In this paper the relationship between the surface relaxations and the electron density distributions of surface states of Cu（100）, Cu（110）, and Cu（111） surfaces is obtained by first-principles calculations. The...In this paper the relationship between the surface relaxations and the electron density distributions of surface states of Cu（100）, Cu（110）, and Cu（111） surfaces is obtained by first-principles calculations. The calculations indicate that relaxations mainly occur in the layers at which the surface states electrons are localized, and the magnitudes of the multilayer relaxations correspond to the difference of electron density of surface states between adjacent layers. The larger the interlayer relaxation is, the larger the difference of electron density of surface states between two layers is.展开更多
The experiments reveal the characteristics of stable damping in a multiphasic Al-Zn eutectoid alloy:（1）Thewhole damping(Q<sup>-1</sup>)has the same dependence on measured frequency（f）,i.e.Q<sup>-...The experiments reveal the characteristics of stable damping in a multiphasic Al-Zn eutectoid alloy:（1）Thewhole damping(Q<sup>-1</sup>)has the same dependence on measured frequency（f）,i.e.Q<sup>-1</sup>ocf<sup>-n</sup>,where n is a parameterand is independent of temperature.（2）In a low-temperature（low-T）and low-strain-amplitude（low-A<sub>）</sub>region,Q<sup>-1</sup>=（B/）exp（-nH/kT）,where B is a parameter,H the atomic diffusion activation energy,k Boltzmann′sconstant,and T the absolute temperature.n,H<sub>o</sub>（=nH）and H are all independent of A<sub>.</sub>The damping comesfrom an anelastic motion of the phase-interface.（3）In an intermediate region including a low-Tand a high-A<sub>,</sub>a middle-T and middle A<sub> </sub>and a high-T and low-A<sub> </sub>regions,the equation Q<sup>-1</sup>=（C/f<sup>n</sup>）exp（nH/kT）stillholds,but the damping has a normal amplitude effect C,n,and H all vary with A<sub>;</sub>the damping results from anonlinear relaxation of phase-interface.（4）In a high-T and high-A<sub> </sub>region,there is no longer a linear relationship between InQ<sup>-1</sup> and T<sup>-1</sup>,whereas the relation Q<sup>-1</sup>f<sup>-n</sup> is still satisfied,where n increases as A<sub> </sub>increases,andthe damping has a normal amplitude effect but one which is weaker than that in the case（3）.The damping maybe attributed to another kind of nonlinear relaxation between phase-interfaces.展开更多
For a few years it has been realized that nanocrystalline phases can be formed during crystallization of amorphous alloys annealed isothermally below the crystallization temperature of usual heating experiments. Data ...For a few years it has been realized that nanocrystalline phases can be formed during crystallization of amorphous alloys annealed isothermally below the crystallization temperature of usual heating experiments. Data of this transformation monitored by the measurement of magnetic susceptibility are presented. A method using a magnetic balance with electronic stabilisation and combined computer facilities is applied. Constant heating and cooling rates as well as isothermal heat treatments are used. Magnetic measurements are able to detect the onset of the transformation of amorphous NI-P alloys much earlier than was possible with differential scanning calorimetry. The transformation kinetics can be analyzed by means of the Avrami plot based on the Johnson-Mehl-Avrami equation. The kinetics of solid state reactions in the nanostructured material can be investigated similarly. Formation of a Ni-phase in a nanostructured Hf-Ni alloy could be detected in a very early stage, where calorimetric methods are not sensitive. Segregation phenomena could be detected from the experiments even after long time. The sensitivity of the applied method is not dependent on the heating rate as the sensitivity of scanning calorimetry is.展开更多
Decoupling the complicated vibrational-vibrational （V-V） coupling of a multimode vibrational relaxation remains a challenge for analyzing the sound relaxational absorption in multi-component gas mixtures. In our pre...Decoupling the complicated vibrational-vibrational （V-V） coupling of a multimode vibrational relaxation remains a challenge for analyzing the sound relaxational absorption in multi-component gas mixtures. In our previous work [Acta Phys. Sin. 61 174301 （2012）], an analytical model to predict the sound absorption from vibrational relaxation in a gas medium is proposed. In this paper, we develop the model to decouple the V-V coupled energy to each vibrationaltranslational deexcitation path, and analyze how the multimode relaxations form the peaks of sound absorption spectra in gas mixtures. We prove that a multimode relaxation is the sum of its decoupled single-relaxation processes, and only the decoupled process with a significant isochoric-molar-heat can be observed as an absorption peak. The decoupling model clarifies the essential processes behind the peaks in spectra arising from the multimode relaxations in multi-component gas mixtures. The simulation validates the proposed decoupling model.展开更多
A class of nonidentical parallel machine scheduling problems are considered in which the goal is to minimize the total weighted completion time. Models and relaxations are collected. Most of these problems are NP-hard...A class of nonidentical parallel machine scheduling problems are considered in which the goal is to minimize the total weighted completion time. Models and relaxations are collected. Most of these problems are NP-hard, in the strong sense, or open problems, therefore approximation algorithms are studied. The review reveals that there exist some potential areas worthy of further research.展开更多
It’s never too early in the year to start planning a break from the stress of city life,and southwest China’s charming Guizhou Province is a destination that should be right at the top of your list.
Recently,high-entropy alloys(HEAs)have attracted wide attention due to their extraordinary materials properties.A main challenge in identifying new HEAs is the lack of efficient approaches for exploring their huge com...Recently,high-entropy alloys(HEAs)have attracted wide attention due to their extraordinary materials properties.A main challenge in identifying new HEAs is the lack of efficient approaches for exploring their huge compositional space.Ab initio calculations have emerged as a powerful approach that complements experiment.However,for multicomponent alloys existing approaches suffer from the chemical complexity involved.In this work we propose a method for studying HEAs computationally.Our approach is based on the application of machine-learning potentials based on ab initio data in combination with Monte Carlo simulations.The high efficiency and performance of the approach are demonstrated on the prototype bcc NbMoTaW HEA.The approach is employed to study phase stability,phase transitions,and chemical short-range order.The importance of including local relaxation effects is revealed:they significantly stabilize single-phase formation of bcc NbMoTaW down to room temperature.Finally,a so-far unknown mechanism that drives chemical order due to atomic relaxation at ambient temperatures is discovered.展开更多
Optimal power flow(OPF) is the fundamental mathematical model to optimize power system operations.Based on conic relaxation, Taylor series expansion and McCormick envelope, we propose three convex OPF models to improv...Optimal power flow(OPF) is the fundamental mathematical model to optimize power system operations.Based on conic relaxation, Taylor series expansion and McCormick envelope, we propose three convex OPF models to improve the performance of the second-order cone alternating current OPF(SOC-ACOPF) model. The underlying idea of the proposed SOC-ACOPF models is to drop assumptions of the original SOC-ACOPF model by convex relaxation and approximation methods.A heuristic algorithm to recover feasible ACOPF solution from the relaxed solution of the proposed SOC-ACOPF models is developed. The proposed SOC-ACOPF models are examined through IEEE case studies under various load scenarios and power network congestions. The quality of solutions from the proposed SOC-ACOPF models is evaluated using MATPOWER(local optimality) and LINDOGLOBAL(global optimality). We also compare numerically the proposed SOC-ACOPF models with other two convex ACOPF models in the literature.The numerical results show robust performance of the proposed SOCACOPF models and the feasible solution recovery algorithm.展开更多
Two dinuclear lanthanide (Ln) complexes, formulated as [phen2Ln2(HCOO)4(HCOO)2 2x(NO3)2x] (1, Ln = Gd and x = 0.52; 2, Ln = Er and x = 0.90; phen = 1,10-phenanthroline), were synthesized and characterized. They are is...Two dinuclear lanthanide (Ln) complexes, formulated as [phen2Ln2(HCOO)4(HCOO)2 2x(NO3)2x] (1, Ln = Gd and x = 0.52; 2, Ln = Er and x = 0.90; phen = 1,10-phenanthroline), were synthesized and characterized. They are isostructural. The dinuclear molecule consists of two Ln3+ bridged by four formate groups and chelated by phen and formate/nitrate ligands, and the Ln3+ possesses a coordination environment of distorted tri-capped trigonal prism of LnOTN2. Both compounds behave as paramag- nets between 2 and 300 K, but display two static field induced magnetic relaxation processes. One is slow and of spin-lattice type, and it results from the lifting of Kramer's degeneracy of the ground-states of both Gd3+ and Er3+, and the other is fast, and it might be spin-spin type.展开更多
Reducing parameter spaces via exploiting symmetries has greatly accelerated and increased the quality of electronic-structure calculations.Unfortunately,many of the traditional methods fail when the global crystal sym...Reducing parameter spaces via exploiting symmetries has greatly accelerated and increased the quality of electronic-structure calculations.Unfortunately,many of the traditional methods fail when the global crystal symmetry is broken,even when the distortion is only a slight perturbation(e.g.,Jahn-Teller like distortions).Here we introduce a flexible and generalizable parametric relaxation scheme and implement it in the all-electron code FHI-aims.This approach utilizes parametric constraints to maintain symmetry at any level.After demonstrating the method’s ability to relax metastable structures,we highlight its adaptability and performance over a test set of 359 materials,across 13 lattice prototypes.Finally we show how these constraints can reduce the number of steps needed to relax local lattice distortions by an order of magnitude.The flexibility of these constraints enables a significant acceleration of high-throughput searches for novel materials for numerous applications.展开更多
Recently, researchers have been interested in studying the semidefinite programming （SDP） relaxation model, where the matrix is both positive semidefinite and entry-wise nonnegative, for quadratically constrained qu...Recently, researchers have been interested in studying the semidefinite programming （SDP） relaxation model, where the matrix is both positive semidefinite and entry-wise nonnegative, for quadratically constrained quadratic programming （QCQP）. Comparing to the basic SDP relaxation, this doubly-positive SDP model possesses additional O（n2） constraints, which makes the SDP solution complexity substantially higher than that for the basic model with O（n） constraints. In this paper, we prove that the doubly-positive SDP model is equivalent to the basic one with a set of valid quadratic cuts. When QCQP is symmetric and homogeneous （which represents many classical combinatorial and non- convex optimization problems）, the doubly-positive SDP model is equivalent to the basic SDP even without any valid cut. On the other hand, the doubly-positive SDP model could help to tighten the bound up to 36%, but no more. Finally, we manage to extend some of the previous results to quartic models.展开更多
Although the plastic loading can enhance creep deformation and yield strength,the anisotropic Stress Relaxation Aging(SRA)behavior and mechanism under plastic loading remain unclear,which presents a significant challe...Although the plastic loading can enhance creep deformation and yield strength,the anisotropic Stress Relaxation Aging(SRA)behavior and mechanism under plastic loading remain unclear,which presents a significant challenge in accurately shaping aluminum alloy panels.In this study,the SRA behavior of 2195-T4 Al-Cu-Li alloys were thoroughly studied under initial loading stresses within the elastic(210/250 MPa)and plastic(380/420 MPa)ranges at 180℃by stress relaxation and tensile tests as well as microstructure characterization.The findings reveal that compared with those under elastic loadings,in-plane anisotropy(IPA)values of the stress relaxation amount,yield strength and fracture elongation under plastic loadings are reduced by 60%–80%,70%–90% and 72%–89%,respectively.Similarly,IPA values of precipitate size in grains and PrecipitationFree Zones(PFZ)width at grain boundaries under plastic loading decrease by 31.4%and 94.4%respectively.These results indicate plastic loading significantly weakens the anisotropic SRA behavior,owing to numerous uniformly distributed fine T1phases and small IPA values of both T1precipitates size and PFZ width in various loading directions.Compared with those of elastic loadingaged alloys,yield strength of plastic loading-aged alloys shows high strength-ductility because of the combined effect of closely dispersed fine T1precipitates,narrowed PFZ and numerous sheared and rotated T1phases at different locations during tensile process.The uniformly distributed larger Kernel Average Misorientation(KAM)and Schmidt factor values of the plastic loading-aged alloy,as well as the cross-slip generated,also help to enhance the strength and ductility of the alloy.展开更多
Due to batteries inconsistencies and potential faults in battery management systems,slight overcharging remains a common yet insufficiently understood safety risk,lacking effective warning methods.To illuminate the de...Due to batteries inconsistencies and potential faults in battery management systems,slight overcharging remains a common yet insufficiently understood safety risk,lacking effective warning methods.To illuminate the degradation behavior and failure mechanism of various overcharged states(100%SOC,105%SOC,110%SOC,and 115%SOC),multiple advanced in-situ characterization techniques(accelerating rate calorimeter,electrochemical impedance spectroscopy,ultrasonic scanning,and expansion instrument)were utilized.Additionally,re-overcharge-induced thermal runaway(TR)tests were conducted,with a specific emphasis on the evolution of the expansion force signal.Results indicated significant degradation at 110%SOC including conductivity loss,loss of lithium inventory,and loss of active material accompanied by internal gas generation.These failure behaviors slow down the expansion force rate during reovercharging,reducing the efficacy of active warnings that depend on rate thresholds of expansion force.Specifically,the warning time for 115%SOC battery is only 144 s,which is 740 s shorter than that for fresh battery,and the time to TR is advanced by 9 min.Moreover,the initial self-heating temperature(T1)is reduced by 62.4℃compared to that of fresh battery,reaching only 70.8℃.To address the low safety of overcharged batteries,a passive overcharge warning method utilizing relaxation expansion force was proposed,based on the continued gas generation after stopping charging,leading to a sustained increase in force.Compared to active methods that rely on thresholds of expansion force rate,the passive method can issue warnings 115 s earlier.By combining the passive and active warning methods,guaranteed effective overcharge warning can be issued 863-884 s before TR.This study introduces a novel perspective for enhancing the safety of batteries.展开更多
BACKGROUND Most patients who were included in previous studies on achalasia had increased lower esophageal sphincter(LES)pressure.Peroral endoscopic myotomy(POEM)has been confirmed to be effective at relieving the cli...BACKGROUND Most patients who were included in previous studies on achalasia had increased lower esophageal sphincter(LES)pressure.Peroral endoscopic myotomy(POEM)has been confirmed to be effective at relieving the clinical symptoms of achalasia associated with increased LES pressure.AIM To identify the safety and efficacy of POEM for patients with normal LES integrated relaxation pressure(LES-IRP).METHODS The clinical data of patients who underwent POEM successfully in The First Medical Center of Chinese PLA General Hospital were retrospectively analyzed.A total of 481 patients who underwent preoperative high-resolution manometry(HRM)at our hospital were ultimately included in this research.According to the HRM results,the patients were divided into two groups:71 patients were included in the normal LES-IRP group(LES-IRP<15 mmHg)and 410 patients were included in the increased LES-IRP group(LES-IRP≥15 mmHg).Clinical characteristics,procedure-related parameters,adverse events,and outcomes were compared between the two groups to evaluate the safety and efficacy of POEM for patients with normal LES-IRP.RESULTS Among the 481 patients included in our study,209 were males and 272 were females,with a mean age of 44.2 years.All patients underwent POEM without severe adverse events.The median pre-treatment Eckardt scores of the normal LES-IRP and increased LES-IRP groups were 7.0 and 7.0(P=0.132),respectively,decreasing to 1.0 and 1.0 post-treatment(P=0.572).The clinical success rate of the normal LES-IRP group was 87.3%(62/71),and that of the increased LES-IRP group was 91.2%(374/410)(P=0.298).Reflux symptoms were measured by the GerdQ questionnaire,and the percentages of patients with GerdQ scores≥9 in the normal LES-IRP and increased LES-IRP groups were 8.5%and 10.7%,respectively(P=0.711).After matching,the rates of clinical success and the rates of GerdQ score≥9 were not significantly different between the two groups.CONCLUSION Our results suggest that POEM is safe and effective for achalasia and patients with normal LES-IRP.In addition,in patients with normal LES-IRP,compared with those with increased LES-IRP,POEM was not associated with a greater incidence of reflux symptoms.展开更多
All-solid-state lithium batteries(ASSLBs)are strongly considered as the next-generation energy storage devices for their high energy density and intrinsic safety.The solid-solid contact between lithium metal and solid...All-solid-state lithium batteries(ASSLBs)are strongly considered as the next-generation energy storage devices for their high energy density and intrinsic safety.The solid-solid contact between lithium metal and solid electrolyte plays a vital role in the performance of working ASSLBs,which is challenging to investigate quantitatively by experimental approach.This work proposed a quantitative model based on the finite element method for electrochemical impedance spectroscopy simulation of different solid-solid contact states in ASSLBs.With the assistance of an equivalent circuit model and distribution of relaxation times,it is discovered that as the number of voids and the sharpness of cracks increase,the contact resistance Rcgrows and ultimately dominates the battery impedance.Through accurate fitting,inverse proportional relations between contact resistance Rcand(1-porosity)as well as crack angle was disclosed.This contribution affords a fresh insight into clarifying solid-solid contact states in ASSLBs.展开更多
In this manuscript,we propose an analytical equivalent linear viscoelastic constitutive model for fiber-reinforced composites,bypassing general computational homogenization.The method is based on the reduced-order hom...In this manuscript,we propose an analytical equivalent linear viscoelastic constitutive model for fiber-reinforced composites,bypassing general computational homogenization.The method is based on the reduced-order homogenization(ROH)approach.The ROH method typically involves solving multiple finite element problems under periodic conditions to evaluate elastic strain and eigenstrain influence functions in an‘off-line’stage,which offers substantial cost savings compared to direct computational homogenization methods.Due to the unique structure of the fibrous unit cell,“off-line”stage calculation can be eliminated by influence functions obtained analytically.Introducing the standard solid model to the ROH method enables the creation of a comprehensive analytical homogeneous viscoelastic constitutive model.This method treats fibrous composite materials as homogeneous,anisotropic viscoelastic materials,significantly reducing computational time due to its analytical nature.This approach also enables precise determination of a homogenized anisotropic relaxation modulus and accurate capture of various viscoelastic responses under different loading conditions.Three sets of numerical examples,including unit cell tests,three-point beam bending tests,and torsion tests,are given to demonstrate the predictive performance of the homogenized viscoelastic model.Furthermore,the model is validated against experimental measurements,confirming its accuracy and reliability.展开更多
Introduction Pure NBT exhibits the frequency-dependent Curie temperature,indicating that its dielectric properties are affected by temperature,measurement frequency,and material processing condition.To enhance the die...Introduction Pure NBT exhibits the frequency-dependent Curie temperature,indicating that its dielectric properties are affected by temperature,measurement frequency,and material processing condition.To enhance the dielectric and relaxor properties of NBT,various dopants such as Sr,K,Li and Bi are incorporated into the NBT structure.These modifications significantly alter the dielectric constant and relaxation behavior,demonstrating a dominant influence of dopant on the material properties.Among these,the solid solution of BaTiO_(3)(BT)with NBT is widely investigated due to its ability to stabilize the perovskite structure and improve dielectric performance.However,the temperature-dependent stability of dielectric properties remains a critical challenge for high-temperature applications.In this study,(1-x)(0.75Na_(0.5)Bi_(0.5)TiO_(3)-0.25BaTiO_(3))-xBaZrO_(3)(NBT-BT-xBZ,x=0,0.08,0.14,and 0.20)ceramics were prepared by a solid-state reaction method.The effect of BaZrO_(3)(BZ)addition on the structural,dielectric,and energy storage properties was systematically investigated.In addition,the phase transition and relaxation behaviors were also analyzed based on the modified Curie-Weiss law,Vogel-Fulcher relation,and Lorentz-type empirical law.Methods The starting materials were powders of high purity Na_(2)CO_(3),Bi_(2)O_(3),TiO_(2),BaCO_(3),and ZrO_(2).The powders were weighed according to a stoichiometric ratio(with 1%excess of Na and Bi)and ground with ethanol in a ball mill at 300 r/min for more than 12 h,and the weight ratio of raw material to ethanol and zirconium balls was 1:1:2.The dried material was heat-treated at 850℃ for 2 h to promote the formation of NBT-BT-BZ.After further grinding for 12 h,the samples were mixed with a small amount of polyvinyl alcohol(PVA).The samples were sintered in air at 1150℃for 2 h and cooled to room temperature.The phase composition of the ceramic samples was determined by an model D8 ADVANDCE X-ray diffractometer(D8 ADVANDCEXRD,Bruker AXS Ltd.,Germany)with Cu target Kαrays,at X-ray wavelengthλof 1.5406Å,2θin the range of 10°to 80°,applied voltage of 40 kV,and a current of 500 mA.A silver paste was coated on the two surfaces as electrodes and heat-treated at 700℃ for 10 min.The dielectric properties of the ceramic samples were determined at different frequencies by a model DMS-1000 high-temperature dielectric temperature spectroscope(BALAB Tech.Co.,China)with at a ramp rate of 3(°)/min in a temperature range from room temperature to 450℃.The overdamped(200Ω)discharge tests for bulk ceramic samples were performed by a model CFD-005 discharge tester(Gogo(GG)Instruments Technology,China)).Results and discussion The XRD patterns indicate that all the ceramic samples have a perovskite structure without any detectable secondary phase,proving that zirconium ions can completely enter the lattice and form a solid solution.Based on the locally magnified XRD peaks,the XRD peak shape shifts towards lower angles as a whole as the BZ content increases.This indicates that the overall volume of the crystal cell shows an expansion as the Zr ions replace Ti ions due to different ionic radii of Zr and Ti ions.The SEM images show that the grain size gradually increases with increasing the BZ content.The addition of BZ promotes the grain growth.However,this gradually slows down with the increase of content up to x of 0.20.The limited grain size variation appears in the latter two samples.All the samples show a relatively dense morphology.The Curie temperature of the NBT-0.25BT ceramic samples is 256℃,which is similar to the reported results.The Curie temperature decreases gradually with the increase of BZ additive,and the dielectric temperature spectrum flattens out,indicating that the enhanced structural and temperature stability of the NBT-BT-BZ ceramics.The maximum values of all dielectric constants correspond to temperatures that increase with frequency,indicating a dielectric relaxor behavior.A frequency dispersion is accompanied at near the Curie temperature,which can be ascribed to the thermal evolution of the tetragonal polar nanoregions(PNRs)and the mixing effect of the transition from tripartite to tetragonal PNRs.Theγvalues obtained from the experimental data at 100 kHz are 1.79,1.83,1.89,and 1.92 for NBT-BT,NBT-BT-0.08BZ,NBT-BT-0.14BZ,and NBT-BT-0.20BZ,respectively.Theγvalue increases gradually with the addition of the BZ content,showing an enhanced relaxation of the NBT-BT-BZ ceramics.The comparison of discharge current curves and energy density of all the ceramics indicate that the addition of BZ significantly improves the discharge current and energy storage performance.A high discharging energy density(Wd)of 1.6 J·cm^(-3) with a fast discharging speed(τ0.9)of 75 ns is obtained for the ceramic samples with x of 0.14.This can be attributed to an increased relaxation as the BZ content increases.Conclusions NBT-BT-BZ ceramics were prepared by a solid-state reaction method.The XRD patterns revealed a phase transition from a tetragonal phase to a pseudocubic phase as the BZ content increased.The dielectric relaxation behavior of the ceramics could be described by three empirical laws(i.e.,modified Curie-Weiss law,Vogel-Fulcher relation and Lorentz-type empirical law).The dielectric relaxation followed the modified Curie-Weiss law and the Vogel-Fulcher relationship.The parametersγand Ea,which were obtained to evaluate the relaxation behavior,increased at a higher BZ content.The Lorentz-type relationship effectively described the temperature dependence of the dielectric constant on both the low-and high-temperature sides within a specific temperature range for all the ceramics.展开更多
In this paper,we introduce the real pairwise completely positive(RPCP)matrices with one of them is necessarily positive semidefinite while the other one is necessarily entrywise nonnegative,which has a real pairwise c...In this paper,we introduce the real pairwise completely positive(RPCP)matrices with one of them is necessarily positive semidefinite while the other one is necessarily entrywise nonnegative,which has a real pairwise completely positive(RPCP)decomposition.We study the properties of RPCP matrices and give some necessary and sufficient conditions for a matrix pair to be RPCP.First,we give an equivalent decomposition for the RPCP matrices,which is different from the RPCP-decomposition and show that the matrix pair(X,X)is RPCP if and only if X is completely positive.Besides,we also prove that the RPCP matrices checking problem is equivalent to the separable completion problem.A semidefinite algorithm is also proposed for detecting whether or not a matrix pair is RPCP.The asymptotic and finite convergence of the algorithm are also discussed.If it is RPCP,we can further give a RPCP-decomposition for it;if it is not,we can obtain a certificate for this.展开更多
The dynamics of biomolecules span across a wide range of timescales,reflecting the complexity of free energy landscapes of biomolecules.Among these,the microsecond-tomillisecond(μs-ms)timescale dynamics are particula...The dynamics of biomolecules span across a wide range of timescales,reflecting the complexity of free energy landscapes of biomolecules.Among these,the microsecond-tomillisecond(μs-ms)timescale dynamics are particularly significant,offering detailed insights into the kinetic,thermodynamic,and structural aspects of biological function.Many critical biological processes,including enzyme catalysis,protein folding,ligand binding,and allosteric regulation,operate within this timescale.Nuclear magnetic resonance(NMR)spectroscopy is a powerful technique for probing molecular dynamics in this time window,commonly used NMR methods for investigatingμs-ms timescale dynamics include Carr-Purcell-Meiboom-Gill(CPMG)relaxation dispersion,chemical exchange saturation transfer(CEST),and rotating-frame longitudinal relaxation dispersion(R_(1ρ)relaxation dispersion).This review provides a brief ove rview of the fundamental principles and some recent advances of these methods,highlighting their interrelationships and applications in elucidating biomolecular dynamics.展开更多
The heavy-atom effect of halogen(Br and I)has been widely employed for boosting spin-crossover in organic molecules,while recent investigation indicated halogen-substitution can also enhance fluorescence and even lead...The heavy-atom effect of halogen(Br and I)has been widely employed for boosting spin-crossover in organic molecules,while recent investigation indicated halogen-substitution can also enhance fluorescence and even lead to aggregation-induced emission(AIE).In this work,we investigated ultrafast excited state dynamics of a halogen-substituted model system,i.e.squaryliums NSQ-R(R=H,Cl,Br,I),by using femtosecond spectroscopy and theoretical approach.Fast external reorganization(Ex-re,~3 ps)and slow internal reorganization(In-re,5-20 ps)were observed,while quantitative fitting indicated halogen-substitution leads to a slower non-radiative S1→S0 decay(k_(NR)^(s))and subsequently enhanced fluorescence emitting.By analyzing the extracted k_(NR)^(s)within theoretical framework of non-radiative transition in the strong coupling regime,a plausible AIE mechanism of NSQs was revealed.Our work provides a clear picture on non-radiative dynamics of halogen-substituted squaryliums,which might be useful for future development of organic dyes.展开更多
基金Project substantially supported by the National Natural Science Foundation of China （Grant No 60471034） and partially by the National Natural Science Foundation of China and the Science Foundation of China Academy of Engineering Physics （Grant No 10576004）.
文摘In this paper the relationship between the surface relaxations and the electron density distributions of surface states of Cu（100）, Cu（110）, and Cu（111） surfaces is obtained by first-principles calculations. The calculations indicate that relaxations mainly occur in the layers at which the surface states electrons are localized, and the magnitudes of the multilayer relaxations correspond to the difference of electron density of surface states between adjacent layers. The larger the interlayer relaxation is, the larger the difference of electron density of surface states between two layers is.
文摘The experiments reveal the characteristics of stable damping in a multiphasic Al-Zn eutectoid alloy:（1）Thewhole damping(Q<sup>-1</sup>)has the same dependence on measured frequency（f）,i.e.Q<sup>-1</sup>ocf<sup>-n</sup>,where n is a parameterand is independent of temperature.（2）In a low-temperature（low-T）and low-strain-amplitude（low-A<sub>）</sub>region,Q<sup>-1</sup>=（B/）exp（-nH/kT）,where B is a parameter,H the atomic diffusion activation energy,k Boltzmann′sconstant,and T the absolute temperature.n,H<sub>o</sub>（=nH）and H are all independent of A<sub>.</sub>The damping comesfrom an anelastic motion of the phase-interface.（3）In an intermediate region including a low-Tand a high-A<sub>,</sub>a middle-T and middle A<sub> </sub>and a high-T and low-A<sub> </sub>regions,the equation Q<sup>-1</sup>=（C/f<sup>n</sup>）exp（nH/kT）stillholds,but the damping has a normal amplitude effect C,n,and H all vary with A<sub>;</sub>the damping results from anonlinear relaxation of phase-interface.（4）In a high-T and high-A<sub> </sub>region,there is no longer a linear relationship between InQ<sup>-1</sup> and T<sup>-1</sup>,whereas the relation Q<sup>-1</sup>f<sup>-n</sup> is still satisfied,where n increases as A<sub> </sub>increases,andthe damping has a normal amplitude effect but one which is weaker than that in the case（3）.The damping maybe attributed to another kind of nonlinear relaxation between phase-interfaces.
文摘For a few years it has been realized that nanocrystalline phases can be formed during crystallization of amorphous alloys annealed isothermally below the crystallization temperature of usual heating experiments. Data of this transformation monitored by the measurement of magnetic susceptibility are presented. A method using a magnetic balance with electronic stabilisation and combined computer facilities is applied. Constant heating and cooling rates as well as isothermal heat treatments are used. Magnetic measurements are able to detect the onset of the transformation of amorphous NI-P alloys much earlier than was possible with differential scanning calorimetry. The transformation kinetics can be analyzed by means of the Avrami plot based on the Johnson-Mehl-Avrami equation. The kinetics of solid state reactions in the nanostructured material can be investigated similarly. Formation of a Ni-phase in a nanostructured Hf-Ni alloy could be detected in a very early stage, where calorimetric methods are not sensitive. Segregation phenomena could be detected from the experiments even after long time. The sensitivity of the applied method is not dependent on the heating rate as the sensitivity of scanning calorimetry is.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60971009 and 61001011)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20090142110019)+1 种基金the Natural Science Foundation of Hubei Province, China (Grant No. 2010CDB02701)the Fundamental Research Funds for the Central Universities, China (Grant No. 2012QN083)
文摘Decoupling the complicated vibrational-vibrational （V-V） coupling of a multimode vibrational relaxation remains a challenge for analyzing the sound relaxational absorption in multi-component gas mixtures. In our previous work [Acta Phys. Sin. 61 174301 （2012）], an analytical model to predict the sound absorption from vibrational relaxation in a gas medium is proposed. In this paper, we develop the model to decouple the V-V coupled energy to each vibrationaltranslational deexcitation path, and analyze how the multimode relaxations form the peaks of sound absorption spectra in gas mixtures. We prove that a multimode relaxation is the sum of its decoupled single-relaxation processes, and only the decoupled process with a significant isochoric-molar-heat can be observed as an absorption peak. The decoupling model clarifies the essential processes behind the peaks in spectra arising from the multimode relaxations in multi-component gas mixtures. The simulation validates the proposed decoupling model.
基金the National Natural Science Foundation of China (70631003)the Hefei University of Technology Foundation (071102F).
文摘A class of nonidentical parallel machine scheduling problems are considered in which the goal is to minimize the total weighted completion time. Models and relaxations are collected. Most of these problems are NP-hard, in the strong sense, or open problems, therefore approximation algorithms are studied. The review reveals that there exist some potential areas worthy of further research.
文摘It’s never too early in the year to start planning a break from the stress of city life,and southwest China’s charming Guizhou Province is a destination that should be right at the top of your list.
基金This collaboration might not have been possible had the authors not met at a number of research programs at the Institute of Pure and Applied Mathematics,UCLA.T.K.and A.S.were supported by the Russian Science Foundation(Grant number 18-13-00479)F.K.acknowledges funding from the Deutsche Forschungsgemeinschaft(SPP 2006)+1 种基金the Netherlands Organization for Scientific Research NWO/STW(VIDI grant 15707)J.N.acknowledges financial support by the DFG under project number NE 428/19-1.
文摘Recently,high-entropy alloys(HEAs)have attracted wide attention due to their extraordinary materials properties.A main challenge in identifying new HEAs is the lack of efficient approaches for exploring their huge compositional space.Ab initio calculations have emerged as a powerful approach that complements experiment.However,for multicomponent alloys existing approaches suffer from the chemical complexity involved.In this work we propose a method for studying HEAs computationally.Our approach is based on the application of machine-learning potentials based on ab initio data in combination with Monte Carlo simulations.The high efficiency and performance of the approach are demonstrated on the prototype bcc NbMoTaW HEA.The approach is employed to study phase stability,phase transitions,and chemical short-range order.The importance of including local relaxation effects is revealed:they significantly stabilize single-phase formation of bcc NbMoTaW down to room temperature.Finally,a so-far unknown mechanism that drives chemical order due to atomic relaxation at ambient temperatures is discovered.
文摘Optimal power flow(OPF) is the fundamental mathematical model to optimize power system operations.Based on conic relaxation, Taylor series expansion and McCormick envelope, we propose three convex OPF models to improve the performance of the second-order cone alternating current OPF(SOC-ACOPF) model. The underlying idea of the proposed SOC-ACOPF models is to drop assumptions of the original SOC-ACOPF model by convex relaxation and approximation methods.A heuristic algorithm to recover feasible ACOPF solution from the relaxed solution of the proposed SOC-ACOPF models is developed. The proposed SOC-ACOPF models are examined through IEEE case studies under various load scenarios and power network congestions. The quality of solutions from the proposed SOC-ACOPF models is evaluated using MATPOWER(local optimality) and LINDOGLOBAL(global optimality). We also compare numerically the proposed SOC-ACOPF models with other two convex ACOPF models in the literature.The numerical results show robust performance of the proposed SOCACOPF models and the feasible solution recovery algorithm.
基金supported by the National Natural Science Foundation of China (21171010, 20871007)the National Basic Research Program of China (2009CB929403)
文摘Two dinuclear lanthanide (Ln) complexes, formulated as [phen2Ln2(HCOO)4(HCOO)2 2x(NO3)2x] (1, Ln = Gd and x = 0.52; 2, Ln = Er and x = 0.90; phen = 1,10-phenanthroline), were synthesized and characterized. They are isostructural. The dinuclear molecule consists of two Ln3+ bridged by four formate groups and chelated by phen and formate/nitrate ligands, and the Ln3+ possesses a coordination environment of distorted tri-capped trigonal prism of LnOTN2. Both compounds behave as paramag- nets between 2 and 300 K, but display two static field induced magnetic relaxation processes. One is slow and of spin-lattice type, and it results from the lifting of Kramer's degeneracy of the ground-states of both Gd3+ and Er3+, and the other is fast, and it might be spin-spin type.
基金This project was supported by TEC1p(the European Research Council(ERC)Horizon 2020 research and innovation programme,grant agreement No.740233)BigMax(the Max Planck Society’s Research Network on Big-Data-Driven Materials-Science)+1 种基金the NOMAD pillar of the FAIR-DI e.V.association.SC and DH acknowledges U.S.DOD-ONR(Grants No.N00014-17-1-2090)D.H.acknowledges support from the U.S.DOD through the National Defense Science and Engineering Graduate(NDSEG)Fellowship Program.
文摘Reducing parameter spaces via exploiting symmetries has greatly accelerated and increased the quality of electronic-structure calculations.Unfortunately,many of the traditional methods fail when the global crystal symmetry is broken,even when the distortion is only a slight perturbation(e.g.,Jahn-Teller like distortions).Here we introduce a flexible and generalizable parametric relaxation scheme and implement it in the all-electron code FHI-aims.This approach utilizes parametric constraints to maintain symmetry at any level.After demonstrating the method’s ability to relax metastable structures,we highlight its adaptability and performance over a test set of 359 materials,across 13 lattice prototypes.Finally we show how these constraints can reduce the number of steps needed to relax local lattice distortions by an order of magnitude.The flexibility of these constraints enables a significant acceleration of high-throughput searches for novel materials for numerous applications.
基金The second author＇s research was supported by Program for Innovative Research Team of Shanghai University of Finance and Economics （IRTSHUFE） and by National Natural Science Foundation of China （NSFC） Project 11471205 the third author＇s research was supported in part by NSF GOALI 0800151.
文摘Recently, researchers have been interested in studying the semidefinite programming （SDP） relaxation model, where the matrix is both positive semidefinite and entry-wise nonnegative, for quadratically constrained quadratic programming （QCQP）. Comparing to the basic SDP relaxation, this doubly-positive SDP model possesses additional O（n2） constraints, which makes the SDP solution complexity substantially higher than that for the basic model with O（n） constraints. In this paper, we prove that the doubly-positive SDP model is equivalent to the basic one with a set of valid quadratic cuts. When QCQP is symmetric and homogeneous （which represents many classical combinatorial and non- convex optimization problems）, the doubly-positive SDP model is equivalent to the basic SDP even without any valid cut. On the other hand, the doubly-positive SDP model could help to tighten the bound up to 36%, but no more. Finally, we manage to extend some of the previous results to quartic models.
基金support from the Key Program of the National Natural Science Foundation of China(No.51235010)。
文摘Although the plastic loading can enhance creep deformation and yield strength,the anisotropic Stress Relaxation Aging(SRA)behavior and mechanism under plastic loading remain unclear,which presents a significant challenge in accurately shaping aluminum alloy panels.In this study,the SRA behavior of 2195-T4 Al-Cu-Li alloys were thoroughly studied under initial loading stresses within the elastic(210/250 MPa)and plastic(380/420 MPa)ranges at 180℃by stress relaxation and tensile tests as well as microstructure characterization.The findings reveal that compared with those under elastic loadings,in-plane anisotropy(IPA)values of the stress relaxation amount,yield strength and fracture elongation under plastic loadings are reduced by 60%–80%,70%–90% and 72%–89%,respectively.Similarly,IPA values of precipitate size in grains and PrecipitationFree Zones(PFZ)width at grain boundaries under plastic loading decrease by 31.4%and 94.4%respectively.These results indicate plastic loading significantly weakens the anisotropic SRA behavior,owing to numerous uniformly distributed fine T1phases and small IPA values of both T1precipitates size and PFZ width in various loading directions.Compared with those of elastic loadingaged alloys,yield strength of plastic loading-aged alloys shows high strength-ductility because of the combined effect of closely dispersed fine T1precipitates,narrowed PFZ and numerous sheared and rotated T1phases at different locations during tensile process.The uniformly distributed larger Kernel Average Misorientation(KAM)and Schmidt factor values of the plastic loading-aged alloy,as well as the cross-slip generated,also help to enhance the strength and ductility of the alloy.
基金supported by the National Natural Science Foundation of China(52476200,52106244)the Guangdong Basic and Applied Basic Research Foundation(2024A1515030124)+1 种基金the Science and Technology Project of China Southern Power Grid under Grant GDKJXM20230246(030100KC23020017)the Fundamental Research Funds for the Central Universities。
文摘Due to batteries inconsistencies and potential faults in battery management systems,slight overcharging remains a common yet insufficiently understood safety risk,lacking effective warning methods.To illuminate the degradation behavior and failure mechanism of various overcharged states(100%SOC,105%SOC,110%SOC,and 115%SOC),multiple advanced in-situ characterization techniques(accelerating rate calorimeter,electrochemical impedance spectroscopy,ultrasonic scanning,and expansion instrument)were utilized.Additionally,re-overcharge-induced thermal runaway(TR)tests were conducted,with a specific emphasis on the evolution of the expansion force signal.Results indicated significant degradation at 110%SOC including conductivity loss,loss of lithium inventory,and loss of active material accompanied by internal gas generation.These failure behaviors slow down the expansion force rate during reovercharging,reducing the efficacy of active warnings that depend on rate thresholds of expansion force.Specifically,the warning time for 115%SOC battery is only 144 s,which is 740 s shorter than that for fresh battery,and the time to TR is advanced by 9 min.Moreover,the initial self-heating temperature(T1)is reduced by 62.4℃compared to that of fresh battery,reaching only 70.8℃.To address the low safety of overcharged batteries,a passive overcharge warning method utilizing relaxation expansion force was proposed,based on the continued gas generation after stopping charging,leading to a sustained increase in force.Compared to active methods that rely on thresholds of expansion force rate,the passive method can issue warnings 115 s earlier.By combining the passive and active warning methods,guaranteed effective overcharge warning can be issued 863-884 s before TR.This study introduces a novel perspective for enhancing the safety of batteries.
文摘BACKGROUND Most patients who were included in previous studies on achalasia had increased lower esophageal sphincter(LES)pressure.Peroral endoscopic myotomy(POEM)has been confirmed to be effective at relieving the clinical symptoms of achalasia associated with increased LES pressure.AIM To identify the safety and efficacy of POEM for patients with normal LES integrated relaxation pressure(LES-IRP).METHODS The clinical data of patients who underwent POEM successfully in The First Medical Center of Chinese PLA General Hospital were retrospectively analyzed.A total of 481 patients who underwent preoperative high-resolution manometry(HRM)at our hospital were ultimately included in this research.According to the HRM results,the patients were divided into two groups:71 patients were included in the normal LES-IRP group(LES-IRP<15 mmHg)and 410 patients were included in the increased LES-IRP group(LES-IRP≥15 mmHg).Clinical characteristics,procedure-related parameters,adverse events,and outcomes were compared between the two groups to evaluate the safety and efficacy of POEM for patients with normal LES-IRP.RESULTS Among the 481 patients included in our study,209 were males and 272 were females,with a mean age of 44.2 years.All patients underwent POEM without severe adverse events.The median pre-treatment Eckardt scores of the normal LES-IRP and increased LES-IRP groups were 7.0 and 7.0(P=0.132),respectively,decreasing to 1.0 and 1.0 post-treatment(P=0.572).The clinical success rate of the normal LES-IRP group was 87.3%(62/71),and that of the increased LES-IRP group was 91.2%(374/410)(P=0.298).Reflux symptoms were measured by the GerdQ questionnaire,and the percentages of patients with GerdQ scores≥9 in the normal LES-IRP and increased LES-IRP groups were 8.5%and 10.7%,respectively(P=0.711).After matching,the rates of clinical success and the rates of GerdQ score≥9 were not significantly different between the two groups.CONCLUSION Our results suggest that POEM is safe and effective for achalasia and patients with normal LES-IRP.In addition,in patients with normal LES-IRP,compared with those with increased LES-IRP,POEM was not associated with a greater incidence of reflux symptoms.
基金supported by the Beijing Natural Science Foundation(Z200011,L233004)the National Key Research and Development Program(2021YFB2500300)+3 种基金the National Natural Science Foundation of China(52394170,52394171,22109011,22393900,and 22108151)the Tsinghua-Jiangyin Innovation Special Fund(TJISF)(2022JYTH0101)the S&T Program of Hebei(22344402D)the Tsinghua University Initiative Scientific Research Program.
文摘All-solid-state lithium batteries(ASSLBs)are strongly considered as the next-generation energy storage devices for their high energy density and intrinsic safety.The solid-solid contact between lithium metal and solid electrolyte plays a vital role in the performance of working ASSLBs,which is challenging to investigate quantitatively by experimental approach.This work proposed a quantitative model based on the finite element method for electrochemical impedance spectroscopy simulation of different solid-solid contact states in ASSLBs.With the assistance of an equivalent circuit model and distribution of relaxation times,it is discovered that as the number of voids and the sharpness of cracks increase,the contact resistance Rcgrows and ultimately dominates the battery impedance.Through accurate fitting,inverse proportional relations between contact resistance Rcand(1-porosity)as well as crack angle was disclosed.This contribution affords a fresh insight into clarifying solid-solid contact states in ASSLBs.
基金support by the National Key R&D Program of China(Grant No.2023YFA1008901)the National Natural Science Foundation of China(Grant Nos.11988102,12172009)is gratefully acknowledged.
文摘In this manuscript,we propose an analytical equivalent linear viscoelastic constitutive model for fiber-reinforced composites,bypassing general computational homogenization.The method is based on the reduced-order homogenization(ROH)approach.The ROH method typically involves solving multiple finite element problems under periodic conditions to evaluate elastic strain and eigenstrain influence functions in an‘off-line’stage,which offers substantial cost savings compared to direct computational homogenization methods.Due to the unique structure of the fibrous unit cell,“off-line”stage calculation can be eliminated by influence functions obtained analytically.Introducing the standard solid model to the ROH method enables the creation of a comprehensive analytical homogeneous viscoelastic constitutive model.This method treats fibrous composite materials as homogeneous,anisotropic viscoelastic materials,significantly reducing computational time due to its analytical nature.This approach also enables precise determination of a homogenized anisotropic relaxation modulus and accurate capture of various viscoelastic responses under different loading conditions.Three sets of numerical examples,including unit cell tests,three-point beam bending tests,and torsion tests,are given to demonstrate the predictive performance of the homogenized viscoelastic model.Furthermore,the model is validated against experimental measurements,confirming its accuracy and reliability.
基金国家自然科学基金(12104188,12474095 and 52402323)开放基金(2023KF03,KYCX24-4102)。
文摘Introduction Pure NBT exhibits the frequency-dependent Curie temperature,indicating that its dielectric properties are affected by temperature,measurement frequency,and material processing condition.To enhance the dielectric and relaxor properties of NBT,various dopants such as Sr,K,Li and Bi are incorporated into the NBT structure.These modifications significantly alter the dielectric constant and relaxation behavior,demonstrating a dominant influence of dopant on the material properties.Among these,the solid solution of BaTiO_(3)(BT)with NBT is widely investigated due to its ability to stabilize the perovskite structure and improve dielectric performance.However,the temperature-dependent stability of dielectric properties remains a critical challenge for high-temperature applications.In this study,(1-x)(0.75Na_(0.5)Bi_(0.5)TiO_(3)-0.25BaTiO_(3))-xBaZrO_(3)(NBT-BT-xBZ,x=0,0.08,0.14,and 0.20)ceramics were prepared by a solid-state reaction method.The effect of BaZrO_(3)(BZ)addition on the structural,dielectric,and energy storage properties was systematically investigated.In addition,the phase transition and relaxation behaviors were also analyzed based on the modified Curie-Weiss law,Vogel-Fulcher relation,and Lorentz-type empirical law.Methods The starting materials were powders of high purity Na_(2)CO_(3),Bi_(2)O_(3),TiO_(2),BaCO_(3),and ZrO_(2).The powders were weighed according to a stoichiometric ratio(with 1%excess of Na and Bi)and ground with ethanol in a ball mill at 300 r/min for more than 12 h,and the weight ratio of raw material to ethanol and zirconium balls was 1:1:2.The dried material was heat-treated at 850℃ for 2 h to promote the formation of NBT-BT-BZ.After further grinding for 12 h,the samples were mixed with a small amount of polyvinyl alcohol(PVA).The samples were sintered in air at 1150℃for 2 h and cooled to room temperature.The phase composition of the ceramic samples was determined by an model D8 ADVANDCE X-ray diffractometer(D8 ADVANDCEXRD,Bruker AXS Ltd.,Germany)with Cu target Kαrays,at X-ray wavelengthλof 1.5406Å,2θin the range of 10°to 80°,applied voltage of 40 kV,and a current of 500 mA.A silver paste was coated on the two surfaces as electrodes and heat-treated at 700℃ for 10 min.The dielectric properties of the ceramic samples were determined at different frequencies by a model DMS-1000 high-temperature dielectric temperature spectroscope(BALAB Tech.Co.,China)with at a ramp rate of 3(°)/min in a temperature range from room temperature to 450℃.The overdamped(200Ω)discharge tests for bulk ceramic samples were performed by a model CFD-005 discharge tester(Gogo(GG)Instruments Technology,China)).Results and discussion The XRD patterns indicate that all the ceramic samples have a perovskite structure without any detectable secondary phase,proving that zirconium ions can completely enter the lattice and form a solid solution.Based on the locally magnified XRD peaks,the XRD peak shape shifts towards lower angles as a whole as the BZ content increases.This indicates that the overall volume of the crystal cell shows an expansion as the Zr ions replace Ti ions due to different ionic radii of Zr and Ti ions.The SEM images show that the grain size gradually increases with increasing the BZ content.The addition of BZ promotes the grain growth.However,this gradually slows down with the increase of content up to x of 0.20.The limited grain size variation appears in the latter two samples.All the samples show a relatively dense morphology.The Curie temperature of the NBT-0.25BT ceramic samples is 256℃,which is similar to the reported results.The Curie temperature decreases gradually with the increase of BZ additive,and the dielectric temperature spectrum flattens out,indicating that the enhanced structural and temperature stability of the NBT-BT-BZ ceramics.The maximum values of all dielectric constants correspond to temperatures that increase with frequency,indicating a dielectric relaxor behavior.A frequency dispersion is accompanied at near the Curie temperature,which can be ascribed to the thermal evolution of the tetragonal polar nanoregions(PNRs)and the mixing effect of the transition from tripartite to tetragonal PNRs.Theγvalues obtained from the experimental data at 100 kHz are 1.79,1.83,1.89,and 1.92 for NBT-BT,NBT-BT-0.08BZ,NBT-BT-0.14BZ,and NBT-BT-0.20BZ,respectively.Theγvalue increases gradually with the addition of the BZ content,showing an enhanced relaxation of the NBT-BT-BZ ceramics.The comparison of discharge current curves and energy density of all the ceramics indicate that the addition of BZ significantly improves the discharge current and energy storage performance.A high discharging energy density(Wd)of 1.6 J·cm^(-3) with a fast discharging speed(τ0.9)of 75 ns is obtained for the ceramic samples with x of 0.14.This can be attributed to an increased relaxation as the BZ content increases.Conclusions NBT-BT-BZ ceramics were prepared by a solid-state reaction method.The XRD patterns revealed a phase transition from a tetragonal phase to a pseudocubic phase as the BZ content increased.The dielectric relaxation behavior of the ceramics could be described by three empirical laws(i.e.,modified Curie-Weiss law,Vogel-Fulcher relation and Lorentz-type empirical law).The dielectric relaxation followed the modified Curie-Weiss law and the Vogel-Fulcher relationship.The parametersγand Ea,which were obtained to evaluate the relaxation behavior,increased at a higher BZ content.The Lorentz-type relationship effectively described the temperature dependence of the dielectric constant on both the low-and high-temperature sides within a specific temperature range for all the ceramics.
文摘In this paper,we introduce the real pairwise completely positive(RPCP)matrices with one of them is necessarily positive semidefinite while the other one is necessarily entrywise nonnegative,which has a real pairwise completely positive(RPCP)decomposition.We study the properties of RPCP matrices and give some necessary and sufficient conditions for a matrix pair to be RPCP.First,we give an equivalent decomposition for the RPCP matrices,which is different from the RPCP-decomposition and show that the matrix pair(X,X)is RPCP if and only if X is completely positive.Besides,we also prove that the RPCP matrices checking problem is equivalent to the separable completion problem.A semidefinite algorithm is also proposed for detecting whether or not a matrix pair is RPCP.The asymptotic and finite convergence of the algorithm are also discussed.If it is RPCP,we can further give a RPCP-decomposition for it;if it is not,we can obtain a certificate for this.
基金financially supported by funds from the Natural Science Foundation of Beijing Municipality(Grant Number 7232251)the National Natural Science Foundation of China(Grant Number 22474006)。
文摘The dynamics of biomolecules span across a wide range of timescales,reflecting the complexity of free energy landscapes of biomolecules.Among these,the microsecond-tomillisecond(μs-ms)timescale dynamics are particularly significant,offering detailed insights into the kinetic,thermodynamic,and structural aspects of biological function.Many critical biological processes,including enzyme catalysis,protein folding,ligand binding,and allosteric regulation,operate within this timescale.Nuclear magnetic resonance(NMR)spectroscopy is a powerful technique for probing molecular dynamics in this time window,commonly used NMR methods for investigatingμs-ms timescale dynamics include Carr-Purcell-Meiboom-Gill(CPMG)relaxation dispersion,chemical exchange saturation transfer(CEST),and rotating-frame longitudinal relaxation dispersion(R_(1ρ)relaxation dispersion).This review provides a brief ove rview of the fundamental principles and some recent advances of these methods,highlighting their interrelationships and applications in elucidating biomolecular dynamics.
基金support by the National Key R&D Program of China(Nos.2020YFA0714603 and 2020YFA0714604)。
文摘The heavy-atom effect of halogen(Br and I)has been widely employed for boosting spin-crossover in organic molecules,while recent investigation indicated halogen-substitution can also enhance fluorescence and even lead to aggregation-induced emission(AIE).In this work,we investigated ultrafast excited state dynamics of a halogen-substituted model system,i.e.squaryliums NSQ-R(R=H,Cl,Br,I),by using femtosecond spectroscopy and theoretical approach.Fast external reorganization(Ex-re,~3 ps)and slow internal reorganization(In-re,5-20 ps)were observed,while quantitative fitting indicated halogen-substitution leads to a slower non-radiative S1→S0 decay(k_(NR)^(s))and subsequently enhanced fluorescence emitting.By analyzing the extracted k_(NR)^(s)within theoretical framework of non-radiative transition in the strong coupling regime,a plausible AIE mechanism of NSQs was revealed.Our work provides a clear picture on non-radiative dynamics of halogen-substituted squaryliums,which might be useful for future development of organic dyes.
