Genetic Programming is a heuristic search algorithm inspired by evolutionary techniques that has been shown to produce satisfactory solutions to problems related to several scientific domains [1]. Presented here is a methodology for the creation of Quantitative Structure-Activity Relationship (QSAR) models for the prediction of chemical activity, using Genetic Programming. QSAR analysis is crucial for drug discovery since good QSAR models enable human experts to select compounds with increased chances of being active for further investigations. Our technique has been tested using the Selwood dataset, a benchmark dataset for the QSAR field [2]. The results indicate that the QSAR models created are accurate, reliable and simple and can thus be used to identify molecular descriptors correlated with measured activity and for the prediction of the activity of untested molecules. The QSAR models we generated predict the activity of untested molecules with an error ranging between 0.46-0.8 on the scale [-1,1]. These results compare favourably with results sited in the literature for the same dataset [3], [4]. Our models are constructed using any combination of the arithmetic operators {+,-, /, *}, the descriptors available and constant values.
This work investigates the performance of an envelope detector under high peak‐to‐average power ratio (PAPR) waveform excitations. First, the use of multi‐stage rectifiers is investigated in wireless power transfer systems, as a method to increase the DC output voltage. It is shown that at low input powers, a large number of stages can reduce the efficiency dramatically. Then, high PAPR waveforms are presented as an alternative method to multi‐stage rectifiers that can increase the DC output voltage without decreasing the efficiency at low input powers. Simulations and experimental measurements with different multi‐tone waveforms and modulation schemes are shown. The results demonstrate that the PAPR and complementary cumulative distribution functions (CCDF) of a waveform significantly influence the RF‐to‐DC conversion. Using a 5‐tone input waveform with −10 dBm power and a 100 kΩ load, the DC output voltage was increased by 32.3%, while using a 256 QAM modulation the output voltage was increased by 12.6%. The results show similar behaviour to that of multi‐stage topologies but without decreased efficiencies at low input powers. These results suggest that the use of high PAPR waveforms can decrease the required number of rectifier stages, and hence increase the rectifier efficiency at extremely low input powers.
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