A Hamiltonian Boussinesq model with horizontally sheared currents

We are interested in the numerical modeling of wave-current interactions around beaches’ surf zones. Any model to predict the onset of wave breaking at the breaker line needs to capture both the nonlinearity of the wave and its dispersion. We have formulated the Hamiltonian dynamics of a new water wave model. This model incorporates both the shallow water model and the potential flow model as limiting systems. The variational model derived by Cotter and Bokhove (2010) is such a model, but the variables used have been difficult to work with. Our new model has a three-dimensional velocity field consisting of the full three-dimensional potential field plus horizontal velocity components, such that the vertical component of vorticity is nonzero. Our aims are to augment the new model locally with bores and to derive a numerical finite element discretization of the new model including the capturing of bores. As a preliminary step, the variational finite element discretization of Miles’ variational principle coupled to an elliptic mesh generator is shown

Variational space-time (dis)continuous Galerkin method for nonlinear free surface waves

A new variational finite element method is developed for nonlinear free surface gravity water waves. This method also handles waves generated by a wave maker. Its formulation stems from Miles' variational principle for water waves together with a space-time finite element discretization that is continuous in space and discontinuous in time. The key features of this formulation are: (i) a discrete variational approach that gives rise to conservation of discrete energy and phase space and preservation of variational structure; and (ii) a space-time approach that guarantees satisfaction of the geometric conservation law which is crucial in handling the deforming flow domain due to the wave maker and free surface motion. The numerical discretization is a combination of a second order finite element discretization in space and a second order symplectic Stormer-Verlet discretization in time. The resulting numerical scheme is verified against nonlinear analytical solutions and discrete energy conservation is demonstrated for long time simulations. We also validated the scheme with experimental data of waves generated in a wave basin of the Maritime Research Institute Netherlands

How oral texts are organized in monolingual and heritage Russian

Peer reviewe

Revisiting Hele-Shaw dynamics to better understand beach evolution

Wave action, particularly during storms, drives the evo lution of beaches. Beach evolution by non-linear break ing waves is poorly understood due to its three-dimensional character, the range of scales involved, and our limited understanding of particle-wave interactions. We show how a novel, three-phase extension to the classic “Hele-Shaw” laboratory experiment can be designed that creates beach morphologies with breaking waves in a quasi-two-dimensional setting. Our thin Hele-Shaw cell simplifies the inherent complexity of three-phase dynamics: all dynamics become clearly visible and measurable. We show that beaches can be created in tens of minutes by several types of breaking waves, with about one-second periods. Quasi-steady beach morphologies emerge as function of initial water depth, at-rest bed level and wave-maker frequency. These are classified mathematically and lead to beaches, berms and sand bars

Bore Soliton Splash-van spektakel tot oceaangolf?

Het nieuwe universiteitsplein van Twente heeft een intrigerende golfgoot. Midden september 2010 was ons gevraagd om in deze goot een soliton te maken om het nieuwe plein feestelijk te openen. Een soliton is een enkelvoudige golf, een gelokaliseerde opeenhoping van zich snel voortstuwend water. “Dat kan”, zeiden we, “maar vanwege de ondoorzichtige gootwanden is een soliton saai als openingsspektakel”. We besloten daarom onze theoretische kennis van solitonen, hydraulische sprongen, en stromingen te combineren om een spetterend spektakel te verzorgen

Towards a numerical laboratory for investigations of gravity-wave 2 mean-ow interactions in the atmosphere

Idealized integral studies of the dynamics of atmospheric inertia-gravity waves (IGWs) from their sources in the troposphere (e.g., by spontaneous emission from jets and fronts) to dissipation and mean- ow e�ects at higher altitudes could contribute to a better treatment of these processes in IGW parameterizations in numerical weather prediction and climate simulation. It seems important that numerical codes applied for this purpose are e�cient and focus on the essentials. Therefore a previously published staggered-grid solver for f-plane soundproof pseudo-incompressible dynamics is extended here by two main components. These are 1) a semi-implicit time stepping scheme for the integration of buoyancy and Coriolis e�ects, and 2) the incorporation of Newtonian heating consistent with pseudo-incompressible dynamics. This heating function is used to enforce a temperature pro�le that is baroclinically unstable in the troposphere and it allows the background state to vary in time. Numerical experiments for several benchmarks are compared against a buoyancy/Coriolis-explicit third-order Runge-Kutta scheme, verifying the accuracy and ef- �ciency of the scheme. Preliminary mesoscale simulations with baroclinic-wave activity in the troposphere show intensive small-scale wave activity at high altitudes, and they also indicate there the expected reversal of the zonal-mean-zonal winds

Pharmacoeconomic evaluation of the tixagevimab and cilgavimab combination using for pre-exposure prophylaxis of COVID-19

Aim. To evaluate pharmacoeconomic feasibility using of the tixagevimab and cilgavimab combination for pre-exposure prophylaxis of COVID-19 in immunocompromised patients. Materials and methods. Cost-effectiveness of tixagevimab and cilgavimab in persons 12 years old who weigh 40 kg and have either a history of allergy that prevents their vaccination against COVID-19 or moderate or immunocompromised was assessed based on PROVENT phase III study results. The quantity of life years or quality-adjusted life years gained was calculated. Direct medical cost associated with prophylaxis of COVID-19, treatment of infected patients and those experiencing long COVID post infection were assessed. Results were compared with wiliness-to-pay threshold, measured as tripled gross domestic product per capita and equal to 2.69 mln RUB in 2022. Results. Pre-exposure prophylaxis of COVID-19 results in additional 0.0287 life years or 0.0247 quality-adjusted life years. The cost of additional life year gained is equal to 1.12 mln RUB, the cost of additional quality-adjusted life years is 1.30 mln RUB. Both costs of additional life year and cost of quality-adjusted life years appeared to be significantly less compared to wiliness-to-pay threshold. Conclusion. Pre-exposure prophylaxis of COVID-19 with combination of tixagevimab and cilgavimab is economically feasible and may be recommended for wide use in Russian healthcare system

Hele-Shaw beach creation by breaking waves: a mathematics-inspired experiment

Fundamentals of nonlinear wave-particle interactions are studied experimentally in a Hele-Shaw configuration with wave breaking and a dynamic bed. To design this configuration, we determine, mathematically, the gap width which allows inertial flows to survive the viscous damping due to the side walls. Damped wave sloshing experiments compared with simulations confirm that width-averaged potential-flow models with linear momentum damping are adequately capturing the large scale nonlinear wave motion. Subsequently, we show that the four types of wave breaking observed at real-world beaches also emerge on Hele-Shaw laboratory beaches, albeit in idealized forms. Finally, an experimental parameter study is undertaken to quantify the formation of quasi-steady beach morphologies due to nonlinear, breaking waves: berm or dune, beach and bar formation are all classified. Our research reveals that the Hele-Shaw beach configuration allows a wealth of experimental and modelling extensions, including benchmarking of forecast models used in the coastal engineering practice, especially for shingle beaches

Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

Variational approaches to water wave simulations

This thesis starts with the study the theoretical aspects of water wave modelling using a variational framework, which is directly associated with phase space and energy conservation laws. In particular, we focus on a new variational model based on the work of Cotter and Bokhove. The new model includes accurate dispersion and incorporates the vertical component of vorticity and breaking waves modelled as bores. The Hamiltonian structure of the new water wave model is derived. A novel approach to find jump conditions at a bore is presented.\ud \ud In Chapter 3 we use a variational approach to derive a class of symplectic time integrators. We start with a Hamiltonian system with coordinate and momentum as canonically conjugated variables. A discrete variational principle in time is constructed, which is discretized with a discontinuous Galerkin finite element method. Following this approach we are able to obtain known time integrators as well as some new integrators.\ud \ud The next topic considered in this thesis is the construction of a numerical wave tank, which is discussed in Chapter 4. A second order accurate variational finite element method for the nonlinear potential flow water wave equations is developed. An important aspect is that the free surface and wave maker motion changes the computational domain each time step.\ud A detailed validation using experimental wave tank data demonstrates the excellent capabilities of the numerical method to simulate realistic wave experiments. In particular, wave focussing is simulated accurately, catching both the location and time when a freak wave occurred in the experiment. The results for an uneven bottom and irregular waves are also found to be excellent. These results provide a suitable basis for the extension of the method to a fast moving ship in waves. \ud \ud In Chapter 4 we also combine the novel third order time integrator developed in Chapter 3 with the discrete variational method constructed earlier in Chapter 4 for nonlinear free surface water waves. A long time calculation reveals no energy or amplitude decay, which provides an adequate base for a further usage of the third order time integrator for more complicated water wave problems