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Gyroremanent magnetization (GRM) has previously been studied in connection with the well-known technique of ac demagnetization, which is used extensively in rock magnetism, palaeomagnetism and magnetic materials research. The 'normal' GRM effect was explained by Stephenson in 1980, but recently a 'reversed' GRM was obtained in a Cr[O.sub.2] particle system by Madsen. We have studied samples of [gamma]-[Fe.sub.2][O.sub.3] particles (commercial magnetic recording tapes) and have identified samples with both 'normal' and 'reversed' GRM. The amplitude of the ac field was found to essentially influence the character of the GRM. In this paper, we also present micromagnetic simulations of the GRM in systems of single-domain particles and the results are discussed. Both 'normal' and 'reversed' GRM have been obtained in the simulations. Index Terms--Gyroremanent magnetization (GRM), magnetization processes, micromagnetic model, particulate media, rock magnetism.

Focuses on a study that described the shock consolidation of diamond and graphite mixtures to fused polycrystalline diamond. Phase diagram of carbon; Experimental details; Examination of recovered samples.

Distributed sensing systems can transform an optical fiber cable into an array of sensors, allowing users to detect and monitor multiple physical parameters such as temperature, vibration and strain with fine spatial and temporal resolution over a long distance. Fiber-optic distributed acoustic sensing (DAS) and distributed temperature sensing (DTS) systems have been developed for various applications with varied spatial resolution, and spectral and sensing range. Rayleigh scattering-based phase optical time domain reflectometry (OTDR) for vibration and Raman/Brillouin scattering-based OTDR for temperature and strain measurements have been developed over the past two decades. The key challenge has been to find a methodology that would enable the physical parameters to be determined at any point along the sensing fiber with high sensitivity and spatial resolution, yet within acceptable frequency range for dynamic vibration, and temperature detection. There are many applications, especially in geophysical and mining engineering where simultaneous measurements of vibration and temperature are essential. In this article, recent developments of different hybrid systems for simultaneous vibration, temperature and strain measurements are analyzed based on their operation principles and performance. Then, challenges and limitations of the systems are highlighted for geophysical applications. [ABSTRACT FROM AUTHOR]

The measurement of special-core-analysis (SCAL) parameters in the laboratory can be a very time-consuming and costly process. The purpose of the present study was to see whether neural networks could be applied to predict a SCAL parameter, such as resistivity index (RI), from minimal training data, because this approach could potentially be used in the future to save time and costs. Our study was undertaken in the Nubian sandstone formation of two Libyan oil fields (A-Libya and B-Libya). A series of different neural-network predictors, to predict the parameter RI, was trained in Well A-02 by use of laboratory measurements undertaken on SCAL plugs together with different combinations of associated wireline logs. The performance of the predictors was then tested in two test wells (Well A-01 in the same oil field as Well A-02, and Well B-01 in a different neighboring oil field). One set of neural-network predictors was trained on a data set containing all 55 SCAL plugs, along with the corresponding wireline-log data, from the Training Well A-02. This training data set is in itself relatively small compared with many previous neuralnet studies in the petroleum industry. The predictions were then compared with another set of genetically-focused-neural-net (GFNN) predictors trained on a much smaller subset of just 14 SCAL plugs, again with the corresponding wireline-log data, from a representative genetic unit (RGU) in Well A-02. The RGU contained representative core plugs from each global hydraulic element (GHE) in that well. Remarkably, the predictors trained on the smaller subset of 14 representative SCAL plugs gave slightly better predictions, compared with the measured values throughout the test wells, than the predictors trained on the larger data set comprising 55 SCAL plugs. For Test Well A-01, we obtained even better results when the GFNN predictors were tested only in the interval equivalent to the RGU of Training Well A-02. We subsequently also obtained very good results from GFNN predictors of the Amott-Harvey wettability index in Test Wells A-01 and B-01 when tested in the intervals equivalent to the RGU of Training Well A-02. This study demonstrates that the SCAL parameters investigated here can be reasonably well-predicted from neural nets, and that the training data set can be quite small if one carefully chooses SCAL plugs that are representative of the petrophysical properties in the reservoir. This approach has the potential of saving both time and costs, because it requires only minimal SCAL data, and would be particularly useful for wells where no core material is available. [ABSTRACT FROM AUTHOR]

With the expansion in the production of shale oil and gas, there is a desire to obtain detailed information of the downhole environment resulting from hydraulic fracturing (fracking). Nanomagnetite (nMag) has been proposed as a suitable contrast agent for magnetic imaging. In order to determine its suitability, 15 nm oleic acid-stabilised magnetite nanoparticles were synthesised and the magnetic susceptibility was measured and compared against two types of proppant. Although frac sand is diamagnetic (−0.20 × 10−5SI), ceramic proppant is paramagnetic (25.7 × 10−5SI) due to the presence of Fe2O3. The quantity of the nanoparticles that would be required for differentiation against the background levels in the proppant pack was calculated to be 0.269 g/L for sand and 1.01 g/L for ceramic, which correlates to a minimum of 15,000 kg and 56,000 kg per well, respectively. In order to determine the contrast with the reservoir rock itself, the magnetic susceptibility was mapped for cores from two typical shale gas reservoirs (Harrison and Rackley, Arkansas), which show a general low level of paramagnetism (ca. 45 × 10−5SI). However, regions are observed with higher susceptibility (>200 × 10−5SI) necessitating the use of 242,000 kg nMag per well in order to provide contrast with the reservoir. [ABSTRACT FROM PUBLISHER]

Thermosets obtained by reacting highly functionalized maleic anhydride-grafted polyethylene and a polyetherdiamine at several NH2/MA molar ratios were characterized for their gel content, thermal, mechanical, and thermo-mechanical behavior. Gel content varied with composition and a maximum (57%) observed when NH2/MA molar ratio was 1.5. Two melting transitions were observed for thermosets, representing the semicrystalline polyethylene fraction in the gel and sol part of the material in contrast to a single transition for the starting polyethylene. Overall crosslinking suppressed the crystallinity of the polyethylene in the thermoset. A single T g observed in the DMA analysis suggested phase mixing between the polyethylene and polyether chains. A shift in the T g observed was related to the degree of crosslinking in the thermosets. Tensile properties of the thermosets were observed to be a strong function of composition and the degree of crosslinking and the optimum mechanical performance was shown by thermosets when NH2/MA molar ratio was 1.5 and 2.0. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]