965 research outputs found
Nuclear Astrophysics with Radioactive Beams
The quest to comprehend how nuclear processes influence astrophysical
phenomena is driving experimental and theoretical research programs worldwide.
One of the main goals in nuclear astrophysics is to understand how energy is
generated in stars, how elements are synthesized in stellar events and what the
nature of neutron stars is. New experimental capabilities, the availability of
radioactive beams and increased computational power paired with new
astronomical observations have advanced the present knowledge. This review
summarizes the progress in the field of nuclear astrophysics with a focus on
the role of indirect methods and reactions involving beams of rare isotopes.Comment: 121 pages, 27 figures, 510 references, to appear in Physics Reports.
Minor typos and references fixe
Is the structure of 42Si understood?
A more detailed test of the implementation of nuclear forces that drive shell
evolution in the pivotal nucleus \nuc{42}{Si} -- going beyond earlier
comparisons of excited-state energies -- is important. The two leading
shell-model effective interactions, SDPF-MU and SDPF-U-Si, both of which
reproduce the low-lying \nuc{42}{Si}() energy, but whose predictions for
other observables differ significantly, are interrogated by the population of
states in neutron-rich \nuc{42}{Si} with a one-proton removal reaction from
\nuc{43}{P} projectiles at 81~MeV/nucleon. The measured cross sections to the
individual \nuc{42}{Si} final states are compared to calculations that combine
eikonal reaction dynamics with these shell-model nuclear structure overlaps.
The differences in the two shell-model descriptions are examined and linked to
predicted low-lying excited states and shape coexistence. Based on the
present data, which are in better agreement with the SDPF-MU calculations, the
state observed at 2150(13)~keV in \nuc{42}{Si} is proposed to be the ()
level.Comment: accepted in Physical Review Letter
Delay-induced Synchronization Phenomena in an Array of Globally Coupled Logistic Maps
We study the synchronization of a linear array of globally coupled identical
logistic maps. We consider a time-delayed coupling that takes into account the
finite velocity of propagation of the interactions. We find globally
synchronized states in which the elements of the array evolve along a periodic
orbit of the uncoupled map, while the spatial correlation along the array is
such that an individual map sees all other maps in his present, current, state.
For values of the nonlinear parameter such that the uncoupled maps are chaotic,
time-delayed mutual coupling suppress the chaotic behavior by stabilizing a
periodic orbit which is unstable for the uncoupled maps. The stability analysis
of the synchronized state allows us to calculate the range of the coupling
strength in which global synchronization can be obtained.Comment: 8 pages, 7 figures, changed content, added reference
Griffiths effects and quantum critical points in dirty superconductors without spin-rotation invariance: One-dimensional examples
We introduce a strong-disorder renormalization group (RG) approach suitable
for investigating the quasiparticle excitations of disordered superconductors
in which the quasiparticle spin is not conserved. We analyze one-dimensional
models with this RG and with elementary transfer matrix methods. We find that
such models with broken spin rotation invariance {\it generically} lie in one
of two topologically distinct localized phases. Close enough to the critical
point separating the two phases, the system has a power-law divergent
low-energy density of states (with a non-universal continuously varying
power-law) in either phase, due to quantum Griffiths singularities. This
critical point belongs to the same infinite-disorder universality class as the
one dimensional particle-hole symmetric Anderson localization problem, while
the Griffiths phases in the vicinity of the transition are controlled by lines
of strong (but not infinite) disorder fixed points terminating in the critical
point.Comment: 14 pages (two-column PRB format), 9 eps figure
Spectral and Transport Properties of d-Wave Superconductors With Strong Impurities
One of the remarkable features of disordered d-wave superconductors is strong
sensitivity of long range properties to the microscopic realization of the
disorder potential. Particularly rich phenomenology is observed for the --
experimentally relevant -- case of dilute distributions of isolated impurity
centers. Building on earlier diagrammatic analyses, the present paper derives
and analyses a low energy effective field theory of this system. Specifically,
the results of previous diagrammatic T-matrix approaches are extended into the
perturbatively inaccessible low energy regimes, and the long range (thermal)
transport behaviour of the system is discussed. It turns out that in the
extreme case of a half-filled tight binding band and infinitely strong
impurities (impurities at the unitary limit), the system is in a delocalized
phase.Comment: 14 pages, two figures include
Spectroscopy of P using the one-proton knockout reaction
The structure of P was studied with a one-proton knockout reaction
at88~MeV/u from a S projectile beam at NSCL. The rays from
thedepopulation of excited states in P were detected with GRETINA,
whilethe P nuclei were identified event-by-event in the focal plane of
theS800 spectrograph. The level scheme of P was deduced up to 7.5 MeV
using coincidences. The observed levels were attributed to
protonremovals from the -shell and also from the deeply-bound
orbital.The orbital angular momentum of each state was derived from the
comparisonbetween experimental and calculated shapes of individual
(-gated)parallel momentum distributions. Despite the use of different
reactions andtheir associate models, spectroscopic factors, , derived
from theS knockout reaction agree with those obtained earlier
fromS(,\nuc{3}{He}) transfer, if a reduction factor , as
deducedfrom inclusive one-nucleon removal cross sections, is applied to the
knockout transitions.In addition to the expected proton-hole configurations,
other states were observedwith individual cross sections of the order of
0.5~mb. Based on their shiftedparallel momentum distributions, their decay
modes to negative parity states,their high excitation energy (around 4.7~MeV)
and the fact that they were notobserved in the (,\nuc{3}{He}) reaction, we
propose that they may resultfrom a two-step mechanism or a nucleon-exchange
reaction with subsequent neutronevaporation. Regardless of the mechanism, that
could not yet be clarified, thesestates likely correspond to neutron core
excitations in \nuc{35}{P}. Thisnewly-identified pathway, although weak, offers
the possibility to selectivelypopulate certain intruder configurations that are
otherwise hard to produceand identify.Comment: 5 figures, 1 table, accepted for publication in Physical Review
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