Science

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Maximizing the power conversion efficiency (PCE) of perovskite-silicon tandem solar cells that can exceed the Shockley-Queisser single-cell limit requires a high performing, stable perovskite top cell with a wide band gap. We developed a stable perovskite solar cell with a band gap of ~1.7 electron volt that retained over 80% of its initial PCE of 20.7% after 1000 hours of continuous illumination. Anion engineering of phenethylammonium (PEA)-based two-dimensional (2D) additives was critical for controlling the structural and electrical properties of 2D passivation layers based on a PbI2 -framework...

Dissipation is a general feature of non-Hermitian systems. But rather than being an unavoidable nuisance, non-Hermiticity can be precisely controlled and, hence, used for sophisticated applications such as optical sensors with enhanced sensitivity. In our work, we implement a non-Hermitian photonic mesh lattice by tailoring the anisotropy of the inter-site coupling. The appearance of an interface results in a complete collapse of the entire eigenmode spectrum, leading to an exponential localization of all modes at the interface...

Manipulation of DNA by CRISPR-Cas enzymes requires the recognition of a protospacer adjacent motif (PAM), limiting target site recognition to a subset of sequences. To remove this constraint, we engineered variants of Streptococcus pyogenes Cas9 (SpCas9) to eliminate the NGG PAM requirement. We developed a variant named SpG capable of targeting an expanded set of NGN PAMs, and further optimized this enzyme to develop a near-PAMless SpCas9 variant named SpRY (NRN>NYN PAMs). SpRY nuclease and base-editor variants can target almost all PAMs, exhibiting robust activities on a wide range of sites with NRN PAMs in human cells and lower but substantial activity on those with NYN PAMs...

Transcription polymerases can exhibit an unusual mode of regenerating certain RNA templates from RNA, yielding systems that can replicate and evolve with RNA as information carrier. Two classes of pathogenic RNAs (Hepatitis delta virus in animals and viroids in plants) are copied by host transcription polymerases. Using in vitro RNA replication by the transcription polymerase of T7 bacteriophage as an experimental model, we identify hundreds of new replicating RNAs, define three mechanistic hallmarks of replication (subterminal de novo initiation, RNA shape-shifting and interrupted rolling circle synthesis) and describe emergence from DNA seeds as a mechanism for the origin of novel RNA replicons...

Ribonucleotide reductases (RNRs) are a diverse family of enzymes that are alone capable of generating 2'-deoxynucleotides de novo and are thus critical in DNA biosynthesis and repair. The nucleotide reduction reaction in all RNRs requires the generation of a transient active site thiyl radical, and in class I RNRs this process involves a long-range radical transfer between two subunits, α and β. Due to the transient subunit association, an atomic resolution structure of an active α2β2 RNR complex has been elusive...

The ongoing COVID-19 outbreak expanded rapidly throughout China. Major behavioral, clinical, and state interventions have been undertaken to mitigate the epidemic and prevent the persistence of the virus in human populations in China and worldwide. It remains unclear how these unprecedented interventions, including travel restrictions, affected COVID-19 spread in China. We use real-time mobility data from Wuhan and detailed case data including travel history to elucidate the role of case importation on transmission in cities across China and ascertain the impact of control measures...

No abstract text is available yet for this article.

No abstract text is available yet for this article.

No abstract text is available yet for this article.

No abstract text is available yet for this article.

The COVID-19 pandemic caused by SARS-CoV-2 is a global health emergency. An attractive drug target among coronaviruses is the main protease (Mpro , 3CLpro ), due to its essential role in processing the polyproteins that are translated from the viral RNA. We report the X-ray structures of the unliganded SARS-CoV-2 Mpro and its complex with an α-ketoamide inhibitor. This was derived from a previously designed inhibitor but with the P3-P2 amide bond incorporated into a pyridone ring to enhance the half-life of the compound in plasma...

The Hayabusa2 spacecraft investigated the small asteroid Ryugu, which has a rubble pile structure. We describe an impact experiment on Ryugu using Hayabusa2's Small Carry-on Impactor (SCI). The impact produced an artificial crater with a diameter >10 m, which has a semicircular shape, an elevated rim and a central pit. Images of the impact and resulting ejecta were recorded by the Deployable CAMera 3 (DCAM3) for >8 min, showing the growth of an ejecta curtain (the outer edge of the ejecta) and deposition of ejecta onto the surface...

The endoplasmic reticulum (ER) engages mitochondria at specialized ER domains known as mitochondria-associated membranes (MAMs). Here, we used three-dimensional high-resolution imaging to investigate the formation of pleomorphic "megamitochondria" with altered MAMs in brown adipocytes lacking the Sel1L-Hrd1 protein complex of ER-associated protein degradation (ERAD). Mice with ERAD deficiency in brown adipocytes were cold sensitive and exhibited mitochondrial dysfunction. ERAD deficiency affected ER-mitochondria contacts and mitochondrial dynamics, at least in part, by regulating the turnover of the MAM protein, sigma receptor 1 (SigmaR1)...

While there have been no cases of type-2 wild poliovirus for over 20 years, transmission of type-2 vaccine-derived poliovirus (VDPV2) and associated paralytic cases in several continents represent a threat to eradication. The withdrawal of the type-2 component of oral poliovirus vaccine (OPV2) was implemented in April 2016 to stop VDPV2 emergence and secure eradication of all poliovirus type 2. Globally, children born after this date have limited immunity to prevent transmission. Using a statistical model, we estimate the emergence date and source of VDPV2s detected between May 2016 and November 2019...

The two tandem bromodomains of the BET proteins enable chromatin binding to facilitate transcription. Drugs that inhibit both bromodomains equally have shown efficacy in certain malignant and inflammatory conditions. To explore the individual functional contributions of the first (BD1) and second (BD2) bromodomains in biology and therapy, we developed selective BD1 and BD2 inhibitors. We found that steady-state gene expression primarily requires BD1 whereas the rapid increase of gene expression induced by inflammatory stimuli requires both BD1 and BD2 of all BET proteins...

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Estimation of the prevalence and contagiousness of undocumented novel coronavirus (SARS-CoV2) infections is critical for understanding the overall prevalence and pandemic potential of this disease. Here we use observations of reported infection within China, in conjunction with mobility data, a networked dynamic metapopulation model and Bayesian inference, to infer critical epidemiological characteristics associated with SARS-CoV2, including the fraction of undocumented infections and their contagiousness. We estimate 86% of all infections were undocumented (95% CI: [82%-90%]) prior to 23 January 2020 travel restrictions...

Spin-orbit coupling has proven indispensable in realizing topological materials and more recently Ising pairing in two-dimensional superconductors. This pairing mechanism relies on inversion symmetry breaking and sustains anomalously large in-plane polarizing magnetic fields whose upper limit is predicted to diverge at low temperatures. Here we show that the recently discovered superconductor few-layer stanene, i.e., epitaxially strained α-Sn, exhibits a distinct type of Ising pairing between carriers residing in bands with different orbital indices near the Γ-point...

Motivated by the rapid spread of COVID-19 in Mainland China, we use a global metapopulation disease transmission model to project the impact of travel limitations on the national and international spread of the epidemic. The model is calibrated based on internationally reported cases, and shows that at the start of the travel ban from Wuhan on 23 January 2020, most Chinese cities had already received many infected travelers. The travel quarantine of Wuhan delayed the overall epidemic progression by only 3 to 5 days in Mainland China, but has a more marked effect at the international scale, where case importations were reduced by nearly 80% until mid February...