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.