Thermal Structure Research Articles

PRODIGE - Planet-forming disks in Taurus with NOEMA. II. Modeling the CO (2-1) isotopologue emission of the Class II T Tauri disks in Taurus

To understand how planets form in protoplanetary disks, it is necessary to characterize their gas and dust distribution and masses. This requires a combination of high-resolution dust continuum and molecular line interferometric observations, coupled with advanced theoretical models of protoplanetary disk physics, chemical composition, and radiative transfer. We aim to constrain the gas density and temperature distributions as well as gas masses in several T Tauri protoplanetary disks located in Taurus. We use the 12CO, 13CO, and C18O (2-1) isotopologue emission observed at $0.9 with the IRAM NOrthern Extended Millimeter Array (NOEMA) as part of the MPG-IRAM Observatory Program PRODIGE (PROtostars and DIsks: Global Evolution \, PIs: P. Caselli Th. Henning). Our sample consists of Class II disks with no evidence of strong radial substructures. We use these data to constrain the thermal and chemical structure of these disks through theoretical models for gas emission. To fit the combined optically thick and thin CO line data in Fourier space, we developed the DiskCheF code, which includes the parameterized disk physical structure, machine-learning (ML) accelerated chemistry, and the RADMC-3D line radiative transfer module. A key novelty of DiskCheF is the fast and feasible ML-based chemistry trained on the extended grid of the disk physical-chemical models precomputed with the ANDES2 code. This ML approach allows complex chemical kinetics models to be included in a time-consuming disk fitting without the need to run a chemical code. We present a novel approach to incorporate chemistry into disk modeling without the need to explicitly calculate a chemical network every time. Using this new disk modeling tool, we successfully fit the 12CO, 13CO, and C$ $O (2-1) data from the CI, CY, DL, DM, DN, and IQ Tau disks. The combination of optically thin and optically thick CO lines allows us to simultaneously constrain the disk temperature and mass distribution, and derive the CO-based gas masses. The best-fit disk gas masses range between 0.005 and $0.04 M_ sun $. These values are in reasonable agreement with the disk dust masses rescaled by a factor of 100 as well as with other indirect gas measurements via, for example, modeling of the wavelength dependence of the dust continuum emission radii, and HD and CO isotopologue emission.

Effect of sodium hydroxide treatment on the fracture toughness of luffa natural fiber reinforced epoxy epikote 828

AbstractMicro‐sized luffa natural fibers (MLNFs) were derived from raw luffa natural fibers from Vietnam by undergoing treatment with sodium hydroxide. This study examined the impact of sodium hydroxide concentration, temperature, and treatment duration on the fracture toughness of epoxy resin 828 reinforced with MLNFs. The results showed that the fracture toughness of the composite, as measured by the critical‐stress‐intensity factor (KIC) and Izod impact strength, was improved after the treatment of the MLNFs with sodium hydroxide. Specifically, with the optimal sodium hydroxide treatment parameters of 6% NaOH at 70 °C for 6 h, the critical‐stress‐intensity factor increased by 93% (from 2.0 to 3.86 MPa m1/2) and the Izod impact strength rose by 44.6% (from 3.81 to 5.51 kJ/m2). The thermal properties and surface structure of MLNFs treated with NaOH were analyzed using thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) images.

EMISSA: Exploring millimetre indicators of solar-stellar activity III. Comparison of Ca II indices and millimetre continua in a 3D model atmosphere

Amongst several spectral lines, some of the strongest chromospheric diagnostics are offered by the Ca II H K lines. These lines can be used to gauge the temperature stratification of the atmosphere since the line core and wings are formed in different regions of the solar atmosphere. Furthermore, the Ca II lines act as tracers for the magnetic structure of the solar atmosphere, as the line cores are formed in the upper chromosphere even though they are formed in non-local thermodynamic equilibrium (NLTE). In contrast, the formation of millimetre (mm) continuum radiation occurs under local thermodynamic equilibrium (LTE) conditions. As a result, the brightness temperatures obtained from observations with the Atacama Large Millimetre/Submillimetre Array (ALMA) offer a complementary perspective on the activity and thermal structure of stellar atmospheres. The overall aim is to establish more robust solar/stellar activity indicators using ALMA observations in comparison with classical diagnostics, such as the s index and infrared triplet (IRT) index. We employed the 1.5D radiative transfer codes RH1.5D and advanced radiative transfer (ART) to compute the synthetic spectra for the Ca II lines and the millimetre (mm) continua, respectively. These calculations were performed using an enhanced network atmosphere model, which incorporates non-equilibrium hydrogen ionisation generated by the state-of-the-art 3D radiation magnetohydrodynamics (rMHD) Bifrost code. To account for the limited spatial resolution of ALMA, we simulated the effect using a Gaussian point spread function (PSF). Additionally, we analysed the correlations and slopes of scatter plots between the Ca II indices and mm continuum for the original and degraded resolutions, focusing on the entire simulation box, quiet Sun regions, and enhanced network patches separately. The activity indices generated from these lines could further be used to compare the spectra of Sun-like stars with the solar spectrum. We present a comparative study between synthetic continuum brightness temperature maps at mm wavelengths (0.3 mm to 8.5 mm) and the Ca II activity indices; namely, the s index and infrared triplet (IRT) index. The Ca II activity indices and mm brightness temperatures are weakly correlated at the high resolution, with the highest correlation observed at a wavelength of 0.3 mm, corresponding to ALMA band 10. As the resolution decreases, the correlation consistently increases. Conversely, the slopes exhibit a decreasing trend with increasing wavelength, while the degradation of resolution does not noticeably affect the calculated slopes. As the spatial resolution decreases, the standard deviations of the Ca II activity indices and brightness temperatures decrease, while the correlations between them increase. However, the slopes do not exhibit significant changes. Consequently, these relationships could be valuable for calibrating the mm continuum maps obtained through ALMA observations.

Room-Temperature Phase Transition Material with Switchable Second-Order Nonlinear Optical Properties.

Phase transition materials with switchable second-order nonlinear optical (NLO) properties have attracted extensive attention because of their great application potential in photoelectric switches, sensors, and modulators, while metal-free organics with NLO switchability near room temperature remain scarce. Herein, we report a hydrogen-bonded metal-free organic crystal, 2-methylpropan-2-aminium 2,2-dimethylpropanoate (1), exhibiting a room-temperature phase transition and favorable NLO switchability. Through investigations on its thermal anomalies, dielectric properties, and crystal structures, we uncover that 1 holds a near-room-temperature phase transition at 303 K from noncentrosymmetric point group C2v to centrosymmetric one D2h, which is attributed to the order-disorder transformations of both tert-butylamine cations and dimethylpropionic acid anions. Accompanied by symmetry change during the phase transition, 1 exhibits reversible and repeatable NLO "on-off" switchability with a desirable switching contrast ratio of ca. 19 between high and low NLO states. This discovery demonstrates a metal-free organic crystal with NLO switching behavior near room temperature, serving as a promising candidate in smart and ecofriendly photoelectric functional materials and devices.

Shining bright: B@S-codoped graphitic carbon nitride nanorods illuminate enhanced catalytic C-N bond formation under visible-light

Graphitic carbon nitride as a photocatalyst seeking attention nowadays, due to its thermal stability, band structure, and chemical properties. Herein, we reported a boron sulfur co-doped graphitic carbon nitride (B@S-g-C3N4) photocatalyst synthesized by a one-pot thermal polycondensation mechanism. However, it was observed that due to co-doping in native carbon nitride structure the photocatalytic behavior and the band structure enhanced which was capable of fascinating the demand of organic transformations i.e. photocatalytic and charge transfer capability. The synthesized B@S-g-C3N4 photocatalyst was characterized by UV–vis DRS, FT-IR, XRD, SEM, EDX, HR-TEM, XPS and electrochemical properties. In addition, the synthesized B@S-g-C3N4 photocatalyst is a metal-free carbon nitride photocatalyst proven to be highly effective in performing organic transformations (conversion yield 98 %) like C-N bond formation under visible light source.

Aquatic photosynthetic carbon pump driven by periodic temperature variations affects dissolved inorganic carbon and hydrochemical characteristics in a groundwater-fed reservoir

Under the influence of periodic temperature variations, biogeochemical cycling in water bodies is markedly affected by the periodic thermal stratification processes in subtropical reservoirs or lakes. In current studies, there is insufficient research on the influence and mechanism of dissolved inorganic carbon (DIC) distribution in karst carbon-rich groundwater-fed reservoirs under the coupled effects of thermal structure stratification and the biological carbon pump (BCP) effect. To address this issue, the Dalongdong (DLD) reservoir in the subtropical region of southern China was chosen as the site for long-term monitoring and research on relevant physicochemical parameters of water, DIC, and its stable carbon isotope (δ13CDIC), CO2 emission flux, as well as the reservoir's thermal stratification index. The results show that: (1) the DLD reservoir is a typical warm monomictic reservoir, which exhibits regular variations of mixing period-stratification period-mixing period on a yearly scale due to thermal structure changes; (2) DIC was consumed by aquatic photosynthetic organisms in the epilimnion during the stratification period, leading to a decrease in DIC concentration, partial pressure of CO2 (pCO2) and CO2 emission flux, and an increase in stable carbon isotope (δ13CDIC). During the mixing period, the trend was reversed; (3) During the thermal stratification, aquatic photosynthesis and water temperature were the primary factors controlling DIC variations in both the epilimnion and thermocline. Regarding the hypolimnion, calcite dissolution, organic matter decomposition, and water temperature were the dominant controlling factors. These results indicate that although carbon-rich karst groundwater provides a plentiful supply of DIC in the DLD reservoir, its availability is still influenced by variations in the reservoir's thermal structure and the metabolic processes of aquatic photosynthetic organisms. Therefore, to better estimate the regional carbon budget in a reservoir or lake, future studies should especially consider the combined effects of BCP and thermal structure variations on carbon variations.

A simple model for predicting oxygen depletion in lakes under climate change

ABSTRACT The advent of climate change has placed aquatic ecosystems at risk for potential declines in water quality, including an increase in the number of lakes experiencing substantial dissolved oxygen (O2) depletion. Through its influence on the thermal structure of lakes via elevated water temperatures and alterations in stratification phenology, climate change intensifies biogeochemical and ecological processes involved in O2 consumption, giving rise to conditions like hypoxia/anoxia. However, predicting O2 dynamics is difficult, with in situ O2 depletion rates showing considerable lake-dependent variability, underpinned by distinct underlying mechanisms. Our study attempts to overcome these lake-specific features and targets distilling key components of O2 depletion into a simple and transferable conceptual model applicable across a diverse array of lakes and at large scales. Using O2 depletion rates from literature reflecting variability in trophic state, we quantified the typical O2 depletion rate ranges for oligotrophic, mesotrophic, and eutrophic lakes and assessed their temperature sensitivity for a broader climate impact assessment. Our model gave reasonable estimates for O2 depletion and risks of anoxia through 3 explanatory variables: trophic state, stratification duration, and hypolimnion temperature. We validated our model predictions using data from 5 German lakes and assessed the relative importance of the 3 influencing factors. This easy-to-use approach has potential for lake management to attain rapid assessments of possible future problems with O2 dynamics in a given lake, even in the absence of in situ data. Moreover, it allows scaling of O2 dynamics continentally/globally without lake-specific hydrological or morphological details.

The contradiction between lithospheric thermal and seismic structures reveals a nonsteady thermal state – A case study from Northeast China

The nature of the lithosphere, as the outermost layer of the solid Earth, has long been a focus of the Earth sciences. Many methods have been used to study the properties and structure of the lithosphere, including gravity, magnetism, electricity, seismic, and geothermics. Since the 1970 s, a coupled heat-flow heat-production steady-state model has been employed to study the thermal structure of the continental lithosphere and has helped researchers explain many geothermal observations. However, the steady-state model does not work well in some areas. Taking Northeast China as a case study, we systematically calculated the lithospheric thermal structure, compared the result with seismic research, and concluded that the lithospheric thermal state is nonsteady in the southern Songliao Basin, the southern Greater Xing’an Range and the Changbai Volcano. The lithosphere in southern Songliao Basin features a hot top and a cold bottom. The lithosphere in southern Greater Xing’an Range and the Changbai Volcano feature a cold top and a hot bottom. Our numerical simulation has demonstrated that the response of surface heat flow to thermal disturbance at the bottom of the lithosphere often lags by more than 20 Myr, resulting in a significant disparity between the thermal structure calculated based on surface heat flow and the velocity structure of seismic waves. In addition, this study of the thermal structure in Northeast China shows that the temperature of the Moho in Songliao Basin is very high (>600 °C), which may be an important cause of the lack of Cenozoic volcanism in the Songliao Basin.

Representation of Thermomechanical Damage in Fiber-Reinforced Ceramic Composites at High Thermal Gradients

Ceramic matrix composites (CMCs) are the core strategic materials for the thermal structure of new-generation hypersonic aircraft. The unclear understanding of the cross-scale thermomechanical behavior and failure mechanism of materials and structures in high-temperature transient environments is a key scientific issue that restricts the reliable design and safe operation of hypersonic aircraft. In this study, a high-temperature test module in a supersonic wind tunnel with integrated various test systems was independently designed to systematically investigate the thermal mechanical damage evolution of CMCs used in astronautics applications under high-temperature transient conditions. Furthermore, a numerical method for fluid-heat-solid coupling based on an iterative solution strategy was developed and compared with an algorithm based on a wall modification strategy in terms of computational efficiency and accuracy. Besides, a comparative analysis was conducted with the temperature field distribution of the sample obtained in the hypersonic wind tunnel integration test to verify the correctness of the developed thermal-fluid-solid coupling calculation method. Finally, through thermoelastic coupling computational models, the high-thermal-gradient-induced thermomechanical damage mechanism of the CMCs was revealed, providing support for further optimizing the material system and thermal structure design of the CMCs.

Effect of composition on the thermal properties and structure of M-Al-Si-O-N glasses, M = Na, Mg, Ca

The primary objective of this study is to explore the relationship between the composition, structure, and thermal characteristics of M-Al-Si-O-N glasses, with M representing sodium (Na), magnesium (Mg), or calcium (Ca). The glasses were prepared by melting in a quartz crucible at 1650 °C and AlN precursor (powder) was utilized as a nitrogen source. The measured thermal properties studied were glass transition temperature (Tg), crystallization temperature (Tc), glass stability, viscosity, and thermal expansion coefficient (α). The findings indicate that increasing the aluminum content leads to higher glass transition, crystallization temperatures, and viscosities. In contrast, fragility values increase with the Al contents, while modifier elements and silicon content influence thermal expansion coefficient values. FTIR analysis revealed that in all glasses, the dominant IR bands are attributed to the presence of Q2 and Q3 silicate units. The effect of Al is observed as a progressive polymerization of the silicate network resulting from the glass-forming role of Al2O3. In most samples, the Q4 silicate mode was also observed, strongly related to the high Al content. Overall, the study shows that the complexity of composition-property correlations where the structural changes affect the properties of Mg/Ca-based oxynitride glasses has potential implications for their use in various technological fields.

Anomalous Characteristics of Water Vapor Budget on the Tibetan Plateau under the Influence of Tropical Cyclones over the Bay of Bengal during Early Summer

Abstract Early summer is a peak time for tropical cyclone (TC) activities over the Bay of Bengal (BoB) and a period of South Asian monsoon onset, and the TCs during this time have a significant impact on the water vapor transport associated with monsoons. This study investigates the anomalous characteristics of the dynamic–thermal atmospheric circulation structure and water vapor budget over the Tibetan Plateau (TP) under the influence of BoB TCs generated in May from 1979 to 2020 with JTWC best track data and ERA5 data. Results reveal that a significant southerly water vapor channel forms from the BoB to the southeastern TP with a water vapor convergence near the Yarlung Zangbo Grand Canyon. A part of the water vapor is transported directly to the TP by deep southerly jet, while the other part is lifted by TCs and then climbs upward to the TP by two uplift processes occurring on the southern slope of the TP and over the TP respectively, which makes the whole troposphere over the southeastern TP warmer and wetter. It is found that anomalous southeasterly airflow in the northeast of TC circulation turns to anomalous southwesterly airflow forming an abnormal anticyclonic circulation over the southern TP in the middle and upper troposphere due to the diabatic heating effect. In this process, the TP acts as an anomalous water vapor sink with remarkable water vapor inflow through its southern boundary, with the main water vapor outflow through the eastern boundary, but a weak easterly water vapor backflow to the eastern TP in the lower troposphere. Significance Statement This study attempts to investigate the anomalous features of the water vapor budget over the Tibetan Plateau (TP) under the influence of the Bay of Bengal (BoB) tropical cyclones (TCs) during early summer. Results show that a significant southerly water vapor channel forms from the BoB to the southeastern TP with a water vapor convergence near the Yarlung Zangbo Grand Canyon. The TP acts as an anomalous water vapor sink with more and higher water vapor inflows through the southern boundary of the TP. A positive temperature and humidity anomaly can be found over the southeastern TP extending upward into the middle and upper troposphere. The results are helpful to understand how the BoB TCs affect the weather process over the TP.

Characterizing the 3D Structure of Molecular Cloud Envelopes in the Cloud Factory Simulations

We leverage recent numerical simulations of highly resolved star-forming regions in a Milky Way–like galaxy to explore the nature of extended gaseous envelopes around molecular clouds. We extract a sample of two dozen star-forming clouds from the feedback-dominated suite of Cloud Factory simulations. With the goal of exploring the 3D thermal and chemical structure of the gas, we measure and fit the clouds’ radial profiles with multiple tracers, including nHI , nH2 , nHtot , n CO, and gas temperature. We find that while solar neighborhood clouds recently detected via 3D dust mapping have radially symmetric, low-density envelopes that extend ∼10–15 pc, the simulated cloud envelopes are primarily radially asymmetric with low-density envelopes that extend only ∼2–3 pc. One potential explanation for the absence of extended envelopes in the simulated clouds may be the lack of magnetic fields, while a stronger local feedback prescription compared to solar neighborhood conditions may drive the radially asymmetric cloud morphologies. We make the pipeline used to extract and characterize the radial profiles of the clouds publicly available, which can be used in complementary and future simulations to shed additional light on the key physics shaping the formation and evolution of star-forming structures in the Milky Way.

Effect of covalently functionalized Indian bentonite clay on thermal, mechanical strength and morphology structure of extrusion/injection‐molded nylon 6 composites

AbstractThe research and development of functional polymer composites and their production have posed significant challenges, particularly in creating high mechanical strength and thermal stability composites. In this study, we utilized a micro corotation extruder and injection molding to produce covalently functionalized Indian bentonite clay‐nylon 6 high‐strength nanocomposites. For comparison, two different amines, 3‐aminopropyl trimethoxysilane and N‐[3‐(trimethoxysilyl) propyl] ethylene di‐amine, were used to functionalize bentonite clay. Additionally, 3% and 5% less amino clay filler was added in the nanocomposite to manufacture the polymer composite. Analytical techniques such as Powder X‐Ray Diffraction, Fourier transform infrared, thermal gravimetric analysis, and Brunauer–Emmett–Teller surface area were used to characterize the molecular orientation of amine functionalization on clay minerals. Wide‐angle X‐ray diffraction, atomic force microscopy, and transmission electron microscope were used to characterize the nylon 6 intercalated in amino clay nanocomposite and the polymer structure morphology. Thermogravimetric analysis and differential scanning calorimetry were used to investigate the crystalline thermal behavior of clay‐nylon 6 composites. From the results, it was observed that the composition containing 5 wt.% amino clay demonstrated a significant improvement in tensile strength when compared with the composition containing 3 wt.% amino clay. The mechanical strength and the thermal behavior showed a significant improvement of ⁓200% for 5% amino clay‐nylon 6 nanocomposite.

Synthesis, crystallization behavior and mechanical property of biodegradable Poly(butylene succinate-co-2-methyl succinate) copolyesters

In this research, a series of biodegradable poly(butylene succinate-co-2-methyl succinate) (PBSMS) random copolyesters with butylene 2-methyl succinate (BMS) unit content from about 10 to 90 mol% were successfully synthesized. Both the homopolymers poly(butylene succinate) (PBS), poly(butylene 2-methyl succinate) (PBMS), and PBSMS copolyesters showed relatively high intrinsic viscosity values of over 0.8 dL/g. The basic thermal parameters, crystallization behavior, crystal structure, spherulitic morphology and growth rate, and mechanical properties of PBSMS copolyesters were extensively studied and compared with those of PBS. The incorporation of methyl group not only effectively increased the toughness of PBSMS copolyesters but also significantly restrained the crystallizability of these copolyesters, showing that PBSMS copolyesters with the BMS unit content higher than 50 mol% were amorphous. Among these copolyesters, PBSMS30 (BMS unit content = 30 mol%) exhibited the most outstanding mechanical properties, with a Young's modulus of 188.0 ± 19.1 MPa, a tensile strength of 19.1 ± 1.8 MPa, and an elongation at break of 714.5 ± 23.2 %. By randomly introducing methyl as a side group into the PBS main chain, the mechanical properties of PBSMS copolyesters have been significantly improved. From the perspective of structure and properties, this study should be interesting and crucial for the development and research of biodegradable polymers.

Impact of Planetary Parameters on Water Clouds Microphysics

Potentially habitable exoplanets are targets of great interest for the James Webb Space Telescope and upcoming mission concepts such as the Habitable Worlds Observatory. Clouds strongly affect climate and habitability, but predicting their properties is difficult. In Global Climate Models (GCMs), especially those aiming at simulating Earth, cloud microphysics is often crudely approximated by assuming that all cloud particles have a single, constant size or a prescribed size distribution and that all clouds in a grid cell are identical. For exoplanets that range over a large phase space of planetary properties, this method could result in large errors. In this work, our goal is to determine how cloud microphysics on terrestrial exoplanets, whose condensable is mainly water vapor, depend on aerosol properties and planetary parameters such as surface pressure, surface gravity, and incident stellar radiation. We use the Community Aerosol and Radiation Model for Atmospheres as a 1D microphysical model to simulate the formation and evolution of clouds including the processes of nucleation, condensation, evaporation, coagulation, and vertical transfer. In these 1D idealized experiments, we find that the parameters that determine the macrophysical thermal structure of the atmospheres, including surface pressure and stellar flux, impact cloud radiative effect (CRE) most significantly. Parameters such as gravity and number density of aerosols working as cloud condensation nuclei affect the microphysical processes of cloud formation, including activation and vertical transfer. They also have a significant, though weaker effect on CRE. This work motivates the development of more accurate GCM cloud schemes and should aid in the interpretation of future observations.

Preparation, thermal properties, and structures of ionic plastic crystals with sandwich and half-sandwich Ru complexes

We have recently been investigating the phase behavior of salts of cationic sandwich complexes in pursuit of novel ionic plastic crystals (IPCs). In this study, we synthesized salts containing sandwich complexes [Ru(Cp)(C6H6)]X ([1]X; X = CPFSA− (1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide), SbCl6−) and half-sandwich complexes [Ru(Cp)(DMSO)3]X ([2]X; X = CPFSA−, FSA− ((FSO2)2N−), PF6−). In addition, we examined their thermal properties and crystal structures. Among them, [1]CPFSA exhibited an IPC phase between 365 and 630 K, whereas the others did not undergo phase transitions at 123–403 K. The cations and anions were alternately arranged in the crystals of [1]X, whereas [2]X did not exhibit the alternating arrangement except for [2]PF6. The results showed that alternating molecular arrangements are crucial for the IPC formation, although low symmetry of the ion environment and intermolecular steric hindrance may inhibit it.

A Graph Neural Network Approach to the Inverse Design for Thermal Transparency with Periodic Interparticle System

Abstract Recent years have witnessed significant advancements in utilizing machine learningbased techniques for thermal metamaterial-based structures and devices to attain favorable thermal transport behavior. Among the various thermal transport behaviors, achieving thermal transparency stands out as particularly desirable and intriguing. Our earlier work demonstrated the use of a thermal metamaterial-based periodic interparticle system as the underlying structure for manipulating thermal transport behavior and achieving thermal transparency. In this paper, we introduce an approach based on graph neural network to address the complex inverse design problem of determining the design parameters for a thermal metamaterial-based periodic interparticle system with the desired thermal transport behavior. Our work demonstrates that combining graph neural network modeling and inference is an effective approach for solving inverse design problems associated with attaining desirable thermal transport behaviors using thermal metamaterials.

Climate warming effects in stratified reservoirs: Thorough assessment for opportunities and limits of machine learning techniques versus process-based models in thermal structure projections

It is nowadays a hot topic to apply machine learning (ML) algorithms to illustrate water temperature dynamics in lentic waters. Due to the limited amount of in-situ temperature measurements from traditional sampling programmes, most of the related studies, however, restricted their analysis within the surface and rarely checked the results for whole depth profiles. Moreover, capability of such methods in projecting thermal dynamics under future climate conditions is even less illustrated. To fill the gap, we collected an unparalleled huge database including 9 million water temperature measurements, from 2013 to 2022, in Rappbode Reservoir, Germany as well as the corresponding climatic and hydrological observations, to train three commonly used ML models (Random Forest, XGBoost, and Long Short-Term Memory) and comprehensively evaluate their performance in reproducing thremal structure within the whole water column. We also systemically compared such simulation results with a well-established process-driven model (CE-QUAL-W2). Going beyond a pure reproduction of observatiosn, we further evaluated the ability of CE-QUAL-W2 and ML models in projecting thermal dynamics under RCP8.5 climate scenario up to 2100. Our results suggested three ML methods yielded high accuracy in capturing water temperature dynamics from the surface (epilimnion) to bottom (hypolimnion), and also satisfactorily reproduced temporal development of the stratification pattern, with the results corresponding well with those from CE-QUAL-W2. By contrast, the projections by ML models were rather insensitive to future climate warming under RCP8.5 comparing with those by CE-QUAL-W2, pointing to an important risk whenever ML-based models are extrapolated beyond their training data range. Supported by millions of in situ measurements, our research clearly illustrated the opportunities (limits) of ML models in projecting thermal dynamics in deep waters, and the conclusion also provides key guidance for scientists to select the appropriate tools in projecting water temperature, and other environmental factors, under changing climate.

Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Planetary and cometary atmospheres

The study of planets and small bodies within our Solar System is fundamental for understanding the formation and evolution of the Earth and other planets. Compositional and meteorological studies of the giant planets provide a foundation for understanding the nature of the most commonly observed exoplanets, while spectroscopic observations of the atmospheres of terrestrial planets, moons, and comets provide insights into the past and present-day habitability of planetary environments, and the availability of the chemical ingredients for life. While prior and existing (sub)millimeter observations have led to major advances in these areas, progress is hindered by limitations in the dynamic range, spatial and temporal coverage, as well as sensitivity of existing telescopes and interferometers. Here, we summarize some of the key planetary science use cases that factor into the design of the Atacama Large Aperture Submillimeter Telescope (AtLAST), a proposed 50-m class single dish facility: (1) to more fully characterize planetary wind fields and atmospheric thermal structures, (2) to measure the compositions of icy moon atmospheres and plumes, (3) to obtain detections of new, astrobiologically relevant gases and perform isotopic surveys of comets, and (4) to perform synergistic, temporally-resolved measurements in support of dedicated interplanetary space missions. The improved spatial coverage (several arcminutes), resolution (~ 1.2′′ − 12′′), bandwidth (several tens of GHz), dynamic range (~ 105) and sensitivity (~ 1 mK km s−1) required by these science cases would enable new insights into the chemistry and physics of planetary environments, the origins of prebiotic molecules and the habitability of planetary systems in general.

Improved photocatalytic performance of Sn/Cl co-doped TiO2 nanoparticles via a novel volatilization solid solution method

Sn/Cl co-doped TiO2 nanoparticles were synthesized via a novel volatile solid solution method. The effect of SnCl2·2H2O concentration (0–35.4 mol.%) and calcination temperature on thermal effect, crystal structure, morphology, composition, light absorption and photocatalytic performance of TiO2 nanoparticles was investigated by TG-DSC, XRD, SEM, EDS, TEM, HRTEM, SAED, UV–Vis, PL, photocurrent test, EIS and XPS. Results indicate that Sn and Cl are co-doped into TiO2 crystal lattice forming a mixed anatase-rutile TiO2 phase without SnO2 phase when SnCl2·2H2O concentration is below 17.7 mol.%, and excess SnCl2·2H2O caused the rutile SnO2 generation and simultaneous rutile TiO2 disappearance. The degradation efficiency of methyl orange reaches 98.7 % using 17.7 mol.% SnCl2·2H2O modified TiO2 calcined at 380 °C after 2 h of 15 W UV light irradiation, which is 19.72 % and increases by two times compared with that of pure TiO2 (8.98 %) after 2 h of 15 W visible light irradiation, both showing the maximum photocatalytic performance possibly due to the simultaneous increased active surface sites, enhanced light absorption and improved separation efficiency of photogenerated electron-hole pairs resulted from small particle size, reduced energy band gap and formation of mixed anatase-rutile TiO2 phases. Reactive species scavenging experiments revealed that O.-2 and h+ play a dominant role in photodegradation process.