Threshold devices

Now, to be sure, McCulloch-Pitts neurons are unrealistically rendered versions of the real thing. For example, the assumption that neuronal firing occurs synchronously throughout the net at well defined discrete points in time is simply wrong. The tacit assumption that the structure of a neural net (i.e. its connectivity, as defined by the set of synaptic weights) remains constant over time is known be false as well. Moreover, while the input-output relationship for real neurons is nonlinear, real neurons are not the simple threshold devices the McCulloch-Pitts model assumes them to be. In fact, the output of a real neuron depends on its weighted input in a nonlinear but continuous manner. Despite their conceptual drawbacks, however, McCulloch-Pitts neurons are nontrivial devices. McCulloch-Pitts were able to show that for a suitably chosen set of synaptic weights wij, a synchronous net of their model neurons is capable of universal computation. This means that, in principle, McCulloch-Pitts nets possess the same raw computational power as a conventional computer (see section 6.4). 

Direct conversion systems are threshold devices, that is, there is a minimum photon energy which can initiate the photochemical reaction. This is called the band-gap ei rgy Eg with a corresponding band-gap wavelength Xg. Eg usually corresponds to the 0-0 transition to the lowest excited singlet state of the absorber (see Fig. 1). Hence, it is important to know what fraction of the incident solar power is available at the band-gap energy. 

The device diameter defined by the radius of the active region is also a very important parameter for low threshold devices. We have to decrease the diameter to realise a low threshold VCSEL. In... 

When we wish to verify the lasing operation of a new and/or ultra-low threshold device, the non-linear relation in the injection current versus light output characteristics is an easy method of testing the threshold criterion. However, sometimes this is observed even on non-lasing samples owing to the filtering effect and electron-hole plasma emission. Methods used to definitively confirm laser operation for vertical cavity devices are as follows [37] ... 

Fig. S. Matrix-addressed liquid crystal display using an FET as an extrinsic threshold device. The capacitor (dashed) is optional.

For the c-Si MISS p+-n i threshold device the values of threshold voltage are predicted (Simmons and El-Badry, 1978) to depend on (d — W)2, where d is the thickness of the n layer and W is the width of the depletion region, and for low donor concentrations this dependence is supported experimentally. In contrast, the results in Fig. 6 show that in the a-Si devices the forming voltage varies linearly with d . It is difficult to decide at present... 

More than fast threshold devices Na channels can function... 

The current-versus-voltage dependence for a single-threshold device is written as... 

The ISOMNOSFET has two features which are not in the conventional MNOSFET. It has a stepped oxide in the channel region, and an ion implanted region adjacent to the channel. By using a stepped oxide with two oxide thicknesses in the channel, two constant threshold thick-oxide FETs in series with the thin oxide variable threshold device ensures that the composite device maintains operation in the enhancement mode in both the high and low threshold states. 

Plaisance, R, Lurie, K.G., Vicaut, E., Martin, D., Gueugniaud, P.Y., Petit, J.L., and Payen, D. Evaluation of an impedance threshold device in patients receiving active compression ecompression cardiopulmonary resuscitation for out of hospital cardiac arrest. Resuscitation, 61,265 271,2004. 

Pitts [1943] proposed neuron models in the form of binary threshold devices and stochastic algorithms involving sudden 0-1 and 1-0 changes of states in neurons as the bases for modeling neural system. Subsequent work by Hebb [1949] was based on mathematical models that attempted to capture the concept of learning by reinforcement or association. 

The spectral response of most NE A emitters with thresholds above 1 pm are shaped similarly to one another regardless of the bandgap of the material. A typical curve is that for (cooled) NEA InGaAsP in Fig. 5.18, where a sharp threshold is followed by a flat quantum efficiency plateau. For longer wavelength threshold devices and in particular for InGaAs, the response curves show inflection points which do vary with bandgap (see Fig. 5.16). At present... 

The functions AND and OR are trivially realized by algebraic addition, in the presence of a threshold. Now any flip-flop is a threshold device. Hence any pair of convergent reactions (leading to the same product) realizes these functions in a straightforward manner. If both influxes are required for the setting (or resetting, respectively) of the flip-flop, AND is realized, and if either is sufficient, OR. 

Liquid-crystal displays have also been constructed on a matrix of single-crystal silicon MOS FET s. Pictorial-gray-scale images have been created on a 1 inch display although line defects were present. Though large arrays of TFT s should be much more economical than silicon MOS FET s, TFT s have suffered in the past from stability and reliability problems. More experimentation is necessary to prove their capabilities as the threshold devices in a liquid-crystal panel. 

Aufderheide, T.R, Kudenchuk, P.J., Hedges, J.R. et al. 2008. Resuscitation outcomes consortium (ROC) PRIMED cardiac arrest trial methods Part 1 Rationale and methodology for the impedance threshold device (ITD) protocol. Resuscitation 78(2) 179-185. 

Pirrallo, R.G., Aufderheide, T.P., Provo, T.A., Keith G. Lurie, K.G. 2005. Effect of an inspiratory impedance threshold device on hemodynamics during conventional manual cardiopulmonary Resuscitation. Resuscitation 66(1) 13-20. 

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