Ionospheric threat simulation for GNSS using the Spirent hardware signal simulator     

Thomas Dautermann  Matteo Sgammini  Sam Pullen 《GPS Solutions》2014,18(3):365-373

Ionospheric disturbances present a considerable hazard to single-frequency satellite navigation systems for airborne users. We discuss our implementation of three ionospheric threat models in the DLR “multi-output advanced signal test environment for receivers” global navigation satellite system simulator, which is based on Spirent GSS 7780/7790 signal generator. These threat models include the standard front-based threat model developed for the integrity assessment of ground-based augmentation systems (GBAS), a simplified plasma bubble model, and ionospheric scintillation, which can be combined with either of the two previously mentioned models. These effects can now straightforwardly be simulated at the German Aerospace Center’s research facilities. As an example, we simulate a GBAS ground facility with code–carrier divergence monitoring, affected by an ionospheric front, and we show the results of a simulation with coincidental occurrence of a plasma bubble and scintillation with an S ₄ index of 0.4.  相似文献   

The oldest evidence for birds in Northern Gondwana? Small tridactyl footprints from the Middle Jurassic of Msemrir (Morocco)     

Matteo Belvedere  Gareth Dyke  Majid Hadri  Shinobu Ishigaki 《Gondwana Research》2011,19(2):542-549

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In situ observation of crystal growth in a basalt melt and the development of crystal size distribution in igneous rocks     

Huaiwei Ni  Hans Keppler  Nicolas Walte  Federica Schiavi  Yang Chen  Matteo Masotta  Zhenjiang Li 《Contributions to Mineralogy and Petrology》2014,167(5):1-13

The speciation of CO₂ in dacite, phonolite, basaltic andesite, and alkali silicate melt was studied by synchrotron infrared spectroscopy in diamond anvil cells to 1,000 °C and more than 200 kbar. Upon compression to 110 kbar at room temperature, a conversion of molecular CO₂ into a metastable carbonate species was observed for dacite and phonolite glass. Upon heating under high pressure, molecular CO₂ re-appeared. Infrared extinction coefficients of both carbonate and molecular CO₂ decrease with temperature. This effect can be quantitatively modeled as the result of a reduced occupancy of the vibrational ground state. In alkali silicate (NBO/t = 0.98) and basaltic andesite (NBO/t = 0.42) melt, only carbonate was detected up to the highest temperatures studied. For dacite (NBO/t = 0.09) and phonolite melts (NBO/t = 0.14), the equilibrium CO₂ + O^2? = CO₃ ^2? in the melt shifts toward CO₂ with increasing temperature, with ln K = ?4.57 (±1.68) + 5.05 (±1.44) 10³ T ^?1 for dacite melt (ΔH = ?42 kJ mol^?1) and ln K = ?6.13 (±2.41) + 7.82 (±2.41) 10³ T ^?1 for phonolite melt (ΔH = ?65 kJ mol^?1), where K is the molar ratio of carbonate over molecular CO₂ and T is temperature in Kelvin. Together with published data from annealing experiments, these results suggest that ΔS and ΔH are linear functions of NBO/t. Based on this relationship, a general model for CO₂ speciation in silicate melts is developed, with ln K = a + b/T, where T is temperature in Kelvin and a = ?2.69 ? 21.38 (NBO/t), b = 1,480 + 38,810 (NBO/t). The model shows that at temperatures around 1,500 °C, even depolymerized melts such as basalt contain appreciable amounts of molecular CO₂, and therefore, the diffusion coefficient of CO₂ is only slightly dependent on composition at such high temperatures. However, at temperatures close to 1,000 °C, the model predicts a much stronger dependence of CO₂ solubility and speciation on melt composition, in accordance with available solubility data.  相似文献   

The Lyman α forest opacity and the metagalactic hydrogen ionization rate at z∼ 2–4     

James S. Bolton  Martin G. Haehnelt  Matteo Viel  Volker Springel 《Monthly notices of the Royal Astronomical Society》2005,357(4):1178-1188

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The properties of the absorbing and line-emitting material in IGR J16318 − 4848     

Giorgio Matt  Matteo Guainazzi 《Monthly notices of the Royal Astronomical Society》2003,341(3):L13-L17

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Robust optimization for ship conceptual design     

Matteo Diez  Daniele Peri 《Ocean Engineering》2010,37(11-12):966-977

The paper presents an approach for the robust optimization of a bulk carrier conceptual design, subject to uncertain operating and environmental conditions. The uncertainties involved in the optimization process are addressed and a general formulation for robust design is given. Specifically, the uncertainties involved in the decision making process are taken into account by means of their probabilistic distributions. The expected values and the standard deviations of the relevant quantities are assessed and included in the optimization objectives, whereas the constraints are evaluated in the worst case. This leads to a robust design able to keep a good performance in the whole probabilistic operating scenario. A particle swarm optimization algorithm is used for the global minimization process, minimizing the expectation and the standard deviation of the unit transportation cost.  相似文献   

Cosmological and astrophysical parameters from the Sloan Digital Sky Survey flux power spectrum and hydrodynamical simulations of the Lyman α forest     

Matteo Viel  Martin G. Haehnelt 《Monthly notices of the Royal Astronomical Society》2006,365(1):231-244

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A unified model for AGN feedback in cosmological simulations of structure formation     

Debora Sijacki  Volker Springel  Tiziana Di Matteo  Lars Hernquist 《Monthly notices of the Royal Astronomical Society》2007,380(3):877-900

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Vertical structure of hyper-accreting disks and consequences for gamma-ray burst outflows     

Elena M. Rossi  Philip J. Armitage  Tiziana Di Matteo 《Astrophysics and Space Science》2007,311(1-3):185-190

We discuss the physics of the power source for gamma-ray bursts (GRBs). There is a great variety of stellar systems proposed as progenitors of long and short GRBs, but any current model for the engine ultimately involves the formation of a hyper-accreting disk around a newly-formed black hole of a few solar masses. The study of such disks can shed light onto the burst composition and energy content. We present preliminary results from disk vertical structure calculations. These include neutrino transport, a height-dependent determination of the nuclear composition, and a simplified treatment of turbulent mixing. We find that vertical mixing is rapid enough to largely erase compositional gradients, and as a consequence the upper layers of the disk reflect the neutron-rich composition of the midplane close to the black hole. We review the implications of this for the nuclear composition of outflows in GRBs. Our models suggest an increasing role for pairs in the upper regions of the disk, and we speculate that a pair-driven wind could be a significant source of cooling. Elena M. Rossi is a Chandra Fellow  相似文献   

Size and shape characteristics of drumlins,derived from a large sample,and associated scaling laws     

Chris D. Clark  Anna L.C. Hughes  Sarah L. Greenwood  Matteo Spagnolo  Felix S.L. Ng 《Quaternary Science Reviews》2009,28(7-8):677-692

Ice sheets flowing across a sedimentary bed usually produce a landscape of blister-like landforms streamlined in the direction of the ice flow and with each bump of the order of 10² to 10³ m in length and 10¹ m in relief. Such landforms, known as drumlins, have mystified investigators for over a hundred years. A satisfactory explanation for their formation, and thus an appreciation of their glaciological significance, has remained elusive. A recent advance has been in numerical modelling of the land-forming process. In anticipation of future modelling endeavours, this paper is motivated by the requirement for robust data on drumlin size and shape for model testing.From a systematic programme of drumlin mapping from digital elevation models and satellite images of Britain and Ireland, we used a geographic information system to compile a range of statistics on length L, width W, and elongation ratio E (where E = L/W) for a large sample. Mean L, is found to be 629 m (n = 58,983), mean W is 209 m and mean E is 2.9 (n = 37,043). Most drumlins are between 250 and 1000 metres in length; between 120 and 300 metres in width; and between 1.7 and 4.1 times as long as they are wide. Analysis of such data and plots of drumlin width against length reveals some new insights. All frequency distributions are unimodal from which we infer that the geomorphological label of ‘drumlin’ is fair in that this is a true single population of landforms, rather than an amalgam of different landform types. Drumlin size shows a clear minimum bound of around 100 m (horizontal). Maybe drumlins are generated at many scales and this is the minimum, or this value may be an indication of the fundamental scale of bump generation (‘proto-drumlins’) prior to them growing and elongating. A relationship between drumlin width and length is found (with r² = 0.48) and that is approximately W = 7 L ^1/2 when measured in metres. A surprising and sharply-defined line bounds the data cloud plotted in E–W–L space, and records a scale-dependent maximum elongation limit (approximated by E_max = L^1/3, when L measured in metres). For a given length, for some reason as yet unknown, drumlins do not exceed the elongation ratio defined by this scaling law. We also report and compare our statistics to an amalgamated sample (25,907 drumlins) of measures derived from around 50 published investigations. Any theory must be able to explain the drumlin statistics and fundamental scaling properties reported herein and they thus provide powerful tests for drumlin modelling.  相似文献