摘要：我们人类生活的三维空间（实空间）是连续的吗？换句话说，实空间是无限可分的么？在宏观世界里，答案无疑是肯定的，因为日常生活的经验，如看到的流水，奔跑的动物，空中的飞鸟，以及自由下落的物体，无一例外的给予人们连续轨迹的印象。在经典力学中，用连续的坐标来描写运动物体被认为是理所当然的。 在量子世界里面，情况会发生戏剧性的变化。例如，当一个粒子的运动受到限制的时候，它的稳定态的能量只能取一些的离散值。一些尝试统一量子力学和引力的现代理论预测了一个最小长度的存在，通常取为普朗克尺度，这个长度大约是1.6×10-35米。然而，这个长度的实验检验是极具挑战性的，因为它远小于LIGO能测量的最小长度(大约是10-19米)。 在本项工作中，作者研究了任意形状的双势垒体系的量子隧穿现象并证明了一个定理。这个定理表明，如果两个势垒之间的间距可以连续变化，即实空间是连续的，则只要适当地调节势垒间距，入射粒子就可以完全穿透双势垒体系。这种现象通常被称为共振隧穿。反之，如果实空间是不连续的，即存在一个非零的最小尺度，则当势垒的尺寸超过某个上限值的时候，共振隧穿现象就不再发生。这个工作揭示了量子隧穿现象和量子引力理论中最小尺度的深刻联系，开辟了检验最小尺度的存在性的新途径。
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The notion of information and complexity are important concepts in many scientific fields such as molecular biology, evolutionary theory, and exobiology. Most measures of these quantities, such as Shannon entropy and related complexity measures, are only defined for objects drawn from a statistical ensemble and cannot be computed for single objects. Based on assembly theory, we attempt to fill this gap by introducing the notion of a ladderpath which describes how an object can be decomposed into a hierarchical structure using repetitive elements. From the ladderpath two measures naturally emerge: the ladderpath-index and the order-index, which represent two axes of complexity. We show how the ladderpath approach can be applied to both strings and spatial patterns and argue that all systems that undergo evolution can be described as ladderpaths. Further, we discuss possible applications to human language and the origins of life. The ladderpath approach provides a novel characterization of the information that is contained in a single object (or a system) and could aid in our understanding of evolving systems and the origin of life in particular.
非厄米的引入扩展了传统厄米量子系统中的概念并诱导出许多新奇的物理现象, 比如非厄米系统所独有的非厄米趋肤效应, 这使得对非厄米量子模型的模拟成为大家关注的热点. 相比于量子平台, 经典系统具有成本低廉、技术成熟、室温条件等优势, 而其中的经典电路系统则更加灵活, 原则上可以模拟任意维度、任意格点间跃迁、任意边界条件下的量子紧束缚模型, 已经成为模拟量子物态的有力平台. 本文利用经典电路通过 SPICE 成功模拟了一个重要的非厄米量子模型 —— 非互易 Aubry-Andr\'e 模型 —— 的稳态性质, 此模型同时具有非互易的格点跃迁和准周期的格点在位势. 以此为例, 详细介绍了如何建立经典电路的拉普拉辛形式与量子紧束缚模型哈密顿矩阵在不同边界条件下的映射, 尤其是如何利用电流型负阻抗变换器构建模型的非互易性. 然后, 根据电路的格林函数, 通过 AC 电流驱动并测量电压响应的方式, 用 SPICE 模拟了周期边界条件下的复能谱和相应的能谱缠绕数, 以及开边界条件下的趋肤与局域模式的竞争. 其中, 为了使电路的响应不发散, 本文还解析地给出辅助元件的设置原则. 结果显示, SPICE 模拟与理论计算很好地吻合, 为进一步的实验实现提供了详细的指导. 由于本文电路设计与测量方案的普适性, 原则上可以直接应用于其他非厄米量子模型的电路模拟.
摘要：磁和磁单极子是物理学中的经典问题。传统磁体通常由刚性材料组成，在回答极端问题时可能面临挑战。这里，我们首次从不同于刚性磁体的导电性流体物质出发，提出通过调控液态金属机器来产生流态化内生磁性并由此构造磁单极子。基于理论解释和概念性实验证据，我们阐明了当溶液中的镓基液态金属在电驱动下发生旋转时，其内部会形成一个内生磁场，这很好地解释了两个这样分离的金属液滴能很容易融合在一起的实验现象，原因在于二者通过各自对应的N极和S极相互吸引。此外，我们还阐明了自驱动型液态金属机器也以一种内生流态化磁体出现且具有电磁同源性；当溶液中的液态镓吞食铝时，会形成一个旋转马达和在体动态变化的电荷分布，从而在内部产生内生磁性；这就解释了运动中的液态金属马达之间经常发生反射性碰撞和吸引性融合的现象，这两种现象分别是由于马达之间N极和S极的动态调整引起的。最后，我们设想可通过这种流态化内生磁体制造磁单极子，并提出了实现这一目标的四条技术路线：1. 匹配液态金属机器的内部流场；2. 基于外电场效应与磁场的叠加效应；3. 借助磁颗粒与液态金属马达之间的复合结构；4. 化学途径，如通过原电池反应。总的来说，本文理论和提供的实验证据揭示了液态金属机器作为流体型内生磁体的机制，并指出了实现磁单极的一些有希望的途径。在不久的将来，在此基础上建立一些非传统型磁电器件和应用是可能的。
摘要： In the past decade, electronic devices based on graphene and the related two-dimensional (2D) materials have exhibited outstanding figures of merit. However, so far, the fabrication of two-dimensional diodes, as elementary building blocks of electronic devices, still relies on manual or semi-automated handling processing. To unleash their commercial potential, the integration of 2D materials into a fully-automated fabrication line is a critical step. Here, we elucidate the focused ion-beam writing as an automated approach to construct lateral diodes on a 2D heterostructure (MoSe2/G) consisting of the stacked monolayer graphene and MoSe2. Se-defects generated by focused ion writing endow the 2D heterostructure with unique electronic properties like the adjustable work function and the quasi-metallic state, which allows for the construction of the barrier at the boundary of the writing and non-writing region. Benefiting from this feature, the ion-beam-written heterostructure is used to realize rectifying and current regulating diodes. Exhibiting comparable performance to traditional diodes, the rectifying diode has a rectification ratio of ~104, while the current regulative diode has a dynamic resistance larger than 4.5 MΩ. Furthermore, to illustrate practical applications of these diodes in digital logic electronics, AND and OR logic gates are directly inscribed on the heterostructure by ion beams. Our work demonstrates the focused ion-beam writing as an additional strategy for direct-writing of 2D diodes on graphene-based heterostructures.
摘要：The past decade has witnessed a surge of interest in exploring emergent particles in condensed matter systems. Novel particles, emerged as excitations around exotic band degeneracy points, continue to be reported in real materials and artificially engineered systems, but so far, we do not have a complete picture on all possible types of particles that can be achieved. Here, via systematic symmetry analysis and modeling, we accomplish a complete list of all possible particles in time reversal-invariant systems. This includes both spinful particles such as electron quasiparticles in solids, and spinless particles such as phonons or even excitations in electric-circuit and mechanical networks. We establish detailed correspondence between the particle, the symmetry condition, the effective model, and the topological character. This obtained encyclopedia concludes the search for novel emergent particles and provides concrete guidance to achieve them in physical systems.
摘要：The unified processing and research of multiple network models are implemented, and a new theoretical breakthrough is made, which sets up two new theorems on evaluating the exact electrical characteristics (potential and resistance) of the complex m×n resistor networks by the Recursion-Transform method with potential parameters (RT-V), applies to a variety of different types of lattice structure with arbitrary boundaries such as the nonregular m×n rectangular networks and the nonregular m×n cylindrical networks. Our research gives the analytical solutions of electrical characteristics of the complex networks (finite, semi-infinite and infinite), which has not been solved before. As applications of the theorems, a series of analytical solutions of potential and resistance of the complex resistor networks are discovered. In particular, three novel mathematical propositions are discovered when comparing the resistance in two resistor networks, and many interesting trigonometric identities are discovered as well.
摘要：Synthesis of low-cost, highly-active and durable non-platinum metal catalysts for methanol oxidation reaction (MOR) is always full of challenge. Here, Ni nanoparticles modified reduced graphene oxide (Ni/rGO) as an efficient non-platinum catalyst were synthesized by laser ablation of Ni target in graphene oxide (GO) solution and the following in situ reduction process. It found that GO played an important role to restrict the growth and aggregation of ultrafine nickel colloids (< 5 nm) in the process of laser ablation. The resulting Ni/rGO catalyst showed advantageous in active sites and charge transport resulting from the small particle size, uniform dispersion and electronic effect arising from the electron interactions between reduced graphene oxide (rGO) and Ni. The obtained Ni/rGO exhibited the ultrahigh catalytic mass activity of 1600 mA/mg, methanol saturation concentration (4 M), which was superior to that of the reported Ni-based catalysts. Remarkably the mass activities of Ni/rGO before and after 1000 cycles exceed that of the commercial Pt/C catalyst, indicating excellent catalytic activity and stability.
摘要：Co-Ni layered double hydroxides (LDHs), as promising supercapacitor electrode materials with high specific capacity, have suffered poor rate property and cycle stability. By doping and topochemical oxidation of Ni ions is considered as efficivent rout to overcome these drawbacks. In this work, Ni3+ doped cobalt-nickel layered double hydroxides (Co-Ni-LDHs) were synthesized by pluse laser ablation of Ni taget in CoCl2 aqeous solution. The existence of Ni3+ ions doped in Co-Ni-LDHs decline the conductive resistance, and increase the mobility of surface charge and transfer rate of electrolyte. As a results, the Ni3+ doped Co-Ni-LDHs display a maximum specific capacitance of 2275 F/g and 1450 F/g at the current density of 1 A/g and 20 A/g, respectivly, indicating a high rate specific capacitance. Moreover, the capacitance retention is to be 80% after 1800 cycles at the current density of 6 A/g, manifesting good cycling stability of Ni3+ doped Co-Ni-LDHs.
摘要：Agglomeration-triggered deactivation of supported platinum electrocatalysts markedly hinders their application in methanol oxidation reaction (MOR). In this study, graphene-supported nickel–iron layered double hydroxide (NiFe–LDH/rGO), in which Fe3+ was introduced to replace Ni2+ partially in the Ni(OH)2 lattice to provide stronger metal–support bonding sites, was utilized to immobilize Pt nanoparticles (NPs). Given the optimized metal–support interfacial contact (Fe3+–O(H)–Pt) between Pt NPs and NiFe–LDH/rGO nanosheets for Pt/NiFe–LDH/rGO electrocatalysts, the Pt/NiFe–LDH/rGO electrocatalysts displayed dramatically enhanced durability than that of Pt/Ni(OH)2/rGO counterpart as well as commercial Pt/C, and 86.5% of its initial catalytic activity can be maintained even after 1200 cycles of cyclic voltammetry (CV) tests during MOR. First-principle calculations toward the resultant M–O(H)–Pt (M = Fe3+, Ni2+) interfacial structure further corroborates that the NiFe–LDH nanosheets can provide stronger bonding sites (via the Fe3+–O(H)–Pt bonds) to immobilize Pt NPs than those of Ni(OH)2 nanosheets (via the Ni2+–O(H)–Pt bonds).
摘要：Herein, nanoparticles SnSe are prepared by fusion method together with ball-milling technique and the effect of hot-pressing temperatures on the thermoelectric properties of the dense materials is explored. Due to the optimization of carrier concentration, the peak figure of merit (ZT) value of the compacted material reaches 0.73 for SnSe sample hot-pressed at 400°C and 450°C. The present investigation indicates that the thermoelectric performance of the SnSe compound can be significantly improved by sintering with suitable temperature.
摘要：AgSbTe2 bulk sample is obtained by hot-pressing under different fabrication parameters, and their thermoelectric properties are investigated in the temperature range of 300-550K. The highest ZT=0.86 is achieved at 475K for the sample hot-pressed at 423K and 500MPa due to the lower thermal conductivity and higher power factor. The results indicate that the optimized thermoelectric properties can be obtained for AgSbTe2 compound at the sintering temperature of 423K under the pressure of 500MPa.
摘要：Recently, single crystalline SnSe and its sodium doped compound were reported to have an ultralow thermal conductivity and high thermoelectric figure of merit. However, the highest high thermoelectric figure of merit for polycrystalline SnSe-based materials is not larger than unity. In this study, we report a high thermoelectric figure of merit 1.21 at 903K along the hot pressing direction for polycrystalline SnSe, realized by incorporating a proper proportion of carbon black as nano-inclusions. The exceptional performance arises from the ultra-high power factor, which comes from a high electrical conductivity and an enhanced Seebeck coefficient through energy-dependent scattering.
摘要：Gd-doped compounds CuGa1-xGdxTe2 (0x0.02) incorporated with tellurium nanoparticles are synthesized by fusion method. Their thermoelectric properties are investigated in the temperature range of 300-800K. The results indicate that the synergistic effect of Gd-doping and Te incorporation remarkably enhances the thermoelectric performance of CuGaTe2. Specially, the thermal conductivity of the specimen CuGa0.98Gd0.02Te2/0.7vol.%Te reduces to 0.45 Wm-1K-1 at 684K, which is ~74% smaller than that of pure CuGaTe2 (=1.76 Wm-1K-1 at 684K) due to the incorporation of nanostructure Te. The thermoelectric figure of merit value (ZT) reaches 0.75 at 737K for the specimen CuGa0.99Gd0.01Te2/0.7vol.%Te, which is ~115% larger than that of pure CuGaTe2.
摘要：CuGaTe2 based composites incorporated with graphite nanosheets(GNs) CuGaTe2/x G (G=GNs, 0x3.04 vol.%) were prepared, and the thermoelectric properties of the composites were studied from 300 to 875 K. The results show that the incorporation of GNs into the CuGaTe2 matrix can enhance the Seebeck coefficient and power factor over the whole temperature range investigated due to energy filtering effects, and the reduction of thermal conductivity below 750K owing to interface scattering. Although the resistivity increases, energy filtering significantly raises the Seebeck component, and the overall effect on power factor is positive. The sample with 2.28 vol.% GNs had the largest ZT value, reaching 0.93 at 873K, which is a ~21% improvement on pure CuGaTe2.
摘要：Transition metal/nitrogen/carbon (M-N/C) catalysts are considered as one of the most promising candidates to replace Pt/C catalysts for oxygen reduction reactions (ORR). Here, we have designed novel reduced graphene oxides (rGO) supported Fe-N-doped carbon (Fe-N-C/rGO) catalysts via simple pyrolysis of polypyrrole(Ppy)-FeO-GO composites. The as-prepared catalysts induced an onset potential of 0.94 V, a half-wave potential of 0.81 V in alkaline solutions, which is much better than that of the counterpart N-C and N-C/rGO catalysts, and comparable to that of Pt/C catalysts. Moreover, the Fe-N-C/rGO catalysts showed improved durability and higher tolerance against methanol crossover than Pt/C in alkaline solutions. This superior ORR perfomance can be ascribed to the combined catalytic effect of both Fe-based nanoparticles (Fe3O4, Fe4C) and Fe-Nx sites, as well as fast mass transfer and accessible active sites benefitting from the mesporous structure and high specific surface area. This work provides new insight for synthesis of a more promising non-platinum electrocatalyst for metal-air batteries and fuel-cell applications.