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A model to describe the transport across membranes of chemical species dissolved in an incompressible flow is developed via homogenization. The asymptotic matching between the microscopic and macroscopic solute concentration fields leads to a solute flux jump across the membrane, quantified through the solution of diffusion problems at the microscale. The predictive model, written in a closed form, covers a wide range of membrane behaviors, in the limit of negligible Reynolds and Peclet numbers inside the membrane. The closure problem at the microscale, found via homogenization, allows one to link the membrane microstructure to its effective macroscopic properties, such as solvent permeability and solute diffusivity. After a validation of the model through comparison with the corresponding full-scale solution, an immediate application is provided, where the membrane behavior is a priori predicted through an analysis of its microscopic properties. The introduced tools and considerations may find applications in the design of thin microstructured membranes. Published under an exclusive license by AIP Publishing.

The wave equation $\left(\partial_{tt} - c^2 \Delta_x\right) u(x,t) = e^{-t} f(x,t)$ is shown to have a unique solution if $u$ and its partial derivatives in $x$ are in $L^2(e^{-t})$ on the cone, and the solution can be explicit given in the Fourier series of orthogonal polynomials on the cone. This provides a particular solution for the boundary value problems of the non-homogeneous wave equation on the cone, which can be combined with a solution to the homogeneous wave equation in the cone to obtain the full solution.

Sports contexts are increasingly used in management research to test and develop theory and explore managerially relevant phenomena. This growth in publications is likely driven by a series of advantages that sports data offers to management researchers. However, such positive features are not a panacea, as several drawbacks are also associated with leveraging sports data, which can limit their usefulness for management scholars. In this paper, we aim to provide management researchers guidance to leverage the advantages and avoid the drawbacks of leveraging sports contexts. To do so, we identify and review 249 papers published over the last 50 years that used sports data to advance management theories and shed light on managerial phenomena. After outlining how these works contributed to the growth of several key conversations in management research, we discuss the advantages of using sports data by outlining how they can advance management research both conceptually (e.g., theory building and radical theorizing) and empirically (e.g., triangulation and replication). We then discuss the potential drawbacks of research using sports data and suggest ways to compensate for them. We close by outlining several new directions in which scholars can leverage sports data to further advance management research.

Potts shunt (PS) was suggested as palliation for patients with suprasystemic pulmonary arterial hypertension (PAH) and right ventricular (RV) failure. PS, however, can result in poorly understood mortality. Here, a patient-specific geometrical multiscale model of PAH physiology and PS is developed for a paediatric PAH patient with stent-based PS. In the model, 7.6mm-diameter PS produces near-equalisation of the aortic and PA pressures and $$Q_p/Q_s$$ Q p / Q s (oxygenated vs deoxygenated blood flow) ratio of 0.72 associated with a 16% decrease of left ventricular (LV) output and 18% increase of RV output. The flow from LV to aortic arch branches increases by 16%, while LV contribution to the lower body flow decreases by 29%. Total flow in the descending aorta (DAo) increases by 18% due to RV contribution through the PS with flow into the distal PA branches decreasing. PS induces 18% increase of RV work due to its larger stroke volume pumped against lower afterload. Nonetheless, larger RV work does not lead to increased RV end-diastolic volume. Three-dimensional flow assessment demonstrates the PS jet impinging with a high velocity and wall shear stress on the opposite DAo wall with the most of the shunt flow being diverted to the DAo. Increasing the PS diameter from 5mm up to 10mm results in a nearly linear increase in post-operative shunt flow and a nearly linear decrease in shunt pressure-drop. In conclusion, this model reasonably represents patient-specific haemodynamics pre- and post-creation of the PS, providing insights into physiology of this complex condition, and presents a predictive tool that could be useful for clinical decision-making regarding suitability for PS in PAH patients with drug-resistant suprasystemic PAH.

This paper proposes a novel hybrid FDTD method for solving the time-dependent Schrodinger equation, which is fundamental for modeling materials and designing nanoscale devices. The wave function is propagated on nonuniform grids by applying explicit updates in part of the grid and implicit updates elsewhere. The latter are based on the Alternating-Direction Implicit (ADI) scheme while the former are constructed with a central difference for the time derivative. A rigorous stability analysis proves that spatial steps can be selectively removed from the stability criterion thus combining the unconditional stability of the ADI scheme with fast explicit calculations. The scheme excels in its flexibility by efficiently discretizing and balancing explicit with implicit updates, as such expediting the computations. Moreover, it retains the linear complexity of explicit schemes with respect to space and time, making it especially scalable to numerically large problems. Several numerical experiments, including a laterally tunnel coupled quantum wire and a nanowire double-barrier resonant-tunneling diode, show the validity of the scheme by demonstrating its high accuracy and decreased CPU time compared to traditional methods. (C) 2021 Elsevier B.V. All rights reserved.

Line-driven winds of hot, luminous stars are intrinsically unstable due to the line-deshadowing instability (LDI). In non-magnetic hot stars, the LDI leads to the formation of an inhomogeneous wind consisting of small-scale, spatially separated clumps that can have great effects on observational diagnostics. However, for magnetic hot stars the LDI generated structures, wind dynamics, and effects on observational diagnostics have not been directly investigated so far. We investigated the non-linear development of LDI generated structures and dynamics in a magnetic line-driven wind of a typical O-supergiant. We employed two-dimensional axisymmetric magnetohydrodynamic (MHD) simulations of the LDI using the Smooth Source Function approximation for evaluating the assumed one-dimensional line force. To facilitate the interpretation of these magnetic models, they were compared with a corresponding non-magnetic LDI simulation as well as a magnetic simulation neglecting the LDI. A central result obtained is that the wind morphology and wind clumping properties change strongly with increasing wind-magnetic confinement. Most notably, in magnetically confined flows, the LDI leads to large-scale, shellular sheets ('pancakes') that are quite distinct from the spatially separate, small-scale clumps in non-magnetic line-driven winds. We discuss the impact of these findings for observational diagnostic studies and stellar evolution models of magnetic hot stars., 14 pages, 7 figures, accepted for publication in A&A

Quantitative assessment of the complex hemodynamic environment in type B aortic dissection (TBAD) through computational fluid dynamics (CFD) simulations can provide detailed insights into the disease and its progression. As imaging and computational technologies have advanced, methodologies have been developed to increase the accuracy and physiological relevance of CFD simulations. This study presents a patient-specific workflow to simulate blood flow in TBAD, utilising the maximum amount of in vivo data available in the form of CT images, 4D-flow MRI and invasive Doppler-wire pressure measurements, to implement the recommended current best practice methodologies in terms of patient-specific geometry and boundary conditions. The study aimed to evaluate and verify this workflow through detailed qualitative and quantitative comparisons of the CFD and in vivo data. Based on data acquired from five TBAD patients, a range of essential model inputs was obtained, including inlet flow waveforms and 3-element Windkessel model parameters, which can be utilised in further studies where in vivo flow data is not available. Local and global analysis showed good consistency between CFD results and 4D-MRI data, with the maximum velocity in the primary entry tear differing by up to 0.3 m/s, and 80% of the analysed regions achieving moderate or strong correlations between the predicted and in vivo velocities. CFD predicted pressures were generally well matched to the Doppler-wire measurements, with some deviation in peak systolic values. Overall, this study presents a validated comprehensive workflow with extensive data for CFD simulation of TBAD.

Coral mounds formed by framework-forming cold-water corals pierce the seabed along most continental margins of the Atlantic Ocean and new sites are continuously being discovered. Here, we describe an extremely high accumulation of coral mounds at the NW Moroccan Atlantic margin between 35 degrees N and 35.5 degrees N. Within an area of only 1440 km(2), > 3400 mounds were found exposed at the seabed. The coral mounds are nowadays characterized by an almost complete lack of living cold-water corals. In addition, numerous buried mounds were identified in hydroacoustic sub-bottom profiles, and are estimated to be similar to 3.7 times more frequent than the exposed mounds. Consequently, a total of similar to 16,000 buried and exposed mounds is estimated for the entire study area. The exposed mounds are rather small with a mean height of 18 m and show a conspicuous arrangement in two slope-parallel belts that centre in water depths between 720 and 870 m and 890-980 m, respectively, putting them among the deepest mound occurrences discovered so far in the Atlantic. The mostly elongated mounds largely stretch downslope pointing to a significant influence of internal waves in the mound formation process. Moreover, based on their average dimensions, the entire coral mound volume can be estimated as 1.3 km(3), which means the mounds store a considerable amount of coral carbonate highlighting their potentially important role as regional carbonate factories. In combination with further occurrences of coral mounds along the Moroccan margin, both in the Mediterranean and in the Atlantic Ocean, these new findings underline Morocco's role as a hotspot for the occurrence of cold-water coral mounds.

Quantum Field Theories (QFTs) in Anti-de Sitter (AdS) spacetime are often strongly coupled when the radius of AdS is large, and few methods are available to study them. In this work, we develop a Hamiltonian truncation method to compute the energy spectrum of QFTs in two-dimensional AdS. The infinite volume of constant timeslices of AdS leads to divergences in the energy levels. We propose a simple prescription to obtain finite physical energies and test it with numerical diagonalization in several models: the free massive scalar field, $\phi^4$ theory, Lee-Yang and Ising field theory. Along the way, we discuss spontaneous symmetry breaking in AdS and derive a compact formula for perturbation theory in quantum mechanics at arbitrary order. Our results suggest that all conformal boundary conditions for a given theory are connected via bulk renormalization group flows in AdS., Comment: 63 pages + appendices, 44 figures

This paper presents image velocimetry measurements on turbulent flows adjacent to a permeable bed made of randomly packed glass particles. For measuring flow velocities inside the bed, the refractive index of the glass particles was matched with that of the fluid. By continuously scanning in the transverse direction, we measured the streamwise and vertical velocity components within a three-dimensional domain (3D2C-PIV), including first- and second-order turbulent statistics. We established how the scanning travel speed is associated with the laser sheet thickness and the space-time velocity fluctuations for collecting reliable measurements. The methodology was applied to free-surface flows over a sloping bed under low relative submergence and supercritical conditions. Space- and time-averaged profiles were obtained in a representative elementary volume as defined by thedouble-averagingprocedure (Nikora et al. in J Hydraulic Eng.127(2):123–133, 2001). A turbulent boundary layer over the rough bed was observed when experiments were run at intermediate Reynolds numbers Re =$$O(1000)$$O(1000). Apart from measuring subsurface velocities, this method shed light on the part played by the rough bed in the overall flow dynamics: the roughness layer was a buffer region within which porosity varied sharply and turbulent stress was rapidly dampened.Graphic abstract

This work predicts the evolution of self-excited thermo-acoustic instabilities in a gas turbine model combustor using large eddy simulation. The applied flow solver is fully compressible and comprises a transported sub-grid probability density function approach in conjunction with the Eulerian stochastic fields method. An unstable operating condition in the PRECCINSTA test case—known to exhibit strong flame oscillations driven by thermo-acoustic instabilities—is the chosen target configuration. Good results are obtained in a comparison of time-averaged flow statistics against available measurement data. The flame’s self-excited oscillatory behaviour is successfully captured without any external forcing. Power spectral density analysis of the oscillation reveals a dominant thermo-acoustic mode at a frequency of 300 Hz; providing remarkable agreement with previous experimental observations. Moreover, the predicted limit-cycle amplitude is found to closely match its respective measured value obtained from experiments with rigid metal combustion chamber side walls. Finally, a phase-resolved study of the oscillation cycle is carried out leading to a detailed description of the physical mechanisms that sustain the closed feedback loop.

In this study, free vibration analyses of embedded carbon and silica carbide nanotubes lying on an elastic matrix are performed based on Eringen’s nonlocal elasticity theory. These nanotubes are modeled as nanobeam and nanorod. Elastic matrix is considered as Winkler–Pasternak elastic foundation and axial elastic media for beam and rod models, respectively. The vibration formulations of the beam and rod are derived by utilizing Hamilton’s principle. The obtained equations of motions are solved by the method of separation of variables and finite element-based Hermite polynomials for various boundary conditions. The effects of boundary conditions, system modeling, structural sizes such as length, cross-sectional sizes, elastic matrix, mode number, and nonlocal parameters on the natural frequencies of these nanostructures are discussed in detail. Moreover, the availability of size-dependent finite element formulation is investigated in the vibration problem of nanobeams/rods resting on an elastic matrix.

The interaction between a fluid and a poroelastic structure is a complex problem that couples the Navier-Stokes equations with the Biot system. The finite element approximation of this problem is involved due to the fact that both subproblems are indefinite. In this work, we first design residual-based stabilization techniques for the Biot system, motivated by the variational multiscale approach. Then, we state the monolithic Navier-Stokes/Biot system with the appropriate transmission conditions at the interface. For the solution of the coupled system, we adopt both monolithic solvers and heterogeneous domain decomposition strategies. Different domain decomposition methods are considered and their convergence is analyzed for a simplified problem. We compare the efficiency of all the methods on a test problem that exhibits a large added-mass effect, as it happens in hemodynamics applications. (C) 2009 Elsevier Inc. All rights reserved.

[Left: Onshore palaeo‐digital elevation model (palaeoDEM) for the Cenomanian North American continent. Key palaeogeographic features are labelled, including the Sevier orogenic highlands, Laramidian landmass, Western Interior Seaway, Appalachian landmass, Hudson Seaway (HS) and Labrador Seaway (LS). Modern North American coastlines and country borders (solid black lines) have been palaeo‐rotated onto palaeoDEMs. Right: Spatial distributions of suspended sediment discharges (Qs) for the Cenomanian North American continent. Qs values overlay palaeoDEM hillshades for comparison with palaeotopography. , Abstract Depositional stratigraphy represents the only physical archive of palaeo‐sediment routing and this limits analysis of ancient source‐to‐sink systems in both space and time. Here, we use palaeo‐digital elevation models (palaeoDEMs; based on high‐resolution palaeogeographic reconstructions), HadCM3L general circulation model climate data and the BQART suspended sediment discharge model to demonstrate a predictive, forward approach to palaeo‐sediment routing system analysis. To exemplify our approach, we use palaeoDEMs and HadCM3L data to predict the configurations, geometries and climates of large continental catchments in the Cenomanian and Turonian North American continent. Then, we use BQART to estimate suspended sediment discharges and catchment‐averaged erosion rates and we map their spatial distributions. We validate our estimates with published geologic constraints from the Cenomanian Dunvegan Formation, Alberta, Canada, and the Turonian Ferron Sandstone, Utah, USA, and find that estimates are consistent or within a factor of two to three. We then evaluate the univariate and multivariate sensitivity of our estimates to a range of uncertainty margins on palaeogeographic and palaeoclimatic boundary conditions; large uncertainty margins (≤50%/±5°C) still recover estimates of suspended sediment discharge within an order of magnitude of published constraints. PalaeoDEMs are therefore suitable as a first‐order investigative tool in palaeo‐sediment routing system analysis and are particularly useful where stratigraphic records are incomplete. We highlight the potential of this approach to predict the global spatio‐temporal response of suspended sediment discharges and catchment‐averaged erosion rates to long‐period tectonic and climatic forcing in the geologic past.]

The mid-Cretaceous period was one of the warmest intervals of the past 140 million years1–5, driven by atmospheric carbon dioxide levels of around 1,000 parts per million by volume6. In the near absence of proximal geological records from south of the Antarctic Circle, it is disputed whether polar ice could exist under such environmental conditions. Here we use a sedimentary sequence recovered from the West Antarctic shelf—the southernmost Cretaceous record reported so far—and show that a temperate lowland rainforest environment existed at a palaeolatitude of about 82° S during the Turonian–Santonian age (92 to 83 million years ago). This record contains an intact 3-metre-long network of in situ fossil roots embedded in a mudstone matrix containing diverse pollen and spores. A climate model simulation shows that the reconstructed temperate climate at this high latitude requires a combination of both atmospheric carbon dioxide concentrations of 1,120–1,680 parts per million by volume and a vegetated land surface without major Antarctic glaciation, highlighting the important cooling effect exerted by ice albedo under high levels of atmospheric carbon dioxide. Multi-proxy core data and model simulations support the presence of temperate rainforests near the South Pole during mid-Cretaceous warmth, indicating very high CO2 levels and the absence of Antarctic ice.

© 2018 Elsevier Ltd Meteorological measurements are conducted in Antwerp, Belgium in July 2013, followed by CFD urban microclimate simulations considering the same city and time period. The simulations are found to be able to reproduce measured air temperatures inside central Antwerp with an average absolute difference of 0.88 °C. The simulation results supplemented with measurements are used to generate location-specific Microclimatic Conditions (MCs) in three locations: (1) a rural location outside Antwerp; (2) an urban location inside Antwerp, away from an urban park; and (3) another urban location, close to the same park. Building Energy Simulations (BES) are performed for 36 cases based on three different MCs, two building use types and six sets of construction characteristics, ranging from pre-1946 buildings to new, low-energy buildings. Monthly Cooling Demands (CDs) are extracted for each case and compared with each other. The results demonstrate that compared to the air temperatures in the rural area, on average, air temperatures at the urban sites away and close to the park are 3.3 °C and 2.4 °C higher, respectively. This leads to an additional monthly CD of up to 90%. CDs of buildings with better thermal insulation and lower infiltration rates can increase by 48% once moved from the rural location to an urban location, which may lead to the reconsideration of design guidelines of low-energy buildings exposed to an urban MC. Although the proximity of an urban park cannot fully compensate the increased CD by an urban MC, residential buildings close to the park are found to have on average 13.9% less CD during July 2013, compared with buildings away from the same park. The influence of the urban park on the CDs of buildings in its vicinity is strongly linked to the meteorological wind direction. Professionals focusing on energy-efficient buildings in cities are advised to conduct energy predictions with location-specific MC data, instead of only using city-averaged meteorological data. ispartof: APPLIED ENERGY vol:228 pages:852-872 status: published

A backward facing micro-step is a building block for many microfluidic devices. Due to micron sized characteristic dimensions, the gas flow in such a geometry is rarefied in nature. Such rarefied gas flows are widely solved using the Direct Simulation Monte Carlo (DSMC) technique. Flow separation, circulation and re-attachment are some of the basic characteristics of step flows. The objective of this study is to analyze the effect of rarefaction on the flow properties and the separation of the flow. The range of selected Knudsen number (Kn) covers the slip and transition regime from a value of 0.0311–13.25. The pressure ratios employed are 3 and 5. It is observed that the slip velocity continuously increases while the centre-line velocity first decreases, then remains constant and finally increases with increase in Kn. At the step, separation of the flow is seen for Kn 0.1325 while no such separation is observed in the range of Kn from 0.198 to 13.25. The corresponding Re for these ranges are 6.43 to 0.67 and 0.392 to 0.012 respectively. The re-attachment length decreases with increase in Kn whereas it increases with increase in Re. A stronger pressure force and a weaker diffusion effect leads to flow separation in the slip regime whereas stronger diffusion and weaker pressure force lead to an absence of flow separation in the transition regime. Finally, this work presents for the first time the existence of the Knudsen minimum for such a backward step geometry.

This paper presents an experimental study of heat transfer in a slightly rarefied gas flowing in a circular tube with constant wall temperature boundary condition. Local temperature measurements are carried out for the first time in rarefied gas flows to investigate into the anomalous values of Nusselt number (Nu) obtained by a previous experimental study (Demsis et al., 2009). The present measurements agree well with the low Nu reported by Demsis et al. (2009) when the Nu is obtained using their procedure; additionally, the measurements reveal the importance of end effects in determining the Nusselt number in rarefied gases. The Nusselt number obtained in the present experiments tends to zero with increasing axial conduction. Nu shows a weak dependence on Knudsen number for the range investigated here (0.001 < Kn < 0.012).

This study concerns with the free vibration analyses for centrifugally stiffened cracked beams modelled as functionally graded material in the axial direction. The variation of material properties along the cracked beam is expressed in terms of the power law distribution. Analyses are carried out by the Rayleigh–Ritz method that uses shape functions and energy expressions written for centrifugally stiffened Euler-Bernoulli beams. The influence of the hub radius, angular velocity, crack location to beam length ratio and crack depth to thickness ratio and cross-section size ratio and inhomogeneity on natural frequencies are examined for the beams with the clamped-free boundary condition. The results are verified by using the data available in the open literature and/or the outputs of finite element analyses performed for an axially functionally graded solid beam. The results show that the fundamental frequency parameters reduce with the increasing the ratio of crack depth to thickness. The highest natural frequency droop exists close to the root of the beam for flap-wise and chord-wise vibrations. Another important finding is that reduction of natural frequency parameters in chord-wise modes is larger than that in flap-wise modes when the crack location is varied. This new research should help to improve predictions of the impact of the crack on free vibrations for the rotating cracked axially functionally graded beams.

Coral mounds formed by framework-forming scleractinian cold-water corals (CWC; mainly Lopheliapertusa) are a common seabed feature along the Atlantic continental margins. While coral mound areas in the NE Atlantic reveal a climate-dependent temporal pattern of CWC occurrence and mound aggradation that is related to distinct environmental conditions (e.g., productivity, water mass properties, hydrodynamics), the long-term development of CWC and coral mounds at the western side of the Atlantic is less well documented and understood. Here, we present a 260-kyr coral record from the recently described Campeche CWC province in the southern Gulf of Mexico, combined with a reconstruction of the paleo-environmental conditions for the last 140 kyr. Uranium-series dating of 26 coral samples reveals that CWC growth predominantly coincided with interglacial periods. Highest vertical mound aggradation rates of 34 to 40 cm kyr(-1) occurred during the Holocene. The reduced occurrence of CWC and the concurrent almost complete stagnation in mound aggradation during glacial periods could be linked to a diminished presence of Antarctic Intermediate Water at those intermediate depths in which the coral mounds occur. Such setting would have caused a less dynamic bottom current regime resulting in a reduced food supply to the CWC along the Campeche Bank. Deutsche Forschungsgemeinschaft (DFG) [HE 3412/17-1] Fundacao para a Ciencia e Tecnologia (FCT) [SFRH/BD/72149/2010] GLOMAR - the Bremen International Graduate School for Marine Sciences info:eu-repo/semantics/publishedVersion

The theory of analytical modeling of periodic metasurfaces for normal incidence is extended to the general oblique case. The metasurface is considered as a periodic planar array with electrically small dipolar scatterers. The induced polarization currents are calculated by combining the information obtained from the response of individual scatterer to the incident wave and the interaction of scatterers with each other. All required interaction coefficients for the most general analysis of metasurfaces are analytically derived. The expressions in terms of the polarization currents are presented for the reflected/transmitted fields from metasurfaces at oblique illumination. Although theoretically known that adding normal polarization currents to the tangential ones will not provide extra degrees of freedom in the manipulation of the reflection and transmission properties of metasurfaces, in most practical applications, it is required to consider both tangential as well as normal polarization currents. Thus, the effect of oblique illumination in the modification of normal and tangential polarization currents is clarified. Our theory is used to analyze two canonical examples of bianisotropic metasurfaces composed of chiral and omega inclusions. The results of this paper provide an effective tool to push the analysis as well as the synthesis of metasurfaces one step forward.

Air-core&ndash, liquid-ring (ACLR) atomization presents a specific type of internal mixing pneumatic atomization. It can be used for disintegration of high viscous feed liquids into small droplets at relatively low gas consumptions. However, the specific principle of ACLR atomization is still under research and no guidelines for process and atomizer design are available. Regarding literature on pre-filming atomizers, it can be hypothesized for ACLR atomization that the liquid film thickness inside the exit orifice of the atomizer, as well as the resulting spray droplet sizes decrease with increasing air-to-liquid ratio (ALR) and decreasing feed viscosity. In this study, the time dependent liquid film thickness inside the exit orifice of the atomizer was predicted by means of computational fluid dynamics (CFD) analysis. Results were compared to high speed video images and correlated to measured spray droplet sizes. In conclusion, the hypothesis could be validated by simulation and experimental data, however, at high viscosity and low ALR, periodic gas core breakups were detected in optical measurements. These breakups could not be predicted in CFD simulations, as the simplification of an incompressible gas phase was applied in order to reduce computational costs and time. Nevertheless, the presented methods show good potential for improvement of atomizer geometry and process design as well as for further investigation of the ACLR atomization principle.

Numerical blood flow simulations are typically set up from anatomical medical images and calibrated using velocity measurements. However, the accuracy of the computational geometry itself is limited by the resolution of the anatomical image. We first show that applying standard no‐slip boundary conditions on inaccurately extracted boundaries can cause large errors in the results, in particular the pressure gradient. In this work, we therefore propose to augment the flow model calibration by slip/transpiration boundary conditions, whose parameters are then estimated using velocity measurements. Numerical experiments show that this methodology can considerably improve the accuracy of the estimated pressure gradients and 3D velocity fields when the vessel geometry is uncertain.

We use non-equilibrium molecular dynamics simulations to study dipolar dumbbell fluids in a thermal gradient. We study the relative orientation of size asymmetric molecules with respect to the thermal gradient, and the sensitivity of the orientation to whether the Wolf method or Ewald summation is employed to compute the electrostatic interactions. For these systems, we find that the Wolf method overestimates the degree of molecular orientation. We also present new data on fluids with very small dipole moments which give novel insight into how the molecular asymmetry influences the polarisation response in the thermal gradient.

The present investigation concerns the numerical solution of elliptic partial differential equations (PDEs) governing physical phenomena in heat transfer and fluid flow by the lattice Boltzmann method (LBM). A general form of dimensionless conservation equations and appropriate source terms to be included in the elliptic PDE are identified. Specific problems considered in this article include heat conduction in a composite domain characterised by a very high thermal conductivity ratio between components and the presence of a partially inclined interface between them. With respect to this problem, the influence of representing oblique interfaces by the simple staircase approximation is studied. On the other hand, hydrodynamically as well as thermally fully-developed laminar flow through rectangular duct and shrouded array of fins is also investigated, where the aspect ratio of the duct cross-section and the height of fins along with the ratio of thermal conductivities of the fin and the fluid are varied. Dimensionless quantities characterising considered problems are determined by LBM and compared with either analytical solutions (if available) or reference data obtained from the finite volume method (FVM). The two relaxation times (TRT) collision scheme with the specific eigenvalue combination fixed to a constant value within a typical range of validity is employed for solving the present problems. The appropriate implementation of boundary conditions and, if required, interface conditions is essential in order to maintain second order accuracy of LBM. It is observed that the accuracy of determination depends strongly on the employed specific eigenvalue combination and relatively weakly on the discrete velocity stencil. As a result, in most of the cases for a considered physical condition, an optimum (range of) specific eigenvalue combination(s) could be detected. Nevertheless, from the acquired results, the potential of LBM with the simple D2Q4 stencil for solving considered problems becomes evident. Therefore, the method proves to be promising for optimisation of duct cross-sections and fin shapes in channels with useful applications in the design of heat exchangers. (C) 2015 Elsevier Masson SAS. All rights reserved.

A joint experimental and computational study of thermoacoustic instabilities in a model swirl-stabilised combustor is presented. This paper aims to deliver a better characterisation of such instabilities through the examination of measurements in conjunction with the numerical results obtained via Large Eddy Simulation (LES). The experimental configuration features a cylindrical combustion chamber where the lean premixed methane/air flame experiences self-sustained thermoacoustic oscillations. The nonlinear behaviour of the acoustically excited flame is experimentally investigated by broadband chemiluminescence and dynamic pressure measurements. In LES, the Eulerian stochastic field method is employed for the unknown turbulence/chemistry interaction of the gas-phase. Comparisons of the predicted frequency spectrum and phase-resolved flame structure with measurements are found to be in good agreement, confirming the predictive capabilities of the LES methodology. The presence of Period 2 thermoacoustic oscillations, as a consequence of period-doubling bifurcation, is also confirmed in LES. Through the application of nonlinear analysis both to the experimental and numerical acoustic fluctuations, it is highlighted that the nonlinear behaviour of combustion instabilities in the burner under investigation follows a pattern typical of Period 2 oscillations. Furthermore, the current work demonstrates a useful approach, through the use of dynamic mode decomposition (DMD), for the investigation of unstable flame modes at a specific frequency of interest. The experimental and numerical DMD reconstructions suggest that hot combustion products are convected azimuthally at a rate dictated by the subharmonic frequency.

This paper presents a comparative study of numerical, experimental and empirical techniques on the effect of localised air blast loads on mild steel and armour steel plates. The blast load effects on monolithic plates have been accounted for by using different approaches provided in the Finite Element hydrocode ABAQUS 6.13, namely an Eulerian Lagrangian and a Coupled Eulerian Lagrangian model. In the first model, the air and the explosive were modelled using multi-material Eulerian grids while the plate was modelled using a rigid Lagrangian mesh, while in the second model the rigid target was replaced with deformable plate.\ud \ud \ud \ud The transient deformation of the plate, strain localisation, pressure distribution on the plate have been investigated in the FE models, which have been validated against small scale experimental data for a limited range of charge sizes for both the mild steel and armoured steel. Despite the lower deflection of armour steel compared to mild steel plates, both plates were shown to undergo rupture upon similar charge mass and stand-off. For this purpose, a non-dimensional analysis was carried out with consideration of stand-off distance and slenderness ratio to predict the rupture impulse.

3D Numerical study of temperature variation for subsonic rarefied gas flow in a microchannel is carried out using an in-house MPI-based parallelized DSMC code. The temperature drop in the microchannel decreases with an increase in the aspect ratio whereas it increases with an increase in the pressure ratio, the cross-aspect ratio (CAR), and the Knudsen number. 3D and 2D simulations results are compared and effect of the CAR and Knudsen number are brought out. Finally, a correlation that predicts the temperature drop is formulated along with a list of conditions that ensures a near isothermal flow.

Despite decades of research, the modeling of moving contact lines has remained a formidable challenge in fluid dynamics whose resolution will impact numerous industrial, biological, and daily life applications. On the one hand, molecular dynamics (MD) simulation has the ability to provide unique insight into the microscopic details that determine the dynamic behavior of the contact line, which is not possible with either continuum-scale simulations or experiments. On the other hand, continuum-based models provide a link to the macroscopic description of the system. In this Feature Article, we explore the complex range of physical factors, including the presence of surfactants, which governs the contact line motion through MD simulations. We also discuss links between continuum- and molecular-scale modeling and highlight the opportunities for future developments in this area., Comment: 54 pages, 11 figures

We derive a residual a posteriori estimator for the Kirchhoff plate bending problem. We consider the problem with a combination of clamped, simply supported, and free boundary conditions subject to both distributed and concentrated (point and line) loads. Extensive numerical computations are presented to verify the functionality of the estimators.

We consider the two-dimensional Ising model with long-range pair interactions of the form $J_{xy}\sim|x-y|^{-\alpha}$ with $\alpha>2$, mostly when $J_{xy} \geq 0$. We show that Dobrushin states (i.e. extremal non-translation-invariant Gibbs states selected by mixed $\pm$-boundary conditions) do not exist. We discuss possible extensions of this result in the direction of the Aizenman-Higuchi theorem, or concerning fluctuations of interfaces. We also mention the existence of rigid interfaces in two long-range anisotropic contexts., Comment: revised version

High temperature gradients in heat sinks of micro devices cause substantial properties variations in gas-micro-convection; which constitutes an important strategic research area in non-rarefaction scaling effects. In present analysis, compressible Navier-Stokes equations incorporating temperature dependent density and thermal conductivity variations, for steady, viscous flow of gas at subsonic speeds (Mach number << 1) are numerically solved. Circular micro-pipe geometry, subjected to constant wall heat flux was chosen, The key observations are: In addition to known effects, two additional physical mechanisms increasingly surface at micro scale; and also determine the micro convection characteristics within continuum regime. They are, induced radial convection due to density variations in radial and axial directions and axial conduction induced due to thermal conductivity variations along the flow. High density variations in radial and axial directions, cause velocity gradients and increase fluid friction irreversibility. High thermal conductivity variations cause flattening of temperature profile, induce axial conduction and substantially increase in entropy generation. The results highlight the need for incorporating fluid properties variation in thermal designs of heat sinks for micro devices. Two-way link between velocity profile and temperature, influence entropy generation. Corner effects at entrance and exit influence entropy generation in all cases studied. (C) 2014 Elsevier Ltd. All rights reserved.

This article presents a three-dimensional numerical framework for the simulation of fluid-fluid immiscible compounds in complex geometries, based on the multiple-relaxation-time lattice Boltzmann method to model the fluid dynamics and the color-gradient approach to model multicomponent flow interaction. New lattice weights for the lattices D3Q15, D3Q19, and D3Q27 that improve the Galilean invariance of the color-gradient model as well as for modeling the interfacial tension are derived and provided in the Appendix. The presented method proposes in particular an approach to model the interaction between the fluid compound and the solid, and to maintain a precise contact angle between the two-component interface and the wall. Contrarily to previous approaches proposed in the literature, this method yields accurate solutions even in complex geometries and does not suffer from numerical artifacts like nonphysical mass transfer along the solid wall, which is crucial for modeling imbibition-type problems. The article also proposes an approach to model inflow and outflow boundaries with the color-gradient method by generalizing the regularized boundary conditions. The numerical framework is first validated for three-dimensional (3D) stationary state (Jurin's law) and time-dependent (Washburn's law and capillary waves) problems. Then, the usefulness of the method for practical problems of pore-scale flow imbibition and drainage in porous media is demonstrated. Through the simulation of nonwetting displacement in two-dimensional random porous media networks, we show that the model properly reproduces three main invasion regimes (stable displacement, capillary fingering, and viscous fingering) as well as the saturating zone transition between these regimes. Finally, the ability to simulate immiscible two-component flow imbibition and drainage is validated, with excellent results, by numerical simulations in a Berea sandstone, a frequently used benchmark case used in this field, using a complex geometry that originates from a 3D scan of a porous sandstone. The methods presented in this article were implemented in the open-source PALABOS library, a general C++ matrix-based library well adapted for massive fluid flow parallel computation.

A common problem in lattice QCD simulations on the torus is the extremely long autocorrelation time of the topological charge, when one approaches the continuum limit. The reason is the suppressed tunneling between topological sectors. The problem can be circumvented by replacing the torus with a different manifold, so that the connectivity of the configuration space is changed. This can be achieved by using open boundary conditions on the fields, as proposed earlier. It has the side effect of breaking translational invariance strongly. Here we propose to use a non-orientable manifold, and show how to define and simulate lattice QCD on it. We demonstrate in quenched simulations that this leads to a drastic reduction of the autocorrelation time. A feature of the new proposal is, that translational invariance is preserved up to exponentially small corrections. A Dirac-fermion on a non-orientable manifold poses a challenge to numerical simulations: the fermion determinant becomes complex. We propose two approaches to circumvent this problem., Comment: 9 pages, 8 figures; v2: matches accepted version

Multiscale modeling of 3D layer-to-layer orthogonal interlock woven composite structure for elastic and strength behavior is presented. Due to the inherent nature of weaving, 3D woven composites can be represented by repetitive unit cells at the meso level. The present study focuses on identifying different types of repetitive unit cells considering both the geometry and the boundary conditions. For a typical 3D layer-to-layer orthogonal interlock woven composite, there are eight types of meso repetitive unit cells taking into account both the geometry and the boundary conditions. Additionally, for a practical situation, fiber volume fraction (Vf) in the impregnated strand is not uniform throughout the cross-section. In other words, Vf would be different for different micro repetitive unit cells. The properties of the macro structure, i.e. the 3D woven composite structure has been determined by applying periodic boundary conditions at micro and meso levels and iso-strain conditions at the macro level using finite element analysis. The continuity between the blocks is provided by merging the nodes in the intersection regions. The effect of different Vf at different locations in the transverse cross-section of the strand on the elastic and the strength properties of 3D layer-to-layer woven composite structure is presented.

We simulate the fracture processes of ferroelectric polycrystals in three dimensions using a phase-field model. In this model, the grain boundaries, cracks and ferroelectric domain walls are represented in a diffuse way by three phase-fields. We thereby avoid the difficulty of tracking the interfaces in three dimensions. The resulting model can capture complex interactions between the crack and the polycrystalline and ferroelectric domain microstructures. The simulation results show the effect of the microstructures on the fracture response of the material. Crack deflection, crack bridging, crack branching and ferroelastic domain switching are observed to act as the main fracture toughening mechanisms in ferroelectric polycrystals. Our fully 3-D simulations illustrate how the combination of these mechanisms enhances the fracture toughness of the material, and pave the way for further systematic studies, including fracture homogenization.

Daily summer precipitation over Belgium from the Aire Limitée Adaptation Dynamique Développement International (ALADIN) model and a version of the model that has been updated with physical parameterizations, the so-called ALARO-0 model [ALADIN and AROME (Application de la Recherche à l'Opérationnel à Meso-Echelle) combined model, first baseline version released in 1998], are compared with respect to station observations for the period 1961–90. The 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40) is dynamically downscaled using both models on a horizontal resolution of 40 km, followed by a one-way nesting on high spatial resolutions of 10 and 4 km. This setup allows us to explore the relative importance of spatial resolution versus parameterization formulation on the model skill to correctly simulate extreme daily precipitation. Model performances are assessed through standard statistical errors and density, frequency, and quantile distributions as well as extreme value analysis, using the peak-over-threshold method and generalized Pareto distribution. The 40-km simulations of ALADIN and ALARO-0 show similar results, both reproducing the observations reasonably well. For the high-resolution simulations, ALARO-0 at both 10 and 4 km is in better agreement with the observations than ALADIN. The ALADIN model consistently produces too high precipitation rates. The findings demonstrate that the new parameterizations within the ALARO-0 model are responsible for a correct simulation of extreme summer precipitation at various horizontal resolutions. Moreover, this study shows that ALARO-0 is a good candidate model for regional climate modeling.

This paper is concerned with the continuous-time Vickrey model, which was first introduced in Vickrey (1969). This model can be described by an ordinary differential equation (ODE) with a right-hand side which is discontinuous in the unknown variable. Such a formulation induces difficulties with both theoretical analysis and numerical computation. Moreover it is widely suspected that an explicit solution to this ODE does not exist. In this paper, the authors advance the knowledge and understanding of the continuous-time Vickrey model by reformulating it as a partial differential equation (PDE) and by applying a variational method to obtain an explicit solution representation. Such an explicit solution is then shown to be the strong solution to the ODE in full mathematical rigor. The authors' methodology also leads to the notion of generalized Vickrey model (GVM), which allows the flow to be a distribution, instead of an integrable function. As explained by Han et al. (in press), this feature of traffic modeling is desirable in the context of analytical dynamic traffic assignment (DTA). The proposed PDE formulation provides new insights into the physics of The Vickrey model, which leads to a number of modeling extensions as well as connection with first-order traffic models such as the Lighthill–Whitham–Richards (LWR) model. The explicit solution representation also leads to a new computational method, which will be discussed in an accompanying paper, Han et al. (in press).

This work presents an analysis methodology based on the use of the Finite Element Method (FEM) nowadays considered one of the main numerical tools for solving Boundary Value Problems (BVPs). The proposed methodology, so-called cg-FEM (Cartesian grid FEM), has been implemented for fast and accurate numerical analysis of 2D linear elasticity problems. The traditional FEM uses geometry-conforming meshes; however, in cg-FEM the analysis mesh is not conformal to the geometry. This allows for defining very efficient mesh generation techniques and using a robust integration procedure, to accurately integrate the domain's geometry. The hierarchical data structure used in cg-FEM together with the Cartesian meshes allow for trivial data sharing between similar entities. The cg-FEM methodology uses advanced recovery techniques to obtain an improved solution of the displacement and stress fields (for which a discretization error estimator in energy norm is available) that will be the output of the analysis. All this results in a substantial increase in accuracy and computational efficiency with respect to the standard FEM. cg-FEM has been applied in structural shape optimization showing robustness and computational efficiency in comparison with FEM solutions obtained with a commercial code, despite the fact that cg-FEM has been fully implemented in MATLAB., This work has been developed within the framework of research project DPI2010-20542 of the Ministerio de Economia y Competitividad (Spain). The financial support of the FPU program (AP2008-01086), the funding from Universitat Politecnica de Valencia, and Generalitat Valenciana (PROMETEO/2012/023) are also acknowledged. The authors also thank the support of the Framework Programme 7 Initial Training Network Funding under Grant no. 289361 "Integrating Numerical Simulation and Geometric Design Technology."

A new set of generalized transport equations is derived for higher-order moments which are generated in evolution equation for stress tensor and heat flux vector in 13-moment equations. The closure we employ satisfies Onsager's symmetry principle. In the derivation, we do not employ a phase density function based on Hermite polynomial series in terms of higher-order moments, unlike Grad's approach. The distribution function is rather chosen to satisfy collision invariance, and H-theorem and capture relatively strong deviations from equilibrium. The phase density function satisfies the linearized Boltzmann equation and provides the correct value of the Prandtl number for monatomic gas. The derived equations are compared with Grad's 13-moments equations for gas modeled as Maxwellian molecule. The merits of the proposed equations against Grad's and R13 equations are discussed. In particular, it is noted that the proposed equations contain higher-order terms compared to these equations but require a fewer number of boundary conditions as compared to the R13 equations. The Knudsen number envelope which can be covered to describe flows with these equations is therefore expected to be larger as compared to the earlier equations.

International audience; The Kerr solution in coordinates corotating with the horizon is studied as a testbed for a spacetime with a helical Killing vector in the Ernst picture. The solution is numerically constructed by solving the Ernst equation with a spectral method and a Newton iteration. We discuss convergence of the iteration for several initial iterates and different values of the Kerr parameters.

It is common knowledge that diffusion theory cannot describe light propagation in semitransparent media, i.e., media with a low optical thickness. However, even in an optically thin slab, late-time transport will be eventually determined by a multiple scattering process whose characteristics are still largely unexplored. We numerically demonstrate that, even for an optical thickness as low as 1, after a short transient, propagation along the slab plane becomes diffusive. Nonetheless, we show that such a diffusion process is governed by modified statistical distributions which result from a highly nontrivial interplay with boundary conditions.

Background: Coronary hemodynamics and physiology specific for bifurcation lesions was not well understood. To investigate the influence of the bifurcation angle on the intracoronary hemodynamics of side branch (SB) lesions computational fluid dynamics simulations were performed. Methods: A parametric model representing a left anterior descending-first diagonal coronary bifurcation lesion was created according to the literature. Diameters obeyed fractal branching laws. Proximal and distal main branch (DMB) stenoses were both set at 60 %. We varied the distal bifurcation angles (40 degrees, 55 degrees, and 70 degrees), the flow splits to the DMB and SB (55 %: 45 %, 65 %: 35 %, and 75 %: 25 %), and the SB stenoses (40, 60, and 80 %), resulting in 27 simulations. Fractional flow reserve, defined as the ratio between the mean distal stenosis and mean aortic pressure during maximal hyperemia, was calculated for the DMB and SB (FFRSB) for all simulations. Results: The largest differences in FFRSB comparing the largest and smallest bifurcation angles were 0.02 (in cases with 40 % SB stenosis, irrespective of the assumed flow split) and 0.05 (in cases with 60 % SB stenosis, flow split 55 %: 45 %). When the SB stenosis was 80 %, the difference in FFRSB between the largest and smallest bifurcation angle was 0.33 (flow split 55 %: 45 %). By describing the Delta P-SB-Q(SB) relationship using a quadratic curve for cases with 80 % SB stenosis, we found that the curve was steeper (i.e. higher flow resistance) when bifurcation angle increases (Delta P = 0.451*Q + 0.010*Q(2) and Delta P = 0.687*Q + 0.017*Q(2) for 40 degrees and 70 degrees bifurcation angle, respectively). Our analyses revealed complex hemodynamics in all cases with evident counter-rotating helical flow structures. Larger bifurcation angles resulted in more pronounced helical flow structures (i.e. higher helicity intensity), when 60 or 80 % SB stenoses were present. A good correlation (R-2 = 0.80) between the SB pressure drop and helicity intensity was also found. Conclusions: Our analyses showed that, in bifurcation lesions with 60 % MB stenosis and 80 % SB stenosis, SB pressure drop is higher for larger bifurcation angles suggesting higher flow resistance (i.e. curves describing the Delta P-SB-Q(SB) relationship being steeper). When the SB stenosis is mild (40 %) or moderate (60 %), SB resistance is minimally influenced by the bifurcation angle, with differences not being clinically meaningful. Our findings also highlighted the complex interplay between anatomy, pressure drops, and blood flow helicity in bifurcations.

Symmetric differential expressions @? of order n=2k with real valued coefficients give rise to self adjoint operators in the space of weighted square integrable functions. Characterization theorems exist in the literature that describe such self-adjoint operators. All such characterizations begin by constructing the maximal domain of definition of the expression @?. The Glazman-Krein-Naimark theorem constructs the maximal domain in terms of eigenfunctions corresponding to a nonreal parameter @l. Representations in terms of certain functions related to a real parameter @l can also be found in the literature. In this paper we construct the maximal domain from two complementary self-adjoint realizations of @?. One operator is assumed to be known and the other one is computed explicitly. From these two operators we explicitly give all other self-adjoint operators associated with @?. A special class of operators associated with @? is what we call Type I operators. They arise in connection with a certain bilinear form that results from the weak formulation of the expression @?. Depending on the deficiency index of @? and the properties of the bilinear form we can have two complementary self-adjoint operators (two Type I operators) and, as it turns out, one of them is the celebrated Friedrich Extension. The other operator appears to be new. As in the general case, using these two operators we give an explicit characterization of all other operators of the same Type I.