Hormone-sleep interactions predict cerebellar connectivity and behavior in aging females

Sex hormones fluctuate over the course of the female lifespan and are associated with brain health and cognition. Thus, hormonal changes throughout female adulthood, and with menopause in particular, may contribute to sex differences in brain function and behavior. Further, sex hormones have been correlated with sleep patterns, which also exhibit sex-specific impacts on the brain and behavior. As such, the interplay between hormones and sleep may contribute to late-life brain and behavioral outcomes in females. Here, in a sample of healthy adult females (n = 79, ages 35-86), we evaluated the effect of hormone-sleep interactions on cognitive and motor performance as well as cerebellar-frontal network connectivity. Salivary samples were used to measure 17β-estradiol, progesterone, and testosterone levels while overnight actigraphy was used to quantify sleep patterns. Cognitive behavior was quantified using the composite average of standardized scores on memory, processing speed, and attentional tasks, and motor behavior was indexed with sequence learning, balance, and dexterity tasks. We analyzed resting-state connectivity correlations for two specific cerebellar-frontal networks: a Crus I to dorsolateral prefrontal cortex network and a Lobule V to primary motor cortex network. In sum, results indicate that sex hormones and sleep patterns interact to predict cerebellar-frontal connectivity and behavior in aging females. Together, the current findings further highlight the potential consequences of endocrine aging in females and suggest that the link between sex hormones and sleep patterns may contribute, in part, to divergent outcomes between sexes in advanced age.

Network segregation in aging females and evaluation of the impact of sex steroid hormones

Males and females show differential patterns in connectivity in resting-state networks (RSNs) during normal aging, from early adulthood to late middle age. Age-related differences in network integration (effectiveness of specialized communication at the global network level) and segregation (functional specialization at the local level of specific brain regions) may also differ by sex. These differences may be due at least in part to endogenous hormonal fluctuation, such as that which occurs in females during midlife with the transition to menopause when levels of estrogens and progesterone drop markedly. A limited number of studies that have investigated sex differences in the action of steroid hormones in brain networks. Here we investigated how sex steroid hormones relate to age-network relationships in both males and females, with a focus on network segregation. Females displayed a significant quadratic relationship between age and network segregation for the cerebellar-basal ganglia and salience networks. In both cases, segregation was still increasing through adulthood, highest in midlife, and with a downturn thereafter. However, there were no significant relationships between sex steroid hormone levels and network segregation levels in females, and they did not exhibit significant associations between progesterone or 17β-estradiol and network segregation. Patterns of connectivity between the cerebellum and basal ganglia have been associated with cognitive performance and self-reported balance confidence in older adults. Together, these findings suggest that network segregation patterns with age in females vary by network, and that sex steroid hormones are not associated with this measure of connectivity in this cross-sectional analysis. Though this is a null effect, it remains critical for understanding the extent to which hormones relate to brain network architecture.

Characterisation and optimisation of foams for varicose vein sclerotherapy

BACKGROUND

Foam sclerotherapy is the process of using an aqueous foam to deliver surfactant to a varicose vein to damage vein wall endothelial cells, causing the vein to spasm, collapse and ultimately be re-absorbed into the body. Aqueous foams are complex fluids that can exhibit a significant yield stress and high effective viscosity which depend on their composition, particularly the bubble size and liquid fraction.

OBJECTIVE

To characterise the properties of foams used for varicose vein sclerotherapy and determine their effectiveness in the displacement of blood during sclerotherapy.

METHODS

Foams are modelled as yield stress fluids and their flow profiles in a model vein are predicted. Values of the yield stress are determined from experimental data for three different foams using the Sauter mean of the bubble size distribution. Along with the measured liquid fraction of the foams, this information is collected into a Bingham number which entirely characterises the process of sclerotherapy.

RESULTS

Polydispersity in bubble size has a strong effect on the yield stress of a foam and the Sauter mean of the size distribution better captures the effects of a few large bubbles. Reducing the polydispersity increases the yield stress, and a higher yield stress results in a larger plug region moving along the vein, which is more effective in displacing blood. The width of the plug region is proportional to the Bingham number, which also has a quadratic dependence on the liquid fraction of the foam. Assuming typical values for the rate of injection of a foam, we predict that for a vein of diameter 5 mm, the most effective foams have low liquid fraction, a narrow size distribution, and a Bingham number B ≈ 4.5.

CONCLUSIONS

The Sauter mean radius provides the most appropriate measure of the bubble size for sclerotherapy and the Bingham number then provides a simple measure of the efficacy of foam sclerotherapy in a vein of a given size, and explains the ability of different foams to remove varicose veins. Foams containing small bubbles, with a narrow size distribution, and a low liquid fraction are beneficial for sclerotherapy.

Simulation of surfactant transport during the rheological relaxation of two-dimensional dry foams

We describe a numerical model to predict the rheology of two-dimensional dry foams. The model accurately describes soap film curvature and viscous friction with the walls, and includes the transport of surfactant within the films and across the vertices where films meet. It accommodates the changes in foam topology that occur when a foam flows and, in particular, accurately represents the relaxation of the foam following a topological change. The model is validated against experimental data, allowing the prediction of elastic and viscous parameters associated with different surfactant solutions.

Ideal wet two-dimensional foams and emulsions with finite contact angle

We present simulations that show that the equilibrium structure of an ideal two-dimensional foam with a finite contact angle develops an inhomogeneity for high liquid fraction φ. In liquid-liquid emulsions this inhomogeneity is known as flocculation. In the case of an ordered foam this requires a perturbation, but in a disordered foam inhomogeneity grows steadily and spontaneously with φ, as demonstrated in our simulations performed with the Surface Evolver.

Curvature driven motion of a bubble in a toroidal Hele-Shaw cell

We investigate the equilibrium properties of a single area-minimizing bubble trapped between two narrowly separated parallel curved plates. We begin with the case of a bubble trapped between concentric spherical plates. We develop a model which shows that the surface energy of the bubble is lower when confined between spherical plates than between flat plates. We confirm our findings by comparing against Surface Evolver simulations. We then derive a simple model for a bubble between arbitrarily curved parallel plates. The energy is found to be higher when the local Gaussian curvature of the plates is negative and lower when the curvature is positive. To check the validity of the model, we consider a bubble trapped between concentric tori. In the toroidal case, we find that the sensitivity of the bubble's energy to the local curvature acts as a geometric potential capable of driving bubbles from regions with negative to positive curvature.

Quasicrystalline three-dimensional foams

We present a numerical study of quasiperiodic foams, in which the bubbles are generated as duals of quasiperiodic Frank-Kasper phases. These foams are investigated as potential candidates to the celebrated Kelvin problem for the partition of three-dimensional space with equal volume bubbles and minimal surface area. Interestingly, one of the computed structures falls close to (but still slightly above) the best known Weaire-Phelan periodic candidate. In addition we find a correlation between the normalized bubble surface area and the root mean squared deviation of the number of faces, giving an additional clue to understanding the main geometrical ingredients driving the Kelvin problem.

Nonequivalence of updating rules in evolutionary games under high mutation rates

Moran processes are often used to model selection in evolutionary simulations. The updating rule in Moran processes is a birth-death process, i. e., selection according to fitness of an individual to give birth, followed by the death of a random individual. For well-mixed populations with only two strategies this updating rule is known to be equivalent to selecting unfit individuals for death and then selecting randomly for procreation (biased death-birth process). It is, however, known that this equivalence does not hold when considering structured populations. Here we study whether changing the updating rule can also have an effect in well-mixed populations in the presence of more than two strategies and high mutation rates. We find, using three models from different areas of evolutionary simulation, that the choice of updating rule can change model results. We show, e. g., that going from the birth-death process to the death-birth process can change a public goods game with punishment from containing mostly defectors to having a majority of cooperative strategies. From the examples given we derive guidelines indicating when the choice of the updating rule can be expected to have an impact on the results of the model.

Comparative study of non-invasive force and stress inference methods in tissue

In the course of animal development, the shape of tissue emerges in part from mechanical and biochemical interactions between cells. Measuring stress in tissue is essential for studying morphogenesis and its physical constraints. For that purpose, a possible new approach is force inference (up to a single prefactor) from cell shapes and connectivity. It is non-invasive and can provide space-time maps of stress in a whole tissue, unlike existing methods. To validate this approach, three force-inference methods, which differ in their approach of treating indefiniteness in an inverse problem between cell shapes and forces, were compared. Tests using two artificial and two experimental data sets consistently indicate that our Bayesian force inference, by which cell-junction tensions and cell pressures are simultaneously estimated, performs best in terms of accuracy and robustness. Moreover, by measuring the stress anisotropy and relaxation, we cross-validated the force inference and the global annular ablation of tissue, each of which relies on different prefactors. A practical choice of force-inference methods in different systems of interest is discussed.

The transition from three-dimensional to two-dimensional foam structures

A two-dimensional foam consists of a monolayer of bubbles. It can be created by squeezing the more familiar three-dimensional foam between two parallel glass plates. We describe and explain the minimum plate separation H which must be reached to fully effect the transition from three- to two- dimensional foam. We find that H/V(1/3) is close to one, where V is the average bubble volume, and increases slightly when the side-walls of the container are taken into account.

Elastoplastic flow of a foam around an obstacle

We simulate quasistatic flows of an ideal two-dimensional monodisperse foam around different obstacles, both symmetric and asymmetric, in a channel. We record both pressure and network contributions to the drag and lift forces and study them as a function of obstacle geometry. We show that the drag force increases linearly with the cross section of an obstacles. The lift on an asymmetric aerofoil-like shape is negative and increases with its arc length, mainly due to the pressure contribution.

The Dynamic Response of Railway Track With Unsupported Sleepers

The dynamic response of railway track with a section of unsupported sleepers is examined experimentally and a mathematical model of such track is presented. The principal function of ballast at frequencies above 100 Hz is to damp vibration of the track while the resilience of the railpad attenuates forces transmitted to the sleeper. In the absence of ballast, concrete sleepers are likely to crack if there are modest wheel or railhead irregularities.

Free-energy-based method for step size detection of processive molecular motors

We report a free-energy-based algorithm to estimate the step size of processive molecular motors from noisy, experimental time position traces. In our approach, the problem of estimating step sizes reduces to the evaluation of the free energy of directed lattice polymers in a random potential. The present approach is Bayesian in spirit as we do not aim to determine the most likely underlying time trace but rather to determine the step size and stepping frequency that are most likely to yield the observed data. We test this method on synthetic data for the simple case of noisy traces with fixed underlying step size and Poissonian stepping statistics. We find that the present scheme can work at signal-to-noise levels that are about 40% worse than those where the best existing step detection methods fail. More importantly, the present approach yields a much more accurate estimate of the step size. Although we focus on the case of non-reversing walks with a single step size, we show that we can detect if this assumption is violated. In principle, the method can be extended to more complex stepping scenarios but we find that for noisy data, multi-parameter fits are not reliable.

Discrete rearranging disordered patterns: prediction of elastic and plastic behavior, and application to two-dimensional foams

We study the elasto-plastic behavior of materials made of individual (discrete) objects such as a liquid foam made of bubbles. The evolution of positions and mutual arrangements of individual objects is taken into account through statistical quantities such as the elastic strain of the structure, the yield strain, and the yield function. The past history of the sample plays no explicit role except through its effect on these statistical quantities. They suffice to relate the discrete scale with the collective global scale. At this global scale, the material behaves as a continuous medium; it is described with tensors such as elastic strain, stress, and velocity gradient. We write the differential equations which predict their elastic and plastic behavior in both the general case and the case of simple shear. An overshoot in the shear strain or shear stress is interpreted as a rotation of the deformed structure, which is a purely tensorial effect that exists only if the yield strain is at least of order 0.3. We suggest practical applications including the following: when to choose a scalar formalism rather than a tensorial one; how to relax trapped stresses; and how to model materials with a low, or a high, yield strain.

Simulation of defects in bubble clusters

Topological defects in a foam, either isolated (disclinations and dislocations) or in pairs, affect the energy and stress, and play an important role in foam deformation. Surface evolver simulations were performed on large finite clusters of bubbles. These allow us to evaluate the effect of the topology of the defects, and the distance between defects, on the energy and pressure of foam clusters of different sizes. The energy of such defects follows trends similar to known analytical results for a continuous medium.

Theory of surface-potential-mediated photorefractivelike effects in liquid crystals

We make a phenomenological model of optical two-beam interaction in a model planar liquid crystal cell. The liquid crystal is subject to homeotropic anchoring at the cell walls, is surrounded by thin photosensitive layers, and is subject to a variable potential across the cell. These systems are often known as liquid crystal photorefractive systems. The interference between the two obliquely incident beams causes a time-independent periodic modulation in electric field intensity in the direction transverse to the cell normal. Our model includes this field phenomenologically by supposing an effect on the electric potential at the cell walls. The transverse periodic surface potential causes spatially periodic departures from a pure homeotropic texture. The texture modulation acts as a grating for the incident light. The incident light is both directly transmitted and also subject to diffraction. The lowest order diffracted beams correspond to energy exchange between the beams. We find that the degree of energy exchange can be strongly sensitive to the mean angle of incidence, the angle between the beams, and the imposed potential across the cell. We use the model to speculate about what factors optimize nonlinear optical interaction in liquid crystalline photorefractive systems.

Relationship between job strain and smoking cessation: the Finnish Public Sector Study

AIMS

To examine whether job strain (ie, excessive demands combined with low control) is related to smoking cessation.

METHODS

Prospective cohort study of 4928 Finnish employees who were baseline smokers. In addition to individual scores, coworker-assessed work unit level scores were calculated. A multilevel logistic regression analysis, with work units at the second level, was performed.

RESULTS

At follow-up, 21% of baseline smokers had quit smoking. After adjustment for sex, age, employer and marital status, elevated odds ratios (ORs) for smoking cessation were found for the lowest vs the highest quartile of work unit level job strain (OR 1.43, 95% CI 1.17 to 1.75) and for the highest vs the lowest quartile of work unit level job control (OR 1.61, 95% CI 1.31 to 1.96). After additional adjustment for health behaviours and trait anxiety, similar results were observed. Further adjustment for socioeconomic position slightly attenuated these associations, but an additional adjustment for individual strain/control had little effect on the results. The association between job strain and smoking cessation was slightly stronger in light than in moderate/heavy smokers. The results for individual job strain and job control were in the same direction as the work unit models, although these relationships became insignificant after adjustment for socioeconomic position. Job demands were not associated with smoking cessation.

CONCLUSIONS

Smoking cessation may be less likely in workplaces with high strain and low control. Policies and programs addressing employee job strain and control might also contribute to the effectiveness of smoking cessation interventions.

Simulations of two-dimensional foam rheology: localization in linear Couette flow and the interaction of settling discs

Surface Evolver simulations of flowing two-dimensional foams are described. These are used for two purposes. Firstly, to extract the location of the T 1s, the changes in bubble topology that occur during plastic flow. It is shown that in linear Couette flow the T1 s are localized in space, becoming more so as the polydispersity of the foam decreases. Secondly, the sedimentation of two circular discs through a foam under gravity is studied. If the discs are sufficiently close, they begin to interact and one moves behind the other during their descent.

Thermographic measurement of the emittance plot of a single positive ion beamlet

Measurements have been made of the emittance plot of a partly neutralized positive ion beamlet, using a slit, a polymer target, and an infrared camera. This thermographic approach is intrinsically linear and absolute (since the properties of the target are known and approximately independent of temperature). It is sufficiently sensitive that only one short pulse is required to capture the entire range of the angular coordinate y('). Ions and neutral atoms are both detected with equal sensitivity. The measurement is unaffected by secondary electrons emitted by the target and by electrons traveling with the positive ion beam, as both types of electron carry very little energy. No specialized electronics or beam deflection devices are required. Providing the region downstream of the mask is free of fields, the target can be several meters away from the mask, allowing good resolution in the y(') axis. The target can be as large as required.

Modelling studies to estimate the prevalence of foot-and-mouth disease carriers after reactive vaccination

Foot-and-mouth disease (FMD) is a highly contagious and economically significant viral disease of cloven-hoofed animals. Vaccination can be used to help restrict the spread of the infection, but evidence must be provided to show that the infection has been eradicated in order to regain the FMD-free status. While serological tests have been developed, which can identify animals that have been infected regardless of vaccination status, it is vital to know the probable prevalence of herds with FMD carriers and the within-herd prevalence of those carriers in order to design efficient post-epidemic surveillance strategies that establish freedom from disease. Here, we present the results of a study to model the expected prevalence of carriers after application of emergency vaccination and the impact of this on the sensitivity of test systems for their detection. Results showed that the expected prevalence of carrier-containing herds after reactive vaccination is likely to be very low, approximately 0.2%, and there will only be a small number of carriers, most likely one, in the positive herds. Therefore, sensitivity for carrier detection can be optimized by adopting an individual-based testing regime in which all animals in all vaccinated herds are tested and positive animals rather than herds are culled.

Branching dendrites with resonant membrane: a "sum-over-trips" approach

Dendrites form the major components of neurons. They are complex branching structures that receive and process thousands of synaptic inputs from other neurons. It is well known that dendritic morphology plays an important role in the function of dendrites. Another important contribution to the response characteristics of a single neuron comes from the intrinsic resonant properties of dendritic membrane. In this paper we combine the effects of dendritic branching and resonant membrane dynamics by generalising the "sum-over-trips" approach (Abbott et al. in Biol Cybernetics 66, 49-60 1991). To illustrate how this formalism can shed light on the role of architecture and resonances in determining neuronal output we consider dual recording and reconstruction data from a rat CA1 hippocampal pyramidal cell. Specifically we explore the way in which an Ih current contributes to a voltage overshoot at the soma.

Steady drainage in emulsions: corrections for surface Plateau borders and a model for high aqueous volume fraction

We compare extensive experimental results for the gravity-driven steady drainage of oil-in-water emulsions with two theoretical predictions, both based on the assumption of Poiseuille flow. The first is from standard foam drainage theory, applicable at low aqueous volume fractions, for which a correction is derived to account for the effects of the confinement of the emulsion. The second arises from considering the permeability of a model porous medium consisting of solid sphere packings, applicable at higher aqueous volume fractions. We find quantitative agreement between experiment and the foam drainage theory at low aqueous volume fractions. At higher aqueous volume fractions, the reduced flow rate calculated from the permeability theory approaches the master curve of the experimental data. Our experimental data demonstrates the analogy between the problem of electrical flow and liquid flow through foams and emulsions.

Shear modulus of two-dimensional foams: the effect of area dispersity and disorder

We use the Surface Evolver to determine the shear modulus G of a dry 2D foam of 2500 bubbles, using both extensional and simple shear. We examine G for a range of monodisperse, bidisperse and polydisperse foams, and relate it to various measures of the structural disorder of each foam. In all cases, the shear modulus of a foam decreases with increasing disorder.

Effect of emergency FMD vaccine antigen payload on protection, sub-clinical infection and persistence following direct contact challenge of cattle

Previous work, in sheep vaccinated with emergency foot-and-mouth disease (FMD) vaccine, indicated the benefit of increasing the antigen payload in inhibiting local virus replication and consequently persistence following an indirect aerosol challenge with a virus homologous to the vaccine strain. The work presented here investigates this possibility further using cattle and a more severe semi-heterologous direct contact challenge. The quantitative dynamics of virus replication and excretion in both vaccinated and non-vaccinated cattle following challenge are examined. Two experiments were carried out each involving 20 vaccinated and 5 non-vaccinated cattle. An O(1) Manisa vaccine (18 PD(50)) was used for the first, previously reported experiment [Cox SJ, Voyce C, Parida S, Reid SM, Hamblin PA, Paton DJ, et al. Protection against direct contact challenge following emergency FMD vaccination of cattle and the effect on virus excretion from the oropharynx. Vaccine 2005;23:1106-13]. The same vaccine was used for the second experiment described in this paper except the antigen payload was increased 10-fold per bovine dose, resulting in significantly higher FMD virus neutralising antibody titres prior to challenge. Twenty-one days post-vaccination the cattle received a 5-day direct contact challenge with FMD virus from five further non-vaccinated cattle infected 24h earlier with O UKG 34/2001. All vaccinated cattle regardless of antigen payload were protected against clinical disease. Sub-clinical oropharyngeal infection was detected in animals from both experiments but the level of virus replication shortly after direct contact challenge was significantly reduced in vaccinated animals. Cattle immunised with the 10-fold antigen payload cleared the virus more readily and consequently at 28 days post-challenge fewer animals were persistently infected compared to the single strength vaccine. Following a severe challenge, the results from both experiments show that use of emergency vaccine can prevent or decrease local virus replication and thereby dramatically reduce the amount of virus released into the environment, particularly during the early post-exposure period. Additionally, increasing the antigen payload of the vaccine may reduce sub-clinical infection, leading to fewer persistently infected virus carrier animals.

The Dynamic Response of Railway Track With Flexible Sleepers to High Frequency Vertical Excitation

A model of railway track is presented which allows examination of the behaviour of the track support. Large sleeper strains are associated with poorly damped sleeper resonances.

Interferon-γ production in vitro from whole blood of foot-and-mouth disease virus (FMDV) vaccinated and infected cattle after incubation with inactivated FMDV

Studies were performed to determine whether a rapid method to detect cell mediated immune responses to foot-and-mouth disease virus (FMDV) could be used either as a diagnostic test or provide a correlate of protection in animals post-vaccination. Using protocols based on the BOVIGAM assay for tuberculosis, whole blood samples from FMDV vaccinated or control animals, before and after challenge infection, were stimulated overnight with inactivated FMDV antigen. The quantity of interferon gamma (IFN-gamma) produced in the supernatants was measured using an ELISA. Specific induction of IFN-gamma was detected in samples from vaccinated, infected and vaccinated-then-infected cattle. Further development of this assay may provide a useful tool for the diagnosis of FMDV immune animals, including the identification of vaccinated animals that have been subsequently infected with FMDV. In these studies, combining the results of the IFN-gamma assay with virus neutralising antibody titre, in groups of vaccinated animals, provided a correlation with the capacity to control virus replication after subsequent challenge.

Drainage induced convection rolls in foams I. Convective bubble motion in a tilted tube

When liquid is added to a foam at sufficiently large flow rates, convective bubble motion will occur. Experiments are described in which the foam is confined in a tube which is tilted from the vertical. The theory of foam drainage is applied to this problem to show that the critical angle of tilt theta(c) at which convection occurs is related to the liquid flow-rate Q by theta(c) proportional to Q(-3/4).

The application of new techniques to the improved detection of persistently infected cattle after vaccination and contact exposure to foot-and-mouth disease

Detection of antibodies to the non-structural proteins (NSP) of foot-and-mouth disease virus (FMDV) was compared with conventional serological and virological methods and with RT-PCR for the identification of FMDV carrier animals obtained after experimental contact challenge of vaccinated cattle. Transmission from carriers to sentinels was also monitored. Twenty FMDV vaccinated and five unvaccinated cattle were challenged by direct contact with five donor cattle excreting FMDV and monitored until 28 days post challenge-exposure . Twelve vaccinated and three unvaccinated animals were retained up to 24 weeks post exposure to FMDV in order to monitor viral persistence, transmission and antibody responses. In nine vaccinated animals, infection persisted beyond 28 days post exposure, virus being detected more frequently and for longer in oesophagopharyngeal samples from these animals when examined by RT-PCR rather than by virus isolation. Although recovery of FMDV RNA became increasingly sporadic over time, the number of RNA copies detected in positive samples declined only slowly. Two naïve sentinel cattle housed with the persistently infected animals between 93 and 168 days after the latter had been challenge-exposed to FMDV did not become infected. There were differences in the ability of commercially available serological tests to detect antibodies to FMDV non-structural proteins (NSP) in vaccinated and subsequently challenged cattle. Although no single test could identify all of the vaccinated cattle that became persistently infected, the most poorly recognised animals were those with the least evidence of virus replication based on other tests. The potential of the detection of antibodies to the 2B NSP of FMDV for diagnosing persistent FMDV infection was demonstrated.

Detection of antibody to the foot-and-mouth disease virus (FMDV) non-structural polyprotein 3ABC in sheep by ELISA

The specificity and sensitivity of an ELISA for detecting IgG to the 3ABC non-structural protein of foot-and-mouth disease (FMD) virus was evaluated in FMD naive, aerosol-infected, aerosol plus direct contact infected and field-exposed sheep. All 12 sheep that were experimentally infected without prior vaccination seroconverted in the test, although fewer field sera from FMD-exposed sheep were scored seropositive compared to test results for structural protein antibodies. The 3ABC test specificity was 98 or 100% according to whether sera reacting in the doubtful range were scored as positive or negative. The test was then used to investigate the antibody response of sheep vaccinated against FMD and exposed to the virus by an aerosol challenge 4-14 days later. The response of individual animals varied. Whether immunised with high or low doses of vaccine, the development of 3ABC antibody was most likely in sheep from which live virus was recovered at or beyond 9 days post-challenge. Non-structural responses were also more frequent in animals from which multiple incidences of live FMD virus isolation (perhaps more indicative of true virus replication) were demonstrated.

Protection against direct-contact challenge following emergency FMD vaccination of cattle and the effect on virus excretion from the oropharynx

The ability of emergency foot-and-mouth disease (FMD) vaccine to protect cattle from a heterologous direct-contact challenge and the effect on virus excretion from the oropharynx were examined. An oil adjuvant O1 Manisa FMD vaccine protected 20 cattle from clinical disease following 5 days of direct-contact exposure to five infected cattle at 21 days post vaccination. The donor cattle had been infected by tongue inoculation with a different FMD virus of the same serotype (O UKG 2001). Protection from clinical disease did not prevent localised sub-clinical infection at the oropharynx in most animals, although quantitative reverse transcriptase polymerase chain reaction (RT-PCR) showed that the level of virus replication shortly after direct-contact challenge was greatly reduced in vaccinated animals. Nevertheless, 45% of the vaccinated cattle became persistently infected with 10(3)-10(6) RNA copies per millilitre of oropharyngeal fluid at 28 days post challenge. However, since live virus could not be readily isolated, the risk of these animals transmitting disease was probably very low. The findings show that even after an extremely severe challenge, use of an emergency vaccine will prevent or reduce local virus replication and thereby dramatically reduce the amount of virus released into the environment in the all-important early post-exposure period. These data should help to model the dynamics of virus transmission in future outbreaks of disease where vaccination is considered.

Two-dimensional viscous froth model for foam dynamics

The two-dimensional viscous froth model is a simple tractable model for foam rheology and coarsening. It includes, but is not confined to, the quasistatic regime. Here we present a detailed analysis and implementation of the model, illustrated with various examples. With certain simplifying assumptions, it provides significant insight into strain-rate-dependent effects in foam rheology and elsewhere, particularly in relation to recent experiments.

Three-dimensional bubble clusters: shape, packing, and growth rate

We consider three-dimensional clusters of equal-volume bubbles packed around a central bubble and calculate their energy and optimal shape. We obtain the surface area and bubble pressures to improve on existing growth laws for three-dimensional bubble clusters. We discuss the possible number of bubbles that can be packed around a central one: the "kissing problem," here adapted to deformable objects.

Evidence that high potency foot-and-mouth disease vaccine inhibits local virus replication and prevents the ‘carrier’ state in sheep

The ability of a single administration of a high, medium and low potency foot-and-mouth disease (FMD) vaccine to decrease or inhibit local virus replication and excretion in the oropharynx of sheep following aerosol challenge with homologous live virus 14 days later was examined. Unvaccinated sheep showed signs of clinical FMD, whereas all of the vaccinated sheep, regardless of antigen payload, were protected against clinical disease and development of viraemia. Virological and serological results confirmed that there had been no local virus replication in the oropharynx of sheep from the high potency vaccine group in contrast to moderate or substantial virus replication in the oropharynx of the low potency vaccinated or unvaccinated sheep respectively. The vaccines showed no evidence of promoting a local mucosal antibody response at the time of virus challenge, but were capable of stimulating a systemic gamma interferon response, the level of which was related to the antigen payload. This suggests that the systemic gamma interferon response could be a useful indicator of the ability of a FMD vaccine to elicit a sterile immunity and indicates that further work is warranted to investigate the role of systemic gamma interferon in this immunity. This is the first experiment to clearly show that high potency, high payload, FMD vaccines are capable of inhibiting local virus replication and consequently persistence and the carrier state in this target species.

The accumulation of deleterious mutations within the frozen niche variation hypothesis

The frozen niche variation hypothesis proposes that asexual clones exploit a fraction of a total resource niche available to the sexual population from which they arise. Differences in niche breadth may allow a period of coexistence between a sexual population and the faster reproducing asexual clones. Here, we model the longer term threat to the persistence of the sexual population from an accumulation of clonal diversity, balanced by the cost to the asexual population resulting from a faster rate of accumulation of deleterious mutations. We use Monte-Carlo simulations to quantify the interaction of niche breadth with accumulating deleterious mutations. These two mechanisms may act synergistically to prevent the extinction of the sexual population, given: (1) sufficient genetic variation, and consequently niche breadth, in the sexual population; (2) a relatively slow rate of accumulation of genetic diversity in the clonal population; (3) synergistic epistasis in the accumulation of deleterious mutations.

Topological changes in a two-dimensional foam cluster

Experiments on a small cluster of bubbles in a nominally two-dimensional foam show an instability in which a topological change forces one of the bubbles to be ejected to the outside of the cluster at a point where this is not predicted by a two-dimensional model of a foam. This is interpreted in terms of the energy of the initial and ejected states and of the finite liquid content of the experimental system. A description of the distribution of liquid in various experimental set-ups suggests that the exact response may depend critically upon the type of system used. This is demonstrated experimentally with reference to small clusters of bubbles undergoing a single topological change.

Longevity of antibody and cytokine responses following vaccination with high potency emergency FMD vaccines

The ability of high potency emergency foot-and-mouth disease (FMD) vaccines to promote sustainable immune responses in sheep and pigs following a single application was examined. All vaccine formulations induced a rapid seroconversion in both species, as expected, which was maintained at near peak titres for up to 6 months in sheep and 7 months in pigs. The Montanide ISA 206 formulation gave the best results in sheep. Vaccinated pigs challenged with homologous FMDV were protected from disease at 7 months post vaccination. Systemic levels of cytokines IL-6, IL-8, and in some pigs IL-12, increased following vaccination and were often maintained at an increased level for the duration of the trials. These initial results suggest that high potency vaccines may promote longer lasting immunity than the conventional lower potency vaccines in ruminants and a comparable response in pigs. Results indicate that in an outbreak situation, should emergency vaccination be done with these high potency vaccines, protection should be conferred for a long enough period for the outbreak to be brought under control without the need to revaccinate. Given the increased interval for re-vaccination the use of high potency vaccines for routine prophylactic campaigns could provide a more cost-effective and efficient means of maintaining herd immunity and is an area thus worthy of further examination.

Further studies on the early protective responses of pigs following immunisation with high potency foot and mouth disease vaccine

The ability of an emergency oil adjuvanted foot-and-mouth disease (FMD) vaccine to elicit early protective immunity in pigs against direct contact homologous challenge was examined. All vaccinates showed reduced viraemia and shedding of FMDV, and certain animals were protected, showing no clinical signs. IL-6, IL-8 and IL-12 were consistently detected in challenged animals that had been vaccinated. Other cytokines--IL-1, IL-2, TNF, TGF and interferons--were not detected. This demonstrates that the vaccine did not induce a systemic inflammatory response, nor a systemic elevation of T lymphocyte activity. Although the IL-6 and IL-8 did not relate to protection, IL-12 production was highest in the protected vaccinated pigs. Thus, the induction of monocytic cell activity, demonstrable by the production of IL-6, IL-8 and IL-12, appears to play a critical role in FMDV emergency vaccine induction of the innate immune defences which relate to early protection against FMD. The possible modes of defence in which such cytokine activity would be involved are discussed.

The transition from two-dimensional to three-dimensional foam structures

Small cells in an experimental sample of two-dimensional foam, such as that which is contained between two glass plates, may undergo a transition to a three-dimensional form, becoming detached from one boundary. We present the first detailed observations of this phenomenon, together with computer simulations. The transition is attributed to an instability of the Rayleigh-Plateau type. A theoretical analysis is given which shows that an individual cell is susceptible to this instability only if it has less than six sides.

Recovering quasi-active properties of dendritic neurons from dual potential recordings

We develop the theory and accompanying algorithm for the recovery of a dendritic neuron's cytoplasmic resistivity, membrane capacitance, leakage conductance, and two maximal channel conductances from weighted averages of simultaneous recordings of somatic and dendritic potential following a somatic current stimulus. We test our results on two model systems with distinct, though prescribed, channel kinetics and branching patterns.

Discerning ionic currents and their kinetics from input impedance data

The excitable nature of a biological cell is manifested in the many voltage gated ion channels that perforate its membrane. The forms of the associated ionic currents, and in particular the functions that govern their kinetics, permit one to distinguish, electrophysiologically, between various cell types. We show, in the context of FitzHugh-Nagumo and Morris-Lecar models and without recourse to voltage or space clamping, that such currents and kinetics may be stably inferred from a cell's voltage response to a specified input current.

Adaptive mesh refinement techniques for electrical impedance tomography

Adaptive mesh refinement techniques can be applied to increase the efficiency of electrical impedance tomography reconstruction algorithms by reducing computational and storage cost as well as providing problem-dependent solution structures. A self-adaptive refinement algorithm based on an a posteriori error estimate has been developed and its results are shown in comparison with uniform mesh refinement for a simple head model.

Identification of the cable parameters in the somatic shunt model

We show that the first five moments of the soma potential and soma current uniquely and stably determine the soma conductance and capacitance and the dendritic electrotonic length, conductance, and capacitance in the so-called somatic shunt model of the passive behavior of a neuron. We test our resulting input admittance algorithm on synthetic data and demonstrate the regularizing effect of knowledge of the ratio of soma to dendrite surface areas.

The ecological cost of sex

Why sex prevails in nature remains one of the great puzzles of evolution. Sexual reproduction has an immediate cost relative to asexual reproduction, as males only express their contribution to population growth through females. With no males to sustain, an asexual mutant can double its relative representation in the population in successive generations. This is the widely accepted 'twofold cost of males'. Many studies have attempted to explain how sex can recoup this cost from fitness benefits associated with the recombination of parental genotypes, but these require complex biological environments that cycle over evolutionary timescales. In contrast, we have considered the ecological dynamics that govern asexual invasion. Here we show the existence of a threshold growth rate for the sexual population, above which the invasion is halted by intraspecific competition. The asexual population then exerts a weaker inhibitory effect on the carrying capacity of the sexual population than on its own carrying capacity. The stable outcome of this is coexistence on a depleted resource base. Under these ecological circumstances, longer-term benefits of sex may eventually drive out the asexual competitor.

High fidelity imaging and high performance computing in nonlinear EIT

We show that nonlinear EIT provides images with well defined characteristics when smoothness of the image is used as a constraint in the reconstruction process. We use the gradient of the logarithm of resistivity as an effective measure of image smoothness, which has the advantage that resistivity and conductivity are treated with equal weight. We suggest that a measure of the fidelity of the image to the object requires the explicit definition and application of such a constraint. The algorithm is applied to the simulation of intra-ventricular haemorrhaging (IVH) in a simple head model. The results indicate that a 5% increase in the blood content of the ventricles would be easily detectable with the noise performance of contemporary instrumentation. The possible implementation of the algorithm in real time via high performance computing is discussed.

Ethnicity, bioethics, and prenatal diagnosis: the amniocentesis decisions of Mexican-origin women and their partners

Bioethical standards and counseling techniques that regulate prenatal diagnosis in the United States were developed at a time when the principal constituency for fetal testing was a self-selected group of White, well-informed, middle-class women. The routine use of alpha-fetoprotein (AFP) testing, which has become widespread since the mid-1980s, introduced new constituencies to prenatal diagnosis. These new constituencies include ethnic minority women, who, with the exception of women from certain Asian groups, refuse amniocentesis at significantly higher rates than others. This study examines the considerations taken into account by a group of Mexican-origin women who had screened positive for AFP and were deciding whether to undergo amniocentesis. We reviewed 379 charts and interviewed 147 women and 120 partners to test a number of factors that might explain why some women accept amniocentesis and some refuse. A woman's attitudes toward doctors, medicine, and prenatal care and her assessment of the risk and uncertainty associated with the procedure were found to be most significant. Case summaries demonstrate the indeterminacy of the decision-making process. We concluded that established bioethical principles and counseling techniques need to be more sensitive to the way ethnic minority clients make their amniocentesis choices.

The role of small ruminants in the epidemiology and transmission of foot-and-mouth disease

Despite representing the largest part of the world's foot-and-mouth disease (FMD)-susceptible domestic livestock, sheep and goats have generally been neglected with regard to their epidemiological role. This is partly due to the often inapparent nature of the disease in these hosts. Nevertheless, their ability to become carriers represents a reservoir for further infection and spread of disease, and so trade of live sheep and goats present a major risk of entry of FMD to disease-free countries. Research and epidemiological studies continue to be necessary in order both to prevent the entry of the virus and to assist in control should the disease reoccur. This review concentrates primarily on more recent studies relating to sheep and goats and, in particular, considers the importance of these hosts in the overall epidemiology of FMD.

Emergency vaccination of sheep against foot-and-mouth disease: protection against disease and reduction in contact transmission

The ability of several emergency FMD vaccine formulations to elicit early protective immunity in sheep was examined. All vaccine formulations were shown to protect sheep against airborne challenge with homologous FMDV within 4 days of vaccination. Protection was associated in part with the induction of serum antibody responses but was also demonstrated in the absence of any detectable antibody response at the time of challenge. Aqueous Al(OH)3/saponin vaccine formulations and oil emulsion vaccines based on Montanide ISA 206 adjuvant reduced virus replication and the numbers of animals subclinically infected up to 28 days post-challenge, when compared with non-vaccinated animals, consequently limiting transmission of the disease or infection to in-contact susceptible animals.

Evidence of partial protection against foot-and-mouth disease in cattle immunized with a recombinant adenovirus vector expressing the precursor polypeptide (P1) of foot-and-mouth disease virus capsid proteins

A recombinant live vector vaccine was produced by insertion of cDNA encoding the structural proteins (P1) of foot-and-mouth disease virus (FMDV) into a replication-competent human adenovirus type 5 vaccine strain (Ad5 wt). Groups of cattle (n = 3) were immunized twice, by the subcutaneous and/or intranasal routes, with either the Ad5 wt vaccine or with the recombinant FMDV Ad5-P1 vaccine. All animals were challenged by intranasal instillation of FMDV 4 weeks after the second immunizations. In the absence of a detectable antibody response to FMDV, significant protection against viral challenge was seen in all of the animals immunized twice by the subcutaneous route with the recombinant vaccine. The observed partial protection against clinical disease was not associated with a reduction in titre of persistent FMDV infections in the oropharynx of challenged cattle.

A new method for extracting cable parameters from input impedance data

We establish conditions under which the input impedance and its first two derivatives, evaluated at the origin, uniquely determine the axial resistance, membrane capacitance, and membrane conductance of a finite uniform cable with one sealed end. We argue that these impedance data are readily available to the experimentalist and we demonstrate the recovery of a cable's electrical parameters from synthetic noisy measurements.