Probability of precision micro-machining of insulating Si3N4 ceramics by EDM

Electrical discharge machining (EDM) is used as a precision machining method for the electrically conductive hard materials with a soft electrode material. But recently we succeeded to machine on insulating material by EDM. The technology is named as an assisting electrode method. The EDMed surface is covered with the electrical conductive layer during discharge. The layer holds the electrical conductivity during discharge. For micro-EDM, the wear of tool electrode becomes lager ratio than the normal machining. So the micro-machining is extremely difficult to get the precision sample.

In this paper to obtain a fine and precise ceramics sample, some trials were carried out considering the EDM conditions, tool electrodes material and assisting electrode materials. Insulating Si₃N₄ ceramics were used for workpiece. The machining properties were estimated by the removal rate and tool wear ratio. To confirm the change of micro-machining process, the discharge waveforms were observed. The micro-machining of the Ø0.05 mm hole could be machined with the commercial sinking electrical discharge machine.     

Simplified robust control for nonlinear uncertain systems: a method of projection and online estimation

Robust control based on an online estimation of uncertainty is presented for a class of nonlinear uncertain systems. The estimation is done via a robust observer after the uncertainty vector is projected onto a one-dimensional subspace. The proposed combination of dynamics projection and online estimation is to relax the knowledge about the size of uncertainty and required in the robust control design, to make robust control less conservative while being effective, and to ensure robust stability without undue complexity.     

<Emphasis Type="SmallCaps">d</Emphasis>-Maltose Synthesized Silver Nanoparticles for Biofilm Eradication

Biofilms are complex bacterial communities have a mechanism for antibiotic resistance leading to human health problems. It remains challenging to treat and eradicate biofilms. In this work, the use of d-maltose synthesized silver nanoparticles (AgNPs) was investigated in an effort to eradicate a biofilm. AgNPs were synthesized using a modified Tollen’s method. d-maltose was used in synthesizing AgNPs with different concentrations of d-maltose (0.01, 0.05 and 0.1 M), referred to as NP1, NP2 and NP3, respectively. TEM images revealed that the particles were polygon shaped. The particle sizes were found to be 86.81?±?13.39, 54.94?±?11.63 and 31.43?±?31.76 nm depending on their sugar concentrations. UV–Vis, ATR–FTIR, and XRD patterns were employed to characterize the AgNPs. Then, these AgNPs were investigated for their anti-bacterial effects against Escherichia coli and Staphylococcus aureus. Evaluation of the minimum inhibitory concentration and minimal bactericidal concentration revealed that S. aureus was inhibited by all AgNPs and killed by NP1 and NP3, and E. coli was inhibited and killed at all AgNPs doses. Furthermore, anti-biofilm activity against these two bacteria was observed using SEM and confocal laser scanning microscopy. This sugar coated AgNPs is a promising material for use in eradication of biofilms.     

2-D Shape Recognition using Recursive Landmark Determination and Fuzzy ART Network Learning

In this Letter, 2-D shape recognition is done using a combination of recursive search of landmarks, landmark-based invariant features, and a fuzzy ART neural-network classifier. To make this novel combination work well, an upper limit is imposed on the number of total landmarks allowed, and this maximum size is then translated into fixed dimensions of invariant features and into the neural processing of the features. It is shown that the recursive landmark search approximates very well any smooth 2-D shape contour, that the shape features used are independent of perspective transformation, and that, when combinedwitha fuzzy ART classifier, unknown features can be efficiently learned on-line to identify multiple distinct objects. An illustrative example is used to demonstrate effectiveness of the proposed algorithm.     

Dramatically enhanced non-Ohmic properties and maximum stored energy density in ceramic-metal nanocomposites: CaCu3Ti4O12/Au nanoparticles

Non-Ohmic and dielectric properties of a novel CaCu₃Ti₄O₁₂/Au nanocomposite were investigated. Introduction of 2.5 vol.% Au nanoparticles in CaCu₃Ti₄O₁₂ ceramics significantly reduced the loss tangent while its dielectric permittivity remained unchanged. The non-Ohmic properties of CaCu₃Ti₄O₁₂/Au (2.5 vol.%) were dramatically improved. A nonlinear coefficient of ≈ 17.7 and breakdown electric field strength of 1.25 × 10⁴ V/m were observed. The maximum stored energy density was found to be 25.8 kJ/m³, which is higher than that of pure CaCu₃Ti₄O₁₂ by a factor of 8. Au addition at higher concentrations resulted in degradation of dielectric and non-Ohmic properties, which is described well by percolation theory.     

Catalytic performance of ZnO nanoparticle in formation of LLDPE/ZnO nanocomposites

ZnO nanoparticle was used for preparing supported catalyst, which was applied in copolymerization of ethylene and 1-octene to obtain LLDPE/ZnO nanocomposite. There were two different impregnation methods (in situ and ex situ) in preparing the nano-ZnO supported catalyst. The investigation to compare both methods was conducted by employing various 1-octene initial concentrations in copolymerization. It was found that a heterogeneous catalytic system comprised a supported catalyst, prepared by in situ impregnation, provided higher catalytic activities and 1-octene incorporations compared to those of ex situ impregnation under similar condition perhaps due to closer similarity to a homogeneous system. For the ex situ impregnation, it was found that when zirconocene was directly impregnated onto the support, the catalytic activity decreased. This was due to zirconocene close vicinity to the supports and even deep into the support structure proved by XPS and TGA measurements. Therefore, it was more inaccessible to monomer attack and reducing the catalytic activity. The separate study on each catalytic system relating to the comonomer effect was also conducted by applying initial comonomer concentrations varied between 0 and 18?mmol. The increase in catalytic activity with increasing comonomer concentration can be considered as a positive comonomer effect, and the opposite was true for a negative comonomer effect. It was found that both positive and negative comonomer effects occurred in in situ impregnation and ex situ impregnation systems with Zn/(Al?+?Zr) support, whereas only positive comonomer effect was found in an ex situ impregnation system with Zn/Al support. This suggested that the comonomer effect was varied according to the nature of each system. The polymer properties, such as relative crystallinity and thermal properties were also investigated and found to alter with 1-octene concentration.     

Robust fault-tolerant self-recovering control of nonlinear uncertain systems

In this paper, the problem of devising a fault-tolerant robust control for a class of nonlinear uncertain systems is investigated. Possible failures of the sensor measuring the state variables are considered, and a robust measure is developed to identify the stability- and performance-vulnerable failures. Based on evaluation of the robust measure, a fault-tolerant robust control will switch itself between one robust control strategy designed under normal operation and another under the faulty condition. It is shown that, under two input-to-state stability conditions, the proposed scheme guarantees not only the desired performance under normal operations but also robust stability and best achievable performance when there is a sensor failure of any kind.