Model turbulent floods with the Smagorinski large eddy closure

Floods, tides and tsunamis are turbulent, yet conventional models are based upon depth averaging inviscid irrotational flow equations. We propose to change the base of such modelling to the Smagorinksi large eddy closure for turbulence in order to appropriately match the underlying fluid dynamics. Our approach allows for large changes in fluid depth to cater for extreme inundations. The key to the analysis underlying the approach is to choose surface and bed boundary conditions that accommodate a constant turbulent shear as a nearly neutral mode. Analysis supported by slow manifold theory then constructs a model for the coupled dynamics of the fluid depth and the mean turbulent lateral velocity. The model resolves the internal turbulent shear in the flow and thus may be used in further work to rationally predict erosion and transport in turbulent floods

The effect of rheology with gas bubbles on linear elastic waves in fluid-saturated granular media

Elastic waves in fluid-saturated granular media depend on the grain rheology, which can be complicated by the presence of gas bubbles. We investigated the effect of the bubble dynamics and their role in rheological scheme, on the linear Frenkel-Biot waves of P1 type. For the wave with the bubbles the scheme consists of three segments representing the solid continuum, fluid continuum and bubbles surrounded by the fluid. We derived the Nikolaevskiy-type equation describing the velocity of the solid matrix in the moving reference system. The equation is linearized to yield the decay rate λ as a function of the wave number k. We compared the λ(k)-dependence for the cases with and without the bubbles, using typical values of the input mechanical parameters. For both the cases, the λ(k) curve lies entirely below zero, which implies a global decay of the wave. We found that the increase of the radius of the bubbles leads to a faster decay, while the increase in the number of the bubbles leads to slower decay of the wave

Numerical modelling of thermoelastic processes using nonlinear theories with thermal relaxation time

A nonlinear model of thermoelasticity is solved for a ring-shaped body with special attention given to the effect of relaxation time on the body dynamics. A spectral Galerkin method is used to accurately resolve spatial structures of temperature and displacement. A sequence of solutions is obtained for gradually increasing initial amplitude of the thermoelastic wave, showing a transition from a steady harmonic wave to singular solutions. Larger values of the relaxation time are shown to result in smoother temperature profiles. The dynamics generated by a localised heat release from an external source is studied. It is observed that the source excites a standing-like wave of the displacement while temperature monotonically decays

Coupled thermomechanical waves in hyperbolic thermoelasticity

Using models incorporating a thermal relaxation time (hyperbolic models), we study the properties of spatially periodic thermoelastic waves propagating in an infinite rod. Analyzing the Lord-Schulman and Green-Lindsay linear models, we reveal dependencies of decay rates and frequency shifts of temperature and displacement upon the wave number for the case of weak thermoelastic coupling. We explore numerically a general nonlinear hyperbolic model, describing the time evolution of initially sinusoidal distributions of displacement and temperature. Mechanisms of nonlinear interaction between thermal and mechanical fields are qualitatively analyzed. It is demonstrated that larger relaxation times may provide smoother temperature profiles at an intermediate stage of the dynamics

Range of validity and intermittent dynamics of the phase of oscillators with nonlinear self-excitation

A range of active systems, particularly of chemical nature, are known to perform self-excited oscillations coupled by diffusion. The role of the diffusion is not trivial so that the differences in the phase of the oscillations through space may persist, depending on the values of the controlling parameters of the system. Firstly, we analyse a 6th-order nonlinear partial differential equation describing such dynamics. We evaluate the range of the parameters leading to different finite versions of the equation, specifically a version based on nonlinear excitation and a version based on linear excitation. In the second part of the work we solve the equation in two spatial dimensions by finite difference discretization in space and subsequent numerical integration of a system of ordinary differential equations in time. A forced variant of the equation is derived and selected exact solutions are presented. They are also used to verify the numerical code. For the unforced equation, irregular dynamics intermitting with periods of slow evolution are recorded and discussed

A pragmatic cluster randomised trial evaluating three implementation interventions

Background Implementation research is concerned with bridging the gap between evidence and practice through the study of methods to promote the uptake of research into routine practice. Good quality evidence has been summarised into guideline recommendations to show that peri-operative fasting times could be considerably shorter than patients currently experience. The objective of this trial was to evaluate the effectiveness of three strategies for the implementation of recommendations about peri-operative fasting. Methods A pragmatic cluster randomised trial underpinned by the PARIHS framework was conducted during 2006 to 2009 with a national sample of UK hospitals using time series with mixed methods process evaluation and cost analysis. Hospitals were randomised to one of three interventions: standard dissemination (SD) of a guideline package, SD plus a web-based resource championed by an opinion leader, and SD plus plan-do-study-act (PDSA). The primary outcome was duration of fluid fast prior to induction of anaesthesia. Secondary outcomes included duration of food fast, patients' experiences, and stakeholders' experiences of implementation, including influences. ANOVA was used to test differences over time and interventions. Results Nineteen acute NHS hospitals participated. Across timepoints, 3,505 duration of fasting observations were recorded. No significant effect of the interventions was observed for either fluid or food fasting times. The effect size was 0.33 for the web-based intervention compared to SD alone for the change in fluid fasting and was 0.12 for PDSA compared to SD alone. The process evaluation showed different types of impact, including changes to practices, policies, and attitudes. A rich picture of the implementation challenges emerged, including inter-professional tensions and a lack of clarity for decision-making authority and responsibility. Conclusions This was a large, complex study and one of the first national randomised controlled trials conducted within acute care in implementation research. The evidence base for fasting practice was accepted by those participating in this study and the messages from it simple; however, implementation and practical challenges influenced the interventions' impact. A set of conditions for implementation emerges from the findings of this study, which are presented as theoretically transferable propositions that have international relevance. Trial registration ISRCTN18046709 - Peri-operative Implementation Study Evaluation (POISE

Современные подходы к визуализации головного мозга при наркомании (обзор литературы)

Background. Brain neuroimaging studies provided information about the neurobiological effects of narcotic substances, and established the mechanisms of their systematic use, as well as provided important information about the subjective experience and behavior of people with drug addiction, including their struggle for recovery. Until recently, five main methods of brain neuroimaging were considered – structural magnetic resonance imaging (MRI), functional MRI (fMRI), magnetic resonance spectroscopy (MRS), positron emission tomography (PET) and single-photon emission computed tomography (SPECT). These methods allow us to identify various aspects of the structure or function of the brain. Microwave thermometry (MR thermometry) is also used as a neuroimaging method of the brain, which allows us to study the temperature homeostasis of the brain in various human conditions.Materials and methods. The search for domestic publications was carried out in the database on the RSCI website, foreign – in the PubMed, Google Scholar databases in the period 1990–2022. When analyzing the PubMed database, the query «neuroimaging drug addiction» found 16066 links. We also studied works on the following keywords: «neurotransmitters and drug abuse». Publications describing the clinical picture, diagnosis, and poisoning with psychoactive substances were analyzed. A total of 45 articles were analyzed.Conclusion. The obtained results strongly confirm that drug addiction is a brain disease that causes important disorders in many areas, including pathways affecting encouragement and cognition. Neuroimaging methods allow researchers to observe the effect of drug substances on the brain and compare the structure, functions and metabolism of the brain in people who abuse and do not abuse drug’s substances. MR thermometry allows measuring the temperature of the brain, which is a reflection of the metabolism of the brain and allows assessing the effect of various substances on the brain. However, nowadays, there is not enough information about the change in cerebral temperature when using psychoactive substances.Актуальность. Исследования нейровизуализации мозга предоставили информацию о нейробиологических эффектах наркотических веществ и установили механизмы возникновения систематического их употребления, а также позволили получить важные сведения о субъективном опыте и поведении людей с наркозависимостью, включая их борьбу за выздоровление. До недавнего времени рассматривалось 5 основных методов нейровизуализации мозга – структурная магнитно-резонансная томография (МРТ), функциональная МРТ (фМРТ), магнитно-резонансная спектроскопия (МРС), позитронно-эмиссионная томография (ПЭТ) и однофотонная эмиссионная компьютерная томография (ОФЭКТ). Данные методы позволяют выявить различные аспекты структуры или функции мозга. Также в качестве нейровизуализационного метода головного мозга используется микроволновая термометрия (МР-термометрия), которая позволяет изучить температурный гомеостаз головного мозга при различных состояниях человека.Материалы и методы. Поиск отечественных публикаций проводился в базе данных на сайте РИНЦ, зарубежных – в базах PubMed, Google Scholar в период 1990–2022 гг. При анализе базы данных PubMed запрос «neuroimaging drug addiction» обнаружил 16066 ссылок. Также изучали работы по ключевым словам «neurotransmitters and drug abuse». Были проанализированы публикации, описывающие клиническую картину, диагностику при отравлении психоактивными веществами. Всего было проанализировано 45 статей.Заключение. Полученные на сегодняшний день результаты твердо подтверждают, что наркомания – это болезнь мозга, вызывающая важные нарушения во многих областях, включая пути, влияющие на поощрение и познание. Методы нейровизуализации позволяют исследователям наблюдать за действием наркотических веществ на мозг и сравнивать структуру, функции и метаболизм головного мозга у людей, злоупотребляющих и не злоупотребляющих наркотическими веществами. МР-термометрия позволяет измерить температуру головного мозга, что является отображением его метаболизма и позволяет оценить влияние различных веществ на головной мозг. Однако на данный момент нет достаточно информации об изменении церебральной температуры при употреблении психоактивных веществ

AIDing Contraception: HIV and Recent Trends in Abortion Rates

Since the onset of HIV/AIDS awareness in the early 1980s, much attention has centered around the substantial negative effects of the disease throughout the world. This paper provides evidence of a secondary effect the disease has had on sexual behavior in the United States. Using a difference-in-differences estimation framework and state level data, we show that the perceived threat of HIV resulted in a drop in unwanted pregnancies, as demonstrated by a lower incidence of abortions. Our results suggest that each additional reported case of HIV per 1,000 individuals resulted in 85.5 fewer abortions per 1,000 live births

Two-dimensional particle solution of the extended Hamilton-Jacobi equation

In classical mechanics the Hamilton-Jacobi equation for a free particle has the property of reducing a perturbation of spatially uniform solution into a point. In the late 1970s Sivashinsky proposed an extension of the equation so that it takes the form of the Kuramoto-Sivashinsky equation under which a smooth soliton is formed instead of the point. The soliton was proposed as a model for spatially extended elementary particle. However, this solution is unstable. Developing the Sivashinsky's idea further, we propose a different extension which ensures stability. We performed two-dimensional computational experiments demonstrating the soliton formation and stability