Search Results (20)

As part of the ongoing transition from fossil fuels to renewable energies, advances are particularly expected in terms of safe and cost-effective solutions. Publicising instances of such advances and emphasising global safety considerations constitute the rationale for this communication. Knowing that high-strength steels can prove economically relevant in the foreseeable future for transporting hydrogen in pipelines by limiting the pipe wall thickness required to withstand high pressure, one advance relates to a bench designed to assess the safe transport or renewable-energy-related buffer storage of hydrogen gas. That bench has been implemented at the technology readiness level TRL 6 to test initially intact, damaged, or pre-notched 500 mm-long pipe sections with nominal diameters ranging from 300 to 900 mm in order to appropriately validate or question the use of reputedly satisfactory predictive models in terms of hydrogen embrittlement and potential corollary failure. The other advance discussed herein relates to the reactivation of a previously fruitful applied research into safe mass solid-state hydrogen storage by magnesium hydride through a new public–private partnership. This latest development comes at a time when markets have started driving the hydrogen economy, bearing in mind that phase-change materials make it possible to level out heat transfers during the absorption/melting and solidification/desorption cycles and to attain an overall energy efficiency of up to 80% for MgH₂-based compacts doped with expanded natural graphite. Full article

A novel double-cycle alternating-flow diode-pumped potassium vapor laser is proposed, theoretically modeled and simulated. The results show that the optical-to-optical efficiency of the laser increases with increasing gas flow rates, although at high flow rates the rate of increase in efficiency decreases. The optical-to-optical efficiency reaches 74.8% at a pump power density of 30 kW/cm² and a gas flow rate of 50 m/s. The optical-to-optical efficiency of the laser is greater with a narrow linewidth pump and high buffer gas pressure. The optical-to-optical efficiency of a flow gas cell is higher than that of a static gas cell. There is an optimal gas cell length that provides the highest optical-to-optical efficiency. At higher pump power densities, higher flow rates are required to obtain higher optical-to-optical efficiencies. Full article

The Neoproterozoic Bure adakitic rock in the western Ethiopia shield is a newly discovered magmatic rock type. However, the physicochemical conditions during its formation, and its source characteristics are still not clear, restricting a full understanding of its petrogenesis and geodynamic evolution. In this study, in order to shed light on the physicochemical conditions during rock formation and provide further constraints on the petrogenesis of the Bure adakitic rock, we conduct electron microprobe analysis on K-feldspar, plagioclase, and biotite. Additionally, we investigate the trace elements and Hf isotopes of zircon, and the Sr-Nd isotopes of the whole rock. The results show that the K-feldspar is orthoclase (Or = 89.08~96.37), the plagioclase is oligoclase (Ab = 74.63~85.99), and the biotite is magnesio-biotite. Based on the biotite analysis results, we calculate that the pressure during rock formation was 1.75~2.81 kbar (average value of 2.09 kbar), representing a depth of approximately 6.39~10.2 km (average value of 7.60 km). The zircon thermometer yields a crystallization temperature of 659~814 °C. Most of the (Ce/Ce*)_D values in the zircons plotted above the Ni-NiO oxygen buffer pair, and the calculated magmatic oxygen fugacity (logfO₂) values vary from −18.5 to −4.9, revealing a relatively high magma oxygen fugacity. The uniform contents of FeO, MgO, and K₂O in the biotite suggest a crustal magma source for the Bure adakitic rock. The relatively low (⁸⁷Sr/⁸⁶Sr)_i values of 0.70088 to 0.70275, positive ε_Nd(t) values of 3.26 to 7.28, together with the positive ε_Hf(t) values of 7.64~12.99, suggest that the magma was sourced from a Neoproterozoic juvenile crust, with no discernable involvement of a pre-Neoproterozoic continental crust, which is coeval with early magmatic stages in the Arabian Nubian Shield elsewhere. Additionally, the mean Nd model ages demonstrate an increasing trend from the northern parts (Egypt, Sudan, Afif terrane of Arabia, and Eritrea and northern Ethiopia; 0.87 Ga) to the central parts (Western Ethiopia shield; 1.03 Ga) and southern parts (Southern Ethiopia Shield, 1.13 Ga; Kenya, 1.2 Ga) of the East African Orogen, which indicate an increasing contribution of pre-Pan-African crust towards the southern part of the East African Orogen. Based on the negative correlation between MgO and Al₂O₃ in the biotite, together with the Lu/Hf-Y and Yb-Y results of the zircon, we infer that the Bure adakitic rock was formed in an arc–arc collision orogenic environment. Combining this inference with the whole rock geochemistry and U-Pb age of the Bure adakitic rock, we further propose that the rock is the product of thickened juvenile crust melting triggered by the Neoproterozoic Pan-African Orogeny. Full article

A multi-stack fuel cell system (MFCS) is a promising solution for high-power PEM fuel cell applications. This paper proposes an optimized stack allocation approach for power allocation, considering economy and dynamics to establish integrated subsystems with added functional components. The results show that an MFCS with target powers of 20 kW, 70 kW, and 120 kW satisfies lifetime and efficiency factors. The common rail buffer at the air supply subsystem inlet stabilizes pressure, buffers, and diverts. By adjusting the volume of the common rail buffer, it is possible to reduce the maximum instantaneous power and consumption of the air compressor. The integrated hydrogen supply subsystem improves hydrogen utilization and reduces parasitic power consumption. However, the integrated thermal subsystem does not have the advantages of integrated gas supply subsystems, and its thermal management performance is worse than that of a distributed thermal subsystem. This MFCS provides a solution for high-power non-average distribution PEM fuel cell systems. Full article

Pyroelectric materials, are those materials with the property that in the absence of any externally applied electric field, develop a built-in spontaneous polarization in their unit cell structure. They are regarded as ideal detector elements for infrared applications because they can provide fast response time and uniform sensitivity at room temperature over all wavelengths. Crystals of the perovskite Lead Titanate (PbTi${\mathrm{O}}_3$) family show pyroelectric characteristics and undergo structural phase transitions. They have a high Curie temperature (the temperature at which the material changes from the ferroelectric (polar) to the paraelectric (nonpolar) phase), high pyroelectric coefficient, high spontaneous polarization, low dielectric constant, and constitute important component materials not only useful for infrared detection, but also with vast applications in electronic, optic, and Micro-electromechanical systems (MEMS) devices. However, the preparation of large perfect, and pure single crystals of PbTi${\mathrm{O}}_3$ is challenging. Additionally, difficulties arise in the application of such bulk crystals in terms of connection to processing circuits, large size, and high voltages required for their operation. A number of thin film fabrication techniques have been proposed to overcome these inadequacies, among which, magnetron sputtering has demonstrated many potentials. By addressing these aspects, the review article aims to contribute to the understanding of the challenges in the field of pyroelectric materials, highlight potential solutions, and showcase the advancements and potentials of pyroelectric perovskite series including PbZrTiO₃ (PZT), ${\mathrm{P}\mathrm{b}}_{\mathrm{x}}{\mathrm{C}\mathrm{a}}_{1-\mathrm{x}}$ (PZN-PT), etc. for which PbTi${\mathrm{O}}_3$ is the end member. The review is presented in two parts. Part 1 focuses on material aspects, including preparation methods using magnetron sputtering and material characterization. We take a tutorial approach to discuss the progress made in epitaxial growth of lead titanate-based ceramics prepared by magnetron sputtering and examine how processing conditions may affect the crystalline quality of the growing film by linking to the properties of the substrate/buffer layer, growth substrate temperature, and the oxygen partial pressure in the gas mixture. Careful control and optimization of these parameters are crucial for achieving high-quality thin films with desired structural and morphological characteristics. Full article

The production of thin films has been extensively studied due to their unique properties that make them highly useful in a wide range of scientific and technological applications. Obtaining thin films with well-defined stoichiometry and crystallinity is a challenging task, especially when dealing with materials of complex stoichiometry. Among diverse methodologies for the manufacture of thin films, pulsed laser deposition (PLD) stands out as a versatile technique for producing crystalline films with complex chemical compositions. In this study, nanosecond PLD was employed to manufacture thin films of Ta-doped Li₇La₃Zr₂O₁₂ (LLZTO), a garnet-like oxide that has been proposed as solid electrolyte for Li-ion solid state batteries. Two distinct deposition atmospheres were investigated: vacuum conditions at 10⁻³ Pa and an oxygen-enriched environment with 10 Pa of O₂ gas buffer. To mitigate lithium losses during deposition, a minor addition of lithium oxide was incorporated into the target. The effects of deposition atmosphere and the impact of post-deposition annealing on the structural, compositional, and morphological properties of LLZTO thin films were analysed through a multi-technique approach. The results suggest deposition under oxygen pressure led to the growth of compact, crystalline films characterized by homogenous elemental distribution across the surface and throughout the film’s depth. These films closely resemble the composition of the target LLZTO material, offering valuable insights for the fabrication of high-quality complex oxide thin films. Full article

A high-pressure (HP) GaN nucleation layer (NL) was inserted between AlGaN buffer and an unintentionally doped (UID) GaN layer of an AlGaN/GaN HEMT on Si. The XRD and TEM showed that when the V/III ratio was optimized during the HP-GaN NL growth, the edge dislocation density in the HP-GaN NL layer could be reduced significantly. Experimental results exhibited a lower off-state leakage current, higher maximum I_D and G_m (corresponding to 22.5% and 21.7% improvement, respectively), and lower on-state resistance. These results demonstrate that the electrical properties of the AlGaN/GaN HEMT can be improved through the insertion of a HP-GaN NL. Full article

Inside a spin-exchange relaxation-free (SERF) co-magnetometer with a high-pressure buffer gas atomic cell, the magnetic field gradient causes the decoherence of atomic spins to produce magnetic-field gradient relaxation. This paper presents a new method for the accurate measurement of magnetic field gradient relaxation of alkali metal atoms and inert atoms of strongly coupled spin systems under triaxial magnetic field gradients in the K-Rb-²¹Ne co-magnetometer. The magnetic field gradient relaxation of alkali metal atoms is measured using a step magnetic field modulation method, and the magnetic field gradient relaxation of inert atoms is measured using a combined free induction decay and spin growth method. The method does not require the use of large background magnetic fields and RF fields to maintain the atoms in the SERF state, does not require additional optics, and is not affected by the pumping or detecting of optical power. A kinetic model that considers a large electron-equivalent magnetic field was designed and a gradient relaxation model was developed. The quadratic coefficients of the experimentally measured gradient relaxation curves fit the theoretical model well over the range of the applied magnetic field gradients, confirming the validity of the proposed method. Full article

Developing low-carbon advanced processes for sustainable wastewater treatment is of great importance to increase bioenergy recovery and to reduce the greenhouse gas effect. In this study, the influence of adding 25 g/L of granular activated carbon (GAC) on the process performance was studied with a lab-scale GAC amended anaerobic dynamic membrane (G-AnDMBR) used to treat real domestic wastewater, which was compared to a control bioreactor without the GAC addition (C-AnDMBR). Due to the initial adsorption effect of GAC and the high microbial activity of the attached biomass of GAC, the G-AnDMBR achieved a better removal of the total chemical oxygen demand (TCOD) and turbidity compared to the C-AnDMBR, with the average removal rate increasing from 82.1% to 86.7% and from 88.7% to 93.2%. The gaseous methane production increased from 0.08 ± 0.05 to 0.14 ± 0.04 L/d, and the total methane production rate was enhanced from 0.21 ± 0.11 to 0.23 ± 0.09 LCH₄/gCOD. Thus, the treatment performance of the G-AnDMBR was superior to that of the C-AnDMBR, and the addition of GAC could improve the effluent quality during the initial dynamic membrane formation process. In addition, the buffering effect of GAC made the G-AnDMBR maintain a relatively stable solution environment. The G-AnDMBR showed a transmembrane pressure (TMP) increasing rate of 0.045 kPa/d, which was obviously lower than that of the C-AnDMBR (0.057 kPa/d) because the nonfluidized GAC could trap fine sludge particles and adsorb soluble extracellular polymer substances (SEPSs), thus inhibiting the over formation of the dynamic membrane layer. A microbial property analysis indicated that GAC induced a change in the microbial community and enhanced the gene abundance of type IV pili and that it also potentially accelerated the direct interspecific electron transfer (DIET) among syntrophic bacteria and methanogens by enriching specific functional microorganisms. The results indicated that the integration of GAC and the AnDMBR process can be a cost-effective and promising alternative for domestic wastewater treatment and bioenergy recovery. Full article

Sulfur dioxide (SO₂) is a key indicator for fault diagnosis in sulfur hexafluoride (SF₆) gas-insulated equipment. In this work, an in situ photoacoustic detection system using an ultraviolet (UV) LED light as the excitation source was established to detect SO₂ in high-pressure SF₆ buffer gas. The selection of the SO₂ absorption band is discussed in detail in the UV spectral regions. Based on the result of the spectrum selection, a UV LED with a nominal wavelength of 285 nm and a bandwidth of 13 nm was selected. A photoacoustic cell, as well as a high-pressure sealed gas vessel containing it, were designed to match the output optical beam and to generate a PA signal in the high-pressure SF6 buffer gas. The performance of the proposed system was assessed in terms of linearity and detection limit. An SO₂ detection limit (1σ) of 0.17 ppm was achieved. Additionally, a correction method was supplied to solve PA signal derivation induced by pressure fluctuation. The method can reduce the derivation from about 5% to 1% in the confirmation experiment. Full article

Cyanotoxins are toxic metabolites produced by most cyanobacteria. In recent years, the occurrence of cyanobacterial blooms in aquatic ecosystems has temporally and spatially increased because of nutrient oversupply caused by human and also by climatic changes. This increase has a negative impact on water quality, ecosystem integrity, and human health. Cyanotoxins constitute a group of compounds with diverse physicochemical properties and their presence in drinkable, fishable, and recreational water is the main health-damaging cause. They are also able to bioaccumulate in plants and vegetables irrigated with contaminated water. Research on the development of suitable analytical methods is needed to establish early-warning strategies for the improved protectionof humans and ecosystems health. Liquid chromatography coupled with mass spectrometry (LC-MS) has been the preferred option for the control of these compounds, mainly using reverse-phase mode or hydrophilic interaction liquid chromatography (HILIC) in order to separate multiclass cyanotoxins of varying polarity, which cannot be handled by the commonly used reverse phase columns. In this work, we propose the use of capillary electrophoresis (CE) coupled with tandem mass spectrometry using triple quadrupole and positive electrospray ionization (CE-(ESI)-MS/MS) to determine a mixture of cyanotoxins with different polarity. CE is an advantageous alternative to LC given its short analysis times, high resolution, low sample and reagent volumes, and the use of silica capillaries and buffers as separation media, resulting in lower cost and low environmental impact. Moreover, CE allows the analysis of molecules hardly affordable by LC, such as polar and very similar compounds (e.g., isomers). The method is designed for the simultaneous determination of eight cyanotoxins belonging to three different classes: cyclic peptides (microcystin-LR, microcystin-RR, and nodularin), alkaloids (cylindrospermopsin, anatoxin-a), and three non-protein amino acids isomers (β-methylamino-L-alanine, 2,4-diaminobutyric acid, and N-(2-aminoethyl) glycine). Separation was achieved using an acidic background electrolyte (BGE) consisting in 2 M of formic acid (FA) and 20% acetonitrile in water. The proper separation and resolution of the three non-protein amino acid isomers was one of the main challenges of the method. This was overcome by applying a voltage of 30 kV in a 90 cm length capillary at 20 °C. Parameters affecting MS detection and the sheath–liquid interface were also studied. Finally, the fixed values were: a sheath gas flow rate of 5 L/min at 195 °C; sheath–liquid consists of MeOH/H2O/FA (50:49.95:0.05 v/v/v), a flow rate of 15 μL/min; and a nozzle voltage of 2000 V; N₂ dry gas rate of 11 L/min at 150 °C; a nebulizer pressure of 10 psi; and a capillary voltage of 2000 V. Online pre-concentration approaches were tested in order to achieve higher sensitivity, obtaining a enrichment factor of 4 with a mixed technique of pH-junction and Field Amplied Sample Stacking (FASS). Full article

The application of oxygen carriers as alternative bed material in fluidized bed combustion originates from chemical lopping processes. They serve as oxygen transport agents undergoing consecutive redox cycles. Thereby, oxygen carriers can provide surplus oxygen in oxygen-lean areas of fluidized bed combustion processes. In turn, re-oxidation takes place in oxygen-rich reactor parts. A more homogeneous combustion and reduced CO emissions follow during steady-state operation. However, especially regarding solid biomass conversion, inhomogeneous fuel qualities result in transient combustion conditions. Therefore, this research deals with the influence of the oxygen carrier ilmenite on solid biomass conversion. Separated batch experiments with methane (volatile), char and wood pellets took place in a laboratory bubbling fluidized bed reactor. They reveal that ilmenite enhances the in-bed CO₂ yield by up to 63% during methane combustion. Batch char experiments confirm that solid–solid reactions with ilmenite are negligible. However, heterogeneous gas–solid reactions reduce the O₂ partial pressure and limit the char conversion rate. The batch wood pellet experiments show that the ilmenite oxygen buffering effect is mitigated due to high local oxygen demand around the pellets and limited pellet distribution in the bed. Finally, the continuous operation in a 100 kW_th BFB with inhomogeneous fuel input indicates a higher in-bed fuel conversion and confirms lower CO emissions and less fluctuation in the flue gas during inhomogeneous fuel supply. Full article

In 2013, UAE imported around 772 million kilograms of rice, making it one of the largest consumers of this popular grain in the world. However, 40% of rice available in the market is discarded, contributing to the country’s CO₂ footprint. Given that CO₂ emissions are recognized as a significant contributor to climate change and efforts aimed at their reduction are proving insufficient for combatting the global increase in temperature, various approaches aimed at its removal from the atmosphere have been proposed. The goal of this study is to contribute to this initiative by proposing a new method for CO₂ removal based on a special gas contact device filled with buffered puffed rice cakes obtained by heating in a purposely designed sealed chamber at high pressure to obtain layers with 9−12 mm thickness. The resulting cakes are subsequently immersed in a sodium hydroxide liquor (0.25−2.5 M) to increase the moisture content to 5% and pH to >11.0. In the experiments, different rice structures (stacked layers, rice grains, and multi-spaced layers) were tested, varying the CO₂ percentage in the simulated effluent gas (1−15%). The highest CO₂ uptake value (7.52 × 10⁻³ mole CO₂/cm² rice cake surface area) was achieved using 10% CO₂ and a 500 mL/min flow rate with rice cakes of 80 mm diameter, comprising 12 mm thick layers that occupied 20% of the device volume. These results indicate that the proposed design exhibits high CO₂ removal efficiency and should be further optimized in future investigations. Full article

Herein, a microfabricated millimeter-level vapor alkali cell with a high hermeticity is fabricated through a wet etching and single-chip anodic bonding process. The vapor cell, containing Rb and N₂, was investigated in a coherent population trapping (CPT) setup for the application of a chip-scale atomic clock (CSAC). The contrast of CPT resonance is up to 1.1% within the only 1 mm length of light interacting with atom. The effects of some critical external parameters on the CPT resonance, such as laser intensity, cell temperature, and buffer gas pressure, are thoroughly studied and optimized. The improved microfabricated vapor cell also exhibited great potential for other chip-scale atomic devices. Full article

During the fast-filling of a high-pressure hydrogen tank, the temperature of hydrogen would rise significantly and may lead to failure of the tank. In addition, the temperature rise also reduces hydrogen density in the tank, which causes mass decrement into the tank. Therefore, it is of practical significance to study the temperature rise and the amount of charging of hydrogen for hydrogen safety. In this paper, the change of hydrogen temperature in the tank according to the pressure rise during the process of charging the high-pressure tank in the process of a 82-MPa hydrogen filling system, the final temperature, the amount of filling of hydrogen gas, and the change of pressure of hydrogen through the pressure reducing valve, and the performance of heat exchanger for cooling high-temperature hydrogen were analyzed by theoretical and numerical methods. When high-pressure filling began in the initial vacuum state, the condition was called the “First cycle”. When the high-pressure charging process began in the remaining condition, the process was called the “Second cycle”. As a result of the theoretical analysis, the final temperatures of hydrogen gas were calculated to be 436.09 K for the first cycle of the high-pressure tank, and 403.55 for the second cycle analysis. The internal temperature of the buffer tank increased by 345.69 K and 32.54 K in the first cycle and second cycles after high-pressure filling. In addition, the final masses were calculated to be 11.58 kg and 12.26 kg for the first cycle and second cycle of the high-pressure tank, respectively. The works of the paper can provide suggestions for the temperature rise of 82 MPa compressed hydrogen storage system and offer necessary theory and numerical methods for guiding safe operation and construction of a hydrogen filling system. Full article