Wave propagation reversal for wavy vortices in wide-gap counter-rotating cylindrical Couette flow.

We present a numerical study of wavy supercritical cylindrical Couette flow between counter-rotating cylinders in which the wavy pattern propagates either prograde with the inner cylinder or retrograde opposite the rotation of the inner cylinder. The wave propagation reversals from prograde to retrograde and vice versa occur at distinct values of the inner cylinder Reynolds number when the associated frequency of the wavy instability vanishes. The reversal occurs for both twofold and threefold symmetric wavy vortices. Moreover, the wave propagation reversal only occurs for sufficiently strong counter-rotation. The flow pattern reversal appears to be intrinsic in the system as either periodic boundary conditions or fixed end wall boundary conditions for different system sizes always result in the wave propagation reversal. We present a detailed bifurcation sequence and parameter space diagram with respect to retrograde behavior of wavy flows. The retrograde propagation of the instability occurs when the inner Reynolds number is about two times the outer Reynolds number. The mechanism for the retrograde propagation is associated with the inviscidly unstable region near the inner cylinder and the direction of the global average azimuthal velocity. Flow dynamics, spatio-temporal behavior, global mean angular velocity, and torque of the flow with the wavy pattern are explored.

Effect of elongational flow on ferrofuids under a magnetic field.

To set up a mathematical model for the flow of complex magnetic fluids, noninteracting magnetic particles with a small volume or an even point size are typically assumed. Real ferrofluids, however, consist of a suspension of particles with a finite size in an almost ellipsoid shape as well as with particle-particle interactions that tend to form chains of various lengths. To come close to the realistic situation for ferrofluids, we investigate the effect of elongational flow incorporated by the symmetric part of the velocity gradient field tensor, which could be scaled by a so-called transport coefficient λ(2). Based on the hybrid finite-difference and Galerkin scheme, we study the flow of a ferrofluid in the gap between two concentric rotating cylinders subjected to either a transverse or an axial magnetic field with the transport coefficient. Under the influence of a transverse magnetic field with λ(2)=0, we show that basic state and centrifugal unstable flows are modified and are inherently three-dimensional helical flows that are either left-winding or right-winding in the sense of the azimuthal mode-2, which is in contrast to the generic cases. That is, classical modulated rotating waves rotate, but these flows do not. We find that under elongational flow (λ(2)≠0), the flow structure from basic state and centrifugal instability flows is modified and their azimuthal vorticity is linearly changed. In addition, we also show that the bifurcation threshold of the supercritical centrifugal unstable flows under a magnetic field depends linearly on the transport coefficient, but it does not affect the general stabilization effect of any magnetic field.

Elongational flow effects on the vortex growth out of Couette flow in ferrofluids.

The growth behavior of stationary axisymmetric vortices and of oscillatory, nonaxisymmetric spiral vortices in Taylor-Couette flow of a ferrofluid in between differentially rotating cylinders is analyzed using a numerical linear stability analysis. The investigation is done as a function of the inner and outer cylinder's rotation rates, the axial wave number of the vortex flows, and the magnitude of an applied homogeneous axial magnetic field. In particular, the consequences of incorporating elongational flow effects in the magnetization balance equation on the marginal control parameters that separate growth from decay behavior are determined. That is done for several values of the transport coefficient that measures the strength of these effects.

Fully nonlinear mode competitions of nearly bicritical spiral or Taylor vortices in Taylor-Couette flow.

Interactions between nearly bicritical modes in Taylor-Couette flow, which have been concerned with the framework of weakly nonlinear theory, are extended to fully nonlinear Navier-Stokes computation. For this purpose, a standard Newton solver for axially periodic flows is generalized to compute any mixed solutions having up to two phases, which typically arise from interactions of two spiral or Taylor vortex modes. Also, a simple theory is developed in order to classify the mixed solutions. With these methods, we elucidate pattern formation phenomena, which have been observed in a Taylor-Couette flow experiment. Focusing on the counter-rotating parameter range, all possible classes of interaction of various solutions with different azimuthal and axial wave numbers are considered within our computational restriction, and we observe numerous connection branches, e.g., footbridge solutions. Some of the mixed solutions result in a three-dimensional wavy spiral solution with axial relative periodicity or an axially doubly periodic toroidally closed vortex solution. The possible connection of the former solution family to spiral turbulence, which has been observed in highly counter-rotating Taylor-Couette flow, is discussed.

Symmetry-breaking Hopf bifurcations to 1-, 2-, and 3-tori in small-aspect-ratio counterrotating Taylor-Couette flow.

The nonlinear dynamics of Taylor-Couette flow in a small-aspect-ratio wide-gap annulus in the counterrotating regime is investigated by solving the full three-dimensional Navier-Stokes equations. The system is invariant under arbitrary rotations about the axis, reflection about the annulus midplane, and time translations. A systematic investigation is presented both in terms of the flow physics elucidated from the numerical simulations and from a dynamical system perspective provided by equivariant normal form theory. The dynamics are primarily associated with the behavior of the jet of angular momentum that emerges from the inner cylinder boundary layer at about the midplane. The sequence of bifurcations as the differential rotation is increased consists of an axisymmetric Hopf bifurcation breaking the reflection symmetry of the basic state leading to an axisymmetric limit cycle with a half-period-flip spatiotemporal symmetry. This undergoes a Hopf bifurcation breaking axisymmetry, leading to quasiperiodic solutions evolving on a 2-torus that is setwise symmetric. These undergo a further Hopf bifurcation, introducing a third incommensurate frequency leading to a 3-torus that is also setwise symmetric. On the 3-torus, as the differential rotation is further increased, a saddle-node-invariant-circle bifurcation takes place, destroying the 3-torus and leaving a pair of symmetrically related 2-tori states on which all symmetries of the system have been broken.

Influence of an inhomogeneous internal magnetic field on the flow dynamics of a ferrofluid between differentially rotating cylinders.

The influence of a magnetic field on the dynamics of the flow of a ferrofluid in the gap between two concentric, independently rotating cylinders is investigated numerically. The Navier-Stokes equations are solved using a hybrid finite difference and Galerkin method. We show that the frequently used assumption that the internal magnetic field within a ferrofluid is equal to the external applied field is only a leading-order approximation. By accounting for the ferrofluid's magnetic susceptibility, we show that a uniform externally imposed magnetic field is modified by the presence of the ferrofluid within the annulus. The modification to the magnetic field has an r(-2) radial dependence and a magnitude that scales with the susceptibility. For ferrofluids typically used in laboratory experiments of the type simulated in this paper, the modification to the imposed magnetic field can be substantial. This has significant consequences on the structure and stability of the basic states, as well as on the bifurcating solutions.

Islands of instability for growth of spiral vortices in the Taylor-Couette system with and without axial through flow.

We present numerical calculations of the linearized Navier-Stokes equations for axially extended and axially localized spiral structures in the Taylor-Couette system. The eigenvalue surface for spiral vortices with azimuthal wave number M=2 shows significantly more structure than that for vortices with M=0 and 1. Islands are found in parameter space where axially periodic vortex perturbations can grow. Bicriticality of different axial wave numbers is observed. Furthermore, parameter islands of absolute instability are found where wave packets consisting of near-critical extended perturbations can grow and expand via oppositely moving fronts. Some results are compared with those of the Ginzburg-Landau approximation.

End wall effects on the transitions between Taylor vortices and spiral vortices.

We present numerical simulations as well as experimental results concerning transitions between Taylor vortices and spiral vortices in the Taylor-Couette system with rigid, nonrotating lids at the cylinder ends. These transitions are performed by wavy structures appearing via a secondary bifurcation out of Taylor vortices and spirals, respectively. In the presence of these axial end walls, pure spiral solutions do not occur as for axially periodic boundary conditions but are substituted by primary bifurcating, stable wavy spiral structures. Similarly to the periodic system, we found a transition from Taylor vortices to wavy spirals mediated by so-called wavy Taylor vortices and, on the other hand, a transition from wavy spirals to Taylor vortices triggered by a propagating defect. We furthermore observed and investigated the primary bifurcation of wavy spirals out of the basic circular Couette flow with Ekman vortices at the cylinder ends.

Influence of homogeneous magnetic fields on the flow of a ferrofluid in the Taylor-Couette system.

We investigate numerically the influence of a homogeneous magnetic field on a ferrofluid in the gap between two concentric, independently rotating cylinders. The full Navier-Stokes equations are solved with a combination of a finite difference method and a Galerkin method. Structure, dynamics, symmetry properties, bifurcation, and stability behavior of different vortex structures are investigated for axial and transversal magnetic fields, as well as combinations of them. We show that a transversal magnetic field modulates the Taylor vortex flow and the spiral vortex flow. Thus, a transversal magnetic field induces wavy structures: wavy Taylor vortex flow (wTVF) and wavy spiral vortex flow. In contrast to the classic wTVF, which is a secondarily bifurcating structure, these magnetically generated wavy Taylor vortices are pinned by the magnetic field, i.e., they are stationary and they appear via a primary forward bifurcation out of the basic state of circular Couette flow.

Stability of the circular Couette flow of a ferrofluid in an axial magnetic field: influence of polydispersity.

The gap between two concentric rotating cylinders is filled with a ferrofluid. A homogeneous magnetic field is applied parallel to the cylinder axis. The stability of the circular Couette flow is analyzed with different models that take into account the polydispersity of the ferrofluid to a varying degree. Their results are compared and their merits are discussed.

Nonlinear defects separating spiral waves in Taylor-Couette flow.

Stable domain walls which are realized by a defect between oppositely traveling spiral waves in a pattern-forming hydrodynamic system, i.e., Taylor-Couette flow, are studied numerically as well as experimentally. A nonlinear mode coupling resulting from the nonlinearities in the underlying momentum balance is found to be essential for the stability of the defects. These nonlinearly driven defects separate spiral domains and act either as a phase generating or annihilating defect. Specific phase differences of either 0 or pi between the participating traveling waves are a characteristic feature of this defect. The influence of a symmetry breaking externally imposed flow on the spiral domains and the defects is studied. The numerical and experimental results are in excellent agreement.

The stochastic evolution of catalysts in spatially resolved molecular systems.

A fully stochastic chemical modelling technique is derived which describes the influence of spatial separation and discrete population size on the evolutionary stability of coupled amplification in biopolymers. The model is analytically tractable for an infinite-dimensional space (simplex geometry), which also provides insight into evolution in normal Euclidean space. The results are compared with stochastic simulations describing the co-evolution of combinatorial families of molecular sequences both in the simplex geometry and in lower (one, two and three) space dimensions. They demonstrate analytically the generic limits which exploitation place on co-evolving multi-component amplification systems. In particular, there is an optimal diffusion (or migration) coefficient for cooperative amplification and minimal and maximal threshold values for stable cooperation. Over a bounded range of diffusion rates, the model also exhibits stable limit cycles. Furthermore, the co-operatively coupled system has a maximum tolerable error rate at intermediate rates of diffusion. A tractable model is thereby established which demonstrates that spatial effects can stabilize catalytic biological information. The analytic behaviour in infinite-dimensional simplex space is seen to provide a reasonable guide to the spatial dependence of the error threshold in physical space. Nanoscale possibilities for the evolution of catalysis on the basis of the model are outlined. We denote the modelling technique by PRESS, Probability Reduced Evolution of Spatially-discrete Species.

Error threshold for spatially resolved evolution in the quasispecies model.

The error threshold for quasispecies in 1, 2, 3, and infinity dimensions is investigated by stochastic simulation and analytically. The results show a monotonic decrease in the maximal sustainable error probability with decreasing diffusion coefficient, independently of the spatial dimension. It is thereby established that physical interactions between sequences are necessary in order for spatial effects to enhance the stabilization of biological information. The analytically tractable behavior in an infinity-dimensional (simplex) space provides a good guide to the spatial dependence of the error threshold in lower dimensional Euclidean space.

Decreased sleep quality and increased sleep related movements in patients with Tourette's syndrome.

OBJECTIVE: Sleep quality and movement patterns across sleep stages in patients with Tourette's syndrome were examined to determine the influence of syndrome severity on sleep quality and the differential effect of sleep stages on tic and non-tic movements. METHODS: Twenty five patients with Tourette's syndrome (mean age 29 (SD 7) years) and 11 control subjects (29 (5) years) were studied by polysomnography and simultaneous split screen video monitoring to record standard sleep variables as well as to evaluate movements to differentiate between tics and regular movements. Severity of Tourette's syndrome during the day was assessed with the Tourette's syndrome severity scale. RESULTS: Sleep was significantly more disturbed in patients with Tourette's syndrome than in controls, with decreased sleep efficiency and slow wave sleep percentage, increased sleep latency, percentage of stage I, percentage of awakeness, number of awakenings, and sleep stage changes and more overall movements during sleep. Severity of Tourette's syndrome during the day correlated significantly and positive with number of awakenings and sleep stage changes and negatively with sleep efficiency. In addition to an increased number of regular movements patients had tics in all sleep stages. Tic frequency as well as frequency of regular movements was significantly higher in REM than in non-REM sleep which was also the case for regular movements of the controls. No disturbance of either REM sleep percentage or REM latency was found. CONCLUSION: Despite normal total sleep time and unaltered REM sleep variables patients with Tourette's syndrome have markedly disturbed sleep. Severity of the syndrome during the day is an important predictor of sleep alteration in patients. The increased rate of tics during REM sleep parallels the overall increased movement activity of patients during REM as well as non-REM sleep. The increased motor activity may be attributable to a state of hyperarousal rather than a disturbed cholinergic system.

CGH analysis of radon-induced rat lung tumors indicates similarities with human lung cancers.

Epidemiological studies have shown that inhalation of radon, a radioactive gas, is associated with an increased risk for lung cancer. We have developed a model of radon-induced rat lung tumors to characterize cytogenetic and molecular events involved in radon-induced lung tumorigenesis. Using comparative genomic hybridization (CGH), gains and losses of genetic material were investigated in a series of 13 carcinomas and four adenomas of the lung. Frequent losses occurred at 4q12-21, 5q11-33, and 15q, which are homologous to human chromosome (HSA) bands 7q21-36, 1p31-36/9p21-31, and 13q14.1-14.3/3p14.2, respectively. These regions are frequently (30-80%) deleted in human lung cancer and contain tumor suppressor genes or proto-oncogenes such as MET, CDKN2A/p16/MTS1, CDKN2B/p15/MTS2, FHIT, and RB1 or yet to be identified genes. Frequent gains involved 6, 7q34-qter, and 19q; chromosomes 6 and 7 being homologous to human 2p21-25 and 8q21-24 where the MYCN and MYC oncogenes are located. The genetic similarities between rat and human lung cancer suggest common underlying mechanisms for tumor evolution in both species. Moreover, cytogenetic and molecular genetic analyses of radon-induced rat lung tumors could help to better understand the development and progression of radon-induced lung cancer in man.

Influence of exposure rate on lung cancer induction in rats exposed to radon progeny.

Animal studies were used in addition to epidemiological studies to investigate the effects of exposure, exposure rate and other factors in predicting risks resulting from exposures to radon progeny. A trend toward increasing tumor risk with decreasing exposure rate was observed in rats exposed at a cumulative exposure varying from about 0.72 J h m(-3) (200 WLM) up to 10.8 J h m(-3) (3,000 WLM) and high exposure rates varying from 25 WLM per week to 500 WLM per week. In contrast, at low cumulative exposure, comparable to lifetime domestic indoor exposures or lifetime occupational exposure in uranium mines, no evidence of an inverse exposure-rate effect was found. Chronic radon exposure at 0.09 J h m(-3) (25 WLM), protracted over 18 months, at a potential alpha-particle energy concentration (PAEC) of 0.042 mJ m(-3) (2 WL), resulted in fewer lung carcinomas in rats than a similar cumulative exposure protracted over 4 to 6 months at a PAEC of 2.1 mJ m(-3) (100 WL). The preliminary results of a new series of experiments carried out at relatively low cumulative exposures of 0.36 J h m(-3) (100 WLM) and PAEC varying from 0.21 mJ m(-3) (10 WL) to 3.15 mJ m(-3) (150 WL) indicate that at cumulative exposures comparable to lifetime indoor or occupational exposures, the risk of lung cancer in rats decreases with decreasing PAEC, i.e. exposure rate. These data suggest that the risk of radon-induced lung cancer results from a complex interplay between cumulative exposure and exposure rate at a given exposure level.

Sustained nontumorigenic phenotype correlates with a largely stable chromosome content during long-term culture of the human keratinocyte line HaCaT.

Altered growth and differentiation and a highly abnormal karyotype are generally believed to be indicators for tumorigenic conversion of human cells. Inactivation of TP53 is supposedly one possible mechanism for accelerated genetic aberrations via reduced control of the genetic integrity. To examine the significance of this functional relationship, we investigated the long-term development of the spontaneously immortalized human skin keratinocyte line HaCaT, carrying UV-specific mutations in both alleles of the TP53 tumor suppressor gene. During > 300 passages, proliferation, clonogenicity, and serum-independent growth potential increased. In addition, HaCaT cells gained anchorage independence and at late passages showed reduced differentiation. Karyotypic analysis up to passage 225 revealed a high frequency of translocations and deletions, with a particular increase during passages 30 and 50. Nevertheless, the HaCaT cells remained nontumorigenic when injected subcutaneously, and noninvasive in surface transplants in nude mice. By comparative genomic hybridization, we confirmed the karyotypically identified phase of increased chromosomal aberrations between passages 30 and 50. However, before and thereafter, the CGH profiles of the individual chromosomes were largely unchanged, demonstrating that those translocations-also maintained in later passages-did not cause a gross chromosomal imbalance. Thus, our data suggest that multiple changes often correlated with a "transformed phenotype," including extensive karyotypic alterations and mutational inactivation of TP53, are well compatible with a nontumorigenic phenotype of the HaCaT cells, and that preserved chromosomal balance may be crucial for this stability during long-term propagation.

[Life threatening salicylate poisoning caused by percutaneous absorption in severe ichthyosis vulgaris]. / Lebensbedrohliche Salicylatintoxikation durch perkutane Resorption bei einer schweren Ichthyosis vulgaris.

In a 7-year-old boy, ichthyosis vulgaris was treated with a 10% ointment for application over a large area of the body surface. In this way, the child received 400 g salicylic acid (0.6 g/kg body weight per day) percutaneously over a period of 4 weeks. The patient was referred to hospital by the family doctor: he was in a deep somnolent state, apparently caused by hyperventilation following wheezing, vomiting, tinnitus and vertigo. Salicylate intoxication was suspected because of metabolic acidosis, an anion gap and respiratory overcompensation. The diagnosis was confirmed by a serum salicylate level of 985 micrograms/ml (therapeutic level 150-300 micrograms/ml). Following forced diuresis and alkalization with sodium bicarbonate, haemodialysis was unnecessary. As the salicylate level declined to values within the therapeutic range, the patient started to recover consciousness, waking on the 4th day. By day 6 there were still obvious neurological deficiencies. Fecal incontinence, bilateral ptosis and intermittent diverging strabismus on the right persisted for some weeks. It was 6 months before complete neurological resolution was achieved. The pathogenesis of salicylate toxicity and the need for safer therapies for ichthyosis vulgaris are discussed.

[Effects of dose rate on carcinogenesis after exposure of rats to low doses of neutron irradiation]. / Effets du débit de dose sur la cancérogenèse après exposition de rats à de faibles doses d'irradiation neutronique.

In this experiment we compared the efficiency of fission neutrons of californium 252 at doses of 25 or 53 mGy in function of the dose rate. Two groups of male Sprague-Dawley rats were exposed at 100 or 420 days of age to fission neutrons with dose rates of 950 or 760 microGy/h for 26 or 33 h, and 2 other groups were irradiated over a year from 3 months to 15 months of age with dose rates of 3.58 or 7.72 microGy/h. The 4 groups of animals were compared with a control group of 501 rats. The reduction of effectiveness on cancer induction that we have previously shown at low dose rate with rats exposed to gamma rays or to alpha particles was not observed for low dose rate exposure with fission neutrons.

[Relationship between irradiation and appearance of brain tumors in rats]. / Relations entre l'irradiation et l'apparition des tumeurs cérbrales chez le rat.

Sprague-Dawley rats were exposed to Co 60 irradiation (3 Gy) at different ages. Rats were distributed among sham-control (618 males and 120 females) and exposed groups: foetus (66 males and 65 females), 3 month-old (304 males), and 9 month-old (120 males and 60 females). The incidence of brain tumours was 5.3% in male control rats and nil in female control rats. Brain tumour incidence decreased in 9 month-old rats (3.3%), and increased from 6.6% in 3 month-old rats to 15.2% in male foetuses and 12.3% in female foetuses. Age at incidence of brain tumours decreased in irradiatiated animals. Astrocytomas were the more susceptible type of brain tumours to radiocarcinogenesis.