417 research outputs found
Vection-induced gastric dysrhythmias and motion sickness
Gastric electrical and mechanical activity during vection-induced motion sickness was investigated. The contractile events of the antrum and gastric myoelectric activity in healthy subjects exposed to vection were measured simultaneously. Symptomatic and myoelectric responses of subjects with vagotomy and gastric resections during vection stimuli were determined. And laboratory based computer systems for analysis of the myoelectric signal were developed. Gastric myoelectric activity was recorded from cutaneous electrodes, i.e., electrogastrograms (EGGs), and antral contractions were measured with intraluminal pressure transducers. Vection was induced by a rotating drum. gastric electromechanical activity was recorded during three periods: 15 min baseline, 15 min drum rotation (vection), and 15 to 30 min recovery. Preliminary results showed that catecholamine responses in nauseated versus symptom-free subjects were divergent and pretreatment with metoclopramide HC1 (Reglan) prevented vection-induced nausea and reduced tachygastrias in two previously symptomatic subjects
Aerospace Medicine and Biology: A continuing bibliography with indexes (supplement 274)
This bibliography lists 128 reports, articles, and other documents introduced into the NASA scientific and technical information system in July 1985
Raised electrical uterine activity and shortened cervical length could predict preterm delivery in a low-risk population
PURPOSE:
To compare diagnostic accuracy of sonographic cervical length (CL) measurement and uterine electric activity assessed by electromyography (EMG) in second trimester regarding prediction of preterm delivery (PTD). ----- METHODS:
Prospective study of 308 low-risk women. Shortened CL was defined as ≤25 mm (≤5th centile), while raised EMG activity was defined as the presence of ≥20 action potentials in 20 min of assessment (≥95th centile). Outcome measures were diagnostic accuracy of both tests alone or in combination for prediction of PTD and early PTD (≤34 weeks). ----- RESULTS:
The incidence of PTD was 23/308 (7.4%) while the incidence of early PTD was 9/308 (2.9%). Shortened CL and raised EMG activity were significantly related to PTD [prevalence-weighted likelihood ratio (pw-LR) 1.9, 95% CI 1.0-3.5 vs. 9.5, 95% CI 2.5-35.7], but not to early PTD (pw-LR 0.4, 95% CI 0.2-0.8 vs. 0.6, 95% CI 0.3-1.7). Significant predictive value for early PTD was found only if both tests were combined (pw-LR 4, 95% CI 1.3-14.3). ----- CONCLUSION:
Shortened CL and raised EMG activity in second trimester have significant diagnostic accuracy regarding prediction of PTD in a low-risk population. However, in order to be useful as a predictor for early PTD both tests must be positive
Materials for hydrogen storage
In the present article two systems studied theoretically in the Physics De-partment of the Universidad Nacional del Sur are presented. Both are related to the Physics of Ma-terials, more specifically to intermetallic hydrogen storage materials, and have been developed using self-consistent Density Functional Theory (DFT) calculations. DFT is a phenomenally successful approach to finding solutions to the fundamental expression that describes the quantum behaviour of atoms and molecules, the Schrödinger equation, in settings of practical value.Laves phases, under the representative forms cubic MgCu2 (C15) and hexagonal MgZn2 (C14) and MgNi2 (C36), have been extensively studied due to their promising behavior as solid state hy-drogen storage materials, ease of synthesis by the conventional cast methods, flexibility in tailoring the thermodynamic properties and good absorp-tion/desorption kinetics and cycle life. However, they cannot be used for technological applications because of its too strong hydride stability at room temperature.In this work we studied the hydrogen absorp-tion for Zr(Cr0.5Ni0.5)2, isostructural with the MgZn2 Laves phase, with the aim to find the most energetically favorable interstitial sites to locate hydrogen. Bulk modulus and volume cell changes due to the hydrogenation process were also ana-lyzed for this phase.According to literature, the most stable were the A2B2 sites, with an absorption energy average of -0.25 eV, followed by the AB3 sites. Bulk Modu-lus fluctuated in the range of 150 and165 GPa.Fil: Robina Merlino, Ariana Melisa. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Pronsato, Maria Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentin
Towards local electromechanical probing of cellular and biomolecular systems in a liquid environment
Electromechanical coupling is ubiquitous in biological systems with examples
ranging from simple piezoelectricity in calcified and connective tissues to
voltage-gated ion channels, energy storage in mitochondria, and
electromechanical activity in cardiac myocytes and outer hair cell stereocilia.
Piezoresponse force microscopy (PFM) has originally emerged as a technique to
study electromechanical phenomena in ferroelectric materials, and in recent
years, has been employed to study a broad range of non-ferroelectric polar
materials, including piezoelectric biomaterials. At the same time, the
technique has been extended from ambient to liquid imaging on model
ferroelectric systems. Here, we present results on local electromechanical
probing of several model cellular and biomolecular systems, including insulin
and lysozyme amyloid fibrils, breast adenocarcinoma cells, and
bacteriorhodopsin in a liquid environment. The specific features of SPM
operation in liquid are delineated and bottlenecks on the route towards
nanometer-resolution electromechanical imaging of biological systems are
identified.Comment: 37 pages (including refs), 8 figure
Dynamic Behavior in Piezoresponse Force Microscopy
Frequency dependent dynamic behavior in Piezoresponse Force Microscopy (PFM)
implemented on a beam-deflection atomic force microscope (AFM) is analyzed
using a combination of modeling and experimental measurements. The PFM signal
comprises contributions from local electrostatic forces acting on the tip,
distributed forces acting on the cantilever, and three components of the
electromechanical response vector. These interactions result in the bending and
torsion of the cantilever, detected as vertical and lateral PFM signals. The
relative magnitudes of these contributions depend on geometric parameters of
the system, the stiffness and frictional forces of tip-surface junction, and
operation frequencies. The dynamic signal formation mechanism in PFM is
analyzed and conditions for optimal PFM imaging are formulated. The
experimental approach for probing cantilever dynamics using frequency-bias
spectroscopy and deconvolution of electromechanical and electrostatic contrast
is implemented.Comment: 65 pages, 15 figures, high quality version available upon reques
Differentiation of endothelin-1 and endothelin-3 concentrations
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