Hydrogen/nitrogen/oxygen defect complexes in silicon from computational searches

Point defect complexes in crystalline silicon composed of hydrogen, nitrogen, and oxygen atoms are studied within density-functional theory (DFT). Ab initio Random Structure Searching (AIRSS) is used to find low-energy defect structures. We find new lowest-energy structures for several defects: the triple-oxygen defect, {3O}, triple oxygen with a nitrogen atom, {N, 3O}, triple nitrogen with an oxygen atom, {3N,O}, double hydrogen and an oxygen atom, {2H,O}, double hydrogen and oxygen atoms, {2H,2O} and four hydrogen/nitrogen/oxygen complexes, {H,N,O}, {2H,N,O}, {H,2N,O} and {H,N,2O}. We find that some defects form analogous structures when an oxygen atom is replaced by a NH group, for example, {H,N,2O} and {3O}, and {H,N} and {O}. We compare defect formation energies obtained using different oxygen chemical potentials and investigate the relative abundances of the defects.Comment: 9 pages, 13 figure

An analysis of two variable rational approximants

AbstractWe present two determinants whose ratio is the Hughes Jones approximant to a power series in two variables. They are generalizations of Jacobi's determinants for Padé approximants. They are useful in certain circumstances when the defining equations are degenerate. We analyze the indeterminacies associated with degenerate approximants, at least one of which is quite different in nature from the degeneracies of the single variable Padé approximants. We are led to suggest a modification of the symmetrizing equations which leads to numerical stability

Anomaly Detection in Paleoclimate Records using Permutation Entropy

Permutation entropy techniques can be useful in identifying anomalies in paleoclimate data records, including noise, outliers, and post-processing issues. We demonstrate this using weighted and unweighted permutation entropy of water-isotope records in a deep polar ice core. In one region of these isotope records, our previous calculations revealed an abrupt change in the complexity of the traces: specifically, in the amount of new information that appeared at every time step. We conjectured that this effect was due to noise introduced by an older laboratory instrument. In this paper, we validate that conjecture by re-analyzing a section of the ice core using a more-advanced version of the laboratory instrument. The anomalous noise levels are absent from the permutation entropy traces of the new data. In other sections of the core, we show that permutation entropy techniques can be used to identify anomalies in the raw data that are not associated with climatic or glaciological processes, but rather effects occurring during field work, laboratory analysis, or data post-processing. These examples make it clear that permutation entropy is a useful forensic tool for identifying sections of data that require targeted re-analysis---and can even be useful in guiding that analysis.Comment: 15 pages, 7 figure

An Assessment of the Mathematics Information Processing Scale: A Potential Instrument for Extending Technology Education Research

Many argue that the United States is falling behind other countries in technology innovation. Some attribute this situation to ineffective education in the areas of math, science, and technology. Research using affective measures has provided evidence of links between student attitudes in math and technology education. With the aim of extending the research, this study examines the psychometric properties of the Mathematics Information Processing Scale1 (MIPS). The MIPS uses both cognitive and affective measures to explore various dimensions of students’ approaches to learning statistics and mathematics. The original study used exploratory factor analysis, while this study uses confirmatory factor analysis to revise the MIPS instrument. By combining both cognitive and affective measures in a single instrument, the MIPS offers the potential to contribute new research knowledge toward the goal of improving math and technology education

Effect of work:rest ratio on cycling performance following sprint interval training: A randomised control trial

Sprint interval training (SIT) has been shown to improve performance measures in a range of individuals, and it is understood that different responses can be elicited from different training protocols. However, consideration of changes in work: rest ratios could offer important insight into optimising training programmes. The purpose of this study was to investigate the effect of three different work: rest ratios on exercise performance. Thirty-six male and female participants were randomly allocated to one of three training groups, or a non-training control group. Training consisted of 10x6 second ‘all-out’ sprints on a cycle ergometer, with a 1:8, 1:10 or 1:12 work: rest ratio. Performance data, including peak power output, performance decrement, and 10km time trial performance data were collected before and after 2-weeks of SIT. There were significant (p ≤ 0.05) improvements in all parameters for the training groups, but no changes in the control condition. Peak power increased by 57.2W, 50.7W and 53.7W in the 1:8, 1:10 and 1:12 groups respectively, with no significant differences in response between conditions. Time trial performance improved significantly in all three training conditions (29.4s, 8.7s, and 25.1s in the 1:8, 1:10 and 1:12 groups), while worsening in the control group. All training conditions resulted in significant improvements in performance, but there were no significant differences in improvement for any of the groups. Any of the three stated work: rest ratios would be appropriate for use with athletes and allow some level of personal preference for those interested in using the protocol

Long-term cigarette smoke exposure increases uncoupling protein expression but reduces energy intake

The appetite suppressing effect of tobacco is a major driver of smoking behaviour; however few studies have addressed the effects of chronic cigarette smoke exposure (SE) on appetite, body weight and metabolic markers. We compared the effects of SE to equivalent food restriction (pair-fed, PF), against sham-exposure, on body weight, adiposity, cytokines, and levels of uncoupling proteins (UCP) and brain neuropeptide Y (NPY) in male Balb/C mice. SE rapidly induced anorexia, and after 12 weeks, SE and PF groups were lighter than control animals (23.9 ± 0.2, 25.5 ± 0.5, 26.8 ± 0.4 g respectively, P < 0.05). White fat (WAT) masses were reduced by both SE and PF. Plasma leptin and insulin were reduced in SE mice; insulin was further reduced by PF. Brown fat UCP1 and 3 mRNA were increased in SE animals relative to PF animals, possibly promoting thermogenesis. WAT mRNA expression of the inflammatory cytokine, TNFα was doubled by SE, while IL-6 was reduced by both PF and SE. Hypothalamic NPY content was increased by SE (89.3 ± 2.8 vs. 75.9 ± 2.4 ng control, P < 0.05), and more by PF (100.7 ± 3.4 ng, P < 0.05 compared to both groups), suggesting disinhibition due to reduced adipose derived leptin. In contrast to equivalent food restriction, cigarette smoke exposure reduced body weight and total hypothalamic NPY, and increased thermogenesis and markers of inflammation. The suppressed hypothalamic NPY and increased UCPs may contribute to the spontaneous hypophagia and extra weight loss in SE animals. These findings contribute to our understanding of weight loss in smoking-related lung disease, suggesting a greater impact than that due to anorexia alone. Crown Copyright © 2008

On the Exchange of Kinetic and Magnetic Energy Between Clouds and the Interstellar Medium

We investigate, through 2D MHD numerical simulations, the interaction of a uniform magnetic field oblique to a moving interstellar cloud. In particular we explore the transformation of cloud kinetic energy into magnetic energy as a result of field line stretching. Some previous simulations have emphasized the possible dynamical importance of a ``magnetic shield'' formed around clouds when the magnetic field is perpendicular to the cloud motion (Jones et al. 1996, Miniati et al. 1998). It was not clear, however, how dependent those findings were to the assumed field configuration and cloud properties. To expand our understanding of this effect, we examine several new cases by varing the magnetic field orientation angle with respect to the cloud motion (\theta), the cloud-background density contrast, and the cloud Mach number. We show that in 2D and with \theta large enough, the magnetic field tension can become dominant in the dynamics of the motion of high density contrast, low Mach number clouds. In such cases a significant fraction of cloud kinetic energy can be transformed into magnetic energy with the magnetic pressure at the cloud nose exceeding the ram pressure of the impinging flow. We derive a characteristic timescale for this process of energy ``conversion''. We find also that unless the cloud motion is highly aligned to the magnetic field, reconnection through tearing mode instabilities in the cloud wake limit the formation of a strong flux rope feature following the cloud. Finally we attempt to interpret some observational properties of the magnetic field in view of our results.Comment: 24 pages in aaspp4 Latex and 7 figures. Accepted for publication in The Astrophysical Journa