7,168 research outputs found
Slide-Down Prevention for Wheeled Mobile Robots on Slopes
Wheeled mobile robots on inclined terrain can slide down due to loss of traction and gravity. This type of instability, which is different from tip-over, can provoke uncontrolled motion or get the vehicle stuck. This paper proposes slide-down prevention by real-time computation of a straightforward stability margin for a given ground-wheel friction coefficient. This margin is applied to the case study of Lazaro, a hybrid skid-steer mobile robot with caster-leg mechanism that allows tests with four or five wheel contact points. Experimental results for both ADAMS simulations and the actual vehicle demonstrate the effectiveness of the proposed approach.Universidad de Málaga. Campus de Excelencia Internacional AndalucÃa Tech
The origin of scale-scale correlations of the density perturbations during inflation
We show that scale-scale correlations are a generic feature of slow-roll
inflation theories. These correlations result from the long-time tails
characteristic of the time dependent correlations because the long wavelength
density perturbation modes are diffusion-like. A relationship between the
scale-scale correlations and time-correlations is established providing a way
to reveal the time correlations of the perturbations during inflation. This
mechanism provides for a testable prediction that the scale-scale correlations
at two different spatial points will vanish.Comment: Accepted for publication, International Journal of Modern Physics,
vol. 8 No.6 (Dec 1999
Enhancement of cooperation in highly clustered scale-free networks
We study the effect of clustering on the organization of cooperation, by
analyzing the evolutionary dynamics of the Prisoner's Dilemma on scale-free
networks with a tunable value of clustering. We find that a high value of the
clustering coefficient produces an overall enhancement of cooperation in the
network, even for a very high temptation to defect. On the other hand, high
clustering homogeneizes the process of invasion of degree classes by defectors,
decreasing the chances of survival of low densities of cooperator strategists
in the network.Comment: 4 pages, 3 figure
A generic persistence model for CLP systems (and two useful implementations)
This paper describes a model of persistence in (C)LP languages and two different and practically very useful ways to implement this model in current systems. The fundamental idea is that persistence is a characteristic of certain dynamic predicates (Le., those which encapsulate
state). The main effect of declaring a predicate persistent is that the dynamic changes made to such predicates persist from one execution to the next one. After proposing a syntax for declaring persistent predicates, a simple, file-based implementation of the concept is presented and
some examples shown. An additional implementation is presented which stores persistent predicates in an external datábase. The abstraction of the concept of persistence from its implementation allows developing applications
which can store their persistent predicates alternatively in files or databases with only a few simple changes to a declaration stating the location and modality used for persistent storage. The paper presents the model, the implementation approach in both the cases of using files
and relational databases, a number of optimizations of the process (using information obtained from static global analysis and goal clustering), and performance results from an implementation of these ideas
Validación de los procesos de determinación de estándares de interpretación (EE) para pruebas de rendimiento educativo
En este trabajo se presenta una revisión del
estado de la cuestión acerca de los métodos para desarrollar
procesos de validación de la determinación de
Estándares en pruebas de rendimiento educativo. Se
analiza el concepto de Validez de los Estándares, asÃ
como estrategias de validación, y algunos indicadores
de juicio
Insulin-like growth factor I (IGF-I) and liver cirrhosis
Insulin-like growth factor I (IGF-I) is a polypeptide hormone secreted
by multiple tissues in response to growth hormone (GH). It
is partly responsible for GH activity, and also has glucose-lowering
and anabolizing effects. Ninety percent of circulating IGF-I originates
in the liver and has autocrine, paracrine, and endocrine effects,
the latter on multiple tissues. Liver cirrhosis results in a progressive
decline of hepatic IGF-I output, and this factor may
become undetectable in advanced disease. Some cirrhosis complications,
mainly those nutritional and metabolic in nature (insuline
resistance, malnutrition, osteopenia, hypogonadism, intestinal disorders),
may be at least partly related to this IGF-I deficiency, since
some IGF-I effects represent a reverse image of cirrhosis complications.
Despite this, IGF-I replacement therapy has been never
suggested for cirrhosis. A number of experimental studies in cirrhotic
rats showed that therapy using low-dose recombinant IGF-I
exerts two types of effect on experimental cirrhosis: a) liver improvement
driven by improved hepatocellular function, portal hypertension,
and liver fibrosis; and b) cirrhosis-related extrahepatic disorder
improvement driven by improved food efficiency, muscle
mass, bone mass, gonadal function and structure, and intestinal
function and structure, with a normalization of sugar and amino
acid malabsorption, and improved intstinal barrier function, manifested
by reduced endotoxemia and bacterial translocation. Subsequently,
the first randomized, double-blind, placebo-controlled, pilot
clinical trial in a small number of cirrhotic patients showed
increased serum albumin and improved energy metabolism as a
result of IGF-I use. Further clinical trials are needed to identify adequate
IGF-I doses, administration duration and frequency, and the
subgroup of cirrhotic patients who will benefit most from this replacement
therapy
Observation of a continuous interior crisis in the Hindmarsh-Rose neuron model.
Interior crises are understood as discontinuous changes of the size of a chaotic attractor that occur when an unstable periodic orbit collides with the chaotic attractor. We present here numerical evidence and theoretical reasoning which prove the existence of a chaos-chaos transition in which the change of the attractor size is sudden but continuous. This occurs in the Hindmarsh¿Rose model of a neuron, at the transition point between the bursting and spiking dynamics, which are two different dynamic behaviors that this system is able to present. Moreover, besides the change in attractor size, other significant properties of the system undergoing the transitions do change in a relevant qualitative way. The mechanism for such transition is understood in terms of a simple one-dimensional map whose dynamics undergoes a crossover between two different universal behavior
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