Dynamic analysis of flexible rotor-bearing systems using a modal approach

The generalized dynamic equations of motion were obtained by the direct stiffness method for multimass flexible rotor-bearing systems. The direct solution of the equations of motion is illustrated on a simple 3-mass system. For complex rotor-bearing systems, the direct solution of the equations becomes very difficult. The transformation of the equations of motion into modal coordinates can greatly simplify the computation for the solution. The use of undamped and damped system mode shapes in the transformation are discussed. A set of undamped critical speed modes is used to transform the equations of motion into a set of coupled modal equations of motion. A rapid procedure for computing stability, steady state unbalance response, and transient response of the rotor-bearing system is presented. Examples of the application of this modal approach are presented. The dynamics of the system is further investigated with frequency spectrum analysis of the transient response

Exploring the Way to Approach the Efficiency Limit of Perovskite Solar Cells by Drift-Diffusion Model

Drift-diffusion model is an indispensable modeling tool to understand the carrier dynamics (transport, recombination, and collection) and simulate practical-efficiency of solar cells (SCs) through taking into account various carrier recombination losses existing in multilayered device structures. Exploring the way to predict and approach the SC efficiency limit by using the drift-diffusion model will enable us to gain more physical insights and design guidelines for emerging photovoltaics, particularly perovskite solar cells. Our work finds out that two procedures are the prerequisites for predicting and approaching the SC efficiency limit. Firstly, the intrinsic radiative recombination needs to be corrected after adopting optical designs which will significantly affect the open-circuit voltage at its Shockley-Queisser limit. Through considering a detailed balance between emission and absorption of semiconductor materials at the thermal equilibrium, and the Boltzmann statistics at the non-equilibrium, we offer a different approach to derive the accurate expression of intrinsic radiative recombination with the optical corrections for semiconductor materials. The new expression captures light trapping of the absorbed photons and angular restriction of the emitted photons simultaneously, which are ignored in the traditional Roosbroeck-Shockley expression. Secondly, the contact characteristics of the electrodes need to be carefully engineered to eliminate the charge accumulation and surface recombination at the electrodes. The selective contact or blocking layer incorporated nonselective contact that inhibits the surface recombination at the electrode is another important prerequisite. With the two procedures, the accurate prediction of efficiency limit and precise evaluation of efficiency degradation for perovskite solar cells are attainable by the drift-diffusion model.Comment: 32 pages, 11 figure

Economic sustainability of palm oil plantations among smallholders in Lahad Datu, Sabah

This study examines the economic sustainability indicators of oil palm smallholders in Lahad Datu, Sabah. A survey based on a set of questionnaires with 58 smallholder respondents were carried out. The findings indicated that majority smallholders have income above the poverty income level,, The income earned by the smallholders can be considered as sustainable.as they initiate measures to ensure that their agricultural activities are carried out via sustainable practices. The respondents spend within their income limit and have savings. They attended training programmes and the skills gained can help to enhance theirefficiency and skills in their cultivation.Keywords: Economic sustainability; Palm oil plantations; Smallholder

The role of thermal and lubricant boundary layers in the transient thermal analysis of spur gears

An improved convection heat-transfer model has been developed for the prediction of the transient tooth surface temperature of spur gears. The dissipative quality of the lubricating fluid is shown to be limited to the capacity extent of the thermal boundary layer. This phenomenon can be of significance in the determination of the thermal limit of gears accelerating to the point where gear scoring occurs. Steady-state temperature prediction is improved considerably through the use of a variable integration time step that substantially reduces computer time. Computer-generated plots of temperature contours enable the user to animate the propagation of the thermal wave as the gears come into and out of contact, thus contributing to better understanding of this complex problem. This model has a much better capability at predicting gear-tooth temperatures than previous models

Correlates of Smoke-Free Policies in Homes and Cars Among Hawaii Residents

The detrimental health effects of environmental tobacco smoke (ETS) have been well established. Cars and homes are two of the primary places that nonsmokers, particularly children, are exposed to ETS. This study examined the prevalence of smoke-free policies in homes and cars among 4,557 residents of Hawaii using cross-sectional data collected from a random-digit dial telephone survey. Smokers were much less likely than nonsmokers and former smokers to have smoke-free policies. Multivariate analysis of current smokers revealed that significant predictors of banning smoking in the home were: disagreeing that it is okay to smoke indoors, smoking fewer cigarettes per day, and higher confidence in ability to quit smoking. Significant predictors of banning smoking in the car were: disagreeing that it is okay to smoke indoors, smoking fewer cigarettes per day, and having children in the household. This study indicates that changing smokers’ attitudes about ETS may be an important component of a comprehensive program to increase smoke-free homes and cars