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81.
82.
83.
Marek Kacewicz 《Mathematical Geology》1994,26(8):985-994
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. 相似文献
84.
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 相似文献
85.
86.
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. 相似文献
87.
Jing-Zhao Qi Shuo Cao Marek Biesiada Teng-Peng Xu Yan Wu Si-Xuan Zhang Zong-Hong Zhu 《天文和天体物理学研究(英文版)》2018,(6)
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. 相似文献
88.
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)... 相似文献
89.
David L. McCollum Volker Krey Keywan Riahi Peter Kolp Arnulf Grubler Marek Makowski Nebojsa Nakicenovic 《Climatic change》2013,119(2):479-494
This paper assesses three key energy sustainability objectives: energy security improvement, climate change mitigation, and the reduction of air pollution and its human health impacts. We explain how the common practice of narrowly focusing on singular issues ignores potentially enormous synergies, highlighting the need for a paradigm shift toward more holistic policy approaches. Our analysis of a large ensemble of alternate energy-climate futures, developed using MESSAGE, an integrated assessment model, shows that stringent climate change policy offers a strategic entry point along the path to energy sustainability in several dimensions. Concerted decarbonization efforts can lead to improved air quality, thereby reducing energy-related health impacts worldwide: upwards of 2–32 million fewer disability-adjusted life years in 2030, depending on the aggressiveness of the air pollution policies foreseen in the baseline. At the same time, low-carbon technologies and energy-efficiency improvements can help to further the energy security goals of individual countries and regions by promoting a more dependable, resilient, and diversified energy portfolio. The cost savings of these climate policy synergies are potentially enormous: $100–600 billion annually by 2030 in reduced pollution control and energy security expenditures (0.1–0.7 % of GDP). Novel aspects of this paper include an explicit quantification of the health-related co-benefits of present and future air pollution control policies; an analysis of how future constraints on regional trade could influence energy security; a detailed assessment of energy expenditures showing where financing needs to flow in order to achieve the multiple energy sustainability objectives; and a quantification of the relationships between different fulfillment levels for energy security and air pollution goals and the probability of reaching the 2 °C climate target. 相似文献
90.
In urbanized areas, particularly in lowland terrains and floors of large river valleys, the natural land configuration is often hard to recognize due to a long history of human activity. Accordingly, archaeological works in cities, which supply knowledge on settlement conditions, are usually accompanied by geological and geomophological research. Lately, data from light detection and ranging (LiDAR) have become a valuable source of information on urban land configuration. Geophysical methods are also becoming increasingly popular in background studies. The paper presents a method of using and linking these sources of spatial information about landforms in such areas. The main aim is to identify to what extent these complementary sources of data and the proposed method can be used in such a specific environment to reconstruct natural, buried terrain morphology. The city of Wroc?aw in Central Europe serves as an example. To this end geomorphometric studies were conducted with the use of digital elevation models (DEMs) based on LiDAR scanning and derivated land-surface parameters—SAGA Wetness Index, Channel Network Base Level and Altitude above Channel Network. The study also involved determining morphological edges and measurements of the meanders of the Odra, as well as expanding information on the spatial distribution of alluvia and the structure of slope breaks. To this end, geophysical measurements were conducted using the Two-Dimensional Electrical Resistivity Tomography method. Additionally, five typical sequences of man-made ground present within the perimeter of the city were distinguished. As a result, a map of the main landforms of Wroc?aw is presented. Finally, we argue that although high resolution DEM and derivate land-surface parameters are very useful in terrain analysis, places with thick man-made ground or strongly levelled areas must be recognized by geoarchaeological excavations or geological bore holes. The geophysical survey is useful to identify buried morphological edges and older relief elements in open areas. 相似文献