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81.
López-Díaz D García-Mateos I Velázquez MM 《Journal of colloid and interface science》2006,299(2):858-866
To study the influence of the head group in the properties of the mixed monolayers adsorbed at the air-water interface, the surface tension and surface potential of binary mixtures of surfactant have been determined as a function of the surfactant composition. Experiments were carried out with anionic-zwitterionic sodium dodecyl sulfate and dodecyl dimethyl ammoniopropane sulfonate (SDS/DDPS), and cationic-zwitterionic dodecyl trimethylammonium bromide and dodecyl dimethyl ammoniopropane sulfonate (DTAB/DDPS), and dodecyl trimethylammonium bromide and tetradecyl dimethyl ammoniopropane sulfonate (DTAB/TDPS). It was shown that mixed monolayers of cationic-zwitterionic surfactant exhibit small negative deviations of ideal behavior, whereas for SDS/DDPS monolayers show strong negative deviation from the ideality. Deviations of ideal behavior are interpreted by regular solution theory. The surface potential values agree very well with the concentration of the ionic component at the interface. The dynamic surface tension values show that the adsorption kinetics on the interface is a diffusion-controlled process. In monolayers with significant deviation of the ideal behavior, anionic-zwitterionic, there is some evidence of intermolecular attractions after diffusion of both surfactants at the interface. 相似文献
82.
Velázquez E Rivas R del Villar M Valverde A Peix A Mateos PF Velázquez E Martínez-Molina E 《Electrophoresis》2006,27(9):1732-1738
Low-molecular-weight (LMW) RNA profiles, which include ribosomal and transfer RNA molecules with similar small sizes, are molecular signatures of microorganisms with a great potential in microbial identification. The greatest resolution of these profiles was achieved by staircase electrophoresis in sequencing gels. Nevertheless, this technique is difficult to use because it takes 7 h, the gels have large sizes and it is necessary to heat the system and to recycle the buffer to maintain the denaturing conditions and avoid smile effects. Most available sequencing slabs have no internal temperature control or homogenizing devices, which by contrast are present in some newly designed non-sequencing slabs. Nevertheless, these slabs present two important problems for separating LMW RNA molecules, the size of gels is only 20 cm (instead of 40 cm) and the maximum voltage that can be reached is only 840 V (instead 2400 V). Staircase electrophoresis follows a model in which the external polarization is incrementally modified with a constant time step value. In the present work, we experimentally confirmed that by reducing the time step and increasing the total number of steps a suitable resolution is achieved. Under these conditions, despite the smaller size of the gels and the lower values of the electric field, the intensity reaches higher values than in sequencing gels and the LMW RNA profiles are correctly separated in 5 h. The resolution of these profiles obtained in non-sequencing gels is similar to that obtained in sequencing ones facilitating the analysis of large populations of microorganisms in any laboratory. 相似文献
83.
Igor Vel?i? 《Journal of Elasticity》2012,108(2):125-150
We present a nonlinear model of weakly curved rod, namely the type of curved rod where the curvature is of the order of the diameter of the cross-section. We use an approach analogous to the one for rods and curved rods and start from the strain energy functional of three dimensional nonlinear elasticity. We do not impose any constitutional behavior of the material and work in a general framework. To derive the model, by means of ??-convergence, we need to set the order of strain energy (i.e., its relation to the thickness of the body h). We analyze the situation when the strain energy (divided by the order of volume) is of the order h 4. This is the same approach as the one used in F?ppl-von Kármán model for plates and the analogous model for rods. The obtained model is analogous to Marguerre-von Kármán for shallow shells and its linearization is the linear shallow arch model which can be found in the literature. 相似文献
84.
Beatriz Martín‐García Prof. M. Mercedes Velázquez Dr. Francesco Rossella Prof. Vittorio Bellani Prof. Enrique Diez Prof. Jose Luis García Fierro Jose Antonio Pérez‐Hernández Juan Hernández‐Toro Sergi Claramunt Prof. Albert Cirera 《Chemphyschem》2012,13(16):3682-3690
Films of a few layers in thickness of reduced graphite oxide (RGO) sheets functionalized by the zwitterionic surfactant N‐dodecyl‐N,N‐dimethyl‐3‐ammonio‐1‐propanesulfonate (DDPS) are obtained by using the Langmuir–Blodgett method. The quality of the RGO sheets is checked by analyzing the degrees of reduction and defect repair by means of X‐ray photoelectron spectroscopy, atomic force microscopy (AFM), field‐emission scanning electron microscopy (SEM), micro‐Raman spectroscopy, and electrical conductivity measurements. A modified Hummers method is used to obtain highly oxidized graphite oxide (GO) together with a centrifugation‐based method to improve the quality of GO. The GO samples are reduced by hydrazine or vitamin C. Functionalization of RGO with the zwitterionic surfactant improves the degrees of reduction and defect repair of the two reducing agents and significantly increases the electrical conductivity of paperlike films compared with those prepared from unfunctionalized RGO. 相似文献
85.
J. J. Velázquez V. D. Rodríguez A. C. Yanes J. del Castillo J. Méndez-Ramos 《Applied physics. B, Lasers and optics》2012,108(3):577-583
95SiO2?C5LaF3 sol-gel derived nano-glass-ceramics single doped with Eu3+ or Sm3+ and codoped with both of them were successfully obtained. XRD measurements confirm the precipitation of LaF3 nanocrystals after the ceramming process, with mean size ranging from 10 to 20?nm which increases with the thermal treatment temperature. The incorporation of rare-earth ions into precipitated LaF3 nanocrystals was confirmed from luminescence spectra. Intense yellow-red emissions were detected under UV and blue light excitation in single and codoped samples. The effect of codoping with Eu3+ and Sm3+ ions and the energy transfer mechanism between them have been analyzed in order to increase the yellow-red emissions. 相似文献
86.
Vel Berzin Michael Kiriukhin Michael Tyurin 《Applied biochemistry and biotechnology》2012,168(6):1384-1393
Acetogen strain Clostridium sp. MT1121 produced 300?mM acetate (p?<?0.005) and 321?mM ethanol (p?<?0.005) from synthesis gas (syngas) blend 60?% CO and 40?%?H2. Clostridium sp. MT1121 was metabolically engineered to eliminate production of either acetate or acetaldehyde during syngas fermentation. We used Cre-lox66/lox71-based gene removal system to eliminate either phosphotransacetylase (pta), or acetaldehyde dehydrogenase (aldh). The resulted biocatalyst with eliminated pta increased ethanol yield to 610?mM (p?<?0.005). Inactivation of pta rendered only 502?mM of ethanol (p?<?0.005). The acetogen biocatalyst with eliminated aldh produced 450?mM acetate (p?<?0.005). The role of cell energy pool preservation for re-directed carbon flux is discussed. This is the first report on time- and cost-efficient gene elimination in acetogens using lox66/lox71 gene elimination system. 相似文献
87.
T. D. Kolomiitsova K. F. Savvateev K. G. Tokhadze D. N. Shchepkin P. G. Sennikov I. A. Vel’muzhova A. D. Bulanov 《Optics and Spectroscopy》2012,112(4):563-573
IR absorption spectra of monoisotopic 28SiH4 and 76GeH4 are studied in Ar and N2 matrices at 10 K. It is shown that the absorption spectra of silane and germane are similar in the regions of the stretching
ν3 and bending ν4 vibrations. Four groups of bands can be separated out in the spectra of each molecule: (1) narrow bands characteristic of
the matrix isolation studies, (2) broad bands, (3) diffuse absorption with a large value of the spectral moment M
2* the intensity of which increases upon annealing, and (4) bands of dimers the intensity of which increases quadratically with
concentration. The spectra of 28SiH4 and 76GeH4 in nitrogen matrices contain a triplet in the stretching region and a doublet in the bending region, which is explained by
the change in the molecular symmetry from T
d
to C
3V
on passage from the gas phase to solid nitrogen. 相似文献
88.
Mesa JA Velázquez-Palenzuela A Brillas E Coll J Torres JL Juliá L 《The Journal of organic chemistry》2012,77(2):1081-1086
The condensation reaction of D-maltose to free radicals of the series of tris(2,4,6-trichlorophenyl)methyl (TTM) and tris(perchlorophenyl)methyl (PTM) has been described for the first time. The new persistent radicals 1 and 2 are very stable and have been characterized by EPR. Their cyclic voltammograms show a quasi-reversible process in the cathode, being reduced to the corresponding anions, with redox potentials a little lower than those of TTM and PTM, respectively. Their oxidant activity is in close relation with their reduction potentials. Therefore, while 2 is reduced by ascorbic acid, 1 remains unaltered. 相似文献
89.
Hyung Ju Hwang Juan J. L. Velázquez 《Archive for Rational Mechanics and Analysis》2010,195(3):763-796
In this paper we prove global existence for solutions of the Vlasov–Poisson system in convex bounded domains with specular
boundary conditions and with a prescribed outward electrical field at the boundary. 相似文献
90.
L. Velázquez G.N. Phillips Jr. R.A. Tapia Y. Zhang 《Computational Optimization and Applications》2001,20(3):299-315
In this paper, we consider approximating global minima of zero or small residual, nonlinear least-squares problems. We propose a selective search approach based on the concept of selective minimization recently introduced in Zhang et al. (Technical Report TR99-12, Rice University, Department of Computational and Applied Mathematics MS-134, Houston, TX 77005, 1999). To test the viability of the proposed approach, we construct a simple implementation using a Levenberg-Marquardt type method combined with a multi-start scheme, and compare it with several existing global optimization techniques. Numerical experiments were performed on zero residual nonlinear least-squares problems chosen from structural biology applications and from the literature. On the problems of significant sizes, the performance of the new approach compared favorably with other tested methods, indicating that the new approach is promising for the intended class of problems. 相似文献