1,662 research outputs found
Muon Capture on Deuteron and 3He: A Personal Review
The present status of theoretical and experimental studies of muon capture
reactions on light nuclei is reviewed. In particular, the recent results for
the two reactions 2H(\mu^-,\nu_\mu)nn and 3He(\mu^-,\nu_\mu)3H are presented,
and the unresolved discrepancies among different measurements and calculations,
open problems, and future developments are discussed.Comment: 19 pages, submitted to International Journal of Modern Physics
Weak proton capture on 3He
The astrophysical S-factor for the proton weak capture on 3He is calculated
with correlated-hyperspherical-harmonics bound and continuum wave functions
corresponding to realistic Hamiltonians consisting of the Argonne v14 or
Argonne v18 two-nucleon and Urbana-VIII or Urbana-IX three-nucleon
interactions. The nuclear weak charge and current operators have vector and
axial-vector components, that include one- and many-body terms. All possible
multipole transitions connecting any of the p 3He S- and P-wave channels to the
4He bound state are considered. The S-factor at a p 3He center-of-mass energy
of 10 keV, close to the Gamow-peak energy, is predicted to be 10.1 10^{-20} keV
b with the AV18/UIX Hamiltonian, a factor of about 4.5 larger than the value
adopted in the standard solar model. The P-wave transitions are found to be
important, contributing about 40 % of the calculated S-factor. The energy
dependence is rather weak: the AV18/UIX zero-energy S-factor is 9.64 10^{-20}
keV b, only 5 % smaller than the 10 keV result quoted above. The model
dependence is also found to be weak: the zero-energy S-factor is calculated to
be 10.2 10^{-20} keV b with the older AV14/UVIII model, only 6 % larger than
the AV18/UIX result. Our best estimate for the S-factor at 10 keV is therefore
(10.1 \pm 0.6) 10^{-20} keV b, when the theoretical uncertainty due to the
model dependence is included. This value for the calculated S-factor is not as
large as determined in fits to the Super-Kamiokande data in which the hep flux
normalization is free. However, the precise calculation of the S-factor and the
consequent absolute prediction for the hep neutrino flux will allow much
greater discrimination among proposed solar neutrino oscillation solutions.Comment: 54 pages RevTex file, 6 PostScript figures, submitted to Phys. Rev.
The nuclear matter equation of state with consistent two- and three-body perturbative chiral interactions
We compute the energy per particle of infinite symmetric nuclear matter from
chiral N3LO (next-to-next-to-next-to-leading order) two-body potentials plus
N2LO three-body forces. The low-energy constants of the chiral three-nucleon
force that cannot be constrained by two-body observables are fitted to
reproduce the triton binding energy and the 3H-3He Gamow-Teller transition
matrix element. In this way, the saturation properties of nuclear matter are
reproduced in a parameter-free approach. The equation of state is computed up
to third order in many-body perturbation theory, with special emphasis on the
role of the third-order particle-hole diagram. The dependence of these results
on the cutoff scale and regulator function is studied. We find that the
inclusion of three-nucleon forces consistent with the applied two-nucleon
interaction leads to a reduced dependence on the choice of the regulator only
for lower values of the cutoff.Comment: 9 pages, 12 figures, 3 tables, to be published in Physical Review C.
arXiv admin note: text overlap with arXiv:1209.553
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Connecting Green Infrastructure with Transportation Planning
The development of green infrastructure planning is increasingly espoused by landscape, conservation, and metropolitan planners as an effective way to create a network of ecological functionality in regions that are otherwise highly impacted by anthropogenic changes. The most common condition is one of expanding metropolitan growth transforming cultivated and natural landscapes into developed ones. Despite its promise, several critical problems arise with green infrastructure planning. We will consider three. The first is that the definition of green infrastructure within the public realm remains highly variable if not embryonic. The second is green infrastructure is a long-term investment whose effects will not be able to be measured until years after implementation, yet there are very few cases of green infrastructure planning that have actually resulted in adopted and implemented plans, which can be used as models of success. And third, although the public benefits of green infrastructure are positive, other forms of regional scale planning have more dominant influence and impacts, most notably transportation planning.
Concerning this last point, our thesis is that green infrastructure and transportation infrastructure have important interactions. Furthermore, transportation infrastructure potentially degrades green infrastructure networks through fragmentation, ecosystem impairment, and loss of connectivity. Mitigating the impacts of transportation infrastructure could potentially be an important asset to green infrastructure planning. Coordination of transportation and green infrastructure holds promise for sustainable development across regional landscapes. We address this thesis by assessing the landscape significance of both green and transportation infrastructure planning and presenting a case study from Maryland, USA.
The case study indicates that there are numerous logical connections between the two types of plans, some of them conflicting. However, it also indicates that there is much research still necessary on green infrastructure, especially in the areas of implementation and efficacy
Chiral nucleon-nucleon forces in nuclear structure calculations
Realistic nuclear potentials, derived within chiral perturbation theory, are
a major breakthrough in modern nuclear structure theory, since they provide a
direct link between nuclear physics and its underlying theory, namely the QCD.
As a matter of fact, chiral potentials are tailored on the low-energy regime of
nuclear structure physics, and chiral perturbation theory provides on the same
footing two-nucleon forces as well as many-body ones. This feature fits well
with modern advances in ab-initio methods and realistic shell-model. Here, we
will review recent nuclear structure calculations, based on realistic chiral
potentials, for both finite nuclei and infinite nuclear matter.Comment: 10 pages, 8 figures, plenary talk presented at "Nucleus-Nucleus 2015"
Conference, 21-26 June 2015, Catania, to be published in the "Conference
Proceedings" Series of the Italian Physical Societ
Break-up channels in muon capture on 3He
The mu + 2H -> nu + n + n, mu + 3He -> nu + 3H, mu + 3He -> nu + n + d and mu
+ 3He -> nu + n + n + p capture reactions are studied with various realistic
potentials under full inclusion of final state interactions. Our results for
the two- and three-body break-up of 3He are calculated with a variety of
nucleon-nucleon potentials, among which is the AV18 potential, augmented by the
Urbana~IX three-nucleon potential. Most of our results are based on the single
nucleon weak current operator. As a first step, we have tested our calculation
in the case of the mu + 2H -> nu + n + n and mu + 3He -> nu + 3H reactions, for
which theoretical predictions obtained in a comparable framework are available.
Additionally, we have been able to obtain for the first time a realistic
estimate for the total rates of the muon capture reactions on 3He in the
break-up channels: 544 1/s and 154 1/s for the n + d and n + n + p channels,
respectively. Our results have also been compared with the most recent
experimental data, finding a rough agreement for the total capture rates, but
failing to reproduce the differential capture rates.Comment: 29 pages, 18 figure
Inclusive neutrino scattering off deuteron from threshold to GeV energies
Background: Neutrino-nucleus quasi-elastic scattering is crucial to interpret
the neutrino oscillation results in long baseline neutrino experiments. There
are rather large uncertainties in the cross section, due to insufficient
knowledge on the role of two-body weak currents. Purpose: Determine the role of
two-body weak currents in neutrino-deuteron quasi-elastic scattering up to GeV
energies. Methods: Calculate cross sections for inclusive neutrino scattering
off deuteron induced by neutral and charge-changing weak currents, from
threshold up to GeV energies, using the Argonne potential and
consistent nuclear electroweak currents with one- and two-body terms. Results:
Two-body contributions are found to be small, and increase the cross sections
obtained with one-body currents by less than 10% over the whole range of
energies. Total cross sections obtained by describing the final two-nucleon
states with plane waves differ negligibly, for neutrino energies
MeV, from those in which interaction effects in these states are fully
accounted for. The sensitivity of the calculated cross sections to different
models for the two-nucleon potential and/or two-body terms in the weak current
is found to be weak. Comparing cross sections to those obtained in a naive
model in which the deuteron is taken to consist of a free proton and neutron at
rest, nuclear structure effects are illustrated to be non-negligible.
Conclusion: Contributions of two-body currents in neutrino-deuteron
quasi-elastic scattering up to GeV are found to be smaller than 10%. Finally,
it should be stressed that the results reported in this work do not include
pion production channels.Comment: 30 pages, 17 figures; publishe
Rationale and design of the PeriOperative ISchemic Evaluation-3 (POISE-3) : a randomized controlled trial evaluating tranexamic acid and a strategy to minimize hypotension in noncardiac surgery
Background For patients undergoing noncardiac surgery, bleeding and hypotension are frequent and associated with increased mortality and cardiovascular complications. Tranexamic acid (TXA) is an antifibrinolytic agent with the potential to reduce surgical bleeding; however, there is uncertainty about its efficacy and safety in noncardiac surgery. Although usual perioperative care is commonly consistent with a hypertension-avoidance strategy (i.e., most patients continue their antihypertensive medications throughout the perioperative period and intraoperative mean arterial pressures of 60 mmHg are commonly accepted), a hypotension-avoidance strategy may improve perioperative outcomes. Methods The PeriOperative Ischemic Evaluation (POISE)-3 Trial is a large international randomized controlled trial designed to determine if TXA is superior to placebo for the composite outcome of life-threatening, major, and critical organ bleeding, and non-inferior to placebo for the occurrence of major arterial and venous thrombotic events, at 30 days after randomization. Using a partial factorial design, POISE-3 will additionally determine the effect of a hypotension-avoidance strategy versus a hypertension-avoidance strategy on the risk of major cardiovascular events, at 30 days after randomization. The target sample size is 10,000 participants. Patients ≥45 years of age undergoing noncardiac surgery, with or at risk of cardiovascular and bleeding complications, are randomized to receive a TXA 1 g intravenous bolus or matching placebo at the start and at the end of surgery. Patients, health care providers, data collectors, outcome adjudicators, and investigators are blinded to the treatment allocation. Patients on ≥ 1 chronic antihypertensive medication are also randomized to either of the two blood pressure management strategies, which differ in the management of patient antihypertensive medications on the morning of surgery and on the first 2 days after surgery, and in the target mean arterial pressure during surgery. Outcome adjudicators are blinded to the blood pressure treatment allocation. Patients are followed up at 30 days and 1 year after randomization. Discussion Bleeding and hypotension in noncardiac surgery are common and have a substantial impact on patient prognosis. The POISE-3 trial will evaluate two interventions to determine their impact on bleeding, cardiovascular complications, and mortality
Perioperative Bluttransfusion: Nutzen, Risiken und Richtlinien
Zusammenfassung: Chirurgisch und traumatisch bedingte Blutverluste sind die häufigsten Ursachen von allogenen Bluttransfusionen, welche nach wie vor mit beträchtlichen Risiken verbunden sind. Nach Korrektur der Hypovolämie ist der Anästhesist häufig mit einer normovolämischen Anämie konfrontiert. Die klinische Relevanz dieses isolierten Hämoglobinabfalls besteht darin, dass die globale und/oder regionale Sauerstoffversorgung über eine kritische Schwelle hinaus beeinträchtigt sein kann, wonach sich eine Gewebshypoxie einstellt. Diese kritische Schwelle ist von Patient zu Patient verschieden und abhängig von dessen Kapazität, den Abfall des Sauerstoffgehaltes zu kompensieren. Aus diesem Grunde sollten primär physiologische Transfusionskriterien angewandt werden und nicht rigide nummerische Transfusionskriterien wie die Hämoglobinkonzentration, welche die individuelle Reserve eines Patienten weitgehend außer Acht lasse
Observation of Fermi-Pasta-Ulam-Tsingou Recurrence and Its Exact Dynamics
One of the most controversial phenomena in nonlinear dynamics is the reappearance of initial
conditions. Celebrated as the Fermi-Pasta-Ulam-Tsingou problem, the attempt to understand how these
recurrences form during the complex evolution that leads to equilibrium has deeply influenced the entire
development of nonlinear science. The enigma is rendered even more intriguing by the fact that integrable
models predict recurrence as exact solutions, but the difficulties involved in upholding integrability for a
sufficiently long dynamic has not allowed a quantitative experimental validation. In natural processes,
coupling with the environment rapidly leads to thermalization, and finding nonlinear multimodal systems
presenting multiple returns is a long-standing open challenge. Here, we report the observation of more than
three Fermi-Pasta-Ulam-Tsingou recurrences for nonlinear optical spatial waves and demonstrate the
control of the recurrent behavior through the phase and amplitude of the initial field. The recurrence period
and phase shift are found to be in remarkable agreement with the exact recurrent solution of the nonlinear
Schrödinger equation, while the recurrent behavior disappears as integrability is lost. These results identify
the origin of the recurrence in the integrability of the underlying dynamics and allow us to achieve one of
the basic aspirations of nonlinear dynamics: the reconstruction, after several return cycles, of the exact
initial condition of the system, ultimately proving that the complex evolution can be accurately predicted in
experimental conditions
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