充分发展湍流场中Pr数对被动标量输运的影响

采用直接数值模拟方法,研究壁湍流中分子Pr数对湍流被动标量输运的影响.发现在槽道湍流的外层,湍流雷诺平均普朗特数PrT与分子普朗特数的倒数呈线性关系;湍流亚格子普朗特数PrT与分子普朗特数的关系较为复杂,在分子普朗特数为1附近时,湍流亚格子Prt数出现极小值.     

人类活体颈椎生物力学性能测试仪器的研制

颈部疼痛和运动障碍是人类的常见病症。不管起因如何，受伤和退化将使颈椎的力学性能发生变化。由于颈椎的生理结构复杂。描述其在三维坐标系的运动状态需要3个平移参数和3个转角参数。为此，我们在颈椎运动力学性能研究时做如下的力学模型简化；把人体的胸部和头部看成是两个刚体，它们之间仅由颈椎相连，当人体的胸部被固定时，头部做曲伸，旋转，侧弯运动，简化为头部绕第一胸椎（T1）的转动。为实现这一运动，我们研制了一套专用的测试装置。测试者接受的是被动测试，头部的旋转是由扭力扳手产生的，当扭力扳手对某轴施加一力偶时，就向被试者头部传递了一力矩T，而此力矩可通过安装在扭力扳后上的力传感器将信号传递到应变仪上测出；头部在这力矩作用下的转角θ则由安装于测试装置上的转角指示器显示，我们分别对四位受试者进行了测试，得到了对应的T-θ曲线图。测试表明，尽管受试个体间存在着特异性，但也能找到一些明显的规律。例如每个受试者颈椎旋转的运动角度要大于其它的几种运动。     

Modeling of isothermal processes in porous materials on the basis of the concept of an ensemble of pores

A class of models of porous media based on the concept of an ensemble of pores with a certain distribution of the main geometric parameters (for example, the pore size) is considered. The cases of pores saturated with single-and two-phase multicomponent liquid mixtures are investigated. The properties of equilibrium states of the mixture are derived from the minimum free energy condition and the transfer laws from the decreasing free energy condition. The hydrodynamic connectivity of the pores is described by two types of kernels: one describes the spatial connectivity and the other the connectivity in an elementary macrovolume. Analytically and numerically, the one-dimensional problems of establishment of a steady-state regime, propagation of a passive admixture, and two-phase flow (an analog of the Buckley-Leverett problem) are investigated. A relationship between the models in question and relaxational filtration models is demonstrated. A simple model of capillary hysteresis related with the non-monotonicity of the pore area to volume ratio function is proposed.     

Designing a Linear Structure with a Local Nonlinear Attachment for Enhanced Energy Pumping

We present a design procedure for enhancing nonlinear energy pumping from a mode of a linear-damped substructure to a weakly coupled, essentially nonlinear oscillator. By this we denote the one way, irreversible passive transfer of vibrational energy from the mode to the nonlinear attachment. The design relies in the asymptotic expansion for large energies of a nonlinear normal mode of the underlying conservative system that provides an analytic estimate of the level of the amplitude reached by the nonlinear attachment in the energy pumping regime. The analytical findings are validated by direct numerical simulations.     

Monitoring of tropospheric ozone in the ambient air with passive samplers

Two sampling campaigns in suburban places in the north zone of Santa Clara city, Cuba, have been carried out on a weekly base with the use of Radiello passive diffusion tubes in order to monitor the tropospheric ozone (O₃) levels in 2010. The first campaign was scheduled from February to April (cold season) and the second one in August and October (warm season), both of them at two sampling sites, i.e., Farm and School of Art Instructors. After aqueous extraction, the samples were analyzed by UV–VIS spectrophotometry.A seasonal trend was observed with the maximum O₃ concentrations in the cold season and the minimum levels in the warm season. Samples collected during the cold season showed the highest O₃ levels. Higher levels were reached at the Farm site with average values of about 58 ± 12 μg/m³, which exceeded the limit of the Cuban Standard 99:1999. In the warm season, the O₃ concentrations were similar for both sites, but lower than those observed in the cold season. The overall, seasonal average value was found to be 24 μg/m³. Despite the higher weekly average temperatures in August, the O₃ concentrations during this month showed the lowest values of the whole sampling period, which finding is in agreement with that reported by the Meteorological Institute of Cuba.Mathematical models, based on the Cochrane-Orcutt algorithm, were fitted to the acquired data set to explain the change in the tropospheric ozone concentrations under various meteorological conditions during the two campaigns. The correlation coefficients for both the cold and the warm seasons demonstrated a strong correlation, i.e., 0.779 and 0.951, respectively. The high correlation of wind speed in the model from the first sampling campaign explains the sharp decrease in O₃ concentrations at the SAI sampling site from the sixth week of sampling.     

甲醇浓度对被动式自呼吸直接甲醇燃料电池性能的影响

依据单电池测试结果和甲醇传质理论考察了甲醇溶液的浓度对被动式自呼吸直接甲醇燃料电池（DMFC）性能的影响.研究结果表明,电池的法拉第效率和能量转化效率会随着浓度的增大而降低,采用4mol/L的甲醇溶液实现了最大的放电功率13.9mW/cm^2,并能在60mA下稳定放电长达20h.这取决于电池运行过程中电极内部的甲醇传质和甲醇透过的共同作用.     

Observer-based passive control for uncertain linear systems with delay in state and control input

This paper deals with the robust passivity synthesis problem for a class of uncertain linear systems with time-varying delay in state and control input. The parameter uncertainties are norm-bounded and allowed to appear in all matrices of the model. The problem aims at designing an observer-based dynamic output-feedback controller that robustly stabilizes the uncertain systems and achieves the strict passivity of closed-loop systems for all admissible uncertainties. By converting the problem at hand into a class of strictly passive control problem for a parameterized system, the explicit solution is established and expressed in terms of a linear matrix inequality. A numerical example is provided to demonstrate the validity of the proposed approach.     

Cr^4＋：YAG的可饱和吸收特性与被动Q开关性能研究

运用速率方程计算了Ｃｒ＾４＋：ＹＡＧ晶体的可饱和吸收特性参数，包括初始吸收系数，饱和吸收系数，饱和光强和损耗调制度，用Ｃｒ＾４＋：ＹＡＧ对脉冲和连续Ｎｄ：ＹＡＧ激光器进行了被动调Ｑ，在脉冲Ｎｄ：ＹＡＧ激光器上得到了８ｎｓ的调Ｑ激光脉冲，在连续Ｎｄ：ＹＡＧ激光器的调Ｑ中得到了间隔和幅度抖动小于５％的输出脉冲充列。     

Fractional Differentiation in Passive Vibration Control

From a single-degree-of-freedom model used to illustrate the concept ofvibration isolation, a method to transform the design for suspensioninto a design for robust controller is presented. Fractionaldifferentiation is used to model viscoelastic behaviour of suspension.The use of fractional differentiation not only permits optimisation ofjust four suspension parameters, showing the `compactness' of thefractional derivative operator, but also leads to robustness ofsuspension performance to uncertainty of the sprung mass. As an example,an engine suspension is studied.     

The heat transfer problem in the wall region of a turbulent boundary layer

The problem of heat transfer in the wall region of a turbulent boundary layer has been investigated. The resonant triad in the theory of hydrodynamic stability was used to obtain the velocity field induced by the coherent structures in the wall region of the turbulent boundary layer, while the small scale turbulence was represented by a simple model. By such a new approach of modeling, the 3-D temperature field is calculated, the mean temperature profile in the wall region and the Nusselt number characterizing the heat flux, which was found to be in good agreement with the experimental observations are obtained. The instantaneous temperature field had streaky structures, thus offering a mechanism for their generation found in numerical simulations. Project supported by the National Natural Science Foundation of China (Grant No. 19132011).