Experimental study on the flow behaviour of water-sand mixtures in fractured rock specimens

The study of flow behaviour of water-sand mixtures in fractured rocks is of great necessity to understand the producing mechanism and prevention of water inrush and sand gushing accidents.A self-developed seepage test system is used in this paper to conduct laboratory experiments in order to study the influence of the particle size distribution,the void ratio,and the initial mass of Aeolian sand on the flow behavior.It is concluded that the water flow velocity is insensitive to the initial mass of the Aeolian sand but increases with the power exponent in the Talbot formula and the specimen height.The outflow of the Aeolian sand increases with the power exponent in the Talbot formula,the specimen height,and the initial mass of the Aeolian sand.Besides,the outflow of the Aeolian sand changes exponentially with the water flow velocity.Finally,it is found that the fractured specimen has a maximum sand filtration capacity beyond which the outflow of the Aeolian sand significantly increases with the initial mass of the Aeolian sand.

Microcrack fracturing of coal specimens under quasi-static combined compression-shear loading

Coal pillars are usually loaded under combined compression-shear stresses at underground coal mines.Their long-term stability is critical to the utilization of underground structures,such as underground reservoirs at coal mines.In this study,a modified rock property testing system was used to explore the mechanical properties of coal specimens under quasi-static combined compression-shear loading conditions.The acoustic emission technique was applied to investigating the microcrack fracturing of coal specimens at various inclination angles.The experimental results show that specimen inclination has remarkable effects on the microcrack initiation,microcrack damage and ultimate failure of the coal specimen.The failure mode of the coal specimen tends to transit from axial splitting to shear failure with increasing specimen inclination,and its peak strength is closely associated with the microcrack damage threshold.In practice,it is recommended to consider coal strength under combined compression-shear loading when using empirical pillar strength formulae so that the effect of pillar inclination can be included.

血清甲胎蛋白阳性胃癌患者临床病理特征与预后关系的研究

目的:探讨血清AFP阳性胃癌(alpha-fetoprotein producing gastric cancer,AFPGC)与普通型胃癌的差异以及其临床病理特征和预后的关系。方法:回顾性分析2013年1月至2018年12月在中国人民解放军联勤保障部队第九四〇医院行胃癌手术的患者1321例,经筛选纳入研究1144例,分为血清AFP阳性组(53例)与血清AFP阴性组(1091例)。结果:AFPGC占同期胃癌患者的4.6%,AFPGC与血清AFP阴性胃癌1、3、5年累计生存率分别为64.2%与92.2%、20.8%与45.1%、13.2%与25.7%,两者术前血清AFP、肿瘤大小、免疫组织化学HER2、肿瘤部位、浸润深度、淋巴结转移、临床分期、脉管侵犯、手术方式、术后肝转移相比,均差异具有统计学意义(P<0.05)。AFPGC单因素以及Cox多因素生存分析显示:临床分期、脉管侵犯、手术方式、术后肝转移以及术后血清AFP再次升高是影响AFPGC预后的危险因素。结论:AFPGC是一种特殊性的胃癌,具有临床分期晚、易发生术后肝转移和脉管侵犯且预后差,AFPGC患者即使肿瘤原发灶被切除后,仍有较高的肝转移风险,且术前血清AFP水平与患者预后无关,而术后监测血清AFP水平可及时发现肿瘤复发及术后肝转移,此外,早期行胃癌根治术有助于改善患者预后。

Stress and deformation analysis of gob-side pre-backfill driving procedure of longwall mining:a case study

At present,non-pillar entry protection in longwall mining is mainly achieved through either the gob-side entry retaining(GER)procedure or the gob-side entry driving(GED)procedure.The GER procedure leads to difficulties in maintaining the roadway in mining both the previous and current panels.A narrow coal pillar about 5-7 m must be left in the GED procedure;therefore,it causes permanent loss of some coal.The gob-side pre-backfill driving(GPD)procedure effectively removes the wasting of coal resources that exists in the GED procedure and finds an alternative way to handle the roadway maintenance problem that exists in the GER procedure.The FLAC^(3D) software was used to numerically investigate the stress and deformation distributions and failure of the rock mass surrounding the previous and current panel roadways during each stage of the GPD procedure which requires"twice excavation and mining".The results show that the stress distribution is slightly asymmetric around the previous panel roadway after the"primary excavation".The stronger and stiffer backfill compared to the coal turned out to be the main bearing body of the previous panel roadway during the"primary mining".The highest vertical stresses of 32.6 and 23.1 MPa,compared to the in-situ stress of 10.5 MPa,appeared in the backfill wall and coal seam,respectively.After the"primary mining",the peak vertical stress under the coal seam at the floor level was slightly higher(18.1 MPa)than that under the backfill(17.8 MPa).After the"secondary excavation",the peak vertical stress under the coal seam at the floor level was slightly lower(18.7 MPa)than that under the backfill(19.8 MPa);the maximum floor heave and maximum roof sag of the current panel roadway were 252.9 and 322.1 mm,respectively.During the"secondary mining",the stress distribution in the rock mass surrounding the current panel roadway was mainly affected by the superposition of the front abutment pressure from the current panel and the side abutment pressure from the previous panel.The floor heave of the current panel roadway reached a maximum of 321.8 mm at 5 m ahead of the working face;the roof sag increased to 828.4 mm at the working face.The peak abutment pressure appeared alternately in the backfill and the coal seam during the whole procedure of"twice excavation and mining"of the GPD procedure.The backfill provided strong bearing capacity during all stages of the GPD procedure and exhibited reliable support for the roadway.The results provide scientific insight for engineering practice of the GPD procedure.

Early changes to the extracellular space in the hippocampus under simulated microgravity conditions

The smooth transportation of substances through the brain extracellular space(ECS)is crucial to maintaining brain function;however,the way this occurs under simulated microgravity remains unclear.In this study,tracer-based magnetic resonance imaging(MRI)and DECS-mapping techniques were used to image the drainage of brain interstitial fluid(ISF)from the ECS of the hippocampus in a tail-suspended hindlimb-unloading rat model at day 3(HU-3)and 7(HU-7).The results indicated that drainage of the ISF was accelerated in the HU-3 group but slowed markedly in the HU-7 group.The tortuosity of the ECS decreased in the HU-3 group but increased in the HU-7 group,while the volume fraction of the ECS increased in both groups.The diffusion rate within the ECS increased in the HU-3 group and decreased in the HU-7 group.The alterations to ISF drainage and diffusion in the ECS were recoverable in the HU-3 group,but neither parameter was restored in the HU-7 group.Our findings suggest that early changes to the hippocampal ECS and ISF drainage under simulated microgravity can be detected by tracer-based MRI,providing a new perspective for studying microgravity-induced nano-scale structure abnormities and developing neuroprotective approaches involving the brain ECS.