Design and control of an ethyl acetate process: coupled reactor/column configuration

In this paper, design and control of a realistic coupled reactor/column process to produce ethyl acetate is studied. The process design is more complicated because the ethyl acetate product is neither the lightest nor the heaviest component in the system. A search procedure is proposed to obtain the optimum process design and operating condition of this process. The optimum process design is the one that minimize the Total Annual Cost (TAC) of this process while satisfying the stringent product impurity specifications. The optimum overall process design includes a continuous-stirred tank reactor (CSTR) coupled with a rectifier, a decanter, another stripper, and a recycle stream. After the process design is established, the next step is to use dynamic simulation to test the appropriate control strategy for this process. Sensitivity analysis is performed to obtain the suitable temperature control points for the columns. The proposed control strategy is very simple containing only one temperature control loop in each column. This recommended simpler control strategy uses the ratio of acetic acid feed rate to ethanol feed rate to control the 5th stage temperature of the rectifier and uses the stripper reboiler duty to control the 5th stage temperature of the stripper. The proposed control strategy does not need any on-line composition measurements and can properly hold product purity in spite of feed flow rate and feed composition disturbances. For small deviations of the product impurity compositions during disturbances, a slow cascade outer composition loop structure can be implemented using off-line composition measurements from the quality lab.     

Long‐term memory colors of Korean and Hungarian observers

Long‐term memory colors have been discussed extensively in the literature but previous articles focused on reflecting color samples. In this work, we studied six important long‐term memory colors, skin (both Caucasian and Oriental), green grass, blue sky, deciduous foliage, orange, and banana, in the viewing situation of a self‐luminous color monitor, for two different observer groups, Koreans and Hungarians. We quantified the long‐term memory colors of both observer groups in terms of CIE L*,a*,b* values, in a given viewing situation, and estimated interobserver variability. We used a comprehensive psychophysical experimental methodology including both the method of constant stimuli and the method of adjustment. In many cases, we found significant differences (t tests, P < 0.05) between the Korean and the Hungarian long‐term memory colors. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 176–183, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20192     

Converting baluns into broad-band impedance-transforming 180/spl deg/ hybrids

A technique for converting baluns into 180/spl deg/ hybrids by adding an in-phase power splitter is presented in this paper. Incorporating the broad-band antiphase and in-phase power splitting characteristics of the balun and power splitter results in a 180/spl deg/ hybrid with broad-band characteristics. This technique also provides a means of achieving perfect matching and output isolation for three-port lossless baluns. Applying this technique to a Marchand balun will result in a broad-band impedance-transforming 180/spl deg/ hybrid. Simple design equations based on the scattering matrix are presented. These theoretical results are validated by an experimental 180/spl deg/ hybrid using a coupled line Marchand balun. It achieves amplitude balance of 0.5 dB and phase balance of less than 5/spl deg/ from 1.2 to 3.2 GHz.     

用于锁模光纤激光陀螺的相敏检测

通过采用锁相放大器,演示了一种性能明显提高的锁模光纤激光陀螺.结果表明锁相放大器的输出与转动速率之间具有理想的线性关系,并对两脉冲(在时间间隔测量过程中引起相位误差)之间的光强差不敏感.与以往报道的时间间隔测量相比,演示了长期稳定性提高了二个数量级.     

Improved burn scar assessment with use of a new scar-rating scale

The subjective assessment of scar appearance is a widely used method in the evaluation of burn outcomes and the efficacy of treatment methods. The purpose of this study is to design a numeric scar-rating scale with better interrater reliability than has previously been reported. The rating scale assesses scar surface, thickness, border height, and color differences between a scar and the adjacent normal skin. Eight raters were trained with use of a standardized set of photographs that provide examples of the scores to be assigned to each level of severity of each scar characteristic. The raters then rated 10 photographs of different scars, referring to the teaching set of pictures for comparison. The intraclass correlation (interrater reliability) was 0.94, 0.95, 0.90, and 0.85 for scar surface, border height, thickness, and color, respectively. This rating system has proved to be a useful tool for the evaluation of scar surface, thickness, border height, and color.     

Exhaustive Output Arbitration of Input Buffered Switch with Buffered Crossbar

We propose a new arbitration method for an input buffered switch with a buffered crossbar. In the proposed method, an exhaustive polling method is used to decrease the synchronization. Using an approximate analysis, we explain how the proposed method improves the switch performance. Also, using computer simulations, we show the proposed method outperforms the previous methods under burst traffic.     

SIMPLE INSTABILITY CRITERION FOR A CLASS OF SINGULAR SYSTEMS WITH MULTIPLE TIME DELAYS

In this paper, the instability for a class of singular systems with discrete and distributed time delays is investigated. Simple instability criterion, which is a delay‐dependent criterion, is derived to guarantee the instability of such systems. Finally, a numerical example is given to illustrate the use of the main result.     

Finite element simulation of package stress in transfer molded MEMS pressure sensors

The goal of this paper is to investigate the effect of residual packaging stress resulting from transfer molding of a micro electro mechanical system pressure sensor. A model of a silicon diaphragm micro electro mechanical system pressure sensor geometry was used to simulate the stresses developed during the molding process. The analyses were carried out with an assumption that the epoxy molding compound was a temperature dependent elastic material. Finite element analysis was used to calculate the residual packaging stress. The stress values were used to obtain the electrical output signal and sensitivity of the packaged sensor. In this way, a direct link was established between package stress and device performance.The calculated output signal and sensitivity were compared with experimental data to verify the simulated stress and hence determine the effect of the packaging process on the pressure sensor. Four different service temperatures were considered to examine the temperature effects on the output signal and the sensitivity for the packaged sensor.     

Nanocomposite-based controlled release formulation of an herbicide, 2,4-dichlorophenoxyacetate incapsulated in zinc–aluminium-layered double hydroxide

Controlled release formulation of an herbicide, 2,4-dichlorophenoxyacetate (24D) was developed by the virtue of the formation of organic–inorganic nanohybrid material and its ion exchange property. The inorganic Zn–Al layered double hydroxide (ZAL) was used as a matrix, hosting an active agent or a guest, 24D by self-assembly technique. The resulting material (ZAD) was subsequently used to study the release property of 24D into aqueous solutions containing chloride, carbonate as well as distilled water. The release of the guest 24D was found to be rapid initially followed by a more sustained release thereafter and this behavior was dependent on the type of anions and their concentrations in the release medium, the aqueous solution. The mechanism of release has been interpreted on the basis of the ion exchange process between the 24D anion intercalated into the interlamellae host and carbonate or chloride and/or hydroxyl anions in the aqueous solution.     

Correlative High‐Resolution Mapping of Strain and Charge Density in a Strained Piezoelectric Multilayer

A key to strain engineering of piezoelectric semiconductor devices is the quantitative assessment of the strain‐charge relationship. This is particularly demanding in current InGaN/GaN‐based light‐emitting diode (LED) designs as piezoelectric effects are known to degrade the device performance. Using the state‐of‐the‐art inline electron holography, we have obtained fully quantitative maps of the two‐dimensional strain tensor and total charge density in conventional blue LEDs and correlated these with sub‐nanometer spatial resolution. We show that the In_0.15Ga_0.85N quantum wells are compressively strained and elongated along the polar growth direction, exerting compressive stress/strain on the GaN quantum barriers. Interface sheet charges arising from a polarization gradient are obtained directly from the strain data and compared with the total charge density map, quantitatively verifying only 60% of the polarization charges are screened by electrons, leaving a substantial piezoelectric field in each In_0.15Ga_0.85N quantum well. The demonstrated capability of inline electron holography provides a technical breakthrough for future strain engineering of piezoelectric optoelectronic devices.