Time-lapse reconstruction of the fracture front from diffracted waves arrivals in laboratory hydraulic fracture experiments

4D acoustic imaging via an array of 32 sources / 32 receivers is used to monitor hydraulic fracture propagating in a 250~mm cubic specimen under a true-triaxial state of stress. We present a method based on the arrivals of diffracted waves to reconstruct the fracture geometry (and fluid front when distinct from the fracture front). Using Bayesian model selection, we rank different possible fracture geometries (radial, elliptical, tilted or not) and estimate model error. The imaging is repeated every 4 seconds and provide a quantitative measurement of the growth of these low velocity fractures. We test the proposed method on two experiments performed in two different rocks (marble and gabbro) under experimental conditions characteristic respectively of the fluid lag-viscosity (marble) and toughness (gabbro) dominated hydraulic fracture propagation regimes. In both experiments, about 150 to 200 source-receiver combinations exhibit clear diffracted wave arrivals. The results of the inversion indicate a radial geometry evolving slightly into an ellipse towards the end of the experiment when the fractures feel the specimen boundaries. The estimated modelling error with all models is of the order of the wave arrival picking error. Posterior estimates indicate an uncertainty of the order of a millimeter on the fracture front location for a given acquisition sequence. The reconstructed fracture evolution from diffracted waves is shown to be consistent with the analysis of $90^{\circ}$ incidence transmitted waves across the growing fracture.Comment: submitted to Geophys. J. In

Filmmaking education and enterprise culture: an ethnographic exploration of two filmmaking education contexts and their relation to bedroom culture and the creative workplace

Filmmaking education has never been firmly integrated into schooling and in past years has suffered from cuts to funding for youth work and formal and non-formal arts education. It continues to exist only by drawing on creative industry and cultural consumption practices as well as state funding. In this paper we explore the filmmaking education contexts we encountered while doing our own pieces of year-long ethnographic research. These contexts import 'enterprising' ways of thinking, doing and being from the creative workplace and 'bedroom culture'. Located across life's domains, they address enterprising subjects who take pleasure in work, make use of leisure, and who are always learning. We argue that these filmmaking education contexts support young people to develop their private creative practice and introduce them to the possibility of work in the creative industries but, because of the enterprise culture in which they are entangled, uncritically address these young people as enterprising subjects

Observations of Radiation Belt Losses Due to Cyclotron Wave-Particle Interactions

Electron loss to the atmosphere plays a critical role in driving dynamics of the Earths Van Allen radiation belts and slot region. This is a review of atmospheric loss of radiation belt electrons caused by plasma wave scattering via Doppler-shifted cyclotron resonance. In particular, the focus is on observational signatures of electron loss, which include direct measurements of precipitating electrons, measured properties of waves that drive precipitation, and variations in the trapped population resulting from loss. We discuss wave and precipitation measurements from recent missions, including simultaneous multi-payload observations, which have provided new insight into the dynamic nature of the radiation belts

Project X: Physics Opportunities

Part 2 of "Project X: Accelerator Reference Design, Physics Opportunities, Broader Impacts". In this Part, we outline the particle-physics program that can be achieved with Project X, a staged superconducting linac for intensity-frontier particle physics. Topics include neutrino physics, kaon physics, muon physics, electric dipole moments, neutron-antineutron oscillations, new light particles, hadron structure, hadron spectroscopy, and lattice-QCD calculations. Part 1 is available as arXiv:1306.5022 [physics.acc-ph] and Part 3 is available as arXiv:1306.5024 [physics.acc-ph]

Neutrinos

229 pages229 pages229 pagesThe Proceedings of the 2011 workshop on Fundamental Physics at the Intensity Frontier. Science opportunities at the intensity frontier are identified and described in the areas of heavy quarks, charged leptons, neutrinos, proton decay, new light weakly-coupled particles, and nucleons, nuclei, and atoms

QCD and strongly coupled gauge theories : challenges and perspectives

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe

Acoustic monitoring of laboratory hydraulic fracture growth under stress and pore pressure

Fluid-driven fracturing is used in a wide range of applications, including oil and gas extraction, geothermal energy recovery, and CO2 sequestration. In order to efficiently fracture the targeted rock formation, theoretical models provide estimates of the fracture size and shape. Carrying properly scaled laboratory experiments, on the other hand, allows to validate theoretical predictions by providing complete datasets of individual experiments performed under controlled conditions, and therefore to better understand the physics of fluid-driven fracturing. The DelFrac Consortium at TU Delft pioneered this field by building an acoustic monitoring setup inside a triaxial press applying three independent stresses on a cubic specimen (Groenenboom, 1998). At the Geo-Energy Lab, we intend to further investigate the solid and fluid mechanics of hydraulic fractures by building a novel experimental setup in our EPFL facility. The fracturing setup will consist in a triaxial frame designed to accommodate cubic-shaped specimens of up to 250 mm in length, and to apply up to 20 MPa independently on each axis. We will also have the ability to pressurize a pore fluid up to 5 MPa inside the frame in order to simulate in-situ conditions. Our current high-pressure pump can inject fluids with a maximum pressure of 51 MPa and a flow rate ranging from 1 μL/min to 90 mL/min through a high-pressure line and a cased wellbore inside the specimen. We will monitor the growth of the fracture with a combination of compressional and shear piezoelectric transducers for a total of 64 units, that can be used to both generate and measure acoustic energy. We use a function generator connected to a high-power amplifier to generate an excitation signal, which is then routed to one of 32 excitation transducers through a multiplexer. The other 32 transducers are connected to a high-speed acquisition board in order to simultaneously record the measured ultrasonic signals. By carefully placing the transducers on all six faces of the specimen to be fractured, we expect to record transmitted, reflected and diffracted acoustic events (Figure 1). We intend to use these three types of event in order to estimate the spatial extent of the fracture, as well as its thickness along raypaths. Transmission measurements, where the wave travels across the specimen, provide fracture thickness information (Groenenboom & Fokkema, 1998; Kovalyshen et al., 2014). Diffraction events, where the wave propagates to the tip of the fracture and then towards the side of the block, carry information about the tip position, and in turn give an estimate of the fracture size (Groenenboom et al., 2001). Reflection events, where the acoustic energy is reflected back toward the same side of the block, let us discriminate between dry and fluid-filled fracture in the case where a fluid lag is present at the fracture tip