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ECEN 5341/4341 Lecture 13 Feb 14, 2014

. ECEN 5341/4341 Lecture 13 Feb 14, 2014. 1 Nonlinear Effects A. Rectification and Second Harmonic s B. Mode Locking C. Coherence D. Minimum Detectable Fields E. Neural Networks 2. Thermal Effects. Nonlinear Characteristics . Currents through a membrane . .

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ECEN 5341/4341 Lecture 13 Feb 14, 2014

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  1. . ECEN 5341/4341Lecture 13 Feb 14, 2014 1 Nonlinear Effects A. Rectification and Second Harmonic s B. Mode Locking C. Coherence D. Minimum Detectable Fields E. Neural Networks 2. Thermal Effects

  2. Nonlinear Characteristics Currents through a membrane. Note the membrane is a poor rectifier at frequencies Below approximately 1to 10MHz At high frequency have not detected nonlinear characteristics at low Power levels with very sensitive receivers.

  3. Injection of 0.6nA into a Pacemaker Cellas a Function of Frequency

  4. Phase Locking for Injected Current in a Pacemaker Cell • 1 • Another expression for phase lock conditions

  5. Phase locking at Harmonics and Sub harmonics.

  6. Coherence. • 1 Litovtiz showed that 10µT at 55 or 65 Hz for 10sec or longer over a 4hr period doubled the specific activity of ornithine decarboxylase cells. • This effect decreases with increasing signal to noise ratios. Over all he shows a need for both space and time coherence.

  7. Increase ODC with Coherence Time. Also shows abnormalities in Chick Embryos for 1µT pulses. Add noise and it goes away.

  8. Mechanism for Bio Effects of Magnetic Fields • 1. Induced Electric Fields ( Ion currents, Molecular Orientation and Configuration • 2. Direct Effects (Free radical Lifetimes and Concentrations.) • 3. Coherence for Good Signal to Noise • 4. Thermal Effects • 5. Amplification • 6.Measured Effects at E = 0.1 V/m and B= 1µT

  9. Frequency Effects • Maximum sensitivity of 5mA/m2 at 10Hz and E= 4mV/m for reduction in growth of neonatal fiber blast cells. Asymmetry with cell length and width.

  10. Time Delay Between Voltage and Current

  11. Variations in Capacity and Conductance With Frequency

  12. Neural Network

  13. Number of Training Runs for 97% Accuracy for Detecting 60Hz vs S/N

  14. Conductance Variations with Frequency • 1

  15. Some Sources of Nonlinearities 1. The Nernst Equation for membrane currents • 2 Changes in Synaptic Junction Thresholds by neural transmitters.( Reduction with repetitive firing) • 3. Changes in gap junction resistances. (Reduction with repetitive firing) • 4. Nonlinear conductance and dielectric constants. • 5. Saturation of chemical reactions • 6. Time delays and changes in initial conditions resulting form feedback and feed forward signals.

  16. Thermal Effects • 1. Power P= R I2 or P = σ J2 • 2. For short pulses where blood cooling is not significant • 3. For a sphere of water in water

  17. Thermal Coefficients • 1. The thermal diffusivity Where K’ is the thermal conductivity, ρ’ is the density, and Cpis the thermal capacity. • 2. For short pulses compared to τcΔtmax • Where H is the total Energy

  18. Changes in Conductivity for Saline

  19. Changes in Heat Capacity of Erythrocyte Membranes

  20. Changes in Chemical Reactions • 1 ΔH’ is the Free Energy and ΔS is the change in entropy. R’ is the gas constant. S = Soe-K’t So we have and exponential of an exponential

  21. Significant Temperatures • 1. More than 2o C for hours • 2. More than 5o C for seconds • 3. More than 10o C for 10-6 sec.

  22. Rate of Temperature Rise • Change in K+ current with change in temperature rate of rise. Changes seen with as little as 0.1 o C at rates of 1o C/sec • Slow changes lead to increases in firing rate fast changes shut down the pacemaker cells.

  23. Fast Temperature Changes • 1. Thermal expansion and acoustic waves. • 2. Microwave hearing

  24. . ECEN 5341/4341Lecture 14Feb 14,2014 1 Noise Sources 2. Minimal levels of signal detection. 3. Some characteristic of Neurons. 4. Logic with Neural Networks that have some of the properties of neurons. An Important Reference “Controlling Cell Behavior Electrically Current views and Future Potential” C. McCaig , A Rajnicek , B Song, M.Zhao Physiol Rev. 85 943-978 (2005)

  25. Signal to Noise and Signal Detection • 1. Some sources of noise. • A. Thermal Noise Pn = kTB • B. Negative Temperatures and Population inversion • E2 N2 • E1 N1

  26. Sources of Noise • 3. Shot Noise • 4. 1/f Noise is seen in Membranes etc.

  27. Noise at the Node of Ranvier in a Frog as a Function of Voltage

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