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1.
The article gives an overview of areas where computers and electronics have made a particular impact on the postharvest industry. These include environmental control and storage, quality monitoring, quality management, grading systems, inventory control, and management of product. Specific examples of the application of electronic systems have been given to illustrate the current state of postharvest technology, and some future predictions have been given. It is likely that consumer demand for improved quality, longer storage life, and guaranteed product safety will continue to grow. In a highly competitive market the industry will need to meet these demands, and electronic technology will play an increasingly important role. Improved sensors to assess quality are still needed, and handling and storage systems are likely to become increasingly sophisticated. In the latter half of the twentieth century technology has contributed much to improve the world's food supply, but it has also generated problems for the wider society, which will require attention in the next millennium. 相似文献
2.
In a time of growing need for catalysts, perovskites have been rediscovered as a family of catalysts of such great diversity that a broad spectrum of scientific disciplines have been brought to bear in their study and application. Because of the wide range of ions and valences which this simple structure can accommodate, the perovskites lend themselves to chemical tailoring. It is relatively simple to synthesize perovskites because of the flexibility of the structure to diverse chemistry. Many of the techniques of ceramic powder preparation are applicable to perovskite catalysts. In their own right, they are therefore of interest as a model system for the correlation of solid-state parameters and catalytic mechanisms. Such correlations [See figure in the PDF file] have recently been found between the rate and selectivity of oxidation-reduction reactions and the thermodynamic and electronic parameters of the solid. For commercial processes such as those mentioned in the introduction, perovskite catalysts have not yet proven to be practical. Much of the initial interest in these catalysts related to their use in automobile exhaust control. Current interest in this field centers on noble metalsubstituted perovskites resistant to S poisoning for single-bed, dual-bed, and three-way catalyst configurations. The formulations commercially tested to date have shown considerable promise, but long-term stability has not yet been achieved. A very large fraction of the elements that make up presently used commercial catalysts can be incorporated in the structure of perovskite oxides. Conversely, it is anticipated that perovskite oxides, appropriately formulated, will show catalytic activity for a large variety of chemical conversions. Even though this expectation is by no means a prediction of commercial success in the face of competition by existing catalyst systems, it makes these oxides attractive models in the study of catalytic chemical conversion. By appropriate formulation many desirable properties can be tailored, including the valence state of transition metal ions, the binding energy and diffusion of O in the lattice, the distance between active sites, and the magnetic and conductive properties of the solid. Only a very small fraction of possible perovskite formulations have been explored as catalysts. It is expected that further investigation will greatly expand the scope of perovskite catalysis, extend the understanding of solid-state parameters in catalysis, and contribute to the development of practical catalytic processes. 相似文献
3.
针对电子节气门系统的非线性环节和外部干扰复杂多变的问题,结合电子节气门的结构特点,建立了电子节气门数学模型,提出了一种基于指数趋近律的非线性鲁棒滑模控制,并对其进行了控制仿真.实验结果表明,基于指数趋近律的滑模鲁棒控制不仅能满足快速到达期望节气门开度,实现高精度控制等要求,而且可以增强电子节气门系统对外界干扰的鲁棒性. 相似文献
4.
Goddard WA 《Science (New York, N.Y.)》1985,227(4689):917-923
During the last decade, advances in computational techniques and in the extraction of chemically useful concepts from electronic wave functions have put theorists into the mainstream of chemistry. Some recent examples of the prediction of spectroscopic quantities and the elucidation of catalytic processes for homogeneous and heterogeneous reactions from theoretical calculations are used to illustrate how theory and experiment are now full partners in chemical research. It is expected that during the next decade the thrust of theoretical chemistry will be to combine the knowledge of fundamental chemical steps and fundamental interactions with advances in chemical dynamics and irreversible statistical mechanics and in computer technology to produce simulations of chemical systems with competing reactions taking place simultaneously at various reaction sites. The promise of such simulation is illustrated by a study of the enzyme thermolysin. 相似文献
5.
汽车起重机全力矩限制器的研制 总被引：1，自引：0，他引：1
利用Intel16位单片机 80C196KC技术 ,研制了汽车起重机全力矩限制器。该全力矩限制器能够实时监测汽车起重机的工作参数 ,并将数据显示在液晶模块上 ;当实测起重力矩达到相应工况下的额定值时 ,全力矩限制器报警并强制停机 ,同时 ,自动将此状态下的工作参数以及相对应的时间记录在时钟芯片的RAM内 ;断电后 ,限制器仍能保护数据的安全。该全力矩限制器符合我国有关技术标准 ,通过改变软件参数和传感器的测量范围 ,可运用于不同型号的汽车起重机。 相似文献
6.
利用脉冲镇定理论，研究了某类汽车系统在协同制动控制并不能达到系统稳定的情况下，加入脉冲干扰使系统达到预期稳定效果.运用Lyapunov方法和常数变易法公式，得到车辆系统在脉冲作用下的稳定性条件为A(t)在［t0,+∞)上连续，∫∞t0|~C(t)|2dt<+∞. 相似文献
7.
当电控门锁意外锁住,车钥匙丢失或锁在车内等意外时,利用汽车诊断仪,进入车身控制系统,或启动安全气囊的运行功能,在不损坏汽车的情况下,能够顺利打开电控门锁. 相似文献
8.
In countries, like the former German Democratic Republic (GDR), where ‘industrialized’ milk production in large herds was the goal to be reached, research on automation of machine milking was started more than 30 years ago. Initially, the main goal was to mechanize operations at the end of the milking process. This work finally resulted in milking devices that do not apply uniform parameters to all cows, but operate according to the milk flow obtained from the cow actually to be milked. This evolution towards ‘controlled milking’ would not have been possible without application of electricity and electronic components for sensors and control units. Also depending on the technical evolution of electronic control systems are devices for recording milk yield and for taking samples for milk analysis, which were available around the year 1980. At that time initial projects for automatic milk recording were evaluated, which had an obvious influence on further development of milk meters. The most demanding step of application of electronic control systems up to now was the introduction of automatic milking systems. Here not only application of teat cups has to be executed, it also is necessary to enable automatic checks of udder condition, milk quality and other operations which may be challenging even for trained human operators. Further evolution of electronic measurement procedures may be important for the milk-producing farmer too, especially when on-line milk analysis is to be introduced within the near future. 相似文献
9.
便携式遥控自动立木整枝机控制系统电源的使用效率是整个系统的一个重要指标及可靠工作的前提.该文在分析控制逻辑的基础上,从节能的观点出发,合理地研制了自动立木整枝机发射与接收系统电源控制电路.电源供电能力测试的结果证明:该电源控制电路可以有效地提高整个系统电源的效率,能够很好地满足自动立木整枝机的工作需要. 相似文献
10.
汽车真空助力器性能测试装置的研制 总被引：2，自引：0，他引：2
朱晨 《内蒙古农业大学学报(自然科学版)》2008,29(2)
本文从汽车真空助力器的工作原理出发,利用80C51单片机完成了汽车真空助力器性能测试装置的数据采集、数据处理、测试结果显示和控制系统的软硬件设计.根据汽车真空助力器在各种工作条件下控制驱动装置的动作.完成了汽车真空助力器密封性、输入-输出特性、空行程等主要性能指标的测试. 相似文献
11.
划分了中国汽车排放标准化发展阶段，对每一阶段汽车排放标准的控制特点进行了分析。研究了随着中国汽车排放标准化进程的发展，中国汽车排放标准逐步严格、不断完善、与国际接轨的控制历程。 相似文献
12.
Coral reefs under rapid climate change and ocean acidification 总被引：13，自引：0，他引：13
Hoegh-Guldberg O Mumby PJ Hooten AJ Steneck RS Greenfield P Gomez E Harvell CD Sale PF Edwards AJ Caldeira K Knowlton N Eakin CM Iglesias-Prieto R Muthiga N Bradbury RH Dubi A Hatziolos ME 《Science (New York, N.Y.)》2007,318(5857):1737-1742
Atmospheric carbon dioxide concentration is expected to exceed 500 parts per million and global temperatures to rise by at least 2 degrees C by 2050 to 2100, values that significantly exceed those of at least the past 420,000 years during which most extant marine organisms evolved. Under conditions expected in the 21st century, global warming and ocean acidification will compromise carbonate accretion, with corals becoming increasingly rare on reef systems. The result will be less diverse reef communities and carbonate reef structures that fail to be maintained. Climate change also exacerbates local stresses from declining water quality and overexploitation of key species, driving reefs increasingly toward the tipping point for functional collapse. This review presents future scenarios for coral reefs that predict increasingly serious consequences for reef-associated fisheries, tourism, coastal protection, and people. As the International Year of the Reef 2008 begins, scaled-up management intervention and decisive action on global emissions are required if the loss of coral-dominated ecosystems is to be avoided. 相似文献
13.
Future surveys for transiting extrasolar planets are expected to detect hundreds of jovian-mass planets and tens of terrestrial-mass planets. For many of these newly discovered planets, the intervals between successive transits will be measured with an accuracy of 0.1 to 100 minutes. We show that these timing measurements will allow for the detection of additional planets in the system (not necessarily transiting) by their gravitational interaction with the transiting planet. The transit-time variations depend on the mass of the additional planet, and in some cases terrestrial-mass planets will produce a measurable effect. In systems where two planets are seen to transit, the density of both planets can be determined without radial-velocity observations. 相似文献
14.
为寻求根据汽车尾气参数来诊断汽车故障的方法，利用径向基函数（RBF）神经网络，对丰田雷克萨斯（LEXUS）400电控发动机进行故障诊断研究。研究结果表明，径向基函数神经网络对发动机故障的诊断是迅速、准确的。 相似文献
15.
Branscomb LM 《Science (New York, N.Y.)》1979,203(4376):143-147
Although long-term forecasting is best left to science fiction writers, scientists can illumine basic technological trends, as in the 100-year scenario presented here. Computers will continue the "small is beautiful" trend, but they are not likely to follow the semilog trail because extrapolation from the current base would lead to absurdities such as a computer cost of 3/100 of a cent. To achieve inexpensive high speed and Lilliputian size, new techniques are likely to replace silicon technology. The ultimate computer might be biological and patterned on DNA. Future computers will reacquire information when needed rather than store it, and we will see personalized products at mass production prices. Light wave communication will broaden communications exchange, but software that is more friendly to human users will be needed. By taking over knowledge distribution, electronic information systems will let universities concentrate on new knowledge. More importantly, they will expand everyone's right to information and free expression through the existing media system and to protection from misuse of information by others. 相似文献
16.
针对永磁同步电机及电动汽车电子差速控制系统存在的问题,以前轮独立驱动电动汽车为研究对象,建立了一种基于离散小波变换的驱动轮等功率分配电子差速控制策略.基于永磁同步电机数学模型,设计了基于离散小波变换的电流控制器,并建立了驱动轮等功率分配电子差速控制策略,为了验证所提出控制策略的有效性,基于Matlab/Simulink和Carsim联合仿真平台,建立了基于离散小波变换的等功率分配电子差速控制策略模型,并与传统PID电流控制器及驱动轮等转矩分配策略进行对比,仿真结果表明,相比于PID电流控制器,基于离散小波变换的电流控制器具有更快的响应速度和较好的鲁棒性,与驱动轮等转矩分配策略相比,基于等功率分配的电子差速控制策略能够实现转矩间的不等分配,降低驱动轮滑转率,有效提高了车辆行驶稳定性与安全性. 相似文献
17.
CaIrO3-type MgSiO3 is the planet-forming silicate stable at pressures and temperatures beyond those of Earth's core-mantle boundary. First-principles quasiharmonic free-energy computations show that this mineral should dissociate into CsCl-type MgO cotunnite-type SiO2 at pressures and temperatures expected to occur in the cores of the gas giants + and in terrestrial exoplanets. At approximately 10 megabars and approximately 10,000 kelvin, cotunnite-type SiO2 should have thermally activated electron carriers and thus electrical conductivity close to metallic values. Electrons will give a large contribution to thermal conductivity, and electronic damping will suppress radiative heat transport. 相似文献
18.
Agricultural Automation in the new Millennium 总被引：1，自引：0，他引：1
Agricultural automation is expected to continue in the new millennium. Reasons are given why a number of prototype automation systems developed in the 20th century have not yet proceeded to commercialisation. Some barriers that have deterred this are identified, and it is suggested that research to overcome these barriers will be a focus of future activity. 相似文献
19.
王丽波 《西北农林科技大学学报(自然科学版)》1993,21(2):25-32
渠系非恒定流的数学处理目前尚无精确的解法。本文用数值方法对灌区渠系的水流运动要素进行了计算并与实测资料进行对比,认为直接差分方法和特征线方法可供渠系优化调控时使用。 相似文献
20.
浅谈燃油组分对汽车尾气排放的影响 总被引：1，自引：0，他引：1
在汽车新技术不断发展,排放法规日趋严格的情况下,燃油质量正成为制约汽车新技术、排放控制技术应用的重要因素。对不同燃油及其组分对汽车尾气排放的影响进行了分析,指出了各种燃油的未来发展方向,为燃油组分的优化提供一定的参考依据。 相似文献