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  • Electronic Resource  (23)
  • 1995-1999  (11)
  • 1985-1989  (12)
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  • Electronic Resource  (23)
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  • 1
    Electronic Resource
    Electronic Resource
    Cell-suspension culture of Arachis hypogaea L.: model system of specific enzyme induction in secondary metabolism (1987)
    Springer
    Planta 172 (1987), S. 238-244 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00394593
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  • 2
    Electronic Resource
    Electronic Resource
    The cross section of14N(n, p)14C at stellar energies and its role as a neutron poison forS-process nucleosynthesis (1988)
    Springer
    The European physical journal 330 (1988), S. 167-172 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01293392
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  • 3
    Electronic Resource
    Electronic Resource
    The3He(d,p) α reaction at astrophysical energies (1989)
    Springer
    The European physical journal 333 (1989), S. 219-227 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01565154
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  • 4
    Electronic Resource
    Electronic Resource
    Screening corrections in cold deuterium fusion rates (1989)
    Springer
    The European physical journal 333 (1989), S. 317-318 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01294522
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  • 5
    Electronic Resource
    Electronic Resource
    Helium burning of22Ne (1989)
    Springer
    The European physical journal 334 (1989), S. 491-510 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01294757
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  • 6
    Electronic Resource
    Electronic Resource
    Prospects for underground accelerator research (1995)
    Springer
    The European physical journal 350 (1995), S. 289-301 
    Details
    ISSN: 1434-601X
    Keywords: 29.00
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A summer institute was convened at the Gran Sasso Laboratory (Italy), 27. June to 7. July 1994, in part to explore the advantages of an accelerator laboratory deep underground, particularly for crucial nuclear-astrophysics measurements presently limited at low energies by cosmic-ray backgrounds. Here we review specific reactions identified as needing further study in a low-background environment, and outline suitable facilities to carry out such studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01291186
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  • 7
    Electronic Resource
    Electronic Resource
    The S(E) factor of7Li(p, γ)8Be and consequences for S(E) extrapolation in7Be(p, γ0)8B (1995)
    Springer
    The European physical journal 351 (1995), S. 229-236 
    Details
    ISSN: 1434-601X
    Keywords: 25.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Excitation functions and forward-backward anisotropies have been measured for the7Li(p, γ)8Be capture reaction over the proton energy rangeE p =100 to 1500 keV, using a 4π summing crystal and Ge(Li) detectors, respectively. The data show at all energies the presence of El and M1 capture amplitudes arising from the direct capture (DC) process and theE R =441 and 1030 keV resonances, respectively. Due to the observed DC process, the present data increase significantly the reaction rates (up to a factor of 110) compared to values given in the compilation. The data and their analyses remove the recent criticism on DC model calculations, which had implied a significant reduction in the extrapolated S(E) factor for7Be(p,γ)B and thus in the predicted flux of high-energy solar neutrinos; thus, the solar neutrino problem is still with us.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01289534
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  • 8
    Electronic Resource
    Electronic Resource
    The E1 and E2 capture amplitudes in 12C(α,γ0)16O (1999)
    Springer
    The European physical journal 6 (1999), S. 451-461 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Excitation functions of the γ0 capture transition in 12C(α,γ)16O at θγ= 90˚ were obtained using a 4 × 4'' BGO crystal in close geometry (E= 0.94 to 3.39 MeV) and a 2 × 2'' BGO crystal in far geometry (E= 1.69 to 3.29 MeV), where the study of the reaction was initiated in inverse kinematics involving a windowless gas target. The small crystal detected essentially the E1 multipole component in the γ0 capture transition, while the large crystal observed approximately the angle-integrated sum of the E1 and E2 multipole components. Analysis of the two data sets together with data from previous work provided strong evidence that both multipoles are of equal importance at the relevant stellar energy E 0= 0.3 MeV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100500050369
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  • 9
    Electronic Resource
    Electronic Resource
    Recoil separator ERNA: ion beam specifications (1999)
    Springer
    The European physical journal 6 (1999), S. 471-477 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. For improved measurements of the key astrophysical reaction 12C(α,γ)16O in inverted kinematics, a recoil separator ERNA is being developed at the 4 MV Dynamitron tandem accelerator in Bochum to detect directly the 16O recoils with about 50% efficiency. Calculations of the ion beam optics including all filtering and focusing elements of ERNA are presented. Since the 12C projectiles and the 16O recoils have essentially the same momentum, and since the 12C ion beam emerging from the accelerator passes through a momentum filter (analysing magnet), the 12C ion beam must be as free as possible from 16O contamination for ERNA to succeed. In the present work, the 16O contamination was reduced from a level of 1 × 10−11 to a level below 2 × 10−29 by the installation of Wien filters both before and after the analysing magnet. The measurement of these and other beam specifications involved other parts of the final ERNA layout – sequentially a Wien filter, a 60˚ dipole magnet, another Wien filter, and a ΔE-E telescope. The setup led to a measured suppression factor of 5 × 10−18 for the 12C ion beam. The experiments also indicate that an almost free choice of the charge state for the 16O recoils is possible in the separator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100500050371
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  • 10
    Electronic Resource
    Electronic Resource
    Absolute cross section of the3He(α,γ)7Be reaction (1988)
    Springer
    The European physical journal 329 (1988), S. 243-254 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01283781
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