Turbulent kinetic energy equation and free mixing

Calculation of free shear flows was carried out to investigate the usefulness of several concepts which were previously successfully applied to wall flows. The method belongs to the class of differential approaches. The turbulence is taken into account by the introduction of one additional partial differential equation, the transport equation for the turbulent shear stress. The structure of turbulence is modeled after Bradshaw et al. This model was used successfully in boundary layers and its applicability to other flows is demonstrated. The work reported differs substantially from that of an earlier attempt to use this approach for calculation of free flows. The most important difference is that the region around the center line is treated by invoking the interaction hypothesis (concerning the structure of turbulence in the regions separated by the velocity extrema). The compressibility effects on shear layer spreading at low and moderate Mach numbers were investigated. In the absence of detailed experiments in free flows, the evidence from boundary layers that at low Mach numbers the structure of turbulence is unaffected by the compressibility was relied on. The present model was tested over a range of self-preserving and developing flows including pressure gradients using identical empirical input. The dependence of the structure of turbulence on the spreading rate of the shear layer was established

Assessment of closure coefficients for compressible-flow turbulence models

A critical assessment is made of the closure coefficients used for turbulence length scale in existing models of the transport equation, with reference to the extension of these models to compressible flow. It is shown that to satisfy the compressible 'law of the wall', the model coefficients must actually be functions of density gradients. The magnitude of the errors that result from neglecting this dependence on density varies with the variable used to specify the length scale. Among the models investigated, the k-omega model yields the best performance, although it is not completely free from errors associated with density terms. Models designed to reduce the density-gradient effect to an insignificant level are proposed

Emergence of Kinetic Behavior in Streaming Ultracold Neutral Plasmas

We create streaming ultracold neutral plasmas by tailoring the photoionizing laser beam that creates the plasma. By varying the electron temperature, we control the relative velocity of the streaming populations, and, in conjunction with variation of the plasma density, this controls the ion collisionality of the colliding streams. Laser-induced fluorescence is used to map the spatially resolved density and velocity distribution function for the ions. We identify the lack of local thermal equilibrium and distinct populations of interpenetrating, counter-streaming ions as signatures of kinetic behavior. Experimental data is compared with results from a one-dimensional, two-fluid numerical simulation.Comment: 8 pages, 6 figure

Inference of heating properties from "hot" non-flaring plasmas in active region cores. I. Single nanoflares

The properties that are expected of “hot” non-flaring plasmas due to nanoflare heating in active regions are investigated using hydrodynamic modeling tools, including a two-fluid development of the Enthalpy Based Thermal Evolution of Loops code. Here we study a single nanoflare and show that while simple models predict an emission measure distribution extending well above 10 MK, which is consistent with cooling by thermal conduction, many other effects are likely to limit the existence and detectability of such plasmas. These include: differential heating between electrons and ions, ionization non-equilibrium, and for short nanoflares, the time taken for the coronal density to increase. The most useful temperature range to look for this plasma, often called the “smoking gun” of nanoflare heating, lies between 10 6.6 and 10 7 K. Signatures of the actual heating may be detectable in some instances.Publisher PDFPeer reviewe

Design of a low-noise aeroacoustic wind tunnel facility at Brunel University

This paper represents the design principle of a quiet, low turbulence and moderately high speed aeroacoustic wind tunnel which was recently commissioned at Brunel University. A new hemi-anechoic chamber was purposely built to facilitate aeroacoustic measurements. The wind tunnel can achieve a maximum speed of about 80 ms-1. The turbulence intensity of the free jet in the potential core is between 0.1–0.2%. The noise characteristic of the aeroacoustic wind tunnel was validated by three case studies. All of which can demonstrate a very low background noise produced by the bare jet in comparison to the noise radiated from the cylinder rod/flat plate/airfoil in the air stream.The constructions of the aeroacoustic wind tunnel and the hemi-anechoic chamber are financially supported by the School of Engineering and Design at Brunel University

Examining potential school contextual influences on gambling among high school youth

Background and Objectives: Gambling is an increasing concern among adolescence, yet there has been limited investigation into school-level factors that may increase the risk for gambling. The current study examined the relationship between substance use and gambling, and explored the influence of school context on adolescent gambling. Methods: Data come from 25,456 students in 58 high schools participating in the Maryland Safe and Supportive Schools Initiative. Youth-reports of socio-demographics, lifetime gambling, and past-month substance use (ie, alcohol, cigarette, marijuana, non-medical prescription drug) were collected. School-level characteristics were student suspension rate, student mobility, percentage of students receiving free/reduce-priced meals, percentage of African American students, urbanicity, gambling prevalence, gambling problem prevalence, and substance use prevalence. Weighted multilevel analyses were conducted. Results: One-third (n = 8,318) reported lifetime gambling, and 10% (n = 2,580) of the full sample, or 31% of the gamblers, experienced gambling problems. Being male and alcohol, marijuana, and non-medical prescription drug use were associated with twice the odds of gambling. Among gamblers, being male, African American, and cigarette, marijuana, and non-medical prescription drug use were associated with higher odds of gambling problems. The school-level factors of suspension rate and percentage of African American had minimal, inverse associations with gambling; however, none were related to gambling problems. Conclusions: Multilevel results indicated that adolescents that are male and use substances are more likely to gamble and have gambling problems. Scientific Significance: The findings indicate a need for prevention programs targeting risky behaviors to also target gambling as such behaviors often co-occur among adolescents

Possible Jurassic age for part of Rakaia Terrane: implications for tectonic development of the Torlesse accretionary prism

Greywacke sandstone and argillite beds comprising Rakaia Terrane (Torlesse Complex) in mid Canterbury, South Island, New Zealand, are widely regarded as Late Triassic (Norian) in age based on the occurrence of Torlessia trace fossils, Monotis, and other taxa. This paleontological age assignment is tested using published 40Ar/39Ar mica and U-Pb zircon ages for these rocks and published and new zircon fission track (FT) ages. The youngest U-Pb zircon ages in the Rakaia Terrane rocks in mid Canterbury are Norian, whereas 10-20% of the 40Ar/39Ar muscovite ages are younger than Norian. Numerical modelling of these mica ages shows that they cannot have originated from partial thermal overprinting in the Torlesse prism if the thermal maximum was short-lived and early in the prism history (210-190 Ma), as commonly inferred for these rocks. The young component of mica ages could, however, be explained by extended residence (200-100 Ma) at 265-290deg.C in the prism. Early Jurassic (c. 189 Ma) zircon FT ages for sandstone beds from Arthur's Pass, the Rakaia valley, and the Hermitage (Mt Cook) are interpreted not to have experienced maximum temperatures above 210deg.C, and therefore cannot have been reduced as a result of partial annealing in the Torlesse prism. This is based on identification of a fossil Cretaceous, zircon FT, partial annealing zone in low-grade schists to the west, and the characteristics of the age data. The Early Jurassic zircon FT ages and the young component of 40Ar/39Ar mica ages are regarded therefore as detrital ages reflecting cooling in the source area, and constrain the maximum depositional age of parts of the Rakaia Terrane in mid Canterbury. The zircon FT data also show the initiation (c. 100 Ma) of marked and widespread Late Cretaceous cooling of Rakaia Terrane throughout Canterbury, which is attributed to uplift and erosion of inboard parts of the Torlesse prism due to continuing subduction accretion at its toe. The critical wedge concept is proposed as a new framework for investigating the development of the Torlesse Complex. The Rakaia Terrane may have formed the core of an accretionary wedge imbricated against the New Zealand margin during the Middle or Late Jurassic. Late Jurassic nonmarine sediments (e.g., Clent Hills Formation) accumulated upon the inner parts of the prism as it enlarged, emerged, and continued to be imbricated. Exhumation of Otago Schist from c. 135 Ma may mark the development of a balance (steady state) between sediments entering the prism at the toe and material exiting at the inboard margin. The enlargement of the area of exhumation to all of Canterbury from c. 100 Ma may reflect a dynamic response to widening of the prism through the accretion of Cretaceous sediments. The model of a dynamic critical wedge may help to explain the various expressions of the Rangitata Orogeny

Disaster Preparedness and Response: A Survey of U.S. Dental Hygienists

Purpose: The purpose of this study was to assess dental hygienists’ interests, current involvement, formal education, views, comfort levels, and intentions for involvement with disaster preparedness and response. Methods: Dental hygienists (n=400) were asked to respond to a 21-item online survey. Data was analyzed using descriptive statistics, chi-square goodness-of-fit tests, and a paired-samples t-test. Common themes were identified and categorized from open-ended questions. Results: A response rate of 84% (n=334) was obtained. Most respondents (97%) reported no involvement with disaster preparedness and response; however, a majority (86%) reported interest. Of those who indicated an interest in disaster preparedness and response, 92% had intentions for becoming involved. A majority of dental hygienists (93%) had not received formal education in disaster preparedness and response; yet, 95% shared the view that dental hygienists could have a vital role in this specialty area. Although results indicated a mean difference of 9% increased comfort with activities not requiring physical contact with human remains, dental hygienists were relatively comfortable with activities requiring contact: taking photographs (76%, n=254), taking radiographs (83%, n=273), resecting the mandible (55%, n=184), cleaning skeletonized remains (67%, n=221). Conclusion: Dental hygienists view themselves as professionals who could have a vital role in disaster preparedness and response. Efforts should be made to increase dental hygiene formal education in disaster preparedness and response with needed curriculum models and competencies for best outcomes when dental hygienists are serving their communities

Tracking mortality in near to real time provides essential information about the impact of the COVID-19 pandemic in South Africa in 2020

Background. Producing timely and accurate estimates of the impact of COVID-19 on mortality is challenging for most countries, but impossible for South Africa (SA) from cause-of-death statistics. Objectives. To quantify the excess deaths and likely magnitude of COVID-19 in SA in 2020 and draw conclusions on monitoring the epidemic in 2021. Methods. Basic details of deaths registered on the National Population Register by the Department of Home Affairs (DoHA) are provided to the South African Medical Research Council weekly. Adjustments are made to the numbers of weekly deaths to account for non-registration on the population register, as well as late registration of death with the DoHA. The weekly number of deaths is compared with the number predicted based on the Holt-Winters time-series analysis of past deaths for provinces and metropolitan areas. Excess deaths were calculated for all-causes deaths and natural deaths, using the predicted deaths as a baseline. In addition, an adjustment was made to the baseline for natural deaths to account for the drop in natural deaths due to lockdown. Results. We estimated that just over 550 000 deaths occurred among persons aged ≥1 year during 2020, 13% higher than the 485 000 predicted before the pandemic. A pronounced increase in weekly deaths from natural causes peaked in the middle of July across all ages except <20 years, and across all provinces with slightly different timing. During December, it became clear that SA was experiencing a second wave of COVID-19 that would exceed the death toll of the first wave. In 2020, there were 70 000 - 76 000 excess deaths from natural causes, depending on the base. Using the adjusted base, the excess death rate from natural causes was 122 per 100 000 population, with a male-to-female ratio of 0.78. Deaths from unnatural causes halved for both males and females during the stringent lockdown level 5. The numbers reverted towards the predicted number with some fluctuations as lockdown restrictions varied. Just under 5 000 unnatural deaths were averted. Conclusions. Tracking the weekly numbers of deaths in near to real time has provided important information about the spatiotemporal impact of the pandemic and highlights that the ~28 000 reported COVID-19 deaths during 2020 substantially understate the death toll from COVID-19. There is an urgent need to re-engineer the system of collecting and processing cause-of-death information so that it can be accessed in a timely way to inform public health actions