Standard method for performing positron emission particle tracking (PEPT) measurements of froth flotation at PEPT Cape Town.

Positron emission particle tracking (PEPT) is a technique for measuring the motion of tracer particles in systems of flow such as mineral froth flotation. An advantage of PEPT is that tracer particles with different physical properties can be tracked in the same experimental system, which allows detailed studies of the relative behaviour of different particle classes in flotation. This work describes the standard operating protocol developed for PEPT experiments in a flotation vessel at PEPT Cape Town in South Africa. A continuously overflowing vessel with constant air recovery enables several hours of data acquisition at steady state flow and consistent flotation conditions. Tracer particles are fabricated with different coatings to mimic mineral surface hydrophobicity and size, and a data treatment derived from a rotating disk study is utilized to produce high frequency (1 kHz) location data relative to the tracer activity. Time averaging methods are used to represent the Eulerian flow field and occupancy of the tracer behaviour based on voxel schemes in different co-ordinate systems. The average velocity of the flow in each voxel is calculated as the peak of the probability density function to represent the peak of asymmetrical or multimodal distributions.•A continuously overflowing flotation vessel was developed for extended data acquisition at steady state flow.•The data treatment enabled the direct comparison of different particle classes in the flotation vessel.•The solids flow fields was described by the probability density function of tracer particle velocity measured in different voxel schemes.

Speech intelligibility while wearing full-facepiece air-purifying respirators.

Intelligible speech communication while wearing air-purifying respirators is critical for law enforcement officers, particularly when they are communicating with each other or the public. The National Institute for Occupational Safety and Health (NIOSH) requires a 70% overall performance rating to pass speech intelligibility certification for commercial chemical, biological, radiological, and nuclear air-purifying respirators. However, the speech intelligibility of certified respirators is not reported and the impact on operational performance is unknown. The objective of this effort was to assess the speech intelligibility of 12 certified air-purifying respirators and to predict their impact on operational performance. The NIOSH respirator certification standard testing procedures were followed. Regression equations were fit to data from studies that examined the impact of degraded speech intelligibility on operational performance of simple and complex missions. The impact of the tested respirators on operational performance was estimated from these equations. Performance ratings observed for each respirator were: MSA Millennium (90%), 3M FR-M40 (88%), MSA Ultra Elite (87%), Scott M110 (86%), North 5400 (85%), Scott M120 (85%), Avon C50 (84%), Avon FM12 (84%), Survivair Optifit (81%), Drager CDR 4500 (81%), Peltor-AOSafety M-TAC (79%), and 3M FR-7800B (78%). The Millennium and FR-M40 had statistically significantly higher scores than the FR-7800B. The Millennium also scored significantly higher than the M-TAC. All of the tested respirators were predicted to have little impact on simple and complex mission performance times and on simple mission success rate. However, the regression equations showed that 75% of missions that require complex communications would be completed while wearing the Millennium, FR-M40, or Ultra Elite but that only 60% would be completed successfully while wearing the FR-7800B. These results suggest that some certified respirators may have a greater impact on speech communications than others.

Effects of respirator ambient air cooling on thermophysiological responses and comfort sensations.

This investigation assessed the thermophysiological and subjective impacts of different respirator ambient air cooling options while wearing chemical and biological personal protective equipment in a warm environment (32.7 ± 0.4°C, 49.6 ± 6.5% RH). Ten volunteers participated in 90-min heat exposure trials with and without respirator (Control) wear and performed computer-generated tasks while seated. Ambient air cooling was provided to respirators modified to blow air to the forehead (FHC) or to the forehead and the breathing zone (BZC) of a full-facepiece air-purifying respirator using a low-flow (45 L·min(-1)) mini-blower. An unmodified respirator (APR) trial was also completed. The highest body temperatures (TTY) and least favorable comfort ratings were observed for the APR condition. With ambient cooling over the last 60 min of heat exposure, TTY averaged 37.4 ± 0.6°C for Control, 38.0 ± 0.4°C for APR, 37.8 ± 0.5°C for FHC, and 37.6 ± 0.7°C for BZC conditions independent of time. Both the FHC and BZC ambient air cooling conditions reduced facial skin temperatures, reduced the rise in body temperatures, and led to more favorable subjective comfort and thermal sensation ratings over time compared to the APR condition; however statistical differences among conditions were inconsistent. Independent of exposure time, average breathing apparatus comfort scores with BZC (7.2 ± 2.5) were significantly different from both Control (8.9 ± 1.4) and APR (6.5 ± 2.2) conditions when ambient cooling was activated. These findings suggest that low-flow ambient air cooling of the face under low work rate conditions and mild hyperthermia may be a practical method to minimize the thermophysiological strain and reduce perceived respirator discomfort.

Importance of ß-Catenin in glucose and energy homeostasis.

In settings of increased insulin demand, failure to expand pancreatic ß-cells mass leads to diabetes. Genome-wide scans of diabetic populations have uncovered several genes associated with susceptibility to type 2 diabetes and a number of them are part of the Wnt signaling. ß-Catenin, a Wnt downstream effector participates in pancreatic development, however, little is known about its action in mature ß-cells. Deletion of ß-Catenin in Pdx1 pancreatic progenitors leads to a decreased ß-cell mass and impaired glucose tolerance. Surprisingly, loss of ß-catenin made these mice resistant to high fat diet because of their increased energy expenditure and insulin sensitivity due to hyperactivity. The complexity of this phenotype was also explained in part by ectopic expression of Cre recombinase in the hypothalamus. Our data implicates ß-Catenin in the regulation of metabolism and energy homeostasis and suggest that Wnt signaling modulates the susceptibility to diabetes by acting on different tissues.

The validation of a self-report measure and physical activity of Australian Aboriginal and Torres Strait Islander and non-Indigenous rural children.

PURPOSE: To validate a self-report measure of physical activity for both Australian Aboriginal and Torres Strait Islander and non-Indigenous rural children, and to describe their physical activity participation. METHODS: In this cross-sectional study, 84 Aboriginal and Torres Strait Islander and 146 non-Indigenous children aged 10-12 years old completed the Many Rivers Physical Activity Recall Questionnaire (MRPARQ), a modified version of the Adolescent Physical Activity Recall Questionnaire (APARQ). A sub-group (n=86) wore an accelerometer for seven consecutive days in order to validate the instrument. RESULTS: Pearson and Intra Class Correlation coefficients between the survey and acceleromtery for weekdays only are 0.31 and 0.16, respectively, for Aboriginal and Torres Strait Islander children, and 0.38 and 0.31, respectively, for non-Indigenous children, and demonstrate a modest (p<0.05) correlation. Self-reported MVPA for Aboriginal and Torres Strait Islander children is between 162 and 172 minutes/day, and is 125 minutes by accelerometer; for non-Indigenous children MVPA is between 123 and 149 minutes (survey) and 107 minutes (accelerometer). CONCLUSION: Australian Aboriginal and Torres Strait Islander children's self-report of physical activity is at least as valid as non-Indigenous children, given culturally appropriate support; they tend to be more active than non-Indigenous children. IMPLICATIONS: The MRPARQ can be administered with Aboriginal and Torres Strait Islander and non-Indigenous children.

Regulation of pancreas plasticity and malignant transformation by Akt signaling.

BACKGROUND & AIMS: Extensive evidence suggests that Akt signaling plays an important role in beta-cell mass and function, although its function in the regulation of the different pancreatic fates has not been adequately investigated. The goal of these studies was to assess the role of Akt signaling in the pancreatic differentiation programs. METHODS: For these experiments, we have generated a double reporter mouse model that provides activation of Akt signaling in a cell type-specific manner. This mouse model conditionally overexpresses a constitutively active form of Akt upon Cre-mediated recombination. Activation of Akt signaling in pancreatic progenitors and acinar and beta-cells was achieved by crossing this animal model to specific Cre-lines. RESULTS: We showed that overexpression of a constitutively active Akt in pancreatic and duodenal homeobox 1 (Pdx1) progenitors induced expansion of ductal structures expressing progenitor markers. This expansion resulted in part from increased proliferation of the ductal epithelium. Lineage-tracing experiments in mice with activation of Akt signaling in mature acinar and beta-cells suggested that acinar-to-ductal and beta-cell-to-acinar/ductal transdifferentiation also contributed to the expansion of the ductal compartment. In addition to the changes in cell plasticity, these studies demonstrated that chronic activation of Akt signaling in Pdx1 progenitors induced the development of premalignant lesions and malignant transformation in old mice. CONCLUSIONS: The current work unravels some of the molecular mechanisms of cellular plasticity and reprogramming, and demonstrates for the first time that activation of Akt signaling regulates the fate of differentiated pancreatic cells in vivo.

Differential effects of p27 in regulation of beta-cell mass during development, neonatal period, and adult life.

beta-Cell cycle progression and proliferation are critical to maintain beta-cell mass in adult mice. Of the cell cycle inhibitors, p27Kip1 is thought to be the primary modulator of the proliferative status in most cell types. p27 plays a role in beta-cell adaptation in genetic models of insulin resistance. To study the role of p27 in beta-cells during physiological conditions and at different stages of beta-cell differentiation, we studied mice deficient of or overexpressing p27. Experiments in p27-deficient mice showed improved glucose tolerance and hyperinsulinemia. These changes were associated with increased islet mass and proliferation. The experiments overexpressing p27 in beta-cells were performed using a doxycycline-inducible model. Interestingly, overexpression of p27 for 16 weeks in beta-cells from adult mice had no effect on glucose tolerance, beta-cell mass, or proliferation. In contrast, induction of p27 expression during beta-cell development or early neonatal period resulted in severe glucose intolerance and reduced beta-cell mass by decreased proliferation. These changes were reversible upon discontinuation of doxycycline. These experiments suggest that p27 is a critical molecule for beta-cell proliferation during beta-cell development and early postnatal life but not for maintenance of adult mass.