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An approach for correcting optical paths of different wavelength lasers in diffusive medium based on Monte Carlo simulation
摘要： Near-infrared spectroscopy (NIRS) generally uses multiple wavelengths of light to obtain functional information. When different wavelengths are employed together, their optical paths are different in the medium and it can potentially cause errors. In this study, we introduced an approach of correcting optical paths when laser sources are used. Laser can be approximated by a point source in a diffusive medium and its depth depends on the wavelength. By multiplying the ratio of detected weights emitted from different point sources, they are conceptually moved to the same position. Monte Carlo simulation was implemented to accumulate required data. As an example for verifying this method, optical properties of the white matter of the brain was used. All combinations of four wavelengths (400, 550, 700, and 850 nm) and six source-detector distances (0.5 mm to 3.0 mm at intervals of 0.5 mm) were simulated. Under the same example conditions, the difference between the simulation results and this method was about ‘1.28%’. The results showed that this approach is applicable to short source-detector distance conditions.
关键词： Monte Carlo simulation,Point source approximation,Near infrared spectroscopy,Light diffusion,Optical path,Penetration depth
更新于2025-09-12 10:27:22
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Spin-orbit-coupled quantum memory of a double quantum dot
摘要： The concept of quantum memory plays an incisive role in the quantum information theory. As confirmed by the several recent rigorous mathematical studies, the quantum memory inmate in the bipartite system ρAB can reduce the uncertainty about part B, after measurements done on part A. In the present work, we extend this concept to systems with a spin-orbit coupling and introduce the notion of spin-orbit quantum memory. We self-consistently explore the Uhlmann fidelity, the pre- and the post-measurement entanglement entropy, and the post-measurement conditional quantum entropy of the system with spin-orbit coupling and show that measurement performed on the spin subsystem decreases the uncertainty of the orbital part. The uncovered effect enhances with the strength of the spin-orbit coupling. We study the concept of macroscopic realism introduced by Leggett and Garg [Phys. Rev. Lett. 54, 857 (1985)] and observe that POVM measurements done on the system under the particular protocol are noninvasive. For the extended system, we perform quantum Monte Carlo calculations and consider the reshuffling of the electron densities due to an external electric field.
关键词： quantum Monte Carlo,spin-orbit coupling,entanglement entropy,POVM measurements,conditional quantum entropy,quantum memory,Uhlmann fidelity
更新于2025-09-12 10:27:22
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Elucidating the effects of guest-host energy level alignment on charge transport in phosphorescent OLEDs
摘要： The correct choice of guest and host molecules in the light-emitting layer is essential for developing high performance phosphorescent organic light emitting devices. However, the effects of the energy level alignment between the guest and the host are yet to be fully elucidated. In this Letter, we use kinetic Monte Carlo simulations to investigate guest-host systems in which the energy gap of the guest and host is fixed, and only the relative energies of the ionization potential/electron affinity are changed to elucidate their effect on charge transport. It was determined that the mobility balance in the blend was sensitive to the energy level alignment, allowing balanced active layer mobility to be achieved despite the hole and electron mobilities being different by around one order of magnitude. It was also found that the mobility of the faster carrier was more sensitive to the energy level alignment than that of the slower carrier due to reduced slower carrier thermalization under deep charge trapping on the guest.
关键词： guest-host energy level alignment,phosphorescent OLEDs,kinetic Monte Carlo simulations,charge transport
更新于2025-09-12 10:27:22
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Gamma spectral analysis by artificial neural network coupled with Monte Carlo simulations
摘要： Neutron activation analysis has been widely used for quantitative analysis. It can quantify elements in parts per million or billion. Artificial neural network is an attractive technique to analyze complex gamma spectra obtained from neutron activation. This study offers an improved methodology to analyze neutron activation gamma spectra using an artificial neural network. The methodology was demonstrated by quantifying five trace elements (Br, Na, Zn, K, Au) in common kidney stones. First, Monte Carlo simulations were used to create a large training data set. Then, an artificial neural network was employed for chemical elements identification analysis. For quantitative analysis, a Levenberg–Marquardt algorithm with 5 ? 23 ? 5 structure artificial neural network was used. The artificial neural network for analysis of simulated gamma spectra resulted in estimated element concentrations. The differences between true and estimated concentrations are 1.8% for Br, 3.4% for Na, 5.4% for Zn, 2.8% for K, and 1.6% for Au. For real gamma spectral analysis, the largest difference was found to be 28.2% for Zn in a calcium oxalate monohydrate type of kidney stones.
关键词： Kidney stone,Monte Carlo,Neural network,Gamma spectroscopy
更新于2025-09-12 10:27:22
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Holographic interferences in strong-field ionization beyond the dipole approximation: The influence of the peak and focal-volume-averaged laser intensities
摘要： In strong-?eld ionization, interferences between electron trajectories create a variety of interference structures in the ?nal momentum distributions. Among them, the interferences between electron pathways that are driven directly to the detector and those that rescatter signi?cantly with the parent ion lead to holography-type interference patterns that have received great attention in recent years. In this work, we study the in?uence of the laser magnetic-?eld component onto the holographic interference pattern, an effect beyond the electric-dipole approximation, in experiment and theory. The experimentally observed nondipole signatures are analyzed via quantum trajectory Monte Carlo simulations. We provide explanations for the experimentally demonstrated asymmetry in the holographic interference pattern and its nonuniform photoelectron energy dependence as well as for the variation of the topology of the holography-type interference pattern along the laser-?eld direction. Analytical scaling laws of the interference features are derived, and their direct relation to either the focal-volume-averaged laser intensities, or to the peak intensities are identi?ed. The latter, in particular, provides direct access to the peak intensity in the focal volume.
关键词： laser magnetic-?eld,nondipole effects,strong-?eld ionization,quantum trajectory Monte Carlo simulations,holographic interference
更新于2025-09-12 10:27:22
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Non-equilibrium electronic transport through a quantum dot with strong Coulomb repulsion in the presence of a magnetic field
摘要： The non-equilibrium electronic transport through a nanoscale device composed of a single quantum dot between two metallic contacts is studied theoretically within the framework of the Keldysh formalism. The quantum dot consists of a single energy level subject to an applied magnetic field. Correlations due to the Coulomb repulsion between electrons on the dot are treated with a Green’s function decoupling scheme which, although similar to the Hubbard-I approximation, captures some of the dynamics beyond. The scheme is exact in the so-called atomic limit, defined by vanishing tunneling between contacts and dot, and in the non-interacting limit, where the on-dot Coulomb repulsion is zero. Explicit analytic solutions, valid for arbitrary magnetic fields, are obtained for two important setups: (i) the stationary regime, with constant voltage bias between the leads, and (ii) the time-dependent regime for metallic leads with constant density of states of infinite width. In these regimes, the current through the dot is evaluated numerically for various parameter sets and its main features interpreted in terms of the underlying physical processes. The results are compared to the non-crossing approximation (NCA) and diagrammatic non-equilibrium quantum Monte-Carlo (QMC) where available.
关键词： Coulomb repulsion,magnetic field,non-equilibrium electronic transport,Hubbard-I approximation,non-crossing approximation,quantum dot,quantum Monte-Carlo,Keldysh formalism
更新于2025-09-12 10:27:22
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Monte Carlo Study of Slot-waveguide Liquid Crystal Phase Shifters
摘要： We present detailed Monte Carlo simulations of a simple model of a nematic liquid crystal slot waveguide shifter, investigating the effect of an applied electric external field. The simulations are based on the Lebwohl-Lasher lattice spin model with boundary conditions chosen to mimic the planar alignment as in Silicon Organic Hybrid waveguides anchoring appropriate for Polydimethylsiloxane polymer walls. The external field is modeled by adding a term to the Hamiltonian which describes its coupling to the mesogenic molecules. We have investigated the effect of the external field on the optical transmission and the ordering across the cell.
关键词： Monte Carlo,confined nematic liquid crystals,anchoring,waveguide shifters
更新于2025-09-12 10:27:22
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Spin-polarization effects of an ultrarelativistic electron beam in an ultraintense two-color laser pulse
摘要： Spin-polarization effects of an ultrarelativistic electron beam head-on colliding with an ultraintense two-color laser pulse are investigated comprehensively in the quantum radiation-dominated regime. We employ a Monte Carlo method, derived from the recent work of Li et al. [Phys. Rev. Lett. 122, 154801 (2019)], to calculate the spin-resolved electron dynamics and photon emissions in the local constant field approximation. We find that electron radiation probabilities in adjacent half cycles of a two-color laser field are substantially asymmetric due to the asymmetric field strengths and, consequently, after interaction the electron beam can obtain a total polarization of about 11% and a partial polarization of up to about 63% because of radiative spin effects, with currently achievable laser facilities, which may be utilized in high-energy physics and nuclear physics. Moreover, the considered effects are shown to be crucially determined by the relative phase of the two-color laser field and robust with respect to other laser and electron-beam parameters.
关键词： radiative spin effects,Monte Carlo method,quantum radiation-dominated regime,spin-polarization,two-color laser pulse,ultrarelativistic electron beam
更新于2025-09-11 14:15:04
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Bayesian 3D Reconstruction of Subsampled Multispectral Single-photon Lidar Signals
摘要： Light detection and ranging (Lidar) single-photon devices capture range and intensity information from a 3D scene. This modality enables long range 3D reconstruction with high range precision and low laser power. A multispectral single-photon Lidar system provides additional spectral diversity, allowing the discrimination of different materials. However, the main drawback of such systems can be the long acquisition time needed to collect enough photons in each spectral band. In this work, we tackle this problem in two ways: first, we propose a Bayesian 3D reconstruction algorithm that is able to find multiple surfaces per pixel, using few photons, i.e., shorter acquisitions. In contrast to previous algorithms, the novel method processes jointly all the spectral bands, obtaining better reconstructions using less photon detections. The proposed model promotes spatial correlation between neighbouring points within a given surface using spatial point processes. Secondly, we account for different spatial and spectral subsampling schemes, which reduce the total number of measurements, without significant degradation of the reconstruction performance. In this way, the total acquisition time, memory requirements and computational time can be significantly reduced. The experiments performed using both synthetic and real single-photon Lidar data demonstrate the advantages of tailored sampling schemes over random alternatives. Furthermore, the proposed algorithm yields better estimates than other existing methods for multi-surface reconstruction using multispectral Lidar data.
关键词： Poisson noise,Bayesian inference,multispectral imaging,Lidar,3D reconstruction,Markov chain Monte Carlo
更新于2025-09-11 14:15:04
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Radiation Tolerant Nanowire Array Solar Cells
摘要： Space power systems require photovoltaics that are lightweight, efficient, reliable, and capable of operating for years or decades in space environment. Current solar panels use planar multijunction, III-V based solar cells with very high efficiency, but their specific power (power to weight ratio) is limited by the added mass of radiation shielding (e.g. coverglass) required to protect the cells from the high-energy particle radiation that occurs in space. Here we demonstrate that III-V nanowire-array solar cells have dramatically superior radiation performance relative to planar solar cell designs and show this for multiple cell geometries and materials, including GaAs and InP. Nanowire cells exhibit damage thresholds ranging from ~10-40 times higher than planar control solar cells when subjected to irradiation by 100-350 keV protons and 1 MeV electrons. Using Monte Carlo simulations, we show that this improvement is due in part to a reduction in the displacement density within the wires arising from their nanoscale dimensions. Radiation tolerance, combined with the efficient optical absorption and the improving performance of nanowire photovoltaics, indicates that nanowire arrays could provide a pathway to realize high-specific-power, substrate-free, III-V space solar cells with substantially reduced shielding requirements. More broadly, the exceptional reduction in radiation damage suggests that nanowire architectures may be useful in improving the radiation tolerance of other electronic and optoelectronic devices.
关键词： space environment,irradiation-induced defects,radiation hard,space solar cells,Monte Carlo simulations,nanowire solar cells,high specific power
更新于2025-09-11 14:15:04