Dangerous connections: on binding site models of infectious disease dynamics

We formulate models for the spread of infection on networks that are amenable to analysis in the large population limit. We distinguish three different levels: (1) binding sites, (2) individuals, and (3) the population. In the tradition of Physiologically Structured Population Models, the formulation starts on the individual level. Influences from the `outside world' on an individual are captured by environmental variables. These environmental variables are population level quantities. A key characteristic of the network models is that individuals can be decomposed into a number of conditionally independent components: each individual has a fixed number of `binding sites' for partners. The Markov chain dynamics of binding sites are described by only a few equations. In particular, individual-level probabilities are obtained from binding-site-level probabilities by combinatorics while population-level quantities are obtained by averaging over individuals in the population. Thus we are able to characterize population-level epidemiological quantities, such as $R_0$, $r$, the final size, and the endemic equilibrium, in terms of the corresponding variables

The Extent of Involvement in Cybercrime activities among Studentsa in Tertiary Institutions in Enugu State of Nigeria

The researcher investigated the extent of involvement in Cybercrime activities among students2019; in tertiary institutions in Enugu state of Nigeria using cross sectional survey design. Questionnaires were used for data collection. A sample of 175 students was drawn from a population of 18,340 final year students in higher institutions in Enugu State using cluster sampling procedure. The instrument contains 12 items with 4 point scale of Most-times, Sometimes, Seldom and Never. The findings showed that students of higher institutions in Enugu state are involved in cybercrime. It also showed that students2019; involvement in cybercrime is dependent on gender and Institution type. The implication of the finding for knowledge and development is that the present level of students2019; involvement in cybercrime has a negative effect on the value of education and by extension, has lead to the setback in economic development of the State. It was recommended that government should empower the law enforcement agencies to checkmate and deal with perpetrators of cybercrime

Mean field at distance one

To be able to understand how infectious diseases spread on networks, it is important to understand the network structure itself in the absence of infection. In this text we consider dynamic network models that are inspired by the (static) configuration network. The networks are described by population-level averages such as the fraction of the population with $k$ partners, $k=0,1,2,\ldots$ This means that the bookkeeping contains information about individuals and their partners, but no information about partners of partners. Can we average over the population to obtain information about partners of partners? The answer is `it depends', and this is where the mean field at distance one assumption comes into play. In this text we explain that, yes, we may average over the population (in the right way) in the static network. Moreover, we provide evidence in support of a positive answer for the network model that is dynamic due to partnership changes. If, however, we additionally allow for demographic changes, dependencies between partners arise. In earlier work we used the slogan `mean field at distance one' as a justification of simply ignoring the dependencies. Here we discuss the subtleties that come with the mean field at distance one assumption, especially when demography is involved. Particular attention is given to the accuracy of the approximation in the setting with demography. Next, the mean field at distance one assumption is discussed in the context of an infection superimposed on the network. We end with the conjecture that an extension of the bookkeeping leads to an exact description of the network structure.Comment: revised versio

Structured populations with distributed recruitment: from PDE to delay formulation

In this work first we consider a physiologically structured population model with a distributed recruitment process. That is, our model allows newly recruited individuals to enter the population at all possible individual states, in principle. The model can be naturally formulated as a first order partial integro-differential equation, and it has been studied extensively. In particular, it is well-posed on the biologically relevant state space of Lebesgue integrable functions. We also formulate a delayed integral equation (renewal equation) for the distributed birth rate of the population. We aim to illustrate the connection between the partial integro-differential and the delayed integral equation formulation of the model utilising a recent spectral theoretic result. In particular, we consider the equivalence of the steady state problems in the two different formulations, which then leads us to characterise irreducibility of the semigroup governing the linear partial integro-differential equation. Furthermore, using the method of characteristics, we investigate the connection between the time dependent problems. In particular, we prove that any (non-negative) solution of the delayed integral equation determines a (non-negative) solution of the partial differential equation and vice versa. The results obtained for the particular distributed states at birth model then lead us to present some very general results, which establish the equivalence between a general class of partial differential and delay equation, modelling physiologically structured populations.Comment: 28 pages, to appear in Mathematical Methods in the Applied Science

CHARACTERIZATION OF METRONIDAZOLE- AND VANCOMYCIN-RESISTANT CLINICAL ISOLATES OF CLOSTRIDIUM DIFFICILE

Characterization of Metronidazole- and Vancomycin-Resistant Clinical Isolates of Clostridium difficile Chioma Odo, MS. Supervisory Professor: Charles Darkoh, Ph.D. ABSTRACT The incidence of C. difficile infections (CDI) has been increasing at an alarming rate. This was precipitated by the emergence of strains with increased virulence, disease severity, and high recurrence rates. These strains also exhibit high propensity for resistance to antibiotics such as fluoroquinolones and beta lactams, which has made the treatment of CDI very challenging. Currently, metronidazole and vancomycin are the most commonly used drugs for the treatment of primary CDI. Metronidazole is used for the treatment of mild to non-severe cases of CDI while vancomycin is reserved for severe CDI cases. In 25-30% of the patients treated with these antibiotics, the infection may recur, and this further complicates CDI treatment. Because C. difficile strains have an intrinsic ability to resist multiple antibiotics, it was hypothesized that there may be strains with high resistance to metronidazole and vancomycin circulating in the patient population. To investigate this hypothesis, 536 clinical CDI stool samples obtained from patients who presented with diarrhea at St. Luke’s Episcopal Hospital at the Texas Medical Center Houston, Texas, Kenyatta National Hospital, Nairobi, and Kisii Teaching and Referral Hospital, Kisii, Kenya were screened for resistant C. difficile strains. The stool samples were analyzed on C. difficile-specific differential medium containing either metronidazole (8 µg/ml) or vancomycin (4 µg/ml). These are concentrations designated by the Clinical and Laboratory Standards Institute to be the resistant breakpoint for each of the antibiotics. Stools that grew resistant colonies were identified and colonies were selected for further analysis. The minimum inhibitory concentration (MIC) of the isolates was determined by E-test and broth microdilution. The results showed that 33.1% (145/438) of the CDI patients from Texas had C. difficile strains in their stools that were resistant to both metronidazole and vancomycin. Remarkably, 93.9% of the CDI patient stools from Kenya had both metronidazole- and vancomycin-resistant C. difficile strains. The resistant strains from both patient populations also exhibit high level of tolerance for these antibiotics that far exceed the previously reported MICs (˃1024 µg/ml compared to 256 µg/ml for metronidazole and \u3e1024 µg/ml compared to 16 µg/ml for vancomycin). All of the vancomycin-resistant strains isolated from the patients in both populations had the homologue of vanA gene, which has been shown to confer a high degree of vancomycin resistance in Gram-positive bacteria. Together, the results demonstrate high prevalence of metronidazole- and vancomycin-resistant C. difficile strains circulating in the patient populations from Texas and Kenya. The spread of C. difficile strains that are resistant to these two antibiotics of last resort may have serious public health implications and underscores the urgent need for a more in-depth analysis of the circulating resistant strains to help inform clinical decisions

Collision Protection of Nuclear Ships: A Survey of the State of the Art

http://deepblue.lib.umich.edu/bitstream/2027.42/96596/1/39015087358738.pd

The Impact and Consequences of Corruption on the Nigerian Society and Economy

There is no doubt that corruption has eaten deep into the fabric of the Nigerian society. Successive governments in the country since independence in 1960 had in recognition of the evil of corruption established programmes and agencies to deal with it. These include the War Against Indiscipline and Corruption (WAIC); Independent Corrupt Practices and other Related Offences Commission (ICPC); the Economic and Financial Crimes Commission (EFCC); etc. Despite the establishment of these agencies and targeted programmes, corruption has continued to ruin every aspect of the country’s national life with serious damages to her image before the international community. Corruption has not only become pervasive in Nigeria but it is more or less a way of life, much to the detriment of the Nigerian society and economy. The paper interrogates the nature of corruption and its implications for national development efforts in Nigeria. The paper concludes that without effectively dealing with corruption in a holistic manner, there can be no meaningful socio-economic and political development of the country. This is because in the opinion of the paper, corruption is evil, which is not reformable but must be removed in its entirety.Key words: Corruption, Impact, Consequences, Society, and Econom