Periodic Variations Research Articles

Regionalized ensemble estimation of wave periods for assessing wave energy resources across Canada. Part II: Wave-period and wave-energy analyses

The cornerstone for harnessing and utilizing wave energy resources lies in the precise and thorough estimation and assessment of wave energy fluxes through advanced modeling of wave periods. This study implements the developed macroscale regionalized ensemble wave-period modeling (MREWPM) method to accomplish the initial integrated estimation and analysis of wave periods and wave energy fluxes across Canada, complemented by advanced estimations of wave heights and wind speeds. The results indicate that Canadian wave periods lengthen in shallow, low-backscatter, southern, remote, or eastern waters, and exhibit temporal variability in breezy, low-backscatter, southern, remote, or eastern regions. The trend of wave periods exhibited fluctuations, decreasing before and increasing after the trough (9.06 s in 2004) during cool seasons. Temporal variabilities and trends of wave periods were more fragmented and heterogeneous compared to averages. Canadian wave energy fluxes generally exhibit an increase southward with latitudes. The wave energy typically diminishes from offshore (deep waters) to nearshore areas (shallow waters), with this attenuation being more pronounced in winter months. There is a rough decrease from winter, autumn, and spring to summer months, mirroring the seasonal variations of wave periods. This seasonality tends to be more pronounced in highly energetic regions, such as the Pacific and Atlantic oceans. This study enhances reliability and feasibility of macroscale wave-period and wave-energy estimation and analyses, offering scientific support for wave energy development, wave climatology, and ocean engineering.

High performance SERS boosting by Fabry- Pérot cavities of silica-gold-silicon multilayers

Surface-enhanced Raman scattering (SERS), an advanced technique for molecular spectroscopy, relies heavily on the preparation of SERS active materials that can significantly enhance the Raman scattering signals for highly sensitive detection of trace molecules. Traditionally, SERS measurements are performed on silicon or silica substrates, the SERS performance is determined by the structure of SERS materials. Here, we show that the SERS signal can be amplified and modulated using Fabry-Pérot (F-P) cavities made of silica-silicon (SiO2-Si) or silica-gold-silicon (SiO2-Au-Si) multilayers as substrates. Periodic SERS signal variations as SiO2 thickness increases are observed, exhibiting optimal enhancement with the SiO2 thickness of 250 nm due to the optical interference in the cavity. Although the signal enhancement by optical interference is weaker than that by plasmonic resonance, additional signal amplification is essential for highly sensitive SERS materials. Moreover, we applied this strategy to detect thiram in bean sprout extracts, demonstrating that the detection sensitivity is two orders of magnitude higher than that using Si substrates. The utilization of the pseudo-internal standard intensity calibration method facilitates the quantitative analysis of thiram concentrations. Our results provide a promising approach for further amplification of SERS signals with great potential for practical applications.

Effects of climate variability and urbanization on spatiotemporal patterns of vegetation in the middle and lower Yangtze River Basin, China.

Vegetation serves as a crucial indicator of ecological environment and plays a vital role in preserving ecosystem stability. However, as urbanization escalates rapidly, natural vegetation landscapes are undergoing continuous transformation. Paradoxically, vegetation is pivotal in mitigating the ecological and environmental challenges posed by urban sprawl. The middle and lower Yangtze River Basin (MLYRB) in China, particularly its economically thriving lower reaches, has witnessed a surge in urbanization. Consequently, this study explored the spatiotemporal variations of normalized difference vegetation index (NDVI) in the MLYRB, with an emphasis on elucidating the impact of climate change and urbanization on vegetation dynamics. The results indicate that a significant increasing trend in NDVI across the MLYRB from 2000 to 2020, a pattern that is expected to persist. An improvement in vegetation was observed in 94.12% of the prefecture-level cities in the study area, predominantly in the western and southern regions. Temperature and wind speed stand out as dominant contributors to this improvement. Nevertheless, significant vegetation degradation was detected in some highly urbanized cities in the central and eastern parts of the study area, mainly attributed to the negative effects of escalating urbanization. Interestingly, a positive correlation between NDVI and the urbanization rate was observed, which may be largely related to proactive ecological preservation policies. Additionally, global climatic oscillations were identified as a key force driving periodic NDVI variations. These findings hold significant importance in promoting harmonious urbanization and ecological preservation, thereby providing invaluable insights for future urban ecological planning efforts.

A Gaussian Variogram‐Based Model of Total Electron Content in the Regional Ionosphere of China

AbstractThis study utilizes ionospheric total electron contents (TECs) data from China and its surrounding areas to compute the regional ionospheric semi‐variance using the Gaussian variogram. The regional ionospheric model is then constructed by introducing an additional stochastic term, named adjusted Spherical Harmonics Adding KrigING method (SHAKING), in which the stochastic Vertical Total Electron Content estimated using Kriging interpolation based on Ionospheric Variogram Model Parameters (IVMP) predict model. In the IVMP prediction model, two notable periodic patterns, that is, diurnal and annual signals with periods of 365.25/i days and 24/j hours, are recognized as Fourier series decompositions. These patterns capture the regular daily and yearly periodic variations in variogram parameters, and the IVMP prediction model is established using harmonic estimation methods. IVMP‐SHAKING is employed to generate the regional ionospheric map in China using multi‐GNSS data from 27 reference stations during days of the year 150–250 in 2022, with 14 rover stations used for evaluation. Results indicate that the proposed model exhibits a standard deviation of 4.85 TECu compared to the difference of slant TEC extracted from rover stations. Compared to existing models, including BDS‐3 broadcast ionospheric model (BDGIM), GPS broadcast model (Klobuchar), Galileo broadcast model (NeQuickG) and post‐processing Global Ionospheric Map released by IGS (IGSG), the accuracy of IVMP‐SHAKING improves by 6%–52%. Additionally, the Standard Point Positioning performance with different ionospheric corrections is analyzed on test stations. Results demonstrate that the horizontal and vertical positioning accuracy of the IVMP‐SHAKING model improves by 31%–55% and 16%–33%, respectively, compared to other three solutions.

An equivalent analysis of unsteady sand transport in a wind tunnel

This study investigates the effect of unsteady wind on sand transport in a wind tunnel using sinusoidally varying wind velocity to represent the unsteady wind. By comparing sand transport fluxes under steady and unsteady winds, we demonstrate that cumulative sand transport flux varies sinusoidally with the sinusoidally varying wind velocity. In addition to the time-averaged wind velocity, the sand transport rate is also affected by the amplitude and period of wind velocity variations. We then propose an ‘equivalent’ steady aeolian sand transport process as a substitute for the actual unsteady transport process. In terms of wind velocity amplitude and period variations, an equivalent wind friction velocity factor u*′ is defined to capture differences caused by wind velocity variations with the same time-averaged wind velocity and friction velocity. Finally, a unified equation for aeolian sand transport is derived, demonstrating applicability for both steady and unsteady flow conditions. The results of this study contribute to a deeper understanding of aeolian sand transport under unsteady flow.

A Possible Explanation of W-type Phenomena in V694 Peg

Three sets of complete multicolor light curves of V694 Peg observed in 2013, 2015, and 2019 were presented and analyzed. Our photometric solutions show that this system was an A-type shallow contact binary in 2013 and 2015 while it converted to a W-type one in 2019. A large cool spot on the component of this binary could explain the conversion, implying the W-type phenomena may be caused by the magnetic activity of the components. We have collected available data on this binary and calculated 505 times of light minimum, which spans 17 yr. The orbital period investigation based on these timings shows there is a long-term period increase at a rate of dP/dt = 4.3(±0.3)×10−9 day yr−1 superposed on a periodic variation with a period of 11.81(±0.06) yr. The cyclic orbital variation may be the result of magnetic activity cycles or the existence of a third body. Until now, only eight transformed systems, including V694 Peg, have been reported. Compared with other converting contact systems between A-type and W-type, V694 Peg is recorded as the shortest-period one. All of these converting systems are late-type (later than F7) contact binaries with the O’Connell effect and show cyclic period variation, which indicates that magnetic activity may be the reason for the conversion between the two types of contact binaries. For investigating the nature of A-type and W-type phenomena, the discovery of more converting contact binaries is essential.

A high precision 3-D tropospheric delay model over China using ERA5 data

The zenith tropospheric delay (ZTD) is an important error in Global Navigation Satellite System (GNSS) navigation and positioning. The current most empirical tropospheric delay models are two-dimensional with low spatial and temporal resolution and cannot capture high-frequent accurate ZTD variations in small areas and short periods, particularly in Mainland China with diverse climate changes and large terrain differences. In this paper, a high precision three-dimensional (3-D) tropospheric delay grid model (ZTD_3D) over China with a horizontal resolution of 0.25° × 0.25° and a time resolution of 1 hour was established with the piecewise function describing the height change of ZTD from 2016-2019 fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data (ERA5). The performance of the proposed model is verified by using radiosonde data and ZTD products from the Crustal Movement Observation Network of China (CMONOC), as well as the global pressure and temperature models (GPT2, GPT3-1 and GPT3-5). Results show that the RMS of ZTD_3D model is 2.04 cm when compared to radiosonde observations, and the accuracy is 55.1 %, 54.7 % and 63.1 % higher than that of GPT3-1 model, GPT3-5 model and GPT2 model, respectively, while the RMS of ZTD_3D model is 3.66 cm when compared to GPS ZTD from CMONOC, and the accuracy is 1.6 % and 29.7 % higher than that of GPT3-5 mode and GPT2 model, respectively. The application of the ZTD_3D model in GNSS precise point positioning (PPP) has showed accuracy improvement in the vertical direction. The model proposed in this study can provide accurate ZTD information and a reliable tropospheric delay correction model for precise GNSS positioning.

A comprehensive analysis of groundwater quality: Geospatial and multivariate approaches in Dindigul District, Tamil Nadu, India

This study focuses on a comprehensive analysis of groundwater quality by integrating hydrogeochemical, geospatial, Multivariate Statistical Approaches (MSA), and water quality indices (WQI), along with visualization techniques, in the Dindigul district of Tamil Nadu, India. A total of 69 water samples, collected during pre-monsoon (PRM) and post-monsoon (POM) periods by the Public Works Department, Tharamani, were analyzed for major cations (Na+, Ca+, Mg+, K+), anions (Cl-, SO4-, HCO3-, NO3-), and various physical and chemical parameters such as pH, Total Dissolved Solids (TDS), and Electrical Conductivity (EC). The Water Quality Index (WQI) for Bureau of Indian Standard was calculated to assess water quality for drinking purposes. PRM samples showed poorer water quality due to ion dilution and agricultural influence compared to POM samples. The WQI revealed that 3.4 % of the PRM area had excellent water quality, 40.72 % good, 35.54 % poor, 18.41 % very poor, and 1.91 % unsuitable for drinking. In the POM period, 6.34 % of the area was classified as excellent, 51.03 % good, 40.09 % poor, 2.45 % very poor, and 0.08 % unsuitable. Irrigation water quality indices, including Sodium Percentage (Na%), Sodium Adsorption Ratio (SAR), Kelly's Ratio (KR), Magnesium Hazard (MH), Residual Sodium Carbonate (RSC), and Permeability Index (PI), were also computed to identify suitable zones for sustainable agriculture. Correlation analysis indicated significant positive relationships between TDS and other parameters, like Bicarbonate, Total Hardness, Chloride, and EC during PRM, and Sulphate, Total Hardness, Calcium, Chloride, Sodium, and EC during POM, suggesting that TDS is a key indicator of water quality variations in both periods.

The curious case of 2MASS J15594729+4403595, an ultra-fast M2 dwarf with possible Rieger cycles

Context. RACE-OC (Rotation and ACtivity Evolution in Open Clusters) is a project aimed at characterising the rotational and magnetic activity properties of the late-type members of open clusters, stellar associations, and moving groups of different ages. The evolution in time of rotation and activity at different masses sheds light on the evolution of the stellar internal structure, on magneto-hydrodynamic processes operating in the stellar interior, and on the coupling and decoupling mechanisms between the radiative core and the external convective envelope. As part of this project, in the present paper we present the results of an investigation of a likely member of the AB Doradus association, the M-type star 2MASS J15594729+4403595. Aims. In the present study, we aim to reveal the real nature of our target, which turned out to be a hierarchical triple system, to derive the stellar rotation period and surface differential rotation, and to characterise its photospheric magnetic activity. Methods. We have collected radial velocity and photometric time series, complemented with archive data, to determine the orbital parameters and the rotation period and we have used the spot modelling technique to explore what causes its photometric variability. Results. We found 2MASS J15594729+4403595 to be a hierarchical triple system consisting of a dwarf, SB1 M2, and a companion, M8. The M2 star has a rotation period of P = 0.37 d, making it the fastest among M-type members of AB Dor. The most relevant result is the detection of a periodic variation in the spotted area on opposite stellar hemispheres, which resembles a sort of Rossby wave or Rieger-like cycles on an extremely short timescale. Another interesting result is the occurrence of a highly significant photometric periodicity, P = 0.443 d, which may be related to the stellar rotation in terms of either a Rossby wave or surface differential rotation. Conclusions. 2MASS J15594729+4403595 may be the prototype of a new class of extremely fast rotating stars exibiting short Rieger-like cycles. We shall further explore what may drive these short-duration cycles and we shall also search for similar stars to allow for a statistical analysis.

Study on the Spatio-temporal Evolutionary Properties of Gas-liquid Two-phase Flow in Centrifugal Pump as Turbine (PAT)

With the increasing complexity of the industrial production process, the transmission medium of the hydraulic turbine is no longer satisfied, and the gas-liquid two-phase mixed medium has to be considered. The presence of gas in the transmission medium will alters the internal flow structure of the hydraulic turbine and affect its operational stability. Therefore, for the purpose of clarifying the influence of inlet gas content on the internal flow of PAT, the unsteady flow of the PAT is simulated in this paper using numerical simulation. Based on the numerical simulation results, the influence of inlet gas content on the internal flow characteristics, characteristics of pressure fluctuation in impeller and volute, and vortex evolution of flow field are analyzed. The accumulation of gas phase leads to the emergence of vortices, and regions with low pressure values appear at the vortex generation. The major factor of the periodic variation of pressure fluctuation between volute and cut-water is the dynamic and static interference of impeller. The increase of gas content causes more flow disorder in the cut-water region and the volute contraction section. Since the gas in the flow channel is predominantly on the suction side of blades, the flow field on the suction side is more complex than that on the pressure side, and the amplitude of pressure fluctuation increases appropriately. The vortex structure is mainly distributed on balance hole, inlet area of impeller and suction side of blade. As the blade rotates, there are new shedding and growth of vortices, and finally attached to the volute wall. Increasing gas content enhances the influence of blade rotation on the vortex evolution characteristics in the volute and impeller.

Research on the aero-hydro coupling characteristics of the floating twin-rotor wind turbine system

The concept of installing two wind turbines on a floating platform, known as a floating twin-rotor wind turbine system, has recently garnered significant interest. This configuration can harness greater wind energy resources, reduce installation and mooring costs by sharing mooring lines, and minimize losses due to wake effects between turbines through yaw control. However, previous research has not sufficiently addressed the dynamic performance analysis of such systems. This study focuses on a high-capacity floating twin-rotor wind turbine system and develops an aero-hydrodynamic coupled analysis method based on the free vortex wake method and potential flow theory, specifically tailored for the twin-rotor configuration. This method facilitates real-time iterative calculations of wind and wave loads acting on the system and suggests optimization strategies for its design. Our findings indicate that the design of high-capacity floating twin-rotor systems can significantly reduce costs. Furthermore, the twin-rotor floating system design enhances wake recovery and achieves optimal comprehensive performance when the rotor spacing ratio (S/D) is 1.2 for the IEA 15 MW turbine. The coupled interactions induce periodic variations in aerodynamic performance, with the amplitude of these variations increasing with turbulence intensity. This research lays a theoretical foundation for advancing the design, platform optimization, and coupled computational analyses of large-capacity, large-scale floating twin-rotor wind turbine systems.

Spatial-temporal analysis and trend prediction of regional crop disease based on electronic medical records

Intelligent diagnosis of individual crop diseases has matured. How to understand the evolution patterns and predict regional disease trends remains a significant challenge. Plant Electronic Medical Records (PEMRs) offer valuable spatial-temporal characteristics about crop diseases, presenting a new opportunity for predicting the occurrence of regional diseases. In this study, we used a large prescription database from Beijing (2018–2021) to reframe regional disease prediction as a time series forecasting task. Firstly, to analyze spatial-temporal evolution patterns, we use ArcGIS to extract key information and identify potential connections between different disease occurrence points. Then, we developed a novel deep learning combined model SV-CBA, which combines Seasonal and Trend decomposition (STL) with Variational Mode Decomposition (VMD) to identify trend, seasonal, and residual components, and re-decomposes the residuals. STL-VMD can capture long-term trends and periodic variations while managing nonlinear and volatile characteristics. The CNN-BiLSTM-Attention model calculates disease trends by linearly integrating predictions of each sub-series. To reduce computational complexity while maintaining predictive performance, we propose an improved simplified attention mechanism. Our model demonstrates superior performance in both comparative and ablation experiments using the PEMRs dataset, outperforming numerous other models. This study provides accurate disease trend predictions, aiding farmers and regional managers in agricultural production management.

Searching for orbital period modulation in X-ray observations of the symbiotic X-ray binary GX 1+4

The symbiotic X-ray binary GX 1+4 possesses a number of peculiar properties that have been studied since the early 1970s. In particular, the orbital period has been a point of debate for many years, until radial velocity measurements were able to settle the debate. These radial velocity findings have so far not been confirmed using X-ray data, even though multiple factors would cause a periodic variation on the same timescale as the orbital period at these energies. Because the orbit of GX 1+4 is eccentric and not seen face-on, changes in the accretion rate and column density along the line of sight could cause a periodic variation in the spin-frequency measurements, X-ray light curves, and hardness ratios of the source. Furthermore, for a high inclination of the orbital plane, the neutron star could be eclipsed by the companion, which would lead to periodic decreases in brightness. We used data from a number of different X-ray telescopes to search directly for periodicity by applying the Lomb-Scargle and epoch-folding approaches to long-term light-curve and spin-frequency measurement data of the source. We support our findings using folded light curves, hardness ratios, and images. We find that our results agree with the radial velocity findings, and we form a self-consistent model that is supported by folded hardness-ratios and light curves. We find that the source is clearly detected in X-rays during the predicted eclipse. Motivated by this absence of an eclipse in the system, we constrain the inclination of the system to $ and the mass of the neutron star in the system to $ - 1.45M_ using the constraints on the red giant mass and surface gravity provided in the literature. Furthermore, we constrain the radius of the red giant to $ 60R_ - 150R_ odot$.

The impact of hydroclimate-driven periodic runoff on hydropower production and management

This study evaluates the impact of hydroclimate-driven periodic runoff on hydropower operations and production, with a focus on how the forecasted biennial periodicity of runoff time series could affect the efficiency of hydropower generation. Hydrologic stochastic processes are utilized to forecast long-term runoff, and seven hydroclimate scenarios are developed to be input into a production management model, allowing for an analysis of how periodic hydroclimate variations influence hydropower management and output. The results reveal that the biennial alternation between wet and dry years is a key factor affecting hydropower operations in the Dalälven River Basin. Notable differences between wet- and dry-year scenarios were observed in terms of power efficiency, production output, and forecasting accuracy. Operating hydropower systems based on dry-year runoff forecasts in wet years results in a 1.63% decrease in production efficiency and a reduction of 9,104 MWh in power generation. Conversely, applying wet-year forecasts in dry years slightly boosts production efficiency by 0.31% and increases power generation by 7,832 MWh. Scenarios that adhere to biennial periodicity offer the highest forecasting accuracy, particularly when applying dry-year forecasts in dry years in winter and spring, which produce the most precise predictions. In contrast, using dry-year forecasts in wet years results in the lowest forecasting accuracy.

Numerical simulation of molten pool flow behavior in ultrasonic vibration-assisted gas tungsten arc welding of low-alloy high-strength steel

The beneficial effects of ultrasonic vibration-assisted arc welding on the performance of welded joints have been experimentally confirmed. However, the mechanism of the influence of ultrasonic vibration on the temperature and flow fields of the welding pool is still not clear, which also limits further application prospects of this technology. The present study established a three-dimensional molten pool model for ultrasonic vibration-assisted gas tungsten arc (UV-GTA) welding of low-alloy high-strength steel, considering free deformation of the molten pool surface and different ultrasonic vibration amplitudes. The temperature field evolution and the molten pool flow behavior under various ultrasonic vibration amplitudes were systematically analyzed. Compared with GTA welding, the ultrasonic vibration in UV-GTA welding enhanced uniformity of the temperature distribution in molten pool. Moreover, the larger the ultrasonic amplitude in UV-GTA welding, the smaller the depth of the molten pool and the time required for the molten pool to reach a quasi-steady state, but the larger the maximum flow rate at the surface as well as at the center of the molten pool. At an ultrasonic vibration amplitude of 40 µm, the molten pool depth in UV-GTA welding decreased by 34.8 % compared with GTA molten pool depth. The time for this UV-GTA molten pool to reach a quasi-steady state was just 0.57 s, and the maximum velocity at its center increased by 88.1 % over that of the GTA molten pool. Comparative analysis of the UV-GTA molten pool and the GTA molten pool revealed a shorter circulating flow field on the upper surface and periodic variations in the internal flow field motion. The simulation outcomes closely align with the experimental findings, confirming both the validity of the model and the accuracy of the pertinent conclusions. This research may lay a solid theoretical foundation for further systematic exploration of the wider application prospects of ultrasonic vibration-assisted arc welding.

Flow field analysis of self-sustained flutter of a wide-slotted bridge deck

This study delves into the flutter mechanism of a 5,000 m bridge with a wide-slotted deck, finding that the motion is self-sustained and not violently destructive. The system damping ratio is not fixed, and only one stable orbit exists. High-resolution PIV experiments at an experimental wind speed of 10.5 m/s measured the static and dynamic flow fields on the windward and leeward decks. The static results showed leading-edge separation on the windward deck within the reference range, while separation on the leeward deck was difficult to observe. Dynamic testing identified instantaneous vortices around the windward/leeward deck at each phase, with no signs of vortices in the wind speed vectors at all phases after phase-averaging, indicating that the vortex drift hypothesis is not valid. The analysis of the streamline pattern revealed periodic variations in leading-edge separation size and reattachment length on the windward deck during the vibration process, while the leeward deck showed consistently inconspicuous changes. Further examination uncovered a peculiar behavior in the horizontal wind speed profile on the leeward deck during the vibration process, attributed to dynamic changes in the height difference between the windward and leeward decks during flutter. The study suggests that the unusual wind speed profile on the leeward deck is caused by the dynamic changes in height difference between the windward and leeward decks during the flutter process, resulting in additional wind loading. These findings shed light on the complex dynamics of bridge flutter and have implications for the design and maintenance of long-span bridges.

Numerical simulation of flow around a transversely oscillating square cylinder at Re=22000

The study utilized OpenFOAM software, combined with the k-ω shear stress transport (SST) turbulence model and Arbitrary Lagrangian-Eulerian (ALE) dynamic mesh method, to investigate the influence of the oscillation amplitude on the flow dynamics around a square cylinder at Re = 2.2 × 104. It was found that various oscillation amplitudes affect the non-Gaussian characteristics of fluctuating pressure differently along the cylinder's surface: diminishing at the leading edge while intensifying at the trailing-edge corner. Concurrently, secondary recirculation bubbles near the cylinder's leading and trailing edges gradually diminish and eventually disappear with increasing oscillation amplitudes. Analysis of the amplitude spectrum of transverse velocity indicates the exclusive presence of odd-order harmonics along the central axis, while both odd and even-order harmonics are observed on either side of the central axis. Additionally, heightened oscillation amplitudes result in increased energy transfer from the cylinder to the fluid, with the energy density function predominantly exhibiting negative values and periodic variations occurring at twice the frequency of cylinder displacement or lift coefficient. As the oscillation amplitude increases, the vortex in the wake region transitions from a single-row to a double-row configuration. The research results provide important theoretical guidance for deepening the understanding of the flow characteristics around the oscillating square cylinder.

Theoretical predictions of CO2, H2 and H2O adsorption mechanisms on M2C-MXene: Selectivity and potential application insights

M2C-MXenes, owing to their abundant adsorption sites, exhibit significant potential in CO2 capture, utilization, and storage (CCUS) and hydrogen energy applications, contributing to hydrogen utilization and global carbon reduction, and thus solving intractable energy and environmental problems. However, the extensive variety of M2C compounds poses challenges to the systematic evaluation of their applications in these fields. The exploration of the adsorption properties of M2Cs is a key fundamental aspect of these studies, and therefore, this study employs calculations across 456 adsorption systems to elucidate the adsorption mechanisms of 19 M2C compounds for small molecules (CO2, H2 and H2O). The results indicate that these M2C materials possess structural stability and metallic characteristics, with periodic variations in the d-band center aligning with trends in CO2 adsorption energy. Notably, molecular orientation impacts adsorption energy more significantly than adsorption sites, particularly for CO2, while M2C compounds primarily exhibit physical adsorption towards H2. Specifically, Sc2C preferentially adsorbs CO2 in atmospheric conditions, and shows chemical adsorption towards H2O, but exhibits negligible adsorption for H2; conversely, Cr2C demonstrates higher adsorption potential for H2. Both materials exhibit favorable thermodynamic stability, suggesting Sc2C is suitable for CCUS applications, while Cr2C holds promising prospects for hydrogen storage.

Evaluating the performance of carbon dioxide and methane observations from carbon-monitoring satellite products over China

As the primary greenhouse gases contributing to climate change, carbon dioxide (CO₂) and methane (CH4) play a critical role in the Earth's radiative balance and temperature regulation. Continuous and accurate satellite monitoring of CO₂ and CH₄ is essential for developing effective policies and strategies to mitigate their impacts. This study utilizes ground-based Fourier-transform infrared measurements from the Total Carbon Column Observing Network (TCCON) to evaluate the performance of current mainstream carbon-monitoring satellites over China, the world's largest carbon emitter. Our findings show that TanSat performs excellently for CO₂ observations at both Hefei and Xianghe sites, achieving a standard deviation (SD) of about 2 ppm and a maximum bias of 0.25 ppm, dropping to 0.02 ppm at Xianghe. In contrast, Orbiting Carbon Observatory (OCO)-3 and Greenhouse Gases Observing Satellite (GOSAT)-2 CO2 measurements are slightly less reliable. For CH₄ monitoring, GOSAT outperforms GOSAT-2, with a SD of around 14 ppb and bias within 2 ppb, compared to GOSAT-2's 17.58 ppb SD and 2.15 ppb bias at Hefei. These results indicate that the latest carbon-monitoring satellites are less precise and accurate than their predecessors. Additionally, we provide detailed assessments of the data products based on different spatial matching criteria. We also discuss the variation in satellite accuracy over time, revealing periodic bias variations and the instability in satellite performance. Furthermore, while the spatial distribution trends of satellite acquisitions are generally consistent on an annual scale, we observe non-negligible differences in the annual averages across specific land surfaces. Our study presents a meticulous evaluation of the reliability of satellite-based carbon-monitoring products over the Chinese region and provides scientific evidence for analyzing uncertainty in carbon source-sink studies.

Temperature-modulated dilatometry as tool for studying precipitation kinetics: Case example Al-Mg

Temperature-modulated dilatometry is implemented as a tool for studying phase equilibration processes in alloys. The potential of this method is demonstrated using a two-phase Al-Mg alloy consisting of the saturated solid solution Al(Mg) and intermetallic Al3Mg2. The relative length change upon sinusoidal temperature modulation around 380∘C with amplitude of 6∘C is monitored for different modulation periods between 1 h and 8 h. The temperature modulation and the thereby varying solubility of Mg in Al imposes a modulation of the relative fractions of the two phases, which can sensitively be detected by dilatometry owing to the different atomic volumes of the two phases. The phase equilibration process causes a characteristic phase lag of the periodic length variation with respect to the temperature modulation. From the variation of the phase shift with the modulation frequency, a reaction rate of k = 1.85 × 10−4 s−1 for the equilibration of the phase equilibrium can be deduced in the framework of a simple kinetic model. This value is in quantitative agreement with the kinetics expected for an equilibration process that is controlled by the diffusion of Mg in Al upon modulation-induced growth or shrinkage of the intermetallic Al3Mg2-phase.