龙游石窟砂岩风化特征研究

风化是龙游石窟保护和向游人开放参观时所面临的主要病害和急待解决的问题.在对浙江省龙游石窟砂岩岩矿分析、泥质胶结物中黏土矿物和地表、洞室渗水分析研究的基础上,模拟石窟客观环境条件,对石窟砂岩在盐溶液中反复浸泡,进行加速风化试验.其试验研究方法是,设置NaCl,Na2SO4饱和溶液和蒸馏水作为对比试验的浸泡液,将石窟砂岩试样在浸泡液中进行反复浸泡-干燥循环试验,每次试样干燥后测定其弹性波速.试验研究表明:Na2SO4,NaCl等可溶盐的参与,大大加速砂岩的风化速度;在洞室的渗水中所含,等离子的浓度越高,加速砂岩风化速度的作用越明显;较加速砂岩风化的作用更大.     

Duality and lower bounds in optimal stochastic control

A dual problem is proposed for an optimal stochastic control problem whose dynamical system is described by a linear stochastic differential equation. Relationships between the extreme values of the original and dual problems are discussed and two duality theorems are obtained The dual problem furnishes lower bounds for the extreme value of the original problem.     

Performance of Counterflow,Parallel Plate Heat Exchangers under Laminar Flow Conditions

Multilayered heat exchangers were analyzed theoretically and their heat transfer characteristics were clarified. The problem was treated as a two-dimensional, conjugated one with three phases-two fully developed laminar flows and the exchanger wall. From numerical results, the exchanger effectiveness was found to be definitely influenced by the following parameters: Graetz number, heat capacity flow rate ratio, dimensionless wall thickness, and conductance ratios between fluid and wall and between both fluids. Examination of mixed-mean temperature distributions in the exchanger showed that longitudinal wall conduction significantly reduces exchanger effectiveness in the low-Graetz-number region. Experimental results were in fairly good agreement with theoretical predictions.     

城市冠层模型的扩展与验证

本文首先介绍了一维简易多层城市冠层模型的概要。该模型以理想化的街区为对象,可进行建筑周边微环境的温湿度、风速的垂直分布变化。然后与实测进行了对比,发现虽然存在一定误差,但城市冠层模型可较好地把握室外温度的变化趋势。可适用于长期动态的室外气候定性分析。