Steep Temperature Research Articles

Elevational partitioning in species distribution, abundance and body size of Australian alpine grasshoppers (Kosciuscola)

AbstractChanges in the physical environment with elevation can influence species distributions and their morphological traits. In mountainous regions, steep temperature gradients can result in patterns of ecological partitioning among species that potentially increases their vulnerability to climate change. We collected data on species distributions, relative abundance and body size for three grasshopper species of the genus Kosciuscola (K. usitatus, K. tristis and K. cognatus) at three locations within the mountainous Kosciuszko National Park in Australia (Thredbo, Guthega and Jagungal). All three species showed differences in their distributions according to elevation, with K. usitatus ranging from 1400 to 2000 m asl, K. tristis from 1600 to 2000 m asl and K. cognatus from 1550 to 1900 m asl. Decreasing relative abundance with increasing elevation was found for K. usitatus, but the opposite pattern was found for K. tristis. The relative abundance of K. cognatus did not change with elevation but was negatively correlated with foliage cover. Body size decreased with elevation in both male and female K. usitatus, which was similarly observed in female K. tristis and male K. cognatus. Our results demonstrate spatial partitioning of species distributions and clines in body size in relation to elevational gradients. Species‐specific sensitivities to climatic gradients may help to predict the persistence of this grasshopper assemblage under climate change.

Resolution Study for Three-dimensional Supernova Simulations with the Prometheus-Vertex Code

Abstract We present a carefully designed, systematic study of the angular resolution dependence of simulations with the Prometheus-Vertex neutrino-hydrodynamics code. Employing a simplified neutrino heating–cooling scheme in the Prometheus hydrodynamics module allows us to sample the angular resolution between 4° and 0.°5. With a newly implemented static mesh refinement (SMR) technique on the Yin-Yang grid, the angular coordinates can be refined in concentric shells, compensating for the diverging structure of the spherical grid. In contrast to previous studies with Prometheus and other codes, we find that higher angular resolution and therefore lower numerical viscosity provides more favorable explosion conditions and faster shock expansion. We discuss the possible reasons for the discrepant results. The overall dynamics seem to converge at a resolution of about 1°. Applying the SMR setup to marginally exploding progenitors is disadvantageous for the shock expansion, however, because the kinetic energy of downflows is dissipated to internal energy at resolution interfaces, leading to a loss of turbulent pressure support and a steeper temperature gradient. We also present a way to estimate the numerical viscosity on grounds of the measured turbulent kinetic energy spectrum, leading to smaller values that are better compatible with the flow behavior witnessed in our simulations than results following calculations in previous literature. Interestingly, the numerical Reynolds numbers in the turbulent, neutrino-heated postshock layer (some 10 to several hundred) are in the ballpark of expected neutrino drag effects on the relevant length scales. We provide a formal derivation and quantitative assessment of the neutrino drag terms in an appendix.

Analysis of wintertime O3 variability using a random forest model and high-frequency observations in Zhangjiakou—an area with background pollution level of the North China Plain

The short-term health effects of ozone (O3) have highlighted the need for high-temporal-resolution O3 observations to accurately assess human exposure to O3. Here, we performed 20-s resolution observations of O3 precursors and meteorological factors to train a random forest model capable of accurately predicting O3 concentrations. Our model performed well with an average validated R2 of 0.997. Unlike in typical linear model frameworks, variable dependencies are not clearly modelled by random forest model. Thus, we conducted additional studies to provide insight into the photochemical and atmospheric dynamic processes driving variations in O3 concentrations. At nitrogen oxides (NOx) concentrations of 10–20 ppb, all the other O3 precursors were in states that increased the production of O3. Over a short timescale, nitrogen dioxide (NO2) can almost track each high-frequency variation in O3. Meteorological factors play a more important role than O3 precursors do in predicting O3 concentrations at a high temporal resolution; however, individual meteorological factors are not sufficient to track every high-frequency change in O3. Nevertheless, the sharp variations in O3 related to flow dynamics are often accompanied by steep temperature changes. Our results suggest that high-temporal-resolution observations, both ground-based and vertical profiles, are necessary for the accurate assessment of human exposure to O3 and the success and accountability of the emission control strategies for improving air quality.

Micro-Texture Analyses of a Cold-Work Tool Steel for Additive Manufacturing.

Small objects of an alloy tool steel were built by selective laser melting at different scan speeds, and their microstructures were analyzed using electron backscatter diffraction (EBSD). To present an explicit correlation with the local thermal cycles in the objects, prior austenite grains were reconstructed using the EBSD mapping data. Extensive growth of austenitic grains after solidification could be detected by the disagreement between the networks of carbides and austenite grain boundaries. A rapid laser scan at 2000 mm/s led to less growth, but retained a larger amount of austenite than a slow one at 50 mm/s. The rapid scan also exhibited definite evolution of Goss-type textures in austenite, which could be attributed to the growth of austenitic grains under a steep temperature gradient. The local variations in the microstructures and the textures enabled us to speculate the locally different thermal cycles determined by the different process conditions, that is, scan speeds.

Assessment of Cu, Zn, Mn, and Fe enrichment in Mt. Kenya soils: evidence for atmospheric deposition and contamination.

Mountains are the preferred sites for studying long-range atmospheric transportation and deposition of heavy metals, due to their isolation and steep temperature decrease that favors cold trapping and condensation of particulate forms of heavy metals. Any enrichment of heavy metals in mountains is presumed to primarily occur through atmospheric deposition. In this particular study, we assessed the status of 27 subsurface soils collected along two elevation gradients of Mt. Kenya using enrichment factors (EFs) as the ecological risk assessments. The collected soils were analyzed for total organic carbon, zinc (Zn), iron (Fe), manganese (Mn), and copper (Cu). The mean concentration of Mn, Fe, Zn, and Cu was 0.376mg/kg, 47.6mg/kg, 12.3mg/kg, and 4.88mg/kg in Chogoria and 0.560mg/kg, 113mg/kg, 12.7mg/kg, and 2.70mg/kg in Naro Moru respectively. These concentrations were below the US-EPA maximum permissible levels for soils, implying that the levels recorded had low toxicity. Meanwhile, the mean enrichment factors for Mn, Cu, and Zn were 0.447, 131, and 78.8 in Chogoria and 0.463, 38.9, and 53.0 in Naro Moru respectively. This implied that Zn and Cu in Chogoria sites were extremely enriched, while in Naro Moru, enrichment levels ranged from significant to extreme. However, Mn was found to have minimal enrichment in all the sites. Lower montane forest and bamboo zone recorded relatively high enrichment due to distance from source of pollution. Ericaceous zone also had high mean enrichment due to influence of wind which favors higher deposition at mid-elevations.

A selection of theoretical results in the context of laser-plasma interaction and inertial fusion

I recall a selection of my results of the last 40 years. I first present a theoretical model of absorption of laser light by a plasma, with an emphasis on its dependence on the laser intensity and wavelength. A second topic concerns the nonlinear and nonlocal electron transport in steep temperature gradients. Thirdly, I present the work on the propagation of a short intense laser pulse in tenuous plasmas. Finally, I discuss the plasma expansion into a vacuum, in particular the structure of the ion front and the prediction of the maximum velocity attained by the ions in the expansion.

Analytical modeling of residual stress in direct metal deposition considering scan strategy

Existence of high tensile residual stress in the additively manufactured parts result in part failure due to crack initiation and propagation. Herein, a physics-based analytical model is proposed to predict the stress distribution much faster than experimentation and numerical methods. A moving point heat source approach is used to predict the in-process temperature field within the build part. Thermal stresses induced by steep temperature gradient is determined using the Green’s functions of stresses due to the point body load in a homogeneous semi-infinite medium. Then, both the in-plane and out of plane residual stress distributions are found from incremental plasticity and kinematic hardening behavior of the metal, in coupling with the equilibrium and compatibility conditions. Due to the steep temperature gradient in this process, material properties vary significantly. Hence, material properties are considered temperature dependent. Moreover, the specific heat is modified to include the latent heat of fusion required for the phase change. Furthermore, the multi-layer and multi-scan aspects of the direct metal deposition process are considered by incorporating the temperature history from the layers and scans. Results from the analytical residual stress model showed good agreement with X-ray diffraction measurements, which is used to determine the residual stresses in the IN718 specimens.

Finite element analysis of temperature and residual stress profiles of porous cubic Ti-6Al-4V titanium alloy by electron beam melting

The temperature and stress profiles of porous cubic Ti-6Al-4V titanium alloy grids by additive manufacturing via electron beam melting (EBM) based on finite element (FE) method were investigated. Three-dimensional FE models were developed to simulate the single-layer and five-layer girds under annular and lateral scanning. The results showed that the molten pool temperature in five-layer girds was higher than that in single-layer grids owing to the larger mass and higher heat capacity. More energies accumulated by the longer scanning time for annular path than lateral path led to the higher temperature and steeper temperature gradient. The thermal stress drastically fluctuated during EBM process and the residual stress decreased with the increase of powder layer where the largest stress appeared at the first layer along the build direction. The stress under lateral scanning was slightly larger but relatively more homogeneous distribution than those under annular scanning. The stress distribution showed anisotropy and the maximum Von Mises stress occurred around the central node. The stress profiles were explained by the temperature fields and grids structure.

Remotely-sensed L4 SST underestimates the thermal fingerprint of coastal upwelling

Sea Surface Temperature (SST) is an essential variable for understanding key physical and biological processes. Blended and interpolated L4 SST products offer major advantages over alternative SST data sources due to their spatial and temporal completeness, yet their ability to discriminate upwelling-induced steep temperature transitions in coastal waters remains largely unassessed. Here we analysed the performance of eleven L4 GHRSST-compliant products in estimating in situ water temperatures recorded by a large network of shallow subtidal and intertidal temperature loggers deployed in shores covering regimes with a wide range of upwelling intensities. Results indicate that while most products perform satisfactorily for most of the year, performance is severely affected during the upwelling season in locations with strong upwelling. We show that upwelling negatively impacts all four metrics used to assess dataset performance (average bias, correlation, centred root-mean-square error and normalized standard deviation), leading to a considerable overestimation of coastal water temperatures (with average bias exceeding 2 °C in some cases). We also show that while the use of L3 data (i. e., prior to blending and interpolation) leads to an increase in performance compared to L4 GHRSST-compliant products, the gain is probably not substantial enough to offset issues related with their spatial and temporal inconsistency along coastlines. Our results suggest that the use of L4 GHRSST-compliant products can lead to a misrepresentation of the thermal fingerprint of upwelling, and thus should be limited (or even avoided) in locations dominated by its effects. Conversely, the use of L4 GHRSST-compliant products on locations with little to no upwelling appears to be warranted. The mismatch between in situ and remotely-sensed sea water temperatures here reported also highlights the need for implementation of long-term monitoring networks of in situ temperature loggers.

The diel vertical migration of the nuisance alga Gonyostomum semen is controlled by temperature and by a circadian clock

Gonyostomum semen is a bloom-forming freshwater raphidophyte that is currently on the increase, which concerns stakeholders and ecologists alike. Much indicates that the success of G. semen is linked to its diel vertical migration (DVM). The DVM was therefore studied in its natural setting using environmental sensors with data logging. DVM happened partly in the absence of light detectable by sensors, suggesting that the DVM involved gravitaxis, although an involvement of phototaxis could not be fully excluded. G. semen migrated downwards the earlier the warmer the water was. The upwards migration showed features of endogenous rhythms, implying that the temporal control of the DVM also has a circadian component that ensures synchronization with the day-night cycle. It is hypothesized that by causing an early descent, exposure to warm water may give G. semen more time to exploit the nutrient-rich lower part of the water column before the circadian control initiates upwards migration. The warming of lakes, caused by global warming or by the more effective conversion of light energy into heat due to the brownification of lakes, may therefore be of advantage to G. semen. In addition, the steep temperature gradient, which is typical for humic lakes during summer stratification, may help avoid the desynchronizing effect that turbulence can have on gravitactic DVMs. Above features of the DVM of G. semen therefore provide putative explanations for why the alga is particularly successful in humic lakes and why it profits from lake brownification and global warming.

Collisional gyrokinetic full‐f particle‐in‐cell simulations on open field lines with PICLS

AbstractApplying gyrokinetic simulations in theoretical turbulence and transport studies for the plasma edge and scrape‐off layer (SOL) presents significant challenges. To particularly account for steep density and temperature gradients in the SOL, the “full‐f” code PICLS was developed. PICLS is a gyrokinetic particle‐in‐cell (PIC) code, is based on an electrostatic model with a linearized field equation, and uses kinetic electrons. In previously published results, we applied PICLS to the well‐studied 1D parallel transport problem during an edge‐localized mode (ELM) in the SOL without collisions. As an extension to this collision‐less case and in preparation for 3D simulations, in this work, a collisional model will be introduced. The implemented Lenard–Bernstein collision operator and its Langevin discretization will be shown. Conservation properties of the collision operator, as well as a comparison of the collisional and non‐collisional case, will be discussed.

Processes Shaping the Frontal-Scale Time-Mean Surface Wind Convergence Patterns around the Kuroshio Extension in Winter

AbstractHigh-resolution satellite observations and numerical simulations have revealed that climatological-mean surface wind convergence and precipitation are enhanced locally around the midlatitude warm western boundary currents (WBCs) with divergence slightly to their poleward side. While steep sea surface temperature (SST) fronts along the WBCs have been believed to play an important role in shaping those frontal-scale atmospheric structures, the mechanisms and processes involved are still under debate. The present study explores specific daily scale atmospheric processes that are essential for shaping the frontal-scale atmospheric structure around the Kuroshio Extension (KE) in winter, taking advantage of a new product of global atmospheric reanalysis. Cluster analysis and case studies reveal that a zonally extending narrow band of surface wind convergence frequently emerges along the KE, which is typically observed under the surface northerlies after the passage of a developed synoptic-scale cyclone. Unlike its counterpart around the cyclone center and associated cold front, the surface convergence tends to be in moderate strength and more persistent, contributing dominantly to the distinct time-mean convergence/divergence contrast across the SST front. Accompanying ascent and convective precipitation, the band of convergence is a manifestation of a weak stationary atmospheric front anchored along the SST front or generation of a weak meso-α-scale cyclone. By reinforcing the ascent and convergence, latent heating through convective processes induced by surface convergence plays an important role in shaping the frontal-scale atmospheric structure around the KE.

Hypersonic aerodynamic interference investigation for a two-stage-to-orbit model

To investigate the aerodynamic interference challenges for hypersonic vehicles, a new type of conceptual TSTO model is considered, which consists of a trapezoid wing as the booster and a hemisphere-cone-cylinder wing as the orbiter. Based on the three-dimensional hybrid LES/RANS numerical simulation method, the mechanism of high surface heat flux and the effect of stage separation between booster and aircraft in hypersonic flight are studied in detail. The results show that the oblique shock generated by the booster impinges on the bow shock in a three-dimensional region around the orbiter nose. Obviously, this interaction brings about a steep temperature gradient and high peak values of pressure and heat flux. When the bow shock under the orbiter is incident to the upper surface of the booster, it will trigger a shock-wave/boundary-layer interaction, which gives rise to the peak pressure and heat flux. When the reflected bow shock impacts the lower surface of the orbiter, it will initiate another interaction. When the two stages separate from each other, the increase in the normal distance between two stages results in a decrease in pressure and heat flux. When the vertical distance is large enough, the reflected bow shock impinges on the rear of the orbiter without producing an interaction. At that moment, the pressure and heat flux maintain low values.

Short- and long-term near-infrared spectroscopic variability of eruptive protostars from VVV

ABSTRACT Numerous eruptive variable young stellar objects (YSOs), mostly Class I systems, were recently detected by the near-infrared Vista Variables in the Via Lactea (VVV) survey. We present an exploratory near-infrared spectroscopic variability study of 14 eruptive YSOs. The variations were sampled over one-day and one-to-two-year intervals and analysed in combination with VVV light curves. CO overtone absorption features are observed on three objects with FUor-like spectra: all show deeper absorption when they are brighter. This implies stronger emission from the circumstellar disc with a steeper vertical temperature gradient when the accretion rate is higher. This confirms the nature of fast VVV FUor-like events, in line with the accepted picture for classical FUors. The absence of Brγ emission in a FUor-like object declining to pre-outburst brightness suggests that reconstruction of the stellar magnetic field is a slow process. Within the one-day time-scale, 60 per cent of H2-emitting YSOs show significant but modest variation, and 2/6 sources have large variations in Brγ. Over year-long time-scales, H2 flux variations remain modest despite up to 1.8 mag variation in Ks. This indicates that emission from the molecular outflow usually arises further from the protostar and is unaffected by relatively large changes in accretion rate on year-long time-scales. Two objects show signs of on/off magnetospheric accretion traced by Brγ emission. In addition, a 60 per cent inter-night brightening of the H2 outflow is detected in one YSO.

Self-Healing of Photocurrent Degradation in Perovskite Solar Cells: The Role of Defect-Trapped Excitons.

Solution-processed lead halide perovskites have emerged as one of the most promising materials in optoelectronic applications. However, the perovskites are not stable over prolonged solar illumination. A recent experimental study has revealed light-activated photocurrent degradation and self-healing in lead halide perovskites, which has important implications in tackling the photostability problems of the perovskites. Unfortunately, the physical origin of the experimental observations is unclear. In this work, we propose a first-principles theory that can elucidate all key experimental observations. By focusing on defect-trapped excitons, the theory can rationalize both fast and slow time scales of self-healing, contrasting dynamics of the photocurrent degradation and its recovery, and the steep temperature dependence of the two competing processes. We further predict that the same phenomenon of self-healing could also be observed in other lead halide perovskites with even faster time scales of recovery. The work provides a general framework for elucidating defect-controlled excitation dynamics in perovskites.

The water line emission and ortho-to-para ratio in the Orion Bar photon-dominated region

Context. The ortho-to-para ratio (OPR) of water in the interstellar medium (ISM) is often assumed to be related to the formation temperature of water molecules, making it a potentially interesting tracer of the thermal history of interstellar gas. Aims. A very low OPR of 0.1–0.5 was previously reported in the Orion Bar photon-dominated region (PDR), based on observations of two optically thin H218O lines which were analyzed by using a single-slab large velocity gradient (LVG) model. The corresponding spin temperature does not coincide with the kinetic temperature of the molecular gas in this UV-illuminated region. This was interpreted as an indication of water molecules being formed on cold icy grains which were subsequently released by UV photodesorption. Methods. A more complete set of water observations in the Orion Bar, including seven H216O lines and one H218O line, carried out using Herschel/HIFI instrument, was reanalyzed using the Meudon PDR code to derive gas-phase water abundance and the OPR. The model takes into account the steep density and temperature gradients present in the region. Results. The model line intensities are in good agreement with the observations assuming that water molecules formed with an OPR corresponding to thermal equilibrium conditions at the local kinetic temperature of the gas and when solely considering gas-phase chemistry and water gas-grain exchanges through adsorption and desorption. Gas-phase water is predicted to arise from a region deep into the cloud, corresponding to a visual extinction of AV ~ 9, with a H216O fractional abundance of ~2 × 10−7 and column density of (1.4 ± 0.8) × 1015 cm−2 for a total cloud depth of AV = 15. A line-of-sight average OPR of 2.8 ± 0.2 is derived. Conclusions. The observational data are consistent with a nuclear spin isomer repartition corresponding to the thermal equilibrium at a temperature of 36 ± 2 K, much higher than the spin temperature previously reported for this region and close to the gas kinetic temperature in the water-emitting gas.

Influence of Keyhole Mode of Plasma Arc Welding on Microstructure and Mechanical Properties of Similar Butt-Welded Incoloy 800H

The keyhole mode of plasma arc welding (K-PAW) was employed to weld Incoloy 800H plates of 6 mm thickness. A nickel–chromium-based superalloy, Incoloy 800H is a fully austenitic face-centered cubic structure and imparts better tensile strength, fatigue strength, and creep properties at higher temperatures. Full-penetration weld was achieved by a single-pass welding, and no defects were observed in X-ray radiography testing. Microstructural studies revealed fine equiaxed dendritic structure present in the weld metals due to the steep temperature gradient induced by the K-PAW. Due to fine grain structure, no solidification cracking was observed in the weldment. Mechanical properties studies confirmed that weldments attained the minimal requirements of tensile strength, hardness, ductility, and toughness as per the boiler pressure vessel fabrication requirement norms.

Lumped analysis criteria for heat transfer in a diluted co – current moving bed heat exchanger with isothermal walls

In this study, a mathematical method was applied to establish modelling selection criteria for lumped parameter analysis (LPA), in the solid phase, of a diluted co-current moving bed heat exchanger (MBHE), with isothermal walls. Simplified expressions for particle temperature errors are obtained, showing, for certain parametric ranges, excellent agreement with the exact solution results. Another remarkable result is that for a MBHE with isothermal walls and very low particle Biot numbers, the possibility of steep intraparticle temperature gradients is demonstrated. Through a scale analysis, this behavior is explained, along with the physical foundations guiding the LPA selection criteria. The differences between two basic forms of approximation in MBHE modelling, that is, the uniform particle temperature assumption (UPTA) and LPA, are characterized. Also, new contributions are provided by the determination of parametric condition for the equality between the temperatures of the fluid and the particle surface and by limiting solutions.

Effects of Different Steeping Temperatures on the Leaching of Aroma Components in Black Tea by SPME–GC–MS Coupled with Chemometric Method

Abstract Background: Black tea is famous for its unique aroma. The analysis of aroma components has attracted considerable attention worldwide because of its complex chemical composition and low concentration. Objective: Steeping temperature is one of the most important factors affecting the aroma of black tea. This study aims to evaluate the effects of four steeping temperatures [60, 70, 80, and 95°C (boiling water)]. Methods: Two major factors affecting extraction performance, including the type of extraction method [direct headspace injection (HS) and solid-phase microextraction (SPME)] and extraction time (50, 60, and 70 min), were optimized to enrich and analyze the aroma components of Congou black tea by GC–MS. In addition, heuristic evolving latent projection (HELP), an effective chemometric resolution method, was employed to resolve the overlapped peaks. Results: A total of 83 aroma components were tentatively identified by GC–MS, such as alcohol (42.06–50.52%), aldehyde (12.09–15.97%), and hydrocarbon (4.79–15.32%). Linalool and its oxides (25.49–36.24%) were the most abundant aroma components, followed by geraniol (2.55–8.54%), methyl salicylate (1.84–9.50%), and nerol (1.93–4.41%). Conclusions: The black tea steeped at 95°C smelled more pleasant with mild green, roast, and fruity aroma. Moreover, at 80°C, the tea had sweeter fragrance with floral aroma, while steeping at 60 and 70°C resulted in more reinforced woody and fatty aroma. Highlights: A total of 83 aroma components of black tea were tentatively identified by SPME–GC–MS. The overlapped peaks were resolved by the HELP method. Aroma characteristics of different steeping temperatures were revealed.

Formation Temperature Distribution of the Turonian- Maastrichtian Fika Shale Formation from Wireline Logs, in Part of Borno Basin, Northeastern Nigeria

The distribution of Formation Temperature of the Fika Shale Formation within part of Borno basin from five wireline logs was investigated. The area under studied covered about 20 by 40 kilometre square of the total land mass of the basin. The Fika shale sequence were identified at 865m to 1795m in Kinasar well, 640m to 1990m in Krumta, 980m to 1620m in Masu, 700m to 2710m in Tuma, 710m to 2220m in Wadi. The plot of the entire Formation Temperature of the study area reveals remarkable steep variations in temperature with increased range from 680C to 1280C starting from the southern eastern region to the north western region. This is possibly due to substantial temperature enhancing effects of the underlying basement complex. Interestingly, it was also observed that the minimal temperature variation occurred approximately 20C/ meter across the field and this also lays credence to the fact that the notable subsurface geothermal variation may be recent events initiated by the near- surface magmatic intrusive events which may have had adverse effects on the overlying sedimentary cover. Furthermore, it was deduced that the probability of hydrocarbon accumulation is better in the south eastern region than the north western region although the steep temperature variation of 20C/ meter within some part of the study area may perhaps reduce this possibility.