Investigation of scattering of elastic waves by cylinders in 1-3 piezocomposites

The scattering behavior of P-waves in piezoelectric composites with 1–3 connectivity is studied. The method of wave function expansion is adopted for the theoretical derivations. Analytical expressions are obtained for the distributions of mechanical displacement in z-direction along the circumferences of piezoelectric cylinders. These solutions are used to study the influence of each element of the stiffness matrix and the piezoelectric matrix on the various resonant modes of vibration. Numerical results obtained indicate that perturbations of the elements c₄₄ and e₁₅ significantly affect resonant frequencies and amplitudes, perturbations of c₁₁ and c₁₂ have pronounced effects on resonant modes of high frequencies also. However, the resonant modes are not so sensitive to the perturbations of c₁₃, e₃₁ and e₃₃. The dynamic characteristics of 1–3 connectivity piezoelectric composites exposed here are meaningful for the design and manufacture of sensor/actuator elements by this kind of composites as well as the on-line health monitoring of the mechanical properties variations of the composites itself.     

Effect of vacuum-induced coherence on lasing without inversion in an equispaced three-level ladder system

The effects of vacuum-induced coherence (VIC) on the properties of the absorption and gain of the probe field in an equispaced three-level ladder atomic system are investigated. It is found that lasing without inversion (LWI) is remarkably enhanced due to the effect of VIC in the case of the small incoherent pump rate.     

Energy-loss near-edge fine structures of iron nanoparticles

Body centered cubic (bcc) Fe nanoparticles were fabricated by in situ decomposition of iron fluoride films in a transmission electron microscope. Electron energy-loss near edge structure (ELNES) was used to characterize this exposure process. In particular, the L(3)/L(2) white-line intensity ratio (WLR) was used to monitor the iron valence state during exposure, and as an indicator of other properties of the iron nanoparticles. Iron nanoparticles with sizes between 2 and 20nm exhibit a constant WLR, whose value is same as that for a continuous bcc iron film, suggesting little or no dependence of the local magnetic moment or structure on the particle size. A broad but prominent peak which occurs 40eV after the L(3)-ionization threshold in the iron fluoride, is absent for a metallic iron film but reappears when the iron is converted to an oxide. Long-range ferromagnetic coupling was observed in samples densely populated with iron nanoparticles. Because there is little interaction between particles and the supporting carbon substrate, these samples provide an ideal model system for studying the influence of particle size and interparticle distance on magnetic properties.     

Investigation of lubricant induced pre-ignition and knocking combustion in an optical spark ignition engine

An experimental study was performed to investigate lubricant oil induced pre-ignition and knocking combustion process in a single cylinder spark ignition (SI) engine with full bore overhead optical access. Lubricant oil was deliberately injected to the exhaust area through a specially modified direct injector to trigger the stochastic pre-ignition in a premixed air and fuel mixture. Simultaneous heat release analysis and high speed combustion imaging were used to study the pre-ignition and combustion processes. Outlier detection based on robust statistical methods was validated as an effective and efficient approach to identify sporadic pre-ignition. When pre-ignition occurred, the pre-ignited flame-front exhibited much faster propagating speed than that of the normal spark-ignited flame-front in the first stage of flame development. In several cycles, pre-ignition was followed by the pre-ignited propagating flame-front and then a separate spark-ignited flame-front before they subsequently merged together. In a few other cycles, pre-ignition led to heavy knocking combustion caused either by the auto-ignition close to the flame-front or near the cylinder wall, or both. The ultimate knock intensity of such cycles was determined by the timing, size, and location of end-gas auto-ignition of the unburned gas. Furthermore, optical detection of the oil droplet entrained combustion in the cycle subsequent to the knocking combustion cycle implied that high frequency oscillation pressure waves ejected lubricant from the piston-ring crevice.     

Tunable local surface plasmon resonance in liquid-crystal-coated Ag nanoparticles

The far-field and near-field properties of a spherical nematic liquid crystal (NLC) coated metal nanoparticle (NPs) have been investigated in an external field, basing on the quasistatic theory. The resonant wavelength is tunable by varying metallic material of core, anisotropy extent and thickness of liquid crystals (LCs). The field enhancement is along the incident polarization near the outer surface of the shell. The direction of field is reverse in the inner surface comparing with the one if outer shell. In contrast to isotropy shell, the surface plasmon resonance (SPR) shows an obvious red shift and field enhancement near outer surface of the shell always is stronger.     

Pyrolysis study of poplar biomass by tunable synchrotron vacuum ultraviolet photoionization mass spectrometry

Pyrolysis is one of the most important methods to convert biomass into biofuel, which is a potential substitute for fossil fuel. The pyrolysis process of poplar biomass, a potential biofuel feedstock, has been studied with tunable synchrotron vacuum ultraviolet (SVUV) photoionization mass spectrometry (PIMS). The mass spectra at different photon energies, temperatures, and time-evolved profiles of selected species during poplar pyrolysis process were measured. Our results reveal that poplar is typical of hardwood according to its relative contents of three lignin monomeric precursors. As temperature increases from 300 to 700 °C, the overall intensities of pyrolysis products decrease due to the gas-phase cracking. Observed intensities of syringyl and guaiacyl subunits of lignin in poplar at low temperature present different trends: the intensities of syringyl subunits of lignin undergo an increase firstly and then a decrease, whereas those of guaiacyl subunits of lignin show decrease continuously. Time-dependent data demonstrate that hemicellulose pyrolysis is faster than lignin in poplar. This work reports a new application of SVUV PIMS in biomass pyrolysis, which performs very well in products analysis.