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991.
P. E. S. De Oliveira L. M. Conserva C. A. De Simone M. A. Pereira V. R. S. Malta D. O. Imbroisi 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(12):o900-o902
X‐ray diffraction studies carried out on single crystals of the monomeric, viz. 5,6‐dimethoxy‐2H‐furo[2,3‐h][1]benzopyran‐2‐one, C13H10O5, and dimeric, viz. 5,5′,6,6′‐tetramethoxy‐3,3′,4,4′‐tetrahydro‐2H,2′H‐3,3′:4,4′‐bi(furo[2,3‐h][1]benzopyran)‐2,2′‐dione, C26H20O10, forms of pimpinellin have revealed that, following cyclodimerization, the carbonyl groups are head‐to‐head with respect to one another. In the monomer, the heterocyclic ring is planar, but it exhibits a twisted‐boat conformation in the dimer. Both the monomer and the dimer interact through C—H⋯O interactions. 相似文献
992.
Danieli Cátia Ceni Laura Alegria Martins Andréa Garcia Pereira Pedro Eduardo Fr?ehlich Ana Maria Bergold 《Chromatographia》2009,69(Z2):189-194
A reversed-phase ion-pairing liquid chromatographic method was developed and validated for the assay of Fe(II) in ferrous
bisglycinate (Fe-bis-gly) capsules using 4-(2-pyridylazo) resorcinol reagent. The analysis was carried out using a Gemini
RP-18 (150 mm × 4.6 mm I.D., particle size 5 μm) analytical column; the mobile phase consisted of a mixture of acetonitrile–water
(28:72 v/v) containing 1 mM tetrabutylammonium hydrogensulfate and 1% phosphate buffer (pH 8.0). The flow rate was 1.0 mL min−1 and the detection was achieved with a photodiode array (PDA) detector at 706 nm. The specificity of the method was proved
using stress conditions and evaluated using a PDA detector. The data validation showed that the method is specific, fast,
accurate, and reproducible for the determination of Fe-bis-gly in dosage form. The response was linear over a range of 1.0–2.6 μg mL−1 (r = 0.9999). The accuracy of the method ranged from 98.02 to 102.75%. The RSD values for intra- and inter-day precision studies
were below 1.3 and 1.1%, respectively. There was no interference of the excipients on the determination of the active pharmaceutical
ingredient. 相似文献
993.
Luis Adrio José M. Antelo Juan M. Ortigueira Jesús J. Fernández Alberto Fernández Ma. Teresa Pereira José M. Vila 《Journal of organometallic chemistry》2009,694(9-10):1273-1282
The reaction of the tetranuclear halide-bridged complexes 1?2(a?d) with Ph2PCH2PPh2 (dppm) or Ph2PC(CH2)PPh2 (vdpp) in 1:2 molar ratio and NH4PF6 afforded the novel tetarnuclear palladacycles 3?6 (a, c, d) as 1:2 electrolytes with bridging diphosphine and halogen ligands. The structure of 4a has been determined by X-ray diffraction analysis, and represents the first example of a tetranuclear palladacycle with bridging dppm and halogen ligands. Reaction of 1?2(a?d) with (Ph2PCH2CH2)2PPh (triphos) in 1:2 molar ratio gave 7(a?d) bearing two pentacoordinated palladium atoms. The structure of 7a, as determined by X-ray diffraction analysis, shows the distorted square pyramidal geometry around the metal centers. Treatment of 1?2(a?d) with dppm, vdpp or Ph2PN(Me)PPh2 (dppma) in 1:4 molar ratio gave the dinuclear palladacycles 8?10(a?d) with a chelating diphosphine ligand at each metal center; further treatment of 9(a?c) with the nucleophiles pyrrolidine, piperidine, morpholine or 4-methyl-piperidine gave the Michael addition derivatives 11?12(a?c), 13b, 13c and 14c, promoted by the withdrawing effect of the palladacycle which activates the CCH2 double bond. 相似文献
994.
The simple assembly line balancing problem is the simplification of a real problem associated to the assignment of the elementary tasks required for assembly of a product in an assembly line. This problem has been extensively studied in the literature for more than half a century. The present work proposes a new procedure to solve the problem we call Bounded Dynamic Programming. This use of the term Bounded is associated not only with the use of bounds to reduce the state space but also to the reduction of such space based on heuristics. This procedure is capable of obtaining an optimal solution rate of 267 out of 269 instances, which have been used in previous works, thus obtaining the best-known performance for the problem. These results are an improvement from any previous procedure found in the literature even when using smaller computing times. 相似文献
995.
Rajendra M. Srivastava Maria C. Pereira Wagner W. M. Faustino Kaline Coutinho Janaína V. dos Anjos Sebasti?o J. de Melo 《Monatshefte für Chemie / Chemical Monthly》2009,15(2):1319-1324
Abstract
A simple and easy synthesis of ten arylamidoximes from arylnitriles and hydroxylamine is described. The formation of the arylamides has been observed to a much lesser extent in the present work. A new mechanism for the formation of arylamidoximes, as well as arylamides, from arylnitriles and hydroxylamine is suggested. Quantum mechanical calculations have been carried out to support this mechanism. The enthalpy of formation in conjunction with atomic charges of the reactants and intermediates helped to understand more about the generation of the products. 相似文献996.
Antônio Pereira BrandãoJr Plamen Koshlukov Alexei Krasilnikov 《Monatshefte für Mathematik》2009,157(3):247-256
Let K be an infinite integral domain, and let A = M
2(K) be the matrix algebra of order two over K. The algebra A can be given a natural -grading by assuming that the diagonal matrices are the 0-component while the off-diagonal ones form the 1-component. In
this paper we study the graded identities and the graded central polynomials of A. We exhibit finite bases for these graded identities and central polynomials. It turns out that the behavior of the graded
identities and central polynomials in the case under consideration is much like that in the case when K is an infinite field of characteristic 0 or p > 2. Our proofs are characteristic-free so they work when K is an infinite field, char K = 2. Thus we describe finite bases of the graded identities and graded central polynomials for M
2(K) in this case as well.
A. Krasilnikov has been partially supported by CNPq and FINATEC. 相似文献
997.
Luísa Pereira 《Journal of Theoretical Probability》2018,31(2):853-866
This paper deals with the asymptotic independence of the normalized kth upper- and rth lower-order statistics and their locations, defined on some strictly stationary sequences \(\left\{ X_n\right\} _{n\ge 1}\) admitting clusters of both high and low values. The main result is the asymptotic independence of the joint locations of the k-largest extremes and the joint locations of the r-smallest extremes of \(\left\{ X_{n}\right\} _{n\ge 1}\), which allows us to censor a sample, by ensuring that the set of observations that we selected contains the k-largest and r-smallest order statistics of the stationary sequence \(\left\{ X_{n}\right\} _{n\ge 1}\) with a predetermined probability. 相似文献
998.
Leonardo Zimmer Fernando Marcelo Pereira Jeroen Adrianus van Oijen Laurentius Philippus Hendrika de Goey 《Combustion Theory and Modelling》2017,21(2):358-379
A numerical model is developed aiming at investigating soot formation in ethylene counterflow diffusion flames. The mass and energy coupling between soot solid particles and gas-phase species is investigated in detail. A semi-empirical two-equation model is chosen for predicting soot mass fraction and number density. The model describes particle nucleation, surface growth, and oxidation. A detailed kinetic mechanism is considered for the gas phase and the effect of considering radiation heat losses is also evaluated. Simulations were done for a range of conditions that produce low-to-significant amounts of soot using three strategies: first by changing the strain rate imposed on the flow field, second, by changing the oxygen content in the oxidant stream, and third, by changing the pressure. Additionally, the effect of the transport model chosen was analysed. The results showed that, for the flames studied and within the limits of the present work, the soot and gas radiation terms are of primary importance for numerical simulations. Additionally, it was shown that the soot mass and thermodynamic properties coupling terms are, in general, a second-order effect, with an importance that increases as soot amount increases. As a general recommendation, the radiation terms have always to be considered, whereas full coupling has to be employed only when the soot mass fraction, YS, is equal to or larger than 0.008. If a higher precision is required, with errors less than 1%, full coupling should be taken into account for YS ≥ 0.002. For lower soot amounts, the coupling through soot mass and thermodynamic properties may be neglected as a first approximation, but an error on the total mass conservation will be present. Additionally, discrepancies from considering different transport models (detailed or simplified) are larger than those found from not fully coupling the phases. 相似文献
999.
Thamiris Machado Magalhães Rodrigo Cinti Guerra Rosane Aguiar da Silva San Gil Ana Paula Valente Renata Antoun Simão Bluma Guenther Soares Thamara de Carvalho Mendes Alexandre dos Santos Pyrrho Valeria Pereira de Sousa Vanessa Lúcia Rodrigues-Furtado 《Journal of nanoparticle research》2017,19(8):277
We report the preparation, characterization, and drug release kinetics of a pH-responsive hydrogel film from a dendrimer megamer. The megamer (GP32) is a three-dimensional reticulated structure with a mean diameter of 71.16 nm (PDI 0.150) and was prepared by the reaction between Poly(amidoamine) generation4 (PAMAM G4) dendrimer and glutaraldehyde (G:P molar ratio 32). The crosslinking units in the megamer are provided mainly by the bicyclic dimer 2-hydroxy-3,4,4a,7,8,8a–hexahydro-2H-chromene-6-carbaldehyde as determined by high-resolution (800 MHz) 1H NMR and FTIR. The hydrogel film (F[GP32]) is formed upon evaporation of a methanolic solution of the megamer and has a high degree of organization and homogeneity. Further crosslinking with glutaraldehyde (CLF[GP32]) enhanced the mechanical properties of the hydrogel film. The chemical constitution and unique megamer architecture enable the hydrogel film to carry both lipophilic and hydrophilic substances. The film did not cause any dermal irritation or clinical signs of toxicity in tests on rabbits, allowed for a sustained release of ketoprofen and played an important role in the process of drug delivery into the receptor medium. This performance taken together with the absence of toxicity makes this hydrogel film a good choice for dermal sustained drug release. 相似文献
1000.
Iram Gleria Tarcísio M. Rocha Filho Annibal D. Figueiredo Neto José David M. Vianna 《Brazilian Journal of Physics》2017,47(4):441-446
In this paper, we discuss the conditions for the existence of first integrals of movement and the Liouville theorem on integrable systems. We revise the core results of the Hamilton-Jacobi theory and discuss the extension of the formalism to encompass constrained systems using Dirac brackets, originally developed in the context of the canonical quantization of constrained systems. As an application, we analyze a Hamiltonian that represents the classical limit of a Fermionic system of oscillators. 相似文献