Endogenous Quasicycles and Stochastic Coherence in a Closed Endemic Model

We study the role of demographic fluctuations in typical endemics as exemplified by the stochastic SIRS model. The birth-death master equation of the model is simulated using exact numerics and analysed within the linear noise approximation. The endemic fixed point is unstable to internal demographic noise, and leads to sustained oscillations. This is ensured when the eigenvalues ($\lambda$) of the linearised drift matrix are complex, which in turn, is possible only if detailed balance is violated. In the oscillatory state, the phases decorrelate asymptotically, distinguishing such oscillations from those produced by external periodic forcing. These so-called quasicycles are of sufficient strength to be detected reliably only when the ratio $|Im(\lambda)/Re(\lambda)|$ is of order unity. The coherence or regularity of these oscillations show a maximum as a function of population size, an effect known variously as stochastic coherence or coherence resonance. We find that stochastic coherence can be simply understood as resulting from a non-monotonic variation of $|Im(\lambda)/Re(\lambda)|$ with population size. Thus, within the linear noise approximation, stochastic coherence can be predicted from a purely deterministic analysis. The non-normality of the linearised drift matrix, associated with the violation of detailed balance, leads to enhanced fluctuations in the population amplitudes.Comment: 21 pages, 8 figure

Escherichia coli Bacteriocins: Antimicrobial Efficacy and Prevalence among Isolates from Patients with Bacteraemia

Bacteriocins are antimicrobial peptides generally active against bacteria closely related to the producer. Escherichia coli produces two types of bacteriocins, colicins and microcins. The in vitro efficacy of isolated colicins E1, E6, E7, K and M, was assessed against Escherichia coli strains from patients with bacteraemia of urinary tract origin. Colicin E7 was most effective, as only 13% of the tested strains were resistant. On the other hand, 32%, 33%, 43% and 53% of the tested strains exhibited resistance to colicins E6, K, M and E1. Moreover, the inhibitory activity of individual colicins E1, E6, E7, K and M and combinations of colicins K, M, E7 and E1, E6, E7, K, M were followed in liquid broth for 24 hours. Resistance against individual colicins developed after 9 hours of treatment. On the contrary, resistance development against the combined action of 5 colicins was not observed. One hundred and five E. coli strains from patients with bacteraemia were screened by PCR for the presence of 5 colicins and 7 microcins. Sixty-six percent of the strains encoded at least one bacteriocin, 43% one or more colicins, and 54% one or more microcins. Microcins were found to co-occur with toxins, siderophores, adhesins and with the Toll/Interleukin-1 receptor domain-containing protein involved in suppression of innate immunity, and were significantly more prevalent among strains from non-immunocompromised patients. In addition, microcins were highly prevalent among non-multidrug-resistant strains compared to multidrug-resistant strains. Our results indicate that microcins contribute to virulence of E. coli instigating bacteraemia of urinary tract origin

Effective websites for small and medium-sized enterprises

This is an accepted manuscript of an article published by MCB UP Ltd in Journal of Small Business and Enterprise Development on 01/06/2000, available online: https://doi.org/10.1108/EUM0000000006836 The accepted version of the publication may differ from the final published version.In the UK, millions are now online and many are prepared to use the Internet to make and influence purchasing decisions. Businesses should, therefore, consider whether the Internet could provide them with a new marketing opportunity. Although increasing numbers of businesses now have a website, there seems to be a quality problem that is leading to missed opportunities, particularly for smaller enterprises. This belief is backed up by an automated survey of 3,802 predominantly small UK business sites, believed to be by far the largest of its kind to date. Analysis of the results reveals widespread problems in relation to search engines. Most Internet users find new sites through search engines, yet over half of the sites checked were not registered in the largest one, Yahoo!, and could therefore be missing a sizeable percentage of potential customers. The underlying problem with business sites is the lack of maturity of the medium as evidenced by the focus on technological issues amongst designers and the inevitable lack of Web-business experience of managers. Designers need to take seriously the usability of the site, its design and its ability to meet the business goals of the client. These issues are perhaps being taken up less than in the related discipline of software engineering, probably owing to the relative ease of website creation. Managers need to dictate the objectives of their site, but also, in the current climate, cannot rely even on professional website design companies and must be capable of evaluating the quality of their site themselves. Finally, educators need to ensure that these issues are emphasised to the next generation of designers and managers in order that the full potential of the Internet for business can be realised

A general model for the marketing of seasonal products

We discuss a general model for the marketing of seasonal products, namely products for which the time intervals devoted to production and sales are distinct. The firm can advertise the product, thus affecting the sales in two different ways, namely directly (customer effect) and indirectly (retailers effect). A two-dimensional goodwill variable represents the (retailes, customers)-advertising capital stock. The dynamics of the system in the sales interval only is analysed, in order to determine the levels of goodwill and inventory at the beginning of such time intervla and subsequent advertising policy, so as to maximize the discounted net profit

The web of things - Challenges and enabling technologies

The Internet of Things (IoT) is an active research area, focusing on connecting real-world things over TCP/IP. This trend has recently triggered the research community to adopt the interoperability of the Web (HTTP) as an application platform for integrating ‘things’ on the Internet. Harnessing physical things into the virtual world using Web standards is also enriching the arena of conventional Web services to unleash data and functions of real-world things as service providers and consumers on the Internet. This evolution of the Web as a highly interoperable application platform for connecting real-world things has raised many research challenges and problems, leading to the fast growing research area called the Web of Things (WoT). Current research on WoT is a catalyst for the realization of IoT, opening up the possibilities of creating ambient spaces (AS), where people and things seamlessly communicate over the Web. In this chapter we discuss the state of the art in WoT research, focusing on the various challenges, and enabling technologies that are driving this research. We discuss architectural frameworks, models and technologies to build applications for future ambient spaces with the WoT. We present case studies that reflect the feasibility and applicability of the WoT technology. We also discuss future trends and research directions within this domain to throw light on existing problems and challenges.Sujith Samuel Mathew, Yacine Atif, Quan Z. Sheng, and Zakaria Maama