Photovoltaic measurements in single-nanowire silicon solar cells

Single-nanowire solar cells were created by forming rectifying junctions in electrically contacted vapor-liquid-solid-grown Si nanowires. The nanowires had diameters in the range of 200 nm to 1.5 microm. Dark and light current-voltage measurements were made under simulated Air Mass 1.5 global illumination. Photovoltaic spectral response measurements were also performed. Scanning photocurrent microscopy indicated that the Si nanowire devices had minority carrier diffusion lengths of approximately 2 microm. Assuming bulk-dominated recombination, this value corresponds to a minimum carrier lifetime of approximately 15 ns, or assuming surface-dominated recombination, to a maximum surface recombination velocity of approximately 1350 cm s(-1). The methods described herein comprise a valuable platform for measuring the properties of semiconductor nanowires, and are expected to be instrumental when designing an efficient macroscopic solar cell based on arrays of such nanostructures.     

High-yield production of graphene by liquid-phase exfoliation of graphite

Fully exploiting the properties of graphene will require a method for the mass production of this remarkable material. Two main routes are possible: large-scale growth or large-scale exfoliation. Here, we demonstrate graphene dispersions with concentrations up to approximately 0.01 mg ml(-1), produced by dispersion and exfoliation of graphite in organic solvents such as N-methyl-pyrrolidone. This is possible because the energy required to exfoliate graphene is balanced by the solvent-graphene interaction for solvents whose surface energies match that of graphene. We confirm the presence of individual graphene sheets by Raman spectroscopy, transmission electron microscopy and electron diffraction. Our method results in a monolayer yield of approximately 1 wt%, which could potentially be improved to 7-12 wt% with further processing. The absence of defects or oxides is confirmed by X-ray photoelectron, infrared and Raman spectroscopies. We are able to produce semi-transparent conducting films and conducting composites. Solution processing of graphene opens up a range of potential large-area applications, from device and sensor fabrication to liquid-phase chemistry.     

Killer whales (Orcinus orca) face protracted health risks associated with lifetime exposure to PCBs

Polychlorinated biphenyl (PCB) concentrations declined rapidly in environmental compartments and most biota following implementation of regulations in the 1970s. However, the metabolic recalcitrance of PCBs may delay responses to such declines in large, long-lived species, such as the endangered and highly PCB-contaminated resident killer whales (Orcinus orca) of the Northeastern Pacific Ocean. To investigate the influence of life history on PCB-related health risks, we developed models to estimate PCB concentrations in killer whales during the period from 1930 forward to 2030, both within a lifetime (approximately 50 years) and across generations, and then evaluated these in the context of health effects thresholds established for marine mammals. Modeled PCB concentrations in killer whales responded slowly to changes in loadings to the environment as evidenced by slower accumulation and lower magnitude increases in PCB concentrations relative to prey, and a delayed decline that was particularly evident in adult males. Since PCBs attained peak levels well above the effects threshold (17 mg/kg lipid) in approximately 1969, estimated concentrations in both the northern and the more contaminated southern resident populations have declined gradually. Projections suggest that the northern resident population could largely fall below the threshold concentration by 2030 while the endangered southern residents may not do so until at least 2063. Long-lived aquatic mammals are therefore not protected from PCBs by current dietary residue guidelines.     

One-pot pyrolysis synthesis of highly active Ru/RuOx nanoclusters for water splitting

Using simple methods to obtain efficient catalysts has been a long-standing goal for researchers.In this work,the employment of a one-pot pyrolysis reaction to achieve molecular confinement,has led to the preparation of ruthenium(Ru)-based nanoclusters in a carbon matrix.A unique feature of the synthetic approach employed is that solvent and substrates were calcined together.As solvent evaporates,during calcination,the substrates form a dense solid which has the effect of limiting the aggregation of Ru centers during the carbonization process.The catalyst prepared in this simple manner showed an impressively high activity with respect to the hydrogen/oxygen evolution reaction(HER/OER).The Ru nanoclusters(Ru NCs),as the hydrogen evolution reaction(HER)catalysts,require ultralow overpotentials of 5 mV and 5.1 mV at-10 mA·cm^-2 in 1.0 M KOH,and 0.5 M H₂SO₄,respectively.Furthermore,the catalyst prepared by the one-pot method has higher crystallinity,a higher Ru content and an ultrafine cluster size,which contributes to its exceptional electrochemical performance.Meanwhile,the RuO_x nanoclusters(RuO_x NCs),obtained by oxidizing the aforementioned Ru NCs,exhibited good oxygen evolution reaction(OER)performance with an overpotential of 266 mV at 10 mA·cm^-2.When applied to overall water splitting,Ru/RuO_x nanoclusters as the cathode and anode catalysts can reach 10 mA·cm^-2 at cell voltages of only 1.49 V in 1 M KOH.     

Development of thin‐film composite hollow‐fiber membranes from modified polyphenylene oxide for gas separation applications

The effect of sulfonation and bromination‐sulfonation on the gas transport properties of polyphenylene oxide has been investigated. These high‐performance modified polymers have been studied in the form of TFC membranes by solution coating on the skin side of polyetherimide hollow fibers. TFC membrane modules prepared from sulfonated‐brominated polyphenylene oxide as the active layer coated on polyetherimide hollow fibers. Stability of the TFC membranes was greatly improved when a wet feed stream was used instead of a dry one. Water vapor in the feed stream most likely prevented the active layer from stress cracking on drying. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 275–282, 2001     

Nalidixic acid resistance influences sensitivity to ionizing radiation among Salmonella isolates

Nalidixic acid (Nal) resistance has been used as a selective marker for studies of pathogen-inoculated fruits and vegetables. A collection of 24 Salmonella isolates were screened for natural resistance to Nal (50 microg/ml). The resistance to ionizing radiation was determined and compared for i) three naturally Nal-resistant (Nal(R)) strains, ii) three naturally Nal-sensitive (Nal(S)) strains, and iii) three strains derived from Nals strains that were made resistant to Nal (Nal(Ri)) by successive culturing and selection in Nal-amended broth. The radiation D10-values (the radiation dose required to achieve a 1-log reduction in population) were determined in buffer solution and in orange juice. D10-values were significantly (P < 0.05) different among the Salmonella isolates tested. When considered as a group, Nal(R) isolates were significantly more sensitive to ionizing radiation than Nals isolates in both media tested. In buffer, D10 of Nal(R) was 0.210 kGy versus 0.257 kGy for Nals. In orange juice, D10 of Nal(R) was 0.581 versus 0.764 for Nals. Inducing resistance to Nal altered the response to irradiation. D10-value of Nal(Ri) was 0.234 kGy in buffer, a 9% reduction relative to Nals parents. In orange juice, the D10-value of Nal(Ri) was 0.637 kGy, a reduction of 17% relative to Nals parents. These results suggest that natural and/or induced resistance to Nal may predispose Salmonella isolates to greater sensitivity to ionizing radiation,and that this effect is influenced by the suspending medium and by the nature of the isolates evaluated.     

The World of Michael Fried's Antiquity

Antiquity occupies a surprisingly central role in Michael Fried's account of contemporary art photography. More specifically, on Fried's account, photographs of antiquity by Thomas Struth and Patrick Faigenbaum stand at the vanguard of contemporary photographic practice. This essay examines the place of these photographs in Fried's work. The essay suggests that close attention to them can illuminate not only unclear turns in Fried's otherwise stunning argument, but also our understanding of the phenomenology of ‘beholding’ in antiquity, a problem that recent work in ancient aesthetics has made considerably more philosophically fraught.     

Maximum likelihood estimation of higher‐order integer‐valued autoregressive processes

Abstract. In this article, we extend the earlier work of Freeland and McCabe [Journal of time Series Analysis (2004) Vol. 25, pp. 701–722] and develop a general framework for maximum likelihood (ML) analysis of higher‐order integer‐valued autoregressive processes. Our exposition includes the case where the innovation sequence has a Poisson distribution and the thinning is binomial. A recursive representation of the transition probability of the model is proposed. Based on this transition probability, we derive expressions for the score function and the Fisher information matrix, which form the basis for ML estimation and inference. Similar to the results in Freeland and McCabe (2004) , we show that the score function and the Fisher information matrix can be neatly represented as conditional expectations. Using the INAR(2) specification with binomial thinning and Poisson innovations, we examine both the asymptotic efficiency and finite sample properties of the ML estimator in relation to the widely used conditional least squares (CLS) and Yule–Walker (YW) estimators. We conclude that, if the Poisson assumption can be justified, there are substantial gains to be had from using ML especially when the thinning parameters are large.     

The degradation of electrochemically polymerised poly (3-aminophenol) films in sodium hydroxide solutions for the production of microelectrode ensembles

Poly (3-aminophenol) films have been grown electrochemically from solutions of 3-aminophenol at pH 7. These pinhole free films passivate the electrode surface and are less than 10 nm thick. The films are stable in 1 M solutions of sulphuric acid. However, they are rapidly degraded in solutions of sodium hydroxide. It is demonstrated that initially the polymer removal results in the creation of an electrode that exhibits the characteristics of a microelectrode ensemble. However, as further polymer is removed these characteristics are lost and response of the electrode resembles that of a large planar electrode. This chemical treatment of poly (3-aminophenol) films allows for the cost-effective production of microelectrode ensembles.