近日，清华大学交叉信息研究院邓东灵研究组与浙江大学物理学院王浩华、宋超研究组等合作，在超导系统中首次制备了斐波那契非阿贝尔拓扑态并实现了斐波那契任意子的编织操作。自然界中常见的基础粒子分为玻色子和费米子两种，交换两个基础粒子的位置会导致系统波函数产生+1（玻色子，如光子）或-1（费米子，如电子）的相位。这是由于在三维空间中，粒子A绕粒子B一圈（等价于交换位置两次）的环路可以在不经过粒子B的情况下连续变形至消失。这限制了系统在粒子交换两次后必须回到最初的量子态，因此每交换一次系统波函数只能产生+1或-1的相因子，相应的粒子被称为玻色子或费米子，满足玻色-爱因斯坦或费米-狄拉克统计规律。而在二维空间中，粒子A绕粒子B一圈的环路无法在不经过粒子B的情况下连续变形至消失，因此没有粒子交换两次后必须回到最初的量子态的限制。在此情形下，粒子的交换可以产生任意的相位，这样的粒子被称作阿贝尔任意子（Anyon），其交换位置的过程被称作编织（braiding）。更一般地，如果系统基态存在简并，交换两个粒子甚至可以改变系统波函数的振幅，导致系统整体的幺正演化而非仅获得一个全局相位。这种粒子被称为非阿贝尔任意子。非阿贝尔任意子的研究具有重要基础理论意义和潜在应用价值。此类粒子满足非阿贝尔统计规律，是与传统玻色子和费米子有着根本不同的奇异粒子。非阿贝尔任意子也是拓扑量子计算的基石。在拓扑量子计算中，量子门由非阿贝尔任意子的编织实现，计算结果的测量则由任意子的融合（fusion）完成。任意子的拓扑性质使得这种量子计算机天生对局域错误免疫，提供了硬件层面的容错量子计算方案。尽管存在多种理论方案，非阿贝尔任意子的实验实现十分困难，直到近年来才出现在量子处理器上模拟非阿贝尔任意子的工作。然而之前所有模拟的非阿贝尔任意子其编织操作所对应的量子门均不具备通用量子计算的能力。而斐波那契任意子则拥有更加复杂的统计性质，其实验实现更为困难。斐波那契任意子量子维度为黄金分割率1.618，与数学中的斐波那契序列息息相关（图1）。其编织能实现任意量子门，可以用于构建通用的容错量子计算机。实验制备斐波那契非阿贝尔拓扑态以及实现斐波那契任意子的编织操作被广泛认为极为困难。该实验采用弦网凝聚模型，通过几何变换使得超导量子芯片方形格子上的量子比特与弦网模型中蜂窝形状的“弦”相吻合（图2）。在该模型中，系统哈密顿量由所有涡旋算符Qv和所有块算符Bp之和构成，基态中所有的弦均为闭合，而激发态中斐波那契任意子分布在开弦的两端（图2）。该实验使用了27个超导量子比特，单（双）比特门精度为99.96%（99.5%），通过115层量子线路制备了系统基态。在制备基态之后，实验通过将系统分成不同区域的方法测量了拓扑纠缠熵，所得结果与理论预言吻合。在此基础上，实验通过弦算符操作产生了两对斐波那契任意子并展示了其编织操作（图3）。实验设计了多种不同的编织次序来测试斐波那契任意子的特性（图3a），分别为：（i）斐波那契任意子与其反粒子湮灭；（ii）编织改变融合结果；（iii）和（iv）融合结果相同验证Yang-Baxter方程；（v）测量斐波那契任意子的量子维度。实验所得结果均与理论预测吻合得很好（图3b），其中根据编制次序（v）的实验结果所得的斐波那契任意子量子维度为1.598，十分接近理论预言的黄金分割率1.618。作为拓扑量子计算领域重要的基础模型，斐波那契任意子的成功模拟与编织是实现通用拓扑量子计算的基础。该研究首次制备了斐波那契非阿贝尔拓扑态并实现了斐波那契任意子的编织操作，向最终实现通用拓扑量子计算迈出了重要一步。 查看详细>>

The current method for assessing medication-related liver injury is not providing an accurate picture of some medications’toxicity—or lack thereof—to the liver,according to anew study led by researchers from the Perelman School of Medicine.Classification of amedication’s potential to damage the liver,termed“hepatotoxicity,”has been historically determined by counting individual reported cases of acute liver injury(ALI).Instead,the researchers used real-world health care data to measure rates of ALI within apopulation and uncovered that some medications’levels of danger to the liver are being misclassified,in apaper published in JAMA Internal Medicine.“Incidence rates of severe ALI can be avaluable tool for determining amedication’s toxicity to the liver and when patients should be monitored,since incidence rates provide atruer,real-world look at this toxicity.Case reports did not accurately reflect observed rates of ALI because they do not consider the number of persons exposed to amedication,and cases of drug-induced liver injury are often underreported,”says senior author Vincent Lo Re.Within the study,17 different medications had rates that exceeded five severe ALI events per 10,000“person-years,”a measure that reflects both the amount of people in agroup and how long the study observes them.The team determined that 11 of these medications were in lower categories of hepatoxicity by case counts that were likely not reflective of their true risk,since their incidence rates revealed higher levels of toxicity.To determine incidence rates,Lo Re and his team,including lead author Jessie Torgersen,an assistant professor of medicine,examined electronic medical record data on almost 8million people.Each person did not have pre-existing liver or biliary disease when they began taking any of the 194 medications that were studied.Each of those medications were analyzed due to suspicion that they could cause harm to the liver,since each had more than four published reports of liver toxicity associated with their use.On the other side of the hepatotoxicity coin,the researchers found eight medications that were classified as the most hepatotoxic based on the number of published case reports,but should actually be in the least liver-toxic group,with incidence rates of less than one severe ALI event per 10,000 person-years.With these findings,the researchers hope that there might soon be mechanisms established within electronic medical records to alert clinicians to closely monitor the liver-related laboratory tests of patients who start amedication with ahigh observed rate of severe ALI. 查看详细>>

Sean Peters is leading amajor multi-institutional initiative to develop power efficient passive radar systems that could peek under the surface of Mars.Peters has earned a$2.45 million,three-year NASA grant to create adrone-based system to map subsurface areas.The project includes field-testing on Earth with an eye toward potential future deployments on missions to the red planet.The work will be carried out in collaboration with NASA’s Jet Propulsion Laboratory,the University of Arizona,and the Reykjavik University in Iceland.“This will allow us to understand the properties of the surface,the depth of ice deposits,and areas that have potential for astro-biological studies on indicators that may support life”said Peters,an assistant professor in the Ann and H.J.Smead Department of Aerospace Engineering Sciences at the University of Colorado Boulder.Utilizing radar on adrone presents unique challenges,and Peters’team has ideas how to solve this challenging problem.Most radar technology actively transmits signals,sending out pings and tracking the response to map nearby terrain or objects.This technology has been applied to various industries,such as military,air traffic control,and the geosciences.Aboard adrone,such systems are not always practical,as they are large and power hungry.Peters has proposed amuch smaller passive radar system that,instead of emitting its own signals,would pick up natural electromagnetic waves emitted by the sun and Jupiter to conduct measurements.“You’re listening for radio noise,essentially the unwanted part in atraditional active radar,to implement this low-resource technology onboard an uncrewed aerial system for altimetry and sounding,”Peters said.“We’ve done preliminary tests with the sun,and we know this is possible.It should be possible for Jupiter too.”Taking advantage of ambient radio waves from radio-astronomical bodies was afocus of Peters’PhD thesis and has been an area of active work for nearly adecade at NASA’s Jet Propulsion Laboratory,which is apartner on the grant.“Jupiter produces radio bursts at the same frequencies as traditional ground penetrating radars,and we can measure them here on Earth.They penetrate into the ground,and our goal is to pick up and analyze the reflected signals to observe what’s below the surface,”Peters said.Peters’PhD student,Thorsteinn Kristinsson,is conducting early work on the grant.“We feel electromagnetic waves coming from the sun just going outside.You wouldn’t think looking at the sky that there are waves hitting your body from Jupiter too,but at certain times there are.”The project is incorporating both the sun and Jupiter because their electromagnetic waves cover different areas of the frequency spectrum.Jupiter’s waves are lower frequency and penetrate deeper into the ground,allowing the team to conduct additional subsurface analysis.The team will design and build the radar system and conduct initial field-testing on the ground in California within the next year.By the third year of the grant,the radar system will be incorporated into adrone for flight tests in Iceland,which has terrain analogous to Martian volcanoes.The Iceland portion of the grant is particularly exciting for Kristinsson,who grew up there and has conducted previous research in the same area.“It’s amazing.It gives me the opportunity to do work in my home country and field testing in an environment Iknow,and that is also so beautiful to be in,”Kristinsson said. 查看详细>>

Artificial intelligence models often play arole in medical diagnoses,especially when it comes to analyzing images such as X-rays.However,studies have found that these models don’t always perform well across all demographic groups,usually faring worse on women and people of color.These models have also been shown to develop some surprising abilities.In 2022,MIT researchers reported that AI models can make accurate predictions about apatient’s race from their chest X-rays—something that the most skilled radiologists can’t do.That research team has now found that the models that are most accurate at making demographic predictions also show the biggest“fairness gaps”—that is,discrepancies in their ability to accurately diagnose images of people of different races or genders.The findings suggest that these models may be using“demographic shortcuts”when making their diagnostic evaluations,which lead to incorrect results for women,Black people,and other groups,the researchers say.“It’s well-established that high-capacity machine-learning models are good predictors of human demographics such as self-reported race or sex or age.This paper re-demonstrates that capacity,and then links that capacity to the lack of performance across different groups,which has never been done,”says Marzyeh Ghassemi,an MIT associate professor of electrical engineering and computer science,a member of MIT’s Institute for Medical Engineering and Science,and the senior author of the study.The researchers also found that they could retrain the models in away that improves their fairness.However,their approached to“debiasing”worked best when the models were tested on the same types of patients they were trained on,such as patients from the same hospital.When these models were applied to patients from different hospitals,the fairness gaps reappeared.“I think the main takeaways are,first,you should thoroughly evaluate any external models on your own data because any fairness guarantees that model developers provide on their training data may not transfer to your population.Second,whenever sufficient data is available,you should train models on your own data,”says Haoran Zhang,an MIT graduate student and one of the lead authors of the new paper.MIT graduate student Yuzhe Yang is also alead author of the paper,which appears today in Nature Medicine.Judy Gichoya,an associate professor of radiology and imaging sciences at Emory University School of Medicine,and Dina Katabi,the Thuan and Nicole Pham Professor of Electrical Engineering and Computer Science at MIT,are also authors of the paper. 查看详细>>

目前普遍认为，人胚胎干细胞（hESCs）存在两种不同的多能性状态，即原始态（naive）和始发态（primed）。naive状态的干细胞类似于胚胎植入前的外胚层，具有最高的发育潜能。primed状态的干细胞类似于植入后的外胚层，在发育阶段比naïve干细胞较晚，多能性相对较低。这两种状态的干细胞在形态、克隆形成能力、信号通路、表观遗传特征和代谢等方面存在诸多差异。因此探索不同状态干细胞的稳态维持、分化以及相互转化的分子机制在发育生物学和再生医学领域十分重要。尽管近年对人胚胎干细胞的研究取得了诸多进展，但对于其多能性的调控，尤其是naïve和primed状态之间相互转化的分子事件，依然不清楚。乙酰葡萄糖胺修饰（O-GlcNAc）是真核细胞内普遍存在的一种非经典的蛋白糖基化修饰方式。由O-GlcNAc糖基转移酶（OGT）负责在蛋白上添加O-GlcNAc，O-GlcNAc糖苷酶（OGA）将O-GlcNAc从蛋白上去除，具有高度动态性；此外，它与多种信号通路相互串扰，并调节包括转录、翻译、信号转导、代谢重编程、细胞分化和胚胎发育等在内的多种重要的生理过程，以维持细胞及机体的稳态。之前针对O-GlcNAc在干细胞中的研究主要集中于OGT，而对于OGA在其中的作用却鲜有报道。2024年6月27日，浙江大学生命科学学院生物化学研究所易文教授课题组在Stem Cell Reports杂志在线发表题为“O-GlcNAcase Regulates Pluripotency States of Human Embryonic Stem Cells”的研究论文。该论文被选为7月份出版期刊的封面文章（图1）。该研究以naïve和primed两种状态的hESCs为研究对象，深入探讨OGA对naïve和primed hESCs两种多能性状态维持和相互转化的影响，以及调控primed和naïve两种状态转变的分子机制。该研究扩展了目前对人胚胎干细胞稳态调控的理解，为制备高多能性的胚胎干细胞提供了重要的实验基础。该研究中，作者首先发现OGA作为去除O-GlcNAc修饰的关键酶，其表达水平在naïve干细胞中显著高于primed干细胞（图2A）。敲低OGA显著抑制naïve干细胞的多能性，但对primed细胞的多能性没有影响；OGA的缺失促进naïve hESCs向primed方向转化（图2B）。此外，作者发现EP300转录调控OGA进而影响naïve多能性，并进一步发现EP300可结合到OGA启动子区域，其可能通过对OGA启动子结合区域的表观遗传组蛋白乙酰化修饰来介导OGA转录。进一步的转录组测序发现OGA可以调控干细胞中全局基因表达，通过调节转录调控网络、分化发育通路、MAPK/ERK以及代谢通路等影响干细胞的多能性维持及状态间转化（图3）。最后，作者通过糖基化蛋白组学揭示了primed和naïve两种状态干细胞的糖基化差异蛋白（图4），为进一步阐明O-GlcNAc糖基化在胚胎干细胞多能性的维持及两种状态相互转化中的重要作用提供了基础。 查看详细>>

Cassini observations of Saturn provide the most extensive dataset available to characterize the atmosphere of any giant planet.I will celebrate the 20th anniversary of Cassini orbit insertion at Saturn(July 1)by presenting results based on the analysis of observations of the middle and upper atmosphere obtained by the UVIS and CIRS instruments during the last two years of the Cassini mission in 2016-2017.These results provide asnapshot of the middle and upper atmosphere around the northern summer solstice,including apole-to-pole map of temperatures as well as the distribution of methane and its photochemical products.They provide evidence that the seasonal circulation pattern in the stratosphere penetrates to the thermosphere and allow us,for the first time,infer neutral wind speeds in the upper atmosphere.The retrieved temperatures and winds also demonstrate the importance auroral electrodynamics and heating in controlling both the dynamics and energy balance of the thermosphere.They indicate that polar auroral heating followed by redistribution of energy to lower latitudes(stirring),enabled by momentum deposition by gravity waves and other sources of drag(shaking),is afeasible mechanism to explain the higher than expected temperatures in the thermosphere and therefore to solve the long-standing“energy crisis”on Saturn.Given the similarity of the subsequently observed temperatures on Jupiter,the same mechanism may also explain the temperatures observed in Jupiter’s thermosphere.Finally,we conclude by providing preliminary estimates of what is required to explain the observed temperatures in the upper atmosphere of Uranus,as afirst step towards apossible common mechanism to explain the higher than expected upper atmosphere temperatures on the giant planets. 查看详细>>

Drug development is typically slow:The pipeline from basic research discoveries that provide the basis for anew drug to clinical trials and then production of awidely available medicine can take decades.But decades can feel impossibly far off to someone who currently has afatal disease.Broad Institute of MIT and Harvard Senior Group Leader Sonia Vallabh is acutely aware of that race against time,because the topic of her research is aneurodegenerative and ultimately fatal disease—fatal familial insomnia,a type of prion disease—that she will almost certainly develop as she ages.Vallabh and her husband,Eric Minikel,switched careers and became researchers after they learned that Vallabh carries adisease-causing version of the prion protein gene and that there is no effective therapy for fatal prion diseases.The two now run alab at the Broad Institute,where they are working to develop drugs that can prevent and treat these diseases,and their deadline for success is not based on grant cycles or academic expectations but on the ticking time bomb in Vallabh’s genetic code.That is why Vallabh was excited to discover,when she entered into acollaboration with Whitehead Institute for Biomedical Research member Jonathan Weissman,that Weissman’s group likes to work at full throttle.In less than two years,Weissman,Vallabh,and their collaborators have developed aset of molecular tools called CHARMs that can turn off disease-causing genes such as the prion protein gene—as well as,potentially,genes coding for many other proteins implicated in neurodegenerative and other diseases—and they are refining those tools to be good candidates for use in human patients.Although the tools still have many hurdles to pass before the researchers will know if they work as therapeutics,the team is encouraged by the speed with which they have developed the technology thus far.“The spirit of the collaboration since the beginning has been that there was no waiting on formality,”Vallabh says.“As soon as we realized our mutual excitement to do this,everything was off to the races.”Co-corresponding authors Weissman and Vallabh and co-first authors Edwin Neumann,a graduate student in Weissman’s lab,and Tessa Bertozzi,a postdoc in Weissman’s lab,describe CHARM—which stands for Coupled Histone tail for Autoinhibition Release of Methyltransferase—in apaper published today in the journal Science.“With the Whitehead and Broad Institutes right next door to each other,I don’t think there’s any better place than this for agroup of motivated people to move quickly and flexibly in the pursuit of academic science and medical technology,”says Weissman,who is also aprofessor of biology at MIT and aHoward Hughes Medical Institute Investigator.“CHARMs are an elegant solution to the problem of silencing disease genes,and they have the potential to have an important position in the future of genetic medicines.” 查看详细>>

If there’s one thing we humans are good at,it’s producing heat.Significant amounts,and in many cases most of the energy we generate and put into our systems we lose as heat,whether it be our appliances,our transportation,our factories,even our electrical grid.“Waste heat is everywhere,”said UC Santa Barbara mechanical engineering professor Bolin Liao,who specializes in thermal science and renewable energy.“Our power plants,our car exhaust pipes—there are so many places where we create excess heat waste.”For the moment,we’re fairly limited as to how we can make the most out of this dissipating heat.But Liao and UCSB colleagues,alongside collaborators from Ohio State University and University of Hong Kong are making headway toward putting that heat to use,with afirst-time comprehensive characterization of the thermoelectric properties of high-quality cadmium arsenide thin films.“If we could harvest that waste heat then that would be fantastic,”he said.“That would really increase our energy efficiency and it’s also areally sustainable energy source.”The team’s research is published in the journal Advanced Materials.A better thermoelectric material“To obtain high efficiency,we need the material to conduct electricity well,conduct heat poorly and generate ahigh voltage for agiven temperature difference,”Liao said.Poor heat conduction minimizes heat dissipation while maintaining atemperature difference across the material,resulting in an electric current enhanced by the material’s high-performing electric conductivity.The voltage resulting from atemperature gradient is known as the Seebeck effect.This combination of electrical and thermal transport properties is ideal but,according to Liao,“very hard to achieve in practice.”Enter cadmium arsenide(Cd3As2),a Dirac semimetal with promising transport properties,in particular,a low thermal conductivity and high electron mobility.“We were pretty excited about this material,and we thought‘okay,this is really acombination of these two great properties,”Liao said.“But there is only one problem.“This problem was that in addition to good electric conduction and poor thermal conduction,you also need this material to be able to generate enough voltage under atemperature gradient.”As asemimetal,cadmium arsenide is excellent at conducting electricity very rapidly,but it only generates avery small Seebeck voltage.To create auseful voltage,Liao explained,one would need to open up aband gap.“You want this material to have acertain energy range where the electrons cannot conduct.That’s called aband gap,”he said.Because of the gap,which essentially blocks the free flow of electrons,enough electrical“pressure”(a.k.a.voltage)can build up as aresponse to atemperature difference across the material.In bulk cadmium arsenide crystals,there is no band gap. 查看详细>>

6月27日下午，西安交大与吉尔吉斯斯坦国际大学签署医学教育合作备忘录。吉尔吉斯斯坦国际大学校长艾达拉利耶夫，副校长拜霍乔耶夫、阿纳巴耶夫及其驻华代表吴晨曦，西安交大副校长、一附院院长吕毅，国际教育学院院长温广瑞出席签约仪式，一附院相关部门负责人参加签约仪式，签约仪式由西安交大国际合作与交流处副处长李文华主持。吕毅副校长致欢迎词，对艾达拉利耶夫校长一行来访表示欢迎，并对吉方选择一附院作为国际医学生临床实习基地表示感谢。他讲到，西安交大医学留学生教育底蕴深厚、体系完善，一附院作为国家医学中心首批“辅导类”单位，规模体量大、医疗技术先进、科研能力突出，相信通过双方合作一定能实现资源共享、优势互补。同时，希望双方在医学人才联合培养的基础上，进一步拓展在医疗、教学和科研方面的作，为“一带一路”国家和地区医疗卫生事业发展作出应有贡献。艾达拉利耶夫校长致辞指出，吉尔吉斯斯坦国际大学已经加入了“一带一路”医科大学联盟等多个组织，借助平台力量积极发展教育事业，开展多项国际合作项目。希望在中国-中亚合作的大框架下，通过拓展双方在本硕博等领域的教育合作，提升医学生教育品质，为推动中亚研究中心的发展发挥作用，也欢迎中方校院领导访吉，深化友谊，共谋发展。国际教育学院温广瑞院长简要介绍了学校留学生情况。他提到，国际教育学院作为留学生招生、管理、就业指导部门，整体负责留学生学习生活等各方面工作。西安交大留学生体量大，留学生教育在全国一千多所开设留学生课程的院校中名列前茅，已累计培养吉尔吉斯斯坦留学生172人。 查看详细>>

Dark energy—a mysterious force pushing the universe apart at an ever-increasing rate—was discovered 26 years ago,and ever since,scientists have been searching for anew and exotic particle causing the expansion.Pushing the boundaries of this search,University of California,Berkeley physicists have now built the most precise experiment yet to look for minor deviations from the accepted theory of gravity that could be evidence for such aparticle,which theorists have dubbed achameleon or symmetron.The experiment,which combines an atom interferometer for precise gravity measurements with an optical lattice to hold the atoms in place,allowed the researchers to immobilize free-falling atoms for seconds instead of milliseconds to look for gravitational effects,besting the current most precise measurement by afactor of five.Though the researchers found no deviation from what is predicted by the theory spelled out by Isaac Newton 400 years ago,expected improvements in the precision of the experiment could eventually turn up evidence that supports or disproves theories of ahypothetical fifth force mediated by chameleons or symmetrons.The ability of the lattice atom interferometer to hold atoms for up to 70 seconds—and potentially 10 times longer—also opens up the possibility of probing gravity at the quantum level,said Holger Müller,UC Berkeley professor of physics.While physicists have well-tested theories describing the quantum nature of three of the four forces of nature—electromagnetism and the strong and weak forces—the quantum nature of gravity has never been demonstrated.“Most theorists probably agree that gravity is quantum.But nobody has ever seen an experimental signature of that,”Müller said.“It’s very hard to even know whether gravity is quantum,but if we could hold our atoms 20 or 30 times longer than anyone else,because our sensitivity increases with the second or fourth power of the hold time,we could have a400 to 800,000 times better chance of finding experimental proof that gravity is indeed quantum mechanical.”Aside from precision measurements of gravity,other applications of the lattice atom interferometer include quantum sensing.“Atom interferometry is particularly sensitive to gravity or inertial effects.You can build gyroscopes and accelerometers,”said UC Berkeley postdoctoral fellow Cristian Panda,who is first author of apaper about the gravity measurements set to be published this week in the journal Nature and is co-authored by Müller.“But this gives anew direction in atom interferometry,where quantum sensing of gravity,acceleration and rotation could be done with atoms held in optical lattices in acompact package that is resilient to environmental imperfections or noise.”Because the optical lattice holds atoms rigidly in place,the lattice atom interferometer could even operate at sea,where sensitive gravity measurements are employed to map the geology of the ocean floor.Screened forces can hide in plain sight Dark energy was discovered in 1998 by two teams of scientists:a group of physicists based at Lawrence Berkeley National Laboratory,led by Saul Perlmutter,now aUC Berkeley professor of physics,and agroup of astronomers that included UC Berkeley postdoctoral fellow Adam Riess.The two shared the 2011 Nobel Prize in Physics for the discovery. 查看详细>>