6715_Lecture5 - V-1 Lecture V 1. 2. 3. 4. 5. Cell -...

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1 PHYS 6715 - Lecture V 1 Lecture V Cell - Response 1. Introduction 2. Response to Electric Excitation 3. Response to Optical Excitation 4. Modeling of Light Scattering 5. Applications of Light Scattering PHYS 6715 - Lecture V 2 V-1 Introduction Excitation source – EM fields • High frequency EM fields: plane waves with phase vary rapidly in space Æ E ( r ,t) =Re{ E 0 exp[i( k r - ω t)]} with λ < 1m or f > 1GHz • DC or low frequency EM fields: quasi-static fields with constant or slow- varying phase in space Æ E ( r ,t) = Re{ E 0 ( r ) const exp(-i ω t)} λ > 1m or f < 1GHz PHYS 6715 - Lecture V 3 V-1 Introduction Excitation source – EM fields • Electric response = cellular response to DC/low frequency EM fields Æ electric potential V is defined as E =- V and often used in place of field because x E 0. • Optical response = cellular response to high frequency EM fields Æ V is no longer useful, ( E,B ) are needed. PHYS 6715 - Lecture V 4 V-1 Introduction Excitation source – acoustic fields Æ The linear acoustic wave equation in 3D space is given by where p and u is the pressure and displacement vector fields, respectively, and v is the speed of sound wave. Æ In 1D space, the plane-wave solution of the wave equation can be found as 2 2 1 0 v ⎛⎞ −≅ ⎜⎟ ⎝⎠ pp uu 0 (,) s i n (2 2 ) xt uxt A T π ϕ λ =− + PHYS 6715 - Lecture V 5 V-1 Introduction The parameters of an acoustic wave u = displacement at the equilibrium location x and time t λ = propagation wavelength T = oscillation period φ 0 = initial phase f = 1/T = frequency k= 1/ λ = wave number 0 s i n 2 ) A T + Excitation source – acoustic fields PHYS 6715 - Lecture V 6 V-1 Introduction The important relations (i) Dispersion relation: v = λ /T = f λ = f/k (ii) Medium characterization: v = Wave energy: average energy density carried by an acoustic wave E=A 2 (2 π f) 2 ρ /2 (iii) Wave intensity: incident power per unit of area I = E.v = A 2 (2 π 2 ρ v/2 p 2 K ρ Adiabatic bulk elastic modulus Mass density Excitation source – acoustic fields
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2 PHYS 6715 - Lecture V 7 V-1 Introduction The ranges of parameters Æ Frequency f: 20 Hz f 20kHz: sound audible to human ear f > 20kHz: ultrasound f ~ 1 to 10 MHz medical ultrasound Æ Velocity (m/s): depends on material properties air Water fat Soft tissues Bone Al 331.5 1482 ~1450 ~1540 ~4100 3000 to 6000 Excitation source – acoustic fields PHYS 6715 - Lecture V 8 V-2 Response to electric excitation Historical development Quantitative study of EM fields can be thought literarily to start from the investigations of electric current in frog’s muscle by a physician Luigi Galvani and the debate over “animal electricity” by physicist Alessandro Volta in Italy in 1780s and 1890s. Santiago Ramón y Cajal studied histological slides of brain and nervous tissues and developed the doctrine that human’s nerve system is made of network of cells with long fine branches in late 1880s, which was later coined with the name “neurons” by Waldeyer in 1891. Cajal received the 1906 Nobel prize for this work which laid the foundation for the electric modeling of the nerve signal transmission.
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This note was uploaded on 01/21/2012 for the course PHYS 6720 taught by Professor Hu during the Spring '10 term at East Carolina University .

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6715_Lecture5 - V-1 Lecture V 1. 2. 3. 4. 5. Cell -...

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