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 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
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
Background:We compared the treatment of small unruptured intracranial aneurysms(UIAs)with flow diverter and LVIS-assisted coiling to determine the effects of hemodynamic changes caused by different stent and coil pack...Background:We compared the treatment of small unruptured intracranial aneurysms(UIAs)with flow diverter and LVIS-assisted coiling to determine the effects of hemodynamic changes caused by different stent and coil packing in endovascular treatment.Methods:Fifty-one UIAs in 51 patients treated with pipeline embolization device(PED)were included in this study and defined as the PED group.We matched controls 1:1 and enrolled 51 UIAs who were treated with LVIS stent,which were defined as the LVIS group.Computational fluid dynamics were performed to assess hemodynamic alterations between PED and LVIS.Clinical analysis was also performed between these two groups after the match.Results:There was no difference in procedural complications between the two groups(P=0.558).At the first angiographic follow-up,the complete occlusion rate was significantly higher in the LVIS group compared with that in the PED group(98.0%vs.82.4%,P=0.027).However,during the further angiographic follow-up,the complete occlusion rate in the PED group achieved 100%,which was higher than that in the LVIS group(98.0%).Compared with the LVIS group after treatment,cases in the PED group showed a higher value of velocity in the aneurysm(0.03±0.09 vs.0.01±0.01,P=0.037)and WSS on the aneurysm(2.32±5.40 vs.0.33±0.47,P=0.011).Consequently,the reduction ratios of these two parameters also showed statistical differences.These parameters in the LVIS group showed much higher reduction ratios.However,the reduction ratio of the velocity on the neck plane was comparable between two groups.Conclusions:Both LVIS and PED were safe and effective for the treatment of small UIAs.However,LVIS-assisted coiling produced greater hemodynamic alterations in the aneurysm sac compared with PED.The hemodynamics in the aneurysm neck may be a key factor for aneurysm outcome.展开更多
Flow diverter(FD)devices have been widely employed to treat cerebral aneurysms.Despite the well-documented clinical benefits,considerable inter-patient variability in clinical outcome has been reported,which implies t...Flow diverter(FD)devices have been widely employed to treat cerebral aneurysms.Despite the well-documented clinical benefits,considerable inter-patient variability in clinical outcome has been reported,which implies the necessity of patient-specifically evaluating hemodynamic changes following FD treatment,especially those associated with posttreatment intra-aneurysmal thrombus formation or complications.Computational fluid dynamics(CFD)methods,owing to the advantages in hemodynamic quantification,cost,and flexibility over traditional in vivo measurement or in vitro experiment methods,have increasingly become a major means for addressing hemodynamic problems related to FD treatment.Relevant CFD-based studies have extensively demonstrated that the results of hemodynamic computation can reasonably explain the clinical outcomes in different patient cohorts and provide useful insights for guiding the selection or optimization of FD devices.Nevertheless,CFD models are inherently unable to predict FD implantation-induced mechanical changes in the walls of aneurysm and its parent artery.In addition,the boundary conditions of most existing CFD models were not fully personalized for purpose of simplicity or due to the difficulty of measuring flow velocity in nearaneurysm regions,which may however considerably compromise the fidelity of the models in reproducing in vivo hemodynamics.To address these issues,the following studies would be expected:(1)perform fluid structure interaction simulations to explore the associations between wall stress/tension and posttreatment adverse vascular remodeling or aneurysm rupture,and(2)develop geometrical multiscale models based on available in vivo data to generate patient-specific boundary conditions for CFD models localized to aneurysm regions.展开更多
The application of fluid diversion during hydraulic fracturing is an evolving technology and has become popular amongst E&P operators over the past few years.The primary objective of the fluid diversion is to impr...The application of fluid diversion during hydraulic fracturing is an evolving technology and has become popular amongst E&P operators over the past few years.The primary objective of the fluid diversion is to improve hydraulic fracturing treatment by increasing stimulated reservoir volume and improving hydrocarbon recovery.This is possible by achieving any of the following objectives:creating uniform distribution of treatment slurry within the target zone;treating unstimulated and under-stimulated zones;or by increasing fracture density by creating a complex fracture network.The fluid diversion application is also helpful in decreasing the number of stages(by increasing stage length)for multi-stage plug-n-perf(PnP)fracturing treatment.It is also applied to prevent fracture-driven interactions between adjacent wells,which is currently a major issue,especially in shale.In addition,for successful refracturing treatment,the diverter application is essential for isolating the existing fractures and redirecting the treatment slurry to the desired unstimulated zones.The diversion methods can be broadly categorized into the mechanical and chemical diversion.Several established mechanical diversion techniques are frac plugs,expandable casing patches,expandable liners,swellable packers,straddle packer assembly,sand plugs,frac sleeves,perforation ball sealers,and limited entry technique.The different chemical diversion techniques are particulates,fibers,gels,surfactants,perforation pods,and composite diverting.This paper describes the current status of established mechanical and chemical diverter technologies and examines their comparative advantages and challenges.Various techniques are suitable for diverter application,but the technique is selected based on the desired objective and conditions of the wellbore and reservoir.The general guidelines for selecting diversion techniques and operational considerations are also provided in the paper.The diagnosis of diversion treatment plays an essential role in diversion technique selection and optimization of selection parameters for the subsequent treatments.Therefore,the application of conventional surface pressure monitoring techniques and advanced diagnostic tools to evaluate diversion effectiveness are briefly described.Presently no standard laboratory testing method is established for the performance evaluation of diverting agents.Therefore,researchers have implemented various laboratory methods,which are briefly summarized in the paper.Significant insight into the diversion technology and guidelines for its selection and successful implementation is provided to help engineers to increase the effectiveness of hydraulic fracturing treatments.The limitations of individual diversion techniques are clarified,which provide the future scope of research for improvement in various diversion technologies.展开更多
Yanhu Lake basin(YHB)is a typical alpine lake on the northeastern Tibetan Plateau(TP).Its continuous expansion in recent years poses serious threats to downstream major projects.As a result,studies of the mechanisms u...Yanhu Lake basin(YHB)is a typical alpine lake on the northeastern Tibetan Plateau(TP).Its continuous expansion in recent years poses serious threats to downstream major projects.As a result,studies of the mechanisms underlying lake expansion are urgently needed.The elasticity method within the Budyko framework was used to calculate the water balance in the Yanhu Lake basin(YHB)and the neighboring Tuotuo River basin(TRB).Results show intensification of hydrological cycles and positive trends in the lake area,river runoff,precipitation,and potential evapotranspiration.Lake expansion was significant between 2001 and 2020 and accelerated between 2015 and 2020.Precipitation increase was the key factor underlying the hydrological changes,followed by glacier meltwater and groundwater.The overflow of Yanhu Lake was inevitable because it was connected to three other lakes and the water balance of all four lakes was positive.The high salinity lake water diverted downstream will greatly impact the water quality of the source area of the Yangtze River and the stability of the permafrost base of the traffic corridor.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
Stent insertion for cerebral aneurysm has been studied using ideal and realistic aneurysms in recent years. Stent insertion aims at reducing the flow in an aneurysm. To minimize the average velocity in an aneurysm, we...Stent insertion for cerebral aneurysm has been studied using ideal and realistic aneurysms in recent years. Stent insertion aims at reducing the flow in an aneurysm. To minimize the average velocity in an aneurysm, we applied optimization to the strut position in a realistic aneurysm based on computational fluid dynamics. The result shows the effect on velocity reduction of strut placement in the inflow area.展开更多
Purpose: Flow diversion is a relatively novel technique to treat some intracranial aneurysms. With new techniques, unusual complications can occur. We described a case of Pipeline Embolization Device (PED) migration, ...Purpose: Flow diversion is a relatively novel technique to treat some intracranial aneurysms. With new techniques, unusual complications can occur. We described a case of Pipeline Embolization Device (PED) migration, strategy for its recognition, and a technical point to prevent its occurrence. Publication of these rare events is important to make physicians aware of potential complications. Methods: A patient with a previously coiled giant superior cerebellar aneurysm presented with brainstem compression symptoms. Imaging verified progressive aneurysm growth. A decision was made to treat the aneurysm with PED. Results: Development of new neurologic symptoms prompted a computed tomography that showed hydrocephalus. An angiogram also showed recanalization of the aneurysm secondary to upward migration/retraction of the flow diverter. A ventriculo-peritoneal shunt was implemented and planning for placement of a second flow diverter was made. Unfortunately, the patient expired while waiting for the endovacular intervention. Conclusions: PED migration may occur even after correct placement of the device. Early recognition of this complication is essential. When clinical changes occur, it is paramount that this uncommon, but potentially deadly, complication is suspected. Appropriate sizing and deployment technique are important for the long-term stability of the device.展开更多
Every colorectal surgeon during his or her career is faced with anastomotic leakage(AL); one of the most dreaded complications following any type of gastrointestinal anastomosis due to increased risk of morbidity, mor...Every colorectal surgeon during his or her career is faced with anastomotic leakage(AL); one of the most dreaded complications following any type of gastrointestinal anastomosis due to increased risk of morbidity, mortality, overall impact on functional and oncologic outcome and drainage on hospital resources. In order to understand and give an overview of the AL risk factors in laparoscopic colorectal surgery, we carried out a careful review of the existing literature on this topic and found several different definitions of AL which leads us to believe that the lack of a consensual, standard definition can partly explain the considerable variations in reported rates of AL in clinical studies. Colorectal leak rates have been found to vary depending on the anatomic location of the anastomosis with reported incidence rates ranging from 0 to 20%, while the laparoscopic approach to colorectal resections has not yet been associated with a significant reduction in AL incidence. As well, numerous risk factors, though identified, lack unanimous recognition amongst researchers. For example, the majority of papers describe the risk factors for left-sided anastomosis, the principal risk being male sex and lower anastomosis, while little data exists defining AL risk factors in a right colectomy. Also, gut microbioma is gaining an emerging role as potential risk factor for leakage.展开更多
AIM: To assess the efficacy and safety of diverting colostomy in treating severe hemorrhagic chronic radiation proctitis(CRP). METHODS: Patients with severe hemorrhagic CRP who were admitted from 2008 to 2014 were enr...AIM: To assess the efficacy and safety of diverting colostomy in treating severe hemorrhagic chronic radiation proctitis(CRP). METHODS: Patients with severe hemorrhagic CRP who were admitted from 2008 to 2014 were enrolled into this study. All CRP patients were diagnosed by a combination of pelvic radiation history, clinical rectal bleeding, and endoscopic findings. Inclusion criteria were CRP patients with refractory bleeding with moderate to severe anemia with a hemoglobin level < 90 g/L. The study group included patients who were treated by diverting colostomy, while the control group included patients who received conservative treatment. The remission of bleeding was defined as complete cessation or only occasional bleeding that needed no further treatment. The primary outcome was bleeding remission at 6 mo after treatment. Quality of life beforetreatment and at follow-up was evaluated according to EORTC QLQ C30. Severe CRP complications were recorded during follow-up.RESULTS: Forty-seven consecutive patients were enrolled, including 22 in the colostomy group and 27 in the conservative treatment group. When compared to conservative treatment, colostomy obtained a higher rate of bleeding remission(94% vs 12%), especially in control of transfusion-dependent bleeding(100% vs 0%), and offered a better control of refractory perianal pain(100% vs 0%), and a lower score of bleeding(P < 0.001) at 6 mo after treatment. At 1 year after treatment, colostomy achieved better remission of both moderate bleeding(100% vs 21.5%, P = 0.002) and severe bleeding(100% vs 0%, P < 0.001), obtained a lower score of bleeding(0.8 vs 2.0, P < 0.001), and achieved obvious elevated hemoglobin levels(P = 0.003), when compared to the conservative treatment group. The quality of life dramatically improved after colostomy, which included global health, function, and symptoms, but it was not improved in the control group. Pathological evaluation after colostomy found diffused chronic inflammation cells, and massive fibrosis collagen depositions under the rectal wall, which revealed potential fibrosis formation. CONCLUSION: Diverting colostomy is a simple, effective and safe procedure for severe hemorrhagic CRP. Colostomy can improve quality of life and reduce serious complications secondary to radiotherapy.展开更多
Due to the reservoir heterogeneity and the stress shadow effect, multiple hydraulic fractures within one fracturing segment cannot be initiated simultaneously and propagate evenly, which will cause a low effectiveness...Due to the reservoir heterogeneity and the stress shadow effect, multiple hydraulic fractures within one fracturing segment cannot be initiated simultaneously and propagate evenly, which will cause a low effectiveness of reservoir stimulation. Temporary plugging and diverting fracturing(TPDF) is considered to be a potential uniform-stimulation method for creating multiple fractures simultaneously in the oilfield. However, the multi-fracture propagation morphology during TPDF is not clear now. The purpose of this study is to quantitatively investigate the multi-fracture propagation morphology during TPDF through true tri-axial fracturing experiments and CT scanning. Critical parameters such as fracture spacing, number of perforation clusters, the viscosity of fracturing fluid, and the in-situ stress have been investigated. The fracture geometry before and after diversion have been quantitively analyzed based on the two-dimensional CT slices and three-dimensional reconstruction method. The main conclusions are as follows:(1) When injecting the high viscosity fluid or perforating at the location with low in-situ stress, multiple hydraulic fractures would simultaneously propagate. Otherwise, only one hydraulic fracture was created during the initial fracturing stage(IFS) for most tests.(2) The perforation cluster effectiveness(PCE) has increased from 26.62% during the IFS to 88.86% after using diverters.(3) The diverted fracture volume has no apparent correlation with the pressure peak and peak frequency during the diversion fracturing stage(DFS) but is positively correlated with water-work.(4) Four types of plugging behavior in shale could be controlled by adjusting the diverter recipe and diverter injection time, and the plugging behavior includes plugging the natural fracture in the wellbore, plugging the previous hydraulic fractures, plugging the fracture tip and plugging the bedding.展开更多
Temporary fecal diversion by a diverting colostomy or ileostomy is occasionally performed for serious complex fistulas.The main indications are highly complex and extensive cryptoglandular anal fistula,anal fistula as...Temporary fecal diversion by a diverting colostomy or ileostomy is occasionally performed for serious complex fistulas.The main indications are highly complex and extensive cryptoglandular anal fistula,anal fistula associated with severe anorectal Crohn’s disease,recurrent rectovaginal fistula,radiation-induced fistula and anal fistula with associated necrotizing fasciitis.The purpose of stoma formation is to divert the fecal stream away from the anorectum and the perianal region so as to control the infective process and prevent trauma to the operated repaired tissues.Once the fistula has healed,the diverting stoma is closed.However,two questions are relevant.First,is it certain that the same disease would not relapse(or the fistula would not recur)once the colostomy is closed?Second,is there a non-surgical method which can obviate the need for a diverting colostomy?An attempt is made to answer both these questions in this review.展开更多
Background: The introduction of pipeline embolisation device (PED) has improved the feasibility of endovascular treatment of intracranial aneurysms. The device allows for endoluminal reconstruction across the aneurysm...Background: The introduction of pipeline embolisation device (PED) has improved the feasibility of endovascular treatment of intracranial aneurysms. The device allows for endoluminal reconstruction across the aneurysm neck but is permeable enough that flow is preserved across the pressure gradients into sidebranch arteries. In spite of higher rates of aneurysm occlusion, there is lack of data concerning medium to long-term clinical and imaging results. Methods: This study was a prospective single center analysis of complications, imaging results, and medium term clinical outcomes after PED treatment of intracranial aneurysms. We included cases over a 17-month period in a tertiary interventional neuroradiology center. We collected data on demographics, vascular risk factors, clinical presentation, angiographic results post treatment, angiographic follow-up and clinical follow-up. Results: Thirty-three patients were included, 25 females and 8 males, with mean age of 55 years;3 presented with acute subarachnoid hemorrhage and 30 for elective treatment. Thirty-seven aneurysms were treated: 35 Internal Carotid Artery (ICA), 1 basilar trunk fusiform, and 1 vertebral artery intradural dissecting aneurysms. No deaths have occurred. Five patients suffered transient neurological complications (15%). Overall aneurysm occlusion was demonstrated in 85% of patients at the end of one year. Discussion:?Overall, the technique of flow diversion and endoluminal reconstruction differs greatly from the established endosaccular packing techniques of standard coiling, balloon remodeling, or stent assisted coiling. Our midterm follow-up confirms that, the rates of clinically significant complications compare favorably with published data on stent assisted coiling, potentially making these devices a truly revolutionizing technique.展开更多
Tight oil reservoirs in Songliao Basin were taken as subjects and a novel idealized refracturing well concept was proposed by considering the special parameters of volume fracturing horizontal wells, the refracturing ...Tight oil reservoirs in Songliao Basin were taken as subjects and a novel idealized refracturing well concept was proposed by considering the special parameters of volume fracturing horizontal wells, the refracturing potential of candidate wells were graded and prioritized, and a production prediction model of refracturing considering the stress sensitivity was established using numerical simulation method to sort out the optimal refracturing method and timing. The simulations show that: with the same perforation clusters, the order of fracturing technologies with contribution to productivity from big to small is refracturing between existent fractured sections, orientation diversion inside fractures, extended refracturing, refracturing of existent fractures; and the later the refracturing timing, the shorter the effective time. Based on this, the prediction model of breakdown pressure considering the variation of formation pressure was used to find out the variation pattern of breakdown pressure of different positions at different production time. Through the classification of the breakdown pressure, the times of temporary plugging and diverting and the amount of temporary plugging agent were determined under the optimal refracturing timing. Daily oil production per well increased from 2.3 t/d to 16.5 t/d in the field test. The research results provide important reference for refracturing optimization design of similar tight oil reservoirs.展开更多
Einstein’s weak equivalence principle suggests that gravity and acceleration (centrifugal force) are indistinguishable from each other and, therefore, equivalent. We maintain that they are not only equivalent, but ev...Einstein’s weak equivalence principle suggests that gravity and acceleration (centrifugal force) are indistinguishable from each other and, therefore, equivalent. We maintain that they are not only equivalent, but even identical, or to rephrase the main statement of this work: A gravitational force does not exist. Rather, gravity is a fictitious force, or, more pointedly: Gravity is the centrifugal force which acts upon material bodies within the rotating S3-hypersphere of the Universe. These in turn warp the adjacent space-fabric, shaping it to the well-known field geometry of general relativity.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
Background:Giant serpentine aneurysms(GSA)originate from saccular or spindle aneurysm,dissimilar from dissected aneurysm,that are defined as partially thrombosed giant aneurysms with tortuous internal vascular channel...Background:Giant serpentine aneurysms(GSA)originate from saccular or spindle aneurysm,dissimilar from dissected aneurysm,that are defined as partially thrombosed giant aneurysms with tortuous internal vascular channel.The clinical and neuroradiologic characteristics are clarified and the mechanism of formation and the efficacy of double stent implantation in GSA are discussed.Case presentation:An 18-year-old man presented himself with a GSA arising from the internal cerebral artery(ICA).In addition,a mandibular aneurysm(MA)arose from the external cerebral artery(ECA).Success was achieved in treating GSA through endovascular treatment with double stents implanted in the parent artery,which were LEO stent and Tubridge flow diverter.After 1 year of follow-up,three-dimensional reconstruction of blood vessels revealed the disappearance of the serpentine access of GSA,which was found to be replaced with a roughly normal vascular structure.Conclusions:Double stent implantation has provided a feasible treatment option for giant serpentine internal carotid aneurysms and eliminated the possibility of causing collateral circulation occlusion.Therefore,it represents a simple and suitable treatment method for anatomical structure and operation.展开更多
AC loss is one of the critical issues for designing REBCO fast‐ramping magnets operating at cryogenic temperatures.There are many ways to reduce AC loss for coil windings.However,it is not clear which method is the m...AC loss is one of the critical issues for designing REBCO fast‐ramping magnets operating at cryogenic temperatures.There are many ways to reduce AC loss for coil windings.However,it is not clear which method is the most effective way to minimize AC loss in the coil windings for a given Ampere‐turns.In this work,we numerically studied coil configurations of several small superconducting magnets constructed from 12 mm SuperPower REBCO coated conductors,for fast‐ramping application with the same Ampere‐turns to identify the lowest AC loss among them.The HTS magnets have a total turn number of 50 and inner diameter of 30 cm,carrying AC current operating in the temperature range of 20–40 K at 25 Hz.We incorporated several existing loss reduction strategies including spacing between the turns for single pancake coils,grading Ic values for the solenoid configuration,and applying flux diverters to shape the magnetic field around the coil windings.The simulation was implemented using a homogenized H‐formulation.Across all studied loss reduction methods,the use of flux diverters has the largest impact in AC loss reduction.The AC loss values in the solenoid winding comprising a stack of five single pancake coils with 0.1 mm turn‐to‐turn gap with the flux diverters agree well with those in the single pancake coil for 2 mm turn‐to‐turn gap with the flux diverters.Solenoid type coil configurations with flux diverters generate much smaller AC loss than the single pancake type with flux diverters when they generate the same center magnetic field.展开更多
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%.
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.
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.
基金This work was supported by the National Natural Science Foundation of China(grant numbers: 81801156, 81801158 and 82072036)Beijing Hospitals Authority Youth Programme(code: QML20190503)
文摘Background:We compared the treatment of small unruptured intracranial aneurysms(UIAs)with flow diverter and LVIS-assisted coiling to determine the effects of hemodynamic changes caused by different stent and coil packing in endovascular treatment.Methods:Fifty-one UIAs in 51 patients treated with pipeline embolization device(PED)were included in this study and defined as the PED group.We matched controls 1:1 and enrolled 51 UIAs who were treated with LVIS stent,which were defined as the LVIS group.Computational fluid dynamics were performed to assess hemodynamic alterations between PED and LVIS.Clinical analysis was also performed between these two groups after the match.Results:There was no difference in procedural complications between the two groups(P=0.558).At the first angiographic follow-up,the complete occlusion rate was significantly higher in the LVIS group compared with that in the PED group(98.0%vs.82.4%,P=0.027).However,during the further angiographic follow-up,the complete occlusion rate in the PED group achieved 100%,which was higher than that in the LVIS group(98.0%).Compared with the LVIS group after treatment,cases in the PED group showed a higher value of velocity in the aneurysm(0.03±0.09 vs.0.01±0.01,P=0.037)and WSS on the aneurysm(2.32±5.40 vs.0.33±0.47,P=0.011).Consequently,the reduction ratios of these two parameters also showed statistical differences.These parameters in the LVIS group showed much higher reduction ratios.However,the reduction ratio of the velocity on the neck plane was comparable between two groups.Conclusions:Both LVIS and PED were safe and effective for the treatment of small UIAs.However,LVIS-assisted coiling produced greater hemodynamic alterations in the aneurysm sac compared with PED.The hemodynamics in the aneurysm neck may be a key factor for aneurysm outcome.
基金supported by the National Natural Science Foundation of China(Grant no.11972231)the China Postdoctoral Science Foundation(Grant no.2018M640385)the SJTU Medical-Engineering Cross-cutting Research Project(Grant nos.YG2015MS53,YG2017MS45).
文摘Flow diverter(FD)devices have been widely employed to treat cerebral aneurysms.Despite the well-documented clinical benefits,considerable inter-patient variability in clinical outcome has been reported,which implies the necessity of patient-specifically evaluating hemodynamic changes following FD treatment,especially those associated with posttreatment intra-aneurysmal thrombus formation or complications.Computational fluid dynamics(CFD)methods,owing to the advantages in hemodynamic quantification,cost,and flexibility over traditional in vivo measurement or in vitro experiment methods,have increasingly become a major means for addressing hemodynamic problems related to FD treatment.Relevant CFD-based studies have extensively demonstrated that the results of hemodynamic computation can reasonably explain the clinical outcomes in different patient cohorts and provide useful insights for guiding the selection or optimization of FD devices.Nevertheless,CFD models are inherently unable to predict FD implantation-induced mechanical changes in the walls of aneurysm and its parent artery.In addition,the boundary conditions of most existing CFD models were not fully personalized for purpose of simplicity or due to the difficulty of measuring flow velocity in nearaneurysm regions,which may however considerably compromise the fidelity of the models in reproducing in vivo hemodynamics.To address these issues,the following studies would be expected:(1)perform fluid structure interaction simulations to explore the associations between wall stress/tension and posttreatment adverse vascular remodeling or aneurysm rupture,and(2)develop geometrical multiscale models based on available in vivo data to generate patient-specific boundary conditions for CFD models localized to aneurysm regions.
文摘The application of fluid diversion during hydraulic fracturing is an evolving technology and has become popular amongst E&P operators over the past few years.The primary objective of the fluid diversion is to improve hydraulic fracturing treatment by increasing stimulated reservoir volume and improving hydrocarbon recovery.This is possible by achieving any of the following objectives:creating uniform distribution of treatment slurry within the target zone;treating unstimulated and under-stimulated zones;or by increasing fracture density by creating a complex fracture network.The fluid diversion application is also helpful in decreasing the number of stages(by increasing stage length)for multi-stage plug-n-perf(PnP)fracturing treatment.It is also applied to prevent fracture-driven interactions between adjacent wells,which is currently a major issue,especially in shale.In addition,for successful refracturing treatment,the diverter application is essential for isolating the existing fractures and redirecting the treatment slurry to the desired unstimulated zones.The diversion methods can be broadly categorized into the mechanical and chemical diversion.Several established mechanical diversion techniques are frac plugs,expandable casing patches,expandable liners,swellable packers,straddle packer assembly,sand plugs,frac sleeves,perforation ball sealers,and limited entry technique.The different chemical diversion techniques are particulates,fibers,gels,surfactants,perforation pods,and composite diverting.This paper describes the current status of established mechanical and chemical diverter technologies and examines their comparative advantages and challenges.Various techniques are suitable for diverter application,but the technique is selected based on the desired objective and conditions of the wellbore and reservoir.The general guidelines for selecting diversion techniques and operational considerations are also provided in the paper.The diagnosis of diversion treatment plays an essential role in diversion technique selection and optimization of selection parameters for the subsequent treatments.Therefore,the application of conventional surface pressure monitoring techniques and advanced diagnostic tools to evaluate diversion effectiveness are briefly described.Presently no standard laboratory testing method is established for the performance evaluation of diverting agents.Therefore,researchers have implemented various laboratory methods,which are briefly summarized in the paper.Significant insight into the diversion technology and guidelines for its selection and successful implementation is provided to help engineers to increase the effectiveness of hydraulic fracturing treatments.The limitations of individual diversion techniques are clarified,which provide the future scope of research for improvement in various diversion technologies.
基金funded by the National Natural Science Foundation of China(42002264)the China Geological Survey Program(DD20230537)the Fundamental Research Funds for the Central Public Research Institutes(SK202006).
文摘Yanhu Lake basin(YHB)is a typical alpine lake on the northeastern Tibetan Plateau(TP).Its continuous expansion in recent years poses serious threats to downstream major projects.As a result,studies of the mechanisms underlying lake expansion are urgently needed.The elasticity method within the Budyko framework was used to calculate the water balance in the Yanhu Lake basin(YHB)and the neighboring Tuotuo River basin(TRB).Results show intensification of hydrological cycles and positive trends in the lake area,river runoff,precipitation,and potential evapotranspiration.Lake expansion was significant between 2001 and 2020 and accelerated between 2015 and 2020.Precipitation increase was the key factor underlying the hydrological changes,followed by glacier meltwater and groundwater.The overflow of Yanhu Lake was inevitable because it was connected to three other lakes and the water balance of all four lakes was positive.The high salinity lake water diverted downstream will greatly impact the water quality of the source area of the Yangtze River and the stability of the permafrost base of the traffic corridor.
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.
文摘Stent insertion for cerebral aneurysm has been studied using ideal and realistic aneurysms in recent years. Stent insertion aims at reducing the flow in an aneurysm. To minimize the average velocity in an aneurysm, we applied optimization to the strut position in a realistic aneurysm based on computational fluid dynamics. The result shows the effect on velocity reduction of strut placement in the inflow area.
文摘Purpose: Flow diversion is a relatively novel technique to treat some intracranial aneurysms. With new techniques, unusual complications can occur. We described a case of Pipeline Embolization Device (PED) migration, strategy for its recognition, and a technical point to prevent its occurrence. Publication of these rare events is important to make physicians aware of potential complications. Methods: A patient with a previously coiled giant superior cerebellar aneurysm presented with brainstem compression symptoms. Imaging verified progressive aneurysm growth. A decision was made to treat the aneurysm with PED. Results: Development of new neurologic symptoms prompted a computed tomography that showed hydrocephalus. An angiogram also showed recanalization of the aneurysm secondary to upward migration/retraction of the flow diverter. A ventriculo-peritoneal shunt was implemented and planning for placement of a second flow diverter was made. Unfortunately, the patient expired while waiting for the endovacular intervention. Conclusions: PED migration may occur even after correct placement of the device. Early recognition of this complication is essential. When clinical changes occur, it is paramount that this uncommon, but potentially deadly, complication is suspected. Appropriate sizing and deployment technique are important for the long-term stability of the device.
文摘Every colorectal surgeon during his or her career is faced with anastomotic leakage(AL); one of the most dreaded complications following any type of gastrointestinal anastomosis due to increased risk of morbidity, mortality, overall impact on functional and oncologic outcome and drainage on hospital resources. In order to understand and give an overview of the AL risk factors in laparoscopic colorectal surgery, we carried out a careful review of the existing literature on this topic and found several different definitions of AL which leads us to believe that the lack of a consensual, standard definition can partly explain the considerable variations in reported rates of AL in clinical studies. Colorectal leak rates have been found to vary depending on the anatomic location of the anastomosis with reported incidence rates ranging from 0 to 20%, while the laparoscopic approach to colorectal resections has not yet been associated with a significant reduction in AL incidence. As well, numerous risk factors, though identified, lack unanimous recognition amongst researchers. For example, the majority of papers describe the risk factors for left-sided anastomosis, the principal risk being male sex and lower anastomosis, while little data exists defining AL risk factors in a right colectomy. Also, gut microbioma is gaining an emerging role as potential risk factor for leakage.
基金Supported by National Natural Science Foundation of China,No.81201581,No.81573078 and No.81372566Support Program from Ministry of Science and Technology of China,No.2014BAI09B06Natural Science Foundation of Guangdong Province,China,No.2016A030311021
文摘AIM: To assess the efficacy and safety of diverting colostomy in treating severe hemorrhagic chronic radiation proctitis(CRP). METHODS: Patients with severe hemorrhagic CRP who were admitted from 2008 to 2014 were enrolled into this study. All CRP patients were diagnosed by a combination of pelvic radiation history, clinical rectal bleeding, and endoscopic findings. Inclusion criteria were CRP patients with refractory bleeding with moderate to severe anemia with a hemoglobin level < 90 g/L. The study group included patients who were treated by diverting colostomy, while the control group included patients who received conservative treatment. The remission of bleeding was defined as complete cessation or only occasional bleeding that needed no further treatment. The primary outcome was bleeding remission at 6 mo after treatment. Quality of life beforetreatment and at follow-up was evaluated according to EORTC QLQ C30. Severe CRP complications were recorded during follow-up.RESULTS: Forty-seven consecutive patients were enrolled, including 22 in the colostomy group and 27 in the conservative treatment group. When compared to conservative treatment, colostomy obtained a higher rate of bleeding remission(94% vs 12%), especially in control of transfusion-dependent bleeding(100% vs 0%), and offered a better control of refractory perianal pain(100% vs 0%), and a lower score of bleeding(P < 0.001) at 6 mo after treatment. At 1 year after treatment, colostomy achieved better remission of both moderate bleeding(100% vs 21.5%, P = 0.002) and severe bleeding(100% vs 0%, P < 0.001), obtained a lower score of bleeding(0.8 vs 2.0, P < 0.001), and achieved obvious elevated hemoglobin levels(P = 0.003), when compared to the conservative treatment group. The quality of life dramatically improved after colostomy, which included global health, function, and symptoms, but it was not improved in the control group. Pathological evaluation after colostomy found diffused chronic inflammation cells, and massive fibrosis collagen depositions under the rectal wall, which revealed potential fibrosis formation. CONCLUSION: Diverting colostomy is a simple, effective and safe procedure for severe hemorrhagic CRP. Colostomy can improve quality of life and reduce serious complications secondary to radiotherapy.
基金the National Natural Science Foundation of China fund (Project number: 52174045 and No. 52104011)Research Foundation of China University of Petroleum-Beijing at Karamay (No. XQZX20210001)PetroChina Innovation Foundation (2020D50070207)。
文摘Due to the reservoir heterogeneity and the stress shadow effect, multiple hydraulic fractures within one fracturing segment cannot be initiated simultaneously and propagate evenly, which will cause a low effectiveness of reservoir stimulation. Temporary plugging and diverting fracturing(TPDF) is considered to be a potential uniform-stimulation method for creating multiple fractures simultaneously in the oilfield. However, the multi-fracture propagation morphology during TPDF is not clear now. The purpose of this study is to quantitatively investigate the multi-fracture propagation morphology during TPDF through true tri-axial fracturing experiments and CT scanning. Critical parameters such as fracture spacing, number of perforation clusters, the viscosity of fracturing fluid, and the in-situ stress have been investigated. The fracture geometry before and after diversion have been quantitively analyzed based on the two-dimensional CT slices and three-dimensional reconstruction method. The main conclusions are as follows:(1) When injecting the high viscosity fluid or perforating at the location with low in-situ stress, multiple hydraulic fractures would simultaneously propagate. Otherwise, only one hydraulic fracture was created during the initial fracturing stage(IFS) for most tests.(2) The perforation cluster effectiveness(PCE) has increased from 26.62% during the IFS to 88.86% after using diverters.(3) The diverted fracture volume has no apparent correlation with the pressure peak and peak frequency during the diversion fracturing stage(DFS) but is positively correlated with water-work.(4) Four types of plugging behavior in shale could be controlled by adjusting the diverter recipe and diverter injection time, and the plugging behavior includes plugging the natural fracture in the wellbore, plugging the previous hydraulic fractures, plugging the fracture tip and plugging the bedding.
文摘Temporary fecal diversion by a diverting colostomy or ileostomy is occasionally performed for serious complex fistulas.The main indications are highly complex and extensive cryptoglandular anal fistula,anal fistula associated with severe anorectal Crohn’s disease,recurrent rectovaginal fistula,radiation-induced fistula and anal fistula with associated necrotizing fasciitis.The purpose of stoma formation is to divert the fecal stream away from the anorectum and the perianal region so as to control the infective process and prevent trauma to the operated repaired tissues.Once the fistula has healed,the diverting stoma is closed.However,two questions are relevant.First,is it certain that the same disease would not relapse(or the fistula would not recur)once the colostomy is closed?Second,is there a non-surgical method which can obviate the need for a diverting colostomy?An attempt is made to answer both these questions in this review.
文摘Background: The introduction of pipeline embolisation device (PED) has improved the feasibility of endovascular treatment of intracranial aneurysms. The device allows for endoluminal reconstruction across the aneurysm neck but is permeable enough that flow is preserved across the pressure gradients into sidebranch arteries. In spite of higher rates of aneurysm occlusion, there is lack of data concerning medium to long-term clinical and imaging results. Methods: This study was a prospective single center analysis of complications, imaging results, and medium term clinical outcomes after PED treatment of intracranial aneurysms. We included cases over a 17-month period in a tertiary interventional neuroradiology center. We collected data on demographics, vascular risk factors, clinical presentation, angiographic results post treatment, angiographic follow-up and clinical follow-up. Results: Thirty-three patients were included, 25 females and 8 males, with mean age of 55 years;3 presented with acute subarachnoid hemorrhage and 30 for elective treatment. Thirty-seven aneurysms were treated: 35 Internal Carotid Artery (ICA), 1 basilar trunk fusiform, and 1 vertebral artery intradural dissecting aneurysms. No deaths have occurred. Five patients suffered transient neurological complications (15%). Overall aneurysm occlusion was demonstrated in 85% of patients at the end of one year. Discussion:?Overall, the technique of flow diversion and endoluminal reconstruction differs greatly from the established endosaccular packing techniques of standard coiling, balloon remodeling, or stent assisted coiling. Our midterm follow-up confirms that, the rates of clinically significant complications compare favorably with published data on stent assisted coiling, potentially making these devices a truly revolutionizing technique.
基金Supported by the National Natural Science Foundation of China(51525404,51504203)China National Science and Technology Major Project(2016ZX05002002)
文摘Tight oil reservoirs in Songliao Basin were taken as subjects and a novel idealized refracturing well concept was proposed by considering the special parameters of volume fracturing horizontal wells, the refracturing potential of candidate wells were graded and prioritized, and a production prediction model of refracturing considering the stress sensitivity was established using numerical simulation method to sort out the optimal refracturing method and timing. The simulations show that: with the same perforation clusters, the order of fracturing technologies with contribution to productivity from big to small is refracturing between existent fractured sections, orientation diversion inside fractures, extended refracturing, refracturing of existent fractures; and the later the refracturing timing, the shorter the effective time. Based on this, the prediction model of breakdown pressure considering the variation of formation pressure was used to find out the variation pattern of breakdown pressure of different positions at different production time. Through the classification of the breakdown pressure, the times of temporary plugging and diverting and the amount of temporary plugging agent were determined under the optimal refracturing timing. Daily oil production per well increased from 2.3 t/d to 16.5 t/d in the field test. The research results provide important reference for refracturing optimization design of similar tight oil reservoirs.
文摘Einstein’s weak equivalence principle suggests that gravity and acceleration (centrifugal force) are indistinguishable from each other and, therefore, equivalent. We maintain that they are not only equivalent, but even identical, or to rephrase the main statement of this work: A gravitational force does not exist. Rather, gravity is a fictitious force, or, more pointedly: Gravity is the centrifugal force which acts upon material bodies within the rotating S3-hypersphere of the Universe. These in turn warp the adjacent space-fabric, shaping it to the well-known field geometry of general relativity.
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.
文摘Background:Giant serpentine aneurysms(GSA)originate from saccular or spindle aneurysm,dissimilar from dissected aneurysm,that are defined as partially thrombosed giant aneurysms with tortuous internal vascular channel.The clinical and neuroradiologic characteristics are clarified and the mechanism of formation and the efficacy of double stent implantation in GSA are discussed.Case presentation:An 18-year-old man presented himself with a GSA arising from the internal cerebral artery(ICA).In addition,a mandibular aneurysm(MA)arose from the external cerebral artery(ECA).Success was achieved in treating GSA through endovascular treatment with double stents implanted in the parent artery,which were LEO stent and Tubridge flow diverter.After 1 year of follow-up,three-dimensional reconstruction of blood vessels revealed the disappearance of the serpentine access of GSA,which was found to be replaced with a roughly normal vascular structure.Conclusions:Double stent implantation has provided a feasible treatment option for giant serpentine internal carotid aneurysms and eliminated the possibility of causing collateral circulation occlusion.Therefore,it represents a simple and suitable treatment method for anatomical structure and operation.
基金supported in part by New Zealand Ministry of Business,Innovation and Employment(MBIE)by the Strategic Science Investment Fund“Advanced Energy Technology Platforms”under Contract RTVU20042020 Google Excellence Research University ProgramUS DOE Ernst Courant Traineeship in Accelerator Sciences and Engineering,the educational program of next generation of accelerator physicists and engineer,US Department of Energy,HEP office.
文摘AC loss is one of the critical issues for designing REBCO fast‐ramping magnets operating at cryogenic temperatures.There are many ways to reduce AC loss for coil windings.However,it is not clear which method is the most effective way to minimize AC loss in the coil windings for a given Ampere‐turns.In this work,we numerically studied coil configurations of several small superconducting magnets constructed from 12 mm SuperPower REBCO coated conductors,for fast‐ramping application with the same Ampere‐turns to identify the lowest AC loss among them.The HTS magnets have a total turn number of 50 and inner diameter of 30 cm,carrying AC current operating in the temperature range of 20–40 K at 25 Hz.We incorporated several existing loss reduction strategies including spacing between the turns for single pancake coils,grading Ic values for the solenoid configuration,and applying flux diverters to shape the magnetic field around the coil windings.The simulation was implemented using a homogenized H‐formulation.Across all studied loss reduction methods,the use of flux diverters has the largest impact in AC loss reduction.The AC loss values in the solenoid winding comprising a stack of five single pancake coils with 0.1 mm turn‐to‐turn gap with the flux diverters agree well with those in the single pancake coil for 2 mm turn‐to‐turn gap with the flux diverters.Solenoid type coil configurations with flux diverters generate much smaller AC loss than the single pancake type with flux diverters when they generate the same center magnetic field.
