Effects of semiconductor-optical-amplifier nonlinearity on theperformance of high-speed intensity-modulation lightwave systems

It is shown that when the amplifier is driven near saturation, its inherent nonlinearity causes significant bit-pattern-dependent pulse distortion, particularly in the bit-rate range between about 2 and 32 GB/s. Without proper countermeasures, this distortion can degrade system performance appreciably due to two basic mechanisms. The first, which can result in a system power penalty of as much as 10 dB, occurs in a standard decision circuit that automatically sets the threshold voltage to the average signal level, rather than in the middle of the eye opening. The second mechanism, which occurs even with the threshold set properly, is due to the nonlinear enhancement of the simple linear intersymbol interference (ISI) within the receiver filter. For example, computations of system performance at 8 Gb/s using an RC filter that gives a quite acceptable 10% of eye closure under linear conditions show that when the amplifier is driven to its saturation output power level, this mechanism causes a system power penalty of about 1 dB, which increases to about 4.5 dB when the power is doubled. Interestingly, with the proper threshold setting, an ideal integrate-and-dump receiver, which introduces no ISI, is shown to suffer no power penalty due to amplifier nonlinearity     

Fundamental limit on number of channels in subcarrier-multiplexed lightwave CATV system

A fundamental limit on the number of channels in an SCM lightwave CATV system is derived by considering an idealised link consisting of a shot-noise-limited receiver and a laser transmitter with a linear light/current characteristic. For VSB-AM TV, the limit is only 50 channels per milliwatt of received optical power.<>     

Photodegradation of phenol red in the presence of oxyhydroxide of Fe(III) (Goethite) under artificial and a natural light

The (α‐FeOOH) Goethite composite is a stable and an efficient catalyst in aqueous suspension under irradiation at 365 nm and by solar light. The photocatalytic activities of this composite were evaluated using Phenol Red (PR) dye (phenolsulfonphthalein class). In the dark, controlling factors, such as the pH and the adsorption of PR on Goethite surface were evaluated (before starting the photochemical experiments). It was found that the system PR‐Goethite present a small decrease in the main band of the dye (435 nm) which was explained by the low rate of adsorption of this dye on the Goethite. Also, we note that 40% of PR decolourisation was obtained after 200 min by the system PR‐Goethite‐hydrogen peroxide (H₂O₂) in dark due to the formation of ^?OH by thermal decomposition of H₂O₂ on the surface of Goethite. The effects of various experimental parameters, such as initial dye concentration, pH, photocatalyst amount, tert‐Butyl alcohol effect and H₂O₂ addition were investigated in the study of photodegradation of the dye. The results showed that the photodegradation of PR under UV‐A (365 nm) irradiation could be enhanced greatly in the presence of H₂O₂. Natural radiation tests (under sunlight) showed that degradation was faster comparing with that obtained using the artificial one at 365 nm. Studies of the mineralization using total organic carbon method under naturel light certify that this method, compatible with the environment, may be considered in the treatment of wastewater and generally in the process of removal of this kind of pollutant.     

Feasibility of Treatment of Refinery Wastewater by a Pilot Scale MF/UF and UF/RO System for Reuse at Boilers and Cooling Towers

A pilot-scale hybrid membrane system, consisting of a ceramic microfilter (MF), two differentpolyvinyl chloride (PVC) and polyacrylonitrile (PAN) ultrafilters (UF), and a polyamide reverse osmosis (RO) filter, has been utilized to decrease harmful and damaging components in wastewater produced from Tehran Refinery with aim to be reused at boilers and cooling towers. Taguchi method was employed to find optimum operating conditions including transmembrane pressure, cross flow velocity (CFV), temperature, and backwash time. Further, analysis of variance (ANOVA) was performed to determine the significance of controlling factors on total organic carbon rejection and normalized permeate flux. MF (ceramic)/UF (PVC) system reduced, %: oil 99.7; chemical oxygen demand (COD) 82; biochemical oxygen demand (BOD) 79.3; conductivity 60.5; total dissolved solids (TDS) 52.6; turbidity 99.7 and total hardness 73.2. MF(ceramic)/UF (PAN) system reduced: oil, COD, BOD, conductivity, TDS, turbidity, and total hardness by 99.8; 84.2; 80.8; 62.72; 55; 99.9 and 78.4%, respectively. UF (PAN)/RO system decreased, %: oil 99.5; COD 99; BOD 99; conductivity 98; TDS 98; turbidity 98.7 and total hardness 99.94. Obtained treated wastewater by this system can be reused as feed water of boilers.     

Glycerol removal from biodiesel using membrane separation technology

Membrane separation technology was used to remove free glycerol from biodiesel in order to meet the ASTM D6751 and EN 14214 standards. Fatty acid methyl esters (FAME) produced from canola oil and methanol were purified using ultra-filtration. The effect of different materials present in the transesterification reaction, such as water, soap, and methanol, on the final free glycerol separation was studied. A modified polyacrylonitrile (PAN) membrane, with 100 kD molecular weight cut-off was used in all runs. Tests were performed at 25 °C and 552 kPa operating pressure. The free glycerol content in the feed, retentate and permeate of the membrane system was analyzed using gas chromatography according to ASTM D6584. Results showed low concentrations of water had a considerable effect in removing glycerol from the FAME even at approx. 0.08 mass%. This is four orders of magnitude less than the amount of water required in a conventional biodiesel purification process using water washing. It is suggested that the mechanism of separation of free glycerol from FAME was due to the removal of an ultrafine dispersed glycerol-rich phase present in the untreated FAME. This was confirmed by the presence of particulates in the untreated FAME. The size of the particles and the free glycerol separation both increased with increasing water content of the FAME. The trends of separation and particle size vs. water content in the FAME phase were very similar and exhibited a sudden increase at 0.08 mass% water in the untreated FAME. This supports the conclusion that water increased the size of the distributed glycerol phase in the untreated FAME leading to its separation by the ultra-filtration membrane. The technology for the removal of free glycerol from biodiesel was found to use 2.0 g of water per L of treated FAME (0.225 mass% water) vs. the current 10 L of water per L of treated FAME.     

Integrated electrokinetic-soil flushing to remove mixed organic and metal contaminants

The integrated use of hydraulic flushing and electrokinetic treatment was investigated for the remediation of silty sand contaminated by both PAHs and heavy metals. The soil was collected from a polluted former manufactured gas plant (MGP). Four bench-scale experiments were conducted to analyze the ability of the combined hydraulic flushing and the electrokinetic treatment for the simultaneous removal of PAHs and heavy metals. Sequential flushing with ethylenediaminetetraacetic acid (EDTA) or Igepal CA-720 were tested with or without the simultaneous application of a low intensity direct electric field (1 VDC cm⁻¹). The best results were obtained with 0.2 M EDTA flushing in two stages (without and with voltage gradient, 1 VDC cm⁻¹), followed by 5% Igepal flushing in two stages (without and with 1 VDC cm⁻¹). Heavy metals were removed mainly during the EDTA flushing, with removal efficiencies of about 60% for Zn, 80% for Pb, and 30% for Cu. During Igepal flushing, no heavy metals were removed, but PAHs were removed, including 40% phenanthrene, 30% pyrene, and 20% benzo[a]pyrene. Overall, this study showed that a carefully designed sequential hydraulic flushing scheme with selected chelant and surfactant is needed for the removal of both heavy metals and PAHs from MGP silty sands. Combining electrokinetics with hydraulic flushing may not necessarily improve contaminant removal from such soils.     

An Environmentally Benign,Highly Efficient Catalytic Reduction of p‐Nitrophenol using a Nano‐Sized Nickel Catalyst Supported on Silica‐Alumina

A green and effective method is reported for the reduction of p‐nitrophenol to p‐aminophenol using a nano‐sized nickel catalyst supported on silica‐alumina in the presence of hydrazine hydrate as an alternative source of hydrogen. It was found that nickel loaded on a silica‐alumina support is a very effective catalyst in the hydrogenation of p‐nitrophenol to p‐aminophenol. Thus it attained 100% conversion in only 69 seconds instead of 260 seconds for commercial Raney nickel. In addition, the possibility to reuse it more than one time with great efficiency gives it another advantage over commercial Rainey nickel which cannot be used more than once. This economical and environmentally friendly method provides a potentially new approach for the synthesis of the intermediate product of paracetamol in industry, which overcomes the drawbacks of the known reduction methods. The prepared catalysts were fully characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X‐ray (EDX), and electron spin resonance (ESR) tehniques.     

Planning for a Large Dam Project: The Case of Traveston Crossing Dam

The approval for a large dam project proposal these days predominantly involves satisfying broadly the criteria of economic development, social equity, and environmental sustainability. It is justified that the criterion of economic development seeks full project cost recovery as well as significant contribution to economic growth of a region. Cost–benefit analysis is normally used as the yardstick for economic development but it has limitations and a better method is warranted. Social equity considerations should embody the need to address the concerns of all sections in communities to be impacted by a project and involve them in the decision-making process. The lapse of this aspect in project planning of the past has led, at least as being partly responsible, to disastrous consequences. Environmental sustainability should seek to ensure that the vital components of the environment are preserved such that the future generation can use the natural resources to their benefit at least as much as the current generation. Environmental sustainability is arguably the most contentious criteria among these. The vagueness in the concept of environmental sustainability and the tendency of the society to err on the safe side have caused many large dam project proposals not reach their fruition. An attempt is made in this paper to define environmental sustainability in a more meaningful way from an analytic viewpoint. The case of Traveston Crossing Dam project in southeast Queensland, Australia is presented as an illustrative example and to evaluate the performance and relevance of the three broad criteria in a real-world application. The case study is also an example of the fact that environmental awareness can lead to enormous level of socio-political forces which can create many hurdles to cross by a democratic government.     

New Type Anode for Calcium Ion Batteries Based on Silicon Carbide Monolayer

Silicon - A theoretical research study was conducted into the possibility of using a two-dimensional graphene-like material silicon carbide nano-sheet (2D-SiCNS) as an anode in rechargeable Ca-ion...