Twisted multilayers of two-dimensional materials attract widespread research interest due to their intriguing electronic and optical properties related to their chiral symmetry breaking and moiréeffects.The two-d...Twisted multilayers of two-dimensional materials attract widespread research interest due to their intriguing electronic and optical properties related to their chiral symmetry breaking and moiréeffects.The two-dimensional transition metal dichalcogenide MoSe_(2) is a particularly promising material for twisted multilayers,capable of sustaining moiréexcitons.Here,we report on a rational bottomup synthesis approach for twisted MoSe_(2) flakes by chemical vapor transport(CVT).Screw dislocation-driven growth was forced by surface-fused SiO_(2)nanoparticles on the substrates that serve as potential nucleation points in low supersaturation condition.Thus,crystal growth by in-situ CVT under addition of MoCl_(5) leads to bulk 2H-MoSe_(2) in a temperature gradient from 900 to 820℃ with a dwell time of 96 h.Hexagonally shaped 2H-MoSe_(2) flakes were grown from 710 to 685℃ with a dwell time of 30 min on SiO_(2)@Al_(2)O_(3)(0001)substrates.Electron backscatter diffraction as well as electron microscopy reveals the screw dislocation-driven growth of triangular 3R-MoSe_(2) with individual step heights between 0.9 and 2.9 nm on SiO_(2)@Si(100)under the same conditions.Finally,twisted MoSe_(2) flakes exhibiting a twist angle of 19°with respect to the[010]zone axis could be synthesized.展开更多
In two-dimensional bilayer systems,twist-angle-dependent electronic and thermoelectric properties have garnered significant scientific interest in recent years.In this work,based on a combination of density functional...In two-dimensional bilayer systems,twist-angle-dependent electronic and thermoelectric properties have garnered significant scientific interest in recent years.In this work,based on a combination of density functional theory and nonequilibrium Green’s function method,we explore the electronic and thermoelectric properties in blue-phosphorene nanoribbon-based heterojunction(BPNRHJ)with and without blue-phosphorene nanoribbon(BPNR)stack.Our calculations find that the electronic conductance and power factor can be strongly enhanced by the BPNR stack,and their enhancements can be further observed with the twist between the layers.The main reason for this is the electronic hybridization between the layers can provide new transport channels,and the twist can modulate the strength of interlayer electronic hybridization,resulting in extremely violent fluctuations in electron transmission and hence an enhanced power factor.While the phonon thermal conductance exhibits very low dependence on the layer stack and twist.Combining these factors,our results reveal that the thermoelectric performance can be greatly modulated and enhanced in twist bilayer BPNRHJ:the figure of merit will be over 2.5 in 4-4-ZBPNR@ZGNR-AA-8.8∘at 500 K.展开更多
We presents a generalized(2+1)-dimensional Sharma-Tasso-Olver-Burgers(STOB)equation,unifying dissipative and dispersive wave dynamics.By introducing an auxiliary potential𝑦as a new space variable and employing...We presents a generalized(2+1)-dimensional Sharma-Tasso-Olver-Burgers(STOB)equation,unifying dissipative and dispersive wave dynamics.By introducing an auxiliary potential𝑦as a new space variable and employing a simpler deformation algorithm,we deform the(1+1)-dimensional STOB model to higher dimensions.The resulting equation is proven Lax-integrable via introducing strong and weak Lax pairs.Traveling wave solutions of the(2+1)-dimensional STOB equation are derived through an ordinary differential equation reduction,with implicit solutions obtained for a special case.Crucially,we demonstrate that the system admits dispersionless decompositions into two types:Case 1 yields non-traveling twisted kink and bell solitons,while Case 2 involves complex implicit functions governed by cubic-algebraic constraints.Numerical visualizations reveal novel anisotropic soliton structures,and the decomposition methodology is shown to generalize broadly to other higher dimensional dispersionless decomposition solvable integrable systems.展开更多
Twist,the very degree of freedom in van der Waals heterostructures,offers a compelling avenue to manipulate and tailor their electrical and optical characteristics.In particular,moirépatterns in twisted homobilay...Twist,the very degree of freedom in van der Waals heterostructures,offers a compelling avenue to manipulate and tailor their electrical and optical characteristics.In particular,moirépatterns in twisted homobilayer transition metal dichalcogenides(TMDs)lead to zone folding and miniband formation in the resulting electronic bands,holding the promise to exhibit inter-layer excitonic optical phenomena.Although some experiments have shown the existence of twist-angle-dependent intra-and inter-layer excitons in twisted MoSe2 homobilayers,electrical control of the interlayer excitons in MoSe_(2) is relatively under-explored.Here,we show the signatures of the moiréeffect on intralayer and interlayer excitons in 2H-stacked twisted MoSe2 homobilayers.Doping-and electric field-dependent photoluminescence mea-surements at low temperatures give evidence of the momentum-direct K-K intralayer excitons,and the momentum-indirect Г-K and Г-Q interlayer excitons.Our results suggest that twisted MoSe_(2) homobilayers are an intriguing platform for engineering interlayer exciton states,which may shed light on future atomically thin optoelectronic applications.展开更多
In this paper,we compute sub-Riemannian limits of some important curvature variants associated with the connection with torsion for four dimensional twisted BCV spaces and derive a Gauss-Bonnet theorem for four dimens...In this paper,we compute sub-Riemannian limits of some important curvature variants associated with the connection with torsion for four dimensional twisted BCV spaces and derive a Gauss-Bonnet theorem for four dimensional twisted BCV spaces.展开更多
Twisted polymer artificial muscles activated by thermal heating represent a new class of soft actuators capable of generating torsional actuation.The thermal torsion effect,characterized by the reversible untwisting o...Twisted polymer artificial muscles activated by thermal heating represent a new class of soft actuators capable of generating torsional actuation.The thermal torsion effect,characterized by the reversible untwisting of twisted fibers as temperature increases due to greater radial than axial thermal expansion,is crucial to the actuation performance of these artificial muscles.This study explores the thermal torsion effect of polymer muscles made of twisted Nylon 6 fibers in experimental and theoretical aspects,focusing on the interplay between material properties and temperature.It is revealed that the thermal torsion effect enhances the actuation performance of the twisted polymer actuator while the thermal softening effect diminishes it.A thermal-mechanical model incorporating both the thermal torsion effect and thermal softening effect is used to predict the recovered torque of the twisted polymer actuators.An optimal bias angle and operating temperature are identified to maximize the recovered torque.Analysis of strain and stress distributions in the cross-section of the twisted polymer fiber shows that the outer layers of the fiber predominantly contribute to the torsional actuation.This work aids in the precise control and structural optimization of the thermally-activated twisted polymer actuators.展开更多
In recent years,there has been a surge of interest in higher-order topological phases(HOTPs)across various disciplines within the field of physics.These unique phases are characterized by their ability to harbor topol...In recent years,there has been a surge of interest in higher-order topological phases(HOTPs)across various disciplines within the field of physics.These unique phases are characterized by their ability to harbor topological protected boundary states at lower-dimensional boundaries,a distinguishing feature that sets them apart from conventional topological phases and is attributed to the higher-order bulk-boundary correspondence.Two-dimensional(2D)twisted systems offer an optimal platform for investigating HOTPs,owing to their strong controllability and experimental feasibility.Here,we provide a comprehensive overview of the latest research advancements on HOTPs in 2D twisted multilayer systems.We will mainly review the HOTPs in electronic,magnonic,acoustic,photonic and mechanical twisted systems,and finally provide a perspective of this topic.展开更多
Recent advancements in two-dimensional van der Waals moir´e materials have unveiled the captivating landscape of moir´e physics.In twisted bilayer graphene(TBG)at‘magic angles’,strong electronic correlatio...Recent advancements in two-dimensional van der Waals moir´e materials have unveiled the captivating landscape of moir´e physics.In twisted bilayer graphene(TBG)at‘magic angles’,strong electronic correlations give rise to a diverse array of exotic physical phenomena,including correlated insulating states,superconductivity,magnetism,topological phases,and the quantum anomalous Hall(QAH)effect.Notably,the QAH effect demonstrates substantial promise for applications in electronic and quantum computing devices with low power consumption.This article focuses on the latest developments surrounding the QAH effect in magic-angle TBG.It provides a comprehensive analysis of magnetism and topology—two crucial factors in engineering the QAH effect within magic-angle TBG.Additionally,it offers a detailed overview of the experimental realization of the QAH effect in moir´e superlattices.Furthermore,this review highlights the underlying mechanisms driving these exotic phases in moir´e materials,contributing to a deeper understanding of strongly interacting quantum systems and facilitating the manipulation of new material properties to achieve novel quantum states.展开更多
In recent years,the study of higher-order topological states and their material realizations has become a research frontier in topological condensed matter physics.We demonstrate that twisted bilayer graphene with sma...In recent years,the study of higher-order topological states and their material realizations has become a research frontier in topological condensed matter physics.We demonstrate that twisted bilayer graphene with small twist angles behaves as a second-order topological insulator possessing topological corner charges.Using a tight-binding model,we compute the topological band indices and corner states of finite-sized twisted bilayer graphene flakes.It is found that for any small twist angle,whether commensurate or incommensurate,the gaps both below and above the flat bands are associated with nontrivial topological indices.Our results not only extend the concept of second-order band topology to arbitrary small twist angles but also confirm the existence of corner states at acute-angle corners.展开更多
Heat transfer,friction factor and thermal enhancement factor characteristics of a double pipe heat exchanger fitted with square-cut twisted tapes（STT） and plain twisted tapes（PTT） are investigated experimentally u...Heat transfer,friction factor and thermal enhancement factor characteristics of a double pipe heat exchanger fitted with square-cut twisted tapes（STT） and plain twisted tapes（PTT） are investigated experimentally using the water as working fluid.The tapes（STT and PTT） have three twist ratios（y=2.0,4.4 and 6.0） and the Reynolds number ranges from 2000 to 12000.The experimental results reveal that heat transfer rate,friction factor and thermal enhancement factor in the tube equipped with STT are significantly higher than those fitted with PTT. The additional disturbance and secondary flow in the vicinity of the tube wall generated by STT are higher compared to that induced by the PTT is referred as the reason for better performance.Over the range considered,the Nusselt number,friction factor and thermal enhancement factor in a tube with STT are respectively,1.03 to 1.14,1.05 to 1.25 and 1.02 to 1.06 times of those in tube with PTT.An empirical correlation is also formulated to match with experimental data of Nusselt number and friction factor for STT and PTT.展开更多
Although helical and twisted reinforcement has been used to reinforce concrete for more than two decades, its rationale still remains unclear. With a brief review of current researches on the helical and twisted reinf...Although helical and twisted reinforcement has been used to reinforce concrete for more than two decades, its rationale still remains unclear. With a brief review of current researches on the helical and twisted reinforcement properties, this paper describes some new phenomenon of the helical and twisted reinforcement in concrete and other matrix by experimental studies, and then discusses on mechanism of helical effect of strengthening. This paper also discusses the mechanism of accessional helical effect of strengthening and its significance in industrial practice. Extensive tests indicate that twisting is the most effective way to improve reinforcement mechanical properties. The main results are： （1） They can greatly enhance bond anchorage in base material. In some pull-out tests, the pull-out resistance increases with reinforcement slip within the specimens, which results not only in a higher pull-out load but also a larger slip up to 70%-80% of reinforcement embedded length. （2） Concrete reinforced by twisted bars demonstrates certain ductility at failure. （3） The bond strength depends on the pitch space directly. （4） The twisted effect on material strengthening is from a three-dimensional interlocking force which is formed from material untwisting when they were pulled out from base specimens.展开更多
In order to study algebraic structures of parallelizable sphere s7, the notions of quasimodules and biquasimodnle algebras over Hopf quasigroups, which are not required to be associative, are introduced. The lack of a...In order to study algebraic structures of parallelizable sphere s7, the notions of quasimodules and biquasimodnle algebras over Hopf quasigroups, which are not required to be associative, are introduced. The lack of associativity of quasimodules is compensated for by conditions involving the antipode. The twisted smash product for Hopf quasigroups is constructed using biquasimodule algebras, which is a generalization of the twisted smash for Hopf algebras. The twisted smash product and tensor coproduct is turned into a Hopf quasigroup if and only if the following conditions （h1→a） h2 = （h2→a） h1, （a←S（h1）） h2 = （a←S（h2）） h1, hold. The obtained results generalize and improve the corresponding results of the twisted smash product for Hopf algebras.展开更多
In this paper, we describe the variety defined by the twisted transfer ideal. It turns out that this variety is nothing but the union of reflecting hyperplanes and the fixed subspaces of the elements of order p in G.
In this paper, we study the twisted Poisson homology of truncated polynomials algebra A in four variables, and we calculate exactly the dimension of i-th (i = 1, 2, 3, 4) twisted Poisson homology group over A by the i...In this paper, we study the twisted Poisson homology of truncated polynomials algebra A in four variables, and we calculate exactly the dimension of i-th (i = 1, 2, 3, 4) twisted Poisson homology group over A by the induction on the length. The calculation methods provided in this paper can also solve truncated polynomials algebra in a few variables.展开更多
This paper deals with the experimental investigation on Nusselt number,friction factor and thermal en-hancement factor of a double pipe heat exchanger equipped with twisted tape consisting wire nails(WN-TT) and plain ...This paper deals with the experimental investigation on Nusselt number,friction factor and thermal en-hancement factor of a double pipe heat exchanger equipped with twisted tape consisting wire nails(WN-TT) and plain twisted tapes(P-TT) with three different twist ratios of y 2.0,4.4 and 6.0. Test runs are conducted using the water as the working fluid with Reynolds number range between 2000 and 12000 for WN-TT and P-TT. It is found that Nusselt number,friction factor and thermal enhancement factor in the tube equipped with WN-TT appreciably higher than those in the tube fitted with P-TT and plain tube. Over the range considered Nusselt number,friction factor and thermal enhancement factor in a tube with WN-TT are respectively,1.08 to 1.31,1.1 to 1.75 and 1.05 to 1.13 times of those in tube with P-TT. The better performance of WN-TT is due to combined effects of the follow-ing factors:(1) common swirling flow generated by P-TT,(2) additional turbulence offered by the wire nails. Em-pirical correlations for Nusselt number,friction factor and thermal enhancement factor are also formulated from the experimental results of WN-TT and P-TT.展开更多
This paper gives a sufficient and necessary condition for twisted products to be weak Hopf algebras, moreover, gives a description for smash products to be weak Hopf algebras. It respectively generalizes R.K.Molnar...This paper gives a sufficient and necessary condition for twisted products to be weak Hopf algebras, moreover, gives a description for smash products to be weak Hopf algebras. It respectively generalizes R.K.Molnar's major result and I.Boca's result.展开更多
基金funding from SFB 1415 subproject B04(Deutsche Forschungsgemeinschaft,No.417590517)supported by the Deutsche Forschungsgemeinschaft through the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter-ct.qmat(EXC 2147,No.390858490)the support provided by the DRESDEN-concept alliance of research institutions.
文摘Twisted multilayers of two-dimensional materials attract widespread research interest due to their intriguing electronic and optical properties related to their chiral symmetry breaking and moiréeffects.The two-dimensional transition metal dichalcogenide MoSe_(2) is a particularly promising material for twisted multilayers,capable of sustaining moiréexcitons.Here,we report on a rational bottomup synthesis approach for twisted MoSe_(2) flakes by chemical vapor transport(CVT).Screw dislocation-driven growth was forced by surface-fused SiO_(2)nanoparticles on the substrates that serve as potential nucleation points in low supersaturation condition.Thus,crystal growth by in-situ CVT under addition of MoCl_(5) leads to bulk 2H-MoSe_(2) in a temperature gradient from 900 to 820℃ with a dwell time of 96 h.Hexagonally shaped 2H-MoSe_(2) flakes were grown from 710 to 685℃ with a dwell time of 30 min on SiO_(2)@Al_(2)O_(3)(0001)substrates.Electron backscatter diffraction as well as electron microscopy reveals the screw dislocation-driven growth of triangular 3R-MoSe_(2) with individual step heights between 0.9 and 2.9 nm on SiO_(2)@Si(100)under the same conditions.Finally,twisted MoSe_(2) flakes exhibiting a twist angle of 19°with respect to the[010]zone axis could be synthesized.
基金supported by the Key Projects of Department of Education of Hunan Province,China(Grant No.21A0167)the Natural Science Foundation of Hunan Province,China(Grant No.2019JJ40532)the Talent Introducing Foundation of Central South University of Forestry and Technology(Grant No.104-0160)。
文摘In two-dimensional bilayer systems,twist-angle-dependent electronic and thermoelectric properties have garnered significant scientific interest in recent years.In this work,based on a combination of density functional theory and nonequilibrium Green’s function method,we explore the electronic and thermoelectric properties in blue-phosphorene nanoribbon-based heterojunction(BPNRHJ)with and without blue-phosphorene nanoribbon(BPNR)stack.Our calculations find that the electronic conductance and power factor can be strongly enhanced by the BPNR stack,and their enhancements can be further observed with the twist between the layers.The main reason for this is the electronic hybridization between the layers can provide new transport channels,and the twist can modulate the strength of interlayer electronic hybridization,resulting in extremely violent fluctuations in electron transmission and hence an enhanced power factor.While the phonon thermal conductance exhibits very low dependence on the layer stack and twist.Combining these factors,our results reveal that the thermoelectric performance can be greatly modulated and enhanced in twist bilayer BPNRHJ:the figure of merit will be over 2.5 in 4-4-ZBPNR@ZGNR-AA-8.8∘at 500 K.
基金supported by the National Natural Science Foundations of China(Grant Nos.12235007,12375003,and 11975131).
文摘We presents a generalized(2+1)-dimensional Sharma-Tasso-Olver-Burgers(STOB)equation,unifying dissipative and dispersive wave dynamics.By introducing an auxiliary potential𝑦as a new space variable and employing a simpler deformation algorithm,we deform the(1+1)-dimensional STOB model to higher dimensions.The resulting equation is proven Lax-integrable via introducing strong and weak Lax pairs.Traveling wave solutions of the(2+1)-dimensional STOB equation are derived through an ordinary differential equation reduction,with implicit solutions obtained for a special case.Crucially,we demonstrate that the system admits dispersionless decompositions into two types:Case 1 yields non-traveling twisted kink and bell solitons,while Case 2 involves complex implicit functions governed by cubic-algebraic constraints.Numerical visualizations reveal novel anisotropic soliton structures,and the decomposition methodology is shown to generalize broadly to other higher dimensional dispersionless decomposition solvable integrable systems.
基金supported by the National Key R&D Program of China(No.2023YFF1500600)the National Natural Science Foun-dation of China(Nos.12004259,12204287)+3 种基金China Postdoc-toral Science Foundation(Grant No.2022M723215)Zheng Vitto Han acknowledges the support of the Fund for Shanxi“1331 Project”Key Subjects Construction,and the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302003)Kenji Watanabe and Takashi Taniguchi acknowledge support from the JSPS KAKENHI(Grant Nos.20H00354 and 23H02052)the World Premier International Research Center Initiative(WPI),MEXT,Japan.
文摘Twist,the very degree of freedom in van der Waals heterostructures,offers a compelling avenue to manipulate and tailor their electrical and optical characteristics.In particular,moirépatterns in twisted homobilayer transition metal dichalcogenides(TMDs)lead to zone folding and miniband formation in the resulting electronic bands,holding the promise to exhibit inter-layer excitonic optical phenomena.Although some experiments have shown the existence of twist-angle-dependent intra-and inter-layer excitons in twisted MoSe2 homobilayers,electrical control of the interlayer excitons in MoSe_(2) is relatively under-explored.Here,we show the signatures of the moiréeffect on intralayer and interlayer excitons in 2H-stacked twisted MoSe2 homobilayers.Doping-and electric field-dependent photoluminescence mea-surements at low temperatures give evidence of the momentum-direct K-K intralayer excitons,and the momentum-indirect Г-K and Г-Q interlayer excitons.Our results suggest that twisted MoSe_(2) homobilayers are an intriguing platform for engineering interlayer exciton states,which may shed light on future atomically thin optoelectronic applications.
基金Supported by National Natural Science Foundation of China(Grant No.11771070).
文摘In this paper,we compute sub-Riemannian limits of some important curvature variants associated with the connection with torsion for four dimensional twisted BCV spaces and derive a Gauss-Bonnet theorem for four dimensional twisted BCV spaces.
基金support from the National Natural Science Foundation of China(Grant No.12272146)the Fundamental Research Funds for the Central Universities(Grant No.2024BRA009)the Young Top-notch Talent Cultivation Program of Hubei Province,is appreciated.
文摘Twisted polymer artificial muscles activated by thermal heating represent a new class of soft actuators capable of generating torsional actuation.The thermal torsion effect,characterized by the reversible untwisting of twisted fibers as temperature increases due to greater radial than axial thermal expansion,is crucial to the actuation performance of these artificial muscles.This study explores the thermal torsion effect of polymer muscles made of twisted Nylon 6 fibers in experimental and theoretical aspects,focusing on the interplay between material properties and temperature.It is revealed that the thermal torsion effect enhances the actuation performance of the twisted polymer actuator while the thermal softening effect diminishes it.A thermal-mechanical model incorporating both the thermal torsion effect and thermal softening effect is used to predict the recovered torque of the twisted polymer actuators.An optimal bias angle and operating temperature are identified to maximize the recovered torque.Analysis of strain and stress distributions in the cross-section of the twisted polymer fiber shows that the outer layers of the fiber predominantly contribute to the torsional actuation.This work aids in the precise control and structural optimization of the thermally-activated twisted polymer actuators.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12304539,12074108,12474151,12347101)the Natural Science Foundation of Chongqing(Grant No.CSTB2022NSCQ-MSX0568)Beijing National Laboratory for Condensed Matter Physics(Grant No.2024BNLCMPKF025)。
文摘In recent years,there has been a surge of interest in higher-order topological phases(HOTPs)across various disciplines within the field of physics.These unique phases are characterized by their ability to harbor topological protected boundary states at lower-dimensional boundaries,a distinguishing feature that sets them apart from conventional topological phases and is attributed to the higher-order bulk-boundary correspondence.Two-dimensional(2D)twisted systems offer an optimal platform for investigating HOTPs,owing to their strong controllability and experimental feasibility.Here,we provide a comprehensive overview of the latest research advancements on HOTPs in 2D twisted multilayer systems.We will mainly review the HOTPs in electronic,magnonic,acoustic,photonic and mechanical twisted systems,and finally provide a perspective of this topic.
基金supported by the Science Research Project of Hebei Education Department(Grant No.BJK2024168)the National Natural Science Foundation of China(Grant No.11904076)+1 种基金the Natural Science Foundation of Hebei(Grant No.A2019205313)Science Foundation of Hebei Normal University(Grant No.L2024J02).
文摘Recent advancements in two-dimensional van der Waals moir´e materials have unveiled the captivating landscape of moir´e physics.In twisted bilayer graphene(TBG)at‘magic angles’,strong electronic correlations give rise to a diverse array of exotic physical phenomena,including correlated insulating states,superconductivity,magnetism,topological phases,and the quantum anomalous Hall(QAH)effect.Notably,the QAH effect demonstrates substantial promise for applications in electronic and quantum computing devices with low power consumption.This article focuses on the latest developments surrounding the QAH effect in magic-angle TBG.It provides a comprehensive analysis of magnetism and topology—two crucial factors in engineering the QAH effect within magic-angle TBG.Additionally,it offers a detailed overview of the experimental realization of the QAH effect in moir´e superlattices.Furthermore,this review highlights the underlying mechanisms driving these exotic phases in moir´e materials,contributing to a deeper understanding of strongly interacting quantum systems and facilitating the manipulation of new material properties to achieve novel quantum states.
基金supported by the National Natural Science Foundation of China(Grant Nos.12104232 and 12074156).
文摘In recent years,the study of higher-order topological states and their material realizations has become a research frontier in topological condensed matter physics.We demonstrate that twisted bilayer graphene with small twist angles behaves as a second-order topological insulator possessing topological corner charges.Using a tight-binding model,we compute the topological band indices and corner states of finite-sized twisted bilayer graphene flakes.It is found that for any small twist angle,whether commensurate or incommensurate,the gaps both below and above the flat bands are associated with nontrivial topological indices.Our results not only extend the concept of second-order band topology to arbitrary small twist angles but also confirm the existence of corner states at acute-angle corners.
文摘Heat transfer,friction factor and thermal enhancement factor characteristics of a double pipe heat exchanger fitted with square-cut twisted tapes（STT） and plain twisted tapes（PTT） are investigated experimentally using the water as working fluid.The tapes（STT and PTT） have three twist ratios（y=2.0,4.4 and 6.0） and the Reynolds number ranges from 2000 to 12000.The experimental results reveal that heat transfer rate,friction factor and thermal enhancement factor in the tube equipped with STT are significantly higher than those fitted with PTT. The additional disturbance and secondary flow in the vicinity of the tube wall generated by STT are higher compared to that induced by the PTT is referred as the reason for better performance.Over the range considered,the Nusselt number,friction factor and thermal enhancement factor in a tube with STT are respectively,1.03 to 1.14,1.05 to 1.25 and 1.02 to 1.06 times of those in tube with PTT.An empirical correlation is also formulated to match with experimental data of Nusselt number and friction factor for STT and PTT.
基金the National Natural Science Foundation of China(No.50578119)
文摘Although helical and twisted reinforcement has been used to reinforce concrete for more than two decades, its rationale still remains unclear. With a brief review of current researches on the helical and twisted reinforcement properties, this paper describes some new phenomenon of the helical and twisted reinforcement in concrete and other matrix by experimental studies, and then discusses on mechanism of helical effect of strengthening. This paper also discusses the mechanism of accessional helical effect of strengthening and its significance in industrial practice. Extensive tests indicate that twisting is the most effective way to improve reinforcement mechanical properties. The main results are： （1） They can greatly enhance bond anchorage in base material. In some pull-out tests, the pull-out resistance increases with reinforcement slip within the specimens, which results not only in a higher pull-out load but also a larger slip up to 70%-80% of reinforcement embedded length. （2） Concrete reinforced by twisted bars demonstrates certain ductility at failure. （3） The bond strength depends on the pitch space directly. （4） The twisted effect on material strengthening is from a three-dimensional interlocking force which is formed from material untwisting when they were pulled out from base specimens.
基金The National Natural Science Foundation of China( No. 10971188 )the Natural Science Foundation of Zhejiang Province(No.Y6110323)+2 种基金Jiangsu Planned Projects for Postdoctoral Research Funds(No. 0902081C)Zhejiang Provincial Education Department Project (No.Y200907995)Qiantang Talents Project of Science Technology Department of Zhejiang Province (No. 2011R10051)
文摘In order to study algebraic structures of parallelizable sphere s7, the notions of quasimodules and biquasimodnle algebras over Hopf quasigroups, which are not required to be associative, are introduced. The lack of associativity of quasimodules is compensated for by conditions involving the antipode. The twisted smash product for Hopf quasigroups is constructed using biquasimodule algebras, which is a generalization of the twisted smash for Hopf algebras. The twisted smash product and tensor coproduct is turned into a Hopf quasigroup if and only if the following conditions （h1→a） h2 = （h2→a） h1, （a←S（h1）） h2 = （a←S（h2）） h1, hold. The obtained results generalize and improve the corresponding results of the twisted smash product for Hopf algebras.
文摘In this paper, we describe the variety defined by the twisted transfer ideal. It turns out that this variety is nothing but the union of reflecting hyperplanes and the fixed subspaces of the elements of order p in G.
文摘In this paper, we study the twisted Poisson homology of truncated polynomials algebra A in four variables, and we calculate exactly the dimension of i-th (i = 1, 2, 3, 4) twisted Poisson homology group over A by the induction on the length. The calculation methods provided in this paper can also solve truncated polynomials algebra in a few variables.
文摘This paper deals with the experimental investigation on Nusselt number,friction factor and thermal en-hancement factor of a double pipe heat exchanger equipped with twisted tape consisting wire nails(WN-TT) and plain twisted tapes(P-TT) with three different twist ratios of y 2.0,4.4 and 6.0. Test runs are conducted using the water as the working fluid with Reynolds number range between 2000 and 12000 for WN-TT and P-TT. It is found that Nusselt number,friction factor and thermal enhancement factor in the tube equipped with WN-TT appreciably higher than those in the tube fitted with P-TT and plain tube. Over the range considered Nusselt number,friction factor and thermal enhancement factor in a tube with WN-TT are respectively,1.08 to 1.31,1.1 to 1.75 and 1.05 to 1.13 times of those in tube with P-TT. The better performance of WN-TT is due to combined effects of the follow-ing factors:(1) common swirling flow generated by P-TT,(2) additional turbulence offered by the wire nails. Em-pirical correlations for Nusselt number,friction factor and thermal enhancement factor are also formulated from the experimental results of WN-TT and P-TT.
基金This work is supported by National Natural Science Foundation of Chinaby the excellent doctorate fund of Nanjing agricultural university
文摘This paper gives a sufficient and necessary condition for twisted products to be weak Hopf algebras, moreover, gives a description for smash products to be weak Hopf algebras. It respectively generalizes R.K.Molnar's major result and I.Boca's result.
