Reactivity of epoxy resin in dispersed dicyandiamide system and dynamic viscoelasticity of the resulting product

A study was made on the curing reaction, leading to a cross-linked network, of bisphenol A diglycidyl either in a dispersed dicyandiamide (DICY) system containing benzyl dimethylamine accelerator and on the dynamic viscoelasticity of the resulting product as related to the DICY particle size (Ds), and compared with a dissolved DICY system. The curing reaction rate varied inversely with logarithmic Ds and directly with the total surface area of the DICY particles, and the finally attainable extent of reaction of the epoxide group decreased with increasing Ds. Activation energy ranged from 14 to 17 kcal/mole depending slightly on Ds. The dynamic viscoelasticity of the cured product was also affected greatly by Ds. Cured product from the system with a 3 μm DICY displayed only a primary transition peak around 180°C in plots of viscoelastic decrement as a function of temperature. With DICY of larger than 10 μm Ds, the number of transition peaks increased to two or three, with a primary peak, a secondary peak around 140μC, and a tertiary peak around 90μC. The relative height of the secondary or tertiary peak increased with increasing Ds. The reaction of the dissolved DICY system proceeded at much the same rate as the 25 μm Ds system, but yielded a cured product with viscoelasticity similar to that of the 3 μm Ds system.     

Recovery of vanadium and molybdenum from heavy oil desulphurization waste catalyst

Sodium chloride-water vapour roasting of calcined catalyst for 2 h at 850°C (water vapour pressure 0.253 bar, N₂ atmosphere) and subsequent leaching of the roasted catalyst with water at its boiling point for 1 h dissolved 81.85% V and 81.78% Mo and minor amounts of other constituents. The separation of V from the leach solution has been carried out efficiently by precipitation (as NH₄VO₃), liquid-liquid extraction using di(2-ethylhexyl)phosphoric acid (D2EHPA) and tri-n-octylamine (TOA) and subsequent strippings and precipitations. The overall recoveries of V and Mo from the waste catalyst are 75.5 and 77%, respectively.     

Behavior of Two Kinds of Particles in Rotary Barrel with Planetary Rotation

Barrel polishing is an extremely efficient processing method for the surface smoothing treatment of a large number of workpieces. However, workpieces and grinding materials may separate depending on processing conditions. Since barrel polishing is carried out while mixing workpieces and grinding materials, the occurrence of segregation should be avoided. The processing conditions inside a planetary barrel which simultaneously rotates around the horizontal axis and revolves around the vertical axis include many unknown factors as well as the occurrence of segregation. The motions of workpieces and grinding materials in this barrel are basically the same as those of particles undergoing planetary rotation in a cylindrical barrel. However, in order to calculate the behavior of a large number of particles, a numerical method that can be applied to a discrete body is necessary. Therefore, in this study, two kinds of particles of different materials and sizes were filled into a planetary barrel, and the behavior of those particles was examined through experiments and simulations using the Discrete Element Method (DEM). As a result, it was demonstrated that certain combinations of length and inside diameter of the rotary barrel could prevent the segregation.     

Strained epilayers effectively reduce plasma-induced fluorine damage in P-HEMTs

We intentionally inserted several strained epilayers, namely In/sub 0.5/Ga/sub 0.5/As, InAs, and InSb, as fluorine-trapping barriers in a conventional pseudomorphic high electron mobility transistor (P-HEMT) structure and investigated their effectiveness against plasma-induced fluorine damage using Hall measurements and secondary ion mass spectrometry (SIMS) analysis. The strained barriers effectively diminished plasma-induced fluorine incorporation into deeper layers than the /spl delta/-doped layer and improved the carrier density and electron mobility compared with those of the conventional P-HEMT. In particular, when the most strained InSb barrier was inserted into the P-HEMT using post-thermal annealing, the carrier density and electron mobility remarkably recovered to 85% and 97% of their respective values before processing because of diminished fluorine incorporation and reduction of incorporated fluorine from the channel layer to the upper layers. This confirms that highly strained barriers are very effective at suppressing plasma-induced fluorine damage in P-HEMTs.     

A PWM strategy for reducing torque-ripple in inverter-fed inductionmotor

A new PWM strategy suitable for an inverter-fed induction motor is described. The output waveforms in the proposed PWM inverter are investigated both theoretically and experimentally. Although the output waveform is a nonsinusoidal waveform, the induction motor driven by the proposed modulating signal produces approximately constant torque. A modulating signal for the three-phase PWM inverter is obtained by superposing a rectangular wave on the specific trapezoidal wave whose flat portion is 120 degrees. By using the proposed modulating signal, the amplitude of the fundamental component is increased by about 17 percent more than that of a conventional sine wave inverter. The new system reduces the torque ripple as well as achieving the effective utilization of the DC supply voltage for the inverter     

Expansion of operating limits for permanent magnet motor by currentvector control considering inverter capacity

The current vector control method of PM (permanent magnet) motors is examined to expand the operating limits associated with inverter capacity. This control method is optimum in the sense of deriving maximum output torque within the voltage and current constraints. The effects of motor parameters are examined by computer simulation. The operating limits are greatly expanded by controlling the d- and q-axis components of the armature current according to the rotor speed. The operating limits are examined considering the demagnetization of the permanent magnet. If the permanent magnet has a straight demagnetization curve, like a rare-earth permanent magnet, the PM motor can be safely operated until the demagnetizing coefficient becomes 1.0. If wide speed range or constant power operation is desirable, a permanent magnetic with a high coercivity and a linear demagnetization curve must be used for the PM motor     

NOVEL TERAHERTZ PHOTOCONDUCTIVE ANTENNAS

The photoconductive (PC) antenna is a key device for the recent terahertz (THz) photonics based on laser-pumped generation and detection of THz radiation. In this paper we report on two new types of PC antennas: the Schottky PC antenna and the multi-contacts PC antenna. The former one is able to detect THz radiation intensity without the time-delay scan and useful for applications where spectroscopic information is not important, such as the THz intensity imaging. The latter one is useful for the polarization sensitive THz spectroscopy, such as the THz ellipsometry. The characteristic features of these new types of PC antennas are studied by using a THz time-domain spectroscopy system.     

X-ray Investigation for α′-(BEDT-TTF)2BrICl at Low Temperature

The organic semiconductor α′-(BEDT-TTF)₂BrICl which exhibits an abrupt decrease of static magnetic susceptivity at Tc (approximately 200 K) with decreasing temperature was investigated by X-ray diffraction experiments. The drastic first-order structural phase transition at Tc was found. The unitcell volume became approximately half of that above Tc. The result of crystal structure analysis at 25 K indicated that the donor molecular arrangement was no longer “α′-type” but “β″-type” below Tc.