bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vortices interacting with nonslip walls: Stirring and mixing of primary and secondary vorticity
Authors: Orlandi Paolo 
Published: July 2002

The interaction of vortices with fixed boundaries is an important problem in many areas of practical interest. During the approach of the vortices to the wall, vorticity is created at the wall, and then mixing and stirring of primary and secondary vorticity lead to different scenarios that depend on the Re number. This problem is relevant to bursting in turbulent boundary layers, which is responsible for turbulence production. In the near-wall region of turbulent flows, vortex stretching plays a fundamental role. As a prelude to attempting the solution by direct simulation of 3-D Navier–Stokes equations, it is convenient to describe the mechanism associated with 2-D or axisymmetric flows. In the present study, axisymmetric vortex rings and vortex dipoles approaching a nonslip flat wall have been considered. In both cases, experimental results based on flow visualization are available.1,2 The purpose of the present paper is to do a numerical simulation with the same conditions used in the real experiments and follow the flow evolution for a much longer time than has been possible in such experiments. Both for axisymmetric and 2-D cases the numerical simulation shows, as revealed by the experiments, that, at the initial stage, very thin layers of vorticity of sign opposite to that of the primary vortex are generated at the wall.
This mechanism is almost independent of Re. This thin and intense layer immediately becomes unstable and rolls up creating a secondary vortex. This vortex interacts with the primary vortex and different flow structures are generated, depending on Re. The location where these structures form depends, in large measure, on whether vortex stretching is present or not. Particularly relevant to the bursting phenomenon is the case at intermediate Re (e.g., Re=1600). Here, a new dipole is created near the wall after multiple rebounding and pairing of secondary vortices. This new structure has sufficient strength to move itself away from the wall. We conclude that mixing and stirring of vorticity are the relevant mechanisms influencing the whole process in a two-dimensional simulation. This ejection of a new structure was previously noticed in the interaction of vortex rings with a wall. From flow visualization, Walker et al., at Re=Γ/ν&gt;3500, observed the occurrence of azimuthal instabilities and, immediately after that, they noticed a new vortex ring was rapidly ejected away from the wall.2 From these observations, those authors argued that the ejection was due to the azimuthal instabilities. In the present paper, axisymmetric calculations have been done in the same range of numbers used in the experiment of Walker et al.2 From the time evolution of the vorticity distribution, we argue that vortex pairing is the main mechanism that contributes to the generation of the new ring rather than azimuthal instabilities. The numerical simulations clearly show that this new ring is created above the primary ring and not at its interior.
The dispersion of particles in a separated backward-facing step flow
Authors: Ruck B. , Makiola B. 
Published: July 2002

Flows in technical and natural circuits often involve a particulate phase. To measure the dynamics of suspended, naturally resident or artificially seeded particles in the flow, optical measuring techniques, e.g., laser Doppler anemometry (LDA) can be used advantageously. In this paper the dispersion of particles in a single-sided backward-facing step flow is investigated by LDA. The investigation is of relevance for both, two-phase flow problems in separated flows with the associated particle diameter range of 1–70 μm and the accuracy of LDA with tracer particles of different sizes. The latter is of interest for all LDA applications to measure continuous phase properties, where interest for experimental restraints require tracer diameters in the upper micrometer range, e.g., flame resistant particles for measurements inside reactors, cylinders, etc. For the experiments, a closed-loop wind tunnel with a step expansion was used. Part of this tunnel, the test section, was made of glass.
The step had a height H=25 mm (channel height before the step 25 mm, after 50 mm, i.e., an expansion ratio of 2). The width of the channel was 500 mm. The length of the glass test section was chosen as 116 step heights. The wind tunnel, driven by a radial fan, allowed flow velocities up to 50 m/sec which is equivalent to ReH=105. Seeding was performed with particles of well-known size: 1, 15, 30, and 70 μm in diameter. As 1 μm tracers oil droplets were used, whereas for the upper micron range starch particles (density 1.500 kg/m3) were chosen. Starch particles have a spherical shape and are not soluble in cold water. Particle velocities were measured locally using a conventional 1-D LDA system. The measurements deliver the resultant ‘‘flow’’ field information stemming from different particle size classes. Thus, the particle behavior in the separated flow field can be resolved. The results show that with increasing particle size, the particle velocity field differs increasingly from the flow field of the continuous phase (inferred from the smallest tracers used). The velocity fluctuations successively decrease with increasing particle diameter. In separation zones, bigger particles have a lower mean velocity than smaller ones.
The opposite holds for the streamwise portions of the particle velocity field, where bigger particles show a higher velocity. The measurements give detailed insight into the particle dynamics in separated flow regions. LDA-measured dividing streamlines and lines of zero velocity of different particle classes in the recirculation region have been plotted and compared. In LDA the use of tracer particles in the upper micrometer size range leads to erroneous determinations of continuous phase flow characteristics. It turned out that the dimensions of the measured recirculation zones are reduced with increasing particle diameter. The physical reasons for these findings (relaxation time of particles, Stokes numbers, etc.) are explained in detail.
The kinematics of quasi-2-D freely decaying turbulence in a stratified fluid
Authors: Caperan Ph. , Maxworthy T. , Spedding G. 
Published: July 2002

We have studied experimentally the dynamics of freely decaying turbulence in a stratified fluid. At low Froude number this flow has a quasi-2-D behavior1 that modifies the mixing (Fr=0.004, Re=1000; based on the integral scales). We characterize the vorticity evolution in the range scales where the enstrophy cascade is taking place. The quasi-2-D period of this turbulence is studied by photographic analysis of the velocity field V, which is interpolated on a regular grid (128×128). We are able to decompose it into its internal wave and turbulent component, and to compute its derivative fields up to the vector η=curlHΩV (related to the enstrophy cascade; where ΩV is the vertical vorticity). An enstrophy transfer model is developed by generalizing the model of Weiss to slightly divergent flows: the tensor F=∇HVH−DivH VHI2 (where H denotes the horizontal component, and I2 is the identity tensor of order 2) enters the equation of evolution for η as dtη=ηF+ΩV curlH (DivHVH). (1) An elongation of η corresponds to an increase of the local vorticity gradient, which is the mechanism of the enstrophy cascade to small scales.
We neglect the second term of (1) since it occurs at the measurement noise scale. Thus eigenvalues λi and eigenvectors of F characterize Eq. (1) and we present maps of these functions. The analysis of these eigenvalues of F gives us the ‘‘coherent’’ zones of the flow where λ is complex, i.e., where the local effect of rotation counteracts the local strain induced by the whole vorticity field. In the remaining zones the λi are generally of opposite sign. Under this condition, the histogram of the angle α between the elongating (V+) and the contracting (V−) eigenvectors shows broad peaks centered on ±π/2, Where the separating curve of ΩV=0 on an Ω map corresponds to α=±π/2. In these regions the strain provokes a deformation of the vorticity field, which corresponds to the enstrophy cascade phenomenon. Statistics on the angles β±=∠(η,V±) reveals a mean alignment of η with V+ (elongation) and a mean right angle with V−. Thus, the relations between F and η are clearly shown in our experimental case.
The main effect of vertical compression or expansion at every point of the field, due for instance to a weak internal wave, is to modify the eigenvalues of F, thus inhibiting or favoring the local enstrophy cascade. In some cases, it is able to impose its sign onto the two eigenvalues: this is observed at the border of the coherent zone.
Turbulent mixing and the selectivity of fast chemical reactions
Authors: Bourne J. R. 
Published: July 2002

Assuming that complete information is available about (a) the chemical reactions (mechanism, stoichiometry, thermodynamics, and kinetics) and (b) the turbulent flow field in a reactor (mean velocities and turbulence parameters), we would like to calculate directly the time evolution of the temperature and the concentrations of all species present. No general method is yet available to satisfy this goal. Starting from the phenomena of reaction, molecular diffusion, and laminar deformation in laminated structures, which are formed by the action of vorticity, mixing in liquids at sub-Kolmogorov scales can be quantitatively described. This approach requires the compositions of the fluids incorporated into the vortices to be known. Thus, for example, when a reagent solution (B) is slowly added to a huge volume of a second reagent solution (A) in a stirred tank reactor, fresh B mixes with the average A composition. (Slowly means that the addition time is much greater than the time needed for turbulent and molecular transport to homogenize the tank contents.) Progress of the reactions is then determined essentially by the interaction between the fine-scale mixing (near the Batchelor concentration scale) and the chemical kinetics.
A convenient way to evaluate this modeling compares predicted and measured product distributions (or selectivities) for fast multiple reactions. (Up to now, this has been done for dilute solutions, which exhibited concentration, rather than also temperature segregation.) Advantages compared to working with single reactions can include enhanced sensitivity, inclusion of a wider range of flow fields than turbulent pipe flow, e.g., well-stirred systems, and practical relevance of controlling product distributions in the manufacture of chemicals. The effects on the product distributions of fast reactions of operating parameters such as stoichiometric and volumetric feed ratios, reagent concentrations, feed location, impeller speed, size and shape, viscosity, and type of reaction can be well described. Present efforts concentrate on relaxing the assumption of slow feed addition and of describing reactors where not only fine-scale, but also coarse-scale inhomogeneities occur. A simplified model for the engulfment frequency between fluids having different compositions is being evaluated. Some progress has been made, but the way in which fluid elements mix with each other is still not fully known.
Ironies of Emancipation: Changing Configurations of ‘Women's Work’ in the ‘Mission of Sisterhood’ to Indian Women
Authors: Haggis Jane 
Published: July 2002

On her arrival in Travancore in 1819 Mrs Mault, as wife of the new missionary, immediately set about establishing a school for convert girls and a ‘lace industry’ to employ convert women. Her actions reflect that pattern of activism and organization historians of gender and imperialism have identified as the ‘mission of domesticity’ conducted by European and North American Christian missionary women to their non-Christian ‘sisters’ in the colonial empires being established by their respective nation-states throughout the nineteenth century. Mrs Mault was herself among the first generation of missionary women to pioneer this specifically female branch of colonizing endeavour, designed to ‘emancipate’ Indian women in terms of the norms of metropolitan ideologies of femininity and womanhood. Drawing on a case study of the London Missionary Society's activities in South Travancore, South India during the nineteenth and early twentieth centuries, I argue that this ‘mission of domesticity’ was not a straightforward transfer of conventions of marriage and motherhood to the colonial context. On the contrary, the project was from the start caught in a complex and contradictory web of agency and discourse which ‘remade’ not only convert women but missionary women as well. Central to this process of refiguring femininity on the imperial fulcrum were changes to the meanings of ‘work’ in relation to both ‘home’ and womanhood, articulated through a religious idiom and framework of action. The consequences of these processes, the article argues, were somewhat contrary. On the one hand, the Indian Christian woman is reconstructed as a wife, mother and worker, while on the other, the missionary women are bifurcated: the missionary wife increasingly viewed as an amateur appendage to her husband, firmly secured in the domestic sphere, while the single woman attains a new status as a professional worker.
Education of a Civil Servant's Daughter: Readings from Monica Chanda's Memoirs
Authors: Karlekar Malavika 
Published: July 2002

Nineteenth-century Bengal was a period of change, conflict and accommodation both among the bhadralok – literally translated to mean the gentle folk, the middle classes – as well as between them and the British rulers. The world view of the bhadralok and its search for a new paradigm had its material basis in changes in existing land relations, the emergence of the market and of urban spaces as well as the spread of education and literacy. Often changes in familial patterns, new roles for girls and women, their education and introduction to wider society, reflected developments in Britain. As the colonial encounter brought about a range of changes in a rapidly evolving social, economic and geographic scenario, it is important to try and understand inter-personal dynamics and at the level of individual consciousnesses. Women started reflecting and writing about their lives by the middle of the last century; the preferred form was the journal or diary. Several wrote many years later, often in widowhood. Monica Chanda was one such woman: the only daughter of Sarala and J.N. Gupta, a member of the Indian Civil Service, she was persuaded, at the age of 70, to write about her childhood, a period of her life she loved reminiscing about to her children and grandchildren. Life in the districts, her mother's role as civil service wife par excellence, early schooling and its later denial are evocatively sketched in this brief memoir. The present article will deal with constructions of a post-Victorian Indo-Anglian girlhood as perceived by Monica, using extensive quotations from the unpublished text. It will also try to trace the symbiotic relationship with the British Raj – viewed often with mixed feelings by the colonized.
Prostitution Policy in Europe: A Time of Change?
Authors: Kilvington Judith , Day Sophie , Ward Helen 
Published: July 2002

There has been considerable recent debate about prostitution in Europe that reflects concerns about health, employment and human rights. Legal changes are being introduced in many countries. We focus on two examples in order to discuss the likely implications. A new law in The Netherlands is normalizing aspects of the sex industry through decriminalizing both workers and businesses. In Sweden, on the other hand, prostitution is considered to be a social problem, and a new law criminalizes the purchasers of sexual services in an attempt to reduce demand. Both reforms appear to have had their desired effect at one level; in The Netherlands, health and safety regulations will be introduced as in any other job, and EU sex workers gain full social, legal and employment rights; in Sweden there was initially a tenfold decrease in the numbers of women working visibly on the streets, and some workers have left the industry. However, in both countries, the new legislation has also driven some sex work underground. Many sex workers are excluded by the Dutch system and move underground to become effectively invisible to the authorities. In Sweden sex workers and their clients also become less visible in order that the latter can avoid sanction. Social and economic changes, such as increased migration and the growing use of the Internet will also render the sex industry less visible both to state regulation and to health care workers. The major problems of prostitution for the workers remain exploitation, stigma, abuse and criminalization. These are not unique to the industry, and can only be tackled effectively by the self-organization of sex workers into unions and rights groups, along with full decriminalization. An alternative vision is promised through self-organization and anti-racist actions by sex workers in Germany; normalization and workers’ rights are tackled alongside training programmes for those seeking alternatives. Policy makers throughout Europe would do well to look at their experience and not simply at the clash of legal reforms.
Women, Wives and the Campaign against Pit Closures in County Durham: Understanding the Vane Tempest Vigil
Authors: Spence Jean 
Published: July 2002

The majority of the women who campaigned to save the Vane Tempest Colliery from closure in 1993 were involved because of their political understanding and allegiances rather than as a consequence of their practical involvement in mining life. Even those women who were married to miners did not conform to the stereotypical conception of ‘miner's wife’. However, the supporting labour movement and the media persisted in conceptualizing the Women's Vigil through romantic and masculinist discourses of miners and mining communities which could only locate the women as ‘wives’, which confined the campaign within historical stereotypes no longer appropriate to the actual situation and which persistently set the idea of socialism against that of feminism. This not only situated the women's campaign as secondary and subject to that of the NUM but it also subverted the possibilities of the women fully articulating their own experience and understanding within the campaign. The situation was further complicated by memories of the miners’ strike of 1984–5 in which women played such an important role. One aspect of this role, that of maintaining mining families in the face of hardship, continued to inform understanding of the women's role in the fight to prevent closure, although it was no longer appropriate. The Women's Vigil engaged with a much wider set of concerns and with a wider range of individuals and groups than did that of the miners themselves. There were serious possibilities for broadening the political campaign around the women's slogan of ‘Jobs, community and environment’ which were never fully exploited because of the difficulties of admitting that women could inhabit any position other than that of ‘miners’ wives’. This experience of the Vane Tempest Vigil indicates the significance and the centrality of gender issues within class based political action.
‘Getting Out and Getting Away’: Women's Narratives of Class Mobility
Authors: Lawler Steph 
Published: July 2002

This article is concerned with the ways in which women narrate a move from a ‘working-class’ position to a position marked (in however fragmentary and complex a way) as ‘middle class’. While such a move might be seen in terms of a straightforward escape from a disadvantaged social position, I argue here that what has to be analysed is the pain and the sense of estrangement associated with this class movement. Drawing on the class narratives of a group of seven white British women, the article uses Bourdieu's concepts of symbolic capital and habitus to explore the cultural and symbolic configurations of class. These configurations may be inscribed into the self, so that the self, itself, is class marked. Since working-class selves are frequently marked in pathological terms, this raises particular difficulties for the idea of an ‘escape’ from such a position. Class in this sense is embedded in people's history and so cannot be so easily ‘escaped’. The usual conventions of life-narratives – in which the self remains the same entity from birth to death and later events are a culmination of earlier ones – are also disrupted in this case. But if a working-class position is marked as pathological, so too is taking on the markers of middle-class existence. To do so is not only to risk ‘getting it wrong’, but it is also to risk the scorn attached to ‘pretentiousness’. There is a particular jeopardy here for women, since it is women who have been especially associated with desires for artefacts associated with bourgeois existence. The article argues for a focus for classed desires and class envy, not in pathological terms, but in terms of a coherent response to political and social exclusions.
Targeted Deletion of the PEX2 Peroxisome Assembly Gene in Mice Provides a Model for Zellweger Syndrome, a Human Neuronal Migration Disorder
Authors: Faust Phyllis L. , Hatten Mary E. 
Published: July 2002

Zellweger syndrome is a peroxisomal biogenesis disorder that results in abnormal neuronal migration in the central nervous system and severe neurologic dysfunction. The pathogenesis of the multiple severe anomalies associated with the disorders of peroxisome biogenesis remains unknown. To study the relationship between lack of peroxisomal function and organ dysfunction, the PEX2 peroxisome assembly gene (formerly peroxisome assembly factor-1) was disrupted by gene targeting.
Homozygous PEX2-deficient mice survive in utero but die several hours after birth. The mutant animals do not feed and are hypoactive and markedly hypotonic. The PEX2-deficient mice lack normal peroxisomes but do assemble empty peroxisome membrane ghosts. They display abnormal peroxisomal biochemical parameters, including accumulations of very long chain fatty acids in plasma and deficient erythrocyte plasmalogens. Abnormal lipid storage is evident in the adrenal cortex, with characteristic lamellar–lipid inclusions. In the central nervous system of newborn mutant mice there is disordered lamination in the cerebral cortex and an increased cell density in the underlying white matter, indicating an abnormality of neuronal migration. These findings demonstrate that mice with a PEX2 gene deletion have a peroxisomal disorder and provide an important model to study the role of peroxisomal function in the pathogenesis of this human disease.