Laser multipass welding techniques for thick section steels have been developed using a new type of UV combined narrow groove. The shape and sizes at the bottom of groove are determined by analyzing the plasma behavio...Laser multipass welding techniques for thick section steels have been developed using a new type of UV combined narrow groove. The shape and sizes at the bottom of groove are determined by analyzing the plasma behavior using high speed photographic equipment. A stable autogenous CO2 laser welding process and greater penetration are generated at the root pass because of strong reduction of the plasma volume. According to the waveforms of welding current and arc voltage, and the interaction between the arc and the laser induced plasma, a suitable groove angle is obtained. Laser-double MIG hybrid welding process is studied and the optimum distances between the laser and two arcs are determined. By using autogenous CO2 laser welding, CO2 laser-MIG hybrid welding and laser-double MIG hybrid welding, 28 mm thick steel plates are welded with four passes. The welds produced are assessed by X-ray. No crack is found and there is only a small amount of pores. The experimental results show that the multipuss welding procedures proposed can realize the joining of thick section steels with high efficiency and good quality.展开更多
The development of alternative casting processes is essential for the high demand of light weight magnesium components to be used in the automotive industry, which often contain different section thicknesses. Squeeze ...The development of alternative casting processes is essential for the high demand of light weight magnesium components to be used in the automotive industry, which often contain different section thicknesses. Squeeze casting with its inherent advantages has been approved for the capability of minimizing the gas porosity in magnesium alloys. For advanced engineering design of light magnesium automotive applications, it is critical to understand the effect of section thickness on mechanical properties of squeeze cast magnesium alloys. In this study, magnesium alloy AM60 with different section thicknesses of 6, 10 and 20 mm squeeze cast under an applied pressure of 30 MPa was investigated. The prepared squeeze cast AM60 specimens were tensile tested at room termperature. The results indicate that the mechanical properties including yield strength （YS）, ultimate tensile strength （UTS） and elongation （A） decrease with an increase in section thickness of squeeze cast AM6O. The microstructure analysis shows that the improvement in the tensile behavior of squeeze cast AM60 is primarily attributed to the low-gas porosity level and fine grain strucuture which result from the variation of cooling rate of different section thickness. The numerical simulation （Magmasoft） was employed to determine the solidification rates of each step, and the simulated results show that the solidification rate of the alloy decreases with an increase in the section thickness. The computed solidification rates support the experimental observation on grain structural development.展开更多
The dependence between neutron skin thickness and neutron abrasion cross section （σnabr） for neutron-rich nuclei is investigated within the framework of the statistical abrasion ablation model. Assuming that the de...The dependence between neutron skin thickness and neutron abrasion cross section （σnabr） for neutron-rich nuclei is investigated within the framework of the statistical abrasion ablation model. Assuming that the density distributions for proton and neutron are of Fermi-type, and adjusting the diffuseness parameter of neutron density distribution in the droplet model, we find out the good linear correlation between the neutron skin thickness and the abrasion cross section σnabr for neutron-rich nuclei. The uncertainty of neutron skin thickness determined from σnabr is very small. It is suggested that σnabr can be used as a new experimental observable to extract the neutron skin thickness for neutronrich nucleus. The scaling behaviours between neutron skin thickness and σnabr, separately, for isotopes of ^26-35Na, ^44-56Ar, ^48-60Ca, ^67-78Ni are also investigated.展开更多
Measurements were performed of K-shell ionization cross sections of Ti element by 10～30 keV positron impact using the thick-target method. The effects of multiple scattering of incident positron and from bremsstrahlu...Measurements were performed of K-shell ionization cross sections of Ti element by 10～30 keV positron impact using the thick-target method. The effects of multiple scattering of incident positron and from bremsstrahlung photons and annihilation photons with the thick-target method are discussed with the Monte Carlo code PENELOPE. Meanwhile, the Monte Carlo method is also applied to determine the detection efficiencies of X- and γ-ray detectors. Our experimental K-shell ionization cross sections for Ti element are compared with the distorted-wave Born approximation （DWBA） theoretical predictions, and it is found that the agreement of the experimental data and theoretical values is good and this indicates that the experimental method adopted in this study is applicable.展开更多
To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel （HSS）, six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with di...To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel （HSS）, six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with different width-to-thickness ratios and loaded under different axial load ratios. For each specimen, the failure mode was observed and hysteretic curve was measured. Comparison of different specimens on hysteretic characteristic, energy dissipation capacity and deformation capacity were further investigated. Test results showed that the degradation of bearing capacity was due to local buckling of flange and web. Under the same axial load ratio, as width-to-thickness ratio increased, the deformation area of local buckling became smaller. And also, displacement level at both peak load and failure load became smaller. In addition, the full extent of hysteretic curve, energy dissipation capacity, ultimate story drift angle decreased, and capacity degradation occurred more rapidly with the increase of width-to-thickness ratio or axial load ratio. Based on the capacity of story drift angle, limiting values which shall not be exceeded are suggested respectively for flange and web plate of 460 MPa HSS I-section columns when used in SMFs and in IMFs in the case of axial load ratio no more than 0.2. Such values should be smaller when the axial load ratio increases.展开更多
In order to predict the flattening rate of the cross-section accurately during the tube ben- ding, the generation principle, the solution and the influence factor of the cross-section flattening were studied. On the b...In order to predict the flattening rate of the cross-section accurately during the tube ben- ding, the generation principle, the solution and the influence factor of the cross-section flattening were studied. On the basis of the plane-stress and the assumption that the plastic volume is con- stant, three-dimensionai strain formulas were established in consider of the cross-section flattening. Considering the wail-thickness change, the approximate calculation formulas of short axis flattening rate were deduced, with the outer diameter and the inner diameter as parameters. Because different materials have different cross-section flattening rates, a material correction factor was introduced to modify the formula based on experiments. Finally, the validity of the theoretical formulas was proved according to the calculation and the experiment results, which can provide a reference for the forming quality prediction in tube bending.展开更多
Background: The myometrium at the location of the CS (caesarean section) scars, also known as residual myometrium thickness (RMT), is larger after a double-layer uterine closure procedure than following a single-layer...Background: The myometrium at the location of the CS (caesarean section) scars, also known as residual myometrium thickness (RMT), is larger after a double-layer uterine closure procedure than following a single-layer one. It may lessen the formation of a niche that is the myometrium’s disruption at the location of the scar of the uterus. Gynecological manifestations, obstetric problems in a future pregnancy and birth, and maybe subfertility are linked to thin RMT and a niche. Objective: To ascertain if double-layer unlocked closure of the uterus is better than single-layer one in terms of post-menstrual spotting and niche development following a first CS. Patients and Methods: In this randomized clinical study, 287 patients were evaluated for qualifying. Of all eligible individuals, 57 patients were excluded from the study based on the inclusion criteria. Results: The variation in ages, gestational age, body mass index (BMI), and cesarean section indications between the two assigned groups is statistically insignificant. However, postmenstrual spotting was statistically significantly more common in single-layer group compared to in double-group. The current study revealed ultrasound findings suggestive of niche formation was statistically significantly more common in single-layer group compared to in double-layer group. Conclusion: As evident from the current study, it demonstrates the advantages of double-layer unlocked closure of the uterus over single-layer one in terms of post-menstrual spotting and niche development following first-time cs. Thus, we deduced that fewer niches are formed, and fewer menstrual spotting occurs in the presence of double unlocked layers closure. To ascertain the impact of uterus closure method on post-operative niche development and the risk of obstetrics and gynaecological problems, further prospective trials with extended follow-up periods are required.展开更多
Objectives: This study focused on evaluating the value of transvaginal 3D ultrasound for the diagnosis and prognostic assessment of post-cesarean section uterine diverticulum. Materials and Methods: We retrospectively...Objectives: This study focused on evaluating the value of transvaginal 3D ultrasound for the diagnosis and prognostic assessment of post-cesarean section uterine diverticulum. Materials and Methods: We retrospectively analyzed the data from 32 patients with post-cesarean section uterine diverticulum over three recent years. In all patients, transvaginal 3D ultrasound was used to measure the size of the uterine diverticulum and the thickness of the lower uterine segment (LUS) and myometrium. Patients with a LUS with a myometrial thickness under 4 mm underwent resection and repair surgery;those with a LUS with a myometrial thickness over 4 mm underwent hysteroscopic resection. The postoperative sonograms were compared with preoperative images to evaluate the efficacy of various treatments. Results: The mean length, width and depth of the uterine diverticula were 18.30 ± 2.80 mm, 9.14 ± 3.20 mm and 11.49 ± 2.71 mm, respectively. The average LUS myometrial thickness was 3.40 ± 0.80 mm (with a range of 1.6 mm - 6.3 mm). After surgery, two patients’ sonograms still showed diverticula at the post-cesarean section scar, measuring 6 mm × 7 mm × 6 mm and 6 mm × 8 mm × 4 mm. There were significant differences in the size of uterine diverticula between preoperative and postoperative sonograms (P < 0.05) and the effective rate of surgery was 93.75% (30/32). Conclusions: Transvaginal 3D ultrasound is an accurate method for detecting post-cesarean section uterine diverticulum and is helpful for assessing surgical options and prognosis. The LUS myometrial thickness, which is considered as an optional index of post-cesarean section uterine diverticulum, should be measured routinely.展开更多
Caesarean section is dramatically increased throughout the world in recent years. Rupture of the uterus is a devastating complication in trial of labour following previous Caesarean section. Evidence suggests that the...Caesarean section is dramatically increased throughout the world in recent years. Rupture of the uterus is a devastating complication in trial of labour following previous Caesarean section. Evidence suggests that the size of the uterine scar and the residual myometrial thickness (RMT) are associated directly with the risk of uterine rupture and risk of dehiscence in subsequent deliveries. Impact of the prelabour and labour Cesarean section on the RMT has not been studied in detail. Objectives: To compare RMT, Caesarean scar defects and to evaluate the elasticity of the Caesarean scar between women who underwent prelabour and labour Caesarean sections. Methods: This was a Cross sectional analytical study. Women who underwent Caesarean section in their first pregnancy were recruited. Sample was stratified to prelabour and labour Caesarean section groups. Transvaginal ultrasound scan was performed six months following the Caesarean section. Dimensions of the uterus, uterine scar defect, RMT and elastosonography of the uterine scar were assessed. Results: A total of 240 postpartum women were analyzed. Uterine niche was detectable in 194 subjects. Prelabour CS group had demonstrated 91.7% (n = 110) scar defects (uterine niche) out of 120 cases and the rate among labour CS group was 70% (n = 84). There was a significant difference in the presence of uterine niche among 2 groups as Prelabour group was found to have more scar defects (p mm (SD 1.2) and 4.99 mm (SD 1.3) respectively and there was no significant difference (t = 0.38, p = 0.71). There was no significant difference between the dimensions of the uterine CS defects of the studied groups. Prelabour CS group had significantly higher Target strain [0.28 vs. 0.24 (t = 2.12, p = 0.04)] and significantly less strain ratio [1.45 vs. 1.55 (t -2.42, p = 0.04)] than labour CS group indicating a better scar in prelabour group. Conclusion: There was no significant difference in RMT and uterine scar defects between prelabour and labour Caesarean section groups. But prelabour Caesarean section scars were less stiff than labour Caesarean section scars. Further studies are warranted to elaborate on the association.展开更多
文摘Laser multipass welding techniques for thick section steels have been developed using a new type of UV combined narrow groove. The shape and sizes at the bottom of groove are determined by analyzing the plasma behavior using high speed photographic equipment. A stable autogenous CO2 laser welding process and greater penetration are generated at the root pass because of strong reduction of the plasma volume. According to the waveforms of welding current and arc voltage, and the interaction between the arc and the laser induced plasma, a suitable groove angle is obtained. Laser-double MIG hybrid welding process is studied and the optimum distances between the laser and two arcs are determined. By using autogenous CO2 laser welding, CO2 laser-MIG hybrid welding and laser-double MIG hybrid welding, 28 mm thick steel plates are welded with four passes. The welds produced are assessed by X-ray. No crack is found and there is only a small amount of pores. The experimental results show that the multipuss welding procedures proposed can realize the joining of thick section steels with high efficiency and good quality.
文摘The development of alternative casting processes is essential for the high demand of light weight magnesium components to be used in the automotive industry, which often contain different section thicknesses. Squeeze casting with its inherent advantages has been approved for the capability of minimizing the gas porosity in magnesium alloys. For advanced engineering design of light magnesium automotive applications, it is critical to understand the effect of section thickness on mechanical properties of squeeze cast magnesium alloys. In this study, magnesium alloy AM60 with different section thicknesses of 6, 10 and 20 mm squeeze cast under an applied pressure of 30 MPa was investigated. The prepared squeeze cast AM60 specimens were tensile tested at room termperature. The results indicate that the mechanical properties including yield strength （YS）, ultimate tensile strength （UTS） and elongation （A） decrease with an increase in section thickness of squeeze cast AM6O. The microstructure analysis shows that the improvement in the tensile behavior of squeeze cast AM60 is primarily attributed to the low-gas porosity level and fine grain strucuture which result from the variation of cooling rate of different section thickness. The numerical simulation （Magmasoft） was employed to determine the solidification rates of each step, and the simulated results show that the solidification rate of the alloy decreases with an increase in the section thickness. The computed solidification rates support the experimental observation on grain structural development.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10775168,10405032,10535010,10405033,10605036 and 10475108)the Shanghai Development Foundation for Science and Technology (Grant Nos 06QA14062,06JC14082 and 05XD14021)+1 种基金the State Key Program of Basic Research of China (Grant No 2007CB815004)the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No KJCX3.SYW.N2)
文摘The dependence between neutron skin thickness and neutron abrasion cross section （σnabr） for neutron-rich nuclei is investigated within the framework of the statistical abrasion ablation model. Assuming that the density distributions for proton and neutron are of Fermi-type, and adjusting the diffuseness parameter of neutron density distribution in the droplet model, we find out the good linear correlation between the neutron skin thickness and the abrasion cross section σnabr for neutron-rich nuclei. The uncertainty of neutron skin thickness determined from σnabr is very small. It is suggested that σnabr can be used as a new experimental observable to extract the neutron skin thickness for neutronrich nucleus. The scaling behaviours between neutron skin thickness and σnabr, separately, for isotopes of ^26-35Na, ^44-56Ar, ^48-60Ca, ^67-78Ni are also investigated.
基金supported by National Natural Science Foundation of China (Nos.10674097,10774106)
文摘Measurements were performed of K-shell ionization cross sections of Ti element by 10～30 keV positron impact using the thick-target method. The effects of multiple scattering of incident positron and from bremsstrahlung photons and annihilation photons with the thick-target method are discussed with the Monte Carlo code PENELOPE. Meanwhile, the Monte Carlo method is also applied to determine the detection efficiencies of X- and γ-ray detectors. Our experimental K-shell ionization cross sections for Ti element are compared with the distorted-wave Born approximation （DWBA） theoretical predictions, and it is found that the agreement of the experimental data and theoretical values is good and this indicates that the experimental method adopted in this study is applicable.
基金the National Natural Science Foundation of China under Grant No.51478244
文摘To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel （HSS）, six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with different width-to-thickness ratios and loaded under different axial load ratios. For each specimen, the failure mode was observed and hysteretic curve was measured. Comparison of different specimens on hysteretic characteristic, energy dissipation capacity and deformation capacity were further investigated. Test results showed that the degradation of bearing capacity was due to local buckling of flange and web. Under the same axial load ratio, as width-to-thickness ratio increased, the deformation area of local buckling became smaller. And also, displacement level at both peak load and failure load became smaller. In addition, the full extent of hysteretic curve, energy dissipation capacity, ultimate story drift angle decreased, and capacity degradation occurred more rapidly with the increase of width-to-thickness ratio or axial load ratio. Based on the capacity of story drift angle, limiting values which shall not be exceeded are suggested respectively for flange and web plate of 460 MPa HSS I-section columns when used in SMFs and in IMFs in the case of axial load ratio no more than 0.2. Such values should be smaller when the axial load ratio increases.
基金Supported by the National Natural Science Foundation of China(50805009)Twelve Five-Year Plan Basic Research Item of National Defense of China(A2220110008)
文摘In order to predict the flattening rate of the cross-section accurately during the tube ben- ding, the generation principle, the solution and the influence factor of the cross-section flattening were studied. On the basis of the plane-stress and the assumption that the plastic volume is con- stant, three-dimensionai strain formulas were established in consider of the cross-section flattening. Considering the wail-thickness change, the approximate calculation formulas of short axis flattening rate were deduced, with the outer diameter and the inner diameter as parameters. Because different materials have different cross-section flattening rates, a material correction factor was introduced to modify the formula based on experiments. Finally, the validity of the theoretical formulas was proved according to the calculation and the experiment results, which can provide a reference for the forming quality prediction in tube bending.
文摘Background: The myometrium at the location of the CS (caesarean section) scars, also known as residual myometrium thickness (RMT), is larger after a double-layer uterine closure procedure than following a single-layer one. It may lessen the formation of a niche that is the myometrium’s disruption at the location of the scar of the uterus. Gynecological manifestations, obstetric problems in a future pregnancy and birth, and maybe subfertility are linked to thin RMT and a niche. Objective: To ascertain if double-layer unlocked closure of the uterus is better than single-layer one in terms of post-menstrual spotting and niche development following a first CS. Patients and Methods: In this randomized clinical study, 287 patients were evaluated for qualifying. Of all eligible individuals, 57 patients were excluded from the study based on the inclusion criteria. Results: The variation in ages, gestational age, body mass index (BMI), and cesarean section indications between the two assigned groups is statistically insignificant. However, postmenstrual spotting was statistically significantly more common in single-layer group compared to in double-group. The current study revealed ultrasound findings suggestive of niche formation was statistically significantly more common in single-layer group compared to in double-layer group. Conclusion: As evident from the current study, it demonstrates the advantages of double-layer unlocked closure of the uterus over single-layer one in terms of post-menstrual spotting and niche development following first-time cs. Thus, we deduced that fewer niches are formed, and fewer menstrual spotting occurs in the presence of double unlocked layers closure. To ascertain the impact of uterus closure method on post-operative niche development and the risk of obstetrics and gynaecological problems, further prospective trials with extended follow-up periods are required.
文摘Objectives: This study focused on evaluating the value of transvaginal 3D ultrasound for the diagnosis and prognostic assessment of post-cesarean section uterine diverticulum. Materials and Methods: We retrospectively analyzed the data from 32 patients with post-cesarean section uterine diverticulum over three recent years. In all patients, transvaginal 3D ultrasound was used to measure the size of the uterine diverticulum and the thickness of the lower uterine segment (LUS) and myometrium. Patients with a LUS with a myometrial thickness under 4 mm underwent resection and repair surgery;those with a LUS with a myometrial thickness over 4 mm underwent hysteroscopic resection. The postoperative sonograms were compared with preoperative images to evaluate the efficacy of various treatments. Results: The mean length, width and depth of the uterine diverticula were 18.30 ± 2.80 mm, 9.14 ± 3.20 mm and 11.49 ± 2.71 mm, respectively. The average LUS myometrial thickness was 3.40 ± 0.80 mm (with a range of 1.6 mm - 6.3 mm). After surgery, two patients’ sonograms still showed diverticula at the post-cesarean section scar, measuring 6 mm × 7 mm × 6 mm and 6 mm × 8 mm × 4 mm. There were significant differences in the size of uterine diverticula between preoperative and postoperative sonograms (P < 0.05) and the effective rate of surgery was 93.75% (30/32). Conclusions: Transvaginal 3D ultrasound is an accurate method for detecting post-cesarean section uterine diverticulum and is helpful for assessing surgical options and prognosis. The LUS myometrial thickness, which is considered as an optional index of post-cesarean section uterine diverticulum, should be measured routinely.
文摘Caesarean section is dramatically increased throughout the world in recent years. Rupture of the uterus is a devastating complication in trial of labour following previous Caesarean section. Evidence suggests that the size of the uterine scar and the residual myometrial thickness (RMT) are associated directly with the risk of uterine rupture and risk of dehiscence in subsequent deliveries. Impact of the prelabour and labour Cesarean section on the RMT has not been studied in detail. Objectives: To compare RMT, Caesarean scar defects and to evaluate the elasticity of the Caesarean scar between women who underwent prelabour and labour Caesarean sections. Methods: This was a Cross sectional analytical study. Women who underwent Caesarean section in their first pregnancy were recruited. Sample was stratified to prelabour and labour Caesarean section groups. Transvaginal ultrasound scan was performed six months following the Caesarean section. Dimensions of the uterus, uterine scar defect, RMT and elastosonography of the uterine scar were assessed. Results: A total of 240 postpartum women were analyzed. Uterine niche was detectable in 194 subjects. Prelabour CS group had demonstrated 91.7% (n = 110) scar defects (uterine niche) out of 120 cases and the rate among labour CS group was 70% (n = 84). There was a significant difference in the presence of uterine niche among 2 groups as Prelabour group was found to have more scar defects (p mm (SD 1.2) and 4.99 mm (SD 1.3) respectively and there was no significant difference (t = 0.38, p = 0.71). There was no significant difference between the dimensions of the uterine CS defects of the studied groups. Prelabour CS group had significantly higher Target strain [0.28 vs. 0.24 (t = 2.12, p = 0.04)] and significantly less strain ratio [1.45 vs. 1.55 (t -2.42, p = 0.04)] than labour CS group indicating a better scar in prelabour group. Conclusion: There was no significant difference in RMT and uterine scar defects between prelabour and labour Caesarean section groups. But prelabour Caesarean section scars were less stiff than labour Caesarean section scars. Further studies are warranted to elaborate on the association.
