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Causo MS Ciccotti G Montemayor D Bonella S Coker DF 《The journal of physical chemistry. B》2005,109(14):6855-6865
We generalize the linearized path integral approach to evaluate quantum time correlation functions for systems best described by a set of nuclear and electronic degrees of freedom, restricting ourselves to the adiabatic approximation. If the operators in the correlation function are nondiagonal in the electronic states, then this adiabatic linearized path integral approximation for the thermal averaged quantum dynamics presents interesting and distinctive features, which we derive and explore in this paper. The capability of these approximations to accurately reproduce the behavior of physical systems is demonstrated by calculating the diffusion constant for an excess electron in a metal-molten salt solution. 相似文献
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A. A. Rodríguez-Rodríguez O. S. Rodríguez-Fernández J. G. Osuna-Alarcón Sagrario M. Montemayor 《Journal of Sol-Gel Science and Technology》2012,61(3):534-540
Ferrites of composition M0.2Co0.4Zn0.4Fe2O4 with M = Cu2+, Mn2+ and Ni2+ were prepared by citrate complex method. Later, their composites with silica have also been obtained by a simple route. The
citrate complex precursors of multielement ferrites were characterized by FTIR spectroscopy and thermal analysis, been found
a similar behavior for the three systems. The thermal treatment (at 400, 600 and 800 °C) of precursors gives, as result, the
spinel type cubic ferrite pure when the ions substituted were copper and nickel; when manganese was used an hematite phase
was obtained as contaminant at 800 °C. The presence of all ions involved and the particle size was corroborated by EDX analysis
and measured from a TEM micrograph, respectively. The magnetic parameters related to magnetic properties, magnetization and
coercivity, were different depending of the chemical composition of the ferrite and the thermal treatment temperature, as
it was expected. At room temperature, the values obtained were near to those reported for Co-ferrite in bulk. The synthesis
route of the composites M0.2Co0.4Zn0.4Fe2O4-SiO2, proposed in this work, gives as result magnetic nanoparticles in an amorphous silica matrix. Their magnetic properties were
depending on weight percentage of the magnetic phase in the composite. 相似文献
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Sagrario M. Montemayor L. A. García-Cerda J. R. Torres-Lubián O. S. Rodríguez-Fernández 《Journal of Sol-Gel Science and Technology》2007,42(2):181-186
In this work the synthesis of CoFe2O4-SiO2 and NiFe2O4-SiO2 nanocomposites was studied via the sol–gel method, using the polymerized complex route. The polymerized precursors obtained
by the reaction of citric acid, ethylene glycol, tetraethylorthosilicate, ferric nitrate, and cobalt nitrate or nickel chloride
were characterized by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. NMR and IR spectra of the precursors,
without and with metallic ions, show the formation of polymeric chains with ester and ether groups and complexes of metal-polymeric
precursor. The nanocomposites were obtained by the thermal decomposition of the organic fraction and characterized by X-ray
diffraction (XRD) and vibrating sample magnetometry (VSM). XRD patterns show the formation of CoFe2O4 and NiFe2O4 in an amorphous silica matrix above 400 °C in both cases. When the calcination temperature was 800 °C the particle size of
the crystalline phases, calculated using the Scherrer equation, reached ∼35 nm for the two oxides. VSM plots show the ferrimagnetic
behavior that is expected for this type of magnetic material; the magnetization at 12.5 KOe of the CoFe2O4-SiO2 and NiFe2O4-SiO2 compounds was 29.5 and 17.4 emu/g, respectively, for samples treated at 800 °C. 相似文献
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Dr. J. Reyes Flores Dr. Griselda Castruita-De León Dr. Gleb Turlakov Dr. Eduardo Arias Dr. Ivana Moggio Dr. Sagrario M. Montemayor Dr. Román Torres Dr. Raquel Ledezma Dr. Ronald F. Ziolo Dr. Julio González-Torres 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(7):2493-2505
Two series of 2,5-di(butoxy)phenyleneethynylenes, one halogenated ( n PEC4-X ; n=2, 3, or 4) and the other boron-dipyrromethene (BODIPY) terminated ( n PEC4-By ; n=3, 4, or 5; By=BODIPY), were synthesized monodirectionally by the step-by-step approach and the molecular structure was corroborated by NMR spectroscopy (1H, 13C-DEPTQ-135, COSY, HSQC, HMBC, 11B, 19F) and MALDI-TOF mass spectrometry. The multiplicity and J-coupling constants of 1H, 11B, and 19F/11B NMR signals revealed, in the n PEC4-By series, that the phenyl in the meso position of BODIPY becomes electronically part of the conjugation of the phenyleneethynylene chain, whereas BODIPY is electronically isolated. The photophysical, electrochemical, and theoretical studies confirm this finding because the properties of n PEC4-By are comparable to those of the n PEC4-X oligomers and BODIPY, indicating negligible electron communication between BODIPY and the n PEC4 moieties. Nevertheless, energy transfer (ET) from n PEC4 to BODIPY was rationalized by spectroscopy and theoretical calculations. Its yield decreases with the n PEC4 conjugation length, according to the increase in distance between the two chromophores, resulting in dual emission for the longest oligomer in which ET is quenched. 相似文献
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We discuss a large class of phenomenological models incorporating quantum gravity motivated corrections to electrodynamics.
The framework is that of electrodynamics in a birefringent and dispersive medium with non-local constitutive relations, which
are considered up to second order in the inverse of the energy characterizing the quantum gravity scale. The energy-momentum
tensor, Green functions and frequency dependent refraction indices are obtained, leading to departures from standard physics.
The effective character of the theory is also emphasized by introducing a frequency cutoff Ω. The analysis of its effects
upon the standard notion of causality is performed, showing that in the radiation regime (Ω R ≫ 1) the expected corrections of the order (ω/Ω)
n
get further suppressed by highly oscillating terms proportional to , thus forbiding causality violations to show up in the corresponding observational effects.
Dedicated to Octavio Obregón on his sixtieth birthday. 相似文献