Selective oxidation of methanol in exhaust gas containing aromatic compounds

The activity of exhaust catalysts of methanol and gasoline mixture fueled automobiles is inhibited by coexistent aromatic compounds contained in the exhaust stream. One approach to avoid this inhibition could be the utilization of a molecular-sieve effect. It seems probable that the migration of aromatic compounds, which have larger molecular sizes than that of methanol, will be blocked by these supports and methanol will selectively reach the active sites of the catalysts. Thus, we examined the simultaneous oxidation of methanol and toluene over some ion-exchanged Pt/zeolite catalysts. Experimental results showed that ion-exchanged Pt/zeolite catalysts are less affected by coexistent toluene and have a higher selectivity for methanol oxidation compared with an alumina-supported platinum catalyst, suggesting that the use of these catalysts is effective for oxidizing methanol in the exhaust stream containing aromatic compounds. Among the catalysts tested, a Pt/H-MOR catalyst was found to be the most effective for the oxidation of methanol and effectively catalyzed the reaction in the presence of toluene even at low temperature.     

A Performance Analysis of Microprocessor-Based Control Systems Applied to Adjustable Speed Motor Drives

Speed regulators for motor drives can be classified into four types according to the degree of accuracy and the response time required for a given application. Formulas are presented which can be used to determine the number of bits and the sampling time which are required of a microprocessor for a thyristor drive microprocessor-based speed regulating system. A systematic approach is also proposed which application engineers can use to evaluate and select the most adequate microprocessor from those commercially available for different types of digital speed regulators.     

Caution when applying eddy current inversion to stress corrosion cracking

This study evaluates the applicability of computer-aided eddy current inversion techniques to the profile evaluation of stress corrosion cracking in Inconel welds. Welded plate specimens, which model head penetration welds of pressurized water reactors, are fabricated; notches and stress corrosion cracks are artificially introduced into the weld metal of the specimens. Eddy current inspections are performed using a uniform eddy current probe driven at frequencies of 10 and 40 kHz. Since weld noise is observed uniformly along the weld line, a simple signal processing is applied to eliminate it. First, the artificial notches are reconstructed and good agreements between reconstructed and true profiles are provided, which demonstrates that the computer-aided eddy current inversion technique can deal with defects in welds. Then, numerical simulations are performed to evaluate the profiles of the stress corrosion cracks. In the numerical simulations, the stress corrosion cracks are modeled as a conductive region with a fixed width of 0.3 mm. The cross-sectional profiles of the cracks are reconstructed from measured eddy current signals directly above and along a crack. Although eddy current signals calculated from the reconstructed profiles agree well with measured ones, the true profiles revealed by destructive testing are found to be very different from the reconstructed ones. Whereas the most plausible reason for the difference is the unexpectedly volumetric profile of the stress corrosion cracks, this study has revealed that computer-aided eddy current inversion techniques that have been used to consider cracks in thin structures would not at this point be directly applicable to those in thick structures. It is also important to know in advance those crack features that can adversely impact accurate crack sizing including whether a detected crack is volumetric or not, namely there are many parallel cracks in a cluster or not.     

Detection of embedded fatigue cracks in Inconel weld overlay and the evaluation of the minimum thickness of the weld overlay using eddy current testing

This study evaluates the applicability of eddy current testing to the detection and sizing of fatigue cracks embedded in Inconel weld overlays. Welded plate specimens, which model head penetration welds and their weld overlays, are fabricated, and fatigue cracks are artificially introduced into the specimens. Eddy current inspections are performed using a uniform eddy current probe driven with 10 kHz, and all of the fatigue cracks are detected with clear signals. Subsequent numerical inversions estimate that the minimum thicknesses of the weld overlays are 1.47, 2.17, and 2.23 mm, whereas true thicknesses revealed through destructive testing are 1.51, 3.25, and 2.10 mm, respectively. Thicknesses are also evaluated using potential drop and ultrasonic testing methods; the results demonstrate that eddy current testing is the most efficient of the three methods.     

Hyperproduction of sebaceous cis-6-hexadecenoic acid by esterase-reduced mutant of Rhodococcus sp. strain

cis-6-Hexadecenoic acid is a major component of human sebaceous lipids that is involved in skin self-sterilization and atopic dermatitis amelioration. It can be prepared by hydrolysis of isopropyl cis-6-hexadecenoate produced by resting cells of Rhodococcus sp. strain KSM-MT66. To devise an economical industrial-scale process for the production of this rare fatty acid, we optimized the conditions for growing rhodococcal cells. Mg(2+) and Fe(2+) ions are essential for the efficient production of isopropyl cis-6-hexadecenoate. To further increase the production of isopropyl cis-6-hexadecenoate, we created a mutant strain (T64) with reduced esterase activity by random mutagenesis using UV irradiation of MT66. Under an optimized condition, the mutant T64 produced more than 60 g l(-1) isopropyl cis-6-hexadecenoate in a 4-d cultivation, corresponding to about 52 g l(-1)cis-6-hexadecenoate.     

Sequence‐Specific DNA Photosplitting of Crosslinked DNAs Containing the 3‐Cyanovinylcarbazole Nucleoside by Using DNA Strand Displacement

An oligodeoxynucleotide (ODN) containing the ultrafast reversible 3‐cyanovinylcarbazole (^CNVK) photo‐crosslinker was photo‐crosslinked to a complementary strand upon exposure to 366 nm irradiation and photosplit by use of 312 nm irradiation. In this paper we report that the photoreaction of ^CNVK on irradiation at 366 nm involves a photostationary state and that its reaction can be controlled by temperature. Guided by this new insight, we proposed and have now demonstrated previously unknown photosplitting of ^CNVK aided by DNA strand displacement as an alternative to heating. The photo‐crosslinked double‐stranded DNA (dsDNA) underwent >80 % photosplitting aided by DNA strand displacement on irradiation at 366 nm without heating. In this photosplitting based on DNA strand displacement, the relative thermal stability of the invader strand with respect to the template strands plays an important role, and an invader strand/template strand system that is more stable than the passenger strand/template strand system induces photosplitting without heating. This new strand‐displacement‐aided photosplitting occurred in a sequence‐specific manner through irradiation at 366 nm in the presence of an invader strand.     

Fluid flow and heat transfer of natural convection over upward‐facing,horizontal, heated plate shrouded by a parallel insulated plate

The present paper describes experimental results on the fluid flow and heat transfer of natural convection between a horizontal, heated plate facing upward and an insulated cover plate. The experiments were carried out with water. The width of the test plates W and their gaps H were changed from W = 50 to 250 mm and H = 10 to 30 mm and ∞ (no cover plate). The visualization studies with dye and liquid crystal thermometry revealed that the roll cells whose axes are perpendicular to the flow direction appear and become dominant over the heated plate on decreasing the gap. These roll cells inhibit the heat transfer, and thus, the heat transfer coefficients become smaller than those without a cover plate. It was found that the flow and heat transfer in the region near the plate edges are unaffected by the cover plate. The conditions of the above reduced heat transfer were determined empirically. Moreover, nondimensional correlations for the local and the overall heat transfer coefficients of the heated plates are proposed based on the present heat transfer results. © 2000 Scripta Technica, Heat Trans Asian Res, 29(4): 333–346, 2000     

Layer-by-layer growth of graphene layers on graphene substrates by chemical vapor deposition

We demonstrate a synthesis of graphene layers on graphene templates prepared by the mechanical exfoliation of graphite crystals using a developed chemical vapor deposition (CVD) apparatus that has a furnace with three temperature zones and can regulate the temperatures separately in each zone. This results in individual control over the decomposition reaction of the carbon feedstock and the growth of graphene layers by activated carbon species. CVD growth using multi-temperature zones provides wider temperature windows appropriate to grow graphene layers. We observed that graphene layers proceed by a layer-by-layer growth mode using an optical microscopy, an atomic force microscopy, and Raman spectroscopy. This result suggests that a graphene growth technique using the CVD apparatus is a potential approach for making graphene sheets with precise control of the layer numbers.     

Locomotion Control of a Hydraulically Actuated Hexapod Robot by Robust Adaptive Fuzzy Control with Self-Tuned Adaptation Gain and Dead Zone Fuzzy Pre-compensation

Hydraulically actuated robotic mechanisms are becoming popular for field robotic applications for their compact design and large output power. However, they exhibit nonlinearity, parameter variation and flattery delay in the response. This flattery delay, which often causes poor trajectory tracking performance of the robot, is possibly caused by the dead zone of the proportional electromagnetic control valves and the delay associated with oil flow. In this investigation, we have proposed a trajectory tracking control system for hydraulically actuated robotic mechanism that diminishes the flattery delay in the output response. The proposed controller consists of a robust adaptive fuzzy controller with self-tuned adaptation gain in the feedback loop to cope with the parameter variation and disturbances and a one-step-ahead fuzzy controller in the feed-forward loop for hydraulic dead zone pre-compensation. The adaptation law of the feedback controller has been designed by Lyapunov synthesis method and its adaptation rate is varied by fuzzy self-tuning. The variable adaptation rate helps to improve the tracking performance without sacrificing the stability. The proposed control technique has been applied for locomotion control of a hydraulically actuated hexapod robot under independent joint control framework. For tracking performance of the proposed controller has also been compared with classical PID controller, LQG state feedback controller and static fuzzy controller. The experimental results exhibit a very accurate foot trajectory tracking with very small tracking error with the proposed controller.