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991.
Bachir Bentria Djamal Benbertal Zoulikha Hebboul Muriel Bagieu‐Beucher Alain Mosset 《无机化学与普通化学杂志》2005,631(5):894-901
The investigation of CdCl2‐HIO3 system, in aqueous and HNO3 solutions, revealed that anhydrous cadmium iodate presents a marked polymorphism. No less than four new Cd(IO3)2polymorphs have been isolated and characterized, two of which showing second harmonic generation activity. Single crystals of ε‐Cd(IO3)2 are obtained by slowly evaporating, at 60 °C, a saturated solution of γ‐Cd(IO3)2 in 30 % nitric acid. This compound crystallizes in the orthorhombic space group Pca21 [a = 17.581(2), b = 5.495(2), c = 11.163(2) Å]. The basic structural unit can be described as the connection of two cadmium polyhedrons with a short metal – metal distance of 3.88Å. These units are further linked through two other iodate bridges resulting in layers parallel to the (100) plane. The 3D linkage is ensured by short bonds of the fourth iodate group. 相似文献
992.
Lucie Lorrain Michel Havaux Alain Tessier Roger M. Leblanc 《Photochemistry and photobiology》1990,51(4):491-496
Abstract— This Technical Note describes the design of a photothermal beam deflection apparatus which allows the easy and rapid measurement of thermal dissipation of absorbed light energy in various photosynthetic materials including whole plant leaves. This system is based on the "mirage effect" in which the refractive index gradient induced in a fluid in contact with the sample, irradiated with an intensity-modulated light, causes the periodic deflection of a laser beam parallel to the sample surface. The deflection of the probe laser beam is detected by a position sensor, the output of which is processed by a lock-in amplifier. Photothermal deflection signals can be monitored in vivo in intact leaves placed in various (liquid or gaseous) environments with a satisfactory signal-to-noise ratio between 100 (in water) and 50 (in air) at low modulation frequencies (ca 30 Hz). It is shown that this new and simple photothermal technique is a very sensitive tool for the measurement of absorption spectra of photosynthetic pigments both in vivo (leaves, algae or chloroplasts) and in model systems (Langmuir-Blodgett and solid films of chlorophyll). 相似文献
993.
Alain Joye 《Communications in Mathematical Physics》2007,275(1):139-162
We consider the adiabatic regime of two parameters evolution semigroups generated by linear operators that are analytic in
time and satisfy the following gap condition for all times: the spectrum of the generator consists in finitely many isolated
eigenvalues of finite algebraic multiplicity, away from the rest of the spectrum. The restriction of the generator to the
spectral subspace corresponding to the distinguished eigenvalues is not assumed to be diagonalizable.
The presence of eigenilpotents in the spectral decomposition of the generator typically leads to solutions which grow exponentially
fast in some inverse power of the adiabaticity parameter, even for real spectrum. In turn, this forbids the evolution to follow
all instantaneous eigenprojectors of the generator in the adiabatic limit. Making use of superadiabatic renormalization, we
construct a different set of time-dependent projectors, close to the instantaneous eigenprojectors of the generator in the
adiabatic limit, and an approximation of the evolution semigroup which intertwines exactly between the values of these projectors
at the initial and final times. Hence, the evolution semigroup follows the constructed set of projectors in the adiabatic
regime, modulo error terms we control. 相似文献
994.
Le Clézio I Gornitzka H Escudier JM Vigroux A 《The Journal of organic chemistry》2005,70(5):1620-1629
Four dinucleotide building units of nucleic acids in which three out of six backbone torsion angles are included in a dioxaphosphorinane ring structure (D-CNA family) have been synthesized: two diastereoisomeric alpha,beta,gamma-D-CNA {cis and trans} and two diastereoisomeric delta,epsilon,zeta-D-CNA {(S(C4'),R(P)) and (S(C4'),S(P))}. The structural analysis of these conformationally restricted dinucleotides, using NMR spectroscopy and X-ray crystallography, shows that these D-CNA structural elements allow the stabilization of torsion angle combinations, alpha/beta/gamma and delta/epsilon/zeta, that are significantly different from those typically observed in canonical A- or B-form duplexes. 相似文献
995.
Boschetti F Denat F Espinosa E Tabard A Dory Y Guilard R 《The Journal of organic chemistry》2005,70(18):7042-7053
[reaction: see text] Bisaminal type compounds obtained by condensation of pyruvic aldehyde with the suitable open-chain tetraamine followed by cyclization with either dibromoethane or dibromopropane can be regioselectively quaternized by a wide range of alkylating agents. Removal of the bisaminal bridge yields the monosubstituted tetraazamacrocycle or bismacrocycle. Further functionalization allows the preparation of bifunctional ligands or trisubstituted macrocycles. The structure of six compounds was solved by X-ray diffraction, and the unexpected results are rationalized according to the molecular modeling calculations. 相似文献
996.
997.
Lemierre V Chrostowska A Dargelos A Chermette H 《The journal of physical chemistry. A》2005,109(37):8348-8355
With the help of various theoretical methods, ionization potentials (IPs) have been computed for a panel of small molecules containing atoms of group 14, 15, or 16 and representing different singly, doubly, or triply bonded systems with or without an interacting heteroatom lone pair. Comparison of experimental IP values to theoretical results indicates that (i) the standard outer valence green function (OVGF), density functional theory (DFT), and DeltaSCF methods lead to rather accurate values, (ii) the CASPT2 method systematically underestimates IPs, (iii) the method of deducing IPs from a shift of some standard DFT eigenvalue spectrum is a straightforward approach leading to rather accurate IPs, (iv) the eigenvalue spectrum obtained with the so-called statistical average of different orbital model potential (SAOP) exchange-correlation model potential is an efficient approach leading directly to quite accurate IPs, and (v) a good prediction of the IP spectrum can be obtained from the shifted excitation spectra of the system calculated by the time-dependent DFT (TD-DFT) method. It is also shown that the TD-DFT calculations of the ionized species bring a significant improvement over the calculations of the neutral molecules, indicating that a great part of the electronic relaxation is already taken into account (in a similar way for all ionizations). Finally, in the case of TD-DFT calculations of neutral molecules, the statistical average of different orbital model potential (SAOP) functional does not lead to significantly better results than the B3LYP functional. 相似文献
998.
We study the effect of the connectivity pattern of complex networks on the propagation dynamics of epidemics. The growth time scale of outbreaks is inversely proportional to the network degree fluctuations, signaling that epidemics spread almost instantaneously in networks with scale-free degree distributions. This feature is associated with an epidemic propagation that follows a precise hierarchical dynamics. Once the highly connected hubs are reached, the infection pervades the network in a progressive cascade across smaller degree classes. The present results are relevant for the development of adaptive containment strategies. 相似文献
999.
For the first time a very weak N-N stretching band (ν5) of hydrazine was unambiguously assigned in the Fourier-transform infrared spectrum. Almost 1500 transitions with a resolution of for K′ from 0 to 6 and for all symmetry species have been analyzed. Despite some perturbations a global fit has been carried out successfully and the band center was determined at , much higher than previously expected. 相似文献
1000.
Bounds on isocurvature perturbations from cosmic microwave background and large scale structure data
We obtain very stringent bounds on the possible cold dark matter, baryon, and neutrino isocurvature contributions to the primordial fluctuations in the Universe, using recent cosmic microwave background and large scale structure data. Neglecting the possible effects of spatial curvature, tensor perturbations, and reionization, we perform a Bayesian likelihood analysis with nine free parameters, and find that the amplitude of the isocurvature component cannot be larger than about 31% for the cold dark matter mode, 91% for the baryon mode, 76% for the neutrino density mode, and 60% for the neutrino velocity mode, at 2sigma, for uncorrelated models. For correlated adiabatic and isocurvature components, the fraction could be slightly larger. However, the cross-correlation coefficient is strongly constrained, and maximally correlated/anticorrelated models are disfavored. This puts strong bounds on the curvaton model. 相似文献