to sluggish actuation speed (response time typically on the order of minutes). Conventional one-way SMPs do not remember the temporary shapes and the recovery speed is relatively slow (response time from tens of seconds to minutes) since it is heat-activated. LCEs, in contrast, owning to their inherent anisotropy, offer promises for fast (e.g., 10 ms [11]) and reversible actuation, large actuation strain, and high energy conversion efficiency. [12] LCEs are lightly crosslinked polymer networks containing main-chain or sidechain mesogenic units. [13] The deformation

Identifying prehistoric irrigated rice fields and characterizing the beginning of paddy soil development are important for a better understanding of human development and agricultural history. In 2003, paddy soils and irrigated rice fields buried at a depth of 100-130 cm were excavated at Chuo-dun-shan in the Yangtze River Delta, close to Suzhou, China. The fields of sizes between 1.4 and 16 m(2) were surrounded with ridges that were connected to ditches/ponds via outlets to control the water level within the fields. Many carbonized and partly carbonized rice grains with an age of 3,903 B.C. (measured (14)C age 5,129+/-45 a BP) were recovered. The surface layers of these buried paddy fields showed a high content of soil organic matter and a considerable high density of rice opals. The latter were identified to derive from Oryza spp. Solid-state (13)C nuclear magnetic resonance spectroscopy revealed aromatic carbon (C) as the predominant organic C form in the fossil surface layer. This is expected, if the major source represents burnt rice and straw. In summary, our data are in agreement with new evidences indicating that in China, paddy soils and irrigated rice cultivation were initiated and developed more than 6,000 years ago.

optoelectronic applications. Specifically, because of the broken inversion symmetry in few-layer MX 2 (M = Mo, W; X = S, Se) flakes with odd layer thicknesses, considerable second harmonic generations (SHGs) are observed, though their bulk materials were well recognized without second-order nonlinearity. [22][23][24][25][26] It is also possible to design spiral nanostructures during the material growth, which not only maintains the broken symmetry in each monolayer but also increases the effective material thickness to greatly strengthen SHGs in 2D TMDs. [27] When the two-photon energy of the pump laser is on-resonance with the exciton of monolayer WSe 2 , a high second-order nonlinear susceptibility of 1000 pm V −1 is estimated, which is about three orders of magnitude higher than those in conventional bulk materials. [28] Combining with the electrical tunability and valley selectivity of the strong excitons in monolayer MX 2 , this exciton-enhanced SHG could be modulated by an order of magnitude with an application of a vertical electrical field, which is also verified to have counter-circular polarization to the pump laser. [29] The extraordinary and tunable SHGs in 2D TMDs provide new possibilities to construct nonlinear optoelectronic devices, including nonlinear electro-optic modulators, coherent light source generators, etc.Most of the SHG studies of 2D TMDs were implemented on mono-and few-layer MoS 2 , MoSe 2 , and their tungsten analogs. In this paper, we report the measurements of SHGs in monoand few-layer MoTe 2 , which has recently arisen as an appealing 2D TMD semiconductor for photonic and electronic devices. In contrast to the MoS 2 and MoSe 2 , the indirect-to-direct bandgap crossover in atomically thin MoTe 2 occurs before reaching the monolayer thickness. [30] And the photoluminescence emission and excitonic absorption are located in the near-infrared range around 1.1 eV, bridging the comparatively large bandgap of other monolayer TMDs and zero-bandgap graphene. Another important property of MoTe 2 is its large exciton-binding energy around 0.6 eV, [31] providing a unique opportunity for achieving the first 2D material-based nanolaser at room temperature. [32] The spin-orbit coupling in MoTe 2 is much stronger than that in MoS 2 or MoSe 2 , which could contribute to a longer decoherence time for exciton valley and spin indexes and new valleytronic devices. [33] Those intriguing attributes are revealed in the semiconducting hexagonal (2H)-MoTe 2 . Note that stable MoTe 2 could also exist in a semimetal monoclinic (1T′) phase, which endows more opportunities for electronic and optoelectronic applications. 2H-to-1T′ phase changes in MoTe 2 could be experimentally realized through laser irradiation, electrostatic gating, and thermal synthesis, and the distinctly modulated Optical second harmonic generations (SHGs) from atomically thin MoTe 2 flakes with 2H and 1T′ phases are studied. From 2H-MoTe 2 samples with odd (even) numbers of layers, strong (negligible) SHGs are observed due to the layer-dep...

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