二维渗流相关长度ξ(p)的幂估计(英文)

相关长度ξ(p)是渗流理论中最重要的一个量。本文对它给出了一个幂估计     

STABILITY NUMBER IN SUBCLASSES OF P5-FREE GRAPHS

Two new hereditary classes of P5-free graphs where the stability number can be found in polynomial time are proposed. They generalize several known results.     

Photochemistry of the alkaloids eudistomin N (6-bromo-nor-harmane) and eudistomin O (8-bromo-nor-harmane) and other bromo-beta-carbolines

The UV-absorption, fluorescence excitation and emission spectra of the alkaloids eudistomin N (6-bromo-nor-harmane) and eudistomin O (8-bromo-nor-harmane) were described. In order to perform a comparative analysis, we also studied other bromo-beta-carbolines and the corresponding non-substituted-carboline. Thus, 6-bromo-, 8-bromo-, 6,8-dibromo-, 3,6-dibromo- and 3,6,8-tribromo-derivatives of nor-harmane, harmane and harmine were studied. These studies were performed in EtOH and in EtOH + 1% perchloric acid solutions (pa). Furthermore, fluorescence quantum yields (phi(f)) in acetonitrile and acetonitrile + 1% perchloric acid solutions at 298 K were measured. The HOMO and LUMO energy, the positions (lambda(max)) and oscillator strength (f) of the (1)S(1) <--(1)S(0) band for all the neutral and protonated beta-carbolines studied was calculated and compared with the experimental data. The pK(a) values in aqueous solution for eudistomin N and O (6-bromo- and 8-bromo-nor-harmane), for 6-bromo-, 8-bromo- and 6,8-dibromo-harmane, and for 6-bromo- and 8-bromo-harmine were spectrophotometrically measured (pK((a)(H(2)O))) . The change of the acid-base character of these compounds on going from the ground state (pK(a)) to the first electronic excited singlet state (pK(a)(*)) as DeltapK(a) = pK(a)(*)-pK(a) = 0.625 Deltanu /T, in ethanol solution at 298 K were calculated (DeltapK(a(EtOH))). Proton affinities (PA) for all the compounds studied defined as minus the enthalpy change of the reaction M+H(+)--> MH(+) (gas state) were calculated. Basicity relative to pyridine (DeltaH(rPy)) defined as the enthalpy change of the isodesmic reaction MH(+) + Py--> M + PyH(+) (gas state) was also calculated. The effect of bromine as substituent on the properties of the beta-carboline moiety in nor-harmane, harmane and harmine is discussed.     

Effect of chlorine as substituent on the photochemistry and acid-base properties of beta-carboline alkaloids

The UV-absorption, fluorescence excitation and emission spectra of the 6-chloro-, 8-chloro-, 6,8-dichloro-derivatives of nor-harmane, harmane and harmine and the 8-chloro-derivative of harmol were studied. These studies were performed in EtOH and in EtOH+1% perchloric acid solutions (pa). Furthermore, fluorescence quantum yields (phi(f)) in both media and in acetonitrile and acetonitrile + 1% perchloric acid solutions at 298 K were measured. The HOMO and LUMO energy, the positions (lambda(max)) and oscillator strength (f) of the 1S1 <-- 1S0 band for all the neutral and protonated beta-carbolines studied were calculated and compared with the experimental data. The pK(a) values in aqueous solution for for 6-chloro-, 8-chloro- and 6,8-dichloro-nor-harmane, harmane and harmine and 8-chloro-harmol were spectrophotometrically measured (pK(a(H2O)). The change of the acid-base character of these compounds on going from the ground state (pK(a)) to the first electronic excited singlet state (pKa*) as DeltapKa = pKa*-pKa, in ethanol solution at 298 K were calculated (DeltapK(a(EtOH))). Ground-state proton affinity (PA) for all the compounds studied defined as minus the enthalpy change of the reaction M + H(+) --> MH+ (gas state) were calculated. Basicity relative to pyridine (DeltaH(rPy)) defined as the enthalpy change of the isodesmic reaction MH(+) + Py --> M + PyH+ in gas state and in water solution, were also calculated (ab initio calculations). The effect of chlorine as substituent on the photochemistry and acid-base properties of the beta-carboline alkaloids is discussed.     

The effect of temperature on the stability of compounds used as UV‐MALDI‐MS matrix: 2,5‐dihydroxybenzoic acid, 2,4,6‐trihydroxyacetophenone, α‐cyano‐4‐hydroxycinnamic acid, 3,5‐dimethoxy‐4‐hydroxycinnamic acid,nor‐harmane and harmane

The thermal stability of several commonly used crystalline matrix‐assisted ultraviolet laser desorption/ionization mass spectrometry (UV‐MALDI‐MS) matrices, 2,5‐dihydroxybenzoic acid (gentisic acid; GA), 2,4,6‐trihydroxyacetophenone (THA), α‐cyano‐4‐hydroxycinnamic acid (CHC), 3,5‐dimethoxy‐4‐hydroxycinnamic acid (sinapinic acid; SA), 9H‐pirido[3,4‐b]indole (nor‐harmane; nor‐Ho), 1‐methyl‐9H‐pirido[3,4‐b]indole (harmane; Ho), perchlorate of nor‐harmanonium ([nor‐Ho + H]⁺) and perchlorate of harmanonium ([Ho + H]⁺) was studied by heating them at their melting point and characterizing the remaining material by using different MS techniques [electron ionization mass spectrometry (EI‐MS), ultraviolet laserdesorption/ionization‐time‐of‐flight‐mass spectrometry (UV‐LDI‐TOF‐MS) and electrospray ionization‐time‐of‐flight‐mass spectrometry (ESI‐TOF‐MS)] as well as by thin layer chromatography analysis (TLC), electronic spectroscopy (UV‐absorption, fluorescence emission and excitation spectroscopy) and ¹H nuclear magnetic resonance spectroscopy (¹H‐NMR). In general, all compounds, except for CHC and SA, remained unchanged after fusion. CHC showed loss of CO₂, yielding the trans‐/cis‐4‐hydroxyphenylacrilonitrile mixture. This mixture was unambiguously characterized by MS and ¹H‐NMR spectroscopy, and its sublimation capability was demonstrated. These results explain the well‐known cluster formation, fading (vanishing) and further recovering of CHC when used as a matrix in UV‐MALDI‐MS. Commercial SA (SA 98%; trans‐SA/cis‐SA 5 : 1) showed mainly cis‐ to‐trans thermal isomerization and, with very poor yield, loss of CO₂, yielding (3′,5′‐dimethoxy‐4′‐hydroxyphenyl)‐1‐ethene as the decarboxilated product. These thermal conversions would not drastically affect its behavior as a UV‐MALDI matrix as happens in the case of CHC. Complementary studies of the photochemical stability of these matrices in solid state were also conducted. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and isolation of chloro‐β‐carbolines obtained by chlorination of β‐carboline alkaloids in solution and in solid state

β‐Carbolines (1‐5) undergo electrophilic aromatic substitution with N‐chlorosuccinimide and N‐chlorobenzotriazole under different experimental conditions. Although 6‐chloro and 8‐chloro‐nor‐har‐mane ( 1a and 1b ) and 6‐chloro and 8‐chloro‐harmane ( 2a and 2b ) obtained by chlorination with sodium hypochlorite of nor‐harmane (1) and harmane (2) were isolated and fully characterized recently, other chloroderivatives of nor‐harmane and harmane have never been described. The preparation and subsequent isolation, purification and full characterization of the dichloroderivatives 1c and 2c are reported (mp, R_f, ¹H nmr, ¹³C nmr and ms) together with the preparation, isolation and charaterization, for the first time, of the chloroderivatives obtained from harmine (3a‐3c) , harmol (4a‐4b) and 7‐acetylharmol (5a‐5c) . As chlorinating reagent N‐chlorosuccinimide and N‐chlorobenzotriazole in solution as well as the β‐carboline ‐N‐chlorosuccinimide solid mixture have been used and their uses have been compared. Gc (t_R) and gc‐ms (m/z) data for other monochloro derivative of nor‐harmane (1d) and monochloro‐ and dichloroderivatives of harmane ( 2d and 2e‐2f ), obtained in trace amounts, are also included (Scheme 1 and Table I). Semiempirical AM1 and PM3 calculations have been performed in order to predict reactivity in terms of the energies of HOMO‐LUMO difference and in terms of the charge density of β‐carbolines (1‐5) and chloro‐β‐carbolines ( 1a‐1c, 2a‐2c, 3a‐3c, 4a‐4b , and 5a‐5c ) (Scheme 1). Theoretical and experimental results are discussed briefly.     

循环流化床气固曳力模型

气固曳力是稠密气固两相流动,尤其是垂直流动中的主要作用力,相应的模型也是数值模拟中准确描述气固两相运动的关键.为了解决现有经验或半经验模型的普适性问题,合理描述流动中经常发生的颗粒团聚现象及其对气固曳力的影响,从理论分析入手,运用最小能量的概念,将传统的CFD方法与宏观的系统分析方法相结合,建立了一个新的计及颗粒团聚效应的气固曳力理论模型.与现有模型相比,新模型不仅具有相同的函数变化关系,可合理地描述气固两相相互作用的物理过程,而且避免了以往经验系数不准确导致的各种误差,为稠密气固两相流动的数值描述提供了重要依据.     

Pyrromethene derivatives in three‐component photoinitiating systems for free radical photopolymerization

1,3,5,7,8‐pentamethyl pyrromethene difluoroborate complex (HMP) and 2,6‐diethyl‐8‐phenyl‐1,3,5,7‐tetramethylpyrromethene difluoroborate complex (EPP) were used to initiate the polymerization of a diacrylate in a two‐ and a three‐component photoinitiating system (PIS), together with an amine (ethyl‐4‐dimethylaminobenzoate, EDB) and triazine A (2‐(4‐methoxyphenyl)‐4,6‐bis(trichloromethyl)‐1,3,5‐triazine, TA) as coinitiators. For both pyrromethene dyes, the highest conversion was achieved with the three‐component PIS. As these dyes have high‐fluorescence quantum yields, steady state and time‐resolved techniques were used to study the possible fluorescence quenching by the amine and the triazine, as well as laser flash photolysis to investigate the electron transfer process that occurs in these PIS from either the singlet or triplet excited states. The electron transfer reaction is evidenced by using time‐resolved photoconductivity. Experiments show that the main interaction between the dye and both coinitiators is through its excited singlet state and the process is more efficient when TA is present. The beneficial effect noted when both coinitiators are used in a three‐component system is ascribed to secondary reactions between the coinitiators and intermediates that lead to the generation of higher amount of initiating species and the recovery of the initial dye. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2594–2603, 2010     

High‐Performance Photoinitiating Systems for Free Radical Photopolymerization. Application to Holographic Recording

The photoinitiating systems (PIS) usable in free radical photopolymerization are briefly reviewed. Apart conventional Type I and Type II photoinitiators, three‐component PIS exhibiting a photocyclic behavior are discussed. The mechanisms of photoreaction are presented, highlighting the role of a redox additive which reacts with the photoinitiator photoproduct. Recent applications in holography recording are described showing that the selection of a PIS plays a crucial role in this application.     

Limits of cubes

The celebrated Urysohn space is the completion of a countable universal homogeneous metric space which can itself be built as a direct limit of finite metric spaces. It is our purpose in this paper to give another example of a space constructed in this way, where the finite spaces are scaled cubes. The resulting countable space provides a context for a direct limit of finite symmetric groups with strictly diagonal embeddings, acting naturally on a module which additively is the “Nim field” (the quadratic closure of the field of order 2). Its completion is familiar in another guise: it is the set of Lebesgue-measurable subsets of the unit interval modulo null sets. We describe the isometry groups of these spaces and some interesting subgroups, and give some generalisations and speculations.