In the impact tests of soft materials, we sometimes observe a thorn shape in the rising segment of the impact force waveform. However, the reason for the occurrence of the thorn shape has not been made clear. In this ...In the impact tests of soft materials, we sometimes observe a thorn shape in the rising segment of the impact force waveform. However, the reason for the occurrence of the thorn shape has not been made clear. In this study, thorn-shape waveforms of several soft materials are measured using compact drop test equipment under the condition of a flat frontal impact. A flat frontal impact is the condition where a drop hammer with a flat bottom surface strikes a plate-like soft material in the normal direction. Synchronized impact forces are measured using two sensors installed on both the drop hammer side and the floor side. The examined soft materials are a sponge sheet, sponge rubber sheet, gel sheet, rubber sheet, flat oil clay, low-rebound urethane foam, cork sheet, sliced ham, pork ham steak, and pork. Based on the test results, the features of the thorn-shape waveforms are discussed from a bird’s-eye view. Furthermore, the occurrence mechanism of the thorn-shape waveforms is discussed from the viewpoint of viscosity discontinuity and the double-strike phenomenon.展开更多
Formation and flow of emulsions in porous media are common in all enhanced oil recovery tech- niques. In most cases, oil-in-water （O/W） emulsions are formed in porous media due to oil-water interaction. Even now, de...Formation and flow of emulsions in porous media are common in all enhanced oil recovery tech- niques. In most cases, oil-in-water （O/W） emulsions are formed in porous media due to oil-water interaction. Even now, detailed flow mechanisms of emulsions through porous media are not well understood. In this study, variation of rate of flow of O/W emulsions with pressure drop was studied experimentally, and rheological pa- rameters were calculated. The pressure drop increases with an increase in oil concentration in the O/W emulsion due to high viscosity. The effective viscosity of the emulsion was calculated from the derived model and expressed as a function of shear rate while flowing through porous media. Flow of O/W emulsions of different concentrations was evaluated in sand packs of different sand sizes. Emulsions were characterized by analyzing their stability, rheological properties, and tem- perature effects on rheological properties.展开更多
基于2008—2015年龙门山地区的强震动记录,采用广义线性反演法计算了龙门山地区的震源参数、品质因子以及83个强震动台站的局部场地放大系数。结果显示:芦山地震发生之前,汶川地震余震的应力降随时间的增加而逐渐增大;芦山地震发生之后...基于2008—2015年龙门山地区的强震动记录,采用广义线性反演法计算了龙门山地区的震源参数、品质因子以及83个强震动台站的局部场地放大系数。结果显示:芦山地震发生之前,汶川地震余震的应力降随时间的增加而逐渐增大;芦山地震发生之后,龙门山断裂带上余震的应力降明显减小,并在之后随时间呈缓慢增大的趋势;部分M_S≥4.7余震事件的加速度震源谱中出现明显的高频衰减现象。通过对应力降随时间变化规律的分析认为,这种高频衰减现象可能与震级大小和震源破裂滑动的最大速率有关。此外,反演得到了山区和盆地地区的品质因子分别为Q(f)=264 f 0.75和Q(f)=223 f 1.01;同时获取了龙门山地区83个强震动台站的局部场地放大系数,并计算了基于NGA场地分类标准的A类、B类和C类场地的平均场地放大系数。结果显示,以上3类场地的平均场地放大系数具有相似的峰值,但是随着场地趋于软弱,峰值平台区向低频部分发育。展开更多
A three-dimensional computational fluid dynamics （CFD） model for gas flow through a serrated valve tray was presented. The flow field, as well as the dry-pressure drop of the valve under the full-opening condition w...A three-dimensional computational fluid dynamics （CFD） model for gas flow through a serrated valve tray was presented. The flow field, as well as the dry-pressure drop of the valve under the full-opening condition was simulated based on the proposed model by using FLUENT 6.0 software. Compared with the values of dry-pressure dro.p in different turbulent models, the.simulated.results using RNG κ-ε model are in reasonable agreement with experimental data, indicating that RNG κ-ε model is suitable in simulating gas flow through the serrated valve tray. Then the CFD model combining RNG κ-ε model was used to study the three-dimensional gas flow through the considered serrated valve tray. The simulated results showed that various eddies existed on the serrated valve tray, and both the eddy and the non-eddy areas were nearly equal. The existence of addendum can decrease the eddy area caused by gas passing through the lateral outlet slots. The size of eddies can be reduced by optimizing the distance between valves.展开更多
Scientific research provides essential information for conservation of threatened species.Data deficiency due to insufficient research impedes the design of conservation plans,and research bias may mistakenly direct l...Scientific research provides essential information for conservation of threatened species.Data deficiency due to insufficient research impedes the design of conservation plans,and research bias may mistakenly direct limited resources to low biodiversity regions or less threatened species.Here,we conducted a systematic review of published papers,grants,and graduate student training on carnivorans in China to identify species bias and research gaps.Furthermore,we collected intrinsic and extrinsic features of carnivorans,and identified features that impact research intensity using generalized linear models.We found that the amount of research on carnivorans increased markedly after 2000,but species bias existed.Bears and big cats received the greatest research attention,while most small-and medium-sized carnivorans received little attention,thus showing the 80-20 phenomenon.Species with a higher level of endemism and protection under Chinese law received more consideration.As an animal conservation icon in China,the giant panda(Ailuropoda melanoleuca)attracted more than 50%of overall carnivoran research resources.However,the giant panda also showed spillover effects,i.e.,post-doctoral graduates who studied the giant panda shifted their research focus to other species after graduation,which may help improve research on other species.Thus,to improve and strengthen Carnivora research and conservation,we suggest investing greater effort in species of less concern,training of more graduate students,and reinforcing academic exchange.If such actions are not taken,many carnivoran species will continue being data deficient and threatened.展开更多
文摘In the impact tests of soft materials, we sometimes observe a thorn shape in the rising segment of the impact force waveform. However, the reason for the occurrence of the thorn shape has not been made clear. In this study, thorn-shape waveforms of several soft materials are measured using compact drop test equipment under the condition of a flat frontal impact. A flat frontal impact is the condition where a drop hammer with a flat bottom surface strikes a plate-like soft material in the normal direction. Synchronized impact forces are measured using two sensors installed on both the drop hammer side and the floor side. The examined soft materials are a sponge sheet, sponge rubber sheet, gel sheet, rubber sheet, flat oil clay, low-rebound urethane foam, cork sheet, sliced ham, pork ham steak, and pork. Based on the test results, the features of the thorn-shape waveforms are discussed from a bird’s-eye view. Furthermore, the occurrence mechanism of the thorn-shape waveforms is discussed from the viewpoint of viscosity discontinuity and the double-strike phenomenon.
文摘Formation and flow of emulsions in porous media are common in all enhanced oil recovery tech- niques. In most cases, oil-in-water （O/W） emulsions are formed in porous media due to oil-water interaction. Even now, detailed flow mechanisms of emulsions through porous media are not well understood. In this study, variation of rate of flow of O/W emulsions with pressure drop was studied experimentally, and rheological pa- rameters were calculated. The pressure drop increases with an increase in oil concentration in the O/W emulsion due to high viscosity. The effective viscosity of the emulsion was calculated from the derived model and expressed as a function of shear rate while flowing through porous media. Flow of O/W emulsions of different concentrations was evaluated in sand packs of different sand sizes. Emulsions were characterized by analyzing their stability, rheological properties, and tem- perature effects on rheological properties.
文摘基于2008—2015年龙门山地区的强震动记录,采用广义线性反演法计算了龙门山地区的震源参数、品质因子以及83个强震动台站的局部场地放大系数。结果显示:芦山地震发生之前,汶川地震余震的应力降随时间的增加而逐渐增大;芦山地震发生之后,龙门山断裂带上余震的应力降明显减小,并在之后随时间呈缓慢增大的趋势;部分M_S≥4.7余震事件的加速度震源谱中出现明显的高频衰减现象。通过对应力降随时间变化规律的分析认为,这种高频衰减现象可能与震级大小和震源破裂滑动的最大速率有关。此外,反演得到了山区和盆地地区的品质因子分别为Q(f)=264 f 0.75和Q(f)=223 f 1.01;同时获取了龙门山地区83个强震动台站的局部场地放大系数,并计算了基于NGA场地分类标准的A类、B类和C类场地的平均场地放大系数。结果显示,以上3类场地的平均场地放大系数具有相似的峰值,但是随着场地趋于软弱,峰值平台区向低频部分发育。
基金Supported by the Natural Science Foundation of Zhejiang Province （Y404052）.
文摘A three-dimensional computational fluid dynamics （CFD） model for gas flow through a serrated valve tray was presented. The flow field, as well as the dry-pressure drop of the valve under the full-opening condition was simulated based on the proposed model by using FLUENT 6.0 software. Compared with the values of dry-pressure dro.p in different turbulent models, the.simulated.results using RNG κ-ε model are in reasonable agreement with experimental data, indicating that RNG κ-ε model is suitable in simulating gas flow through the serrated valve tray. Then the CFD model combining RNG κ-ε model was used to study the three-dimensional gas flow through the considered serrated valve tray. The simulated results showed that various eddies existed on the serrated valve tray, and both the eddy and the non-eddy areas were nearly equal. The existence of addendum can decrease the eddy area caused by gas passing through the lateral outlet slots. The size of eddies can be reduced by optimizing the distance between valves.
基金This study was supported by the National Natural Science Foundation of China(31900372,31822049)。
文摘Scientific research provides essential information for conservation of threatened species.Data deficiency due to insufficient research impedes the design of conservation plans,and research bias may mistakenly direct limited resources to low biodiversity regions or less threatened species.Here,we conducted a systematic review of published papers,grants,and graduate student training on carnivorans in China to identify species bias and research gaps.Furthermore,we collected intrinsic and extrinsic features of carnivorans,and identified features that impact research intensity using generalized linear models.We found that the amount of research on carnivorans increased markedly after 2000,but species bias existed.Bears and big cats received the greatest research attention,while most small-and medium-sized carnivorans received little attention,thus showing the 80-20 phenomenon.Species with a higher level of endemism and protection under Chinese law received more consideration.As an animal conservation icon in China,the giant panda(Ailuropoda melanoleuca)attracted more than 50%of overall carnivoran research resources.However,the giant panda also showed spillover effects,i.e.,post-doctoral graduates who studied the giant panda shifted their research focus to other species after graduation,which may help improve research on other species.Thus,to improve and strengthen Carnivora research and conservation,we suggest investing greater effort in species of less concern,training of more graduate students,and reinforcing academic exchange.If such actions are not taken,many carnivoran species will continue being data deficient and threatened.
