News on China's scientific and technological development.

Scientists from SJTU and HKU created a jellyfish like phototactic artificial creature.

"The untethered, electronics-free, ambient-powered hydrogel vehicle manoeuvres through obstacles agilely, following illumination cues of moderate intensities, similar to that of natural sunlight."

Paper:

Self-regulated underwater phototaxis of a photoresponsive hydrogel-based phototactic vehicle​

Abstract​

Incorporating a negative feedback loop in a synthetic material to enable complex self-regulative behaviours akin to living organisms remains a design challenge. Here we show that a hydrogel-based vehicle can follow the directions of photonic illumination with directional regulation inside a constraint-free, fluidic space. By manipulating the customized photothermal nanoparticles and the microscale pores in the polymeric matrix, we achieved strong chemomechanical deformation of the soft material. The vehicle swiftly assumes an optimal pose and creates directional flow around itself, which it follows to achieve robust full-space phototaxis. In addition, this phototaxis enables a series of complex underwater locomotions. We demonstrate that this versatility is generated by the synergy of photothermofluidic interactions resulting in closed-loop self-control and fast reconfigurability. The untethered, electronics-free, ambient-powered hydrogel vehicle manoeuvres through obstacles agilely, following illumination cues of moderate intensities, similar to that of natural sunlight.

News release:

钱小石教授团队研发自决策软体载具实现水下全空间的趋光性运动

近日，上海交通大学机械与动力工程学院前瞻交叉研究中心的钱小石教授团队与香港大学机械工程系Nicholas X. Fang教授合作开发了一种整体的、刺激响应的趋光软体载具（PTV），具有类似水母的对称性几何结构，能够迅速的朝向任意方向的稳定光源自主运动，并根据光源方向的变化，实时准确追踪。该研究工作以题为“Self-regulated underwater phototaxis of photoresponsive hydrogel-based phototactic vehicle”的研究论文发表在《Nature Nanotechnology》上。博士研究生侯国栋为该论文的第一作者，钱小石教授为通讯作者，香港大学Nicholas X. Fang教授为共同通讯作者。

在海洋中，有一些漂浮的小生物能感知到水中光线的变化。它们可以根据光线的强弱，自主调整自己的运动，以便捕捉到食物、寻找繁殖的机会，并远离危险。这些生物的调整运动有很多种，包括趋光性、趋涡性、趋流性和趋化性等，让它们可以根据环境的变化，自主选择移动的方向。这种能力让它们看起来有点像在做“决策”。要实现这种“决策”，生物体需要在受到刺激时产生驱动力，并在合适的时候停止驱动。目前，人类制造的一些人工系统也有类似的反馈控制功能，但这些功能往往需要依赖预先编程的电子电路控制，或者人为的遥控操作。 然而，如果不依赖电子控制或人工干预，仅仅使用均匀的材料，我们还很难实现像这些小生物一样，可以无拖线、自主决策地在整个空间内进行趋光性运动。这个领域仍有许多挑战等待我们去克服和研究。

在光照条件下，PTV利用定向光子能量引发温度、流场和几何形态上的非对称性。光子诱导的多场可逆非对称性使PTV能够对任何入射方向做出响应（图1a），从而产生可提供动力的向光流体运动（图1b），并自发地采取最佳姿态进行低阻力的向光游动（图1c）。为了避免因受热表面引起的上升流而产生的偏移运动，PTV能够自适应地增强受热表面的对流换热，从而为纠正方向偏差提供负反馈（图1d）。此智能系统采用一种快速驱动和恢复的刺激响应水凝胶为基质材料，对来自不同方向的光照能做出快速响应（图1e）。高灵敏度和可逆的化学机械反应使其能够在温和的光照条件下（＜1 Sun），实现对全空间的向光性和精准操纵（见图1g、h）。

一旦受到光照，PTV的三种非对称特性同时被激发，从而形成新的温度梯度、流场梯度和机械应变梯度（图2a-d）。为了实现长期且对等的驱动和恢复，作者通过控制材料制备的化学和物理过程来改变凝胶的孔隙度。在16°的角度下，冰模板辅助下混合交联的水凝胶柱在不到一秒的时间内完全恢复原状（图2f），其恢复速度与其收缩速度相当，比之前报道的最佳值快了30倍。PTV中内嵌的光热响应材料r-GO和AuNPs有效地将光能转化为热能，当从上方照射光线时，PTV迅速上升至水面（图2i）。表面的温升引发向上的对流，传递了方向信息（图2j）。PIV测试结果与CFD模拟结果相当吻合（图2j、k）。水平光照时，右侧的水平辐照引起温度和流场的非对称性，在光照一侧产生更高的温度和流速（图2o）。被加热的表面反映了入射光的方向信息，但也会引发上升流，使PTV向右上方移动（图2m）。CFD和PIV结果（图2n、o）表明，流场中的大部分是向上对流，这可能导致水平光线照射时的准确性降低（图2m）。

在白光照射下，与r-GO耦合的PTV表现出自主向上和向右的跃迁，然后回到底部，实现了水平趋光性（见图3a）。分析结果表明，PTV加速时遇到环境冷流体的速度更快，随之而来的冷却终止了上升流，使PTV重新回到正常运动轨迹。大量的对流传热向环境中释放的热量(q=-hA(T_s-T_f ))超过了输入光子的功率（P），因此引发了表面温度的振荡，从而构建了负反馈回路（图3b，3c）。在阳光照射下，PTV始终停留在容器底部（图3e）。一旦受到光照，PTV立即开始游向水面（图3f）。与AuNPs结合的PTV同样也能够向光源方向跳跃（图3g）。由于光束宽度相对较窄，上升的PTV会通过远离照明的方式降低表面温度，从而完成负反馈循环。作者定量研究了无量纲理查森数（Ri=Gr/Re2）来探究自然对流和强制对流的相对权重。尽管在两种情况下努塞尔特数（Nu=16.9）相当，但激光照射时的Ri为144.0（≫1），从而证实了自然对流在冷却中占主导地位。而在宽光束照射下，Ri=6.8，说明速度诱导的混合对流在自适应调节中扮演重要角色（图3i）。

桨状触手获取动量时容易与激光束错位，由光-热-流体驱动的PTV在较长距离上表现出鲁棒的趋光性却几乎没有方向偏差（图4a、b）。将六根偏离中心位置的触手巧妙地级联，PTV能够自适应的旋转前进（图4c）。响应性触手会向光源方向弯曲并抵消倾覆力矩，从而在PTV爬上坡道时提供额外的稳定性（图4d）。由于聚合物基体自发诱导的非对称性和快速恢复特性，PTV的定向响应是即时的。PTV具备灵活操控的能力的同时还具有出色的方向和位置分辨率。在恒定光源的连续变化角度下，PTV可以完美地模仿中国书法汉字“自然”（图4e）中复杂的笔画运动。与在水面浸没时的趋光性不同，由于马兰戈尼对流效应，当PTV浮在气水界面上时，会避开光线（图4f）。

在这项研究中，团队通过调整水凝胶纳米复合材料内部的光-热-机械-流体相互作用，成功实现了人工趋光性。这种趋光性不依赖于对光源或边界条件的特殊要求，通过建立负反馈回路来调控水凝胶系统的运动，PTV能够在没有明显远距离偏离的情况下追踪光线，并能够在适度而持续的光照下精确地转向复杂的路径。考虑到PTV仅具有一个负反馈回路，因此探索涉及更多控制回路的策略可能会使这种不受约束、不需要电子元件、能够自给自足能源的材料系统具备多功能的调节行为。

该研究依托材料科学、热科学、光学、流体力学、机械制造等多个领域的交叉合作，上海交通大学机械与动力工程学院的孟光教授、陈江平教授、吴亚东副研究员、汪华苗副教授、杨光副教授、刘振宇副教授以及南方科技大学机械与能源工程系的葛锜副教授也参与了该项研究。研究工作得到了国家重点研发计划项目，国家自然科学基金项目，上海市自然科学基金项目，机械系统与振动全国重点实验室开放课题等项目的支持。

A team led by Prof. Qian Xiaoshi who created the artificial jellyfish above also made breakthrough in electrocaloric (EC) materials which can lead to more efficient EC cooling devices.

Paper:

Molecular interface regulation enables order-disorder synergy in electrocaloric nanocomposites​

• Flexible nanocomposites maintaining both high ECE and high thermal conductivity
• Covalent linked organic-inorganic interfaces enhance free space for phase transition
• A figure of merit (EPCQ) is proposed for evaluating electrocaloric nanocomposites
• High thermal conductivity enables great performance enhancement in EC cooling devices

Summary​

High thermal conductivities are highly desired for electrocaloric (EC) materials to improve the key performances of EC devices, including cooling power density (CPD) and coefficient of performance (COP). However, despite the large EC effect (ECE), the state-of-the-art EC polymer exhibits low thermal conductivity. The simple mixture of the EC polymer and two-dimensional (2D) high-thermal-conductivity nanofillers would dramatically reduce ECE by increasing long-range ordering. To free dipole orientations, we introduced 3-sulfurouspropyltrimethoxysilane (SPTMS) to covalently graft boron-nitride nanosheets on the EC polymer. The interface-regulated nanocomposite exhibited the EC entropy change of 30.94 Jkg−1K−1 under 100 MVm−1 and thermal conductivity of 0.72 Wm−1K−1, and utilizing which, the standard model of EC refrigerator achieved a 5.23 Wg−1 CPD, 6.8-fold higher than the one operating a simple mixture. A figure of merit of electrocaloric nanocomposites was proposed to assess their overall capability in the heat-pumping applications.


News release:

钱小石教授团队实现纳米复合电卡聚合物材料的有序-无序协同调控

近日，上海交通大学机械与动力工程学院前瞻交叉研究中心的钱小石教授团队在Joule期刊在线发表题为“Molecular interface regulation enables order-disorder synergy in electrocaloric nanocomposites”的研究论文。博士研究生韩东霖是论文第一作者，钱小石教授是通讯作者。

电卡效应来源于电偶极子熵变，往往需要材料偶极的混乱，然而热导率的提升则依赖有序晶格结构，在一般的复合材料中同时实现高偶极无序度与高热导率是较为矛盾的。针对这个问题，该研究通过一种复合材料界面调控的策略，将功能化的高导热BNNS作为填料，通过点击化学方法将SPTMS硅烷分子共价链接到电卡聚合物P(VDF-TrFE-CFE)分子链上，合成了BNNS-SPTMS-TP复合材料，增加了BNNS与聚合物链段的间距，避免了BNNS的高度有序结构对复合材料电卡效应的钳制作用，在大幅提升聚合物的热导率的同时维持了聚合物在低电场下的高熵变，实现了高热导率有序排列与电卡高熵无序排列之间的协同调控。

电卡（Electrocaloric，EC）制冷能够直接高效利用电能，易于实现高COP和低TEWI。EC聚合物材料凭借其柔性、自修复、低成本等优点受到学术界的广泛关注。然而，低热导率是掣肘EC聚合物应用的关键问题。在聚合物中添加高热导率纳米填料是改善其热导率的有效手段。在这项工作中，为了避免填料的EC效应对聚合物性能带来的干扰，钱小石教授团队将电学惰性的BNNS作为填料，掺杂至P(VDF-TrFE-CFE)三元共聚物（terpolymer），并通过界面调控合成了BNNS-SPTMS-TP，这种材料兼具高热导率、高熵变、宽工作温度窗口、高击穿场和高机械模量等特性，有效提高了EC制冷器件的制冷功率密度和温宽，为EC制冷器件的设计提供了便利。

团队以该复合材料为制冷核心制备了电卡制冷器件，其中高分子复合材料在系统热沉与热源之间形成布雷顿循环。在相同材料厚度的条件下，更高的热导率能有效缩短热传递时间，进而输出更大的制冷量和COP。器件实际运行结果表明，简单地将BNNS与terpolymer掺杂虽然可以有效提高热导率，但得到的BNNS/TP电致熵变显著恶化，这再次指出了高导热率要求的结构有序性和高电致熵变要求的极性无序性之间存在矛盾。作者利用SPTMS分子限制将BNNS与弛豫铁电高分子交联，撑开了并限制了BNNS和聚合物链之间的空间，让有序结构与无序结构各司其职，同时实现了材料的大电卡熵变和高热导率。

在100MV/m的电场下，terpolymer的熵变为29 J/kgK，而BNNS/TP的熵变降低至16 J/kgK，BNNS-SPTMS-TP的熵变增加至31 J/kgK。SAXS的表征结果合理解释了这一现象。BNNS/TP在32 nm和16 nm附近出现了明显的长程序峰，而BNNS-SPTMS-TP的峰值相比terpolymer更弱。DFT计算结果一方面佐证了SAXS数据，另一方面说明BNNS-SPTMS-TP的相变能垒更低。进一步地，在原位WAXD测试中发现BNNS-SPTMS-TP的相转变比例更大，结晶晶粒尺寸更小。

通过介电性能表征发现，由于相同电场下BNNS-SPTMS-TP的极化强度更低，其介电损耗大幅下降。在不同温度和频率下对聚合物的介电常数进行测试，发现BNNS-SPTMS-TP的介电常数更低。高熵变与低极化说明BNNS-SPTMS-TP的beta系数更大，即更符合极化高熵体系的要求。进一步地，不同温度下的熵变测试结果表明，BNNS-SPTMS-TP能在更宽的温度区间内维持高熵变性能。

在薄膜EC制冷器件中，由于BNNS-SPTMS-TP兼具高导热性和高熵变特性，与简单混合的BNNS/TP和terpolymer相比，使用BNNS-SPTES-TP的器件具有更大的制冷功率密度。

团队设计了基于电卡主动回热（AER）循环的制冷系统。在AER循环中，通过使用多物理场有限元分析平台，分别对器件在绝热Neumann条件下的温度跨度和Dirichlet条件下的制冷功率密度（CPD）及COP进行分析。BNNS-SPTMS-TP可以在更高的频率下充分完成热量交换，具有最高的温度跨度，优势更加明显。在1 Hz下，使用BNNS-SPTMS-TP的器件温跨达到了50 K，terpolymer为36.5 K，而BNNS/TP只有26 K。使用BNNS-SPTMS-TP的器件在4 Hz频率下的CPD达到了5.23 W/g，而terpolymer只有2.90 W/g。BNNS/TP难以维持10 K的温度跨度，它在1 Hz时只有0.77 W/g的峰值CPD，并且在3 Hz后无法提供有效的制冷功率。

为了从热力学、传热学、制造工艺和电学稳定性等多个角度综合评价EC复合材料，该工作进一步提出了电卡复合材料质量因子（EPCQ）。EPCQ综合考虑了材料的熵变、温变、击穿特性、填料比例、密度以及损耗等物理参数，是一种综合评价电卡复合材料的优值。

此项研究工作得到了国家重点研发计划“变革性技术关键科学问题”重点专项、国家自然科学基金项目、上海市自然科学基金项目、机械系统与振动国家重点实验室项目、上海交通大学“深蓝计划”面上项目和“重点前瞻布局基金”项目以及常州市领军人才计划等的支持。上海同步辐射光源BL19U2和BL16B1线站、上海交通大学学生创新中心和分析测试中心提供了表征技术支持。

Chinese firm Changsheng Technology Co Ltd achieved mass production of T1000 carbon fiber, which had previously been monopolized by Japan and the US. Capacity is 1700 tons per year with a 95% yield rate.

This research was led by a team from the University of Hong Kong, along with China’s National Nanoscience Centre and British superlens pioneer John Pendry..

Chinese and British scientists create highest-resolution superlens​

• New technique creates lens that can detect images that are just tens of nanometres in size, far beyond the limits of traditional microscopes
• The research was led by a team from the University of Hong Kong, along with China’s National Nanoscience Centre and British superlens pioneer John Pendry

A team of Chinese and British scientists have created the highest-resolution optical imaging lens to date.

Since the 19th century, physicians have assumed that optical microscopes have a resolution limit beyond which they cannot see objects clearly.
When items are smaller than about 200 nanometers, such as some viruses, they become indistinguishable under an optical microscope.
But in 2000 the Imperial College London scientist John Pendry came up with the concept of a superlens that could get round this problem.


Superlenses, which are made of plasmonic materials that mix metals with other substances, can create images on a subwavelength scale.

“The ultimate goal of optical imaging technology is resolution. Superlenses broke this limit and astonished physicists. However, the mixed surface made with metal and electrolyte can cause severe optical loss and the problem has existed for 20 years,” said Zheng Guoxing, a Wuhan University professor who was not involved in the research.

In the latest study, an international team led by Professor Zhang Shuang from the University of Hong Kong and Professor Zhang Xiang, the university’s current president, along with Pendry and researchers from China’s National Nanoscience Centre, found a way to lower the resolution limit by an order of magnitude to tens of nanometres.

The team used a combination of multiple frequencies to virtually increase resolution and offset the optical loss of the superlens. Their work was published in the peer-reviewed journal Science on Saturday.

They used a mathematical formula to turn a complicated light wave into a mix of simpler waves and then used the information from these simpler waves to make up for losses in the image quality

In other words, it is like using different colours of the spectrum to create a new colour that can reveal more details than the original colours alone. By using this method, it is possible to obtain ultra-high resolution imaging.

“We first proved this approach theoretically and then validated it with an experiment at microwave frequency. The imaging effect was highly consistent with our theoretical expectations,” Zhang Shuang told Science and Technology Daily.

Based on this, the team successfully designed a superlens and improved its imaging resolution by about an order of magnitude in the laboratory.

“This is a beautiful and universal method, usable across multiple optical frequencies, and extendable to other wave systems like sound waves, elastic waves and quantum waves to solve the loss problem,” Zhang Xiang told Science and Technology Daily report.

Ian S Osborne, the editor of Science, wrote in the journal that the technique “shows practical ways to overcome intrinsic losses in superlenses systems, offering potential for substantial improvements in imaging and sensing capabilities”.

The superlenses can be applied in various fields where high-resolution imaging is required, such as biomedicine, fibre optic communications and nanotechnology.

They can reveal features at a sub-wavelength scale that are not visible with conventional optical imaging techniques.

HW & Ericksson renewed cross licensing agreement. Which problem means Ericksson is paying HW a lot of money to use its patents

China has mastered the advanced control technology of high-limited nuclear fusion

China National Nuclear Corporation's public account announced that the new generation of artificial sun "China Circulation No. 3" has made significant scientific research progress, and for the first time achieved a high-constraint mode operation under a plasma current of 1 million amperes. Key technical problems such as high-current high-constraint mode operation control, high-power heating system injection coupling, and advanced divertor configuration control are important milestones in the development of nuclear fusion energy in my country, marking the development of magnetic confinement nuclear fusion research in China. Major step forward for fusion plasma operation

It seems the tech gap in carbon fiber has mostly disappeared already. I remember this being a big discussion topic 10 years ago.

China aims to accelerate the industrialization of new materials such as superconducting materials, graphene and liquid metal，which are the cornerstone and precursor of the future development of high-tech industries, the country’s top industry regulator said on Monday.

The Ministry of Industry and Information Technology and State-owned Assets Supervision and Administration Commission jointly released a list of important new materials that they will focus on advancing.

These materials represent the direction and trend of the development of the new material industry, which is an important entry point for building new growth engines, the ministries said.

For instance, the ministries called for their subordinate bodies to encourage enterprises to advance the industrialization of graphene in potential sectors such as rail traffic, aerospace equipment, new energy and new-generation information technologies.

Also, more efforts are needed to promote the industrialization of superconducting materials in potential sectors such as nuclear engineering, electronic equipment and new energy vehicles.

The China-US science pact signed in 1979 is arguably more important to the US than China.

US extends science pact with China: what it means for research​

The move is a stop-gap measure, and scientists warn that lack of a full renewal could damage research collaborations.

But some scientists have campaigned for the US government to continue the agreement. In a letter sent to Biden on 24 August, physicists Steven Kivelson and Peter Michelson at Stanford University in California wrote that the agreement provides an important framework for cooperation between the two countries and that cutting off ties with China “would directly and negatively impact” their own research. More than 1,000 academics signed the letter.

Kivelson, a theoretical physicist researching quantum materials, told Nature that many of his best graduate students and postdocs come from China.

“Much of the physics that I think about is based on experimental work that is done in China,” he says. “The entire field is highly dependent on and benefits from cooperation with colleagues in China.”
...
Jenny Lee, a higher-education researcher and vice-president for international affairs at the University of Arizona, Tucson, says that, if the agreement is scrapped, it could hurt research and higher education in the United States more than in China. This year, China overtook the United States as the nation publishing the largest number of high-quality research articles. The impact will probably be felt in future when new collaborations fail to form, she says. “It will signal to the next generation of scientists that we don’t want to actively cooperate with China,” she says.

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