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931.
This paper develops an analytical dynamic model for cracked beams including bending, axial stiffness, rotational inertia, shear deformation and the coupling of the last two effects. The damage is modelled using a rotational spring that simulates the crack based on fracture mechanics theory. The developed model is used to predict variations on natural frequencies for several crack sites and damage magnitude along the beam. The importance of this work lies in the development of an analytical model that has no approximation due to discretization of the displacement field. This initial theoretical approach describes the expected behaviour for changes in the natural frequencies for simply-supported and clamped-free beams with the precision that only analytical methods allow. The results provide a useful benchmark to compare with approximate numerical methods that can be used to model and analyse the problem. The model showed similar results for long span beams, but the inclusion of rotational inertia and shear deformation effects rendered improvements in the dynamic behaviour mainly in the case of slender and short span beams when compared with the simplified Euler–Bernoulli model. 相似文献
932.
The use of a combination of IrCl3 with a series of ligands derived from the C2-symmetric diamine diphenylethanediamine (DPEN) forms a catalyst capable of the asymmetric hydrogenation of ketones in up to 85% ee. 相似文献
933.
Fernando Silveira Maria do Carmo Martins Alves Fernanda C. Stedile Sibele B. C. Pergher João Henrique Zimnoch dos Santos 《大分子反应工程》2009,3(4):139-147
A series of supports – differing in their textural properties, the nature of their surface sites, and in their crystallinities – were investigated in the sequential grafting reaction of Cp2ZrCl2 and (nBuCp)2ZrCl2 mixtures. The catalyst systems were analyzed by Rutherford backscattering spectrometry, AFM, EXAFS, and nitrogen adsorption. All systems were shown to be active in ethylene polymerization reactions when methylaluminoxane was used as the cocatalyst. Experimental results are discussed in terms of the relationships between the grafted metal content, the catalyst activity, the surface roughness and polarity, the interatomic Zr–C and Zr–O distances of the grafted species and the molecular weights of the resulting polyethylenes.
934.
Jorge Ginja Teixeira Cristina Barrocas Dias Dora Martins Teixeira 《Electroanalysis》2009,21(21):2345-2353
The electrochemical behavior of pomiferin, a natural isoflavone with significant antioxidant, antidiabetic and antitumor properties, is reported here for the first time at a glassy carbon electrode (GCE). In order to understand the redox processes of this compound, its response was compared with the nonantioxidant isoflavone osajin. Based on cyclic and square‐wave voltammetric methods it was observed that pomiferin presents a quasireversible anodic peak, which was attributed to the oxidation of the catechol group, and that is strongly influenced by pH. This anodic process yields a well‐defined DPV response, which can be used for the analytical determination of this potential pharmotherapeutic isoflavone. 相似文献
935.
Helio G. Bonacorso Guilherme P. Bortolotto Jussara Navarini Liliane M.F. Porte Carson W. Wiethan Nilo Zanatta Marcos A.P. Martins Alex F.C. Flores 《Journal of fluorine chemistry》2010,131(12):1297-1301
This study describes a simple and efficient procedure to synthesize a novel series of fourteen 4-substituted N-(5-pyridinyl-1H-1,2,4-triazol-3-yl)-6-(trifluoromethyl)pyrimidin-2-amines, where the 4-substituents are H, CH3, C6H5, 4-FC6H4, 4-CH3C6H4, 4-CH3OC6H4 and 2-Furyl; from the cyclocondensation reaction of N-[5-(pyridinyl)-1H-1,2,4-triazol-3-yl]guanidines with 4-alkoxy-4-alkyl(aryl/heteroaryl)-1,1,1-trifluoroalk-3-en-2-ones. The reactions were carried out in ethanol under reflux for 18 h and led to 40-68% yields. N-(Pyridyl-triazolyl)guanidine precursors were further obtained from reactions of cyanoguanidine with nicotinic or isonicotinic acid hydrazides and the halogenated enones from trifluoroacetylation of enolethers or acetals. 相似文献
936.
937.
M. Augusta Antunes Cristina G. de Azevedo M. Teresa Duarte Ana M. Martins 《Journal of organometallic chemistry》2010,695(9):1328-6561
Complexes [MHCpBz(CO)2(PR3)] (R = CH3, M = Mo (1); M = W (2); R = Ph, M = Mo (3); CpBz = C5(CH2Ph)5) were prepared by thermal decarbonylation of the corresponding [MHCpBz(CO)3] in the presence of trimethyl- or triphenyl-phosphine. In solution the NMR spectra of all compounds show the presence of cis and trans isomers that interconvert at room temperature. In the solid state the molecular structures obtained for compounds 1 and 2 correspond to the trans isomers, while for 3 the cis isomer is present.The electrochemistry of [MoHCpBz(CO)2(PMe3)] (1), [MoHCpBz(CO)3] (5), [WHCpBz(CO)3] (6), [WCpBz(CO)3]2 (7), and [MCpBz(CO)3(CH3CN)]BF4 (8), is described. The cleavage of M-H bonds takes place upon oxidation or reduction. Cations [MCpBz(CO)2L(CH3CN)]+ form in solvent-assisted M-H bond breaking upon oxidation of [MHCpBz(CO)2L] (L = PMe3, CO). Reduction of [MHCpBz(CO)3] gives [MCpBz(CO)3]− and H2. The presence of one PMe3 ligand lowers the reduction potential and precludes the observation of reduction waves. 相似文献
938.
Isarita Martins Larissa de Souza Canaes Keity Margareth Doretto Susanne Rath 《Electroanalysis》2010,22(4):455-462
The applicability of boron‐doped diamond (BDD) as a working electrode in an amperometric cell, coupled to HPLC, was demonstrated, for determining benzodiazepines in pharmaceutical preparations. The separation of the benzodiazepines was achieved using a Waters XTerra RP18 column (250×4.6 mm, 5 μm) with a mobile phase sodium phosphate (pH 3.5; 0.10 mol L?1)‐acetonitrile (65 : 35, v/v) at flow of 1.2 mL min?1. The measurements were performed in a system 871 Advanced Bioscan (Metrohm) with a BDD (8000 ppm) adapted to the thin layer mode cell. Stainless steel and platinum wire were used as reference and auxiliary electrodes, respectively. The cell was operated in pulse mode, using ?1.9 V as initial potential. The method presented linearity, repeatability and ruggedness and it represents a novel, alternative electroanalytical method for benzodiazepines determination. 相似文献
939.
Filomena Martins Luís Moreira Nélson Nunes Ruben E. Leitão 《Journal of Thermal Analysis and Calorimetry》2010,100(2):483-491
Solution enthalpies of 1-bromoadamantane, 1-adamantanol, and 2-adamantanone in a large set of protic and aprotic solvents
are reported at 298.15 K. Solvent effects on the solution processes of these solutes are analyzed in terms of a modified TAKA
equation, involving δcav
h
s as the cavity term. The nature and magnitude of the major interactions which influence these processes are assessed and discussed
in terms of the solutes’ characteristics. New insights on the solution processes under scrutiny are presented. 相似文献
940.
A selective molecularly imprinted polymer-solid phase extraction for the determination of fenitrothion in tomatoes 总被引:1,自引:0,他引:1
Leonardo Augusto de Barros Isarita Martins Susanne Rath 《Analytical and bioanalytical chemistry》2010,397(3):1355-1361
A new and selective sorbent for molecularly imprinted solid-phase extraction (MISPE) was developed and applied for the determination
of residues of fenitrothion (FNT) in tomatoes, using HPLC coupled to photodiode array detection (HPLC-DAD). Using FNT as the
template molecule, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker, toluene
as the porogenic solvent, and bulk polymerization as the synthetic method, a molecularly imprinted polymer (MIP) was synthesized.
In order to choose the medium which promotes the best molecular recognition of FNT by the MIP, the adsorption of FNT by the
MIP was studied in different media containing acetonitrile and toluene. Besides FNT, three structurally related compounds
were used to evaluate the selectivity of the FNT-molecularly imprinted polymer. The MIP exhibited the highest selective rebinding
to FNT. The method developed was validated, using fortified blank tomato samples. The extraction efficiency was 96%. The limits
of detection and quantitation were 0.050 and 0.130 μg g−1, respectively. The intra-day precision was 5.9% and the inter-day precision 8.1%. The accuracy was higher than 89% for a
concentration level around the maximum residue limit of 0.5 μg g−1. 相似文献