bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution and instability of unsteady nonlinear streaks generated by free-stream vortical disturbances
Authors: RICCO PIERRE , LUO JISHENG , WU XUESONG
Published: April 2011

We investigate the influence of free-stream vortical disturbances on the evolution and instability of an incompressible laminar boundary layer, focusing on components of sufficiently long wavelength, which are known to penetrate into the boundary layer to generate streamwise elongated streaks. The free-stream disturbance is assumed to be sufficiently strong (but still of small amplitude) that the induced streaks acquire an O(1) streamwise velocity in the region where the boundary-layer thickness becomes comparable with the spanwise wavelength of the perturbation. The formation and evolution of the streaks are governed by the nonlinear unsteady boundary-region equations supplemented by appropriate upstream and far-field boundary conditions. This initial-boundary-value problem is solved for the special case where the free-stream disturbance is modelled by a pair of oblique vortical modes with the same frequency but opposite spanwise wavenumbers. Nonlinearity is found to inhibit the response. The nonlinear interaction alters the mean-flow profile appreciably, the shape of which is in quantitative agreement with experimental measurements. Wall-normal inflection points are detected in the instantaneous streamwise velocity profiles. The secondary stability analysis indicates that in the presence of free-stream disturbance with an intensity of 2.8%, the resulting streaky boundary layer becomes inviscidly unstable. The characteristic frequency, phase and group velocities, and growth rate of unstable sinuous modes are found to be in broad agreement with recent experiments. The present theoretical framework allows in principle a quantitative relation to be established between the characteristics of free-stream turbulence and the secondary instability, and this relation may be exploited to develop an efficient and physics-based approach for predicting bypass transition.
Measurements and simulations of time-dependent flow fields within an electrokinetic micromixer
Authors: BARZ DOMINIK P. J. , ZADEH HAMID FARANGIS , EHRHARD PETER
Published: April 2011

We investigate the flow field in an electrokinetic micromixer. The concept of the micromixer is based on the combination of an alternating electrical field applied to a pressure-driven base flow in a meander–channel geometry. The presence of the electrical field leads to an additional electro-osmotic velocity contribution, which results in a complex flow field within the meander bends. The velocity fields within the meander are measured by means of a microparticle-image velocimetry method. Furthermore, we introduce a mathematical model, describing the electrical and fluid-mechanical phenomena present within the device, and perform simulations comparable to the experiments. The comparison of simulations and experiments reveals good agreement, with minor discrepancies in flow topology, obviously caused by small but crucial differences between experimental and numerical geometries. In detail, simulations are performed for sharp corners of the bends, while in the experiments these corners are rounded due to the microfabrication process.
Oblique route to turbulence
Authors: MALIK MUJEEB R.
Published: April 2011

Direct numerical simulations have been performed by Mayer, Von Terzi & Fasel (J. Fluid Mech., this issue, vol. 674, 2011, pp. 5–42) to demonstrate that oblique-mode breakdown leads to fully turbulent flow for a Mach 3 flat-plate boundary layer. Since very low level of initial disturbances is required for this transition scenario, oblique-mode breakdown is the most potent mechanism for transition in two-dimensional supersonic boundary layers in low-disturbance environments relevant to flight.
Analysis of mechanisms for platelet near-wall excess under arterial blood flow conditions
Authors: CROWL L. , FOGELSON A. L.
Published: April 2011

The concentration of platelets near the blood vessel wall is important because platelets survey the condition of the vessel wall and respond to injuries to it. Under arterial flow conditions, platelets are non-uniformly distributed across the vessel lumen and have a high concentration within a few microns of the vessel wall. This is believed to be a consequence of the complex motion of red blood cells which constitute a large fraction of the blood's volume. We use a novel lattice Boltzmann-immersed boundary method to simulate, in two dimensions, the motion of dense red blood cell suspensions and their effect on platelet-sized particles. We track the development of a red blood cell-free layer near the wall and the later development of the platelet near-wall excess. We find that the latter develops more quickly at high wall shear rates and that the magnitude of the excess and its proximity to the wall are dependent on haematocrit. Treating the simulation data as if it were generated by a drift–diffusion process, we find that the effective lateral platelet diffusivity depends strongly on lateral position; it has a magnitude of order of 10−6 cm2 s−1 over much of the lumen but drops to almost zero close to the wall. This large effective diffusivity over the core of the lumen combined with reduced space for platelets in this region because of the inward migration of red blood cells largely but not completely accounts for the observed platelet-concentration profiles. We present evidence for a highly localized red blood cell-induced platelet drift at the edge of the red cell-free layer and suggest a physical mechanism that may generate it.
Shock-wave surfing
Authors: LAURENCE S. J. , DEITERDING R.
Published: April 2011

A phenomenon referred to as ‘shock-wave surfing’, in which a body moves in such a way as to follow the shock wave generated by another upstream body, is investigated numerically and analytically. During the surfing process, the downstream body can accumulate a significantly higher lateral velocity than would otherwise be possible. The surfing effect is first investigated for interactions between a sphere and a planar oblique shock. Numerical simulations are performed and a simple analytical model is developed to determine the forces acting on the sphere. A phase-plane description is employed to elucidate features of the system dynamics. The analytical model is then generalised to the more complex situation of aerodynamic interactions between two spheres, and, through comparisons with further computations, is shown to adequately predict the final separation velocity of the surfing sphere in initially touching configurations. Both numerical simulations and a theoretical analysis indicate a strong influence of the sphere radius ratio on the separation process and predict a critical radius ratio that delineates entrainment of the smaller body within the flow region bounded by the larger body's shock from expulsion. Furthermore, it is shown that an earlier scaling law does not accurately describe the separation behaviour. The surfing effect has important implications for meteoroid fragmentation: in particular, a large fraction of the variation in the separation velocity deduced by previous authors from an analysis of terrestrial crater fields can be explained by a combination of surfing and a modest rotation rate of the parent body.
Dynamic effects on the transition between two-dimensional regular and Mach reflection of shock waves in an ideal, steady supersonic free stream
Authors: NAIDOO K. , SKEWS B. W.
Published: April 2011

There have been numerous studies on the steady-state transition criteria between regular and Mach reflection of shock waves generated by a stationary, two-dimensional wedge in a steady supersonic flow, since the original shock-wave reflection research by Ernst Mach in 1878. The steady, two-dimensional transition criteria between regular and Mach reflection are well established. There has been little done to consider the dynamic effect of a rapidly rotating wedge on the transition between regular and Mach reflection. This paper presents the results of an investigation on the effect of rapid wedge rotation on regular to Mach reflection transition in the weak- and strong-reflection ranges with the aid of experiment and computational fluid dynamics. The experimental set-up includes a novel facility to rotate a pair of large aspect ratio wedges in a 450 mm × 450 mm supersonic wind tunnel at wedge rotation speeds up to 11000 deg s−1. High-speed images and measurements are presented. A numerical solution of the inviscid governing flow equations was used to mimic the experimental motion and to extend the investigation beyond the limits of the current facility to explore the influence of variables in the parameter space. There is good agreement between experimental measurements and numerical simulation. This paper includes the first experimental evidence of the regular to Mach reflection transition beyond the steady-state detachment condition in the weak- and strong-reflection ranges. It also presents results of simulations for the dynamic regular to the Mach reflection transition which show a difference between the sonic, length-scale and detachment conditions. This paper includes experimental evidence of the Mach to regular reflection transition below the steady-state von Neumann condition.
Contributions of the wall boundary layer to the formation of the counter-rotating vortex pair in transverse jets
Authors: SCHLEGEL FABRICE , WEE DAEHYUN , MARZOUK YOUSSEF M. , GHONIEM AHMED F.
Published: April 2011

Using high-resolution 3-D vortex simulations, this study seeks a mechanistic understanding of vorticity dynamics in transverse jets at a finite Reynolds number. A full no-slip boundary condition, rigorously formulated in terms of vorticity generation along the channel wall, captures unsteady interactions between the wall boundary layer and the jet – in particular, the separation of the wall boundary layer and its transport into the interior. For comparison, we also implement a reduced boundary condition that suppresses the separation of the wall boundary layer away from the jet nozzle. By contrasting results obtained with these two boundary conditions, we characterize near-field vortical structures formed as the wall boundary layer separates on the backside of the jet. Using various Eulerian and Lagrangian diagnostics, it is demonstrated that several near-wall vortical structures are formed as the wall boundary layer separates. The counter-rotating vortex pair, manifested by the presence of vortices aligned with the jet trajectory, is initiated closer to the jet exit. Moreover tornado-like wall-normal vortices originate from the separation of spanwise vorticity in the wall boundary layer at the side of the jet and from the entrainment of streamwise wall vortices in the recirculation zone on the lee side. These tornado-like vortices are absent in the case where separation is suppressed. Tornado-like vortices merge with counter-rotating vorticity originating in the jet shear layer, significantly increasing wall-normal circulation and causing deeper jet penetration into the crossflow stream.
Generation of internal solitary waves in a pycnocline by an internal wave beam: a numerical study
Authors: GRISOUARD N. , STAQUET C. , GERKEMA T.
Published: April 2011

Oceanic observations from western Europe and the south-western Indian ocean have provided evidence of the generation of internal solitary waves due to an internal tidal beam impinging on the pycnocline from below – a process referred to as ‘local generation’ (as opposed to the more direct generation over topography). Here we present the first direct numerical simulations of such a generation process with a fully nonlinear non-hydrostatic model for an idealised configuration. We show that, depending on the parameters, different modes can be excited and we provide examples of internal solitary waves as first, second and third modes, trapped in the pycnocline. A criterion for the selection of a particular mode is put forward, in terms of phase speeds. In addition, another simpler geometrical criterion is presented to explain the selection of modes in a more intuitive way. Finally, results are discussed and compared with the configuration of the Bay of Biscay.
A turbulent patch arising from a breaking internal wave
Authors: YAKOVENKO SERGEY N. , THOMAS T. GLYN , CASTRO IAN P.
Published: April 2011

Results of direct numerical simulations of the development of a breaking internal gravity wave are presented. The wave was forced by the imposition of an appropriate bottom boundary shape (a two-dimensional cosine hill) within a density-stratified domain having a uniform upstream velocity and density gradient. The focus is on turbulence generation and maintenance within the turbulent patch generated by the wave breaking. Pathlines, density contours, temporal and spatial spectra, and second moments of the velocity and density fluctuations and turbulent kinetic energy balance terms obtained from the data averaged over the span in the mixed zone are all used in the analysis of the flow. Typical Reynolds numbers, based on the vertical scale of the breaking region and the upstream velocity, were around 6000 and the fully resolved computations yielded sufficient resolution to capture the fine-scale transition processes as well as the subsequent fully developed turbulence. It is shown that globally, within the turbulent patch, there is an approximate balance in the production, dissipation and transport processes for turbulent kinetic energy, so that the patch remains quasi-steady over a significant time. Although it is far from being axially homogeneous, with turbulence generation occurring largely near the upstream bottom part of the patch where the mean velocity shear is particularly large, it has features not dissimilar to those of a classical turbulent wake.
Columnar eddy formation in freely decaying homogeneous rotating turbulence
Authors: YOSHIMATSU K. , MIDORIKAWA M. , KANEDA Y.
Published: April 2011

The roles of the Coriolis force and the convection associated with the fluid motion in the formation of columnar eddies in freely decaying homogeneous rotating turbulence at a moderate Rossby number are studied by direct numerical simulation of the Navier–Stokes equations in a periodic box. The simulated field is compared with a series of artificial fields generated by switching off the nonlinear and viscous terms in the Navier–Stokes equation at given instants. The comparison shows that, without the nonlinear convection effect, the Coriolis force cannot sustain the substantial growth in the direction parallel to the rotational axis of the length scale defined on the basis of the two-point correlation of the square of the vorticity, i.e. cannot sustain the formation of the columnar eddies. The length scale characterizes well the intuitive impression from visualization of flow obeying the dynamics with or without the nonlinear effect. It is shown that the lack of substantial growth is insensitive to the scale of the eddies, the box size and viscosity, at least in the case studied here.
Flexibility effects on vortex formation of translating plates
Authors: KIM DAEGYOUM , GHARIB MORTEZA
Published: April 2011

Vortex structures made by impulsively translating low aspect-ratio plates are studied experimentally using defocusing digital particle image velocimetry. The investigation of translating plates with a 90° angle of attack is important since it is a fundamental model for a better understanding of drag-based propulsion systems. Rectangular flat-rigid, flexible and curved-rigid thin plates with the same aspect ratio are studied in order to develop qualitative and quantitative understanding of their vortex structures and hydrodynamic forces. We find that the vortex formation processes of all three cases are drastically different from each other. The interaction of leading-edge vortices and tip flow near the tip region is an important mechanism to distinguish vortex patterns among these three cases. The drag trends of three cases are correlated closely with vortex structure and circulation. The initial peak of hydrodynamic force in the flexible plate case is not as large as the initial peak of the flat and curved rigid plate cases during the acceleration phase. However, after the initial peak, the flexible plate generates a large force comparable to that of the flat-rigid plate case in spite of its deformed shape, which results from the slow development of the vortex structure.
The Lighthill–Weis-Fogh clap–fling–sweep mechanism revisited
Authors: KOLOMENSKIY D. , MOFFATT H. K. , FARGE M. , SCHNEIDER K.
Published: April 2011

The Lighthill–Weis-Fogh ‘clap–fling–sweep’ mechanism for lift generation in insect flight is re-examined. The novelty of this mechanism lies in the change of topology (the ‘break’) that occurs at a critical instanttcwhen two wings separate at their ‘hinge’ point as ‘fling’ gives way to ‘sweep’, and the appearance of equal and opposite circulations around the wings at this critical instant. Our primary aim is to elucidate the behaviour near the hinge point as timetpasses throughtc. First, Lighthill's inviscid potential flow theory is reconsidered. It is argued that provided the linear and angular accelerations of the wings are continuous, the velocity field varies continuously through the break, although the pressure field jumps instantaneously att=tc. Then, effects of viscosity are considered. Near the hinge, the local Reynolds number is very small and local similarity solutions imply a logarithmic (integrable) singularity of the pressure jump across the hinge just before separation, in contrast to the ‘negligible pressure jump’ of inviscid theory invoked by Lighthill. We also present numerical simulations of the flow using a volume penalization technique to represent the motion of the wings. For Reynolds number equal to unity (based on wing chord), the results are in good agreement with the analytical solution. At a realistic Reynolds number of about 20, the flow near the hinge is influenced by leading-edge vortices, but local effects still persist. The lift coefficient is found to be much greater than that in the corresponding inviscid flow.
Experiments on the elliptic instability in vortex pairs with axial core flow
Authors: ROY CLÉMENT , LEWEKE THOMAS , THOMPSON MARK C. , HOURIGAN KERRY
Published: April 2011

Results are presented from an experimental study on the dynamics of pairs of vortices, in which the axial velocity within each core differs from that of the surrounding fluid. Co- and counter-rotating vortex pairs at moderate Reynolds numbers were generated in a water channel from the tips of two rectangular wings. Measurement of the three-dimensional velocity field was accomplished using stereoscopic particle image velocimetry, revealing significant axial velocity deficits in the cores. For counter-rotating pairs, the long-wavelength Crow instability, involving symmetric wavy displacements of the vortices, could be clearly observed using dye visualisation. Measurements of both the axial wavelength and the growth rate of the unstable perturbation field were found to be in good agreement with theoretical predictions based on the full experimentally measured velocity profile of the vortices, including the axial flow. The dye visualisations further revealed the existence of a short-wavelength core instability. Proper orthogonal decomposition of the time series of images from high-speed video recordings allowed a precise characterisation of the instability mode, which involves an interaction of waves with azimuthal wavenumbers m = 2 and m = 0. This combination of waves fulfils the resonance condition for the elliptic instability mechanism acting in strained vortical flows. A numerical three-dimensional stability analysis of the experimental vortex pair revealed the same unstable mode, and a comparison of the wavelength and growth rate with the values obtained experimentally from dye visualisations shows good agreement. Pairs of co-rotating vortices evolve in the form of a double helix in the water channel. For flow configurations that do not lead to merging of the two vortices over the length of the test section, the same type of short-wave perturbations were observed. As for the counter-rotating case, quantitative measurements of the wavelength and growth rate, and comparison with previous theoretical predictions, again identify the instability as due to the elliptic mechanism. Importantly, the spatial character of the short-wave instability for vortex pairs with axial flow is different from that previously found in pairs without axial flow, which exhibit an azimuthal variation with wavenumber m = 1.
Dynamics of fingering convection. Part 1 Small-scale fluxes and large-scale instabilities
Authors: TRAXLER A. , STELLMACH S. , GARAUD P. , RADKO T. , BRUMMELL N.
Published: April 2011

Double-diffusive instabilities are often invoked to explain enhanced transport in stably stratified fluids. The most-studied natural manifestation of this process, fingering convection, commonly occurs in the ocean's thermocline and typically increases diapycnal mixing by 2 orders of magnitude over molecular diffusion. Fingering convection is also often associated with structures on much larger scales, such as thermohaline intrusions, gravity waves and thermohaline staircases. In this paper, we present an exhaustive study of the phenomenon from small to large scales. We perform the first three-dimensional simulations of the process at realistic values of the heat and salt diffusivities and provide accurate estimates of the induced turbulent transport. Our results are consistent with oceanic field measurements of diapycnal mixing in fingering regions. We then develop a generalized mean-field theory to study the stability of fingering systems to large-scale perturbations using our calculated turbulent fluxes to parameterize small-scale transport. The theory recovers the intrusive instability, the collective instability and the γ-instability as limiting cases. We find that the fastest growing large-scale mode depends sensitively on the ratio of the background gradients of temperature and salinity (the density ratio). While only intrusive modes exist at high density ratios, the collective and γ instabilities dominate the system at the low density ratios where staircases are typically observed. We conclude by discussing our findings in the context of staircase-formation theory.
BIRDS AND KHOESĀN: LINKING SPIRITS AND HEALING WITH DAY-TO-DAY LIFE
Authors: Low Chris
Published: April 2011

It is not surprising that animals have played a significant role in KhoeSān cosmology but identifying exactly what that role is and how it relates to different contexts of belief and action is more challenging. This article identifies a special role for birds in KhoeSān thought and practice, which is tightly bound to matters of spirit and healing, seems relatively cohesive and is distinctive and widespread, both culturally and historically. Working out from a detailed KhoeSān medical ethnography and using bird examples taken from a wide range of KhoeSān, I argue that bird relationships are best understood by re-framing popular ideas of ‘supernatural potency’ within persistent habits of perception and the opportunities or challenges they present. I further highlight how KhoeSān interaction with birds must be linked to particular relationships with knowledge in order to understand why birds are so salient. I conclude by emphasizing the dangers of explaining KhoeSān bird relationships within potentially distorting categories of ‘metaphor’.
DEATH ‘ON THE MOVE’: FUNERALS, ENTREPRENEURS AND THE RURAL–URBAN NEXUS IN SOUTH AFRICA
Authors: Lee Rebekah
Published: April 2011

This article primarily concerns the intersection of the changing management of death with the problems and possibilities presented by the growing mobility of the African, and specifically Xhosa-speaking, population in South Africa from the latter half of the twentieth century to the present day. I am interested in how shifts in the practices and beliefs around death are mediated by individuals, households and businesses who have an historical affinity towards movement, particularly across what has been called the ‘rural–urban nexus’. In what ways has this more mobile orientation influenced the perception of rites and responsibilities surrounding death? And how have more mobile ‘ways of dying’ in turn created new subjectivities and new ways in which to imagine relations between the living and the dead? I argue that African funeral directors based in Cape Town and the rural areas of the Eastern Cape – a steadily more numerous and prominent group of entrepreneurs – are well-placed to shape these processes, through their role as cultural mediators and technological innovators, and their particular emphasis on maintaining a flow of bodies (both dead and alive) between rural and urban areas. I focus on two aspects of contemporary South African funerals – embalming and exhumations – that are suggestive of how the migration dynamic, and the continuing demands from mobile mourners for innovations via the funeral industry, have encouraged new perceptions of and relations to the dead body.
Embracing the Ummah: Student Politics beyond State Power in Pakistan
Authors: NELSON MATTHEW J.
Published: April 2011

Studies of student politics in Pakistan often focus on the competition between ‘secular’ and ‘religious’ student groups—for example, the leftward-leaning National Students Federation, regional parties with a broadly secular orientation like the Pakhtun Students Federation, the Islami Jamiat-e-Tuleba (Islamic Students Association), and sectarian groups like the (Shi'a) Imamia Students Organization. This paper describes the emergence of an increasingly violent stalemate between and amongst these groups since the 1960s. It then argues that for a growing number of students this stalemate produced a certain disenchantment with exclusionary efforts to control the ‘state-based Muslim nationalism’ that lay behind the formation of Pakistan itself. Seeking alternatives, these disenchanted students developed an interest in non-state-based forms of Muslim solidarity—forms that rejected the constraints of territorial Muslim nationalism in favour of transnational movements focused on the revitalization of Muslim solidarity on a truly global scale—movements like the (Deobandi) Tablighi Jama'at and the (Barelwi) Da'wat-e-Islami. Tracing this development, this paper takes up one application of Talal Asad's argument that alternative expressions of religion (and religious solidarity) are ‘produced’ by specific political circumstances. It also examines this formulation in the light of other theories that take an interest in the effects—indeed the potentially ‘democratizing’ effects—of protracted political stalemates.
Afternoon shedding of a new species ofIsospora(Apicomplexa) in the endangered Regent Honeyeater (Xanthomyza phrygia)
Authors: MORIN-ADELINE VICTORIA , VOGELNEST LARRY , DHAND NAVNEET K. , SHIELS MICHAEL , ANGUS WARRICK , ŠLAPETA JAN
Published: April 2011

The Regent Honeyeater (Xanthomyza phyrigia) is an endangered Australian bird species. Breeding populations have been established at Australian zoos in support of re-introduction programmes. This species is the host of a new species ofIsospora(Apicomplexa). Oocysts are spherical, 25·8 (22·5–28·75) by 23·8 (20–26·25)μm with a colourless to pale yellow smooth wall undergoing rapid exogenous sporulation, 90% sporulated oocysts in 8 h at 20°C. Each oocyst contains 1 polar granule. Sporocysts are ovoid, 18·67 (17–19) by 9·49 (9–10)μm with a flat Stieda body and spherical substieda body devoid of a hyaline body. The asexual stages and sexual phase is within the enterocytes of the duodenum and jejunum. Faeces collected in the morning (AM,n=84) and in the afternoon (PM,n=90) revealed significant diurnal periodicity in oocyst shedding; 21% (18 of 84) of the AM were positive with the mean of 499 oocysts.g−1compared to the PM with 91% (82 of 90) bird faeces positive with the mean of 129 723 oocysts.g−1. Therefore, parasite checks for these birds should be carried out in the afternoon to obtain an accurate result. The ecological significance of the high parasite burden in captive birds requires further investigation and comparison to the wild counterparts.
Study on ovine abortion associated withToxoplasma gondiiin affected herds of Khorasan Razavi Province, Iran based on PCR detection of fetal brains and maternal serology
Authors: RASSOULI M. , RAZMI G. R. , BASSAMI M. R. , MOVASSAGHI A. R. , AZIZZADEH M.
Published: April 2011

Toxoplasma gondii, an obligatory intracellular protozoan parasite, is one of the causative agents of ovine abortion, as reported in many countries. Different techniques are being used to detect this pathogen in infected ovine fetuses. One of the most sensitive and specific diagnostic techniques is Nested-PCR amplification of the B1 target gene of the organism. In total, 200 brain samples of aborted ovine fetuses and maternal sera submitted from different parts of Khorasan Razavi province, Iran were investigated to track the role ofToxoplasma gondiiin ovine abortion by a slightly modified Nested-PCR and IFAT assays, respectively. Among all samples, 27 (13·5%) were PCR-positive and 31 (15·5%) were IFAT-positive and theToxoplasma-induced abortion prevalence calculated was 8·8% to18·2% with 95% confidence interval. Results show that high levels of congenital transmission may occur in 27/31(87%) of pregnancies with an excellent logical agreement (ĸ=0·9) between 2 different tests. According to the results of this study, the Nested-PCR employed in this investigation could be recommended as an applied routine test for the routine examination and confirmation ofToxoplasma gondii-induced ovine abortion.
Parasites in a man-made landscape: contrasting patterns of trematode flow in a fishpond area in Central Europe
Authors: SOLDÁNOVÁ M. , FALTÝNKOVÁ A. , SCHOLZ T. , KOSTADINOVA A.
Published: April 2011

We have explored a large body of novel data focusing on small-scale temporal and spatial patterns in the composition and structure of larval trematode communities inLymnaea stagnalis(L.) from a typical Central European agricultural landscape. The 5 eutrophic fishponds studied provide excellent environments for the development of species-rich and abundant trematode communities. Nine prevalent species were consistently present in component communities, but had differential contribution to the parasite flow in the 5 ponds resulting in significant contrasting patterns of community similarity and the prevalence of the 3 major transmission guilds driving this similarity. Component communities split into 2 groups: (i) those from the large pond dominated by anatid and larid generalists with active miracidial transmission; and (ii) those from the smaller ponds dominated by 2 plagiorchioideans infecting snailsviaegg ingestion. We put forward 3 hypotheses for the remarkable differences in larval trematode flow in the similar and closely located eutrophic ponds: (i) species-specific differences in parasite colonization potential displayed by an ‘active-passive’ dichotomy in miracidial transmission strategies of the species; (ii) top-down effects of pond context on transmission pathways of the trematodes; and (iii) competition as an important mechanism in eutrophic environments with a bottom-up effect on component community structure.
The influence of water on the migration of infective trichostrongyloid larvae onto grass
Authors: van DIJK J. , MORGAN E. R.
Published: April 2011

Detailed knowledge of the effects of water on the migration of infective larvae of economically important trichostrongyloid species is urgently needed to feed into prediction models of future epidemiology. The influence of water on the migration of the parasitic nematodes Nematodirus battus, Haemonchus contortus and Teladorsagia circumcincta from sheep dung onto grass was examined in a series of laboratory experiments. Turf plots were seeded with larvae, which were recovered from grass clippings by serial sampling. Free water was necessary for larvae to escape from dung, but not for vertical migration onto grass. When temperature and relative humidity were held constant, the proportion of a population of live larvae present on herbage reached a plateau of around 2 (1–10)% after 24 h, and then changed little over time. Larvae in soil and dung formed a reservoir, such that a similar proportion of the larval population was maintained on grass after clipping. These findings suggest continuing random movement of free larvae. Implications for the epidemiology of trichostrongyloid species are discussed in the context of trade-offs faced by the parasites.
Biogeographical region and host trophic level determine carnivore endoparasite richness in the Iberian Peninsula
Authors: ROSALINO L. M. , SANTOS M. J. , FERNANDES C. , SANTOS-REIS M.
Published: April 2011

We address the question of whether host and/or environmental factors might affect endoparasite richness and distribution, using carnivores as a model. We reviewed studies published in international peer-reviewed journals (34 areas in the Iberian Peninsula), describing parasite prevalence and richness in carnivores, and collected information on site location, host bio-ecology, climate and detected taxa (Helminths, Protozoa andMycobacteriumspp.). Three hypotheses were tested (i) host based, (ii) environmentally based, and (iii) hybrid (combination of environmental and host). Multicollinearity reduced candidate variable number for modelling to 5: host weight, phylogenetic independent contrasts (host weight), mean annual temperature, host trophic level and biogeographical region. General Linear Mixed Modelling was used and the best model was a hybrid model that included biogeographical region and host trophic level. Results revealed that endoparasite richness is higher in Mediterranean areas, especially for the top predators. We suggest that the detected parasites may benefit from mild environmental conditions that occur in southern regions. Top predators have larger home ranges and are likely to be subjected to cascading effects throughout the food web, resulting in more infestation opportunities and potentially higher endoparasite richness. This study suggests that richness may be more affected by historical and regional processes (including climate) than by host ecological processes.
Schizophrenia patients are impaired in empathic accuracy
Authors: Lee J. , Zaki J. , Harvey P.-O. , Ochsner K. , Green M. F.
Published: April 2011

Background

Empathy is crucial for successful social relationships. Despite its importance for social interactions, little is known about empathy in schizophrenia. This study investigated the degree to which schizophrenia patients can accurately infer the affective state of another person (i.e. empathic accuracy).

Method

A group of 30 schizophrenia patients and 22 healthy controls performed an empathic accuracy task on which they continuously rated the affective state of another person shown in a video (referred to as the ‘target’). These ratings were compared with the target's own continuous self-rating of affective state; empathic accuracy was defined as the correlation between participants' ratings and the targets' self-ratings. A separate line-tracking task was administered to measure motoric/attentional factors that could account for group differences in performance. Participants' self-rated empathy was measured using the Interpersonal Reactivity Index, and targets' self-rated emotional expressivity was measured using the Berkeley Expressivity Questionnaire.

Results

Compared with controls, schizophrenia patients showed lower empathic accuracy although they performed the motoric tracking task at high accuracy. There was a significant group×target expressivity interaction such that patients showed a smaller increase in empathic accuracy with higher levels of emotional expressivity by the target, compared with controls. Patients' empathic accuracy was uncorrelated with self-reported empathy or clinical symptoms.

Conclusions

Schizophrenia patients showed lower empathic accuracy than controls, and their empathic accuracy was less influenced by the emotional expressivity of the target. These findings suggest that schizophrenia patients benefit less from social cues of another person when making an empathic judgement.
Alexis de Tocqueville and the Two-Founding Thesis
Authors: Ceaser James W.
Published: April 2011

Alexis de Tocqueville's account of the formation of the American regime identifies two constitutive moments: the Puritan colonization and the Revolution and the Constitution (1775–1789). Contrary to historians of the day, Tocqueville gave as much credit to the Puritans as to the Founders. Yet far from being a pure history, Tocqueville's narrative also had the purpose of promoting a new political foundation that replaced the philosophical doctrine of natural rights with an account based on “Customary History.” Tocqueville's approach was intended to further a great theoretical project inaugurated by Montesquieu that offered an alternative model to the mainstream Enlightenment position for how political philosophy should enter into and influence political life. This article analyzes the two-founding thesis, explores the underlying theoretical project on foundations of Tocqueville and Montesquieu, and presents and assesses the debate on the merits of attempting to change the political foundation of the American regime.
Defending the Union: Andrew Jackson's Nullification Proclamation and American Federalism
Authors: Brogdon Matthew S.
Published: April 2011

This essay contends that we can better understand Andrew Jackson's distinctive account of federalism by looking outside the Jeffersonian and Jacksonian political traditions. More appropriate peers for Jackson, as a constitutional statesman, are John Marshall and Abraham Lincoln. Existing treatments of Jackson miss these connections because they focus primarily on his roles as party leader and reformer, to the neglect of his constitutional statesmanship. A major cause of this neglect is the apparent inconsistency between Jackson's “nationalist” account of the Union in the Nullification Proclamation and his advocacy of “states' rights” elsewhere, a tension that can be resolved by a closer reading of Jackson's rhetoric. Among other things, this redefinition of Jackson's legacy demonstrates that there is no necessary tension between a strong union and meaningful limits on federal power; nor is there a necessary affinity between narrow construction of federal power and state-compact theory.
A Reply to Orren and Skowronek
Authors: Thomas George
Published: April 2011

I write to note a fundamental area of agreement with Professors Orren and Skowronek. And yet given this shared concern I think the study of ideas should be at the center of developmental approaches to politics. Professors Orren and Skowronek write, “The time has passed when familiar claims about constitutional foundations and normative commitments can be ventured confidently without serious consideration of confounding evidence. Making inquiries into these areas specific and empirically tractable will be, we think, value added.” I agree with this general assessment. Indeed, I have written a book,The Madisonian Constitution, which seeks to examine tensions within American constitutionalism and empirically trace how constitutional understandings and constitutional change have necessarily been partial and incomplete. In fact, I suggest that constitutional conflict has been an ordinary feature of American constitutionalism precisely because the American constitutional order is structured around agonistic principles and institutions. From the perspective of political science, understanding these tensions might also prove helpful in sustaining the American polity. But let me be clear: I do not think there is an easy foundation to be arrived at in the study of the American polity, or any other polity. Nor do I long for a world untroubled by “facing the facts,” nor for a time untroubled by historicism, positivism, or social science. I do think, however, an at times uncritical acceptance of historicism and positivism has led political scientists unnecessarily to turn away from the study of ideas and values that make up the political community.
Dimensions of stable sets and scrambled sets in positive finite entropy systems
Authors: FANG CHUN , HUANG WEN , YI YINGFEI , ZHANG PENGFEI
Published: April 2011

We study the dimensions of stable sets and scrambled sets of a dynamical system with positive finite entropy. We show that there is a measure-theoretically ‘large’ set containing points whose sets of ‘hyperbolic points’ (i.e. points lying in the intersections of the closures of the stable and unstable sets) admit positive Bowen dimension entropies; under the continuum hypothesis, this set also contains a scrambled set with positive Bowen dimension entropies. For several kinds of specific invertible dynamical systems, the lower bounds of the Hausdorff dimension of these sets are estimated. In particular, for a diffeomorphism on a smooth Riemannian manifold with positive entropy, such a lower bound is given in terms of the metric entropy and Lyapunov exponent.
Ergodic measures of Markov semigroups with the e-property
Authors: SZAREK TOMASZ , WORM DANIËL T. H.
Published: April 2011

We study the set of ergodic measures for a Markov semigroup on a Polish state space. The principal assumption on this semigroup is the e-property, an equicontinuity condition. We introduce a weak concentrating condition around a compact set K and show that this condition has several implications on the set of ergodic measures, one of them being the existence of a Borel subset K0 of K with a bijective map from K0 to the ergodic measures, by sending a point in K0 to the weak limit of the Cesàro averages of the Dirac measure on this point. We also give sufficient conditions for the set of ergodic measures to be countable and finite. Finally, we give a quite general condition under which the Cesàro averages of any measure converge to an invariant measure.
Watching Exotic Animals Next Door: “Scientific” Observations at the Zoo (ca. 1870–1910)
Authors: Hochadel Oliver
Published: April 2011

Argument

The nineteenth century witnessed the advent of the modern zoo. Nearly everyone who came to watch the exotic animals was a “lay person” in the sense that virtually none had formal training in zoology. This paper provides a typology of these observers: the zoo directors, assistants, keepers, animal painters, and the “common” visitor. What did they observe and what were their motivations? Did they pursue a certain agenda? What kind of knowledge, if any, did they produce? Soon the issue of the reliability of these observations emerged. Lay observers insisted on the veracity of their intimate and personal knowledge of animals while academics complained that their claims could not be generalized and were tainted by anthropomorphism. Hence the focus on the observations of these laymen will reveal contemporary assumptions on what may count as “scientific.” This is closely linked to the question of how far the zoo may qualify as a site of scientific investigation in the first place. The constraints on doing research on animals in a public space such as the zoo were numerous. Yet despite these obstacles the zoological garden contributed to the rise of ecological thinking as well as to the formation of ethology as a scientific discipline.
The Art of Authority: Exhibits, Exhibit-Makers, and the Contest for Scientific Status in the American Museum of Natural History, 1920–1940
Authors: Cain Victoria
Published: April 2011

Argument

In the 1920s and 1930s, the growing importance of habitat dioramas at the American Museum of Natural History forced staff members to reconsider what counted as scientific practice and knowledge. Exhibit-makers pressed for more scientific authority, citing their extensive and direct observations of nature in the field. The museum's curators, concerned about their own eroding status, dismissed this bid for authority, declaring that older traditions of lay observation were no longer legitimate. By the 1940s, changes inside and outside the museum had destroyed any lingering notions that what exhibit-makers garnered from observing raw materials constituted scientific knowledge.
Collecting Standards: Teaching Botanical Skills in Sweden, 1850–1950
Authors: Beckman Jenny
Published: April 2011

Argument

Standards of botanical practice in Sweden between 1850 and 1950 were set, not only in schools and universities, but also in naturalist societies and botanical exchange clubs, and were articulated in handbooks and manuals produced for schoolboys. These standards were maintained among volunteer naturalists in the environmental movement in the 1970s, long after the decline and disappearance of collecting from the curriculum. School science provides a link between the laboratory, the classroom, and the norms and practices of everyday life: between the various “insides” and “outsides” of educational and research settings.
Lay Observers, Telegraph Lines, and Kansas Weather: The Field Network as a Mode of Knowledge Production
Authors: Vetter Jeremy
Published: April 2011

Argument

This paper examines the field network – linking together lay observers in geographically distributed locations with a central figure who aggregated their locally produced observations into more general, regional knowledge – as a historically emergent mode of knowledge production. After discussing the significance of weather knowledge as a vital domain in which field networks have operated, it describes and analyzes how a more robust and systematized weather observing field network became established and maintained on the ground in the early twentieth century. This case study, which examines two Kansas City-based local observer networks supervised by the same U.S. Weather Bureau office, demonstrates some of the key issues involved in maintaining field networks, such as the role of communications infrastructure, especially the telegraph, the procedures designed to make local observation more systematic and uniform, and the centralized, hierarchical power relations that underpinned even a low-status example of knowledge production on the periphery.
Clinical significance of methicillin-resistantStaphylococcus aureuscolonization in residents in community long-term-care facilities in Spain
Authors: MANZUR A. , DE GOPEGUI E. RUIZ , DOMINGUEZ M. , MARISCAL D. , GAVALDA L. , PEREZ J. L. , SEGURA F. , PUJOL M. ,   the Spanish Network for Research in Infectious Diseases
Published: April 2011

Methicillin-resistantStaphylococcus aureus(MRSA) is highly prevalent in Spanish hospitals and community long-term-care facilities (LTCFs). This longitudinal study was performed in community LTCFs to determine whether MRSA colonization is associated with MRSA infections and overall mortality. Nasal and decubitus ulcer cultures were performed every 6 months for an 18-month period on 178 MRSA-colonized residents (86 490 patient-days) and 196 non-MRSA carriers (97 470 patient-days). Fourteen residents developed MRSA infections and 10 of these were skin and soft tissue infections. Two patients with respiratory infections required hospitalization. The incidence rate of MRSA infection was 0·12/1000 patient-days in MRSA carriers and 0·05/1000 patient-days in non-carriers (P=0·46). No difference in MRSA infection rate was found according to the duration of MRSA colonization (P=0·69). The mortality rate was 20·8% in colonized residents and 16·8% in non-carriers; four residents with MRSA infection died. Overall mortality was statistically similar in both cohorts. Our results suggest that despite a high prevalence of MRSA colonization in LTCFs, MRSA infections are neither frequent nor severe while colonized residents remain at the facility. The epidemiological impact of an MRSA reservoir is more relevant than the clinical impact of this colonization for an individual resident and supports current recommendations to control MRSA spread in community LTCFs.