Why do we need 14C inter-comparisons?: The Glasgow 14C inter-comparison series, a reflection over 30 years

Radiocarbon measurement is a well-established, routinely used, yet complex series of inter-linked procedures. The degree of sample pre-treatment varies considerably depending on the material, the methods of processing pre-treated material vary across laboratories and the detection of 14C at low levels remains challenging. As in any complex measurement process, the questions of quality assurance and quality control become paramount, both internally, i.e. within a laboratory and externally, across laboratories. The issue of comparability of measurements (and thus bias, accuracy and precision of measurement) from the diverse laboratories is one that has been the focus of considerable attention for some time, both within the 14C community and the wider user communities. In the early years of the technique when there was only a small number of laboratories in existence, inter-comparisons would function on an ad hoc basis, usually involving small numbers of laboratories (e.g.Otlet et al, 1980). However, as more laboratories were set-up and the detection methods were further developed (e.g. new AMS facilities), the need for more systematic work was recognised. The international efforts to create a global calibration curve also requires the use of data generated by different laboratories at different times, so that evidence of laboratory offsets is needed to inform curve formation. As a result of these factors, but also as part of general good laboratory practice, including laboratory benchmarking and quality assurance, the 14C community has undertaken a wide-scale, far-reaching and evolving programme of global inter-comparisons, to the benefit of laboratories and users alike. This paper looks at some of that history and considers what has been achieved in the past 30 years

SSME main combustion chamber life prediction

Typically, low cycle fatigue life is a function of the cyclic strain range, the material properties, and the operating temperature. The reusable life is normally defined by the number of strain cycles that can be accrued before severe material degradation occurs. Reusable life is normally signified by the initiation or propagation of surface cracks. Hot-fire testing of channel wall combustors has shown significant mid-channel wall thinning or deformation during accrued cyclic testing. This phenomenon is termed cyclic-creep and appears to be significantly accelerated at elevated surface temperatures. This failure mode was analytically modelled. The cyclic life of the baseline SSME-MCC based on measured calorimeter heat transfer data, and the life sensitivity of local hot spots caused by injector effects were determined. Four life enhanced designs were assessed

On the capacity and normalisation of ISI channels

[Abstract]: We investigate the capacity of various ISI channels with additive white Gaussian noise. Previous papers showed a minimum Eb/N0 of −4.6 dB, 3 dB below the capacity of a flat channel, is obtained using the water-pouring capacity formulas for the 1 + D channel. However, these papers did not take into account that the channel power gain can be greater than unity when water-pouring is used. We present a generic power normalization method of the channel frequency response, namely peak bandwidth normalisation, to facilitate the fair capacity comparison of various ISI channels. Three types of ISI channel, i.e., adder channels, RC channels and magnetic recording channels, are examined. By using our channel power gain normalization, the capacity curves of these ISI channels are shown

A period of calm in Scottish seas: a comprehensive study of ΔR values for the northern British Isles coast and the consequent implications for archaeology and oceanography

The Marine Radiocarbon Reservoir Effect (MRE) is a 14C age offset between contemporaneous marine- and terrestrially-derived carbon. In Northern Hemisphere surface waters it is of the order of 400 years but temporal and spatial deviations, known as ΔR, occur. This study provides a comprehensive dataset of 21 ΔR and MRE values for the east coast of Scotland and 21 recalculated values for the west coast of Scotland and Ireland, for the period c. 3500 BC to 1450 AD. They are presented as mean, site-specific ΔR and MRE values, together with their associated uncertainties, calculated as standard errors for predicted values. The ΔR values range from -320 ± 35 to +150 ± 28 14C years and show no spatial or temporal trends. The MRE values range from 59 ± 40 to 531 ± 26, show an almost identical distribution pattern to the ΔR values and again show no spatial or temporal trends. Results show that ΔR values calculated for a single site using statistically indistinguishable groups of terrestrial and marine radiocarbon age measurements can produce variability of up to 225 14C years. ΔR is an important factor in the accurate calibration of samples containing marine-derived carbon for archaeological interpretation but is often also used as an indicator of changes in 14C specific activity of the oceans, and therefore a proxy for changes in ocean circulation and/or climate. Using the methods outlined in this paper, it is apparent that ΔR values for the northern part of the British Isles have been relatively stable, within our ability to quantify non-random variation in the data. The fact that significant climatic shifts have been recorded during this time, yet these are not visible in the ΔR data, presents a cautionary tale regarding the use of ΔR to infer large-scale oceanographic or climatic changes. Upon the exclusion of 5 outliers from the 42 values, the remaining ΔR values are statistically indistinguishable from one another and range from -142 ± 61 to +40 ± 47 14C years. 34 of these values are from Scottish archaeological sites and can be combined to produce a mean value for Scotland of -47 ± 52 14C years for the period 3500 BC to 1450 AD, to be used only in the absence of site- and period-specific data

CD4+ T cell hyporesponsiveness after repeated exposure to Schistosoma mansoni larvae is dependent upon interleukin-10

The effect that multiple percutaneous exposures to Schistosoma larvae has on the development of early CD4+ lymphocyte reactivity is unclear, yet it is important in the context of humans living in areas where schistosomiasis is endemic. In a murine model of multiple infections, we show that exposure of mice to repeated doses (4×) of Schistosoma mansoni cercariae, compared to a single dose (1×), results in CD4+ T cell hyporesponsiveness within the skin-draining lymph nodes (sdLN), manifested as reduced CD4+ cell proliferation and cytokine production. FoxP3+ CD4+ regulatory T cells were present in similar numbers in the sdLN of 4× and 1× mice and thus are unlikely to have a role in effecting hyporesponsiveness. Moreover, anergy of the CD4+ cell population from 4× mice was slight, as proliferation was only partly circumvented through the in vitro addition of exogenous interleukin-2 (IL-2), and the in vivo blockade of the regulatory molecule PD1 had a minimal effect on restoring responsiveness. In contrast, IL-10 was observed to be critical in mediating hyporesponsiveness, as CD4+ cells from the sdLN of 4× mice deficient for IL-10 were readily able to proliferate, unlike those from 4× wild-type cohorts. CD4+ cells from the sdLN of 4× mice exhibited higher levels of apoptosis and cell death, but in the absence of IL-10, there was significantly less cell death. Combined, our data show that IL-10 is a key factor in the development of CD4+ T cell hyporesponsiveness after repeated parasite exposure involving CD4+ cell apoptosis

New CP-violation and preferred-frame tests with polarized electrons

We used a torsion pendulum containing $\sim 9 \times 10^{22}$ polarized electrons to search for CP-violating interactions between the pendulum's electrons and unpolarized matter in the laboratory's surroundings or the sun, and to test for preferred-frame effects that would precess the electrons about a direction fixed in inertial space. We find $|g_{\rm P}^e g_{\rm S}^N|/(\hbar c)< 1.7 \times 10^{-36}$ and $|g_{\rm A}^e g_{\rm V}^N|/(\hbar c) < 4.8 \times 10^{-56}$ for $\lambda > 1$AU. Our preferred-frame constraints, interpreted in the Kosteleck\'y framework, set an upper limit on the parameter $|\bm{\tilde {b}}^e| \leq 5.0 \times 10^{-21}$ eV that should be compared to the benchmark value $m_e^2/M_{\rm Planck}= 2 \times 10^{-17}$ eV.Comment: 4 figures, accepted for publication in Physical Review Letter

Management Production Systems and Timing Strategies for Cull Cows

Replaced with revised version of paper 06/04/09.Cattle, cull cows, management, marketing, production systems, timing, Farm Management, Marketing,

Holocene variations in the Scottish marine radiocarbon reservoir effect

We assessed the evidence for variations in the marine radiocarbon reservoir effect (MRE) at coastal, archaeological Iron Age sites in north and west Scotland by comparing AMS measurements of paired marine and terrestrial materials (4 pairs per context). DeltaR values were calculated from measurements on material from 3 sites using 6 sets of samples, all of which were deposited around 2000 BP. The weighted mean of the DeltaR determinations was -79 +/- 17 C-14 yr, which indicates a consistent, reduced offset between atmospheric and surface ocean C-14 specific activity for these sites during this period, relative to the present day (DeltaR = similar to0 C-14 yr). We discuss the significance of this revised AR correction by using the example of wheelhouse chronologies at Hornish Point and their development in relation to brochs. In addition, we assess the importance of using the concepts of MRE correction and AR variations when constructing chronologies using C-14 measurements made on materials that contain marine- derived carbon

Influence of Beginning Body Condition Scores on Net Returns From Feeding Cull Cows

The impact of beginning body condition scores on returns from feeding cull cows was investigated in a two year experiment. In each of two culling years, physical performance data and financial data were measured at approximately monthly intervals for culls on pasture versus dry lot. Specifically, data was collected for cows culled in October 2007 and held through April 2008 and for cows culled in October 2008 and held through March 2009. We examine the sensitivity of net returns relative to the choice of body condition score as a sorting trigger for heavy versus thin cows. In this two year study, while a pasture system was generally more profitable than a drylot system, thin cows were typically more profitable than cows with higher BCS, regardless of the feeding system. The importance of the sorting criteria is highlighted in year two. Using the lower BCS criteria for sorting is the only scenario that generates positive net returns, albeit small. Thus, decisions regarding cull cow retention and feeding should consider body condition scores.Agricultural and Food Policy,