共查询到20条相似文献，搜索用时 250 毫秒
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《发明与创新》2001,(5)
在国家“863”超导攻关项目——“高温超导输电电缆”研究过程中 ,西北有色金属研究院组织精干队伍在Bi系超导体的成像机理、加工技术及热处理技术等方面进行了扎实的基础性研究 ,通过改进关键工艺技术 ,首先在短样上取得突破 ,横截面为 4 .0 mm× 0 .2 6mm的 Bi系带材的临界电流 ( Ic)达到 81安培 ,工程临界电流密度达 780 0 A/cm2 ( 77K,自场 ) ,在此基础上 ,又研制出了多根 Ic大于 30安培、长度约为50米的带材 ,并成功用于 6m电缆制造。作为实用高温超导带材 ,2 0 0米的长带可满足在磁体、电缆、电机、变压器及故障电流限制器等电工、… 相似文献
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湖泊湿地利用与保护临界的经济学准则探讨 总被引：1，自引：1，他引：1
湖泊湿地资源开发利用与保护临界（简称“湿地临界”）的经济学准则是指湿地开发利用的边际净收益应不低于边际净损耗，也就是当生态损失发生特大变化，超出净收益，或者直接经济效益下降，小于净损耗时的湿地利用规模。其核心是生态服务功能之间的相容性分析及其效益的经济评估，即与开发利用功能相容的服务效益作为净收益的组成部分，与开发利用功能不相容或有条件相容的服务作为净损耗的组成部分。宝应湖围网养蟹的净收益包括围网养蟹、调节小气候和吸收二氧化碳的效益，净损耗包括供水、净化水质、调蓄洪水、生物多样性保育、科研教育、休闲娱乐的效益。经计算得到，宝应湖围网养殖的年净收益为37 304元/hm2，净损耗为16 222元/hm2，ΔE值为21 082元/hm2，因此认为，在目前的社会经济水平下，宝应湖围网养蟹的利用方式尚未超出湖泊湿地开发利用临界的经济学准则，仍具有一定的开发利用潜力。 相似文献
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利用高温超导材料制成的电力传输电缆,已可以在较经济运行的工作温区,在无阻损耗的情况下实现高电流密度传输。在直流输电系统中引入 高温超导技术,可以实现更高的电流传输密度,近乎为零的线路电阻损耗,大为降低的线路电压等级,并因而降低的所需绝缘材料和换流站的成本。因此可使 直流输电具有更普遍的实际应用意义。 相似文献
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《科技通报》2018,(12)
针对电路启动阶段的瞬态浪涌电流产生过冲的问题,提出基于能量再生的瞬态浪涌电流抑制方法。构建瞬态浪涌电流过冲产生与抑制交流的等效模型,利用电路理论对构建的等效模型进行分析,利用能量再生的电流抑制的方法,基于传输线的理论与反射的理论,在对变频器输出的脉冲在电流上传输与反射的过程进行分析的基础上,对电机端的瞬态浪涌电流产生的机理以及幅值进行分析计算。当与浪涌单元进行连接之后,对浪涌抑制单元工作的原理进行分析,得出各器件电流与电压的波形,完成对电路启动阶段的瞬态浪涌电流抑制方法的研究。实验的结果表明,本文提出的方法能有效抑制瞬态浪涌电流产生的过冲谐波,且适应性比较强。 相似文献
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通过对AC高通量筛选过程的分析，建立了AC技术筛选药物的定性及定量模型，为高通量药物筛选提供了必要的理论指导。 相似文献
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Dazhong Ma Qiuye Sun Xiangpeng Xie Xiaoyu Li 《Journal of The Franklin Institute》2019,356(3):1225-1246
The power sharing of AC/DC micro-grids is researched in this paper. The proposed strategy mainly include two parts: the primary power event triggering control with secondary control and an adaptive quasi sliding mode voltage control in inner-loop. Firstly, a event triggering power sharing control (ETPSC) based on droop curve is developed to regulate the voltage and frequency of AC and voltage of DC with the aim of the proportional power sharing between AC and DC micro-grids. The triggered threshold of ETPSC can be chosen to decide the transmitted power between AC and DC micro-grids. When the difference power between AC and DC micro-grids is less than the triggered threshold of power flow, there is no power sharing between AC and DC micro-grids, which can less the number of switching the power flow direction and the transmitted line power loss. The ETPSC has a great robust for the disturbances of load and improve the stability of the system. An adaptive quasi-sliding-mode control,which is implemented easily and flexibly with small computational burden and only based on input/output (I/O) measurement data but not the model any more, is used to control voltage in inner-loop. The effectiveness of the proposed control schemes is demonstrated by some numerical simulations and experimental results. 相似文献
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Chandrika D. Nayak Vaibhav Agarwal Dinesh M. Nayak 《Indian journal of clinical biochemistry : IJCB》2013,28(2):152-157
Objective: Fetus with intrauterine stress may exhibit programmed changes that can alter its metabolism and bear severe risk for diseases in adult life. The current study was designed to assess the correlation between cord blood lipid profile with the anthropometric data in neonates. Materials and methods: 146 newborn babies born at Dr. T M A Pai Hospital, Udupi were screened and their birth weight, length, head circumference and abdominal circumference were noted at birth. Umbilical cord blood samples were analyzed for total cholesterol, triglycerides (TG), high density lipoprotein (HDL) and low density lipoprotein (LDL). Infants were also grouped further based on gestational age (GA) and sex-adjusted birth weight percentiles into three groups i.e. Small for gestational age (SGA), Appropriate for gestational age (AGA) and Large for gestational age (LGA) for comparison of their lipid profiles. Inclusion criteria were normal fetal heart rate at birth and an APGAR score >7. Statistical significance of relation between lipid profile and anthropometry was done using ANOVA and Pearson correlation coefficient. Results: Triglycerides were significantly higher in babies with higher ponderal index (PI) than those with lower PI (P = 0.011). The TG level of SGA babies were significantly higher as compared to AGA group (P = 0.001). The LDL levels in neonates with higher abdominal circumference were significantly lower than those with lower AC (P = 0.019). Mean HDL levels were higher in neonates with larger AC, but not statistically significant. Maternal BMI had no influence on neonates’ lipid profile. Conclusion: Abnormal intrauterine milieu created by maternal changes during gestation may bear a profound impact on lipid metabolism in neonates, which may account for their differences in lipid profile and anthropometry at birth. 相似文献
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《Journal of The Franklin Institute》2022,359(17):9473-9491
A novel distributed secondary voltage and frequency control strategy is proposed with the Zeno-free event-triggered scheme for an island alternating current (AC) microgrid under Denial-of-Service (DoS) attacks. A DoS attack compensation mechanism and an event-triggered mechanism on the basis of the checking scheme are developed. Then, a secure event-checked based event-triggered secondary control method is explored to guarantee the tracking performance of the microgrid under DoS attacks. Further, some linear matrix inequalities (LMIs)-based sufficient conditions are derived to design the controller. What’s more, the proposed asynchronous periodic triggering method can efficiently save communication resources and further reduce the update number of the controller. Finally, the efficiency of this work is verified by an islanded AC microgrid with comparisons. 相似文献
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To analyze the jamming and unjamming transition of oil-in-water emulsions under continuous temperature change, we simulated an emulsion system whose critical volume fraction was 0.3, which was validated with experimental results under oscillatory shear stress. In addition, we calculated the elastic modulus using the phase lag between strain and stress. Through heating and cooling, the emulsion experienced unjamming and jamming. A phenomenon—which is when the elastic modulus does not reach the expected value at the isothermal system—occurred when the emulsion system was cooled. We determined that this phenomenon was caused by the frequency being faster than the relaxation of the deformed droplets. We justified the relation between the frequency and relaxation by simulating the frequency dependency of the difference between the elastic modulus when cooled and the expected value at the same temperature. 相似文献
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介绍了适用于环上椭圆曲线的加法公式,完善了局部环Z/pnZ上椭圆曲线密码学的基础理论,构造了环Z/pnZ上的基于角色的椭圆曲线密码系统.根据环Z/pnZ的结构特点,简化了其上椭圆曲线的加法完备系统,从而大大提高了环Z/pnZ上的椭圆曲线计算点加的效率;另外,给出了E(Z/pnZ)上密码群生成元的选取方法;证明Z/pnZ上的密码体系与有限域Fp的椭圆曲线密码体系有相同的安全程度;最后在环Z/pnZ上给出一个基于角色的椭圆曲线密码方案. 相似文献
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基于晶体塑性理论并利用有限元方法对镍基单晶含缺口平板的应力应变场进行了分析,研究了外载荷、厚度和缺口半径等对平板缺口部分的等效应力、最大分切应力和应变的影响。结果表明:外载荷的变化不会影响三变量的分布规律,各变量随载荷的增加都呈增大的趋势;厚度和缺口半径是影响缺口尖端应力应变状态的两个重要因素,厚度增大和缺口半径减小都会增加缺口尖端的应力应变集中程度,且应力最大值位置不随厚度发生变化,但随缺口半径的减少其位置也随之向远离缺口尖端方向移动。最后从理论上对缺口的应力应变进行了推导,其结论与有限元分析结果基本相符。 相似文献
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卫星自主导航中25～60公里星光大气折射模型研究 总被引：5，自引：0，他引：5
星光大气折射法是卫星自主导航技术发展起来的一种新的导航方法,直接影响其精度的主要因素是星光大气折射模型的不确定性。本文在研究卫星自主导航方法和大气折射原理及平流层大气的实际状态和基本变化规律的基础上,基于地球大气密度的实验数据,给出了平流层大气密度随高度变化的模型。采用球形大气分层的研究方法,根据光在湍流大气中的传播机理和卫星、地球、星光切线高度之间的几何关系以及光学定律推导出的折射角与大气密度的关系式,建立了星光大气折射模型．给出了影响导航精度的高度范围25～60公里的星光大气折射角随切线高度变化的经验公式。仿真结果表明,符合大气折射的变化规律,与现有的经验公式吻合较好,而且考虑了大气密度实际变化的影响．并有较大的实际应用价值。 相似文献