Energy–exergy analysis and modernization suggestions for a combined‐cycle power plant

Energy and exergy analysis were carried out for a combined‐cycle power plant by using the data taken from its units in operation to analyse a complex energy system more thoroughly and to identify the potential for improving efficiency of the system. In this context, energy and exergy fluxes at the inlet and the exit of the devices in one of the power plant main units as well as the energy and exergy losses were determined. The results show that combustion chambers, gas turbines and heat recovery steam generators (HRSG) are the main sources of irreversibilities representing more than 85% of the overall exergy losses. Some constructive and thermal suggestions for these devices have been made to improve the efficiency of the system. Copyright © 2005 John Wiley & Sons, Ltd.     

Science and technology policy in Turkey. National strategies for innovation and change during the 1983-2003 period and beyond

Summary An evaluation of Turkey's science and technology (S & T) policy in the last two decades has been made by using various indicators of S & T and technological innovation. National trends in inputs for research and development (R & D) activities, publication output and patent data have been studied for the implications of the S & T policy from 1983 to 2003. Some of the findings on the outcomes of policy measures in terms of inputs to R & D and publication output are as follows: (1) Total R & D expenditure, as percent of gross domestic product (GDP), increased from 0.32% in 1990 to 0.67% in 2002, (2) the fraction of R & D in the total expenditure for technological innovation increased from 6.6% in 1995-1997 to 29.2% in 1998-2000, and (3) the number of papers in the journals covered in the Science Citation Index (SCI) of the Institute for Scientific Information (ISI) increased from 464 in 1983 to 12160 in 2003 - a more than 26-fold increase in the last two decades.     

Reductive ethylation in ethereal solvents

Organic compounds, in particular anthracene and naphthalene, and two coals have been reductively ethylated in tetrahydrofuran (THF) and diglyme using alkali metals to form anions and ethyl iodide to produce ethylates. Product distributions were sensitive to experimental conditions. The rate of anion formation was controlled by their rate of desorption, probably as contact ion pairs, from the alkali metal surface. The enthalpy of formation of a solvated contact ion pair was ≈500 kJ mole^?1 mainly due to dipole-solvent interaction. 18-crown-6 ether was used to diagnose that, when treated with potassium in THF, anthracepe gave solvated contact ion pairs and probably di-anions whose reactions were characterized by the formation of ethyldihydroanthracene. Naphthalene under identical conditions gave loosely solvated mono-anions which reacted by electron transfer to give diethyldihydronaphthalene. With other alkali metals anthracene and naphthalene gave similar product distributions. The behaviour of other polynuclear aromatic hydrocarbons and of two coals was classified in the same way. It is suggested that when coals are readily solubilized by reductive alkylation mono-alkyldihydro products will predominate.     

An ATM queue manager handling multiple delay and loss priorities

The asynchronous transfer mode (ATM) technique has been widely accepted as a flexible and effective scheme to transport various traffic over the future broadband network. To fully utilize network resources while still providing satisfactory quality of service (QOS) to all network users, prioritizing the user's traffic according to their service requirements becomes necessary. During call setup or service provisioning, each service can be assigned a service class determined by a delay priority and a loss priority. A queue manager in ATM network nodes will schedule ATM cells departing and discarding sequence based on their delay and loss priorities. Most queue management schemes proposed so far only consider either one of these two priority types. The queue manager handles multiple delay and loss priorities simultaneously. Moreover, a cell discarding strategy, called push-out, that allows the buffer to be completely shared by all service classes, has been adopted in the queue manager. We propose a practical architecture to implement the queue manager by using available VLSI sequencer chips     

Solubility of chlorine in aqueous hydrochloric acid solutions

The solubility of chlorine in aqueous hydrochloric acid solutions was studied. The effects of HCl concentration and temperature on the solubility were evaluated, and the thermodynamic parameters of the dissolution were calculated. It was found that the solubility isotherms had a minimum at about 0.5M HCl concentration at all the temperatures studied and that solubility decreased with the increase of temperature at all the HCl concentration range investigated.     

Degradation of 17beta-estradiol and bisphenol A in aqueous medium by using ozone and ozone/UV techniques

Decomposition and complete degradation of two endocrine disrupters, namely 17beta-estradiol (E2) and bisphenol A (BPA) in aqueous medium by using ozone (O3) only and O3/UV advanced oxidation techniques (AOT) has been studied. The efficiency of the O3 systems used were determined based on the initial conversion and complete degradation of the substrates. Within the limits of the O3 dosages used, coupling of UV decreased the O3 consumption by 22.5% in converting the same amount of E2. Also the time to convert the same amount of E2 was considerably decreased. It was observed that there is no significant difference in O3 amount consumed for complete conversion of BPA by O3 and O3/UV systems. However, when O3 dosage decreased the amount of BPA conversion exhibits significant differences between two processes. The intermediate products formed during the oxidation of E2 were determined to be formed by oxidation of aromatic side of E2 with O3/*OH radical.     

Residual and recurrent shunts after implantation of Cook detachable duct occlusion coils

Cough and chest wall pain at high altitude have only received passing mention in the medical literature. Increased minute ventilation of cold dry air at very high altitude is likely to cause airway irritation. This in turn may result in airway drying, mucus production, postnasal drip from vasomotor rhinitis, and bronchospasm acting individually or in combination to stimulate the vagal cough reflex. The cough is exacerbated further at extreme altitudes above 5500 m, and may result in intercostal muscle strain and single or multiple rib fractures. We present a case of multiple cough induced stress fractures and arthropathy documented by technetium-99 bone scan in a high altitude climber and suggest the addition of the term High Altitude Cough Syndrome (HACS) to the medical syntax to identify this discrete medical problem of exposure to very high altitude.     

Muscarinic receptors in rat cortex, hippocampus, hypothalamus and brainstem following transient forebrain ischemia and hemorrhagic shock

[3H]Quinuclidinyl benzilate binding properties of cerebral cortex, hippocampus, hypothalamus and brainstem of rats subjected to transient forebrain ischemia or severe hemorrhagic shock were investigated. Maximal binding capacities (Bmax) were not significantly different from control animals in either model. On the other hand, significant increases in binding affinities at all four brain regions in the ischemia-reperfusion group and at hypothalamic and brainstem membranes in the hemorrhagic shock group were observed. Kd values obtained in cortex and hippocampus of animals in shock were similar to control values. It was concluded that in brain ischemia models, the number of brain muscarinic receptors do not change at early stages, but binding affinities increase most likely due to systemic hypotension rather than reperfusion. The well-developed circle of Willis seems to protect cortical and hippocampal muscarinic receptors from hypoxia-induced changes.     

Purification and characterisation of a polyphenol oxidase from Boletus erythropus and investigation of its catalytic efficiency in selected organic solvents

Polyphenol oxidase (PPO) was purified from Boletus erythropus using a Sepharose 4B-L-tyrosine-p-amino benzoic acid affinity column. Optimum pH and temperature were found to be 8.0 and 20 °C, respectively, using 4-methylcatechol as a substrate. The enzyme was extremely stable between pH 3.0 and 9.0 after 24 h incubation at 4 °C. B. erythropus PPO was also quite stable between 10 and 30 °C after 4 h incubation. The K_m and V_max values were calculated as 2.8 mM and 1430 U/mg protein by Lineweaver–Burk curve, respectively. The enzyme activity was inhibited by sodium metabisulfite, ascorbic acid, sodium azide and benzoic acid. It was seen that the mushroom PPO was an effective biocatalyst in selected organic solvents, such as dichloromethane, dichloroethane and toluene, when catechin was used as a substrate. All data support that B. erythropus has a highly active PPO, possessing similar biochemical and kinetic characteristics to other plant PPOs.