News on China's scientific and technological development.

SanWenYu

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Scientists from Tsinghua created an inorganic optical hydrogel that can "stably and contiuously modulate deep ultra-violet light" with varying machanic strain (compression or stretch). It is an ideal material for making birefringent optical elements that have wide uses in solar-blind ultraviolet communication, semiconductor manufacturing, lithography and biomedicine.

Paper:
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Deep ultraviolet hydrogel based on 2D cobalt-doped titanate​

Abstract​

Birefringent optical elements that work in deep ultraviolet (DUV) region become increasingly important these years. However, most of the DUV optical elements have fixed birefringence which is hard to be tuned. Here, we invent a birefringence-tunable optical hydrogel with mechano-birefringence effect in the DUV region, based on two-dimensional (2D) low-cobalt-doped titanate. This 2D oxide material has an optical anisotropy factor of 1.5 × 10–11 C2 J−1 m−1, larger than maximum value obtained previously, leading to an extremely large specific magneto-optical Cotton-Mouton coefficient of 3.9 × 106 T−2 m−1. The extremely large coefficient enables the fabrication of birefringent hydrogel in a small magnetic field with an ultra-low concentration of 2D oxide material. The hydrogel can stably and continuously modulate 303 nm DUV light with large phase tunability by varying the strain (compression or stretching) from 0 to 50%. Our work opens the door to design and fabricate new proof-of-concept DUV birefringence-tunable element, as demonstrated by optical hydrogels capable of DUV modulation by mechanical stimuli.

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透射式深紫外(波长λ<350 nm)双折射元件可在不改变光路的情况下实现深紫外光调制,在日盲区光通信、半导体加工、光刻及生物医学等领域具有重要应用价值。目前,虽然研究人员已开发出一系列深紫外双折射单晶并实现了商业化应用,但受限于固定的双折射值,目前尚难以实现深紫外光信号的动态连续调制,且限制了其在一些新兴领域的应用。液晶材料具有可受外场(电场/磁场/应力)调控的双折射,有望解决这一问题。目前主流液晶器件由有机小分子或高分子构成,在深紫外光照射下吸收率高、材料不稳定,导致器件难以在深紫外波段工作,开发深紫外波段透光率高、双折射可调及紫外光照射下稳定的双折射元件意义重大。

近日,清华大学深圳国际研究生院刘碧录团队及合作者研制出一种基于无机二维材料液晶的光学水凝胶,该水凝胶在深紫外区具有优异的稳定性,并展现出可调的力致双折射效应,实现了深紫外光的连续稳定调制。研究人员首先采用自上而下的离子插层剥离法制备出无机钴掺杂二维氧化钛液晶,该材料具有3.9 eV的宽带隙,在深紫外波段具有高透射率及稳定性,同时还具有极大的几何各向异性与磁各向异性,以及目前报道最高的光学各向异性因子(达1.5× 10–11 C2 J−1 m−1),三者共同赋予其极大的磁场响应灵敏度(Cotton-Mouton系数,达3.9 × 106 T-2 m-1)。研究人员进而发现在1 T以内的低磁场下即可实现二维材料液晶分子的高度有序排列,且这种磁控排列方式具有毫秒级的快速响应、良好的可逆性及循环稳定性。基于此,研究团队在磁场作用下通过光聚合反应将无机二维钴掺杂氧化钛液晶与聚合物基质交联制成水凝胶。该水凝胶保留了二维材料液晶分子的定向排布,对其施加应力,可进一步调控光程及排布程度,从而实现深紫外偏振光相位延迟的连续调控,呈现出动态可调的力致双折射效应。

该工作中,研究人员结合了无机钴掺杂二维氧化钛材料结构可控、磁性可控、光学带隙宽的特征和水凝胶小巧轻便、可精确加工及操控等特性,为透射式、机械操控、连续稳定的深紫外光调制提供了一种可行的原型器件。该研究可为新型深紫外双折射器件的开发提供参考,有望应用在光通信、柔性紫外光学设备及生物医学等领域。
 

SanWenYu

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Chinese scientists created a low density, electro-conductive B4C ceramic with excellent mechanical properties.

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Highly electro-conductive B4C–TiB2 composites with three-dimensional interconnected intergranular TiB2 network​

To achieve lightweight B4C-based composite ceramics with high electrical conductivities and hardness, B4C–TiB2 ceramics were fabricated by reactive spark plasma sintering (SPS) using B4C, TiC, and amorphous B as raw materials. During the sintering process, fine B4C–TiB2 composite particles are firstly in situ synthesized by the reaction between TiC and B. Then, large raw B4C particles tend to grow at the cost of small B4C particles. Finally, small TiB2 grains surround large B4C grains to create a three-dimensional interconnected intergranular TiB2 network, which is beneficial for an electro-conductive network and greatly improves the conductivity of the ceramics. The effect of the B4C particle size on the mechanical and electrical properties of the ceramics was investigated. When the particle size of initial B4C powders is 10.29 µm, the obtained B4C–15 vol% TiB2 composite ceramics exhibit an electrical conductivity as high as 2.79×104 S/m and a density as low as 2.782 g/cm3, together with excellent mechanical properties including flexural strength, Vickers hardness (HV), and fracture toughness (KIC) of 676 MPa, 28.89 GPa, and 5.28 MPa·m1/2, respectively.

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安徽工大团队成功研发低硼化钛含量新型陶瓷

近日,安徽工业大学材料科学与工程学院教授冉松林团队分别在国际期刊《先进陶瓷(英文)》 (Journal of Advanced Ceramics)和《美国陶瓷协会会刊》《Journal of the American Ceramic Society》发表结构功能一体化复相陶瓷的最新研究成果。

据悉,碳化硼(B4C)陶瓷具有熔点高、密度低、化学稳定性强以及耐磨性好等优良性能,广泛应用于耐磨、装甲防护等领域。在碳化硼基体中引入第二相硼化钛(TiB2),形成B4C-TiB2复相陶瓷,不仅能有效提高碳化硼陶瓷的力学性能,还能显著降低复相陶瓷的电阻率,实现结构功能一体化。然而,由于硼化钛比碳化硼比重更大,本征硬度更低,硼化钛的加入也增加了材料的比重,降低了材料的硬度。

经过一系列研究,冉松林团队发现在保证高致密度和良好导电性能的前提下,降低B4C-TiB2复相陶瓷中硼化钛的比例,可进一步满足工业和军工领域对超轻、超硬材料的需求。团队通过化学反应协同基体晶粒选择性吸收生长法,设计并制备了一种低硼化钛含量的超轻、超硬、导电B4C-TiB2复相陶瓷,并通过探索复相陶瓷的显微结构与其导电性能、力学性能间的关系,实现了对B4C-TiB2复相陶瓷在结构和功能性能上的可控调节。本研究为结构功能一体化材料的制备及性能研究提供了一种新的思路。
 

sunnymaxi

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A Chinese research team has developed a software package called "HIBLUP" following five years of study, which helps improve big data calculations for genomic breeding. The findings have been published in the journal Nucleic Acids Research...

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siegecrossbow

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The concern with TikTok is that Chinese law allows the government to order ByteDance to give it TikTok’s US user data or spread propaganda or misinformation to US users. ByteDance and TikTok have denied ever doing this, and there’s no public evidence that they have. But for TikTok’s opponents, the potential is enough. They’ve also cited past controversies over
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that’s banned in China and ByteDance employees
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of a few US TikTok users in order to investigate employees suspected of leaking information to journalists (ByteDance said this surveillance wasn’t authorized by the company and the employees responsible were fired).

Holy crap literally 1984! Why is no one talking about this?
 
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