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Search Results: 1 - 10 of 1113 matches for " Instability "
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Control of Karman Vortex Street behind a Thin Airfoil at Low Reynolds Number  [PDF]
Shohei Takagi, Yasufumi Konishi, Shigeru Obayashi, Masato Asai
Journal of Flow Control, Measurement & Visualization (JFCMV) , 2016, DOI: 10.4236/jfcmv.2016.43011
Abstract: To control the Karman vortex street formed behind a thin airfoil at a certain incidence, a control cylinder was placed at the suction side apart from the airfoil in the downstream region. Both smoke visualization and hot-wire measurements confirmed that the Karman vortex street was completely suppressed. The mechanism for suppression of the vortex street was examined with a hot-wire survey.
Evolution of Hydrodynamic Instability on Planar Jelly Interface Driven by Explosion  [PDF]
Tao Wang, Jingsong Bai, Wenbin Huang, Yang Jiang, Liyong Zou, Ping Li, Duowang Tan
World Journal of Mechanics (WJM) , 2012, DOI: 10.4236/wjm.2012.23018
Abstract: A high precision numerical algorithm MVPPM (multi-viscous-fluid piecewise parabolic method) is proposed and applied to study the multi-viscous-fluid dynamics problems. Three planar jelly experiments with periodic cosine perturbation on the initial interface have been conducted and numerically simulated by MVPPM. Good agreement between experimental and numerical results has been achieved, including the shape of jelly interface, the displacements of front face of jelly layer, bubble top and spike head. The effects of initial conditions (including amplitude and wave length of perturbation, thickness of jelly layer, etc.) on the evolution of the jelly interface have been numerically analyzed. It is found that the key affecting factors are the perturbation amplitude and thickness of jelly layer. The hydrodynamic instability on double planar jelly layers driven by explosion has been investigated numerically to examine their laws of evolution, and an interesting phenomenon is observed.
About the Prospects for Passage to Instability  [PDF]
I. V. Lebed
Open Journal of Fluid Dynamics (OJFD) , 2013, DOI: 10.4236/ojfd.2013.33027

The results of the direct numerical integration of the Navier-Stokes equations are evaluated against experimental data for problem on a flow around bluff bodies in an unstable regime. Experiment records several stable medium states for flow past a body. Evolution of each of these states, after losing the stability, inevitably goes by periodic vortex shedding modes. Calculations based on the Navier-Stokes equations satisfactorily reproduced all observed stable medium states. They were, however, incapable of reproducing any of a vortex shedding modes recorded experimentally. The solutions to the classic hydrodynamics equations successfully reach the boundary of instability field. However, classic solutions are unable to cross this boundary. Most likely, the reason for this is the Navier-Stokes equations themselves. The classic hydrodynamics equations directly follow from the Boltzmann equation and naturally contain the error involved in the derivation of classic kinetic equation. Just the Boltzmann hypothesis, which closed kinetic equation, allowed us to con- struct classic hydrodynamics on only three lower principal hydrodynamic values. The use of the Boltzmann hypothesis excludes higher principal hydrodynamic values from the participation in the formation of classic hydrodynamics equations. The multimoment hydrodynamics equations are constructed using seven lower principal hydrodynamic values. The numerical integration of the multimoment hydrodynamics equations in the problem on flow around a sphere shows that the solutions to these equations cross the boundary and enter the instability field. The boundary crossing is accompanied by appearance of very uncommon acts in scenario of system evolution.

Kinetic Foundation for the Multimoment Hydrodynamics Equations  [PDF]
Igor V. Lebed
Open Journal of Fluid Dynamics (OJFD) , 2015, DOI: 10.4236/ojfd.2015.51010
Abstract: The equations for the pair distribution functions are derived directly from the second equation of the Bogolyubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy. The derivation is fulfilled within the frameworks of the multiscale method. The equations for the pair distribution functions are the kinetic foundation for the multimoment hydrodynamics equations. Solutions to the equations for the pair distribution functions predetermine the possibility of constructing the hydrodynamics equations with an arbitrary number of principle hydrodynamic values specified beforehand. The tendency to increase the number of principal hydrodynamic values is caused by the necessity of interpreting the behavior of the system after the loss of stability. Solutions to the classic hydrodynamics equations constructed for only three principle hydrodynamic values are unable to predict the direction of instability evolution. Solutions to the multimoment hydrodynamics equations are capable of reproducing correctly the phenomenon of emergence and development of instability.
Initial Treatment of Knee Dislocation at Yopougon Teaching Hospital/Abidjan, Ivory Coast  [PDF]
Traoré Alidou, Kouassi Kouamé Jean Eric, Kouassi Aya Adela?de Natacha, Mbende Alban Slim, Sie Essoh Jean Baptiste, Bamba Insa, Lambin Yves
Open Journal of Orthopedics (OJO) , 2016, DOI: 10.4236/ojo.2016.611045
Abstract: Knee dislocation is a serious and rare injury. Its rarity and the variety of injuries that result from it mean that there is no adequate management that is universally accepted. The aim of this study was to evaluate our emergency care strategy for these injuries. Materials and methodology: This was a retrospective study conducted from January 1992 to December 2004 on nine cases of knee dislocation. It consisted of six men and three women. The average age of these subjects was 35, ranging from 15 to 50 years. The causes for these injuries included: public road accidents (n = 4), household accidents (n = 3), a sporting accident and a dislocation that occurred following a fight. The dislocations were anteromedial (n = 4), posterolateral (n = 2), posterior (n = 2) and anterior (n = 1). Associated injuries were sore joint (n = 2), contusion of the common peroneal nerve (n = 1) and vascular injury (n = 1). An angiography was performed on one patient for a vascular injury and an Elecmyography (EMG) for a common peroneal nerve injury. Closed reduction was used for eight patients and open reduction for one patient. Results: Five knees were stable with normal range of motion and some residual pain. Four patients had knee instability; two anterior, one anteroposterior and one lateral. In three of these patients, the CT arthrography/arthro-scan confirmed central pivot damage, with meniscal damage in two of them. The four patients were referred to a knee surgeon in a private practice. The post-operational effects were minimal in vascular injury. The EMG performed for the common peroneal nerve detected a nerve contusion. Conclusion: Our emergency care strategy remains closed reduction. This therapeutic management is consistent, at least in the first 15 days, with the literature.
Producers’ Preference for Price Instability?  [PDF]
Andrew Schmitz
Theoretical Economics Letters (TEL) , 2018, DOI: 10.4236/tel.2018.810114
Abstract: The debate over whether producers prefer price instability to price stability continues, especially where policies are often endorsed that aim at generating stability. Such policies include the holding of agriculture commodity stocks by government to bring about price stability. But why would producers support such a policy given that producers prefer price instability, or do they? Oi argues that producers prefer price instability, which is opposite to the conclusion reached by Massell. In this paper, we take up the issue as to producers’ preference for price instability using the classic welfare economic framework used by Massell and Just et al. We develop a producer price expectation model that brings about price stability, which is possible without storage. We use this as the basis upon which to compare price stability to price instability. Our conclusion is that producers prefer price instability regardless of whether it is due to demand or supply shocks.
The Instability of Political and Administrative Institutions in the Democratic Republic of the Congo  [PDF]
Chelo Kpats Guyguy, Xiaojun Xu
Open Journal of Social Sciences (JSS) , 2019, DOI: 10.4236/jss.2019.72005
Abstract: This article uses a historical approach to identify and analyze the factors leading to the instability of political and administrative institutions of the Democratic Republic of Congo from independence to the year 2017. There are multiple factors related to institutional instability in the DRC. Key among them includes the inadequate constitutional provisions, the difficulties caused by the non-application of democratic principles, the heterogeneity of the populace and frequent conflicts. Other contributors to the institutional instability experienced in the DRC include the politicization of the administration, the prevailing social-economic situation, poor governance, the non-observance of the laws, the poor distribution of the national wealth, foreign pressures and macroeconomic influences. The challenges due to institutional and political instability in the DRC provide opportunities for the Congolese state and its populace to re-invent itself to be a truly democratic space where the ambitions to develop and improve the living conditions of the people can be improved through stabilized and functional institutions.
Surface-wave instabilities in a plasma rotating with step-like frequency profile
Mikhailovskii, A.B.;Pustovitov, V.D.;Galv?o, R.M.O.;Amador, C.H.S.;Lominadze, J.G.;Churikov, A.P.;Kharshiladze, O.A.;
Brazilian Journal of Physics , 2009, DOI: 10.1590/S0103-97332009000100014
Abstract: an approach for the theory of nonlocal magnetorotational and convective instabilities in a rotating plasma is developed, on the basis of the surface wave concept, which allows the derivation of useful analytical results.it is assumed that the rotation frequency has a step-like profile, so that a narrow transition layer separates two regions with different rotation frequencies. the one-fluid magnetohydrodynamic (mhd) model for description of the perturbed plasma dynamics is used. it is shown that in the case of magnetized plasma the main properties of the nonlocal (surface-wave) instabilities are similar to those of the local ones.
Posturographic Evaluation of Dizziness Complaining Patients under Suspicion to Develop Parkinson's Disease  [PDF]
Hyun Cho
Neuroscience & Medicine (NM) , 2011, DOI: 10.4236/nm.2011.21004
Abstract: Although the typical clinical signs of Parkinson disease (PD) are tremor, rigidity, bradykinesia, and postural instability, PD is preceded by a preclinical phase during which neuronal degeneration develops without typical symptoms. More general nonspecific symptoms including dizziness have also been described to predate the typical PD signs for several years. All subjects were selected among patients in the Willis Hospital (Pusan, South of Korea), with complaints of diz-ziness from September 2009 to September 2010 and the baseline neurological screening and clinical ENT examination, to which the results were within the normal range. At baseline, 113 participants underwent neurological screening and provided information on dizziness. Of those participants, 103 were enrolled including 63 subjects in the control group. We used posturography. It allows quantitative assessment of vestibular-spinal component of body balance. The parame-ter of average speed of pressure center displacement to the lateral plan (VMX) and antero-posterior plan (VMY), which presented statistically significant differences between the groups except VMX with closed eyes. (p = 0.008 and p = 0.012, with closed eyes). With open eyes, only VMY showed significant difference between the groups (p = 0.010). In this study, the patients with dizziness and subjective complaints related to typical clinical signs of PD complaints presented higher instability in the orthostatic position than the control group of patients with dizziness and without such complaint. It could suggest that dizziness may be one symptom of preclinical PD and progress to overt postural instability. It is believed that a stepwise approach with a simple and inexpensive initial screening test of preclinical PD is required.
Quantum Effects on the Rayleigh-Taylor Instability of Viscoelastic Plasma Model through a Porous Medium  [PDF]
Gamal A. Hoshoudy
Journal of Modern Physics (JMP) , 2011, DOI: 10.4236/jmp.2011.210142
Abstract: The stability of stratified of incompressible, viscoelastic plasma through a porous medium in the presence of the quantum mechanism is considered. The dispersion relation is obtained using the normal mode technique. The behavior of growth rate with respect to the quantum effect, strain retardation time and stress relaxation time are examined in the presence of porosity of the porous medium, the medium permeability, kinematic viscosity. It is shown that, the presence of quantum term stabilizes a certain wave number band, whereas the system is unstable for all wave numbers in the absence of quantum term. The considered parameters beside the quantum term will bring about more stability on the considered system.
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