Model-free estimation of fracture aperture with neural networks

The feedforward backpropagation technique provides a model-free estimation with neural networks. The algorithm was used to estimate fracture aperture of natural fractures in three dimensional space. A three-layer neural network with at least 5 nodes in a hidden layer was trained on a data set consisting of formation imaging microscanner logs (FMS)from horizontal boreholes. Sensitivity studies were performed to account for the rate of learning convergence, convergence to local error minima, etc. Among the factors contributing mostly to the overall good or bad performance of the network, the following are worth mentioning: number of data points, data spacing, and data variability. It is shown that a smoothing operation applied to aperture data along the wellbore often helps to reduce disorientation of the network and to switch from oscillations or chaotic jumps to convergence.     

Analysis of the high-resolution Mg XI X-ray spectra

In Part IV of the series of papers about the analysis of the INTERCOSMOS 16 ADP spectra a method is developed to evaluate plasma densities from measured resonance, intercombination, and forbidden helium-like Mg xi line intensities, using plots of the so-called G and R ratios. The density is close to the low-density limit. For the active region McMath 14352 a correlation between mean plasma density and electron temperature has been found, in agreement with earlier results. In an appendix systematic differences between measured and calculated line fluxes in all bands A to F are discussed.     

LEO GPS attitude determination algorithm for a micro-satellite using boom-arm deployed antennas

This paper describes a low earth orbiter micro-satellite attitude determination algorithm using GPS phase and pseudorange data as the only observables. It is designed to run in real-time, at a rate of 10 Hz, on-board the spacecraft, using minimal chip and memory resources. The spacecraft design includes four GPS antennas deployed on boom arms to improve the antenna separations. The boom arms feature smart sensors, from which time-varying deformation data are used to calculate changes in the body-fixed system (BFS) co-ordinates of the attitude antennas. These data are used as input to the attitude algorithm to improve the accuracy of the output. The conventional double-difference phase observation equations have been re-arranged so that the only unknown parameters in the functions (once the ambiguities have been determined) are the spacecraft Euler angles. This greatly increases the redundancy in the mathematical model, and is exploited to enhance the algorithm's ability to trap observations contaminated by unmodelled multipath. This approach has been shown to be successful in identifying phase outliers at the 5–10 mm level. Speed of execution of the program is improved by utilising numerical differentiation of the model equations in the linearisation process. Furthermore, as the number of solve-for parameters is reduced to three by the chosen mathematical model, matrix inversion requirements are minimised. A novel approach to ambiguity resolution and determination of initial estimates of the attitude parameters has been developed utilising a heuristic technique and the known, and time varying, BFS co-ordinates of the antenna array. Algorithm testing is based on a simulation of the micro-satellite trajectory combined with variations in attitude derived from spin-stabilisation and periodic roll and pitch parameters. The trajectory of the spacecraft centre of mass was calculated by numerical integration of a force model using Earth gravity field parameters, third body effects due to the Sun and the Moon, dynamic Earth tide effects (solar and lunar), and a solar radiation pressure model. Frame transformations between J2000 and ITRF97 used the IERS conventions. A similar approach was used to calculate the trajectories of all available GPS satellites during the same period, using initial conditions of position and velocity from IGS precise orbits. RMS differences between the published precise orbit and the integrated satellite positions were at the 5-mm level. Phase observables are derived from these trajectories, biased by simulation of receiver and satellite clock errors, cycle slips, random or systematic noise and initial integer ambiguities. In the actual simulation of the attitude determination process in orbit, GPS satellite positions are calculated using broadcast ephemerides. The results show that the aim of 0.05° (two sigma) attitude precision can be met provided that the phase noise can be reduced to the level of 1–2 mm. Attitude precision was found to vary strongly with constellation geometry, which can change quite rapidly depending on the variations in spacecraft attitude. The redundancy in the mathematical model was found to be very effective in trapping and isolating cycle slips to the double difference observations that are contaminated. This allows for the possibility of correcting for cycle slips without full recourse to the ambiguity resolution algorithm. Electronic Publication     

A dendroclimatological study of east- and west-facing slopes in mountainous areas subjected to strong air pollution (the Sudetes,Central Europe)

The Sudetes Mountains (Central Europe) were under a particularly intense long-term air pollution load during the 1970s and 1980s. Intense industrial activity in this area led to large-scale forest dieback and reductions in tree growth rates, potentially limiting the use of tree-ring data from this region in dendroclimatic research. In this paper, ring-width chronologies were constructed for 493 Norway spruce trees (Picea abies L. Karst.) from 17 sampling sites within five major mountain ranges in the Sudetes Mountains of Poland. Growth-climate response data indicate that April?July temperatures are the main factor affecting radial growth of trees in the study area. Our data also indicate the strong influence of slope aspect on temperature signal strength. The lowest correlation values were obtained for sites located on western slopes with effective fog deposition, which are strongly affected by pollution. An appropriate sampling strategy resulted in the creation of a temperature-sensitive proxy record (rAMJJ = 0.70), exceptional for areas under strong pressure from human activity. Based on a regional master chronology, growing season (April?July) temperatures over the past 200 years were then reconstructed. Four warm and four cold periods were distinguished and compared with other reconstructions and long-term instrumental data.     

What do parameterized Om(z) diagnostics tell us in light of recent observations?

In this paper, we propose a new parametrization for Om(z) diagnostics and show how the most recent and significantly improved observations concerning the H(z) and SN Ia measurements can be used to probe the consistency or tension between the ΛCDM model and observations. Our results demonstrate that H0 plays a very important role in the consistency test of ΛCDM with H(z)data. Adopting the Hubble constant priors from Planck 2013 and Riess, one finds considerable tension between the current H(z) data and ΛCDM model and confirms the conclusions obtained previously by others. However, with the Hubble constant prior taken from WMAP9, the discrepancy between H(z) data and ΛCDM disappears, i.e., the current H(z) observations still support the cosmological constant scenario. This conclusion is also supported by the results derived from the Joint Lightcurve Analysis(JLA) SN Ia sample. The best-fit Hubble constant from the combination of H(z)+JLA(H00 = 68.81+1.5-1.49 km s-1 Mpc-1) is very consistent with results derived both by Planck 2013 and WMAP9, but is significantly different from the recent local measurement by Riess.     

Flare Characteristics from X-ray Light Curves

A new methodology is given to determine basic parameters of flares from their X-ray light curves. Algorithms are developed from the analysis of small X-ray flares occurring during the deep solar minimum of 2009, between Solar Cycles 23 and 24, observed by the Polish Solar Photometer in X-rays (SphinX) on the Complex Orbital Observations Near-Earth of Activity of the Sun-Photon (CORONAS-Photon) spacecraft. One is a semi-automatic flare detection procedure that gives start, peak, and end times for single (“elementary”) flare events under the assumption that the light curve is a simple convolution of a Gaussian and exponential decay functions. More complex flares with multiple peaks can generally be described by a sum of such elementary flares. Flare time profiles in the two energy ranges of SphinX (1.16?–?1.51 keV, 1.51?–?15 keV) are used to derive temperature and emission measure as a function of time during each flare. The result is a comprehensive catalogue – the SphinX Flare Catalogue – which contains 1600 flares or flare-like events and is made available for general use. The methods described here can be applied to observations made by Geosynchronous Operational Environmental Satellites (GOES), the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and other broad-band spectrometers.     

Concentrated, ‘pulsed’ axial glacier flow: structural glaciological evidence from Kvíárjökull in SE Iceland

A detailed structural glaciological study carried out on Kvíárjökull in SE Iceland reveals that recent flow within this maritime glacier is concentrated within a narrow corridor located along its central axis. This active corridor is responsible for feeding ice from the accumulation zone on the south‐eastern side of Öræfajökull to the lower reaches of the glacier and resulted in a c. 200 m advance during the winter of 2013–2014 and the formation of a push‐moraine. The corridor comprises a series of lobes linked by a laterally continuous zone of highly fractured ice characterised by prominent flow‐parallel crevasses, separated by shear zones. The lobes form highly crevassed topographic highs on the glacier surface and occur immediately down‐ice of marked constrictions caused by prominent bedrock outcrops located on the northern side of the glacier. Close to the frontal margin of Kvíárjökull, the southern side of the glacier is relatively smooth and pock‐marked by a number of large moulins. The boundary between this slow moving ice and the active corridor is marked by a number of ice flow‐parallel strike‐slip faults and a prominent dextral shear zone which resulted in the clockwise rotation and dissection of an ice‐cored esker exposed on the glacier surface. It is suggested that this concentrated style of glacier flow identified within Kvíárjökull has affinities with the individual flow units which operate within pulsing or surging glaciers. © 2017 The Authors Earth Surface Processes and Landforms © 2017 John Wiley & Sons, Ltd.     

3D bearing capacity probabilistic analyses of footings on spatially variable c–φ soil

Acta Geotechnica - The paper examines three-dimensional (3D) analyses of the load bearing capacity of square and strip footings on a spatially variable cohesive–frictional (c–φ)...