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91.
Antonio García Martínez Enrique Teso Vilar Florencio Moreno Jiménez Paloma Martínez‐Ruiz Ricardo Bernárdez Vilaboa 《Rapid communications in mass spectrometry : RCM》2009,23(6):856-862
The electron ionisation (EI) mass spectra of a series of bridgehead‐fused Δ2‐norbornanethiazolines, a new class of bridgehead‐norbornane derivatives, have been studied and their cleavage mechanisms rationalised on the basis of the substituent shifts as well as on the identification of relevant peaks through accurate mass measurements and collision‐induced dissociation tandem mass spectrometric experiments. The fragmentation patterns of isomeric pairs of 6,6‐ and 10,10‐dimethylnorbornanethiazolines are almost identical, probably due to an initial isomerisation of molecular ion previous to the fragmentation. In general, the dominant peaks in the spectra of all the studied compounds originate from initial α‐cleavages of C(5)–C(6) or C(1)–C(10) bonds, followed by concomitant homolytic cleavage of C(1)–C(9) and C(7)–C(10) bonds. The driving force for this fragmentation pathway, directed by the gem‐dimethyl group, is the formation of a highly stabilised thiazolilmethyl cation which constitutes the base peak in all the spectra and allows the identification of these interesting ligands. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
92.
M.C. Arenas L. Fernando Rodríguez-Núnez Domingo Rangel Omar Martínez-Álvarez Claudia Martínez-Alonso V.M. Castaño 《Ultrasonics sonochemistry》2013,20(2):777-784
In this work, hybrid nanocomposites based on anatase titania:polypyrrole (TiO2:PPy) were directly obtained from a simple, one-step, ultrasonic (UT)-assisted synthesis. The properties of these crystalline nanocomposites were compared with those of others fabricated using cold (Cold)-assisted synthesis without any UT assistance, which required a hydrothermal treatment (HT) to yield crystalline anatase titania in the nanocomposite (TiO2:PPy) at low temperature (130 °C) and in a short time (3 h). The SEM results demonstrated that the UT-assisted synthesis is a feasible method to obtain anatase TiO2:PPy nanocomposites with controlled morphology using low energy. The Fourier transform infrared (FT-IR) bands of the crystalline nanocomposites exhibited a shift with respect to neat components, which was attributed to the strong interaction between the secondary amine groups (N–H) of PPy and the oxygen from TiO2. The acceptable absorption in the visible region (λmax = 670 nm) indicates that these nanocomposites are good candidates for harvesting energy in solar cells. Devices based on these nanocomposites were built to evaluate their electrical properties. An increase in the photocurrent was observed for the devices prepared with the nanocomposites from the UT-assisted synthesis. 相似文献
93.
94.
M.I. Idiart F. Willot Y.-P. Pellegrini P. Ponte Castañeda 《International Journal of Solids and Structures》2009,46(18-19):3365-3382
This paper presents a combined numerical-theoretical study of the macroscopic behavior and local field distributions in a special class of two-dimensional periodic composites with viscoplastic phases. The emphasis is on strongly nonlinear materials containing pores or rigid inclusions. Full-field numerical simulations are carried out using a fast Fourier transform algorithm [Moulinec, H., Suquet, P., 1994. A fast numerical method for computing the linear and nonlinear properties of composites. C. R. Acad. Sci. Paris II 318, 1417–1423.], while the theoretical results are obtained by means of the ‘second-order’ nonlinear homogenization method [Ponte Castañeda, P., 2002. Second-order homogenization estimates for nonlinear composites incorporating field fluctuations. I. Theory. J. Mech. Phys. Solids 50, 737–757]. The effect of nonlinearity and inclusion concentration is investigated in the context of power-law (with strain-rate sensitivity m) behavior for the matrix phase under in-plane shear loadings. Overall, the ‘second-order’ estimates are found to be in good agreement with the numerical simulations, with the best agreement for the rigidly reinforced materials. For the porous systems, as the nonlinearity increases (m decreases), the strain field is found to localize along shear bands passing through the voids (the strain fluctuations becoming unbounded) and the effective stress exhibits a singular behavior in the dilute limit. More specifically, for small porosities and fixed nonlinearity , the effective stress decreases linearly with increasing porosity. However, for ideally plastic behavior , the dependence on porosity becomes non-analytic. On the other hand, for rigidly-reinforced composites, the strain field adopts a tile pattern with bounded strain fluctuations, and no singular behavior is observed (to leading order) in the dilute limit. 相似文献
95.
In this paper we give conditions on an implication algebra A so that two congruences θ
1, θ
2 on A permute, i.e. θ
1 ∘ θ
2 = θ
2 ∘ θ
1. We also provide simpler conditions for permutability in finite implication algebras. Finally we present some applications
of these characterizations.
The support of Universidad Nacional del Sur and CONICET is gratefully acknowledged. 相似文献
96.
97.
98.
99.
A. Pérez-Pacheco R. Casta?eda-Guzmán C. Oliva?Montes?de?Oca A. Esparza-García S. J. Pérez?Ruiz 《Applied Physics A: Materials Science & Processing》2011,102(3):699-704
In this work, we present characterization of titanium oxide thin films by photoacoustic measurements to determine the ablation
threshold and phase transitions from amorphous to crystalline states. The important advantages of this method are that it
does not require amplification at the detection stage and that it is a non-destructive technique. The correlation analysis
of the photoacoustic signals allows us to visualize the ablation threshold and the phase transitions with enhanced sensitivity.
This correlation analysis clearly exhibits the changes in the thin-film morphology due to controlled variations of the fluence
(energy/area) and the temperature of the surrounding medium. This is particularly important for those cases where the crystalline
changes caused by temperature variations need to be monitored. The thin-film samples were prepared by the sputtering technique
at room temperature in the amorphous state. The phase transformations were induced by controlled temperature scanning and
then corroborated with Raman spectroscopy measurements. 相似文献
100.
R. Estrada R. Rodríguez V. M. Casta?o 《Applied Physics A: Materials Science & Processing》2010,99(4):723-728
A new kind of synthetic membrane was designed with the capacity to adjust the pore diameter in a wide range of sizes (from 0.8 to 22.3 microns) just by changing the pH of the aqueous medium where it is immersed; in this way it is possible to control externally the pore size of the membrane. A non-linear mathematical model, based on the overlap of the electrical double layers of charged particles, was developed to explain the oscillatory behavior of the pore size when the pH was varied. This model fits correctly this oscillatory behavior. Scanning electron microscope images were obtained in low-vacuum conditions to reduce, as much as possible, possible changes in the external conditions after the immersion in water. 相似文献