Effects of Ambience on Thermal-Diffusion Type Ga-doping Process for ZnO Nanoparticles

Various annealing atmospheres were employed during our unique thermal-diffusion type Ga-doping process to investigate the surface, structural, optical, and electrical properties of Ga-doped zinc oxide (ZnO) nanoparticle (NP) layers. ZnO NPs were synthesized using an arc-discharge-mediated gas evaporation method, followed by Ga-doping under open-air, N2, O2, wet, and dry air atmospheric conditions at 800 °C to obtain the low resistive spray-coated NP layers. The I–V results revealed that the Ga-doped ZnO NP layer successfully reduced the sheet resistance in the open air (8.0 × 102 Ω/sq) and wet air atmosphere (8.8 × 102 Ω/sq) compared with un-doped ZnO (4.6 × 106 Ω/sq). Humidity plays a key role in the successful improvement of sheet resistance during Ga-doping. X-ray diffraction patterns demonstrated hexagonal wurtzite structures with increased crystallite sizes of 103 nm and 88 nm after doping in open air and wet air atmospheres, respectively. The red-shift of UV intensity indicates successful Ga-doping, and the atmospheric effects were confirmed through the analysis of the defect spectrum. Improved electrical conductivity was also confirmed using the thin-film-transistor-based structure. The current controllability by applying the gate electric-field was also confirmed, indicating the possibility of transistor channel application using the obtained ZnO NP layers.

Atmospheric effects of air pollution during dry and wet periods in São Paulo

Air pollutants reach high concentrations in developing countries, such as Brazil. The state of São Paulo is the economic and demographic center of Brazil and presents high levels of urbanization,...

Millimetre wave 3-D channel modelling for next generation 5G networks

<abstract><p>Millimetre wave (mm-wave) spectrum (30-300GHz) is a key enabling technology in the advent of 5G. However, an accurate model for the mm-wave channel is yet to be developed as the existing 4G-LTE channel models (frequency below 6 GHz) exhibit different propagation attributes. In this paper, a spatial statistical channel model (SSCM) is considered that estimates the characteristics of the channel in the 28, 60, and 73 GHz bands. The SSCM is used to mathematically approximate the propagation path loss in different environments, namely, Urban-Macro, Urban-Micro, and Rural-Macro, under Line-of-Sight (LOS) and Non-Line-of-Sight (NLOS) conditions. The New York University (NYU) channel simulator is utilised to evaluate the channel model under various conditions including atmospheric effects, distance, and frequency. Moreover, a MIMO system has been evaluated under mm-wave propagation. The main results show that the 60 GHz band has the highest attenuation compared to the 28 and 73 GHz bands. The results also show that increasing the number of antennas is proportional to the condition number and the rank of the MIMO channel matrix.</p></abstract>

Investigation of OH radical kinetics with glycine, alanine, serine and threonine in the aqueous phase

&lt;p&gt;Amino acids are key substances in biological activities and can be emitted into the atmosphere as constituents of primary aerosols. Understanding the radical kinetics of amino acids is necessary to evaluate their atmospheric effects. In the present study, the hydroxyl radical (OH) reaction kinetics of glycine, alanine, serine and threonine were investigated in the aqueous phase. The temperature and pH dependent rate constants were measured by a laser flash photolysis-long path absorption setup using the competition kinetics method. Based on the measurements and speciation calculations, the OH radical reaction rate constants of the fully protonated (H&lt;sub&gt;2&lt;/sub&gt;A&lt;sup&gt;+&lt;/sup&gt;) and neutral (HA&lt;sup&gt;&amp;#177;&lt;/sup&gt;) form were determined. The following T-dependent Arrhenius expressions were derived for the OH radical reactions with glycine, &lt;em&gt;k&lt;/em&gt;(&lt;em&gt;T&lt;/em&gt;, H&lt;sub&gt;2&lt;/sub&gt;A&lt;sup&gt;+&lt;/sup&gt;) = (9.1 &amp;#177; 0.3) &amp;#215; 10&lt;sup&gt;9&lt;/sup&gt; &amp;#215; exp[(-2360 &amp;#177; 230 K)/&lt;em&gt;T&lt;/em&gt;], &lt;em&gt;k&lt;/em&gt;(&lt;em&gt;T&lt;/em&gt;, HA&lt;sup&gt;&amp;#177;&lt;/sup&gt;) = (1.3 &amp;#177; 0.1) &amp;#215; 10&lt;sup&gt;10&lt;/sup&gt; &amp;#215; exp[(-2040 &amp;#177; 240 K)/&lt;em&gt;T&lt;/em&gt;]; alanine, &lt;em&gt;k&lt;/em&gt;(&lt;em&gt;T&lt;/em&gt;, H&lt;sub&gt;2&lt;/sub&gt;A&lt;sup&gt;+&lt;/sup&gt;) = (1.0 &amp;#177; 0.1) &amp;#215; 10&lt;sup&gt;9&lt;/sup&gt; &amp;#215; exp[(-1030 &amp;#177; 340 K)/&lt;em&gt;T&lt;/em&gt;], &lt;em&gt;k&lt;/em&gt;(&lt;em&gt;T&lt;/em&gt;, HA&lt;sup&gt;&amp;#177;&lt;/sup&gt;) = (6.8 &amp;#177; 0.4) &amp;#215; 10&lt;sup&gt;10&lt;/sup&gt; &amp;#215; exp[(-2020 &amp;#177; 370 K)/&lt;em&gt;T&lt;/em&gt;]; serine, &lt;em&gt;k&lt;/em&gt;(&lt;em&gt;T&lt;/em&gt;, H&lt;sub&gt;2&lt;/sub&gt;A&lt;sup&gt;+&lt;/sup&gt;) = (1.1 &amp;#177; 0.1) &amp;#215; 10&lt;sup&gt;9&lt;/sup&gt; &amp;#215; exp[(-470 &amp;#177; 150 K)/&lt;em&gt;T&lt;/em&gt;], &lt;em&gt;k&lt;/em&gt;(&lt;em&gt;T&lt;/em&gt;, HA&lt;sup&gt;&amp;#177;&lt;/sup&gt;) = (3.9 &amp;#177; 0.1) &amp;#215; 10&lt;sup&gt;9&lt;/sup&gt; &amp;#215; exp[(-720 &amp;#177; 130 K)/&lt;em&gt;T&lt;/em&gt;]; and threonine, &lt;em&gt;k&lt;/em&gt;(&lt;em&gt;T&lt;/em&gt;, H&lt;sub&gt;2&lt;/sub&gt;A&lt;sup&gt;+&lt;/sup&gt;) = (5.0 &amp;#177; 0.1) &amp;#215; 10&lt;sup&gt;10&lt;/sup&gt; &amp;#215; exp[(-1500 &amp;#177; 100 K)/&lt;em&gt;T&lt;/em&gt;], &lt;em&gt;k&lt;/em&gt;(&lt;em&gt;T&lt;/em&gt;, HA&lt;sup&gt;&amp;#177;&lt;/sup&gt;) = (3.3 &amp;#177; 0.1) &amp;#215; 10&lt;sup&gt;10&lt;/sup&gt; &amp;#215; exp[(-1320 &amp;#177; 90 K)/&lt;em&gt;T&lt;/em&gt;] (in units of L mol&lt;sup&gt;-1&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;).&lt;/p&gt; &lt;p&gt;The density functional theory calculation was performed using GAUSSIAN to simulate the energy barriers (&lt;em&gt;E&lt;sub&gt;Barrier&lt;/sub&gt;&lt;/em&gt;) of OH radical induced H-atom abstraction. According to the simulated results, amino and carboxyl group increase the &lt;em&gt;E&lt;sub&gt;Barrier&lt;/sub&gt;&lt;/em&gt; at the adjacent C&amp;#8209;atom and thus reduce the OH radical reactivity. Hydroxide and methyl group decrease the &lt;em&gt;E&lt;sub&gt;Barrier&lt;/sub&gt;&lt;/em&gt; at the adjacent C-atom, leading to an increase in the OH radical rate constant.&lt;/p&gt;

Atmospheric Correction of Airborne Hyperspectral CASI Data Using Polymer, 6S and FLAASH

Airborne hyperspectral data play an important role in remote sensing of coastal waters. However, before their application, atmospheric correction is required to remove or reduce the atmospheric effects caused by molecular and aerosol scattering and absorption. In this study, we first processed airborne hyperspectral CASI-1500 data acquired on 4 May 2019 over the Uljin coast of Korea with Polymer and then compared the performance with the other two widely used atmospheric correction approaches, i.e., 6S and FLAASH, to determine the most appropriate correction technique for CASI-1500 data in coastal waters. Our results show the superiority of Polymer over 6S and FLAASH in deriving the Rrs spectral shape and magnitude. The performance of Polymer was further evaluated by comparing CASI-1500 Rrs data with those obtained from the MODIS-Aqua sensor on 3 May 2019 and processed using Polymer. The spectral shapes of the derived Rrs from CASI-1500 and MODIS-Aqua matched well, but the magnitude of CASI-1500 Rrs was approximately 0.8 times lower than MODIS Rrs. The possible reasons for this difference were time difference (1 day) between CASI-1500 and MODIS data, higher land adjacency effect for MODIS-Aqua than for CASI-1500, and possible errors in MODIS Rrs from Polymer.

Atmospheric Effects on the Isotopic Composition of Ozone

The delta values of the isotope composition of atmospheric ozone is ~100‰ (referenced to atmospheric O2). Previous photochemical models, which considered the isotope fractionation processes from both formation and photolysis of ozone, predicted δ49O3 and δ50O3 values, in δ49O3 versus δ50O3 space, that are >10‰ larger than the measurements. We propose that the difference between the model and observations could be explained either by the temperature variation, Chappuis band photolysis, or a combination of the two and examine them. The isotopic fractionation associated with ozone formation increases with temperature. Our model shows that a hypothetical reduction of ~20 K in the nominal temperature profile could reproduce the observations. However, this hypothesis is not consistent with temperatures obtained by in situ measurements and NCEP Reanalysis. Photolysis of O3 in the Chappuis band causes O3 to be isotopically depleted, which is supported by laboratory measurements for 18O18O18O but not by recent new laboratory data made at several wavelengths for 49O3 and 50O3. Cloud reflection can significantly enhance the photolysis rate and affect the spectral distribution of photons, which could influence the isotopic composition of ozone. Sensitivity studies that modify the isotopic composition of ozone by the above two mechanisms are presented. We conclude isotopic fractionation occurring in photolysis in the Chappuis band remains the most plausible solution to the model-observation discrepancy. Implications of our results for using the oxygen isotopic signature for constraining atmospheric chemical processes related to ozone, such as CO2, nitrate, and the hydroxyl radical, are discussed.

LEO Satellites Constellation-to-Ground QKD Links: Greek Quantum Communication Infrastructure Paradigm

Quantum key distribution (QKD) has gained a lot of attention over the past few years, but the implementation of quantum security applications is still challenging to accomplish with the current technology. Towards a global-scale quantum-secured network, satellite communications seem to be a promising candidate to successfully support the quantum communication infrastructure (QCI) by delivering quantum keys to optical ground terminals. In this research, we examined the feasibility of satellite-to-ground QKD under daylight and nighttime conditions using the decoy-state BB84 QKD protocol. We evaluated its performance on a hypothetical constellation with 10 satellites in sun-synchronous Low Earth Orbit (LEO) that are assumed to communicate over a period of one year with three optical ground stations (OGSs) located in Greece. By taking into account the atmospheric effects of turbulence as well as the background solar radiance, we showed that positive normalized secure key rates (SKRs) up to 3.9×10−4 (bps/pulse) can be obtained, which implies that satellite-to-ground QKD can be feasible for various conditions, under realistic assumptions in an existing infrastructure.

Modified Vegetation Detection Index Using Different-Spectral Signature

The Normalization Difference Vegetation Index (NDVI), for many years, was widely used in remote sensing for the detection of vegetation land cover. This index uses red channel radiances (i.e., 0.66 μm reflectance) and near-IR channel (i.e., 0.86 μm reflectance). In the heavy chlorophyll absorption area, the red channel is located, while in the high reflectance plateau of vegetation canopies, the Near-IR channel is situated. Senses of channels (Red & Near- IR) read variance depths over vegetation canopies. In the present study, a further index for vegetation identification is proposed. The normalized difference vegetation shortwave index (NDVSI) is defined as the difference between the cubic bands of Near- IR and Shortwave infrared radiation (SWIR) divided by their sums. The radiances or reflectances are included in this index from the Near-IR channel and WSIR2 channel (2.1 μm). The NDVSI is less sensitivite to atmospheric effects as compared to NDVI. By comparing the one NDVSI index with the two indexes (NDVI, SAVI) of vegetation cover, good correlations were found between NDVI and NDVSI (R2=0.917) and between SAVI and NDVSI (R2=0.809. Accordingly, the proposed index can be taken into consideration as an independent vegetation index

The TROPOSIF global sun-induced fluorescence dataset from the Sentinel-5P TROPOMI mission

The first satellite-based global retrievals of terrestrial sun-induced chlorophyll fluorescence (SIF) were achieved in 2011. Since then, a number of global SIF datasets with different spectral, spatial, and temporal sampling characteristics have become available to the scientific community. These datasets have been useful to monitor the dynamics and productivity of a range of vegetated areas worldwide, but the coarse spatiotemporal sampling and low signal-to-noise ratio of the data hamper their application over small or fragmented ecosystems. The recent advent of the Copernicus Sentinel-5P TROPOMI mission and the high quality of its data products promise to alleviate this situation, as TROPOMI provides daily global measurements at a much denser spatial and temporal sampling than earlier satellite instruments. In this work, we present a global SIF dataset produced from TROPOMI measurements within the TROPOSIF project funded by the European Space Agency. The current version of the TROPOSIF dataset covers the time period between May 2018 and April 2021. Baseline SIF retrievals are derived from the 743–758 nm window. A secondary SIF dataset derived from an extended fitting window (735–758 nm window) is included. This provides an enhanced signal-to-noise ratio at the expense of a higher sensitivity to atmospheric effects. Spectral reflectance spectra at seven 3 nm windows devoid of atmospheric absorption within the 665–785 nm range are also included in the TROPOSIF dataset as an important ancillary variable to be used in combination with SIF. The methodology to derive SIF and ancillary data as well as results from an initial data quality assessment are presented in this work. The TROPOSIF dataset is available through the following digital object identifier (DOI): https://doi.org/10.5270/esa-s5p_innovation-sif-20180501_20210320-v2.1-202104 (Guanter et al., 2021).

Modelling the control of groundwater on landslides triggering: the respective role of atmosphere and rainfall during typhoons

Landslides are often triggered by catastrophic events, among which earthquakes and rainfall are the most depicted. However, very few studies have focused on the effect of atmospheric pressure on slope stability, even though weather events such as typhoons are associated with significant atmospheric pressure changes. Indeed, both atmospheric pressure changes and rainfall-induced groundwater level change can generate pore pressure changes with similar amplitude. In this paper, we assess the respective impacts of atmospheric effects and rainfall over the stability of a hillslope. An analytical model of transient groundwater dynamics is developed to compute slope stability for finite hillslopes. Slope stability is evaluated through a safety factor based on the Mohr-Coulomb failure criterion. Both rainfall infiltration and atmospheric pressure variations, which impact slope stability by modifying the pore pressure of the media, are described by diffusion equations. The models have then been forced by weather data from different typhoons that were recorded over Taiwan. While rainfall infiltration can induce pore pressure change up to hundred kPa, its effects is delayed in time due to diffusion. To the contrary, atmospheric pressure change induces pore pressure changes not exceeding a few kPa, but its effect is instantaneous. Moreover, the effect of rainfall infiltration on slope stability decreases towards the toe of the hillslope and is cancelled where the water table reaches the surface, leaving atmospheric pressure change as the main driver of slope instability. This study allows for a better insight of slope stability through pore pressure analysis, and shows that atmospheric effects shouldn’t always be neglected.