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Wearable Solar Systems
Published in Denise Wilson, Wearable Solar Cell Systems, 2019
What can 9.1 W/m2 achieve? The answer to that question certainly depends on the technology and method by which PV cells are made wearable for the average consumer. Consider first the use of highly efficient but rigid crystalline silicon with 26.1% power conversion efficiency in ideal AM 1.5 conditions (Table 9.1). Because of a lack of flexibility, the rigid panel might be designed to be worn across the outward-facing side of a backpack with a surface area of about 0.1 m2. Under fluorescent lighting, silicon is only 34% as efficient as it is when exposed to sunlight (Table 9.2). Thus, for every watt of light reaching the panel, a maximum of 0.09 W is successfully harvested (34% of the 26.1% power conversion efficiency in response to sunlight). 9.1 W/m2 over 0.1 m2 of area amounts to 0.91 W and at 9% efficiency, yields 0.082 W, which over 16 hours of exposure to artificial fluorescent light, yields 1.3 Wh of energy. Compared to the per capita electricity consumption per day in the United States (U.S. Energy Information Administration 2017), this seems like a trivial amount of energy. However, compared to the energy demand of wearables and portables (Tables 8.1 through 8.5), 1.3 Wh of energy is enough to support an MP3 player, a wireless headset, a smartwatch, a fitness band, a sports watch for many hours, or a hearing aid for multiple days,. And, if the office worker goes outside for lunch, the 0.1 m2 backpack panel will enjoy an additional 82.7 W/m2 (Table 9.4) for an hour, adding 2.2 Wh to the energy harvested bringing the total to approximately 3.5 Wh over a 16-hour day, enough to power a laptop or tablet computer for an hour or two or a smartphone for most of the day. Leaving the backpack on a sunny window ledge can increase the total energy harvested even further.
Neural engineering
Published in Alex Mihailidis, Roger Smith, Rehabilitation Engineering, 2023
The peripheral nerve can be stimulated either non-invasively using (1) transcutaneous/surface electrodes or invasively using (2) percutaneous or (3) implanted electrodes. The transcutaneous electrode can be placed on the skin surface above a nerve branch, a muscle belly, or a group of muscle bellies (Figure 22.1). The size of the transcutaneous electrode should be selected depending on the target. The electrodes have traditionally been connected with flexible leads to a stimulator that may be worn on the body trunk or a limb. However, several manufacturers now have designs resembling large band-aids, where the stimulator is mounted onto the surface electrodes and controlled wirelessly with hand-held devices such as a smartphone or tablet computer. Some systems require the transcutaneous electrodes placed above a nerve branch aiming to activate the whole nerve branch, such as a foot drop stimulator. Other systems are designed to place transcutaneous electrodes on a specific point of a muscle belly, that is, the motor point. The motor point is the site that produces the strongest contraction with the lowest level of stimulation. When the transcutaneous electrode is placed over the motor point of the target muscle, we can expect to induce muscle contraction efficiently. However, to do so, the location of the motor point must be identified manually using a probe electrode, which requires skill, time, and specialized devices. Therefore, in clinical settings, motor point stimulation is not used very often. Instead, FES is achieved by electrically stimulating a group of muscles with a pair of large electrodes covering the entire muscle group. For example, in the case of activating quadriceps femoris, a pair of large electrodes located at the proximal and distal ends of the thigh is often used instead of locating multiple electrodes over specific motor points of each muscle head. Since the transcutaneous FES is a non-invasive treatment method, it can be easily applied to patients and is relatively inexpensive, which is beneficial for therapeutic applications. However, the transcutaneous FES requires knowledge and skillsets to place electrodes at appropriate locations to induce isolated, ideal limb movements, while it is also difficult to activate deep muscles. In addition, the transcutaneous FES can be significantly limited by discomfort/pain caused by the electrical activation of cutaneous sensory receptors.
Influence of virtual keyboard design and usage posture on typing performance and muscle activity during tablet interaction
Published in Ergonomics, 2020
Ming-I Brandon Lin, Ruei-Hong Hong, Yu-Ping Huang
This study demonstrated that the split virtual keyboard allows better task performance with reduced muscle activity of the right EDC muscle than the standard virtual keyboard when performing text entry activities with two hands on a tablet computer. Using tablets on a desk increased muscle activity in the neck and shoulder region, whereas typing with tablets on the lap showed greater and more dynamic EDC and FDS muscle activity and increased typing speed. Regarding the duration of tablet use, the typing performance decreased over time with a significant increase in right CES muscle activity. These findings suggest that the effects of usage postures on the musculoskeletal system were further compounded by the virtual keyboard design. To improve the user experience of using tablets outside a traditional office setting, it is important to gain a better understanding of the relationships between design features of virtual keyboards, task performance, and musculoskeletal outcomes incurred under various usage scenarios.
Exploring the usability of the text-based CAPTCHA on tablet computers
Published in Connection Science, 2019
The experiment for the usability analysis of the text-based CAPTCHA on tablet computer was conducted on a population of 125 Internet users who were recruited by email and tested in real-life contexts. All participants had normal or corrected to normal colour vision. The participation in the study was voluntary and all users agreed to an online consent form before participating. In particular, participants were informed that the provided data and their interactions with the system would be processed and anonymously used as a part of an experimental user study of the research group. No further details about the aim of the study or the type of recorded interaction data (e.g. time to complete the challenge) were provided to the participants in order to avoid bias effects. After that, an investigator asked each user to solve two types of text-based CAPTCHA on tablet computer: (i) containing only text and (ii) containing only numbers. The used CAPTCHAs were composed of six lowercased alphanumeric characters altered with complex coloured background, waving and extra lines in background (see Figures 1 and 2). The used tablet computer had a Liquid Crystal Display (LCD) 7” wide in its diagonal, internal virtual keyboard and Android operating system. The investigator measured using a chronometer the CAPTCHA response time from the beginning to the end of the process. This time was given in seconds. After solving the CAPTCHA, it was checked if the result is accurate. If the CAPTCHA was not successfully solved, then the success was given as no. Otherwise, the success in solving the CAPTCHA was given as yes.