Photonic skins enable a direct and intuitive visualization of various physical and mechanical stimuli with eye‐readable colorations by intimately laminating to target substrates. Their development is ...still at infancy compared to that of electronic skins. Here, an ultra‐adaptable, large‐area (10 × 10 cm2), multipixel (14 × 14) photonic skin based on a naturally abundant and sustainable biopolymer of a shape‐memory, responsive multiphase cellulose derivative is presented. The wearable, multipixel photonic skin mainly consists of a photonic sensor made of mesophase cholesteric hydroxypropyl cellulose and an ultra‐adaptable adhesive layer made of amorphous hydroxypropyl cellulose. It is demonstrated that with multilayered flexible architectures, the multiphase cellulose derivative–based integrated photonic skin can not only strongly couple to a wide range of biological and engineered surfaces, with a maximum of ≈180 times higher adhesion strengths compared to those of the polydimethylsiloxane adhesive, but also directly convert spatiotemporal stimuli into visible color alterations in the large‐area, multipixel array. These colorations can be simply converted into 3D strain mapping data with digital camera imaging.
An ultra‐adaptable and wearable photonic skin based on a shape‐memory and stimuli‐responsive cellulose derivative is presented. The cellulose derivative–based photonic skin can not only intimately laminate to a wide range of biological and engineered surfaces, with exceptional adhesion strengths, but also directly convert spatiotemporal stimuli into visible color alterations in the large‐area, multipixel array.
Vibration-based Structural Health Monitoring (SHM) techniques are among the most common approaches for structural damage identification. The presence of damage in structures may be identified by ...monitoring the changes in dynamic behavior subject to external loading, and is typically performed by using experimental modal analysis (EMA) or operational modal analysis (OMA). These tools for SHM normally require a limited number of physically attached transducers (e.g. accelerometers) in order to record the response of the structure for further analysis. Signal conditioners, wires, wireless receivers and a data acquisition system (DAQ) are also typical components of traditional sensing systems used in vibration-based SHM. However, instrumentation of lightweight structures with contact sensors such as accelerometers may induce mass-loading effects, and for large-scale structures, the instrumentation is labor intensive and time consuming. Achieving high spatial measurement resolution for a large-scale structure is not always feasible while working with traditional contact sensors, and there is also the potential for a lack of reliability associated with fixed contact sensors in outliving the life-span of the host structure. Among the state-of-the-art non-contact measurements, digital video cameras are able to rapidly collect high-density spatial information from structures remotely. In this paper, the subtle motions from recorded video (i.e. a sequence of images) are extracted by means of Phase-based Motion Estimation (PME) and the extracted information is used to conduct damage identification on a 2.3-m long Skystream® wind turbine blade (WTB). The PME and phased-based motion magnification approach estimates the structural motion from the captured sequence of images for both a baseline and damaged test cases on a wind turbine blade. Operational deflection shapes of the test articles are also quantified and compared for the baseline and damaged states. In addition, having proper lighting while working with high-speed cameras can be an issue, therefore image enhancement and contrast manipulation has also been performed to enhance the raw images. Ultimately, the extracted resonant frequencies and operational deflection shapes are used to detect the presence of damage, demonstrating the feasibility of implementing non-contact video measurements to perform realistic structural damage detection.
Exploiting the distinct excitation and emission properties of concomitant electrochemiluminophores in conjunction with the inherent color selectivity of a conventional digital camera, we create a new ...strategy for multiplexed electrogenerated chemiluminescence detection, suitable for the development of low-cost, portable clinical diagnostic devices. Red, green and blue emitters can be efficiently resolved over the three-dimensional space of ECL intensity versus applied potential and emission wavelength. As the relative contribution ratio of each emitter to the photographic RGB channels is constant, the RGB ECL intensity versus applied-potential curves could be effectively isolated to a single emitter at each potential.
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•Interfacial dynamics of droplet breakup with tunnels in a T-junction was studied.•Four breakup stages were observed in the droplet breakup process.•The relations between scaling laws ...and influencing factors were clarified.•Viscosity effect on the droplet breakup process was highlighted.•The formation of satellite droplets in a T-junction was investigated.
Dynamics for droplet breakup with tunnels and formation of satellite droplets in a symmetric microfluidic T-junction are investigated using a high-speed digital camera. The breakup process of droplet could be divided into four sequential stages: squeezing, transition, pinch-off, and thread rupture stages. Effects of the viscosity ratio of both phases λ, the capillary number of the continuous phase Cac, and the dimensionless droplet length l0/wc on the breakup process of droplet are analyzed. In the squeezing stage controlled by squeezing pressure, the variation of the minimum width of the droplet neck with time could be scaled as a power-law relationship with exponent related to λ and l0/wc. The transition stage is dominated by the velocity of the fluid, and the pinch-off stage is mainly driven by the capillary force. For these two stages, the evolution of the minimum width of the droplet neck with the remaining time could be described as other power-law relationship with exponent related to λ. In the thread rupture stage controlled by viscous stresses of both phases and the surface tension, the minimum width of droplet neck decreases linearly with time, and the coefficient of the linear function depends on λ. Additionally, for the formation of satellite droplets, the size of satellite droplet increases with the increase of superficial velocity of the fluid and droplet viscosity. Furthermore, a critical capillary number 0.03 is observed in low viscosity of the droplet, which divides the variation of the size of the main satellite droplet with the capillary number into constant area and growth zone.
Nowadays, the cyberspace consists of an increasing number of IoT devices, such as net-printers, webcams, and routers. Illuminating the nature of online devices would provide insights into detecting ...potentially vulnerable devices on the Internet. However, there is a lack of device discovery in large-scale due to the massive number of device models (i.e., types, vendors, and products). In this paper, we propose an efficient approach to generate fingerprints of IoT devices. We observe that device manufacturers have different network system implementations on their products. We explore features spaces of IoT devices in three network layers, including the network-layer, transport-layer, and application-layer. Utilizing the feature of network protocols, we generate IoT device fingerprints based on neural network algorithms. Furthermore, we implement the prototype system and conduct real experiments to validate the performance of device fingerprints. Results show that our classification can generate device class labels with a 94% precision and 95% recall. We use those device fingerprints to discover 15.3 million network-connected devices and analyze their distribution characteristics in cyberspace.
One of the largest impediments in the development of microfluidic-based smart sensing systems is the manufacturability of integrated, complex devices. Here we propose multimaterial 3D printing for ...the fabrication of such devices in a single step. A microfluidic device containing an integrated porous membrane and embedded liquid reagents was made by 3D printing and applied for the analysis of nitrate in soil. The manufacture of the integrated, sealed device was realized as a single print within 30 min. The body of the device was printed in transparent acrylonitrile butadiene styrene (ABS) and contained a 400 μm wide structure printed from a commercially available composite filament. The composite filament can be turned into a porous material through dissolution of a water-soluble material. Liquid reagents were integrated by briefly pausing the printing before resuming for sealing the device. The devices were evaluated by the determination of nitrate in a soil slurry containing zinc particles for the reduction of nitrate to nitrite using the Griess reagent. Using a consumer digital camera, the linear range of the detector response ranged from 0 to 60 ppm, covering the normal range of nitrate in soil. To ensure that the sealing of the reagent chamber is maintained, aqueous reagents should be avoided. When using the nonaqueous reagent, the multimaterial device containing the Griess reagent could be stored for over 4 days but increased the detection range to 100–500 ppm. Multimaterial 3D printing is a potentially new approach for the manufacture of microfluidic devices with multiple integrated functional components.
We report on improvements made on our previously introduced technique of cavity-enhanced Raman spectroscopy (CERS) with optical feedback cw-diode lasers in the gas phase, including a new ...mode-matching procedure which keeps the laser in resonance with the optical cavity without inducing long-term frequency shifts of the laser, and using a new CCD camera with improved noise performance. With 10 mW of 636.2 nm diode laser excitation and 30 s integration time, cavity enhancement achieves noise-equivalent detection limits below 1 mbar at 1 bar total pressure, depending on Raman cross sections. Detection limits can be easily improved using higher power diodes. We further demonstrate a relevant analytical application of CERS, the multicomponent analysis of natural gas samples. Several spectroscopic features have been identified and characterized. CERS with low power diode lasers is suitable for online monitoring of natural gas mixtures with sensitivity and spectroscopic selectivity, including monitoring H2, H2S, N2, CO2, and alkanes.
Fatigue cracks developed under repetitive loads are one of the major threats to structural integrity of steel bridges. Human inspection is the most commonly applied approach for fatigue crack ...detection, but is time consuming, labor intensive, and lacks reliability. In this study, we propose a computer vision‐based fatigue crack detection approach using a short video stream taken by a consumer‐grade digital camera. A feature tracking technology is applied to the video for tracking the surface motion of the monitored structure under repetitive load. Then, a crack detection and localization algorithm is established to effectively search differential features at different video frames caused by the crack opening and closing. The effectiveness of the proposed approach is validated through testing two experimental specimens with in‐plane and out‐of‐plane fatigue cracks, respectively. Results indicate that the proposed approach can robustly identify the fatigue crack, even when the crack is under ambient lighting conditions, surrounded by other crack‐like edges, covered by complex surface textures, or invisible to human eyes due to crack closure. Furthermore, our proposed approach enables accurate quantification of the crack opening under fatigue loading with submillimeter accuracy. However, due to the capacity of the camera resolution in this study, accurate detection of crack tip remains challenging.
Artificial light at night has affected most of the natural nocturnal landscapes worldwide and the subsequent light pollution has diverse effects on flora, fauna and human well-being. To evaluate the ...environmental impacts of light pollution, it is crucial to understand both the natural and artificial components of light at night under all weather conditions. The night sky brightness for clear skies is relatively well understood and a reference point for a lower limit is defined. However, no such reference point exists for cloudy skies. While some studies have examined the brightening of the night sky by clouds in urban areas, the published data on the (natural) darkening by clouds is very sparse. Knowledge of reference points for the illumination of natural nocturnal environments however, is essential for experimental design and ecological modeling to assess the impacts of light pollution. Here we use differential all-sky photometry with a commercial digital camera to investigate how clouds darken sky brightness at two rural sites. The spatially resolved data enables us to identify and study the nearly unpolluted parts of the sky and to set an upper limit on ground illumination for overcast nights at sites without light pollution.
The concept of a comfort zone, most often defined as a psychological space of safety that sets boundaries for our day-to-day functioning, can also find its reference in the process of learning a ...foreign language. The experiences of the pandemic distance learning show that the turned off camera is the basic element constituting the comfort zone of students during synchronous language classes. The status of the camera often becomes a bone of contention between teachers, who perceive it as a tool that allows for building a positive relationship and contact with class participants, and students who identify it with a lack of a sense of security, freedom or privacy. This paper will present the results of an online survey conducted among teachers (13) and students (36) of Dutch philology, made of 13 questions concerning the function, reception and purposefulness of turned on / off cameras during remote classes. The collected data was subjected to qualitative and quantitative analysis, which revealed that an on-camera in remote language classes evokes mostly negative emotions in students, while an off-camera evokes mostly positive emotions; for teachers, the relationship is largely reversed. However, for both groups of respondents, the predominant belief is that there is a positive correlation between the camera being on and effectiveness of the class.
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