1,280 research outputs found
Electroproductions of Light - and -Hypernuclei
Theoretical estimations of production cross sections of light and
hypernuclei in reactions at around CEBAF energies are
given. Because of dominant spin-flip amplitudes and large momentum transfers,
unnatural parity states and stretched states of hypernuclei are favorably
excited. They are compared with quasifree hyperon productions.Comment: 12 pages in Latex(6 figures are available on reques
An Algorithmic Framework for Computing Validation Performance Bounds by Using Suboptimal Models
Practical model building processes are often time-consuming because many
different models must be trained and validated. In this paper, we introduce a
novel algorithm that can be used for computing the lower and the upper bounds
of model validation errors without actually training the model itself. A key
idea behind our algorithm is using a side information available from a
suboptimal model. If a reasonably good suboptimal model is available, our
algorithm can compute lower and upper bounds of many useful quantities for
making inferences on the unknown target model. We demonstrate the advantage of
our algorithm in the context of model selection for regularized learning
problems
Full-Coupled Channel Approach to Doubly Strange -Shell Hypernuclei
We describe {\it ab initio} calculations of doubly strange, , -shell
hypernuclei (H, H,
He and He) as a first attempt to
explore the few-body problem of the {\it full}-coupled channel scheme for these
systems. The wave function includes , ,
and channels. Minnesota , D2 , and
simulated potentials based on the Nijmegen hard-core model, are used.
Bound state solutions of these systems are obtained. We find that a set of
phenomenological interactions among the octet baryons in and
-2 sectors, which is consistent with all of the available experimental binding
energies of and -2 -shell (hyper-)nuclei, can predict a particle
stable bound state of H.
For H and He,
and potentials enhance the net
coupling, and a large probability is obtained even for a weaker
potential.Comment: 4 pages, 1 figur
Can We Extract Lambda-Lambda Interaction from Two-Particle Momentum Correlation ?
We analyze the invariant mass spectrum of Lambda-Lambda in reaction at P(K^+)=1.65 GeV/c by using a combined framework of
IntraNuclear Cascade (INC) model and the correlation function technique. The
observed enhancement at low-invariant masses can be well reproduced with
attractive Lambda-Lambda interactions with the scattering length either in the
range a = -6 \sim -4 fm (no bound state) or a = 7 \sim 12 fm (with bound
state). We also discuss Lambda-Lambda correlation functions in central
relativistic heavy-ion collisions as a possible way to eliminate this discrete
ambiguity.Comment: 4 Pages, LaTeX with psfig, embedded 4 ps figures. Talk given at
KEK-Tanashi Int. Symp. on "Physics of Hadrons and Nuclei", 14-17 Dec. 1998,
Tokyo, Japan, Nuclear Physics A, to appea
Lambda Lambda-XiN Coupling Effects in Light Hypernuclei
The significance of -N coupling in double-
hypernuclei has been studied. The Pauli suppression effect due to this coupling
in He has been found to be 0.43 MeV for the coupling
strength of the NSC97e potential. This indicates that the free-space
interaction is stronger by about phase shift than
that deduced from the empirical data of He without
including the Pauli suppression effect. In He and
H, an attractive term arising from -N
conversion is enhanced by the formation of an alpha particle in intermediate
states. According to this enhancement, we have found that the
binding energy () of
He is about 0.27 MeV larger than that of
He for the NSC97e coupling strength. This finding deviates
from a general picture that the heavier is the core nucleus, the larger is
.Comment: 16 pages with 2 figure
Comparison of conservative treatment versus transcatheter arterial embolisation for the treatment of spontaneously ruptured hepatocellular carcinoma
Purpose: To elucidate the prognostic factors in the spontaneous rupture of hepatocellular carcinoma (HCC) and to determine whether transcatheter arterial embolisation (TAE) is associated with better prognosis compared to conservative treatment. Material and methods: A retrospective multicentre study was conducted involving 71 patients with spontaneous rupture of HCC. A conservative treatment group (Cons T group) included 20 patients, while a transcatheter arterial embolisation group (TAE group) included 51 patients. Results: The median survival time (MST) in the Cons T group was only 16 days and the survival rate was 39% at one month, whereas the MST in the TAE group was 28 days and the one month survival rate was 63%. However, there is no statistically significant difference in the overall survival between Cons T and TAE groups (p = 0.213). Multivariable analysis identified only the presence of distant metastasis as an independent prognostic factor (p = 0.023). A subanalysis including patients without distant metastasis showed that the presence of portal vein tumour thrombosis was a significant prognostic factor (p = 0.015). Conclusions: Distant metastasis appears to be a prognostic factor in spontaneous rupture of HCC. In cases without distant metastasis, portal vein tumour thrombosis could influence the prognosis. Our data failed to prove any benefit of TAE as the primary management
Exclusive production in proton-nucleus collisions
The exclusive meson production in a proton-nucleus collision, leading
to two body final states, is investigated in a fully covariant two-nucleon
model based on the effective Lagrangian picture. The explicit kaon production
vertex is described via creation, propagation and decay into relevant channel
of (1650), (1710) and (1720) intermediate baryonic states in the
initial collision of the projectile nucleon with one of its target counterparts
which is modeled by the one-pion exchange process. The calculated cross
sections show strong sensitivity to the medium effects on pion propagator and
to the final hypernuclear state excited in the reaction.Comment: Two new figures, version accepted for publication by Phys. Rev.
Ab initio approach to s-shell hypernuclei 3H_Lambda, 4H_Lambda, 4He_Lambda and 5He_Lambda with a Lambda N-Sigma N interaction
Variational calculations for s-shell hypernuclei are performed by explicitly
including degrees of freedom. Four sets of YN interactions (SC97d(S),
SC97e(S), SC97f(S) and SC89(S)) are used. The bound-state solution of
He is obtained and a large energy expectation value of the tensor
transition part is found. The internal energy of the
He subsystem is strongly affected by the presence of a particle
with the strong tensor transition potential.Comment: Phys. Rev. Lett. 89, 142504 (2002
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