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21.
Dispersive liquid–liquid microextraction based on solidification of floating organic droplet for the determination of triazine and triazoles in mineral water samples 下载免费PDF全文
Cátia M. Bolzan Sergiane S. Caldas Bruno S. Guimarães Ednei G. Primel 《Journal of separation science》2016,39(17):3410-3417
A simple, rapid, and sensitive method for the determination of atrazine, simazine, cyproconazole, tebuconazole, and epoxiconazole in mineral water employing the dispersive liquid–liquid microextraction with solidification of a floating organic drop with determination by liquid chromatography tandem mass spectrometry has been developed. A mixed solution of 250 μL 1‐dodecanol and 1250 μL methanol was injected rapidly into 10 mL aqueous solution (pH 7.0) with 2% w/v NaCl. After centrifugation for 5 min at 2000 rpm, the organic solvent droplets floated on the surface of the aqueous solution and the floating solvent solidified. The method limits of detection were between 3.75 and 37.5 ng/L and limits of quantification were between 12.5 and 125 ng/L. The recoveries ranged from 70 to 118% for repeatability and between 76 and 95% for intermediate precision with a relative standard deviation from 2 to 18% for all compounds. Low matrix effect was observed. The proposed method can be successfully applied in routine analysis for determination of pesticide residues in mineral water samples, allowing for monitoring of triazine and triazoles at levels below the regulatory limits set by international and national legislations. 相似文献
22.
Alves-Santos M Dávila LY Petrilli HM Capaz RB Caldas MJ 《Journal of computational chemistry》2006,27(2):217-227
We present a detailed analysis of the application of density functional theory (DFT) methods to the study of structural properties of molecular and supramolecular systems, using as a paradigmatic example three para-phenylene-based systems: isolated biphenyl, single chain poly-para-phenylene, and crystalline biphenyl. We use different functionals for the exchange correlation potential, the local density (LDA), and generalized gradient approximations (GGA), and also different basis sets expansions, localized, plane waves (PW), and mixed (localized plus PW), within the reciprocal space formulation for the hamiltonian. We find that regardless of the choice of basis functions, the GGA calculations yield larger interring distances and torsion angles than LDA. For the same XC approximation, the agreement between calculations with different basis functions lies within 1% (LDA) or 0.5% (GGA) for distances, and while PW and mixed basis calculations agree within 1 degrees for torsion angles, the localized basis results show larger angles by approximately 8 degrees and a nonmonotonic dependence on basis size, with differences within 6 degrees. The most prominent features, namely the torsion between rings for isolated molecule and infinite chain, and planarity for the molecule in crystalline environment, are well reproduced by all DFT calculations. 相似文献
23.
We analytically describe the complex scenario of homoclinic bifurcations in the Chua's circuit. We obtain a general scaling law that gives the ratio between bifurcation parameters of different nearby homoclinic orbits. As an application of this theoretical approach, we estimate the number of higher order subsidiary homoclinic orbits that appear between two consecutive lower order subsidiary orbits. Our analytical finds might be valid for a large class of dynamical systems and are numerically confirmed in the parameter space of the Chua's circuit. 相似文献
24.
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
25.
Evidences of internal particle transport barriers have been observed in plasma discharges with reversed plasma flow. To investigate the influence of the radial electric field profile on these barriers, we apply a drift wave map that describe the plasma particle transport and allows the integration of particle drift in the presence of a given electrostatic turbulence spectrum. With this procedure we show that transport barriers due to the shearless flow invariant lines are created inside the plasma. Moreover, by varying the radial electric field profile, we observe the formation and destruction of internal transport barriers constituted by shearless invariant lines, as well as its effects on the transport in the map's phase space. Applicability of our results are discussed for the Texas Helimak, a toroidal plasma device in which the radial electric field can be changed by application of bias potential. 相似文献
26.
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
27.
Multi-residue analytical methods for the determination of pesticides and PPCPs in water by LC-MS/MS: a review 总被引:1,自引:0,他引:1
Ednei G. Primel Sergiane S. Caldas Ana L. V. Escarrone 《Central European Journal of Chemistry》2012,10(3):876-899
Residues of pesticides, pharmaceutical and personal care products (PPCPs) are contaminants of world-wide concern. Consequently,
there is a growing need to develop reliable analytical methods, which enable rapid, sensitive and selective determination
of these pollutants in environmental samples, at trace levels. In this paper, a review of the liquid chromatography-tandem
mass spectrometry (LC-MS/MS) based methods for the determination of pesticides and PPCPs in the environment is presented.
Advanced aspects of current LC-MS/MS methodology, including sample preparation and matrix effects, are discussed. 相似文献
28.
29.
D.S. Covita C.D.R. AzevedoC.C. Caldas J.F.C.A. Veloso 《Physics letters. [Part B]》2011,701(2):151-154
Photoelectron extraction efficiency is a key parameter in gaseous detectors design requiring CsI photocathodes, particularly in pressurized applications for rare event experiments. Within this work we report on our measurements of the photoelectron extraction efficiency from a CsI photocathode into argon and xenon up to 10 atm. It is demonstrated that the photoelectron extraction efficiency is independent from pressure when scaling the electric field accordingly. This measurement provides experimental validation to the Monte Carlo predictions. 相似文献
30.
The Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) states, characterized by Cooper pairs condensed at finite-momentum are, at the same time, exotic and elusive. It is partially due to the fact that the FFLO states allow superconductivity to survive even in strong magnetic fields at the mean-field level. The effects of induced interactions at zero temperature are calculated in both clean and dirty cases, and it is found that the critical field at which the quantum phase transition to an FFLO state occurs at the mean-field level is strongly suppressed in imbalanced Fermi gases. This strongly shrinks the phase space region where the FFLO state is unstable and more exotic ground state is to be found. In the presence of high level impurities, this shrinkage may destroy the FFLO state completely. 相似文献