Radiation Density Research Articles

Radiative–Convective Heating of the Surface of the Martian Descent Vehicle MSL with Taking into Account the Turbulent Nature of Flow

The three-dimensional computer model based on the Reynolds-averaged Navier–Stokes equations together with the Baldwin–Lomax and Prandtl algebraic models of turbulent mixing is used to calculate radiative–convective heat transfer on the surface of the MSL descent space vehicle. The intensification of convective heat transfer on the leeward side of the frontal aerodynamic shield and the superiority of the radiative heat flux density over the convective one on the rear surface are demonstrated. The calculations are performed using the physically and chemically nonequilibrium gas model. The results are compared with the calculations based on other computational models and the flight data on the heat load to the descent vehicle obtained during MSL descent in the dense layers of the Martian atmosphere.

Evaluation of Direct Terahertz Radiation on Prospective Communication Applications

The continuous development of information and communication technology has brought rapid changes, especially developments in cellular technology, starting with 1G and reaching the fifth development in 2020, 5G. This development continues, as evidenced by the start of 6G technology development in early 2020. The Terahertz (THz) spectrum, which has not been used optimally so far for communication technologies, is one candidate to support the next cellular technology developments. THz Waves offers far wider bandwidth than the existing technologies. Apart from the advantages of THz wave radiation, this research studies THz wave radiation intensity and its potential for communication. By calculating the Atmospheric Attenuation, FSPL and considering the minimum received power of user equipment (UE), THz wave radiation characteristics will be more optimal for use less than 500 meters at 0.1 THz and less than 100 meters at 3 THz. The highest Power density of THz radiation is 7.99 × 10-11 Watt/m2 when using 0.1 THz as frequency and a power transmitter of 10 Watts. The results show that exposure to THz waves in communication applications is safe and acceptable for practical communication use.

Photovoltaic AlGaAs/GaAs devices for conversion of high-power density laser (800–860 nm) radiation

Photovoltaic converters of high-power (λ = 800–860 nm, ELR = 150–550 W/cm2) laser radiation (PhotoVoltaic Laser Power Converters – PVLPCs) based on AlGaAs/GaAs heterostructures grown by metalorganic vapor-phase epitaxy have been developed. To increase the output voltage, the space charge region of p-GaAs/n-AlхGa1-хAs heterojunction was shifted to the n-AlхGa1-хAs wide-gap layer with a gradual “x”. The technology for embedding a rear reflector based on TiOx/SiO2/Ag into the photovoltaic converter structure by “transferring” the heterostructure to a supporting substrate and the method of bonding to form a monolithic structure of the PVLPC has been elaborated. To operate the heterostructures at an increased power density of laser radiation, they have been designed to eliminate possible potential barriers at the heterointerfaces and the frontal contact topology with a high density of the metal grid (50 μm and 125 μm contact pitch are under consideration) has been employed. PVLPCs with efficiency of 62% were obtained at the power density of monochromatic radiation (λ = 850 nm) ELR = 170 W/cm2. The finger pitch of 50 μm allows keeping efficiency more than 56% even with a fivefold increase in laser radiation (up to ELR = 500 W/cm2).

An efficient asymptotic preserving Monte Carlo method for radiative transfer equations

In this work, an efficient asymptotic preserving Monte Carlo method is developed for nonlinear thermal radiative transfer equations. We derive a new approximate macroscopic equation for the radiation energy density, from an integral solution of the radiation intensity along characteristics of the microscopic equation. We will solve a coupled macro-micro system with a hybrid numerical method. The macroscopic radiation and material energy densities are updated first by using a deterministic finite volume method. The microscopic equation, with the emission source provided from the macroscopic variables, can then be efficiently solved using a particle-based Monte Carlo method. This new approach is uniformly stable, with large time steps independent of scaling parameters and the speed of light. Besides, it can be shown that the method is asymptotic preserving in the diffusive limit for an optically thick regime. Numerical experiments are performed to demonstrate the high efficiency and good performances of our proposed method.

Radiation hydrodynamical self-similar accretion disc winds

ABSTRACT Self-similar supersonic winds from an accretion disc around a central object are examined with/without radiation fields under the fully self-similar treatment of two-dimensional outflows. The thermal pressure and viscosity are ignored for simplicity. In the case without radiation fields, many solutions are not outflowing winds, but bound flows, except for limited cases which satisfy the escape condition with sufficiently large initial launch speed and rotational one. In the case with radiation fields, the radiation force acts as a driving force, and therefore, the winds blow easier. However, several solutions are unphysical, since the radiative energy density becomes negative. As a result, depending on the rotational motion and boundary conditions, the radiatively driven self-similar cold disc winds are divided into three types; bound solutions lacking launch speed or radiative acceleration, unphysical ones with a negative energy density, and escaping winds confined in the conical region or extending in the whole space as a special type.

Radiative-convective heating of the surface of the Martian descent vehicle MSL with allowance for the turbulent nature of the flow

A spatial computer model based on the Reynolds-averaged Navier-Stokes equations together with the Baldwin-Lomax and Prandtl algebraic models of turbulent mixing was used to calculate the radiative-convective heat transfer on the surface of the MSL descent vehicle. The intensification of convective heat transfer on the leeward side of the frontal aerodynamic shield and the superiority of the radiative heat flux density over the convective one on the rear surface are shown. The calculations were performed using the model of a physically and chemically nonequilibrium gas. A comparison is made with the results of calculations using other computational models and with flight data on the heat load on the descent vehicle obtained during the MSL descent in the dense layers of the Martian atmosphere.

Local Structural Investigation of Near-Infrared-Reflective Black Ca2(Mn,Ti)O4 Pigments Using Synchrotron Radiation X-Ray and Density Functional Theory Calculations.

Layered perovskite black Ca2(Mn,Ti)O4 ceramics were studied by using synchrotron radiation X-rays (SRX) and density functional theory (DFT) calculations to investigate the valence states of the cations, average/local structures, and electronic states. The crystallographic data were obtained by the Rietveld refinement of the obtained synchrotron radiation X-ray powder diffraction patterns. X-ray absorption near edge structure (XANES) spectroscopy measurements revealed that the ratios of Mn4+ and Ti4+ were about 82 and 95%, respectively, in all samples, and the Mn/Ti valences were not affected by the introduction of Ti4+. In addition, two pre-edge peaks were observed in the Mn-XANES spectra, but their peak positions and intensities were affected by doping with Ti4+, indicating that the symmetry of the MnO6 octahedra was changed. A comparison of the atomic distances estimated from the Rietveld analysis and radial distribution function (RDF) revealed that there were large differences between the M-M distances (M = Mn, Ti). Therefore, XANES simulations were carried out to obtain models of the local structure. The experimental and theoretical data indicate that the Mn atoms were configured in a zigzagging arrangement, and the distortion of the MnO6 octahedra increased with the increase in the degree of Ti4+ doping. The origin of the changes to the pre-edge peaks was not only the crystal field strength around Mn but also the symmetry of the MnO6 octahedra.

Temporal‐Spatial‐Resolved Lasing Dynamics in Customized Solution Grown Perovskite Single‐Crystal Microcavities

AbstractSingle‐crystal halide perovskites are among the most promising semiconductor candidates for highly efficient optoelectronic devices due to their higher stability against moisture and light radiation and lower trap density than their polycrystalline counterparts. In this work, single‐crystal MAPbBr3 microcavities with controllable geometries and sizes are fabricated using a template‐limited method combined with an anti‐solvent diffusion growth method. The single‐crystal microcavities emit lasers around 550 nm under femtosecond laser excitation, with a lasing threshold of ≈35 µJ cm−2 and a quality factor of 1135, as well as excellent long‐term operation stability. The temporal‐spatial evolution of the lasing process in an individual microcavity is achieved by the microscopic optical Kerr‐gating technique. The temporal behaviors including pulse duration and build‐up time, emission spectra shift, and lasing mode evolution as a function of pump fluence are unveiled, and the complex relationship between the light‐induced carrier dynamics and lasing properties is clarified. Spatial heterogeneous lasing dynamics are also observed in an individual microdisk, which is attributed to the non‐uniform optical losses and carrier densities driven by structural imperfections. This study can provide a fabrication strategy for perovskite on‐chip optoelectronic devices, as well as a deeper understanding of the carrier‐density‐driven lasing dynamics in microcavities.

Dual Control of Enhanced Quasi-Bound States in the Continuum Emission from Resonant c-Si Metasurfaces.

Optical bound states in the continuum (BICs) offer strong interactions with quantum emitters and have been extensively studied for manipulating spontaneous emission, lasing, and polariton Bose-Einstein condensation. However, the out-coupling efficiency of quasi-BIC emission, crucial for practical light-emitting devices, has received less attention. Here, we report an adaptable approach for enhancing quasi-BIC emission from a resonant monocrystalline silicon (c-Si) metasurface through lattice and multipolar engineering. We identify dual-BICs originating from electric quadrupoles (EQ) and out-of-plane magnetic dipoles, with EQ quasi-BICs exhibiting concentrated near-fields near the c-Si nanodisks. The enhanced fractional radiative local density of states of EQ quasi-BICs overlaps spatially with the emitters, promoting efficient out-coupling. Furthermore, coupling the EQ quasi-BICs with Rayleigh anomalies enhances directional emission intensity, and we observe inherent opposite topological charges in the multipolarly controlled dual-BICs. These findings provide valuable insights for developing efficient nanophotonic devices based on quasi-BICs.

Development of a new hybrid energy system based on a microturbine and parabolic trough collector for usage in sports stadiums

The use of solar technologies is expanding day by day due to easy access and its easiness in combining with other systems. The low density of solar radiation in some places has caused a quiet acceptance of this type of energy, which can be overcome by concentrating solar radiation in a specific area. One of the other problems of renewable energy is the lack of access at all hours of the day and night, and to solve this problem, a gas microturbine system has been used. The purpose of this research is to supply the thermal and electrical energy needed by the sports stadium. The purpose of this research is to investigate the hybrid gas microturbine system with a capacity of 30 kW with a linear parabolic concentrator collector. To achieve this goal, thermodynamic modeling was done and the effect of effective parameters on electrical and thermal power production was evaluated. Among the significant results of this research, the decrease of 0.1% in mechanical power due to the increase of 5 °C in the ambient temperature is noticeable, and on the other hand, according to the obtained results, it can be said that the electrical and mechanical efficiencies increase by 3% due to the increase in the annual radiation intensity to the amount of 1100 W/m2.

Transformational features of the vein wall during a long-term period of endovenous laser ablation using 1910 nm laser radiation. Results of in-vivo experiments.

In this paper, results of in-vivo experiments on the animals of endovenous laser ablation (EVLA) using laser radiation with the wavelength 1910 nm are reported. The results of histological studies of the vein segments removed immediately after the procedure and in a long-term period (30 days and 3 months) are presented. Their structural transformation and the obliteration degree of the vein lumen using different values of the linear energy density of laser radiation (LEED=7.5; 15; 20 J/cm) are estimated. Edilbay breed of sheep (males) were used as experimental animals. Laser radiation with a wavelength of λ=1910 nm and power of Р<inf>rad</inf> = 1.5, 3, 4 W was used for EVLA experiments, and speed of fiber traction (v) was 2 mm/s. 8 days after EVLA stitches and an elastic bandage were removed. Animals were observed for 3 months in the vivarium. Animals have duplex ultrasound scanning of coagulation veins under anesthesia, after analysis vein segments were excised for histological examination. As a result, the damage degree to the vein wall tissues (intima, media, adventitia) and peri-venous tissues was revealed. It is shown that in the long-time period, the intima and partial muscle layer transformed to connective tissue. EVLA using laser radiation with a higher value of LEED led to the growth of connective tissue, oedema of all vein layers and peri-venous tissue. The lumen closure occurred due to clot and the vein wall transformation, a maximum value was 25% using LEED=20 J/cm. The connective-tissue transformation of the coagulated vein occurs in a long-term period and more pronounced for higher LEED. However, features of vein hemodynamics of animals and differences between the clot formation process of human varicose veins and healthy animal veins lead to incomplete occlusion. These features should be taken into account during extrapolation results of experiments on animals in clinical practice.

Dependence of light absorption on temperature changes in tattoo pigments

Purpose: to study the quantitative intensity of optical density and light absorption of the electromagnetic radiation with tattoo pigment aqueous solution depending on its temperature.Material and methods. One hundred twenty-three of the most common commercial tattoo pigments were selected for the trial; 369 samples of aqueous solutions were made of them. Optical density of each pigment sample was determined at 14 and 77 °C. Then, each sample was exposed to optical radiation (IPL xenon lamp with pulsed light) at 14 and 77 °C.Results and discussion. Electromagnetic radiation with wavelengths 532 and 1064 nm increased tattoo pigment destruction from 78,27 to 84,37 % under temperature rise from 14 to 77 °C.Conclusion. Electromagnetic radiation of the optical range with wavelengths 532 and 1064 nm cannot destroy all tattoo pigments; however, optical density of solutions changes under temperature rise which promotes destruction of coloring agents.

Super‐Resolved Bulk States of Photonic Crystals With Cathodoluminescence Microscopy

AbstractProgress in photonic crystals (PhCs) enables the advanced manipulation of light propagation, leading to strong light–matter interactions and unconventional applications. To explore the physical nature and realize the precise and efficient control of position‐dependent light–matter interactions, the direct deep‐subwavelength characterization of PhC states is pivotal. Here, the super‐resolved visualization of bulk states in the z‐direction asymmetric dielectric PhC is realized by characterizing the radiative local density of optical states, including the etched hole area. An accelerating voltage scanning approach is proposed to selectively probe bulk states and substrates, elucidating the electron–matter interactions affected by the electron‐beam energy. The bulk state energy is demonstrated to be confined inside structure holes as shown by the cathodoluminescence intensity mappings of PhCs with different geometrical parameters, enabling the design of a silicon‐based high‐quality cavity in the visible range. This work provides a deep investigation of the depth‐dependent interaction between the electron beam and dielectric PhCs, promoting the characterization of PhC delocalized modes. The deep‐subwavelength detail of bulk state benefits the future nanoscale manipulation of light–matter interactions and the optimization of quantum emission devices.

Improving water use efficiency in vertical farming: Effects of growing systems, far-red radiation and planting density on lettuce cultivation

Vertical farms (VFs) are innovative urban production facilities consisting of multi-level indoor systems equipped with artificial lighting in which all the environmental conditions are controlled independently from the external climate. VFs are generally provided with a closed loop fertigation system to optimize the use of water and nutrients. The objective of this study, performed within an experimental VF at the University of Bologna, was to quantify the water use efficiency (WUE, ratio between plant fresh weight and the volume of water used) for a lettuce (Lactuca sativa L.) growth cycle obtained in two different growing systems: an ebb-and-flow substrate culture and a high pressure aeroponic system. Considering the total water consumed (water used for irrigation and climate management), WUE of ebb-and-flow and aeroponics was 28.1 and 52.9 g L−1 H2O, respectively. During the growing cycle, the contribution generated by the recovery of internal air moisture from the heating, ventilation and air conditioning (HVAC) system, was quantified. Indeed, by recovering water from the dehumidifier, water use decreases dramatically (by 67 %), while WUE increased by 206 %. Further improvement of WUE in the ebb-and-flow system was obtained through ameliorated crop management strategies, in particular, by increasing planting densities (e.g., 153, 270 and 733 plants m−2) and by optimizing the light spectrum used for plant growth (e.g., adjusting the amount of far-red radiation in the spectrum). Strategies for efficient use of water in high-tech urban indoor growing systems are therefore proposed.

Optimization of 12Х18Н9Т-Steel Processing by Ring Laser Beams

Using the MOGA genetic algorithm built into the DesignXplorer module of the ANSYS Workbench program, optimization of laser processing of 12Х18Н9Т-steel by annular beams has been performed. The calculation of temperature fields has been carried out taking into account the dependence of the thermophysical properties of the material on temperature by the finite element method in the ANSYS Workbench program. A regression model has been obtained for processing 12Х18Н9Т-steel by annular laser beams using a face-centered variant of the central compositional plan of the experiment. The power density and duration of laser radiation pulses, the outer and inner diameters of the laser beam in the processing plane were used as variable factors. The penetration depths of the material and the maximum temperatures in the laser processing zone were used as responses. The influence of processing parameters on the penetration depths of the material in the laser impact zone and the maximum temperature values has been evaluated. It has been established that the depth of penetration of the material and the maximum temperatures are most affected by the power density of laser radiation. Optimization of laser processing of 12Х18Н9Т-steel by annular beams was carried out by setting the limiting values of the maximum tempe-rature in the processing zone for three variants of the minimum penetration depth. The parameters obtained as a result of optimization using the MOGA algorithm and the parameters obtained as a result of finite element modeling are compared. The maximum relative error of the results when determining the maximum temperatures did not exceed 1 % and when determining the maximum penetration depths did not exceed 6 %.

Effect of UV, IR and microwave radiation on Tween-80 porogen based low-k films

Low dielectric constant (low-k) films due to their potential application as an inter-layer dielectric (ILD) attracted significant attention of researchers and scientists. Porous low-k films like xerogel, aerogel, porogen based and hybrid films are extensively investigated as they have dielectric constant value less than that of SiO2. Considering the advantages of porous low-k films, current investigation focused onto the study of porogen based porous low-k films. To obtain low-k films, solgel based spin-on technique is used. Incorporation of Tween-80 porogen in deposited low-k films is confirmed through the presence of –CH2-CH3 group around 2856–2916 cm−1 in FTIR spectra. Removal of porogen material from film matrix was done by using radiation exposure of samples and is confirmed through FTIR analysis. Refractive indices (RI) of deposited porogen based films treated with UV, IR and microwave radiations are observed to be 1.28, 1.29 and 1.33, respectively. Further, density of IR, UV and microwave radiation is calculated from RI, and is observed to be decreased for UV radiation up to 1.38 gm/cm3. Dielectric constant value k = 2.7 was achieved for UV treated samples. Investigation suggests that low-k films having lower k value may have potential applications as ILD for ULSI technology.

Effects of thermal radiation and variable density of nanofluid heat transfer along a stretching sheet by using Keller Box approach under magnetic field

Effects of thermal radiation and variable density of nanofluid heat transfer along a stretching sheet by using Keller Box approach under magnetic field

New Inogranic Scintillators’ Application in the Electromagnetic Calorimetry in High-Energy Physics

Scintillation crystals Gd3Al2Ga3O12 (GAGG) are an excellent candidate for application in ionizing-radiation detectors because of their high radiation resistance, density and light yield. These crystals can be used in combination with lead tungstate (PbWO4 or PWO) crystals for the development of a new generation of electromagnetic calorimeter with advanced spatial and energy resolutions in a broad energy range. PWO crystals enable the accurate detection of high-energy photons, while GAGG crystals provide the possibility of precisely measuring photon energies, down to a few MeV. Different options for a composite electromagnetic calorimeter based on PWO and GAGG crystals are considered to optimize spatial and energy resolutions in a broad energy range (from 1 MeV to 100 GeV). In particular, different lengths of the GAGG section of the calorimeter are considered, from 0.5 to 10 cm. The separation of signals from photons and hadrons is also taken into consideration through the study of shower shape in the calorimeter. The optimization is based on Geant4 simulations, considering light collection as well as the use of different photodetectors and electronic noise. Simulations are verified with light yield measurements of GAGG samples obtained using radioactive sources and test beam measurements of the prototype of the PWO-based Photon Spectrometer of the ALICE experiment at CERN.

Impact of pre-sowing red laser irradiation of corn seeds on quality and quantity of harvest yield

As the population increases, more people need to be fed. In order to find a physical method that influence the corn production, this work is dedicated to evaluating the impact of pre-sowing red laser irradiation of corn (Zea mays L.) seeds on harvest yield. The aim was to analyze the influence of red laser radiation on corn seeds, on the quantity and quality of yield, on large-scale and open field production. It is hypothesized that at least one red laser irradiation treatment could improve corn crop yield. In radiation, a red laser diode at 660 nm with a power of 100 mW was used, two radiation densities were used (D1: 2 mW cm-2 and D2: 4 mW cm-2), applied during 4 exposure times (T1: 15, T2: 30, T3: 60 and T4: 120 s) and a control group without treatment (C). A random arrangement was used, in a 2 x 4 factorial scheme, totaling 8 treatments and control, with four replications. The data were subjected to an ANOVA and the means were compared with the Tukey test (HSD; p ≤ 0.05). The D2-T4 treatment produced the most significant impact concerning the control, improving yield by 19±1% (3 t ha-1), cob length 18±1%, cob diameter 22±3%, weight (16±2%) and corn kernels size (14±2%). We also find negative effects on yield, D2-T1 decreased crop yield around 16±1% (2.24 t ha-1). The results show a way to include this technique as a technique that can to increase or decrease corn yield. Keywords: Cob length; Maize; open field; Thousand kernel weight.

Optimization of energy parameters for laser-induced PDT of cervical tissues using numerical simulation and fluorescent monitoring

The main problem in the photodynamic therapy (PDT) of tumors is insufficient light exposure to tissue or the appearance of undesirable surface effects. The reason is the irregular distribution of the absorbed light dose by depth. The influence of the spot diameter on the relative fluence rate in the near-surface layer of the cervical tissue was studied by Monte Carlo simulation. Photodynamic exposure with chlorine-type photosensitizer (PS) was carried out on the tissue model with laser 660 nm at the same power density with a change in spot diameter from 5 to 15 mm and radiation energy density from 100 to 300 J cm−2. The distributions of the fluorescence indices of the PS and the hemoglobin oxygenation degree by depth were obtained. The dependence of PS photobleaching on the energy density was established at the same power density and different spot diameters. The developed method increased the efficiency of PDT by delivering a sufficient energy density of laser radiation to the entire tumor tissue by depth without thermal damage, that allowed minimizing side effects and prevent possible growth and recurrence of the disease.