41 research outputs found
Benchmark Calculation of the Three-Nucleon Photodisintegration
A benchmark is set on the three-nucleon photodisintegration calculating the total cross section with modern realistic two- and three-nucleon forces (AV18, UrbIX) using both the Faddeev equations and the Lorentz Integral Transform method. This test shows that the precision of three-body calculations involving continuum states is considerably higher than experimental uncertainties. Effects due to retardations, higher multipoles, meson exchange currents and Coulomb force are studied
Is there a Pronounced Giant Dipole Resonance in ^4He?
A four-nucleon calculation of the total ^4He photodisintegration cross
section is performed. The full final-state interaction is taken into account
for the first time. This is achieved via the method of the Lorentz integral
transform. Semi-realistic NN interactions are employed. Different from the
known partial two-body ^4He(\gamma,n)^3He and ^4He(\gamma,p)^3H cross sections
our total cross section exhibits a pronounced giant resonance. Thus, in
contrast to older data, we predict quite a strong contribution of
the channel at the giant resonance peak energy.Comment: 10 pages, Latex (REVTEX), 4 Postscript figures, to appear in Phys.
Rev. Let
Electromagnetic response functions of few-nucleon systems
Inclusive electromagnetic reactions in few-nucleon systems are studied basing
on accurate three- and four-body calculations. The longitudinal 4He(e,e')
response function obtained at q\le 600 MeV/c completely agrees with experiment.
The exact 4He spectral function obtained in a semirealistic potential model is
presented, and the accuracy of the quasielastic response calculated with its
help is assessed, as well as the accuracy of some simpler approximations for
the response. The photodisintegration cross section of 3He obtained with the
realistic AV14 NN force plus UrbanaVIII NNN force agrees with experiment. It is
shown that this cross section is very sensitive to underlying nuclear dynamics
in the E_\gamma\simeq 70-100 MeV region. In particular, the NNN nuclear force
clearly manifests itself in this region.Comment: 10 pages, Latex, style file is included, 7 ps figures, to appear in
Proc. of the 2nd Int. Conf. on Perspectives in Hadronic Physics, ITCP,
Triest, May 1999, World Sci., Singapor
Higher-Order Nuclear-Polarizability Corrections in Atomic Hydrogen
Nuclear-polarizability corrections that go beyond unretarded-dipole
approximation are calculated analytically for hydrogenic (atomic) S-states.
These retardation corrections are evaluated numerically for deuterium and
contribute -0.68 kHz, for a total polarization correction of 18.58(7) kHz. Our
results are in agreement with one previous numerical calculation, and the
retardation corrections completely account for the difference between two
previous calculations. The uncertainty in the deuterium polarizability
correction is substantially reduced. At the level of 0.01 kHz for deuterium,
only three primary nuclear observables contribute: the electric polarizability,
, the paramagnetic susceptibility, , and the third Zemach
moment, . Cartesian multipole decomposition of the virtual
Compton amplitude and its concomitant gauge sum rules are used in the analysis.Comment: 26 pages, latex, 1 figure -- Submitted to Phys. Rev. C -- epsfig.sty
require
Threshold 3He and 3H Transverse Electron Scattering Response Functions
The threshold transverse response functions R_T(q,omega) for 3He and 3H are
calculated using the AV18 nucleon-nucleon potential, the UrbanaIX three-body
force, and the Coulomb potential. Final states are completely taken into
account via the Lorentz integral transform technique. Consistent two-body pi-
and rho-meson exchange currents as deduced using the Arenh\"ovel-Schwamb
technique are included. The convergence of the method is shown and a comparison
of the corresponding MEC contribution is made to that of a consistent MEC for
the meson theoretical r-space BonnA potential. The response R_T is calculated
in the threshold region at q=174, 324, and 487 MeV/c and compared with
available data. The strong MEC contributions in the threshold region are nicely
confirmed by the data at q=324 and 487 MeV/c although some differences between
theoretical and experimental results remain. A comparison is also made with
other calculations, where the same theoretical input is used. The agreement is
generally rather good, but leaves also some space for further improvement.Comment: 16 pages, 5 figure
No systematic effects of sampling direction on climate-growth relationships in a large-scale, multi-species tree-ring data set
Ring-width series are important for diverse fields of research such as the study of past climate, forest ecology, forest genetics, and the determination of origin (dendro-provenancing) or dating of archaeological objects. Recent research suggests diverging climate-growth relationships in tree-rings due to the cardinal direction of extracting the tree cores (i.e. direction-specific effect). This presents an understudied source of bias that potentially affects many data sets in tree-ring research. In this study, we investigated possible direction-specific growth variability based on an international (10 countries), multi-species (8 species) tree-ring width network encompassing 22 sites. To estimate the effect of direction-specific growth variability on climate-growth relationships, we applied a combination of three methods: An analysis of signal strength differences, a Principal Component Gradient Analysis and a test on the direction-specific differences in correlations between indexed ring-widths series and climate variables. We found no evidence for systematic direction-specific effects on tree radial growth variability in high-pass filtered ring-width series. In addition, direction-specific growth showed only marginal effects on climate-growth correlations. These findings therefore indicate that there is no consistent bias caused by coring direction in data sets used for diverse dendrochronological applications on relatively mesic sites within forests in flat terrain, as were studied here. However, in extremely dry, warm or cold environments, or on steep slopes, and for different life-forms such as shrubs, further research is advisable.</p
Analiza porównawcza stopnia uszkodzenia jesionu wyniosłego (Fraxinus excelsior L.) i olszy czarnej (Alnus glutinosa (L.) Gaertn.), rosnących w zmieszaniu lub bliskim sąsiedztwie
The paper presents a comparative analysis of the degree of damage to common ash and black alder trees growing in mixture or a close neighbourhood. Three variants of the damage assessment method were applied in the analysis: defoliation−based variant I, vitality variant II and synthetic damage indicator−based variant III. It was demonstrated that on average ash stands were more damaged than alder stands. This allowed to put forward a hypothesis that there is an alternative to replace ash with black alder on some, especially wet habitats where the dieback process is largely advanced