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Solvolytic Reactions in Fluorinated Alcohols. Role of Nucleophilic and Other Solvation Effects
Ryu, Zoon Ha,Llewellyn, Gareth,Bentley, T. William 동의대학교 기초과학연구소 1999 基礎科學硏究論文集 Vol.9 No.1
Rate constants and products for solvolyses of chlorodiphenylmethane (Ph₂CHCl) and p-methoxybenzyl chloride in 2,2,2-trifluoroethanol (TFE)/water and TFE/ethanol are reported, along with additional kinetic data for solvolyses of tert-butyl and other alkyl halides (RX) in 97% w/w TFE/water and in 97% w/w hexafluoropropan-2-ol/water (HFIP). Results are discussed in terms of the solvent ionizing power(Y) and the solvent nucleophilicity(N), and contributions from other solvation effects are considered. Comparisons with other S_N1 solvolyses show that solvolyses of Ph₂CHCl in TFE mixtures are unexpectedly fast, but product ratios are unexceptional. An additional solvation effect influences solvolyses leading to delocalized cations, and a delocalized cationic transition state for concerted elimination may explain the recent results of Takeuchi et al., (J. Org. Chem. 1997, 62, 4904) without the need to postulate additional specific solvation effects for adamantyl systems, such as Bronsted-base solvation of α- and β-hydrogen atoms; concerted elimination may occur because simple tertiary alkyl cations are too unstable to form in predominantly aqueous media. Iodide/bromide and bromide/chloride rate ratios are very similar for 1-adamantyl halides and corresponding solvolyses of tert-butyl halides; these ratios decrease in the order aq EtOH $gt; TFE $gt; HFIP, as expected for an electrophilic solvation effect (this effect can readily be incorporated into Y values). From kinetic data for a series of tertiary alkyl chlorides in 97% TFE/water, it is shown that the susceptibility of rates of solvolyses of RCl to N decreases with an increase in steric hindrance or with an increase in charge stabilization. Also, the small kinetic solvent isotope effects for typical solvolyses (e.g., methyl tosylate) indicate that nucleophilic attack lags behind heterolysis of the C-X bond.
Tanita Sirirat,Terdthai Vatanatham,Nanthiya Hansupalak,Garry Llewellyn Rempel,Wanvimon Arayapranee 한국화학공학회 2015 Korean Journal of Chemical Engineering Vol.32 No.5
A graft copolymerization model for using cumene hydroperoxide/tetraethylenepentamine (CHPO/TEPA) as a redox initiator was developed to describe the grafting of methyl methacrylate onto natural rubber latex as a coreshell particle. The model allows estimating the effects of the initiator concentration, monomer-rubber weight ratio, and temperature on the properties of graft product, e.g., % grafting efficiency and the % monomer composition in the graft copolymer and free polymer. The rate expressions of polymer chain formation are developed by taking into account a reduction of CHPO by TEPA and a population event of radicals between core/shell phases. The parameter estimation is performed to find the kinetic parameters. Validation with experimental results demonstrates a good applicability of the proposed model. The model results reveal that the formation of grafted polymer chains rather form by the chain transfer reaction to rubber chains from homopolymer radicals and the initiation reaction of cumyloxy radicals to rubber chains.
Leong, Lester Chee Hao,Sim, Llewellyn Shao-Jen,Jara-Lazaro, Ana Richelia,Tan, Puay Hoon Asian Pacific Journal of Cancer Prevention 2016 Asian Pacific journal of cancer prevention Vol.17 No.5
Background: It is unclear as to whether the size ratio elastographic technique is useful for assessing ultrasound-detected ductal carcinoma-in-situ (DCIS) masses since they commonly lack a significant desmoplastic reaction. The objectives of this study were to determine the accuracy of this elastographic technique in DCIS and examine if there was any histopathological correlation with the grey-scale strain patterns. Materials and Methods: Female patients referred to the radiology department for image-guided breast biopsy were prospectively evaluated by ultrasound elastography prior to biopsy. Histological diagnosis was the gold standard. An elastographic size ratio of more than 1.1 was considered malignant. Elastographic strain patterns were assessed for correlation with the DCIS histological architectural patterns and nuclear grade. Results: There were 30 DCIS cases. Elastographic sensitivity for detection of malignancy was 86.7% (26/30). 10/30 (33.3%) DCIS masses demonstrated predominantly white elastographic strain patterns while 20/30 (66.7%) were predominantly black. There were 3 (10.0%) DCIS masses that showed had a co-existent bull's-eye sign and 7 (23.3%) other masses had a co-existent toothpaste sign, a strain pattern that has never been reported in the literature. Four out of 4/5 comedo DCIS showed a predominantly white strain pattern (p=0.031) while 6/7 cases with the toothpaste sign were papillary DCIS (p=0.031). There was no relationship between the strain pattern and the DCIS nuclear grade. Conclusions: The size ratio elastographic technique was found to be very sensitive for ultrasound-detected DCIS masses. While the elastographic grey-scale strain pattern should not be used for diagnostic purposes, it correlated well with the DCIS architecture.
Resonance of a flexible plate immersed in a von Kármán vortex street
Erika Sandoval Hernández,Stefan G. Llewellyn Smith,Anne Cros 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.4
This work presents a theoretical and experimental study of a flexible plate immersed in a von Kármán vortex street. The wake is generated in a water flow using a cylindrical obstacle with a Reynolds number lower than 200. The vortices provoke oscillations of a flexible plate whose leading edge is clamped a few cylinder diameters downstream of the obstacle. The oscillation amplitude of the free edge is examined experimentally as the plate length is varied with respect to the wavelength. The value of the peak of the amplitude and the phase shift between the forcing vortices and the plate deflection are consistent with theoretical predictions. These predictions use an Euler-Bernoulli model for the motion of the plate produced by the pressure difference over the plate due to the combined effect of the vortex street and the deflection of the plate. The ratio between the plate length and the wake wavelength for which resonance occurs is fixed by the condition that the natural frequency of the plate is equal to the vortex frequency.
Wiersum, Andrew D.,Chang, Jong-San,Serre, Christian,Llewellyn, Philip L. American Chemical Society 2013 Langmuir Vol.29 No.10
<P>An adsorbent performance indicator (API) is proposed in an effort to initially highlight porous materials of potential interest for PSA separation processes. This expression takes into account working capacities, selectivities, and adsorption energies and additionally uses weighting factors to reflect the specific requirements of a given process. To demonstrate the applicability of the API, we have performed the adsorption of carbon dioxide and methane at room temperature on a number of metal–organic frameworks, a zeolite and a molecular sieve carbon. The API is calculated for two different CO<SUB>2</SUB>/CH<SUB>4</SUB> separation case scenarios: “bulk separation” and “natural gas purification”. This comparison highlights how the API can be more versatile than previously proposed comparison factors for an initial indication of potential adsorbent performance.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2013/langd5.2013.29.issue-10/la3044329/production/images/medium/la-2012-044329_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la3044329'>ACS Electronic Supporting Info</A></P>
Yokoyama, Ryuzo,Tamba, Sumio,Soma, Takashi,Jones, David Llewellyn,Parkes, Isabelle,Dunlon, Craig 대한원격탐사학회 1996 International Symposium on Remote Sensing Vol.12 No.1
The first Mutsu Bay Sea Surface Temperature Validation Experiment (MUBEX'95), which is joint research and observation experiment together with United Kingdom and Japan, has performed during the period 20th July to 27th August 1995 in Mutsu Bay, northern Honshu, Japan. The joint validation experiment has been planned to continue during three years from 1995. The stated objectives of MUBEX'95 are: (1). To validate the sea surface temperature (SST) observations made by four satellite radiometer systems, which are ERS-1/ATSR-1, ERS-2/ATSR-2, NOAA-12/AVHRR and NOAA-14lAVHRR, (2). To investigate the surface fluxes of heat and momentum and other processes thought to define the radiometric signal measured by infrared radiometry, (3). To investigate the sub pixel temperature and variability of the radiometric SST with reference to the SST at depth.
Hydrogen Storage in the Giant-Pore Metal–Organic Frameworks MIL-100 and MIL-101
Latroche, Michel,Surblé,, Suzy,Serre, Christian,Mellot-Draznieks, Caroline,Llewellyn, Philip L.,Lee, Jin-Ho,Chang, Jong-San,Jhung, Sung Hwa,Fé,rey, Gé,rard WILEY-VCH Verlag 2006 Angewandte Chemie Vol.45 No.48
<B>Graphic Abstract</B> <P>Large hydrogen-storage capacity at liquid-nitrogen temperature is exhibited by the metal–organic framework MIL-101. In the zeotype architecture of this porous solid (see picture) each intersection of the cages is occupied by a supertetrahedron formed by trimers of chromium octahedra assembled with benzene-1,4-dicarboxylate ligands. <img src='wiley_img/14337851-2006-45-48-ANIE200600105-content.gif' alt='wiley_img/14337851-2006-45-48-ANIE200600105-content'> </P>