No abstract

The piezoresistive response of n-and p-type hydrogenated nanocrystalline silicon thin films, deposited by hot-wire (HW) and plasma-enhanced chemical vapor deposition (PECVD) on thermally oxidized silicon wafers, has been studied using four-point bending tests. The piezoresistive gauge factor (GF) was measured on patterned thin-film micro-resistors rotated by an angle θ with respect to the principal strain axis. Both longitudinal (GF L) and transverse (GF T) GFs, corresponding to θ = 0º and 90º, respectively, are negative for n-type and positive for p-type films. For other values of θ (30º, 45º, 120º and 135º) GFs have the same signal as GF L and GF T and their value is proportional to the normal strain associated with planes rotated by θ relative to the principal strain axis. It is concluded that the films are isotropic in the growth plane since the GF-values follow a Mohr's circle with the principal axes 2 coinciding with those of the strain tensor. The strongest p-type pirezoresistive response (GF L = 41.0, GF T = 2.84) was found in a film deposited by PECVD at a substrate temperature of 250ºC and working pressure of 0.250 Torr, with dark conductivity 1.6 Ω-1 cm-1. The strongest n-type response (GF L =-28.1, GF T =-5.60) was found in a film deposited by PECVD at 150ºC and working pressure of 3 Torr, with dark conductivity 9.7 Ω-1 cm-1. A model for the piezoresistivity of nc-Si is proposed, based on a mean-field approximation for the conductivity of an ensemble of randomly oriented crystallites and neglecting grain boundary effects. The model is able to reproduce the measured GF L values for both n-and p-type films. It fails however to explain the transversal GF T data. Both experimental and theoretical data show that nanocrystalline silicon can have an isotropic piezoresistive effect of the order of 40% of the maximum response of crystalline silicon.

The agriculture sector is the backbone of Pakistan’s economy, reflecting 26% of its GPD and 43% of the entire labor force. Smart and precise agriculture is the key to producing the best crop yield. Moreover, emerging technologies are reducing energy consumption and cost-effectiveness for saving agricultural resources in control and monitoring systems, especially for those areas lacking these resources. Agricultural productivity is thwarted in many areas of Pakistan due to farmers’ illiteracy, lack of a smart system for remote access to farmland, and an absence of proactive decision-making in all phases of the crop cycle available in their native language. This study proposes an internet of agricultural things (IoAT) based smart system armed with a set of economical, accessible devices and sensors to capture real-time parameters of farms such as soil moisture level, temperature, soil pH level, light intensity, and humidity on frequent intervals of time. The system analyzes the environmental parameters of specific farms and enables the farmers to understand soil and environmental factors, facilitating farmers in terms of soil fertility analysis, suitable crop cultivation, automated irrigation and guidelines, harvest schedule, pest and weed control, crop disease awareness, and fertilizer guidance. The system is integrated with an android application ‘Kistan Pakistan’ (prototype) designed in bilingual, i.e., ‘Urdu’ and ‘English’. The mobile application is equipped with visual components, audio, voice, and iconic and textual menus to be used by diverse literary levels of farmers.

We start by presenting an overview of the various definitions of heat and work found in the literature. Then, we consider several examples for analysis and show that the theory of Thermodynamics requires a precise definition of such quantities. The comparison regarding the Second Law of the system-based and surroundings-based definitions of heat and work is undertaken leading to the conclusion that the definitions of such concepts should be based on variables external to the system.