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Light penetration in seawater polluted by dispersed oil: results of radiative transfer modelling
摘要： The downwelling light in seawater is shaped by natural seawater constituents as well as by some external substances which can occur locally and temporally. In this study we focused on dispersed oil droplets which can be found in seawater after an oil spill or in the consequence of intensive shipping, oil extraction and transportation. We applied our modi?ed radiative transfer model based on Monte Carlo code to evaluate the magnitude of potential in?uence of dispersed oil droplets on the downwelling irradiance and the depth of the euphotic zone. Our model was validated on the basis of in situ measurements for natural (unpolluted) seawater in the Southern Baltic Sea, resulting in less than 5% uncertainty. The optical properties of dispersed Petrobaltic crude oil were calculated on the basis of Mie theory and involved into radiative transfer model. We found that the changes in downwelling light caused by dispersed oil depend on several factors such as oil droplet concentration, size distribution, and the penetration depth (i.e. vertical range of oil droplets occurrence below sea surface). Petrobaltic oil droplets of submicron sizes and penetration depth of 5 m showed a potentially detectable reduction in the depth of the euphotic zone of 5.5% at the concentration of only 10 ppb. Micrometer-sized droplets needed 10 times higher concentration to give a similar effect. Our radiative transfer model provided data to analyse and discuss the in?uence of each factor separately. This study contributes to the understanding of the change in visible light penetration in seawater affected by dispersed oil.
关键词： radiative transfer,droplet size distribution,dispersed oil,Oil pollution,downwelling irradiance
更新于2025-09-04 15:30:14
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Towards quantum communication from global navigation satellite system
摘要： Satellite-based quantum communication (QC) is an invaluable resource for the realization of a quantum network at the global scale. In this regard, the use of satellites well beyond the low Earth orbit gives the advantage of long communication time with a ground station. However, high-orbit satellites pose a great technological challenge due to the high diffraction losses of the optical channel, and the experimental investigation of such quantum channels is still lacking. Here, we report on the first experimental exchange of single photons from a global navigation satellite system (GNSS) at a slant distance of 20 000 km, by exploiting the retroreflector array mounted on GLONASS satellites. We also observed the predicted temporal spread of the reflected pulses due to the geometrical shape of the array. Finally, we estimated the requirements needed for an active source on a GNSS satellite, aiming towards QC from GNSS with state-of-the-art technology.
关键词： global navigation satellite system,quantum key distribution,quantum communication
更新于2025-09-04 15:30:14
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Adjustment of Sentinel-2 Multi-Spectral Instrument (MSI) Red-Edge Band Reflectance to Nadir BRDF Adjusted Reflectance (NBAR) and Quantification of Red-Edge Band BRDF Effects
摘要： Optical wavelength satellite data have directional re?ectance effects over non-Lambertian surfaces, described by the bidirectional re?ectance distribution function (BRDF). The Sentinel-2 multi-spectral instrument (MSI) acquires data over a 20.6? ?eld of view that have been shown to have non-negligible BRDF effects in the visible, near-infrared, and short wave infrared bands. MSI red-edge BRDF effects have not been investigated. In this study, they are quanti?ed by an examination of 6.6 million (January 2016) and 10.7 million (April 2016) pairs of forward and back scatter re?ectance observations extracted over approximately 20? × 10? of southern Africa. Non-negligible MSI red-edge BRDF effects up to 0.08 (re?ectance units) across the 290 km wide MSI swath are documented. A recently published MODIS BRDF parameter c-factor approach to adjust MSI visible, near-infrared, and short wave infrared re?ectance to nadir BRDF-adjusted re?ectance (NBAR) is adapted for application to the MSI red-edge bands. The red-edge band BRDF parameters needed to implement the algorithm are provided. The parameters are derived by a linear wavelength interpolation of ?xed global MODIS red and NIR BRDF model parameters. The ef?cacy of the interpolation is investigated using POLDER red, red-edge, and NIR BRDF model parameters, and is shown to be appropriate for the c-factor NBAR generation approach. After adjustment to NBAR, red-edge MSI BRDF effects were reduced for the January data (acquired close to the solar principal where BRDF effects are maximal) and the April data (acquired close to the orthogonal plane) for all the MSI red-edge bands.
关键词： Landsat,NBAR,POLDER,bidirectional re?ectance distribution function (BRDF),Africa,Sentinel-2,red-edge,MODIS
更新于2025-09-04 15:30:14
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An entanglement-based wavelength-multiplexed quantum communication network
摘要： Quantum key distribution has reached the level of maturity required for deployment in real-world scenarios. It has previously been shown to operate alongside classical communication in the same telecommunication fibre and over long distances in fibre and in free-space links. Despite these advances, the practical applicability of quantum key distribution is curtailed by the fact that most implementations and protocols are limited to two communicating parties. Quantum networks scale the advantages of quantum key distribution protocols to more than two distant users. Here we present a fully connected quantum network architecture in which a single entangled photon source distributes quantum states to many users while minimizing the resources required for each. Further, it does so without sacrificing security or functionality relative to two-party communication schemes. We demonstrate the feasibility of our approach using a single source of bipartite polarization entanglement, which is multiplexed into 12 wavelength channels. Six states are then distributed between four users in a fully connected graph using only one fibre and one polarization analysis module per user. Because no adaptations of the entanglement source are required to add users, the network can readily be scaled to a large number of users, without requiring trust in the provider of the source. Unlike previous attempts at multi-user networks, which have been based on active optical switches and therefore limited to some duty cycle, our implementation is fully passive and thus has the potential for unprecedented quantum communication speeds.
关键词： Entanglement,Quantum key distribution,Quantum communication,Quantum networks,Wavelength-multiplexed
更新于2025-09-04 15:30:14
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Measurement-Device-Independent Quantum Key Distribution over asymmetric channel and unstable channel
摘要： We show that a high key rate of Measurement-Device-Independent Quantum Key Distribution (MDIQKD) over asymmetric and unstable quantum channel can be obtained by full optimization and compensation. Employing a gradient optimization method, we make the full optimization taking both the global optimization for the 12 independent parameters and the joint constraints for statistical fluctuations. We present a loss-compensation method by monitoring the channel loss for an unstable channel. The numerical simulation shows that the method can produce high key rate for both the asymmetric channel and the unstable channel. Compared with the existing results of independent constraints, our result here improves the key rate by 1 to tens of times in typical experimental conditions.
关键词： unstable channel,asymmetric channel,Quantum Key Distribution,loss-compensation method,Measurement-Device-Independent,full optimization
更新于2025-09-04 15:30:14
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RADIATION FIELD AND OPTICAL COUPLING EVALUATION USING A NEW MATHEMATICAL MODEL
摘要： The mathematical model elaborated in this paper is based on the concept of intrinsic modes in order to analyze and synthesize optical wave propagation along a non-uniform optical structure which is used in integrated optics communication as tapered optical coupler. The new mathematical model is simply developed by introducing modi?cations to the intrinsic integral, and its numerical evaluation illustrates the electromagnetic ?eld distribution inside a taper thin ?lm and also outside the waveguide constituted by the substrate and the cladding of lower refractive index. The proposed method permits e?ciently tracking the behaviour of the optical waves both inside and outside the optical waveguide, and quantifying the radiation and optical coupling occurring from the taper thin ?lm of higher refractive index to adjacent mediums until a total energy transfer; this happens at thicknesses lower than waveguide cuto? thickness of each mode. The new model can be applied to all types of tapered optical coupler, made from di?erent optical materials and having di?erent wedge angles.
关键词： intrinsic modes,tapered optical coupler,mathematical model,optical wave propagation,electromagnetic ?eld distribution,radiation and optical coupling
更新于2025-09-04 15:30:14
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Modeling and Simulation of High-Frequency Solar Irradiance
摘要： As the use of solar power as a source of electricity is increasing, so is the interest in modeling radiation at high temporal resolutions. High-dimensional remote sensing data products depend on cloud cover variability, atmosphere aerosol levels, and other atmospheric parameters. Because of weather fronts and aerosols, it is difficult to quantify solar power variability based on distributed solar networks. The global horizontal irradiance (GHI) component in the National Solar Radiation Database (NSRDB) is available at a 30-min time resolution. The algorithm proposed in this paper produces 1-min-resolution GHI samples at locations where NSRDB data are available. The synthetic irradiance datasets are produced using log-additive non-Gaussian mixture models and resampling techniques. The model is trained over historical data, and predicted values are compared with in situ data. This approach allows for estimating the solar irradiance at subhourly temporal resolutions, while featuring variability for locations where measurements are otherwise not available.
关键词： irradiance generation,stochastic modeling,mixture distribution,Downscaling
更新于2025-09-04 15:30:14
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Ionic Current Rectification by Laminated Bipolar Silica Isoporous Membrane
摘要： Ionic current rectification (ICR) is one of interesting characteristics displayed by nanochannels with asymmetric ge-ometry, ionic concentration or charge distribution, which has been utilized for the development of chemical sensors and biosensors. Herein we report the ICR phenomenon observed with ultrathin silica isoporous membrane (SIM), which was prepared by laminat-ing two layers of SIM with opposite charges and different pore dimeters, designated as bipolar SIM (bp-SIM). The negatively charged layer, called as n-SIM, was 86-nm-thick and consisted of channels with a diameter of 2–3 nm. The positively charged layer with a thickness of 59 nm, termed as p-SIM, was comprised of channels of 4.5–5.5 nm in diameter. They were primarily grown on the solid surface using the St?ber-solution and biphasic-stratification growth approaches, respectively, and then exfoliated to obtain perforated structures by the polymer-protected chemical etching and transfer method. The negative charges of n-SIM and positive ones of p-SIM were generated by the deprotonation of pristine surface silanol and post-modified ammonium groups, respectively. Neither n-SIM nor p-SIM alone displays the ICR characteristic, because of their symmetric structure and uniform charge distribu-tion. When laminating two of them, an apparent ICR characteristic was observed for the bp-SIM with a typical diode-like current-voltage response. This behavior was rationalized to arise from the asymmetric charge distribution on two layers by finite element simulations. Considering the facile preparation and diverse surface functionalities, as well as its uniform and highly porous structure, the bp-SIM provides an attractive platform for designing ICR-based sensors.
关键词： bipolar SIM,nanochannels,asymmetric charge distribution,Ionic current rectification,silica isoporous membrane
更新于2025-09-04 15:30:14
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Twin-field quantum key distribution with large misalignment error
摘要： Based on the novel idea of twin-field quantum key distribution [TF-QKD; Lucamarini et al., Nature (London) 557, 400 (2018)], we present a protocol named the "sending or not sending TF-QKD" protocol, which can tolerate large misalignment error. A revolutionary theoretical breakthrough in quantum communication, TF-QKD changes the channel-loss dependence of the key rate from linear to square root of channel transmittance. However, it demands the challenging technology of long-distance single-photon interference, and also, as stated in the original paper, the security proof was not finalized there due to the possible effects of the later announced phase information. Here we show by a concrete eavesdropping scheme that the later phase announcement does have important effects and the traditional formulas of the decoy-state method do not apply to the original protocol. We then present our "sending or not sending" protocol. Our protocol does not take postselection for the bits in Z-basis (signal pulses), and hence the traditional decoy-state method directly applies and automatically resolves the issue of security proof. Most importantly, our protocol presents a negligibly small error rate in Z-basis because it does not request any single-photon interference in this basis. Thus our protocol greatly improves the tolerable threshold of misalignment error in single-photon interference from the original a few percent to more than 45%. As shown numerically, our protocol exceeds a secure distance of 700, 600, 500, or 300 km even though the single-photon interference misalignment error rate is as large as 15%, 25%, 35%, or 45%.
关键词： misalignment error,single-photon interference,quantum key distribution,twin-field,decoy-state method
更新于2025-09-04 15:30:14
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[IEEE 2018 53rd International Universities Power Engineering Conference (UPEC) - Glasgow, United Kingdom (2018.9.4-2018.9.7)] 2018 53rd International Universities Power Engineering Conference (UPEC) - Manage Reverse Power Flow and Fault Current Level in LV Network with High Penetration of Small Scale Solar and Wind Power Generation
摘要： High penetration level of rooftop small-scale renewable energy generation (REG) such as solar and wind power into the existing low voltage (LV) network would cause the flow of power in reverse direction. This would also vary the level of short-circuit current required for relays to operate. Relay settings would be required to properly detect the unpredictable isolate the faulty section. This paper investigates the impact of residential distributed generation (DG) penetration level on the typical UK low voltage network protection system. Studies were commenced to properly charge and discharge the home connected energy storage battery (ESB). ESB is used as a remedial measure to confine the flow of reverse power due to rooftop DGs. Penetration level DGs are modeled based on proper ESB charging and discharging states in daily load cycle. Short circuit analysis results are compared with the UK passive network to investigate the impact of the DG on the short circuit currents at distribution transformer.
关键词： UK distribution network,short circuit analysis,Rooftop DG penetration,energy storage batteries,reverse power flow
更新于2025-09-04 15:30:14