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971.
Jessica L. Carvalho Michael E. Somers Kari Dalnoki‐Veress 《Journal of Polymer Science.Polymer Physics》2011,49(10):712-716
Ellipsometry is used to measure the crystallization and melting temperature of a bidisperse blend of a crystalline‐amorphous diblock copolymer. Binary blends of sphere‐forming poly(butadiene‐ethylene oxide) (PB‐PEO) of two different molecular weights are prepared. The two PB‐PEO diblocks that are used share the same amorphous majority PB block length but different crystalline PEO minority block length. As the concentration of higher molecular weight diblock in the blend is increased, the size of the PEO spherical domains swell, providing access to the full range of domain sizes between the limits of the two neat diblock components. The change in domain size is consistent with a monotonic change in both the crystallization and melting temperatures. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 相似文献
972.
Lyubomira Ivanov Jessica Rosenholm Tanya Tsoncheva Mika Linden Daniela Paneva Ivan Mitov 《Reaction Kinetics and Catalysis Letters》2008,95(2):329-336
Iron modified NH2- or COOH- functionalized SBA-15 is characterized by XRD, N2-physisorption, TPR-TG, FTIR, M?ssbauer spectroscopy and methanol decomposition. The material obtained from COOH-functionalized
silica exhibits the highest catalytic activity. 相似文献
973.
Irina P. Smoliakova Jessica L. Wood Valeria A. Stepanova Relindis Y. Mawo 《Journal of organometallic chemistry》2010,695(3):360-8772
Tertiary, secondary and primary benzylamines, as well as structurally different oxazolines readily reacted with Pd(OAc)2 on silica gel to form cyclopalladated complexes containing a five or six-membered palladacycle with a (sp2)C-Pd or (sp3)C-Pd bond. The complexes were obtained in 45-98% yield, which is comparable with or exceeds the yields reported for preparation of the same compounds in solution. Aliphatic (sp3)C-H bond activation took place in the cyclopalladation of (S)-2-tert-butyl-4-phenyl-2-oxazoline on SiO2 leading to the exclusive formation of the corresponding endo palladacycle, whereas two products were reported for the same reaction performed in AcOH. 相似文献
974.
Thomas A. Spencer Janeta Popovici-Müller Bobbijo van Beusichem Celeste Viscardi MacMillan Carolee F. Lavey Jessica M. Sin Robert Ditchfield 《Tetrahedron》2010,66(25):4441-4451
Toward the goal of gaining further insight into carbocation-π interactions, bridged-ring aromatic alkene model systems are being investigated in which one isomer will permit π complexation of an intramolecular tertiary carbocation with a benzene ring, but the other isomer will not. The syntheses of three sets of such isomers, having, respectively, benzobicyclo[3.2.1]octene, benzobicyclo[2.2.1]heptene, and benzobicyclo[4.2.1]nonene structures, are described. 相似文献
975.
Célia M. Silveira Jessica Baur Michael Holzinger José J. G. Moura Serge Cosnier M. Gabriela Almeida 《Electroanalysis》2010,22(24):2973-2978
Single‐walled carbon nanotubes (SWCNTs) deposits on glassy carbon and pyrolytic graphite electrodes have dramatically enhanced the direct electron transfer of the multihemic nitrite reductase from Desulfovibrio desulfuricans ATCC 27774, enabling a 10‐fold increase in catalytic currents. At optimal conditions, the sensitivity to nitrite and the maximum current density were 2.4±0.1 A L mol?1 cm?2 and 1500 µA cm?2, respectively. Since the biosensor performance decreased over time, laponite clay and electropolymerized amphiphilic pyrrole were tested as protecting layers. Both coating materials increased substantially the bioelectrode stability, which kept about 90 % and 60 % of its initial sensitivity to nitrite after 20 and 248 days, respectively. 相似文献
976.
Duane E. Weisshaar Gary W. Earl Eric M. Villa Jessica L. Zierke Christopher J. Fry Kara L. Becvar Shik Ki Li Matthew C. Schafer 《国际化学动力学杂志》2010,42(4):221-225
Quaternary ammonium compounds are produced worldwide in hundreds of millions of pound volume annually for a plethora of end‐uses from fabric‐care formulations to asphalt emulsifiers, typically from nongreen alkylating reagents. The kinetics of a reaction employing dimethyl carbonate (DMC) as a green alkylating agent was investigated using three trialkylamines (tributylamine, trihexylamine, and trioctylamine) at several temperatures. Arrhenius and Eyring analysis of the data showed that values of Ea (79 kJ/mol), ΔH? (75 kJ/mol), and ΔS? (220 J/(mol K)) were the same for all three amine reactants, consistent with a report that Ea is independent of alkyl chain length when the chain length is greater than three carbons. Although rates are significantly slower with DMC than with other alkylating reagents, the resulting methyl carbonate anion has advantages for clean anion metathesis, which is important for some applications, especially those involving ionic liquids. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 221–225, 2010 相似文献
977.
Aaron Bostwick Jessica McChesney Taisuke Ohta Eli Rotenberg Thomas Seyller Karsten Horn 《Progress in Surface Science》2009,84(11-12):380-413
Graphene, the single layer of hexagonally coordinated carbon, is a two-dimensional material with many unusual properties; its physical realization a few years ago has caused a storm of activities in the solid state physics and materials science communities. The intriguing “massless Dirac Fermion” character of its charge carriers renders graphene a unique study object in condensed matter physics, and we discuss how surface-related techniques such as photoemission, STM and LEED play a prominent role in these investigations. We report on experimental studies of the growth and electronic structure of epitaxial single and few layer graphene on silicon carbide. The unusual band structure of single layer graphene and its evolution as layers are added towards bulk graphite is studied. In the special case of the bilayer, the opening of a gap by inducing an asymmetry through the influence of doping is examined. Finally, the influence of many body processes on the spectral function is discussed on the basis of high resolution photoemission data. The discussion of these aspects gives a comprehensive overview of the electronic structure of graphene as examined by experiment. 相似文献
978.
An imaging mass spectrometric method using laser ablation inductively coupled plasma spectrometry (LA-ICP-MS) was developed to determine Cu, Zn, Cd, Hg and Pb and metal distribution in longitudinal tissue sections of the marine snail Nassarius reticulatus (Gastropoda, Prosobranchia). Snails were sampled in northern Brittany (France) at three stations with different contamination levels.The quantification of metal distribution (imaging or mapping) in a thin slice of the snail tissue was carried out using different strategies: by one-point calibration and via matrix-matched laboratory standards using different biological materials (BCR 278, snail tissue, and rat brain). Together with the imaging of metals the distribution of two non-metals (carbon and sulfur) was analyzed. The imaging LA-ICP-MS analysis yielded an inhomogeneous distribution for all elements investigated. The detection limits for the distribution analysis of Cu, Zn, Cd, Hg and Pb measured by LA-ICP-MS were in the low μg g−1 range. 相似文献
979.
This paper is devoted to the study of specific statistical methods for extremal events in the markovian setup, based on the regenerative method and the Nummelin technique. Exploiting ideas developed in Rootzén (Adv Appl Probab 20:371–390, 1988), the principle underlying our methodology consists of first generating a random number l of approximate pseudo-renewal times τ 1, τ 2, ..., τ l for a sample path X 1, ..., X n drawn from a Harris chain X with state space E, from the parameters of a minorization condition fulfilled by its transition kernel, and then computing submaxima over the approximate cycles thus obtained: $\max_{1+\tau_1\leq i \leq \tau_2}f(X_i),\;\ldots ,\;\max_{1+\tau_{l-1}\leq i \leq \tau_l}f(X_i)This paper is devoted to the study of specific statistical methods for extremal events in the markovian setup, based on the
regenerative method and the Nummelin technique. Exploiting ideas developed in Rootzén (Adv Appl Probab 20:371–390, 1988), the principle underlying our methodology consists of first generating a random number l of approximate pseudo-renewal times τ
1, τ
2, ..., τ
l
for a sample path X
1, ..., X
n
drawn from a Harris chain X with state space E, from the parameters of a minorization condition fulfilled by its transition kernel, and then computing submaxima over the approximate cycles thus obtained: max1+t1 £ i £ t2f(Xi), ?, max1+tl-1 £ i £ tlf(Xi)\max_{1+\tau_1\leq i \leq \tau_2}f(X_i),\;\ldots ,\;\max_{1+\tau_{l-1}\leq i \leq \tau_l}f(X_i) for any measurable function f:E→ℝ. Estimators of tail features of the sample maximum max1 ≤ i ≤ n
f(X
i
) are then constructed by applying standard statistical methods, tailored for the i.i.d. setting, to the submaxima as if they
were independent and identically distributed. In particular, the asymptotic properties of extensions of popular inference
procedures based on the conditional maximum likelihood theory, such as Hill’s method for the index of regular variation, are
thoroughly investigated. Using the same approach, we also consider the problem of estimating the extremal index of the sequence
{f(X
n
)}
n ∈ ℕ under suitable assumptions. Eventually, practical issues related to the application of the methodology we propose are discussed
and preliminary simulation results are displayed. 相似文献
980.
Michael A. Parkes Jessica F. Lockyear Stephen D. Price 《International journal of mass spectrometry》2009,280(1-3):85
The reaction between Ar2+ and C2H2 has been studied, at centre-of-mass collision energies ranging from 3 to 7 eV, using a position-sensitive coincidence technique to detect the monocation pairs, which are formed. Sixteen different reaction channels generating pairs of monocations have been observed, these channels arise from double-electron-transfer, single-electron-transfer and chemical reactions forming ArC+. Examination of the scattering diagrams and energetic information extracted from the coincidence data indicate that double-electron-transfer is a direct process, which does not involve a collision complex, and the derived energetics point towards a concerted, not stepwise, mechanism for the two-electron-transfer. As is commonly observed, single-electron-transfer from C2H2 to Ar2+ takes place via a direct mechanism, again not involving complexation. Most of the C2H2+ products that are formed in the single-electron-transfer reactions possess significant (12–15 eV) internal energy and fragment rapidly within the electric field of the partner Ar+ ion. The chemical reactions appear to proceed via a direct mechanism involving the initial formation of ArCH+, which subsequently fragments to form ArC+. 相似文献