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•Novel porous covalent organic framework was used as SPME adsorbent.•The synthesized COF showed high thermal stability, large surface area, and high crystallinity.•A GC-CD-IMS ...instrument was used to determine chlorpyrifos and trifluralin, simultaneously.
Novel porous covalent organic framework (COF) based on condensation reaction between cyanuric chloride, 4,4′-ethylendianiline, and 3,4,9,10-perylenetetracarboxylic dianhydride was synthesized via sealed tube condition. The results COF was used as a new adsorbent for solid-phase microextraction (SPME) for extracting trifluralin and chlorpyrifos from vegetables, fruit samples, and wastewater. Gas chromatograph with a corona discharge-ion mobility spectrometer as the detector was also used for analyzing the target analytes. Some parameters that affected the extraction, such as stirring rate, time and temperature of extraction and pH were investigated, exhaustively. The detection limits were 0.13, and 0.15 µg/L and the linear ranges of 0.45–20 and 0.50–25 µg/L with a linearity coefficient of 0.9965 and 0.9987 were also obtained for trifluralin and chlorpyrifos, respectively. The method was applied successfully to analyze some real samples of cucumber, carrot, grape, and agriculture wastewater, and the results showed a relative recovery in the range of 87% to 110%.
Treating PEDOT:PSS (Clevios) with certain additives, such as ethylene glycol (EG), dimethyl sulfoxide (DMSO) and sorbitol, has been shown to increase the conductivity of this material from roughly 1 ...to nearly 1000 S/cm. Using a slow drying method, we show that the additive induced a separation between free PSS and reorganized PEDOT:PSS complexes in the highly conductive PEDOT:PSS films. Additives (DMSO, DEG, and PEG 400) were included in PEDOT:PSS aqueous dispersions at large volume fractions. The mixtures were slowly dried under room conditions. During drying, the evaporation of water resulted in an additive-rich solvent mixture from which the reorganized PEDOT:PSS complexes aggregated into a dense film while free PSS remained in the solution. Upon complete drying, PSS formed a transparent rim film around the conducting PEDOT film. The chemical compositions of the two phases were studied using an infrared microscope. This removal of PSS resulted in more compact packing of PEDOT molecules, as confirmed by X-ray diffraction measurements. X-ray photoelectron spectroscopy and atomic force microscope measurements suggested the enrichment of PEDOT on the film surface after PSS separation. Through a simple drying process in an additive-containing dispersion, the conductivity of PEDOT films increased from 0.1 to 200–400 S/cm. Through this method, we confirmed the existence of two phases in additive-treated and highly conductive PEDOT:PSS films. The proper separation between PSS and PEDOT will be of relevance in designing strategies to process high-performance plastic electrodes.
Wind turbine power curve modeling is an important tool in turbine performance monitoring and power forecasting. There are several statistical techniques to fit the empirical power curve of a wind ...turbine, which can be classified into parametric and nonparametric methods. In this paper, we study four of these methods to estimate the wind turbine power curve. Polynomial regression is studied as the benchmark parametric model, and issues associated with this technique are discussed. We then introduce the locally weighted polynomial regression method, and show its advantages over the polynomial regression. Also, the spline regression method is examined to achieve more flexibility for fitting the power curve. Finally, we develop a penalized spline regression model to address the issues of choosing the number and location of knots in the spline regression. The performance of the presented methods is evaluated using two simulated data sets as well as an actual operational power data of a wind farm in North America.
Sildenafil, approved two decades ago, is the inhibitor of phosphodiesterase 5 (PDE5). First of all, it was designated for angina pectoris, but soon it showed a wonderful efficacy in erectile ...dysfunction (ED) and then pulmonary arterial hypertension (PAH). Due to the distribution of phosphodiesterase (PDE) in almost all organs, maybe it effects other diseases. Hence, a great number of investigations began to understand the role of PDEi in different organs. Preliminary research on sildenafil in cell culture and animal models has yielded promising results. Soon, a greater number of animal researches and clinical trials joined them. The results disclosed sildenafil can have beneficial effects in each organ such as heart, liver, kidney, brain, and intestines. Furthermore, it has significantly improved the prognosis of organ ischemia in various animal models. Clinical trials in several diseases, such as recurrent spontaneous miscarriage, fatty liver disease, bronchopulmonary dysplasia (BPD), heart failure, and premature ejaculation (PE) brought promising results. Although some clinical trials are available on the effects of sildenafil on various diseases, further studies on humans are needed to consolidate the ultimate effects of sildenafil. The aim of this review was to describe the effects of sildenafil on each organ and explain its mechanisms of action. Further, other PDE inhibitors such as tadalafil and vardenafil have been briefly discussed in parts of this review.
Carbon nanotubes (CNTs) are among the most promising materials for applications in future nanotechnology. The combination of excellent physical and mechanical properties beside chemical resistance ...seems very interesting for different industrial applications. However, the commercialization of nanotube-based nanocomposites has been hampered by their high cost and minuscule production. In the present study, we have tried to understand the fundamental aspects of multiwall carbon nanotubes (MWCNTs) direct growth on metal catalyst particles via thermal chemical vapor deposition (T.CVD) in the presence of zirconium hydride (ZrH2) and aluminum nanoparticles. The effects of different parameters such as gas flow rates, metal catalyst systems, and temperature on the quality and quantity of the obtained MWCNTs were investigated and some interesting results were obtained. It was found that at moderate temperatures, MWCNTs growth rate on iron-based (Fe) catalyst was much more than that on nickel (Ni) and cobalt (Co) particles. Transmission electron microscopy (TEM) results and TGA analysis revealed that metal nanoparticles as the nucleation sites come from the fragmentation of catalyst surfaces and the application of relatively small amounts of ZrH2 significantly enhances this mechanism. Besides, crystalline structure of MWCNTs was performed by Raman spectroscopy, X-ray diffraction (XRD) and selected area electron diffraction (SAED) technique. This method shows great promise for achieving the goal of mass-production due to its high quality and yield; simplicity, and ease of scale-up.
•The effect of different parameters on direct growth of MWCNTs with various metal particles was investigated by thermal CVD.•The performance of catalysts was in the order of Iron > nickel > cobalt.•The presence of zirconium hydride was tried as an in situ hydrogen generator and co-catalyst system.
Seismicity parameters can simplify the understanding of the intrinsic complications that arise in the state of stress across the hypocentral areas of interest. We studied variations of the spatial ...and temporal changes of these parameters by three different methods: maximum curvature, entire magnitude range, and hierarchical space time point process model across the July 2019 Ridgecrest earthquake region. In order to verify the estimations, the Utsu’s test has also been applied. According to the results, seismicity parameters show heterogeneous distribution in this area. The implemented methods provide comparable
b
-values; however, the
b
-value displays relatively lower values in northwest and higher values in southeast. Seismicity rate comparison for two periods before and after the M7.1 shock favors change in the
b
-value. Based on the employed catalog, seismic activity accelerated about half an hour before the M6.4 event. Whereas 2 days before the M7.1 earthquake, seismic activity was low and accelerated approximately 1 day prior to the same event. So there is a clear difference in pre M6.4 and pre M7.1 seismic activity patterns. Moreover, the
b
-value and magnitude of completeness show decrease before the M7.1 shock, and spatial changes of the
b
-value expose obvious differences with depth.
Carbon sheets were attached to magnetite (Fe
3
O
4
) nanoparticles. The resulting nanocomposite is shown to be a viable sorbent for use in magnetic dispersive solid-phase microextraction of three ...organophosphorus pesticides. The sorbent was synthesized via the sol-gel process followed by calcination and was characterized by an X-ray diffractometer, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and Raman spectrometry techniques. The affecting parameters in the adsorption and desorption steps were assessed and optimized via response surface methodology. Following desorption with dichloromethane, the OPPs were quantified by gas chromatography along with ion mobility spectrometry detection. Under optimized conditions, the limits of detection were 1.00, 0.46 and 0.85 μg L
−1
for fenthion, malathion and chlorpyrifos, respectively. Response is linear in the concentration range of 2–500 μg L
−1
for fenthion and malathion, and 2–1000 μg L
−1
for chlorpyrifos with the determination coefficient larger than 0.9969. The intra-day and inter-day precision were from 3 to 9% and 5 to 16%, respectively. The enrichment factor was greater than 142 for all the studied pesticides. The sorbent was used for analyze spiked water and vegetable samples and gave relative recovery higher than 82%.
Graphical abstract
A flowchart of the synthesis of porous magnetized carbon sheet nanocomposites and the process of the magnetic dispersive solid-phase microextraction (MD-μ-SPE) of three organophosphorus pesticides prior to analysis by gas chromatography-ion mobility spectrometry (GC-IMS).
The water entry of hollow cylinders is investigated experimentally. Three hollow cylindrical projectiles with the same mass, surface coating, outer diameter, holes' average diameter, and length are ...considered. They have three different holes in the shape of a cylinder, an upward cone, and a downward cone. Hence, all non-dimensional parameters are identical for the same impact velocity. A Pco-DimaxS high-speed camera records the projectiles' trajectory. Given the released heights (from 0.5 cm to 95 cm), the impact velocity approximately varies from 0.31ms−1 to 4.32ms−1. Different air-entrainment characteristics like cavity closure patterns, cavity dimensions/shapes, pinch-off time/depth, water jets, cavity shedding, etc., are detected and discussed. Also, the projectiles' kinetics (velocity, acceleration, and coefficient of hydrodynamic force) is examined. The results show different closure patterns with the change of impact velocity and hole geometry: (1) the deep-seal, (2) the surface-seal on the through-hole-jet, and on the cylinder wall. The through-hole-jet for the cylinder with the downward conical hole has the highest height of the other two projectiles. In addition, as the cylinder with the downward conical hole has the largest impact cross-section, it draws a larger volume of air, and as a result, it shows more resistance to cavity sealing.
•An experimental study concerning the water entry of hollow cylinders is done.•These cylinders have three different holes in the shape of a cylinder, an upward cone and a downward cone.•According to the dimensions of the cylinders, all dimensionless parameters are identical for the same impact velocity.•Different closure patterns with impact velocity and hole geometry change are observed.•The cylinder with a downward conic hole draws a larger air volume, showing more resistance to cavity sealing.
We consider the Bayesian estimation of the parameters of a finite mixture model from independent order statistics arising from imperfect ranked set sampling designs. As a cost‐effective method, ...ranked set sampling enables us to incorporate easily attainable characteristics, as ranking information, into data collection and Bayesian estimation. To handle the special structure of the ranked set samples, we develop a Bayesian estimation approach exploiting the Expectation‐Maximization (EM) algorithm in estimating the ranking parameters and Metropolis within Gibbs Sampling to estimate the parameters of the underlying mixture model. Our findings show that the proposed RSS‐based Bayesian estimation method outperforms the commonly used Bayesian counterpart using simple random sampling. The developed method is finally applied to estimate the bone disorder status of women aged 50 and older.
•Carbon-silica hybrid nanofiber was used for solid-phase microextraction of pesticides.•Two-dimensional separation structure of GC-IMS was used as the detection system.•The method provides the ...acceptable sensitivity and accuracy as well as the rapid analysis.
Carbon-silica hybrid nanofibers as high performance coatings for solid-phase microextraction fibers were used for analyzing some pesticides by using gas chromatography-corona discharge ion mobility spectrometry. To that end, the fibers were prepared by carbonizing sol-gel based on electrospun polyacrylonitrile and tetraethyl orthosilicate nanofibers as carbon and silica precursors, respectively. Different parameters affecting the electrospinning and the extraction processes including spinning distance, voltage, feeding rate, stirring rate, salt concentration, temperature and extraction time were optimized by response surface methodology. The method involved deionized water samples spiked with pesticides at different concentration levels. The calibration curves were linear in the ranges of 0.1–20 and 0.05–20 μg L−1 with determination coefficients (R2) of 0.9976 and 0.9928 for malathion and chlorpyrifos, respectively. The limits of detection of 0.032 and 0.019 μg L−1 and the limits of quantification of 0.1 and 0.05 μg L−1 were found for malathion and chlorpyrifos, respectively. Acceptable reproducibility values were obtained with relative standard deviations (RSD, n = 3) lower than 6 and 15%, for intra-day and inter-day precision, respectively. Finally, the relative recoveries of the proposed method were calculated in the range of 80–111% for real samples.
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