Analysis of Strength Characteristics and Energy Dissipation of Improved-Subgrade Soil of High-Speed Railway above Mined-Out Areas

To reveal the effect of sand content on the mechanical performance and energy dissipation of cement improved subgrade soil, using universal testing machine and SHPB test device, unconfined compressive strength (UCS) and impact compression strength under different impact load (0.2, 0.3, 0.4, and 0.5 MPa) were carried out for the cement improved subgrade soil with different sand content (0%, 5%, 10%, 15%, and 20%). Results show that the dynamic and static stress-strain curves of the cement improved soil have similar variation trend. With the increase of the sand content, the UCS and impact compressive strength of the cement improved soil both increase first, then decrease later, showing the form of a quadratic function. The strength growth rate and the dynamic increase factor (DIF) reach the maximum values when the sand content is 10%, which is 64.7% and 18.6% larger than that of ordinary improved subgrade soil, respectively. In addition, when the sand content increases from 0% to 20%, the specific dissipation energy increases first, and decreases later. Mixing 10% natural sand is the optimal proportion to obtain better energy dissipation capacity of the sand-cement-improved soil

Mechanical Properties of Steel Fiber-Reinforced Magnesium Phosphate Cement Mortar

A new cement-based mortar with high early strength and toughness was developed by adding micro steel fibers (MSF) in magnesium phosphate cement (MPC) mortar. The compressive and flexural tests were carried out to investigate the effect of curing time, MSF volume fraction, sand-cement mass ratio, and water-cement mass ratio on the strength and flexural toughness of MSF-reinforced MPC mortar (MSFRMM). Also, the flexural toughness and ductility of MSFRMM were evaluated according to ASTM C1609. The results of this study showed that the addition of MSF from 0% to 1.6% by volume significantly improved the compressive strength of MSFRMM. The MSFRMM showed high early strength, especially during the first 3 days. The addition of MSFs changed the flexural failure mode of MPC-based mortar from brittleness to ductility, and the flexural toughness of MSFRMM remarkably increased with the increase of MSF volume fraction from 0% to 1.6%. The toughness and ductility of MSFRMM slightly increased with the increase of the dosage of cement. The toughness and ductility of MSFRMM increased with the decrease of the water-cement mass ratio due to the improved density of the mortar caused by the reduction of water

Analysis and implementation of fractional-order chaotic system with standard components

This paper is devoted to the problem of uncertainty in fractional-order Chaotic systems implemented by means of standard electronic components. The fractional order element (FOE) is typically substituted by one complex impedance network containing a huge number of discrete resistors and capacitors. In order to balance the complexity and accuracy of the circuit, a sparse optimization based parameter selection method is proposed. The random error and the uncertainty of system implementation are analyzed through numerical simulations. The effectiveness of the method is verified by numerical and circuit simulations, tested experimentally with electronic circuit implementations. The simulations and experiments show that the proposed method reduces the order of circuit systems and finds a minimum number for the combination of commercially available standard components.This work was supported in part by the National Natural Science Foundation of China under Grant 61501385, in part by the National Nuclear Energy Development Project of State Administration for Science, Technology and Industry for National Defense, PRC under Grant 18zg6103, and in part by Sichuan Science and Technology Program under Grant 2018JY0522. We would like to thank Xinghua Feng for meaningful discussion.info:eu-repo/semantics/publishedVersio

Front and Back‐Junction Carbon Nanotube‐Silicon Solar Cells with an Industrial Architecture

In the past, the application of carbon nanotube-silicon solar cell technology to industry has been limited by the use of a metallic frame to define an active area in the middle of a silicon wafer. Here, industry standard device geometries are fabricated with a front and back-junction design which allow for the entire wafer to be used as the active area. These are enabled by the use of an intermixed Nafion layer which simultaneously acts as a passivation, antireflective, and physical blocking layer as well as a nanotube dopant. This leads to the formation of a hybrid nanotube/Nafion passivated charge selective contact, and solar cells with active areas of 1–16 cm$^{2}$ are fabricated. Record maximum power conversion efficiencies of 15.2% and 18.9% are reported for front and back-junction devices for 1 and 3 cm$^{2}$ active areas, respectively. By placing the nanotube film on the rear of the device in a back-junction architecture, many of the design-related challenges for carbon nanotube silicon solar cells are addressed and their future applications to industrialized processes are discussed

Differentiable Robot Neural Distance Function for Adaptive Grasp Synthesis on a Unified Robotic Arm-Hand System

Grasping is a fundamental skill for robots to interact with their environment. While grasp execution requires coordinated movement of the hand and arm to achieve a collision-free and secure grip, many grasp synthesis studies address arm and hand motion planning independently, leading to potentially unreachable grasps in practical settings. The challenge of determining integrated arm-hand configurations arises from its computational complexity and high-dimensional nature. We address this challenge by presenting a novel differentiable robot neural distance function. Our approach excels in capturing intricate geometry across various joint configurations while preserving differentiability. This innovative representation proves instrumental in efficiently addressing downstream tasks with stringent contact constraints. Leveraging this, we introduce an adaptive grasp synthesis framework that exploits the full potential of the unified arm-hand system for diverse grasping tasks. Our neural joint space distance function achieves an 84.7% error reduction compared to baseline methods. We validated our approaches on a unified robotic arm-hand system that consists of a 7-DoF robot arm and a 16-DoF multi-fingered robotic hand. Results demonstrate that our approach empowers this high-DoF system to generate and execute various arm-hand grasp configurations that adapt to the size of the target objects while ensuring whole-body movements to be collision-free.Comment: Under revie

Effect of supercritical CO2 extraction on pore characteristics of coal and its mechanism

Abundant pore space in coal is not only the place for the accumulation of coalbed methane (CBM), but also the tunnel for gas migration. In this study, five sets of coal samples before and after the second coalification were selected from the eastern margin of Ordos Basin to simulate supercritical CO2 (Sc-CO2) extraction in supercritical extraction equipment. The evolutions of pore structure and porosity were tested by mercury intrusion porosimetry and nuclear magnetic resonance spectroscopy to compare the changes of pore structure and porosity due to the Sc-CO2 extraction, and to explain the related mechanism. The results show that: (1) Pore volume, pore specific surface area, and connectivity characteristics changed significantly due to Sc-CO2 extraction, and the increment of pore volume and pore specific surface area presented a law of increase–decrease–increase with the increase in the coal rank, and the turning point was near the second coalification. (2) The porosity increment change trend due to Sc-CO2 extraction was increase–decrease–increase with increasing coal rank, and the turning point was again near the second coalification, which supports the mercury intrusion porosimetry results. (3) The changes were observed in the porosity characteristics due to Sc-CO2 extraction through pore-increasing and expanding effects. Before the second coalification, the pore-increasing and expanding effects co-existed in the micropores, and after the second coalification, the pore-expanding effect mainly existed in the transitional pores and above. (4) The variation model for the pore structure of coal due to Sc-CO2 extraction was established. The conclusions offer not only important theoretical significance for the CO2-enhanced CBM (CO2-ECBM) mechanism but also important significance for CO2-ECBM engineering

Methyl 2-(5-fluoro-1H-indol-3-yl)-2-oxoacetate

The indolyl portion of the title mol­ecule, C11H8FNO3, is flat, the five- and six-membered rings making a dihedral angle of 0.815 (6)°. Inter­molecular N—H⋯O hydrogen bonds link adjacent mol­ecules into a linear chain. Slipped π–π stacking inter­actions between two neighboring indole groups further consolidate the mol­ecules into a three-dimensional supra­molecular architecture [centroid–centroid distances = 3.555 (10) and 3.569 (10) Å]

The numerical prediction of the Earth’s polar motion based on an advanced multivariate algorithm

Since there are complicated changes in the polar motion (PM) from sub-annual to decadal, precisely predicting it is challenging. Here, we provide an advanced multivariate algorithm by combining an iterative oblique singular spectrum analysis (IOSSA) with pseudo data (IOSSApd) and consider more periodic and quasi-periodic signals, especially long-period oscillations (Ding et al., Geophys. Res. Lett., 2019, 46, 13765–13774) and multi-frequency Chandler wobble (Pan, International Journal of Geosciences, 2012, 3, 930–951), than previous studies. The IOSSA in oblique coordinates, due to its weak separability conditions, has a better separation performance than general singular spectrum analysis (SSA), and the IOSSApd approach further solved the shift problem. Upon using the IOSSApd method, the PM data can be separated into deterministic and stochastic components, extrapolated by the multiple-harmonic (MH) and autoregressive integrated moving average (ARIMA) models, respectively. Based on the IERS EOPC04 PM series, we produced multiple sets of PM predictions with a 1-year leading time and reported the IERS Bulletin A predictions as a comparison. For 90-day leading time predictions, the mean absolute errors (MAEs) of the x- and y-components were 7.69 and 5.12 mas, respectively, while the corresponding MAEs obtained by IERS Bulletin A were 9.45 and 5.69 mas, respectively. For up to 360 days, our algorithm obtains the MAEs of PM slowly accumulating to 12.98 mas on average, far better than the 19.14 mas for Bulletin A’s predictions (also significantly superior to the corresponding results given by previous studies). The prediction performance in the middle- and long-term prediction is further compared against the general SSA predictor. By virtue of weak periodic error, our results show that combining the IOSSApd + MH + ARIMA models improved the prediction success rate up to 75.39% and 69.58% for the x- and y-component, respectively