We report comprehensive angle-resolved photoemission investigations on the electronic structures and nematicity of the parent compounds of the iron-based superconductors including CeFeAsO, BaFe2As2, NaFeAs, FeSe and u...We report comprehensive angle-resolved photoemission investigations on the electronic structures and nematicity of the parent compounds of the iron-based superconductors including CeFeAsO, BaFe2As2, NaFeAs, FeSe and undoped FeSe/SrTiO3 films with 1, 2 and 20 layers. While the electronic structure near tile Brillouin zone center F varies dramatically among different materials, the electronic structure near the Brillouin zone corners （M points）, as well as their temperature dependence, are rather similar. The electronic structure near the zone corners is dominated by the electronic nematicity that gives rise to a band splitting of the dxz and dyz bands below the nematie transition temperature. A clear relation is observed between the band splitting magnitude arid the onset temperature of nematicity. Our results may shed light on the origin of nematicity, its effect on the electronic structures, and its relation with superconductivity in the iron-based superconductors.展开更多
The driving mechanism of nematicity and its twist with superconductivity in iron-based superconductors are still under debate.Recently,a dominant B1g-type strain effect on superconductivity is observed in underdoped i...The driving mechanism of nematicity and its twist with superconductivity in iron-based superconductors are still under debate.Recently,a dominant B1g-type strain effect on superconductivity is observed in underdoped iron-pnictides superconductors Ba(Fe_(1-x)Co_(x))_(2)As_(2),suggesting a strong interplay between nematicity and superconductivity.Since the long-range spin order is absent in FeSe superconductor,whether a similar strain effect could be also observed or not is an interesting question.Here,by utilizing a flexible film as substrate,we successfully achieve a wide-range-strain tuning of FeSe thin flake,in which both the tensile and compressive strain could reach up to~0.7%,and systematically study the strain effect on both superconducting and nematic transition(T_(c)and Ts)in the FeSe thin flake.Our results reveal a predominant A1g-type strain effect on T_(c).Meanwhile,Ts exhibits a monotonic anti-correlation with T_(c)and the maximum T_(c)reaches to 12 K when Ts is strongly suppressed under the maximum compressive strain.Finally,in comparison with the results in the underdoped Ba(Fe_(1-x)Co_(x))_(2)As_(2),the absence of B1g-type strain effect in FeSe further supports the role of stripe-type spin fluctuations on superconductivity.In addition,our work also supports that the orbital degree of freedom plays a key role to drive the nematic transition in FeSe.展开更多
Subject Code:A04With the support by the National Natural Science Foundation of China,a collaborative study by the research groups led by Profs.Li Wei(李渭),Chen Xi(陈曦)and Xue Qikun(薛其坤)from Tsinghua University an...Subject Code:A04With the support by the National Natural Science Foundation of China,a collaborative study by the research groups led by Profs.Li Wei(李渭),Chen Xi(陈曦)and Xue Qikun(薛其坤)from Tsinghua University and Prof.Shen Zhixun(沈志勋)from Stanford University,demonstrates stripes developed展开更多
Understanding the nature of the mysterious pseudogap phenomenon is one of the most important issues associated with cuprate high-T_(c) superconductors.Here,we report 17O nuclear magnetic resonance(NMR) studies on two ...Understanding the nature of the mysterious pseudogap phenomenon is one of the most important issues associated with cuprate high-T_(c) superconductors.Here,we report 17O nuclear magnetic resonance(NMR) studies on two planar oxygen sites in stoichio?metric cuprate YBa_(2)Cu_(4)O_(8) to investigate the symmetry breaking inside the pseudogap phase.We observe that the Knight shifts of the two oxygen sites are identical at high temperatures but different below T_(nem) ~185 K,which is close to the pseudogap temperature T^(*).Our result provides a microscopic evidence for intra-unit-cell electronic nematicity.The difference in quadrupole resonance frequency between the two oxygen sites is unchanged below T_(nem),which suggests that the observed nematicity does not directly stem from the local charge density modulation.Furthermore,a short-range charge density wave(CDW) order is observed below T=150 K.The additional broadening in the 17O-NMR spectra because of this CDW order is determined to be inequivalent for the two oxygen sites,which is similar to that observed in case of nematicity.These results suggest a possible connection between nematicity,CDW order,and pseudogap.展开更多
Active matter exhibits collective motions at various scales.Geometric confinement has been identified as an effective way to control and manipulate active fluids,with much attention given to external factors.However,t...Active matter exhibits collective motions at various scales.Geometric confinement has been identified as an effective way to control and manipulate active fluids,with much attention given to external factors.However,the impact of the inherent properties of active particles on collective motion under confined conditions remains elusive.Here,we use a highly tunable active nematics model to study active systems under confinement,focusing on the effect of the self-driven speed of active particles.We identify three distinct states characterized by unique particle and flow fields within confined active nematic systems,among which circular rotation emerges as a collective motion involving rotational movement in both particle and flow fields.The theoretical phase diagram shows that increasing the self-driven speed of active particles significantly enhances the region of the circular rotation state and improves its stability.Our results provide insights into the formation of high quality vortices in confined active nematic systems.展开更多
Cell division is a fundamental biological process in which a parent cell divides into two daughter cells.The cell cortex,a thin layer primarily composed of actin filaments and myosin motors beneath the plasma membrane...Cell division is a fundamental biological process in which a parent cell divides into two daughter cells.The cell cortex,a thin layer primarily composed of actin filaments and myosin motors beneath the plasma membrane,plays a critical role in ensuring proper cell division.In this study,we apply a hydrodynamic model to describe the actin cortex as an active nematic surface,incorporating orientational order arising from actin filament alignment and anisotropic active stress produced by myosin motors.By analyzing the linearized dynamics,we investigate how shape,flow,and stress regulators evolve over time when the surface deviates slightly from a sphere.Our findings reveal that the active alignment of actin filaments,often overlooked in previous studies,is crucial for successful division.Furthermore,we demonstrate that a cortical chiral flow naturally emerges as a consequence of this active alignment.Overall,our results provide a mechanistic explanation for key phenomena observed during cell division,offering new insights into the role of active stress and filament alignment in cortical dynamics.展开更多
Fe-based superconductors represent a fascinating class of materials,extensively studied for their complex interplay of superconductivity,magnetism,spin density waves,and nematicity,along with the interactions among th...Fe-based superconductors represent a fascinating class of materials,extensively studied for their complex interplay of superconductivity,magnetism,spin density waves,and nematicity,along with the interactions among these orders.An intriguing yet unexplained phenomenon observed in Fe-based superconductors is the emergence of superconductivity below 25K in the non-superconducting parent compound SrFe_(2)As_(2)following exposure to water at its surface.In this study,we employed in situ angle-resolved photoemission spectroscopy and low-energy electron diffraction to meticulously examine the electronic structure evolution of SrFe_(2)As_(2)upon in situ water dosing.Our findings indicate that water dosing markedly attenuates the spin density wave phase and surface Sr reconstruction while preserving the nematic order in SrFe_(2)As_(2).Furthermore,we detected an enhancement in the spectral weight of bands near the Fermi level.Our observations highlight the critical role of the intricate interplay among various orders induced by water dosing,which effectively modifies the band structure and favors the emergence of superconductivity in SrFe_(2)As_(2).展开更多
A programmable low-profile array antenna based on nematic liquid crystals(NLCs)is proposed.Each antenna unit comprises a square patch radiating structure and a tunable NLC-based phase shifter capable of achieving a ph...A programmable low-profile array antenna based on nematic liquid crystals(NLCs)is proposed.Each antenna unit comprises a square patch radiating structure and a tunable NLC-based phase shifter capable of achieving a phase shift exceeding 360°with high linearity.First,the above 64 antenna units are periodically arranged into an 8×8 NLC-based antenna array,and the bias voltage of the NLC-based phase shifter loaded on the antenna unit is adjusted through the control of the field-programmable gate array(FPGA)programming sequences.This configuration enables precise phase changes for all 64 channels.Numerical simulation,sample processing,and experimental measurements of the antenna array are conducted to validate the performance of the antenna.The numerical and experimental results demonstrate that the proposed antenna performs well within the frequency range of 19.5-20.5 GHz,with a 3 dB relative bandwidth of 10%and a maximum main lobe gain of 14.1 dBi.A maximum scanning angle of±34°is achieved through the adjustment of the FPGA programming sequence.This NLC-based programmable array antenna shows promising potential for applications in satellite communication.展开更多
A series of novel thermotropic liquid crystalline polyesters bearing nonlinear optical azobenzene side group were synthesized by high temperature solution polycondensation and their structures,thermal stability, phas...A series of novel thermotropic liquid crystalline polyesters bearing nonlinear optical azobenzene side group were synthesized by high temperature solution polycondensation and their structures,thermal stability, phase transition behavior and crystallinity were characterized by IR,elemental analysis, TG-DTA, polarizing optical microscope (POM) equipped with a hot stage and X-ray diffraction techniques. The results demonstrate that all the synthesized polyesters exhibit nematic liquid crystalline phases and show relatively high glass transition temperatures and good thermal stability.展开更多
In this article, we prove the global existence of weak solutions to the non- isothermal nematic liquid crystal system on T2, on the basis of a new approximate system which is different from the classical Ginzburg-Land...In this article, we prove the global existence of weak solutions to the non- isothermal nematic liquid crystal system on T2, on the basis of a new approximate system which is different from the classical Ginzburg-Landau approximation. Local in space energy inequalities are employed to recover the estimates on the second order spatial derivatives of the director fields locally in time, which cannot be derived from the basic energy balance. It is shown that these weak solutions satisfy the temperature equation, and also the total energy equation but away from at most finite many ＂singular＂ times, at which the energy concentration occurs and the director field losses its second order derivatives.展开更多
A detailed theoretical analysis of determining the sum of flexoelectric coefficients in nematic liquid crystals using the capacitance method is given. In the strong anchoring parallel aligned nematic （PAN） and hybri...A detailed theoretical analysis of determining the sum of flexoelectric coefficients in nematic liquid crystals using the capacitance method is given. In the strong anchoring parallel aligned nematic （PAN） and hybrid aligned nematic （HAN） cells, the dependences of the capacitance on the sum of flexoelectric coefficients and the applied voltage are obtained by numerical simulations, and the distributions of the director and the electric potential for different applied voltages and flexoelectric coefficients are also given. Based on this theoretical analysis, we propose an experimental design for measuring the capacitance of a liquid crystal cell using the improved precision LCR meter E4980A （Agilent）. Through comparing the experimental data with the simulated results, the sum of flexoeletric coefficients can be determined.展开更多
Ultra high molar mass polyethylene(UHPE)powder as polymerized in a slurry process has been studied,in its nascent state,after recrystallization on rapid cooling from the melt and after hot compression molding to a fil...Ultra high molar mass polyethylene(UHPE)powder as polymerized in a slurry process has been studied,in its nascent state,after recrystallization on rapid cooling from the melt and after hot compression molding to a film,by DSC,effect of annealing the recrystallized specimen at 120 similar to 130 degreesC,morphology by polarizing optical microscopy and small angle X-ray scattering.Based on the experimental results obtained the macromolecular condensed state of the nascent UHPE powder is a rare case of a multi-chain condensed state of non-interpenetrating chains,involving interlaced extended chain crystalline layers and relaxed parallel chain amorphous layers.On melting,a nematic rubbery state of nanometer size domain resulted.The nematic-isotropic transition temperature was judged from literature data to be at least 220 degreesC,possibly higher than 300 ℃,the exact temperature is however not sue because of chain degradation at such high temperatures.The recrystallization process from the melt is a crystallization from a nematic rubbery state.The drop of remelting peak temperature by 10 K of the specimen recrystallized from its melt as compared to the nascent state has its origin in the decrease both of the crystalline chain stem length and of the degree of crystallinity.The remelting peak temperature could be returned close to that of the nascent state by annealing at 120~130 ℃.展开更多
A homologous series of heterocycles,6-methyl-2-（4-alkoxybenzylidenamino）benzothiazoles,were synthesized and characterized using FT-IR,^1H and ^（13）C NMR and mass spectrometric analysis.Enantiotropic nematic phase ...A homologous series of heterocycles,6-methyl-2-（4-alkoxybenzylidenamino）benzothiazoles,were synthesized and characterized using FT-IR,^1H and ^（13）C NMR and mass spectrometric analysis.Enantiotropic nematic phase was observed for shorter members.Smectic A phase only emerged from octyloxy derivative onwards.The terminal methyl group at the benzothiazole fragment and the Schiff base linkage influenced the mesomorphic behavior of the present series.展开更多
We provide an analytical study on the stability of equilibria of rigid rodlike nematic liquid crystalline polymers （LCPs） governed by the Smoluchowski equation with the Maier-Saupe intermolecular potential. We simpl...We provide an analytical study on the stability of equilibria of rigid rodlike nematic liquid crystalline polymers （LCPs） governed by the Smoluchowski equation with the Maier-Saupe intermolecular potential. We simplify the expression of the free energy of an orientational distribution function of rodlike LCP molecules by properly selecting a coordinate system and then investigate its stability with respect to perturbations of orientational probability density. By computing the Hessian matrix explicitly, we are able to prove the hysteresis phenomenon of nematic LCPs： when the normalized polymer concentration b is below a critical value b＊ （6.T314863965）, the only equilibrium state is isotropic and it is stable; when b＊ 〈 b 〈 15/2, two anisotropic （prolate） equilibrium states occur together with a stable isotropic equilibrium state. Here the more aligned prolate state is stable whereas the less aligned prolate state is unstable. When b 〉 15/2, there are three equilibrium states： a stable prolate state, an unstable isotropie state and an unstable oblate state.展开更多
Nematic liquid crystal system of interacting biaxial particles via dispersion forces is studied.The molecular orienting potential form in a magnetic field is given for the first time.Weakly ordered isotropic phase is ...Nematic liquid crystal system of interacting biaxial particles via dispersion forces is studied.The molecular orienting potential form in a magnetic field is given for the first time.Weakly ordered isotropic phase is treated in the two-particle cluster approximation.Taking account of the molecular biaxiality,it is found that the ratio of the lowest supercooling temperature T^(*)to the nematic-isotropic phase transition temperature TC approaches the observed value,and the validity of the mean field theory is clarified.展开更多
A kinetics approach is developed for the geometrically nonlinear analysis of photo-induced wrinkling of glassy twist nematic films on soft elastic substrates.In this way,the problem is reduced to finding the steady st...A kinetics approach is developed for the geometrically nonlinear analysis of photo-induced wrinkling of glassy twist nematic films on soft elastic substrates.In this way,the problem is reduced to finding the steady state of an overdamped evolution system according to a kinetic law,rather than directly solving the coupled nonlinear equations.This enables one to account for the complicated director distribution and obtain the precise wrinkling morphology of the film.Though the approach proposed here is for a twist nematic film,it can be extended to study glassy nematic films with other director distributions.展开更多
In this paper,we study a nematic liquid crystals system in three-dimensional whole space R3 and obtain the time decay rates of the higher-order spatial derivatives of the solution by the method of spectral analysis an...In this paper,we study a nematic liquid crystals system in three-dimensional whole space R3 and obtain the time decay rates of the higher-order spatial derivatives of the solution by the method of spectral analysis and energy estimates if the initial data belongs to L1（R3） additionally.展开更多
In this paper we derive LPS＇s criterion for the breakdown of classical solutions to the incompressible nematic liquid crystal flow, a simplified version of Ericksen-Leslie system modeling the hydrodynamic evolution o...In this paper we derive LPS＇s criterion for the breakdown of classical solutions to the incompressible nematic liquid crystal flow, a simplified version of Ericksen-Leslie system modeling the hydrodynamic evolution of nematic liquid crystals in R^3. We show that if 0 〈 T 〈 ＋∞ is the maximal time interval for the unique smooth solution u ∈ C^∞（[0, T）,R^3）,then ｜u｜＋｜△d｜∈L^q（[0,T],L^p（R^3））,where p and q satisfy the Ladyzhenskaya-Prodi-Serrin＇s condition：3/p＋2/q=1 and p∈（3,＋∞].展开更多
In this paper, a rotational invariant of interaction energy between two biaxial-shaped molecules is assumed and in the mean field approximation, nine elastic constants for simple distortion patterns in biaxial nematic...In this paper, a rotational invariant of interaction energy between two biaxial-shaped molecules is assumed and in the mean field approximation, nine elastic constants for simple distortion patterns in biaxial nematics are derived in terms of the thermal average （Dmn^（l）） （Dm＇n＇^（l＇））, where Dmn^（l） is the Wigner rotation matrix. In the lowest order terms, the elastic constants depend on coefficients Γ,Γ＇, λ, order parameters Q0 = Q0（D00^（2）） ＋Q2（D02^（2）＋D0-2^（2）） and Q2 = Q0（D20^（2）） ＋ Q2（D22^（2）＋D2-2^（2））. Here Γ and Γ＇ depend on the function form of molecular interaction energy vj′j″j （τ12） and probability function fk′k″k （τ12）, where r12 is the distance between two molecules, and λ is proportional to temperature. Q0 and Q2 are parameters related to multiple moments of molecules. Comparing these results with those obtained from Landau-de Gennes theory, we have obtained relationships between coefficients, order parameters used in both theories. In the special case of uniaxial nematics, both results are reduced to a degenerate case where K11=K33.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 11190022,11334010 and 11534007the National Basic Research Program of China under Grant No 2015CB921000the Strategic Priority Research Program(B)of Chinese Academy of Sciences under Grant No XDB07020300
文摘We report comprehensive angle-resolved photoemission investigations on the electronic structures and nematicity of the parent compounds of the iron-based superconductors including CeFeAsO, BaFe2As2, NaFeAs, FeSe and undoped FeSe/SrTiO3 films with 1, 2 and 20 layers. While the electronic structure near tile Brillouin zone center F varies dramatically among different materials, the electronic structure near the Brillouin zone corners （M points）, as well as their temperature dependence, are rather similar. The electronic structure near the zone corners is dominated by the electronic nematicity that gives rise to a band splitting of the dxz and dyz bands below the nematie transition temperature. A clear relation is observed between the band splitting magnitude arid the onset temperature of nematicity. Our results may shed light on the origin of nematicity, its effect on the electronic structures, and its relation with superconductivity in the iron-based superconductors.
基金Project supported by the National Key R&D Program of China(Grant Nos.2017YFA0303000 and 2016YFA0300201)the National Natural Science Foundation of China(Grant No.11888101)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB25000000)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY160000).
文摘The driving mechanism of nematicity and its twist with superconductivity in iron-based superconductors are still under debate.Recently,a dominant B1g-type strain effect on superconductivity is observed in underdoped iron-pnictides superconductors Ba(Fe_(1-x)Co_(x))_(2)As_(2),suggesting a strong interplay between nematicity and superconductivity.Since the long-range spin order is absent in FeSe superconductor,whether a similar strain effect could be also observed or not is an interesting question.Here,by utilizing a flexible film as substrate,we successfully achieve a wide-range-strain tuning of FeSe thin flake,in which both the tensile and compressive strain could reach up to~0.7%,and systematically study the strain effect on both superconducting and nematic transition(T_(c)and Ts)in the FeSe thin flake.Our results reveal a predominant A1g-type strain effect on T_(c).Meanwhile,Ts exhibits a monotonic anti-correlation with T_(c)and the maximum T_(c)reaches to 12 K when Ts is strongly suppressed under the maximum compressive strain.Finally,in comparison with the results in the underdoped Ba(Fe_(1-x)Co_(x))_(2)As_(2),the absence of B1g-type strain effect in FeSe further supports the role of stripe-type spin fluctuations on superconductivity.In addition,our work also supports that the orbital degree of freedom plays a key role to drive the nematic transition in FeSe.
文摘Subject Code:A04With the support by the National Natural Science Foundation of China,a collaborative study by the research groups led by Profs.Li Wei(李渭),Chen Xi(陈曦)and Xue Qikun(薛其坤)from Tsinghua University and Prof.Shen Zhixun(沈志勋)from Stanford University,demonstrates stripes developed
基金supported by the National Natural Science Foundation of China (Grant Nos. 11974405, 11674377, and 11634015)the Ministry of Science and Technology of China (Grant Nos. 2016YFA0300502, and 2017YFA0302904)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB33010100)。
文摘Understanding the nature of the mysterious pseudogap phenomenon is one of the most important issues associated with cuprate high-T_(c) superconductors.Here,we report 17O nuclear magnetic resonance(NMR) studies on two planar oxygen sites in stoichio?metric cuprate YBa_(2)Cu_(4)O_(8) to investigate the symmetry breaking inside the pseudogap phase.We observe that the Knight shifts of the two oxygen sites are identical at high temperatures but different below T_(nem) ~185 K,which is close to the pseudogap temperature T^(*).Our result provides a microscopic evidence for intra-unit-cell electronic nematicity.The difference in quadrupole resonance frequency between the two oxygen sites is unchanged below T_(nem),which suggests that the observed nematicity does not directly stem from the local charge density modulation.Furthermore,a short-range charge density wave(CDW) order is observed below T=150 K.The additional broadening in the 17O-NMR spectra because of this CDW order is determined to be inequivalent for the two oxygen sites,which is similar to that observed in case of nematicity.These results suggest a possible connection between nematicity,CDW order,and pseudogap.
基金supported by the National Key Research and Development Program of China under Grant No.2022YFA1405000Innovation Program for Quantum Science and Technology under Grant No.2024ZD0300101the National Natural Science Foundation of China under Grant Nos.12274212,12174184,12347102。
文摘Active matter exhibits collective motions at various scales.Geometric confinement has been identified as an effective way to control and manipulate active fluids,with much attention given to external factors.However,the impact of the inherent properties of active particles on collective motion under confined conditions remains elusive.Here,we use a highly tunable active nematics model to study active systems under confinement,focusing on the effect of the self-driven speed of active particles.We identify three distinct states characterized by unique particle and flow fields within confined active nematic systems,among which circular rotation emerges as a collective motion involving rotational movement in both particle and flow fields.The theoretical phase diagram shows that increasing the self-driven speed of active particles significantly enhances the region of the circular rotation state and improves its stability.Our results provide insights into the formation of high quality vortices in confined active nematic systems.
基金support from the National Nat-ural Science Foundation of China(Grant No.12474199)the Fundamental Research Funds for Central Universities of China(Grant No.20720240144),and 111 Project(B16029).
文摘Cell division is a fundamental biological process in which a parent cell divides into two daughter cells.The cell cortex,a thin layer primarily composed of actin filaments and myosin motors beneath the plasma membrane,plays a critical role in ensuring proper cell division.In this study,we apply a hydrodynamic model to describe the actin cortex as an active nematic surface,incorporating orientational order arising from actin filament alignment and anisotropic active stress produced by myosin motors.By analyzing the linearized dynamics,we investigate how shape,flow,and stress regulators evolve over time when the surface deviates slightly from a sphere.Our findings reveal that the active alignment of actin filaments,often overlooked in previous studies,is crucial for successful division.Furthermore,we demonstrate that a cortical chiral flow naturally emerges as a consequence of this active alignment.Overall,our results provide a mechanistic explanation for key phenomena observed during cell division,offering new insights into the role of active stress and filament alignment in cortical dynamics.
基金supported by the National Nature Science Foundation of China[Grant Nos.92365204 and 12274298(Z.K.Liu)]the National Key R&D program of China[Grant No.2022YFA1604400/03(Z.K.Liu)]Zhangjiang Laboratory(Y.M.Zhang).The authors thank BL02B at the Shanghai Synchrotron Radiation Facility supported by the National Natural Science Foundation of China(Contract No.11227902).
文摘Fe-based superconductors represent a fascinating class of materials,extensively studied for their complex interplay of superconductivity,magnetism,spin density waves,and nematicity,along with the interactions among these orders.An intriguing yet unexplained phenomenon observed in Fe-based superconductors is the emergence of superconductivity below 25K in the non-superconducting parent compound SrFe_(2)As_(2)following exposure to water at its surface.In this study,we employed in situ angle-resolved photoemission spectroscopy and low-energy electron diffraction to meticulously examine the electronic structure evolution of SrFe_(2)As_(2)upon in situ water dosing.Our findings indicate that water dosing markedly attenuates the spin density wave phase and surface Sr reconstruction while preserving the nematic order in SrFe_(2)As_(2).Furthermore,we detected an enhancement in the spectral weight of bands near the Fermi level.Our observations highlight the critical role of the intricate interplay among various orders induced by water dosing,which effectively modifies the band structure and favors the emergence of superconductivity in SrFe_(2)As_(2).
基金The National Natural Science Foundation of China(No.62401168,62401139,62401170)China Postdoctoral Science Foundation(No.2023MD744197)+2 种基金Postdoctoral Fellowship Program of CPSF(No.GZC20230631)Project for Enhancing Young and Middle-aged Teacher’s Research Basis Ability in Colleges of Guangxi(No.2023KY0218)Guangxi Key Laboratory Foundation of Optoelectronic Information Processing(No.GD23102)。
文摘A programmable low-profile array antenna based on nematic liquid crystals(NLCs)is proposed.Each antenna unit comprises a square patch radiating structure and a tunable NLC-based phase shifter capable of achieving a phase shift exceeding 360°with high linearity.First,the above 64 antenna units are periodically arranged into an 8×8 NLC-based antenna array,and the bias voltage of the NLC-based phase shifter loaded on the antenna unit is adjusted through the control of the field-programmable gate array(FPGA)programming sequences.This configuration enables precise phase changes for all 64 channels.Numerical simulation,sample processing,and experimental measurements of the antenna array are conducted to validate the performance of the antenna.The numerical and experimental results demonstrate that the proposed antenna performs well within the frequency range of 19.5-20.5 GHz,with a 3 dB relative bandwidth of 10%and a maximum main lobe gain of 14.1 dBi.A maximum scanning angle of±34°is achieved through the adjustment of the FPGA programming sequence.This NLC-based programmable array antenna shows promising potential for applications in satellite communication.
文摘A series of novel thermotropic liquid crystalline polyesters bearing nonlinear optical azobenzene side group were synthesized by high temperature solution polycondensation and their structures,thermal stability, phase transition behavior and crystallinity were characterized by IR,elemental analysis, TG-DTA, polarizing optical microscope (POM) equipped with a hot stage and X-ray diffraction techniques. The results demonstrate that all the synthesized polyesters exhibit nematic liquid crystalline phases and show relatively high glass transition temperatures and good thermal stability.
基金Hong Kong RGC Earmarked Research Grants 14305315,CUHK4041/11P and CUHK4048/13PThe Chinese University of Hong Kong,a Croucher Foundation-CAS Joint Grant,and a NSFC/RGC Joint Research Scheme(N-CUHK443/14)
文摘In this article, we prove the global existence of weak solutions to the non- isothermal nematic liquid crystal system on T2, on the basis of a new approximate system which is different from the classical Ginzburg-Landau approximation. Local in space energy inequalities are employed to recover the estimates on the second order spatial derivatives of the director fields locally in time, which cannot be derived from the basic energy balance. It is shown that these weak solutions satisfy the temperature equation, and also the total energy equation but away from at most finite many ＂singular＂ times, at which the energy concentration occurs and the director field losses its second order derivatives.
基金supported by the National Natural Science Foundation of China(Grant Nos.11274088,11374087,and 11304074)the Natural Science Foundation of Hebei Province,China(Grant No.A2014202123)+2 种基金the Research Project of Hebei Education Department,China(Grant Nos.Z2012061 and QN2014130)the Science and Technology Plan Project of Hebei Province,China(Grant No.134576260)the Key Subject Construction Project of Hebei Province University,China
文摘A detailed theoretical analysis of determining the sum of flexoelectric coefficients in nematic liquid crystals using the capacitance method is given. In the strong anchoring parallel aligned nematic （PAN） and hybrid aligned nematic （HAN） cells, the dependences of the capacitance on the sum of flexoelectric coefficients and the applied voltage are obtained by numerical simulations, and the distributions of the director and the electric potential for different applied voltages and flexoelectric coefficients are also given. Based on this theoretical analysis, we propose an experimental design for measuring the capacitance of a liquid crystal cell using the improved precision LCR meter E4980A （Agilent）. Through comparing the experimental data with the simulated results, the sum of flexoeletric coefficients can be determined.
基金This work was supported by the National Key Projects for Fundamental Research-“Macromoleular Condensed State”,Ministry of Science and Technology,China
文摘Ultra high molar mass polyethylene(UHPE)powder as polymerized in a slurry process has been studied,in its nascent state,after recrystallization on rapid cooling from the melt and after hot compression molding to a film,by DSC,effect of annealing the recrystallized specimen at 120 similar to 130 degreesC,morphology by polarizing optical microscopy and small angle X-ray scattering.Based on the experimental results obtained the macromolecular condensed state of the nascent UHPE powder is a rare case of a multi-chain condensed state of non-interpenetrating chains,involving interlaced extended chain crystalline layers and relaxed parallel chain amorphous layers.On melting,a nematic rubbery state of nanometer size domain resulted.The nematic-isotropic transition temperature was judged from literature data to be at least 220 degreesC,possibly higher than 300 ℃,the exact temperature is however not sue because of chain degradation at such high temperatures.The recrystallization process from the melt is a crystallization from a nematic rubbery state.The drop of remelting peak temperature by 10 K of the specimen recrystallized from its melt as compared to the nascent state has its origin in the decrease both of the crystalline chain stem length and of the degree of crystallinity.The remelting peak temperature could be returned close to that of the nascent state by annealing at 120~130 ℃.
基金Universiti Tunku Abdul Rahman and Ministry of Higher Education (MOHE) for the financial supports via LRGS(No.LR003-2011A)and research facilities
文摘A homologous series of heterocycles,6-methyl-2-（4-alkoxybenzylidenamino）benzothiazoles,were synthesized and characterized using FT-IR,^1H and ^（13）C NMR and mass spectrometric analysis.Enantiotropic nematic phase was observed for shorter members.Smectic A phase only emerged from octyloxy derivative onwards.The terminal methyl group at the benzothiazole fragment and the Schiff base linkage influenced the mesomorphic behavior of the present series.
基金supported by the National Science Foundation and by the Office of Naval Research
文摘We provide an analytical study on the stability of equilibria of rigid rodlike nematic liquid crystalline polymers （LCPs） governed by the Smoluchowski equation with the Maier-Saupe intermolecular potential. We simplify the expression of the free energy of an orientational distribution function of rodlike LCP molecules by properly selecting a coordinate system and then investigate its stability with respect to perturbations of orientational probability density. By computing the Hessian matrix explicitly, we are able to prove the hysteresis phenomenon of nematic LCPs： when the normalized polymer concentration b is below a critical value b＊ （6.T314863965）, the only equilibrium state is isotropic and it is stable; when b＊ 〈 b 〈 15/2, two anisotropic （prolate） equilibrium states occur together with a stable isotropic equilibrium state. Here the more aligned prolate state is stable whereas the less aligned prolate state is unstable. When b 〉 15/2, there are three equilibrium states： a stable prolate state, an unstable isotropie state and an unstable oblate state.
基金Supported by the Hebei Province Natural Science Foundation of China under Grant No.198002.
文摘Nematic liquid crystal system of interacting biaxial particles via dispersion forces is studied.The molecular orienting potential form in a magnetic field is given for the first time.Weakly ordered isotropic phase is treated in the two-particle cluster approximation.Taking account of the molecular biaxiality,it is found that the ratio of the lowest supercooling temperature T^(*)to the nematic-isotropic phase transition temperature TC approaches the observed value,and the validity of the mean field theory is clarified.
基金supported by the National Natural Science Foundation of China(Grant 11072231)Collaborative Innovation Center of Suzhou Nano Science and Technology
文摘A kinetics approach is developed for the geometrically nonlinear analysis of photo-induced wrinkling of glassy twist nematic films on soft elastic substrates.In this way,the problem is reduced to finding the steady state of an overdamped evolution system according to a kinetic law,rather than directly solving the coupled nonlinear equations.This enables one to account for the complicated director distribution and obtain the precise wrinkling morphology of the film.Though the approach proposed here is for a twist nematic film,it can be extended to study glassy nematic films with other director distributions.
基金supported by NNSFC(11271381and 11501373)China 973 Program(2011CB808002)+5 种基金the Natural Science Foundation of Guangdong Province(2016A0300310019 and 2016A030307042)Guangdong Provincial culture of seedling of China(2013LYM0081)the Education research platform project of Guangdong Province(2014KQNCX208)the Education Reform Project of Guangdong Province(2015558)the Shaoguan Science and Technology Foundation(20157201)Education Reform Project of Shaoguan University(SYJY20121361 and SYJY20141576)
文摘In this paper,we study a nematic liquid crystals system in three-dimensional whole space R3 and obtain the time decay rates of the higher-order spatial derivatives of the solution by the method of spectral analysis and energy estimates if the initial data belongs to L1（R3） additionally.
基金Supported by National Natural Science Foundation of China (10976026, 11271305, 11301439, 11226174)
文摘In this paper we derive LPS＇s criterion for the breakdown of classical solutions to the incompressible nematic liquid crystal flow, a simplified version of Ericksen-Leslie system modeling the hydrodynamic evolution of nematic liquid crystals in R^3. We show that if 0 〈 T 〈 ＋∞ is the maximal time interval for the unique smooth solution u ∈ C^∞（[0, T）,R^3）,then ｜u｜＋｜△d｜∈L^q（[0,T],L^p（R^3））,where p and q satisfy the Ladyzhenskaya-Prodi-Serrin＇s condition：3/p＋2/q=1 and p∈（3,＋∞].
基金Project supported by the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(Grant No07JKD140095)
文摘In this paper, a rotational invariant of interaction energy between two biaxial-shaped molecules is assumed and in the mean field approximation, nine elastic constants for simple distortion patterns in biaxial nematics are derived in terms of the thermal average （Dmn^（l）） （Dm＇n＇^（l＇））, where Dmn^（l） is the Wigner rotation matrix. In the lowest order terms, the elastic constants depend on coefficients Γ,Γ＇, λ, order parameters Q0 = Q0（D00^（2）） ＋Q2（D02^（2）＋D0-2^（2）） and Q2 = Q0（D20^（2）） ＋ Q2（D22^（2）＋D2-2^（2））. Here Γ and Γ＇ depend on the function form of molecular interaction energy vj′j″j （τ12） and probability function fk′k″k （τ12）, where r12 is the distance between two molecules, and λ is proportional to temperature. Q0 and Q2 are parameters related to multiple moments of molecules. Comparing these results with those obtained from Landau-de Gennes theory, we have obtained relationships between coefficients, order parameters used in both theories. In the special case of uniaxial nematics, both results are reduced to a degenerate case where K11=K33.
