Efficiency analysis of Turkish natural gas distribution companies by using data envelopment analysis method

This paper analyzes the performance of 38 Turkish natural gas distribution companies by using a non-parametric method, Data Envelopment Analysis (DEA). The results are used to determine the most proper model specification, to detect the important criteria affecting the efficiency levels, and to find the common characteristics of the most inefficient firms. We find that public firms compared to private firms, non-tender firms compared to tender firms, large firms compared to small firms and firms operating in more developed areas compared to firms operating in underdeveloped areas that utilize resources and manage costs more efficiently. However, we cannot reach a certain conclusion about the comparison of old firms versus the new firms. Lastly, we try to detect the common characteristics of the most inefficient firms and find that most of these firms are immature and low scale companies. Therefore, we think these firms can increase efficiency level either by increasing their delivery amounts through higher penetration rates or by merging or doing both together.     

Protective effect of Funalia trogii crude extract on deltamethrin-induced oxidative stress in rats

In this study the protective effects of cold buffer extract of Funalia trogii ATCC 200800 (FtE) and vitamin E (VitE) on oxidative stress induced with deltamethrin using oral administration in rats were investigated. Deltamethrin treatment caused an increase in liver enzyme activities of aspartate transaminase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP) (p < 0.05); however, it caused a decrease in activities of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GRd) when compared to control group (p < 0.05). Activities of AST, ALT, ALP enzymes and level of thiobarbituric acid reactive substances (TBARS) decreased significantly after VitE administration (p < 0.05). Both enzyme activities and TBARS levels were found similar in VitE and FtE treated rats shortly after pesticide administration (p < 0.05). In conclusion, it appears that FtE prepared in cold buffer has capability to prevent the liver damage like VitE against the toxic effect of deltamethrin.     

Covalent immobilization of α‐amylase onto thermally crosslinked electrospun PVA/PAA nanofibrous hybrid membranes

Poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) nanofibers with the fiber diameter of 100–150 nanometers were fabricated by electrospinning. PVA/PAA nanofibers were crosslinked by heat‐induced esterification and resulting nanofiber mats insoluble in water. α‐Amylase was covalently immobilized onto the PVA/PAA nanofiber surfaces via the activation of amine groups in the presence of 1,1′‐carbonyldiimidazole. The immobilized α‐amylase has more resistance to temperature inactivation than that of the free form and showed maximum activity at 50°C. pH‐dependent activities of the free and immobilized enzymes were also investigated, and it was found that the pH of maximum activity for the free enzyme was 6.5, while for the optimal pH of the immobilized enzyme was 6.0. Reuse studies demonstrated that the immobilized enzyme could reuse 15 times while retaining 81.7% of its activity. Free enzyme lost its activity completely within 15 days. Immobilized enzyme lost only 17.1% of its activity in 30 days. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Polymerization of N-vinylcarbazole initiated by UV-radiation

The solid-state polymerization of N-vinylcarbazole initiated by UV-radiation at 25, 32.5, and 45°C was studied. The rate of polymerization increased with increase in temperature. The limiting conversion at all temperatures is 56%. The molecular weight, determined by viscosity measurements, first increased, reached a maximum, then decreased. The molecular weight distribution, studied by GPC, was broad with a shoulder on the low molecular weight side. The morphology of partially polymerized single crystals was studied by electron scanning microscopy to determine the propagation mode of polymerization with respect to the monomer structure. The high activation energy of 71-9kJ/mol and ESR spectrum suggest a radical mechanism of polymerization.     

铜添加对近共晶Al-Si-xCu合金的微观组织和硬度的影响

研究铜含量对Al-Si-xCu（x=2%,3%,4%and5%）合金的微观组织和硬度的影响。不同铜含量的铝合金经熔炼后于690°C铸造成湿砂模并固化,于500°C保温7h进行固溶处理后对样品进行水冷。随后于190°C进行时效处理,分别保温5,10和15h,研究时效时间对基体硬度的影响。采用差热分析法,在冷却速度30K/min下确定平衡相的转变温度,并研究铜含量对四元共晶合金的形成和α（Al）＋Si熔点的影响。结果表明,随着铜含量的增加,发生析出硬化从而导致基体硬度增加,α（Al）＋Si的熔点降低,共晶相的含量增加。当铜含量超过2%时,生成熔点为507°C的四元共晶相。     

Partial characterization of lettuce (Lactuca sativa L.) polyphenol oxidase

Polyphenol oxidase (PPO) from garden lettuce (Lactuca sativa L.) was partially purified by ammonium sulphate ((NH₄)₂SO₄) precipitation and dialysis, and then some of its kinetic properties such as optimum pH and temperature, substrate specificity, thermal inactivation and inhibition were investigated. The total phenolic and protein contents of Lactuca sativa L. extracts were determined according to the Folin-Ciocalteu and Bradford methods, and found to be 304 mg/100 g on a fresh weight basis and 494 μg/mL, respectively. PPO activity was determined using 4-methylcatechol, catechol and pyrogallol as substrates. Kinetic parameters, K _m and V _max, were calculated from Lineweaver–Burk plots. According to V _max/K _m ratio, pyrogallol was the most suitable substrate, followed by catechol and 4-methylcatechol. The optimum temperature and pH values were 30, 40 and 30 °C; and 6.5, 8.0 and 7.5 for 4-methylcatechol, catechol and pyrogallol substrates, respectively. The thermal inactivation of PPO was investigated at 35, 55 and 75 °C. The enzyme activity decreased with increasing temperature. The effect of different inhibitors on partially purified Lactuca sativa L. PPO was spectrophotometrically investigated. For this purpose, tropolone, glutathione, ascorbic acid and 4-aminobenzoic acid were used to inhibit the activity of Lactuca sativa L. PPO at different concentrations. From the experimental results, it was found that glutathione was found to be the most potent inhibitor for Lactuca sativa L. PPO.     

DNA adsorption on a poly‐L‐lysine‐immobilized poly(2‐hydroxyethyl methacrylate) membrane

The DNA adsorption properties of poly‐L ‐lysine‐immobilized poly(2‐hydroxyethyl methacrylate) (pHEMA) membrane were investigated. The pHEMA membrane was prepared by UV‐initiated photopolymerization and activated with epichlorohydrin. Poly‐L ‐lysine was then immobilized on the activated pHEMA membrane by covalent bonding, via a direct chemical reaction between the amino group of poly‐L ‐lysine and the epoxy group of pHEMA. The poly‐L ‐lysine content of the membrane was determined as 1537 mg m^?2. The poly‐L ‐lysine‐immobilized membrane was utilized as an adsorbent in DNA adsorption experiments. The maximum adsorption of DNA on the poly‐L ‐lysine‐immobilized pHEMA membrane was observed at 4 °C from phosphate‐buffered salt solution (pH 7.4, 0.1 M; NaCl 0.5 M) containing different amounts of DNA. The non‐specific adsorption of DNA on the plain pHEMA membrane was low (about 263 mg m^?2). Higher DNA adsorption values (up to 5849 mg m^?2) were obtained in which the poly‐L ‐lysine‐immobilized pHEMA membrane was used. Copyright © 2003 Society of Chemical Industry     

Isolation of volatile oil from thyme (Thymbra spicata) by steam distillation

The effects of steam flow rate (1.03 and 0.64 L/h), distillation time, and particle size (0.50, 1.00, 2.05 mm) of Thymbra spicata on essential oil yield and sequence of extraction of compounds were studied. A logarithmic model fitted well to experimental data. The composition of the essential oil obtained by steam distillation was investigated for whole leaves only since the grinding had an adverse effect on yield. The oil obtained was very rich with respect to its carvacrol content. For both steam flow rates, oxygenated monoterpenes were recovered the most rapidly. Using whole leaves (2.05 mm) and a higher steam flow rate (1.03 L/h) for 75 min of distillation was chosen as the optimum which gives the lowest amount of monoterpene hydrocarbons, the complete recovery of oxygenated compounds, and the highest yield in a shorter time. Yield was 1.57% at this optimum condition. The oil was composed of 53.1% oxygenated compounds, 25.7% monoterpene hydrocarbons, 4.4% sesquiterpenes, and 14.1% p-cymene.     

A NEURAL NETWORK-BASED SYSTEM FOR PREDICTION OF COMPUTER USER COMFORT

This article proposes a neural network-based system for prediction of computer user comfort with respect to the existing settings of the workstation. In this context, anthropometric measures and the existing measures of a computer workstation were related to back-support comfort, distance comfort, keyboard comfort, monitor comfort, and seat comfort using two distinct modeling approaches—multiple linear regression and artificial neural network. The purpose of this article was to compare and contrast the resulting models. The data from 144 computer workstations were used and a total of 12 different data types such as shoulder to elbow, eye to buttock, pan height, monitor height, or distance from the chair were recorded. While multiple linear regression could not be used to adequately predict the computer workstation comfort, the neural network was deemed superior. This approach allows ergonomists to aid in the decision-making process of computer environment design and the prediction of the health risk in an occupational environment.