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生物电阻抗法(BIA)是一种安全非侵入式的、结果可靠有效的人体组成成分(脂肪含量)测量方法。以此为原理,设计了一款便携式无线人体脂肪率测量仪。硬件上,系统以高集成化、低功耗的阻抗测量芯片AD5933为核心,通过蓝牙实现与上位机的无线通信,大大降低了设备的复杂度。软件部分提出一种单频点小阻抗范围的增益系数校准方式,计算量小且容易实现。将新测量仪和欧姆龙体脂仪HBF-358进行对比实验,并作Bland-Altman一致性分析。结果表明,二者的相关系数为0.997。此外,该测量仪还具有易操作、小型化的特点。 相似文献
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The propagation of hollow Gaussian beams in strongly nonlocal nonlinear media is studied in detail.Two analytical expressions are derived.For hollow Gaussian beams,the intensity distribution always evolves periodically.However the second-order moment beam width can keep invariant during propagation if the input power is equal to the critical power.The interaction of two hollow Gaussian beams and the vortical hollow Gaussian beams are also discussed.The vortical hollow Gaussian beams with an appropriate topological charge can keep their shapes invariant during propagation. 相似文献
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Characteristic improvements of thin film AlGaInP red light emitting diodes on a metallic substrate 下载免费PDF全文
We report a type of thin film Al Ga In P red light emitting diode(RLED) on a metallic substrate by electroplating copper(Cu) to eliminate the absorption of Ga As grown substrate.The fabrication of the thin film RLED is presented in detail.Almost no degradations of epilayers properties are observed after this substrate transferred process.Photoluminescence and electroluminescence are measured to investigate the luminous characteristics.The thin film RLED shows a significant enhancement of light output power(LOP) by improving the injection efficiency and light extraction efficiency compared with the reference RLED on the Ga As parent substrate.The LOPs are specifically enhanced by 73.5% and 142% at typical injections of 2 A/cm~2 and 35 A/cm~2 respectively from electroluminescence.Moreover,reduced forward voltages,stable peak wavelengths and full widths at half maximum are obtained with the injected current increasing.These characteristic improvements are due to the Cu substrate with great current spreading and the back reflection by bottom electrodes.The substrate transferred technology based on electroplating provides an optional way to prepare high-performance optoelectronic devices,especially for thin film types. 相似文献
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利用空问诱导色散补偿介质色散 总被引:2,自引:1,他引:1
研究了超短脉冲贝塞尔光束在色散介质中的传输特性,指出空间诱导色散效应可以用来补偿介质色散作用,从而可以在色散介质中实现无衍射无色散的类时空孤子波的传输。用理论推导和数值模拟的方法得到的具有反常色散性质的空间诱导色散可以有效地补偿介质色散。数值模拟的结果表明,由于超短脉冲贝塞尔光束的无衍射无色散传输距离受到高阶色散效应和贝塞尔光束空间受限两方面的限制,无衍射无色散传输只能在有限距离内近似实现。通过增加脉冲长度可以减小高阶色散效应的影响。在传输距离小于衍射距离时,空间诱导色散效应可以很好地描述脉冲演化和色散补偿过程。 相似文献
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研究了超短啁啾脉冲光束在真空中的传输行为以及在传输过程中时空奇异性的形成. 结果表 明,对于脉冲时间较长(相对于一个光学周期)的超短啁啾脉冲光束,啁啾导致的脉冲光谱 展宽仍然会导致脉冲光束空间奇异性的出现. 脉冲啁啾比脉冲长度对脉冲光束空间奇异性的 出现影响更大. 给出了超短啁啾高斯脉冲光束在不同参数下的数值模拟、空间奇异性出现的 条件等,并用复解析信号理论消除了空间奇异性的出现.
关键词:
单周期
缓变包络近似
奇异性
啁啾脉冲 相似文献
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本文报道了以1313nmNd:YLF激光脉冲泵浦掺饵(Er3+)单模GeO2/SiO2光纤而产生多波长可见光的实验,在该光纤中观察到(463~510)nm间的多波长放大自发辐射过程,此过程对应于Er3+离子的2G7/2等几个激发态到4I13/2亚稳态的跃迁.其激发过程是分步的四光子吸收过程,同时,掺饵光纤的红外发射峰1530nm(4I13/2-4I15/2)与1313nm泵浦光之间的三波混频过程也对这一区间的连续多峰的光谱结构有贡献.实验中还观察到540nm附近的绿光辐射. 相似文献
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