Effect of leakage transformer on laser power and mode pattern of CO2 laser excited by 60 Hz AC discharges

The 60 Hz AC discharges generated by a leakage transformer instead of an isolation one, which is usually used in the power supply of DC CO₂ laser, are employed as a pumping source in this experiment. The laser performance characteristics as functions of pressure and discharge current have been investigated. The maximum laser power is about 40 W at conditions of 18 Torr and 35 mA. The output power is not less than that of DC discharge at the same condition. In addition, the laser outputs of 60 Hz AC discharges obtained by different transformers such as a leakage type and an isolation one have been measured. It was found that the laser power obtained by the leakage transformer is saturated at the higher current compared with the isolation transformer.     

Microelectrofluidic bench using UV-curable rigid polymer fabricated by rapid and low-temperature process

We present a rapid and low-temperature polymer fabrication method based on the direct patterning by UV light. Compared to the conventional polymer micromolding method for polydimethylsiloxane (PDMS) and cyclic olefin copolymers (COC), the present method has advantages of rapid fabrication in low-temperature environment. We used an AEO3000, UV-curable low-stress hyper-branched polymer (HBP), as a polymer material. The AEO3000 layer was selectively exposed to UV light by a photomask at room temperature for 3 min. Using the present method, we designed the rigid substrate for the microelectrofluidic bench. The measured electrical and fluidic interconnection characteristics in the bench were 0.75 ± 0.44 Ω and 8.3 kPa (at the flow rate of 100 μl/min), respectively. Both electric and fluidic characteristics were equivalent or lower than the sum of individual devices. We also successfully verified the bio-sample analysis through the interconnected devices on the microelectrofluidic bench using yeast cell samples. The proposed method offers fast and bio-compatible process applicable to biomedical micro total analysis systems.     

Iterative algorithms for part grouping and loading in cellular reconfigurable manufacturing systems

A reconfigurable manufacturing system (RMS), one of state-of-the-art manufacturing system technologies, is the one designed at the outset for rapid changes in its hardware and software components in order to quickly adjust its production capacity and functionality in response to market or system changes. In this study, we consider a cellular RMS with multiple reconfigurable machining cells (RMCs), each of which has numerical control machines, a setup station, and an automatic material handling and storage system. Each machine within the RMC has an automatic tool changer and a tool magazine of a limited capacity. Two important operational problems, part grouping and loading, are considered in this study. Part grouping is the problem of allocating parts to RMCs, and loading is the problem of allocating operations and their cutting tools to machines within the RMC. An integer programming model is suggested to represent the two problems at the same time for the objective of balancing the workloads assigned to machines. Then, due to the complexity of the problem, we suggest two iterative algorithms in which the two problems are solved repeatedly until a solution is obtained. Computational experiments were done on various test instances and the results are reported.     

Variable energy gap of SiCN nanopowders

SiCN and SiC nanopowders were prepared by infrared laser pyrolysis of gaseous precursors starting from a SiH₄C₂H₂NH₃ gas mixture. The SiCN powders were composed of an amorphous phase ascribed to the ternary compound with a β-SiC crystalline phase, while the SiC powders consisted of β phase only. The chemical bonding and the local atomic order in the SiCN powders are much more complicated than those of pure SiCSi₃N₄ mixtures and are strongly dependent on the variation in the initial gas composition. The average grain size was estimated from X-raydiffraction (XRD) patterns and atomic force microscopy (AFM). The UV-VIS transmittance data were used for the bandgap determination in these new materials. Absorption studies suggested that the direct energy gap is more favourable in SiCN and SiC nanoparticles and is blueshifted with regard to the crystalline bulk (SiC). The change of type of band-to-band transition in SiC nanopowders, due to the size effects, and increasing of the energy gap value in SiCN powders with different local atomic arrangement, makes them attractive for blue-UV optoelectronic applications. PACS 61.46.+w; 78.70.Ck; 68.3.Ps; 78.40.-q     

Visualizations of the transitional flow patterns at the mid-span between shrouded co-rotating disks

Transitional air flow patterns at the mid-plane of gap between co-rotating disks in a stationary cylindrical enclosure are visualized under the acceleration condition of disks. The flow visualization is performed using olive oil particles with a laser sheet and CCD camera. On disk spinning-up, the transition flow patterns are clearly observed. The affect of magnitude of acceleration on the onset of transition and the relations of the number of vortex cells in fully turbulent regime of the flow in an outer region of the flow field to the rotating speed are also investigated. The centrifugal effect of particle is evaluated from the comparison with visualization results using hollow glass spheres.     

Dynamical analysis of an anemoscope in the phase plane

We study the dynamical aspects of an anemoscope indicating a wind direction by constructing a model in the discrete view of fluid. Due to the non-linearity of the rotational equation, the geometrical method is applied for the qualitative analysis. For a given wind direction, there are two fixed points of the parallel and anti-parallel configurations. Near the anti-parallel configuration of the stable fixed point, the anemoscope performs a damped harmonic oscillation. It can be noteworthy that there is always the damping term for both the configurations even in the absence of the non-aerodynamic frictional force from, for example, the axis of rotation. The argument using the index of a closed curve in the phase portrait seems to support the non-existence of periodic solution.     

Quasi-Baer Rings with Essential Prime Radicals

A ring R is called “quasi-Baer” if the right annihilator of every right ideal is generated, as a right ideal, by an idempotent. It can be seen that a quasi-Baer ring cannot be a right essential extension of a nilpotent right ideal. Birkenmeier asked: Does there exist a quasi-Baer ring which is a right essential extension of its prime radical? We answer this question in the affirmative. Moreover, we provide an example of a quasi-Baer ring in which the right essentiality of the prime radical does not imply the left essentiality of the prime radical.     

Rapid synthesis and consolidation of nanostructured 2MgAl2O4–MgAl2Ti3O10 composite and its mechanical properties

Rapid sintering of nanostructured 2MgAl₂O₄–MgAl₂Ti₃O₁₀ composite in a pulsed current activated sintering process was investigated. The advantage of this process is that it enables very rapid densification to near theoretical density and prevents grain growth in nanostructured materials. Highly dense nanostructured 2MgAl₂O₄–MgAl₂Ti₃O₁₀ composite was produced by simultaneous application of 80 MPa pressure and a pulsed current of 2,800 A for 2 min. The sintering behavior, grain size, and mechanical properties of the 2MgAl₂O₄–MgAl₂Ti₃O₁₀ composite were investigated.