Low Temperature Regime Research Articles

Topological kinetic crossover in a nanomagnet array

Ergodic kinetics, which are critical to equilibrium thermodynamics, can be constrained by a system's topology. We studied a model nanomagnetic array in which such constraints visibly affect the behavior of the magnetic moments. In this system, magnetic excitations connect into thermally active one-dimensional strings whose motion can be imaged in real time. At high temperatures, our data showed the merging, breaking, and reconnecting of strings, resulting in the system transitioning between topologically distinct configurations. Below a crossover temperature, the string motion is dominated by simple changes in length and shape. In this low-temperature regime, the system is energetically stable because of its inability to explore all possible topological configurations. This kinetic crossover suggests a generalizable conception of topologically broken ergodicity and limited equilibration.

Bimetallic NiFe Nanoparticles Supported on CeO2 as Catalysts for Methane Steam Reforming.

Ni-Fe nanocatalysts supported on CeO2 have been prepared for the catalysis of methane steam reforming (MSR) aiming for coke-resistant noble metal-free catalysts. The catalysts have been synthesized by traditional incipient wetness impregnation as well as dry ball milling, a green and more sustainable preparation method. The impact of the synthesis method on the catalytic performance and the catalysts' nanostructure has been investigated. The influence of Fe addition has been addressed as well. The reducibility and the electronic and crystalline structure of Ni and Ni-Fe mono- and bimetallic catalysts have been characterized by temperature programmed reduction (H2-TPR), in situ synchrotron X-ray diffraction (SXRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Their catalytic activity was tested between 700 and 950 °C at 108 L gcat-1 h-1 and with the reactant flow varying between 54 and 415 L gcat-1 h-1 at 700 °C. Hydrogen production rates of 67 mol gmet-1 h-1 have been achieved. The performance of the ball-milled Fe0.1Ni0.9/CeO2 catalyst was similar to that of Ni/CeO2 at high temperatures, but Raman spectroscopy revealed a higher amount of highly defective carbon on the surface of Ni-Fe nanocatalysts. The reorganization of the surface under MSR of the ball-milled NiFe/CeO2 has been monitored by in situ near-ambient pressure XPS experiments, where a strong reorganization of the Ni-Fe nanoparticles with segregation of Fe toward the surface has been observed. Despite the catalytic activity being lower in the low-temperature regime, Fe addition for the milled nanocatalyst increased the coke resistance and could be an efficient alternative to industrial Ni/Al2O3 catalysts.

High temperature increases 2,4-D metabolism in resistant Amaranthus palmeri

AbstractPalmer amaranth (Amaranthus palmeri S. Watson) is a troublesome weed in several cropping systems in the United States. The evolution of resistance to multiple herbicides is a challenge for the management of this weed. Recently, we reported metabolic resistance to 2,4-D possibly mediated by cytochrome P450 (P450) activity in a six-way-resistant A. palmeri population (KCTR). Plant growth temperature can influence the herbicide efficacy and level of resistance. The effect of temperature on 2,4-D resistance in A. palmeri is unknown. In the present research, we investigated the response of KCTR and a known susceptible (MSS) A. palmeri response to 2,4-D grown under low-temperature (LT, 24/14 C, day/night [d/n]) or high-temperature (HT, 34/24 C, d/n) regimes. When MSS and KCTR plants were 8- to 10-cm tall, they were treated with 0, 140, 280, 560 (field recommended dose), 1,120, and 2,240 g ai ha−1 of 2,4-D. Further, 8- to 10-cm-tall MSS and KCTR plants grown at LT and HT were also treated with [14C]2,4-D to assess the metabolism of 2,4-D at LT and HT. The results of dose–response experiments suggest that KCTR A. palmeri exhibits 23 times more resistance to 2,4-D at HT than MSS. Nonetheless, at LT, the resistance to 2,4-D in KCTR was only 2-fold higher than in MSS. Importantly, there was enhanced metabolism of 2,4-D in both KCTR and MSS A. palmeri at HT compared with LT. Further, treatment with the P450 inhibitor malathion, followed by 2,4-D increased the susceptibility of KCTR at HT. Overall, rapid metabolism of 2,4-D increased KCTR resistance to 2,4-D at HT compared with LT. Therefore, the application of 2,4-D when temperatures are cooler can improve control of 2,4-D–resistant A. palmeri.

Quantum statistical mechanics of dissolving Abelian Higgs vortices

The quantum partition function for Abelian Higgs vortices at high density—the regime of dissolving vortices—is calculated explicitly, using spectral data for the Beltrami Laplacian on the N-vortex moduli space with a scaled Fubini–Study metric. From the partition function, the pressure of the vortex gas is derived. There are three asymptotic regimes—High, Intermediate and Low Temperature. The phase crossover from Intermediate to Low Temperature is modelled by a Bessel function. In the Low Temperature regime the free energy is not extensive but is proportional to N 2.

Tunable electron-flexural phonon interaction in graphene heterostructures.

Peculiar electron-phonon interaction characteristics underpin the ultrahigh mobility1, electron hydrodynamics2-4, superconductivity5 and superfluidity6,7 observed in graphene heterostructures. The Lorenz ratio between the electronic thermal conductivity and the product of the electrical conductivity and temperature provides insight into electron-phonon interactions that is inaccessible to past graphene measurements. Here we show an unusual Lorenz ratio peak in degenerate graphene near 60 kelvin and decreased peak magnitude with increased mobility. When combined with ab initio calculations of the many-body electron-phonon self-energy and analytical models, this experimental observation reveals that broken reflection symmetry in graphene heterostructures can relax a restrictive selection rule8,9 to allow quasielastic electron coupling with an odd number of flexural phonons, contributing to the increase of the Lorenz ratio towards the Sommerfeld limit at an intermediate temperature sandwiched between the low-temperature hydrodynamic regime and the inelastic electron-phonon scattering regime above 120 kelvin. In contrast to past practices of neglecting the contributions of flexural phonons to transport in two-dimensional materials, this work suggests that tunable electron-flexural phonon couping can provide a handle to control quantum matter at the atomic scale, such as in magic-angle twisted bilayer graphene10 where low-energy excitations may mediate Cooper pairing of flat-band electrons11,12.

Effect of solute distribution on the screw dislocation motion in bcc Fe-based systems

Screw dislocation motion in bcc Fe plays an important role in establishing the strong temperature and strain rate sensitivity of flow stress, which in turn promotes the ductile to brittle transition phenomenon in steel. Addition of solute atoms, possessing attractive interaction with screw dislocations, is believed to reduce the flow stress sensitivity of Fe. The present work intends to study the effect of Ni and Cu solute atom distribution on the screw dislocation motion in bcc Fe using molecular statics (MS) and molecular dynamics (MD) simulations. MS simulation results predict that the local distribution of Ni atoms around the screw dislocation greatly influences the Peierls stress of Fe at 0 K temperature, while Cu atom distribution has marginal effect. Moreover, the presence of Ni/Cu atoms ahead of the dislocation line helps to reduce the Peierls stress due to the dislocation-solute attractive interaction. MD simulation was performed on random Fe-Ni and Fe-Cu alloys to determine the effect of solute concentration on the temperature sensitivity of flow stress of Fe. The results showed that addition of Ni/Cu reduces the flow stress sensitivity of Fe by inducing solid solution softening effect at low temperature regime. Ni was found to be more effective than Cu in reducing the flow stress temperature sensitivity of Fe. The rationale behind the softening action of Ni and Cu is discussed in terms of changing the differential displacement plot and unstable stacking fault energy of Fe.

Berezinskii-Kosterlitz-Thouless phase transition with Rabi-coupled bosons

We theoretically investigate the superfluid-normal-state Berezinskii-Kosterlitz-Thouless transition in a binary mixture of bosonic atoms with Rabi coupling under balanced densities. We find the nonmonotonic behavior of the transition temperature with respect to the intercomponent coupling and amplification of the transition temperature for finite values of Rabi coupling, but for small intracomponent couplings. We develop the Nelson-Kosterlitz renormalization-group equations in the two-component Bose mixture and obtain the Nelson-Kosterlitz criterion modified by a fractional parameter, which is responsible for half-integer vortices, and by Rabi coupling. Adopting the renormalization-group approach, we clarify the dependence of the Berezinskii-Kosterlitz-Thouless transition temperature on the Rabi coupling and the intercomponent coupling. Analysis of the first and second sound velocities also reveals the suppression of quasicrossing of the two sound modes with a finite Rabi coupling in the low-temperature regime. Our results for a two-dimensional binary Bose superfluid contribute to the understanding of a broad range of multicomponent quantum systems such as two-dimensional multiband superconductors.

Superconductivity and fermionic dissipation in quantum Hall edges

Proximity-induced superconductivity in fractional quantum Hall edges is a prerequisite to proposed realizations of parafermion zero modes. A recent experimental work [G\"ul et al., Phys. Rev. X 12, 021057 (2022)] provided evidence for such coupling, in the form of a crossed Andreev reflection signal, in which electrons enter a superconductor from one chiral mode and are reflected as holes to another, counterpropagating chiral mode. Remarkably, while the probability for crossed Andreev reflection was small, it was stronger for $\ensuremath{\nu}=1/3$ fractional quantum Hall edges than for integer ones. We theoretically explain these findings, including the relative strengths of the signals in the two cases and their qualitatively different temperature dependencies. An essential part of our model is the coupling of the edge modes to normal states in the cores of Abrikosov vortices induced by the magnetic field, which provide a fermionic bath. We find that the stronger crossed Andreev reflection in the fractional case originates from the suppression of electronic tunneling between the fermionic bath and the fractional quantum Hall edges. Our theory shows that the mere observation of crossed Andreev reflection signal does not necessarily imply the presence of localized parafermion zero modes, and suggests ways to identify their presence from the behavior of this signal in the low-temperature regime.

Modern non-thermal method of processing plant raw materials used to increase its storability

Along with thermal methods of processing plant raw materials, non-thermal processing methods have been actively developed in recent decades, which make it possible to preserve the qualitative characteristics of the initial raw materials to the maximum and increase the shelf life of the finished product. When using these methods, slight heating of the product can occur, for example, as in the processing by ultraviolet radiation (UVR). In the case of using such a type of processing as filtration, heating is completely absent; under the conditions of high pressure processing of the product (hereinafter HPP), a low temperature regime is observed. These methods are distinguished by minimizing the impact on the organoleptic characteristics of the finished product (texture, appearance, color, odor), as well as the preservation of micro- and macronutrients. The article discusses the main non-thermal methods of processing plant materials: high pressure (HPP), processing in a pulsed electric field (PEF), radioactive radiation, ultraviolet radiation (UVR), filtration. The advantages and factors hindering their widespread use on an industrial scale are noted. It is noted that high pressure, ultraviolet radiation and filtration to one degree or another are widely used in food production, while processing in a pulsed electric field and radioactive radiation are of extremely limited use due to the need to ensure the safety of processing for service personnel. It should also be noted that processing only by non-thermal methods leads to a limited shelf life of finished products and often requires lower storage temperatures. If it is necessary to increase the shelf life, it makes sense to combine thermal and non-thermal processing methods, for example, microfiltration (ultrafiltration) of juice, bottling into consumer packaging, gentle pasteurization. The undoubted advantage of this combination can be a reduction in the thermal load on a product, since the initial microbiological contamination is reduced by filtration. And, as a result, we get a stably stored product with minimal quality loss and preserved native potential.

Ni nanoparticles supported on Al2O3 + La2O3 yolk-shell catalyst for photo-assisted thermal decomposition of methane

Catalytic methane decomposition (CMD) has emerged as an appealing technology for large-scale production of H2 and carbon nanostructures from natural gas. As the CMD process is mildly endothermic, the application of concentrated renewable energy sources such as solar energy under a low-temperature regime could potentially represent a promising approach towards CMD process operation. Herein, Ni/Al2O3-La2O3 yolk-shell catalysts are fabricated using a straightforward single-step hydrothermal approach and tested for their performance in photothermal CMD. We show that the morphology of the resulting materials, dispersion and reducibility of Ni nanoparticles, and nature of metal-support interactions can be tuned by addition of varying amounts of La. Notably, the addition of an optimal amount of La (Ni/Al-20La) improved the H2 yield and catalyst stability relative to the base Ni/Al2O3 material, while also favoring base growth of carbon nanofibers. Additionally, we show for the first time a photothermal effect in CMD, whereby the introduction of 3 suns light irradiation at a constant bulk temperature of 500 °C reversibly increased the H2 yield of catalyst by about 1.2 times relative to the rate in the dark, accompanied by a decrease in apparent activation energy from 41.6 kJ mol−1 to 32.5 kJ mol−1. The light irradiation further suppressed undesirable CO co-production at low temperatures. Our work reveals photothermal catalysis as a promising route for CMD while providing an insightful understanding of the roles of modifier in enriching methane activation sites on Al2O3-based catalysts.

Flame regimes in DI diesel combustion: LES study for light- and heavy-duty injectors

Experimental and numerical studies contributed significantly to the overall understanding of diesel spray combustion phenomena over recent decades. In particular, the conceptual model proposed by Dec (1997) [1] and its extensions, describing the mechanisms behind spray formation, vaporization, mixing, ignition, as well as pollutant formation and consumption, have provided new insights for DI diesel engine applications. However, the literature still lacks detailed studies on the local flame regimes of diesel spray combustion. This study presents a comprehensive flame regime analysis of two benchmark cases of the Engine Combustion Network, Spray A and Spray D, which represent light- and heavy-duty applications. To this end, the established gradient-free regime identification (GFRI) approach is extended to cover diesel spray flames and applied to numerical LES data, based on tabulated chemistry, using the unsteady flamelet progress variable (UFPV) approach. The applicability of the tabulated chemistry approach for flame regime identification is validated based on DNS data. For both light- and heavy-duty diesel injectors, a different ignition behavior and temporal evolution of the flame regime distribution is observed. In both configurations the main ignition is dominated by multi-regime combustion, which governs the flame stabilization, and non-premixed combustion, most prominent when approaching steady-state. However, the spatial separation of flame regimes, especially multi-regime and the low-temperature regime, significantly differs when comparing the two spray flames. Based on this qualitative analysis, the impact of the single flame regimes on the overall heat release is analyzed. This is followed by a conditional flame structure analysis, with respect to the mixture fraction and flame regime, for representative times, e.g., early and main ignition as well as quasi steady-state combustion. Finally, the outcome of the local flame regime analysis is consolidated, and an extended conceptual model is proposed, including a detailed understanding of the predominant flame regimes.

Modelling of the impact of climate change on the transformation of nitrogen forms in the soil and N2O emissions from the agroecosystems of Eastern Ukraine

The moisture-temperature regime influences the nitrogen status of the soil and the microbiological processes of the transformation of nitrogen forms. Therefore, we assumed that ongoing climate change may affect the emission of nitrous oxide N2O, which is formed in the course of the transformation of nitrogen forms in the soil and is one of the most aggressive greenhouse gases that determine the global warming potential. To test this hypothesis and make a quantitative assessment of the impact of climate change on the transformation of nitrogen forms in the soil and N2O emissions from the agroecosystem soils, we used a complex model of greenhouse gas emissions from an agroecosystem soil that we developed and the RCP4.5 climate change scenario. The research was performed for the chernozem soils of Eastern Ukraine, with winter wheat being the cultivated crop. ‘Dry’ and ‘wet’ years typical for the period of 2021–2050 were selected among climate conditions in accordance with the climate change scenario. A ‘dry’ year was considered to be a year with a precipitation of 60% or less of the long-term average, a ‘wet’ year was a year with a precipitation of 130% or more of the long-term average for the studied period. The level of ammonification during the growing season for both ‘dry’ and partially ‘wet’ years was mainly controlled by temperature. At the beginning of the period, at negative temperatures below –3 °C ammonification and nitrification almost stopped, and at temperatures above –2 °C they slightly increased. Indices for the intensity of these processes increased with a rise in temperature from 0 °C to 10–11 °C. In the conditions of a ‘dry’ year an increment in temperature to the level of 22.4–27.8 °C caused a sharp increase in the rate of ammonification and caused a high level of the rate of nitrification. For the conditions of a ‘wet’ year with a sufficiently low (compared to a ‘dry’ year) temperature regime, a relatively significant rise in temperature with still quite good humidification increased the intensity of the ammonification process. The dependence of the intensity of the ammonification and nitrification processes on the moisture reserves in the soil is traced. The high level of moisture reserves in the arable layer at the beginning of the growing season in both ‘dry’ and ‘wet’ years formed anaerobic conditions in the upper layer of the soil. Against the background of rising temperatures, this called forth the denitrification process. N2O emission was 0.03–0.29 g N-N2O/ha•day due to the denitrification process in a ‘dry’ year, and 0.7–5.2 g N-N2O/ha•day in a ‘wet’ year. The highest level of N2O emission due to nitrification was observed in a ‘dry’ year in the middle of the vegetation period at high temperatures (22.7–27.8 °С) and amounted to 8.2–11.2 g N-N2O/ha•day. A decrease in soil moisture reserves during the second half of the growing season reduced the level of N2O emissions. Nitrification was the main process producing N2O. The emissions of N2O with moisture reserves greater than 55 mm in the arable layer occurred due to denitrification. A rise in temperature increases the level of N2O emissions. The peculiarities of the influence of moisture and temperature conditions of ‘dry’ and ‘wet’ years on the processes of ammonification, nitrification, denitrification, and N2O emissions from chernozem soils according to the RCP4.5 climate change scenario in Eastern Ukraine were assessed.

Trap analysis on Pt-AlGaN/GaN Schottky barrier diode through deep level transient spectroscopy

Trap characterization on GaN Schottky barrier diodes (SBDs) has been carried out using deep-level transient spectroscopy (DLTS). Selective probing by varying the ratio of the rate window values (r) incites different trap signatures at similar temperature regimes. Electron traps are found to be within the values: 0.05–1.2 eV from the conduction band edge whereas the hole traps 1.37–2.66 eV from the valence band edge on the SBDs. In the lower temperature regime, the deeper electron traps contribute to the capacitance transients with increasing r values, whereas at the higher temperatures >300 K, a slow variation of the trap levels (both electrons and holes) is observed when r is varied. These traps are found to be mainly contributed to dislocations, interfaces, and vacancies within the structure.

Johari–Goldstein β relaxation in glassy dynamics originates from two-scale energy landscape

Supercooled liquids undergo complicated structural relaxation processes, which have been a long-standing problem in both experimental and theoretical aspects of condensed matter physics. In particular, past experiments widely observed for many types of molecular liquids that relaxation dynamics separated into two distinct processes at low temperatures. One of the possible interpretations is that this separation originates from the two-scale hierarchical topography of the potential energy landscape; however, it has never been verified. Molecular dynamics simulations are a promising approach to tackle this issue, but we must overcome laborious difficulties. First, we must handle a model of molecular liquids that is computationally demanding compared to simple spherical models, which have been intensively studied but show only a slower process: α relaxation. Second, we must reach a sufficiently low-temperature regime where the two processes become well-separated. Here, we handle an asymmetric dimer system that exhibits a faster process: Johari-Goldstein β relaxation. Then, we employ the parallel tempering method to access the low-temperature regime. These laborious efforts enable us to investigate the potential energy landscape in detail and unveil the first direct evidence of the topographic hierarchy that induces the β relaxation. We also successfully characterize the microscopic motions of particles during each relaxation process. Finally, we study the correlation between low-frequency modes and two relaxation processes. Our results establish a fundamental and comprehensive understanding of experimentally observed relaxation dynamics in supercooled liquids.

Quantum Stirling heat engine with squeezed thermal reservoir

We analyze the performance of a quantum Stirling heat engine (QSHE), using a two-level system and a harmonic oscillator as the working medium, that is in contact with a squeezed thermal reservoir and a cold reservoir. First, we derive closed-form expressions for the produced work and efficiency, which strongly depend on the squeezing parameter r h. Then, we prove that the effect of squeezing heats the working medium to a higher effective temperature, which leads to better overall performance. In particular, the efficiency increases with the degree of squeezing, surpassing the standard Carnot limit when the ratio of the temperatures of the hot and cold reservoirs is small. Furthermore, we derive the analytical expressions for the efficiency at maximum work and the maximum produced work in the high and low temperature regimes, and we find that at extreme temperatures the squeezing parameter r h does not affect the performance of the QSHE. Finally, the performance of the QSHE depends on the nature of the working medium.

Utility of Shockley–Read–Hall analysis to extract defect properties from semiconductor minority carrier lifetime data

The semiconductor minority carrier lifetime contains information about several important material properties, including Shockley–Read–Hall defect levels/concentrations and radiative/Auger recombination rates, and the complex relationships between these parameters produce a non-trivial temperature-dependence of the measured lifetime. It is tempting to fit temperature-dependent lifetime data to extract the properties of the Shockley–Read–Hall recombination centers; however, without a priori knowledge of the distribution of the Shockley–Read–Hall states across the bandgap, this fit problem is under-constrained in most circumstances. Shockley–Read–Hall lifetime data are not well-suited for the extraction of Shockley–Read–Hall defect levels but can be used effectively to extract minority carrier recombination lifetimes. The minority carrier recombination lifetime is observed at temperatures below 100 K in a Si-doped n-type InGaAs/InAsSb superlattice, and deviation from its expected temperature-dependence indicates that the capture cross section of the defect associated with Si-doping has an activation energy of 1.5 meV or a characteristic temperature of 17 K. This lower temperature regime is also preferrable for the analysis of the physics of defect introduction with displacement-damage-generating particle irradiation.

Calculation of ablation instabilities during MCCI with the TIM model

The Transient Interface Model (TIM) (Seiler and Combeau, 2014; Seiler and Jamet, 2019) dedicated to Molten Core-Concrete Interaction simulation is used to investigate ablation instabilities. The ablation instability leads to concrete ablation in preferential directions, potentially jeopardizing the mitigation criterion based on residual concrete thickness. The ablation instability occurs when all the corium/concrete interfaces do not undergo the same ablation regime. These regimes are specific of the interface temperature; in the homogeneous Low Interface Temperature (LIT) regime, the interface temperature is close to the liquidus temperature of concrete matrix, whereas in the homogeneous High Interface Temperature (HIT) regime, the interface as well as the pool temperatures are close to the pool liquidus temperature. When these different ablation regimes are present simultaneously (non-homogeneous situation), only the surfaces under LIT regime are ablated. It is shown that ablation instabilities are favored at low power dissipation and at small test scale. Calculations suggest that the limit between HIT and LIT dominant regimes can be represented in the pseudo-binary phase diagram. The surfaces initially under HIT regime (not ablated) may return to the LIT regime (with ablation) after a time delay which depends on the extension of the surface initially under HIT regime, on the value of the mass transfer coefficient and, to some extent, on the melt to interface heat transfer. Finally, the calculation at reactor scale with siliceous concrete indicates that an ablation instability may occur in the initial stage of the MCCI transient. Such ablation instability does not induce significant preferential ablation in the reactor configuration if it is limited to the horizontal surface of the reactor pit. If it affects the lateral walls, and due to the small thickness of the corium layer, a significant ablation depth could be reached (∼1 m in a reactor pit of 6 m inner diameter).

Catalytic oxidation of acetone and ethanol on a platinum wire

The current-voltage characteristics of a thin long platinum wire in air with acetone or ethanol small admixtures were obtained. Using the quadratic dependence of platinum resistance on temperature, the temperature-current dependences for the wire were calculated. At concentrations of combustible gas vapors above a certain value, these dependences show a hysteresis character. Using the assumption of acetone and ethanol complete oxidation on platinum, as a catalyst, and the first order of the oxidation reaction, temperature-current dependences was analysised. The temperature difference between the high and low-temperature stationary regimes of catalytic oxidation on the wire makes it possible to estimate the admixture concentration. As a result, the experimental dependence of the critical current value by catalytic ignition and extinction gas mixture on platinum on the admixture concentration was constructed. With its analytical description, it is possible to fairly accurately estimate the apparent values ​​of the activation energy and the pre-exponential multiplier for the oxidation reaction in a wide temperature range. A method of determining the kinetic parameters for the oxidation reaction based on the experimentally found parameters of degeneracy critical conditions is proposed.

The Combined Impact of Ni-Based Catalysts and a Binary Carbonate Salts Mixture on the CO2 Gasification Performance of Olive Kernel Biomass Fuel

In the present work, the individual or synergistic effect of Ni-based catalysts (Ni/CeO2, Ni/Al2O3) and an eutectic carbonate salt mixture (MS) on the CO2 gasification performance of olive kernels was investigated. It was found that the Ni/CeO2 catalyst presented a relatively superior instant gasification reaction rate (Rco) compared to Ni/Al2O3, in line with the significant redox capability of CeO2. On the other hand, the use of the binary eutectic carbonate salt mixture (MS) lowered the onset and maximum CO2 gasification temperatures, resulting in a notably higher carbon conversion efficiency (81%) compared to the individual Ni-based catalysts and non-catalytic gasification tests (60%). Interestingly, a synergetic catalyst-carbonate salt mixture effect was revealed in the low and intermediate CO2 gasification temperature regimes, boosting the instant gasification reaction rate (Rco). In fact, in the temperature range of 300 to 550 °C, the maximum Rco value for both MS-Ni/Al2O3 and MS-Ni/CeO2 systems were four times higher (4 × 10−3 min−1 at 460 °C) compared to the individual counterparts. The present results demonstrated for the first time the combined effect of two different Ni-based catalysts and an eutectic carbonate salt mixture towards enhancing the CO production rate during CO2 gasification of olive kernel biomass fuel, especially in the devolatilization and tar cracking/reforming zones. On the basis of a systematic characterization study and lab-scale gasification experiments, the beneficial role of catalysts and molten carbonate salts on the gasification process was revealed, which can be ascribed to the catalytic activity as well as the improved mass and heat transport properties offered by the molten carbonate salts.

Physicochemical Conditions of the Devonian-Jurassic Continental Deep Biosphere Tracked by Carbonate Clumped Isotope Temperatures of Granite-Hosted Carbonate Veins

Previous studies have shown that microorganisms thrive in oligotrophic fracture systems, and metabolisms include consumption and production of methane. In the Laxemar, Götemar, and Forsmark areas of Sweden, ancient microbial activity has previously been demonstrated by large δ13CVPDB variability of carbonate vein infillings within granitic host rocks. Here, we apply carbonate clumped isotope thermometry to reconstruct the temperature of precipitation of the carbonate within these veins. The carbonate clumped isotope temperatures indicate that mineralization took place between 46°C and 108°C, in line with previously published fluid inclusion data (<50°C to 113°C). The new carbonate clumped isotope data more accurately narrows temperatures at the lower end of this range as fluid inclusions are not easily applicable below 80°C, a temperature regime of high importance for paleobiological reconstructions. Our results demonstrate that large volumes of biogenic carbonate cement were formed from low-temperature microbial processes in low-salinity water, succeeding calcite of deep brine origin. The known burial and thermal history of the region combined with our carbonate clumped isotope data place the microbial activity at the end of the Variscan orogeny and later events (e.g., Jurassic). Thus, carbonate clumped isotope thermometry reduces uncertainties in deep biosphere studies by providing more accurate temperature constraints in the low-temperature regime, the biogenic processes, and the origin of the diagenetic fluids.