Characterization of natural cellulosic fibers from Yucca aloifolia L. leaf as potential reinforcement of polymer composites

Cellulose - In this work lignocellulosic fibers were obtained from Yucca aloifolia L. leaves and their chemical, morphological, thermal and mechanical properties were studied. The fibers were...     

Directed lattices: site-to-bond conversion and its uses for the percolation and dilute polymer transitions

A method for conversion of directed site animals to their bond counterparts is used to significantly extend the number of such configurations in 2, 3, 4 dimensions, obtain their loop partition and study the singularity structure (for both dominant and subdominant singularities) of the corresponding dilute polymer transitions. A special property of bond directed configurations (equivalence lence of loop and bond perimeter partition) is exploited to obtain longer susceptibility series in 3 and 4 dimensions and the gap exponent estimate is refined into the intervals TANOPartly funded by SBF 341 (Aachen-Julich-Koln) and Reitoria Uni. Porto (Project 1-87)     

Novel Bisphosphonates Derived from 1H‐Indazole, 1H‐Pyrazolo[3,4‐b]Pyridine,and 1H‐Pyrazolo[3,4‐b]Quinoline

Novel tetraethyl ethylene‐1,1‐bisphosphonate esters derived from 1H‐indazole, 1H‐pyrazolo[3,4‐b]pyridine, and 1H‐pyrazolo[3,4‐b]quinoline were synthesized by a Michael addition reaction of tetraethyl ethylidene‐1,1‐bisphosphonate with the corresponding heterocycle, using conventional heating and microwave‐assisted methods. The microwave‐assisted method provides shorter reaction times and better yields. The hydrolysis of bisphosphonates afforded the corresponding bisphosphonic acids or salt, using concentrated hydrochloric acid or TMSBr/collidine, respectively. All new compounds were fully characterized, and their structures were assigned using ¹H, ³¹P, and ¹³C NMR and IR spectroscopies and mass spectrometry. The molecular structure of compound 6 was confirmed by X‐ray diffraction studies.     

Self‐assembled Monolayers of Alkylphosphonic Acids on Aluminum Oxide Surfaces – A Theoretical Study

Density‐functional based calculations were used to investigate self‐assembled monolayers of different alkylphosphonic acids on corundum α‐Al₂O₃ (0001), bayerite β‐Al(OH)₃ (001) and boehmite γ‐AlOOH (010) surface models. Mono‐, bi‐, and tridentate adsorption modes were considered. In addition, the organization of single adsorbed molecules was compared to the organization at full surface coverage. The height (thickness) of the self‐assembled monolayers is always shorter than the length of the phosphonic acid molecules due to tilting of the alkyl chains. Tilt angles at full surface coverage are very similar to the tilt angle of a single adsorbed molecule, which indicates that the density of the self‐assembled monolayers is limited by the density of adsorption sites. The lateral interactions between alkyl chains are evidenced by small torsions of the adsorbed molecules, which may serve to minimize the repulsion forces between interchain hydrogen atoms. Similar tilt angles were obtained for mono‐, bi‐, and tridentate adsorptions. Hence, the coordination mode cannot be characterized by the molecule tilting.     

The influence of adsorption phenomena on the impedance spectroscopy of an electrolytic cell

In this work we investigate the influence of the adsorption of ions on the impedance spectroscopy of an electrolytic cell. We consider that the positive and negative ions present in a dielectric liquid are adsorbed in the electrode surfaces with different adsorption energies. This difference in adsorption energies causes an additional plateaux in the limit of the low-frequency range of the real part of the impedance Z . In the same frequency range, a second minimum in the imaginary part of Z is predicted. The theory is illustrated with measurements of the impedance of an electrolytic solution in the frequency range from 10^-2Hz to 1KHz. A comparison between the present model and others from the literature to describe the experimental results is also made.     

Determination of cobalt marker in cow ruminal fluid by EDXRF and SRTXRF

This article describes a comparison of conventional energy‐dispersive X‐ray fluorescence (EDXRF) and synchrotron radiation total‐reflection X‐ray fluorescence (SRTXRF) for Co determination in ruminal fluid from Holstein cow. This element is used as marker for animal nutrition studies. For EDXRF, 200 µl of the sample were dried on 6.35 µm Mylar film at 60 °C. The excitation was carried out using an X‐ray tube with Mo target and Zr filter operated at 30 kV/20 mA. For SRTXRF, 10 µl of the sample were pipetted on a Lucite carrier and dried at 60 °C. In both the techniques, Ga was used as internal standard and the acquisition time was 200 s. The trueness of both techniques was evaluated through the standard addition method, the recoveries obtained by SRTXRF and EDXRF were 76 and 99%, and the limits of detection, 13 and 240 µg l^?1, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

GRASP with path relinking for the orienteering problem

In this paper, we address an optimization problem resulting from the combination of the well-known travelling salesman and knapsack problems. In particular, we target the orienteering problem, originated in the context of sport, which consists of maximizing the total score associated with the vertices visited in a path within the available time. The problem, also known as the selective travelling salesman problem, is NP-hard and can be formulated as an integer linear program. Since the 1980s, several solution methods for this problem have been developed and applied to a variety of fields, particularly in routing and tourism. We propose a heuristic method—based on the Greedy Randomized Adaptive Search Procedure (GRASP) and the Path Relinking methodologies—for finding approximate solutions to this optimization problem. We explore different constructive methods and combine two neighbourhoods in the local search of GRASP. Our experimentation with 196 previously reported instances shows that the proposed procedure obtains high-quality solutions employing short computing times.     

Influence of hydrogen bonds on the molecular structure and conformations of two (C30H48O2) pentacyclic triterpene isomers

The structural study of two (C₃₀H₄₈O₂) pentacyclic triterpene (PCTT) isomers is presented. These terpenes, known as 30-hydroxy-lup-20(29)-en-3-one (1) and (11α)-11-hydroxy-lup-20(29)-en-3-one (2), were isolated from Maytenus imbricata Mart. Ex Reissek (Celastraceae). The molecular structure of 1 and 2 differs in the position of the hydroxyl group. Both compounds crystallize in non-centrosymmetric space groups with two molecules in the asymmetric unit. The crystal structure of 1 shows a triclinic P1 space group (a = 9.5518(1) ?, b = 9.7083(1) ?, c = 14.4696(2) ?, α = 93.832(1)°, β = 102.833(1)°, and γ = 103.307(1)°), while compound 2 crystallizes in a monoclinic P2₁ one (a = 13.4439(16) ?, b = 14.4463(14) ?, c = 13.5224(9) ? and β = 99.703(8)°). The two molecules independent by symmetry of 1 differ slightly due to the presence of static disorder in oxygen atoms. In addition, the intermolecular geometries of 1 and 2 were analysed, and in each isomer the crystal packing is stabilized by O-H…O intermolecular hydrogen bonds and van der Waals forces.