58 research outputs found
Tuning the average path length of complex networks and its influence to the emergent dynamics of the majority-rule model
We show how appropriate rewiring with the aid of Metropolis Monte Carlo
computational experiments can be exploited to create network topologies
possessing prescribed values of the average path length (APL) while keeping the
same connectivity degree and clustering coefficient distributions. Using the
proposed rewiring rules we illustrate how the emergent dynamics of the
celebrated majority-rule model are shaped by the distinct impact of the APL
attesting the need for developing efficient algorithms for tuning such network
characteristics.Comment: 10 figure
Coarse-Grained Analysis of Microscopic Neuronal Simulators on Networks: Bifurcation and Rare-events computations
We show how the Equation-Free approach for mutliscale computations can be
exploited to extract, in a computational strict and systematic way the emergent
dynamical attributes, from detailed large-scale microscopic stochastic models,
of neurons that interact on complex networks. In particular we show how the
Equation-Free approach can be exploited to perform system-level tasks such as
bifurcation, stability analysis and estimation of mean appearance times of rare
events, bypassing the need for obtaining analytical approximations, providing
an "on-demand" model reduction. Using the detailed simulator as a black-box
timestepper, we compute the coarse-grained equilibrium bifurcation diagrams,
examine the stability of the solution branches and perform a rare-events
analysis with respect to certain characteristics of the underlying network
topology such as the connectivity degre
On the effect of the path length and transitivity of small-world networks on epidemic dynamics
We show how one can trace in a systematic way the coarse-grained solutions of
individual-based stochastic epidemic models evolving on heterogeneous complex
networks with respect to their topological characteristics. In particular, we
have developed algorithms that allow the tuning of the transitivity (clustering
coefficient) and the average mean-path length allowing the investigation of the
"pure" impacts of the two characteristics on the emergent behavior of detailed
epidemic models. The framework could be used to shed more light into the
influence of weak and strong social ties on epidemic spread within small-world
network structures, and ultimately to provide novel systematic computational
modeling and exploration of better contagion control strategies
Analytical and Numerical Bifurcation Analysis of a Forest-Grassland Ecosystem Model with Human Interaction
We perform both analytical and numerical bifurcation analysis of a
forest-grassland ecosystem model coupled with human interaction. The model
consists of two nonlinear ordinary differential equations incorporating the
human perception of forest/grassland value. The system displays multiple steady
states corresponding to different forest densities as well as regimes
characterized by both stable and unstable limit cycles. We derive analytically
the conditions with respect to the model parameters that give rise to various
types of codimension-one criticalities such as transcritical, saddle-node, and
Andronov-Hopf bifurcations and codimension-two criticalities such as cusp and
Bogdanov-Takens bifurcations. We also perform a numerical continuation of the
branches of limit cycles. By doing so, we reveal turning points of limit cycles
marking the appearance/disappearance of sustained oscillations. These
far-from-equilibrium criticalities that cannot be detected analytically give
rise to the abrupt loss of the sustained oscillations, thus leading to another
mechanism of catastrophic shift
Synthesis and Characterization of Greener Ceramic Materials with Lower Thermal Conductivity Using Olive Mill Solid Byproduct
In the current research, the valorization of olive mill solid waste as beneficial admixture into clay bodies for developing greener ceramic materials with lower thermal conductivity, thus with increased thermal insulation capacity towards energy savings, is investigated. Various clay/waste mixtures were prepared. The raw material mixtures were characterized and subjected to thermal gravimetric analysis, in order to optimize the mineral composition and maintain calcium and magnesium oxides content to a minimum. Test specimens were formed employing extrusion and then sintering procedure at different peak temperatures. Apparent density, water absorption capability, mechanical strength, porosity and thermal conductivity were determined on sintered specimens and examined in relation to the waste percentage and sintering temperature. The experimental results showed that ceramic production from clay/olive-mill solid waste mixtures is feasible. In fact, the mechanical properties are not significantly impacted with the incorporation of the waste in the ceramic body. However, the thermal conductivity decreases significantly, which can be of particular interest for thermal insulating materials development. Furthermore, the shape of the produced ceramics does not appear to change with the sintering temperature increase
Deep brain stimulation for movement disorder treatment: Exploring frequency-dependent efficacy in a computational network model
A large scale computational model of the basal ganglia (BG) network is
proposed to describes movement disorder including deep brain stimulation (DBS).
The model of this complex network considers four areas of the basal ganglia
network: the subthalamic nucleus (STN) as target area of DBS, globus pallidus,
both pars externa and pars interna (GPe-GPi), and the thalamus (THA).
Parkinsonian conditions are simulated by assuming reduced dopaminergic input
and corresponding pronounced inhibitory or disinhibited projections to GPe and
GPi. Macroscopic quantities can be derived which correlate closely to thalamic
responses and hence motor programme fidelity. It can be demonstrated that
depending on different levels of striatal projections to the GPe and GPi, the
dynamics of these macroscopic quantities switch from normal conditions to
parkinsonian. Simulating DBS on the STN affects the dynamics of the entire
network, increasing the thalamic activity to levels close to normal, while
differing from both normal and parkinsonian dynamics. Using the mentioned
macroscopic quantities, the model proposes optimal DBS frequency ranges above
130 Hz.Comment: 40 pages, 16 figure
Wound dehiscence: is still a problem in the 21th century: a retrospective study
<p>Abstract</p> <p>Background</p> <p>The aim of this study was to evaluate the risk factors of wound dehiscence and determine which of them can be reverted.</p> <p>Methods</p> <p>We retrospectively analyzed 3500 laparotomies. Age over 75 years, diagnosis of cancer, chronic obstructive pulmonary disease, malnutrition, sepsis, obesity, anemia, diabetes, use of steroids, tobacco use and previous administration of chemotherapy or radiotherapy were identified as risk factors</p> <p>Results</p> <p>Fifteen of these patients developed wound dehiscence. Emergency laparotomy was performed in 9 of these patients. Patients who had more than 7 risk factors died.</p> <p>Conclusion</p> <p>It is important for the surgeon to know that wound healing demands oxygen consumption, normoglycemia and absence of toxic or septic factors, which reduces collagen synthesis and oxidative killing mechanisms of neutrophils. Also the type of abdominal closure may plays an important role. The tension free closure is recommended and a continuous closure is preferable. Preoperative assessment so as to identify and remove, if possible, these risk factors is essential, in order to minimize the incidence of wound dehiscence, which has a high death rate.</p
SYNTHESIS AND CHARACTERIZATION OF GREENER CERAMIC MATERIALS WITH LOWER THERMAL CONDUCTIVITY USING OLIVE MILL SOLID BYPRODUCT
In the current research, the valorization of olive mill solid waste as beneficial admixture into clay bodies for developing greener ceramic materials with lower thermal conductivity, thus with increased thermal insulation capacity towards energy savings, is investigated. Various clay/waste mixtures were prepared. The raw material mixtures were characterized and subjected to thermal gravimetric analysis, in order to optimize the mineral composition and maintain calcium and magnesium oxides content to a minimum. Test specimens were formed employing extrusion and then sintering procedure at different peak temperatures. Apparent density, water absorption capability, mechanical strength, porosity and thermal conductivity were determined on sintered specimens and examined in relation to the waste percentage and sintering temperature. The experimental results showed that ceramic production from clay/olive-mill solid waste mixtures is feasible. In fact, the mechanical properties are not significantly impacted with the incorporation of the waste in the ceramic body. However, the thermal conductivity decreases significantly, which can be of particular interest for thermal insulating materials development. Furthermore, the shape of the produced ceramics does not appear to change with the sintering temperature increase
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