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《科学》（20220722出版）一周论文导读2022-07-24 21:40·科学网编译 | 冯维维Science, 22 July 2022, Volume 377 Issue 6604《科学》2022年7月22日，第377 卷，6604期物理化学Physical chemistryQuantum effects in thermal reaction rates at metal surfaces金属表面热反应速率的量子效应▲ 作者：DMITRIY BORODIN, NILS HERTLG. BARRATT PARK, MICHAEL SCHWARZERJAN, ALEC M. WODTKE, etc.▲ 链接：https://www.science.org/doi/10.1126/science.abq1414▲ 摘要：准确描述表面化学反应的基本步骤是一个长期的挑战，因为缺乏可靠的实验测量相应的速率常数，这使它不可能严格验证理论估计。即使是像氢原子在铂表面的热复合这样简单的反应，以前的实验速率常数也只是在很大的不确定性下得到的。使用速度分辨动力学和基于离子成像的绝对分子束通量校准，作者克服了实验困难，报告了该反应在宽温度范围内的空前准确的速率常数。他们还展示了一个定量再现实验的无参数模型，为日益增长的计算多相催化领域开辟了新的前景。▲ Abstract：Accurate description of elementary steps of chemical reactions at surfaces is a long-standing challenge because of the lack of reliable experimental measurements of the corresponding rate constants, which also makes it impossible to rigorously validate theoretical estimates. Even for reactions as simple as thermal recombination of hydrogen atoms on platinum surfaces, previous experimental rate constants have only been obtained with large uncertainties. Using velocity-resolved kinetics and ion imaging–based calibration of absolute molecular beam fluxes, Borodin et al. managed to overcome established experimental difficulties and report unprecedentedly accurate rate constants for this reaction over a wide temperature range. They also demonstrate a parameter-free model that quantitatively reproduces the experiment, opening up new vistas for the growing field of computational heterogeneous catalysis.High ambipolar mobility in cubic boron arsenide revealed by transient reflectivity microscopy用瞬态反射率显微镜观察立方砷化硼的高双极性迁移率▲ 作者：SHUAI YUE, FEI TIAN, XXINYU SUIMOHAMMADJAVAD MOHEBINIA, XIANXIN WUTIAN TONGZHIMING WANG, BO WU, QING ZHANG, XINFENG LIU▲ 链接：https://www.science.org/doi/10.1126/science.abn4727▲ 摘要：在室温条件下，半导体立方砷化硼（c-BAs）对电子的载流子迁移率为1400平方厘米/伏特秒，对空穴的载流子迁移率为2100平方厘米/伏特秒。利用泵探针瞬态反射率显微镜观察光激发载流子在单晶c-BAs中的扩散，以获得其迁移率。通过对近带隙的600纳米泵浦脉冲，作者发现高的双极迁移率为1550±120平方厘米/伏特秒，与理论预测一致。在同一地点进行的400纳米泵的额外实验显示，迁移率为>3000平方厘米/伏特秒，作者将其归因于热电子在发挥作用。高载流子迁移率的观察，结合高热导率，使c-BAs在高性能电子和光电子领域的大量器件应用成为可能。▲ Abstract：Semiconducting cubic boron arsenide (c-BAs) has been predicted to have carrier mobility of 1400 square centimeters per volt-second for electrons and 2100 square centimeters per volt-second for holes at room temperature. Using pump-probe transient reflectivity microscopy, we monitored the diffusion of photoexcited carriers in single-crystal c-BAs to obtain their mobility. With near-bandgap 600-nanometer pump pulses, we found a high ambipolar mobility of 1550 ± 120 square centimeters per volt-second, in good agreement with theoretical prediction. Additional experiments with 400-nanometer pumps on the same spot revealed a mobility of >3000 square centimeters per volt-second, which we attribute to hot electrons. The observation of high carrier mobility, in conjunction with high thermal conductivity, enables an enormous number of device applications for c-BAs in high-performance electronics and optoelectronics.High ambipolar mobility in cubic boron arsenide立方砷化硼的高双极性迁移率▲ 作者：JUNGWOO SHI, GEETHAL AMILA GAMAGE, ZHIWEI DING, KE CHEN, FEI TIAN, HWIJONG LEE, GANG CHEN, etc.▲ 链接：https://www.science.org/doi/10.1126/science.abn4290▲ 摘要：具有高热导率和高电子-空穴迁移率的半导体对于电子器件和光子器件以及基础研究具有重要意义。在这些超高导热材料中，立方砷化硼（c-BAs）的电子和空穴迁移率将同时达到>1000厘米平方/伏特/秒。利用光学瞬变光栅技术，作者在室温下实验测量了c-BAs样品的相同位置，其热导率为每米每开尔文1200瓦，双极迁移率为每伏特每秒1600平方厘米。从头计算表明，降低电离杂质浓度和中性杂质浓度是获得高迁移率和高热导率的关键。由于具有高的双极性移动性和超高的热导率，c-BAs有望成为下一代电子产物的候选材料。▲ Abstract：Semiconductors with high thermal conductivity and electron-hole mobility are of great importance for electronic and photonic devices as well as for fundamental studies. Among the ultrahigh–thermal conductivity materials, cubic boron arsenide (c-BAs) is predicted to exhibit simultaneously high electron and hole mobilities of >1000 centimeters squared per volt per second. Using the optical transient grating technique, we experimentally measured thermal conductivity of 1200 watts per meter per kelvin and ambipolar mobility of 1600 centimeters squared per volt per second at the same locations on c-BAs samples at room temperature despite spatial variations. Ab initio calculations show that lowering ionized and neutral impurity concentrations is key to achieving high mobility and high thermal conductivity, respectively. The high ambipolar mobilities combined with the ultrahigh thermal conductivity make c-BAs a promising candidate for next-generation electronics.化学ChemistryPhysical mixing of a catalyst and a hydrophobic polymer promotes CO hydrogenation through dehydration催化剂和疏水聚合物的物理混合通过脱水促进一氧化碳氢化▲ 作者：WEI FANG, CHENGTAO WANG, LIANG WANG, LU LIU, HANGJIE LI, FENG-SHOU XIAO, etc.▲ 链接：https://www.science.org/doi/10.1126/science.abo0356▲ 摘要：在许多受水限制的反应中，选择性地从反应系统中去除水至关重要，通常需要膜反应器。作者发现，疏水聚二乙烯苯与钴锰碳化物的简单物理混合物可以调节催化剂的局部环境，以快速运输合成气转化中的水产物。这能够改变催化剂表面的水吸附平衡，导致更大比例的自由表面，反过来将合成气转化率提高近2倍。在250℃条件下，一氧化碳转化率达到63.5%，71.4%的烃类产物为轻烯烃，优于同等条件下的无聚二乙烯苯催化剂。物理混合钴锰碳/聚二乙烯苯催化剂在120小时的连续测试中具有良好的耐久性。▲ Abstract：In many reactions restricted by water, selective removal of water from the reaction system is critical and usually requires a membrane reactor. We found that a simple physical mixture of hydrophobic poly(divinylbenzene) with cobalt-manganese carbide could modulate a local environment of catalysts for rapidly shipping water product in syngas conversion. We were able to shift the water-sorption equilibrium on the catalyst surface, leading to a greater proportion of free surface that in turn raised the rate of syngas conversion by nearly a factor of 2. The carbon monoxide conversion reached 63.5%, and 71.4% of the hydrocarbon products were light olefins at 250°C, outperforming poly(divinylbenzene)-free catalyst under equivalent reaction conditions. The physically mixed CoMn carbide/poly(divinylbenzene) catalyst was durable in the continuous test for 120 hours.物理学PhysicsAmplified emission and lasing in photonic time crystals光子时间晶体中的放大发射和激光▲ 作者：MARK LYUBAROV, YAAKOV LUMERALEX DIKOPOLTSEV, ERAN LUSTIG, YONATAN SHARABIAND MORDECHAI SEGEV▲ 链接：https://www.science.org/doi/10.1126/science.abo3324▲ 摘要：规则光子晶体是一种折射率具有空间周期性的结构，可以抑制结构中嵌入的发射器的自发光发射。在光子时间晶体中，折射率在超快时间尺度上周期性地调制。作者从理论上探索了当一个发射器被放置在这样一个时间晶体中会发生什么。与常规光子晶体相比，作者发现时间晶体应该放大发射，产生激光。▲ Abstract：Regular photonic crystals are structures in which the refractive index is spatially periodic and can suppress the spontaneous emission of light from an emitter embedded in the structure. In photonic time crystals, the refractive index is periodically modulated in time on ultrafast time scales. Lyubarov et al. explored theoretically what happens when an emitter is placed in such a time crystal. In contrast to the regular photonic crystals, the authors found that time crystals should amplify emission, leading to lasing.生物多样性BiodiversityInterspecific competition limits bird species’ ranges in tropical mountains种间竞争限制了热带山区鸟类的活动范围▲ 作者：BENJAMIN G. FREEMAN, MATTHEW STRIMAS-MACKEY AND ELIOT T. MILLER▲ 链接：https://www.science.org/doi/10.1126/science.abl7242▲ 摘要：物种的地理范围受到气候和物种相互作用的限制。气候是解释为什么物种只能生活在极具生物多样性的热带山脉的狭窄海拔范围内的普遍原因，但竞争也会限制物种的海拔范围。作者通过在31个山地地区进行鸟类海拔范围大小的全球比较测试来检验这些假设的对比预测，使用来自全球公民项目eBird的440多万公民科学记录，来定义每个地区物种的海拔范围。他们找到了强有力的证据，证明竞争、而非气候，是狭窄海拔范围的主要驱动因素。这些结果强调了物种相互作用在塑造热带山区物种分布范围中的重要性，热带山区是地球上最热门的生物多样性热点地区。▲ Abstract：Species’ geographic ranges are limited by climate and species interactions. Climate is the prevailing explanation for why species live only within narrow elevational ranges in megadiverse biodiverse tropical mountains, but competition can also restrict species’ elevational ranges. We test contrasting predictions of these hypotheses by conducting a global comparative test of birds’ elevational range sizes within 31 montane regions, using more than 4.4 million citizen science records from eBird to define species’ elevational ranges in each region. We find strong support that competition, not climate, is the leading driver of narrow elevational ranges. These results highlight the importance of species interactions in shaping species’ ranges in tropical mountains, Earth’s hottest biodiversity hotspots.
2025年01月17日，这样设置应该是为了比较长的公交车掉头，因为转弯半径太大的缘故。
《原纱央莉之重装上阵》免费HD在线播放 -华惠影院《驯服小姨子》全集完整版免费在线观看_电影_八戒影院
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传记作家沃尔特·艾萨克森如此形容刚参加工作时的乔布斯：光脚，长发，套着嬉皮士风格的外套，全身散发半个月不洗澡的异味。民警在涵洞内查找了一圈，最终将目标锁定在一个编织袋上面，腐败的味道就是从这个编织袋散发出来的，当打开这个编织袋，发现里面是一具被肢解的尸体。