5,472 research outputs found
Small and meso-scale properties of a substorm onset auroral arc
No full textInternational audienceWe present small and meso-scale properties of a substorm onset arc observed simultaneously by the Reimei and THEMIS satellites together with ground-based observations by the THEMIS GBO system. The optical observations revealed the slow equatorward motion of the growth-phase arc and the development of a much brighter onset arc poleward of it. Both arcs showed the typical particle signature of electrostatic acceleration in an inverted-V structure together with a strong Alfvén wave acceleration signature at the poleward edge of the onset arc. Two THEMIS spacecraft encountered earthward flow bursts around the times the expanding optical aurora reached their magnetic footprints in the ionosphere. The particle and field measurements allowed for the reconstruction of the field-aligned current system and the determination of plasma properties in the auroral source region. Auroral arc properties were extracted from the optical and particle measurements and were used to compare measured values to theoretical predictions of the electrodynamic model for the generation of auroral arcs. Good agreement could be reached for the meso-scale arc properties. A qualitative analysis of the internal structuring of the bright onset arc suggests the operation of the tearing instability which provides a 'rope-like' appearance due to advection of the current in the sheared flow across the arc. We also note that for the observed parameters ionospheric conductivity gradients due to electron precipitation will be unstable to the feedback instability in the ionospheric Alfvén resonator that can drive structuring in luminosity over the range of scales observed
Protein recognition of ammonium cations using side-chain aromatics: a structural variation for secondary ammonium ligands.
No full textNon-linear relationship between maternal work hours and child body weight: Evidence from the Western Australian Pregnancy Cohort (Raine) Study
Full text linkUsing longitudinal data from the Western Australia Pregnancy Cohort (Raine) Study and both random-effects and fixed-effects models, this study examined the connection between maternal work hours and child overweight or obesity. Following children in two-parent families from early childhood to early adolescence, multivariate analyses revealed a non-linear and developmentally dynamic relationship. Among preschool children (ages 2 to 5), we found lower likelihood of child overweight and obesity when mothers worked 24 h or less per week, compared to when mothers worked 35 or more hours. This effect was stronger in low-to-medium income families. For older children (ages 8 to 14), compared to working 35–40 h a week, working shorter hours (1–24, 25–34) or longer hours (41 or more) was both associated with increases in child overweight and obesity. These non-linear effects were more pronounced in low-to-medium income families, particularly when fathers also worked long hours.We acknowledge the University of Western Australia (UWA), the Raine Medical Research Foundation, the UWA Faculty of Medicine, Dentistry and Health Sciences, the Women’s and Infant’s Research Foundation (KEMH), Curtin University and Edith Cowan University for providing funding for the Core Management of the Raine Study. Lyndall Strazdins is supported by an Australian Research Council Future Fellowship FT110100686, and this paper was part of a visiting fellowship supported by WZB Berlin Social Science Center (Wissenschaftszentrum Berlin für Sozialforschung)
A series-parallel load-resonant converter for a controlled-current arc-welding power supply
Full text linkA power supply incorporating a series-parallel load-resonant converter, capable of very
efficient operation over a wide range of output power is presented. The series-parallel
load-resonant converter is shown to have three pairs of resonant frequencies.
Operation of the circuit at each of these resonant frequencies maintains zero current
switching and high frequency operation. Design mathematics is developed which
allow series-parallel load-resonant converters to be designed with specific resonant
frequencies and circuit resistances. A new method of power control for series-parallel
load-resonant converters is presented; the power delivered to the circuit and hence the
load is shown to var substantially depending on which resonant frequency the circuit
is excited at. Two series-parallel load-resonant converters are designed simulated,
constructed and tested. There is good agreement between the simulation and
experimental results. One of the circuits produces an output current of 200 A while
the second demonstrates the new power control technique pulsing between 55 A and
145 A while running at frequencies of 63 kHz and 100 kHz. The new power supply
is particularly suited to arc-welding. It contains an active rectifier and draws near
unity power factor
Soluble tau species, not neurofibrillary aggregates, disrupt neural system integration in a tau transgenic model
Full text linkNeurofibrillary tangles are a feature of Alzheimer disease and other tauopathies, and although they are generally believed to be markers of neuronal pathology, there is little evidence evaluating whether tangles directly impact neuronal function. To investigate the response of cells in hippocampal circuits to complex behavioral stimuli, we used an environmental enrichment paradigm to induce expression of an immediate-early gene, Arc, in the rTg4510 mouse model of tauopathy. These mice reversibly overexpress P301L tau and exhibit substantial neurofibrillary tangle deposition, neuronal loss, and memory deficits. Using fluorescent in situ hybridization to detect Arc messenger RNA, we found that rTg4510 mice have impaired hippocampal Arc expression both without stimulation and in response to environmental enrichment; this likely reflects the combination of functional impairments of existing neurons and loss of neurons. However, tangle-bearing cells were at least as likely as non-tangle-bearing neurons to exhibit Arc expression in response to enrichment. Transgene suppression with doxycycline for 6 weeks resulted in increased percentages of Arc-positive cells in rTg4510 brains compared with untreated transgenics, restoring enrichment-induced Arc messenger RNA levels to that of wild-type controls despite the continued presence of neurofibrillary pathology. We interpret these data to indicate that soluble tau contributes to impairment of hippocampal function, although tangles do not preclude neurons from responding in a functional circuit
Arc Root Attachment on the Anode Surface of Arc Plasma Torch Observed with a Novel Method
No full textThe arc-root attachment on the anode surface of a dc non-transferred arc plasma torch has been successfully observed using a novel approach. A specially designed copper mirror with a boron nitride film coated on its surface central-region is employed to avoid the effect of intensive light emitted from the arc column upon the observation of weakly luminous arc root. It is found that the arc-root attachment is diffusive on the anode surface of the argon plasma torch, while constricted arc roots often occur when hydrogen or nitrogen is added into argon as the plasma-forming gas
Numerical-simulation of ac plasma-arc thermodynamics
No full textA mathematical model and approximate analysis for the energy distribution of an ac plasma arc with a moving boundary is developed. A simplified electrical conductivity function is assumed so that the dynamic behavior of the arc may be determined, independent of the gas type. The model leads to a reduced set of non-linear partial differential equations which governs the quasi-steady ac arc. This system is solved numerically and it is found that convection plays an important role, not only in the temperature distribution, but also in arc disruptions. Moreover, disruptions are found to be influenced by convection only for a limited frequency range. The results of the present studies are applicable to the frequency range of 10-10(2) Hz which includes most industry ac arc frequencies. (C) 1994 Academic Press, Inc
Increased power density plasma arc welding: The effect of an added radial gas flow around the arc root
No full textAdditional constriction of the arc in plasma arc welding has been investigated. By additionally constricting the arc, the power density at the work piece can be increased. If successful, it is hoped that this increase will approach values achieved in laser beam welding at a fraction of the costs of the latter. A survey of the available literature on plasma arc welding was made. An experimental torch incorporating facilities for additional constriction was custom-designed and built. Experiments with an arc on a non-melting anode were carried out to assess the functioning of the experimental torch, explore the possibility of additional arc constriction and assess some of the changes to the arc as a result. Subsequently, preliminary keyhole welding trials were executed to determine the performance of the experimental torch under welding conditions and to obtain a first indication of the effect of additional arc constriction on a keyhole weld. Additional constriction of the arc in plasma arc welding has been proven to be possible. The power density was increased by a factor of two. Weld narrowing due to additional arc constriction was observed.Technische MateriaalwetenschappenMechanical, Maritime and Materials Engineerin
Characteristics of Gliding Arc Discharge Plasma
Full text linkA gliding arc discharge plasma and its characteristics are described. Analysis on the production principle of the plasma is presented. Some experimental results about two novel types of the gliding arc plasma generator were obtained. These types of gliding arc plasma are potentially used in chemical industry and environment engineering
The monocot fossil pollen record of New Zealand and its implications for palaeoclimates and environments
No full textPublished online: 19 May 2015Cretaceous;Eocene;Miocene;palaeoecology;palaeoenvironment;palynology The record of fossil monocotyledonous pollen in New Zealand is summarized and discussed in terms of age and palaeoecological implications. The fossil monocot pollen record covers reports of taxa variously ranging from the Palaeogene to the present, with diverse groups represented, including Alstroemeriaceae: Luzuriagoideae (Luzuriaga), Amaryllidaceae (aff. Hymenocallis?), Arecaceae (including Nypa and aff. Metroxylon), Asparagaceae: Lomandroideae (Arthropodium, Cordyline), Asteliaceae (Astelia and Collospermum), Cyperaceae, Anarthriaceae (including Hopkinsiaceae and Lyginiaceae) or Flagellariaceae?, Orchidaceae, Pandanaceae, Poaceae, Restionaceae (aff. Empodisma), Ripogonaceae (Ripogonum), Typhaceae (Typha and Sparganium) and Asphodelaceae (= Xanthorrhoeaceae): Hemerocallidoideae (Dianella and Phormium). There are also monosulcate and reticulate lilioid and echinate and gemmate arecoid palynomorphs known from the Late Cretaceous. The possible biogeographical and palaeoecological implications of these records, especially for tropical or subtropical taxa occurring at mid to high southern latitudes, are also discussed. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 00, 000–000.John G. Conran, Dallas C. Mildenhall, J. Ian Raine, Elizabeth M. Kennedy and Daphne E. Le
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