《科學》（20240329出版）一周論文導讀

Science, 29 MAR 2024, VOL 383, ISSUE 6690

《科學》2024年3月29日，第383卷，6690期

物理學Physics

Ultrafast Kapitza-Dirac effect

超快卡皮查—狄拉克效應

▲ 作者：Kang Lin, Sebastian Eckart, Hao Liang, Alexander Hartung, Sina Jacob, Qinying Ji, et al.

▲ 鏈接：

https://www.science.org/doi/10.1126/science.adn1555

▲ 摘要：

類似于光通過材料光柵的光學衍射，當電子被駐波光場衍射時，就會發生卡皮查—狄拉克效應。在最初的描述中，這種效應與時間無關。

研究組將卡皮查—狄拉克效應擴展到時域。通過跟蹤60飛秒（其中1飛秒= 10?15秒）駐波脈沖衍射的脈沖電子波包在泵浦探測方案中的時空演化，觀察到了隨時間變化的衍射模式。

觀察到的模式條紋間距與傳統卡皮查—狄拉克效應產生的條紋間距不同。通過利用這種時間分辨衍射方案，研究組可獲得自由電子相位特性的時間演化，并有望成像離子勢和電子退相干。

▲ Abstract：

Similar to the optical diffraction of light passing through a material grating, the Kapitza-Dirac effect occurs when an electron is diffracted by a standing light wave. In its original description, the effect is time independent. Here, we extended the Kapitza-Dirac effect to the time domain. By tracking the spatiotemporal evolution of a pulsed electron wave packet diffracted by a 60-femtosecond (where one femtosecond = 10?15 seconds) standing wave pulse in a pump-probe scheme, we observed time-dependent diffraction patterns. The fringe spacing in the observed pattern differs from that generated by the conventional Kapitza-Dirac effect. By exploiting this time-resolved diffraction scheme, we can access the time evolution of the phase properties of a free electron and potentially image ionic potentials and electronic decoherences.

材料科學Materials Science

A hyperelastic hydrogel with an ultralarge reversible biaxial strain

具有超大可逆雙軸應變的超彈性水凝膠

▲ 作者：Lili Chen, Zhekai Jin, Wenwen Feng, Lin Sun, Hao Xu & Chao Wang

▲ 鏈接：

https://www.science.org/doi/10.1126/science.adh3632

▲ 摘要：

超彈性材料對大應變表現出非線性彈性響應，而水凝膠由于交聯不均勻和交聯間鏈段有限，通常具有較低的彈性范圍。

研究組通過引入可逆的珍珠項鏈結構（珠子由繩子連接）開發了一種具有更寬彈性范圍的超彈性水凝膠。亞納米微珠在循環機械應變下能高效展開并重新折疊；因此，水凝膠在被拉伸至面應變超過10000%后可迅速恢復。

此外，水凝膠可從輕微機械損傷（如針扎和割傷）中快速愈合。這些進展使該離子水凝膠成為多功能氣動夾具材料的理想選擇，可同時提供超大抓握范圍、自我感知能力和快速愈合能力。

▲ Abstract：

Hyperelastic materials exhibit a nonlinear elastic response to large strains, whereas hydrogels typically possess a low elastic range due to the nonuniform cross-linking and limited chain segments among cross-links. We developed a hyperelastic hydrogel that possesses a broader elastic range by introducing a reversible pearl-necklace structure, in which beads are connected by strings. The subnanometric beads can efficiently unfold and refold under cyclic mechanical strains; thus, the hydrogel can rapidly recover after being stretched to an areal strain of more than 10,000%. Additionally, the hydrogel can quickly heal from minor mechanical damages such as needle punctures and cuts. These advancements make our ionic hydrogels ideal for multifunctional pneumatic gripper materials; they simultaneously offer an ultralarge gripping range, self-sensing capabilities, and fast healing abilities.

化學Chemistry

Biodegradable ferroelectric molecular crystal with large piezoelectric response

具有大壓電響應的可生物降解鐵電分子晶體

▲ 作者：Han-Yue Zhang, Yuan-Yuan Tang, Zhu-Xiao Gu, Peng Wang, Xiao-Gang Chen, Hui-Peng Lv, et al.

▲ 鏈接：

https://www.science.org/doi/10.1126/science.adj1946

▲ 摘要：

瞬態可植入壓電材料是生物傳感、藥物傳遞、組織再生、抗菌和腫瘤治療的理想材料。為了在人體中使用，這種壓電材料必須表現出靈活性、生物相容性和生物可降解性。這些要求對傳統的無機壓電氧化物和壓電聚合物而言頗具挑戰。

研究組發現分子晶體HOCH2(CF2)3CH2OH [2,2,3,3,4,4—六氟戊烷—1,5—二醇（HFPD）]具有高壓電性，無需極化處理的大壓電系數d33約為138 pC/N，壓電電壓常數g33約為2450 × 10?3 Vm/N，具有良好的生物細胞相容性，在生理環境中表現出良好的生物降解性和生物安全性。

HFPD可與聚乙烯醇復合，以形成d33為34.3 pC/N的柔性壓電薄膜。該材料證明了分子晶體具有吸引人的壓電特性，且有望應用于瞬態可植入機電設備。

▲ Abstract：

Transient implantable piezoelectric materials are desirable for biosensing, drug delivery, tissue regeneration, and antimicrobial and tumor therapy. For use in the human body, they must show flexibility, biocompatibility, and biodegradability. These requirements are challenging for conventional inorganic piezoelectric oxides and piezoelectric polymers. We discovered high piezoelectricity in a molecular crystal HOCH2(CF2)3CH2OH [2,2,3,3,4,4-hexafluoropentane-1,5-diol (HFPD)] with a large piezoelectric coefficient d33 of ~138 picocoulombs per newton and piezoelectric voltage constant g33 of ~2450 ×10?3?volt-meters per newton under no poling conditions, which also exhibits good biocompatibility toward biological cells and desirable biodegradation and biosafety in physiological environments. HFPD can be composite with polyvinyl alcohol to form flexible piezoelectric films with a d33 of 34.3 picocoulombs per newton. Our material demonstrates the ability for molecular crystals to have attractive piezoelectric properties and should be of interest for applications in transient implantable electromechanical devices.

人工智能Artificial Intelligence

Mechanism for feature learning in neural networks and backpropagation-free machine learning models

神經網絡中的特征學習機制與無反向傳播機器學習模型

▲ 作者：Adityanarayanan Radhakrishnan, Daniel Beaglehole, Parthe Pandit & Mikhail Belkin

▲ 鏈接：

https://www.science.org/doi/10.1126/science.adi5639

▲ 摘要：

了解神經網絡如何學習數據中的特征或相關模式以進行預測，對于其在技術和科學應用中的可靠使用至關重要。

在這項工作中，研究組提出了一種統一的數學機制，稱為平均梯度外積（AGOP），以表征神經網絡中的特征學習。他們提供了AGOP可捕獲各種神經網絡架構所學習特征的經驗證據，包括基于轉換器的語言模型、卷積網絡、多層感知器和遞歸神經網絡。

此外，還證明了無反向傳播的AGOP在機器學習模型（如內核機器）中實現了特征學習，而先驗不能識別特定于任務的特征。總而言之，研究組建立了一個基本機制，可在神經網絡中捕獲特征學習，并在通用機器學習模型中實現特征學習。

▲ Abstract：

Understanding how neural networks learn features, or relevant patterns in data, for prediction is necessary for their reliable use in technological and scientific applications. In this work, we presented a unifying mathematical mechanism, known as average gradient outer product (AGOP), that characterized feature learning in neural networks. We provided empirical evidence that AGOP captured features learned by various neural network architectures, including transformer-based language models, convolutional networks, multilayer perceptrons, and recurrent neural networks. Moreover, we demonstrated that AGOP, which is backpropagation-free, enabled feature learning in machine learning models, such as kernel machines, that a priori could not identify task-specific features. Overall, we established a fundamental mechanism that captured feature learning in neural networks and enabled feature learning in general machine learning models.

地球科學Earth Science

Quantifying methane emissions from United States landfills

量化美國垃圾填埋場的甲烷排放

▲ 作者：Daniel H. Cusworth, Riley M. Duren, Alana K. Ayasse, Ralph Jiorle, Katherine Howell, Andrew Aubrey, et al.

▲ 鏈接：

https://www.science.org/doi/10.1126/science.adi7735

▲ 摘要：

來自固體廢物的甲烷排放可能占全球人為預算的很大一部分，但很少有全面研究來評估存量假設。

研究組使用空中成像光譜儀對2016年至2022年間美國18個州數百個大型垃圾填埋場的排放量進行了量化。該研究覆蓋了美國20%的開放垃圾填埋場，代表了對廢物部門甲烷點源最系統的測量研究。

研究組在大多數（52%）站點檢測到顯著的點源甲烷排放，其中許多站點的排放持續多次檢測（數周至數年）。將這些數據與15個垃圾填埋場的獨立同期原位航空觀測數據進行比較，并建立了良好的一致性。

該研究結果表明，在氣候變化減緩政策的背景下，有必要對垃圾填埋場甲烷排放進行長期的天氣尺度監測。

▲ Abstract：

Methane emissions from solid waste may represent a substantial fraction of the global anthropogenic budget, but few comprehensive studies exist to assess inventory assumptions. We quantified emissions at hundreds of large landfills across 18 states in the United States between 2016 and 2022 using airborne imaging spectrometers. Spanning 20% of open United States landfills, this represents the most systematic measurement-based study of methane point sources of the waste sector. We detected significant point source emissions at a majority (52%) of these sites, many with emissions persisting over multiple revisits (weeks to years). We compared these against independent contemporaneous in situ airborne observations at 15 landfills and established good agreement. Our findings indicate a need for long-term, synoptic-scale monitoring of landfill emissions in the context of climate change mitigation policy.

公共衛生Public Health

Design of a SARS-CoV-2 papain-like protease inhibitor with antiviral efficacy in a mouse model

在小鼠模型中設計具有抗病毒功效的SARS-CoV-2木瓜酶樣蛋白酶抑制劑

▲ 作者：Bin Tan, Xiaoming Zhang, Ahmadullah Ansari, Prakash Jadhav, Haozhou Tan, Kan Li, et al.

▲ 鏈接：

https://www.science.org/doi/10.1126/science.adm9724

▲ 摘要：

SARS-CoV-2變異株和耐藥突變體的出現要求使用更多的口服抗病毒藥物。SARS-CoV-2木瓜酶樣蛋白酶（PLpro）是一個有前景但頗具挑戰性的藥物靶點。

研究組設計并合成了85種非共價PLpro抑制劑，其與最近發現的泛素結合位點和S4亞位點附近的已知BL2凹槽袋相結合。先導物抑制PLpro的抑制常數Ki值為13.2至88.2納摩爾。八種先導物的PLpro共晶結構揭示了其相互作用模式。

體內先導Jun12682抑制SARS-CoV-2及其變異株，包括耐尼馬特瑞韋株，EC50在0.44至2.02微摩爾之間。在SARS-CoV-2感染小鼠模型中，口服Jun12682可改善生存，減少肺部病毒載量和病變，這表明PLpro抑制劑是頗有前景的口服SARS-CoV-2抗病毒候選藥物。

▲ Abstract：

The emergence of SARS-CoV-2 variants and drug-resistant mutants calls for additional oral antivirals. The SARS-CoV-2 papain-like protease (PLpro) is a promising but challenging drug target. We designed and synthesized 85 noncovalent PLpro inhibitors that bind to a recently discovered ubiquitin binding site and the known BL2 groove pocket near the S4 subsite. Leads inhibited PLpro with the inhibitory constant Ki values from 13.2 to 88.2 nanomolar. The co-crystal structures of PLpro with eight leads revealed their interaction modes. The in vivo lead Jun12682 inhibited SARS-CoV-2 and its variants, including nirmatrelvir-resistant strains with EC50 from 0.44 to 2.02 micromolar. Oral treatment with Jun12682 improved survival and reduced lung viral loads and lesions in a SARS-CoV-2 infection mouse model, suggesting that PLpro inhibitors are promising oral SARS-CoV-2 antiviral candidates.