Achieving long spin coherence times is crucial for quantum precision measurements,and closed-loop control techniques are often employed to accomplish this goal.Here,we demonstrate the impact of closed-loop feedback co...Achieving long spin coherence times is crucial for quantum precision measurements,and closed-loop control techniques are often employed to accomplish this goal.Here,we demonstrate the impact of closed-loop feedback control on nuclear spin precession in a metastability exchange optical pumping(MEOP)-based polarized^(3)He system.We analyze the effects of feedback theoretically and validate our predictions experimentally.With optimized feedback parameters,the spin coherence time T_(2)is extended by an order of magnitude.When the feedback strength surpasses a critical threshold,robust maser oscillations are spontaneously excited,demonstrating remarkable resistance to environmental noise and maintaining stable oscillation.This proof-of-principle experiment highlights the viability of MEOP-based^(3)He spin oscillators,especially in low-frequency domains.The operational simplicity and easy integration associated with MEOP-based systems make them particularly promising for fast,high-precision magnetic field measurements.展开更多
In this paper, the equilibrium properties of spin-1 Blume–Emery–Griffiths model are studied by using constant-coupling approximation. The dipolar and quadrupolar order parameters, the stable, metastable and unstable...In this paper, the equilibrium properties of spin-1 Blume–Emery–Griffiths model are studied by using constant-coupling approximation. The dipolar and quadrupolar order parameters, the stable, metastable and unstable states and free energy of the model are investigated. The states are defined in terms of local minima of the free energy of system. The numerical calculations are presented for several values of exchange interactions on the simple cubic lattice with q = 6.展开更多
Metastability,disorder and jamming are the typical characteristics of amorphous systems,while the related structure changes remain unclear.Sphere packing is often used as a structure model for amorphous and crystallin...Metastability,disorder and jamming are the typical characteristics of amorphous systems,while the related structure changes remain unclear.Sphere packing is often used as a structure model for amorphous and crystalline states.In this article,sphere packing systems with packing densities ranging from 0.50 to 0.74 were simulated by using Discrete Element Method(DEM),and the obtained packing structures were assessed to investigate the densification process and jamming properties.An order parameter that can effectively distinguish the order and disorder of packing structures was proposed based on the distribution characteristics of jamming angles.Then the evolution of jamming characteristics during the transition from Random Loose Packing(RLP)to Random Close Packing(RCP)and the jamming-jamming relations of different packing structures were demonstrated.On this basis,a correlation between order-jamming-metastable states from the microscopic structural perspective was established,which is of valuable theoretical and practical implications for the characterization and synthesis of crystalline and amorphous materials.展开更多
A family of irreducible Markov chains on a finite state space is considered as an exponential perturbation of a reducible Markov chain. This is a generalization of the Freidlin-Wentzell theory, motivated by studies of...A family of irreducible Markov chains on a finite state space is considered as an exponential perturbation of a reducible Markov chain. This is a generalization of the Freidlin-Wentzell theory, motivated by studies of stochastic Ising models, neural network and simulated annealing. It is shown that the metastability is a universal feature for this wide class of Markov chains. The metastable states are simply those recurrent states of the reducible Markov chain. Higher level attractors, related attractive basins and their pyramidal structure are analysed. The logarithmic asymptotics of the hitting time of various sets are estimated. The hitting time over its mean converges in law to the unit exponential distribution.展开更多
The molecular mechanisms controlling mouse embryonic stem cell(ESC)metastability,i.e.their capacity to fluctuate between different states of pluripotency,are not fully resolved.We developed and used a novel automation...The molecular mechanisms controlling mouse embryonic stem cell(ESC)metastability,i.e.their capacity to fluctuate between different states of pluripotency,are not fully resolved.We developed and used a novel automation platform,the Cellmaker,to screen a library of metabolites on two ESC-based phenotypic assays(i.e.proliferation and colony phenotype)and identified two metabolically related amino acids,namely L-proline(L-Pro)and L-ornithine(L-Orn),as key regulators of ESC metastability.Both compounds,but mainly L-Pro,force ESCs toward a novel epiblast stem cell(EpiSC)-like state,in a dose-and time-dependent manner.Unlike EpiSCs,L-Pro-induced cells(PiCs)contribute to chimeric embryos and rely on leukemia inhibitor factor(LIF)to self-renew.Furthermore,PiCs revert to ESCs or differentiate randomly upon removal of either L-Pro or LIF,respectively.Remarkably,PiC generation depends on both L-Pro metabolism(uptake and oxidation)and Fgf5 induction,and is strongly counteracted by antioxidants,mainly L-ascorbic acid(vitamin C,Vc).ESCs↔PiCs phenotypic transition thus represents a previously undefined dynamic equilibrium between pluripotent states,which can be unbalanced either toward an EpiSC-like or an ESC phenotype by L-Pro/L-Orn or Vc treatments,respectively.All together,our data provide evidence that ESC metastability can be regulated at a metabolic level.展开更多
Hyperpolarized^(3)He nuclei have emerged as a significantly important approach in quantum precision measurement techniques,with extensive applications in fundamental physics,magnetometry,metrology,and beyond.In this s...Hyperpolarized^(3)He nuclei have emerged as a significantly important approach in quantum precision measurement techniques,with extensive applications in fundamental physics,magnetometry,metrology,and beyond.In this study,we report on the design and implementation of a^(3)He polarization system at the China Mianyang Research Reactor(CMRR),utilizing the metastabilityexchange optical pumping(MEOP)method.We employed a Merritt coil system consisting of four square coils to furnish a uniform holding field.We deployed a 2 W fiber laser to pump the metastable^(3)He atoms and conducted free induction decay(FID)detection of the polarized^(3)He nuclei using both pickup coil and optical methods.For the optical method,we used a50 m W linearly polarized distributed Bragg reflector(DBR)laser as the probe.We applied transverse light absorption polarimetry to measure the absolute nuclear polarization of the ground-state^(3)He.We have developed cell fabrication capabilities at the CMRR,and cells at various pressures ranging from 100 to 1000 Pa have been fabricated and evaluated.For a typical borosilicate cell with 100 Pa pressure,the absolute polarization is measured as Pn≈70%,and the transverse relaxation time is estimated as T2≈0.5 s.Moreover,we constructed a few aluminosilicate cells,each carefully filled with pure^(3)He at a pressure of 100 Pa.Subsequently,we conducted a comprehensive evaluation of their performance in the context of MEOP.展开更多
Planar cations or anions can form stacks in crystals or solutions,where the surrounding or environment plays a decisive role as demonstrated in previous studies.However,it remains unclear whether these counterintuitiv...Planar cations or anions can form stacks in crystals or solutions,where the surrounding or environment plays a decisive role as demonstrated in previous studies.However,it remains unclear whether these counterintuitive interactions possess any inherent stability or are thoroughly repulsive if the constraint of environment is removed.In this work,we explored the inherent stability ofπ-πstacking between closed-shell ions of like charges with prototypes derived from experimental studies.The inherent metastability was identified by the characteristic local minima and the transition states preventing their dissociation and verified by ab initio molecular dynamics(AIMD)simulations.The nature of involved interactions was deciphered with the energy decomposition approach based on the block-localized wavefunction method(BLW-ED).Like the conventional neutralπ-πstacking interactions,electron correlation is the most attractive energy component.But it is overturned by the Coulombic repulsion between net charges for all modes of dimerization,resulting in the overall repulsive inter-cation or anion in-teractions.Contributions from van der Waals interactions were also observed in the reduced density gradient analysis.The origin of the metastability was elucidated by examining the contributions of individual physical factors to the well-depths.The inherent metastability originates from the electron correlation,which dramatically increases due to the enhanced overlap between ions from a transition state to its corresponding minimum.展开更多
This work studies the stability and metastability of stationary patterns in a diffusionchemotaxis model without cell proliferation.We first establish the interval of unstable wave modes of the homogeneous steady state...This work studies the stability and metastability of stationary patterns in a diffusionchemotaxis model without cell proliferation.We first establish the interval of unstable wave modes of the homogeneous steady state,and show that the chemotactic flux is the key mechanism for pattern formation.Then,we treat the chemotaxis coefficient as a bifurcation parameter to obtain the asymptotic expressions of steady states.Based on this,we derive the sufficient conditions for the stability of one-step pattern,and prove the metastability of two or more step patterns.All the analytical results are demonstrated by numerical simulations.展开更多
The sequence of ground states for SrTiO_(3) film subjected to epitaxial strain as well as to mechanical stress along the[001]and[110]axes is calculated from first principles within the density functional theory.Under ...The sequence of ground states for SrTiO_(3) film subjected to epitaxial strain as well as to mechanical stress along the[001]and[110]axes is calculated from first principles within the density functional theory.Under the fixed-strain boundary conditions,an increase in the lattice parameter of a substrate results in the I4cm→I4/mcm→Ima2→Cm→Fmm2→Ima2(II)sequence of ground states.Under the fixed-stress boundary conditions,the phase sequence is different and depends on how the stress is applied.It is revealed that the simultaneous presence of competing ferroelectric and antiferrodistortive instabilities in SrTiO_(3) gives rise to the appearance of metastable phases,whose number increases dramatically under the fixed-stress conditions.In the metastable phases,the octahedral rotation patterns are shown to differ substantially from those in the ground state.It is suggested that in systems with competing instabilities,each polar phase has its optimal octahedral rotation pattern which stabilizes this phase and creates a potential barrier preventing this phase to be transformed into other structures.展开更多
The phase metastability and precipitation are now considered to be an important strategy in designing Fe-rich high entropy alloys(HEAs).In this study,the influence of silicon addition on the initial and straininduced ...The phase metastability and precipitation are now considered to be an important strategy in designing Fe-rich high entropy alloys(HEAs).In this study,the influence of silicon addition on the initial and straininduced microstructure evolution and related mechanical property of Fe52−xMn27Cr15Co6Six(x=0,0.3,0.5,1.0,1.5,at.%)HEAs was systematically investigated by utilizing the in-depth microstructural characterization coupled with X-ray diffractometer(XRD),secondary electron microscopy(SEM),and transmission electron microscopy(TEM).The addition of Si to Fe52−xMn27Cr15Co6Six HEAs facilitates the triplex structure consisting of fcc-γmatrix,thermally-inducedε-martensite and sigma phase(σ).The lattice distortion energy by Si atoms is suggested to promote the formation ofσphase consisting of Cr,Si and Co and consequently influence the metastability of the matrix.In 0.3 at.%Si HEA,the strain-induced bodycentered tetragonal(bct)-typeα’-martensite were observed at the intersection of bi-directional straininducedε-martensite laths,enhancing the ultimate tensile strength to∼851 MPa from∼618.3 MPa with ductility increment(∼73.1%from∼71%).In 0.3 at.%Si and 0.5 at.%Si alloys,the granular-typeσphase was observed both at grain boundaries and in grain interior,and the size of granular-typeσphase at grain boundary and intra-granularσphase were found to be similar.The deformation mode altered from the transformation-induced plasticity(TRIP)to twinning-induced plasticity(TWIP)with an increase of Si content to 1.5 at.%,due to the enhanced fcc-γstability induced by the compositional modulation driven by increasedσphase formation.The propagation of microcracks inside brittleσphase could be suppressed by homogeneous slip through strain-induced martensite transformation(SIMT)in HEAs with low Si addition of 0.3at.%-0.5 at.%.展开更多
This study investigates the development of novel high-entropy alloys(HEAs)with enhanced mechanical properties through an innovative fabrication method of direct energy deposition(DED).The focus is on the creation of m...This study investigates the development of novel high-entropy alloys(HEAs)with enhanced mechanical properties through an innovative fabrication method of direct energy deposition(DED).The focus is on the creation of metastable core-shell precipitation-strengthened HEAs that exhibit a unique multi-stage terrace-like slip wave toughening mechanism,a novel approach to improving both strength and ductility simultaneously.Mechanical testing reveals that the developed HEAs exhibit superior mechanical proper-ties,including high yield strength,ultimate tensile strength,and exceptional ductility.The improvement in these properties is attributed to the multi-stage terrace-like slip wave toughening mechanism activated by the unique microstructural features.This toughening mechanism involves the sequential activation of slip systems,facilitated by the stress concentration around the core-shell precipitates and the subsequent propagation of slip waves across the material.The terrace-like pattern of these slip waves enhances the material's ability to deform plastically,providing a significant toughening effect while maintaining high strength levels.Furthermore,the study delves into the fundamental interactions between the microstruc-tural elements and the deformation mechanisms.It elucidates how the core-shell precipitates and the matrix cooperate to distribute stress uniformly,delay the onset of necking,and prevent premature failure.This synergistic interaction between the microstructural features and the slip wave toughening mecha-nism is central to the remarkable balance of strength and ductility achieved in the HEAs.The introduction of a multi-stage terrace-like slip wave toughening mechanism offers a new pathway to designing HEAs with an exceptional amalgamation of strength and ductility.展开更多
The effect of hot deformation onα-phase precipitation during the subsequent heat treatment,as well as the mechanical properties of TB18 Ti-alloy,was investigated.Results show that the round bar obtained by the dual-p...The effect of hot deformation onα-phase precipitation during the subsequent heat treatment,as well as the mechanical properties of TB18 Ti-alloy,was investigated.Results show that the round bar obtained by the dual-phase field forging of the cast ingot exhibits uniform composition distribution on its cross-section.However,various degrees of deformation are detected at different positions on the cross-section,which is attributed to the characteristics of the forging process.Under the forging condition,the microstructure is mainly composed ofβ-phase matrix and coarsened discontinuous primaryα-phases.After solution and following artificial aging treatment,the primaryα-phases disappear,while needle-like secondaryα-phases precipitate in the matrix.Additionally,dispersed white zones are observed in the samples after aging,which are analyzed to be the precipitation-free zones of secondaryα-phase.Despite a uniform compositional distribution among various regions,these dispersed white zones exhibit higher content and larger size in the positions that have undergone lower forging deformation.It indicates that the insufficient forging deformation inhibits the precipitation of the secondaryα-phase,ultimately resulting in the lower strengthening effect by heat treatment.Thus,consistent with the characteristics of the forging process,a periodic variation of sample in strength is detected along the circumferential direction of the forged round bar.展开更多
High-pressure β-Sn germanium may transform into diverse metastable allotropes with distinctive nanostructures and unique physical properties via multiple pathways under decompression.However,the mechanism and transit...High-pressure β-Sn germanium may transform into diverse metastable allotropes with distinctive nanostructures and unique physical properties via multiple pathways under decompression.However,the mechanism and transition kinetics remain poorly understood.Here,we investigate the formation of metastable phases and nanostructures in germanium via controllable transition pathways of β-Sn Ge under rapid decompression at different rates.High-resolution transmission electron microscopy reveals three distinct metastable phases with the distinctive nanostructures:an almost perfect st12 Ge crystal,nanosized bc8/r8 structures with amorphous boundaries,and amorphous Ge with nanosized clusters (0.8–2.5 nm).Fast in situ x-ray diffraction and x-ray absorption measurements indicate that these nanostructured products form in certain pressure regions via distinct kinetic pathways and are strongly correlated with nucleation rates and electronic transitions mediated by compression rate,temperature,and stress.This work provides deep insight into the controllable synthesis of metastable materials with unique crystal symmetries and nanostructures for potential applications.展开更多
Laboratory and field observations have suggested a correlation between contact dynamics and slow dynamics.The underlying mechanical mechanisms at the contact level require investigation at the nanoscale.This study use...Laboratory and field observations have suggested a correlation between contact dynamics and slow dynamics.The underlying mechanical mechanisms at the contact level require investigation at the nanoscale.This study uses molecular dynamics(MD)simulations to investigate the interactions between two quartz plates separated by a water film,focusing on the relationship between adhesion force and separation distance.The density and orientation angle profiles were calculated from simulation data to investigate the relationship between the interfacial structure of the water film and contact potential.The simulations reveal multiple metastable states of the contact potential,consistent with existing theoretical models.The results show that the contact force is influenced by the structure of the water film,including oscillation forces and stratification.This provided verification and development for existing theoretical models based on metastable contacts.展开更多
The spray-deposition was used to produce billets of Mg-4Al-1.5Zn-3Ca-1Nd(A alloy)and Mg-13Al-3Zn-3Ca-1Nd(B alloy),and evolution of deformation substructure and Mg_(x)Zn_(y)Ca_(z)metastable phase in fine-grained(3μm)M...The spray-deposition was used to produce billets of Mg-4Al-1.5Zn-3Ca-1Nd(A alloy)and Mg-13Al-3Zn-3Ca-1Nd(B alloy),and evolution of deformation substructure and Mg_(x)Zn_(y)Ca_(z)metastable phase in fine-grained(3μm)Mg alloys was investigated by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),and electron backscattered diffraction(EBSD).It was found that different dislocation configurations were formed in A and B alloys.Redundant free dislocations(RFDs)and dislocation tangles were the ways to form deformation substructure in A alloy,no RFDs except dislocation tangles were found in B alloy.The interaction between nano-scale second phase particles(nano-scale C15 andβ-Mg_(17)(Al,Zn)_(12)phase)and different dislocation configurations had a significant effect on the deformation substructures formation.The mass transfer of Mg_(x)Zn_(y)Ca_(z)metastable phases and the stacking order of stacking faults were conducive to the Mg-Nd-Zn typed long period stacking ordered(LPSO)phases formation.Nano-scale C15 phases,Mg-Nd-Zn typed LPSO phases,c/a ratio,β-Mg_(17)(Al,Zn)_(12)phases were the key factors influencing the formation of textures.Different textures and grain boundary features(GB features)had a significant effect on k-value.The non-basal textures were the main factor affecting k-value in A alloy,while the high-angle grain boundary(HAGB)was the main factor affecting k-value in B alloy.展开更多
The electrolysis of alkaline seawater is critical for sustainable hydrogen production but is hindered by the sluggish oxygen evolution reaction in saline environments.Advanced electrocatalysts with tailored structures...The electrolysis of alkaline seawater is critical for sustainable hydrogen production but is hindered by the sluggish oxygen evolution reaction in saline environments.Advanced electrocatalysts with tailored structures and electronic properties are essential,and phase engineering provides a transformative approach by modulating crystallographic symmetry and electronic configurations.Two-dimensional(2D)LaMnO_(3) perovskites show promise due to their exposed active sites and tunable electronic properties.However,the conventional stable rhombohedral phase limits oxygen diffusion despite good electron transport.Unconventional metastable phases with superior symmetry enhance lattice oxygen activity in saline environments but are challenging to synthesize.Herein,we propose a microwave shock method incorporating Co atoms to rapidly produce 2D LaMnO_(3) in rhombohedral,hexagonal,and metastable cubic phases.This strategy circumvents the limitations of high-temperature synthesis,preserving the 2D morphology while enabling the formation of metastable cubic phases.The metastable cubic phase exhibits superior OER activity and stability even in alkaline seawater due to optimal symmetry,interlayer spacing,and Mn-O covalency.X-ray absorption spectroscopy and theoretical calculations further highlight its balanced oxygen adsorption and desorption.This work underscores the role of metastable phase engineering in advancing seawater electrolysis and establishes a scalable route for designing high-performance 2D electrocatalysts.展开更多
The extensive applications of cubic silicon in flexible transistors and infrared detectors are greatly hindered by its intrinsic properties.Metastable silicon phases,such as Si-Ⅲ,Ⅳ,andⅫ,prepared using extreme press...The extensive applications of cubic silicon in flexible transistors and infrared detectors are greatly hindered by its intrinsic properties.Metastable silicon phases,such as Si-Ⅲ,Ⅳ,andⅫ,prepared using extreme pressure methods,provide a unique“genetic bank”with diverse structures and exotic characteristics.However,exploration of their inherent physical properties remains underdeveloped.Herein,we demonstrate the phase engineering strategy to modulate the thermal conductivity and mechanical properties of metastable silicon.The thermal conductivity,obtained via the Raman optothermal approach,exhibits broad tunability across various Si-Ⅰ,Ⅲ,Ⅻ,andⅣphases.The hardness and Young's modulus of Si-Ⅳare significantly greater than those of the Si-Ⅲ/Ⅻmixture,as confirmed by the nanoindentation technique.Moreover,it was found that pressure-induced structural defects can substantially degrade the thermal and mechanical properties of silicon.This systematic investigation offers a feasible route for designing novel semiconductors and further advancing their desirable applications in advanced nanodevices and mechanical transducers.展开更多
In recent years,aqueous aluminum ion batteries have been widely studied owing to their abundant energy storage and high theo retical capacity.An in-depth study of vanadium oxide materials is necessary to address the p...In recent years,aqueous aluminum ion batteries have been widely studied owing to their abundant energy storage and high theo retical capacity.An in-depth study of vanadium oxide materials is necessary to address the precipitation of insoluble products covered cathode surface and the slow reaction kinetics.Therefore,a method using a simple one-step hydrothermal preparation and oxalic acid to regulate oxygen vacancies has been reported.A high starting capacity(400 mAh g^(-1))can be achieved by Ov-V2O5,and it is capable of undergoing 200 cycles at 0.4 A g^(-1),with a termination discharge capacity of103 mAh g^(-1).Mechanism analysis demonstrated that metastable structures(AlxV2O5and HxV2O5)were constructed through the insertion of Al^(3+)/H^(+)during discharging,which existed in the lattice intercalation with V2O5.The incorporation of oxygen vacancies lowers the reaction energy barrier while improving the ion transport efficiency.In addition,the metastable structure allows the electrostatic interaction between Al3+and the main backbone to establish protection and optimize the transport channel.In parallel,this work exploits ex-situ characterization and DFT to obtain a profound insight into the instrumental effect of oxygen vacancies in the construction of metastable structures during in-situ electrochemical activation,with a view to better understanding the mechanism of the synergistic participation of Al3+and H+in the reaction.This work not only reports a method for cathode materials to modulate oxygen vacancies,but also lays the foundation for a deeper understanding of the metastable structure of vanadium oxides.展开更多
Reinforcing bars in concrete structures in marine environment are prone to pitting corrosion,which threatens the safety of engineering structures.In order to effectively mitigate the pitting corrosion of reinforcing b...Reinforcing bars in concrete structures in marine environment are prone to pitting corrosion,which threatens the safety of engineering structures.In order to effectively mitigate the pitting corrosion of reinforcing bars,the electrochemical testing and atomic force microscopy are adopted,the effect of triethanolamine dodecylbenzene sulfonate(TDS)on metastable pitting behavior of 304 stainless steel(304 SS)in simulated concrete pore solutions(SCPS)with chlorine contamination was studied.The results show that the corrosion potential(Ecorr)and breakdown potential(Eb)increased with the growth of the TDS concentrations.Statistical cha-racteristics of metastable pits suggested that as the TDS concentrations increased in the SCPS,the parameters were all decreased.The Mott-Schottky tests exhibited that,although the donor density(ND)diminished,the thickness of the space charge layer(W)increased with increasing TDS concentrations.Investigation results showed that TDS inhibited the sprouting and growth of metastable pits,and with greater TDS concentration,it becomes more difficult for metastable pits to transfer into stable pits in the SCPS,the generated stable passive film prevented the sprouting of pitting corrosion,It is recommended to use TDS with a concentration of not less than 3.364×10^(-4) mol/L in engineering,so that the sensitivity of passivation film of 304SS to chloride erosion is reduced.展开更多
To overcome the strength-plasticity trade-offin the structural titanium alloys,a novel metastableβti-tanium alloy Ti-5Mo-4Cr-1V-1Zr(Ti-5411)with high strength and high plasticity was designed by the d-electrons theor...To overcome the strength-plasticity trade-offin the structural titanium alloys,a novel metastableβti-tanium alloy Ti-5Mo-4Cr-1V-1Zr(Ti-5411)with high strength and high plasticity was designed by the d-electrons theory,average electron-to-atom ratio(e/α^(-))and atomic radius difference(Δr^(-))theory.Com-bined in-situ scanning electron microscope(SEM)and electron backscatter diffraction(EBSD),the defor-mation mechanisms of the novel Ti-5411 metastableβtitanium alloy were systematically investigated.The results show that the Ti-5411 alloy exhibits excellent yield strength(∼689 MPa),tensile strength(∼930 MPa)and total elongation(∼39%).The in-situ tension indicates that slip activities,crystal rota-tion,stress induced martensite(SIM)α''transformation and{332}<113>deformation twin are the major deformation mechanisms of Ti-5411 alloy.Besides,with the increase of strain degree(0-0.5 mm displace-ment),deformation twins increase,widen and interlace.At 0.35 mm tensile displacement,the orientation of theβgrains rotates∼6.65°to accommodate the increased macrostrain.Additionally,martensiteα''also assists the nucleation of twins.Some{332}<113>twins grow and merge by consuming martensiteα''during deformation,and the residual martensiteα''remains in the merged twins.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.U2230207)。
文摘Achieving long spin coherence times is crucial for quantum precision measurements,and closed-loop control techniques are often employed to accomplish this goal.Here,we demonstrate the impact of closed-loop feedback control on nuclear spin precession in a metastability exchange optical pumping(MEOP)-based polarized^(3)He system.We analyze the effects of feedback theoretically and validate our predictions experimentally.With optimized feedback parameters,the spin coherence time T_(2)is extended by an order of magnitude.When the feedback strength surpasses a critical threshold,robust maser oscillations are spontaneously excited,demonstrating remarkable resistance to environmental noise and maintaining stable oscillation.This proof-of-principle experiment highlights the viability of MEOP-based^(3)He spin oscillators,especially in low-frequency domains.The operational simplicity and easy integration associated with MEOP-based systems make them particularly promising for fast,high-precision magnetic field measurements.
文摘In this paper, the equilibrium properties of spin-1 Blume–Emery–Griffiths model are studied by using constant-coupling approximation. The dipolar and quadrupolar order parameters, the stable, metastable and unstable states and free energy of the model are investigated. The states are defined in terms of local minima of the free energy of system. The numerical calculations are presented for several values of exchange interactions on the simple cubic lattice with q = 6.
基金the National Natural Science Foundation of China(grant No.51374070)Liaoning Revitalization Talents Program(grant No.XLYC1805007)of ChinaNatural Science Foundation of Jiangsu Province(grant No.BK20200269)for the financial support to this work.
文摘Metastability,disorder and jamming are the typical characteristics of amorphous systems,while the related structure changes remain unclear.Sphere packing is often used as a structure model for amorphous and crystalline states.In this article,sphere packing systems with packing densities ranging from 0.50 to 0.74 were simulated by using Discrete Element Method(DEM),and the obtained packing structures were assessed to investigate the densification process and jamming properties.An order parameter that can effectively distinguish the order and disorder of packing structures was proposed based on the distribution characteristics of jamming angles.Then the evolution of jamming characteristics during the transition from Random Loose Packing(RLP)to Random Close Packing(RCP)and the jamming-jamming relations of different packing structures were demonstrated.On this basis,a correlation between order-jamming-metastable states from the microscopic structural perspective was established,which is of valuable theoretical and practical implications for the characterization and synthesis of crystalline and amorphous materials.
基金Project partially supported by the National Natural Science Foundation of China and a Postdoctoral Fellowship of the State Education Commission.
文摘A family of irreducible Markov chains on a finite state space is considered as an exponential perturbation of a reducible Markov chain. This is a generalization of the Freidlin-Wentzell theory, motivated by studies of stochastic Ising models, neural network and simulated annealing. It is shown that the metastability is a universal feature for this wide class of Markov chains. The metastable states are simply those recurrent states of the reducible Markov chain. Higher level attractors, related attractive basins and their pyramidal structure are analysed. The logarithmic asymptotics of the hitting time of various sets are estimated. The hitting time over its mean converges in law to the unit exponential distribution.
基金This work was supported by Associazione Italiana Ricerca sul Cancro[IG-6128 to G.M.and IG-4840 to S.D.F.]Telethon[GGP-08120 to G.M.]+1 种基金Regione Campania-Programma Operativo Regionale[CRdC WP11 to S.F.,S.D.F,D.D.C.,G.M.and E.J.P.]Ministero Istruzione Universita Ricerca[Medical Research in Italy RBNE08HM7T_003 to E.J.P.].
文摘The molecular mechanisms controlling mouse embryonic stem cell(ESC)metastability,i.e.their capacity to fluctuate between different states of pluripotency,are not fully resolved.We developed and used a novel automation platform,the Cellmaker,to screen a library of metabolites on two ESC-based phenotypic assays(i.e.proliferation and colony phenotype)and identified two metabolically related amino acids,namely L-proline(L-Pro)and L-ornithine(L-Orn),as key regulators of ESC metastability.Both compounds,but mainly L-Pro,force ESCs toward a novel epiblast stem cell(EpiSC)-like state,in a dose-and time-dependent manner.Unlike EpiSCs,L-Pro-induced cells(PiCs)contribute to chimeric embryos and rely on leukemia inhibitor factor(LIF)to self-renew.Furthermore,PiCs revert to ESCs or differentiate randomly upon removal of either L-Pro or LIF,respectively.Remarkably,PiC generation depends on both L-Pro metabolism(uptake and oxidation)and Fgf5 induction,and is strongly counteracted by antioxidants,mainly L-ascorbic acid(vitamin C,Vc).ESCs↔PiCs phenotypic transition thus represents a previously undefined dynamic equilibrium between pluripotent states,which can be unbalanced either toward an EpiSC-like or an ESC phenotype by L-Pro/L-Orn or Vc treatments,respectively.All together,our data provide evidence that ESC metastability can be regulated at a metabolic level.
基金supported by the National Natural Science Foundation of China(Grant Nos.U2230207,U2030209,12305114,and 12305125)Sichuan Science and Technology Program(Grant No.2024NSFSC1356)the National Key Research and Development Program of China(Grant Nos.2020YFA0406001,and 2020YFA0406002)。
文摘Hyperpolarized^(3)He nuclei have emerged as a significantly important approach in quantum precision measurement techniques,with extensive applications in fundamental physics,magnetometry,metrology,and beyond.In this study,we report on the design and implementation of a^(3)He polarization system at the China Mianyang Research Reactor(CMRR),utilizing the metastabilityexchange optical pumping(MEOP)method.We employed a Merritt coil system consisting of four square coils to furnish a uniform holding field.We deployed a 2 W fiber laser to pump the metastable^(3)He atoms and conducted free induction decay(FID)detection of the polarized^(3)He nuclei using both pickup coil and optical methods.For the optical method,we used a50 m W linearly polarized distributed Bragg reflector(DBR)laser as the probe.We applied transverse light absorption polarimetry to measure the absolute nuclear polarization of the ground-state^(3)He.We have developed cell fabrication capabilities at the CMRR,and cells at various pressures ranging from 100 to 1000 Pa have been fabricated and evaluated.For a typical borosilicate cell with 100 Pa pressure,the absolute polarization is measured as Pn≈70%,and the transverse relaxation time is estimated as T2≈0.5 s.Moreover,we constructed a few aluminosilicate cells,each carefully filled with pure^(3)He at a pressure of 100 Pa.Subsequently,we conducted a comprehensive evaluation of their performance in the context of MEOP.
基金support from the Natural Science Foundation of China(No.22073060)support from the Natural Science Foundation of China(No.22273054)This work was performed in part at the Joint School of Nanoscience and Nanoengineering,a member of the National Nanotechnology Coordinated Infrastructure(NNCI),which is supported by the US National Science Foundation(Grant ECCS-2025462).
文摘Planar cations or anions can form stacks in crystals or solutions,where the surrounding or environment plays a decisive role as demonstrated in previous studies.However,it remains unclear whether these counterintuitive interactions possess any inherent stability or are thoroughly repulsive if the constraint of environment is removed.In this work,we explored the inherent stability ofπ-πstacking between closed-shell ions of like charges with prototypes derived from experimental studies.The inherent metastability was identified by the characteristic local minima and the transition states preventing their dissociation and verified by ab initio molecular dynamics(AIMD)simulations.The nature of involved interactions was deciphered with the energy decomposition approach based on the block-localized wavefunction method(BLW-ED).Like the conventional neutralπ-πstacking interactions,electron correlation is the most attractive energy component.But it is overturned by the Coulombic repulsion between net charges for all modes of dimerization,resulting in the overall repulsive inter-cation or anion in-teractions.Contributions from van der Waals interactions were also observed in the reduced density gradient analysis.The origin of the metastability was elucidated by examining the contributions of individual physical factors to the well-depths.The inherent metastability originates from the electron correlation,which dramatically increases due to the enhanced overlap between ions from a transition state to its corresponding minimum.
基金Manjun Ma was supported by the National Natural Science Foundation of China(Nos.12071434 and 11671359).
文摘This work studies the stability and metastability of stationary patterns in a diffusionchemotaxis model without cell proliferation.We first establish the interval of unstable wave modes of the homogeneous steady state,and show that the chemotactic flux is the key mechanism for pattern formation.Then,we treat the chemotaxis coefficient as a bifurcation parameter to obtain the asymptotic expressions of steady states.Based on this,we derive the sufficient conditions for the stability of one-step pattern,and prove the metastability of two or more step patterns.All the analytical results are demonstrated by numerical simulations.
基金supported by Russian Foundation for Basic Research grant No.13-02-00724.
文摘The sequence of ground states for SrTiO_(3) film subjected to epitaxial strain as well as to mechanical stress along the[001]and[110]axes is calculated from first principles within the density functional theory.Under the fixed-strain boundary conditions,an increase in the lattice parameter of a substrate results in the I4cm→I4/mcm→Ima2→Cm→Fmm2→Ima2(II)sequence of ground states.Under the fixed-stress boundary conditions,the phase sequence is different and depends on how the stress is applied.It is revealed that the simultaneous presence of competing ferroelectric and antiferrodistortive instabilities in SrTiO_(3) gives rise to the appearance of metastable phases,whose number increases dramatically under the fixed-stress conditions.In the metastable phases,the octahedral rotation patterns are shown to differ substantially from those in the ground state.It is suggested that in systems with competing instabilities,each polar phase has its optimal octahedral rotation pattern which stabilizes this phase and creates a potential barrier preventing this phase to be transformed into other structures.
基金financially supported by the National Research Foundation of Korea(NRF)grants funded by the Korean Govern-ment(Nos.RS-2023-00281246 and RS-2024-00398068)the grant(No.360-05-01-PNK9690)by the Department of Hydrogen Materials Evaluation at Korea Institute of Materials Science(KIMS).
文摘The phase metastability and precipitation are now considered to be an important strategy in designing Fe-rich high entropy alloys(HEAs).In this study,the influence of silicon addition on the initial and straininduced microstructure evolution and related mechanical property of Fe52−xMn27Cr15Co6Six(x=0,0.3,0.5,1.0,1.5,at.%)HEAs was systematically investigated by utilizing the in-depth microstructural characterization coupled with X-ray diffractometer(XRD),secondary electron microscopy(SEM),and transmission electron microscopy(TEM).The addition of Si to Fe52−xMn27Cr15Co6Six HEAs facilitates the triplex structure consisting of fcc-γmatrix,thermally-inducedε-martensite and sigma phase(σ).The lattice distortion energy by Si atoms is suggested to promote the formation ofσphase consisting of Cr,Si and Co and consequently influence the metastability of the matrix.In 0.3 at.%Si HEA,the strain-induced bodycentered tetragonal(bct)-typeα’-martensite were observed at the intersection of bi-directional straininducedε-martensite laths,enhancing the ultimate tensile strength to∼851 MPa from∼618.3 MPa with ductility increment(∼73.1%from∼71%).In 0.3 at.%Si and 0.5 at.%Si alloys,the granular-typeσphase was observed both at grain boundaries and in grain interior,and the size of granular-typeσphase at grain boundary and intra-granularσphase were found to be similar.The deformation mode altered from the transformation-induced plasticity(TRIP)to twinning-induced plasticity(TWIP)with an increase of Si content to 1.5 at.%,due to the enhanced fcc-γstability induced by the compositional modulation driven by increasedσphase formation.The propagation of microcracks inside brittleσphase could be suppressed by homogeneous slip through strain-induced martensite transformation(SIMT)in HEAs with low Si addition of 0.3at.%-0.5 at.%.
文摘This study investigates the development of novel high-entropy alloys(HEAs)with enhanced mechanical properties through an innovative fabrication method of direct energy deposition(DED).The focus is on the creation of metastable core-shell precipitation-strengthened HEAs that exhibit a unique multi-stage terrace-like slip wave toughening mechanism,a novel approach to improving both strength and ductility simultaneously.Mechanical testing reveals that the developed HEAs exhibit superior mechanical proper-ties,including high yield strength,ultimate tensile strength,and exceptional ductility.The improvement in these properties is attributed to the multi-stage terrace-like slip wave toughening mechanism activated by the unique microstructural features.This toughening mechanism involves the sequential activation of slip systems,facilitated by the stress concentration around the core-shell precipitates and the subsequent propagation of slip waves across the material.The terrace-like pattern of these slip waves enhances the material's ability to deform plastically,providing a significant toughening effect while maintaining high strength levels.Furthermore,the study delves into the fundamental interactions between the microstruc-tural elements and the deformation mechanisms.It elucidates how the core-shell precipitates and the matrix cooperate to distribute stress uniformly,delay the onset of necking,and prevent premature failure.This synergistic interaction between the microstructural features and the slip wave toughening mecha-nism is central to the remarkable balance of strength and ductility achieved in the HEAs.The introduction of a multi-stage terrace-like slip wave toughening mechanism offers a new pathway to designing HEAs with an exceptional amalgamation of strength and ductility.
基金Qin Chuangyuan Cites High-Level Innovation,Entrepreneurship Talent Project(QCYRCXM-2023-003)Innovation Capability Support Program of Shaanxi(2022KJXX-84)。
文摘The effect of hot deformation onα-phase precipitation during the subsequent heat treatment,as well as the mechanical properties of TB18 Ti-alloy,was investigated.Results show that the round bar obtained by the dual-phase field forging of the cast ingot exhibits uniform composition distribution on its cross-section.However,various degrees of deformation are detected at different positions on the cross-section,which is attributed to the characteristics of the forging process.Under the forging condition,the microstructure is mainly composed ofβ-phase matrix and coarsened discontinuous primaryα-phases.After solution and following artificial aging treatment,the primaryα-phases disappear,while needle-like secondaryα-phases precipitate in the matrix.Additionally,dispersed white zones are observed in the samples after aging,which are analyzed to be the precipitation-free zones of secondaryα-phase.Despite a uniform compositional distribution among various regions,these dispersed white zones exhibit higher content and larger size in the positions that have undergone lower forging deformation.It indicates that the insufficient forging deformation inhibits the precipitation of the secondaryα-phase,ultimately resulting in the lower strengthening effect by heat treatment.Thus,consistent with the characteristics of the forging process,a periodic variation of sample in strength is detected along the circumferential direction of the forged round bar.
基金supported by the National Nature Science Foundation of China(NSFC)(Grant No.11974033)Xuqiang Liu acknowledges support from the National Postdoctoral Foundation Project of China under Grant No.GZC20230215+2 种基金the National Nature Science Foundation of China under Grants No.12404001The XRD measurements at room and high temperatures were performed at the 4W2 HPStation of the Beijing Synchrotron Radiation Facility(BSRF)and beamline 15U1 of the Shanghai Synchrotron Radiation Facility(SSRF)In situ high-pressure,low-temperature XRD measurements were conducted at sector 16 ID-B,HPCAT of the Advanced Photon Source,and were supported by DOE-NNSA under Award No.DE-NA0001974.
文摘High-pressure β-Sn germanium may transform into diverse metastable allotropes with distinctive nanostructures and unique physical properties via multiple pathways under decompression.However,the mechanism and transition kinetics remain poorly understood.Here,we investigate the formation of metastable phases and nanostructures in germanium via controllable transition pathways of β-Sn Ge under rapid decompression at different rates.High-resolution transmission electron microscopy reveals three distinct metastable phases with the distinctive nanostructures:an almost perfect st12 Ge crystal,nanosized bc8/r8 structures with amorphous boundaries,and amorphous Ge with nanosized clusters (0.8–2.5 nm).Fast in situ x-ray diffraction and x-ray absorption measurements indicate that these nanostructured products form in certain pressure regions via distinct kinetic pathways and are strongly correlated with nucleation rates and electronic transitions mediated by compression rate,temperature,and stress.This work provides deep insight into the controllable synthesis of metastable materials with unique crystal symmetries and nanostructures for potential applications.
文摘Laboratory and field observations have suggested a correlation between contact dynamics and slow dynamics.The underlying mechanical mechanisms at the contact level require investigation at the nanoscale.This study uses molecular dynamics(MD)simulations to investigate the interactions between two quartz plates separated by a water film,focusing on the relationship between adhesion force and separation distance.The density and orientation angle profiles were calculated from simulation data to investigate the relationship between the interfacial structure of the water film and contact potential.The simulations reveal multiple metastable states of the contact potential,consistent with existing theoretical models.The results show that the contact force is influenced by the structure of the water film,including oscillation forces and stratification.This provided verification and development for existing theoretical models based on metastable contacts.
基金financial support by the National Natural Science Foundation of China(No.51364032)the Inner Mongolia Natural Science Foundation(No.2022MS05028)。
文摘The spray-deposition was used to produce billets of Mg-4Al-1.5Zn-3Ca-1Nd(A alloy)and Mg-13Al-3Zn-3Ca-1Nd(B alloy),and evolution of deformation substructure and Mg_(x)Zn_(y)Ca_(z)metastable phase in fine-grained(3μm)Mg alloys was investigated by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),and electron backscattered diffraction(EBSD).It was found that different dislocation configurations were formed in A and B alloys.Redundant free dislocations(RFDs)and dislocation tangles were the ways to form deformation substructure in A alloy,no RFDs except dislocation tangles were found in B alloy.The interaction between nano-scale second phase particles(nano-scale C15 andβ-Mg_(17)(Al,Zn)_(12)phase)and different dislocation configurations had a significant effect on the deformation substructures formation.The mass transfer of Mg_(x)Zn_(y)Ca_(z)metastable phases and the stacking order of stacking faults were conducive to the Mg-Nd-Zn typed long period stacking ordered(LPSO)phases formation.Nano-scale C15 phases,Mg-Nd-Zn typed LPSO phases,c/a ratio,β-Mg_(17)(Al,Zn)_(12)phases were the key factors influencing the formation of textures.Different textures and grain boundary features(GB features)had a significant effect on k-value.The non-basal textures were the main factor affecting k-value in A alloy,while the high-angle grain boundary(HAGB)was the main factor affecting k-value in B alloy.
文摘The electrolysis of alkaline seawater is critical for sustainable hydrogen production but is hindered by the sluggish oxygen evolution reaction in saline environments.Advanced electrocatalysts with tailored structures and electronic properties are essential,and phase engineering provides a transformative approach by modulating crystallographic symmetry and electronic configurations.Two-dimensional(2D)LaMnO_(3) perovskites show promise due to their exposed active sites and tunable electronic properties.However,the conventional stable rhombohedral phase limits oxygen diffusion despite good electron transport.Unconventional metastable phases with superior symmetry enhance lattice oxygen activity in saline environments but are challenging to synthesize.Herein,we propose a microwave shock method incorporating Co atoms to rapidly produce 2D LaMnO_(3) in rhombohedral,hexagonal,and metastable cubic phases.This strategy circumvents the limitations of high-temperature synthesis,preserving the 2D morphology while enabling the formation of metastable cubic phases.The metastable cubic phase exhibits superior OER activity and stability even in alkaline seawater due to optimal symmetry,interlayer spacing,and Mn-O covalency.X-ray absorption spectroscopy and theoretical calculations further highlight its balanced oxygen adsorption and desorption.This work underscores the role of metastable phase engineering in advancing seawater electrolysis and establishes a scalable route for designing high-performance 2D electrocatalysts.
基金supported by the National Natural Science Foundation of China(Grant Nos.52472040,52072032,and 12090031)the 173 JCJQ program(Grant No.2021JCJQ-JJ-0159)。
文摘The extensive applications of cubic silicon in flexible transistors and infrared detectors are greatly hindered by its intrinsic properties.Metastable silicon phases,such as Si-Ⅲ,Ⅳ,andⅫ,prepared using extreme pressure methods,provide a unique“genetic bank”with diverse structures and exotic characteristics.However,exploration of their inherent physical properties remains underdeveloped.Herein,we demonstrate the phase engineering strategy to modulate the thermal conductivity and mechanical properties of metastable silicon.The thermal conductivity,obtained via the Raman optothermal approach,exhibits broad tunability across various Si-Ⅰ,Ⅲ,Ⅻ,andⅣphases.The hardness and Young's modulus of Si-Ⅳare significantly greater than those of the Si-Ⅲ/Ⅻmixture,as confirmed by the nanoindentation technique.Moreover,it was found that pressure-induced structural defects can substantially degrade the thermal and mechanical properties of silicon.This systematic investigation offers a feasible route for designing novel semiconductors and further advancing their desirable applications in advanced nanodevices and mechanical transducers.
基金financially supported by the National Natural Science Foundation of China(52102233)Science and Technology Project of Hebei Education Department(QN2023019).
文摘In recent years,aqueous aluminum ion batteries have been widely studied owing to their abundant energy storage and high theo retical capacity.An in-depth study of vanadium oxide materials is necessary to address the precipitation of insoluble products covered cathode surface and the slow reaction kinetics.Therefore,a method using a simple one-step hydrothermal preparation and oxalic acid to regulate oxygen vacancies has been reported.A high starting capacity(400 mAh g^(-1))can be achieved by Ov-V2O5,and it is capable of undergoing 200 cycles at 0.4 A g^(-1),with a termination discharge capacity of103 mAh g^(-1).Mechanism analysis demonstrated that metastable structures(AlxV2O5and HxV2O5)were constructed through the insertion of Al^(3+)/H^(+)during discharging,which existed in the lattice intercalation with V2O5.The incorporation of oxygen vacancies lowers the reaction energy barrier while improving the ion transport efficiency.In addition,the metastable structure allows the electrostatic interaction between Al3+and the main backbone to establish protection and optimize the transport channel.In parallel,this work exploits ex-situ characterization and DFT to obtain a profound insight into the instrumental effect of oxygen vacancies in the construction of metastable structures during in-situ electrochemical activation,with a view to better understanding the mechanism of the synergistic participation of Al3+and H+in the reaction.This work not only reports a method for cathode materials to modulate oxygen vacancies,but also lays the foundation for a deeper understanding of the metastable structure of vanadium oxides.
基金supports from the National Natural Science Foundation of China(Nos.51509081,52208241).
文摘Reinforcing bars in concrete structures in marine environment are prone to pitting corrosion,which threatens the safety of engineering structures.In order to effectively mitigate the pitting corrosion of reinforcing bars,the electrochemical testing and atomic force microscopy are adopted,the effect of triethanolamine dodecylbenzene sulfonate(TDS)on metastable pitting behavior of 304 stainless steel(304 SS)in simulated concrete pore solutions(SCPS)with chlorine contamination was studied.The results show that the corrosion potential(Ecorr)and breakdown potential(Eb)increased with the growth of the TDS concentrations.Statistical cha-racteristics of metastable pits suggested that as the TDS concentrations increased in the SCPS,the parameters were all decreased.The Mott-Schottky tests exhibited that,although the donor density(ND)diminished,the thickness of the space charge layer(W)increased with increasing TDS concentrations.Investigation results showed that TDS inhibited the sprouting and growth of metastable pits,and with greater TDS concentration,it becomes more difficult for metastable pits to transfer into stable pits in the SCPS,the generated stable passive film prevented the sprouting of pitting corrosion,It is recommended to use TDS with a concentration of not less than 3.364×10^(-4) mol/L in engineering,so that the sensitivity of passivation film of 304SS to chloride erosion is reduced.
基金supported by the National Natural Science Foundation of China(Nos.52104372,52374332)the Postdoctoral Research Foundation of China(Nos.2019M651129,2019TQ0053)the Fundamental Research Funds for the Central Universities(No.N2324003-02).
文摘To overcome the strength-plasticity trade-offin the structural titanium alloys,a novel metastableβti-tanium alloy Ti-5Mo-4Cr-1V-1Zr(Ti-5411)with high strength and high plasticity was designed by the d-electrons theory,average electron-to-atom ratio(e/α^(-))and atomic radius difference(Δr^(-))theory.Com-bined in-situ scanning electron microscope(SEM)and electron backscatter diffraction(EBSD),the defor-mation mechanisms of the novel Ti-5411 metastableβtitanium alloy were systematically investigated.The results show that the Ti-5411 alloy exhibits excellent yield strength(∼689 MPa),tensile strength(∼930 MPa)and total elongation(∼39%).The in-situ tension indicates that slip activities,crystal rota-tion,stress induced martensite(SIM)α''transformation and{332}<113>deformation twin are the major deformation mechanisms of Ti-5411 alloy.Besides,with the increase of strain degree(0-0.5 mm displace-ment),deformation twins increase,widen and interlace.At 0.35 mm tensile displacement,the orientation of theβgrains rotates∼6.65°to accommodate the increased macrostrain.Additionally,martensiteα''also assists the nucleation of twins.Some{332}<113>twins grow and merge by consuming martensiteα''during deformation,and the residual martensiteα''remains in the merged twins.
