Synthesis and characterization of hydroxyl terminated poly(butadiene)-g-poly(glycidyl azide) copolymer as a new energetic propellant binder

Summary Poly(glycidyl azide), PGA, was grafted onto Hydroxyl Terminated Poly(butadiene), HTPB, via free radical mechanism. PGA-macro azoinitator and HTPB polymer mixture was casted from solution and the polymer film was kept at 90°C for 4 hours. The grafted polymer was isolated from the product by fractional precipitation and characterized by NMR and FT-IR spectroscopy. Graft copolymer structure was also confirmed that volume ratio of nonsolvent to the solution of the graft copolymer was between those of corresponding homopolymers. TGA traces of the block polymers were containing two different maxima at 253°C (for PGA units) and 469°C (for HTPB units). Because of the incompatibility of the blocks, DSC curve showed two T_g's which belong to the related segments.     

Electrochemical performance and modeling of lithium‐sulfur batteries with varying carbon to sulfur ratios

Lithium‐sulfur batteries have attracted much research interest because of their high theoretical energy density and low‐cost raw materials. While the electrodes are composed of readily available materials, the processes that occur within the cell are complex, and the electrochemical performance of these batteries is very sensitive to a number of cell processing parameters. Herein, a simple electrochemical model will be used to predict, with quantitative agreement, the electrochemical properties of lithium‐sulfur cathodes with varying carbon to sulfur ratios. The discharge capacity and the polarization were very similar for the lowest sulfur loadings, while above 23.2 wt% sulfur the gravimetric capacity dropped significantly, and there was an increase in the cell polarization. In addition, a transition in the electrode morphology, from well dispersed to aggregated sulfur at the surface, will be reflected in the change in a critical model parameter demonstrating the sensitivity and functionality of even this simple model in predicting complex behavior in the lithium‐sulfur cells.     

The interplay between leadership and organizational culture in the Turkish construction sector

Organizational culture and leadership are purported to be deeply integrated and intertwined within an organization. Although there is a substantial amount of research demonstrating the importance of the interplay of culture and leadership, there exist few empirical examinations of the nature of this link. To examine this link, based on Cameron and Quinn's Organizational Culture Assessment Instrument and Hofstede's Values Survey Module, a questionnaire survey was conducted. The sample consists of 499 managerial personnel out of 107 contracting firms. With the aim of achieving a better understanding of how leadership style is influenced by organizational culture, Multinomial Logistic Regression was used. The findings demonstrate that managers in the contracting companies with different cultural characteristics tend to adopt different leadership styles to lead their employees to succeed in their business. Information contained in this paper will feed into country-specific understanding of leadership and organizational culture within the construction industry.     

Changes in the texture,physicochemical properties and volatile compound profiles of fresh Kashar cheese (<90 days) during ripening

In this study, four different fresh Kashar cheese samples were ripened for 90 days. The physicochemical properties, texture attributes, fatty acid composition and volatile compound profiles of the samples were measured every 30 days of ripening. The texture properties of the cheese samples were significantly affected by the duration of the ripening period. The results of this study highlighted that texture parameters as a function of ripening period should be considered for both fresh and aged Kashar cheeses to determine the ripening period as they are very important for consumer acceptability and consumption of the end product.     

Free radical crosslinking of unsaturated bacterial polyesters obtained from soybean oily acids

Summary Poly(-3-hydroxy alkanoate) containing unsaturated side chains, PHA-soybean, were produced by feeding Pseudomonas oleovorans with soybean oily acids obtained from soybean oil. Unsaturation of PHA-soybean were found to be 10 mol-% of unsaturated side chains. Main saturated part of the biopolymer was Poly(3-hydroxy octanoate) with minor hexanoate and decanoate units. PHA films were crosslinked via free radical mechanism by means of thermally or under UV irradiation in the presence of benzoyl peroxide, benzophenon, and /or ethylene glycol dimethacrylate (EGDM). Crosslinking yield of the PHA films were found to be from 81 to 93 wt.-% from the sol-gel analysis. Swelling properties of the crosslinked PHA films in chloroform and toluene were also studied. Mc values of crosslinked PHAs were also calculated using Flory-Rehner equation. The crosslinked biopolyester obtained by thermally at 60 °C with benzoyl peroxide indicated the highest crosslinking density. Glass transition temperatures (Tg) of crosslinked biopolyester samples were changed from −33 to −45 °C while that of PHA-soybean was −60 °C. Received: 16 June 2000/Revised version: 22 January 2001/Accepted: 20 May 2001     

Effective factors improving catalyst layers of PEM fuel cell

Cathode catalyst layer has an important role on water management across the membrane electrode assembly (MEA). Effect of Pt percentage in commercial catalyst and Pt loading from the viewpoint of activity and water management on performance was investigated. Physical and electrochemical characteristics of conventional and hydrophobic catalyst layers were compared. Performance results revealed that power density of conventional catalyst layers (CLs) increased from 0.28 to 0.64 W/cm² at 0.45 V with the increase in Pt amount in commercial catalyst from 20% to 70% Pt/C for H₂/Air feed. In the case of H₂/O₂ feed, power density of CLs increased from 0.64 to 1.29 W/cm² at 0.45 V for conventional catalyst layers prepared with Tanaka. Increasing Pt load from 0.4 to 1.2 mg/cm², improved kinetic activity at low current density region in both feeding conditions. Scattering electron microscopy (SEM) images revealed that thickness of the catalyst layers (CLs) increases by increasing Pt load. Electrochemical impedance spectroscopy (EIS) results revealed that thinner CLs have lower charge transfer resistance than thicker CLs. Inclusion of 30 wt % Polytetrafluoroethylene (PTFE) nanoparticles in catalyst ink enhanced cell performance for the electrodes manufactured with 20% Pt/C at higher current densities. However, in the case of 70% Pt/C, performance enhancement was not observed. Cyclic voltammetry (CV) results revealed that 20% Pt/C had higher (77 m²/g) electrochemical surface area (ESA) than 70% Pt/C (65 m²/g). In terms of hydrophobic powders, ESA of 30PTFE prepared with 70% Pt/C was higher than 30PTFE prepared with 20 %Pt/C. X-Ray Diffractometer (XRD) results showed that diameter of Pt particles of 20% Pt/C was 2.5 nm, whereas, it was 3.5 nm for 70% Pt/C, which confirms CV results. Nitrogen physisorption results revealed that primary pores of hydrophobic catalyst powder prepared with 70% Pt/C was almost filled (99%) with Nafion and PTFE.     

Nitrogen Transformations during Soil–Aquifer Treatment of Wastewater Effluent—Oxygen Effects in Field Studies

Depth-dependent oxygen concentrations and aqueous-phase total ammonia and nitrate/nitrite ion concentrations were measured in the field during the infiltration of wastewater effluent. Measurements illustrated the dependence of nitrogen fate and transport on oxygen availability. Infiltration basins were operated by alternating wet (infiltration) and dry periods. During infiltration periods, ammonia was removed within the top few feet of sediments via adsorption. Biochemical activity rapidly eliminated residual molecular oxygen in the infiltrate, making the soil profile anoxic. During dry periods, oxygen reentered the basin profile and sorbed ammonia was converted to nitrate via nitrification. Oxygen penetrated to a depth of about 0.6?m?(2?ft) within the first few days of dry periods. At greater depths, oxygen levels increased more slowly due to a combination of slow transport kinetics and biochemical (nitrogenous) oxygen demand. During normal wet/dry basin cycles consisting of about 4 wet and 4 dry days, the local vadose zone remained anoxic at depths greater than about 1.5?m?(5?ft) below land surface. As a consequence, conditions for denitrification were satisfied in the deeper sediments. That is, the nitrate nitrogen produced in near surface sediments moved freely downward with infiltrating water where it encountered an extensive anoxic zone before reaching local monitoring or extraction wells. The relative importance of dissolved organics and sorbed ammonia as electron donors for denitrification reactions remains to be established.