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61.
62.
Background
Recently several studies have shown that people use contextual information to make predictions about the rest of the sentence or story as the text unfolds. Using event related potentials (ERPs) we tested whether these on-line predictions are based on a message-level representation of the discourse or on simple automatic activation by individual words. Subjects heard short stories that were highly constraining for one specific noun, or stories that were not specifically predictive but contained the same prime words as the predictive stories. To test whether listeners make specific predictions critical nouns were preceded by an adjective that was inflected according to, or in contrast with, the gender of the expected noun. 相似文献63.
Molecules are created from a Bose-Einstein condensate of atomic 87Rb using a Feshbach resonance. A Stern-Gerlach field is applied, in order to spatially separate the molecules from the remaining atoms. For detection, the molecules are converted back into atoms, again using the Feshbach resonance. The measured position of the molecules yields their magnetic moment. This quantity strongly depends on the magnetic field, thus revealing an avoided crossing of two bound states at a field value slightly below the Feshbach resonance. This avoided crossing is exploited to trap the molecules in one dimension. 相似文献
64.
Mode-mismatched thermal lens (TL) measurements in Cr3+-doped fluoride crystals (LiSrAIF6 and LiSrGaF6) are reported. A nonlinear increase of the TL signal, and decrease of quantum efficiency, with increasing excitation power was observed and attributed to energy-transfer upconversion (ETU). Assuming an upconversion rate that is proportional to the excited-state population, Wup = gammaN(e), the theoretical model developed fits the experimental data well. The ETU parameters (gamma) were determined with unprecedented accuracy for low Cr concentrations. Thermo-optical parameters (K, ds/dT) were also obtained. 相似文献
65.
N. Karayianis D.E. Wortman H.P. Jenssen 《Journal of Physics and Chemistry of Solids》1976,37(7):675-682
The energy levels for Ho3+ in single crystal LiYF4 from 0–21,300 cm?1 have been determined from polarized absorption and fluorescence spectra using crystals at temperatures between 4 and 300°K. Energy level assignments were made initially by comparing the crystal spectra with energy levels calculated by using crystal field parameters interpolated from previously reported analyses of Nd3+, Er3+ and Tm3+ in LiYF4. The energy level scheme identifies energy levels in the 10 lowest J-multiplets and gives calculated energies for the next six higher J-multiplets. The crystal field parameters were varied to obtain a best fit between experimental and theoretical energies, and the final values B20 = 410, B40 = ? 615, B44 = 819, B60 = ? 27.9 and B64 = 677 ± i32.8 cm?1 give an r.m.s. fit of 2.78 cm?1. The calculations were made by diagonalizing the crystal field Hamiltonian, Hx = ΣkmBkmCkm, in the space of ten lowest J-multiplets spanned by intermediate coupled free-ion wavefunctions calculated using the free-ion parameters of Carnall et al. for Ho in aqueous solution. The calculated g∥ for the Γ3.4 ground state of 13.63 compares favorably with a previously reported value of 13.3 ± 0.1. 相似文献
66.
In this work we used the Thermal Lens (TL) technique to discriminate two important processes responsible to reduce the upper-state population and fluorescence quantum efficiency (η) in Cr3+ doped colquiriite crystals: the thermal quenching of the fluorescence (TQF) and the Auger upconversion (ETU). We observed a nonlinear increase of the TL signal with laser power due to the decrease of η by ETU and/or TQF. The analysis of these curves allowed the determination of the thermal load, the increase of the crystal temperature as a function of the pump excitation and the discrimination between ETU and TQF processes. 相似文献
67.
Dr. Marte Sofie Martinsen Holmsen Dr. Ainara Nova Dr. Sigurd Øien-Ødegaard Dr. Richard H. Heyn Prof. Mats Tilset 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(4):1532-1536
A highly asymmetric AuIII η3-allyl complex has been generated by treating Au(η1-allyl)Br(tpy) (tpy=2-(p-tolyl)pyridine) with AgNTf2. The resulting η3-allyl complex has been characterized by NMR spectroscopy and X-ray crystallography. DFT calculations and variable temperature 1H NMR suggest that the allyl ligand is highly fluxional. 相似文献
68.
Dr. Alessandro Longo Dr. Ewoud J. J. de Boed Dr. Nisha Mammen Dr. Marte van der Linden Prof. Dr. Karoliina Honkala Prof. Dr. Hannu Häkkinen Prof. Dr. Petra E. de Jongh Dr. Baira Donoeva 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(31):7051-7058
Controlling the size and uniformity of metal clusters with atomic precision is essential for fine-tuning their catalytic properties, however for clusters deposited on supports, such control is challenging. Here, by combining X-ray absorption spectroscopy and density functional theory calculations, it is shown that supports play a crucial role in the evolution of monolayer-protected clusters into catalysts. Based on the acidic nature of the support, cluster-support interactions lead either to fragmentation of the cluster into isolated Au–ligand species or ligand-free metallic Au0 clusters. On Lewis acidic supports that bind metals strongly, the latter transformation occurs while preserving the original size of the metal cluster, as demonstrated for various Aun sizes. These findings underline the role of the support in the design of supported catalysts and represent an important step toward the synthesis of atomically precise supported nanomaterials with tailored physico-chemical properties. 相似文献
69.
Balchen M Gjelstad A Rasmussen KE Pedersen-Bjergaard S 《Journal of chromatography. A》2007,1152(1-2):220-225
Electrokinetic cross membrane extraction of acidic drugs was demonstrated for the first time. The acidic drugs were extracted from an alkaline aqueous donor solution (300 microl), through a thin supported liquid membrane of 1-heptanol sustained in the pores of the wall of a porous hollow fiber, and into an aqueous alkaline acceptor solution (30 microl) present inside the lumen of the hollow fiber by the application of a d.c. electrical potential. The negative electrode was placed in the donor solution, and the positive electrode was placed in the acceptor solution. Optimal extractions were accomplished with 1-heptanol as the supported liquid membrane, with 50 V as the driving force, and with pH 12.0 in both the donor and acceptor solutions, respectively (NaOH). Equilibrium extraction conditions were obtained after 5 min of operation with the whole assembly agitated at 1200 rpm. Eleven different acidic drugs were extracted with recovery values between 8 and 100%, and initial data supported that electrokinetic cross membrane extraction provided repeatable data and linear response between original donor concentration and final acceptor concentration of the acidic model compounds. 相似文献
70.
Seip KF Stigsson J Gjelstad A Balchen M Pedersen-Bjergaard S 《Journal of separation science》2011,34(23):3410-3417
A large screening of different components in the supported liquid membrane (SLM) in electromembrane extraction (EME) was performed to test the extraction efficiency on eight model peptides. Electromembrane extraction from a 500 μL acidified aqueous sample containing the model peptides in the concentration 10 μg/mL was used. Extraction time was 5 min with an electric potential of 10 V and 900 rpm agitation of the sample vial. The samples were extracted through a hollow fiber-based SLM with different compositions of organic solvents and carriers. A small volume of acidified acceptor solution (25 μL) was after extraction analyzed directly, or with some dilution, on CE or HPLC. This article has identified mono- or di-substituted phosphate groups as the prominent group of carrier molecules needed to obtain acceptable recoveries. For the organic solvents, primary alcohols and ketones have shown promise regarding recovery and reproducibility, with some differences in selectivity. A new composition of the SLM, namely 2-octanone and tridecyl phosphate (90:10 w/w) has proved to give higher extraction recoveries and lower standard deviation than SLMs previously reported in the literature. 相似文献