Uniaxial compression of dense granular materials: Stress distribution and permeability

A uniaxial compression apparatus designed to investigate the dynamics of proppant particle packing is described. This dynamic compression device (DCD) uses a small charge of particles, approximately 3.5–7 cm³ depending upon the configuration of an experiment. The DCD allows simultaneous measurement of boundary stresses on the packing and permeability of the packing to fluid flow. Visualization of the packing at compressive stress levels up to σ_A = 7100 psi (49 MPa) is also demonstrated. The stresses measured are the normal stress at both walls on the axis of compression, with their difference providing a measure of the shear (or friction) force from the walls, and the transverse normal stress on one orthogonal axis, σ_T. Permeability may be determined by either a fixed pressure drop or fixed flow rate experiment, with results presented from the fixed pressure drop approach by imposing a small gravity head of the flowing liquid; liquid flow is gravimetrically measured.The behaviors of packings of hard particles, both uncoated and when coated with a very viscous and tacky polyamide resin, are reported. The packing materials include a ceramic material used as a proppant in hydraulic fracturing of petroleum wells, and glass beads. The proppant and glass beads have mean diameters of approximately 700 μm and 500 μm, respectively, with the proppant less spherical and more polydisperse than the glass beads. The proppant particles undergo only limited breakage up to the maximum stress imposed here. The glass beads undergo significant breakage. Protocols for the compression can be varied. The reported results use a single loading and unloading at the same speed in each segment (increasing and decreasing stress), as well as a cyclic loading of differing numbers of cycles. The rate of loading is specified and can be varied from 0.56 μm/s–1.7 mm/s, with results here focusing on the range of 1–30 μm/s. Measured stress and permeability are shown as a function of axial load and loading rate, as well as the behavior in cyclic loading. The results are shown to be highly reproducible, establishing the ability to determine the properties of a proppant pack in a small charge device with imposed deformation. The influence of the resin coating on the properties is reported.Direct visualization is one of the key features of the DCD. Local motions and overall rearrangements of particles can be monitored by digital camera. These have been presented using particle image velocimetry (PIV).     

Oxygen vacancy diffusion in alumina: New atomistic simulation methods applied to an old problem

Understanding diffusion in alumina is a long-standing challenge in ceramic science. The present article applies a novel combination of metadynamics and kinetic Monte Carlo simulation approaches to the investigation of oxygen vacancy diffusion in alumina. Three classes of diffusive jumps with different activation energies were identified, the resulting diffusion coefficient being best fitted by an Arrhenius equation having a pre-exponential factor of 7.88 × 10⁻² m² s⁻¹ and an activation energy of 510.83 kJ mol⁻¹. This activation energy is very close to values for the most pure aluminas studied experimentally (activation energy 531 kJ mol⁻¹). The good agreement indicates that the dominating atomic-scale diffusion mechanism in alumina is vacancy diffusion.     

Community energy planning in Canada: The role of renewable energy

An emerging trend in Canada is the creation of community energy plans, where decisions that used to be left to regional level energy agencies or private individuals are now being considered at the community level. A desire to reduce greenhouse gas emissions and to become more energy self-sufficient is driving this change. Theoretically, local level management is desirable because it achieves these goals through improvements in the three areas of energy efficiency, energy conservation and switching to renewable energy sources. The analysis of 10 of the first community energy plans in Canadian communities, ranging in population size from 500 to one million, finds that communities are choosing policies and programs centred on increasing energy efficiency and conservation while renewable energy receives much less attention. Municipal operations were called upon to set higher targets than the general community. Communities that recognized the substantial potential of renewable energy often focused on technologies that the municipal sector could implement, such as bio-fuels for their transportation fleet. Wind, passive solar design, solar photovoltaics and solar thermal options were only recommended in a few cases. Overall, only one of the five larger communities (Calgary) recommended implementing multiple renewable energy technologies while three of the five smaller communities proposed multiple renewable energy sources. The implication is that smaller and more remote communities may be the most willing to lead in the planned introduction of renewable energy systems.     

Cyanobacterial blooms in the central basin of Lake Erie: Potentials for cyanotoxins and environmental drivers

Lake Erie western basin (WB) cyanobacterial blooms are a yearly summer occurrence; however, blooms have also been reported in the offshore waters of the central basin (CB), and very little is known about what drives these blooms or their potential for cyanobacterial toxins. Cyanobacteria Index was quantified using MODIS and MERIS data for the CB between 2003 and 2017, and water samples were collected between 2013 and 2017. The goals were to 1) quantify cyanobacteria, 2) determine environmental drivers of CB blooms, and 3) determine the potential for cyanobacterial toxins in the CB. Dolichospermum (Anabaena) occurred in the CB during July before the onset of the WB bloom, and then in August and September, the cyanobacteria community shifted towards Microcystis. The largest Dolichospermum blooms (2003, 2012, 2013, and 2015) were associated with reduced water clarity (Secchi disk depth?<?4?m), whereas large CB Microcystis blooms (2011 and 2015) were associated with large WB blooms. Dolichospermum blooms occurred in high nitrate concentrations (>20?μmol/L) and high nitrogen-to?phosphorus ratios (>100), which indicate nutrient concentrations or ratios did not select for Dolichospermum. Additionally, the sxtA gene, but not mcyE or microcystins, were detected in the CB during July 2016 and 2017. The mcyE gene and microcystins were detected in the CB during August 2016 and 2017. The results indicate the CB's potential for cyanotoxins shifts from saxitoxins to microcystins throughout the summer. Continued monitoring of cyanobacteria and multiple cyanobacterial toxins is recommended to ensure safe drinking water for CB coastal communities.     

Comparison of phonetic judgments and electropalatographic measurements of articulatory place of production

Judgments of articulatory place of production were obtained for a set of consonant-vowel nonsense syllables spoken with a known place of production by two normal speakers. Correspondence between judgments and actual place of production was poor.     

Oncocytic lesions of the caruncle and other ocular adnexa

This is a clinicopathologic study of 18 oncocytic lesions involving the ocular adnexa. These lesions most commonly occur in elderly patients (median age 73), and there is a striking predilection for women. The broad spectrum of lesions included oncocytic adenomatous hyperplasia, oncocytomas, and oncocytic carcinoma. Ten lesions, all of which were oncocytomas, involved the caruncle, four the conjunctiva, and one the mucocutaneous junction of the eyelid. Two tumors involved the lacrimal sac and one the lacrimal gland. A review of the literature disclosed only 17 previously reported oncocytic lesions of the ocular adnexa. A small yellowish-tan or reddish caruncular mass, especially in an elderly woman, should alert the ophthalmologist to consider the possibility of oncocytoma in his differential diagnosis.     

The interaction of dietary fibers and cholesterol upon the plasma lipids and lipoproteins, sterol balance, and bowel function in human subjects

To identify any metabolic effects of dietary fiber upon cholesterol metabolism in man, six adult volunteer subjects were fed eucaloric cholesterol-free formula diets, with and without added dietary fiber for two 4-wk periods. A large quantity of dietary fiber was fed, some 60 g of plant cell wall material (or 16 g of crude fiber) derived from corn, beans, bran, pectin, and purified cellulose. This provided about five times the fiber intake of the typical American diet. The addition of fiber to the cholesterol-free diet did not change either the plasma cholesterol level (171+/-21 mg/dl, SEM, to 167+/-18) or the triglyceride (103+/-39 to 93+/-27 mg/dl). The excretion of both endogenous neutral steroids and bile acids were unchanged with fiber (505+/-41 to 636+/-75 mg/day and 194+/-23 to 266+/-47 mg/day, respectively.) However, total fecal steroid excretion was increased 699+/-29 to 902+/-64 mg/day, P < 0.025). With fiber, intestinal transit time was decreased (59+/-9 to 35+/-8 h, P < 0.005), and both the wet and dry stool weights were greatly increased.A second group of six subjects was fed similar diets containing 1,000 mg cholesterol derived from egg yolk. The addition of fiber to the 1,000-mg cholesterol diet did not alter either plasma cholesterol level (233+/-26 to 223+/-36 mg/dl) or triglyceride (102+/-19 to 83+/-11 mg/dl). The excretion of endogenous neutral steroids (618+/-84 to 571+/-59 mg/day), of bile acids (423+/-122 to 401+/-89 mg/day), and of total fecal steroids (1,041+/-175 to 972+/-111 mg/day) were unchanged by fiber. The absorption of dietary cholesterol was not altered when fiber was added to the 1,000-mg cholesterol diet (44.0+/-3.3 to 42.9+/-2.5%). A two-way analysis of variance utilizing both groups of subjects indicated a significant (P < 0.001) effect of dietary cholesterol upon the plasma cholesterol concentration. We concluded that a large quantity of dietary fiber from diverse sources had little or no effect upon the plasma lipids and sterol balance in man in spite of the fact that intestinal transit time and stool bulk changed greatly.