BACKGROUND Diverting stoma(DS)is routinely proposed in intersphincteric resection for ultra-low rectal cancer,but it is associated with increased stoma-related complications and economic burden.Appropriate patient sel...BACKGROUND Diverting stoma(DS)is routinely proposed in intersphincteric resection for ultra-low rectal cancer,but it is associated with increased stoma-related complications and economic burden.Appropriate patient selection and operative strategies to avoid stoma formation need further elucidation.METHODS This study enrolled 505 consecutive patients,including 84 who underwent stoma-free(SF)intersphincteric resection.After matching,patients were divided into SF(n=78)and DS(n=78)groups.The primary endpoint was the anastomotic leakage(AL)rate within 6 months and its protective factors for both the total and SF cohorts.The secondary endpoints included overall survival and disease-free survival.RESULTS The AL rate was greater in the SF group than in the DS group(12.8%vs 2.6%,P=0.035).Male sex[(odds ratio(OR)=2.644,P=0.021],neoadjuvant chemoradiotherapy(nCRT)(OR=6.024,P<0.001),and tumor height from the anal verge≤4 cm(OR=4.160,P=0.007)were identified as independent risk factors.Preservation of the left colic artery(LCA)was protective in both the total cohort(OR=0.417,P=0.013)and the SF cohort(OR=0.312,P=0.027).The female patients who did not undergo nCRT and had preservation of the LCA experienced a significantly lower incidence of AL(2/97,2.1%).The 3-year overall survival or disease-free survival did not significantly differ be-tween the groups.CONCLUSION Female patients who do not receive nCRT may avoid the need for DS by preserving the LCA without increasing the risk of AL or compromising oncological outcomes.展开更多
Objective:To summarize the nursing treatment of patients who underwent implantation of a blood flow diverter to treat complex intracranial aneurysms.Methods:Data from 22 patients with complex aneurysms,diagnosed at an...Objective:To summarize the nursing treatment of patients who underwent implantation of a blood flow diverter to treat complex intracranial aneurysms.Methods:Data from 22 patients with complex aneurysms,diagnosed at an interventional center for blood flow diverter implantation between February 2015 and February 2016,treated in the Henan Provincial People’s Hospital(Zhengzhou,China),were retrospectively analyzed.Nursing methods,including preoperative,intraoperative,and postoperative care,were analyzed.Results:All 22 patients underwent successful surgery,with no related complications or hospital mortality,and were cured in hospital.Conclusion:Interventional flow diverter therapy for patients with complex intracranial aneurysms is a new technology,and involves intensive care by nursing staff and appears to be a promising new treatment method.展开更多
Storage modulus and loss modulus is the main performance index of visco-elastic properties.In this paper the storage modulus and loss modulus of a new diverting acid and their influencing factors were systematically i...Storage modulus and loss modulus is the main performance index of visco-elastic properties.In this paper the storage modulus and loss modulus of a new diverting acid and their influencing factors were systematically investigated.Besides,the constitutive equations of the diverting acid at different temperatures were elicited from shearing experiments,which show that the visco-elastic surfactant(VES)acid system is a non-Newtonian power law fluid at low temperature and a Newtonian fluid at high temperature.The storage modulus and loss modulus at different temperatures,pH,and VES content in the acid are critical for the design of acid stimulation for oil well,especially when the VES acid is used in this field only on trial and the basic data are in urgent needed for the design and construction of the acidification stimulation.展开更多
In order to research segmented diverters for aircraft lightning protection, a transient 2 D multiphysics model based on magnetohydrodynamics theory is proposed to predict the location of the arc plasma discharge and l...In order to research segmented diverters for aircraft lightning protection, a transient 2 D multiphysics model based on magnetohydrodynamics theory is proposed to predict the location of the arc plasma discharge and lightning channel, and to simulate the electrothermal behavior.Based on numerical calculation and preliminary analysis, factors that affect the breakdown voltage of the segmented diverter are discussed. The results show that the voltage increase rate of the voltage source, the width of the air gap between metal segments and the geometry of these segments influence the breakdown voltage of the strip. High-voltage tests of the segmented diverter are performed to reveal air breakdown of the strip and redirect the lightning current.Experimental and numerical results are compared to verify the correctness of the numerical model. The ionization of the air gap between metal segments and the breakdown voltage of the strip calculated by the model are qualitatively consistent with experimental results. The breakdown voltage of the segmented diverter is far lower than the lightning voltage. When a lightning strike occurs, the segmented diverter can be quickly ionized to form a plasma channel which can guide the lightning current well.展开更多
A compact pneumatic pulse-jet pump with a Venturi-like reverse flow diverter,which consists of a nozzle and diffuser,is designed for lifting and transporting a hazardous fluid through a narrow mounting hole.The pumpin...A compact pneumatic pulse-jet pump with a Venturi-like reverse flow diverter,which consists of a nozzle and diffuser,is designed for lifting and transporting a hazardous fluid through a narrow mounting hole.The pumping performance for a liquid mixture or a liquid-solid mixture is examined in terms of the effects of liquid viscosity,particle mass concentration,lifting height,and compression pressure.Results reveal that the pumping performance of the compact pneumatic pulse-jet pump is controlled by jet inertia and the flow resistance of the riser tube positioned after the diffuser.The capacity of the compact pneumatic pulse-jet pump increases with compression pressure and decreases with liquid viscosity.However,even for a liquid mixture with a high viscosity of 7.38 mPa·s,a pumping capacity of 170.7 L·h-1 was observed.For a liquid mixture,two dimensionless indices of performance were found to be the ratio of Euler numbers Euout/EuDV and the suction factor q.As the liquid-solid mixture was lifted to elevation of 6.74 m by the compact pump,the particle size distributions of the liquid-solid mixture in the tank and from the riser tube outlet were determined by a particle size analyzer and found to coincide well.展开更多
The effective plugging of artificial fractures is key to the success of temporary plugging and diverting fracturing technology,which is one of the most promising ways to improve the heat recovery efficiency of hot dry...The effective plugging of artificial fractures is key to the success of temporary plugging and diverting fracturing technology,which is one of the most promising ways to improve the heat recovery efficiency of hot dry rock.At present,how temporary plugging agents plug artificial fractures under high temperature remains unclear.In this paper,by establishing an improved experimental system for the evaluation of temporary plugging performance at high temperature,we clarified the effects of high temperature,injection rate,and fracture width on the pressure response and plugging efficiency of the fracture.The results revealed that the temporary plugging process of artificial fractures in hot dry rock can be divided into four main stages:the initial stage of temporary plugging,the bridging stage of the particles,the plugging formation stage,and the high-pressure dense plugging stage.As the temperature increases,the distribution distance of the temporary plugging agent,the number of pressure fluctuations,and the time required for crack plugging increases.Particularly,when the temperature increases by 100℃,the complete plugging time increases by 90.7%.展开更多
In order to obtain the dynamic characteristics of a differential piston warm gas selfpressurization system for liquid attitude and divert propulsion system, a transient model is developed using the modular modeling me...In order to obtain the dynamic characteristics of a differential piston warm gas selfpressurization system for liquid attitude and divert propulsion system, a transient model is developed using the modular modeling method. The system includes the solid start cartridge,pressure-amplified tank with liquid monopropellant, liquid regulator, gas generator, and pipes.The one-dimensional finite-element state-variable model is applied to the pipes and the lumped parameter method is adopted for the other modules. The variations of the system operation parameters over time during the startup, steady-state, and pulsing operational processes are obtained from the transient model, and the characteristics of starting time changing with different system parameters are also analyzed. It is shown that the system startup process can be divided into three distinct processes. The starting time monotonically changes with variations of the liquid regulator parameters, first decreasing and then increasing with the mass change of the solid propellant charge of the start cartridge, initial gas cavity volume of the pressure amplified tank and initial gas cushion of the propellant tank. The starting time can be reduced to less than 1.0 s（0.68–0.75 s for the current system）. For meeting the deviation requirements of ±10% of the steady-state propellant tank pressure, the positive deviation requirement is assured by the self-locking pressure and the negative deviation can be assured within an allowable maximum propellant tank volume flowrate（1.6 times the design value for the proposed system） for downstream thrusters for a designed system. The results from the simulation are useful as a guide for further system design and testing.展开更多
The reverse flow diverter (RFD) consisting of a nozzle and a diffuser is a key component in pneumatic pulse jet pumps. We investigated the effects of suction gap and diffuser configurations on RFD performance during t...The reverse flow diverter (RFD) consisting of a nozzle and a diffuser is a key component in pneumatic pulse jet pumps. We investigated the effects of suction gap and diffuser configurations on RFD performance during the reverse flow mode. Three suction gap configurations were examined: (1) an axisymmetrical cylinder, (2) a cuboid whose bottom plane had no half-circle groove and was level with the diffuser entrance lower border, and (3) a cuboid with a half-circle groove on the bottom plane. Among them, the second one resulted in the highest RFD pumping capacity. The effect of receiver presence before the diffuser was also examined. RFD pumping efficiency was found to be enhanced in the presence of a receiver before the diffuser when the suction gap length is small and the jet outlet velocity at the nozzle exit is high enough. Based on experimental data, a dimensionless performance curve of the suction factor q versus the ratio of Euler numbers in sections out-out and 0-0 Eu out /Eu 0 was derived. This curve is insensitive to suction gap configurations.展开更多
An analytical expression of the peeling mode in the near separatrix region of diverted tokamak plasma is derived. It is shown that in diverted plasmas both with single and double X points, though the perturbed potenti...An analytical expression of the peeling mode in the near separatrix region of diverted tokamak plasma is derived. It is shown that in diverted plasmas both with single and double X points, though the perturbed potential energy of the unstable peeling mode tends to be large, its growth rate becomes very small due to the even larger kinetic energy. Compared to some recent studies that give qualitatively correct results about this growth rate, our result is directly related with the diverted equilibrium quantities suitable for application to realistic experiments.展开更多
The Lower Cambrian Longwangmiao dolomite gas reservoirs in the Sichuan Basin are characterized by well-developed natural micro-fractures and dissolved pores and cavities.Due to the strong heterogeneity of reservoirs a...The Lower Cambrian Longwangmiao dolomite gas reservoirs in the Sichuan Basin are characterized by well-developed natural micro-fractures and dissolved pores and cavities.Due to the strong heterogeneity of reservoirs and the serious damage of drilling and completion fluids,acid placement is difficult,and especially the acidizing stimulation of long-interval highly deviated wells or horizontal wells is more difficult.In this paper,the diverting mechanism and rheological behavior of viscoelastic surfactant(VES)based diverting acid was firstly investigated,and the diverting acid with good diversion performance and low secondary damage was selected as the main acid.Then,based on the experimental results of its rheological behaviors,an empirical model of effective viscosity was fitted and a two-scale wormhole propagation model was coupled.And accordingly,a mathematical model for the acidizing of self-diverting acid was established to simulate the pH value,Ca^(2+)concentration,effective viscosity and wormhole shape under the effect of diverting acid in long-interval highly deviated wells that are non-uniformly damaged.Finally,gelled acid and 5%VES diverting acid were compared in terms of their etched wormhole shapes,flow rate dis-tribution and acid imbibition profiles.It is shown that the diverting acid can obviously improve the acid imbibition profile of strong-heterogeneity reservoirs to intensify low-permeability reservoir stimulation.In view of the strong heterogeneity of Longwangmiao dolomite reservoirs and the complexities of drilling and completion fluid damage in the Sichuan Basin,a placement technology was developed for variable VES concentration diverting acid in horizontal wells and long-interval highly deviated wells completed with slotted liners.This acid placement technology has been practically applied in 8 wells and their cumulative gas production rate tested at the wellhead is 1233.46×10^(4)m^(3)/d.The average production stimulation ratio per well is up to 1.95.It provides a support for the efficient development of the Longwangmiao giant gas reservoir.展开更多
The semi-analytical method, previously used to construct model double-null and single-null diverted tokamak equi- libria （Bingren Shi, Plasma Phys. Control Fusion 50 （2008） 085006, 51 （2009） 105008, Nucl. Fusion ...The semi-analytical method, previously used to construct model double-null and single-null diverted tokamak equi- libria （Bingren Shi, Plasma Phys. Control Fusion 50 （2008） 085006, 51 （2009） 105008, Nucl. Fusion 51 （2011） 023004）, is extended to describe diverted tokamak equilibria with nonzero edge current, including the Pfirsch Schliiter（PS） cur- rent. The PS current density is expressed in a way suitable to describe a diverted tokamak configuration in the near separatrix region. The model equilibrium is expressed by only two terms of the exact separable solutions of the Grad Shafranov equation, one of which is governed by a homogeneous ordinary differential equation, and the other by an inhomogeneous one. The particular merits of such a model configuration are that the internal region inside the separa- trix and a suitable scrape-off layer can be simultaneously described by this exact solution. To investigate the physics in the region near the X-point, the magnetic surfaces can be satisfactorily described by approximate hyperbolic curves.展开更多
Flow diverting stents are braided,metallic endoluminal devices widely used to treat intracranial aneurysms.Bioresorbable flow diverters(BRFDs)are gaining traction as the next generation of flow diverter technology.BRF...Flow diverting stents are braided,metallic endoluminal devices widely used to treat intracranial aneurysms.Bioresorbable flow diverters(BRFDs)are gaining traction as the next generation of flow diverter technology.BRFDs aim to occlude and heal the aneurysm before safely dissolving into the body,mitigating or eliminating complications associated with the permanent presence of conventional flow diverters such as thromboembolism and stenosis.Additional putative advantages of a BRFD include a reduction in metal induced medical imaging artifacts,a restoration of physiological vasoreactivity,and allowing physicians to re-access the aneurysm if an additional procedure is required.In this current study,iron-manganese-nitrogen(FeMnN)alloy BRFDs and permanent control FDs composed of an industry standard Cobalt-Nickel-Chromium alloy were deployed in the rabbit aorta.MicroCT and SEM corrosion analysis determined the FeMnN wire volumes and cross-sectional areas had reduced approximately 85%and 95%after 3-and 6-months implantation duration,respectively.Histo-logical analysis demonstrated the BRFDs exhibited suitable biocompatibility,with no cases of in-stent throm-bosis,clinically significant stenosis,or adverse tissue responses observed.Immunohistochemistry revealed the neointimas surrounding the BRFDs featured a confluent endothelium covering several layers of smooth muscle cells,with macrophages adjacent to the device wires.The macrophages were able to penetrate the corrosion product and were observed transporting corrosion products away from the implant site.This current work provides primary in vivo corrosion and biocompatibility data to the field for FeMn alloys,which we feel will stimulate and inform the design of next-generation bioresorbable endovascular devices.展开更多
Marine natural products represent an important class of biologically active compounds critical for drug discovery.To date,17 marine-derived drugs,including trabectedin and eribulin,have been approved by the US FDA for...Marine natural products represent an important class of biologically active compounds critical for drug discovery.To date,17 marine-derived drugs,including trabectedin and eribulin,have been approved by the US FDA for clinical use and 33 others are in clinical trials[1].However,their medicinal investigation and clinical trials are often hampered by the scarcity of natural sources and by the difficulties of their harvesting in the delicate marine environment.Therefore,efficient and scalable approaches for the synthesis of promising marine natural products are essential to overcome supply issues for drug development.展开更多
Flow diverter intervention is a cutting-edge treatment for intracranial aneurysms by altering the flow field and reducing the pressure in the aneurysm sac.However,the rupture rate and complications rate are still high...Flow diverter intervention is a cutting-edge treatment for intracranial aneurysms by altering the flow field and reducing the pressure in the aneurysm sac.However,the rupture rate and complications rate are still high.In this study,a new design of flow diverter based on Bernoulli’s equation was proposed and hemodynamics evaluation of it was conducted.The numerical model of a patient specific internal carotid aneurysm was established based on computed tomography scan images(Model C).The aneurysm models with normal diverter(ND)and local stenosed diverter(LSD)were modified from the patient-specific model.The blood flow characteristics were obtained and analyzed by numerical simulation while the in vitro experiments were conducted using three-dimensional printed silicone models and pressure measurement system.In both ND and LSD models,the blood flow into the aneurysm have been significantly blocked by the diverters and the pressure in the aneurysm sac have been decreased.The pressure drop and the wall shear stress on the aneurysm wall in the LSD model are higher than that in the ND model.The oscillatory shear index and relative residence time in the aneurysm wall of LSD are lower than that in the ND model.The pressure measurement in the vitro experiment also qualitatively verified the results of pressure comparison in the numerical simulation.In conclusion,the simulation results and in vitro experiments verified that diverter can certainly reduce the pressure in the aneurysm,and the newly design diverter with local stenosis can strengthening this effect.展开更多
During the life of a well,treatments are carried out to boost productivity by stimulating initially unproduced zones.These treatments include hydraulic fracturing,matrix acidization,and acid fracturing,among others.Hy...During the life of a well,treatments are carried out to boost productivity by stimulating initially unproduced zones.These treatments include hydraulic fracturing,matrix acidization,and acid fracturing,among others.Hydraulic fracturing treatment is generally applied to deeper reservoirs of oil or natural gas for enhanced recovery.By infusing proppant,water,and chemicals under extreme pressure during the fracturing procedure,fissures in and beneath the reservoir layer can be accessed and expanded.Another stimulating procedure,matrix acidization,involves injecting acid down the drilling hole to permeate the rock fissures at stresses lower than the fracture stress.In addition,carbonate reservoir acid fracturing stimulation is commonly used as an acid treatment technique whereby a pressure greater than the formation disintegration pressure or spontaneous fracture closure pressure is used to compress acid into the reservoir.These treatments allow existing wells to sustain hydrocarbon production without new wells being drilled.Diverters,when employed efficiently,can prevent the need to use a rig to provide momentary physical barriers,thus lowering the cost of the workover.Recent improvements in diversion technology make use of a variety of degradable particles that act as momentary bridges,either at the perforation entries or inside the existing fractures.The aim of this study is to introduce different types of mechanical and chemical diverters used to enhance the productivity of wells.This study explains the concepts of different types of diverters and their applications in several formations,it will also help readers to understand the selection procedures based on the suitability and requirements of diverter use by case studies from around the world.展开更多
基金Supported by Beijing Natural Science Foundation,No.L222054 and No.4232058.
文摘BACKGROUND Diverting stoma(DS)is routinely proposed in intersphincteric resection for ultra-low rectal cancer,but it is associated with increased stoma-related complications and economic burden.Appropriate patient selection and operative strategies to avoid stoma formation need further elucidation.METHODS This study enrolled 505 consecutive patients,including 84 who underwent stoma-free(SF)intersphincteric resection.After matching,patients were divided into SF(n=78)and DS(n=78)groups.The primary endpoint was the anastomotic leakage(AL)rate within 6 months and its protective factors for both the total and SF cohorts.The secondary endpoints included overall survival and disease-free survival.RESULTS The AL rate was greater in the SF group than in the DS group(12.8%vs 2.6%,P=0.035).Male sex[(odds ratio(OR)=2.644,P=0.021],neoadjuvant chemoradiotherapy(nCRT)(OR=6.024,P<0.001),and tumor height from the anal verge≤4 cm(OR=4.160,P=0.007)were identified as independent risk factors.Preservation of the left colic artery(LCA)was protective in both the total cohort(OR=0.417,P=0.013)and the SF cohort(OR=0.312,P=0.027).The female patients who did not undergo nCRT and had preservation of the LCA experienced a significantly lower incidence of AL(2/97,2.1%).The 3-year overall survival or disease-free survival did not significantly differ be-tween the groups.CONCLUSION Female patients who do not receive nCRT may avoid the need for DS by preserving the LCA without increasing the risk of AL or compromising oncological outcomes.
基金National Natural Science Foundation of China(81601583).
文摘Objective:To summarize the nursing treatment of patients who underwent implantation of a blood flow diverter to treat complex intracranial aneurysms.Methods:Data from 22 patients with complex aneurysms,diagnosed at an interventional center for blood flow diverter implantation between February 2015 and February 2016,treated in the Henan Provincial People’s Hospital(Zhengzhou,China),were retrospectively analyzed.Nursing methods,including preoperative,intraoperative,and postoperative care,were analyzed.Results:All 22 patients underwent successful surgery,with no related complications or hospital mortality,and were cured in hospital.Conclusion:Interventional flow diverter therapy for patients with complex intracranial aneurysms is a new technology,and involves intensive care by nursing staff and appears to be a promising new treatment method.
基金Supported by the Acidification for Heterogeneous Carbonate Reservoirs Program of Petro China Company Limited
文摘Storage modulus and loss modulus is the main performance index of visco-elastic properties.In this paper the storage modulus and loss modulus of a new diverting acid and their influencing factors were systematically investigated.Besides,the constitutive equations of the diverting acid at different temperatures were elicited from shearing experiments,which show that the visco-elastic surfactant(VES)acid system is a non-Newtonian power law fluid at low temperature and a Newtonian fluid at high temperature.The storage modulus and loss modulus at different temperatures,pH,and VES content in the acid are critical for the design of acid stimulation for oil well,especially when the VES acid is used in this field only on trial and the basic data are in urgent needed for the design and construction of the acidification stimulation.
基金supported by National Natural Science Foundation of China (No. 51475369)the Natural Science Basic Research Plan in Shaanxi Province of China (No. 2018JM1001)
文摘In order to research segmented diverters for aircraft lightning protection, a transient 2 D multiphysics model based on magnetohydrodynamics theory is proposed to predict the location of the arc plasma discharge and lightning channel, and to simulate the electrothermal behavior.Based on numerical calculation and preliminary analysis, factors that affect the breakdown voltage of the segmented diverter are discussed. The results show that the voltage increase rate of the voltage source, the width of the air gap between metal segments and the geometry of these segments influence the breakdown voltage of the strip. High-voltage tests of the segmented diverter are performed to reveal air breakdown of the strip and redirect the lightning current.Experimental and numerical results are compared to verify the correctness of the numerical model. The ionization of the air gap between metal segments and the breakdown voltage of the strip calculated by the model are qualitatively consistent with experimental results. The breakdown voltage of the segmented diverter is far lower than the lightning voltage. When a lightning strike occurs, the segmented diverter can be quickly ionized to form a plasma channel which can guide the lightning current well.
文摘A compact pneumatic pulse-jet pump with a Venturi-like reverse flow diverter,which consists of a nozzle and diffuser,is designed for lifting and transporting a hazardous fluid through a narrow mounting hole.The pumping performance for a liquid mixture or a liquid-solid mixture is examined in terms of the effects of liquid viscosity,particle mass concentration,lifting height,and compression pressure.Results reveal that the pumping performance of the compact pneumatic pulse-jet pump is controlled by jet inertia and the flow resistance of the riser tube positioned after the diffuser.The capacity of the compact pneumatic pulse-jet pump increases with compression pressure and decreases with liquid viscosity.However,even for a liquid mixture with a high viscosity of 7.38 mPa·s,a pumping capacity of 170.7 L·h-1 was observed.For a liquid mixture,two dimensionless indices of performance were found to be the ratio of Euler numbers Euout/EuDV and the suction factor q.As the liquid-solid mixture was lifted to elevation of 6.74 m by the compact pump,the particle size distributions of the liquid-solid mixture in the tank and from the riser tube outlet were determined by a particle size analyzer and found to coincide well.
基金supported financially by the Beijing Natural Science Foundation Project(No.3222030)the National Natural Science Foundation of China(No.51936001,No.52274002 and No.52192622)+1 种基金the PetroChina Science and Technology Innovation Foundation Project(2021DQ02–0201)Award Cultivation Foundation from Beijing Institute of Petrochemical Technology(No.BIPTACF-002).
文摘The effective plugging of artificial fractures is key to the success of temporary plugging and diverting fracturing technology,which is one of the most promising ways to improve the heat recovery efficiency of hot dry rock.At present,how temporary plugging agents plug artificial fractures under high temperature remains unclear.In this paper,by establishing an improved experimental system for the evaluation of temporary plugging performance at high temperature,we clarified the effects of high temperature,injection rate,and fracture width on the pressure response and plugging efficiency of the fracture.The results revealed that the temporary plugging process of artificial fractures in hot dry rock can be divided into four main stages:the initial stage of temporary plugging,the bridging stage of the particles,the plugging formation stage,and the high-pressure dense plugging stage.As the temperature increases,the distribution distance of the temporary plugging agent,the number of pressure fluctuations,and the time required for crack plugging increases.Particularly,when the temperature increases by 100℃,the complete plugging time increases by 90.7%.
文摘In order to obtain the dynamic characteristics of a differential piston warm gas selfpressurization system for liquid attitude and divert propulsion system, a transient model is developed using the modular modeling method. The system includes the solid start cartridge,pressure-amplified tank with liquid monopropellant, liquid regulator, gas generator, and pipes.The one-dimensional finite-element state-variable model is applied to the pipes and the lumped parameter method is adopted for the other modules. The variations of the system operation parameters over time during the startup, steady-state, and pulsing operational processes are obtained from the transient model, and the characteristics of starting time changing with different system parameters are also analyzed. It is shown that the system startup process can be divided into three distinct processes. The starting time monotonically changes with variations of the liquid regulator parameters, first decreasing and then increasing with the mass change of the solid propellant charge of the start cartridge, initial gas cavity volume of the pressure amplified tank and initial gas cushion of the propellant tank. The starting time can be reduced to less than 1.0 s（0.68–0.75 s for the current system）. For meeting the deviation requirements of ±10% of the steady-state propellant tank pressure, the positive deviation requirement is assured by the self-locking pressure and the negative deviation can be assured within an allowable maximum propellant tank volume flowrate（1.6 times the design value for the proposed system） for downstream thrusters for a designed system. The results from the simulation are useful as a guide for further system design and testing.
文摘The reverse flow diverter (RFD) consisting of a nozzle and a diffuser is a key component in pneumatic pulse jet pumps. We investigated the effects of suction gap and diffuser configurations on RFD performance during the reverse flow mode. Three suction gap configurations were examined: (1) an axisymmetrical cylinder, (2) a cuboid whose bottom plane had no half-circle groove and was level with the diffuser entrance lower border, and (3) a cuboid with a half-circle groove on the bottom plane. Among them, the second one resulted in the highest RFD pumping capacity. The effect of receiver presence before the diffuser was also examined. RFD pumping efficiency was found to be enhanced in the presence of a receiver before the diffuser when the suction gap length is small and the jet outlet velocity at the nozzle exit is high enough. Based on experimental data, a dimensionless performance curve of the suction factor q versus the ratio of Euler numbers in sections out-out and 0-0 Eu out /Eu 0 was derived. This curve is insensitive to suction gap configurations.
基金Project supported by the National Magnetic Confinement Fusion Science Program of China （Grant No. 2009GB 101002）.
文摘An analytical expression of the peeling mode in the near separatrix region of diverted tokamak plasma is derived. It is shown that in diverted plasmas both with single and double X points, though the perturbed potential energy of the unstable peeling mode tends to be large, its growth rate becomes very small due to the even larger kinetic energy. Compared to some recent studies that give qualitatively correct results about this growth rate, our result is directly related with the diverted equilibrium quantities suitable for application to realistic experiments.
基金Project supported by the National Science and Technology Major Project“Large-scale Oil and Gas Fields and CBM Development:Demonstration Project of Large-scale Carbonate Gas Fields in Sichuan Basin”(Code:2016ZX05052)CNPC Major Science and Technology Project“Research and Application of Deep-Temperature and High-Pressure Sulfur Gas Reservoir Reformation Technology in Sichuan Basin”(Code:2016E-0609).
文摘The Lower Cambrian Longwangmiao dolomite gas reservoirs in the Sichuan Basin are characterized by well-developed natural micro-fractures and dissolved pores and cavities.Due to the strong heterogeneity of reservoirs and the serious damage of drilling and completion fluids,acid placement is difficult,and especially the acidizing stimulation of long-interval highly deviated wells or horizontal wells is more difficult.In this paper,the diverting mechanism and rheological behavior of viscoelastic surfactant(VES)based diverting acid was firstly investigated,and the diverting acid with good diversion performance and low secondary damage was selected as the main acid.Then,based on the experimental results of its rheological behaviors,an empirical model of effective viscosity was fitted and a two-scale wormhole propagation model was coupled.And accordingly,a mathematical model for the acidizing of self-diverting acid was established to simulate the pH value,Ca^(2+)concentration,effective viscosity and wormhole shape under the effect of diverting acid in long-interval highly deviated wells that are non-uniformly damaged.Finally,gelled acid and 5%VES diverting acid were compared in terms of their etched wormhole shapes,flow rate dis-tribution and acid imbibition profiles.It is shown that the diverting acid can obviously improve the acid imbibition profile of strong-heterogeneity reservoirs to intensify low-permeability reservoir stimulation.In view of the strong heterogeneity of Longwangmiao dolomite reservoirs and the complexities of drilling and completion fluid damage in the Sichuan Basin,a placement technology was developed for variable VES concentration diverting acid in horizontal wells and long-interval highly deviated wells completed with slotted liners.This acid placement technology has been practically applied in 8 wells and their cumulative gas production rate tested at the wellhead is 1233.46×10^(4)m^(3)/d.The average production stimulation ratio per well is up to 1.95.It provides a support for the efficient development of the Longwangmiao giant gas reservoir.
基金supported by the National Magnetic Confinement Fusion Science Program of China (Grant No. 2009GB101002)
文摘The semi-analytical method, previously used to construct model double-null and single-null diverted tokamak equi- libria （Bingren Shi, Plasma Phys. Control Fusion 50 （2008） 085006, 51 （2009） 105008, Nucl. Fusion 51 （2011） 023004）, is extended to describe diverted tokamak equilibria with nonzero edge current, including the Pfirsch Schliiter（PS） cur- rent. The PS current density is expressed in a way suitable to describe a diverted tokamak configuration in the near separatrix region. The model equilibrium is expressed by only two terms of the exact separable solutions of the Grad Shafranov equation, one of which is governed by a homogeneous ordinary differential equation, and the other by an inhomogeneous one. The particular merits of such a model configuration are that the internal region inside the separa- trix and a suitable scrape-off layer can be simultaneously described by this exact solution. To investigate the physics in the region near the X-point, the magnetic surfaces can be satisfactorily described by approximate hyperbolic curves.
基金National Institutes of Health grant#R01 NS076491supported by American Heart Association grant 23PRE1012781.
文摘Flow diverting stents are braided,metallic endoluminal devices widely used to treat intracranial aneurysms.Bioresorbable flow diverters(BRFDs)are gaining traction as the next generation of flow diverter technology.BRFDs aim to occlude and heal the aneurysm before safely dissolving into the body,mitigating or eliminating complications associated with the permanent presence of conventional flow diverters such as thromboembolism and stenosis.Additional putative advantages of a BRFD include a reduction in metal induced medical imaging artifacts,a restoration of physiological vasoreactivity,and allowing physicians to re-access the aneurysm if an additional procedure is required.In this current study,iron-manganese-nitrogen(FeMnN)alloy BRFDs and permanent control FDs composed of an industry standard Cobalt-Nickel-Chromium alloy were deployed in the rabbit aorta.MicroCT and SEM corrosion analysis determined the FeMnN wire volumes and cross-sectional areas had reduced approximately 85%and 95%after 3-and 6-months implantation duration,respectively.Histo-logical analysis demonstrated the BRFDs exhibited suitable biocompatibility,with no cases of in-stent throm-bosis,clinically significant stenosis,or adverse tissue responses observed.Immunohistochemistry revealed the neointimas surrounding the BRFDs featured a confluent endothelium covering several layers of smooth muscle cells,with macrophages adjacent to the device wires.The macrophages were able to penetrate the corrosion product and were observed transporting corrosion products away from the implant site.This current work provides primary in vivo corrosion and biocompatibility data to the field for FeMn alloys,which we feel will stimulate and inform the design of next-generation bioresorbable endovascular devices.
文摘Marine natural products represent an important class of biologically active compounds critical for drug discovery.To date,17 marine-derived drugs,including trabectedin and eribulin,have been approved by the US FDA for clinical use and 33 others are in clinical trials[1].However,their medicinal investigation and clinical trials are often hampered by the scarcity of natural sources and by the difficulties of their harvesting in the delicate marine environment.Therefore,efficient and scalable approaches for the synthesis of promising marine natural products are essential to overcome supply issues for drug development.
基金This work was supported by the National Key Research and Development Plan of China(2017YFB0702501)the National Natural Science Foundation of China(No.11872096,11772036,31870940),the “111” Project(B13003).
文摘Flow diverter intervention is a cutting-edge treatment for intracranial aneurysms by altering the flow field and reducing the pressure in the aneurysm sac.However,the rupture rate and complications rate are still high.In this study,a new design of flow diverter based on Bernoulli’s equation was proposed and hemodynamics evaluation of it was conducted.The numerical model of a patient specific internal carotid aneurysm was established based on computed tomography scan images(Model C).The aneurysm models with normal diverter(ND)and local stenosed diverter(LSD)were modified from the patient-specific model.The blood flow characteristics were obtained and analyzed by numerical simulation while the in vitro experiments were conducted using three-dimensional printed silicone models and pressure measurement system.In both ND and LSD models,the blood flow into the aneurysm have been significantly blocked by the diverters and the pressure in the aneurysm sac have been decreased.The pressure drop and the wall shear stress on the aneurysm wall in the LSD model are higher than that in the ND model.The oscillatory shear index and relative residence time in the aneurysm wall of LSD are lower than that in the ND model.The pressure measurement in the vitro experiment also qualitatively verified the results of pressure comparison in the numerical simulation.In conclusion,the simulation results and in vitro experiments verified that diverter can certainly reduce the pressure in the aneurysm,and the newly design diverter with local stenosis can strengthening this effect.
文摘During the life of a well,treatments are carried out to boost productivity by stimulating initially unproduced zones.These treatments include hydraulic fracturing,matrix acidization,and acid fracturing,among others.Hydraulic fracturing treatment is generally applied to deeper reservoirs of oil or natural gas for enhanced recovery.By infusing proppant,water,and chemicals under extreme pressure during the fracturing procedure,fissures in and beneath the reservoir layer can be accessed and expanded.Another stimulating procedure,matrix acidization,involves injecting acid down the drilling hole to permeate the rock fissures at stresses lower than the fracture stress.In addition,carbonate reservoir acid fracturing stimulation is commonly used as an acid treatment technique whereby a pressure greater than the formation disintegration pressure or spontaneous fracture closure pressure is used to compress acid into the reservoir.These treatments allow existing wells to sustain hydrocarbon production without new wells being drilled.Diverters,when employed efficiently,can prevent the need to use a rig to provide momentary physical barriers,thus lowering the cost of the workover.Recent improvements in diversion technology make use of a variety of degradable particles that act as momentary bridges,either at the perforation entries or inside the existing fractures.The aim of this study is to introduce different types of mechanical and chemical diverters used to enhance the productivity of wells.This study explains the concepts of different types of diverters and their applications in several formations,it will also help readers to understand the selection procedures based on the suitability and requirements of diverter use by case studies from around the world.
