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排序方式: 共有159条查询结果,搜索用时 15 毫秒
141.
Barker A Briere RA Gibbons LK Makoff G Papadimitriou V Patterson JR Somalwar S Wah YW Winstein B Winston R Woods M Yamamoto H Swallow EC Bock GJ Coleman R Enagonio J Hsiung YB Tschirhart R Stanfield K Stefanski R Yamanaka T Gollin GD Karlsson M Okamitsu JK Debu P Peyaud B Turlay R Vallage B 《Physical review D: Particles and fields》1990,41(11):3546-3547
142.
An unexpected rearrangement was observed during the treatment of tritylamine with n-butyllithium, leading to the formation of an imine. 相似文献
143.
Kennedy P Kennedy H Papadimitriou S 《Rapid communications in mass spectrometry : RCM》2005,19(8):1063-1068
We investigated the effects of sample acidification on the stable carbon and nitrogen isotopic composition (delta13C and delta15N), as well as the organic carbon (OC) and total nitrogen (TN) composition, of an algal culture and a marine sediment. Replicate measurements of untreated and acid-treated samples were made using 1 M, 2 M and 6 M HCl, 6% H2SO3 and 1 M H3PO4. For all treatments the precision of the analysis for the acid-treated sample was equal to or less than that in the non-acidified sample. For the algae, analysis of variance (ANOVA) indicated no significant differences in the mean OC and TN concentration, or delta13C and delta15N composition, between any acid treatment and non-acidified samples. For the sediment sample a comparison could only be made between the different acid treatments because the untreated contained significant amounts ( approximately 30%) of carbonate carbon. ANOVA indicated that the mean OC determined in sediment samples after the 1 M HCl treatment and the mean delta13C values after the 6% H2SO3 and 1 M H3PO4 treatments were significantly different (p < 0.013 and < .05, respectively) from all other treatments. Mass balance calculations indicate that in some instances delta13C values were biased due to a contribution from unreacted carbonate carbon. There were no significant differences in the mean TN between any acid-treated and non-acidified samples. The mean delta15N values after 6 M HCl, 6% H2SO3 and 1 M H3PO4 treatments were significantly different from the untreated sediment sample (p < 0.044). Based on the significant bias observed for the delta15N and delta13C values, a weak (1-2 M) HCl solution is confirmed as the most appropriate acid for the removal of inorganic carbon from natural materials requiring elemental and isotopic analysis. 相似文献
144.
A simple method for the alkaline hydrolysis of esters 总被引:1,自引:0,他引:1
Vassiliki Theodorou Konstantinos Skobridis Valentine Ragoussis 《Tetrahedron letters》2007,48(46):8230-8233
A very mild and rapid procedure for the efficient alkaline hydrolysis of esters in non-aqueous conditions has been developed, by the use of dichloromethane/methanol (9:1) as solvent. This method conveniently provides both carboxylic acids and alcohols from the corresponding esters and sodium hydroxide in a few minutes at room temperature. A plausible reaction mechanism is proposed. 相似文献
145.
Gergely Kovács Tas Szász-Vadász Vassilis C. Papadimitriou Sándor Dóbé Tibor Bérces Ferenc Márta 《Reaction Kinetics and Catalysis Letters》2005,87(1):129-138
Summary Pulsed laser photolysis with resonance fluorescence monitoring of OH radicals was applied at T = 300±2 K to obtain the rate constants of k1= (3.38±0.60)x10-12, k2= (2.52±0.44)x10-13and k3 = (1.06±0.30)x10-13cm3molecule-1s-1with 2σprecision given for the overall reactions OH + CH3CH2OH (1), OH + CF2HCH2OH (2) and OH + CF3CH2OH (3), respectively. k2is the first direct kinetic data for the reaction of OH radicals with CF2HCH2OH reported in the literature.</o:p> 相似文献
146.
Dr. Guoju Yang Dr. Sneha A. Akhade Xi Chen Dr. Yue Liu Dr. Mal‐Soon Lee Dr. Vassiliki‐Alexandra Glezakou Dr. Roger Rousseau Prof. Dr. Johannes A. Lercher 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(11):3565-3570
The thermodynamic state of H2 adsorbed on Pt in the aqueous phase was determined by kinetic analysis of H2 reacting with D2O to HDO, HD, and D2, and by DFT‐based ab initio molecular dynamics simulations of H2 adsorption on Pt(111), Pt(110), and Pt nanoparticles. Dissociative adsorption of H2 on Pt is significantly weakened in the aqueous phase compared to adsorption at gas–solid interfaces. Water destabilizes the adsorbed H atoms, decreasing the heat of adsorption by 19–22 kJ while inducing an additional entropy loss of 50–70 J K?1. Upon dissociative adsorption of H2, the average distance of water from the Pt surface increases and the liquid adopts a structure that is more ordered than before close to the Pt surface, which limits the translation mobility of the adsorbed H atoms. The presence of hydrated hydronium ions next to the Pt surface further lowers the H?Pt bond strength. 相似文献
147.
Aristotelis Xenakis Vassiliki Papadimitriou Theodore G. Sotiroudis 《Current Opinion in Colloid & Interface Science》2010,15(1-2):55-60
Natural oils are in general mixtures of triglycerides of various fatty acids containing also small quantities of a multitude of other molecules, the minor components. Their composition depends on the type of their sources, either vegetable or animal, and on agronomic and climatic conditions. Extraction process highly influences the final composition of the natural oils. The bulk triglyceride phase presents some structural order due to the internal polarity of these molecules. The presence of the minor components, which are either amphiphilic or even hydrophilic together with some remaining moisture, induces colloidal association within the lipophilic triglyceride phase. These local organizates host proteins and antioxidants that preserve their activity influencing the quality and stability of the edible oils. Of specific interest is the case of the veiled virgin olive oil, the untreated juice of the olives. Veiled virgin olive oil is unique among vegetable oils that is consumed without any refining process and consequently possesses colloidal structure. It is remarkable that this unfiltered oil presents higher resistance to oxidation than the filtered ones, indicating the significance of internal structure to the final quality of the product. 相似文献
148.
149.
Sofia A. Papadimitriou 《European Polymer Journal》2008,44(7):2356-2366
A series of novel poly(ε-caprolactone-co-propylene succinate) P(CL-co-PSu) copolymers having low propylene succinate content and high molecular weight were synthesized following a combinatory scheme of ring opening and polycondensation reactions, in an attempt to obtain copolymers of sufficient performance and increased biodegradation rates. Enzymatic hydrolysis of the copolymers was studied in the presence of mixture of Rhizopus delemar and Pseudomonas cepacia lipases. Much higher hydrolysis rates, comparing to neat PCL, were proved by both mass loss measurements and scanning electron microscopy (SEM) observations of the degraded film surfaces. Thermodynamics of cocrystallization and wide-angle X-ray diffraction (WAXD) patterns were investigated to estimate the extent of comonomer cocrystallization. Results of the study showed that comonomer inclusion may hold, though the molar fraction of the comonomer in the PCL crystals is lower than in the bulk. This means that not only the observed decrease of the degree of crystallinity from about 48% for PCL to about 29% for the P(CL-co-PSu) 75/25 favours enzymatic hydrolysis, but also the enrichment of the amorphous phase in the fast degrading propylene succinate units plays its role. The non-isothermal crystallization rates of the copolymers, like the melting points, decreased substantially when the propylene succinate content exceeded 8 mol%. The activation energy of crystallization was calculated using the isoconversional method of Friedman, over the whole range of crystallization temperatures. An increase was found in the activation energy with increasing the comonomer content in the copolymers also proving the reduced symmetry along the copolymer chains due to the presence of comonomer units. 相似文献
150.
Akio Imai Etsuko Nishimura Masahiro Hattori Stratos Papadimitriou 《European Journal of Operational Research》2007
This paper addresses the berth allocation problem at a multi-user container terminal with indented berths for fast handling of mega-containerships. In a previous research conducted by the authors, the berth allocation problem at a conventional form of the multi-user terminal was formulated as a nonlinear mathematical programming, where more than one ship are allowed to be moored at a specific berth if the berth and ship lengths restriction is satisfied. In this paper, we first construct a new integer linear programming formulation for easier calculation and then the formulation is extended to model the berth allocation problem at a terminal with indented berths, where both mega-containerships and feeder ships are to be served for higher berth productivity. The berth allocation problem at the indented berths is solved by genetic algorithms. A wide variety of numerical experiments were conducted and interesting findings were explored. 相似文献