Cold State Research Articles

Ocean-forcing of cool season precipitation drives ongoing and future decadal drought in southwestern North America

The US Southwest is in a drought crisis that has been developing over the past two decades, contributing to marked increases in burned forest areas and unprecedented efforts to reduce water consumption. Climate change has contributed to this ongoing decadal drought via warming that has increased evaporative demand and reduced snowpack and streamflows. However, on the supply side, precipitation has been low during the 21st century. Here, using simulations with an atmosphere model forced by imposed sea surface temperatures, we show that the 21st century shift to cooler tropical Pacific sea surface temperatures forced a decline in cool season precipitation that in turn drove a decline in spring to summer soil moisture in the southwest. We then project the near-term future out to 2040, accounting for plausible and realistic natural decadal variability of the Pacific and Atlantic Oceans and radiatively-forced change. The future evolution of decadal variability in the Pacific and Atlantic will strongly influence how wet or dry the southwest is in coming decades as a result of the influence on cool season precipitation. The worst-case scenario involves a continued cold state of the tropical Pacific and the development of a warm state of the Atlantic while the best case scenario would be a transition to a warm state of the tropical Pacific and the development of a cold state of the Atlantic. Radiatively-forced cool season precipitation reduction is strongest if future forced SST change continues the observed pattern of no warming in the equatorial Pacific cold tongue. Although this is a weaker influence on summer soil moisture than natural decadal variability, no combination of natural decadal variability and forced change ensures a return to winter precipitation or summer soil moisture levels as high as those in the final two decades of the 20th century.

Elaborative collection of condensed combustion products of solid propellants: Towards a real Solid Rocket Motor (SRM) operational environment

A novel constant-pressure and constant-quenching distance Condensed Combustion Products (CCPs) collection system was developed, coupled with a timing control system, to collect the CCPs formed in the course of burning of aluminum-based composite propellants. The effects of adiabatic graphite plating, collection zone, quenching distance, time series of collection, and propellant burning rate on the microscopic morphology, particle size distribution and unburned aluminum content of CCPs were investigated. It was verified that the graphite plating can provide a high-fidelity high-temperature environment for propellant combustion. The combustion efficiency is improved by 2.44% compared to the bare propellant case. The time series of collection has a significant effect on the combustion efficiency of aluminum, and the combustion efficiency of aluminum in the thermal state (1.2–2.4 s) is 2.75% higher than that in the cold state (0–1.2 s). Similarly, the characteristics of the CCPs in different collection zones are different. At the quenching distance of 5 mm, the combustion efficiency of aluminum in the core zone (85.39%) is much lower than that in the outer zone (92.07%), while the particle size of the CCPs in the core zone (172 μm) is larger than that in the outer zone (41 μm). This indicates that the core zone is more likely to produce large-sized and incompletely burned agglomerates during the propellant combustion process. Different burning rates also lead to a significant difference in particle size distribution and combustion efficiency. High burning rates result in higher combustion efficiency. A detailed sequence of the elaborative collection process of CCPs is proposed, mainly including the setting of ignition delay time, burning rate, working pressure, plating length and time series of collection. The findings of this study are expected to provide a reliable tool for the evaluation of the combustion efficiency of solid propellants.

A novel measurement method for ash deposition based on coplanar capacitance principle: Theoretical, numerical and experimental studies

Monitoring for the fouling and slagging is critical to ensure the stable operation of gasification system. This paper proposes a novel measurement method for the ash deposition based on coplanar capacitance principle. A theoretical analysis of electrostatic field is conducted to obtain the correlation between the coplanar capacitance value and the deposition thickness. A finite element simulation is carried out to discuss the electric field characteristics of ash depositing on the coplanar capacitor. It shows that the capacitance value initially increases and tends to be constant with the increase of deposition thickness. The lower distance between positive and negative electrodes is favorable to the capacitance value (signal strength) but unfavorable to the maximum measurable thickness. Furthermore, a cold state experiment is conducted to verify the correctnesses of the theoretical and numerical models, and a hot state experiment is carried out to study the capacitance characteristics of sensor in the high temperature range of 700 °C–1200 °C. Results show that the permittivity of the material is lower under the higher test frequency, which leads to the lower capacitance value of sensor. The complex impedance curve of ash is conformed to IBLC dielectric model, this explains that the sensor capacitance increases with the test temperature increasing caused by the increase of permittivity due to the enlargement of ash grain. The change of Si/Al content has little effect on the dielectric properties of ash, however, the higher Fe2O3 content or the lower CaO content results into the lower ash fusion point, larger grain size, and thence higher permittivity and sensor capacitance. The maximum measurable thicknesses of the sensors in the cold state and hot state are 11.2 mm and 10.0 mm, respectively, which are independent with the test frequency, test temperature, and ash component.

Numerical Analysis of Metals Under The Influence of Electromagnetic Field at Different Current Values

The primary factors of the widespread use of induction melting furnaces are uniform metal and heat distribution due to its mixing features, low alloy losses, excellent temperature and composition control, versatility in processing different materials, the ability to quickly start the process from a cold state when needed, and the absence of air pollution problems. In induction heating, not all sides of the part to be heated receive an equal amount of heat. Only if the part to be heated is of the type that conducts heat very well can all sides of the part be heated close to each other. Induction heating produces high heat on the surface, less on the inner parts, and least on the center of the material. This heating varies depending on the frequency of the current source and the penetration depth. In this study, a model was created in ANSYS numerical analysis program by taking the current, which is one of the electromagnetic and thermal parameters affecting the temperature distribution in the metalic material in induction heating, at different values. In the simulation model created, three-dimensional numerical analysis results of a cylindrical metallic material were obtained. In the simulation program, the power and frequency required for the design of the induction coil and the magnetic permeability, resistivity, heat transfer coefficient of the material and the position of the material in the inductor are determined as boundary conditions. Depending on these variables, the temperature and magnetic field distributions on the material were obtained. In addition to the numerical analysis, a cylindrical metallic material with known properties was placed in a specially manufactured induction coil and the temperature values on the material were measured to verify the numerical analysis. ANSYS modeling results with the same material dimensions, properties, and other parameters used in the experiment, were given and examined in comparison with the experimental results.

Proof of Concept of a Novel Solid–Solid Heat Exchanger Based on a Double L-Valve Concept

A proof of concept of a novel parallel-flow solid–solid heat exchanger consisting of two L-Valves with concentric vertical tubes, named as Double L-Valve, is presented for the case of the Carbonate Looping process, as a CO2 capture technology. The operational objective of the solid–solid heat exchanger is to heat up the relatively cold solid stream coming from the carbonator reactor by absorbing heat from the hotter stream coming from the calciner. This novel solid–solid heat exchanger concept has been constructed on a small scale to study the hydrodynamic response of the system experimentally at different designs and airflow rates in its cold state. Based on the experimental data from the small prototype, a scaled-up hydrodynamic model is proposed that provides estimations for the operational requirements at an industrial scale. Apart from the cold flow pilot model, the heat exchanger is being assessed in the current work for an industrial case study in terms of the following: (a) the heat transfer via rigorous one-dimensional thermal modelling, (b) the structural integrity of the design through Finite Element Method (FEM) analysis, and (c) a parametric study for its expected cost. The purpose of this work is to provide a holistic approach of this novel solid–solid heat exchanger concept, the main advantage of which is its simple design and relatively low cost.

High emissive contrast of adaptive, thin-film, tungsten-doped VO2 composites

There is a significant interest in developing advanced materials technologies that will reduce the consumption of fossil fuel resources. One efficient way of reducing energy consumption for heating and cooling applications is the development of a passive and adaptive thermal management system that radiates heat at high temperatures while providing insulation under cooler conditions. Vanadium dioxide (VO2) is a candidate material for this type of adaptive behavior since it transitions from a low temperature reflective state to a high temperature emissive state at 68 °C when deposited upon a dielectric-coated ground plane. Additionally, by doping VO2 with high valence tungsten (W6+), the transition temperature can be reduced to values that are close to room temperature (22 °C). In this Letter, W6+-doped VO2 multilayer composites are designed to utilize thin film interference in order to maximize the infrared (IR) emission contrast between the hot and cold states of VO2 while also reducing the transition temperature. Through careful engineering of the thickness and doping of the VO2 layer within the multilayer film, a 50% emissive contrast was maintained across the 8–13 μm spectral region, while the transition temperature was reduced from 68 °C in the undoped film to 29 °C in the 1.7 at. % W6+.

Experimental research on micro thrust measurement of ion thruster under variable working conditions

In view of the application requirements for accurately measuring the micro thrust of ion thrusters in space electric propulsion, an experimental study of micro thrust measurement under variable working conditions was carried out based on an 8 cm ion thruster. By combining highly sensitive thrust response parameters such as gas flow, anode voltage and grid voltage, the ion thruster can achieve high-precision continuous thrust adjustment in the range of 1–18.6 mN. The calibration results of the thrust measuring device were compared in the cold state and the stable state of thermal equilibrium of the ion thruster, respectively, and the measured thrust was compared with the thrust value calculated based on beam current characteristic measurement. The experimental results showed that compared with the cold calibration, the calibration results of the thrust measuring device in the stable state of thermal equilibrium of the ion thruster are more suitable for measuring the thrust of the ion thruster, and the measured thrust value is in good agreement with the thrust value calculated based on beam current characteristic measurement, and the relative error of the two within the research range is less than 4%.

Enhanced Hydrogen Escape on Mars during the 2018 Global Dust Storm: Impact of Horizontal Wind Field

Mars has undergone a substantial water loss, transforming from the early warm and wet state to the current cold and arid state. Observations and modeling efforts suggest that hydrogen escape is a metric of water loss on Mars. As a consequence of the vertical transport of water vapor by deep convection, hydrogen escape is significantly enhanced during Martian global dust storms. Motivated by the established scenario that the horizontal wind field could substantially enhance thermal escape, here we evaluate, for the first time, how the escape of H and H2 on Mars during a typical global dust storm is modified by the enhanced horizontal wind field during the period. By combining kinetic model calculations and the Mars Climate Database outputs, we reach the conclusion that a nonnegligible enhancement of the H and H2 escape flux could be driven by horizontal winds near the exobase, reaching 15% for H and 60% for H2 at dawn near the equator during the dust storm. Although the enhancement of the global hydrogen escape rate by the horizontal wind is insignificant, it plays a crucial role in the redistribution of H and H2 escape flux. The results presented here make useful contributions to a thorough understanding of enhanced hydrogen escape during the global dust storms.

Influence of aging heat treatment at 180 °C on cavitation erosion for aluminum alloy type 5083 in cold rolled state

Aluminum-based alloys have wide applicability in the construction of aircraft, vehicles, and ships. Some of their components, during operation, such as the radiators and the rotors of the cooling pumps in the vehicles, and the propellers of fishing and pleasure boats are affected by the abrasive, chemical and cavitational corrosive action of the water. At certain hydrodynamic flow regimes, the most dangerous becomes the corrosion through cavitation. Operation in such regimes inevitably leads to damaging the structure, due to cyclic stresses of the micro-jets and shock waves generated by the implosion of cavitation bubbles. Although the chemical constitution and alloying with other chemical elements increase the mechanical properties, the service life is still limited when operating in high-intensity cavitation flows. Therefore, researchers are looking for solutions to improve this resistance through various treatments, such as bulk heat. Research heading the same direction, but, made on 5083 alloy, is presented in this paper. The results highlight the behavior of a modified structure compared to the semi-fabricated state (obtained by rolling), through three durations regimes (one hours, 12 hours and 24 hours) of aging heat treatment to 180 °C temperature, after hardening treatment at 450 °C. The cavitation tests were performed in the Laboratory of the Polytechnic University of Timisoara, on the standard vibrating device with piezoceramic crystals. The results were expressed by curves and parameters specific to the evaluation of cavitation resistance, and by macro and microscopic images, showing the unique aspects of the connection between the structure and the mechanical properties obtained through heat treatment regimes. Thus, comparison of the results, including with the delivery state (laminated product), shows that the highest resistance is provided by the treatment at 24 hours. At the same time, the erosion, of pitting and caverns type, and differs from one structure to another.

Navigating Performance-Efficiency Tradeoffs in Serverless Computing: Deduplication to the Rescue!

Navigating the performance and efficiency trade-offs is critical for serverless platforms, where the providers ideally want to give the illusion of warm function startups while maintaining low resource costs. Limited controls, provided via toggling sandboxes between warm and cold states and keepalives, force operators to sacrifice significant resources to achieve good performance.

Effects of Si on the stress rupture life and microstructure of a novel austenitic stainless steel

A novel Si-bearing austenitic stainless steel was designed as the cladding material for lead-cooled fast reactors with an operating temperature range of 450 °C–550 °C, and the effects of Si (1.0 wt% - 2.0 wt%) on the creep life and fractured microstructure of material were studied at 550 °C and 650 °C. Results show that the addition of Si increased the stress rupture life of steel at 550 °C whereas brought in an opposite effect at 650 °C, which was closely related to the precipitation behavior of σ phase at these two temperatures during creep. At 550 °C the precipitation of σ phase was quite slow, but it was substantially accelerated at 650 °C. Since the experimental materials used in this work were in a cold worked state, so deformation twins existed and they were discovered to be able to promote the nucleation and growth of σ phase on the grain boundaries. With the increase of Si content at 550 °C, σ phase became larger in quantity and denser in distribution on the grain boundary, which improved the anti-cracking ability of grain boundary and enhanced the creep life of material. However, at 650 °C, σ particles apparently coarsened and congregated on the grain boundary under thermal activation, leading to an evident drop in the stress rupture property of steel.

Interfacial heat transfer with non-condensable gas in ASTEC V2.2: Application to severe accidents study during PWR cold shutdown states

In a diphasic flow, the presence of non-condensable gas has an important impact on interfacial heat transfer, especially at low global pressure. In severe accidents studies, such flow can be commonly encountered. For example, in pressurised water reactors, high concentration of non-condensable gas can be found in the reactor coolant system in case of late core reflooding with a high oxidation rate (high hydrogen concentration) or in case of accidents happening during the cold shutdown of the reactor, when the reactor coolant system has been partly drained (high air concentration). Such flows with non-condensable gas are challenging to compute for severe accident system codes. A new model is implemented in ASTEC v2.2 to improve the interfacial heat transfer calculation in presence of non-condensable gas. The model gives a more accurate estimation of the heat transfer by assuming that it is mainly driven by vapour diffusion in the gas phase. The new model is applied to study cold shutdown states for 1300 MWe pressurized water reactors. A complete calculation of the cooling, depressurisation and draining of the reactor can be successfully performed. In order to show ASTEC new capabilities, a first accident scenario with loss of the residual heat removal system is also presented.

Bell's palsy was associated with TRPV2 downregulation of Schwann cell by cold stress

ObjectiveEpidemiological and clinical studies have shown that sharp changes in the ambient temperature are associated with the occurrence and development of Bell's palsy. However, the specific pathogenesis of peripheral facial paralysis remains nebulous. This study investigated the effect of cold stress on transient receptor potential cation channel subfamily V member 2 (TRPV2) secretion by Schwann cells and its role in Bell's palsy. Materials and methodsSchwann cell morphology was observed using transmission electron microscopy (TEM). Cell proliferation, apoptosis and cell cycle were analysed using CCK8 and flow cytometry. ELISA, Reverse transcription-quantitative PCR, western blotting and immunocytochemical fluorescence staining were used to detect the effects of cold stress on TRPV2, neural cell adhesion molecule (NCAM) and nerve growth factor (NGF) expression in Schwann cells. ResultsCold stress resulted in a widening of the intercellular space, and the particles on the membrane showed different degrees of loss. Cold stress may cause Schwann cells to enter a cold dormant state. ELISA, RT-qPCR, western blotting and immunocytochemical fluorescences staining indicated that cold stress inhibited the expression of TRPV2, NCAM, and NGF. ConclusionsDrastic temperature difference between cold and heat can downregulate TRPV2 and the secretome of Schwann cells. The imbalance of Schwann cell homeostasis under such stress may contribute to nerve signalling dysfunction leading to the development of facial paralysis.

Experiment and numerical study on combustion characteristics of low-nitrogen burners

Low nitrogen combustion has always been an essential topic in energy conservation and environmental protection. This paper proposes a new type of low-nitrogen burner, which aims to optimize the burner structure and reduce NOx emission. Fuel and air staged combustion and central swirl technology are adopted in the burner to reduce local high-temperature areas and NOx generation. The effects of the new low-nitrogen burner's structural parameters and operating parameters on the temperature distribution, velocity distribution and NOx concentration distribution in the furnace are analyzed by cold state experiment and numerical simulation. The results show that: the cyclone blade deflection angle of 30 and the main combustion stage gas nozzle of 3 are the optimal structural parameters. The secondary combustion stage gas ratio of 0.1, the excess air coefficient of 1.05, and the air preheating temperature of 298 K are the optimal working condition parameters. At this moment, the furnace has the highest average temperature, the best combustion efficiency and the lowest NOx emission. These indicates that the novel low-nitrogen burner can be a suitable device for reducing NOx emission.

Searching for phase transitions in neutron stars with modified Gaussian processes

Gaussian processes provide a promising framework by which to extrapolate the equation of state (EoS) of cold, catalyzed matter beyond 1 – 2 times nuclear saturation density. Here we discuss how to extend Gaussian processes to include nontrivial features in the speed of sound, such as bumps, kinks, and plateaus, which are predicted by nuclear models with exotic degrees of freedom. Using a fully Bayesian analysis incorporating measurements from X-ray sources, gravitational wave observations, and perturbative QCD results, we show that these features are compatible with current constraints and report on how the features affect the EoS posteriors.

Deglacial climate changes as forced by different ice sheet reconstructions

Abstract. During the last deglaciation, the climate evolves from a cold state at the Last Glacial Maximum (LGM) at 21 ka (thousand years ago) with large ice sheets to the warm Holocene at ∼9 ka with reduced ice sheets. The deglacial ice sheet melt can impact the climate through multiple ways: changes of topography and albedo, bathymetry and coastlines, and freshwater fluxes (FWFs). In the PMIP4 (Paleoclimate Modelling Intercomparison Project – Phase 4) protocol for deglacial simulations, these changes can be accounted for or not depending on the modelling group choices. In addition, two ice sheet reconstructions are available (ICE-6G_C and GLAC-1D). In this study, we evaluate all these effects related to ice sheet changes on the climate using the iLOVECLIM model of intermediate complexity. We show that the two reconstructions yield the same warming to a first order but with a different amplitude (global mean temperature of 3.9 ∘C with ICE-6G_C and 3.8 ∘C with GLAC-1D) and evolution. We obtain a stalling of temperature rise during the Antarctic Cold Reversal (ACR, from ∼14 to ∼12 ka) similar to proxy data only with the GLAC-1D ice sheet reconstruction. Accounting for changes in bathymetry in the simulations results in a cooling due to a larger sea ice extent and higher surface albedo. Finally, freshwater fluxes result in Atlantic meridional overturning circulation (AMOC) drawdown, but the timing in the simulations disagrees with proxy data of ocean circulation changes. This questions the causal link between reconstructed freshwater fluxes from ice sheet melt and recorded AMOC weakening.

Study of the thermal expansion effects of a space nuclear reactor with an integrated honeycomb core design using OpenMC and ANSYS

The negative reactivity feedback in the nuclear fuel plays an important role in maintaining the stable operation of nuclear reactors. For heat pipe cooled space reactors using highly enriched U, the fuel temperature reactivity feedback mainly due to Doppler effect and the thermal expansion of solid fuel. In this paper, based on an integrated heat pipe space reactor design, a one-way coupling of the Monte Carlo code OpenMC and finite element method ANSYS is used to evaluate the reactor expansion and the impacts to the reactor reactivity. The average expansion was 0.126 cm for the fuel block from cold state to full power operation state. The fuel thermal expansion introduces a negative reactivity feedback of −59 pcm, and the reflector expansion introduces another −675 pcm, resulting a temperature coefficient of −0.638 pcm/K.

Research for the Process of Forming the Metal during its Cyclic Deformation

Use the devices for the implementation of the combined casting process and deformation of non-ferrous alloys is a relatively new direction in the technology of materials processing by pressure. For an adequate description of the shaping processes implemented in such devices on the basis of certain mathematical models, experimental data on the energy-force parameters of deformation are required, as well as data for the nature of the distribution and intensity of deformations arising in the process during cyclic deformation of a metal product. The cyclical nature of the process of forming a metal product, coupled with large plastic deformations, does not allow directly using the traditional methods of experimental research of its stress-strain state adopted in the theory of metalworking by pressure. This gap is partly intended to fill by this study. The paper proposes a complex technique based on the registration (according to the electrical characteristics of the drive motor) of the instantaneous power of irreversible deformation for the material of a metal product. Prone to strain hardening in a cold state, a method for directly establishing the components of plastic deformation of the workpiece based on the method of rolled dividing grids with subsequent calculations according to Siebel's method. Analysis of the experimental results allows us to establish a qualitative picture of the deformation mechanism. The obtained experimental values are necessary for the verification of mathematical models and software systems for calculating the stress-strain state of materials under complex loading and finite deformations.

Red Squirrel Tests: Air Products' ammonia field experiments

AbstractThe Red Squirrel ammonia field experiments were conducted at the DNV Spadeadam site in the UK in 2022. Field test data currently exists for high‐pressure (ambient temperature) two‐phase releases of ammonia from Desert Tortoise (1983) and FLADIS (1996) experiments. No field tests have ever been done for cold (refrigerated) ammonia liquid spills on dry land or into water. The handling of liquified ammonia, during storage/processing and transportation, in a cold (refrigerated) state is inherently safer than in a high‐pressure (ambient temperature) liquified state. The main objective of the Air Products’ Red Squirrel Tests was to determine the source term and dispersion characteristics for high‐pressure (ambient temperature) liquified ammonia and low‐pressure (cold/refrigerated) liquified ammonia in form of two‐phase releases and liquid spills, respectively. Liquid spills on concrete and water were studied, along with the process conditions that led to the transition from liquid spills to two‐phase flow regimes based on discharge pressures for cold liquified ammonia. Details on the equipment, instrumentation, secondary containment, and ammonia sensors and their layout are presented. An initial analysis of the source terms and dispersion behavior for two‐phase releases and contained liquid spills over a range of weather conditions is also provided.

Deep learning approach for recognizing cold and warm thermal discomfort cues from videos

Reducing building energy consumption while maintaining individual thermal comfort levels is a challenge. Energy-efficiency strategies that control indoor conditions, with the aim of reducing energy waste and increasing occupant comfort, require the capture of personal thermal comfort preferences in their feedback loop. However, direct feedback from surveys and invasive methods, which have been proposed to collect personal thermal comfort preferences, are impractical in real-world settings due to the decay of commitment, need for repeated feedback, and invasiveness. To address this challenge, this paper proposes a novel non-invasive approach for automated thermal discomfort detection using a deep learning-based model for thermal discomfort cue recognition. The model recognizes nine discomfort cues from video recordings of occupants in indoor work settings, which could be associated with the cold or warm thermal discomfort states. In developing the model, the architectures of two different residual neural networks (ResNets) that learn spatial and local information were tested using data augmentation and transfer learning techniques, and then compared with the performance of (1) traditional machine learning classifiers that used video frames mapped to the feature space of the ResNets; and (2) the ResNets extended with a long short-term memory (LSTM) layer that learns temporal information from the frame sequence. Approaches that accounted for temporal and spatial information outperformed those that only took spatial information into consideration. The final thermal discomfort cue recognition model achieved a weighted F1-measure of 85% in correctly classifying the cues. The proposed approach could help provide rapid and effortless feedback in building energy management systems to reduce building energy waste while providing comfortable indoor conditions towards increased occupant health and productivity.