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Ablation behavior of SiCp/AA2024 composites irradiated by a single-pulse nanosecond laser
摘要： In this study, homogenous Al alloy and SiC materials and SiCp/AA2024 composites with mean particle diameters of 5 μm and 30 μm were irradiated by a single-pulse nanosecond fiber laser with a 200 ns pulse width and 1064 nm wavelength. Using a laser pulse, regular circular heat-affected zones (HAZ) were formed in the homogenous materials. For the composites, an Al allloy matrix was melted and sputtered, and the SiC particles bulged when irradiated by the laser pulse. According to the measured results, the HAZ increased with the pulse energy density in a logarithmic pattern. Nonlinear fitting results demonstrated that the damage thresholds of the composites and SiC homogenous materials were the lowest and highest, respectively. SiCp/AA2024 composites with different mean particle diameters exhibited similar damage thresholds. The measured etching depths of the SiC particles and Al alloy matrix were smaller than the respective values of the homogenous materials. Thermal simulation results revealed that thermal-mechanical coupling occurred between the SiC particles and Al alloy matrix. The SiC particles in the composite heated more rapidly under a nanosecond laser, and the heat was then transferred to the matrix. Large SiC particles constrained the matrix’s molten pool, which accelerated its gasification but hindered further etching.
关键词： Composites materials,Phase transitions,Ablation mechanism,Nanosecond laser irradiating,Interface effect
更新于2025-09-19 17:13:59
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<i>Ab initio</i> study of temperature- and laser-induced phase transitions in
摘要： We analyze the bulk phase transitions of the three titanium dioxide polymorphs anatase, rutile, and brookite in thermodynamical equilibrium and after ultrafast laser excitation using the generalized solid-state nudged elastic band (G-SSNEB) method. For calculating the forces and stresses needed for G-SSNEB, we use electronic-temperature dependent density functional theory calculations. Our results show that the anatase-rutile and brookite-rutile phase transitions have a considerably lower energy barrier than the anatase-brookite phase transition in the thermodynamical equilibrium and upon laser excitation. The obtained transition temperatures in thermodynamical equilibrium are consistent with experimentally observed ones. Furthermore, our calculations show that the pathways of the phase transition are not affected considerably by the applied laser pulse. Although the pathways do not change considerably we see that the rutile phase is stabilized by the laser pulse.
关键词： phase transitions,density functional theory,G-SSNEB method,titanium dioxide,laser excitation
更新于2025-09-12 10:27:22
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Magnetic phase transitions of insulating spin-orbit coupled Bose atoms in one-dimensional optical lattices
摘要： We consider the insulating spin-orbit coupled Bose atoms con?ned within one-dimensional optical lattices and explore their ground-state magnetic phase transitions. Under strong interactions, the charge degrees of atoms are frozen and the system can be described by an anisotropic XXZ Heisenberg chain with Dzyaloshinskii-Moriya interaction and transverse ?eld. We apply the matrix product state method to obtain the ground states, and analyze spiral correlation functions, spin-spin correlation functions, and ?rst energy gap. Under weakly transverse ?elds, the ground state is a ferromagnetic phase if the interspin s-wave interaction strength is stronger than that of the intraspin ones, otherwise, it is a paramagnetic phase, an antiferromagnetic phase, or a gapless spiral phase with algebraic decaying spin correlations. When the transverse ?eld is strengthened, the gapless spiral phase is broken and a new spiral phase with long-range spin-spin correlations emerges.
关键词： optical lattices,XXZ Heisenberg chain,Bose atoms,magnetic phase transitions,Dzyaloshinskii-Moriya interaction,spin-orbit coupling,matrix product state method,transverse ?eld
更新于2025-09-12 10:27:22
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Light propagation in inhomogeneous media, coupled quantum harmonic oscillators and phase transitions
摘要： this contribution has two main purposes. first, using classical optics we show how to model two coupled quantum harmonic oscillators and two interacting quantized fields. Second, we present classical analogs of coupled harmonic oscillators that correspond to anisotropic quadratic graded indexed media in a rotated reference frame, and we use operator techniques, common to quantum mechanics, to solve the propagation of light through a particular type of graded indexed medium. Additionally, we show that the system presents phase transitions.
关键词： inhomogeneous media,phase transitions,quantum harmonic oscillators,light propagation
更新于2025-09-11 14:15:04
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Electro-optical, dielectric and optical properties of graphene oxide dispersed nematic liquid crystal composites
摘要： Graphene oxide (GO) in various concentrations (0.04 wt.%, 0.1 wt.% and 0.3 wt.%) was dispersed into nematic liquid crystal (LC) 5CB and studied for electro-optical, dielectric and optical responses. The textural and phase transition studies were investigated by optical polarising microscopy in the nematic phase. The effect of GO concentration on the micro-texture, phase transition temperatures, birefringence, threshold voltage, contrast ratio, dielectric permittivity, dielectric loss and conductivity was also investigated. The nematic–isotropic transition temperature slight increases (~3%) in the 0.04 wt.% and 0.1 wt.% GO dispersed 5CB composites as compared to 5CB. Threshold voltage decreases in the GO–5CB composites with the increase of GO concentration. Additionally, the effect of GO concentration on the optical absorbance of UV–visible light and energy bandgap is also considered.
关键词： graphene oxide,phase transitions,birefringence,threshold voltage,Nematic liquid crystals
更新于2025-09-11 14:15:04
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Beyond the molecular movie: Dynamics of bands and bonds during a photoinduced phase transition
摘要： Ultrafast nonequilibrium dynamics offer a route to study the microscopic interactions that govern macroscopic behavior. In particular, photoinduced phase transitions (PIPTs) in solids provide a test case for how forces, and the resulting atomic motion along a reaction coordinate, originate from a nonequilibrium population of excited electronic states. Using femtosecond photoemission, we obtain access to the transient electronic structure during an ultrafast PIPT in a model system: indium nanowires on a silicon(111) surface. We uncover a detailed reaction pathway, allowing a direct comparison with the dynamics predicted by ab initio simulations. This further reveals the crucial role played by localized photoholes in shaping the potential energy landscape and enables a combined momentum- and real-space description of PIPTs, including the ultrafast formation of chemical bonds.
关键词： Silicon surface,Photoinduced phase transitions,Chemical bonds,Electronic structure,Indium nanowires,Femtosecond photoemission,Ultrafast dynamics
更新于2025-09-10 09:29:36
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Influence of additives on structure and ferroelectric properties of NBT-BT-BMT ceramics
摘要： Influence of various over stoichiometric additives on phase formation, unit cell parameters, microstructure, dielectric and ferroelectric properties of solid solutions 0.8[0.8(Na0.5Bi0.5)TiO3-0.2BaTiO3]-0.2Bi(Mg0.5Ti0.5)O3 system has been studied. The unit cell volume slightly decreased in case of the V2O5 additives but did not change in case of Bi2O3, LiF, and KCl additives. Increase in dielectric parameters ert and tandrt values at the room temperature was revealed for compositions doped by KCl additives, while these parameters decreased in compositions doped by the V2O5 additives. Linear correlation between piezoelectric coefficient d33 measured for separate grains using the Piezoresponse Force Microscopy method and dielectric permittivity ert values at the room temperature was confirmed.
关键词： ferroelectric phase transitions,additives,dielectric properties,perovskite structure,Ceramics (Na0.5Bi0.5)TiO3 - BaTiO3 - Bi(Mg0.5Ti0.5)O3
更新于2025-09-10 09:29:36
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[Springer Tracts in Modern Physics] Parity-time Symmetry and Its Applications Volume 280 || Construction of Non- P T $$\mathbb {PT}$$ -Symmetric Complex Potentials with All-Real Spectra
摘要： We review recent work on the generalization of PT symmetry. We show that, in addition to PT -symmetric complex potentials, there are also large classes of non-PT -symmetric complex potentials which also feature all-real spectra. In addition, some classes of these non-PT -symmetric potentials allow phase transitions which do or do not go through exceptional points. These non-PT -symmetric potentials are constructed by a variety of methods, such as the symmetry and supersymmetry methods and the soliton theory. A generalization of PT symmetry in multi-dimensions is also reviewed.
关键词： all-real spectra,exceptional points,soliton theory,symmetry methods,supersymmetry methods,non-PT -symmetric potentials,PT symmetry,phase transitions
更新于2025-09-10 09:29:36
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The Influence of the V2O5 · GeO2 Glass Phase on the Properties of AgI Nanolayers
摘要： Using X-ray phase analysis and impedance monitoring, it was shown that for a nanolayered structure, softened glass (V2O5 ? GeO2) can take an imprint from AgI lattice and retain it while being cooled to temperatures below Tg.
关键词： nanolayers,solid electrolytes,phase transitions,interfacial interactions,ionic conductivity
更新于2025-09-10 09:29:36
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Outstanding piezoelectric properties, phase transitions and domain configurations of 0.963(K0.48Na0.52)(Nb0.955Sb0.045)O3?0.037(Bi0.50Na0.50)HfO3 ceramics
摘要： Requirements for substituting the current lead-based piezoelectric materials with lead-free ones are becoming increasingly strong from environmental concerns. In this article, we report piezoelectric properties, phase transitions and domain configurations of a dense 0.963(K0.48Na0.52)(Nb0.955Sb0.045)O3?0.037(Bi0.50Na0.50)HfO3 lead-free ceramic prepared through solid-state reaction by two-step sintering. It has a large piezoelectric coefficient d33 = 512 pC/N and a planner eletromechanical coupling coefficient kp ≈ 0.54 at room temperature. Dielectric measurement indicates that rhombohedral-orthorhombic, orthorhombic-tetragonal, and tetragonal-cubic phase transitions upon heating process occur at ?30 °C, 57 °C and 238 °C, respectively. X-ray diffraction analysis shows that the crystalline structure is dominantly of orthorhombic phase at room temperature. Domain configurations were investigated by acid etching technique. The poled ceramic shows domain patterns of long parallel stripes with hierarchical nanodomain structure existing in some broad stripes. The observed outstanding piezoelectric properties are ascribed to the rhombohedral-orthorhombic and orthorhombic-tetragonal phase transitions, and to the characteristic domain structure.
关键词： Phase transitions,Piezoelectricity,Lead-free ceramics,Ceramics,Ferroelectrics,Domain structure
更新于2025-09-10 09:29:36