and with a less steep increase than found for phenylalanine ammonia-lyase and stilbene synthase.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-601X
    Keywords: 25.90 ; 95.90
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The26Al(n, p)26Mg reaction has been studied using neutron spectra which closely resembled Maxwell-Boltzmann (M.-B.) distributions with thermal energies ofkT=40 ×10−6, 31 and 71 keV and also forE n =270–350 keV. These energies correspond to stellar temperaturesT 9=4.6×10−7, 0.36, 0.82 and 3.1–4.1, whereT 9 is in units of 109 K. The partial cross sections for thep 0-(p 1-)transition are found to equal 26±10(1,850 ±150), 13±6(124±17), 16±13(84±14) and 21±8(72±15) mb for the above neutron spectra, respectively. The astrophysical reaction rate is determined for the combinedp 0- andp 1-transitions to beN A 〈σν〉=(0.324±0.026, 20.5±2.7, 22.6±4.3 and 38.7±11.1) ×106 cm3 mole−1 s−1. The results are compared with previous investigations and with statistical model calculations.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 328 (1987), S. 291-299 
    ISSN: 1434-601X
    Keywords: 23.20 ; 21.10.-k
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In the framework of a potential model we have calculated the various bremsstrahlung cross sections into the5Li ground state, includingM 1 andE 2 γ-transitions leading from the high energy wing of the5Li ground state resonance into states belonging to the same resonance at lower energy (intrastate transition). Our calculation supports the hypothesis of Schmalbrock et al. [1] that intrastate transitions ofM 1 andE 2 multipolarity exist. While we find a maximum cross section of roughly 1.4 nb for theE 2 transition, we predict the cross sections forM 1 intrastate transition to be less than 3·10−5nb. An experimental observation of the intrastate γ-ray emission appears to be very difficult due to the dominance of competing resonant (M 1) and direct (E 1) capture processes. Schmalbrock et al. have suggested to deduce magnetic dipole and electric quadrupole moments of resonant states from the measurements of the respectiveM 1 andE 2 intrastate transitions. We will show that theM 1 intrastate cross sections do not yield the appropriate information to determine the magnetic dipole moment. We will also discuss thatE 2 intrastate transitions do not seem to be a suited tool to find the quadrupole moment of an unstable state.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 329 (1988), S. 243-254 
    ISSN: 1434-601X
    Keywords: 25.55.-e ; 27.10 ; 27.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The absolute cross section σ(E) of the3He(α, γ)7Be reaction has been measured fromE c.m. =195 to 686 keV. The studies employed both a supersonic jet gas target and an extended gas target, and were carried out by the observation of the prompt capture γ-ray transitions as well as the7Be residual nuclei. The absolute cross sections deduced from the capture γ-rays are in good agreement with most previous work and remove a discrepancy with other earlier work. In comparison, the σ(E) values obtained from the7Be residual nuclei are systematically higher, suggesting a small production of additional7Be by contaminant reactions.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1434-601X
    Keywords: 95.30.C ; 97.10.C ; 25.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The absolute average cross section 〈σ〉 of the14N(n, p)14C reaction has been measured using neutron spectra that closely resemble Maxwell-Boltzmann distributions with thermal energies of kT=25.0 and 52.4 keV: 〈σ〉=0.81±0.05 and 0.52±0.06 mb, respectively. The resulting reaction rates are nearly the same at T9=0.29 and 0.61, and their average, NA〈συ〉=(1.3±0.1)×105 cm3 s−1 mol−1, is about a factor of three smaller than the previously adopted values obtained by extrapolation between thermal and higher-energy data. Thus, the14N(n, p)14C reaction plays a correspondingly smaller role as a neutron poison fors-process nucleosynthesis.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 325 (1986), S. 193-196 
    ISSN: 1434-601X
    Keywords: 23.20 ; 27.10
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied theD(α, γ)6Li reaction at stellar energies within a potential model. Our calculation improves previous investigations as we explicitely take into account the internal quadrupole moment of the deuteron and ad-state component in the6Li ground state. We reproduce the experimental data for energiesE〈3 MeV. We find, however, that our improvements represent only minor corrections.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 333 (1989), S. 219-227 
    ISSN: 1434-601X
    Keywords: 21.60.Gx ; 25.55.-e ; 24.10.Eq
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have performed a microscopic study of the3He(d,p) α reaction at astrophysical energies within the framework of the Resonating Group Method adopting three different effective nucleon-nucleon interactions. The calculations suggest that the low-energy3He(d,p) α cross section is in good approximation given by the contribution arising from the 3/2+ resonant state atE R =245 keV. In fact, the low-energy data can be better (and more physically) described by a single Breit-Wigner resonance parametrization than by a polynomial fit. Our fit to the3He(d,p) α cross section results in a noticeable reduction in the uncertainties of the resonance parameters of the 3/2+ resonant state as well as in a significantly improved extrapolation of the data to astrophysically important energies. On the basis of this extrapolation we were able to quantitatively deduce the enhancement of the low-energy cross section due to electron screening effects from the data of Krauss et al. and Engstler et al. These experimental enhancement factors were compared with various theoretical models which are all based on the Born-Oppenheimer approximation. As the models underestimate the observed enhancement we suggest that the theoretical study of electron screening effects requires a dynamical treatment.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 333 (1989), S. 317-318 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have recalculated the fusion rates of the free deuterium molecule, ion and mesomolecule taking into account the shielding of the Coulomb barrier by the electrons and muon. Electron screening increases the rates by several orders of magnitude. The fusion of hydrogen nuclei is known to be the source of energy of stars occuring in their high-temperature, high-pressure interiors. In terrestrial conditions, one attempts currently to tap this source of nuclear fusion energy by alternative techniques, i.e. high-temperature plasmas or muon-catalyzed fusion. Very recently cold fusion in solids has achieved worldwide attention, since experimental evidence for increased hydrogenic fusion rates in palladium and titanium has been reported[1,2]. These reports have motivated us to reconsider the fusion probability of free hydrogen molecules, ions and mesomolecules, following closely the studies of Refs. [3,4,5]. Our aim however is to improve the previous estimates of the respective fusion rates by taking account of the screening effects of the electrons and muons on the nuclear Coulomb barrier which will turn out to be quite important. As in Ref. [5] we will restrict our numerical results to deuterium only.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 334 (1989), S. 491-510 
    ISSN: 1434-601X
    Keywords: 25.55 ; 97.10
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The22Ne(α, γ)26Mg and22Ne(α, n)25Mg reactions were investigated forE α(lab) from 0.71 to 2.25 MeV. Neon gas enriched to 99% in22Ne was recirculated in a differentially pumped gas target system of the extended type. Theγ-ray transitions were observed with Ge(Li) detectors and the neutrons with3He ionization chambers. A previously known resonance at ER(lab)=2.05 MeV was verified and 15 new resonances were found in the energy range covered, with the lowest at ER(lab)=0.83 MeV. Information on resonance energies, widths, strengths,γ-ray branching ratios, as well asJ π assignments, is reported. The energy range investigated corresponds to the important temperature range ofT 9 from 0.3 to 1.4 (109 K), for which the astrophysical rates were determined for both reactions. The results show that the ratios of the rates for22Ne(α, n)25Mg and22Ne(α, γ)26Mg are significantly smaller than the previously adopted values, e.g., by at least a factor of 60 nearT 9=0.65. Thus, the22Ne(α, n)25Mg reaction will likely play a smaller role as a neutron source fors-process nucleosynthesis, than has frequently been assumed.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 324 (1986), S. 307-310 
    ISSN: 1434-601X
    Keywords: 23.20 ; 27.10 ; 21.60G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied resonant, intrastate and non-resonant bremsstrahlungγ-ray transitions leading to the 2+ state in8Be atE x=2.94 MeV. We find aγ-width of Γ γ =0.45 eV for the 4+ state in8Be, corresponding to anE 2 strength of 19 W.u. For the intrastateγ-ray transition within the 2+ resonance we predict a maximum cross section of 2.5 nb atE≈3.3 MeV. An experimental observation of this novel type ofγ-ray emission, however, appears to be difficult due to the dominance of competing resonant and direct capture processes.
    Type of Medium: Electronic Resource
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