Enzymatic Synthesis of Glucose- and Xylose Laurate Esters Using Different Acyl Donors,Higher Substrate Concentrations,and Membrane Assisted Solvent Recovery

Glucose- and xylose laurate esters are enzymatically synthesized using equimolar substrate concentrations in 2-methyl-2-butanol, comparing free lauric acid with methyl- and vinyl-laurate as acyl donors. All reactions result in ≥70% acyl donor conversions after 72 h but the activated donors are also partially hydrolyzed to lauric acid, highlighting the difficulty in controlling water presence in this particular reaction system. The esterification of xylose generates a complex product profile, with several regioisomers of monoesters and diesters. The esterification of glucose is quite selective, forming mainly the 6-O monoester (≥96%) with a small presence of two diester isomers (4%). Increasing substrate concentration up to 800 millimoles kg⁻¹ results in lower conversion values (down to 58%) but shows that the reaction proceeds successfully even in the presence of high amounts of insoluble glucose. However, the reaction is less selective and the proportion of diester increases, becoming up to 46% (molar fraction) of the final product. Solvent recovery after esterification can be achieved by organic solvent nanofiltration through a polymeric membrane able to retain ≥80% of all reaction substrates and products. Practical Applications: The use of high substrate concentrations during the enzymatic synthesis of sugar ester biosurfactants leads to product titers that are more industrially appealing, without the need to find a solvent that can solubilize all initial substrate. The sustainability of the enzymatic conversion at mild temperatures can be enhanced by recycling of the reaction solvent through organic solvent nanofiltration, an energy efficient alternative to other traditional methods like distillation.     

The mechanical properties of epoxy resins

Crack propagation in a series of epoxy resins described in Part 1 has been studied as a function of testing rate and temperature. It has been found that crack propagation is continuous at low temperatures but that as the temperature is raised the mode of propagation becomes unstable (stick/slip). Features on the fracture surfaces at the crack arrest lines have been shown to be of the same dimensions as those expected for a Dugdale plastic zone. It has been suggested that the slip process takes place by slow growth of a crack through the plastic zone followed by rapid propagation through virgin material. It has been shown that the stick/slip behaviour is due to blunting of the crack which is controlled by the yield behaviour of the resin. A unique fracture criterion has been shown to be applicable to epoxy resins which is that a critical stress of the order of three times the yield stress must be achieved at a critical distance ahead of the crack. Electron microscope replicas of the fracture surfaces have been obtained and an underlying nodular structure can be resolved. However, no direct correlation between the nodule size and fracture properties has been found.     

Crack propagation in and fractography of epoxy resins

The relationship between the stability of crack propagation in, and the fracture surface appearance of, DGEBA epoxy resins cured with TETA has been investigated using a linear elastic fracture mechanics approach. In particular, the effect of varying the amount of curing agent and curing conditions and altering external variables such as testing rate, temperature and environment have been studied. Under certain conditions, propagation is found to be stable and fracture surfaces have a smooth appearance. Under other conditions the cracks propagate in an unstable stick-slip manner. In this case, arrest lines can be seen on the fracture surfaces and their intensity and roughness increases with the magnitude of the crack jumps. The roughness of the fracture surfaces has been measured using a Talysurf and this has been shown to be due principally to deviation of the cracks from the original fracture plane rather than any gross plastic deformation.     

Modelling useful energy demand system as derived from basic needs in the household sector

Inter-fuel substitution in the household sector depends on whether their target energy use is similar or not. To account for the effect of end-use application on energy demand, the concept of useful energy is utilized in which energy carriers are grouped according to their end-use applications. Useful energy is assumed as a commodity demanded to satisfy needs. Therefore, it should possess certain characteristics in accordance with the nature of basic needs. These characteristics were investigated through a two-level budgeting system with demographic variables indicating rural and urban households of Iran. The model has been applied to estimate the behavioural parameters such as income and price elasticities of useful energy demand. The estimated values of income and own-price elasticity show that all categories of useful energy are necessities with a relatively inelastic demand. Among them, cooling and non-substitutable electricity has the highest income and own-price elasticity, while lighting and water heating are ranked as the most necessary types of useful energy due to their low-income elasticity. In addition, small values of cross price elasticities support the idea that different types of useful energy are almost independent. Therefore, the results confirm that useful energy demands could be considered as basic needs.     

Corrosion and time dependent passivation of Al 5052 in the presence of H<Subscript>2</Subscript>O<Subscript>2</Subscript>

Corrosion and time–dependent oxide film growth on AA5052 Aluminum alloy in 0.25M Na₂SO₄ solution containing H₂O₂ was studied using electrochemical impedance spectroscopy, potentiodynamic polarization, chronoamperometric and open circuit potential monitoring. It was found that sequential addition of H₂O₂ provokes passivation of AA5052 which ultimately thickens the oxide film and brings slower corrosion rates for AA5052. H2O2 facilitates kinetics of oxide film growth on AA 5052 at 25° and 60 °C which is indicative of formation of a thick barrier film that leads to an increment in the charge transfer resistance. Pitting incubation time increases by introduction of H₂O₂ accompanied by lower pitting and smoother surface morphologies. At short exposure (up to 8 h) to H₂O₂–containing solution, the inductive response at low frequencies predominantly determined the corrosion mechanism of AA5052. On the other hand, at prolonged exposure times (more than 24 h) to 0.25M Na₂SO₄+1vol% H₂O₂ solution, thicker oxide layers resulted in the mixed inductive–Warburg elements in the spectra.     

A Comparison between Industry’s and Academia’s Perceptions of a Career in Construction Education

It is well documented that real-world experience is essential in teaching the applied sciences. However, it has also been shown that faculty positions are being filled with candidates with strong research agendas but less industry experience. The aim of this study is to understand what industry’s perception of a career in academia is like and compare it to the perceptions of those actually in the profession. This is viewed as a needed first step in attracting more industry practitioners into construction education. The study surveys practitioners and faculty on how satisfying a career in CM academia is at meeting 16 factors identified as important to overall job satisfaction. The responses of both groups were compared to evaluate where industry’s perceptions did not align with those of faculty. The study also compared the workplace attributes that industry indicated they valued most and what faculty indicated a career in education provided. The study found that a terminal degree, interest in research and publishing, interest in teaching, and salary were the greatest barriers for industry practitioners to enter CM academia. The comparison of work place priority and barriers to entry was used to provide potential strategies to encourage more industry practitioners into CM education.     

Impact of innovation programs on development of energy system: Case of Iranian electricity-supply system

The paper presents further experiments with an extended version of a comprehensive model for assessment of energy technologies and research and development (R&D) planning to evaluate the impact of innovation programs on development of Iranian electricity-supply system. This analytical instrument is a model of energy R&D resource allocation with an explicit perspective of developing countries which has been linked to a bottom-up energy-systems model. Three emerging electricity generation technologies of solar PV, wind turbine and gas fuel cell are considered in the model and the impact of innovation programs on cost-reducing innovation for them is examined. The main results provided by the modeling approach include optimal allocation of R&D resources, induced capacity expansion policies to guarantee the effectiveness of R&D activities, competitive cost of emerging technologies, impact of innovation programs on optimal structure of electricity-supply system and benefits of innovation programs in the long-run.     

Combination of supercritical fluid extraction with dispersive liquid-liquid microextraction for extraction of organophosphorus pesticides from soil and marine sediment samples

Supercritical fluid extraction (SFE) coupled with dispersive liquid-liquid microextraction (DLLME) and followed by gas chromatography-flame ionization detection (GC-FID) was applied for extraction and determination of ultra-trace amounts of seven organophosphorus pesticides (OPPs) (o,o,o-triethyl phosphorothioate, thionazin, sulfotepp, disulfoton, methyl parathion, parathion, and famphur) in soil and marine sediment samples. Supercritical CO₂ at 150 bar, 60 °C, 10 min static and 30 min dynamic extraction times was used to extract the pesticides. The extracts were collected in 1.0 mL of acetonitrile. Seventeen μL of carbon tetrachloride was dissolved in the collecting solvent and the mixture was then injected rapidly into 5.0 mL of aqueous solution. About (5.0 ± 0.2 μL) of sediment phase was collected after centrifuging and finally 2.0 μL of it was injected into gas chromatography (GC) injection port for analyses. The extraction recoveries for the target analytes were in the range of 44.4% and 95.4% and relative standard deviation (RSD%) for four-replicate measurements was below 7.5%. The limit detections of the method for determining the pesticides were in the range of 0.001-0.009 mg kg⁻¹. The method was successfully applied for analysis of OPPs in real soil and marine sediment samples and satisfactory results were obtained.