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The conformations of protonated RA15K, RA20K and RA15H (R = arginine, A = alanine, K = lysine, and H = histidine) have been examined in the gas phase as a function of temperature. These peptides were designed so that intramolecular proton transfer will trigger conformational changes between a helix (proton sequestered at the C-terminus) and globule (proton sequestered at the N-terminus). Kinetically controlled structural transitions occur below 400 K (from helix to globule for RA15H, and from globule to helix for RA15K and RA20K). As the temperature is raised, the compact globule found at room temperature expands, accesses more configurations, and becomes entropically favored. At around 500 K, the RA15K and RA20K helices undergo a melting transition. The transition is broad, as expected for a phase transition in a finite system, and becomes narrower as the peptide size increases. In the helical conformation, the two basic residues are well separated; as a result, the proton transfer necessary to drive the melting transition probably involves a mobile proton. For doubly protonated RA15K, a dumbbell-like conformation (resulting from repulsion between the two protonated basic residues) is found at high temperature.

Purpose Recent developments in wearable technologies have paved the way for continuous monitoring of the electrocardiogram (ECG) signal, without the need for any laboratory settings. A number of wearable sensors ranging from wet electrode sensors to dry sensors, textile-based sensors, knitted integrated sensors (KIS) and planar fashionable circuit boards are used in ECG measurement. The purpose of this study is to carry out a comparative study of the different sensors used for ECG measurements. The current challenges faced in developing wearable ECG sensors are also reviewed. Design/methodology/approach This study carries out a comparative analysis of different wearable ECG sensors on the basis of four important aspects: materials and methods used to develop the sensors, working principle, implementation and performance. Each of the aspects has been reviewed with regard to the main types of wearable ECG sensors available. Findings A comparative study of the sensors helps understand the differences in their operating principles. While some sensors may have a higher efficiency, the others might ensure more user comfort. It is important to strike the right balance between the various aspects influencing the sensor performance. Originality/value Wearable ECG sensors have revolutionized the world of ambulatory ECG monitoring and helped in the treatment of many cardiovascular diseases. A comparative study of the available technologies will help both doctors and researchers gain an understanding of the shortcomings in the existing systems.

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