The aging adult voice

Advancing age produces physiologic changes that may alter voice. Some of these changes are inevitable; others may be avoidable or reversible. In addition, many treatable medical conditions may cause voice changes similar to those of aging. It is essential that all voice care providers be familiar with the expected changes of aging, and be alert to reversible conditions that may adversely affect phonation and be mistaken for presbyphonia.     

一类非线性周期种群系统的最优收获控制

研究一类具有周期系数和年龄结构的生物动力系统的最优收获问题．应用冻结系数法和不动点原理讨论了状态系统的适定性．借助法锥概念得到了控制问题的Pontryagin极值原理，推广了文献中的一个结果．     

Comparison of maintenance policies with monotone failure rate distributions

We compare different maintenance policies assuming that the system lifetime has either increasing failure rate (IFR), or decreasing failure rate (DFR) distribution. We show that these assumptions yield strongly stochastic comparisons between the process' intensities. This yields weaker stochastic comparison between the processes than the stochastic comparison that hold when the system lifetime is new better than used (NBU) or new worse than used (NWU). Copyright © 2002 John Wiley & Sons, Ltd.     

悬浮液进样-FAAS测定不同年限党参中的4种微量元素

为了探讨不同生长年限对党参质量控制的影响,同时建立快速测定党参中微量铁、铜、锌、锰的方法.采用悬浮液进样-FAAS用于党参样品的测定,悬浮于琼脂胶体中,直接喷入空气-乙炔火焰中,用标准加入法测定.不同生长年限的党参中微量元素的含量变化存在一定的规律性,这主要与中药材的生长年限有关,其次与中药材的产地有关;Fe元素含量较...     

Stability and bifurcation of an SIVS epidemic model with treatment and age of vaccination

In this paper, we consider a two-dimensional SIS model with vaccination. It is assumed that vaccinated individuals become susceptible again when vaccine loses its protective properties with time. Here the rate at which vaccinated individual move to susceptible class again, depends upon vaccine age and hence it is assumed to be a variable. This SIVS model with treatment exhibits backward bifurcation under certain conditions on treatment which complicate the criteria for the success of the treatment by making it possible to have stable endemic states. We also show how the infectivity and the recovery function affect the existence of backward bifurcation.     

Recent advances in the metallurgy of aluminum alloys. Part II: Age hardening

In this paper are reviewed some recent progress on the understanding and simulation of aluminum alloy age hardening. The main phenomena governing the formation of precipitate microstructures in aluminum alloys are presented; they provide a qualitative understanding of the relationship between alloy chemistry, processing and final precipitate microstructure at the nanoscale. In a second part, we describe how modeling approaches are capable of predicting these microstructures, from simple models to more advanced ones. A particular emphasis is put on the limits of these models and the strategies that are being developed to overcome them. In a third part, the mechanisms for precipitation strengthening will be discussed, as well as the models available to quantify this strengthening. Finally, in the last part, we will give some general prospects for the main developing areas of research.     

Diffusion-weighted magnetic resonance imaging of human skeletal muscles: gender-, age- and muscle-related differences in apparent diffusion coefficient

Purpose

To evaluate the apparent diffusion coefficient (ADC) of skeletal muscle based on signal intensity (SI) attenuation vs. increasing b values and to determine ADC differences in skeletal muscles between genders, age groups and muscles.

Materials and Methods

Diffusion-weighted images (b values in the range of 0–750 s/mm² at increments of 50 s/mm²) of the ankle dorsiflexors (116 subjects) and the erector spinae muscles (86 subjects) were acquired with a 1.5-T MR device. From the two different slopes obtained in SI vs. b-value logarithmic plots, ADC^b0–50 (b values=0 and 50 s/mm²) reflected diffusion and perfusion, while ADC^b50–750 (b values in the range of 50–750 s/mm² at increments of 50 s/mm²) approximated the true diffusion coefficient. Moreover, to evaluate whether this b-value combination is appropriate for assessing the flow component within muscles, diffusion-weighted images of the ankle dorsiflexors (10 subjects) were obtained before and during temporal arterial occlusion.

Results

ADC^b0–50 and ADC^b50–750 were found to be 2.64×10^–3 and 1.44×10^–3 mm²/s in the ankle dorsiflexors, and 3.02×10^–3 and 1.49×10^–3 mm²/s in the erector spinae muscles, respectively. ADC^b0–50 was significantly higher than ADC^b50–750 in each muscle (P<.01). The erector spinae muscles showed significantly higher ADC values than the ankle dorsiflexors (P<.01). However, for each muscle, there were few significant gender- and age-related ADC differences. Following temporal occlusion, ADC^b0–50 of the ankle dorsiflexors decreased significantly from 2.49 to 1.6×10^–3 mm²/s (P<.01); however, ADC^b50–750 showed no significant change.

Conclusion

Based on the SI attenuation pattern, muscle ADC could be divided into ADC that reflects both diffusion and perfusion, and ADC that approximates a true diffusion coefficient. There were significant differences in ADC of functionally distinct muscles. However, we barely found any gender- or age-related ADC differences for each muscle.     

The dynamics of pest control pollution model with age structure and time delay

In this paper, by using pollution model and impulsive delay differential equation, we investigate the dynamics of a pest control model with age structure for pest by introducing a constant periodic pesticide input and releasing natural enemies at different fixed moment. We assume only the pests are affected by pesticide. We show that there exists a global attractive pest-extinction periodic solution when the periodic natural enemies release amount μ₁ and pesticide input amount μ₂ are larger than some critical value. Further, the condition for the permanence of the system is also given. By numerical analyses, we also show that constant maturation time delay, pulse pesticide input and pulse releasing of the natural enemies can bring obvious effects on the dynamics of system. We believe that the results will provide reliable tactic basis for the practical pest management.     

年龄分布下种群资源开发动态博弈的Nash均衡

研究具有年龄结构的种群资源开发中的动态博弈问题.应用~Kakutani~多值映射不动点定理证明了Nash均衡的存在性,借助切锥－法锥和共轭系统技巧刻画了均衡策略.结果表明,在一定条件下,均衡策略具有Bang-Bang结构.