Constriction size distributions of granular filters: a numerical study

The retention capability of granular filters is controlled by the narrow constrictions connecting the voids within the filter. The theoretical justification for empirical filter rules used in practice includes consideration of an idealised soil fabric in which constrictions form between co-planar combinations of spherical filter particles. This idealised fabric has not been confirmed by experimental or numerical observations of real constrictions. This paper reports the results of direct, particle-scale measurement of the constriction size distribution (CSD) within virtual samples of granular filters created using the discrete-element method (DEM). A previously proposed analytical method that predicts the full CSD using inscribed circles to estimate constriction sizes is found to poorly predict the CSD for widely graded filters due to an over-idealisation of the soil fabric. The DEM data generated are used to explore quantitatively the influence of the coefficient of uniformity, particle size distribution and relative density of the filter on the CSD. For a given relative density CSDs form a narrow band of similarly shaped curves when normalised by characteristic filter diameters. This lends support to the practical use of characteristic diameters to assess filter retention capability

AN INVESTIGATION OF THE ACTIVATION OF THE SUBDIVISIONS OF GLUTEUS MEDIUS DURING ISOMETRIC HIP CONTRACTIONS

Gluteus medius is involved in movement and stability of the hip and gluteus medius dysfunction is commonly implicated in many lower limb pathologies (Fredericson et al 2000). It is proposed that functional subdivisions exist within the gluteus medius muscle (Conneely and O’Sullivan 2008). There is however a lack of empirical evidence examining the role of the subdivisions of gluteus medius. This study compared the muscle activation of these subdivisions (anterior, middle and posterior) during isometric contractions of hip abduction, internal and external rotation in normal subjects

Canine dystocia in 50 UK first-opinion emergency-care veterinary practices: prevalence and risk factors

Dystocia can represent a major welfare issue for dogs of certain breeds and morphologies. First-opinion emergency-care veterinary caseloads represent a useful data resource for epidemiological research because dystocia can often result in emergency veterinary care. The study analysed a merged database of clinical records from 50 first-opinion emergency-care veterinary practices participating in the VetCompass Programme. Multivariable logistic regression modelling was used for risk factors analysis. There were 701 dystocia cases recorded among 18,758 entire female dogs, resulting in a dystocia prevalence of 3.7 per cent (95 per cent CI 3.5–4.0 per cent). Breeds with the highest odds of dystocia compared with crossbred bitches were French Bulldog (OR: 15.9, 95 per cent CI 9.3 to 27.2, P<0.001), Boston Terrier (OR: 12.9, 95 per cent CI 5.6 to 29.3, P<0.001), Chihuahua (OR: 10.4, 95 per cent CI 7.0 to 15.7, P<0.001) and Pug (OR: 11.3, 95 per cent CI 7.1 to 17.9, P<0.001). Bitches aged between 3.0 and 5.9 years had 3.1 (95 per cent CI 2.6 to 3.7, P<0.001) times the odds of dystocia compared with bitches aged under 3.0years. Certain breeds, including some brachycephalic and toy breeds, appeared at high risk of dystocia. Opportunities to improve this situation are discussed

Influence of particle size distribution on the proportion of stress-transmitting particles and implications for measures of soil state

It is generally accepted that the use of void ratio and bulk density as measures of soil8state have limitations in the case of gap-graded soils as the finer grains may not 9transmit stress. However, hitherto no one has systematically explored whether this 10issue also emerges for soils with continuous gradings. Building on a number of experimental and discrete element method (DEM) studies that have considered the idea of an effective void ratio for gap-graded or bi-modal soils, this contribution extends consideration of this concept to a broader range of particle size distributions. By exploiting high performance computers, this study considers a range of ideal isotropically compressed samples of spherical particles with linear, fractal and gap-graded (bimodal and trimodal) particle size distributions. The materials’ initial packing densities are controlled by varying the inter-particle coefficient of friction. The results show that even for soils with continuous particle size distributions, a significant proportion of the finer particles may not transmit stress and be inactive. Drawing on ideas put forward in relation to gap-graded soils, both a mechanical void ratio and mechanical bulk density that consider the inactive grains as part of the void space are determined. Even for the linear and fractal gradings considered here, the difference between the conventional measures and the mechanical measures is finite and density dependent. The difference is measurably larger in the looser samples considered. These data highlight a conceptual/fundamental limitation of using the global void ratio26as a measure of state in expressions to predict granular material behaviou

Increasing concentrations of dichloromethane, CH2Cl2, inferred from CARIBIC air samples collected 1998–2012

Atmospheric concentrations of dichloromethane, CH2Cl2, a regulated toxic air pollutant and minor contributor to stratospheric ozone depletion, were reported to have peaked around 1990 and to be declining in the early part of the 21st century. Recent observations suggest this trend has reversed and that CH2Cl2 is once again increasing in the atmosphere. Despite the importance of ongoing monitoring and reporting of atmospheric CH2Cl2, no time series has been discussed in detail since 2006. The CARIBIC project (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) has analysed the halocarbon content of whole-air samples collected at altitudes of between ~10–12 km via a custom-built container installed on commercial passenger aircraft since 1998, providing a long-term record of CH2Cl2 observations. In this paper we present this unique CH2Cl2 time series, discussing key flight routes which have been used at various times over the past 15 years. Between 1998 and 2012 increases were seen in all northern hemispheric regions and at different altitudes, ranging from ~7–10 ppt in background air to ~13–15 ppt in regions with stronger emissions (equating to a 38–69% increase). Of particular interest is the rising importance of India as a source of atmospheric CH2Cl2: based on CARIBIC data we provide regional emission estimates for the Indian subcontinent and show that regional emissions have increased from 3–14 Gg yr^-1 (1998–2000) to 16–25 Gg yr^-1 (2008). Potential causes of the increasing atmospheric burden of CH2Cl2 are discussed. One possible source is the increased use of CH2Cl2 as a feedstock for the production of HFC-32, a chemical used predominantly as a replacement for ozone-depleting substances in a variety of applications including air conditioners and refrigeration

Particle Impact Analysis of Bulk Powder During Pneumatic Conveyance

Fragmentation of powders during transportation is a common problem for manufacturers of food and pharmaceutical products. We illustrate that the primary cause of breakage is due to inter-particle collisions, rather than particle-wall impacts, and provide a statistical mechanics model giving the number of collisions resulting in fragmentation

Using ultrasonic reflection resonance to probe stress wave velocity in assemblies of spherical particles

A high-sensitivity method to measure acoustic wave speed in soils by analyzing the reflected ultrasonic signal from a resonating layered interface is proposed here. Specifically, an ultrasonic transducer which can be used to both transmit and receive signals is installed on a low-high acousticimpedance layered structure of hard PVC and steel, which in turn is placed in contact with the soil deposit of interest. The acoustic impedance of the soil (the product of density and wave velocity) is deduced from analysis of the waves reflected back to the transducer. A system configuration design is enabled by developing an analytical model that correlates the objective wave speed with the measurable reflection coefficient spectrum. The physical viability of this testing approach is demonstrated by means of a one-dimensional compression device that probes the stress-dependence of compression wave velocity of different sizes of glass ballotini particles. Provided the ratio of the wavelength of the generated wave to the soil particle size is sufficiently large the data generated are in agreement with data obtained using conventional time-of-flight measurements. In principle, this high-sensitivity approach avoids the need for the wave to travel a long distance between multiple transmitterreceiver sensors as is typically the case in geophysical testing of soil. Therefore it is particularly suited to in-situ observation of soil properties in a highly compact setup, where only a single transducer is required. Furthermore, high spatial resolution of local measurements can be achieved, and the data are unaffected by wave attenuation as transmitted in soil

Acoustic emission enabled particle size estimation via low stress-varied axial interface shearing

Acoustic emission (AE) refers to a rapid release of localized stress energy that propagates as a transient elastic wave and is typically used in geotechnical applications to study stick-slip during shearing, and breakage and fracture of particles. This article develops a novel method of estimating the particle size, an important characteristic of granular materials, using axial interface shearing-induced AE signals. Specifically, a test setup that enables axial interface shearing between a one-dimensional compression granular deposit and a smooth shaft surface is developed. The interface sliding speed (up to 3mm/s), the compression stress (0-135kPa), and the particle size (150μm-5mm) are varied to test the acoustic response. The start and end moments of a shearing motion, between which a burst of AE data is produced, are identified through the variation of the AE count rates, before key parameters can be extracted from the bursts of interests. Linear regression models are then built to correlate the AE parameters with particle size, where a comprehensive evaluation and comparison in terms of estimation errors is performed. For granular samples with a single size, it is found that both the AE energy related parameters and AE counts, obtained using an appropriate threshold voltage, are effective in differentiating the particle size, exhibiting low fitting errors. The value of this technique lies in its potential application to field testing, for example as an add-on to cone penetration test systems and to enable in-situ characterization of geological deposits