Single excitons in InGaN quantum dots on GaN pyramid arrays

Fabrication of single InGaN quantum dots (QDs) on top of GaN micropyramids is reported. The formation of single QDs is evidenced by showing single sub-millielectronvolt emission lines in microphotoluminescence (μPL) spectra. Tunable QD emission energy by varying the growth temperature of the InGaN layers is also demonstrated. From μPL, it is evident that the QDs are located in the apexes of the pyramids. The fact that the emission lines of the QDs are linear polarized in a preferred direction implies that the apexes induce unidirected anisotropic fields to the QDs. The single emission lines remain unchanged with increasing the excitation power and/or crystal temperature. An in-plane elongated QD forming a shallow potential with an equal number of trapped electrons and holes is proposed to explain the absence of other exciton complexes.     

Disease transmission in territorial populations: the small-world network of Serengeti lions

Territoriality in animal populations creates spatial structure that is thought to naturally buffer disease invasion. Often, however, territorial populations also include highly mobile, non-residential individuals that potentially serve as disease superspreaders. Using long-term data from the Serengeti Lion Project, we characterize the contact network structure of a territorial wildlife population and address the epidemiological impact of nomadic individuals. As expected, pride contacts are dominated by interactions with neighbouring prides and interspersed by encounters with nomads as they wander throughout the ecosystem. Yet the pride–pride network also includes occasional long-range contacts between prides, making it surprisingly small world and vulnerable to epidemics, even without nomads. While nomads increase both the local and global connectivity of the network, their epidemiological impact is marginal, particularly for diseases with short infectious periods like canine distemper virus. Thus, territoriality in Serengeti lions may be less protective and non-residents less important for disease transmission than previously considered.     

One-step production of superhydrophobic coatings on flat substrates via atmospheric Rf plasma process using non-fluorinated hydrocarbons

This paper describes the direct deposition of hydrocarbon coatings with a static water contact angle higher than 150 using simple C6 hydrocarbons as a reactive gas in helium plasma generated in ambient air without any preroughening of the silicon (100) substrate. The film morphology and hydrophobicity are found to strongly depend on the structure of the reagent hydrocarbon. The films deposited with n-hexane and cyclohexane exhibited relatively smooth morphology and the water contact angle was only ～95°, similar to polypropylene. When benzene was used as a main reactive gas, the deposited film surface showed nanoscale textured morphology and superhydrophobicity with a water contact angle as high as 167°. Because the plasma is generated in air, all films show some degree of oxygen incorporation. These results imply that the incorporation of a small amount of oxygenated species in hydrocarbon films due to excitation of ambient air is not detrimental for superhydrophobicity, which allows the atmospheric rf plasma with the benzene precursor to produce rough surface topography needed for superhydrophobicity.     

Facile fabrication of all-SWNT field-effect transistors

Field-effect transistors (FETs) have been fabricated using as-grown single-walled carbon nanotubes (SWNTs) for the channel as well as both source and drain electrodes. The underlying Si substrate was employed as the back-gate electrode. Fabrication consisted of patterned catalyst deposition by surface modification followed by dip-coating and synthesis of SWNTs by alcohol chemical vapor deposition (CVD). The electrodes and channel were grown simultaneously in one CVD process. The resulting FETs exhibited excellent performance, with an I _ON/I _OFF ratio of 10⁶ and a maximum ON-state current (I _ON) exceeding 13 μA. The large I _ON is attributed to SWNT bundles connecting the SWNT channel with the SWNT electrodes. Bundling creates a large contact area, which results in a small contact resistance despite the presence of Schottky barriers at metallic-semiconducting interfaces. The approach described here demonstrates a significant step toward the realization of metal-free electronics.      

Two improvements to the dynamic wake meandering model: including the effects of atmospheric shear on wake turbulence and incorporating turbulence build‐up in a row of wind turbines

The dynamic wake meandering (DWM) model is an engineering wake model designed to physically model the wake deficit evolution and the unsteady meandering that occurs in wind turbine wakes. The present study aims at improving two features of the model:

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Metal complexation properties of freshwater dissolved organic matter are explained by its aromaticity and by anthropogenic ligands

Dissolved organic matter (DOM) in surface waters affects the fate and environmental effects of trace metals. We measured variability in the Cd, Cu, Ni, and Zn affinity of 23 DOM samples isolated by reverse osmosis from freshwaters in natural, agricultural, and urban areas. Affinities at uniform pH and ionic composition were assayed at low, environmentally relevant free Cd, Cu, Ni, and Zn activities. The C-normalized metal binding of DOM varied 4-fold (Cu) or about 10-fold (Cd, Ni, Zn) among samples. The dissolved organic carbon concentration ranged only 9-fold in the waters, illustrating that DOM quality is an equally important parameter for metal complexation as DOM quantity. The UV-absorbance of DOM explained metal affinity only for waters receiving few urban inputs, indicating that in those waters, aromatic humic substances are the dominant metal chelators. Larger metal affinities were found for DOM from waters with urban inputs. Aminopolycarboxylate ligands (mainly EDTA) were detected at concentrations up to 0.14 μM and partly explained the larger metal affinity. Nickel concentrations in these surface waters are strongly related to EDTA concentrations (R2=0.96) and this is underpinned by speciation calculations. It is concluded that metal complexation in waters with anthropogenic discharges is larger than that estimated with models that only take into account binding on humic substances.     

Effects of fluid–fluid interfacial elasticity on droplet formation in microfluidic devices

Biomolecules adsorb at fluid–fluid interfaces and can form a cohesive interfacial network imparting distinctive local interfacial mechanics. This modification of interfacial behavior is empirically known to significantly affect the stability and flow behavior of foams and emulsions. Droplet formation in the presence of interfacial networks is investigated in a flow‐focusing microfluidic device using designed peptide surfactants, which allow decoupled control of interfacial rheology and interfacial tension. The influence of interfacial elasticity on droplet breakup, satellite droplet formation and droplet size are reported. The presence of high interfacial elasticity strongly affects the mechanism of droplet breakup by delaying neck thinning and altering interfacial shape at the point of droplet detachment, resulting in the suppression of satellite droplet formation and a decrease in droplet size. We report a correlation between dimensionless droplet size and a new dimensionless grouping which combines flow‐rate ratio with the ratio of interfacial tension and interfacial elasticity. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Purification,Stereoisomeric Analysis and Quantification of Sex Pheromone Precursors in Female Whole Body Extracts from Pine Sawfly Species

A GC-MS method to analyze the stereoisomeric composition of chiral secondary alcohols found in whole body extracts of pine sawfly females was developed. The tested alcohols were derivatized with optically pure (S)-2-acetoxypropionyl chloride prior to GC-MS analysis. Baseline separation was obtained for all sixteen stereoisomers of 3,7,9-trimethyltridecan-2-ol and for the four 3-methylpentadecan-2-ol stereoisomers. For 3,7-dimethyltridecan-2-ol, 3,7-dimethyltetradecan-2-ol and 3,7-dimethylpentadecan-2-ol baseline separation was obtained for 6 of the possible 8 stereoisomers. When a mixture of 16 stereoisomers of 3,7,11-trimethyltridecan-2-ol was tested, baseline separation of 7 peaks out of 16 possible was obtained. The investigated alcohols are pheromone precursors for some pine sawfly species that are severe defoliators of pine. Females from several Diprion, Neodiprion, Macrodiprion, Microdiprion, and Gilpinia species emit esters of such secondary alcohols as sex pheromones that attract males for mating. To quantify the small amounts of the precursor alcohol and its stereoisomeric composition found in whole body extracts from female pine sawflies, a purification method was optimized. An extract of 20 females of D. pini contained about 8 ng of (2S,3R,7R)-3,7-dimethyltridecan-2-ol per female, and three extracts of 18, 20, and 90 females of N. sertifer contained between 5 and 13 ng of (2S,3S,7S)-3,7-dimethylpentadecan-2-ol per female.