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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Microrheology ： ウィキペディア英語版 Microrheology Microrheology〔 〕 is a technique used to measure the rheological properties of a medium, such as microviscosity, via the measurement of the trajectory of a flow tracer (a micrometre-sized particle). It is a new way of doing rheology, traditionally done using a rheometer. There are two types of microrheology: ''passive microrheology'' and ''active microrheology''. Passive microrheology uses inherent thermal energy to move the tracers, whereas active microrheology uses externally applied forces, such as from a magnetic field or an optical tweezer, to do so. Microrheology can be further differentiated into 1- and 2-particle methods.〔 〕 〔 〕 == Passive microrheology== '' Passive microrheology '' uses the thermal energy (''kT'') to move the tracers, although recent evidence suggest that active random forces inside cells may instead move the tracers in a diffusive-like manner.〔 The trajectories of the tracers are measured optically either by microscopy or by diffusing-wave spectroscopy (DWS). From the mean squared displacement with respect to time (noted MSD or <Δ''r''2> ), one can calculate the visco-elastic moduli ''G''′(''ω'') and ''G''″(''ω'') using the generalized Stokes–Einstein relation (GSER). Here is a view of the trajectory of a particle of micrometer size. Image:Brownian_trajectory.png|Typical trajectory of a Brownian particle (simulation) Image:examples_MSD_pure_viscous_and_elastic.png|Two examples of MSD: one for a purely viscous fluid (free diffusion) and one for a viscolelastic fluid (trapped by elastic network) Image:Film particule ds polymere.gif|Animation of a particle in a polymer-like network Observing the MSD for a wide range of time scales gives information on the microstructure of the medium where are diffusing the tracers. If the tracers are having a free diffusion, one can deduce that the medium is purely viscous. If the tracers are having a sub-diffusive mean trajectory, it indicates that the medium presents some viscoelastic properties. For example, in a polymer network, the tracer may be trapped. The excursion ''δ'' of the tracer is related to the elastic modulus ''G''′ with the relation ''G''′ = ''k''B''T''/(6''πaδ''2).〔 〕 Microrheology is another way to do linear rheology. Since the force involved is very weak (order of 10−15 N), microrheology is guaranteed to be in the so-called linear region of the strain/stress relationship. It is also able to measure very small volumes (biological cell). Given the complex viscoelastic modulus $G(\backslash omega)=G\text{'}(\backslash omega)+i\; G\text{'}\text{'}(\backslash omega)\backslash ,$ with ''G''′(''ω'') the elastic (conservative) part and ''G''″(''ω'') the viscous (dissipative) part and ''ω''=2''πf'' the pulsation. The GSER is as follows: :$\backslash tilde(s)=\backslash frac(s)\backslash rangle\}$ with :$\backslash tilde(s)$: Laplace transform of ''G'' :''k''B: Boltzmann constant :''T'': temperature in kelvins :''s'': the Laplace frequency :''a'': the radius of the tracer :$\backslash langle\backslash Delta\; \backslash tilde^(s)\backslash rangle$: the Laplace transform of the mean squared displacement A related method of passive microrheology involves the tracking positions of a particle at a high frequency, often with a quadrant photodiode.〔 〕 From the position, $x(t)$, the power spectrum, can be found, and then related to the real and imaginary parts of the response function, $\backslash alpha(\backslash omega)$.〔 〕 The response function leads directly to a calculation of the complex shear modulus, $G(\backslash omega)$ via: :$G(\backslash omega)\; =\; \backslash frac$ 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Microrheology」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.