Search Results (8)

The geochemical monitoring of volcanic activity today relies largely on remote sensing, but the combination of this approach together with soil gas monitoring, using the appropriate parameters, is still not widely used. The main purpose of this study was to correlate data from crater gas emissions with flank emissions of soil gases at Mt. Etna volcano from June 2006 to December 2020. Crater SO₂ fluxes were measured from fixed stations around the volcano using the DOAS technique and applying a modeled clear-sky spectrum. The SO₂/HCl ratio in the crater plume was measured with the OP-FTIR technique from a transportable instrument, using the sun as an IR source. Soil CO₂ efflux coupled with the ²²⁰Rn/²²²Rn activity ratio in soil gases (named SGDI) were measured at a fixed monitoring site on the east flank of Etna. All signals acquired were subject both to spectral analysis and to filtering of the periodic signals discovered. All filtered signals revealed changes that were nicely correlated both with other geophysical signals and with volcanic eruptions during the study period. Time lags between parameters were explained in terms of different modes of magma migration and storage inside the volcano before eruptions. A comprehensive dynamic degassing model is presented that allows for a better understanding of magma dynamics in an open-conduit volcano. Full article

Previous researchers have detailed the problems in measuring the thermal resistance value of a whole roof assembly under hot conditions due to the uncertainty of the outdoor environment. Currently, no established method exists to experimentally investigate an entire thermal roof performance under a steady-state condition. This article details the properties of the indoor solar simulator and the research methods undertaken to measure the thermal resistance value of roof assembly. The indoor solar simulator utilizes 40 halogen bulbs to accurately replicate sun radiation. Thermocouples and heat flux sensors are installed at several locations on the roof assembly to quantify the heat transmission occurring through it. The thermal resistance value is determined by adding up the average difference in temperature across the external and internal roof surfaces and dividing the total amount by the total of all averaged heat fluxes. Subsequently, this study investigates the thermal efficiency of residential roof assemblies that comprise various insulation materials frequently employed in Malaysia, including stone wool, mineral glass wool, reflective bubble foil insulation, and radiant barriers. The analysis showed that the roof configurations with bubble foil reflective insulation produce superior thermal resistance values when coupled with enclosed air space or mass insulation, with thermal resistance values ranging between 2.55 m²K/W and 3.22 m²K/W. It can be concluded that roof configurations with bubble foil reflective insulation resulted in high total thermal resistance and passed the minimum thermal resistance value of 2.5 m²K/W under the Malaysian Uniform Building By-Law 38 (A) requirements. Furthermore, the radiant barrier produced a high thermal resistance value of 2.50 m²K/W when installed parallel to a 50 mm enclosed air space, emphasising the crucial function of an enclosed air space next to a reflective foil to resist the incoming heat radiation. The findings from this research can help building professionals determine the optimum insulation for residential building roofs in Malaysia. Full article

In order to establish a transferring chain from a photon flux of a single-photon source in quantum radiometry, the nonlinearity of the photodetector needs to be accurately measured. Using the flux superposition method, a nonlinearity measurement setup has been designed. The measurement setup consists of two tungsten halogen lamps, parent–child integrating spheres, an adjustable aperture, a diaphragm tube, and an optical filter. It has the advantage of low polarization error, low interference error, and low stray light effect. The Si photodiode to be measured is cooled to −40 °C to obtain a low noise level for low-flux radiation measurement. The nonlinearity of the Si photodetector is measured for photocurrent ranges from 10⁻¹² A~10⁻⁶ A level, with a relative standard uncertainty from 0.0092~0.023%. The relative standard uncertainty of the nonlinearity correction factor ranged from 0.023~0.049%. Full article

Sodium hypochlorite (NaClO) solution is wildly used to remove membrane fouling-derived organic materials and restore membrane flux, which can result in the formation of halogenated by-products. To reduce the halogenated by-products, a combined cleaning process with NaClO and peroxides including hydrogen peroxide (H₂O₂), peroxydisulfate (PDS), and peroxymonosulfate (PMS) were applied in offline mode to remove the organic fouling. It was found that all the combined cleaning processes could effectively restore the membrane flux. Compared with the process of NaClO cleaning followed by peroxide cleaning (NaClO–peroxide), fewer halogenated by-products were generated in the NaClO post-combined cleaning process (peroxide–NaClO), and the PDS–NaClO cleaning process exhibited the best performance in controlling by-products. Overall, most by-product generation showed a positive correlation with reaction time and temperature. Full article

Dynamical processes and changes in the ozone layer in the Arctic stratosphere during the winter of 2019–2020 were analyzed using numerical experiments with a chemistry-transport model (CTM) and reanalysis data. The results of numerical calculations using CTM with Dynamic parameters specified from the Modern Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) reanalysis data, carried out according to several scenarios of accounting for the chemical destruction of ozone, demonstrated that both Dynamic and chemical processes contribute significantly to ozone changes over the selected World Ozone and Ultraviolet Radiation Data Centre network stations, both in the Eastern and in the Western hemispheres. Based on numerical experiments with the CTM, the specific Dynamic conditions of winter–spring 2019–2020 described a decrease in ozone up to 100 Dobson Units (DU) in the Eastern Hemisphere and over 150 DU in the Western Hemisphere. In this case, the photochemical destruction of ozone in both the Western and Eastern Hemispheres at a maximum was about 50 DU with peaks in April in the Eastern Hemisphere and in March and April in the Western Hemisphere. Heterogeneous activation of halogen gases on the surface of polar stratospheric clouds, on the one hand, led to a sharp increase in the destruction of ozone in chlorine and bromine catalytic cycles, and, on the other hand, decreased its destruction in nitrogen catalytic cycles. Analysis of wave activity using 3D Plumb fluxes showed that the enhancement of upward wave activity propagation in the middle of March over the Gulf of Alaska was observed during the development stage of the minor sudden stratospheric warming (SSW) event that led to displacement of the stratospheric polar vortex to the north of Canada and decrease of polar stratospheric clouds’ volume. Full article

The changes in the morphology and the electrophysical properties of the Cr/n-Si (111) structure depending on the rapid thermal treatment were considered in this study. The chromium films of about 30 nm thickness were deposited via magnetron sputtering. The rapid thermal treatment was performed by the irradiation of the substrate’s back side with the incoherent light flux of the quartz halogen lamps in nitrogen medium up to 200–550 °C. The surface morphology was investigated, including the grain size, the roughness parameters and the specific surface energy using atomic force microscopy. The resistivity value of the chromium films on silicon was determined by means of the four-probe method. It was established that at the temperatures of the rapid thermal treatment up to 350 °C one can observe re-crystallization of the chromium films with preservation of the fine grain morphology of the surface, accompanied by a reduction in the grain sizes, specific surface energy and the value of specific resistivity. At the temperatures of the rapid thermal treatment from 400 to 550 °C there originates the diffusion synthesis of the chromium disilicide CrSi₂ with the wave-like surface morphology, followed by an increase in the grain sizes, roughness parameters, the specific surface energy and the specific resistivity value. Full article

To make Europe competitive in the field of astronomical sensors and detectors, the main goal of this research is to provide the capability to manufacture high performance infrared focal plane arrays (FPA) devoted to scientific and astronomical ground and space telescope missions. This paper presents the main outcome of an international project with the highest standard of quality for this detector. The resulting detector is a sensor with a hybridized MCT (HgCdTe) epilayer on a CdZnTe substrate of 2 k × 2 k pixels and 15 μm of pixel pitch. On this framework, an optical setup has been developed at the IFAE optical laboratory with the capabilities to perform the characterization of a near-infrared (NIR) detector covering the range from 800 to 2500 nm. The optical setup is mainly composed of a power controlled quartz–halogen (QTH) lamp and an astigmatism-corrected Czerny–Turner monochromator with two diffraction gratings covering the detector wavelength range with a minimum resolution of ∼1 nm. A temperature stabilized gold-coated integration sphere provides a uniform and monochromatic illumination, while an InGaAs photodiode located at the north pole of the integration sphere is used to measure the radiant flux toward the detector. The whole setup is fully controlled by a Labview™ application and synchronized with the detector’s readout electronic (ROE). Full article

The 2014–2015 Bárðarbunga fissure eruption at Holuhraun in central Iceland was distinguished by the high emission of gases, in total 9.6 Mt SO₂, with almost no tephra. This work collates all ground-based measurements of this extraordinary eruption cloud made under particularly challenging conditions: remote location, optically dense cloud with high SO₂ column amounts, low UV intensity, frequent clouds and precipitation, an extensive and hot lava field, developing ramparts, and high-latitude winter conditions. Semi-continuous measurements of SO₂ flux with three scanning DOAS instruments were augmented by car traverses along the ring-road and along the lava. The ratios of other gases/SO₂ were measured by OP-FTIR, MultiGAS, and filter packs. Ratios of SO₂/HCl = 30–110 and SO₂/HF = 30–130 show a halogen-poor eruption cloud. Scientists on-site reported extremely minor tephra production during the eruption. OPC and filter packs showed low particle concentrations similar to non-eruption cloud conditions. Three weather radars detected a droplet-rich eruption cloud. Top of eruption cloud heights of 0.3–5.5 km agl were measured with ground- and aircraft-based visual observations, web camera and NicAIR II infrared images, triangulation of scanning DOAS instruments, and the location of SO₂ peaks measured by DOAS traverses. Cloud height and emission rate measurements were critical for initializing gas dispersal simulations for hazard forecasting. Full article