Human behaviors are extremely sophisticated, relying on the adaptive, plastic and event-driven network of sensory neurons. Such neuronal system analyzes multiple sensory cues efficiently to establish ...accurate depiction of the environment. Here, we develop a bimodal artificial sensory neuron to implement the sensory fusion processes. Such a bimodal artificial sensory neuron collects optic and pressure information from the photodetector and pressure sensors respectively, transmits the bimodal information through an ionic cable, and integrates them into post-synaptic currents by a synaptic transistor. The sensory neuron can be excited in multiple levels by synchronizing the two sensory cues, which enables the manipulating of skeletal myotubes and a robotic hand. Furthermore, enhanced recognition capability achieved on fused visual/haptic cues is confirmed by simulation of a multi-transparency pattern recognition task. Our biomimetic design has the potential to advance technologies in cyborg and neuromorphic systems by endowing them with supramodal perceptual capabilities.
Soft electronics that seamlessly interface with skin are of great interest in health monitoring and human–machine interfaces. However, achieving mechanical softness, skin adhesiveness, and high ...conductivity concurrently has always been a major challenge due to the difficulty in bonding dissimilar materials while retaining their respective properties. Herein, the mechanically interlocked hydrogel–elastomer hybrid is reported as a viable solution to this problem. Hydrogels with low moduli and high adhesiveness are employed as the substrate, while porous elastomer webs are used as matrices to load conductive films and lock the hydrogels through a mechanically interlocked structure. The bonding strength between the hydrogel and elastomer in the interlocking hybrid structure is 14.3 times of that obtained via the physical stacking method. As a proof of concept, interlocking hybrids are used as on‐skin electrodes for electrophysiological signal recording including electromyography and electrocardiography. The robust hybrid electrodes are able to detect signals after multiple cycles. The proposed strategy not only is an effective approach to achieve interlocking structures, but also provides a new perspective for soft and stretchable electronics.
A novel hydrogel–elastomer hybrid is developed by mechanical interlocking. Porous elastomer webs are used as matrices to load conductive materials and lock hydrogels through an interlocking structure to achieve mechanically soft and skin‐adhesive electrodes. The interlocking hybrid is used as an on‐skin electrode for recording electrophysiological signals.
Fiber‐shaped stretchable strain sensors with small testing areas can be directly woven into textiles. This paves the way for the design of integrated wearable devices capable of obtaining real‐time ...mechanical feedback for various applications. However, for a simple fiber that undergoes uniform strain distribution during deformation, it is still a big challenge to obtain high sensitivity. Herein, a new strategy, surface strain redistribution, is reported to significantly enhance the sensitivity of fiber‐shaped stretchable strain sensors. A new method of transient thermal curing is used to achieve the large‐scale fabrication of modified elastic microfibers with intrinsic microbeads. The proposed strategy is independent of the active materials utilized and can be universally applied for various active materials. The strategy used here will shift the vision of the sensitivity enhancement method from the active materials design to the mechanical design of the elastic substrate, and the proposed strategy can also be applied to nonfiber‐shaped stretchable strain sensors.
Surface strain redistribution in substrates significantly enhances sensitivity of fiber‐shaped stretchable strain sensors fabricated by thermal‐transient‐curing and Plateau–Rayleigh instability. Poly(dimethylsiloxane) (PDMS) microfibers with beads are produced in large scale. The beads regulate strain distribution. Novel sensors are well adhered to textiles for monitoring sports activities. This study opens up a new perspective of fiber‐shaped sensors and a method to enhance sensitivity.
Stretchable strain sensors have aroused great interest for their application in human activity recognition, health monitoring, and soft robotics. For various scenarios involving the application of ...different strain ranges, specific sensitivities need to be developed, due to a trade‐off between sensor sensitivity and stretchability. Traditional stretchable strain sensors are developed based on conductive sensing materials and still lack the function of customizable sensitivity. A novel strategy of mechanocombinatorics is proposed to screen the sensor sensitivity based on mechanically heterogeneous substrates. Strain redistribution over substrates is optimized by mechanics and structure parameters, which gives rise to customizable sensitivity. As a proof of concept, a local illumination method is used to fabricate heterogeneous substrates with customizable mechanics and structure parameters. A library of mechanocombinatorial strain sensors is created for extracting the specific sensitivity. Thus, not only is an effective strategy for screening of sensor sensitivity demonstrated, but a contribution to the mechanocombinatorial strategy for personalized stretchable electronics is also made.
A novel strategy of mechanocombinatorics is developed to screen the sensitivity of stretchable strain sensors. Mechanically heterogeneous substrates, defined as substrates comprising low and high modulus regions, are incorporated into strain sensors. Strain distributions over substrates are controlled by combined parameters of mechanics and structure. A library of strain sensors based on heterogeneous substrates is created for screening of sensitivity.
Applications under extreme conditions, such as solid circuit breakers and electromagnetic launching systems, are great challenges to semiconductor power devices. The die-attach solder joint is as one ...of the most vulnerable structures and critical to the reliability of insulated-gate bipolar transistor (IGBT) modules. In this paper, IGBT modules were cross sectioned and tested under pulse high-current power cycling. The failure mechanism of the die-attach solder in IGBTs at pulse high-current modes was investigated. Evolution of microdefects in the die-attach solder during power cycling was characterized and factors for the failure of die-attach solder joints was discussed. The results revealed that voids, cracks, and detachment of interface were the major microdefects in the die-attach solder layer. A detachment of the Si/Sn-Ag-Cu (SAC) interface is verified as the major failure mode under pulse high-current power cycling. Interface cracks between the Si-chip and die-attach solder layer were found to initiate first at the solder layer edges and then extended to the center of the solder layer with the increase of power cycles. The detachment of Si/SAC interface was more similar to the brittle fracture. The junction temperature swing and heating rate were the key factors for detachment of the Si/SAC interface.
This paper provides the first meta-analytic examination of the relationship between leadership and followers' intrinsic motivation. In particular, we examined 6 leadership variables ...(transformational, ethical, leader-member exchange, servant, empowering, and abusive supervision) using data from 50 independent samples and 21,873 participants. We found that transformational leadership, ethical leadership, leader-member exchange (LMX), servant leadership, and empowering leadership were positively related to intrinsic motivation, whereas abusive supervision was negatively linked to intrinsic motivation. Although these leadership styles were associated with intrinsic motivation, they varied considerably in their relative importance. Empowering, ethical, and servant leadership emerged as the more important contributors to intrinsic motivation than transformational leadership. LMX showed a similar contribution with transformational leadership to intrinsic motivation. Effectiveness of leadership styles in relation to intrinsic motivation varied by power distance, publication year, and journal quality. Drawing on our findings, we discuss the theoretical and practice implications.
Stretchable conductors are the basic units of advanced flexible electronic devices, such as skin‐like sensors, stretchable batteries and soft actuators. Current fabrication strategies are mainly ...focused on the stretchability of the conductor with less emphasis on the huge mismatch of the conductive material and polymeric substrate, which results in stability issues during long‐term use. Thermal‐radiation‐assisted metal encapsulation is reported to construct an interlocking layer between polydimethylsiloxane (PDMS) and gold by employing a semipolymerized PDMS substrate to encapsulate the gold clusters/atoms during thermal deposition. The stability of the stretchable conductor is significantly enhanced based on the interlocking effect of metal and polymer, with high interfacial adhesion (>2 MPa) and cyclic stability (>10 000 cycles). Also, the conductor exhibits superior properties such as high stretchability (>130%) and large active surface area (>5:1 effective surface area/geometrical area). It is noted that this method can be easily used to fabricate such a stretchable conductor in a wafer‐scale format through a one‐step process. As a proof of concept, both long‐term implantation in an animal model to monitor intramuscular electric signals and on human skin for detection of biosignals are demonstrated. This design approach brings about a new perspective on the exploration of stretchable conductors for biomedical applications.
Thermal‐radiation‐assisted metal encapsulation is used to prepare large‐scale high‐performance stretchable conductors that possess high stretchability, stability and adhesion and large surface area. They are used to simultaneously monitor electromyography and skin deformation and implanted to detect intramuscular signals. This study offers a new path for highly stable stretchable conductors and related biointerface applications.
Lifting-off of Al bonding wires is one common failure mode of insulated-gate bipolar transistor (IGBT) modules during long-time operation. In the present work, the failure mechanism of Al wires ...lifting-off was investigated and the major factors were discussed based on both experiments and finite element (FE) simulations. It indicates that lifting-off of Al-wires is mainly determined by the interfacial thermal stress at the bonding interface. Thermal expansion of Al-wires and thermal mismatch of Al-Si interfaces contribute to the interfacial thermal stress which is affected by the resistance heat of Al-wires and power loss of Si-chips. Accordingly, a new lifetime model for the Al wires lifting-off failure mode of IGBT modules is proposed and verified through power cycling tests. The conduction current <inline-formula> <tex-math notation="LaTeX">I_{c} </tex-math></inline-formula>, the heating time <inline-formula> <tex-math notation="LaTeX">t_{\mathrm{\scriptscriptstyle ON}} </tex-math></inline-formula>, and the junction temperature swing <inline-formula> <tex-math notation="LaTeX">\Delta T_{j} </tex-math></inline-formula> are three major factors for the fatigue life model of IGBTs under Al wires lifting-off failure mode.
Fatigue of die-attach solder joints is quite critical to reliability of IGBT modules. In the present work, physics of failure of die-attach joints in IGBTs was discussed based on the evolution of ...micro-defects in materials under accelerated aging through experiments and Finite element (FE) simulations. It shows that voids, cracks of Sn-Ag-Cu (SAC) alloys and detachment of Si/SAC interfaces are three major micro-defects in the die-attach solder. Voids could accelerate evolution of other two micro-defects. Cracking of SAC alloys is the major failure mode of die-attach solder under power cycling and detachment of Si/SAC interfaces turns to be the dominant failure mode under transient electrical/thermal shocks. FE simulations indicate that the shear thermal stress τshear at Si/SAC interfaces is the decisive factor for switching between the two failure modes. When ΔTj > 105 °C, the average shear stress τshear_ave at Si/SAC interfaces exceeds the bonding strength and detachment of Si/SAC interfaces plays a major role in failure of die-attach solder. Based on physics of failure, two physical life models for die-attach joints under various accelerated aging conditions were proposed.
•Failure mechanism of die-attach solders were studied by experiments and FE simulations.•Cracking of solder is the major failure mode for die-attach solders under power cycling.•the chip/solder interface detachment becomes the root cause under electrical/thermal shocks.•Voids in the solder layer could accelerate the above two failure modes.•Life models for die-attach solder in IGBTs were proposed based on the physics of failure.
Abstract
Ionization sources other than H
ii
regions give rise to the right-hand branch in the standard (N
ii
) BPT diagram, populated by Seyfert 2s and LINERs. However, because the majority of ...Seyfert/LINER hosts are star-forming (SF), H
ii
regions contaminate the observed lines to some extent, making it unclear if the position along the branch is merely due to various degrees of mixing between pure Seyferts/LINERs and SF, or whether it reflects the intrinsic diversity of Seyfert/LINER ionizing sources. In this study, we empirically remove SF contributions in ∼100,000 Seyferts/LINERs from SDSS using the doppelganger method. We find that mixing is not the principal cause of the extended morphology of the observed branch. Rather, Seyferts/LINERs intrinsically have a wide range of line ratios. Variations in ionization parameter and metallicity can account for much of the diversity of Seyfert/LINER line ratios, but the hardness of the ionization field also varies significantly. Furthermore, our
k
-means classification on seven decontaminated emission lines reveals that LINERs are made up of two populations, which we call soft and hard LINERs. The Seyfert 2s differ from both types of LINERs primarily by higher ionization parameter, whereas the two LINER types mainly differ from each other (and from star-forming regions) in the hardness of the radiation field. We confirm that the N
ii
BPT diagram more efficiently identifies LINERs than S
ii
and O
i
diagnostics, because in the latter many LINERs, especially soft ones, occupy the same location as pure starformers, even after the SF has been removed from LINER emission.
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