bluuebunny/crossref_metadata_2025_split huggingface dataset:
The nonlinear evolution of zonally symmetric equatorial inertial instability
Authors: GRIFFITHS STEPHEN D. 
Published: January 2005

The inertial instability of equatorial shear flows is studied, with a view to understanding observed phenomena in the Earth's stratosphere and mesosphere. The basic state
is a zonal flow of stratified fluid on an equatorial β-plane, with latitudinal shear. The
simplest self-consistent model of the instability is used, so that the basic state and
the disturbances are zonally symmetric, and a vertical diffusivity provides the scale
selection. We study the interaction between the inertial instability, which takes the
form of periodically varying disturbances in the vertical, and the mean flow, where
‘mean’ is a vertical mean.The weakly nonlinear regime is investigated analytically, for flows with an arbitrary
dependence on latitude. An amplitude equation of the form dA/dt = A−k2A∫[mid ]A[mid ]2dt
is derived for the disturbances, and the evolving stability properties of the mean
flow are discussed. In the final steady state, the disturbances vanish, but there is a
persistent mean flow change that stabilizes the flow. However, the magnitude of the
mean flow change depends strongly on the initial conditions, so that the system has a
long memory. The analysis is extended to include the effects of Rayleigh friction and
Newtonian cooling, destroying the long-memory property.A more strongly nonlinear regime is investigated with the help of numerical
simulations, extending the results up to the point where the instability leads to
density contour overturning. The instability is shown to lead to a homogenization of
fQ¯ around the initially unstable region, where f is the Coriolis parameter, and Q¯ is
the vertical mean of the potential vorticity. As the instability evolves, the line of zero
Q¯ moves polewards, rather than equatorwards as might be expected from a simple
self-neutralization argument.
Mathematical modelling of the overflowing cylinder experiment
Authors: HOWELL P. D. , BREWARD C. J. W. 
Published: January 2005

The overflowing cylinder (OFC) is an experimental apparatus designed to generate
a controlled straining flow at a free surface, whose dynamic properties may then be
investigated. Surfactant solution is pumped up slowly through a vertical cylinder.
On reaching the top, the liquid forms a flat free surface which expands radially
before over flowing down the side of the cylinder. The velocity, surface tension and
surfactant concentration on the expanding free surface are measured using a variety
of non-invasive techniques.A mathematical model for the OFC has been previously derived by Breward et al.
(2001) and shown to give satisfactory agreement with experimental results. However, a
puzzling indeterminacy in the model renders it unable to predict one scalar parameter
(e.g. the surfactant concentration at the centre of the cylinder), which must be therefore
be taken from the experiments.In this paper we analyse the OFC model asymptotically and numerically. We show
that solutions typically develop one of two possible singularities. In the first, the
surface concentration of surfactant reaches zero a finite distance from the cylinder
axis, while the surface velocity tends to infinity there. In the second, the surfactant
concentration is exponentially large and a stagnation point forms just inside the rim
of the cylinder. We propose a criterion for selecting the free parameter, based on
the elimination of both singularities, and show that it leads to good agreement with
experimental results.
The unsteady Kármán problem for a dilute particle suspension
Authors: FOSTER M. R. , DUCK P. W. , HEWITT R. E. 
Published: January 2005

We consider the unsteady three-dimensional Kármán flow induced by the impulsive
rotation of an infinite rotating plane immersed in an incompressible viscous fluid
with a dilute suspension of small solid monodisperse spherical particles. The flow is
described in terms of a ‘dusty gas’ model, which treats the discrete phase (particles)
and the continuous phase (fluid) as two continua occupying the same space and
interacting through a Stokes drag mechanism. The model is extended to allow for a
local gravitational acceleration in a direction parallel to the axis of rotation, and is
valid for cases in which gravity acts either in the same direction as or in the opposite
direction to the Ekman axial flow induced by the rotation of the plane.Analysis based on the theory of characteristics shows that the role of gravity is
crucial to the treatment of the discrete-phase equations, particularly in regard to the
appropriate boundary conditions to be applied at the solid surface. Other notable
features include the presence of an essential singularity in the solution when gravity
is absent; indeed this phenomenon may help to explain some of the difficulties
encountered in previous studies of this type. If the gravitational force is directed away
from the rotating surface, a number of other interesting features arise, including the
development of discontinuities in the particle distribution profiles, with corresponding
particle-free regions contained between the interface and the rotating boundary. These
‘shock’ features can be associated with a critical axial location in the boundary layer
at which a balance is achieved between Ekman suction induced by the rotating
boundary and the influence of gravitational effects acting to move particles away
from the boundary.
Nonlinear dynamics over rough
topography: homogeneous and stratified
quasi-geostrophic theory
Authors: VANNESTE JACQUES 
Published: January 2005

The weakly nonlinear dynamics of quasi-geostrophic flows over a one-dimensional,
periodic or random, small-scale topography is investigated using an asymptotic approach. Averaged (or homogenized) evolution equations which account for the flow–topography interaction are derived for both homogeneous and continuously stratified
quasi-geostrophic fluids. The scaling assumptions are detailed in each case; for stratified fluids, they imply that the direct influence of the topography is confined within
a thin bottom boundary layer, so that it is through a new bottom boundary condition that the topography affects the large-scale flow. For both homogeneous and
stratified fluids, a single scalar function entirely encapsulates the properties of the
topography that are relevant to the large-scale flow: it is the correlation function of
the topographic height in the homogeneous case, and a linear transform thereof in
the continuously stratified case.Some properties of the averaged equations are discussed. Explicit nonlinear solutions in the form of one-dimensional travelling waves can be found. In the homogeneous case, previously studied by Volosov, they obey a second-order differential equation; in the stratified case on which we focus they obey a nonlinear pseudodifferential equation, which reduces to the Peierls–Nabarro equation for sinusoidal
topography. The known solutions to this equation provide examples of nonlinear
periodic and solitary waves in continuously stratified fluid over topography.The influence of bottom topography on large-scale baroclinic instability is also
examined using the averaged equations: they allow a straightforward extension of
Eady's model which demonstrates the stabilizing effect of topography on baroclinic
instability.
The shape of vortices in quasi-geostrophic turbulence
Authors: REINAUD J. N. , DRITSCHEL D. G. , KOUDELLA C. R. 
Published: January 2005

The present work discusses the most commonly occurring shape of the coherent
vortical structures in rapidly rotating stably stratified turbulence, under the quasi-geostrophic approximation. In decaying turbulence, these vortices – coherent regions of
the materially-invariant potential vorticity – dominate the flow evolution, and indeed
the flow evolution is governed by their interactions. An analysis of several exceptionally high-resolution simulations of quasi-geostrophic turbulence is performed. The
results indicate that the population of vortices exhibits a mean height-to-width aspect
ratio less than unity, in fact close to 0.8.This finding is justified here by a simple model, in which vortices are taken to
be ellipsoids of uniform potential vorticity. The model focuses on steady ellipsoids
within a uniform background strain flow. This background flow approximates the
effects of surrounding vortices in a turbulent flow on a given vortex. It is argued that
the vortices which are able to withstand the highest levels of strain are those most
likely to be found in the actual turbulent flow. Our calculations confirm that the
optimal height-to-width aspect ratio is close to 0.8 for a wide range of background
straining flows.
Strong solitary internal waves in a 2.5-layer model
Authors: VORONOVICH ALEXANDER G. 
Published: January 2005

A theoretical model for internal solitary waves for stratification consisting of two
layers of incompressible fluid with a constant Brunt–Väisälä frequency and a density
jump at the boundary between layers (‘2.5-layer model’) is presented. The equation
of motion for solitary waves in the case of a constant Brunt–Väisälä frequency N
is linear, and nonlinearity appears due only to boundary conditions between layers.
This allows one to obtain in the case of long waves a single ordinary differential
equation for an internal solitary wave profile. In the case of nearly homogeneous
layers the solitons obtained here coincide with the solitons calculated by Choi &
Camassa (1999), and in the weakly nonlinear case they reduce to KdV solitons. In the
general situation strong 2.5-layer solitons can correspond to higher modes. Sufficiently
strong solitons could also possess a recirculating core (at least, as a formal solution).The model was applied to the data collected during the COPE experiment. The
results are in reasonable agreement with experimental data.
The motion of a fluid ellipsoid in a general linear background flow
Authors: McKIVER WILLIAM J. , DRITSCHEL DAVID G. 
Published: January 2005

The study of the motion of a fluid ellipsoid has a long and fascinating history
stretching back originally to Laplace in the late 18th century. Recently, this subject
has been revived in the context of geophysical fluid dynamics, where it has been shown
that an ellipsoid of uniform potential vorticity remains an ellipsoid in a background
flow consisting of horizontal strain, vertical shear, and uniform rotation. The object of
the present work is to present a simple, appealing, and practical way of investigating
the motion of an ellipsoid not just in geophysical fluid dynamics but in general. The
main result is that the motion of an ellipsoid may be reduced to the evolution of a
symmetric, 3×3 matrix, under the action of an arbitrary 3×3 ‘flow’ matrix. The latter
involves both the background flow, which must be linear in the Cartesian coordinates
at the surface of the ellipsoid, and the self-induced flow, which was given by Laplace.The resulting simple dynamical system lends itself ideally to both numerical and
analytical study. We illustrate a few examples and then present a theory for the
evolution of a vortex within a slowly varying background flow. We show that a
vortex may evolve quasi-adiabatically, that is, it stays close to an equilibrium form
associated with the instantaneous background flow. The departure from equilibrium,
on the other hand, is proportional to the rate of change of the background flow.
Rates of treated schizophrenia and its clinical and cultural features in the population isolate of the Iban of Sarawak: a tri-diagnostic approach
Authors: BARRETT ROBERT , LOA PETER , JERAH EDWARD , NANCARROW DEREK , CHANT DAVID , MOWRY BRYAN 
Published: January 2005

Background. We present results of a study of treated rates of schizophrenia among the Iban of Sarawak, Malaysia. Most Iban live in longhouses, each comprising a kindred group of up to 300 individuals. Cultural practices such as minimal intermarriage with members of adjacent ethnic groups and in-depth genealogical knowledge make them a population suitable for genetic investigation. Iban culture is conducive to a focus on symptoms and illness, and to patterns of treatment-seeking behaviour that are enthusiastic and persistent.Method. We identified all known cases of psychotic disorder within a defined catchment area based on an exhaustive survey of available medical records. From corresponding Malaysian census data (91056 persons), we report rates of treated schizophrenia in the Iban population, using three diagnostic systems, as well as the demographic and clinical characteristics of these individuals.Results. The most frequent presenting complaints were insomnia and aggression. We found higher treated rates for narrowly defined schizophrenia among males, but no significant gender difference for age of onset. Estimates of treated rates to age 55 years (per 10000) for narrow schizophrenia were 41·9 (ICD-10), 56·5 (DSM-IV), and 83 (RDC), while the rates for broad schizophrenia were 105·5, 103·2, and 107·5 respectively.Conclusions. Treated rates of schizophrenia were higher than the reported prevalence for many populations at risk, including many small-scale societies, although different methodological approaches may partly explain these findings. Given the cultural patterns of Iban treatment-seeking behaviour, treated rates of schizophrenia reported here may closely approximate the population prevalence of this disorder.
Psychiatric and social aspects of suicidal behaviour in prisons
Authors: JENKINS RACHEL , BHUGRA DINESH , MELTZER HOWARD , SINGLETON NICOLA , BEBBINGTON PAUL , BRUGHA TRALOACH , COID JEREMY , FARRELL MIKE , LEWIS GLYN , PATON JO 
Published: January 2005

Background. Suicidal behaviour and completed suicide are serious problems within British prisons, leading to significant morbidity and mortality, and are the focus of major efforts towards their prevention.Aim. To explore the demographic, social and psychiatric correlates of suicidal behaviour in prisons in England and Wales and their relationship with health service use; and to develop a combined psychosocial model of risk.Method. This report analyses the prevalence of suicidal ideation and suicide attempts in the ONS National Prison Survey, and their association with the presence of psychiatric disorders, personality disorder, substance abuse and social risk factors. These data were compared with data from the second national survey of psychiatric morbidity in adults living at home. In both surveys, a two-phase interviewing procedure was used, covering general health, health service use, assessment of psychiatric disorders, life events, social supports, suicidal behaviour, activities of daily living, sociodemographic data, substance abuse and intelligence.Results. Suicidal thoughts and suicide attempts were commoner in prisons than in the general population and these were significantly associated with higher rates of psychosis, neurosis and personality disorder in prisons. In addition, demographic and factors such as being young, single, white, leaving school early and experiencing poor social support and significant social adversity were important risk factors for suicidal thoughts. Crucially, there was no separate category of people at suicidal risk who did not have psychiatric disorders.Conclusions. The high rates of suicidal behaviour in prisons cannot be addressed without adequate attention to the high rates of psychiatric disorder and vulnerability factors in prisoners.
Neurophysiological correlates of increased verbal working memory in high-dissociative participants: a functional MRI study
Authors: VELTMAN DICK J. , De RUITER MICHIEL B. , ROMBOUTS SERGE A. R. B. , LAZERON RICHARD H. C. , BARKHOF FREDERIK , VAN DYCK RICHARD , DOLAN RAYMOND J. , HANS PHAF R. 
Published: January 2005

Background. Dissociation, defined as a disruption in usually integrated mental functions, is found not only in DSM-IV dissociative disorders, but also in post-traumatic stress disorder and eating disorders. Dissociative phenomena are also common in the general population, and may reflect a constitutionally determined cognitive style rather than a pathological trait acquired through experiencing adverse life events. In pathological dissociation, evidence has been presented for episodic memory dysfunction. In contrast, in high-dissociative subjects increased performance has been found for episodic memory and dual task performance. These findings have been linked to changes in working memory capacity.Method. In the present study, the authors sought to extend these findings by using functional magnetic resonance imaging during performance of two parametric working memory tasks. We tested 21 healthy low- and high-dissociative participants.Results. High-dissociative participants performed slightly better during both tasks. Imaging data showed that both groups activated similar networks for both tasks, i.e. (bilateral) dorsolateral (DL) and ventrolateral prefrontal cortex (PFC), parietal cortex, and supplementary motor area. Group×task interactions were found in the high-dissociative group in L DLPFC and L parietal cortex; in the low-dissociative group in R fusiform gyrus. The differences in the high-dissociative group were independent from performance differences, implying that high-dissociative subjects generally recruit this network to a greater extent.Conclusions. These results confirm earlier findings using a verbal WM task in high-dissociative participants, and are compatible with the conceptualization of non-pathological dissociation as an information-processing style, characterized by distinct attentional and mnemonic abilities.
Clinical and functional outcomes of depression treatment in patients with and without chronic medical illness
Authors: SIMON GREGORY E. , VON KORFF MICHAEL , LIN ELIZABETH 
Published: January 2005

Background. In patients with chronic medical conditions, depression can be viewed as an expected reaction to illness or an independent condition requiring active treatment. We examine how clinical and functional outcomes of depression treatment compare in primary-care patients with and without chronic medical illness.Method. Health plan administrative data were used to identify primary-care patients initiating antidepressant treatment, including a general sample (n=204) and cohorts with ischemic heart disease (n=68), diabetes (n=93), or obstructive lung disease (n=74). Telephone interviews at baseline, 2 months, and 6 months assessed depression (Structured Clinical Interview for DSM-IV, Hopkins Symptom Checklist depression scale), functional status (SF-36) and days of disability because of to illness.Results. At baseline, depression severity in patients with diabetes and obstructive lung disease was similar to those without medical co-morbidity, but significantly lower in those with ischemic heart disease. Social and emotional functioning were similar across all groups, but those with chronic medical illness reported greater physical impairment. All groups showed significant improvement in depression over six months, but the rate of improvement was significantly slower in those with heart disease. All groups showed significant and similar improvement in social and emotional functioning, but physical functioning showed little change. Days of disability and restricted activity improved significantly in all groups. Improvement in depression during treatment was strongly related to change in disability.Conclusions. Patients with chronic medical illness and co-morbid depression show significant improvements in mood, social and emotional functioning, and disability following initiation of depression treatment. Depression may be a stronger determinant of disability than is stable chronic medical illness.
Correlation between different memory systems and striatal dopamine D2/D3 receptor density: a single photon emission computed tomography study
Authors: CHEN PO SEE , KUANG YANG YEN , LEE YUH-SHIOW , YEH TZUNG LIEH , LEE I. HUI , CHIU NAN TSING , CHU CHING LIN 
Published: January 2005

Objective. Although studies have indicated that the human basal ganglia have a specific role in different memory systems, the functional significance of the striatal dopamine activities for the basal ganglia remains less clear. This study assessed the relationship between measures of striatal dopamine activities and indices of different memory systems in healthy individuals.Method. Single photon emission computed tomography and [123I]IBZM (iodobenzamide) were used to assess the striatal dopamine D2/D3 receptor density in 62 healthy volunteers aged between 19 and 61 years. All subjects underwent a Wechsler Memory Scale – Revised test.Results. Dopamine D2/D3 receptor densities in the striatum decline with age. Stepwise regression analysis showed that verbal delayed recall and working memory account for most of the variance in dopamine D2/D3 measurements. These relationships remain significantly after controlling for age effects.Conclusions. Brain striatal dopamine activities are also significantly associated with various memory systems, in addition to motor functions. This may explain why patients with neuropsychiatric disorders may have both memory and motor impairments.
Dysfunction of a distributed neural circuitry in schizophrenia patients during a working-memory performance
Authors: MENDREK A. , KIEHL K. A. , SMITH A. M. , IRWIN D. , FORSTER B. B. , LIDDLE P. F. 
Published: January 2005

Background. In a recent longitudinal study of first-episode schizophrenia patients, we found that while dysfunction of the right dorsolateral prefrontal cortex (DLPFC), right thalamus, left cerebellum and cingulate gyrus normalized with antipsychotic treatment and significant reduction in symptomatology, the left DLPFC, left thalamus, and right cerebellum remained disturbed. In the present study we investigated whether these abnormalities are also present in clinically stable, relatively well-functioning schizophrenia patients in comparison to control subjects during performance of the N-back working-memory task.Method. Twelve schizophrenia and 12 control subjects completed the study. The functional images collected during scanning were analyzed using a random-effects model in a restricted set of six regions of interest (ROIs). In addition, the exploratory search in the entire brain volume was performed.Results. The ROI analyses revealed relative underactivation in the region of the left DLPFC and the right cerebellum, as well as overactivation in the left cerebellum. The exploratory whole-brain search exposed additional overactivation in the medial frontal, anterior cingulate, and left parietal cortices.Conclusions. The present study provides evidence of significant underactivations in stable schizophrenia patients in regions that we have previously observed to be dysfunctional in acutely psychotic and partially remitted patients, together with extensive overactivations in several regions that potentially reflect some compensatory mechanism or increased effort on the working-memory task.