1,720,970 research outputs found
Identifying the dynamic model used by the KUKA LWR: A reverse engineering approach
No full textAn approach is presented for the model identification of the so-called link dynamics used by the KUKA LWR-IV, a lightweight manipulator with elastic joints that is very popular in robotics research but for which a complete and reliable dynamic model is not yet publicly available. The control software interface of this robot provides numerical values of the link inertia matrix and the gravity vector at each configuration, together with link position and joint torque sensor data. Taking advantage of this information, a general procedure is set up for determining the structure and identifying the value of the relevant dynamic coefficients used by the manufacturer in the evaluation of these robot model terms. We call this a reverse engineering approach, because our main goal is to match the numerical data provided by the software interface, using a suitable symbolic model of the robot dynamics and the inertial and gravity coefficients that are being estimated. Only configuration-dependent terms are involved in this process, and thus static experiments are sufficient for this task. The main issues of dynamic model identification for robots with elastic joints are discussed in general, highlighting the pros and cons of the approach taken for this class of KUKA lightweight manipulators. The main identification results, including training and validation tests, are reported together with additional dynamic validation experiments that use the complete identified model and joint torque sensor data
A geometrical approach to the PKPD modelling of inhaled bronchodilators
No full textThe present work introduces a new method to model the pharmacokinetics and pharmacodynamics (PKPD) of an inhaled dose of bronchodilator. This method provides an alternative approach to classic compartmental representations or computational fluid dynamics.
A five compartment lung model comprising the upper airways, bronchial tree mucosa, bronchial muscles, alveoli and plasma has been modified to take into account anatomical, geometrical features such as bronchial branching and smooth muscle distribution. Many anatomical and physiological features of the bronchial tree depend, as a first approximation, on bronchial generation or on mean distance from the larynx. Among these are diameters, resistances, and receptor density, which work together in determining the local response to the inhaled dose; integrating these local responses over the whole bronchial tree allows an approximation of total broncodilator response, particularly with respect to airflow resistance.
While the PK part of the model reflects classical compartmental assumptions, the PD part substitutes a simplified geometrical and functional description of the bronchial tree for the typical PD models of effect, leading to the direct computation of the approximate FEV1.
In the present work the construction of the model is detailed, and literature data are used to derive the anatomical approximations used. Simulation of two asthmatic subjects is employed to illustrate the behaviour of the model in representing the evolution over time of the distribution and effect of an inhaled dose of bronchodilator. The relevance of formulation diffusivity on therapeutic efficacy is discussed and conclusions regarding the applicability of the model in interpreting single-subject and population experiments are drawn
Simulation of Trauma Incidents: Modelling the Evolution of Patients and Resources
No full textMathematical modeling and simulation with medical applications has gained much interest in the last few years, mainly due to the widespread availability of low-cost technology and computational power. This paper presents an integrated platform for the in-silico simulation of trauma incidents, based on a suite of interacting mathematical models. The models cover the generation of a scenario for an incident, a model of physiological evolution of the affected individuals, including the possible effect of the treatment, and a model of evolution in time of the required medical resources. The problem of optimal resource allocation is also investigated. Model parameters have been identified according to the expertise of medical doctors and by reviewing some related literature. The models have been implemented and exposed as web services, while some software clients have been built for the purpose of testing. Due to its extendability, our integrated platform highlights the potential of model-based simulation in different health-related fields, such as emergency medicine and personal health systems. Modifications of the models are already being used in the context of two funded projects, aiming at evaluating the response of health systems to major incidents with and without model-based decision support
A unifying organ model of pancreatic insulin secretion
Full text linkThe secretion of insulin by the pancreas has been the object of much attention over the past several decades. Insulin is known to be secreted by pancreatic β-cells in response to hyperglycemia: its blood concentrations however exhibit both high-frequency (period approx. 10 minutes) and low-frequency oscillations (period approx. 1.5 hours). Furthermore, characteristic insulin secretory response to challenge maneuvers have been described, such as frequency entrainment upon sinusoidal glycemic stimulation; substantial insulin peaks following minimal glucose administration; progressively strengthened insulin secretion response after repeated administration of the same amount of glucose; insulin and glucose characteristic curves after Intra-Venous administration of glucose boli in healthy and prediabetic subjects as well as in Type 2 Diabetes Mellitus. Previous modeling of β-cell physiology has been mainly directed to the intracellular chain of events giving rise to single-cell or cell-cluster hormone release oscillations, but the large size, long period and complex morphology of the diverse responses to whole-body glucose stimuli has not yet been coherently explained. Starting with the seminal work of Grodsky it was hypothesized that the population of pancreatic β-cells, possibly functionally aggregated in islets of Langerhans, could be viewed as a set of independent, similar, but not identical controllers (firing units) with distributed functional parameters. The present work shows how a single model based on a population of independent islet controllers can reproduce very closely a diverse array of actually observed experimental results, with the same set of working parameters. The model's success in reproducing a diverse array of experiments implies that, in order to understand the macroscopic behaviour of the endocrine pancreas in regulating glycemia, there is no need to hypothesize intrapancreatic pacemakers, influences between different islets of Langerhans, glycolitic-induced oscillations or β-cell sensitivity to the rate of change of glycemia
Enhancing force feedback in teleoperated needle insertion through on-line identification of the needle-tissue interaction parameters
No full textThis paper proposes an approach for displaying
the needle-tip interaction force exchanged between the needle
tip and the tissues to the remote operator of a teleoperated
needle insertion procedure. As known, the measures of the
needle tip interaction force with tissues obtained through
F/T sensor at the robot wrist do not provide a transparent
perception of the needle-tissue interaction at the tip mainly
because of the friction between the needle shaft and the
traversed tissues. Current literature mainly proposes hardware
solutions to the problem of measuring the forces at the needle
tip. In this work we aim instead at cleaning the F/T sensor
information for rendering only the estimated force exchanged at
the needle tip. The approach is based on an online identification
of the parameters of a needle-tissue interaction force model to
isolate offset force values mainly due to friction. The approach,
validated through simulations and experiments, is expected to
increase the sensitivity of the rendered force to tissue transitions
thus improving safety and accuracy in needle placement
Novel patterns and methods for zooming camera calibration
No full textCamera calibration is a necessary step in order to develop applications that need to establish a relationship between image pixels and real world points. The goal of camera calibration is to estimate the extrinsic and intrinsic camera parameters. Usually, for non-zooming cameras, the calibration is carried out by using a grid pattern of known dimensions (e.g., a chessboard). However, for cameras with zoom functions, the use of a grid pattern only is not sufficient, because the calibration has to be effective at multiple zoom levels and some features (e.g., corners) could not be detectable. In this paper, a calibration method based on two novel calibration patterns, specifically designed for zooming cameras, is presented. The first pattern, called in-lab pattern, is designed for intrinsic parameter recovery, while the second one, called on-field pattern, is conceived for extrinsic parameter estimation. As an application example, on-line virtual advertising in sport events, where the objective is to insert virtual advertising images into live or pre-recorded television shows, is considered. A quantitative experimental evaluation shows an increase of performance with respect to the use of standard calibration routines considering both re-projection accuracy and calibration time
An islet population model of pancreatic insulin production
No full textGlucose-induced pancreatic insulin release is the fundamental mechanism responsible for glucose homeostasis, its failure determining the clinical picture of Diabetes Mellitus. The details of the feedback loop controlling glycemia through insulin secretion have been an important subject of investigation and modeling for decades. In this note, a recently published population model is considered, whose purpose is to replicate in silico different observed phenomena such as low frequency glycemia-insulinemia oscillations, as well as concordant induction of high-frequency insulin oscillations. The basic idea underlying this model is that the pancreas behaves like a population of independent controllers (each consisting of a fundamental secreting unit, a pancreatic islet), all reacting to the same glucose stimulus, but with varying perfomance characteristics. This idea has been supported by a relatively wide range of simulations, aiming to replicate most important in vivo experiments concerning pancreatic insulin release. It will be shown in this note that the same mathematical structure can also replicate a set of in vitro experiments, provided that the model context is adapted to the structure of the different experiments to be simulated. More in details, the model will be shown to reproduce the double phase of insulin release during a prolonged glucose stimulus: A first phase of impulsive insulin release, immediately upon glucose administration, and a second phase of more gradual release, dependent on the potentiation effect of the secretory units. ©2013 IEEE
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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