Dielectric, elastic, anelastic and conductivity behaviour of ferroelectromagnetic composites, Ni0·5Zn0·5Fe1·95O4?δ + Ba0·8Pb0·2TiO3

Ferroelectromagnetic composites with compositions, X Ni_0·5Zn_0·5Fe_1·95O_4−δ + (1 − X) Ba_0·8Pb_0·2TiO₃, in which X varies as 0, 0·005, 0·010, 0·015, 0·020, 0·040, 0·060, 0·080 and 1 in mole %, were prepared by conventional ceramic double sintering process. The presence of two phases was confirmed by X-ray diffraction. The temperature variation of dielectric constant, ɛ′, dielectric loss, tan δ, d.c. conductivity, a.c. conductivity, elastic and anelastic behaviour of ferrite-ferroelectric composites were studied in the temperature range 30–350°C. The a.c. conductivity measurements on these composites in the frequency range 100 Hz-1 MHz at room temperature reveal that the conduction mechanism is due to small polaron hopping. The dielectric and elastic data were discussed in the light of phase transitions.     

Synthesis of gold nanorods in organic media

A seed mediated approach for the synthesis of anisotropic rod shaped gold nanoparticles in organic media (toluene) is demonstrated. Pre-formed gold nanoparticles stabilized in toluene by 4-hexadecylaniline (HDA) are used as seeds. These when reacted with 1-octadecylamine (ODA) hydrophobised chloroaurate ions in toluene lead to the formation of gold nanorods. ODA or alkylamines of different chain lengths which are the chloroaurate ion phase transfer agent have been found to play a key role in the formation of the nanorods. The gold nanorods that have a five-fold symmetry evolve from multiply twinned particles and are bound at the tips by [1 11] faces and at the sides by [100] faces. The gold nanorods have been shown to grow under the shape directing effect of the alkylamines which stabilize the high energy [100] faces. The concentration of the alkylamines has been found to play a critical role in the formation of the gold nanorods. Higher concentrations of the alkylamines lead to formation of spherical particles, at times of narrow size distribution.     

Effects of sintering temperature on structural and electromagnetic properties of MgCuZn ferrite prepared by microwave sintering

Nanocrystalline magnesium–copper–zinc (Mg_0.30Cu_0.20Zn_0.50Fe₂O₄) ferrites were prepared by microwave sintering technique. The effects of the sintering temperature on particle size and magnetic properties were investigated. In this article, optimum sintering temperature required for MgCuZn ferrite system for obtaining good electromagnetic properties, suitable for applications in low temperature co-fired ceramics (LTCC) chip components was studied. The grain size, initial permeability, dielectric constant and saturation magnetisations were found to increase, and dielectric loss was found to decrease with the increasing sintering temperature. Mg–Cu–Zn ferrites with a permeability of μ?=?1110 (at 1?MHz) were fully densified at the standard LTCC sintering temperature of 950°C.     

用粘附过滤法净化选矿,冶金工业的废液及生产过程的溶液

本文讨论了苏联研制的以自松散纤维滤层粘附过滤低浓度悬浮液及废液的方法,阐述了此方法的理论规律及实际应用。指出了加重的新型纤维材料能获得高的过滤速度,同时可以保持吸附能力和过滤循环时间分别超过粒状过滤器(granular filter)5～7倍及3～4倍,在滤层上的压头损失十分小,实际上,在整个过滤期间保持不变。     

A buck-boost integrated high gain non-isolated half-bridge series resonant converter for solar PV/battery fed multiple load LED lighting applications

Solar photovoltaic (SPV) or battery fed multiple load LED lighting applications are gaining importance these days, which require independent voltage regulation and dimming control. Half-bridge resonant converters are mostly used due to their simple structure. In this paper, a buck-boost integrated high gain non-isolated symmetrical half-bridge series resonant converter is proposed for multiple load LED lighting applications. With the aid of integrated buck-boost operation, the output voltage can be regulated below and above the nominal input voltage effectively and can produce twice the gain as compared with classical half-bridge converters. Frequency modulation is implemented for output voltage regulation. Pulse width modulation (PWM) dimming has been adopted for illumination control. The proposed driver results in several advantages such as low cost, compact size, improved efficiency due to soft-switching, simple control, independent dimming, and effective operation for multiple loads. Thus, the proposed non-isolated driver configuration is well suited for SPV/battery fed multiple load LED lighting applications. The proposed configuration is tested with single LED load of 22 W and dual-LED loads of 22 W and 43 W. There is an excellent consensus between the simulation and the experimental outcomes.     

Investigation on flocculation characteristics of polysaccharide-based graft copolymers in coal fines suspension

The article deals with the synthesis of two polysaccharide-based graft copolymers of acrylamide, namely, starch-g-polyacrylamide (St-g-PAM) and amylopectin-g-polyacrylamide (Ap-g-PAM). Intrinsic viscosity of the graft copolymers was determined. A flocculation jar test was carried out with −200# ASTM particles for two coking and two noncoking coal samples from Indian coalfields. It is observed that both the grafted products are very effective flocculants in bringing down the turbidity of supernatant liquid of coking coal fines suspension. Though they are effective flocculants in the case of noncoking coal suspension as well, the supernatant turbidity remains somewhat high. Ap-g-PAM performed better than St-g-PAM, which is distinctly apparent in the case of noncoking coal suspension. This may be ascribed to the presence of longer grafted polyacrylamide chains in case of Ap-g-PAM. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2619–2625, 1998     

Pyroelectricity in calcium substituted sodium bismuth titanate layer structured ferroelectric ceramics

Pyroelectric properties of bismuth layer structured calcium substituted sodium bismuth titanate (Na_0·5Bi_0·5)_1−x Ca _x Bi₄Ti₄O₁₅ withx=0 (NBT) andx=0·1 (0·1 NCBT) were studied by measuring the current under short circuit condition. Spontaneous polarization and figures of merit were evaluated from the measured values of pyroelectric coefficients, dielectric constant and loss tangent. The pyroelectric properties were studied in poled and short circuit condition from 30°C to 700°C. The results obtained were discussed in the light of dielectric and conductivity properties of the samples.     

Chemically modified fibrin–gelatin composites: Preparation and characterization

The crude fibrin which is hitherto discarded as waste in slaughterhouses was recovered and purified. Using this fibrin, fibrin–gelatin composites were prepared and crosslinked with either basic chromium sulfate or glutaraldehyde. These composites were also graft-copolymerized with polyhydroxyethyl methacrylate using hydrogen peroxide–ferrous ammonium sulfate initiation technique. The graft copolymers were characterized for their moisture content, water absorption capacity, tensile strength, infrared spectroscopy, scanning electron microscopy, and thermogravimetric profile. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1109–1115, 1998     

Accelerated and environmental weathering studies on polyethylene–starch blend films

Biodegradable polymers are desirable for a variety of applications, such as in packaging, agriculture, and medicine. Polyethylene (PE) blended with starch is already found to be a potential candidate to replace nondegradable thermoplastics in the areas of packaging. Films of polyethylene (PE)–starch blends with and without vegetable oil as a compatibilizer were prepared. The degradation of the films under thermooxidative treatment, ultraviolet light exposure, high temperature, high humidity, and natural ambience (soil burial) were monitored. It is seen that vegetable oil as an additive has a dual role: as a plasticizer, it improves the film quality; as a prooxidant, it accelerates degradation of the film. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2251–2257, 1998     

Packaging and Performance of 980nm Broad Area Semiconductor Lasers

<正>High power broad area semiconductor lasers have found increasing applications in pumping of solid state laser systems and fiber amplifiers, frequency doubling, medical systems and material processing. Packaging including the assembly design, process and thermal management, has a significant impact on the optical performance and reliability of a high power broad area laser. In this paper, we introduce the package structures and assembling process of 980nm broad area lasers and report the performances including output power, thermal behavior and far fields.We will report two types of high power broad area laser assemblies. One is a microchannel liquid cooled assembly and the other is a conduction cooled CT-mount assembly .Optical powers of 15W and 10W were achieved from a 980nm broad area laser with a 120μm stripe width in a microchannel liquid cooled assembly and conduction cooled CT-mount assembly, respectively .Furthermore, a high power of 6.5 W out of fiber was demonstrated from a pigtailed, fully packaged butterfly-type module without TEC ( Thermoelectric cooler ).The measurement results showed that thermal management is the key in not only improving output power, but also significantly improving beam divergence and far field distribution. The results also showed that the die attach solder can significant impact the reliability of high power broad area lasers and that indium solder is not suitable for high power laser applications due to electromigration at high current densities and high temperatures.