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In recent years, major natural disasters and public safety accidents have frequently occurred worldwide. In order to deal with various disasters and accidents using rapidly deployable, reliable, efficient, and stable emergency com...
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In recent years, major natural disasters and public safety accidents have frequently occurred worldwide. In order to deal with various disasters and accidents using rapidly deployable, reliable, efficient, and stable emergency communication networks, all countries in the world are strengthening and improving emergency communication network construction and related technology research. Motivated by these situations, in this paper, we provide a state-of-the-art survey of the current situation and development of emergency communication networks. In this detailed investigation, our primary focus is the extensive discussion of emergency communication network technology, including satellite networks, ad hoc networks, cellular networks, and wireless private networks. Then, we explore and analyze the networks currently applied in emergency rescue, such as the 370M narrowband private network, broadband cluster network, and 5G constellation plan. We propose a broadband-narrowband integrated emergency communication network to provide an effective solution for visual dispatch of emergency rescue services. The main findings derived from the comprehensive survey on the emergency communication network are then summarized, and possible research challenges are noted. Lastly, we complete this survey by shedding new light on future directions for the emergency communication network. In the future, the emergency network will develop in the direction of intelligence, integration, popularization, and lower cost, and space-air-ground-sea integrated networks. This survey provides a reference basis for the construction of networks to mitigate major natural disasters and public safety accidents.
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Solar thermophotovoltaics (STPV) system is a technique that uses absorber and emitter to remold wide-band solar radiation into narrowband infrared emission and then convert it into electric energy in order to get high energy conve...
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Solar thermophotovoltaics (STPV) system is a technique that uses absorber and emitter to remold wide-band solar radiation into narrowband infrared emission and then convert it into electric energy in order to get high energy conversion efficiency. In this study, we fabricated an integrated silicon-based intermediate structure to enable the spectral reshaping. The absorber is a hierarchical Si NW structure, which exhibits excellent absorption performance of over 95 % in the spectral range of 220-1100 nm and a low heat loss in the long-wavelength band. The emitter is planar Si-W-SiN/SiNO structure, exhibiting a selective narrowband absorption (i.e., emission) peak in the target wavelength. When the emission peak of emitter is at 1800 nm, the overall efficiency of the STPV system based on this silicon-based intermediate structure can theoretically exceed 29 % with an achievable solar concentration of 1000 and an emitter-to-absorber area ratio of 4. We also test the prepared spectral reshaping intermediate structures on real systems and discuss further optimizations.
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A method was investigated to estimate broadband surface shortwave albedo from the narrowband refiectances obtained by the Advanced Very High Resolution Radiometers (AVHRRs) on board the polar orbiting satellites. Field experiments...
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A method was investigated to estimate broadband surface shortwave albedo from the narrowband refiectances obtained by the Advanced Very High Resolution Radiometers (AVHRRs) on board the polar orbiting satellites. Field experiments were conducted to measure simultaneously multispectral narrowband refiectances and broadband albedo over various vegetation and soil surfaces. These data were combined to examine the behavior of narrowband-to-broadband (NTB) conversion factors for different surfaces. Many previous studies have used constant NTB conversion factors for the AVHRR data. The results from this investigation indicate that the optimal NTB conversion factors for AVHRR channels I and 2 have a strong dependence on the amount of green vegetation within the field of view. Two conversion factors, f_1 and f_2, were established to quantify, respectively, I) the relationship between the reflectance in the narrow red wave band and the total refiectance within the whole visible subregion (0.3-O.685 #mu#m) and 2) the relationship between the reflectance in the narrow near- infrared wave band and the total reflectance within the whole near-infrared subregion (0.695-2.8 #mu#m). Values of f_1 and f_2, calculated from field data, correlated well with the normalized difference vegetation index (NDVI), largely because of the unique characteristics of light absorption and scattering within the red and near-infrared wave bands by green leaves. The f_1-NDVI and f_2-NDVI relationships developed from this study were used to infer empirical coefficients needed to estimate surface albedo from AVHRR data. The surface alhedo values calculated by the new method agreed with ground-based measurements within a root-mean-square error of 0.02, which is better than other methods that use constant empirical coefficients. Testing with albedo measurements made by unmanned aerospace vehicles during a field campaign also indicates that the new method provides an improved estimate of surface albedo.
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Broadband and narrowband time-domain asymptotics are proposed for pulse propagation in range-independent ocean environments. The broadband approximation results by applying the stationary-phase method to the Fourier transform of t...
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Broadband and narrowband time-domain asymptotics are proposed for pulse propagation in range-independent ocean environments. The broadband approximation results by applying the stationary-phase method to the Fourier transform of the Green's function, expressed in terms of normal modes. The narrowband approximation is obtained by incorporating the shape function of the emitted signal — assumed Gaussian — into the phase term and applying the steepest-descent method. The roots of the frequency-derivative of the phase are located in the complex plane by using a second-order expansion of the eigenvalues. The performance of the two approximations is studied numerically. While the broadband approximation improves with increasing bandwidth, the narrowband approximation improves when the bandwidth decreases. Both approximations improve with increasing range, and they can be used for delivering time-domain results more efficiently than with standard Fourier synthesis.
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Wavelength-selective light detection is becoming more and more prevalent as
new sectors emerge, such as imaging, wearable electronic devices, the
Internet of Things, machine vision, and biosensing. Traditional narrowband
RGB de...
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Wavelength-selective light detection is becoming more and more prevalent as
new sectors emerge, such as imaging, wearable electronic devices, the
Internet of Things, machine vision, and biosensing. Traditional narrowband
RGB detection necessitates several separate devices for different colors by
changing the active layer materials or applying color filters ahead of the
broadband detector, which increases the architectural complexity and limits
the quality of color sensing. Here, this work devises a novel dual-mode
perovskite photodetector with both narrowband and broadband light sensing
based on the imbalance transportation of carriers in the perovskite:
Rhodamine B (RhB) active layer. In Mode 1, under light illumination from ITO,
a narrowband response in 600–700 nm is obtained with a specific detectivity
(D*) of 6.7 × 10~(11) Jones, responsivity (R) of 7.6 mA W~(−1), and a full-width at
half-maximum (FWHM) of 80 nm. In Mode 2, under light illumination from
Ag, the visible broadband response of 400–700 nm is achieved with a D* of
10~(12) Jones and R over 80 mA W~(−1). Furtherly, by designing a simple optical
system and signal processing, RGB light signals are detected independently
and panchromatic image sensing and rebuilding are realized. This work will
give inspiration to architecture design for multi-band integrated
photodetectors.
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We propose and demonstrate a novel perfect absorber platform by combining the colloidal crystal and refractory metal layer. Dual-band absorption with the efficiency up to 99.8% (0.336 mu m) and 99.1% (1.382 mu m) is achieved. More...
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We propose and demonstrate a novel perfect absorber platform by combining the colloidal crystal and refractory metal layer. Dual-band absorption with the efficiency up to 99.8% (0.336 mu m) and 99.1% (1.382 mu m) is achieved. Moreover, the absorption bandwidths are 81 nm and 1237 nm for the two bands in the UV and near-infrared ranges, suggesting the simultaneous achievement of narrowband and ultra-broadband absorption. Furthermore, the resonant wavelengths in the two bands are with the geometric multiples up to 3 similar to 6, indicating the large differential frequency responses. In addition, the absorption properties can be artificially adjusted via the structural parameters. These features can hold potential applications in the nonlinear optics such as frequency multiplication, difference and mixing, and the selective spectral filtering and manipulation, etc.
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A lithography-free, double-functional single bismuth (Bi) metal nanostructure is designed, fabricated, and characterized for ultrabroadband absorption in the visible (vis) and near-infrared (NIR) ranges, and for a narrowband respo...
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A lithography-free, double-functional single bismuth (Bi) metal nanostructure is designed, fabricated, and characterized for ultrabroadband absorption in the visible (vis) and near-infrared (NIR) ranges, and for a narrowband response with ultrahigh refractive index sensitivity in the mid-infrared (MIR) range. To achieve a large-scale fabrication of the design in a lithography-free route, the oblique-angle deposition approach is used to obtain densely packed and randomly spaced/oriented Bi nanostructures. It is shown that this fabrication technique can provide a bottom-up approach to controlling the length and spacing of the design. The characterization findings reveal a broadband absorbance above 0.8 in vis and NIR, and a narrowband absorbance centered around 6.54 mu m. Dense architecture and extraordinary permittivity of Bi provide strong field confinement in ultrasmall gaps between nanostructures, and this can be utilized for a sensing application. An ultrahigh sensitivity of 2151 nm refractive-index unit (RIU-1) is acquired, which is, as far as it is known, the experimentally highest sensitivity attained so far. The simple and large-scale compatible fabrication route of the design together with the extraordinary optical response of Bi coating makes this design promising for many optoelectronic and sensing applications.
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Two-dimensional transition metal dichalcogenides materials (TMDCs) have gathered attention because of their special features like absorption. In order to increase absorption in narrowband or broadband wavelength, heterostructures,...
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Two-dimensional transition metal dichalcogenides materials (TMDCs) have gathered attention because of their special features like absorption. In order to increase absorption in narrowband or broadband wavelength, heterostructures, which consist of two TMDC, monolayers, and spacers, are suggested and probed in the entire visible wavelength range. In this paper, the effectiveness of TMDC monolayers permutation, spacer number, spacer place, spacer thickness, incident angle, and polarization on absorption have been investigated, and concluded that usage of the spacer would almost double the absorption comparing to having no spacer, while the structure is simple. The suggested structure is able to invite attentions to utilize them in devices like optoelectronic and nanophotonic.
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Most reported spatially combined or quasioptical amplifier arrays exhibit resonant narrowband performance (>10%) and have not addressed thermal management issues. We report a waveguide-based spatial combining scheme using broadban...
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Most reported spatially combined or quasioptical amplifier arrays exhibit resonant narrowband performance (>10%) and have not addressed thermal management issues. We report a waveguide-based spatial combining scheme using broadband tapered-slot transitions, capable of realizing full waveguide band coverage (40% fractional bandwidth) with good thermal properties. An X-band prototype using eight medium-power GaAs monolithic microwave integrated circuits (MMICs) produced an output power of 2.4 W and 9-dB power gain at 1-dB compression, with a combining efficiency of 68% and >/spl plusmn/1-dB gain variation over the full waveguide band (8-12 GHz).
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Indoor broadband power-line noise is composed of three main terms: impulsive components, narrowband interferences, and background noise. Most impulsive components have a cyclostationary behavior. However, while some of them consis...
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Indoor broadband power-line noise is composed of three main terms: impulsive components, narrowband interferences, and background noise. Most impulsive components have a cyclostationary behavior. However, while some of them consist of impulses of considerable amplitude, width, and repetition rates of 50/100 Hz (in Europe), others have lower amplitude and shorter width but repetition rates of up to hundreds of kilohertz. Classical studies compute statistics of the impulse characteristics without taking into account these significant differences. This paper presents a detailed analysis of these noise terms with a clear distinction between their constituent terms. A classification of the narrowband interferences according to their power spectral density and their statistical behavior is also given. Finally, the instantaneous power spectral density of the background noise and its probability distribution are investigated. Some of the results presented in this paper are available for download from the web site http://www.plc.uma.es/index_eng.htm.
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