20,109 research outputs found

### Angular Momentum Projected Configuration Interaction with Realistic Hamiltonians

The Projected Configuration Interaction (PCI) method starts from a collection
of mean-field wave functions, and builds up correlated wave functions of good
symmetry. It relies on the Generator Coordinator Method (GCM) techniques, but
it improves the past approaches by a very efficient method of selecting the
basis states. We use the same realistic Hamiltonians and model spaces as the
Configuration Interaction (CI) method, and compare the results with the full CI
calculations in the sd and pf shell. Examples of 24Mg, 28Si, 48Cr, 52Fe and
56Ni are discussed.Comment: 10 pages, 10 figures. Revised version. To be published in Physical
Review

### Towards a practical approach for self-consistent large amplitude collective motion

We investigate the use of an operatorial basis in a self-consistent theory of
large amplitude collective motion. For the example of the
pairing-plus-quadrupole model, which has been studied previously at
equilibrium, we show that a small set of carefully chosen state-dependent basis
operators is sufficient to approximate the exact solution of the problem
accuratly. This approximation is used to study the interplay of quadrupole and
pairing degrees of freedom along the collective path for realistic examples of
nuclei. We show how this leads to a viable calculational scheme for studying
nuclear structure, and discuss the surprising role of pairing collapse.Comment: 19 pages, 8 figures Revised version To be published in Phys. Rev.

### Central depression in nuclear density and its consequences for the shell structure of superheavy nuclei

The influence of the central depression in the density distribution of
spherical superheavy nuclei on the shell structure is studied within the
relativistic mean field theory. Large depression leads to the shell gaps at the
proton Z=120 and neutron N=172 numbers, while flatter density distribution
favors N=184 for neutrons and leads to the appearance of a Z=126 shell gap and
to the decrease of the size of the Z=120 shell gap. The correlations between
the magic shell gaps and the magnitude of central depression are discussed for
relativistic and non-relativistic mean field theories.Comment: 5 page

### Collective dipole excitations in sodium clusters

Some properties of small and medium sodium clusters are described within the
RPA approach using a projected spherical single particle basis. The oscillator
strengths calculated with a Schiff-like dipole transition operator and folded
with Lorentzian functions are used to calculate the photoabsorbtion cross
section spectra. The results are further employed to establish the dependence
of the plasmon frequency on the number of cluster components. Static electric
polarizabilities of the clusters excited in a RPA dipole state are also
calculated.
Comparison of our results with the corresponding experimental data show an
overall good agreement.Comment: 23 pages, 5 figure

### Description of superdeformed bands in light N=Z nuclei using the cranked HFB method

Superdeformed states in light $N=Z$ nuclei are studied by means of the
self-consistent cranking calculation (i.e., the P + QQ model based on the
cranked Hartree-Fock-Bogoliubov method). Analyses are given for two typical
cases of superdeformed bands in the $A \simeq 40$ mass region, that is, bands
where backbending is absent ($^{40}$Ca) and present ($^{36}$Ar). Investigations
are carried out, particularly for the following points: cross-shell excitations
in the sd and pf shells; the role of the g$_{9/2}$ and d$_{5/2}$ orbitals; the
effect of the nuclear pairing; and the interplay between triaxiality and band
termination.Comment: 17 pages, 18 figures, accepted in Phys. Rev.

### Pairing in Nuclei

Simple generic aspects of nuclear pairing in homogeneous medium as well as in
finite nuclei are discussed. It is argued that low-energy nuclear structure is
not sensitive enough to resolve fine details of nuclear nucleon-nucleon (NN)
interaction in general and pairing NN interaction in particular what allows for
regularization of the ultraviolet (high-momentum) divergences and a consistent
formulation of effective superfluid local theory. Some aspects of
(dis)entanglement of pairing with various other effects as well as forefront
ideas concerning isoscalar pairing are also briefly discussed.Comment: Invited talk presented at the International Conference on Finite
Fermionic Systems, Nilsson Model 50 Years,Lund, Sweden, June 14-18, 2005, 7
LaTeX pages, 4 encapsulated postscript figure

### The effects of deformation and pairing correlations on nuclear charge form factor

A set of moderately deformed $s-d$ shell nuclei is employed for testing the
reliability of the nuclear ground state wave functions which are obtained in
the context of a BCS approach and offer a simultaneous consideration of
deformation and pairing correlations effects. In this method, the mean field is
assumed to be an axially symmetric Woods-Saxon potential and the effective
two-body interaction is a monopole pairing force. As quantities of main
interest we have chosen the nuclear form factors, the occupancies of the active
(surface) orbits and the Fermi sea depletion, which provide quite good tests
for microscopic descriptions of nuclei within many body theories. For our
comparisons with results emerging from other similar methods, an axially
deformed harmonic oscillator field is also utilized.Comment: 20 pages, 12 figures, 2 table

### Ecosystem properties and principles of living systems as foundation for sustainable agriculture â€“ Critical reviews of environmental assessment tools, key findings and questions from a course process

With increasing demands on limited resources worldwide, there is a growing interest in sustainable patterns of utilisation and production. Ecological agriculture is a response to these concerns.
To assess progress and compliance, standard and comprehensive measures of resource requirements, impacts and agro-ecological health are needed. Assessment tools should also be rapid, standardized, userfriendly, meaningful to public policy and applicable to management. Fully considering these requirements confounds the development of integrated methods.
Currently, there are many methodologies for monitoring performance, each with its own foundations, assumptions, goals, and outcomes, dependent upon agency agenda or academic orientation. Clearly, a concept of sustainability must address biophysical, ecological, economic, and sociocultural foundations.
Assessment indicators and criteria, however, are generally limited, lacking integration, and at times in conflict with one another. A result is that certification criteria, indicators, and assessment methods are not based on a consistent, underlying conceptual framework and often lack a management focus.
Ecosystem properties and principles of living systems, including self-organisation, renewal, embeddedness, emergence and commensurate response provide foundation for sustainability assessments and may be appropriate focal points for critical thinking in an evaluation of current methods and standards. A systems framework may also help facilitate a comprehensive approach and promote a context for meaningful discourse. Without holistic accounts, sustainable progress remains an illdefined concept and an elusive goal.
Our intent, in the work with this report, was to use systems ecology as a pedagogic basis for learning and discussion to:
- Articulate general and common characteristics of living systems.
- Identify principles, properties and patterns inherent in natural ecosystems.
- Use these findings as foci in a dialogue about attributes of sustainability to:
a. develop a model for communicating scientific rationale.
b. critically evaluate environmental assessment tools for application in land-use.
c. propose appropriate criteria for a comprehensive assessment and expanded definition of ecological land use

### Parametrizations of triaxial deformation and E2 transitions of the wobbling band

By the very definition the triaxial deformation parameter $\gamma$ is related
to the expectation values of the K=0 and K=2 components of the intrinsic
quadrupole tensor operator. On the other hand, using the same symbol
"$\gamma$", various different parametrizations of triaxial deformation have
been employed, which are suitable for various types of the mean-field
potentials. It is pointed out that the values of various "$\gamma$" are quite
different for the same actual triaxial deformation, especially for the large
deformation; for example, the difference can be almost a factor two for the
case of the triaxial superdeformed bands recently observed in the Hf and Lu
nuclei. In our previous work, we have studied the wobbling band in Lu nuclei by
using the microscopic framework of the cranked Nilsson mean-field and the
random phase approximation, where the most serious problem is that the
calculated B(E2) value is about factor two smaller. It is shown that the origin
of this underestimation can be mainly attributed to the small triaxial
deformation; if is used the same triaxial deformation as in the analysis of the
particle-rotor model, the calculated B(E2) increases and gives correct
magnitude compared with the experimental data.Comment: 10 pages, 9 figure

### Nilsson diagrams for light neutron-rich nuclei with weakly-bound neutrons

Using Woods-Saxon potentials and the eigenphase formalism for one-particle
resonances, one-particle bound and resonant levels for neutrons as a function
of quadrupole deformation are presented, which are supposed to be useful for
the interpretation of spectroscopic properties of some light neutron-rich
nuclei with weakly-bound neutrons. Compared with Nilsson diagrams in text books
which are constructed using modified oscillator potentials, we point out a
systematic change of the shell structure in connection with both weakly-bound
and resonant one-particle levels related to small orbital angular momenta
$\ell$. Then, it is seen that weakly-bound neutrons in nuclei such as
$^{15-19}$C and $^{33-37}$Mg may prefer to being deformed as a result of
Jahn-Teller effect, due to the near degeneracy of the 1d$_{5/2}$-2s$_{1/2}$
levels and the 1f$_{7/2}$-2p$_{3/2}$ levels in the spherical potential,
respectively. Furthermore, the absence of some one-particle resonant levels
compared with the Nilsson diagrams in text books is illustrated.Comment: 12 pages, 5 figure

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