Epidemiological aspects of Aeromonas salmonicida in the marine environment.

The epidemiology of Aeromonas salmonicida subsp. salmonicida in the marine environment was investigated. Nutrient resuscitation and infectivity studies did not support a previous claim of dormancy in A. salmonicida and validated the use of colony-forming units (cfu) in survival studies. Survival of A. salmonicida in seawater was assessed and found to be of short duration «10 days). Survival of the bacterium in non-sterile sediment, obtained from beneath a salmon cage, appeared to be limited. The minimum infective dose of A. salmonicida to Atlantic salmon in short duration (1-3 days) bath exposure in sea water was 10' cfu ml-I. Prolonged exposure for three weeks resulted in infection with 102 cfu ml- I. Intragastric intubation of the bacterium established infection with doses >105 cfu. Shedding of A. salmonicida from infected salmon was 105-108 cfu/fish/hr. Survival and shedding results were combined in a computer model. A. salmonicida was predicted to travel >6 km suspended within the water column of a sea loch. Covert infection in freshwater farmed salmon was assessed by ELISA and the standard stress test. Results indicated that ELISA may be useful as a routine monitor of furunculosis infection. The efficacy of dot-blot immunoassay was found to be 108 cfu A. salmonicida in fish kidney tissue. Rainbow trout (Oncorhynchus mykiss) and salmon mucus were not found to inhibit the growth of A. salmonicida supporting recent evidence that fish skin is a site of carriage. In vitro studies suggested that trout serum proteins do not confer protection from fish antibody on A. salmonicida in covert infections. Preliminary work was undertaken to develop a specific DNA probe for A. salmonicida which will allow its detection in environmental samples and carrier fish. A gene library of A. salmonicida was constructed in lambda gtll and screened for" A "-protein with antibodies

Velocity map imaging of the dynamics of the CH3 + HCl -> CH4 + Cl reaction using a dual molecular beam method

International audienceThe reactions CH3 + HCl → CH4 + Cl(²P_3/2) and CD₃ + HCl → CD₃H + Cl(²P_3/2) have been studied by photo-initiation (by CH₃I or CD₃I photolysis at 266 nm) in a dual molecular beam apparatus. Product Cl(²P</sub>3/2</sub>) atoms were detected using resonance enhanced multi-photon ionisation and velocity map imaging, revealing product translational energy and angular scattering distributions in the centre-of-mass frame. Image analysis is complicated by the bimodal speed distribution of CH₃ (and CD₃) radicals formed in coincidence with I(²P_3/2) and I(²P_1/2) atoms from CH₃I (CD₃I) photodissociation, giving overlapping Newton diagrams with displaced centre of mass velocities. The relative reactivities to form Cl atoms are greater for the slower CH₃ speed group than the faster group by factors of ~1.5 for the reaction of CH₃ and ~2.5 for the reaction of CD₃, consistent with the greater propensity of the faster methyl radicals to undergo electronically adiabatic reactions to form Cl(²P_1/2). The average fraction of the available energy becoming product translational energy is = 0.48 ± 0.05 and 0.50 ± 0.03 for reaction of the faster and slower sets of CH₃ radicals, respectively. The Cl atoms are deduced to be preferentially forward scattered with respect to the HCl reagents, but the angular distributions from the dual beam imaging experiments require correction for under-detection of forward scattered Cl products

You never surf alone. Ubiquitous tracking of users' browsing habits

In the early age of the internet users enjoyed a large level of anonymity. At the time web pages were just hypertext documents; almost no personalisation of the user experience was o ered. The Web today has evolved as a world wide distributed system following specific architectural paradigms. On the web now, an enormous quantity of user generated data is shared and consumed by a network of applications and services, reasoning upon users expressed preferences and their social and physical connections. Advertising networks follow users' browsing habits while they surf the web, continuously collecting their traces and surfing patterns. We analyse how users tracking happens on the web by measuring their online footprint and estimating how quickly advertising networks are able to pro le users by their browsing habits

Modelling heterogeneity in scale directly: implications for estimates of influence in freight decision-making groups

The state of practice in the modelling of heterogeneous preferences does not separate the effects of scale from estimated mean and standard deviation preference measures. This restriction could lead to divergent behavioural implications relative to a flexible modelling structure that accounts for scale effects independently of estimated distributions of preference measures. The generalised multinomial logit (GMNL) model is such an econometric tool, enabling the analyst to identify the role that scale plays in impacting estimated sample mean and standard deviation preference measures, including confirming whether the appropriate model form approaches standard cases such as mixed logit. The GMNL model is applied in this paper to compare the behavioural implications of the minimum information group inference (MIGI) model within a study of interdependent road freight stakeholders in Sydney, Australia. MIGI estimates within GMNL models are compared with extant mixed logit measures (see Hensher and Puckett, 2008) to confirm whether the implications of the restrictive (with respect to scale) mixed logit model are consistent to those from the more flexible GMNL model. The results confirm the overall implication that transporters appear to hold relative power over supply chain responses to variable road-user charges. However, the GMNL model identifies a broader range of potential group decision-making outcomes and a restricted set of attributes over which heterogeneity in group influence is found than the mixed logit model. Hence, this analysis offers evidence that failing to account for scale heterogeneity may result in inaccurate representations of the bargaining set, and the nature of preference heterogeneity, in general

Biochemically realistic MD and kinetic models of the Rhodobacter sphaeroides bc1 complex

This work seeks to duplicate a realistic membrane for a more natural model of the Rb. sphaeroides bc1 complex which in past studies has lacked several details in composition of the fatty acids and relative quantities of each lipid. Past studies have shown some distortion on MD relaxation relating to a large void volume in the protein structures. In this model we have set up the membrane with the complement of lipids reported for the chromatophore membrane, and have taken steps to ameliorate the structural distortions on relaxation of the protein by populating the void with a complement of lipids. The MD model is used to determine diffusion constants and motions of the system in preparation for calculating potentials of mean force for wild type and ISP tether mutants. The current kinetic model provides a kinetic and thermodynamic understanding of the rate-limiting reaction, and associated partial processes that lead to successive turnovers. Since both bacterial and mitochondrial complexes have essentially the same catalytic core, their mechanisms are essentially similar, and a better understanding of the bacterial system can be extrapolated to the context of mitochondrial function, and medically important roles in cellular physiology, cardiovascular disease, apoptosis, and diseases associated with aging

Observing thermal Schwinger pair production

We study the possibility of observing Schwinger pair production enhanced by a thermal bath of photons. We consider the full range of temperatures and electric field intensities from pure Schwinger production to pure thermal production, and identify the most promising and interesting regimes. In particular, we identify temperatures of similar to 20 keV/k(B) and field intensities of similar to 10(23) W cm(-2) where pair production would be observable. In this case, the thermal enhancement over the Schwinger rate is exponentially large and due to effects which are not visible at any finite order in the loop expansion. Pair production in this regime can thus be described as more nonperturbative than the usual Schwinger process, which appears at one loop. Unfortunately, such high temperatures appear to be out of reach of foreseeable technologies, though nonthermal photon distributions with comparable energy densities are possible. We suggest the possibility that similar nonperturbative enhancements may extend out of equilibrium and propose an experimental scheme to test this.Peer reviewe

Mutual information-based binarisation of multiple images of an object: an application in medical imaging

A new method for image thresholding of two or more images that are acquired in different modalities or acquisition protocols is proposed. The method is based on measures from information theory and has no underlying free parameters nor does it require training or calibration. The method is based on finding an optimal set of global thresholds, one for each image, by maximising the mutual information above the thresholds while minimising the mutual information below the thresholds. Although some assumptions on the nature of images are made, no assumptions are made by the method on the intensity distributions or on the shape of the image histograms. The effectiveness of the method is demonstrated both on synthetic images and medical images from clinical practice. It is then compared against three other thresholding method

Maximum Power Efficiency and Criticality in Random Boolean Networks

Random Boolean networks are models of disordered causal systems that can occur in cells and the biosphere. These are open thermodynamic systems exhibiting a flow of energy that is dissipated at a finite rate. Life does work to acquire more energy, then uses the available energy it has gained to perform more work. It is plausible that natural selection has optimized many biological systems for power efficiency: useful power generated per unit fuel. In this letter we begin to investigate these questions for random Boolean networks using Landauer's erasure principle, which defines a minimum entropy cost for bit erasure. We show that critical Boolean networks maximize available power efficiency, which requires that the system have a finite displacement from equilibrium. Our initial results may extend to more realistic models for cells and ecosystems.Comment: 4 pages RevTeX, 1 figure in .eps format. Comments welcome, v2: minor clarifications added, conclusions unchanged. v3: paper rewritten to clarify it; conclusions unchange