Nitrate and nitrite in vegetables on the Danish market: content and intake

The contents of nitrate and nitrite in lettuce, leek, potato, beetroot, Chinese cabbage and white cabbage on the Danish market were determined for 3 years in the period 1993-1997 as part of the Danish food monitoring programme. These vegetables are supposed to provide the major contribution to the intake of nitrate from the diet. Results for nitrate and nitrite in fresh and frozen spinach are also shown. The highest content of nitrate was found in lettuce followed by beetroot, Chinese cabbage, fresh spinach, leek, frozen spinach, white cabbage and potatoes. For all the products a great variation in the content of nitrate was found. For lettuce a characteristic variation throughout the year is clearly seen with the highest content in the winter period the lowest content in the summer period. Generally, the content of nitrite was low but in spinach high contents were found, probably due to improper storage conditions during transportation. The intake of nitrate and nitrite from these vegetables is calculated on the basis of two different consumption surveys. For both surveys the average intake of nitrate from the vegetables included in the monitoring programme is estimated to be approximately 40mg day^-1, whereas for nitrite the average intake is approximately 0.09mg day^-1. The total intake of nitrate and nitrite is estimated to be respectively 61mg day^-1 and 0.5mg day^-1.     

Modelling Approach for Planar Self‐Breathing PEMFC and Comparison with Experimental Results

This paper presents a model‐based analysis of a proton exchange membrane fuel cell (PEMFC) with a planar design as the power supply for portable applications. The cell is operated with hydrogen and consists of an open cathode side allowing for passive, self‐breathing, operation. This planar fuel cell is fabricated using printed circuit board (PCB) technology. Long‐term stability of this type of fuel cell has been demonstrated. A stationary, two‐dimensional, isothermal, mathematical model of the planar fuel cell is developed. Fickian diffusion of the gaseous components (O₂, H₂, H₂O) in the gas diffusion layers and the catalyst layers is accounted for. The transport of water is considered in the gaseous phase only. The electrochemical reactions are described by the Tafel equation. The potential and current balance equations are solved separately for protons and electrons. The resulting system of partial differential equations is solved by a finite element method using FEMLAB (COMSOL Inc.) software. Three different cathode opening ratios are realized and the corresponding polarization curves are measured. The measurements are compared to numerical simulation results. The model reproduces the shape of the measured polarization curves and comparable limiting current density values, due to mass transport limitation, are obtained. The simulated distribution of gaseous water shows that an increase of the water concentration under the rib occurs. It is concluded that liquid water may condense under the rib leading to a reduction of the open pore space accessible for gas transport. Thus, a broad rib not only hinders the oxygen supply itself, but may also cause additional mass transport problems due to the condensation of water.     

Pollutant emissions,performance and combustion behaviour assessment of an Si gas engine fuelled with Lcv gas containing carbon monoxide and hydrogen diluted by nitrogen

This paper includes the experimental test data of an SI engine fuelled with simulated LCV gas (Low Calorific Value), which resembles synthesis gas in composition. The LCV gas was simulated by a mixture of carbon monoxide, hydrogen and nitrogen. During the experiment, the lower heating value of the LCV gas was altered by dilution with nitrogen. A single-cylinder Honda GX270 engine was adopted in the experiment to assess the impact of LCV gas on the system performance. This engine is typically used to power various machines and for electrical energy production in small generator sets. A modified engine was connected to an electric generator, which was loaded with an electric resistor. Engine operation was controlled using a microprocessor controller. All tests were performed at constant engine speed (3000 rpm). The engine was working at wide-open throttle for all mixtures. All mixtures were burned at stoichiometric conditions and with fixed value of ignition timing (30 deg bTDC). The indicated performance of the SI engine was evaluated based on the in-cylinder pressure measurements. No significant impact on the main internal parameters of the tested SI engine fuelled with simulated LCV gas diluted by nitrogen was observed. The experimental tests showed that the combustion duration increased for the mixtures with higher content of inert gas. Increase in the LHV raised the specific emissions of NO_x and decreased specific emissions of CO and HC.     

Effect of pipe orientation on dense-phase transport in inclined upward and downward flows

A physical model is presented to describe the flow characteristics of cocurrent two-layer upflow and downflow through inclined tubes. The influence of inclination angle on these two kinds of flow patterns has been investigated. For inclined upflow, the solids/gas velocity ratio is less than unity and decreases slightly with the increase of inclination angle, whereas for inclined downflow, this velocity ratio is, in general, greater than unity and increases with the inclination angle. The average voidage increases as the inclination angle decreases for inclined upflow while an opposite trend exists for inclined downflow. The pressure gradient is invariably negative for inclined upflow at various inclination angles and for inclined downflow of low inclination; however, the gradient becomes positive for inclined downflow at higher inclination angles. A flow regime map has also been presented. The present predictions agree well with the existing published experimental results.     

近代河流沉积与地震地层学解释

对近代沉积的研究工作帮助了地震地层学解释人员在地震部面上理解和追索地下地层的岩性、岩相变化。但是，特别是对于陆相地层，解释人员往往忽略了河流沉积的历史性侧向侵蚀作用、搬运作用及再沉积作用。本文作者以黄河及长江的沉积历史变迁为两个典型实例，说明了下列事实：在一条瓣状河或曲流域中的河道、天然堤、心滩、曲流沙坝、牛轭湖及泛滥平原等等，它们的平面位置在地史中每几百年就会显著地改变。然而盆地的沉积速率却很慢     

基于特征自由度变动的装配误差累积建模研究

利用基于装配功能对于各零件装配特征变动的雅可比矩阵,结合特征自由度和变动理论,建立表示装配功能要求的特征变动与装配零件特征变动联系的数学模型。运用该数学模型,可以定量地表示装配特征的变动对产品装配功能要求的影响,为设计者指出对装配功能影响较大的零件公差并有针对性地对其进行公差分析。