Unstable periodic orbits in a chaotic meandering jet flow

We study the origin and bifurcations of typical classes of unstable periodic orbits in a jet flow that was introduced before as a kinematic model of chaotic advection, transport and mixing of passive scalars in meandering oceanic and atmospheric currents. A method to detect and locate the unstable periodic orbits and classify them by the origin and bifurcations is developed. We consider in detail period-1 and period-4 orbits playing an important role in chaotic advection. We introduce five classes of period-4 orbits: western and eastern ballistic ones, whose origin is associated with ballistic resonances of the fourth order, rotational ones, associated with rotational resonances of the second and fourth orders, and rotational-ballistic ones associated with a rotational-ballistic resonance. It is a new kind of nonlinear resonances that may occur in chaotic flow with jets and/or circulation cells. Varying the perturbation amplitude, we track out the origin and bifurcations of the orbits for each class

Ellipsoidal vortex in a nonuniform flow: Dynamics and chaotic advections

Quasi-geostrophic dynamics of an ellipsoidal vortex embedded in a nonuniform flow is studied in the approximation of the infinitely deep rotating ocean with a constant buoyancy frequency. The vortex core is an ellipsoid with a constant vorticity different from the background vorticity value. The core is shown to move along with the flow and to deform under the effect of it. Regimes of the core\u27s behavior depend on the flow characteristics and the initial values of the vortex parameters (the shape and the orientation relative to the flow). These regimes are (i) rotation (along with the eccentricity oscillation), (ii) oscillation about one of the two specific directions (along with the eccentricity oscillation), and (iii) infinite horizontal elongation of the core. The localized regimes (rotation and oscillation) of the core motion are analyzed. It is shown, that zones of the water mass capturing can appear in the induced velocity field. The mechanisms of fluid particle trajectory chaotization are revealed; in particular, it is shown that, owing to the double periodicity of the core motion, all the nonlinear resonances appear as pairs of two resonance islands with the same winding number

Floating tracer clustering in divergent random flows modulated by an unsteady mesoscale ocean field

Clustering of tracers floating on the ocean surface and evolving due to combined velocity fields consisting of a deterministic mesoscale component and a kinematic random component is analysed. The random component represents the influence of submesoscale motions. A theory of exponential clustering in random velocity fields is applied to characterise the obtained clustering scenarios in both steady and unsteady time-dependent mesoscale flows, as simulated by a comprehensive realistic, eddy-resolving, general circulation model for the Japan/East Sea. The mesoscale flow field abounds in transient eddy-like patterns modulating and branching the main currents, and the underlying time-mean flow component features closed recirculation zones that can entrap the tracer. The submesoscale flow component is modelled kinematically, as a divergent random velocity field with a prescribed correlation radius and variance. The combined flow induces tracer clustering, that is, the exponential growth of tracer density in patches with vanishing areas. The statistical topography methodology, which provides integral characteristics to quantify the emerging clusters, uncovers drastic dependence of the clustering rates on whether the mesoscale flow component is taken to be steady or time-dependent. The former situation favours robust exponential clustering, similar to the theoretically understood case of purely divergent and zero-mean random velocity. The latter situation, on the contrary, hinders exponential clustering due to significant advection of the tracer out of the nearly enclosed eddies, at the rate faster than the clustering rate

Particle entrapment as a feedback effect

We consider a suspension of polarizable particles under the action of traveling wave dielectrophoresis (DEP) and focus on particle induced effects. In a situation where the particles are driven by the DEP force, but no external forces are exerted on the fluid, the joint motion of the particles can induce a steady fluid flow, which leads to particle entrapment. This feedback effect is proven to be non-negligible even for small volume concentration of particles.Comment: 4 pages, 4 figures, submitte

Язвенная болезнь желудка и двенадцатиперстной кишки: выбор тактики при кровотечении

Ulcerative gastroduodenal bleedings remain the actual problem of emergency surgery because of quite frequency and high mortality. The analysis of treatment results in 782 patients was conducted. There were 239 patients with gastric ulcers, 488 patients with duodenal ulcers, 37 patients with combined ulcers and 18 patients with bleeding peptic ulcers of gastroenteranastomosis. The choice of surgical policy was based on emergency fibrogastroscopy findings. According to these findings the locality and severity of bleeding were defined using J. Forrest scale. The treatment began in intensive care with obligatory endoscopic control "by the program". Emergency operations were performed in 5,9% cases and urgent operations were performed in 16.4% cases of all patients who suffered with bleeding. There were 21,7% patients with operative treatment in remote and planned order. Postoperative mortality was 3,8%. Postoperative complications were in 12,2% patients. There were consider that the treatment of ulcerative gastroduodenal bleedings should be based on the individual active and waiting policy concluding in somatic patient's condition, duration of ulcerative anamnesis, presence of gastroduodenal bleedings in the past, ulcer location, and bleeding intensity (using J. Forrest scale) and effectiveness of conservative hemostasis.Язвенные гастродуоденальные кровотечения являются актуальной проблемой экстренной хирургии в связи с частой встречаемостью и высокой летальностью. Проведен анализ результатов лечения 782 больных с язвенной болезнью желудка (239), двенадцатиперстной кишки (488), а также больных с сочетанными язвами (37) и пептической язвой гастроэнтероанастомоза (18), осложненной кровотечением. Выбор тактики лечения основывался на данных экстренной фиброгастроскопии, с помощью которой устанавливали локализацию и тяжесть кровотечения по шкале J. Forrest. Лечение начинали в условиях отделения интенсивной терапии с обязательным эндоскопическим контролем «по программе». В экстренном порядке оперировано 5,9% больных, в срочном порядке - 16,4% пациентов от всех поступивших с кровотечением. В отсроченном и плановом порядке оперативное лечение проведено у 21,7% больных. Послеоперационная летальность составила 3,8%. Осложнения после операции имели место у 12,2% больных. По результатам исследования сделан вывод, что в лечении язвенных гастродуоденальных кровотечений следует придерживаться индивидуальной активно-выжидательной тактики, основанной на соматическом состоянии пациента, длительности язвенного анамнеза и локализации язвы, наличии эпизодов гастродуоденального кровотечения в прошлом, а также интенсивности кровотечения (по J. Forrest) и эффективности консервативного гемостаза