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[0] BASMAJIAN JV, Control and training of individual motor units.Science 141no Issue 440-1 (1963 Aug 2)

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ref: -0 tags: Na Ji 2p two photon fluorescent imaging pulse splitting damage bleaching date: 05-31-2019 19:55 gmt revision:5 [4] [3] [2] [1] [0] [head]

PMID-18204458 High-speed, low-photodamage nonlinear imaging using passive pulse splitters

  • Core idea: take a single pulse and spread it out to N=2 kN= 2^k pulses using reflections and delay lines.
  • Assume two optical processes, signal SI αS \propto I^{\alpha} and photobleaching/damage DI βD \propto I^{\beta} , β>α>1\beta \gt \alpha \gt 1
  • Then an NN pulse splitter requires N 11/αN^{1-1/\alpha} greater average power but reduces the damage by N 1β/α.N^{1-\beta/\alpha}.
  • At constant signal, the same NN pulse splitter requires N\sqrt{N} more power, consistent with two photon excitation (proportional to the square of the intensity: N pulses of N/N\sqrt{N}/N intensity, 1/N per pulse fluorescence, Σ1\Sigma \rightarrow 1 overall fluorescence.)
  • This allows for shorter dwell times, higher power at the sample, lower damage, slower photobleaching, and better SNR for fluorescently labeled slices.
  • Examine the list of references too, e.g. "Multiphoton multifocal microscopy exploiting a diffractive optical element" (2003)

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ref: -0 tags: asynchronous design Rajit Manohar Octasic date: 06-12-2013 00:19 gmt revision:5 [4] [3] [2] [1] [0] [head]

At Cornell I took a VLSI design class taught by Rajit Manohar (*), and even then - 2002/2003 - he was very excited about asynchronous circuit design. I was uncertain about the technology at the time, but generally I trusted his instinct. Seems that there is certainly some oil in those hills - Octasic has just released a new basestation IC based on asynchronous processor cores: http://www.octasic.com/en/products/oct2200/oct2224w.php

The associated product-brief/technology whitepaper gives some good motivations for why asynchronous design is superior to classical synchronous design: (I'll quote, since I find this fascinating, hope they don't mind!)

  • Elimination of clock trees - Synchronous high-speed processors require large clock trees to keep sequential blocks synchronized. These clock trees require high-power buffers to drive complex high-capacitance networks that cover most of the chip. Clocks change state twice per cycle, consuming power on both positive and negative edges. These clock trees do not perform any information processing, thus provide no useful computing work, yet they consume a significant portion of the total power. Eliminating the clock trees alone can reduce power consumption by as much as 40% in a high-performance processor.
  • Elimination of pipeline state elements - Modern synchronous high-performance processors rely heavily on pipeline design techniques. Those pipelines require the use of a very large number of inter-stage flip-flops and state elements to support a high clock frequency operation. However, these inter-stage flip-flops and state elements also dont contribute to the actual data processing and computing tasks performed by the processor. In an asynchronous design these storage elements are discarded, saving the silicon space they occupy and the large amount of power they consume.
  • Elimination of lost margin timing - These inter-stage flip-flops require set-up and hold times which force a significant portion of the time between clock edges to be unusable for computation in high-frequency synchronous designs. Moreover given that each sub-micron technology shrink tends to increase path timing uncertainty, this further shortens the active period that can be used to achieve useful work between clock edges. This also means that in a synchronous design, the inter-stage circuit logic needs to be designed to operate increasingly faster than a single clock period to perform the same work. This requires the increased use of larger, higher power buffers in the datapath. In an asynchronous processor design, the logic does not have to deal with such small time steps. They can be built using slower, smaller and lower power circuits, while still delivering the same level of overall performance. Because the gates can be slower, it allows more use of low-leakage high-threshold voltage (HVT) gates, which drastically reduces leakage and further reduces power consumption and die area.
  • Reducing wire interconnect length -The silicon area savings discussed above translate into even more power savings, because wires connecting two elements get shorter as the circuits between these elements shrink. Shorter wires have less capacitance, thus switching them requires less power by using smaller buffers

Cool! I expect to see these techniques in many processors in the future - from embedded, very power sensitive MCUs to GPUs!

(*) Rajit was a cool guy. Not only did he give us a good grade, but he even drove us 'downtown' (in the sense of down the hill, Ithaca doesn't really have a downtown) at one point to pick up some resistors and other electronic parts so we could test out MOSIS-fabricated ASIC.

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ref: BASMAJIAN-1963.08 tags: original BMI M1 human EMG tuning operant control Basmajian date: 01-05-2012 00:49 gmt revision:6 [5] [4] [3] [2] [1] [0] [head]

PMID-13969854[0] Control and Training of Individual Motor Units

  • humans have the ability to control the firing rate of peripheral motor units with a high resolution.
  • "The quality of control over anterior horn cells may determine the rates of learning" yup!
  • "Some learn such esquisite control that they soon can produce rhythms of contraction in one unit, imitating drum rolls etc"
  • the youngest persons were among both the best and worst learners.
  • after about 30 minutes the subject was required to learn how to repress the first unit and to recruit another one.
    • motor unit = anterior horn cell, its axon, and all the muscle fibers on which the terminal branches of the axon end. max rate ~= 50hz.
    • motor units can be discriminated, much like cortical neurons, by their shape.
    • some patients could recruit 3-5 units altogether - from one bipolar electrode!
      • in playback mode (task: trigger the queried unit), several subjects had particular difficulty in recruiting the asked-for units. "They groped around in their conscious efforts to find them sometimes, it seemed, only succeded by accident"
    • some patients could recruit motor units in the absence of feedback, but they were unable to explain how they do it.
  • 0.025 (25um) nylon-insulated Karma alloy EMG recording wire.
  • feedback: auditory & visual (oscilloscope).
  • motor units have a maximum rate, above which overflow takes place and other units are recruited (in accord with the size principle).
  • "The controls (are) learned so quickly, are so esquisite, are so well retained after the feedbacks are eliminated that one must not dismiss them as tricks"