Although the late Quaternary slip rate of the Northern Margin Fault of the Huaizhuo Basin(NFHB)was studied approximately 30 years ago using thermoluminescence and geomorphic methods,the underlying uncertainty cannot b...Although the late Quaternary slip rate of the Northern Margin Fault of the Huaizhuo Basin(NFHB)was studied approximately 30 years ago using thermoluminescence and geomorphic methods,the underlying uncertainty cannot be neglected,considering the limitations resulting from age and displacement measurements.Accordingly,we attempted to re-estimate the late Quaternary slip rate of the NFHB using high-precision remote sensing image interpretation,large-scale geological and geomorphic mapping,paleoseismic analysis,and Quaternary geochronology testing.The results,based on stratigraphic dislocation and age constraint in the trenches,show that the present deformation of the NFHB has been dominated by the extension,with a vertical slip rate~0.04-0.11 mm/a.We estimate a vertical slip rate of~0.06 mm/a,with an R^(2) value of~0.91,which is much lower than the~0.5 mm/a result estimated previously.There are three possible reasons for this discrepancy.The fi rst is the limitation resulting from dating and displacement measurements in earlier studies;the second is the slip decomposition caused by multiple branches of the NFHB,which leads to the low slip rate observed at a single fault;and third possible explanation is that the fault may be locked at present with a low slip rate,which means that the earthquake hazard of the NFHB cannot be ignored,and more in-depth research,such as geodetic and intensive observations of earthquake precursors,is urgently needed.This discovery poses a new challenge for the active study of the NFHB and the northeast corner of the Ordos Plateau in the North China Block.展开更多
The relationships of cooling rate with microstructure and thermal conductivity of vermicular graphite cast iron(VGI) cylinder block were studied, which are important for design and optimization of the casting process ...The relationships of cooling rate with microstructure and thermal conductivity of vermicular graphite cast iron(VGI) cylinder block were studied, which are important for design and optimization of the casting process of VGI cylinder blocks. Cooling rates at different positions in the cylinder block were calculated based on the cooling curves recorded with a solidification simulation software. The metallographic structure and thermal conductivity were observed and measured using optical microscopy(OM), scanning electrical microscopy(SEM) and laser flash diffusivity apparatus, respectively. The effects of the cooling rate on the vermicularity, total and average areas of all graphite particles, and the pearlite fraction in the VGI cylinder block were investigated. It is found that the vermicularity changes in parabola trend with the increase of cooling rate. The total area of graphite particles and the cooling rate at eutectoid stage can be used to predict pearlite fraction well. Moreover, it is found that the thermal conductivity at room temperature is determined by the average area of graphite particles and pearlite fraction when the range of vermicularity is from 80% to 93%. Finally, the quantitative models are established to calculate the vermicularity, pearlite fraction, and thermal conductivity of the VGI cylinder block.展开更多
Purpose: Whether or not right and left stellate ganglion blocks (SGB) affect blood pressure (BP) and heart rate (HR) differently has been controversial. The aim of this study was to analyze BP and HR changes after lar...Purpose: Whether or not right and left stellate ganglion blocks (SGB) affect blood pressure (BP) and heart rate (HR) differently has been controversial. The aim of this study was to analyze BP and HR changes after large numbers of right or left SGBs. Methods: A total of 16,404 right SGBs and 13,766 left SGBs were performed with 6 ml of 1% mepivacaine using the anterior paratracheal approach at C6. Changes in systolic BP and HR 30 min after SGBs were compared to the baseline values. Results: Systolic BP decreased by 25 to 49 mmHg in 10.93% and more than 50 mmHg in 0.67% of 16,404 right SGBs. Those percentages were significantly higher than corresponding percentages;8.43% and 0.49% of 13,766 left SGBs (P < 0.0001 and P < 0.05, respectively). On the other hand, systolic BP increased by 25-49 mmHg in 5.74% and more than 50 mmHg in 0.52% of left SGBs, and in 4.15% and 0.18% of right SGBs (P < 0.0001and P < 0.0001 between left and right SGBs, respectively). Right SGB caused marked reduction in HR (greater than 30 beats/min), more than left SGB (4.22% versus 2.70%, P Conclusions: Both right and left SGBs could produce clinically significant hypertension and hypotension, and also severe bradycardia. However, right SGB produces a higher incidence of significant reductions in systolic BP and HR, compared to left SGB. On the other hand, left SGB produces a significant increase in systolic BP compared to right SGB. Those differences likely stem from the hemispheric asymmetry in autonomic cardiovascular control.展开更多
In this paper, using the 1999 ~ 2007 GPS velocity field data, and by choosing the optimal block model, we obtained the deformation models applicable to the boundary zones of major blocks and the slip rates of block bo...In this paper, using the 1999 ~ 2007 GPS velocity field data, and by choosing the optimal block model, we obtained the deformation models applicable to the boundary zones of major blocks and the slip rates of block boundary faults on the mid-southern segment of the North-South Seismic Belt. The results show that： on the Longmenshan fault zone, the tensional and compressive slip rate is small on the Baoxing-Wenchuan segment, about 0. 5 ~ 1.8mm·a^-1, and the rate is relatively significant on the segment of the Wenchuan--Maoxian, as 1.8 ~3.8mm·a^-1; on the Xianshuihe fault belt, there is a certain difference in spatial distribution between the tensional slip rag.e and strike-slip rate： the tensional slip rate （ 8. lmm^a-1） is bigger than the sinistral strike-slip rate （ 4.8mm·a^-1） at the north of the Luhuo region; the tension and compression slip rate is basically the same as the strike-slip rate at Luhuo-Dawu; the Dawu-Kangding section presents a trend of decreased strike-slip rate and increased tensional slip rate; the Kangding-ghimian segment shows a strike-slip nature; the strike-slip rate is significantly greater than the tension/compression rate on the Xiaojiang fault zone; the slip rate on the Red River fault zone shows obvious spatial segmentation, the slip rate is smaller in its northwest part, but with a certain amount of tensional/compression component, 4. 7mm·a^-1 on the Jingdong segment. The segment east of Jingdong （ western Gejiu） is mainly of strike-slip, with a slip rate of 4. 5mm·a^-1.展开更多
Global Positioning System (GPS) observations during four measurement campaigns from 1992 to 1999 are used in a study of the temporal and spatial variation characteristics of crustal deformation of active tectonic bloc...Global Positioning System (GPS) observations during four measurement campaigns from 1992 to 1999 are used in a study of the temporal and spatial variation characteristics of crustal deformation of active tectonic blocks in North China. The Euler vectors for these active blocks are determined on the basis of GPS velocities of a group relative stable points in 1992,1995,1996 and in 1996,1999 respectively. We have studied the relative motion between blocks at the boundaries and the intra block deformation field. We have also inverted the strain rate fields for these active blocks by bi cubic spline model based on the GPS velocity field. The results show that the intra block deformation rates are different from those in block boundary zones, and are also different in different periods; the deformational field is generally characterized by intra-block extension in North China.展开更多
In order to study the mechanics,acoustic emission(AE)and electromagnetic emission(EME)response law of bursting liability coal at different loading rates,uniaxial compression tests were carried out on coal mass from Ko...In order to study the mechanics,acoustic emission(AE)and electromagnetic emission(EME)response law of bursting liability coal at different loading rates,uniaxial compression tests were carried out on coal mass from Konggu Coal Mine.The corresponding relations among mechanical properties,AE and EME signals in the process of coal failure under loading were analyzed,and the energy evolution law of coal failure with bursting liability under loading rate was discussed.The results show that within a certain range of loading rate,the higher the loading rate,the higher the compressive strength and peak load of bursting liability coal,and the shorter the time for coal to reach the peak load.Under different loading rates,the mechanics,AE and EME signals of coal samples can be well corresponded.When the loading rate is low,the number of blocks destroyed of coal sample is large and the block size is relatively small,and the blocks are mainly scattered around the test platform.When the loading rate is high,the number of damaged blocks is relatively small and the block size is relatively large,and the blocks are far away from the test bench.When loading at a low rate,the internal cracks in coal can be fully developed and connected,and the energy release rate is relatively uniform in the process of loading and failure of coal sample.In the case of high loading rate,the energy release rate of coal sample in the loading process is much smaller than that in the moment of failure.Combining the above test results with the actual situation of the working face,it can be concluded that the total energy stored in the coal of fast mining increases and the threshold of impact decreases compared with that of slow mining.Therefore,under the disturbance of external dynamic load,rapid mining is more likely to induce rock burst.展开更多
Due to the high complexity of the pairwise decoding algorithm and the poor performance of zero forcing（ ZF） /minimum mean square error（ MMSE） decoding algorithm, two low-complexity suboptimal decoding algorithms, ...Due to the high complexity of the pairwise decoding algorithm and the poor performance of zero forcing（ ZF） /minimum mean square error（ MMSE） decoding algorithm, two low-complexity suboptimal decoding algorithms, called pairwisequasi-ZF and pairwise-quasi-MMSE decoders, are proposed. First,two transmit signals are detected by the quasi-ZF or the quasiMMSE algorithm at the receiver. Then, the two detected signals as the decoding results are substituted into the two pairwise decoding algorithm expressions to detect the other two transmit signals. The bit error rate（ BER） performance of the proposed algorithms is compared with that of the current known decoding algorithms.Also, the number of calculations of ZF, MMSE, quasi-ZF and quasi-MMSE algorithms is compared with each other. Simulation results showthat the BER performance of the proposed algorithms is substantially improved in comparison to the quasi-ZF and quasiMMSE algorithms. The BER performance of the pairwise-quasiZF（ pairwise-quasi-MMSE） decoder is equivalent to the pairwiseZF（ pairwise-MMSE） decoder, while the computational complexity is significantly reduced.展开更多
Objective:To understand the characteristic parameters and radon exhalation rates of aerated concrete blocks.Methods:A total of 39 nationally inspected samples were measured.Their dry density was determined based on th...Objective:To understand the characteristic parameters and radon exhalation rates of aerated concrete blocks.Methods:A total of 39 nationally inspected samples were measured.Their dry density was determined based on their mass and volumes,their porosities were measured on the principle of volumetric expansion,and their radium content was determined using a high-purity germanium(HPGe)detector for gamma-ray spectroscopy.Furthermore,their diffusion lengths were quantified by establishing a combined cumulative and diffusion chamber,and their radon exhalation rates were measured through closed-box testing using a continuous radon monitor.Results:The aerated concrete blocks exhibited dry densities ranging from 464 to 840 kg/m^(3)[average:(654.0±82.5)kg/m^(3)],open porosities from 67.1%to 81.1%[average:(74.3±3.3)%],radium(^(226)Ra)content from 12.3 to 136 Bq/kg[average:(63.0±30.4)Bq/kg],diffusion lengths from 0.49 to 1.01 m[average:(0.70±0.15)m],and radon exhalation rates from 0.6 to 22.8 Bq·m^(-2)·h^(-1)[average:(7.3±5.3)Bq·m^(-2)·h^(-1)].Conclusion:Aerated concrete blocks exhibit significantly higher porosities,diffusion lengths,and radon exhalation rates than traditional concrete and clay bricks.These blocks might contribute to the high indoor radon concentration observed in modern buildings in China.展开更多
After hydraulic fracturing treatment,a reduction in permeability caused by the invasion of fracturing fluids is an inevitable problem,which is called water blocking damage.Therefore,it is important to mitigate and eli...After hydraulic fracturing treatment,a reduction in permeability caused by the invasion of fracturing fluids is an inevitable problem,which is called water blocking damage.Therefore,it is important to mitigate and eliminate water blocking damage to improve the flow capacities of formation fluids and flowback rates of the fracturing fluid.However,the steady-state core flow method cannot quickly and accurately evaluate the effects of chemical agents in enhancing the fluid flow capacities in tight reservoirs.This paper introduces a time-saving and accurate method,pressure transmission test(PTT),which can quickly and quantitatively evaluate the liquid flow capacities and gas-drive flowback rates of a new nanoemulsion.Furthermore,scanning electron microscopy(SEM)was used to analyze the damage mechanism of different fluids and the adsorption of chemical agents on the rock surface.Parallel core flow experiments were used to evaluate the effects of the nanoemulsion on enhancing flowback rates in heterogeneous tight reservoirs.Experimental results show that the water blocking damage mechanisms differ in matrices and fractures.The main channels for gas channeling are fractures in cracked cores and pores in non-cracked cores.Cracked cores suffer less damage from water blocking than non-cracked cores,but have a lower potential to reduce water saturation.The PTT and SEM results show that the permeability reduction in tight sandstones caused by invasion of external fluids can be list as guar gum fracturing fluid>slickwater>brine.Parallel core flow experiments show that for low-permeability heterogenous s andstone reservoirs with a certain permeability ratio,the nanoemulsion can not only reduce reverse gas channeling degree,but also increase the flowback rate of the fracturing fluid.The nanoemulsion system provides a new solution to mitigate and eliminate water blocking damage caused by fracturing fluids in tight sandstone gas reservoirs.展开更多
A brain-computer interface(BCI)-based electric wheelchair control system was developed, which enables the users to move the wheelchair forward or backward, and turn left or right without any pre-learning. This control...A brain-computer interface(BCI)-based electric wheelchair control system was developed, which enables the users to move the wheelchair forward or backward, and turn left or right without any pre-learning. This control system makes use of the amplitude enhancement of alpha-wave blocking in electroencephalogram(EEG) when eyes close for more than 1 s to constitute a BCI for the switch control of wheelchair movements. The system was formed by BCI control panel, data acquisition, signal processing unit and interface control circuit. Eight volunteers participated in the wheelchair control experiments according to the preset routes. The experimental results show that the mean success control rate of all the subjects was 81.3%, with the highest reaching 93.7%. When one subject's triggering time was 2.8 s, i.e., the flashing time of each cycle light was 2.8 s, the average information transfer rate was 8.10 bit/min, with the highest reaching 12.54 bit/min.展开更多
基金The research and development project of Beijing Disaster Prevention Technology Co.,Ltd.(FZKJYF202201)funded this work.
文摘Although the late Quaternary slip rate of the Northern Margin Fault of the Huaizhuo Basin(NFHB)was studied approximately 30 years ago using thermoluminescence and geomorphic methods,the underlying uncertainty cannot be neglected,considering the limitations resulting from age and displacement measurements.Accordingly,we attempted to re-estimate the late Quaternary slip rate of the NFHB using high-precision remote sensing image interpretation,large-scale geological and geomorphic mapping,paleoseismic analysis,and Quaternary geochronology testing.The results,based on stratigraphic dislocation and age constraint in the trenches,show that the present deformation of the NFHB has been dominated by the extension,with a vertical slip rate~0.04-0.11 mm/a.We estimate a vertical slip rate of~0.06 mm/a,with an R^(2) value of~0.91,which is much lower than the~0.5 mm/a result estimated previously.There are three possible reasons for this discrepancy.The fi rst is the limitation resulting from dating and displacement measurements in earlier studies;the second is the slip decomposition caused by multiple branches of the NFHB,which leads to the low slip rate observed at a single fault;and third possible explanation is that the fault may be locked at present with a low slip rate,which means that the earthquake hazard of the NFHB cannot be ignored,and more in-depth research,such as geodetic and intensive observations of earthquake precursors,is urgently needed.This discovery poses a new challenge for the active study of the NFHB and the northeast corner of the Ordos Plateau in the North China Block.
文摘The relationships of cooling rate with microstructure and thermal conductivity of vermicular graphite cast iron(VGI) cylinder block were studied, which are important for design and optimization of the casting process of VGI cylinder blocks. Cooling rates at different positions in the cylinder block were calculated based on the cooling curves recorded with a solidification simulation software. The metallographic structure and thermal conductivity were observed and measured using optical microscopy(OM), scanning electrical microscopy(SEM) and laser flash diffusivity apparatus, respectively. The effects of the cooling rate on the vermicularity, total and average areas of all graphite particles, and the pearlite fraction in the VGI cylinder block were investigated. It is found that the vermicularity changes in parabola trend with the increase of cooling rate. The total area of graphite particles and the cooling rate at eutectoid stage can be used to predict pearlite fraction well. Moreover, it is found that the thermal conductivity at room temperature is determined by the average area of graphite particles and pearlite fraction when the range of vermicularity is from 80% to 93%. Finally, the quantitative models are established to calculate the vermicularity, pearlite fraction, and thermal conductivity of the VGI cylinder block.
文摘Purpose: Whether or not right and left stellate ganglion blocks (SGB) affect blood pressure (BP) and heart rate (HR) differently has been controversial. The aim of this study was to analyze BP and HR changes after large numbers of right or left SGBs. Methods: A total of 16,404 right SGBs and 13,766 left SGBs were performed with 6 ml of 1% mepivacaine using the anterior paratracheal approach at C6. Changes in systolic BP and HR 30 min after SGBs were compared to the baseline values. Results: Systolic BP decreased by 25 to 49 mmHg in 10.93% and more than 50 mmHg in 0.67% of 16,404 right SGBs. Those percentages were significantly higher than corresponding percentages;8.43% and 0.49% of 13,766 left SGBs (P < 0.0001 and P < 0.05, respectively). On the other hand, systolic BP increased by 25-49 mmHg in 5.74% and more than 50 mmHg in 0.52% of left SGBs, and in 4.15% and 0.18% of right SGBs (P < 0.0001and P < 0.0001 between left and right SGBs, respectively). Right SGB caused marked reduction in HR (greater than 30 beats/min), more than left SGB (4.22% versus 2.70%, P Conclusions: Both right and left SGBs could produce clinically significant hypertension and hypotension, and also severe bradycardia. However, right SGB produces a higher incidence of significant reductions in systolic BP and HR, compared to left SGB. On the other hand, left SGB produces a significant increase in systolic BP compared to right SGB. Those differences likely stem from the hemispheric asymmetry in autonomic cardiovascular control.
基金jointly sponsored by the National Key Technology R&D Program of the 12th "Five-year Plan" of PRC(2012BAK19B02)the Special Fund for Earthquake-related Scientific Research of China Earthquake Administration(201108009)the Youth Earthquake Regime Tracing Project for 2012(2012020212)
文摘In this paper, using the 1999 ~ 2007 GPS velocity field data, and by choosing the optimal block model, we obtained the deformation models applicable to the boundary zones of major blocks and the slip rates of block boundary faults on the mid-southern segment of the North-South Seismic Belt. The results show that： on the Longmenshan fault zone, the tensional and compressive slip rate is small on the Baoxing-Wenchuan segment, about 0. 5 ~ 1.8mm·a^-1, and the rate is relatively significant on the segment of the Wenchuan--Maoxian, as 1.8 ~3.8mm·a^-1; on the Xianshuihe fault belt, there is a certain difference in spatial distribution between the tensional slip rag.e and strike-slip rate： the tensional slip rate （ 8. lmm^a-1） is bigger than the sinistral strike-slip rate （ 4.8mm·a^-1） at the north of the Luhuo region; the tension and compression slip rate is basically the same as the strike-slip rate at Luhuo-Dawu; the Dawu-Kangding section presents a trend of decreased strike-slip rate and increased tensional slip rate; the Kangding-ghimian segment shows a strike-slip nature; the strike-slip rate is significantly greater than the tension/compression rate on the Xiaojiang fault zone; the slip rate on the Red River fault zone shows obvious spatial segmentation, the slip rate is smaller in its northwest part, but with a certain amount of tensional/compression component, 4. 7mm·a^-1 on the Jingdong segment. The segment east of Jingdong （ western Gejiu） is mainly of strike-slip, with a slip rate of 4. 5mm·a^-1.
文摘Global Positioning System (GPS) observations during four measurement campaigns from 1992 to 1999 are used in a study of the temporal and spatial variation characteristics of crustal deformation of active tectonic blocks in North China. The Euler vectors for these active blocks are determined on the basis of GPS velocities of a group relative stable points in 1992,1995,1996 and in 1996,1999 respectively. We have studied the relative motion between blocks at the boundaries and the intra block deformation field. We have also inverted the strain rate fields for these active blocks by bi cubic spline model based on the GPS velocity field. The results show that the intra block deformation rates are different from those in block boundary zones, and are also different in different periods; the deformational field is generally characterized by intra-block extension in North China.
基金Supported by the National Natural Science Foundation of China(52304203,52374180 and 52327804).
文摘In order to study the mechanics,acoustic emission(AE)and electromagnetic emission(EME)response law of bursting liability coal at different loading rates,uniaxial compression tests were carried out on coal mass from Konggu Coal Mine.The corresponding relations among mechanical properties,AE and EME signals in the process of coal failure under loading were analyzed,and the energy evolution law of coal failure with bursting liability under loading rate was discussed.The results show that within a certain range of loading rate,the higher the loading rate,the higher the compressive strength and peak load of bursting liability coal,and the shorter the time for coal to reach the peak load.Under different loading rates,the mechanics,AE and EME signals of coal samples can be well corresponded.When the loading rate is low,the number of blocks destroyed of coal sample is large and the block size is relatively small,and the blocks are mainly scattered around the test platform.When the loading rate is high,the number of damaged blocks is relatively small and the block size is relatively large,and the blocks are far away from the test bench.When loading at a low rate,the internal cracks in coal can be fully developed and connected,and the energy release rate is relatively uniform in the process of loading and failure of coal sample.In the case of high loading rate,the energy release rate of coal sample in the loading process is much smaller than that in the moment of failure.Combining the above test results with the actual situation of the working face,it can be concluded that the total energy stored in the coal of fast mining increases and the threshold of impact decreases compared with that of slow mining.Therefore,under the disturbance of external dynamic load,rapid mining is more likely to induce rock burst.
基金The National Natural Science Foundation of China(No.6157110861201248)+1 种基金the Open Research Fund of National Mobile Communications Research Laboratory of China(No.2011D18)China Postdoctoral Science Foundation(No.2012M511175)
文摘Due to the high complexity of the pairwise decoding algorithm and the poor performance of zero forcing（ ZF） /minimum mean square error（ MMSE） decoding algorithm, two low-complexity suboptimal decoding algorithms, called pairwisequasi-ZF and pairwise-quasi-MMSE decoders, are proposed. First,two transmit signals are detected by the quasi-ZF or the quasiMMSE algorithm at the receiver. Then, the two detected signals as the decoding results are substituted into the two pairwise decoding algorithm expressions to detect the other two transmit signals. The bit error rate（ BER） performance of the proposed algorithms is compared with that of the current known decoding algorithms.Also, the number of calculations of ZF, MMSE, quasi-ZF and quasi-MMSE algorithms is compared with each other. Simulation results showthat the BER performance of the proposed algorithms is substantially improved in comparison to the quasi-ZF and quasiMMSE algorithms. The BER performance of the pairwise-quasiZF（ pairwise-quasi-MMSE） decoder is equivalent to the pairwiseZF（ pairwise-MMSE） decoder, while the computational complexity is significantly reduced.
基金financially supported by the National Natural Science Foundation of China(No.11375164 and 12105274).
文摘Objective:To understand the characteristic parameters and radon exhalation rates of aerated concrete blocks.Methods:A total of 39 nationally inspected samples were measured.Their dry density was determined based on their mass and volumes,their porosities were measured on the principle of volumetric expansion,and their radium content was determined using a high-purity germanium(HPGe)detector for gamma-ray spectroscopy.Furthermore,their diffusion lengths were quantified by establishing a combined cumulative and diffusion chamber,and their radon exhalation rates were measured through closed-box testing using a continuous radon monitor.Results:The aerated concrete blocks exhibited dry densities ranging from 464 to 840 kg/m^(3)[average:(654.0±82.5)kg/m^(3)],open porosities from 67.1%to 81.1%[average:(74.3±3.3)%],radium(^(226)Ra)content from 12.3 to 136 Bq/kg[average:(63.0±30.4)Bq/kg],diffusion lengths from 0.49 to 1.01 m[average:(0.70±0.15)m],and radon exhalation rates from 0.6 to 22.8 Bq·m^(-2)·h^(-1)[average:(7.3±5.3)Bq·m^(-2)·h^(-1)].Conclusion:Aerated concrete blocks exhibit significantly higher porosities,diffusion lengths,and radon exhalation rates than traditional concrete and clay bricks.These blocks might contribute to the high indoor radon concentration observed in modern buildings in China.
基金financially supported by the National Science Foundation of China(Grant No.51804033)China Postdoctoral Science and Foundation(Grant No.2018M641254)the National Science and Technology Major Projects of China(Grant Nos.2016ZX05051,2016ZX05014-005,and 2017ZX05030)。
文摘After hydraulic fracturing treatment,a reduction in permeability caused by the invasion of fracturing fluids is an inevitable problem,which is called water blocking damage.Therefore,it is important to mitigate and eliminate water blocking damage to improve the flow capacities of formation fluids and flowback rates of the fracturing fluid.However,the steady-state core flow method cannot quickly and accurately evaluate the effects of chemical agents in enhancing the fluid flow capacities in tight reservoirs.This paper introduces a time-saving and accurate method,pressure transmission test(PTT),which can quickly and quantitatively evaluate the liquid flow capacities and gas-drive flowback rates of a new nanoemulsion.Furthermore,scanning electron microscopy(SEM)was used to analyze the damage mechanism of different fluids and the adsorption of chemical agents on the rock surface.Parallel core flow experiments were used to evaluate the effects of the nanoemulsion on enhancing flowback rates in heterogeneous tight reservoirs.Experimental results show that the water blocking damage mechanisms differ in matrices and fractures.The main channels for gas channeling are fractures in cracked cores and pores in non-cracked cores.Cracked cores suffer less damage from water blocking than non-cracked cores,but have a lower potential to reduce water saturation.The PTT and SEM results show that the permeability reduction in tight sandstones caused by invasion of external fluids can be list as guar gum fracturing fluid>slickwater>brine.Parallel core flow experiments show that for low-permeability heterogenous s andstone reservoirs with a certain permeability ratio,the nanoemulsion can not only reduce reverse gas channeling degree,but also increase the flowback rate of the fracturing fluid.The nanoemulsion system provides a new solution to mitigate and eliminate water blocking damage caused by fracturing fluids in tight sandstone gas reservoirs.
基金Supported by the National Natural Science Foundation of China(No.81222021,No.30970875,No.90920015,No.61172008 and No.81171423)National Key Technology Research and Development Program of the Ministry of Science and Technology of China(No.2012BAI34B02)Program for New Century Excellent Talents in University of the Ministry of Education of China(No.NCET-10-0618)
文摘A brain-computer interface(BCI)-based electric wheelchair control system was developed, which enables the users to move the wheelchair forward or backward, and turn left or right without any pre-learning. This control system makes use of the amplitude enhancement of alpha-wave blocking in electroencephalogram(EEG) when eyes close for more than 1 s to constitute a BCI for the switch control of wheelchair movements. The system was formed by BCI control panel, data acquisition, signal processing unit and interface control circuit. Eight volunteers participated in the wheelchair control experiments according to the preset routes. The experimental results show that the mean success control rate of all the subjects was 81.3%, with the highest reaching 93.7%. When one subject's triggering time was 2.8 s, i.e., the flashing time of each cycle light was 2.8 s, the average information transfer rate was 8.10 bit/min, with the highest reaching 12.54 bit/min.
