Tritium supply and use: a key issue for the development of nuclear fusion energy

Full power operation of the International Thermonuclear Experimental Reactor (ITER) has been delayed and will now begin in 2035. Delays to the ITER schedule may affect the availability of tritium for subsequent fusion devices, as the global CANDU-type fission reactor fleet begins to phase out over the coming decades. This study provides an up to date account of future tritium availability by incorporating recent uncertainties over the life extension of the global CANDU fleet, as well as considering the potential impact of tritium demand by other fusion efforts. Despite the delays, our projections suggest that CANDU tritium remains sufficient to support the full operation of ITER. However, whether there is tritium available for a DEMO reactor following ITER is largely uncertain, and is subject to numerous uncontrollable externalities. Further tritium demand may come from any number of private sector “compact fusion” start-ups which have emerged in recent years, all of which aim to accelerate the development of fusion energy. If the associated technical challenges can be overcome, compact fusion programmes have the opportunity to use tritium over the next two decades whilst it is readily available, and before full power DT operation on ITER starts in 2035. Assuming a similar level of performance is achievable, a compact fusion development programme, using smaller reactors operating at lower fusion power, would require smaller quantities of tritium than the ITER programme, leaving sufficient tritium available for multiple concepts to be developed concurrently. The development of concurrent fusion concepts increases the chances of success, as it spreads the risk of failure. Additionally, if full tritium breeding capability is not expected to be demonstrated in DEMO until after 2050, an opportunity exists for compact fusion programmes to incorporate tritium breeding technology in nearer-term devices. DD start-up, which avoids the need for external tritium for reactor start-up, is dependent upon full tritium breeding capability, and may be essential for large-scale commercial roll-out of fusion energy. As such, from the standpoint of availability and use of external tritium, a compact route to fusion energy may be more advantageous, as it avoids longer-term complications and uncertainties in the future supply of tritium

Grazing Effects on the Seed Pool of \u3cem\u3eStipa Krylovii\u3c/em\u3e and Its Genetic Diversity in Relationship to the Plant Population on a Typical Steppe Community in Inner Mongolia

Stipa krylovii is an important tufted forage species on the typical steppe in Inner Mongolia and is sensitive to heavy grazing pressure. Vegetative recovery of plant density is dependent on the seed bank, which is a genetic reservoir that supports the vegetative expression of the species thus enhancing its resilience (McCue and Holtsford 1998). The ability of the seed bank to support the Stipa krylovii population is dependent on its size and genetic diversity. Therefore, we conducted a study to determine the effects of heavy grazing pressure on its seed reserves and examine its genetic diversity in relation to surviving plants

Grazing Effects on Genetic Diversity of \u3cem\u3eFestuca Campestris\u3c/em\u3e Rydb. And \u3cem\u3eStipa Grandis\u3c/em\u3e L. On the Native Grasslands in Canada and China, Respectively

Genetic drift or selectively neutral mutation in finite populations may result in genetic diversity within a natural population (Kimura, 1986). Genetic diversity influences the resilience of a species to survive perturbations or adapt to changes in its environment. Grazing by livestock may affect genetic diversity by exerting selection pressure on grazing sensitive species. In this study, we examine the effects of heavy sustained grazing pressure on the genetic diversity of Festuca campestris Rydb. and Stipa grandis L. These species are found on the Canadian Plains and the steppes of Inner Mongolia, respectively. Each is an important forage species that dominates their respective grasslands but decline readily when subjected to heavy grazing pressure

Test of a DC-HTS Busbar Demonstrator for Power Distribution in Hybrid-Electric Propulsion Systems for Aircraft

In the framework of the German project TELOS (Thermo-Electrically Optimised Aircraft Propulsion Systems) a high-temperature superconducting 40 MVA DC demonstrator busbar for hybrid-electric propulsion systems for aircraft has been developed. The design current for a temperature below 25 K is 13.3 kA and the rated voltage is 3 kV. The 2-pole busbar contains 2 stacks of REBCO coated conductors which are supported by a 3D-printed structure allowing compensation of thermal length changes of the superconductor. It fits in a cryostat tube with an inner diameter of 25 mm. A special focus has been put on low-resistive joints that are necessary to connect single elements of the busbar system. The special layout of the joints allows an effective current redistribution between the different tapes in a stack. We present results for the test of the DC busbar demonstrator in liquid nitrogen at 77 K. The design current for this temperature is 3.3 kA which corresponds to a rated power of 10 MW. We applied currents up to 3.5 kA and measured the I-V characteristics and contact resistances of 90° and 180° joints in a virgin and in a strained state thus simulating thermal length changes. We also present results of Lorentz-Force tests with short AC current pulses up to 20 kA to demonstrate the viability of the design for application with currents up to 13.3 k

A Comparison of Production and Soils in Modified Mixed Prairie Community

This study examined the effects of reseeding a Stipa-Agropyron- Bouteloua community to monocultures of crested wheatgrass (Agropyron cristatum (L.) Geartn.), Russian wild rye grass (Elymus junceus Fisch.), and wheat (Triticum aestivum L.) on above and below ground biomass and indicators of soil quality. Summer fallowed wheat produced 10817 kg ha-1 and 4090 kg ha-1 of above ground below ground biomass respectively whereas the native community produced 3191 kg ha-1 above ground and 13013 kg ha-1 of below ground biomass. However wheat, crested wheatgrass and Russian wildrye grass generally showed a lower biological index, phosphatase and dehydrogenase activity

Indicated Truancy Interventions: Effects on School Attendance Among Chronic Truant Students.

BACKGROUNDTruancy is a significant problem in the U.S. and in other countries around the world. Truancy has been linked to serious immediate and far-reaching consequences for youth, families, and schools and communities, leading researchers, practitioners, and policy makers to try to understand and to address the problem. Although numerous and significant steps have been taken at the local, state, and national levels to reduce truancy, the rates of truancy have at best remained stable or at worst been on the rise, depending on the indicator utilized to assess truancy rates. The costs and impact of chronic truancy are significant, with both short- and long-term implications for the truant youth as well as for the family, school, and community. Although several narrative reviews and one meta-analysis of attendance and truancy interventions have attempted to summarize the extant research, there are a number of limitations to these reviews. It is imperative that we systematically synthesize and examine the evidence base to provide a comprehensive picture of interventions that are being utilized to intervene with chronic truants, to identify interventions that are effective and ineffective, and to identify gaps and areas in which more research needs to be conducted to better inform practice and policy.OBJECTIVESThe main objective of this systematic review was to examine the effects of interventions on school attendance to inform policy, practice, and research. The questions guiding this study were: 1) Do truancy programs with a goal of increasing student attendance for truant youth affect school attendance behaviors of elementary and secondary students with chronic attendance problems?2) Are there differences in the effects of school-based, clinic/community-based, and court-based programs?3) Are some modalities (i.e., family, group, multimodal) more effective than others in increasing student attendance? SEARCH STRATEGYA systematic and comprehensive search process was employed to locate all possible studies between 1990 and 2009, with every effort made to include both published and unpublished studies to minimize publication bias. A wide range of electronic bibliographic databases and research registers was searched, websites of relevant research centers and groups were mined for possible reports, over 200 e-mails and letters were sent to programs listed in large databases of truancy programs compiled by the National Center for School Engagement and the National Dropout Prevention Center, and contact with researchers in the field of truancy and absenteeism was attempted. In addition, we examined reference lists of all previous reviews as well as citations in research reports for potential studies.SELECTION CRITERIAStudies eligible for this review were required to meet several eligibility criteria. Studies must have utilized a randomized, quasi-experimental, or single-group pre-posttest design with the aim of evaluating the effectiveness of interventions with a stated primary goal of increasing student attendance (or decreasing absenteeism) among chronic truant students. Studies must have measured an attendance outcome and reported sufficient data to calculate an effect size. Finally, studies must have been published between 1990 and 2009 in the United States, United Kingdom, Australia, or Canada. DATA COLLECTION AND ANALYSISA total of 28 studies, reported in 26 reports, met final eligibility criteria and were included in this review and meta-analysis. Of the studies that were included, 5 utilized a randomized design (RCT), 11 utilized a quasi-experimental design (QED), and 12 utilized a single group pre-posttest design (SGPP). All eligible studies were coded using a structured coding instrument, with 20% of studies coded by a second coder. Descriptive analysis was conducted to examine and describe data related to the characteristics of the included studies. Analysis of the mean effect size, the heterogeneity of effect sizes, and the relationship between effect size and methodological and substantive characteristics of the interventions was also conducted separately for the RCT/QED studies and the SGPP studies. The effect sizes were calculated using the standardized mean difference effect size statistic, correcting for small sample size using Hedges’ g (Hedges, 1992). Assuming a mixed effects model, the analog to the ANOVA and bivariate meta-regression frameworks were used to examine potential moderating variables related to study, participant, and intervention characteristics. RESULTSThe meta-analytic findings demonstrated a significant overall positive and moderate mean effect of interventions on attendance outcomes. The mean effect size for interventions examined in the included RCT studies was .57 and the mean effect size for the QED studies was .43. No significant differences were observed between the RCT and QED studies in the magnitude of the treatment effect (Qb= .28, p \u3e.05). The mean effect size of interventions examined using an SGPP design was .95. A moderate effect on attendance outcomes is encouraging; however, the overall mean effect size is masked by a large amount of heterogeneity, indicating significant variance in effect sizes between studies. Moderator analyses found no significant differences in mean effects between studies on any moderating variable tested. No differences were found between school-, court-, or community-based programs or between different modalities of programs. The duration of the intervention also did not demonstrate any association with effect size. Collaborative programs and multimodal interventions produced statistically similar effects on attendance as non-collaborative and single-modality programs, which runs counter to the prevailing beliefs and recommendations for best practices in truancy reduction found in the literature.Other significant findings from this study relate to methodological shortcomings, the absence of important variables as well as gaps in the evidence base. These findings include the lack of inclusion of minority students and a lack of reporting and statistical analysis of demographic variables, particularly race/ethnicity and socioeconomic status (SES). Given that race and SES have been linked to absenteeism, the absence of this data was surprising. The majority of studies also lacked adequate descriptions of the interventions, making replication of the intervention difficult, and failed to measure and report long-term outcomes. AUTHORS’ CONCLUSIONSOverall, the findings from this study suggest that chronic truant students benefit from interventions targeting attendance behaviors; thus it is important and worthwhile to intervene with chronic truant youth. Given the minimal differences in effects across program types and modalities, no one program type or modality stands out as being more effective than any other. Although no statistically significant differences in effects were found between types and modalities of interventions included in this review, there was a lack of available evidence to support the general belief (and popular “best-practice” recommendations) that collaborative and multimodal interventions are more effective than programs that are not collaborative and single modal interventions. Due to the small sample size and large heterogeneity between studies and within groups of studies, caution must be used when interpreting and applying the findings from this meta-analysis. Overall, the studies included in the review improved attendance by an average of 4.69 days, almost a full school week. However, although the interventions included in this study were, overall, found to be effective, the mean rates of absenteeism at posttest in most studies remained above acceptable levels. This finding indicates the need for additional work and research. Developing more effective interventions and policies as well as studying outcomes of interventions, particularly with vulnerable and at-risk populations, is crucial to combating absenteeism. The gaps and deficiencies identified in this study also affirm the need for increasing and strengthening the evidence base on which current policies and practices rest. Although additional outcome research is necessary, more of the same is not sufficient. Significant improvements in the quality of truancy intervention research are required and identified gaps need to be addressed. Recommendations to improve the quality and fill gaps in truancy intervention research are discussed here. In addition, given the significant and pervasive deficiencies in the extant research, a critical analysis of the practices, assumptions, and sociopolitical contexts underlying truancy intervention research seems warranted

An energy balance model for paleoclimate transitions

A new energy balance model (EBM) is presented and is used to study paleoclimate transitions. While most previous EBMs only dealt with the globally averaged climate, this new EBM has three variants: Arctic, Antarctic and tropical climates. The EBM incorporates the greenhouse warming effects of both carbon dioxide and water vapour, and also includes ice–albedo feedback and evapotranspiration. The main conclusion to be inferred from this EBM is that the climate system may possess multiple equilibrium states, both warm and frozen, which coexist mathematically. While the actual climate can exist in only one of these states at any given time, the EBM suggests that climate can undergo transitions between the states via mathematical saddle-node bifurcations. This paper proposes that such bifurcations have actually occurred in Paleoclimate transitions. The EBM is applied to the study of the Pliocene paradox, the glaciation of Antarctica and the so-called warm, equable climate problem of both the mid-Cretaceous Period and the Eocene Epoch. In all cases, the EBM is in qualitative agreement with the geological record.</p