531 research outputs found
Crack paths under mixed mode loading
Long fatigue cracks that initially experience mixed mode displacements usually change direction in response to cyclic elastic stresses. Eventually the cracks tend to orient themselves into a pure mode I condition, but the path that they take can be complex and chaotic. In this paper, we report on recent developments in techniques for tracking the crack path as it grows and evaluating the strength of the mixed mode crack tip stress field
Control Policies for a Dynamic Storage System With Multiple Lifts and Shuttles
New types of Automated Storage and Retrieval Systems, able to achieve high throughput levels, are continuously being developed and require new control polices to take full advantage of the developed system. In this paper we study a dynamic storage system as developed by Vanderlande Industries consisting of a conveyor, two lifts, multiple transfer shuttles, and a storage rack. One of the decision problems for this system is the scheduling problem of the two lifts. In other words, which lift is going to handle which request and in which order. In this paper, we derive an integrated look-ahead heuristic based on enumeration to simultaneously assign a set of pre-defined requests to the lifts and to schedule the lifts. As main performance measure we use the total time required to serve all requests
6Li direct breakup lifetimes
alpha-d coincidence data were studied for the 6Li + 59Co reaction at E(lab) =
29.6 MeV. By using a kinematic analysis, it was possible to identify which
process, leading to the same final state, has the major contribution for each
of the selected angular regions. Contributions of the 6Li sequential and direct
breakup to the incomplete fusion/transfer process were discussed by considering
the lifetimes obtained by using a semiclassical approach, for both breakup
components.Comment: 5 pages, 4 figures, Invited Talk (Parrallel Sessions) of A. Szanto de
Toledo, prepared for the Proccedings of the 10th International Conference on
Nucleus-Nucleus Collisions, August 16-21, 2009, Beijing, China; submitted to
Nucl. Phys. A (Proceedings of NN2009
Reaction mechanisms for weakly-bound, stable nuclei and unstable, halo nuclei on medium-mass targets
An experimental overview of reactions induced by the stable, but weakly-bound
nuclei 6Li, 7Li and 9Be, and by the exotic, halo nuclei 6He, 8B, 11Be and 17F
on medium-mass targets, such as 58Ni, 59Co or 64Zn, is presented. Existing data
on elastic scattering, total reaction cross sections, fusion processes, breakup
and transfer channels are discussed in the framework of a CDCC approach taking
into account the breakup degree of freedom.Comment: 7 pages, 6 figures, Invited Talk given by C. Beck to the 10th
International Conference on Nucleus-Nucleus Collisions, August 16-21, 2009
Beijing, China; Paper submitted to the NN2009 Proceedings, Nuclear Physics A
(to be published
Sub- and above barrier fusion of loosely bound Li with Si
Fusion excitation functions are measured for the system Li+Si
using the characteristic -ray method, encompassing both the sub-barrier
and above barrier regions, viz., = 7-24 MeV. Two separate experiments
were performed, one for the above barrier region (= 11-24 MeV) and
another for the below barrier region (= 7-10 MeV). The results were
compared with our previously measured fusion cross section for the
Li+Si system. We observed enhancement of fusion cross section at
sub-barrier regions for both Li and Li, but yield was substantially
larger for Li. However, for well above barrier regions, similar type of
suppression was identified for both the systems.Comment: 8 pages, 6 figures, as accepted for publication in Eur.Phys.J.
Reaction mechanisms in the 6Li+59Co system
The reactions induced by the weakly bound 6Li projectile interacting with the
intermediate mass target 59Co were investigated. Light charged particles
singles and - coincidence measurements were performed at the near
barrier energies E_lab = 17.4, 21.5, 25.5 and 29.6 MeV. The main contributions
of the different competing mechanisms are discussed. A statistical model
analysis, Continuum-Discretized Coupled-Channels calculations and two-body
kinematics were used as tools to provide information to disentangle the main
components of these mechanisms. A significant contribution of the direct
breakup was observed through the difference between the experimental sequential
breakup cross section and the CDCC prediction for the non-capture breakup cross
section.Comment: 30 pages, 8 figure
Projectile breakup dynamics for Li + Co: kinematical analysis of - coincidences
A study of the kinematics of the - coincidences in the Li +
Co system at a bombarding energy of MeV is presented.
With exclusive measurements performed over different angular intervals it is
possible to identify the respective contributions of the sequential projectile
breakup and direct projectile breakup components. A careful analysis using a
semiclassical approach of these processes provides information on both their
lifetime and their distance of occurrence with respect to the target. Breakup
to the low-lying (near-threshold) continuum is delayed, and happens at large
internuclear distances. This suggests that the influence of the projectile
breakup on the complete fusion process can be related essentially to direct
breakup to the Li high-lying continuum spectrum. %Comment: Revised version including new Fig.3 and Fig.4 with new CDCC
calculations. Accepted for publication at Eur. Phys. Jour. A. 11 pages, 6
figure
Radioterapia en cáncer de recto localmente avanzado: situación actual y desarrollo terapéutico
La radioterapia es uno de los elementos integrantes del tratamiento radical del cáncer de recto localmente avanzado. La radioterapia preoperatoria y la radioterapia postoperatoria en combinación con quimioterapia han demostrado aumento del control local y la supervivencia. La tendencia actual es el uso de quimioirradiación preoperatoria por su mejor tolerancia y porque a los beneficios en control local y supervivencia se le podrían añadir los de mayor tasa de respuesta (downstaging) y un aumento de cirugía preservadora del esfínter anal. El desarrollo terapéutico en cáncer de recto localmente avanzado se sitúa en conseguir una mayor intensificación terapéutica sobre el tumor y las regiones de riesgo de recidiva sin aumentar la toxicidad sobre los tejidos sanos: esquemas de radioterapia con fraccionamientos modificados, radioterapia intraoperatoria, radioterapia con intensidad modulada de dosis, nuevos agentes quimioterápicos en combinación con radioterapia. En el presente artículo se revisan los datos más relevantes de esta modalidad terapéutica.Radiotherapy is one of the integral elements of the radical treatment of locally advanced rectal cancer. Combined chemotherapy and postoperative radiotherapy or preoperative radiotherapy has demonstrated an increase in local control and survival. The present trend is the use of preoperative chemoradiotherapy: this scheme seems to have a better tolerance and downstaging with an increase in sphincter-preserving surgery rates. Current therapeutic development in locally advanced rectal cancer focuses on obtaining a greater therapeutic ratio: with modified fractionation, intraoperative radiation therapy, intensity modulated radiation therapy, new chemoradiation regimens. The present work reviews the state of the art and the most significant advances in radiation in rectal cancer
Coupled-Channel Effects in Collisions between Heavy Ions near the Coulomb Barrier
With the recent availability of state-of-the-art heavy-ion stable and
radioactive beams, there has been a renew interest in the investigation of
nuclear reactions with heavy ions. I first present the role of inelastic and
transfer channel couplings in fusion reactions induced by stable heavy ions.
Analysis of experimental fusion cross sections by using standard
coupled-channel calculations is discussed. The role of multi-neutron transfer
is investigated in the fusion process below the Coulomb barrier by analyzing
S+Zr as benchmark reactions. The enhancement of fusion cross
sections for S+Zr is well reproduced at sub-barrier energies by
NTFus code calculations including the coupling of the neutron-transfer channels
following the Zagrebaev semi-classical model. Similar effects for
Ca+Zr and Ca+Zr fusion excitation functions are
found. The breakup coupling in both the elastic scattering and in the fusion
process induced by weakly bound stable projectiles is also shown to be crucial.
In this lecture, full coupled-channel calculations of the fusion excitation
functions are performed by using the breakup coupling for the more neutron-rich
reaction and for the more weakly bound projectiles. I clearly demonstrate that
Continuum-Discretized Coupled-Channel calculations are capable to reproduce the
fusion enhancement from the breakup coupling in Li+Co.Comment: 14 pages. 6 figure
The PAMELA Positron Excess from Annihilations into a Light Boson
Recently published results from the PAMELA experiment have shown conclusive
evidence for an excess of positrons at high (~ 10 - 100 GeV) energies,
confirming earlier indications from HEAT and AMS-01. Such a signal is generally
expected from dark matter annihilations. However, the hard positron spectrum
and large amplitude are difficult to achieve in most conventional WIMP models.
The absence of any associated excess in anti-protons is highly constraining on
any model with hadronic annihilation modes. We revisit an earlier proposal,
whereby the dark matter annihilates into a new light (<~GeV) boson phi, which
is kinematically constrained to go to hard leptonic states, without
anti-protons or pi0's. We find this provides a very good fit to the data. The
light boson naturally provides a mechanism by which large cross sections can be
achieved through the Sommerfeld enhancement, as was recently proposed.
Depending on the mass of the WIMP, the rise may continue above 300 GeV, the
extent of PAMELA's ability to discriminate electrons and positrons.Comment: 4 pages, 2 figures; v3 separated pions plot, references adde
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