Structural of BCTZ nanowires and high performance BCTZ-based nanogenerator for biomechanical energy harvesting

Owing to its excellent piezoelectric and ferroelectric properties, (Ba,Ca)(Ti,Zr)O₃ (BCTZ) family is considered as one of the most promising piezoelectric materials to replace the lead-based piezoelectrics, such as Pb(Zr,Ti)O₃ et al.. In this study, a BCTZ nanowires (NWs) based piezoelectric nanogenerator (NG) was fabricated. BCTZ NWs were prepared by an electrospinning technique. The NG achieved an excellent piezoelectric performance with a maximum open-circuit voltage of 0.65 V and short-circuit current of 2.2 nA by bending periodically. Furthermore, the NG obtained a maximum voltage of 2.2 V and current of 90 nA by tapping it. Results indicate that the lead-free BCTZ has a huge application potential in biomechanical energy harvesting.     

Multiaxial wavy top-emission organic light-emitting diodes on thermally prestrained elastomeric substrates

In this work, we report the fabrication process of wavy top-emission organic light-emitting diodes (WOLEDs), which can sustain multiaxial tensile and compressive strains. The devices are fabricated using standard procedures, comprised of the conventional stacks of OLED materials and transfer printing process. Transferring these devices onto thermally prestrained elastomeric substrates and then releasing this strain configure the devices into random, two-dimensional (2D) wavy layouts. The performance of the WOLEDs is analyzed at ±1.5% (strain ratio = 1.16) and ±3% (strain ratio = 2.33) strain with respect to the prestrain value. The fabricated WOLEDs demonstrate good performance in the green light region within ±1.5% and show comparable results even at ±3% tensile and compression strains, which indicates that the fabricated devices can accommodate high strain ratios without inducing significant stresses in the devices. Finite element simulation demonstrates strong coherence with the experimental results and provides a valuable insight into the strain effects on each layer utilized for the device fabrication. Along with that, the neutral plane is generated around the upper region of emission and cathode layers in the devices. A slight blue shift observed by the electroluminescence analysis reveals that luminescence of various colors can be obtained by changing the dimensions of the wavy buckles. This research work can remarkably contribute to the fabrication of multicolored flexible, wearable indicators or curvilinear displays that require the ability not only to bend and stretch, but also to compress in multiple directions with a high strain ratio.     

Design and characterization of a real-time,wearable, endosomatic electrodermal system

This paper presents the design and characterization of a compact wearable system for long-term assessment of skin potential response, with the aim of monitoring mental stress in a variety of applications. Literature reports that the expected skin potential has peak-to-peak amplitudes of few millivolts in the frequency band [0.1, 10] Hz. The designed system is characterized by a slightly wider bandwidth of [0.08, 40] Hz, and it is based on a 12-bit ADC working with a sampling rate of 200 Sa/s, which can be increased up to 3.5 kSa/s. Data can be continuously acquired for up to 40 h with a battery of 3.7 V/1800 mAh. A Graphical User Interface was also developed for the host computer in .NET framework. The system, to our knowledge the first example of wearable endosomatic electrodermal activity sensor, joins to several skin conductance wearable measuring systems recently proposed in literature, and opens up opportunities for future comparisons of endosomatic and exosomatic responses in real life.The device is thoroughly characterized in accordance with the state-of-the-art of the metrological research in the field.     

Power and efficiency analysis of high-frequency Wireless Power Transfer Systems

This paper discusses the losses analysis of low power high-frequency Wireless Power Transfer Systems (WPTSs). Ideal models for efficiency evaluation of WPTS can predict performances that are quite far from the real ones. The model proposed in this paper includes semiconductor devices losses, as well as modulation of duty-cycle and phase for the secondary side rectifier. The global influence of semiconductor devices and control parameters on the overall WPTS performances is numerically determined by solving the herein discussed non linear equations system. Experimental measurements realized on a 2 W@6.78 MHz WPTS demonstrate the validity of this analysis.     

Designing wearable vibrotactile notifications for information communication

Visual and auditory stimuli are frequently used for information communication on mobile devices. These feedback modalities, however, are less suitable for emerging wearable devices that are intended to support multitasking with minimum interruption. Use of vibrotactile stimuli is great alternatives due to their low disruption and high ability to attract attention.Currently, effective vibration notifications are still elusive. In the present study, we explored a vibration notification mechanism by using a singular vibration motor to generate various vibration stimuli. This solution is appropriate for existing wearable devices that have a small form factor, limited internal space, and low battery capacity. Our first experiment investigated individuals’ vibration perception in order to select a set of vibration stimuli that were detectable and discriminable. In our second experiment, we mapped the 5 vibration stimuli that were identified in the first experiment to various mobile application events and evaluated user performance using a wrist mounted prototype device. Results indicate that our vibration notification design achieved an average response accuracy rate of 82.3% (SD=18.0%) and an average response time of 2.83 (SD=0.83) s. Moreover, results of the post-test questionnaire revealed that the average perceived usefulness towards the vibration notification design was rated 5.5 (SD=1.18) and the average perceived ease of use was rated 5.0 (SD=1.36) when using a 7-point rating scale. Overall, results indicated the present vibration notification design was perceived as useful and highlighted opportunities for improving perceptions of ease of use. Our findings inform the design of future vibration notifications on wearable devices and highlight the importance of increasing pair-wise dissimilarities, perceived usefulness, and perceived ease of use in designing effective vibration notifications.     

Unsupervised understanding of location and illumination changes in egocentric videos

Wearable cameras stand out as one of the most promising devices for the upcoming years, and as a consequence, the demand of computer algorithms to automatically understand the videos recorded with them is increasing quickly. An automatic understanding of these videos is not an easy task, and its mobile nature implies important challenges to be faced, such as the changing light conditions and the unrestricted locations recorded. This paper proposes an unsupervised strategy based on global features and manifold learning to endow wearable cameras with contextual information regarding the light conditions and the location captured. Results show that non-linear manifold methods can capture contextual patterns from global features without compromising large computational resources. The proposed strategy is used, as an application case, as a switching mechanism to improve the hand-detection problem in egocentric videos.     

Disseminating trust information in wearable communities

This paper describes a framework for managing and distributing trust information in a community of mobile and wearable computer users. Trust information in the form of reputations are used to aid users during their social interactions with the rest of the community.     

铜对水泵叶轮耐磨性能的影响

加入＜0.8%的Cu显著减少叶轮叶片尖角薄断面白口,改善叶轮可切削性能;加入Cu的铸铁,流动性改善,有利于提高铸件致密度.所以Cu能有效地提高水泵叶轮的耐磨性能.     

Exploring MARS: developing indoor and outdoor user interfaces to a mobile augmented reality system

We describe an experimental mobile augmented reality system (MARS) testbed that employs different user interfaces to allow outdoor and indoor users to access and manage information that is spatially registered with the real world. Outdoor users can experience spatialized multimedia presentations that are presented on a head-tracked, see-through, head-worn display used in conjunction with a hand-held pen-based computer. Indoor users can get an overview of the outdoor scene and communicate with outdoor users through a desktop user interface or a head- and hand-tracked immersive augmented reality user interface.