田间条件下土壤氮素运移的模拟模型Ⅱ田间检验与应用

本文通过冬小麦春季生长阶段的田间试验检验了土壤水、热和氮素联合模拟模型，结果表明土壤含水量、土壤温度以及土壤无机氮含量的模拟计算值与实测值吻合程度较好．应用经检验的模型和有关参数，模拟计算了不同灌水条件下土壤氮素动态，结果看出：在本试验条件下，在冬小麦返青到收获期间，各灌水处理１ｍ深处总体上不存在土壤无机氮淋洗渗漏，而是不同程度的上升补给．反硝化和氮挥发是氮素损失的主要途径．     

基于实验成绩评定分析的实验教学改革探讨

为了进一步提高学院实验教学质量,基于实验教学成绩评定标准,分析学院土力学实验课程教学现状和存在的问题,查找实验教学体系设计缺陷,在以往专业实验基础上增设专业基础实验,修订实验成绩评定方案,探讨实验教学改革及实验管理方式,优化实验教学成绩评定体系。结果表明,基于实验课成绩评定的实验教学改革能较好地改善实验教学效果,进一步完善实验教学方法,切实提高学生的创新和动手能力,培养其独立开展科学研究的能力和素养。     

开路缺陷的软故障关键面积研究

从软故障的产生机制出发,研究了软故障的作用模式.为了计算软     

An Efficient Algorithm to Solve the Problem of Dropped Call in CDMA Cellular Systems

1 Introduction For any multi-user communication system, it is a big problem that the call drops out to the user and service provider. The propagation conditions required for a satisfactory communication can not always be met owing to irregularities in cel…     

Mechanically Programmable Dip Molding of High Aspect Ratio Soft Actuator Arrays

This work presents multiple methods of creating high aspect ratio fluidic soft actuators that can be formed individually or in large arrays via dip coating. Within this methodology, four strategies are provided to mechanically program the motion of these actuators, including the use of fiber inclusions, gravity, surface tension, and electric fields. The modular nature of this dip coating fabrication technique is inexpensive, easy to modify, and scalable. These techniques are used to demonstrate the fabrication of soft actuators with aspect ratios up to 200:1 and integrated arrays of up to 256 actuators. Furthermore, these methods have the potential to achieve higher aspect ratios and larger array sizes. Operating pressure, curvature, and curling strength tests reveal the design space in which fabrication parameters can be selected to tune the input and output parameters of soft bending actuators. An individual bending actuator made with these methods weighs between 0.15 and 0.5 g, can hold up to 2 N, and can be designed to work in groups to increase curling strength with distributed contact forces. Arrays of these actuators may be useful in atypical grasping and manipulation tasks, fluid manipulation, and locomotion.     

High‐Tensile Strength,Composite Bijels through Microfluidic Twisting

Rope making is a millennia old technique to collectively assemble numerous weak filaments into flexible and high tensile strength bundles. However, delicate soft matter fibers lack the robustness to be twisted into bundles by means of mechanical rope making tools. Here, weak microfibers with tensile strengths of a few kilopascals are combined into ropes via microfluidic twisting. This is demonstrated for recently introduced fibers made of bicontinuous interfacially jammed emulsion gels (bijels). Bijels show promising applications in use as membranes, microreactors, energy and healthcare materials, but their low tensile strength make reinforcement strategies imperative. Hydrodynamic twisting allows to produce continuous bijel fiber bundles of controllable architecture. Modelling the fluid flow field reveals the bundle geometry dependence on a subtle force balance composed of rotational and translational shear stresses. Moreover, combining multiple bijel fibers of different compositions enables the introduction of polymeric support fibers to raise the tensile strength to tens of megapascals, while simultaneously preserving the liquid like properties of the bijel fibers for transport applications. Hydrodynamic twisting shows potentials to enable the combination of a wide range of materials resulting in composites with features greater than the sum of their parts.     

Integrated Optimal Cell Site Selection and Frequency Allocation for Cellular Radio Networks

Two major planning problems are encountered when designing a cellular radio network. The initial question is where to locate the base transmitter stations such that full coverage is achieved at low interference. This is relevant for frequency division (FDMA) as well as code division multiple access (CDMA) technology. If the locations of base stations are given, then for an FDMA-system frequencies have to be assigned such that there is a sufficient number of channels per cell available at a low total interference level. Since cell site selection and frequency allocation have mutual influences on each other, the ultimate goal is to deal with both problems in a single design step. The main intention of this paper is to model the above planning issues as linear integer programs, and to discuss solution methods for the corresponding NP-hard problems. According to their increasing complexity we proceed from channel allocation via cell site selection to an integrated single setup.     

Transparent Soft Robots for Effective Camouflage

Transparency is a surprisingly effective method to achieve camouflage and has been widely adapted by natural animals. However, it is challenging to replicate in synthetic systems. Herein, a transparent soft robot is developed, which can achieve effective camouflage. Specifically, this robot is driven by transparent dielectric elastomer actuators (DEAs). Transparent and stretchable conductive polymers, based on blends of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and water‐borne polyurethane (WPU), are employed as compliant solid‐state electrodes in the DEAs. The electrode exhibits large stretchability, low stiffness, excellent conductivity at large strain, and high transmittance. Consequently, the DEA can achieve a large voltage‐induced area strain of 200% and a high transmittance of 85.5%. Driven by these soft actuators, the robot can realize translations using its asymmetric vibration mode, which can be explained by dynamics analysis and is consistent with finite element modeling. This soft robot can achieve effective camouflage, due to its high transparency as well as thin structure. Furthermore, the robot can become completely flat for even better camouflage by converting its 3D structure to 2D. The transparent soft robot is potentially useful in many applications such as robots for battlefield, reconnaissance, and security surveillance, where effective camouflage is required in dynamic and/or unstructured environments.     

A new ZVT–ZCT quasi-resonant DC link for soft switching inverters

In this article, the new ZVT–ZCT Quasi-Resonant DC Link, which ensures zero crossings at any time required for soft switching (SS) and provides zero voltage transition (ZVT) turn-on and zero current transition (ZCT) turn-off together for the main switch of active snubber cell in pulse width modulated or space vector modulated operation of inverter is presented. The new circuit combines the most desirable features of the circuits presented previously and overcomes most drawbacks of these circuits by using only one auxiliary switch with fewer other components. Consequently, new ZVT–ZCT Quasi-Resonant DC Link, which is verified by a prototype of a 1.2 kW and 50 kHz circuit, is analysed in detail. All semiconductor devices operate under SS, the main switch is subjected to no additional voltage and current stresses, and the stress on the auxiliary switch is very low in the proposed new inverter.     

Fe73.5Cu1Nb3Si13.5B9纳米晶软磁粉体的制备工艺与微波电磁性能

研究热处理工艺、材料粒度对Fe73.5Cu1Nb3Si13.5B9材料微波电磁性能的影响,对该类材料的微波电磁性能和吸波性能进行测试。结果表明:热处理工艺对材料的微波电磁性能产生较大的影响,达到晶化条件的热处理工艺有利于提高材料的电磁性能;随着材料粒度的减小,微波电磁性能提高,电磁参数之间的匹配性提高;Ⅴ级粒度材料的最低反射率达到-12 dB,低于-5 dB的频宽达12.5 GHz。