Simple analytical Green's functions for ray perturbations in layered media

The total Green's function for two‐point boundary‐value problems can be related to the propagator for initial‐value problems. A very simple expression for the Green's function is obtained when the unperturbed medium may be described by material with a constant gradient in quadratic slowness. The derivation requires a correct understanding of assumptions made in the propagator solution. Expressions are also obtained for Green's function in multilayered media. Copyright © 1993, Wiley Blackwell. All rights reserve

The disappearing women: North West ICT project final report

Project Context The Disappearing Women: Northwest ICT project was embarked upon to further understand why more women leave the sector than are being recruited, 36% of new ICT recruits in the UK (in the first quarter of 2002) were women, yet in the same period, women accounted for 46% of all leavers or ‘disappearing’ women (The DTI Women in IT Champions report 2003, Grey and Healy 2004). This continuing trend shows a decline from 27% of women making up the ICT workforce in 1997 with a drop to 21% in 2004 (The DTI Women in IT Industry report 2005b). The number of women in the ICT sector remains disappointingly small considering that women make up around 50% of the total UK workforce and significantly this figure has gradually continued to fall despite numerous initiatives to attract more women into the sector (see Griffiths and Moore 2006 for a list of high profile ‘women in ICT’ initiatives). The research team’s first gender research project - Women in IT (WINIT) - ran for two years from January 2004 until March 2006 at the Information Systems Institute at The University of Salford and dealt solely with women who worked in the ICT sector in England. The WINIT Project via an online questionnaire and in-depth interviews gathered the stories and experiences of up to 500 participants and 19 interviewees respectively. The project enabled these women’s voices to be heard but the research team were constantly aware that a certain part of the female ICT workforce - the ‘disappearing’ women who had left ICT vowing never to return - had been overlooked and effectively silenced. It was these women who once found, may be able to facilitate a more in-depth understanding of why women were leaving the ICT sector. Having amassed skills and expertise, qualifications in ICT and crossed ICT recruitment barriers (DTI 2005a) the ‘disappearing’ women for whatever reasons decided to change their career trajectories and leave the sector. What ‘chilly’ (Falkner 2004) workplaces, disinterested organisational cultures and indifferent working conditions had these women encountered that became determining factors in leaving the ICT sector? There has been little (if any) research conducted involving this specific cohort of women and The Disappearing Women: North West ICT (DW: NW ICT) project seeks to make a research contribution to what is a continuing statistical and symbolic under-representation of women in the ICT labour market. The DW: NW ICT project was partly funded by the European Social Fund (ESF) from April 2006 until December 2006 under ESF Objective 3, Policy Field 5.1: Improving the Participation of Women. The DW: NW ICT project contributes research to priority 5 and its strategic objective to reduce the level of disadvantage faced by women in the labour market. The project was run in the Information Systems Group, Salford Business School of The University of Salford, Greater Manchester, UK. The report is structured as follows. The first section presents the backdrop for the research, looking in general at women in the ICT labour market in England and then women leaving the ICT sector focussing on the North West of England and more explicitly women leaving ICT employment in the North West of England. The research aims of the project form the following section; they have been loosely classified in to two groupings, the push and pull factors that are contributing to the high attrition rate of women leaving ICT. The methodology follows with the route taken in how this ‘hard to reach’ target sample were finally located, once contacted the life history interview process and procedures adopted is explained in full. The vignettes of the ‘disappearing’ women are included to allow the reader an opportunity to ‘get to know’ these women a little more closely. Key themes that have naturally emerged throughout the interview data analysis process are presented, including hostilities in the ICT workplace, significant events and the process of leaving ICT workplaces and finally stories of the ‘appearing’ women and their current situations are heard. A discussion regarding the findings of the DW: NW ICT project concludes this report

Maternal nutritional status, C1 metabolism and offspring DNA methylation: a review of current evidence in human subjects.

: Evidence is growing for the long-term effects of environmental factors during early-life on later disease susceptibility. It is believed that epigenetic mechanisms (changes in gene function not mediated by DNA sequence alteration), particularly DNA methylation, play a role in these processes. This paper reviews the current state of knowledge of the involvement of C1 metabolism and methyl donors and cofactors in maternal diet-induced DNA methylation changes in utero as an epigenetic mechanism. Methyl groups for DNA methylation are mostly derived from the diet and supplied through C1 metabolism by way of choline, betaine, methionine or folate, with involvement of riboflavin and vitamins B6 and B12 as cofactors. Mouse models have shown that epigenetic features, for example DNA methylation, can be altered by periconceptional nutritional interventions such as folate supplementation, thereby changing offspring phenotype. Evidence of early nutrient-induced epigenetic change in human subjects is scant, but it is known that during pregnancy C1 metabolism has to cope with high fetal demands for folate and choline needed for neural tube closure and normal development. Retrospective studies investigating the effect of famine or season during pregnancy indicate that variation in early environmental exposure in utero leads to differences in DNA methylation of offspring. This may affect gene expression in the offspring. Further research is needed to examine the real impact of maternal nutrient availability on DNA methylation in the developing fetus

High precision zinc stable isotope measurement of certified biological reference materials using the double spike technique and multiple collector-ICP-MS

Biological reference materials with well-characterized s table isotope compositions are lacking in the field of ‘isotope biochemistry’, which seeks to understand bodily processes that rely on essential metals by determining metal stable isotope ratios. Here, we present Zn stable isotope data for six biological reference materials with certified trace metal concentrations, fish muscle, bovine muscle, pig kidney, human hair, human blood serum and human urine. Replicate analyses of multiple aliquots of each material achieved reproducibilities (2sd) of 0.04-0.13 ‰ for δ66/64Zn 22 (which denotes the deviation of the 66 Zn/64Zn ratio of a sample from a pure Zn reference material in parts per 1000). This implies only very minor isotopic heterogeneities within the samples, rendering them suitable as quality control materials for Zn isotopeanalyses. This endorsement is reinforced by (i) the close agreement of our Zn isotope data for two of the samples (bovine 2 muscle and human blood serum) to previously published results for different batches of the same material and (ii) the similarity of the isotopic data for the samples (δ66/64Zn≈ –0.8 to 0.0 ‰) to previously published Zn isotope results for similar biological materials. Further tests revealed that the applied Zn separation procedure is sufficiently effective to enable accurate data acquisition even at low mass resolving power (M/ΔM ≈ 400), as measurements and analyses conducted at much higher mass resolution (M/ΔM ≈ 8500) delivered essentially identical results

The Mathematics Problem and Mastery Learning for First-Year, Undergraduate STEM Students

In the 2014 academic year Mastery Learning was implemented in four first-year mathematics subjects in an effort to address a lack of preparedness and poor outcomes of increasing numbers of undergraduate students in science, engineering and mathematics programs. This followed partial success in the use of diagnostic testing and pre-teaching, active learning, and a greater emphasis on problem solving in context - under-prepared students were still more likely to fail the pre-teaching subject and to struggle with subsequent mathematics subjects. Also, failure rates overall were higher than benchmarks required. This paper describes the learning design used, and the outcomes achieved, with implementing Mastery Learning – the positive: improved academic success, time management, and attitudes towards learning and Mathematics, an increased sense of independence, confidence and retention of content, and reduced stress and anxiety; and the negative: students having a sense of being taught how to pass a test rather than having a deeper understanding of the content. It will be seen that this negative is a consequence of a small but important difference in implementation

Violent video games and morality: a meta-ethical approach

This paper considers what it is about violent video games that leads one reasonably minded person to declare "That is immoral" while another denies it. Three interpretations of video game content a re discussed: reductionist, narrow, and broad. It is argued that a broad interpretation is required for a moral objection to be justified. It is further argued that understanding the meaning of moral utterances – like "x is immoral" – is important to an understanding of why there is a lack of moral consensus when it comes to the content of violent video games. Constructive ecumenical expressivism is presented as a means of explaining what it is that we are doing when we make moral pronouncements and why, when it comes to video game content, differing moral attitudes abound. Constructive ecumenical expressivism is also presented as a means of illuminating what would be required for moral consensus to be achieved

Experimental evaluation of the extractability of Fe-bound organic carbon in sediments as a function of carboxyl content

The majority of organic carbon (OC) burial in marine sediments occurs on continental shelves, of which an estimated 10–20% is associated with reactive iron (FeR). The association of OC with FeR (OC-FeR) is thought to facilitate preservation of organic matter (OM) in sediments and therefore represents an important carbon sink. The citrate-bicarbonate-dithionite (CBD) method is used to quantify OC-FeR in marine sediments by reductively dissolving FeR, thereby releasing bound OC. While the CBD method is widely used, it may be less efficient at measuring OC-FeR than currently thought, due to the incomplete reduction of FeR, resulting from the neutral pH conditions required to prevent OM hydrolysis. Additionally, the typical range of values reported for OC-FeR in marine sediments is narrow, despite variation in OM and FeR inputs, OM source types and chemical compositions. This suggests a limitation exists on the amount of OC that can become associated with FeR, and/or that the CBD method is limited in the OC-FeR that it is able to quantify. In assessing the efficiency of the CBD method, we aimed to understand whether methodological errors or (mis)interpretation of these extraction results may contribute to the apparent limitation on OC-FeR values. Here, we synthesised OC-FeR composites with a known FeR phase and known OM moieties, varying in carboxyl content, at neutral pH. These were spiked into OC-free marine sediment, and subject to a CBD extraction to investigate i) the efficiency of CBD for OC extraction; ii) the efficiency of CBD for FeR extraction; ii) how the OC moiety affects the physical parameters of associated FeR minerals; and iii) the impact of OM moiety on OC and Fe release. We show that the CBD method results in only partial dissolution of the most susceptible FeR phase (ferrihydrite) and therefore incomplete removal of bound OC. While as little as ~20% of Fe is released from OC-free ferrihydrite, structural disorder of the mineral phase increases with the inclusion of more OC, resulting in greater losses of up to 62% Fe for carboxyl rich OC-FeR complexes. In addition, our results show that the NaCl control step performed in the CBD method is capable of removing weakly bound OC from FeR, such that inclusion of this OC in the total OC-FeR fraction may increase marine sediments OC-FeR estimates by ~33%. Finally, we suggest that the structure of OC involved in OC-FeR binding can affect quantification of the OC-FeR pool. Our results have important implications for assessing the FeR bound OC fraction in marine sediments and the fate of this OC in the global carbon cycle

Technical note: Uncovering the influence of methodological variations on the extractability of iron-bound organic carbon

Association of organic carbon (OC) with reactive iron (FeR) represents an important mechanism by which OC is protected against remineralisation in soils and marine sediments. Recent studies indicate that the molecular structure of organic compounds and/or the identity of associated FeR phases exert a control on the ability of an OC–FeR complex to be extracted by the citrate–bicarbonate–dithionite (CBD) method. However, many variations of the CBD extraction are used, and these are often uncalibrated to each other, rendering comparisons of OC–FeR values extracted via the different methods impossible. Here, we created synthetic ferrihydrite samples coprecipitated with simple organic structures and subjected these to modifications of the most common CBD method. We altered some of the method parameters (reagent concentration, time of the extraction and sample preparation methods) and measured FeR recovery to determine which (if any) modifications affected the release of FeR from the synthetic sample. We provide an assessment of the reducing capacity of Na dithionite in the CBD method (the amount of Fe reduced by a fixed amount of dithionite) and find that the concentration of dithionite deployed can limit OC–FeR extractability for sediments with a high FeR content. Additionally, we show that extending the length of any CBD extraction offers no benefit in removing FeR. Moreover, we demonstrate that for synthetic OC–FeR samples dominated by ferrihydrite, freeze-drying samples can significantly reduce OC–FeR extractability; this appears to be less of an issue for natural marine sediments where natural ageing mechanisms may mimic the freeze-drying process for more stable Fe phases. While our study is not an all-inclusive method comparison and is not aimed at delivering the “perfect” extraction setup, our findings provide a collected summary of critical factors which influence the efficiency of the CBD extraction for OC–FeR. As such, we provide a platform from which OC–FeR values obtained under different methods can be interpreted and future studies of sediment carbon cycling can build upon