Seasonal variation in the C,N and S stable isotope composition of retail organic and conventional Irish beef

The objective of this study was to investigate seasonal variation in the C, N and S stable isotope composition of retail organic and conventional Irish beef. A total of 242 beef samples (127 organic, 115 conventional) was collected in a one-year survey and analysed by isotope ratio mass spectrometry. The δ¹³C time series in conventional beef was significantly non-random, with a pronounced seasonal positive shift of >2‰ between December and June, whilst δ¹³C in organic beef was less variable and significantly more negative. In conventional beef, δ¹⁵N was remarkably invariant (remaining close to 7‰) throughout the year, while organic beef was more variable and also significantly lower in δ¹⁵N. The S isotope composition (δ³⁴S) exhibited a complex seasonal pattern in both types of beef. These results show that seasonal patterns can occur in the isotopic composition of beef, probably reflecting seasonality in animal feeding practices modulated by tissue turnover rates. Such seasonal variation needs to be considered in the isotopic authentication of beef and other animal-derived products.     

VECSEL threshold and output power-shutoff dependence on the carrier recombination rates

We compute the lasing threshold and thermally driven power-shutoff characteristics of optically pumped vertical-external-cavity surface-emitting lasers. Using a quantitative numerical model, variations in the threshold and shutoff power levels are contrasted for the two approaches to the computation of the carrier recombination rates: using the AN+BN/sup 2/+CN/sup 3/ model with the temperature and carrier density independent coefficients, versus using recombination rates precomputed within the framework of the microscopic many-body theory.     

Measuring anthropometric indicators through nutrition surveillance in humanitarian settings: options, issues, and ways forward

The technical discourse on nutrition surveillance started decades ago, and the first technical guidelines were proposed in mid-1970s. In spite of this long history, little evidence and consensus exists on the best methods for conducting nutrition surveillance, and on the validity of data produced by these approaches. Multiple nutrition surveillance systems exist in humanitarian settings; however, the validity and usefulness of data produced by these systems are often questionable. In this paper, we outline and define five major methodological approaches to collecting child anthropometric data through surveillance: repeated surveys, community-based sentinel sites, mass screenings, admission data from feeding centers, and data from health clinics. We discuss outstanding methodological and practical challenges with direct implications for quality, validity, and interpretability of collected data and highlight comparative advantages and disadvantages of different methods. We also propose ways forward to building a better evidence base by documenting the strengths and limitations of different approaches, with the eventual goal of achieving consensus on the best ways to collect anthropometric data through surveillance.     

Two kinds of division polynomials for twisted Edwards curves

This paper presents two kinds of division polynomials for twisted Edwards curves. Their chief property is that they characterise the n-torsion points of a given twisted Edwards curve. We present recursions for the division polynomials, which differ in their flavour. We prove a uniqueness form for elements of the function field of an Edwards curve. We also present results concerning the coefficients of these polynomials, which may aid computation.     

Tapered-cavity surface-emitting distributed-Bragg-reflector semiconductor lasers: modeling and experiment

We report on the design and fabrication of tapered cavity grating coupled surface-emitting distributed Bragg reflector (DBR) lasers in the 980-nm regime. A curved second-order grating is used at the end of a tapered gain section to provide feedback as well as collimated surface out-coupling. A detailed numerical analysis shows that operation up to approximately twice the threshold is possible without significant degradation of the far field. Near diffraction-limited collimated surface-emitting output with moderate power of about 150 mW is obtained under continuous operation.     

Interface toughness of carbon nanotube reinforced epoxy composites

Traditional single-fiber pull-out type experiments were conducted on individual multiwalled carbon nanotubes (MWNT) embedded in an epoxy matrix using a novel technique. Remarkably, the results are qualitatively consistent with the predictions of continuum fracture mechanics models. Unstable interface crack propagation occurred at short MWNT embedments, which essentially exhibited a linear load-displacement response prior to peak load. Deep embedments, however, enabled stable crack extension and produced a nonlinear load-displacement response prior to peak load. The maximum pull-out forces corresponding to a wide range of embedments were used to compute the nominal interfacial shear strength and the interfacial fracture energy of the pristine MWNT-epoxy interface.     

Systems-of-systems methodology for strategic infrastructure decision making: Ireland as a case study

Infrastructure development is a long term process, which cannot easily adapt to sudden change; and infrastructure assets can have long lifetimes. Poor investment choices risk locking in poor policy choices for substantial periods of time. The ‘need’ for a new infrastructure asset arises due to demographic, economic or policy changes. But historically Ireland’s infrastructure investment has also been driven, in part, by the pursuit of political / economic policies which have themselves ‘created’ infrastructure needs; and often decided on an isolated project-by-project basis. In contrast, a systems-of-systems (SoS) approach is a fusion of network modelling, consideration of various policy options, and appraisal of the impact of alternative demographic and economic scenarios on multiple systems. This paper assesses Ireland’s readiness to adopt a SoS approach to infrastructure decision-making, proposes a methodology for its development and implementation. This would enable the demand for new infrastructure to be tested under various policy scenarios, providing evidence for investment decisions.     

Molecular genetic and biochemical analysis of Brassica napus proliferating cell nuclear antigen function

A cDNA encoding the proliferating cell nuclear antigen (PCNA) from Brassica napus (oilseed rape) was shown to complement the lethal deletion mutation in the PCNA gene (delta POL30) of Saccharomyces cerevisiae. We provide unequivocal evidence that the B. napus PCNA can perform all the essential functions of the yeast PCNA in DNA replication, although some species-specific differences may exist. In addition, the B. napus PCNA expressed as a fusion polypeptide with glutathione S-transferase (GST) was shown to stimulate the activity and processivity of two delta-like DNA polymerases from wheat in vitro. These experiments provide direct biochemical evidence that the B. napus PCNA may function as an auxiliary factor in plant cell DNA replication.