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The dynamics of a fluid-filled square cavity with stable thermal stratification subjected to harmonic vertical oscillations is investigated numerically. The nonlinear responses to this parametric excitation are studied over a comprehensive range of forcing frequencies up to two and a half times the buoyancy frequency. The nonlinear results are in general agreement with the Floquet analysis, indicating the presence of nested resonance tongues corresponding to the intrinsic
eigenmodes of the stratified cavity. For the lowest-order subharmonic
tongue, the responses are analysed in great detail, with complex dynamics identified near onset, most of which involves interactions with unstable saddle states of a homoclinic or heteroclinic nature.
Stereo-electroencephalography (SEEG) has been shown to be a valuable tool for the anatomo-electroclinic definition of the epileptogenic zone (EZ) in some patients with medically refractory epilepsy considered for surgery. In Spain, many of those patients are not offered this diagnostic procedure. The objective of our health technology assessment (HTA) report was to evaluate the effectiveness, safety and cost-effectiveness of SEEG to define the EZ in patients with refractory epilepsy considered for surgery compared to no SEEG intervention (i.e. remaining with further antiepileptic drugs).
We undertook a systematic review with meta-analyses on the effectiveness and safety of SEEG. A cost-effectiveness analysis was conducted using a Markov model which simulates the costs and health outcomes of individuals for a lifetime horizon from the perspective of the Spanish National Health Service (NHS). The effectiveness measure was quality-adjusted life years (QALYs). We ran extensive sensitivity analyses, including a probabilistic sensitivity analysis.
The EZ was found in 92 percent of patients who underwent SEEG, 72 percent were eligible for epilepsy surgery and 33 percent were free of seizures after surgery (47 percent of those who received surgery). Any complications related to insertion and monitoring of SEEG and the subsequent intervention occurred in 1.3 percent of patients. In the base case analysis, SEEG led to higher QALYs and healthcare costs with an estimated incremental cost-effectiveness ratio of EUR 10,368 (USD 12,217) per QALY. The sensitivity analyses showed that the results of the study were robust.
SEEG is a cost-effective technology in patients with refractory epilepsy considered for surgery when compared to no SEEG intervention.
The dynamic response to shear of a fluid-filled square cavity with stable temperature stratification is investigated numerically. The shear is imposed by the constant translation of the top lid, and is quantified by the associated Reynolds number. The stratification, quantified by a Richardson number, is imposed by maintaining the temperature of the top lid at a higher constant temperature than that of the bottom, and the side walls are insulating. The Navier–Stokes equations under the Boussinesq approximation are solved, using a pseudospectral approximation, over a wide range of Reynolds and Richardson numbers. Particular attention is paid to the dynamical mechanisms associated with the onset of instability of steady state solutions, and to the complex and rich dynamics occurring beyond.
The linear stability of a stably stratified fluid-filled cavity subject to vertical oscillations is determined via Floquet analysis. Retaining the viscous and diffusion terms in the Navier–Stokes–Boussinesq equations, with no-slip velocity boundary conditions, no-flux temperature conditions on the sidewalls and constant temperatures on the top and bottom walls, we find that the instabilities are primarily subharmonic (as is typical in many parametrically forced systems), except for in a few low-forcing-frequency ranges where the instabilities are synchronous. When the viscosity is small, the Floquet modes resemble the inviscid eigenmodes of the unforced problem, except in boundary layers. We establish scaling laws quantifying how viscosity regularizes the degeneracy associated with the inviscid idealization, and how it scales the thickness and intensity of the boundary layers. The product of boundary layer thickness and intensity remains constant with decreasing viscosity, leading to a delta distribution of vorticity on the walls in the limit of zero viscosity. This is in contrast to the zero wall vorticity in the inviscid case.
The flow response of a rapidly rotating fluid-filled cube to low-amplitude librational forcing is investigated numerically. Librational forcing is the harmonic modulation of the mean rotation rate. The rotating cube supports inertial waves which may be excited by libration frequencies less than twice the rotation frequency. The response is comprised of two main components: resonant excitation of the inviscid inertial eigenmodes of the cube, and internal shear layers whose orientation is governed by the inviscid dispersion relation. The internal shear layers are driven by the fluxes in the forced boundary layers on walls orthogonal to the rotation axis and originate at the edges where these walls meet the walls parallel to the rotation axis, and are hence called edge beams. The relative contributions to the response from these components is obscured if the mean rotation period is not small enough compared to the viscous dissipation time, i.e. if the Ekman number is too large. We conduct simulations of the Navier–Stokes equations with no-slip boundary conditions using parameter values corresponding to a recent set of laboratory experiments, and reproduce the experimental observations and measurements. Then, we reduce the Ekman number by one and a half orders of magnitude, allowing for a better identification and quantification of the contributions to the response from the eigenmodes and the edge beams.
The bryozoan genus Aspidostoma Hincks, 1881 has been regarded as the only representative of the Aspidostomatidae Jullien, 1888 in Argentina to date. Its type species, Aspidostoma giganteum (Busk, 1854), is presently distributed in the Magellanic Region (Argentina and Chile) and has been recorded in Oligocene and Miocene fossil deposits of Santa Cruz and Chubut, respectively. New material from San Julián (late Oligocene), Monte León (early Miocene), Chenque (early to middle Miocene), and Puerto Madryn (late Miocene) formations suggests, however, that A. giganteum is not represented in the fossil record. Material from Puerto Madryn Formation previously regarded as A. giganteum is here recognized as Aspidostoma roveretoi new species. Aspidostoma ortmanni Canu, 1904 is revalidated for the species from the San Julián Formation. Aspidostoma armatum new species and Aspidostoma tehuelche new species are introduced for material from the Monte León and Chenque formations, respectively. Aspidostoma incrustans Canu, 1908, from the early Miocene, is redescribed. Melychocella Gordon and Taylor, 1999, which differs from Aspidostoma in having vicarious avicularia and lacking a median ridge and a quadrangular process proximal to the opesia-orifice, is so far represented by three Paleogene species from the Chatham Islands (Southwest Pacific). The material from Monte León allowed us to transfer Aspidostoma flammulum Canu, 1908 to Melychocella, resulting in the new combination Melychocella flammula (Canu, 1908). Melychocella biperforata new species is described from the lower Miocene Monte León and Chenque formations. The presence of Melychocella in the Neogene of Patagonia extends its geographic distribution and its temporal range.
Contained rotating flows subject to precessional forcing are well known to exhibit rapid and energetic transitions to disorder. Triadic resonance of inertial modes has been previously proposed as an instability mechanism in such flows, and that idea was developed into a successful model for predicting instability in a cylindrical container when departures from solid-body rotation are sufficiently small. Using direct numerical simulation and dynamic mode decomposition, we analyse instabilities of precessing cylinder flows whose three-dimensional basic states, steady in the gimbal frame of reference, may depart substantially from solid-body rotation. In the gimbal frame, the instability can be interpreted as resulting from a supercritical Hopf bifurcation that results in a limit-cycle flow. In the cylinder frame of reference, the basic state is a rotating wave with azimuthal wavenumber
, and the instability satisfies triadic-resonance conditions with the instability mode maintaining a fixed orientation with respect to the basic state. Thus, we are able to demonstrate the existence of two alternative but congruent explanations for the instability. Additionally, we show that basic states may depart substantially from solid-body rotation even with modest cylinder tilt angles, and growth rates for instabilities may be sufficiently large that nonlinear saturation to disordered states can occur within approximately ten cylinder revolutions, in agreement with experimental observations.
Rapidly rotating cylinder flows subjected to low-amplitude precessional forcing are studied numerically over a range of cylinder and precessional rotation rates. For sufficiently small rotation rates, viscous effects lead to a forced overturning flow that is steady in the precession (table) frame of reference. Increasing the rotation rates, this forced flow loses stability in a Hopf bifurcation, which can be either supercritical or subcritical, and may preserve or break the symmetry of the system, depending on the parameter regime studied. Regardless of these details of the Hopf bifurcation, it is found that the Hopf instability is associated with a slightly detuned triadic resonance between the forced overturning flow and two free Kelvin modes (inviscid eigenmodes of the rotating cylinder). Further increases in rotation rates lead to a sequence of secondary instabilities which also follow a generic pattern irrespective of the parameter regime investigated. The relationship between this sequence of instabilities and the resultant nonlinear dynamics with the experimentally observed phenomenon of resonant collapse is discussed.
Palivizumab is the standard immunoprophylaxis against serious disease due to respiratory syncytial virus infection. Current evidence-based prophylaxis guidelines may not address certain children with CHD within specific high-risk groups or clinical/management settings.
An international steering committee of clinicians with expertise in paediatric heart disease identified key questions concerning palivizumab administration; in collaboration with an additional international expert faculty, evidence-based recommendations were formulated using a quasi-Delphi consensus methodology.
Palivizumab prophylaxis was recommended for children with the following conditions: <2 years with unoperated haemodynamically significant CHD, who are cyanotic, who have pulmonary hypertension, or symptomatic airway abnormalities; <1 year with cardiomyopathies requiring treatment; in the 1st year of life with surgically operated CHD with haemodynamically significant residual problems or aged 1–2 years up to 6 months postoperatively; and on heart transplant waiting lists or in their 1st year after heart transplant. Unanimous consensus was not reached for use of immunoprophylaxis in children with asymptomatic CHD and other co-morbid factors such as arrhythmias, Down syndrome, or immunodeficiency, or during a nosocomial outbreak. Challenges to effective immunoprophylaxis included the following: multidisciplinary variations in identifying candidates with CHD and prophylaxis compliance; limited awareness of severe disease risks/burden; and limited knowledge of respiratory syncytial virus seasonal patterns in subtropical/tropical regions.
Evidence-based immunoprophylaxis recommendations were formulated for subgroups of children with CHD, but more data are needed to guide use in tropical/subtropical countries and in children with certain co-morbidities.
The origins of the large Classic and Postclassic urban centres of Central Mexico remain poorly understood. Archaeological investigations at the Formative site of Tlalancaleca in Puebla (Mexico) provide the first detailed study of a large-scale urban centre of that period. Preliminary results suggest that the growth and development of this particular site may have influenced the subsequent growth of Teotihuacan itself. This study explores how urbanisation can be identified archaeologically by tracing the expansion of population and the emergence of monumental architecture.
The flow in a split cylinder with each half in exact counter rotation is studied numerically. The exact counter rotation, quantified by a Reynolds number
based on the rotation rate and radius, imparts the system with an
symmetry (invariance to azimuthal rotations as well as to an involution consisting of a reflection about the mid-plane composed with a reflection about any meridional plane). The
symmetric basic state is dominated by a shear layer at the mid-plane separating the two counter-rotating bodies of fluid, created by the opposite-signed vortex lines emanating from the two endwalls being bent to meet at the split in the sidewall. With the exact counter rotation, the additional involution symmetry allows for steady non-axisymmetric states, that exist as a group orbit. Different members of the group simply correspond to different azimuthal orientations of the same flow structure. Steady states with azimuthal wavenumber
(the value of
depending on the cylinder aspect ratio
) are the primary modes of instability as
are varied. Mode competition between different steady states ensues, and further bifurcations lead to a variety of different time-dependent states, including rotating waves, direction-reversing waves, as well as a number of slow–fast pulse waves with a variety of spatio-temporal symmetries. Further from the primary instabilities, the competition between the vortex lines from each half-cylinder settles on either a
steady state or a limit cycle state with a half-period-flip spatio-temporal symmetry. By computing in symmetric subspaces as well as in the full space, we are able to unravel many details of the dynamics involved.
The arterial switch operation is currently the gold standard technique for repair of transposition of the great arteries. Some atypical coronary patterns such as intramural, interarterial, and a unique posterior button are associated with more complexity and surgical risk. We report a successful Aubert operation for transposition of the great arteries associated with a single and interarterial coronary artery arising from a posterior sinus.
In countless biological and technological processes, the flow of Newtonian liquids with a non-Newtonian interface is a common occurrence, such as in monomolecular films in ‘solid’ phases atop of aqueous bulk fluid. There is a lack of models that can predict the flow under conditions different from those used to measure the rheological response of the interface. Here, we present a model which describes interfacial hydrodynamics, including two-way coupling to a bulk Newtonian fluid described by the Navier–Stokes equations, that allows for shear-thinning response of the interface. The model includes a constitutive equation for the interface under steady shear that takes the Newtonian functional form but where the surface shear viscosity is generalized to be a function of the local shear rate. In the limit of a highly viscous interface, the interfacial hydrodynamics is decoupled from the bulk flow and the model can be solved analytically. This provides not only insight into the flow but also a means to validate the numerical technique for solving the two-way coupled problem. The numerical results of the coupled problem shed new light on existing experimental results on steadily sheared monolayers of dipalmitoylphosphatidylcholine (DPPC), the primary constituent of lung surfactant and the bilayers of mammalian cell walls. For low packing density DPPC monolayers, a Newtonian shear-independent surface shear viscosity model can reproduce the interfacial flows, but at high packing density, the shear-thinning properties of the new model presented here are needed.
The nonlinear dynamics of the flow in a differentially rotating split cylinder is investigated numerically. The differential rotation, with the top half of the cylinder rotating faster than the bottom half, establishes a basic state consisting of a bulk flow that is essentially in solid-body rotation at the mean rotation rate of the cylinder and boundary layers where the bulk flow adjusts to the differential rotation of the cylinder halves, which drives a strong meridional flow. There are Ekman-like layers on the top and bottom end walls, and a Stewartson-like side wall layer with a strong downward axial flow component. The complicated bottom corner region, where the downward flow in the side wall layer decelerates and negotiates the corner, is the epicentre of a variety of instabilities associated with the local shear and curvature of the flow, both of which are very non-uniform. Families of both high and low azimuthal wavenumber rotating waves bifurcate from the basic state in Eckhaus bands, but the most prominent states found near onset are quasiperiodic states corresponding to mixed modes of the high and low azimuthal wavenumber rotating waves. The frequencies associated with most of these unsteady three-dimensional states are such that spiral inertial wave beams are emitted from the bottom corner region into the bulk, along cones at angles that are well predicted by the inertial wave dispersion relation, driving the bulk flow away from solid-body rotation.
Although there is increasing evidence for the effects on wildlife of primary infrastructure (paved roads and human settlements), the effect of secondary infrastructure (tracks and isolated buildings) is generally assumed to be low in sparsely developed areas. We hypothesized that secondary infrastructure may have a negative effect similar to that of primary infrastructure, and hence may be the source of extended impacts in landscapes that are otherwise relatively undisturbed. We studied multi-year breeding site data for a community of large birds (raptors and storks) in the Monfragüe Biosphere Reserve, in the south-west Iberian Peninsula. Using a bootstrap model selection approach we modelled the distribution of breeding sites, using as predictors measures of habitat accessibility (relief, hydrography) and various types of infrastructure (primary and secondary) at different scales. Distance effect functions were developed. Secondary infrastructure exerted a negative effect on breeding sites that was equivalent to that of primary infrastructure, in terms of both transport (track vs road) and dwellings (scattered vs aggregated). The negative effect was distance (rather than density) mediated, and remained within the 1 km scale. The potential impact of secondary infrastructure is greater than that of primary infrastructure as it occupies more extensive areas and includes richer communities, with significant proportions of threatened populations. Our results contradict common assumptions about the negligible impact of secondary infrastructure on biodiversity, reveal new challenges for biodiversity conservation, and provide insights relevant for the spatial planning of isolated buildings and tracks in sparsely developed areas with species of conservation interest.
The presence of endwalls in Taylor–Couette flows has far reaching effects, leading to dynamics that are qualitatively different from those associated with the idealized situation involving infinitely long cylinders. This is well known in the classical situation where the inner cylinder is rotating and the outer cylinder is stationary. The effects of endwalls in the centrifugally stable situation with stationary inner cylinder and rotating outer cylinder have not been previously considered in detail. The meridional flows induced by the endwalls lead to the formation of a thin sidewall boundary layer on the inner cylinder wall if the endwalls are rotating, or on the outer cylinder wall if they are stationary. At sufficiently high Reynolds numbers (non-dimensional rotation rate of the outer cylinder), the sidewall boundary layer has concentrated shear, the pressure gradient in the azimuthal direction (which is the streamwise direction for the boundary layer flow) is zero (the flow is axisymmetric) and the boundary layer thickness is constant. At a critical Reynolds number, the sidewall boundary layer loses stability at a subcritical Hopf bifurcation, breaking the axisymmetry of the basic state flow, and for Reynolds numbers slightly above critical, the basic state is unstable to a packet of Hopf modes with azimuthal wavenumbers clustered about the critical wavenumber. The early time evolution of the critical Hopf mode is a rotating wave whose behaviour is analogous to a Tollmien–Schlichting wave. As the Hopf modes grow with time, nonlinear interactions lead to modulations in the waves, localization of the disturbances and the evolution of concentrated streamwise vortical streaks which become very intense via vortex stretching.
In this work, the effect of three principal and independent parameters of Atmospheric Plasma Spray on the properties of coatings deposited using mixtures of commercial powders of titanium dioxide (TiO2) and chromium oxide (Cr2O3) was studied. The results of this work are used for special applications on turbomachinery components such as wear protection in sliding seals and in steam valves for turbines, chemical protection for centrifugal compressor members, and special seal applications.
The design of experiments (DoE) technique has proved to be very useful to study the influence factors and optimization. Pierlot et al.  demonstrated that the application of the Hadamard and two factorial design techniques are useful for the optimization of thermal spray processes. An example of the application of the DoE is the one mentioned by Murugan et al. . In their work, a factorial design was used to study the interactions between gas flow, oxygen flow, powder rate and spray distance on the percentage of porosity and hardness of TiO2 - Cr2O3 composite coatings generated by High Velocity Oxy-Fuel.
The ½ fractional two-level factorial DoE technique was used to analyze and optimize the Atmospheric Plasma Spray process parameters. In the current research, experiments were conducted varying the deposition velocity, gas flow and stand-off distance. The effect of these process variables were evaluated by thickness, hardness and microstructure analysis. In this study, an empirical relationship between process variables and response parameters was developed. The entire relationship was made using the results of the DoE.
A very realistic 1:17 scale physical model of a 140-ton gas-stirred industrial steel ladle was used to evaluate flow patterns measured by Particle Image Velocimetry (PIV), considering a three-phase system (air-water-oil) to simulate the argon-steel-slag system and to quantify the effect of the slag layer on the flow patterns. The flow patterns were evaluated for a single injector located at the center of the ladle bottom with a gas flow rate of 2.85 l/min, with the presence of a slag phase with a thickness of 0.0066 m. The experimental results obtained in this work are in excellent agreement with the trends reported in the literature for these gas-stirred ladles. Additionally, a mathematical model was developed in a 2D gas-stirred ladle considering the three-phase system built in the physical model. The model was based on the Eulerian approach in which the continuity and the Navier Stokes equations are solved for each phase. Therefore, there were three continuity and six Navier-Stokes equations in the system. Additionally, turbulence in the ladle was computed by using the standard k-epsilon turbulent model. The agreement between numerical simulations and experiments was excellent with respect to velocity fields and turbulent structure, which sets the basis for future works on process analysis with the developed mathematical model, since there are only a few three-phase models reported so far in the literature to predict fluid dynamics in gas-stirred steel ladles.
During the Middle Paleolithic period, carnivores and hominids periodically occupied the same areas at different times and each predator generated significant palimpsests, rendering difficult their archaeological interpretation. Teixoneres Cave, a carnivore den site, located in the northeastern part of the Iberian Peninsula, demonstrates that it is possible to overcome these problems by using a careful strategy in selecting samples for radiocarbon dating, in order to produce an accurate chronology of the site in question and certainly attest the human occupation.
The flow in the bulk driven by a viscous interfacial film set in motion by a rotating sharp circular knife edge has been examined through experiments and computations. In the experiments, the water surface is covered by an insoluble monomolecular film of dipalmitoylphosphatidylcholine (DPPC), a molecule of wide interest in biology and medicine. It is shown that the viscous coupling between the interfacial film and the bulk liquid leads to a strong bulk flow. Depending on the surface packing and corresponding surface tension, DPPC monolayers exhibit a wide range of phase morphologies. Upon shearing the monolayer, its viscous response varies from that of an essentially inviscid film at low surface packing, to that of a highly viscous non-Newtonian (shear thinning) film when the packing is dense. The more viscous the film, the stronger the driven bulk flow. We have examined this behaviour for hydrodynamic regimes straddling the Stokes flow regime and where flow inertia is important.