7,396 research outputs found
Direct Use of Low Enthalpy Deep Geothermal Resources in the East African Rift Valley
Geothermal energy is already harnessed across East Africa to provide hundreds of megawatts of electricity, with significant plans for future expansion towards generation at the gigawatt scale. This power generation utilizes the high steam temperatures (typically more than 200 °C) that are available in several locations in Kenya, Ethiopia and elsewhere. The presence of these high enthalpy resources has deflected attention from the often attractive low and medium enthalpy resources present across a more extensive portion of the region. Geothermally heated water at cooler temperatures (less than 90 °C) could be widely produced by drilling shallower and cheaper boreholes than those required for power production. This low enthalpy resource could be widely exploitable throughout the Rift Valley, offering a low carbon, sustainable, reliable and commercially competitive source of heating, drying and cooling (via absorption chillers) to local farmers and growers, and for low temperature commercial and industrial uses. Applications of this type would displace expensive fossil fuels, reducing costs and carbon emissions as well as improving the region’s energy and food security. The power input for pump systems can be accommodated by relatively small generators, so direct heat projects could be beneficial to consumers in areas with no grid access
Surveying structural complexity in quantum many-body systems
Quantum many-body systems exhibit a rich and diverse range of exotic
behaviours, owing to their underlying non-classical structure. These systems
present a deep structure beyond those that can be captured by measures of
correlation and entanglement alone. Using tools from complexity science, we
characterise such structure. We investigate the structural complexities that
can be found within the patterns that manifest from the observational data of
these systems. In particular, using two prototypical quantum many-body systems
as test cases - the one-dimensional quantum Ising and Bose-Hubbard models - we
explore how different information-theoretic measures of complexity are able to
identify different features of such patterns. This work furthers the
understanding of fully-quantum notions of structure and complexity in quantum
systems and dynamics.Comment: 9 pages, 5 figure
Memory-efficient tracking of complex temporal and symbolic dynamics with quantum simulators
Tracking the behaviour of stochastic systems is a crucial task in the
statistical sciences. It has recently been shown that quantum models can
faithfully simulate such processes whilst retaining less information about the
past behaviour of the system than the optimal classical models. We extend these
results to general temporal and symbolic dynamics. Our systematic protocol for
quantum model construction relies only on an elementary description of the
dynamics of the process. This circumvents restrictions on corresponding
classical construction protocols, and allows for a broader range of processes
to be modelled efficiently. We illustrate our method with an example exhibiting
an apparent unbounded memory advantage of the quantum model compared to its
optimal classical counterpart.Comment: 15 pages, 5 figure
Quantifying the Origin and Distribution of Intracluster Light in a Fornax-like Cluster
Using a cosmological -body simulation, we investigate the origin and
distribution of stars in the intracluster light (ICL) of a Fornax-like cluster.
In a dark matter only simulation we identify a halo which, at , has and , and replace infalling
subhalos with models that include spheroid and disc components. As they fall
into the cluster, the stars in some of these galaxies are stripped from their
hosts, and form the ICL. We consider the separate contributions to the ICL from
stars which originate in the haloes and the discs of the galaxies. We find that
disc ICL stars are more centrally concentrated than halo ICL stars. The
majority of the disc ICL stars are associated with one initially disc-dominated
galaxy that falls to the centre of the cluster and is heavily disrupted,
producing part of the cD galaxy. At radial distances greater than 200kpc, well
beyond the stellar envelope of the cD galaxy, stars formerly from the stellar
haloes of galaxies dominate the ICL. Therefore at large distances, the ICL
population is dominated by older stars.Comment: Paper published as MNRAS , 2017, 467, 4501 This version corrects a
small typo in the authors fiel
Social networking site use in young adolescents: association with health-related quality of life and behavioural difficulties
Despite Social Networking Sites (SNS) having a minimum age of 13, younger adolescents are using them. In this study, we examine self-reported overall SNS use and SNS use if awake at night in relation to Health-Related Quality of Life (HRQOL, measured by KIDSCREEN-10) and behaviour (measured by Strengths and Difficulties Questionnaire, SDQ) in 5229 adolescents aged 11–12 in the Study of Cognition, Adolescents and Mobile Phones (SCAMP) cohort. Two-thirds of the study population used SNS. Weekday and weekend SNS use on mobile phones and other devices was significantly associated with lower HRQOL in females (all p-values for linear trend < 0.01) but not males. Using SNS if awake at night was also significantly associated with lower HRQOL in females (adjusted β-coefficient - 2.20 (95% CI - 3.18, - 1.22)). Higher SNS use on mobile phones and other devices was associated with increased behavioural difficulties in both genders (p-value for trend < 0.001). Similarly, SNS use if awake at night was associated with greater behavioural difficulties (adjusted β-coefficient 2.54 (95% CI 2.09, 2.98)). We recommend further longitudinal research in this area in order have a better understanding of the direction of relationships between SNS and wellbeing and behaviour in adolescents
Direct Use of Low Enthalpy Deep Geothermal Resources in the East African Rift Valley
Geothermal energy is already harnessed across East Africa to provide hundreds of megawatts of electricity, with significant plans for future expansion towards generation at the gigawatt scale. This power generation utilizes the high steam temperatures (typically more than 200 °C) that are available in several locations in Kenya, Ethiopia and elsewhere. The presence of these high enthalpy resources has deflected attention from the often attractive low and medium enthalpy resources present across a more extensive portion of the region. Geothermally heated water at cooler temperatures (less than 90 °C) could be widely produced by drilling shallower and cheaper boreholes than those required for power production. This low enthalpy resource could be widely exploitable throughout the Rift Valley, offering a low carbon, sustainable, reliable and commercially competitive source of heating, drying and cooling (via absorption chillers) to local farmers and growers, and for low temperature commercial and industrial uses. Applications of this type would displace expensive fossil fuels, reducing costs and carbon emissions as well as improving the region’s energy and food security. The power input for pump systems can be accommodated by relatively small generators, so direct heat projects could be beneficial to consumers in areas with no grid access
The effects of oral contraceptives on exercise performance in women: a systematic review and meta-analysis
Background: Oral contraceptive pills (OCPs) are double agents, which downregulate endogenous concentrations of oestradiol and progesterone whilst simultaneously providing daily supplementation of exogenous oestrogen and progestin during the OCP-taking days. This altered hormonal milieu differs significantly from that of eumenorrheic women and might impact exercise performance, due to changes in ovarian hormone-mediated physiological processes.
Objective: To explore the effects of OCPs on exercise performance in women and to provide evidence-based performance recommendations to users.
Methods: This review complied with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A between-group analysis was performed, wherein performance of OCP users was compared with naturally menstruating women, and a within-group analysis was conducted, wherein performance during OCP consumption was compared with OCP withdrawal. For the between-group analysis, women were phase matched in two ways: (1) OCP withdrawal versus the early follicular phase of the menstrual cycle and (2) OCP consumption versus all phases of the menstrual cycle except for the early follicular phase. Study quality was assessed using a modified Downs and Black Checklist and a strategy based on the recommendations of the Grading of Recommendations Assessment Development and Evaluation working group. All meta-analyses were conducted within a Bayesian framework to facilitate probabilistic interpretations.
Results: 42 studies and 590 participants were included. Most studies (83%) were graded as moderate, low or very low quality, with 17% achieving high quality. For the between-group meta-analysis comparing OCP users with naturally menstruating women, posterior estimates of the pooled effect were used to calculate the probability of at least a small effect (d ≥ 0.2). Across the two between-group comparison methods, the probability of a small effect on performance favouring habitual OCP users was effectually zero (p < 0.001). In contrast, the probability of a small effect on performance favouring naturally menstruating women was moderate under comparison method (1) (d ≥ 0.2; p = 0.40) and small under comparison method (2) (d ≥ 0.2; p = 0.19). Relatively large between-study variance was identified for both between-group comparisons (0.5 = 0.16 [95% credible interval (CrI) 0.01-0.44] and 0.5 = 0.22 [95% CrI 0.06-0.45]). For the within-group analysis comparing OCP consumption with withdrawal, posterior estimates of the pooled effect size identified almost zero probability of a small effect on performance in either direction (d ≥ 0.2; p ≤ 0.001).
Conclusions: OCP use might result in slightly inferior exercise performance on average when compared to naturally menstruating women, although any group-level effect is most likely to be trivial. Practically, as effects tended to be trivial and variable across studies, the current evidence does not warrant general guidance on OCP use compared with non-use. Therefore, when exercise performance is a priority, an individualised approach might be more appropriate. The analysis also indicated that exercise performance was consistent across the OCP cycle
Horava-Lifshitz gravity: a status report
This is intended to be a brief introduction and overview of Horava-Lifshitz
gravity. The motivation and all of the various version of the theory (to date)
are presented. The dynamics of the theory are discussed in some detail, with a
focus on low energy viability and consistency, as these have been the issues
that attracted most of the attention in the literature so far. Other properties
of the theory and developments within its framework are also covered, such as:
its relation to Einstein-aether theory, cosmology, and future perspectives.Comment: 17 pages, no figures, based on talk given at the 14th Conference on
Recent Developments in Gravity (NEBXIV), Ioannina, Greece, 8-11 Jun 2010; v2:
minor changes to match published version, references adde
Evolving surface finite element method for the Cahn-Hilliard equation
We use the evolving surface finite element method to solve a Cahn- Hilliard equation on an evolving surface with prescribed velocity. We start by deriving the equation using a conservation law and appropriate transport for- mulae and provide the necessary functional analytic setting. The finite element method relies on evolving an initial triangulation by moving the nodes according to the prescribed velocity. We go on to show a rigorous well-posedness result for the continuous equations by showing convergence, along a subse- quence, of the finite element scheme. We conclude the paper by deriving error estimates and present various numerical examples
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