Learning to Rank from Implicit Feedback

Whenever access to information is mediated by a computer, we can easily record how users respond to the information with which they are presented. These normal interactions between users and information systems are implicit feedback. The key question we address is -- how can we use implicit feedback to automatically improve interactive information systems, such as desktop search and Web search? Contrasting with data collected from external experts, which is assumed as input in most previous research on optimizing interactive information systems, implicit feedback gives more accurate and up-to-date data about the needs of actual users. While another alternative is to ask users for feedback directly, implicit feedback collects data from all users, and does not require them to change how they interact with information systems. What makes learning from implicit feedback challenging, is that the behavior of people using interactive information systems is strongly biased in several ways. These biases can obscure the useful information present, and make standard machine learning approaches less effective. This thesis shows that implicit feedback provides a tremendous amount of practical information for learning to rank, making four key contributions. First, we demonstrate that query reformulations can be interpreted to provide relevance information about documents that are presented to users. Second, we describe an experiment design that provably avoids presentation bias, which is otherwise present when recording implicit feedback. Third, we present a Bayesian method for collecting more useful implicit feedback for learning to rank, by actively selecting rankings to show in anticipation of user responses. Fourth, we show how to learn rankings that resolve query ambiguity using multi-armed bandits. Taken together, these contributions reinforce the value of implicit feedback, and present new ways it can be exploited

Pore size distribution and accessible pore size distribution in bituminous coals

The porosity and pore size distribution of coals determine many of their properties, from gas release to their behavior on carbonization, and yet most methods of determining pore size distribution can only examine a restricted size range. Even then, only accessible pores can be investigated with these methods. Small-angle neutron scattering (SANS) and ultra small-angle neutron scattering (USANS) are increasingly used to characterize the size distribution of all of the pores non-destructively. Here we have used USANS/SANS to examine 24 well-characterized bituminous and subbituminous coals: three from the eastern US, two from Poland, one from New Zealand and the rest from the Sydney and Bowen Basins in Eastern Australia, and determined the relationships of the scattering intensity corresponding to different pore sizes with other coal properties. The range of pore radii examinable with these techniques is 2.5nm to 7μm. We confirm that there is a wide range of pore sizes in coal. The pore size distribution was found to be strongly affected by both rank and type (expressed as either hydrogen or vitrinite content) in the size range 250nm to 7μm and 5 to 10nm, but weakly in intermediate regions. The results suggest that different mechanisms control coal porosity on different scales. Contrast-matching USANS and SANS were also used to determine the size distribution of the fraction of the pores in these coals that are inaccessible to deuterated methane, CD4, at ambient temperature. In some coals most of the small (~10nm) pores were found to be inaccessible to CD4 on the time scale of the measurement (~30min–16h). This inaccessibility suggests that in these coals a considerable fraction of inherent methane may be trapped for extended periods of time, thus reducing the effectiveness of methane release from (or sorption by) these coals. Although the number of small pores was less in higher rank coals, the fraction of total pores that was inaccessible was not rank dependent. In the Australian coals, at the 10nm to 50nm size scales the pores in inertinites appeared to be completely accessible to CD4, whereas the pores in the vitrinite were about 75% inaccessible. Unlike the results for total porosity that showed no regional effects on relationships between porosity and coal properties, clear regional differences in the relationships between fraction of closed porosity and coal properties were found. The 10 to 50nm-sized pores of inertinites of the US and Polish coals examined appeared less accessible to methane than those of the inertinites of Australian coals. This difference in pore accessibility in inertinites may explain why empirical relationships between fluidity and coking properties developed using Carboniferous coals do not apply to Australian coals

Tracking metamorphic dehydration reactions in real time with transmission small- and wide-angle synchrotron X-ray scattering: the case of gypsum dehydration

We present a review of a unique non-destructive method for the real-time monitoring of phase transformations and nano-pore evolution in dehydrating rocks: transmission small- and wide-angle synchrotron X-ray scattering (SAXS/WAXS). It is shown how SAXS/WAXS can be applied to investigating rock samples dehydrated in a purpose-built loading cell that allows the coeval application of high temperature, axial confinement, and fluid pressure or flow to the specimen. Because synchrotron sources deliver extremely bright monochromatic X-rays across a wide energy spectrum, they enable the in situ examination of confined rock samples with thicknesses of ≤ 1 mm at a time resolution of order seconds. Hence, fast kinetics with reaction completion times of about hundreds of seconds can be tracked. With beam sizes of order tens to hundreds of micrometres, it is possible to monitor multiple interrogation points in a sample with a lateral extent of a few centimetres, thus resolving potential lateral spatial effects during dehydration and enlarging sample statistics significantly. Therefore, the SAXS/WAXS method offers the opportunity to acquire data on a striking range of length scales: for rock samples with thicknesses of ≤ 10-3 m and widths of 10-2 m, a lateral interrogation-point spacing of ≥ 10-5 m can be achieved. Within each irradiated interrogation-point volume, information concerning pores with sizes between 10-9 and 10-7 m and the crystal lattice on the scale of 10-10 m is acquired in real time. This article presents a summary of the physical principles underpinning transmission X-ray scattering with the aim of providing a guide for the design and interpretation of time-resolved SAXS/WAXS experiments. It is elucidated (1) when and how SAXS data can be used to analyse total porosity, internal surface area, and pore-size distributions in rocks on length scales from ∼1 to 300 nm; (2) how WAXS can be employed to track lattice transformations in situ; and (3) which limitations and complicating factors should be considered during experimental design, data analysis, and interpretation. To illustrate the key capabilities of the SAXS/WAXS method, we present a series of dehydration experiments on a well-studied natural gypsum rock: Volterra alabaster. Our results demonstrate that SAXS/WAXS is excellently suited for the in situ tracking of dehydration kinetics and the associated evolution of nano-pores. The phase transformation from gypsum to bassanite is correlated directly with nano-void growth on length scales between 1 and 11 nm for the first time. A comparison of the SAXS/WAXS kinetic results with literature data emphasises the need for future dehydration experiments on rock specimens because of the impact of rock fabric and the generally heterogeneous and transient nature of dehydration reactions in nature. It is anticipated that the SAXS/WAXS method combined with in situ loading cells will constitute an invaluable tool in the ongoing quest for understanding dehydration and other mineral replacement reactions in rocks quantitatively. </p

Assessing the potential for CO2 adsorption in a subbituminous coal, Huntly Coalfield, New Zealand, using small angle scattering techniques

Small angle scattering techniques (SAXS and SANS) have been used to investigate the microstructural properties of the subbituminous coals (R-max 0.42-0.45%) from the Huntly Coalfield, New Zealand. Samples were collected from the two thick (>5 m) coal seams in the coalfield and have been analysed for methane and carbon dioxide sorption capacity, petrography, pore size distribution, specific surface area and porosity

Accessibility of pores in coal to methane and carbon dioxide

Fluid–solid interactions in natural and engineered porous solids underlie a variety of technological processes, including geological storage of anthropogenic greenhouse gases, enhanced coal bed methane recovery, membrane separation, and heterogeneous catalysis. The size, distribution and interconnectivity of pores, the chemical and physical properties of the solid and fluid phases collectively dictate how fluid molecules migrate into and through the micro- and meso-porous media, adsorb and ultimately react with the solid surfaces. Due to the high penetration power and relatively short wavelength of neutrons, smallangle neutron scattering (SANS) as well as ultra small-angle scattering (USANS) techniques are ideally suited for assessing the phase behavior of confined fluids under pressure as well as for evaluating the total porosity in engineered and natural porous systems including coal. Here we demonstrate that SANS and USANS can be also used for determining the fraction of the pore volume that is actually accessible to fluids as a function of pore sizes and study the fraction of inaccessible pores as a function of pore size in three coals from the Illinois Basin (USA) and Bowen Basin (Australia). Experiments were performed at CO2 and methane pressures up to 780 bar, including pressures corresponding to zero average contrast condition (ZAC), which is the pressure where no scattering from the accessible pores occurs. Scattering curves at the ZAC were compared with the scattering from same coals under vacuum and analysed using a newly developed approach that shows that the volume fraction of accessible pores in these coals varies between �90% in the macropore region to �30% in the mesopore region and the variation is distinctive for each of the examined coals. The developed methodology may be also applied for assessing the volume of accessible pores in other natural underground formations of interest for CO2 sequestration, such as saline aquifers as well as for estimating closed porosity in engineered porous solids of technological importance

Small-Angle and Ultrasmall-Angle Neutron Scattering (SANS/USANS) Study of New Albany Shale: A Treatise on Microporosity

Small-angle neutron scattering (SANS) and ultrasmall-angle neutron scattering (USANS) techniques were applied to study the microstructure of several New Albany shales of different maturity. It has been established that the total porosity decreases with maturity and increases somewhat for post-mature samples. A new method of SANS data analysis was developed, which allows the extraction of information about the size range and number density of micropores from the relatively flat scattering intensity observed in the limit of the large scattering vector <i>Q</i>. Macropores and significant number of mesopores are surface fractals, and their structure can be described in terms of the polydisperse spheres (PDSP) model. The model-independent Porod invariant method was employed to estimate total porosity, and the results were compared with the PDSP model results. It has been demonstrated that independent evaluation of incoherent background is crucial for accurate interpretation of the scattering data in the limit of large <i>Q</i>-values. Pore volumes estimated by the N₂ and CO₂ adsorption, as well as via the mercury intrusion technique, have been compared with those measured by SANS/USANS, and possible reasons for the observed discrepancies are discussed

Pore structure characterization of North American shale gas reservoirs using USANS/SANS, gas adsorption, and mercury intrusion

Small-angle and ultra-small-angle neutron scattering (SANS and USANS), low-pressure adsorption (N2 and CO2), and high-pressure mercury intrusion measurements were performed on a suite of North American shale reservoir samples providing the first ever comparison of all these techniques for characterizing the complex pore structure of shales. The techniques were used to gain insight into the nature of the pore structure including pore geometry, pore size distribution and accessible versus inaccessible porosity. Reservoir samples for analysis were taken from currently-active shale gas plays including the Barnett, Marcellus, Haynesville, Eagle Ford, Woodford, Muskwa, and Duvernay shales. Low-pressure adsorption revealed strong differences in BET surface area and pore volumes for the sample suite, consistent with variability in composition of the samples. The combination of CO2 and N2 adsorption data allowed pore size distributions to be created for micro–meso–macroporosity up to a limit of �1000 Å. Pore size distributions are either uni- or multi-modal. The adsorption-derived pore size distributions for some samples are inconsistent with mercury intrusion data, likely owing to a combination of grain compression during high-pressure intrusion, and the fact that mercury intrusion yields information about pore throat rather than pore body distributions. SANS/USANS scattering data indicate a fractal geometry (power-law scattering) for a wide range of pore sizes and provide evidence that nanometer-scale spatial ordering occurs in lower mesopore–micropore range for some samples, which may be associated with inter-layer spacing in clay minerals. SANS/USANS pore radius distributions were converted to pore volume distributions for direct comparison with adsorption data. For the overlap region between the two methods, the agreement is quite good. Accessible porosity in the pore size (radius) range 5 nm–10 lm was determined for a Barnett shale sample using the contrast matching method with pressurized deuterated methane fluid. The results demonstrate that accessible porosity is pore-size dependent

Fingerprint of hydrocarbon generation in the southern Georgina Basin, Australia, revealed by small angle neutron scattering

Small angle neutron scattering (SANS) and ultra-small angle neutron scattering (USANS) are used to directly detect the processes of hydrocarbon generation in the 10 nm to 10 μm size pores in Middle Cambrian carbonate and siliciclastic rocks which contain no land-plant material suitable for conventional maturity determination by vitrinite reflectance. The method takes advantage of the pore-size-specific variation of neutron scattering contrast between the solid rock matrix and pore-space content with depth, which is caused by thermal maturation of organic matter through the oil and gas generation windows. SANS and USANS measurements were performed on bedding plane-orientated core slices, extracted from a series of 10 to 12 depth intervals for three wells CKAD0001, MacIntyre 1 and Baldwin 1, in the southern Georgina Basin, central Australia. The depth intervals, intersecting the organic-rich basal ‘hot’ shales of the middle Cambrian Arthur Creek Formation, were selected based on Rock-Eval pyrolysis data. SANS and USANS results indicate that oil generation has occurred in the past in nanometer-sized pores in rocks that are now at depths of around 538.4 m in CKAD0001 and 799.3 m in MacIntyre 1. Furthermore, in the CKAD0001 well, the oil-wet pores extend into the larger pore-size range (at least up to 10 μm) due to the efficient expulsion of oil. At around 880 m in Baldwin 1, the influence of pyrobitumen reverts pore space from gas wet to oil wet. These hydrocarbons have remained in situ since the Devonian when the Neoproterozoic to Paleozoic section was exhumed in the Alice Springs Orogeny and subsequently eroded, preserving only remnants of the once extensive basin sediments.\ud \ud Keywords\ud \ud Hydrocarbon generation; Hydrocarbon expulsion; SANS; USANS; Georgina Basin; Cambrian; Arthur Creek Formatio

Characterization of tight gas reservoir pore structure using USANS/SANS and gas adsorption analysis

Small-angle and ultra-small-angle neutron scattering (SANS and USANS) measurements were performed on samples from the Triassic Montney tight gas reservoir in Western Canada in order to determine the applicability of these techniques for characterizing the full pore size spectrum and to gain insight into the nature of the pore structure and its control on permeability. The subject tight gas reservoir consists of a finely laminated siltstone sequence; extensive cementation and moderate clay content are the primary causes of low permeability. SANS/USANS experiments run at ambient pressure and temperature conditions on lithologically-diverse sub-samples of three core plugs demonstrated that a broad pore size distribution could be interpreted from the data. Two interpretation methods were used to evaluate total porosity, pore size distribution and surface area and the results were compared to independent estimates derived from helium porosimetry (connected porosity) and low-pressure N2 and CO2 adsorption (accessible surface area and pore size distribution). The pore structure of the three samples as interpreted from SANS/USANS is fairly uniform, with small differences in the small-pore range (<2000 Å), possibly related to differences in degree of cementation, and mineralogy, in particular clay content. Total porosity interpreted from USANS/SANS is similar to (but systematically higher than) helium porosities measured on the whole core plug. Both methods were used to estimate the percentage of open porosity expressed here as a ratio of connected porosity, as established from helium adsorption, to the total porosity, as estimated from SANS/USANS techniques. Open porosity appears to control permeability (determined using pressure and pulse-decay techniques), with the highest permeability sample also having the highest percentage of open porosity. Surface area, as calculated from low-pressure N2 and CO2 adsorption, is significantly less than surface area estimates from SANS/USANS, which is due in part to limited accessibility of the gases to all pores. The similarity between N2 and CO2-accessible surface area suggests an absence of microporosity in these samples, which is in agreement with SANS analysis. A core gamma ray profile run on the same core from which the core plug samples were taken correlates to profile permeability measurements run on the slabbed core. This correlation is related to clay content, which possibly controls the percentage of open porosity. Continued study of these effects will prove useful in log-core calibration efforts for tight gas