1,365 research outputs found
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 , , 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
partners, 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
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