Stability in high-output-voltage push-pull current-fed converters

The relationship between the magnetizing inductances of a transformer and of a choke coil in high-voltage power supplies is studied. The analysis defines the conditions for high switching frequency and stable operation of high-voltage power supplies without power loss increases. This approach is confirmed by the implementation of a high-voltage power supply operating at 200 kHz with an efficiency of 86%     

Realization of ultrahigh coherence in semiconductor lasers bynegative electrical feedback

To be useful, an ultrahigh-coherence semiconductor laser source requires high frequency stability, narrow linewidth, the capability of frequency tracking to a master laser, and stable frequency tuning. Negative electrical feedback is proposed to meet these four requirements simultaneously. Although the degree of frequency fluctuation that can be reduced by negative electrical feedback is limited by the noise contained in the feedback signal, theoretical calculations show that the fluctuations can be lower than the quantum noise limit. Experimental results obtained recently by the author are reviewed     

Performances of a frequency offset locked He-Xe laser system at 3.51 µm

A highly stabilized frequency offset locked He-Xe laser system was constructed for high resolution laser spectroscopy of H2CO [5_{1,5}(upsilon = 0) rightarrow 6_{0,6}(upsilon_{5}= 1)] at 3.51μm. It is composed of three He-Xe lasers. The first laser is H2CO-stabilized and is used as a frequency reference in the system. The second laser is frequency offset locked to the first laser by using the beat frequency between these lasers, and is used as a local oscillator. The third laser is frequency offset locked to the second laser, and is used to observe the H2CO spectrum by slowly varying the beat frequency between these lasers. The frequency stability of the first laser, measured against a similarly stabilized and synchronously modulated laser, was1.0times10^{-14}attau = 100s, where τ represents the integration time. The frequency traceability of the second laser to the first laser was expressed as8.0times10^{-13} cdot tau^{-1}for 10 msleq tau leq 100s. It was found that this value of the traceability was independent of the frequency modulation of the first and second lasers. The frequency traceability of the third laser to the second laser was nearly equal to that of the second laser described previously. The variable range of the frequency of the third laser was 19 MHz. In this range, the frequency traceability of the third laser to the second laser was independent of the beat frequency between these two lasers. From these results, it was concluded that this system can be used for the observation of the H2CO spectrum.     

An Allan variance real-time processing system for frequencystability measurements of semiconductor lasers

A real-time frequency stability measurement system for semiconductor lasers was developed. Since the frequency of the input signal is measured successively without clearing the counter, measurements of the Allan variance made with this system are more accurate than those made with conventional instruments. The Allan variance can be measured for integration times τ from 1 μs to 10000 s, and the number N of measured frequencies averaged over the integration time τ can be arbitrarily selected up to N=707 for each integration time. The highest measurable frequency was 90 MHz. It was demonstrated experimentally that this system can be used for measurements of the frequency stability of semiconductor lasers     

Interface Structure and Bond Strength of Copper-Bonded Alumina Substrates

Copper-bonded alumina substrates with different interface structures were studied to elucidate their effect on the bond strength and the resistance to hydrogen embrittlement and thermal cracking. The substrates were made by bonding copper either directly to alumina using Cu-O eutectic reaction or indirectly with an interlayer of cuprous aluminate between the metal and the ceramic. The substrate with the aluminate interlayer shows somewhat lower bond strength, still adequate for its use, than the directly bonded substrate. However, the substrate with the aluminate layer has greater resistance to hydrogen embrittlement and thermal cracking. The cause of such improvement is ascribed to the porosity of the aluminate layer and the compressive stress induced in alumina.     

Synthesis and properties of ethylene‐substituted styrene copolymers

The copolymerization of ethylene and substituted styrenes [RSt's; p‐methylstyrene (MSt), p‐tert‐butylstyrene (BSt), 2‐vinylnaphthalene (VN), and p‐(tert‐butyldimethylsilyloxy)styrene (BMSiOSt)] were investigated with dimethylsilylene(tetramethylcyclopentadienyl)(N‐tert‐butyl)titanium dichloride to yield the corresponding ethylene–RSt copolymers. The substituent on the styrene (St) monomers did not affect the monomer reactivity ratio. The effect of the substituent structure of RSt on the thermal and mechanical properties was studied with differential scanning calorimetry, dynamic mechanical thermal spectroscopy, and elongation testing. The glass‐transition temperature (T_g) of the copolymers increased with increasing RSt content, and the order of T_g was as follows: BSt > VN > MSt = St. A copolymer with p‐hydroxystyrene (HOSt) was successively synthesized by means of deprotection of the copolymer with BMSiOSt. The copolymer showed a much higher T_g than the other copolymers because of the hydrogen connection of its OH groups. The mechanical properties of the copolymer in the glass state, at a lower temperature than T_g, were almost independent of the nature of the RSt. The substituent of the St monomers affected the pattern of the stress–strain curve in the elongation testing in the amorphous state. An improvement in the shape memory effect was observed in poly(ethylene‐co‐BSt). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of Preparation Conditions on the Structural and Optical Properties of Spark Plasma-Sintered PLZT (8/65/35) Ceramics

Transparent lanthanum-doped lead zirconate titanate (PLZT) ceramics with high density were fabricated using spark plasma sintering (SPS), a recently developed hot-pressing method. A wet–dry combination method was used to prepare the fine PLZT powders. The average grain size of the PLZT ceramics was less than 1 μm, because of a relatively low sintering temperature and a very short sintering time. The transmittance of PLZT ceramics increased with an increase of calcination temperature up to 700°C and then it slightly decreased with further increase of calcination temperature. The transmittance strongly depended on the SPS temperature and heat-treatment temperature. The pellet sintered at 900°C for 10 min and heat treated at 800°C for 1 h with a thickness of 0.5 mm showed a transmittance of 31% at a wavelength of 700 nm. The relationships between the transmittance and the microstructure were investigated.     

Using color reach histogram for object search in colour and/or depth scene

A method is proposed for object search in cluttered color and/or depth scene, which is based on color reach histogram. The histogram features an image by the distribution of pixel colors with their two- and three-dimensional locations. In real situation, it is sometimes difficult to keep illumination unchanged or stable, and then color distributions can address an another effective cue for object identification. The color reach histograms reveal strong robustness for illumination change and/or on-plane rotation. In comparison with conventional histogram-based methods, the stability and robustness in object search and tracking could be obtained and verified through many experiments with real objects.