目前国内头痛专病继续教育缺乏统一规范的标准方法,因此以解放军总医院神经内科目前开展的2种头痛继续教育模式(头痛学校和头痛进修教育)为例来探索头痛专病继续教育方法。头痛学校:以短期培训班形式招募培训对头痛诊疗有兴趣的医师,教...目前国内头痛专病继续教育缺乏统一规范的标准方法,因此以解放军总医院神经内科目前开展的2种头痛继续教育模式(头痛学校和头痛进修教育)为例来探索头痛专病继续教育方法。头痛学校:以短期培训班形式招募培训对头痛诊疗有兴趣的医师,教授头痛诊疗基础知识、头痛系统性疾病管理模式(screen,migraine,aura,red flag and treatment,SMART)和计算机临床决策支持系统(computerized clinical decision support system,CDSS);头痛进修教育:以神经内科头痛病房、头痛门诊为实践基地开展为期半年到1年的头痛专病进修教育。头痛学校可在相对短的时间培训出大量头痛专病医师,部分优秀学员具备开办头痛专病门诊的资质和能力,但缺乏诊疗实践能力的培训;头痛进修教育:在培养头痛专病专家方面更有优势,但其时间、人力成本更高。头痛专病继续教育可有效促进头痛诊疗规范化、同质化,是减轻头痛专病所致负担的必要途径。不同头痛专病继续教育方法各有优缺点,在实践中可互为有效补充。展开更多
Liver transplantation is the primary therapeutic intervention for end-stage liver disease.However,vascular complications,particularly those involving the hepatic artery,pose significant risks to patients.The clinical ...Liver transplantation is the primary therapeutic intervention for end-stage liver disease.However,vascular complications,particularly those involving the hepatic artery,pose significant risks to patients.The clinical manifestations associated with early arterial complications following liver transplantation are often non-specific.Without timely intervention,these complications can result in graft fai-lure or patient mortality.Therefore,early diagnosis and the formulation of an op-timal treatment plan are imperative.Ultrasound examination remains the pre-dominant imaging modality for detecting complications post liver transplan-tation.This article comprehensively reviews common causes and clinical present-ations of early hepatic artery complications in the post-transplantation period and delineates abnormal sonographic findings for accurate diagnosis of these con-ditions.Overall,ultrasound offers the advantages of convenience,safety,effect-iveness,and non-invasiveness.It enables real-time,dynamic,and precise evalua-tion,making it the preferred diagnostic method for post-liver transplantation assessments.INTRODUCTION Liver transplantation stands as the primary therapeutic approach for end-stage liver disease.Continuous advancements in surgical techniques and the application of novel immunosuppressive agents contribute to ongoing improvements in the success rate and overall survival in patients undergoing liver transplantation procedures.Despite these advan-cements,vascular complications,particularly those involving the hepatic artery,pose significant risks to patients.During the early stages following liver transplantation(within the first 30 d),proper hepatic artery function is crucial for hepatic arterial blood flow.During later stages,collateral circulation,including arteries such as the phrenic artery,right gastric artery,and gastroduodenal artery,becomes important for maintaining hepatic blood supply.It is now understood that the establishment of effective collateral circulation is pivotal for determining the prognosis of hepatic artery complic-ations.The clinical manifestations of these complications are closely linked to factors such as timing,severity,and the specific type of onset.Insufficient hepatic arterial blood flow can lead to abnormal liver function,hepatic infarction,and the formation of hepatic abscesses.Additionally,since the hepatic artery is the sole blood supply to the biliary tract,hepatic artery-related ischemia may result in biliary stricture,obstruction,and the formation of bile ducts.Ultrasound examination remains the primary imaging modality for diagnosing complications post liver transplantation.This article comprehensively reviews common causes and clinical presentations of early hepatic artery complications in the post-transplantation period and outlines abnormal sonographic findings for accurately diagnosing these conditions.NORMAL HEPATIC ARTERY During the intraoperative phase,an ultrasound examination is typically conducted to evaluate the hepatic artery anas-tomosis.The normal internal diameter of the hepatic artery typically ranges from 2 to 5 mm.Two strong echo points are typically identified near the anastomosis.To assess blood flow dynamics,peak systolic velocity,end-diastolic velocity,and resistance index are measured at the donor and recipient sides of the anastomosis following angle correction.Anastomotic stenosis presence and severity can be evaluated by comparing the velocity at the anastomotic site with that at the recipient side.Postoperatively,direct visualization of the anastomosis site through gray ultrasound scans is often challenging.The surgical approach has a significant impact on the proper hepatic artery’s position,resulting in a lower overall success rate of continuous visualization.Color Doppler ultrasound is primarily employed to trace the artery’s path,and spectral measurements are taken at the brightest position of the Color Doppler blood flow signal,primarily used to identify the presence of high-speed turbulence.Hepatic artery spectrum examination plays a crucial role,as a favorable arterial spectral waveform and appropriate hepatic artery flow velocity typically indicate a successful anastomosis,even in cases where the hepatic artery anastomosis cannot be directly visualized by ultrasound.The hepatic artery runs alongside the portal vein,often selected as a reference due to its larger inner diameter.A normal hepatic artery spectrum displays a regular pulsation pattern with a rapid rise in systole and a slow decline in diastole.Parameters for assessing hepatic artery resistance include a resistance index between 0.5 to 0.8 and an artery systolic acceleration of less than 80 ms.Instantaneous increases in the resistance index(RI>0.8)often occur within 2 d after surgery,followed by a subsequent return to normal hepatic arterial parameters.It has been established that the maximum blood flow velocity during systole in the hepatic artery should not exceed 200 cm/s[1].展开更多
Hot water flooding is an effective way to develop heavy oil reservoirs.However,local channeling channels may form,possibly leading to a low thermal utilization efficiency and high water cut in the reservoir.The pore s...Hot water flooding is an effective way to develop heavy oil reservoirs.However,local channeling channels may form,possibly leading to a low thermal utilization efficiency and high water cut in the reservoir.The pore structure heterogeneity is an important factor in forming these channels.This study proposes a method that mixes quartz sand with different particle sizes to prepare weakly heterogeneous and strongly heterogeneous models through which hot water flooding experiments are conducted.During the experiments,computer tomography(CT)scanning identifies the pore structure and micro remaining oil saturation distribution to analyze the influence of the pore structure heterogeneity on the channeling channels.The oil saturation reduction and average pore size are divided into three levels to quantitatively describe the relationship between the channeling channel distribution and pore structure heterogeneity.The zone where oil saturation reduction exceeds 20%is defined as a channeling channel.The scanning area is divided into 180 equally sized zones based on the CT scanning images,and threedimensional(3D)distributions of the channeling channels are developed.Four micro remaining oil distribution patterns are proposed,and the morphology characteristics of micro remaining oil inside and outside the channeling channels are analyzed.The results show that hot water flooding is more balanced in the weakly heterogeneous model,and the oil saturation decreases by more than 20%in most zones without narrow channeling channels forming.In the strongly heterogeneous model,hot water flooding is unbalanced,and three narrow channeling channels of different lengths form.In the weakly heterogeneous model,the oil saturation reduction is greater in zones with larger pores.The distribution range of the average pore size is larger in the strongly heterogeneous model.The network remaining oil inside the channeling channels is less than outside the channeling channels,and the hot water converts the network remaining oil into cluster,film,and droplet remaining oil.展开更多
According to the report from the Chinese Center for Disease Control and Prevention,the prevalence of human immunodeficiency virus(HIV)infection exceeded 1.2 million individuals by the year 2022,with an annual increase...According to the report from the Chinese Center for Disease Control and Prevention,the prevalence of human immunodeficiency virus(HIV)infection exceeded 1.2 million individuals by the year 2022,with an annual increase of about 80000 cases.The overall prevalence of hepatitis B surface antigen among individuals co-infected with HIV reached 13.7%,almost twice the rate of the general population in China.In addition to the well-documented susceptibility to opportunistic infections and new malignancies,HIV infected patients frequently experience liver-related organ damage,with the liver and kidneys being the most commonly affected.This often leads to the development of end-stage liver and kidney diseases.Therefore,organ transplantation has emerged as an important part of active treatment for HIV infected patients.However,the curative effect is not satisfactory.HIV infection has been considered a contraindication for organ transplantation.Until the emergence of highly active anti-retroviral therapy in 1996,the once intractable replication of retrovirus was effectively inhibited.With prolonged survival,the failure of important organs has become the main cause of death among HIV patients.Therefore,transplant centers worldwide have resu-med exploration of organ transplantation for HIV-infected individuals and reached a positive conclusion.This study provides an overview of the current landscape of HIV-positive patients receiving liver transplantation(LT)in main-land China.To date,our transplant center has conducted LT for eight end-stage liver disease patients co-infected with HIV,and all but one,who died two months postoperatively due to sepsis and progressive multi-organ failure,have survived.Comparative analysis with hepatitis B virus-infected patients during the same period revealed no statistically significant differences in acute rejection reactions,cytomegalovirus infection,bacteremia,pulmonary infections,acute kidney injury,new-onset cancers,or vascular and biliary complications.展开更多
Time-encoded imaging is useful for identifying potential special nuclear materials and other radioactive sources at a distance.In this study,a large field-of-view time-encoded imager was developed for gamma-ray and ne...Time-encoded imaging is useful for identifying potential special nuclear materials and other radioactive sources at a distance.In this study,a large field-of-view time-encoded imager was developed for gamma-ray and neutron source hotspot imaging based on a depth-of-interaction(DOI)detector.The imager primarily consists of a DOI detector system and a rotary dual-layer cylindrical coded mask.An EJ276 plastic scintillator coupled with two SiPMs was designed as the DOI detector to increase the field of view and improve the imager performance.The difference in signal time at both ends and the log of the signal amplitude ratio were used to calculate the interaction position resolution.The position resolution of the DOI detector was calibrated using a collimated Cs-137 source,and the full width at half maximum of the reconstruction position of the Gaussian fitting curve was approximately 4.4 cm.The DOI detector can be arbitrarily divided into several units to independently reconstruct the source distribution images.The unit length was optimized via Am-Be source-location experiments.A multidetector filtering method is proposed for image denoising.This method can effectively reduce image noise caused by poor DOI detector position resolution.The vertical field of view of the imager was(-55°,55°)when the detector was placed in the center of the coded mask.A DT neutron source at 20 m standoff could be located within 2400 s with an angular resolution of 3.5°.展开更多
Acoustic models of railway vehicles in standstill and pass-by conditions can be used as part of a virtual certification process for new trains.For each piece of auxiliary equipment,the sound power measured on a test b...Acoustic models of railway vehicles in standstill and pass-by conditions can be used as part of a virtual certification process for new trains.For each piece of auxiliary equipment,the sound power measured on a test bench is combined with meas-ured or predicted transfer functions.It is important,however,to allow for installation effects due to shielding by fairings or the train body.In the current work,fast-running analytical models are developed to determine these installation effects.The model for roof-mounted sources takes account of diffraction at the corner of the train body or fairing,using a barrier model.For equipment mounted under the train,the acoustic propagation from the sides of the source is based on free-field Green’s functions.The bottom surfaces are assumed to radiate initially into a cavity under the train,which is modelled with a simple diffuse field approach.The sound emitted from the gaps at the side of the cavity is then assumed to propagate to the receivers according to free-field Green’s functions.Results show good agreement with a 2.5D boundary element model and with measurements.Modelling uncertainty and parametric uncertainty are evaluated.The largest variability occurs due to the height and impedance of the ground,especially for a low receiver.This leads to standard deviations of up to 4 dB at low frequencies.For the roof-mounted sources,uncertainty over the location of the corner used in the equivalent barrier model can also lead to large standard deviations.展开更多
Purpose – The vibration of the rails is a significant source of railway rolling noise, often forming the dominantcomponent of noise in the important frequency region between 400 and 2000 Hz. The purpose of the paper ...Purpose – The vibration of the rails is a significant source of railway rolling noise, often forming the dominantcomponent of noise in the important frequency region between 400 and 2000 Hz. The purpose of the paper is toinvestigate the influence of the ground profile and the presence of the train body on the sound radiation fromthe rail.Design/methodology/approach – Two-dimensional boundary element calculations are used, in which therail vibration is the source. The ground profile and various different shapes of train body are introduced in themodel, and results are observed in terms of sound power and sound pressure. Comparisons are also made withvibro-acoustic measurements performed with and without a train present.Findings – The sound radiated by the rail in the absence of the train body is strongly attenuated by shieldingdue to the ballast shoulder. When the train body is present, the sound from the vertical rail motion is reflectedback down toward the track where it is partly absorbed by the ballast. Nevertheless, the sound pressure at thetrackside is increased by typically 0–5 dB. For the lateral vibration of the rail, the effects are much smaller. Oncethe sound power is known, the sound pressure with the train present can be approximated reasonably well withsimple line source directivities.Originality/value – Numerical models used to predict the sound radiation from railway rails have generallyneglected the influence of the ground profile and reflections from the underside of the train body on the soundpower and directivity of the rail. These effects are studied in a systematic way including comparisons with measurements.展开更多
BACKGROUND Given the current organ shortage crisis,split liver transplantation(SLT)has emerged as a promising alternative for select end-stage liver disease patients.AIM To introduce an ex-vivo liver graft splitting a...BACKGROUND Given the current organ shortage crisis,split liver transplantation(SLT)has emerged as a promising alternative for select end-stage liver disease patients.AIM To introduce an ex-vivo liver graft splitting approach and evaluate its safety and feasibility in SLT.METHODS A retrospective analysis was conducted on the liver transplantation data from cases performed at our center between April 1,2022,and May 31,2023.The study included 25 SLT cases and 81 whole liver transplantation(WLT)cases.Total ex-vivo liver splitting was employed for SLT graft procurement in three steps.Patient outcomes were determined,including liver function parameters,postoperative complications,and perioperative mortality.Group comparisons for categorical variables were performed using theχ²-test.RESULTS In the study,postoperative complications in the 25 SLT cases included hepatic artery thrombosis(n=1)and pulmonary infections(n=3),with no perioperative mortality.In contrast,among the 81 patients who underwent WLT,complications included perioperative mortality(n=1),postoperative pulmonary infections(n=8),abdominal infection(n=1),hepatic artery thromboses(n=3),portal vein thrombosis(n=1),and intra-abdominal bleeding(n=5).Comparative analysis demonstrated significant differences in alanine aminotransferase(176.0 vs 73.5,P=0.000)and aspartate aminotransferase(AST)(42.0 vs 29.0,P=0.004)at 1 wk postoperatively,and in total bilirubin(11.8 vs 20.8,P=0.003)and AST(41.5 vs 26.0,P=0.014)at 2 wk postoperatively.However,the overall incidence of complications was comparable between the two groups(P>0.05).CONCLUSION Our findings suggest that the total ex-vivo liver graft splitting technique is a safe and feasible approach,especially under the expertise of an experienced transplant center.The approach developed by our center can serve as a valuable reference for other transplantation centers.展开更多
文摘目前国内头痛专病继续教育缺乏统一规范的标准方法,因此以解放军总医院神经内科目前开展的2种头痛继续教育模式(头痛学校和头痛进修教育)为例来探索头痛专病继续教育方法。头痛学校:以短期培训班形式招募培训对头痛诊疗有兴趣的医师,教授头痛诊疗基础知识、头痛系统性疾病管理模式(screen,migraine,aura,red flag and treatment,SMART)和计算机临床决策支持系统(computerized clinical decision support system,CDSS);头痛进修教育:以神经内科头痛病房、头痛门诊为实践基地开展为期半年到1年的头痛专病进修教育。头痛学校可在相对短的时间培训出大量头痛专病医师,部分优秀学员具备开办头痛专病门诊的资质和能力,但缺乏诊疗实践能力的培训;头痛进修教育:在培养头痛专病专家方面更有优势,但其时间、人力成本更高。头痛专病继续教育可有效促进头痛诊疗规范化、同质化,是减轻头痛专病所致负担的必要途径。不同头痛专病继续教育方法各有优缺点,在实践中可互为有效补充。
基金Supported by the Shenzhen Science and Technology R&D Fund,No.JCYJ20220530163011026and Shenzhen Third People’s Hospital,No.G2022008 and No.G2021008。
文摘Liver transplantation is the primary therapeutic intervention for end-stage liver disease.However,vascular complications,particularly those involving the hepatic artery,pose significant risks to patients.The clinical manifestations associated with early arterial complications following liver transplantation are often non-specific.Without timely intervention,these complications can result in graft fai-lure or patient mortality.Therefore,early diagnosis and the formulation of an op-timal treatment plan are imperative.Ultrasound examination remains the pre-dominant imaging modality for detecting complications post liver transplan-tation.This article comprehensively reviews common causes and clinical present-ations of early hepatic artery complications in the post-transplantation period and delineates abnormal sonographic findings for accurate diagnosis of these con-ditions.Overall,ultrasound offers the advantages of convenience,safety,effect-iveness,and non-invasiveness.It enables real-time,dynamic,and precise evalua-tion,making it the preferred diagnostic method for post-liver transplantation assessments.INTRODUCTION Liver transplantation stands as the primary therapeutic approach for end-stage liver disease.Continuous advancements in surgical techniques and the application of novel immunosuppressive agents contribute to ongoing improvements in the success rate and overall survival in patients undergoing liver transplantation procedures.Despite these advan-cements,vascular complications,particularly those involving the hepatic artery,pose significant risks to patients.During the early stages following liver transplantation(within the first 30 d),proper hepatic artery function is crucial for hepatic arterial blood flow.During later stages,collateral circulation,including arteries such as the phrenic artery,right gastric artery,and gastroduodenal artery,becomes important for maintaining hepatic blood supply.It is now understood that the establishment of effective collateral circulation is pivotal for determining the prognosis of hepatic artery complic-ations.The clinical manifestations of these complications are closely linked to factors such as timing,severity,and the specific type of onset.Insufficient hepatic arterial blood flow can lead to abnormal liver function,hepatic infarction,and the formation of hepatic abscesses.Additionally,since the hepatic artery is the sole blood supply to the biliary tract,hepatic artery-related ischemia may result in biliary stricture,obstruction,and the formation of bile ducts.Ultrasound examination remains the primary imaging modality for diagnosing complications post liver transplantation.This article comprehensively reviews common causes and clinical presentations of early hepatic artery complications in the post-transplantation period and outlines abnormal sonographic findings for accurately diagnosing these conditions.NORMAL HEPATIC ARTERY During the intraoperative phase,an ultrasound examination is typically conducted to evaluate the hepatic artery anas-tomosis.The normal internal diameter of the hepatic artery typically ranges from 2 to 5 mm.Two strong echo points are typically identified near the anastomosis.To assess blood flow dynamics,peak systolic velocity,end-diastolic velocity,and resistance index are measured at the donor and recipient sides of the anastomosis following angle correction.Anastomotic stenosis presence and severity can be evaluated by comparing the velocity at the anastomotic site with that at the recipient side.Postoperatively,direct visualization of the anastomosis site through gray ultrasound scans is often challenging.The surgical approach has a significant impact on the proper hepatic artery’s position,resulting in a lower overall success rate of continuous visualization.Color Doppler ultrasound is primarily employed to trace the artery’s path,and spectral measurements are taken at the brightest position of the Color Doppler blood flow signal,primarily used to identify the presence of high-speed turbulence.Hepatic artery spectrum examination plays a crucial role,as a favorable arterial spectral waveform and appropriate hepatic artery flow velocity typically indicate a successful anastomosis,even in cases where the hepatic artery anastomosis cannot be directly visualized by ultrasound.The hepatic artery runs alongside the portal vein,often selected as a reference due to its larger inner diameter.A normal hepatic artery spectrum displays a regular pulsation pattern with a rapid rise in systole and a slow decline in diastole.Parameters for assessing hepatic artery resistance include a resistance index between 0.5 to 0.8 and an artery systolic acceleration of less than 80 ms.Instantaneous increases in the resistance index(RI>0.8)often occur within 2 d after surgery,followed by a subsequent return to normal hepatic arterial parameters.It has been established that the maximum blood flow velocity during systole in the hepatic artery should not exceed 200 cm/s[1].
基金supported by the National Key Research and Development Program of China (Grant No.2018YFA0702400)the National Natural Science Foundation of China (Grant No.52174050)+1 种基金the Natural Science Foundation of Shandong Province (Grant No.ZR2020ME088)the National Natural Science Foundation of Qingdao (Grant No.23-2-1-227-zyyd-jch)。
文摘Hot water flooding is an effective way to develop heavy oil reservoirs.However,local channeling channels may form,possibly leading to a low thermal utilization efficiency and high water cut in the reservoir.The pore structure heterogeneity is an important factor in forming these channels.This study proposes a method that mixes quartz sand with different particle sizes to prepare weakly heterogeneous and strongly heterogeneous models through which hot water flooding experiments are conducted.During the experiments,computer tomography(CT)scanning identifies the pore structure and micro remaining oil saturation distribution to analyze the influence of the pore structure heterogeneity on the channeling channels.The oil saturation reduction and average pore size are divided into three levels to quantitatively describe the relationship between the channeling channel distribution and pore structure heterogeneity.The zone where oil saturation reduction exceeds 20%is defined as a channeling channel.The scanning area is divided into 180 equally sized zones based on the CT scanning images,and threedimensional(3D)distributions of the channeling channels are developed.Four micro remaining oil distribution patterns are proposed,and the morphology characteristics of micro remaining oil inside and outside the channeling channels are analyzed.The results show that hot water flooding is more balanced in the weakly heterogeneous model,and the oil saturation decreases by more than 20%in most zones without narrow channeling channels forming.In the strongly heterogeneous model,hot water flooding is unbalanced,and three narrow channeling channels of different lengths form.In the weakly heterogeneous model,the oil saturation reduction is greater in zones with larger pores.The distribution range of the average pore size is larger in the strongly heterogeneous model.The network remaining oil inside the channeling channels is less than outside the channeling channels,and the hot water converts the network remaining oil into cluster,film,and droplet remaining oil.
基金Supported by the Shenzhen Science and Technology R&D Fund,No.JCYJ20220530163011026Shenzhen Third People’s Hospital,No.G2022008 and No.G2021008.
文摘According to the report from the Chinese Center for Disease Control and Prevention,the prevalence of human immunodeficiency virus(HIV)infection exceeded 1.2 million individuals by the year 2022,with an annual increase of about 80000 cases.The overall prevalence of hepatitis B surface antigen among individuals co-infected with HIV reached 13.7%,almost twice the rate of the general population in China.In addition to the well-documented susceptibility to opportunistic infections and new malignancies,HIV infected patients frequently experience liver-related organ damage,with the liver and kidneys being the most commonly affected.This often leads to the development of end-stage liver and kidney diseases.Therefore,organ transplantation has emerged as an important part of active treatment for HIV infected patients.However,the curative effect is not satisfactory.HIV infection has been considered a contraindication for organ transplantation.Until the emergence of highly active anti-retroviral therapy in 1996,the once intractable replication of retrovirus was effectively inhibited.With prolonged survival,the failure of important organs has become the main cause of death among HIV patients.Therefore,transplant centers worldwide have resu-med exploration of organ transplantation for HIV-infected individuals and reached a positive conclusion.This study provides an overview of the current landscape of HIV-positive patients receiving liver transplantation(LT)in main-land China.To date,our transplant center has conducted LT for eight end-stage liver disease patients co-infected with HIV,and all but one,who died two months postoperatively due to sepsis and progressive multi-organ failure,have survived.Comparative analysis with hepatitis B virus-infected patients during the same period revealed no statistically significant differences in acute rejection reactions,cytomegalovirus infection,bacteremia,pulmonary infections,acute kidney injury,new-onset cancers,or vascular and biliary complications.
基金supported by the National Natural Science Foundation of China(Nos.11975121,12205131)the Fundamental Research Funds for the Central Universities(No.lzujbky-2021-sp58)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.KYCX22_0354)。
文摘Time-encoded imaging is useful for identifying potential special nuclear materials and other radioactive sources at a distance.In this study,a large field-of-view time-encoded imager was developed for gamma-ray and neutron source hotspot imaging based on a depth-of-interaction(DOI)detector.The imager primarily consists of a DOI detector system and a rotary dual-layer cylindrical coded mask.An EJ276 plastic scintillator coupled with two SiPMs was designed as the DOI detector to increase the field of view and improve the imager performance.The difference in signal time at both ends and the log of the signal amplitude ratio were used to calculate the interaction position resolution.The position resolution of the DOI detector was calibrated using a collimated Cs-137 source,and the full width at half maximum of the reconstruction position of the Gaussian fitting curve was approximately 4.4 cm.The DOI detector can be arbitrarily divided into several units to independently reconstruct the source distribution images.The unit length was optimized via Am-Be source-location experiments.A multidetector filtering method is proposed for image denoising.This method can effectively reduce image noise caused by poor DOI detector position resolution.The vertical field of view of the imager was(-55°,55°)when the detector was placed in the center of the coded mask.A DT neutron source at 20 m standoff could be located within 2400 s with an angular resolution of 3.5°.
基金The work described here has been supported by the TRANSIT project(funded by EU Horizon 2020 and the Europe’s Rail Joint Undertaking under grant agreement 881771).
文摘Acoustic models of railway vehicles in standstill and pass-by conditions can be used as part of a virtual certification process for new trains.For each piece of auxiliary equipment,the sound power measured on a test bench is combined with meas-ured or predicted transfer functions.It is important,however,to allow for installation effects due to shielding by fairings or the train body.In the current work,fast-running analytical models are developed to determine these installation effects.The model for roof-mounted sources takes account of diffraction at the corner of the train body or fairing,using a barrier model.For equipment mounted under the train,the acoustic propagation from the sides of the source is based on free-field Green’s functions.The bottom surfaces are assumed to radiate initially into a cavity under the train,which is modelled with a simple diffuse field approach.The sound emitted from the gaps at the side of the cavity is then assumed to propagate to the receivers according to free-field Green’s functions.Results show good agreement with a 2.5D boundary element model and with measurements.Modelling uncertainty and parametric uncertainty are evaluated.The largest variability occurs due to the height and impedance of the ground,especially for a low receiver.This leads to standard deviations of up to 4 dB at low frequencies.For the roof-mounted sources,uncertainty over the location of the corner used in the equivalent barrier model can also lead to large standard deviations.
基金supported by the TRANSIT project(funded by EU Horizon 2020 and the Europe’s Rail Joint Undertaking under Grant Agreement 881771).
文摘Purpose – The vibration of the rails is a significant source of railway rolling noise, often forming the dominantcomponent of noise in the important frequency region between 400 and 2000 Hz. The purpose of the paper is toinvestigate the influence of the ground profile and the presence of the train body on the sound radiation fromthe rail.Design/methodology/approach – Two-dimensional boundary element calculations are used, in which therail vibration is the source. The ground profile and various different shapes of train body are introduced in themodel, and results are observed in terms of sound power and sound pressure. Comparisons are also made withvibro-acoustic measurements performed with and without a train present.Findings – The sound radiated by the rail in the absence of the train body is strongly attenuated by shieldingdue to the ballast shoulder. When the train body is present, the sound from the vertical rail motion is reflectedback down toward the track where it is partly absorbed by the ballast. Nevertheless, the sound pressure at thetrackside is increased by typically 0–5 dB. For the lateral vibration of the rail, the effects are much smaller. Oncethe sound power is known, the sound pressure with the train present can be approximated reasonably well withsimple line source directivities.Originality/value – Numerical models used to predict the sound radiation from railway rails have generallyneglected the influence of the ground profile and reflections from the underside of the train body on the soundpower and directivity of the rail. These effects are studied in a systematic way including comparisons with measurements.
基金Supported by the Shenzhen Science and Technology Research and Development Fund,No.JCYJ20220530163011026.
文摘BACKGROUND Given the current organ shortage crisis,split liver transplantation(SLT)has emerged as a promising alternative for select end-stage liver disease patients.AIM To introduce an ex-vivo liver graft splitting approach and evaluate its safety and feasibility in SLT.METHODS A retrospective analysis was conducted on the liver transplantation data from cases performed at our center between April 1,2022,and May 31,2023.The study included 25 SLT cases and 81 whole liver transplantation(WLT)cases.Total ex-vivo liver splitting was employed for SLT graft procurement in three steps.Patient outcomes were determined,including liver function parameters,postoperative complications,and perioperative mortality.Group comparisons for categorical variables were performed using theχ²-test.RESULTS In the study,postoperative complications in the 25 SLT cases included hepatic artery thrombosis(n=1)and pulmonary infections(n=3),with no perioperative mortality.In contrast,among the 81 patients who underwent WLT,complications included perioperative mortality(n=1),postoperative pulmonary infections(n=8),abdominal infection(n=1),hepatic artery thromboses(n=3),portal vein thrombosis(n=1),and intra-abdominal bleeding(n=5).Comparative analysis demonstrated significant differences in alanine aminotransferase(176.0 vs 73.5,P=0.000)and aspartate aminotransferase(AST)(42.0 vs 29.0,P=0.004)at 1 wk postoperatively,and in total bilirubin(11.8 vs 20.8,P=0.003)and AST(41.5 vs 26.0,P=0.014)at 2 wk postoperatively.However,the overall incidence of complications was comparable between the two groups(P>0.05).CONCLUSION Our findings suggest that the total ex-vivo liver graft splitting technique is a safe and feasible approach,especially under the expertise of an experienced transplant center.The approach developed by our center can serve as a valuable reference for other transplantation centers.
