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.     

Phase evolution and electrical behaviour of samarium-substituted bismuth ferrite ceramics

Bi_1-xSm_xFeO₃ (x?=?0.15–0.18) ceramics with high density were produced using spark plasma sintering. The effects of composition, synthesis conditions and temperature on the phase evolution were studied, using XRD, TEM and dielectric spectroscopy. The coexistence of the ferroelectric R3c, antiferroelectric Pnam and paraelectric Pnma phases was revealed, with relative phase fractions affected by both calcination conditions and Sm concentration. Experiments on powdered samples calcined at different temperatures up to 950?°C suggest higher calcination temperatures promote Sm diffusion, allowing samples to reach compositional homogeneity. The structural transitions from the Pnam and R3c phases to the Pnma phase were comprehensively investigated, with phase transition temperatures clearly identified. The dielectric permittivity, electrical resistivity and breakdown strength were increased upon Sm-substitution, while ferroelectric switching was suppressed. The polarization-electric field loop became increasingly narrow with increasing Sm-content, but double hysteresis loops, which may reflect a reversible antiferroelectric to ferroelectric transformation, were not observed.     

Hybrid power markets in Africa: Generation planning,procurement and contracting challenges

African power sectors are generally characterised by insufficient generation capacity.     

Mobile information systems and organisational control: beyond the panopticon metaphor?

With their ubiquity, mobile information systems (IS) may be used in ways that challenge the dynamics of organisational control, forcing IS scholars to revisit the panopticon metaphor and possibly offer new conceptual tools for theorising about information technology (IT)-based organisational control. Yet little IS research has offered critical reflections on the use of the panopticon to represent the control potential of mobile IS. This study investigates whether the way mobile IS are engaged in the workplace reinforce panoptic control systems or generate other types of control logics, requiring another conceptual lens. A qualitative exploratory case study investigated a consulting company whose professionals equipped themselves with mobile IS. The study reveals the emergence of a subtle, invisible form of ‘free control’ through mobile IS. Although consultants are mobile, flexible, and autonomous, a powerful communication and information network keeps them in a position of ‘allowed subjection’. Free control is characterised by a shift in the location of authority, a time-related discipline, a deep sense of trust, and adherence to organisational norms that the professionals themselves co-construct. These characteristics, which render such control even more pernicious than panoptic arrangements, deserve more attention in further IS research.     

Reduced-order PCA models for chemical reacting flows

One of the most challenging aspects of turbulent combustion research is the development of reduced-order combustion models which can accurately reproduce the physics of real systems. The identification and utilization of the low dimensional manifolds in these system is paramount to understand and develop robust models which can account for turbulence–chemistry interactions. Recently, principal components analysis (PCA) has been given notable attention in its analysis of reacting systems, and its potential in reducing the number of dimensions with minimum reconstruction error. The present work provides a methodology which has the ability of exploiting the information obtained from PCA. Two formulations of the approach are shown: Manifold Generated from PCA (MG-PCA), based on a global analysis, and Manifold Generated from Local PCA (MG-L-PCA), based on performing the PCA analysis locally. The models are created using the co-variance matrix of a data-set which is representative of the system of interest. The reduced models are then used as a predictive tool for the reacting system of interest by transporting only a subset of the original state-space variables on the computational grid and using the PCA basis to reconstruct the non-transported variables. The present study first looks into the optimal selection of the subset of transported variables and analyzes the effect of this selection on the approximation of the state space and chemical species source terms. Then, a demonstration of various a posteriori cases is presented.     

Effect of hot air,vacuum and infrared drying methods on quality of rose hip (Rosa rubiginosa) leathers

For the development of fruit leathers, a formulation containing rose hip pulp, sucrose and citric acid was used as initial material for the drying process. Three dehydration techniques were tested: forced hot air, infrared and vacuum, all carried out at 60 and 70 °C. All methods led to flexible, translucent fruit leathers at both temperatures. Colour and water activity were not affected by the dehydration method nor by the temperatures tested. Nutritional parameters such as antioxidant capacity (TEAC) and content of phenolic substances were measured. The best retention was achieved with vacuum drying at 60 °C being of 57.5% and 25.1%, respectively. ESEM observations were conducted to assess the effect of drying methods and conditions on microstructure of leathers. Various extents of sucrose crystallisation were inferred from surface images. Cross‐sectional micrographs showed that the size of pores was affected by the drying technique but not by temperature in the range studied.     

Buffer Standards for the Biological pH of the Amino Acid N-[2 hydroxyethyl]piperazine-N'-[3-propanesulfonic acid], HEPPS, From (278.15 to 328.15) K

For the HEPPS buffer under investigation, there are seven buffer solutions without NaCl and eight buffer solutions that contain Cl(-) and have an ionic strength (I = 0.16 mol·kg(-1)), which is similar to that of blood plasma. These buffer solutions have been evaluated in the temperature range of (278.15 to 328.15) K using the extended Debye- Hückel equation and the Bates-Guggenheim convention. The previously determined E(j) values have been used to determine the operational pH values of HEPPS buffer solutions at (298.15 and 310.15) K. These are recommended as secondary standard reference solutions for pH measurements in saline media with an isotonic ionic strength of I = 0.16 mol·kg(-1).