Desiccation of a clay film: Cracking versus peeling

Cracking and peeling of a layer of clay on desiccation has been simulated using a spring model. A vertical section through the layer with finite thickness is represented by a rectangular array of nodes connected by linear springs on a square lattice. The effect of reduction of the natural length of the springs, which mimics the drying is studied. Varying the strength of adhesion between sample and substrate and the rate of penetration of the drying front produces an interesting phase diagram, showing cross-over from peeling to cracking behavior. Changes in the number and width of cracks on varying the layer thickness is observed to reproduce experimental reports.Comment: 4 figure

Optimisation using central composite design (CCD) and the desirability function for sorption of methylene blue from aqueous solution onto Lemna major

AbstractWater pollution due to contamination of dye containing effluents is a great threat to water body. A study on the biosorption of methylene blue (MB) onto low-cost Lemna major biomass was conducted and the process parameters were optimized by response surface methodology (RSM). A two-level, four-factor central composite design (CCD) has been employed to determine the effect of various process parameters namely initial concentration (600–1000 mg L−1), bioadsorbent dose (0.20–1.50 g/100 mL), pH (5–12) and stirring rate (250–800 rpm) on MB uptake from aqueous solution. By using this design a total of 30 biosorption experimental data were fitted. The regression analysis showed good fit of the experimental data to the second-order polynomial model with coefficient of determination (R2) value of 0.9978 and model F-value of 953.48. The optimum conditions of initial concentration (1000 mg L−1), adsorbent dose (0.2 g), pH (5) and stirring rate (251.51 rpm) were recorded from desirability function. The adsorption isotherm data were best described by both Freundlich and Langmuir models with a maximum adsorption capacity of 488 mg MB g−1 L. major biomass at 30 °C which is higher than that available with adsorbents used by past researchers. Finally the pseudo second order kinetic model described the MB biosorption process with a good fitting (R2 = 0.999). The adsorbent was characterised by scanning electron micrograph (SEM) and Fourier transform infrared spectroscopy (FTIR)

Similarities between the structure functions of thermal convection and hydrodynamic turbulence

In this paper, we analyze the scaling of velocity structure functions of turbulent thermal convection. Using high-resolution numerical simulations, we show that the structure functions scale similar to those of hydrodynamic turbulence, with the scaling exponents in agreement with She and Leveque's predictions [Phys. Rev. Lett. 72, 336-339 (1994)]. The probability distribution functions of velocity increments are non-Gaussian with wide tails in the dissipative scales and become close to Gaussian in the inertial range. The tails of the probability distribution follow a stretched exponential. We also show that in thermal convection, the energy flux in the inertial range is less than the viscous dissipation rate. This is unlike in hydrodynamic turbulence where the energy flux and the dissipation rate are equal.Comment: 21 pages, 9 figure

Vulnerable Path Determination in mobile ad-hoc networks using Markov Model

Security threats are of major concern in information sensitive ad-hoc networks like emergency military communication networks. We propose a Proactive Information Security Management System (PISMS) framework with vulnerable path determination module (VPDM) for such mobile ad-hoc networks. The chief security officer can use it to identify the most vulnerable paths, so that they can be patched using suitable security technologies before the hackers actually attack and compromise them. Our PISMS computes (i) the probability of transitioning from each node to its adjacent neighbors, using two key indicators (angle and distance); (ii) number of steps required to reach a pre-determined destination from different sources using Markov model. The path that requires minimum number of steps to reach a destination is the most vulnerable path. This mechanism of identifying vulnerable path is incorporated as an integral part of the Information systems acquisition, development and maintenance (ISADM) module of ISMS framework ISO27001

Dynamics of market states and risk assessment

Based on previous developments of the concept of market states using correlation matrices, in the present paper we address the dynamical evolution of correlation matrices in time. This will imply minor modifications to the market states themselves, due to increased attention to the transition matrix between the states. We will introduce trajectories of the correlation matrices by considering one day shifts for the epoch used to calculate the correlation matrices and will visualize both the states and the trajectories after dimensional scaling. This approach using dynamics improves the options of risk assessment and opens the door to dynamical treatments of markets and shows noise suppression in a new light.Comment: 22 pages and 27 figures. arXiv admin note: text overlap with arXiv:2003.0705