Amplitude Of Temperature Fluctuations Research Articles

Thermal performance analysis of lightweight phase change envelopes

To improve indoor thermal comfort and achieve building energy saving, a new envelope structure based on phase change material (PCM) was proposed. Firstly, an experimental platform was built around the room model, and the effects of ambient temperatures and PCM layout on the room temperature at different times were explored. Subsequently, a room numerical model heat transfer was constructed and the experimental verification was completed. The effects of PCM thickness, position, arrangement, and melting point difference on the room temperature at each time were analyzed based on the latent heat utilization rate, temperature fluctuation amplitude, and delay time. The experimental results show that when the walls all around the room contain PCM, the maximum indoor temperature can drop to 29.5 °C, and the maximum temperature drop is 3.2 °C. In addition, the greater the heat flow, the less effective the PCM is at controlling the temperature in the room. The simulation results show that when the PCM with a thickness of 15 mm is placed on the interior side of the wall, the maximum indoor temperature can be reduced to 29 °C, the maximum temperature drop is 2.9 °C, and the peak indoor temperature is extended by 0.8 h. When the PCM is arranged in series and the melting point difference is 3 K, the temperature control effect is the best, the maximum indoor temperature can be reduced to 25.7 °C, the maximum temperature drop is 2.9 °C, and the temperature fluctuation is the minimum, 2.6 °C.

On the kinetic temperature of a one-dimensional crystal on the long-time scale

We investigate the dynamics of the kinetic temperature of a finite one-dimensional harmonic chain, the evolution of which is initiated by a thermal shock. We demonstrate that the kinetic temperature returns arbitrarily close to its initial state (the one immediately following the thermal shock) infinitely many times, and we give an estimate for the time elapsed until the recurrence. This assertion is closely related to the Poincare recurrence theorem and we discuss their relation. To estimate the recurrence time we use its averaging along system’s trajectory and provide a rigorous mathematical definition of the mean recurrence time. It turns out that the mean recurrence time exponentially increases with the number of particles in the chain. A connection is established between this problem and the local theorems of large deviations theory.Previous studies have shown that in such a one-dimensional harmonic chain, at times of order N, a thermal echo phenomenon is observed — a sharp increase in the amplitude of kinetic temperature fluctuations. In the present work, we give a rigorous mathematical formulation to this phenomenon and estimate the amplitude of the fluctuations.The research is partially funded by the Ministry of Science and Higher Education of the Russian Federation within the framework of the Research Center of World-Class Program: Advanced Digital Technologies (agreement №075-15-2020-311 dated 04.20.2022).

Unsteady-state modeling and analysis of a spray-assisted low-temperature desalination system

The spray-assisted low-temperature desalination (SLTD) technology driven by low-grade heat sources has demonstrated excellent thermodynamic and economic performances. However, existing studies are based on steady-state analyses and cannot describe dynamic system performance under fluctuations of the operating conditions. This work presents an unsteady-state analysis of the SLTD system driven by low-grade waste-heat sources. A dynamic model is developed and validated against experimental data. The model is observed to predict dynamic temperature profiles accurately with a maximum absolute error of ±0.3 °C. Then, the model is applied to analyze the responses of the SLTD system to different disturbances. Results show that the first evaporator is the most sensitive to the heat source temperature fluctuation, while locations farther away from the disturbance have longer response times and smaller fluctuations. When the heat source temperature for a 4-effect system fluctuates by 10 %, the response time and temperature fluctuation amplitude of the 1st effect are 579 s and 8 %, respectively, while those of the 4th effect are 1007 s and 3 %, respectively. Besides, the systems with smaller heat transfer areas, fewer numbers of effect, and higher heat source temperatures have faster response speeds. The results provide useful information for system operation and control strategy exploitation.

Characterization of PCM-PCHE and its effect on the suppression of temperature fluctuations in the SCO2 Brayton cycle

Supercritical CO2 Brayton cycles are now widely used in industrial power generation systems based on various energy sources. In order to solve the temperature problem that is prone to occur at the outlet of the turbine, a printed circuit heat exchanger (PCHE) with phase change materials (PCM) incorporated in it is intended to minimize system temperature fluctuations at the cost of extremely low heat exchange loss.. In this paper, a numerical simulation method is used to study this PCM-embedded PCHE to investigate the overall heat exchanger performance. It is found that when the phase shift between the inlet fluctuations of the hot and cold sides is 180°, this PCHE with embedded PCM has the best reduction of the outlet temperature fluctuation amplitude. Then it was put into an overall supercritical CO2 Brayton cycle, and it was found that PCM-PCHE could reduce the amplitude of efficiency fluctuations by roughly 40.8 %, the overall stability of the system was significantly improved, average power generation was increased by about 1.6 kW based on the reduced power consumption of the two-stage compressor.

Yellow hypergiant V509 Cas: Stable in the ‘yellow void’

Context. The yellow hypergiant star V509 Cas is currently undergoing an extreme phase of evolution. Having experienced eruptive mass-loss outbursts in the 20th century, the star’s effective temperature reached record high values in the early 2000s. However, since then, the star’s behaviour has displayed an unprecedented level of stability. In spite of that, the star could be traversing through the ‘yellow void’ instability region. Aims. To describe the current evolutionary state of V509 Cas, we analysed its variability using photometric and spectroscopic data collected over recent years. By comparing our findings with historical records, we aim to determine whether the star’s surface shows signs of stabilisation. Additionally, we investigate the variability of emission components in the wings of certain spectral lines to highlight the contribution of the circumstellar gaseous disc to this phenomenon. Methods. Our spectroscopic monitoring observations were carried out at Tartu Observatory over the course of seven years, supplemented by echelle spectra obtained at the Nordic Optical Telescope, as well as publicly available photometric data from Gaia, AAVSO, and AAVSO’s Bright Star Monitor programme. We estimated the variability of effective temperature and radial velocity from the spectral time series and correlated it with the brightness variability of V509 Cas. Results. The results indicate that the star’s average brightness level has remained stable throughout the observed period, with an amplitude of variability ∼0.1 mag. While the amplitude of short-term temperature fluctuations has decreased compared to the early 2000s, the variability of the radial velocity remains similar to historical values from the early 20th century. Moreover, we show how the variable radial velocity affects the emission components in some absorption lines (e.g. Sc II) and how that follows the hypothesis of a disc surrounding the star.

Sizes of Active Galactic Nucleus Inhomogeneous Disks—Large in Microlensing, Small in Reverberation Mapping

Magnetohydrodynamic turbulence can drive significant temperature fluctuations in the accretion disk of an active galactic nucleus (AGN). As a result, the disk can be highly inhomogeneous and has a half-light radius larger than the static Shakura and Sunyaev disk (SSD), in agreement with quasar microlensing observations. Meanwhile, the accretion-disk sizes can also be determined using continuum reverberation mappings that measure interband cross-correlations and time lags. The interband time lags are often understood in the X-ray reprocessing scenario. Here we show that the interband continuum time lags of the X-ray reprocessing of an inhomogeneous disk are similar to or even smaller than those of a static SSD. Consequently, the X-ray reprocessing of an inhomogeneous disk cannot account for the recent continuum reverberation mappings of some Seyfert 1 AGNs, whose measured time lags are larger than those of a static SSD. In contrast to the tight correlation between UV/optical variations, the cross-correlation between X-ray and disk emission is rather weak in this model; this behavior is consistent with recent continuum reverberation mappings. Moreover, the time lags in this model are anticorrelated with the amplitude of disk temperature fluctuations. Our results suggest that the temperature fluctuations should be properly considered when modeling interband continuum time lags.

A novel microfluidic chip integrated with Pt micro-thermometer for temperature measurement at the single-cell level

Noninvasive and sensitive thermometry of a single cell during the normal physiological process is crucial for analyzing fundamental cellular metabolism and applications to cancer treatment. However, current thermometers generally sense the average temperature variation for many cells, thereby failing to obtain real-time and continuous data of an individual cell. In this study, we employed platinum (Pt) electrodes to construct an integrated microfluidic chip as a single-cell thermometer. The single-cell isolation unit in the microchip consisted of a main channel, which was connected to the inlet and outlet of a single-cell capture funnel. A single cell can be trapped in the funnel and the remaining cells can bypass and flow along the main channel to the outlet. The best capture ratio of a single MCF7 cell at a single-cell isolation unit was 90 % under optimal condition. The thermometer in the micro-chip had a temperature resolution of 0.007 °C and showed a good linear relationship in the range of 20–40 °C (R2 = 0.9999). Slight temperature increment of different single tumor cell (MCF7 cell, H1975 cell, and HepG2 cell) cultured on the chip was continuously recorded under normal physiological condition. In addition, the temperature variation of single MCF7 cell in-situ after exposure to a stimulus (4 % paraformaldehyde treatment) was also monitored, showing an amplitude of temperature fluctuations gradually decreased over time. Taken together, this integrated microchip is a practical tool for detecting the change in the temperature of a single cell in real-time, thereby offering valuable information for the drug screening, diagnosis, and treatment of cancer.

Model-based prediction of frost formation inside frozen food packages under temperature fluctuations

Abstract Frozen storage of food products is widely accepted not only in the industry but also by households. Frost formation during long-term storage is recognized as a phenomenon that causes changes in product characteristics and quality losses. However, quantitative prediction and control of frost formation remains a challenge. In this study, a mathematical model was developed to predict frost formation inside frozen food products (i.e., frozen minced meat packed in a polyvinylidene chloride (PVDC) film) under fluctuating temperature conditions in a domestic refrigerator. The proposed model is based on heat transfer and energy balance equations, and the amount of frost formation is estimated from the heat generated by condensation. The heat transfer coefficients were experimentally obtained and applied to the developed model. The interactions between the amplitude and frequency of temperature fluctuations and the corresponding amount of frost formation were visualized using contour plots. Both the amplitude and frequency were found to increase frost formation. For the range of fluctuations tested (temperature amplitudes of 0.5–2.5 K and cooling rates of 0.0125–0.2 K/min when connected to the compressor), the simulation predicted that the amount of frost in the packages varied up to approximately 4.5 times (0.48–2.18 g/month for packages containing 300 g of minced meat) depending on the different temperature fluctuation settings.

Complex Microlandscape as a Structural Unit of the Study of Spatiotemporal Development of an Ombrotrophic Suboceanic Bog

Ombrotrophic suboceanic bogs are distinguished by a high diversity of complex microlandscapes within the bog massif. Each complex microlandscape is a separate intrabog ecosystem with a specific set of parameters and relationships. This study aims to assess the specifics of the characteristics and parameters of the complex microlandscapes as part of an ombrotrophic suboceanic Sphagnum bog and as stages of bog morphogenesis, and to establish the internal relationships and their relationship with external environmental factors. A comprehensive multidisciplinary approach was used to assess the functioning of the complex microlandscapes. It was found that the relationship with the air temperature is closer than with the bog water table dynamics. It was shown that the morphometric parameters of perennial dwarf shrubs can serve as indicators of the stages of development of bogs. The processes of the self-regulation of complex microlandscapes are weakened with the age of the complex microlandscape, as evidenced by an increase in the amplitude of temperature fluctuations and the level of bog waters, as well as the key physicochemical parameters of the peat deposit. This leads to a gradual, slow reorientation of the physicochemical processes occurring in the deposit, from the deposition of organic matter to the decomposition of peat biomass.

Laser Weld Seam Curved Path Effect on 6063 Aluminum Alloy Strength and Temperature Distributions: COMSOL Numerical Simulation

To improve the welding performance of aluminum alloys, a thermal source model of an irregular weld seam was established. COMSOL software was used for numerical simulation of the weld seam geometry effect on the temperature and stress fields in laser welding, which results were experimentally validated. The results show that the ellipsoidal laser welding melted micropool exhibited quasi-steady-state temperature field characteristics. The temperature gradient and thermal stress showed an increase followed by a decline. The temperature fluctuation amplitude of the square-tooth-shaped weld seam exceeded that of the arc-toothshaped one. The temperature evolution of the broken line tooth-shaped weld seam showed a slightly increasing trend, except for the inflection point. The experimental average tensile strength of the weld seam was the highest, reaching about 210 MPa, i.e., roughly 85% of the base material (245 MPa), which coincided with the COMSOL-based temperature field simulation results. With increasing deformation amplitude and transition radius, the maximum tensile force, tensile strength, and elongation at fracture showed an increasing trend. However, the deformation amplitude should be below a certain limit because its increase elongates the welding path and reduces the distance between weld seams, resulting in serious heat accumulation. The tensile fracture morphology of the 6063-T6 base material was curved shear, with shallow toughness pits, small tearing edges at the edges, and small granular objects, indicating small plastic deformation during the fracture process. The tensile fracture of the welded part spanned the weld seam and the base material, and the fracture occurred along the tangent direction of the weld seam. The fracture surface was smooth, the tearing edges at the edge of the toughness pit shifted along the weld seam direction, forming many co-directional slip bands, with highly pronounced plastic deformation.

Performance of Spodoptera litura (Lepidoptera: Noctuidae) in responses to different amplitudes of alternating temperatures across permissive warm temperature regimes.

Climate change involves changes in the pattern of temperature fluctuations and the frequency and magnitude of thermal extremes. It is essential to investigate how insects respond to increased temperature variations, especially for species that usually experience diel temperature variations extending to thermal performance limits. To explicitly elucidate the effects of sizes of amplitudes of temperature variations, we used daily alternating temperatures with an equivalent mean of 28 °C to investigate the impact of different fluctuation amplitudes (± 0 °C, ± 2 °C, ± 4 °C, and ± 6 °C) across permissive temperature regimes on the performance of Spodoptera litura FabriciusFabricius, a highly destructive polyphagous pest of crops and vegetables in tropical and temperate climates. Amplitudes of temperature fluctuations significantly affected developmental durations, adult life spans, pupal weights, fecundity, and fertility of S. litura. The survival rates from the egg stage to the adult eclosion did not differ significantly across different temperature treatments. The developmental durations of individual life cycles significantly increased with larger amplitudes in 3 fluctuating temperature treatments. The pupal weight was significantly lower and the adult life span was significantly shorter in the ± 6 °C treatment in all treatments. Fecundity and fertility were significantly reduced in the ± 6 °C treatment, making the continuation of generations nearly impossible. The results should provide critical information for understanding the ecology of this widespread pest under diel, seasonal, and global climate changes.

Climatology of gravity wave activity based on two Martian years from ACS/TGO observations

Context. Gravity waves redistribute energy and momentum between the lower and upper atmosphere, thus providing vertical coupling between layers, and they affect the state, dynamics, and variability of the upper atmosphere. The statistics of gravity wave activity on Mars is poorly explored but is required in order to characterize the atmospheric circulation and to constrain numerical models. Aims. We present the gravity wave statistics accumulated over two Martian years: from the second half of Martian year 34 to the middle of Martian year 36 (May 2018 to February 2022). The statistics includes seasonal and latitude distributions of the wave potential energy and drag, serving to represent the wave activity and impact on the atmospheric dynamics. Methods. The observations were performed by the middle- and near-infrared spectrometers of the Atmospheric Chemistry Suite on board the ExoMars Trace Gas Orbiter. The temperature profiles we obtained independently from both channels during simultaneous measurements show a good agreement, thus providing verification and enhancing confidence in the data. The gravity wave parameters included amplitudes of temperature fluctuations, potential energy per unit mass, and wave drag. These parameters were retrieved at altitudes up to 160 and 100 km from the middle- and near-infrared channels, respectively. Results. A comparison of the data obtained during the global dust storm of Martian year 34 with the corresponding period of Martian year 35 without a storm revealed a reduction of wave activity in mid-latitudes, which is in agreement with previous observations, and enhancement in the polar regions of the southern hemisphere, which was not predicted by simulations with a high-resolution circulation model.

Verification experiment of maximum hydraulic diameter in a novel three-dimensional asymmetric oscillating heat pipe

A novel three-dimensional asymmetric oscillating heat pipe (3DAOHP) with unequal curvature radius of upper and lower bends has been designed. Setting the basic factor of diameter from 1.9 mm to 6.2 mm, a verification experiment on the criterion of conventional maximum hydraulic diameter (MHD) has been conducted. The results show that the 3DAOHP can still perform normally and transfer heat effectively, even if the diameter exceeds the MHD by 98.1 %. And the temperature profiles at each end does not show obvious abnormalities. The thermal performance also does not show any deterioration, which still follows the rule that the larger the diameter, the stronger the heat transfer capability. The thermal resistance of the 6.2 mm 3DAOHP can reach 0.07 °C/W at 1300 W without touching the dry-out limit. Moreover, the frequency and amplitude of hot end temperature fluctuation show suppression as the diameter increases. Therefore, the conventional MHD is not a diameter limitation of oscillating heat pipe (OHP) in enhancing heat transfer. Thus, the availability of OHP in high heat loads can be improved by further increasing the tube diameter. These findings are important for the OHP application in higher heat flux.

Comparing temperature fluctuation attenuation capabilities and feasible parameter regions of indirect- and direct-contact heat exchangers for an ultra-high precision constant-temperature chilled water system: An experimental and Modelica-based study

Constant temperature and humidity rooms have widespread applications in high-end manufacturing and scientific research. Conventional wisdom primarily focuses on controlling the air temperature at the terminals, i.e., the supplied outlets. For achieving ultra-high precision (e.g., ±0.1 °C), it becomes essential to pre-control the temperature of the chilled water of the air-conditioning system. Nevertheless, there is still limited understanding of this matter. This paper investigated two common temperature fluctuation attenuators for the chilled water system: indirect- and direct-contact heat exchangers, e.g., a plate heat exchanger (PHE) and a water mixing pump (WMP), respectively, as follows. First, Modelica models of the two systems were established and validated by an experimental set-up capable of switching between the PHE and WMP loops. Second, an orthogonal analysis was conducted to evaluate the attenuation effects of four key factors. Results indicated that both attenuators can provide the required constant temperature precision with nuanced differences. The MWP system demonstrated faster settling time, primarily affected by valve adjustment accuracy. In contrast, PHE exhibited superior fluctuation control, with valve adjustment accuracy and input chilled water temperature fluctuation amplitude as critical factors. Finally, feasible parameter regions for the two types of attenuators under ultra-high precision targets were delineated and analyzed.

МЕРЫ БОРЬБЫ С СОРНОЙ РАСТИТЕЛЬНОСТЬЮ НА ПОСЕВАХ СОИ

In the forest-steppe zone of the Republic of North Ossetia-Alania on soybean crops (Iriston varieties), the effect of the soil herbicide Harness and insurance herbicides Galaxy Top, Illoxan, Frontier was studied. The aim of the research was to study the effect of various herbicides on the contamination of crops and the species composition of weed vegetation of promising soybean varieties in the conditions of the forest-steppe zone of the Russian Federation. Scientific novelty of research. The influence of various herbicides on the growth, development and productivity of promising soybean varieties has been studied; the effect of herbicides on the contamination of crops has been shown; The removal of basic nutrients by individual species of weeds has been established. Every year, more and more new herbicides appear on the market, so studying the properties of herbicides and their effect on weeds is an urgent task. The methodology. On the leached chernozems of the forest-steppe zone of the Russian Federation-Alania in 2020-2022, on the experimental fields of the SCNIIGPSH VNC RAS. The sowing method is wide–row (row spacing – 45 cm), with a seeding rate of 400 thousand germinating seeds per 1 hectare. The research area is hot, mostly well-humidified. The sum of temperatures is 3000-3200 °C. The climate of the described territory is continental, the absolute annual amplitude of air temperature fluctuations is 64 ° C. On the territory of the experiment, the soil is represented by medium-sized, heavy-loamy leached chernozem, underlain by pebbles. The soil is mechanically loamy, with a depth that turns into light and medium loamy- rocky. The authors found that chemical protection of crops from weeds in the forest-steppe zone should be carried out with combinations of herbicides Pivot 0.9 + Bazagran 1.1. At the same time, weed death reaches from 79.4 to 92.9%. After harvesting soybeans, the soil is quite suitable for the cultivation of any agricultural crop, since (in specified doses) herbicides do not accumulate in products and are safe for the environment.

System multi-scale analysis of temperature control for spaceborne electronic devices

<sec>To improve the simulation resolution and accuracy in thermal analysis of spaceborne electronic devices and the temperature control performance of passive thermal control devices, a system multi-scale model is established, thereby obtaining the temperature field and heat flux of electronic devices inside the satellite on different scales as illustrated in the below figure. The temperature fluctuation mechanism inside the satellite is analyzed on different physical scales. The thermal analysis resolution of spaceborne electronic equipment is improved, and a method to reduce the power fluctuation of spaceborne equipment is proposed based on the results of system multi-scale thermal analysis.</sec><sec>The results indicate that the accuracy deviation between the multi-scale model of the system and the actual model is less than 9%. However, the system multi-scale model saves 99.67% of the mesh generation time, which greatly improves the computation efficiency. The system multi-scale model can capture the thermal information about device-level chip microstructures at a lower computational cost. The system-level model can evaluate the temperature control and insulation performance of passive thermal control materials on a macroscale. The temperature fluctuation amplitude of the platform compartment is 7.95 K, while the temperature fluctuation amplitude of the load compartment decreases to 2.43 K after the temperature of the composite phase change insulation material has been controlled, which is 69.43% lower than that of the platform compartment. Compared with traditional vacuum insulation panels, the composite phase change materials are very superior in controlling the temperature of the chamber and suppressing temperature fluctuations. The temperature fluctuation signal after being insulated by the composite phase change insulation materials shows a characteristic of shifting to the high-frequency domain. After selecting the cabins that require key insulation and temperature control through multiple regression analysis, a simplified model at device level is employed to obtain temperature fields under different thermal control device layouts as a training dataset. A neural network genetic algorithm is used to predict the optimal installation position of passive thermal control device on the device scale and a thermal control layout scheme is obtained, which reduces the maximum temperature fluctuation of the device by 2.74 K. If the temperature uniformity coefficient is taken as the optimization goal, the temperature of each device on PCB board can be reduced to 14.39% of the average temperature of all devices through optimizations.</sec>

A phase change material based annular thermoelectric energy harvester from ambient temperature fluctuations: Transient modeling and critical characteristics

Annular thermoelectric power generator has been increasingly considered in application of ambient energy harvesting owing to the advantages of simple structure and no pollution. To improve thermal stability and energy harvesting performance of this system, the latent heat of phase change materials to improve thermal management and the high thermal conductivity of the heat sink to enhance heat transfer with the ambient are harness to annular thermoelectric power generator. Motivated by this, a phase change material based annular thermoelectric energy harvester (PCM-ATEH) with fins is developed for ambient energy harvesting and its three-dimensional transient model is also built up through jointly with thermo-electric and phase change processes. This paper considers the influence of key parameters such as temperature fluctuation amplitude, temperature fluctuation period, height ratio of PCM and thermoelectric generator (TEG) and melting temperature on liquid fraction, temperature difference, voltage and power density. Moreover, the comparison of PCM-ATEH and PCM based thermoelectric energy harvester (PCM-TEH) with/without fins is further conducted in this study to explore thermal management and energy harvesting performance. The energy harvesting characteristics of PCM-ATEH with fins is developed concerning the combination of power generation of TEG and melting process of PCM. Based on the results, it is found that the temperature difference and power density of PCM-ATEH with fins vary periodically with the sinusoidal temperature boundary, and results show that increasing temperature fluctuation period is not always feasible. Additionally, the comparative results indicate that the peak power density and energy efficiency of PCM-ATEH with fins are increased by 0.126 W/m2 and 0.02 % compared with PCM-TEH with fins, and increased by 0.195 W/m2 and 0.041 % compared with PCM-ATEH without fins. The results of energy harvesting characteristics show that a maximum of 0.77$ per watt can be reached to power generation cost of PCM-ATEH with fins. This paper can provide theoretical guidance for thermal management and energy conversion of energy harvesting system.

Various disturbances propagation analysis of district heating system based on the standardized thermal resistance method

AbstractVarious heating disturbances and faults in the heating network are necessary to be controlled and handled by some intelligent heating strategies with the increasing complexity of the heating network. This paper constructed the dynamic modeling of the heating system using standard thermal resistance and obtained a dynamic heat current model of the heating system. On this basis, we analyzed the heat transfer performance of the heating system. Five disturbances are selected, including the behavior of users, indoor heat source, heat exchanger heat transfer performance deterioration, pipe blockage, and pipe leakage. The effects of different disturbances on the overall system and user side water supply temperature were obtained by establishing a dynamic model for segmented heating pipelines. Feasible control methods for the heating network and load side are sorted out, mainly changing the water supply's temperature and the water supply's flow rate to reduce the water supply's fluctuation. Five specific control strategies are proposed for five types of disturbances. Comparing the case without control and the case with control, the results show that the fluctuation of water supply temperature is significantly reduced, and the control strategies can reduce the impact of disturbances on the heat network system and customers and improve the comfort of customers in the presence of disturbances. under the disturbance of pipeline leakage, the method proposed in this article reduces the temperature fluctuation amplitude by 75% and the fluctuation duration by 60%.

Formation mechanism of aluminum and its carbides under wobbling laser melting injection with carbon nanotubes-SiC hybrid particles

The softening problem of fusion zone (FZ) impede the widespread application of wobbling laser welding (WLW) which plays an essential role in aluminum alloy welding. The introduction of carbon nano tubes (CNTs) and SiC particles (SiCp) has the potential to alleviate this problem, whereas the mechanism of aluminum solidification and carbides synthesis under wobbling laser with multiple reinforcers is still unknown. Accordingly, CNTs-SiCp reinforced aluminum FZ is fabricated by wobbling laser melting injection (WLMI) for the first time. The numerical simulation of WLW and WLMI is incorporated in microstructure characterization, kinetic-thermodynamic calculation is innovatively carried out to determine the critical synthesis condition of carbides. The new insights into the nucleation/growth and orientations principle of aluminum with its carbides are demonstrated comprehensively. Firstly, the process of WLMI makes preferred growth of Al in FZ more diversified than that under WLW due to the undulate liquid-mushy interface. Secondly, carbides of Al4C3 and Al4SiC4 can exhibit a coupled growth in FZ edge due to high frequency and large amplitude of temperature fluctuation, rather than that have an independent growth in FZ center with relatively stable temperature. Thirdly, the coherent orientation relationships (ORs) that <0001>Al4C3//<0001>Al4SiC4 and <0001>Al4C3//<100>Al is preferred to be formed under oscillating heat-flow field of WLMI. Finally, the desired orientation of Al, Al4C3 and Al4SiC4 with fine grain can be gained in FZ, its strength has even exceeded base metal by more than 10%. This paper can be regarded as a breakthrough in strengthening FZ under WLW, by WLMI with CNTs-SiCp hybrid particles, and provide a theoretical guidance of microstructure and property optimization.

Pre-landing Assessment of the Surface and Shallow Subsurface Thermal Setting of Mare Crisium of the Moon for the Heat Flow Measurement Planned on the Blue Ghost 1 Mission

In 2024, under NASA’s Commercial Lunar Payload Services initiative, a robotic lander will touch down in Mare Crisium of the Moon and deploy a heat flow probe. Ideally, the probe should penetrate the regolith deep enough (1.5–2 m) to avoid the influence of insolation, but it is a major challenge to excavate such a hole on a robotic mission. The present study assesses the insolation-induced temperature fluctuation in the shallower subsurface of the landing site in case the heat flow probe does not reach past that depth. The assessment was based on a newly constructed, one-dimensional heat conduction model, which accounted for the history of solar heat intake at the landing site for the past 100 yr. The thermal properties of the subsurface regolith of the model were constrained by the previous surface temperature observations by flyovers of NASA’s Lunar Reconnaissance Orbiter and the subsurface thermal measurement data from Apollo 17. The model showed that the amplitude of the insolation-induced annual subsurface temperature fluctuation is modulated by the 18.6 yr period precession of the Moon. The model also showed that the amplitude of this annual wave would be at (or close to) its minimum in 2024, when the mission would take place. Even though the thermal wave may be felt at depths greater than 1.5 m, because of its small amplitude, the thermal gradient in the depth range from 1 to 1.5 m would be within several percent of the gradient representative of the endogenic heat flow.