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1
Kitov, B. I. « Fluorescence of anisotropic primary X-ray radiation ». Аналитика и контроль 26, no 1 (2022) : 6–12. http://dx.doi.org/10.15826/analitika.2022.26.1.002.
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In the X-ray spectral fluorescence analysis, the anisotropy of primary radiation results in an uneven radiation of a sample’s surface, strengthening the role of some sections and weakening the role of others. The goal of the current work was to determine the minimal distance from the window of the X-ray tube with a cone-shaped anode at which the intensity of the sample’s radiation becomes homogeneous. The research method was the computer modeling of the X-ray fluorescence experiment. The working model was built on the basis of two equations for the densities of the fluxes of braking and characteristic radiations of the massive anode, which took into account the absorption of primary radiation by the anode’s material and the back-scattering of electrons. The ring source was represented in the model as the sum of infinitely small linear elements of equal power, and the sample was disc-shaped and coaxial with the source. The calculation diagram was very well consistent with the experimental diagram of radiation’s direction described in the research literature. Two spatial distributions were calculated. The first one described the distribution of primary radiation’s intensity on the surface of the sample, while the second one described the distribution of the fluorescent radiation, which was more valuable for the X-ray spectrometry. The calculations showed that although the second distribution, unlike the first one, considered the absorption of the primary radiation and secondary radiation in the sample, the shapes of both radiations were close. It was demonstrated that the area of the sample, which carried the most information on the composition of the irradiated material, was ring-shaped, and the width of this ring depended on the distance to the X-ray tube’s window. As the distance increased, the diagram of the spatial distribution of the radiation’s intensity became smoother, and, when the distance exceeded two diameters of the anode, the radiation became homogeneous. The constructed model, which considered the anisotropy of the primary analysis, could be applied in the method of fundamental parameters of X-ray fluorescence analysis for a spectrometer with compressed geometry.
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Schwarz, Benjamin, Matthias Sammer, Nicole Matejka, Sarah Rudigkeit et Judith Reindl. « High-LET targeted microbeam irradiation induces local chromatin reorganization in living cells showing active basal mechanisms at highly complex DNA damage sites ». Journal of Radiation Research and Imaging 2, no 1 (9 mai 2023) : 1–8. http://dx.doi.org/10.46439/radiation.2.006.
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DNA repair eukaryotic cells have additional protective mechanisms that avoid uncontrolled interaction of different parts of the chromatin and damaged regions. Key factors here are the regulation of chromatin density and mobility. The 4D (temporal and spatial) organization of chromatin is controlling this security barrier by regulating the accessibility of genes, flexibility of DNA, and its ability to move inside the nucleus. How this regulation mechanisms are involved in DNA repair upon radiation damage is until now rarely known but an important part to understand the enhanced effectiveness of high linear energy transfer (LET) particles. The damage recognition via PARP1 and the subsequent chromatin decondensation via PARylation is a crucial step in the DNA damage response (DDR). Upon We used the SNAKE microbeam with a beam spot size of <1 µm to induce highly localized DNA damage in living cells using 55 MeV Carbon ions to investigate the chromatin rearrangements in the early stage of DDR. The nuclei were irradiated with a cross pattern consisting of 1000 ions per spot and 25 spots per cell either with one (11 000 Gy), two (22 000 Gy), or three crosses (33 000 Gy). The chromatin rearrangement was imaged live for several minutes after irradiation at the beam using SiR chromatin stain. Upon 91% of the cells show a localized decondensation starting from a few seconds up to minutes after irradiation. The chromatin is decondensed by 6%-8% in the beam path with a local condensation at the edges of up to 8%. Our results suggest that chromatin decondensation is a fast process in the first few seconds after damage induction. Furthermore, decondensation status does not change over minutes, which gives evidence that this process and therefore DDR is paused or even stopped. In combination with the existing knowledge about early reactions to damage induction our data support the model of PARP induced chromatin decondensation. Furthermore, it is evident that also ultra-high doses of radiation are, in first place not able to inactivate initial basal mechanisms as response to damage induction.
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Volosyuk, V. K., S. S. Zhyla, V. V. Pavlikov, A. D. Abramov et V. G. Yakovlev. « Оptimal algorithm of radio brightness estimation in the spatial distributed radiometric sys-tems ». Radiotekhnika, no 191 (22 décembre 2017) : 143–49. http://dx.doi.org/10.30837/rt.2017.4.191.13.
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Optimization of processing of radio thermal radiation noise processes in multichannel spatially-distributed radiometric systems is performed. The received algorithms applicable in the systems of aperture synthesis are received within the maximum likelihood method in the assumption that spectral brightness of radiation within the frequency band of the receiver is constant, but as the image of a radiating object it depends on spatial (angular) coordinates. Feature of the solved tasks consists in using spectral VF -transforms which do not require execution of the spatiotemporal band-limitedness (quasi monochromatic approximation) condition and make it possible to solve the problem of synthesis of algorithms for processing wideband and ultra wideband processes.
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Karabekova, D. Zh. « VARIATION OF SPATIALLY HETEROGENEOUS RADIATION BY COORDINATE-SENSITIVE RECEIVER ». Eurasian Physical Technical Journal 17, no 1 (juin 2020) : 113–18. http://dx.doi.org/10.31489/2020no1/113-118.
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Bratman, Vladimir, Yuri Lurie, Yuliya Oparina et Andrey Savilov. « Capabilities of Terahertz Cyclotron and Undulator Radiation from Short Ultrarelativistic Electron Bunches ». Instruments 3, no 4 (11 octobre 2019) : 55. http://dx.doi.org/10.3390/instruments3040055.
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Mechanisms of coherent spontaneous cyclotron and undulator radiations of short dense bunches, in which electrons move along the same stationary helical trajectories, but have different dynamic properties, have been compared in detail. The results are based on the simplest 1D model in the form of a plane consisting of uniformly distributed synchronously moving and in-phase emitting particles, as well as numerical 3D codes developed to study the dynamics of bunches in waveguides taking into account the effects of the radiation and spatial charge fields. For cyclotron radiation under group synchronism conditions, the Coulomb expansion of a bunch occurs along the surface of a constant wave phase with the formation of an effectively radiating coherent structure. A significantly higher radiation frequency, but with a lower efficiency, can be obtained in the regime of simultaneous excitation of high-frequency (autoresonant) and low-frequency waves; in the field of the latter, stabilization of the bunch phase size can be achieved. Such a two-wave generation is much more efficient when the bunches radiate in the combined undulator and strong guiding magnetic fields under conditions of the negative mass instability, when both the Coulomb interaction of the particles and the radiation field stabilize the longitudinal size of the bunch.
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Mordachev, V. I. « Assessment of the Contribution of Radiations of User Equipment to the Anthropogenic Electromagnetic Background Created by Mobile (Cellular) Communications ». Doklady BGUIR 21, no 5 (26 octobre 2023) : 50–58. http://dx.doi.org/10.35596/1729-7648-2023-21-5-50-58.
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The declared increase in spatial density of user (terminal, peripheral, etc.) radiating equipment (UE) of mobile communications up to 0.1 UE/m2 in 4G (LTE) networks, up to 1.0 UE/m2 in 5G (NR) networks and up to 10 UE/m2 in promising 6G networks may cause an unacceptable increase in electromagnetic background and in corresponding forced risks to public health. The paper proposes a method for assessing the contribution of UE radiations to the level of anthropogenic electromagnetic background created by mobile communications. This method is based on the analysis of the electromagnetic loading on the area created by stationary and mobile radiation sources of mobile communications and determined by the area density of mobile traffic, its asymmetry in downlink and uplink data transmission, the degree of UE concentration in the observation point vicinity, the radio channels spectral efficiency, the size of base stations service areas and other characteristics. The calculated data are given, indicating that in places of UE concentration, the component of electromagnetic background formed by UE radiations may be predominant, many times exceeding the contribution of base station radiations, and determining the actual level of forced risks to public health, which requires consideration in the system of their hygienic rationing.
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Kang, Sinkyu, Sungwoo Kim et Dowon Lee. « Spatial and temporal patterns of solar radiation based on topography and air temperature ». Canadian Journal of Forest Research 32, no 3 (1 mars 2002) : 487–97. http://dx.doi.org/10.1139/x01-221.
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Incident solar radiation is a driving force for many ecological and hydrological processes. For this study, we developed TopoRad, a new radiation model, to describe spatial and temporal patterns of daily radiation based on topography and daily temperature regimes. The model was applied to the Mount Jumbong Forest, located in the mid-eastern area of the Korean peninsula; and the model calculations were evaluated by varying the spatial scales of the digital elevation models (DEMs). In the TopoRad, a clearness index was used to calculate global radiation on a horizontal surface and to partition direct and diffuse radiation. Topographic corrections were separately calculated for each direct and diffuse radiation, using daily topographic modifiers calculated from a DEM. TopoRad predicted daily global radiation of five weather stations with a mean absolute error of 3.1 MJ·m2·day1 and a mean bias of 0.3 MJ·m2·day1. In the spatial application for Mount Jumbong Forest, distinctively different patterns between direct and diffuse radiations were found where direct radiation (5.2 MJ·m2·day1) had more influence than diffuse radiation (4.6 MJ·m2·day1) on annual mean daily radiation. When the scaling effect was inspected across different spatial resolutions, the predicted global radiation was nonlinearly related to spatial resolutions. As the spatial resolution became more coarse, the predicted radiation decreased for south-facing slopes and increased for north-facing slopes, indicating that the predictions from the models cannot be generalized for gradients. TopoRad is better suited to predict daily radiation in rugged landscapes where fine-scale prediction is required.
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Linder, Hans Peter. « Plant species radiations : where, when, why ? » Philosophical Transactions of the Royal Society B : Biological Sciences 363, no 1506 (25 juin 2008) : 3097–105. http://dx.doi.org/10.1098/rstb.2008.0075.
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The spatial and temporal patterns of plant species radiations are largely unknown. I used a nonlinear regression to estimate speciation and extinction rates from all relevant dated clades. Both are surprisingly high. A high species richness can be the result of either little extinction, thus preserving the diversity that dates from older radiations (a ‘mature radiation’), or a ‘recent and rapid radiation’. The analysis of radiations from different regions (Andes, New Zealand, Australia, southwest Africa, tropics and Eurasia) revealed that the diversity of Australia may be largely the result of mature radiations. This is in sharp contrast to New Zealand, where the flora appears to be largely the result of recent and rapid radiations. Mature radiations are characteristic of regions that have been climatically and geologically stable throughout the Neogene, whereas recent and rapid radiations are more typical of younger (Pliocene) environments. The hyperdiverse Cape and Neotropical floras are the result of the combinations of mature as well as recent and rapid radiations. Both the areas contain stable environments (the Amazon basin and the Cape Fold Mountains) as well as dynamic landscapes (the Andes and the South African west coast). The evolution of diversity can only be understood in the context of the local environment.
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KAWAMURA, TOHRU, KAZUHIKO HORIOKA et FUMIHIRO KOIKE. « Potential of Kα radiation by energetic ionic particles for high energy density plasma diagnostics ». Laser and Particle Beams 24, no 2 (juin 2006) : 261–67. http://dx.doi.org/10.1017/s0263034606060393.
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In this paper, potential of diagnostics with the use ofKα radiation for an energy deposition process from an intense ion-beam to background plasma is considered quantitatively.Kα radiation is a good candidate for the purpose. The wavelength ofKα radiation is varied according to the charge state of an emitter atom, and the diagnostics spatially resolved with radiations from various kinds of charge states can give us a profile of plasma temperature in a target material. For the calculation ofKα yield, an atomic population kinetics code is developed, and the result shows thatKα radiation has potential to get information of a plasma profile heated by an intense ion-beam.
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Essery, Richard, Peter Bunting, Aled Rowlands, Nick Rutter, Janet Hardy, Rae Melloh, Tim Link, Danny Marks et John Pomeroy. « Radiative Transfer Modeling of a Coniferous Canopy Characterized by Airborne Remote Sensing ». Journal of Hydrometeorology 9, no 2 (1 avril 2008) : 228–41. http://dx.doi.org/10.1175/2007jhm870.1.
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Abstract Solar radiation beneath a forest canopy can have large spatial variations, but this is frequently neglected in radiative transfer models for large-scale applications. To explicitly model spatial variations in subcanopy radiation, maps of canopy structure are required. Aerial photography and airborne laser scanning are used to map tree locations, heights, and crown diameters for a lodgepole pine forest in Colorado as inputs to a spatially explicit radiative transfer model. Statistics of subcanopy radiation simulated by the model are compared with measurements from radiometer arrays, and scaling of spatial statistics with temporal averaging and array size is discussed. Efficient parameterizations for spatial averages and standard deviations of subcanopy radiation are developed using parameters that can be obtained from the model or hemispherical photography.
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Nagathil, Neeraja, Vineethkumar Vadakkemattathil, Shimod Kundu Parambil et Prakash Vamanan. « Spatial analysis of radionuclide concentration in the high background radiation regions of Kerala, India ». Radiation Protection Dosimetry 199, no 20 (décembre 2023) : 2554–58. http://dx.doi.org/10.1093/rpd/ncad195.
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Abstract Every creature on earth undergoes continuous exposure to natural background radiation. Hence, it is crucial to monitor systematically, the degree of radioactivity in the ecosystem and possible radiological health hazards. The present study attempt to investigate the dynamics of prominent radionuclides and various radiological parameters associated with terrestrial gamma radiations along the littoral regions of the Kollam district, a well-reported high background radiation area in India. The gamma radiation exposure rate along the coastal belt of Kollam was measured using a portable Micro-R-survey meter and associated radiological parameters have been calculated and compared with the global average values. The result indicates that the radiological parameters cross the safe limits recommended by the UNSCEAR 2000. A high value is found in the shoreline of Chavara, with a maximum absorbed dose rate of 11 945.1nGyh−1. The monazite-enriched black sand widely distributed all along the coast, which contains natural radioisotopes such as 40K, 226Ra and 232Th, has greatly contributed to the increase in radiation levels in the regions.
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Bakhtiari, Farhad, Shole Golmohammady, Masoud Yousefi, Fatemeh D. Kashani et Bijan Ghafary. « Generation of terahertz radiation in collisional plasma by beating of two dark hollow laser beams ». Laser and Particle Beams 33, no 3 (10 juin 2015) : 463–72. http://dx.doi.org/10.1017/s026303461500049x.
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AbstractThis paper presents a scheme of terahertz radiation generation based on beating of two dark hollow laser beams with different frequencies, the same electric field amplitudes, in actual plasma with spatially periodic density that electron–neutral collisions have taken into account. The main feature of considered hollow laser beams is, having the same power at different beam orders. Because of special distribution in beam intensity gradient in dark hollow laser beam, the produced terahertz radiation has special field profile. The effects of laser and plasma parameters on terahertz radiation generation are investigated analytically. It can be deduced that by increasing beating frequency, efficiency of terahertz generation decreases which can be compensated by manipulating density ripple magnitudes and dark-size adjusting parameter. The intensity of the emitted radiations is found to be highly sensitive to the beam order. Based on the results of this paper, optimization of laser and plasma parameters can increase the efficiency of terahertz radiation generation strongly.
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Mazzotti, Giulia, Johanna Malle, Sarah Barr et Tobias Jonas. « Spatially Continuous Characterization of Forest Canopy Structure and Subcanopy Irradiance Derived from Handheld Radiometer Surveys ». Journal of Hydrometeorology 20, no 7 (1 juillet 2019) : 1417–33. http://dx.doi.org/10.1175/jhm-d-18-0158.1.
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Abstract Small-scale variations in radiative transfer through forest canopies are strongly linked to canopy structural heterogeneity. To date, upscaling of radiative transfer parameterizations developed at the point scale is hampered by (i) poor representation of canopy structure variability and (ii) limited spatially explicit subcanopy irradiance data to assess the performance of radiative transfer schemes at typical resolutions of land surface models. This study presents a novel approach for efficient in situ characterization of canopy structure and subcanopy irradiance over large spatial extents. The method involves a handheld radiometer assembly mounted on a motorized gimbal developed for nonstationary continuous measurements of shortwave and longwave radiation along forest transects. In combination with radiation and temperature data from a stationary reference station, spatially resolved estimates of sky-view fraction, canopy transmissivity, and longwave enhancement could be obtained. Under favorable meteorological conditions, validation against sky-view fraction data from hemispherical photographs yielded an RMSE of 0.03 (i.e., 3%). Irradiance measurements under heterogeneous canopy cover revealed strong spatial coherence between longwave radiation enhancement, shortwave radiation attenuation, and sky-view fraction on overcast days. Under clear-sky conditions, however, sun flecks caused highly variable shortwave radiation transmissivity patterns. This study demonstrates the potential of handheld radiometer surveys to deliver valuable spatially distributed datasets of collocated canopy structure and subcanopy irradiance which can be used (i) as reference data for alternative approaches to derive canopy structure parameters, (ii) to improve modeling of subcanopy radiation across a wide range of canopy distributions, and (iii) to support respective model upscaling efforts.
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GUS'KOV, S. Yu, Yu S. KAS'ANOV, M. O. KOSHEVOI, V. B. ROZANOV, A. A. RUPASOV et A. S. SHIKANOV. « Scattering and transmission of laser radiation at the heating of low-density foam targets ». Laser and Particle Beams 17, no 2 (avril 1999) : 287–91. http://dx.doi.org/10.1017/s0263034699172148.
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Experimental study of the radiation scattered at the laser heating of low-density foam targets and transmitted through the targets is presented. The scattered and transmitted radiations were investigated using spectrometers and streak cameras providing spatial, angular, spectral and temporal resolutions that enabled us to study the dynamics of the process of burning-through of the thick foam targets, the velocities of the plasma critical density motion as well as mass velocity of the plasma.
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Liu, M., A. Bárdossy, J. Li et Y. Jiang. « Physically-based modeling of topographic effects on spatial evapotranspiration and soil moisture patterns through radiation and wind ». Hydrology and Earth System Sciences 16, no 2 (6 février 2012) : 357–73. http://dx.doi.org/10.5194/hess-16-357-2012.
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Abstract. In this paper, simulations with the Soil Water Atmosphere Plant (SWAP) model are performed to quantify the spatial variability of both potential and actual evapotranspiration (ET), and soil moisture content (SMC) caused by topography-induced spatial wind and radiation differences. To obtain the spatially distributed ET/SMC patterns, the field scale SWAP model is applied in a distributed way for both pointwise and catchment wide simulations. An adapted radiation model from r.sun and the physically-based meso-scale wind model METRAS PC are applied to obtain the spatial radiation and wind patterns respectively, which show significant spatial variation and correlation with aspect and elevation respectively. Such topographic dependences and spatial variations further propagate to ET/SMC. A strong spatial, seasonal-dependent, scale-relevant intra-catchment variability in daily/annual ET and less variability in SMC can be observed from the numerical experiments. The study concludes that topography has a significant effect on ET/SMC in the humid region where ET is a energy limited rather than water availability limited process. It affects the spatial runoff generation through spatial radiation and wind, therefore should be applied to inform hydrological model development. In addition, the methodology used in the study can serve as a general method for physically-based ET estimation for data sparse regions.
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Wang, Qi, Jun Lan, Zhaoyu Deng, Yun Lai et Xiaozhou Liu. « Acoustic source localization based on acoustic leaky-wave antenna with heterogeneous structure ». Journal of the Acoustical Society of America 153, no 1 (janvier 2023) : 487–95. http://dx.doi.org/10.1121/10.0016815.
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In this study, an acoustic leaky-wave antenna (LWA) with heterogeneous structure is proposed and the functions of the spatial directional radiation and acoustic source localization are achieved via utilizing the presented antenna configuration. In the radiating mode, the designed antenna possesses peculiar frequency-scanning characteristics, which enable it to determine the directional radiation of sound waves with diverse incident frequencies. Considering the receiving mode, the antenna emerges with explicit directional frequency characteristics, which ensure its function of spatial acoustic source localization. Additionally, compared with the traditional acoustic LWA, the proposed antenna structure exhibits sharper directivity and has potential applications in high-precision acoustic source localization.
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Tian, Lin, Lin Chen, Peng Zhang, Bo Hu, Yang Gao et Yidan Si. « The Ground-Level Particulate Matter Concentration Estimation Based on the New Generation of FengYun Geostationary Meteorological Satellite ». Remote Sensing 15, no 5 (5 mars 2023) : 1459. http://dx.doi.org/10.3390/rs15051459.
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The new-generation FengYun geostationary meteorological satellite has a high spatial and temporal resolution, which is advantageous in environmental assessments and air pollution monitoring. This study researched the ground-level particulate matter concentration estimation, based on satellite-observed radiations. The radiation of ground-level particulate matter is separate from the apparent radiation observed by satellites. The positive correlation between PM2.5 and PM10 is also considered to improve the accuracy of inversion results and the interpretability of the estimation model. Then, PM2.5 and PM10 concentrations were estimated synchronously every 5 min in mainland China based on FY-4A satellite directly observed radiations. The validation results showed that the improved model estimated results were close to the ground site measured results, with a high determination coefficient (R2) (0.89 for PM2.5, and 0.90 for PM10), and a small Root Mean Squared Error (RMSE) (4.69 μg/m3 for PM2.5 concentrations, and 13.77 μg/m3 for PM10 concentrations). The estimation model presented a good performance in PM2.5 and PM10 concentrations during typical haze and dust storm cases, indicating that it is applicable in different weather conditions and regions.
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Kang, S., D. Lee et J. S. Kimball. « The effects of spatial aggregation of complex topography on hydroecological process simulations within a rugged forest landscape : development and application of a satellite-based topoclimatic model ». Canadian Journal of Forest Research 34, no 3 (1 mars 2004) : 519–30. http://dx.doi.org/10.1139/x03-213.
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We evaluated the effects of topographic complexity on landscape carbon and hydrologic process simulations within a rugged mixed hardwood forest by developing and applying a satellite-based hydroecological model at multiple spatial scales. The effects of topographic variability were evaluated by aggregating raster-based digital elevation model and satellite-derived leaf area index inputs across eight different spatial resolutions from 30 m (62 208 pixels) to 2160 m (12 pixels). Our modeling analysis showed that the effect of topography was the strongest on solar radiation and temperature, intermediate on soil water and evapotranspiration, and ambiguous on soil respiration. Spatial aggregation of model inputs smoothed heterogeneous spatial patterns of modeled output variables relative to fine-scale results. Model outputs varied nonlinearly with different levels of spatial aggregation, while spatial variability of model inputs and outputs were dampened at increasingly coarse aggregation levels. Biases in spatially aggregated model predictions were generally less than ±10%, except for solar radiation, which showed biases of up to +50% at coarser spatial scales. The large positive bias in the solar radiation implies that overestimation of biophysical variables that are sensitive to solar radiation (e.g., photosynthesis and net primary production) may be considerable in rugged forested landscapes unless subgrid scale effects are accounted for.
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Алгазинов, Э. К., В. А. Шульгин, И. А. Лавриненко et А. А. Сирота. « Анализатор спектра флуоресценции на основе оптоволоконного Y-циркулятора ». Письма в журнал технической физики 44, no 14 (2018) : 50. http://dx.doi.org/10.21883/pjtf.2018.14.46344.17238.
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AbstractWe consider a method of probe analysis employing fiber-optic a composite Y-circulator design for the implementation of laser-induced fluorescence (LIF) spectroscopy diagnostics. The proposed principle of the LIF analyzer is based on spatially separated directed optical beams of excitation and fluorescence radiations. Conditions of the effective Y-circulator operation as a passive fiber-optic switch are determined. Experimental investigation of the switched radiation losses is performed. An example of using the proposed analyzer for LIF diagnostics of biological media is presented.
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Xue, Chaofan, Xiangyu Meng, Yanqing Wu, Yong Wang, Liansheng Wang, Shumin Yang, Jun Zhao et Renzhong Tai. « The wave optical whole process design of the soft X-ray interference lithography beamline at SSRF ». Journal of Synchrotron Radiation 25, no 6 (26 octobre 2018) : 1869–76. http://dx.doi.org/10.1107/s1600577518012833.
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A new spatially coherent beamline has been designed and constructed at the Shanghai Synchrotron Radiation Facility. Here, the design of the beamline is introduced and the spatial coherence is analyzed throughout the whole process by wave optics. The simulation results show good spatial coherence at the endstation and have been proven by experiment results.
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He, Bing, Xi Wu, Kang Liu, Yuanzhi Yao, Wenjiang Chen et Wei Zhao. « Trends in Forest Greening and Its Spatial Correlation with Bioclimatic and Environmental Factors in the Greater Mekong Subregion from 2001 to 2020 ». Remote Sensing 14, no 23 (25 novembre 2022) : 5982. http://dx.doi.org/10.3390/rs14235982.
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Understanding trends of vegetation evolution and its spatial characteristics is critical for sustainable social development in the Greater Mekong Subregion (GMS), which is densely populated and still has uneven economic development. Through Theil–Sen/Mann–Kendall tests, polynomial regression and bivariate local autocorrelation analyses, we investigated vegetation greening trends and their spatial correlation with bioclimatic and environmental variables. The study yielded the following results: (1) Land cover in the GMS has changed significantly over the last 20 years. Conversion between forest and grassland was the main type of change. (2) The upward trend in the forest enhanced vegetation index (EVI) significantly exceeded the downward trend in countries over 20 years. In GMS, the spatial variation in forest trend slope values ranged from −0.0297 a−1 to 0.0152 a−1. (3) Anthropogenic activities have played an important role in forest greening; planted, plantation and oil palm forests exhibit the largest contributions to greening. (4) Changes in forest EVI were most spatially correlated with radiation (12.19% for surface net solar radiation and 12.14% for surface solar radiation downwards) and least spatially correlated with seasonality precipitation (8.33%) and mean annual temperature (8.19%). The results of the analysis of EVI trends in vegetation and their spatial correlation with bioclimatic and environmental variables can provide a reference for strategies aimed for protecting the vegetation ecology.
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Mueller, E. R., et J. Waldman. « Power and spatial mode measurements of sideband generated, spatially filtered, submillimeter radiation ». IEEE Transactions on Microwave Theory and Techniques 42, no 10 (1994) : 1891–95. http://dx.doi.org/10.1109/22.320770.
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Bakhtiari, Farhad, Masoud Yousefi, Shole Golmohammady, Seyed Masoud Jazayeri et Bijan Ghafary. « Generation of terahertz radiation by beating of two circular flat-topped laser beams in collisional plasma ». Laser and Particle Beams 33, no 4 (15 octobre 2015) : 713–22. http://dx.doi.org/10.1017/s026303461500083x.
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AbstractThis paper presents a scheme of terahertz (THz) radiation generation based on beating of two flat-topped laser beams by different frequencies and the same electric field amplitudes in actual plasma with spatially periodic density that electron–neutral collisions have been taken into account. Flat-topped laser beams have the exclusive features such as steep gradient in distribution of laser intensities, wider cross-section in comparison with other profiles, which make stronger ponderomotive force and lead to stronger nonlinear current and hence, THz radiation of higher field. The effects of laser and plasma parameters on THz radiation generation are investigated analytically. It is shown that by increasing the order of flatness of incident laser beams, because of their steep gradient, good enhancement in emitted THz radiation take place. It can be deduced that by increasing beating frequency, efficiency of THz generation decreases which can be compensated by manipulating in density ripple magnitudes. The intensity of the emitted radiations is found to be highly sensitive to the order of flatness. Based on the results of this paper, optimization of laser and plasma parameters can increase the efficiency of THz radiation generation strongly.
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Wenqiang Hua, Wenqiang Hua, Guangzhao Zhou Guangzhao Zhou, Yuzhu Wang Yuzhu Wang, Ping Zhou Ping Zhou, Shumin Yang Shumin Yang, Chuanqian Peng Chuanqian Peng, Fenggang Bian Fenggang Bian, Xiuhong Li Xiuhong Li et and Jie Wang and Jie Wang. « Measurement of the spatial coherence of hard synchrotron radiation using a pencil beam ». Chinese Optics Letters 15, no 3 (2017) : 033401–33405. http://dx.doi.org/10.3788/col201715.033401.
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Wang Junjie, 王俊杰, 杨艳芳 Yang Yanfang, 何英 He Ying, 李琦 Li Qi et 王昆峰 Wang Kunfeng. « 基于偶极子天线辐射反向创建空间球形聚焦光斑 ». Acta Optica Sinica 44, no 10 (2024) : 1026033. http://dx.doi.org/10.3788/aos231679.
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Kubyshkin, Evgenii P., et Vladimir A. Kulikov. « On a Mechanism for the Formation of Spatially Inhomogeneous Structures of Light Waves in Optical Information Transmission Systems ». Modeling and Analysis of Information Systems 27, no 2 (24 juin 2020) : 152–63. http://dx.doi.org/10.18255/1818-1015-2020-2-152-163.
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Spatially inhomogeneous structures of light waves are used as a mechanism of compacting information in optical and fiber-optic communication systems. In this paper, we consider a mathematical model of an optical radiation generator with a nonlinear delayed feedback loop and a stretching (compression) operator of the spatial coordinates of the light wave in a plane orthogonal to the radiation direction. It is shown that the presence of a delay in the feedback loop can lead to the generation of stable periodic spatially inhomogeneous oscillations. In the space of the main parameters of the generator, the spaces of generation of stable spatially non-uniform oscillations are constructed, the mechanism of their occurrence is studied, and approximate asymptotic formulas are constructed.
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GOMERO, G. I., M. J. REBOUÇAS, A. F. F. TEIXEIRA et A. BERNUI. « TOPOLOGICAL REVERBERATIONS IN FLAT SPACE–TIMES ». International Journal of Modern Physics A 15, no 26 (20 octobre 2000) : 4141–62. http://dx.doi.org/10.1142/s0217751x00002081.
Texte intégralRésumé :
We study the role played by multiply-connectedness in the time evolution of the energy E(t) of a radiating system that lies in static flat space–time manifolds ℳ4 whose t= const spacelike sections ℳ3 are compact in at least one spatial direction. The radiation reaction equation of the radiating source is derived for the case where ℳ3 has any nontrivial flat topology, and an exact solution is obtained. We show that the behavior of the radiating energy E(t) changes remarkably from exponential damping, when the system lies in ℛ3, to a reverberation pattern (with discontinuities in the derivative Ė(t) and a set of relative minima and maxima) followed by a growth of E(t), when ℳ3 is endowed with any one of the 17 multiply-connected flat topologies. It emerges from this result that the compactness in at least one spatial direction of Minkowski space–time is sufficient to induce this type of topological reverberation, making clear that topological fragilities can arise not only in the usual cosmological modelling, but also in ordinary flat space–time manifolds. An explicit solution of the radiation reaction equation for the case where [Formula: see text] is discussed in detail, and graphs which reveal how the energy varies with the time are presented and analyzed.
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Gureyev, Timur E., Alexander Kozlov, Yakov I. Nesterets, David M. Paganin, Andrew V. Martin et Harry M. Quiney. « Signal-to-noise, spatial resolution and information capacity of coherent diffraction imaging ». IUCrJ 5, no 6 (15 septembre 2018) : 716–26. http://dx.doi.org/10.1107/s2052252518010941.
Texte intégralRésumé :
It is shown that the average signal-to-noise ratio (SNR) in the three-dimensional electron-density distribution of a sample reconstructed by coherent diffractive imaging cannot exceed twice the square root of the ratio of the mean total number of scattered photons detected during the scan and the number of spatially resolved voxels in the reconstructed volume. This result leads to an upper bound on Shannon's information capacity of this imaging method by specifying the maximum number of distinguishable density distributions within the reconstructed volume when the radiation dose delivered to the sample and the spatial resolution are both fixed. If the spatially averaged SNR in the reconstructed electron density is fixed instead, the radiation dose is shown to be proportional to the third or fourth power of the spatial resolution, depending on the sampling of the three-dimensional diffraction space and the scattering power of the sample.
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Pietras-Szewczyk, Małgorzata, et Leszek Szewczyk. « Modelling of real solar radiation spatial distribution as a tool for solar energy cadastre in the cities ». Energy & ; Environment 29, no 2 (5 décembre 2017) : 204–15. http://dx.doi.org/10.1177/0958305x17745272.
Texte intégralRésumé :
The increasing needs of energy and decreasing traditional energy sources are becoming one of the biggest issues of our civilization. The provision of stable energy supply is a matter of state security. The energy consumption keeps growing especially in big cities. Therefore, it became reasonable to produce energy directly in cities. To optimize the use of the solar energy in the city areas, a fundamental issue is to find and estimate the amount of solar radiations at a specified location by using available tools and data. The main goal of this work is to demonstrate the potential of the r.sun model, a component of GRASS software, in calculating real solar radiation for the selected location. The work starts with demonstrating the effect of cloud cover for the amount of solar radiation reaching the Earth’s surface and the usage of GIS software and Ogimet website in the spatial analysis of real solar radiation distribution. For this purpose, data concerning cloud cover for selected locations were analysed. The study is based on the synoptic data obtained from Ogimet. Average daily cloud cover totals and long-term values were calculated. Apart from the cloud cover data, a significant variable, the Linke turbidity factor, describing the weakening of solar radiation due to the presence of aerosols and water vapour in the atmosphere, was taken into consideration. The obtained results were used to develop a map of real solar radiation distribution for a part of Wrocław. The results obtained by that model with the acquired data by the local meteorological station show compatibility.
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Kwon, You Jin, et Dong Kun Lee. « Thermal Comfort and Longwave Radiation over Time in Urban Residential Complexes ». Sustainability 11, no 8 (15 avril 2019) : 2251. http://dx.doi.org/10.3390/su11082251.
Texte intégralRésumé :
Large cities with a high concentration of high-rise buildings are shaded by urban canyon. This brings a cooling effect compared to the space exposed to the sun, but is not always cool due to the longwave radiation emitted from buildings and the built environment. We tested the micro-scale effects of major external spatial factors, trees, and buildings, under shade on longwave radiation shifts to understand the effects of large shaded areas in megacities. Incoming and outgoing longwave radiations (ILR and OLR, respectively) were found to decrease the overall observation by time zone. Longwave radiation on a micro-scale was also inversely proportional to the tree volume. From mean radiant temperature (MRT) analysis, we found that about a 10% decrease in MRT could be achieved by increasing tree volume by around 50%. Larger tree volumes corresponded to greater blocking effects on longwave radiation. Considering the tree volume, a multilayer urban tree canopy composition can more favorably improve the thermal environment and energy sustainability of a city compared to a single-layer canopy. Larger trees planted with harmonious shrubs are the most effective in reducing longwave radiation.
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Bauerle, William L., Nilakantan S. Rajaraman, Shruthi Anantharamu et Joseph D. Bowden. « TREESTRESS : A Within Canopy Spatial Distribution Model for Simulating the Carbon and Water Exchange Response to Atmospheric Thermal and Rhizospheric Water Stress ». HortScience 40, no 4 (juillet 2005) : 1130A—1130. http://dx.doi.org/10.21273/hortsci.40.4.1130a.
Texte intégralRésumé :
A model (TREESTRESS, a spatially explicit 3-D process-based model) for simulating the spatial distribution of intracanopy photosynthetic and transpirational responses to multiple stress factors is presented. The model includes intracrown validation on both deciduous and coniferous radiation transfer, incorporation of temperature response functions of Rubisco-, mesophyll-, and RuBP-limited photosynthesis to the widely used Farquhar et al. (1980) photosynthesis model, and a rhizospheric water stress submodel to constrain the Ball-Berry stomatal conductance submodel. The model also includes functions that account for acclimation and/or no acclimation to growth temperature. Taken together, the model aims at predicting spatially explicit intracrown response to multiple stresses (primarily temperature, water, and radiation stress). The model was parameterized for red maple trees under nursery conditions and validated by sap flow, photosynthesis, and radiation measurements. The integration of multiple stress response functions in a spatially explicit process-based model could provide a proficient method to simulate stress interactions and predict carbon uptake and water use in crowns, canopies, ecosystems, and landscapes.
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Alekseeva, I., A. Budnik et M. Sliuniaev. « MOVING IRRADIATED BY NEUTRONS CONTAINING URANIUM NANOPARTICLES GAS MEDIUM AMPLIFICATION PROPERTIES RESEARCH ». PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. SERIES : NUCLEAR AND REACTOR CONSTANTS 2020, no 2 (26 juin 2020) : 49–60. http://dx.doi.org/10.55176/2414-1038-2020-2-49-60.
Texte intégralRésumé :
The search for promising ways of nuclear energy usage has led to the emergence of a whole line of research on the direct conversion of the nuclear reaction products energy into laser radiation. In the present work, the amplifying properties of a spatially inhomogeneous nuclear-excited containing uranium nanoparticles moving argon-xenon medium irradiated by an inhomogeneous neutron field were studied. This work purpose is to investigate the dependence of the laser active medium amplifying properties on the initial gas mixture velocity, neutron pulse duration, and the neutron flux space-time distribution. As a short result, we could present the radial dependence of the laser radiation intensity gain at different points in time showed on the picture below. Summarizing laser radiation intensity gain calculations results: an active laser- medium with a length of 1 m provides a significant amplification (10 or more times) of the laser radiation in one pass. And it seems to be reasonable to continue studying the amplifying properties of such laser-active medium, considering the laser radiation’s wave nature.
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Tamburini, Fabrizio, Mariafelicia De Laurentis et Ignazio Licata. « Radiation from charged particles due to explicit symmetry breaking in a gravitational field ». International Journal of Geometric Methods in Modern Physics 15, no 07 (24 mai 2018) : 1850122. http://dx.doi.org/10.1142/s0219887818501220.
Texte intégralRésumé :
The paradox of a free falling radiating charged particle in a gravitational field is a well-known fascinating conceptual challenge that involves classical electrodynamics and general relativity (GR). We discuss this paradox considering the emission of radiation as a consequence of an explicit space/time symmetry breaking involving the electric field within the trajectory of the particle seen from an external observer. This occurs in certain particular cases when the relative motion of the charged particle does not follow a geodesic of the motion dictated by the explicit Lagrangian formulation of the problem and thus from the metric of spacetime. The problem is equivalent to the breaking of symmetry within the spatial configuration of a radiating system like an antenna: when the current is not conserved at a certain instant of time within a closed region, then emission of radiation occurs [D. Sinha and G. A. J. Amaratunga, Phys. Rev. Lett. 114(7) (2015) 147701]. Radiation from a system of charges is possible only when there is explicit breaking of symmetry in the electric field in space and time.
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Zaramella, Mattia, Marco Borga, Davide Zoccatelli et Luca Carturan. « TOPMELT 1.0 : a topography-based distribution function approach to snowmelt simulation for hydrological modelling at basin scale ». Geoscientific Model Development 12, no 12 (13 décembre 2019) : 5251–65. http://dx.doi.org/10.5194/gmd-12-5251-2019.
Texte intégralRésumé :
Abstract. Enhanced temperature-index distributed models for snowpack simulation, incorporating air temperature and a term for clear sky potential solar radiation, are increasingly used to simulate the spatial variability of the snow water equivalent. This paper presents a new snowpack model (termed TOPMELT) which integrates an enhanced temperature-index model into the ICHYMOD semi-distributed basin-scale hydrological model by exploiting a statistical representation of the distribution of clear sky potential solar radiation. This is obtained by discretizing the full spatial distribution of clear sky potential solar radiation into a number of radiation classes. The computation required to generate a spatially distributed water equivalent reduces to a single calculation for each radiation class. This turns into a potentially significant advantage when parameter sensitivity and uncertainty estimation procedures are carried out. The radiation index may be also averaged in time over given time periods. Thus, the model resembles a classical temperature-index model when only one radiation class for each elevation band and a temporal aggregation of 1 year is used, whereas it approximates a fully distributed model by increasing the number of the radiation classes and decreasing the temporal aggregation. TOPMELT is integrated within the semi-distributed ICHYMOD model and is applied at an hourly time step over the Aurino Basin (also known as the Ahr River) at San Giorgio (San Giorgio Aurino), a 614 km2 catchment in the Upper Adige River basin (eastern Alps, Italy) to examine the sensitivity of the snowpack and runoff model results to the spatial and temporal aggregation of the radiation fluxes. It is shown that the spatial simulation of the snow water equivalent is strongly affected by the aggregation scales. However, limited degradation of the snow simulations is achieved when using 10 radiation classes and 4 weeks as spatial and temporal aggregation scales respectively. Results highlight that the effects of space–time aggregation of the solar radiation patterns on the runoff response are scale dependent. They are minimal at the scale of the whole Aurino Basin, while considerable impact is seen at a basin scale of 5 km2.
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Rüdisser, Daniel, Tobias Weiss et Lukas Unger. « Spatially Resolved Analysis of Urban Thermal Environments Based on a Three-Dimensional Sampling Algorithm and UAV-Based Radiometric Measurements ». Sensors 21, no 14 (16 juillet 2021) : 4847. http://dx.doi.org/10.3390/s21144847.
Texte intégralRésumé :
A new method and workflow to assess outdoor thermal comfort and thermal stress in urban areas is developed. The new methodology is applied to a case of an urban quarter in the city of Graz. The method recognises the significance of detailed and accurate spatially resolved determination of mean radiant temperatures taking into account all relevant radiative components, comprising thermal radiation, as well as global radiation. The method relies on radiometric imaging data that are mapped onto a three-dimensional model. The image data are acquired by means of drones (UAVs) equipped with multispectral and thermographic cameras to capture short- and long-wave radiation. Pre-existing city models and a Monte Carlo raytracing algorithm to perform anisotropic sampling based on a 3D model with human topology are used to determine local radiation temperatures with high spatial resolution. Along with spot measurements carried out on the ground simultaneously, the spatially resolved and three-dimensionally determined mean radiation temperatures are used to calculate thermal comfort indicator maps using UTCI and PMV calculation. Additional ground measurements are further used to validate the detection, as well as the entire evaluation process.
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Mordachev, V. I., et D. A. Tsyanenka. « Influence of Spatial Selectivity of Radiation of Mobile Communication Base Stations on the Level of Electromagnetic Background Introduced by them ». Doklady BGUIR 20, no 7 (12 décembre 2022) : 56–64. http://dx.doi.org/10.35596/1729-7648-2022-20-7-56-64.
Texte intégralRésumé :
Radio frequency electromagnetic radiation from base stations is the main source of electromagnetic background generated by mobile (cellular) communication systems in residential areas; its intensity makes a significant contribution to the level of electromagnetic pollution of the habitat and determines the level of electromagnetic safety of the population. The previously proposed technique for estimating the average intensity of this background, based on the analysis of the territorial intensity of mobile traffic, takes into account the spatial selectivity of base station radiation in a simplified form by introducing the radiation directivity parameter U, equal to the inverse of the number of base station service sectors, assuming that the width of the main lobe of the radiation pattern is equal to the width of this sector and without taking into account the radiation directivity in the vertical plane, which determines the pessimistic nature of these estimates. The paper presents a refined analysis of the values of the parameter U for a two-level models of antenna radiation patterns, which reflects the real values of the width of their main lobes in horizontal and vertical planes, the relative levels of side lobes and the ratio of radiation power of the main and side lobes. The analysis was performed both for stationary sector antennas of cellular communication systems and for adaptive phased antenna arrays of 4G/5G systems capable of providing service using narrow beams. The analysis showed that the value of the U parameter of sector antennas is 5–15 dB less than the inverse of the number of sectors of base stations, and for narrow beams of adaptive antenna arrays, this difference reaches 20 dB. If tilt angles of main lobes of antenna radiation patterns with respect to the horizon are less than 30°, then at estimation of the average electromagnetic background intensity the inverse of their antenna gain in the main lobe can be used as the U parameter value of the spatial selectivity (directivity) of base stations radiations.
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Sahu, Kiran Chandra, et Jukka Tuhkuri. « Active structural acoustic control of transmitted sound through a double panel partition by weighted sum of spatial gradients ». Journal of Low Frequency Noise, Vibration and Active Control 36, no 1 (mars 2017) : 27–42. http://dx.doi.org/10.1177/0263092317693479.
Texte intégralRésumé :
Active control of harmonic sound transmission through an acoustically baffled, rectangular, simply supported double panel partition has been analytically studied. Velocity potential method is used for the vibro-acoustic modeling unlike the commonly used cavity mode method. It is very well-known that at high frequencies uncontrolled double panel partition mostly radiates sound due to the dipole-type motion of the radiating panel, which the volume velocity method can't be able to detect, therefore, weighted sum of spatial gradients is used to control these modes and achieves sound attenuation in a broad frequency band. A piezoceramic actuator (lead zirconate titanate) is attached on one side of the panel surface, and the optimal magnitude and phase of the voltage supplied to the lead zirconate titanate for minimizing the weighted sum of spatial gradients and volume velocity at the error sensor locations are calculated using a simple-gradient based algorithm. Numerical results of sound power transmission ratio and averaged quadratic velocity of panels indicate that lead zirconate titanate should be placed on the incident panel and minimization of the control quantities should be done on the radiating panel to achieve better sound attenuation. The acoustic radiation mode analysis shows that the weighted sum of spatial gradients is able to control multiple acoustic radiation modes and, thereby, accomplishes better reduction of sound power transmission compared to volume velocity.
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Ishchenko, E. F., et A. L. Sokolov. « Spatially depolarised laser radiation ». Quantum Electronics 34, no 1 (31 janvier 2004) : 91–94. http://dx.doi.org/10.1070/qe2004v034n01abeh002588.
Texte intégral
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Brunner, W., R. W. John, H. Paul et H. Steudel. « Radiation reabsorption in a laser-produced plasma ». Laser and Particle Beams 6, no 4 (novembre 1988) : 723–29. http://dx.doi.org/10.1017/s0263034600005668.
Texte intégralRésumé :
Taking into account the emission and absorption of resonance radiation in a recombining laser-produced plasma of intermediate density, the system of rate equations for the population densities coupled with the radiative transfer equation is approximately treated. In the case of spatially varying absorption we derive an approximate form of the rate equation determining the population density of the upper resonance level. By applying this relation to an axially symmetric plasma a simple formula that describes the effect of radiation reabsorption on the spatial behaviour of the population density is obtained.
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Al-Allaq, Zaid Jabbar, Haidar Zaeer Dhaam, Mohammed Jawad Al Dujaili Al-Khazraji et Muntadhar Hameed Ismael Al-Khuzaie. « Discovering the spatial locations of the radio frequency radiations effects around mobile towers ». International Journal of Electrical and Computer Engineering (IJECE) 13, no 2 (1 avril 2023) : 1629. http://dx.doi.org/10.11591/ijece.v13i2.pp1629-1638.
Texte intégralRésumé :
<span lang="EN-US">Nowadays, smart devices have become a major part of human life, and this need has led to an increase in the demand for these devices, prompting major telecommunications companies to compete with each other to acquire the bulk of this market. This competition led to a significant increase in the number of mobile towers, to expand the coverage area. Each communication tower has transmitters and receivers to connect subscribers within the mobile network and other networks. The receivers and transmitters of each mobile tower operate on radio frequency waves. These waves can cause harm to humans if the body tissues absorb the radiation resulting from these waves. Headache, discomfort, and some other diseases are among the effects resulting from the spatial proximity to the mobile towers. In this paper, a model based on geographic information systems (GIS) software is proposed for the purpose of discovering the area of exposure to radio frequency radiation. This model can assists mitigate the opportunities of exposure to these radiations, thus reducing its danger. Real data of the levels of electromagnetic pollution resulting from mobile towers were analyzed during this study and compared with international safety standards.</span>
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Cheong, Patrick Chi-Kit, Harry Ho-Yin Ng, Alan Tsz-Lok Lam et Tjonnie Guang Feng Li. « General-relativistic Radiation Transport Scheme in Gmunu. I. Implementation of Two-moment-based Multifrequency Radiative Transfer and Code Tests ». Astrophysical Journal Supplement Series 267, no 2 (1 août 2023) : 38. http://dx.doi.org/10.3847/1538-4365/acd931.
Texte intégralRésumé :
Abstract We present the implementation of a two-moment-based general-relativistic multigroup radiation transport module in the General-relativistic multigrid numerical (Gmunu) code. On top of solving the general-relativistic magnetohydrodynamics and the Einstein equations with conformally flat approximations, the code solves the evolution equations of the zeroth- and first-order moments of the radiations in the Eulerian-frame. An analytic closure relation is used to obtain the higher order moments and close the system. The finite-volume discretization has been adopted for the radiation moments. The advection in spatial space and frequency-space are handled explicitly. In addition, the radiation–matter interaction terms, which are very stiff in the optically thick region, are solved implicitly. The implicit–explicit Runge–Kutta schemes are adopted for time integration. We test the implementation with a number of numerical benchmarks from frequency-integrated to frequency-dependent cases. Furthermore, we also illustrate the astrophysical applications in hot neutron star and core-collapse supernovae modelings, and compare with other neutrino transport codes.
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Chen, Jingdong, Jin Xiang, Shuai Jiang, Qiaofeng Dai, Shaolong Tie et Sheng Lan. « Multipole Radiations from Large Gold Nanospheres Excited by Evanescent Wave ». Nanomaterials 9, no 2 (31 janvier 2019) : 175. http://dx.doi.org/10.3390/nano9020175.
Texte intégralRésumé :
We proposed the use of the evanescent wave generated in a total internal reflection configuration to excite large gold nanospheres and investigated the radiations of the high-order plasmon modes supported in gold nanospheres. It was revealed that the evanescent wave excitation is equivalent to the excitation by using both the incident and reflected light, offering us the opportunity to control the orientation of the electric field used to excite nanoparticles. In addition, it was found that the scattering light intensity is greatly enhanced and the background noise is considerably suppressed, making it possible to detect the radiations from high-order plasmon modes. Moreover, the influence of the mirror images on the scattering induced by a metal substrate is eliminated as compared with the surface plasmon polariton excitation. By exciting a gold nanosphere with s-polarized light and detecting the scattering light with a p-polarized analyzer, we were able to reveal the radiation from the electric quadrupole mode of the gold nanosphere in both the spatial and the frequency domains. Our findings are important for characterizing the radiations from the high-order modes of large nanoparticles and useful for designing nanoscale photonic devices.
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Rashid Niaghi, Ali, Oveis Hassanijalilian et Jalal Shiri. « Estimation of Reference Evapotranspiration Using Spatial and Temporal Machine Learning Approaches ». Hydrology 8, no 1 (2 février 2021) : 25. http://dx.doi.org/10.3390/hydrology8010025.
Texte intégralRésumé :
Evapotranspiration (ET) is widely employed to measure amounts of total water loss between land and atmosphere due to its major contribution to water balance on both regional and global scales. Considering challenges to quantifying nonlinear ET processes, machine learning (ML) techniques have been increasingly utilized to estimate ET due to their powerful advantage of capturing complex nonlinear structures and characteristics. However, limited studies have been conducted in subhumid climates to simulate local and spatial ETo using common ML methods. The current study aims to present a methodology that exempts local data in ETo simulation. The present study, therefore, seeks to estimate and compare reference ET (ETo) using four common ML methods with local and spatial approaches based on continuous 17-year daily climate data from six weather stations across the Red River Valley with subhumid climate. The four ML models have included Gene Expression Programming (GEP), Support Vector Machine (SVM), Multiple Linear Regression (LR), and Random Forest (RF) with three input combinations of maximum and minimum air temperature-based (Tmax, Tmin), mass transfer-based (Tmax, Tmin, U: wind speed), and radiation-based (Rs: solar radiation, Tmax, Tmin) measurements. The estimates yielded by the four ML models were compared against each other by considering spatial and local approaches and four statistical indicators; namely, the root means square error (RMSE), the mean absolute error (MAE), correlation coefficient (r2), and scatter index (SI), which were used to assess the ML model’s performance. The comparison between combinations showed the lowest SI and RMSE values for the RF model with the radiation-based combination. Furthermore, the RF model showed the best performance for all combinations among the four defined models either spatially or locally. In general, the LR, GEP, and SVM models were improved when a local approach was used. The results showed the best performance for the radiation-based combination and the RF model with higher accuracy for all stations either locally or spatially, and the spatial SVM and GEP illustrated the lowest performance among the models and approaches.
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Dunn, Paul Christian, et Leonhard Blesius. « Modeling Insolation, Multi-Spectral Imagery and LiDAR Point-Cloud Metrics to Predict Plant Diversity in a Temperate Montane Forest ». Geographies 1, no 2 (23 août 2021) : 79–103. http://dx.doi.org/10.3390/geographies1020006.
Texte intégralRésumé :
Incident solar radiation (insolation) passing through the forest canopy to the ground surface is either absorbed or scattered. This phenomenon, known as radiation attenuation, is measured using the extinction coefficient (K). The amount of radiation reaching the ground surface of a given site is effectively controlled by the canopy’s surface and structure, determining its suitability for plant species. Menhinick’s and Simpson’s biodiversity indexes were selected as spatially explicit response variables for the regression equation using canopy structure metrics as predictors. Independent variables include modeled area solar radiation, LiDAR-derived canopy height, effective leaf area index data derived from multi-spectral imagery and canopy strata metrics derived from LiDAR point-cloud data. The results support the hypothesis that (1) canopy surface and strata variability may be associated with understory species diversity due to radiation attenuation and the resultant habitat partitioning and that, (2) such a model can predict both this relationship and biodiversity clustering. The study data yielded significant correlations between predictor and response variables and were used to produce a multiple–linear model comprising canopy relief, the texture of heights, and vegetation density to predict understory plant diversity. When analyzed for spatial autocorrelation, the predicted biodiversity data exhibited non-random spatial continuity.
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Hock, Regine. « A distributed temperature-index ice- and snowmelt model including potential direct solar radiation ». Journal of Glaciology 45, no 149 (1999) : 101–11. http://dx.doi.org/10.3189/s0022143000003087.
Texte intégralRésumé :
AbstractHourly melt and discharge of Storglaciären, a small glacier in Sweden, were computed for two melt seasons, applying temperature-index methods to a 30 m resolution grid for the melt component. The classical degree-day method yielded a good simulation of the seasonal patient of discharge, but the pronounced melt-induced daily discharge cycles were not captured. Modelled degree-day factors calculated for every hour and each gridcell from melt obtained from a distributed energy-balance model varied substantially, both diurnally and spatially. A new distributed temperature-index model is suggested, attempting to capture both the pronounced diurnal melt cycles and the spatial variations in melt due to the effects of surrounding topography. This is accomplished by including a radiation index in terms of potential clear-sky direct solar radiation, and thus, without the need for other data besides air temperature. This approach improved considerably the simulation of diurnal discharge fluctuations and yielded a more realistic spatial distribution of melt rates. The incorporation of measured global radiation to account for the reduction in direct solar radiation due to cloudiness did not lead to additional improvement in model performance.
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Hock, Regine. « A distributed temperature-index ice- and snowmelt model including potential direct solar radiation ». Journal of Glaciology 45, no 149 (1999) : 101–11. http://dx.doi.org/10.1017/s0022143000003087.
Texte intégralRésumé :
AbstractHourly melt and discharge of Storglaciären, a small glacier in Sweden, were computed for two melt seasons, applying temperature-index methods to a 30 m resolution grid for the melt component. The classical degree-day method yielded a good simulation of the seasonal patient of discharge, but the pronounced melt-induced daily discharge cycles were not captured. Modelled degree-day factors calculated for every hour and each gridcell from melt obtained from a distributed energy-balance model varied substantially, both diurnally and spatially. A new distributed temperature-index model is suggested, attempting to capture both the pronounced diurnal melt cycles and the spatial variations in melt due to the effects of surrounding topography. This is accomplished by including a radiation index in terms of potential clear-sky direct solar radiation, and thus, without the need for other data besides air temperature. This approach improved considerably the simulation of diurnal discharge fluctuations and yielded a more realistic spatial distribution of melt rates. The incorporation of measured global radiation to account for the reduction in direct solar radiation due to cloudiness did not lead to additional improvement in model performance.
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Kozak, Kenneth H., David W. Weisrock et Allan Larson. « Rapid lineage accumulation in a non-adaptive radiation : phylogenetic analysis of diversification rates in eastern North American woodland salamanders (Plethodontidae : Plethodon ) ». Proceedings of the Royal Society B : Biological Sciences 273, no 1586 (6 décembre 2005) : 539–46. http://dx.doi.org/10.1098/rspb.2005.3326.
Texte intégralRésumé :
Adaptive radiations have served as model systems for quantifying the build-up of species richness. Few studies have quantified the tempo of diversification in species-rich clades that contain negligible adaptive disparity, making the macroevolutionary consequences of different modes of evolutionary radiation difficult to assess. We use mitochondrial-DNA sequence data and recently developed phylogenetic methodologies to explore the tempo of diversification of eastern North American Plethodon , a species-rich clade of woodland salamanders exhibiting only limited phenotypic disparity. Lineage-through-time analysis reveals a high rate of lineage accumulation, 0.8 species per million years, occurring 11–8 million years ago in the P. glutinosus species group, followed by decreasing rates. This high rate of lineage accumulation is exceptional, comparable to the most rapid of adaptive radiations. In contrast to classic models of adaptive radiation where ecological niche divergence is linked to the origin of species, we propose that phylogenetic niche conservatism contributes to the rapid accumulation of P. glutinosus -group lineages by promoting vicariant isolation and multiplication of species across a spatially and temporally fluctuating environment. These closely related and ecologically similar lineages persist through long-periods of evolutionary time and form strong barriers to the geographic spread of their neighbours, producing a subsequent decline in lineage accumulation. Rapid diversification among lineages exhibiting long-term maintenance of their bioclimatic niche requirements is an under-appreciated phenomenon driving the build-up of species richness.
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Ma, Shaoqing, Peng Ding, Zhengxuan Zhou, Huilong Jin, Xiaoli Li et Yingwei Li. « Terahertz Radiation Modulates Neuronal Morphology and Dynamics Properties ». Brain Sciences 14, no 3 (14 mars 2024) : 279. http://dx.doi.org/10.3390/brainsci14030279.
Texte intégralRésumé :
Terahertz radiation falls within the spectrum of hydrogen bonding, molecular rotation, and vibration, as well as van der Waals forces, indicating that many biological macromolecules exhibit a strong absorption and resonance in this frequency band. Research has shown that the terahertz radiation of specific frequencies and energies can mediate changes in cellular morphology and function by exciting nonlinear resonance effects in proteins. However, current studies have mainly focused on the cellular level and lack systematic studies on multiple levels. Moreover, the mechanism and law of interaction between terahertz radiation and neurons are still unclear. Therefore, this paper analyzes the mechanisms by which terahertz radiation modulates the nervous system, and it analyzes and discusses the methods by which terahertz radiation modulates neurons. In addition, this paper reviews the laws of terahertz radiation’s influence on neuronal morphology and kinetic properties and discusses them in detail in terms of terahertz radiation frequency, energy, and time. In the future, the safety of the terahertz radiation system should be considered first to construct the safety criterion of terahertz modulation, and the spatial resolution of the terahertz radiation system should be improved. In addition, the systematic improvement of the laws and mechanisms of terahertz modulation of the nervous system on multiple levels is the key to applying terahertz waves to neuroscience. This paper can provide a platform for researchers to understand the mechanism of the terahertz–nervous system interaction, its current status, and future research directions.
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Ludovici, Gian Marco, Andrea Chierici, Susana Oliveira de Souza, Francesco d’Errico, Alba Iannotti et Andrea Malizia. « Effects of Ionizing Radiation on Flora Ten Years after the Fukushima Dai-ichi Disaster ». Plants 11, no 2 (15 janvier 2022) : 222. http://dx.doi.org/10.3390/plants11020222.
Texte intégralRésumé :
The aim of this work is to analyze the effects of ionizing radiation and radionuclides (like 137Cs) in several higher plants located around the Fukushima Dai-ichi Nuclear Power Plant (FNPP), evaluating both their adaptive processes and evolution. After the FNPP accident in March 2011 much attention was focused to the biological consequences of ionizing radiation and radionuclides released in the area surrounding the nuclear plant. This unexpected mishap led to the emission of radionuclides in aerosol and gaseous forms from the power plant, which contaminated a large area, including wild forest, cities, farmlands, mountains, and the sea, causing serious problems. Large quantities of 131I, 137Cs, and 134Cs were detected in the fallout. People were evacuated but the flora continued to be affected by the radiation exposure and by the radioactive dusts’ fallout. The response of biota to FNPP irradiation was a complex interaction among radiation dose, dose rate, temporal and spatial variation, varying radiation sensitivities of the different plants’ species, and indirect effects from other events. The repeated ionizing radiations, acute or chronic, guarantee an adaptation of the plant species, demonstrating a radio-resistance. Consequently, ionizing radiation affects the genetic structure, especially during chronic irradiation, reducing genetic variability. This reduction is associated with the different susceptibility of plant species to chronic stress. This would confirm the adaptive theory associated with this phenomenon. The effects that ionizing radiation has on different life forms are examined in this review using the FNPP disaster as a case study focusing the attention ten years after the accident.
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Ravanat, J. L. « Endogenous natural and radiation-induced DNA lesions : differences and similarities and possible implications for human health and radiological protection ». Radioprotection 53, no 4 (octobre 2018) : 241–48. http://dx.doi.org/10.1051/radiopro/2018039.
Texte intégralRésumé :
During the last few decades, a considerable amount of work has been done to better assess the effects of ionizing radiation on living organisms. In particular a lot of attention has been focused on the consequences of modifications of the DNA macromolecule, the support of the genetic information. Detailed information is now available on the formation of radiation-induced DNA lesions at the physical, chemical and biological levels. Emphasis will be placed in this review article on the differences and similarities, in term of DNA lesions formation and outcome, between endogenous oxidative stress and ionizing radiation, both stresses that could produce oxidative DNA lesions through similar mechanistic pathways involving mostly reactive oxygen species. If the chemical nature of the generated lesions is similar, the differences in term of biological consequences could be attributed to their spatial distribution in genomic DNA, since ionizing radiations produce lesions in cluster. These clusters of lesions represent a challenge for the DNA repair machinery. In contrast, endogenous oxidative stress generates scattered lesions that could be repaired with a much higher efficacy and fidelity. Possible implication of the use of DNA damage and repair for human health purposes and radiological protection will be discussed.