Search results for "Instability"
showing 10 items of 724 documents
On the thermal instability in a horizontal rectangular porous channel heated from below by a constant flux
2014
Published version of an article in the journal: Journal of Physics: Conference Series. Also available from the publisher at: http://dx.doi.org/10.1088/1742-6596/501/1/012003 Open Access The onset of thermoconvective instability in a rectangular horizontal channel filled with a fluid-saturated porous medium is studied. The channel is heated from below with a constant flux. The top wall is maintained at a uniform constant temperature, while the lateral boundaries are permeable and perfectly conducting. The stability of the basic motionless state is analysed with respect to small-amplitude disturbances. The eigenvalue problem for the neutral stability condition is solved analytically for the n…
Global Linear Stability Analysis of the Flow Around a Superhydrophobic Circular Cylinder
2016
International audience; Over the last few years, superhydrophobic (SH) surfaces have been receiving an increasing attention in many scientific areas by virtue of their ability to enhance flow slip past solid walls and reduce the skin-friction drag. In the present study, a global linear-stability analysis is employed to investigate the influence of the SH-induced slip velocity on the primary instability of the 2D flow past a circular cylinder. The flow regions playing the role of 'wavemaker' are identified by considering the structural sensitivity of the unstable mode, thus highlighting the effect of slip on the global instability of the considered flow. In addition, a sensitivity analysis t…
Turing Instability and Pattern Formation for the Lengyel–Epstein System with Nonlinear Diffusion
2014
In this work we study the effect of density dependent nonlinear diffusion on pattern formation in the Lengyel---Epstein system. Via the linear stability analysis we determine both the Turing and the Hopf instability boundaries and we show how nonlinear diffusion intensifies the tendency to pattern formation; in particular, unlike the case of classical linear diffusion, the Turing instability can occur even when diffusion of the inhibitor is significantly slower than activator's one. In the Turing pattern region we perform the WNL multiple scales analysis to derive the equations for the amplitude of the stationary pattern, both in the supercritical and in the subcritical case. Moreover, we c…
Challenges in truncating the hierarchy of time-dependent reduced density matrices equations
2012
In this work, we analyze the Born, Bogoliubov, Green, Kirkwood, and Yvon (BBGKY) hierarchy of equations for describing the full time evolution of a many-body fermionic system in terms of its reduced density matrices (at all orders). We provide an exhaustive study of the challenges and open problems linked to the truncation of such a hierarchy of equations to make them practically applicable. We restrict our analysis to the coupled evolution of the one- and two-body reduced density matrices, where higher-order correlation effects are embodied into the approximation used to close the equations. We prove that within this approach, the number of electrons and total energy are conserved, regardl…
Nucleation and accretion of bioelastomeric fibers at biological temperatures and low concentrations.
1988
Quasi-elastic light scattering (QELS) studies are reported, which address the early stages of aggregation of the polypentamer poly(VPGVG). This reflects the major primary structural feature of native elastin. The study is focused on the region of the phase diagram which in both its temperature and concentration range is closest to the state of affairs occurring in the course of bioelastogenesis by progressive synthesis of the precursor protein. Results here reported allow for the first time a self-consistent view of the physics of elastogenesis, and specify the role of the region of metastability and of that of instability of the phase diagram in the non-chaotic, orderly formation of elasto…
Hydrogeological hazards and weather events: Triggering and evolution of shallow landslides
2014
Abstract Landslides are the most intense and serious manifestations of the degradation of slopes and they are the main causes of geological hazard when they, directly or indirectly, involving towns and infrastructures. They are a global environment problem; there are several examples that have produced untold damages and loss of human lives in many parts of the world. In 1920 the landslides mobilization, as a result of a strong earthquake in China, in the province of Kansu, killed 200,000 people; in 1938 fast debris flow, triggered by heavy rainfalls in Japan, caused the death of 600 people; in 1963 in Italy the Vajont disaster caused the death of 1,899 people, as a result of a landslide lo…
Eckhaus instability of stationary patterns in hyperbolic reaction–diffusion models on large finite domains
2022
AbstractWe have theoretically investigated the phenomenon of Eckhaus instability of stationary patterns arising in hyperbolic reaction–diffusion models on large finite domains, in both supercritical and subcritical regime. Adopting multiple-scale weakly-nonlinear analysis, we have deduced the cubic and cubic–quintic real Ginzburg–Landau equations ruling the evolution of pattern amplitude close to criticality. Starting from these envelope equations, we have provided the explicit expressions of the most relevant dynamical features characterizing primary and secondary quantized branches of any order: stationary amplitude, existence and stability thresholds and linear growth rate. Particular em…
The role of depression and impulsivity in the psychopathology of bulimia nervosa.
2013
Introduction: The study aimed to analyze the role of depression and impulsivity in the psychopathology of bulimia nervosa (BN). Materials and methods: Seventy female patients with DSM-IV BN, purging subtype, were assessed for eating-related symptoms, body dissatisfaction, affective symptoms, impulsivity, and personality traits. Factor analysis and structural equation modeling methods were used for statistical analysis. Results: BN appeared as a condition which incorporated 5 general dimensions: a) binge eating and compensatory behaviours; b) restrictive eating; c) body dissatisfaction; d) dissocial personality traits; and e) a cluster of features which was called "emotional instability" The…
Model Exploration and Computer Experiments
2017
This chapter contains a description of a set of simulation experiments for exploration of the agent-based model proposed in the present work, devised to illustrate the model’s generative capacity and highlight the influence of the newly introduced mechanisms on the complexity of the solutions. The first experiment shows the influence of the critical “cop”-to-“active” ratio ρ c in the risk perception model on the size, duration, and recurrence of rebellion peaks. The relationship between ρ c , the occurrence of cascades and the maximum possible peak size was demonstrated analytically and then studied via computer simulations. It was shown that the value of ρ c has a strong impact on the stab…
Locking Reconstruction Double Plating of Distal Humeral Fractures: How Many Screws in the Distal Ulnar Column Segment in A3 Fracture Provide Superior…
2009
Objectives: Two 90-degree configurations of locking reconstruction plates with different numbers of screws in the distal ulnar column segment of distal extra-articular humeral fractures with metaphyseal comminution (A3) were biomechanically investigated. Methods: Eight pairs of fresh-frozen human humeri were used. For paired comparison, the humeri were divided into 2 randomized groups. In both groups, double-plate osteosyntheses with locking reconstruction plates were performed in 90-degree configurations. In group 1, the posteriorly placed radial column plate exceeded the capitellum and the ulnar column plate extended into the ulnar sulcus. The ulnar plate was molded around the medial epic…