Monitoring landfill volatile organic compounds emissions by an uncrewed aerial vehicle platform with infrared and visible-light cameras, remote monitoring, and sampling systems.

An uncrewed aerial vehicle (UAV) platform equipped with dual imaging cameras, a gas sampling system, and a remote synchronous monitoring system was developed to sample and analyze volatile organic compounds (VOCs) emitted from landfills. The remote synchronous monitoring system provided real-time video to administrators with specific permissions to assist in identifying sampling sites within extensive landfill areas. The sampling system included four kits capable of collecting samples from different locations during a single flight mission. Each kit comprised a 1 L Tedlar bag for measuring landfill VOC concentrations according to the TO-15 method prescribed by the US Environmental Protection Agency. The air sample was introduced into a Tedlar bag via pumping. A known volume of the sample was subsequently concentrated using a solid multisorbent concentrator. Following this, the sample underwent cold trap concentration and thermal desorption. The concentrated sample was then transferred to a chromatography-mass spectrometry system for separation and analysis. Since the anaerobic catabolism of organic waste is exothermic and emits VOCs, this study employed UAV thermal imaging to locate principal emission sources for sampling. Visible-light imaging helped identify newer or older landfill sections, aiding in the selection of appropriate sampling sites, particularly when surfaces were thermally disturbed by solar radiation. Field measurements were conducted under three meteorological conditions: sunny morning, cirrus morning, and thin cloud evening (2 h after sunset), identifying 119, 122, and 111 chemical species respectively. The sequence of total VOC concentrations measured correlated with the meteorological conditions as follows: cirrus morning > thin cloud evening > sunny morning. The results indicated that ambient temperature and global solar radiation significantly influenced daytime gas emissions from landfills. Evening thermal images, unaffected by solar heating, facilitated more accurate identification of major VOC emission points, resulting in higher VOC concentrations compared to those recorded in the sunny morning. VOCs from the landfill were categorized into nine organic groups: alkanes, alkenes, carbonyls, aromatics, alcohols, esters, ethers, organic oxides, and others. The classification was based on carbon-containing compounds (Cn, where the compound contains n carbon atoms). Alkanes were predominant in terms of Cn presence, followed by alcohols and carbonyls. Among the organic groups, organic oxides, particularly 2-heptyl-1,3-dioxolane, exhibited the highest concentrations, succeeded by alkenes. Sampling under cloudy conditions or in the evening is recommended to minimize the effects of surface temperature anomalies caused by solar radiation, which vary due to differences in land composition.

Design of Inner Matching Three-Stage High-Power Doherty Power Amplifier Based on GaN HEMT Model.

This paper introduces the structure and characteristics of an internal-matching high-power Doherty power amplifier based on GaN HEMT devices with 0.25 µm process platforms from the Nanjing Electronic Devices Institute. Through parameter extraction and load-pull testing of the model transistor, an EE_HEMT model for the 1.2 mm gate-width GaN HEMT device was established. This model serves as the foundation for designing a high-power three-stage Doherty power amplifier. The amplifier achieved a saturated power gain exceeding 9 dB in continuous wave mode, with a saturated power output of 49.7 dBm. The drain efficiency was greater than 65% at 2.6 GHz. At 9 dB power back-off point, corresponding to an output power of 40.5 dBm, the drain efficiency remained above 55%. The performance of the amplifier remains consistent within the 2.55-2.62 GHz frequency range. The measured power, efficiency, and gain of the designed Doherty power amplifier align closely with the simulation results based on the EE_HEMT model, validating the accuracy of the established model. Furthermore, the in-band matching design reduces the size and weight of the amplifier. The amplifier maintains normal operation even after high and low-temperature testing, demonstrating its reliability. In conjunction with DPD (digital pre-distortion) for the modulated signal test, the amplifier exhibits extremely high linearity (ACLR < -50.93 dBc). This Doherty power amplifier holds potential applications in modern wireless communication scenarios.

Prediction and analysis of atmospheric visibility in five terrain types with artificial intelligence.

Scattering visiometers are widely used to measure atmospheric visibility; however, visibility is difficult to measure accurately because the extinction coefficient decays exponentially with visual range according to the Koschmid's law. Moreover, models for predicting visibility are lacking due to the lack of accurate visibility observations to verify. This study formulated an artificial intelligence method for measuring atmospheric visibility in five topographical regions: hills, basins, plains, alluvial plains, and rift valleys. Four air pollution factors and five meteorological factors were selected as independent variables for predicting visibility by using three artificial intelligence models, namely a support vector machine (SVM) model, a multilayer perceptron (MLP) model, and an extreme gradient boosting (XGBoost) model. The GridSearchCV function was used to automatically tune model hyperparameters to determine the optimal parameter values of the three models for the five target areas. The predictions of the aforementioned three models underwent considerable considerably scale shrinking relative to observed values. The inappropriately low predicted visibility values might have been caused by the use of inaccurate observations for training. To solve this problem, formulas of scale ratio and downshift were used to adjust the predicted values. Statistical measurements of model performance measures by five quantitative methods (e.g., correlation coefficient, mean absolute error) showed that adjusted predictions were in strong agreement with the observation data for the five target areas. Therefore, the adjusted prediction has high reliability. Because of obvious differences in the topography, weather, and air quality of the five target areas, different models provided optimal predictions for different areas. In densely populated western Taiwan, the MLP model is most suitable for predicting visibility on hills whereas the XGBoost model is most suitable for predicting visibility on basins and plains. In eastern Taiwan, the SVM model is most suitable for predicting visibility on alluvial plains and rift valleys. Thus, the optimal prediction model should be identified according to the conditions in each area. These results can inform decision-making processes or improve visibility predicting in specific areas.

The impacts of air quality and secondary organic aerosols formation on traffic accidents in heavy fog-haze weather.

This study estimated changes in the levels of three components of regional haze, namely fine particulate matter (PM2.5), relative humidity (RH), and secondary organic aerosols (SOAs), at the time of two severe traffic accidents on a coastal expressway and a freeway in the Jianan Plain in southwestern Taiwan to understand the impact of weather and air quality factors on the low visibility. Monitoring data and surveillance images from four nearby air quality monitoring stations were collected to determine the precise causes of the poor visibility-related accidents. The study applied a haze extraction method to the images to achieve demisting, and the processed data were used to assess the relationship between the haze components and visibility during the accidents. The correlation between visibility and the haze components was assessed. The results revealed that the RH levels dropped significantly at the time of the accidents, signifying that moisture was not the main haze-fog component. The haze components can be ordered as follows in terms of their correlation with (and thus effect on) local visibility: PM2.5 > SOAs > RH. The spatial distributions and evolutions of the three components indicated that the PM2.5 concentrations remained high from midnight until early morning but decreased slightly at the time of both accidents. By contrast, the concentration of ultrafine SOA particles, which can scatter and absorb light to reduce road visibility, increased rapidly before both accidents. Therefore, PM2.5 and SOAs were two non-negligible factors of low visibility during the accidents, especially SOAs.

Mn-incorporated ferrihydrite for Cr(VI) immobilization: Adsorption behavior and the fate of Cr(VI) during aging.

Chromium(VI) (Cr(VI)) is an environmental priority pollutant, and its mobility in natural environment is strongly controlled by ferrihydrite. Ferrihydrite always contains various ions, which may change the properties of ferrihydrite, thereby affecting the behavior of pollutants. This study aims to investigate the adsorption of Cr(VI) by Mn-incorporated ferrihydrite and the mobility behavior of Cr(VI) during aging. Results showed that the incorporation of Mn enhanced the adsorption of Cr(VI) on ferrihydrite, and the adsorption performance increased with the increase of Mn content. The maximum adsorption capacity for Cr(VI) reached to 48.5 mg/g with molar ratio of Mn/Fe 5%, while it was 36.1 mg/g for pure ferrihydrite. After aging for 7 days, ferrihydrite transformed into goethite and hematite. The adsorbed Cr(VI) on the surface of ferrihydrite was released into the solution during aging. The incorporation of Mn retarded the transformation of ferrihydrite, which inhibited the migration of adsorbed Cr(VI). Nevertheless, the incorporation of Mn resulted in the transformation of adsorbed Cr(VI) to non-desorbed Cr(VI), thereby enhancing the retention of Cr(VI). Our results suggest that the incorporation of Mn into ferrihydrite has an important role on the mobility of Cr(VI), which enhances our understanding of the behavior of Cr(VI) in the environment.

Mobility and transformation of Cr(VI) on the surface of goethite in the presence of oxalic acid and Mn(II).

Goethite is an effective adsorbent for hexavalent chromium (Cr(VI)). Oxalic acid and other organic acids will affect the release, immobilization, and bioavailability of Cr(VI) in nature on the mineral surface. Mn(II) can accelerate the reduction of Cr(VI) with oxalic acid. Herein, the effects of oxalic acid and Mn(II) on the mobilization and transformation of adsorbed Cr(VI) on the surface of goethite were investigated in this study. The results revealed that Mn(II) could increase the adsorption of Cr(VI) by increasing the positive charge on the surface of goethite. The complexation of oxalic acid with the surface of goethite caused the adsorbed Cr(VI) to be released into the solution. Moreover, oxalic acid could undergo redox with adsorbed Cr(VI) through electron conduction on the surface of goethite, thereby resulting in the transformation of adsorbed Cr(VI) to Cr(III). During the reaction in the presence of oxalic acid, the concentration of Cr(III) increased from 0 to 13.9 mg/L. In addition, Mn(II), oxalic acid, and Cr(VI) could form unstable ester-like species in the solution, which accelerated the reduction of Cr(VI) to Cr(III). These findings of this study may enrich our understanding of the behaviors of Cr(VI) in the coexistence of goethite, oxalic acid, and Mn(II).

The scale-free network behavior of ambient volatile organic compounds.

A scale-free network model with surface and vertical field measurements was used to identify the connectivity distribution of the scale-free network behavior of ambient volatile organic compounds (VOCs). The results show that the carbon number (C(n)) with the total amount of C(n) compounds (P(C(n))) possesses an explicit relationship with the scale-free network behavior. The proportionate coefficient (α) and exponent (γ) of the scale-free network model with spatial and temporal variations are estimated and discussed. The analytical results demonstrate that although photochemical reactions cause the VOCs fraction variation, they do not alter the fraction of C(n) compounds observably. Therefore, the values of α and of γ did not vary with time, but with local regional characteristics. The results indicate that the influence of local VOCs emissions occurs at a height of 100 m, but becomes insufficient at a height of 300 m. Air mass mixing increases with greater height; thus, the influence of regional characteristics at a height of 700 m is low. Finally, a successful empirical model was established to evaluate the distribution of surface VOCs in various regions.

A new scale-free network model for simulating and predicting epidemics.

The course of epidemics often resembles a scale-free network, but some specific elements should be considered in developing a new model. This study introduces a time-shifting and discontinuous forcing function H into the scale-free network model to fit the specific period and intensity of the infection, and redefines the probability p as abortive infection rate. For the non-human vectors or hosts, three new factors (new connectivity K(i)(t), new links M, and time delay τ) were introduced in the proposed model of this study. The simulation results of six types of epidemic transmissions show that the proposed Scale-Free Epidemic Models, SFE-1 and SFE-2, are accurate. SFE-1 model and SFE-2 model are useful for the transmission categories from human and insects/vertebrates, respectively. Further comparisons of different races/ethnicities and different transmission categories of AIDS cases in the United States were also analyzed. Both SFE models can be used to predict epidemics and can suggest the results more clearly, irrespective of whether the epidemics are under control. Therefore, the proposed SFE models can help the government determine the level of caution required and predict the results of policy decisions, thus helping to balance socioeconomic and health concerns.

Epitaxial photostriction-magnetostriction coupled self-assembled nanostructures.

Self-assembled vertical nanostructures take advantage of high interface-to-volume ratio and can be used to design new functionalities by the choice of a proper combination of constituents. However, most of the studies to date have emphasized the functional controllability of the nanostructures using external electric or magnetic fields. In this study, to introduce light (or photons) as an external control parameter in a self-assembled nanostructure system, we have successfully synthesized oxide nanostructures with CoFe(2)O(4) nanopillars embedded in a SrRuO(3) matrix. The combination of photostrictive SrRuO(3) and magnetostrictive CoFe(2)O(4) in the intimately assembled nanostructures leads to a light-induced, ultrafast change in magnetization of the CoFe(2)O(4) nanopillars. Our work demonstrates a novel concept on oxide nanostructure design and opens an alternative pathway for the explorations of diverse functionalities in heteroepitaxial self-assembled oxide nanostructures.

Local conduction at the BiFeO(3)-CoFe(2)O(4) tubular oxide interface.

In strongly correlated oxides, heterointerfaces, manipulating the interaction, frustration, and discontinuity of lattice, charge, orbital, and spin degrees of freedom, generate new possibilities for next generation devices. In this study, existing oxide heterostructures are examined and local conduction at the BiFeO(3)-CoFe(2)O(4) vertical interface is found. In such hetero-nanostructures the interface cannot only be the medium for the coupling between phases, but also a new state of the matter. This study demonstrates a novel concept on for oxide interface design and opens an alternative pathway for the exploration of diverse functionalities in complex oxide interfaces.

Synthesis, control, and characterization of surface properties of Cu2O nanostructures.

The ability to control nanostructure shape can strongly affect the overall properties of that system. Here we report the ability to deterministically control nanostructure shape, surface facet orientation, and surface potentials of the oxide semiconductor Cu(2)O. Epitaxial Cu(2)O nanostructures with different shapes and geometries-from boxes to pyramids to huts-have been grown via pulsed laser deposition. By varying the adatom energy and flux per laser pulse we can tune the nature of the nanostructure geometry, the total density of features, the relative surface area to volume ratio, and can create polar, nonequilibrium surfaces. In addition to detailed structural analysis of the nanostructures, high-resolution Kelvin probe force microscopy has been used to systematically analyze the surface potential and electronic structure of the (100), (110), and (111) surfaces of Cu(2)O. These studies suggest that each surface, possessing a unique atomic structure, gives rise to different surface energy levels of conduction and valence bands and the formation of electronic surface junctions. The implication of these findings in terms of a range of applications is discussed.

Misorientation control and functionality design of nanopillars in self-assembled perovskite-spinel heteroepitaxial nanostructures.

In this study, advanced control of crystallographic orientations and magnetic properties of self-assembled nanostructures via rational selections of substrates is demonstrated. We show that in the perovskite-spinel BiFeO(3)-CoFe(2)O(4) model system the crystal orientation of self-assembled CoFe(2)O(4) nanopillars can be tuned among (001), (011), and (111), while that of the BiFeO(3) matrix is fixed in (001). Moreover, the resultant CoFe(2)O(4) nanopillars appear in various shapes: pyramid, roof, and triangular platform, respectively. The tunable nanostructures through this approach enable the control of material functionality such as the magnetic anisotropy of CoFe(2)O(4). This study opens a new pathway for the engineering of self-assembled heteroepitaxial nanostructures.

A molecular quantized charge pump.

A novel single electron pump based on individual molecules (a single wall carbon nanotube) is discussed in terms of the hybrid superconducting-normal conducting pumping principle. A concept demonstration device has been built based on a carbon nanotube contacted by Nb-Ti leads. Charge current quantization is achieved through rf modulation of the back gate voltage. The device is able to transfer a given number of electrons per pumping cycle. Single electron pumping is achieved for pumping frequencies up to 80 MHz.

Electrical and optical transport of GaAs/carbon nanotube heterojunctions.

Heterojunctions consisting of nanotubes and an industrialized semiconductor-GaAs have been produced, and their transport properties were studied. We found that the p-doped GaAs forms an ohmic contact with a nanotube but the n-doped GaAs/nanotube heterojunction is rectifying. Analysis of measurement results at various temperatures shows that tunneling transport plays an important role. We also observed photovoltaic effects in n-GaAs/nanotube junction with the illumination of a green laser or desk lamp.