Thrusting and exhumation of the southern Mongolian Plateau: Joint thermochronological constraints from the Langshan Mountains, western Inner Mongolia, China

The Mongolian Plateau has undergone multi-stage denudation since the Late Triassic, and the NE-trending Langshan Mountains in the southern margin of the Mongolian Plateau is crucial to unraveling the Meso-Cenozoic cooling and exhumation history of the Mongolian Plateau. The Langshan Mountains are dominated by Precambrian gneiss and Permian–Middle Triassic granitic plutons crosscut by a set of NE-striking thrust faults. A joint thermochronological study was conducted on 31 granitic and gneissic samples along the HQ and CU transects across the Langshan Mountains and other two samples from the BQ in the north of the Langshan Mountains. Four biotite/muscovite and three K-feldspar 40Ar/39Ar plateau ages range from 205 ± 1 to 161 ± 1 and 167 ± 1 to 131 ± 1 Ma, respectively. Thirty-three apatite fission track (AFT) ages are between 184 ± 11 and 79 ± 4 Ma, with mean track lengths from 11.1 ± 1.8 to 13.1 ± 1.4 μm of mostly unimodal distributions. Thirty-one single-grain raw AHe ages are in a range of 134 ± 8 to 21 ± 1 Ma. The AFT ages decrease monotonously from NW to SE until thrust faults along the two transects, with an age-jump across thrust F35. Joint thermal history modelling shows a three-stage cooling history as a result of denudation, especially with spatial differentiation in the first stage. Relative slow cooling at c. 0.6–1.0 °C/Ma occurred in the BQ and the northern part of the HQ transect during 220–100 Ma and the northern part of the CU transect during 160–100 Ma, respectively, with an amount of c. 2–3 km denudation between 160 and 100 Ma, implying little movement along the thrusts F13 and F33. In the middle and southern parts of the HQ transect and the southern part of the CU transect, rapid cooling at c. 4.0–7.0 °C/Ma, with c. 6–9 km denudation during 170–130 or 160–100 Ma, respectively, is probably influenced by thrusting of F35, F38 and F42 and the resultant tilting. A combination of thrusting, tilting, and denudation led to the youngering trends towards thrusts in different parts. However, there was no significant denudation across the Langshan Mountains in the second stage from c. 100 or 80 Ma until the last stage of rapid denudation (c. 2 km) since 20–10 Ma, which is simultaneous with the rapid uplift of the northern part of the Tibetan Plateau at c. 15 Ma. A youngering trend of AFT ages from the inner to the peripherals of the Mongolian Plateau implies the outward propagation of the Mongolian Plateau since the Mesozoic

Suspension and Measurement of Graphene and Bi2Se3 Atomic Membranes

Coupling high quality, suspended atomic membranes to specialized electrodes enables investigation of many novel phenomena, such as spin or Cooper pair transport in these two dimensional systems. However, many electrode materials are not stable in acids that are used to dissolve underlying substrates. Here we present a versatile and powerful multi-level lithographical technique to suspend atomic membranes, which can be applied to the vast majority of substrate, membrane and electrode materials. Using this technique, we fabricated suspended graphene devices with Al electrodes and mobility of 5500 cm^2/Vs. We also demonstrate, for the first time, fabrication and measurement of a free-standing thin Bi2Se3 membrane, which has low contact resistance to electrodes and a mobility of >~500 cm^2/Vs

Numerical simulation and experimental research of spectral noise characteristics for the four-wheel landing gear

Numerical simulation and wind tunnel experiment were conducted for flow field and flow noise characteristics of four-wheel landing gear. Under the landing speed, large eddy simulation method was applied to simulate the unsteady turbulent flow field around the landing gear. In addition, vortex-acoustic theory was also employed to compute the intensity and position of sound source, and integral method of FW-H equation was used to solve the sound field generated from different components and their combinations, analyze the noise generation mechanism, spectral characteristics and far-field directivity. Meanwhile, the contribution of each component to the total noise was assessed. The aerodynamic acoustic experiment was conducted for landing gear in the wind tunnel, and a microphone was applied to measure and obtain the spectral characteristics of noise, which was compared with the numerical computation result. As shown from the result, a good agreement was found between the experimental and numerical results. Besides, it was shown from the simulation result that small parts ignored in the computational sound field played a greater impact on prediction result of noise, especially high-frequency noise. As shown from landing gear vorticity and sound pressure distribution, sound source was mainly distributed in the solid surface of various components for the landing gear. Additionally, sound source was also occurred in the vortex shedding positions behind each component. Greater energy and density of the sound source were found in the gap formed between tire and bogie and in the pillar stairs. The tire noise showed maximum contribution to the total noise, followed by the bogie noise, while the pillar noise was minimal. The total noise spectrum was closest to the tire noise spectrum