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排序方式: 共有151条查询结果,搜索用时 15 毫秒
1.
Adina I. Ciuciu Dr. Lucia Flamigni Dr. Roman Voloshchuk Prof. Dr. Daniel T. Gryko 《化学:亚洲杂志》2013,8(5):1004-1014
An assembly consisting of three units, that is, a meso‐substituted corrole ( C3 ), 1,8 naphthaleneimide ( NIE ), and a Zn porphyrin ( ZnP ), has been synthesized. NIE is connected to C3 through a 1,3‐phenylene bridge and to the ZnP unit through a direct C? C bond. The convergent synthetic strategy includes the preparation of a trans‐A2B‐corrole possessing the imide unit, followed by Sonogashira coupling with a meso‐substituted A3B‐porphyrin. The photophysical processes in the resulting triad ZnP-NIE-C3 are examined and compared with those of the corresponding C3-NIE dyad and the constituent reference models C3 , NIE , and ZnP . Excitation of the NIE unit in C3-NIE leads to a fast energy transfer of 98 % efficiency to C3 with a rate ken=7.5×1010 s?1, whereas excitation of the corrole unit leads to a reactivity of the excited state identical to that of the model C3 , with a deactivation rate to the ground state k=2.5×108 s?1. Energy transfer to C3 and to ZnP moieties follows excitation of NIE in the triad ZnP-NIE-C3 . The rates are ken=7.5×1010 s?1 and ken=2.5×1010 s?1 for the sensitization of the C3 and ZnP unit, respectively. The light energy transferred from NIE to Zn porphyrin unit is ultimately funneled to the corrole component, which is the final recipient of the excitation energy absorbed by the different components of the array. The latter process occurs with a rate ken=3.4×109 s?1 and 89 % efficiency. Energy transfer processes take place in all cases by a Förster (dipole–dipole) mechanism. The theory predicts quite satisfactorily the rate for the ZnP/C3 couple, where components are separated by about 23 Å, but results in calculated rates that are one to two orders of magnitude higher for the couples NIE/ZnP (D/A) and NIE/C3, which are separated by distances of about 14 and 10 Å, respectively. 相似文献
2.
The purpose of this paper is to provide a new, unified and complete study for uniform dichotomy and exponential dichotomy
on the half-line. First we deduce conditions for the existence of uniform dichotomy, using classes of function spaces over
_+{\mathbb {R}_+} which are invariant under translations. After that, we obtain a classification of the main classes of function spaces over
\mathbb R+{\mathbb {R}_+}, in order to deduce necessary and sufficient conditions for the existence of exponential dichotomy, emphasizing on the main
technical qualitative properties of the underlying spaces. We motivate our approach by illustrative examples and show that
the main hypotheses cannot be dropped. We provide optimal methods regarding the input space in the study of dichotomy and
deduce as particular cases some interesting situations as well as several dichotomy results published in the past few years. 相似文献
3.
The gas phase infrared spectrum of monoisotopic H3Si37Cl has been reinvestigated in the ν1/ν4 region near 2200 cm−1, using a Fourier transform spectrometer, with a nominal resolution of 0.0027 cm−1. The rovibrational analysis confirms, besides the weak Coriolis x, y resonance between the (v1 = 1) and (v4 = 1) levels, the existence of two strong local perturbations in the ν4 band. These are caused by rotational (Δk = Δl = ±1) type resonances with and , respectively. Another local perturbation of the 12 ? KΔK ? 14 subbands of the ν4 band, probably due to a (Δk = Δl = ±1) interaction with , was detected and analyzed. All these local perturbations have been studied individually using a simple model of two interacting sublevels. Without the transitions involved in the local perturbations, more than 2000 lines of the ν1/ν4 band system were used to obtain a complete set of vibration-rotation parameters set for the v1 = 1 and v4 = 1 states. By means of a band contour simulation, both the transition moment ratio ∣M4:M1∣ = 1.25 and a positive sign of the Coriolis intensity perturbation were determined.The present results, together with the accurate existing data for ν2, ν3, ν5, and ν6 bands, allowed us to derive the experimental values, Ae = 2.8722945(37) cm−1 and Be = 0.2182248(22) cm−1, which are compared with those of ab initio calculations. 相似文献
4.
Abstract The problem of the mean square exponential stability for a class of discrete-time linear stochastic systems subject to independent random perturbations and Markovian switching is investigated. The case of the linear systems whose coefficients depend both to present state and the previous state of the Markov chain is considered. Three different definitions of the concept of exponential stability in mean square are introduced and it is shown that they are not always equivalent. One definition of the concept of mean square exponential stability is done in terms of the exponential stability of the evolution defined by a sequence of linear positive operators on an ordered Hilbert space. The other two definitions are given in terms of different types of exponential behavior of the trajectories of the considered system. In our approach the Markov chain is not prefixed. The only available information about the Markov chain is the sequence of probability transition matrices and the set of its states. In this way one obtains that if the system is affected by Markovian jumping the property of exponential stability is independent of the initial distribution of the Markov chain. The definition expressed in terms of exponential stability of the evolution generated by a sequence of linear positive operators, allows us to characterize the mean square exponential stability based on the existence of some quadratic Lyapunov functions. The results developed in this article may be used to derive some procedures for designing stabilizing controllers for the considered class of discrete-time linear stochastic systems in the presence of a delay in the transmission of the data. 相似文献
5.
Adina Raducan Alexandra Olteanu Mihaela Puiu Dumitru Oancea 《Central European Journal of Chemistry》2008,6(1):89-92
The kinetics of the reaction between malachite green (MG) and sodium hydroxide (MG fading) was studied using a spectrophotometric
method in the presence of two cationic surfactants, cetyl-benzyl-dimethyl-ammonium chloride (CBDAC) and hexadecyl-trimethylammonium
bromide (HTAB) and one anionic surfactant, sodium dodecyl sulphate (SDS) at concentrations below and above critical micellar
concentrations. The cationic surfactants have a catalytic effect, while the anionic surfactant has an inhibitory effect on
the reaction. A kinetic model describing the influence of surfactant on reaction rate was developed. The results are discussed
on the basis of electrostatic and hydrophobic interactions between the kinetic micelles and malachite green.
相似文献
6.
Jérôme Gualbert Patrick Shahgaldian Adina Lazar Anthony W. Coleman 《Journal of inclusion phenomena and macrocyclic chemistry》2004,48(1-2):37-44
Solid Lipid Nanoparticles (SLNs) have been prepared fromc-2,c-8,c-14,c-20-tetraundecyl-4,6,10,12,16,18,22,24-octahydroxyresorc[4]areneas colloidal suspensions. Photon Correlation Spectroscopy studies revealed aparticle hydrodynamic diameter of 150 nm. Non-contact mode Atomic ForceMicroscopy allows observation of the particles as slightly flattened sphericalobjects of 236 (±40) nm diameter and 145 (±40) nm height. Thestudy of the preparation parameters showed that shear force does not affectthe hydrodynamic size of the SLNs. In contrast, the viscosity and the pH ofthe aqueous phase, the amphiphile concentration in the organic phase and thevolume of organic phase used, all lead to variation in the size of the particles.In term of post preparation parameters only the ionic strength has been shownto affect significantly the particle size; while the pH of the storing solution,microwave, ultrasonic and thermal treatments do not. Short and long-termstability studies have been performed to measure the effect of the ionic strengthon the stability of the particles. The use of carbohydrate cryoprotectants does notallow re-dispersion of the colloidal suspension after freeze-drying. 相似文献
7.
Jeanina Pandele Cusu Adina Magdalena Musuc Mihaela Matache Dumitru Oancea 《Journal of Thermal Analysis and Calorimetry》2012,110(3):1259-1266
In this study, the thermal stability and exothermal decomposition of some ketone-2,4-dinitrophenylhydrazones have investigated using the DSC technique. The synthesized and purified crystalline solids are thermally stable and start to decompose after melting. Non-isothermal DSC curves, recorded at several heating rates, were used to evaluate the melting properties and the kinetics of thermal decomposition. The isoconversional and model-fitting methods were applied to determine the activation parameters from the common analysis of multiple curves measured at different heating rates. Based on the results of the model??free method, a kinetic model was derived, and the kinetic parameters were obtained by means of a multivariate nonlinear regression. The results are discussed in relation to the effect of the ketone structure. 相似文献
8.
The H5PV2Mo10O40 polyoxometalate in a polyethylene glycol solvent was effective for a series of aerobic oxidation reactions including oxydehydrogenation of alcohols and cyclic dienes, oxidation of sulfides and the Wacker reaction; the solvent-catalyst phase can be recovered and recycled. 相似文献
9.
Mihail?MeganEmail author Adina?Lumini?a?Sasu Bogdan?Sasu 《Integral Equations and Operator Theory》2004,50(4):489-504
The aim of this paper is to give necessary and sufficient conditions for pointwise and uniform exponential dichotomy of linear skew-product flows. We shall obtain that the pointwise exponential dichotomy of a linear skew-product flow is equivalent to the pointwise admissibility of the pair
As a consequence, we prove that a linear skew-product flow on
is uniformly exponentially dichotomic if and only if the pair
is uniformly admissible for . 相似文献
10.
Connections between uniform exponential expansiveness and complete admissibility of the pair
are studied. A discrete version for a theorem due to Van Minh, Räbiger and Schnaubelt is presented. Equivalent characterizations of Perron type for uniform exponential expansiveness of evolution families in terms of complete admissibility are given. 相似文献