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41.
We have investigated plasma turbulence at the edge of a tokamak plasma using data from electrostatic potential fluctuations measured in the Brazilian tokamak TCABR. Recurrence quantification analysis has been used to provide diagnostics of the deterministic content of the series. We have focused our analysis on the radial dependence of potential fluctuations and their characterization by recurrence-based diagnostics. Our main result is that the deterministic content of the experimental signals is most pronounced at the external part of the plasma column just before the plasma radius. Since the chaoticity of the signals follows the same trend, we have concluded that the electrostatic plasma turbulence at the tokamak plasma edge can be partially explained by means of a deterministic nonlinear system. 相似文献
42.
de Melo JV Vasconcelos RH Furtado AF Peixoto CA Silva-Filha MH 《Micron (Oxford, England : 1993)》2008,39(8):1342-1350
The larvicidal action of the entomopathogen Bacillus sphaericus towards Culex quinquefasciatus is due to the binary (Bin) toxin present in crystals, which are produced during bacterial sporulation. The Bin toxin needs to recognize and bind specifically to a single class of receptors, named Cqm1, which are 60-kDa α-glucosidases attached to the apical membrane of midgut cells by a glycosylphosphatidylinositol anchor. C. quinquefasciatus resistance to B. sphaericus has been often associated with the absence of the α-glucosidase Cqm1 in larvae midgut microvilli. In this work, we aimed to investigate, at the ultrastructural level, the midgut cells from C. quinquefasciatus larvae whose resistance relies on the lack of the Cqm1 receptor. The morphological analysis showed that midgut columnar cells from the resistant larvae are characterized by a pronounced production of lipid inclusions, throughout the 4th instar. At the end of this stage, resistant larvae had an increased size and number of these inclusions in the midgut cells, while only a small number were observed in the cells from susceptible larvae. The morphological differences in the midgut cells of resistant larvae found in this work suggested that the lack of the Cqm1 receptor, which also has a physiological role as being an α-glucosidase, can be related to changes in the cell metabolism. The ultrastructural effects of Bin toxin on midgut epithelial cells from susceptible and resistant larvae were also investigated. The cytopathological alterations observed in susceptible larvae treated with a lethal concentration of toxin included breakdown of the endoplasmic reticulum, mitochondrial swelling, microvillar disruption and vacuolization. Some effects were observed in cells from resistant larvae, although those alterations did not lead to larval death, indicating that the receptor Cqm1 is essential to mediate the larvicidal action of the toxin.This is the first ultrastructural study to show differences in the cell morphology of resistant larvae and further investigation is needed to understand the impact of the lack of expression of midgut enzymes on the physiology of resistant insects. 相似文献
43.
The origin of paramagnetic centers in graphite-like amorphous carbon is investigated. The films were deposited by the ion beam assisted deposition (IBAD) and have a concentration of sp2 sites of about 90% and zero energy band gap. The density of the film and the electrical resistivity are close to these of crystalline graphite. However, the hardness and stress of the films are similar to those of diamond-like carbon. Electron spin resonance (ESR) performed at the X-band (9.4 GHz) revealed an unexpected low density of paramagnetic centers, ascribed to conduction electrons with a g-value of about 2.003. 相似文献
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45.
Felipe A. C. Viana Valder SteffenJr. Sergio Butkewitsch Marcus de Freitas Leal 《Journal of Global Optimization》2009,45(3):427-449
In this work, a flat pressure bulkhead reinforced by an array of beams is designed using a suite of heuristic optimization
methods (Ant Colony Optimization, Genetic Algorithms, Particle Swarm Optimization and LifeCycle Optimization), and the Nelder-Mead
simplex direct search method. The compromise between numerical performance and computational cost is addressed, calling for
inexpensive, yet accurate analysis procedures. At this point, variable fidelity is proposed as a tradeoff solution. The difference
between the low-fidelity and high-fidelity models at several points is used to fit a surrogate that corrects the low-fidelity
model at other points. This allows faster linear analyses during the optimization; whilst a reduced set of expensive non-linear
analyses are run “off-line,” enhancing the linear results according to the physics of the structure. Numerical results report
the success of the proposed methodology when applied to aircraft structural components. The main conclusions of the work are
(i) the variable fidelity approach enabled the use of intensive computing heuristic optimization techniques; and (ii) this
framework succeeded in exploring the design space, providing good initial designs for classical optimization techniques. The
final design is obtained when validating the candidate solutions issued from both heuristic and classical optimization. Then,
the best design can be chosen by direct comparison of the high-fidelity responses. 相似文献
46.
Michele Mugnaine Adriane S. Reis Fernando S. Borges Rafael R. Borges Fabiano A. S. Ferrari Kelly C. Iarosz Ibere L. Caldas Ewandson L. Lameu Ricardo L. Viana Jose D. SzezechJr. Jürgen Kurths Antonio M. Batista 《The European physical journal. Special topics》2018,227(10-11):1151-1160
The human cerebral cortex can be separated into cortical areas forming a clustered network structure. We build two different clustered networks, where one network is based on a healthy brain and the other according to a brain affected by a neurodegenerative process. Each cortical area has a subnetwork with small-world properties. We verify that both networks exhibit rich-club organisation and phase synchronisation. Due to the fact that neuronal synchronisation can be related to brain diseases, we consider the delayed feedback control as a method to suppress synchronous behaviours. In this work, it is presented that depending on the feedback parameters, intensity and time delay, phase synchronisation in both networks can be suppressed. Therefore, one of our main results is to show that delayed feedback control can be used to suppress undesired synchronous behaviours not only in the healthy brain, but also in the brain marked by neurodegenerative processes. 相似文献
47.
A liquid chromatography‐atmospheric pressure photoionization tandem mass spectrometric (LC‐APPI‐MS/MS) method for the determination of triterpenoids in medicinal plant extracts 下载免费PDF全文
Luciana Assis Gobo Carine Viana Osmar Alves Lameira Leandro Machado de Carvalho 《Journal of mass spectrometry : JMS》2016,51(8):558-565
An analytical method using liquid chromatography‐atmospheric pressure photoionization tandem mass spectrometry with toluene as a dopant was developed for the determination of triterpenes in medicinal plant extracts. The 12 compounds determined have been shown to exhibit biological activity, such as gastroprotective, hepatoprotective, anti‐inflammatory, antiviral and anti‐tumor effects. The parameters of the atmospheric pressure photoionization interface were optimized to obtain the highest possible sensitivity for all of the compounds. The limits of detection and quantification ranged from 0.4 to 157.9 µg l?1 and 1.3 to 526.4 µg l?1, respectively. The method was validated and applied to extracts of five medicinal plants species (Mansoa alliacea (Lam.) A.H.Gentry, Bauhinia variegata var variegata, Bauhinia variegata var alboflava, Cecropia obtuse Trécul and Cecropia palmate Willd) from the Amazonian region. The concentrations of the six triterpenes quantified in the samples ranged from 0.424 mg kg?1 for ursolic acid to 371.96 mg kg?1 for β‐amyrin, which were quantified by using the standard addition method (n = 3). Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
48.
Trigueiro João Paulo C. Figueiredo Rute C. Rojo Javier Viana Renato M. R. Schnitzler Mariane C. Silva Glaura G. 《Journal of Solid State Electrochemistry》2016,20(7):1991-2000
Journal of Solid State Electrochemistry - Carbon nanotubes (CNTs) were surface-modified by a glycodendrimer with four glucose units (4-Gl). Electrodes for supercapacitors based on CNT/4-Gl hybrids... 相似文献
49.
50.
K.C. IaroszA.M. Batista R.L. Viana S.R. LopesI.L. Caldas T.J.P. Penna 《Physica A》2012,391(3):819-827
We study the firing rate properties of a cellular automaton model for a neuronal network with chemical synapses. We propose a simple mechanism in which the nonlocal connections are included, through electrical and chemical synapses. In the latter case, we introduce a time delay which produces self-sustained activity. Nonlocal connections, or shortcuts, are randomly introduced according to a specified connection probability. There is a range of connection probabilities for which neuron firing occurs, as well as a critical probability for which the firing ceases in the absence of time delay. The critical probability for nonlocal shortcuts depends on the network size according to a power-law. We also compute the firing rate amplification factor by varying both the connection probability and the time delay for different network sizes. 相似文献