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Rui M. S. Loureiro Robert A. W. Johnstone Gaël Labat 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(6):o306-o308
Fusion of 4‐nitrophenol and acetamide in a 1:1 molar ratio gives the title product, C6H5NO3·C2H5NO, (III), which has the character of a pure covalently bonded compound, having a high sharp melting point. Complex (III) (m.p. 371.9–372.9 K) can be recrystallized from various solvents and forms eutectics with either acetamide or 4‐nitrophenol. Similar fusion of mixtures of acetamide and 2‐nitrophenol yields no complex similar to (III) and mixtures of acetamide and 3‐nitrophenol produce only a weak low‐melting complex. The significance of this study lies in its demonstration, via graph set analysis, that some of the patterns found individually in crystalline acetamide or 4‐nitrophenol have been preserved in crystals of complex (III), while several higher order graph sets are produced in (III) due to new hydrogen bonds involving the nitro group. In particular, large hydrogen‐bonded rings are formed together with helical chains. 相似文献
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Andreia S. Oliveira João C. Silva Mónica V. Loureiro Ana C. Marques Nicholas A. Kotov Rogério Colaço Ana P. Serro 《Macromolecular bioscience》2023,23(2):2200240
Cartilage replacement materials exhibiting a set of demanding properties such as high water content, high mechanical stiffness, low friction, and excellent biocompatibility are quite difficult to achieve. Here, poly(p-phenylene-2,6-benzobisoxazole) (PBO) nanofibers are combined with polyvinyl alcohol (PVA) to form a super-strong structure with a performance that surpasses the vast majority of previously existing hydrogels. PVA–PBO composites with water contents in the 59–76% range exhibit tensile and compressive moduli reaching 20.3 and 4.5 MPa, respectively, and a coefficient of friction below 0.08. Further, they are biocompatible and support the viability of chondrocytes for 1 week, with significant improvements in cell adhesion, proliferation, and differentiation compared to PVA. The new composites can be safely sterilized by steam heat or gamma radiation without compromising their integrity and overall performance. In addition, they show potential to be used as local delivery platforms for anti-inflammatory drugs. These attractive features make PVA–PBO composites highly competitive engineered materials with remarkable potential for use in the design of load-bearing tissues. Complementary work has also revealed that these composites will be interesting alternatives in other industrial fields where high thermal and mechanical resistance are essential requirements, or which can take advantage of the pH responsiveness functionality. 相似文献
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Roseany V. V. Lopes Nuno Pedro D. Loureiro José R. Zamian Pâmela S. Fonseca Júlio L. Macedo Maria L. dos Santos Maria J. A. Sales 《Macromolecular Symposia》2009,286(1):89-94
Although the petrochemical polymers have revolutionized the technological development, the intensive use of these materials have contributed to the global pollution. In this context, researches involving ecofriendliness materials are growing up, as well as, a current interest in developing materials from inexpensive and renewable resources, such as vegetable oils. In this work, is described the synthesis of polymeric materials by thermal polymerization from linseed oil (Linum usitatissimum L.) and passion fruit oil (Passiflora edulis) and their characterization by gas chromatographic (GC), Fourier transform infrared (FTIR) spectroscopy, solubility in organic solvents, thermogravimetry (TG), differential scanning calorimetry (DSC) and Raman spectroscopy. The TG curve shows that those polymeric materials present two stages of decomposition. DSC plots of the vegetable oils showed some endothermic and exothermic transitions which are not present in the DSC curves corresponding to oil-based polymers. The Raman spectra of the polymers indicate declining of absorbance in the region of CC stretching (∼1600 cm−1). This absorption was used to estimate the degree of polymerization (79% and 67.5% for linseed and passion fruit oils, respectively). 相似文献
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Marcos Pereira Estellita Lins Luiz Fernando de Lyra Novaes Luiz Fernando Loureiro Legey 《Annals of Operations Research》2005,138(1):79-96
This paper proposes a new methodology for the assessment of the value range for real estate units. The theoretical basis of
the methodology is built on the Data Envelopment Analysis—DEA approach, which has its original concept adapted to the case
where the units under assessment consist of transactions among sellers and buyers. The proposed approach—christened Double
Perspective-Data Envelopment Analysis (DP-DEA)—is applied to a database comprising the prices and features of the units under
assessment. It is shown that the DP-DEA presents some specific advantages when compared to the usual regression analysis method
employed in real estate value assessment. 相似文献
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We bring a new proof for showing that an orthogonal polynomial sequence is classical if and only if any of its polynomial fulfils a certain differential equation of order 2k, for some k?1. So, we build those differential equations explicitly. If k=1, we get the Bochner's characterization of classical polynomials. With help of the formal computations made in Mathematica, we explicitly give those differential equations for k=1,2 and 3 for each family of the classical polynomials. Higher order differential equations can be obtained similarly. 相似文献
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本文报导了采用氩离子激光器来泵浦Pr3+:YLF晶体,应用声光调制器实现了主动锁模;同时应用振动─高反射平面镜也实现了被动锁模,两种锁模均得到了ps光脉冲.据作者了解这是这种晶体材料的第一次锁模运转. 相似文献
29.
We present a general method for the linear least-squares solutionof overdetermined and underdetermined systems. The method isparticularly efficient when the coefficient matrix is quasi-square,that is when the number of rows and number of columns is almostthe same. The numerical methods for linear least-squares problemsand minimum-norm solutions do not generally take account ofthis special characteristic. The proposed method is based onLU factorization of the original quasi-square matrix A, assumingthat A has full rank. In the overdetermined case, the LU factorsare used to compute a basis for the null space of AT. The right-handside vector b is then projected onto this subspace and the least-squaressolution is obtained from the solution of this reduced problem.In the case of underdetermined systems, the desired solutionis again obtained through the solution of a reduced system.The use of this method may lead to important savings in computationaltime for both dense and sparse matrices. It is also shown inthe paper that, even in cases where the matrices are quite small,sparse solvers perform better than dense solvers. Some practicalexamples that illustrate the use of the method are included. 相似文献
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