Strict doubly ergodic infinite transformations

We give examples of rank-one transformations that are (weak) doubly ergodic and rigid (so all their Cartesian products are conservative), but with non-ergodic two-fold Cartesian product. We give conditions for rank-one infinite measure-preserving transformations to be (weak) doubly ergodic and for their k-fold Cartesian product to be conservative. We also show that a (weak) doubly ergodic nonsingular group action is ergodic with isometric coefficients, and that the latter strictly implies W-measurable sensitivity.     

Free vibration of triple-walled carbon nanotubes

Natural frequencies of triple-walled carbon nanotubes (TWCNTs) are determined both exactly and approximately. For the case of a TWCNT simply supported at its ends, closed-form solutions are obtained. It is shown that there are three series of natural frequencies corresponding to the cubic polynomial equation for natural frequency squares. For a TWCNT that has other boundary conditions approximate Bubnov?CGalerkin and Petrov?CGalerkin methods are used with simple polynomial functions. Each of these methods yields three natural frequencies corresponding to the lower end of each frequency spectrum.     

Development of maize cob‐based biochar filter for water purification

The study aimed at biochar production from maize cob and its performance in improving water physiochemical attributes. Three feedstock masses (2, 2.5, 3 kg) were used for biochar production. Nine treatment combinations of T1L1, T1L2, T1L3, T2L1, T2L2, T2L3, T3L1, T3L2 and T3L3 in triplicate were used for biochar performance. Biochar yield of 50% was averagely achieved at slow pyrolysis conditions (300 to 600°C) and 120 min residence time. Biochar had 4.13% moisture content, 6.86% ash, 17.70% volatile matter, 71.28% fixed carbon, and a pH of 10.27. Odour, colour, and total hardness of the wastewater improved after filtration using biochar to acceptable levels for potable water use. Total hardness reduced by 51.9% in T2L2 and 44.4% in T3L2. Findings front maize cob biochar as a purification technology for domestic potable water use. There is need for maize cob biochar performance on heavy metals and when it is sandwiched with other materials.     

Adaptive interpolation of images using a new nonlinear cell-average scheme

We present a new method for image interpolation which combines a cell average version of the nonlinear interpolatory technique called PPH (Piecewise Polynomial Harmonic) and subcell resolution techniques. It is designed to perform more accurately at discontinuities, avoiding the evaluation of any extrapolation technique. Numerical experiments are shown validating the theoretical aspects of the algorithm.     

Towards benchmarking routing protocols in wireless mesh networks

Wireless mesh networks (WMNs) establish a new, quick and low-cost alternative to provide communications when deploying a fixed infrastructure that could result prohibitive in terms of either time or money. During last years, the specification of multi-hop routing protocols for WMNs has been promoted, leading to their recent exploitation in commercial solutions. The selection of routing protocols for integration in WMNs requires the evaluation, comparison and ranking of eligible candidates according to a representative set of meaningful measures. In this context, the development of suitable experimental techniques to balance different features of each protocol is an essential requirement. This paper copes with this challenging task by proposing a benchmarking methodology to experimentally evaluate and compare the behaviour of these protocols. The feasibility of the proposed approach is illustrated through a simple but real (non-simulated) case study and reflects to what extent this methodology can be useful in increasing our knowledge on how real WMNs behave in practice.     

Experimental and numerical simulations of the hydraulic flushing of reservoir sedimentation for planning and design of a hydropower project

Hydropower projects located on rivers transporting heavy sediment loads require design and operation criteria based on sediment management as a means of sustaining the project life. Sediment management is achieved by designing projects as a run‐of‐the‐river scheme, with provision for drawdown flushing, noting hydraulic model simulations are essential for optimizing the design of these projects. Sediment deposition levels are generally predicted with long‐term simulations using 1‐D numerical models, as well as experiments with scaled physical models that simulate drawdown flushing. The present study presents experiments with scaled model and 3‐D numerical model simulations conducted for hydraulic flushing of a reservoir. Experiments were conducted for various durations and discharges to finalize the intake alignment and optimize the flushing. The results of the 3‐D numerical model simulations are in agreement with the results of the experimental study (4%–6% variation). The results also indicate a combination of a 1‐D numerical model for sedimentation and a 3‐D numerical model for flushing can be effectively used to simulate the sedimentation and flushing of reservoirs during the planning and design stages.