3,818 research outputs found
Neural Network Methods for Boundary Value Problems Defined in Arbitrarily Shaped Domains
Partial differential equations (PDEs) with Dirichlet boundary conditions
defined on boundaries with simple geometry have been succesfuly treated using
sigmoidal multilayer perceptrons in previous works. This article deals with the
case of complex boundary geometry, where the boundary is determined by a number
of points that belong to it and are closely located, so as to offer a
reasonable representation. Two networks are employed: a multilayer perceptron
and a radial basis function network. The later is used to account for the
satisfaction of the boundary conditions. The method has been successfuly tested
on two-dimensional and three-dimensional PDEs and has yielded accurate
solutions
Selective Reflection Spectroscopy on the UV Third Resonance Line of Cs : Simultaneous Probing of a van der Waals Atom-Surface Interaction Sensitive to Far IR Couplings and of Interatomic Collisions
We report on the analysis of FM selective reflection experiments on the
6S1/2->8P3/2 transition of Cs at 388 nm, and on the measurement of the surface
van der Waals interaction exerted by a sapphire interface on Cs(8P3/2). Various
improvements in the systematic fitting of the experiments have permitted to
supersede the major difficulty of a severe overlap of the hyperfine components,
originating on the one hand in a relatively small natural structure, and on the
other hand on a large pressure broadening imposed by the high atomic density
needed for the observation of selective reflection on a weak transition. The
strength of the van der Waals surface interaction is evaluated to be 7310
kHz.m3. An evaluation of the pressure shift of the transition is also
provided as a by-product of the measurement. We finally discuss the
significance of an apparent disagreement between the experimental measurement
of the surface interaction, and the theoretical value calculated for an
electromagnetic vacuum at a null temperature. The possible influence of the
thermal excitation of the surface is evoked, because, the dominant
contributions to the vW interaction for Cs(8P3/2) lie in the far infrared
range.Comment: submitted to Laser Physics - issue in the memory of Herbert Walther
Benjamin-Ono Kadomtsev-Petviashvili’s models in interfacial electro-hydrodynamics
Three-dimensional nonlinear potential free surface flows in the presence of vertical electric fields are considered. Both the effects of gravity and surface tension are included in the dynamic boundary condition. An asymptotic analysis (based on the assumptions of small depth and small free surface displacements) is presented. It is shown that the problem can be modelled by a Benjamin-Ono Kadomtsev-Petviashvili equation. Furthermore a fifth order Benjamin-Ono Kadomtsev-Petviashvili equation is derived to describe the flows in the particular case of values of the Bond number close to 1/3
Evaluating the Effects of Match-Induced Fatigue on Landing Ability; the Case of the Basketball Game
International Journal of Exercise Science 14(6): 768-778, 2021. This paper examines the effect of match–induced fatigue on lower limb biomechanics, in the case of a basketball game. For this purpose, sixteen male basketball athletes, ages 18 to 22, performed a jump-landing task prior and post a recreational basketball game. The Landing Error Scoring System (LESS) was used to examine the biomechanics of landing. The Vertical jump (VJ) and the Borg Rating of Perceived Exertion (RPE) scale pre- and post-game were employed to assess the level of fatigue induced by the basketball game. In order to compare pre and post measurements, t-tests for dependent samples were used. The performance of the VJ test post-game was found to be significantly lower (t (15) = 3.83, p = 0.002) showing a large effect (Cohen’s d = 0.9) compared to pre-game measurements. Further, the LESS scores were significantly (t (15) = 2.33, p = 0.034) higher post-game with a medium effect (d = 0.5). The differences in LESS scores were due to errors in the landing technique which is bound to be influenced by biomechanics. Moreover, the Borg RPE scale was found to be significantly higher (t (15) = 10.77, p \u3c 0.001) post-game showing a very large effect (d =2.6). It is important to note, that these significant differences occurred with a merely medium level of fatigue (6.6 ± 0.3 pre-game vs 11.9 ± 1.0 post-game). The results of this study would be of great benefit to sports science teams and coaches for formulating effective strategies to improve athletes’ performance and reduce the likelihood of injury
Adaptive Memetic Particle Swarm Optimization with Variable Local Search Pool Size
We propose an adaptive Memetic Particle Swarm Optimization algorithm where local search is selected from a pool of different algorithms. The choice of local search is based on a probabilistic strategy that uses a simple metric to score the efficiency of local search. Our study investigates whether the pool size affects the memetic algorithm’s performance, as well as the possible benefit of using the adaptive strategy against a baseline static one. For this purpose, we employed the memetic algorithms framework provided in the recent MEMPSODE optimization software, and tested the proposed algorithms on the Benchmarking Black Box Optimization (BBOB 2012) test suite. The obtained results lead to a series of useful conclusions
Early versus Late Tracheostomy Promotes Weaning in Intensive Care Unit Patients
Background and aim of the study: The time interval between the patients’ intubation and the performance of a tracheostomy has been considered as critical for the disease prognosis and outcome. The aim of the present study was to compare and contrast the outcomes of early vs late tracheostomy with regard to intensive care unit (ICU) patients’ weaning from respiratory support. Methods: This retrospective observational study, involved patients who were hospitalized in two general and one Covid-19 ICUs of two tertiary hospitals in Athens and were subjected to tracheostomy. Data were collected from the patients’ medical records in order to estimate the duration of patient weaning and the number of days from the patients’ intubation until the time of tracheostomy. In the present study the term early tracheostomy denotes tracheostomy performed within 14 days from patient intubation and late tracheostomy defines the tracheostomy carried out after 14 days. For Covid-19 patients, guidelines suggested that tracheostomies should be performed 21 days following intubation, due to the high risk of virus transmission. Results: One hundred and thirty-one patients who underwent tracheostomy participated in the study. Most tracheostomies were performed using the percutaneous technique. The group of patients tracheostomized within 14 days after their admission in ICU weaned faster from respiratory support compared to ones who were tracheostomized after 14 days. Conclusions: The most common distinction between early and late tracheostomy is 14 days, with early tracheostomy being more beneficial in terms of patients’ outcomes, and specifically ICU patients’ weaning. (www.actabiomedica.it)
Modeling and Simulation of Multi-Lane Traffic Flow
A most important aspect in the field of traffic modeling is the simulation of
bottleneck situations. For their realistic description a macroscopic multi-lane
model for uni-directional freeways including acceleration, deceleration,
velocity fluctuations, overtaking and lane-changing maneuvers is systematically
deduced from a gas-kinetic (Boltzmann-like) approach. The resulting equations
contain corrections with respect to previous models. For efficient computer
simulations, a reduced model delineating the coarse-grained temporal behavior
is derived and applied to bottleneck situations.Comment: For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.htm
Selective Reflection Spectroscopy at the Interface between a Calcium Fluoride Window and Cs Vapour
A special vapour cell has been built, that allows the measurement of the
atom-surface van der Waals interaction exerted by a CaF2 window at the
interface with Cs vapour. Mechanical and thermal fragility of fluoride windows
make common designs of vapour cells unpractical, so that we have developed an
all-sapphire sealed cell with an internal CaF2 window. Although impurities were
accidentally introduced when filling-up the prototype cell, leading to a
line-broadening and shift, the selective reflection spectrum on the Cs D1 line
(894 nm) makes apparent the weak van der Waals surface interaction. The
uncertainties introduced by the effects of these impurities in the van der
Waals measurement are nearly eliminated when comparing the selective reflection
signal at the CaF2 interface of interest, and at a sapphire window of the same
cell. The ratio of the interaction respectively exerted by a sapphire interface
and a CaF2 interface is found to be 0.55 0.25, in good agreement with the
theoretical evaluation of ~0.67.Comment: soumis \`a Appl Phys B MS 4734
Perceptions, attitudes and training needs of primary healthcare professionals in identifying and managing frailty: a qualitative study
PURPOSE: Although frailty can be delayed or prevented by appropriate interventions, these are often not available in countries lacking formal education and infrastructure in geriatrics. The aim of this study was to: (a) explore ideas, perceptions and attitudes of primary health care (PHC) professionals towards frailty in a country where geriatrics is not recognised as a specialty; (b) explore PHC professionals' training needs in frailty; and (c) define components of a frailty educational programme in PHC. METHODS: Qualitative design, using two focus groups with PHC professionals conducted in Thessaloniki, Greece. Focus groups were audio recorded and transcribed. Data were analysed with thematic analysis. RESULTS: In total 31 PHC professionals (mean age: 46 years; gender distribution: 27 females, 4 males) participated in the study (physicians n = 17; nurses n = 12; health visitors n = 2). Four main themes were identified: (1) Perceptions and understanding of frailty; (2) Facilitators and barriers to frailty identification and management; (3) Motivation to participate in a frailty training programme; (4) Education and training. The main barriers for the identification and management of frailty were associated with the healthcare system, including duration of appointments, a focus on prescribing, and problems with staffing of allied health professionals, but also a lack of education. Training opportunities were scarce and entirely based on personal incentive. Professionals were receptive to training either face-to-face or online. A focus on learning practical skills was key. CONCLUSION: Education and training of professionals and interdisciplinary collaboration are essential and much needed for the delivery of person-centred care for people with frailty living in the community
Microwave Absorption of Surface-State Electrons on Liquid He
We have investigated the intersubband transitions of surface state electrons
(SSE) on liquid He induced by microwave radiation at temperatures from 1.1
K down to 0.01 K. Above 0.4 K, the transition linewidth is proportional to the
density of He vapor atoms. This proportionality is explained well by Ando's
theory, in which the linewidth is determined by the electron - vapor atom
scattering. However, the linewidth is larger than the calculation by a factor
of 2.1. This discrepancy strongly suggests that the theory underestimates the
electron - vapor atom scattering rate. At lower temperatures, the absorption
spectrum splits into several peaks. The multiple peak structure is partly
attributed to the spatial inhomogeneity of the static holding electric field
perpendicular to the electron sheet.Comment: 15 pages, 7 figures, submitted to J. Phys. Soc. Jp
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