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排序方式: 共有911条查询结果,搜索用时 648 毫秒
901.
Rosa Ana Pérez Beatriz Albero Consuelo Sánchez-Brunete José Luis Tadeo 《International journal of environmental analytical chemistry》2013,93(14):1666-1678
A method for the analysis of chlorotoluenes (CTs) in soil has been developed based on ultrasonic assisted extraction with a low volume of organic solvent and determination by gas chromatography-tandem mass spectrometry (GC–MS/MS). A simultaneous clean-up on an alumina–anhydrous sodium sulphate mixture was carried out to remove soil interferences. However, an additional clean-up with graphitised carbon was needed for some very dirty samples. Several solvents were assayed and a mixture of ethyl acetate:hexane (80?:?20, v/v) was selected to carry out soil extractions. Recovery studies were performed at 0.2, 0.1, 0.05 and 0.02?ng?g?1 fortification levels, and recoveries obtained for all the compounds and concentrations were higher than 81% with standard deviations fulfilling the requirements of the IUPAC. LODs from 0.7 to 5.2?ng?kg?1 and LOQs from 2.2 to 17.5?ng?kg?1 were achieved for the analysed compounds, being pentachlorotoluene the compound with the highest limits, followed by the monochlorinated toluenes. The proposed analytical method was applied to determine CT levels in agricultural and industrial soils. These compounds were found in all the industrial soils analysed and some CTs were present in agricultural soils at lower levels. 相似文献
902.
The interaction between carboxylic acid-stabilised gold nanoparticles (AuNP) and pH-responsive microgels is shown. The microgel particles are a copolymer of N-[3-(dimethylamino)propyl]methacrylamide (DMAPMA) and N-isopropylacrylamide (NIPAM). The microgel properties are presented by their hydrodynamic diameter and electrophoretic mobility in response to pH. These microgel particles are pH-responsive under neutral conditions decreasing in diameter beyond pH 7. The dispersion characteristics of AuNP adsorbed onto the microgel network are shown with respect to adsorbed amount and the pH-responsive properties of the AuNP. This data is presented between pH 3 and 6 where the microgel properties remain constant. Asymmetric adsorption of AuNP onto poly(DMAPMA-co-NIPAM) microgels is achieved by adsorption of nanoparticles, from the aqueous phase, onto microgel-stabilised oil-in-water emulsions. These asymmetrically modified microgels display very different dispersion behaviour, in response to pH, due to their dipolar nature. 相似文献
903.
904.
Santos J Illescas BM Martín N Adrio J Carretero JC Viruela R Ortí E Spänig F Guldi DM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(10):2957-2964
The synthesis of the first fully conjugated tetrathiafulvalene–tetracyano‐p‐quinodimethane ((TTF)–TCNQ)‐type system has been carried out by means of a Julia–Kocienski olefination reaction. In particular, a tetracyanoanthraquinodimethane (TCAQ) formyl derivative and two new sulfonylmethyl‐exTTFs (exTTF=2‐[9‐(1,3‐dithiol‐2‐ylidene)anthracen‐10(9H)‐ylidene]‐1,3‐dithiole)—prepared as new building blocks—were linked. A variety of experimental conditions reveal that the use of sodium hexamethyldisilazane (NaHMDS) as base in THF afforded the E olefins with excellent stereoselectivity. Theoretical calculations at the B3LYP/6‐31G** level point to highly distorted exTTF and TCAQ that form an almost planar stilbene unit between them. Although calculations predicted appreciable electronic communication between the donor and the acceptor, cyclic voltammetric studies did not substantiate this effect. It was only in photophysical assays that the electronic communication emerged in the form of a charge‐transfer (CT) absorption and emission. Once photoexcited (i.e., the locally excited state or excited charge‐transfer state), an ultrafast, subpicosecond charge separation leads to a radical ion pair state in which the spectroscopic features of the radical cation of exTTF as well as the radical anion of TCAQ are discernable. The radical ion pair is metastable and undergoes a fast ((1.0±0.2) ps) charge recombination to reconstitute the electronic ground state. Such ultrafast charge separation and recombination processes come as a consequence of the very short vinyl linkage between the two electroactive units. 相似文献
905.
María José Castro-Castro Dolors Dot-Bach Beatriz Candás-Estébanez Ruth Cano-Corres Xavier Fuentes-Arderiu 《Accreditation and quality assurance》2011,16(12):643-647
In the clinical laboratory, one of the most objective ways to perform the final review of patients’ measured values is the
use of computerized plausibility control (i.e., set of procedures used to decide whether a patient’s measured value is valid according to established clinical and
biological criteria). This study is focused on the estimation of alert and change limits to be applied to detect doubtful
patients’ measured values. These limits are useful to improve the final review of patients’ measured values since these limits
are produced objectively and are selected according to the clinical laboratory needs, letting the clinical laboratory professional
staff to save time and effort. 相似文献
906.
Beatriz Luna 《Physica D: Nonlinear Phenomena》2008,237(21):2685-2695
Discrete-time regulatory networks are dynamical systems on directed graphs with a structure that is inspired on natural systems of interacting units. Using a notion of determination between vertices, we define sets of dominant vertices, and we prove that in the asymptotic regime, the projection of the dynamics on a dominant set allows us to determine the state of the whole system at all times. We provide an algorithm to find sets of dominant vertices, and we test its accuracy on several examples. We also explore the possibility of using the dominant set characteristics as a measure of the structural complexity of networks. 相似文献
907.
We study the possibility for a global unitary applied on an arbitrary number of qubits to be decomposed in a sequential unitary procedure, where an ancillary system is allowed to interact only once with each qubit. We prove that sequential unitary decompositions are in general impossible for genuine entangling operations, even with an infinite-dimensional ancilla, being the controlled-NOT gate a paradigmatic example. Nevertheless, we find particular nontrivial operations in quantum information that can be performed in a sequential unitary manner, as is the case of quantum error correction and quantum cloning. 相似文献
908.
L. Beatriz Castro-Gómez Dr. José Campos-Martínez Dr. Marta I. Hernández Dr. Ramón Hernández-Lamoneda 《Chemphyschem》2023,24(23):e202300387
We present a detailed theoretical study of the molecular oxygen trimer where the potential energy surfaces of the seven multiplet states have been calculated by means of a pair approximation with very accurate dimer ab initio potentials. In order to obtain all the states a matrix representation of the potential using the uncoupled spin representation has been applied. The and states are nearly degenerate and low-lying isomers appear for most multiplicities. A crucial point in deciding the relative stabilities is the zero-point energy which represents a sizable fraction of the electronic well-depth. Therefore, we have performed accurate diffusion Monte Carlo studies of the lowest state in each multiplicity. Analysis of the wavefunction allows a deeper interpretation of the cluster structures, finding that they are significantly floppy in most cases. 相似文献
909.
910.
Rafaela Osuna-Gómez Tiago Mendonca da Costa Beatriz Hernández-Jiménez Gabriel Ruiz-Garzón 《Mathematical Methods in the Applied Sciences》2023,46(2):2319-2333
This paper presents necessary and sufficient conditions for generalized Hukuhara differentiability of interval-valued functions and counterexamples of some equivalences previously presented in the literature, for which important results are based on. Moreover, applications of interval generalized Hukuhara differentiability are presented. 相似文献