半直线上L~p-Poincaré不等式最优常数的估计

运用分析方法给出半直线上测度有限时在Dirichlet边界条件下L~p-Poincaré不等式最优常数的变分公式,并运用迭代方法结合变分公式得到了最优常数的显式估计.     

Functionalisation of fluorescent BODIPY dyes by nucleophilic substitution

The BODIPY chromophore can be easily modified by nucleophilic mono- or disubstitution of 3,5-dichloroBODIPY with O-, N-, S- and C-nucleophiles. Absorption and fluorescence spectral data of the new BODIPY derivatives are also reported.     

Synthesis of mixed sequence borane phosphonate DNA

A novel solid-phase phosphoramidite-based method has been developed for the synthesis of borane phosphonate DNA. Keys to this new approach are replacement of the common 5'-dimethoxytrityl blocking group with a 5'-silyl ether and the use of new protecting groups on the bases (adenine, N6-dimethoxytrityl; cytosine, N4-trimethoxytrityl; guanine, N2-[9-fluorenylmethoxycarbonyl]; thymine, N3-anisoyl). Because of these developments, it is now possible for the first time to synthesize oligodeoxynucleotides having any combination of the four 2'-deoxynucleosides and both phosphate and borane phosphonate internucleotide linkages (including oligomers having exclusively borane phosphonate linkages).     

Détonabilité de mélanges stoechiométriques méthane–hydrogène–oxygène–azoteDetonation characteristics of stoichiometric mixtures of methane–hydrogen–oxygen–nitrogen

The goal of this Note is to determine the influence of H₂ addition on the detonation and detonability of stoichiometric CH₄/O₂/N₂ mixtures for three values of the nitrogen dilution $\beta ={\mathrm{N}}_2/{\mathrm{O}}_2$ ($\beta =0$ (oxygen); 2; 3.76 (air)) and also of the influence of the initial temperature. It is based on the measurement of the mean cell size of the steady self-sustained detonation in these mixtures, this characteristic length being representative of the mixture detonability. Results indicate that the detonability of the (CH₄H₂) mixture is mainly controlled by the heavier fuel, i.e., CH₄ and for instance the detonability of the mixture where 20% of CH₄ volume has been replaced by H₂ is nearly the same as that of the mixture where CH₄ is the only fuel. The influence of the initial temperature on the detonability depends on N₂ concentration. To cite this article: C. Matignon et al., C. R. Mecanique 334 (2006).     

Interaction Mechanisms Between Ar–O<Subscript>2</Subscript> Post-Discharge and Stearic Acid I: Behaviour of Thin Films

We study the interaction of thick films (~4 mm) of stearic acid (SA), a C₁₈ alkane skeleton with an acid function, with late Ar–O₂ post-discharge. Contrary to what is observed with thin films of SA (~2–3 μm) which are efficiently etched (part I), only functionalization is observed over the first 2 h of treatment with a plasma source operated in the continuous mode, whatever the temperature. The heat released by surface reactions affects non-linearly the temperature of the substrate. Pulsing the source at a frequency ranging from 0.1 to 1 kHz slows down the functionalization process but does not allow any etching of the material. On the contrary, the SA can be etched as thick films by pulsing the oxygen flow rate at a frequency below 50 mHz. By pulsing the reactive gas, the time averaged value of the [O]/[O₂] ratio is decreased, limiting the functionalization processes due to oxygen atoms, and the mean temperature is lowered, decreasing the diffusion length of O₂ (and/or possibly O₂*) species in the SA which are responsible for the scission of C–C bonds of radicals.     

Kinetic parameter estimation of solvent‐free reactions monitored by 13C NMR spectroscopy,a case study: Mono‐ and di‐(hydroxy)ethylation of aniline with ethylene carbonate

The kinetics of solvent‐free reactions can be followed in situ by ¹³C nuclear magnetic resonance (NMR) spectroscopy, provided that the reaction mixture can be maintained liquid at the monitoring temperature. The pros and cons of the technique and the correct translation of the signal intensities into concentrations are discussed. A good model for this investigation is the reaction of ethylene carbonate ( 1 ) with aniline ( 2 ) at 140°C, two alkylation products of N‐mono‐ and N, N‐bis‐(2‐hydroxy)ethylation of aniline form (compounds 3 and 4 , respectively). The overall reaction occurs with heavy volume shrinking, so that the physical as well as the chemical features evolve during the course of the process. The chemical evolution is described by the kinetic constants k₁ and k₂ of the two N‐alkylation steps, the physical evolution by the time‐dependent activity coefficients α(t). Two complementary procedures are utilized for the determination of these parameters. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 154–160, 2011