Lapping of ultra-precision ball surfaces. Part I. Concentric V-groove lapping system

A general closed-form analytical solution is derived for the lapping tracks with its kinematics for the concentric V-groove lapping system. Based on the kinematics, the theoretical prediction in the prediction of the ball-spin angle β is in very good agreement with the experimental results from the observation of the contact track, where a small slip ratio occurs at the contact points. The lapping tracks on the ball surface for the three contact points are fixed circles, and their lengths of the lapping tracks are linearly proportional to |sin(θ₁+β)|, |sin(θ₂+β)|, and |cos β|, respectively. To understand the generation mechanism of spherical surface, the ball is enforced to rotate a certain degree of δ with respect to its previous orientation when it enters the lap again. Results show that the lapped area ratio, Lr, is significantly influenced by the angular speed ratio, w_b/Ω_b, and δ. When the angular speed ratio is integer and δ is small enough or randomized, the lapped area ratios at the contact points of A, B, and C are linearly proportional to [sin θ+sin(θ+2β)], [sin θ+sin(θ−2β)], and (1+cos 2β), respectively. In practice, if the orientation is randomized as the ball enters the lap again, then the distribution of the lapping tracks are dense after many cycles, and the larger the lapping length in each cycle, the smaller is the number of cycles required to achieve the maximum lapped area ratio. In the geometry design of ball lapping, the V-groove half-angle should be larger than 45°, but to prevent the splash of abrasives, it should be less than 75°.     

Nitride-based flip-chip p-i-n photodiodes

Nitride-based flip-chip p-i-n photodiodes were fabricated and characterized. It was found that we could achieve a small dark current of 5/spl times/10/sup -10/ A at -5 V and a large rejection ratio larger than three orders of magnitude. It was also found that the photodiodes only detect optical signals with wavelengths between 365 and 378 nm. Furthermore, it was found that peak responsivity occurs at around 370 nm with a value of 0.21 A/W at zero bias which corresponds to 70% external quantum efficiency.     

Conceptual Structural Design in SEED

Although there are many computer-based tools for analyzing structures whose geometry, topology, and member properties have already been determined, there are very few general-purpose tools to assist structural designers in synthesizing structural configurations to be subsequently sized, analyzed, and detailed. The comceptual-structural-design submodule of the Software Environment to Support the Early Phases in Building Design (SEED-Config) is intended to fill this void. The process starts with a geometric model of the building's massing, a set of functional requirements to be satisfied, and a toolkit of technologies capable of generating potential structural system and subsystem alternatives. Structural alternatives can be rapidly generated under designer control to the level of detail desired and evaluated against a range of criteria. Provisions are made to store design cases as well as to retrieve and adapt these to meet new requirements.     

Electromechanical and electrothermal behaviours of carbon whisker reinforced elastomer composites

The electromechanical and electrothermal properties of conducting carbon whisker reinforced thermoplastic elastomer (TPE) composites were investigated. The carbon whiskers were derived by a catalytic chemical vapour Deposition (CCVD) process and the TPE was a styrene-ethylene-butylene-styrene (S-EB-S) block copolymer. The electrical resistivity (ϱ) of the composites can be varied either by uniaxial deformation (10¹–10⁸ Ω cm) or by temperature (10¹–10⁵ Ω cm). The temperature-resistivity studies indicated that the resistivity of these composites was influenced by the glass transition temperature (T _g) of the TPE. The ϱ versus 1/T curves exhibited two distinct regimes each with a different negative slope which intersected at the T _g of the elastomer. This was correlated to the T _gof the EB segments in the S-EB-S block copolymer (∼ -50°C) by the dynamic mechanical thermal analysis. Further, uniaxial deformation studies at room temperature (20 °C) demonstrated that the resistivity increased exponentially with the deformation. Processing technique considerations and electron micrographs of the morphology of the composites indicated the formation of polymeric film on the carbon whiskers. Thus, the electrical conduction between carbon whiskers in these highly loaded (33 and 52 vol % fraction) composites occurred through the elastomeric film by electron tunnelling. This is explained on the basis of Mott's electron hopping theory, for conduction through several carbon-polymer-carbon (C-P-C) junctions. Further studies by scanning electron microscopy, dielectric thermal analysis and voltage-current characteristics confirmed this observation. Mechanical and electrical properties of the composites indicated that CCVD carbon whiskers can be used to improve the strength and electrical conductivity of TPEs. The change in resistivity (up to five orders of magnitude) of the composites with respect to the deformation or temperature can find use in electromechanical and electrothermal device applications.     

Shrinkage estimation of scale parameter of the extreme-valuedistribution

The author studies the usual preliminary test estimator of the scale parameter of the extreme-value distribution in censored samples. The optimum levels of significance and their corresponding critical values for the preliminary test are obtained based on the minimax regret criterion. A preliminary test shrinkage estimator that is smoother than the usual preliminary test estimator is proposed as well. The optimum values of shrinkage coefficients for the preliminary test shrinkage estimator are obtained, and are also based on the minimax regret criterion. Comparison of these two estimators shows that if the mean square error is a criterion of goodness of estimation then the preliminary test shrinkage estimator is better than the usual preliminary test estimator     

Migration behavior and separation of sulfonamides in capillary zone electrophoresis. I. Influence of buffer pH and electrolyte modifier

UDPG-pyrophosphorylase (EC 2.7.7.9) from Saccharomyces cerevisiae was studied and the presence of isoforms investigated. Its activity was monitored during growth of cultures in rich media containing glucose, galactose, sucrose, maltose or glycerol as carbon sources. The results suggest that UDPG-pyrophosphorylase is subject to both catabolite repression and catabolite inactivation. The inactivation process seems to be complex: in order to produce maximum inactivation, glucose and ammonium sulfate must be added together. Addition of glucose or ammonium sulfate separately produced little effect upon enzyme activity. Adsorption to and elution from a DEAE-Sephacel column of a crude protein extract prepared from yeast cells collected in stationary phase from a glucose medium showed three activity peaks, which we denominated isoform I, II, and III. Isoform I is constitutive, it was the only form present during exponential growth on glucose medium, and did not suffer any alteration after glucose exhaustion, heat shock or by growing cells on maltose. On the other hand, isoforms II and III were shown to be repressed by glucose, and induced by heat shock. Furthermore, isoform II of UDPG-pyrophosphorylase was present together with isoform I when yeast cells were grown on maltose. The presence of a MAL4C allele rendered isoform II constitutive. Interestingly, a gal3 mutant strain had low UDPG-pyrophosphorylase activity and isoforms I and II were not expressed. These results are discussed in relation to trehalose metabolism.     

The effect of spring pad loading and head penetration on the flight of flexible disk over a spherical head

A flexible disk, spinning at relatively low speed (80-600 r/min) and locally sandwiched between a spherical head and a spring loaded pressure pad, is investigated by stroboscopic white light interferometry. The contours of the disk in the vicinity of the head in general, and the minimum head/disk spacing in particular, are determined for various values of parameters such as disk speed, head penetration, and the pad loading force. Based on the topology of the contours, various modes of flight with distinctive characteristics are classified, and the effects of the head penetration and the pad loading force are thoroughly analyzed. Qualitative explanations of the observed phenomena are given and the problems associated with the optimum head design are discussed.     

Effect of reactive ion etching and post-etching annealing on the electrical characteristics of indium-tin oxide/silicon junctions

Indium tin oxide (ITO) films were deposited onto p-type Si wafers with radio frequency (r.f.) magnetron sputtering. The effect of the silicon surface treatment with reactive ion etching (RIE) on the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of the ITO/Si junction are investigated. When the Si substrate is etched by RIE prior to the deposition of ITO film, the I–V characteristics of the ITO/p-Si junction transfer from an ohmic contact for the unetched-Si to a rectifying contact for the etched Si. In addition, the barrier height, ideality factor, and series resistance increase with increasing etching power. This is attributed to the net positive ion charge and defects on the damaged surface. Thermal annealing can eliminate the damage caused by RIE. The I–V curves of ITO/etched p-Si become more ohmic as samples are annealed in N2 at 300 °C. Secondary ion mass spectroscopy (SIMS) depth profiles indicate that some impurity defects migrate and/or disappear after post-etching annealing. © 1998 Chapman & Hall     

High detectivity InGaN-GaN multiquantum well p-n junction photodiodes

InGaN-GaN multiquantum well (MQW) p-n junction photodiodes with semi-transparent Ni-Au electrodes were fabricated and characterized. It was found that the fabricated InGaN-GaN p-n junction photodiodes exhibit a 20-V breakdown voltage and a photocurrent to dark current contrast ratio of /spl sim/10/sup 5/ when a 0.4-V reverse bias was applied. The peak responsivity at 380 nm was 1.28 and 1.76 A/W with a 0.1- and 3-V applied reverse bias, respectively. Furthermore, an internal gain was found from our InGaN-GaN MQW p-n junction photodiodes possibly due to the long-lifetime of GaN based materials. Also, it was found that the low frequency noise of our photodiodes was dominated by the 1/f type noise. For a given bandwidth of 500 Hz, the corresponding noise equivalent power and normalized detectivity D/sup */ were found to be 6.34/spl times/10/sup -13/ W and 4.45/spl times/10/sup 11/ cm/spl middot/Hz/sup 0.5/ W/sup -1/, respectively.     

Optimum slope for solar insolation on a flat surface tilted toward the equator in heating season

A simple equation is developed for the explict determination of the optimum slope for solar insolation on a flat surface tilted toward the equator during the heating season. This equation applies for both northern and southern hemispheres. The relationships between the optimum slope of the surface and related parameters are presented and discussed.