Bilayer self-assembly on a hydrophilic, deterministically nanopatterned surface

We present measurements of the in situ, microscopic architecture of a self- assembled bilayer at the interface between a regularly nanopatterned surface and an aqueous sub-phase using neutron reflectometry. The substrate is patterned with a rectangular array of nanoscale holes. Because of the high quality of the pattern, using neutron reflectometry, we are able to map the surface-normal density distribution of the patterned silicon, the penetration of water into the pattern, and the distribution of a deposited film inside and outside of the etched holes. In this stud; 1,2-dilauroyl-sn-glycero-3-phosphocholine （DLPC） single bilayers were deposited on the hydrophilic patterned surface. For bilayers deposited either by vesicle fusion （VF） or by the Langmuir-Schaefer （L-S） technique, the most consistent model found to fit the data shows that the lipids form bilayer coatings on top of the substrate as well as the bottoms of the holes in an essentially conformal fashion. However, while there is a single bilayer on the unetched silicon surface, the lipids coating the bottoms of the holes form a complex bimodal structure consistent with a rough surface produced by the etching process. This study provides insight into film transfer both outside and inside regular nanopatterned features.     

Design of a novel flat-plate photobioreactor system for green algal hydrogen production

Some green microalgae have the ability to harness sunlight to photosynthetically produce molecular hydrogen from water. This renewable, carbon-neutral process has the additional benefit of sequestering carbon dioxide and accumulating biomass during the algal growth phase. We document the details of a novel one-litre vertical flat-plate photobioreactor that has been designed to facilitate green algal hydrogen production at the laboratory scale. Coherent, non-heating illumination is provided by a panel of cool-white light-emitting diodes. The reactor body consists of two compartments constructed from transparent polymethyl methacrylate sheets. The primary compartment holds the algal culture, which is agitated by means of a recirculating gas-lift. The secondary compartment is used to control the temperature of the system and the wavelength of radiation. The reactor is fitted with probe sensors that monitor the pH, dissolved oxygen, temperature and optical thickness of the algal culture. A membrane-inlet mass spectrometry system has been developed and incorporated into the reactor for dissolved hydrogen measurement and collection. The reactor is hydrogen-tight, modular and fully autoclaveable.     

Prevalence of tobacco use in Eritrea: results from a noncommunicable disease risk factor survey.

The prevalence of noncommunicable diseases in Eritrea is increasing. Tobacco use is a recognized risk factor for most of these diseases, especially cardiovascular disease. No data have been published on tobacco use in Eritrea. The present study sought to establish the prevalence of tobacco smoking in Eritrea. The World Health Organization STEPwise approach was used for the survey, conducted in 2004 on a random national sample size of 2,460 subjects (response rate = 93.7%). The prevalence of tobacco smoking in the general population was 8.1%; the prevalence was 15% among men, compared with 0.6% among women. Prevalence rates were higher in those older than 45 years of age. The prevalence of tobacco smoking was higher among Muslims (11.4%) than Orthodox Christians (5.8%), and among alcohol drinkers (10.2%) than nondrinkers (6.6%). The majority of tobacco users (89.3%) used commercially available cigarettes. A study on knowledge, attitudes, and practices regarding tobacco use is needed to determine the behavioral factors leading to tobacco smoking among the vulnerable groups.     

Propene Epoxidation over K-Promoted Ag/CaCO3 Catalysts: The Effect of Metal Particle Size

With increasing loading of potassium promoter, Ag/CaCO₃ catalysts exhibit a clear maximum in selectivity towards propene epoxide formation. This behavior correlates with changes in silver particle size distribution as revealed by HREM and XPS. Maximum selectivity and activity are achieved when the catalyst contains a large proportion of Ag particles whose size lies in the intermediate range 20-40 nm. Ag particles that are either much smaller or much larger than this are less selective towards epoxidation. The mechanistic implications of these findings are discussed and comparison is made with the corresponding properties of Ag/-alumina catalysts normally used for ethene epoxidation.     

A novel nutrient control method to deprive green algae of sulphur and initiate spontaneous hydrogen production

The green alga Chlamydomonas reinhardtii has the ability to produce clean and renewable molecular hydrogen through the biophotolysis of water. Hydrogen production takes place under anaerobic conditions, which may be imposed metabolically by depriving the algae of sulphur. Sulphur-deprivation typically requires the spatial and temporal separation of the algal growth and hydrogen production stages. This would typically require separate photobioreactors for each stage as well as a costly and energy intensive medium exchange technique such as centrifugation, making the process difficult to scale up.     

Understanding the role of agricultural practices in the potential colonization and contamination by Escherichia coli in the rhizospheres of fresh produce

To better protect consumers from exposure to produce contaminated with Escherichia coli, the potential transfer of E. coli from manure or irrigation water to plants must be better understood. We used E. coli strains expressing bioluminescence (E. coli O157:H7 lux) or multiantibiotic resistance (E. coli2(+)) in this study. These marked strains enabled us to visualize in situ rhizosphere colonization and metabolic activity and to track the occurrence and survival of E. coli in soil, rhizosphere, and phyllosphere. When radish and lettuce seeds were treated with E. coli O157:H7 lux and grown in an agar-based growth system, rapid bacterial colonization of the germinating seedlings and high levels of microbial activity were seen. Introduction of E. coli2(+) to soil via manure or via manure in irrigation water showed that E. coli could establish itself in the lettuce rhizosphere. Regardless of introduction method, 15 days subsequent to its establishment in the rhizosphere, E. coli2(+) was detected on the phyllosphere of lettuce at an average number of 2.5 log CFU/g. When E. coli2(+) was introduced 17 and 32 days postseeding to untreated soil (rather than the plant surface) via irrigation, it was detected at low levels (1.4 log CFU/g) on the lettuce phyllosphere 10 days later. While E. coli2(+) persisted in the bulk and rhizosphere soil throughout the study period (day 41), it was not detected on the external portions of the phyllosphere after 27 days. Overall, we find that E. coli is mobile in the plant system and responds to the rhizosphere like other bacteria.     

Parameters affecting the growth and hydrogen production of the green alga Chlamydomonas reinhardtii

The green alga Chlamydomonas reinhardtii has the ability to photosynthetically produce molecular hydrogen (H₂) under anaerobic conditions. It offers a biological route to renewable H₂ production from sunlight and water. Algal growth and H₂ production kinetics must be understood in order to determine appropriate system parameters and develop photobioreactors. Algal biomass should be grown efficiently and economically to attain the high cell densities necessary for H₂ production. The nutrient requirements and process conditions that encourage the growth of dense and healthy algal cultures were explored. Anaerobic conditions were imposed by sulphur deprivation, which requires an exchange of the algal growth medium by centrifugation or dilution. A tubular flow photobioreactor featuring a large surface-to-volume ratio was used to monitor and control the key parameters in the H₂ production process, including pH, dissolved oxygen, optical density, temperature, agitation and light intensity. A cumulative H₂ yield of 3.1 ± 0.3 ml/l of culture was measured.     

Assessment of fog-water collection on the eastern escarpment of Eritrea

Fog can be considered a potential water resource for certain semi-arid and arid countries. In Eritrea, a fog-water collection project was implemented in 2007 in the villages of Arborobue and Nefasit. This study presents an assessment of the project after five years of implementation and identifies the main strengths to be technical viability, since it is simple and manageable by communities, and reasonable in areas where conventional water delivery systems are not feasible. The main limitations are that it is not economically viable unless its initial cost is subsidized; moreover, fog capture is seasonal, and net damage occurs during strong winds.