Temperature Region Research Articles

Fabrication of NBI Ion Source Back Plate and its High Heat Flux Experiment

The back plate is an important component of the ion source because of its multiple roles including heat load removal during beam operation. The main components of the back plate are (1) a Type 304L stainless steel (SS304L) magnet positioning plate that holds samarium cobalt permanent magnets required for the confinement of ion source plasma, (2) an oxygen-free electronic copper cooling plate with 35 inner and 8 outer cooling channel grooves (each of which is 4 × 1.8 mm2) that is vacuum brazed with a SS304L magnet positioning plate, and (3) a SS304L magnet cover plate. In this paper, the back plate is successfully fabricated, and a high heat flux experiment is done at the High Heat Flux Test Facility Center with an electron beam power of 200 kW for 458 s. The uniform incident heat flux is 2.5 MW/m2. Demineralized water at 34°C is supplied at the rate of 1 kg/s to the cooling plate at inlet pressure of 8.2 bars to remove the high heat load. The surface temperature of the copper plate is measured by an infrared camera, and three temperature regions are observed. The measured average surface temperature of the cooling plate is ~152°C. The bulk water temperature rise ΔTw is ~39.42°C. The estimated absorbed heat flux is ~2.04 MW/m2, and the heat absorption coefficient is 81.6%. The measured leak rate after the heat flux test is 1.6 × 10−8 mbars∙L/s. These High Heat Flux Test experimental results will be useful to study the thermomechanical performance of the back plate and to understand the effect of increasing the beam pulse length.

Fabrication of ultra-precise flexible electrothermal film by direct-write printing porous graphene-Ag structure

In this study, graphene oxide (GO)‑silver nitrate (AgNO3) composite ink was prepared with stable printability, which could match the direct-write print technique for patterning GO-AgNO3 composite structure. Reduced graphene oxide (rGO)‑silver (Ag) porous structure could be obtained with a freeze-drying and gas phase reduction process. The rGO-Ag porous structure could reach a conductivity of 3.2 × 105 S/m through quantum penetration effect with the bridging action. Subsequently, polydimethylsiloxane (PDMS) encapsulated the rGO-Ag porous structure, and a special composite structure of PDMS/ rGO-Ag/PDMS films could be obtained by adjusting the wetting effect. PDMS provided a good tensile property and excellent bending resistance, and then a relative resistance changes within 5 % could be achieved after the number of 10,000 bending times. With the rGO-Ag porous structure compressed into a thinner film, an ultra-precise flexible electrothermal performance could be realized with the conductive network and flexible package structure. The surface temperature of fabricated composite film could reach 201.3 °C at the voltage of 7 V, within a heating time of 25 s, and maintaining the temperature for 1800 s. Meanwhile, the flexible electrothermal film could keep a stable temperature after 120 power on/power off cycles. Furthermore, the flexible electrothermal film also has a linear temperature control ability, which could carry out the linear temperature control with different temperature regions. At last, the ultra-precise flexible electrothermal film exhibits an excellent applying effect for the wrist hot compress, pipeline heating and window cleaning with uneven ice thickness. Therefore, the direct-write printed porous graphene-Ag structure presents a special property for fabricating ultra-precise flexible electrothermal film, which could provide a great research significance and application value in printing electronic structure and manufacturing electronic device.

Isothermal Amplification Using Temperature-Controlled Frequency Mixing Magnetic Detection-Based Portable Field-Testing Platform.

Sensitive magnetic nucleic acid (NA) detection via frequency mixing magnetic detection (FMMD) requires amplified NA samples for which a reliable temperature control is necessary. The feasibility of recombinase polymerase amplification (RPA) was studied within a newly integrated temperature-controlled sensor unit of a mobile FMMD based setup. It has been demonstrated that the inherently generated heat of the low frequency (LF) excitation signal of FMMD can be utilized and controlled by means of pulse width modulation (PWM). To test control performance in a point of care (PoC) setting with changing ambient conditions, a steady state and dynamic response model for the thermal behavior at the sample position of the sensor were developed. We confirmed that in the sensor unit of the FMMD device, RPA performs similar as in a temperature-controlled water bath. For narrow steady state temperature regions, a linear extrapolation suffices for estimation of the sample position temperature, based on the temperature feedback sensor for PWM control. For any other ambient conditions, we identified and validated a lumped parameter model (LPM) performing with high estimation accuracy. We expect that the method can be used for NA amplification and magnetic detection using FMMD in resource-limited settings.

Fabrication and Characterization of PLA/PBAT Blends, Blend-Based Nanocomposites, and Their Supercritical Carbon Dioxide-Induced Foams.

In this study, a twin-screw extruder was used to fabricate poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate) (PBAT) blends and blend-based nanocomposites with carbon nanotube (CNT) or nanocarbon black (CB) as nanofillers. The fabricated samples were subsequently treated with supercritical carbon dioxide (scCO2) to fabricate the corresponding foams. Bi-phasic morphology and selective distribution of CNTs or CBs in the PBAT phase were observed in the blends/composites through scanning electron microscopy. After the scCO2 treatment, the selective foaming of the PBAT phase in the prepared blends/composites was confirmed. The cellular structure of PBAT phase in scCO2-treated blends is similar to the size/shape of PBAT domains in untreated blends or treated neat PBAT foam. The addition of CNTs or CBs in the blends led to a slight reduction in cell size of the foamed PBAT phase, demonstrating CNT/CB-induced cell nucleation. Differential scanning calorimetry (DSC) results showed that CNTs and CBs played as nucleating agents and increased the initial crystallization temperature up to 14 °C compared with neat PBAT for PBAT in different composites during cooling. The scCO2 treatment induced the bimodal stability of PBAT crystals in different samples, which melted mainly in two temperature regions in DSC studies. Thermogravimetric analyses revealed that compared with parent blends, the addition of CNTs or CBs increased the temperature at 80 wt.% loss (degradation of PBAT portion) up to 6 °C. The electrical resistivity decreased by more than six orders of magnitude for certain CNT- or CB-added composites compared with the parent blends. The hardness of the blends slightly increased after forming the corresponding composites and then declined after the scCO2 treatment.

Heat transfer enhancement mechanics of different micro-disturbing structures for transcritical hydrocarbon fuel using 3-D secondary flow intensity analysis

Heat transfer enhancement based upon micro-disturbing structures becomes increasingly important for thermal protection of air-breathing propulsion systems. To explore the influence mechanism of different structures on heat transfer in regenerative cooling channels of scramjet engines, flow structures and heat transfer of supercritical-pressure n-Decane in mini-channels with dimple and micro-rib arrays are numerically investigated. Results indicate effective heat transfer enhancement inside the channels depends more on efficient transverse turbulence disturbance rather than longitudinal or perpendicular turbulence disturbance. Severe thermal stratification generates strong shear layers in channels, where transverse secondary flows bring much intenser flow mixing than longitudinal secondary flows, especially in transcritical temperature region where the best heat transfer enhancement is obtained. With same characteristic dimensions, longitudinal micro-disturbing structures like dimples have lower flow resistance, but transverse micro-disturbing structures like micro-ribs achieve stronger heat transfer enhancement. Besides, the performance of micro-ribs is much more sensitive to the dimensional change. Therefore, micro-ribs have larger working excursion for enhancing performance factor than dimples. With optimal structure parameters: hr = e = 0.3 mm, pr = 3 mm, hd = 0.225 mm, dd = 1.5 mm, overall performance factor in micro-ribbed channel is 1.14 times of that in dimpled channel. Those conclusions provide effective support for optimization design for the regenerative cooling structures.

An Experimental Investigation Of Local Thermo-Fluidic Heat Transfer In A U-Shaped Mini-Channel Sink

This study investigates experimentally a heated U-shaped mini-channel heat sink using Infrared Thermography and Particle Image Velocimetry for a water coolant flow of Reynolds numbers of 280, 650, and 1350 (based on the hydraulic channel diameter). The choice of this cell geometry is based on its role as a simplified unit of a serpentine heat exchanger, which is proved to be one of the most promising for cooling processes. The use of the infrared camera allows the detection of temperature fields on top of the external surface of the cell. Therefore, aiming to derive the temperature distribution on the channel roof, a dedicated transfer function is implemented. Moreover, we employed the lumped capacitance model for thermal analysis on both infrared measurements and thermocouple data. The latter are recorded to capture the cooling process of the aluminium base and water temperature at the end of the outlet tube. As a result, thermal transient rate, cooling magnitude and equilibrium temperature are obtained. These parameters indicate that higher Reynolds numbers correspond to increased thermal transient rates, enhanced cooling effects, and lower equilibrium temperatures. A non-uniform distribution of heat transfer along the channel is reported, with the most efficient cooling area localized close to the first 90-degree corner. These findings are consistent with numerical simulations and previous experimental observations. PIV results reveal the presence of two fluid acceleration zones following both 90-degree corners, which contribute to improve the water cooling ability in their respective regions. Additionally, the formation of two recirculating bubbles is reported at the inner wall from corners vertices, whose intensity is dependent on Reynolds number, pushing the main flow towards the outer channel wall and reducing the local heat transfer. Turbulent kinetic energy distributions are also investigated, pointing out the presence of intense areas that better match with regions of minimum equilibrium temperature than maximum velocity zones. This suggests the presence of local turbulent unsteadiness and three-dimensional phenomena, which contributes significantly to cooling enhancement.

IMPROVING THE ACCURACY OF CALCULATING THE SUPER-COMPRESSIBILITY COEFFICIENT OF HELIUM BASED ON STATE EQUATIONS

To date, the Russian gas industry is developing a large number of deposits with a high helium content in the composition of the extracted gas, such as Chayandinskoye, Kovyktinskoye, Yaraktinskoye oil and gas condensate fields. Helium has never before been the object of detailed study during gathering and treatment, but today helium is an important resource that is used in many fields: military industry, medicine, shipbuilding, laser technology, space technology. The high demand for the component of the extracted gas has created requirements for the creation of a technology for separating it from gas. In addition, helium is a «cold» gas due to the weak interaction of its molecules, so it is difficult to model phase equilibrium at extremely low temperatures. As a result, improving the simulation of condensation of a helium mixture is undoubtedly an urgent task of the industry today. The purpose of the study is to increase the accuracy of calculating the thermodynamic properties of helium based on one of the modifications of the Peng-Robinson equation of state for thermobaric conditions corresponding to helium liquefaction processes.As the methods used in this work, a software module for calculating the selection of the Peneloux correction in the Java programming language was implemented. The results are tested on known experimental data, as well as a specialized software product for calculating the thermodynamic properties of fluids.The features of calculating the superconductivity coefficient of helium based on the cubic equation of state are presented. The optimal range of the Peneloux correction for the Peng-Robinson equation of state has been found, as well as an approximation formula that allows us to find the correction in the low temperature region. The results obtained will allow us to calculate the thermodynamic properties of helium with high accuracy. This will allow us to predict the volume of production and condensation of helium from natural gas, which is certainly an important task for the development of the country's economy.

Cover Image, Volume 62, Issue 13

The cover image is based on the Research Article Synthesis and chiroptical properties of β‐1,2‐linked glycopolymers prepared by click polymerization by Misaki Suzuki et al., https://doi.org/10.1002/pol.20230746In the cover image, Yasuhito Koyama and coworkers show the design, synthesis, and folding behaviors of β‐1,2‐linked glycopolymers as a bioconjugate‐based foldamer. The glycopolymers are synthesized via the click polymerization of alkyne‐containing β‐glycosyl azides. The galactose‐based polymer adopts a helically folded structure in ClCH2CH2Cl or THF. It is indicated that the glucose‐based polymer can possibly form the helical folded structure in ClCH2CH2Cl at a low temperature region and adopt a random coil structure at 50 °C. In THF, the glucose‐based polymer does not fold the conformation at all in the observed temperature region. image

Extreme temperature gradient promoting oxygen diffusion in yttria‐stabilized zirconia: A molecular dynamics study

AbstractThe oxidation resistance of yttria‐stabilized zirconia (YSZ) thermal barrier coatings and conductivity of YSZ solid oxide fuel cells are closely related to the diffusion of oxygen ions () in YSZ, but the diffusion behavior in small‐sized YSZ samples under non‐isothermal condition where the temperature gradient () could be significant remaining elusive. Herein, we disclose the previously unrevealed effect of extreme on the self‐diffusion behavior of in both pristine and strained YSZ. It is found that the self‐diffusion coefficient () experiences a nearly one‐fold increase under an extreme around 60 K/Å. The diffusion direction tends to be toward regions of high temperature. Uniaxial stress is revealed to reduce due to the increased activation energy of ions, whereas promotes the self‐diffusion in the stressed system. These results underscore the role of in influencing the self‐diffusion behavior of YSZ, providing a theoretical guideline for examining ceramics serving in extreme environments.

Geographic patterns and climatic drivers of the mean genus age of liverworts in North America

Phylogenetic niche conservatism posits that species tend to retain ancestral ecological traits and distributions, which has been broadly tested for lineages originating in tropical climates but has been rarely tested for lineages that originated and diversified in temperate climates. Liverworts are thought to originate in temperate climates. Mean lineage age reflects evolutionary history of biological communities. Here, using regional liverwort floras across a long latitudinal gradient from tropical to arctic climates in North America, we test the age-component of the temperate niche conservatism hypothesis. Mean genus age (MGA) was estimated for each of 76 regional floras of liverworts. We related MGA to climatic variables for North America as a whole and for its eastern and western parts separately, and used variation partitioning analysis to assess the relative importance of temperature- versus precipitation-related variables and of climate extremes versus seasonality on MGA. We found that older genera of liverworts tend to concentrate in humid regions of intermediate temperatures in the range of 10 °C–20 °C, from which liverworts have adapted to and diversified into more arid, colder, and hotter regions, supporting the temperate niche conservatism hypothesis. We also found that across North America the MGA of liverwort assemblages is more strongly affected by precipitation-related variables than by temperature-related variables, and is more strongly affected by climate extremes than by climate seasonality. Geographic patterns of the MGA of liverworts are consistent with the temperate niche conservatism hypothesis, rather than the tropical niche conservatism hypothesis, the latter of which is broadly supported by angiosperms.

Simulation of ordering and diffusion in CrxMoNbTaVW alloys within the framework of the N-body approach when specifying interatomic interactions

Purpose. Development of interatomic potentials for atomistic simulation of alloys based on refractory metals of the V-Cr-Nb-Mo-Ta-W system and atomistic simulation using these ordering and diffusion potentials in CrxMoNbTaVW alloys. Methods. The development of the interatomic potentials of the V-Cr-Nb-Mo-Ta-W system was carried out within the framework of the 𝑁-body approach; To optimize the parameters of the potentials, the results of calculations within the framework of the electron density functional theory using the VASP software package were used as target values; the simulations of ordering and diffusion was carried out using methods of molecular dynamics and the developed We have previously used the combined method of molecular dynamics and the Monte Carlo method (MD+MK). Results. Within the framework of the 𝑁-body approach, potentials are constructed that complement the V-Nb-Mo-W potential system that we built earlier to the V-Cr-Nb-Mo-Ta-W system. The constructed potentials predict the characteristics of alloys in good agreement with experimental data, CALPHAD data and density functional theory data. Using these potentials by the MD+MC method, CrxMoNbTaVW alloys were modeled, where 𝑥 = 0, 0.5, 1, 2 and 3, in the temperature range from 500 ºC to 2300 ºC. The MD+MC calculations and CALPHAD data agreed in the temperature and concentration regions containing one phase of BCC. At a temperature of 1000ºC, MD + MC calculations show the presence of a single BCC phase, which contradicts CALPHAD data, but is consistent with experimental data. The simulation showed that the atomic structure of the CrMoNbTaVW model alloy is self-sufficient to realize the diffusion of components without artificial introduction of vacancies. The absolute values of the diffusion coefficients of the components and the values of the effective activation energy of diffusion in a solid solution of CrMoNbTaVW were calculated for the first time by the method of molecular dynamics. Analysis of the calculated diffusion characteristics indicates that a diffusion mechanism is implemented in the CrMoNbTaVW alloy, which includes coordinated movement of atoms of various grades. Conclusion. The development of methods for atomistic simulations of alloys based on refractory metals of the V-Cr-Nb-Mo-Ta-W system and the results of atomistic simulation of ordering and diffusion in CrxMoNbTaVW alloys have shown their importance for explaining and predicting heat resistance caused by diffusion processes in multicomponent alloys at high temperatures.

Elucidating the influence mechanisms of splat cooling on microstructure evolution in friction stir welding of 2195 Al–Li alloy by multi-scale simulation

Al–Li alloy has been widely used in the manufacture of aerospace aircraft structural parts due to its high specific strength and excellent comprehensive performance. Friction stir welding (FSW), as a solid-state joining technique, generates comparatively lower heat generation in contrast to fusion welding. However, even with this reduced heat input, the welded joints of 2195 Al–Li alloy still exhibit noticeable thermal softening. FSW is very sensitive to welding heat input, and the thermal cycle of high peak temperature coarsens the grain in the weld zone, thereby reducing joint properties. To overcome these problems, external cooling can be applied to reduce peak temperature and increase cooling speed, improving the performance of FSW joints. In order to study the mechanism of external cooling on the microstructure evolution of joints, this work established a multi-scale simulation of splat cooling assisted friction stir welding (SCaFSW) of 2195 Al–Li alloy. The temperature change and material deformation data in SCaFSW were calculated in the macroscopic finite element model and used for further Monte Carlo microstructure evolution simulation, and compared with the conventional FSW process. Results reveal that the splat cooling significantly reduces the area of the high temperature region of the workpiece, decreasing the temperature at the same location 10 mm behind the tool by approximately 50 °C compared to FSW. While the local temperature field around the tool pin is not affected by the splat cooling, which mainly accelerates the cooling rate of the welded joint and reduces the plastic strain. In addition, the dislocation density in the weld nugget zone (WNZ) of SCaFSW joint is higher than that in conventional FSW, which promotes the process of grain nucleation and finally refines the grain in the WNZ. The simulated average grain size and thermal cycling results are in good agreement with the experimental results.

Assessment of Look-up tables for the prediction of heat transfer coefficient distribution in rod bundles cooled by supercritical water

The evaluation of available Look-Up Tables for prediction of heat transfer coefficient distribution in rod bundles cooled by supercritical water with the aim of their further use in computational analyses of various Fuel Assembles of Supercritical Water-Cooled Reactors is made. The comparison between the calculations based on Look-Up Tables with the values from empirical correlations and experimental data for smooth and wire-wrapped rod bundles was presented. The obtained results showed that Look-Up Table of the University of Ottawa, which was created to describe improved and deteriorated heat transfer regimes in round tubes, allows describing available data points with 30 % of the mean square deviation. It is noted that the presence of wire intensifies heat transfer exchange near pseudocritical temperature region but existing versions of Look-Up Tables cannot take into account this effect. Nevertheless, there is potential for further improvement in predicting the heat transfer coefficient using Look-Up Table by introducing additional correction factors.

Thermonuclear 28P(p, γ)29S reaction rate and astrophysical implication in ONe nova explosion

Context. An accurate 28P(p, γ)29S reaction rate is crucial to defining the nucleosynthesis products of explosive hydrogen burning in ONe novae. Using the recently released nuclear mass of 29S, together with a shell model and a direct capture calculation, we reanalyzed the 28P(p, γ)29S thermonuclear reaction rate and its astrophysical implication. Aims. We focus on improving the astrophysical rate for 28P(p, γ)29S based on the newest nuclear mass data. Our goal is to explore the impact of the new rate and associated uncertainties on the nova nucleosynthesis. Methods. We evaluated this reaction rate via the sum of the isolated resonance contribution instead of the previously used Hauser-Feshbach statistical model. The corresponding rate uncertainty at different energies was derived using a Monte Carlo method. Nova nucleosynthesis is computed with the 1D hydrodynamic code SHIVA. Results. The contribution from the capture on the first excited state at 105.64 keV in 28P is taken into account for the first time. We find that the capture rate on the first excited state in28 P is up to more than 12 times larger than the ground-state capture rate in the temperature region of 2.5 × 107 K to 4 × 108 K, resulting in the total 28P(p, γ)29S reaction rate being enhanced by a factor of up to 1.4 at ~1 × 109 K. In addition, the rate uncertainty has been quantified for the first time. It is found that the new rate is smaller than the previous statistical model rates, but it still agrees with them within uncertainties for nova temperatures. The statistical model appears to be roughly valid for the rate estimation of this reaction in the nova nucleosynthesis scenario. Using the 1D hydrodynamic code SHIVA, we performed the nucleosynthesis calculations in a nova explosion to investigate the impact of the new rates of 28P(p, γ)29S. Our calculations show that the nova abundance pattern is only marginally affected if we use our new rates with respect to the same simulations but statistical model rates. Finally, the isotopes whose abundance is most influenced by the present 28P(p, γ)29S uncertainty are 28Si, 33,34S, 35,37Cl, and 36Ar, with relative abundance changes at the level of only 3% to 4%.

Electrical conductivity of copper in the low temperature region of warm dense matter

In this study, electrical conductivity of copper in the low temperature part of a warm dense matter regime is investigated utilizing underwater electrical wire explosion. Specifically, for the vapor/plasma region with a density of ∼0.01 normal density, temperature up to 10 kK, and the liquid–vapor two-phase region below the binodal curve, the electrical conductivity of copper is measured as a function of density and temperature by means of shadowgraph imaging, spectroscopy, and electrical measurements. In this region, anomalous temperature dependence and characteristics originated from a phase transition are found. Based on the careful analysis of experiments and model calculations, it is revealed that bound electrons, in addition to free electrons, contribute significantly to the electrical conductivity in the vapor/plasma region, and that the associated phase transition kinetics play a substantial role in adequately describing the behavior in the liquid–vapor two-phase region. An improved electrical conductivity model emerging from our combined experimental and theoretical study that accounts for the characteristics in the low temperature regime of the warm dense matter is presented.

Deciphering the influence of support in the performance of NiFe2O4 catalyst for the production of hydrogen fuel and nanocarbon by methane decomposition

Wet chemical synthesis route was used to synthesis nickel ferrite (NiFe2O4) nanoparticle. Later on the synthesized NiFe2O4 were supported on the surface of three traditional supports such as Al2O3, MgO and TiO2 to get NiFe2O4/Al2O3, NiFe2O4/TiO2 and NiFe2O4/MgO catalysts. The activity profile of each catalyst was evaluated in a fixed-bed reactor for direct methane decomposition at 800 °C. For both fresh and spent catalysts, many characterization techniques have been employed mainly XRD, FESEM, HRTEM, Raman spectroscopy, TGA, and nitrogen adsorption-desorption isotherm. X-ray powder diffraction studies revealed that all synthesized catalysts have a cubic spinel crystal structure. The XRD confirm the presence of NiFe2O4 particles in the component of fresh NiFe2O4/MgO, NiFe2O4/TiO2 and NiFe2O4/Al2O3 catalysts. Temperature Program Reduction (TPR) unveiled the presence of Ni oxides and Fe oxides by displaying reduction peaks in their respective temperature regions. The N2 adsorption-desorption isotherms of the fresh all catalysts reveal that these catalysts have a mesoporous structure. Activity data concluded NiFe2O4/MgO to be the most active catalysts among the tested catalysts methane conversion magnitude of 41.13 % and H2 formation rate of 84.40 × 10−5 mol H2 g−1 min−1. On the other hand, the H2 formation rate drastically declined and very poor activity of both NiFe2O4/TiO2 and NiFe2O4/Al2O3 catalysts was observed in the current work. XRD patterns, FESEM images and TGA analysis of spent NiFe2O4/MgO catalyst shown the filamentous carbon formation which secondarily confirm its higher activity, while its absence in catalysts of NiFe2O4/TiO2 and NiFe2O4/Al2O3. TGA analysis of the carbon deposited on the NiFe2O4/MgO catalyst showed that the amount of carbon was approximately 64 wt%. It was suggested that the formation of nickel-iron carbide revealed by XRD studies of spent catalysts may be the factor related to their poor activity while discussing the structure-activity relationship. Likewise, the higher degree of dispersion related to NiFe2O4/MgO as displayed by XRD, FESEM and TPR investigations, played a vital role in accelerating the rate of hydrogen formation.

In Ukrainian

The CMs were obtained in argon in three stages: 1) heating (4 grad/min) to the specified temperature t in the range of 350–825 °С; 2) isothermal exposure 1 h; 3) cooling, washing from alkali and drying. Samples are denoted as CM(t). The CM yield (Y, %) and CMs elemental composition are determined. Based on low-temperature (77 K) nitrogen adsorption-desorption isotherms, integral and differential dependences of the specific surface area SDFT (m2/g) and pore volume V (cm3/g) on the average pore diameter (D, nm) were calculated by 2D-NLDFT-НS method (SAIEUS program). They were used to define volumes of ultramicropores (Vumi), supermicropores (Vsmi) and micropores (Vmi). The total pore volume V was calculated from the nitrogen amount adsorbed at a relative pressure p/p0 ~ 1.0. The S values of ultramicropores (Sumi), supermicropores (Ssmi) and micropores (Smi) were similarly determined. The CM yield was established to decrease linearly (R2 = 0.979) from 70.2 to 45.3 % with an increase in temperature from 350 to 825 °С. The carbon content decreases to a minimum value at 500 °С (72.6 %), and then increases to a maximum value (87.5 %) at 825 °С; the oxygen content changes antibatically. Two temperature regions were identified: region I (≤ 500 °С) of increasing the oxygen content due to reactions in which KOH acts as a donor of O atoms; region II (≥ 500 °C) of dominating the thermal destruction of functional groups (carboxyl, lactone, ester) with the release of CO and CO2, and condensation increasing the size of polyarenes of the CM secondary framework and formsng single Сar-Саr bonds between them. The CM(350) sample was found to contain only mesopores (D ≥ 10 nm) and macropores. An activation temperature increase to 400 °C initiates the additional formation of small-diameter micropores and mesopores. In samples CM(400) - CM(825), the main portion of newly formed pores falls on pores with D ≤ 5 nm. With increasing temperature, the micropores volume increases almost linearly (R2 = 0.992). The Vumi and Vsmi volumes increase up to 600 °C. At higher temperatures the ultramicropores volume decreases due to transforming ultramicropores (D ≤ 0.7 nm) into supermicropores (D = 0.7–2.0 nm). Portion of the ultramicropores volume changes with a maximum (23.9 %) in the CM(600) sample. The SBET specific surface area linearly (R2 = 0.992) increases with temperature up to 1729 m2/g. The SDFT values are close to SBET, but noticeably lower (1514–1530 m2/g) for CM(785)-CM(825). The micropores specific surface area increases to 1415 m2/g, and ultramicropore surface Sumi changes extremely with a maximum (526 m2/g) for the CM(600) sample, which should be expected based on the temperature dependence of the Vumi parameter. The decrease in Sumi values after the maximum is compensated by an increase in the supermicropore surface. Such an effect - the redistribution of pores by size in the microporous range (D ≤ 2 nm) with an increase in the alkaline activation temperature is not described in the literature. The portion of the micropores surface is dominant (92.6–97.0 %) in samples prepared at t ≥ 450 °C. The portion of the ultramicropore surface is maximum (56.3 %) in CM(500). Pores are revealed that do not form at all at 450–750 °C. These are supermicropores (D = 0.96–2.00 nm) and mesopores of small diameters (D = 2.0–2.82 nm). This effect was assumed to be due to the properties of the CM supramolecular framework, which is formed from polyarene fragments of the initial and activated coals having polyarenes with diameters of the same order (1.68–2.54 nm).

The comparative study of structural, optoelectronic and thermoelectric properties of Li-based half-Heusler alloys via GGA and meta-GGA functionals

The present work aims to investigate the effects of meta-GGA functionals on the structural, optoelectronic and thermoelectric properties of LiXY(X=Be, Mg, Zn, Cd and Y=N, P, As, Sb, Bi) half-Heusler alloys using density functional theory (DFT) and classical Boltzmann transport theory. The obtained lattice constants of these alloys are in good agreement with the experimental values, exhibiting a slight decrease slightly with meta-GGA functionals compared with GGA-PBE. Band structure calculations demonstrate that the materials exhibit semiconductor character and provide validation for the use of meta-GGA functionals, particularly the r2SCAN and rSCAN, to predict the band gap values of LiXY more accurately. Optical and thermoelectric properties are calculated and discussed in detail. The results reveal that the meta-GGA functionals predict a significant change compared with GGA-PBE in the low energy and temperature region, while in the high energy and temperature regions, all four functionals present almost the same change trends.

Decrease in MJO Predictability Following Indo–Pacific Warm Pool Expansion

AbstractThe characteristics of the Madden–Julian oscillation (MJO) have changed and are projected to continue changing with the expansion of the Indo–Pacific warm pool, which is the Earth's largest region of warm sea surface temperatures (SSTs). However, the likelihood of a change in MJO predictability following warm pool expansion remains unaddressed. Therefore, this study investigated the effect of warm pool expansion on MJO variability and predictability using the highly idealized aquaplanet configuration of Community Earth System Model 2 (CESM2). By expanding the warm pool in the Indo–Pacific, MJO‐like waves become more regionally confined, short‐lived convective events with weaker magnitude and less robust eastward propagating signals, possibly due to stronger zonal SST gradients and wider meridional widths of the warm pool. Perfect‐model ensemble forecast experiments revealed that the MJO predictability decreased by approximately 5 days, the forecast error proliferated, and the signal rapidly reduced following warm pool expansion.

Choice of reaction progress variable under preferential diffusion effects in turbulent syngas combustion based on detailed chemistry direct numerical simulations

The combustion of hydrogen and carbon-monoxide mixtures, so-called syngas, plays an increasingly important role in the safety context of non-fossil energy generation, more specifically in the risk management of incidents in process engineering plants for ammonia synthesis and in nuclear power plants. In order to characterize and simulate syngas/air combustion on industrially relevant scales, subgrid modelling is required, which is often based on a reaction progress variable. To understand the influence of different fuel compositions, turbulence intensities and flame topologies on different possible definitions of reaction progress variable, detailed chemistry direct numerical simulations data of premixed, lean hydrogen/air and syngas/air flames has been considered. A reaction progress variable based on normalized molecular oxygen mass fraction has been found not to capture the augmentation of the normalized burning rate per unit flame surface area in comparison to the corresponding 1D unstretched premixed flame due to preferential diffusion effects. By contrast, reaction progress variables based on other individual species, such as hydrogen, can capture the augmentation of the rate of burning well, but exhibit a pronounced sensitivity to preferential diffusion effects, especially in response to flame curvatures. However, a reaction progress variable based on the linear combination of the main products can accurately represent the temperature evolution of the flame for different mixtures, turbulence intensities and varying local flame topology, while effectively capturing the augmentation of burning rate due to preferential diffusion effects. However, its tendency to assume values larger than 1.0 in the regions of super-adiabatic temperatures poses challenges for future modeling approaches, whereas the reaction progress variable based on hydrogen mass fraction remains bound between 0.0 and 1.0 despite showing deviations in comparison to corresponding variations obtained from the unstretched laminar flame depending on flame curvature variations.