Fibers on a graph with local load sharing

We study a random fiber bundle model with tips of the fibers placed on a graph having co-ordination number 3. These fibers follow local load sharing with uniformly distributed threshold strengths of the fibers. We have studied the critical behaviour of the model numerically using a finite size scaling method and the mean field critical behaviour is established. The avalanche size distribution is also found to exhibit a mean field nature in the asymptotic limit.Comment: 9 pages, 6 figures, To appear in International Journal of Modern Physics

Morphological Bedload Transport in Gravel-Bed Braided Rivers

Gravel-bed braided rivers, defined by their multi-thread planform and dynamic morphology, are commonly found in proglacial mountainous areas. With little cohesive sediment and a lack of stabilizing vegetation, the dynamic morphology of these rivers is fundamentally the result of bedload transport processes but our understanding of the fundamental relationships between channel form and bedload processes remains incomplete. For example, the area of the bed actively transporting bedload, known as the active width, is strongly linked to bedload transport rates but these relationships have not been investigated systematically in braided rivers. This research builds on previous research to investigate the relationships between morphology, bedload transport rates, and bed-material mobility using physical models of braided rivers over a range of constant channel-forming discharges and event hydrographs. Morphology changes were estimated using the morphological method, which infers information from changes in channel topography over time, from an extensive dataset of digital elevation models (DEMs) generated using digital photogrammetry and ‘Structure-from-Motion’ principles. Results suggest that the morphological active width is highly variable even at constant discharge, but increases with stream power and is positively related to bedload transport rates, bulk change (i.e. total volume of erosion and deposition), and active braiding intensity. Morphologically-derived sediment budgets provided reasonable estimates of bedload transport rates that were similar to independent measurements of bedload transport rates from sediment baskets. In addition, grain size distributions and bed mobility evolved from a state of partial mobility towards equal mobility with increasing discharge. This is rare in most gravel-bed rivers but in braided rivers the high levels of sediment supply and lack of armouring allow for greater mobility of the channel bed and subsurface. Finally, the lower detection threshold for the morphological active width, bedload transport, and transition to selective mobility all coincided with a dimensionless stream power of ~0.08. Overall, these results suggest that while braided rivers are dynamic, they may be restricted in ways like their single-threaded counterparts so that measures of morphology (i.e. the active width) can be used as general predictors of bedload transport rates and the morphological stability of the river. This knowledge contributes to our overall understanding of braided river morphodynamics while also building on theory for use in applied geomorphology and engineering practices for the management, conservation, and restoration of complex braided rivers systems

Value and risk reporting practice among listed companies in Belgium.

In this report we describe the general practices, among Belgian public firms, re voluntary disclosure. We provide an overall score, a subtotal for each of ten information categories, and individual scores. We find that only two subtotals, Management & Performance and Organization & Strategy, fare rather well almost across the board. The value drivers, in contrast, tend to come in among the lowest-ranked items, as does Risk Management. For two value drivers, Brands and Customers, around half of the companies even remain utterly silent. Across firms, there often is a pronounced right-skewness among the rankings for one subcategory. On more than half the items that could logically help determine value, more than half of the firms provide no information whatsoever.The top-performing companies are doing spectacularly better on Risk Management, and (relatively) worse on macro information. Manufacturing firms do best, both in terms of total rating as well as on most subcategories, followed by retail/distribution/media (RDM) and then Technology.Optimal; Value; Risk; Reporting; Companies; Firms; Disclosure; Information; Management; Performance; Strategy; Risk management; Brands; Manufacturing;

Dynamic model of fiber bundles

A realistic continuous-time dynamics for fiber bundles is introduced and studied both analytically and numerically. The equation of motion reproduces known stationary-state results in the deterministic limit while the system under non-vanishing stress always breaks down in the presence of noise. Revealed in particular is the characteristic time evolution that the system tends to resist the stress for considerable time, followed by sudden complete rupture. The critical stress beyond which the complete rupture emerges is also obtained

Comparison of Two Detailed Models of Aedes aegypti Population Dynamics

The success of control programs for mosquito-­borne diseases can be enhanced by crucial information provided by models of the mosquito populations. Models, however, can differ in their structure, complexity, and biological assumptions, and these differences impact their predictions. Unfortunately, it is typically difficult to determine why two complex models make different predictions because we lack structured side-­by-­side comparisons of models using comparable parameterization. Here, we present a detailed comparison of two complex, spatially explicit, stochastic models of the population dynamics of Aedes aegypti, the main vector of dengue, yellow fever, chikungunya, and Zika viruses. Both models describe the mosquito?s biological and ecological characteristics, but differ in complexity and specific assumptions. We compare the predictions of these models in two selected climatic settings: a tropical and weakly seasonal climate in Iquitos, Peru, and a temperate and strongly seasonal climate in Buenos Aires, Argentina. Both models were calibrated to operate at identical average densities in unperturbedconditions in both settings, by adjusting parameters regulating densities in each model (number of larval development sites and amount of nutritional resources). We show that the models differ in their sensitivityto environmental conditions (temperature and rainfall) and trace differences to specific model assumptions.Temporal dynamics of the Ae. aegypti populations predicted by the two models differ more markedly under strongly seasonal Buenos Aires conditions. We use both models to simulate killing of larvae and/or adults with insecticides in selected areas. We show that predictions of population recovery by the models differ substantially, an effect likely related to model assumptions regarding larval development and (director delayed) density dependence. Our methodical comparison provides important guidance for model improvement by identifying key areas of Ae. aegypti ecology that substantially affect model predictions, and revealing the impact of model assumptions on population dynamics predictions in unperturbed and perturbed conditions.Fil: Legros, Mathieu. University of North Carolina; Estados UnidosFil: Otero, Marcelo Javier. Universidad de Buenos Aires; ArgentinaFil: Romeo Aznar, Victoria Teresa. Universidad de Buenos Aires; ArgentinaFil: Solari, Hernan Gustavo. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Gould, Fred. National Institutes of Health; Estados UnidosFil: Lloyd, Alun L.. National Institutes of Health; Estados Unido

Effect of discontinuity in threshold distribution on the critical behaviour of a random fiber bundle

The critical behaviour of a Random Fiber Bundle Model with mixed uniform distribution of threshold strengths and global load sharing rule is studied with a special emphasis on the nature of distribution of avalanches for different parameters of the distribution. The discontinuity in the threshold strength distribution of fibers non-trivially modifies the critical stress as well as puts a restriction on the allowed values of parameters for which the recursive dynamics approach holds good. The discontinuity leads to a non-universal behaviour in the avalanche size distribution for smaller values of avalanche size. We observe that apart from the mean field behaviour for larger avalanches, a new behaviour for smaller avalanche size is observed as a critical threshold distribution is approached. The phenomenological understanding of the above result is provided using the exact analytical result for the avalanche size distribution. Most interestingly,the prominence of non-universal behaviour in avalanche size distribution depends on the system parameters.Comment: 6 pages, 4 figures, text and figures modifie

Dynamic model for failures in biological systems

A dynamic model for failures in biological organisms is proposed and studied both analytically and numerically. Each cell in the organism becomes dead under sufficiently strong stress, and is then allowed to be healed with some probability. It is found that unlike the case of no healing, the organism in general does not completely break down even in the presence of noise. Revealed is the characteristic time evolution that the system tends to resist the stress longer than the system without healing, followed by sudden breakdown with some fraction of cells surviving. When the noise is weak, the critical stress beyond which the system breaks down increases rapidly as the healing parameter is raised from zero, indicative of the importance of healing in biological systems.Comment: To appear in Europhys. Let

A random fiber bundle with many discontinuities in the threshold distribution

We study the breakdown of a random fiber bundle model (RFBM) with $n$-discontinuities in the threshold distribution using the global load sharing scheme. In other words, $n+1$ different classes of fibers identified on the basis of their threshold strengths are mixed such that the strengths of the fibers in the $i-th$ class are uniformly distributed between the values $\sigma_{2i-2}$ and $\sigma_{2i-1}$ where $1 \leq i \leq n+1$. Moreover, there is a gap in the threshold distribution between $i-th$ and $i+1-th$ class. We show that although the critical stress depends on the parameter values of the system, the critical exponents are identical to that obtained in the recursive dynamics of a RFBM with a uniform distribution and global load sharing. The avalanche size distribution (ASD), on the other hand, shows a non-universal, non-power law behavior for smaller values of avalanche sizes which becomes prominent only when a critical distribution is approached. We establish that the behavior of the avalanche size distribution for an arbitrary $n$ is qualitatively similar to a RFBM with a single discontinuity in the threshold distribution ($n=1$), especially when the density and the range of threshold values of fibers belonging to strongest ($n+1$)-th class is kept identical in all the cases.Comment: 6 pages, 4 figures, Accepted in Phys. Rev.

Crossover Behavior in Burst Avalanches of Fiber Bundles: Signature of Imminent Failure

Bundles of many fibers, with statistically distributed thresholds for breakdown of individual fibers and where the load carried by a bursting fiber is equally distributed among the surviving members, are considered. During the breakdown process, avalanches consisting of simultaneous rupture of several fibers occur, with a distribution D(Delta) of the magnitude Delta of such avalanches. We show that there is, for certain threshold distributions, a crossover behavior of D(Delta) between two power laws D(Delta) proportional to Delta^(-xi), with xi=3/2 or xi=5/2. The latter is known to be the generic behavior, and we give the condition for which the D(Delta) proportional to Delta^(-3/2) behavior is seen. This crossover is a signal of imminent catastrophic failure in the fiber bundle. We find the same crossover behavior in the fuse model.Comment: 4 pages, 4 figure

Tailoring laser pulses with spectral and fluence constraints using optimal control theory

Within the framework of optimal control theory we develop a simple iterative scheme to determine optimal laser pulses with spectral and fluence constraints. The algorithm is applied to a one-dimensional asymmetric double well where the control target is to transfer a particle from the ground state, located in the left well, to the first excited state, located in the right well. Extremely high occupations of the first excited state are obtained for a variety of spectral and/or energetic constraints. Even for the extreme case where no resonance frequency is allowed in the pulse the algorithm achieves an occupation of almost 100%