1,192 research outputs found
Flow along a long thin cylinder
No full textTwo different approaches have been used to calculate turblent flow along a long thin culinder where the flow is aligned with the cylinder. A boundary-layer code is used to predict the mean flow for very long cylinders (length to ratio of up to O(106)), with the effects of the turbulence estimated through a turbulence model. Detailed comparison with experimental results shows that the mean properties of the flow are predicted within experimental accuracy. The boundary-layer model predicts that, sufficiently far downstream, the surface shear stress will be (almost) constant. This is consistent with experimental results from long cylinders in the form of sonar arrays. A periodic Navier-Stokes problem is formulated, and solutions generated for the boundary-layer model and experiments. Strongly turbulent flow occurs only near the surface of the cylinder, with relatively weak turbulence over most of the boundary layer. For a thick boundary layer with the boundary-layer thickness much larger than the cylinder radius, the mean flow is effectively constant near the surface, in both temporal and spatial frameworks, while the outer flow continues to develop in time or space. Calculations of the circumferentially averaged surface pressure spectrum sho that, in physical terms, as the radius of the cylinder decreases, the surface noise from the turbulence increases, with the maximum noise at a Reynolds number of O(103). An increase in noise with a decrease in radius (Reynolds number) is consistent with experimental results
Recurrence of travelling waves in transitional pipe flow
No full textThe recent theoretical discovery of families of unstable travelling-wave solutions in pipe flow at Reynolds numbers lower than the transitional range, naturally raises the question of their relevance to the turbulent transition process. Here, a series of numerical experiments are conducted in which we look for the spatial signature of these travelling waves in transitionary flows. Working within a periodic pipe of 5D (diameters) length, we find that travelling waves with low wall shear stresses (lower branch solutions) are on a surface in phase space which separates initial conditions which uneventfully relaminarize and those which lead to a turbulent evolution. This dividing surface (a separatrix if turbulence is a sustained state) is then minimally the union of the stable manifolds of all these travelling waves. Evidence for recurrent travelling-wave visits is found in both 5D and 10D long periodic pipes, but only for those travelling waves with low-to-intermediate wall shear stress and for less than about 10% of the time in turbulent flow at Re = 2400. Given this, it seems unlikely that the mean turbulent properties such as wall shear stress can be predicted as an expansion solely over the travelling waves in which their individual properties are appropriately weighted. Instead the onus is on isolating further dynamical structures such as periodic orbits and including them in any such expansion
Boundary layer flow on a long thin cylinder
No full textThe development of the boundary layer along a long thin cylinder aligned with the flow is considered. Numerical solutions are presented and compared with previous asymptotic results. Very near the leading edge the flow is given by the Blasius solution for a flat plate. However, there is soon a significant deviation from Blasius flow, with a thinner boundary layer and higher wall shear stress. Linear normal mode stability of the flow is investigated. It is found that for Reynolds numbers less than a critical value of 1060 the flow is unconditionally stable. Also, axisymmetric modes are only the fourth least stable modes for this problem, with the first three three-dimensional modes all having a lower critical Reynolds number. Further, for Reynolds numbers above the critical value, the flow is unstable only for a finite distance, and returns to stability sufficiently far downstream
Pathogenic treatment of the inflammatory diseases of the urogenital tract in women of reproductive age
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O.I. Letyaeva, O.R. Ziganshin
South Ural State Medical University, Chelyabinsk, Russian Federation
This paper discusses one of the important gynecological issues, inflammatory diseases of the urogenital tract caused by opportunistic microbes. The treatment and long-term control over these conditions are challenging and depend on their occurrence and high risk of complications. Impaired local anti-infectious protection is one of the risk factors of chronic inflammation. Since the disease may recur even after successful treatment, domestic and foreign authors increasingly focus on immunotherapy as a part of complex strategy and isolated entity. Local immunotherapy may prevent recurrences and activate host defense. This paper describes the management of two women with mixed infections. The first woman with chronic recurrent inflammation (cervicitis caused by U. urealyticum, vulvovaginal candidiasis, and aerobic vaginitis) in whom prior etiological therapy was ineffective received immunotherapy which resulted in long-term remission. The second woman with coexistent papillomavirus infection (genital warts) and bacterial vaginosis received immunotherapy and topical etiological treatment. As a result, clinical symptoms, the size and number of genital warts reduced which greatly facilitated their chemical destruction.
Keywords: genital tract, urogenital infections, papillomavirus infection, bacterial vaginosis, local immunity, biofilms.
For citation: Letyaeva O.I., Ziganshin O.R. Pathogenic treatment of the inflammatory diseases of the urogenital tract in women of reproductive age. Russian Journal of Woman and Child Health. 2021;4(1):59–64. DOI: 10.32364/2618-8430-2021-4-1-59-64.
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Current trends in surgical treatment for infertility associated with polycystic ovary syndrome
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I.I. Grishin, T.G. Chirvon, O.R. Oguede
Pirogov Russian National Research Medical University, Moscow, Russian Federation
Polycystic ovary syndrome (PCOS) is a common endocrine disorder and one of the main causes of anovulation in women of childbearing age. Surgical procedures for infertility treatment in women with PCOS have been used in clinical practice for a long time. As a rule, they are considered as a second-line therapy after the first-line pharmacological treatment. Since recently the focus has shifted to the comparison of different types of surgical treatment techniques, their effects on the ovarian function, and the development of adhesions. The article reviews the most common surgical options for PCOS treatment in various patient groups and the key results obtained in the top importance studies undertaken in this area. Surgical treatment of PCOS in properly selected patients seems to be a cost-effective therapeutic option that has comparable success rates to ovulation induction with gonadotropins. Laparoscopic ovarian drilling is one of the preferable minimally invasive techn iques. This procedure is recommended for patients who have other indications for laparoscopy, or if there is a high risk of ovarian hyperstimulation syndrome and multiple pregnancy, or if there are contraindications to multiple pregnancy. At the same time, it is emphasized that the uniform regimens and standards of PCOS surgical treatment have not been optimized so far. Their outcomes are understudied and the issue is still open for discussion.
Keywords: laparoscopic ovarian drilling, polycystic ovary syndrome, ovarian hyperstimulation syndrome, anovulation, infertility, adhesions.
For citation: Grishin I.I., Chirvon T.G., Oguede O.R. Current trends in surgical treatment for infertility associated with polycystic ovary syndrome. Russian Journal of Woman and Child Health. 2022;5(3):209–214 (in Russ.). DOI: 10.32364/2618-8430-2022-5-3-209-214.
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Embedding machine learning into passivity theory: A port-Hamiltonian approach.
No full textPassivity-based control (PBC) is a control methodology that achieves its control objective by rendering a system passive with respect to a desired storage function. A key feature of PBC is that it exploits structural properties of the system. In this thesis, the PBC of systems endowed with a special structure, called port-Hamiltonian (PH) systems, has been investigated. The geometric structure of PH systems allows reformulating the PBC problem in terms of solving a generally complex partial differential equation (PDE). Reinforcement learning (RL), on the other hand, is a learning control method that can solve complex nonlinear (stochastic) control problems without the need for a process model or explicitly solving a set of equations. In RL the controller receives an immediate numerical reward as a function of the process state and possibly control action. The goal is to find an optimal control policy that maximizes the cumulative long-term rewards, which corresponds to maximizing a value function. In this thesis, actor-critic techniques have been used, which are a class of RL methods in which a separate actor (the control law) and critic (a "memory") function are learned. A disadvantage of RL is that without having a process model it can be slow at learning and computationally expensive. In this thesis, the goal was to design a theoretical framework using PBC techniques subject to control saturation that incorporates knowledge about the PH system and learns (optimal) control policies using actor-critic reinforcement learning. Therefore, actor-critic reinforcement learning methods have been combined with different types of PBC, e.g. EB-PBC and IDA-PBC. The combination of EB-PBC with an actor-critic method, energy-balancing actor-critic (EBAC), showed its effectiveness in the pendulum swing-up problem, which was used as a benchmark test. The advantages of the method from a PBC perspective are that no PDE has to be explicitly solved, control saturation can be incorporated, the geometric structure of the PH system is preserved, (numerical) stability can be assessed using passivity theory and the learned controllers can be interpreted in terms of energy-shaping strategies. From a RL perspective, the learning is speeded up because model knowledge is available.Delft Center for Systems and ControlMechanical, Maritime and Materials Engineerin
Fluctuation in Stock Properties of Arcto-Norwegian Cod Related to Long-term Environmental Changes.
No full textFrom a historic perspective the cod in the Barents Sea-Svalbard region has been the most productive gadoid stock in the Atlantic. Variation in catches has always been large, but during the last 10-15 years catches and stock abundance have reached the lowest level on record. Three major causes of variation have been discussed; stock reduction through exploitation, environmental influences on recruitment, and species interaction effects on maturation, growth and mortality. In addition, interactions between these three sources might be important. The influence of each specific factor is difficult to evaluate from incidental observations and short-term time series. In that respect, the time series on catches and on biological and environmental information of this stock, which partly goes back to the 19th century assumes a unique position in comparison with data on most other stocks. In this paper fluctuations in catches and stock abundance will be compared with changes in recruitment, size/age composition and growth. This information is discussed in view of historic variation in ecological and environmental parameters. The stock has been under particularly high exploitation pressure since the mid-seventies. Further, large changes in growth rates and poor recruitment to the commercially exploited stock have characteristic for the end of the 1980s and the 1990s. The analysis here shows that substantial long-term variation might underlie short-term variability, and, more importantly, that long-term changes roughly coincide with similar fluctuations in the environment. Consequently, it is suggested that inserting on a steady-state perspective on the population dynamics of this stock may lead to mismanagement and to a reduction of long-term yield.
Fluctuation in stock properties of north-east Arctic cod related to long-term environmental changes
No full textFrom a historic perspective, the north-east Arctic cod stock, which is found in the Barents SeaSvalbard region, has been the most productive gadoid stock in the Atlantic. Variation in catch has always been large, but during the last 1015 years catch and stock abundance have reached the lowest level on record. Three major causes of variation have been discussed: (i) stock reduction through exploitation; (ii) environmental influences on recruitment; and (iii) species interaction effects on maturation, growth and mortality. In addition, interactions among these three sources might be important. The influence of each specific factor is difficult to evaluate from incidental observations and short-term time series. In this respect, the time series on catches and on biological and environmental information of this stock, which partly extend back to the 19th century, occupy a unique position in comparison to data on most other stocks.
In this paper, fluctuations in catch and stock abundance are compared with changes in recruitment, size/age and growth. This information is discussed in view of historic variation in ecology and environment. The stock has been under particularly high exploitation pressure since the mid-1970s. Further, large changes in growth rates and poor recruitment to the commercially exploited stock are characteristic of late 1980s and throughout the 1990s. The analysis shows that substantial long-term variation might underlie short-term variability, and more importantly, that long-term changes roughly coincide with similar fluctuations in the environment. Such factors might substantially affect the relationship between spawning stock and recruitment, which is also apparent from the difference in conclusions reached by various published studies. Consequently, it is suggested that using a steady-state perspective for the population dynamics may lead to mismanagement and to a reduction of the long-term yield from this stock
A critical assessment of the institutionalisation of Performance Management Systems in Local Government: a special focus on political office bearers and senior managers in O.R Tambo District Municipality
No full textService delivery is at the centre of South Africa’s developmental local government. Thus with such a high calling to development, local municipalities play an important role in enhancing development in their areas of jurisdiction. In the area under this study, the Local Government Department has initiated Performance Management as a response to the service delivery hardships and as a bottom up approach to socio economic development of their communities. In the view of Performance Management being used as a tool for enhancing Service delivery, the study therefore sought to discover the role that the Performance Management System is playing in the Local Municipality Development of O.R District. It also sought to find out the extent of support that has been afforded by government and other stakeholders within the context of the cooperative governance. To establish this, the researcher employed the quantitative approach guided by a primary research design. The review of primary data allowed for a close assessment of the Performance Management System in detail. Available data on PMS gave an easier task of assessing the impact of PMS in the district and the constraints they have faced so far. The findings from the study revealed that PMS in the district show a great potential for better performance if performance management systems were to be understood by all staff members of the municipality. It has been also observed that they lack information on performance management, proper finance management, and diversification and value addition for their service delivery so as to increase their competitiveness. It is imperative therefore to recommend further training on good Performance management skills and sourcing for employees and understanding new PMS. This form of support will go a long way in ensuring the sustainability of Performance Management System in the O.R. District Municipality. Keywords: Performance Management System, Political office bearers and Senior Manager O.R District
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