A high-frequency electronic ballast for HID lamps based on aλ/4-long distributed constant line

A novel type of solid-state ballast, which operates in the megahertz-range frequency, is presented in this paper. A circuit composed of a voltage-source half-bridge inverter, a distributed constant line and a parallel LC resonant circuit has been developed for this purpose. The high-intensity discharge (HID) lamp is connected to the output terminal of the inverter through the distributed constant line. Here, since the length of the line is adjusted to 1/4 of the propagation wavelength λ (λ/4 condition), the output voltage of the voltage-source inverter can be converted to a current source on the load side. Therefore, the ballast can supply not only high voltage to the HID lamp for initiating discharge, but also stable current to it during discharge condition. The modification of the proposed circuit is also proposed in order to expand the operating frequency without increasing the undesirable harmonic current. The experimental results from a prototype system verify the theoretical procedure     

Long-term and collapse tests on a timber-concrete composite beam with glued-in connection

The paper reports the results of a comprehensive experimental test performed on a 6 m span timber-concrete composite beam with glued re-bar connection. The beam had first been subjected to sustained load in unsheltered outdoor conditions for 5 years. Eventually a ramp loading test up to failure was performed. The long-term test showed an increase in deflection mainly during the first two years, while the slip rose during the whole testing period. Thermo-hygrometric variations of environment caused an important fluctuation of all quantities on both yearly and daily scale. By comparing experimental and analytical results, it is highlighted that composite beams in outdoor conditions should be assigned to the 3rd service class according to the Eurocode 5 (EC5). Analytical predictions based on approximate formulae suggested by such regulation are found to be not conservative for the long-term behaviour and fairly accurate for the collapse behaviour. Since the simplified formulae proposed by the latest versions of the EC5-Parts 1.1 and 2 largely underestimate the actual connection stiffness and strength, it is recommended that realistic values of these properties, such as those obtained through push-out tests, be used when designing timber-concrete composite beams.     

Fabrication and anisotropic electronic property for oriented Li1+x−yNb1−x−3yTix+4yO3 solid solution by slip casting in a high magnetic field

The Li_1+x?yNb_1?x?3yTi_x+4yO₃ (0.06 ≤ x ≤ 0.33, 0 ≤ y ≤ 0.09) (hereafter LNT), forms a unique and periodical structure in the Li₂O-Nb₂O₅-TiO₂ ternary system. In this work, toward application of the unique qualities of an electro-ceramic, we fabricated oriented LNT balk ceramics by slip casting in a strong magnetic field of 12 T using various sizes of particles. The c-axis of the LNT powders was aligned parallel to the magnetic field. As a result, we found anisotropic- and unique- electric properties which were caused by a superstructure with intergrowth layers of corundum-type [Ti₂O₃]²⁺. The Qf value parallel to the c-axis was about five times greater than that of perpendicular to the c-axis. We first clarified the mechanism showing that the anisotropic Qf value was caused by the anisotropic electron conductivity and the anisotropic bonding strength in the superstructure.     

Crystal structure and dielectric properties of Ca(0.85)Nd(0.1)TiO(3) - LnAlO(3) ceramics

The microwave dielectric properties of Ca(0.85)Nd(0.1)TiO(3) - LnAlO(3) (Ln = Sm, Gd, Dy, Er) ceramics are investigated in this paper. The structural characteristics of the specimens were evaluated by Rietveld refinement of Xray diffraction (XRD) patterns and high-resolution transmission electron microscopy (HRTEM). Solid solution limits were dependent on the ionic radius of Ln(3+) ions. With the decrease of the ionic radius of the Ln(3+) ions, the thermal stability of the resonant frequency decreases. This can be attributed to the increased level of oxygen octahedral distortion caused by the increase in the B-site bond valence in the ABO(3) perovskite structure. The dielectric constant (K) and the quality factor (Qf) of the specimens were dependent on the polarizability and grain size, respectively.     

Controlling temperature coefficient of resistivity in La1−xSrxMnO3 ceramics

We propose La_1−xSr_xMnO₃ as a new lead-free and ruthenium-free conductive oxide used for thick film resistors. The temperature coefficient of resistivity (TCR) of the La_1−xSr_xMnO₃ was controlled systematically by changing the composition x. The TCR behavior depended on the change of the crystal symmetries and the average valence of Mn ions. The highest value of 9356 ppm/°C was obtained at the x = 0.35. Zero TCR was realized around 0.200 < x < 0.225 and 0.45 < x < 0.50, where the critical x values were related to the characteristic change from Mott-insulator to metallic behavior. The systematical controlling TCR and the zero TCR are the first to be demonstrated for conductive oxide.