Variations of the amplitudes of oscillation of the Be star Achernar

We report on finding variations in amplitude of the two main oscillation frequencies found in the Be star Achernar, over a period of 5 years. They were uncovered by analysing photometric data of the star from the SMEI instrument. The two frequencies observed, 0.775 c/d and 0.725 c/d, were analysed in detail and their amplitudes were found to increase and decrease significantly over the 5-year period, with the amplitude of the 0.725 c/d frequency changing by up to a factor of eight. The nature of this event has yet to be properly understood, but the possibility of it being due to the effects of a stellar outburst or a stellar cycle are discussed.Comment: 6 pages, 6 figures, 1 table, to be published in MNRA

Healing of simulated fault gouges aided by pressure solution: results from rock analogue experiments

see Abstract Volum

Extending Holding Time for Hot Foods

Humidifying the air inside a hot holding cabinet can greatly extend the holding time for hot foods by retarding the quality degradation of the food due to moisture loss. Not all cabinets are equally effective in maintaining temperature and humidity. A rudimentary understanding of how heat and moisture are transferred to the food will help operators select the cabinet that best meets operation’s needs. The authors address what works and why

Permeability evolution in sorbing media. Analogies between organic-rich shale and coal

Shale gas reservoirs like coalbed methane (CBM) reservoirs are promising targets for geological sequestration of carbon dioxide (CO2). However, the evolution of permeability in shale reservoirs on injection of CO2 is poorly understood unlike CBM reservoirs. In this study, we report measurements of permeability evolution in shales infiltrated separately by nonsorbing (He) and sorbing (CO2) gases under varying gas pressures and confining stresses. Experiments are completed on Pennsylvanian shales containing both natural and artificial fractures under nonpropped and propped conditions. We use the models for permeability evolution in coal (Journal of Petroleum Science and Engineering, Under Revision) to codify the permeability evolution observed in the shale samples. It is observed that for a naturally fractured shale, the He permeability increases by approximately 15% as effective stress is reduced by increasing the gas pressure from 1 MPa to 6 MPa at constant confining stress of 10 MPa. Conversely, the CO2 permeability reduces by a factor of two under similar conditions. A second core is split with a fine saw to create a smooth artificial fracture and the permeabilities are measured for both nonpropped and propped fractures. The He permeability of a propped artificial fracture is approximately 2- to 3fold that of the nonpropped fracture. The He permeability increases with gas pressure under constant confining stress for both nonpropped and propped cases. However, the CO2 permeability of the propped fracture decreases by between one-half to one-third as the gas pressure increases from 1 to 4 MPa at constant confining stress. Interestingly, the CO2 permeability of nonpropped fracture increases with gas pressure at constant confining stress. The permeability evolution of nonpropped and propped artificial fractures in shale is found to be similar to those observed in coals but the extent of permeability reduction by swelling is much lower in shale due to its lower organic content. Optical profilometry is used to quantify the surface roughness. The changes in surface roughness indicate significant influence of proppant indentation on fracture surface in the shale sample. The trends of permeability evolution on injection of CO2 in coals and shales are found analogous; therefore, the permeability evolution models previously developed for coals are adopted to explain the permeability evolution in shales

Characterisation of red-giant stars in the public Kepler data

The first public release of long-cadence stellar photometric data collected by the NASA Kepler mission has now been made available. In this paper we characterise the red-giant (G-K) stars in this large sample in terms of their solar-like oscillations. We use published methods and well-known scaling relations in the analysis. Just over 70% of the red giants in the sample show detectable solar-like oscillations, and from these oscillations we are able to estimate the fundamental properties of the stars. This asteroseismic analysis reveals different populations: low-luminosity H-shell burning red-giant branch stars, cool high-luminosity red giants on the red-giant branch and He-core burning clump and secondary-clump giants.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journa

Imaging elastodynamic and hydraulic properties of in situ fractured rock. An experimental investigation exploring effects of dynamic stressing and shearing

We describe laboratory experiments to elucidate the relationship between nonlinear elasticity and permeability evolution in fractured media subjected to local stress perturbations. This study is part of an effort to measure fluid pathways and fracture properties using active-source acoustic monitoring during fluid injection and shear of rough fractures. Experiments were conducted with L-shaped samples of Westerly granite fractured in situ under triaxial conditions with deionized water subsequently circulated through the resulting fractures. After in situ fracturing, we separately imposed oscillations of the applied normal stress and pore pressure with amplitudes ranging from 0.2 to 1 MPa and frequencies from 0.1 to 40 Hz. In response to normal stress and pore pressure oscillations, fractured Westerly granite samples exhibit characteristic transient softening, acoustic velocity fluctuations, and slow recovery, together with permeability enhancement or decay, informing us about the coupled nonlinear elastodynamic and poromechanical rock properties. Fracture interface properties (contact asperity stiffness, aperture) are then altered in situ by shearing, which generally decreases the measured elastic nonlinearity and permeability change for both normal stress and pore pressure oscillations

The universal red-giant oscillation pattern; an automated determination with CoRoT data

The CoRoT and Kepler satellites have provided thousands of red-giant oscillation spectra. The analysis of these spectra requires efficient methods for identifying all eigenmode parameters. The assumption of new scaling laws allows us to construct a theoretical oscillation pattern. We then obtain a highly precise determination of the large separation by correlating the observed patterns with this reference. We demonstrate that this pattern is universal and are able to unambiguously assign the eigenmode radial orders and angular degrees. This solves one of the current outstanding problems of asteroseismology hence allowing precise theoretical investigation of red-giant interiors.Comment: Accepted in A&A letter

Reliability of P mode event classification using contemporaneous BiSON and GOLF observations

We carried out a comparison of the signals seen in contemporaneous BiSON and GOLF data sets. Both instruments perform Doppler shift velocity measurements in integrated sunlight, although BiSON perform measurements from the two wings of potassium absorption line and GOLF from one wing of the NaD1 line. Discrepancies between the two datasets have been observed. We show,in fact, that the relative power depends on the wing in which GOLF data observes. During the blue wing period, the relative power is much higher than in BiSON datasets, while a good agreement has been observed during the red period.Comment: 7 pages, HELAS II: Helioseismology, Asteroseismology, and MHD Connections, conference proceedin

Breakdown pressure and fracture surface morphology of hydraulic fracturing in shale with H2O, CO2 and N2

Slick-water fracturing is the most routine form of well stimulation in shales; however N2, LPG and CO2 have all been used as “exotic” stimulants in various hydrocarbon reservoirs. We explore the use of these gases as stimulants on Green River shale to compare the form and behavior of fractures in shale driven by different gas compositions and states and indexed by breakdown pressure and the resulting morphology of the fracture networks. Fracturing is completed on cylindrical samples containing a single blind axial borehole under simple triaxial conditions with confining pressure ranging from 10 to 25 MPa and axial stress ranging from 0 to 35 MPa (σ1 > σ2 = σ3). Results show that: (1) under the same stress conditions, CO2 returns the highest breakdown pressure, followed by N2, and with H2O exhibiting the lowest breakdown pressure; (2) CO2 fracturing, compared to other fracturing fluids, creates nominally the most complex fracturing patterns as well as the roughest fracture surface and with the greatest apparent local damage followed by H2O and then N2; (3) under conditions of constant injection rate, the CO2 pressure build-up record exhibits condensation between ~5 and 7 MPa and transits from gas to liquid through a mixed-phase region rather than directly to liquid as for H2O and N2 which do not; (4) there is a positive correlation between minimum principal stress and breakdown pressure for failure both by transverse fracturing (σ3axial) and by longitudinal fracturing (σ3radial) for each fracturing fluid with CO2 having the highest correlation coefficient/slope and lowest for H2O. We explain these results in terms of a mechanistic understanding of breakdown, and through correlations with the specific properties of the stimulating fluids