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1.
2.
A. Cannizzo R. Boscaino F.M. Gelardi M. Leone 《Journal of Physics and Chemistry of Solids》2003,64(12):2437-2443
We report an experimental study on the relationship between the optical activity of Ge-oxygen deficient centers and dynamic properties and conformational heterogeneity of vitreous matrix in silica. We focus our attention on the absorption band at ∼5.2 eV (B2β) and on the two related emissions at ∼4.2 eV (αE) and at ∼3.1 eV (β). From the temperature dependence of B2β band we estimate a mean energy value of 26 meV for local vibrational modes coupled to the electronic transition, suggesting that the chromophore and its surrounding have access to low frequency dynamics. From the thermal behavior of the two emissions we distinguish the two competitive relaxation processes from the first singlet excited state S1: the radiative one, giving rise the αE band, and the thermally activated intersystem-crossing process between S1 and the triplet state T1, originating the β band. The intersystem-crossing rate increases on increasing the temperature, determining an opposite thermal behavior of the intensity of the two emissions. However, this temperature dependence cannot be rationalized by a simple Arrhenius law and the αE decay kinetics at high temperatures do not follow a single exponential law, suggesting a complex landscape of configurational energies of the process. 相似文献
3.
Given an arbitrary point (x, u) inR
n
× R
+
m
, we give bounds on the Euclidean distance betweenx and the unique solution
to a strongly convex program in terms of the violations of the Karush-Kuhn-Tucker conditions by the arbitrary point (x, u). These bounds are then used to derive linearly and superlinearly convergent iterative schemes for obtaining the unique least 2-norm solution of a linear program. These schemes can be used effectively in conjunction with the successive overrelaxation (SOR) methods for solving very large sparse linear programs.Sponsored by the United States Army under Contract No. DAAG29-80-C-0041. This material is based on research sponsored by National Science Foundation Grant No. DCR-8420963 and Air Force Office of Scientific Research Grant No. AFOSR-ISSA-85-00080.On leave from CRAI, via Bernini 5, Rende, Cosenza, Italy. 相似文献
4.
Sandro Faetti Leone Fronzoni Paolo Grigolini Vincenzo Palleschi Girolamo Tropiano 《Journal of statistical physics》1988,52(3-4):979-1003
Two models for the Freedericksz transition in a fluctuating magnetic field are considered: one is based on a dichotomic and the other on a nonlinear Gaussian noise. Both noises are characterized by a finite correlation time. It is shown that the linear response assumption leading to the best Fokker-Planck approximation in the dichotomic and nonlinear Gaussian cases can be trusted only up to the order
1 and
0, respectively. The role of the corrections to the linear response approximation is discussed and it is shown how to replace the non-Fokker-Planck terms stemming from these corrections with equivalent terms of standard type. This technique is shown to produce perfect agreement with the exact analytical results (dichotomic noise) and to satisfactorily fit the results of analog simulation (nonlinear Gaussian noise). 相似文献
5.
Sandro Faetti Leone Fronzoni Paolo Grigolini Riccardo Mannella 《Journal of statistical physics》1988,52(3-4):951-978
It is shown that the Fokker-Planck operator can be derived via a projection-perturbation approach, using the repartition of a more detailed operator into a perturbation
1 and an unperturbed part
0. The standard Fokker-Planck structure is recovered at the second order in
1, whereas the perturbation terms of higher order are shown to provoke the breakdown of this structure. To get rid of these higher order terms, a key approximation, local linearization (LL), is made. In general, to evaluate at the second order in
1 the exact expression of the diffusion coefficient which simulates the influence of a Gaussian noise with a finite correlation time, a resummation up to infinite order in must be carried out, leading to what other authors call the best Fokker-Planck approximation (BFPA). It is shown that, due to the role of terms of higher order in
1, the BFPA leads to predictions on the equilibrium distributions that are reliable only up to the first order in t. The LL, on the contrary, in addition to making the influence of terms of higher order in
1 vanish, results in a simple analytical expression for the term of second order that is formally coincident with the complete resummation over all the orders in t provided by the Fox theory. The corresponding diffusion coefficient in turn is shown to lead in the limiting case to exact results for the steady-state distributions. Therefore, over the whole range 0 the LL turns out to be an approximation much more accurate than the global linearization proposed by other authors for the same purpose of making the terms of higher order in
1 vanish. In the short- region the LL leads to results virtually coincident with those of the BFPA. In the large- region the LL is a more accurate approximation than the BFPA itself. These theoretical arguments are supported by the results of both analog and digital simulation. 相似文献
6.
Becattini B Sareth S Zhai D Crowell KJ Leone M Reed JC Pellecchia M 《Chemistry & biology》2004,11(8):1107-1117
Bid is a key member of the Bcl-2 family proteins involved in the control of the apoptotic cascade in cells, leading to cell death. Uncontrolled cell death is associated with several human pathologies, such as neurodegenerative diseases and ischemic injuries. Therefore, Bid represents a potential yet unexplored and challenging target for strategies aimed at the development of therapeutic agents. Here we show that a multidisciplinary NMR-based approach that we named SAR by ILOEs (structure activity relationships by interligand nuclear Overhauser effect) allowed us to rationally design a series of 4-phenylsulfanyl-phenylamine derivatives that are capable of occupying a deep hydrophobic crevice on the surface of Bid. These compounds represent the first antiapoptotic small molecules targeting a Bcl-2 protein as shown by their ability to inhibit tBid-induced SMAC release, caspase-3 activation, and cell death. 相似文献
7.
Jackson WG Dickie AJ McKeon JA Spiccia L Brudenell SJ Hockless DC Willis AC 《Inorganic chemistry》2005,44(2):401-409
The bis(pentadentate) ligand tmpdtne binds two Co(II) centers, and the entity is readily oxidized to the dicobalt(III) derivative [Co(2)(tmpdtne)Cl(2)](4+) which has been separated into two isomeric forms. NMR studies establish these as meso and rac isomers arising from the different or same absolute configurations for the asym configuration about each Co(III) center. Each dinuclear ion base hydrolyses to the dihydroxo derivative [Co(2)(tmpdtne)(OH)(2)](4+) with retained asym configurations about each metal ion and also retained rac or meso configurations. The kinetics for the stepwise loss of the two Cl(-) ligands is uniphasic, and data are presented to show that the loss of the first chloride is rate determining and is followed by very rapid intramolecular and loss of the second Cl(-) via a hydroxo-bridged species to yield the observed dihydroxo derivative. Meso and rac forms of the latter have been crystallized. The X-ray crystal structure of the rac-dihydroxo complex is reported, and it establishes the configurations of all the complexes reported. The (1)H NMR spectra for the hydroxo ions show very high field Co-OH resonances (ca. delta-0.5 ppm) not observed previously for such ions, and this result is discussed in the context of published (1)H NMR data for bridged Co-OH-Co species. The base hydrolysis kinetics for the dichloro ions are first order in [OH(-)], and deprotonation at an alpha-CH(2) center (alpha to a pyridyl) is identified as the source of the catalysis, since there is no NH center available for deprotonation on the ligand. These data further support the new pseudoaminate base hydrolysis mechanism first reported in 2003. The values of k(OH) for the second-order base-catalyzed reaction are ca. 4.0 M(-1) s(-1) for both the rac and meso isomers, and these results are discussed in terms of the increased acidities of these 4+ cations compared to their 2+ ion counterparts. 相似文献
8.
Thomas Merakis Annette Murphy Leone Spiccia Alan Beguin Werner Marty 《Helvetica chimica acta》1989,72(5):993-995
Crystalline salts of the hydrolytic dimer of Cr(III), [Cr2(μ-OH)2(H2O)8]X4·n H2O (X = p-toluenesulfonate (tos) or mesitylene-2-sulfonate (dmtos)) have been prepared in good yields via a simple two-step procedure: H+ oxidation of Cr metal to give Cr2+ (T ≈? 70°) followed by O2 oxidation, of Cr2+ to give the dimer (T ≈? 25°). The mechanism of conversion of Cr2+ into the dimer is discussed. 相似文献
9.
In this paper we study a variable coefficient Sine-Gordon (vSG) equation given by theta(tt)-theta(xx)+F(x,t)sin theta=0 where F(x,t) is a real function. To establish if it may be integrable we have performed the standard test of Weiss, Tabor, and Carnevale (WTC). We have got that the (vSG) equation has the Painleve' property (Pp) if the function F(x,t) satisfies a well-defined nonlinear partial differential equation. We have found the general solution of this last equation and, consequently, the functions F(x,t) such that the (vSG) equation possesses the (Pp), are given by F(x,t)=F(1)(x+t)F(2)(x-t) where F(1)(x+t) and F(2)(x-t) are arbitrary functions. Using this last result we have obtained some particular solutions of the vSG equation. (c) 1995 American Institute of Physics. 相似文献
10.
Leone AM Tibodeau JD Bull SH Feldberg SW Thorp HH Murray RW 《Journal of the American Chemical Society》2003,125(22):6784-6790
Polypyridyl complexes of Co decorated with 350-Da polyether chains (Co(350)(2+)) form molten phases of nucleic acids when paired with DNA counterions (Co(350)DNA) or 25-mer oligonucleotides. Analysis of voltammetry and chronoamperometry of mixtures of these phases with complexes having ClO(4)(-) counterions (Co(350)(ClO(4))(2)) and no other diluent provides charge transport rates from the oxidation and reduction currents for the complexes. As the mole fraction of the Co(350)(ClO(4))(2) complex in the mixture is varied from ca. 0.25 to 1, the physical diffusion constants derived from the Co(III/II) wave increase from 1 x 10(-11) cm(2)/s to 5 x 10(-10) cm(2)/s, and apparent diffusion constants dominated by the Co(II/I) electron self-exchange increase from 1 x 10(-10) cm(2)/s to 2 x 10(-8) cm(2)/s. Pure Co(350)DNA melts, containing no Co(350)(ClO(4))(2) complex, do not exhibit recognizable voltammetric waves; DNA suppresses the Co(II/I) electron transfer reactions of Co complexes for which it is the counterion. There are therefore two microscopically distinct kinds of Co(350) complexes, those with DNA and those with ClO(4)(-) counterions, with respect to their Co(II/I) electron-transfer dynamics, leading to percolative behavior in their mixtures. The electron-transfer rates of the Co(II/I) couple are controlled by the diffusive relaxation of the ionic atmosphere around the reaction pair, and the inactivity of the bound Co complexes can be attributed to the very low mobility of the anionic phosphate groups in the DNA counterion. Substitution of sulfonated polystyrene for DNA produced similar results, suggesting that this phenomenon is general to other polymer counterions of low mobility. We conclude that the measured Co(II/I) charge transport and electron-transfer rate constants reflect more the diffusive mobility of the perchlorate counterion than the intrinsic Co(II/I) electron hopping rate. 相似文献