Shi J, Yuan C, Huang H-L, Johnson J, Chae C, Wang S, Hanus R, Kim S, Cheng Z, Hwang J. Thermal Transport across Metal/β-Ga2O3 Interfaces. ACS Applied Materials & Interfaces. 2021;13(24):29083–29091.
Over the past years, perylenediimide (PDI)-based polymers have emerged as one of the widely studied polymer acceptors applicable to all-polymer solar cells (PSCs) due to their outstanding photovoltaic properties. Covalently fused PDI units, such as naphthodiperylenetetraimide (NDP), are proven beneficial to increasing the regularity of polymer backbones and enhancing the molecular packing in blend films, thus optimizing the active-layer morphology and improving the device performance. However, most investigated PDI polymers commonly demonstrated low open-circuit voltage (V-oc) in solar cells due to their low-lying lowest unoccupied molecular orbital (LUMO), which greatly limited the power-conversion efficiencies (PCEs) of their devices. Herein, we design and synthesize two new polymer acceptors (PTP-TT and PTP-Th) using thiophene-fused dimeric PDI (i.e., PTP) as the key building block. Both polymers exhibit much elevated LUMO levels at ca. -3.8 eV and achieve higher V-oc in devices compared with NDP-derived polymers. In particular, PTP-TT exhibits stronger light-absorption ability than PTP-Th and a presumably more planar backbone conformation, which are favorable for molecular packing and charge carrier transport in the active layer. Using PTB7-Th as the donor, PTP-TT-based devices achieve the best PCE of 7.04%, with a V-oc of 0.86 V, a short-circuit current density of 14.96 mA/cm(2), and a fill factor of 54%. The current results demonstrate that fusing PDIs with a proper electron-rich moiety can synergistically elevate the LUMO level and optimize the backbone regularity of polymer acceptors to obtain desirable efficiencies of PSCs.
Predicting spatial patterns in thermal tolerance and vulnerability of species under climate warming remains a challenge. Current knowledge is mainly from experiment-based thermal physiology of limited numbers of ectotherms, yet large-scale evaluations on plants remain elusive. Here, using distribution maps with spatial resolutions of 20 × 20 km for 5628 woody species in China, we propose a novel approach, i.e. thermal distribution curves, to describe species' realized thermal niches and then estimate their thermal tolerance and warming risks under projected climate warming in 2050s and 2070s. We find that species' vulnerability and potential local extinction risks within grid cells decrease with latitude and increase with aridity due to narrow thermal tolerance of species located at low latitudes and arid regions. Over 90% of species could still tolerate future warming in most areas, indicating relatively optimistic expectation of potential local extinctions. Our study presents a new framework to quantify climate warming impacts on a large number of species without sufficient physiological information and provides fundamental references for conservation planning under climate change.
Past decades have witnessed the extension of the Wi-Fi signals as a useful tool sensing human activities. One common assumption behind it is that there is a one-to-one mapping between human activities and Wi-Fi received signal patterns. However, this assumption does not hold when the user conducts activities in different locations and orientations. Actually, the received signal patterns of the same activity would become inconsistent when the relative location and orientation of the user with respect to transceivers change, leading to unstable sensing performance. This problem is known as the position-dependent problem, hindering the actual deployment of Wi-Fi-based sensing applications. In this paper, to tackle this fundamental problem, we develop a new position-independent sensing strategy and use gesture recognition as an application example to demonstrate its effectiveness. The key idea is to shift our observation from the traditional transceiver view to the hand-oriented view, and extract features that are irrespective of position-specific factors. Following the strategy, we design a position-independent feature, denoted as Motion Navigation Primitive(MNP). MNP captures the pattern of moving direction changes of the hand, which shares consistent patterns when the user performs the same gesture with different position-specific factors. By analyzing the pattern of MNP, we convert gestures into sequences of strokes (e.g, line, arc and corner) which makes them easy to be recognized. We build a prototype WiFi gesture recognition system, i.e., WiGesture to validate the effectiveness of the proposed strategy. Experiments show that our system can outperform the start-of-arts significantly in different settings. Given its novelty and superiority, we believe the proposed method symbolizes a major step towards gesture recognition and would inspire other solutions to position-independent activity recognition in the future.
In this article, we present the capacitance–voltage ( C – V ) characteristics of Hfx Zr1−x O2 metal–ferroelectric–metal (MFM) thin-film capacitors with various Zr doping, thicknesses, and annealing temperatures. The influence of doping, electric field cycling, and annealing temperature on tuning characteristics (tunability) was analyzed and an optimized bias region for the maximum tunability was defined. Additional focus was made on an antiferroelectric-like (AFE) behavior, which occurs for > 50% Zr doping. The presence of both the ferroelectric and the AFE phase manifests itself in specific C – V behavior, where a reduced bias range is required for tuning, however, at the cost of a smaller tunability. The suitability of this behavior for varactor applications is also discussed.
