Estimation of soil and crop parameters for wheat from airborne radar backscattering data in C and X bands

The study of radar backscattering signatures of wheat fields was investigated, using data collected on the Orgeval agricultural watershed (France) by the airborne scatterometer ERASME in C and X bands, HH and VV polarizations, at incidence angles from 15° to 45°, during two years for different soil moisture conditions with simultaneous ground-based measurements. A simple parameterization as water-cloud model with two driving parameters (the surface soil moisture and the plant water content) gives satisfactory results to estimate radar cross sections of wheat for a wide range of frequencies (C and X bands) and incidence angles (20° and 40°) within 1 dB in CHH and XHH and 2 dB in CVV and XVV. At the lower frequency (C band) the attenuated soil backscattering by the vegetation is dominant. It is shown that simple linear relations in C band between radar cross section and soil moisture are insufficient. A correction term for the vegetation attenuation is needed and is determined. Low contrast between the backscattering of dry and wet soil (around 6 dB) for a given vegetation density leads to a relatively high error in the estimation of soil moisture by radar (0.06 cm³ / cm³). At the higher frequency (X band), the radar backscattering is negatively correlated to the vegetation water content with a saturation of the radar cross section as the plant grows (about 6 dB of dynamic range between low and fully grown canopy) with no dependence on the soil signal. The achievable accuracy in the estimation of crop water content is the same at 20° and 40° and higher in XHH (about 0.5 kg/m²) than in XVV.     

Amperometric biosensor for formic acid in air

The possibility of developing a simple, inexpensive and specific personal passive “real-time” air sampler incorporating a biosensor for formic acid was investigated. The sensor is based on the enzymatic reaction between formic acid and formate dehydrogenase (FDH) with nicotinamide adenine dinucleotide (NAD⁺) as a co-factor and Meldola's blue as mediator. An effective way to immobilise the enzyme, co-factor and Meldola's blue on screen-printed, disposable, electrodes was found to be in a mixture of glycerol and phosphate buffer covered with a gas-permeable membrane. Steady-state current was reached after 4–15 min and the limit of detection was calculated to be below 1 mg/m³. However, the response decreased by 50% after storage at −15°C for 1 day.     

High sensitivity ethanol gas sensor integrated with a solid-state heater and thermal isolation improvement structure for legal drink-drive limit detecting

The paper reports the successful fabrication of ethanol gas sensors with tin-dioxide (SnO₂) thin films integrated with a solid-state heater, which is realized with technologies of micro-electro-mechanical systems (MEMS), and are compatible with VLSI processes. The main sensing part with dimensions of 450×400 μm² in this developed device is composed of a sensing SnO₂ film, which is fabricated by electron-gun evaporation with proper annealing in ambient oxygen gas to yield fine particles and good structure. An integrated solid-state heater with a 4.5 μm-thick cantilever bridge (1000×500 μm²) structure is made of silicon carbide (SiC) material by MEMS technologies. The sensitivity for 1000 ppm ethanol gas reaches as high as 90 with 10 s and 2 min for the response and recovery time, respectively, at an operating temperature of 300°C. Those experimental results also exhibit a much superior performance to that of a popular commercial ethanol gas sensor TGS-822. Therefore, the developed sensor with high performance is a good candidate for some specific application in automobile to detect drink-drive limit and allows an array integration available with various films for controlling each element at separate resistance.     

中国东部沿海四省一市PM2.5浓度遥感估算方法研究

卫星遥感反演的气溶胶光学深度（AOD）产品已被广泛应用于近地面PM_2.5浓度的估算。已有研究表明通过构建AOD和PM_2.5之间的高级统计模型—线性混合效应模型（LME）可以有效获取近地面PM_2.5浓度的空间分布,但由于引入了大量的气象和土地利用等因子,使得模型对变量的解译能力有所降低。为此,基于MODIS AOD（空间分辨率：3 km）,以我国东部长江三角洲—福建—广东（YRD-FJ-GD）为研究区,构建了两种非参数机器学习模型,即支持向量机（SVM）和随机森林（RF）模型,来估算2018年YRD-FJ-GD地区的近地面PM_2.5浓度,并将其与线性混合效应模型（LME）的估算结果进行对比。研究发现,3种模型估算的PM_2.5浓度与地面实测值之间的R²均高于0.6,其中,RF模型的估算精度最优,模型拟合的R²高达0.91,比SVM模型（R²=0.79）和LME模型（R²=0.64）的估算结果分别提高了13%和30%;且RMSE（~9.07 μg/m³）也远低于LME（~19.09 μg/m³）和SVM模型（~17.29 μg/m³）。此外,由随机森林（RF）模型估算的2018年YRD-FJ-GD地区的PM_2.5空间分布显示,长江三角洲（YRD）地区的年均PM_2.5浓度最高（>46 μg/m³）,其次为广东省（GD）,福建地区（FJ）的年均PM_2.5浓度最低（<37 μg/m³）;4个季节的平均PM_2.5浓度则呈现冬季（46.32 μg/m³）>春季（38.80 μg/m³）>秋季（36.15 μg/m³）>夏季（30.16 μg/m³）的分布格局。研究结果表明：与高级统计模型（LME）和机器学习（SVM）相比,随机森林（RF）模型能更好地应用于YRD-FJ-GD地区的PM_2.5浓度估算。     

生态系统模型模拟中国叶面积指数变化趋势及驱动因子的不确定性

为了厘清中国近30 a来植被生长趋势及其对不同环境变化的响应,使用了3套长时间序列遥感叶面积指数（Leaf area index, LAI）数据集以及8套生态系统模型,对LAI变化趋势从总量、空间分布以及不同植被类型进行了分析与归因。总量上,1982~2015年遥感观测的LAI趋势（9.8×10^-3m²/m²·a）高于生态系统模型模拟的趋势（4.2×10^-3m²/m²·a）,大气二氧化碳浓度上升是主要驱动因素（（3.5×10^-3m²/m²·a）;遥感观测到全国79.5%的区域LAI都呈现显著增长的趋势,而生态系统模型模拟LAI的增长面积占比为33.1%;除草地外,生态系统模型低估了其他植被类型的LAI变化趋势。模型对降雨变化的响应过于敏感以及对人为活动模拟能力不足是模型模拟中国LAI变化趋势不确定性的重要来源。本研究定量分析了近30 a中国各种植被变化情况及其驱动因子,并对模型低估中国植被生长进行了解释,为后续中国地区植被相关研究提供了参考。     

Sentinel-1 based Soil Moisture Estimation in Middle Reaches of Heihe River Basin

In this study, a change detection model, constructed using the Sentinel-1 Synthetic Aperture Radar (SAR) data and the simultaneous Normalized Difference Vegetation Index (NDVI) products from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Landsat 8 sensors, is applied to estimate soil moisture in middle reaches of the Heihe River Basin, and the effects of two key parameters on retrieval accuracy are comprehensively investigated. The results show that: (1) when constructing the empirical relationship between backscattering coefficient difference ( \mathrm{\Delta } \sigma ) and Vegetation Index (VI) required by change detection model, the optimal sampling ratios in the ( \mathrm{\Delta } \sigma - V I ) space are approximately 2% and 4% for MODIS NDVI and Landsat 8 NDVI, respectively; (2) the Landsat 8 NDVI-based change detection model slightly outperforms the MODIS NDVI-based model in soil moisture retrieval accuracy, with Root Mean Square Error(RMSE) of 0.040 m³/m³ and 0.044 m³/m³respectively; (3) for the key parameters of the change detection method, replacing the ground-based initial soil moisture and scaling factor (maximum soil moisture difference between two adjacent dates \mathrm{\Delta } M s_{max} ) by the low-resolution SMAP/Sentinel-1 L2_SM_SP data will increase the RMSE by 0.01 m³/m³ and 0.04 m³/m³ respectively. Comparing to the parameter of initial soil moisture, the error in soil moisture scaling factor will lead to more significant degradation in the performance of the change detection method, thus it is recommended to use the high precision scaling factor for soil moisture estimation. This study confirms the promising potential of Sentinel-1 data for retrieving high-resolution soil moisture via change detection method and provides practical insight into its application.     

基于Sentinel-1数据的黑河中游土壤水分反演

基于Sentinel-1合成孔径雷达 (SAR) 数据及相同时段的中分辨率成像光谱仪（MODIS）和Landsat 8两种归一化植被指数（NDVI）,构建变化检测模型以估算黑河中游的高分辨率土壤水分,并探讨模型中具体参数设置对估算精度的影响。结果表明：①在对后向散射系数时间序列的差值 ( \mathrm{\Delta } \sigma ) 和植被指数 ( \mathrm{V} \mathrm{I} ) 进行线性建模过程中,MODIS NDVI和Landsat 8 NDVI这两种植被产品所构建的模型在 \mathrm{\Delta } \sigma - \mathrm{V} \mathrm{I} 空间中所选取的采样点比例分别为2%和4%时,各自取得最优精度; ②以土壤水分反演为目标,使用Landsat 8 NDVI构建的变化检测模型略优于使用MODIS NDVI构建的变化检测模型,两种模型的均方根误差RMSE分别为0.040 m³/m³和0.044 m³/m³,相关系数R分别为0.86和0.83; ③对于变化检测方法的关键参数,若使用低分辨率的SMAP/Sentinel-1 L2_SM_SP土壤水分数据分别代替站点观测的土壤水分初始值和缩放因子 (即两个连续时相土壤水分变化的最大值 \mathrm{\Delta } M s_{max} ) 这两个参数,则土壤水分RMSE将分别增加0.01 m³/m³和0.04 m³/m³。即土壤水分缩放因子这一参数的误差对反演结果的影响大于土壤水分初始值误差对反演结果的影响,故采用高精度的缩放因子进行变化检测估算。研究结论对于利用新兴的Sentinel-1 SAR数据,通过变化检测算法准确获取高分辨率土壤水分信息具有实际参考价值。     

Fiber composite thin shells subjected to thermal buckling loads

The results of parametric studies to assess the effects of various parameters on the buckling behavior of angle-ply, laminated thin shells in a hot environment are presented in this paper. These results were obtained by using a three-dimensional finite element analysis. An angle-ply, laminated thin shell with fiber orientation of [θ/ −θ]₂ was subjected to compressive mechanical loads. The laminated thin shell has a cylindrical geometry. The laminate contained T300 graphite fibers embedded in an intermediate-modulus, high-strength (IMHS) matrix. The fiber volume fraction was 55% and the moisture content was 2%. The residual stresses induced into the laminated structure during the curing were taken into account. Parametric studies were performed to examine the effect on the critical buckling load of the following parameters: cylinder length and thickness, internal hydrostatic pressure, different ply thicknesses, different temperature profiles through the thickness of the structure, and different layup configurations and fiber volume fractions. In conjunction with these parameters the ply orientation varied from 0° to 90°. Seven ply angles were examined: 0°, 15°, 30°, 45°, 60°, 75°, and 90°. The results show that the ply angle θ and the laminate thickness had significant effects on the critical buckling load. The fiber volume fraction and the internal hydrostatic pressure had important effects on the critical buckling load. The cylinder length had a moderate influence on the buckling load. The thin shell with [θ/−θ]₂ or [θ/−θ]^s angle-ply laminate had better buckling-load performance than the thin shell with [θ]₄ off-axis laminate. The temperature profiles through the laminate thickness and various laminates with the same thickness but with the different ply thickness had insignificant effects on the buckling behavior of the thin shells.     

使用光谱平滑提高浑浊水体叶绿素a浓度估算模型的应用精度

水体叶绿素a浓度估算是水质参数遥感监测的重要内容,由于采样时间和地点的限制,传统估算模型的参数和形式具有较大的时间和空间依赖性。光谱平滑可以突出不同数据集的共同特征,从而增加模型的预测精度,因此考虑使用平滑方法来提高水体叶绿素a浓度估算模型的应用精度。利用太湖2004年夏季和2011年春季共4个月的数据,对比分析了移动平均、多项式平滑和核回归平滑处理前后浑浊水体实测反射光谱的变化,以及该变化对叶绿素a浓度三波段遥感估算模型和模型应用精度的影响。结果表明：核回归平滑处理后的光谱数据建立的三波段模型的残差正态分布更好,估算模型更为稳健。将2004年7月数据建立的模型用于8月数据,估算的叶绿素a浓度的RMSE从平滑前的33.56 mg/m³降低到了平滑后的25.60 mg/m³;将2011年3月建立的模型用于4月数据,估算的叶绿素a浓度的RMSE从平滑前的16.68 mg/m³降低到了平滑后的10.57 mg/m³。由此可以认为,实测光谱的核回归平滑处理有助于提高叶绿素a浓度三波段模型的应用精度,且对于叶绿素a浓度变化较大的夏季数据的改进效果更显著。     

Determination of maximum acceptable weight of lift by adult Indian female workers

A study on maximum acceptable weight limit (MAWL) was conducted on ten adult Indian female building construction workers (CW) and eight household workers (HW), following the psychophysical methodology. All these workers were in the age group of 28–32 years. In this study, three different body heights (i.e. knee, waist and maximum reach) in sagittal plane were considered. The lifting frequency was fixed at 1 lift min⁻¹. The subjects were instructed to lift the load from the ground. Each set of experiments was conducted for 45 min work period using free-style lifting technique. Subjects were using a load container with no handle, which is typically used in the field. Both the working heart rates (WHR) and pause heart rates (with 4.4 s interval) were collected for the entire duration. The subjects were requested to rate their perceived exertion level after each load adjustment. The average MAWL working heart rates of CW group are 106.2(±8.3), 108.7(±9.3) and 106.8(±11.0) beats min⁻¹ for knee, waist and maximum reach heights, where the load levels were estimated as 18.2(±0.8), 17.4(±1.4) and 16.3(±1.2) kg, respectively. For HW group, the MAWL working heart rates obtained were 101.3(±8.0), 99.6(±6.2) and 105.2(±6.1) beats min⁻¹ for knee, waist and maximum reach heights and the corresponding load levels were 15.4(±0.5), 14.4(±0.7) and 13.9(±1.2) kg, respectively. Both the groups psychophysically rated the work in moderate to heavy category. A best-fit curve was obtained from average normalized baseline pause heart rates with work duration (t) as Avg. N.H.R._base=k.t. It has been observed that with extrapolation of the work duration to 8 h from 45 min experimental observation, the heart rate would increase to about 6–8 beats min⁻¹ for both the groups of workers. This equation can be used to approximate the effect of work-duration on heart rate.

Relevance to industry

MAWL study was performed on industrial female workers, which is rarely reported in the literature. Moreover, earlier studies were mainly conducted on the Americans. This study is focused on Indian population to compare the applicability of NIOSH guidelines in Indian context.     

内蒙古草原叶面积指数时空格局与水热影响

叶面积指数(Leaf Area Index,LAI)是表征植被状况的重要参数,与植被的生长和变化状况密切相关。探究内蒙古草原LAI长时间序列时空格局特征及水热条件对LAI的影响,可为准确掌握内蒙古草原分布与生长状况差异提供数据支撑,对了解内蒙古草原生产能力的空间分布特征具有参考价值。基于2000～2019年GEOV2 LAI产品数据集,结合气温和降水资料,选取变化斜率、变异系数和相关性系数3个指标对内蒙古草原LAI展开分析。结果显示,内蒙古草原LAI由东北向西南递减,多年均值为1.34 m²/m²,在不同草原类型中,荒漠草原(0.28 m²/m²)<典型草原(0.96 m²/m²)<草甸草原(2.27 m²/m²)<草甸(2.60 m²/m²),且与变异系数呈反比,荒漠草原年际间波动最剧烈。近20 a内蒙古草原LAI呈波动中上升趋势(0.02 m     

Temporal-Spatial Variation Analysis of Net Primary Productivity and its Relationship with Climate in Central Asia

The Net Primary Productivity (NPP) of vegetation and its response to climate change is one of the key areas in research of global change. The study on spatial and temporal changes of NPP in central Asia is important to understand the mechanism of vegetation-environment action and to cope with global change. Therefore, based on the MOD17A3 dataset and meteorological data and GIS analysis method, this paper is intended to analyze the spatial pattern, temporal variation and the driving factors to NPP in Central Asia during 2000~2014. The results shows that: ①the spatial variation of NPP in Central Asia is ranged from 0 to 874 gC/m²·a, with an average of 151.90 gC/m²·a. The average annual total NPP is 482.41TgC (1 Tg=10¹² g), and both the average NPP and total NPP showed a decrease trend. ②The average NPP was higher in southeastern alpine regions and high latitudes areas than in central and southern desert areas in Central Asia. ③From 2000 to 2014, the annual NPP in central Asia showed a decrease trend with a rate of -2.05 gC/m²·a², covering 39.89% of the region with significant reduction. The areas in which NPP decreased were mainly distributed in Kazakhstan, with typical steppe zone being the most significant in five ecological zones. ④The effect of precipitation on NPP in Central Asia was stronger than that of temperature. Precipitation influenced NPP of typical steppe，desert and desert steppe more seriously, while alpine meadow and alpine forest were jointly affected by precipitation and temperature.     

中亚地区植被净初级生产力时空动态及其与气候因子关系

植被净初级生产力(Net Primary Productivity,NPP)及其对气候变化的响应是全球变化的核心研究内容之一,研究中亚地区NPP的时空格局变化对理解植被—环境的作用机理以及应对全球变化具有重要的意义。基于MOD17A3数据集、气象数据结合GIS分析方法研究中亚地区2000~2014年的植被NPP时空动态特征及其与气候因子的关系。结果表明：①中亚地区空间上NPP的变化范围在0~874 gC/m²·a之间,平均值为151.90 gC/m²·a,NPP年总量平均值为482.41TgC (1 Tg=10¹² g),NPP平均值与总量均呈现出下降趋势;②中亚地区NPP的高值区主要分布在高纬度地区和东南部高山地区,中部和南部荒漠区则为NPP的低值区;③中亚地区2000~2014年间NPP在空间上总体呈现下降趋势,达到显著下降的区域总体面积的39.89%。NPP呈下降趋势的区域主要集中在哈萨克斯坦的大部分区域,不同分区内以典型草原区最为显著;④中亚地区NPP受降水量的影响作用高于气温,荒漠草原区、典型草原区以及荒漠区主要受到降水量的控制,高山草甸区与高山林地区则受到降水和气温的共同作用。     

Human–seat interface analysis of upper and lower body weight distribution

The human–seat interfaces were analyzed to determine the differential distribution of the body weight to the components of seat. Fifteen volunteers were tested on a simulated seat system with two piezoelectric force platforms, one placed as chair seat pan and the other placed on the floor surface as footrest. The seated configurations included back inclines (75° and 80°), upright (90°) and reclines (95°, 105° and 115°), absence or presence of armrest (adjusted at 62–68 cm of height), forward and backward sloping of the seat pan, and supported and unsupported back. The armrest and backrest assemblies were isolated from the force platforms. The difference in the body weight (kgf) to the sum of forces recorded at seat pan and feet yielded the extent of weight transferred to other features (e.g., backrest and armrest). The weight distributed at seat was 10–12% less at back inclines (p<0.01) as compared to upright unsupported sitting. With the backrest reclined beyond 95°, the weight at seat gradually decreased by 9% at 115° recline. The load distributed at feet varied narrowly; however, it was significantly greater (p<0.01) at upright supported back, compared to unsupported back. The height of the armrest was optimized at 68 cm, since the weight distribution at seat pan consistently reduced by 12% at that height, as compared to the absence of armrest (F_(4,524)=8.80, p<0.05). The suggested height of the armrest corresponded to 40% of the body stature of the selected volunteers. The load distributed at feet was 18% greater with the presence of armrest, indicating that a part of the weight of the upper leg fell on the seat pan, when the armrest was absent. The weight fell on the seat in slouch posture was 5% less than in upright sitting, while the weight at feet was marginally higher in slouch than in upright posture. The study maintained that the horizontal as well as 5° forward slope of the seat might be the preferred choice, since the load distributed at seat was highest at backward sloping seat for all conditions of supported and unsupported back. The study reaffirms that the backrest and armrest have conjoint influence in reducing the load distributed at seat, which in turn might help in mitigating stress on the spinal and other paraspinal structures.

Relevance to Industry

The human–seat interface analysis and understanding of body weight distribution to the components of seat may be beneficial for ergo-design application in optimizing parameters for chair configurations that provide comfort and safety to the user.     

The analysis of heart rate variability in unrestrained rats. Validation of method and results

An experimental setting and software were developed to evaluate cardiac autonomic function in unrestrained rats. Subcutaneously implanted ECG electrodes and an indwelling venous catheter were tunneled to a tail cuff in five rats. The ECG was A/D converted at 1000 Hz. After peak detection, a time series of RR intervals was obtained. Programs for the analysis of heart rate variability (HRV) were implemented in LabVIEW. Statistical properties were determined in the time domain. After cubic spline function curve fitting, resampling at 0.1 s and test for stationarity, power spectral analysis was performed on sampled records of 30 min duration after applying a sliding Hanning window (Welch method: 256 points (duration 25.6 s), 50% overlap and 0.039 Hz resolution). Algorithms were tested with simulated signals consisting of isolated frequency components, which were retrieved at their exact locations. Physiological validation of the system was performed by, β-adrenergic and cholinergic blockade and by forced breathing at a fixed rate. Measurements were performed on five unrestrained rats under basal conditions. Mean RR was 174.2±3.6 ms; S.D., 13.3±4.6 ms; rMSSD, 5.2±1.2 ms; pNN10, 3.5±1.9% and pNN5, 18.7±6.4%. Low (0.19–0.74 Hz) and high frequency (0.78–2.5 Hz) power were determined (and also percent of low to total and high to total): 18.42±10.74 ms² (22.9±6.5%) and 15.66±5.56 ms² (19.9±2.7%), and the ratio low/high: 1.16±0.39. In conclusion, HRV analysis programs were developed and thoroughly tested through simulations and in vivo, under basal conditions and after pharmacological blockades. Using this software, HRV data from unrestrained rats were obtained.     

基于背包激光雷达的单木材积估测方法研究

背包式激光雷达(Backpack Laser Scanning,BLS)在森林资源调查中具有很大的应用潜力,但在复杂地表情景下,单木材积和林分蓄积量提取精度存在较大不确定性。以广西高峰林场为研究区,利用随机森林方法,基于BLS点云数据对单木材积和样地蓄积量进行估测。首先,对BLS点云进行单木分割,提取单木胸径(DBH)、树高(Htree)、冠幅直径(CD)、冠幅面积(CA)、冠幅体积(CV)、郁闭度(CC)、间隙率(GF)和叶面积指数(LAI)共8个特征参数,并计算56个分层高度指标(高度百分比、累积高度百分比、变异系数、冠层起伏率等)。然后,通过随机森林算法构建单木材积估测模型,并对比各种参数组合的预测精度。得到结果：(1)仅用8个单木结构特征参数进行建模,估测精度为：R²=0.83、RMSE=0.097 m³;(2)加入分层高度指标的模型估测精度有所提升：R²=0.87、RMSE=0.087 m³;(3)通过Boruta算法进行变量筛选,输入参数从64个减少至52个,估测精度差异不大：R     

Titania NOx sensors for exhaust monitoring

Oxide semiconductors have been examined to develop NO_x sensors for exhaust monitoring. Titania doped with trivalent elements, such as Al³⁺, Sc³⁺, Ga³⁺ or In³⁺, has a good sensitivity and selectivity to NO between 450 and 550 °C, and shows rapid response. A sensor probe for monitoring exhaust NO_x has been fabricated. Many kinds of interference gases, such as C₃H₆, CO and SO₂, have been found to have only a slight influence on the sensor response to NO. The influence of O₂ and H₂O is also negligible, except for the cases of 0% H₂O and fuel-rich conditions. In accordance with these results, the sensor probe operates satisfactority in the exhaust gas of various combustion conditions without interference from the various kinds of gas species in the exhaust gases.     

One-handed dynamic pulling strength with special reference to speed, handle height and angles of pulling

A laboratory study was conducted to determine the effects of pulling speed, handle height and angle of pull from the horizontal plane on one-handed dynamic pulling strength. The dynamic strength of nineteen male subjects for a 1 m pull was measured at four different handle heights (40%, 50%, 60% and 70% of shoulder height), at three different angles above the horizontal plane (15°, 25° and 35°), and at three different speeds of pulling (mean speed = 0.7, 1 and 1.1 ms⁻¹). In addition, ratings of perceived exertion were recorded for elbow, shoulder and back. Also, the subjects were required to rate the overall comfort for the pull.

Pulling speed, handle height and angle all had a significant effect on both mean and peak dynamic pulling strengths (p 0.01). Among the three variables, pulling speed was found to be the most critical. The mean dynamic strength was 360, 250 and 180 N and the peak strength was 600, 425 and 320 N at 0.7, 1 and 1.1 ms⁻¹, respectively. The strengths decreased with an increase in handle height from 100% at 40% shoulder height to 83% at 70% of shoulder height and were the highest at an angle of 25° from the horizontal plane.

The ratings of perceived exertion for all three body parts decreased with an increase in speed of pulling (p 0.01). The high speed pulls were perceived as being more comfortable than low speed pulls (p 0.01). The handles at 50% and 60% of shoulder height and at an angle of 25° were perceived as being more comfortable than those at other heights and angles (p 0.01).

It is suggested that biomechanical stresses need to be considered along with physical strength and ratings of perceived exertion and comfort to determine optimum speed, height and angle of pulling for high speed pulling tasks.     

Pyroelectric and dielectric properties of sol–gel derived barium–strontium–titanate (Ba0.64Sr0.36TiO3) thin films

The barium–strontium–titanate (BST, Ba_0.64Sr_0.36TiO₃) thin films have been prepared by the sol–gel method on a platinum-coated silicon substrate. The resulting thin films show very good dielectric and pyroelectric properties. The dielectric constant and dissipation factor for Ba_0.64Sr_0.36TiO₃ thin film at a frequency of 200 Hz were 592 and 0.028, respectively. The dependence of the capacitance as a function of the voltage shows a strongly non-linear character, and two peaks characterizing spontaneous polarization switching can be clearly seen in this curve, indicating that the films have a ferroelectric nature. The capacitance changed from 495 to 1108 pF with the applied voltage in the −5 to +5 V range at a frequency of 100 kHz. The peak pyroelectric coefficient at 30 °C is 1080 μC/m² K. The pyroelectric coefficient at room temperature (25 °C) is 1860 μC/m² K, and the figure-of-merit of this film is 37.4 μC/m³ K. The high pyroelectric coefficients and the greater figures-of-merit of Ba_0.64Sr_0.36TiO₃ thin films make it possible to be used for thermal infrared detection and imaging.     

Evaluation of three gas collection devices

Traditionally, the mouthpiece, nose-clip, and headgear arrangement (MN) used in indirect calorimetry is uncomfortable for some subjects, interferes with communications, and often interrupts tests if the nose-clip is lost. Gas collection masks (MASK) offer the possibility of alleviating the problems of MN but leakage and increased air dead space have been problematic. The present study compares the use of MN with two MASK designs (with nose-dam which prevents nasal breathing (MASKnd), and without nose-dam (MASKwo), from light to peak work rates in 20 well-trained subjects (M=12, F=8). Ventilation rate (Ve), oxygen uptake (VO₂), respiratory exchange ratio (RER) and heart rate (HR) were measured and comfort was assessed with a questionnaire. At the highest work rate, subjects achieved higher (as determined by repeated measures ANOVA) Ve for MASKnd(114.0±27 L min⁻¹) and MASKwo=(115.0±29 L min⁻¹) than for MN (108±28 L min⁻¹). Likewise, VO₂ in both MASKnd (55.0±10 ml kg min⁻¹) and MASKwo (56.2±11 ml kg min⁻¹) were higher than in the MN (53.7±12 ml kg min⁻¹)(p<0.05). Both MASKnd and MASKwo MASKs resulted in greater subject comfort than that for MASKmn. These data suggest that true maximal VO₂ can be more often attained with a MASK than an MN, since Ve and VO₂ were higher in MASK compared to that in MN.

Relevance to industry

This study will provide an evaluation of gas masks as an alternative to the traditional but uncomfortable mouth-piece and nose-clip used in indirect calorimetry.