Maximum Reflectivity Research Articles

Mechanical, electronic, and optoelectronic properties of RE3+MoN3 (RE3+ = La, Ce, Nd, Pr, Sm) perovskites

AbstractThe electronic structure, mechanical, and optical properties of RE3+MoN3 (RE3+ = La, Ce, Pr, Nd, Sm) perovskites were calculated by the Full Potential method (FP‐LAPW) based on density functional theory. The unit cell structure (space group ) was optimized using the PBE‐GGA functional. Furthermore, the calculated tolerance factor is found in the permissible range for a cubic perovskite. Elastic properties of these compounds confirm the mechanical stability, anisotropic, ductile, metallic, stiffer, and rigid nature. The electronic structure calculations were then performed using the mBJ functional followed by hybrid functional & Hubbard correction U. The electron charge density plots revealed ionic and covalent bonding in RE3+MoN3. The total density of states and band structure calculations display metallic behavior for the RE3+MoN3 compounds. Maximum refractive index (4.8), reflectivity (.72), and optical conductivity (8.21) were obtained for LaMoN3 perovskites. Different optical properties have been calculated; therefore, we anticipate the identification of highly useful optoelectronic applications.

Solar Dish Concentrator: A Case Study at the Energy Center Rooftop

Concentrating solar technology plays a role, albeit a niche role compared to commercial solar systems (photovoltaics and thermal collectors). Within the context of sustainable development and within the green transition phase, it could be a respectable player. The main purpose of this study is to create and validate a model that approximates the temperature trend of a receiver installed in a CSP (concentrated solar plant). A method to approximate optical and thermal performance is discussed. The paraboloid installed in the Energy Center (Turin, Italy) was taken as a reference, creating a model that could simulate real operating conditions. The Monte Carlo (MC) method for ray tracing was adopted developing two models. The first model sets the maximum reflectivity of the paraboloid and neglects the loss of “limb darkening,” while the second one sets a reflectivity of 80%. Once the incident flux was obtained, the optical performance was analytically calculated and compared to the value provided by the manufacturer. The thermal performance was also studied, reproducing the dimensions of the receiver consisting of a sintered alumina tube placed at a focal distance from the paraboloid. Two configurations were analyzed: one neglecting the losses due to radiation and natural convection, the other one including the losses due to radiation and considering the atmospheric wind condition. Finally, the model was validated by comparing the obtained temperatures with those measured by thermocouples placed on the receiver. Analyzing two random days in the year 2020, an average error of 7% and 2% was obtained.

Identifikasi Sebaran Asap Kebakaran Hutan di Wilayah Jambi dengan Menggunakan Radar C-BAND

Forest and land fires along with the distribution of smoke are one of the disasters threats in the Jambi region which has tropical forests. By knowing the lowest level of visibility from observations, this study was conducted on September 23, 2015. Weather and satellite radar have ability to detect particles and the distribution of smoke from forest and land fires with great spatial and temporal resolution, supported by HIMAWARI-8 satellite data as comparison. C-Band Doppler radar and default strategy scanning are used to identify smoke in Jambi. Wind layer analysis uses CAPPI V products to display smoke distribution and CMAX dBZ with palette changes to identify smoke particles, which then will be carried out vertical cross section to see smoke reflectivity values, identify smoke vertical profiles, and patterns of smoke distribution of forest and land fires. The smoke reflectivity index value can be seen from the dBZ value. The results of the identification show that the smoke material reaches a maximum reflectivity value of 30 dBZ at the centre of the fire point and the minimum value of very fine smoke particles reaches -24.4 dBZ which scattered with the dominant velocity distribution direction to the northwest.

Deep convective clouds observed by ground-based radar over Naqu, Qinghai–Tibet Plateau

The deep convective clouds (DCCs, 20 dBZ echo top exceeding 14 km) and intense DCCs (IDCCs, 40 dBZ echo top exceeding 10 km) over Naqu, a city featuring the most active convection in the central Qinghai–Tibet Plateau, were analyzed on the basis of data derived from the Naqu C-band radar within a radius of 100 km. The most frequent DCCs occur in July and at 15:00 LT (local time), in terms of monthly and diurnal variations, respectively. The geographic distribution of the DCCs seems to be related to the topography. The centers featuring the most frequent DCCs correspond to some certain hilly areas, while the ratio of IDCC to DCC is greater in some specific flat areas, which may be because the hilly topography is conducive to triggering convection but is unfavorable to the full accumulation of unstable energy. The DCCs (IDCCs) have average 20, 30 and 40 dBZ echo tops of approximately 15.8 (16.5), 12.3 (14.1) and 9.9 (11.3) km, and average areas of the regions with a composite reflectivity >20, 30 and 40 dBZ of approximately 120.3 (196.1), 37.4 (75.3) km2 and 9.2 (14.6) km2, respectively. The maximum reflectivity and horizontal extents of 20 and 30 dBZ radar echoes tend to occur at the level around −20 °C. The average horizontal extent of DCCs is much smaller than that suggested by the satellite-based radar data. In the diurnal variations in the vertical and horizontal extents of DCCs, the parameters related to 30 dBZ always increase more slowly and decrease more rapidly than those related to 20 dBZ in the afternoon, which is attributed to the generally weak convection characteristics of DCCs. The strongest convection may be around 16:00 LT in Naqu.

Analysis of Cloud Growth Phases When Nocturnal Hail Occurs (Case Study: Sekadau, 22 August 2020)

On August 22 2020, hail was reported in Sekadau, West Kalimantan at 21:23 WIB. The phenomenon of hail does not usually occur at night. So, further research is needed to find out how the cloud growth phase and Cumulonimbus (Cb) cloud structure are in this phenomenon. This research utilizes remote sensing instruments in the form of a C-Band type weather radar for the Supadio Meteorological Station and the Himawari 8 Satellite, as well as a radiosonde instrument that is closest to the time and location of the hail events. The results of satellite imagery show that nocturnal hail occurs before the clouds reach the mature phase, with the cloud top temperature at the time of hail less than -60 ºC. The maximum reflectivity detected by the radar using CMAX products shows a less significant value with an intensity of up to 52 dBZ. The VCUT product shows the maximum intensity altitude is at an altitude of 5 – 8 km. This shows that there is a process of ice condensation on the freezing level layer. The ZHAIL product image shows that there is a potential for hail in the Sekadau area with a probability of more than 80%. The occurrence of ice rain at Sekadau at night is caused by the presence of Cumulonimbus clouds with very cold peak temperatures and the mixing process above the freezing level which supports the formation of ice condensation in Cb clouds.

Analysis of Atmospheric Conditions during the Occurrence of Mesoscale Convective Complex (MCC) in East Kalimantan and Surrounding Area (Case Study: December 26, 2021)

Mesoscale Convective Complex (MCC) was first introduced in 1980 through research on infrared (IR) satellite images by Maddox. The MCC phenomenon can caused rain with a long period of time. This study aims to determine the atmospheric conditions when MCC occurred in East Kalimantan and surroundings area on December 26, 2021. The research data used in this study is Himawari-8 satellite data to display cloud top temperatures and convective cloud distribution using the CCO method and image interpretation using RGB method. Analysis of atmospheric conditions was also carried out on air humidity, vertical velocity, and reflectivity in the atmosphere obtained from weather radar data from the Stasiun Meteorologi Sultan Aji Muhammad Sulaiman - Sepinggan. Based on the results of the analysis, MCC was identified as a mature phase on December 26, 2021 at 12.00 UTC. Airmass RGB analysis shows the presence of clouds which are known as Cb clouds through CCO analysis as well as warm air masses with high humidity in East Kalimantan. Negative value of vertical velocity also indicates an updraft of moist air masses and the maximum reflectivity value of the CMAX product, which is 53 dBz, indicates strong convection activity.

Measurement of Time Dependent Reflection, Transmission, and Absorption in Laser Driven Silicon and GaAs Switches for 250 GHz Radiation.

The reflectance and transmittance of Si and GaAs wafers irradiated by a 6 ns pulsed, 532 nm laser have been studied for s- and p-polarized 250 GHz radiation as a function of laser fluence and time. The measurements were carried out using precision timing of the and signals, allowing an accurate determination of the absorptance where . Both wafers had a maximum reflectance above 90% for a laser fluence . Both also showed an absorptance peak of ~50% lasting ~2 ns during the risetime of the laser pulse. Experimental results were compared with a stratified medium theory using the Vogel model for the carrier lifetime and the Drude model for permittivity. Modeling showed that the large absorptance at the early part of the rise of the laser pulse was due to the creation of a lossy, low carrier density layer. For Si, the measured and were in very good agreement with theory on both the nanosecond time scale and the microsecond scale. For GaAs, the agreement was very good on the nanosecond scale but only qualitatively correct on the microsecond scale. These results may be useful for planning applications of laser driven semiconductor switches.

Fractal characteristics for coal chemical structure: Principle, methodology and implication

Despite coal chemical structure's importance as the organic backbone for hydrocarbon production, the fractal characteristics for coal chemical structure remains unexplored. Therefore, this paper proposed a novel method to calculate the fractal dimension Df for coal chemical structure. The principle and methodology of the proposed method were deduced and summarized in detail. This method was applied to calculate the fractal dimension Df for the coal chemical structure from lignite to anthracite. The research results indicate that the fractal dimension Df for coal chemical structure decreases first and then increases with coalification. The turning point of the variation trend of fractal dimension Df and coalification corresponds to the second coalification jump (maximum vitrinite reflectance Ro, max = 1.30 %). This study has achieved the micro characterization on coal chemical structure at molecular scale, which has potential application value on the functional properties analysis and molecular synthesis design of coal-based material research fields.

Electromagnetic wave absorption properties of hot‐pressed Si3N4‐SiC ceramic nanocomposites

AbstractHigh‐density Si3N4‐SiC ceramic nanocomposites have exceptional mechanical properties, but little is known about their electromagnetic wave absorption (EMA) capabilities. In this paper, the effects of sintering temperature and starting material compositions on the dielectric and EMA properties of hot‐pressed Si3N4‐SiC ceramic nanocomposites were investigated. The real and imaginary permittivities of Si3N4‐SiC ceramic nanocomposites increase with increasing sintering temperature or SiC content, particularly at the sintering temperature of 1850°C and SiC content of 50 wt.%. This is primarily due to the improvement of interfacial and defect polarizations, which is caused by the doping of nitrogen into the SiC nanocrystals during the solution‐precipitation process. The real and imaginary permittivities of Si3N4‐SiC ceramic nanocomposites show decreasing trends as sintering aid content increases. Si3N4‐SiC ceramic composites have both good EMA and mechanical properties when they are sintered at 1850°C with 30 wt.% SiC and 5–8 wt.% sintering aids. The minimum reflection loss and maximum flexural strength reach ‐58 dB and 586 MPa, respectively. Materials with multilayered structural designs have both strong and broad EMA properties.

Enhanced physical properties of nickel telluride metal chalcogenide material with molybdenum dopant

ABSTRACT In the study, nickel telluride and molybdenum dopants were synthesised using an electrochemical deposition approach. The nanoparticle of the material shows the reaction between the transition metal and chalcogenide material, and the nickel telluride pristine demonstrates that the film surface provides a clean image of melted wax with splattered evidence of oil on the film. The film that was deposited at 0.1 mol% clearly shows how the dopant changed the melted wax to nanoparticles, demonstrating the compatibility of the two materials. The structural patterns showed diffraction peaks at the (111), (200), (210), (211), (300), and (311) diffraction planes, which are equivalent to 13.22 °, 16.95 °, 18.85 °, 25.93 °, 30.84 °, and 32.98 ° for nickel telluride and 13.38 °, 16.93 °, 19.02 °, 25.95 °, 30.85, and 33.02 ° for molybdenum-doped nickel telluride. Both nickel telluride and molybdenum-doped nickel telluride materials produced similar peaks. When the dopant was added, the thickness of the molybdenum-doped nickel telluride films grew from 132.02 to 147.57 nm. The UV area of the spectra was found to have the maximum absorbance and reflectance, however, the transmittance increased as the wavelength of the incident radiation increased. The absorbance, transmittance, and reflectance of nickel telluride and molybdenum-doped nickel telluride thin film material are improved by the addition of molybdenum as a dopant. The energy bandgap of the synthesised films; the nickel telluride has 1.18 eV, while the doped nickel telluride has an energy bandgap of 1.50–1.55 eV which shows that the energy bandgap narrows as molybdenum-dopant concentration rises.

Fano-Like Resonance from Disorder Correlation in Vacancy-Doped Photonic Crystals.

By preparing colloidal crystals with random missing scatterers, crystals are created where disorder is embodied as vacancies in an otherwise perfect lattice. In this special system, there is a critical defect concentration where light propagation undergoes a transition from an all but perfect reflector (for the spectral range defined by the Bragg condition), to a metamaterial exhibiting an enhanced transmission phenomenon. It is shown that this behavior can be phenomenologically described in terms of Fano-like resonances. The results show that the Fano's parameter q experiences a sign change signaling the transition from a perfect crystal exhibiting a reflectance Bragg peak, through a state where background scattering is maximum and Bragg reflectance reaches a minimum to a point where the system reenters a low scattering state recovering ordinary Bragg diffraction. A simple dipolar model considering the correlation between scatterers and vacancies is proposed and the reported evolution of the Fano-like scattering is explained in terms of the emerging covariance between the optical paths and polarizabilities and the effect of field enhancement in photonic crystal (PhC) defects.

The organic petrology of vitrinite-like maceral in the Lower Paleozoic shales: Implications for the thermal maturity evaluation

Vitrinite-like maceral (VLM) is a type of autochthonous, synsedimentary, dispersed organic matter, which is ubiquitous in many Lower Paleozoic marine shales. The VLM reflectance has been used as an alternative tool to evaluate the thermal maturity of pre-Devonian marine sediments lacking a classical vitrinite, however, the existing knowledge about its optical properties and reflectance characteristics is still relatively limited. In this study, the optical properties of VLM were examined by means of organic-petrological methods applied to a series of naturally and artificially matured VLM-rich shales samples and their reflectance crossplots. The strong positive correlation between the true maximum reflectance (Rmax) and bireflectance of VLM indicates the increasing anisotropy of VLM with increasing thermal maturity. VLM shows a linear coalification path in the studied shales. It displays biaxial neutral features in the samples with Rmax ≤ 2%, but shows obvious optically biaxial negative characteristics in the samples with Rmax > 2%. The shape of VLM reflectance indicating surface (VLMRIS) gradually becomes oblate with increasing maturity. These results indicate that VLM exhibits appearance and optical properties similar to vitrinite, and its reflectance can be used as a reliable indicator for thermal maturity evaluation. The equivalent vitrinite reflectance (EqVRo) values, which were calculated based on the mean measured maximum reflectance of VLM (VLMR¯max), evidence that the Niutitang Formation shales from China and Alum shales from Denmark are post-over mature, and the Yurtus Formation shales in Tarim Basin and the Alum shales from Sweden are still within the oil window.

Was coal metamorphism an influence on the minor element chemistry of the Middle Pennsylvanian Springfield (No. 9) coal in Western Kentucky?

Coal rank in the Middle Pennsylvanian Carbondale Formation Springfield coal in the Western Kentucky coalfield, part of the Illinois Basin, ranges from high volatile A bituminous in southern Union and Webster counties to high volatile C bituminous in the rest of the region. The chlorine content closely follows the coal rank, being highest in the high volatile A bituminous coals. High concentrations of V and Cr are evident in the top benches at all sites and is particularly strong in the higher rank sites. Zinc and other elements (Ni, Mo, among others) are enriched in some benches, but the trend is not as consistent as with V and Cr. Zirconium (+ Nb) and TiO2, both serving as proxies for a detrital influx, show differentiation among the quadrangles, with the high volatile C bituminous Spottsville quadrangle coals having the highest Zr + Nb content. The correlation between Y and Zr indicates that the highest Y occurs in the Spottsville samples. The Spottsville samples have highest REE. Principal components analysis using both a rank parameter (vitrinite maximum reflectance) and the set of geochemical parameters showed that the coal rank axis (Rmax) (with the highest rank being in the Providence quadrangle) is orthogonal to the overlapping LREE/HREE and GdN/GdN* axes and is opposite to the REE, Zr + Nb, and Zn axes. Hydrothermal metamorphism certainly influenced coal rank, the chlorine content of the coals, and, perhaps, some aspects of the minor element chemistry. Coal metamorphism, however, was not the sole influence and not even the dominant influence on the concentration of REE in the Springfield coal in western Kentucky since other factors, such as the greater concentrations of detrital minerals in the Spottsville quadrangle samples, seem to have had a greater influence on the REE chemistry.

Microstructure, mechanical properties and optical reflectance of TiNiN films deposited on silicon substrates using cathodic arc evaporation

Variations in applied substrate bias during cathodic arc deposition may impose intriguing consequences on the mechanical and optical properties of TiNiN coatings. Here, TiNiN films were fabricated onto Si substrates using a Ti95Ni5 (at.%) alloy target via cathodic arc evaporation employing a range of substrate bias voltages varying from 0 to -150 V. The aim of this study was to investigate the microstructures, mechanical performance, and optical properties of the TiNiN films in terms of the employed substrate potential. A significant enhancement (57%) in hardness for the TiNiN film was attained at -50 V as compared to zero substrate potential. This was principally attributed to the evolution of a fine, equiaxed nanocomposite structure, in association with the induction of a very high compressive residual stress at -50 V. In contrast, a maximum optical reflectance of 73% in the near-infrared range was determined for the coating synthesised at -150 V. It is speculated that incidence of fewer macroparticles on the film surface at elevated negative potentials, due to the induction of a higher repulsive force, may reduce the scattering of light incident on the coating's surface, promoting improved spectral reflectivity.

Investigation of optoelectronic & thermoelectric features of ZnCrX2 (X = S Se Te) chalcopyrite semiconductor using mBJ potential

In the present investigation, we have examined the structural, optoelectronic and thermoelectric properties of the compound ZnCrX2 (X = S, Se, Te) using the full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA-PBEsol) and the modified Becke–Johnson (mBJ) implemented on Wien2k code. By calculating the electronic structure, we observed that the indirect band gap was 1.76 eV, 1.68 eV, and 1.59 eV, for these selected compounds and the type of chemical bonding was ionic between Zn-X and Cr-X. For the three ternary chalcopyrites their optical properties including optical conductivity, complex dielectric functions, complex refractive index, reflectivity, energy loss, and absorption coefficient were examined. The calculated optical conductivity indicates that the studied compounds are suitable for optoelectronic applications as they have good absorbance and less energy loss in the low energy range of the electromagnetic spectrum. For ZnCrTe2, the maximum reflectivity was in the low energy range (0.48 or 48% at 9 eV). The BoltzTrap code was executed for the calculation of the thermoelectric properties and thermal efficiency of the compounds investigated, depending upon the Seebeck coefficient, thermal conductivity and electrical conductivity. The high value of the figure of merit and the Seebeck coefficient (260 uV/k) defines the high efficiency of the materials studied. Hence, the studied chalcopyrite compounds offer applications in solar cell devices and p-type semiconducting nature predictive in transport investigations.

Monolithic high contrast grating on GaSb/AlAsSb based epitaxial structures for mid-infrared wavelength applications.

We demonstrate monolithic high contrast gratings (MHCG) based on GaSb/AlAs0.08Sb0.92 epitaxial structures with sub-wavelength gratings enabling high reflection of unpolarized mid-infrared radiation at the wavelength range from 2.5 to 5 µm. We study the reflectivity wavelength dependence of MHCGs with ridge widths ranging from 220 to 984 nm and fixed 2.6 µm grating period and demonstrate that peak reflectivity of above 0.7 can be shifted from 3.0 to 4.3 µm for ridge widths from 220 to 984 nm, respectively. Maximum reflectivity of up to 0.9 at 4 µm can be achieved. The experiments are in good agreement with numerical simulations, confirming high process flexibility in terms of peak reflectivity and wavelength selection. MHCGs have hitherto been regarded as mirrors enabling high reflection of selected light polarization. With this work, we show that thoughtfully designed MHCG yields high reflectivity for both orthogonal polarizations simultaneously. Our experiment demonstrates that MHCGs are promising candidates to replace conventional mirrors like distributed Bragg reflectors to realize resonator based optical and optoelectronic devices such as resonant cavity enhanced light emitting diodes and resonant cavity enhanced photodetectors in the mid-infrared spectral region, for which epitaxial growth of distributed Bragg reflectors is challenging.

Optically controllable high-frequency photonic band gaps using modified superradiance lattice

We report that modified superradiance lattice (2023, Phys. Scr. 98 015 105) can be used to obtain high-frequency photonic band gaps which are controllable using low-frequency light. Here, we also notice that the maximum reflectivity of these photonic band gaps can be achieved via low-frequency light control. This maximum reflectivity remains constant for a certain range of probe detuning depending upon the strength of the control field. We also report that this can lead to experimental realization of the soft x-ray regime (high-frequency) via 61st-order low-frequency light using Be2+ ions, the corresponding reflectivity in this case is 96%. Therefore, one can construct controllable x-ray photonic band gaps which can further be used to devise optical switches, beam splitters, and frequency combs. Moreover, this scheme holds the promise of working efficiently in all types of other configurations where reflection of high-frequency light is needed using nth order low-frequency light.

Transport and thermoelectric performance of Fluorine functionalized Ge-carbide sheets

Based on density functional theory simulations, GW approximation + BSE and the semi-classical Boltzmann transport theory, electronic ,optical and thermoelectric response of bidimensional fluorinated Ge-carbides are investigated. Three configurations are considered, namely F-CGe, CGe-F, F-CGe-F to explore the effect of both fluorination distribution and coverage. It is shown that the conduction (valence) band is shifted upwards (downwards) when F decorates C-atoms (Ge-atoms) which tunes the gap energy. Furthermore, full fluorination makes CGe sheet better dielectric structure. The maximum reflectivity and absorption reveal that F-CGe-F structure exhibits better optical response, unlike its two counterparts constrained to absorb incident photon energy to the UV region only. The maximum polarization values are found in the visible region for the half fluorinated structure F-CGe and in the UV spectrum for F-CGe-F and CGe-F. The Fluorination also improves the transport properties of CGe which significantly increases its merit factor (ZT) at room temperature. Th three compounds are found to exhibit an ultralow lattice conductivity which leads and a record high ZT up to 0.65, 0.77, and 0.81 at 900 K in CGe-F, F-CGe and F-CGe-F respectively. Our results evaluate the potential of fluorinated CGe sheets as suitable thermoelectric materials at the ambient temperature.

Research on Reflection Mechanism of Nonuniform Plasma

The surface of the near-space hypersonic vehicle is covered with a plasma sheath (PSh) with fluid properties. During the radar detection of hypersonic vehicles, the spatial distribution characteristics of PSh parameters affect the reflected wave intensity and the position of the maximum reflection layer of plasma in the vehicle’s different areas, resulting in significant differences in the intensity and frequency offset of echo signals in various areas. In order to further study the reflection characteristics of nonuniform plasma, this article uses the equivalent wave impedance method to calculate the reflection and transmission coefficients of each layer of plasma, analyzes the reflection intensity distribution mechanism of nonuniform plasma, and reveals the EM shielding effect (ES-effect) of plasma. Based on the typical carrier frequency, collision frequency, electron density, and electron density distribution gradient, the variation law of maximum reflection position and maximum reflection intensity in nonuniform plasma is revealed. The research results lay a theoretical foundation for analyzing echo signal characteristics of the PSh-covered target, radar detection anomaly suppression, and EM stealth.

Accuracy of scanning interrogation of FBG sensors

Abstract Progress in the fibre optic technology spurred the development of optical fibre-based sensors. A successful fibre optics-based element for sensorial systems is fibre Bragg grating. It allows to read the measured value by the spectral shift of light, which is the variable with a good potential for accurate measurement. Various types of the interrogation of the light spectrum reflected from the measuring grating are discussed in this article and the work concentrates on the spectrum scanning that gives the good chances to diminish measuring errors by a proper choice of parameters. The focal point is the accuracy of establishing the correct value of the maximum reflectance wavelength. The significance of the noise in the photoelectric scanning signal for the measuring accuracy is analysed and the crucial factor is found in the minimizing the reflectance spectral width of the measuring grating and using the spectrum of the scanning light with the same or smaller spectral width. An important aspect is the relation of the maximal reflectance and the wavelength width of the measuring grating reflectance spectrum. The article also shows the potentiality of the apodized gratings for improving the scanning interrogation. A specific index apodization profile was analysed and its advantages are discussed.