Hybrid offset‐time and burst assembly algorithm (H‐OTBA) for delay sensitive applications over optical burst switching networks

Optical burst switching (OBS) is the most favourable switching paradigm for future all‐optical networks. Burst assembly is the first process in OBS and it consists of aggregating clients packets into bursts. Assembled bursts wait for an offset time before being transmitted to their intended destinations. Offset time is used to allow burst control packet reserve required resources prior to burst arrival. Burst assembly process and offset‐time create extra delay in OBS networks. To make OBS suitable for real time applications, this extra latency needs to be controlled. This paper proposes and evaluates a novel offset time and burst assembly scheme to address this issue. Constant bit rate (CBR) traffic that has stringent end‐to‐end delay QoS requirements is used in this study. The proposed scheme is called hybrid offset‐time and burst assembly algorithm (H‐OTBA). The objective of the paper is achieved by controlling maximum burst transfer delay parameters of CBR. The proposed scheme was evaluated via network simulation. Simulation results demonstrate that, H‐OTBA has effectively reduced end‐to‐end delay for CBR traffic compared with current solutions. Copyright © 2014 John Wiley & Sons, Ltd.     

Experimental evaluation of a vibration-based leak detection technique for water pipelines

Conventional water pipeline leak detection surveys employ labour-intensive acoustic techniques, which are usually expensive and not amenable for continuous monitoring of distribution systems. Many previous studies attempted to address these limitations by proposing and evaluating a myriad of continuous, long-term monitoring techniques. However, these techniques have difficulty to identify leaks in the presence of pipeline system complexities (e.g. T-joints), offered limited compatibility with popular pipe materials (e.g. PVC), and were in some cases intrusive in nature. Recently, a non-intrusive pipeline surface vibration-based leak detection technique has been proposed to address some of the limitations of the previous studies. This new technique involves continuous monitoring of the change in the cross-spectral density of surface vibration measured at discrete locations along the pipeline. Previously, the capabilities of this technique have been demonstrated through an experimental campaign carried out on a simple pipeline set-up. This paper presents a follow-up evaluation of the new technique in a real-size experimental looped pipeline system located in a laboratory with complexities, such as junctions, bends and varying pipeline sizes. The results revealed the potential feasibility of the proposed technique to detect and assess the onset of single or multiple leaks in a complex system.     

Indole Alkaloids of Alstonia angustifolia var. latifolia as Green Inhibitor for Mild Steel Corrosion in 1 M HCl Media

The inhibition effect of mild steel (MS) corrosion in 1 M HCl was studied by the addition of indole alkaloids (crude) isolated from Alstonia angustifolia var. latifolia (A. latifolia) leaves at 303 K. Potentiodynamic polarization, impedance spectroscopy, scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) analyses were used for this study. Results show that the isolated alkaloid extract of A. latifolia is a good inhibitor and exhibited maximum inhibition efficiency (above 80%) at concentrations between 3 and 5 mg/L. Polarization measurements indicated that the inhibitor does not alter the mechanism of either anodic or cathodic reactions and acted as mixed-type inhibitor. The inhibition efficiencies of both electrochemical techniques are found to be in good agreement and adsorption of inhibitor follows Langmuir isotherm. Adsorption of inhibitor over metal surface was well supported by the SEM studies, while FTIR studies evidenced the presence of indole alkaloids as green inhibitor that reduces the rate of corrosion.     

Effect of CaO on tar reforming to hydrogen-enriched gas with in-process CO2 capture in a bubbling fluidized bed biomass steam gasifier

Previous studies showed that calcium oxide (CaO), when added to a biomass steam gasifier, could play the role of both CO₂ sorbent and tar reforming catalyst, and thereby produce more hydrogen. However, most of these works focused on the former role with little attention to tar reforming aspect of CaO. Therefore, this work aims primarily at studying the tar reforming effect of in-bed CaO. To this end, an in-depth analysis of the effect of CaO on tar yield and composition is presented. The present work also studies the role of CaO as a CO₂ sorbent to enhance hydrogen production from steam gasification of biomass in a bubbling fluidized bed. The influence of different operating parameters, temperature (T) and steam to biomass (S/B) ratio, as well as the effect of using in-bed CaO on gas and tar production is investigated. Results show that the maximum H₂ and minimum CO₂ concentration of 63.07% and 18.68%, respectively are obtained at T = 650 °C and S/B = 3.41. The maximum H₂ yield of 256.81 ml g⁻¹-biomass was obtained at T = 700 °C and S/B = 3.41, at which the minimum tar content of 6.45 g N m⁻³ was also received. Compared to a bed of sand alone, a 20% higher H₂ concentration, an almost double H₂ yield and a 67% reduction in tar content were obtained when a bed of CaO was used. Moreover, shifting the tar species from higher to fewer ring structures as a result of in-bed CaO can reduce tar dew point by 11 °C and tar carcinogenic potential by almost 60%.     

Climate-based empirical model for PV module temperature estimation in tropical environment

The paper proposes new mathematical models to estimating PV module temperature for poly and mono crystalline technologies in tropical climate such as in Malaysia. The developed models are based on measured hourly global solar radiation, ambient temperature, relative humidity, wind speed and module temperature. All data were collected over the year 2009 at GreenTech 92 kWp installed PV system in Selangor, Malaysia. The models were compared using r, MBE, RMSE, and MPE. The results showed that the proposed models give the highest value of correlation coefficient r, and good result when considering statistical indicators i.e. low RMSE, low MBE, and low MPE values. The results show that the proposed regression models have advantages over the conventional approaches for calculating the hourly and day-average PV module temperature, and give the closest results comparing to the actual measurements. The proposed approaches can be used as effective tools for predicting the PV module temperature, whether a simple PV module, open rack system, BIPV installations, or even PV/Thermal collector, in remote and rural locations with no direct measurement equipment. The proposed models can be very useful in studying PV system performance and estimating its energy output.     

Optimization of Process Parameters for the Preparation of CaO/CaSO4/Coal Fly Ash Sorbent for Sulfur Dioxide (SO2) Removal: Part II

A two-step optimization strategy was employed to optimize the surface area of sorbent prepared from coal fly ash, calcium oxide (CaO) and calcium sulfate (CaSO₄) for flue gas desulfurization. In the first step, a 3 level full factorial design of experiment was used to develop a regression model equation to correlate the significant experimental sorbent preparation variables to the surface area of the resulting sorbent. The three experimental sorbent preparation variables studied are hydration period (x ₁), ratio of CaO to fly ash (x ₂) and amount of CaSO₄ (x ₃). In the subsequent step, response surface methodology was used to identify the experimental sorbent preparation variables that maximize the surface area of the sorbent. Through this two-step optimization strategy, it was found that at a hydration period of 10 hrs and drying temperature of 100°C, optimum surface area of 67.0 m²/g could be attained by using 5 grams of CaO, 13.7 grams of fly ash, and 7.4 grams of CaSO₄ in the preparation mixture. The prediction was verified with experimental runs.     

Effect of processing routes on mechanical and thermal properties of copper–graphene composites

In this paper, copper–graphene composites were fabricated by using two different processing routes (ball milling (BM) and ultrasonication) followed by spark plasma sintering. Vickers hardness and anisotropic thermal conductivity of the composites were measured and observed that ultrasonicated fabricated composites gave better result compared with BM composite and even from pure copper. The hardness values obtained for ultrasonicated copper–graphene composite were 69?HV (57% higher) and thermal conductivity 387?W/m?K (13% higher) by using only 0.5?wt-% of graphene, while for pure copper the values were 44?HV and 341?W/m?K. The value of anisotropic thermal conductivity ultrasonicated composites was also 1.97 which is much higher than pure copper 0.94.     

An intermediate range solution to a diffraction problem with impedance conditions

An intermediate range solution for the problem of plane wave diffraction by a finite plate with impedance boundaries is presented. Initially, the problem is expressed in terms of two Wiener–Hopf equations with the help of Fourier transform and the boundary conditions in the transformed domain. The consideration of the intermediate range approximation in terms of source position renders integrals that are generally elusive to tackle because of the presence of branch points. These integrals are evaluated by invoking a modified stationary phase method, thereby a field valid over an intermediate range is calculated. The graphical analysis is preformed for various parameters of physical interest for both intermediate and far-field solutions.     

Morphology, structural and optical characterization of electron beam evaporated bromoaluminium phthalocyanine (BrAlPc) thin films

Bromoaluminium phthalocyanine (BrAlPc) thin films have been deposited onto pre-cleaned glass substrates by electron beam evaporation technique. Thin films have been characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and optical absorption (UV–Vis) spectra. XRD studies of BrAlPc thin film deposited at room temperature shows the indication of the α-phase. FESEM images have shown that the most of particles are spherical in shape with an average size about 26–34 nm. Using UV–Visible spectra over the wavelength range 300–800 nm, the optical band gap, absorption coefficient and extinction coefficient of BrAlPc thin films are evaluated. The optical absorption measurements of thin films show that the absorption mechanism is due to direct transition.