旋翼/平尾非定常气动干扰是导致直升机纵向"抬头(Pitch-up)"现象的主要原因。为在直升机设计阶段准确分析旋翼/平尾非定常气动干扰以及由此引起的低速纵向操纵特性变化,通过涡量等效原则和Neumann物面边界条件建立了适用于旋...旋翼/平尾非定常气动干扰是导致直升机纵向"抬头(Pitch-up)"现象的主要原因。为在直升机设计阶段准确分析旋翼/平尾非定常气动干扰以及由此引起的低速纵向操纵特性变化,通过涡量等效原则和Neumann物面边界条件建立了适用于旋翼/平尾气动干扰分析的非定常面元/黏性涡粒子混合法。该方法耦合了考虑尾迹时变效应的非定常面元法、黏性涡粒子法及涡量镜面法,以准确模拟旋翼和平尾的非定常气动载荷、旋翼尾迹的非定常特性以及旋翼尾迹对平尾的气动干扰效应。首先通过计算NASA ROBIN(Rotor Body Interaction)旋翼尾迹几何和诱导速度分布,并与实验测量值、时间精确自由尾迹及CFD计算结果对比验证方法的准确性。相比于时间精确自由尾迹,本文方法计算精度更高。随后分析了旋翼/平尾非定常气动干扰对平尾向下气动载荷和气动导数的影响,并分析了平尾构型对旋翼/平尾非定常气动干扰的影响规律。分析表明:旋翼尾迹与平尾干扰导致低速状态的平尾载荷突增,气动导数反号;低平尾气动载荷突增较大,高平尾较小,但高速气动导数反号;前置平尾载荷突增量减小,但对应速度范围较宽;右旋直升机右平尾载荷突增量较小,但气动导数特性基本不变。展开更多
共轴刚性双旋翼系统提高直升机最大前飞速度,但旋翼振动载荷明显增大。为研究高速共轴刚性双旋翼系统振动载荷特性,须首先分析共轴刚性双旋翼气动干扰下的非定常气动载荷。基于非定常面元法建立满足桨叶前缘和后缘边界条件的旋翼反流区...共轴刚性双旋翼系统提高直升机最大前飞速度,但旋翼振动载荷明显增大。为研究高速共轴刚性双旋翼系统振动载荷特性,须首先分析共轴刚性双旋翼气动干扰下的非定常气动载荷。基于非定常面元法建立满足桨叶前缘和后缘边界条件的旋翼反流区气动模型以体现高速共轴刚性双旋翼后行边反流区影响,且增加共轴刚性双旋翼桨尖涡-桨叶气动干扰模型以体现共轴刚性双旋翼非定常气动干扰影响,并结合基于黏性涡粒子法的共轴刚性双旋翼尾迹模型,构建高速共轴刚性双旋翼气动干扰下的气动载荷分析方法。通过计算前飞状态下的X2共轴刚性双旋翼特征剖面非定常气动载荷时间历程,并与PRASADUM以及基于NASA OVERFLOW和CREATE AV Helios的CFD/CSD计算结果对比,验证本文共轴刚性双旋翼非定常气动载荷分析方法的有效性。相比于PRASADUM,本文分析更好地体现上、下旋翼在前行边和后行边非定常气动载荷的变化特性,并与CFD/CSD计算结果更吻合。分析X2上、下旋翼气动干扰对共轴刚性双旋翼桨叶非定常气动载荷的影响,以及单旋翼与共轴刚性双旋翼非定常气动载荷差异。分析表明,低速状态下的共轴刚性双旋翼非定常气动载荷受双旋翼桨尖涡干扰显著,而高速前飞状态受双旋翼桨叶干扰明显,且表现出桨叶片数整数倍的辐射状干扰特征。展开更多
To further investigate the one-dimensional(1D)rheological consolidation mechanism of double-layered soil,the fractional derivative Merchant model(FDMM)and the non-Darcian flow model with the non-Newtonian index are re...To further investigate the one-dimensional(1D)rheological consolidation mechanism of double-layered soil,the fractional derivative Merchant model(FDMM)and the non-Darcian flow model with the non-Newtonian index are respectively introduced to describe the deformation of viscoelastic soil and the flow of pore water in the process of consolidation.Accordingly,an 1D rheological consolidation equation of double-layered soil is obtained,and its numerical analysis is performed by the implicit finite difference method.In order to verify its validity,the numerical solutions by the present method for some simplified cases are compared with the results in the related literature.Then,the influence of the revelent parameters on the rheological consolidation of double-layered soil are investigated.Numerical results indicate that the parameters of non-Darcian flow and FDMM of the first soil layer greatly influence the consolidation rate of double-layered soil.As the decrease of relative compressibility or the increase of relative permeability between the lower soil and the upper soil,the dissipation rate of excess pore water pressure and the settlement rate of the ground will be accelerated.Increasing the relative thickness of soil layer with high permeability or low compressibility will also accelerate the consolidation rate of double-layered soil.展开更多
AIM： To study the protective effect of Astragalus rnernbranaceus on intestinal mucosa reperfusion injury and its mechanism after hemorrhagic shock in rats. METHODS： A total of 32 SD rats were randomly divided into f...AIM： To study the protective effect of Astragalus rnernbranaceus on intestinal mucosa reperfusion injury and its mechanism after hemorrhagic shock in rats. METHODS： A total of 32 SD rats were randomly divided into four groups （n = 8, each group）： normal group, model group, low dosage group （treated with 10 g/kg Astragalus membranaceus） and high dosage group （treated with 20 g/kg Astragalus membranaceus）. The model of hemorrhagic shock for 60 min and reperfusion for 90 min was established. Therapeutic solution （3 mL） was administrated before reperfusion. At the end of the study, the observed intestinal pathology was analyzed. The blood concentrations of lactic acid （LD）, nitric oxide （NO）, endothelin-1 （ET-1）, malondialdehyde （MDA） and the activity of superoxide dismutase （SOD）, glutathione peroxidase （GSH-PX） in intestinal mucosa were determined. RESULTS： The intestinal mucosa pathology showed severe damage in model group and low dosage group, slight damage in high dosage group and no obvious damage in normal group. The Chiu＇s score in low dose group and high dose group was significantly lower than that in model group. The content of MDA in model group was higher than that in low and high dose groups, while that in high dose group was almost the same as in normal group. The activity of SOD and GSH-PX was the lowest in model group and significantly higher in high dose group than in normal and low dose groups. The concentrations of LD and ET-1 in model group were the highest. The concentrations of NO in model group and low dose group were significantly lower than those in high dose group and normal group. CONCLUSION： High dose Astraga/us membranaeus has much better protective effect on hemorrhagic shockreperfusion injury of intestinal mucosa than low dose Astragalus membranaceus. The mechanism may be that Astragalus membranaceus can improve antioxidative effect and regulate NO/ET level during hemorrhagic reperfusion.展开更多
The diagnosis of inflammatory bowel disease(IBD) depends on direct endoscopic visualization of the colonic and ileal mucosa and the histological study of the obtained samples.Radiological and scintigraphic methods are...The diagnosis of inflammatory bowel disease(IBD) depends on direct endoscopic visualization of the colonic and ileal mucosa and the histological study of the obtained samples.Radiological and scintigraphic methods are mainly used as an adjunct to endoscopy.In this review,we focus on the diagnostic potential of nuclear medicine procedures.The value of all radiotracers is described with special reference to those with greater experience and more satisfactory results.Tc-99m hexamethylpropylene amine oxime white blood cells remain a widely acceptable scintigraphic method for the diagnosis of IBD,as well as for the evaluation of disease extension and severity.Recently,pentavalent Tc-99m dimercaptosuccinic acid has been recommended as an accurate variant and a complementary technique to endoscopy for the follow-up and assessment of disease activity.Positron emission tomography alone or with computed tomography using fluorine-18 fluorodeoxyglucose appears to be a promising method of measuring inflammation in IBD patients.展开更多
We describe the case of a 68-year-old otherwise healthy male who presented to our emergency room with signs and symptoms of acute appendicitis. Exploratory surgery revealed a normal appendix. Further examination revea...We describe the case of a 68-year-old otherwise healthy male who presented to our emergency room with signs and symptoms of acute appendicitis. Exploratory surgery revealed a normal appendix. Further examination revealed an enlarged lymph node-like mass of tissue near the appendix, in the ileocecal mesentery. This mass was removed and was found to be inflamed heterotopic gastric tissue. Although reports of heterotopic gastric tissue in the literature are common, we believe that this case represents the first report of inflamed heterotopic gastric tissue simulating appendicitis.展开更多
The use of electro-osmotic chemical is an effective method to improve the clayey soil foundation.Various boundary conditions can be adopted in this method.In this work,two electrode–clay contacts,three solution condi...The use of electro-osmotic chemical is an effective method to improve the clayey soil foundation.Various boundary conditions can be adopted in this method.In this work,two electrode–clay contacts,three solution conditioners,and four anode solution supply times were used for clayey soil improvement.Based on the experimental data,electro-osmotic consolidation theory,and transport of ion theory,it is found that the electro-osmotic chemical effect of the separation of electrode–clay(E_S)is more beneficial for the transport of Ca^(2+),production of cementing material,and reduction of water content than that of electrode–clay(E_C)joining;through electrode–clay contact separation,the anode solution conditioner(NaPO3)6(E_SHMP)delayed the cementing reaction and then increased the transport of Ca^(2+)near the cathode,which increased the amount of cementing material and the electro-osmotic chemical effect;and when the anode conditioner(NaPO3)6 was used,two days of anode solution supply followed by three days cut off from the anode solution led to the highest undrained shear strength increase after the application of electro-osmotic chemical,which resolved the uneven electro-osmotic chemical effect in the E_SHMP.展开更多
文摘旋翼/平尾非定常气动干扰是导致直升机纵向"抬头(Pitch-up)"现象的主要原因。为在直升机设计阶段准确分析旋翼/平尾非定常气动干扰以及由此引起的低速纵向操纵特性变化,通过涡量等效原则和Neumann物面边界条件建立了适用于旋翼/平尾气动干扰分析的非定常面元/黏性涡粒子混合法。该方法耦合了考虑尾迹时变效应的非定常面元法、黏性涡粒子法及涡量镜面法,以准确模拟旋翼和平尾的非定常气动载荷、旋翼尾迹的非定常特性以及旋翼尾迹对平尾的气动干扰效应。首先通过计算NASA ROBIN(Rotor Body Interaction)旋翼尾迹几何和诱导速度分布,并与实验测量值、时间精确自由尾迹及CFD计算结果对比验证方法的准确性。相比于时间精确自由尾迹,本文方法计算精度更高。随后分析了旋翼/平尾非定常气动干扰对平尾向下气动载荷和气动导数的影响,并分析了平尾构型对旋翼/平尾非定常气动干扰的影响规律。分析表明:旋翼尾迹与平尾干扰导致低速状态的平尾载荷突增,气动导数反号;低平尾气动载荷突增较大,高平尾较小,但高速气动导数反号;前置平尾载荷突增量减小,但对应速度范围较宽;右旋直升机右平尾载荷突增量较小,但气动导数特性基本不变。
文摘共轴刚性双旋翼系统提高直升机最大前飞速度,但旋翼振动载荷明显增大。为研究高速共轴刚性双旋翼系统振动载荷特性,须首先分析共轴刚性双旋翼气动干扰下的非定常气动载荷。基于非定常面元法建立满足桨叶前缘和后缘边界条件的旋翼反流区气动模型以体现高速共轴刚性双旋翼后行边反流区影响,且增加共轴刚性双旋翼桨尖涡-桨叶气动干扰模型以体现共轴刚性双旋翼非定常气动干扰影响,并结合基于黏性涡粒子法的共轴刚性双旋翼尾迹模型,构建高速共轴刚性双旋翼气动干扰下的气动载荷分析方法。通过计算前飞状态下的X2共轴刚性双旋翼特征剖面非定常气动载荷时间历程,并与PRASADUM以及基于NASA OVERFLOW和CREATE AV Helios的CFD/CSD计算结果对比,验证本文共轴刚性双旋翼非定常气动载荷分析方法的有效性。相比于PRASADUM,本文分析更好地体现上、下旋翼在前行边和后行边非定常气动载荷的变化特性,并与CFD/CSD计算结果更吻合。分析X2上、下旋翼气动干扰对共轴刚性双旋翼桨叶非定常气动载荷的影响,以及单旋翼与共轴刚性双旋翼非定常气动载荷差异。分析表明,低速状态下的共轴刚性双旋翼非定常气动载荷受双旋翼桨尖涡干扰显著,而高速前飞状态受双旋翼桨叶干扰明显,且表现出桨叶片数整数倍的辐射状干扰特征。
基金Project(51578511)supported by the National Natural Science Foundation of China。
文摘To further investigate the one-dimensional(1D)rheological consolidation mechanism of double-layered soil,the fractional derivative Merchant model(FDMM)and the non-Darcian flow model with the non-Newtonian index are respectively introduced to describe the deformation of viscoelastic soil and the flow of pore water in the process of consolidation.Accordingly,an 1D rheological consolidation equation of double-layered soil is obtained,and its numerical analysis is performed by the implicit finite difference method.In order to verify its validity,the numerical solutions by the present method for some simplified cases are compared with the results in the related literature.Then,the influence of the revelent parameters on the rheological consolidation of double-layered soil are investigated.Numerical results indicate that the parameters of non-Darcian flow and FDMM of the first soil layer greatly influence the consolidation rate of double-layered soil.As the decrease of relative compressibility or the increase of relative permeability between the lower soil and the upper soil,the dissipation rate of excess pore water pressure and the settlement rate of the ground will be accelerated.Increasing the relative thickness of soil layer with high permeability or low compressibility will also accelerate the consolidation rate of double-layered soil.
基金Supported by the Chinese Traditional Medicine Foundation of Guangdong Province, China, No. 102061
文摘AIM： To study the protective effect of Astragalus rnernbranaceus on intestinal mucosa reperfusion injury and its mechanism after hemorrhagic shock in rats. METHODS： A total of 32 SD rats were randomly divided into four groups （n = 8, each group）： normal group, model group, low dosage group （treated with 10 g/kg Astragalus membranaceus） and high dosage group （treated with 20 g/kg Astragalus membranaceus）. The model of hemorrhagic shock for 60 min and reperfusion for 90 min was established. Therapeutic solution （3 mL） was administrated before reperfusion. At the end of the study, the observed intestinal pathology was analyzed. The blood concentrations of lactic acid （LD）, nitric oxide （NO）, endothelin-1 （ET-1）, malondialdehyde （MDA） and the activity of superoxide dismutase （SOD）, glutathione peroxidase （GSH-PX） in intestinal mucosa were determined. RESULTS： The intestinal mucosa pathology showed severe damage in model group and low dosage group, slight damage in high dosage group and no obvious damage in normal group. The Chiu＇s score in low dose group and high dose group was significantly lower than that in model group. The content of MDA in model group was higher than that in low and high dose groups, while that in high dose group was almost the same as in normal group. The activity of SOD and GSH-PX was the lowest in model group and significantly higher in high dose group than in normal and low dose groups. The concentrations of LD and ET-1 in model group were the highest. The concentrations of NO in model group and low dose group were significantly lower than those in high dose group and normal group. CONCLUSION： High dose Astraga/us membranaeus has much better protective effect on hemorrhagic shockreperfusion injury of intestinal mucosa than low dose Astragalus membranaceus. The mechanism may be that Astragalus membranaceus can improve antioxidative effect and regulate NO/ET level during hemorrhagic reperfusion.
文摘The diagnosis of inflammatory bowel disease(IBD) depends on direct endoscopic visualization of the colonic and ileal mucosa and the histological study of the obtained samples.Radiological and scintigraphic methods are mainly used as an adjunct to endoscopy.In this review,we focus on the diagnostic potential of nuclear medicine procedures.The value of all radiotracers is described with special reference to those with greater experience and more satisfactory results.Tc-99m hexamethylpropylene amine oxime white blood cells remain a widely acceptable scintigraphic method for the diagnosis of IBD,as well as for the evaluation of disease extension and severity.Recently,pentavalent Tc-99m dimercaptosuccinic acid has been recommended as an accurate variant and a complementary technique to endoscopy for the follow-up and assessment of disease activity.Positron emission tomography alone or with computed tomography using fluorine-18 fluorodeoxyglucose appears to be a promising method of measuring inflammation in IBD patients.
文摘We describe the case of a 68-year-old otherwise healthy male who presented to our emergency room with signs and symptoms of acute appendicitis. Exploratory surgery revealed a normal appendix. Further examination revealed an enlarged lymph node-like mass of tissue near the appendix, in the ileocecal mesentery. This mass was removed and was found to be inflamed heterotopic gastric tissue. Although reports of heterotopic gastric tissue in the literature are common, we believe that this case represents the first report of inflamed heterotopic gastric tissue simulating appendicitis.
基金Project(41902280)supported by the National Natural Science Foundation of ChinaProject(300102219105)supported by the Fundamental Research Funds for the Central Universities,China+1 种基金Project(LP1922)supported by the Open Foundation of State Key Laboratory of Coastal and Offshore Engineering,ChinaProject(XJKFJJ201805)supported by the Open Foundation of Shaanxi Key Laboratory of Safety and Durability of Concrete Structures,China。
文摘The use of electro-osmotic chemical is an effective method to improve the clayey soil foundation.Various boundary conditions can be adopted in this method.In this work,two electrode–clay contacts,three solution conditioners,and four anode solution supply times were used for clayey soil improvement.Based on the experimental data,electro-osmotic consolidation theory,and transport of ion theory,it is found that the electro-osmotic chemical effect of the separation of electrode–clay(E_S)is more beneficial for the transport of Ca^(2+),production of cementing material,and reduction of water content than that of electrode–clay(E_C)joining;through electrode–clay contact separation,the anode solution conditioner(NaPO3)6(E_SHMP)delayed the cementing reaction and then increased the transport of Ca^(2+)near the cathode,which increased the amount of cementing material and the electro-osmotic chemical effect;and when the anode conditioner(NaPO3)6 was used,two days of anode solution supply followed by three days cut off from the anode solution led to the highest undrained shear strength increase after the application of electro-osmotic chemical,which resolved the uneven electro-osmotic chemical effect in the E_SHMP.
