Magnetohydrodynamic(MHD)radiative chemically reactive mixed convection flow of a hybrid nanofluid(Al_(2)O_(3)–Cu/H_(2)O)across an inclined,porous,and stretched sheet is examined in this study,along with its unsteady ...Magnetohydrodynamic(MHD)radiative chemically reactive mixed convection flow of a hybrid nanofluid(Al_(2)O_(3)–Cu/H_(2)O)across an inclined,porous,and stretched sheet is examined in this study,along with its unsteady heat and mass transport properties.The hybrid nanofluid’s enhanced heat transfer efficiency is a major benefit in high-performance engineering applications.It is composed of two separate nanoparticles suspended in a base fluid and is chosen for its improved thermal properties.Thermal radiation,chemical reactions,a transverse magnetic field,surface stretching with time,injection or suction through the porous medium,and the effect of inclination,which introduces gravity-induced buoyancy forces,are all important physical phenomena that are taken into account in the analysis.A system of nonlinear ordinary differential equations(ODEs)is derived from the governing partial differential equations for mass,momentum,and energy by applying suitable similarity transformations.This simplifies the modeling procedure.The bvp4c solver in MATLAB is then used to numerically solve these equations.Different governing parameters modify temperature,concentration,and velocity profiles in graphs and tables.These factors include radiation intensity,chemical reaction rate,magnetic field strength,unsteadiness,suction/injection velocity,inclination angle,and nanoparticle concentration.A complex relationship between buoyancy and magnetic factors makes hybrid nanofluids better at heat transmission than regular ones.Thermal systems including cooling technologies,thermal coatings,and electronic heat management benefit from these findings.展开更多
This paper discusses the model of the boundary layer(BL)flow and the heat transfer characteristics of hybrid nanofluid(HNF)over shrinking/stretching disks.In addition,the thermal radiation and the impact of velocity a...This paper discusses the model of the boundary layer(BL)flow and the heat transfer characteristics of hybrid nanofluid(HNF)over shrinking/stretching disks.In addition,the thermal radiation and the impact of velocity and thermal slip boundary conditions are also examined.The considered hybrid nano-fluid contains silver(Ag)and iron oxide(Fe_(3)O_(4))nanoparticles dispersed in the water to prepare the Ag-Fe_(3)O_(4)/water-based hybrid nanofluid.The requisite posited partial differential equations model is converted to ordinary differential equations using similarity transformations.For a numerical solution,the shooting method in Maple is employed.Moreover,the duality in solutions is achieved for both cases of the disk(stretching(λ>0)and shrinking(λ<0)).At the same time,a unique solution is observed for λ=0.No solution is found for them at λ<λ_(c),whereas the solutions are split at the λ=λ_(c).Besides,the value of the λ_(c) is dependent on the φ_(hnf).Meanwhile,the values of f″(0)and -θ′(0)intensified with increasing φ_(hnf).Stability analysis has been applied using bvp4c in MATLAB software due to a dual solution.Furthermore,analysis shows that the first solution is stable and feasible physically.For the slip parameters,an increase in the velocity slip parameter increases the velocity and shear stress profiles while increasing the temperature profile in the first solutions.While the rise in thermal slip parameter reduces the temperature profile nanoparticle volume fractions increase it.展开更多
In this work,a morphology transition mode is revealed in ultra-high molecular weight polyethylene(UHMWPE)when stretching at 120℃:moving from the slightly deformed region to the necked region,the morphology transfers ...In this work,a morphology transition mode is revealed in ultra-high molecular weight polyethylene(UHMWPE)when stretching at 120℃:moving from the slightly deformed region to the necked region,the morphology transfers from small spherulites to a mixture of transcrystalline and enlarged spherulites,and finally to pure transcrystalline;meanwhile,the lamellae making up the transcrystalline or spherulite were fragmented into smaller ones;spatial scan by wide-angle X-ray scattering(WAXS)and small angle X-ray scattering(SAXS)revealed that the crystallinity is increased from 25.3%to 30.1%and the crystal orientation was enhanced greatly,but the lamellae orientation was quite weak.The rise of enlarged spherulites or a mixture of transcrystalline and spherulites can also be found in UHMWPE stretched at 140 and 148℃,whereas absent in UHMWPE stretched at 30℃.In situ WAXS/SAXS measurements suggest that during stretching at 30℃,the crystallinity is reduced drastically,and a few voids are formed as the size increases from 50 nm to 210 nm;during stretching at 120℃,the crystallinity is reduced only slightly,and the kinking of lamellae occurs at large Hencky strain;during stretching at 140 and 148℃,an increase in crystallinity with stretching strain can be found,and the lamellae are also kinked.Taking the microstructure and morphology transition into consideration,a mesoscale morphology transition mode is proposed,in the stretching-induced crystallization the fragmented lamellae can be rearranged into new supra-structures such as spherulite or transcrystalline during hot stretching.展开更多
In this paper,the authors examine various slip effects on themagnetic field and thermal radiative impacts on the flow,mass and heat transfer of a Jeffrey nanofluid over a 2-dimensional inclined stretching sheet by a p...In this paper,the authors examine various slip effects on themagnetic field and thermal radiative impacts on the flow,mass and heat transfer of a Jeffrey nanofluid over a 2-dimensional inclined stretching sheet by a porous media.The offered work is modelled to be in the form of a combination of coupled highly nonlinear partial differential equations in dimensional contexts.Governing equations were obtained,dimensionless parameters were defined in terms of similarity parameters,and the solutionswere obtained by the Homotopy Analysis Method(HAM).The analysis is significant as the effects of viscosity are identified and the important parameters are to be determined that could eventually control a type of flowbehaviour,especially in promoting the flowand inhibiting flowof velocity,temperature,and concentrations.The findings show that such an increase in themagnetic parameter decreases the velocity profile by approximately 15%due to more Lorentz forces,and thermal radiation increases the temperature profile by up to 25%,therefore,enhancing the rate of heat transfer.The process of Brownian motion and thermophoresis increases the depth of the thermal boundary layer by 10–20 percent and reduces in concentration profiles by 12 percent when the Brownian motion parameter increases.A velocity slip parameter lowers the velocity field by about 18 percent,and a parameter of permeability lowers the momentum of flow by another 10 percent.The HAM solutions show very high accuracy levels,having an order of convergence at level 15 and errormargins are well below 0.01 percent compared to the earlier studies.All these findings can provide profound knowledge in improving heat transmission in non-Newtonian fluid systems and can be used in biomedical engineering,thermal insulation,and industrial processes such as polymer extrusion and cooling technology.Principles of heat and mass transfer give us the crucial foundation on which to study the behavior of heat andmaterial flows in other engineering and scientific disciplines.Such principles apply to various fields of study,including the following engineering fields:mechanical,chemical,aerospace,civil,and environmental.展开更多
Highly oriented poly(vinylidene fluoride)(PVDF)ultrathin films with differentβ-phase contents were prepared using the melt-draw method.The effect ofβ-phase content onα-βphase transition of highly oriented PVDF ult...Highly oriented poly(vinylidene fluoride)(PVDF)ultrathin films with differentβ-phase contents were prepared using the melt-draw method.The effect ofβ-phase content onα-βphase transition of highly oriented PVDF ultrathin films induced by stretching was investigated using transmission electron microscopy(TEM)and Fourier transform infrared(FTIR)spectroscopy.The results show that stretching can enhance the crystallinity and increase the average thickness of the lamellae.A fullα-βphase transition can be achieved for PVDF ultrathin films of 20.6%βphase stretched to aλ(stretching ratio)of 1.5,while fewαphases still exist for ultrathin films of 35.0%βphase,together with bent and tilted lamellae.Compared to thicker PVDF films undergoing stretching-inducedα-βphase transition,the higherα-βphase transition efficiency of the PVDF ultrathin films can be attributed to the parallel aligned lamellar structure.Moreover,a higherβ-phase content can suppressα-βphase transition because of the stress concentration effect ofβ-phase.Ultimately,these results provide valuable insights into the stretching-inducedα-βphase transition of PVDF ultrathin films.展开更多
Background:Stretching has wide appeal,but there seems to exist some mismatch between its purported applications and what the evidence shows.There is compelling evidence for some stretching applications,but for others,...Background:Stretching has wide appeal,but there seems to exist some mismatch between its purported applications and what the evidence shows.There is compelling evidence for some stretching applications,but for others,the evidence seems heterogeneous or unsupportive.The discrepancies even affect some systematic reviews,possibly due to heterogeneous eligibility criteria and search strategies.This consensus paper seeks to unify the divergent findings on stretching and its implications for both athletic performance and clinical practices by delivering evidence-based recommendations.Methods:A panel of 20 experts with a blend of practical experience and scholarly knowledge was assembled.The panel meticulously reviewed existing systematic reviews,defined key terminologies(e.g.,consensus definitions for different stretching modes),and crafted guidelines using a Delphi consensus approach(minimum required agreement:80%).The analysis focused on 8 topics,including stretching's acute and chronic(long-term)effects on range of motion,strength performance,muscle hypertrophy,stiffness,injury prevention,muscle recovery,posture correction,and cardiovascular health.Results:There was consensus that chronic and acute stretching(a)improves range of motion(although alternatives exist)and(b)reduces muscle stiffness(which may not always be desirable);the panel also agreed that chronic stretching(c)may promote vascular health,but more research is warranted.In contrast,consensus was found that stretch training does not(a)contribute substantively to muscle growth,(b)serve as an allencompassing injury prevention strategy,(c)improve posture,or(d)acutely enhance post-exercise recovery.Conclusion:These recommendations provide guidance for athletes and practitioners,highlighting research gaps that should be addressed to more comprehensively understand the full scope of stretching effects.展开更多
Maximizing the efficiency of thermal engineering equipment involves minimizing entropy generation,which arises from irreversible processes.This study examines thermal transport and entropy generation in viscous flow o...Maximizing the efficiency of thermal engineering equipment involves minimizing entropy generation,which arises from irreversible processes.This study examines thermal transport and entropy generation in viscous flow over a radially stretching disk,incorporating the effects of magnetohydrodynamics(MHD),viscous dissipation,Joule heating,and radiation.Similarity transformations are used to obtain dimensionless nonlinear ordinary differential equations(ODEs)from the governing coupled partial differential equations(PDEs).The converted equations are then solved by using the BVP4C solver in MATLAB.To validate the findings,the results are compared with previously published studies under fixed parameter conditions,demonstrating strong agreement.Various key parameters are analyzed graphically to assess their impact on velocity and temperature distributions.Additionally,Bejan number and entropy generation variations are presented for different physical parameters.The injection parameter(S<0)increases the heat transfer rate,while the suction parameter(S>0)reduces it,exhibiting similar effects on fluid velocity.The magnetic parameter(M)effectively decreases entropy generation within the range of approximately 0≤η≤0.6.Beyond this interval,its influence diminishes as entropy generation values converge,with similar trends observed for the Bejan number.Furthermore,increased thermal radiation intensity is identified as a critical factor in enhancing entropy generation and the Bejan number.展开更多
In this work,the lamellar structural evolution and microvoids variations of βpolypropylene(β-PP)during the processing of two different stretching methods,sequential biaxial stretching and simultaneous biaxial stretc...In this work,the lamellar structural evolution and microvoids variations of βpolypropylene(β-PP)during the processing of two different stretching methods,sequential biaxial stretching and simultaneous biaxial stretching,were investigated in detail.It was found that different stretching methods led to significantly different lamellae deformation modes,and the microporous membranes obtained from the simultaneous biaxial stretching exhibited better mechanical properties.For the sequential biaxial stretching,abundant coarse fibers originated from the tight accumulation of the lamellae parallel to the longitudinal stretching direction,whereas the lamellae perpendicular to the stretching direction were easily deformed and separated.Those coarse fibers were difficult to be separated to form micropores during the subsequent transverse stretching process,resulting in a poor micropores distribution.However,for the simultaneous biaxial stretching,theβcrystal had the same deformation mode,that is,the lamellae distributed in different directions were all destroyed,forming abundant microvoids and little coarse fibers.展开更多
Purpose： The present study aimed to examine the effect of static stretching （SS） and a sport-specific dynamic stretching （DS） session at two specific post-stretch time intervals in highly trained female athletes ...Purpose： The present study aimed to examine the effect of static stretching （SS） and a sport-specific dynamic stretching （DS） session at two specific post-stretch time intervals in highly trained female athletes （age 19.90 ± 1.60 years; height 1.80 ±0.06 m; mass 76.87 ± 9.95 kg） on kinetic parameters of peak force, time-to-takeoff, and rate of force development. Methods： The data were collected over 3 days （randomized within subject design with control session）. Following each stretch session （SS vs. DS vs. control） of equal duration （7 min total： 30 s per targeted muscle group） participants performed countermovement jumping on a force platform at 1 and 15 rain after stretching. Results： The DS session significantly improved upon kinetic variables of rate of force development, peak force, and time-to-takeoffrelative to SS at 1 min after stretching. No significant effect was found at 15 min. Conclusion： Together these findings suggest that when training and competing to jump quickly and maximally the female athlete should incorporate DS instead of SS as part of their pre-competition warm-up, but conduct performance within 15 min of their warm-up to elicit maximal gains展开更多
BACKGROUND Flexibility,agility and muscle strength are key factors to either win or lose a game.Recently the effect of a new technique,deep transverse friction massage(DTFM)on muscle extensibility as compared to tradi...BACKGROUND Flexibility,agility and muscle strength are key factors to either win or lose a game.Recently the effect of a new technique,deep transverse friction massage(DTFM)on muscle extensibility as compared to traditional stretching techniques has been examined.AIM To compare the effect of DTFM vs static and dynamic stretching techniques on the hamstring’s extensibility,agility,and strength amongst Lebanese and Syrian football players.Recording the incidence of non-contact hamstring muscle injury was a secondary objective.METHODS This study is a single-blinded prospective longitudinal randomized controlled trial.The experiment took place over a period of four weeks.Football players were randomized into three intervention groups(static stretching;dynamic stretching;DTFM).Participants of each group were followed-up carefully by assessors during their intervention sessions three times per week,for a total of 12 sessions and during the data collection.Extensibility,agility,and strength were compared between intervention groups at(baseline;acute;and chronic)phases.Straight leg raise and 1 repetition maximum tests were used to measure the dominant leg hamstring muscle extensibility and maximal strength respectively.T-drill test was used to assess the lower extremities agility.RESULTS Of 103 Lebanese and Syrian male football players aged between 18 and 35 were sampled from Damascus-Syria and South of Lebanon to participate in this study.Between-groups measures of acute strength(P=0.011)and chronic extensibility(P=0.000)solely showed a significant difference,and the static group showed to be superior as compared to the other groups.No loss to follow-up or protocol violation was recorded.CONCLUSION Static stretching is showing to be superior to the other techniques used,regarding gaining long-term extensibility and short-term maximal muscle strength.In addition,DTFM showed improvements but did not outweigh the effects on footballers’performance when comparing it to static and dynamic techniques.Finally,no difference between the interventions is recorded regarding the rate of muscle injuries incidence.展开更多
Purpose： The purpose of this study was to determine the extent that a static stretching program could increase heart rate （HR） and oxygen consumption （VO2）, and if the increases were sufficient to serve as a warm...Purpose： The purpose of this study was to determine the extent that a static stretching program could increase heart rate （HR） and oxygen consumption （VO2）, and if the increases were sufficient to serve as a warm-up for aerobic activity. Methods： The HR and VO2 of 15 male and 16 female college students were measured after either 12 min of passive static stretching （SS）, or 12 rain pseudo-stretching （PS）, which consisted of moving through the stretching positions without placing the muscles on stretch. Four different lower body stretches were used with each stretch held for 30 s before the participant moved to a different position, with the circuit being repeated four times. VO2 was determined by averaging breath-by-breath measures over the total 12 min. HR was obtained every 30 s and the 24 values were averaged. Warm-up benefit was determined from the 02 deficit accrued during 7-min cycling at 60% VOzmax. Results： HR （beats/rain, mean 4. SD） for SS （84 ± 11） was a significant （p 〈 0.05） 9% greater than PS （78 ± 12）. Similarly, VO2 （mL/min, mean 4. SD） for SS （0.53 ± 0.13） was a significant 44% greater than PS （0.38 ± 0.11）. The O2 deficit （L, mean 4, SD） for SS （0.64 ± 1.54） was not different from PS （0.72 ± 1.61）. Conclusion： These data indicate that passive static stretching increases both HR and VO2, indicating that metabolic activity can be increased without muscle activation. The magnitude of the increases, however, is not sufficient to elicit a warm-up effect.展开更多
Changes of dyeing behavior of wool after stretching - setting treatment are studied.Effects of stretching - setting on wool structure are analyzed.It is concluded that stretching - setting treatment not only reduces w...Changes of dyeing behavior of wool after stretching - setting treatment are studied.Effects of stretching - setting on wool structure are analyzed.It is concluded that stretching - setting treatment not only reduces wool diameter and increases wool length,but also brings about low-temperature dyeing of wool.展开更多
he lithosphere stretching, subsidence and basement thermal history of the Songliao, Yinggehai and Qiongdongnan basins in East China have been investigated by using backstripping technique and stretching models. ...he lithosphere stretching, subsidence and basement thermal history of the Songliao, Yinggehai and Qiongdongnan basins in East China have been investigated by using backstripping technique and stretching models. The subsidence curve of the Songliao basin characterizes a rift basin history evolving from synrift rapid subsidence to postrift thermal subsidence. The calculated stretching factor of the basin is about 1.8 to 2.0 and the horizontal extension is about 55-60 km. The reconstructed subsidence curves of the Qiongdongnan and Yinggehai basins show that the basins underwent several rapid subsidence episodes, which has been interpreted as the result of a multiple stretching of the lithosphere. The total mean stretching factors of the Qiongdongnan and Yinggehai basins, calculated by using a multiple instantaneous stretching model, are about 1.7-1.9 and 2.5-3.0 respectively. The stretching factors of these basins, estimated from subsidence, are consistent with those determined from crustal thinning. The reconstructed thermal histories of these basins are in agreement with the geological observation.展开更多
The problem of the steady magnetohydrodynamic （MHD） stagnation-point flow of an incompressible viscous fluid over a stretching sheet is studied. The effect of an induced magnetic field is taken into account. The non...The problem of the steady magnetohydrodynamic （MHD） stagnation-point flow of an incompressible viscous fluid over a stretching sheet is studied. The effect of an induced magnetic field is taken into account. The nonlinear partial differential equations are transformed into ordinary differential equations via the similarity transformation. The transformed boundary layer equations are solved numerically using the shooting method. Numerical results are obtained for various magnetic parameters and Prandtl numbers. The effects of the induced magnetic field on the skin friction coefficient, the local Nusselt number, the velocity, and the temperature profiles are presented graphically and discussed in detail.展开更多
A boundary layer analysis is presented for non-Newtonian fluid flow and heat transfer over a nonlinearly stretching surface. The Casson fluid model is used to characterize the non-Newtonian fluid behavior. By using su...A boundary layer analysis is presented for non-Newtonian fluid flow and heat transfer over a nonlinearly stretching surface. The Casson fluid model is used to characterize the non-Newtonian fluid behavior. By using suitable transformations, the governing partial differential equations corresponding to the momentum and energy equations are converted into non-linear ordinary differential equations. Numerical solutions of these equations are obtained with the shooting method. The effect of increasing Casson parameter is to suppress the velocity field. However the temperature is enhanced with the increasing Casson parameter.展开更多
The steady flow and heat transfer of a hybrid nanofluid past a permeable stretching/shrinking wedge with magnetic field and radiation effects are studied. The governing equations of the hybrid nanofluid are converted ...The steady flow and heat transfer of a hybrid nanofluid past a permeable stretching/shrinking wedge with magnetic field and radiation effects are studied. The governing equations of the hybrid nanofluid are converted to the similarity equations by techniques of the similarity transformation. The bvp4c function that is available in MATLAB software is utilized for solving the similarity equations numerically. The numerical results are obtained for selected different values of parameters. The results discover that two solutions exist, up to a certain value of the stretching/shrinking and suction strengths. The critical value in which the solution is in existence decreases as nanoparticle volume fractions for copper and wedge angle parameter increase. It is also found that the hybrid nanofluid enhances the heat transfer rate compared with the regular nanofluid. The reduction of the heat transfer rate is observed with the increase in radiation parameter. The temporal stability analysis is performed to analyze the stability of the dual solutions, and it is revealed that only one of them is stable and physically reliable.展开更多
This article studies the influence of polymers on drag reduction and heat transfer enhancement of a nanofluid past a uniformly heated permeable vertically stretching surface. Our prime focus is on analyzing the possib...This article studies the influence of polymers on drag reduction and heat transfer enhancement of a nanofluid past a uniformly heated permeable vertically stretching surface. Our prime focus is on analyzing the possible effects of polymer inclusion in the nanofluid on drag coefficient, Nusselt number and Sherwood number. Dispersion model is considered to study the behavior of fluid flow and heat transfer in the presence of nanoparticles. Molecular approach is opted to explore polymer addition in the base fluid. An extra stress arises in the momentum equation as an outcome of polymer stretching. The governing boundary layer equations are solved numerically. Dependence of physical quantities of engineering interest on different flow parameters is studied. Reduction in drag coefficient, Nusselt number and Sherwood number is noticed because of polymer additives.展开更多
文摘Magnetohydrodynamic(MHD)radiative chemically reactive mixed convection flow of a hybrid nanofluid(Al_(2)O_(3)–Cu/H_(2)O)across an inclined,porous,and stretched sheet is examined in this study,along with its unsteady heat and mass transport properties.The hybrid nanofluid’s enhanced heat transfer efficiency is a major benefit in high-performance engineering applications.It is composed of two separate nanoparticles suspended in a base fluid and is chosen for its improved thermal properties.Thermal radiation,chemical reactions,a transverse magnetic field,surface stretching with time,injection or suction through the porous medium,and the effect of inclination,which introduces gravity-induced buoyancy forces,are all important physical phenomena that are taken into account in the analysis.A system of nonlinear ordinary differential equations(ODEs)is derived from the governing partial differential equations for mass,momentum,and energy by applying suitable similarity transformations.This simplifies the modeling procedure.The bvp4c solver in MATLAB is then used to numerically solve these equations.Different governing parameters modify temperature,concentration,and velocity profiles in graphs and tables.These factors include radiation intensity,chemical reaction rate,magnetic field strength,unsteadiness,suction/injection velocity,inclination angle,and nanoparticle concentration.A complex relationship between buoyancy and magnetic factors makes hybrid nanofluids better at heat transmission than regular ones.Thermal systems including cooling technologies,thermal coatings,and electronic heat management benefit from these findings.
基金the Researchers Supporting Project number(RSPD2025R997),King Saud University,Riyadh,Saudi Arabia.
文摘This paper discusses the model of the boundary layer(BL)flow and the heat transfer characteristics of hybrid nanofluid(HNF)over shrinking/stretching disks.In addition,the thermal radiation and the impact of velocity and thermal slip boundary conditions are also examined.The considered hybrid nano-fluid contains silver(Ag)and iron oxide(Fe_(3)O_(4))nanoparticles dispersed in the water to prepare the Ag-Fe_(3)O_(4)/water-based hybrid nanofluid.The requisite posited partial differential equations model is converted to ordinary differential equations using similarity transformations.For a numerical solution,the shooting method in Maple is employed.Moreover,the duality in solutions is achieved for both cases of the disk(stretching(λ>0)and shrinking(λ<0)).At the same time,a unique solution is observed for λ=0.No solution is found for them at λ<λ_(c),whereas the solutions are split at the λ=λ_(c).Besides,the value of the λ_(c) is dependent on the φ_(hnf).Meanwhile,the values of f″(0)and -θ′(0)intensified with increasing φ_(hnf).Stability analysis has been applied using bvp4c in MATLAB software due to a dual solution.Furthermore,analysis shows that the first solution is stable and feasible physically.For the slip parameters,an increase in the velocity slip parameter increases the velocity and shear stress profiles while increasing the temperature profile in the first solutions.While the rise in thermal slip parameter reduces the temperature profile nanoparticle volume fractions increase it.
基金supported by the National Natural Science Foundation of China(Nos.52003249,12072325 and 52273027)the Natural Science Foundation of Henan(No.242300421236).
文摘In this work,a morphology transition mode is revealed in ultra-high molecular weight polyethylene(UHMWPE)when stretching at 120℃:moving from the slightly deformed region to the necked region,the morphology transfers from small spherulites to a mixture of transcrystalline and enlarged spherulites,and finally to pure transcrystalline;meanwhile,the lamellae making up the transcrystalline or spherulite were fragmented into smaller ones;spatial scan by wide-angle X-ray scattering(WAXS)and small angle X-ray scattering(SAXS)revealed that the crystallinity is increased from 25.3%to 30.1%and the crystal orientation was enhanced greatly,but the lamellae orientation was quite weak.The rise of enlarged spherulites or a mixture of transcrystalline and spherulites can also be found in UHMWPE stretched at 140 and 148℃,whereas absent in UHMWPE stretched at 30℃.In situ WAXS/SAXS measurements suggest that during stretching at 30℃,the crystallinity is reduced drastically,and a few voids are formed as the size increases from 50 nm to 210 nm;during stretching at 120℃,the crystallinity is reduced only slightly,and the kinking of lamellae occurs at large Hencky strain;during stretching at 140 and 148℃,an increase in crystallinity with stretching strain can be found,and the lamellae are also kinked.Taking the microstructure and morphology transition into consideration,a mesoscale morphology transition mode is proposed,in the stretching-induced crystallization the fragmented lamellae can be rearranged into new supra-structures such as spherulite or transcrystalline during hot stretching.
文摘In this paper,the authors examine various slip effects on themagnetic field and thermal radiative impacts on the flow,mass and heat transfer of a Jeffrey nanofluid over a 2-dimensional inclined stretching sheet by a porous media.The offered work is modelled to be in the form of a combination of coupled highly nonlinear partial differential equations in dimensional contexts.Governing equations were obtained,dimensionless parameters were defined in terms of similarity parameters,and the solutionswere obtained by the Homotopy Analysis Method(HAM).The analysis is significant as the effects of viscosity are identified and the important parameters are to be determined that could eventually control a type of flowbehaviour,especially in promoting the flowand inhibiting flowof velocity,temperature,and concentrations.The findings show that such an increase in themagnetic parameter decreases the velocity profile by approximately 15%due to more Lorentz forces,and thermal radiation increases the temperature profile by up to 25%,therefore,enhancing the rate of heat transfer.The process of Brownian motion and thermophoresis increases the depth of the thermal boundary layer by 10–20 percent and reduces in concentration profiles by 12 percent when the Brownian motion parameter increases.A velocity slip parameter lowers the velocity field by about 18 percent,and a parameter of permeability lowers the momentum of flow by another 10 percent.The HAM solutions show very high accuracy levels,having an order of convergence at level 15 and errormargins are well below 0.01 percent compared to the earlier studies.All these findings can provide profound knowledge in improving heat transmission in non-Newtonian fluid systems and can be used in biomedical engineering,thermal insulation,and industrial processes such as polymer extrusion and cooling technology.Principles of heat and mass transfer give us the crucial foundation on which to study the behavior of heat andmaterial flows in other engineering and scientific disciplines.Such principles apply to various fields of study,including the following engineering fields:mechanical,chemical,aerospace,civil,and environmental.
基金financially supported from the National Natural Science Foundation of China(Nos.52203026 and 52027804)。
文摘Highly oriented poly(vinylidene fluoride)(PVDF)ultrathin films with differentβ-phase contents were prepared using the melt-draw method.The effect ofβ-phase content onα-βphase transition of highly oriented PVDF ultrathin films induced by stretching was investigated using transmission electron microscopy(TEM)and Fourier transform infrared(FTIR)spectroscopy.The results show that stretching can enhance the crystallinity and increase the average thickness of the lamellae.A fullα-βphase transition can be achieved for PVDF ultrathin films of 20.6%βphase stretched to aλ(stretching ratio)of 1.5,while fewαphases still exist for ultrathin films of 35.0%βphase,together with bent and tilted lamellae.Compared to thicker PVDF films undergoing stretching-inducedα-βphase transition,the higherα-βphase transition efficiency of the PVDF ultrathin films can be attributed to the parallel aligned lamellar structure.Moreover,a higherβ-phase content can suppressα-βphase transition because of the stress concentration effect ofβ-phase.Ultimately,these results provide valuable insights into the stretching-inducedα-βphase transition of PVDF ultrathin films.
文摘Background:Stretching has wide appeal,but there seems to exist some mismatch between its purported applications and what the evidence shows.There is compelling evidence for some stretching applications,but for others,the evidence seems heterogeneous or unsupportive.The discrepancies even affect some systematic reviews,possibly due to heterogeneous eligibility criteria and search strategies.This consensus paper seeks to unify the divergent findings on stretching and its implications for both athletic performance and clinical practices by delivering evidence-based recommendations.Methods:A panel of 20 experts with a blend of practical experience and scholarly knowledge was assembled.The panel meticulously reviewed existing systematic reviews,defined key terminologies(e.g.,consensus definitions for different stretching modes),and crafted guidelines using a Delphi consensus approach(minimum required agreement:80%).The analysis focused on 8 topics,including stretching's acute and chronic(long-term)effects on range of motion,strength performance,muscle hypertrophy,stiffness,injury prevention,muscle recovery,posture correction,and cardiovascular health.Results:There was consensus that chronic and acute stretching(a)improves range of motion(although alternatives exist)and(b)reduces muscle stiffness(which may not always be desirable);the panel also agreed that chronic stretching(c)may promote vascular health,but more research is warranted.In contrast,consensus was found that stretch training does not(a)contribute substantively to muscle growth,(b)serve as an allencompassing injury prevention strategy,(c)improve posture,or(d)acutely enhance post-exercise recovery.Conclusion:These recommendations provide guidance for athletes and practitioners,highlighting research gaps that should be addressed to more comprehensively understand the full scope of stretching effects.
文摘Maximizing the efficiency of thermal engineering equipment involves minimizing entropy generation,which arises from irreversible processes.This study examines thermal transport and entropy generation in viscous flow over a radially stretching disk,incorporating the effects of magnetohydrodynamics(MHD),viscous dissipation,Joule heating,and radiation.Similarity transformations are used to obtain dimensionless nonlinear ordinary differential equations(ODEs)from the governing coupled partial differential equations(PDEs).The converted equations are then solved by using the BVP4C solver in MATLAB.To validate the findings,the results are compared with previously published studies under fixed parameter conditions,demonstrating strong agreement.Various key parameters are analyzed graphically to assess their impact on velocity and temperature distributions.Additionally,Bejan number and entropy generation variations are presented for different physical parameters.The injection parameter(S<0)increases the heat transfer rate,while the suction parameter(S>0)reduces it,exhibiting similar effects on fluid velocity.The magnetic parameter(M)effectively decreases entropy generation within the range of approximately 0≤η≤0.6.Beyond this interval,its influence diminishes as entropy generation values converge,with similar trends observed for the Bejan number.Furthermore,increased thermal radiation intensity is identified as a critical factor in enhancing entropy generation and the Bejan number.
基金supported by the National Natural Science Foundation of China(No.51721091).
文摘In this work,the lamellar structural evolution and microvoids variations of βpolypropylene(β-PP)during the processing of two different stretching methods,sequential biaxial stretching and simultaneous biaxial stretching,were investigated in detail.It was found that different stretching methods led to significantly different lamellae deformation modes,and the microporous membranes obtained from the simultaneous biaxial stretching exhibited better mechanical properties.For the sequential biaxial stretching,abundant coarse fibers originated from the tight accumulation of the lamellae parallel to the longitudinal stretching direction,whereas the lamellae perpendicular to the stretching direction were easily deformed and separated.Those coarse fibers were difficult to be separated to form micropores during the subsequent transverse stretching process,resulting in a poor micropores distribution.However,for the simultaneous biaxial stretching,theβcrystal had the same deformation mode,that is,the lamellae distributed in different directions were all destroyed,forming abundant microvoids and little coarse fibers.
文摘Purpose： The present study aimed to examine the effect of static stretching （SS） and a sport-specific dynamic stretching （DS） session at two specific post-stretch time intervals in highly trained female athletes （age 19.90 ± 1.60 years; height 1.80 ±0.06 m; mass 76.87 ± 9.95 kg） on kinetic parameters of peak force, time-to-takeoff, and rate of force development. Methods： The data were collected over 3 days （randomized within subject design with control session）. Following each stretch session （SS vs. DS vs. control） of equal duration （7 min total： 30 s per targeted muscle group） participants performed countermovement jumping on a force platform at 1 and 15 rain after stretching. Results： The DS session significantly improved upon kinetic variables of rate of force development, peak force, and time-to-takeoffrelative to SS at 1 min after stretching. No significant effect was found at 15 min. Conclusion： Together these findings suggest that when training and competing to jump quickly and maximally the female athlete should incorporate DS instead of SS as part of their pre-competition warm-up, but conduct performance within 15 min of their warm-up to elicit maximal gains
文摘BACKGROUND Flexibility,agility and muscle strength are key factors to either win or lose a game.Recently the effect of a new technique,deep transverse friction massage(DTFM)on muscle extensibility as compared to traditional stretching techniques has been examined.AIM To compare the effect of DTFM vs static and dynamic stretching techniques on the hamstring’s extensibility,agility,and strength amongst Lebanese and Syrian football players.Recording the incidence of non-contact hamstring muscle injury was a secondary objective.METHODS This study is a single-blinded prospective longitudinal randomized controlled trial.The experiment took place over a period of four weeks.Football players were randomized into three intervention groups(static stretching;dynamic stretching;DTFM).Participants of each group were followed-up carefully by assessors during their intervention sessions three times per week,for a total of 12 sessions and during the data collection.Extensibility,agility,and strength were compared between intervention groups at(baseline;acute;and chronic)phases.Straight leg raise and 1 repetition maximum tests were used to measure the dominant leg hamstring muscle extensibility and maximal strength respectively.T-drill test was used to assess the lower extremities agility.RESULTS Of 103 Lebanese and Syrian male football players aged between 18 and 35 were sampled from Damascus-Syria and South of Lebanon to participate in this study.Between-groups measures of acute strength(P=0.011)and chronic extensibility(P=0.000)solely showed a significant difference,and the static group showed to be superior as compared to the other groups.No loss to follow-up or protocol violation was recorded.CONCLUSION Static stretching is showing to be superior to the other techniques used,regarding gaining long-term extensibility and short-term maximal muscle strength.In addition,DTFM showed improvements but did not outweigh the effects on footballers’performance when comparing it to static and dynamic techniques.Finally,no difference between the interventions is recorded regarding the rate of muscle injuries incidence.
文摘Purpose： The purpose of this study was to determine the extent that a static stretching program could increase heart rate （HR） and oxygen consumption （VO2）, and if the increases were sufficient to serve as a warm-up for aerobic activity. Methods： The HR and VO2 of 15 male and 16 female college students were measured after either 12 min of passive static stretching （SS）, or 12 rain pseudo-stretching （PS）, which consisted of moving through the stretching positions without placing the muscles on stretch. Four different lower body stretches were used with each stretch held for 30 s before the participant moved to a different position, with the circuit being repeated four times. VO2 was determined by averaging breath-by-breath measures over the total 12 min. HR was obtained every 30 s and the 24 values were averaged. Warm-up benefit was determined from the 02 deficit accrued during 7-min cycling at 60% VOzmax. Results： HR （beats/rain, mean 4. SD） for SS （84 ± 11） was a significant （p 〈 0.05） 9% greater than PS （78 ± 12）. Similarly, VO2 （mL/min, mean 4. SD） for SS （0.53 ± 0.13） was a significant 44% greater than PS （0.38 ± 0.11）. The O2 deficit （L, mean 4, SD） for SS （0.64 ± 1.54） was not different from PS （0.72 ± 1.61）. Conclusion： These data indicate that passive static stretching increases both HR and VO2, indicating that metabolic activity can be increased without muscle activation. The magnitude of the increases, however, is not sufficient to elicit a warm-up effect.
文摘Changes of dyeing behavior of wool after stretching - setting treatment are studied.Effects of stretching - setting on wool structure are analyzed.It is concluded that stretching - setting treatment not only reduces wool diameter and increases wool length,but also brings about low-temperature dyeing of wool.
文摘he lithosphere stretching, subsidence and basement thermal history of the Songliao, Yinggehai and Qiongdongnan basins in East China have been investigated by using backstripping technique and stretching models. The subsidence curve of the Songliao basin characterizes a rift basin history evolving from synrift rapid subsidence to postrift thermal subsidence. The calculated stretching factor of the basin is about 1.8 to 2.0 and the horizontal extension is about 55-60 km. The reconstructed subsidence curves of the Qiongdongnan and Yinggehai basins show that the basins underwent several rapid subsidence episodes, which has been interpreted as the result of a multiple stretching of the lithosphere. The total mean stretching factors of the Qiongdongnan and Yinggehai basins, calculated by using a multiple instantaneous stretching model, are about 1.7-1.9 and 2.5-3.0 respectively. The stretching factors of these basins, estimated from subsidence, are consistent with those determined from crustal thinning. The reconstructed thermal histories of these basins are in agreement with the geological observation.
基金supported by the Fundamental Research Grant Scheme (FRGS) of the Ministry of Higher Education (MOHE) of Malaysia (No. UKM-ST-07-FRGS0036-2009)
文摘The problem of the steady magnetohydrodynamic （MHD） stagnation-point flow of an incompressible viscous fluid over a stretching sheet is studied. The effect of an induced magnetic field is taken into account. The nonlinear partial differential equations are transformed into ordinary differential equations via the similarity transformation. The transformed boundary layer equations are solved numerically using the shooting method. Numerical results are obtained for various magnetic parameters and Prandtl numbers. The effects of the induced magnetic field on the skin friction coefficient, the local Nusselt number, the velocity, and the temperature profiles are presented graphically and discussed in detail.
基金UGC,New Delhi,India under the Special Assistance Programme DSA Phase-1
文摘A boundary layer analysis is presented for non-Newtonian fluid flow and heat transfer over a nonlinearly stretching surface. The Casson fluid model is used to characterize the non-Newtonian fluid behavior. By using suitable transformations, the governing partial differential equations corresponding to the momentum and energy equations are converted into non-linear ordinary differential equations. Numerical solutions of these equations are obtained with the shooting method. The effect of increasing Casson parameter is to suppress the velocity field. However the temperature is enhanced with the increasing Casson parameter.
基金the Ministry of Education of Malaysia(No.FRGS/1/2019/STG06/UKM/01/4)Ministry of Science of Romania(No.PN-III-P4-ID-PCE-2016-0036)。
文摘The steady flow and heat transfer of a hybrid nanofluid past a permeable stretching/shrinking wedge with magnetic field and radiation effects are studied. The governing equations of the hybrid nanofluid are converted to the similarity equations by techniques of the similarity transformation. The bvp4c function that is available in MATLAB software is utilized for solving the similarity equations numerically. The numerical results are obtained for selected different values of parameters. The results discover that two solutions exist, up to a certain value of the stretching/shrinking and suction strengths. The critical value in which the solution is in existence decreases as nanoparticle volume fractions for copper and wedge angle parameter increase. It is also found that the hybrid nanofluid enhances the heat transfer rate compared with the regular nanofluid. The reduction of the heat transfer rate is observed with the increase in radiation parameter. The temporal stability analysis is performed to analyze the stability of the dual solutions, and it is revealed that only one of them is stable and physically reliable.
基金Project(IFP-A-2022-2-5-24) supported by Institutional Fund Projects,University of Hafr Al Batin,Saudi Arabia。
文摘This article studies the influence of polymers on drag reduction and heat transfer enhancement of a nanofluid past a uniformly heated permeable vertically stretching surface. Our prime focus is on analyzing the possible effects of polymer inclusion in the nanofluid on drag coefficient, Nusselt number and Sherwood number. Dispersion model is considered to study the behavior of fluid flow and heat transfer in the presence of nanoparticles. Molecular approach is opted to explore polymer addition in the base fluid. An extra stress arises in the momentum equation as an outcome of polymer stretching. The governing boundary layer equations are solved numerically. Dependence of physical quantities of engineering interest on different flow parameters is studied. Reduction in drag coefficient, Nusselt number and Sherwood number is noticed because of polymer additives.
