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Two-photon absorption in a two-level system enabled by noise
摘要： We address the textbook problem of dynamics of a spin placed in a dc magnetic field and subjected to an ac drive. If the drive is polarized in the plane perpendicular to the dc field, then the drive photons are resonantly absorbed when the spacing between the Zeeman levels is close to the photon energy. This is the only resonance when the drive is circularly polarized. For a linearly polarized drive, additional resonances corresponding to absorption of three, five, and multiple odd numbers of photons is possible. Interaction with the environment causes the broadening of the absorption lines. We demonstrate that the interaction with environment enables the forbidden two-photon absorption. We adopt a model of the environment in the form of random telegraph noise produced by a single fluctuator. As a result of the synchronous time fluctuations of different components of the random field, the shape of the two-photon absorption line is non-Lorentzian and depends dramatically on the drive amplitude. This shape is a monotonic curve at strong drive, while, at weak drive, it develops a two-peak structure reminiscent of an induced transparency on resonance.
关键词： environment interaction,absorption spectrum,noise,two-photon absorption,telegraph noise,Floquet description,two-level system
更新于2025-09-12 10:27:22
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[IEEE 2019 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech) - St. Petersburg, Russia (2019.10.17-2019.10.18)] 2019 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech) - The Multi-Criteria Optimization in the LTspice Simulation Software of a JFet class AB Buffer Amplifier for Operation at Low Temperatures
摘要： A high-speed buffer amplifier (BA) for analog microcircuits field-effect transistors is proposed. The scheme differs from the known circuit solutions by a small number of elements and can operate within the range of cryogenic temperatures. In the LTSpice simulation software, the optimal control parameters were selected using the DEAP (Distributed Evolutionary Algorithm in Python) library of distributed evolutionary calculations and the NSGA-II multi-criteria optimization algorithm. Minimization of offset voltage, static current consumption and dead band width on the amplitude characteristic at low temperatures were chosen as the priority parameters of the control unit.
关键词： low-temperature electronics,class AB operation,optimization of analog electronic circuit,operational amplifier,LTspice environment,buffer amplifier,junction field-effect transistors
更新于2025-09-12 10:27:22
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Evaluation of the photovoltaic potential in built environment using spatial data captured by unmanned aerial vehicles
摘要： In this paper, a spatial photovoltaic (PV) potential evaluation method based on the combination of aerial photogrammetry and Geographic Information System (GIS) is proposed for PV potential evaluation of built environment (BE). The method can be applied to PV potential evaluation of not only building roofs, but also built environments such as carpark. The point cloud model of the studied field is established by processing images captured by unmanned aerial vehicles (UAV), which are then imported into GIS to estimate the available area for PV installation based on sunlight analysis after offsetting the identified borders of the urban and ecological infrastructures. The PV potential is determined based on the installation configurations of PV modules. With the help of the PVSYST software simulation, the proposed method in this paper is used to evaluate the PV potential of a carpark and a rooftop of a building in Singapore.
关键词： geographic information system,low‐altitude aerial photography,photovoltaic potential evaluation,photogrammetry,built environment
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
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New Techniques for Sizing Solar Photovoltaic Panels for Environment Monitoring Sensor Nodes
摘要： The development of perpetually powered sensor networks for environment monitoring to avoid periodic battery replacement and to ensure the network never goes offline due to power is one of the primary goals in sensor network design. In many environment-monitoring applications, the sensor network is internet-connected, making the energy budget high because data must be transmitted regularly to a server through an uplink device. Determining the optimal solar panel size that will deliver sufficient energy to the sensor network in a given period is therefore of primary importance. The traditional technique of sizing solar photovoltaic (PV) panels is based on balancing the solar panel power rating and expected hours of radiation in a given area with the load wattage and hours of use. However, factors like the azimuth and tilt angles of alignment, operating temperature, dust accumulation, intermittent sunshine and seasonal effects influencing the duration of maximum radiation in a day all reduce the expected power output and cause this technique to greatly underestimate the required solar panel size. The majority of these factors are outside the scope of human control and must be therefore be budgeted for using an error factor. Determining of the magnitude of the error factor to use is crucial to prevent not only undersizing the panel, but also to prevent oversizing which will increase the cost of operationalizing the sensor network. But modeling error factors when there are many parameters to consider is not trivial. Equally importantly, the concept of microclimate may cause any two nodes of similar specifications to have very different power performance when located in the same climatological zone. There is then a need to change the solar panel sizing philosophy for these systems. This paper proposed the use of actual observed solar radiation and battery state of charge data in a realistic WSN-based automatic weather station in an outdoor uncontrolled environment. We then develop two mathematical models that can be used to determine the required minimum solar PV wattage that will ensure that the battery stays above a given threshold given the weather patterns of the area. The predicted and observed battery state of charge values have correlations of 0.844 and 0.935 and exhibit Root Mean Square Errors of 9.2% and 1.7% for the discrete calculus model and the transfer function estimation (TFE) model respectively. The results show that the models perform very well in state of charge prediction and subsequent determination of ideal solar panel rating for sensor networks used in environment monitoring applications.
关键词： battery state of charge,environment monitoring,solar radiation,discrete calculus model,transfer function estimation,solar photovoltaic panels,sensor nodes
更新于2025-09-11 14:15:04
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Electrodeposited AgAu nanoalloy enhancing photoelectric conversion efficiency of dye sensitized solar cells
摘要： In this study, an equivalent mechanical model was established for the clogging induced by soil suction under negative pressure during root-zone infiltration irrigation in a crop-free pot, and a state diagram was plotted for the clogging process induced by a single soil suction factor under negative pressure. Three groups of impact factor experiments were conducted using three different emitters: a flow-adjustable emitter with eight horizontal outlets (emitter L), a flow-adjustable emitter with two vertical outlets (emitter Q), and an anti-clogging material wrapped around the outer surface of emitter L (emitter K). The first group of experiments investigated the influence of irrigation pressure, the variation of irrigation pressure (range of 0.02 to 0.12 MPa), and the amount of sediment inside emitter L in Yunnan laterite. For the second group of experiments, two soil types (Yunnan laterite and yellow sand), two single-event irrigation volumes (170 and 250 mL), and two numbers of irrigation events (8 and 16) were used to quantitatively analyze the sediment content in emitter L. The third group of experiments used emitters L, Q, and K and involved quantitative analysis of the clogging differences in the different emitter types with two soil types (Yunnan laterite and yellow sand) and two numbers of irrigation events (24 and 64). Statistical analysis showed that irrigation pressure, soil type, irrigation pattern, and emitter type were significant (p < 0.05) for the amount of sediment due to negative suction inside the emitter. The results demonstrate that emitter clogging induced by negative pressure tends to first decrease and then increase with increasing irrigation pressure. The amount of sediment that accumulates within an emitter is influenced by both the soil suction effect under negative pressure as well as soil flushing under positive pressure. Within emitter L, clogging induced by soil suction under negative pressure was more likely to occur when using Yunnan laterite rather than yellow sand soil. When both soil types were used in the test, emitter L was observed to be more prone to clogging induced by negative pressure compared to emitter Q, whereas emitter K exhibited the best anti-clogging performance. This study provides a quantitative account of the factors associated with clogging induced by negative pressure, and it provides a theoretical and experimental basis for gaining an in-depth understanding of emitter clogging during root-zone infiltration irrigation in Yunnan laterite.
关键词： Negative-pressure clogging,Emitter,Yunnan laterite,Pot environment,Root-zone infiltration irrigation
更新于2025-09-11 14:15:04
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Characterization and analysis on micro-hardness and microstructure evolution of brass subjected to laser shock peening
摘要： In view of the temperature distribution of the high-temperature geothermal tunnels, the surrounding rock temperature was divided into four grades (40 (cid:1)C, 60 (cid:1)C, 80 (cid:1)C and 100 (cid:1)C) to simulate the hot-dry environment. Using the standard curing environment as a reference condition, the mechanical properties and pore structure characteristics of concrete for shotcrete use under hot-dry environments at different temperatures were studied by mechanical and mercury intrusion porosimetry (MIP) tests. Fractal dimension of pore structure was calculated through the fractal model based on thermodynamic method. Bivariate correlation analysis was conducted on the curing temperature and the pore structure parameters. The results show that the 40 (cid:1)C hot-dry environment is conducive to enhance the mechanical properties of concrete and optimize its pore structure at the age of 1d. However, the hot-dry environments after 7 days will deteriorate the mechanical properties and pore structure of concrete, and the higher the temperature, the more obvious the deterioration. There is a significant correlation between curing temperature and porosity of capillary pores, median pore diameter, average pore diameter and fractal dimension.
关键词： Pore structure,Surrounding rock temperature,Mechanical property,Fractal dimension,Concrete for shotcrete use,High-temperature geothermal tunnel,Hot-dry environment
更新于2025-09-11 14:15:04
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Cryogenic Characterization of RF Low-Noise Amplifiers Utilizing Inverse-Mode SiGe HBTs for Extreme Environment Applications
摘要： The cryogenic performance of radiation-hardened radio-frequency (RF) low-noise amplifiers (LNAs) is presented. The LNA, which was originally proposed for the mitigation of single-event transients (SETs) in a radiation environment, uses inverse-mode silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) in its core cascode stages. In this prototype, the upper common-base SiGe HBT is configured in inverse mode for balanced RF performance and reduced SET sensitivity. In order to better exploit the inverse-mode LNAs in a variety of extreme-environment applications, the RF performance of the LNA was characterized using liquid nitrogen to evaluate cryogenic operation down to 78 K. While the SiGe LNA exhibits acceptable RF performance for all temperature conditions, there is a noticeable gain drop observed at 78 K compared to the conventional forward-mode design. This is attributed to the limited high-frequency performance of an inverse-mode SiGe HBT. As a guideline, compensation techniques including layout modifications and profile optimization are discussed for the mitigation of the observed gain degradation.
关键词： low-noise amplifier (LNA),heterojunction bipolar transistor (HBT),cascode,inverse mode,extreme environment,cryogenic measurement,silicon-germanium (SiGe)
更新于2025-09-11 14:15:04
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[IEEE 2018 International Conference on 3D Vision (3DV) - Verona (2018.9.5-2018.9.8)] 2018 International Conference on 3D Vision (3DV) - Multi-scale Direct Sparse Visual Odometry for Large-Scale Natural Environment
摘要： In this paper, we describe a multi-scale monocular direct sparse visual odometry (DSO) system to recover large-scale trajectories in unstructured natural environments in real time, while building a consistent metric map of the visited scenes. In contrast to the current state-of-the-art DSO system, the proposed method allows for more robust motion estimation and more accurate reconstruction in distant scenes by exploiting the characteristics of short- and long-range pixels, respectively. The long-range pixels, which are less sensitive to small camera translations, are used to initialize the camera rotation, so as to boost the tracking robustness in challenging natural environments. A multi-scale reconstruction framework is developed to recover short-range structure over successive frames, as well as the long-range structure over distant frames, hence allowing for a more consistent mapping precision. The reconstruction precision, the tracking accuracy, and the robustness of the proposed system are extensively evaluated with a publicly available vKITTI dataset, as well as the challenging Devon Island dataset, and Symphony Lake dataset. A detailed performance comparison between the proposed method and the state-of-the-art DSO system is presented.
关键词： multi-scale,large-scale natural environment,monocular vision,3D mapping,direct sparse visual odometry,real-time tracking
更新于2025-09-10 09:29:36
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Investigation of Natural Ecological Enviroment Using Remote Sensing Based Integrated Index at a City Scale
摘要： It is of great importance to monitor and evaluate the dynamics of ecological environment due to severe human activities. In our study, three remote sensing based ecological factors were selected to generate an integrated index for estimating the natural ecological environment at a city scale, specifically including vegetation coverage, soil index and slope. Vegetation coverage was derived from Normalized Difference Vegetation Index (NDVI) of Landsat 8 OLI (Operational Land Imager) imagery. Soil index was generated by the greenness above bare soil (GRABS). Slope was derived from 30 meters resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM). An integrated index with the method of weighting average was obtained by normalizing the three indicators. The results show that Hefei has a relatively good ecological environment. The ratio of excellent and good levels accounts for 71.00% of the study area. In general, the ecological environment is better in the southern part than that in the northern part.
关键词： NDVI,Integrated index,Remote sensing,Landsat 8 OLI,Ecological environment
更新于2025-09-10 09:29:36