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31.
We have fitted the π? spectra from the reactions π±p → π?+ anything using an expression which exhibits the differing forward-backward slopes of the x-distributions, the turnover near (but not exactly at) x = 0 and the correlations between P1 and p2T. The expression is a generalized Bose-Einstein distribution which is covariant with respect to Lorentz transformation along the incident beam direction. 相似文献
32.
John P. Linsky Thomas R. Paul Malcolm E. Kenney 《Journal of Polymer Science.Polymer Physics》1971,9(1):143-160
Work on two sheet organosilicon polymers, one derived from the mineral chrysotile and the other from the mineral apophyllite, is described. This work provides direct evidence that both these polymers are composed of sheets. In addition, it shows that in the chrysotile-derived polymer the sheets curl into scrolls, and that in the apophyllite-derived polymer the sheets are essentially flat. 相似文献
33.
34.
Edithe Selwa Ian M. Kenney Oliver Beckstein Bogdan I. Iorga 《Journal of computer-aided molecular design》2018,32(10):1203-1216
Macroscopic pKa values were calculated for all compounds in the SAMPL6 blind prediction challenge, based on quantum chemical calculations with a continuum solvation model and a linear correction derived from a small training set. Microscopic pKa values were derived from the gas-phase free energy difference between protonated and deprotonated forms together with the Conductor-like Polarizable Continuum Solvation Model and the experimental solvation free energy of the proton. pH-dependent microstate free energies were obtained from the microscopic pKas with a maximum likelihood estimator and appropriately summed to yield macroscopic pKa values or microstate populations as function of pH. We assessed the accuracy of three approaches to calculate the microscopic pKas: direct use of the quantum mechanical free energy differences and correction of the direct values for short-comings in the QM solvation model with two different linear models that we independently derived from a small training set of 38 compounds with known pKa. The predictions that were corrected with the linear models had much better accuracy [root-mean-square error (RMSE) 2.04 and 1.95 pKa units] than the direct calculation (RMSE 3.74). Statistical measures indicate that some systematic errors remain, likely due to differences in the SAMPL6 data set and the small training set with respect to their interactions with water. Overall, the current approach provides a viable physics-based route to estimate macroscopic pKa values for novel compounds with reasonable accuracy. 相似文献
35.
Smita Dayal Jun Li Ying-Syi Li Hongqiao Wu Anna C S Samia Malcolm E Kenney Clemens Burda 《Photochemistry and photobiology》2008,84(1):243-249
This study examines the electronic coupling between quantum dots (QDs) and molecules on their surfaces as a function of the modality of their interaction. As a probe, the energy transfer (ET) between CdSe QDs and phthalocyanines (Pcs) was monitored and evaluated with regard to the functionalization of the axial phthalocyanine ligand, bulkiness of the functional group bridging the QD donor and Pc acceptor, and the number of the functionalized axial ligands. New silicon PCs and their conjugates with CdSe QDs were synthesized. The ET efficiency and kinetics were studied by steady state and femtosecond time-resolved absorption spectroscopy. We observed a decrease in ET efficiency with the increase in functional group bulkiness, which could be explained by increasing steric hindrance between the ET pair. In addition, a higher ET efficiency was observed for amino and thiol functionalized Pcs compared to Pcs without functional group on the axial alkyl chain. 相似文献
36.
The gas-phase thermolysis of the guanidinato aluminum amide precursor [Me2NC(NiPr)2]Al(NMe2)2 (1) in the oven temperature range of ambient temperatures to 600 °C has been investigated with matrix-isolation FTIR spectroscopy and time-of-flight mass spectrometry (argon as carrier gas). Precursor 1 fragments above 300 °C to form iPrCNCiPr (2) and monomeric Al(NMe2)3 (3m). Independent thermolysis series with 2 and the aluminum amide dimer 3d, [Al(NMe2)3]2, were conducted and been used to interpret the results of the fragmentation of precursor 1. Compound 3m was present in the thermolysis range of 350–450 °C and has been identified for the first time. Through a comparison of measured FTIR spectra with the calculated spectrum of 3m (D3 point group symmetry; B3LYP/6-31G(d) level of theory) all expected IR bands were found and could be assigned to normal modes. At thermolysis temperatures of ?500 °C signals indicative for H2CNCH3 (4) were found, showing that 3m fragments further at higher temperature. The thermolysis product 2 (iPrCNCiPr) withstands the higher thermolysis temperatures. From our study one can conclude that precursor 1 cleanly delivers the monomeric aluminum alane 3m, which then acts as the reactive material forming species. 相似文献
37.
Dayal S Lou Y Samia AC Berlin JC Kenney ME Burda C 《Journal of the American Chemical Society》2006,128(43):13974-13975
The effect of linker chain length on the energy transfer from CdSe quantum dots (QDs) to silicon phthalocyanine (Pc) photodynamic therapy agents was investigated by steady-state and femtosecond time-resolved spectroscopy with 500 nm light for the specific excitation of the QD energy donor. The conjugation between the QD and the Pc was achieved with linker chains varying from 4 to 9 bond lengths by incorporating 1-6 methylene groups into the axial ligand of the Pc. With increasing chain length, the energy-transfer efficiency increased, which appears to be opposed to a purely F?rster-type resonance energy-transfer behavior that is commonly discussed for the energy transfer in QD conjugates. The obtained results provide strong evidence for a capping-layer-mediated energy transfer in the QD-based donor-acceptor conjugates. 相似文献
38.
Stephen Kenney Kade Poper Ganesh Chapagain Gordon F. Christopher 《Rheologica Acta》2013,52(5):485-497
Viscoelastic flow around a confined cylinder at high Deborah numbers is studied using microfluidic channels. By varying fluid properties and flow rates, a systematic study of the roles of elasticity and inertia is accomplished. Two new elastic flow instabilities that occur at high Deborah numbers are identified. A downstream instability of disordered and temporally varying streamlines is observed at a Deborah number above 10. This instability is a precursor to an unsteady vortex that develops upstream of the cylinder at higher Deborah numbers. Both instabilities occur at moderate Reynolds numbers but are fundamentally elastic. The size and steadiness of the upstream vortex are primarily controlled by the Deborah and the elasticity number. 相似文献
39.
40.
C. Jacobsen J. M. Kenney J. Kirz I. McNulty R. J. Rosser F. Cinotti H. Rarback D. Shu 《Photochemistry and photobiology》1986,44(3):421-423
Scanning soft X-ray microscopy offers several advantages over other forms of X-ray microscopy. It subjects the specimen to the lower doses of radiation and by digitally recording the image, gives direct quantitative information on the absorption of the specimen as a function of position. Elemental maps can be produced easily by comparing images taken at different wavelengths, chosen to exploit X-ray absorption edges or resonances. This technique was used to explore the distribution of calcium in 0.2 μm-thick bone specimens, detecting concentrations of 5% by weight, with a spatial resolution of 0.2 μm. Progress in X-ray sources in the form of undulators and in X-ray optics indicates that soon the range of elements that can be mapped will be extended and the spatial resolution and elemental sensitivity will be improved by an order of magnitude. 相似文献