Konzept zur Maßstabsübertragung beim Suspendieren im Rührbehälter

Concept for Scale-up on Suspension in a Stirred Tank. The relationships derived for the suspension of solids in a propeller loop can be applied to corresponding processes in a stirred tank by means of analogy considerations. Accordingly, the ratio of stirrer power to slip power of laminar flow state is inversely proportional to the vessel diameter. In contrast, the power ratio remains constant in turbulent flow. There is a pronounced transition range between these two limiting states. The author's own experimental studies performed over a wide range of Re numbers for the recycling flow confirm this relationship. The observations presented explain why numerous authors have determined scale-up rules lying between these two extremes. The experiments shows that the power input for suspension is always significantly greater than the slip power. Under otherwise identical conditions, the necessary stirrer power is smaller by a factor of three for a propeller stirrer than for a disk impeller. The suspension of small solids concentrations can also be approximated by the flow model presented. The somewhat different physical relations valid in this case are substantiated by the author's experiments. The model also provided information relevant to scale-up when the particle properties are unknown. This is demontrated for an example in a 21 m³ vessel.     

车床静刚度计算机测试系统研制

在分析了车床的结构特点和车削工艺系统的受力情况和借鉴传统车床静刚度仪优点的基础上，研制了一套基于计算机控制的车床静刚度测试系统。系统由计算机作为信号检测、数据处理和控制核心，并配以精密位移传感器、压力传感器和步进电机及其驱动器等。实现了自动加载、卸载，采样，数据处理，直接绘制、显示和打印刚度曲线等功能。系统的成功研制为车床静刚度的测试提供了一种先进手段。实测结果表明，该系统具有自动化程度高、测试效率高、精度高、可靠性高、测试性能稳定的优点。     

用虚拟仪器技术验证牛顿第二定律

牛顿第二定律是经典力学的基本定律之一,为了形象、直观、准确地验证牛顿第二定律,本文利用数字实验系统生动地展示F=ma的关系。通过本实验可以使学生获得更直观的教学感受。     

食品安全检测数据仓库技术的应用与研究

主要利用数据仓库技术,以山东地区进出口食品检测实验室的检测数据为分析对象,初次构建了进出口食品农产品实验室检测数据仓库系统,为食品安全风险分析提供了准确科学的数据支持,为实现数据的进一步挖掘和系统平台的开发做好了准备工作。     

PVC塑窗型材锯铣中心设计研究

介绍了已开发成功的PVC塑窗型材锯铣加工中心,从模块化设计、刀具布局设计、绿色设计和适应性设计几个方面对这一新技术产品的设计思想、方法和关键技术进行了探讨.     

Estimation of mercury vapor flux from natural substrate in Nevada

The contribution of mercury to the atmosphere from natural sources is not well-quantified, particularly at the regional scale. This modeling study employed a Geographic Information Systems (GIS) approach to estimate mercury flux from substrate in Nevada, which lies within one of the global belts of geologic Hg enrichment. In situ mercury flux measurements were taken from a variety of substrate types with a wide range of mercury concentrations. This empirical data forms the basis of equations applied to a database of over 71,000 rock and soil samples used in scaling mercury flux for Nevada. The GIS was employed to spatially model estimated flux values according to sample type, geology, presence/absence of hydrothermal alteration, and meteorological conditions. The area average flux calculated for Nevada adjusted for meteorological conditions is 4.2 +/- 1.4 ng m-2 h-1, which corresponds to a approximately 29 kg daily emission of mercury. Areas of hydrothermal alteration emit 12.9 +/- 3.6 ng m-2 h-1, accounts for 22% of net mercury emissions yet represents only 7% of the area of Nevada. Unaltered geologic units have low fluxes (3.5 +/- 1.2 ng m-2 h-1) but, because of their large area, emit 78% of the total mercury.     

Atmospheric mercury emissions and speciation at the sulphur bank mercury mine superfund site, Northern California

One pathway for release of mercury (Hg) from naturally enriched sites is emission to the atmosphere. Elemental Hg, when emitted, will enter the global atmospheric pool. In contrast, if reactive gaseous Hg or Hg2+ (as HgCl2, HgBr2, or HgOH2) is formed, it will most likely be deposited locally. This study focused on the measurement of elemental Hg flux and reactive gaseous Hg concentrations at the Sulphur Bank Superfund Site, an area of natural Hg enrichment with anthropogenic disturbance and ongoing geothermal activity. Mean Hg emissions ranged from 14 to 11000 ng m(-2) h(-1), with the highest emissions from anthropogenically disturbed materials. Reactive gaseous Hg concentrations were the highest ever reported for a natural setting (0.3-76 ng m(-3)). Measured Hg fluxes were used within a Geographic Information System to estimate mercury releases to the atmosphere from the site. Results indicated approximately 17 kg of Hg y(-1) of is emitted to the atmosphere from the 3.8 km2 area, with half from mine waste, ore, and tailing piles and half from relatively undisturbed naturally enriched substrate.     

堤防防汛闸门设计浅析

濒江临海的特殊地理位置使上海常常受到来自海洋、内陆的潮水或洪水的侵袭,大堤和闸门共同组成的防汛体系保障了市民生命财产的安全.该文分析了上海市防汛闸门的类型和特点,并结合工程实例分析防汛闸门止水设置的必要性,提出一种横拉防汛闸门的改进设计型式,在确保大堤防汛安全的同时,美化了景观,方便了市民和游客的进出.