The honeycomb magnet Na_(3)Co_(2)SbO_(6)recently emerged as a promising candidate for realizing Kitaev quantum spin liquid with relatively low levels of structural disorder.While the precise spin Hamiltonian remains c...The honeycomb magnet Na_(3)Co_(2)SbO_(6)recently emerged as a promising candidate for realizing Kitaev quantum spin liquid with relatively low levels of structural disorder.While the precise spin Hamiltonian remains controversial,the potential existence of a quantum spin liquid or other novel quantum magnetic phases continues to stimulate investigation.Here,we study the temperature and magnetic field-dependent spin excitations of Na_(3)Co_(2)SbO_(6)on a twin-free single crystal using magneto-terahertz(THz)spectroscopy,focusing on magnetic anisotropy and field-induced unusual phases.We observe a low-energy continuum excitation above T_(N)and a 0.5 THz(2 meV)spin wave excitation in magnetic order under zero field.Upon applying an in-plane magnetic field,the spin waves transform to a magnetic continuum over an intermediate field range,above which the system enters a spin-polarized state.Crucially,the spin excitation spectra reveal striking anisotropy between the a and b crystallographic axes,demanding description by a strongly anisotropic spin model.These findings establish Na_(3)Co_(2)SbO_(6)as a model system for investigating field-tunable quantum magnetism and potential spin liquid behavior in highly anisotropic systems.展开更多
With the improvement of electricity markets,the gradual aggravation of energy shortage and the environment pollution,it is urgent to formulate a new model to precisely satisfy the system demand for energy and reserve....With the improvement of electricity markets,the gradual aggravation of energy shortage and the environment pollution,it is urgent to formulate a new model to precisely satisfy the system demand for energy and reserve.Currently,power system opti-mization dispatching is always formulated as a discrete-time scheduling model.In this paper,we first demonstrate through an example that the upper and lower bounds of spinning reserve offered by a unit,given in the discrete-time model framework as constraints,is unreachable.This causes the problem that the reserve delivery obtained by the discrete-time scheduling model cannot be carried out precisely.From the detailed analysis of the ramp rate constraints,it is proved that the reachable upper and lower bounds of spinning reserve in every period can be expressed as functions of two variables,i.e.,generation level of unit at the start and end of this period.Thus,a new method is provided to calculate the upper and lower bounds of spinning reserve which are reachable in average.Furthermore,a new model based on this proposed method for joint scheduling of generation and reserve is presented,which considers the ability to realize the scheduled energy and reserve delivery.It converts the opti-mization based accurate scheduling for generation and reserve of power system from a continuous-time optimal control prob-lem to a nonlinear programming problem.Therefore,the proposed model can avoid the difficulties in solving a continu-ous-time optimal control problem.Based on the sequential quadratic programming method,numerical experiments for sched-uling electric power production systems are performed to evaluate the model and the results show that the new model is highly effective.展开更多
基金supported by National Natural Science Foundation of China(Grant Nos.12488201,12250008,12474138,and 12274004)the National Key Research and Development Program of China(Grant No.2021YFA1401901,2022YFA1403901,2023YFA1406002,and 2024YFA1408301)。
文摘The honeycomb magnet Na_(3)Co_(2)SbO_(6)recently emerged as a promising candidate for realizing Kitaev quantum spin liquid with relatively low levels of structural disorder.While the precise spin Hamiltonian remains controversial,the potential existence of a quantum spin liquid or other novel quantum magnetic phases continues to stimulate investigation.Here,we study the temperature and magnetic field-dependent spin excitations of Na_(3)Co_(2)SbO_(6)on a twin-free single crystal using magneto-terahertz(THz)spectroscopy,focusing on magnetic anisotropy and field-induced unusual phases.We observe a low-energy continuum excitation above T_(N)and a 0.5 THz(2 meV)spin wave excitation in magnetic order under zero field.Upon applying an in-plane magnetic field,the spin waves transform to a magnetic continuum over an intermediate field range,above which the system enters a spin-polarized state.Crucially,the spin excitation spectra reveal striking anisotropy between the a and b crystallographic axes,demanding description by a strongly anisotropic spin model.These findings establish Na_(3)Co_(2)SbO_(6)as a model system for investigating field-tunable quantum magnetism and potential spin liquid behavior in highly anisotropic systems.
基金supported by the National Natural Science Foundation of China(Grant Nos.60921003,60736027,61174161,60974101)the Spe-cialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20090121110022)+3 种基金the Fundamental Research Funds for the Central Universities of Xiamen University(Grant Nos.2011121047,201112G018,CXB2011035)the Key Research Project of Fujian Province of China(Grant No.2009H0044)Xiamen University National 211 3rd Period Project of China)(Grant No.0630-E72000)the Natural Sci-ence Foundation of Fujian Province,China(Grant No.2011J05154)
文摘With the improvement of electricity markets,the gradual aggravation of energy shortage and the environment pollution,it is urgent to formulate a new model to precisely satisfy the system demand for energy and reserve.Currently,power system opti-mization dispatching is always formulated as a discrete-time scheduling model.In this paper,we first demonstrate through an example that the upper and lower bounds of spinning reserve offered by a unit,given in the discrete-time model framework as constraints,is unreachable.This causes the problem that the reserve delivery obtained by the discrete-time scheduling model cannot be carried out precisely.From the detailed analysis of the ramp rate constraints,it is proved that the reachable upper and lower bounds of spinning reserve in every period can be expressed as functions of two variables,i.e.,generation level of unit at the start and end of this period.Thus,a new method is provided to calculate the upper and lower bounds of spinning reserve which are reachable in average.Furthermore,a new model based on this proposed method for joint scheduling of generation and reserve is presented,which considers the ability to realize the scheduled energy and reserve delivery.It converts the opti-mization based accurate scheduling for generation and reserve of power system from a continuous-time optimal control prob-lem to a nonlinear programming problem.Therefore,the proposed model can avoid the difficulties in solving a continu-ous-time optimal control problem.Based on the sequential quadratic programming method,numerical experiments for sched-uling electric power production systems are performed to evaluate the model and the results show that the new model is highly effective.
