科研成果

In-Memory Computing (IMC), which takes advantage of analog multiplication-accumulation (MAC) insides memory, is promising to alleviate the Von-Neumann bottleneck and improve the energy efficiency of deep neural networks (DNNs). Since the time-domain (TD) computing is also an energy-efficient analog computing paradigm, we present an 8kb mixed-signal IMC macro, TD-SRAM, by combining IMC with TD computing. A dual-edge single input (DESI) TD computing topology is proposed, which can significantly improve the area and power efficiencies of TD cell. The TD-SRAM bitcell consisting of a 6T DESI based TD cell and a 6T-SRAM cell supports binary DNNs. In the IMC mode, 60 columns work in parallel and 96-input binary-MAC operations are processed in each column. Implemented in a standard 40-nm CMOS process, the TD-SRAM achieves the high energy efficiency of 537 TOPS/W at 0.9-V supply. With different DNN topologies, the test chips achieve the accuracy of 95.90%-98.00% with a dual 2-bit time-to-digital converter (TDC) in the MNIST dataset.

Passive radiative cooling technology uses the infrared atmospheric window to allow outer space to be a cold sink for heat. However, this effect is one that is only helpful for energy savings in the warmer months. Wang et al. and Tang et al. used the metal-insulator transition in tungsten-doped vanadium dioxide to create window glass and a rooftop coating that circumvents this problem by turning off the radiative cooling at lower temperatures. Because the transition is simply temperature dependent, this effect also happens passively. Model simulations suggest that these materials would lead to energy savings year-round across most of the climate zones in the United States. —BG A smart radiative coating automatically switches thermal radiation power in response to ambient temperature. The sky is a natural heat sink that has been extensively used for passive radiative cooling of households. A lot of focus has been on maximizing the radiative cooling power of roof coating in the hot daytime using static, cooling-optimized material properties. However, the resultant overcooling in cold night or winter times exacerbates the heating cost, especially in climates where heating dominates energy consumption. We approached thermal regulation from an all-season perspective by developing a mechanically flexible coating that adapts its thermal emittance to different ambient temperatures. The fabricated temperature-adaptive radiative coating (TARC) optimally absorbs the solar energy and automatically switches thermal emittance from 0.20 for ambient temperatures lower than 15°C to 0.90 for temperatures above 30°C, driven by a photonically amplified metal-insulator transition. Simulations show that this system outperforms existing roof coatings for energy saving in most climates, especially those with substantial seasonal variations.

A highly solar active nanocomposite with sheet-like WO3 skeleton and evenly loaded TiO2 and carbon quantum dots (CQDs) was synthesized by facile hydrothermal-calcining process, which showed 3.1- and 46.6- times activity on antibiotic (cephalexin) degradation than TiO2 and WO3, respectively. The construction of TiO2/WO3 heterojunction narrowed the band gap and facilitated the electrons-holes separation. The π conjugated CQDs was found to further improve the charge separation and extend the visible light response by photosensitization. However, the promoted charge separation predominantly contributed to the improved photocatalytic activity. The contributions of detected reactive species follows the order of: O2–>1O2>OH>h+. The cephalexin degradation mechanism and pathway were proposed based on DFT (density functional theory) calculation and experimental analysis. The photocatalytic mineralization efficiency can reach 92.4% in 4 h, indicating the efficient reduction of ecotoxicity of cephalexin and its intermediates. This new composite proved to have great potentials for emerging contaminants degradation in water.

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.