... Risk Factors Is shoulder instability the same as shoulder dislocation? No. The signs of dislocation and instability might ... the same to you--weakness and pain. However, dislocation occurs when your shoulder goes completely out of place. The shoulder ligaments ...
International Nuclear Information System (INIS)
In the shoulder, the advantages of range of motion are traded for the disadvantages of vulnerability to injury and the development of instability. Shoulder instability and the lesion it produces represent one of the main causes of shoulder discomfort and pain. Shoulder instability is defined as a symptomatic abnormal motion of the humeral head relative to the glenoid during active shoulder motion. Glenohumeral instabilities are classified according to their causative factors as the pathogenesis of instability plays an important role with respect to treatment options: instabilities are classified in traumatic and atraumatic instabilities as part of a multidirectional instability syndrome, and in microtraumatic instabilities. Plain radiographs ('trauma series') are performed to document shoulder dislocation and its successful reposition. Direct MR arthrography is the most important imaging modality for delineation the different injury patterns on the labral-ligamentous complex and bony structures. Monocontrast CT-arthrography with use of multidetector CT scanners may be an alternative imaging modality, however, regarding the younger patient age, MR imaging should be preferred in the diagnostic work-up of shoulder instabilities. (orig.)
Smith, Matthew V; Sekiya, Jon K
2010-06-01
Hip instability is becoming a more commonly recognized source of pain and disability in patients. Traumatic causes of hip instability are often clear. Appropriate treatment includes immediate reduction, early surgery for acetabular rim fractures greater than 25% or incarcerated fragments in the joint, and close follow-up to monitor for avascular necrosis. Late surgical intervention may be necessary for residual symptomatic hip instability. Atraumatic causes of hip instability include repetitive external rotation with axial loading, generalized ligamentous laxity, and collagen disorders like Ehlers-Danlos. Symptoms caused by atraumatic hip instability often have an insidious onset. Patients may have a wide array of hip symptoms while demonstrating only subtle findings suggestive of capsular laxity. Traction views of the affected hip can be helpful in diagnosing hip instability. Open and arthroscopic techniques can be used to treat capsular laxity. We describe an arthroscopic anterior hip capsular plication using a suture technique. PMID:20473129
Joly, Laurent; Chassaing, Patrick; Chapin, Vincent; Reinaud, Jean; Micallef, J; Suarez, Juan; Bretonnet, L
2003-01-01
1. Introduction - Illustrative examples from experiments and simulations 2. The baroclinic torque in high Froude number flows, its organization, scale and order of magnitude 3. Stability of the inhomogeneous mixing-layer 4. Transition of the inhomogeneous mixing-layer and the 2D secondary baroclinic instability 5. The strain field of 2D light jets 6. Transition to three-dimensionality in light jets and the question of side-jets 7. Baroclinic instability of heavy vortices and...
Energy Technology Data Exchange (ETDEWEB)
Schmitt, R.; Froehner, S.; Coblenz, G.; Christopoulos, G. [Institut fuer Diagnostische und Interventionelle Radiologie, Herz- und Gefaessklinik GmbH, Bad Neustadt an der Saale (Germany)
2006-10-15
This review addresses the pathoanatomical basics as well as the clinical and radiological presentation of instability patterns of the wrist. Carpal instability mostly follows an injury; however, other diseases, like CPPD arthropathy, can be associated. Instability occurs either if the carpus is unable to sustain physiologic loads (''dyskinetics'') or suffers from abnormal motion of its bones during movement (''dyskinematics''). In the classification of carpal instability, dissociative subcategories (located within proximal carpal row) are differentiated from non-dissociative subcategories (present between the carpal rows) and combined patterns. It is essential to note that the unstable wrist initially does not cause relevant signs in standard radiograms, therefore being ''occult'' for the radiologic assessment. This paper emphasizes the high utility of kinematographic studies, contrast-enhanced magnetic resonance imaging (MRI) and MR arthrography for detecting these predynamic and dynamic instability stages. Later in the natural history of carpal instability, static malalignment of the wrist and osteoarthritis will develop, both being associated with significant morbidity and disability. To prevent individual and socio-economic implications, the handsurgeon or orthopedist, as well as the radiologist, is challenged for early and precise diagnosis. (orig.)
International Nuclear Information System (INIS)
Shoulder instability is a common clinical feature leading to recurrent pain and limitated range of motion within the glenohumeral joint. Instability can be due a single traumatic event, general joint laxity or repeated episodes of microtrauma. Differentiation between traumatic and atraumatic forms of shoulder instability requires careful history and a systemic clinical examination. Shoulder laxity has to be differentiated from true instability followed by the clinical assessment of direction and degree of glenohumeral translation. Conventional radiography and CT are used for the diagnosis of bony lesions. MR imaging and MR arthrography help in the detection of soft tissue affection, especially of the glenoid labrum and the capsuloligamentous complex. The most common lesion involving the labrum is the anterior labral tear, associated with capsuloperiostal stripping (Bankart lesion). A number of variants of the Bankart lesion have been described, such as ALPSA, SLAP or HAGL lesions. The purpose of this review is to highlight different forms of shoulder instability and its associated radiological findings with a focus on MR imaging. (orig.)
Rumolo, G
2014-01-01
When a beam propagates in an accelerator, it interacts with both the external fields and the self-generated electromagnetic fields. If the latter are strong enough, the interplay between them and a perturbation in the beam distribution function can lead to an enhancement of the initial perturbation, resulting in what we call a beam instability. This unstable motion can be controlled with a feedback system, if available, or it grows, causing beam degradation and loss. Beam instabilities in particle accelerators have been studied and analysed in detail since the late 1950s. The subject owes its relevance to the fact that the onset of instabilities usually determines the performance of an accelerator. Understanding and suppressing the underlying sources and mechanisms is therefore the key to overcoming intensity limitations, thereby pushing forward the performance reach of a machine.
Systematics of shoulder instability
International Nuclear Information System (INIS)
Shoulder instability is defined as a symptomatic abnormal motion of the humeral head relative to the glenoid during active shoulder motion. Glenohumeral instabilities are classified according to the causative factors as the pathogenesis of instability plays an important role with respect to treatment options. Instabilities are classified into traumatic and atraumatic instabilities as part of a multidirectional instability syndrome and into microtraumatic instabilities. For diagnostics plain radiographs (''trauma series'') are performed to document shoulder dislocation and its successful repositioning. Direct magnetic resonance (MR) arthrography is the most important imaging modality for delineation of the different injury patterns of the labral-ligamentous complex and bony structures. Monocontrast computed tomography (CT) arthrography with the use of multidetector CT scanners represents an alternative imaging modality; however, MR imaging should be preferred in the work-up of shoulder instabilities due to the mostly younger age of patients. (orig.)
Evaluating shoulder instability treatment
Linde, J. A.
2016-01-01
Shoulder instability common occurs. When treated nonoperatively, the resulting societal costs based on health care utilization and productivity losses are significant. Shoulder function can be evaluated using patient reported outcome measurements (PROMs). For shoulder instability, these include the Western Ontario Shoulder Instability index (WOSI) and the Oxford Shoulder Instability Score (OSIS). When translated and validated for the dutch population, both have good measurment properties. Sco...
Earnings instability and tenure
Cappellari, Lorenzo; Leonardi, Marco
2007-01-01
We study the effect of tenure on earnings instability in Italy using two alternative estimation strategies. First we use a descriptive measure of earnings instability and fixed effects regressions. Second, we develop a formal model of earnings dynamics distinguishing permanent from transitory earnings, and exploit variation of tenure and instability over time and across birth cohorts in estimation. We use the two approaches also to evaluate earnings instability associated with temporary contr...
Shoulder instability; Schulterinstabilitaeten
Energy Technology Data Exchange (ETDEWEB)
Kreitner, Karl-Friedrich [Mainiz Univ. (Germany). Klinik und Poliklinik fuer Diagnostische und Interventionelle Radiologie
2014-06-15
In the shoulder, the advantages of range of motion are traded for the disadvantages of vulnerability to injury and the development of instability. Shoulder instability and the lesion it produces represent one of the main causes of shoulder discomfort and pain. Shoulder instability is defined as a symptomatic abnormal motion of the humeral head relative to the glenoid during active shoulder motion. Glenohumeral instabilities are classified according to their causative factors as the pathogenesis of instability plays an important role with respect to treatment options: instabilities are classified in traumatic and atraumatic instabilities as part of a multidirectional instability syndrome, and in microtraumatic instabilities. Plain radiographs ('trauma series') are performed to document shoulder dislocation and its successful reposition. Direct MR arthrography is the most important imaging modality for delineation the different injury patterns on the labral-ligamentous complex and bony structures. Monocontrast CT-arthrography with use of multidetector CT scanners may be an alternative imaging modality, however, regarding the younger patient age, MR imaging should be preferred in the diagnostic work-up of shoulder instabilities. (orig.)
Joint instability and osteoarthritis.
Blalock, Darryl; Miller, Andrew; Tilley, Michael; Wang, Jinxi
2015-01-01
Joint instability creates a clinical and economic burden in the health care system. Injuries and disorders that directly damage the joint structure or lead to joint instability are highly associated with osteoarthritis (OA). Thus, understanding the physiology of joint stability and the mechanisms of joint instability-induced OA is of clinical significance. The first section of this review discusses the structure and function of major joint tissues, including periarticular muscles, which play a significant role in joint stability. Because the knee, ankle, and shoulder joints demonstrate a high incidence of ligament injury and joint instability, the second section summarizes the mechanisms of ligament injury-associated joint instability of these joints. The final section highlights the recent advances in the understanding of the mechanical and biological mechanisms of joint instability-induced OA. These advances may lead to new opportunities for clinical intervention in the prevention and early treatment of OA. PMID:25741184
Modelling Financial Instability
Franklin Allen
2005-01-01
Financial instability can have large adverse effects on an economy. One major cause of instability is asset price bubbles. This paper starts by considering how such bubbles can arise due to the expansion of money and credit. The ways in which subsequent financial instability occurs are then discussed. Banking crises can arise due to panics or as a result of the business cycle. Contagion and financial fragility can cause small disturbances to have large effects. Finally, policy issues are touc...
Dynamics of explosive instability
International Nuclear Information System (INIS)
It was shown that in general case explosive instability dynamics should be described as four wave interaction. The main difference from three wave interaction is that this dynamics may not contain explosive instability. Besides it may by irregular. If the characteristics of one of the wave is closed to one of the interacting wave and they are connected linearly then explosive instability may be suppressed.
Instability in evolutionary games.
Directory of Open Access Journals (Sweden)
Zimo Yang
Full Text Available BACKGROUND: Phenomena of instability are widely observed in many dissimilar systems, with punctuated equilibrium in biological evolution and economic crises being noticeable examples. Recent studies suggested that such instabilities, quantified by the abrupt changes of the composition of individuals, could result within the framework of a collection of individuals interacting through the prisoner's dilemma and incorporating three mechanisms: (i imitation and mutation, (ii preferred selection on successful individuals, and (iii networking effects. METHODOLOGY/PRINCIPAL FINDINGS: We study the importance of each mechanism using simplified models. The models are studied numerically and analytically via rate equations and mean-field approximation. It is shown that imitation and mutation alone can lead to the instability on the number of cooperators, and preferred selection modifies the instability in an asymmetric way. The co-evolution of network topology and game dynamics is not necessary to the occurrence of instability and the network topology is found to have almost no impact on instability if new links are added in a global manner. The results are valid in both the contexts of the snowdrift game and prisoner's dilemma. CONCLUSIONS/SIGNIFICANCE: The imitation and mutation mechanism, which gives a heterogeneous rate of change in the system's composition, is the dominating reason of the instability on the number of cooperators. The effects of payoffs and network topology are relatively insignificant. Our work refines the understanding on the driving forces of system instability.
Genomic instability following irradiation
Energy Technology Data Exchange (ETDEWEB)
Hacker-Klom, U.B.; Goehde, W. [Inst. fuer Strahlenbiologie, Muenster Univ. (Germany)
2001-07-01
Ionising irradiation may induce genomic instability. The broad spectrum of stress reactions in eukaryontic cells to irradiation complicates the discovery of cellular targets and pathways inducing genomic instability. Irradiation may initiate genomic instability by deletion of genes controlling stability, by induction of genes stimulating instability and/or by activating endogeneous cellular viruses. Alternatively or additionally it is discussed that the initiation of genomic instability may be a consequence of radiation or other agents independently of DNA damage implying non nuclear targets, e.g. signal cascades. As a further mechanism possibly involved our own results may suggest radiation-induced changes in chromatin structure. Once initiated the process of genomic instability probably is perpetuated by endogeneous processes necessary for proliferation. Genomic instability may be a cause or a consequence of the neoplastic phenotype. As a conclusion from the data available up to now a new interpretation of low level radiation effects for radiation protection and in radiotherapy appears useful. The detection of the molecular mechanisms of genomic instability will be important in this context and may contribute to a better understanding of phenomenons occurring at low doses <10 cSv which are not well understood up to now. (orig.)
Genomic instability following irradiation
International Nuclear Information System (INIS)
Ionising irradiation may induce genomic instability. The broad spectrum of stress reactions in eukaryontic cells to irradiation complicates the discovery of cellular targets and pathways inducing genomic instability. Irradiation may initiate genomic instability by deletion of genes controlling stability, by induction of genes stimulating instability and/or by activating endogeneous cellular viruses. Alternatively or additionally it is discussed that the initiation of genomic instability may be a consequence of radiation or other agents independently of DNA damage implying non nuclear targets, e.g. signal cascades. As a further mechanism possibly involved our own results may suggest radiation-induced changes in chromatin structure. Once initiated the process of genomic instability probably is perpetuated by endogeneous processes necessary for proliferation. Genomic instability may be a cause or a consequence of the neoplastic phenotype. As a conclusion from the data available up to now a new interpretation of low level radiation effects for radiation protection and in radiotherapy appears useful. The detection of the molecular mechanisms of genomic instability will be important in this context and may contribute to a better understanding of phenomenons occurring at low doses <10 cSv which are not well understood up to now. (orig.)
The Collisionless Magnetothermal Instability
Islam, Tanim
2013-01-01
It is likely that nearly all central galactic massive and supermassive black holes are nonradiative: their accretion luminosities are orders of magnitude below what can be explained by efficient black hole accretion within their ambient environments. These objects, of which Sagittarius A* is the best-known example, are also dilute (mildly collisional to highly collisionless) and optically thin. In order for accretion to occur, magnetohydrodynamic instabilities must develop that not only transport angular momentum, but also gravitational energy generated through matter infall, outwards. A class of new magnetohydrodynamical fluid instabilities -- the magnetoviscous-thermal instability (MVTI) (Islam12) -- was found to transport angular momentum and energy along magnetic field lines through large (fluid) viscosities and thermal conductivities. This paper describes the collisionless and mildly collisional analogue to the MVTI, the collisional magnetothermal instability (CMTI), that similarly transports energy and ...
... ankle surgeon will ask you about any previous ankle injuries and instability. Then s/he will examine your ankle ... Weak ankles may be a result of previous ankle injuries, but in some cases they are a congenital ( ...
Kuehn, Christian
2015-01-01
High-dimensional computational challenges are frequently explained via the curse of dimensionality, i.e., increasing the number of dimensions leads to exponentially growing computational complexity. In this commentary, we argue that thinking on a different level helps to understand, why we face the curse of dimensionality. We introduce as a guiding principle the curse of instability, which triggers the classical curse of dimensionality. Furthermore, we claim that the curse of instability is a...
Rotor internal friction instability
Bently, D. E.; Muszynska, A.
1985-01-01
Two aspects of internal friction affecting stability of rotating machines are discussed. The first role of internal friction consists of decreasing the level of effective damping during rotor subsynchronous and backward precessional vibrations caused by some other instability mechanisms. The second role of internal frication consists of creating rotor instability, i.e., causing self-excited subsynchronous vibrations. Experimental test results document both of these aspects.
Streaming gravity mode instability
International Nuclear Information System (INIS)
In this paper, we study the stability of a current sheet with a sheared flow in a gravitational field which is perpendicular to the magnetic field and plasma flow. This mixing mode caused by a combined role of the sheared flow and gravity is named the streaming gravity mode instability. The conditions of this mode instability are discussed for an ideal four-layer model in the incompressible limit. (author). 5 refs
International Nuclear Information System (INIS)
The heliopause (HP) separates the tenuous hot heliosheath plasma from the relatively dense cool magnetized plasma of the local interstellar medium (LISM). Fluid acceleration in the HP region can therefore drive Rayleigh-Taylor-like and Kelvin-Helmholtz- like instabilities. Charge exchange coupling of plasma ions and primary interstellar neutral atoms provides an effective gravity, suggesting the possibility of Rayleigh Taylor-like (RT-like) instabilities. Shear flow due to the velocity difference between the heliosheath and the interstellar flows drives Kelvin Helmholtz-like (KH-like) modes on the heliopause. Magnetic fields damp the classical KH instability. However, we show that energetic neutral atoms (ENAs) destabilize KH-modes,even in the presence of interplanetary and interstellar magnetic fields. We consider a model that includes a number of effects that are important in the heliosphere such as resonant change exchange between the primary neutrals and the solar wind plasma, ENAs from the inner heliosheath, plasma flows along the heliopause and magnetic fields in the inner and outer heliosheath. We find that the nose region is unstable to RT-like modes for HP parameters, while the shoulder region is unstable to a new instability that has the characteristics of a mixed RT-KH-like mode. These instabilities are not stabilized by typical values of the magnetic fields in the inner and outer heliosheath close to the nose and shoulder regions. Whereas ENAs have a stabilizing influence on the RT instability in the vicinity of the nose region (due to counter streaming), they have a destabilizing influence on the KH instability in the vicinity of the flanks. We find that even in the presence of interplanetary and interstellar magnetic fields, ENAs can drive a new form of KH-like instability on the flanks. An analysis of the collisional and anomalous magnetic field diffusion time scales shows that ideal MHD is an appropriate model at the HP. The interstellar magnetic
Plasma physics and instabilities
International Nuclear Information System (INIS)
These lectures procide an introduction to the theory of plasmas and their instabilities. Starting from the Bogoliubov, Born, Green, Kirkwood, and Yvon (BBGKY) hierarchy of kinetic equations, the additional concept of self-consistent fields leads to the fundamental Vlasov equation and hence to the warm two-fluid model and the one-fluid MHD, or cold, model. The properties of small-amplitude waves in magnetized (and unmagnetized) plasmas, and the instabilities to which they give rise, are described in some detail, and a complete chapter is devoted to Landau damping. The linear theory of plasma instabilities is illustrated by the current-driven electrostatic kind, with descriptions of the Penrose criterion and the energy principle of ideal MHD. There is a brief account of the application of feedback control. The non-linear theory is represented by three examples: quasi-linear velocity-space instabilities, three-wave instabilities, and the stability of an arbitrarily largeamplitude wave in a plasma. (orig.)
Mackenzie's Demon with instabilities
International Nuclear Information System (INIS)
MacKenzie's Maxwell Demon, consisting of positively biased thin wires, heats plasma electrons without significantly affecting the plasma potential. Experiments were performed on the Maxwell Demon in a multi-dipole confined filament discharge. It is shown that given adequate bias, the Demon reduces a bi-Maxwellian electron distribution function to a single Maxwellian electron distribution function. It is shown that a small planar electrode can perform identical heating as the Demon, provided that the electrode has the area of approximately three times the Demon's conductive surface area. The instability that limits the Demon's operation is investigated. Time-resolved measurements of changes in global electron temperature, plasma density and plasma potential within a cycle of the instability are considered. It is found that the Demon's instability is a repeating pulsed anode spot. Density measurements indicate that the frequency of the instability is dependent on plasma production and loss rates. The neutral pressure dependence of the anode spot instability is measured and modeled for the first time. (paper)
Neutrino beam plasma instability
Indian Academy of Sciences (India)
Vishnu M Bannur
2001-10-01
We derive relativistic ﬂuid set of equations for neutrinos and electrons from relativistic Vlasov equations with Fermi weak interaction force. Using these ﬂuid equations, we obtain a dispersion relation describing neutrino beam plasma instability, which is little different from normal dispersion relation of streaming instability. It contains new, nonelectromagnetic, neutrino-plasma (or electroweak) stable and unstable modes also. The growth of the instability is weak for the highly relativistic neutrino ﬂux, but becomes stronger for weakly relativistic neutrino ﬂux in the case of parameters appropriate to the early universe and supernova explosions. However, this mode is dominant only for the beam velocity greater than 0.25 and in the other limit electroweak unstable mode takes over.
Instabilities in astrophysical jets
International Nuclear Information System (INIS)
Instabilities in astrophysical jets are studied in the nonlinear regime by performing 2D numerical classical gasdynamical calculations. The instabilities which arise from unsteadiness in output from the central engine feeding the jets, and those which arise from a beam in a turbulent surrounding are studied. An extra power output an order of magnitude higher than is normally delivered by the engine over a time equal to (nozzle length)/(sound velocity at centre) causes a nonlinear Kelvin-Helmholtz instability in the jet walls. Constrictions move outwards, but the jet structure is left untouched. A beam in turbulent surroundings produces internal shocks over distances of a few beam widths. If viscosity is present the throughput of material is hampered on time scales of a few beam radius sound travel times. The implications are discussed. (Auth.)
Rincon, F; Cowley, S C
2014-01-01
Slow dynamical changes in magnetic-field strength and invariance of the particles' magnetic moments generate ubiquitous pressure anisotropies in weakly collisional, magnetized astrophysical plasmas. This renders them unstable to fast, small-scale mirror and firehose instabilities, which are capable of exerting feedback on the macroscale dynamics of the system. By way of a new asymptotic theory of the early nonlinear evolution of the mirror instability in a plasma subject to slow shearing or compression, we show that the instability does not saturate quasilinearly at a steady, low-amplitude level. Instead, the trapping of particles in small-scale mirrors leads to nonlinear secular growth of magnetic perturbations, $\\delta B/B \\propto t^{2/3}$. Our theory explains recent collisionless simulation results, provides a prediction of the mirror evolution in weakly collisional plasmas and establishes a foundation for a theory of nonlinear mirror dynamics with trapping, valid up to $\\delta B/B =O(1)$.
DEFF Research Database (Denmark)
Langie, Sabine A S; Koppen, Gudrun; Desaulniers, Daniel;
2015-01-01
Genome instability is a prerequisite for the development of cancer. It occurs when genome maintenance systems fail to safeguard the genome's integrity, whether as a consequence of inherited defects or induced via exposure to environmental agents (chemicals, biological agents and radiation). Thus......, genome instability can be defined as an enhanced tendency for the genome to acquire mutations; ranging from changes to the nucleotide sequence to chromosomal gain, rearrangements or loss. This review raises the hypothesis that in addition to known human carcinogens, exposure to low dose of other...... chemicals present in our modern society could contribute to carcinogenesis by indirectly affecting genome stability. The selected chemicals with their mechanisms of action proposed to indirectly contribute to genome instability are: heavy metals (DNA repair, epigenetic modification, DNA damage signaling...
Photomultiplier time instability
International Nuclear Information System (INIS)
A short-time and slow instability of anode photocurrent in photoelectron multiplier is investigated. The analysis of sorption and desorption processes stimulated by electron excitation allowed to propose an adsorption-desorption mechanism of devices instability. Transient response and drift of photomultiplier anode photocurrent are measured as well as the curves of spent variations of spectral sensitivity of photocathode and individual amplifier cascades of the multiplying system depending on anode current. The results of calculating the proposed model are in good agreement with the experimental data
Ringed accretion disks: instabilities
Pugliese, D
2016-01-01
We analyze the possibility that several instability points may be formed, due to the Paczy\\'nski mechanism of violation of mechanical equilibrium, in the orbiting matter around a supermassive Kerr black hole. We consider recently proposed model of ringed accretion disk, made up by several tori (rings) which can be corotating or counterrotating relative to the Kerr attractor due to the history of the accretion process. Each torus is governed by the general relativistic hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. We prove that the number of the instability points is generally limited and depends on the dimensionless spin of the rotating attractor.
Longitudinal microwave instability
International Nuclear Information System (INIS)
A derivation of the relationship between growth rate and impedance is given. The only other instability considered here is the resonance effect produced by excessive tune shift due to space charge. We assume, without discussion, the (Δν)/sub max/ = .25; that is, this resonance growth is avoided (stability) by limiting the ring charge. On the other hand, the longitudinal microwave instability is assumed to be present (cannot be stabilized). Thus, the latter involves a limiting impedance to keep the growth rate low enough. The maximum allowed impedance for a maximum allowed growth rate is listed
Ringed Accretion Disks: Instabilities
Pugliese, D.; Stuchlík, Z.
2016-04-01
We analyze the possibility that several instability points may be formed, due to the Paczyński mechanism of violation of mechanical equilibrium, in the orbiting matter around a supermassive Kerr black hole. We consider a recently proposed model of a ringed accretion disk, made up by several tori (rings) that can be corotating or counter-rotating relative to the Kerr attractor due to the history of the accretion process. Each torus is governed by the general relativistic hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. We prove that the number of the instability points is generally limited and depends on the dimensionless spin of the rotating attractor.
Fluidelastic instability in tube arrays
International Nuclear Information System (INIS)
When an array of tubes is subjected to crossflow, the tubes can experience dynamic instability, generally called fluidelastic instability. Instability initiates when the crossflow velocity exceeds a threshold value above which energy input from the flow exceeds that dissipated by system damping. Catastrophic failures of reactor and process plant equipment have been attributed to fluidelastic instability. As a result, extensive research studies have been conducted in the last 15 years with the objective of understanding the instability mechanisms and developing general design guidelines to avoid instability. Argonne National Laboratory has a continuing research program in this area which includes both mathematical model development and experimentation. This paper describes recent developments and accomplishments
Tracking Code for Microwave Instability
Energy Technology Data Exchange (ETDEWEB)
Heifets, S.; /SLAC
2006-09-21
To study microwave instability the tracking code is developed. For bench marking, results are compared with Oide-Yokoya results [1] for broad-band Q = 1 impedance. Results hint to two possible mechanisms determining the threshold of instability.
Shock instability in dissipative gases
Radulescu, Matei I.; Sirmas, Nick
2011-01-01
Previous experiments have revealed that shock waves in thermally relaxing gases, such as ionizing, dissociating and vibrationally excited gases, can become unstable. To date, the mechanism controlling this instability has not been resolved. Previous accounts of the D'yakov-Kontorovich instability, and Bethe-Zel'dovich-Thompson behaviour could not predict the experimentally observed instability. To address the mechanism controlling the instability, we study the propagation of shock waves in a ...
Nonlinear evolution of MHD instabilities
International Nuclear Information System (INIS)
A 3-D nonlinear MHD computer code was used to study the time evolution of internal instabilities. Velocity vortex cells are observed to persist into the nonlinear evolution. Pressure and density profiles convect around these cells for a weak localized instability, or convect into the wall for a strong instability. (U.S.)
Genetic instability in Gynecological Cancer
Institute of Scientific and Technical Information of China (English)
ZHAO Qing-hua; ZHOU Hong-lin
2003-01-01
Defects of mismatch repair (MMR) genes also have beenidentified in many kinds of tumors. Loss of MMR functionhas been linked to genetic instability especially microsatelliteinstability that results in high mutation rate. In this review, wediscussed the microsatellite instability observed in thegynecological tumors. We also discussed defects in the DNAmismatch repair in these tumors and their correlation to themicrosatellite instability, as well as the gene mutations due tothe microsatellite instability in these tumors. From thesediscussion, we tried to understand the mechanism ofcarcinogenesis in gynecological tumors from the aspect ofgenetic instability due to mismatch repair defects.
International Nuclear Information System (INIS)
The interaction between energetic charged particles and thermal plasma, which forms the basis of diffusive shock acceleration, leads also to interesting dynamical phenomena. For a compressional mode propagating in a system with homoeneous energetic particle pressure it is well known that friction with the energetic particles leads to damping. The linear theory of this effect has been analyzed in detail by Ptuskin. Not so obvious is that a non-uniform energetic particle pressure can in addition amplify compressional disturbances. If the pressure gradient is sufficiently steep this growth can dominate the frictional damping and lead to an instability. It is important to not that this effect results from the collective nature of the interaction between the energetic particles and the gas and is not connected with the Parker instability, nor with the resonant amplification of Alfven waves
Whistler modulational instability.
Brinca, A. L.
1973-01-01
Derivation of the modulational instability characteristics of whistlers in cold and hot plasmas. The cold-plasma analysis considers both ion motion and relativistic effects; the unstable band, with a growth rate proportional to (B/B sub zero)squared, is contiguous to Omega sub e/4 and, depending on the plasma density, lies above or below that frequency (Omega sub e is the electron cyclotron frequency of the static magnetic field; B and B sub zero are the whistler and static magnetic fields). In hot plasmas, stability occurs between Omega sub e/4 and Omega prime (less than Omega sub e), with Omega prime depending mainly on the mean energy and anisotropy of the energetic electron population; the complementary unstable band has a growth rate proportional to (B/B sub zero) to the 1/2 power. The relevance of the instability to whistlers in the magnetosphere is discussed.
Chiodi, Filippo; Andreotti, Bruno; Claudin, Philippe
2012-01-01
The river bar instability is revisited, using a hydrodynamical model based on Reynolds averaged Navier-Stokes equations. The results are contrasted with the standard analysis based on shallow water Saint-Venant equations. We first show that the stability of both transverse modes (ripples) and of small wavelength inclined modes (bars) predicted by the Saint-Venant approach are artefacts of this hydrodynamical approximation. When using a more reliable hydrodynamical model, the dispersion relati...
Hogg, Tad; Huberman, Bernardo A.; Youssefmir, Michael
1995-01-01
Recent developments in the global liberalization of equity and currency markets, coupled to advances in trading technologies, are making markets increasingly interdependent. This increased fluidity raises questions about the stability of the international financial system. In this paper, we show that as couplings between stable markets grow, the likelihood of instabilities is increased, leading to a loss of general equilibrium as the system becomes increasingly large and diverse.
Huberman, B A; Huberman, Bernardo A; Youssefmir, Michael
1995-01-01
Recent developments in the global liberalization of equity and currency markets, coupled to advances in trading technologies, are making markets increasingly interdependent. This increased fluidity raises questions about the stability of the international financial system. In this paper, we show that as couplings between stable markets grow, the likelihood of instabilities is increased, leading to a loss of general equilibrium as the system becomes increasingly large and diverse.
Non-conventional fishbone instabilities
International Nuclear Information System (INIS)
New instabilities of the fishbone type are predicted. The first is a trapped-particle-induced m = n = 1 instability with a mode structure that has nothing in common with the conventional rigid kink displacement. This instability takes place when the magnetic field is weak, so that the precession frequency of the energetic ions is not small as compared to the frequency of the corresponding Alfven continuum at r=0 and the magnetic shear is small inside the q = 1 radius (the case relevant to spherical tori). The second predicted instability is an Energertic Particle Mode fishbone instability driven by circulating particles, and the third is a double-kink-mode instability driven by the circulating energetic ions. In particular, the latter can have two frequencies simultaneously: we refer to it as 'doublet' fishbones. This instability can occur when the radial profile of the energetic ions has an off-axis maximum inside the region of the mode localization. (author)
Shoulder instability; Schultergelenkinstabilitaet
Energy Technology Data Exchange (ETDEWEB)
Sailer, J.; Imhof, H. [Abteilung Osteoradiologie, Univ.-Klinik fuer Radiodiagnostik Wien (Austria)
2004-06-01
Shoulder instability is a common clinical feature leading to recurrent pain and limitated range of motion within the glenohumeral joint. Instability can be due a single traumatic event, general joint laxity or repeated episodes of microtrauma. Differentiation between traumatic and atraumatic forms of shoulder instability requires careful history and a systemic clinical examination. Shoulder laxity has to be differentiated from true instability followed by the clinical assessment of direction and degree of glenohumeral translation. Conventional radiography and CT are used for the diagnosis of bony lesions. MR imaging and MR arthrography help in the detection of soft tissue affection, especially of the glenoid labrum and the capsuloligamentous complex. The most common lesion involving the labrum is the anterior labral tear, associated with capsuloperiostal stripping (Bankart lesion). A number of variants of the Bankart lesion have been described, such as ALPSA, SLAP or HAGL lesions. The purpose of this review is to highlight different forms of shoulder instability and its associated radiological findings with a focus on MR imaging. (orig.) [German] Die Schultergelenkinstabilitaet ist haeufig fuer wiederholt auftretende Schmerzen sowie eine eingeschraenkte Beweglichkeit im Glenohumeralgelenk verantwortlich. Sie kann als Folge eines vorangegangenen Traumas, einer generellen Hyperlaxitaet oder infolge wiederholter Mikrotraumen entstehen. Die Differenzierung zwischen traumatischer und atraumatischer Form der Gelenkinstabilitaet erfordert eine sorgfaeltige Anamnese und eine genaue klinische Untersuchung. Die Gelelenklaxitaet als Differenzialdiagnose muss von der echten Instabilitaet unterschieden werden, die Instabilitaet wird dann im Rahmen des klinischen Status nach Grad und Richtung der glenohumeralen Translation unterteilt. Zur Diagnose knoecherner Laesionen werden das konventionelle Roentgen sowie die CT herangezogen. MRT sowie MR-Arthrographie dienen zur Detektion
Vijg, Jan; Suh, Yousin
2013-01-01
Genome instability has long been implicated as the main causal factor in aging. Somatic cells are continuously exposed to various sources of DNA damage, from reactive oxygen species to UV radiation to environmental mutagens. To cope with the tens of thousands of chemical lesions introduced into the genome of a typical cell each day, a complex network of genome maintenance systems acts to remove damage and restore the correct base pair sequence. Occasionally, however, repair is erroneous, and such errors, as well as the occasional failure to correctly replicate the genome during cell division, are the basis for mutations and epimutations. There is now ample evidence that mutations accumulate in various organs and tissues of higher animals, including humans, mice, and flies. What is not known, however, is whether the frequency of these random changes is sufficient to cause the phenotypic effects generally associated with aging. The exception is cancer, an age-related disease caused by the accumulation of mutations and epimutations. Here, we first review current concepts regarding the relationship between DNA damage, repair, and mutation, as well as the data regarding genome alterations as a function of age. We then describe a model for how randomly induced DNA sequence and epigenomic variants in the somatic genomes of animals can result in functional decline and disease in old age. Finally, we discuss the genetics of genome instability in relation to longevity to address the importance of alterations in the somatic genome as a causal factor in aging and to underscore the opportunities provided by genetic approaches to develop interventions that attenuate genome instability, reduce disease risk, and increase life span. PMID:23398157
Non-conventional Fishbone Instabilities
International Nuclear Information System (INIS)
New instabilities of fishbone type are predicted. First, a trapped-particle-induced m = n = 1 instability with the mode structure having nothing to do with the conventional rigid kink displacement. This instability takes place when the magnetic field is weak, so that the precession frequency of the energetic ions is not small as compared to the frequency of the corresponding Alfven continuum at r = 0 and the magnetic shear is small inside the q = 1 radius [the case relevant to spherical tori]. Second, an Energetic Particle Mode fishbone instability driven by circulating particles. Third, a double-kink-mode instability driven by the circulating energetic ions. In particular, the latter can have two frequencies simultaneously: we refer to it as ''doublet'' fishbones. This instability can occur when the radial profile of the energetic ions has an off-axis maximum inside the region of the mode localization
Modulational instability of nematic phase
Indian Academy of Sciences (India)
T Mithun; K Porsezian
2014-02-01
We numerically observe the effect of homogeneous magnetic field on the modulationally stable case of polar phase in = 2 spinor Bose–Einstein condensates (BECs). Also we investigate the modulational instability of uniaxial and biaxial (BN) states of polar phase. Our observations show that the magnetic field triggers the modulational instability and demonstrate that irrespective of the magnetic field effect the uniaxial and biaxial nematic phases show modulational instability.
Summary of longitudinal instabilities workshop
International Nuclear Information System (INIS)
A five-day ISABELLE workshop on longitudinal instabilities was held at BNL, August 9--13, 1976. Heavy emphasis was put on single bunched beam instabilities in the microwave region extending above the cut-off frequency of the ISABELLE vacuum chamber. A discussion is given of the mechanism governing the instability, and calculations as well as measurements of the longitudinal coupling impedances in the ISABELLE rings are described
Instability in Shocked Granular Gases
Sirmas, Nick; Falle, Sam; Radulescu, Matei
2013-01-01
Shocks in granular media, such as vertically oscillated beds, have been shown to develop instabilities. Similar jet formation has been observed in explosively dispersed granular media. Our previous work addressed this instability by performing discrete-particle simulations of inelastic media undergoing shock compression. By allowing finite dissipation within the shock wave, instability manifests itself as distinctive high density non-uniformities and convective rolls within the shock structur...
Instability of enclosed horizons
Kay, Bernard S
2013-01-01
We study the classical massless scalar wave equation on the region of 1+1-dimensional Minkowski space between the two branches of the hyperbola $x^2-t^2=1$ with vanishing boundary conditions on it. We point out that there are initially finite-energy initially, say, right-going waves for which the stress-energy tensor becomes singular on the null-line $t+x=0$. We also construct the quantum theory of this system and show that, while there is a regular Hartle-Hawking-Israel-like state, there are coherent states built on this for which there is a similar singularity in the expectation value of the renormalized stress-energy tensor. We conjecture that in 1+3-dimensional situations with 'enclosed horizons' such as a (maximally extended) Schwarzschild black hole in equilibrium in a stationary box or the (maximally extended) Schwarzschild-AdS spacetime, there will be a similar singularity at the horizon and that would signal an instability when matter perturbations and/or gravity are switched on. Such an instability ...
Libration driven multipolar instabilities
Cébron, David; Herreman, Wietze
2014-01-01
We consider rotating flows in non-axisymmetric enclosures that are driven by libration, i.e. by a small periodic modulation of the rotation rate. Thanks to its simplicity, this model is relevant to various contexts, from industrial containers (with small oscillations of the rotation rate) to fluid layers of terrestial planets (with length-of-day variations). Assuming a multipolar $n$-fold boundary deformation, we first obtain the two-dimensional basic flow. We then perform a short-wavelength local stability analysis of the basic flow, showing that an instability may occur in three dimensions. We christen it the Libration Driven Multipolar Instability (LDMI). The growth rates of the LDMI are computed by a Floquet analysis in a systematic way, and compared to analytical expressions obtained by perturbation methods. We then focus on the simplest geometry allowing the LDMI, a librating deformed cylinder. To take into account viscous and confinement effects, we perform a global stability analysis, which shows that...
Cohabitation and Children's Family Instability
Kelly Raley, R.; Wildsmith, Elizabeth
2004-01-01
This study estimates how much children's family instability is missed when we do not count transitions into and out of cohabitation, and examines early life course trajectories of children to see whether children who experience maternal cohabitation face more family instability than children who do not. Using data from the 1995 National Survey of…
Microsatellite instability in bladder cancer
DEFF Research Database (Denmark)
Gonzalez-Zulueta, M; Ruppert, J M; Tokino, K; Tsai, Y C; Spruck, C H; Miyao, N; Nichols, P W; Hermann, G G; Horn, T; Steven, K
1993-01-01
Somatic instability at microsatellite repeats was detected in 6 of 200 transitional cell carcinomas of the bladder. Instabilities were apparent as changes in (GT)n repeat lengths on human chromosome 9 for four tumors and as alterations in a (CAG)n repeat in the androgen receptor gene on the X chr...
Cinerama sickness and postural instability
Bos, J.E.; Ledegang, W.D.; Lubeck, A.J.A.; Stins, J.F.
2013-01-01
Motion sickness symptoms and increased postural instability induced by motion pictures have been reported in a laboratory, but not in a real cinema. We, therefore, carried out an observational study recording sickness severity and postural instability in 19 subjects before, immediately and 45 min af
Instability of liquid crystal elastomers
An, Ning; Li, Meie; Zhou, Jinxiong
2016-01-01
Nematic liquid crystal elastomers (LCEs) contract in the director direction but expand in other directions, perpendicular to the director, when heated. If the expansion of an LCE is constrained, compressive stress builds up in the LCE, and it wrinkles or buckles to release the stored elastic energy. Although the instability of soft materials is ubiquitous, the mechanism and programmable modulation of LCE instability has not yet been fully explored. We describe a finite element method (FEM) scheme to model the inhomogeneous deformation and instability of LCEs. A constrained LCE beam working as a valve for microfluidic flow, and a piece of LCE laminated with a nanoscale poly(styrene) (PS) film are analyzed in detail. The former uses the buckling of the LCE beam to occlude the microfluidic channel, while the latter utilizes wrinkling or buckling to measure the mechanical properties of hard film or to realize self-folding. Through rigorous instability analysis, we predict the critical conditions for the onset of instability, the wavelength and amplitude evolution of instability, and the instability patterns. The FEM results are found to correlate well with analytical results and reported experiments. These efforts shed light on the understanding and exploitation of the instabilities of LCEs.
Genome instability in Alzheimer disease
DEFF Research Database (Denmark)
Hou, Yujun; Song, Hyundong; Croteau, Deborah L;
2016-01-01
to the development of noninvasive treatment strategies. Further investigations into the molecular mechanisms connecting DNA damage to AD pathology may help to develop novel treatment strategies for this debilitating disease. Here we provide an overview of the role of genome instability and DNA repair deficiency...... in AD pathology and discuss research strategies that include genome instability as a component....
Chiodi, Filippo; Claudin, Philippe
2012-01-01
The river bar instability is revisited, using a hydrodynamical model based on Reynolds averaged Navier-Stokes equations. The results are contrasted with the standard analysis based on shallow water Saint-Venant equations. We first show that the stability of both transverse modes (ripples) and of small wavelength inclined modes (bars) predicted by the Saint-Venant approach are artefacts of this hydrodynamical approximation. When using a more reliable hydrodynamical model, the dispersion relation does not present any maximum of the growth rate when the sediment transport is assumed to be locally saturated. The analysis therefore reveals the fundamental importance of the relaxation of sediment transport towards equilibrium as it it is responsible for the stabilisation of small wavelength modes. This dynamical mechanism is characterised by the saturation number, defined as the ratio of the saturation length to the water depth Lsat/H. This dimensionless number controls the transition from ripples (transverse patte...
Plateau Rayleigh instability simulation.
Mead-Hunter, Ryan; King, Andrew J C; Mullins, Benjamin J
2012-05-01
The well-known phenomena of Plateau-Rayleigh instability has been simulated using computational fluid dynamics (CFD). The breakup of a liquid film into an array of droplets on a cylindrical element was simulated using a volume-of-fluid (VOF) solver and compared to experimental observations and existing theory. It is demonstrated that the VOF method can correctly predict the breakup of thins films into an array of either axisymmetric droplets or clam-shell droplets, depending on the surface energy. The existence of unrealistically large films is precluded. Droplet spacing was found to show reasonable agreement with theory. Droplet motion and displacement under fluid flow was also examined and compared to that in previous studies. It was found that the presence of air flow around the droplet does not influence the stable film thickness; however, it reduces the time required for droplet formation. Novel relationships for droplet displacement were derived from the results. PMID:22512475
Patzelt, Felix
2015-01-01
Many complex systems exhibit extreme events far more often than expected for a normal distribution. This work examines how self-similar bursts of activity across several orders of magnitude can emerge from first principles in systems that adapt to information. Surprising connections are found between two apparently unrelated research topics: hand-eye coordination in balancing tasks and speculative trading in financial markets. Seemingly paradoxically, locally minimising fluctuations can increase a dynamical system's sensitivity to unpredictable perturbations and thereby facilitate global catastrophes. This general principle is studied in several domain-specific models and in behavioural experiments. It explains many findings in both fields and resolves an apparent antinomy: the coexistence of stabilising control or market efficiency and perpetual instabilities resembling critical phenomena in physical systems.
From instabilities to multifragmentation
International Nuclear Information System (INIS)
The main purpose of this article is to show that, in many physical situations, the spinodal decomposition of unstable systems can be correctly described by stochastic mean-field approaches. Such theories predict that the occurrence of spinodal instability leading the multifragmentation of an expended nuclear system, can be signed through the observation of time scales for the fragment formation of the order of 100 fm/c and of typical fragment size around A=20. We will finally discuss the fact that these fragments are formed at finite temperature and so can subsequently decay in flight. Finally, we will give some hints about possible experimental signals of such first order phase transitions. (authors). 12 refs., 5 figs
Structural and Material Instability
DEFF Research Database (Denmark)
Cifuentes, Gustavo Cifuentes
This work is a small contribution to the general problem of structural and material instability. In this work, the main subject is the analysis of cracking and failure of structural elements made from quasi-brittle materials like concrete. The analysis is made using the finite element method. Three...... program based on the finite element method for the analysis of cracks in structural elements is presented; in this program the interface and elements with embedded discontinuities are implemented....... use of interface elements) is used successfully to model cases where the path of the discontinuity is known in advance, as is the case of the analysis of pull-out of fibers embedded in a concrete matrix. This method is applied to the case of non-straight fibers and fibers with forces that have...
Internal rotor friction instability
Walton, J.; Artiles, A.; Lund, J.; Dill, J.; Zorzi, E.
1990-01-01
The analytical developments and experimental investigations performed in assessing the effect of internal friction on rotor systems dynamic performance are documented. Analytical component models for axial splines, Curvic splines, and interference fit joints commonly found in modern high speed turbomachinery were developed. Rotor systems operating above a bending critical speed were shown to exhibit unstable subsynchronous vibrations at the first natural frequency. The effect of speed, bearing stiffness, joint stiffness, external damping, torque, and coefficient of friction, was evaluated. Testing included material coefficient of friction evaluations, component joint quantity and form of damping determinations, and rotordynamic stability assessments. Under conditions similar to those in the SSME turbopumps, material interfaces experienced a coefficient of friction of approx. 0.2 for lubricated and 0.8 for unlubricated conditions. The damping observed in the component joints displayed nearly linear behavior with increasing amplitude. Thus, the measured damping, as a function of amplitude, is not represented by either linear or Coulomb friction damper models. Rotordynamic testing of an axial spline joint under 5000 in.-lb of static torque, demonstrated the presence of an extremely severe instability when the rotor was operated above its first flexible natural frequency. The presence of this instability was predicted by nonlinear rotordynamic time-transient analysis using the nonlinear component model developed under this program. Corresponding rotordynamic testing of a shaft with an interference fit joint demonstrated the presence of subsynchronous vibrations at the first natural frequency. While subsynchronous vibrations were observed, they were bounded and significantly lower in amplitude than the synchronous vibrations.
Combustion Instabilities Modeled
Paxson, Daniel E.
1999-01-01
NASA Lewis Research Center's Advanced Controls and Dynamics Technology Branch is investigating active control strategies to mitigate or eliminate the combustion instabilities prevalent in lean-burning, low-emission combustors. These instabilities result from coupling between the heat-release mechanisms of the burning process and the acoustic flow field of the combustor. Control design and implementation require a simulation capability that is both fast and accurate. It must capture the essential physics of the system, yet be as simple as possible. A quasi-one-dimensional, computational fluid dynamics (CFD) based simulation has been developed which may meet these requirements. The Euler equations of mass, momentum, and energy have been used, along with a single reactive species transport equation to simulate coupled thermoacoustic oscillations. A very simple numerical integration scheme was chosen to reduce computing time. Robust boundary condition procedures were incorporated to simulate various flow conditions (e.g., valves, open ends, and choked inflow) as well as to accommodate flow reversals that may arise during large flow-field oscillations. The accompanying figure shows a sample simulation result. A combustor with an open inlet, a choked outlet, and a large constriction approximately two thirds of the way down the length is shown. The middle plot shows normalized, time-averaged distributions of the relevant flow quantities, and the bottom plot illustrates the acoustic mode shape of the resulting thermoacoustic oscillation. For this simulation, the limit cycle peak-to-peak pressure fluctuations were 13 percent of the mean. The simulation used 100 numerical cells. The total normalized simulation time was 50 units (approximately 15 oscillations), which took 26 sec on a Sun Ultra2.
Dynamical Instability and Soliton Concept
International Nuclear Information System (INIS)
The problem of dynamical instability and clustering (stable fragments formation) in a breakup of excited nuclear systems are considered from the points of view of the soliton concept. It is noted that the volume (spinodal) instability can be associated with nonlinear terms, and the surface (Rayleigh-Taylor type) instability, with the dispersion terms in the evolution equations. The spinodal instability and the Rayleigh-Taylor instability may compensate each other and lead to stable quasi-soliton type objects. The simple analytical model is presented to illustrate this physical picture. The time evolution of an initially compressed cold nuclear system is analysed in the framework of the inverse mean-field method. It is demonstrated that the nonlinearity and dispersion terms of the evolution equations can lead to clusterization in the final channel. 8 p
Nonlinear evolution of MHD instabilities
International Nuclear Information System (INIS)
The problems of nonlinear theory of MHD instability, some analytical solutions of one-dimensional dynamic and two-dimensional kinematic problems and the problems of helical MHD instability in a plasma cylinder and axially-symmetric MHD instability in a Z-pinch are considered. The initial configuration is assumed to be equilibrium but unstable and its motion is initiated by a small initial disturbance. Instability evolution at a nonlinear stage is investigated by means of computer numerical integrating of the total system of MHD equations of motion. Limiting by two-dimensional motions class allows using the visual apparatus of freezed in functions satisfying in ideal gasodynamics the equation deltaPSIsub(i)/deltat+vector Vgrad PSIsub(i)=0. The investigation of evolution of axially symmetric MHD-instability in Z-pinch systems allows to construct on uncontradictory scheme of physical processes occuring in them from the initial discharge state to cylindrical equilibrium state
Gravitational Instabilities in Circumstellar Disks
Kratter, Kaitlin M
2016-01-01
[Abridged] Star and planet formation are the complex outcomes of gravitational collapse and angular momentum transport mediated by protostellar and protoplanetary disks. In this review we focus on the role of gravitational instability in this process. We begin with a brief overview of the observational evidence for massive disks that might be subject to gravitational instability, and then highlight the diverse ways in which the instability manifests itself in protostellar and protoplanetary disks: the generation of spiral arms, small scale turbulence-like density fluctuations, and fragmentation of the disk itself. We present the analytic theory that describes the linear growth phase of the instability, supplemented with a survey of numerical simulations that aim to capture the non-linear evolution. We emphasize the role of thermodynamics and large scale infall in controlling the outcome of the instability. Despite apparent controversies in the literature, we show a remarkable level of agreement between analyt...
Equilibrium Electro-osmotic Instability
Rubinstein, Isaak
2014-01-01
Since its prediction fifteen years ago, electro-osmotic instability has been attributed to non-equilibrium electro-osmosis related to the extended space charge which develops at the limiting current in the course of concentration polarization at a charge-selective interface. This attribution had a double basis. Firstly, it has been recognized that equilibrium electro-osmosis cannot yield instability for a perfectly charge-selective solid. Secondly, it has been shown that non-equilibrium electro-osmosis can. First theoretical studies in which electro-osmotic instability was predicted and analyzed employed the assumption of perfect charge-selectivity for the sake of simplicity and so did the subsequent numerical studies of various time-dependent and nonlinear features of electro-osmotic instability. In this letter, we show that relaxing the assumption of perfect charge-selectivity (tantamount to fixing the electrochemical potential in the solid) allows for equilibrium electro-osmotic instability. Moreover, we s...
Beam instability Workshop - plenary sessions
International Nuclear Information System (INIS)
The purpose of this workshop was to provide a review of the mechanisms of limiting beam instabilities, their cures, including feedback, and beam measurement for synchrotron radiation light sources. 12 plenary sessions took place whose titles are: 1) challenging brilliance and lifetime issues with increasing currents; 2) limiting instabilities in multibunch; 3) experience from high currents in B factories; 4) longitudinal dynamics in high intensity/bunch; 5) Transverse instabilities for high intensity/bunch; 6) working group introduction from ESRF experience; 7) impedance modelling: simulations, minimization; 8) report on the broadband impedance measurements and modelling workshop; 9) feedback systems for synchrotron light sources; 10) beam instabilities diagnostics; 11) harmonic cavities: the pros and cons; and 12) experimental study of fast beam-ion instabilities at PLS. This document gathers the 12 articles that were presented during these sessions
Instability in Shocked Granular Gases
Sirmas, Nick; Radulescu, Matei
2013-01-01
Shocks in granular media, such as vertically oscillated beds, have been shown to develop instabilities. Similar jet formation has been observed in explosively dispersed granular media. Our previous work addressed this instability by performing discrete-particle simulations of inelastic media undergoing shock compression. By allowing finite dissipation within the shock wave, instability manifests itself as distinctive high density non-uniformities and convective rolls within the shock structure. In the present study we have extended this work to investigate this instability at the continuum level. We modeled the Euler equations for granular gases with a modified cooling rate to include an impact velocity threshold necessary for inelastic collisions. Our results showed a fair agreement between the continuum and discrete-particle models. Discrepancies, such as higher frequency instabilities in our continuum results may be attributed to the absence of higher order effects.
Instability in shocked granular gases
International Nuclear Information System (INIS)
Shocks in granular media, such as vertically oscillated beds, have been shown to develop instabilities. Similar jet formation has been observed in explosively dispersed granular media. Our previous work addressed this instability by performing discrete-particle simulations of inelastic media undergoing shock compression. By allowing finite dissipation within the shock wave, instability manifests itself as distinctive high density non-uniformities and convective rolls within the shock structure. In the present study we have extended this work to investigate this instability at the continuum level. We modeled the Euler equations for granular gases with a modified cooling rate to include an impact velocity threshold necessary for inelastic collisions. Our results showed a fair agreement between the continuum and discrete-particle models. Discrepancies, such as higher frequency instabilities in our continuum results may be attributed to the absence of higher order effects.
Instabilities of advection-dominated accretion flows
Chen, X
1996-01-01
Accretion disk instabilities are briefly reviewed. Some details are given to the short-wavelength thermal instabilities and the convective instabilities. Time-dependent calculations of two-dimensional advection-dominated accretion flows are presented.
Instabilities of Advection-Dominated Accretion Flows
Chen, Xingming
1996-01-01
Accretion disk instabilities are briefly reviewed. Some details are given to the short-wavelength thermal instabilities and the convective instabilities. Time-dependent calculations of two-dimensional advection-dominated accretion flows are presented.
Nonlinear ideal magnetohydrodynamics instabilities
International Nuclear Information System (INIS)
Explosive phenomena such as internal disruptions in toroidal discharges and solar flares are difficult to explain in terms of linear instabilities. A plasma approaching a linear stability limit can, however, become nonlinearly and explosively unstable, with noninfinitesimal perturbations even before the marginal state is reached. For such investigations, a nonlinear extension of the usual MHD (magnetohydrodynamic) energy principle is helpful. (This was obtained by Merkel and Schlueter, Sitzungsberichted. Bayer. Akad. Wiss., Munich, 1976, No. 7, for Cartesian coordinate systems.) A coordinate system independent Eulerian formulation for the Lagrangian allowing for equilibria with flow and with built-in conservation laws for mass, magnetic flux, and entropy is developed in this paper which is similar to Newcomb's Lagrangian method of 1962 [Nucl. Fusion, Suppl., Pt. II, 452 (1962)]. For static equilibria nonlinear stability is completely determined by the potential energy. For a potential energy which contains second- and nth order or some more general contributions only, it is shown in full generality that linearly unstable and marginally stable systems are explosively unstable even for infinitesimal perturbations; linearly absolutely stable systems require finite initial perturbations. For equilibria with Abelian symmetries symmetry breaking initial perturbations are needed, which should be observed in numerical simulations. Nonlinear stability is proved for two simple examples, m=0 perturbations of a Bennet Z-pinch and z-independent perturbations of a θ pinch. The algebra for treating these cases reduces considerably if symmetries are taken into account from the outset, as suggested by M. N. Rosenbluth (private communication, 1992)
WELLBORE INSTABILITY: CAUSES AND CONSEQUENCES
Directory of Open Access Journals (Sweden)
Borivoje Pašić
2007-12-01
Full Text Available Wellbore instability is one of the main problems that engineers meet during drilling. The causes of wellbore instability are often classified into either mechanical (for example, failure of the rock around the hole because of high stresses, low rock strength, or inappropriate drilling practice or chemical effects which arise from damaging interaction between the rock, generally shale, and the drilling fluid. Often, field instances of instability are a result of a combination of both chemical and mechanical. This problem might cause serious complication in well and in some case can lead to expensive operational problems. The increasing demand for wellbore stability analyses during the planning stage of a field arise from economic considerations and the increasing use of deviated, extended reach and horizontal wells. This paper presents causes, indicators and diagnosing of wellbore instability as well as the wellbore stresses model.
Size effects on cavitation instabilities
DEFF Research Database (Denmark)
Niordson, Christian Frithiof; Tvergaard, Viggo
2006-01-01
growth is here analyzed for such cases. A finite strain generalization of a higher order strain gradient plasticity theory is applied for a power-law hardening material, and the numerical analyses are carried out for an axisymmetric unit cell containing a spherical void. In the range of high stress......In metal-ceramic systems the constraint on plastic flow leads to so high stress triaxialities that cavitation instabilities may occur. If the void radius is on the order of magnitude of a characteristic length for the metal, the rate of void growth is reduced, and the possibility of unstable cavity...... triaxiality, where cavitation instabilities are predicted by conventional plasticity theory, such instabilities are also found for the nonlocal theory, but the effects of gradient hardening delay the onset of the instability. Furthermore, in some cases the cavitation stress reaches a maximum and then decays...
Summary of longitudinal instabilities workshop
Energy Technology Data Exchange (ETDEWEB)
Chasman, R.
1976-01-01
A five-day ISABELLE workshop on longitudinal instabilities was held at Brookhaven, August 9-13, 1976. About a dozen outside accelerator experts, both from Europe and the U.S.A., joined the local staff for discussions of longitudinal instabilities in ISABELLE. An agenda of talks was scheduled for the first day of the workshop. Later during the week, a presentation was given on the subject ''A more rigorous treatment of Landau damping in longitudinal beam instabilities''. A few progress meetings were held in which disagreements regarding calculations of coupling impedances were clarified. A summary session was held on the last day. Heavy emphasis was put on single bunched beam instabilities in the microwave region extending above the cut-off frequency of the ISABELLE vacuum chamber.
Intrinsic Instability of Coronal Streamers
Chen, Y; Song, H Q; Shi, Q Q; Feng, S W; Xia, L D; 10.1088/0004-637X/691/2/1936
2009-01-01
Plasma blobs are observed to be weak density enhancements as radially stretched structures emerging from the cusps of quiescent coronal streamers. In this paper, it is suggested that the formation of blobs is a consequence of an intrinsic instability of coronal streamers occurring at a very localized region around the cusp. The evolutionary process of the instability, as revealed in our calculations, can be described as follows: (1) through the localized cusp region where the field is too weak to sustain the confinement, plasmas expand and stretch the closed field lines radially outward as a result of the freezing-in effect of plasma-magnetic field coupling; the expansion brings a strong velocity gradient into the slow wind regime providing the free energy necessary for the onset of a subsequent magnetohydrodynamic instability; (2) the instability manifests itself mainly as mixed streaming sausage-kink modes, the former results in pinches of elongated magnetic loops to provoke reconnections at one or many loc...
Baryon Instability in SUSY Models
Nath, Pran; Arnowitt, R.
1996-01-01
Comment: 14 pages, latex, 1 fig, to be published in proceedings of the International Workshop on " Future Prospects of Baryon Instability Search in p-Decay and n-nbar Oscillation Experiments", Oak Ridge, Tennessee, March 28-30,1996
Thermal instability of gold nanowires
Energy Technology Data Exchange (ETDEWEB)
Karim, Shafqat [Fachbereich Chemie, Marburg University (Germany); Toimil-Molares, Maria E.; Cornelius, Thomas; Neumann, Reinhard [Gesellschaft fuer Schwerionenforschung (GSI), Darmstadt (Germany); Balogh, Adam; Ensinger, Wolfgang [Institute of Materials Science, Darmstadt University of Technology (Germany)
2007-07-01
The technological implementation of nanostructures in future nano- and opto-electronic devices requires the capability to withstand elevated temperatures often encountered during routine operation. However, due to their reduced size and high surface to volume ratio, nanowires are expected to display structural and morphological instabilities. The Rayleigh instability concept, introduced to describe the instability of liquid jets, is applied to the fragmentation of metal nanowires during heating. Gold nanowires are electrochemically deposited in etched ion track membranes. After dissolving the template, the wires are put on a substrate and heated to temperatures between 300 and 600 C. The wires decay driven by Rayleigh instability, and the process depends on annealing temperature, wire diameter, and crystallinity. Wires of diameter 20 nm already fragment at 300 C being far below the bulk melting temperature of 1064 C.
Waves and instabilities in plasmas
International Nuclear Information System (INIS)
The contents of this book are: Plasma as a Dielectric Medium; Nyquist Technique; Absolute and Convective Instabilities; Landau Damping and Phase Mixing; Particle Trapping and Breakdown of Linear Theory; Solution of Viasov Equation via Guilding-Center Transformation; Kinetic Theory of Magnetohydrodynamic Waves; Geometric Optics; Wave-Kinetic Equation; Cutoff and Resonance; Resonant Absorption; Mode Conversion; Gyrokinetic Equation; Drift Waves; Quasi-Linear Theory; Ponderomotive Force; Parametric Instabilities; Problem Sets for Homework, Midterm and Final Examinations
Midcarpal instability: a radiological perspective
International Nuclear Information System (INIS)
Midcarpal instability (MCI) is the result of complex abnormal carpal motion at the midcarpal joint of the wrist. It is a form of non-dissociative carpal instability (CIND) and can be caused by various combinations of extrinsic ligament injuries that then result in one of several subtypes of MCI. The complex patterns of injury and the kinematics are further complicated by competing theories, terminology and classifications of MCI. Palmar, dorsal, ulna midcarpal instability, and capitolunate or chronic capitolunate instability are all descriptions of types of MCI with often overlapping features. Palmar midcarpal instability (PMCI) is the most commonly reported type of MCI. It has been described as resulting from deficiencies in the ulna limb of the palmar arcuate ligament (triquetrohamate-capitate) or the dorsal radiotriquetral ligaments, or both. Unstable carpal articulations can be treated with limited carpal arthrodesis or the ligamentous defects can be treated with capsulorrhaphy or ligament reconstruction. Conventional radiographic abnormalities are usually limited to volar intercalated segment instability (VISI) patterns of carpal alignment and are not specific. For many years stress view radiographs and videofluoroscopy have been the methods of choice for demonstrating carpal instability and abnormal carpal kinematics respectively. Dynamic US can be also used to demonstrate midcarpal dyskinesia including the characteristic triquetral ''catch-up'' clunk. Tears of the extrinsic ligaments can be demonstrated with MR arthrography, and probably with CT arthrography, but intact yet redundant ligaments are more difficult to identify. The exact role of these investigations in the diagnosis, categorisation and management of midcarpal instability has yet to be determined. (orig.)
Stability and instability in evolution.
Benci, V; Galleni, L
1998-10-21
In this paper we propose a mechanism which tries to explain the presence of periods of stability and instability which occur during the evolution of living forms. According to the Gaia hypothesis there are feedback mechanisms which stabilise the biosphere. Adding the presence of parameters which are out of control of the biosphere and of different time-scales, we propose a model which might explain the periods of instability. PMID:9790828
Photomultiplier short-term instability
International Nuclear Information System (INIS)
The present paper gives a description of the apparatus and method to measure PM gain short-term instability under the condition of pulsed light source simulating the operation at proton synchrotrons. Experimental results are presented for FEU-84, FEU-85, FEU-110, FEU-115 and XP2010 photomultipliers. It is shown that the short-term gain instability can be described by a simple mathematical model. (Auth.)
Equilibrium Electro-osmotic Instability
Rubinstein, Isaak; Zaltzman, Boris
2014-01-01
Since its prediction fifteen years ago, electro-osmotic instability has been attributed to non-equilibrium electro-osmosis related to the extended space charge which develops at the limiting current in the course of concentration polarization at a charge-selective interface. This attribution had a double basis. Firstly, it has been recognized that equilibrium electro-osmosis cannot yield instability for a perfectly charge-selective solid. Secondly, it has been shown that non-equilibrium elect...
Instability of enclosed horizons
Kay, Bernard S.
2015-03-01
We point out that there are solutions to the scalar wave equation on dimensional Minkowski space with finite energy tails which, if they reflect off a uniformly accelerated mirror due to (say) Dirichlet boundary conditions on it, develop an infinite stress-energy tensor on the mirror's Rindler horizon. We also show that, in the presence of an image mirror in the opposite Rindler wedge, suitable compactly supported arbitrarily small initial data on a suitable initial surface will develop an arbitrarily large stress-energy scalar near where the two horizons cross. Also, while there is a regular Hartle-Hawking-Israel-like state for the quantum theory between these two mirrors, there are coherent states built on it for which there are similar singularities in the expectation value of the renormalized stress-energy tensor. We conjecture that in other situations with analogous enclosed horizons such as a (maximally extended) Schwarzschild black hole in equilibrium in a (stationary spherical) box or the (maximally extended) Schwarzschild-AdS spacetime, there will be similar stress-energy singularities and almost-singularities—leading to instability of the horizons when gravity is switched on and matter and gravity perturbations are allowed for. All this suggests it is incorrect to picture a black hole in equilibrium in a box or a Schwarzschild-AdS black hole as extending beyond the past and future horizons of a single Schwarzschild (/Schwarzschild-AdS) wedge. It would thus provide new evidence for 't Hooft's brick wall model while seeming to invalidate the picture in Maldacena's ` Eternal black holes in AdS'. It would thereby also support the validity of the author's matter-gravity entanglement hypothesis and of the paper ` Brick walls and AdS/CFT' by the author and Ortíz.
Elastic instabilities in rubber
Gent, Alan
2009-03-01
Materials that undergo large elastic deformations can exhibit novel instabilities. Several examples are described: development of an aneurysm on inflating a rubber tube; non-uniform stretching on inflating a spherical balloon; formation of internal cracks in rubber blocks at a critical level of triaxial tension or when supersaturated with a dissolved gas; surface wrinkling of a block at a critical amount of compression; debonding or fracture of constrained films on swelling, and formation of ``knots'' on twisting stretched cylindrical rods. These various deformations are analyzed in terms of a simple strain energy function, using Rivlin's theory of large elastic deformations, and the results are compared with experimental measurements of the onset of unstable states. Such comparisons provide new tests of Rivlin's theory and, at least in principle, critical tests of proposed strain energy functions for rubber. Moreover the onset of highly non-uniform deformations has serious implications for the fatigue life and fracture resistance of rubber components. [4pt] References: [0pt] R. S. Rivlin, Philos. Trans. Roy. Soc. Lond. Ser. A241 (1948) 379--397. [0pt] A. Mallock, Proc. Roy. Soc. Lond. 49 (1890--1891) 458--463. [0pt] M. A. Biot, ``Mechanics of Incremental Deformations'', Wiley, New York, 1965. [0pt] A. N. Gent and P. B. Lindley, Proc. Roy. Soc. Lond. A 249 (1958) 195--205. [0pt] A. N. Gent, W. J. Hung and M. F. Tse, Rubb. Chem. Technol. 74 (2001) 89--99. [0pt] A. N. Gent, Internatl. J. Non-Linear Mech. 40 (2005) 165--175.
Elliptic and magneto-elliptic instabilities
Directory of Open Access Journals (Sweden)
Lyra Wladimir
2013-04-01
Full Text Available Vortices are the fundamental units of turbulent flow. Understanding their stability properties therefore provides fundamental insights on the nature of turbulence itself. In this contribution I briely review the phenomenological aspects of the instability of elliptic streamlines, in the hydro (elliptic instability and hydromagnetic (magneto-elliptic instability regimes. Vortex survival in disks is a balance between vortex destruction by these mechanisms, and vortex production by others, namely, the Rossby wave instability and the baroclinic instability.
Fermi liquids near Pomeranchuk instabilities
Reidy, Kelly Elizabeth
We explore features of a Fermi liquid near generalized Pomeranchuk instabilities (PIs) starting from both ordered and disordered phases. These PIs can be viewed as quantum critical points in parameter space, and thus provide an alternate viewpoint on quantum criticality. We employ the tractable crossing symmetric equation method, which is a non-perturbative diagrammatic many-particle method used to calculate the Fermi liquid interaction functions and scattering amplitudes. We consider both repulsive and attractive underlying interactions of arbitrary strength. Starting from a ferromagnetically ordered ground state, we find that upon approach to an s-wave instability in one critical channel, the system simultaneously approaches instabilities in non-critical channels. We study origins and implications of this "quantum multicriticality". We also find that a nematic (non-s-wave) instability precedes and is driven by Pomeranchuk instabilities in both the s-wave spin and density channels. Finally, we discuss potential applications of our results to physical systems, such as ferromagnetic superconductors.
Radiation-induced chromosomal instability
Energy Technology Data Exchange (ETDEWEB)
Ritter, S. [GSI, Biophysics, Darmstadt (Germany)
1999-03-01
Recent studies on radiation-induced chromosomal instability in the progeny of exposed mammalian cells were briefly described as well as other related studies. For the analysis of chromosomal damage in clones, cells were seeded directly after exposure in cell well-dish to form single cell clones and post-irradiation chromosome aberrations were scored. Both exposure to isoeffective doses of X-ray or 270 MeV/u C-ions (13 keV/{mu}m) increased the number of clones with abnormal karyotype and the increase was similar for X-ray and for C-ions. Meanwhile, in the progeny of cells for mass cultures, there was no indication of a delayed expression of chromosomal damage up to 40 population doublings after the exposure. A high number of aberrant cells were only observed directly after exposure to 10.7 MeV/u O-ions, i.e. in the first cycle cells and decreased with subsequent cell divisions. The reason for these differences in the radiation-induced chromosomal instability between clonal isolates and mass culture has not been clarified. Recent studies indicated that genomic instability occurs at a high frequency in the progeny of cells irradiated with both sparsely and densely ionizing radiation. Such genomic instability is thought likely to increase the risk of carcinogenesis, but more data are required for a well understanding of the health risks resulting from radiation-induced delayed instability. (M.N.)
Compressive Instability Phenomena During Springback
International Nuclear Information System (INIS)
Springback in sheet metal product makes difficulties in die design because small strain causes large displacement. Especially for the sheet metal product having small geometric constraints, springback displacement may become severe. After first stage of stamping of outer case of washing machine, a large amount of springback is observed. The stamping depth of the outer case is small while stamping area is very large compared to the stamping depth, and therefore, there exists small geometric constraints in the formed part. Also, a compressive instability during the elastic recovery takes place and this instability enlarged the elastic recovery and dimensional error. In this paper, the compressive instability during the elastic recovery is analyzed using bifurcation theory. The final deformed shape after springback is obtained by bifurcating the solution path from primary to secondary. The deformed shapes obtained by the finite element analysis are in good agreement with the experimental data. The bifurcation behavior and the springback displacement for different forming depth are investigated
Kinetic theory of tearing instability
International Nuclear Information System (INIS)
The guiding-center kinetic equation with Fokker-Planck collision term is used to study, in cylindrical geometry, a class of dissipative instabilities of which the classical tearing mode is an archetype. Variational solution of the kinetic equation obviates the use of an approximate Ohm's law or adiabatic assumption, as used in previous studies, and it provides a dispersive relation which is uniformly valid for any ratio of wave frequency to collision frequency. One result of using the rigorous collision operator is the prediction of a new instability. This instability, driven by the electron temperature gradient, is predicted to occur under the long mean-free path conditions of present tokamak experiments, and has significant features in common with the kink-like oscillations observed in such experiments
Interfacial Instability during Granular Erosion
Lefebvre, Gautier; Merceron, Aymeric; Jop, Pierre
2016-02-01
The complex interplay between the topography and the erosion and deposition phenomena is a key feature to model granular flows such as landslides. Here, we investigated the instability that develops during the erosion of a wet granular pile by a dry dense granular flow. The morphology and the propagation of the generated steps are analyzed in relation to the specific erosion mechanism. The selected flowing angle of the confined flow on a dry heap appears to play an important role both in the final state of the experiment, and for the shape of the structures. We show that the development of the instability is governed by the inertia of the flow through the Froude number. We model this instability and predict growth rates that are in agreement with the experiment results.
Longitudinal instability in HIF beams
International Nuclear Information System (INIS)
In contrast to an electron induction accelerator, in which the particle velocity is virtually constant, the resistive and inductive components of accelerating module impedances can cause instability for an intense non-relativistic heavy ion beam accelerated in a similar structure. Since focusing requirements at the fusion pellet imply a momentum spread approx-lt 3 x 10-4 at the end of the accelerator, it is essential to understand and suppress this instability. There is also an economic issue involved for this application; selection of parameters to control the instability must not unduly affect the efficiency and cost of the accelerator. This paper will present the results of analytic and computational work on module impedances, growth rates and feed back (forward) systems. 2 refs., 3 figs
Interfacial instabilities and Kapitsa pendula
Krieger, Madison
2015-11-01
Determining the critera for onset and amplitude growth of instabilities is one of the central problems of fluid mechanics. We develop a parallel between the Kapitsa effect, in which a pendulum subject to high-frequency low-amplitude vibrations becomes stable in the inverted position, and interfaces separating fluids of different density. It has long been known that such interfaces can be stabilized by vibrations, even when the denser fluid is on top. We demonstrate that the stability diagram for these fluid interfaces is identical to the stability diagram for an appopriate Kapitsa pendulum. We expand the robust, ``dictionary''-type relationship between Kapitsa pendula and interfacial instabilities by considering the classical Rayleigh-Taylor, Kelvin-Helmholtz and Plateau instabilities, as well as less-canonical examples ranging in scale from the micron to the width of a galaxy.
Performance through Deformation and Instability
Bertoldi, Katia
2015-03-01
Materials capable of undergoing large deformations like elastomers and gels are ubiquitous in daily life and nature. An exciting field of engineering is emerging that uses these compliant materials to design active devices, such as actuators, adaptive optical systems and self-regulating fluidics. Compliant structures may significantly change their architecture in response to diverse stimuli. When excessive deformation is applied, they may eventually become unstable. Traditionally, mechanical instabilities have been viewed as an inconvenience, with research focusing on how to avoid them. Here, I will demonstrate that these instabilities can be exploited to design materials with novel, switchable functionalities. The abrupt changes introduced into the architecture of soft materials by instabilities will be used to change their shape in a sudden, but controlled manner. Possible and exciting applications include materials with unusual properties such negative Poisson's ratio, phononic crystals with tunable low-frequency acoustic band gaps and reversible encapsulation systems.
Modulational instability of drift waves
International Nuclear Information System (INIS)
The instability of drift waves against zonal flows and streamers is discussed. Unlike in previous treatments, we do not make the assumption that their frequency is resonant with drift wave packets. In this more general treatment we find at least two unstable roots even in the simple case of a monochromatic pump drift wave, and potentially an infinite multitude of roots for a more complicated drift wave spectrum. One of them is the well known modulational instability in resonance with the drift wave packets; the other is a new instability corresponding to the inelastic refraction of drift waves at the streamer. It is nontrivial which of the many roots is the most unstable one
Hydrodynamick instabilities on ICF capsules
International Nuclear Information System (INIS)
This article summarizes our current understanding of hydrodynamic instabilities as relevant to ICF. First we discuss classical, single mode Rayleigh-Taylor instability, and nonlinear effects in the evolution of a single mode. Then we discuss multimode systems, considering: (1) the onset of nonlinearity; (2) a second order mode coupling theory for weakly nonlinear effects, and (3) the fully nonlinear regime. Two stabilization mechanisms relevant to ICF are described next: gradient scale length and convective stabilization. Then we describe a model which is meant to estimate the weakly nonlinear evolution of multi-mode systems as relevant to ICF, given the short-wavelength stabilization. Finally, we discuss the relevant code simulation capability, and experiments. At this time we are quite optimistic about our ability to estimate instability growth on ICF capsules, but further experiments and simulations are needed to verify the modeling. 52 refs
Telomere dysfunction and chromosome instability
Energy Technology Data Exchange (ETDEWEB)
Murnane, John P., E-mail: jmurnane@radonc.ucsf.edu [Department of Radiation Oncology, University of California San Francisco, 2340 Sutter Street, San Francisco, CA 94143-1331 (United States)
2012-02-01
The ends of chromosomes are composed of a short repeat sequence and associated proteins that together form a cap, called a telomere, that keeps the ends from appearing as double-strand breaks (DSBs) and prevents chromosome fusion. The loss of telomeric repeat sequences or deficiencies in telomeric proteins can result in chromosome fusion and lead to chromosome instability. The similarity between chromosome rearrangements resulting from telomere loss and those found in cancer cells implicates telomere loss as an important mechanism for the chromosome instability contributing to human cancer. Telomere loss in cancer cells can occur through gradual shortening due to insufficient telomerase, the protein that maintains telomeres. However, cancer cells often have a high rate of spontaneous telomere loss despite the expression of telomerase, which has been proposed to result from a combination of oncogene-mediated replication stress and a deficiency in DSB repair in telomeric regions. Chromosome fusion in mammalian cells primarily involves nonhomologous end joining (NHEJ), which is the major form of DSB repair. Chromosome fusion initiates chromosome instability involving breakage-fusion-bridge (B/F/B) cycles, in which dicentric chromosomes form bridges and break as the cell attempts to divide, repeating the process in subsequent cell cycles. Fusion between sister chromatids results in large inverted repeats on the end of the chromosome, which amplify further following additional B/F/B cycles. B/F/B cycles continue until the chromosome acquires a new telomere, most often by translocation of the end of another chromosome. The instability is not confined to a chromosome that loses its telomere, because the instability is transferred to the chromosome donating a translocation. Moreover, the amplified regions are unstable and form extrachromosomal DNA that can reintegrate at new locations. Knowledge concerning the factors promoting telomere loss and its consequences is
Stretching Instability of Helical Springs
Kessler, David A.; Rabin, Yitzhak
2003-01-01
We show that when a gradually increasing tensile force is applied to the ends of a helical spring with sufficiently large ratios of radius to pitch and twist to bending rigidity, the end-to-end distance undergoes a sequence of discontinuous stretching transitions. Subsequent decrease of the force leads to steplike contraction, and hysteresis is observed. For finite helices, the number of these transitions increases with the number of helical turns but only one stretching and one contraction instability survive in the limit of an infinite helix. We calculate the critical line that separates the region of parameters in which the deformation is continuous from that in which stretching instabilities occur.
Hydromagnetic Instabilities in Neutron Stars
Lasky, Paul D; Kokkotas, Kostas D; Glampedakis, Kostas
2011-01-01
We model the non-linear ideal magnetohydrodynamics of poloidal magnetic fields in neutron stars in general relativity assuming a polytropic equation of state. We identify familiar hydromagnetic modes, in particular the 'sausage/varicose' mode and 'kink' instability inherent to poloidal magnetic fields. The evolution is dominated by the kink instability, which causes a cataclysmic reconfiguration of the magnetic field. The system subsequently evolves to new, non-axisymmetric, quasi-equilibrium end-states. The existence of this branch of stable quasi-equilibria may have consequences for magnetar physics, including flare generation mechanisms and interpretations of quasi-periodic oscillations.
Modulational instabilities in discrete lattices
International Nuclear Information System (INIS)
We study analytically and numerically modulational instabilities in discrete nonlinear chains, taking the discrete Klein-Gordon model as an example. We show that discreteness can drastically change the conditions for modulational instability; e.g., at small wave numbers a nonlinear carrier wave is unstable to all possible modulations of its amplitude if the wave amplitude exceeds a certain threshold value. Numerical simulations show the validity of the analytical approach for the initial stage of the time evolution, provided that the harmonics generated by the nonlinear terms are considered. The long-term evolution exhibits chaoticlike states
Mechanical Instabilities of Biological Tubes
Hannezo, Edouard; Prost, Jacques; Joanny, Jean-François
2012-07-01
We study theoretically the morphologies of biological tubes affected by various pathologies. When epithelial cells grow, the negative tension produced by their division provokes a buckling instability. Several shapes are investigated: varicose, dilated, sinuous, or sausagelike. They are all found in pathologies of tracheal, renal tubes, or arteries. The final shape depends crucially on the mechanical parameters of the tissues: Young’s modulus, wall-to-lumen ratio, homeostatic pressure. We argue that since tissues must be in quasistatic mechanical equilibrium, abnormal shapes convey information as to what causes the pathology. We calculate a phase diagram of tubular instabilities which could be a helpful guide for investigating the underlying genetic regulation.
Faraday instability in deformable domains
International Nuclear Information System (INIS)
Hydrodynamical instabilities are usually studied either in bounded regions or free to grow in space. In this article we review the experimental results of an intermediate situation, in which an instability develops in deformable domains. The Faraday instability, which consists in the formation of surface waves on a liquid experiencing a vertical forcing, is triggered in floating liquid lenses playing the role of deformable domains. Faraday waves deform the lenses from the initial circular shape and the mutual adaptation of instability patterns with the lens boundary is observed. Two archetypes of behaviour have been found. In the first archetype a stable elongated shape is reached, the wave vector being parallel to the direction of elongation. In the second archetype the waves exceed the response of the lens border and no equilibrium shape is reached. The lens stretches and eventually breaks into fragments that have a complex dynamics. The difference between the two archetypes is explained by the competition between the radiation pressure the waves exert on the lens border and its response due to surface tension.
Waves and instabilities in plasmas
Chen Liu
1987-01-01
The topics covered in these notes are selective and tend to emphasize more on kinetic-theory approaches to waves and instabilities in both uniform and non-uniform plasmas, students are assumed to have some basic knowledge of plasma dynamics in terms of single-particle and fluid descriptions.
Arthroscopic Management of Scapholunate Instability
Geissler, William B.
2013-01-01
Wrist arthroscopy plays a valuable role in the management of scapholunate instability. A spectrum of injuries can occur to the scapholunate interosseous ligament, which may be difficult to detect with imaging studies. Wrist arthroscopy enables detection and management of injury to the scapholunate ligament under bright light and magnified conditions, in both acute and chronic situations.
GENETIC INSTABILITY IN CERVICAL CARCINOMA
Institute of Scientific and Technical Information of China (English)
赵旻; 伍欣星; 邱小萍; 李晖; 戴天力; 谭云
2002-01-01
Objective: The role of human papillomavirus (HPV) in the development of cervical carcinoma has been clearly established but other factors could be involved in cervical tumorigenesis such as loss of heterozygosity (LOH) and microsatellite instability (MI). The aim of the present study was to investigate the genetic instability in cervical carcinoma tissues and provide evidence for discoveringnew tumor suppressor genes and screening diagnostic molecular marker of cervical carcinoma. Methods: Fifty primary cervical carcinoma samples from high-incidence area were analyzed by PCR for HPV16 infection, LOH and microsatellite instability. Results: HPV16 was detected in 88% of the cases. Sixty-six percent of total cases showed LOH with no more than 3 different loci per case. The highest frequency of the allelic loss was found in D18S474 (18q21, 40.5%). MI was detected in 4 cases (8%) only. Conclusion: Different percentages of LOH on specific chromosomal regions were found and MI was very infrequent in cervical carcinoma. The putative suppressor gene(s) could be located on specific chromosome regions such as 18q, and genetic instability could be involved in cervical tumorigenesis.
Lending sociodynamics and economic instability
Hawkins, Raymond J.
2011-11-01
We show how the dynamics of economic instability and financial crises articulated by Keynes in the General Theory and developed by Minsky as the Financial Instability Hypothesis can be formalized using Weidlich’s sociodynamics of opinion formation. The model addresses both the lending sentiment of a lender in isolation as well as the impact on that lending sentiment of the behavior of other lenders. The risk associated with lending is incorporated through a stochastic treatment of loan dynamics that treats prepayment and default as competing risks. With this model we are able to generate endogenously the rapid changes in lending opinion that attend slow changes in lending profitability and find these dynamics to be consistent with the rise and collapse of the non-Agency mortgage-backed securities market in 2007/2008. As the parameters of this model correspond to well-known phenomena in cognitive and social psychology, we can both explain why economic instability has proved robust to advances in risk measurement and suggest how policy for reducing economic instability might be formulated in an experimentally sound manner.
Edge instabilities of topological superconductors
Hofmann, Johannes S.; Assaad, Fakher F.; Schnyder, Andreas P.
2016-05-01
Nodal topological superconductors display zero-energy Majorana flat bands at generic edges. The flatness of these edge bands, which is protected by time-reversal and translation symmetry, gives rise to an extensive ground-state degeneracy. Therefore, even arbitrarily weak interactions lead to an instability of the flat-band edge states towards time-reversal and translation-symmetry-broken phases, which lift the ground-state degeneracy. We examine the instabilities of the flat-band edge states of dx y-wave superconductors by performing a mean-field analysis in the Majorana basis of the edge states. The leading instabilities are Majorana mass terms, which correspond to coherent superpositions of particle-particle and particle-hole channels in the fermionic language. We find that attractive interactions induce three different mass terms. One is a coherent superposition of imaginary s -wave pairing and current order, and another combines a charge-density-wave and finite-momentum singlet pairing. Repulsive interactions, on the other hand, lead to ferromagnetism together with spin-triplet pairing at the edge. Our quantum Monte Carlo simulations confirm these findings and demonstrate that these instabilities occur even in the presence of strong quantum fluctuations. We discuss the implications of our results for experiments on cuprate high-temperature superconductors.
Cavitation instabilities in hydraulic machines
International Nuclear Information System (INIS)
Cavitation instabilities in hydraulic machines, hydro turbines and turbopump inducers, are reviewed focusing on the cause of instabilities. One-dimensional model of hydro turbine system shows that the overload surge is caused by the diffuser effect of the draft tube. Experiments show that this effect also causes the surge mode oscillations at part load. One dimensional model of a cavitating turbopump inducer shows that the mass flow gain factor, representing the cavity volume increase caused by the incidence angle increase is the cause of cavitation surge and rotating cavitation. Two dimensional model of a cavitating turbopump inducer shows that various modes of cavitation instabilities start to occur when the cavity length becomes about 65% of the blade spacing. This is caused by the interaction of the local flow near the cavity trailing edge with the leading edge of the next blade. It was shown by a 3D CFD that this is true also for real cases with tip cavitation. In all cases, it was shown that cavitation instabilities are caused by the fundamental characteristics of cavities that the cavity volume increases with the decrease of ambient pressure or the increase of the incidence angle
The Chemistry of Beer Instability
Stewart, Graham G.
2004-01-01
Brewing of beer, one of the oldest biotechnology industries was one of the earliest processes to be undertaken on commercial basis. Biological instability involves contamination of bacteria, yeast, or mycelia fungi and there is always a risk in brewing that beer can become contaminated by micro-organisms.
Singlet and triplet instability theorems
Energy Technology Data Exchange (ETDEWEB)
Yamada, Tomonori; Hirata, So, E-mail: sohirata@illinois.edu [Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801 (United States); CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan)
2015-09-21
A useful definition of orbital degeneracy—form-degeneracy—is introduced, which is distinct from the usual energy-degeneracy: Two canonical spatial orbitals are form-degenerate when the energy expectation value in the restricted Hartree–Fock (RHF) wave function is unaltered upon a two-electron excitation from one of these orbitals to the other. Form-degenerate orbitals tend to have isomorphic electron densities and occur in the highest-occupied and lowest-unoccupied molecular orbitals (HOMOs and LUMOs) of strongly correlated systems. Here, we present a mathematical proof of the existence of a triplet instability in a real or complex RHF wave function of a finite system in the space of real or complex unrestricted Hartree–Fock wave functions when HOMO and LUMO are energy- or form-degenerate. We also show that a singlet instability always exists in a real RHF wave function of a finite system in the space of complex RHF wave functions, when HOMO and LUMO are form-degenerate, but have nonidentical electron densities, or are energy-degenerate. These theorems provide Hartree–Fock-theory-based explanations of Hund’s rule, a singlet instability in Jahn–Teller systems, biradicaloid electronic structures, and a triplet instability during some covalent bond breaking. They also suggest (but not guarantee) the spontaneous formation of a spin density wave (SDW) in a metallic solid. The stability theory underlying these theorems extended to a continuous orbital-energy spectrum proves the existence of an oscillating (nonspiral) SDW instability in one- and three-dimensional homogeneous electron gases, but only at low densities or for strong interactions.
Singlet and triplet instability theorems
International Nuclear Information System (INIS)
A useful definition of orbital degeneracy—form-degeneracy—is introduced, which is distinct from the usual energy-degeneracy: Two canonical spatial orbitals are form-degenerate when the energy expectation value in the restricted Hartree–Fock (RHF) wave function is unaltered upon a two-electron excitation from one of these orbitals to the other. Form-degenerate orbitals tend to have isomorphic electron densities and occur in the highest-occupied and lowest-unoccupied molecular orbitals (HOMOs and LUMOs) of strongly correlated systems. Here, we present a mathematical proof of the existence of a triplet instability in a real or complex RHF wave function of a finite system in the space of real or complex unrestricted Hartree–Fock wave functions when HOMO and LUMO are energy- or form-degenerate. We also show that a singlet instability always exists in a real RHF wave function of a finite system in the space of complex RHF wave functions, when HOMO and LUMO are form-degenerate, but have nonidentical electron densities, or are energy-degenerate. These theorems provide Hartree–Fock-theory-based explanations of Hund’s rule, a singlet instability in Jahn–Teller systems, biradicaloid electronic structures, and a triplet instability during some covalent bond breaking. They also suggest (but not guarantee) the spontaneous formation of a spin density wave (SDW) in a metallic solid. The stability theory underlying these theorems extended to a continuous orbital-energy spectrum proves the existence of an oscillating (nonspiral) SDW instability in one- and three-dimensional homogeneous electron gases, but only at low densities or for strong interactions
Coupled Bunch Instabilities in the LHC
Angal-Kalinin, Deepa
2002-01-01
In the LHC, the coupled bunch instabilities will be mainly driven by the RF cavities and the resistive wall effect. The growth times of these instabilities have been estimated taking into consideration the undamped and damped higher order modes of these cavities. These estimates show that the rise times of the longitudinal coupled bunch instabilities are under control. The proposed transverse feed-back system allows the same conclusion to be drawn for the transverse resistive wall instability.
Measurements of fast transition instability in RHIC
Energy Technology Data Exchange (ETDEWEB)
Ptitsyn, V.; Blaskiewicz, M.; Fischer, W.; Lee, R.; Zhang, S.Y.
2010-05-23
A fast transition instability presents a limiting factor for ion beam intensity in RHIC. Several pieces of evidence show that electron clouds play an important role in establishing the threshold of this instability. In RHIC Runs8 the measurements of the instability, using a button BPM, were done in order to observe details of the instability development on the scale over hundreds and thousands turns. The paper presents and discusses the results of those measurements in time and frequency domains.
Perception of job instability in Europe
Böckerman, Petri
2002-01-01
The perception of job instability is an important measure of subjective well-being of individuals, because most people derive their income from selling their labour services. The study explores the determination of perception of job instability in Europe. The study is based on a large-scale survey from the year 1998. There are evidently large differences in the amount of perceived job instability from country to country. The lowest level of perceived job instability is in Denmark (9%). In con...
Media Freedom and Socio-Political Instability
Pal Sudeshna
2011-01-01
Free media may reduce incidents of socio-political instability. Different types of socio-political instability have been shown to have a negative effect on investment and economic growth. This study examines the effect of free media on various indicators of socio-political instability. Using a panel of 98 countries over 1994-2005, this study shows that media free from government control and interference may decrease different forms of socio-political instability because it puts internal and e...
Surge Instability on a Cavitating Propeller
Duttweiler, Mark E.; Brennen, Christopher E.
2001-01-01
This study details experiments investigating a previously unrecognized surge instability on a cavitating propeller in a water tunnel. The surge instability is furst explored through visual observation of the cavitation on the propeller blades and in the tip vortices. Similarities between the instability and previously documented cavitation phenomena are noted. Measurements of the radiated pressure are then obtained, and the acoustic signature of the instability is identified. The magnitud...
Solitons versus parametric instabilities during ionospheric heating
Nicholson, D. R.; Payne, G. L.; Downie, R. M.; Sheerin, J. P.
1984-01-01
Various effects associated with ionospheric heating are investigated by numerically solving the modified Zakharov (1972) equations. It is shown that, for typical ionospheric parameters, the modulational instability is more important than the parametric decay instability in the spatial region of strongest heater electric field. It is concluded that the modulational instability leads to the formation of solitons, as originally predicted by Petviashvili (1976).
Observation of Parametric Instability in Advanced LIGO
Evans, Matthew; Fritschel, Peter; Miller, John; Barsotti, Lisa; Martynov, Denis; Brooks, Aidan; Coyne, Dennis; Abbott, Rich; Adhikari, Rana; Arai, Koji; Bork, Rolf; Kells, Bill; Rollins, Jameson; Smith-Lefebvre, Nicolas; Vajente, Gabriele; Yamamoto, Hiroaki; Derosa, Ryan; Effler, Anamaria; Kokeyama, Keiko; Betzweiser, Joseph; Frolov, Valera; Mullavey, Adam; O`Reilly, Brian; Dwyer, Sheila; Izumi, Kiwamu; Kawabe, Keita; Landry, Michael; Sigg, Daniel; Ballmer, Stefan; Massinger, Thomas J; Staley, Alexa; Mueller, Chris; Grote, Hartmut; Ward, Robert; King, Eleanor; Blair, David; Ju, Li; Zhao, Chunnong
2015-01-01
Parametric instabilities have long been studied as a potentially limiting effect in high-power interferometric gravitational wave detectors. Until now, however, these instabilities have never been observed in a kilometer-scale interferometer. In this work we describe the first observation of parametric instability in an Advanced LIGO detector, and the means by which it has been removed as a barrier to progress.
Localized Rayleigh Instability in Evaporation Fronts
Diamant, Haim; Agam, Oded
2009-01-01
A qualitatively different manifestation of the Rayleigh instability is demonstrated, where, instead of the usual extended undulations and breakup of the liquid into many droplets, the instability is localized, leading to an isolated narrowing of the liquid filament. The localized instability, caused by a nonuniform curvature of the liquid domain, plays a key role in the evaporation of thin liquid films off solid surfaces.
Mood instability: significance, definition and measurement
Broome, M.R.; Saunders, K.E.A.; Harrison, P. J.; MARWAHA S.
2015-01-01
Mood instability is common, and an important feature of several psychiatric disorders. We discuss the definition and measurement of mood instability, and review its prevalence, characteristics, neurobiological correlates and clinical implications. We suggest that mood instability has underappreciated transdiagnostic potential as an investigational and therapeutic target.
Basic instabilities of collisionless gravitating systems.
Polyachenko, V. L.
1995-05-01
The paper presents a short summary of basic instabilities in stellar systems, namely: the Jeans, bar-mode and fire-hose (bending) instabilities. A classification of bar-mode instabilities according to a ratio of the bar pattern angular velocity and the maximal precession speed of nearly-circular stellar orbits is proposed.
Introduction to instabilities in natural circulation systems
International Nuclear Information System (INIS)
This lecture reviews the various natural circulation instabilities and their classification instabilities observed during various stages of natural circulation such as single-phase, boiling inception and fully developed two-phase flow are described. The mechanisms causing the instabilities are also briefly described. (author)
On modulational instability of two coupled waves
International Nuclear Information System (INIS)
The modulational instability of two waves propagating in a cubically nonlinear medium is considered. It is shown that the correct theory in the case of comparatively small instability rates operates with ''renormalized'' equations as for a linear dielectric function, so for an effective third-order medium response. This renormalization is due to so-called interference terms. The appearance of the interference terms is a specific feature of the two-mode modulational instability in comparison with the well-known instability of a single mode. The instability of two pump Langmuir waves is investigated. (orig.)
Placing Marangoni instabilities under arrest
Bhamla, M Saad
2016-01-01
Soap bubbles occupy the rare position of delighting and fascinating both young children and scientific minds alike. Sir Isaac Newton, Joseph Plateau, Carlo Marangoni, and Pierre-Gilles de Gennes, not to mention countless others, have discovered remarkable results in optics, molecular forces and fluid dynamics from investigating this seemingly simple system. We present here a compilation of curiosity-driven experiments that systematically investigate the surface flows on a rising soap bubble. From childhood experience, we are familiar with the vibrant colors and mesmerizing display of chaotic flows on the surface of a soap bubble. These flows arise due to surface tension gradients, also known as Marangoni flows or instabilities. In Figure 1, we show the surprising effect of layering multiple instabilities on top of each other, highlighting that unexpected new phenomena are still waiting to be discovered, even in the simple soap bubble.
Statistical theory of thermal instability
Illarionov, A F
1997-01-01
A new statistical approach is presented to study the thermal instability process of optically thin unmagnetized plasma. In this approach the time evolution of mass distribution function over temperature is calculated. This function characterizes the statistical properties of the multiphase medium of arbitrary spaced three-dimensional structure of arbitrary temperature perturbations. We construct our theory under the isobarical condition (P=const over space), which is satisfied in the short wavelength limit. The developed theory is illustrated in the case of thermal instability of a slowly expanding interstellar cloud. Numerical solutions of equations of the statistical theory are constucted and compared with hydrodynamical solutions. The results of both approaches are identical in the short wavelength range when the isobarity condition is satisfied. Also the limits of applicability of the statistical theory are estimated. The possible evolution of initial spectrum of perturbations is discussed. The proposed t...
Instability of supersymmetric microstate geometries
Eperon, Felicity C; Santos, Jorge E
2016-01-01
We investigate the classical stability of supersymmetric, asymptotically flat, microstate geometries with five non-compact dimensions. Such geometries admit an "evanescent ergosurface": a timelike hypersurface of infinite redshift. On such a surface, there are null geodesics with zero energy relative to infinity. These geodesics are stably trapped in the potential well near the ergosurface. We present a heuristic argument indicating that this feature is likely to lead to a nonlinear instability of these solutions. We argue that the precursor of such an instability can be seen in the behaviour of linear perturbations: nonlinear stability would require that all linear perturbations decay sufficiently rapidly but the stable trapping implies that some linear perturbation decay very slowly. We study this in detail for the most symmetric microstate geometries. By constructing quasinormal modes of these geometries we show that generic linear perturbations decay slower than any inverse power of time.
On dynamical (black hole) instabilities
Coutant, Antonin; Parentani, Renaud
2016-01-01
Black hole dynamical instabilities have been mostly studied in specific models. To display their common features, we study the general properties of the complex frequency modes which are responsible for such instabilities. We show that they are square integrable, have a vanishing conserved norm, and appear in mode doublets or quartets. We also study how they appear in the spectrum and how their complex frequencies subsequently evolve when varying some external parameter. When working on an infinite domain, they appear from the reservoir of quasi-normal modes obeying outgoing boundary conditions. This is illustrated by generalizing, in a non-positive definite Krein space, a solvable model (Friedrichs model) which originally describes the appearance of a resonance when coupling an isolated system to a mode continuum. In a finite spatial domain instead, they arise from the fusion of two real frequency modes with opposite norms, through a process that closely resembles avoided crossing.
Stretching Folding Instability and Nanoemulsions
Chan, Chon U
2009-01-01
Here we show a folding-stretching instability in a microfluidic flow focusing device using silicon oil (100cSt) and water. The fluid dynamics video demonstrates an oscillating thread of oil focused by two co-flowing streams of water. We show several high-speed sequences of these oscillations with 30,000 frames/s. Once the thread is decelerated in a slower moving pool downstream an instability sets in and water-in-oil droplets are formed. We reveal the details of the pinch-off with 500,000 frames/s. The pinch-off is so repeatable that complex droplet patterns emerge. Some of droplets are below the resolution limit, thus smaller than 1 micrometer in diameter.
Mechanical Instabilities of Biological Tubes
Hannezo, Edouard; Prost, Jacques; 10.1103/PhysRevLett.109.018101
2012-01-01
We study theoretically the shapes of biological tubes affected by various pathologies. When epithelial cells grow at an uncontrolled rate, the negative tension produced by their division provokes a buckling instability. Several shapes are investigated : varicose, enlarged, sinusoidal or sausage-like, all of which are found in pathologies of tracheal, renal tubes or arteries. The final shape depends crucially on the mechanical parameters of the tissues : Young modulus, wall-to-lumen ratio, homeostatic pressure. We argue that since tissues must be in quasistatic mechanical equilibrium, abnormal shapes convey information as to what causes the pathology. We calculate a phase diagram of tubular instabilities which could be a helpful guide for investigating the underlying genetic regulation.
Instability investigation for storage mode
International Nuclear Information System (INIS)
The Amsterdam Pulse Stretcher (AmPS) will be used in storage mode for internal target (IT) physics. It demands the beam lifetime at least at the order of half an hour and the stored beam current of 200 mA. Bunched beam instabilities have been observed in many storage rings. The low-Q broadband impedance drives the single-bunch instability. The single bunch treshold and the equilibrium bunch length as the function of energies, RF voltages, and RF frequencies are investigated. The code ZAP has been used for investigating the stability thresholds for AmPS in storage mode. This note presents the simulation results. They gave useful information for choosing the RF parameters of AmPS. (author). 3 refs.. 6 figs.. 3 tabs
Modulational instability of two waves
International Nuclear Information System (INIS)
The stability of a plasma in the presence of two propagating waves (modulation interaction) is considered. It is shown under what circumstances it is necessary to use open-quotes renormalizedclose quotes expressions for both the linear dielectric function and the effective third-order response. The typical behavior of both kinds of interaction are found for the specific case of Langmuir waves in a uniform and isotropic collisionless plasma. Criteria are established under which it is possible to disregard the effect of the interference terms in both the zeroth approximation and in the equations for the modulational perturbations when studying the modulational interaction of two pump waves. The calculated modulational instability growth rates are compared with the growth rates of the modulational instability for a single monochromatic mode. 13 refs
Fluctuations and Instability in Sedimentation
Guazzelli, Élisabeth
2011-01-21
This review concentrates on the fluctuations of the velocities of sedimenting spheres, and on the structural instability of a suspension of settling fibers. For many years, theoretical estimates and numerical simulations predicted the fluctuations of the velocities of spheres to increase with the size of the container, whereas experiments found no such variation. Two ideas have increased our understanding. First, the correlation length of the velocity fluctuations was found experimentally to be 20 interparticle separations. Second, in dilute suspensions, a vertical variation in the concentration due to the spreading of the front with the clear fluid can inhibit the velocity fluctuations. In a very dilute regime, a homogeneous suspension of fibers suffers a spontaneous instability in which fast descending fiber-rich columns are separated by rising fiber-sparse columns. In a semidilute regime, the settling is hindered, more so than for spheres. © 2011 by Annual Reviews. All rights reserved.
Feedback control of resistive instabilities
International Nuclear Information System (INIS)
Resistive instabilities are responsible for much of the global behavior and the determination of the possible domains of operation of tokamaks. Their successful control could have definite advantages, even making available new regimes of operation. Elimination of sawtoothing might allow operation with higher currents and more peaked current profiles, with q on axis well below unity. In this work different feedback schemes are explored. Simple analytical derivations of the effects of local heating and current drive feedback are presented. Although control of modes with m greater than or equal to 2 is fairly straightforward, the control of the m = 1 mode is more difficult because of its proximity to ideal instability. The most promising scheme utilizes high energy trapped particles. 20 refs., 3 figs
Instability of colliding metastable strings
International Nuclear Information System (INIS)
We investigate the collision dynamics of two metastable strings which can be viewed as tube-like domain walls with winding numbers interpolating a false vacuum and a true vacuum. We find that depending on the relative angle and speed of two strings, instability of strings increases and the false vacuum is filled out by rapid expansion of the strings or of a remnant of the collision.
Interfacial Instability during Granular Erosion
Lefebvre, Gautier; Merceron, Aymeric; Jop, Pierre
2016-01-01
The complex interplay between the topography and the erosion and deposition phenomena is a key feature to model granular flows such as landslides. Here, we investigated the instability that develops during the erosion of a wet granular pile by a dry dense granular flow. The morphology and the propagation of the generated steps are analyzed in relation to the specific erosion mechanism. The selected flowing angle of the confined flow on a dry heap appears to play an important role both in the ...
Single-bunch longitudinal instability
International Nuclear Information System (INIS)
A theoretical analysis is given of the recently observed microwave instability in storage rings. It is shown that one expects a threshold proportional to impedance R/sub S/ in the limit of very large or small resonator bandwidths, with the threshold lower by the bunching factor for the large bandwidth case. For intermediate bandwidths, the threshold should be proportional to the area under the resonance curve, so de-Qing resonators will have little effect in this region
Statistical instability of physical processes
Gorban, I. I.
2011-01-01
New parameters describing destructions of statistical stability in finite observation interval have been proposed. For known and new statistical instability parameters, metric units that open possibility to characterize destructions of statistical stability in terms of quantity have been introduced. It is shown that essential rule in disturbances of statistical stability plays fluctuations of expectation of the process that lead to change expectation of average, and also fluctuations of varia...
Chromosomal instability determines taxane response
Swanton, Charles; Nicke, Barbara; Schuett, Marion; Eklund, Aron C.; Ng, Charlotte; Li, Qiyuan; Hardcastle, Thomas; Lee, Alvin; Roy, Rajat; East, Philip; Kschischo, Maik; Endesfelder, David; Wylie, Paul; Kim, Se Nyun; Chen, Jie-Guang
2009-01-01
Microtubule-stabilizing (MTS) agents, such as taxanes, are important chemotherapeutics with a poorly understood mechanism of action. We identified a set of genes repressed in multiple cell lines in response to MTS agents and observed that these genes are overexpressed in tumors exhibiting chromosomal instability (CIN). Silencing 22/50 of these genes, many of which are involved in DNA repair, caused cancer cell death, suggesting that these genes are involved in the survival of aneuploid cells....
Polygonal instabilities on interfacial vorticities
Labousse, Matthieu
2015-01-01
We report the results of a theoretical investigation of the stability of a toroidal vortex bound by an interface. Two distinct instability mechanisms are identified that rely on, respectively, surface tension and fluid inertia, either of which may prompt the transformation from a circular to a polygonal torus. Our results are discussed in the context of three experiments, a toroidal vortex ring, the hydraulic jump, and the hydraulic bump.
Polygonal instabilities on interfacial vorticities.
Labousse, M; Bush, J W M
2015-10-01
We report the results of a theoretical investigation of the stability of a toroidal vortex bound by an interface. Two distinct instability mechanisms are identified that rely on, respectively, surface tension and fluid inertia, either of which may prompt the transformation from a circular to a polygonal torus. Our results are discussed in the context of three experiments, a toroidal vortex ring, the hydraulic jump, and the hydraulic bump. PMID:26537726
Experiences with Extreme Monetary Instability
Dornbusch, Rudiger
1990-01-01
In early 1990, Argentina, Brazil, Peru, Yugoslavia and Poland were experiencing extreme instability or, at least, the early stages of stabilization. Other countries, like Bolivia, had already run the course and stabilized or, like Mexico, had avoided the extreme experience and opted for stabilization promptly and decisively. The lessons from these case studies, and from the earlier experiences of the 1920s and 1940s, have still to be drawn. Exactly the same themes come up each time. The paper...
Finite temperature instability for compactification
International Nuclear Information System (INIS)
We consider finite temperature effects upon theories with extra dimensions compactified via vacuum stress energy (Casimir) effects. For sufficiently high temperature, a static configuration for the internal space is impossible. At somewhat lower temperatures, there is an instability due to thermal fluctuations of radius of the compact dimensions. For both cases, the Universe can evolve to a de Sitter-like expansion of all dimensions. Stability to late times constrains the initial entropy of the universe. 28 refs., 1 fig., 2 tabs
Laser driven hydrodynamic instability experiments
International Nuclear Information System (INIS)
An extensive series of experiments has been conducted on the Nova laser to measure hydrodynamic instabilities in planar foils accelerated by x-ray ablation. Single mode experiments allow a measurement of the fundamental growth rates from the linear well into the nonlinear regime. Two-mode foils allow a first direct observation of mode coupling. Surface-finish experiments allow a measurement of the evolution of a broad spectrum of random initial modes
Bifurcations, instabilities, degradation in geomechanics
Exadaktylos, George
2007-01-01
Leading international researchers and practitioners of bifurcations and instabilities in geomechanics debate the developments and applications which have occurred over the last few decades. The topics covered include modeling of bifurcation, structural failure of geomaterials and geostructures, advanced analytical, numerical and experimental techniques, and application and development of generalised continuum models etc. In addition analytical solutions, numerical methods, experimental techniques, and case histories are presented. Beside fundamental research findings, applications in geotechni
MD 751: Train Instability Threshold
Carver, Lee Robert; Metral, Elias; Salvant, Benoit; Levens, Tom; Nisbet, David; Zobov, M; CERN. Geneva. ATS Department
2016-01-01
The purpose of this MD is to measure the octupole current thresholds for stability for a single bunch, and then make an immediate comparison (with the same operational settings) for a train of 72 bunches separated by 25ns. From theory, the expected thresholds should be similar. Any discrepancy between the two cases will be of great interest as it could indicate the presence of additional mechanisms that contribute to the instability threshold, for example electron cloud.
Pattern Generation by Dissipative Parametric Instability
Perego, A. M.; Tarasov, N.; Churkin, D. V.; Turitsyn, S. K.; Staliunas, K.
2016-01-01
Nonlinear instabilities are responsible for spontaneous pattern formation in a vast number of natural and engineered systems, ranging from biology to galaxy buildup. We propose a new instability mechanism leading to pattern formation in spatially extended nonlinear systems, which is based on a periodic antiphase modulation of spectrally dependent losses arranged in a zigzag way: an effective filtering is imposed at symmetrically located wave numbers k and -k in alternating order. The properties of the dissipative parametric instability differ from the features of both key classical concepts of modulation instabilities, i.e., the Benjamin-Feir instability and the Faraday instabiltyity. We demonstrate how the dissipative parametric instability can lead to the formation of stable patterns in one- and two-dimensional systems. The proposed instability mechanism is generic and can naturally occur or can be implemented in various physical systems.
Modes of storage ring coherent instabilities
International Nuclear Information System (INIS)
Longitudinal impedance in a beam and various modes of longitudinal coherent instabilities are discussed. The coasting beam coherent instability, microwave instability, and single-bunch longitudinal coherent instabilities are considered. The Vlasov equation is formulated, and a method of solving it is developed. The synchrotron modes are treated, which take the possible bunch shape distortion fully into consideration. A method of treating the synchrotron mode coupling in the case of a small bunch is discussed which takes advantage of the fact that only a few of the synchrotron modes can contribute in such a case. The effect of many bunches on the coherent motion of the beam and the longitudinal symmetric coupled bunch modes are discussed. The transverse impedance is then introduced, and the transverse coasting beam instability is discussed. Various bunched beam instabilities are discussed, including both single bunch instabilities and coupled bunch instabilities. The Vlasov equation for transverse as well as longitudinal motion of particles is introduced as well as a method of solving it within a linear approximation. Head-tail modes and short bunch instabilities and strong coupling instabilities in the long bunch case are covered
Material and structural instabilities of single-wall carbon nanotubes
Institute of Scientific and Technical Information of China (English)
J. Wu; K. C. Hwang; J. Song; Y. Huang
2008-01-01
The nonlinear atomistic interactions usually involve softening behavior. Instability resulting directly from this softening are called the material instability, while those unrelated to this softening are called the structural instability. We use the finite-deformation shell theory based on the interatomic potential to show that the tension instability of single-wall carbon nanotubes is the material instability, while the compression and torsion instabilities are structural instability.
Passive mitigation of mode instabilities
Jauregui, C.; Otto, H.-J.; Stutzki, F.; Jansen, F.; Limpert, J.; Tünnermann, A.
2014-03-01
The phenomenon of mode instabilities has quickly become the most limiting effect for a further scaling of the average power of fiber laser systems. Consequently it is of great importance to find solutions for this problem. In this work we propose two concrete possible passive mitigation strategies: the first one is based on the reduction of the heat load in the fiber, whereas the second one is based on the reduction of the pump absorption. In both cases a significant increase of the threshold is expected.
Carpal instability of the wrist.
Caggiano, Nicholas; Matullo, Kristofer S
2014-01-01
The scaphoid is stabilized by the scapholunate ligament (directly) and lunotriquetral ligament (indirectly). Disruption of either of these ligaments leads to a pattern of instability that, left untreated, leads to altered mechanics of the wrist and ultimately debilitating arthritis and collapse. Although arthroscopy remains the gold standard for diagnosis of these injuries, plain films and advanced imaging are useful adjuncts. In the acute setting, conservative treatment may be attempted, but recalcitrant cases require surgical stabilization. Salvage procedures are also available for those patients who fail initial stabilization or present with late degeneration. PMID:24267214
Instability of ties in compression
DEFF Research Database (Denmark)
Buch-Hansen, Thomas Cornelius
2013-01-01
Masonry cavity walls are loaded by wind pressure and vertical load from upper floors. These loads results in bending moments and compression forces in the ties connecting the outer and the inner wall in a cavity wall. Large cavity walls are furthermore loaded by differential movements from the...... temperature gradient between the outer and the inner wall, which results in critical increase of the bending moments in the ties. Since the ties are loaded by combined compression and moment forces, the loadbearing capacity is derived from instability equilibrium equations. Most of them are iterative, since...
Sheet Beam Klystron Instability Analysis
Energy Technology Data Exchange (ETDEWEB)
Bane, K.L.F.; Jensen, A.; Li, Z.; Stupakov, G.; Adolphsen, C.; /SLAC
2009-05-08
Using the principle of energy balance we develop a 2D theory for calculating growth rates of instability in a two-cavity model of a sheet beam klystron. An important ingredient is a TE-like mode in the gap that also gives a longitudinal kick to the beam. When compared with a self-consistent particle-in-cell calculation, with sheet beam klystron-type parameters, agreement is quite good up to half the design current, 65 A; at full current, however, other, current-dependent effects come in and the results deviate significantly.
The instability of Wilton ripples
Trichtchenko, Olga; Wilkening, Jon
2015-01-01
Wilton ripples are a type of periodic traveling wave solution of the full water wave problem incorporating the effects of surface tension. They are characterized by a resonance phenomenon that alters the order at which the resonant harmonic mode enters in a perturbation expansion. We compute such solutions using non-perturbative numerical methods and investigate their stability by examining the spectrum of the water wave problem linearized about the resonant traveling wave. Instabilities are observed that differ from any previously found in the context of the water wave problem.
Fingering Instabilities in Dewetting Nanofluids
Pauliac-Vaujour, E.; Stannard, A.; Martin, C. P.; Blunt, M. O.; Notingher, I.; Moriarty, P. J.; Vancea, I.; Thiele, U.
2008-05-01
The growth of fingering patterns in dewetting nanofluids (colloidal solutions of thiol-passivated gold nanoparticles) has been followed in real time using contrast-enhanced video microscopy. The fingering instability on which we focus here arises from evaporatively driven nucleation and growth in a nanoscopically thin precursor solvent film behind the macroscopic contact line. We find that well-developed isotropic fingering structures only form for a narrow range of experimental parameters. Numerical simulations, based on a modification of the Monte Carlo approach introduced by Rabani et al. [Nature (London)NATUAS0028-0836 426, 271 (2003)10.1038/nature02087], reproduce the patterns we observe experimentally.
Transverse Instabilities in the Fermilab Recycler
Energy Technology Data Exchange (ETDEWEB)
Prost, L.R.; Burov, A.; Shemyakin, A.; Bhat, C.M.; Crisp, J.; Eddy, N.; /Fermilab
2011-07-01
Transverse instabilities of the antiproton beam have been observed in the Recycler ring soon after its commissioning. After installation of transverse dampers, the threshold for the instability limit increased significantly but the instability is still found to limit the brightness of the antiprotons extracted from the Recycler for Tevatron shots. In this paper, we describe observations of the instabilities during the extraction process as well as during dedicated studies. The measured instability threshold phase density agrees with the prediction of the rigid beam model within a factor of 2. Also, we conclude that the instability threshold can be significantly lowered for a bunch contained in a narrow and shallow potential well due to effective exclusion of the longitudinal tails from Landau damping.
Transverse Instabilities in the FERMILAB Recycler
Prost, L R; Shemyakin, A; Bhat, C M; Crisp, J; Eddy, N
2012-01-01
Transverse instabilities of the antiproton beam have been observed in the Recycler ring soon after its commissioning. After installation of transverse dampers, the threshold for the instability limit increased significantly but the instability is still found to limit the brightness of the antiprotons extracted from the Recycler for Tevatron shots. In this paper, we describe observations of the instabilities during the extraction process as well as during dedicated studies. The measured instability threshold phase density agrees with the prediction of the rigid beam model within a factor of 2. Also, we conclude that the instability threshold can be significantly lowered for a bunch contained in a narrow and shallow potential well due to effective exclusion of the longitudinal tails from Landau damping.
Radiation induced chromosome instability in human fibroblasts
International Nuclear Information System (INIS)
Evidence has been arising that some biological effects can manifest many cell divisions after irradiation. We have demonstrated that de novo chromosome instability can be detected 10- 15 mean population doubling after heavy ion irradiations. This chromosome instability is characterized by end to end fusions between specific chromosomes. The specificity of the instability may differ from one donor to another but for the same donor, the same instability should be observed after irradiation, during the senescence process and after SV40 transfection (before crisis). In irradiated primary culture fibroblasts, the expression of the delayed chromosomal instability lasts for several cell divisions without inducing cell death. Several rounds of fusions- breakage-fusions can be performed and unbalanced clones emerge (gain or loss of chromosomes with the shorter telomeres would become unstable first.. The difference in the chromosomal instability among donors could be due to a polymorphism in telomere lengths. This could induce large variation in long term response to irradiation among individuals. (author)
Mode-locking via dissipative Faraday instability
Tarasov, Nikita; Perego, Auro M.; Churkin, Dmitry V.; Staliunas, Kestutis; Turitsyn, Sergei K.
2016-08-01
Emergence of coherent structures and patterns at the nonlinear stage of modulation instability of a uniform state is an inherent feature of many biological, physical and engineering systems. There are several well-studied classical modulation instabilities, such as Benjamin-Feir, Turing and Faraday instability, which play a critical role in the self-organization of energy and matter in non-equilibrium physical, chemical and biological systems. Here we experimentally demonstrate the dissipative Faraday instability induced by spatially periodic zig-zag modulation of a dissipative parameter of the system--spectrally dependent losses--achieving generation of temporal patterns and high-harmonic mode-locking in a fibre laser. We demonstrate features of this instability that distinguish it from both the Benjamin-Feir and the purely dispersive Faraday instability. Our results open the possibilities for new designs of mode-locked lasers and can be extended to other fields of physics and engineering.
Instability of SmS under pressure
International Nuclear Information System (INIS)
It is suggested that electron-phonon (EP) interaction is a suitable mechanism to explain the instability of the semiconducting phase in SmS under pressure. The f reversible d and d reversible d scattering processes due to EP interaction avoid the introduction of negative renormalized f-d hybridization assumed by some other models as the source of the first order instability. Moreover this instability is shown as occuring for a non-zero energy gap. (orig.)
Kelvin-Helmholtz instabilities with Godunov SPH
Cha, Seung-Hoon; Inutsuka, Shu-Ichiro; Nayakshin, Sergei
2009-01-01
Numerical simulations for the non-linear development of Kelvin-Helmholtz instability in two different density layers have been performed with the particle-based method (Godunov SPH) developed by Inutsuka (2002). The Godunov SPH can describe the Kelvin-Helmholtz instability even with a high density contrast, while the standard SPH shows the absence of the instability across a density gradient (Agertz et al. 2007). The interaction of a dense blob with a hot ambient medium has been performed als...
Cultural diversity, economic development and societal instability
Daniel Nettle; Grace, James B.; Marc Choisy; Howard V Cornell; Jean-François Guégan; Michael E Hochberg
2007-01-01
BACKGROUND: Social scientists have suggested that cultural diversity in a nation leads to societal instability. However, societal instability may be affected not only by within-nation or alpha diversity, but also diversity between a nation and its neighbours or beta diversity. It is also necessary to distinguish different domains of diversity, namely linguistic, ethnic and religious, and to distinguish between the direct effects of diversity on societal instability, and effects that are media...
Instabilities and transition in boundary layers
Indian Academy of Sciences (India)
N Vinod; Rama Govindarajan
2005-03-01
Some recent developments in boundary layer instabilities and transition are reviewed. Background disturbance levels determine the instability mechanism that ultimately leads to turbulence. At low noise levels, the traditional Tollmien–Schlichting route is followed, while at high levels, a `by-pass' route is more likely. Our recent work shows that spot birth is related to the pattern of secondary instability in either route.
Instabilities of flows and transition to turbulence
Sengupta, Tapan K
2012-01-01
Introduction to Instability and TransitionIntroductionWhat Is Instability?Temporal and Spatial InstabilitySome Instability MechanismsComputing Transitional and Turbulent FlowsFluid Dynamical EquationsSome Equilibrium Solutions of the Basic EquationBoundary Layer TheoryControl Volume Analysis of Boundary LayersNumerical Solution of the Thin Shear Layer (TSL) EquationLaminar Mixing LayerPlane Laminar JetIssues of Computing Space-Time Dependent FlowsWave Interaction: Group Velocity and Energy FluxIssues of Space-Time Scale Resolution of FlowsTemporal Scales in Turbulent FlowsComputing Time-Averag
Analysis of fluid structural instability in water
International Nuclear Information System (INIS)
Recent flow testing of stainless steel hardware in a high pressure/high temperature water environment produced an apparent fluid-structural instability. The source of instability was investigated by studying textbook theory and by performing NASTRAN finite element analyses. The modal analyses identified the mode that was being excited, but the flutter instability analysis showed that the design is stable if minimal structural damping is present. Therefore, it was suspected that the test hardware was the root cause of the instability. Further testing confirmed this suspicion
Rayleigh-Taylor instability in compressible fluids
Energy Technology Data Exchange (ETDEWEB)
Sturtevant, B. (California Inst. of Tech., Pasadena, CA (USA). Graduate Aeronautical Labs.)
1990-11-05
This is a report of the progress during the past year of the shock-tube study of the Richtmyer-Meshkov instability, initiated under the sponsorship of the Lawrence Livermore National Laboratory in September, 1982. The purpose of this research program, as stated in the original proposal, is: to investigate the nonlinear processes initiated by shock wave interaction with gas-gas interfaces. In particular, the nonlinear stage of shock-initiated Rayleigh-Taylor instability, the secondary instabilities (e.g., Kelvin-Helmholtz instability) arising therefrom and the concomitant mixing of the two fluids are of interest.''
Combustion instability modeling and analysis
Energy Technology Data Exchange (ETDEWEB)
Santoro, R.J.; Yang, V.; Santavicca, D.A. [Pennsylvania State Univ., University Park, PA (United States)] [and others
1995-10-01
It is well known that the two key elements for achieving low emissions and high performance in a gas turbine combustor are to simultaneously establish (1) a lean combustion zone for maintaining low NO{sub x} emissions and (2) rapid mixing for good ignition and flame stability. However, these requirements, when coupled with the short combustor lengths used to limit the residence time for NO formation typical of advanced gas turbine combustors, can lead to problems regarding unburned hydrocarbons (UHC) and carbon monoxide (CO) emissions, as well as the occurrence of combustion instabilities. Clearly, the key to successful gas turbine development is based on understanding the effects of geometry and operating conditions on combustion instability, emissions (including UHC, CO and NO{sub x}) and performance. The concurrent development of suitable analytical and numerical models that are validated with experimental studies is important for achieving this objective. A major benefit of the present research will be to provide for the first time an experimentally verified model of emissions and performance of gas turbine combustors.
Instability of a penetrating blade
Bigoni, D.; Bosi, F.; Dal Corso, F.; Misseroni, D.
2014-03-01
Application of a dead compressive load at the free end of an elastic rod (the ‘blade') induces its penetration into a sliding sleeve ending with a linear elastic spring. Bifurcation and stability analysis of this simple elastic system shows a variety of unexpected behaviors: (i) an increase of buckling load at decreasing of elastic stiffness; (ii) a finite number of buckling loads for a system with infinite degrees of freedom (leading to a non-standard Sturm-Liouville problem); (iii) more than one bifurcation load associated to each bifurcation mode; (iv) a restabilization of the straight configuration after the second bifurcation load associated to the first instability mode; (v) the presence of an Eshelby-like (or configurational) force, deeply influencing stability. Only the first of these behaviors was previously known, the second and third ones disprove common beliefs, the fourth highlights a sort of ‘island of instability', and the last one shows surprising phenomena and effects on stability.
Rogue Waves and Modulational Instability
Zakharov, V. E.; Dyachenko, A.
2015-12-01
The most plausible cause of rogue wave formation in a deep ocean is development of modulational instability of quasimonochromatic wave trains. An adequate model for study of this phenomenon is the Euler equation for potential flow of incompressible fluid with free surface in 2-D geometry. Numerical integration of these equations confirms completely the conjecture of rogue wave formation from modulational instability but the procedure is time consuming for determination of rogue wave appearance probability for a given shape of wave energy spectrum. This program can be realized in framework of simpler model using replacement of the exact interaction Hamiltonian by more compact Hamiltonian. There is a family of such models. The popular one is the Nonlinear Schrodinger equation (NLSE). This model is completely integrable and suitable for numerical simulation but we consider that it is oversimplified. It misses such important phenomenon as wave breaking. Recently, we elaborated much more reliable model that describes wave breaking but is as suitable as NLSE from the point of numerical modeling. This model allows to perform massive numerical experiments and study statistics of rogue wave formation in details.
Langmuir turbulence and modulational instability
International Nuclear Information System (INIS)
The authors discuss the turbulent state of an unmagnetized, completed ionized hydrogen plasma for the case when the electron temperature is much higher than the ion temperature so that the main modes to be considered are the Langmuir and ion-sound modes, while the transverse electromagnetic mode can for most purposes be neglected. The authors sketch Zakharov's derivation of the basic equations which in their linear form describe the three modes mentioned earlier and which describe the nonlinear modulational instability (M.I.). The linear analysis of the equations derived is given and it is shown that the decay instability of finite-amplitude Langmuir waves is fully covered by these equations. A brief discussion of various soliton-bearing equations such as the Kortweg-de Vries equation (KdV), the sine-Gordon equation (SG), and the non-linear Schroedinger equation (NLS) is given. It is shown that in three-dimensions soliton-like structures are unstable against adiabatic collapse, and the dynamics of such collapsing 'cavitons' are discussed. Finally, the few relevant experiments performed are discussed, and some ideas for future research are mentioned. (Auth.)
Hydrodynamic instabilities and neutron scattering
International Nuclear Information System (INIS)
The flow pattern in a liquid layer heated from below changes character as the vertical temperature gradient is increased. A review is given for the sequence of instabilities connected with the different flow regimes, with emphasis on their phase-transition aspects. Utilizing the coupling that exists between the molecular orientation and flow in a liquid crystal, we have used neutron scattering to explore these phenomena. The special features of liquid crystals in this respect are pointed out. Experiments near the lowest lying instability, the Rayleigh-Benard transition, verify the mean-field predictions for the change of the threshold gradient with the applied magnetic field, the behaviour of the order parameter (the fluid velocity) versus epsilon (the reduced gradient scale), the time-dependent growth and the critical slowing down of the growth rate of the order parameter. A pre-transitional tail of intensity is analysed within the same formalism and it is suggested that it arises from hydrodynamic fluctuations driven by the microscopic fluctuations of the liquid. Experiments at higher gradients reveal a time-periodic flow regime with frequencies down to cycles per hour. These observations lend support to modern theories for the transition to turbulence. (author)
Interfacial instabilities in vibrated fluids
Porter, Jeff; Laverón-Simavilla, Ana; Tinao Perez-Miravete, Ignacio; Fernandez Fraile, Jose Javier
2016-07-01
Vibrations induce a range of different interfacial phenomena in fluid systems depending on the frequency and orientation of the forcing. With gravity, (large) interfaces are approximately flat and there is a qualitative difference between vertical and horizontal forcing. Sufficient vertical forcing produces subharmonic standing waves (Faraday waves) that extend over the whole interface. Horizontal forcing can excite both localized and extended interfacial phenomena. The vibrating solid boundaries act as wavemakers to excite traveling waves (or sloshing modes at low frequencies) but they also drive evanescent bulk modes whose oscillatory pressure gradient can parametrically excite subharmonic surface waves like cross-waves. Depending on the magnitude of the damping and the aspect ratio of the container, these locally generated surfaces waves may interact in the interior resulting in temporal modulation and other complex dynamics. In the case where the interface separates two fluids of different density in, for example, a rectangular container, the mass transfer due to vertical motion near the endwalls requires a counterflow in the interior region that can lead to a Kelvin-Helmholtz type instability and a ``frozen wave" pattern. In microgravity, the dominance of surface forces favors non-flat equilibrium configurations and the distinction between vertical and horizontal applied forcing can be lost. Hysteresis and multiplicity of solutions are more common, especially in non-wetting systems where disconnected (partial) volumes of fluid can be established. Furthermore, the vibrational field contributes a dynamic pressure term that competes with surface tension to select the (time averaged) shape of the surface. These new (quasi-static) surface configurations, known as vibroequilibria, can differ substantially from the hydrostatic state. There is a tendency for the interface to orient perpendicular to the vibrational axis and, in some cases, a bulge or cavity is induced
Metals near a magnetic instability
International Nuclear Information System (INIS)
The ground state of a number of metals is in close proximity to a magnetic instability. In these metals, often pronounced deviations from Fermi-liquid behavior are observed, which are commonly referred to as non-Fermi-liquid (NFL) behavior. The scenario of incipient magnetic order is exemplified by CeCu6 with a nonmagnetic ground state, and long-range incommensurate antiferromagnetism in CeCu6-xAux for x > xc 0.1. The magnetic instability can be tuned by alloying or applying external pressure. At the quantum critical point (QCP), where the Neel temperature TN vanishes, the specific heat C varies as C/T ∝ ln(T/T0), independent of whether TN is tuned to zero by variation of x or p, and one observes a linear resistivity contribution Δρ ∝ T. These NFL features can be explained by quasi two-dimensional critical fluctuations, as observed for x = 0.1 with inelastic neutron scattering. In addition, unusual dynamic scaling laws are found in the vicinity of the QCP in CeCu6-xAux which are incompatible with simple spin-fluctuation scenarios. Here we compare in detail the QCP tuned by alloying with new data for x = 0.2, inducing a magnetic instability by a magnetic field. The observation that in case the specific heat and the resistivity at the critical field can be described by the three-dimensional spin fluctuation the latter scenario finds its correspondence in Lorentzian quasi-elastic linewidths observed with inelastic neutron scattering. The archetypal weak ferromagnet ZrZn2 has long been considered a candidate for p-wave superconductivity if samples can be made sufficiently pure. We recently found evidence for superconductivity in ZrZn2 single crystals of unpredicted purity. Surprisingly, superconductivity (with Tc ≅ 0.3 K) exists over the entire pressure range where ferromagnetism exists, and vanishes when ferromagnetism is suppressed at sufficiently high pressure
On hydrodynamic instability of the ozone layer
International Nuclear Information System (INIS)
We show that instability may be arisen when the large-scale waves propagate in the ozone layer of Earth's atmosphere. The instability criterion suitable both for the acoustic waves and for the Rossby waves is found. Moreover, the possibility of the spatially located dissipative Rossby vortical structures formation in this layer is established
Electron beam instabilities in gyrotron beam tunnels
International Nuclear Information System (INIS)
Electron beam instabilities occurring in a gyrotron electron beam can induce an energy spread which might significantly deteriorate the gyrotron efficiency. Three types of instabilities are considered to explain the important discrepancy found between the theoretical and experimental efficiency in the case of quasi-optical gyrotrons (QOG): the electron cyclotron maser instability, the Bernstein instability and the Langmuir instability. The low magnetic field gradient in drift tubes of QOG makes that the electron cyclotron maser instability can develop in the drift tube at very low electron beam currents. Experimental measurements show that with a proper choice of absorbing structures in the beam tunnel, this instability can be suppressed. At high beam currents, the electrostatic Bernstein instability can induce a significant energy spread at the entrance of the interaction region. The induced energy spread scales approximately linearly with the electron beam density and for QOG one observes that the beam density is significantly higher than the beam density of an equivalent cylindrical cavity gyrotron. (author) figs., tabs., refs
Travelling-wave-induced instability of structures
International Nuclear Information System (INIS)
The effect of transmission time of propagating disturbances on the dynamic instability of structures is discussed in this paper. Through a parametric study it is shown that for certain values of transmission time and wave frequency parameters, the structure may become dynamically unstable. An example is worked out, and graphical results depicting the regions of instability are presented
Comparison of instability theory with simulation results
International Nuclear Information System (INIS)
The results of a quantitative comparison between linear instability theory and simulation results for a third order charge fluctuation mode in a quadrupole - focused beam are summarized. The theory is found to provide a good account of the initial instability exhibited by the simulation computations
Cultural diversity, economic development and societal instability.
Directory of Open Access Journals (Sweden)
Daniel Nettle
Full Text Available BACKGROUND: Social scientists have suggested that cultural diversity in a nation leads to societal instability. However, societal instability may be affected not only by within-nation or alpha diversity, but also diversity between a nation and its neighbours or beta diversity. It is also necessary to distinguish different domains of diversity, namely linguistic, ethnic and religious, and to distinguish between the direct effects of diversity on societal instability, and effects that are mediated by economic conditions. METHODOLOGY/PRINCIPAL FINDINGS: We assembled a large cross-national dataset with information on alpha and beta cultural diversity, economic conditions, and indices of societal instability. Structural equation modeling was used to evaluate the direct and indirect effects of cultural diversity on economics and societal stability. Results show that different types and domains of diversity have interacting effects. As previously documented, linguistic alpha diversity has a negative effect on economic performance, and we show that it is largely through this economic mechanism that it affects societal instability. For beta diversity, the higher the linguistic diversity among nations in a region, the less stable the nation. But, religious beta diversity has the opposite effect, reducing instability, particularly in the presence of high linguistic diversity. CONCLUSIONS: Within-nation linguistic diversity is associated with reduced economic performance, which, in turn, increases societal instability. Nations which differ linguistically from their neighbors are also less stable. However, religious diversity between neighboring nations has the opposite effect, decreasing societal instability.
On the descriptions of beam instabilities
Maillard, Antoine
2016-01-01
We investigate two interesting features of beam instabilities in accelerators : First, we provide the equivalence between two models to describe transverse instabilities, the circulant matrix model (based on a longitudinal phase space discretization) and the Vlasov formalism. Secondly, we show how to derive dispersion integrals for transverse detuning effects in the Vlasov formalism, thus allowing for Landau damping mechanism.
Stability and instability in quantum mechanics
International Nuclear Information System (INIS)
This work is an attempt to describe the problem of stability and instabilities of quantum systems and involving very delicate experiments in molecular physics and solid state physics. A kind of transition to chaos occurs and few theoretical models have been proposed to investigate such a transition but it is better to use the term instabilities waiting for calling such an effect quantum chaos
Plasma instabilities in high electric fields
DEFF Research Database (Denmark)
Morawetz, K.; Jauho, Antti-Pekka
1994-01-01
expression is derived for the nonequilibrium dielectric function epsilon(K, omega). For certain values of momenta K and frequency omega, Imepsilon(K, omega) becomes negative, implying a plasma instability. This new instability exists only for strong electric fields, underlining its nonequilibrium origin....
On viscoelastic instability in polymeric filaments
DEFF Research Database (Denmark)
Rasmussen, Henrik Koblitz; Hassager, Ole
The 3D Lagrangian Integral Method is used to simulate the effects of surface tension on the viscoelastic end-plate instability, occuring in the rapid extension of some polymeric filaments between parallel plates. It is shovn that the surface tension delays the onset of the instability. Furthermore...
Cultural diversity, economic development and societal instability
Nettle, D.; Grace, J.B.; Choisy, M.; Cornell, H.V.; Guegan, J.-F.; Hochberg, M.E.
2007-01-01
Background. Social scientists have suggested that cultural diversity in a nation leads to societal instability. However, societal instability may be affected not only by within-nation on ?? diversity, but also diversity between a nation and its neighbours or ?? diversity. It is also necessary to distinguish different domains of diversity, namely linguistic, ethnic and religious, and to distinguish between the direct effects of diversity on societal instability, and effects that are mediated by economic conditions. Methodology/Principal Findings. We assembled a large cross-national dataset with information on ?? and ?? cultural diversity, economic conditions, and indices of societal instability. Structural equation modeling was used to evaluate the direct and indirect effects of cultural diversity on economics and societal stability. Results show that different type and domains of diversity have interacting effects. As previously documented, linguistic ?? diversity has a negative effect on economic performance, and we show that it is largely through this economic mechanism that it affects societal instability. For ?? diversity, the higher the linguistic diversity among nations in a region, the less stable the nation. But, religious ?? diversity has the opposite effect, reducing instability, particularly in the presence of high linguistic diversity. Conclusions. Within-nation linguistic diversity is associated with reduced economic performance, which, in turn, increases societal instability. Nations which differ linguistically from their neighbors are also less stable. However, religious diversity between, neighboring nations has the opposite effect, decreasing societal instability.
The Magnetoviscous-thermal Instability
Islam, Tanim
2011-01-01
Accretion flows onto underluminous black holes, such as Sagittarius A* at the center of our galaxy, are dilute (mildly collisional to highly collisionless), optically thin, and radiatively inefficient. Therefore, the accretion properties of such dilute flows are expected to be modified by their large viscosities and thermal conductivities. Second, turbulence within these systems needs to transport angular momentum as well as thermal energy generated through gravitational infall outwards in order to allow accretion to occur. This is in contrast to classical accretion flows, in which the energy generated through accretion down a gravitational well is locally radiated. In this paper, using an incompressible fluid treatment of an ionized gas, we expand on previous research by considering the stability properties of a magnetized rotating plasma wherein the thermal conductivity and viscosity are not negligible and may be dynamically important. We find a class of MHD instabilities that can transport angular momentum...
Short wavelength magnetic buoyancy instability
Mizerski, K A; Hughes, D W
2013-01-01
Magnetic buoyancy instability plays an important role in the evolution of astrophysical magnetic fields. Here we revisit the problem introduced by \\citet{Gilman_1970} of the short wavelength linear stability of a plane layer of compressible isothermal fluid permeated by a horizontal magnetic field of strength decreasing with height. Dissipation of momentum and magnetic field is neglected. By the use of a Rayleigh-Schr\\"odinger perturbation analysis, we explain in detail the limit in which the transverse horizontal wavenumber of the perturbation, denoted by $k$, is large (i.e.\\ short horizontal wavelength) and show that the fastest growing perturbations become localized in the vertical direction as $k$ is increased. The growth rates are determined by a function of the vertical coordinate $z$ since, in the large $k$ limit, the eigenmodes are strongly localized in the vertical direction. We consider in detail the case of two-dimensional perturbations varying in the directions perpendicular to the magnetic field,...
Instability Threshold “Hysteresis”
Directory of Open Access Journals (Sweden)
Agnes Muszynska
1999-01-01
Full Text Available The transient process which starts at the instability threshold of a rotor rotating in a fluid environment, and ends up in the limit cycle of self-excited vibrations known as fluid whirl or fluid whip, is discussed in this paper. A one-lateral-mode, isotropic, nonlinear model of the rotor with fluid interaction allows for exact particular solutions and an estimation of the transient process. The fluid interacting with the rotor is contained in a small radial clearance area, such as in bearings, seals, or rotor-to-stator clearances, and its effects are represented by fluid film radial stiffness, damping, and fluid inertia rotating at a different angular velocities.
Shear instabilities in granular flows.
Goldfarb, David J; Glasser, Benjamin J; Shinbrot, Troy
2002-01-17
Unstable waves have been long studied in fluid shear layers. These waves affect transport in the atmosphere and oceans, in addition to slipstream stability behind ships, aeroplanes and heat-transfer devices. Corresponding instabilities in granular flows have not been previously documented, despite the importance of these flows in geophysical and industrial systems. Here we report that breaking waves can form at the interface between two streams of identical grains flowing on an inclined plane downstream of a splitter plate. Changes in either the shear rate or the angle of incline cause such waves to appear abruptly. We analyse a granular flow model that agrees qualitatively with our experimental data; the model suggests that the waves result from competition between shear and extensional strains in the flowing granular bed. We propose a dimensionless shear number that governs the transition between steady and wavy flows. PMID:11797003
Evolution of genetic instability in heterogeneous tumors.
Asatryan, Ani D; Komarova, Natalia L
2016-05-01
Genetic instability is an important characteristic of cancer. While most cancers develop genetic instability at some stage of their progression, sometimes a temporary rise of instability is followed by the return to a relatively stable genome. Neither the reasons for these dynamics, nor, more generally, the role of instability in tumor progression, are well understood. In this paper we develop a class of mathematical models to study the evolutionary competition dynamics among different sub-populations in a heterogeneous tumor. We observe that despite the complexity of this multi-component and multi-process system, there is only a small number of scenarios expected in the context of the evolution of instability. If the penalty incurred by unstable cells (the decrease in the growth due to deleterious mutations) is high compared with the gain (the production rate of advantageous mutations), then instability does not evolve. In the opposite case, instability evolves and comes to dominate the system. In the intermediate parameter regime, instability is generated but later gives way to stable clones. Moreover, the model also informs us of the patterns of instability for cancer lineages corresponding to different stages of progression. It is predicted that mutations causing instability are merely "passengers" in tumors that have undergone only a small number of malignant mutations. Further down the path of carcinogenesis, however, unstable cells are more likely to give rise to the winning clonal wave that takes over the tumor and carries the evolution forward, thus conferring a causal role of the instability in such cases. Further, each individual clonal wave (i.e. cells harboring a fixed number of malignant driver mutations) experiences its own evolutionary history. It can fall under one of three types of temporal behavior: stable throughout, unstable to stable, or unstable throughout. Which scenario is realized depends on the subtle (but predictable) interplay among
Parametric instabilities in the LCGT arm cavity
Yamamoto, K.; Uchiyama, T.; Miyoki, S.; Ohashi, M.; Kuroda, K.; Numata, K.
2008-07-01
We evaluated the parametric instabilities of LCGT (Japanese interferometric gravitational wave detector project) arm cavity. The number of unstable modes of LCGT is 10-times smaller than that of Advanced LIGO (USA). Since the strength of the instabilities of LCGT depends on the mirror curvature more weakly than that of Advanced LIGO, the requirement of the mirror curvature accuracy is easier to be achieved. The difference in the parametric instabilities between LCGT and Advanced LIGO is because of the thermal noise reduction methods (LCGT, cooling sapphire mirrors; Advanced LIGO, fused silica mirrors with larger laser beams), which are the main strategies of the projects. Elastic Q reduction by the barrel surface (0.2 mm thickness Ta2O5) coating is effective to suppress instabilities in the LCGT arm cavity. Therefore, the cryogenic interferometer is a smart solution for the parametric instabilities in addition to thermal noise and thermal lensing.
Parametric instabilities in the LCGT arm cavity
Yamamoto, K; Miyoki, S; Ohashi, M; Kuroda, K; Numata, K
2008-01-01
We evaluated the parametric instabilities of LCGT (Japanese interferometric gravitational wave detector project) arm cavity. The number of unstable modes of LCGT is 10-times smaller than that of Advanced LIGO (U.S.A.). Since the strength of the instabilities of LCGT depends on the mirror curvature more weakly than that of Advanced LIGO, the requirement of the mirror curvature accuracy is easier to be achieved. The difference in the parametric instabilities between LCGT and Advanced LIGO is because of the thermal noise reduction methods (LCGT, cooling sapphire mirrors; Advanced LIGO, fused silica mirrors with larger laser beams), which are the main strategies of the projects. Elastic Q reduction by the barrel surface (0.2 mm thickness Ta$_2$O$_5$) coating is effective to suppress instabilities in the LCGT arm cavity. Therefore, the cryogenic interferometer is a smart solution for the parametric instabilities in addition to thermal noise and thermal lensing.
Aeroelastic instability problems for wind turbines
Energy Technology Data Exchange (ETDEWEB)
Hansen, M. E. [Wind Energy Department, Riso National Laboratory, Technical University of Denmark, Frederiksborgvej 399, DK-4000 Roskilde, (Denmark)
2007-09-05
This paper deals with the aeroelastic instabilities that have occurred and may still occur for modern commercial wind turbines: stall-induced vibrations for stall-turbines, and classical flutter for pitch-regulated turbines. A review of previous works is combined with derivations of analytical stability limits for typical blade sections that show the fundamental mechanisms of these instabilities. The risk of stall-induced vibrations is mainly related to blade airfoil characteristics, effective direction of blade vibrations and structural damping; whereas the blade tip speed, torsional blade stiffness and chordwise position of the center of gravity along the blades are the main parameters for flutter. These instability characteristics are exemplified by aeroelastic stability analyses of different wind turbines. The review of each aeroelastic instability ends with a list of current research issues that represent unsolved aeroelastic instability problems for wind turbines. (Author).
Control of interfacial instabilities using flow geometry
Al-Housseiny, Talal T.; Tsai, Peichun A.; Stone, Howard A.
2012-10-01
The displacement of one fluid by another is one of the most common processes involving interfacial instabilities. It is universally accepted that, in a uniform medium, flow displacement is unstable when a low-viscosity fluid invades a fluid of higher viscosity: the classical viscous fingering instability. Consequently, once fluid properties are specified, opportunities for control become very limited. However, real systems where displacement instabilities occur, such as porous structures, lung airways and printing devices, are rarely uniform. We find that the simplest heterogeneity--a gradient in the flow passage--can lead to fundamentally different displacement behaviours. We use this finding to either inhibit or trigger an instability and, hence, to devise a strategy to manipulate instabilities in fluid-fluid systems. The control setting we identify has a wide spectrum of applications ranging from small-scale technologies such as microfluidics to large-scale operations such as enhanced oil recovery.
Taming contact line instability for pattern formation
Deblais, A.; Harich, R.; Colin, A.; Kellay, H.
2016-08-01
Coating surfaces with different fluids is prone to instability producing inhomogeneous films and patterns. The contact line between the coating fluid and the surface to be coated is host to different instabilities, limiting the use of a variety of coating techniques. Here we take advantage of the instability of a receding contact line towards cusp and droplet formation to produce linear patterns of variable spacings. We stabilize the instability of the cusps towards droplet formation by using polymer solutions that inhibit this secondary instability and give rise to long slender cylindrical filaments. We vary the speed of deposition to change the spacing between these filaments. The combination of the two gives rise to linear patterns into which different colloidal particles can be embedded, long DNA molecules can be stretched and particles filtered by size. The technique is therefore suitable to prepare anisotropic structures with variable properties.
Treatment of the subject of tearing instability
International Nuclear Information System (INIS)
A simple approach is taken to the mechanics of potential instability associated with the steady tearing portion of J-Integral R-curves. The analysis is developed from simple examples of structural component (or test specimen) configurations with cracks, examining their instability possibilities individually, in order to draw more general conclusions about elastic-plastic cracking instability as contrasted to linear-elastic behavior. Finally, an attempt is made to model a more local cleavage-like instability for material in the fracture process zone just ahead of a crack tip. Results are then presented of a testing program which clearly demonstrates the appropriateness of the tearing instability analysis and which illustrates its broad potential for future application, as well as presenting guidelines for its further development. The material selected for analysis was Ni-Cr-Mo-V rotor steel
Surface instabilities during straining of anisotropic materials
DEFF Research Database (Denmark)
Legarth, Brian Nyvang; Richelsen, Ann Bettina
2006-01-01
The development of instabilities in traction-free surfaces is investigated numerically using a unit cell model. Full finite strain analyses are conducted using isotropic as well as anisotropic yield criteria and both plane strain tension and compression are considered. In the load range of tension...... investigated, it is found that isotropic plasticity can only predict surface instabilities if non-associated plastic flow is accounted for. However, for anisotropic plasticity a surface instability is observed for associated plastic flow if the principal axes of anisotropy coincide with the directions...... of principal overall strain. For other orientations surface instabilities are seen when non-associated plastic flow is taken into account. Compared to tension, smaller compressive deformations are needed in order to initiate a surface instability....
The modulational instability of colinear waves
International Nuclear Information System (INIS)
A brief review is given of the modulational instability of a single wave. Some aspects of the modulational instability of two colinear waves are then studied. In general, the waves are modulationally unstable with a maximal growth rate which is larger than the modulational growth rate of either wave alone. Moreover, waves which are modulationally stable by themselves are often unstable in the other's presence. This is true for both copropagating and counterpropagating waves. An important property of an instability is whether it is absolute of convective in nature. The modulational instability of two equal-amplitude copropagating waves is usually, but not always, convective. The modulational instability of two equal-amplitude counter-propagating waves is always absolute. Some applications of current interest are discussed. (orig.)
On modulational instability of turbulent spectra
International Nuclear Information System (INIS)
The character of the modulational instability of a Langmuir wave packet is usually assumed to be similar to that of the instability of a monochromatic pump Langmuir wave if the width of the packet is small when compared to the rate of the instability. This assumption has been confirmed only for the case corresponding to the ''hydrodynamical'' development of the modulational instability, i.e., for the case when the phase velocity of the modulational perturbations exceeds the ion thermal velocity. Here we consider the opposite case (when the phase velocity of the modulational perturbations is less than the ion thermal velocity) which corresponds to the ''static'' development of the instability. We demonstrate that the above assumption is valid for the situation considered. (orig.)
Rayleigh-Taylor instability in elastic solids.
Piriz, A R; Cela, J J López; Cortázar, O D; Tahir, N A; Hoffmann, D H H
2005-11-01
We present an analytical model for the Rayleigh-Taylor instability that allows for an approximate but still very accurate and appealing description of the instability physics in the linear regime. The model is based on the second law of Newton and it has been developed with the aim of dealing with the instability of accelerated elastic solids. It yields the asymptotic instability growth rate but also describes the initial transient phase determined by the initial conditions. We have applied the model to solid/solid and solid/fluid interfaces with arbitrary Atwood numbers. The results are in excellent agreement with previous models that yield exact solutions but which are of more limited validity. Our model allows for including more complex physics. In particular, the present approach is expected to lead to a more general theory of the instability that would allow for describing the transition to the plastic regime. PMID:16383751
Flowtran assessment for predicting flow instability
International Nuclear Information System (INIS)
FLOWTRAN is a thermal-hydraulic assembly code for simulating Savannah River Site (SRS) reactor assemblies and predicting flow instability. Reactor power and flow transient modelling is critical in determining safe operating limits at which a reactor could be shut down without damage to the fuel assemblies. FLOWTRAN models an individual assembly's thermal-hydraulic behavior and can determine the operating power limit to avoid flow instability when the flow regime through the assembly is single-phase. Tests were conducted at Columbia University in 1988--89 with downward flow through single tubes to examine fluid flow instability. FLOWTRAN cannot predict actual flow instability because it cannot model two-phase flow. FLOWTRAN modelled the heated tubes to predict Onset of Significant Voiding (OSV) using the Saha-Zuber's correlation modified for SRS reactors; data analyses for the Columbia tests showed that the modified correlation OSV is a conservative predictor for downward flow instability
Experimental study on low pressure flow instability
International Nuclear Information System (INIS)
The experiment was performed on the test loop (HRTL-5), which simulates the geometry and system design of the 5 MW reactor. The flow behavior for a wide range of inlet subcooling, in which the flow undergoes from single phase to two phase, is described in a natural circulation system at low pressure (p = 0.1, 0.24 MPa). Several kinds of flow instability, e.g. subcooled boiling instability, subcooled boiling induced flashing instability, pure flashing instability as well as flashing coupled density wave instability and high frequency flow oscillation, are investigated. The mechanism of flashing and flashing concerned flow instability, which has never been studied well in this field, is especially interpreted. The experimental results show that, firstly, for a low pressure natural circulation system the two phase flow is unstable in most of inlet subcooling conditions, the two phase stable flow can only be reached at very low inlet subcooling; secondly, at high inlet subcooling the flow instability is dominated by subcooled boiling in the heated section, and at middle inlet subcooling is dominated by void flashing in the adiabatic long riser; thirdly, in two phase stable flow region the condition for boiling out of the core, namely, single phase flow in the heated section, two phase flow in the riser due to vapor flashing, can be realized. The experimental results are very important for the design and accident analysis of the vessel and swimming pool type natural circulation nuclear heating reactor. (7 refs., 10 figs., 1 tab.)
Instability of refrigeration system - A review
International Nuclear Information System (INIS)
It is essential to ensure the stability for the normal operation of refrigeration systems. This paper reviews the researches on the theory and solutions of the instability of refrigeration systems. The instability of refrigeration systems includes two aspects: the two-phase flow instability in refrigeration system, the instability on refrigeration system control characteristics. As an inherent characteristic of two-phase evaporating flow, several separate explanations for the formation of oscillation of mixture-vapor transition point in the evaporation process by different scholars had been given but there is no general explanation till now. The investigation of instability on refrigeration system control characteristics focused on both static and dynamic researches. The minimum stable signal line theory, as a very important finding for the static instability of the evaporator and thermal expansion valve control loop, presented the different result to other researches. Dynamic researches on simulation and frequency-domain analysis provided various means for forecast and validation with considerable precision while their application range was still confined. With the development of variable capacity compressor and electronic expansion valve, further researches should be carried out to analyze the instability of the variable capacity refrigeration system with considering the influence of parameter coupling and control algorithm.
Instabilities of black strings and branes
Energy Technology Data Exchange (ETDEWEB)
Harmark, Troels [The Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen Oe (Denmark); Niarchos, Vasilis [Centre de Physique Theorique, Ecole Polytechnique, 91128 Palaiseau (France); Obers, Niels A [The Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen Oe (Denmark)
2007-04-21
We review recent progress on the instabilities of black strings and branes both for pure Einstein gravity as well as supergravity theories which are relevant for string theory. We focus mainly on Gregory-Laflamme instabilities. In the first part of the review, we provide a detailed discussion of the classical gravitational instability of the neutral uniform black string in higher-dimensional gravity. The uniform black string is part of a larger phase diagram of Kaluza-Klein black holes which will be discussed thoroughly. This phase diagram exhibits many interesting features including new phases, non-uniqueness and horizon-topology changing transitions. In the second part, we turn to charged black branes in supergravity and show how the Gregory-Laflamme instability of the neutral black string implies via a boost/U-duality map similar instabilities for non- and near-extremal smeared branes in string theory. We also comment on instabilities of D-brane bound states. The connection between classical and thermodynamic stability, known as the correlated stability conjecture, is also reviewed and illustrated with examples. Finally, we examine the holographic implications of the Gregory-Laflamme instability for a number of non-gravitational theories including Yang-Mills theories and little string theory. (topical review)
Instabilities of black strings and branes
International Nuclear Information System (INIS)
We review recent progress on the instabilities of black strings and branes both for pure Einstein gravity as well as supergravity theories which are relevant for string theory. We focus mainly on Gregory-Laflamme instabilities. In the first part of the review, we provide a detailed discussion of the classical gravitational instability of the neutral uniform black string in higher-dimensional gravity. The uniform black string is part of a larger phase diagram of Kaluza-Klein black holes which will be discussed thoroughly. This phase diagram exhibits many interesting features including new phases, non-uniqueness and horizon-topology changing transitions. In the second part, we turn to charged black branes in supergravity and show how the Gregory-Laflamme instability of the neutral black string implies via a boost/U-duality map similar instabilities for non- and near-extremal smeared branes in string theory. We also comment on instabilities of D-brane bound states. The connection between classical and thermodynamic stability, known as the correlated stability conjecture, is also reviewed and illustrated with examples. Finally, we examine the holographic implications of the Gregory-Laflamme instability for a number of non-gravitational theories including Yang-Mills theories and little string theory. (topical review)
Radiative heat transport instability in ICF plasmas
Rozmus, W.; Bychenkov, V. Yu.
2015-11-01
A laser produced high-Z plasma in which an energy balance is achieved due to radiation losses and radiative heat transfer supports ion acoustic wave instability. A linear dispersion relation is derived and instability is compared to the radiation cooling instability. This instability develops in the wide range of angles and wavenumbers with the typical growth rate on the order of cs/LT (cs is the sound speed, LT is the temperature scale length). In addition to radiation dominated systems, a similar thermal transport driven ion acoustic instability was found before in plasmas where the thermal transport coefficient depends on electron density. However, under conditions of indirect drive ICF experiments the driving term for the instability is the radiative heat flux and in particular, the density dependence of the radiative heat conductivity. A specific example of thermal Bremsstrahlung radiation source has been considered corresponding to a thermal conductivity coefficient that is inversely proportional to the square of local particle density. In the nonlinear regime this instability may lead to plasma jet formation and anisotropic x-ray generation.
Study of sausage instability in semiconductor plasma
International Nuclear Information System (INIS)
As a perturbation of the adiabatically compressed linear pinch, a theory of the sausage instability is developed on the basis of the magnetohydrodynamic equations of motion and the particle conservation combined with Maxwell's equations. A dispersion relation of the instability and the explicit dependence of wave parameters on the fields are obtained by linearizing the equations for axially symmetrical harmonic perturbation. The critical field between a convective and an absolute instability is numerically obtained, and spatial growth rates associated with the instability are also derived in its convectively unstable region. The excitation of the sausage instability is made in an impact ionized plasma of n-InSb. The linear pinch effect of the samples is confirmed through the magnetic field dependence of current-voltage characteristics, and sinusoidal coherent oscillations are observed after a complete confinement of a pinch without an external magnetic field. Oscillation frequencies and currents on the threshold of excitations are obtained for various samples as a function of the applied electric field. The stabilization of instability by an axial magnetic field is also investigated theoretically and experimentally. The possibility of the stabilization is discussed through an evaluation of the magnetic Reynolds number in an impact ionized plasma pinch, and the critical magnetic field is derived from the hydromagnetic energy principle of the stabilization. Waveforms of the excited instability are observed under various axial magnetic fields in order to find the critical magnetic field for stabilization. The developed theories of the sausage instability on the dispersion relation and on the stabilization by axial magnetic fields are in good qualitative and quantitative agreements with the experiments. It is found that the sausage instability is excited in an impact ionized plasma of n-InSb and is explained well by the developed theory. (J.P.N.)
Understanding carpal instability: a radiographic perspective.
Kani, Kimia Khalatbari; Mulcahy, Hyojeong; Chew, Felix S
2016-08-01
The wrist is disposed to a variety of instability patterns owing to its complex anatomical and biomechanical properties. Various classification schemes have been proposed to describe the different patterns of carpal instability, of which the Mayo classification is the most commonly used. Understanding the concepts and pertinent terminology of this classification scheme is important for the correct interpretation of images and optimal communication with referring physicians. Standard wrist radiographs are the first line of imaging in carpal instability. Additional information may be obtained with the use of stress radiographs and other imaging modalities. PMID:27085694
Two stream instabilities in degenerate quantum plasmas
Son, S
2013-01-01
The quantum mechanical effect on the plasma two-stream instability is studied based on the dielectric function approach. The analysis suggests that the degenerate plasma relevant to the inertial confinement fusion behaves differently from classical plasmas when the electron drift velocity is comparable to the Fermi velocity. For high wave vector comparable to the Fermi wave vector, the degenerate quantum plasma has larger regime of the two-stream instabilities than the classical plasma. A regime, where the plasma waves with the frequency larger than 1.5 times of the Langmuir wave frequency become unstable to the two-stream instabilities, is identified.
Analyses of cavitation instabilities in ductile metals
DEFF Research Database (Denmark)
Tvergaard, Viggo
Cavitation instabilities have been predicted for a single void in a ductile metal stressed under high triaxiality conditions. In experiments for a ceramic reinforced by metal particles a single dominant void has been observed on the fracture surface of some of the metal particles bridging a crack...... for the influence of such size-effects on cavitation instabilities are presented. When a metal contains a distribution of micro voids, and the void spacing compared to void size is not extremely large, the surrounding voids may affect the occurrence of a cavitation instability at one of the voids...
Nonlinear stage of the modulational instability
International Nuclear Information System (INIS)
The modulational instability of a broad spectrum of plasma waves with random phases is studied. Equations describing the inital stage of the instability are derived. Conditions for suppressing the instability are determined from these equations. The stabilizing effect is the scattering of plasmons by growing density perturbations. This scattering leads to an ergodic spectrum and weakens the stability condition. The possibility of a statistical description of Langmuir turbulence is discussed for the case of large amplitude and an arbitrary characteristic dimension for the modulational perturbations
Taylor Instability of Incompressible Liquids
Fermi, E.; von Neumann, J.
1955-11-01
A discussion is presented in simplified form of the problem of the growth of an initial ripple on the surface of an incompressible liquid in the presence of an acceleration, g, directed from the outside into the liquid. The model is that of a heavy liquid occupying at t = 0 the half space above the plane z = 0, and a rectangular wave profile is assumed. The theory is found to represent correctly one feature of experimental results, namely the fact that the half wave of the heavy liquid into the vacuum becomes rapidly narrower while the half wave pushing into the heavy liquid becomes more and more blunt. The theory fails to account for the experimental results according to which the front of the wave pushing into the heavy liquid moves with constant velocity. The case of instability at the boundary of 2 fluids of different densities is also explored. Similar results are obtained except that the acceleration of the heavy liquid into the light liquid is reduced.
Chromosomal instability determines taxane response.
Swanton, Charles; Nicke, Barbara; Schuett, Marion; Eklund, Aron C; Ng, Charlotte; Li, Qiyuan; Hardcastle, Thomas; Lee, Alvin; Roy, Rajat; East, Philip; Kschischo, Maik; Endesfelder, David; Wylie, Paul; Kim, Se Nyun; Chen, Jie-Guang; Howell, Michael; Ried, Thomas; Habermann, Jens K; Auer, Gert; Brenton, James D; Szallasi, Zoltan; Downward, Julian
2009-05-26
Microtubule-stabilizing (MTS) agents, such as taxanes, are important chemotherapeutics with a poorly understood mechanism of action. We identified a set of genes repressed in multiple cell lines in response to MTS agents and observed that these genes are overexpressed in tumors exhibiting chromosomal instability (CIN). Silencing 22/50 of these genes, many of which are involved in DNA repair, caused cancer cell death, suggesting that these genes are involved in the survival of aneuploid cells. Overexpression of these "CIN-survival" genes is associated with poor outcome in estrogen receptor-positive breast cancer and occurs frequently in basal-like and Her2-positive cases. In diploid cells, but not in chromosomally unstable cells, paclitaxel causes repression of CIN-survival genes, followed by cell death. In the OV01 ovarian cancer clinical trial, a high level of CIN was associated with taxane resistance but carboplatin sensitivity, indicating that CIN may determine MTS response in vivo. Thus, pretherapeutic assessment of CIN may optimize treatment stratification and clinical trial design using these agents. PMID:19458043
Linear theory of drift instability
International Nuclear Information System (INIS)
Drift wave instability was studied theoretically. Low frequency waves are influenced by plasma inhomogeneity when the phase velocity of the waves perpendicular to magnetic field is comparable to the drift velocity. The low-ν plasma in a homogeneous magnetic field B parallel to z-axis was considered for the analysis, and it was assumed that the plasma density varies along X-axis. Electrostatic fluctuations were assumed. The dispersion relation of drift waves was derived from the continuity equation of ions. If Coulomb collisions or resonant particles prevent electrons from following the Boltzmann distribution, various free energy sources make the drift waves unstable. The effects of resonant particles and finite Larmor radii were examined with the Vlasov equation. The stability analysis of the drift mode in a sheared magnetic field has been one of the important objects of thermonuclear fusion researches. A model magnetic field was considered and analyzed. The stability of the drift mode in toroidal systems was studied. (Kato, T.)
Valence instabilities in cerium intermetallics
International Nuclear Information System (INIS)
The primary purpose of this investigation was to study the magnetic behaviour of cerium in intermetallic compounds, that show an IV behaviour, e.g. CeSn3. In the progress of the investigations, it became of interest to study the effect of changes in the lattice of the IV compound by substituting La or Y for Ce, thus constituting the Cesub(1-x)Lasub(x)Sn3 and Cesub(1-x)Ysub(x)Sn3 quasibinary systems. A second purpose was to examine the possibility of introducing instabilities in the valency of a trivalent intermetallic cerium compound: CeIn3, also by La and Y-substitutions in the lattice. Measurements on the resulting Cesub(1-x)Lasub(x)In3 and Cesub(1-x)Ysub(x)In3 quasibinaries are described. A third purpose was to study the (gradual) transition from a trivalent cerium compound into an IV cerium compound. This was done by examining the magnetic properties of the CeInsub(x)Snsub(3-x) and CePbsub(x)Snsub(3-x) systems. Finally a new possibility was investigated: that of the occurrence of IV behaviour in CeSi2, CeSi, and in CeGa2. (Auth.)
Careers in conditions of instability
Directory of Open Access Journals (Sweden)
Hohlova Valentina Vasil'evna
2016-04-01
Full Text Available The purpose of this work is the research of the social-economic phenomenon of a career as a result of conscious human position and behaviour in the field of employment, which is connected with job and professional growth, as a chain of events which are components of life, the sequence of professional activities and other biographical roles, which all together express the commitment of a person’s activity according to his generalized model of self-development. On the basis of the theoretical analysis the dependence of making a career in the condition of instability and indefiniteness on job market flexibility, erosion and even the destruction of the usual way of life and labor relations. The career concepts under the conditions of flexible capitalism and of career policy as the typology of empiric differences of job biographic models are considered. The peculiarity of the proposed career policy concept is that its individual alternatives of career making oppose to organization management and personal demands: the difference between a professional’s wishes and a specific strategy of the development phases are quite noticeable. According to the results of empiric research carried out through the methods of interview, polling, expert assessment, the analysis of the received results, the mathematical data processing the basic types of the career policy and its connection with the organization’s personal development are revealed.
Instability of viscoelastic compound jets
Ye, Han-Yu; Yang, Li-Jun; Fu, Qing-Fei
2016-04-01
This paper investigates the axisymmetric instability of a viscoelastic compound jet, for which the constitutive relation is described by the Oldroyd B model. It is found that a viscoelastic compound jet is more unstable than a Newtonian compound jet, regardless of whether the viscoelastic compound jet is inner-Newtonian-outer-viscoelastic, inner-viscoelastic-outer-Newtonian, or fully viscoelastic. It is also found that an increase in the stress relaxation time of the inner or outer fluid renders the jet more unstable, while an increase in the time constant ratio makes the jet less unstable. An analysis of the energy budget of the destabilization process is performed, in which a formulation using the relative rate of change of energy is adopted. The formulation is observed to provide a quantitative analysis of the contribution of each physical factor (e.g., release of surface energy and viscous dissipation) to the temporal growth rate. The energy analysis reveals the mechanisms of various trends in the temporal growth rate, including not only how the growth rate changes with the parameters, but also how the growth rate changes with the wavenumber. The phenomenon of the dispersion relation presenting two local maxima, which occurred in previous research, is explained by the present energy analysis.
Pulsational-Pair Instability Supernovae
Woosley, S E
2016-01-01
The final evolution of stars in the mass range 60 - 150 solar masses is explored. Depending upon their mass loss and rotation rates, many of these stars will end their lives as pulsational pair-instability supernovae. Even a non-rotating 70 solar mass star is pulsationally unstable during oxygen shell burning and can power a sub-luminous supernova. Rotation decreases the limit further. For more massive stars, the pulsations are less frequent, span a longer time, and are more powerful. Violent pulsations eject not only any residual low density envelope, but also that fraction of the helium core mass outside about 35 - 50 solar masses. The remaining core of helium and heavy elements continues to evolve, ultimately forming an iron core of about 2.5 solar masses that probably collapses to a black hole. A variety of observational transients result with total durations ranging from days to 10,000 years, and luminosities from 10$^{41}$ to 10$^{44}$ erg s$^{-1}$. Many transients resemble ordinary Type IIp supernovae,...
Condition for convective instability of dark solitons
International Nuclear Information System (INIS)
Simple derivation of the condition for the transition point from absolute instability of plane dark solitons to their convective instability is suggested. It is shown that unstable wave packet expands with velocity equal to the minimal group velocity of the disturbance waves propagating along a dark soliton. The growth rate of the length of dark solitons generated by the flow of Bose-Einstein condensate past an obstacle is estimated. Analytical theory is confirmed by the results of numerical simulations. -- Highlights: → Conditions for absolute or convective instability of dark solitons are derived. → Velocity of expansion of instability front equals to the minimal group velocity. → Growth rate of length of dark solitons generated by the flow is estimated.
E region instabilities in the polar ionosphere
International Nuclear Information System (INIS)
Some typical examples of electron-density profiles are presented and discussed. The instabilities observed in different cases of horizontal and vertical gradients of density, are analysed and an attempt of explanation is made
Aeroelastic instability problems for wind turbines
DEFF Research Database (Denmark)
Hansen, Morten Hartvig
2007-01-01
stiffness and chordwise position of the center of gravity along the blades are the main parameters for flutter. These instability characteristics are exemplified by aeroelastic stability analyses of different wind turbines. The review of each aeroelastic instability ends with a list of current research......This paper deals with the aeroelostic instabilities that have occurred and may still occur for modem commercial wind turbines: stall-induced vibrations for stall-turbines, and classical flutter for pitch-regulated turbines. A review of previous works is combined with derivations of analytical...... stability limits for typical blade sections that show the fundamental mechanisms of these instabilities. The risk of stall-induced vibrations is mainly related to blade airfoil characteristics, effective direction of blade vibrations and structural damping, whereas the blade tip speed, torsional blade...
Interfacial fluid instabilities and Kapitsa pendula
Krieger, Madison Ski
2015-01-01
The onset and development of instabilities is one of the central problems in fluid mechanics. Here we develop a connection between instabilities of free fluid interfaces and inverted pendula. When acted upon solely by the gravitational force, the inverted pendulum is unstable. This position can be stabilised by the Kapitsa phenomenon, in which high-frequency low-amplitude vertical vibrations of the base creates a fictitious force which opposes the gravitational force. By transforming the dynamical equations governing a fluid interface into an appropriate pendulum, we demonstrate how stability can be induced in fluid systems by properly tuned vibrations. We construct a "dictionary"-type relationship between various pendula and the classical Rayleigh-Taylor, Kelvin-Helmholtz, Rayleigh-Plateau and the self-gravitational instabilities. This makes several results in control theory and dynamical systems directly applicable to the study of "tunable" fluid instabilities, where the critical wavelength depends on the e...
Axial instability of rotating relativistic stars
Friedman, J L; Friedman, John L.; Morsink, Sharon M.
1998-01-01
Perturbations of rotating relativistic stars can be classified by their behavior under parity. For axial perturbations (r-modes), initial data with negative canonical energy is found with angular dependence $e^{im\\phi}$ for all values of $m\\geq 2$ and for arbitrarily slow rotation. This implies instability (or marginal stability) of such perturbations for rotating perfect fluids. This low $m$-instability is strikingly different from the instability to polar perturbations, which sets in first for large values of $m$. The timescale for the axial instability appears, for small angular velocity $\\Omega$, to be proportional to a high power of $\\Omega$. As in the case of polar modes, viscosity will again presumably enforce stability except for hot, rapidly rotating neutron stars. This work complements Andersson's numerical investigation of axial modes in slowly rotating stars.
Plasma equilibrium and instabilities in tokamaks
International Nuclear Information System (INIS)
A phenomenological introduction of some of the main theoretical and experimental features on equilibrium and instabilities in tokamaks is presented. In general only macroscopic effects are considered, being the plasma described as a fluid. (L.C.)
Shear instabilities in shallow-water magnetohydrodynamics
Mak, Julian; Hughes, D W
2016-01-01
Within the framework of shallow-water magnetohydrodynamics, we investigate the linear instability of horizontal shear flows, influenced by an aligned magnetic field and stratification. Various classical instability results, such as H{\\o}iland's growth rate bound and Howard's semi-circle theorem, are extended to this shallow-water system for quite general profiles. Two specific piecewise-constant velocity profiles, the vortex sheet and the rectangular jet, are studied analytically and asymptotically; it is found that the magnetic field and stratification (as measured by the Froude number) are generally both stabilising, but weak instabilities can be found at arbitrarily large Froude number. Numerical solutions are computed for corresponding smooth velocity profiles, the hyperbolic-tangent shear layer and the Bickley jet, for a uniform background field. A generalisation of the long-wave asymptotic analysis of Drazin & Howard (1962) is employed in order to understand the instability characteristics for both ...
Cancer chromosomal instability: therapeutic and diagnostic challenges
McGranahan, Nicholas; Burrell, Rebecca A.; Endesfelder, David; Novelli, Marco R; Swanton, Charles
2012-01-01
This review provides a much-needed translational perspective into the issue of aneuploidy and chromosomal instability, discussing the prognostic value of CIN assessment in human tumours, methods to analyze it and how it could be therapeutically targeted.
Size-effects on cavitation instabilities
DEFF Research Database (Denmark)
Niordson, Christian Frithiof; Tvergaard, Viggo
2005-01-01
growth is here analyzed for such cases. A finite strain generalization of a higher order strain gradient plasticity theory is applied for a power-law hardening material, and the numerical analyses are carried out for an axisymmetric unit cell containing a spherical void. In the range of high stress......In metal-ceramic systems the constraint on plastic flow leads to so high stress triaxialities that cavitation instabilities may occur. If the void radius is on the order of magnitude of a characteristic length for the metal, the rate of void growth is reduced, and the possibility of unstable cavity...... triaxiality, where cavitation instabilities are predicted by conventional plasticity theory, such instabilities are also found for the nonlocal theory, but the effects of gradient hardening delay the onset of the instability. Furthermore, in some cases the cavitation stress reaches a maximum and then decays...
On nonlinear development of beam instability
International Nuclear Information System (INIS)
Radiation-resonance interactions are taken into account in the problem of dynamics of an electron beam inb plasma. The beam characteristics to be taken into account are determined. Stabilization conditions for beam instability are established
The universal instability in general geometry
Energy Technology Data Exchange (ETDEWEB)
Helander, P.; Plunk, G. G. [Max-Planck-Institut für Plasmaphysik, Wendelsteinstr. 1, 17491 Greifswald (Germany)
2015-09-15
The “universal” instability has recently been revived by Landreman et al. [Phys. Rev. Lett. 114, 095003 (2015)], who showed that it indeed exists in plasma geometries with straight (but sheared) magnetic field lines. Here, it is demonstrated analytically that this instability can be presented in more general sheared and toroidal geometries. In a torus, the universal instability is shown to be closely related to the trapped-electron mode, although the trapped-electron drive is usually dominant. However, this drive can be weakened or eliminated, as in the case in stellarators with the maximum-J property, leaving the parallel Landau resonance to drive a residual mode, which is identified as the universal instability.
The universal instability in general geometry
International Nuclear Information System (INIS)
The “universal” instability has recently been revived by Landreman et al. [Phys. Rev. Lett. 114, 095003 (2015)], who showed that it indeed exists in plasma geometries with straight (but sheared) magnetic field lines. Here, it is demonstrated analytically that this instability can be presented in more general sheared and toroidal geometries. In a torus, the universal instability is shown to be closely related to the trapped-electron mode, although the trapped-electron drive is usually dominant. However, this drive can be weakened or eliminated, as in the case in stellarators with the maximum-J property, leaving the parallel Landau resonance to drive a residual mode, which is identified as the universal instability
An hydrodynamic shear instability in stratified disks
Dubrulle, B; Normand, C; Richard, D; Hersant, F; Zahn, J P; Normand, Ch.
2004-01-01
We discuss the possibility that astrophysical accretion disks are dynamically unstable to non-axisymmetric disturbances with characteristic scales much smaller than the vertical scale height. The instability is studied using three methods: one based on the energy integral, which allows the determination of a sufficient condition of stability, one using a WKB approach, which allows the determination of the necessary and sufficient condition for instability and a last one by numerical solution. This linear instability occurs in any inviscid stably stratified differential rotating fluid for rigid, stress-free or periodic boundary conditions, provided the angular velocity $\\Omega$ decreases outwards with radius $r$. At not too small stratification, its growth rate is a fraction of $\\Omega$. The influence of viscous dissipation and thermal diffusivity on the instability is studied numerically, with emphasis on the case when $d \\ln \\Omega / d \\ln r =-3/2$ (Keplerian case). Strong stratification and large diffusivit...
Hydrodynamic instability in eccentric astrophysical discs
Barker, Adrian J
2014-01-01
Eccentric Keplerian discs are believed to be unstable to three-dimensional hydrodynamical instabilities driven by the time-dependence of fluid properties around an orbit. These instabilities could lead to small-scale turbulence, and ultimately modify the global disc properties. We use a local model of an eccentric disc, derived in a companion paper, to compute the nonlinear vertical ("breathing mode") oscillations of the disc. We then analyse their linear stability to locally axisymmetric disturbances for any disc eccentricity and eccentricity gradient using a numerical Floquet method. In the limit of small departures from a circular reference orbit, the instability of an isothermal disc is explained analytically. We also study analytically the small-scale instability of an eccentric neutrally stratified polytropic disc with any polytropic index using a WKB approximation. We find that eccentric discs are generically unstable to the parametric excitation of small-scale inertial waves. The nonlinear evolution o...
Instability in hydraulic machines demonstration rig
Muszynska, A.; Braun, M. J.
1985-01-01
In fluid flow machines, the working fluid involved in rotative motion due to shaft rotation significantly modifies the rotor synchronous response. This can result in the rotor maintaining the high vibration amplitude that occurs at resonance over an extended rotative speed range. The phase changes in this range are typically very small. The fluid may also create rotor instability, i.e., subsynchronous self-excited vibrations, when the rotative speed is sufficiently high. This rotor instability is often related and increases with higher rotor unbalance (Opposite to other types of instability such as oil whirl/whip, internal friction, etc.). The rotor rig demonstrates typical dynamic behavior of hydraulic machines. At lower speeds the effect of amplitude/phase mentioned above is noticeable; at higher speeds the subsynchronous instability occurs.
Magnetorotational decay instability in Keplerian disks.
Shtemler, Yuri; Liverts, Edward; Mond, Michael
2013-12-01
The saturation of the magnetorotational instability (MRI) in thin Keplerian disks through three-wave resonant interactions is introduced and discussed. That mechanism is a natural generalization of the fundamental decay instability discovered five decades ago for infinite, homogeneous, and immovable plasmas. The decay instability relies on the energy transfer from the MRI to stable slow Alfvén-Coriolis as well as magnetosonic waves. A second-order forced Duffing amplitude equation for the initially unstable MRI as well as two first-order equations for the other two waves are derived. The solutions of those equations exhibit bounded bursty nonlinear oscillations for the MRI as well as unbounded growth for the linearly stable slow Alfvén-Coriolis and magnetosonic perturbations, thus giving rise to the magnetorotational decay instability. PMID:24476249
Elliptical instability in terrestrial planets and moons
Cébron, David; Moutou, Claire; Gal, Patrice Le; 10.1051/0004-6361/201117741
2012-01-01
The presence of celestial companions means that any planet may be subject to three kinds of harmonic mechanical forcing: tides, precession/nutation, and libration. These forcings can generate flows in internal fluid layers, such as fluid cores and subsurface oceans, whose dynamics then significantly differ from solid body rotation. In particular, tides in non-synchronized bodies and libration in synchronized ones are known to be capable of exciting the so-called elliptical instability, i.e. a generic instability corresponding to the destabilization of two-dimensional flows with elliptical streamlines, leading to three-dimensional turbulence. We aim here at confirming the relevance of such an elliptical instability in terrestrial bodies by determining its growth rate, as well as its consequences on energy dissipation, on magnetic field induction, and on heat flux fluctuations on planetary scales. Previous studies and theoretical results for the elliptical instability are re-evaluated and extended to cope with ...
Bankart Repair to Correct Shoulder Instability
Full Text Available ... instability, or the shoulder dislocating again with other activities. Nonetheless, we always approach these patients first with physical therapy and rehab. So, Joe, maybe if you ...
Bankart Repair to Correct Shoulder Instability
Full Text Available ... Hospital. Over the next hour you'll see a Bankart repair to correct shoulder instability. Bankart lesions ... three small incisions. You'll also hear from a patient who has undergone the surgery, and meet ...
Magnetorotational Explosive Instability in Keplerian Disks
Shtemler, Yuri; Mond, Michael
2015-01-01
In this paper it is shown that deferentially rotating disks that are in the presence of weak axial magnetic field are prone to a new nonlinear explosive instability. The latter occurs due to the near-resonance three-wave interactions of a magnetorotational instability with stable Alfven-Coriolis and magnetosonic modes. The dynamical equations that govern the temporal evolution of the amplitudes of the three interacting modes are derived. Numerical solutions of the dynamical equations indicate that small frequency mismatch gives rise to two types of behavior: 1. explosive instability which leads to infinite values of the three amplitudes within a finite time, and 2. bounded irregular oscillations of all three amplitudes. Asymptotic solutions of the dynamical equations are obtained for the explosive instability regimes and are shown to match the numerical solutions near the explosion time.
Can dust coagulation trigger streaming instability?
Drazkowska, Joanna
2014-01-01
Streaming instability can be a very efficient way of overcoming growth and drift barriers to planetesimal formation. However, it was shown that strong clumping, which leads to planetesimal formation, requires a considerable number of large grains. State-of-the-art streaming instability models do not take into account realistic size distributions resulting from the collisional evolution of dust. We investigate whether a sufficient quantity of large aggregates can be produced by sticking and what the interplay of dust coagulation and planetesimal formation is. We develop a semi-analytical prescription of planetesimal formation by streaming instability and implement it in our dust coagulation code based on the Monte Carlo algorithm with the representative particles approach. We find that planetesimal formation by streaming instability may preferentially work outside the snow line, where sticky icy aggregates are present. The efficiency of the process depends strongly on local dust abundance and radial pressure g...
Early Prevention Method for Power Systems Instability
DEFF Research Database (Denmark)
Dmitrova, Evgenia
a given operational conditions and predicts the resulting stability margins for the new steady state, while avoiding time consuming time domain simulations. The method has been validated on the Western Danish power system model, containing 464 buses. The case study of aperiodic small signal angular......In the scope of this work, a method capable of fast identification of the proper countermeasure, that prevents emerging instability, has been developed. The focus is placed on the prevention of aperiodic small signal angular instability by means of manipulations applied to load nodes (nodes...... instability was created. Utilizing synthetic PMU data, the early prevention method proposed a location and an amount of the countermeasure which will prevent instability; the prediction of the resulting stability margins corresponding to application of the suggested countermeasure was carried out. The...
Bankart Repair to Correct Shoulder Instability
Full Text Available BANKART REPAIR TO CORRECT SHOULDER INSTABILITY AKRON CHILDREN'S HOSPITAL AKRON, OHIO February 21, 2008 00:00:11 NARRATOR: Welcome to Akron Children's Hospital. Over the next hour you'll see a ...
Double contrast CT diagnosis of shoulder instability
International Nuclear Information System (INIS)
Purpose: To study clinical importance of double contrast CT arthrography in the diagnosis of shoulder instability. Materials and methods: Eight patients were diagnosed as having shoulder instability with double contrast CT. The technique involved injection of 4 ml, 76% urografin and 10 ml of room air through an anterior shoulder puncture. The CT images were obtained with the patients supine and prone position. Results: The results of the CT arthrography were confirmed during the surgical operation afterward. The characteristics of abnormal double contrast CT arthrograms. They included anterior labral tear: the rounded anterior glenoid labrum, detached anterior labrum and anterior labral fragment; anterior capsular stripping off the anterior scapular glenoid neck; and enlargement of anterior and posterior capsular stripping off the anterior scapular glenoid neck; and enlargement of anterior and posterior capsular cavity. Conclusion: The current CT arthrography provides important X-ray information for both diagnosis of shoulder instability and anatomical repair of shoulder instability
Model of surface instabilities induced by stress
Mueller, Judith; Grant, Martin
1998-01-01
We propose a model based on a Ginzburg-Landau approach to study a strain relief mechanism at a free interface of a non-hydrostatically stressed solid, commonly observed in thin-film growth. The evolving instability, known as the Grinfeld instability, is studied numerically in two and three dimensions. Inherent in the description is the proper treatment of nonlinearities. We find these nonlinearities can lead to competitive coarsening of interfacial structures, corresponding to different waven...
Electromechanical instability in suspended carbon nanotubes
Jonsson, L. M.; Gorelik, L. Y.; Shekhter, R. I.; Jonson, M.
2005-01-01
We have theoretically investigated electromechanical properties of freely suspended carbon nanotubes when a current is injected into the tubes using a scanning tunneling microscope. We show that a shuttle-like electromechanical instability can occur if the bias voltage exceeds a dissipation-dependent threshold value. An instability results in large amplitude vibrations of the carbon nanotube bending mode, which modify the current-voltage characteristics of the system.
Convective Instabilities in Two Liquid Layers
McFadden, G. B.; Coriell, S. R.; Gurski, K. F.; Cotrell, D. L.
2007-01-01
We perform linear stability calculations for horizontal fluid bilayers, taking into account both buoyancy effects and thermocapillary effects in the presence of a vertical temperature gradient. To help understand the mechanisms driving the instability, we have performed both long-wavelength and short-wavelength analyses. The mechanism for the large wavelength instability is complicated, and the detailed form of the expansion is found to depend on the Crispation and Bond numbers. The system al...
Dispersion Instability in Strongly Interacting Electron Liquids
Zhang, Ying; Yakovenko, V. M.; Sarma, S. Das
2004-01-01
We show that the low-density strongly interacting electron liquid, interacting via the long-range Coulomb interaction, could develop a dispersion instability at a critical density associated with the approximate flattening of the quasiparticle energy dispersion. At the critical density the quasiparticle effective mass diverges at the Fermi surface, but the signature of this Fermi surface instability manifests itself away from the Fermi momentum at higher densities. For densities below the cri...
Energetic particle instabilities in fusion plasmas
Sharapov, S E; Berk, H L; Borba, D N; Breizman, B N; Challis, C D; Classen, I G J; Edlund, E M; Eriksson, J; Fasoli, A; Fredrickson, E D; Fu, G Y; Garcia-Munoz, M; Gassner, T; Ghantous, K; Goloborodko, V; Gorelenkov, N N; Gryaznevich, M P; Hacquin, S; Heidbrink, W W; Hellesen, C; Kiptily, V G; Kramer, G J; Lauber, P; Lilley, M K; Lisak, M; Nabais, F; Nazikian, R; Nyqvist, R; Osakabe, M; von Thun, C Perez; Pinches, S D; Podesta, M; Porkolab, M; Shinohara, K; Schoepf, K; Todo, Y; Toi, K; Van Zeeland, M A; Voitsekhovich, I; White, R B; Yavorskij, V; TG, ITPA EP; Contributors, JET-EFDA
2013-01-01
Remarkable progress has been made in diagnosing energetic particle instabilities on present-day machines and in establishing a theoretical framework for describing them. This overview describes the much improved diagnostics of Alfven instabilities and modelling tools developed world-wide, and discusses progress in interpreting the observed phenomena. A multi-machine comparison is presented giving information on the performance of both diagnostics and modelling tools for different plasma conditions outlining expectations for ITER based on our present knowledge.
Studies of elastic-plastic instabilities
DEFF Research Database (Denmark)
Tvergaard, Viggo
1999-01-01
Analyses of plastic instabilities are reviewed, with focus on results in structural mechanics as well as continuum mechanics. First the basic theories for bifurcation and post-bifurcation behavior are briefly presented. Then, localization of plastic flow is discussed, including shear band formation...... in solids, localized necking in biaxially stretched metal sheets, and the analogous phenomenon of buckling localization in structures. Also some recent results for cavitation instabilities in elastic-plastic solids are reviewed....
Global Financial Instability: Framework, Events, Issues
Mishkin, Frederic S.
1999-01-01
Two of the key questions facing policymakers today are how to reduce the risk of global financial instability and how to cope with it when it occurs. This paper starts by defining financial instability and then showing how it harms economic activity. It then uses this framework to describe what happened during the recent financial crises in Mexico and East Asia. The paper ends by raising several key policy issues; not coincidentally, these issues are addressed in the remaining papers in the s...
Two stream instabilities in degenerate quantum plasmas
Son, S.
2013-01-01
The quantum mechanical effect on the plasma two-stream instability is studied based on the dielectric function approach. The analysis suggests that the degenerate plasma relevant to the inertial confinement fusion behaves differently from classical plasmas when the electron drift velocity is comparable to the Fermi velocity. For high wave vector comparable to the Fermi wave vector, the degenerate quantum plasma has larger regime of the two-stream instabilities than the classical plasma. A reg...
Delayed chromosomal instability induced by DNA damage.
Marder, B A; Morgan, W. F.
1993-01-01
DNA damage induced by ionizing radiation can result in gene mutation, gene amplification, chromosome rearrangements, cellular transformation, and cell death. Although many of these changes may be induced directly by the radiation, there is accumulating evidence for delayed genomic instability following X-ray exposure. We have investigated this phenomenon by studying delayed chromosomal instability in a hamster-human hybrid cell line by means of fluorescence in situ hybridization. We examined ...
Computational methods for probability of instability calculations
Wu, Y.-T.; Burnside, O. H.
1990-01-01
This paper summarizes the development of the methods and a computer program to compute the probability of instability of a dynamic system than can be represented by a system of second-order ordinary linear differential equations. Two instability criteria based upon the roots of the characteristics equation or Routh-Hurwitz test functions are investigated. Computational methods based on system reliability analysis methods and importance sampling concepts are proposed to perform efficient probabilistic analysis. Numerical examples are provided to demonstrate the methods.
Elliptical instability of compressible flow in ellipsoids
Clausen, N.; A. Tilgner
2014-01-01
Context. Elliptical instability is due to a parametric resonance of two inertial modes in a fluid velocity field with elliptical streamlines. This flow is a simple model of the motion in a tidally deformed, rotating body. Elliptical instability typically leads to three-dimensional turbulence. The associated turbulent dissipation together with the dissipation of the large scale mode may be important for the synchronization process in stellar and planetary binary systems. Aims. In order to ...
Regional Banking Instability and FOMC Voting
Eichler, Stefan; Lähner, Tom; Noth, Felix
2016-01-01
This study analyzes if regionally affiliated Federal Open Market Committee (FOMC) members take their districts' regional banking sector instability into account when they vote. Considering the period from 1978 to 2010, we find that a deterioration in a district's bank health increases the probability that this district's representative in the FOMC votes to ease interest rates. According to member-specific characteristics, the effect of regional banking sector instability on FOMC voting behavi...
Perception and self-organized instability
Friston, Karl,; Breakspear, Michael; Deco, Gustavo
2012-01-01
This paper considers state-dependent dynamics that mediate perception in the brain. In particular, it considers the formal basis of self-organized instabilities that enable perceptual transitions during Bayes-optimal perception. The basic phenomena we consider are perceptual transitions that lead to conscious ignition (Dehaene and Changeux, 2011) and how they depend on dynamical instabilities that underlie chaotic itinerancy (Breakspear, 2001; Tsuda, 2001) and self-organized criticality (Begg...
Studies of elastic-plastic instabilities
DEFF Research Database (Denmark)
Tvergaard, Viggo
1999-01-01
Analyses of plastic instabilities are reviewed, with focus on results in structural mechanics as well as continuum mechanics. First the basic theories for bifurcation and post-bifurcation behavior are briefly presented. Then, localization of plastic flow is discussed, including shear band formati...... in solids, localized necking in biaxially stretched metal sheets, and the analogous phenomenon of buckling localization in structures. Also some recent results for cavitation instabilities in elastic-plastic solids are reviewed....
A hydrodynamic approach to QGP instabilities
Calzetta, E
2013-01-01
We show that the usual linear analysis of QGP Weibel instabilities based on the Maxwell-Boltzmann equation may be reproduced in a purely hydrodynamic model. The latter is derived by the Entropy Production Variational Method from a transport equation including collisions, and can describe highly nonequilibrium flow. We find that, as expected, collisions slow down the growth of Weibel instabilities. Finally, we discuss the strong momentum anisotropy limit.
Systematics of shoulder instability; Systematik der Schulterinstabilitaet
Energy Technology Data Exchange (ETDEWEB)
Kreitner, K.F.; Maehringer-Kunz, A. [Johannes-Gutenberg-Universitaet Mainz, Klinik und Poliklinik fuer Diagnostische und Interventionelle Radiologie, Mainz (Germany)
2015-03-01
Shoulder instability is defined as a symptomatic abnormal motion of the humeral head relative to the glenoid during active shoulder motion. Glenohumeral instabilities are classified according to the causative factors as the pathogenesis of instability plays an important role with respect to treatment options. Instabilities are classified into traumatic and atraumatic instabilities as part of a multidirectional instability syndrome and into microtraumatic instabilities. For diagnostics plain radiographs (''trauma series'') are performed to document shoulder dislocation and its successful repositioning. Direct magnetic resonance (MR) arthrography is the most important imaging modality for delineation of the different injury patterns of the labral-ligamentous complex and bony structures. Monocontrast computed tomography (CT) arthrography with the use of multidetector CT scanners represents an alternative imaging modality; however, MR imaging should be preferred in the work-up of shoulder instabilities due to the mostly younger age of patients. (orig.) [German] Unter einer Schulterinstabilitaet versteht man jede zu Beschwerden fuehrende Translation des Humeruskopfs in Relation zur Gelenkpfanne waehrend einer aktiven Bewegung der Schulter. Glenohumerale Instabilitaeten werden heute nach ihrer Aetiologie eingeteilt, da bei der Wahl der Therapie der Entstehungsmechanismus der Instabilitaet eine wichtige Rolle spielt. Danach unterscheidet man primaer traumatisch von atraumatisch entstandenen Instabilitaeten sowie Mikroinstabilitaeten. Bei der Diagnostik dienen konventionelle Roentgenuebersichtsaufnahmen nur noch zur Dokumentation einer Luxation und zur Beurteilung der Reposition. Die durch eine Instabilitaet hervorgerufenen Verletzungsfolgen am labroligamentaeren Komplex und den knoechernen Strukturen werden heute bevorzugt mit der direkten MR-Arthrographie dargestellt. Hierbei koennen unterschiedliche Verletzungsmuster dargestellt werden. Nach
Studies on electron cloud instability in BEPCⅡ
Institute of Scientific and Technical Information of China (English)
LIU Yu-Dong; YUE Jun-Hui; WANG Na
2009-01-01
Electron Cloud Instability has been studied in the operation of BEPC.The BEPC Ⅱ began the commissioning in November 2006 and the positron beam current has reached 500 mA.Because of such a high beam current,some instabilities such as ECI,bunch lengthening et al,have appeared during the operation.The experimental investigation on ECI during the commissioning of BEPC Ⅱ will be reported in this paper.
Instabilities and shape analyses of elastic shells
Knoche, Sebastian
2014-01-01
This thesis presents research results on the deformation of elastic shells, especially concerning buckling and wrinkling instabilities. The theoretical description of such deformations is used to develop methods of shape analysis, which serve to infer material properties from simple experimental observations of deformed shells. When an initially spherical shell is deflated, two successive instabilities can typically be observed. In a first buckling transition, an axisymmetric dimple appears....
Modulational instability and spatiotemporal transition to chaos
International Nuclear Information System (INIS)
The one-dimensional generalized modified complex Ginzburg-Landau equation [Malomed BA, Stenflo L. J Phys A: Math Gen 1991;24:L1149] is considered. The linear stability analysis is used in order to derive the conditions for modulational instability. We obtained the generalized Lange and Newell's criterion for modulational instability. Numerical simulation shows the validity of the analytical approach. The model presents a rich variety of patterns propagating in the system and a spatiotemporal transition to chaos
Relativistically modulational instability by strong Langmuir waves
Energy Technology Data Exchange (ETDEWEB)
Liu, X. L.; Liu, S. Q. [Department of Physics, Nanchang University, Jiangxi, Nanchang 330031 (China); Li, X. Q. [Department of Physics, Nanjing Normal University, Nanjing 210097 (China)
2012-09-15
Based on the set of nonlinear coupling equations, which has considered the relativistic effects of electrons, modulational instability by strong Langmuir waves has been investigated in this paper. Both the characteristic scale and maximum growth rate of the Langmuir field will enhance with the increase in the electron relativistic effect. The numerical results indicate that longitudinal perturbations induce greater instability than transverse perturbations do, which will lead to collapse and formation of the pancake-like structure.
ON THE INSTABILITY OF THE RAILWAY VEHICLES
Directory of Open Access Journals (Sweden)
Traian MAZILU
2011-11-01
Full Text Available The railway vehicles have two sources of instability. The most common is the hunting induced by the reversed conic shape of the rolling surfaces of the wheels. The other one is related by the anomalous Doppler effect that can occurs when the train velocity exceeds the phase velocity of the waves induced in the track structure. Some aspects regarding the two sources of instability are presented.
Microbunching Instability Modeling in the SPARX configurations
International Nuclear Information System (INIS)
The modeling of the microbunching instability has been carried out for the SPARX FEL accelerator, two configurations have been considered and compared: hybrid compression scheme (velocity bunching plus magnetic compressor) and purely magnetic. The effectiveness of a lattice tuning together with the use of a laser heather has been exploited to reduce the instability drawbacks on the electron beam quality. Analytical predictions and start to end simulation results are reported in this paper.
The relationship between modulational instability and oscillating two-stream instability
International Nuclear Information System (INIS)
The stability of a finite-amplitude monochromatic Langmuir wave is considered in one dimension. A dispersion relation is obtained which includes the decay, purely growing and modulational instabilities. It is shown that for an infinite-wavelength Langmuir pump wave the modulational and oscillating two-stream instabilities are the same. It is also pointed out that the threshold for the modulational instability is equal to the threshold for the inverse oscillating two-stream instability, in which the Langmuir wave energy is converted into electromagnetic radiation. (author)
On the chiral imbalance and Weibel instabilities
Kumar, Avdhesh; Bhatt, Jitesh R.; Kaw, P. K.
2016-06-01
We study the chiral-imbalance and the Weibel instabilities in presence of the quantum anomaly using the Berry-curvature modified kinetic equation. We argue that in many realistic situations, e.g. relativistic heavy-ion collisions, both the instabilities can occur simultaneously. The Weibel instability depends on the momentum anisotropy parameter ξ and the angle (θn) between the propagation vector and the anisotropy direction. It has maximum growth rate at θn = 0 while θn = π / 2 corresponds to a damping. On the other hand the pure chiral-imbalance instability occurs in an isotropic plasma and depends on difference between the chiral chemical potentials of right and left-handed particles. It is shown that when θn = 0, only for a very small values of the anisotropic parameter ξ ∼ξc, growth rates of the both instabilities are comparable. For the cases ξc < ξ ≪ 1 or ξ ≳ 1 at θn = 0, the Weibel modes dominate over the chiral-imbalance instability if μ5 / T ≤ 1. However, when μ5 / T ≥ 1, it is possible to have dominance of the chiral-imbalance modes at certain values of θn for an arbitrary ξ.
Resistive instabilities in toroidal confinement
International Nuclear Information System (INIS)
Low-m tearing modes constitute the dominant instability problem in present-day tokamaks. In this paper, the stability criteria for representative current profiles with q(0) values in the vicinity of unity are reviewed; sawtooth reconnection to q(0) values just at, or slightly exceeding, unity is generally destabilizing to the m = 2, n = 2 and m = 3, n = 2 modes and limits the range of stable profile shapes. Major disruptions can be produced by the simultaneous growth of m = 2, n = 1 and m = 3, n = 2 magnetic islands, leading to destabilization of higher-order modes and to the overlapping of several island chains. Internal disruptions---or sawteeth---arise in a variety of forms other than that produced by the classically reconnecting m = 1 mode. In some case, the q(r) value is apparently close to unity over a large central part of the plasma; in other cases, the q(0) value remains substantially below unity throughout a sawtooth cycle. Toroidal effects are sufficient to stabilize the resistive m = 1 mode in the latter case. Feedback stabilization of m ≥ 2 modes by rf heating or current drive, applied locally at the magnetic islands, appears feasible; feedback by island current drive is much more efficient, in terms of the radio-frequency power required, than feedback by island heating. Feedback stabilization of the m = 1 resistive mode---although yielding particularly beneficial effects for resistive-tearing and high-beta stability by allowing q(0) values substantially below unity---is more problematical, unless the m = 1 ideal MHD mode can be given sufficient positive stability. This appears possible, however, either by strong triangular shaping of the central flux surfaces or by appropriate tailoring of the current profile in the vicinity of the q = 1 surface
Two-stream instability model with electrons trapped in quadrupoles
Channell, P. J.
2009-08-01
We formulate the theory of the two-stream instability (e-cloud instability) with electrons trapped in quadrupole magnets. We show that a linear instability theory can be sensibly formulated and analyzed. The growth rates are considerably smaller than the linear growth rates for the two-stream instability in drift spaces and are close to those actually observed.
Two-stream instability model with electrons trapped in quadrupoles
Energy Technology Data Exchange (ETDEWEB)
Channell, P J [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)], E-mail: pchannell@lanl.gov
2009-08-15
We formulate the theory of the two-stream instability (e-cloud instability) with electrons trapped in quadrupole magnets. We show that a linear instability theory can be sensibly formulated and analyzed. The growth rates are considerably smaller than the linear growth rates for the two-stream instability in drift spaces and are close to those actually observed.
Shoulder instability : A clinical and MRI-based analysis
Salomonsson, Björn
2009-01-01
Shoulder instability is a common but complex and challenging area of shoulder pathology, and new diagnostic methods and treatments are continuously developed. We conducted this study to evaluate the clinical outcome of shoulder instability with respect to different diagnostic possibilities and surgical treatments. We have studied the patient material from our department, consisting of atraumatic instability, posttraumatic recurrent anterior instability, and primary shoul...
Modulational instability in a plasma-filled magnetized waveguide
International Nuclear Information System (INIS)
Theoretical investigation into effect of plasma restriction on modulational instability development in magnetized plasma waveguide with perfectly conducting walls is conducted in hydrodynamic approximation. Conditions for instability occurrence are found and the area of its development is specified. Expressions for this instability increment are obtained. It is shown that an area of wave phase rates exists for which modulational instability does not develop
Beam-Ion Instability in PEP-II
Energy Technology Data Exchange (ETDEWEB)
Heifets, S.; Kulikov, A.; Wang, Min-Huey; Wienands, U.; /SLAC
2007-11-07
The instability in the PEP-II electron ring has been observed while reducing the clearing gap in the bunch train. We study the ion effects in the ring summarizing existing theories of the beam-ion interaction, comparing them with observations, and estimating effect on luminosity in the saturation regime. Considering the gap instability we suggest that the instability is triggered by the beam-ion instability, and discuss other mechanisms pertinent to the instability.
Model of oscillatory instability in vertically-homogeneous atmosphere
Rutkevich, P. B.; Rutkevych, P. P.
2009-01-01
Existence and repeatability of tornadoes could be straightforwardly explained if there existed instability, responsible for their formation. However, it is well known that convection is the only instability in initially stable air, and the usual convective instability is not applicable for these phenomena. In the present paper we describe an instability in the atmosphere, which can be responsible for intense vortices. This instability appears in a fluid with Coriolis force and dissipation and...
Multiphase Instabilities in Explosive Dispersal of Particles
Rollin, Bertrand; Ouellet, Frederick; Annamalai, Subramanian; Balachandar, S. ``Bala''
2015-11-01
Explosive dispersal of particles is a complex multiphase phenomenon that can be observed in volcanic eruptions or in engineering applications such as multiphase explosives. As the layer of particles moves outward at high speed, it undergoes complex interactions with the blast-wave structure following the reaction of the energetic material. Particularly in this work, we are interested in the multiphase flow instabilities related to Richmyer-Meshkov (RM) and Rayleigh-Taylor (RM) instabilities (in the gas phase and particulate phase), which take place as the particle layer disperses. These types of instabilities are known to depend on initial conditions for a relatively long time of their evolution. Using a Eulerian-Lagrangian approach, we study the growth of these instabilities and their dependence on initial conditions related to the particulate phase - namely, (i) particle size, (ii) initial distribution, and (iii) mass ratio (particles to explosive). Additional complexities associated with compaction of the layer of particles are avoided here by limiting the simulations to modest initial volume fraction of particles. A detailed analysis of the initial conditions and its effects on multiphase RM/RT-like instabilities in the context of an explosive dispersal of particles is presented. This work was supported by the U.S. Department of Energy, National Nuclear Security Administration, Advanced Simulation and Computing Program, as a Cooperative Agreement under the Predictive Science Academic Alliance Program, Contract No. DE-NA0002378.
Kelvin-Helmholtz instabilities with Godunov SPH
Cha, Seung-Hoon; Nayakshin, Sergei
2009-01-01
Numerical simulations for the non-linear development of Kelvin-Helmholtz instability in two different density layers have been performed with the particle-based method (Godunov SPH) developed by Inutsuka (2002). The Godunov SPH can describe the Kelvin-Helmholtz instability even with a high density contrast, while the standard SPH shows the absence of the instability across a density gradient (Agertz et al. 2007). The interaction of a dense blob with a hot ambient medium has been performed also. The Godunov SPH describes the formation and evolution of the fingers due to the combinations of Rayleigh-Taylor, Richtmyer-Meshkov, and Kelvin-Helmholtz instabilities. The blob test result coincides well with the results of the grid-based codes. An inaccurate handling of a density gradient in the standard SPH has been pointed out as the direct reason of the absence of the instabilities. An unphysical force happens at the density gradient even in a pressure equilibrium, and repulses particles from the initial density di...
Tidal instability in exoplanetary systems evolution
Directory of Open Access Journals (Sweden)
Le Gal P.
2011-02-01
Full Text Available A new element is proposed to play a role in the evolution of extrasolar planetary systems: the tidal (or elliptical instability. It comes from a parametric resonance and takes place in any rotating ﬂuid whose streamlines are (even slightly elliptically deformed. Based on theoretical, experimental and numerical works, we estimate the growth rate of the instability for hot-jupiter systems, when the rotation period of the star is known. We present the physical process, its application to stars, and preliminary results obtained on a few dozen systems, summarized in the form of a stability diagram. Most of the systems are trapped in the so-called "forbidden zone", where the instability cannot grow. In some systems, the tidal instability is able to grow, at short timescales compared to the system evolution. Implications are discussed in the framework of misaligned transiting systems, as the rotational axis of the star would be unstable in systems where this elliptical instability grows.
Radiologic signs of detrusor instability in children
International Nuclear Information System (INIS)
Purpose: To revalue radiologic signs of detrusor instability in children. Material and Methods: Retrospective analysis of videourodynamic studies performed in 85 children consulting for urinary incontinence and/or infection. Patients were free from neuropathic diseases, alterations of the urinary tract, previous surgery or anticholinergic treatment. Images of the bladder coinciding to the peaks of unstable detrusor contractions in patients with unstable bladders, and those at the end of filling in stable bladders were analyzed. Results: Bladder outlets were open in 38 patients and close in 47. Detrusor instability was found in 97 % of those with an open bladder outlet and in 36 % when close. Bladder outlets were open in all cases with contractions stronger than 60 cm.water. All 'spinning-top' urethras were associated to contractions stronger than 70 cm.water. Most false negatives (close bladder outlet in unstable bladders) corresponded to contractions lower than 30 cm.water. Different shapes of the bladder were found irrespective of detrusor instability. Conclusions: 1) An open bladder outlet observed during bladder filling is a reliable sign of significant detrusor instability in children without neuropathy; 2) It is highly specific of instability; 3) Most false negatives coincide with low amplitude contractions; 4) 'Spinning-top' images indicate strong contractions. (author)
On the Chiral imbalance and Weibel Instabilities
Kumar, Avdhesh; Kaw, Predhiman K
2016-01-01
We study the chiral-imbalance and the Weibel instabilities in presence of the quantum anomaly using the Berry-curvature modified kinetic equation. We argue that in many realistic situations, e.g. relativistic heavy-ion collisions, both the instabilities can occur simultaneously. The Weibel instability depends on the momentum anisotropy parameter $\\xi$ and the angle ($\\theta_n$) between the propagation vector and the anisotropy direction. It has maximum growth rate at $\\theta_n=0$ while $\\theta_n=\\pi/2$ corresponds to a damping. On the other hand the pure chiral-imbalance instability occurs in an isotropic plasma and depends on difference between the chiral chemical potentials of right and left-handed particles. It is shown that when $\\theta_n=0$, only for a very small values of the anisotropic parameter $\\xi\\sim \\xi_c$, growth rates of the both instabilities are comparable. For the cases $\\xi_c<\\xi\\ll1$, $\\xi\\approx 1$ or $\\xi \\geq 1$ at $\\theta_n=0$, the Weibel modes dominate over the chiral-imbalance ins...
Instability localization with artificial neural networks (ANNs)
International Nuclear Information System (INIS)
The aim of this piece of research is to investigate the potential of artificial neural networks (ANNs) for tackling the problem of instability localization. The instability is modeled by a variable strength absorber (point-source) in a two-dimensional bare reactor model with a one neutron-energy group. The proposed approach constitutes an exercise in simplicity in that: (1) an arbitrarily simplified model is employed for ANN training and validation; (2) few training and validation patterns of low complexity are utilized; (3) the ANN inputs are derived directly from the neutron noise signals, the proposed location of instability is given on-line via an uncomplicated combination of ANN outputs; (4) the ANN architecture is independent of the number of possible locations of instability. In fact, unlike previous approaches which employ hundreds of outputs (one for each fuel assembly), only two ANN outputs are employed representing the X- and Y-coordinates (location) of instability; (5) the responses of only a few detectors are employed; (6) a measure of confidence in the prediction is assigned. The results of ANN testing, which is performed on patterns from both actual and simplified models, are reported and analyzed
Kinetic Simulations of Rayleigh-Taylor Instabilities
Sagert, Irina; Bauer, Wolfgang; Colbry, Dirk; Howell, Jim; Staber, Alec; Strother, Terrance
2014-09-01
We report on an ongoing project to develop a large scale Direct Simulation Monte Carlo code. The code is primarily aimed towards applications in astrophysics such as simulations of core-collapse supernovae. It has been tested on shock wave phenomena in the continuum limit and for matter out of equilibrium. In the current work we focus on the study of fluid instabilities. Like shock waves these are routinely used as test-cases for hydrodynamic codes and are discussed to play an important role in the explosion mechanism of core-collapse supernovae. As a first test we study the evolution of a single-mode Rayleigh-Taylor instability at the interface of a light and a heavy fluid in the presence of a gravitational acceleration. To suppress small-wavelength instabilities caused by the irregularity in the separation layer we use a large particle mean free path. The latter leads to the development of a diffusion layer as particles propagate from one fluid into the other. For small amplitudes, when the instability is in the linear regime, we compare its position and shape to the analytic prediction. Despite the broadening of the fluid interface we see a good agreement with the analytic solution. At later times we observe the development of a mushroom like shape caused by secondary Kelvin-Helmholtz instabilities as seen in hydrodynamic simulations and consistent with experimental observations.
Coherent Instabilities of ILC Damping Ring
Energy Technology Data Exchange (ETDEWEB)
Heifets, S.; Stupakov, G.; Bane, K.; /SLAC
2006-09-27
The paper presents the first attempt to estimates the ILC damping ring impedance and compare thresholds of the classical instabilities for several designs initially proposed for the DR. The work was carried out in the spring of 2006. Since then the choice of the DR is narrowed. Nevertheless, the analysis described may be useful for the next iterations of the beam stability. Overall, the conventional instabilities will have little impact on the ring performance provided the careful design of the ring minimizes the impedance below acceptable level indicated above. The only exception is the transverse CB instability. The longitudinal CB is less demanding. However, even the transverse CB instability would have threshold current above nominal provided the aperture in the wigglers is increased from 8 mm to 16 mm. The microwave instability needs more studies. Nevertheless, we should remember that the ILC DR is different from existing high-current machines at least in two respects: absence of the beam-beam tune spread stabilizing beams in colliders, and unusual strict requirements for low emittance. That may cause new problems such as bunch emittance dilution due to high-frequency wakes (BPMs, grooves), etc. Even if such a possibility exists, it probably universal for all machines and ought be addressed in the design of vacuum components rather than have effect on the choice of the machine design.
Effects of electron temperature anisotropy on proton mirror instability evolution
Ahmadi, Narges; Raeder, Joachim
2016-01-01
Proton mirror modes are large amplitude nonpropagating structures frequently observed in the magnetosheath. It has been suggested that electron temperature anisotropy can enhance the proton mirror instability growth rate while leaving the proton cyclotron instability largely unaffected, therefore causing the proton mirror instability to dominate the proton cyclotron instability in Earth's magnetosheath. Here, we use particle-in-cell simulations to investigate the electron temperature anisotropy effects on proton mirror instability evolution. Contrary to the hypothesis, electron temperature anisotropy leads to excitement of the electron whistler instability. Our results show that the electron whistler instability grows much faster than the proton mirror instability and quickly consumes the electron free energy, so that there is no electron temperature anisotropy left to significantly impact the evolution of the proton mirror instability.
Electromagnetic heavy-ion/proton instabilities
International Nuclear Information System (INIS)
Ion/ion instabilities are driven by the relative velocity v0 of two distinct ion components. This manuscript reports linear theory and simulation studies of electromagnetic ion/ion instabilities for a warm proton component streaming against a cool, heavy ion component in a homogeneous, magnetized, collisionless plasma in which v0 is parallel or antiparallel to the background magnetic field. Under these conditions linear Vlasov dispersion theory predicts that the fastest growing mode is usually the right-hand polarized proton resonant instability. Two-dimensional initial value hybrid simulations of this growing mode are carried out, yielding scaling relations for the maximum fluctuating magnetic field energy density and the proton pickup time. The latter is proportional to the inverse of the maximum growth rate for a wide range of plasma parameters. (c) 1999 American Geophysical Union
Bunched beam longitudinal instability: Coherent dipole motion
International Nuclear Information System (INIS)
In this paper, the authors present a new formulation for the longitudinal coherent dipole motion, where a quadrature response of the environmental impedance is shown to be the effective longitudinal impedance for the beam instability. The Robinson-Pedersen formulation for the longitudinal dipole motion is also presented, the difference of the two approaches is discussed in the comparison. The results by using the Sacherer integral equation for the coherent dipole motion can generate the same results as by using the other two approaches, except for a scaling difference. The formulation is further generalized to the rigid bunch motion using signal analysis method, where a form factor shows up naturally. Finally, the formulation is applied to solve the coupled bunch instabilities. Examples of the AGS Booster and the AGS coupled bunch instabilities are used to illustrate the applications of the formulation
Kinematical and Dynamical Approaches to Gravitational Instability
Bertschinger, E
1993-01-01
This paper reviews the essential physics of gravitational instability in a Robertson-Walker background spacetime. Three approaches are presented in a pedagogical manner, based on (1) the Eulerian fluid equations, (2) the Lagrangian description of trajectories, and (3) the Lagrangian fluid equations. Linear and nonlinear limits are discussed for each case. Shear and tides are shown to play a key role in nonlinear gravitational instability. The Lagrangian fluid approach is used to show that several widely held beliefs about gravitational instability are false. The following collapse theorem is proven: for a given initial density fluctuation and growth rate, the spherical tophat perturbation collapses more slowly than any other configuration. We also show that density maxima are not the first points to collapse and that underdense regions may collapse if their initial shear is sufficiently high. The Lagrangian fluid approach leads to an almost closed set of local evolution equations for individual mass elements....
Instabilities in non-expanding glasma
Fujii, H; Iwazaki, A
2009-01-01
A homogeneous color magnetic field is known to be unstable for the fluctuations perpendicular to the field in the color space (the Nielsen-Olesen instability). We argue that these unstable modes, exponentially growing, generate an azimuthal magnetic field with the original field being in the $z$-direction, which causes the Nielsen-Olesen instability for another type of fluctuations. The growth rate of the latter unstable mode increases with the momentum $p_z$ and can become larger than the former's growth rate which decreases with increasing $p_z$. These features may explain the interplay between the primary and secondary instabilities observed in the real-time simulation of a non-expanding glasma, i.e., stochastically generated anisotropic Yang-Mills fields without expansion.
Knee instability scores for ACL reconstruction.
Rahnemai-Azar, Ata A; Naendrup, Jan-Hendrik; Soni, Ashish; Olsen, Adam; Zlotnicki, Jason; Musahl, Volker
2016-06-01
Despite abundant biological, biomechanical, and clinical research, return to sport after anterior cruciate ligament (ACL) injury remains a significant challenge. Residual rotatory knee laxity has been identified as one of the factors responsible for poor functional outcome. To improve and standardize the assessment of knee instability, a variety of instability scoring systems is available. Recently, devices to objectively quantify static and dynamic clinical exams have been developed to complement traditional subjective grading systems. These devices enable an improved evaluation of knee instability and possible associated injuries. This additional information may promote the development of new treatment algorithms and allow for individualized treatment. In this review, the different subjective laxity scores as well as complementary objective measuring systems are discussed, along with an introduction of injury to an individualized treatment algorithm. PMID:26980119
Elbow joint instability: A kinematic model.
Olsen, B S; Henriksen, M G; Søjbjerg, J O; Helmig, P; Sneppen, O
1994-05-01
The effect of simultaneous ulnar and radial collateral ligament division on the kinematics of the elbow joint is studied in a cadaveric model. Severance of the anterior part of the ulnar collateral ligament and the annular ligament led to significant elbow joint instability in valgus and varus stress and in forced external and internal rotation. The mean maximum laxity in valgus stress and forced external rotation were 5.7° and 13.2°. The forearms of the elbow joint specimens were transfixed in maximum pronation. During valgus and varus stress the corresponding spontaneous ulnar rotation of the specimens was recorded. The reproducibility of the instability pattern suggests that this model is suitable for evaluating stabilizing procedures aimed at correction of elbow joint instability before these procedures are introduced into patient care. PMID:22959690
Nodal analysis of two-phase instabilities
International Nuclear Information System (INIS)
Nodal models having moving nodal boundaries have been developed for the analysis of two-phase flow instabilities in a boiling channel. The first model, which was based on a Galerkin method for the discretization, has been found to be accurate in the prediction of the onset of instabilities as well as the frequency of oscillations. This model however, had some problems with the prediction of chaotic phenomena and did not allow for flow reversal in the channel. A second nodal model, based on a finite difference approach, has been found to perform better for the prediction of non-linear response and it also allows for flow reversal. Both models are numerically more efficient than the existing fixed grid models for instabilities analysis
Twisted magnetic structures emerging from buoyancy instabilities
Jouve, L; Proctor, M R E
2012-01-01
We here report calculations of magnetic buoyancy instabilities of a sheared magnetic layer where two separate zones are unstable. The idea is to study the possible generation of large-scale helical structures which could then rise through a stellar convection zone and emerge at the surface to create active regions. The calculations shown here are a follow-up of the work of Favier et al. (2012) where the instability developed in a weakly magnetized atmosphere, consisting of a uniform field oriented in a different direction from the unstable layer below. Here, the top layer representing the atmosphere is itself unstable to buoyancy instabilities and thus quickly creates a more complex magnetic configuration with which the layer below will interact. We also find in this case that the accumulation of magnetic tension between the two unstable layers favors the creation of large-scale helical structures.
Twisted magnetic structures emerging from buoyancy instabilities
Jouve, L.; Silvers, L. J.; Proctor, M. R. E.
2012-12-01
We here report calculations of magnetic buoyancy instabilities of a sheared magnetic layer where two separate zones are unstable. The idea is to study the possible generation of large-scale helical structures which could then rise through a stellar convection zone and emerge at the surface to create active regions. The calculations shown here are a follow-up of the work of Favier et al. (2012) where the instability developed in a weakly magnetized atmosphere, consisting of a uniform field oriented in a different direction from the unstable layer below. Here, the top layer representing the atmosphere is itself unstable to buoyancy instabilities and thus quickly creates a more complex magnetic configuration with which the layer below will interact. We also find in this case that the accumulation of magnetic tension between the two unstable layers favors the creation of large-scale helical structures.
Buoyancy Instabilities in Degenerate, Collisional, Magnetized Plasmas
Chang, P
2009-01-01
In low-collisionality plasmas, anisotropic heat conduction due to a magnetic field leads to buoyancy instabilities for any nonzero temperature gradient. We study analogous instabilities in degenerate {\\it collisional} plasmas, i.e., when the electron collision frequency is large compared to the electron cyclotron frequency. Although heat conduction is nearly isotropic in this limit, the small residual anisotropy ensures that collisional degenerate plasmas are also convectively unstable independent of the sign of the temperature gradient. We show that the range of wavelengths that are unstable is independent of the magnetic field strength, while the growth time increases with decreasing magnetic field strength. We discuss the application of these collisional buoyancy instabilities to white dwarfs and neutron stars. Magnetic tension and the low specific heat of a degenerate plasma significantly limit their effectiveness; the most promising venues for growth are in the liquid oceans of young, weakly magnetized n...
Rational Instability in the Natural Coalition Forming
Vinogradova, Galina
2012-01-01
We are investigating a paradigm of instability in coalition forming among countries, which indeed is intrinsic to any collection of individual groups or other social aggregations. Coalitions among countries are formed by the respective attraction or repulsion caused by the historical bond propensities between the countries, which produced an intricate circuit of bilateral bonds. Contradictory associations into coalitions occur due to the independent evolution of the bonds. Those coalitions tend to be unstable and break down frequently. The model extends some features of the physical theory of Spin Glasses. Within the frame of this model, the instability is viewed as a consequence of decentralized maximization processes searching for the best coalition allocations. In contrast to the existing literature, a rational instability is found to result from forecast rationality of countries. Using a general theoretical framework allowing to analyze the countries' decision making in coalition forming, we feature a sys...
Turing instabilities on Cartesian product networks
Asllani, Malbor; Busiello, Daniel M.; Carletti, Timoteo; Fanelli, Duccio; Planchon, Gwendoline
2015-08-01
The problem of Turing instabilities for a reaction-diffusion system defined on a complex Cartesian product network is considered. To this end we operate in the linear regime and expand the time dependent perturbation on a basis formed by the tensor product of the eigenvectors of the discrete Laplacian operators, associated to each of the individual networks that build the Cartesian product. The dispersion relation which controls the onset of the instability depends on a set of discrete wavelengths, the eigenvalues of the aforementioned Laplacians. Patterns can develop on the Cartesian network, if they are supported on at least one of its constitutive sub-graphs. Multiplex networks are also obtained under specific prescriptions. In this case, the criteria for the instability reduce to compact explicit formulae. Numerical simulations carried out for the Mimura-Murray reaction kinetics confirm the adequacy of the proposed theory.
Instability of a water-spout flow
Carrión, Luis; Herrada, Miguel A.; Shtern, Vladimir N.
2016-03-01
The paper studies the linear stability of a steady axisymmetric air-water motion in a vertical sealed cylinder, driven by the rotating top disk, motivated by possible applications in aerial bioreactors. As the flow strength Re increases, a vortex breakdown bubble (VBB) emerges near the bottom center and expands toward the interface. Regions of clockwise meridional circulation of air and water become separated by a thin anticlockwise circulation layer (TCL) adjacent to the interface in water. This study reveals that instability develops for larger Re than those at which VBB and TCL emerge. The instability focuses in the air region being typically of shear-layer type. The instability is centrifugal if the air volume fraction is small.
Instabilities of structured metal films on nanoscale
Dong, Nanyi; Wu, Yueying; Fowlkes, Jason; Rack, Philip; Kondic, Lou
2014-11-01
We consider instabilities of metal films on nanoscale, with particular focus on the interplay between the initial geometry and instability development. In experiments, metal films are deposited lithographically, allowing for precise control of the initial shape, and then exposed to laser pulses that liquefy them. The considered geometries involve various shapes (cylinders or prisms) superimposed on top of a flat film. We consider this problem within the framework of the long wave (lubrication) theory. Our simulations show that the main features of the instability development could be captured, as long as destabilizing liquid-solid interaction is considered in the model. We conclude by discussing the influence of the distance between the imposed perturbations, their shape, as well as experimental noise on the evolution. Supported by NSF Grant No. CBET-1235710.
Prediction of flow instability during natural convection
International Nuclear Information System (INIS)
The occurrence of flow excursion instability during passive heat removal for Tehran Research Reactor (TRR) has been analyzed at low-pressure and low-mass rate of flow conditions without boiling taking place. Pressure drop-flow rate characteristics in the general case are determined upon a developed code for this purpose. The code takes into account variations of different pressure drop components caused by different powers as well as different core inlet temperatures. The analysis revealed the fact that the instability can actually occur in the natural convection mode for a range of powers per fuel plates at a predetermined inlet temperature with fixed geometry of the core. Low mass rate of flow and high sub-cooling are the two important conditions for the occurrence of static instability in the TRR. The calculated results are compared with the existing data in the literature. (author)
Transverse modulational instability of collinear waves
International Nuclear Information System (INIS)
The transverse modulational instability, or filamentation, of two collinear waves is investigated using a coupled nonlinear Schro at sign;udinger-equation model. For infinite media it is shown that the presence of the second laser field increases the growth rate of the instability and decreases the scale length of the most unstable filaments. Systems of two copropagating waves are shown to be convectively unstable and systems of two counterpropagating waves are shown to be absolutely unstable, even when the ratio of backward- to forward-wave intensity is small. For two counterpropagating waves in finite media, the threshold intensities for the absolute instability depend only weakly on the ratio of wave intensities. The general theory is applied to the pondermotive filamentation of two light waves in homogeneous plasma
Modulational instability of Langmuir wave packets
International Nuclear Information System (INIS)
The broad spectra of random waves in unmagnetized plasmas are considered. A universal nonlinear formalism is developed for description of the nonlinear effects (modulational instability, etc.) in which random plasma waves take part. The integral equations for perturbations of wave field correlation functions are obtained. In a description of the modulational instability of random wave packets these equations play the same role as the set of coupled equations for the fields of modulational perturbations in the case of a single monochromatic pump wave. On the basis of these integral dispersion equations the modulational instability of broad wave spectra is investigated for the one-dimensional situation (when directions of propagation of the random waves coincide with that of the modulational perturbations) and for isotropic wave turbulence
Control and simulation of thermoacoustic instabilities
Poinsot, Thierry
2014-11-01
Combustion instabilities (CI), due to thermoacoustic coupling between acoustic waves and chemical reaction, constitute a major danger for all combustion systems. They can drive the system to unstable states where the whole combustor can oscillate, vibrate, quench or in extreme cases explode or burn. Such phenomena are commonly observed in the final phases of development programs, leading to major difficulties and significant additional costs. One of the most famous examples of combustion instabilities is the F1 engine of the Apollo program which required more than 1000 engine tests to obtain a stable regime satisfying all other constraints (performance, ignition, etc). CIs constitute one of the most challenging problems in fluid mechanics: they combine turbulence, acoustics, chemistry, unsteady two-phase flow in complex geometries. Since combustion instabilities have been identified (more than hundred years ago), the combustion community has followed two paths: (1) improve our understanding of the phenomena controlling stability to build engines which would be ``stable by design'' and (2) give up on a detailed understanding of mechanisms and add control systems either in open or closed loop devices to inhibit unstable modes. Of course, understanding phenomena driving combustion instabilities to suppress them would be the most satisfying approach but there is no fully reliable theory or numerical method today which can predict whether a combustor will be stable or not before it is fired. This talk will present an overview of combustion instabilities phenomenology before focusing on: (1) active control methods for combustion instabilities and (2) recent methods to predict unstable modes in combustors. These methods are based on recent Large Eddy Simulation codes for compressible reacting flows on HPC systems but we will also describe recent fully analytical methods which provide new insights into unstable modes in annular combustion chambers. Support: European
Analysis of microscopic instability for rotating LIB
International Nuclear Information System (INIS)
The instability of a neutral hollow beam is investigated within the framework of the Vlasov-Maxwell equations. It is assumed that the hollow beam is thin with the radial thickness a which is much smaller than the major radius R0, and that the equilibrium beam charge is neutralized by the background electron charge. The stability analysis is carried out for perturbations about the beam equilibrium distribution function fsub(b)0. The detailed instability properties are calculated for a variety of system parameters. (author)
Metal pad instabilities in liquid metal batteries
Zikanov, Oleg
2015-01-01
A mechanical analogy is used to analyze the interaction between the magnetic field, electric current and deformation of interfaces in liquid metal batteries. It is found that, during charging or discharging, a sufficiently large battery is prone to instabilities of two types. One is similar to the metal pad instability known for aluminum reduction cells. Another type is new. It is related to the destabilizing effect of the Lorentz force formed by the azimuthal magnetic field induced by the base current and the current perturbations caused by the local variations of the thickness of the electrolyte layer.
Energy Technology Data Exchange (ETDEWEB)
Stupakov, G.V. [Stanford Linear Accelerator Center, Menlo Park, CA (United States)
1996-08-01
The ionization of residual gas by an electron beam in an accelerator generates ions that can resonantly couple to the beam through a wave propagating in the beam-ion system. Results of the study of a beam-ion instability are presented for a multi-bunch train taking into account the decoherence of ion oscillations due to the ion frequency spread and spatial variation of the ion frequency. It is shown that the combination of both effects can substantially reduce the growth rate of the instability. (author)
Methods for Simulating the Heavy Core Instability
Directory of Open Access Journals (Sweden)
Chang Philip
2013-04-01
Full Text Available Vortices have been proposed as the sites of planet formation, where dust collects and grows into planetesimals, the building blocks of planets. However, for very small dust particles that can be treated as a pressure-less fluid, we have recently discovered the “heavy core” instability, driven by the density gradient in the vortex. In order to understand the eventual outcome of this instability, we need to study its non-linear development. Here, we describe our ongoing work to develop highly accurate numerical models of a vortex with a density gradient embedded within a protoplanetary disk.
Heuristic explanation of journal bearing instability
Crandall, S. H.
1982-01-01
A fluid-filled journal bearing is viewed as a powerful pump circulating fluid around the annular space between the journal and the bearing. A small whirling motion of the journal generates a wave of thickness variation progressing around the channel. The hypothesis that the fluid flow drives the whirl whenever the mean of the pumped fluid velocity is greater than the peripheral speed of the thickness variation wave is discussed and compared with other simple explanations of journal bearing instability. It is shown that for non-cavitation long bearings the hypothesis predicts instability onset correctly for unloaded bearings but gradually overpredicts the onset speed as the load is increased.
Critical ionization velocity and electrostatic instabilities
International Nuclear Information System (INIS)
The role of electrostatic instabilities in the interaction between a plasma and a neutral gas in relative motion is investigated. The analysis is an extension of the theory developed by Sherman to account for the physical process leading to Alfven's critical velocity. The way in which the energy associated with the two-stream instability is distributed between the ions and electrons in the linear phase is determined. The electron energy is estimated and compared with that required for ionization of the neutral gas. The significance of the restriction of the electron motion by the magnetic field is emphasized by the introduction of an effective mass parameter for the electrons. (Auth.)
INTRINSIC INSTABILITY OF THE LATTICE BGK MODEL
Institute of Scientific and Technical Information of China (English)
熊鳌魁
2002-01-01
Based on the stability analysis with no linearization and expansion,it is argued that instability in the lattice BGK model is originated from the linearrelaxation hypothesis of collision in the model. The hypothesis stands up only whenthe deviation from the local equilibrium is weak. In this case the computation is abso-lutely stable for real fluids. But for flows of high Reynolds number, this hypothesis isviolated and then instability takes place physically. By performing a transformationa quantified stability criteria is put forward without those approximation. From thecriteria a sufficient condition for stability can be obtained and serve as an estimationof the limited Reynolds number as high as possible.
Instability of large solitary water waves
Lin, Zhiwu
2008-01-01
We consider the linearized instability of 2D irrotational solitary water waves. The maxima of energy and the travel speed of solitary waves are not obtained at the highest wave, which has a 120 degree angle at the crest. Under the assumption of non-existence of secondary bifurcation which is confirmed numerically, we prove linear instability of solitary waves which are higher than the wave of maximal energy and lower than the wave of maximal travel speed. It is also shown that there exist uns...
Envelope instability as a source of diffusion
International Nuclear Information System (INIS)
Electron cooling increases the phase space density of the cooled particles up to a certain limit. This limit is normally characterized by a strong space charge tune shift, about 0.2-0.3. This tune shift is high enough to bring the cooled beam to the threshold of the envelope instability. The envelope instability can be in a kind of dynamic equilibrium with the cooling, keeping the cooled beam at a threshold with a high level of the coherent noise. This noise acts as a diffusion for the halo particles which puts a limit on the stored current
THREE-BEAM INSTABILITY IN THE LHC*
Burov, A
2013-01-01
In the LHC, a transverse instability is regularly observed at 4TeV right after the beta-squeeze, when the beams are separated by about their ten transverse rms sizes [1-3], and only one of the two beams is seen as oscillating. So far only a single hypothesis is consistent with all the observations and basic concepts, one about a third beam - an electron cloud, generated by the two proton beams in the high-beta areas of the interaction regions. The instability results from a combined action of the cloud nonlinear focusing and impedance.
Envelope instability as a source of diffusion
Burov, A
2000-01-01
Electron cooling increases the phase space density of the cooled particles up to a certain limit. This limit is normally characterized by a strong space charge tune shift, about 0.2-0.3. This tune shift is high enough to bring the cooled beam to the threshold of the envelope instability. The envelope instability can be in a kind of dynamic equilibrium with the cooling, keeping the cooled beam at a threshold with a high level of the coherent noise. This noise acts as a diffusion for the halo particles which puts a limit on the stored current.
Adjacent Instability after Instrumented Lumbar Fusion.
Directory of Open Access Journals (Sweden)
Wen-Jer Chen
2003-11-01
Full Text Available The invention of pedicle screw instrumentation has greatly improved outcomes ofspinal fusion, which has become the treatment of choice for lumbar spondylolisthesis. Asresearchers accumulate experience, both theoretical and clinical advances are continuallybeing reported. A review of the literature and the experience of the authors show that thedevelopment of adjacent instability, as in the breakdown of a neighboring unfixed motionsegment, is a common consequence of an instrumented lumbar spine. This article reviewsthe risk factors and surgical treatment of adjacent instability. The authors believe that properpreoperative planning and complete surgical procedures are imperative to prevent adjacentinstability. For those who need revision surgery, meticulous surgical techniques can achievesatisfactory results.
Modulational instability in periodic quadratic nonlinear materials
DEFF Research Database (Denmark)
Corney, Joel Frederick; Bang, Ole
2001-01-01
We investigate the modulational instability of plane waves in quadratic nonlinear materials with linear and nonlinear quasi-phase-matching gratings. Exact Floquet calculations, confirmed by numerical simulations, show that the periodicity can drastically alter the gain spectrum but never completely...... removes the instability. The low-frequency part of the gain spectrum is accurately predicted by an averaged theory and disappears for certain gratings. The high-frequency part is related to the inherent gain of the homogeneous non-phase-matched material and is a consistent spectral feature....
Modulational instability of two colliding whistlers
International Nuclear Information System (INIS)
It is shown that the dynamics of two colliding whistlers is governed by a pair of coupled nonlinear Schroedinger equations. The latter exhibit a modulational instability of constant amplitude whistlers that are nonlinearly interacting through quasistationary density perturbations created by the combined action of the ponderomotive forces of two whistlers. It has been found that the growth rate of the modulational instability increases with the intensity of any of the colliding whistlers, but decreases with the wave number per unit length of the modulated wave packet
Cometary ion instabilities in the solar wind
Czech Academy of Sciences Publication Activity Database
Matteini, L.; Schwartz, S. J.; Hellinger, Petr
2015-01-01
Roč. 119, Special Is. (2015), s. 3-12. ISSN 0032-0633 R&D Projects: GA ČR GA15-10057S Institutional support: RVO:67985815 Keywords : cometary plasma * hybrid simulations * pick-up ion instabilities Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.875, year: 2014
Control of Coherent Instabilities by Linear Coupling
Cappi, R; Möhl, D
2001-01-01
One of the main challenges in the design of high-energy colliders is the very high luminosity necessary to provide significant event rates. This imposes strong constraints to achieve and preserve beams of high brightness, i.e. intensity to emittance ratio, all along the injector chain. Amongst the phenomena that can blow up and even destroy the beam are transverse coherent instabilities. Two methods are widely used to damp these instabilities. The first one is Landau damping by non-linearities. The second consists in using an electronic feedback system. However, non-linearities are harmful to single-particle motion due to resonance phenomena, and powerful wideband feedback systems are expensive. It is shown in this paper that linear coupling is a further method that can be used to damp transverse coherent instabilities. The theory of collective motion is outlined, including the coupling of instability rise and damping rates, chromaticity and Landau damping. Experimental results obtained at the CERN PS are rep...
Perception and self-organized instability.
Friston, Karl; Breakspear, Michael; Deco, Gustavo
2012-01-01
This paper considers state-dependent dynamics that mediate perception in the brain. In particular, it considers the formal basis of self-organized instabilities that enable perceptual transitions during Bayes-optimal perception. The basic phenomena we consider are perceptual transitions that lead to conscious ignition (Dehaene and Changeux, 2011) and how they depend on dynamical instabilities that underlie chaotic itinerancy (Breakspear, 2001; Tsuda, 2001) and self-organized criticality (Beggs and Plenz, 2003; Plenz and Thiagarajan, 2007; Shew et al., 2011). Our approach is based on a dynamical formulation of perception as approximate Bayesian inference, in terms of variational free energy minimization. This formulation suggests that perception has an inherent tendency to induce dynamical instabilities (critical slowing) that enable the brain to respond sensitively to sensory perturbations. We briefly review the dynamics of perception, in terms of generalized Bayesian filtering and free energy minimization, present a formal conjecture about self-organized instability and then test this conjecture, using neuronal (numerical) simulations of perceptual categorization. PMID:22783185
Remittances, spending, and political instability in Ukraine
Czech Academy of Sciences Publication Activity Database
Kuntsevych, Iuliia
2016-01-01
Roč. 64, č. 1 (2016), s. 42-57. ISSN 0722-480X Institutional support: PRVOUK-P23 Keywords : Ukraine * remittances * political instability Subject RIV: AH - Economics http://www.degruyter.com/view/j/soeu.2016.64.issue-1/soeu-2016-0004/soeu-2016-0004.xml
Who is afraid of political instability?
Czech Academy of Sciences Publication Activity Database
Campos, Nauro; Nugent, J. B.
-, č. 2555 (2000), s. 1-29. ISSN 0265-8003 Institutional research plan: CEZ:AV0Z7085904 Keywords : economic growth * political instability Subject RIV: AH - Economics http://www.cepr.org/pubs/new-dps/dplist.asp?dpno=2555
Streaming instability of aggregating slime mold amoebae
Levine, Herbert; Reynolds, William
1991-05-01
We propose a new model of aggregation in the cellular slime mold D. Discoideum. Our approach couples the excitable signaling system to amoeba chemotaxis; the resultant system of equations is tractable to analytical and numerical approaches. Using our model, we derive the existence of a streaming instability for the concentric target aggregation pattern.
The disruptive instability in Tokamak plasmas
Salzedas, F.J.B.
2001-01-01
Studies performed in RTP (Rijnhuizen Tokamak Project) of the most violent and dangerous instability in tokamak plasmas, the major disruption, are presented. A particular class of disruptions is analyzed, namely the density limit disruption, which occur in high density plasmas. The radiative te
Jeans instability in classical and modified gravity
Arbuzova, E. V.; Dolgov, A. D.; L. Reverberi
2014-01-01
Gravitational instability in classical Jeans theory, General Relativity, and modified gravity is considered. The background density increase leads to a faster growth of perturbations in comparison with the standard theory. The transition to the Newtonian gauge in the case of coordinate dependent background metric functions is studied. For modified gravity a new high frequency stable solution is found.
Jeans instability in classical and modified gravity
Energy Technology Data Exchange (ETDEWEB)
Arbuzova, E.V., E-mail: arbuzova@uni-dubna.ru [Novosibirsk State University, Novosibirsk, 630090 (Russian Federation); Department of Higher Mathematics, University “Dubna”, 141980 Dubna (Russian Federation); Dolgov, A.D., E-mail: dolgov@fe.infn.it [Novosibirsk State University, Novosibirsk, 630090 (Russian Federation); ITEP, Bol. Cheremushkinsaya ul., 25, 113259 Moscow (Russian Federation); Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Ferrara, Polo Scientifico e Tecnologico – Edificio C, Via Saragat 1, 44122 Ferrara (Italy); Reverberi, L., E-mail: reverberi@fe.infn.it [Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Ferrara, Polo Scientifico e Tecnologico – Edificio C, Via Saragat 1, 44122 Ferrara (Italy); Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Ferrara, Polo Scientifico e Tecnologico – Edificio C, Via Saragat 1, 44122 Ferrara (Italy)
2014-12-12
Gravitational instability in classical Jeans theory, General Relativity, and modified gravity is considered. The background density increase leads to a faster growth of perturbations in comparison with the standard theory. The transition to the Newtonian gauge in the case of coordinate dependent background metric functions is studied. For modified gravity a new high frequency stable solution is found.
Jeans instability in classical and modified gravity
Directory of Open Access Journals (Sweden)
E.V. Arbuzova
2014-12-01
Full Text Available Gravitational instability in classical Jeans theory, General Relativity, and modified gravity is considered. The background density increase leads to a faster growth of perturbations in comparison with the standard theory. The transition to the Newtonian gauge in the case of coordinate dependent background metric functions is studied. For modified gravity a new high frequency stable solution is found.
Bar instabilities in Coma cluster galaxies
International Nuclear Information System (INIS)
The radial distribution of bar versus nonbar galaxies within the Coma cluster shows that a significantly larger fraction of bar galaxies are members of the cluster core. This result can be used either to estimate the time scale for the decay of bar instabilities or to argue that galaxies in the core of Coma are confined within the core
Peeling Instability in the Pegasus ST
Bongard, M. W.; Barr, J. L.; Fonck, R. J.; Redd, A. J.; Schlossberg, D. J.
2011-10-01
Ohmic plasmas in PEGASUS are often initially unstable to peeling modes, an instability underlying deleterious edge localized mode (ELM) activity in fusion-grade plasmas. These edge-localized instabilities are observed under conditions of high parallel edge current density (J∥ ~ 0 . 1 MA/m2) and low magnetic field (B ~ 0 . 1 T) present at near-unity aspect ratio, corresponding to high peeling instability drive (~J∥ / B) . They generate electromagnetic MHD activity with low toroidal mode numbers n PEGASUS discharges permit time-resolved measurements of the edge current density profile Jedge using an insertable Hall probe. Peeling MHD fluctuation amplitudes scale strongly with measured J∥ / B , consistent with theory. Ideal stability analysis of Hall-constrained equilibrium reconstructions with DCON finds instability to peeling modes. Filaments form from an initial Jedge ``current-hole'' perturbation and carry currents ~100-250 A. Their radial trajectories feature transient acceleration due to magnetostatic repulsion followed by constant-velocity motion, consistent with models of ELM dynamics. Work supported by US DOE Grant DE-FG02-96ER54375.
The short circuit instability in protoplanetary disks
DEFF Research Database (Denmark)
Hubbard, A.; McNally, C.P.; Mac Low, M.M.;
2013-01-01
and lightning, as it concentrates the dissipation of magnetic energy by means of the enhanced release of free electrons. This instability can generate very high temperatures, making it an excellent candidate for thermally processing protoplanetary disk solids, from annealing silicates to melting...
High temperature instability of hollow nanoparticles
Czech Academy of Sciences Publication Activity Database
Fischer, F. D.; Svoboda, Jiří
2008-01-01
Roč. 10, č. 2 (2008), s. 255-261. ISSN 1388-0764 R&D Projects: GA AV ČR IAA200410601 Institutional research plan: CEZ:AV0Z20410507 Keywords : hollow nanoparticle * instability * modelling Subject RIV: BJ - Thermodynamics Impact factor: 2.299, year: 2008
Kelvin Helmholtz Instability in Planetary Magnetospheres
Johnson, Jay R.; Wing, Simon; Delamere, Peter A.
2014-11-01
Kelvin-Helmholtz instability plays a particularly important role in plasma transport at magnetospheric boundaries because it can control the development of a turbulent boundary layer, which governs the transport of mass, momentum, and energy across the boundary. Waves generated at the interface can also couple into body modes in the plasma sheet and inner magnetosphere where they can play an important role in plasma sheet transport and particle energization in the inner magnetosphere. Kinetic and electron-scale effects are important for the development of K-H instability, leading to secondary instabilities and plasma mixing. The development of vortices that entwine magnetosheath field lines with magnetospheric field lines also allows reconnection and the interchange of plasma blobs from open to closed field lines. Dawn-dusk asymmetries in Kelvin-Helmholtz development at planetary boundary layers may result from several effects including plasma corotation, kinetic effects, magnetic geometry, or asymmetric distribution of plasma. Examples are provided throughout the solar system illustrating the pervasive effects of the Kelvin-Helmholtz instability on plasma transport.
Microtearing Instability In The ITER Pedestal
International Nuclear Information System (INIS)
Unstable microtearing modes are discovered by the GS2 gyrokinetic siimulation code, in the pedestal region of a simulated ITER H-mode plasma with approximately 400 WM DT fusion power. Existing nonlinear theory indicates that these instabilities should produce stochastic magnetic fields and broaden the pedestal. The resulted electron thermal conductivity is estimated and the implications of these findings are discussed.
Treatment of glenohumeral instability in rugby players.
Funk, Lennard
2016-02-01
Rugby is a high-impact collision sport, with impact forces. Shoulder injuries are common and result in the longest time off sport for any joint injury in rugby. The most common injuries are to the glenohumeral joint with varying degrees of instability. The degree of instability can guide management. The three main types of instability presentations are: (1) frank dislocation, (2) subluxations and (3) subclinical instability with pain and clicking. Understanding the exact mechanism of injury can guide diagnosis with classical patterns of structural injuries. The standard clinical examination in a large, muscular athlete may be normal, so specific tests and techniques are needed to unearth signs of pathology. Taking these factors into consideration, along with the imaging, allows a treatment strategy. However, patient and sport factors need to be also considered, particularly the time of the season and stage of sporting career. Surgery to repair the structural damage should include all lesions found. In chronic, recurrent dislocations with major structural lesions, reconstruction procedures such as the Latarjet procedure yields better outcomes. Rehabilitation should be safe, goal-driven and athlete-specific. Return to sport is dependent on a number of factors, driven by the healing process, sport requirements and extrinsic pressures. Level of evidence V. PMID:26786164
Time-resonant tokamak plasma edge instabilities?
Webster, A. J.; Dendy, R. O.; Calderon, F. A.; Chapman, S. C.; Delabie, E.; Dodt, D.; Felton, R.; Todd, T. N.; Maviglia, F.; Morris, J.; Riccardo, V.; Alper, B.; Brezinsek, S.; Coad, P.; Likonen, J.; Rubel, M.; JET-EFDA Contributors,
2014-01-01
For a two week period during the Joint European Torus 2012 experimental campaign, the same high confinement plasma was repeated 151 times. The dataset was analysed to produce a probability density function (pdf) for the waiting times between edge-localized plasma instabilities (ELMs). The result was
Kinetic Simulations of Rayleigh-Taylor Instabilities
Sagert, Irina; Colbry, Dirk; Howell, Jim; Staber, Alec; Strother, Terrance
2014-01-01
We report on an ongoing project to develop a large scale Direct Simulation Monte Carlo code. The code is primarily aimed towards applications in astrophysics such as simulations of core-collapse supernovae. It has been tested on shock wave phenomena in the continuum limit and for matter out of equilibrium. In the current work we focus on the study of fluid instabilities. Like shock waves these are routinely used as test-cases for hydrodynamic codes and are discussed to play an important role in the explosion mechanism of core-collapse supernovae. As a first test we study the evolution of a single-mode Rayleigh-Taylor instability at the interface of a light and a heavy fluid in the presence of a gravitational acceleration. To suppress small-wavelength instabilities caused by the irregularity in the separation layer we use a large particle mean free path. The latter leads to the development of a diffusion layer as particles propagate from one fluid into the other. For small amplitudes, when the instability is i...
Genomic instability and cancer: an introduction
Institute of Scientific and Technical Information of China (English)
Zhiyuan Shen
2011-01-01
@@ Genomic instability as a major driving force of tumorigenesis.The ultimate goal of cell division for most non-cancerous somatic cells is to accurately duplicate the genome and then evenly divide the duplicated genome into the two daughter cells.This ensures that the daughter cells will have exactly the same genetic material as their parent cell.
Possible instabilities in the beat wave accelerator
International Nuclear Information System (INIS)
In this article the concept of the beat wave accelerator is studied with emphasis put on the plasma physics. An important effect is the relativistic nature of the electrons oscillating in the electric field of the beat wave. Various instabilities are presented which could limit the overall efficiency of the accelerating process. (author)
Note on modulational instability of Boussinesq wavetrains
Directory of Open Access Journals (Sweden)
S. Roy Choudhury
1992-06-01
Full Text Available It is demonstrated that modulational instability may occur in Boussinesq wavetrains for wavenumbers k2>1, in contrast to the result found by Shivamoggi and Debnath. Both Whitham's averaged Lagrangian formulation and the technique of Benjamin and Feir are used.
Modulational instability in nonlocal nonlinear Kerr media
DEFF Research Database (Denmark)
Krolikowski, Wieslaw; Bang, Ole; Juul Rasmussen, Jens; Wyller, John
2001-01-01
We study modulational instability (MI) of plane waves in nonlocal nonlinear Kerr media. For a focusing nonlinearity we show that, although the nonlocality tends to suppress MI, it can never remove it completely, irrespective of the particular profile of the nonlocal response function. For a...
Dynamical instabilities of hot and compressed nuclei
International Nuclear Information System (INIS)
The dynamical evolution of a hot and compressed nucleus is described by means of an extended liquid drop model. Using only the continuity equation and the energy conservation we show that the system expands after a while. The possible global instabilities of the drop are studied by applying the general conditions of stability of dynamical systems. We find that the nucleus is unstable if it can reach a low density configuration (≅ 0.07 nucleon/fm3). Such a configuration is obtained if the initial compression of the nucleus is large enough. It is shown that the thermal excitation energy has much less influence than the compressional energy. These instability conditions are in good agreement with those obtained previously within the framework of lattice percolation and the same model for the dynamical expansion. Since local instabilities may also very likely be present, we propose to study them using a restructured aggregation model. They lead to a multifragmentation of the system, a mechanism which is known experimentally to exist. We find that the local instabilities occur at essentially the same density values than the global ones. A moment analysis of the calculated multifragmentation events allows to extract a critical exponent in excellent agreement with the one deduced experimentally from Au induced reactions
Genome organization, instabilities, stem cells, and cancer
Directory of Open Access Journals (Sweden)
Senthil Kumar Pazhanisamy
2009-01-01
Full Text Available It is now widely recognized that advances in exploring genome organization provide remarkable insights on the induction and progression of chromosome abnormalities. Much of what we know about how mutations evolve and consequently transform into genome instabilities has been characterized in the spatial organization context of chromatin. Nevertheless, many underlying concepts of impact of the chromatin organization on perpetuation of multiple mutations and on propagation of chromosomal aberrations remain to be investigated in detail. Genesis of genome instabilities from accumulation of multiple mutations that drive tumorigenesis is increasingly becoming a focal theme in cancer studies. This review focuses on structural alterations evolve to raise a variety of genome instabilities that are manifested at the nucleotide, gene or sub-chromosomal, and whole chromosome level of genome. Here we explore an underlying connection between genome instability and cancer in the light of genome architecture. This review is limited to studies directed towards spatial organizational aspects of origin and propagation of aberrations into genetically unstable tumors.
Plasma instabilities multifrequency study in equatorial electrojet
International Nuclear Information System (INIS)
In this thesis, multifrequential HF coherent radar results are presented, in the field plasma instabilities in equatorial electrojet. In a first part, characteristics of the irregularities observed either at the 3 meter wavelength by VHF radars, either at other wavelengths during pinpoint experiments, or in-situ by probe rockets are recalled. Theoretical studies progressed and are presented, at the same time with these experimental observations: instability linear theory, non linear theories, HF radar specificity, and problems associated to HF waves propagation and refraction in ionosphere. Original experimental results from Ethiopia are gathered in the second part. Plasma instability has been studied in different geophysical conditions and Doppler spectra characteristics are presented for each one of them. These characteristics are completely different according to the various cases; they are also different according to wether observations are made during the day in normal conditions (electric field pointed to the east at the equator) or in counter-electrojet conditions (electric field pointed to the west). The last part is concerned with theoretical interpretation of the previous results. A comprehensive view of the instability physical mechanisms, according to the geophysical conditions encountered, has been allowed by our results, VHF radar measurements at Jicamarca, or in situ probe measurements on the whole. Irregularities study has been limited to the E region
Instabilities in the Mean Field Limit
Han-Kwan, Daniel; Nguyen, Toan T.
2016-03-01
Consider a system of N particles interacting through Newton's second law with Coulomb interaction potential in one spatial dimension or a {C}^2 smooth potential in any dimension. We prove that in the mean field limit N → + ∞, the N particles system displays instabilities in times of order log N, for some configurations approximately distributed according to unstable homogeneous equilibria.
Eliminating Computational Instability In Multibody Simulations
Watts, Gaines L.
1994-01-01
TWOBODY implements improved version of Lagrange multiplier method. Program ultilizes programming technique eliminating computational instability in multibody simulations in which Lagrange multipliers used. In technique, one uses constraint equations, instead of integration, to determine coordinates that are not independent. To illustrate technique, it includes simple mathematical model of solid rocket booster and parachute connected by frictionless swivel. Written in FORTRAN 77.
Study of Fast Instability in Fermilab Recycler
Energy Technology Data Exchange (ETDEWEB)
Antipov, Sergey [Chicago U.; Adamson, Philip [Fermilab; Nagaitsev, Sergei [Fermilab; Yang, Ming-Jen [Fermilab
2016-06-01
One of the factors which may limit the intensity in the Fermilab Recycler is a fast transverse instability. It develops within a hundred turns and, in certain conditions, may lead to a beam loss. Various peculiar features of the instability: its occurrence only above a certain intensity threshold, and only in horizontal plane, as well as the rate of the instability, suggest that its cause is electron cloud. We studied the phenomena by observing the dynamics of stable and unstable beam. We found that beam motion can be stabilized by a clearing bunch, which confirms the electron cloud nature of the instability. The findings suggest electron cloud trapping in Recycler combined function mag-nets. Bunch-by-bunch measurements of betatron tune show a tune shift towards the end of the bunch train and allow the estimation of the density of electron cloud and the rate of its build-up. The experimental results are in agreement with numerical simulations of electron cloud build-up and its interaction with the beam.
A computer simulation of chromosomal instability
Goodwin, E.; Cornforth, M.
The transformation of a normal cell into a cancerous growth can be described as a process of mutation and selection occurring within the context of clonal expansion. Radiation, in addition to initial DNA damage, induces a persistent and still poorly understood genomic instability process that contributes to the mutational burden. It will be essential to include a quantitative description of this phenomenon in any attempt at science-based risk assessment. Monte Carlo computer simulations are a relatively simple way to model processes that are characterized by an element of randomness. A properly constructed simulation can capture the essence of a phenomenon that, as is often the case in biology, can be extraordinarily complex, and can do so even though the phenomenon itself is incompletely understood. A simple computer simulation of one manifestation of genomic instability known as chromosomal instability will be presented. The model simulates clonal expansion of a single chromosomally unstable cell into a colony. Instability is characterized by a single parameter, the rate of chromosomal rearrangement. With each new chromosome aberration, a unique subclone arises (subclones are defined as having a unique karyotype). The subclone initially has just one cell, but it can expand with cell division if the aberration is not lethal. The computer program automatically keeps track of the number of subclones within the expanding colony, and the number of cells within each subclone. Because chromosome aberrations kill some cells during colony growth, colonies arising from unstable cells tend to be smaller than those arising from stable cells. For any chosen level of instability, the computer program calculates the mean number of cells per colony averaged over many runs. These output should prove useful for investigating how such radiobiological phenomena as slow growth colonies, increased doubling time, and delayed cell death depend on chromosomal instability. Also of
Muscle activation patterns in patients with recurrent shoulder instability
Directory of Open Access Journals (Sweden)
Anju Jaggi
2012-01-01
Conclusion: The DEMG results suggest that increased activation of LD may play a role in both anterior and posterior shoulder instability; increased activation of PM may play a role in anterior instability.
Corona-induced electrohydrodynamic instabilities in low conducting liquids
Energy Technology Data Exchange (ETDEWEB)
Vega, F.; Perez, A.T. [Depto. Electronica y Electromagnetismo, Facultad de Fisica, Universidad de Sevilla, Avda. Reina Mercedes, s/n. 41012, Sevilla (Spain)
2003-06-01
The rose-window electrohydrodynamic (EHD) instability has been observed when a perpendicular field with an additional unipolar ion injection is applied onto a low conducting liquid surface. This instability has a characteristic pattern with cells five to 10 times greater than those observed in volume instabilities caused by unipolar injection. We have used corona discharge from a metallic point to perform some measurements of the rose-window instability in low conducting liquids. The results are compared to the linear theoretical criterion for an ohmic liquid. They confirmed that the minimum voltage for this instability is much lower than that for the interfacial instability in high conducting liquids. This was predicted theoretically in the dependence of the critical voltage as a function of the non-dimensional conductivity. It is shown that in a non-ohmic liquid the rose window appears as a secondary instability after the volume instability. (orig.)
Prevalence of knee instability in relation to sports activity
DEFF Research Database (Denmark)
Hahn, Thomas; Foldspang, Anders; Hansen, Thorsten Ingemann
2001-01-01
The objective was to estimate the prevalence of knee instability among active athletes and to investigate potential associations to type, amount and duration of sports participation. Based on a questionnaire, 339 athletes provided information about different features of occupation, sports activity...... and knee instability. The 12-month period prevalence of knee instability and constant or recurrent knee instability, and absence from sport and absence from work due to knee instability, was 22%, 14%, 5% and 1%, respectively. Knee instability as such, and constant or recurrent knee instability were...... found to be positively associated with female gender and different features of occupational work. In conclusion, knee instability is a commonly reported phenomenon among active athletes. It was found to be independent of the type and the amount of sports activity but highly dependent on female gender...
The subcritical baroclinic instability in local accretion disc models
Lesur, G
2009-01-01
(abridged) Aims: We present new results exhibiting a subcritical baroclinic instability (SBI) in local shearing box models. We describe the 2D and 3D behaviour of this instability using numerical simulations and we present a simple analytical model describing the underlying physical process. Results: A subcritical baroclinic instability is observed in flows stable for the Solberg-Hoiland criterion using local simulations. This instability is found to be a nonlinear (or subcritical) instability, which cannot be described by ordinary linear approaches. It requires a radial entropy gradient weakly unstable for the Schwartzchild criterion and a strong thermal diffusivity (or equivalently a short cooling time). In compressible simulations, the instability produces density waves which transport angular momentum outward with typically alpha<3e-3, the exact value depending on the background temperature profile. Finally, the instability survives in 3D, vortex cores becoming turbulent due to parametric instabilities...
Rembiasz, Tomasz; Cerdá-Durán, Pablo; Müller, Ewald; Aloy, Miguel-Ángel
2015-01-01
The magnetorotational instability (MRI) can be a powerful mechanism amplifying the magnetic field in core collapse supernovae. However, whether initially weak magnetic fields can be amplified by this instability to dynamically relevant strengths is still a matter of active scientific debate. One of the main uncertainties concerns the process that terminates the growth of the instability. Parasitic instabilities of both Kelvin-Helmholtz (KH) and tearing-mode type have been suggested to play a crucial role in this process, disrupting MRI channel flows and quenching magnetic field amplification. We performed two-dimensional and three-dimensional sheering-disc simulations of a differentially rotating proto-neutron star layer in non-ideal MHD with unprecedented high numerical resolution. Our simulations show that KH parasitic modes dominate tearing modes in the regime of large hydrodynamic and magnetic Reynolds numbers, as encountered in proto-neutron stars. They also determine the maximum magnetic field stress ac...
Morphological instabilities of stratified epithelia: a mechanical instability in tumour formation
Risler, Thomas
2013-01-01
Interfaces between stratified epithelia and their supporting stromas commonly exhibit irregular shapes. Undulations are particularly pronounced in dysplastic tissues and typically evolve into long, finger-like protrusions in carcinomas. In a previous work (Basan et al., Phys. Rev. Lett. 106, 158101 (2011)), we demonstrated that an instability arising from viscous shear stresses caused by the constant flow due to cell turnover in the epithelium could drive this phenomenon. While interfacial tension between the two tissues as well as mechanical resistance of the stroma tend to maintain a flat interface, an instability occurs for sufficiently large viscosity, cell-division rate and thickness of the dividing region in the epithelium. Here, extensions of this work are presented, where cell division in the epithelium is coupled to the local concentration of nutrients or growth factors diffusing from the stroma. This enhances the instability by a mechanism similar to that of the Mullins-Sekerka instability in single...
Trisomy 21 and facial developmental instability.
Starbuck, John M; Cole, Theodore M; Reeves, Roger H; Richtsmeier, Joan T
2013-05-01
The most common live-born human aneuploidy is trisomy 21, which causes Down syndrome (DS). Dosage imbalance of genes on chromosome 21 (Hsa21) affects complex gene-regulatory interactions and alters development to produce a wide range of phenotypes, including characteristic facial dysmorphology. Little is known about how trisomy 21 alters craniofacial morphogenesis to create this characteristic appearance. Proponents of the "amplified developmental instability" hypothesis argue that trisomy 21 causes a generalized genetic imbalance that disrupts evolutionarily conserved developmental pathways by decreasing developmental homeostasis and precision throughout development. Based on this model, we test the hypothesis that DS faces exhibit increased developmental instability relative to euploid individuals. Developmental instability was assessed by a statistical analysis of fluctuating asymmetry. We compared the magnitude and patterns of fluctuating asymmetry among siblings using three-dimensional coordinate locations of 20 anatomic landmarks collected from facial surface reconstructions in four age-matched samples ranging from 4 to 12 years: (1) DS individuals (n = 55); (2) biological siblings of DS individuals (n = 55); 3) and 4) two samples of typically developing individuals (n = 55 for each sample), who are euploid siblings and age-matched to the DS individuals and their euploid siblings (samples 1 and 2). Identification in the DS sample of facial prominences exhibiting increased fluctuating asymmetry during facial morphogenesis provides evidence for increased developmental instability in DS faces. We found the highest developmental instability in facial structures derived from the mandibular prominence and lowest in facial regions derived from the frontal prominence. PMID:23505010
Dynamic instability of the hard turning process
Directory of Open Access Journals (Sweden)
J. Kopač
2006-04-01
Full Text Available Purpose: Purpose of this paper is consideration of dynamic behavior of the hard turning process. There are several indicators which could confirm assumption of turning instability (depth of cutting, high ratio of forces Fc/Fp, small tool nose radius, and non-uniform stress distribution over tool/workpiece contact. Lead edge angle and passive force Fp are strongly depend on depth of cutting in hard turning what additionally increase instability.Design/methodology/approach: Numerical calculation and experimental tests have been done to evaluate the rate of cutting instability while using and comparing different process monitoring sensors, and acquisition techniques based on PC platform.Findings: It was found that high chip thickness alteration occur because of cutting depth vary for a value of some 60 % and even more if Fp force signal is analyzing when machine tool has inadequate stiffness.Research limitations/implications: Results and findings presented in this paper are qualitative and might be slightly different in other cutting condition (e.g. if wiper inserts are used. Also there are no experiences with coated workpieces or with workpiece material with low deformation energy.Practical implications: Assuming that a hard turning is a semi finishing or finishing process, surface finish is of big relevance. Surface roughness is a consequence of both cutting instability and of tool/workpiece loading condition. Results of test indicates an optimal cutting depth for final pass when minimum surface roughness can be achieved what can be valuable for cutting regime determination. Furthermore, more effective use of the machine tool performances might be achieved.Originality/value: Originality of the paper is in analysis of sources of turning instability (variable depth of cutting combined with side edge angle and tool nose radius which lead primary to condition where Fp sensing data does not fit to the normal distribution and secondary to cyclic push
The dynamic instability of adiabatic blast waves
Ryu, Dongsu; Vishniac, Ethan T.
1991-01-01
Adiabatic blastwaves, which have a total energy injected from the center E varies as t(sup q) and propagate through a preshock medium with a density rho(sub E) varies as r(sup -omega) are described by a family of similarity solutions. Previous work has shown that adiabatic blastwaves with increasing or constant postshock entropy behind the shock front are susceptible to an oscillatory instability, caused by the difference between the nature of the forces on the two sides of the dense shell behind the shock front. This instability sets in if the dense postshock layer is sufficiently thin. The stability of adiabatic blastwaves with a decreasing postshock entropy is considered. Such blastwaves, if they are decelerating, always have a region behind the shock front which is subject to convection. Some accelerating blastwaves also have such region, depending on the values of q, omega, and gamma where gamma is the adiabatic index. However, since the shock interface stabilizes dynamically induced perturbations, blastwaves become convectively unstable only if the convective zone is localized around the origin or a contact discontinuity far from the shock front. On the other hand, the contact discontinuity of accelerating blastwaves is subject to a strong Rayleigh-Taylor instability. The frequency spectra of the nonradial, normal modes of adiabatic blastwaves have been calculated. The results have been applied to the shocks propagating through supernovae envelopes. It is shown that the metal/He and He/H interfaces are strongly unstable against the Rayleigh-Taylor instability. This instability will induce mixing in supernovae envelopes. In addition the implications of this work for the evolution of planetary nebulae is discussed.
Mamatsashvili, George
2016-01-01
The helical magnetorotational instability is known to work for resistive rotational flows with comparably steep negative or extremely steep positive shear. The corresponding lower and upper Liu limits of the shear are continuously connected when some axial electrical current is allowed to flow through the rotating fluid. Using a local approximation we demonstrate that the magnetohydrodynamic behavior of this dissipation-induced instability is intimately connected with the nonmodal growth and the pseudospectrum of the underlying purely hydrodynamic problem.
Instability of capitalism inflation, unemployment, and business cycles
Adil H. Mouhammed
2006-01-01
This paper investigates the instability of capitalism defined as a condition under which capitalism creates inflation, unemployment, and business cycles. Great economists such as Marx, Veblen, and Schumpeter have examined this problem, concluding that capitalist instability will transform capitalism. A model is developed in this paper to investigate instability, and the finding is that the basic cause behind instability is the conflict on income share: wages and profits. The fluctuations i...
Instability of capitalism inflation, unemployment, and business cycles
Adil H. Mouhammed
2006-01-01
This paper investigates the instability of capitalism defined as a condition under which capitalism creates inflation, unemployment, and business cycles. Great economists such as Marx, Veblen, and Schumpeter have examined this problem, concluding that capitalist instability will transform capitalism. A model is developed in this paper to investigate instability, and the finding is that the basic causebehind instability is the conflict on income share: wages and profits. The fluctuations in th...
EARLY WARNING INDICATORS OF ECONOMIC AND FINANCIAL INSTABILITY INDEXES
Rodica Oana Ioniţă
2013-01-01
This paper is an empirical study which analyzes economic and financial instability periods. I composed two early warning indicators: one for a period of economic instability and other for a period of financial instability. The index of economic instability periods is called EWI (Economic Warning Index) and it is defined with the aid of an intermediary indicator CII – defined in terms of industrial production growth, external trade growth and unemployment growth – and of a basket of significan...
TRANSMISSION LINE-WIRE DANCING (GALLOPING) – LYAPUNOV INSTABILITY
V. I. Vanko; I. K. Marchevski
2015-01-01
This article describes aerodynamic losses of damping, or aerodynamic instability, which we observe in experiments and in engineering practice. As applied to industrial high-voltage lines this phenomenon is usually called galloping (dancing) of phase line wires. This phenolmenon can be explained by Lyapunov’s instability of equilibrium state of wires profile (cross-section). In addition to known condition of Grauert-den-Hartog’s instability there was obtained practical condition of instability...
Role of oxidative DNA damage in genome instability and cancer
International Nuclear Information System (INIS)
Inactivation of mismatch repair (MMR) is associated with a dramatic genomic instability that is observed experimentally as a mutator phenotype and micro satellite instability (MSI). It has been implicit that the massive genetic instability in MMR defective cells simply reflects the accumulation of spontaneous DNA polymerase errors during DNA replication. We recently identified oxidation damage, a common threat to DNA integrity to which purines are very susceptible, as an important cofactor in this genetic instability
Ageostrophic instability in rotating, stratified interior vertical shear flows
Wang, Peng; Mcwilliams, James C.; Menesguen, Claire
2014-01-01
The linear instability of several rotating, stably stratified, interior vertical shear flows (U) over bar (z) is calculated in Boussinesq equations. Two types of baroclinic, ageostrophic instability, AI1 and AI2, are found in odd-symmetric (U) over bar (z) for intermediate Rossby number (R-0). AI1 has zero frequency; it appears in a continuous transformation of the unstable mode properties between classic baroclinic instability (BCI) and centrifugal instability (CI). It begins to occur at int...
Development and Reliability of the Ankle Instability Instrument
Docherty, Carrie L; Gansneder, Bruce M; Arnold, Brent L; Hurwitz, Shepard R.
2006-01-01
Context: Functional ankle instability has been defined in a variety of ways. Factors that are frequently used in this definition include a history of a severe ankle sprain, a history of multiple ankle sprains, and a recurrent feeling of instability or “giving way.” With all the variations in defining functional ankle instability, it becomes increasingly important to develop a more consistent framework for assessing this instability.
Analysis of Instabilities in Non-Equilibrium Plasmas
Institute of Scientific and Technical Information of China (English)
LIN Lie; WU Bin; ZHANG Peng; WANG Yong-Qing
2004-01-01
Plasma instabilities with charged particle production processes in non-equilibrium plasma are analysed. A criterion on plasma instabilities is deduced by first-order perturbation theory. The relationship between plasma instabilities and certain factors (degree of non-equilibrium in plasma, the electron attachment rate coefficient and electron temperature) are described.
Aeroelastic instability of a flexible plate in a uniform flow
Eloy, Christophe; Souilliez, Claire; Schouveiler, Lionel
2008-01-01
The flutter instability of a flexible plate immersed in an axial flow is experimentally investigated. This instability is similar to flag flutter and results from the competition between destabilizing pressure forces and stabilizing bending stiffness. The instability threshold is measured as a function of the experimental parameters (plate size and aspect ratio) and compared to different theoretical predictions.
Current-Driven Filament Instabilities in Relativistic Plasmas. Final report
International Nuclear Information System (INIS)
This grant has supported a study of some fundamental problems in current- and flow-driven instabilities in plasmas and their applications in inertial confinement fusion (ICF) and astrophysics. It addressed current-driven instabilities and their roles in fast ignition, and flow-driven instabilities and their applications in astrophysics
Current-Driven Filament Instabilities in Relativistic Plasmas. Final report
Energy Technology Data Exchange (ETDEWEB)
Ren, Chuang
2013-02-13
This grant has supported a study of some fundamental problems in current- and flow-driven instabilities in plasmas and their applications in inertial confinement fusion (ICF) and astrophysics. It addressed current-driven instabilities and their roles in fast ignition, and flow-driven instabilities and their applications in astrophysics.
Nonlinear drift wave instability due to nonlinear structures
International Nuclear Information System (INIS)
A nonlinear instability due to zonal flows and magnetic islands has been found. The instability has the character of a dissipative drift instability due to an anomalous resistivity. The anomalous resistivity is typically two orders of magnitude larger than the classical at the edge. (author)
Transverse nonlinear instability for two-dimensional dispersive models
Rousset, F.; N. Tzvetkov
2006-01-01
We present a method to prove nonlinear instability of solitary waves in dispersive models. Two examples are analyzed: we prove the nonlinear long time instability of the KdV solitary wave (with respect to periodic transverse perturbations) under a KP-I flow and the transverse nonlinear instability of solitary waves for the cubic nonlinear Schr\\"odinger equation.
Implications of the PSR instability for the SNS
International Nuclear Information System (INIS)
The Los Alamos Proton Storage Ring suffers from a violent, high frequency, transverse instability at high beam current. The Spallation Neutron Source will be similar to the PSR and one must insure that the PSR instability will not keep SNS from reaching its design goal. Efforts toward understanding the instability are described
Subwavelength modulational instability and plasmon oscillons in nanoparticle arrays.
Noskov, Roman E; Belov, Pavel A; Kivshar, Yuri S
2012-03-01
We study modulational instability in nonlinear arrays of subwavelength metallic nanoparticles and analyze numerically nonlinear scenarios of the instability development. We demonstrate that modulational instability can lead to the formation of regular periodic or quasiperiodic modulations of the polarization. We reveal that such nonlinear nanoparticle arrays can support long-lived standing and moving oscillating nonlinear localized modes--plasmon oscillons. PMID:22463637
Trapped particle effect on modulational instability of plasma wave
International Nuclear Information System (INIS)
A problem of stability of high amplitude plasma wave, in which field acceleration of particles takes place, is important in physics of high-energy plasma accelerators. Instabilities (modulational instability in particular) are factors restricting acceleration time and hindering realization of the main metric of charge density waves - extremely high acceleration rate. Trapped particle effect on modulational instability of plasma wave is considered
The Viscoelastic End Plate Instability in the Stretch of Concentrated Polymer Solutions
DEFF Research Database (Denmark)
Rasmussen, Henrik Koblitz; Longin, Pierre-Yves; Bach, Anders; Hassager, Ole
2001-01-01
We consider here a particular instability, an axis symmetry breaking meniscus instability that occurs etc.......We consider here a particular instability, an axis symmetry breaking meniscus instability that occurs etc....
Radiative heat transport instability in a laser produced inhomogeneous plasma
International Nuclear Information System (INIS)
A laser produced high-Z plasma in which an energy balance is achieved due to radiation emission and radiative heat transfer supports ion acoustic instability. A linear dispersion relation is derived, and instability is compared to the radiation cooling instability [R. G. Evans, Plasma Phys. Controlled Fusion 27, 751 (1985)]. Under conditions of indirect drive fusion experiments, the driving term for the instability is the radiative heat flux and, in particular, the density dependence of the radiative heat conductivity. A specific example of thermal Bremsstrahlung radiation source has been considered. This instability may lead to plasma jet formation and anisotropic x-ray generation, thus affecting inertial confinement fusion related experiments
Modulation Instability in Biased Photorefractive-Photovoltaic Crystals
Institute of Scientific and Technical Information of China (English)
LU Ke-Qing; ZHAO Wei; YANG Yan-Long; SUN Chuan-Dong; GAO Hong-Wen; LI Jin-Ping; ZHANG Yan-Peng
2004-01-01
@@ We show the modulation instability of broad optical beams in biased photorefractive-photovoltaic crystals under steady-state conditions. This modulation instability growth rate depends on the external bias field, the bulk photovoltaic effect, and the ratio of the optical beam intensity to that of the dark irradiance. Under appropriate conditions, this modulation instability growth rate is the modulation instability growth rate studied previously in biased photorefractive-nonphotovoltaic crystals, and the modulation instability growth rate in open- and closed-circuit photorefractive-photovoltaic crystals can be predicted.
Recent progress in the understanding of mode instabilities
Jauregui, Cesar; Otto, Hans-Jürgen; Modsching, Norbert; Limpert, Jens; Tünnermann, Andreas
2015-03-01
In this work the latest progress in the understanding of mode instabilities is reviewed. Particular emphasis is put on the recently established influence of photodarkening on the mode instability threshold and its behavior. It is shown, for example, that even degradations of the output power in the order of a few percent can lead to very significant reductions of the mode instability threshold. Moreover, our analysis shows that photodarkening also alters the expected behavior of the mode instability threshold with respect to the signal wavelength and the seed power. Thus photodarkening is revealed as one of the main effects shaping the behavior of the mode instability threshold observed in experiments.
Radiative heat transport instability in a laser produced inhomogeneous plasma
Energy Technology Data Exchange (ETDEWEB)
Bychenkov, V. Yu. [P. N. Lebedev Physics Institute, Russian Academy of Sciences, Moscow 119991 (Russian Federation); Center for Fundamental and Applied Research, VNIIA, ROSATOM, Moscow 127055 (Russian Federation); Rozmus, W. [Theoretical Physics Institute, University of Alberta, Edmonton T6G 2E1 Alberta (Canada)
2015-08-15
A laser produced high-Z plasma in which an energy balance is achieved due to radiation emission and radiative heat transfer supports ion acoustic instability. A linear dispersion relation is derived, and instability is compared to the radiation cooling instability [R. G. Evans, Plasma Phys. Controlled Fusion 27, 751 (1985)]. Under conditions of indirect drive fusion experiments, the driving term for the instability is the radiative heat flux and, in particular, the density dependence of the radiative heat conductivity. A specific example of thermal Bremsstrahlung radiation source has been considered. This instability may lead to plasma jet formation and anisotropic x-ray generation, thus affecting inertial confinement fusion related experiments.
Modulational instability of a large-amplitude lower hybrid wave
International Nuclear Information System (INIS)
Modulation instability of a longwave low-hybride high amplitude wave is considered. A new method for investigating the cold plasma parametric instabilities, based on regularization of finiteless determinants by the Hill method is developed, using which an obvious expression for instability increment is obtained without making use of low parameters. It is shown that without regard to plasma particle thermal spread, increment grows monotonously with the growth of Bessel function argument. Instability increment calculations for plasma with Maxwell distribution by rates are performed using a numeric solution of a standard system describing parametric instabilities. 10 refs.; 6 figs
Modulational instability of Langmuir waves in dense plasmas
International Nuclear Information System (INIS)
The modulational instability development of Langmuir waves is investigated in highly collisional plasmas where the characteristic frequency Ω of the modulated perturbations is much less than νeff, the effective electron collision frequency. It is demonstrated that the modulational instability for the situation considered is mostly determined by collisional effects (differential Joule heating nonlinearity), in contrast to the well-known modulational instability in collisionless plasmas (where ponderomotive force nonlinearity dominates). Rates and thresholds of the instability are found in various limits. The modulational instability is most effective when the angles between a pump wave vector and wave vectors of the modulational perturbations are of order unity
Transverse "Monopole" Instability Driven by Electron Cloud?
Benedetto, Elena; Zimmermann, Frank; Ohmi, K; Papaphilippou, Y; Rumolo, Giovanni
2003-01-01
We simulate the long-term emittance growth of a proton beam due to an electron cloud of moderate density. This emittance growth is sometimes characterized by a rapid blow up of the bunch tail, and it appears to be different from the strong head-tail instability, which is observed at higher electron densities. We study whether this instability can occur in the absence of transverse dipole motion along the bunch, and its sensitivity to various simulation parameters, such as the number of beam-electron interaction points (IPs) and the phase advances between them. Using a frozen-potential model, we compute tune footprints, which reveal the resonances contributing to the incoherent part of the emittance growth.
Arthroscopic Reverse Remplissage for Posterior Instability.
Lavender, Chad D; Hanzlik, Shane R; Pearson, Sara E; Caldwell, Paul E
2016-02-01
Posterior shoulder dislocation is an unusual injury often associated with electrical shock or seizure. As with anterior instability, patients frequently present with an impaction injury to the anterior aspect of the humeral head known as a "reverse Hill-Sachs lesion." The treatment of this bony defect is controversial, and multiple surgical procedures to fill the defect in an effort to decrease recurrence have been described. Most of the reports have focused on an open approach using variations of lesser tuberosity and subscapularis transfers, bone allograft, and even arthroplasty to assist with persistent instability. We advocate an arthroscopic technique that involves a suture anchor-based distal tenodesis of the subscapularis tendon or a reverse remplissage procedure. PMID:27073776
Arthroscopic Reverse Remplissage for Posterior Instability
Lavender, Chad D.; Hanzlik, Shane R.; Pearson, Sara E.; Caldwell, Paul E.
2016-01-01
Posterior shoulder dislocation is an unusual injury often associated with electrical shock or seizure. As with anterior instability, patients frequently present with an impaction injury to the anterior aspect of the humeral head known as a “reverse Hill-Sachs lesion.” The treatment of this bony defect is controversial, and multiple surgical procedures to fill the defect in an effort to decrease recurrence have been described. Most of the reports have focused on an open approach using variations of lesser tuberosity and subscapularis transfers, bone allograft, and even arthroplasty to assist with persistent instability. We advocate an arthroscopic technique that involves a suture anchor–based distal tenodesis of the subscapularis tendon or a reverse remplissage procedure. PMID:27073776
Gravitational Instability and Tsallis' Nonextensive Statistics
Lima, J A S; Silva, R
2002-01-01
The concept of Jeans gravitational instability is rediscussed in the framework of the nonextensive statistics proposed by Tsallis. A simple analytical formula generalizing the Jeans criterion is derived by assuming that the unperturbed self-gravitating collisionless gas is described by the $q$-parametrized class of nonextensive velocity distribution. It is shown that the critical values of wavelenght and mass depend explicitly on the nonextensive $q$-parameter. The standard Jeans wavelenght derived for a Maxwellian distribution is recovered in the limiting case $q$=1. For power-law distributions with cutoff, the instability condition is weakneed with the system becoming unstable even for wavelenghts of the disturbance smaller than the standard Jeans lenght $\\lambda_J$.
CFD simulation of Kelvin-Helmholtz instability
International Nuclear Information System (INIS)
Kelvin-Helmholtz instability appears in stratified two-fluid flow at surface. When the relative velocity is higher than the critical relative velocity, the growth of waves occurs. The experiment of Thorpe [1] used as a benchmark in the present paper, is made in a rectangular glass tube filled with two immiscible fluids of various densities. We simulated the growth of instability with CFX-5.7 code and compared simulation with analytical solution. It was found that surface tension force, which stabilizes growth of waves, actually has a destabilizing effect in simulation, unless very small timestep and residual is used. In CFX code system of nonlinear Navier-Stokes equations is linearised and solved iterative in each timestep, until prescribed residual is achieved. On the other hand, simulation without surface tension force is more stable than analytical result predicts. (author)
Instabilities in power law gradient hardening materials
DEFF Research Database (Denmark)
Niordson, Christian Frithiof; Tvergaard, Viggo
2005-01-01
Tension and compression instabilities are investigated for specimens with dimensions in the micron range. A finite strain generalization of a higher order strain gradient plasticity theory is implemented in a finite element scheme capable of modeling power law hardening materials. Effects of grad...... gradient hardening are found to delay the onset of localization under plane strain tension, and significantly reduce strain gradients in the localized zone. For plane strain compression gradient hardening is found to increase the load-carrying capacity significantly.......Tension and compression instabilities are investigated for specimens with dimensions in the micron range. A finite strain generalization of a higher order strain gradient plasticity theory is implemented in a finite element scheme capable of modeling power law hardening materials. Effects of...
Subtalar joint instability: current clinical concepts.
Budny, Adam
2004-07-01
There has been extensive research and investigation into the subtalar joint (STJ), yet the biomechanics that relate to its anatomic function, especially instability after injury, are surrounded by controversy. With a mechanism of injury closely related to the classic inversion ankle sprain, chronic instability can result following trauma to the lateral ligamentous support network of either joint. Over the past decades there have been countless examples in the literature challenging the current standard of evaluation and treatment of the "subtalar sprain." New technologies have offered varied approaches to diagnostic capability, each with its own strengths and weaknesses, ranging from standard radiographs to CT and MRI. A review of the literature should aid in deciphering the controversy surrounding this aspect of podiatric medicine. PMID:15246150
Transverse Mode Coupling Instability with Space Charge
Energy Technology Data Exchange (ETDEWEB)
Balbekov, V. [Fermilab
2016-03-11
Transverse mode coupling instability of a bunch with space charge and wake field is considered in frameworks of the boxcar model. Eigenfunctions of the bunch without wake are used as the basis for solution of the equations with the wake field included. Dispersion equation for the bunch eigentunes is obtained in the form of an infinite continued fraction. It is shown that influence of space charge on the instability essentially depends on the wake sign. In particular, threshold of the negative wake increases in absolute value until the space charge tune shift is rather small, and goes to zero at higher space charge. The explanation of this behavior is developed by analysis of the bunch spectrum. A comparison of the results with published articles is represented.
Hydrodynamic instability in warped astrophysical discs
Ogilvie, Gordon I
2013-01-01
Warped astrophysical discs are usually treated as laminar viscous flows, which have anomalous properties when the disc is nearly Keplerian and the viscosity is small: fast horizontal shearing motions and large torques are generated, which cause the warp to evolve rapidly, in some cases at a rate that is inversely proportional to the viscosity. However, these flows are often subject to a linear hydrodynamic instability, which may produce small-scale turbulence and modify the large-scale dynamics of the disc. We use a warped shearing sheet to compute the oscillatory laminar flows in a warped disc and to analyse their linear stability by the Floquet method. We find widespread hydrodynamic instability deriving from the parametric resonance of inertial waves. Even very small, unobservable warps in nearly Keplerian discs of low viscosity can be expected to generate hydrodynamic turbulence, or at least wave activity, by this mechanism.
Nonideal magnetohydrodynamic instabilities and toroidal magnetic confinement
International Nuclear Information System (INIS)
The marked divergence of experimentally observed plasma instability phenomena from the predictions of ideal magnetohydrodynamics led in the early 1960s to the formulations of finite-resistivity stability theory. Beginning in the 1970s, advanced plasma diagnostics have served to establish a detailed correspondence between the predictions of the finite-resistivity theory and experimental plasma behavior - particularly in the case of the resistive kink mode and the tokamak plasma. Nonlinear resistive-kink phenomena have been found to govern the transport of magnetic flux and plasma energy in the reversed-field pinch. The other predicted finite-resistivity instability modes have been more difficult to identify directly and their implications for toroidal magnetic confinement are still unresolved
General Theory of the Plasmoid Instability
Comisso, L; Huang, Y -M; Bhattacharjee, A
2016-01-01
A general theory of the onset and development of the plasmoid instability is formulated by means of a principle of least time. The scaling relations for the final aspect ratio, transition time to rapid onset, growth rate, and number of plasmoids are derived, and shown to depend on the initial perturbation amplitude $\\left({\\hat w}_0\\right)$, the characteristic rate of current sheet evolution $\\left(1/\\tau\\right)$, and the Lundquist number $\\left(S\\right)$. They are not simple power laws, and are proportional to $S^{\\alpha} \\tau^{\\beta} \\left[\\ln f(S,\\tau,{\\hat w}_0)\\right]^\\sigma$. The detailed dynamics of the instability is also elucidated, and shown to comprise of a period of quiescence followed by sudden growth over a short time scale.
Electromagnetic instabilities in rotating magnetized viscous objects
Nekrasov, Anatoly
2009-01-01
We study electromagnetic streaming instabilities in thermal viscous regions of rotating astrophysical objects, such as, magnetized accretion disks, molecular clouds, their cores, and elephant trunks. The obtained results can also be applied to any regions of interstellar medium, where different equilibrium velocities between charged species can arise. We consider a weakly ionized multicomponent plasma consisting of neutrals and magnetized electrons, ions, and dust grains. The effect of perturbation of collisional frequencies due to density perturbations of species is taken into account. We obtain general expressions for perturbed velocities of species involving the thermal pressure and viscosity in the case in which perturbations propagate perpendicular to the background magnetic field. The dispersion relation is derived and investigated for axisymmetric perturbations. New compressible instabilities generated due to different equilibrium velocities of different charged species are found in the cold and therma...
Dissipative drift instability in dusty plasma
Directory of Open Access Journals (Sweden)
Nilakshi Das
2012-03-01
Full Text Available An investigation has been done on the very low-frequency electrostatic drift waves in a collisional dusty plasma. The dust density gradient is taken perpendicular to the magnetic field B0⃗, which causes the drift wave. In this case, low-frequency drift instabilities can be driven by E1⃗×B0⃗ and diamagnetic drifts, where E1⃗ is the perturbed electric field. Dust charge fluctuation is also taken into consideration for our study. The dust- neutral and ion-neutral collision terms have been included in equations of motion. It is seen that the low-frequency drift instability gets damped in such a system. Both dust charging and collision of plasma particles with the neutrals may be responsible for the damping of the wave. Both analytical and numerical techniques have been used while developing the theory.
Transverse Mode Coupling Instability with Space Charge
Balbekov, V
2016-01-01
Transverse mode coupling instability of a bunch with space charge and wake field is considered in frameworks of the boxcar model. Eigenfunctions of the bunch without wake are used as the basis for solution of the equations with the wake field included. Dispersion equation for the bunch eigentunes is obtained in the form of an infinite continued fraction. It is shown that influence of space charge on the instability essentially depends on the wake sign. In particular, threshold of the negative wake increases in absolute value until the space charge tune shift is rather small, and goes to zero at higher space charge. The explanation of this behavior is developed by analysis of the bunch spectrum. A comparison of the results with published articles is represented.
Mirror Instability: Quasi-linear Effects
Hellinger, P.; Travnicek, P. M.; Passot, T.; Sulem, P.; Kuznetsov, E. A.
2008-12-01
Nonlinear properties of the mirror instability are investigated by direct integration of the quasi-linear diffusion equation [Shapiro and Shevchenko, 1964] near threshold. The simulation results are compared to the results of standard hybrid simulations [Califano et al., 2008] and discussed in the context of the nonlinear dynamical model by Kuznetsov et al. [2007]. References: Califano, F., P. Hellinger, E. Kuznetsov, T. Passot, P. L. Sulem, and P. M. Travnicek (2008), Nonlinear mirror mode dynamics: Simulations and modeling, J. Geophys. Res., 113, A08219, doi:10.1029/2007JA012898. Kuznetsov, E., T. Passot and P. L. Sulem (2007), Dynamical model for nonlinear mirror modes near threshold, Phys. Rev. Lett., 98, 235003 . Shapiro, V. D., and V. I. Shevchenko (1964), Quasilinear theory of instability of a plasma with an anisotropic ion velocity distribution, Sov. JETP, 18, 1109.
Semiconductor Lasers Stability, Instability and Chaos
Ohtsubo, Junji
2013-01-01
This third edition of “Semiconductor Lasers, Stability, Instability and Chaos” was significantly extended. In the previous edition, the dynamics and characteristics of chaos in semiconductor lasers after the introduction of the fundamental theory of laser chaos and chaotic dynamics induced by self-optical feedback and optical injection was discussed. Semiconductor lasers with new device structures, such as vertical-cavity surface-emitting lasers and broad-area semiconductor lasers, are interesting devices from the viewpoint of chaotic dynamics since they essentially involve chaotic dynamics even in their free-running oscillations. These topics are also treated with respect to the new developments in the current edition. Also the control of such instabilities and chaos control are critical issues for applications. Another interesting and important issue of semiconductor laser chaos in this third edition is chaos synchronization between two lasers and the application to optical secure communication. One o...
Elastic instability in stratified core annular flow
Bonhomme, Oriane; Leng, Jacques; Colin, Annie
2010-01-01
We study experimentally the interfacial instability between a layer of dilute polymer solution and water flowing in a thin capillary. The use of microfluidic devices allows us to observe and quantify in great detail the features of the flow. At low velocities, the flow takes the form of a straight jet, while at high velocities, steady or advected wavy jets are produced. We demonstrate that the transition between these flow regimes is purely elastic -- it is caused by viscoelasticity of the polymer solution only. The linear stability analysis of the flow in the short-wave approximation captures quantitatively the flow diagram. Surprisingly, unstable flows are observed for strong velocities, whereas convected flows are observed for low velocities. We demonstrate that this instability can be used to measure rheological properties of dilute polymer solutions that are difficult to assess otherwise.
Instability in electromagnetically driven flows Part I
Gissinger, Christophe; Fauve, Stephan
2016-01-01
The MHD flow driven by a travelling magnetic field (TMF) in an annular channel is investigated numerically. For sufficiently large magnetic Reynolds number Rm, or if a large enough pressure gradient is externally applied, the system undergoes an instability in which the flow rate in the channel dramatically drops from synchronism with the wave to much smaller velocities. This transition takes the form of a saddle-node bifurcation for the time-averaged quantities. In this first paper, we characterize the bifurcation, and study the stability of the flow as a function of several parameters. We show that the bifurcation of the flow involves a bistability between Poiseuille-like and Hartman-like regimes, and relies on magnetic flux expulsion. Based on this observation, new predictions are made for the occurrence of this stalling instability.
Electromagnetic instability induced by Neutrino interaction
Bhatt, Jitesh R
2016-01-01
A kinetic theory of spin plasma in a neutrino background is developed. Equations of motion of a charged particle in the presence of electromagnetic field and the neutrino asymmetry are derived using the effective low-energy Lagrangian. Modified Vlasov equation is obtained by extending the regular phase-space to incorporate the spin degree of freedom. We apply this formalism to the early Universe to study collective modes in the plasma after the neutrino decoupling. It is shown that the parity violating term in the Lagrangian leads to a plasma instability which can generate magnetic fields. We find that that at the temperatures below the neutrino decoupling the instability can produce magnetic field of 10 Gauss in the Universe. We discuss cosmological implications of the results.
Thin film instability with thermal noise
Diez, Javier A; Fernández, Roberto
2016-01-01
We study the effects of stochastic thermal fluctuations on the instability of the free surface of a flat liquid film upon a solid substrate. These fluctuations are represented as a standard Brownian motion that can be added to the deterministic equation for the film thickness within the lubrication approximation. Here, we consider that while the noise term is white in time, it is coloured in space. This allows for the introduction of a finite correlation length in the description of the randomized intermolecular interaction. Together with the expected spatial periodicity of the flow, we find a dimensionless parameter, $\\beta$, that accounts for the relative importance of the spatial correlation. We perform here the linear stability analysis (LSA) of the film under the influence of both terms, and find the corresponding power spectra for the amplitudes of the normal modes of the instability. We compare this theoretical result with the numerical simulations of the complete non-linear problem, and find a good ag...
Thermal instability in the interstellar medium
Directory of Open Access Journals (Sweden)
J. Ghanbari
2000-06-01
Full Text Available This study demonstrates how thermal structures in the interstellar medium can emerge as a result of thermal instability. For a two-dimensional case, the steady state thermal structures was investigeted and it was shown that a large class of solutions exist. For a one –dimensional case the conductivity was found to be negligible. The effects of to cal cooling on the thermal instability were explored in some depth. In this case analytical results for time-dependent cooling function were presented, too. We studied nonlinear wave phenomena in thermal fluid systems, with a particular emphasis on presenting analytical results. When conductivity is proportional to temperature, the beliavior of thermal waves is soliton like. For slow thermal waves, approximate analytical results were presented. Extensions of this work are discussed briefly, together with possible astrophysical applications.
Front instabilities in evaporatively dewetting nanofluids
Vancea, I.; Thiele, U.; Pauliac-Vaujour, E.; Stannard, A.; Martin, C. P.; Blunt, M. O.; Moriarty, P. J.
2008-10-01
Various experimental settings that involve drying solutions or suspensions of nanoparticles—often called nanofluids—have recently been used to produce structured nanoparticle layers. In addition to the formation of polygonal networks and spinodal-like patterns, the occurrence of branched structures has been reported. After reviewing the experimental results we use a modified version of the Monte Carlo model first introduced by Rabani [Nature 426, 271 (2003)] to study structure formation in evaporating films of nanoparticle solutions for the case that all structuring is driven by the interplay of evaporating solvent and diffusing nanoparticles. After introducing the model and its general behavior we focus on receding dewetting fronts which are initially straight but develop a transverse fingering instability. We analyze the dependence of the characteristics of the resulting branching patterns on the driving effective chemical potential, the mobility and concentration of the nanoparticles, and the interaction strength between liquid and nanoparticles. This allows us to understand the underlying instability mechanism.
Baroclinic Instability on Hot Extrasolar Planets
Polichtchouk, Inna
2012-01-01
We investigate baroclinic instability in flow conditions relevant to hot extrasolar planets. The instability is important for transporting and mixing heat, as well as for influencing large-scale variability on the planets. Both linear normal mode analysis and non-linear initial value calculations are carried out -- focusing on the freely-evolving, adiabatic situation. Using a high-resolution general circulation model (GCM) which solves the traditional primitive equations, we show that large-scale jets similar to those observed in current GCM simulations of hot extrasolar giant planets are likely to be baroclinically unstable on a timescale of few to few tens of planetary rotations, generating cyclones and anticyclones that drive weather systems. The growth rate and scale of the most unstable mode obtained in the linear analysis are in qualitative, good agreement with the full non-linear calculations. In general, unstable jets evolve differently depending on their signs (eastward or westward), due to the chang...
Nonlinear evolution of the sausage instability
International Nuclear Information System (INIS)
Sausage instabilities of an incompressible, uniform, perfectly conducting Z pinch are studied in the nonlinear regime. In the long wavelength limit (analogous to the ''shallow water theory'' of hydrodynamics), a simplified set of universal fluid equations is derived, with no radial dependence, and with all parameters scaled out. Analytic and numerical solutions of these one-dimensional equations show that an initially sinusoidal perturbation grows into a ''spindle'' or cylindrical ''spike and bubble'' shape, with sharp radial maxima. In the short wavelength limit, the problem is shown to be mathematically equivalent to the planar semi-infinite Rayleigh--Taylor instability, which also grows into a spike-and-bubble shape. Since the spindle shape is common to both limits, it is concluded that it probably obtains in all cases. The results are in agreement with dense plasma focus experiments
A STUDY ON MICROWAVE INSTABILITY INDUCED RADIATION.
Energy Technology Data Exchange (ETDEWEB)
MURPHY,J.B.; WANG,J.M.
1999-03-29
It has been shown in the context of a solvable model that the microwave instability can be described in terms of ''coherent states'' [1]. Building on this model, we first show that the simplicity of the model arises from the fact that the key integral-differential equation can be reduced to the Karhunen-Loeve equation of the theory of stochastic processes. We present results on the correlation functions of the electric field. In particular, for the second order correlation function, we show that a relation akin to the Hanbury Brown-Twiss correlation holds for the coherent states of the microwave-instability induced radiation. We define an entropy-like quantity and we introduce a Wigner distribution function representation.
Wakefields and Instabilities in Linear Accelerators
Ferrario, M; Palumbo, L
2014-01-01
When a charged particle travels across the vacuum chamber of an accelerator, it induces electromagnetic fields, which are left mainly behind the generating particle. These electromagnetic fields act back on the beam and influence its motion. Such an interaction of the beam with its surro undings results in beam energy losses, alters the shape of the bunches, and shifts the betatron and synchrotron frequencies. At high beam current the fields can even lead to instabilities, thus limiting the performance of the accelerator in terms of beam quality and current intensity. We discuss in this lecture the general features of the electromagnetic fields, introducing the concepts of wakefields and giving a few simple examples in cylindrical geometry. We then show the effect of the wakefields on the dynamics of a beam in a linac, dealing in particular with the beam breakup instability and how to cure it.
Modulational instability in wind-forced waves
Energy Technology Data Exchange (ETDEWEB)
Brunetti, Maura [GAP-Climate and Institute for Environmental Sciences, University of Geneva, Route de Drize 7, 1227 Carouge (Switzerland); Kasparian, Jérôme [GAP-Nonlinear, University of Geneva, Chemin de Pinchat 22, 1227 Carouge (Switzerland)
2014-11-14
We consider the wind-forced nonlinear Schrödinger (NLS) equation obtained in the potential flow framework when the Miles growth rate is of the order of the wave steepness. In this case, the form of the wind-forcing terms gives rise to the enhancement of the modulational instability and to a band of positive gain with infinite width. This regime is characterised by the fact that the ratio between wave momentum and norm is not a constant of motion, in contrast to what happens in the standard case where the Miles growth rate is of the order of the steepness squared. - Highlights: • We start from the nonlinear Schrödinger equation (NLSE) for fast-growing waves. • The wind-forcing terms give rise to the enhancement of the modulational instability. • In this regime the ratio between wave momentum and norm is not conserved in time.
Nonideal magnetohydrodynamic instabilities and toroidal magnetic confinement
Energy Technology Data Exchange (ETDEWEB)
Furth, H.P.
1985-05-01
The marked divergence of experimentally observed plasma instability phenomena from the predictions of ideal magnetohydrodynamics led in the early 1960s to the formulations of finite-resistivity stability theory. Beginning in the 1970s, advanced plasma diagnostics have served to establish a detailed correspondence between the predictions of the finite-resistivity theory and experimental plasma behavior - particularly in the case of the resistive kink mode and the tokamak plasma. Nonlinear resistive-kink phenomena have been found to govern the transport of magnetic flux and plasma energy in the reversed-field pinch. The other predicted finite-resistivity instability modes have been more difficult to identify directly and their implications for toroidal magnetic confinement are still unresolved.
A Joint Chow Test for Structural Instability
Directory of Open Access Journals (Sweden)
Bent Nielsen
2015-03-01
Full Text Available The classical Chow test for structural instability requires strictly exogenousregressors and a break-point specified in advance. In this paper, we consider twogeneralisations, the one-step recursive Chow test (based on the sequence of studentisedrecursive residuals and its supremum counterpart, which relaxes these requirements. We useresults on the strong consistency of regression estimators to show that the one-step test isappropriate for stationary, unit root or explosive processes modelled in the autoregressivedistributed lags (ADL framework. We then use the results in extreme value theory to developa new supremum version of the test, suitable for formal testing of structural instability withan unknown break-point. The test assumes the normality of errors and is intended to be usedin situations where this can be either assumed nor established empirically. Simulations showthat the supremum test has desirable power properties, in particular against level shifts latein the sample and against outliers. An application to U.K. GDP data is given.
Nonlinear evolution of whistler wave modulational instability
DEFF Research Database (Denmark)
Karpman, V.I.; Lynov, Jens-Peter; Michelsen, Poul; Juul Rasmussen, J.
1995-01-01
The nonlinear evolution of the modulational instability of whistler waves coupled to fast magnetosonic waves (FMS) and to slow magnetosonic waves (SMS) is investigated. Results from direct numerical solutions in two spatial dimensions agree with simplified results from a set of ordinary...... differential equations obtained from a Hamiltonian formulation of the governing equations. The long-time evolution of the modulational instability for the FMS-coupling shows a quasi-recurrent behavior with a slow spreading of the energy to higher and higher mode numbers. For the SMS-coupling, no recurrent...... behavior is found and the energy is gradually leaking to higher mode numbers while the spatial evolution of the modulation tends to develop small scale ''spikes.'' (C) 1995 American Institute of Physics....
Semiquantum chaotic manifestations of modulational instability
International Nuclear Information System (INIS)
The modulational perturbations of the amplitude and phase for the time evolution of plane waves are studied in the semiquantum approach. Beyond the stability criterion from the nonlinear Schrödinger equation, there arise signatures of chaos in the dynamics of the associated cubic–quartic effective potential. The extended classical system described by fluctuation variables, nonlinearly coupled to the average ones, undergoes time-dependent variational approximation and foresees rooms of surprising regularity in the instability zone and chaos within the stable region of the wave number. The question of modulational instability (MI) for physical systems exhibits semiquantum chaotic features numerically observed with standard indicators. A dynamical quantum MI criterion is derived to resize the regions for stability with the correspondent momentum. (paper)
Nonlinear evolution of whistler wave modulational instability
International Nuclear Information System (INIS)
The nonlinear evolution of the modulational instability of whistler waves coupled to fast magnetosonic waves (FMS) and to slow magnetosonic waves (SMS) is investigated. Results from direct numerical solutions in two spatial dimensions agree with simplified results from a set of ordinary differential equations obtained from a Hamiltonian formulation of the governing equations. The long-time evolution of the modulational instability for the FMS-coupling shows a quasi-recurrent behavior with a slow spreading of the energy to higher and higher mode numbers. For the SMS-coupling, no recurrent behavior is found and the energy is gradually leaking to higher mode numbers while the spatial evolution of the modulation tends to develop small scale ''spikes.'' copyright 1995 American Institute of Physics
Feedback control of coupled-bunch instabilities
International Nuclear Information System (INIS)
The next generation of synchrotron light sources and particle accelerators will require active feedback systems to control multi-bunch instabilities. Stabilizing hundreds or thousands of potentially unstable modes in these accelerator designs presents many technical challenges. Feedback systems to stabilize coupled-bunch instabilities may be understood in the frequency domain (mode-based feedback) or in the time domain (bunch-by-bunch feedback). In both approaches an external amplifier system is used to create damping fields that prevent coupled-bunch oscillations from growing without bound. The system requirements for transverse (betatron) and longitudinal (synchrotron) feedback are presented, and possible implementation options developed. Feedback system designs based on digital signal-processing techniques are described. Experimental results are shown from a synchrotron oscillation damper in the SSRL/SLAC storage ring SPEAR that uses digital signal-processing techniques
Does Easing Monetary Policy Increase Financial Instability?
Cesa-Bianchi, Ambrogio; Rebucci, Alessandro
2013-01-01
This paper develops a model featuring both a macroeconomic and a financial stability objective that speaks to the interaction between monetary and macroprudential policies. First, we find that interest rate rigidities in a monopolistic banking system have an asymmetric impact on financial stability: they lead to greater financial instability in response to contractionary shocks, while they act as an automatic financial stabilizer in response to expansionary shocks. Second, we find that when t...
SOCIAL PSYCHOLOGY OF INSTABILITY WITHIN ORGANIZATIONAL REALITY
Takhir Yu. Bazarov
2012-01-01
Since modern organizations inevitably face constant changes in internal and external environment, can anything be done in order for the strategy of changes to become “proactive" and to prevent naturally determined crisis situations and recession? Featuring empirical data, the article discusses the possibility of socio- psychological research in the situation of instability. Among other aspects, there is suggested an answer to the question of whether social psychology can help a person to real...
Rayleigh-Taylor Instability in Viscoelastic Fluids
Joshi, Amey
2013-01-01
In this paper I analyze the onset of Rayleigh-Taylor instability between two linear viscoelastic fluids assuming that the perturbations at the interface are small. In the first half, the paper analyzes a stratified viscoelastic fluid in which I prove that the perturbations rise or fall exponentially without oscillating. The second half of the paper examines the effect of electric and magnetic fields on viscoelastic fluids. I show that it is possible to choose electric or magnetic field gradie...
Coherent instabilities of a relativistic bunched beam
Energy Technology Data Exchange (ETDEWEB)
Chao, A.W.
1982-06-01
A charge-particle beam contained in an accelerator vacuum chamber interacts electromagnetically with its environment to create a wake field. This field than acts back on the beam, perturbing the particle motion. If the beam intensity is high enough, this beam-environment interaction may lead to an instability and to subsequent beam loss. The beam and its environment form a dynamical system, and it is this system that will be studied. 84 references.
Variational approach to the modulational instability.
Rapti, Z; Kevrekidis, P G; Smerzi, A; Bishop, A R
2004-01-01
We study the modulational stability of the nonlinear Schrödinger equation using a time-dependent variational approach. Within this framework, we derive ordinary differential equations (ODE's) for the time evolution of the amplitude and phase of modulational perturbations. Analyzing the ensuing ODE's, we rederive the classical modulational instability criterion. The case (relevant to applications in optics and Bose-Einstein condensation) where the coefficients of the equation are time dependent, is also examined. PMID:14995759
Large-scale instabilities of helical flows
Cameron, Alexandre; Alexakis, Alexandros; Brachet, Marc-Étienne
2016-01-01
Large-scale hydrodynamic instabilities of periodic helical flows are investigated using $3$D Floquet numerical computations. A minimal three-modes analytical model that reproduce and explains some of the full Floquet results is derived. The growth-rate $\\sigma$ of the most unstable modes (at small scale, low Reynolds number $Re$ and small wavenumber $q$) is found to scale differently in the presence or absence of anisotropic kinetic alpha (\\AKA{}) effect. When an $AKA$ effect is present the s...
Coherent instabilities of a relativistic bunched beam
International Nuclear Information System (INIS)
A charge-particle beam contained in an accelerator vacuum chamber interacts electromagnetically with its environment to create a wake field. This field than acts back on the beam, perturbing the particle motion. If the beam intensity is high enough, this beam-environment interaction may lead to an instability and to subsequent beam loss. The beam and its environment form a dynamical system, and it is this system that will be studied. 84 references
Flow and instability in quantum gravity
International Nuclear Information System (INIS)
We study the flow from the m=3 multicritical matrix theory, unambiguously defined by Brezin, Marinari and Parisi, to the m=2 pure gravity theory. We find behavior in the flow indicative of a non-perturbative instability in this definition of non-perturbative pure quantum gravity. We expect a similar situation for all m even theories. Other definitions of these theories are briefly discussed. (orig.)
The Growth Effects of Institutional Instability
DEFF Research Database (Denmark)
Berggren, Niclas; Bergh, Andreas; Bjørnskov, Christian
. While institutional instability is negatively related to growth in the baseline case, there are indications that the effect can be positive in rich countries, suggesting that institutional reform is not necessarily costly even during a transition period. Sensitivity analysis, e.g., decomposing the...... political risk index by using both its constituting components and the results of a principal components analysis, using other measures of institutional quality and excluding outliers, confirm the general results, with qualifications....
Erosion waves: transverse instabilities and fingering
Malloggi, F.; Lanuza, J.; Andreotti, B.; Clément, E.
2005-01-01
Two laboratory scale experiments of dry and under-water avalanches of non-cohesive granular materials are investigated. We trigger solitary waves and study the conditions under which the front is transversally stable. We show the existence of a linear instability followed by a coarsening dynamics and finally the onset of a fingering pattern. Due to the different operating conditions, both experiments strongly differ by the spatial and time scales involved. Nevertheless, the quantitative agree...
Phase instability and coarsening in two dimensions
Misbah, Chaouqi; Politi, Paolo
2009-01-01
Instabilities and pattern formation is the rule in nonequilibrium systems. Selection of a persistent lengthscale, or coarsening (increase of the lengthscale with time) are the two major alternatives. When and under which conditions one dynamics prevails over the other is a longstanding problem, particularly beyond one dimension. It is shown that the challenge can be defied in two dimensions, using the concept of phase diffusion equation. We find that coarsening is related to the \\lambda-depen...
Characterization of gas-lift instabilities
Hu, Bin
2005-01-01
This dissertation mainly investigates the occurrence and characteristics of density-wave instability in gas-lift wells. The investigation is based on a simplified gas-lift system, in which water and air are used as producing fluid and lifting gas respectively, and heat transfer effect is neglected.To carry out the investigation, both linear stability analysis and numerical simulation are performed. The linear stability analysis is based on a homogenous two-phase flow model and the numerical s...
Space Propagation of Instabilities in Zakharov Equations
Metivier, Guy
2007-01-01
39 p International audience In this paper we study an initial boundary value problem for Zakharov's equations, describing the space propagation of a laser beam entering in a plasma. We prove a strong instability result and prove that the mathematical problem is ill-posed in Sobolev spaces. We also show that it is well posed in spaces of analytic functions. Several consequences for the physical consistency of the model are discussed.
Pisotriquetral arthrodesis for pisotriquetral instability: case report.
Singer, Georg; Eberl, Robert; Hoellwarth, Michael E
2011-02-01
A 22-year-old professional downhill mountain bike rider developed increasing posttraumatic pisotriquetral instability. To preserve full function of the pisiform bone, we performed pisotriquetral arthrodesis using a Herbert screw. Ten months after the splint was removed, the patient was free of symptoms and returned to professional downhill mountain biking without limitations. This uncommon method seems to be a feasible treatment strategy and can be recommended in high-demand patients. PMID:21168980
Neurodegeneration-associated instability of ribosomal DNA
Hallgren, Justin; Pietrzak, Maciej; Rempala, Grzegorz; Nelson, Peter T.; Hetman, Michal
2014-01-01
Homologous recombination (HR)-mediated instability of the repetitively organized ribosomal DNA (rDNA) has been proposed as a mediator of cell senescence in yeast triggering the DNA damage response. High individual variability in the content of human rDNA suggests that this genomic region remained relatively unstable throughout evolution. Therefore, quantitative real time PCR was used to determine the genomic content of rDNA in post mortem samples of parietal cortex from 14 young- and 9 elderl...
Chromosomal instability determines taxane sensitivity - supplementary materials
Swanton, Charles; Nicke, Barbara; Schuett, Marion; Eklund, Aron C.; Ng, Charlotte; Li, Qiyuan; Hardcastle, Thomas; Lee, Alvin; Roy, Rajat; East, Philip; Kschischo, Maik; Endesfelder, David; Wylie, Paul; Kim, Se Nyun; Chen, Jie-Guang
2009-01-01
Microtubule-stabilizing (MTS) agents, such as taxanes, are important chemotherapeutics with a poorly understood mechanism of action. We identified a set of genes repressed in multiple cell lines in response to MTS agents and observed that these genes are overexpressed in tumors exhibiting chromosomal instability (CIN). Silencing 22/50 of these genes, many of which are involved in DNA repair, caused cancer cell death, suggesting that these genes are involved in the survival of aneuploid cells....
Instability of nonlinear dispersive solitary waves
Lin, Zhiwu
2008-01-01
We consider linear instability of solitary waves of several classes of dispersive long wave models. They include generalizations of KDV, BBM, regularized Boussinesq equations, with general dispersive operators and nonlinear terms. We obtain criteria for the existence of exponentially growing solutions to the linearized problem. The novelty is that we dealt with models with nonlocal dispersive terms, for which the spectra problem is out of reach by the Evans function technique. For the proof, ...
A Visual Observation of Cavitating Inducer Instability
Kamijo, Kenjiro; Shimura, Takashi; 渡辺, 光男; WATANABE, Mitsuo; 上条, 謙二郎; 志村, 隆
1980-01-01
This paper presents the results of experiments on the instability of a cavitating inducer, which is considered to be closely related with the POGO phenomena in liquid propellant rockets. The present experiment employed a high speed camera for visual observations. The dynamic pressure of both the inducer upstream and downstream was also measured. The difference between rotating cavitation and cavitation induced low cycle oscillations was examined. The cavities moved around the periphery of the...
Aerodynamic instabilities in transonic centrifugal compressor
Buffaz, Nicolas; Trébinjac, Isabelle
2014-01-01
International audience This paper presents the analysis of the instabilities inception in a transonic centrifugal com-pressor for different rotation speeds. The analysis was conducted from experimental results obtained with unsteady pressure sensors implanted in the inducer, vaneless diffuser and vaned diffuser. Beyond the stability limit the compressor enters into a deep surge without any precursor, whatever the speed. The surge process is initiated in the vaned diffuser by a massive boun...
Infrared instability from nonlinear QCD evolution
Enberg, R.; Peschanski, R.
2005-01-01
Using the Balitsky-Kovchegov (BK) equation as an explicit example, we show that nonlinear QCD evolution leads to an instability in the propagation toward the infrared of the gluon transverse momentum distribution, if one starts with a state with an infrared cut-off. This effect takes the mathematical form of rapidly moving traveling wave solutions of the BK equation, which we investigate by numerical simulations. These traveling wave solutions are different from those governing the transition...
Instability Resistance Training Across the Exercise Continuum
Behm, David G.; Colado Sanchez, Juan Carlos
2013-01-01
Context: Instability resistance training (IRT; unstable surfaces and devices to strengthen the core or trunk muscles) is popular in fitness training facilities. Objective: To examine contradictory IRT recommendations for health enthusiasts and rehabilitation. Data Sources: A literature search was performed using MEDLINE, SPORT Discus, ScienceDirect, Web of Science, and Google Scholar databases from 1990 to 2012. Study Selection: Databases were searched using key terms, including “balance,” “s...
Instability Criteria and Growth of Baroclinic Disturbances
Fleagle, Robert G.
2011-01-01
The instability criterion and the rate of growth of long baroclinic disturbances in horizontally uniform zonal flow is derived for a sloping streamsurface. Both quantities are expressed by one explicit and simple function. Unstable disturbances are characterized by upward motion toward the cold air and downward motion toward the warm air. The slope of the streamsurface is eliminated, and the growth equation is compared with the results of other studies. The maximum rate of growth is small eno...
Transient Instability of Rapidly Rotating Black Holes
Gralla, Samuel E; Zimmerman, Peter
2016-01-01
We analytically study the linear response of a near-extremal Kerr black hole to external scalar, electromagnetic, and gravitational field perturbations. We show that the energy density, electromagnetic field strength, and tidal force experienced by infalling observers exhibit transient growth near the horizon. The growth lasts arbitrarily long in the extremal limit, reproducing the horizon instability of extremal Kerr. We explain these results in terms of near-horizon geometry and discuss potential astrophysical implications.
Thermodynamic instability of doubly spinning black objects
Astefanesei, D.; Rodriguez, M.; S. Theisen
2010-01-01
We investigate the thermodynamic stability of neutral black objects with (at least) two angular momenta. We use the quasilocal formalism to compute the grand canonical potential and show that the doubly spinning black ring is thermodynamically unstable. We consider the thermodynamic instabilities of ultra-spinning black objects and point out a subtle relation between the microcanonical and grand canonical ensembles. We also find the location of the black string/membrane phases of doubly spinn...
Financial instability from local market measures
Marco Bardoscia; Giacomo Livan; Matteo Marsili
2012-01-01
We study the emergence of instabilities in a stylized model of a financial market, when different market actors calculate prices according to different (local) market measures. We derive typical properties for ensembles of large random markets using techniques borrowed from statistical mechanics of disordered systems. We show that, depending on the number of financial instruments available and on the heterogeneity of local measures, the market moves from an arbitrage-free phase to an unstable...
A subject-specific postural instability parameter.
Argatov, I
2013-01-01
A mathematical modeling approach is applied for deriving subject-specific stabilometric parameters associated with center-of-pressure sway measurements for assessing balancing ability of subjects in quiet standing on a force platform. Based on the inverted pendulum model, a new combined stabilometric parameter including anthropometric characteristics (body height and mass) is obtained which represents a measure of postural instability. A physical meaning of the subject-specific parameter is related to the effective stiffness of the inverted pendulum model. PMID:22795475
A Joint Chow Test for Structural Instability
Bent Nielsen; Andrew Whitby
2012-01-01
The classical Chow test for structural instability requires strictly exogenousregressors and a break-point specified in advance. In this paper, we consider twogeneralisations, the one-step recursive Chow test (based on the sequence of studentisedrecursive residuals) and its supremum counterpart, which relaxes these requirements. We useresults on the strong consistency of regression estimators to show that the one-step test isappropriate for stationary, unit root or explosive processes modelle...
White-light parametric instabilities in plasmas
Santos, J. E.; Silva, L. O.; Bingham, R.
2007-01-01
Parametric instabilities driven by partially coherent radiation in plasmas are described by a generalized statistical Wigner-Moyal set of equations, formally equivalent to the full wave equation, coupled to the plasma fluid equations. A generalized dispersion relation for Stimulated Raman Scattering driven by a partially coherent pump field is derived, revealing a growth rate dependence, with the coherence width $\\sigma$ of the radiation field, scaling with $1/\\sigma$ for backscattering (thre...
Flow instabilities within an urban intersection
Czech Academy of Sciences Publication Activity Database
Kellnerová, Radka; Jaňour, Zbyněk
2011-01-01
Roč. 47, 1-4 (2011), s. 268-277. ISSN 0957-4352 Institutional research plan: CEZ:AV0Z20760514 Keywords : wind-tunnel * street canyon * flow instability * urban intersection * environmental pollution * quadrant analysis Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 0.361, year: 2011 http://inderscience.metapress.com/content/e301241p70566w5w/
Summary of working group on collective instabilities
International Nuclear Information System (INIS)
In this paper we summarize the efforts of the Working Group on Collective Instabilities at the Workshop on the RHIC Performance. Impedance estimates have been made for some of the main hardware in RHIC, including bellows, pickup electrodes, abort kicker, and transverse damper. In general, these impedances are not expected to limit the beam intensity for Au ions, but might limit the proton intensity. We have also calculated the higher-order modes of the standard 26.7-MHz rf cavity for use in estimating coupled-bunch instability growth rates. Predictions of intrabeam scattering confirm the results in the RHIC Conceptual Design Report. For the standard assumptions, there is a threefold growth in transverse emittance. Varying the initial transverse emittance by a factor of two changes the final emittance value (after 10 hours) by less than 20%. If a 214-MHz rf system is considered, the growth is more severe---about a factor of five---and a beam lifetime of 10 hours requires an rf voltage in excess of 32 MV. Coupled-bunch calculations show that the transverse instabilities are dominated by the resistive-wall impedance for either rf choice. A modest damping system should be adequate to deal with this. Longitudinal growth times of about 20 ms are expected for the low-frequency rf case; growth times for the high-frequency rf system are a factor of 10 longer and the instability is predicted to be Landau damped. Copper plating of the dipole vacuum chambers has been found to have no deleterious effects, provided the coating is uniform and not overly thick. 14 refs., 3 tabs
Studies of intense-laser plasma instabilities
Czech Academy of Sciences Publication Activity Database
Láska, Leoš; Krása, Josef; Badziak, J.; Jungwirth, Karel; Krouský, Eduard; Margarone, Daniele; Parys, P.
2013-01-01
Roč. 272, May (2013), 94-98. ISSN 0169-4332 R&D Projects: GA MŠk(CZ) 7E09092; GA MŠk(CZ) LC528; GA AV ČR IAA100100715 Institutional research plan: CEZ:AV0Z10100523 Keywords : laser plasma instabilities * self-generated magnetic field * longitudinal structure of the expanding plasma Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.538, year: 2013
Influence of Ion Streaming Instabilities on Transport Near Plasma Boundaries
Baalrud, Scott D
2015-01-01
Plasma boundary layers are susceptible to electrostatic instabilities driven by ion flows in presheaths and, when present, these instabilities can influence transport. In plasmas with a single species of positive ion, ion-acoustic instabilities are expected under conditions of low pressure and large electron-to-ion temperature ratio ($T_e/T_i \\gg 1$). In plasmas with two species of positive ions, ion-ion two-stream instabilities can also be excited. The stability phase-space is characterized using the Penrose criterion and approximate linear dispersion relations. Predictions for how these instabilities affect ion and electron transport in presheaths, including rapid thermalization due to instability-enhanced collisions and an instability-enhanced ion-ion friction force, are also briefly reviewed. Recent experimental tests of these predictions are discussed along with research needs required for further validation. The calculated stability boundaries provide a guide to determine the experimental conditions at ...
Influence of ion streaming instabilities on transport near plasma boundaries
Baalrud, Scott D.
2016-04-01
Plasma boundary layers are susceptible to electrostatic instabilities driven by ion flows in presheaths and, when present, these instabilities can influence transport. In plasmas with a single species of positive ion, ion-acoustic instabilities are expected under conditions of low pressure and large electron-to-ion temperature ratio ({{T}e}/{{T}i}\\gg 1 ). In plasmas with two species of positive ions, ion-ion two-stream instabilities can also be excited. The stability phase-space is characterized using the Penrose criterion and approximate linear dispersion relations. Predictions for how these instabilities affect ion and electron transport in presheaths, including rapid thermalization due to instability-enhanced collisions and an instability-enhanced ion-ion friction force, are briefly reviewed. Recent experimental tests of these predictions are discussed along with research needs required for further validation. The calculated stability boundaries provide a guide to determine the experimental conditions at which these effects can be expected.
Instabilities in a Self-Gravitating Magnetized Gas Disk
Lee, S M; Lee, Sang Min; Hong, Seung Soo
1999-01-01
A linear stability analysis has been performed onto a self-gravitating magnetized gas disk bounded by external pressure. The resulting dispersion relation is fully explained by three kinds of instability: a Parker-type instability driven by self-gravity, usual Jeans gravitational instability and convection. In the direction parallel to the magnetic fields, the magnetic tension completely suppresses the convection. If the adiabatic index $\\gamma$ is less than a certain critical value, the perturbations trigger the Parker as well as the Jeans instability in the disk. Consequently, the growth rate curve has two maxima: one at small wavenumber due to a combination of the Parker and Jeans instabilities, and the other at somewhat larger wavenumber mostly due to the Parker instability. In the horizontal direction perpendicular to the fields, the convection makes the growth rate increase monotonically upto a limiting value as the perturbation wavenumber gets large. However, at small wavenumbers, the Jeans instability...
Model of oscillatory instability in vertically-homogeneous atmosphere
Directory of Open Access Journals (Sweden)
P. B. Rutkevich
2009-02-01
Full Text Available Existence and repeatability of tornadoes could be straightforwardly explained if there existed instability, responsible for their formation. However, it is well known that convection is the only instability in initially stable air, and the usual convective instability is not applicable for these phenomena. In the present paper we describe an instability in the atmosphere, which can be responsible for intense vortices. This instability appears in a fluid with Coriolis force and dissipation and has oscillatory behaviour, where the amplitude growth is accompanied by oscillations with frequency comparable to the growth rate of the instability. In the paper, both analytical analysis of the linear phase of the instability and nonlinear simulation of the developed stage of the air motion are addressed. This work was supported by the RFBR grant no. 09-05-00374-a.
Imaging findings in posterior instability of the shoulder
International Nuclear Information System (INIS)
Posterior shoulder instability refers to the symptoms and signs resulting from excessive posterior translation of the humerus. Magnetic resonance (MR) imaging is the radiological modality of choice in the diagnostic assessment of posterior instability. Computed tomography (CT) is useful in the evaluation of osseous abnormalities associated with posterior instability. A detailed description of the posterior osseous and labroligamentous abnormalities has evolved recently, and many variant lesions of the posteroinferior labrum and/or capsular structures have been described. As the recommended surgical management of lesions associated with posterior instability is a lesion-specific approach, awareness of the specific lesions that have been described in association with posterior instability helps in pre-surgical planning. The purpose of this article is to review the classification of, and injury mechanisms leading to, posterior shoulder instability and to describe imaging findings associated with posterior instability, with emphasis on MR imaging. (orig.)
The acoustic instabilities in magnetized collisional dusty plasmas
Energy Technology Data Exchange (ETDEWEB)
Pandey, B. P., E-mail: birendra.pandey@mq.edu.au [Department of Physics and Astrophysics, Macquarie University, Sydney, NSW 2109 (Australia); Vladimirov, S. V., E-mail: s.vladimirov@physics.usyd.edu.au [Metamaterials Laboratory, National Research University of Information Technology, Mechanics, and Optics, St. Petersburg 199034 (Russian Federation); Dwivedi, C. B., E-mail: jagatpurdwivedi@gmail.com [Ved–Vijnanam Pravartanam Samitihi, Pratapgarh (Awadh), Jagatpur, Bharat (India)
2014-09-15
The present work investigates the wave propagation in collisional dusty plasmas in the presence of electric and magnetic field. It is shown that the dust ion-acoustic waves may become unstable to the reactive instability whereas dust-acoustic waves may suffer from both reactive and dissipative instabilities. If the wave phase speed is smaller than the plasma drift speed, the instability is of reactive type whereas in the opposite case, the instability becomes dissipative in nature. Plasma in the vicinity of dust may also become unstable to reactive instability with the instability sensitive to the dust material: dielectric dust may considerably quench this instability. This has implications for the dust charging and the use of dust as a probe in the plasma sheath.
The acoustic instabilities in magnetized collisional dusty plasmas
International Nuclear Information System (INIS)
The present work investigates the wave propagation in collisional dusty plasmas in the presence of electric and magnetic field. It is shown that the dust ion-acoustic waves may become unstable to the reactive instability whereas dust-acoustic waves may suffer from both reactive and dissipative instabilities. If the wave phase speed is smaller than the plasma drift speed, the instability is of reactive type whereas in the opposite case, the instability becomes dissipative in nature. Plasma in the vicinity of dust may also become unstable to reactive instability with the instability sensitive to the dust material: dielectric dust may considerably quench this instability. This has implications for the dust charging and the use of dust as a probe in the plasma sheath
Shear-induced instabilities in layered liquids
Auernhammer, Günter K.; Brand, Helmut R.; Pleiner, Harald
2002-12-01
Motivated by the experimentally observed shear-induced destabilization and reorientation of smectic-A-like systems, we consider an extended formulation of smectic-A hydrodynamics. We include both, the smectic layering (via the layer displacement u and the layer normal pcirc) and the director ncirc of the underlying nematic order in our macroscopic hydrodynamic description and allow both directions to differ in nonequilibrium situations. In an homeotropically aligned sample the nematic director does couple to an applied simple shear, whereas the smectic layering stays unchanged. This difference leads to a finite (but usually small) angle between ncirc and pcirc, which we find to be equivalent to an effective dilatation of the layers. This effective dilatation leads, above a certain threshold, to an undulation instability of the layers. We generalize our earlier approach [G. K. Auernhammer, H. R. Brand, and H. Pleiner, Rheol. Acta 39, 215 (2000)] and include the cross couplings with the velocity field and the order parameters for orientational and positional order and show how the order parameters interact with the undulation instability. We explore the influence of various material parameters on the instability. Comparing our results to recent experiments and molecular dynamic simulations, we find a good qualitative agreement.
Instability patterns between counter-rotating disks
Directory of Open Access Journals (Sweden)
F. Moisy
2003-01-01
Full Text Available The instability patterns in the flow between counter-rotating disks (radius to height ratio R/h from 3.8 to 20.9 are investigated experimentally by means of visualization and Particle Image Velocimetry. We restrict ourselves to the situation where the boundary layers remain stable, focusing on the shear layer instability that occurs only in the counter-rotating regime. The associated pattern is a combination of a circular chain of vortices, as observed by Lopez et al. (2002 at low aspect ratio, surrounded by a set of spiral arms, first described by Gauthier et al. (2002 in the case of high aspect ratio. Stability curve and critical modes are measured for the whole range of aspect ratios. From the measurement of a local Reynolds number based on the shear layer thickness, evidence is given that a free shear layer instability, with only weak curvature effect, is responsible for the observed patterns. Accordingly, the number of vortices is shown to scale as the shear layer radius, which results from the competition between the centrifugal effects of each disk.
Cladding failure by local plastic instability
Energy Technology Data Exchange (ETDEWEB)
Kramer, J.M.; Deitrich, L.W.
1977-12-01
Cladding failure is one of the major considerations in analysis of fuel-pin behavior during hypothetical accident transients since time, location, and nature of failure govern the early postfailure material motion and reactivity feedback. Out-of-pile thermal transient tests of both irradiated and unirradiated fast-reactor cladding show that local plastic instability, or bulging, often precedes rupture and that the extent of local instability limits the initial rip length. To investigate the details of bulge formation and growth, a perturbation analysis of the equations governing large deformation of a cylindrical shell has been developed, resulting in a set of linear differential equations for the bulge geometry. These equations have been solved along with appropriate constitutive equations and various constraints on the ends of the cladding. Sources for bulge formation that have been considered include initial geometric imperfections and thermal perturbations due to either eccentric fuel pellets or nonsymmetric cooling. Of these, only the first is relevant to out-of-pile burst tests. Here it has been found that the most likely imperfection that will grow unstably to failure leads to a bulge around half the circumference with an axial length 1.1 times the deformed diameter. This is in general agreement with burst-test results. For the case of in-reactor fuel pins, it has been found that thermal perturbations can significantly affect local instability, particularly if the deformation process is thermally activated with a high activation energy.
Scaling and uncertainty in BWR instability problems
International Nuclear Information System (INIS)
This paper deals with a critical review of activities, performed at the DCMN of Pisa University, in relation to the thermo-hydraulic oscillations in two-phase systems. Stability analyses, including model development and achievement of experimental data, are generally performed for BWRs in order to achieve the following objectives: to reach a common understanding in relation to the predictive capabilities of system codes and to the influence of various parameters on the instability; to establish a data base for the qualification of the analytical tools already or becoming available; to set-up qualified tools (code/models + nodalization + user assumption) suitable for predicting the unstable behaviour of the nuclear plants of interest (current BWR, SBWR, ABWR and RBMK). These considerations have been the basis for the following researches: 1) proposal of the Boiling Instability Program (BIP) (1) 2) evaluation of stability tests in PIPER-ONE apparatus (2) 3) coupled thermal-hydraulic and neutronic instabilities in the LaSalle-2 BWR plant (3) 4) participation to the NEA-OECD BWR Benchmark (4) The RELAP/MOD2 and RELAP5/MOD3 codes have been used. (author)
Sawtooth Instability in the Compact Toroidal Hybrid
Herfindal, J. L.; Maurer, D. A.; Hartwell, G. J.; Ennis, D. A.; Knowlton, S. F.
2015-11-01
Sawtooth instabilities have been observed in the Compact Toroidal Hybrid (CTH), a current-carrying stellarator/tokamak hybrid device. The sawtooth instability is driven by ohmic heating of the core plasma until the safety factor drops below unity resulting in the growth of an m = 1 kink-tearing mode. Experiments varying the vacuum rotational transform from 0.02 to 0.13 are being conducted to study sawtooth property dependance on vacuum flux surface structure. The frequency of the sawtooth oscillations increase from 2 kHz to 2.8 kHz solely due the decrease in rise time of the oscillation, the crash time is unchanged. CTH has three two-color SXR cameras, a three-channel 1mm interferometer, and a new bolometer system capable of detecting the signatures of sawtooth instabilities. The new bolometer system consists of two cameras, each containing a pair of diode arrays viewing the plasma directly or through a beryllium filter. Electron temperature measurements are found with the two-color SXR cameras through a ratio of the SXR intensities. Impurity radiation can drastically affect the electron temperature measurement, therefore new filters consisting of aluminum and carbon were selected to avoid problematic line radiation while maximizing the signal for a 100 eV plasma. This work is supported by U.S. Department of Energy Grant No. DE-FG02-00ER54610.
Buoyancy instabilities in degenerate, collisional, magnetized plasmas
Chang, Philip; Quataert, Eliot
2010-03-01
In low-collisionality plasmas, anisotropic heat conduction due to a magnetic field leads to buoyancy instabilities for any non-zero temperature gradient. We study analogous instabilities in degenerate collisional plasmas, i.e. when the electron collision frequency is large compared to the electron cyclotron frequency. Although heat conduction is nearly isotropic in this limit, the small residual anisotropy ensures that collisional degenerate plasmas are also convectively unstable independent of the sign of the temperature gradient. We show that the range of wavelengths that are unstable is independent of the magnetic field strength, while the growth time increases with decreasing magnetic field strength. We discuss the application of these collisional buoyancy instabilities to white dwarfs and neutron stars. Magnetic tension and the low specific heat of a degenerate plasma significantly limit their effectiveness; the most promising venues for growth are in the liquid oceans of young, weakly magnetized neutron stars (B <~ 109 G) and in the cores of young, high magnetic field white dwarfs (B ~ 109 G).
Digital instability of a confined elastic meniscus.
Biggins, John S; Saintyves, Baudouin; Wei, Zhiyan; Bouchaud, Elisabeth; Mahadevan, L
2013-07-30
Thin soft elastic layers serving as joints between relatively rigid bodies may function as sealants, thermal, electrical, or mechanical insulators, bearings, or adhesives. When such a joint is stressed, even though perfect adhesion is maintained, the exposed free meniscus in the thin elastic layer becomes unstable, leading to the formation of spatially periodic digits of air that invade the elastic layer, reminiscent of viscous fingering in a thin fluid layer. However, the elastic instability is reversible and rate-independent, disappearing when the joint is unstressed. We use theory, experiments, and numerical simulations to show that the transition to the digital state is sudden (first-order), the wavelength and amplitude of the fingers are proportional to the thickness of the elastic layer, and the required separation to trigger the instability is inversely proportional to the in-plane dimension of the layer. Our study reveals the energetic origin of this instability and has implications for the strength of polymeric adhesives; it also suggests a method for patterning thin films reversibly with any arrangement of localized fingers in a digital elastic memory, which we confirm experimentally. PMID:23858433
Ballooning mode instability at the plasmapause
Lakhina, G. S.; Mond, M.; Hameiri, E.
1990-01-01
The ballooning mode instability, which can excite hydromagnetic waves at the plasmapause, is studied in the presence of azimuthal plasma flows induced during geomagnetically disturbed periods. A general sufficient criterion for the ballooning mode stability is derived, for a change in the potential energy greater than or equal to 0, which involves the integration over an entire field line. A local stability analysis at the equatorial plasmapause region shows that the ballooning modes could be spontaneously generated via instability under at least two conditions: one is similar to the usual interchange condition, and the second to the quasi-interchange modes. Both of these local instability conditions can be derived from the general stability criterion. Finally an exact solution for the equilibrium state with flow is derived analytically, and the change in the potential energy is computed numerically. It is found that, in the cases studied, the flow does not spontaneously excite the ballooning modes; it only further stabilizes (or destabilizes) the ballooning spectrum if originally the system is stable (or unstable). The analysis would be useful for the interpretation of some of the low-frequency modes observed at the ground and near the equatorial plasmapause.
Beam instability studies at the APS
International Nuclear Information System (INIS)
The Argonne Advanced Photon Source, APS (Fig. 1), is a 7-GeV positron storage ring with a circumference of 1104 m. It has a ''third generation, DBA or Chasman-Green'' lattice composed of 40 sectors each having a ∼6 m long zero-dispersion straight-section for accommodating insertion devices. Neighboring straight-sections are connected by a 360 degrees/40 = 9 degrees double-bend-achromatic bending section designed to produce the smallest emittance attainable with reasonable component parameter values and dynamic apertures. Thus, it is a very strongly focusing lattice with vx = 35.22 and vy = 14.30. The beam chamber of the storage ring including all rf, vacuum and photon beam components is designed to ensure that a beam current > 100 mA can be stably stored. We expect that the maximum stable beam current could be as high as 300 mA. This paper will give some details of the studies and computations to ensure the stability of such a beam. The discussions will be organized in the following three parts: Coupled-bunch instability caused by the higher-order modes (HOMs) of the rf cavities; Single-bunch instability due to the resistive wall impedance; and Single-bunch instability due to broadband impedances arising from beam chamber irregularities
Baroclinic instability in the solar tachocline
Energy Technology Data Exchange (ETDEWEB)
Gilman, Peter; Dikpati, Mausumi, E-mail: gilman@ucar.edu, E-mail: dikpati@ucar.edu [High Altitude Observatory, National Center for Atmospheric Research, 3080 Center Green, Boulder, CO 80307-3000 (United States)
2014-05-20
The solar tachocline is likely to be close to a geostrophic 'thermal wind', for which the Coriolis force associated with differential rotation is closely balanced by a latitudinal pressure gradient, leading to a tight relation between the vertical gradient of rotation and the latitudinal entropy gradient. Using a hydrostatic but nongeostrophic spherical shell model, we examine baroclinic instability of the tachocline thermal wind. We find that both the overshoot and radiative parts of the tachocline should be baroclinicly unstable at most latitudes. Growth rates are roughly five times higher in middle and high latitudes compared to low latitudes, and much higher in the overshoot than in the radiative tachocline. They range in e-folding amplification from 10 days in the high latitude overshoot tachocline, down to 20 yr for the low latitude radiative tachocline. In the radiative tachocline only, longitudinal wavenumbers m = 1, 2 are unstable, while in the overshoot tachocline a much broader range of m are unstable. At all latitudes and with all stratifications, the longitudinal scale of the most unstable mode is comparable to the Rossby deformation radius, while the growth rate is set by the local latitudinal entropy gradient. Baroclinic instability in the tachocline competing with instability of the latitude rotation gradient established in earlier studies should be important for the workings of the solar dynamo and should be expected to be found in most stars that contain an interface between radiative and convective domains.
Electromagnetic instability in a magnetic neutral sheet
International Nuclear Information System (INIS)
The structure of electromagnetic perturbations in a magnetic neutral sheet was analyzed within the framework of a Vlasov-Maxwellian picture. In the geomagnetic tail, there exists a stable magnetic neutral sheet of about 10 R-E (earth radius) thick. However, it has been reported that the thickness of this sheet is reduced to about 1 R-E just before the onset of substorms, and this shows the critical thickness of sheet destruction. In the laboratory experiment, a stable neutral sheet is produced by induction, and its thickness also becomes as thin as about the ion Larmor radius, which is defined far outside the sheet region, before the sudden destruction of the sheet current. Tearing instability cannot explain this abrupt destruction. Then it can be considered that the tearing instability is stabilized by some mechanisms. Consequently, it becomes important to look for another perturbation unstable in a thin sheet while stable in a thick sheet. Here, a magnetically compressional mode propagating in the direction of the unperturbed current which produced reverse field is considered. Equilibrium configuration and particle orbits, perturbations, resulted eigenfunctions and dispersion relations are described to show that the above mode becomes unstable in a thin sheet, and the critical thickness is about the ion Larmor radius just outside the sheet region. When the typical field intensity in the geomagnetic tail is taken, the time scale of this instability becomes about 800 sec. This value coincides with the observed flare time scale. (Wakatsuki, Y.)
Gravitomagnetic Instabilities in Anisotropically Expanding Fluids
Kleidis, Kostas; Kuiroukidis, Apostolos; Papadopoulos, Demetrios B.; Vlahos, Loukas
Gravitational instabilities in a magnetized Friedman-Robertson-Walker (FRW) universe, in which the magnetic field was assumed to be too weak to destroy the isotropy of the model, are known and have been studied in the past. Accordingly, it became evident that the external magnetic field disfavors the perturbations' growth, suppressing the corresponding rate by an amount proportional to its strength. However, the spatial isotropy of the FRW universe is not compatible with the presence of large-scale magnetic fields. Therefore, in this paper we use the general-relativistic version of the (linearized) perturbed magnetohydrodynamic equations with and without resistivity, to discuss a generalized Jeans criterion and the potential formation of density condensations within a class of homogeneous and anisotropically expanding, self-gravitating, magnetized fluids in curved space-time. We find that, for a wide variety of anisotropic cosmological models, gravitomagnetic instabilities can lead to subhorizontal, magnetized condensations. In the nonresistive case, the power spectrum of the unstable cosmological perturbations suggests that most of the power is concentrated on large scales (small k), very close to the horizon. On the other hand, in a resistive medium, the critical wave-numbers so obtained, exhibit a delicate dependence on resistivity, resulting in the reduction of the corresponding Jeans lengths to smaller scales (well bellow the horizon) than the nonresistive ones, while increasing the range of cosmological models which admit such an instability.
Nonlinear Instabilities in Shock-Bounded Slabs
Vishniac, E T
1993-01-01
(substantial changes to section 3.2, otherwise minor) We present an analysis of the hydrodynamic stability of a cold slab bounded by two accretion shocks. Previous numerical work has shown that when the Mach number of the shock is large the slab is unstable. Here we show that to linear order both the bending and breathing modes of such a slab are stable. However, nonlinear effects will tend to soften the restoring forces for bending modes, and when the slab displacement is comparable to its thickness this gives rise to a nonlinear instability. The growth rate of the instability, above this threshold but for small bending angles, is $\\sim c_sk (k\\eta)^{1/2}$, where $\\eta$ is the slab displacement. When the bending angle is large the slab will contain a local vorticity comparable to $c_s/L$, where $L$ is the slab thickness. We discuss the implications of this work for gravitational instabilities of slabs. Finally, we examine the cases of a decelerating slab bounded by a single shock and a stationary slab bounde...
PEP-X IMPEDANCE AND INSTABILITY CALCULATIONS
Energy Technology Data Exchange (ETDEWEB)
Bane, K.L.F.; Lee, L.-Q.; Ng, C.; Stupakov, G.; au Wang, L.; Xiao, L.; /SLAC
2010-08-25
PEP-X, a next generation, ring-based light source is designed to run with beams of high current and low emittance. Important parameters are: energy 4.5 GeV, circumference 2.2 km, beam current 1.5 A, and horizontal and vertical emittances, 185 pm by 8 pm. In such a machine it is important that impedance driven instabilities not degrade the beam quality. In this report they study the strength of the impedance and its effects in PEP-X. For the present, lacking a detailed knowledge of the vacuum chamber shape, they create a straw man design comprising important vacuum chamber objects to be found in the ring, for which they then compute the wake functions. From the wake functions they generate an impedance budget and a pseudo-Green function wake representing the entire ring, which they, in turn, use for performing microwave instability calculations. In this report they, in addition, consider in PEP-X the transverse mode-coupling, multi-bunch transverse, and beam-ion instabilities.
Electromagnetic Instabilities Excited by Electron Temperature Anisotropy
Institute of Scientific and Technical Information of China (English)
陆全明; 王连启; 周艳; 王水
2004-01-01
One-dimensional particle-in-cell simulations are performed to investigate the nonlinear evolution of electromagnetic instabilities excited by the electron temperature anisotropy in homogeneous plasmas with different parameters. The results show that the electron temperature anisotropy can excite the two right-hand electromagnetic instabilities, one has the frequency higher than Ωe, the other is the whistler instability with larger amplitude,and its frequency is below Ωe. Their dispersion relations are consistent with the prediction from the cold plasma theory. In the initial growth stage (prediction from linear theory), the frequency of the dominant mode (the mode whose amplitude is large enough) of the whistler wave almost does not change, but in the saturation stage the situation is different. In the case that the ratio of electron plasma frequency to cyclotron frequency is larger than 1, the frequency of the dominant mode of the whistler wave drifts from high to low continuously. However, for the case of the ratio smaller than 1, besides the original dominant mode of the whistler wave whose frequency is about 2.6ωe, another dominant mode whose frequency is about 1.55ωe also begins to be excited at definite time,and its amplitude increases with time until it exceeds the original dominant mode.
Mizuno, Yosuke; Nishikawa, Ken-Ichi; Hardee, Philip E
2009-01-01
We have investigated the development of current-driven (CD) kink instability through three-dimensional relativistic MHD simulations. A static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the kink instability. The instability develops as predicted by linear theory. In the non-linear regime the kink amplitude continues to increase up to the terminal simulation time, albeit at different rates, for all but one simulation. The growth rate and nonlinear evolution of the CD kink instability depends moderately on the density profile and strongly on the magnetic pitch profile. The growth rate of the kink mode is reduced in the linear regime by an increase in the magnetic pitch with radius and the non-linear regime is reached at a later time than for constant helical pitch. On the other hand, the g...
Mizuno, Yosuke; Lyubarsky, Yuri; ishikawa, Ken-Ichi; Hardee, Philip E.
2010-01-01
We have investigated the development of current-driven (CD) kink instability through three-dimensional relativistic MHD simulations. A static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the kink instability. The instability develops as predicted by linear theory. In the non-linear regime the kink amplitude continues to increase up to the terminal simulation time, albeit at different rates, for all but one simulation. The growth rate and nonlinear evolution of the CD kink instability depends moderately on the density profile and strongly on the magnetic pitch profile. The growth rate of the kink mode is reduced in the linear regime by an increase in the magnetic pitch with radius and the non-linear regime is reached at a later time than for constant helical pitch. On the other hand, the growth rate of the kink mode is increased in the linear regime by a decrease in the magnetic pitch with radius and reaches the non-linear regime sooner than the case with constant magnetic pitch. Kink amplitude growth in the non-linear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the non-linear regime nearly ceases for increasing magnetic pitch.
Observations of a tropical instability vortex
Kennan, Sean Christopher
1997-11-01
Observations of an upper ocean vortex associated with tropical instabilities in the tropical Pacific were made in the vicinity of the South Equatorial Current and North Equatorial Counter Current (SEC-NECC) shear at 140oW during November-December of 1990. The dynamic and thermohaline structure of the observed vortex is mapped in three dimensions using a suite of measurements from shipboard, hydrographic, and satellite sensors and drifting buoys. Evidence that the sampled flow field is steady in a frame of reference moving with the disturbance is used to study the underlying dynamical balances and the effects on heat, fresh water, and eddy energy fluxes in the region. The vortex translated westward at 30 cm/s (0.24o/day), less than half the speed of westward propagating meridional oscillations of the Equatorial Undercurrent (EUC) and SEC system. The associated flow deformed the North Equatorial Front through northward advection of cold equatorial water and southward entrainment of warmer tropical water, giving the surface temperature field the cusp-like pattern which is commonly associated with tropical instabilities. A dipole of convergence and divergence had magnitudes comparable to the local inertial frequency and confirms predictions by various numerical models. Relative vorticity advection balanced convergence at the front, allowing northward moving cold water to subduct beneath the warmer tropical water. The growth of the vortex appears to have been limited by the inertial frequency via a vortex instability mechanism. The same features are present in shear vortices in a general circulation model. The vortex transported heat and fresh water equatorward at rates of about 0.2 MW/m2 and 5 g/(m2s), respectively. The heat flux agrees with previous estimates from observations and models. The region from 2-5oN gained heat and fresh water at 2-5 W/m3 and 0.1 μg/(m3s). Eddy kinetic energy increased via barotropic instability at a rate of 0.15 mW/m3 and via baroclinic
Shrefler, John; Dietze, Georg; Narayanan, Ranga
2015-11-01
The classical Marangoni instability problem, principally introduced by Pearson in 1958, takes the interface of two fluids heated from below to be non-deflecting and as a consequence of this assumption thermal inertia is responsible for the onset of convective flows. However, in practical problems where interfacial deflections are uncontrollable and necessarily present, we find that thermal inertia is of very little importance for a broad class of fluids. Neglecting the contribution of thermal inertia, we find that the instability persists as in the classical case. This is shown by way of an integral boundary layer method for long wavelength flows and confirmed by detailed calculations using the full equations. We aim to demonstrate that the principal result that thermal inertia is unimportant continues to hold for the evaporation instability problem, provided pure component phase change is considered. Supported by NSF 0968313 and Marie Curie IRSES grants.
Modulational instability of broad spectra of lower hybrid waves
International Nuclear Information System (INIS)
A universal nonlinear formalism in which the fields are represented as a sum of their regular and random components is applied to derive integral equations describing the modulational instability of the spectra of lower hybrid waves. The modulational instability of the one-dimensional spectra of lower hybrid waves is investigated. It is shown that the 'short-scale' instability of one-dimensional spectra behaves as the 'short-scale' instability of a monochromatic pump wave; in particular, the maximum growth rate of the short-scale instability differs from that of the instability of a monochromatic pump wave by a numerical factor of order unity. It is demonstrated that the 'long-scale' instability of the wave spectra is generally weaker than the instability of a monochromatic pump wave. The instability thresholds can exist only for spectra occupying the entire range of wavenumbers in which the waves can be excited. A transition from a weakly turbulent state to a strongly turbulent state is studied. It is shown that such a transition is physically meaningful only in systems in which the weakly turbulent spectrum of the waves in the space of wave vectors is very broad. The problem of describing the effect of the modulational instability on the lower hybrid current drive is discussed
Posterior glenoid rim deficiency in recurrent (atraumatic) posterior shoulder instability
International Nuclear Information System (INIS)
Objective. To assess the shape of the posterior glenoid rim in patients with recurrent (atraumatic) posterior instability.Design and patients. CT examinations of 15 shoulders with recurrent (atraumatic) posterior instability were reviewed in masked fashion with regard to abnormalities of the glenoid shape, specifically of its posterior rim. The glenoid version was also assessed. The findings were compared with the findings in 15 shoulders with recurrent anterior shoulder instability and 15 shoulders without instability. For all patients, surgical correlation was available.Results. Fourteen of the 15 (93%) shoulders with recurrent (atraumatic) posterior shoulder instability had a deficiency of the posteroinferior glenoid rim. In patients with recurrent anterior instability or stable shoulders such deficiencies were less common (60% and 73%, respectively). The craniocaudal length of the deficiencies was largest in patients with posterior instability. When a posteroinferior deficiency with a craniocaudal length of 12 mm or more was defined as abnormal, sensitivity and specificity for diagnosing recurrent (atraumatic) posterior instability were 86.7% and 83.3%, respectively. There was a statistically significant difference in glenoid version between shoulders with posterior instability and stable shoulders (P=0.01).Conclusion. Recurrent (atraumatic) posterior shoulder instability should be considered in patients with a bony deficiency of the posteroinferior glenoid rim with a craniocaudal length of more than 12 mm. (orig.)
CHF and flow instability in rod bundles
International Nuclear Information System (INIS)
Data for two very different rod bundles have been analyzed using a new CHF correlation and a crude, but simple, subchannel analysis. The CHF correlation was developed for round uniform tubes and has been shown to accurately predict CHF in nonuniform tubes. The first set of data was for a KWU rod bundle (37 rods) with a heated length of 3.00 m and an O.D. (outside diameter) of 12.9 mm over a range of pressure 70 to 150 bar in upflow. The second set of data was for a 5 x 5 TRIGA rod bundle with a heated length of 0.559 m and 13.75 mm O.D. over a range of pressure of 0.945 to 1.372 bar in downflow. In contrast to the KWU data, the correlation greatly over estimates the CHF values for the TRIGA data. The TRIGA CHF data correlate very well with the variable qsat assuming no mixing, qc,exp = 0.955qsat (stdev = 9.87%). This result strongly suggests that these instabilities, which resulted immediately in CHF, are triggered by the Onset of Flow Instability (OFI) rather than CHF. The wide spread in rod power factors, the low pressure, and the downflow condition all contribute to promoting this type of instability (Ledinegg). The crude subchannel analysis has been compared with calculations of exit conditions of the hot channel using COBRA code. The agreement is fair when the homogeneous equilibrium model is used in the COBRA code. This is expected since the exit of the hot channel is always subcooled. Using Zuber's, along with other, void fraction relations in COBRA yields much lower exit velocities and high positive exit qualities, and, in some cases, convergence difficulties arise. The facts indicate that the bundle has already past the OFI point: which is possible since no CHF calculation was made in these COBRA analyses. (J.P.N)
Characterisation of the Montset instability, Valais, Switzerland
Perraudin, Camille; Carrea, Dario; Derron, Marc-Henri; Jaboyedoff, Michel
2013-04-01
The present study focuses on the rock slope of Montset, a 2622 m high summit in the Penninic Alps, in Switzerland. Different features (morpho-structure, size of the phenomenon, present-day rate of displacement, and ancient collapse of the lower part of the slope) suggest that it is a deep-seated slope deformation (DSGSD). The detection and the monitoring of movements are important to understand the deformation mechanisms, the type, and the geometry of rock slope failure and to assess its stability. Terrestrial laser scanning (TLS) provides high resolution point clouds of the topography which is used for structural analysis including an assessment of the discontinuity sets and a detailed geometrical characterization of the study area. Two TLS acquisition were conducted in July and October 2012. The scans are treated and analyzed using PolyWorks software to be first aligned and georeferenced. The alignment of the scans taken at different epochs enables the detection and quantification of slope movements, like rockfalls or sliding area. No significant movements were detected; however, some localized movements such as rockfalls or creep due to permafrost meltdown were shown. Furthermore, forward movement is detected in the upper part of the instability. The comparison between the discontinuity sets from both sides of the fault which is assumed to delimit the instability shows rotational movements. Several more active areas are identified, based on field observations. Based on the recognition of common structural features with a stable reference area, we can compute the rotation or the toppling that characterize the discontinuity planes of the unstable area. Once the movements are detected, quantified and localized, a 3D model of the instability can be proposed. This is realized using Move, modeling software which can integrate various geological data.
Curvature instability of a vortex ring
Fukumoto, Yasuhide; Hattori, Yuji
2005-03-01
A global stability analysis of Kelvin's vortex ring to three-dimensional disturbances of infinitesimal amplitude is made. The basic state is a steady asymptotic solution of the Euler equations, in powers of the ratio ɛ of the core radius to the ring radius, for an axisymmetric vortex ring with vorticity proportional to the distance from the symmetric axis. The effect of ring curvature appears at first order, in the form of a dipole field, and a local straining field, which is a quadrupole field, follows at second order. The eigenvalue problem of the Euler equations, retaining the terms to first order, is solved in closed form, in terms of the Bessel and the modified Bessel functions. We show that the dipole field causes a parametric resonance instability between a pair of Kelvin waves whose azimuthal wavenumbers are separated by 1. The most unstable mode occurs in the short-wavelength limit, under the constraint that the radial and the azimuthal wavenumbers are of the same magnitude, and the limiting value of maximum growth rate coincides with the value 165/256 ɛ obtained by Hattori & Fukumoto (Phys. Fluids, vol. 15, 2003, p. 3151) by means of the geometric optics method. The instability mechanism is traced to stretching of disturbance vorticity in the toroidal direction. In the absence of viscosity, the dipole effect outweighs the straining field effect of O(ɛ2) known as the Moore-Saffman-Tsai-Widnall instability. The viscosity acts to damp the former preferentially and these effects compete with each other.
Magnetorotational Instability of Dissipative MHD Flows
Energy Technology Data Exchange (ETDEWEB)
HERRON, ISOM H
2010-07-10
Executive summary Two important general problems of interest in plasma physics that may be addressed successfully by Magnetohydrodynamics (MHD) are: (1) Find magnetic field configurations capable of confining a plasma in equilibrium. (2) Study the stability properties of each such an equilibrium. It is often found that the length scale of many instabilities and waves that are able to grow or propagate in a system, are comparable with plasma size, such as in magnetically confined thermonuclear plasmas or in astrophysical accretion disks. Thus MHD is able to provide a good description of such large-scale disturbances. The Magnetorotational instability (MRI) is one particular instance of a potential instability. The project involved theoretical work on fundamental aspects of plasma physics. Researchers at the Princeton Plasma Physics Laboratory (PPPL) began to perform a series of liquid metal Couette flow experiments between rotating cylinders. Their purpose was to produce MRI, which they had predicted theoretically 2002, but was only observed in the laboratory since this project began. The personnel on the project consisted of three persons: (1) The PI, who was partially supported on the budget during each of four summers 2005-2008. (2) Two graduate research assistants, who worked consecutively on the project throughout the years 2005-2009. As a result, the first student, Fritzner Soliman, obtained an M.S. degree in 2006; the second student, Pablo Suarez obtained the Ph.D. degree in 2009. The work was in collaboration with scientists in Princeton, periodic trips were made by the PI as part of the project. There were 4 peer-reviewed publications and one book produced.
Stochastically driven instability in rotating shear flows
International Nuclear Information System (INIS)
The origin of hydrodynamic turbulence in rotating shear flows is investigated, with particular emphasis on the flows whose angular velocity decreases but whose specific angular momentum increases with the increasing radial coordinate. Such flows are Rayleigh stable, but must be turbulent in order to explain the observed data. Such a mismatch between the linear theory and the observations/experiments is more severe when any hydromagnetic/magnetohydrodynamic instability and then the corresponding turbulence therein is ruled out. This work explores the effect of stochastic noise on such hydrodynamic flows. We essentially concentrate on a small section of such a flow, which is nothing but a plane shear flow supplemented by the Coriolis effect. This also mimics a small section of an astrophysical accretion disc. It is found that such stochastically driven flows exhibit large temporal and spatial correlations of perturbation velocities and hence large energy dissipations of perturbation, which presumably generate the instability. A range of angular velocity (Ω) profiles of the background flow, starting from that of a constant specific angular momentum (λ = Ωr2; r being the radial coordinate) to a constant circular velocity (vϕ = Ωr), is explored. However, all the background angular velocities exhibit identical growth and roughness exponents of their perturbations, revealing a unique universality class for the stochastically forced hydrodynamics of rotating shear flows. This work, to the best of our knowledge, is the first attempt to understand the origin of instability and turbulence in three-dimensional Rayleigh stable rotating shear flows by introducing additive noise to the underlying linearized governing equations. This has important implications to resolve the turbulence problem in astrophysical hydrodynamic flows such as accretion discs. (paper)
CSR instability in a Bunch Compressor
International Nuclear Information System (INIS)
The coherent synchrotron radiation of a bunch in a bunch compressor may lead to the microwave instability producing longitudinal modulation of the bunch with wavelengths small compared to the bunch length. It can also be a source of an undesirable emittance growth in the compressor. We derive and analyze the equation that describes linear evolution of the microwave modulation taking into account incoherent energy spread and finite emittance of the beam. Numerical solution of this equation for the LCLS bunch compressor gives the amplification factor for different wavelengths of the beam microbunching
Rarefaction solitons initiated by sheath instability
Energy Technology Data Exchange (ETDEWEB)
Levko, Dmitry [Department of Aerospace Engineering and Engineering Mechanics, The University of Texas at Austin, Austin, Texas 78712 (United States)
2015-09-15
The instability of the cathode sheath initiated by the cold energetic electron beam is studied by the one-dimensional fluid model. Numerical simulations show the generation of travelling rarefaction solitons at the cathode. It is obtained that the parameters of these solitons strongly depend on the parameters of electron beam. The “stretched” variables are derived using the small-amplitude analysis. These variables are used in order to obtain the Korteweg-de Vries equation describing the propagation of the rarefaction solitons through the plasma with cold energetic electron beam.
Local instability in BWR reactor simulator
International Nuclear Information System (INIS)
''Local'' oscillations in thermal-hydraulic quantities have been observed while performing system code calculations related to PIPER-ONE BWR simulator; void fraction oscillations were detected at the channel middle elevation but not at channel bottom and top. This paper deals with an experimental investigation of ''local'' instability starting from experimental data obtained with the PIPER-ONE facility. The considered test is PO-SD-5B; the post-test analysis has been carried out by RELAP5/MOD2 code. In particular the analysis concerns the experimental and calculated oscillations of pressure drop in the core region and the calculated oscillations of channel void fraction
Hip Instability: Current Concepts and Treatment Options.
Dumont, Guillaume D
2016-07-01
Instability of the hip can manifest in a wide range of settings, with presenting symptoms including subtle discomfort at end range of motion or more dramatic dislocation of the joint. It can result from traumatic injury with dislocation or subluxation; atraumatic capsular laxity; structural bony abnormality, such as acetabular dysplasia; and iatrogenic injury. Initial treatment of the concentrically reduced joint often begins with physical therapy to strengthen dynamic stabilizers and to allow time for resolution of acute symptoms. Surgical treatment is aimed at repairing injured soft tissue structures, including static stabilizers, and addressing underlying bony structural deficiencies. PMID:27343395
Cancer chromosomal instability: therapeutic and diagnostic challenges.
McGranahan, Nicholas; Burrell, Rebecca A; Endesfelder, David; Novelli, Marco R; Swanton, Charles
2012-06-01
Chromosomal instability (CIN)-which is a high rate of loss or gain of whole or parts of chromosomes-is a characteristic of most human cancers and a cause of tumour aneuploidy and intra-tumour heterogeneity. CIN is associated with poor patient outcome and drug resistance, which could be mediated by evolutionary adaptation fostered by intra-tumour heterogeneity. In this review, we discuss the clinical consequences of CIN and the challenges inherent to its measurement in tumour specimens. The relationship between CIN and prognosis supports assessment of CIN status in the clinical setting and suggests that stratifying tumours according to levels of CIN could facilitate clinical risk assessment. PMID:22595889
Curvature suppresses the Rayleigh-Taylor instability
Trinh, Philippe H; Hammoud, Naima; Howell, Peter D; Chapman, S Jonathan; Stone, Howard A
2014-01-01
The dynamics of a thin liquid film on the underside of a curved cylindrical substrate is studied. The evolution of the liquid layer is investigated as the film thickness and the radius of curvature of the substrate are varied. A dimensionless parameter (a modified Bond number) that incorporates both geometric parameters, gravity, and surface tension is identified, and allows the observations to be classified according to three different flow regimes: stable films, films with transient growth of perturbations followed by decay, and unstable films. Experiments and theory confirm that, below a critical value of the Bond number, curvature of the substrate suppresses the Rayleigh-Taylor instability.
Stochastic stability and instability of model ecosystems
Ladde, G. S.; Siljak, D. D.
1975-01-01
In this work, we initiate a stability study of multispecies communities in stochastic environment by using Ito's differential equations as community models. By applying the direct method of Liapunov, we obtain sufficient conditions for stability and instability in the mean of the equilibrium populations. The conditions are expressed in terms of the dominant diagonal property of community matrices, which is a suitable mechanism for resolving the central problem of 'complexity vs stability' in model ecosystems. As a by-product of this analysis we exhibit important structural properties of the stochastic density-dependent models, and establish tolerance of community stability to a broad class of nonlinear time-varying perturbations.
Topologically Induced Instability in String Theory
McInnes, B
2001-01-01
Using the generalised AdS/CFT correspondence, we show that there are certain ten-dimensional differentiable manifolds such that string theory on such a manifold is unstable [to the emission of "large branes"] no matter what the metric may be. The instability is thus due to the [differential] topology of the manifold, not to any particular choice of its geometry. We propose a precise criterion for this "topology selection mechanism", and prove it in many cases. The techniques employed may be useful in more general cases.
Instability of Bucket Foundations during Installation
DEFF Research Database (Denmark)
Madsen, Søren; Andersen, Lars Vabbersgaard; Ibsen, Lars Bo
The bucket foundation is an upcoming technology for offshore wind turbines. The bucket foundation is a large cylindrical monopod foundation constructed as a thin steel shell structure. A bucket foundation does not require heavy installation equipment since it is installed by suction forces. The...... combination of a thin shell structure and suction forces leads to the fact that instability, in form of buckling, becomes a crucial issue during installation. The hydrostatic buckling pressure of the bucket foundation is addressed using three-dimensional, non-linear finite element analysis. The results of the...
Collisionless trapped ion temperature gradient instabilities
International Nuclear Information System (INIS)
Under the fluid limit, the collisionless trapped ion temperature gradient instabilities with eigenfrequency approaching to ion bounce frequency are investigated by retaining the trapped ion parallel compressibility in the electrostatic case. The unstable eigenmodes are shown in entire range of parameter b. There exists a local unstable slab branch with a moderate ballooning structure at the relatively short wavelengths. Meanwhile, two nonlocal unstable branches, toroidal and slab, with mode structures of periodic oscillation overlapping on a secular variation are found in the relatively long wavelength limit. These unstable modes' eigenfrequencies, propagating properties, and eigenmode structures are given analytically and numerically. The numerical results are in good agreement with the analytical ones. (5 figs.)
Modulational instability in wind-forced waves
Brunetti, Maura
2014-01-01
We consider the wind-forced nonlinear Schroedinger (NLS) equation obtained in the potential flow framework when the Miles growth rate is of the order of the wave steepness. In this case, the form of the wind-forcing terms gives rise to the enhancement of the modulational instability and to a band of positive gain with infinite width. This regime is characterised by the fact that the ratio between wave momentum and norm is not a constant of motion, in contrast to what happens in the standard case where the Miles growth rate is of the order of the steepness squared.
Nitric Oxide: Genomic Instability And Synthetic Lethality
Directory of Open Access Journals (Sweden)
Vasily A. Yakovlev
2015-08-01
Loss or inhibition of Poly(ADP-ribose polymerase 1 (PARP1 activity results in accumulation of DNA single-strand breaks, which are subsequently converted to DSB by the transcription machinery. In BRCA-positive cells, DSB are repaired by HRR, but they cannot be properly repaired in BRCA1-deficient cells, leading to genomic instability, chromosomal rearrangements, and cell death. Our data demonstrated that combination of NO-donors with PARP inhibitors significantly sensitized the BRCA1-positive cancer cells to DNA-damaging agents.
Coping with instabilities - lessons from Japanese architecture
DEFF Research Database (Denmark)
Greve, Anni
This paper offers insight into the role of architecture in coping with instabilities. At its centre is a second generation of Japanese architects who came to maturity after World War II. They questioned the International Style, and asked for a return to architecture in the image of the early...... Japanese idea about an ‘in-between’, place and occasion means an ‘in-between’, the Japanese term ma. The final part of the lecture considers ma in its quality as 1) a formula replicated in different cognitive domains, in language, visual perception, abstract ways of reasoning, emotions and actions, and 2...
Social Psychology of Instability within Organizational Reality
Directory of Open Access Journals (Sweden)
Takhir Yu. Bazarov
2012-01-01
Full Text Available Since modern organizations inevitably face constant changes in internal and externalenvironment, can anything be done in order for the strategy of changesto become “proactive” and to prevent naturally determined crisis situations andrecession? Featuring empirical data, the article discusses the possibility of sociopsychologicalresearch in the situation of instability. Among other aspects, thereis suggested an answer to the question of whether social psychology can help aperson to realize his/her identity in professional and organizational environments.Moreover, a number of fixed behavioral patterns observed in situations of changesare examined specifically.
Kinetic Simulations of Rayleigh-Taylor Instabilities
Sagert, Irina; Bauer, Wolfgang; Colbry, Dirk; Howell, Jim; Staber, Alec; Strother, Terrance
2014-01-01
We report on an ongoing project to develop a large scale Direct Simulation Monte Carlo code. The code is primarily aimed towards applications in astrophysics such as simulations of core-collapse supernovae. It has been tested on shock wave phenomena in the continuum limit and for matter out of equilibrium. In the current work we focus on the study of fluid instabilities. Like shock waves these are routinely used as test-cases for hydrodynamic codes and are discussed to play an important role ...
MR imaging in sports-related glenohumeral instability
International Nuclear Information System (INIS)
Sports-related shoulder pain and injuries represent a common problem. In this context, glenohumeral instability is currently believed to play a central role either as a recognized or as an unrecognized condition. Shoulder instabilities can roughly be divided into traumatic, atraumatic, and microtraumatic glenohumeral instabilities. In athletes, atraumatic and microtraumatic instabilities can lead to secondary impingement syndromes and chronic damage to intraarticular structures. Magnetic resonance (MR) arthrography is superior to conventional MR imaging in the diagnosis of labro-ligamentous injuries, intrinsic impingement, and SLAP (superior labral anteroposterior) lesions, and thus represents the most informative imaging modality in the overall assessment of glenohumeral instability. This article reviews the imaging criteria for the detection and classification of instability-related injuries in athletes with special emphasis on the influence of MR findings on therapeutic decisions. (orig.)
Prediction of alpine glacier sliding instabilities: a new hope
Faillettaz, Jerome; Sornette, Didier
2012-01-01
Mechanical and sliding instabilities are the two processes which may lead to breaking off events of large ice masses. Mechanical instabilities mainly affect unbalanced cold hanging glaciers. For the latter case, a prediction could be achieved based on data of surface velocities and seismic activity. The case of sliding instabilities is more problematic. This phenomenon occurs on temperate glacier tongues. Such instabilities are strongly affected by the subglacial hydrology: melt water may cause (i) a lubrication of the bed and (ii) a decrease of the effective pressure and consequently a decrease of basal friction. Available data from Allalingletscher (Valais) indicate that the glacier tongue experienced an active phase during 2-3 weeks with enhanced basal motion in late summer in most years. In order to scrutinize in more detail the processes governing the sliding instabilities, a numerical model developed to investigate gravitational instabilities in heterogeneous media was applied to Allalingletscher. This ...
Simulation and quasilinear theory of aperiodic ordinary mode instability
International Nuclear Information System (INIS)
The purely growing ordinary (O) mode instability driven by excessive parallel temperature anisotropy for high-beta plasmas was first discovered in the 1970s. This instability receives renewed attention because it may be applicable to the solar wind plasma. The electrons in the solar wind feature temperature anisotropies whose upper values are apparently limited by plasma instabilities. The O-mode instability may be important in this regard. Previous studies of O mode instability have been based on linear theory, but the actual solar wind electrons may be in saturated state. The present paper investigates the nonlinear saturation behavior of the O mode instability by means of one-dimensional particle-in-cell simulation and quasilinear theory. It is shown that the quasilinear method accurately reproduces the simulation results
Theory of local thermal instability in spherical systems
Balbus, Steven A.; Soker, Noam
1989-01-01
The gasdynamical properties of local thermal instability in optically thin astrophysical plasmas as it occurs in spherical accretion and winds is investigated. In a medium characterized by both thermal and hydrostatic equilibrium, if the cooling function is not an explicit function of position and does not display isentropic thermal instability, then isobaric thermal instability by the Field criterion is present if and only if convective instability is present by the Schwarzschild criterion. In this case, thermal overstability cannot occur. Convective instability by the Schwarzschild criterion will also occur in accretion flows locally dominated by external heating or in marginally unbound, radiatively cooling outflows. A very general Lagrangian equation for the development of nonradial thermal instability in flows with spherical symmetry is derived and is solved analytically in certain regimes. The results are applied to cluster X-ray cooling flows.
Nonaxisymmetric linear instability of cylindrical magnetohydrodynamic Taylor-Couette flow
Child, Adam; Hollerbach, Rainer
2015-01-01
We consider the nonaxisymmetric modes of instability present in Taylor-Couette flow under the application of helical magnetic fields, mainly for magnetic Prandtl numbers close to the inductionless limit, and conduct a full examination of marginal stability in the resulting parameter space. We allow for the azimuthal magnetic field to be generated by a combination of currents in the inner cylinder and fluid itself, and introduce a parameter governing the relation between the strength of these currents. A set of governing eigenvalue equations for the nonaxisymmetric modes of instability are derived and solved by spectral collocation with Chebyshev polynomials over the relevant parameter space, with the resulting instabilities examined in detail. We find that by altering the azimuthal magnetic field profiles the azimuthal magnetorotational instability, nonaxisymmetric helical magnetorotational instability, and Tayler instability yield interesting dynamics, such as different preferred mode types, and modes with a...
Experimental study on modulational instability and evolution of crescent waves
Directory of Open Access Journals (Sweden)
Ya-long ZHOU
2012-12-01
Full Text Available A series of experiments on the instability of steep water wave trains in water with finite water depths and infinite water depths in a wide wave basin were performed. It was found that under the coupled development of modulational instability and class-II instability, the initial two-dimensional steep wave trains evolved into three-dimensional crescent waves, followed by the occurrence of disordered water surfaces, and that the wave energy transferred to sidebands in the amplitude spectrum of the water surface elevation. The results also show that water depth has a significant effect on the growth of modulational instability and the evolution of crescent waves. The larger the water depth, the more quickly the modulational instability suppresses class-II instability.
Parametric and modulational instabilities of the discrete nonlinear Schroedinger equation
International Nuclear Information System (INIS)
We examine the parametric and modulational instabilities arising in a non-autonomous, discrete nonlinear Schroedinger equation. The principal motivation for our study stems from the dynamics of Bose-Einstein condensates trapped in a deep optical lattice. We find that under periodic variations of the heights of the interwell barriers (or equivalently of the scattering length), in addition to the modulational instability, a window of parametric instability becomes available to the system. We explore this instability through multiple-scale analysis and identify it numerically. Its principal dynamical characteristic is that, typically, it develops over much larger times than the modulational instability, a feature that is qualitatively justified by comparison of the corresponding instability growth rates
Instabilities in the dissolution of a porous matrix
Szymczak, Piotr; 10.1029/2011GL046720
2011-01-01
A reactive fluid dissolving the surrounding rock matrix can trigger an instability in the dissolution front, leading to spontaneous formation of pronounced channels or wormholes. Theoretical investigations of this instability have typically focused on a steadily propagating dissolution front that separates regions of high and low porosity. In this paper we show that this is not the only possible dissolutional instability in porous rocks; there is another instability that operates instantaneously on any initial porosity field, including an entirely uniform one. The relative importance of the two mechanisms depends on the ratio of the porosity increase to the initial porosity. We show that the "inlet" instability is likely to be important in limestone formations where the initial porosity is small and there is the possibility of a large increase in permeability. In quartz-rich sandstones, where the proportion of easily soluble material (e.g. carbonate cements) is small, the instability in the steady-state equat...
Transverse mode coupling instability for leptons in the CERN SPS
Energy Technology Data Exchange (ETDEWEB)
Linnecar, T.; Shaposhnikova, E.N. [European Organization for Nuclear Research, Geneva (Switzerland)
1996-08-01
The intensity of leptons accelerated in the SPS machine is limited by a vertical transverse instability. The results of measurements of the thresholds for this transverse instability are compared with theoretical predictions for different broad band impedance models of the SPS. The threshold intensities found for the transverse instability and the position of the losses in the cycle enable the parameters of the broadband resonant impedance to be specified. (author)
Large Eddy Simulation of thermoacoustic instabilities in annular combustion chambers
Wolf, Pierre
2011-01-01
Increasingly stringent regulations and the need to tackle rising fuel prices have placed great emphasis on the design of aeronautical gas turbines. This drive towards innovation has resulted sometimes in new concepts being prone to combustion instabilities. Combustion instabilities arise from the coupling of acoustics and combustion. In the particular field of annular combustion chambers, these instabilities often take the form of azimuthal modes. To predict these modes, one must consider the...
Limitation of the ECRIS performance by kinetic plasma instabilities (invited)
Tarvainen, Olli; Kalvas, Taneli; Koivisto, Hannu; Komppula, Jani; Kronholm, Risto; Laulainen, Janne; Izotov, I.; Mansfeld, D.; Skalyga, V.; Toivanen, V.; Machicoane, G.
2015-01-01
Electron cyclotron resonance ion source (ECRIS) plasmas are prone to kinetic instabilities due to anisotropic electron velocity distribution. The instabilities are associated with strong microwave emission and periodic bursts of energetic electrons escaping the magnetic confinement. The instabilities explain the periodic ms-scale oscillation of the extracted beam current observed with several high performance ECRISs and restrict the parameter space available for the optimization o...
Systematic review of chronic ankle instability in children
Mandarakas, Melissa; Pourkazemi, Fereshteh; Sman, Amy; Burns, Joshua; Hiller, Claire E
2014-01-01
Background Chronic ankle instability (CAI) is a disabling condition often encountered after ankle injury. Three main components of CAI exist; perceived instability; mechanical instability (increased ankle ligament laxity); and recurrent sprain. Literature evaluating CAI has been heavily focused on adults, with little attention to CAI in children. Hence, the objective of this study was to systematically review the prevalence of CAI in children. Methods Studies were retrieved from major databas...