Recent photoelectron spectroscopy results from gas phase C 60 exhibit the same partial cross section variation with photon energy as has been observed in its solid phase. We assume that the variations originate from a fullerene specific ability to form a spherical standing wave of the final state electron by intramolecular interference or virtual reflection at the center of the photoionized molecule. The calculated photon energies of the cross section minima based on the boundary conditions of the standing wave agree fairly well with experimental data. [S0031-9007(96)00143-3]
A traveling-wave thermoacoustic electric generator, which is composed of a traveling wave thermoacoustic engine and linear alternators, is promising in solar power generation and energy recovery due to its high efficiency, high reliability, and capability of utilizing low-grade heat. An equivalent acoustic circuit of a linear alternator is first built and analyzed using electro-mechano-acoustical analogy. It is found that the acoustic coupling of the linear alternators to the traveling-wave thermoacoustic engine is crucial to the performance of the system. A traveling-wave thermoacoustic electric generator with a variable electric R-C load is then constructed and experimentally studied. Both the theoretical analysis and the experimental results show the importance of mechanical and electrical resonances to the overall performance of the system. Furthermore, the thermal-to-electric efficiency and the electric power are found to be proportional to the pressure amplitude and the square of it in front of the piston of the linear alternator, respectively. By optimizing the load impedance, the traveling-wave thermoacoustic electric generator has achieved a maximum electric power of 345.3 W with a thermal-to-electric efficiency of 9.34% and a maximum efficiency of 12.33% with an electric power of 321.8 W at around 65 Hz when helium of 3.0 MPa is used as the working gas.
Traveling-wave thermoacoustic electric generator (TWTEG) is promising in efficiently converting the heat of fuel combustion, solar energy, industrial waste heat, etc. into electricity with a very scalable power output. Based on the decoupling method and theoretical analysis, the acoustic impedance requirements of the traveling-wave thermoacoustic engine (TWTE) and linear alternators (LAs) to reach an efficient and powerful operation state were studied quantitatively. A 1 kW level traveling-wave thermoacoustic electric generator was then built for experimental study. Good matching conditions of acoustic impedances were then experimentally demonstrated by modulating the working frequency, load resistance, and electric reactance of the thermoacoustic electric generator, which agreed well with the theoretical analysis. A maximum electric power output of 750.4 W and a highest thermal-to-electric efficiency of 0.163 have been achieved by the acoustically matched thermoacoustic electric generator with helium of 3.16 MPa as the working gas. This work would be instructive for the acoustic matching and designs of high-performance thermoacoustic electric generation systems.
Ultraviolet photoemission spectra of Yb 2.75 C 60 thin films are measured. The valence band is a wide hump centered at ϳ0.8 eV below the Fermi level. The result also indicates the semiconducting property of Yb 2.75 C 60 since no Fermi edge is observed. The hybridization between 6s states of Yb and the lowest-unoccupiedmolecular-orbital ͑LUMO͒ band of C 60 is non-negligible although it should not be considered to be strong. More than 14% of Yb 6s electrons are estimated to be distributed in the covalent bonds between Yb and C 60 . The spectra for submonolayer C 60 on Yb film reveal that Yb 6s electrons can easily transfer to C 60 and such demonstrate that the bonding in Yb 2.75 C 60 is mainly ionic. The LUMOϩ1 orbital of the submonolayer C 60 is partially occupied, which is different from the case in Yb 2.75 C 60 . There is no evidence of trivalent Yb in the spectra.
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