S eventeen years after the severe acute respiratory syndrome (SARS) epidemic, an outbreak of pneumonia, now called coronavirus disease (COVID-19), was reported in Wuhan, China. Some of the early casepatients had a history of visiting the Huanan Seafood Wholesale Market, where wildlife mammals are sold, suggesting a zoonotic origin. The causative agent was rapidly isolated from patients and identified to be a coronavirus, now designated as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by the International Committee on Taxonomy of Viruses (1). SARS-CoV-2 has spread rapidly to other places; 113,702 cases and 4,012 deaths had been reported in 110 countries/areas as of March 10, 2020 (2). In Hong Kong, 130 cases and 3 deaths had been reported. SARS-CoV-2 is a member of subgenus Sarbecovirus (previously lineage b) in the family Coronaviridae, genus Betacoronavirus, and is closely related to SARS-CoV, which caused the SARS epidemic during 2003, and to SARS-related-CoVs (SARSr-CoVs) in horseshoe bats discovered in Hong Kong and mainland China (3-5). Whereas SARS-CoV and Middle East respiratory syndrome coronavirus were rapidly traced to their immediate animal sources (civet and dromedaries, respectively), the origin of SARS-CoV-2 remains obscure. SARS-CoV-2 showed high genome sequence identities (87.6%-87.8%) to SARSr-Rp-BatCoV-ZXC21/ ZC45, detected in Rhinolophus pusillus bats from Zhoushan, China, during 2015 (6). A closer-related strain, SARSr-Ra-BatCoV-RaTG13 (96.1% genome identity with SARS-CoV-2), was recently reported in Rhinolophus affinis bats captured in Pu'er, China, during 2013 (7). Subsequently, Pangolin-SARSr-CoV/ P4L/Guangxi/2017 (85.3% genome identity to SARS-CoV-2) and related viruses were also detected in smuggled pangolins captured in Nanning, China, during 2017 (8) and Guangzhou, China, during 2019 (9). To elucidate the evolutionary origin and pathway of SARS-CoV-2, we performed an in-depth genomic, phylogenetic, and recombination analysis in relation to SARSr-CoVs from humans, civets, bats, and pangolins (10). The Study We downloaded 4 SARS-CoV-2, 16 human/civet-SARSr-CoV, 63 bat-SARSr-CoV and 2 pangolin-SARSr-CoV genomes from GenBank and GISAID (https:// www.gisaid.org). We also sequenced the complete genome of SARS-CoV-2 strain HK20 (GenBank accession no. MT186683) from a patient with COVID-19 in Hong Kong. We performed genome, phylogenetic, and recombination analysis as described (11). The 5 SARS-CoV-2 genomes had overall 99.8%-100% nt identities with each other. These genomes showed 96.1% genome identities with SARSr-Ra-BatCoV-RaTG13, 87.8% with SARSr-Rp-BatCoV-ZC45, 87.6% with SARSr-Rp-BatCoV-ZXC21, 85.3% with pangolin-SARSr-CoV/P4L/Guangxi/2017, and 73.8%-78.6% with other SARSr-CoVs, including human/civet-SARSr-CoVs (Table 1, https://wwwnc. cdc.gov/EID/article/26/7/20-0092-T1.htm). Most predicted proteins of SARS-CoV-2 showed high amino acid sequence identities with that of SARSr-Ra-BatCoV RaTG13, except the receptor-binding

There currently lacks of a way to directly write out electronics, just like printing pictures on paper by an office printer. Here we show a desktop printing of flexible circuits on paper via developing liquid metal ink and related working mechanisms. Through modifying adhesion of the ink, overcoming its high surface tension by dispensing machine and designing a brush like porous pinhead for printing alloy and identifying matched substrate materials among different papers, the slightly oxidized alloy ink was demonstrated to be flexibly printed on coated paper, which could compose various functional electronics and the concept of Printed-Circuits-on-Paper was thus presented. Further, RTV silicone rubber was adopted as isolating inks and packaging material to guarantee the functional stability of the circuit, which suggests an approach for printing 3D hybrid electro-mechanical device. The present work paved the way for a low cost and easygoing method in directly printing paper electronics.

Materials with a temperature‐controlled reversible electrical transition between insulator and conductor are attracting huge attention due to their promising applications in many fields. However, most of them are intrinsically rigid and require complicated fabrication processes. Here, a highly stretchable (680% strain) liquid metal polymer composite as a reversible transitional insulator and conductor (TIC), which is accompanied with huge resistivity changes (more than 4 × 109 times) reversibly through a tuning temperature in a few seconds is introduced. When frozen, the insulated TIC becomes conductive and recovers after warming. Both the phase change of the liquid metal droplets and the rigidity change of the polymer contribute directly to transition between insulator and conductor. A simplified model is established to predict the expansion and connection of liquid metal droplets. Along with high stretchability, straightforward fabrication methods, rapid triggering time, large switching ratio, good repeatability, the TIC offers tremendous possibilities for numerous applications, like stretchable switches, semiconductors, temperature sensors, and resistive random‐access memory. Accordingly, a system that can display numbers and letters via converting alternative TIC temperature to a binary signal on a computer is conceived and demonstrated. The present discovery suggests a general strategy for fabricating and stimulating a stretchable transitional insulator and conductor based on liquid metal and allied polymers.

Printed electronics is becoming increasingly important in a variety of newly emerging areas. However, restricted to the rather limited conductive inks and available printing strategies, the current electronics manufacture is usually confined to industry level. Here, we show a highly cost-effective and entirely automatic printing way towards personal electronics making, through introducing a tapping-mode composite fluid delivery system. Fundamental mechanisms regarding the reliable printing, transfer and adhesion of the liquid metal inks on the substrate were disclosed through systematic theoretical interpretation and experimental measurements. With this liquid metal printer, a series of representative electronic patterns spanning from single wires to desired complex configurations such as integrated circuit (IC), printed-circuits-on-board (PCB), electronic paintings, or more do-it-yourself (DIY) devices, were demonstrated to be printed out with high precision in a moment. And the total machine cost already reached personally affordable price. This is hard to achieve by a conventional PCB technology which generally takes long time and is material, water and energy consuming, while the existing printed electronics is still far away from the real direct printing goal. The present work opens the way for large scale personal electronics manufacture and is expected to generate important value for the coming society.