51 research outputs found
Multilayer shallow water models with locally variable number of layers and semi-implicit time discretization
We propose an extension of the discretization approaches for multilayer
shallow water models, aimed at making them more flexible and efficient for
realistic applications to coastal flows. A novel discretization approach is
proposed, in which the number of vertical layers and their distribution are
allowed to change in different regions of the computational domain.
Furthermore, semi-implicit schemes are employed for the time discretization,
leading to a significant efficiency improvement for subcritical regimes. We
show that, in the typical regimes in which the application of multilayer
shallow water models is justified, the resulting discretization does not
introduce any major spurious feature and allows again to reduce substantially
the computational cost in areas with complex bathymetry. As an example of the
potential of the proposed technique, an application to a sediment transport
problem is presented, showing a remarkable improvement with respect to standard
discretization approaches
A weakly non-hydrostatic shallow model for dry granular flows
A non-hydrostatic depth-averaged model for dry granular flows is proposed,
taking into account vertical acceleration. A variable friction coefficient
based on the rheology is considered. The model is obtained from an
asymptotic analysis in a local reference system, where the non-hydrostatic
contribution is supposed to be small compared to the hydrostatic one. The
non-hydrostatic counterpart of the pressure may be written as the sum of two
terms: one corresponding to the stress tensor and the other to the vertical
acceleration. The model introduced here is weakly non-hydrostatic, in the sense
that the non-hydrostatic contribution related to the stress tensor is not taken
into account due to its complex implementation. A simple and efficient
numerical scheme is proposed. It consists of a three-step splitting procedure,
and it is based on a hydrostatic reconstruction. Two key points are: (i) the
friction force has to be taken into account before solving the non-hydrostatic
pressure. Otherwise, the incompressibility condition is not ensured; (ii) both
the hydrostatic and the non-hydrostatic pressure are taken into account when
dealing with the friction force. The model and numerical scheme are then
validated based on several numerical tests, including laboratory experiments of
granular collapse. The influence of non-hydrostatic terms and of the choice of
the coordinate system (Cartesian or local) is analyzed. We show that
non-hydrostatic models are less sensitive to the choice of the coordinate
system. In general, the non-hydrostatic model introduced here much better
reproduces granular collapse experiments compared to hydrostatic models. An
important result is that the simulated mass profiles up to the deposit and the
front velocity are greatly improved. As expected, the influence of the
non-hydrostatic pressure is shown to be larger for small values of the slope
What is the optimal level of vitamin D in non-dialysis chronic kidney disease population?
AIM: To evaluate thresholds for serum 25(OH)D concentrations in relation to death, kidney progression and hospitalization in non-dialysis chronic kidney disease (CKD) population. METHODS: Four hundred and seventy non-dialysis 3-5 stage CKD patients participating in OSERCE-2 study, a prospective, multicenter, cohort study, were prospectively evaluated and categorized into 3 groups according to 25(OH)D levels at enrollment (less than 20 ng/mL, between 20 and 29 ng/mL, and at or above 30 ng/mL), considering 25(OH)D between 20 and 29 ng/mL as reference group. Association between 25(OH)D levels and death (primary outcome), and time to first hospitalization and renal progression (secondary outcomes) over a 3-year follow-up, were assessed by Kaplan-Meier survival curves and Cox-proportional hazard models. To identify 25(OH)D levels at highest risk for outcomes, receiver operating characteristic (ROC) curves were performed. RESULTS: Over 29 ± 12 mo of follow-up, 46 (10%) patients dead, 156 (33%) showed kidney progression, and 126 (27%) were hospitalized. After multivariate adjustment, 25(OH)D < 20 ng/mL was an independent predictor of all-cause mortality (HR = 2.33; 95%CI: 1.10-4.91; P = 0.027) and kidney progression (HR = 2.46; 95%CI: 1.63-3.71; P < 0.001), whereas the group with 25(OH)D at or above 30 ng/mL did not have a different hazard for outcomes from the reference group. Hospitalization outcomes were predicted by 25(OH) levels (HR = 0.98; 95%CI: 0.96-1.00; P = 0.027) in the unadjusted Cox proportional hazards model, but not after multivariate adjusting. ROC curves identified 25(OH)D levels at highest risk for death, kidney progression, and hospitalization, at 17.4 ng/mL [area under the curve (AUC) = 0.60; 95%CI: 0.52-0.69; P = 0.027], 18.6 ng/mL (AUC = 0.65; 95%CI: 0.60-0.71; P < 0.001), and 19.0 ng/mL (AUC = 0.56; 95%CI: 0.50-0.62; P = 0.048), respectively. CONCLUSION: 25(OH)D < 20 ng/mL was an independent predictor of death and progression in patients with stage 3-5 CKD, with no additional benefits when patients reached the levels at or above 30 ng/mL suggested as optimal by CKD guidelines.Abbott and the Spanish Society of Nephrolog
Evidence for muon neutrino oscillation in an accelerator-based experiment
We present results for muon neutrino oscillation in the KEK to Kamioka (K2K)
long-baseline neutrino oscillation experiment. K2K uses an accelerator-produced
muon neutrino beam with a mean energy of 1.3 GeV directed at the
Super-Kamiokande detector. We observed the energy dependent disappearance of
muon neutrino, which we presume have oscillated to tau neutrino. The
probability that we would observe these results if there is no neutrino
oscillation is 0.0050% (4.0 sigma).Comment: 5 pages, 4 figure
Search for coherent charged pion production in neutrino-carbon interactions
We report the result from a search for charged-current coherent pion
production induced by muon neutrinos with a mean energy of 1.3 GeV. The data
are collected with a fully active scintillator detector in the K2K
long-baseline neutrino oscillation experiment. No evidence for coherent pion
production is observed and an upper limit of is set on
the cross section ratio of coherent pion production to the total
charged-current interaction at 90% confidence level. This is the first
experimental limit for coherent charged pion production in the energy region of
a few GeV.Comment: 5 pages, 4 figure
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