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201.
Sahu A Qi L Kang MS Deng D Norris DJ 《Journal of the American Chemical Society》2011,133(17):6509-6512
A general, one-pot, single-step method for producing colloidal silver chalcogenide (Ag(2)E; E = Se, S, Te) nanocrystals is presented, with an emphasis on Ag(2)Se. The method avoids exotic chemicals, high temperatures, and high pressures and requires only a few minutes of reaction time. While Ag(2)S and Ag(2)Te are formed in their low-temperature monoclinic phases, Ag(2)Se is obtained in a metastable tetragonal phase not observed in the bulk. 相似文献
202.
Matsuura BS Condie AG McBee IA Buff RC Karahalis GJ Stephenson CR 《Organic letters》2011,13(23):6320-6323
An intramolecular cyclization cascade reaction has been developed utilizing a high valent palladium intermediate that generates a carbon-carbon and carbon-oxygen bond in a single transformation. This method provides rapid access to highly functionalized tricyclic scaffolds, including spirocyclic cyclohexadienones. Good yields and mild conditions are reported with high tolerance toward oxygen and water. 相似文献
203.
Petrov AP Dodgson BJ Cherney LT Krylov SN 《Chemical communications (Cambridge, England)》2011,47(27):7767-7769
We introduce a predictive measure of micromixing termed quantitative overlap (QO). QO depends on the distribution of reactants throughout the reactor and can be calculated by solving equations of diffusion. We used a bimolecular reaction and a capillary microreactor to experimentally prove that QO is proportional to the product yield. 相似文献
204.
Wong BM Cordaro JG 《The journal of physical chemistry. C, Nanomaterials and interfaces》2011,115(37):18333-18341
The band structure and electronic properties in a series of vinylene-linked heterocyclic conducting polymers are investigated using density functional theory (DFT). In order to accurately calculate electronic band gaps, we utilize hybrid functionals with fully periodic boundary conditions to understand the effect of chemical functionalization on the electronic structure of these materials. The use of predictive first-principles calculations coupled with simple chemical arguments highlights the critical role that aromaticity plays in obtaining a low band gap polymer. Contrary to some approaches which erroneously attempt to lower the band gap by increasing the aromaticity of the polymer backbone, we show that being aromatic (or quinoidal) in itself does not ensure a low band gap. Rather, an iterative approach which destabilizes the ground state of the parent polymer toward the aromatic ? quinoidal level crossing on the potential energy surface is a more effective way of lowering the band gap in these conjugated systems. Our results highlight the use of predictive calculations guided by rational chemical intuition for designing low band gap polymers in photovoltaic materials. 相似文献
205.
BM Wong D Lacina IM Nielsen J Graetz MD Allendorf 《The journal of physical chemistry. C, Nanomaterials and interfaces》2011,115(15):7778-7786
Knowledge of the relative stabilities of alane (AlH(3)) complexes with electron donors is essential for identifying hydrogen storage materials for vehicular applications that can be regenerated by off-board methods; however, almost no thermodynamic data are available to make this assessment. To fill this gap, we employed the G4(MP2) method to determine heats of formation, entropies, and Gibbs free energies of formation for 38 alane complexes with NH(3-n)R(n) (R = Me, Et; n = 0-3), pyridine, pyrazine, triethylenediamine (TEDA), quinuclidine, OH(2-n)R(n) (R = Me, Et; n = 0-2), dioxane, and tetrahydrofuran (THF). Monomer, bis, and selected dimer complex geometries were considered. Using these data, we computed the thermodynamics of the key formation and dehydrogenation reactions that would occur during hydrogen delivery and alane regeneration, from which trends in complex stability were identified. These predictions were tested by synthesizing six amine-alane complexes involving trimethylamine, triethylamine, dimethylethylamine, TEDA, quinuclidine, and hexamine and obtaining upper limits of ΔG° for their formation from metallic aluminum. Combining these computational and experimental results, we establish a criterion for complex stability relevant to hydrogen storage that can be used to assess potential ligands prior to attempting synthesis of the alane complex. On the basis of this, we conclude that only a subset of the tertiary amine complexes considered and none of the ether complexes can be successfully formed by direct reaction with aluminum and regenerated in an alane-based hydrogen storage system. 相似文献
206.
Melody L. Massar Matthew Fickus Erik Bryan Douglas T. Petkie Andrew J. TerzuoliJr. 《Advances in Computational Mathematics》2011,35(1):83-97
The spectral centroid of a signal is the curve whose value at any given time is the centroid of the corresponding constant-time
cross section of the signal’s spectrogram. A spectral centroid provides a noise-robust estimate of how the dominant frequency
of a signal changes over time. As such, spectral centroids are an increasingly popular tool in several signal processing applications,
such as speech processing. We provide a new, fast and accurate algorithm for the real-time computation of the spectral centroid
of a discrete-time signal. In particular, by exploiting discrete Fourier transforms, we show how one can compute the spectral
centroid of a signal without ever needing to explicitly compute the signal’s spectrogram. We then apply spectral centroids
to an emerging biometrics problem: to determine a person’s heart and breath rates by measuring the Doppler shifts their body
movements induce in a continuous wave radar signal. We apply our algorithm to real-world radar data, obtaining heart- and
breath-rate estimates that compare well against ground truth. 相似文献
207.
Bryan Ek 《Journal of Difference Equations and Applications》2019,25(2):262-293
The q-binomial coefficients were conjectured to be unimodal as early as the 1850's but it remained unproven until Sylvester's 1878 proof using invariant theory. In 1982, Proctor gave an ‘elementary’ proof using linear algebra. Finally, in 1989, Kathy O'Hara provided a combinatorial proof of the unimodality of the q-binomial coefficients. Very soon thereafter, Doron Zeilberger translated the argument into an elegant recurrence. We introduce several perturbations to the recurrence to create a larger family of unimodal polynomials. We analyse how these perturbations affect the final polynomial and analyse some specific cases. 相似文献
208.
Chunhao Zhai Yung P. Koh Bryan D. Vogt Sindee L. Simon 《Journal of polymer science. Part A, Polymer chemistry》2024,62(9):1922-1933
The effect of nanoconfinement on the kinetics of benzyl methacrylate radical polymerization is investigated using differential scanning calorimetry. Controlled pore glass (CPG), ordered mesoporous carbons, and mesoporous silica are used as confinement media with pore sizes from 2 to 8 nm. The initial polymerization rate in CPG and mesoporous silica increases relative to the bulk and increases linearly with reciprocal pore size; whereas, the rate in the carbon mesopores decreases linearly with reciprocal pore size; the changes are consistent with the rate being related to the ratio of the pore surface area to pore volume. Induction times are longer for nanoconfined polymerizations, and in the case of CPG and carbon mesopores, autoacceleration occurs earlier, presumably due to the limited diffusivity and lower termination rates for the confined polymer chains. The molecular weight of the polymer synthesized in the nanopores is generally higher than that obtained in the bulk except at the lowest temperatures investigated. The equilibrium conversion under nanoconfinement decreases with decreasing temperature and with confinement size, exhibiting what appears to be a floor temperature at low temperatures. 相似文献
209.
210.
G. L. Norris 《Fresenius' Journal of Analytical Chemistry》1893,32(1):597
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