Direct determination of the diffusion coefficient variation of coal based on Fick's law and model establishment

Gas diffusion ability directly affects gas exploitation, outburst risk, emission and content determination. In order to study the influence of stress, gas pressure and temperature on gas diffusion coefficient in coal, the gas diffusion coefficient in columnar coal sample was measured with stable concentration difference, which avoided the model dependence that caused by deducing diffusion coefficient through desorption curve. The experimental results shown that the diffusion coefficient was approximately negative linear related to the effective stress for both the adsorbed methane and the non-adsorbed helium, but it was less affected than the permeability. The methane diffusion coefficient decreased as a power function with increasing inlet pressure (concentration gradient), and the relationship with temperature satisfied the Arrhenius formula. The diffusion coefficient measured by the steady-state method was compared with those obtained by the classical model and the time-varying model. It was found that the obtained diffusion coefficients were of the same order of magnitude, the sizes can be several times different, and the variation trend of diffusion coefficient was different with increasing gas pressure. Based on the law of diffusion coefficient affected by pressure (concentration) and temperature, a variable diffusion coefficient model was established. The gas desorption for granular coal at constant and variable temperature was predicted utilizing measured diffusion coefficient for columnar coal, and the prediction results were validated by desorption test. It indicated that the model can well reflect the gas diffusion process in the coal matrix under both constant and variable temperature condition

Moir\'e Fractional Chern Insulators II: First-principles Calculations and Continuum Models of Rhombohedral Graphene Superlattices

The experimental discovery of fractional Chern insulators (FCIs) in rhombohedral pentalayer graphene twisted on hexagonal boron nitride (hBN) has preceded theoretical prediction. Supported by large-scale first principles relaxation calculations at the experimental twist angle of $0.77^\circ$, we obtain an accurate continuum model of $n=3,4,5,6,7$ layer rhombohedral graphene-hBN moir\'e systems. Focusing on the pentalayer case, we analytically explain the robust $|C|=0,5$ Chern numbers seen in the low-energy single-particle bands and their flattening with displacement field, making use of a minimal two-flavor continuum Hamiltonian derived from the full model. We then predict nonzero valley Chern numbers at the $\nu = -4,0$ insulators observed in experiment. Our analysis makes clear the importance of displacement field and the moir\'e potential in producing localized "heavy fermion" charge density in the top valence band, in addition to the nearly free conduction band. Lastly, we study doubly aligned devices as additional platforms for moir\'e FCIs with higher Chern number bands.Comment: Second paper in the moir\'e FCI serie

A 3′ UTR SNP in COL18A1 Is Associated with Susceptibility to HBV Related Hepatocellular Carcinoma in Chinese: Three Independent Case-Control Studies

BACKGROUND: Accumulated evidences indicate that single nucleotide polymorphisms (SNP) in angiogenesis and tumorigenesis related genes are associated with risk of Hepatocellular carcinoma (HCC). COL18A1 encodes the precursor of endostatin, which is a broad-spectrum angiogenesis inhibitor, and we speculate that SNPs in COL18A1 may be associated with susceptibility to HCC. METHODS AND FINDINGS: We carried out a 2-stage association study in 3 independent case-control groups in a total of 1067 chronic hepatitis B (CHB) patients and 808 hepatitis B virus (HBV) related HCC patients in Han Chinese. Four SNPs which can represent all potential functional SNPs with MAF>0.1 recorded in HapMap database were genotyped using TaqMan methods. Levels of total COL18A1 mRNA were also examined using quantitative real-time RT-PCR. We found that rs7499 located in 3'-UTR to be strongly associated with HBV related HCC (P(combined) = 0.0000005, OR = 0.72, 95%CI = 0.63-0.82). COL18A1 mRNA expression was significantly decreased as the disease progressed (P = 0.000026). CONCLUSION: These findings indicate that COL18A1 rs7499 may contribute to the risk of HCC in Han Chinese

Historical trends of forest fires and carbon emissions in China from 1988 to 2012

A larger amount of carbon is stored in forest ecosystems than in the entire atmosphere. Thus, relatively small changes in forest carbon stocks can significantly impact net carbon exchange between the biosphere and atmosphere. Changes in forest stocks can result from various disturbances, such as insect pests, windstorms, flooding, and especially forest fires. Globally, the impact of forest fires has been enhanced due to ongoing warming of the climate. The current study reported an evaluation of carbon emissions from historical forest fires in China during 1988-2012 with observational data collected from national agriculture statistics. Historical fire trends and fire-induced carbon emissions were described over space and time at both national and regional levels. The results indicated that no significant increases in fire occurrence and carbon emissions were observed during the study period at the national level. However, at the regional level, there was a significant increasing trend in fire occurrence, and drought severity was a major driver of fire activity. Most carbon emissions were from north and northeast China, and these emissions contributed significantly to total carbon emissions. The results also showed that annual fire-induced emissions ranged from 0.04TgC to 7.22TgC, with an average of 1.03TgC. Large interannual and spatial variabilities of carbon emissions were also indicated, and these were attributed to spatial and temporal variations in fire regimes. The results improve understanding of fire characteristics and provide significant information for reducing model-related uncertainty of fire-induced carbon emissions

Historical trends of forest fires and carbon emissions in China from 1988 to 2012

A larger amount of carbon is stored in forest ecosystems than in the entire atmosphere. Thus, relatively small changes in forest carbon stocks can significantly impact net carbon exchange between the biosphere and atmosphere. Changes in forest stocks can result from various disturbances, such as insect pests, windstorms, flooding, and especially forest fires. Globally, the impact of forest fires has been enhanced due to ongoing warming of the climate. The current study reported an evaluation of carbon emissions from historical forest fires in China during 1988-2012 with observational data collected from national agriculture statistics. Historical fire trends and fire-induced carbon emissions were described over space and time at both national and regional levels. The results indicated that no significant increases in fire occurrence and carbon emissions were observed during the study period at the national level. However, at the regional level, there was a significant increasing trend in fire occurrence, and drought severity was a major driver of fire activity. Most carbon emissions were from north and northeast China, and these emissions contributed significantly to total carbon emissions. The results also showed that annual fire-induced emissions ranged from 0.04TgC to 7.22TgC, with an average of 1.03TgC. Large interannual and spatial variabilities of carbon emissions were also indicated, and these were attributed to spatial and temporal variations in fire regimes. The results improve understanding of fire characteristics and provide significant information for reducing model-related uncertainty of fire-induced carbon emissions

Novel method for modified interlaminar approach using contralateral oblique view: A technical suggestion.

A modified interlaminar (MIL) approach has been proposed for improved accessibility to the target epidural space. However, even with fluoroscopic guidance, uncertainty about the distance between the needle tip and the epidural space can remain. Using the contralateral oblique (CLO) view, determination of the epidural space can be easier with clearer identification of the interlaminar opening. We inserted the needle at the midpoint of the interlaminar opening on the fluoroscopic anteroposterior (AP) view and made the needle oriented toward the pedicle of the target side. Then, CLO view was created by rotating the intensifier approximately 45 degrees to the contralateral side of the target. Through the CLO view, the ventral interlaminar line (VILL) was confirmed and the needle was able to enter the epidural space more easily. The medical records of 29 patients who were conducted MIL approach using CLO view were retrospectively analyzed to evaluate the effectiveness and safety of this procedure. The accessibility to the ventral epidural space was 93.1%. There was no procedure-related complication. Using CLO view, uncertainty can be reduced during the MIL approach, which in turn shortens procedure time and improves safety

Technologies for Heat Hazard Governance and Thermal Energy Recovery in Deep Mines

As the depth of mines continues to increase, the problems of high temperature and potential heat damage become more prominent. In this study, the characteristics of natural and industrial heat sources in mines were reviewed, and then mainstream heat hazard governance technologies and corresponding utilization methods were discussed and compared. The first category of technologies comprises the optimization of ventilation systems, the insulation of roc heat, and artificial refrigeration. These cooling approaches are limited because the heat resources cannot be recovered. The second category is the utilization of waste industrial heat in mines, including the use of waste heat from the air compressors, drainage water, and foul airflow, but the current applications of these approaches have limited effectiveness in cooling the underground space. The third category is the application of geo-structures to recover natural heat in mines. Based on the principles of the chiller/heat pump cycle and the characteristics of heat sources and sinks in mines, the potential and constraints of each technology were discussed and summarized. This study provides a scientific reference for the selection of suitable heat governance and utilization technologies

Numerical Study of the Thermo-Hydro-Mechanical Coupling Impacts of Shallow Geothermal Borehole Groups in Fractured Rock Mass on Geological Environment

Fractured rock mass is extensively distributed in Karst topography regions, and its geological environment is different from that of the quaternary strata. In this study, the influences on geological environment induced by the construction and operation of a large-scale borehole group of ground source heat pumps are analyzed by a thermo-hydro-mechanical (THM) coupling numerical model. It was found that groundwater is redirected as the boreholes can function as channels to the surface, and the flow velocity in the upstream of borehole group is higher than those downstream. This change in groundwater flow enhances heat transfer in the upstream boreholes but may disturb the original groundwater system and impact the local geological environment. Heat accumulation is more likely to occur downstream. The geo-stress concentration appears in the borehole area, mainly due to exaction and increasing with the depth. On the fracture plane, tensile stress and maximum shear stress simultaneously occur on the upstream of boreholes, inducing the possibility of fracturing or the expansion of existing fractures. There is a slight uplift displacement on the surface after the construction of boreholes. The correlations of the above THM phenomena are discussed and analyzed. From the modeling results, it is suggested that the consolidation of backfills can minimize the environmental disturbances in terms of groundwater redirection, thermal accumulation, occurrence of tensile stress, and possible fracturing. This study provides support for the assessment of impacts on geological environments resulting from shallow geothermal development and layout optimization of ground heat exchangers in engineering practices

The influence of residual stress for the strength of plate-fin structures in the typical operation process of Liquefied Natural Gas (LNG) heat exchanger

In order to ensure the safe operation of heat exchangers in the Liquefied Natural Gas (LNG), the stress analysis model of aluminum Plate-Fin Structure (PFS) is established based on the thermal-elastic-plasticity theory. The residual stress distribution of PFS and its influence on the structural strength is analyzed by the thermal-structural coupling method. The results indicate that the residual stress distribution of PFS is very complex, and the residual stress reaches the peak at the Brazed Joint (BJ). Due to the equivalent stress at BJ near the fin is higher than that at BJ near the plate, cracks are more easily produced at BJ near the fin. Therefore, the existence of residual stress has a negative impact on PFS, which may increase the possibility of strength failure at BJ under the typical operating conditions (normal operation, cut-down and heat-up) of the heat exchanger. In addition, the residual stress gradually decreases with the brazing cooling rate decrease. The residual stress within the PFS will be effectively reduced by properly reducing the brazing cooling rate, which can slow down the strength failure of the PFS. The above research results will provide an important basis for the design and safe operation of the aluminum plate-fin heat exchanger