Random Field and Random Anisotropy Effects in Defect-Free Three-Dimensional XY Models

Monte Carlo simulations have been used to study a vortex-free XY ferromagnet with a random field or a random anisotropy on simple cubic lattices. In the random field case, which can be related to a charge-density wave pinned by random point defects, it is found that long-range order is destroyed even for weak randomness. In the random anisotropy case, which can be related to a randomly pinned spin-density wave, the long-range order is not destroyed and the correlation length is finite. In both cases there are many local minima of the free energy separated by high entropy barriers. Our results for the random field case are consistent with the existence of a Bragg glass phase of the type discussed by Emig, Bogner and Nattermann.Comment: 10 pages, including 2 figures, extensively revise

Predictability in a highly stochastic system: final size of measles epidemics in small populations.

To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked Files. This article is open access.A standard assumption in the modelling of epidemic dynamics is that the population of interest is well mixed, and that no clusters of metapopulations exist. The well-known and oft-used SIR model, arguably the most important compartmental model in theoretical epidemiology, assumes that the disease being modelled is strongly immunizing, directly transmitted and has a well-defined period of infection, in addition to these population mixing assumptions. Childhood infections, such as measles, are prime examples of diseases that fit the SIR-like mechanism. These infections have been well studied for many systems with large, well-mixed populations with endemic infection. Here, we consider a setting where populations are small and isolated. The dynamics of infection are driven by stochastic extinction-recolonization events, producing large, sudden and short-lived epidemics before rapidly dying out from a lack of susceptible hosts. Using a TSIR model, we fit prevaccination measles incidence and demographic data in Bornholm, the Faroe Islands and four districts of Iceland, between 1901 and 1965. The datasets for each of these countries suffer from different levels of data heterogeneity and sparsity. We explore the potential for prediction of this model: given historical incidence data and up-to-date demographic information, and knowing that a new epidemic has just begun, can we predict how large it will be? We show that, despite a lack of significant seasonality in the incidence of measles cases, and potentially severe heterogeneity at the population level, we are able to estimate the size of upcoming epidemics, conditioned on the first time step, to within reasonable confidence. Our results have potential implications for possible control measures for the early stages of new epidemics in small populations.US Department of Homeland Security HSHQDC-12-C-00058 Eunice Kennedy Shriver National Institute of Child Health and Human Development 5R24HD047879 National Institutes of Health 5T32HD007163 Bill and Melinda Gates Foundation RAPIDD program of the Science and Technology Directorate, Department of Homeland Security Fogarty International Center, National Institutes of Healt

Numerical analysis of the venda nova II hydroelectrical complex main caverns and backanalysis of the geomechanical parameters

Neste trabalho é apresentado um modelo numérico 3D para as cavernas principais do complexo da Venda Nova II considerando as diferentes fases de escavação. Os parâmetros geomecânicos do maciço granítico, para os modelos, foram calculados utilizando o software GEOPAT. Este programa é um sistema baseado em conhecimento que permite obter os parâmetros geomecânicos para a modelação de obras subterrâneas em maciços graníticos. Os resultados do modelo são comparados com os deslocamentos observados por intermédio de extensómetros ao longo das várias fases construtivas. Nesta comparação são utilizadas diversas ferramentas estatísticas para a validação dos resultados obtidos. Finalmente, é realizada a retroanálise de parâmetros geomecânicos do maciço rochoso utilizando um algoritmo de optimização inovador. Os resultados obtidos permitiram concluir que a estimativa inicial dos parâmetros apresenta uma precisão bastante aceitável e que o algoritmo possui uma boa robustez e eficiência.In this work a 3D numerical model for the main caverns of the Venda Nova II complex which considers the different excavation stages is presented. The geomechanical parameters for the numerical models were computed using GEOPAT. This software is a knowledge based system which allows evaluating geomechanical parameters for the modelling of underground works built in granite rock masses. The results are compared with the observed displacements measured with extensometers along the different construction stages. In this comparison several statistical tools are used for the validation of the obtained results. Finally, the backanalysis of geomechanical parameters of the interested rock mass is performed using an innovative optimization algorithm. The results show that the initial evaluation of the parameters presents a very acceptable accuracy and that the algorithm posses good robustness and efficiency.Fundação para a Ciência e a Tecnologia (FCT) - Projecto POCI/ECM/57495/2004, intitulado Geotechnical Risk in Tunnels for High Speed Trains.Faculdade de Ciências e Tecnologia da Universidade de Coimbra (FCT-UC

Inverse analysis on two geotechnical works : a tunnel and a cavern

One of the major difficulties for geotechnical engineers during project phase is to estimate in a reliable way the mechanical parameters values of the adopted constitutive model. In project phase, they can be evaluated by laboratory and in situ tests. But, these tests lead to uncertainties due to the soil reworking and to local character of the test which is not representative of the soil mass. Moreover for in situ tests interpretation difficulties exist due to the non homogeneous character of the strain and stress fields applied to the soil mass. In order to reduce these uncertainties, geotechnical engineers can use inverse analysis processes during construction. This article shows the application of two of these processes (a deterministic and a probabilistic method) on convergence leveling measurements realized during the excavation of the Bois de Peu tunnel (France). Moreover, these two processes are also applied on displacements measured by inclinometers during the excavation of the hydroelectric powerhouse cavern Venda Nova II (Portugal). The two inverse analysis methods are coupled with two geotechnical software (CESAR-LCPC and FLAC3D) to identify soil parameters. Numerical and experimental results are compared.(undefined

Stocking activities for the Arctic charr in Lake Geneva: Genetic effects in space and time

Artificial stocking practices are widely used by resource managers worldwide, in order to sustain fish populations exploited by both recreational and commercial activities, but their benefits are controversial. Former practices involved exotic strains, although current programs rather consider artificial breeding of local fishes (supportive breeding). Understanding the complex genetic effects of these management strategies is an importan t challenge with economic and conservation implications, especially in the context of population declines. In this study, we focus on the declining Arctic charr (Salvelinus alpinus) population from Lake Geneva (Switzerland and France), which has initially been restocked with allochtonous fishes in the early eighties, followed by supportive breeding. In this context, we conducted a genetic survey to document the evolution of the genetic diversity and structure throughout the last 50 years, before and after the initiation of hatchery supplementation, using contemporary and historical samples. We show that the introduction of exotic fishes was associated with a genetic bottleneck in the 1980–1990s, a break of Hardy–Weinberg Equilibrium (HWE), a reduction in genetic diversity, an increase in genetic structure among spawning sites, and a change in their genetic composition. Together with better environmental conditions, three decades of subsequent supportive breeding using local fishes allowed to re-establish HWE and the initial levels of genetic variation. However, current spawning sites have not fully recovered their original genetic composition and were extensively h omogenized across the lake. Our study demonstrates the drastic genetic consequ e nces of different restocking tactics in a comprehensive spatiotemporal framewo rk and suggests that genetic alteration by nonlocal stocking may be partly reversible through supportive breeding. We recommend that conservation-based programs consider local diversity and implement adequate protocols to limit the genetic homogenization of this Arctic charr population

Modeling oscillatory Microtubule--Polymerization

Polymerization of microtubules is ubiquitous in biological cells and under certain conditions it becomes oscillatory in time. Here simple reaction models are analyzed that capture such oscillations as well as the length distribution of microtubules. We assume reaction conditions that are stationary over many oscillation periods, and it is a Hopf bifurcation that leads to a persistent oscillatory microtubule polymerization in these models. Analytical expressions are derived for the threshold of the bifurcation and the oscillation frequency in terms of reaction rates as well as typical trends of their parameter dependence are presented. Both, a catastrophe rate that depends on the density of {\it guanosine triphosphate} (GTP) liganded tubulin dimers and a delay reaction, such as the depolymerization of shrinking microtubules or the decay of oligomers, support oscillations. For a tubulin dimer concentration below the threshold oscillatory microtubule polymerization occurs transiently on the route to a stationary state, as shown by numerical solutions of the model equations. Close to threshold a so--called amplitude equation is derived and it is shown that the bifurcation to microtubule oscillations is supercritical.Comment: 21 pages and 12 figure

Numerical analysis of the Venda Nova II powerhouse complex

In the North of Portugal a hydroelectric scheme called Venda Nova II was recently built in order to optimize the resources of the reservoirs created by Venda Nova and Salamonde dams. The scheme, almost fully composed by underground structures and built in a predominantly granite rock mass, include several tunnels with a total length of about 7.5km, inclined and vertical shafts with a total length of 750m and two caverns which compose the powerhouse complex. The complex consists of two caverns interconnected by two galleries at a dept of about 350m. For this complex, 2D and 3D numerical models were developed considering the different construction stages. The geomechanical parameters of the granite formation for the numerical models were obtained using GEOPAT. This software is a knowledge based system which allows obtaining geomechanical parameters for underground structures modelling in granite formations. The 2D model was developed in the Phases2 software while the 3D model in FLAC3D. In this paper results of these models are analysed. Some comparisons are carried out between the models results and the monitored data. The numerical results show in general a good agreement with the monitored ones.Fundação para a Ciência e a Tecnologia (FCT) - projecto POCI/ECM/57495/2004 - Geotechnical Risk in Tunnels for High Speed Trains

Relative seismic velocity variations correlate with deformation at Kīlauea volcano, Hawai'i

Seismic noise interferometry allows the continuous and real-time measurement of relative seismic velocity through a volcanic edifice. Because seismic velocity is sensitive to the pressurization state of the system, this method is an exciting new monitoring tool at active volcanoes. Despite the potential of this tool, no studies have yet comprehensively compared velocity to other geophysical observables on a short-term time scale at a volcano over a significant length of time. We use volcanic tremor (~0.3 to 1.0 Hz) at Kīlauea as a passive source for interferometry to measure relative velocity changes with time. By cross-correlating the vertical component of day-long seismic records between ~230 station pairs, we extract coherent and temporally consistent coda wave signals with time lags of up to 120 s. Our resulting time series of relative velocity shows a remarkable correlation between relative velocity and the radial tilt record measured at Kīlauea summit, consistently correlating on a time scale of days to weeks for almost the entire study period (June 2011 to November 2015). As the summit continually deforms in deflation-inflation events, the velocity decreases and increases, respectively. Modeling of strain at Kīlauea suggests that, during inflation of the shallow magma reservoir (1 to 2 km below the surface), most of the edifice is dominated by compression—hence closing cracks and producing faster velocities—and vice versa. The excellent correlation between relative velocity and deformation in this study provides an opportunity to understand better the mechanisms causing seismic velocity changes at volcanoes, and therefore realize the potential of passive interferometry as a monitoring tool

Fermi Surface as the Driving Mechanism for Helical Antiferromagnetic Ordering in Gd-Y Alloys

The first direct experimental evidence for the Fermi surface (FS) driving the helical antiferromagnetic ordering in a gadolinium-yttrium alloy is reported. The presence of a FS sheet capable of nesting is revealed, and the nesting vector associated with the sheet is found to be in excellent agreement with the periodicity of the helical ordering.Comment: 4 pages, 4 figure

Measurement of masses in the [Formula: see text] system by kinematic endpoints in pp collisions at [Formula: see text].

A simultaneous measurement of the top-quark, W-boson, and neutrino masses is reported for [Formula: see text] events selected in the dilepton final state from a data sample corresponding to an integrated luminosity of 5.0 fb-1 collected by the CMS experiment in pp collisions at [Formula: see text]. The analysis is based on endpoint determinations in kinematic distributions. When the neutrino and W-boson masses are constrained to their world-average values, a top-quark mass value of [Formula: see text] is obtained. When such constraints are not used, the three particle masses are obtained in a simultaneous fit. In this unconstrained mode the study serves as a test of mass determination methods that may be used in beyond standard model physics scenarios where several masses in a decay chain may be unknown and undetected particles lead to underconstrained kinematics