A PDE-based Method for Optimizing Solar Cell Performance

In this paper, we address the optimal design problem for organic solar cells (OSC). In particular, our focus is to enhance short-curcuit photocurrent by optimizing the donor-acceptor interface. To that end, we propose two drift-diffusion models for organic solar cells, both of which account for the physics of OSC\u27s that charge carriers are mostly generated in the region near the donor-acceptor interface. For the first drift-diffusion model, the generation of charge carriers is translated into a boundary condition across the donor-acceptor interface. We apply the theory of shape optimization to compute the shape gradient functional of the photocurrent. In particular, shape differential calculus is extensively applied in the computation. For the second drfit-diffusion model, we parameterize the donor-acceptor interface as a leve set of a function, i.e. the phase field function . The dependence of the second drift-diffusion model on the geometry is therefore transformed into its dependence on the phase field function. Such transformation greatly simplifies the sensitivity analysis and leads to an easy-to-implement numerical optimization algorithm. In numerical examples, it is shown that the maximum output power of the optimized solar cell can be increased by a factor of 3. Our analysis and examples in this paper are in two dimensions, but the generelization of both the analysis and numerical optimization to three dimensions is straightforward

Breastfeeding in China: a review

This review aims to describe changes in breastfeeding and summarise the breastfeeding rates, duration and reasons of discontinuing 'any breastfeeding' or 'exclusive breastfeeding' in P.R. China. Breastfeeding rates in China fell during the 1970s when the use of breast milk substitutes became widespread, and reached the lowest point in the 1980s. As a result many efforts were introduced to promote breastfeeding. The breastfeeding rate in China started to increase in the 1990s, and since the mid-1990s 'any breastfeeding' rates in the majority of cities and provinces, including minority areas, have been above 80% at four months. But most cities and provinces did not reach the national target of 'exclusive breastfeeding' of 80%. The 'exclusive breastfeeding' rates in minority areas were relatively lower than comparable inland provinces. The mean duration of 'any breastfeeding' in the majority of cities or provinces was between seven and nine months. The common reasons for ceasing breastfeeding, or introducing water or other infant food before four months, were perceived breast milk insufficiency, mother going to work, maternal and child illness and breast problems. Incorrect traditional perceptions have a strong adverse influence on 'exclusive breastfeeding' in less developed areas or rural areas. China is a huge country, geographically and in population size, and there is considerable ethnic diversity. Therefore breastfeeding rates in different parts of China can vary considerably

Coherent control of population transfer between vibrational states in an optical lattice via two-path quantum interference

We demonstrate coherent control of population transfer between vibrational states in an optical lattice by using interference between a one-phonon transition at $2\omega$ and a two-phonon transition at $\omega$. The $\omega$ and $2\omega$ transitions are driven by phase- and amplitude-modulation of the lattice laser beams, respectively. By varying the relative phase between these two pathways, we control the branching ratio of transitions to the first excited state and to the higher states. Our best result shows an improvement of the branching ratio by a factor of 3.5$\pm$0.7. Such quantum control techniques may find broad application in suppressing leakage errors in a variety of quantum information architectures.Comment: 5 pages, 4 figure

Systematic Review of Usability Engineering Management Studies for the Aging Population -UEM4Agin

Usability management is one of the core elements of any software to make it efficient and effective. Unfortunately, most of the time usability as well as its management is neglected while developing software that may result as ineffective and inefficient software design. In different eras different researchers performed studies to highlight the management of usability and to show its importance. Due to the increase in the aging population, the concern for the aging population assistances of each equipment becomes to be necessary. Number of Steps has been taken so far to help out the aging population but remained limited to visual considerations, such as stronger contrasts or larger characters on the displays and printing, or such physical characteristics as the ease for pressing buttons. In this paper, our focus is to perform a systematic review (SR) of usability management specifically for the aging population/senior citizens and its limitations. The systematic review aims to address three research questions: 1) What is the current status of usability management/usability engineering management research for the aging population/senior citizen around the globe? As we found that the literature on usability management for the aging population began in 1992 and increased thereafter, there is a lack of organized research teams and dedicated usability management journals for researching the aging population. High-impact theoretical studies are scarce. On the application side, no original and systematic research frameworks have been developed. The understanding and definition of usability and usability management is not well synchronized with international norms. 2) What are the existing methods, approaches, frameworks and practices that are currently being used in usability engineering management for the aging population? 3) What are the limitations of usability engineering management for the aging population/senior citizen? Purpose of this study is to identify the current research problems, existing studies for providing valid solution to these problems and will find out the limitations of existing work for covering the existing problems in usability engineering management specifically for the aging population. This will be done by performing quantitative literature of different databases and all the results will be gathered by analyzing and summarizing the statistical data using “R Studio”. Remedial techniques for handling the limitation of usability engineering management will be planned in future for the aging population

A decade of change in breastfeeding in China's far north-west

BACKGROUND: There have been considerable changes in breastfeeding practices in China over the past forty years. However China is a very large country, and breastfeeding rates in different parts of China vary considerably. The objective of this paper is to identify and compare breastfeeding types and rates between 1994–1996 and 2003–2004 in Shihezi, Xinjiang Uygur Autonomous Region, PR China. METHODS: In 1994–1996, a study of breastfeeding (n = 2197) was undertaken in Shihezi, Xinjiang, PR China. A decade later in 2003–2004, a longitudinal study (n = 545) of infant feeding practices was undertaken in the same area. RESULTS: The 'any breastfeeding' rates at 1, 4 and 6 months were 94%, 82% and 78% respectively in the early 1990s. A decade later, breastfeeding at 1 month was lower, but rates at 4 and 6 months remained the same. In 2004 the 'full breastfeeding' rate at one month was significantly higher (57%) than a decade earlier (38%), but after 3 months there was a rapid decline. This reflected a shift in the way complementary foods are introduced: the initial introduction was later, but by a higher proportion of mothers. CONCLUSION: The rate of breastfeeding at one month is significantly lower in 2003–2004 when compared to 1994–1996. The 'full breastfeeding' rates were initially higher, but after 3 months were then lower. The Chinese national breastfeeding targets were not reached in either period of the study. These studies show the need to further promote full or exclusive breastfeeding and further longitudinal studies are necessary to provide the detailed knowledge about risk factors required for health promotion programs

Fault Diagnosis of Motor Bearing by Analyzing a Video Clip

Conventional bearing fault diagnosis methods require specialized instruments to acquire signals that can reflect the health condition of the bearing. For instance, an accelerometer is used to acquire vibration signals, whereas an encoder is used to measure motor shaft speed. This study proposes a new method for simplifying the instruments for motor bearing fault diagnosis. Specifically, a video clip recording of a running bearing system is captured using a cellphone that is equipped with a camera and a microphone. The recorded video is subsequently analyzed to obtain the instantaneous frequency of rotation (IFR). The instantaneous fault characteristic frequency (IFCF) of the defective bearing is obtained by analyzing the sound signal that is recorded by the microphone. The fault characteristic order is calculated by dividing IFCF by IFR to identify the fault type of the bearing. The effectiveness and robustness of the proposed method are verified by a series of experiments. This study provides a simple, flexible, and effective solution for motor bearing fault diagnosis. Given that the signals are gathered using an affordable and accessible cellphone, the proposed method is proven suitable for diagnosing the health conditions of bearing systems that are located in remote areas where specialized instruments are unavailable or limited

Threshold fine-tuning and 3D characterisation of porous media using X-ray nanotomography

A common challenge in the X-ray nanotomography of porous media, such as fuel cell gas diffusion layers (GDLs), is to binarize nanotomography greyscale images in order to differentiate between solids and voids for structural characterisation and numerical flow analysis. In the process threshold determination is critical. This paper presents a study on determination of and fine-tuning threshold value based on comparison of material porosity and average fibre diameter obtained from nanotomography images with porosity data from density experiments and average fibre diameter achieved from scanning electron microscopy images respectively. The more accurate 3D reconstructed model is then used to calculate pore size distribution and average pore size, while the gas permeability of the representative 3D binary images are calculated using a single phase Lattice Boltzmann (LB) model in the D3Q19 regime