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Plasmonic nanoparticles assemblies templated by helical bacteria and resulting optical activity
摘要： Plasmonic nanoparticles (NPs) adsorbing onto helical bacteria can lead to formation of NP helicoids with micron scale pitch. Associated chiroptical effects can be utilized as bioanalytical tool for bacterial detection and better understanding of the spectral behavior of helical self-assembled structures with different scales. Here, we report that enantiomerically pure helices with micron scale of chirality can be assembled on Campylobacter jejuni, a helical bacterium known for severe stomach infections. These organisms have right-handed helical shapes with a pitch of 1–2 microns and can serve as versatile templates for a variety of NPs. The bacteria itself shows no observable rotatory activity in the visible, red, and near-IR ranges of electromagnetic spectrum. The bacterial dispersion acquires chiroptical activity at 500–750 nm upon plasmonic functionalization with Au NPs. Finite-difference time-domain simulations confirmed the attribution of the chiroptical activity to the helical assembly of gold nanoparticles. The position of the circular dichroism peaks observed for these chiral structures overlaps with those obtained before for Au NPs and their constructs with molecular and nanoscale chirality. This work provides an experimental and computational pathway to utilize chiroplasmonic particles assembled on bacteria for bioanalytical purposes.
关键词： bacteria,simulation,C. jejuni,circular dichroism,plasmonic,mesoscale,gold nanoparticle,biotechnology
更新于2025-09-23 15:19:57
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Emission spectrum control in monolithic blue-cyan dichromatic light-emitting diodes
摘要： InGaN-based dichromatic light emitting diodes (LEDs) emitting in the blue and cyan spectral ranges simultaneously, are investigated both experimentally and theoretically. Two main approaches to controlling the ratio of blue-to-cyan components in the emission spectrum are suggested and analyzed: (i) thickness variation of the GaN barrier between the blue and cyan quantum wells and (ii) optimization of the barrier doping with n- or p-type impurities. Detailed examination of the approaches is carried out in order to understand their capabilities for intentional variation of the blue-to-cyan ratio in a wide range. Based on numerical simulations, a novel mechanism, invoking enhanced Shockley-Read-Hall recombination in the barrier and underlying both approaches, is suggested and discussed. It is shown that proposed design of the monolithic blue-cyan LEDs does not result in substantial decrease of the LED emission efficiency compared to monochromatic blue or cyan reference samples.
关键词： InGaN,simulation,quantum well,doping,emission spectrum,light-emitting diode
更新于2025-09-23 15:19:57
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Photon statistics and dynamics of nanolasers subject to intensity feedback
摘要： Using a fully stochastic numerical scheme, we theoretically investigate the behavior of a nanolaser in the lasing transition region under the influence of intensity feedback. Studying the input-output curves as well as the second-order correlations for different feedback fractions, we obtain an insight into the role played by the fraction of photons reinjected into the cavity. Our results reveal that the transition shrinks and moves to lower pump values with the feedback strength, and irregular pulses can be generated when the feedback is sufficiently large. The interpretation of the observation is strengthened through the comparison with the temporal traces of the emitted photons and with the radio-frequency power spectra. These results provide insight into the physics of nanolasers as well as validating the use of the second-order autocorrelation as a sufficient tool for interpretation of the dynamics. This confirmation offers a solid basis for the reliance on autocorrelations in experiments studying the effects of feedback in nanodevices.
关键词： nanolasers,stochastic simulation,intensity feedback,photon statistics,autocorrelation
更新于2025-09-23 15:19:57
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The time response of plasmonic sensors due to binary adsorption: analytical versus numerical modeling
摘要： In order to allow for multiscale modeling of complex systems, we focus on various approaches to modeling binary adsorption. We consider multiple methods of modeling the temporal response of general plasmonic sensors. We start from the analytical approach. The kinetics of adsorption and desorption is modeled both as a first order reaction and as a second-order reaction. The criteria for their validity and the choice between them in the case of two-component adsorption are established. Due to the nonlinearities of the second-order reactions and the lack of their analytical solutions, computer-aided modeling is considered next, also in multiple ways: the employment of numerical solvers, fitting of experimental results, the stochastic simulation algorithms and the employment of artificial neural networks (ANN). The examples we present illustrate the advantages and disadvantages of the particular approaches. The goal is to aid the concurrent multiscale modeling of adsorption-based devices. Machine learning in ANN performed here is used to estimate the equilibrium values of adsorbed quantities. The obtained results show that to train an ANN for the estimation of the equilibrium adsorption quantities the Levenberg–Marquardt and the Bayesian regularization algorithms are less efficient than the quasi-Newton BFGS (Broyden–Fletcher–Goldfarb–Shanno) algorithm.
关键词： Kinetics,Stochastic simulation algorithms,Adsorption,Machine learning algorithms,Plasmonic sensing
更新于2025-09-23 15:19:57
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FDTD simulation studies on improvement of light absorption in organic solar cells by dielectric nanoparticles
摘要： In this paper, we present a systematic design and analysis of organic solar cell (OSC) by embedding dielectric nanoparticles layer at anode. Using numerical simulations, we show that there is improvement in the light absorption in the active layer of the device using nanoparticles. The nanoparticles will act as scattering medium for the incident light and hence trap the light inside the device. For the light scattered at different angles, the optical path length in the active medium is increased and this leads to more absorption of light in the active layer and thereby increase in the efficiency. The scattering efficiency and hence the absorption of solar radiation for generation of current depends on the particle size, inter-particle separation and the refractive index contrast between the particles and the embedding medium. Mie theory has been used to calculate the scattering efficiency of nanoparticles. The effect on light absorption and current density of OSC due to nanoparticles has been carried out using finite difference time domain analysis. It is shown that the proposed OSC structure increases the light absorption in the active layer of the device by 40% and short circuit current density by 34%.
关键词： Organic solar cell,Dielectric nanoparticles,Light absorption,Scattering efficiency,Optical simulation
更新于2025-09-23 15:19:57
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[IEEE 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Xiamen, China (2019.12.17-2019.12.20)] 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - A 220 GHz GaN HEMT Power Amplifier
摘要： Evolutions of Geant4 code have affected the simulation of electron backscattering with respect to previously published results. Their effects are quantified by analyzing the compatibility of the simulated electron backscattering fraction with a large collection of experimental data for a wide set of physics configuration options available in Geant4. Special emphasis is placed on two electron scattering implementations first released in Geant4 version 10.2: the Goudsmit-Saunderson multiple scattering model and a single Coulomb scattering model based on Mott cross section calculation. The new Goudsmit-Saunderson multiple scattering model appears to perform equally or less accurately than the model implemented in previous Geant4 versions, depending on the electron energy. The new Coulomb scattering model was flawed from a physics point of view, but computationally fast in Geant4 version 10.2; the physics correction released in Geant4 version 10.2p01 severely degrades its computational performance. Problems observed in electron backscattering simulation in previous publications have been addressed by evolutions in the Geant4 geometry domain.
关键词： Electrons,Monte Carlo,simulation,Geant4
更新于2025-09-23 15:19:57
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Effect of laser beam incidence angle on cladding morphology in laser cladding process
摘要： The change of angle θ between laser cladding powder plane and substrate plane will lead to changes in cladding layer's geometric morphology. Therefore, we established a quantitative numerical prediction model for cladding layer geometry. In this model, we consider the variation of θ, the laser energy attenuation rate and the temperature rise of the powder particles. At the same time, the simulation results were verified by experiments. The results show that when θ is in the range of 50°~90°, the initial temperature is 298 K, the scanning speed is 3.75 mm/s, and the laser spot diameter is 4.5 mm, the Fe#1 powder cladding can achieve better forming effect on Q235. In general, with the decrease of θ, the height of the cladding layer decreases and the width of the layer increases. However, when θ is less than 50°, the quality of the formed morphology significantly deteriorated. The experimental results are in good agreement with the simulation results, which verifies the validity and reliability of the model. This work provides a theoretical reference for further understanding the relationship between the laser cladding morphology and the incident angle.
关键词： Numerical simulation,Laser cladding,Geometric morphology,Laser incident angle
更新于2025-09-23 15:19:57
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Assessment of a house affected by ground movement using terrestrial laser scanning and numerical modeling
摘要： This study analyzed the internal mechanical state of houses disturbed by underground coal mining, especially those that are free from damage in subsidence areas. Traditional surveying and terrestrial laser scanning (TLS) were utilized as the external monitoring methods to obtain the outside displacement of the disturbed houses. The results were then used to estimate the internal mechanical state of houses using simulation software. Three high-quality houses in Paifang Village, China were scanned using TLS in their pre- and post-mining stages. The magnitude of movement and deformation was highly related to the location of the building in the panel, which was enlarged near the center of the subsidence basin. ANSYS was used to compute the internal state of the houses with a focus on the structural columns, ring beams, and walls of the houses under changing tensile conditions. Results showed that the structural column and ring beam can resist tensile deformation, whereas the window corner was the principal point of stress concentration with potential risk of cracking. Mastering the internal stress state of undamaged buildings in mining-affected areas can help to strengthen the premaintenance of houses and guide the construction of new anti-deformation houses. The results of this work may benefit the construction of anti-deformation buildings in mining regions.
关键词： Underground coal mine,Internal mechanical state of houses,Terrestrial laser scanning,Numerical simulation,Traditional surveying
更新于2025-09-23 15:19:57
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Simulation-assisted analysis of microstructural evolution of Tia??6Ala??4V during laser powder bed fusion
摘要： A combination of a Multi-Phase Field model and an Orientation Field is proposed to describe the microstructure evolution induced by laser–material interaction in Laser Powder Bed Fusion (LPBF). The relevant phase transformations are covered by nucleation and growth processes driven by free enthalpy. An empiric correction is applied to the phase-field approach to reduce the grid resolution required for the numerical simulation. This contribution focuses on the LPBF processing of the titanium alloy Ti–6Al–4V. Particularly, the transition between β-titanium and melt is emphasized. The results are discussed and compared to measurements. A numerical correction can be applied to the MPF model to avoid a mesh introduct anisotopy in the crystal growth. The simulation shows the β-phase crystal growth with the (1 0 0) direction into the melt. The model for the phase transformation from β-phase to α-phase agrees with the XRD measurements.
关键词： Simulation,Orientation field method,Phase-field method,Selective laser melting,Volume of the fluid method,Laser powder bed fusion
更新于2025-09-23 15:19:57
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Effect of front surface light trapping structures on the PERC solar cell
摘要： Properties of the front textured surface shape and anti-reflection coating have a great impact on the performance of solar cells. In this paper, the simulation model of the minimum unit cell structure is established and validated, which is based on the framework of Silvaco software and basic parameters of the standard pyramid textures single crystalline silicon PERC solar cell. The effect of the front surface light trapping structures on cell performance is discussed. It is found that the slightly concave pyramid-like textures can improve the response for short wavelengths and the short-circuit current density of the cell is increased by 0.3 mA/cm2, which is improved by 0.80%. In addition, by properly controlling the preparation process of the anti-reflection coating, a gradient-index SiOxNy/Si3N4 double-layer anti-reflection coating (DLARC) can be formed, which can significantly reduce the reflectivity for short wavelengths. And the short-circuit current density of the cell can be increased by 0.32 mA/cm2, which is improved by 0.86%. Finally, the optimized slightly concave pyramid-like textures and the SiOxNy/Si3N4 DLARC can improve the photoelectric conversion efficiency of the PERC solar cell by 0.18% and 0.20%, respectively.
关键词： Texturing,PERC solar cell,Light trapping,Device simulation,Anti-reflection coating
更新于2025-09-23 15:19:57