This paper proposes a control scheme that allows doubly fed induction wind generators (DFIWG) to participate effectively in system frequency regulation. In this control approach, wind generators ...operate according to a deloaded optimum power extraction curve such that the active power provided by each wind turbine increases or decreases during system frequency changes. The control strategy defined at the wind generator to supply primary frequency regulation capability exploits a combination of control of the static converters and pitch control, adjusting the rotor speed and the active power according to the deloaded optimum power extraction curve. Results obtained in a small isolated system are presented to demonstrate the effectiveness of the approach.
This paper presents a conceptual framework to successfully integrate electric vehicles into electric power systems. The proposed framework covers two different domains: the grid technical operation ...and the electricity markets environment. All the players involved in both these processes, as well as their activities, are described in detail. Additionally, several simulations are presented in order to illustrate the potential impacts/benefits arising from the electric vehicles grid integration under the referred framework, comprising steady-state and dynamic behavior analysis.
In this study, montmorillonite clay (MC) has been utilized as the adsorbent for the removal of a cationic dye, methylene blue (MB), from aqueous solution by the batch adsorption technique under ...different conditions of initial dye concentration, adsorbent concentration, contact time, solution pH, and temperature. Attempts were made to fit the isothermal data using Langmuir and Freundlich equations. The experimental results have demonstrated that the equilibrium data are fitted well by a Langmuir isotherm equation. Thermodynamic parameters such as the changes in enthalpy, entropy, and Gibbs' free energy were determined, showing adsorption to be an endothermic yet spontaneous process. Pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were considered to evaluate the rate parameters. The experimental data fitted the pseudo-second-order kinetic model, with an activation energy of +28.5 kJ mol
−1. The results indicate that MC adsorbs MB efficiently and could be employed as a low-cost alternative in wastewater treatment for the removal of cationic dyes.
Effect of initial methylene blue concentration on the adsorption onto montmorillonite clay. More MB was retained and the adsorption mechanism became more efficient, as the initial dye concentration increased.
Convectively Driven Vortex Flows in the Sun Bonet, J. A; Márquez, I; Sánchez Almeida, J ...
Astrophysical journal/The Astrophysical journal,
11/2008, Letnik:
687, Številka:
2
Journal Article
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We have discovered small whirlpools in the Sun, with a size similar to terrestrial hurricanes (image0.5 Mm). The theory of solar convection predicts them, but they had remained elusive so far. The ...vortex flows are created at the downdrafts where the plasma returns to the solar interior after cooling down, and we detect them because some magnetic bright points (BPs) follow a logarithmic spiral on their way to being engulfed by a downdraft. Our disk-center observations show 0.9 x 10 super(-2) vortexes per Mm super(2), with a lifetime of the order of 5 minutes, and with no preferred sense of rotation. They are not evenly spread out over the surface, but they seem to trace the supergranulation and the mesogranulation. These observed properties are strongly biased by our type of measurement, unable to detect vortexes except when they are engulfing magnetic BPs.
The mechanisms underlying the initiation/onset of, and the recovery from, depression are still largely unknown; views that neurogenesis in the hippocampus may be important for the pathogenesis and ...amelioration of depressive symptoms have gained currency over the years although the original evidence has been challenged. In this study, an unpredictable chronic mild stress protocol was used to induce a depressive-like phenotype in rats. In the last 2 weeks of stress exposure, animals were treated with the antidepressants fluoxetine, imipramine, CP 156,526 or SSR 1494515, alone or combined with methylazoxymethanol, a cytostatic agent used to arrest neurogenesis. We found that antidepressants retain their therapeutic efficacy in reducing both measured indices of depression-like behavior (learned helplessness and anhedonia), even when neurogenesis is blocked. Instead, our experiments suggest re-establishment of neuronal plasticity (dendritic remodeling and synaptic contacts) in the hippocampus and prefrontal cortex, rather than neurogenesis, as the basis for the restoration of behavioral homeostasis by antidepressants.
Co-encapsulation of drugs directed at commonly associated diseases provides a convenient means for administration, especially if transdermally delivered.
In this work, a comprehensive study for the ...co-encapsulation of drugs with a differential lipophilicity, olanzapine and simvastatin, and their transdermal delivery in a formulation containing nanostructured lipid carriers (NLC) is presented. Focus is given to the evaluation of a strategy in which NLC and chemical permeation enhancers are combined. It comprises in vitro, in silico and cellular viability approaches. The optimization and rationalization of the systems are carried out using a two-step factorial design. It is shown that the external medium in the NLC dispersion strongly influences permeation. It is also seen that the use of NLC determines a synergistic effect with selected permeation enhancers, thus promoting marked flux enhancement ratios (48 and 21, respectively for olanzapine and simvastatin) relative to the drugs in solution. The developed formulations can be considered non-irritant. A correlation between enhancer positioning in a lipid bilayer, partially governed by a H-bonding phenomenon, and enhancement effect is suggested from molecular dynamics studies and experimental observations.
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•Montmorillonite was modified with cetyltrimethylammonium bromide.•The modification was confirmed by FTIR, TG/DTA, XRD, SEM/EDX, specific surface area, and zeta potential ...measurements.•The kinetics of adsorption were described by a pseudo-second order model.•The thermodynamic parameters showed a non-spontaneous, exothermic process.•MCCTA has potential use as an adsorbent of p-nitrophenol from aqueous media.
Montmorillonite clay (MC) yields after modification of the interlamellar spacing and the chemical character of its surface by treatment with cetyltrimethylammonium bromide (CTAB) a solid product (MCCTA). This has been used as an adsorbent for the removal of p-nitrophenol (PNP) from aqueous solutions. The MCCTA samples were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TG/DTA), FT-IR spectroscopy, zeta potential measurements, X-ray diffraction (XRD), and specific surface area. Investigations were also carried out to assess how the adsorption of PNP was affected by factors such as contact time, initial PNP concentration, adsorbent dosage and temperature. Of the two models tried the Freundlich isotherm gave a better account of the equilibrium data than did the Langmuir one. The kinetics could be successfully replicated by a pseudo-second order model with an activation energy of 55.0 kJ mol−1, while the thermodynamic parameters indicated an exothermic (ΔadsHo = −15.8 kJ mol−1), non-spontaneous (ΔadsGo = + 3.9–5.9 kJ mol−1) adsorption process. The experimental results showed MCCTA, unlike natural MC, to have a significant adsorption capacity for PNP removal from aqueous media.
We report strong evidence of the importance of contact hubs (or superspreaders) in mitigating the current COVID-19 pandemic. Contact hubs have a much larger number of contacts than the average in the ...population, and play a key role on the effectiveness of vaccination strategies. By using an age-structures compartmental SEIAHRV (Susceptible, Exposed, Infected symptomatic, Asymptomatic, Hospitalized, Recovered, Vaccinated) model, calibrated from available demographic and COVID-19 incidence, and considering separately those individuals with a much greater number of contacts than the average in the population, we show that carefully choosing who will compose the first group to be vaccinated can impact positively the total death toll and the demand for health services. This is even more relevant in countries with a lack of basic resources for proper vaccination and a significant reduction in social isolation. In order to demonstrate our approach we show the effect of hypothetical vaccination scenarios in two countries of very different scales and mitigation policies, Brazil and Portugal.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Using the k-means cluster analysis algorithm, we carry out an unsupervised classification of all galaxy spectra in the seventh and final Sloan Digital Sky Survey data release (SDSS/DR7). Except for ...the shift to rest-frame wavelengths and the normalization to the g-band flux, no manipulation is applied to the original spectra. The algorithm guarantees that galaxies with similar spectra belong to the same class. We find that 99% of the galaxies can be assigned to only 17 major classes, with 11 additional minor classes including the remaining 1%. The classification is not unique since many galaxies appear in between classes; however, our rendering of the algorithm overcomes this weakness with a tool to identify borderline galaxies. Each class is characterized by a template spectrum, which is the average of all the spectra of the galaxies in the class. These low-noise template spectra vary smoothly and continuously along a sequence labeled from 0 to 27, from the reddest class to the bluest class. Our Automatic Spectroscopic K-means-based (ASK) classification separates galaxies in colors, with classes characteristic of the red sequence, the blue cloud, as well as the green valley. When red sequence galaxies and green valley galaxies present emission lines, they are characteristic of active galactic nucleus activity. Blue galaxy classes have emission lines corresponding to star formation regions. We find the expected correlation between spectroscopic class and Hubble type, but this relationship exhibits a high intrinsic scatter. Several potential uses of the ASK classification are identified and sketched, including fast determination of physical properties by interpolation, classes as templates in redshift determinations, and target selection in follow-up works (we find classes of Seyfert galaxies, green valley galaxies, as well as a significant number of outliers). The ASK classification is publicly accessible through various Web sites.
Biological scaffolds generated from tissue-derived extracellular matrix (ECM) are commonly used clinically for soft tissue regeneration. Such biomaterials can enhance tissue-specific differentiation ...of adult stem cells, suggesting that structuring different ECMs into multi-layered scaffolds can form the basis of new strategies for regenerating damaged interfacial tissues such as the osteochondral unit. In this study, mass spectrometry is used to demonstrate that growth plate (GP) and articular cartilage (AC) ECMs contain a unique array of regulatory proteins that may be particularly suited to bone and cartilage repair respectively. Applying a novel iterative freeze-drying method, porous bi-phasic scaffolds composed of GP ECM overlaid by AC ECM are fabricated, which are capable of spatially directing stem cell differentiation in vitro, promoting the development of graded tissues transitioning from calcified cartilage to hyaline-like cartilage. Evaluating repair 12-months post-implantation into critically-sized caprine osteochondral defects reveals that these scaffolds promote regeneration in a manner distinct to commercial control-scaffolds. The GP layer supports endochondral bone formation, while the AC layer stimulates the formation of an overlying layer of hyaline cartilage with a collagen fiber architecture better recapitulating the native tissue. These findings support the use of a bi-layered, tissue-specific ECM derived scaffolds for regenerating spatially complex musculoskeletal tissues.
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