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971.
Pamela M. Lundin Gaurav Giri Zhenan Bao 《Journal of polymer science. Part A, Polymer chemistry》2013,51(4):908-915
Previous routes to polymers with mono‐alkylated bithiophenes have proceeded through polymerization of monoalkyl‐2,2′‐bithiophene monomers through oxidative or AB‐type cross‐coupling polymerizations. The resulting polymer regiochemistry affects both the location and orientation of the polymer side‐chains. In contrast, AABB‐type cross‐coupling polymerizations can control the location and in some cases the orientation of the side‐chains. To study how this control can impact polymer properties, two poly(monodecyl‐2,2′‐bithiophene) polymers have been synthesized through Stille AABB‐type polycondensations of 2,5‐bis(trimethylstannyl)thiophene with different monomers. The alkyl side‐chains are located on every other thiophene, but polymer 1 consists of both head‐to‐tail and head‐to‐head dyads, whereas polymer 2 is made up of only head‐to‐head dyads. 1H NMR, 13C NMR, and heteronuclear single quantum correlation spectroscopy are used to confirm and contrast the polymer regiochemistries. The physical properties of the two polymers are analyzed using UV–vis spectroscopy, differential scanning calorimetry, and grazing‐incidence X‐ray diffraction. Polymer 2 is found to display significantly more aggregation in solution than 1, and it displays different thermal properties. The film properties of polymers 1 and 2, however, are very similar, with nearly identical UV–vis profiles and d‐spacing values as determined by grazing incidence X‐ray diffraction. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
972.
973.
A decomposition method for approximate evaluation of continuous flow multi-stage lines with general Markovian machines 总被引:1,自引:0,他引:1
In this paper, a decomposition method for evaluating the performance of continuous flow lines with machines characterized by general Markovian fluid models and finite capacity buffers is proposed. This study uses the exact solution of general two-stage Markovian fluid models as a building block. Decomposition equations are provided to propagate the effect of partial and complete blocking and starvation phenomena throughout the system. A decomposition algorithm that solves the new decomposition equations is proposed. Numerical results prove the good accuracy of the developed method. In particular, a comparison with existing techniques shows that our method is generally more accurate, especially in the estimation of the average buffer levels. Moreover, additional information can be collected by the application of our approach which enables a deeper analysis of the system behavior. Finally, the generality of the approach allows for modeling and studying many different system configurations within a unique framework, also including several previously uninvestigated layouts. 相似文献
974.
Christopher L. Fleming Stanley E. Griffis John E. Bell 《European Journal of Operational Research》2013
Routing problems often utilize experimental networks to represent real world scenarios. However most ignore the inclusion of triangle inequality violations, a phenomenon resulting from delays or rounding errors within a network. This work evaluates the effect of both frequency – the number of violations – and severity – the degree of intensity of a violation – of triangle inequality and evaluates both solution quality and solution time based on Simulated Annealing, Ant Colony Optimization and Savings Algorithm methods. Findings indicate that while both frequency and severity degrade solution quality, increased levels of frequency and severity together result in significant adverse affects to solution quality. Solution time, however, is not impacted by the presence of triangle inequality violations within the network. This information should encourage practitioners to identify delays and maintain the presence of triangle inequality violations in a network to ensure accuracy of solution quality. 相似文献
975.
Ruth A. Odhiambo Gerald K. Muthakia Stanley M. Kagwanja 《Transition Metal Chemistry》2012,37(5):431-437
Mo(NO)T p * Cl2 (T p * ?=?3,5-dimethyl pyrazole) when reacted with m-functionalized Fe(III) Schiff base complexes; the Schiff base ligands being derived from condensation of 2,4-dihydroxybenzaldehyde or salicylaldehyde with a variety of ??,??-diamines [1,2-C6H4(NH2)2, NH2(CH2) n NH2; n?=?2?C4] affords bimetallic complexes containing two potential reduction centers. The compounds were characterized by physicochemical and spectroscopic methods. It is shown that as the polymethylene carbon chain of the Schiff base backbone increases, the physicochemical and spectroscopic properties also change gradually. Electrochemical data show that the m-functionalized complexes reduce at potentials less cathodic than their p-substituted analogues. It is also shown that the redox potentials are solvent dependent. 相似文献
976.
Chunmei Ban Natalya A. Chernova M. Stanley Whittingham 《Electrochemistry communications》2009,11(3):522-525
Nanocrystallites of vanadium pentoxide were synthesized by the hydrothermal treatment of electrospun composite nanofibers. Each crystallite of dimension ?100 nm was found to be a single crystal of δ-phase HxV4O10 · nH2O. The crystallinity and morphology was maintained on heating to 500 °C when V2O5 was formed. The electrochemical capacity of the nano-V2O5 in a lithium cell was found to be above 350 mAh/g. The columbic efficiency is close to 100% when small amounts of lithium bis(oxalato)borate is added to the LiPF6 electrolyte. 相似文献
977.
Roderick R. Kunz Kerin Clow Gregory Dennis Hardy Jonathan Oyler Stanley A. Ostazeski Augustus Way Fountain III 《Analytical and bioanalytical chemistry》2009,395(2):357-369
A campaign to measure the amount of trace explosive residues in an operational military environment was conducted on May 27–31,
2007, at the National Training Center at Fort Irwin, CA, USA. The objectives of this campaign were to develop the methods
needed to collect and analyze samples from tactical military settings, to use the data obtained to determine what the trace
explosive signatures suggest about the potential capabilities of chemical-based means to detect IEDs, and, finally, to present
a framework whereby a sound understanding of the signature science can be used to guide development of new sensing technologies
and sensor concepts of operation. Through our use of combined background and threat signature data, we have performed statistical
analyses to estimate upper limits of notional sensor performance that is limited only by the spatial correlation of the signature
chemicals to the threats of interest. 相似文献
978.
Frédéric Bayart Pamela Gorkin Sophie Grivaux Raymond Mortini 《Arkiv f?r Matematik》2009,47(2):205-229
We give several characterizations of those sequences of holomorphic self-maps {φ
n
}
n≥1 of the unit disk for which there exists a function F in the unit ball of H
∞ such that the orbit {F∘φ
n
:n∈ℕ} is locally uniformly dense in . Such a function F is said to be a -universal function. One of our conditions is stated in terms of the hyperbolic derivatives of the functions φ
n
. As a consequence we will see that if φ
n
is the nth iterate of a map φ of into , then {φ
n
}
n≥1 admits a -universal function if and only if φ is a parabolic or hyperbolic automorphism of . We show that whenever there exists a -universal function, then this function can be chosen to be a Blaschke product. Further, if there is a -universal function, we show that there exist uniformly closed subspaces consisting entirely of universal functions. 相似文献
979.
980.
Nalinda Almeida Stanley Hirschi Anja Mueller Leela Rakesh 《Journal of Thermal Analysis and Calorimetry》2010,102(2):647-652
Viscoelastic properties of κ-carrageenan in saline solution at various concentrations and pH were investigated by dynamic
rheological techniques, viscosity, elasticity measurements, and IR spectrometry. The viscosity and elasticity at low concentrations
of κ-carrageenan do not depend on pH, confirming that κ-carrageenan is in a disordered conformation. At 0.7% κ-carrageenan,
the disordered confirmation transforms into an ordered helical confirmation with the possibility of weak-type gel formation.
The transformation is also confirmed by dynamic measurements of loss and storage moduli. Furthermore, at this concentration,
the viscosity and elasticity are highly dependent on pH. At higher concentrations of NaCl (0.5 M) at some pHs, we observed
that storage moduli is greater than loss moduli for the entire frequency region. Hence, there is a possibility of structure
transformation from weak-type gel to a somewhat intermediate gel. The lowest viscosity and elasticity were obtained at extreme
pH, confirming that there are structural changes occurring at these pHs due to hydrolysis. This is confirmed by IR data. 相似文献