Fullerenes have been studied for nearly three decades and enormous advances have been made. Mass spectrometry is commonly used for investigations on the distribution of fullerenes formed from evaporated graphite targets, and soot produced from such targets. We report distributions of fullerenes formed by graphite evaporation by use of a pulsed supersonic cluster source and compare them to certain distributions synthesised by other techniques, such as arc discharge and combustion methods. We highlight the fact that physical processes can occur during the mass spectral analysis of fullerenes under certain conditions that may skew the observed distribution of cage sizes present in a sample. In some cases, an analysis of fullerene-containing soot can greatly exaggerate the relative abundance of large fullerenes compared to C60 and medium-sized fullerenes, depending on the particular experimental setup. 相似文献
Of the many types of catalysis involving two or more catalysts, synergistic catalysis is of great interest because novel reactions or reaction pathways may be discovered when there is synergy between the catalysts. Herein, we describe a synergistic cascade catalysis, in which immobilized Au/Pd bimetallic nanoparticles and Lewis acids work in tandem to achieve the N-alkylation of primary amides to secondary amides with alcohols via hydrogen autotransfer. When Au/Pd nanoparticles were used with metal triflates, a significant rate acceleration was observed, and the desired secondary amides were obtained in excellent yields. The metal triflate is thought to not only facilitate the addition of primary amides to aldehydes generated in situ, but also enhance the returning of hydrogen from nanoparticles to hydrogen-accepting intermediates. This resulted in a more rapid turnover of the nanoparticle catalyst, and ultimately translated into an increase in the overall rate of the reaction. The two catalysts in this co-catalytic system work in a synergistic and cascade fashion, resulting in an efficient hydrogen autotransfer process. 相似文献
Fundamental science, as well as all communications and navigation systems, are heavily reliant on the phase, timing, and synchronization provided by low‐noise and agile frequency sources. Although research into varied photonic and electronic schemes have strived to improve upon the spectral purity of microwave and millimeter‐wave signals, the reliance on conventional electronic synthesis for tuning has resulted in limited progress in broadband sources. Using a digital‐photonic synthesizer architecture that derives its time‐base from a high‐stability optical reference cavity, we generate frequency‐agile and wideband microwave signals with exceptional dynamic range and with a fractional frequency instability of 1 × 10−15 at 1 s. The presented architecture demonstrates digitally controlled, user defined and broadband frequency tuning from RF to 100 GHz with orders‐of‐magnitude improvement in noise performance over room‐temperature electronic wide‐bandwidth synthesis schemes.
Reversible addition‐fragmentation chain transfer polymerization yields reactive block copolymers bearing the pentafluorophenyl ester (PFPA) group, and subsequent Click amidation using 2,2,6,6‐tetramethylpiperidine‐N‐oxyl‐ and imidazolium‐functionalized primary amines produces the corresponding functional block copolymers, leading to installation of statistical radical‐ and ionic sites into the PFPA segment. The monolayered thin film devices fabricated using the obtained block copolymers exhibit repeatable switching of electric conductivity (on/off ratio > 103) under a bias voltage, which reveals that the coexistence of radicals and ions in the same spherical domain of the copolymer layer is a prerequisite for repeatable switching memory.
A new homonuclear and heterodinuclear pyridine-2,6-dicarboxylate complexes, formulated as (enH2)[Cu(dipic)2]·2.5H2O (1) and [Cu(μ-dipic)2Zn(H2O)5]·2H2O (2) (en = ethylenediamine, dipic = pyridine-2,6-dicarboxylate) were synthesized according the reactions between the three species of copper(II) and zinc(II) nitrate, ethylenediamine and pyridine-2,6-dicarboxylic acid. Complexes have been characterized by the methods of elemental, spectroscopic (IR and UV–Vis), thermal (TG/DTG, DTA) analysis, magnetic measurement and single crystal X-ray diffraction. Correlation coefficient, activation energies, E∗; pre-exponential factor, A; entropies, S∗; enthalpies, H∗ and Gibbs free energies, G∗ of the thermal decomposition reactions have been calculated under the derivations from thermogravimetric (TG) and differential thermogravimetric (DTG) curves, using the Coats–Redfern and Horowitz–Metzger methods. Complex 1 belonged to a six-coordinate behavior with a distorted octahedral geometry around Cu(II), that the structure contains two pyridine-2,6-dicarboxylate species as a tridentate ligands and ethylenediaminium cation as a counter ion as well as 2.5 uncoordinated water molecules. On the other hand complex 2 contains six-coordinated Cu(II) and Zn(II) ions, which are linked by two O atoms of the same carboxyl group from dipicolinic acid. The dipicolinate dianions again behave as tridentate ligands in 2. Two uncoordinated water molecules are also present in the structure. The structure units of 1 and 2 are mutually held by the hydrogen bonds and π?π interactions. There is also a C–O?π interaction in 2. The Cu(II) complexes are connected to one another via O–H?O hydrogen bonds, forming water clusters, which play an important role in the stabilization of the crystal structure. In the water clusters, the water molecules are trapped by the cooperative association of coordination interactions as well as hydrogen bonds. 相似文献
The alkaline treatment of the pyridinium salts, readily available from the S-alkylations of 3-amino-4-(1-pyridinio)thiophene-5-thiolates with various alkyl halides, in chloroform at room temperature afforded the corresponding thieno[3',4':4,5]imidazo[1,2-a]pyridine derivatives in low to moderate yields via the intramolecular cyclization of the resulting 1,5-dipoles followed by the aromatization of the primary cycloadducts. Interestingly, the reactions using unsymmetrical 3-amino-4-[1-(3-methylpyridinio)]thiophene-5-thiolates afforded only 8-methylthieno[3',4':4,5]imidazo[1,2-a]pyridines and the other 6-methyl derivatives were not formed at all. In addition the isolation of a byproduct in the condensation reaction of pyridinium salt with the solvent (CHCl?) is also discussed. 相似文献
A simple method for constructing gold nanoparticle‐modified electrodes with three‐dimensional nanostructures is demonstrated. The electrodes were prepared by casting citrate‐reduced AuNPs onto polycrystalline gold electrodes. The resultant electrodes had a large surface area‐to‐volume ratio, adequate for high protein loading and conferring high stability. The gold nanoparticle electrodes were covered with a self‐assembled monolayer of 11‐mercaptoundecanoic acid for electrostatic immobilization of cytochrome c (cyt c). At the electrode, direct, reversible electron transfer from cyt c was observed with remarkable stability. Moreover, an extremely high surface coverage of electrochemically active cyt c, 167 fully packed monolayers, was obtained through use of the electrode. 相似文献
We investigate baryogenesis in the ν MSM, which is the Minimal Standard Model (MSM) extended by three right-handed neutrinos with Majorana masses smaller than the weak scale. In this model the baryon asymmetry of the universe (BAU) is generated via flavour oscillation between right-handed neutrinos. We consider the case when BAU is solely originated from the CP violation in the mixing matrix of active neutrinos. We perform analytical and numerical estimations of the yield of BAU, and show how BAU depends on mixing angles and CP violating phases. It is found that the asymmetry in the inverted hierarchy for neutrino masses receives a suppression factor of about 4% comparing with the normal hierarchy case. It is, however, pointed out that, when θ13=0 and θ23=π/4, baryogenesis in the normal hierarchy becomes ineffective, and hence the inverted hierarchy case becomes significant to account for the present BAU. 相似文献
We evaluated the ability of diffusion-weighted imaging (DWI) to detect bone metastasis by comparing the results obtained using this modality with those obtained using 11C-methionine (MET) positron emission tomography (PET) and bone scintigraphy.
Materials and methods
This retrospective study involved 29 patients with bone metastasis. DWI was obtained using a single-shot echo planar imaging (EPI) sequence with fat suppression using a short inversion time inversion recovery sequence. The detection capabilities of DWI for bone metastases were compared with those of whole body MET PET (in 19 patients) and 99mTc-methylene diphosphonate bone scintigraphy (in 15 patients).
Results
Among the 19 patients who were diagnosed using DWI and PET, the PET identified 39 bone metastases, while the DWI identified 60 metastases out of 69 metastases revealed with conventional magnetic resonance imaging (MRI). Among the 15 patients who were diagnosed using DWI and bone scintigraphy, the bone scintigraphy identified 18 bone metastases, while the DWI identified 72 metastases out of 78 metastases revealed with conventional MRI. The overall bone metastasis detection rates were 56.5% for PET, 23.1% for bone scintigraphy and 92.3% for DWI.
Conclusion
DWI is a very sensitive method for detecting bone metastasis and is superior to MET PET and bone scintigraphy in terms of its detection capabilities. 相似文献
The interaction of atomic H with Ag(1 1 1)/Si(1 1 1)7 × 7 surfaces was studied by thermal desorption (TD) spectroscopy and scanning tunneling microscopy (STM) at room temperature. TD spectroscopy revealed an intense peak from mono H–Si bonds, even though the Si surface was covered by the Ag atoms. This peak was not observed from Ag-coated SiO2/Si substrates. STM observation showed no clear change of the Ag surface morphology resulting from H exposure. All these results indicate that the atomic H adsorbs at neither the Ag surfaces nor Ag bulk sites, but at the Ag/Si interface by diffusing through the Ag film. 相似文献