Cold State Research Articles

ENSO phase locking, asymmetry and predictability in the INMCM Earth system model

Abstract Advanced numerical climate models are known to exhibit biases in simulating some features of El Niño–Southern Oscillation (ENSO), which is a key mode of interannual climate variability. In this study we analyze how two fundamental features of observed ENSO – asymmetry between hot and cold states and phase-locking to the annual cycle – are reflected in two different versions of the INMCM Earth system model (state-of-the-art Earth system model participating in the Coupled Model Intercomparison Project). We identify the above ENSO features using the conventional empirical orthogonal functions (EOF) analysis, which is applied to both observed and simulated upper ocean heat content (OHC) data in the tropical Pacific. We obtain that the observed tropical Pacific OHC variability is described well by two leading EOF-modes, which roughly reflect the fundamental recharge-discharge mechanism of ENSO. These modes exhibit strong seasonal cycles associated with ENSO phase locking while the revealed nonlinear dependencies between amplitudes of these cycles reflect ENSO asymmetry.We also assess and compare the predictability of observed and simulated ENSO based on linear inverse modelling. We find that the improved INMCM6 model has significant benefits in simulating described features of observed ENSO as compared with the previous INMCM5 model. The improvements of the INMCM6 model providing such benefits are discussed. We argue that proper cloud parameterization scheme is crucial for accurate simulation of ENSO dynamics with numerical climate models.

Transforming Growth Factor Beta 2 (TGFB2) and Interferon Gamma Receptor 2 (IFNGR2) mRNA Levels in the Brainstem Tumor Microenvironment (TME) Significantly Impact Overall Survival in Pediatric DMG Patients.

This hypothesis-generating study characterized the mRNA expression profiles and prognostic impacts of antigen-presenting cell (APC) markers (CD14, CD163, CD86, and ITGAX/CD11c) in pediatric brainstem diffuse midline glioma (pbDMG) tumors. We also assessed the mRNA levels of two therapeutic targets, transforming growth factor beta 2 (TGFB2) and interferon gamma receptor 2 (IFNGR2), for their biomarker potentials in these highly aggressive pbDMG tumors. The expressions of CD14, CD163, and ITGAX/CD11c mRNAs exhibited significant decreases of 1.64-fold (p = 0.037), 1.75-fold (p = 0.019), and 3.33-fold (p < 0.0001), respectively, in pbDMG tumors relative to those in normal brainstem/pons samples. The pbDMG samples with high levels of TGFB2 in combination with low levels of APC markers, reflecting the cold immune state of pbDMG tumors, exhibited significantly worse overall survival outcomes at low expression levels of CD14, CD163, and CD86. The expression levels of IFNGR2 and TGFB2 (1.51-fold increase (p = 0.002) and 1.58-fold increase (p = 5.5 × 10-4), respectively) were significantly upregulated in pbDMG tumors compared with normal brainstem/pons samples. We performed multivariate Cox proportional hazards modelling that showed TGFB2 was a prognostic indicator (HR for patients in the TGFB2high group of pbDMG patients = 2.88 (1.12-7.39); p = 0.028) for poor overall survival (OS) and was independent of IFNGR2 levels, the age of the patient, and the significant interaction effect observed between IFNGR2 and TGFB2 (p = 0.015). Worse survival outcomes in pbDMG patients when comparing high versus low TGFB2 levels in the context of low IFNGR2 levels suggest that the abrogation of the TGFB2 mRNA expression in the immunologically cold tumor microenvironment can be used to treat pbDMG patients. Furthermore, pbDMG patients with low levels of JAK1 or STAT1 mRNA expression in combination with high levels of TGFB2 also exhibited poor OS outcomes, suggesting that the inclusion of (interferon-gamma) IFN-γ to stimulate and activate JAK1 and STAT1 in anti-tumor APC cells present the brainstem TME can enhance the effect of the TGFB2 blockade.

Combustion simulations of scramjet combustor using reduced mechanism of surrogate fuel for regenerative cooling pyrolysis products

Taking the surrogate fuel (64% ethylene and 36% methane in mole percentage) for regenerative cooling pyrolysis products used in HIFiRE-2 scramjet combustor as an example, present work systematically explores the workflow of the integrated mechanism reduction for surrogate fuel of pyrolysis products, the kinetic performance verification of the preferred reduced mechanism, and the combustion simulation application of the reduced mechanism in scramjet combustor. A static integrated reduction strategy is performed to obtain reduced mechanism for the surrogate fuel with the NUIGMech1.2 as detailed mechanism under wide conditions for temperature range of 900 - 1800 K, pressure range of 1 - 4 atm, and equivalence ratio range of 0.25 - 5.0. A reduced mechanism (34 species and 181 reactions)with remarkably reduced size is obtained, which presents favorable performance incomprehensive kinetic validations. With this compact and high-fidelity reduced mechanism, the combustion simulations for the scramjet combustor are carried out combining with tabulation of dynamic adaptive chemistry for run-time speed-up. The simulation results of static pressure profiles obtained for cold and hot states match well with the experimental measurements for the two conditions with flight Mach number of 5.84 and 6.50. Meanwhile, the flow and combustion characteristics of the two conditions are investigated based on simulation results. The integrated reduction strategy and systematic kinetic verification used in present work provide reference values for the application of more complex surrogate fuel mechanisms in scramjet combustor combustion simulation.

A location-based advising method in teacher–student frameworks

The integration of a teacher–student framework in multi-agent learning has proven to be an effective approach for improving learning performance. This framework facilitates the exchange of advice among agents, enabling them to learn from each other. However, contemporary advising methods face a common limitation in which teacher agents can only provide poor advice to student agents when the latter are in states that contain limited environmental information. These states are referred to as ”cold states” and are prevalent in multi-agent environments. To overcome this challenge, we propose a novel location-based advising method. This approach utilizes the student agent’s location as well as their current state to generate advice from the teacher agent. By doing so, we can avoid the cold-state issue altogether. Our experimental results demonstrate that this method significantly improves the learning performance of agents when compared to state-of-the-art advising methods. In summary, our proposed location-based advising method addresses the limitations of contemporary advising methods in multi-agent learning, specifically the cold-state issue. Our approach utilizes both the student’s location and state information to generate advice from the teacher, leading to improved learning performance.

Analysis of the Machine-Specific Behavior of Injection Molding Machines.

The performance of an injection molding machine (IMM) influences the process and the quality of the parts manufactured. Despite increasing data collection capabilities, their machine-specific behavior has not been extensively studied. To close corresponding research gaps, the machine-specific behavior of two hydraulic IMMs of different sizes and one electric IMM were compared with each other as part of the investigations. Both the start-up behavior from the cold state and the behavior of the machine at different operating points were considered. To complement this, the influence of various material properties on the machine-specific behavior was investigated by processing an unreinforced and glass-fiber-reinforced polyamide. The results obtained provide crucial insights into machine-specific behavior, which may, for instance, account for disparities between computer fluid dynamic (CFD) simulations and experimental results. Furthermore, it is expected that the description of the machine-specific behavior can contribute to transfer knowledge when applying transfer learning algorithms. Looking ahead to future research, it is advised to create what is referred to as a "machine fingerprint", and this proposal is accompanied by some preliminary recommendations for its development.

The high energy X-ray probe (HEX-P): a new window into neutron star accretion

Accreting neutron stars (NSs) represent a unique laboratory for probing the physics of accretion in the presence of strong magnetic fields (B ≳ 108 G). Additionally, the matter inside the NS itself exists in an ultra-dense, cold state that cannot be reproduced in Earth-based laboratories. Hence, observational studies of these objects are a way to probe the most extreme physical regimes. Here we present an overview of the field and discuss the most important outstanding problems related to NS accretion. We show how these open questions regarding accreting NSs in both low-mass and high-mass X-ray binary systems can be addressed with the High-Energy X-ray Probe (HEX-P) via simulated data. In particular, with the broad X-ray passband and improved sensitivity afforded by a low X-ray background, HEX-P will be able to 1) distinguish between competing continuum emission models; 2) provide tighter upper limits on NS radii via reflection modeling techniques that are independent and complementary to other existing methods; 3) constrain magnetic field geometry, plasma parameters, and accretion column emission patterns by characterizing fundamental and harmonic cyclotron lines and exploring their behavior with pulse phase; 4) directly measure the surface magnetic field strength of highly magnetized NSs at the lowest accretion luminosities; as well as 5) detect cyclotron line features in extragalactic sources and probe their dependence on luminosity in the super-Eddington regime in order to distinguish between geometrical evolution and accretion-induced decay of the magnetic field. In these ways HEX-P will provide an essential new tool for exploring the physics of NSs, their magnetic fields, and the physics of extreme accretion.

Experimental Study on Gas-Solid Two-Phase Flow Characteristics of a Vertical Cyclone Combustor System.

According to the design and operational parameters of the cyclone liquid slag-discharging boiler, an experimental platform for the cyclone burner was designed and constructed in a cold state based on the principle of similarity. The experimental study investigated the effects of parameters, such as swirl-vane angles, coal concentration, operating parameters, and particle size, on the flow distribution and vertical riser resistance characteristics of the vertical cyclone burner. The results showed that there were differences in flow distribution among the cyclone burners, and the most uniform flow distribution was achieved when the swirl-vane angle of the primary air was 30°. The concentration of pulverized coal significantly influenced the pressure drop in the vertical ascending section, which increased with higher concentrations of pulverized coal. When the concentration of pulverized coal remains constant, the pipeline pressure drop is minimized at a primary air velocity of 7.5 m/s. As the secondary wind speed increased, the pressure drop consistently rose; when the secondary wind speed is 22 m/s, the pressure drop of the pipeline is the maximum; however, excessively high secondary wind speeds were found to be detrimental to the formation of an optimal aerodynamic field in the burner. Furthermore, when the pulverized coal concentration was held constant, materials with larger particle sizes exhibited the highest pressure drop. When the particle size increases from 50 to 150 μm, the pressure drop of the vertical riser segment also increases. Finally, based on the Barth additional pressure drop theory, the pressure drop formula of the vertical riser is fitted by a dimensional analysis method, and the correlation formula of the pressure drop test of gas-solid two-phase flow in the vertical riser is obtained.

MANAGEMENT OF FUEL CONSUMPTION OF 200 MW POWER UNIT WHEN OPERATING IN FREQUENT START-UP MODE

In the context of insufficient maneuvering capacities in the United Energy System of Ukraine, 200 MW power units are used to cover peak loads in variable operating modes. At the same time, there is a deterioration in the economic performance of power equipment. The efficiency of power generation directly depends on the operating modes of the power unit. Therefore, the task was set to develop a system to rationalize operating modes in order to increase efficiency. The average annual specific fuel consumption was chosen as the objective function. To calculate the specific consumption during the year, the method of bringing all losses during start-up and stationary operation to similar consumption of conventional fuel was used. The following factors were selected as optimization factors: the power unit operation time during the year, the total number of starts from different thermal states for 1 year, and the proportion of starts from different thermal states. The limits of change in the factors were chosen as follows: the number of hours of power unit operation ti from 2000 to 6500 hours per year; annual number of starts ni from 25 to 75 times per year; the share of starts from the cold state of metal CSi from 0.1 to 0.9; the share of starts from the hot state GSj within the share of all starts (hot and un-cooled) from 0 to 1 The developed mathematical model allows to estimate fuel consumption for all possible combinations of operational factors. To demonstrate the operation of this system, calculations were performed for a specific 200 MW power unit with a TP-100 power boiler and a K-200-130 steam turbine. The main parameters of the power unit operation mode were determined using the start-up map and the operating instructions developed by the manufacturer. The calculations established a rational distribution of operating parameters, at which the consumption of conditional fuel is 334-340 g.c.f./kWh. It has been established that the rational number of hours of power unit operation is ti = 5500-6500 h/year, with the annual number of starts ni = 25-36 year-1, while the share of starts should be: from the cold state of the metal CSi = 0.72-0.9; from the hot state HSj = 0.1-0.28; from the un-cooled state USi,j = 0-0.18, and then the difference between the most rational and irrational operating modes is 16.5 % (fuel consumption of 55 g.c.f /kWh).

Ammonia powered thermal-responsive smart window with spectral regulation of Cu2+ and sodium copper chlorophyllin

Thermal responsive windows are highly promising for the next-generation architecture for their self-powered solar transmittance. However, existing thermochromic techniques, include VO2- and hydrogel-based systems, have not been used for large-scale in window applications, because of the technical obstacles such as low luminous transmittance (Tlum), poor solar modulation ability (ΔTsol), high transition temperature (Tc) and high haze rate. To tackle those issues, a new thermal-responsive design, i.e., the Ammonia Pressure Powered smart (APPs) window, was proposed, with Cu2+ and sodium copper chlorophyllin (SCC) providing solar spectrum management. In comparisons to traditional thermochromic windows, the new concept of APPs window shows significant energy-related advances. Particularly, a feasible Tc (24–36 °C), outstanding ΔTsol (67 %), and high Tlum in both cold (84 %) and hot (47.4 %) states are reported in this study. In addition, outdoor experimental test of the APPs window demonstrated that it could produce a rational daylight level of both photopic effects and melanopic effects, whilst reduce the room temperature by about 4 °C on hot sunny day. Furthermore, energy simulations conducted for the APPs window in three different cities (Singapore, Hong Kong and Harbin) indicate its superior performance, compared to the double-layered low-e glazing windows, across various climatic conditions. With cost-effective materials and excellent performance, the authors believe that this new APPs window represents a smart and sustainable solution for the development of next-generation green buildings.

Neuroinflammation drives sex-dependent effects on pain and negative affect in a murine model of repeated mild traumatic brain injury.

The Center for Disease Control and Prevention estimates that 75% of reported cases of traumatic brain injury (TBI) are mild, where chronic pain and depression are 2 of the most common symptoms. In this study, we used a murine model of repeated mild TBI to characterize the associated pain hypersensitivity and affective-like behavior and to what extent microglial reactivity contributes to these behavioral phenotypes. Male and female C57BL/6J mice underwent sham or repeated mild traumatic brain injury (rmTBI) and were tested for up to 9 weeks postinjury, where an anti-inflammatory/neuroprotective drug (minocycline) was introduced at 5 weeks postinjury in the drinking water. Repeated mild traumatic brain injury mice developed cold nociceptive hypersensitivity and negative affective states, as well as increased locomotor activity and risk-taking behavior. Minocycline reversed negative affect and pain hypersensitivities in male but not female mice. Repeated mild traumatic brain injury also produced an increase in microglial and brain-derived neurotropic factor mRNA transcripts in limbic structures known to be involved in nociception and affect, but many of these changes were sex dependent. Finally, we show that the antiepileptic drug, gabapentin, produced negative reinforcement in male rmTBI mice that was prevented by minocycline treatment, whereas rmTBI female mice showed a place aversion to gabapentin. Collectively, pain hypersensitivity, increased tonic-aversive pain components, and negative affective states were evident in both male and female rmTBI mice, but suppression of microglial reactivity was only sufficient to reverse behavioral changes in male mice. Neuroinflammation in limbic structures seems to be a contributing factor in behavioral changes resulting from rmTBI.

On the drivers of regime shifts in the Antarctic marginal seas, exemplified by the Weddell Sea

Abstract. Recent studies have found evidence for a potential future tipping point, when the density of Antarctic continental shelf waters, specifically in the southern Weddell Sea, will allow for the onshore flow of warm waters of open ocean origin. A cold-to-warm regime shift in the adjacent ice shelf cavities entails a strong enhancement of ice shelf basal melt rates and could trigger instabilities in the ice sheet. From a suite of numerical experiments, aimed to force such a regime shift on the continental shelf, we identified the density balance between the shelf waters formed by sea ice production and the warmer water at the shelf break as the defining element of a tipping into a warm state. In our experiments, this process is reversible but there is evidence for hysteresis behaviour. Using HadCM3 20th-century output as atmospheric forcing, the resulting state of the Filchner–Ronne cavity depends on the initial state. In contrast, ERA Interim forcing pushes even a warm-initialized cavity into a cold state, i.e. it pushes the system back across the reversal threshold to the cold side. However, it turns out that for forcing data perturbations of a realistic magnitude, a unique and universal recipe for triggering a regime shift in Antarctic marginal seas was not found; instead, various ocean states can lead to an intrusion of off-shelf waters onto the continental shelf and into the cavities. Whether or not any given forcing or perturbation yields a density imbalance and thus allows for the inflow of warm water depends on the complex interplay between bottom topography, mean ocean state, sea ice processes, and atmospheric conditions.

Impact of freeze-in on dark matter isocurvature

Dark matter freeze-in is a compelling cosmological production mechanism in which all or some of the observed abundance of dark matter is generated through feeble interactions it has with the Standard Model. In this work we present the first analysis of freeze-in dark matter fluctuations and consider two benchmark models: freeze-in through the direct decay of a heavy vector boson and freeze-in through pair annihilation of Standard Model particles in the thermal bath. We provide a theoretical framework for determining the impact of freeze-in on curvature and dark matter isocurvature perturbations. We determine freeze-in dark matter fluid properties from first principles, tracking its evolution from its relativistic production to its final cold state, and calculate the evolution of the dark matter isocurvature perturbation. We find that in the absence of initial isocurvature, the freeze-in production of dark matter does not source isocurvature. However, for an initial isocurvature perturbation seeded by inflation, the nonthermal freeze-in process may allow for a fraction of the isocurvature to persist, in contrast to the exponential suppression it receives in the case of thermal dark matter. In either case, the evolution of the curvature mode is unaffected by the freeze-in process. We show sensitivity projections of future cosmic microwave background experiments to the amplitude of uncorrelated, totally anticorrelated, and totally correlated dark matter isocurvature perturbations. From these projections, we infer the sensitivity to the abundance of freeze-in dark matter that sustains some fraction of the primordial isocurvature.

Exploring Neutrino Mass Orderings through Supernova Neutrino Detection

Core-collapse supernovae (SNe) are one of the most powerful cosmic sources of neutrinos, with energies of several MeV. The emission of neutrinos and antineutrinos of all flavors carries away the gravitational binding energy of the compact remnant and drives its evolution from the hot initial to the cold final states. Detecting these neutrinos from Earth and analyzing the emitted signals present a unique opportunity to explore the neutrino mass ordering problem. This research outlines the detection of neutrinos from SNe and their relevance in understanding the neutrino mass ordering. The focus is on developing a model-independent analysis strategy, achieved by comparing distinct detection channels in large underground detectors. The objective is to identify potential indicators of mass ordering within the neutrino sector. Additionally, a thorough statistical analysis is performed on the anticipated neutrino signals for both mass orderings. Despite uncertainties in supernova explosion parameters, an exploration of the parameter space reveals an extensive array of models with significant sensitivity to differentiate between mass orderings. The assessment of various observables and their combinations underscores the potential of forthcoming supernova observations in addressing the neutrino mass ordering problem.

Design of a Novel α-Shaped Flue Gas Route Flame Incinerator for the Treatment of Municipal Waste Materials

In order to improve the combustion characteristics of municipal waste materials and reduce excess pollutants generated during the incineration process, this study develops a novel waste incinerator with an α-shaped flue gas route. This has been achieved through the application of momentum vector synthesis theory in order to modify the secondary air structure in a conventional incinerator, resulting in enhanced combustion efficiency of the incinerator. Computational Fluid Dynamics (CFD) based cold state test results demonstrate that with appropriate modifications to the design of the incinerator, the flue gas propagates through a longer α-shaped route rather than conventional L-shaped route. Hot state tests have been carried out on a full scale 750 tons/day waste incinerator. Test rests show that the temperature of the flue gas increases by 138% under the front arch when secondary air supply is being incorporated into the design of the incinerator, resulting in better combustion of the municipal waste materials, lower emissions and higher thermal efficiency of the incinerator. The results obtained in this study confirm the rationality and feasibility of momentum flow rate method for better design of waste incinerators.Graphical

Synthesis of a Bistable Recuperative Pump Powered by Shape Memory Alloys and a Two-Section Involute Cam

The paper discusses the synthesis problem of a bistable piston pump, employing a driving mechanism that comprises shape memory alloy wires, a two-section involute cam, and an energy-recuperating spring. The transition from one stable end position to another in the pump is achieved by heating and subsequently shortening one of the shape memory alloy wires, initiating the motion of the mechanism. This is then followed by the engagement of the recuperative spring to traverse the intermediate unstable equilibrium position and complete the entire stroke. The reversal of motion follows a similar approach, where the second SMA wire shortens while the first wire remains in a cold state. Importantly, the mechanism necessitates a low force within the shape memory alloy wire to initiate motion towards the opposite stable position. This research encompasses the examination of type, geometric, and force synthesis considerations for the pump, leading to the development of fundamental kinematic and force relationships. Moreover, a novel mechanism is proposed and synthesized, incorporating a two-section involute cam with a cusp point, to generate the desired discontinuous moment function produced by the recuperative spring. Further analysis reveals that the thermal time constant, which regulates the dynamic response of the mechanism, is directly proportional to the diameter of the driving SMA and inversely proportional to the square root of the number of SMA branches.

Multiple Dissociation Pathways in HNCO Decomposition Governed by Potential Energy Surface Topography.

The exquisite features of molecular photochemistry are key to any complete understanding of the chemical processes governed by potential energy surfaces (PESs). It is well established that multiple dissociation pathways relate to nonadiabatic transitions between multiple coupled PESs. However, little detail is known about how the single PES determines reaction outcomes. Here we perform detailed experiments on HNCO photodissociation, acquiring the state-specific correlations of the NH (a1Δ) and CO (X1Σ+) products. The experiments reveal a trimodal CO rotational distribution. Dynamics simulations based on a full-dimensional machine-learning-based PES of HNCO unveil three dissociation pathways exclusively occurring on the S1 excited electronic state. One pathway, following the minimum energy path (MEP) via the transition state, contributes to mild rotational excitation in CO, while the other two pathways deviating substantially from the MEP account for relatively cold and hot CO rotational state populations. These peculiar dynamics are unambiguously governed by the S1 state PES topography, i.e., a narrow acceptance cone in the vicinity of the transition state region. The dynamical picture shown in this work will serve as a textbook example illustrating the importance of the PES topography in molecular photochemistry.

Evaluation of the operation status of the residential land market in Beijing-Tianjin-Hebei region of China and its spatiotemporal pattern characteristics.

Exploring the operation status and patterns of urban land markets is an important theoretical and practical topic for promoting coordinated socio-economic development. In this study, the operation status of the residential land market in the Beijing-Tianjin-Hebei region and the characteristics of its pattern were analyzed using the composite index method and the 3σ rule of the normal distribution and taking the 174 counties in Beijing, Tianjin, and Hebei, China, as the research objects. The results show that ① Beijing, Tianjin, Langfang, Zhangjiakou, and Baoding residential land market state composite indexes are all in the middle to upper levels in the Beijing-Tianjin-Hebei city cluster, while Qinhuangdao, Handan, and Chengde residential land market state composite indexes are generally low. The harmony between the residential land price and national economy, the market supply and demand balance, and the structural balance may become the main factors affecting the healthy development of the residential land market in Beijing and Tianjin. ② The proportion of counties with "healthy" residential land market in all dimensions and overall market status reached over 64%, and the residential land market in the Beijing-Tianjin-Hebei region is running well. The rapid increase in residential land prices from 2016 to 2020 was an important driver of the increased heat in the residential land market across the region. ③ The residential land market in the counties around Beijing and Tianjin is significantly hotter than in other regions, and there is an obvious polarization effect in the operation state of the residential land market in the Beijing-Tianjin region. The residential land market is generally cold in the counties in the southern and northeastern parts of the region and other peripheral areas, and there is a risk of marginalization in the development of the residential land market in the counties in the peripheral areas. ④ Both the hot and cold residential land market states exhibit spatial clustering characteristics. Most of the clusters are not consistent with the municipal administrative boundaries, and the states of the residential land market in neighboring counties are very similar.

The role of P2O5 on the stability of β-C2S in AOD slag based on the improvement of hydration activity

The original AOD slag in the cold state contained more than 50 wt% low-hydration activity γ-C2S, which significantly affects the hydration activity. Therefore, the effect of the typical crystal stabilizer P2O5 on the formation of a new phase and the enhancement in the mass fraction of high hydration activity β-C2S in AOD slag were studied, and the internal factors that controlled the doping preference and influenced the hydration activity of the crystal stabilizer P2O5 were revealed. When the addition of P2O5 was 0.6 wt%, the mass fraction of β-C2S in AOD slag was increased by 50.8 wt%. The P5+ and its oxide P2O5 entered the lattice of C2S in solid solution, causing lattice distortion. After P doping, the charge energies of the Ca, Si and O atoms shifted toward the low energy direction by approximately 5 eV, which increased the stability of the electronic structure. In addition, P doping changed the delocalization of the CBM in the pure phase, partially located the LDOS of the VBM and CBM, and increased the numbers of nucleophilic and electrophilic attack sites, thus improving the hydration activity of β-C2S.

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.