GPS multipath mitigation: a nonlinear regression approach

Under the assumption that the surrounding environment remains unchanged, multipath contamination of GPS measurements can be formulated as a function of the sidereal repeatable geometry of the satellite with respect to the fixed receiver. Hence, multipath error estimation amounts to a regression problem. We present a method for estimating code multipath error of GPS ground fixed stations. By formulating the multipath estimation as a regression problem, we construct a nonlinear continuous model for estimating multipath error based on well-known sparse kernel regression, for example, support vector regression. We will empirically show that the proposed method achieves state-of-the-art performance on code multipath mitigation with 79 % reduction on average in terms of standard deviation of multipath error. Furthermore, by simulation, we will also show that the method is robust to other coexisting signals of phenomena, such as seismic signals.     

Natural occurrence of higher thiadiamondoids and diamondoidthiols in a deep petroleum reservoir in the Mobile Bay gas field

A series of higher thiadiamondoids and diamondoidthiols, including thiatetramantanes, tetramantanethiols, thiapentamantanes, pentamantanethiols, thiahexamantanes, hexamantanethiols and thiacylcohexamantane, was discovered in a gas condensate produced from a very deep (6274 m, 20,585 ft) petroleum reservoir in the Bon Secour Bay in the Mobile Bay gas field, located offshore Alabama in the northern Gulf of Mexico, USA. This appears to be the first reported natural occurrence of these compounds. Several isomers of higher thiadiamondoids and diamondoidthiols were identified using full scan gas chromatography-mass spectrometry (GC-MS) coupled with GC-sulfur chemiluminescence detection (GC-SCD) and GC × GC-time of flight mass spectrometry (GC × GC-TOFMS). These higher thiadiamondoids and diamondoidthiols are associated with abundant lower homologs including thiaadamantanes, thiadiamantanes, thiatriamantanes and their thiol groups. The origin of these compounds in petroleum has not been reported. It is speculated that similar to lower thiadiamondoids and diamondoidthiols, higher ones are possibly formed from the sulfurization of their precursor diamondoids during TSR, a conclusion supported by the occurrence of open-cage higher diamondoidthiols and sulfur isotopic data of higher thiadiamondoids and diamondoidthiols isolated from the Mobile Bay condensate. The presence of higher thiadiamondoids and diamondoidthiols is indicative of the occurrence of TSR and can be used to predict sour gas production.     

Simulating the effects of induced anisotropy on liquefaction potential using a new constitutive model

The effects of induced anisotropy on the undrained behaviour of very loose and saturated sands have been a subject of intensive investigation, both experimentally and theoretically, by several authors in the past few years. This paper proposes an original constitutive model well‐adapted to simulate the behaviour of sands subject to complex stress histories, in particular, the preloading cycle along the classical drained stress path in compression. The developed model belongs to the family of critical state models. Its construction is based on a few theoretical concepts taken from the theory of ‘Bounding Surface Plasticity’ developed among others by Y. Dafalias and Popov (1975), the ‘Clay And Sand Model’ (CASM) of H. Yu (2006), the CJS model (B. Cambou and K. Jafari (1988)) and the hyperelastic isotropic model of P. Lade (1987). To accurately simulate volume changes, which represent a key element in soil behaviour, a state‐dependent dilatancy rule is proposed, which can account for the influences of stress and void ratio. The current void ratio depends implicitly on the irreversible strains already accumulated hence the strain history. A kinematic hardening is combined with an isotropic hardening, involving rotation and distortion of the bounding surface, in order to capture correctly the experimental observations. Comparisons of experimental results to numerical simulations show that the model is able to simulate with a good precision the major trends of undrained responses of loose and presheared sands. It predicts correctly rapid static liquefaction at small or null drained preloading, as well as the progressive transition to a completely stable behaviour typical of dense sands, while the sample is loose in reality. At intermediate to large amplitudes of preloadings, the model also predicts correctly the temporary stage of instability when the deviatoric stress decreases slightly before rising up again. Copyright © 2013 John Wiley & Sons, Ltd.     

REDD+ Readiness progress across countries: time for reconsideration

Efforts towards Reducing Emissions from Deforestation and Forest Degradation plus conservation, sustainable management of forests and enhancement of carbon stocks (REDD+) have grown in importance in developing countries following negotiations within the United Nations Framework Convention on Climate Change (UNFCCC). This has favoured investments in processes to prepare countries for REDD+ at the national level (a process referred to as REDD+ Readiness). Yet, little attention has been given to how Readiness can be assessed and potentially improved. This article presents a framework for Readiness assessment and compares progress in REDD+ Readiness across four countries, namely Cameroon, Indonesia, Peru, and Vietnam. The Readiness assessment framework comprises six functions, namely planning and coordination; policy, laws, and institutions; measurement, reporting, verification (MRV), and audits; benefit sharing; financing; and demonstrations and pilots. We found the framework credible and consistent in measuring progress and eliciting insight into Readiness processes at the country level. Country performance for various functions was mixed. Progress was evident on planning and coordination, and demonstration and pilots. However, MRV and audits; financing; benefit sharing; and policies, laws and institutions face major challenges. The results suggest that the way national forest governance has been shaped by historical circumstances (showing path dependency) is a critical factor for progress in Readiness processes. There is need for a rethink of the current REDD+ Readiness infrastructure given the serious gaps observed in addressing drivers of deforestation and forest degradation, linking REDD+ to broader national strategies and systematic capacity building.     

Procedure,selection and application of plasticity models for a soil

A five-step procedure involving mathematical formulation, identification and determination of parameters and verification is presented for development and selection of appropriate and reliable constitutive law(s) for geologic media. Comprehensive analyses are performed toward determination of an appropriate law for a (artificial) soil. The most suitable model is obtained by critical evaluation of four different plasticity models; here verification and comparisons of predictions with observations from laboratory tests, and with those from two boundary value problems are used as the basis of the selection. The model thus selected is found to be appropriate for applications to relevant practical problems.     

Aggregation of small ice crystals in an electric field

Abstract

Small ice crystals with average diameter of about 30 μm are produced in a large cold room and allowed to fall in a settling chamber in the presence of a quasi‐uniform electric field. Aggregates (flakes) of ice crystals are collected by permanent replicas. Results show that an electric field above a threshold value of about 4 × 10⁴ V m^‐1 rapidly increases the growth of flakes by the capture of small ice crystals. The influence of the electric field upon the growth of ice aggregates is maximum at a field strength of about 1.5 × 10⁵ V m^‐1. Comparison of the results with Jiusto's mathematical model of the growth rate gives values of the collection efficiency at different field strengths. It is very likely that the electric field increases the adhesion (aggregation) efficiency rather than the collision (cross‐section) efficiency.     

Biodegradation of diesel oil in marine environment by a floating water droplet

Diesel oil is one of the derivatives of crude oil which resistance to biodegradation due to its complex structure and low solubility in water. A novel concept of enhancement of diesel degradation using floating water droplet is proposed and being investigated to address some key challenges encountered in diesel oil spillages in the aqueous area and wetlands. This study aims to increase the floatability of a floating water droplet on oil. A droplet containing a mixed consortium of 60 different hydrocarbon degrading bacteria and sodium dodecyl sulfate as a surfactant was deposited on the diesel oil surface. Contact angle and contact radius were monitored to observe the effect of bacterial activities on the droplet. The behavior of this droplet on diesel oil was different to a previous study with paraffin oil. In particular, the floatability, bacterial growth and biofilm formation demonstrate significant deviation due to the diesel interactions with biological processes. Nevertheless, the results show this method increase microbial activities within the droplet. The result verifies the applicability of the floating water droplet as an environmentally friendly method for diesel oil spillages.     

Investigation of the accelerated carbonation of a MgO-based binder used to treat contaminated sediment

A MgO-based binder developed to simultaneously solidify/stabilize contaminated sediment and store CO₂ has been described previously. The objectives of the study presented here were to investigate the kinetics of the carbonation reactions of the binder and the extent to which carbonation occurred and to identify the optimal conditions for using the binder. The carbonation reaction was clearly faster and the degree of carbonation higher at CO₂ concentrations of 50 and 100% than in the ambient atmosphere (which contains 0.04% CO₂). A modified unreactive core model adequately described the kinetics. The rate constants were 0.0217–0.319 h^?1 and were proportional to the degree of carbonation. A high degree of carbonation, 93.8%, was achieved at a CO₂ concentration of 100%. The water to sediment ratio strongly affected carbonation, the optimal ratio being around 0.7. The relative humidity did not strongly affect the carbonation performance. The carbonation products were magnesite (MgCO₃) and nesquehonite (MgCO₃·3H₂O). X-ray diffraction analysis showed that brucite (Mg(OH)₂) was not present, suggesting that brucite was very quickly transformed into magnesium carbonates, the presence of which was confirmed by thermal gravimetric analysis. The results indicated that, in 7 d, 1 kg of binder could sequester up to 0.507 kg of CO₂ in a 100% CO₂ atmosphere. The results indicate that the MgO-based binder has great potential to be used to sequester CO₂ under accelerated carbonation conditions.     

Cluster Observes the High-Altitude CUSP Region

This paper gives an overview of Cluster observations in the high-altitude cusp region of the magnetosphere. The low and mid-altitude cusps have been extensively studied previously with a number of low-altitude satellites, but only little is known about the distant part of the magnetospheric cusps. During the spring-time, the trajectory of the Cluster fleet is well placed for dayside, high-altitude magnetosphere investigations due to its highly eccentric polar orbit. Wide coverage of the region has resulted and, depending on the magnetic dipole tilt and the solar wind conditions, the spacecraft are susceptible to encounter: the plasma mantle, the high-altitude cusp, the dayside magnetosphere (i.e. dayside plasma sheet) and the distant exterior cusp diamagnetic cavity. The spacecraft either exit into the magnetosheath through the dayside magnetopause or through the exterior cusp–magnetosheath interface. This paper is based on Cluster observations made during three high-altitude passes. These were chosen because they occurred during different solar wind conditions and different inter-spacecraft separations. In addition, the dynamic nature of the cusp allowed all the aforementioned regions to be sampled with different order, duration and characteristics. The analysis deals with observations of: (1) both spatial and temporal structures at high-altitudes in the cusp and plasma mantle, (2) signatures of possible steady reconnection, flux transfer events (FTE) and plasma transfer events (PTE), (3) intermittent cold (<100 eV) plasma acceleration associated with both plasma penetration and boundary motions, (4) energetic ions (5–40 keV) in the exterior cusp diamagnetic cavity and (5) the global structure of the exterior cusp and its direct interface with the magnetosheath. The analysis is primarily focused on ion and magnetic field measurements. By use of these recent multi-spacecraft Cluster observations we illustrate the current topics under debate pertaining to the solar wind–magnetosphere interaction, for which this region is known to be of major importance.