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The first demonstration of laser action in ruby was made in 1960 by T. H. Maiman of Hughes Research Laboratories, USA. Many laboratories worldwide began the search for lasers using different materials, operating at different wavelengths. In the UK, academia, industry and the central laboratories took up the challenge from the earliest days to develop these systems for a broad range of applications. This historical review looks at the contribution the UK has made to the advancement of the technology, the development of systems and components and their exploitation over the last 60 years.
We examine a turbulent distributed wall-source plume: the flow resulting from a uniform vertical wall source of buoyancy such as that produced by an evenly heated or cooled vertical wall. The vertically distributed buoyancy source is created by forcing dense salt water solution through a porous wall. Velocity measurements on a vertical plane normal to the wall are first presented examining the full height of the wall in order to identify the region in which the bulk flow has become fully turbulent, self-similar and reached an invariant balance between the fluxes of volume, momentum and buoyancy. Simultaneous velocity and buoyancy field measurements are then presented in this region and an entrainment coefficient of $\alpha = 0.068 \pm 0.006$ is determined. This value is small compared to that of buoyancy-driven unbounded flows, e.g. a free line plume, and we reason this to be due to the presence of a rigid boundary restricting meandering and turbulence production, rather than the effect of the vertically distributed source of buoyancy. Turbulent velocity and buoyancy statistics are presented and, in order to gain physical insights into the flow behaviour, the results are compared to those of other canonical buoyancy-driven free and wall-bounded flows. We show that the bulk mixing of distributed wall-source plumes can be captured by consideration of the characteristic vertical velocities and a constant entrainment coefficient. This mixing is inhibited both by the presence of a rigid boundary and the reduced characteristic velocities (compared to those of wall line plumes).
We examine the flow resulting from a vertically distributed wall-source plume in both an unventilated and ventilated space. First, we present experimental ambient buoyancy measurements for an unventilated ‘filling box’ where the developing ambient buoyancy profiles are successfully modelled using an adapted ‘peeling’ model which incorporates results presented in Part 1 of this work. We then present steady-state ambient buoyancy measurements for a ventilated box. Using dye visualisation, it is observed that, in the steady state, negligible ambient vertical transport occurs within the stratified region, implying a linear ambient buoyancy stratification within this region, and we predict the gradient of this linear stratification. Finally, we apply our experimental results to two practical examples. We present a methodology to create a given linear ambient temperature stratification within a room via a prescribed uniform wall heat flux and consider the resulting temperature stratification within a large ventilated atrium with a wall heated by solar radiation.
The Holmboe wave instability is one of the classic examples of a stratified shear instability, usually explained as the result of a resonance between a gravity wave and a vorticity wave. Historically, it has been studied by linear stability analyses at infinite Reynolds number,
, and by direct numerical simulations at relatively low
in the regions known to be unstable from the inviscid linear stability results. In this paper, we perform linear stability analyses of the classical ‘Hazel model’ of a stratified shear layer (where the background velocity and density distributions are assumed to take the functional form of hyperbolic tangents with different characteristic vertical scales) over a range of different parameters at finite
, finding new unstable regions of parameter space. In particular, we find instability when the Richardson number is everywhere greater than
, where the flow would be stable at infinite
by the Miles–Howard theorem. We find unstable modes with no critical layer, and show that, despite the necessity of viscosity for the new instability, the growth rate relative to diffusion of the background profile is maximised at large
. We use these results to shed new light on the wave-resonance and over-reflection interpretations of stratified shear instability. We argue for a definition of Holmboe instability as being characterised by propagating vortices above or below the shear layer, as opposed to any reference to sharp density interfaces.
Operational definitions of mania are based on expert consensus rather than empirical data. The aim of this study is to identify the key domains of mania, as well as the relevance of the different signs and symptoms of this clinical construct.
A review of latent factor models studies in manic patients was performed. Before extraction, a harmonization of signs and symptoms of mania and depression was performed in order to reduce the variability between individual studies.
We identified 12 studies fulfilling the inclusion criteria and comprising 3039 subjects. Hyperactivity was the clinical item that most likely appeared in the first factor, usually covariating with other core features of mania, such as increased speech, thought disorder, and elevated mood. Depressive–anxious features and irritability–aggressive behavior constituted two other salient dimensions of mania. Altered sleep was frequently an isolated factor, while psychosis appeared related to grandiosity, lack of insight and poor judgment.
Our results confirm the multidimensional nature of mania. Hyperactivity, increased speech, and thought disorder appear as core features of the clinical construct. The mood experience could be heterogeneous, depending on the co-occurrence of euphoric (elevated mood) and dysphoric (irritability and depressive mood) emotions of varying intensity. Results are also discussed regarding their relationship with other constitutive elements of bipolar disorder, such as mixed and depressive states.
We present simultaneous two-dimensional measurements of the velocity and buoyancy fields on a central vertical plane in two-dimensional line plumes: a free plume distant from vertical boundaries and a wall plume, adjacent to a vertical wall. Data are presented in both an Eulerian and a plume coordinate system that follow the instantaneous turbulent/non-turbulent interface (TNTI) of the plume. We present measurements in both coordinate systems and compare the entrainment in the two flows. We find that the value of the entrainment coefficient in the wall plume is greater than half that of the free plume. The reduction in entrainment is investigated by considering a decomposition of the entrainment coefficient based on the mean kinetic energy where the relative contributions of turbulent production, buoyancy and viscous terms are calculated. The reduced entrainment is also investigated by considering the statistics of the TNTI and the conditional vertical transport of the ambient and engulfed fluid. We show that the wall shear stress is non-negligible and that the free plume exhibits significant meandering. The effect of the meandering on the entrainment process is quantified in terms of the stretching of the TNTI where it is shown that the length of the TNTI is greater in the free plume and, further, the relative vertical transport of the engulfed ambient fluid is observed to be 15 % greater in the free plume. Finally, the turbulent velocity and buoyancy fluctuations, Reynolds stresses and the turbulent buoyancy fluxes are presented in both coordinate systems.
We study the dynamical system of a two-dimensional, forced, stratified mixing layer at finite Reynolds number
, and Prandtl number
. We consider a hyperbolic tangent background velocity profile in the two cases of hyperbolic tangent and uniform background buoyancy stratifications, in a domain of fixed, finite width and height. The system is forced in such a way that these background profiles are a steady solution of the governing equations. As is well known, if the minimum gradient Richardson number of the flow,
, is less than a certain critical value
, the flow is linearly unstable to Kelvin–Helmholtz instability in both cases. Using Newton–Krylov iteration, we find steady, two-dimensional, finite-amplitude elliptical vortex structures – i.e. ‘Kelvin–Helmholtz billows’ – existing above
. Bifurcation diagrams are produced using branch continuation, and we explore how these diagrams change with varying
. In particular, when
is sufficiently high we find that finite-amplitude Kelvin–Helmholtz billows exist when
for the background flow, which is linearly stable by the Miles–Howard theorem. For the uniform background stratification, we give a simple explanation of the dynamical system, showing the dynamics can be understood on a two-dimensional manifold embedded in state space, and demonstrate the cases in which the system is bistable. In the case of a hyperbolic tangent stratification, we also describe a new, slow-growing, linear instability of the background profiles at finite
, which complicates the dynamics.
We observed pediatric S. aureus hospitalizations decreased 36% from 26.3 to 16.8 infections per 1,000 admissions from 2009 to 2016, with methicillin-resistant S. aureus (MRSA) decreasing by 52% and methicillin-susceptible S. aureus decreasing by 17%, among 39 pediatric hospitals. Similar decreases were observed for days of therapy of anti-MRSA antibiotics.
We present simultaneous two-dimensional velocity and scalar measurements on a central vertical plane in an axisymmetric pure turbulent plume. We use an edge-detection algorithm to determine the edge of the plume, and compare the data obtained in both a fixed Eulerian frame and a frame relative to local coordinates defined in terms of the instantaneous plume edge. In an Eulerian frame we observe that the time-averaged distributions of vertical and horizontal velocity are self-similar, the vertical velocity being well represented by a Gaussian distribution. We condition these measurements on whether fluid is inside or outside of the plume, and whether fluid inside is mixed plume fluid or engulfed ambient fluid. We find that, on average, 5 % of the total vertical volume transport occurs outside the plume and this figure rises to nearly 14 % at heights between large-scale coherent structures. We show that the fluxes of engulfed fluid within the plume envelope are slightly larger than the vertical transport outside the plume – indicating that ambient fluid is engulfed into the plume envelope before being nibbled across the turbulent/non-turbulent interface (TNTI) and then ultimately irreversibly mixed. Our new measurements in the plume coordinate (following the meandering fluctuating plume) show the flow within the plume and in the nearby ambient fluid is strongly influenced by whether an eddy is present locally within the plume, or absent. When an eddy is present and the plume is wide, the vertical velocities near the plume edge are small and hence all vertical transport is inside the plume. In regions where the plume is narrow and there is no eddy, large vertical velocities and hence transport are observed outside the plume suggesting that pressure forces associated with the eddies accelerate ambient fluid which is then engulfed into the plume. Finally, we show that observing significant vertical velocities beyond the scalar edge of the plume does not suggest that the characteristic width of the velocity distribution is greater than that of the scalar field; on the contrary, we show our observations to be consistent with a buoyancy distribution that is up to 20 % wider than that of the velocity. Measurements in the plume coordinates show that the mixing of momentum across the plume results in a distribution for which the differential entropy is close to maximal and the mixing of momentum is uninhibited (i.e. not bounded) by the TNTI of the plume. Furthermore, our measurements suggest that the scalar mixing across the plume may also result in a distribution for which the differential entropy is close to maximal but, in contrast to the momentum, the scalar mixing is strictly bounded by the plume edge.
Introduction: The Canadian CT Head Rules (CCTHR) is the gold standard clinical decision rule for minor head injuries (MHIs) & has been shown to have 100% sensitivity in identifying patients that would have an abnormal CT scan. Within the CCTHR age 65+ is considered to be an independent risk factor for abnormal head CT. However, a previously published Italian study indicated that the rate of pathological findings in otherwise low risk MHI patients under the age of 79 was less than 1% & significantly lower than those over the age of 80, which brings to question whether the traditional age cut off of 65 as a factor in the CCTHR is too conservative when considering the appropriateness for imaging. Therefore this study aimed to quantify the extent to which low risk MHI patients between the ages of 65-79 present with abnormal CT findings or require neurosurgical intervention when compared to patients over 80 years of age as one of the criteria used in the CCTHR is the age threshold of 65. A secondary objective of this study was to explore abnormal CT rates across these age groupings for otherwise low risk patients on anticoagulants. Methods: A retrospective chart review was conducted on all patients over the age of 65 that received a head CT for a MHI in the Kelowna General Hospital ED between 2006-2016. The imaging results for all patients that had no other risk criteria of the CCTHR other than age were reviewed & rates of pathological findings were compared between patients ages 65-79 & 80+ for both patients on anticoagulants & those not on anticoagulants. Differences in rates by age were compared for statistical significance using the chi-squared & Fisher’s exact test. Results: To date 248 patients have been reviewed & meet the criteria of being >65 & with no other CCTHR criteria. 65% of patients were female & 30% of patients were on anticoagulants. For the patients that were not on anticoagulants, 6 of the 75 (8%) individuals between 65-79 & 9 of the 94 (10%) of those over 80 had abnormal findings on CT (p=0.128). Conclusion: Preliminary results of this study population indicate that there are a significant number of abnormal CT findings in patients under the age of 80 suggesting that patients ages 65-79 without any other CCTHR criteria may still benefit from a head CT. Chart reviews are ongoing & updated results including findings for anti-coagulated patients will be presented at CAEP 2017.
The past decade has seen atomic Bose-Einstein condensates emerge as a promising prototype system to explore the quantum mechanical form of turbulence, buoyed by a powerful experimental toolbox to control and manipulate the fluid, and the amenity to describe the system from first principles. This chapter presents an overview of this topic, from its history and fundamental motivations, its characteristics and key results to date, and finally to some promising future directions.
A Quantum Storm in a Teacup
A befitting title to this chapter could have been “a quantum storm in a teacup.” The storm refers to a turbulent state of a fluid, teeming with swirls and waves. Quantum refers to the fact that the fluid is not the classical viscous fluid of conventional storms but rather a quantum fluid in which viscosity is absent and the swirls are quantized. The quantum fluid in our story is a quantum-degenerate gas of bosonic atoms, an atomic Bose-Einstein condensate (BEC), formed at less than a millionth of a degree above absolute zero. And finally the teacup refers to the bowl-like potential used to confine the gas; this makes the fluid inherently inhomogeneous and finite-sized. A typical image of our quantum storm in a teacup is shown in Fig. 17.1a.
This chapter reviews quantum turbulence in atomic condensates, tracing its history (Section 17.2), introducing the main theoretical approach (Section 17.3) and the underyling quantum vortices (Section 17.4).We then turn to describing physical characteristics (Section 17.5), the experimental observations to date (Section 17.6), methods of generating turbulence (Section 17.7), and some exciting research directions (Section 17.8) before presenting an outlook (Section 17.9).
Turbulence refers to a highly agitated, disordered, and nonlinear fluid motion, characterized by the presence of eddies and energy across a range of length and time scales . It occurs ubiquitously in nature, from blood flow and waterways to atmospheres and the interstellar medium, and is of practical importance in many industrial and engineering contexts. Since da Vinci's first scientific study of turbulent flow of water past obstacles, circa 1507, research into turbulence in classical viscous fluids continues with vigor; however, due to its rich complexities, the physical essence and mathematical description of turbulence remain a challenge.
A scaling theory of long-wavelength electrostatic turbulence in a magnetised, weakly collisional plasma (e.g. drift-wave turbulence driven by ion temperature gradients) is proposed, with account taken both of the nonlinear advection of the perturbed particle distribution by fluctuating
flows and of its phase mixing, which is caused by the streaming of the particles along the mean magnetic field and, in a linear problem, would lead to Landau damping. It is found that it is possible to construct a consistent theory in which very little free energy leaks into high velocity moments of the distribution function, rendering the turbulent cascade in the energetically relevant part of the wavenumber space essentially fluid-like. The velocity-space spectra of free energy expressed in terms of Hermite-moment orders are steep power laws and so the free-energy content of the phase space does not diverge at infinitesimal collisionality (while it does for a linear problem); collisional heating due to long-wavelength perturbations vanishes in this limit (also in contrast with the linear problem, in which it occurs at the finite rate equal to the Landau damping rate). The ability of the free energy to stay in the low velocity moments of the distribution function is facilitated by the ‘anti-phase-mixing’ effect, whose presence in the nonlinear system is due to the stochastic version of the plasma echo (the advecting velocity couples the phase-mixing and anti-phase-mixing perturbations). The partitioning of the wavenumber space between the (energetically dominant) region where this is the case and the region where linear phase mixing wins its competition with nonlinear advection is governed by the ‘critical balance’ between linear and nonlinear time scales (which for high Hermite moments splits into two thresholds, one demarcating the wavenumber region where phase mixing predominates, the other where plasma echo does).
Establishing an evidence-based diagnostic system informed by the biological (dys)function of the nervous system is a major priority in psychiatry. This objective, however, is often challenged by difficulties in identifying homogeneous clinical populations. Melancholia, a biological and endogenous subtype for major depressive disorder, presents a canonical test case in the search of biological nosology.
We employed a unique combination of naturalistic functional magnetic resonance imaging (fMRI) paradigms – resting state and free viewing of emotionally salient films – to search for neurobiological signatures of depression subtypes. fMRI data were acquired from 57 participants; 17 patients with melancholia, 17 patients with (non-melancholic) major depression and 23 matched healthy controls.
Patients with melancholia showed a prominent loss of functional connectivity in hub regions [including ventral medial prefrontal cortex, anterior cingulate cortex (ACC) and superior temporal gyrus] during natural viewing, and in the posterior cingulate cortex while at rest. Of note, the default mode network showed diminished reactivity to external stimuli in melancholia, which correlated with the severity of anhedonia. Intriguingly, the subgenual ACC, a potential target for treating depression with deep brain stimulation (DBS), showed divergent changes between the two depression subtypes, with increased connectivity in the non-melancholic and decreased connectivity in the melancholic subsets.
These findings reveal neurobiological changes specific to depression subtypes during ecologically valid behavioural conditions, underscoring the critical need to respect differing neurobiological processes underpinning depressive subtypes.
Agriculture is a largely technical endeavour involving complicated managerial decision-making that affects crop performance. Farm-level modelling integrates crop models with agent behaviour to account for farmer decision-making and complete the representation of agricultural systems. To replicate an important part of agriculture in Central Europe a crop model was calibrated for a unique region's predominant crops: winter wheat, winter and spring barley, silage maize and winter rapeseed. Their cultivation was then simulated over multiple decades at daily resolution to test validity and stability, while adding the dimension of agent behaviour in relation to environmental and economic conditions. After validation against regional statistics, simulated future weather scenarios were used to forecast crop management and performance under anticipated global change. Farm management and crop genetics were treated as adaptive variables in the milieu of shifting climatic conditions to allow projections of agriculture in the study region into the coming decades.
A tuberculosis (TB) case was reported May 2008 in Kelowna, British Columbia, leading to a multi-year outbreak in homeless persons. The epidemiological characteristics and social networks of cases are described. Outbreak-related cases were identified from epidemiological information in medical records and from genotyping of TB isolates. Social network information from case interviews were used to identify potential locations of TB transmission, where symptom screening and tuberculin skin testing was conducted. Fifty-two cases that were predominantly male (47/52), Canadian-born (44/50), and were homeless or associated with homeless individuals (42/52) were reported from May 2008 to May 2014. Many isolates (40/49) had partial resistance to isoniazid. Transmission primarily occurred at two homeless shelters, with potential further transmission at sites visited by the general population. TB outbreaks in homeless populations can occur in small, low-incidence cities. Social network information helped prioritize sites for TB screening, thereby improving detection of persons with TB disease or latent infection for treatment.
Streams draining the Cypress Hills support unique and understudied macroinvertebrate communities in Saskatchewan, Canada. Here, we report the discovery of a species of caddisfly new to the Cypress Hills and Saskatchewan, Neophylax splendens Denning (Trichoptera: Thremmatidae). Larvae were collected early in May 2012, and are found to enter pre-pupal diapause in mid-June until mid-September. Larvae were identified as N. splendens by morphological characters and verified with genetic analysis. Its occurrence strengthens the biogeographical link between the montane regions in British Columbia, Canada and Utah, United States of America with the southwest corner of Saskatchewan. This study highlights the importance of seasonal sampling, resolute species level identifications in biological surveys and the use of genetic analyses to obtain this level of identification.
Dementia is a complex and variable condition which makes recognition of it particularly difficult in a low prevalence primary care setting. This study examined the factors associated with agreement between an objective measure of cognitive function (the revised Cambridge Cognitive Assessment, CAMCOG-R) and general practitioner (GP) clinical judgment of dementia.
This was a cross-sectional study involving 165 GPs and 2,024 community-dwelling patients aged 75 years or older. GPs provided their clinical judgment in relation to each of their patient's dementia status. Each patient's cognitive function and depression status was measured by a research nurse using the CAMCOG-R and the 15-item Geriatric Depression Scale (GDS), respectively.
GPs correctly identified 44.5% of patients with CAMCOG-R dementia and 90% of patients without CAMCOG-R dementia. In those patients with CAMCOG-R dementia, two patient-dependent factors were most important for predicting agreement between the CAMCOG-R and GP judgment: the CAMCOG-R score (p = 0.006) and patient's mention of subjective memory complaints (SMC) to the GP (p = 0.040). A higher CAMCOG-R (p < 0.001) score, female gender (p = 0.005), and larger practice size (p < 0.001) were positively associated with GP agreement that the patient did not have dementia. Subjective memory complaints (p < 0.001) were more likely to result in a false-positive diagnosis of dementia.
Timely recognition of dementia is advocated for optimal dementia management, but early recognition of a possible dementia syndrome needs to be balanced with awareness of the likelihood of false positives in detection. Although GPs correctly agree with dimensions measured by the CAMCOG-R, improvements in sensitivity are required for earlier detection of dementia.
The MRI-based methods for measuring perfusion and related vascular characteristics that are described in this book have multiple research and clinical applications in oncology. The oncological applications specific to the brain are detailed in Chapter 11. This current chapter provides an overview of oncology applications outside the brain, covering both current clinical practice and research techniques. The technical aspects of image acquisition and analysis are only alluded to briefly, except where these details form a critical component of understanding the study data and their interpretation.
Various perfusion MRI techniques are performed in oncology imaging. Outside the brain, the majority of applications are based on T1-weighted dynamic contrast-enhanced (DCE)-MRI, although dynamic susceptibility contrast (DSC) and arterial spin labeling (ASL) are now used increasingly often in research studies. In this section, all ‘MR perfusion imaging’ refers to T1-weighted DCE-based techniques unless explicitly stated otherwise. It is important to appreciate that T1-weighted DCE-MRI is an umbrella term that covers many similar acquisition and analysis approaches, which may have important differences in their practical application and for comparison between studies.
Pelagic ecosystems and their fisheries are of particular economic and social importance to the countries and territories of the Wider Caribbean for various reasons. In some countries (e.g. Barbados, Grenada) commercial pelagic fisheries already contribute significantly to total landings and seafood export foreign exchange earnings. Ports and postharvest facilities service the vessels, ranging from artisanal canoes to industrial longliners, and their catch which often reaches tourists as well as locals (Mahon and McConney 2004). In other places where the focus has previously been on inshore and demersal fisheries (e.g. Antigua and Barbuda, Belize) there is growing interest in the potential of pelagic fisheries development. This potential lies not only in commercial fisheries, but also in the high-revenue and conservation-aware recreational fisheries well established in a few locations (e.g. Puerto Rico, Costa Rica) and undertaken at a lower level in many others.
Underlying all of this is the complexity due to many of the valued pelagics being migratory or highly migratory shared and straddling stocks falling under the 1995 United Nations Fish Stocks Agreement and subject to several international instruments and management regimes, such as those of the International Commission for the Conservation of Atlantic Tunas (ICCAT). The web of linkages across Caribbean marine jurisdictions and organizations is complex (McConney et al. 2007). The related issues call for an ecosystem approach (McConney and Salas Chapter 7; Schuhmann et al. Chapter 8) and some progress has already been made at multiple levels (Fanning and Oxenford Chapter 16; Singh-Renton et al. Chapter 14).
This synthesis chapter presents the outputs of facilitated symposium sessions specifically related to achieving and implementing a shared vision for the pelagic ecosystem in marine ecosystem based management (EBM) in the Wider Caribbean. The methodology was described in Chapter 1 of this volume. This chapter first describes a vision for the pelagic ecosystem and reports on the priorities assigned to the identified vision elements. It then addresses how the vision might be achieved by taking into account assisting factors (those that facilitate achievement) and resisting factors (those that inhibit achievement). The chapter concludes with guidance on the strategic direction needed to implement the vision, identifying specific actions to be undertaken for each of the vision elements.