Measuring effective diffusivities in porous pellets: experimental procedures and FFT calculations

The effective diffusivity, D[subscript] e, of He in N[subscript]2 in ZnS pellets was determined using a dynamic Wicke-Kallenbach diffusion cell at 1.5 atm and 23°C. Pellets were pressed from reagent powders in rings with internal diameters of 25.4 mm. Pellet lengths ranged from 3.43 to 23.34 mm;Diffusivities were calculated by minimizing the sum-of-squares error, in the frequency domain, between the experimental data and a model for diffusion through the pellet. The experimental data were transformed to the frequency domain via the fast Fourier transform (FFT) and the Laplace transform solution of the diffusion equations was used for comparison to the experimental data;Four different configurations of the experimental apparatus were used and the effects of apparatus dead-volumes, chamber volumes, bottom chamber gas feed position, and flow rate through the thermal conductivity detector (TCD) on D[subscript] e, are shown. The height of the tracer dispersion cone above the top face of the pellet affected the value of D[subscript] e calculated. A model was proposed which separated the upper chamber volume into a region of complete mixing and into another region where mass transfer occurred by gaseous diffusion. The model did not adequately describe the effect of cone height above the pellet on the values of D[subscript] e obtained. Sample loop volumes ranged from 0.15 x 10[superscript]-6 to 5.21 x 10[superscript]-6 m[superscript]3 and He/N[subscript]2 tracer gas concentrations of 9.9, 52.5, and 100% He were used, but the differences among the diffusivities attributed to using the different gas concentrations and sample loops were less than 10%;Diffusivities were found to increase with pellet length unless the response-time of the TCD and the dispersion of the gas flow through the apparatus were included in the diffusion model. D[subscript] e values calculated in this manner agreed within 5% of the values calculated using the difference in moments procedure;Tortuosity factors, [tau], were calculated by summing the diffusional contributions over all pores sizes using the results obtained from mercury porosimetry experiments. The best low and high estimates for the tortuosity factor gave reasonable values of 1.56 and 2.84, respectively

The Use of Autologous PRP gel for the Treatment of Diabetic Foot Ulcers

The purpose of this systematic literature review is to examine the efficacy of platelet rich-plasma (PRP) gel as a therapy for diabetic foot ulcers (DFUs). Infections in patients with diabetes, especially diabetic foot ulcers, are challenging to treat due to neurovascular compromise. Searches were done in PubMed utilizing the terms “diabetic foot ulcer”, “platelet rich plasma” and “autologous”. In PubMed, the following limits and terms were used: randomized control trial (RCTs), sample size greater than 30 participants, foot ulcers, and English. A meta-analysis revealed three studies meeting inclusion/exclusion criteria: Li et al, Gude et al, and Ahmed et al. The literature available demonstrates that autologous PRP gel is an effective treatment to increase DFU healing rate when compared to the current standard of care. Further studies may be necessary to determine long term outcomes and consequences of the use of autologous PRP gel

BLAST Autonomous Daytime Star Cameras

We have developed two redundant daytime star cameras to provide the fine pointing solution for the balloon-borne submillimeter telescope, BLAST. The cameras are capable of providing a reconstructed pointing solution with an absolute accuracy < 5 arcseconds. They are sensitive to stars down to magnitudes ~ 9 in daytime float conditions. Each camera combines a 1 megapixel CCD with a 200 mm f/2 lens to image a 2 degree x 2.5 degree field of the sky. The instruments are autonomous. An internal computer controls the temperature, adjusts the focus, and determines a real-time pointing solution at 1 Hz. The mechanical details and flight performance of these instruments are presented.Comment: 8 pages, 6 figures, 1 table. To be published in conference proceedings for the "Ground-based and Airborne Instrumentation for Astronomy" part of the SPIE Astronomical Telescopes and Instrumentation Symposium that will be held 24-31 May 2006 in Orlando, F

Who Is missing-out on school? Exploring socioeconomic inequalities in school absenteeism

The strong relationship between family background and school performance among secondary pupils is a well-established finding in the cross-national comparative literature (Van de Werfhorst and Mijs 2010) and for Scotland (Sosu and Ellis 2014). “Closing the attainment gap” between children from lower and higher socioeconomic backgrounds is the main priority of the Scottish government’s education policy (Scottish Government 2016). A potential mechanism that may help to account for the association between family background and school performance is school absenteeism. Being absent from school may result from legitimate (e.g. sickness) or illegitimate reasons (e.g. truancy), as well as exclusion from school. In the school year 2014/2015, the total rate of absence for secondary schools in Scotland was 8.1% with significant differences between low (12%) and high-income (5.5%) neighbourhoods (Scottish Government, 2015). Several studies have found that school absenteeism is linked to lower educational achievement (Aucejo and Romano 2016; Buscha and Conte 2014; Gottfried 2011; London, Sanchez and Castrechini 2016; Steward et al. 2008). This is because absent students miss out on teacher-led lessons, peer interactions or activities that may stimulate their learning and ultimately their performance in exams. In addition, they might feel less integrated into their class and struggle to participate in classroom activities and interactions with peers and teachers which, in turn, is detrimental to their learning. Importantly, school absenteeism may be particularly harmful for children from lower socio-economic backgrounds as their parents have neither the time nor resources to compensate for school absence by supporting their children in engaging with the content of the missed school lessons. The relationship between family background and school absenteeism may operate through health-related behaviour (e.g. Moonie et al. 2006), environmental hazards (e.g. Currie et al. 2009), residential and school mobility (Nolan et al. 2013), family structure and environment (Evans 2004), and parental employment characteristics (Han 2005). Although a few studies show that students from the lower socio-economic background are more often absent from school (Attwood and Croll 2006; Nolan et al. 2013; Theriot, Craun and Dupper 2010), they do not address if and and to what extent parental resources are associated with absenteeism. Additionally, it is not clear if students from lower socioeconomic backgrounds or specific family structures are more likely to experience particular forms of absenteeism- such as exclusion- possibly due to the tendency for teacher bias towards students from low-income households (Campbell, 2015). Finally, it is not clear if boys and girls from different socioeconomic backgrounds experience absenteeism in the same way. This study attempts to fill the existing knowledge gaps in trying to answer the following questions: 1. To what extent do different socioeconomic factors (parental education, parental class or neighbourhood deprivation) and family structures (Eg. single parent, number of siblings) determine school absenteeism? 2. Do students from lower socioeconomic backgrounds or specific family structures differ in their experience of particular forms of school absenteeism (legitimate absence, truancy and exclusion)? 3. Drawing on the theory of intersectionality, does the relationship between socioeconomic backgrounds and school absenteeism differ between boys and girls

School absenteeism and academic achievement : Is missing-out on school more detrimental to students from lower socioeconomic backgrounds?

Significant social inequalities in academic achievement are well established. Evidence suggests that students from lower socioeconomic backgrounds are more frequently absent from school. Whereas school absenteeism is a potential mechanism for explaining the social inequality in academic achievement, empirical evidence on the link between absenteeism and achievement is sparse. Additionally, it is not clear if different forms of absenteeism have the same detrimental effect on achievement. Absent students miss out on teacher-led lessons, peer interactions or activities that may stimulate their learning and ultimately their performance in exams. In addition, they might feel less integrated into their class and struggle to participate in classroom activities and interactions with peers and teachers which, in turn, is harmful to their learning. Importantly, school absenteeism may be particularly detrimental to children from lower socio-economic backgrounds as their parents have neither the time nor resources to compensate for school absence by supporting their children in engaging with the content of the missed school lessons. In this paper, we first examine the association between different types of school absenteeism (legitimate absence, truancy and exclusion) and academic achievement in secondary school. Besides, we consider whether the association between absenteeism and academic achievement varies between different socioeconomic groups and family structures. We analysed a sample (N=5,000) from the Scottish Longitudinal Study (SLS) by linking census, school administrative and achievement, and administrative health data. The unique SLS data provided us with a rich set of confounders from the Census and health data in estimating the adjusted association between school absenteeism and academic achievement using regression-based approaches. We will discuss the data linkage process as well as the policy and practice implications of our findings

School Absenteeism and Academic Achievement:Does the Reason for Absence Matter?

Studies consistently show associations between school absences and academic achievement. However, questions remain about whether this link depends on the reason for children's absence. Using a sample of the Scottish Longitudinal Study (n = 4,419), we investigated whether the association between school absenteeism and achievement in high-stakes exams at the end of compulsory and post-compulsory schooling varies with the reason for absence. In line with previous research, our findings show that overall absences are negatively associated with academic achievement at both school stages. Likewise, all forms of absences (truancy, sickness absence, exceptional domestic circumstances, family holidays) are negatively associated with achievement at the end of compulsory and post-compulsory schooling. First difference regressions confirm these negative associations, except for family holidays. These results suggest that, in addition to lost instruction, other mechanisms such as behavioral, health-related, and psychosocial pathways may account for the association between absenteeism and achievement. The findings have implications for designing tailored absenteeism interventions to improve pupils' academic achievement

On Complete Sets of Polarization Observables

A new criterion is developed which provides a check as to whether a chosen set of polarization observables is complete with respect to the determination of all independent $T$-matrix elements of a reaction of the type $a+b\to c+d+...$. As an illustrative example, this criterion is applied to the longitudinal observables of deuteron electrodisintegration.Comment: 8 pages revtex, final version, accepted for Nucl. Phys.

Give it up for climate change : a defence of the beneficiary pays principle

This article focuses on the normative problem of establishing how the burdens associated with implementing policies designed to prevent, or manage, climate change should be shared amongst states involved in ongoing international climate change negotiations. This problem has three key features: identifying the nature and extent of the burdens that need to be borne; identifying the type of agent that should be allocated these burdens; and distributing amongst the particular ‘tokens’ of the relevant ‘agent type’ climatic burdens according to principles that none could reasonably reject. The article defends a key role in climatic burden-sharing policy for the principle that states benefiting most from activities that cause climate change should bear the greatest burden in terms of the costs of preventing dangerous climate change. I outline two versions of this ‘beneficiary pays’ principle; examine the strengths and weakness of each version; and explore how the most plausible version (which I call the ‘unjust enrichment’ account) could be operationalized in the context of global climate governance