11,616 research outputs found
Modeling the long term dynamics of pre-vaccination pertussis
The dynamics of strongly immunizing childhood infections is still not well
understood. Although reports of successful modeling of several incidence data
records can be found in the literature, the key determinants of the observed
temporal patterns have not been clearly identified. In particular, different
models of immunity waning and degree of protection applied to disease and
vaccine induced immunity have been debated in the literature on pertussis. Here
we study the effect of disease acquired immunity on the long term patterns of
pertussis prevalence. We compare five minimal models, all of which are
stochastic, seasonally forced, well-mixed models of infection based on
susceptible-infective-recovered dynamics in a closed population. These models
reflect different assumptions about the immune response of naive hosts, namely
total permanent immunity, immunity waning, immunity waning together with
immunity boosting, reinfection of recovered, and repeat infection after partial
immunity waning. The power spectra of the output prevalence time series
characterize the long term dynamics of the models. For epidemiological
parameters consistent with published data for pertussis, the power spectra show
quantitative and even qualitative differences that can be used to test their
assumptions by comparison with ensembles of several decades long
pre-vaccination data records. We illustrate this strategy on two publicly
available historical data sets.Comment: paper (31 pages, 11 figures, 1 table) and supplementary material (19
pages, 5 figures, 2 tables
Public health and economic costs of investigating a suspected outbreak of Legionnaires' disease.
This paper provides one of the first assessments of the burden of both the public health investigation and the economic costs associated with an apparent outbreak of Legionnaires' disease (LD) in South East London. In addition to epidemiological, microbiological and environmental investigations, we collected data on the staff time and resources committed by the 11 main organizations responsible for managing the outbreak. Of the overall estimated costs of 455,856 pounds, only 14% (64,264 pounds) was spent on investigation and control of the outbreak compared with 86% (391,592 pounds) spent on the hospital treatment of the patients. The time and money spent on public health services in this investigation appear to represent good value for money considering the potential costs of a major outbreak, including the high case-fatality rate in LD generally and the high health-care costs. Further research is needed to determine optimum strategies for the cost-effective use of health system resources in investigations of LD. Whether the threshold for investigation of cases should be based on observed incidence rates or the cost-effectiveness of investigations, or both, should be debated further
Neural control of nonlinear systems with composite adaptation for improved convergence of Gaussian networks
The use of composite adaptive laws for control of the ane class of nonlinear systems having unknown dynamics is
proposed. These dynamics are approximated by Gaussian
radial basis function neural networks whose parameters
are updated by a composite law that is driven by both
tracking and estimation errors. This is motivated by the
need to improve the speed of convergence of the unknown
parameters, hence resulting in better system performance.
To ensure global stability despite the inevitable network
approximation errors, the control law is augmented with
a low gain sliding mode component and deadzone adaptation is used for the indirect part of the composite law. The
stability of the system is analyzed and the effectiveness of
the method is demonstrated by simulation.peer-reviewe
Unscented transform-based dual adaptive control of nonlinear MIMO systems
The paper proposes a multilayer perceptron neural network controller for dual adaptive control of a class
of stochastic MIMO nonlinear systems subject to functional
uncertainty. The neural network parameters are adjusted in
real-time using the Unscented Kalman filter algorithm and
no pre-operational training phase is required. Dual adaptive control aims to strike a compromise between the two
control characteristics of caution and probing, leading to
an improved overall performance. The system is evaluated
through numerical simulations and Monte Carlo analysis. The
resulting performance of the dual adaptive controller is not only
consistently superior to non-dual adaptive control schemes, but
also surpasses the performance of similar controllers that are
based on Extended Kalman filter estimators. This reflects the
enhanced accuracy of the Unscented Kalman filter estimator,
despite being a local estimation method. In addition, unlike use
of other estimators, the proposed approach neither requires the
computation of complex Jacobian matrices as part of the design,
nor the evaluation of such matrices in real-time. This renders
the proposed controller inherently amenable and practical for
real-time implementation.peer-reviewe
Experimental evaluation of haptic control for human activated command devices
Haptics refers to a widespread area of research that focuses on the interaction
between humans and machine interfaces as applied to the sense of touch. A haptic interface
is designed to increase the realism of tactile and kinesthetic sensations in applications such
as virtual reality, teleoperation, and other scenarios where situational awareness is considered
important, if not vital. This paper investigates the use of electric actuators and non-linear
algorithms to provide force feedback to an input command device for providing haptics to the
human operator. In particular, this work involves the study and implementation of a special case
of feedback linearization known as inverse dynamics control and several outer loop impedance
control topologies. It also investigates the issues concerned with force sensing and the application
of model based controller functions in order to vary the desired inertia and the desired mass
matrix. Results of the controllersâ abilities to display any desired impedance and provide the
required kinesthetic constraint of virtual environments are shown on two experimental test rigs
designed for this purpose.peer-reviewe
Trajectory tracking in the presence of obstacles using the limit cycle navigation method
This paper proposes a system for effecting trajectory tracking in combination with obstacle avoidance in mobile
robotic systems. In robotics research, these two situations
are typically considered as separate problems. This work
approaches the problem by integrating classical trajectory following control schemes with Kim et al.âs Limit Cycle
Navigation method for obstacle avoidance. The use of Artificial Potential Function methods for obstacle avoidance is
purposely avoided so as to prevent the well-known problems
of local minima associated with such schemes. The paper
also addresses the problem of non-global obstacle sensing and
proposes modifications to Kim et al.âs method for handling
multiple, overlapping obstacles under local sensing conditions.peer-reviewe
Trajectory tracking of a differentially driven wheeled mobile robot in the presence of obstacles
A trajectory following and obstacle avoidance mechanism for a mobile robot is presented for situations where the robot has to follow a specific target trajectory but the task might not be completely possible due to obstacles in the way, which the robot must avoid. After avoiding an obstacle, the robot should catch up with the target trajectory. In the proposed system, this objective is reached by combining a nonlinear control method with an Artificial Potential Function method, leading to trajectory tracking control with obstacle avoidance capabilities.peer-reviewe
Lifting the lid: a clinical audit on commode cleaning
Many healthcare-associated infections (HCAIs) are preventable by infection control procedures designed to interrupt the transmission of organisms from a source. Commodes are in use constantly throughout healthcare facilities. Therefore commode surfaces are constantly handled, and any pathogens present have the potential to be transferred to not only other surfaces but also, more importantly, to patients, thus compromising patient safety. In order to examine the effectiveness and thoroughness of cleaning commodes an audit was undertaken to assess compliance with evidence-based practice. This audit demonstrates a cycle which includes defining best practice, implementing best practice, monitoring best practice and taking action to improve practice. The audit results confirmed an issue that the authors had long suspected. That is, that commodes allocated to individual patients are not always cleaned after every use. Using adenosine triphosphate (ATP) bioluminescence as an indicator of organic soiling also demonstrated that commodes that were considered clean were not always cleaned to a high standard. Implementing the audit recommendations improves staff knowledge through education, standardises cleaning procedures and ultimately improves patient safety
How can onchocerciasis elimination in Africa be accelerated? Modelling the impact of increased ivermectin treatment frequency and complementary vector control
Background: Great strides have been made toward onchocerciasis elimination by mass drug administration (MDA) of ivermectin. Focusing on MDA-eligible areas, we investigated where the elimination goal can be achieved by 2025 by continuation of current practice (annual MDA with ivermectin) and where intensification or additional vector control is required. We did not consider areas hypoendemic for onchocerciasis with loiasis coendemicity where MDA is contraindicated. Methods: We used 2 previously published mathematical models, ONCHOSIM and EPIONCHO, to simulate future trends in microfilarial prevalence for 80 different settings (defined by precontrol endemicity and past MDA frequency and coverage) under different future treatment scenarios (annual, biannual, or quarterly MDA with different treatment coverage through 2025, with or without vector control strategies), assessing for each strategy whether it eventually leads to elimination. Results: Areas with 40%â50% precontrol microfilarial prevalence and â„10 years of annual MDA may achieve elimination with a further 7 years of annual MDA, if not achieved already, according to both models. For most areas with 70%â80% precontrol prevalence, ONCHOSIM predicts that either annual or biannual MDA is sufficient to achieve elimination by 2025, whereas EPIONCHO predicts that elimination will not be achieved even with complementary vector control. Conclusions: Whether elimination will be reached by 2025 depends on precontrol endemicity, control history, and strategies chosen from now until 2025. Biannual or quarterly MDA will accelerate progress toward elimination but cannot guarantee it by 2025 in high-endemicity areas. Long-term concomitant MDA and vector control for high-endemicity areas might be useful
Surveillance for Anthrax Cases Associated with Contaminated Letters, New Jersey, Delaware, and Pennsylvania, 2001
In October 2001, two inhalational anthrax and four cutaneous anthrax cases, resulting from the processing of Bacillus anthracisâcontaining envelopes at a New Jersey mail facility, were identified. Subsequently, we initiated stimulated passive hospital-based and enhanced passive surveillance for anthrax-compatible syndromes. From October 24 to December 17, 2001, hospitals reported 240,160 visits and 7,109 intensive-care unit admissions in the surveillance area (population 6.7 million persons). Following a change to reporting criteria on November 8, the average of possible inhalational anthrax reports decreased 83% from 18 to 3 per day; the proportion of reports requiring follow-up increased from 37% (105/286) to 41% (47/116). Clinical follow-up was conducted on 214 of 464 possible inhalational anthrax patients and 98 possible cutaneous anthrax patients; 49 had additional laboratory testing. No additional cases were identified. To verify the limited scope of the outbreak, surveillance was essential, though labor-intensive. The flexibility of the system allowed interim evaluation, thus improving surveillance efficiency
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