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Transiently changing shape of the photon number distribution in a quantum-dota??cavity system driven by chirped laser pulses
摘要： We have simulated the time evolution of the photon number distribution in a semiconductor quantum-dot–microcavity system driven by chirped laser pulses and compare with unchirped results. When phonon interactions with the dot are disregarded—thus corresponding to the limit of atomic cavity systems—chirped pulses generate photon number distributions that change their shape drastically in the course of time. Phonons have a strong and qualitative impact on the photon statistics. The asymmetry between phonon absorption and emission destroys the symmetry of the photon distributions obtained for positive and negative chirps. While for negative chirps transient distributions resembling thermal ones are observed, for positive chirps the photon number distribution still resembles its phonon-free counterpart but with overall smoother shapes. In sharp contrast, using unchirped pulses of the same pulse area and duration wave packets are found that move up and down the Jaynes-Cummings ladder with a bell shape that changes little in time. For shorter pulses and lower driving strength Rabi-like oscillations occur between low photon number states. For all considered excitation conditions transitions between sub- and super-Poissonian statistics are found at certain times. For resonant driving with low intensity the Mandel parameter oscillates and is mostly negative, which indicates a nonclassical state in the cavity ?eld. Finally, we show that it is possible that the Mandel parameter dynamically approaches zero and still the photon distribution exhibits two maxima and thus is far from being a Poissonian.
关键词： Mandel parameter,photon number distribution,chirped laser pulses,quantum-dot–cavity system,phonon interactions
更新于2025-09-23 15:21:01
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Role of Sb on the vertical-alignment of type-II strain-coupled InAs/GaAsSb multi quantum dots structures
摘要： The implementation of GaAs0.8Sb0.2 as CL to obtain type-II strain-coupled InAs MQD structures has been examined and compared to similar structures without Sb or without strain coupling. First, it has been demonstrated that capping with GaAsSb prevents the formation of In-rich agglomerations that hampered the QD formation as it has been observed in the sample without Sb. Instead, it promotes the vertical alignment (VA) of almost all QDs with a high density of QD columns. Second, there is a preferential Sb accumulation over the dots together with an undulation of the growth front, contrary to the observed in the uncoupled structure. In case of a deficient covering of GaAsSb, as occurs for giant QDs, In-rich agglomerations may develop. Each VAQD column consists of a sequence of alternating quantum blocks of pyramid-shaped In(Ga)As separated by GaAsSb blocks that rest over them. These Sb-rich blocks are not homogeneous accumulating around the pyramidal apex like a collar. Between the columns, there is an impoverishment of In and Sb compared to the uncoupled sample. These columns can behave as self-aligned nanowires with type II band alignment between self-assembled InAs and GaAsSb quantum blocks that opens new opportunities for novel devices.
关键词： GaAsSb capping layer,III-V semiconductors alloys,Transmission electron microscopy,Composition distribution,Vertical aligned quantum dots
更新于2025-09-23 15:21:01
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Formamidinium-based Perovskite Solar Cells with Enhanced Moisture Stability and Performance via Confined Pressure Annealing
摘要： Formamidinium (FA) based perovskite solar cells (PSC) shows enhanced stability comparing to their methylammonium (MA) based counterpart. However, its stability needs to be further enhanced for the potential commercial applications. We demonstrate here that the high-quality thin film can be obtained for FA-based perovskite with remarkably enhanced moisture stability using a confined-pressure annealing (CPA) processing and controlling the amount of Cs introduced into the FAPbI3 perovskite precursor solution. Without additional 2D cation additives, surface passivation or encapsulation, no phase degradation was observed for the Cs0.1FA0.9PbI3 perovskite under a humidity of 70 RH% over 500 hours. The unencapsulated device maintained over 70% performances for 500 hours comparing to <80 h of the conventional processed devices, which is the comparable to the outstanding moisture stability of the 2D/3D perovskites. The FA-based perovskite grain size was promoted to over 1 micrometer with a high static water contact angle up to 112°. The surface cations composition was varied with the concentrated FA cation species at surface while homogenized Cs/FA distribution inside the film. The trapped state density and carrier recombination rate were also reduced with a high fill factor of 82% and the efficiency over 20.23%. This work suggests the intrinsic stability of the 3D perovskite could be further enhanced with adjusting of the surface compositions during the crystallization process.
关键词： Confined pressure annealing,Perovskite solar cells,Cation distribution,Moisture stability,Formamidinium
更新于2025-09-23 15:21:01
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Photovoltaic-Driven SiC MOSFET Circuit Breaker with Latching and Current Limiting Capability
摘要： This paper introduces a Solid State Circuit Breaker with Latching and Current Limiting capabilities for DC distribution systems. The proposed circuit uses very few electronic parts and it is fully analog. A SiC N-MOSFET driven by a photovoltaic driver and a maximum current detector circuit are the core elements of the system. This work details circuit operation under different conditions and includes experimental validation at 1 kVdc. Wide versatility, highly configurable, and very fast response, less than 1 μs in the case of short-circuit, are the most remarkable outcomes.
关键词： SiC MOSFET,Solid State Circuit Breaker (SSCB),fault current limiter,WBG semiconductors,DC power distribution
更新于2025-09-23 15:21:01
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Scattering of an alkali-metal atomic beam on anti-spin-relaxation coatings
摘要： We performed scattering experiments using a rubidium (Rb) atomic beam on paraf?n ?lms and measured the angular and velocity distributions of scattered atoms. The paraf?n ?lms were prepared in various ways and characterized by atomic force microscopy and x-ray diffraction. The ?lms exhibited various roughnesses and crystal structures. The paraf?n ?lms preserved the spin polarization of the scattered atoms. The measured angular distributions of all prepared ?lms were consistent with Knudsen’s cosine law. The velocity distributions were well ?tted by Maxwell’s distribution, characterized by a temperature much closer to the ?lm temperature than to the atomic-beam temperature. We therefore concluded that the translational motion of the scattered atoms was thermalized with the paraf?n ?lms via single-scattering events.
关键词： Knudsen’s cosine law,velocity distributions,scattering experiments,paraf?n ?lms,Maxwell’s distribution,rubidium atomic beam,spin polarization,angular distributions
更新于2025-09-23 15:21:01
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Birefringence measurement of biological tissue based on polarization-sensitive digital holographic microscopy
摘要： We present a polarization-sensitive digital holography to measure the birefringence of biological tissues with complex structures. The birefringence measurement system is established by incorporating the modified Mach–Zehnder interferometer and lab-developed software. Normal and cancerous bladder tissue samples are measured by using the proposed experimental system. The polarization-dependent phase-shifted holograms are recorded by rotating the polarizer. Moreover, the hybrid reconstruction and least-square unwrapping algorithms are used to extract phase information of biological tissues at different polarization states. The birefringence of tissue is obtained from the above-phase distributions. The results show that polarization sensitivity exists in the normal bladder tissue and cancerous bladder tissue, and the median birefringence value of the cancerous tissue is significantly higher than that of the normal tissue. These results will provide reference for pathological research and clinic diagnoses.
关键词： Mach–Zehnder interferometer,birefringence,polarization-sensitive digital holography,biological tissue,phase distribution
更新于2025-09-23 15:21:01
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Digital holographic sizer for coal powder size distribution measurement: preliminary simulation and experiment
摘要： On-line and continuous measurements of coal powder size distribution in coal-fired plants remain challenging. A coal powder size measurement system based on digital holography (DH) is developed. The effects of several factors, i.e. pixel size, recording distance, particle size, and concentration, on particle size measurement by the DH method are quantified by simulation, yielding the suitable pixel size, recording distance and particle concentration. The measurement system is implemented based on the simulation results and applied to measure particle size distribution of pulverized coal samples. Results show that the particles are clearly reconstructed from the hologram, and the measured size distributions agree well with those of the samples measured by laser particle size analyzer. This work shows that the digital holographic sizer has great potential in coal powder size distribution measurement in power plant pipes.
关键词： digital holography,particle size distribution,coal powder,on-line measurement
更新于2025-09-23 15:21:01
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Tunable luminescence and transmittance nature of CdS:PMMA nanocomposites for optoelectronic applications
摘要： Optical and energy storage materials based on semiconductors are of great interest today. The present report explains the semiconductor nanocomposite centered on highly transparent Poly(methyl methacrylate) (PMMA) matrix and Cadmium Sulphide (CdS) nano particles. The solid ?lms of CdS:PMMA composite was prepared using simple and cost e?ective solution casting technique. The surface morphology and the presence of CdS particles in PMMA matrix was analysed using Scanning Electron Microscope (SEM) and Energy Dispersive X-ray spectra (EDX). The size of the particles was analysed using Atomic Force Microscopy (AFM) and Transmission Electron Microscope (TEM) and they revealed the presence of nano sized particles. The narrow size distribution of particles was identi?ed from TEM and AFM analysis. The transmittance of the CdS:PMMA nanocomposite solid ?lms was found to be above 90%. The blue and green emission of CdS:PMMA nanocomposite solid ?lms were observed from Photoluminescence (PL) spectra.
关键词： Composite materials,Polymeric composite,Luminescence,Green emission,Particle distribution,Transmittance
更新于2025-09-23 15:21:01
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[IEEE 2018 IEEE PES/IAS PowerAfrica - Cape Town, South Africa (2018.6.28-2018.6.29)] 2018 IEEE PES/IAS PowerAfrica - A Review of Grid Tied PV Generation on LV Distribution Networks
摘要： Renewable generation, at the customer side of the meter, continue to gain interest worldwide. Distribution network (DN) performance analysis, under distributed photovoltaic generation (DPVG), is paramount important to ensure DN security and reliability. This paper presents a broad review of issues, with an emphasis on grid voltage, associated with DSPVG, and proposed solutions. There has not been a comprehensive literature review of DSPVG, particularly in South Africa (SA). There is a need to quantify impacts and expectations of DSPVG connection on three phase radial low voltage (LV) DNs. In this paper, circuit diagrams and mathematical expressions for voltage rise and drop analyses, are detailed, with a comprehensive range of proposed and commercially available mitigation solutions. These include; active power curtailment (APC), reactive power control (RPC) and droop-based voltage control. APC is more ef?cient and effective for LV DNs. Sophisticated strategies combining different standalone control methods, were proposed in literature, for increase of DSPVG penetration, both locally, in residential home, and globally.
关键词： Distribution network,low voltage,voltage control,photovoltaic
更新于2025-09-23 15:21:01
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Short-term Voltage Stability Enhancement in Residential Grid with High Penetration of Rooftop PV units
摘要： Short-term voltage instability (STVI) imposes a severe threat to modern distribution networks (DNs) where a large number of intermittent distributed generator (DG) units, like rooftop photovoltaic (PV), is being integrated. Consequently, most of the international standards have been revised by incorporating the requirement of dynamic voltage support (DVS) through DG units, which is a promising approach to alleviate the STVI. In this paper, a novel DVS strategy is proposed to improve the short-term voltage stability (STVS) in residential grids. In comparison with other DVS strategies, the proposed DVS scheme maximizes the active power support from PV units following a contingency utilizing maximum allowable current of the PV inverters. Moreover, the inverter design margin is taken into account in designing the proposed scheme to limit the injected grid current within maximum allowable inverter current. The impact of inverter design margin on the STVS is explained, and the effectiveness of the proposed strategy compared with conventional DVS is demonstrated. The feasibility of the DVS control strategies in practical application is studied. Several case studies are carried out on benchmark IEEE 4 bus and IEEE 13 node test feeder systems, and finally on a ring-type DN. The results show that the proposed DVS scheme is feasible, and achieved superior performance compared to the other strategies. Furthermore, it has been shown that implementation of the proposed DVS scheme can avoid the installation of an expensive 1200 kVA D-STATCOM for STVS improvement in the target system.
关键词： Distributed generators,fault induced delayed voltage recovery,low voltage ride-through,dynamic voltage support,short-term voltage stability,distribution system
更新于2025-09-23 15:21:01