1,310 research outputs found
Synchronization of the Frenet-Serret linear system with a chaotic nonlinear system by feedback of states
A synchronization procedure of the generalized type in the sense of Rulkov et
al [Phys. Rev. E 51, 980 (1995)] is used to impose a nonlinear Malasoma chaotic
motion on the Frenet-Serret system of vectors in the differential geometry of
space curves. This could have applications to the mesoscopic motion of
biological filamentsComment: 12 pages, 7 figures, accepted at Int. J. Theor. Phy
LICOR-Liquid Columns' Resonances
The aim of the experiment LICOR was the investigation of the axial resonances oi cylindrical liquid columns supported by equal circular coaxiaJ disks. In preparation ot the D-2 experiment a •heoreiical model has been developed, which exactly describes the small amplitude oscillations of finite cylindrical columns between coaxial circular disks. In addition, in terrestrial experiments the resonance frequencies of small liquid columns with up to 5 mm in diameter have been determined and investigations with density-matched liquids (silicon oil in a waierlmethanol mixture) have been performed. For the D-2 experiment LICOR the front disk and the rear disk lor use in the AFPM have been constructed and equipped with pressure sensors and the necessary electronics. The pressure exerted by the oscillating liquid column on trie supporting disks vsas as low as 10 Pa. Since the data downlink of the Materials Research Laboratory was just one signal oer second and channel, it was necessary to determine amplitude and phase of the pressure already in the LICOR disks. The D-2 experiment has been successfully performed. It has fully confirmed the theoretical models and remarkably supplements the experiments on small liquid columns and on density-matched columns
Optical absorption of divalent metal tungstates: Correlation between the band-gap energy and the cation ionic radius
We have carried out optical-absorption and reflectance measurements at room
temperature in single crystals of AWO4 tungstates (A = Ba, Ca, Cd, Cu, Pb, Sr,
and Zn). From the experimental results their band-gap energy has been
determined to be 5.26 eV (BaWO4), 5.08 eV (SrWO4), 4.94 eV (CaWO4), 4.15 eV
(CdWO4), 3.9-4.4 eV (ZnWO4), 3.8-4.2 eV (PbWO4), and 2.3 eV (CuWO4). The
results are discussed in terms of the electronic structure of the studied
tungstates. It has been found that those compounds where only the s electron
states of the A2+ cation hybridize with the O 2p and W 5d states (e.g BaWO4)
have larger band-gap energies than those where also p, d, and f states of the
A2+ cation contribute to the top of the valence band and the bottom of the
conduction band (e.g. PbWO4). The results are of importance in view of the
large discrepancies existent in prevoiusly published data.Comment: 16 pages, 3 figures, 1 tabl
Supervised physical activity during pregnancy improves fetal cardiac response
Objetivo: Valorar la influencia de un programa de ejercicio fÃsico durante la gestación en la adaptación de la frecuencia cardiaca fetal (FCF). Se espera encontrar una mejor adaptación de la FCF especialmente en cuanto a recuperaciones más rápidas.
Método: 45 gestantes participantes en un ensayo clÃnico aleatorizado sin complicaciones ni contraindicaciones para el ejercicio fueron estudiadas durante el tercer trimestre de embarazo. Se midieron las siguientes variables: FCF en reposo, FCF post-ejercicio y tiempo de recuperación de la FCF a los niveles de reposo.
Resultados: La FCF en reposo fue similar en ambos grupos. La FCF post-ejercicio fue significativamente mayor en el grupo control (GC) que en el grupo ejercicio (GE) en ambas pruebas, al 40% GE=138,5±6,4GE vs 141±7,5 GC (p=0,001), al 60% 141,6±10,8 GE vs 150,3±16,8GC. Lo mismo ocurre en los tiempos de recuperación, al 40% 78,2±95,7GE vs 328,4±315,2GC (p=0,001), al 60% 193,3±257,8 GE vs 542,6±482,9GC (p=0,003).
Conclusión: El ejercicio fÃsico desarrollado durante el embarazo tiene como consecuencia una mejor adaptación de la FCF post-ejercicio, asà como recuperaciones más rápidas.Objective: To assess the influence of a physical activity program during pregnancy on the adaptation of the fetal heart rate (FHR). Greater adaptations and faster recovery are expected to find.
Methods: 45 pregnant women included in a randomized control trial, all with uncomplicated pregnancies for exercise were studied in their third trimester of pregnancy. Rest FHR, post-exercise FHR and recovery time were assessed.
Results: Rest FHR was similar in both groups. Post-exercise FHR were significantly higher in control group (CG) than in exercise group (EG) in both test, 40% 138,5±6,4EG vs 141±7,5CG (p=0,001), 60% 141,6±10,8EG vs 150,3±16,8CG. The same was found in recovery time, 40% 78,2±95,7EG vs 328,4±315,2CG (p=0,001), al 60% 193,3±257,8EG vs 542,6±482,9CG (p=0,003)
La enseñanza de las ciencias en algunas instituciones educativas del estado de jalisco
El objeto de investigación en este estudio es el diagnóstico de las prácticas y los saberes cientÃficos de los agentes educativos, docentes y estudiantes, desde el nivel de educación preescolar hasta la educación superior tecnológica. La perspectiva es desde el marco de la cultura y el significado en uso. La investigación que se expone es descriptiva, de tipo diagnóstica, con un enfoque cualitativo. El método utilizado es la entrevista en grupos focales, con la intención de recuperar los significados referidos a la enseñanza, el aprendizaje y los saberes de las ciencias naturales y las matemáticas de los profesores del estado de Jalisco en México. Los reusltados dan pauta para conocer los significados cientìficos que cotidianamente utilizan los docentes y que se convierten en el referente desde donde enseñan las ciencias y las matemáticas
Exercise during pregnancy. A narrative review asking: What do we know?
Although there is no consensus as to whether exercise is beneficial during pregnancy, most studies report it poses no risk to either the mother or the fetus, and many suggest it to be beneficial to both. This review, which examines the evidence available, also reveals the many differences in study design followed, the type of exercise undertaken and the variables measured, which make it difficult to compare results. Advances in our understanding of the effects of exercise during pregnancy might best be made by undertaking randomised clinical trials with standardised protocols. However, most of the studies examining the relationship between exercise and pregnancy report no complications on maternal or fetal well-being. This is also in line with recent review studies advising that the pregnant population without obstetric contraindications should be encouraged to exercise during pregnancy. Therefore, the results of the present review stimulate those responsible for the healthcare of the pregnant woman to recommend moderate exercise throughout pregnancy without risk to maternal and fetal health
High-pressure structural investigation of several zircon-type orthovanadates
Room temperature angle-dispersive x-ray diffraction measurements on
zircon-type EuVO4, LuVO4, and ScVO4 were performed up to 27 GPa. In the three
compounds we found evidence of a pressure-induced structural phase
transformation from zircon to a scheelite-type structure. The onset of the
transition is near 8 GPa, but the transition is sluggish and the low- and
high-pressure phases coexist in a pressure range of about 10 GPa. In EuVO4 and
LuVO4 a second transition to a M-fergusonite-type phase was found near 21 GPa.
The equations of state for the zircon and scheelite phases are also determined.
Among the three studied compounds, we found that ScVO4 is less compressible
than EuVO4 and LuVO4, being the most incompressible orthovanadate studied to
date. The sequence of structural transitions and compressibilities are
discussed in comparison with other zircon-type oxides.Comment: 34 pages, 2 Tables, 11 Figure
"A Decentralized Operations Concept for the European Payloads on the International Space Station"
The European Module Columbus of the International Space Station (ISS) is planned to be launched 2004. For its exploitation phase as well as for the early utilisation of the Space Station starting from 2003 onwards the operations procedures are now being defined in detail and the implementation of specific infrastructure has started. A decentralised operations concept will allow the investigators to perform their experiments using the telescience technique of remote experiment operations whenever feasible. User Support and Operation Centres (USOCs) will act as Facility Responsible Centres (FRC) performing the operations for multi user experiment facilities. The Columbus Control Centre (COL-CC) will perform the Columbus system operations, co-ordinate the European payload operations and provide the European Communications network. This paper gives an overview on the operations concepts and the tasks and set up of the involved sites
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Farmers' management of rice varietal diversity in the mid-hills of Nepal: implications for on-farm conservation and crop improvement
Season-long monitoring of on-farm rice (Oryza sativa, L.) plots in Nepal explored farmers' decision-making process on the deployment of varieties to agroecosystems, application of production inputs to varieties, agronomic practices and relationship between economic return and area planted per variety. Farmers deploy varieties [landraces (LRs) and modern varieties (MVs)] to agroecosystems based on their understanding of characteristics of varieties and agroecosystems, and the interaction between them. In marginal growing conditions, LRs can compete with MVs. Within an agroecosystem, economic return and area planted to varieties have positive relationship, but this is not so between agroecosystems. LRs are very diverse on agronomic and economic traits; therefore, they cannot be rejected a priori as inferior materials without proper evaluation. LRs have to be evaluated for useful traits and utilized in breeding programmes to generate farmer-preferred materials for marginal environments and for their conservation on-farm
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