Large Temperature Increase Research Articles

Ultrafast photodoping and effective Fermi-Dirac distribution of the Dirac particles in Bi2Se3

We exploit time- and angle-resolved photoemission spectroscopy to determine the evolution of the out-of-equilibrium electronic structure of the topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$. The response of the Fermi-Dirac distribution to ultrashort IR laser pulses has been studied by modeling the dynamics of hot electrons after optical excitation. We disentangle a large increase in the effective temperature (${T}^{*}$) from a shift of the chemical potential (${\ensuremath{\mu}}^{*}$), which is consequence of the ultrafast photodoping of the conduction band. The relaxation dynamics of ${T}^{*}$ and ${\ensuremath{\mu}}^{*}$ are $k$ independent and these two quantities uniquely define the evolution of the excited charge population. We observe that the energy dependence of the nonequilibrium charge population is solely determined by the analytical form of the effective Fermi-Dirac distribution.

A similarity solution for the flow and heat transfer over a moving permeable flat plate in an external free stream: case of strong injection

The previous work of Bachok et al. (Heat Mass Transf. 47:1643–1649, 2011) on the forced convection heat transfer on an isothermal moving surface in an external free stream is extended to the case when fluid injection through the surface, characterized by the parameter γ, is large. The asymptotic solution derived in this limit shows that the boundary layer has a double region structure, with an inviscid inner region of thickness O(γ) and an outer shear layer. Some further aspects of the original problem not treated in Bachok et al. (Heat Mass Transf. 47:1643–1649, 2011) are discussed as well as the analogous problem for a constant surface heat flux, where relatively small injection rates are seen to give rise to large increases in the surface temperature.

Mechanisms for European summer temperature response to solar forcing over the last millennium

Abstract. A simulation of the last millennium is compared to a recent spatio-temporal reconstruction of summer temperature over Europe. The focus is on the response to solar forcing over the pre-industrial era. Although the correlation between solar forcing and the reconstruction remains small, the spatial regression over solar forcing shows statistically significant regions. The meridional pattern of this regression is found to be similar in the model and in the reconstruction. This pattern exhibits a large warming over Northern and Mediterranean Europe and a lesser amplitude response over Central and Eastern Europe. The mechanisms explaining this pattern in the simulation are mainly related to evapotranspiration fluxes. It is shown that the evapotranspiration is larger in summer over Central and Eastern Europe when solar forcing increases, while it decreases over the Mediterranean area. The explanation for the evapotranspiration increase over Central and Eastern Europe is found in the increase of winter precipitation there, leading to a soil moisture increase in spring. As a consequence, the evapotranspiration is larger in summer, which leads to an increase in cloud cover over this region, reducing the surface shortwave flux there and leading to less warming. Over the Mediterranean area, the surface shortwave flux increases with solar forcing, the soil becomes dryer and the evapotranspiration is reduced in summer leading to a larger increase in temperature. This effect appears to be overestimated in the model as compared to the reconstruction. Finally, the warming of Northern Europe is related to the albedo feedback due to sea-ice cover retreat with increasing solar forcing.

Trend analysis of weekly temperatures and oxygen concentrations during summer stratification in Lake Plußsee: A long‐term study

Small dimictic Lake Plußsee in North Germany experienced major changes of the temperature and oxygen regime from 1969 to 2006, which reflected regional and large‐scale changes in meteorological forcing. We used long‐term weekly measurements of the lake's epilimnetic, metalimnetic, and hypolimnetic temperatures and dissolved oxygen concentrations and meteorological forcing variables to estimate long‐term trends for each week. Except for large warming trends of air temperatures in the last week of April (0.14°C yr−1) and the first week of May (0.11°C yr−1), the extent of epilimnetic warming trends during the same time period (∼ 0.06–0.08°C yr−1) was also caused by a cumulative effect resulting from an earlier onset of stratification. Negative hypolimnetic temperature trends at the same time (∼ 0.01°C yr−1) also resulted from an earlier onset of stratification and increased water‐column stability in spring. In summer and autumn, large increases in epilimnetic temperature and water‐column stability were also affected by a shift of the timing of the yearly maxima of epilimnetic temperatures and water‐column stability, which resulted in a later breakdown of stratification. This annual pattern of long‐term trends of epilimnetic and hypolimnetic temperatures agrees with models driven by the expected increase of air temperatures due to anthropogenic greenhouse gases. Due to a prolonged stratification period, oxygen concentrations during the last weeks of the stratified period were lower, although oxygen concentrations in the water column increased within the first weeks of stratification.

Numerical study on ultra-lean rotating counterflow twin premixed flame of hydrogen–air

Rotating counterflow twin premixed flame (RCTF) of hydrogen air was numerically simulated with detailed chemistry to explore the possibility of ultra-lean combustion. As a result, it was found that ultra-lean RCTF of equivalence ratio Φ=0.052, which is far leaner than the generally-recognized flammability limit Φ=0.10, is realized. It was also found that under ultra-lean conditions the flame temperature of RCTF largely exceeds the adiabatic flame temperature; e.g., at Φ=0.06 the former is 1171K, while the latter is 503K. This increase of burned gas temperature is attributed to the so-called low Lewis number effect within the flammability limit, but under an ultra-lean condition some other mechanism to increase temperature is dominant. The “pseudo local equivalence ratio” of burned gas of RCTF differs largely from that of the unburned gas due to the extraordinarily high concentration of H2O. This suggests the possibility that the local condition at the reaction zone is much richer than the unburned gas, which brings about the large temperature increase.

Temperature shocks and ecological implications at a cold-water coral reef

Continuous long-term measurements of temperature, salinity and current velocity, have been recorded over 44 months at the Tisler Reef. The Tisler Reef is a 2 km long cold-water coral reef on the sill of the Kosterfjord, located in the north-eastern Skagerrak, Norway. The reef comprises principally Lophelia pertusa, at depths between 70 and 160 m, and is an important habitat for sponge, crustacean and fish species including a number of species of commercial importance. Analysis of the current velocity data has identified a number of features such as flow reversals. These reversals in flow direction are often associated with significant changes in bottom temperature. During the autumn months of 2006 and 2008, a series of large and rapid increases in bottom temperature were observed, with temperatures seen to rise by approximately 4°C in a 24 hour period on both occasions. The occurrence of the 2006 and 2008 events corresponded with the observation of mass mortality in the long-lived sponge Geodia baretti. Historical temperature records from the region suggest that these temperature shocks are uncharacteristically high. The temperatures observed at the reef exceed the typical short-term physiological limits of L. pertusa thus future temperature shock events may have a swift and negative impact on the cold-water coral reef ecosystems of the Skagerrak.

Effect of size-dependent grain structures on the dynamics of nanoparticle coalescence

The effect of grain structure on the coalescence dynamics of anatase TiO2 nanoparticles at different temperatures is investigated using classical molecular dynamics (MD) simulation. Examination of local-lattice-orientation distributions reveals that the grain morphology of particles is highly dependent on size. For a single anatase nanoparticle below the melting temperature, an amorphous-to-crystalline transition occurs for diameters ranging from 2 to 2.5 nm as temperature increases. Below the transition diameter (for a given temperature), the entire nanoparticle is amorphous. Above the transition diameter, the nanoparticle consists of a crystalline core and an amorphous shell (4–6 Å). Considering that such grain-structure characteristics may lead to different dynamic behaviors, the coalescence between pairs of 2 nm–2 nm, 3 nm–3 nm, and 2 nm–3 nm nanoparticles is investigated. For 2 nm–2 nm nanoparticle coalescence, the process is independent of initial temperature and is seemingly viscosity-controlled with a dynamic temperature rise due to energy transfer from surface to internal kinetic (thermal). For 3 nm–3 nm nanoparticle coalescence, the process is sensitive to initial temperature. Above the melting temperature, the dynamics are similar to the 2 nm–2 nm amorphous case. Just below the melting point, coalescence consists of melting of the crystalline cores with subsequent large increase in temperature due to recrystallization. For 2 nm–3 nm nanoparticle coalescence, recrystallization of the 2 nm particle significantly increases the total temperature compared to the 2 nm–2 nm case.

Nanocomposites based on plasma-polymerized carbon nanotubes and Nylon-6

Un-expected large increase in crystallization temperature (c.a. 53 °C) was found for Nylon-6 nanocomposites with both kind of carbon nanotubes (CNTs) and plasma-polymerized CNTs (CNTM) compared with Nylon-6 homopolymer. This behavior was associated with a high level of dispersion of CNT in all nanocomposites and the ability of CNT to act like a nucleating agent for semi-crystalline polymers. Besides, the steps involved in polymerization procedure help in dispersion of CNT, which is reported for the first time.

Examining evapotranspiration trends in Africa

Surface temperatures are projected to increase 3–4°C over much of Africa by the end of the 21st century. Precipitation projections are less certain, but the most plausible scenario given by the Intergovernmental Panel on Climate Change (IPCC) is that the Sahel and East Africa will experience modest increases (~5%) in precipitation by the end of the 21st century. Evapotranspiration (Ea) is an important component of the water, energy, and biogeochemical cycles that impact several climate properties, processes, and feedbacks. The interaction of Ea with climate change drivers remains relatively unexplored in Africa. In this paper, we examine the trends in Ea, precipitation (P), daily maximum temperature (Tmax), and daily minimum temperature (Tmin) on a seasonal basis using a 31 year time series of variable infiltration capacity (VIC) land surface model (LSM) Ea. The VIC model captured the magnitude, variability, and structure of observed runoff better than other LSMs and a hybrid model included in the analysis. In addition, we examine the inter-correlations of Ea, P, Tmax, and Tmin to determine relationships and potential feedbacks. Unlike many IPCC climate change simulations, the historical analysis reveals substantial drying over much of the Sahel and East Africa during the primary growing season. In the western Sahel, large increases in daily maximum temperature appear linked to Ea declines, despite modest rainfall recovery. The decline in Ea and latent heating in this region could lead to increased sensible heating and surface temperature, thus establishing a possible positive feedback between Ea and surface temperature.

Tipping Points in the Arctic: Eyeballing or Statistical Significance?

Arctic ecosystems have experienced and are projected to experience continued large increases in temperature and declines in sea ice cover. It has been hypothesized that small changes in ecosystem drivers can fundamentally alter ecosystem functioning, and that this might be particularly pronounced for Arctic ecosystems. We present a suite of simple statistical analyses to identify changes in the statistical properties of data, emphasizing that changes in the standard error should be considered in addition to changes in mean properties. The methods are exemplified using sea ice extent, and suggest that the loss rate of sea ice accelerated by factor of ~5 in 1996, as reported in other studies, but increases in random fluctuations, as an early warning signal, were observed already in 1990. We recommend to employ the proposed methods more systematically for analyzing tipping points to document effects of climate change in the Arctic.

Non-covalently modified graphene sheets by imidazolium ionic liquids for multifunctional polymer nanocomposites

Chemical reduction of graphite oxide (GO) to produce graphene nanosheets often results in irreversible agglomeration and precipitation. Herein, stable well-dispersed graphene sheets in solvents were obtained by simultaneous functionalization and reduction of GO under alkaline conditions, in the presence of sodium borohydride and imidazolium ionic liquids (Imi-ILs) containing two vinyl-benzyl groups. In this case, positively charged imidazolium groups of Imi-ILs underwent ion-exchange with negatively charged GO sheets and were linked to their edges, while Imi-ILs were non-covalently attached onto the large surfaces of graphene through π–π and/or cation–π stacking interactions. The vinyl-benzyl reactive sites were then copolymerized in situ with methyl methacrylate to fabricate graphene/poly(methyl methacrylate) (PMMA) composites. Functionalized graphene sheets were uniformly dispersed in the PMMA matrix and contributed to large increases in storage modulus (+58.3%) and glass transition temperature (+19.2 °C) at 2.08 vol.% loading. High electrical conductivity was also achieved at graphene loading levels beyond 1 vol.% (ca. 2.55 Sm−1) with a low percolation threshold (0.25 vol.%) for the composites. Hence, a general methodology which facilitates the development of a multifunctional advanced material has been successfully established. This can be extended to other vinyl polymer-based composites containing graphene.

ANALYSIS OF PROJECTED CLIMATE CHANGE FOR HUNGARY USING ENSEMBLES SIMULATIONS

In order to estimate the future regional climate change for the Carpathian Basin located in Central/Eastern Europe, outputs from several RCMs (from the completed European project ENSEMBLES) are summarized and analyzed using the SRES A1B scenario. Composite maps of the projected annual and seasonal temperature and precipitation changes are generated using RCM simulations (with 25 km spatial resolution) for the reference period 1961-1990, and the target periods 2021-2050, 2071-2100. Overall, the results suggest significant warming in Hungary. Projected seasonal warming is 1-3 °C, and 2-6 °C for 2021-2050, and 2071-2100, respectively. The largest temperature increase is likely to occur in summer. In case of precipitation, the annual sum is not likely to change significantly in the region. However, the summer precipitation is projected to decrease significantly during the 21st century, autumn and winter precipitation amounts are projected to increase.

Screening Analysis for Hazard Assessment of Peroxides Decomposition

In this study, the analysis of the decomposition of four different peroxides (including hydrogen peroxide) by screening calorimetry is proposed. The objective is to analyze the decomposition reactions and evaluate the consequences in particular when the process undergoes to thermal explosion and may be the cause of incidents. Screening calorimetry data allow us to define the conditions and ranges of temperature and pressure evolved during the reaction. In the experimental apparatus used (a screening calorimeter), the experiments have been carried out safely, even when there is a rapid and large increase in temperature and pressure. Scanning and isothermal conditions has been investigated. An Early Warning Detection System (EWDS) for thermal runaway, based on the divergence criterion, has also been applied off-line to the experimental isothermal data, in order to evaluate the sensitivity of the method applied to both temperature and pressure profiles. The results of the application of the EWDS have been co...

Elucidation of the dynamics for hot-spot initiation at nonuniform interfaces of highly shocked materials

The fundamental processes in shock-induced instabilities of materials remain obscure, particularly for detonation of energetic materials. We simulated these processes at the atomic scale on a realistic model of a polymer-bonded explosive (3,695,375 atoms/cell) and observed that a hot spot forms at the nonuniform interface, arising from shear relaxation that results in shear along the interface that leads to a large temperature increase that persists long after the shock front has passed the interface. For energetic materials this temperature increase is coupled to chemical reactions that lead to detonation. We show that decreasing the density of the binder eliminates the hot spot.

Polymorphism and cross-nucleation in poly(1,3-dioxolan)

The isothermal crystallization from the melt of a poly(1,3-dioxolan) having a number-average molecular weight of 5100 was investigated by optical microscopy, differential scanning calorimetric and X-ray diffraction. A single spherulitic morphology (Phase I) of negative sign is observed at crystallization temperatures below 19 °C while multiple morphologies are observed at crystallization temperatures above 19 °C (Phases IIa, IIb and III). Phase IIa crystallizes first and is characterized by a low birefringence until its sporadic transformation into Phase IIb, characterized by a sudden increase in birefringence. Phase IIb acts as a nucleating agent for Phase III (cross-nucleation process). Phases I and III exhibit distinct growth rates that are two orders of magnitude lower than the transformation rate of Phase IIa into Phase IIb. Relationships between the crystalline structures of the different morphologies and their melting temperatures are also discussed. The transformation IIa/IIb is easily detected optically by a huge increase in birefringence but there is a more subtle Ia/Ib transformation which is hardly seen optically, although it gives rise to a large increase in melting temperature of that phase.

Archival and acoustic tags reveal the post-spawning migrations, diving behavior, and thermal habitat of hatchery-origin Sacramento River steelhead kelts (Oncorhynchus mykiss)

Acoustic and geolocating archival tags were deployed on steelhead kelts to study their post-spawning migrations, diving behavior and thermal habitat. Fourteen reconditioned steelhead kelts were surgically implanted with LAT2510 archival and V7-2 L acoustic tags, and released from Coleman National Fish Hatchery. An array of acoustic receivers in the Sacramento River and Delta, and the San Francisco Bay estuary detected the downstream movement of the steelhead. Two steelhead kelts (J and M) with archival tags were recovered at the hatchery after 219 and 285 days at liberty respectively. Based on changes in geolocations, vertical movements, and water temperatures, the migrations of steelhead J and M were divided into five and six phases respectively. Steelhead J moved into coastal California waters while steelhead M remained in freshwater for the majority of its time at liberty. Large increases in temperature and opacity were recorded before and after the ocean phases, likely as the steelhead moved through the Sacramento Delta. Both steelhead kelts remained relatively close to the surface throughout their migration but there were diurnal differences in the vertical movements. In freshwater, the steelhead tended to be deeper during the day (e.g., steelhead J: 3.08 ± 1.50 vs 1.65 ± 1.15 m, day vs night) but in the ocean, the steelhead were typically deeper during the night (1.32 ± 1.61 vs 5.63 ± 6.11 m). Both steelhead kelts appeared to be less oceanic than a previous study in Scott Creek, a small coastal stream approximately 100 km south of the mouth of San Francisco Bay. Although this study has a small sample size, the results suggest that steelhead kelts from a large river and estuary system, like the Sacramento River, may be relatively less oceanic than steelhead kelts from small coastal streams.

Environmental change in the Great Whale River region, Hudson Bay: Five decades of multidisciplinary research by Centre d'études nordiques (CEN)

The Great Whale River region on the eastern shore of Hudson Bay, Canada, encompasses the villages of Whapmagoostui (Cree First Nation) and Kuujjuarapik (Inuit) and surrounding areas. The principal field station of Centre d'études nordiques (CEN: Centre for Northern Studies) has operated at Whapmagoostui-Kuujjuarapik (W-K; 55° 15′ N, 77° 45′ W) since the 1970s, with diverse research projects on past and present environments. The climate at W-K is strongly influenced by the proximity of Hudson Bay, and the recent pronounced loss of sea ice in this sector of northern Canada has been accompanied by large increases in air temperature. Discontinuous or scattered permafrost occurs throughout the region and is degrading rapidly. The W-K region continues to experience particularly rapid isostatic uplift in response to the retreat of the Laurentide Ice Sheet. Parabolic dunes occur along the coast and are strongly influenced by the plant cover. Paleoecological studies have documented the Holocene evolution of landscapes, including lakes, wetlands, and forests. The vegetation type is coastal forest tundra, with some 400 recorded species. Studies on certain insect groups provide a baseline for assessing future ecological change. The first signs of human occupation in the W-K region have been dated at 3800 BP. The arrival of the Hudson's Bay Company in the 18th century marked the onset of continuous occupation. Rapid social, economic, and environmental change initiated in the mid-20th century continues to this day.

Study of rapid ionisation for simulation of soft X-ray lasers with the 2D hydro-radiative code ARWEN

We present our fast ionisation routine used to study transient soft X-ray lasers with ARWEN, a two-dimensional hydrodynamic code incorporating adaptative mesh refinement (AMR) and radiative transport. We compute global rates between ion stages assuming an effective temperature between singly-excited levels of each ion. A two-step method is used to obtain in a straightforward manner the variation of ion populations over long hydrodynamic time steps. We compare our model with existing theoretical results both stationary and transient, finding that the discrepancies are moderate except for large densities. We simulate an existing Molybdenum Ni-like transient soft X-ray laser with ARWEN. Use of the fast ionisation routine leads to a larger increase in temperature and a larger gain zone than when LTE datatables are used.

Reaction hazards of triethylaluminum under closed conditions

We evaluate the reaction hazards of triethylaluminum (TEA) under closed conditions for safe treatment of aluminum alkyls. The explosive reactions of TEA are difficult to be estimated using thermal analysis because the estimate reactions are too slow under these conditions. The results of our closed vessel tests and chemical equilibrium calculations show that the TEA and water system mixture in closed conditions decomposes into lower-molecular-weight compounds than the products by using well-known hydrolysis of TEA. The present work also demonstrates that large temperature and pressure increases could occur because of the existence of TEA and aluminum hydroxide. Since aluminum hydroxide contains water as alumina hydrates, aluminum hydroxide could have been the source of water at high temperatures and could have contributed to the mixed reaction between TEA and water.

Coupled neutronics-fluids modelling of criticality within a MOX powder system

This paper is concerned with the reactivity during a transient of a layered MOX, and moderating lubricant (zinc stearate) mixing system which is used as part of fuel processing. The reactivity effects with increases in temperature and mixing (moderation) are investigated here. The transient and static simulations reveal that large increases in reactivity and temperature are possible. The nuclear criticality modelling of powders is performed using the Finite Element Transient Criticality (FETCH) code. This models criticality transients in spatial and temporal detail using a continuum multi-fluid model of the gas and solid-powder phases. The neutronics model in FETCH solves the neutron transport in full phase space. In this study a number of hypothetical criticality scenarios with the same generic mixing device and MOX powder are investigated in order to gain an understanding of the dynamics of powder criticality. An additive zinc stearate is also introduced. The zinc stearate, can act as a moderator and thus, on mixing, a ramp reactivity can be introduced. The mixing device is introduced into the simulations to help investigate this ramp reactivity.