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Theory of relaxation oscillations in exciton-polariton condensates
摘要： We provide an analytical and numerical description of relaxation oscillations in the nonresonantly pumped polariton condensate. Presented considerations are based on coupled rate equations that are derived from the open dissipative Gross-Pitaevskii model. The evolution of the condensate density can be explained qualitatively by studying the topology of the trajectory in phase space. We use a ?xed points analysis for the classi?cation of the different regimes of condensate dynamics, including fast stabilization, slow oscillations, and ultrashort pulse emission. We obtain an analytical condition for the occurrence of relaxation oscillations. Continuous and pulsed condensate excitations are considered and we demonstrate that, in the latter case, the existence of the second reservoir is necessary for the emergence of oscillations. We show that relaxation oscillations should be expected to occur in systems with relatively short polariton lifetimes.
关键词： phase space,nonresonantly pumped,relaxation oscillations,fixed points analysis,exciton-polariton condensates,Gross-Pitaevskii model
更新于2025-09-09 09:28:46
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Phenomenological approach on electromagnetic waves propagation in normal and diabetic blood, influence of the relative macromolecular structures
摘要： This paper completes the thermodynamic characterization of normal and diabetic blood by the study of the propagation of electromagnetic waves. After a brief introduction on the thermodynamic approach in a biological system, the procedure used is briefly described. The problem of the propagation of electromagnetic waves is faced by deducing an expression of the propagation speed and attenuation of the wave as a function of the frequency. Comparison of results between normal and diabetic blood shows a greater number of permanent dipoles in diabetic blood than in the normal one. Diabetic blood tends to the insolubility because of conformational changes of blood proteins which cannot effectively respond to the stress of the electric field.
关键词： Non-equilibrium thermodynamics,Dielectric relaxation in blood,Blood
更新于2025-09-09 09:28:46
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Dynamic mechanical and electric behaviors of La-doped BiVO4
摘要： Bismuth vanadate (BiVO4) is an important semiconductor with wide applications, but it is still lack of in-depth understanding for its fundamental dynamic behaviors. To address this issue, the comprehensive analysis of structure, internal friction (IF), modulus, dielectric and impedance spectra was employed to unambiguously disclose the dynamic mechanical and electric behaviors for a series of Bi1-xLaxVO4 ceramics (0 ≤ x ≤ 0.15). In the sensitive mechanical measurement, five IF peaks, corresponding modulus anomalies and high-temperature creep behavior have been observed in our Bi1-xLaxVO4 ceramics. Through analyzing their related kinetic parameters, defect formations and evolution processes, the complex evolution model of ferroelastic domains including four different stages and the origin of grain boundary relaxation are well established. As for the electric experiment, there are two apparently different activation processes in low and high temperature regions, respectively. In conjunction with structural and mechanical characterizations, we confirm that the mixed electric/oxide ionic conduction dominates from 433 to 633 K, undergoing a structural change (633-673 K) to the complicated defect conduction at higher temperatures (673-833 K). Our findings smooth the track for better realization of the fundamental dynamic behaviors as well as extending practical application of BiVO4-based material.
关键词： Bismuth vanadate,dynamic mechanical behaviors,electric behaviors,ferroelastic domains,grain boundary relaxation,electric conduction mechanism,BiVO4,La-doped
更新于2025-09-09 09:28:46
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Modeling charge density in AlGaN/AlN/InGaN/GaN-based double heterostructures including InGaN layer strain relaxation
摘要： An analytical model is presented to calculate the two-dimensional electron gas (2DEG) density and barrier height of bare surface AlGaN/AlN/InGaN/GaN double heterostructures, which use InGaN as the conducting layer. The basic model is derived from electrostatic analysis of the di?erent material interfaces. The e?ect of strain relaxation in the InGaN layer is also incorporated here. Further, the impact of a two-dimensional hole gas at the InGaN/GaN interface, formed when the InGaN layer thickness is high, has been considered. The presented results are seen to agree with the available experimental results. Thus, this model can be a useful tool in the design and modeling of InGaN-based III-nitride heterostructures.
关键词： two-dimensional hole gas,AlGaN/InGaN/GaN heterostructure,strain relaxation,two-dimensional electron gas
更新于2025-09-09 09:28:46
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A Fractional Complex Permittivity Model of Media with Dielectric Relaxation
摘要： In this work, we propose a fractional complex permittivity model of dielectric media with memory. Debye’s generalized equation, expressed in terms of the phenomenological coefficients, is replaced with the corresponding differential equation by applying Caputo’s fractional derivative. We observe how fractional order depends on the frequency band of excitation energy in accordance with the 2nd Principle of Thermodynamics. The model obtained is validated with respect to the measurements made on the biological tissues and in particular on the human aorta.
关键词： fractional calculus,fractional ordinary differential equations,media with dielectric relaxation
更新于2025-09-09 09:28:46
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Sensing coated iron-oxide nanoparticles with spectral induced polarization (SIP): Experiments in natural sand packed flow-through columns
摘要： The development of nanoparticle-based soil remediation techniques is hindered by the lack of accurate in situ nanoparticle (NP) monitoring and characterization methods. Spectral induced polarization (SIP), a non-invasive geophysical technique, offers a promising approach to detect and quantify NPs in porous media. However, its successful implementation as a monitoring tool requires an understanding of the polarization mechanisms, the governing NP-associated SIP responses and their dependence on the stabilizing coatings that are typically used for NPs deployed in environmental applications. Herein, we present SIP responses (0.1-10,000 Hz) measured during injection of a poloxamer-coated super-paramagnetic iron-oxide nanoparticle (SPION) suspension in flow-through columns packed with natural sand from the Borden Aquifer. An advective-dispersive transport model is fitted to outflow SPION concentration measurements to compute average concentrations over the SIP spatial response domain (within the columns). The average SPION concentrations are compared with the real and imaginary components of the complex conductivity. Excellent correspondence is found between the average SPION concentrations the columns and the imaginary conductivity values, suggesting that NP-mediated polarization (that is, charge storage) increases proportionally with increasing SPION concentration. Our results support the possibility of SIP monitoring of spatial and temporal NP distributions, which can be immediately deployed in bench-scale studies with the prospect of future real-world field applications.
关键词： Maxwell-Wagner polarization,relaxation time,super paramagnetic iron-oxide nanoparticles (SPIONs),Spectral induced polarization (SIP),chargeability
更新于2025-09-09 09:28:46
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Acceleration techniques in a bi-iterative model for EM scattering from a 3-D object above a 2-D rough surface
摘要： A novel bi-iterative model is proposed to solve the extra large-scale composite electromagnetic (EM) scattering from an object above a rough surface. For the rough surface scattering, the forward-backward methodology and its modi?cation with under-relaxation iteration method are developed to accelerate the convergence of the iterative physical optics (IPO) and improve its robustness. Meanwhile, the local iteration methodology and the fast far ?eld approximation (FaFFA) in the matrix-vector product are proposed to reduce effectively the computational complexity and further improve the ef?ciency of the whole iteration process. Hence, this model can greatly reduce the computational costs, including both RAM memory and CPU time.
关键词： under-relaxation iteration,EM scattering,target above rough surface,fast far ?eld approximation
更新于2025-09-09 09:28:46
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High-Temperature Cycle Durability of Superplastic Al-Zn Eutectoid Solder Joints with Stress Relaxation Characteristics for SiC Power Semiconductor Devices
摘要： We have developed a new high-temperature Al-Zn lead-free soldering process that utilizes superplasticity to realize SiC power devices with high-temperature cycle durability. The joining process consists of an Al-78wt.%Zn preparation being sandwiched by a SiC die and insulation substrate, an interfacial cleaning process at approximately 250-270oC, a heating stage to reach the solid-liquid coexisting temperature of 420-430oC, the ejection of low-melting-temperature β(Zn) from the joining area by press stress, and the transformation to a superplastic composition, i.e., Al-70 wt.% Zn at 270-310oC. Many lamellar phases that enable superplasticity can be formed in this microstructure. This solder joint composition was proven to have a better stress-relaxation effect than eutectic Al-95wt.%Zn, and the composition shows a much higher damping capability at the maximum operating temperature of SiC devices (200oC) than that of other joining candidates. The outstanding temperature cycle durability was verified in temperature cycle tests from -40oC to 300oC for 5000 cycles. This durability is due to the high-stress-relaxation effect from the superplasticity transformation realized by the lamellar structures in the Al-Zn alloy solder.
关键词： lamellar structure,damping capability,power semiconductor,SiC,superplasticity,temperature cycle test,Al-Zn eutectoid solder,lead-free solder,stress relaxation
更新于2025-09-09 09:28:46
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Evolution of ferroelectric and piezoelectric response by heat treatment in pseudocubic BiFeO3–BaTiO3 ceramics
摘要： Heat treatment of ceramics is an important process to tailor the fine electromechanical properties. To explore the criteria for optimized heat treatment in a perovskite structure of (1–x)Bi1.05FeO3–xBaTiO3 (BF–BT100x) system, the structural phase relation, ferroelectric and piezoelectric response of BF–BT36 and BF–BT40 ceramics prepared by furnace cooling (FC) and quenching process were investigated. The X-ray diffraction examination showed single pseudocubic perovskite structure for all the ceramics. The homogenous microstructure was obtained for all ceramics with relatively large grain size in the furnace cooled samples. Well saturated ferroelectric hysteresis loops and enhanced piezoelectric constant (d33 = 97 pC/N) were achieved by quenching process. Dielectric curve of BF–BT36 showed large dielectric constant at its Curie temperature, however, BF–BT40 showed diffused relaxor-like dielectric anomalies. Quenched BF–BT36 samples showed typical butterfly like field induced strain curves, however negative strain decreased in BF–BT40 ceramics. From these investigated study, it is observed that BF–BT ceramics are very sensitive to the heat treatment process (furnace cooling and quenching) on the dielectric, electromechanical properties.
关键词： Quenching process,Electric field induced strain,Dielectric relaxation,BF–BT
更新于2025-09-09 09:28:46
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Ultrapure NIR-to-NIR Single Band Emission of β-PbF2: Yb3+/Tm3+ in Glass Ceramics
摘要： An ultrapure near infrared (NIR) emission entered at 800 nm upon 976 nm laser excitation (NIR-to-NIR) was observed in β-PbF2: Yb3+/Tm3+ glass ceramics (GCs). The ultrapure NIR-to-NIR single band emission originated from the 3H4 → 3H6 transition of Tm3+ with the ratio of NIR emission, and a blue band up to 9,633 was obtained. Through detailed analysis of the crystal structure and the energy transfer between Tm3+ and Yb3+, it is elucidated that the host lattice with low phonon energy cooperative with the energy mismatch results in a dramatic population of the 3H4 state as well as ultrapure NIR-to-NIR single band emission. Moreover, up-conversion (UC) emission properties and the decay lifetimes of β-PbF2: Yb3+/Tm3+ in GCs were explored thoroughly. The results illustrate that efficient cross relaxation (CR) processes between Tm3+ generate the energy redistribution in UC emission spectra, further concentrating energy to NIR emission. These two issues can be treated as crucial factors on ultrapure NIR-to-NIR single band emission in β-PbF2: Yb3+/Tm3+ in GCs. The ultrapure NIR-to-NIR single band emission through 976 nm laser excitation is advantageous for enhancing resolution and has potential application in bio-imaging fields.
关键词： Energy mismatch,Fluoride nanocrystal doped with Tm3+,Glass ceramics,Single band,Cross relaxation
更新于2025-09-09 09:28:46