Boiling heat transfer and critical heat flux of ethanol–water mixtures flowing through a diverging microchannel with artificial cavities

This paper presents an experimental study on the convective boiling heat transfer and the critical heat flux (CHF) of ethanol–water mixtures in a diverging microchannel with artificial cavities. The results show that the boiling heat transfer and the CHF are significantly influenced by the molar fraction (x_m) as well as the mass flux. For the single-phase convection region except for the region near the onset of nucleate boiling with temperature overshoot, the single-phase heat transfer coefficient is independent of the wall superheat and increases with a decrease in the molar fraction. After boiling incipience, the two-phase heat transfer coefficient is much higher than that of single-phase convection. The two-phase heat transfer coefficient shows a maximum in the region of bubbly-elongated slug flow and deceases with a further increase in the wall superheat until approaching a condition of CHF, indicating that the heat transfer is mainly dominated by convective boiling. A flow-pattern-based empirical correlation for the two-phase heat transfer coefficient of the flow boiling of ethanol–water mixtures is developed. The overall mean absolute error of the proposed correlation is 15.5%, and more than 82.5% of the experimental data were predicted within a ±25% error band. The CHF increases from x_m = 0–0.1, and then decreases rapidly from x_m = 0.1–1 at a given mass flux of 175 kg/m² s. The maximum CHF is reached at x_m = 0.1 due to the Marangoni effect, indicating that small additions of ethanol into water could significantly increase the CHF. On the other hand, the CHF increases with increasing the mass flux at a given molar fraction of 0.1. Moreover, the experimental CHF results are compared with existing CHF correlations of flow boiling of the mixtures in a microchannel.     

Cost analysis of a finite capacity queue with server breakdowns and threshold-based recovery policy

This paper analyzes a repairable M/M/1/N queueing system under a threshold-based recovery policy. The threshold-based recovery policy means that the server breaks down only if there is at least one customer in the system, and the recovery can be performed when q (1 ≤ q ≤ N) or more customers are present. For this queueing system, a recursive method is applied to obtain steady-state solutions in neat closed-form expressions. We then develop some important system characteristics, such as the number of customers in the system, the probability that the server is busy, the effective arrival rate and the expected waiting time in the system, etc. A cost model is constructed to determine the optimal threshold value, the optimal system capacity and the optimal service rate at a minimum cost. In order to solve this optimization problem, the direct search method and Newton's method are employed. Sensitivity analysis is also conducted with various system parameters. Finally, we present some managerial insights through an application example.     

Computational procedure of optimal inventory model involving controllable backorder rate and variable lead time with defective units

This article considers that the number of defective units in an arrival order is a binominal random variable. We derive a modified mixture inventory model with backorders and lost sales, in which the order quantity and lead time are decision variables. In our studies, we also assume that the backorder rate is dependent on the length of lead time through the amount of shortages and let the backorder rate be a control variable. In addition, we assume that the lead time demand follows a mixture of normal distributions, and then relax the assumption about the form of the mixture of distribution functions of the lead time demand and apply the minimax distribution free procedure to solve the problem. Furthermore, we develop an algorithm procedure to obtain the optimal ordering strategy for each case. Finally, three numerical examples are also given to illustrate the results.     

高屏溪流域区域降雨特性分析

主要探讨气候变化下高屏溪流域的降雨变化趋势。首先将高屏溪流域依据潮州断层划分为山区与平原两个区域,利用Mann-Whitney-Pettitt(MWP)检定、Mann-Kendall趋势检定及t值检定等非参数统计方法,探讨山区及平原年降雨量、年一日最大降雨量、年降雨天数、年降雨强度及各季节降雨类型的差异及变化趋势。分析结果显示,山区及平原区在降雨强度上具有显著增加趋势,其发生显著变化的变异时间均分布在2000—2004年。因此,将数据变异点划分为前后两个样本,各测站在变异点之后发生超大暴雨事件的频率较变异点前有较大增加,其变异点之前山区平均发生超大暴雨事件的频率约2年一遇,平原区约8年一遇;变异点后山区约1年二遇,平原则2年一遇。各季节降雨类型检定中,台风季具有显著差异,于变异点后呈现增大现象,显示1980—2009年期间的降雨量在丰水期间有显著增加趋势且主要集中在台风季节,而枯水期间则无显著变化趋势。     

In Vivo Functional Assay in Fish Gills: Exploring Branchial Acid-Excreting Mechanisms in Zebrafish

Molecular and physiological analyses in ionoregulatory organs (e.g., adult gills and embryonic skin) are essential for studying fish ion regulation. Recent progress in the molecular physiology of fish ion regulation was mostly obtained in embryonic skin; however, studies of ion regulation in adult gills are still elusive and limited because there are no direct methods for in vivo functional assays in the gills. The present study applied the scanning ion-selective electrode technique (SIET) in adult gills to investigate branchial H⁺-excreting functions in vivo. We removed the opercula from zebrafish and then performed long-term acid acclimation experiments. The results of Western blot and immunofluorescence showed that the protein expression of H⁺-ATPase (HA) and the number of H⁺-ATPase-rich ionocytes were increased under acidic situations. The SIET results proved that the H⁺ excretion capacity is indeed enhanced in the gills acclimated to acidic water. In addition, both HA and Na⁺/H⁺ exchanger (Nhe) inhibitors suppressed the branchial H⁺ excretion capacity, suggesting that H⁺ is excreted in association with HA and Nhe in zebrafish gills. These results demonstrate that SIET is effective for in vivo detection in fish gills, representing a breakthrough approach for studying the molecular physiology of fish ion regulation.     

Insulin management and metabolic control of type 1 diabetes mellitus in childhood and adolescence in 18 countries. Hvid?re Study Group on Childhood Diabetes

Insulin regimens and metabolic control in children and adolescents with Type 1 diabetes mellitus were evaluated in a cross-sectional, non-population-based investigation, involving 22 paediatric departments, from 18 countries in Europe, Japan, and North America. Blood samples and information were collected from 2873 children from March to August 1995. HbA1c was determined once and analysed centrally (normal range 4.4-6.3%, mean 5.4%). Year of birth, sex, duration of diabetes, height, body weight, number of daily insulin injections, types and doses of insulin were recorded. Average HbA1c in children under 11 years was 8.3 +/- 1.3% (mean +/- SD) compared with 8.9 +/- 1.8% in those aged 12-18 years. The average insulin dose per kg body weight was almost constant (0.65 U kg(-1) 24 h(-1)) in children aged 2-9 years for both sexes, but there was a sharp increase during the pubertal years, particularly in girls. The increase in BMI of children with diabetes was much faster during adolescence compared to healthy children, especially in females. Sixty per cent of the children (n = 1707) used two daily insulin injections while 37% (n = 1071) used three or more. Of those on two or three injections daily, 37% used pre-mixed insulins, either alone or in combination with short- and intermediate-acting insulin. Pre-adolescent children on pre-mixed insulin showed similar HbA1c levels to those on a combination of short- and long-acting insulins, whereas in adolescents significantly better HbA1c values were achieved with individual combinations. Very young children were treated with a higher proportion of long-acting insulin. Among adolescent boys, lower HbA1c was related to use of more short-acting insulin. This association was not found in girls. We conclude that numerous insulin injection regimens are currently used in paediatric diabetes centres around the world, with an increasing tendency towards intensive diabetes management, particularly in older adolescents. Nevertheless, the goal of near normoglycaemia is achieved in only a few.     

Thermal modulation spectroscopy of biological films

Thermal modulation spectroscopic techniques have been developed to study the optical properties of copper complexes of spermine and spermidine. Both pure and mixed solutions of the complexes were used to prepare films on special substrate heaters. Measurement techniques were developed to obtain approximately quantitative estimates of the composition of the mixed films from the modulation spectra. It is concluded that modulation spectroscopy is an appropriate tool for obtaining quantitative information on biologically important compounds. The spectra at 77 K and 300 K were significantly different.     

Perception of spatiotemporal random fractals: an extension of colorimetric methods to the study of dynamic texture

Recent work establishes that static and dynamic natural images have fractal-like l/falpha spatiotemporal spectra. Artifical textures, with randomized phase spectra, and 1/falpha amplitude spectra are also used in studies of texture and noise perception. Influenced by colorimetric principles and motivated by the ubiquity of 1/falpha spatial and temporal image spectra, we treat the spatial and temporal frequency exponents as the dimensions characterizing a dynamic texture space, and we characterize two key attributes of this space, the spatiotemporal appearance map and the spatiotemporal discrimination function (a map of MacAdam-like just-noticeable-difference contours).     

TiO2 beads as photocatalyst and photoelectrode for dye‐sensitized solar cells synthesized by a microwave‐assisted hydrothermal method

In this study, a two‐step process involving a sol–gel and microwave‐assisted hydrothermal (MH) techniques has been used to synthesize a novel TiO₂ structure, namely, TiO₂ mesoporous beads. Various hydrothermal synthesis parameters were investigated to study their effects on the resulting beads. It was found that within the processing conditions used, the TiO₂ beads have similar sizes (~325 nm) and contain uniform‐sized anatase TiO₂ nanoparticles (<10 nm), which are single crystals. Crystalline TiO₂ beads are obtained in as short as 15 min at a low temperature of only 140 °C without any post‐process calcination. Less surface oxygen vacancies was obtained at a higher MH temperature. Compare to the commercial P‐25 TiO₂ powders and conventional hydrothermal synthesized TiO₂ beads, MH synthesized TiO₂ beads exhibit much higher values of specific surface areas, pore volumes, and porosities. The use of TiO₂ beads as photocatalyst and photoelectrode for dye‐sensitized solar cells has also been investigated. Copyright © 2015 John Wiley & Sons, Ltd.