Erratum to: Melts of garnet lherzolite: experiments,models and comparison to melts of pyroxenite and carbonated lherzolite     

Timothy?L.?GroveEmail author  Eva?S.?Holbig  Jay?A.?Barr  Christy?B.?Till  Michael?J.?Krawczynski 《Contributions to Mineralogy and Petrology》2014,168(6):1086

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The 40 cm Monitoring Telescope of the Universitätssternwarte Bochum     

M. Ramolla  H. Drass  R. Lemke  C. Westhues  F. Pozo Nuez  A. Barr Dominguez  M. Haas  R. Chini  M. Murphy 《Astronomische Nachrichten》2013,334(10):1115-1120

The new 40cm Bochum Monitoring Telescope (BMT) has started routine operation at the Universitätssternwarte Bochum (USB), located near Cerro Armazones in Chile. It has a 41′ × 27′ field of view (FoV) and is equipped with B and V broad band filters and three narrow band filters at 670, 680, and 690 nm. This makes the BMT ideally suited to perform photometric reverberation mapping of the Hα emission line of active galactic nuclei, where the line is redshifted into the narrow bands, and to monitor bright stars which would be saturated with large telescopes. As a complement to our Robotic Bochum Twin Telescope (RoBoTT) with 2°.7 FoV and 14 filters, the BMT is an efficient instrument to accurately study the variability of individual sources, provided that its smaller FoV covers a sufficient number of suitable comparison stars. Here we describe the telescope and its fully robotic operation, and present science verification data demonstrating the performance of the BMT. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

3D Numerical Simulations of <Emphasis Type="Italic">f</Emphasis>-Mode Propagation Through Magnetic Flux Tubes     

K. Daiffallah  T. Abdelatif  A. Bendib  R. Cameron  L. Gizon 《Solar physics》2011,268(2):309-320

Three-dimensional numerical simulations have been used to study the scattering of a surface-gravity wave packet by vertical magnetic-flux tubes, with radii from 200 km to 3 Mm, embedded in stratified polytropic atmosphere. The scattered wave has been found to consist primarily of m=0 (axisymmetric) and m=1 modes. The ratio of the amplitude of these two modes was found to be strongly dependent on the radius of the flux tube. The kink mode is the dominant mode excited in tubes with a small radius, while the sausage mode is dominant for large tubes. Simulations of this type provide a simple, efficient, and robust way to start to understand the seismic signature of flux tubes, which have recently begun to be observed.  相似文献   

Constructing Semi-Empirical Sunspot Models for Helioseismology     

R. H. Cameron  L. Gizon  H. Schunker  A. Pietarila 《Solar physics》2011,268(2):293-308

One goal of helioseismology is to determine the subsurface structure of sunspots. In order to do so, it is important to understand first the near-surface effects of sunspots on solar waves, which are dominant. Here we construct simplified, cylindrically-symmetric sunspot models that are designed to capture the magnetic and thermodynamics effects coming from about 500 km below the quiet-Sun τ ₅₀₀₀=1 level to the lower chromosphere. We use a combination of existing semi-empirical models of sunspot thermodynamic structure (density, temperature, pressure): the umbral model of Maltby et al. (1986, Astrophys. J. 306, 284) and the penumbral model of Ding and Fang (1989, Astron. Astrophys. 225, 204). The OPAL equation-of-state tables are used to derive the sound-speed profile. We smoothly merge the near-surface properties to the quiet-Sun values about 1 Mm below the surface. The umbral and penumbral radii are free parameters. The magnetic field is added to the thermodynamic structure, without requiring magnetostatic equilibrium. The vertical component of the magnetic field is assumed to have a Gaussian horizontal profile, with a maximum surface field strength fixed by surface observations. The full magnetic-field vector is solenoidal and determined by the on-axis vertical field, which, at the surface, is chosen such that the field inclination is 45° at the umbral – penumbral boundary. We construct a particular sunspot model based on SOHO/MDI observations of the sunspot in active region NOAA 9787. The helioseismic signature of the model sunspot is studied using numerical simulations of the propagation of f, p ₁, and p ₂ wave packets. These simulations are compared against cross-covariances of the observed wave field. We find that the sunspot model gives a helioseismic signature that is similar to the observations.  相似文献   

Constructing and Characterising Solar Structure Models for Computational Helioseismology     

H. Schunker  R. H. Cameron  L. Gizon  H. Moradi 《Solar physics》2011,271(1-2):1-26

In local helioseismology, numerical simulations of wave propagation are useful to model the interaction of solar waves with perturbations to a background solar model. However, the solution to the linearised equations of motion include convective modes that can swamp the helioseismic waves that we are interested in. In this article, we construct background solar models that are stable against convection, by modifying the vertical pressure gradient of Model S (Christensen-Dalsgaard et al., 1996, Science 272, 1286) relinquishing hydrostatic equilibrium. However, the stabilisation affects the eigenmodes that we wish to remain as close to Model S as possible. In a bid to recover the Model S eigenmodes, we choose to make additional corrections to the sound speed of Model S before stabilisation. No stabilised model can be perfectly solar-like, so we present three stabilised models with slightly different eigenmodes. The models are appropriate to study the f and p ₁ to p ₄ modes with spherical harmonic degrees in the range from 400 to 900. Background model CSM has a modified pressure gradient for stabilisation and has eigenfrequencies within 2% of Model S. Model CSM_A has an additional 10% increase in sound speed in the top 1 Mm resulting in eigenfrequencies within 2% of Model S and eigenfunctions that are, in comparison with CSM, closest to those of Model S. Model CSM_B has a 3% decrease in sound speed in the top 5 Mm resulting in eigenfrequencies within 1% of Model S and eigenfunctions that are only marginally adversely affected. These models are useful to study the interaction of solar waves with embedded three-dimensional heterogeneities, such as convective flows and model sunspots. We have also calculated the response of the stabilised models to excitation by random near-surface sources, using simulations of the propagation of linear waves. We find that the simulated power spectra of wave motion are in good agreement with an observed SOHO/MDI power spectrum. Overall, our convectively stabilised background models provide a good basis for quantitative numerical local helioseismology. The models are available for download from http://www.mps.mpg.de/projects/seismo/NA4/ .  相似文献   

RATES OF SEA LEVEL RISE FOR SOUTHERN NEW ENGLAND: A SPACE-TIME CONCEPT     

J. Richard Jones  Barry Cameron 《自然地理学》2013,34(1):46-52

An application of trend surface analysis is presented within a space-time framework to predict the rates of sea-level rise for the southern New England coastal region since 10,000 years B.P. Based on the predicted second order trend surface, 65% of the variance is explained and is significant at the 0.01 level. The results of the analysis also indicate those local areas that have experienced the largest amount of spatial and temporal variation from the regional mean rate of rise since 10,000 years B.P.  相似文献   

Near real-time geoprocessing on the grid: A scalable approach to road traffic monitoring     

Aengus McCullough  Philip James  Stuart Barr 《International journal of geographical information science》2013,27(10):1939-1957

The geospatial sensor web is set to revolutionise real-time geospatial applications by making up-to-date spatially and temporally referenced data relating to real-world phenomena ubiquitously available. The uptake of sensor web technologies is largely being driven by the recent introduction of the OpenGIS Sensor Web Enablement framework, a standardisation initiative that defines a set of web service interfaces and encodings to task and query geospatial sensors in near real time. However, live geospatial sensors are capable of producing vast quantities of data over a short time period, which presents a large, fluctuating and ongoing processing requirement that is difficult to adequately provide with the necessary computational resources. Grid computing appears to offer a promising solution to this problem but its usage thus far has primarily been restricted to processing static as opposed to real-time data sets. A new approach is presented in this work whereby geospatial data streams are processed on grid computing resources. This is achieved by submitting ongoing processing jobs to the grid that continually poll sensor data repositories using relevant OpenGIS standards. To evaluate this approach a road-traffic monitoring application was developed to process streams of GPS observations from a fleet of vehicles. Specifically, a Bayesian map-matching algorithm is performed that matches each GPS observation to a link on the road network. The results show that over 90% of observations were matched correctly and that the adopted approach is capable of achieving timely results for a linear time geoprocessing operation performed every 60 seconds. However, testing in a production grid environment highlighted some scalability and efficiency problems. Open Geospatial Consortium (OGC) data services were found to present an IO bottleneck and the adopted job submission method was found to be inefficient. Consequently, a number of recommendations are made regarding the grid job-scheduling mechanism, shortcomings in the OGC Web Processing Service specification and IO bottlenecks in OGC data services.  相似文献   

Differential rotation on both components of the pre-main-sequence binary system HD 155555     

N. J. Dunstone  G. A. J. Hussain  A. Collier Cameron  S. C. Marsden  M. Jardine  J. R. Barnes  J. C. Ramirez Velez  J.-F. Donati 《Monthly notices of the Royal Astronomical Society》2008,387(4):1525-1536

We present the first measurements of surface differential rotation on a pre-main-sequence binary system. Using intensity (Stokes I) and circularly polarized (Stokes V) time-series spectra, taken over 11 nights at the Anglo-Australian Telescope (AAT), we incorporate a solar-like differential rotation law into the surface imaging process. We find that both components of the young, 18 Myr, HD 155555 (V824 Ara, G5IV + K0IV) binary system show significant differential rotation. The equator–pole lap times as determined from the intensity spectra are 80 d for the primary star and 163 d for the secondary. Similarly, for the magnetic spectra we obtain equator–pole lap times of 44 and 71 d, respectively, showing that the shearing time-scale of magnetic regions is approximately half of that found for stellar spots. Both components are therefore found to have rates of differential rotation similar to those of the same spectral-type main-sequence single stars. The results for HD 155555 are therefore in contrast to those found in other, more evolved, binary systems where negligible or weak differential rotation has been discovered. We discuss two possible explanations for this: first that at the age of HD 155555 binary tidal forces have not yet had time to suppress differential rotation and secondly that the weak differential rotation previously observed on evolved binaries is a consequence of their large convection zone depths. We suggest that the latter is the more likely solution and show that both temperature and convection zone depth (from evolutionary models) are good predictors of differential rotation strength. Finally, we also examine the possible consequences of the measured differential rotation on the interaction of binary star coronae.  相似文献   

Helioseismology of Sunspots: Confronting Observations with Three-Dimensional MHD Simulations of Wave Propagation     

R. Cameron  L. Gizon  T. L. Jr. Duvall 《Solar physics》2008,251(1-2):291-308

The propagation of solar waves through the sunspot of AR?9787 is observed by using temporal cross-correlations of SOHO/MDI Dopplergrams. We then use three-dimensional MHD numerical simulations to compute the propagation of wave packets through self-similar magnetohydrostatic sunspot models. The simulations are set up in such a way as to allow a comparison with observed cross-covariances (except in the immediate vicinity of the sunspot). We find that the simulation and the f-mode observations are in good agreement when the model sunspot has a peak field strength of 3 kG at the photosphere and less so for lower field strengths. Constraining the sunspot model with helioseismology is only possible because the direct effect of the magnetic field on the waves has been fully taken into account. Our work shows that the full-waveform modeling of sunspots is feasible.  相似文献   

Wind‐wave development across a large shallow intertidal estuary: A case study of Manukau Harbour,New Zealand     

Murray J. Smith  Craig L. Stevens  Richard M. Gorman  John A. McGregor  Cameron G. Neilson 《新西兰海洋与淡水研究杂志》2013,47(5):985-1000

Locally generated wind‐waves in estuaries play an important role in the sediment dynamics and the transport of biota. Wave growth in estuaries is complicated by tidally varying depth, fetch, and currents. Wave development was studied at six sites along a transect across Manukau Harbour, New Zealand, which is a large intertidal estuary with a tidal range of up to 4 m. Three meteorological masts were also deployed across the measurement transect to measure wave forcing by the wind. A spatial variation in wind speed by up to a factor of 2 was observed which has a significant effect on wave development at short fetches. The wind variation can be explained by the extreme change in surface roughness at the upwind land‐water boundary. The tidally varying depth results in non‐stationary wave development. At the long fetch sites wave development is dictated by the tidally varying depth with peak frequencies continuing to decrease after high water, whereas wave height is attenuated by bottom friction. The non‐dimensional energy and peak frequency parameters commonly used to describe wave growth, clearly exhibit depth limiting effects, but with wider scatter than in previous studies in simpler environments. The peak frequency predictions of Young & Verhagen (1996a) fit our data well. However, the wide variability of energy limits the usefulness of standard growth prediction curves in such situations, and highlights the requirement for a validated, shallow‐water numerical model.  相似文献