- 标题
- 摘要
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- 实验方案
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Can all the infrared secular growth really be understood as increase of classical statistical variance?
摘要： It is known that in the theory of light scalar ?elds during in?ation, correlation functions su?er from infrared (IR) divergences or large IR loop corrections, leading to the breakdown of perturbation theory. In order to understand the physical meaning of such IR enhancement, we investigate the stochastic properties of an e?ective equation of motion (EoM) for long-wavelength modes of a canonically normalized light scalar ?eld φ with a general su?ciently ?at interaction potential on de Sitter background. Firstly, we provide an alternative re?ned derivation of the e?ective action for long-wavelength modes which leads to the e?ective EoM that correctly reproduces all the IR correlation functions in a good approximation at a late time, by integrating out short-wavelength modes. Next, under the assumption that one can neglect non-local correlations in the in?uence functional exceeding the coarse-graining scale, we show that the e?ective EoM for IR modes of the “average ?eld” in Schwinger-Keldysh formalism φ< c can be interpreted as a classical stochastic process in the present model.
关键词： quantum ?eld theory on curved space,in?ation
更新于2025-09-04 15:30:14
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Tunneling ionization of atoms and ions in a linear electromagnetic wave and a constant magnetic field and the “imaginary time” method
摘要： The tunneling ionization of atoms and negative ions in an intense linearly polarized laser ?eld and a constant uniform magnetic ?eld is discussed in the quasiclassical theory framework. We use the “imaginary time” method, where tunneling is described by the classical equations of motion but with purely imaginary “time” to derive the extremal subbarrier trajectory of the photoelectron. This allows to obtain simple analytical expressions for ionization rates in the tunneling regime for an arbitrary angle between a laser beam and a constant magnetic ?eld accounting for the Coulomb interaction of the photoelectron with the atomic core. The resonance case, when the frequency of a monochromatic electromagnetic wave and the cyclotron frequency are equal, is also considered. The limits of weak and strong magnetic ?elds and the expressions for the barrier width and the emission angle of photoelectrons are discussed. It is shown that a magnetic ?eld in the presence of a linear electromagnetic wave increases the barrier width and thus decreases the ionization probability, i.e., stabilizes the bound level.
关键词： linear electromagnetic wave,imaginary time method,atoms,ions,quasiclassical theory,tunneling ionization,constant magnetic field
更新于2025-09-04 15:30:14
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Ab-initio study on electronic and magnetic properties of (Ga,Co) co-doped ZnO
摘要： Using first-principles calculations based on density functional theory within GGA formalism, we have studied the electronic structure and magnetic properties of (Ga,Co) co-doped ZnO system. The effect of impurity distances on ferromagnetic and antiferromagnetic ground state in Co0.056Zn0.944O has been studied. For the closest Co-Co distance, a ferromagnetic ground state with total magnetic moment of ~3.00μμ’ per Co atom has been found. The electronic structure also displays a nearly halfmetallic order. Conversely, for the farthest Co-Co distance an antiferromagnetic ground state was found for Co0.056Zn0.944O. When Zn2+ ions are replaced by Ga ions in Co0.056Zn0.944O, the new (Ga,Co) co-doped ZnO system is more energetically stable. It has also been found that Ga-doping reduces the Co0.056Zn0.944O band gap due to the sp-d exchange interactions, which is in good agreement with the experimental data. Moreover, the Ga-doping changes the nearly halmetallic order of Co0.056Zn0.944O to metallic. Results also show that Ga0.029Co0.056Zn0.915O is still ferromagnetic with a total magnetic moment of ~3.00μμ’ per Co atom. It was also found that the ferromagnetic ground state in (Ga,Co) co-doped ZnO vanishes as Ga concentration increases.
关键词： GGA formalism,(Ga,ab-initio,density functional theory,electronic structure,Co) co-doped ZnO,magnetic properties
更新于2025-09-04 15:30:14
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-SiC
摘要： Optical charge state switching was previously observed in photoluminescence experiments for the divacancy defect in 4H-SiC. The participating dark charge state could not be identified with certainty. We use constrained density-functional theory to investigate the mechanism of charge state conversion from the bright neutral charge state of the divacancy defect to the positive and negative charge states including corresponding recovery of the neutral charge state. While we can confirm that the positive charge state is dark, we do not find evidence that the negative charge state is dark. We compute similar absorption energies required for conversion of the neutral defect to both charge states. However, the formation of the positive charge state requires a series of excitations involving a 2-photon excitation, while the creation of the negative charge state is achieved through a single 2-photon process. Calculated absorption energies for the recovery of the neutral defect from the positive charge state fit the experimental value better than those from the negative charge state. Defect formation energies as a function of the Fermi energy show a very small Fermi energy range in which the negative charge state is most stable, while the positive charge state exhibits a wide stability range. Overall, our computational results give more support to the identification of the dark charge state as the positive over the negative charge state in the mechanism of optical charge state switching.
关键词： divacancy defect,optical charge state switching,constrained density-functional theory,photoluminescence,4H-SiC
更新于2025-09-04 15:30:14
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Anomalous carrier transport model for broadband infrared absorption in metals
摘要： We derive a model for accurately reproducing the broadband infrared optical response of common engineering metals. Here we use “broadband infrared” to refer to wavelengths beginning at 1 μm and extending to approximately 100 μm or more. The model generalizes the Drude theory to account for sources of anomalous intraband absorption. This is accomplished by modeling these sources as elements of disorder that introduce diffusive perturbations into the local ?eld. In the stationary setting, the memory kernel description of the ?eld relaxation leads to a fractional derivative with an order that corresponds to the memory decay strength. We demonstrate that this model is fully consistent with the Drude theory and that the semiclassical theory is recovered under requisite assumptions on the ?eld relaxation or radiative wavelength. The anomalous model component is shown to reproduce empirically observed anomalous absorption that has been traditionally corrected by models possessing empirical components that have not been formally derived. Results are presented for several common metals for which the proposed model accurately reproduces the data over the entire modeled bandwidth. A comparative analysis con?rms that the proposed model represents a robust, high ?delity alternative to previously proposed models that do not capture the observed physical response over the extended infrared range.
关键词： broadband infrared,anomalous intraband absorption,fractional derivative,Drude theory,memory kernel
更新于2025-09-04 15:30:14
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Effects of spin-orbit coupling on the optical response of a material
摘要： We investigate the effects of spin-orbit coupling on the optical response of materials. In particular, we study the effects of the commutator between the spin-orbit coupling part of the potential and the position operator on the optical matrix elements using density functional theory calculations within the generalized gradient approximation. By means of a formalism that separates a fully relativistic Kleinman-Bylander pseudopotential into the scalar-relativistic and spin-orbit-coupling parts, we calculate the contribution of the commutator arising from spin-orbit coupling to the squared optical matrix elements of isolated atoms, monolayer transition-metal dichalcogenides, and topological insulators. In the case of isolated atoms from H (Z = 1) to Bi (Z = 83), the contribution of spin-orbit coupling to the squared matrix elements can be as large as 14%. On the other hand, in the cases of monolayer transition-metal dichalcogenides and topological insulators, we find that this contribution is less than 1% and that it is sufficient to calculate the optical matrix elements and subsequent physical quantities without considering the commutator arising from spin-orbit coupling.
关键词： optical response,spin-orbit coupling,transition-metal dichalcogenides,topological insulators,density functional theory
更新于2025-09-04 15:30:14
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Uncertain Analysis of a Stationary Solar Compound Parabolic Concentrator PV Collector System Using Fuzzy Set Theory
摘要： The uncertain analysis of fixed solar compound parabolic concentrator (CPC) collector system is investigated for use in combination with solar PV cells. Within solar CPC PV collector systems, any radiation within the collector acceptance angle enters through the aperture and finds its way to the absorber surface by multiple internal reflections. It is essential that the design of any solar collector aims to maximize PV performance since this will elicit a higher collection of solar radiation. In order to analyze uncertainty of the solar CPC collector system in the optimization problem formulation, three objectives are outlined. Seasonal demands are considered for maximizing two of these objectives, the annual average incident solar energy and the lowest month incident solar energy during winter; the lowest cost of the CPC collector system is approached as a third objective. This study investigates uncertain analysis of a solar CPC PV collector system using fuzzy set theory. The fuzzy analysis methodology is suitable for ambiguous problems to predict variations. Uncertain parameters are treated as random variables or uncertain inputs to predict performance. The fuzzy membership functions are used for modeling uncertain or imprecise design parameters of a solar PV collector system. Triangular membership functions are used to represent the uncertain parameters as fuzzy quantities. A fuzzy set analysis methodology is used for analyzing the three objective constrained optimization problems.
关键词： uncertain analysis,solar CPC PV collector system,fuzzy set theory,solar energy,optimization
更新于2025-09-04 15:30:14
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Utilizing History and Philosophy of Science (HPS) to Teach Physics: The Case of Electromagnetic Theory
摘要： Here the paper provides a historical and philosophical analysis of the development of electromagnetic theory in physics teaching for the benefit of scientific literacy. The analysis is described by the paradigms offered by Kuhn. A number of scientists‘ work in electromagnetic theory which is embedded in the tension between engaging in revolutionary science and normal science provides an insight into how scientific work is thought to proceed. The work of revolutionary scientists: Faraday and Maxwell, who were pivotal in developing the understanding of electromagnetic radiation. A group of scientists now known as the Maxwellians were integral to refining and clarifying Maxwell‘s theory. By realizing these things, the students will become inspired and reinforced in resolve to understand the richness of scientific discovery.
关键词： History and philosophy of science,science education,Kuhn‘s theory of paradigms
更新于2025-09-04 15:30:14
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Hyperelastic material modeling of graphene based on density functional calculations
摘要： A new parameter set for the graphene material model of [1] is obtained. The material model is anisotropic hyperelastic and calibrated by a trial dataset generated by density functional theory (DFT). The DFT experiments are one pure dilatation test and two uniaxial stretch tests along the armchair and zigzag directions. The strain energy is computed from ab-initio simulations and used to calibrate the parameters of the hyperelastic model. The strain energy and stresses from the new parameter set are calculated and verified with the results of [1].
关键词： density functional theory,hyperelastic material model,DFT,anisotropic,strain energy,graphene
更新于2025-09-04 15:30:14
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A parallelizable chaos-based true random number generator based on mobile device cameras for the Android platform
摘要： True random number generators are used in high security applications such as cryptography where non-determinism is required. However, they are slower than their pseudorandom counterparts because they need to extract entropy from physical phenomenon. To overcome this drawback, generators have been designed to extract unpredictability from devices such as computer processing units or microphones. This paper introduces a new generator for the Android mobile platform based on images captured by a built-in camera. Although similar generators exist, they suffer from poor performance and a lack of proper security evaluation. The proposed generator implements a chaos-based postprocessing algorithm that eliminates statistical defects and increases its throughput. These goals are achieved by using the inherent properties of a chaotic system to amplify entropy extracted from the captured images. The proposed generator is evaluated in two phases: first, statistical test suites are executed to identify statistical defects. Next, the generator’s forward and backward security is analysed. Results indicate that the proposed true random number generator is able to generate statistically secure true random number sequences faster than existing mobile-based generators. In addition, the generator is designed to support parallel processing, thus allowing its performance to scale according to the mobile device’s multicore architecture.
关键词： Chaos theory,Digital camera,True random number generator,Mobile device,Android
更新于2025-09-04 15:30:14