The circumferentially averaged equation of the inlet flow radial equilibrium in axial compressor was deduced. It indicates that the blade inlet radial pressure gradient is closely related to the radial component of th...The circumferentially averaged equation of the inlet flow radial equilibrium in axial compressor was deduced. It indicates that the blade inlet radial pressure gradient is closely related to the radial component of the circumferential fluctuation（CF） source item. Several simplified cascades with/without aerodynamic loading were numerically studied to investigate the effects of blade bowing on the inlet flow radial equilibrium. A data reduction program was conducted to obtain the CF source from three-dimensional（3D） simulation results. Flow parameters at the passage inlet were focused on and each term in the radial equilibrium equation was discussed quantitatively. Results indicate that the inviscid blade force is the inducement of the inlet CF due to geometrical asymmetry. Blade bowing induces variation of the inlet CF, thus changes the radial pressure gradient and leads to flow migration before leading edge（LE） in the cascades. Positive bowing drives the inlet flow to migrate from end walls to mid-span and negative bowing turns it to the reverse direction to build a new equilibrium. In addition, comparative studies indicate that the inlet Mach number and blade loading can efficiently impact the effectiveness of blade bowing on radial equilibrium in compressor design.展开更多
In this work, the wafer bowing during growth can be in-situ measured by a reflectivity mapping method in the 3×2 Thomas Swan close coupled showerhead metal organic chemical vapor deposition（MOCVD） system. The r...In this work, the wafer bowing during growth can be in-situ measured by a reflectivity mapping method in the 3×2 Thomas Swan close coupled showerhead metal organic chemical vapor deposition（MOCVD） system. The reflectivity mapping method is usually used to measure the film thickness and growth rate. The wafer bowing caused by stresses（tensile and compressive） during the epitaxial growth leads to a temperature variation at different positions on the wafer, and the lower growth temperature leads to a faster growth rate and vice versa. Therefore, the wafer bowing can be measured by analyzing the discrepancy of growth rates at different positions on the wafer. Furthermore, the wafer bowings were confirmed by the ex-situ wafer bowing measurement. High-resistivity and low-resistivity Si substrates were used for epitaxial growth. In comparison with low-resistivity Si substrate, Ga N grown on high-resistivity substrate shows a larger wafer bowing caused by the highly compressive stress introduced by compositionally graded Al Ga N buffer layer. This transition of wafer bowing can be clearly in-situ measured by using the reflectivity mapping method.展开更多
The full potential linear muffin-tin orbital (FP-LMTO) method was applied to study the structural and electronic properties of the compounds MgO, ZnO and their alloy MgxZn1–xO in the zincblende and NaCl structures. R...The full potential linear muffin-tin orbital (FP-LMTO) method was applied to study the structural and electronic properties of the compounds MgO, ZnO and their alloy MgxZn1–xO in the zincblende and NaCl structures. Results are obtained using the local density approximation (LDA), the ground-state properties like lattice constant and bulk modulus obtained agree very well with experimental and other theoretical calculations. The effect of composition on lattice constant from Vegard’s law and the bulk modulus was investigated. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers. It is concluded that the energy band gap bowing is primarily due to chemical charge-transfer effect. Contribution of volume deformation and structural relaxation to the gap bowing parameter is found to be very small.展开更多
On the basis of first principles calculations using density functional theory, we explore the structural and electronic properties of two binaries: CaO and MgO in rock salt structures. Structural properties of the sem...On the basis of first principles calculations using density functional theory, we explore the structural and electronic properties of two binaries: CaO and MgO in rock salt structures. Structural properties of the semiconductor CaχMg1-χO alloys are derived from total-energy minimization within the General Gradient Approximation. The band gap bowing parameters dependence is very powerful Calcium composition. The results offer that an average bowing parameter of CaχMg1-χO alloys is b = ~0.583$ eV. We analyzed the volume deformation, charge transfer and structural relaxation effects of the CaχMg1-χO alloys.展开更多
The effects of blade bowing on the performance of a high pressure-ratio turbocharger centrifugal compressor were studied by experiments and numerical simulation.The results showed that the negative bowing was capable ...The effects of blade bowing on the performance of a high pressure-ratio turbocharger centrifugal compressor were studied by experiments and numerical simulation.The results showed that the negative bowing was capable of increasing the choke mass rate and the efficiency but decreased the surge mass flow rate,while the positive bowing had the opposite effects.When coupling with the self-recirculation casing treatment,the surge mass flow rate of the compressor with negative bowing blade was almost identical with that of the prototype,while the choke mass flow rate was still larger,and the total effect contributed to an increase of the stable flow range by 5.85%at design speed.Besides,the flow mechanism of the coupling effects of blade bowing and self-recirculation casing treatment was discussed.展开更多
Background For some high myopic patients with posterior iris bowing, laser periphery iridectomy should be performed pre-operation to prevent pupil block glaucoma if these patients would have phakic intraocular lens im...Background For some high myopic patients with posterior iris bowing, laser periphery iridectomy should be performed pre-operation to prevent pupil block glaucoma if these patients would have phakic intraocular lens implantation to correct high myopia. So we had the opportunity to analysis the influence of laser iridectomy on posterior iris bowing. Methods Eighteen high myopic patients with posterior iris bowing （11 males and 7 females） were involved in the study in Beijing Tongren Eye Center from March 2008 to July 2008. Phakic intraocular lens were implanted to correct their ametropia. The mean age was （32＋6） years （range, 25-40 years）. The center anterior chamber depth, the pupil diameter, the posterior iris bowing depth and the anterior chamber angle were measured with anterior segment coherence tomography （AS-OCT） under the normal condition, myosis condition induced by 2% pilocarpine, laser periphery iridectomy after myosis, and 2% pilocarpine eluting condition respectively. Results There was no significant difference of center anterior chamber depth under the four conditions （P=0.512）. The pupil constricted after pilocarpine （P=0.001）. After＇ laser iridectomy performed and pilocarpine eluted, posterior iris bowing depth reduced more than that in normal condition （P=0.003）. The anterior chamber angle reduced significantly after laser periphery iridectomy and pilocarpine eluted （P=0.012）. Conclusion Laser periphery iridectomy can reduce the posterior iris bowing, which might be due to the change in aqueous circulate pathway.展开更多
The electronic band structures and band gap bowing parameters of In_xGa_（1-x）N are studied by the firstprinciples method based on the density functional theory. Calculations by employing both the Heyd-ScuseriaErnzer...The electronic band structures and band gap bowing parameters of In_xGa_（1-x）N are studied by the firstprinciples method based on the density functional theory. Calculations by employing both the Heyd-ScuseriaErnzerh of hybrid functional（HSE06） and the Perdew-Burke-Ernzerhof（PBE） one are performed. We found that the theoretical band gap bowing parameter is dependent significantly on the calculation method, especially on the exchange-correlation functional employed in the DFT calculations. The band gap of In_xGa_（1-x）N alloy decreases considerably when the In constituent x increases. It is the interactions of s–s and p–p orbitals between anions and cations that play significant roles in formatting the band gaps bowing. In general, the HSE06 hybrid functional could provide a good alternative to the PBE functional in calculating the band gap bowing parameters.展开更多
The strong crustal magnetic fields significantly alter the structure of the Martian space environment,including all plasma boundaries.The stretches of mini-magnetospheres formed by crustal fields from the location of ...The strong crustal magnetic fields significantly alter the structure of the Martian space environment,including all plasma boundaries.The stretches of mini-magnetospheres formed by crustal fields from the location of the Martian bow shocks were first found from the Mars Atmosphere and Volatile EvolutioN(MAVEN)observations.The present study aims to test whether this effect is also present in the shocks observed by Mars Express(MEX).We find that the bow shocks above the crustal field regions are enlarged,resulting in a north−south asymmetry and a longitude dependence in the shock size.The longitude dependence is more pronounced for near-subsolar shocks,and more dispersed for near-terminator shocks.The enlarged shocks are also observed to have shifted tailward from the longitudes of the strongest crustal fields.Due to a dawnside bias in MEX shock crossings,the enlarged shocks generally display a westward shift from the strongest crustal field region.These results confirm that stretches of the mini-magnetosphere are also present in the MEX shock observations.展开更多
Observational analyses and convection-permitting simulations are conducted to study an extreme event of damaging surface winds within a bow-shaped squall line over South China.Prevailing explanations for the formation...Observational analyses and convection-permitting simulations are conducted to study an extreme event of damaging surface winds within a bow-shaped squall line over South China.Prevailing explanations for the formation of damaging surface winds were applied to investigate the detailed processes at the mature stage of a squall line in a complicated real-world scenario.It is shown that environmental vertical wind shear was adequately strong to cause a shearing vorticity,and the shearing vorticity was comparable to the baroclinic vorticity by a cold pool.The balance led to strong upward motions at the leading edge of the squall line and brought plenty of rainfall.The descending rainfall cooled the surrounding air and entrained the upper-level cold air downward to the lower level,strengthening the cold pool by excessive evaporation and melting.The cold pool accelerated the propagation speed of the squall line and caused extensive wind damage at the surface.Meanwhile,the horizontal vortex lines at the leading edge of the cold pool were lifted by frontal updrafts and tilted to form the anti-cyclonic vortex at the middle level.This maintained and intensified the rearinflow jet behind the apex of bow echo in association with a notable midlevel pressure gradient.The rear-inflow jet was then transported downward to the surface by descending condensate,leading to damaging winds there.Other factors,such as environmental flows,however,contributed less to the damaging surface winds.展开更多
Wave breaking at the bow of a high-speed ship is of great importance to the hydrodynamic performance of high-speed ships,accompanied by complex flow field deformation.In this study,the smoothed particle hydrodynamics(...Wave breaking at the bow of a high-speed ship is of great importance to the hydrodynamic performance of high-speed ships,accompanied by complex flow field deformation.In this study,the smoothed particle hydrodynamics(SPH)method under the Lagrange framework is adopted to simulate the breaking bow wave of the KCS ship model.In order to improve the computational efficiency,the inflow and outflow boundary model is used to establish a numerical tank of current,and a numerical treatment for free surface separation is implemented.Numerical simulations are carried out at Fr=0.35,0.40,0.5,0.6,and different types of wave breaking such as spilling breaker,plunging breaker,and scars are captured by the SPH method,which is consistent with the experimental result,demonstrating that the present SPH method can be robust and reliable in accurately predicting the breaking bow wave phenomenon of high-speed ships.Furthermore,the wave elevation and velocity field in the bow wave region are analyzed,and the evolution of the bow wave breaking is provided.展开更多
Unusual head trauma is rare with various mechanisms of occurrence. The injuries can be similar to those of road accidents but sometimes with significant complexities. The objective was to determine the frequency of th...Unusual head trauma is rare with various mechanisms of occurrence. The injuries can be similar to those of road accidents but sometimes with significant complexities. The objective was to determine the frequency of this pathology in our practice, describe the different mechanisms and report the craniocerebral lesions caused by this type of trauma. Materials and Method: This was a descriptive study with retrospective collection spread over a period of 3 years. After selecting the files, the patients and/or their companions were contacted by telephone to inquire about them and then returned to the consultation for reassessment. Disease history and information were obtained from patients’ medical records. Result: The frequency of this pathology was 1.78% and his incidence was 0.4 cases per month. The average age of the patients was 13.47 years. All the victims were male. 41.17% of patients were in school. The mechanisms of trauma were the hoof blow 47.1%, the horn blow 29.4% and the stone blow 11.7% respectively. 23.5% of patients were confused and 11.7% children were in coma. One patient presented an anisocoria. The motor deficit was present in 5 cases. CT-scan made it possible to highlight a skull depressing fracture 58.8% and confirm a craniocerebral wound in 35.3%. The average time between patient admission to hospital and completion of surgery was 24.5 hours. The surgery had consisted of the trimming of cranio-cerebral wounds, exploration, duroplasty and lifting of skull depressing fracture. After 15 months of follow-up, the evolution was favorable in 53.3%, the morbidity was 33.4% and the mortality 17.6%. Conclusion: These are rare but serious conditions because they are fatal and disabling. An early and multidisciplinary management can hope to have a good favorable.展开更多
Based on previously released data,this paper first presented the criteria for recognizing bow echoes and divided their life cycle into three stages:the development stage,the mature stage,and the attenuation stage.Base...Based on previously released data,this paper first presented the criteria for recognizing bow echoes and divided their life cycle into three stages:the development stage,the mature stage,and the attenuation stage.Based on Doppler weather radar data during 2011-2020,43 bow echo events(including 54 individual bow echoes)in western South China were identified.The spatial and temporal distributions,formation and dissipation modes of these bow echoes,and the severe weather they caused were statistically analyzed.The results show that:(1)The bow echo events were unevenly distributed year-to-year,but all occurred from March to July,with the highest in April and May and the lowest in July.The period from night to early morning was found to be the main period for bow echo generation and intensification.(2)A banded area from Hechi City on the southeastern edge of the Yunnan-Guizhou Plateau to Wuzhou City in southeast Guangxi was identified as a high-incidence area of bow echoes.The length of bow echoes was correlated with their life cycle.(3)The origins of the bow echoes could be divided into five locations,most of which were in the eastern Yunnan-Guizhou Plateau.After entering western South China,their moving paths were categorized into three types,among which most bow echoes moved southeastward,generally because of the effect of cold air.Specifically,bow echoes generally moved eastward when cold air was weak or in the warm zone.Meanwhile,the fewest bow echoes moved northeastward.(4)Four modes of bow echo formation were identified:linearly organized,broken areal,linearly merging,and broken line.Dissipation could also be classified into four types.(5)The probability of convective weather generated by a bow echo was largest in the mature stage.展开更多
The outlet flow fields of a low-speed repeating-stage compressor with bowed stator stages are measured with five-hole probe under the near stall condition when the rotor/stator axial gap varies. The performances of th...The outlet flow fields of a low-speed repeating-stage compressor with bowed stator stages are measured with five-hole probe under the near stall condition when the rotor/stator axial gap varies. The performances of the straight stator stages are investigated and compared to those of the bowed stator stages. The results show that using bowed stator stages could alleviate the flow separation at both upper and low corners of the suction surface and the endwalls, and decrease the losses along the flow passage as well as the outlet flow angle. As the rotor/stator axial gap decreases, although the diffusion capacity of the compressor increases obviously, the outlet flow field in the straight stator stages deteriorates quickly. By contrast, little changes occur in the bowed stator stages, indicating that as the rotor/stator axial gap decreases, improved performance is achieved in the bowed stator stages.展开更多
图像检索的Bag of Words体系存在量化后的视觉词影响局部特征的辨别能力并且缺乏特征之间空间关系的缺点,影响检索效率。针对复杂背景的目标查询,提出了融合显著性信息的图像检索方法和基于显著特征点空间距离比的后验证方法。首先,提...图像检索的Bag of Words体系存在量化后的视觉词影响局部特征的辨别能力并且缺乏特征之间空间关系的缺点,影响检索效率。针对复杂背景的目标查询,提出了融合显著性信息的图像检索方法和基于显著特征点空间距离比的后验证方法。首先,提取图像显著目标区域,使用空间金字塔模型进行图像检索。然后,利用查询图像与检索图像匹配的显著特征对,计算任意两对显著特征点的距离比,保留满足阈值的比值,并求和,用以重新排序结果图像,得到最终的检索结果。实验结果表明:该方法显著提高了检索的精确度,并减少了几何验证过程的运算时间。展开更多
基金supported by the National Natural Science Foundation of China (Nos.51236001,51006005)the National Basic Research Program of China (No. 2012CB720201)Beijing Natural Science Foundation (No. 3151002)
文摘The circumferentially averaged equation of the inlet flow radial equilibrium in axial compressor was deduced. It indicates that the blade inlet radial pressure gradient is closely related to the radial component of the circumferential fluctuation（CF） source item. Several simplified cascades with/without aerodynamic loading were numerically studied to investigate the effects of blade bowing on the inlet flow radial equilibrium. A data reduction program was conducted to obtain the CF source from three-dimensional（3D） simulation results. Flow parameters at the passage inlet were focused on and each term in the radial equilibrium equation was discussed quantitatively. Results indicate that the inviscid blade force is the inducement of the inlet CF due to geometrical asymmetry. Blade bowing induces variation of the inlet CF, thus changes the radial pressure gradient and leads to flow migration before leading edge（LE） in the cascades. Positive bowing drives the inlet flow to migrate from end walls to mid-span and negative bowing turns it to the reverse direction to build a new equilibrium. In addition, comparative studies indicate that the inlet Mach number and blade loading can efficiently impact the effectiveness of blade bowing on radial equilibrium in compressor design.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61274039 and 51177175)the National Basic Research Program of China(Grant No.2011CB301903)+5 种基金the Ph.D.Programs Foundation of Ministry of Education of China(Grant No.20110171110021)the International Science and Technology Collaboration Program of China(Grant No.2012DFG52260)the International Science and Technology Collaboration Program of Guangdong Province,China(Grant No.2013B051000041)the Science and Technology Plan of Guangdong Province,China(Grant No.2013B010401013)the National High Technology Research and Development Program of China(Grant No.2014AA032606)the Opened Fund of the State Key Laboratory on Integrated Optoelectronics,China(Grant No.IOSKL2014KF17)
文摘In this work, the wafer bowing during growth can be in-situ measured by a reflectivity mapping method in the 3×2 Thomas Swan close coupled showerhead metal organic chemical vapor deposition（MOCVD） system. The reflectivity mapping method is usually used to measure the film thickness and growth rate. The wafer bowing caused by stresses（tensile and compressive） during the epitaxial growth leads to a temperature variation at different positions on the wafer, and the lower growth temperature leads to a faster growth rate and vice versa. Therefore, the wafer bowing can be measured by analyzing the discrepancy of growth rates at different positions on the wafer. Furthermore, the wafer bowings were confirmed by the ex-situ wafer bowing measurement. High-resistivity and low-resistivity Si substrates were used for epitaxial growth. In comparison with low-resistivity Si substrate, Ga N grown on high-resistivity substrate shows a larger wafer bowing caused by the highly compressive stress introduced by compositionally graded Al Ga N buffer layer. This transition of wafer bowing can be clearly in-situ measured by using the reflectivity mapping method.
文摘The full potential linear muffin-tin orbital (FP-LMTO) method was applied to study the structural and electronic properties of the compounds MgO, ZnO and their alloy MgxZn1–xO in the zincblende and NaCl structures. Results are obtained using the local density approximation (LDA), the ground-state properties like lattice constant and bulk modulus obtained agree very well with experimental and other theoretical calculations. The effect of composition on lattice constant from Vegard’s law and the bulk modulus was investigated. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers. It is concluded that the energy band gap bowing is primarily due to chemical charge-transfer effect. Contribution of volume deformation and structural relaxation to the gap bowing parameter is found to be very small.
文摘On the basis of first principles calculations using density functional theory, we explore the structural and electronic properties of two binaries: CaO and MgO in rock salt structures. Structural properties of the semiconductor CaχMg1-χO alloys are derived from total-energy minimization within the General Gradient Approximation. The band gap bowing parameters dependence is very powerful Calcium composition. The results offer that an average bowing parameter of CaχMg1-χO alloys is b = ~0.583$ eV. We analyzed the volume deformation, charge transfer and structural relaxation effects of the CaχMg1-χO alloys.
基金supported by the National Natural Science Foundation of China(Grant No.51176087)
文摘The effects of blade bowing on the performance of a high pressure-ratio turbocharger centrifugal compressor were studied by experiments and numerical simulation.The results showed that the negative bowing was capable of increasing the choke mass rate and the efficiency but decreased the surge mass flow rate,while the positive bowing had the opposite effects.When coupling with the self-recirculation casing treatment,the surge mass flow rate of the compressor with negative bowing blade was almost identical with that of the prototype,while the choke mass flow rate was still larger,and the total effect contributed to an increase of the stable flow range by 5.85%at design speed.Besides,the flow mechanism of the coupling effects of blade bowing and self-recirculation casing treatment was discussed.
文摘Background For some high myopic patients with posterior iris bowing, laser periphery iridectomy should be performed pre-operation to prevent pupil block glaucoma if these patients would have phakic intraocular lens implantation to correct high myopia. So we had the opportunity to analysis the influence of laser iridectomy on posterior iris bowing. Methods Eighteen high myopic patients with posterior iris bowing （11 males and 7 females） were involved in the study in Beijing Tongren Eye Center from March 2008 to July 2008. Phakic intraocular lens were implanted to correct their ametropia. The mean age was （32＋6） years （range, 25-40 years）. The center anterior chamber depth, the pupil diameter, the posterior iris bowing depth and the anterior chamber angle were measured with anterior segment coherence tomography （AS-OCT） under the normal condition, myosis condition induced by 2% pilocarpine, laser periphery iridectomy after myosis, and 2% pilocarpine eluting condition respectively. Results There was no significant difference of center anterior chamber depth under the four conditions （P=0.512）. The pupil constricted after pilocarpine （P=0.001）. After＇ laser iridectomy performed and pilocarpine eluted, posterior iris bowing depth reduced more than that in normal condition （P=0.003）. The anterior chamber angle reduced significantly after laser periphery iridectomy and pilocarpine eluted （P=0.012）. Conclusion Laser periphery iridectomy can reduce the posterior iris bowing, which might be due to the change in aqueous circulate pathway.
基金Project supported by the National Natural Science Foundation of China(Nos.11204257,21233004)the China Postdoctoral Science Foundation(No.2012M511447)
文摘The electronic band structures and band gap bowing parameters of In_xGa_（1-x）N are studied by the firstprinciples method based on the density functional theory. Calculations by employing both the Heyd-ScuseriaErnzerh of hybrid functional（HSE06） and the Perdew-Burke-Ernzerhof（PBE） one are performed. We found that the theoretical band gap bowing parameter is dependent significantly on the calculation method, especially on the exchange-correlation functional employed in the DFT calculations. The band gap of In_xGa_（1-x）N alloy decreases considerably when the In constituent x increases. It is the interactions of s–s and p–p orbitals between anions and cations that play significant roles in formatting the band gaps bowing. In general, the HSE06 hybrid functional could provide a good alternative to the PBE functional in calculating the band gap bowing parameters.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFF0503204)the National Natural Science Foundation of China(Grant No.42388101)+3 种基金Youth Innovation Promotion Association CAS(2020065)Young Elite Scientist Sponsorship Program by CAST(YESS20200152)the Key Research Program of the Institute of Geology&Geophysics,CAS(IGGCAS-202102)the Key Research Program of Chinese Academy of Sciences(Grant ZDB-SSW-TLC00103).
文摘The strong crustal magnetic fields significantly alter the structure of the Martian space environment,including all plasma boundaries.The stretches of mini-magnetospheres formed by crustal fields from the location of the Martian bow shocks were first found from the Mars Atmosphere and Volatile EvolutioN(MAVEN)observations.The present study aims to test whether this effect is also present in the shocks observed by Mars Express(MEX).We find that the bow shocks above the crustal field regions are enlarged,resulting in a north−south asymmetry and a longitude dependence in the shock size.The longitude dependence is more pronounced for near-subsolar shocks,and more dispersed for near-terminator shocks.The enlarged shocks are also observed to have shifted tailward from the longitudes of the strongest crustal fields.Due to a dawnside bias in MEX shock crossings,the enlarged shocks generally display a westward shift from the strongest crustal field region.These results confirm that stretches of the mini-magnetosphere are also present in the MEX shock observations.
基金Research(2020B0301030004)National Natural Science Foundation of China(42275002)+3 种基金Natural Science Foundation of Chongqing(CSTB2022NSCQ-MSX0890)Scientific and Technological Project of Chongqing Meteorological Service(YWJSGG-202124)Key Innovation Team of China Meteorological Administration(CMA2022ZD09)Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(SML2023SP209)。
文摘Observational analyses and convection-permitting simulations are conducted to study an extreme event of damaging surface winds within a bow-shaped squall line over South China.Prevailing explanations for the formation of damaging surface winds were applied to investigate the detailed processes at the mature stage of a squall line in a complicated real-world scenario.It is shown that environmental vertical wind shear was adequately strong to cause a shearing vorticity,and the shearing vorticity was comparable to the baroclinic vorticity by a cold pool.The balance led to strong upward motions at the leading edge of the squall line and brought plenty of rainfall.The descending rainfall cooled the surrounding air and entrained the upper-level cold air downward to the lower level,strengthening the cold pool by excessive evaporation and melting.The cold pool accelerated the propagation speed of the squall line and caused extensive wind damage at the surface.Meanwhile,the horizontal vortex lines at the leading edge of the cold pool were lifted by frontal updrafts and tilted to form the anti-cyclonic vortex at the middle level.This maintained and intensified the rearinflow jet behind the apex of bow echo in association with a notable midlevel pressure gradient.The rear-inflow jet was then transported downward to the surface by descending condensate,leading to damaging winds there.Other factors,such as environmental flows,however,contributed less to the damaging surface winds.
基金The Guangdong Basic and Applied Basic Research Foundation(2024B1515020107)the National Natural Science Foundation of China(Grant Nos.52171329)+1 种基金the State Key Laboratory of Disaster Prevention&Mitigation of Explosion&Impact(Grant No.NOLGD-SKL-202201)the Fundamental Research Funds for the Central Universities,Sun Yat-sen University(Grant No.231gbi023).
文摘Wave breaking at the bow of a high-speed ship is of great importance to the hydrodynamic performance of high-speed ships,accompanied by complex flow field deformation.In this study,the smoothed particle hydrodynamics(SPH)method under the Lagrange framework is adopted to simulate the breaking bow wave of the KCS ship model.In order to improve the computational efficiency,the inflow and outflow boundary model is used to establish a numerical tank of current,and a numerical treatment for free surface separation is implemented.Numerical simulations are carried out at Fr=0.35,0.40,0.5,0.6,and different types of wave breaking such as spilling breaker,plunging breaker,and scars are captured by the SPH method,which is consistent with the experimental result,demonstrating that the present SPH method can be robust and reliable in accurately predicting the breaking bow wave phenomenon of high-speed ships.Furthermore,the wave elevation and velocity field in the bow wave region are analyzed,and the evolution of the bow wave breaking is provided.
文摘Unusual head trauma is rare with various mechanisms of occurrence. The injuries can be similar to those of road accidents but sometimes with significant complexities. The objective was to determine the frequency of this pathology in our practice, describe the different mechanisms and report the craniocerebral lesions caused by this type of trauma. Materials and Method: This was a descriptive study with retrospective collection spread over a period of 3 years. After selecting the files, the patients and/or their companions were contacted by telephone to inquire about them and then returned to the consultation for reassessment. Disease history and information were obtained from patients’ medical records. Result: The frequency of this pathology was 1.78% and his incidence was 0.4 cases per month. The average age of the patients was 13.47 years. All the victims were male. 41.17% of patients were in school. The mechanisms of trauma were the hoof blow 47.1%, the horn blow 29.4% and the stone blow 11.7% respectively. 23.5% of patients were confused and 11.7% children were in coma. One patient presented an anisocoria. The motor deficit was present in 5 cases. CT-scan made it possible to highlight a skull depressing fracture 58.8% and confirm a craniocerebral wound in 35.3%. The average time between patient admission to hospital and completion of surgery was 24.5 hours. The surgery had consisted of the trimming of cranio-cerebral wounds, exploration, duroplasty and lifting of skull depressing fracture. After 15 months of follow-up, the evolution was favorable in 53.3%, the morbidity was 33.4% and the mortality 17.6%. Conclusion: These are rare but serious conditions because they are fatal and disabling. An early and multidisciplinary management can hope to have a good favorable.
基金National Natural Science Foundation of China(52239006,41975001,41930972)Natural Science Foundation of Guangxi Zhuang Autonomous Region(2022GXNSFBA035565)。
文摘Based on previously released data,this paper first presented the criteria for recognizing bow echoes and divided their life cycle into three stages:the development stage,the mature stage,and the attenuation stage.Based on Doppler weather radar data during 2011-2020,43 bow echo events(including 54 individual bow echoes)in western South China were identified.The spatial and temporal distributions,formation and dissipation modes of these bow echoes,and the severe weather they caused were statistically analyzed.The results show that:(1)The bow echo events were unevenly distributed year-to-year,but all occurred from March to July,with the highest in April and May and the lowest in July.The period from night to early morning was found to be the main period for bow echo generation and intensification.(2)A banded area from Hechi City on the southeastern edge of the Yunnan-Guizhou Plateau to Wuzhou City in southeast Guangxi was identified as a high-incidence area of bow echoes.The length of bow echoes was correlated with their life cycle.(3)The origins of the bow echoes could be divided into five locations,most of which were in the eastern Yunnan-Guizhou Plateau.After entering western South China,their moving paths were categorized into three types,among which most bow echoes moved southeastward,generally because of the effect of cold air.Specifically,bow echoes generally moved eastward when cold air was weak or in the warm zone.Meanwhile,the fewest bow echoes moved northeastward.(4)Four modes of bow echo formation were identified:linearly organized,broken areal,linearly merging,and broken line.Dissipation could also be classified into four types.(5)The probability of convective weather generated by a bow echo was largest in the mature stage.
基金National Natural Science Foundation of China (50646021)Chinese Specialized Research Fund for the Doctoral Pro-gram of Higher Education (20060213007)
文摘The outlet flow fields of a low-speed repeating-stage compressor with bowed stator stages are measured with five-hole probe under the near stall condition when the rotor/stator axial gap varies. The performances of the straight stator stages are investigated and compared to those of the bowed stator stages. The results show that using bowed stator stages could alleviate the flow separation at both upper and low corners of the suction surface and the endwalls, and decrease the losses along the flow passage as well as the outlet flow angle. As the rotor/stator axial gap decreases, although the diffusion capacity of the compressor increases obviously, the outlet flow field in the straight stator stages deteriorates quickly. By contrast, little changes occur in the bowed stator stages, indicating that as the rotor/stator axial gap decreases, improved performance is achieved in the bowed stator stages.
文摘图像检索的Bag of Words体系存在量化后的视觉词影响局部特征的辨别能力并且缺乏特征之间空间关系的缺点,影响检索效率。针对复杂背景的目标查询,提出了融合显著性信息的图像检索方法和基于显著特征点空间距离比的后验证方法。首先,提取图像显著目标区域,使用空间金字塔模型进行图像检索。然后,利用查询图像与检索图像匹配的显著特征对,计算任意两对显著特征点的距离比,保留满足阈值的比值,并求和,用以重新排序结果图像,得到最终的检索结果。实验结果表明:该方法显著提高了检索的精确度,并减少了几何验证过程的运算时间。
