in this work, nanocomposites made of nanosized zirconia crystallized in situ in an amorphous silicon oxycarbo(nitride) (Sioc(n)) matrix have been designed through a precursor route for visible light photocatalytic applications. the relative volume fraction of the starting precursors and the pyrolysis temperatures not only influences the phase fraction of zirconia crystallites but also stabilizes the tetragonal crystal structure of zirconia (t-Zro 2) at room temperature. the presence of carbon in interstitial sites of zirconia and oxygen vacancy defects led to drastic reduction in the band gap (2.2 eV) of the nanocomposite. Apart from being a perfect host avoiding sintering of the active phase and providing mechanical stability, the amorphous matrix also reduces the recombination rate by forming heterojunctions with t-Zro 2. the reduction in band gap as well as the formation of heterojunctions aids in harnessing the visible light for photocatalytic activity. Large scale industrialization and urbanization has led to extensive pollution and contamination of rivers and water bodies, posing a threat to future generations and sustainable development 1. Chemical industries, leather factories, paint manufactures, dyeing and plating units release harmful untreated waste directly into our water bodies 2-4. These are non-biodegradable and toxic to humans as well as flora and fauna. Filtration with activated carbon, coagulation using chemical agents, ozonization, flocculation and reverse osmosis are some of the techniques that are frequently used to remove these harmful substances 5-8. However, these techniques are not effective in complete removal and merely result in the transfer of chemicals from one source to another. The photocatalytic phenomenon is capable of converting these toxic substances (EDTA, Cr(VI), nitrite) to harmless counterparts such as hydrogen, Cr(III) and nitrates 9-11. This is achieved via a catalyst that upon subsequent excitation produces electrons and holes. These electrons and holes produce superoxide and hydroxyl radicals that are responsible for the oxidation and reduction processes 12-15. But the efficiency of photocatalyst is largely dependent on the recombination rate of these electrons and holes. This drives the need for developing suitable catalysts which could be eventually scaled up for a large-scale clean-up drive 16-19. The wide band gap (3.25-5.1 eV) combined with a negative conduction band potential (−1.0 V vs. NHE at pH 0) 11 has recently spurred a lot of research on zirconia as a photocatalyst 20-23. It is important to note that the band gap value depends on the crystal structure (3.84 eV for cubic, 4.11 eV for tetragonal and 4.51 eV for monoclinic) 24 , defects and processing route of the ceramics 25. From the available limited literature, it is known that the presence of both monoclinic and tetragonal phases of zirconia 26-28 is beneficial for photocatalysis. The high temperature tetragonal phase of zirconia namely t-ZrO 2 can be stabilized at room temperature by using suitable
This paper reports the work done towards planning the trajectory for cooperative crane lifts. The location of the hook points between the pick and place positions are determined using a path-planner. These are inputs to the trajectory planner. The goal of the trajectory planner is to connect all the path-points while ensuring the overshoots, velocities, accelerations and jerk for each degree of freedom to be within acceptable limits for the system. A number of alternate techniques are available for defining the trajectory between the path-points. This paper reports on the evaluation of algebraic and trigonometric splines for trajectory planning. Splines of various orders were initially evaluated for a single joint. This evaluation found that 4 th order trigonometric splines were most appropriate. Hence, this was applied to a lift problem involving the 2x4 DOF cooperative manipulator system and the results are presented.
Cooperative crane lifts are considered as an alternative to specialized heavy crane lifts. However, in executing a cooperative crane lift, the precise coordination among the cranes is critical. This level of precision is better assured through automation of the lift operation. However, due to the drawbacks in current crane technology automated execution is not feasible. The development of a prototype work cell for cooperative lifts is addressed in this paper. The prototype manipulator developed has four degrees of freedom and possess the degrees of freedom of a typical hydraulic crane -swinging, luffing, telescoping and hoisting. For programmable control, the manipulator is interfaced to the computer. Uncoordinated motion among the individual manipulators often occurs when subject to cooperative manipulation. The cooperative manipulation is ensured by means of a typical logic that paves the way for proper control flow sequence between the individual controllers through RS-232 serial port. A series of trials were conducted to investigate the behaviour of the system under different cases.
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