BACKGROUND The clinical impact of post-percutaneous coronary intervention (PCI) quantitative flow ratio (QFR) in patients treated with PCI for chronic total occlusion (CTO) was still undetermined.METHODS All CTO vesse...BACKGROUND The clinical impact of post-percutaneous coronary intervention (PCI) quantitative flow ratio (QFR) in patients treated with PCI for chronic total occlusion (CTO) was still undetermined.METHODS All CTO vessels treated with successful anatomical PCI in patients from PANDA Ⅲ trial were retrospectively measured for postPCI QFR.The primary outcome was 2-year vessel-oriented composite endpoints (VOCEs,composite of target vessel-related cardiac death,target vessel-related myocardial infarction,and ischemia-driven target vessel revascularization).Receiver operator characteristic curve analysis was conducted to identify optimal cutoff value of post-PCI QFR for predicting the 2-year VOCEs,and all vessels were stratified by this optimal cutoff value.Cox proportional hazards models were employed to calculate the hazard ratio (HR) with 95% CI.RESULTS Among 428 CTO vessels treated with PCI,353 vessels (82.5%) were analyzable for post-PCI QFR.31 VOCEs (8.7%) occurred at 2 years.Mean value of post-PCI QFR was 0.92±0.13.Receiver operator characteristic curve analysis shown the optimal cutoff value of post-PCI QFR for predicting 2-year VOCEs was 0.91.The incidence of 2-year VOCEs in the vessel with post-PCI QFR<0.91 (n=91) was significantly higher compared with the vessels with post-PCI QFR≥0.91 (n=262)(22.0%vs.4.2%,HR=4.98,95%CI:2.32–10.70).CONCLUSIONS Higher post-PCI QFR values were associated with improved prognosis in the PCI practice for coronary CTO.Achieving functionally optimal PCI results (post-PCI QFR value≥0.91) tends to get better prognosis for patients with CTO lesions.展开更多
Background Quantitative flow ratio(QFR)based lesion selection for percutaneous coronary intervention(PCI)treatment has shown clinical benefits in terms of reduced risk for myocardial infarction and repeat revasculariz...Background Quantitative flow ratio(QFR)based lesion selection for percutaneous coronary intervention(PCI)treatment has shown clinical benefits in terms of reduced risk for myocardial infarction and repeat revascularization.Whether this benefit is consistent across different age groups still needs further investigation.Methods In this prespecified subgroup study of FAVORⅢChina trial,we compared long-term clinical outcomes between QFR-guided and angiography-guided PCI among different age groups among 3825 enrolled subjects.The primary endpoint was major adverse cardiac events(MACEs),a composite of all-cause death,myocardial infarction,and ischemia-driven revascularization.Results Of the 3825 patients,1717(44.9%)were aged≥65 years.At baseline,patients≥65 had higher rates of hypertension,hyperlipidaemia,stroke history(P<0.0001),and peripheral vascular disease(P=0.024)and had higher SYNTAX scores(P=0.0095).Compared with standard angiography guidance,the QFR-guided strategy consistently reduced the 1-year(≥65 years,6.04%vs.9.19%,HR=0.65,95%CI:0.46–0.92;<65 years,5.53%vs.8.43%,HR=0.65,95%CI:0.47–0.91)and 3-year MACE rates in both age groups(≥65 years,11.8%vs.15.2%,HR:0.75,95%CI:0.58–0.98;<65 years,9.5%vs.14.6%,HR=0.63;95%CI:0.49–0.81),without a significant interaction(Pinteraction=0.99).Within the QFR-guided group,the 3-year MACE rate in patients with deferred vessels was numerically greater in patients aged≥65 years than in those aged<65 years(8.3%vs.3.0%,P=0.10).Conclusions Although with higher rate of comorbidities and more complex coronary anatomy,the long-term benefit of the QFR-guided PCI strategy remained consistent in patients≥65 years,compared with those<65 years.展开更多
Background Quantitative flow ratio(QFR) holds significant value in guiding drug-coated balloon(DCB) treatment and enhancing outcomes. However, the predictive capability of post-angioplasty QFR for long-term clinical e...Background Quantitative flow ratio(QFR) holds significant value in guiding drug-coated balloon(DCB) treatment and enhancing outcomes. However, the predictive capability of post-angioplasty QFR for long-term clinical events in patients with de novo lesions who receive DCB treatment remains uncertain. The aim of this study was to explore the potential significance of post-angioplasty QFR measurements in predicting clinical outcomes in patients underwent DCB treatment for de novo lesions.Methods Patients who underwent DCB-only intervention for de novo lesions were enrolled. QFR was conducted after DCB treatment. The patients were then categorized based on post-angioplasty QFR. The primary endpoint was major adverse cardiac events(MACE), encompassing all-cause death, cardiovascular death, nonfatal myocardial infarction, stroke, and target vessel revascularization.Results A total of 553 patients with 561 lesions were included. The median follow-up period was 505 days, during which 66(11.8%) MACEs occurred. Based on post-procedural QFR grouping, there were 259 cases in the high QFR group(QFR > 0.93) and302 cases in the low QFR group(QFR ≤ 0.93). Kaplan-Meier analysis revealed a significantly higher cumulative incidence of MACE in the low QFR group(log-rank P = 0.004). The multivariate Cox proportional hazards model demonstrated a significant inverse correlation between QFR and the occurrence of MACEs(HR = 0.522, 95%CI: 0.289-0.942, P = 0.031). Landmark analysis indicated that high QFR had a significant reducing effect on the cumulative incidence of MACEs within 1 year(log-rank P = 0.016)and 1-5 years(log-rank P = 0.026).Conclusions In patients who underwent DCB-only treatment for de novo lesions, higher post-procedural QFR values(> 0.93)were identified as an independent protective factor against adverse prognosis.展开更多
Wall-mounted swirling ventilation is a new type of system in mechanized excavation faces with a dust sup-pression performance that is closely related to the blowing-to-suction flow ratio.Physical and simulation models...Wall-mounted swirling ventilation is a new type of system in mechanized excavation faces with a dust sup-pression performance that is closely related to the blowing-to-suction flow ratio.Physical and simulation models were developed according to the No.C103 mechanized excavation face in the Nahe Coal Mine of the Baise Mining Bureau,Guangxi Province to optimize the blowing-to-suction flow ratio for wall-mounted swirling ventilation.Both the k-εturbulence model and the discrete phase model were utilized to simulate airflow field structures and dust concentration distribution patterns at various blowing-to-suction flow ratios.The results suggest that higher blowing-to-suction flow ratios increase the airflow field disturbance around the working face and weaken the intensity of the axial air curtain.On the other hand,both the intensity of the radial air curtain and the dust suppression effect are enhanced.At a blowing-to-suction flow ratio of 0.8,the wall-mounted swirling ventilation system achieved the most favorable dust suppression performance.Both the total dust and respirable dust had their lowest concentrations with maximum efficiencies of reducing both types at 90.33%and 87.16%,respectively.展开更多
Severe coronary stenosis concomitant with congenital coronary myocardial bridge(MB)is a tough scenario for cardiologist to perform revascularization,for which the complication rates including in-stent restenosis,stent...Severe coronary stenosis concomitant with congenital coronary myocardial bridge(MB)is a tough scenario for cardiologist to perform revascularization,for which the complication rates including in-stent restenosis,stent fracture,stent thrombosis and even coronary perforation are still high.[1,2]Meanwhile,the necessity of revascularization in such patients is worth prudent evaluation.Cardiac imaging modalities are crucial and helpful in making revascularized decisions and strategies.Herein,we report a case using quantitative flow ratio(QFR)and intravascular ultrasound(IVUS)to facilitate accurate revascularization in a patient with both severe coronary stenosis and deep coronary MB.展开更多
Objective The study sought to investigate the clinical predictive value of quantitative flow ratio(QFR)for the long-term target vessel failure(TVF)outcome in patients with in-stent restenosis(ISR)by using drug-coated ...Objective The study sought to investigate the clinical predictive value of quantitative flow ratio(QFR)for the long-term target vessel failure(TVF)outcome in patients with in-stent restenosis(ISR)by using drug-coated balloon(DCB)treatment after a long-term follow-up.Methods This was a retrospective study.A total of 186 patients who underwent DCB angioplasty for ISR in two hospitals from March 2014 to September 2019 were enrolled.The QFR of the entire target vessel was measured offline.The primary endpoint was TVF,including target vessel-cardiac death(TV-CD),target vessel-myocardial infarction(TV-MI),and clinically driven-target vessel revascularization(CD-TVR).Results The follow-up time was 3.09±1.53 years,and 50 patients had TVF.The QFR immediately after percutaneous coronary intervention(PCI)was significantly lower in the TVF group than in the no-TVF group.Multivariable Cox regression analysis indicated that the QFR immediately after PCI was an excellent predictor for TVF after the long-term follow-up[hazard ratio(HR):5.15×10−5(6.13×10−8−0.043);P<0.01].Receiver-operating characteristic(ROC)curve analysis demonstrated that the optimal cut-off value of the QFR immediately after PCI for predicting the long-term TVF was 0.925(area under the curve:0.886,95%confidence interval:0.834–0.938;sensitivity:83.40%,specificity:88.00;P<0.01).In addition,QFR≤0.925 post-PCI was strongly correlated with the TVF,including TV-MI and CD-TVR(P<0.01).Conclusion The QFR immediately after PCI showed a high predictive value of TVF after a long-term follow-up in ISR patients who underwent DCB angioplasty.A lower QFR immediately after PCI was associated with a worse TVF outcome.展开更多
Objective:The goal of this study was to examine the prognostic performance of optical flow ratio(OFR)among patients with coronary artery disease(CAD)after percutaneous coronary intervention(PCI).Methods:We recruited p...Objective:The goal of this study was to examine the prognostic performance of optical flow ratio(OFR)among patients with coronary artery disease(CAD)after percutaneous coronary intervention(PCI).Methods:We recruited patients with CAD undergoing optical coherence tomography(OCT)-directed PCI between January 2019 and June 2021 for our single-center,hospital-based,retrospective cohort investigation.We assessed the link between post-PCI OFR and major adverse cardiovascular events(MACE)via multivariate Cox regression analy-sis.Results:Receiver operating characteristic analysis revealed that the best post-PCI OFR threshold for MACE was 0.91,and introduction of OFR into the baseline profile and OCT results markedly enhanced MACE identification after PCI.On the basis of survival curves,patients with OFR≤0.91(P<0.001)and thin-cap fibroatheroma(TCFA)(P=0.007)exhibited higher MACE incidence,and myocardial infarction(MI)incidence was considerably greater among patients with OFR≤0.91(P<0.001),compared with OFR>0.91.Multivariate Cox regression analysis suggested that OFR≤0.91(hazard ratio[HR]:3.60;95%confidence interval[CI]:1.24–10.44;P=0.019),and TCFA(HR:3.63;95%CI:1.42–9.20;P=0.007)were independent risk factors for MACE,and OFR≤0.91 was independently associated with MI(HR:14.64;95%CI:3.27–65.54;P<0.001).Conclusion:OFR after PCI is an independent MACE bio-indicator among patients with CAD.Adding OFR to post-PCI OCT results may potentially enhance MACE prediction.展开更多
Background:The FAVOR(Comparison of Quantitative Flow Ratio Guided and Angiography Guided Percutaneous Intervention in Patients with Coronary Artery Disease)III China trial demonstrated that percutaneous coronary inter...Background:The FAVOR(Comparison of Quantitative Flow Ratio Guided and Angiography Guided Percutaneous Intervention in Patients with Coronary Artery Disease)III China trial demonstrated that percutaneous coronary intervention(PCI)lesion selection using quantitative flow ratio(QFR)measurement,a novel angiography-based approach for estimating fractional flow reserve,improved two-year clinical outcomes compared with standard angiography guidance.This study aimed to assess the cost-effectiveness of QFR-guided PCI from the perspective of the current Chinese healthcare system.Methods:This study is a pre-specified analysis of the FAVOR III China trial,which included 3825 patients randomized between December 25,2018,and January 19,2020,from 26 centers in China.Patients with stable or unstable angina pectoris or those≥72 hours post-myocardial infarction who had at least one lesion with a diameter stenosis between 50%and 90%in a coronary artery with a≥2.5 mm reference vessel diameter by visual assessment were randomized to a QFR-guided strategy or an angiography-guided strategy with 1:1 ratio.During the two-year follow-up,data were collected on clinical outcomes,quality-adjusted life-years(QALYs),estimated costs of index procedure hospitalization,outpatient cardiovascular medication use,and rehospitalization due to major adverse cardiac and cerebrovascular events(MACCE).The primary analysis calculated the incremental cost-effectiveness ratio(ICER)as the cost per MACCE avoided.An ICER of¥10,000/MACCE event avoided was considered economically attractive in China.Results:At two years,the QFR-guided group demonstrated a reduced rate of MACCE compared to the angiography-guided group(10.8%vs.14.7%,P<0.01).Total two-year costs were similar between the groups(¥50,803±21,121 vs.¥50,685±23,495,P=0.87).The ICER for the QFR-guided strategy was¥3055 per MACCE avoided,and the probability of QFR being economically attractive was 64%at a willingness-to-pay threshold of¥10,000/MACCE avoided.Sensitivity analysis showed that QFR-guided PCI would become cost-saving if the cost of QFR were below¥3682(current cost:¥3800).Cost-utility analysis yielded an ICER of¥56,163 per QALY gained,with a 53%probability of being cost-effective at a willingness-to-pay threshold of¥85,000 per QALY gained.Conclusion:In patients undergoing PCI,a QFR-guided strategy appears economically attractive compared to angiographic guidance from the perspective of the Chinese healthcare system.展开更多
Background:Drug-coated balloons(DCBs)have emerged as potential alternatives to drug-eluting stents in specific lesion subsets for de novo coronary lesions.Quantitative flow ratio(QFR)is a method based on the three-dim...Background:Drug-coated balloons(DCBs)have emerged as potential alternatives to drug-eluting stents in specific lesion subsets for de novo coronary lesions.Quantitative flow ratio(QFR)is a method based on the three-dimensional quantitative coronary angiography and contrast flow velocity during coronary angiography(CAG),obviating the need for an invasive fractional flow reserve procedural.This study aimed to assess the serial angiographic changes of de novo lesions post-DCB therapy and further explore the cut-off values of lesion and vessel QFR,which predict vessel restenosis(diameter stenosis[DS]≥50%)at mid-term follow-up.Methods:The data of patients who underwent DCB therapy between January 2014 and December 2019 from the multicenter hospital were retrospectively collected for QFR analysis.From their QFR performances,which were analyzed by CAG images at follow-up,we divided them into two groups:group A,showing target vessel DS≥50%,and group B,showing target vessel DS<50%.The median follow-up time was 287 days in group A and 227 days in group B.We compared the clinical characteristics,parameters during DCB therapy,and QFR performances,which were analyzed by CAG images between the two groups,in need to explore the cut-off value of lesion/vessel QFR which can predict vessel restenosis.Student's t test was used for the comparison of normally distributed continuous data,Mann-Whitney U test for the comparison of non-normally distributed continuous data,and receiver operating characteristic(ROC)curves for the evaluation of QFR performance which can predict vessel restenosis(DS≥50%)at mid-term follow-up using the area under the curve(AUC).Results:A total of 112 patients with 112 target vessels were enrolled in this study.Group A had 41 patients,while group B had 71.Vessel QFR and lesion QFR were lower in group A than in group B post-DCB therapy,and the cut-off values of lesion QFR and vessel QFR in the ROC analysis to predict target vessel DS≥50%post-DCB therapy were 0.905(AUC,0.741[95%confidence interval,CI:0.645,0.837];sensitivity,0.817;specificity,0.561;P<0.001)and 0.890(AUC,0.796[95%CI:0.709,0.882];sensitivity,0.746;specificity,0.780;P<0.001).Conclusions:The cut-off values of lesion QFR and vessel QFR can assist in predicting the angiographic changes post-DCB therapy.When lesion/vessel QFR values are<0.905/0.890 post-DCB therapy,a higher risk of vessel restenosis is potentially predicted at follow-up.展开更多
An online method using continuous flow isotope ratio mass spectrometry （CF-IRMS） interfaced with a Gasbench Ⅱ was presented to determine chlorine stable isotope composition. Silver chloride （AgCl） was quantitativ...An online method using continuous flow isotope ratio mass spectrometry （CF-IRMS） interfaced with a Gasbench Ⅱ was presented to determine chlorine stable isotope composition. Silver chloride （AgCl） was quantitatively derived from chloride by using silver nitrate （AgNO3）, and then was reacted with iodomethane （CH3Ⅰ） to produce methyl chloride （CH3Cl）. A GasBench Ⅱ equipped with a PoraPlot Q column was used to separate CH3Cl from any other gas species. Finally, chlorine stable isotope analysis was carried out on CH3Cl introduced to the IRMS in a helium stream via an active open split. The minimum amount of Cl used in this method is of the order of 1.4 μmol. Inter-laboratory and inter-technique comparisons show that the total uncertainty incorporating both the precision and accuracy of this method is better than 0.007%. Furthermore, ten seawaters sampled from different locations have a narrow δ37Cl value range from -0.008% to 0.010%, with a mean value of （0.000±0.006）%. This supports the assumption that any seawater can be representative of standard mean ocean chloride （SMOC） and used as an international reference material.展开更多
Conventionally,flexible barriers are rated based on their ability to resist a free-falling boulder with a particular input energy.However,there is still no well-accepted approach for evaluating performance of flexible...Conventionally,flexible barriers are rated based on their ability to resist a free-falling boulder with a particular input energy.However,there is still no well-accepted approach for evaluating performance of flexible barrier under debris flow impact.In this study,a large-nonlinear finite-element model was used to back-analyze centrifuge tests to discern the effects of impact material type,barrier stiffness,and flow aspect ratio(flow height to flow length)on the reaction force between the impacting medium and flexible barrier.Results show that,in contrast to flexible barriers for resisting rockfall,the normal impact force induced by the highly frictional and viscous debris is insensitive to barrier stiffness.This is because the elongated distributions of kinetic energy are mainly dissipated by the internal and boundary shearing,and only a small portion is forwarded to the barrier.Furthermore,a new stiffness number is proposed to characterize the equivalent stiffness between a debris flow or a boulder,and a flexible barrier.Under the circumstance of an extremely elongated debris flow event,i.e.,low aspect ratio,the load on a barrier is dominated by the static component and thus not sensitive to the barrier stiffness.展开更多
According to the observational data of viscous debris flows with hyper-concentration, debris flows can be classified into three types:high-viscous, viscous, and sub-viscous debris flows.Distinct formation mechanism of...According to the observational data of viscous debris flows with hyper-concentration, debris flows can be classified into three types:high-viscous, viscous, and sub-viscous debris flows.Distinct formation mechanism of different graded bedding structures in deposits of viscous debris flows was analyzed in this paper by using their yield-stress ratio and flow plug ratio.This paper specially analyzed the effect of Weissenberg which the gravels in squirm condition of hyper-concentration viscous flows would tend to move vertically, and the formation mechanism of the gravels accumulated at surface was also studied.The analysis in this paper can establish a foundation for the studies on differentiation of bedding structures of debris flow deposits and studies on dynamic parameters of debris flows.展开更多
Based on conservation of energy principle and heat flow data in China continent, the upper limit of 1.3 μW/m3 heat production is obtained for continental crust in China. Furthermore, using the data of heat flow and h...Based on conservation of energy principle and heat flow data in China continent, the upper limit of 1.3 μW/m3 heat production is obtained for continental crust in China. Furthermore, using the data of heat flow and helium isotope ratio of underground fluid, the heat productions of different tectonic units in China continent are estimated in range of 0.58-1.12 μW/m3 with a median of 0.85 μW/m3. Accordingly, the contents of U, Th and K20 in China crust are in ranges of 0.83-1.76 μg/g, 3.16-6.69 μg/g, and 1.0%-2.12%, respectively. These results indicate that the abundance of radioactive elements in the crust of China continent is much higher than that of Archean crust; and this fact implies China＇s continental crust is much evolved in chemical composition. Meanwhile, significant lateral variation of crustal composition is also exhibited among different tectonic units in China continent. The crust of eastern China is much enriched in incompatible elements such as U, Th and K than that of western China; and the crust of orogenic belts is more enriched than that of platform regions. It can also be inferred that the crusts of eastern China and orogenic belts are much felsic than those of western China and platform regions, respectively, derived from the positive correlation between the heat production and SiO2 content of bulk crust. This deduction is consistent with the results derived from the crustal seismic velocity data in China. According to the facts of the lower seismic velocity of China than the average value of global crust, and the higher heat production of China continent compared with global crust composition models published by previous studies, it is deduced that the average composition models of global continent crust by Rudnick and Fountain （1995）, Rudnick and Gao （2003）, Weaver and Tarney （1984）, Shaw et al. （1986）, and Wedepohl （1995） overestimate the abundance of incompatible elements such as U, Th and K of continental crust.展开更多
The neutron-to-proton and3 H-to-3 He yield ratios, and the directed flows of particles dependent on a reduced rapidity, the transverse momentum per nucleon,and a reduced impact parameter are investigated for ^(28)S+^(...The neutron-to-proton and3 H-to-3 He yield ratios, and the directed flows of particles dependent on a reduced rapidity, the transverse momentum per nucleon,and a reduced impact parameter are investigated for ^(28)S+^(28)Si and ^(32)S+^(28)Si systems at 50 and 400 MeV/u using an isospin-dependent quantum molecular dynamics model.The results show that these yield ratios of projectile-like fragments are approximately equal to the constituent neutron-to-proton ratio of the projectile. There are clear differences of the directed flows for isospin-related fragments neutron and proton,~3H and ~3He from ^(28)S+^(28)Si collisions.The differences in directed flows for neutrons and protons and ~3H–~3He from a proton-rich nucleus ^(28)S- induced collisions are noticeably larger than those from a stable nucleus ^(32)S- induced reactions under medium impact parameters. Thus, the yield ratios and differences in directed flows for the neutrons and protons and ~3H–~3He under medium impact parameters are proposed as possible observable items for studying isospin physics.展开更多
In modern gas turbines, rim seal located between the stator-disc and rotor-disc is used to prevent hot-gas ingestion into the inner stage-gap of high pressure turbine. However, the purge flow supplied to the cavity th...In modern gas turbines, rim seal located between the stator-disc and rotor-disc is used to prevent hot-gas ingestion into the inner stage-gap of high pressure turbine. However, the purge flow supplied to the cavity through the rim seal interacts with the main flow, producing additional aerodynamic loss due to the mixing process which plays a significant role in the formation, development and evolution of downstream secondary flow. In this paper, a set of cascade representative of low aspect ratio turbine is selected to numerically investigate the influence of upstream cavity purge flow on the hub secondary flow structure and aerodynamic loss. Cascade with/without upstream cavity and four different purge mass flow rates are all taken into account in this simulation. Then, a deep insight into the loss mechanism of interaction between purge flow and main flow is gained. The results show that the presence of cavity and purge flow has a significant impact on the main flow which not only changes the vortex structure in both the passage and upstream cavity, but also alters the cascade exit flow angle distribution along the spanwise. Moreover, aerodynamic loss in the cascade rises with the increase of purge flow rate while the sealing effect is also enhanced. Therefore, the effect of upstream cavity purge flow must be considered in the process of turbine aerodynamic design. What is more, it is necessary to minimize the purge flow rate in order to reduce aerodynamic loss on the premise of satisfying cooling requirements.展开更多
Air flow control is one of the most important control methods for maintaining the stability and reliability of a fuel cell system, which can avoid oxygen starvation or oxygen saturation. The oxygen excess ratio （OER...Air flow control is one of the most important control methods for maintaining the stability and reliability of a fuel cell system, which can avoid oxygen starvation or oxygen saturation. The oxygen excess ratio （OER） is often used to indicate the air flow condition. Based on a fuel cell system model for vehicles, OER performance was analyzed for different stack currents and temperatures in this paper, and the results show that the optimal OER was affected weakly by the stack temperature. In order to ensure the system working in optimal OER, a control scheme that includes an optimal OER regulator and a fuzzy control was proposed. According to the stack current, a reference value of air flow rate was obtained with the optimal OER regulator and then the air compressor motor voltage was controlled with the fuzzy controller to adjust the air flow rate provided by the air compressor. Simulation results show that the control method has good dynamic and static characteristics.展开更多
Rotating flows represent a very interesting area for researchers and industry for their extensive use in industrial and domestic machinery and especially for their great energy potential, annular flows are an example ...Rotating flows represent a very interesting area for researchers and industry for their extensive use in industrial and domestic machinery and especially for their great energy potential, annular flows are an example that draws the attention of researchers in recent years. The best design and optimization of these devices require knowledge of thermal, mechanical and hydrodynamic characteristics of flows circulating in these devices. An example of hydrodynamic parameters is the speed of rotation of the moving walls. This work is to study numerically the influence of the rotating speed ratio Γ of the two moving cylinders on the mean and especially on the turbulent quantities of the turbulent flow in the annular space. The numerical simulation is based on one-point statistical modeling using a low Reynolds number second-order full stress transport closure (RSM model), simulation code is not a black box but a completely transparent code where we can intervene at any step of the calculation. We have varied Γ from -1.0 to 1.0 while maintaining always the external cylinder with same speed Ω. The results show that the turbulence structure, profiles of mean velocities and the nature of the boundary layers of the mobile walls depend enormously on the ratio of speeds. The level of turbulence measured by the kinetic energy of turbulence and the Reynolds stresses shows well that the ratio Γ is an interesting parameter to exploit turbulence in this kind of annular flows.展开更多
A depth_integrated two_dimensional numerical model of current, salinity and sediment transport was proposed and calibrated by the observation data in the Yangtze River Estuary. It was then applied to investigate the f...A depth_integrated two_dimensional numerical model of current, salinity and sediment transport was proposed and calibrated by the observation data in the Yangtze River Estuary. It was then applied to investigate the flow and sediment ratio of the navigation channel, i.e. the North Channel of the Yangtze River Estuary,before and after the first phase waterway project is implemented. Particularly, the influences of groin length and the orientation of the submerged dam on the flow ratio and sediment load discharging into the North Channel were discussed. The numerical results demonstrate that less sediment load discharges into the navigation channel, which unburdens the waterway dredging, but in the meantime the flow ratio is also decreased. The flow and sediment ratio can be adjusted by changing layout and dimensions of the hydro_structures, such as the groin length, the top height, etc. The effect of the orientation of the submerged dam is more obvious than the groin lengh.展开更多
The effects of the aspect ratio on unsteady solutions through the curved duct flow are studied numerically by a spectral based computational procedure with a temperature gradient between the vertical sidewalls for the...The effects of the aspect ratio on unsteady solutions through the curved duct flow are studied numerically by a spectral based computational procedure with a temperature gradient between the vertical sidewalls for the Grashof number 100 ≤ Gr ≤ 2 000. The outer wall of the duct is heated while the inner wall is cooled and the top and bottom walls are adiabatic. In this paper, unsteady solutions are calculated by the time history analysis of the Nusselt number for the Dean numbers Dn = 100 and Dn = 500 and the aspect ratios 1≤γ≤ 3. Water is taken as a working fluid （Pr =7.0）. It is found that at Dn = 100, there appears a steady-state solution for small or large Gr. For moderate Gr, however, the steady-state solution turns into the periodic solution if γ is increased. For Dn = 500, on the other hand, it is analyzed that the steady-state solution turns into the chaotic solution for small and large Gr for any γ lying in the range. For moderate Gr at Dn = 500, however, the steady-state flow turns into the chaotic flow through the periodic oscillating flow if the aspect ratio is increased.展开更多
Hydrogenated microcrystalline silicon(μc-Si:H)films were prepared on glass and silicon substrates by radio frequency magnetron sputtering at 100°C using a mixture of argon(Ar)and hydrogen(H2)gasses as precursor ...Hydrogenated microcrystalline silicon(μc-Si:H)films were prepared on glass and silicon substrates by radio frequency magnetron sputtering at 100°C using a mixture of argon(Ar)and hydrogen(H2)gasses as precursor gas.The effects of the ratio of hydrogen flow(H2/(Ar+H2)%)on the microstructure were evaluated.Results show that the microstructure,bonding structure,and surface morphology of theμc-Si:H films can be tailored based on the ratio of hydrogen flow.An amorphous to crystalline phase transition occurred when the ratio of hydrogen flow increased up to 50%.The crystallinity increased and tended to stabilize with the increase in ratio of hydrogen flow from 40%to 70%.The surface roughness of thin films increased,and total hydrogen content decreased as the ratio of hydrogen flow increased.Allμc-Si:H films have a preferred(111)orientation,independent of the ratio of hydrogen flow.And theμc-Si:H films had a dense structure,which shows their excellent resistance to post-oxidation.展开更多
基金supported by the CAMS Innovation Fund for Medical Sciences(No.2021-I2M-1-008)the National High Level Hospital Clinical Research Funding(No.2023-GSP-GG-2&No.2023-GSP-QN-34&No.2023-GSPRC-05).
文摘BACKGROUND The clinical impact of post-percutaneous coronary intervention (PCI) quantitative flow ratio (QFR) in patients treated with PCI for chronic total occlusion (CTO) was still undetermined.METHODS All CTO vessels treated with successful anatomical PCI in patients from PANDA Ⅲ trial were retrospectively measured for postPCI QFR.The primary outcome was 2-year vessel-oriented composite endpoints (VOCEs,composite of target vessel-related cardiac death,target vessel-related myocardial infarction,and ischemia-driven target vessel revascularization).Receiver operator characteristic curve analysis was conducted to identify optimal cutoff value of post-PCI QFR for predicting the 2-year VOCEs,and all vessels were stratified by this optimal cutoff value.Cox proportional hazards models were employed to calculate the hazard ratio (HR) with 95% CI.RESULTS Among 428 CTO vessels treated with PCI,353 vessels (82.5%) were analyzable for post-PCI QFR.31 VOCEs (8.7%) occurred at 2 years.Mean value of post-PCI QFR was 0.92±0.13.Receiver operator characteristic curve analysis shown the optimal cutoff value of post-PCI QFR for predicting 2-year VOCEs was 0.91.The incidence of 2-year VOCEs in the vessel with post-PCI QFR<0.91 (n=91) was significantly higher compared with the vessels with post-PCI QFR≥0.91 (n=262)(22.0%vs.4.2%,HR=4.98,95%CI:2.32–10.70).CONCLUSIONS Higher post-PCI QFR values were associated with improved prognosis in the PCI practice for coronary CTO.Achieving functionally optimal PCI results (post-PCI QFR value≥0.91) tends to get better prognosis for patients with CTO lesions.
文摘Background Quantitative flow ratio(QFR)based lesion selection for percutaneous coronary intervention(PCI)treatment has shown clinical benefits in terms of reduced risk for myocardial infarction and repeat revascularization.Whether this benefit is consistent across different age groups still needs further investigation.Methods In this prespecified subgroup study of FAVORⅢChina trial,we compared long-term clinical outcomes between QFR-guided and angiography-guided PCI among different age groups among 3825 enrolled subjects.The primary endpoint was major adverse cardiac events(MACEs),a composite of all-cause death,myocardial infarction,and ischemia-driven revascularization.Results Of the 3825 patients,1717(44.9%)were aged≥65 years.At baseline,patients≥65 had higher rates of hypertension,hyperlipidaemia,stroke history(P<0.0001),and peripheral vascular disease(P=0.024)and had higher SYNTAX scores(P=0.0095).Compared with standard angiography guidance,the QFR-guided strategy consistently reduced the 1-year(≥65 years,6.04%vs.9.19%,HR=0.65,95%CI:0.46–0.92;<65 years,5.53%vs.8.43%,HR=0.65,95%CI:0.47–0.91)and 3-year MACE rates in both age groups(≥65 years,11.8%vs.15.2%,HR:0.75,95%CI:0.58–0.98;<65 years,9.5%vs.14.6%,HR=0.63;95%CI:0.49–0.81),without a significant interaction(Pinteraction=0.99).Within the QFR-guided group,the 3-year MACE rate in patients with deferred vessels was numerically greater in patients aged≥65 years than in those aged<65 years(8.3%vs.3.0%,P=0.10).Conclusions Although with higher rate of comorbidities and more complex coronary anatomy,the long-term benefit of the QFR-guided PCI strategy remained consistent in patients≥65 years,compared with those<65 years.
基金supported by grants from the National Natural Science Foundation of China (82070408)the Traditional Chinese Medicine Science and Technology Project of Zhejiang Province (2023ZL496)。
文摘Background Quantitative flow ratio(QFR) holds significant value in guiding drug-coated balloon(DCB) treatment and enhancing outcomes. However, the predictive capability of post-angioplasty QFR for long-term clinical events in patients with de novo lesions who receive DCB treatment remains uncertain. The aim of this study was to explore the potential significance of post-angioplasty QFR measurements in predicting clinical outcomes in patients underwent DCB treatment for de novo lesions.Methods Patients who underwent DCB-only intervention for de novo lesions were enrolled. QFR was conducted after DCB treatment. The patients were then categorized based on post-angioplasty QFR. The primary endpoint was major adverse cardiac events(MACE), encompassing all-cause death, cardiovascular death, nonfatal myocardial infarction, stroke, and target vessel revascularization.Results A total of 553 patients with 561 lesions were included. The median follow-up period was 505 days, during which 66(11.8%) MACEs occurred. Based on post-procedural QFR grouping, there were 259 cases in the high QFR group(QFR > 0.93) and302 cases in the low QFR group(QFR ≤ 0.93). Kaplan-Meier analysis revealed a significantly higher cumulative incidence of MACE in the low QFR group(log-rank P = 0.004). The multivariate Cox proportional hazards model demonstrated a significant inverse correlation between QFR and the occurrence of MACEs(HR = 0.522, 95%CI: 0.289-0.942, P = 0.031). Landmark analysis indicated that high QFR had a significant reducing effect on the cumulative incidence of MACEs within 1 year(log-rank P = 0.016)and 1-5 years(log-rank P = 0.026).Conclusions In patients who underwent DCB-only treatment for de novo lesions, higher post-procedural QFR values(> 0.93)were identified as an independent protective factor against adverse prognosis.
基金support for this work was provided by the National Natural Science Foundation of China(No.51574123)the Scientific Research Project of Hunan Province Office of Education(No.18A185),which are gratefully acknowledged.
文摘Wall-mounted swirling ventilation is a new type of system in mechanized excavation faces with a dust sup-pression performance that is closely related to the blowing-to-suction flow ratio.Physical and simulation models were developed according to the No.C103 mechanized excavation face in the Nahe Coal Mine of the Baise Mining Bureau,Guangxi Province to optimize the blowing-to-suction flow ratio for wall-mounted swirling ventilation.Both the k-εturbulence model and the discrete phase model were utilized to simulate airflow field structures and dust concentration distribution patterns at various blowing-to-suction flow ratios.The results suggest that higher blowing-to-suction flow ratios increase the airflow field disturbance around the working face and weaken the intensity of the axial air curtain.On the other hand,both the intensity of the radial air curtain and the dust suppression effect are enhanced.At a blowing-to-suction flow ratio of 0.8,the wall-mounted swirling ventilation system achieved the most favorable dust suppression performance.Both the total dust and respirable dust had their lowest concentrations with maximum efficiencies of reducing both types at 90.33%and 87.16%,respectively.
基金supported by grants from National Key R&D Program of China (2016YFC1300304)
文摘Severe coronary stenosis concomitant with congenital coronary myocardial bridge(MB)is a tough scenario for cardiologist to perform revascularization,for which the complication rates including in-stent restenosis,stent fracture,stent thrombosis and even coronary perforation are still high.[1,2]Meanwhile,the necessity of revascularization in such patients is worth prudent evaluation.Cardiac imaging modalities are crucial and helpful in making revascularized decisions and strategies.Herein,we report a case using quantitative flow ratio(QFR)and intravascular ultrasound(IVUS)to facilitate accurate revascularization in a patient with both severe coronary stenosis and deep coronary MB.
基金supported by the Nanjing Municipal Science and Technology Bureau(No.201803008)the Cardiocare Sponsored Optimized Antithrombotic Research Fund(No.BJUHFCSOARF201801-13).
文摘Objective The study sought to investigate the clinical predictive value of quantitative flow ratio(QFR)for the long-term target vessel failure(TVF)outcome in patients with in-stent restenosis(ISR)by using drug-coated balloon(DCB)treatment after a long-term follow-up.Methods This was a retrospective study.A total of 186 patients who underwent DCB angioplasty for ISR in two hospitals from March 2014 to September 2019 were enrolled.The QFR of the entire target vessel was measured offline.The primary endpoint was TVF,including target vessel-cardiac death(TV-CD),target vessel-myocardial infarction(TV-MI),and clinically driven-target vessel revascularization(CD-TVR).Results The follow-up time was 3.09±1.53 years,and 50 patients had TVF.The QFR immediately after percutaneous coronary intervention(PCI)was significantly lower in the TVF group than in the no-TVF group.Multivariable Cox regression analysis indicated that the QFR immediately after PCI was an excellent predictor for TVF after the long-term follow-up[hazard ratio(HR):5.15×10−5(6.13×10−8−0.043);P<0.01].Receiver-operating characteristic(ROC)curve analysis demonstrated that the optimal cut-off value of the QFR immediately after PCI for predicting the long-term TVF was 0.925(area under the curve:0.886,95%confidence interval:0.834–0.938;sensitivity:83.40%,specificity:88.00;P<0.01).In addition,QFR≤0.925 post-PCI was strongly correlated with the TVF,including TV-MI and CD-TVR(P<0.01).Conclusion The QFR immediately after PCI showed a high predictive value of TVF after a long-term follow-up in ISR patients who underwent DCB angioplasty.A lower QFR immediately after PCI was associated with a worse TVF outcome.
基金supported by the Outstanding Young Talent Program of Guangdong Provincial People’s Hospital(grant number KJ012019084)the High-level Hospital Construction Project(grant number DFJH2020021).
文摘Objective:The goal of this study was to examine the prognostic performance of optical flow ratio(OFR)among patients with coronary artery disease(CAD)after percutaneous coronary intervention(PCI).Methods:We recruited patients with CAD undergoing optical coherence tomography(OCT)-directed PCI between January 2019 and June 2021 for our single-center,hospital-based,retrospective cohort investigation.We assessed the link between post-PCI OFR and major adverse cardiovascular events(MACE)via multivariate Cox regression analy-sis.Results:Receiver operating characteristic analysis revealed that the best post-PCI OFR threshold for MACE was 0.91,and introduction of OFR into the baseline profile and OCT results markedly enhanced MACE identification after PCI.On the basis of survival curves,patients with OFR≤0.91(P<0.001)and thin-cap fibroatheroma(TCFA)(P=0.007)exhibited higher MACE incidence,and myocardial infarction(MI)incidence was considerably greater among patients with OFR≤0.91(P<0.001),compared with OFR>0.91.Multivariate Cox regression analysis suggested that OFR≤0.91(hazard ratio[HR]:3.60;95%confidence interval[CI]:1.24–10.44;P=0.019),and TCFA(HR:3.63;95%CI:1.42–9.20;P=0.007)were independent risk factors for MACE,and OFR≤0.91 was independently associated with MI(HR:14.64;95%CI:3.27–65.54;P<0.001).Conclusion:OFR after PCI is an independent MACE bio-indicator among patients with CAD.Adding OFR to post-PCI OCT results may potentially enhance MACE prediction.
基金This study is supported by grants from the National High Level Hospital Clinical Research Funding(Nos.2022-GSP-GG-20 and 2023-GSP-GG-3)the Capital’s Funds for Health Improvement and Research(No.2022-2-4033)the Chinese Academy of Medical Sciences(No.2022-I2M-C&T-A-009).
文摘Background:The FAVOR(Comparison of Quantitative Flow Ratio Guided and Angiography Guided Percutaneous Intervention in Patients with Coronary Artery Disease)III China trial demonstrated that percutaneous coronary intervention(PCI)lesion selection using quantitative flow ratio(QFR)measurement,a novel angiography-based approach for estimating fractional flow reserve,improved two-year clinical outcomes compared with standard angiography guidance.This study aimed to assess the cost-effectiveness of QFR-guided PCI from the perspective of the current Chinese healthcare system.Methods:This study is a pre-specified analysis of the FAVOR III China trial,which included 3825 patients randomized between December 25,2018,and January 19,2020,from 26 centers in China.Patients with stable or unstable angina pectoris or those≥72 hours post-myocardial infarction who had at least one lesion with a diameter stenosis between 50%and 90%in a coronary artery with a≥2.5 mm reference vessel diameter by visual assessment were randomized to a QFR-guided strategy or an angiography-guided strategy with 1:1 ratio.During the two-year follow-up,data were collected on clinical outcomes,quality-adjusted life-years(QALYs),estimated costs of index procedure hospitalization,outpatient cardiovascular medication use,and rehospitalization due to major adverse cardiac and cerebrovascular events(MACCE).The primary analysis calculated the incremental cost-effectiveness ratio(ICER)as the cost per MACCE avoided.An ICER of¥10,000/MACCE event avoided was considered economically attractive in China.Results:At two years,the QFR-guided group demonstrated a reduced rate of MACCE compared to the angiography-guided group(10.8%vs.14.7%,P<0.01).Total two-year costs were similar between the groups(¥50,803±21,121 vs.¥50,685±23,495,P=0.87).The ICER for the QFR-guided strategy was¥3055 per MACCE avoided,and the probability of QFR being economically attractive was 64%at a willingness-to-pay threshold of¥10,000/MACCE avoided.Sensitivity analysis showed that QFR-guided PCI would become cost-saving if the cost of QFR were below¥3682(current cost:¥3800).Cost-utility analysis yielded an ICER of¥56,163 per QALY gained,with a 53%probability of being cost-effective at a willingness-to-pay threshold of¥85,000 per QALY gained.Conclusion:In patients undergoing PCI,a QFR-guided strategy appears economically attractive compared to angiographic guidance from the perspective of the Chinese healthcare system.
文摘Background:Drug-coated balloons(DCBs)have emerged as potential alternatives to drug-eluting stents in specific lesion subsets for de novo coronary lesions.Quantitative flow ratio(QFR)is a method based on the three-dimensional quantitative coronary angiography and contrast flow velocity during coronary angiography(CAG),obviating the need for an invasive fractional flow reserve procedural.This study aimed to assess the serial angiographic changes of de novo lesions post-DCB therapy and further explore the cut-off values of lesion and vessel QFR,which predict vessel restenosis(diameter stenosis[DS]≥50%)at mid-term follow-up.Methods:The data of patients who underwent DCB therapy between January 2014 and December 2019 from the multicenter hospital were retrospectively collected for QFR analysis.From their QFR performances,which were analyzed by CAG images at follow-up,we divided them into two groups:group A,showing target vessel DS≥50%,and group B,showing target vessel DS<50%.The median follow-up time was 287 days in group A and 227 days in group B.We compared the clinical characteristics,parameters during DCB therapy,and QFR performances,which were analyzed by CAG images between the two groups,in need to explore the cut-off value of lesion/vessel QFR which can predict vessel restenosis.Student's t test was used for the comparison of normally distributed continuous data,Mann-Whitney U test for the comparison of non-normally distributed continuous data,and receiver operating characteristic(ROC)curves for the evaluation of QFR performance which can predict vessel restenosis(DS≥50%)at mid-term follow-up using the area under the curve(AUC).Results:A total of 112 patients with 112 target vessels were enrolled in this study.Group A had 41 patients,while group B had 71.Vessel QFR and lesion QFR were lower in group A than in group B post-DCB therapy,and the cut-off values of lesion QFR and vessel QFR in the ROC analysis to predict target vessel DS≥50%post-DCB therapy were 0.905(AUC,0.741[95%confidence interval,CI:0.645,0.837];sensitivity,0.817;specificity,0.561;P<0.001)and 0.890(AUC,0.796[95%CI:0.709,0.882];sensitivity,0.746;specificity,0.780;P<0.001).Conclusions:The cut-off values of lesion QFR and vessel QFR can assist in predicting the angiographic changes post-DCB therapy.When lesion/vessel QFR values are<0.905/0.890 post-DCB therapy,a higher risk of vessel restenosis is potentially predicted at follow-up.
基金Projects(40772156, 41072179) supported by the National Natural Science Foundation of China
文摘An online method using continuous flow isotope ratio mass spectrometry （CF-IRMS） interfaced with a Gasbench Ⅱ was presented to determine chlorine stable isotope composition. Silver chloride （AgCl） was quantitatively derived from chloride by using silver nitrate （AgNO3）, and then was reacted with iodomethane （CH3Ⅰ） to produce methyl chloride （CH3Cl）. A GasBench Ⅱ equipped with a PoraPlot Q column was used to separate CH3Cl from any other gas species. Finally, chlorine stable isotope analysis was carried out on CH3Cl introduced to the IRMS in a helium stream via an active open split. The minimum amount of Cl used in this method is of the order of 1.4 μmol. Inter-laboratory and inter-technique comparisons show that the total uncertainty incorporating both the precision and accuracy of this method is better than 0.007%. Furthermore, ten seawaters sampled from different locations have a narrow δ37Cl value range from -0.008% to 0.010%, with a mean value of （0.000±0.006）%. This supports the assumption that any seawater can be representative of standard mean ocean chloride （SMOC） and used as an international reference material.
基金support from the National Natural Science Foundation of China(Grant Nos.51809261,11672318,and 51709052)financial support from the Theme-based Research Grant T22-603/15N+1 种基金the General Research Fund 16209717 provided by the Research Grants Council of the Government of Hong Kong SAR,Chinafinancial support by the Hong Kong Jockey Club Disaster Preparedness and Response Institute(HKJCDPRI18EG01)
文摘Conventionally,flexible barriers are rated based on their ability to resist a free-falling boulder with a particular input energy.However,there is still no well-accepted approach for evaluating performance of flexible barrier under debris flow impact.In this study,a large-nonlinear finite-element model was used to back-analyze centrifuge tests to discern the effects of impact material type,barrier stiffness,and flow aspect ratio(flow height to flow length)on the reaction force between the impacting medium and flexible barrier.Results show that,in contrast to flexible barriers for resisting rockfall,the normal impact force induced by the highly frictional and viscous debris is insensitive to barrier stiffness.This is because the elongated distributions of kinetic energy are mainly dissipated by the internal and boundary shearing,and only a small portion is forwarded to the barrier.Furthermore,a new stiffness number is proposed to characterize the equivalent stiffness between a debris flow or a boulder,and a flexible barrier.Under the circumstance of an extremely elongated debris flow event,i.e.,low aspect ratio,the load on a barrier is dominated by the static component and thus not sensitive to the barrier stiffness.
基金supported by the National Natural Science Foundation of China (Grant No.40671026)
文摘According to the observational data of viscous debris flows with hyper-concentration, debris flows can be classified into three types:high-viscous, viscous, and sub-viscous debris flows.Distinct formation mechanism of different graded bedding structures in deposits of viscous debris flows was analyzed in this paper by using their yield-stress ratio and flow plug ratio.This paper specially analyzed the effect of Weissenberg which the gravels in squirm condition of hyper-concentration viscous flows would tend to move vertically, and the formation mechanism of the gravels accumulated at surface was also studied.The analysis in this paper can establish a foundation for the studies on differentiation of bedding structures of debris flow deposits and studies on dynamic parameters of debris flows.
基金supported by the National Natural Science Foundation of China (Grants Nos. 40376013, 40572128, and 40104003)
文摘Based on conservation of energy principle and heat flow data in China continent, the upper limit of 1.3 μW/m3 heat production is obtained for continental crust in China. Furthermore, using the data of heat flow and helium isotope ratio of underground fluid, the heat productions of different tectonic units in China continent are estimated in range of 0.58-1.12 μW/m3 with a median of 0.85 μW/m3. Accordingly, the contents of U, Th and K20 in China crust are in ranges of 0.83-1.76 μg/g, 3.16-6.69 μg/g, and 1.0%-2.12%, respectively. These results indicate that the abundance of radioactive elements in the crust of China continent is much higher than that of Archean crust; and this fact implies China＇s continental crust is much evolved in chemical composition. Meanwhile, significant lateral variation of crustal composition is also exhibited among different tectonic units in China continent. The crust of eastern China is much enriched in incompatible elements such as U, Th and K than that of western China; and the crust of orogenic belts is more enriched than that of platform regions. It can also be inferred that the crusts of eastern China and orogenic belts are much felsic than those of western China and platform regions, respectively, derived from the positive correlation between the heat production and SiO2 content of bulk crust. This deduction is consistent with the results derived from the crustal seismic velocity data in China. According to the facts of the lower seismic velocity of China than the average value of global crust, and the higher heat production of China continent compared with global crust composition models published by previous studies, it is deduced that the average composition models of global continent crust by Rudnick and Fountain （1995）, Rudnick and Gao （2003）, Weaver and Tarney （1984）, Shaw et al. （1986）, and Wedepohl （1995） overestimate the abundance of incompatible elements such as U, Th and K of continental crust.
基金supported by the National Natural Science Foundation of China(No.11405025)
文摘The neutron-to-proton and3 H-to-3 He yield ratios, and the directed flows of particles dependent on a reduced rapidity, the transverse momentum per nucleon,and a reduced impact parameter are investigated for ^(28)S+^(28)Si and ^(32)S+^(28)Si systems at 50 and 400 MeV/u using an isospin-dependent quantum molecular dynamics model.The results show that these yield ratios of projectile-like fragments are approximately equal to the constituent neutron-to-proton ratio of the projectile. There are clear differences of the directed flows for isospin-related fragments neutron and proton,~3H and ~3He from ^(28)S+^(28)Si collisions.The differences in directed flows for neutrons and protons and ~3H–~3He from a proton-rich nucleus ^(28)S- induced collisions are noticeably larger than those from a stable nucleus ^(32)S- induced reactions under medium impact parameters. Thus, the yield ratios and differences in directed flows for the neutrons and protons and ~3H–~3He under medium impact parameters are proposed as possible observable items for studying isospin physics.
基金Key Laboratory Foundation (9140C4103091003C) for funding this work
文摘In modern gas turbines, rim seal located between the stator-disc and rotor-disc is used to prevent hot-gas ingestion into the inner stage-gap of high pressure turbine. However, the purge flow supplied to the cavity through the rim seal interacts with the main flow, producing additional aerodynamic loss due to the mixing process which plays a significant role in the formation, development and evolution of downstream secondary flow. In this paper, a set of cascade representative of low aspect ratio turbine is selected to numerically investigate the influence of upstream cavity purge flow on the hub secondary flow structure and aerodynamic loss. Cascade with/without upstream cavity and four different purge mass flow rates are all taken into account in this simulation. Then, a deep insight into the loss mechanism of interaction between purge flow and main flow is gained. The results show that the presence of cavity and purge flow has a significant impact on the main flow which not only changes the vortex structure in both the passage and upstream cavity, but also alters the cascade exit flow angle distribution along the spanwise. Moreover, aerodynamic loss in the cascade rises with the increase of purge flow rate while the sealing effect is also enhanced. Therefore, the effect of upstream cavity purge flow must be considered in the process of turbine aerodynamic design. What is more, it is necessary to minimize the purge flow rate in order to reduce aerodynamic loss on the premise of satisfying cooling requirements.
基金supported by the National Natural Science Foundation of China (No. 51177138)the Research Fund for the Doctoral Program of High Education of China (No.20100184110015)Sichuan Province International Technology Cooperation and Exchange Program (No. 2012HH0007)
文摘Air flow control is one of the most important control methods for maintaining the stability and reliability of a fuel cell system, which can avoid oxygen starvation or oxygen saturation. The oxygen excess ratio （OER） is often used to indicate the air flow condition. Based on a fuel cell system model for vehicles, OER performance was analyzed for different stack currents and temperatures in this paper, and the results show that the optimal OER was affected weakly by the stack temperature. In order to ensure the system working in optimal OER, a control scheme that includes an optimal OER regulator and a fuzzy control was proposed. According to the stack current, a reference value of air flow rate was obtained with the optimal OER regulator and then the air compressor motor voltage was controlled with the fuzzy controller to adjust the air flow rate provided by the air compressor. Simulation results show that the control method has good dynamic and static characteristics.
文摘Rotating flows represent a very interesting area for researchers and industry for their extensive use in industrial and domestic machinery and especially for their great energy potential, annular flows are an example that draws the attention of researchers in recent years. The best design and optimization of these devices require knowledge of thermal, mechanical and hydrodynamic characteristics of flows circulating in these devices. An example of hydrodynamic parameters is the speed of rotation of the moving walls. This work is to study numerically the influence of the rotating speed ratio Γ of the two moving cylinders on the mean and especially on the turbulent quantities of the turbulent flow in the annular space. The numerical simulation is based on one-point statistical modeling using a low Reynolds number second-order full stress transport closure (RSM model), simulation code is not a black box but a completely transparent code where we can intervene at any step of the calculation. We have varied Γ from -1.0 to 1.0 while maintaining always the external cylinder with same speed Ω. The results show that the turbulence structure, profiles of mean velocities and the nature of the boundary layers of the mobile walls depend enormously on the ratio of speeds. The level of turbulence measured by the kinetic energy of turbulence and the Reynolds stresses shows well that the ratio Γ is an interesting parameter to exploit turbulence in this kind of annular flows.
文摘A depth_integrated two_dimensional numerical model of current, salinity and sediment transport was proposed and calibrated by the observation data in the Yangtze River Estuary. It was then applied to investigate the flow and sediment ratio of the navigation channel, i.e. the North Channel of the Yangtze River Estuary,before and after the first phase waterway project is implemented. Particularly, the influences of groin length and the orientation of the submerged dam on the flow ratio and sediment load discharging into the North Channel were discussed. The numerical results demonstrate that less sediment load discharges into the navigation channel, which unburdens the waterway dredging, but in the meantime the flow ratio is also decreased. The flow and sediment ratio can be adjusted by changing layout and dimensions of the hydro_structures, such as the groin length, the top height, etc. The effect of the orientation of the submerged dam is more obvious than the groin lengh.
文摘The effects of the aspect ratio on unsteady solutions through the curved duct flow are studied numerically by a spectral based computational procedure with a temperature gradient between the vertical sidewalls for the Grashof number 100 ≤ Gr ≤ 2 000. The outer wall of the duct is heated while the inner wall is cooled and the top and bottom walls are adiabatic. In this paper, unsteady solutions are calculated by the time history analysis of the Nusselt number for the Dean numbers Dn = 100 and Dn = 500 and the aspect ratios 1≤γ≤ 3. Water is taken as a working fluid （Pr =7.0）. It is found that at Dn = 100, there appears a steady-state solution for small or large Gr. For moderate Gr, however, the steady-state solution turns into the periodic solution if γ is increased. For Dn = 500, on the other hand, it is analyzed that the steady-state solution turns into the chaotic solution for small and large Gr for any γ lying in the range. For moderate Gr at Dn = 500, however, the steady-state flow turns into the chaotic flow through the periodic oscillating flow if the aspect ratio is increased.
基金Projects(51505050,51805063) supported by the National Natural Science Foundation of China for Young ScholarsProjects(KJ1500942,KJQN201801134) supported by the Scientific and Technological Research Program of Chongqing Education Commission of ChinaProjects(cstc2017jcyjAX0075,cstc2015jcyj A50033) supported by the Chongqing Research Program of Basic Research and Frontier Technology,China
文摘Hydrogenated microcrystalline silicon(μc-Si:H)films were prepared on glass and silicon substrates by radio frequency magnetron sputtering at 100°C using a mixture of argon(Ar)and hydrogen(H2)gasses as precursor gas.The effects of the ratio of hydrogen flow(H2/(Ar+H2)%)on the microstructure were evaluated.Results show that the microstructure,bonding structure,and surface morphology of theμc-Si:H films can be tailored based on the ratio of hydrogen flow.An amorphous to crystalline phase transition occurred when the ratio of hydrogen flow increased up to 50%.The crystallinity increased and tended to stabilize with the increase in ratio of hydrogen flow from 40%to 70%.The surface roughness of thin films increased,and total hydrogen content decreased as the ratio of hydrogen flow increased.Allμc-Si:H films have a preferred(111)orientation,independent of the ratio of hydrogen flow.And theμc-Si:H films had a dense structure,which shows their excellent resistance to post-oxidation.
