Hybrid and modular multilevel converter designs for isolated HVDC–DC converters

Efficient medium and high-voltage dc-dc conversion is critical for future dc grids. This paper proposes a hybrid multilevel dc-ac converter structure that is used as the kernel of dc-dc conversion systems. Operation of the proposed dc-ac converter is suited to trapezoidal ac-voltage waveforms. Quantitative and qualitative analyses show that said trapezoidal operation reduces converter footprint, active and passive components' size, and on-state losses relative to conventional modular multilevel converters. The proposed converter is scalable to high voltages with controllable ac-voltage slope; implying tolerable dv/dt stresses on the converter transformer. Structural variations of the proposed converter with enhanced modularity and improved efficiency will be presented and discussed with regards to application in front-to-front isolated dc-dc conversion stages, and in light of said trapezoidal operation. Numerical results provide deeper insight of the presented converter designs with emphasis on system design aspects. Results obtained from a proof-of-concept 1-kW experimental test rig confirm the validity of simulation results, theoretical analyses, and simplified design equations presented in this paper. - 2013 IEEE.Scopu

Measurements and physical-layer modelling of transmission loss for gas turbine engine sensor networks

The aim of this study is to extract a physical-layer wireless channel model from a set of channel measurements, in support of the wider, collaborative, WIDAGATE project to assess the potential of wireless sensor networks for the condition monitoring of gas turbine engines. The collaborative partners in WIDAGATE are Rolls-Royce, Selex and University College London. The resulting model is being incorporated into a complete system protocol stack as part of the wider project. The physical layer channel model incorporates interference [1] and noise in addition to signal transmission characteristics

Financial Liberalization, Savings and the Banking Sector in Bangladesh

This article explores the consequences of financial liberalization policy on the banking sector in Bangladesh. Following a motivating portfolio selection theor-etical model on the impact of liberalization, it applies time series techniques with annual banking sector data for the period 1981-2008. The study suggests that the main objective of financial liberalization to promote domestic private savings by raising real interest rates has not worked. No significant positive correlation is observed between domestic private savings and the real deposit interest rate

Formulation of critical micellar concentration of non- phosphate detergents by surface tension measurement

Non-phosphate builders which are environmentally friendly are required for use in detergent formulation to replace the sodium tri-poly phosphate (STPP). Phosphates are excellent fertilizer for algae, bacteria, and other flora and fauna in rivers, lakes and  oceans, making them bloom at very rapid rates. This exhausts the oxygen supply both in the surface and in the bottom layers of water bodies, and leading the death of fishes. Sodium metasilicate a non-phosphate builder from Lokoja Quartzite was used to  formulate a non-phosphate biodegradable synthetic detergent using 25%, 50% and 75% sodium hydroxide concentrations. The critical micellar concentration (CMC) of a non-phosphate  detergent was determined via measurement of surface tension. This method is rapid, reliable and cheap compared to the  fluorescence polarization method which required a sophiscated materials such as 1,6-diphenyl-1,3,5-hexatriene as fluorescence probe. The detergents formulated with 75% and 50% sodium hydroxide concentrations have CMC values of 8.6685 mM and 6.9348 mM respectively. From this study, a non phosphate builder synthesized from Lokoja Quartzite has potential of protecting aquatic animals when compared with the conventional STPP currently used in our detergent formulation. Also, the simple and economical approach for determination of detergent’s CMC has demonstrated it’s potentials. These values agree well with the literature value ranges between 7 to 10 mM.Keywords: Detergent; CMC; Surfactants; Non-phosphate;  1,6-diphenyl-1,3,5-hexatrien

Reduction of Sulphur Content of Urals Crude Oil Prior to Processing Using Oxidative Desulphurization

The presence of sulphur in crude oil poses enormous challenges as regards its negative environmental and economic impacts. As such, the safety of the personnel and the equipment is at high risk during the processing of Urals crude oil in Kaduna Refining and Petrochemical Company (KRPC) because of its sour nature. This study was aimed at reducing the sulphur content of the Urals crude oil prior to processing by subjecting it to oxidative desulphurization where peracetic acid was used as the oxidant in the actual mass-to-stoichiometric mass ratio ranging from 1 to 5. The oxidized sulphur compounds were thereafter extracted using acetic acid as the extraction solvent. Furthermore, atmospheric distillation was carried out on both the raw and the desulphurized crude oil samples. Finally, the sulphur contents of the various crude oil samples and their fractions were analyzed. The results showed drastic reductions in the sulphur contents up to actual mass-to-stoichiometric mass ratio of 2 but the reductions became progressively insignificant afterwards. Meanwhile, the highest reduction in the sulphur content of the crude oil was 61.6 % while those of the gasoline, kerosene, diesel and residue were 32.0, 45.1, 68.9 and 75.0 % respectively. Therefore, peracetic acid is an effective oxidant for oxidative desulphurization of the crude oil.Keywords: Sulphur content, Crude oil, Oxidative desulphurization, Thiophenic compound

Neural servocontroller for nonlinear MIMO plant

A design of a neural servocontroller for a nonlinear MIMO plant has been presented. The control scheme is essentially an error feedback system. However, it also uses the variables representing the plant operating point. Integrators are used in the control loop to ensure low frequency setpoint following and disturbance rejection, and enhance the robustness of the scheme. The neurocontroller may be trained either (a) to minimise a quadratic loss function composed of the filtered setpoint error and the filtered plant input or (b) to induce the closed loop system to follow the output of a reference model. The training is conducted offline for a class of setpoints conforming to the normal operating condition of the plant. Results of simulation studies are also reporte

Levels of Heavy Metals in Soil, Water and Vegetables around Industrial area in Bauchi, Northeastern Nigeria

This study examined the levels of heavy metals in soil, water, and vegetables (amaranthus, hibiscussabdariffa, and allium cepa leaves) around the industrial area Bauchi, Northeastern Nigeria. The composite samples of soil, water, and vegetables were collected and determine the level of heavy metals (Mn, Zn, Cd, Pb, and As) using Atomic Absorption Spectrophotometer (AAS). The level of the heavy metals decreased in the order of Mn > Zn > Pb > Cd, Pb > Zn > Mn > Cd, and Mn > Zn > Mn > Cd in the soil, water, and vegetables respectively. Among the vegetables, amaranthus had the highest heavy metals level followed by allium cepa leaves and hibiscus sabdariffa. The levels of heavy metals obtained were below the tolerance level recommended by the world health organization (WHO). The bio-concentration factors of the heavy metals for the studied samples were below one except Zn in amaranthus. The daily intake of metals for Mn was found to be the highest in amaranthus for children and estimated to be 1.149 mg/person/day. Health risk index of Zn for amaranthus and allium cepa leaves for children and Pb for amaranthus, hibiscus sabdariffa and allium cepa leaves for both children and adults were above 1, except in hibiscus sabdariffa for adults, signifying provable of health risks for the consumption of the vegetables in the study area. Therefore, the consumption of these vegetables as food could pose a health hazard, and regular monitoring is recommended to prevent metal accumulation with their associated health implications in the consuming public

Copper (II) Adsorption by Calcium-alginate Shea Butter Cake

This study investigated the utilization of modified shea butter cake for the removal of Cu(II) ions from aqueous solution. Instrumental analysis such as Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), X-ray Diffractometer (XRD) was used for the characterisation of the solid sorbent. Batch equilibrium study was carried out to evaluate the adsorption capacity, and process parameters such as initial metal ion concentration, time, pH, and adsorbent dosage. An optimum pH of 5, equilibrium time of 30mins and adsorbent dosage of 40 beads was obtained. The Langmuir and Freundlich isotherms were used to fit the experimental data and values fits the Langmuir more adequately with correlation coefficient unity (1.000) at 10mg/l of initial metal ion concentration. The Kinetic study using the Pseudo-first-order and pseudo-second were used to determine the rate constants and experiments data best fits the pseudo-second –order with calculated amount adsorbed approximately equal to the experimental values. The results indicate that modified shea butter cake could be employed as an adsorbent for the removal of copper (II) ions in an aqueous solution. Keywords: Shea butter cake, process parameters, kinetics, Copper (II)

Neural servocontroller for nonlinear MIMO plant

A design of a neural servocontroller for a nonlinear MIMO plant has been presented. The control scheme is essentially an error feedback system. However, it also uses the variables representing the plant operating point. Integrators are used in the control loop to ensure low frequency setpoint following and disturbance rejection, and enhance the robustness of the scheme. The neurocontroller may be trained either (a) to minimise a quadratic loss function composed of the filtered setpoint error and the filtered plant input or (b) to induce the closed loop system to follow the output of a reference model. The training is conducted offline for a class of setpoints conforming to the normal operating condition of the plant. Results of simulation studies are also reporte

Enzymatic Study on the Microbial Degradation of Homocholine

This research was conducted to investigate the enzymatic activities in the degradation pathway of homocholine by bacterial strains isolated from the soil. Screening of the homocholine oxidation activity in the isolated strains, by replica staining method and spectrophotometric assay, showed that NAD+ - dependent dehydrogenase enzymes were predominant in all isolates. Furthermore, dried cell reaction of Pseudomonas sp. strain A9 cells with homocholine in the presence and absence of NAD+ demonstrated that the enzymes responsible for the metabolism of homocholine were alcohol and aldehyde dehydrogenases that require NAD+ as electron acceptor. Moreover, in the cell free extract of Pseudomonas sp. strain A9 an inducible NAD+ - dependent homocholine dehydrogenase was detected. The crude preparation of this enzyme has broad substrate specificity. Although various buffering conditions and stabilizing reagent were applied to stabilize the enzyme activity, the enzyme was unstable in vitro and lost its activity soon after and during the purification processes. Furthermore, an inducible NAD+ - dependent 3- hydroxypropionate dehydrogenase activity was also detected in the cell free extract of Pseudomonas sp. strain A9. This result indicated the presence of 3-hydroxypropionate as an intermediate metabolite in the degradation pathway of homocholine by this strain. Thus, in Pseudomonas sp. strain A9, homocholine is oxidized to trimethylaminopropionaldehyde by a NAD+-dependent homocholine dehydrogenase and consequently, trimethylaminopropionaldehyde oxidized to β-alanine betaine by a NAD+ - dependent aldehyde dehydrogenase. Thereafter, cleavage of β-alanine betaine C-N bond yielded trimethylamine and 3-hydroxypropionate (C-3 moiety). Thereafter, 3- hydroxypropionate was further oxidized to malonate semi-aldehyde by a NAD+ - dependent 3-hydroxypropionate dehydrogenase