共查询到20条相似文献,搜索用时 51 毫秒
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基于迈克尔逊干涉原理设计了金属丝杨氏模量的测量装置。在金属丝上施加持续而又均匀增加的力,引起金属丝细微伸长,通过灵敏杠杆带动移动镜的移动,从而引起光屏上干涉圆环数目的变化;用一种光电传感器捕捉干涉圆环的光强信号,将光信号转换为电信号,再通过模数转换,精确算出干涉圆环的条数,就可以实现对金属丝微小伸长量的测量。采用Origin软件处理实验数据,避免了人为因素所造成的误差,智能化计算出金属丝的杨氏模量。 相似文献
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We investigate the Casimir effect at a finite temperature in the electromagnetic Rindler space, and we find that the Casimir energy is proportional to T(4)/d(2) in the high-temperature limit, where T ≈ 27 °C is the temperature and d ≈ 100 nm is a small cutoff. We propose to make metamaterials to mimic the Rindler space and measure the predicted Casimir effect. Because the parameters of metamaterials we proposed are quite simple, this experiment would be easily implemented in the laboratory. 相似文献
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In this paper we study the macroscopic behavior of nematic side-chain liquid single crystal elastomers exposed to an external electric or magnetic field. For this purpose we use the framework of a continuum model. The geometries investigated comprise the bend and the twist geometry known from the classical Frederiks transition in low molecular weight liquid crystals. For the bend geometry we find a laterally homogeneous and a two-dimensional undulatory instability, which may compete at onset. In the case of the twist geometry three instabilities can occur at onset, two of which are two dimensional and clearly show undulations. As a major result we propose how the values of the twist coefficient K(2) and the values of the material parameters D(1) and D(2) connected to relative rotations between the director field and the polymer network can be determined from experimental observations. In addition, we explain why a twist experiment is probably the most suitable set-up in order to measure the material parameter D(1). 相似文献
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The elastic energy density of Iiquid crystal under the action of external electric field E is given by F=F(ni,ni,j,Ei,Ei,j……)where n is the director and ni,j,,Ei,j the gradients. By a systematic expansion of F in polynomials and the use of material symmetries, we obtain macroscopically for nematics and cholesterics all the possible external field-effects. In addition to the well-known dielectric interaction (n · n)and the flexoelec-tric effects of Meyer,-e1(E · n)(∇ · n)-e3 E · (n ∇ ·)n,we find a new term e0n · (n · ∇)E which corresponds to the flexoelectric effect related to electric quadrupoles introduced microscopically by related to electric quadrupoles introduced microscopically by Prost and Marcerou, This new term is not equivalent to the previous two terms of Meyer. An experiment to measure this new flexoelectric constant eo is proposed. Previous experiments measuring fIexoelectric constants are compared and discussed in the light of our theory, which also applies to other cases of external vector fields. 相似文献
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Magnetic resonance imaging is very sensitive to magnetic field variations. This inherent sensitivity can be exploited to measure small electric currents flowing in the human body. This report describes an experiment in which the magnetic fields produced by small currents applied to the forearm of a living subject have been detected in the tissue. It shows how such measurements have been used to measure current density. The suggested technique is used to measure one component of a current density in a saline solution in vitro. 相似文献
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Kim EA 《Physical review letters》2006,97(21):216404
We compute the temperature, voltage, and magnetic field dependences of the conductance oscillations of a model interferometer designed to measure the fractional statistics of the quasiparticles in the fractional quantum Hall effect. The geometry is the same as that used in recent experiments. With appropriate assumptions concerning the relative areas of the inner and outer rings of the interferometer, we find the theoretical results, including the existence of super periodic Aharonov-Bohm oscillations, to be in remarkably good agreement with experiment. We then make additional experimental predictions with no adjustable parameters which, if verified, would confirm the proposed interpretation of the experiment as a measurement of fractional statistics. 相似文献
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利用正向交流(ac)小信号方法对GaN发光二极管的电容-电压特性进行测量,可以观察到GaN发光二极管中的负电容现象。正向偏压越大,测试频率越低,负电容现象越明显。测量到的负电容现象是表象,不存在负电容;提出GaN发光二极管p-n结的结电容在特定的正向电压范围内等效于可变电容。分析可变电容对正向交流小信号响应得到:特定参数的可变电容使结电容电流相位落后于交流小信号电压相位π/2,使得在测量中表现为负电容。发现表观电容-正向电压曲线的极值点与理论模型相吻合,证明了该理论模型的正确性。 相似文献
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直流稳压电源可以将交流电压变换为直流电压,并使之稳定,在我们现实生活中应用很广泛,在实验中我们利用的电学知识,设计制造了一种直流稳压电源。本文简要介绍了这种直流稳压电源波形演示器的设计目的和电路原理,重点阐述了它的制作流程、滤波和稳压原理以及性能测试输出波形。 相似文献
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在一种猝发高重频的X射线自由电子激光(XFEL)装置中,由于受到光阴极注入器内补偿螺线管与电子枪之间特殊结构的限制,阴极附近电场与磁场为叠加状态。实验中需要对阴极热发射度进行测量,而测量热发射度常用的螺线管扫描法基于几何发射度不变的前提,无法直接应用于电磁场叠加的结构。针对这一问题,考虑到归一化过程可以剔除电场对发射度的影响,基于此,研究归一化相空间中应用的螺线管扫描法,并通过仿真计算与分析,最终证明该方法适用于电磁叠加场中阴极热发射度的测量。 相似文献
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The use of atomic decay rates as a probe of sub-vacuum phenomena will be studied. Because electromagnetic vacuum fluctuations are essential for radiative decay of excited atomic states, decay rates can serve as a measure of the suppression of vacuum fluctuations in non-classical states, such as squeezed vacua. In such states, the renormalized expectation value of the square of the electric field or the energy density can be periodically negative, representing suppression of vacuum fluctuations. We explore the extent to which atomic decays can be used to measure the mean squared electric field or energy density. We consider a scheme in which atoms in an excited state transit a closed cavity whose lowest mode contains photons in a non-classical state. A crucial feature of our analysis is that we do not employ the rotating wave approximation. The change in the decay probability of the atom in the cavity due to the non-classical state can, under certain circumstances, serve as a measure of the mean squared electric field or energy density in the cavity. We make some estimates of the magnitude of this effect, which indicate that an experimental test might be possible, although very challenging. 相似文献
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Using high resolution excitation-emission spectroscopy we investigated the changes occurring in the optical transition of Er3? ions in LiNbO3 during inversion of the ferroelectric axis. In stoichiometric LiNbO3 we find that a drastic reconfiguration among the different defect sites takes places favoring those centers which have already been dominant in the as-grown sample. The reconfiguration is attributed to changes in the arrangement of the local charge compensators. Furthermore, we find a small shift of the emission transition energy, which is consistent with an increase of the intrinsic electric field. These findings make the Er3? ions very suitable probes for 3D imaging of domain structures and for in-situ studies of the dynamics of the domain inversion processes and the defect/domain wall interaction. 相似文献