5,013 research outputs found
Ground state of N=Z doubly closed shell nuclei in CBF theory
The ground state properties of N=Z doubly closed shell nuclei are studied
within correlated basis function theory. A truncated version of the Urbana v14
realistic potential, with spin, isospin and tensor components, is adopted,
together with state dependent correlations. Fermi hypernetted chain integral
equation and single operator chain approximation are used to evaluate density,
distribution function and ground state energy of 16O and 40Ca. The results
favourably compare with the available, variational MonteCarlo estimates and
provide a first substantial check of the accuracy of the cluster summation
method for state dependent correlations. We achieve in finite nuclei at least
the same level of accuracy in the treatment of non central interactions and
correlations as in nuclear matter. This opens the way for a microscopic study
of medium heavy nuclei ground state using present days realistic hamiltonians.Comment: 35 pages (LateX) + 3 figures. Phys.Rev.C, in pres
On the Usability of Probably Approximately Correct Implication Bases
We revisit the notion of probably approximately correct implication bases
from the literature and present a first formulation in the language of formal
concept analysis, with the goal to investigate whether such bases represent a
suitable substitute for exact implication bases in practical use-cases. To this
end, we quantitatively examine the behavior of probably approximately correct
implication bases on artificial and real-world data sets and compare their
precision and recall with respect to their corresponding exact implication
bases. Using a small example, we also provide qualitative insight that
implications from probably approximately correct bases can still represent
meaningful knowledge from a given data set.Comment: 17 pages, 8 figures; typos added, corrected x-label on graph
SU(2) Kinetic Mixing Terms and Spontaneous Symmetry Breaking
The non-abelian generalization of the Holdom model --{\it i.e.} a theory with
two gauge fields coupled to the kinetic mixing term -- is considered. Contrarily to the abelian case, the group
structure is explicitly broken to . For SU(2) this fact implies
that the residual gauge symmetry as well as the Lorentz symmetry is
spontaneusly broken. We show that this mechanism provides of masses for the
involved particles. Also, the model presents instanton solutions with a
redefined coupling constant.Comment: 9pp. typos and clarifications are adde
Are Steroids Still Useful in Immunosuppressed Patients With Inflammatory Bowel Disease? A Retrospective, Population-Based Study
Background: Effectiveness of corticosteroids in immunosuppressed patients with inflammatory bowel disease (IBD) has not been completely elucidated. Aims: To assess the effectiveness and examine the long-term follow-up of systemic or low-bioavailability oral steroid treatment for moderate flare-ups in patients treated with immunosuppressive drugs. Methods: Immunosuppressed patients with inflammatory bowel disease (IBD) from our population-data registry were analyzed. For statistical analysis, the chi-square test, Mann-Whitney U test, and Kaplan-Meier survival analysis were used as appropriate. Results: A total of 392 patients with IBD and a median of 82 (range, 6–271) months of immunosuppressive (IMM) treatment were identified. The mean follow-up was 87 months (range, 6–239 months). A total of 89 patients (23%) needed at least one steroid course during their follow-up. Average time from IMM to steroid treatment was 26 (range, 6–207) months. In patients with CD, fibrostenotic (B2) and fistulizing (B3) behaviors [p = 0.005; odds ratio (OR): 2.284] were risk factors for using steroids after IMM treatment. In patients with UC, no statistically significant variables were identified. Of the 89 patients who received one first steroid course, 49 (55%) stepped up to biological treatment or surgery after a median of 13 months (range, 0–178), 19 (21%) were treated with repeated steroid courses, and 31 (35%) required no further treatment. Patients with CD had a higher risk (p = 0.007; OR: 3.529) of receiving biological treatment or surgery than patients with UC. The longer the patients with UC (more months) spent using steroids, the greater the risk of requiring treatment with biological drugs or surgery (p = 0.009). Conclusion: A total of 23% of the immunosuppressed patients with IBD received at least one course of steroid treatment. In patients under immunosuppression treated with at least a course of steroids, CD patients were more likely stepped up to biologics and/or surgery than UC patients. In patients with CD, B2/B3 behavior pattern were significant risk factors. After one course of steroids only 35% of immunosuppressed IBD patients remained in remission without needing treatment scalation. © Copyright © 2021 Sicilia, Arias, Hontoria, GarcÃa, Badia and Gomollón
Ground State Correlations in 16O and 40Ca
We study the ground state properties of doubly closed shell nuclei O
and Ca in the framework of Correlated Basis Function theory using state
dependent correlations, with central and tensor components. The realistic
Argonne and two-nucleon potentials and three-nucleon
potentials of the Urbana class have been adopted. By means of the Fermi
Hypernetted Chain integral equations, in conjunction with the Single Operator
Chain approximation, we evaluate the ground state energy, one- and two-body
densities and electromagnetic and spin static responses for both nuclei. In
O we compare our results with the available Monte Carlo and Coupled
Cluster ones and find a satisfying agreement. As in the nuclear matter case
with similar interactions and wave functions, the nuclei result under-bound by
2--3 MeV/A.Comment: 33 RevTeX pages + 8 figures, to appear in Phys.Rev.
The Bekenstein Bound in Asymptotically Free Field Theory
For spatially bounded free fields, the Bekenstein bound states that the
specific entropy satisfies the inequality , where
stands for the radius of the smallest sphere that circumscribes the system. The
validity of the Bekenstein bound on the specific entropy in the asymptotically
free side of the Euclidean self-interacting scalar
field theory is investigated. We consider the system in thermal equilibrium
with a reservoir at temperature and defined in a compact spatial
region without boundaries. Using the effective potential, we presented an
exhaustive study of the thermodynamic of the model. For low and high
temperatures the system presents a condensate. We obtain also the renormalized
mean energy and entropy for the system. With these quantities, we shown
in which situations the specific entropy satisfies the quantum bound
Short-range correlations in low-lying nuclear excited states
The electromagnetic transitions to various low-lying excited states of 16O,
48Ca and 208Pb are calculated within a model which considers the short-range
correlations. In general the effects of the correlations are small and do not
explain the required quenching to describe the data.Comment: 6 pages, 2 postscript figures, 1 tabl
Effects of state dependent correlations on nucleon density and momentum distributions
The proton momentum and density distributions of closed shell nuclei are
calculated within a model treating short--range correlations up to first order
in the cluster expansion. The validity of the model is verified by comparing
the results obtained with purely scalar correlations with those produced by
finite nuclei Fermi Hypernetted Chain calculations. State dependent
correlations are used to calculate momentum and density distributions of 12C,
16O, 40Ca, and 48Ca, and the effects of their tensor components are studied.Comment: 16 pages, latex, 8 figures, accepted for publication in Phys. Rev.
Self-similar dynamics of morphogen gradients
We discovered a class of self-similar solutions in nonlinear models
describing the formation of morphogen gradients, the concentration fields of
molecules acting as spatial regulators of cell differention in developing
tissues. These models account for diffusion and self-induced degration of
locally produced chemical signals. When production starts, the signal
concentration is equal to zero throughout the system. We found that in the
limit of infinitely large signal production strength the solution of this
problem is given by the product of the steady state concentration profile and a
function of the diffusion similarity variable. We derived a nonlinear boundary
value problem satisfied by this function and used a variational approach to
prove that this problem has a unique solution in a natural setting. Using the
asymptotic behavior of the solutions established by the analysis, we
constructed these solutions numerically by the shooting method. Finally, we
demonstrated that the obtained solutions may be easily approximated by simple
analytical expressions, thus providing an accurate global characterization of
the dynamics in an important class of non-linear models of morphogen gradient
formation. Our results illustrate the power of analytical approaches to
studying nonlinear models of biophysical processes.Comment: 17 pages, 5 figure
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