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Previous research has shown that using foreign languages reduces cognitive biases. Here, we investigate whether this foreign-language effect extends to self-related cognition – in particular, the self-positivity bias, which refers to automatic association of oneself with positive information and has a facilitation role in maintaining mental health. We applied event-related brain potentials and oscillations in the implicit association test where Chinese–English bilinguals responded to category words (self vs. others) and attribute words (positive vs. negative) in either their native language Chinese or their foreign language English. In response to Chinese words, a self-positivity bias occurred, indexed by a positive D-score in reaction times as well as by smaller N200, larger P3-like/LPC responses, and lower alpha desynchronization when self words were associated with positive relative to negative traits. However, the bias was diminished in the English context. Overall, our findings provide important implications for language choices when self-protective mechanisms should be enhanced.
We report dispersion management based on a mismatched-grating compressor for a 100 PW level laser, which utilizes optical parametric chirped pulse amplification and also features large chirped pulse duration and an ultra-broadband spectrum. The numerical calculation indicates that amplified pulses with 4 ns chirped pulse duration and 210 nm spectral bandwidth can be directly compressed to sub-13 fs, which is close to the Fourier-transform limit (FTL). More importantly, the tolerances of the mismatched-grating compressor to the misalignment of the stretcher, the error of the desired grating groove density and the variation of material dispersion are comprehensively analyzed, which is crucially important for its practical application. The results demonstrate that good tolerances and near-FTL compressed pulses can be achieved simultaneously, just by keeping a balance between the residual second-, third- and fourth-order dispersions in the laser system. This work can offer a meaningful guideline for the design and construction of 100 PW level lasers.
Bathymetric simultaneous localisation and mapping (SLAM) methods yield accurate navigation results for autonomous underwater vehicles (AUVs) and can construct consistent seabed terrain maps. Multiple independently working vehicles can complete tasks like surveying and mapping efficiently, which means cooperative bathymetric SLAM using multiple AUVs is suitable for large-scale seabed mapping. However, the transmission of bathymetric measurements collected using a multi-beam echo sounder over a low bandwidth, noisy, and unreliable acoustic channel is difficult, making cooperative bathymetric SLAM very challenging. This paper develops a graph-based cooperative bathymetric SLAM system that can compress many bathymetric measurements into small-scale acoustic packets and yield accurate navigation results with a 10% loss of acoustic packets caused by unreliable acoustic communication. According to the simulation conducted using the field data, the new algorithm is shown to be robust and capable of providing accurate location and mapping results over a low bandwidth, noisy, and unreliable acoustic channel.
In this study, a high-energy, temporally shaped picosecond ultraviolet (UV) laser running at 100 Hz is demonstrated, with its pulses boosted to 120 mJ by cascaded regenerative and double-pass amplifiers, resulting in a gain of more than 108. With precise manipulation and optimization, the amplified laser pulses were flat-top in the temporal and spatial domains to maintain high filling factors, which significantly improved the conversion efficiency of the subsequent third harmonic generation (THG). Finally, 91 mJ, 470 ps pulses were obtained at 355 nm, corresponding to a conversion efficiency as high as 76%, which, as far as we are aware of, is the highest THG efficiency for a high-repetition-rate picosecond laser. In addition, the energy stability of the UV laser is better than 1.07% (root mean square), which makes this laser an attractive source for a variety of fields including laser conditioning and micro-fabrication.
Narrowband microwave generation with tuneable frequency is demonstrated by illuminating a photoconductive semiconductor switch (PCSS) with a burst-mode fibre laser. The whole system is composed of a high-power linearly polarized burst-mode pulsed fibre laser and a linear-state PCSS. To obtain a high-performance microwave signal, a desired envelope of burst is necessary and a pulse pre-compensation technique is adopted to avoid envelope distortion induced by the gain-saturation effect. Resulting from the technique, homogenous peak power distribution in each burst is ensured. The maximum energy of the laser burst pulse reaches 200 μJ with a burst duration of 100 ns at the average power of 10 W, corresponding to a peak power of 4 kW. When the PCSS is illuminated by the burst-mode fibre laser, narrowband microwave generation with tuneable frequency (0.80–1.12 GHz) is obtained with a power up to 300 W. To the best of the authors’ knowledge, it is the first demonstration of frequency-tuneable narrowband microwave generation based on a fibre laser. The high-power burst-mode fibre laser reported here has great potential for generating high-power arbitrary microwave signals for a great deal of applicable demands such as smart adaptive radar and intelligent high-power microwave systems.
The stability of dynamic fracture is a fundamental and challenging problem in the field of materials science. The grain size effect on dynamic fracture instability in polycrystalline graphene under tear loading is explored via theoretical analysis and molecular dynamics simulations. The fracture stability phase diagram in terms of grain size and crack propagation velocity is obtained, and three regions of crack propagation are identified: stable, metastable, and unstable. For grain size above 2 nm, there exists a critical velocity beyond which fracture instability occurs, and this critical velocity depends linearly on grain size. Decreasing grain size leads to reduced characteristic time for correction of crack path deflection, which plays a dominant role in dynamic fracture instabilities. However, when grain size is below 2 nm, there does not exist a critical velocity for steady propagation of cracks due to discontinuous effects. Our results also provide a valuable insight into dynamic fracture of polycrystalline graphene as well as other 2D and quasi-2D materials.
The evolution of arid environments in northern China was a major environmental change during the Quaternary. Here we present the dating and environmental proxy results from a 35 m long core (A-WL10ZK-1) collected from the Ulan Buh Desert (UBD), along with supplemental data from four other cores. The UBD is one of the main desert dune fields in China and our results indicate the UBD has undergone complex evolution during the late Quaternary. Most of the present UBD was covered by a Jilantai-Hetao Mega-paleolake lasting until ~ 90 ka ago. A sandy desert environment prevailed throughout the UBD during the last glacial period and early Holocene. A wetland environment characterized by the formation of numerous interdunal ponds in the northern UBD occurred at ~ 8–7 ka, although a dune field persisted in the southern UBD. The modern UBD landscape formed after these wetlands dried up. During the last 2000 years, eolian sand from the Badain Jaran Desert has invaded the northern UBD, while farming and overgrazing resulted in the formation of the eastern UBD. We suggest that the formation of UBD landforms is related to the disintegration of the megalake Jilantai-Hetao and to summer monsoon changes during the last glaciation and Holocene.
Arid Central Asia (ACA) lies on a major climatic boundary between the mid-latitude westerlies and the northwestern limit of the Asian summer monsoon, yet only a few high-quality reconstructions exist for its climate history. Here we calibrate a new organic geochemical proxy for lake temperature, and present a 45-yr-resolution temperature record from Hurleg Lake at the eastern margin of the ACA in the northern Tibetan Plateau. Combination with other proxy data from the same samples reveals a distinct warm–dry climate association throughout the record, which contrasts with the warm–wet association found in the Asian monsoon region. This indicates that the climatic boundary between the westerly and the monsoon regimes has remained roughly in the same place throughout the Holocene, at least near our study site. Six millennial-scale cold events are found within the past 9000 yr, which approximately coincide with previously documented events of northern high-latitude cooling and tropical drought. This suggests a connection between the North Atlantic and tropical monsoon climate systems, via the westerly circulation. Finally, we also observe an increase in regional climate variability after the mid-Holocene, which we relate to changes in vegetation (forest) cover in the monsoon region through a land-surface albedo feedback.
Central China has experienced stronger summer monsoon during warm periods such as Marine Isotope Stages (MIS) 1 and 3, and weaker summer monsoon during cool periods such as MIS 2. The evolution history of Dajiuhu subalpine peatland in central China can help investigate how the expansion and shrinkage of peatland were associated with monsoonal strength over the last glacial–interglacial cycle. Here we apply bulk organic carbon and molecular biomarkers (hopane and n-alkane) to reconstruct the evolution history for the Dajiuhu peatland over the past 40,000 yr. The results indicate fluctuations between lacustrine and peat-like deposition during MIS 3, steady lacustrine deposition during MIS 2, and peatland initiation and expansion during MIS 1 in the Dajiuhu peatland. Therefore, at the glacial–interglacial scale, warmer summer and cooler winter conditions in interglacial periods are crucial to trigger peat deposition, whereas reduced evaporation in glacial period instead of decreased monsoonal-driven precipitation would have played a predominant role in the regional effective moisture balance. However, within the Holocene (MIS 1), monsoonal precipitation changes appear to be the main controller on millennial-scale variations of water-table level of the Dajiuhu peatland.
The frictional behaviors of fullerenes C60 and C70 were studied because they were speculated to be solid lubricants. For the sublimated pure C60 films on Si(001), a high friction coefficient (0.55–0.8) was observed under different loads and pin materials. For the C70 film, the friction coefficient showed a pin dependence, which changed from 0.5 with an Al2O3 pin to about 0.9 with a 440 stainless steel pin. The relatively high friction coefficients of C60 and C70 films were due to the tendency of the C60 and C70 particles to clump and compress into high shear strength layers rather than due to the impurities in the fullerenes. The benzene-solvated C60 · 4C6H6 and C70 ·xC6H6 showed a lowered friction coefficient (0.25 for C60 · 4C6H6 and 0.3 for C70 · xC6H6), which might result from the lowered shear strength of the hcp structure of C60 · 4C6H6 and C70 ·xC6H6 molecular crystals in which the benzene molecules were intercalated.
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