6,424 research outputs found
The Galactic Branches as a Possible Evidence for Transient Spiral Arms
With the use of a background Milky-Way-like potential model, we performed
stellar orbital and magnetohydrodynamic (MHD) simulations. As a first
experiment, we studied the gaseous response to a bisymmetric spiral arm
potential: the widely employed cosine potential model and a self-gravitating
tridimensional density distribution based model called PERLAS. Important
differences are noticeable in these simulations, while the simplified cosine
potential produces two spiral arms for all cases, the more realistic density
based model produces a response of four spiral arms on the gaseous disk, except
for weak arms -i.e. close to the linear regime- where a two-armed structure is
formed. In order to compare the stellar and gas response to the spiral arms, we
have also included a detailed periodic orbit study and explored different
structural parameters within observational uncertainties. The four armed
response has been explained as the result of ultra harmonic resonances, or as
shocks with the massive bisymmetric spiral structure, among other. From the
results of this work, and comparing the stellar and gaseous responses, we
tracked down an alternative explanation to the formation of branches, based
only on the orbital response to a self-gravitating spiral arms model. The
presence of features such as branches, might be an indication of transiency of
the arms.Comment: 17 pages, 9 figures. Accepted for publication in MNRA
Enseñanza de Inteligencia Artificial e IngenierĂa del Conocimiento
nivel mundial en la unificaciĂłn de los contenidos que se
imparten en el primer curso que un estudiante de
Informática recibe en Inteligencia Artificial e IngenierĂa
del Conocimiento (INCO). El alcance y la diversidad de
problemas a los que estas materias están dirigidas
incrementa aun más la necesidad de crear un programa
coherente e integrado en sĂ mismo, y con el Plan de
Estudios de la InstituciĂłn en la que se imparte.
Evidentemente, la uniĂłn de todos los temas tratados en
los libros de Inteligencia Artificial e IngenierĂa del
Conocimiento, "comĂşnmente aceptado", serĂa demasiado extenso, mientras que la intersecciĂłn de todos ellos no suele incluir todo aquello que es considerado importante
A conceptual model of check dam hydraulics for gully control: efficiency, optimal spacing and relation with step-pools
There is little information in scientific literature regarding the
modifications induced by check dam systems in flow regimes within restored
gully reaches, despite it being a crucial issue for the design of gully
restoration measures. Here, we develop a conceptual model to classify flow
regimes in straight rectangular channels for initial and dam-filling
conditions as well as a method of estimating efficiency in order to provide
design guidelines. The model integrates several previous mathematical
approaches for assessing the main processes involved (hydraulic jump, impact
flow, gradually varied flows). Ten main classifications of flow regimes were
identified, producing similar results when compared with the IBER model. An
interval for optimal energy dissipation (ODI) was observed when the steepness
factor <i>c</i> was plotted against the design number (DN, ratio between the
height and the product of slope and critical depth). The ODI was
characterized by maximum energy dissipation and total influence conditions.
Our findings support the hypothesis of a maximum flow resistance principle
valid for a range of spacing rather than for a unique configuration. A value
of <i>c</i> = 1 and DN ~ 100 was found to economically meet the ODI
conditions throughout the different sedimentation stages of the structure.
When our model was applied using the same parameters to the range typical of
step-pool systems, the predicted results fell within a similar region to that
observed in field experiments. The conceptual model helps to explain the
spacing frequency distribution as well as the often-cited trend to lower <i>c</i>
for increasing slopes in step-pool systems. This reinforces the hypothesis of
a close link between stable configurations of step-pool units and man-made
interventions through check dams
An Expert Systems for Homeopatic Glaucoma Treatment (SEHO)
In this article, an Expert System for Homeopathic Glaucoma Treatment (SEHO) is presented, the task of which is to assist ophthalmologists in selecting the most appropriate therapy for a patient diagnosed as having glaucoma. It is based on techniques proper to homeopathic medicine, a trend that is gaining more and more supporters all over the world, but in which real experts are few and far between. After a brief overview of the state of the art, the authors describe in detail on the development of the system, for which the IDEAL methodology, designed for knowledge-based system development, was used
El trabajador social como asesor familiar
Se plantea la necesidad social que las familias tienen de recibir asesoramiento sobre sus problemas, en los diferentes momentos por los que pasan en su ciclo vital, y la oportunidad de la figura del trabajador social para desarrollar tareas encaminadas a proporcionar dicho asesoramiento familiar
Diffusion dynamics on multiplex networks
We study the time scales associated to diffusion processes that take place on
multiplex networks, i.e. on a set of networks linked through interconnected
layers. To this end, we propose the construction of a supra-Laplacian matrix,
which consists of a dimensional lifting of the Laplacian matrix of each layer
of the multiplex network. We use perturbative analysis to reveal analytically
the structure of eigenvectors and eigenvalues of the complete network in terms
of the spectral properties of the individual layers. The spectrum of the
supra-Laplacian allows us to understand the physics of diffusion-like processes
on top of multiplex networks.Comment: 6 Pages including supplemental material. To appear in Physical Review
Letter
Artificial neural network algorithm for online glucose prediction from continuous glucose monitoring.
Background and Aims: Continuous glucose monitoring (CGM) devices could be useful for real-time management of diabetes therapy. In particular, CGM information could be used in real time to predict future glucose levels in order to prevent hypo-/hyperglycemic events. This article proposes a new online method for predicting future glucose concentration levels from CGM data.
Methods: The predictor is implemented with an artificial neural network model (NNM). The inputs of the NNM are the values provided by the CGM sensor during the preceding 20 min, while the output is the prediction of glucose concentration at the chosen prediction horizon (PH) time. The method performance is assessed using datasets from two different CGM systems (nine subjects using the Medtronic [Northridge, CA] Guardian® and six subjects using the Abbott [Abbott Park, IL] Navigator®). Three different PHs are used: 15, 30, and 45 min. The NNM accuracy has been estimated by using the root mean square error (RMSE) and prediction delay.
Results: The RMSE is around 10, 18, and 27 mg/dL for 15, 30, and 45 min of PH, respectively. The prediction delay is around 4, 9, and 14 min for upward trends and 5, 15, and 26 min for downward trends, respectively. A comparison with a previously published technique, based on an autoregressive model (ARM), has been performed. The comparison shows that the proposed NNM is more accurate than the ARM, with no significant deterioration in the prediction delay
Evaluation of the changes in working limits in an automobile assembly line using simulation
The aim of the work presented in this paper consists of the development of a decision-making support system, based on discrete-event simulation models, of an automobile assembly line which was implemented within an Arena simulation environment and focused at a very specific class of production lines with a four closed-loop network configuration. This layout system reflects one of the most common configurations of automobile assembly and preassembly lines formed by conveyors. The sum of the number of pallets on the intermediate buffers, remains constant, except for the fourth closed-loop, which depends on the four-door car ratio (x) implemented between the door disassembly and assembly stations of the car body. Some governing equations of the four closed-loops are not compatible with the capacities of several intermediate buffers for certain values of variable x. This incompatibility shows how the assembly line cannot operate in practice for x0,97 in a stationary regime, due to the starvation phenomenon or the failure of supply to the machines on the production line. We have evaluated the impact of the pallet numbers circulating on the first closed-loop on the performance of the production line, translated into the number of cars produced/hour, in order to improve the availability of the entire manufacturing system for any value of x. Until the present date, these facts have not been presented in specialized literature. © 2012 American Institute of Physics
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