Mobility and robustness are two important features for practical applications of robots. Soft robots made of polymeric materials have the potential to achieve both attributes simultaneously. Inspired by nature, this research presents soft robots based on a curved unimorph piezoelectric structure whose relative speed of 20 body lengths per second is the fastest measured among published artificial insect-scale robots. The soft robot uses several principles of animal locomotion, can carry loads, climb slopes, and has the sturdiness of cockroaches. After withstanding the weight of an adult footstep, which is about 1 million times heavier than that of the robot, the system survived and continued to move afterward. The relatively fast locomotion and robustness are attributed to the curved unimorph piezoelectric structure with large amplitude vibration, which advances beyond other methods. The design principle, driving mechanism, and operating characteristics can be further optimized and extended for improved performances, as well as used for other flexible devices.

The literature on IPOs offers a wide variety of explanations to justify the dramatic swings in the volume of IPOs observed in the market. Many theories predict that hot IPO markets are characterized by clusters of firms in particular industries for which a technological innovation has occurred, suggesting that hot and cold market IPO firms will differ in quality, prospects, or types of business. Others suggest hot market IPOs are firms that take advantage of irrational investors. We compare firms that go public in a number of hot and cold markets during 1975-2000, examining them at the time of the IPO and during the following five years. We find that both hot and cold market IPOs are largely concentrated in the same narrow set of industries and hot markets for many industries occur at the same time. We also find few distinctions in quality and scant evidence that hot market IPOs have better growth prospects. Our results suggest that technological innovations are not the primary determinant of hot markets because IPO markets cycle with greater frequency than the underlying innovations, and are more in line with the view that hot markets reflect greater investor optimism, though not necessarily active manipulation by managers.

Real-time and continuous monitoring of physiological signals is essential for mobile health, which is becoming a popular tool for efficient and convenient medical services. Here, an active pulse sensing system that can detect the weak vibration patterns of the human radial artery is constructed with a sandwich-structure piezoelectret that has high equivalent piezoelectricity. The high precision and stability of the system result in possible medical assessment applications, including the capability to identify common heart problems (such as arrhythmia); the feasibility to conduct pulse palpation measurements similar to well-trained doctors in Traditional Chinese Medicine; and the possibility to measure and read blood pressure.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201803413.imitate the TCM practice for health assessments without well-trained, real doctors. Previously, human pulse waves have been measured using sensors based on different detection mechanisms, such as optics, [16,17] image processing, [15,18,19] acoustics, [20] and pressure means, [21][22][23][24][25][26][27][28][29] etc. Among these, active pressure sensors based on the working principles of piezoelectricity [21][22][23][24] or triboelectricity [7,8] are the more intuitive and sensitive method to detect pulse waves, as these sensors can accurately and directly reflect the weak vibration of the radial artery to better imitate the pulse diagnosis in TCM. Several vertical contact-separation and single-electrode triboelectric pressure sensors have been published to detect human motion and physiological signals, with advantages of thin, flexible, and excellent sensitivity. [30] However, vertical contact-separation devices are composed of two separated parts, which increases the difficulty of assembly and operation in practice. Single-electrode triboelectric sensors have been proposed to address this issue but the exposed residual charges on the sensor surface can be easily leaked. Piezoelectret is flexible, lightweight, and have large and stable equivalent piezoelectric coefficient for high sensitivity. [25] Furthermore, sensors based on piezoelectret materials can alleviate the aforementioned issues in triboelectric sensors to detect physiological signals.In this work, we use an active and flexible pulse wave sensing system based on a fluorinated ethylene propylene (FEP)/Ecoflex/FEP sandwich-structured piezoelectret for piezoelectriclike detections. [25,26,31] Several key features are accomplished from the prototype sensing systems: 1) excellent precision and stability capable of differentiating and classifying pulses from different volunteers coupled with the help of big data analyses; 2) the identification of a common heart problem (arrhythmia) from volunteers who were previously diagnosed in hospitals equipped with advanced and bulky electrocardiogram (ECG) setups; 3) the feasibility in recording and revealing the blood pressure using the pulse sensing system instead of a ...

Agility and trajectory control are two desirable features for robotics, but they become very challenging for soft robots without rigid structures to support rapid manipulations. Here, a curved piezoelectric thin film driven at its structural resonant frequency is used as the main body of an insect-scale soft robot for its fast translational movements, and two electrostatic footpads are used for its swift rotational motions. These two schemes are simultaneously executed during operations through a simple two-wire connection arrangement. A high relative centripetal acceleration of 28 body length per square second compared with existing robots is realized on a 65-milligram tethered prototype, which is better than those of common insects, including the cockroach. The trajectory manipulation demonstration is accomplished by navigating the robot to pass through a 120-centimeter-long track in a maze within 5.6 seconds. One potential application is presented by carrying a 180-milligram on-board sensor to record a gas concentration route map and to identify the location of the leakage source. The radically simplified analog motion adjustment technique enables the scale-up construction of a 240-milligram untethered robot. Equipped with a payload of 1660 milligrams to include the control circuit, a battery, and photoresistors, the untethered prototype can follow a designated, 27.9-centimeter-long “S”-shaped path in 36.9 seconds. These results validate key performance attributes in achieving both high mobility and agility to emulate living agile insects for the advancements of soft robots.

hydrogen evolution using sustainably produced electricity has promised a carbonfree production of a chemical fuel. [5] However, most commercial hydrogen is still produced via steam reforming of methane because there are few scalable base-metal replacements for platinum at the scales required for electrocatalysis. [6] Dimensional reduction of 3D materials to 0D, 1D, or 2D nanostructures (thickness vs lateral size < 1%), [7,8] has attracted interest for discovering intriguing new catalytic properties. Notably, including 2D nanostructures comprised of metals, [9] transition metal dichalcogenides, [10][11][12] transition metal oxides, [13,14] and 2D transition metal carbides (TMCs) [15] have been explored for enhanced catalytic performance, and advances in this area have led to reliable and cost-effective fabrication methods ideal for base-metal hydrogen evolution catalysts.Among these materials, 2D TMCs possess excellent electrical conductivity, electrochemical activity, high surface area, and strong chemical resilience. [16] These make them particularly desirable for various clean energy applications such as energy storage [17][18][19] and catalysis. [7,15] The most widely applied method toward 2D TMCs requires a selective etching process from their Low-dimensional (0/1/2 dimension) transition metal carbides (TMCs) possess intriguing electrical, mechanical, and electrochemical properties, and they serve as convenient supports for transition metal catalysts. Large-area single-crystalline 2D TMC sheets are generally prepared by exfoliating MXene sheets from MAX phases. Here, a versatile bottom-up method is reported for preparing ultrathin TMC sheets (≈10 nm in thickness and >100 μm in lateral size) with metal nanoparticle decoration. A gelatin hydrogel is employed as a scaffold to coordinate metal ions (Mo 5+ , W 6+ , Co 2+ ), resulting in ultrathin-film morphologies of diverse TMC sheets. Carbonization of the scaffold at 600 °C presents a facile route to the corresponding MoC x , WC x , CoC x , and to metal-rich hybrids (Mo 2−x W x C and W/Mo 2 C-Co). Among these materials, the Mo 2 C-Co hybrid provides excellent hydrogen evolution reaction (HER) efficiency (Tafel slope of 39 mV dec −1 and 48 mV j = 10 mA cm −2 in overpotential in 0.5 m H 2 SO 4 ). Such performance makes Mo 2 C-Co a viable noble-metal-free catalyst for the HER, and is competitive with the standard platinum on carbon support. This template-assisted, self-assembling, scalable, and low-cost manufacturing process presents a new tactic to construct low-dimensional TMCs with applications in various cleanenergy-related fields. Hydrogen ElectrocatalysisThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Flexible pressure sensors with a high sensitivity in the lower zone of a subtle-pressure regime has shown great potential in the fields of electronic skin, human–computer interaction, wearable devices, intelligent prosthesis, and medical health. Adding microstructures on the dielectric layer on a capacitive pressure sensor has become a common and effective approach to enhance the performance of flexible pressure sensors. Here, we propose a method to further dramatically increase the sensitivity by adding elastic pyramidal microstructures on one side of the electrode and using a thin layer of a dielectric in a capacitive sensor. The sensitivity of the proposed device has been improved from 3.1 to 70.6 kPa−1 compared to capacitive sensors having pyramidal microstructures in the same dimension on the dielectric layer. Moreover, a detection limit of 1 Pa was achieved. The finite element analysis performed based on electromechanical sequential coupling simulation for hyperelastic materials indicates that the microstructures on electrode are critical to achieve high sensitivity. The influence of the duty ratio of the micro-pyramids on the sensitivity of the sensor is analyzed by both simulation and experiment. The durability and robustness of the device was also demonstrated by pressure testing for 2000 cycles.

The $350 billion contraction in the asset-backed commercial paper (ABCP) market in the last five months of 2007 played a central role in transforming concerns about the credit quality of mortgage-related assets into a global financial crisis. This paper attempts to better understand why the substantial contraction in ABCP occurred by measuring and analyzing runs on ABCP programs over the period from August 2007 through December 2007. While it has been suggested that commercial paper programs, like commercial banks, may be prone to runs, we are the first to conduct a comprehensive empirical analysis of runs in the ABCP market using a rich and novel issue-level data set for all ABCP programs in the U.S. market. A program is defined as being run when it does not issue new paper during a week despite having a substantial share of its outstandings scheduled to mature, and then continuing in a run until it issues. We find evidence of extensive runs: more than 100 programs (one-third of all ABCP programs) were in a run within weeks of the onset of the turmoil and the odds of subsequently leaving the run state were very low. We interpret this finding as an indication that the ABCP market was subject to a bank-like "panic." We also find that while runs were linked to credit and liquidity exposures of individual programs, runs were also related importantly to non-program specific variables in the first several weeks of the turmoil, indicating that runs were relatively indiscriminate during the early part of the panic. Thus the ABCP market may be inherently unstable and a source of systemic risk.

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