Evaluation of passive mixing behaviors in a pillar obstruction poly(dimethylsiloxane) microfluidic mixer using fluorescence microscopy

The rapid mixing of fluids passing through a microfluidic channel is very important for various applications of microfluidic systems. It has been a great challenge to achieve highly efficient mixing in a microfluidic system because it is very difficult to generate turbulence in a submillimeter-size channel at low Reynolds numbers (Re). In this paper, we fabricated a pillar obstruction microfluidic mixer and evaluated its mixing efficiency at various flow rates. The mixing behavior of confluent streams was estimated using a fluorescence microscope. Three different sets of miscible solutions (phosphate-buffered solution, gold nanocolloids and 20% glycerol), with Rhodamine 6G aqueous solution, were used as sample laminar flows. According to our experimental results, the pillar obstruction microfluidic mixer shows an excellent mixing performance in the low Re range. Here, the mixing performance was strongly dependent on the characteristic viscosity changes of different sets of miscible solutions. The pillar obstruction microfluidic mixer designed here is expected to benefit a wide range of lab-on-a-chip applications because fabrication is very simple and the mixing efficiency is excellent at low Re.     

Pairwise testing for systems with data derived from real‐valued variable inputs

Pairwise testing is an effective combinatorial test case generation approach in which test cases are developed to execute all possible pairwise combinations of system inputs. It can help reduce the number of test cases and save testing time yet still effective in finding defects. However, it is very difficult for practitioners to effectively apply pairwise testing in the real world because of the lack of suitable techniques and guidelines. To redress this situation, this paper conducts a case study of applying pairwise testing to system data derived from real‐valued variable inputs. In order to apply pairwise testing to this case study, this paper develops a test procedure and a novel partitioning method to test derived data as a naïve application of the conventional pairwise testing that would produce a huge number of test cases. A comparative evaluation shows that the pairwise testing of the proposed approach is more effective than the random testing with a 12–20% higher fault detection ratio. Based on our experience, guidelines for applying pairwise testing in practice are also presented. Copyright © 2014 John Wiley & Sons, Ltd.     

Structural integrity assessment of the reactor pressure vessel under the external reactor vessel cooling condition

Since the suggestion of external reactor vessel cooling (ERVC), the effects of melting and cooling on the response of structural integrity of the reactor pressure vessel (RPV) under core melting accident conditions have been investigated. To investigate the initial behavior of RPV lower head and the effects of analysis conditions on the structural integrity of RPV, the transient analysis is utilized considering the transient state. To obtain an analogy with real phenomena, the material properties were determined by combining and modifying the existing results considering phase transformation and temperature dependency. The temperature and stress analyses are performed for core melting accident by using ABAQUS. Finally, the potential for vessel damage is discussed using the Larson-Miller curve and damage rule. In addition, the results by transient analysis are compared with those by steady state analysis and the effects of analysis conditions on structural integrity are reviewed.     

Aluminum–germanium wafer bonding of (AlGaIn)N thin-film light-emitting diodes

Eutectic aluminum–germanium wafer bonding was used to fabricate (AlGaIn)N thin-film light-emitting diodes (LEDs). Wafer bonding was carried out on 2″ wafer level at a bond temperature of 470 °C using patterned Al bond pads on the GaN-on-sapphire LED epiwafer and plain Ge substrates. The microstructure of the joint formation was characterized via cross-section analysis using scanning electron microscopy and energy dispersive X-ray spectroscopy (EDX). Scanning acoustic microscopy was used to investigate the bond interface. The shear strength was determined to be 1–2 kN/cm². The formation of a liquid Al–Ge phase is evident from cross-section analysis and optical microscopy. During solidification, Al and Ge are separated into distinct phases again, which is revealed by EDX. The obtained bond is not free of micro-voids, yet it is mechanically stable and suited for the fabrication of thin-film LEDs by removing the sapphire substrate via laser lift-off, which is also demonstrated.     

Evaluation of the potential of various spectral indices and textural features derived from satellite images for surficial deposits mapping

The present paper deals with the relevance of spectral and textural indices to surficial deposits identification and mapping. The study area is located in the Cochabamba valley in central Bolivia. Potential of SPOT‐4, Landsat‐7 and Radarsat‐1 data were compared for surficial deposits mapping. Different spectral indices including NDVI (normalized difference vegetation index) and TSAVI (transformed soil adjusted vegetation index) and textural features (mean, standard deviation, angular second moment, entropy, etc.) were extracted from these datasets and used in the mapping process. The results showed that indices exhibit different level of sensitivities according to surficial deposit types. A discriminant analysis was conducted to extract the most significant indices, which were then used in a three‐step linear combination mathematical model to map surficial deposits. We achieved an overall classification rate of 74% using spectral data of land use map in step 1. By adding information on vegetation and soils obtained from evaluation of spectral indices, this rate was improved to 82% during step 2. Finally, it was further slightly improved to 83% by adding textural data in the final step.     

High‐reliability gate driver circuit to prevent ripple voltage

In this paper, a high‐reliability gate driver circuit is proposed to prevent multiple outputs. The proposed circuit ensures reliability of the pull‐up thin‐film transistor (TFT) by periodically discharging the Q node voltage to the low‐level voltage (VGL) in the off stage. In addition, the output node is composed of two pull‐down TFTs that are driven alternately to ensure stability against bias stress. Thus, because the reliabilities of the pull‐up and pull‐down TFTs can be guaranteed simultaneously, the stability of the entire circuit is improved. Based on the simulation results, the rising and falling times of the output pulse are stable within 1.77 and 1.28 μs, respectively, even when the threshold voltage of the entire TFT is shifted by +10.0 V. In addition, the ripple voltage of the proposed circuit is almost eliminated and is within 0.79% of the total swing voltage. Moreover, through current is prevented in the proposed circuit because the turn‐on durations of the pull‐up and pull‐down units are completely nonoverlapping, which suggests that unnecessary power consumption can be eliminated. Therefore, based on 2,160 stages, the total power consumption of the proposed circuit is reduced by 34.7 mW from 276.3 to 241.6 mW.     

The evaluation of reliability and validity of a preliminary version of the Clinical Assessment of Schizophrenic Syndrome (CASS)

This article describes the development, field testing, and evaluation of an interactive computer program, "Life Challenge," developed by the New York State Department of Health as a tool for enhancing adolescents' sense of self-efficacy in HIV/AIDS prevention programs. The computer kiosks were field tested in 13 sites serving high-risk adolescents. The program uses a time travel adventure game format to provide information and nonthreatening skill practice. Users record and play back their responses as they "negotiate" with their chosen partners. A proof of concept evaluation with analysis of 211 audio responses found that users took negotiating tasks seriously; statistically significant learning gains were achieved on knowledge items and in self-efficacy scores (greatest improvement for those with low baseline self-efficacy levels). Challenges and problems encountered in implementing the project are described, and the potential of using computers for skill practice and educational interventions in health education is explored.     

Droplet-Based Microreactions With Oil Encapsulation

This paper reports a microreaction technology for biochemical assay using nanoliter droplets encapsulated inside oil droplets. Microreaction chambers are constructed on a glass substrate by accumulating oil droplets that are dispensed by a directional droplet ejector. Droplets of different aqueous reagents are then directionally ejected (by other directional droplet ejector adjacent to the oil droplet ejector) into the oil microchambers for parallel and combinatory analysis. Because the reagents are encapsulated in oil, the evaporation rate is reduced by several orders of magnitude, and only small amounts of reagents are required for each assay. The microchamber size and the reagent amount are digitally controlled by the number of ejected oil and reagent droplets, respectively. The ejectors for oil and reagents have been integrated on a single chip so that each assay is performed efficiently without any mechanical movement and alignment. We have carried out both physical and chemical microreactions with this method and observed a negligible difference in response from conventional macroreactions.     

Single- and Triaxis Piezoelectric-Bimorph Accelerometers

This paper describes the novel single- and triaxis piezoelectric-bimorph accelerometers that are built on parylene beams with ZnO films. The unamplified sensitivity and the minimum detectable signal of the fabricated single-axis accelerometer are measured to be 7.0 mV/g and 0.01 g, respectively, over a frequency range from 60 Hz to subhertz. The linearity of the sensitivity as a function of acceleration is measured to be 0.9% in the full scale. A highly symmetric quad-beam bimorph structure with a single proof mass is used for triaxis acceleration sensing and is demonstrated to produce high sensitivity, low cross-axial sensitivity, and good linearity, all in a compact size. The unamplified sensitivities of the X-, Y-, and Z-axis electrodes (of the triaxis accelerometer) in response to the accelerations in X-, Y-, and Z-axes are 0.93, 1.13, and 0.88 mV/g, respectively. The worst-case minimum detectable signal of the triaxis accelerometer is measured to be 0.04 g over a bandwidth ranging from subhertz to 100 Hz. The cross-axial sensitivity among the X-, Y-, and Z-axis electrodes is less than 15% in the triaxis accelerometer. The theoretical analyses of the charge sensitivities and resonant frequencies along with the effects of residual stress on the charge sensitivities are presented for both the single- and triaxis accelerometers.