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.<>     

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.     

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.     

Analysis of cooling curve to determine the end point of freezing

The cooling curve method used for the measurement of freezing point of food is further analyzed to explore whether it can be used to identify the end point of freezing or glass transition. In this method, slope of the cooling curve is determined and plotted as a function of time to identify the end point of freezing (T′_m). Initially, the slope is decreased and then reached a minimum value, which is identified as the nucleation of ice. Then the slope is increased until the end point of freezing. The end point of freezing is identified when the slope starts to decrease from its highest value or plateau. Sucrose solutions and starch gels were used to measure its T′_m in identifying validity of the proposed method. The measured values of T′_m by the proposed method is very close to the literature values.     

An empirical model for predicting the length of a capillary tube

Any refrigerant device consists of several parts, and one of the most significant parts is the expansion device. This expansion device can be classified into several types according to the size of the refrigeration system. The capillary tube is used usually with a small refrigerant system size to reduce the higher pressure in the condenser into the low pressure in the evaporator. In this study, the effect of the capillary tube's diameter and that of the temperature of the condenser and evaporator on the length of such a device has been theoretically studied. Furthermore, a validation between the theoretical analysis and experimental findings from the literature review has been carried out. To achieve the theoretical aspect, MATLAB code has been developed. The results showed that the maximum difference between the theoretical and experimental results regarding temperature and pressure refrigeration is around 5% and 3.4%, respectively. Also, the results depict that the inner diameter and the condenser temperature have an effect on the length of the capillary tube. However, the effect of the inner diameter is higher compared with the condenser temperature. In addition, an equation to predict the length of the capillary tube has been developed with an accuracy of 98%. This equation is created as a function of the capillary tube's diameter and the temperature of the condenser and the evaporator. Moreover, this equation can be used to predict the length of the capillary tube for small refrigeration devices, especially those operating under 10 KW. The findings of this study can help make a mathematical approach used for the design of the capillary tube simpler and easier to apply.     

Histological technique to detect the physiological age of the malaria vector mosquito Anopheles pharoensis (Diptera: Culicidae)

The risk of malaria recurrence increases due to the main vector, Anopheles pharoensis. The physiological age of the mosquito population is needed to expect malaria vector dynamics. The number of completed gonotrophic cycles is of great importance in determining the physiological age of females. A technique has been described that focuses on the number of dilatations remaining in the ovarioles after each oviposition to determine how many blood meals have been taken. At each gonotrophic cycle, the chances of infection of the vectors are repeated. The histological changes that occur immediately in the ovarioles and ovulation itself were studied. Under the influence of the contractions of the ovarian muscles, the eggs begin to move over the distal end of the ovariole into the inner oviduct. The terminal pedicle is markedly dilated near the diameter of the eggs. After the expulsion of the mature eggs, ovariole dilations were found at the point of their development in the terminal pedicle due to the accumulation of nurse cell remnants and follicular epithelium. The results were used to develop epidemiological localization and to evaluate the effectiveness of antimalaria interventions. The ovarian inspection often provides a technique to distinguish nulliparous from parous female anophelines. In addition, this study can provide basic entomological knowledge on the physiological age of mosquitoes by considering the histological changes in the ovaries, which allow the evaluation of vector management strategies in the field.     

Dynamic modeling of gas phase propylene homopolymerization in fluidized bed reactors

A new model with comprehensive kinetics for propylene homopolymerization in fluidized bed reactors was developed to investigate the effect of mixing, operating conditions, kinetic and hydrodynamic parameters on the reactor performance as well as polymer properties. Presence of the particles in the bubbles and the excess gas in the emulsion phase was considered to improve the two-phase model, thus, considering the polymerization reaction to take place in both the bubble and emulsion phases. It was shown that in the practical range of superficial gas velocity and catalyst feed rate, the ratio of produced polymer in the bubble phase to the total production rate is roughly between 10% and 13%, which is a substantial amount and cannot be ignored. Simulation studies were carried out to compare the results of the improved two-phase, conventional well-mixed and constant bubble size models. The improved two-phase and well mixed models predicted a narrower and safer window at the same running conditions compared with the constant bubble size model. The improved two-phase model showed close dynamic behavior to the conventional models at the beginning of polymerization, but starts to diverge with the evolution of time.     

Influence of storage,brine concentration and in‐container heat treatment on the stability of white brined Nabulsi cheese

Microbial levels were significantly (P < 0.05) affected by the temperature‐time treatments used during in‐container heat treatment of the curd, brine concentration and storage duration. A heat treatment of 115 °C × 2 min, in the absence of NaCl, was sufficient to eliminate Mesophilic micro‐organisms, Coliforms, Staphylococcus aureus and Yeast and Moulds for the duration of 1 year of storage. Sensory scores for colour, appearance and texture increased significantly (P < 0.05) with the increase in the NaCl in brine concentration regardless of the temperature‐time treatment.