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51.
In this paper, dynamic model of a class of parallel systems, namely, the hexaslides, is proposed. The model developed is based on the concept the decoupled natural orthogonal complement (DeNOC) matrices, introduced elsewhere. The dynamic model of hexslides, though complex due to the existence of multi-loop kinematic chains, is required for actuator power estimation, computed-torque control, optimum tool trajectory generation, etc. The use of DeNOC offers many physical interpretations, recursive algorithms, and parallel computations. Using the proposed dynamic model, a parallel inverse dynamics algorithm has been presented to compute the actuator forces. This is useful to choose suitable motors for an application. An illustration is provided using an existing machine tool based on hexaslides, namely, the HexaM, while it is carrying out a circular contouring. Secondly, the effect of leg and slider inertias is also studied, which clearly suggests that neither of these can be neglected while finding the actuator forces. 相似文献
52.
U V Varadaraju G V Subba Rao K D Chandrasekaran A Baradarajan K Krishnaiah Mukesh Agarwala V S Achutharaman P Venugopal K A Padmanabhan L S Vaidyanathan G Rangarajan 《Bulletin of Materials Science》1989,12(1):63-80
The oxygen-deficient phase of the highT
c superconductor, YBa2Cu3O7, was oxygen-enriched using the fluidization technique to give good superconducting properties. The normal method of oxygen
treatment at 900°C for 24 h and at 600°C for 24 h has been reduced to just one treatment at 600°C for 12 h by the fluidization
technique to achieve almost the same strength of superconducting signal for the YBa2Cu3O7 powder, which establishes the attractiveness of the latter route for the large-scale preparation of superconducting material.
The particle sizes were in the range 0–90, 90–180 and 180–420 μm. The fluidized particles were crystalline with orthorhombic
distortion.T
c
onset
, estimated using the a.c. magnetic susceptibility method, was 91·3 K. The volume fraction of superconducting material in
the product was 83·7–85·3%, one of the highest values reported so far for YBa2Cu3O7. 相似文献
53.
New spectrophotometric methods for the assay of some antioxidants have been developed using potassium permanganate and metol (p-N-methyl amino phenol). Metol is oxidised at pH 3.0 with potassium permanganate and coupled with antioxidants to give λmax at 560 nm for propyl gallate and gallic acid and 510nm for butylated hydroxy anisole. The method is simple, sensitive, reproducible and accurate within ±1% and applicable to the assay of antioxidants (gallic acid, propyl gallate and butylated hydroxy anisole) in oils and fats. 相似文献
54.
55.
Hari B. Goyal M. O. Garg K. R. Rao R. D. Srivastava 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(2):49-56
The kinetics of the reaction of acetic acid and acetylene over zinc acetate-activated carbon catalyst was investigated over a wide range of process variables in a pilot reactor. Although various catalytic reaction mechanisms were postulated, the rate of reaction was most satisfactorily correlated by a mechanism of surface reaction between charged adsorbed acetic acid and acetylene, which assumes that the rate controlling step was the irreversible charged adsorption of acetylene and acetic acid. 相似文献
56.
Uma Maheswar Rao S. S. M. S. Abdul Majeed C. Venkataseshaiah R. Sarathi 《Bulletin of Materials Science》2002,25(6):473-475
In the present work, tracking phenomena has been studied with silicone rubber material under the a.c. and d.c. voltages following
IEC-587 standards. The surface condition of the tracked zone was analysed using wide angle X-ray diffraction (WAXD) and thermogravimetric
differential thermal analysis (TG-DTA) studies. The tracking time was different for a.c. and d.c. voltages. 相似文献
57.
This paper draws attention to the basic principles governing reflections in uniform Bragg reflectors (BR) when measured employing optical low coherence reflectometry (OLCR) technique. Using computations based on transfer matrix method (TMM), we first showed a strong spectral dependence of Bragg reflectograms on an OLCR probe spectrum. Later, this dependence is exploited to evaluate, for the first time, the coupling coefficient κ of a Bragg grating in a distributed Bragg reflector (DBR) laser on InP 相似文献
58.
59.
60.
A. Edwards Mulpuri V. Rao B. Molnar A. E. Wickenden W. Holland P. H. Chi 《Journal of Electronic Materials》1997,26(3):334-339
Doping by ion implantation using Si, O, Mg, and Ca has been studied in single crystal semi-insulating and n-type GaN grown
on a-sapphire substrates. The n-and p-type dopants used in this study are Si and O; Mg and Ca, respectively. Room temperature
activation of Si and O donors has been achieved after 1150°C annealing for 120 s. The activation of Mg and Ca acceptors is
too low to measure at both room temperature and 300°C. Using higher doses to achieve a measurable p-type conduction increases
the amount of damage created by the implantation. Rutherford back scattering measurements on this material indicate that the
damage is still present even after the maximum possible heat treatment. Secondary ion mass spectrometry measurements have
indicated a redistribution in the measured profiles of Mg due to annealing. 相似文献