Entropy and irreversibility in the quantum realm Am. J. Phys. 79, 297 (2011) We propose a method to characterize electrical resistor damage based on entropy measurements. Irreversible entropy and the rate at which it is generated are more convenient parameters than resistance for describing damage because they are essentially positive in virtue of the second law of thermodynamics, whereas resistance may increase or decrease depending on the degradation mechanism. Commercial resistors were tested in order to characterize the damage induced by power surges. Resistors were biased with constant and pulsed voltage signals, leading to power dissipation in the range of 4-8 W, which is well above the 0.25 W nominal power to initiate failure. Entropy was inferred from the added power and temperature evolution. A model is proposed to understand the relationship among resistance, entropy, and damage. The power surge dissipates into heat (Joule effect) and damages the resistor. The results show a correlation between entropy generation rate and resistor failure. We conclude that damage can be conveniently assessed from irreversible entropy generation. Our results for resistors can be easily extrapolated to other systems or machines that can be modeled based on their resistance. V C 2015 AIP Publishing LLC.

An augmentative and alternative communication (AAC) device for people with speech disabilities is presented. This AAC system exhibits the advantages of two currently used systems: 1) usability of the communication boards and 2) natural oral communication of the electronic communicators. To improve comfort in use, robustness and versatility, the system is designed as two separate blocks linked by wireless communication via a wireless network of communication board sheets. The communication sheets, which are the interface with the user, are economical, simple to use, and scalable to adaptation of the number of symbols and the vocabulary of the individuals who use the system. The digital system (record/player system) controls the net, identifies the active sheets and the pushed symbols, and plays and records all sounds. This digital system can be easily replaced by other digital interfaces, such as computers, smartphones, or tablets, and can increase the function of the AAC with the possibility of using the Internet communication (emails and Skype, among others). The prototype has been evaluated in two special education schools, which are attended by children with severe motor disabilities with or without associated disorders and multi-deficiencies. Positive reviews from individuals who use the AAC system open the possibility of the system's use in both home and educational environments.

We propose a method to assess the degradation and aging of light emitting diodes (LEDs) based on irreversible entropy generation rate. We degraded several LEDs and monitored their entropy generation rate (Ṡ) in accelerated tests. We compared the thermoelectrical results with the optical light emission evolution during degradation. We find a good relationship between aging and Ṡ (t), because Ṡ is both related to device parameters and optical performance. We propose a threshold of Ṡ (t) as a reliable damage indicator of LED end-of-life that can avoid the need to perform optical measurements to assess optical aging. The method lays beyond the typical statistical laws for lifetime prediction provided by manufacturers. We tested different LED colors and electrical stresses to validate the electrical LED model and we analyzed the degradation mechanisms of the devices.

Abstract-The purpose of this paper is to analyze the influence of the metallic structures of a realistic car body frame on the specific absorption rate (SAR) produced by a cell phone when a complete human body model is placed at different locations inside the vehicle, and to identify the relevant parameters responsible for these changes. The modeling and analysis of the whole system was conducted by means of computer simulations based on the full wave finite-difference time-domain (FDTD) numerical method. The excitation considered was an 835 MHz 2 dipole located as a handsfree communication device or as a hand-held portable system. We compared the SAR at different planes on the human model, placed inside the vehicle with respect to the free space situation. The presence of the car body frame significantly changes the SAR distributions, especially when the dipole is far from the body. Although the results are not conclusive on this point, this change in SAR distribution is not likely to produce an increase above the limits in current guidelines for partial body exposure, but may be significant for whole-body exposure. The most relevant change found was the change in the impedance of the dipole, affecting the radiated power. A complementary result from the electromagnetic computations performed is the change in the electromagnetic field distribution inside a vehicle when human bodies are present. The whole vehicle model has been optimized to provide accurate results for sources placed inside the vehicle, while keeping low requirements for computer storage and simulation time.

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