108 research outputs found
Low-lying continuum structures in B8 and Li8 in a microscopic model
We search for low-lying resonances in the B8 and Li8 nuclei using a
microscopic cluster model and a variational scattering method, which is
analytically continued to complex energies. After fine-tuning the
nucleon-nucleon interaction to get the known 1+ state of B8 at the right
energy, we reproduce the known spectra of the studied nuclei. In addition, our
model predicts a 1+ state at 1.3 MeV in B8, relative to the Be7+p threshold,
whose corresponding pair is situated right at the Li7+n threshold in Li8.
Lacking any experimental evidence for the existence of such states, it is
presently uncertain whether these structures really exist or they are spurious
resonances in our model. We demonstrate that the predicted state in B8, if it
exists, would have important consequences for the understanding of the
astrophysically important Be7(p,gamma)B8 reaction.Comment: 6 pages with 1 figure. The postscript file and more information are
available at http://nova.elte.hu/~csot
Radiative capture and electromagnetic dissociation involving loosely bound nuclei: the B example
Electromagnetic processes in loosely bound nuclei are investigated using an
analytical model. In particular, electromagnetic dissociation of B is
studied and the results of our analytical model are compared to numerical
calculations based on a three-body picture of the B bound state. The
calculation of energy spectra is shown to be strongly model dependent. This is
demonstrated by investigating the sensitivity to the rms intercluster distance,
the few-body behavior, and the effects of final state interaction. In contrast,
the fraction of the energy spectrum which can be attributed to E1 transitions
is found to be almost model independent at small relative energies. This
finding is of great importance for astrophysical applications as it provides us
with a new tool to extract the E1 component from measured energy spectra. An
additional, and independent, method is also proposed as it is demonstrated how
two sets of experimental data, obtained with different beam energy and/or
minimum impact parameter, can be used to extract the E1 component.Comment: Submitted to Phys. Rev. C. 10 pages, 7 figure
Experience gained at the Ural Turbine Works with retrofitting steam turbine units for thermal power stations
Accuracy and Stability of Computing High-Order Derivatives of Analytic Functions by Cauchy Integrals
High-order derivatives of analytic functions are expressible as Cauchy
integrals over circular contours, which can very effectively be approximated,
e.g., by trapezoidal sums. Whereas analytically each radius r up to the radius
of convergence is equal, numerical stability strongly depends on r. We give a
comprehensive study of this effect; in particular we show that there is a
unique radius that minimizes the loss of accuracy caused by round-off errors.
For large classes of functions, though not for all, this radius actually gives
about full accuracy; a remarkable fact that we explain by the theory of Hardy
spaces, by the Wiman-Valiron and Levin-Pfluger theory of entire functions, and
by the saddle-point method of asymptotic analysis. Many examples and
non-trivial applications are discussed in detail.Comment: Version 4 has some references and a discussion of other quadrature
rules added; 57 pages, 7 figures, 6 tables; to appear in Found. Comput. Mat
The Schwarzian derivative and the Wiman-Valiron property
Consider a transcendental meromorphic function in the plane with finitely many critical values, such that the multiple points have bounded multiplicities and the inverse function has finitely many transcendental singularities. Using the Wiman-Valiron method it is shown that if the Schwarzian derivative is transcendental then the function has infinitely many multiple points, the inverse function does not have a direct transcendental singularity over infinity, and infinity is not a Borel exceptional value. The first of these conclusions was proved by Nevanlinna and Elfving via a fundamentally different method
Non-real zeros of derivatives of meromorphic functions
A number of results are proved concerning non-real zeros of derivatives of real and strictly non-real meromorphic functions in the plane
Transition processes occurring under continuous and stepwise heating of GaAs surface-barrier structures
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