As prestressed concrete(PC)structures age,long-termeffects,e.g.,creep,shrinkage,and prestress losses,compromise their structural performance.Strengthening these aged PC beams has become a crucial matter.One effective ...As prestressed concrete(PC)structures age,long-termeffects,e.g.,creep,shrinkage,and prestress losses,compromise their structural performance.Strengthening these aged PC beams has become a crucial matter.One effective solution is to use externally bonded fiber-reinforced polymer(FRP)sheets;however,limited research has been done on aged PC beams using the FRP,especially for beams with unbonded prestressing strands(UPC beams).Therefore,this research investigates the flexural strengthening efficacy of external FRP sheets on aged UPC beams with unbonded tendons.Aging minimally affected the failure modes of UPC beams,with nonstrengthened beams showing flexural failure via rebar yielding and concrete crushing,and FRP-strengthened beams failing due to FRP debonding and tensile reinforcement yielding,though tendons in the aged beams did not yield due to prestress losses,unlike the new beams.The U-wrap anchor curbed widespread debonding,leading to tensile reinforcement yielding and FRP rupture.Aging hastened crack growth and stiffness loss,increasing deflections and reducing load resistance,but FRP reinforcement mitigated these effects,enhancing cracking resistance by 14%over the unstrengthened aged beams and 7%over the new beams while boosting ultimate resistance by 9%above the non-strengthened new beams.Compared to the new FRP-strengthened beams,the aged counterparts had lower cracking resistance,stiffness and capacity—showing 20%higher deflections,7–9%lower serviceability loads,7%–17%reduced ultimate strength and 17%less deformability—due to prestress losses and premature FRP debonding.展开更多
Finless porpoises(FPs)serve as flagship species and key ecological indicators for assessing environmental quality.However,FPs are challenging to survey due to their elusive behavior and lack of distinctive features.St...Finless porpoises(FPs)serve as flagship species and key ecological indicators for assessing environmental quality.However,FPs are challenging to survey due to their elusive behavior and lack of distinctive features.Stranding and sighting events offer essential information on species diversity,distribution patterns,and potential threats.In this study,records from 1986 to 2023 were analyzed to assess the temporal and spatial distribution patterns of FP strandings and sightings in the Qiantang River Estuary,China.Results show an increase in the number of recorded events over time.Seasonal variations were evident,with a peak in strandings and sightings occurring in late winter.The frequency of records was higher during spring and moderate tides compared to neap tides,particularly in hydrologically normal years.Rapidly receding tides and sediment accumulation appear to restrict the activity space of FPs,thereby increasing the frequency of these events.Localized conditions associated with stranding and sighting events were classified into four categories:bifurcation zones,confluence zones,separation zones,and deep channels adjacent to concave banks.Deep channels,which are optimal for shipping,also elevate the risk of FP strandings.These findings offer valuable insights for the development and design of conservation strategies tailored to the needs of FPs in estuarine environments.展开更多
To tackle the issue of notch frequency and center frequency drift of the L(0,1)mode guided wave in ultra⁃sonic guided wave⁃based stress monitoring of prestressed steel strands,a method using higher⁃order mode plateau ...To tackle the issue of notch frequency and center frequency drift of the L(0,1)mode guided wave in ultra⁃sonic guided wave⁃based stress monitoring of prestressed steel strands,a method using higher⁃order mode plateau fre⁃quencies is adopted.First,the correlation between group velocity peaks and phase velocities at these plateau frequen⁃cies is analyzed.This analysis establishes a quantitative rela⁃tionship between phase velocity and stress in the steel strand,providing a theoretical foundation for stress monitor⁃ing.Then the two⁃dimensional Fourier transform is em⁃ployed to separate wave modes.Dynamic programming techniques are applied in the frequency⁃velocity domain to extract higher⁃order modes.By identifying the group veloc⁃ity peaks of these separated higher⁃order modes,the plateau frequencies of guided waves are determined,enabling indi⁃rect measurement of stress in the steel strand.To validate this method,finite element simulations are conducted under three scenarios.Results show that the higher⁃order modes of transient signals from three different positions can be ac⁃curately extracted,leading to successful cable stress moni⁃toring.This approach effectively circumvents the issue of guided wave frequency drift and improves stress monitoring accuracy.Consequently,it significantly improves the appli⁃cation of ultrasonic guided wave technology in structural health monitoring.展开更多
Strand displacement reaction is a crucial component in the assembly of diverse DNA-based nanodevices,with the toehold-mediated strand displacement reaction representing the prevailing strategy.However,the single-stran...Strand displacement reaction is a crucial component in the assembly of diverse DNA-based nanodevices,with the toehold-mediated strand displacement reaction representing the prevailing strategy.However,the single-stranded Watson-Crick sticky region that serves as the trigger for strand displacement can also cause leakage reactions by introducing crosstalk in complex DNA circuits.Here,we proposed the toeless and reversible DNA strand displacement reaction based on the Hoogsteen-bond triplex,which is compatible with most of the existing DNA circuits.We demonstrated that our proposed reaction can occur at pH 5 and can be reversed at pH 9.We also observed an approximately linear relationship between the degree of reaction and pH within the range of pH 5-6,providing the potential for precise regulation of the reaction.Meanwhile,by altering the sequence orientation,we have demonstrated that our proposed reaction can be initiated or regulated through the same toeless mechanism without the requirement for protonation in low pH conditions.Based on the proposed reaction principle,we further constructed a variety of DNA nanodevices,including two types of DNA logic gates that rely on pH 5/pH 9 changes for initiating and reversing:the AND gate and the OR gate.We also successfully constructed a DNA Walker based on our proposed reaction modes,which can move along a given track after the introduction of a programmable DNA sequence and complete a cycle after 4 steps.Our findings suggest that this innovative approach will have broad utility in the development of DNA circuits,molecular sensors,and other complex biological systems.展开更多
Strand displacement reaction enables the construction of enzyme-free DNA reaction networks,thus has been widely applied to DNA circuit and nanotechnology.It has the characteristics of high efficiency,universality and ...Strand displacement reaction enables the construction of enzyme-free DNA reaction networks,thus has been widely applied to DNA circuit and nanotechnology.It has the characteristics of high efficiency,universality and regulatability.However,the existing regulation tools cannot enable effective control of the reaction sequence,which undoubtedly limits the construction of complex nucleic acid circuits.Herein,we developed a regulation tool,toehold lock,and achieved strict control of reaction sequence without loss of the main reaction signal output.Furthermore,we applied the tool to scenarios such as seesaw circuits,AND/OR logic gates,and entropy-driven circuits,and respectively demonstrated its significant superiority compared to the original method.We believe that the proposed toehold lock has greatly optimized the efficiency of DNA strand displacement-based networks,and we anticipate that the tool will be widely used in multiple fields.展开更多
Fluorescent labels are widely used in the characterizations of DNA-based reaction network operations.We systematically studied the effects of commonly used fluorescent pairs on thermal stabilities of signal-substrate ...Fluorescent labels are widely used in the characterizations of DNA-based reaction network operations.We systematically studied the effects of commonly used fluorescent pairs on thermal stabilities of signal-substrate duplex and the strand displacement kinetics.It is demonstrated that the modifications of duplex with fluorescent pairs stabilize DNA duplex by up to 3.5℃,and the kinetics of DNA strand displacement circuit is also evidently slowed down.These results highlight the importance of fluorescent pairs towards the kinetic modulation in designing nucleic acid probes and complex DNA dynamic circuits.展开更多
In 2022,Yellow Sea green tide caused by Ulva prolifera reached a historic minimum and the coastal areas of Shandong Peninsula were less affected.However,the largest amount of seaweed biomass has been washed ashore on ...In 2022,Yellow Sea green tide caused by Ulva prolifera reached a historic minimum and the coastal areas of Shandong Peninsula were less affected.However,the largest amount of seaweed biomass has been washed ashore on Lianyungang and Rizhao coasts since 2015.We studied the development pattern of Yellow Sea green tide in 2022,and analyzed the key environmental factors on the growth and drifting,then discussed the possible reasons that resulted in the massive stranding of green tide biomass in Lianyungang and Rizhao.Results show under the combined influence of the east to southeast winds and currents with shoreward anomalies,green tide drifted to the coastal waters between Shandong and Jiangsu provinces and the distribution areas located westward compared with previous years(2008–2021).Floating U.prolifera rafts from the coastal waters of Binhai and Sheyang drifted continuously into the coastal waters of Lianyungang and Rizhao,providing important supplements for Yellow Sea green tide.Because green tide in 2022 distributed close to the coastal waters,the abundant nutrients might support their continuous high growth rate.In addition,the amount of rainfall around Shandong Peninsula from late June to early July were significantly higher than in previous years,which might promote the development of green tide to some extent.展开更多
Closing a single nozzle or multiple nozzles for a temporary casting operation(fewer strands casting)was common in a tundish due to insufficient molten steel or equipment failure.However,nozzle clogging usually happens...Closing a single nozzle or multiple nozzles for a temporary casting operation(fewer strands casting)was common in a tundish due to insufficient molten steel or equipment failure.However,nozzle clogging usually happens under the situation of fewer strands casting.Hence,a temperature deviation index was introduced to characterize the temperature stratification of molten steel for a large capacity tundish,and a new calculation method of residence time curve was used to describe the different flow types of molten steel at each outlet.Based on hydraulics experiment and numerical simulation,important parameters of present case and modified case were compared.Under the situation of fewer strands casting,the proportion of internal-recycle flow after modification decreased from 30.68%to 24.55%;the standard deviation of the response time reduced from 27.59 to 13.16,and the interquartile range of temperature deviation index changed from 0.89 to 0.27.展开更多
Objective To explore if strand breaks of DNA in human early chorionic villus cells in uterus were induced by diagnostic ultrasound and to evaluate the method used for detection of single-stranded breaks and double-str...Objective To explore if strand breaks of DNA in human early chorionic villus cells in uterus were induced by diagnostic ultrasound and to evaluate the method used for detection of single-stranded breaks and double-stranded breaks in human DNA. Methods 60 normal pregnant women aged 20-30, who underwent artificial abortion during 6-8 weeks of gestation, were randomly divided into 2 experimental groups: All 30 cases were exposed to diagnostic ultrasound in uterus for 10 minutes, and 24 hours later chorionic villi were extracted; the other 30 cases were taken as the control group. Single-stranded DNA and double-stranded DNA in villus cells in all cases were isolated by the alkaline unwinding combined with hydroxylapatite chromatography, and were quantitatively detected using 32 P-labeled Alu probe for dot-blotting hybridization. Results There was no significant difference in quantity and percentage in single-stranded DNA and double-stranded DNA between 2 groups (P>0.05). 32 P-Alu probe could only hybridize with human DNA, and could detect DNA isolated from as few as 2.5×10 3 chorionic villus cells and 0.45ng DNA in human leukocytes. Conclusion The results suggested that there were no DNA strand damages in human chorionic villus cells when the uterus was exposed to diagnostic ultrasound for 10 minutes. The method,^(32)P-Alu probe for dot-blotting hybridization, was even more specific, sensitive and accurate than conventional approaches.展开更多
A stranded wires helical spring is formed of a multilayer and coaxial strand of several wires twisted together with the same direction of spiral. Compared with the conventional single wire spring, the stranded wires h...A stranded wires helical spring is formed of a multilayer and coaxial strand of several wires twisted together with the same direction of spiral. Compared with the conventional single wire spring, the stranded wires helical spring has the notable predominance in strength, damping and vibration reduction, which is usually used in aircraft engines, automatic weapons, etc. However, due to its complicated structure, the precise computation of its strength and rigidity need be a correct mathematical model, which then will be imported to finite element analysis software for solutions. Equations on solving geometric parameters, such as external diameters of strands and screw pitches of wires, are put forward in the paper. It also proposes a novel methodology on solving geometric parameters and establishing entity models of the stranded wires helical spring, which provides foundation of computing mechanical parameters by FEA. Then mathematical models on the centre line of the strand and the surface curve of each wire, after closing two ends in a spring, are proposed. Finally, geometric parameters are solved in a case study, and a 3D entity model of a spring with 3 layers and 16 wires is established, which has validated the accuracy of the proposed methodology and the 3D entity mathematical model. The method provides a new way to design stranded wire helical spring.展开更多
Ultrasonic guided wave inspection is an effective non-destructive testing method which can be used for stress level evaluation in steel strands.Unfortunately the propagation velocity of ultrasonic guided waves changes...Ultrasonic guided wave inspection is an effective non-destructive testing method which can be used for stress level evaluation in steel strands.Unfortunately the propagation velocity of ultrasonic guided waves changes due to temperature shift making the prestress measurement of steel strands inaccurate and even sometimes impossible.In the course of solving the problem,this paper reports on quantitative research on the temperature dependence of ultrasonic longitudinal guided wave propagation in long range steel strands.In order to achieve the generation and reception of a chosen longitudinal mode in a steel strand with a helical shaped surface,a new type of magnetostrictive transducer was developed,characterized by a group of thin clips and three identical permanent magnets.Excitation and reception of ultrasonic guided waves in a steel strand were performed experimentally.Experimental results shows that in the temperature range from-4 ℃ to 34 ℃,the propagation velocity of the L（0,1） mode at 160 kHz linearly decreased with increasing temperature and its temperature dependent coefficient was 0.90（m·s-1 ·（℃）-1） which is very close to the theoretical prediction.The effect of dimension deviation between the helical and center wires and the effect of the thermal expansion of the steel strand on ultrasonic longitudinal guided wave propagation were also analyzed.It was found that these effects could be ignored compared with the change in the material mechanical properties of the steel strands due to temperature shift.It was also observed that the longitudinal guided wave mode was somewhat more sensitive to temperature changes compared with conventional ultrasonic waves theoretically.Therefore,it is considered that the temperature effect on ultrasonic longitudinal guided wave propagation in order to improve the accuracy of stress measurement in prestressed steel strands.Quantitative research on the temperature dependence of ultrasonic guided wave propagation in steel strands provides an important basis for the compensation of temperature effects in stress measurement in steel strands by using ultrasonic guided wave inspection.展开更多
Rotor-assembled strand works as a typical tube insert to achieve heat transfer augmentation and scale inhibition in a heat exchanger.In this work, the PIV experiment regarding the flow fields in a circular tube insert...Rotor-assembled strand works as a typical tube insert to achieve heat transfer augmentation and scale inhibition in a heat exchanger.In this work, the PIV experiment regarding the flow fields in a circular tube inserted with rotor-assembled strand was conducted and the flow characteristics on transverse section and longitudinal section were analyzed.The results showed that swirling flow was produced in the tube inserted with rotors and it was particularly strong within the swing diameter of the rotor on the section that contains the rotor;the average turbulence intensity and the radial velocity were improved notably; the velocity vectors on the longitudinal section remained along the direction of a straight line; both the swirling flow and average turbulence intensity were higher for the rotor with three blades than for the rotor with two blades except that the radial velocity was approximate, but they were all reduced by enlarging the lead of the rotor.Characterization of the flow patterns in a circular tube contributes to understanding the heat transfer efficiency and scale inhibition performance of the rotor-assembled strand and provides guidance for its application.展开更多
基金support by the Ministry of Education and Training of Vietnam for this research,under grant no.B2023-MBS-02.
文摘As prestressed concrete(PC)structures age,long-termeffects,e.g.,creep,shrinkage,and prestress losses,compromise their structural performance.Strengthening these aged PC beams has become a crucial matter.One effective solution is to use externally bonded fiber-reinforced polymer(FRP)sheets;however,limited research has been done on aged PC beams using the FRP,especially for beams with unbonded prestressing strands(UPC beams).Therefore,this research investigates the flexural strengthening efficacy of external FRP sheets on aged UPC beams with unbonded tendons.Aging minimally affected the failure modes of UPC beams,with nonstrengthened beams showing flexural failure via rebar yielding and concrete crushing,and FRP-strengthened beams failing due to FRP debonding and tensile reinforcement yielding,though tendons in the aged beams did not yield due to prestress losses,unlike the new beams.The U-wrap anchor curbed widespread debonding,leading to tensile reinforcement yielding and FRP rupture.Aging hastened crack growth and stiffness loss,increasing deflections and reducing load resistance,but FRP reinforcement mitigated these effects,enhancing cracking resistance by 14%over the unstrengthened aged beams and 7%over the new beams while boosting ultimate resistance by 9%above the non-strengthened new beams.Compared to the new FRP-strengthened beams,the aged counterparts had lower cracking resistance,stiffness and capacity—showing 20%higher deflections,7–9%lower serviceability loads,7%–17%reduced ultimate strength and 17%less deformability—due to prestress losses and premature FRP debonding.
基金The National Natural Science Foundation of China under contract Nos 42176214 and 42176170the Zhejiang Provincial Natural Science Foundation of China under contract Nos LZJWZ22E090002 and LZJWY22E090006the Key Program of the President of the Zhejiang Institute of Hydraulics and Estuaries under contract No.ZIHE21Z001.
文摘Finless porpoises(FPs)serve as flagship species and key ecological indicators for assessing environmental quality.However,FPs are challenging to survey due to their elusive behavior and lack of distinctive features.Stranding and sighting events offer essential information on species diversity,distribution patterns,and potential threats.In this study,records from 1986 to 2023 were analyzed to assess the temporal and spatial distribution patterns of FP strandings and sightings in the Qiantang River Estuary,China.Results show an increase in the number of recorded events over time.Seasonal variations were evident,with a peak in strandings and sightings occurring in late winter.The frequency of records was higher during spring and moderate tides compared to neap tides,particularly in hydrologically normal years.Rapidly receding tides and sediment accumulation appear to restrict the activity space of FPs,thereby increasing the frequency of these events.Localized conditions associated with stranding and sighting events were classified into four categories:bifurcation zones,confluence zones,separation zones,and deep channels adjacent to concave banks.Deep channels,which are optimal for shipping,also elevate the risk of FP strandings.These findings offer valuable insights for the development and design of conservation strategies tailored to the needs of FPs in estuarine environments.
基金The National Natural Science Foundation of China(No.52278303).
文摘To tackle the issue of notch frequency and center frequency drift of the L(0,1)mode guided wave in ultra⁃sonic guided wave⁃based stress monitoring of prestressed steel strands,a method using higher⁃order mode plateau fre⁃quencies is adopted.First,the correlation between group velocity peaks and phase velocities at these plateau frequen⁃cies is analyzed.This analysis establishes a quantitative rela⁃tionship between phase velocity and stress in the steel strand,providing a theoretical foundation for stress monitor⁃ing.Then the two⁃dimensional Fourier transform is em⁃ployed to separate wave modes.Dynamic programming techniques are applied in the frequency⁃velocity domain to extract higher⁃order modes.By identifying the group veloc⁃ity peaks of these separated higher⁃order modes,the plateau frequencies of guided waves are determined,enabling indi⁃rect measurement of stress in the steel strand.To validate this method,finite element simulations are conducted under three scenarios.Results show that the higher⁃order modes of transient signals from three different positions can be ac⁃curately extracted,leading to successful cable stress moni⁃toring.This approach effectively circumvents the issue of guided wave frequency drift and improves stress monitoring accuracy.Consequently,it significantly improves the appli⁃cation of ultrasonic guided wave technology in structural health monitoring.
基金financially supported by the National Key Research and Development Program of China(No.2021YFC2701402)the Open Research Fund of State Key Laboratory of Bioelectronics,Southeast University(No.Sklb2021-k06)+1 种基金the Open Foundation of NHC Key Laboratory of Birth Defect for Research and Prevention(Hunan Provincial Maternal and Child Health Care Hospital)(No.KF2020007)the Open Foundation of Translational Medicine National Science and Technology Infrastructure(Shanghai)(No.TMSK-2021-141)。
文摘Strand displacement reaction is a crucial component in the assembly of diverse DNA-based nanodevices,with the toehold-mediated strand displacement reaction representing the prevailing strategy.However,the single-stranded Watson-Crick sticky region that serves as the trigger for strand displacement can also cause leakage reactions by introducing crosstalk in complex DNA circuits.Here,we proposed the toeless and reversible DNA strand displacement reaction based on the Hoogsteen-bond triplex,which is compatible with most of the existing DNA circuits.We demonstrated that our proposed reaction can occur at pH 5 and can be reversed at pH 9.We also observed an approximately linear relationship between the degree of reaction and pH within the range of pH 5-6,providing the potential for precise regulation of the reaction.Meanwhile,by altering the sequence orientation,we have demonstrated that our proposed reaction can be initiated or regulated through the same toeless mechanism without the requirement for protonation in low pH conditions.Based on the proposed reaction principle,we further constructed a variety of DNA nanodevices,including two types of DNA logic gates that rely on pH 5/pH 9 changes for initiating and reversing:the AND gate and the OR gate.We also successfully constructed a DNA Walker based on our proposed reaction modes,which can move along a given track after the introduction of a programmable DNA sequence and complete a cycle after 4 steps.Our findings suggest that this innovative approach will have broad utility in the development of DNA circuits,molecular sensors,and other complex biological systems.
基金the financial support from the National Key Research and Development Program of China(No.2021YFC2701402)the Open Research Fund of State Key Laboratory of Bioelectronics,Southeast University(No.Sklb2021-k06)+2 种基金the Open Foundation of NHC Key Laboratory of Birth Defect for Research and Prevention(Hunan Provincial Maternal and Child Health Care Hospital)(No.KF2020007)Hunan Province Assisted Reproduction and Regenerative Medicine Clinical Demonstration Center Funded Project(No.2020SK4019)the Open Foundation of Translational Medicine National Science and Technology Infrastructure(Shanghai)(No.TMSK-2021-141)。
文摘Strand displacement reaction enables the construction of enzyme-free DNA reaction networks,thus has been widely applied to DNA circuit and nanotechnology.It has the characteristics of high efficiency,universality and regulatability.However,the existing regulation tools cannot enable effective control of the reaction sequence,which undoubtedly limits the construction of complex nucleic acid circuits.Herein,we developed a regulation tool,toehold lock,and achieved strict control of reaction sequence without loss of the main reaction signal output.Furthermore,we applied the tool to scenarios such as seesaw circuits,AND/OR logic gates,and entropy-driven circuits,and respectively demonstrated its significant superiority compared to the original method.We believe that the proposed toehold lock has greatly optimized the efficiency of DNA strand displacement-based networks,and we anticipate that the tool will be widely used in multiple fields.
基金This work was supported by the National Natural Science Foundation of China(No.22073090 No.21991132,No.52021002)the National Key R&D Program of China(No.2020YFA0710703)the Funds of Youth Innovation Promotion Association and the Fun damental Research Funds for the Central Universities.
文摘Fluorescent labels are widely used in the characterizations of DNA-based reaction network operations.We systematically studied the effects of commonly used fluorescent pairs on thermal stabilities of signal-substrate duplex and the strand displacement kinetics.It is demonstrated that the modifications of duplex with fluorescent pairs stabilize DNA duplex by up to 3.5℃,and the kinetics of DNA strand displacement circuit is also evidently slowed down.These results highlight the importance of fluorescent pairs towards the kinetic modulation in designing nucleic acid probes and complex DNA dynamic circuits.
基金Supported by the National Key R&D Program of China(No.2022YFC3106005)the Shandong Provincial Natural Science Foundation(No.ZR2021MD122)+1 种基金the MNR Key Laboratory of Eco-Environmental Science and Technology,China(No.MEEST-2023-04)the Shandong Provincial Key Laboratory of Marine Ecological Environment and Disaster Prevention and Mitigation(No.201708)。
文摘In 2022,Yellow Sea green tide caused by Ulva prolifera reached a historic minimum and the coastal areas of Shandong Peninsula were less affected.However,the largest amount of seaweed biomass has been washed ashore on Lianyungang and Rizhao coasts since 2015.We studied the development pattern of Yellow Sea green tide in 2022,and analyzed the key environmental factors on the growth and drifting,then discussed the possible reasons that resulted in the massive stranding of green tide biomass in Lianyungang and Rizhao.Results show under the combined influence of the east to southeast winds and currents with shoreward anomalies,green tide drifted to the coastal waters between Shandong and Jiangsu provinces and the distribution areas located westward compared with previous years(2008–2021).Floating U.prolifera rafts from the coastal waters of Binhai and Sheyang drifted continuously into the coastal waters of Lianyungang and Rizhao,providing important supplements for Yellow Sea green tide.Because green tide in 2022 distributed close to the coastal waters,the abundant nutrients might support their continuous high growth rate.In addition,the amount of rainfall around Shandong Peninsula from late June to early July were significantly higher than in previous years,which might promote the development of green tide to some extent.
基金the National Natural Science Foundation of China(Grant No.51774031).
文摘Closing a single nozzle or multiple nozzles for a temporary casting operation(fewer strands casting)was common in a tundish due to insufficient molten steel or equipment failure.However,nozzle clogging usually happens under the situation of fewer strands casting.Hence,a temperature deviation index was introduced to characterize the temperature stratification of molten steel for a large capacity tundish,and a new calculation method of residence time curve was used to describe the different flow types of molten steel at each outlet.Based on hydraulics experiment and numerical simulation,important parameters of present case and modified case were compared.Under the situation of fewer strands casting,the proportion of internal-recycle flow after modification decreased from 30.68%to 24.55%;the standard deviation of the response time reduced from 27.59 to 13.16,and the interquartile range of temperature deviation index changed from 0.89 to 0.27.
文摘Objective To explore if strand breaks of DNA in human early chorionic villus cells in uterus were induced by diagnostic ultrasound and to evaluate the method used for detection of single-stranded breaks and double-stranded breaks in human DNA. Methods 60 normal pregnant women aged 20-30, who underwent artificial abortion during 6-8 weeks of gestation, were randomly divided into 2 experimental groups: All 30 cases were exposed to diagnostic ultrasound in uterus for 10 minutes, and 24 hours later chorionic villi were extracted; the other 30 cases were taken as the control group. Single-stranded DNA and double-stranded DNA in villus cells in all cases were isolated by the alkaline unwinding combined with hydroxylapatite chromatography, and were quantitatively detected using 32 P-labeled Alu probe for dot-blotting hybridization. Results There was no significant difference in quantity and percentage in single-stranded DNA and double-stranded DNA between 2 groups (P>0.05). 32 P-Alu probe could only hybridize with human DNA, and could detect DNA isolated from as few as 2.5×10 3 chorionic villus cells and 0.45ng DNA in human leukocytes. Conclusion The results suggested that there were no DNA strand damages in human chorionic villus cells when the uterus was exposed to diagnostic ultrasound for 10 minutes. The method,^(32)P-Alu probe for dot-blotting hybridization, was even more specific, sensitive and accurate than conventional approaches.
基金supported by National Natural Science Foundation for Distinguished Young Scholar of China (Grant No. 50925518)National Natural Science Foundation of China (Grant No. 50775226)+1 种基金Key Project of Ministry of Education of China(Grant No. 109129)Chongqing Municipal Key Scientific and Technological Project of China (Grant No. CSTC2009AC3049)
文摘A stranded wires helical spring is formed of a multilayer and coaxial strand of several wires twisted together with the same direction of spiral. Compared with the conventional single wire spring, the stranded wires helical spring has the notable predominance in strength, damping and vibration reduction, which is usually used in aircraft engines, automatic weapons, etc. However, due to its complicated structure, the precise computation of its strength and rigidity need be a correct mathematical model, which then will be imported to finite element analysis software for solutions. Equations on solving geometric parameters, such as external diameters of strands and screw pitches of wires, are put forward in the paper. It also proposes a novel methodology on solving geometric parameters and establishing entity models of the stranded wires helical spring, which provides foundation of computing mechanical parameters by FEA. Then mathematical models on the centre line of the strand and the surface curve of each wire, after closing two ends in a spring, are proposed. Finally, geometric parameters are solved in a case study, and a 3D entity model of a spring with 3 layers and 16 wires is established, which has validated the accuracy of the proposed methodology and the 3D entity mathematical model. The method provides a new way to design stranded wire helical spring.
基金supported by National Natural Science Foundation of China (Grant No. 10602004,Grant No. 50975006)Beijing Municipal Natural Science Foundation of China (Grant No. 2072003)+1 种基金Beijing Municipal Talent Developing Project of China (Grant No.20081B0501500173)Beijing Municipal Nova Program of China(Grant No. 2008A015)
文摘Ultrasonic guided wave inspection is an effective non-destructive testing method which can be used for stress level evaluation in steel strands.Unfortunately the propagation velocity of ultrasonic guided waves changes due to temperature shift making the prestress measurement of steel strands inaccurate and even sometimes impossible.In the course of solving the problem,this paper reports on quantitative research on the temperature dependence of ultrasonic longitudinal guided wave propagation in long range steel strands.In order to achieve the generation and reception of a chosen longitudinal mode in a steel strand with a helical shaped surface,a new type of magnetostrictive transducer was developed,characterized by a group of thin clips and three identical permanent magnets.Excitation and reception of ultrasonic guided waves in a steel strand were performed experimentally.Experimental results shows that in the temperature range from-4 ℃ to 34 ℃,the propagation velocity of the L（0,1） mode at 160 kHz linearly decreased with increasing temperature and its temperature dependent coefficient was 0.90（m·s-1 ·（℃）-1） which is very close to the theoretical prediction.The effect of dimension deviation between the helical and center wires and the effect of the thermal expansion of the steel strand on ultrasonic longitudinal guided wave propagation were also analyzed.It was found that these effects could be ignored compared with the change in the material mechanical properties of the steel strands due to temperature shift.It was also observed that the longitudinal guided wave mode was somewhat more sensitive to temperature changes compared with conventional ultrasonic waves theoretically.Therefore,it is considered that the temperature effect on ultrasonic longitudinal guided wave propagation in order to improve the accuracy of stress measurement in prestressed steel strands.Quantitative research on the temperature dependence of ultrasonic guided wave propagation in steel strands provides an important basis for the compensation of temperature effects in stress measurement in steel strands by using ultrasonic guided wave inspection.
基金Supported by the National Natural Science Foundation of China(51576012)
文摘Rotor-assembled strand works as a typical tube insert to achieve heat transfer augmentation and scale inhibition in a heat exchanger.In this work, the PIV experiment regarding the flow fields in a circular tube inserted with rotor-assembled strand was conducted and the flow characteristics on transverse section and longitudinal section were analyzed.The results showed that swirling flow was produced in the tube inserted with rotors and it was particularly strong within the swing diameter of the rotor on the section that contains the rotor;the average turbulence intensity and the radial velocity were improved notably; the velocity vectors on the longitudinal section remained along the direction of a straight line; both the swirling flow and average turbulence intensity were higher for the rotor with three blades than for the rotor with two blades except that the radial velocity was approximate, but they were all reduced by enlarging the lead of the rotor.Characterization of the flow patterns in a circular tube contributes to understanding the heat transfer efficiency and scale inhibition performance of the rotor-assembled strand and provides guidance for its application.
